Searching for a database for spaceships, satellites, drones, etc.?

Question: Similar to this question except for space technologies—ships, satellites, drones etc.?
Comment: I saw in an earlier question somebody posted an URL to a website for US drone attacks. I kept the url: http://natsec.newamerica.net/drones/pakistan/analysis
Answer: I would guess that scraping lists an timelines linked on the summary page Spaceflight lists and timeline (Wikipedia) will cover most satellites, probes and drones operational today and in the past.
Answer: I found this while googling:
The UCS Satellite Database is a listing of the more than 1000 operational satellites currently in orbit around Earth. Our intent in producing the database is to create a research tool for specialists and non-specialists alike by collecting open-source information on operational satellites and presenting it in a format that can be easily manipulated for research and analysis. It is available as both a downloadable Excel file and in a tab-delimited text format.
http://www.ucsusa.org/nuclear_weapons_and_global_security/solutions/space-weapons/ucs-satellite-database.html
Answer: Nasa have a superb resource at http://ssd.jpl.nasa.gov/?horizons which covers solar system objects. Satellites and spacecraft as well as asteroids, comets, planets etc
Answer: I can't help on the drones -- but NASA has a service called the Satellite Situation Center that will tell you the location of many spacecraft.  I can only assume that they don't track clasified (ie, secrete military) spacecraft.
Another spacecraft location database is the one at N2YO.
Unlike aircraft and surface ships, most spacecraft are one-off builds.  There are constellations of spacecraft such as STEREO, CLUSTER, GPS, and Iridium, and there are a few that are built similar for economy of scale (eg, GOES-N, GOES-O, GOES-P), and maybe some communications satellites.
You can get additional information about scientific spacecraft (both current and older) from the National Space Science Data Center.


Calculating the distance between points and multiple lines?

Question: I have a point shapefile of about 100 points and a polyline shapefile of about 200 lines and I am interested in finding the distance between every point and each individual polyline. My polyline shapefile represents individual fault lines in a region. So for each polyline (or fault line) I want to calculate the distance to each of my points. I know that I can calculate the distance between the points and the closest polyline to each point but I'm not sure how to go about calculating the distance between my points and each individual line. Any ideas?
Answer: You can turn your polyline shapefile into a route using Create Routes in the Linear Referencing Toolbox. Then use the tool, Locate Features Along Routes, also in the Linear Referencing toolbox, to find the distance to the nearest routed polyline and it's nearest perpendicular location along the route. I always use ArcMap's Search button or key Ctrl+F while in your mxd and just type in whatever tool you're looking for.
You'll need to set a large enough search radius so that all your points are captured when using Locate Features Along Routes (and search radius only works for locating points.)
The MEAS field will be the point's perpendicular location along the route in whatever map units your mxd is set in (feet, meters, etc.), and the Distance field, what you're interested in, will contain the nearest distance from the route. A negative (-) number is west of the route, and a positive number is east of the route.
Answer: If you have an ArcInfo/Advanced license then the Generate Near Table tool will calculate the distance (NEAR_DIST) between every point and line combination - with options to output the location of x- and y-coordinates (NEAR_X and NEAR_Y) and angle (NEAR_ANGLE) - be sure to uncheck the closest option to find all. You can use the Join Field tool twice to copy the original attributes from the IN_FID to the in_features object ID, and the NEAR_FID to the near_features object ID.
If you don't need those extra fields calculated and/or for any license level use @caitriggs clever linear referencing answer.
Comment: Thanks for the help! I do not have an ArcInfo license so I used @caitriggs Create Routes method and it worked. That was exactly what I was looking for. Thanks again.


How many keywords are possible in Lightroom without a performance penalty?

