Gökçeada veya 1970 yılına kadar kullanılan adıyla İmroz (,  Imvros), Çanakkale'nin bir ilçesi ve Türkiye'nin en büyük adasıdır. Ege Denizi'nin kuzeyinde, Saros Körfezi girişinde yer almaktadır. 91 km kıyı şeridine sahiptir. Yıllık yağış miktarı metrekareye 950 – 1050 mm arasında değişmektedir. Adanın batısında yer alan İncirburnu Türkiye'nin de en batı noktasını oluşturmaktadır. 2011 ve 2012 yıllarında haftada 2 kez Gökçeada-İstanbul uçak seferleri yapılmış olup, 2013 ve sonrasında ticari yolcu uçuşları yapılmamıştır.

Gökçeada, Türkiye'de 2016 itibarıyla 11 tane olan "sakin kent"lerden (Cittaslow) birisidir. Cittaslow hareketi, Türkiye'ye 2009 yılında Seferihisar ilçesinin katılmasıyla gelmiştir. Seferihisar Belediye Başkanı, Cittaslow Uluslararası Başkan Yardımcısı, Cittaslow Türkiye Koordinatörü olan Tunç Soyer, Cittaslow hareketinin Türkiye'de gelişmesine öncü olmuş, İzmir ili Seferihisar ilçesi dünyanın 129′uncu, Türkiye'nin ilk sakin şehri olmuştur. Bu üyelik, Türkiye'nin tanıtımı için yeni bir vesile olmakla birlikte, sakin kent unvanı almış ilçelerin gelişimi, kültürel ve tarihi değerlerinin korunması için önemli bir adımdır. 2009 yılından 2016 yılına kadar geçen 7 yıl gibi kısa bir süre içerisinde Türkiye'de sakin kent hareketine üye sayısı Mart 2016'da Erzurum ili Uzundere ilçesinin katılmasıyla 11'e yükselmiştir.

Tarihçe
Ada'nın ilk çağlardaki durumu hakkında fazla bilgi mevcut değildir. Bilgiler, Orta Çağ'da başlamıştır. Ada 1204-1261 tarihleri arasında Latin İmparatorluğu'na tabi kalmıştır. Bizans İmparatorluğu'nun son zamanlarında bütünlüğünü koruyamaması üzerine, Cenevizli Gattilusıo Ailesi diğer Ege Adalarında olduğu gibi, bu ada üzerinde de hâkimiyet kurmaya gayret etmiştir. Bu aile o zamana kadar 1. Murat devrinden itibaren siyasi manevralarla Türkleri ada'dan uzak tutmuştur. Fatih 1453 yılında İstanbul'u alıp, Bizans İmparatorluğu'na son vermesi ile imparatorlukla sıkı ilişkileri olan bu Latin devletinin de sonu gelmiş oldu. Dorino Gattilusio ölünce yerine geçen oğlu Dominiko, Dukas'ı Fatih'e elçi olarak gönderdi.

Bunun sebebi, her sene Midilli Adası için verilen 3000, Limni Adası için verilen 2300 altın vergiyi padişaha takdim etmekti. Aslen Limni Adası her sene mezkûr vergiyi vermek için Midilli hakimine ve Gökçeada senede 1200 altın vergi vermek şartı ile Enez hakimine verilmişti. İstanbul'un fethinden sonra, Gattilusio Ailesi'nin davranışına benzer davranışları diğer aileler de göstermişti. Aslen Gökçeada'lı olan Kristobulos'un bu husustaki gayretlerini önemsemek gerekir. Kristobulos, İstanbul'un fethinden sonra bir heyet tanzim ederek, Fatih Sultan Mehmet'e göndermiştir. Bizans'a tabi olan Gökçeada, Limni ve Taşoz Adalarına imparatorluk tarafından tayin edilmiş olan memurlar, İstanbul'un fethini ve imparatorun ölümünü haber alınca, Gökçeada'dakiler Kefaloz Burnundan İtalyan gemilerinden memleketten çıktılar.

Ada halkı da bunun üzerine göç girişiminde bulunuyorlardı. Kristobulos, göçe engel olabilmek için Gelibolu sancak beyi bir elçi göndererek, adalara hücum etmemesi için onunla bir anlaşma yaptı. Hamza Bey'in aracılığı ile de bir başpiskoposu ve kocabaşıdan ibaret sefaret heyetini Fatih'e gönderdi. Heyet hükümdara bağlılıklarını bildirdikten sonra, Fatih'ten şimdiye kadar olduğu gibi idare edilmelerini, yılda muayyen bir vergi vermelerini ve tayin edilen bir kişinin ada idaresinden sorumlu olmasını istediler. Bu sırada Enez Bey'i Palamede, kendi memurlarından birini ve Midilli Bey'i Dorya'nın oğlunu elçi sıfatıyla padişaha göndererek adaların idaresinin kendisine verilmesini rica ettiğinden Kristobulos tarafından gönderilen heyet ile görüşülüp iki taraf anlaştıktan sonra 1453 yılında Ada, Palamede Gattilusio'yu Limni ve Taşoz Adaları ise Dorya'ya verildi. Böylece göç, meşhur tarihçi Gökçeada'lı Kristobulos'un çabaları ile önlenmiş oldu. Aynı yıl içinde Palamede ölünce, bırakmış olduğu vasiyetinde hissenin çoğunu, ölen büyük oğlunun zevcesi ve çocuğuna bırakmakla beraber, Enez şehri, Gökçeada ve Semadirek adalarının idari sorumlusu olan küçük oğlu Dorino, bu vasiyetnameye iltifat etmeyip, babasının bırakmış olduğu bütün hisseye zorla sahip oldu. Onun namına Gökçeada'da Joannes Laskaris Enez'de valilik yaptı. Dorino idaresinde kardeşinin zevcesi ve oğlunu hiç gözetmediğinden, yakınları bu hareketin doğru olmadığını, hissesi olup da payını alamayan bu kadının padişaha şikâyette bulunabileceğini söylediler. Nihayet bu kadın, dayısını elçi olarak padişaha gönderdi. Bu zat, Dorino'nun haksızlığından bahsettikten sonra, padişaha karşı da İtalyanlarla anlaşmakta olduğunu, asker toplayarak Enez ve adalara muhafız tayin ettiğini kötü sonuçlanacağını anlattı.

Bunun üzerine padişah, Dorino'ya müsamaha yapılmamasını buyurdu. Kaptan Yunus Paşa, Dorino'yu getirmek için Semadirek Adası'na 50 çiftelik bir kayık gönderdiğinden, kendi de Dorino'nun memurlarını değiştirip ve idareyi tanzim için ada'nın Kefaloz Koyu'na yanaştı ve haberci göndererek, ada'nın idaresini Kristobulos'a verdiğini bildirdi. Dorino ise, korktuğundan Yunus Paşa'nın gönderdiği kayığa binmeyip önce Enez'e oradan Edirne'ye varıp, padişahın huzuruna çıkarak af diledi ancak Kaptan Yunus Paşa'nın bu kişinin normal biri olmadığını adaları kendi içlerinden birine verilmesinin doğru olduğunu bildirmesi üzerine, Dorino'ya sadece Trakya'da birkaç köy tahsis edilerek, ada'nın idaresi Kristobulos'a verildi. (1456) Gökçeada bu şekilde 1460'a kadar Osmanlı idaresinde kalmıştır.

Doğru ve dürüst bir insan olduğunu ispatlayan Kristobulos, Mistra Despotu Demetrios Paleologos'a mektup yazarak, Midilli ve Gökçeada'nın Osmanlı hükümdarlığı'ndan elde etmenin zamanı olduğunu bildirdi. Bunun üzerine Paleologos, iki adamını Fatih'e gönderdi. O sırada Mora Fethi'ni tamamlamış olan Fatih, Despot Demetrios'a Limni ve Gökçeada'nın idaresini verdi. Gökçeada Venedik ve Osmanlılar arasında cereyan eden bazı olaylara sahne oldu. Papalık donanmasının ada'ya hücumu Kristobulos tarafından diplomasi ile savuşturuldu. Ada 1466'da Venediklilerin eline geçti ise de birkaç yıl sonra, kesin olarak 1470 yılında tekrar Türkler tarafından alındı. Ada halkının vergi haricinde devlete karşı bazı vazifeleri vardı. Ada'nın kalelerini ve yalılarını korumakla görevliydiler. Kendilerine hizmet karşılığı dirlik verilirdi. Ancak, meydana gelen zarar neticesinde dirlikleri ellerinden alınırdı. Gökçeada 17. yy ortalarında Girit Savaşı sebebi ile Venedik Donanması ile yapılan mücadelelere sahne oldu. 1655'de Kaptan-ı Derya olan Ali Paşa, donanma ile, boğaz, Venedik Donanması tarafından kapatılmış iken, Akdeniz'den çıkıp Girit'e gitmeye teşebbüs etmişti. Derya Beylerinin filoları Venedik donanması ile karşılaştığında, top atışları ile başlayan savaşın sonucu bilinmemektedir. Ada Venedik donanmasının, sık sık sığındığı bir yer oldu.

1698 tarihinde 73 parçalık donanma ile ada'nın kömür Limanı'na girip ada halkını haraca kesmiştir. Bu durumu öğrenen Boğazhisar muhafızı Vezir İbrahim Paşa, haberi İstanbul'a ulaştırdı. Bunun üzerine Mustafa Ağa 30 fırkatalık donanma ile Türk kıyılarını savunmak için Gökçeada'ya hareket etti. Bunun üzerine 21 Ağustos 1698'de Venedik donanması çatışmadan korkarak ada'dan kaçtı. Venedik donanmasını Midilli Adası'nın Zeytin Burnunda yakalayan Türk donanması, bu savaşı da zaferle kazandı. Balkan Savaşları sırasında, Kefaloz açıklarında, İmroz Deniz Savaşı adı altında bir savaş olmuştur. Savaşın ilk ateşini 16 Aralık 1912'de Barbaros ve Turgut Reis, Averof zırhlısına açmıştır. Yunan komutan muhabereyi kesip Mondros Limanı'na doğru hareket edince savaş bitmiş oldu. Çeşitli nedenlerle göçlerin yaşandığı Gökçeada, çok değişken bir nüfusa sahip idi; Lozan Anlaşması neticesinde, 22 Eylül 1923'te Türkiye Cumhuriyeti topraklarına fiilen katılmıştır.

Yerleşim birimleri

Merkez / Çınarlı
Adanın merkezidir. Kamu kurumları ve nüfusun çoğu buradadır. Eskiden tarifeli seferler yapılmış olan bir havaalanı mevcuttur. Yunanca adı "Panaghia"'dır. Kaleköy, Zeytinliköy, Eski ve Yeni Bademli köyleri çok yakındır.

Dereköy

Adanın iç batı kesimindedir. Cumhuriyetin ilk yıllarında Türkiye'nin en büyük köyü olarak kabul edilmektedir. 1970'li yıllara kadar Gökçeada'nın en büyük köyü olma niteliğini korumuştur. Yoğun göç vermesi nedeniyle şu anda terk edilmiş durumdadır. Dereköy'ün Yunanca adı "Shinudi"'dir. Meryem Ana bayramında (15 Ağustos) yurtdışına göç edenler, çocukları ve torunlarının geri dönmesiyle köy hareketlenir.

Kaleköy
Adanın kuzeydoğusundadır. Kaleköy iskelesi, I. Dünya Savaşı sırasında Fransız Donanma Kumandanlığı tarafından düzenlenmiş, 1970'li yıllarda Kuzulimanı'na yeni iskele yapılıncaya kadar tüm adanın ulaşımını sağlamıştır. Ancak küçük tonajlı gemilerin ve yatların yanaşması için uygundur. Bu yıllara kadar adanın ulaşımı, Ayvalık ve Gemlik adlı yolcu gemileri ile sağlanmıştır. Yunanca adı "Kastro"'dur.

Haftada iki kez (Çarşamba ve Cumartesi) saat 23:00 civarında adaya ulaşan bu gemiler iskeleye yanaşamadıkları için yaklaşık 1,6 km açıkta demirlemek zorunda kalırlardı. Gemiler ile iskele arasında ulaşım balıkçı/süngerci tekneleri ile sağlanırdı. Kaleköy iskelesinin hemen sağ tarafında yer alan tepenin üzerinde köye eski ismini veren kale yer almaktadır.

