Justifying non-expert lecturer

Question: If a maths lecturer is lecturing a higher-level undergraduate course outside their area (i.e. has not taken a course in themselves or learned themselves over the course of their research), how could you justify to the students that they are suitably qualified to teach and assess them?
Comment: I'm not sure I understand why you should be justifying the lecturer's qualifications to the students. Presumably your department has ascertained that the individual is indeed knowledgeable enough in the area to provide high-level instruction (that is very important). That should be suitable justification in and of itself. To maintain that trust, it is essential to never permit an unqualified individual to instruct a course.
Comment: It depends on the background of the Lecturer. After some point of mathematical maturity it becomes comparatively simple to assimilate new material. Also, if this person is a good teacher and cares about the students then they'll take the time to see how other folks are teaching similar courses at other good institutions. But, the students, well, as long as he doesn't grade too hard they'll be fine.
Comment: Could you contextualize this question a bit more? Right now, you could cross out the word *maths* from the question and it'd read essentially the same; is there some way in which this being *math*-specific should/would/could affect the answer? Also confusing: Is the person a *non-expert* (as in the title) or generally unfamiliar with the material (as in the body)? There's a difference between a non-expert and a total naif. Finally: *Is* the person "suitably qualified" for this position? If yes: Why? If no: This question looks to me like it is asking about tricking students.
Comment: I'd go with "you cannot".
Comment: "I think being in maths rather than another subject could affect the answer." - Based on my discussions with colleagues in other disciplines, I do think it is somewhat peculiar to mathematics that people often are called upon to teach completely out of their 'specialty' (and not just generalist courses).  Plenty of math PhDs with no statistics background whatsoever are asked to teach both intro and mathematical statistics every year!
Comment: Interesting, that would be the opposite of my experience, where e.g. a historian might feel very uncomfortable teaching Modern Asian History if their dissertation was in Medieval European or something, whereas an analyst could be perfectly well expected to teach upper-level number theory or probability in a small department or if someone was on sabbatical, even if they'd never had the course.
Comment: I agree you don't justify it.  More to the point, a person's qualifications only guarantee their expertise in an area and do not necessarily reflect their capacity as teachers.
Comment: @BenjaminDickman Where this question actually comes from is that I'm having a discussion with colleagues from other subjects that basically comes down to the question of what makes you suitably qualified to teach at this level. I think being in maths rather than another subject could affect the answer. I also want to discount the argument 'we haven't got anyone suitable so they will have to do', which I suspect students would complain about if they found out.
Comment: @BenjaminDickman Also, I don't understand your distinction between the title and the body, as they are intended to be the same. I mean someone who is generally sufficiently qualified that they have been hired by the university, but teaching a course far enough from their specialty that is not immediately obvious that they are a suitable choice.
Comment: It may depend on the type of institution, of course; at a Research I might be very different than at tiny liberal arts college X or comprehensive regional state University Y.
Comment: @kcrisman Actually, I would have gone the other way round. I've been talking to people who teach in a completely different subject. But it seems to me that 'statistics' or 'research methods' might translate better between subjects than does in maths, where the content is the maths.
Comment: Huston's [Teaching What You Don't Know](http://www.amazon.com/Teaching-What-You-Dont-Know/dp/0674066170) might be worth picking up.
Comment: @kcrisman, who says the mathematician isn't equally conflicted?
Comment: @vonbrand I'm not sure which of my comments you're specifically referring to, but I only put my thoughts there as a comment because they are anecdotal in any case; my answer below is (I hope) orthogonal to it.  I am sure that in many cases the math instructor may feel pretty unqualified, that is true, and assuredly many of them won't feel it is fair or a good idea.  My point was just that it seems like this might be a more common thing in mathematics teaching than in other disciplines - but no, I don't have comprehensive data either.
Answer: The comments are very interesting, but you are talking about how to justify to students.  That may not always be necessary, but here is a stab at it if someone really asked (which I find somewhat unlikely).

The instructor has a PhD in mathematics, which means that s/he has learned not just how to learn independently, but how to become an expert in mathematical subject matter.  Given the interconnectedness of mathematics, I am confident that Dr. X will do an excellent job not only with the subject at hand, but how it fits into your studies in general, both before and after this class.

Some may disagree with this characterization, but anyway I think it's more true than not.
Obviously the first time won't be the best, but that is something that can be said for any course when taught the first time, including freshman calculus/college algebra/finite mathematics or whatever your "first" college course happens to be.  How many people really "get" the Mean Value Theorem until they have to teach it?  Proving random stuff with it in some undergraduate real analysis course also likely lies years behind instructor Y or Z, not just instructor X.
Comment: (Something you might *not* want to say is that the instructor might actually be more motivated - and hence better - by getting to learn something they didn't learn before but always wanted to, as opposed to something they now find sort of uninspiring or boring.  It's likely to be true reasonably often, but probably students won't like that rationale as much.)
Comment: Not only a non-specialist can be more motivated, but he or she can see more easily what is difficult to understand, not having years of habits to hide difficulties from her or him.
Answer: Usually undergraduate level courses are not very difficult for experienced researchers/lecturers. Even without previous research experience in the specific topic, lecturers can learn the material very fast and be able to teach the topic to students well enough afterwards.
However, it may be the case that the lecturer appears to be unqualified or unfit to teach the material, but based on my personal experience I think this often reflects on the lecturer's ability to teach rather than their knowledge on the subject.
Answer: In France, my answer would be that we only hire faculty who can teach every mathematical subject at every undergraduate level (possibly with quite some work, of course). This is most usually included in the job description, and is pretty accurate in practice.
One thing that makes it relatively easy to ensure that a good majority of faculty have this broadness is that a good majority of us have taken Agrégation, a national competition intended to hire high school teachers of higher mathematical level, where one has to demonstrate a good mastery of a big chunk of undergraduate mathematics.
Another point is that the higher education in Écoles Normales Supérieures is very broad: one does not specialize too much too early; and a good majority of faculty in France went to one of these ENS. Of course, we also hire people whose higher education was at a university, and foreign mathematicians, but many of them are equally broad, and all in all I think the vast majority of faculty is able to teach any undergraduate course, if needed.
Answer: The one thing I would add--hopefully not considered a segue--is to avoid justifying or opening up a discussion of justifying.  The natural impetus of the students is to assume competence of the instructor.  Don't weaken that.
You may feel an urge to confession ("first time teaching this" or "never took this"), but it is likely you are trying to gain sympathy or to set expectations lower.  This is a natural human thing to do, especially for bright people with inverse Dunning-Kreuger.  But don't do it.  Stay positive, stay in control, and just do your best to teach a great course...with a stiff upper lip about your lack of experience.  Nobody wants to hear your issues...they want to learn the topic.
Source: instructor training for first aid and skiing.  Absolutely do not tell your classes, you are a first timer.  And I believe the commonality here is psychology and pedagogy.  Not course content.  IOW, the "educators" part is dominant, not the "mathematics" part.
Comment: I have come across situations where the students do not automatically accept the lecturer. Besides, I don't think it's really appropriate to be doing something like that if it can't be justified to the students.
Answer: Assessment is the easy part, anyone who is well versed in the logic of mathematics should be able to vet the student's proofs and computations.
Teaching is less clear. You want the lecturer to know what the important parts are. If they aren't familiar with the subject, how are they going to know where the most fertile ideas can be found? (This can be remedied if there is a good textbook available.) Still, you can always run the class --- not as a lecture --- but as a seminar where everyone is upfront about the fact that everyone, including the professor, is learning the subject together. I've certainly had classes like that in graduate school, for emerging topics. They were fun!
Comment: I think there are problems with assessment. While in theory you should be able to verify correctness, I find that even in familiar topics it can be hard to spot all the tricks that sound reasonably but are not right for some fairly subtle reason. Judging the value of an incorrect answer seems potentially problematic too. Everyone learning together sounds fine for graduate level, but I find it hard to picture that working so well in an undergraduate context where a mark has to given at the end.

Justifying non-expert lecturer


What tools does a Buddhist have to engender others to take a wiser approach?

Question: Mum is regularly woken in the night by panic attacks which bring on uncomfortable physical sensations that she takes so seriously she has been known to ring the paramedics (always unnecessarily). After many months I am still unable to get her to even entertain the notion of 'staying with the discomfort, just as it is'. Does a Buddhist have any tools (metta/prayer/mantras - sorry I don't know the words) to manifest/stir-up a change in someone else's approach? Or do I have to work on cultivating my own acceptance of the situation - however resigned that might make me feel?
Answer: I'm sorry to hear about your mother's discomforts. I used to have similar panic attacks that would bring on hyperventilation, taking Xanax and in extreme cases calling the paramedics as well, even though I had studied Buddhism academically for many years and I "knew" it should be able to help me.
It was only when I actually started practicing in stead of studying the attacks subsided, mostly because I had learned to recognize their arising in my mind and the cascade of thoughts, feelings and physical reactions that followed out of them.
The best recommendation I can give you from personal experience is not to start with "staying with the discomfort", as this already requires a person to be able to "witness" the arising and setting of thoughts in the mind. I suggest you start with simple breath counting in a comfortable position and once she is comfortable doing this, ask your mother to observe the space in between thoughts. Doing so will allow these spaces to grow and allow your mom to see the arising of thoughts and sensations, in stead of them being constant and unstoppable, like we usually perceive them. Once you get to that stage, you can start focusing on "staying with" the discomfort, as she will no longer experience it as inevitably leading to the subsequent discomfort in her mind.
Hope this helps, best wishes to you and your mother.
Answer: Metta practice, toward all beings seriously, by heart, in action: The Healing Power of the Precepts. Once even right view and right thinking is established, there is no more falling into low states and the path to final liberation opened.
That's by the way the only way to pay the goodness of ones mother, parents back. Good if giving best try and walk the path in front to know it. Mudita, Nyom Robin.
That might be an answer to the text-part. As for the header, it does not really fit to the rest. So maybe good if dividing and make two questions.
One has actually not really any tool to "change" others as beings are heirs of there own actions at least. Much faith in you might help others to take of what you give (and provide just good). If having learned to read mind (formost your own), it might help to provide at more proper time, but also this has it's limits.
[Note: this is a gift of Dhamma, not thought for trade, stakes, exchanges or other gains subject toward decay and should be deleted if it's not giften to give in Dhammic conditions]


Did Ajamila go to swarga or attain moksha?