Question: Does anyone know whether there's an upper limit to the number of keywords possible in Lightroom without experiencing a lack in performance?
Answer: Are you wondering about the distinct list of keywords in an entire catalog or are you wondering about the number of keywords for a single image?
I am doubtful that there is any practical limit to the number of keywords allowed in a Lightroom catalog. It wouldn't make sense to have an artificial limit in the software itself but it is possible. Lightroom is based on the very efficient relational database SQLite which should allow for essentially an endless amount of keywords to be added without any performance implications.
On this site people have argued for and against using a single large catalog, but it is not unheard of to have a catalog(not previews, smart previews, etc.) in the 2GB+ range and still have great performance.
Related:
Does the number of smart collections affect Lightroom's performance?
Comment: Please note that he didn't ask if the program has a hard-coded upper limit. He asked till where is possible to go up **"without experiencing lack in performance"**
Comment: @JohnThomas - I agree. Also without quantifying "lack in performance", it would be easy to argue as soon as you add 1 keyword performance is lacking. It is arbitrary as defined and not very useful for anyone. Your answer for example states "keep your total number of keywords at minimum". What exactly does that mean, 10 keywords? 10,000? 1,000,000? None of this is very useful or practical anyways.
Comment: Hi, thanks for the reply! In ignorance I didn't even consider number of keywords per image, only total number. So, thanks for the head's up on that!
Comment: Sure. In fact any number depends on the concrete hardware and the what means 'acceptable performance' for each user. That's why I tried to give some general guidance/rules to a general question. The actual answer only the one who asked can give.
Answer: Your question isn't correctly written. I'll try to untangle it, tough.
You cannot say that till "n" keywords you won't get any performance degradation and from "n"+1 (ok, "n"+100 or whatever) you suddenly will feel it.
The performance degradation is a quite incremental process. It is rather an oblique line and not a stair-like graph. Also, of course, it depends on the hardware on which you're on.
That said, Lr organizes internally the keywords in several tables which are rather fat (wide - with many fields) in comparison with other programs thing which means that in some situations (queries) it will be (much) slower than other programs. I have practical experience with eg. XnView MP which is much faster in these things because it has just one table for keywords and this is almost a half wide (7 fields vs. 13 in Lightroom).
So, Rule #1: In Lightroom try to keep your total number of keywords at minimum. But if you cannot then there are other, better solutions.
Besides of the keywords table there is another table, the table of keywords assigned to each image.
This table is very narrow but, again, here Lr choose to have 3 fields instead of 2 (which is the minimum). Ok, one can argue that it is 33% increase but frankly because the 3rd field is an integer, I don't think that for 100.000-200.000 rows the performance degradation will be so big.
However, if the cardinality (the number of rows) grows, and this happens quickly if one assigns many keywords to each photo, then the difference in performance increases.
So, Rule #2: In Lightroom try to keep your number of keywords per image low. But if you cannot then there are better solutions, but the difference will show up only from several thousands images above.
Also, we have here a corollary:
Corollary #2a: If you cannot afford leaving Lightroom be sure to keep your catalogs small.
In conclusion we have Rule #3:
Rule #3: Lightroom wasn't designed for scalability in mind. If you want such a thing you can get other DAMs.
Disclaimer: While I tested other programs from performance POV (AfterShotPro is one of the best, Zoner has a hardcoded upper limit, ACDSee has a rather slow DB, like Lightroom), as I said, I personally use XnView MP together with Photoshop and/or Photivo (an awesome free RAW editor). It just happens to know well how XnView MP's DB backend is designed vs Lightroom and how is its performance curve. You can download it to see if it fits for you - it is freeware.
Comment: Thanks for the thorough reply! Leaving Lr isn't an option at the time being, but it's great to know the alternatives :) But is there a performance difference btw a "flat" keyword list and a hierarchichal list, given the same total number?
Comment: @EndreGrünerOfstad: Good question. :) Tried to answer here, I know what to write (there are some points to consider in order to know how to do it/what Lr settings to choose) but here the space simply doesn't help me. Also, IMHO it is a pity to get lost this question in comments. If isn't so hard for you ask a new question with the text above and I will gladly answer you :)
Comment: it has now been given a question of its own  https://photo.stackexchange.com/questions/52813/hierarchical-vs-flat-keyword-lists-and-performance-in-lightroom
Answer: Lightroom uses a SQLite database to hold its keyword information. SQLite does have size limits, but they are so high that it simply isn't worth worrying about them. You can have zillions of keywords in your catalog.
HOWEVER. It is not only possible to make Lightroom slow to a crawl, I can do it at will. Heavy keyword use is one of the easiest and most reliable ways to do it.
Here is a catalog of Lightroom keyword failure modes and myths, all culled from my long experience with Lightroom, going back to the pre-1.0 beta days:

The more keywords you add, the slower Lightroom will get.
I don't mean lots of keywords on a single photo here. I mean that if you take a pile of photos without any keywords on them and add one or two keywords to each, Lightroom will be noticeably slower after one or two hundred keyword additions. If you restart Lightroom, performance returns.
If you continue pushing Lightroom this way, you can get it to the point where it takes many seconds to apply a keyword.
I've seen Lightroom sit there, nearly unresponsive, for a minute or two while it churns through its backlog of work.
The computer is not the problem. I've seen this on several different computers, both Windows and Mac, which ranged from reasonably fast to positively high-end. In fact, if you go open up another program, leaving Lightroom churning away in the background, your new foreground program will be fairly responsive, since Lightroom doesn't use 100% of the computer's resources while it is in such a state. I've spent a fair bit of time playing Borderlands 2 while Lr grinds away in the background. There's a bit of a hit to the frame rate, but it's still playable.
If you want to see this for yourself, here's a sure-fire Lightroom tar baby recipe:

Start with a catalog of many thousand photos, with lots (10+) of keywords on each, selected from a nice deep hierarchy of keywords. Don't bother if you're still using a small, flat keyword list.
Now take one of the most popular photos in your keyword set, and move it somewhere else in the hierarchy. Lightroom will re-keyword every affected photo.
Once that completes, add another keyword to any photo in your library. It doesn't have to be one of those you just touched. See the difference?
Relaunch Lightroom. Performance is back to where it was before you started, isn't it?
Interesting, no?

When you get Lightroom into this state, if you launch Activity Monitor on OS X, you should see that it pegs one CPU core, leaving the others idle. This tells me that keywording is essentially a single-threaded activity. You will also see that disk I/O is fairly low, meaning it isn't being I/O bound. It just isn't using your CPU's full horsepower to rearrange its keyword database.
I assume the same thing happens on Windows, but I haven't tested that.
Reducing the size of your catalog helps, but not all that much.
Whenever I have a big session of heavy keywording to do, I slice the set of photos I want to work on out into a separate temporary catalog. Here's the workflow:

Select all the photos you want to work on
Say File → Export as Catalog...
I recommend that you put it on your Desktop and call it something that clearly marks it as a temporary catalog: temp, foo, x, etc. You want easy access to it, and you don't want to leave it cluttering your disk once you're through with it.
Press Ctrl/Cmd-S to make sure all metadata is saved to disk for those photos.
Do this even if you have "Automatically write changes into XMP" enabled in your Catalog Settings. For reasons that should be increasingly clear to you, dear reader, Lightroom can get badly backlogged. When you quit Lightroom with pending unsaved metadata, it will save only the minimum information it needs to be able to start back up and continue work. You must force it to finish all pending work before you continue, else you risk a mismatch between the information in the catalog and the information stored in the photo via EXIF, IPTC, XMP, etc.
Say Metadata → Export Keywords... You will see why in just a bit.
Exit Lightroom, then double-click the new catalog you just created to open it instead of your default. Alternatively, launch Lightroom with Option/Alt held, so that it prompts you for the catalog to open.
Say Metadata → Import Keywords... and point it at the file you just created above.
If you don't do this, your new catalog will only contain those keywords present in the photos you exported. You presumably want all of your keywords available in the new catalog.
Do your keywording.
Select all the photos, then say Cmd/Ctrl-S to save the changes to disk. You must do this even if you have the "Automatically write changes into XMP" setting enabled in your main catalog. It's a per-catalog setting, and it defaults to "off" for new catalogs.
(See the next major point for more on this.)
Relaunch Lightroom again, opening the main catalog this time.
Say Metadata → Read Metadata From File to load your changes back into the main catalog.
Once you're satisfied that the changes have all made it back into the main catalog, quit Lightroom and delete the temporary catalog. We don't need it any more.