Zeytinli

Adanın kuzey iç kesimlerinde, Merkez ilçeye çok yakın eski bir Rum köyüdür. Hâlen küçük bir Rum kökenli nüfus yaşamaktadır. Ayrıca Fener Rum Patriği Bartholomeos'un doğum yeridir. Yunanca adı "Aya Teodoroi"'dir. Köyde Rum İlkokulu bulunur.

Tepeköy
Adanın kuzeyinde bir Rum köyüdür. Hâlen küçük bir Rum kökenli nüfus yaşamaktadır. Yunanca adı "Agridya"'dır. Köyde Rum Lisesi ve Ortaokulu bulunur.

Uğurlu
Türkiye'nin en batı noktasında yer almaktadır. Köyün adının nereden geldiği ve geçmişi hakkında bilgi yoktur. Muğla ve Burdur illerinden 1970'li yıllarda ailelerin yerleştirilmesi ile köy teşekkül etmiştir. İlçe merkezine 25 km uzaklıktadır.

Ekonomisi tarım, hayvancılık, balıkçılık, ve turizme dayalıdır. Ev pansiyonculuğu başlıca gelir kaynaklarından olup, çok sayıda pansiyon bulunmaktadır. Özellikle kamp severler için deniz ve doğanın birleştiği sakin koylar mevcuttur.

Köyde, ilköğretim okulu ve sağlık ocağı mevcuttur. Köyün içme suyu şebekesi ve kanalizasyon şebekesi bulunmaktadır. Köy içinin yolları taşla kaplıdır. PTT şubesi yoktur ancak PTT acentesi vardır. Köye ulaşımı sağlayan yol asfalt olup köyde elektrik, sabit telefon ve internet vardır. Uğurlu köyü denize 100 metre mesafede olmakla birlikte, adanın iki iskelesinden biri Uğurlu köyünde bulunmaktadır. Limni Adası'na 20 km mesafede bulunması itibarıyla adalar arası turizm, ilerisi için Uğurlu köyünün yeni yüzünü belirleyebilir.

Bademli
Adanın kuzeydoğusunda, merkez ilçe ile Kaleköy arasında yer alır. Bademli'nin Yunanca adı "Gliki"'dir.

Yenibademli
Yeni kurulan köylerdendir, Isparta'lı aileler iskan edilmiştir. Adanın kuzeydoğusundadır, motel ve pansiyon bölgesidir. Denize uzaklığı 500 metredir. Adanın en büyük köyüdür.

Eşelek
Yeni kurulan köylerdendir, Çanakkale'li aileler iskan edilmiştir. Adanın güneydoğusunda olan Eşelek, bir tarım bölgesidir ve sebze meyve üretilir.

Şahinkaya
Adanın yerleşik ilk Türk köyüdür. 1973-1974 yıllarında Trabzon ili Çaykara ilçesi Şahinkaya (Şur) köyünden iskân gelmiştir. Tarım, hayvancılık, son yıllarda pansiyonculuk yapılmaktadır. Köyün tam karşısı çam ormanı ile kaplıdır. Köyün içme suyu 3 farklı yeraltı kaynağının beslediği depodan gelmektedir. Köy adanın güney sahillerine yakın, Laz Koyuna 5 km civarındadır. Köy içinde zeytinyağı, bal, oğlak eti, kuzu eti, keçi peyniri temin edilebilir.

Şirinköy
Yeni kurulan köylerdendir, 80 sonrası Bulgaristan göçmenlerinin iskan edilmiştir.

Fatih
Adanın en kalabalık ve ada merkezinin bir kısmını içine alan bir mahalledir.

Tarihi Yapılar

Camiler

Camiiler, nüfusun etnik yapısına bağlı olarak ada mimarisinde pek yer bulmamıştır. Adadaki Osmanlı Dönemi'ne ait tek cami, Çınarlı Mahallesi'nde yer alan ve bugün Merkez Cami olarak anılan yapıdır.

Caminin kesin yapım tarihi bilinmemektedir. Ancak, 1878 tarihli Osmanlı arşivinde Hamidiye Camii ile birlikte 1885 ve 1889 tarihli arşiv belgelerinde padişahın ismine izafeten yaptırılan bir caminin bahsi geçmektedir. Tarihi yayınlar da 1895 yılında adada yalnızca bir caminin varlığına işaret eder. Söz konusu belge ve yayınlarda bahsi geçen yapının bu günkü cami olması kuvvetle muhtemeldir.

Kayıtlara göre 1907 yılında büyük oranda yenilenen cami yakın zamanda da esaslı bir onarım geçirmiştir. Kuzey-güney yönde dikdörtgen prizmal bir kütle teşkil eden cami kırma çatı ile örtülür. Sonradan eklendiği anlaşılan kuzeydoğu köşedeki minare, cami boyutlarıyla dengeli bir orantıya sahiptir. Kaba yontu ve moloz taşla inşa edilen caminin pencere söve ve lentoları düzgün kesme taştır. Yalın mimarisi ve boyutları ile bir mahalle mescidi özelliği gösteren yapı bölgenin mimari dokusuyla uyum içindedir. Kuzey eksendeki sade bir kapıdan girilen harim ahşap düz tavanla örtülüdür. Sonradan sıvanarak badana edilen iç mekân tarihi dokusunu kaybetmiştir.

Merkez Camisi dışında Gökçeada'da farklı bir tarihi cami bulunmasa da mübadele öncesi Biga'da yer alan Eşelek Köyü, mübadele sonucu adaya yerleştirildiğinde eski köy camisinin minaresini de beraberlerinde getirmişlerdir. Bu iki cami ile birlikte Gökçeada'daki köylerde sonradan yapılan pek çok Gökçeada camileri bulunmaktadır.

Kilise ve manastırlar
Gökçeada, tarihi boyunca farklı uygarlıkların iktidar mücadelelerine sahne olduğu için dilinden, yemeklerine, yapılarından, dinine kadar sürekli köklü değişimler geçirmiştir. Bu yüzden adada camilerle birlikte Rumlardan kalma tarihi kiliseler ve manastırlar bulunur. Resmi kayıtlara göre 19. yüzyılın sonlarında adada sekiz kilise bulunmaktadır. Yapılan araştırmalar ise onbir adet kilisenin varlığına işaret eder.

Gökçeada'nın merkezindeki üç mahalleden biri olan Çınarlı Mahallesi'ndeki Aya Panayia Kilisesi, 1835 yılında inşa edilmiş ve hala kullanılan Gökçeada kiliselerinden biridir. Merkezdeki diğer bir mahalle olan Fatih Mahallesi'nde Metropolitan Kilisesi yer almaktadır. Yeni Mahalle'deki Aya Varvara Kilisesi ise yanındaki eski çeşmesiyle dikkat çekmekte. Gökçeada'da sahil kısmında bulunan tek yerleşim yeri olan Kaleköy'deki Aya Marina Kilisesi, adadaki restore edilmiş kiliselerinden.

Gökçeada'nın en eski kilisesi olan Agios Georgios Zeytinliköy'de bulunmaktadır. Ayrıca dünyadaki 300 milyon Ortodoks Hristiyan'ın ruhani lideri olan 1. Bartholomeos 1940 yılında Zeytinli'de doğmuş. 1991 yılında Patrik ilan edilen Bartholomeos, senede birkaç kez doğduğu evi ziyarete geliyor. Tepeköy'de, 1832 yılında inşa edilen Evangelismos Teotoku Kilisesi ve eski Rum Mezarlığı bulunur. Gökçeada'daki Rum köylerinden olan Dereköy'de ibadete açık iki kilise bulunmaktadır. Köyün girişindeki Hagia Marina Kilisesi ve çarşıdaki Koimesistis Theotokos Kilisesi. İkisi de 1800'lü yılların başında inşa edilmiş.

Manastırlar

Kiliselerle birlikte adada yaklaşık 360 şapelin varlığından söz edilir. Halkın 'manastır' olarak da adlandırdığı şapeller ibadetin yanında, kötülüklerden korumak ve bereket getirmesi amacıyla, başta kent merkezleri olmak üzere adanın her yerine inşa edilmiştir.

Kaya Mezarları
Kaya mezarları adanın birçok noktasında bulunmaktadır, ancak mezarların hepsi tahrip edilmiştir. Mezarların hangi dönemde yapıldıkları bilinmemektedir.

Ada'daki kaya mezarları genellikle tuz gölü yakınında'ki eski askeri bölge ve Kokina Mevkiin'de bulunmaktadır.

Kaleler
Gökçeada'da 2 tane kale bulunmaktadır kalelerden bir tanesi ve en meşhur olanı Kaleköy'de bulunmaktadır diğeri ise pek bilinmemektedir ve Dereköy'de bulunmaktadır.

İskiter (Kastro) Kalesi

Yukarı Kaleköy mevkiinde bulunan İskiter kalesi adanın en eski yapılarından birisidir. Cenevizliler tarafından inşa edilen kalenin surlarının bir kısmı hala ayaktadır. İskiterkalesi, Çınarlı Ovasına hakim bir tepededir. Kalenin bulunduğu mevkiden aşağı Kaleköy, Yeni bademli, Eski bademli ve Zeytinli köyleri net olarak görülebilir.

Ayrıca, yapısı nedeniyle tıpkı bir yelkeni andıran ve ancak denizden ulaşılabilen Yelkenkaya'yı da kuzeydoğu yönüne bakıldığında görmek mümkündür.

İskinit (Paleokastro) Kalesi

Dereköy mevkiinde bulunan İskinit kalesi adanın en eski yapılarından birisidir. Tam olarak ne zaman yapıldığı bilinmemektedir. Halk arasında Şeytan veya Korsan kalesi olarak'da geçmektedir. Gökçeada'ya hakim bir tepede bulunmaktadır kale adanın her noktasını görebilmektedir. Kale'ye ulaşmak ise oldukça zordur yüksek bir nokta'da bulunmaktadır ve bu noktaya giden bir yol veya patika yoktur.

Çamaşırhaneler
Çamaşırhaneler ada geleneğinde önemli bir yere sahipti. Geçmiş yıllarda, her köyün özel bir çamaşır yıkama günü olmakta ve kadınlar arasında aynı zamanda haberleşme ve yiyecek-içecek sunma günü olarak geçmekteydi.

Anadolu'da "yunak" olarak da adlandırılan çamaşırhaneler, kadınların belirli günlerde toplanıp çamaşır yıkadıkları ve sonrasında kapılarını kapatarak yıkandıkları yapılardır.

Ada'daki hemen her köyde birden çok çamaşırhane bulunmaktaydı. Bunlar bir cephesi açık veya kapalı dikdörtgen planlı basit yapılardır. Geleneksel yığma taş duvarla inşa edilen yapıların üzerleri kiremit kaplı kırma çatılarla örtülüdür. İçerisinde yer alan çeşmeler, kazanlarda suların ısıtıldığı ocaklar, çamaşır yıkama tekneleri, sekiler, malzemelerin konduğu nişler ve suların atıldığı açık kanallar bu yapıların temel unsurlarıdır.

Dereköy'deki Hagia Panaghia Kilisesi yanında yer alan çamaşırhane bunların anıtsal bir örneğini teşkil eder.

Nüfus

Gökçeada'da Nüfus Değişimi

Tanınmış Gökçeadalılar

 I. Bartholomeos İstanbul Ortodoks Patrikhanesi Ekümenik Patriği ve İstanbul Başpiskoposu. Tarihten günümüze 270. ve mevcut Ekümenik Patrik ve İstanbul Başpiskoposu'dur.
 Mustafa Ruhi Efendi 19. yüzyılın önemli dini ve siyasi lideri. Mustafa Ruhi Efendi hem bir Nakşibendi şeyhi hem de Arnavut kökenliler için önemli bir siyasi temsilcisidir.
 Amerika Başpiskoposu Lakovos Kuzey ve Güney Amerika Başpiskoposu Iakovos, 1959'dan 1996'daki istifasına kadar Kuzey ve Güney Amerika'daki Yunan Ortodoks Başpiskoposluğunun primatıydı.
 Apostolos Christodoulou İstanbul Ekümenik Patrikhanesi'nin bir rahip, teolog ve Büyükşehir piskoposuydu.
 Michael Critobulus Yunan politikacı, bilgin ve tarihçiydi. Sultan II. Mehmet döneminde Doğu Roma İmparatorluğu'nun Osmanlı fethi tarihinin yazarı olarak bilinir.