Question: He called his son "Narayana" on his deathbed and that amounted to calling the god Narayana and that absolved him of all sins according to the story.  Did he go to Swarga or attain Moksha?
Answer: Ajamila went to abode of Vishnu on heavenly car assuming form of Vishnu's attendant after casting his body.
After chanting name "Narayana"(name of Lord), Lord Vishnu's attendants appeared on spot and saved him from noose of Yama and his attendants.
Chapter 1, sixth Khanda of Bhagavata Purana says: (translated by Dr. G.V. Tagore)

Thus, the ignorant Ajämila led his life. When the time of death actually arrived, he thought of his young son called Näräyana.
(Then) he saw that three extremely terrible male figures with wry faces, and with the hair on their bodies standing erect, and with
  nooses in their hands, had come to take him away.
With his senses greatly agitated, he called out in a prolonged loud voice, his son named Näräyana who was absorbed in his play-things
  at a distance.
Having heard the repetition of the name of Lord Hari, their master, uttered by the dying man, the servants of Näräyapa immediately
  rushed forward, Oh great King.
Angels of Vishnu (intercepted and) forcibly stopped the messengers of Yama who were dragging (thé jiva of) Ajämila, the husband of the
  maid-servant, from the interior of his heart.
Thus prevented (from carrying out their duty) the messengers of Yama demanded, ' 'Who are you who thus defy the order of Yama, the god
  presiding over righteousness.

Vishnu's attendants said chanting name of Lord at death time destroys all sins  at death time (syllables of name of Lord are powerful enough to destroy all sins).
Vishnu's attendants said the following to Yama's attendants: (2nd chapter, 6th Khanda of Bhagavata Purana):

Hence, do not carry him ( the jiva of Ajämila) by the wrong way (the sinner's path leading to Yama's abode). He has completely
  expiated all his sins. (When even a syllable of the Lord's name is
  sufficient to annihilate all sins), he has uttered the complete name
  of the Lord when he was about to die (and there is no time and hence
  possibility of committing a sin after articulating the Lord's name) .
(As to the objection that Ajämila called his son and and not Vishnu, messengers explain). The experts in Sästras say that utterance
  of the Lord's name even if taken to denote another person, or in a
  friendly joke or as an insertion during the recitation of a song, or
  in (an outward, apparent ) disrespect"', completely annihilates all
  sins.

After explaining, Vishnu's attendants disappeared from spot and Ajamila contemplated on the discussion and got Vairagya and through yoga he casted off his body on banks of Ganga.

Sri Suka said :

In this way, through a moment's association with the pious (servants of Vishnu), he felt a thorough aversion to worldly life (and
  its pleasures) and freeing himself from all ties (to his mistress,
  children and property) , he proceeded to Gangädvära.
Settling down in that sacred place (the abode of God), he betook himself to (the path of) Yoga. He withdrew (from worldly pleasures)
  all his senses and organs, and concentrated his mind on the self.
Then, he dissociated his self from ( the product of) the gunas viz. the body, sense-organs etc., and by concentrating his mind, he
  fixed it on the Supreme Brahman, which is the essential form of the
  Lord and is the embodiment of consciousness, and bliss.
When his mind and intellect were thus ( thoroughly) stabilised in the Brahman, the Brähmapa visualized before him those very male
  figures (messengers of Vishnu) , and recognizing them as those as
  having been seen before, he stood up and bowed down his head (to pay
  respect).
After that vision, he cast off his body at the sacred place (Haridvära) in the Gaigä and immediately assumed the (angelic) form of
  the attendant of the Lord.
Along with the servants of Lord Vishnu, the Brähmapa ascended' the heavenly car made of gold and proceeded through heavens to thé abode
  of the Lord of Sri (i.e. Visnu).
Comment: Skandha not khanda
Comment: @moonstar is there difference between Khanda and Skandha? Skandha is branch but Skanda Purana divisions are called khandas.
Comment: Divisions of Mahabhagavatam are called Skandhas. Vishnu Purana are called Amshas, Ramayana are called Sargas. We should not change the names of the divisions. @moonstar is right.
Comment: @Sarvabhouma "Ramayana are called Sargas."  Then why Ramayana is famous for "kanda" like sundara kanda?
Comment: @KrishnaShweta Chapter is called Sarga and Divisions are called Kandas. Chapters can't be called Adhyayas similar to Bhagavad Gita and Vice versa
Answer: Ajamila attained moksha:

Accompanied by the order carriers of Lord Vishnu, Ajāmila boarded a golden aircraft. Passing through the airways, he went directly to the abode of Lord Vishnu, the husband of the goddess of fortune. (Bhagavata Purana 6.2.44)

Since, Ajamila had chanted "Narayana", he attained moksha as promised by Shree Krishna in the Bhagavad Gita:

And the one who, at the last moment, while leaving the body, departs, contemplating upon Me alone, attains My abode; of this, there is no doubt.(Bhagavad Gita 8.5)


Recommended time to finish a cup of coffee for the best caffeine surge?

Question: Is there such thing as a recommended time lapse in which to finish drinking a cup of coffee, in which you get the best kick out of the caffeine?
Answer: Physiologically, as soon as substances enter the body, they are being processed, entering your system and subsequently removed from it. By that logic, you will experience the greatest net effect of the caffeine content of your cup of coffee by finishing it in the shortest amount of time possible. This is assuming that your definition of 'best kick' is indeed attempting to feel the most potent effects of the caffeine available in your cup.
Comment: It's almost nigh impossible to tell since everyone's caffeine tolerance is different and thus you cannot even relate caffeine dosage to it's felt effects on each individual. This question doesn't actually have any useful one-answer-fits-all. All I can say is, to ensure a stable ride through the caffeine, you'll need to be drinking it in uniform mouthfuls, with uniform intervals for a stable caffeine intake. The sizes of the mouthfuls and intervals are the variables that are dependent on the individual and therefore the time taken will also be variable if we assume an 8oz cup.
Comment: You're welcome, I hope I that was helpful!
Comment: Cool. I guess more of what I mean is, how can I maximize the amount of time and effects of a cup of coffee. Sort of like feeling an average kick of caffeine and making the cup of coffee last the longest possible amount of time, while still having an average effect of it's caffeine in the human body.
Comment: Thank you! It very much did!


After America achieved independence, did George Washington continue to wear a military uniform?

Question: After the American Revolution, the founding fathers seem to have adapted their 'costumes' from similar European ones. Like the Europeans, their uniforms often had orders, medallions and 'golden-like'-coloured-epaulet. But some of these symbols were only about civil respect, not about their military descent. So what about George Washington?
Answer: George Washington made a point of NOT wearing a military uniform in civilian life. In his First Inaugural speech, he pointedly wore a "cloth coat" to set an example for other citizens of the fledgling Republic.
Source

http://suite101.com/article/washingtons-american-made-inaugural-clothes-a213962
Answer: Washington conspicuously respected the subordination of military to civilian power as a general, and at his inaugurations and other official appearances as president, always wore civilian clothes. Still, that does not mean he never donned his uniform again. At least one surviving uniform is in the collection of the Smithsonian Institution, and to quote liberally:

This blue wool coat is part of a suit of regimentals made for George Washington in 1789. It has a buff wool rise and fall collar, buff cuffs and lapels, and buff lining; there is a row of yellow metal buttons on each lapel, as well as on each cuff.
This uniform was worn by George Washington from 1789 until his death in 1799; the small clothes or breeches and waistcoat, date from the revolutionary period.
In December 1798, Washington was recorded wearing this uniform when he visited Philadelphia on Provisional Army duty. He wore a similar uniform when he was commissioned by the Continental Congress as Commander-in-Chief of the Continental Army.

Lansdowne's iconic painting of Washington in civilian dress was not produced until 1796.
There are some sources which say he donned his Revolutionary War uniform when reviewing troops suppressing the Whiskey Rebellion, which Joseph Ellis writes is the last time a sitting U.S. president commanded troops in the field. Washington was not charging into battle at the head of the army, however, and I did not turn up any authoritative sources which mention his dress.
Comment: True, but the question was about whether Washington continued to wear a military uniform after independence, not specifically about whether he wore it during his presidency.
Comment: Not a complaint, just a point I thought needed to be made. I've already upvoted the answer. :-)
Comment: I'd like to note that the timing from the quote implies that he never wore that uniform (perhaps didn't even have it made) until after he retired from public office (March 4, 1797).


Do physics laws really apply to anything?

Question: My professor said that a law was stated and announced as a law because it happens in our everyday life. He gave us an example of Newton's 3 laws.  He said that walking possess 3 laws of Newton's.  Is it true that all laws really happen in our daily motion?
Answer: There is no agreed upon definition of "law," or even "theory" in the sciences - including in physics. A better term which describes what scientists actually come up with is "model." A model is a description, usually mathematical, that relates quantities or behaviours that are seen in the world. For example, you will see mathematical formulas relating the acceleration of bodies to the forces impressed upon them, and formulas relating the forces to other quantities like mass or charge and so on. In principle these formulas allow you to compute what is going to happen in any given situation, and if the prediction is right then your model survives. The formulas are not "laws" in the sense that they have some independent existence: they only make sense within the larger model of which they are a part - in this case Newtonian mechanics. Nature doesn't sit down and ask "now how can I obey the laws now" and work out what to do next with a pen and paper like we physicists do. No, nature just does what it does. We try to describe and predict it using models.
Often a model starts with a simple observation, but as more and more observations are brought together the model becomes more general and more powerful, capable of describing more phenomenena. When new things are observed which cannot be incorporated into the model a new model is formed. The hard part is that the new model must still be capable of explaining the old things. It has to explain why the old model worked so well for the phenomena that were seen before. For example, we now know that Newtonian mechanics is an incorrect picture of the world. It works very well in everyday life, but it cannot describe things which are moving very fast or which are very small. For these you need the theory of relativity (an unfortunate name that stuck) and quantum mechanics, respectively. Or a combination of the two (quantum field theory) if things are both very fast and very small. At the moment quantum field theory is the most general framework in which we know how to do physics. But you can recover Newtonian mechanics as an excellent approximation in ordinary situations that you will face every day.
This is the sense in which "laws" apply to the real world. All scientific knowledge is provisional. Nature just is what it is, and does what it does, but we try to describe it. The remarkable thing about physics is that we can describe nature quantitatively to great accuracy. New discoveries may be made which require a new understanding of the world, but the new understanding will always be one that subsumes, or explains, why the old understanding worked well in the past. Newtonian mechanics is still very useful. I wouldn't want my bridge designers to spend a lot of time learning quantum field theory - I'd want them to spend a lot of time mastering the practical application of Newtonian mechanics (that is, applying the formulas well and speedily). But in the end all of our laws, theories or models are at best approximate quantitative and provisional descriptions of nature.
Answer: No.
Opinion:
A true "law" in physics is roughly equivalent to a theorem in Mathematics.  Usually to become a law there needs to be some sort of theoretical or mathematical basis for it as well as be validated experimentally.
Answer (counter example):
A physical law like "nothing can travel faster than the speed of light" is not something we encounter at all in our daily lives.