Having jumped through all those hoops, you should notice that Lightroom is a bit faster when running with the much smaller catalog. I find it to be barely enough of an advantage to bother doing it.
This should convince you that the overall size of the catalog is not the main thing affecting the speed of Lightroom. The keyword set size and the number of keywords per photo have a disproportionate effect on the speed of Lightroom.
Disabling the "Automatically write changes into XMP" setting in your Catalog Settings helps, but not all that much if you have a fast disk.
Tip: Have a fast disk. :)
Ideally, put the catalog file on a fast SSD, and the tree holding your master photos off on a separate fast RAID. (Or if you're really well-heeled, put the masters on a RAID of SSDs!) Keeping the two separate gives the OS opportunities to write to both at the same time, opportunities that aren't available when both requests must go to a single disk.
Smart Collections are a speed hit, particularly if they have keyword-based rules.
The good news is that there's an escape hatch: Smart Collections only hurt performance once they've been opened within a given Lightroom session. If you fold up all your Collection Sets and twist the Collections panel's disclosure triange closed, then re-launch Lightroom, none of your Smart Collections will impact Lightroom's speed.
But beware! If you twist open some of those disclosure triangles and then immediately twist them closed again, the damage is done: the speed hit will continue to affect Lightroom until you re-launch it.
The most reliable way to speed Lightroom up again is to re-launch it.
I spend a lot of time re-launching Lightroom. Sigh.
Answer: The easiest way to check this is to import a controlled vocabulary with large number of files. For example, David Rieck, an author of the ControlledVocabulary.com has a LR's version of his CV that contains several thousands of well-structured keywords.
Performance is a wide termin and it might reflect to different aspects of the program. In your case, you might see a degradation of the first program launching, expanding the keywords tree, searching by keywords, metadata syncyng, etc... Plus different PC configuration will have different thresould for performance degradation.
Using hierarchical keyword structure can improve both: program performance and convenience of keyword's management.
BTW our Daminion Server can import > 20000 keywords and work without performance degradation on i3/4Gb PC configuration.


How to allow a user 'edit' on activities?

Question: Users have ACL 'edit' access to a group, and can access the contacts in the group OK.  They can create an activity, but then cannot edit it - for each activity they just get 'View' and 'File on Case' possibilities and not 'Edit'.  There are no  permissions to edit activities - only view and delete.  How can I allow them to edit activities?  Using 5.6 and Drupal
Comment: Have you tried doing this using Webform CiviCRM?
Comment: You mention "File on Case" - if your users **can** edit activities that are ***not*** associated with cases, check to see if you have either the "CiviCase: access my cases and activities" (view and edit only those cases managed by this user) or the "CiviCase: access all cases and activities" (view and edit all cases for visible contacts) permissions enabled for the given role?
Comment: Tony - this is using the regular back office UI.  Although I guess a webform would also work, so will give it a try
Comment: Tamar - I checked the permission you suggested but it made no difference - they have these permission although the problem here is with regular activities, not case activities.
I notice that this problem has come up before, with no solution, although some users don't have this problem at all so it must be something to with this groups of users access.
Answer: I fixed this problem by changing ACLs.  Originally the user was in role 'A' and the contact where they could create but not edit an activity was in group 'B' - and role 'A' had edit access to group 'B'. By changing the target contact to be in the same group as the 'A' role and giving that role 'edit' access to itself (its group) then they get edit access to activities.  As it happened, putting the target contact into this group is OK but this might not always be the case.  Seems like 'edit activities' should be a permission - this has been discussed before.