Gökçeada'nın önemli yerleri

 Aydıncık/Kefaloz Mevkii ve Plajı: Ada'nın güneydoğusunda uzunca bir plajdır, tesisleri mevcuttur, yelken sörfü için idealdir.
 Kefaloz Burnu: Ada'nın güneydoğusundadır.
 Kapıkaya Mevkii: Ada'nın güneyindedir, tesisi olmayan bir plajı vardır.
 Kaşkaval Burnu/Peynir Kayalıkları: Ada'nın kuzeydoğusundadır, dalış için idealdir.
 Kaynarburun: Ada'nın doğusunda, Kuzulimanı'nın güneyinde burun
 Kokina Mevkii:
 Kömür Burnu: İnceburun'un kuzeyinde burun.
 Kuzulimanı: Adanın doğusundadır, Eceabat Kabatepe'den ve Çanakkale'den feribot seferleri yapılır.
 Mavikoy/Lacivertkoy: Türkiye'nin ilk ve tek su altı millî parkının bulunduğu yörededir, adanın kuzeydoğusundadır, dalış için idealdir.
 Lazkoyu: Ada'nın güneyindedir, tesisi mevcuttur, taşlık bir plajı vardır.
 Marmaros Mevkii: Ada'nın kuzeybatısındadır, şelalesi ile ünlüdür.
 Cugura Mevkii: Ada'nın iç orta kesimlerindedir.
 Gizli Liman: Ada'nın batısındadır, gümrük kurulması durumunda Limni adası ile karşılıklı feribot seferleri başlatılabilecektir, tesisi mevcut olan uzunca bir plajı vardır.
 İnceburun/İncir burnu: Türkiye'nin en batı noktasıdır.
 Pınarbaşı Mevkii
 Yelkenkaya Mevkii: Türkiye'nin ilk ve tek su altı millî parkının bulunduğu yörededir, adanın kuzeydoğusundadır, dalış için idealdir.
 Yıldızkoy: Türkiye'nin ilk ve tek su altı millî parkının bulunduğu yörededir, adanın kuzeydoğusundadır, dalış için idealdir. Tesisi mevcuttur.

Ayrıca bakınız
 Bozcaada
 Ege Adaları

Kaynakça

Dış bağlantılar
 Gökçeada Kaymakamlığı
 Gökçeada Belediyesi.

Gökçeada
Cittaslow

Gökçeada


Kim Jang-hoon (김장훈), né le , est un chanteur sud-coréen connu pour ses ballades rock.

Biographie
Kim Jang-hoon a rapidement quitté l'école pour devenir DJ dans des cafés. En 1991, il sort son premier album.

Discographie
Albums
1991 : Vol 1 always between you and I
1994 : Vol 2 Now
1997 : Vol 3 I just sang my song
1998 : Vol 4 1998 BALLADS FOR TEARS
1999 : Vol 5 Fool
2000 : Vol 6 INNOCENCE
2001 : Vol 7 Natural
2004 : Novelty Hero Newspaper with Cho PD
2005 : Vol A Piece
2006 : Vol 9 It's me
2007 : Project: Maestro
2010 : Letter to Kim Hyun Sik

Singles
2004 : Novelty Hero Newspaper with Cho PD
2010 : Make Me Cry Again (ft. Psy)

Notes et références

Naissance en août 1963
Naissance à Séoul
Chanteur sud-coréen
Chanteur de rock

Kim Jang-hoon


المبطوح، وهي قرية تونسية تقع في ولاية بنزرت.
 قرعة المبطوح، وهي قرعة تقع قرب قرية المبطوح بالشمال الشرقي التونسي.

مبطوح (توضيح)


Yağdere, Aydın'ın Sultanhisar ilçesine bağlı bir mahalledir. 2022 yılı itibarıyla Adrese Dayalı Nüfus Kayıt Sistemi'ne göre mahallenin nüfusu 349'dur.

Kaynakça

Sultanhisar'ın mahalleleri

Yağdere, Sultanhisar


Richard Mauze Burr (født 30. november 1955 i Charlottesville) er en amerikansk republikansk politiker. Han er medlem af USA's senat valgt i North Carolina siden 2005 Han var medlem af Repræsentanternes Hus i perioden 1995–2005.

Eksterne henvisninger

Medlemmer af USA's kongres for det republikanske parti
Medlemmer af Senatet i USA
Personer fra North Carolina

Richard Burr


Taşlıca, Tokat ilinin Reşadiye ilçesine bağlı bir köydür.

Tarihçe
Köyün adı, 1928 kayıtlarında Kotanı olarak geçmektedir.

Coğrafya
Köy, Tokat il merkezine 109 km, Reşadiye ilçe merkezine 20 km uzaklıktadır.

Nüfus

Kaynakça

Dış bağlantılar

Reşadiye belde ve köyleri

Taşlıca, Reşadiye


Kozja ćuprija nalazi se u klancu rijeke Miljacke nekoliko kilometara istočno od starog centra Sarajeva. Cesta na kojoj je premostila rijeku je poznati carigradski put, t.j. put kojim je išao tijekom osmanske vladavine, od Sarajeva do istočnih dijelova Carstva, sve do Carigrada. Kozja ćuprija jedan je od četiri stara mosta na području Grada koji su još uvijek sačuvani. Ostala tri mosta su Šeher-Ćehajina ćuprija, Latinska ćuprija i Rimski most (most na Plandištu kod Blažuja).

Podaci o vremenu gradnje mosta su rijetki, a dokumenti navode samo okvire njegovog porijekla. Ovaj most ima jedan luk s dva kružna otvora. Dug je 42 m, a širok 4,75 m. Raspon svoda je 17,5 m. Izgrađena je od vapnenca i sedre.

U osmansko doba Kozja ćuprija bila je mjesto gdje su se dočekivali carski namjesnici – veziri. Na mostu bi dočekan svaki novi vezir. Svi istaknuti ljudi u Sarajevu izlazili bi pred njega i okupljali bi se obični ljudi, jer je to bio jedan od najvažnijih događaja. Također se spominje da bi u čast novog vezira neki od hrabrijih momaka skočili s mosta u Miljacki, a on bi im dao novac (ovaj skok podvig je divljenja, jer Miljacka nema dubine na tom mjestu, i visina mosta je stvarno velika).

O podrijetlu ovog mosta postoji narodna legenda. Kaže da je siromašni pastir čuvajući koze primijetio da su se neobično dugo zadržavali oko nekih grmova na rijeci. Kad je malo bolje pogledao ispod tog grma, pronašao je staklenku punu zlatnika. Tim je novcem platio školovanje, a nakon mnogo godina, otkako je postao ugledni i bogati podanik Carstva, odlučio je sagraditi most na Miljacki, na istom mjestu gdje su jarci ukazivali na njegovo zlato.

Međutim, danas se vjeruje da je ovaj most nastao tijekom velike akcije uređenja putne mreže, u doba Mehmed-paše Sokolovića (veliki vezir 1565. – 1579.). Tada su u Bosni i Hercegovini izgrađeni još neki poznati mostovi – most Arslanagića kod Trebinja, Stari most u Mostaru i poznata Ćuprija na Drini u Višegradu.

Danas je Kozja ćuprija mjesto gdje se Sarajlije mogu opustiti i uživati u okolnoj prirodi. Do njega vodi pješačka staza uz Miljacku koja započinje na Darivi, u blizini Gradske vijećnice.

Zaštita
Komisija za očuvanje nacionalnih spomenika, na sjednici održanoj od 30. kolovoza do 4. rujna 2004. godine, odlučila je most odrediti nacionalnim spomenikom Bosne i Hercegovine. Tu odluku Komisija je donijela u sljedećem sastavu: Zeynep Ahunbay, Amra Hadžimuhamedović, Dubravko Lovrenović, Ljiljana Ševo (predsjedavajuća), Tina Wik.

Izvori

Pješački mostovi u Sarajevu
Mostovi na Miljacki

Kozja ćuprija


La Organización Panamericana de Río de Janeiro es un complejo residencial inaugurado en 2007, construido especialmente para los Juegos Panamericanos 2007 .

Está ubicada en la Avenida Ayrton Senna en Jacarepaguá. Los inmuebles fueron vendidos al acabar los juegos. Hasta el 10 de mayo de 2007, el 98% de la propiedad había sido vendida. Los precios oscilan entre $ 146.000 y $ 512.000.
Los 17 edificios que conforman la ciudad y fueron residencia de los 5.500 atletas de 42 países que participan en los juegos sumaban un costo total de $ 31.8 millones (casi 16 millones de dólares).

Juegos Panamericanos de 2007
Economía de Brasil

Panamericana (Río de Janeiro)


مريجات قد تعني:

 مريجات (عاليه) القرية اللبنانية في قضاء عاليه.
 مريجات (زحلة) القرية اللبنانية في قضاء زحلة.
 مريجات (الشوف)القرية اللبنانية في قضاء الشوف.

مريجات (توضيح)


An Calamagrostis tacomensis in uska species han Liliopsida nga ginhulagway ni K.L.Marr ngan Hebda. An Calamagrostis tacomensis in nahilalakip ha genus nga Calamagrostis, ngan familia nga Poaceae. Waray hini subspecies nga nakalista.

Mga kasarigan

Calamagrostis

Calamagrostis tacomensis


is a district located in Hiroshima Prefecture, Japan. Currently the district has only the town of Ōsakikamijima.

As of April, 2008, the district has an estimated population of 8,739 and a Density of 202 persons/km2. The total area is 43.28 km2.

The towns and villages within Toyota District (As of the city, town, and village status enforcement in 1889)
 Setoda (瀬戸田町)
 Tadanoumi (忠海町)
 Mitarai (御手洗町)
 Ōkawa (大河村)
 Ōgusa (大草村)
 Ōsakinakano (大崎中野村)
 Ōsakiminami (大崎南村)
 Ōchō (大長村)
 Ōnori (大乗村)
 Kamikitagata (上北方村)
 Kawamoto (川源村)
 Kitaikuchi (北生口村)
 Kidani (木谷村)
 Kuba (久芳村)
 Kuwanashi (椹梨村)
 Koizumi (小泉村)
 Kōnejima (高根島村)
 Kodani (小谷村)
 Saezaki (佐江崎村)
 Sagiura (鷺浦村)
 Shimokitagata (下北方村)
 Sunami (須波村)
 Zennyūji (善入寺村)
 Takasaka (高坂村)
 Takeni (竹仁村)
 Tanoura (田野浦村)
 Tamari (田万里村)
 Tono (戸野村)
 Toyota (豊田村)
 Toyohama (豊浜村)
 Nagatani (長谷村)
 Nishiikuchi (西生口村)
 Nishino (西野村)
 Nyūno (入野村)
 Nutanishi (沼田西村)
 Nutahigashi (沼田東村)
 Nomi (乃美村)
 Higashiikuchi (東生口村)
 Higashino (東野村)
 Hisatomo (久友村)
 Funaki (船木村)
 Hongō (本郷村)
 Minamiikuchi (南生口村)
 Minamigata (南方村)
 Myōga (名荷村)
 Yoshina (吉名村)

(total of 3 towns, 43 villages)