What is the difference between "beweisen" and "nachweisen"?

Question: Is there a difference between these two words? What is it?
As I found they both mean: to prove, demonstrate. They are also reported as a synonym in Duden.
Comment: beweisen - logisch, mit den Argumenten.
nachweisen - mit einem Dokument, einer Untersuchung, ...
Answer: First, beweisen is the term used in mathematics if you prove something. Second, it is also used if you prove yourself. In both cases, you cannot go with nachweisen.
Now let's get to their overlapping meaning of proving something to be true by using facts, evidence.
I don't think there's really a difference in meaning; however, you cannot always interchange these words. Their uses differs slightly.
When you establish proof of something to somebody, you say jemandem etwas nachweisen.

Dem Angeklagten konnte die Tat nachgewiesen werden.

There was a claim that the defendant committed a crime and they were able to give proof. If you'd like to go with beweisen, you must change it a bit:

Die Tat konnte bewiesen werden.

So, beweisen is merely about "give proof of something", while nachweisen can additionally take a dative object to indicate who's guilty.
Though, you can also apply the dative object to beweisen. But it's different and is, for instance, commonly used in the sense of proving yourself.

Ich konnte ihm beweisen, dass ich doch dazu fähig bin.

That simply means, that you proved something to someone. They now believe you that you were right.
Some more examples:
You'd go with "jemandem den Alkoholkonsum nachweisen" (proving that they drank alcohol) rather than "den Alkoholkonsum beweisen" (yes, people drink alcohol... who cares?!).
It's more common to say "jemandes Unschuld beweisen" than "jemandes Unschuld nachweisen" (or even less likely "jemandem seine Unschuld nachweisen", but this is based on the fact that only few people pronounce themselves guilty if they're not). So, you simply prove somebody's innocence.
Basically, you can use "(jemandem) etwas nachweisen" when you make a statement and then, afterwards, you give some prove to 'show' you're right. Thus, nachweisen is typically used when you give proof by merely presenting a document that proves your statement. Beweisen would sound slightly odd in that context.
For the sake of completeness, I'd like to mention that there also the phrases einen Nachweis erbringen and einen Beweis erbringen, respectively.

Für die Tat konnte kein Nachweis erbracht werden.
  Du solltest schon einen Beweis vorlegen, wenn du mit solchen Behauptungen daher kommst.
Comment: So in the context of your example sentence, Tat means specifically crime. This is new to me. I always perceive this word in a more general meaning: deed, act, etc. It is more neutral. According to you, it can also be negative.

Man learnt nie aus.
Comment: @Cary https://www.duden.de/rechtschreibung/Tat 1b) --- But I don't think it's negative. It doesn't have a connotation, it's just describing a crime.
Answer: Well they mean almost the same but you will have to use them differently.
Nachweisen always comes with something, which you have proven or somebody who you have proven to have done something.

Der Wissenschaftler konnte die Existenz von Sauerstoff nachweisen.
  Der Polizist weist dem Dieb eine Straftat nach.
  Der Polizist beweist, dass der Dieb eine Straftat begangen hat.

As you can see there is a grammatical difference but no difference concerning the meaning of the words.
Answer: A good question, but difficult to answer. Duden has seen this problem by only saying beweisen and nachweisen are just variants. The normal word is beweisen.
Nachweisen is typical for certain sectors such as chemistry and  law and authorities.
Authorities need a special Nachweis for the death of a person. It is a special document called "Sterbeurkunde". A physician has to write a "Totenschein" and deliver it to the special authority that in turn gives out a "Sterbeurkunde", which is sent to the son or daughter. This document is a Nachweis for the death for other institutions such as banks etc. And for this special Beweis authorities prefer the special term Nachweis.
There are a lot of Beweise that someone is dead, e.g. when one does not breath anymore or one's body is cold. But authorities need and produce a special Nachweis.

What is the difference between “beweisen” and “nachweisen”?


Water from coffee condensation

Question: Why is it that from a cup of hot coffee, only the water condensates on the inside of the lid? Why aren't there any coffee particles? Does it only have to do with density or is it something else involved?
Comment: To condensate, a compound must evaporate first. Water does that, and coffee particles do not. This has nothing to do with density. Also, welcome to Chem.SE.
Comment: Yes, thank you:). I was thinking more about the actual evaporation process. I know that for water to evaporate, the molecules must have sufficient KE to overcome hydrogen bonding, but what happens to the kinetic energy of coffee molecules? is it just slowly given off as heat or is there even if just "theoretical" evaporation/sublimation.
Answer: I agree with Jan. The "coffee molecules", probably mostly alkaloids like caffeine, have larger and heavier structures than water molecules. I would expect most have dipole-dipole intermolecular forces, and (minor) hydrogen bonding may be present for some.
When you heat the solution with thermal energy, when we zoom in to the molecular scale we see this energy us actually kinetic. The molecules move faster, and some at the surface break free of their attractions to their neighbors. Despite water being held together by the strong hydrogen bonding intermolecular force, water molecules will be first and most to gain enough energy to pop out of the liquid solution. As Jan said, there are many more water molecules that coffee solute molecules. Also, the coffee solute's greater weights will make them harder to bring up to speed (though as a general rule of thumb IMFs like H-bonds actually play a more significant role than mass).
So those water molecules that pop out are far from their neighbors, so they constitute what we call a gas or vapor. There is much more water-gas above the solution than coffee-molecule-gas. This water vapor exerts a pressure based on how many molecules there are (and depending on kinetic energy / temperature), and we call this pressure from the gas above the coffee the "vapor pressure of the solution". The vapor pressure of water, despite being low relative to many organic liquids, is far higher than the vapor pressure of the molecules from coffee.
Think about the coffee residue in your pot, or the grounds - do they evaporate? Essentially no. There is essentially no vapor pressure, they are too bound by their IMFs to pop out and become gas (at temperatures a human usually encounters anyway). But water has a high vapor pressure, it is easily evaporated.
So when the gaseous water molecules encounter cooler surfaces, they will transfer some kinetic energy to the surface and transition from energetic gas state to lower-energy liquid state. This is the meaning of "condense". No coffee molecules condense, because none were in the gas phase to begin with (essentially).
Jan had a great point that these concepts are the foundation of the incredibly important process of distillation.
Answer: Let's analyse the sequence of events.

You have a solution
part of that solution enters the gas phase
the part that enters the gas phase moves until
it finds a surface that it feels comfortable 'settling' on.

It should quickly be mentioned that water is the primary component of coffee by far, hands down. Thus, even assuming approximately equal distribution in the gas phase, there should still be a lot more water than anything else. But that alone doesn't really answer it.
The key quantity you want to be looking at is vapour pressure. The coffee is hot (or at least warm), relatively close to water's boiling point of $100~\mathrm{^\circ C}$ so the vapour pressure of water will be comparatively large. Most other components of coffee have a boiling point that is much higher and would be solids at room temperature. These two factors combined allow us to allocate them a low vapour pressure even at the temperature of hot coffee. Therefore, the amount of water leaving the coffee is even larger.
The basic principle behind this is distillation; a mixture of multiple compounds that can be separated by their vapour pressures (often correlating with their corresponding boiling points). Typically, liquids will be distilled away far before solids.

Water from coffee condensation


can recessive alleles produce codominance?

Question: Maybe I'm confused by the term "codominance", but I wondering if codominance only occurs with two dominant alleles.
Can two recessive alleles produce codominance in an individual?
Likewise, can two recessive alleles produce incomplete dominance?
Answer: An allele is not dominant or recessive by itself. It is dominant or recessive compared to another allele. Therefore, if you consider one locus (position on a sequence) that has two alleles (bi-allelic locus), you cannot have two dominant or two recessive alleles. It is like saying that two things are darker. In reality you can either say that one is darker than the other one or that the color is as dark as the other one. So either one allele is dominant (or partially dominant) and the other is necessarily recessive (or partially recessive) or the two alleles are codominant.