Display all posts of current viewing tag

Question: I'm having problems getting all related posts of the current viewing tag. Does anyone know how you can do this dynamic? I want to create a own kind of 'archive' page for this.
Answer: Ok .. after searching for a while I figured out what I was doing wrong. I wasn't including custom post types in the loop. I ended up constantly with 'not found'.
Whats the solution:
query_posts( array( 'post_type' => 'blog', 'showposts' => 3, 'orderby' => 'rand') );  if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

And it queues all posts with the current viewing tag!
Special thanks to Sven and Kaiser!
Answer: You can use the default get_posts() function from WordPress with taxonomy parameter.
Comment: Nope sven, This is what I did:

When viewing a post, I click on one of the tags (like Android), i'm going to the tag.php page and want to display all related posts with the tag 'Android'..
Comment: Thanks Sven, but how do I get the posts related to the current tag? I've managed to output the single_tag_title(); but don't know how to get the rest..
Comment: So, you need the tag of the current post? You can get the tags with the function get_the_tags() (http://codex.wordpress.org/Function_Reference/get_the_tags)
Answer: Simply use a tag archive for that.
You can grab a term/taxon, then display a link to its archive using get_tag_link().
As you can see from the Template Hierarchy Diagram, there're the following tempalte names, that will trigger (in hierarchical & parent/child theme) order:

tag-{$slug}.php
tag-{$id}.php
tag.php
archive.php

There you will have - depending on your URl/Route - the posts available and can proceed them using a plain loop, like the one you can see in the codex. All filters are available, as well as well as all filters like pre_get_posts, etc. and Conditional Tags like is_tag() that will determine if you're on a tag archive.


Drying and curled up leaves on pluot tree

Question: We planted the tree about 2 months ago. It was thriving beautifully. Last week suddenly the leaves curled up and dried becoming brown. It coincided with dry days (I'm in northeast) so I started watering it every day but so far it hasn't recovered. The main stem and branches look,healthy and their tips are still green.
I tried to give it plant food but noticed no difference.
My neighbor suggested it may have used up all the good soil from the pot where it came and now it is facing the clay soil in my house. Is it possible? Is it dying?
Any suggestions?
Thanks.
Comment: Add a picture please
Comment: Of course, during the day.
Answer: If you only planted it two months ago, the most likely cause is a problem with water supply, as in not enough of it. Do not fertilize the tree at all while its in a critical state, but you should soak it daily with at least 4 gallons a day, or leave a hose trickling at the base of the tree for a couple of hours daily. Do that even if its raining, unless the rain is absolutely torrential and goes on for a day or two. New trees need copious water supplies for their first two years, and particularly so if you plant in spring and not fall. If the weather is hot and sunny and dry, give it more than 4 gallons, until it starts putting out new leaves, then ensure you water it properly ongoing by giving it a good soak of 4-6 gallons every 5-7 days. A little bit of rain or a few showers is not a reason to think the tree has been watered.
The other possibility is whether the tree needed hardening off prior to being planted out - if it was packaged in plastic, or had been kept under shelter or inside, then it would have done.
This answer assumes there's no evidence on the tree of any disease or insect infestation. But one question - when you planted, had you prepared the area beforehand by digging it over and adding composted material or composted manure? Or did you just dig a single hole and put the tree into it? Regardless of the answer to these two questions, carry out the watering as recommended above in the meantime if you want to save your tree.
Comment: Thanks, we are watering it as you suggested. Just dug a hole and put the tree in. And yes, no evidence of any problems.
Comment: if all you did was just dig a hole, as you say, then later on, after the tree has recovered, you should apply a mulch of composted manure or composted organic materials 2 inches deep, all around the tree to a distance of a couple of feet out from the trunk,  but don't let it sit against the trunk of the tree. I don't like the look of the black stem visible in the picture though...how much rain have you had in the last couple of months since you planted it, not counting the latest dry spell?


How to make cairo-dock icons not to hide

Question: How to make my cairo-dock icons not to hide(always shown).
Answer:
Right click on the dock itself and choose 'Cairo Dock'->'Configure'.
Under 'Behaviour' choose 'Visibility'.

You will find a 'visibility of the main Dock' section with a 'visibility' drop down - select 'Always on top'.