Timeline (April 1, 1889~March 31, 1956)
 April 1, 1889 Municipal status enforced. It had 3 towns and 43 villages in the past.
 January 1, 1903 The village of Saezaki added Kuwaki from the village of Tanoura.
 April 1, 1917 The village of Ōsakinakano renamed to the village of Nakano.
 January 1, 1920 Parts of the village of Nakano (Noga, etc.) and Higashino (Dochu, etc.) broke off and created the town of Kinoe within the areas (4 towns, 43 villages).
 April 1, 1924 The village of Ōkawa gained town status to become the town of Kōchi (1st generation) (5 towns, 42 villages)
 April 1, 1924 The village of Hongō gained town status to become the town of Hongō (1st generation) (6 towns, 41 villages).
 April 1, 1929 The village of Saizaki renamed and gained town status to become the town of Saizaki (幸崎町) (7 towns, 40 villages).
 November 15, 1936 The villages of Sunami and Tanoura merged with the towns of Itozaki, Mihara, and the villages of Nishino and Yamanaka, Mitsugi District to form the city of Mihara (1st generation) (7 towns, 38 villages)
 April 1, 1937 The town of Setoda and the village of Nishiikuchi merged to form the town of Setoda (7 towns, 37 villages).
 February 20, 1941 The village of Ōchō changed the pronunciation to Daichō.
 January 1, 1943 The village of Kidani merged with the towns of Mitsu and Hayatahara from Kamo District to form the town of Akitsu in Kamo District (7 towns, 36 villages)
 October 1, 1943 The town of Kinoe (木ノ江町) becomes the town of Kinoe (木江町).
 January 1, 1944 The village of Kawamoto and Nomi merged to form the village of Toyosaka (7 towns, 35 villages).
 April 1, 1944 The town of Setoda and the villages of Kitaikuchi, Kōnejima, and Myōga merged to form the town of Setoda (7 towns, 32 villages)
 August 9, 1947 The village of Daichō changed the pronunciation to Ōchō.
 April 1, 1949 The village of Toyosaka gained town status to become the town of Toyosaka (8 towns, 31 villages)
 June 10, 1950 The village of Zōga (now the city of Higashiiroshima) added Zōga from the village of Tono.
 April 1, 1951 The villages of Kamikitagata, Shimokitagata, and Zennyūji merged to form the village of Kitakata (8 towns, 29 villages).
 April 1, 1951 The village of Sakaibara from Mitsugi District (now the city of Mihara) added parts of the village of Takasaka (Kobayashi, Tsuchitori, Yamanakano).
 November 3, 1951 The village of Ōgusa added Ubagahara from the village of Funaki.
 March 22, 1953 The village of Nagatani along with the village of Yahata from Mitsugi District merged into the city of Mihara (8 towns, 28 villages).
 May 1, 1953 The village of Higashiikuchi merged with the towns of Mitsunoshō, Takuma, Habu, and the villages of Ōhama, Shigei, and Nakanoshō from Mitsugi District to form the city of Innoshima (8 towns, 27 villages).
 March 31, 1954 The village of Ōnori and parts of the village of Minamigata along with the village of Higashino from Kamo District merged into the town of Takehara in Kamo District (8 towns, 26 villages).
 April 1, 1954 The village of Koizumi, Nutanishi, and Nutahigashi merged into the city of Mihara (8 towns, 23 villages).
 November 3, 1954 The town of Hongō and the village of Kitagata, Funaki, and Minamigata to form the town of Hongō (8 towns, 20 villages).
 March 31, 1955 The town of Tamari merged with the town of Takehara along with the village of Shōno from Kamo District to become the town of Takehara in Kamo District (8 towns, 19 villages).
 March 31, 1955 The town of Kōchi (1st generation) and the villages of Tono and parts of Oda in the village of Toyota merged to form the town of Kōchi (8 towns, 18 villages).
 March 31, 1955 The villages of Ōgusa, Kuwanashi, and Toyota (excluding parts of Oda) merged with the village of Kanda from Sera District to form the town of Daiwa. As a result, the village of Toyota dissolved (9 towns, 15 villages).
 March 31, 1955 The villages of Nakano and Higashino merged and gained town status to become the town of Ōsaki (10 towns, 13 villages).
 March 31, 1955 The town of Kinoe and the village of Ōsakiminami merged to form the town of Kinoe (10 towns, 12 villages).
 March 31, 1955 The village of Kodani merged into the village of Takaya in Kamo District (now the city of Higashihiroshima) (10 towns, 11 villages).
 April 1, 1955 The town of Setoda and the village of Minamiikuchi merged to form the town of Setoda (10 towns, 10 villages).
 July 10, 1955 The villages of Kuba and Takeni merged and gained town status to become the town of Fukutomi (11 towns, 8 villages).
 March 31, 1956 The town of Mitarai along with the villages of Ōchō and Hisatomo merged to form the town of Yutaka (11 towns, 6 villages).
 March 31, 1956 The city of Mihara absorbed the village of Takasaka (11 towns, 5 villages)

The towns and villages of Toyota District as of March 31, 1956 (before the change to the municipalities within both Kamo and Toyota Districts)
 Ōsaki (大崎町; -cho) → Remained in Toyota District
 Kinoe (木江町; -cho) → Remained in Toyota District
 Kōchi (河内町; -cho) → Moved to Kamo District (Merged into the city of Higashihiroshima on February 7, 2005)
 Saizaki (幸崎町; -cho) → Remained in Toyota District
 Setoda (瀬戸田町; -cho) → Remained in Toyota District
 Daiwa (大和町; -cho) → Moved to Kamo District (Moved to the city of Mihara (2nd) on March 22, 2005)
 Tadanoumi (忠海町; -cho) → Remained in Toyota District
 Toyosaka (豊栄町; -cho) → Moved to Kamo District (Merged into the city of Higashihiroshima on February 7, 2005)
 Fukutomi (福富町; -cho) → Moved to Kamo District (Merged into the city of Higashihiroshima on February 7, 2005)
 Hongō (本郷町; -cho) → Remained in Toyota District
 Yutaka (豊町; -machi) → Remained in Toyota District
 Sagiura (鷺浦村; -mura) → Remained in Toyota District
 Toyohama (豊浜村; -mura) → Remained in Toyota District
 Nyūno (入野村; -mura) → Moved to Kamo District (Merged into the town of Kōchi, Kamo District, on September 30, 1956)
 Higashino (東野村; -mura) → Remained in Toyota District
 Yoshina (吉名村; -mura) → Remained in Toyota District

(total of 11 towns, 5 villages)

The towns and villages of Toyota District as of April 1, 1956 (after the change to the municipalities within both Kamo and Toyota Districts)
 Akitsu (安芸津町; -cho) → Moved from Kamo District
 Ōsaki (大崎町; -cho)
 Kawajiri (川尻町; -cho) → Moved from Kamo District
 Kinoe (木江町; -cho)
 Saizaki (幸崎町; -cho)
 Setoda (瀬戸田町; -cho)
 Takehara (竹原町; -cho) → Moved from Kamo District
 Tadanoumi (忠海町; -cho)
 Hongō (本郷町; -cho)
 Yasuura (安浦町; -cho) → Moved from Kamo District
 Yutaka (豊町; -machi)
 Ato (安登村; -mura) → Moved from Kamo District
 Kanaga (賀永村; -mura) → Moved from Kamo District
 Sagiura (鷺浦村; -mura)
 Toyohama (豊浜村; -mura)
 Higashino (東野村; -mura)
 Yoshina (吉名村; -mura)

(total of 11 towns, 6 villages)

Timeline (April 1, 1956~Present)
 April 1, 1956 4 towns and 1 village within Toyota District moved to Kamo District, while 4 towns and 2 villages within Kamo District moved to Toyota District. At this time, the district had 11 towns and 6 villages.
 September 30, 1956 The town of Saijō, Kamo District (now: the city of Higashihiroshima) absorbed the parts of Niga in the village of Kanaga.
 September 30, 1956 The town of Takehara, Kamo District, absorbed the villages of Yoshina and Kanaga (excluding parts of Nika). As a result, the village of Kanaga dissolved (11 towns, 4 villages)
 September 30, 1956 The city of Mihara absorbed the town of Saizaki and the village of Sagiura (10 towns, 3 villages)
 April 1, 1958 The village of Ato breaks up, merges into the towns of Kawajiri (小用・水落・竜王山と寒風の一部) and Yasuura (前記以外の部分), and dissolves (10 towns, 2 villages).
 November 3, 1958 The towns of Takehara and Tadanoumi merged and gained city status to become the city of Takehara (8 towns, 2 villages).
 April 1, 1964 The village of Higashino gained town status to become the town of Higashino (9 towns, 1 villages).
 November 3, 1969 The village of Toyohama gained town status to become the town of Toyohama (10 villages)
 April 1, 2003 The towns of Ōsaki, Kinoe, and Higashino merged to form the town of Ōsakikamijima (8 towns).
 April 1, 2004 The city of Kure absorbed the town of Kawajiri (7 towns).
 February 7, 2005 The city of Higashihiroshima absorbed the town of Akitsu (6 towns).
 March 20, 2005 The city of Kure absorbed the towns of Toyohama, Yasuura, and Yutaka (3 towns).
 March 22, 2005 The town of Hongō merged with the city of Mihara, the town of Daiwa, from Kamo District, and the town of Kui, from Mitsugi District, to form the new city of Mihara (2 towns).
 January 10, 2006 The city of Onomichi absorbs the city of Innoshima and the town of Setoda (1 town).

See also
Toyota District, Ibaraki
Toyota District, Tōtomi
Toyota District, Kagawa

Toyota District

Toyota District, Hiroshima


Arthropteris es un género de helechos perteneciente a la familia Tectariaceae.

Taxonomía
El género fue descrito por John Smith (botánico) y publicado en Blumea 30: 3. 1984. La especie tipo es: Aenigmopteris dubia (Copel.) Holttum

Especies aceptadas
A continuación se brinda un listado de las especies del género Arthropteris aceptadas hasta enero de 2013, ordenadas alfabéticamente. Para cada una se indica el nombre binomial seguido del autor, abreviado según las convenciones y usos:

Especies
Arthropteris albopunctata J. Sm.
Arthropteris altescandens J. Sm.
Arthropteris monocarpa (Cordem.) C. Chr.
Arthropteris orientalis (J.F. Gmel.) Posth.
Arthropteris palisotii (Desv.) Alston
Arthropteris parallela C. Chr.
Arthropteris repens (Brack.) C. Chr.
Arthropteris tenella (G. Forst.) J. Sm. ex Hook. f.

Referencias

Enlaces externos

Tectariaceae

Arthropteris


STS-35 was the tenth flight of Space Shuttle Columbia, the 38th shuttle mission.  It was devoted to astronomical observations with ASTRO-1, a Spacelab observatory consisting of four telescopes. The mission launched from Kennedy Space Center in Florida on December 2, 1990.

Crew

Backup crew

Crew seating arrangements

Crew notes
Prior to the Challenger disaster, this mission was slated to launch in March 1986 as STS-61-E. Jon A. McBride was originally assigned to command this mission, which would have been his second spaceflight. He chose to retire from NASA in May 1989 and was replaced as mission commander by Vance D. Brand. In addition, Richard N. Richards (as pilot) and David C. Leestma (as mission specialist), were replaced by Guy S. Gardner and John M. Lounge respectively. Fifty-nine year-old Brand was the oldest astronaut to fly into space until F. Story Musgrave, 61 on STS-80 in 1996, and U.S. Senator John H. Glenn Jr., 77 when he flew on STS-95 in 1998.

Preparations and launch

The much-delayed ASTRO-1 had originally been manifested to fly on what would have been the next shuttle mission after Challenger's ill-fated STS-51-L as STS-61-E in March 1986. The mission was remanifested as STS-35 during the long stand-down after the accident with the addition of the Broad Band X-ray Telescope (BBXRT-01), and the original ASTRO-1 payload was brought out of storage and recertified for flight. Columbia rolled out to Pad 39A in late April 1990 for a scheduled launch date of May 16, 1990. Following the Flight Readiness Review (FRR), announcement of a firm launch date was delayed to change a faulty freon coolant loop proportional valve in the orbiter's coolant system. At the subsequent Delta FRR, the date was set for May 30, 1990. Launch on May 30 was scrubbed during tanking due to a minor hydrogen leak in the tail service mast on the mobile launcher platform and a major leak in the external tank/orbiter quick disconnect assembly. Hydrogen was also detected in the orbiter's aft compartment and believed to be associated with a leak involving the  umbilical assembly.

Leakage at the  umbilical was confirmed by a mini-tanking test on June 6, 1990. The leakage could not be repaired at the pad, and the vehicle was rolled back to the Vehicle Assembly Building (VAB) June 12, 1990, demated, and transferred to the Orbiter Processing Facility (OPF). The orbiter-side  umbilical assembly was replaced with one borrowed from Endeavour, then still under construction. The external tank (ET) was then fitted with new umbilical hardware. The ASTRO-1 payload was reserviced regularly and remained in Columbias cargo bay during orbiter repairs and reprocessing.

Columbia was rolled out to Pad A for the second time on August 9, 1990, to support a September 1, 1990, launch date. Two days before launch, the avionics box on the BBXRT-01 portion of the ASTRO-1 payload malfunctioned and had to be changed and retested. Launch was rescheduled for September 6, 1990. During tanking, high concentrations of hydrogen were again detected in the orbiter's aft compartment, forcing another postponement. NASA managers concluded that Columbia had experienced separate hydrogen leaks from the beginning: one of the umbilical assembly (now replaced) and one or more which had resurfaced in the aft compartment. Suspicion focused on the package of three hydrogen recirculation pumps in the aft compartment. These were replaced and retested. A damaged Teflon cover seal in the main engine number three hydrogen prevalve was replaced. Launch was rescheduled for September 18, 1990. The fuel leak in the aft compartment resurfaced during tanking, and the launch was scrubbed again. The STS-35 mission was put on hold until problem resolved by a special tiger team assigned by the Space Shuttle director.