Think of a gene that influence a phenotypic trait such as tail length for example. This locus is bi-allelic (two different alleles (=variant of a gene) exist (=segregate) at this locus). We'll call the two alleles $A$ and $B$. An individual that homozygous $AA$ has trait value $M_{AA}$. The homozygotes $AB$ have trait value $M_{AB}$ and individuals $BB$ have trait values $M_{BB}$. Viewing this in a table it gives:
$$
\begin{array}{c|lcr}
\text{Genotype} & \text{Tail length} \\
\hline
\text{AA} & M_{AA}\\
\text{AB} & M_{AB}\\
\text{BB} & M_{BB}\\
\end{array}
$$
The following table gives the tail length of the different genotypes under the different types of interactions (dominance, partial dominance and co-dominance).
$$
\begin{array}{c|lcr}
\text{Interaction} & \text{AA} & \text{AB} & \text{BB} \\
\hline
\text{A is dominant and B is recessive} & M_{AA} & M_{AA} = M_{AB} & M_{BB} \\
\\
\\ & & M_{AA} > M_{AB} > M_{BB}\\
\text{Partial Dominance} & M_{AA} & \text{or} & M_{BB}
\\ & & M_{AA} < M_{AB} < M_{BB} \\
\\
\text{Codominance} & M_{AA} & M_{AB} = \frac{M_{AA} + M_{BB}}{2} & M_{BB} \\
\end{array}
$$
Because, in the codominance case $M_{AB}$ is necessarily between the values of $M_{AA}$ and $M_{BB}$ ($M_{AA} > M_{AB} > M_{BB}$ or $M_{AA} < M_{AB} < M_{BB}$), one can consider codominance as being a special case of partial dominance where neither $A$ or $B$ dominates because they both contribute as much to the determination of the tail length.
Various definitions may exist for such concepts as well as for overdominance (also sometimes called heterozygous advantage) or stabilizing selection for examples. Those definitions differ in the sense that they sometimes apply to the value of the quantitative trait, to the fitness value (which is another quantitative trait) or to genetic polymorphism.
Answer: When two alleles show codiminance, they are not described as dominant or recessive relative to each other. They are simply codiminant to each other. The same applies to incomplete dominance.
Note that all these terms are relative to the alleles you're talking about. An allele that is dominant over one allele may be recessive to another and codiminant with yet another.
Answer: Shorter answer:
The dominant/recessive paradigm that is taught in middle school and high school is not universally applicable.  It accurately describes only a small number of phenotypes, compared to all the genotype/phenotype interactions which an organism exhibits.  It was a useful place to start when it came to unraveling the relationship between genes and phenotypes, but it is very limited.
So trying to shoehorn all phenotypes into that paradigm is a serious mistake.  Just because all of your homework problems are solved using it doesn't mean that it's applicable to all real-life situations.


Line breaks in markdown

Question: I have been seeing new users who copy/paste code or information into posts not add extra newlines(or even type without extra newlines) and make posts hard to read, wasting the time of a moderator or editor. Can this behavior be changed to make single linebreaks act as lienbreaks? Or is by design?
Comment: I see far too many users blindly copy-pasting from a forum, termian output, etc, and getting one big mess that will waste about 10 minutes of an editor. in alleviating the situation.
Answer: It is by-design - the Markdown syntax specifies a blank line between paragraphs.
Code should be indicated as such - indented four spaces. There's a button on the toolbar and a shortcut key to accomplish this, and doing so also handles escaping special characters in cases where it otherwise can't be done automatically.

Line breaks in markdown


How can I find this limit?

Question: The question is:
$$\lim_{x\rightarrow0} \frac {(x+1)^{1/3}-1} x$$
Obviously I have to rationalize it such that the x in the denominator is removed, but I'm not sure how to do so. Thanks.
Comment: Hint: What is the value of derivative of $\sqrt[3]{x+1}$ at $x=0$?
Answer: another way could be for you to use a substitution $x+1=t^3$. Then as $x \to 0$, $t \to 1$. Use this and simplify.
Comment: How would I simplify the x in the denominator (that's the main problem I'm having).
Comment: using the substitution I mentioned you get $\lim_{t \to 1}\frac{t-1}{t^3-1}$. Now use the factorization $t^3-1=(t-1)(t^2+t+1)$.
Answer: I'm assuming you've studied differentiation. Let $f(x)=(x+1)^{1/3}$. Now consider $f'(0)$. By definition,
\begin{align} f'(0)&= \lim_{h\to0}\frac{f(h)-f(0)}{h} \\
&=\lim_{h\to0} \frac{(h+1)^{1/3}-1}{h}
\end{align}
This is precisely the limit you want to evaluate. Now $f'(0)$ can be evaluated using your usual rules of differentiation.
$$ f'(x)=\frac{1}{3}(x+1)^{-2/3}$$ and so
$f'(0)=1/3$.
Note: This trick can be used to evaluate limits that looks of the form 'difference quotient'. I think the point of the problem is for you to see that the given limit is the definition for $f'(0)$.
Answer: Let's put $1 + x = y$ so that $y \to 1$ as $x \to 0$. Then we have $$\begin{aligned}L &= \lim_{x \to 0}\frac{(1 + x)^{1/3} - 1}{x}\\
&= \lim_{y \to 1}\frac{y^{1/3} - 1}{y - 1}\\
&= \lim_{z \to 1}\frac{z - 1}{z^{3} - 1}\text{ by putting }y = z^{3}, z\to 1\\
&= \lim_{z \to 1}\frac{1}{z^{2} + z + 1} = \frac{1}{3}\end{aligned}$$
Note that we can prove the more general result in the same manner (i.e. using algebraic manipulation) that $$\lim_{x \to a}\frac{x^{n} - a^{n}}{x - a} = na^{n - 1}\tag {1}$$ if $a > 0$ and $n$ is rational. The result holds even if the number $n$ is irrational, but then the proof is not based on algebraical manipulation but rather on theory of logarithm and exponential functions.
Some answers have used the differentiation technique to get the answer. However to prove that $(x^{n})' = nx^{n - 1}$ we do need to use the limit result (1) I have mentioned above so that the reasoning based on differentiation to calculate this is kind of circular and should be avoided unless the question is kind of multiple choice type (where you have to get the answer and not show the working).
Answer: Use L'Hôpital's rule:
$\lim\limits_{x\rightarrow0} \left[ \frac {(x+1)^{1/3}-1}{x} \right]=\lim\limits_{x\rightarrow0}\left[\frac{\frac{d}{dx}[(x+1)^{1/3}-1]}{\frac{d}{dx}[x]} \right]=\lim\limits_{x\rightarrow0}\left[\frac{\frac{1}{3}(x+1)^{-2/3}-0}{1}\right]=\lim\limits_{x\rightarrow0}\left[\frac{1}{3}(x+1)^{-2/3}\right]=...$

How can I find this limit?


What is this long spiked black piece with rubbery orange tip piece used for?

Question: Missing instructions but it should stand out if you've ever seen it
Comment: Welcome to Bricks.  Do you see LEGO logos on it anywhere?  Can we get a picture of the other side?
Answer: This is part 61406pb04 Plate, Modified 1x2 with Angular Extension and Flexible Orange Tip, which comes in 2 sets:
8076 Deep Sea Striker

70135 Cragger's Fire Striker
Answer: It sounds like you're going through a large collection, so may have this question again.
In general, if you have a LEGO part you don't recognize, the best thing to do is to search for the four or five digit design number on the underside.  (It's small on many parts, molded into the plastic in the recesses.)  In this case, the design number is 61406.  There are several websites you can use to find it based on the design number; Brick Owl is one I'm fond of.
From there, you can look at the sets that used (and others with the same design but different colors) to get a sense of its usual use.


Why not just print money to combat deflation?

Question: If interest rates are zero and inflation is under 2% per year then why not have the fed print money without borrowing until inflation is back at 2% per year? The money could be used to pay off the national debt. Businesses would have a predictable floor of a 2% inflation rate.  The slippery slope argument against that sort of policy could be prevented by having the policy written into law. It's a fix where everyone wins, right?
Comment: So what is the reverse side if inflation rises above 2%? Escalating tax increases or interest rises until the economy crashes?
Comment: Once inflation goes above 2% or interest rates rise above zero then you stop printing money and revert to standard monetary policy- use interest rate hikes to control inflation.
Answer: That's essentially what Quantitative Easing was supposed to be.
However, we've known for about 80 years that it doesn't work in times like these, and like the 1930s, when demand is flat because of a massive debt overhang. The demand for money just isn't there.
In these times, trying to simply expand the money supply is like pushing on a piece of string.
Japan's been battling with non-responsive flat demand for many years now (though driven largely by demographics). Monetary stimulus has failed. Fiscal stimulus has at least steadied the ship.
Comment: This is like a stimulus package that doesn't add anything to the national debt. Printing money can be used to boost public spending, which gets back into the public hands in the form of teacher salaries or transportation engineering jobs. Banks and borrowing are not part of the equation.
Comment: Printing money works if it gets to the publics hands, and if the public decide to spend it. In the case of Japan, people save a lot more than in other countries, and everywhere else where there has been a quantitative easing, the transmission channel was sort of broken, the money didn't get to the public hands, because banks didn't lent the money on fear they won't get it back. That's why, in this kind of situation printing money doesn't fight deflation.
Comment: @user2133034 did you find an answer? I was just going to write the same question... this does indeed not answer it, since the effect concerning deflation, is the same whether bonds are bought or not... so why do it?


What is this bug and how do I keep it from eating my plants' leaves?

Question: Can someone tell me if they know what type of bug this is?  If so, how do I get rid of it as it seems to be eating the leaves.
Click any photo for full size
Comment: That's quite hard to see. If you don't have a better camera, try taking the picture through a magnifying glass.
Comment: Or at least get a picture on a more contrasting background if you can
Answer: That is a katydid, which is any insect in the family Tettigoniidae. Yours is from the  sub-family Phaneropterinae. It's a California Anglewing, Microcentrum californicum. It's probably not causing much damage on your plants, but you can control it with a general insecticide.
Here's a comparison picture:
Comment: My comparison pic even has the antenna missing on the same side. =)
Answer: It is hard to see clearly, but it looks as if the body is shaped rather like an elongated leaf, with the back end narrowing down almost to a point. The eyes are definitely yellowish with black centres, it should have six legs, jointed in the manner of the two I can see in the picture - if I'm seeing it properly, this is a green katydid, and its one of those that does eat plants - usually sticks around on whatever plant it likes most and eats that. Presumably there is some local treatment appropriate for these if you have a heavy infestation, I'm in the UK, so don't know what you'd use - maybe someone else can advise on a suitable pesticide, if its necessary.
Comment: @J.Musser I could see most of it (on my desktop) but  couldn't quite distinguish between the greens for overall body shape - don't forget, my eyes are a lot older than yours!
Comment: @J.Musser blimey, herbicide, of course I meant pesticide. I shall alter that, must have been on automatic pilot when I typed it. Not sure if its necessary or not to use pesticide, depends if its eating too much of the plant. By the way, I only have a dumbphone and a tablet, no smartphone.


Cokin Z Pro filter holder causes vignetting at 18 mm on Nikkon 18-35. Any solutions?