That way, your dock will always be on top of any window.
Answer: Cairo Dock (Docky) is a great alternative to the Unity panel. Docky is highly customizable, and the possibilities are almost endless.
As to your question, there are tons of resources out there to show you how to do this and other cool things. Here are a few that I have encountered recently (I intentionally selected sites with a broader appeal to benefit other surfers):
1) First, a basic tutorial (GLX-DOCK is chockablock with tips and hints.Look around!)
http://glx-dock.org/ww_page.php?p=A%20complete%20tutorial%20on%20how%20to%20customize%20your%20dock&lang=en
2) This one steps you through some cool Ubuntu deskop facelifts with Docky:
http://mylinuxexplore.blogspot.co.il/2013/02/simple-steps-to-decorate-linux-desktop.html
3) Here's another sub-site of askubuntu, dedicated to hot Cairo Dock questions:
https://askubuntu.com/tags/cairo-dock/hot
Have a ball.


Friendstream App do not update Twitter,Facebook

Question: I am unable to get Twitter, Facebook updates in FriendsStream App (HTC Sense) on my Desire HD.
anyone knows how to fix this?Right now only Flickr updates come and I used to get all the above before.
Answer: Please, give more details. Have you saw twitter and facebook messages in the FriendStream before?
I have the same phone. Did you try to take a look at the "Menu->Settings->Show updates" in the FriendStream application? There are checkmarks for every stream-source.


Texture Coordinate vs Geometry Node

Question: When working with generated texture coordinates I see sometimes the Texture Coordinate (generated) and sometimes the Geometry (Position) node used. What is exactly the difference ?
Comment: Geometry position is almost certainly the (X,Y,Z) coordinate of the surface (or interior) point that is to be coloured/textured etc. as part of the render.  Texture Coordinate defines what is to be used for the (U,V) coordinate used to lookup a position on the UV Map and use the pixel information found at that point as the source for the rendered pixel (or the onward journey through node graph).

[link](https://www.blender.org/manual/render/cycles/nodes/input.html)
Answer: The Generated and Position outputs each represent coordinate systems.  These are often used as texture coordinates for procedural textures since they are 3-dimensional, though they can be useful for other effects as well.

Generated Texture Coordinates
Generated coordinates are defined by the bounding box of an object, and are unique to each object.
Generated texture coordinates give the bounding-box-space position across the mesh.  The bottom, left, front of the bounding box is the origin (coordinates [0, 0, 0]), and the top, right, back of the bounding box is [1, 1, 1].

I use generated coordinates when I need the texturing to transform, particularly rotate, with the object.  However when the bounding box is significantly non-cuboidal generated textures will stretch and distort the texturing.  In these cases you may need to manually "un-stretch" the texture with a mapping node, or use Position coordinates.
Generated coordinates can also be useful for non-texturing methods, like creating gradients or other more advanced techniques.

Position Coordinates
The Geometry > Position output gives the position in world-space across the object.  The origin ([0, 0, 0]) is the world origin and all other points are simply their respective position in Blender Units relative to the origin.

I like to use Position coordinates to keep uniform texture scaling across with a material assigned to multiple objects with different sized bounding boxes.  Using Position coordinates also prevents distorted stretching on objects with significantly non-cuboidal bounding boxes.
Comment: I would say it does not matter too much in practical situations to use the one or the other. Or are there situations that it matters which node you use ?
Comment: @JanScherders  See edit.

Texture Coordinate vs Geometry Node


Error Loading Wallpaper

Question: When i press "ctrl+alt+f3" it goes in cli mode
and then when i press "ctrl+alt+f7" error loading wallpaper
All things are working properly
just my desktop wallpaper seems to be crashed
Comment: & how do i paste my pics here so u can see what is the real problem
Comment: Click "edit", then img in the toolbar. Upload the picture and click save edits
Comment: Your'e Welcome!
Answer: I had this problem just yesterday. I removed all my nautilus plugins, thinking that was the problem - but it seemed not to be.
In the end, I ended up noticing that the Desktop had been disabled all together. If you have GNOME-Tweak tool or Ubuntu-Tweak installed, re-enable the option to display Desktop icons, and your Desktop wallpaper will return.
Let me know if you need any further assistance in the comments.
Answer: Are you running 11.04 or 11.10?
Try restarting nautilus with:
<code>nautilus -q </code>
That will quit your current nautilus session. If it doesn't restart automatically, you can run nautilus from the terminal or open a folder. This should work and be less extreme than completely restarting X.
Hope this helps!
Comment: Ubuntu desktop 11.10

Error Loading Wallpaper


Is it normal for focal length to change while focusing?