Columbia was transferred to Pad B on October 8, 1990, to make room for Atlantis on Mission STS-38. Tropical storm Klaus forced another rollback to the VAB on October 9, 1990. The vehicle was transferred to Pad B again on October 14, 1990. Another mini-tanking test was conducted on October 30, 1990, using special sensors and video cameras and employing a see-through Plexiglas aft compartment door. No excessive hydrogen leakage was detected. With the problem resolved, the flight had only to wait for the completion of STS-38, imparting another four-week delay. A scheduled launch date of November 30, 1990, was moved by several days due to concerns that observations of astronomical targets would be adversely affected. Liftoff on December 2, 1990, was delayed by 21 minutes to allow the U.S. Air Force time to observe low-level clouds that might impede the tracking of the Shuttle's ascent. Liftoff finally occurred on December 2, 1990, 1:49:01 a.m. EST, the ninth night launch in shuttle history and the second for Columbia. A nominal ascent to orbit followed. This was one of the most delayed launches of the Space Shuttle program.

Mission highlights

The primary payload of mission STS-35 was ASTRO-1, the fifth flight of the Spacelab system and the second with the Igloo and two pallets train configuration. The primary objectives were round-the-clock observations of the celestial sphere in ultraviolet and X-ray spectral wavelengths with the ASTRO-1 observatory, consisting of four telescopes: Hopkins Ultraviolet Telescope (HUT); Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE); Ultraviolet Imaging Telescope (UIT), mounted on the Instrument Pointing System (IPS). The Instrument Pointing System consisted of a three-axis gimbal system mounted on a gimbal support structure connected to a Spacelab pallet at one end and the aft end of the payload at the other, a payload clamping system for support of the mounted experiment during launch and landing, and a control system based on the inertial reference of a three-axis gyro package and operated by a gimbal-mounted microcomputer. The Broad-Band X-Ray Telescope (BBXRT) and its Two-Axis Pointing System (TAPS) rounded out the instrument complement in the aft payload bay.

The crew split into shifts after reaching orbit, with Gardner, Parker, and Parise comprising the Red Team; the Blue Team consisted of Hoffman, Durrance, and Lounge. Commander Brand was unassigned to either team and helped coordinate mission activities. The telescopes were powered up and raised from their stowed position by the Red Team 11 hours into the flight. Observations began under the Blue Team 16 hours into the mission after the instruments were checked out. In a typical ASTRO-1 ultraviolet observation, the flight crew member on duty maneuvered the Shuttle to point the cargo bay in the general direction of the astronomical object to be observed. The mission specialist commanded the pointing system to aim the telescopes toward the target. They also locked on to guide stars to help the pointing system remain stable despite orbiter thruster firings. The payload specialist set up each instrument for the upcoming observation, identified the celestial target on the guide television, and provided the necessary pointing corrections for placing the object precisely in the telescope's field of view. He then started the instrument observation sequences and monitored the data being recorded. Because the many observations created a heavy workload, the payload and mission specialists worked together to perform these complicated operations and evaluate the quality of observations. Each observation took between 10 minutes to a little over an hour.

Issues with the pointing precision of the IPS and the sequential overheating failures of both data display units (used for pointing telescopes and operating experiments) during the mission impacted crew-aiming procedures and forced ground teams at Marshall Space Flight Center (MSFC) to aim the telescopes with fine-tuning by the flight crew. BBXRT-01 was directed from the outset by ground-based operators at Goddard Space Flight Center (GSFC) and was not affected. The X-ray telescope required little attention from the crew. A crew member would turn on the BBXRT and the TAPS at the beginning of operations and then turn them off when the operations concluded. After the telescope was activated, researchers at Goddard could "talk" to the telescope via computer. Before science operations began, stored commands were loaded into the BBXRT computer system. Then, when the astronauts positioned the Shuttle in the general direction of the source, the TAPS automatically pointed the BBXRT at the object. Since the Shuttle could be oriented in only one direction at a time, X-ray observations had to be coordinated carefully with ultraviolet observations. Despite the pointing problems, the full suite of telescopes obtained 231 observations of 130 celestial objects over a combined span of 143 hours. Science teams at Marshall and Goddard estimated that 70% of the mission objectives were completed. ASTRO-1 was the first shuttle mission controlled in part from the Spacelab Mission Operations Control facility at MSFC in Huntsville, Alabama.

During the flight, the crew experienced trouble dumping waste water due to a blocked waste water line, but managed to compensate using spare containers. Problems also affected one RCC thruster and an onboard text and graphics teleprinter used for receiving flight plan updates.

Additional payloads and experiments

Conducting short-wave radio transmissions between ground-based amateur radio operators and a Shuttle-based amateur radio operator was the basis for the Shuttle Amateur Radio Experiment (SAREX-II). SAREX communicated with amateur stations in line-of-sight of the orbiter in one of four transmission modes: voice, Slow-scan television (SSTV), data or (uplink only) Fast scan television (FSTV). The voice mode was operated in the attended mode while SSTV, data or FSTV could be operated in either attended or unattended modes. During the mission, SAREX was operated by Payload Specialist Ron Parise, a licensed operator (WA4SIR), during periods when he was not scheduled for orbiter or other payload activities. A ground-based experiment to calibrate electro-optical sensors at Air Force Maui Optical Site (AMOS) in Hawaii was also conducted during the mission. The Space Classroom Program, Assignment: The Stars project was carried out to spark student interest in science, mathematics and technology. Mission Specialist Hoffman conducted the first classroom lesson taught from space on December 7, 1990, in support of this objective, covering material on the electromagnetic spectrum and the ASTRO-1 observatory. A supporting lesson was taught from the ASTRO-1 control center in Huntsville.

Landing

The mission was cut short by one day due to impending bad weather at the primary landing site, Edwards Air Force Base, California. The Orbital Maneuvering System (OMS) engines were fired at 8:48 p.m. PST over the Indian Ocean to deorbit the spacecraft, which landed on Runway 22 at Edwards Air Force Base, California, at 9:54 p.m. PST, on December 10, 1990, after a mission duration of 8 days, 23 hours, 5 minutes, and 8 seconds. This was the fourth night landing of the shuttle program. Rollout distance: ). Rollout time: 58 seconds. Columbia returned to KSC on December 20, 1990, on the Shuttle Carrier Aircraft (SCA). Landing weight: .

Image gallery

See also

 List of human spaceflights
 List of Space Shuttle missions
 Outline of space science
 Space Shuttle

References

External links
 NASA mission summary
 STS-35 Video Highlights
 Jack A. Jones Collection, The University of Alabama in Huntsville Archives and Special Collections Files of Jack A. Jones, mission manager for Astro-1.

Space Shuttle missions
Edwards Air Force Base
Crewed space observatories
Spacecraft launched in 1990

STS-35


Topical decongestants are decongestants applied directly to the nasal cavity. Their effectiveness by themselves in the common cold appears to have a small benefit in adults.

Topical decongestants should only be used by patients for a maximum of 5–7 days in a row, because rebound congestion may occur in the form of rhinitis medicamentosa. When used in adults for a short period of time side effects appear to be few.

Mechanism of action
Topical decongestants are vasoconstrictors, and work by constricting the blood vessels within the nasal cavity.

Examples
 Ephedrine
 Levomethamphetamine
 Naphazoline
 Oxymetazoline
 Phenylephrine
 Propylhexedrine
 Pseudoephedrine
 Tramazoline
 Xylometazoline

See also
 Decongestant
 Nasal irrigation
 Nasal spray

References

Topical decongestant


Benz ist eine Dorfschaft der Gemeinde Malente im Kreis Ostholstein in Schleswig-Holstein.

Geographie
Benz liegt in der Endmoränenlandschaft der Holsteinischen Schweiz. Die beiden Benzer Seen, also Großer Benzer See und Kleiner Benzer See, werden auch Benzer Augen genannt. Geologisch sind die Seen zwei Toteisseen, die nach der letzten Eiszeit dort entstanden, wo zwei riesige Gletschereisblöcke liegen blieben.

Durch den Ort verläuft die Kreisstraße 1.

Geschichte

Ostholsteins Besiedlung nach der Eiszeit
In Ostholstein entstand in der letzten Eiszeit, der Weichseleiszeit, eine Endmoränenlandschaft mit Hügeln, Seen, Granitfelsen und unterschiedlichen Ackerböden. Die Rentierjäger waren die ersten Bewohner nach der Weichseleiszeit. Archäologische Funde der frühen Bewohner sind Faustkeile und Speerspitzen aus Flintstein. Aus der Zeit des Ackerbaus finden wir auch Mahlsteine, Schmuck, Bronzeteile, Siedlungsspuren, Megalithgräber und Urnenfelder. Bis etwa 600 n. Chr. hatten die germanischen Holsten das Gebiet sesshaft bewohnt. Im Zuge der Völkerwanderung verließen die Holsten Ostholstein. Etwa ein Jahrhundert lang blieb es siedlungsleer, bis ab 700 n. Chr. die slawischen Wagrier den Raum von Ostholstein bis südlich zur Elbe kampflos besiedelten. Karl der Große überließ das Gebiet später den ebenfalls slawischen Abodriten, da sie sich mit ihm im Kampf gegen die Sachsen verbündet hatten, und einigte sich 810 n. Chr. mit ihnen auf den Limes Saxoniae, den Grenzstreifen des slawischen Siedlungsraums.

Um 970 wurde das Bistum Oldenburg gegründet. Herzog Heinrich der Löwe gab Wagrien als Lehen an den Grafen Adolf II. von Holstein, der ab 1143 mit der Ansiedlung sowohl von Kolonisten aus seinem Herrschaftsbereich als auch Westfalen, Flamen, Friesen, und Sachsen in den mittleren und südlichen Teilen Wagriens begann. Er war auch bemüht, in seinem Herrschaftsbereich die christliche Missionierung zu fördern, worin er durch den Missionar Vizelin unterstützt wurde. Schon bald ging die slawische Bevölkerung in der neuen Mehrheit auf. Um 1150 förderte Heinrich der Löwe Lübeck und das Bistum Oldenburg, dem er 300 Hufen zusprach.

Die ersten Urkunden 1215
Benz, ein wendisches Dorf, wurde 1215/16 als Banzeuiz zusammen mit anderen Dörfern des Bischofs von Lübeck in zwei Urkunden erwähnt. In der Zeit nach Heinrich dem Löwen, von 1201, der Schlacht bei Stellau, bis 1227, der Schlacht von Bornhöved, reichte die dänische Herrschaft bis an die Elbe. Der König Waldemar II. von Dänemark setzte seinen thüringischen Neffen Albrecht von Orlamünde als Grafen von Holstein ein. Der Bischof Bertold von Lübeck bat sowohl die neuen Landesherren Waldemar II. und Albrecht von Orlamünde als auch den Papst Honorius III., seine Besitzungen und Rechte in Holstein mit Urkunden zu bestätigen. Benz gehörte zu den Dörfern des bischöflichen Gerichts in Malente.

2015 wurde "800 Jahre Benz" gefeiert.

Die Herkunft des Namens Benz
Noch heute verraten uns die Namen der Dörfer teilweise die Herkunft der Siedler: Die Namen Utin und Flehm sind niederländisch-flämisch. Der Name Benz ist slawisch.
Die Namen in den Urkunden von 1215 Banzeuiz und 1251 Benzsche kommen nach Haefs von dem altpolabischen Basevici. Die Endsilben -vi-ci sind ein Patronymsuffix, also besitzanzeigend, und Bas ist ein Personenname. Der Name Bas könnte auch die Verkürzung sein von Banz oder Bansch. Also bedeutet der heutige Ortsname Benz: die Siedlung der Leute des Bansch oder das Dorf des Banz.

Landwirtschaft in Benz
Um 1280 hatte Benz laut Tafelgüterverzeichnis 14 Hufner. Die Hufner hatten freie Bauernstellen.

Kaiser Karl V. erhob 1549 für die Kirchspiele Bosau, Neukirchen, Malente, Ratekau, Rensefeld und das Land Oldenburg die Reichstürkensteuer.
Sie diente der Finanzierung der Türkenkriege, die für den Kaiser und das Reich zu einer ständigen Bedrohung geworden sind. Zu dieser Steuer wurden auch die Benzer Hufner: Pasker Tamm (heute Hof Schulte), Pasker Tode (heute Westernreiten Hof Fraider, Markus Oeverdieck, Lammert Oeverdieck und Hans Oeverdieck veranlagt.

Im 17. Jahrhundert entstand schrittweise das Gut Benzerhof aus mehreren Hufen.
Das Dorf Benz gehörte im 19. Jahrhundert zum Allodialgut Benz. Heute ist das Gut Benzerhof ein Teil von Benz.