Question: My Cokin z pro holder causes vignetting at 18 mm on my Nikon 18-35 mm and the problem is accentuated if I have to screw it on top of a polarizer. Anyone else had this problem or have any solutions? I am using the Cokin provided filter holder and the lens thread is 77mm.
Answer: There is a limit to the amount of length you can add to the lens barrel before it starts blocking the light that enters the lens.  The determining factors are the angle of view and how far back the front element is from the filter threads.  The current version of your lens has a front element that's more recessed than its predecessor, so that factor gives you less room to work even though the widest focal lengths are the same.
I think the Z series holder is already good for wide-angle use (the P series has a different holder for that purpose), so the best you can do is get rid of your polarizer or switch to a slim one if you're not using one already.


What reactions occur when mixing copper sulfate and sodium hydroxide?

Question: I tried reacting copper sulfate with sodium hydroxide to get copper hydroxide, which should precipitate, according to the following equation:
$$\ce{2NaOH + CuSO4 -> Cu(OH)2(s) + Na2SO4}$$
I looked on Google Images, and the color of copper hydroxide is light-blue, but something interesting happened when I mixed these two solutions: the precipitate formed - and was originally light-blue, as expected - however, it turned into this black-green sludge within a few seconds. I'm thinking a complex ion might have formed between the $\ce{Na2SO4}$, and the $\ce{Cu(OH)2}$. I just saw a video on this, posted by NileRed, but he doesn't go into detail. Does anyone have an idea of what's going on?
Comment: Well, many compounds of copper are green. There's for example https://pl.wikipedia.org/wiki/Brochantyt
Answer: As noted in your question and in one of the comments, copper forms many different complexes having a variety of colors from red to green to blue to black and probably more.  Of course the situation here is even more "complex" (sorry) as you can end up with mixtures of the different copper complexes, as appears to be the case over the course of your experiment.
The formation of some cupric oxide ($\ce{CuO}$) would account for the appearance of an insoluble black precipitate.  This could happen from the decomposition of some of the $\ce{Cu(OH)2}$.
$\ce{Cu(OH)2}$ itself should be a greenish to pale-blue insoluble precipitate.
It is possible that the original $\ce{Cu(OH)2}$ precipitate appeared more blue than green due to the blue $\ce{CuSO4}$ solution.  As the reaction proceeded, $\ce{CuO}$ and more $\ce{Cu(OH)2}$ precipitated to give the black-green precipitate you observed.
Comment: The wiki link shows Cu(OH)2 as a "blue" solid. It looks blusih-green to me. Sort of turquoise color. I think you also have to consider "wet" vs "dry" Cu(OH)2. Cu(SO4)*(H2O)5 is much darker blue than Cu(SO4).
Comment: Good point about the hydration @MaxW.  I also tried to give a better description of the turquoise-ish color.  It seems to me to change with the angle of my monitor, so I included the description given in the text;)
Comment: Hydroxide ppts are notorious for absorbing other ions. In a strong hydroxide solution I'd expect the ppt to drag extra $\ce{OH^-}$ out of solution. I'd guess that the decomposition of $\ce{Cu(OH)2}$ is base catalyzed. So $$\ce{Cu(OH)2 + OH^- -> CuO(OH)^- + H2O}$$ $$\ce{CuO(OH)^-  -> CuO + OH^-}$$ Out of an ammonia solution the ppt must form slowly enough so as to absorb very little extra $\ce{OH^-}$.
Comment: If I remember correctly, anhydrous copper sulfate is white, but that should hardly be an issue here.
Answer: Yes, as noted by @airhuff, there is not one but two reactions involving, one is formation of greenish-pale blue copper sulfate, $\ce{CuSO4}$ and other one is formation of black-brown copper(II) oxide $\ce{CuO}$. Also, there are also solvation reactions occurring involving formation of solvated complex but we are going to neglect that.
\begin{align}
\ce{CuSO4 + 2NaOH &-> Cu(OH)2 + Na2SO4}\tag{1}\label{one}\\
\ce{2CuSO4 + 2NaOH &-> [CuO + H2O] + Na2SO4}\tag{2}\label{two}
\end{align}
Some copper(II) hydroxide decomposes to form copper(II) oxide and water,
$$\ce{Cu(OH)2 -> CuO + H2O},$$
and that's how reaction $\eqref{two}$ proceeds.


Upgrade to the latest LTS ubuntu server

Question: I've the old OS installed in our server and I needed to install nodejs on the process I was required to update the system so I did apt-get update and in the process it breaks the libudev library and I keep on getting udev requires a kernel >= 2.6.32 not started failed when I start in result I can not login to the server via SSH or run screen command. I'm thinking of upgrading the server OS to ubuntu 12.04 LTS.  My question is how do I achieve this and what are the implications on the running applications on the server? Is there any safe way to upgrade but also ensuring the installed application runs smoothly?
Answer: There's a specific package for that, install it and run the upgrade:
sudo apt-get install update-manager-core
sudo do-release-upgrade

The upgrade will get you a new kernel, 3.2 in the case of 12.04. This means that all packages installed must be upgraded too, to versions compiled against the new kernel. Since 10.04 is now 3 years old, there might be some relevant changes to the software installed. Say that a particular application uses a different configuration method, after the upgrade you must change the old configuration to the new method.
You can do a search for the relevant packages to check the versions available for 10.04 and 12.04. You can then compare what may have changed between the two.

Upgrade to the latest LTS ubuntu server


Altec Lansing iML 237 not Working in 11.10

Question: I have an Altec Lansing iML 237 external USB that was working in 11.04, but does not in 11.10.  When plugged in, a "CM102-A+/102S+ Audio Controller" appears in the sound system settings, but it will not play.  The only profile setting is "Analog Stereo Output", but the speaker uses a digital interface over USB.
The output of lsusb is:
Bus 002 Device 008: ID 0d8c:0103 C-Media Electronics, Inc. CM102-A+/102S+ Audio Controller

The system log when the speaker is plugged in:
Oct 31 20:08:26 TOSHIBA-NB505 kernel: [164035.560115] usb 2-2: new full speed USB device number 8 using uhci_hcd
Oct 31 20:08:26 TOSHIBA-NB505 mtp-probe: checking bus 2, device 8: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-2"
Oct 31 20:08:26 TOSHIBA-NB505 mtp-probe: bus: 2, device: 8 was not an MTP device

Any ideas, or is the driver for this device under linux 3.0 broken?
Answer: Well, just like when your car stops making that funny noise when you take it to the mechanic, the speaker started working!
I am going to attribute it to the mere action of posting to AskUbuntu!
Comment: Glad its working for you!


Link-buttons and button-links

Question: I'd like to hear your opinions whether or not using buttons that look like links (text links, especially when styled the same as links) and links that look like a buttons is a good practice. I feel that making a link look like a button, and vice versa, is materially dishonest and is deceptive. It tells users that links and buttons are the same but they aren't. For example, users might expect to be able to open the buttons that look like links in a new tab or window but that obviously doesn't happen. Links should be navigational and buttons actionable but then again we have buttons labeled "next" to go to a next step in wizards etc. Can anyone help to understand the convoluted science behind these components?
Answer: By general rule, your buttons should look like buttons and your link should look like links. But reality is so that it is not always possible (or even good for your precise situation).
In my opinion, there is no real harm for links to looks like buttons. It's the other way around that is tricky (for the reasons you mentioned).
If you decide to make a button looks like a link however, you should be very clear in you copy that clicking the button will trigger an action. There should be no doubt that it is in fact not a link. Context is crucial here. If you decide to try this for one of your project, I'll also advice you to test your screen with user just to be sure.
Answer: I think it both is okay if the user understands what will happen in the next step. A button is visually easier to scan for the user cause in most cases it has a border, background or something similar and the visible area is larger than the area of a link.
I think there is no perfect rule, should always test it with your target group.

Link-buttons and button-links


When did Spanish develop perfect aspect?

Question: Latin and many other Romance languages do not have perfect aspect, but Greek has perfect aspect and Iberia was a land for Ancient Greek colonies.
So how and when Spanish integrates perfect aspect into others existing Latin aspects (like perfective and imperfective aspects which also exist in Greek)?
Comment: Out of curiosity, why's this question here and not on Spanish SE?
Answer: I think this question is confused
Latin did have a perfect aspect, it was only available in the present, past, and future tenses (these verb forms are usually described as the perfect, pluperfect, and future perfect tenses respectively). This was a true perfect and not a perfective aspect in Classical Latin, that sense developed later as the Classical perfect "tense" evolved into the Spanish preterite (with perfective aspect)
The new perfect aspect using the descendant of habeo (or sum for some verbs, especially intransitive verbs of movement) + inf, which can be conjugated into whatever tense you like, is present in pretty much all Romance languages (although some conservative Romanian varieties prefer the old perfect tense). It seems to be a pretty-much universal feature of Vulgar Latin meaning it would likely already have developed by the end of the Republic
Comment: Wikipedia states that Portuguese had an haver perfect, but that now the use of ter has displaced it. As ter occupies the sense habeo had in vulgar latin, this doesn't seem a problem. The comment about Greek and Germanic was not well thought through or worded and is probably best off removed, I'll edit
Comment: Isn't the Latin perfective available in all three tenses? _Amāveram_ "I had loved", _amāvī_ "I have loved", _amāverō_ "I will have loved"?
Comment: ah yeah, you're right, will correct the post
Comment: Portuguese does not have a periphrastic perfect formed with _habeō_ either; it uses the preterite (= old perfect) as Latin did. It does have a similar construction with _ter_, but this is not a simple perfect: its meaning is more along the lines of 'lately I've been …ing' rather than just 'I have …ed'. Also, what do you mean by "a true perfect and not a perfective aspect in Classical Latin"? The Germanic past tense is not a perfective aspect, and nor is the Greek aorist – but the Classical Latin perfect _is_ a perfective (or rather, aoristic-perfective) aspect.
Comment: what I meant though is that the Germanic past is generally considered to have perfective aspect in most descendants (although I understand that in German it is moreorless just a past tense with no particular aspect and is sometimes called the imperfect to contrast with the compound perfect tense). My understanding was also that the aorist also had perfective aspect but my knowledge of Greek is fairly basic
Comment: @Tristan But the use of _ter_ has not replaced it – the preterite has. The _ter_ construction is not very common and does not correspond to the perfect aspect (or tense); in cases where Spanish would use _he …ado_, Portuguese will nearly always use _…ei_. All Germanic languages express perfect aspect through periphrasis; past is imperfective-aoristic. (Classical) Greek has imperfective, aorist and perfective all as morphological tenses (e.g., 1sg preterites ἔλυον – ἔλυσα – ἔλελύκειν).
Comment: I think we're talking at cross-purposes here. In the compound perfect construction, ter has displaced haver. The fact the sense of that construction has shifted is a separate matter
Answer: Latin did in fact have a perfective aspect! (I'm going to use the term "perfective" for the aspect here, because "perfect" has a different meaning in traditional Latin grammar, but "perfective aspect" and "perfect aspect" are the same thing.)
Classical Latin had a three-way distinction of tense (past, present, future) and a three-way distinction of aspect (perfective, imperfective, aoristic) which could be mixed and matched freely.
Some combinations looked the same as others:
<code>        Imperf. Aoristic Perfective
 Future  amābō   amābō     amāverō
Present   amō     amō       amāvī
   Past amābam   amāvī    amāveram
</code>
In particular, present perfective ("I have loved") and past aoristic ("I loved") look identical, due to two different PIE "tenses" merging in Proto-Italo-Celtic (*). But we know they were distinct functions, because of certain grammatical features that change if a verb is past vs present tense: present perfective acts like a present, and past aoristic acts like a past.
In Vulgar Latin somewhere around the first few centuries CE, a new form was invented for the present perfective (amātum habeō), and the old form was used only for the past aoristic. This is where most Romance languages got their "perfect" tense, though in many cases its meaning has shifted. I'm not very good at Spanish, but I believe Spanish kept the perfect semantics, while e.g. French and Italian didn't—but I would chalk this up to the vagaries of language change, not to any Greek influence.
(*) If you accept the existence of Proto-Italo-Celtic; if you don't, it happened separately in Proto-Italic and Proto-Celtic.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/108881/discussion-on-answer-by-draconis-when-did-spanish-develop-perfect-aspect).