Schule und Feuerwehr
Vor 1836 brannte die erste Schule von Benz ab. Sie war vor dem Brand in einem schlechten Zustand. Die Schule stand am Dorfteich und dort befindet sich jetzt das Haus der Familie Puls. Das zweite Schulhaus wurde 1836 in der Flehmer Straße gebaut und ist zurzeit die Dorfkirche.

1923 brennen beim Benzerhof die alte "Meiereikate", später der Kuhstall, die Scheune, die damalige Meierei (Hauptstraße 35) und die Hufe des Eigentümers Lemke (Schwonauer Weg 2). Der Brandstifter kann nicht ermittelt werden.
1926 wird die Freiwillige Feuerwehr Benz-Nüchel gegründet. Ihr erster Einsatz war 1934 der Brand des Kuhstalls auf dem Benzerhof.
1945 wurden in Benz und Nüchel selbstständige Freiwillige Feuerwehren gegründet.
1979 wurde zunächst eine Jugendfeuerwehr der Gemeinde Malente gegründet und seit 1981 gibt es die Jugendfeuerwehr Benz-Nüchel.

Kirche, Sport, Wasserwerk, Kindergarten
Nach 1945 leben sehr viele Flüchtlinge in Benz; deshalb wurde 1946 für die stark gewachsene Bevölkerung im 1836 erbauten zweiten Schulhaus eine Kirche eingerichtet. Der Kirchraum wird bis heute genutzt.

Von 1948 bis 1957 bestand der Sportverein SV-Benz-Nüchel und 1963 wurde der TSV-Benz-Nüchel gegründet.

1967 wurde das Wasserwerk Benz für die Gemeinde Malente mit zwei 130 m tiefen Brunnen und ca. 25 km Hauptleitungen in Betrieb genommen.

Im Ort gibt es seit 1986 einen Kindergarten im Dörfergemeinschaftshaus, der ehemaligen Schule für Benz und Nüchel, die 1938 als drittes Schulhaus in Benz erbaut wurde.

Verkehr
Benz hatte seit 1890 einen eigenen Bahnhof an der 1892 fertiggestellten Bahnstrecke Malente-Gremsmühlen–Lütjenburg. Am Empfangsgebäude des Bahnhofs gibt es eine Gedenktafel für die Auflösung der Reichsbahndirektion Stettin, die hier im Juli 1945 stattfand: Der "Befehlszug" des Präsidenten der Direktion war hier gestrandet. Da die Länge des Bahnsteigs in Benz für den Zug nicht ausreichte, war er auf drei Bahnhöfe verteilt worden: Benz, Lensahn und Oldenburg. 1976 wurde der Personenverkehr eingestellt, 1996 der Güterverkehr. Von 2006 bis 2008 bestand ein Draisinenbetrieb zwischen Malente und Lütjenburg.

Vereine
 Freiwillige Feuerwehr Benz
 Turn- und Sport-Verein Benz-Nüchel im Dörfergemeinschaftshaus

Weblinks
 Dorfschaft Benz Dorf-Benz.de
 Der Ort Benz auf Malente.de – Dort findet sich auch der Hinweis: 386 Einwohner hat Benz im Okt. 2015
 TSV-Benz-Nüchel auf tsv-benz-nuechel.de

Einzelnachweise

Ort im Kreis Ostholstein
Geographie (Malente)
Ersterwähnung 1215

Benz (Malente)


Foreningen Menneskebiblioteket er en dansk forening, som blev stiftet af Ronni Abergel og afholdte første arrangement på Roskilde Festival 2000. Konceptet er lige så enkelt, som navnet antyder: i stedet for bøger udlånes mennesker, der hver især repræsenterer grupper i samfundet, som på den ene eller anden måde oplever forudfattede holdninger, fordomme, stigma eller diskrimination. Sammen med de mennesker, der låner dem, har de en 30-minutter lang personlig samtale, der kan være om et svært og tabulagt emne. Man kan låne menneskebøger til events på biblioteker, skoler eller til konferencer eller festivaller.

Menneskene, som man kan låne til samtaler, er i overensstemmelse med Menneskebiblioteks koncept og terminologi derfor "åbne bøger" i den forstand, at de har mod på at svare på alle slags spørgsmål. "Bøgerne" har således også titler, som de selv har defineret på baggrund af de fordomme, som de har mødt i deres liv. Bogudvalget byder bl.a. på alt fra ADHD til Polyamorøs. Udvalget varierer ved hvert arrangement, men et overblik kan findes på organisationens hjemmesider.

Siden koncepts start for snart tyve år siden har Menneskebiblioteket udbredt sig til mere end 85 partnerlande verden over. Heraf er der fire etablerede bogdepoter i Danmark.

Referencer

Eksterne henvisninger

 Dansk hjemmeside http://menneskebiblioteket.dk/roskilde-festival-med-donation-til-menneskebiblioteket/
 International hjemmeside http://humanlibrary.org/
 Dansk Facebook side: https://www.facebook.com/menneskebiblioteket/
 International Facebook side: https://www.facebook.com/humanlibraryorg/

Foreninger fra Danmark
Etableret i 2000

Menneskebiblioteket


Nina Åström es una cantante finlandesa de góspel, que representó a Finlandia en el Festival de la Canción de Eurovisión 2000 con la canción "A Little Bit", donde terminó en la 19.ª posición con 18 puntos. Ella comenzó su carrera artística en los años 1980s, y publicó su primer álbum de estudio en 1991.

Vida personal
Åström actualmente vive en Tenerife , España y está casada. Además, ella tiene dos hijas.

Discografía

Álbumes de estudio
 Person 2 Person (1991)
 A Matter of Time (1994)
 Moods (1995)
 A Friend (1999)
 A Little Bit of Love (2000)
 Vierelle jäät (2000)
 Merry Christmas Jesus (2001)
 Real Life (2003)
 Landscape of my Soul (2007)
 Avoin taivas (2012)
 Minun aarteeni (2014)
 Joulun Kuningas (2014)
 Takaisin kotiin (2016)
 Rauhaa ja rohkeutta (2018)

Sencillos
 "The Way We Are" (2010)

Enlaces externos
Sitio web oficial

Participantes en Eurovisión 2000
Cantantes femeninas de Finlandia
Cantantes de góspel

Nina Åström


In computer science, 2-satisfiability, 2-SAT or just 2SAT is a computational problem of assigning values to variables, each of which has two possible values, in order to satisfy a system of constraints on pairs of variables. It is a special case of the general Boolean satisfiability problem, which can involve constraints on more than two variables, and of constraint satisfaction problems, which can allow more than two choices for the value of each variable. But in contrast to those more general problems, which are NP-complete, 2-satisfiability can be solved in polynomial time.

Instances of the 2-satisfiability problem are typically expressed as Boolean formulas of a special type, called conjunctive normal form (2-CNF) or Krom formulas. Alternatively, they may be expressed as a special type of directed graph, the implication graph, which expresses the variables of an instance and their negations as vertices in a graph, and constraints on pairs of variables as directed edges. Both of these kinds of inputs may be solved in linear time, either by a method based on backtracking or by using the strongly connected components of the implication graph. Resolution, a method for combining pairs of constraints to make additional valid constraints, also leads to a polynomial time solution. The 2-satisfiability problems provide one of two major subclasses of the conjunctive normal form formulas that can be solved in polynomial time; the other of the two subclasses is Horn-satisfiability.

2-satisfiability may be applied to geometry and visualization problems in which a collection of objects each have two potential locations and the goal is to find a placement for each object that avoids overlaps with other objects. Other applications include clustering data to minimize the sum of the diameters of the clusters, classroom and sports scheduling, and recovering shapes from information about their cross-sections.

In computational complexity theory, 2-satisfiability provides an example of an NL-complete problem, one that can be solved non-deterministically using a logarithmic amount of storage and that is among the hardest of the problems solvable in this resource bound. The set of all solutions to a 2-satisfiability instance can be given the structure of a median graph, but counting these solutions is #P-complete and therefore not expected to have a polynomial-time solution. Random instances undergo a sharp phase transition from solvable to unsolvable instances as the ratio of constraints to variables increases past 1, a phenomenon conjectured but unproven for more complicated forms of the satisfiability problem. A computationally difficult variation of 2-satisfiability, finding a truth assignment that maximizes the number of satisfied constraints, has an approximation algorithm whose optimality depends on the unique games conjecture, and another difficult variation, finding a satisfying assignment minimizing the number of true variables, is an important test case for parameterized complexity.

Problem representations

A 2-satisfiability problem may be described using a Boolean expression with a special restricted form. It is a conjunction (a Boolean and operation) of clauses, where each clause is a disjunction (a Boolean or operation) of two variables or negated variables. The variables or their negations appearing in this formula are known as literals. For example, the following formula is in conjunctive normal form, with seven variables, eleven clauses, and 22 literals:

The 2-satisfiability problem is to find a truth assignment to these variables that makes the whole formula true. Such an assignment chooses whether to make each of the variables true or false, so that at least one literal in every clause becomes true. For the expression shown above, one possible satisfying assignment is the one that sets all seven of the variables to true. Every clause has at least one non-negated variable, so this assignment satisfies every clause. There are also 15 other ways of setting all the variables so that the formula becomes true. Therefore, the 2-satisfiability instance represented by this expression is satisfiable.

Formulas in this form are known as 2-CNF formulas. The "2" in this name stands for the number of literals per clause, and "CNF" stands for conjunctive normal form, a type of Boolean expression in the form of a conjunction of disjunctions. They are also called Krom formulas, after the work of UC Davis mathematician Melven R. Krom, whose 1967 paper was one of the earliest works on the 2-satisfiability problem.

Each clause in a 2-CNF formula is logically equivalent to an implication from one variable or negated variable to the other. For example, the second clause in the example may be written in any of three equivalent ways:

Because of this equivalence between these different types of operation, a 2-satisfiability instance may also be written in implicative normal form, in which we replace each or clause in the conjunctive normal form by the two implications to which it is equivalent.

A third, more graphical way of describing a 2-satisfiability instance is as an implication graph. An implication graph is a directed graph in which there is one vertex per variable or negated variable, and an edge connecting one vertex to another whenever the corresponding variables are related by an implication in the implicative normal form of the instance. An implication graph must be a skew-symmetric graph, meaning that it has a symmetry that takes each variable to its negation and reverses the orientations of all of the edges.

Algorithms
Several algorithms are known for solving the 2-satisfiability problem. The most efficient of them take linear time.

Resolution and transitive closure
 described the following polynomial time decision procedure for solving 2-satisfiability instances.

Suppose that a 2-satisfiability instance contains two clauses that both use the same variable x, but that x is negated in one clause and not in the other. Then the two clauses may be combined to produce a third clause, having the two other literals in the two clauses; this third clause must also be satisfied whenever the first two clauses are both satisfied. For instance, we may combine the clauses  and  in this way to produce the clause . In terms of the implicative form of a 2-CNF formula, this rule amounts to finding two implications  and , and inferring by transitivity a third implication .

Krom writes that a formula is consistent if repeated application of this inference rule cannot generate both the clauses  and , for any variable . As he proves, a 2-CNF formula is satisfiable if and only if it is consistent. For, if a formula is not consistent, it is not possible to satisfy both of the two clauses  and  simultaneously. And, if it is consistent, then the formula can be extended by repeatedly adding one clause of the form  or  at a time, preserving consistency at each step, until it includes such a clause for every variable. At each of these extension steps, one of these two clauses may always be added while preserving consistency, for if not then the other clause could be generated using the inference rule. Once all variables have a clause of this form in the formula, a satisfying assignment of all of the variables may be generated by setting a variable  to true if the formula contains the clause  and setting it to false if the formula contains the clause .

Krom was concerned primarily with completeness of systems of inference rules, rather than with the efficiency of algorithms. However, his method leads to a polynomial time bound for solving 2-satisfiability problems. By grouping together all of the clauses that use the same variable, and applying the inference rule to each pair of clauses, it is possible to find all inferences that are possible from a given 2-CNF instance, and to test whether it is consistent, in total time , where  is the number of variables in the instance. This formula comes from multiplying the number of variables by the  number of pairs of clauses involving a given variable, to which the inference rule may be applied. Thus, it is possible to determine whether a given 2-CNF instance is satisfiable in time . Because finding a satisfying assignment using Krom's method involves a sequence of  consistency checks, it would take time .  quote a faster time bound of  for this algorithm, based on more careful ordering of its operations. Nevertheless, even this smaller time bound was greatly improved by the later linear time algorithms of  and .

In terms of the implication graph of the 2-satisfiability instance, Krom's inference rule can be interpreted as constructing the transitive closure of the graph. As  observes, it can also be seen as an instance of the Davis–Putnam algorithm for solving satisfiability problems using the principle of resolution. Its correctness follows from the more general correctness of the Davis–Putnam algorithm. Its polynomial time bound follows from the fact that each resolution step increases the number of clauses in the instance, which is upper bounded by a quadratic function of the number of variables.

Limited backtracking
 describe a technique involving limited backtracking for solving constraint satisfaction problems with binary variables and pairwise constraints. They apply this technique to a problem of classroom scheduling, but they also observe that it applies to other problems including 2-SAT.

The basic idea of their approach is to build a partial truth assignment, one variable at a time. Certain steps of the algorithms are "choice points", points at which a variable can be given either of two different truth values, and later steps in the algorithm may cause it to backtrack to one of these choice points. However, only the most recent choice can be backtracked over. All choices made earlier than the most recent one are permanent.

Initially, there is no choice point, and all variables are unassigned. At each step, the algorithm chooses the variable whose value to set, as follows:
If there is a clause both of whose variables are already set, in a way that falsifies the clause, then the algorithm backtracks to its most recent choice point, undoing the assignments it made since that choice, and reverses the decision made at that choice. If there is no choice point, or if the algorithm has already backtracked over the most recent choice point, then it aborts the search and reports that the input 2-CNF formula is unsatisfiable.
If there is a clause in which one of the clause's two variables has already been set, and the clause could still become either true or false, then the other variable is set in a way that forces the clause to become true.
In the remaining case, each clause is either guaranteed to become true no matter how the remaining variables are assigned, or neither of its two variables has been assigned yet. In this case the algorithm creates a new choice point and sets any one of the unassigned variables to an arbitrarily chosen value.

Intuitively, the algorithm follows all chains of inference after making each of its choices. This either leads to a contradiction and a backtracking step, or, if no contradiction is derived, it follows that the choice was a correct one that leads to a satisfying assignment. Therefore, the algorithm either correctly finds a satisfying assignment or it correctly determines that the input is unsatisfiable.

Even et al. did not describe in detail how to implement this algorithm efficiently. They state only that by "using appropriate data structures in order to find the implications of any decision", each step of the algorithm (other than the backtracking) can be performed quickly. However, some inputs may cause the algorithm to backtrack many times, each time performing many steps before backtracking, so its overall complexity may be nonlinear. To avoid this problem, they modify the algorithm so that, after reaching each choice point, it begins simultaneously testing both of the two assignments for the variable set at the choice point, spending equal numbers of steps on each of the two assignments. As soon as the test for one of these two assignments would create another choice point, the other test is stopped, so that at any stage of the algorithm there are only two branches of the backtracking tree that are still being tested. In this way, the total time spent performing the two tests for any variable is proportional to the number of variables and clauses of the input formula whose values are permanently assigned. As a result, the algorithm takes linear time in total.

Strongly connected components
 found a simpler linear time procedure for solving 2-satisfiability instances, based on the notion of strongly connected components from graph theory.

Two vertices in a directed graph are said to be strongly connected to each other if there is a directed path from one to the other and vice versa. This is an equivalence relation, and the vertices of the graph may be partitioned into strongly connected components, subsets within which every two vertices are strongly connected. There are several efficient linear time algorithms for finding the strongly connected components of a graph, based on depth-first search: Tarjan's strongly connected components algorithm and the path-based strong component algorithm each perform a single depth-first search. Kosaraju's algorithm performs two depth-first searches, but is very simple.

In terms of the implication graph, two literals belong to the same strongly connected component whenever there exist chains of implications from one literal to the other and vice versa. Therefore, the two literals must have the same value in any satisfying assignment to the given 2-satisfiability instance. In particular, if a variable and its negation both belong to the same strongly connected component, the instance cannot be satisfied, because it is impossible to assign both of these literals the same value. As Aspvall et al. showed, this is a necessary and sufficient condition: a 2-CNF formula is satisfiable if and only if there is no variable that belongs to the same strongly connected component as its negation.

This immediately leads to a linear time algorithm for testing satisfiability of 2-CNF formulae: simply perform a strong connectivity analysis on the implication graph and check that each variable and its negation belong to different components. However, as Aspvall et al. also showed, it also leads to a linear time algorithm for finding a satisfying assignment, when one exists. Their algorithm performs the following steps:
Construct the implication graph of the instance, and find its strongly connected components using any of the known linear-time algorithms for strong connectivity analysis.
Check whether any strongly connected component contains both a variable and its negation. If so, report that the instance is not satisfiable and halt.
Construct the condensation of the implication graph, a smaller graph that has one vertex for each strongly connected component, and an edge from component  to component  whenever the implication graph contains an edge  such that  belongs to component  and  belongs to component . The condensation is automatically a directed acyclic graph and, like the implication graph from which it was formed, it is skew-symmetric.
Topologically order the vertices of the condensation.  In practice this may be efficiently achieved as a side effect of the previous step, as components are generated by Kosaraju's algorithm in topological order and by Tarjan's algorithm in reverse topological order.
For each component in the reverse topological order, if its variables do not already have truth assignments, set all the literals in the component to be true. This also causes all of the literals in the complementary component to be set to false.

Due to the reverse topological ordering and the skew-symmetry, when a literal is set to true, all literals that can be reached from it via a chain of implications will already have been set to true. Symmetrically, when a literal  is set to false, all literals that lead to it via a chain of implications will themselves already have been set to false. Therefore, the truth assignment constructed by this procedure satisfies the given formula, which also completes the proof of correctness of the necessary and sufficient condition identified by Aspvall et al.

As Aspvall et al. show, a similar procedure involving topologically ordering the strongly connected components of the implication graph may also be used to evaluate fully quantified Boolean formulae in which the formula being quantified is a 2-CNF formula.

Applications

Conflict-free placement of geometric objects
A number of exact and approximate algorithms for the automatic label placement problem are based on 2-satisfiability. This problem concerns placing textual labels on the features of a diagram or map. Typically, the set of possible locations for each label is highly constrained, not only by the map itself (each label must be near the feature it labels, and must not obscure other features), but by each other: every two labels should avoid overlapping each other, for otherwise they would become illegible. In general, finding a label placement that obeys these constraints is an NP-hard problem. However, if each feature has only two possible locations for its label (say, extending to the left and to the right of the feature) then label placement may be solved in polynomial time. For, in this case, one may create a 2-satisfiability instance that has a variable for each label and that has a clause for each pair of labels that could overlap, preventing them from being assigned overlapping positions. If the labels are all congruent rectangles, the corresponding 2-satisfiability instance can be shown to have only linearly many constraints, leading to near-linear time algorithms for finding a labeling.  describe a map labeling problem in which each label is a rectangle that may be placed in one of three positions with respect to a line segment that it labels: it may have the segment as one of its sides, or it may be centered on the segment. They represent these three positions using two binary variables in such a way that, again, testing the existence of a valid labeling becomes a 2-satisfiability problem.

 use 2-satisfiability as part of an approximation algorithm for the problem of finding square labels of the largest possible size for a given set of points, with the constraint that each label has one of its corners on the point that it labels. To find a labeling with a given size, they eliminate squares that, if doubled, would overlap another point, and they eliminate points that can be labeled in a way that cannot possibly overlap with another point's label. They show that these elimination rules cause the remaining points to have only two possible label placements per point, allowing a valid label placement (if one exists) to be found as the solution to a 2-satisfiability instance. By searching for the largest label size that leads to a solvable 2-satisfiability instance, they find a valid label placement whose labels are at least half as large as the optimal solution. That is, the approximation ratio of their algorithm is at most two. Similarly, if each label is rectangular and must be placed in such a way that the point it labels is somewhere along its bottom edge, then using 2-satisfiability to find the largest label size for which there is a solution in which each label has the point on a bottom corner leads to an approximation ratio of at most two.

Similar applications of 2-satisfiability have been made for other geometric placement problems. In graph drawing, if the vertex locations are fixed and each edge must be drawn as a circular arc with one of two possible locations (for instance as an arc diagram), then the problem of choosing which arc to use for each edge in order to avoid crossings is a 2-satisfiability problem with a variable for each edge and a constraint for each pair of placements that would lead to a crossing. However, in this case it is possible to speed up the solution, compared to an algorithm that builds and then searches an explicit representation of the implication graph, by searching the graph implicitly.
In VLSI integrated circuit design, if a collection of modules must be connected by wires that can each bend at most once, then again there are two possible routes for the wires, and the problem of choosing which of these two routes to use, in such a way that all wires can be routed in a single layer of the circuit, can be solved as a 2-satisfiability instance.

 consider another VLSI design problem: the question of whether or not to mirror-reverse each module in a circuit design. This mirror reversal leaves the module's operations unchanged, but it changes the order of the points at which the input and output signals of the module connect to it, possibly changing how well the module fits into the rest of the design. Boros et al. consider a simplified version of the problem in which the modules have already been placed along a single linear channel, in which the wires between modules must be routed, and there is a fixed bound on the density of the channel (the maximum number of signals that must pass through any cross-section of the channel). They observe that this version of the problem may be solved as a 2-satisfiability instance, in which the constraints relate the orientations of pairs of modules that are directly across the channel from each other. As a consequence, the optimal density may also be calculated efficiently, by performing a binary search in which each step involves the solution of a 2-satisfiability instance.

Data clustering
One way of clustering a set of data points in a metric space into two clusters is to choose the clusters in such a way as to minimize the sum of the diameters of the clusters, where the diameter of any single cluster is the largest distance between any two of its points. This is preferable to minimizing the maximum cluster size, which may lead to very similar points being assigned to different clusters. If the target diameters of the two clusters are known, a clustering that achieves those targets may be found by solving a 2-satisfiability instance. The instance has one variable per point, indicating whether that point belongs to the first cluster or the second cluster. Whenever any two points are too far apart from each other for both to belong to the same cluster, a clause is added to the instance that prevents this assignment.

The same method also can be used as a subroutine when the individual cluster diameters are unknown. To test whether a given sum of diameters can be achieved without knowing the individual cluster diameters, one may try all maximal pairs of target diameters that add up to at most the given sum, representing each pair of diameters as a 2-satisfiability instance and using a 2-satisfiability algorithm to determine whether that pair can be realized by a clustering. To find the optimal sum of diameters one may perform a binary search in which each step is a feasibility test of this type. The same approach also works to find clusterings that optimize other combinations than sums of the cluster diameters, and that use arbitrary dissimilarity numbers (rather than distances in a metric space) to measure the size of a cluster. The time bound for this algorithm is dominated by the time to solve a sequence of 2-satisfiability instances that are closely related to each other, and  shows how to solve these related instances more quickly than if they were solved independently from each other, leading to a total time bound of  for the sum-of-diameters clustering problem.

Scheduling
 consider a model of classroom scheduling  in which a set of n teachers must be scheduled to teach each of m cohorts of students. The number of hours per week that teacher  spends with cohort  is described by entry  of a matrix  given as input to the problem, and each teacher also has a set of hours during which he or she is available to be scheduled. As they show, the problem is NP-complete, even when each teacher has at most three available hours, but it can be solved as an instance of 2-satisfiability when each teacher only has two available hours. (Teachers with only a single available hour may easily be eliminated from the problem.) In this problem, each variable  corresponds to an hour that teacher  must spend with cohort , the assignment to the variable specifies whether that hour is the first or the second of the teacher's available hours, and there is a 2-satisfiability clause preventing any conflict of either of two types: two cohorts assigned to a teacher at the same time as each other, or one cohort assigned to two teachers at the same time.

 apply 2-satisfiability to a problem of sports scheduling, in which the pairings of a round-robin tournament have already been chosen and the games must be assigned to the teams' stadiums. In this problem, it is desirable to alternate home and away games to the extent possible, avoiding "breaks" in which a team plays two home games in a row or two away games in a row. At most two teams can avoid breaks entirely, alternating between home and away games; no other team can have the same home-away schedule as these two, because then it would be unable to play the team with which it had the same schedule. Therefore, an optimal schedule has two breakless teams and a single break for every other team. Once one of the breakless teams is chosen, one can set up a 2-satisfiability problem in which each variable represents the home-away assignment for a single team in a single game, and the constraints enforce the properties that any two teams have a consistent assignment for their games, that each team have at most one break before and at most one break after the game with the breakless team, and that no team has two breaks. Therefore, testing whether a schedule admits a solution with the optimal number of breaks can be done by solving a linear number of 2-satisfiability problems, one for each choice of the breakless team. A similar technique also allows finding schedules in which every team has a single break, and maximizing rather than minimizing the number of breaks (to reduce the total mileage traveled by the teams).