Right hand technique for low chromatic notes

Question: I'm teaching myself to play the alto recorder. Since I'm mostly interested in jazz, I have been trying to practice in all keys from the start.
My problem is with the right-hand technique for the low chromatic notes. I found some descriptions mentioning a wrist turning action, where one is supposed to turn one's wrist outward or upward; the fingers sliding to a position where they only cover a half-hole. That more or less worked for me, but I seem to get better results and less right-hand movement when lifting the finger tip to uncover half-holes.
For example, when playing from low F to low Ab, I lift my pinkie and straighten my third finger, such that the tip of it lifts a little and doesn't cover the other half-hole anymore. While the wrist movement is similar to the supposedly proper technique, in this way I manage to keep my pinky closer to its hole, and it seems to minimize movement in general. Also, I find it easier to slur these and similar movements (e.g. Bb to Ab) – there is less chance of squeaking and bending, compared to when I do the sliding finger motion.
Since I don't have a recorder teacher, I'd like to know whether such a technique is acceptable. I suppose the movement might be considered to lead to a less natural finger position or more tension, but it actually feels quite comfortable to me.
Should I go on practicing this technique, or should I stop using it?
Answer: In my opinion, what works for you is what works. Everyone's hands, wrists, and recorders are different. You seem to be analyzing your movements with great attention to detail; keep doing that. Practicing the 'best' movements will get them into your muscle memory and they'll become, if not quite second nature, at least third.
You may find that you'll use both kinds of techniques depending on what you're playing -- going up or down the scale, etc. That's perfectly fine. Practice jumping right to the half-hole notes from all the others, just to see what works in terms of your wrist movement.
Have fun, keep experimenting.
Comment: Thank you very much for the advice. Practicing both techniques and using them when appropriate sounds reasonable. I'm just wondering whether you've ever seen other (good) players using something like this. (By the way, I'll wait a little for other answers before accepting.)
Comment: I wish I could accept more than one answer. I chose Matthew's because he went into a little more detail. (Also, as a beginner, it's reassuring to hear that I'm not the only one using this technique.) Thanks again!
Comment: Glad to be of service. If you watch professionals carefully you'll see them use all possible techniques, but usually the same one for a given transition/passage. At that level, alternative fingerings and breath control gives one even more choices about how handle tricky bits.
Answer: Rule #1 is to do what works for you. I don't do everything on the recorder the same way my teacher does, because I don't get on with some of her playing technique (particularly her method for left-hand thumb placement). You do have to know why you're doing what you're doing though, you can't just say "that looks hard" and do something else because it might be worth it being hard.
That said, you're clearly thinking in the right way about this. I've seen, roughly, three techniques for half-holing with the right hand.

Turning the wrist
Lifting and bending the fingers to close the half-hole with a fingertip (without having to turn the wrist)
Lifting the tip of the finger, as you've described you do

I've seen people play well with all of these techniques. I tend to turn the wrist, but that's just what works for me - my hands and fingers are too big for #3, I end up smothering the 'open' side of the hole. Also, my fingers aren't delicate or precise enough to do method #2.
So you do what works for you, but I don't think you can describe any of these methods as 'wrong'. Some have different advantages, and you're right about keeping your fingers closer to the holes being a good thing. The trick with the wrist-turning technique is to do as little of it as possible else you can't get those rapid movements from F to Ab (for example) which comes up a lot in baroque music. Whatever you do also has to work well for tricky transitions like G->Ab->G at speed (like one of my grade 8 exam pieces, that took a lot of boring drilling to get that sorted out).
But just keep thinking like you're thinking, examining everything you do and experiment a lot and you'll come up with things that work. Do read the literature, watch videos, talk to other recorder players, but it's ultimately your hands, your recorder and your style of music and if you're producing a good sound and not artificially limiting yourself with your technique then I don't see why you should feel compelled to obey everything in a book.
My teacher would claim most of the books are wrong anyway. She keeps saying she's going to write her own...
Comment: Great answer, thanks! I'll mostly stick with method three, then, but also practice method two, trying to minimize movement.


2d Euler manufactured solutions

Question: Where can I find manufactured solutions for the 2d Euler equations, with the complete analytical terms, including the Jacobian of the source term ?
Comment: Welcome to SciComp.SE! The point of manufactured solutions is that you can easily make your own, so it's not quite clear what you're asking for here. You can find analytical (and presumably physical) solutions to Euler's equations in http://www.sciencedirect.com/science/article/pii/S0895717703901105
Comment: I was looking if possible for something more directly implementable, like the analytical expressions of the solutions, their analytical source terms, and the  derivatives of the source terms.
Comment: You just repeated what you wrote in the question.
Answer: This 2004 paper by Roy et. al in Int. J. Numer. Meth. Fluids 2004; 44:599–620 (DOI: 10.1002/d.660) should contain exactly what you're looking for:
ftp://ftp.demec.ufpr.br/CFD/bibliografia/erros_numericos/Roy_et_al_2004.pdf
You can contact the authors to obtain a copy of the FORTRAN code for the source terms (and their derivatives), or generate them yourself using symbolic manipulation software such as Mathematica.
Another paper by the same authors:
http://www.dept.aoe.vt.edu/~cjroy/Conference-Papers/aiaa2002-3110.pdf
Answer: You can find information about Manufactured solutions in this repository. Particularly,
Malaya, Nicholas, et al. "MASA: a library for verification using manufactured and analytical solutions." Engineering with Computers 29.4 (2013): 487-496.
That have the codes in this GitHub repository.

MASA (Manufactured Analytical Solution Abstraction) is a library written in C++ (with C, python and Fortran90 interfaces) which provides a suite of manufactured solutions for the software verification of partial differential equation solvers in multiple dimensions. Example formulations include:
Heat Equation
Laplace's Equation
Euler Equations (with and without thermal equilibrium chemistry)
Navier-Stokes Equations
Reynolds Averaged Navier Stokes with Various Turbulence Models

2d Euler manufactured solutions


Stolen Idea Patented

Question: I think I made a mistake about a month ago and disclosed an idea that I had to a colleague.  I'm in the process of taking the idea to market, but it hasn't gone public yet.  I wasn't planning on patenting it, but it very well might be patentable.  Can the person that I disclosed the idea to patent it?
Comment: Quick summary: I think the answer is technically "no" -- if the other person didn't independently invent it, then it's not his to patent. If he does file for a patent, however, the onus is on you to demonstrate that he did not independently invent it and got the idea directly from you. You must also consider that your disclosure of the idea in a non-confidential setting constitutes a kind of "public disclosure" which can have legal ramifications as well. (But someone else will have to tell you exactly what those are; I don't know.)
Comment: There is a [similar question](http://patents.stackexchange.com/q/12157/14417) that might offer additional insight.
Answer: At least in the US, part of filing a patent application involves an oath/declaration, which includes a provision such as:

I hereby declare that: [...] I believe the inventor(s) named below to be the original and first inventor(s) of the subject matter which is claimed and for which a patent is sought on the invention titled:

Filing such a claim if he knew it to be false (i.e., knew that he was not the original and first inventor of the subject matter) would not only invalidate his application, but is probably1 illegal in itself, and could be subject to prosecution.
There are some provisions to allow (for example) a patent application to be filed if the inventor dies before filing the paperwork, but it doesn't sound like those would apply here.

But note that here I'm assuming US law. I suppose in some countries 1) you might not have to submit such a declaration, or 2) that knowingly lying on such a declaration might not violate any laws. Either of those would surprise me at least a little though.
Comment: An [answer to a related question](http://patents.stackexchange.com/a/13218/14417) contains additional information on the Oath/Declaration, prior to AIA.
Answer: As another answer says, only an actual inventor or someone an actual inventor has assigned their rights to can legally file in the U.S. since the AIA went into effect the declaration has been changed to

I believe that I am the original inventor or an original joint inventor of a claimed invention in the application.

If the disclosure would not be considered confidential it did start a one year clock on when you can file. Also, as mentioned, if you both file and he files first you need to prove he derived it from you. Maybe worse, he can invent something different, inspired by what he leaned from you.

Stolen Idea Patented


When an answer gets a NAA comment From Review, should it include justification?