Discrete tomography

Tomography is the process of recovering shapes from their cross-sections. In discrete tomography, a simplified version of the problem that has been frequently studied, the shape to be recovered is a polyomino (a subset of the squares in the two-dimensional square lattice), and the cross-sections provide aggregate information about the sets of squares in individual rows and columns of the lattice. For instance, in the popular nonogram puzzles, also known as paint by numbers or griddlers, the set of squares to be determined represents the dark pixels in a binary image, and the input given to the puzzle solver tells him or her how many consecutive blocks of dark pixels to include in each row or column of the image, and how long each of those blocks should be. In other forms of digital tomography, even less information about each row or column is given: only the total number of squares, rather than the number and length of the blocks of squares. An equivalent version of the problem is that we must recover a given 0-1 matrix given only the sums of the values in each row and in each column of the matrix.

Although there exist polynomial time algorithms to find a matrix having given row and column sums, the solution may be far from unique: any submatrix in the form of a 2 × 2 identity matrix can be complemented without affecting the correctness of the solution. Therefore, researchers have searched for constraints on the shape to be reconstructed that can be used to restrict the space of solutions. For instance, one might assume that the shape is connected; however, testing whether there exists a connected solution is NP-complete. An even more constrained version that is easier to solve is that the shape is orthogonally convex: having a single contiguous block of squares in each row and column.
Improving several previous solutions,  showed how to reconstruct connected orthogonally convex shapes efficiently, using 2-SAT. The idea of their solution is to guess the indexes of rows containing the leftmost and rightmost cells of the shape to be reconstructed, and then to set up a 2-satisfiability problem that tests whether there exists a shape consistent with these guesses and with the given row and column sums. They use four 2-satisfiability variables for each square that might be part of the given shape, one to indicate whether it belongs to each of four possible "corner regions" of the shape, and they use constraints that force these regions to be disjoint, to have the desired shapes, to form an overall shape with contiguous rows and columns, and to have the desired row and column sums. Their algorithm takes time  where  is the smaller of the two dimensions of the input shape and  is the larger of the two dimensions.  The same method was later extended to orthogonally convex shapes that might be connected only diagonally instead of requiring orthogonal connectivity.

A part of a solver for full nonogram puzzles,  used 2-satisfiability to combine information obtained from several other heuristics. Given a partial solution to the puzzle, they use dynamic programming within each row or column to determine whether the constraints of that row or column force any of its squares to be white or black, and whether any two squares in the same row or column can be connected by an implication relation. They also transform the nonogram into a digital tomography problem by replacing the sequence of block lengths in each row and column by its sum, and use a maximum flow formulation to determine whether this digital tomography problem combining all of the rows and columns has any squares whose state can be determined or pairs of squares that can be connected by an implication relation. If either of these two heuristics determines the value of one of the squares, it is included in the partial solution and the same calculations are repeated. However, if both heuristics fail to set any squares, the implications found by both of them are combined into a 2-satisfiability problem and a 2-satisfiability solver is used to find squares whose value is fixed by the problem, after which the procedure is again repeated. This procedure may or may not succeed in finding a solution, but it is guaranteed to run in polynomial time. Batenburg and Kosters report that, although most newspaper puzzles do not need its full power, both this procedure and a more powerful but slower procedure which combines this 2-satisfiability approach with the limited backtracking of  are significantly more effective than the dynamic programming and flow heuristics without 2-satisfiability when applied to more difficult randomly generated nonograms.

Renamable Horn satisfiability
Next to 2-satisfiability, the other major subclass of satisfiability problems that can be solved in polynomial time is Horn-satisfiability. In this class of satisfiability problems, the input is again a formula in conjunctive normal form. It can have arbitrarily many literals per clause but at most one positive literal.  found a generalization of this class, renamable Horn satisfiability, that can still be solved in polynomial time by means of an auxiliary 2-satisfiability instance. A formula is renamable Horn when it is possible to put it into Horn form by replacing some variables by their negations. To do so, Lewis sets up a 2-satisfiability instance with one variable for each variable of the renamable Horn instance, where the 2-satisfiability variables indicate whether or not to negate the corresponding renamable Horn variables.
In order to produce a Horn instance, no two variables that appear in the same clause of the renamable Horn instance should appear positively in that clause; this constraint on a pair of variables is a 2-satisfiability constraint. By finding a satisfying assignment to the resulting 2-satisfiability instance, Lewis shows how to turn any renamable Horn instance into a Horn instance in polynomial time. By breaking up long clauses into multiple smaller clauses, and applying a linear-time 2-satisfiability algorithm, it is possible to reduce this to linear time.

Other applications
2-satisfiability has also been applied to problems of recognizing undirected graphs that can be partitioned into an independent set and a small number of complete bipartite subgraphs, inferring business relationships among autonomous subsystems of the internet, and reconstruction of evolutionary trees.

Complexity and extensions

NL-completeness
A nondeterministic algorithm for determining whether a 2-satisfiability instance is not satisfiable, using only a logarithmic amount of writable memory, is easy to describe: simply choose (nondeterministically) a variable v and search (nondeterministically) for a chain of implications leading from v to its negation and then back to v. If such a chain is found, the instance cannot be satisfiable. By the Immerman–Szelepcsényi theorem, it is also possible in nondeterministic logspace to verify that a satisfiable 2-satisfiability instance is satisfiable.

2-satisfiability is NL-complete, meaning that it is one of the "hardest" or "most expressive" problems in the complexity class NL of problems solvable nondeterministically in logarithmic space. Completeness here means that a deterministic Turing machine using only logarithmic space can transform any other problem in NL into an equivalent 2-satisfiability problem.  Analogously to similar results for the more well-known complexity class NP, this transformation together with the Immerman–Szelepcsényi theorem allow any problem in NL to be represented as a second order logic formula with a single existentially quantified predicate with clauses limited to length 2. Such formulae are known as SO-Krom.  Similarly, the implicative normal form can be expressed in first order logic with the addition of an operator for transitive closure.

The set of all solutions

The set of all solutions to a 2-satisfiability instance has the structure of a median graph, in which an edge corresponds to the operation of flipping the values of a set of variables that are all constrained to be equal or unequal to each other. In particular, by following edges in this way one can get from any solution to any other solution. Conversely, any median graph can be represented as the set of solutions to a 2-satisfiability instance in this way. The median of any three solutions is formed by setting each variable to the value it holds in the majority of the three solutions. This median always forms another solution to the instance.

 describes an algorithm for efficiently listing all solutions to a given 2-satisfiability instance, and for solving several related problems.
There also exist algorithms for finding two satisfying assignments that have the maximal Hamming distance from each other.

Counting the number of satisfying assignments
#2SAT is the problem of counting the number of satisfying assignments to a given 2-CNF formula. This counting problem is #P-complete, which implies that it is not solvable in polynomial time unless P = NP. Moreover, there is no fully polynomial randomized approximation scheme for #2SAT unless NP = RP and this even holds when the input is restricted to monotone 2-CNF formulas, i.e., 2-CNF formulas in which each literal is a positive occurrence of a variable.

The fastest known algorithm for computing the exact number of satisfying assignments to a 2SAT formula runs in time .

Random 2-satisfiability instances

One can form a 2-satisfiability instance at random, for a given number n of variables and m of clauses, by choosing each clause uniformly at random from the set of all possible two-variable clauses. When m is small relative to n, such an instance will likely be satisfiable, but larger values of m have smaller probabilities of being satisfiable. More precisely, if m/n is fixed as a constant α ≠ 1, the probability of satisfiability tends to a limit as n goes to infinity: if α < 1, the limit is one, while if α > 1, the limit is zero. Thus, the problem exhibits a phase transition at α = 1.

Maximum-2-satisfiability
In the maximum-2-satisfiability problem (MAX-2-SAT), the input is a formula in conjunctive normal form with two literals per clause, and the task is to determine the maximum number of clauses that can be simultaneously satisfied by an assignment. Like the more general maximum satisfiability problem, MAX-2-SAT is NP-hard. The proof is by reduction from 3SAT.

By formulating MAX-2-SAT as a problem of finding a cut (that is, a partition of the vertices into two subsets) maximizing the number of edges that have one endpoint in the first subset and one endpoint in the second, in a graph related to the implication graph, and applying semidefinite programming methods to this cut problem, it is possible to find in polynomial time an approximate solution that satisfies at least 0.940... times the optimal number of clauses. A balanced MAX 2-SAT instance is an instance of MAX 2-SAT where every variable appears positively and negatively with equal weight. For this problem, Austrin has improved the approximation ratio to .

If the unique games conjecture is true, then it is impossible to approximate MAX 2-SAT, balanced or not, with an approximation constant better than 0.943... in polynomial time. Under the weaker assumption that P ≠ NP, the problem is only known to be inapproximable within a constant better than 21/22 = 0.95454...

Various authors have also explored exponential worst-case time bounds for exact solution of MAX-2-SAT instances.

Weighted-2-satisfiability
In the weighted 2-satisfiability problem (W2SAT), the input is an -variable 2SAT instance and an integer , and the problem is to decide whether there exists a satisfying assignment in which exactly  of the variables are true.

The W2SAT problem includes as a special case the vertex cover problem, of finding a set of  vertices that together touch all the edges of a given undirected graph. For any given instance of the vertex cover problem, one can construct an equivalent W2SAT problem with a variable for each vertex of a graph. Each edge  of the graph may be represented by a 2SAT clause  that can be satisfied only by including either  or  among the true variables of the solution. Then the satisfying instances of the resulting 2SAT formula encode solutions to the vertex cover problem, and there is a satisfying assignment with   true variables if and only if there is a vertex cover with  vertices. Therefore, like vertex cover, W2SAT is NP-complete.

Moreover, in parameterized complexity W2SAT provides a natural W[1]-complete problem, which implies that W2SAT is not fixed-parameter tractable unless  this holds for all problems in W[1]. That is, it is unlikely that there exists an algorithm for W2SAT whose running time takes the form . Even more strongly, W2SAT cannot be solved in time  unless the exponential time hypothesis fails.

Quantified Boolean formulae
As well as finding the first polynomial-time algorithm for 2-satisfiability,  also formulated the problem of evaluating fully quantified Boolean formulae in which the formula being quantified is a 2-CNF formula. The 2-satisfiability problem is the special case of this quantified 2-CNF problem, in which all quantifiers are existential. Krom also developed an effective decision procedure for these formulae.  showed that it can be solved in linear time, by an extension of their technique of strongly connected components and topological ordering.

Many-valued logics
The 2-satisfiability problem can also be asked for propositional many-valued logics. The algorithms are not usually linear, and for some logics the problem is even NP-complete. See  for surveys.

References

NL-complete problems
Satisfiability problems

2-satisfiability


Les Cavinulaceae sont une famille d'algues de l'embranchement des Bacillariophyta (Diatomées), de la classe des Bacillariophyceae et de l'ordre des Naviculales.

Étymologie
Le nom de la famille vient du genre type Cavinula, composé du préfixe cav‑ creux, et du suffixe latin ‑ula, petite, littéralement « petite cavité », probablement en référence à la cavité centrale que montre l'espèce holotype Cavinula cocconeiformis.

Description

Distribution

Liste des genres
Selon  :
 Cavinula D.G.Mann & A.J.Stickle, 1990

Systématique
Le nom correct complet (avec auteur) de ce taxon est Cavinulaceae D.G.Mann.

L'espèce holotype Cavinula cocconeiformis avait été précédemment décrite, en 1855, par Robert Greville sous le nom de Navicula cocconeiformis.

Liens externes

 Illustrations
 Spaulding et al. 2009. Cavinula. In Diatoms of North America (Diatomées d'Amérique du Nord), 15/05/2022 : voir en ligne

Notes et références

Famille d'algues (nom scientifique)
Naviculales

Cavinulaceae


Severiano Martínez Anido (21 de maio de 1862 - 24 de dezembro de 1938) foi um general espanhol que ocupou vários cargos governamentais em Espanha durante as ditaduras de Primo de Rivera e de Franco.

Vice-primeiros-ministros da Espanha
Mortos em 1938
Nascidos em 1862
Generais da Espanha
Políticos da Espanha

Severiano Martínez Anido