Question: At present, when an NAA comment "From Review" appears, it includes boilerplate stating that this is not an answer, and critiques or clarification requests should be comments.  In cases where the answer is clearly not either of these, should some justification (or even explanation) for the admonition be included?  If part of the purpose here is to improve the quality of the answers, then identifying what the actual issue would seem to be called for.
Comment: It would be nice if flags could be interpreted again the way they were originally envisioned, before the review queues were added.  It used to mean "Hey, there's something wrong here!  Whomever can do something about it, please have a look".  But it now needs to be all perfectly categorized and mean exactly what the flag says.  Like NAA, ugh.  Far too many times I see answers getting flagged that are troubled only because the question is far too vague to allow a decent answer.  So whack the question, not the answer, and solve two problems.
Comment: If a comment doesn't address the issue in the post it is not constructive. It doesn't matter if the comment comes from the boilerplate. The normal comment policy should apply: if you have something useful to say and are prepared to engage in a conversation, do so. If not, don't comment.
Answer: I remember the days when people actually spoke their mind in comments.
Now, with review comments, it seems we can no longer rely on reviewers actually meaning what they "say" in the canned comments that they keep leaving in their wake, whether or not this was their intention.
The fact that you're now asking if a canned comment should include justification — and I can't think of any other way to include such a justification than for the reviewer to add another, manual comment in response to another comment (from you or someone else) requesting clarification of the original comment and potentially starting a drawn-out comment conversation about the canned comment — just goes to show how ridiculous things have become.
People, if you want to leave a comment on an answer you're reviewing, but the canned comment doesn't quite fit, the "add a comment" link is right there. You can enter a manual comment. And if you don't want to go to the trouble, the option of not leaving a comment is there, too. Last I checked, you are not forced to leave a comment on every answer you review in LQP. When in doubt, don't. Otherwise it just makes you sound stupid.
For everyone else, I refer you to my answer on non-sequitur review comments. In short I agree with rene: just flag them as not constructive. If you really want to get a word in edgewise, just express disagreement with the canned comment and advise the reviewer to be more specific next time. More likely than not, the owner of the answer couldn't care less about the nuances of the review system.
Comment: "And if you don't want to go to the trouble, the option of not leaving a comment is there, too" I think the problem here is that reviewers *don't consciously review* anymore and just want the number to go down or up...
Comment: It's also possible to just edit the auto-comment if it's almost, but not quite, a good fit.
Comment: Fwiw, this is exactly why I was reluctant to add these in the first place: http://meta.stackexchange.com/questions/117963/formal-adoption-of-pro-forma-comments-script-into-se-engine-proper/137363#137363 I do think they do more good than harm on balance, but there's no denying they get misused with some regularity. FWIW, the system automatically deletes these comments after a bit if there's no reply and the post isn't deleted.
Comment: @Braiam: I thought that was the case, but "No comment needed" *is the default option* - they could have just clicked right through the dialog to confirm the review without leaving an irrelevant comment. Unless they somehow managed to incorporate choosing a canned comment into their muscle memory...


how to find whether this paper is already available or not, if authors just changed the Paper title & author name?

Question: I am the editor. I received a paper from some author. I need to check whether that same paper is already published in some other journal or not. For example some authors downloaded a paper from some other journal, they just change the paper title, and author name and they send that paper to us. So in this case how can I find whether this paper is already available or not?
Answer: There are several software available for checking plagiarism, which would also fit the problem you are investigating. The journal (actually the publisher) for which I am editor use iThenticate. I am not in a position to compare the numerous software and services around, some free, some commercial. However, a simple check that can easily be made is to to a Google search on bits of text. I have personally used this to check on similarities between manuscripts and earlier published articles to check on the degree of overlap and it works fine. It will give you a first indication at which stage you can decide on continuing with a more advanced analysis.
See also answers in What is the easiest way to check for plagiarism in student essay papers?
Comment: Some evidence: in the late 1990s and early 2000s I taught courses on crypto and on coding, in which I required a written project. Some plagiarism was hinted at from use of language that I suspected was beyond the ken of the given writer, and follow-ups confirmed. More subtly, some cases came to my attention only later when some phrase in a published paper resonated with a student project. Some discreet inquiries on my part strongly suggested that "clever" people plagiarized considerably more subtly than just cutting-and-pasting...
Comment: ... namely, by making substantial "cosmetic" changes so that a superficial appraisal would be less likely to detect plagiarism. Beginning in the early 2000s, just as search engines could easily find resonating phrases, the "clever" plagiarists would just as easily spend a little time running tests on the match-ability of their plagiarized documents... as I was told. Eventually, I decided to not corrupt my general approach to students... Perfect enforcement is too expensive. General deterrence is feasible, but will be imperfect. I don't know any really strong solution...
Comment: And, of course, a slightly-clever plagiarist will continue tweaking a paper until Google ceases to produce too-good hits.
Comment: Then it seems the effort is more to plagiarize than to actually get another publication. This, on the other hand indicates it only the not so clever ones that can get caught. Do yo have any support that supports your statement? It would be very interesting to check it out in order to get a strategy for catching the more clever ones.


rsync on Lion failing with Perl error

Question: I'm trying to rsync a bunch of photos from one mac to another.
rsync -av /Users/billybobob/Pictures/ firstname.lastname@example.com:/Volumes/Harddrive/Billybobob_Photos

I've got the keys correct because I can ssh from billybobob's computer into sarahsansskirt's computer.  I can also rsync to a freeNAS box I have with no issues.  However when I try to rsync to sarahsansskirt's computer I get
Can't locate local/lib.pm in @INC (@INC contains: /lib/perl5 /Library/Perl/5.12/darwin-thread-multi-2level /Library/Perl/5.12 /Network/Library/Perl/5.12/darwin-thread-multi-2level /Network/Library/Perl/5.12 /Library/Perl/Updates/5.12.3/darwin-thread-multi-2level /Library/Perl/Updates/5.12.3 /System/Library/Perl/5.12/darwin-thread-multi-2level /System/Library/Perl/5.12 /System/Library/Perl/Extras/5.12/darwin-thread-multi-2level /System/Library/Perl/Extras/5.12 .).

BEGIN failed--compilation aborted.
Can't open perl script " -Mlocal::lib": No such file or directory
I didn't think rsync had anything to do with Perl.
What am I doing wrong here?
BTW all that INC@ looks wrong, my Perl is basically broken on billybobob's computer.... but that shouldn't matter I think.
Answer: Probably you have specified LocalCommand option with some perl command in your ~/.ssh/config for host 192.168.1.4

rsync on Lion failing with Perl error


How can I increase resolution for current sensor?

Question: I purchased a ACS711 Hall effect-based linear current sensor (http://www.pololu.com/product/2197) and when i read the input it's basically always the same. After doing some research I think it's because there is only a 10bit AD converter and since the current is only changing a little bit it's not enough to catch the change. For my situation I'm pulling around 40-90ma idle and when the motor turns on it jumps up so I want this sensor to see that but it only jumps up to about 120ma. Any tips on how to fix this? Maybe a different sensor? Can I use an amplifier to boost the analog signal?
Comment: You definitely want a different sensor for this. Your current sensor isn't sensitive enough for the current application.
Comment: Are you sensing the right line? Because, a motor using only 30-80mA doesn't sound right?
Comment: If you have a transistor, simply amplify the voltage. This allows you set different reference voltages
Comment: @Jasmine yeah. I typically have to use 2A adapters for motors. Check that out.
Answer: In default configuration, the Arduino's ADC has a range of 0v-Vcc (5v or 3.3v depending on the model). If you are sure your input voltages will always be way lower than Vcc, spreading the ADC's resolution over that range is a waste of accuracy. What you need to do is to properly configure your analog reference voltage.
Basically, this is a way of telling your Arduino "instead of spreading your ADC's bits over a range of 0v to Vcc, just cram all that accuracy between 0v and [refVoltage]."
So:

Measure the highest analog output your sensor will give.
Setup a voltage divider to output a little more than that
Connect the voltage divider's output to the AREF pin
in setup(), declare analogReference(EXTERNAL);

And that's basically it. As noted, in this specific case you'd probably be better off buying another sensor altogether. However, you won't always have that luxury, and knowing how to set the analog voltage reference always comes in handy.
Comment: The problem with this is that the sensor produces voltage offsets from Vcc/2, so your ADC has to support voltages of 0 to about Vcc/2 - ie: you can get only about a resolution gain of 2.  To do better you need differential inputs rather than single ended (eg: having the ADC 0-1024 counts span 2.2v - 2.7v if Vcc=5V).  That could be done with op amps, or using a different Arduino.  I guess I'll write up the latter, since it takes a bit more explaining.
Answer: First, let's look at where you are now.  The sensor you have reports current changes at 110mV per amp.
That means 40mA => 4.4mv, 90mA => 9.9mv, and 120mA => 13.2mv -- all very small voltages and small changes in voltage.
Let's work backward, tho.  A 5V Arduino in typical ADC mode has a resolution of about 5 mV (5 V / 1024 counts), whilea 3.3V Arduino would have a resolution of about 3.3 mv).  Divide those step sizes by 0.11V/A sensitivity and you'll see that a different of 1 count on the ADC will represent about 45ma (5V Vcc) or 30 ma (3.3V Vcc).  But there is always inaccuracy and noise, so it's going to be hard to reliably distinguish between 90mA and 120 mA (using your figures).
You can improve that somewhat by switching to a sensor with higher sensitivity (and lower maximum range) like https://www.pololu.com/product/1185 which improves the sensitivity to 185 mV per amp.  The step size of the ADC converters would translate to about 26 mA (@5V) or 17.5 mA (@3.3V).  That's still pretty tight.
You might be able to manage with the more sensitive sensor and a 3.3V Arduino - if you use capacitors to filter out the electrical noise on the sensor to ADC input, and you average multiple readings in your code to further smooth the values.  But it would be marginal.
So you need to amplify the sensor.  Yes, you could do that with an external amplifier, like an op Amp.  A transistor is more difficult because you need it to stay fairly linear which gets trickier, and you may need more than one stage - so an op amp is easier.
There's another tricky factor - you need to compare the voltage from the sensor to some reference - Vcc/2 for your sensor, and 2.5V for the more sensitive one.  The current is proportional to the difference between the sensor reading and that reference (the current going one way for sensor output above reference, the other way for sensor output below reference).
I'll mention another option - you could use an Arduino Mega or Leonardo.  These chips offer the option of differential inputs (one pin goes to the signal, and one to the reference), and they have built in selectable amplifiers with up to 200x amplification.  That should give you plenty of resolution, without needing to use external active analog circuitry.
You will still need to filter the sensor output to smooth spikes from the motor (current spikes translated to voltage spikes by the sensor).  You may need to also filter the Arduino Aref input with a cap.
Suppose you were to use an Arduino Mega or Leonard with the sensor you have.  You'd want a Vcc/2 reference, which could simply be two identical resistors (say 10K ohm) between Vcc and Ground as a voltage divider (and maybe a cap to ground for filtering).  You would still probably need to calibrate by finding the ADC value for no current as your reference and subtract that from the reading you get when current is flowing.


Why was Fairy Tail disbanded?

Question: Why suddenly the guild members decided they go each on his way?
As Lucy describeds it, no one opposed the decision of just close the guild.
Comment: do yu mean when they left to train?
Comment: @Dragon Near the end of the anime and before the current arc in the manga Natsu and Happy decided to go on a training journey.
Answer: Your question can be answered only in big spoiler as it is revealed in the next chapters. So...
SPOILER ALERT

 Makarov disbanded Fairy Tail so that its members would not get caught in a fight with the Alvarez Empire. After he disbanded the guild, he went to the Alvarez Empire where it was revealed that the Emperor is none other than Zeref himself. Zeref wanted the Lumen Histoire, which is Mavis' body (or more precisely, her ability to use imagination) in order to fight Acnologia. Lumen Histoire is hidden in the basement of Fairy Tail guild building. If the guild is not disbanded, then the whole members would get killed in the fight due to the sheer difference in power between them. At least this was what Makarov thought.
Answer: I think the reason why Makarov disbanded Fairy Tail is because of Lumen Histoire. It is one of the strongest spell of Fairy Tail including Fairy Sphere and Fairy Glitter. It is still a mystery what Lumen Histoire is hence, the reason why fairy tail got disbanded.
Answer: As far as I know (by the anime) Makarov just disbanded the guild for an unknown reason. Nobody really knows for sure why he did. Maybe many of the guild members just didn't want to argue, or maybe it's because maybe they all thought that it would be best to go their separate ways.
Comment: Didn't he disband the guild so they wouldn't be caught up in the fight?
Comment: How do you mean ?
Comment: It's explained in the answer above, beware for spoilers if you've only seen the anime.
Answer: Based off the anime I think the guild was disbanded because Makorov wasn't able to be the master any more and the only person qualified that would do it was none other than Natsu and because he left Mokorov had no choice but to disowns the guild.
Answer: I think Macarov disbanded the guild because he knew zeref was coming and he wanted to avoid being in a fight with him and keep fairy tail safe
Answer: I think Makarov disbanded the guild because there was probably danger ahead of them and Makarov wanted to protect them, but couldn't bare to tell them that there was more danger after their battle with the Underworld king. Makarov probably wanted to protect them and solve the problem by himself without harming people from the guild.
Comment: Can you add sources to this?
Answer: In chapter 439 of Fairy Tail, it's revealed that the disbanding of Fairy Tail was because of Lumen Histoire.
There's a country (let's just say country A) that has tried to take Lumen Histoire for themselves before by invading the country, but they got stopped by the council at that time. Now, however, (when Fairy Tail was disbanded) the council didn't exist anymore and Fairy Tail and its country needed time to rebuild everything so that country A had gotten the opportunity to do what they couldn't before and Makarov knew that. He also knew that Fairy Tail wasn't strong enough to be their opponent yet, which was why he disbanded the guild and went to that country to stall sometimes.

Why was Fairy Tail disbanded?


What is causing these lines of blotchy white spots in photos from my Instax 100?

Question: I recently started using my uncle's Instax 100. I bought new film and took some pictures with it. However, all of them had this weird lines in them. I wonder what that could be? I'm not familiar with Instax.
Comment: Are you sure the film is new? Those borders look incredibly smeared/scratched banged up; they should be white.  Is it doing this with more than one pack?
Answer: In old instant films, the image you see appears directly where the film was exposed when you took the photo. The wide portion of the border contains developing and fixing chemicals. After the image is exposed, a roller breaks the chemicals free and spreads them across the film. Based on the consistent appearance of the splotches, the rollers are probably damaged and developer is not being spread across the film evenly.
They are unlikely to be a film defect because of their appearance across multiple frames. They are unlikely to be a defect in the lenses or other parts of the camera because of their repeating pattern down each frame.
Although I did not find any tutorials online about fixing the rollers specifically, the following resources may be helpful:

Fujifilm Instax 100 Disassembly
YouTube: Fuji Instax 210 torn down (explains how internal mechanisms work)

It looks like the rollers need to, at least, be cleaned. If they are pitted, they probably need to be replaced. (You could try filling the pits with resin.  Then sand them down.) I wonder whether, a dowel could be used to spread the chemicals around after the film has been ejected from the camera.
Comment: Is there a tutorial somewhere that i can see how to check on the rollers?


How to say "though" and the use of "pourtant"

Question: How do I say "though" like in the sentence "There was food though"?
Could you say "pourtant, il y avait des nourritures" or "Il y avait des nourritures pourtant"?
Comment: I feel to have the right translation in french, we need to understand the context. What is the sentence and situation? Another one is "malgré qu'il y avait de la nourriture"
Answer: To add up to other answers, another possibility that I would use is

Cela dit, il y avait de la nourriture.

which can be translated literally as "That being said, there was food", so it tones potential, previous criticism.
In spoken language, one could also use

Il y avait de la nourriture, cela dit.

which is sloppy phrasing, but might match the original sentence better.
Answer: Both places are correct but you're mistranslating the number of food. Don't put a plural when you don't need it. Food is singular, let it stay and translate by :

Pourtant, il y avait de la nourriture ?

Or :

Il avait de la nourriture pourtant ?

The place where you put it will depend. If the sentence is within a conversation, the first translation is a direct opposition to the predecessing sentence. If the previous speaker said that the last wedding he went to was horrible, the first translation will oppose his argument to yours, the food. The second translation will be more polite.
Note that pourtant is widely used in the familiar language, but a more academic word would be cependant.
If you want to go further, you'll have to invert the verb and the subject :

Y avait-il de la nourriture cependant?

That last sentence is better in the academic way but less used in familiar language.
Answer: Contrarily to @Dranna, I wouldn't put "pourtant" at the end of a sentence like this. The adverb is most often placed just after the verb. It can be placed at the beginning or the end of the phrase, but then it should be separated with a ",".

Il y avait pourtant de la nourriture.
Il y avait de la nourriture, pourtant.
Pourtant, il y avait de la nourriture.

Note that this construction is for an affirmative sentence. You can make it an interrogation with a question mark and a change of intonation.

Il y avait de la nourriture, pourtant ?

but normally you should have an inversion when you build a interrogative sentence (note that in this case the sentence is also negative).

N'y avait-il pourtant pas de nourriture ?

If order to give the same impression as in English, I would suggest

Il y avait de la nourriture, non ?

Last remark : IMHO, "pourtant" is closer to the meaning of "(al)though" and "cependant" is closer to "however". "Pourtant" is not necessarily more familiar than "cependant".


Does block difficulty adjust with different gas limits?

Question: Ethereum has a dynamic gas limit, a market governed by the miners. Does the block difficulty change if the gas limit is changed? For example with an increased gas limit from 3 million GAS to 6 million GAS, would the block difficulty increase, or is the miner reward adjusted, or how is the crypto economic game theory balanced for different gas limits?
Answer: No.
Currently, difficulty is computed as:
adj_factor = max(1 - ((timestamp - parent.timestamp) // 10), -99)
child_diff = int(max(parent.difficulty + (parent.difficulty // BLOCK_DIFF_FACTOR) * adj_factor, min(parent.difficulty, MIN_DIFF)))

As you can see, there is nothing about gas in the formulas.
A Metropolis EIP to adjust the difficulty also does not involve gas:
adj_factor = max((2 if len(parent.uncles) else 1) - ((timestamp - parent.timestamp) // 9), -99)

The block gas limit in Ethereum is similar to the blocksize in Bitcoin, and has similar game theory.  Basically, higher block gas limits mean a miner can include more transactions in a block and thus collect more fees.  But larger blocks take more time to propagate in the network, increasing the chance that one won't be the "winning" miner.  Ethereum also implements some GHOST: basically the added rule that "runner-up" miners still get their blocks included in the blockchain as uncle-blocks and still get a portion of the mining reward.  So the analysis isn't as clear-cut as winning/losing the block reward and see https://blog.ethereum.org/2016/10/31/uncle-rate-transaction-fee-analysis for more analysis such as:

In Ethereum's current environment, block rewards are 5 ETH and will
  stay that way until the algorithm is changed. Accepting 1 million gas
  means a 1.86% chance of the block becoming an uncle. Fortunately,
  Ethereum's uncle mechanism has a happy side effect here: the average
  uncle reward is recently around 3.2 ETH, so 1 million gas only means a
  1.86% chance of putting 1.8 ETH at risk, ie. an expected loss of 0.033 ETH and not 0.093 as would be the case without an uncle mechanism.


How can EOS prevent collusion of block producers?

Question: How can EOS prevent colluding to make it a more decentralized system?
Answer: If you are asking  about how blockproducers make concenses ,aBFT (asynchronous Byzentene faluttolerent)
please follow this article
http://www.information-age.com/gold-standard-security-distributed-systems-like-blockchain-123469395/
Answer: In order to prevent collusion, EOSIO, like many other chains, keeps all on-chain transactions public. Further, it natively supports a constitution through Ricardian clauses and a multisig "admin" account that has various privileges if a supermajority of BPs agree on using it. As such, there are certain rules that participants agree when using the blokchain. For instance, on the EOS mainnet, there is a clause that one implicitly agrees on when using the voteproducer command:

...
I stipulate I have not and will not accept anything of value in exchange for these votes, on penalty of confiscation of these tokens, and other penalties.
...

Thus, this framework can be employed to reduce or prevent collusion, assuming this is possible. For further information about this, the governance section in the whitepaper may provide more details.

However, you also ask:

How can EOS prevent colluding to make it a more decentralized system?

I would note that collusion prevention is not necessarily conducive to creating a more decentralized system. For instance, Dan Larimer mentions:

True decentralization is free market competition among different colluding groups.