Question: When I change the focus distance on my Pentax 55-300mm lens, the focal length appears to change.  More specifically, the lens appears to zoom in as I focus towards the minimum focusing distance.  This is most noticeable at the 55mm end of the lens.  Is this normal?
Comment: No.  This is the other way around.
Comment: possible duplicate of [Does changing the focal length change focus?](http://photo.stackexchange.com/questions/10734/does-changing-the-focal-length-change-focus)
Comment: Oh! Well, it's still basically the same thing from the other side of the equation, right? But also see [How can a prime lens focus on more than one plane?](http://photo.stackexchange.com/questions/12034/how-can-a-prime-lens-focus-on-more-than-one-plane), which also asks a similar question in a slightly different way.
Answer: This is called focus breathing.
With some lenses, especially macro lenses such as the Canon EF 100mm f/2.8 Macro USM, this effect can be substantial—at the minimum focusing distance, the focal length becomes about 70mm. While this is not normally an issue in still photography, it can pose a problem in video shooting as it can cause the angle of view to change while racking or following focus. Cine lenses are generally corrected for focus breathing, but lenses designed for still photography are often not corrected for this behavior.
Comment: Actually, a reduction in focal length while focusing closer, as with most internal-focus (or "rear-focus") lenses, *is* the correction for changing field of view. (Additional floating correction elements may interfere somewhat with a constant FoV in some designs.) In a traditional unit focus lens (where the physical length of the lens changes as you focus) the field of view narrows substantially as you focus closer. A traditional 100mm macro lens would have a 200mm operating length at 1:1.
Comment: No, I'm stating it clearly, not implying it. The lens's focal point (the infinity focus point, if you will) is moved away from the recording medium (sensor), and the resulting image is a smaller crop of the lens's image circle. On unit focus lenses, the field of view will be that of a lens whose focal length is ($infinity_focus + $lens_extension) focused at infinity; IF lenses keep ($infinity_focus + $lens_extension) constant by reducing ($infinity_focus) while increasing ($lens_extension), so FoV is maintained.
Comment: @StanRogers, are you implying that (focal length != field of view) when the lens is not focused at infinity?
Answer: Yes, it is normal.
Closer focusing lenses exhibit this more but it depends on the design of the particular lens. In any case, there is almost always a slight change in focal-length as focus changes. The difference will be more noticeable at the wide-end of a zoom but even prime lenses do that too.
When manufacturers specify things like focal-length and angle-of-view it is always (in my experience) with the lens focus set to infinity.
Comment: Focal length (and thus angle of view) and aperture are by definition given at infinity focus. Which can lead to slightly silly numbers, for example in the case of the Canon MP-E 65 dedicated macro lens which cannot focus to infinity in the first place :)


Difference between AMPscript and SSJS

Question: What is the main difference between AMPscript and SSJS in Marketing Cloud? Can you please give me clear information about the differences between AMPscript and SSJS?
Answer: In everyday life, AMPScript is sufficient for most personalisation tasks, when it comes to emails and landing pages. SSJS offers a larger set of functions, which I mainly use for data integrations to external APIs.
Briefly speaking, AMPScript is for personalisation and SSJS for development/integrations. Here are some more points:

AMPscript simply and efficiently handles inline personalization or simple IF ELSE statements.
AMPscript better handles use cases, where each subscriber needs to see unique content, than SSJS.
AMPscript has a shorter learning curve than SSJS for users new to scripting languages in general.
A great deal of people already know JavaScript and can immediately apply that knowledge to Marketing Cloud
In general, the vast majority of users can handle the tasks they need to perform using AMPscript. Use Core library SSJS functions only to accomplish tasks on landing pages where AMPscript does not provide appropriate functions. Platform SSJS functions can handle messaging tasks as well as landing pages and applications.
Answer: ssjs:
Marketing Cloud executes the JavaScript on the server when rendering. Use Core server-side JavaScript functions to personalize landing pages and create applications to run on Marketing Cloud
Ampscript:
AMPscript is a scripting language that you can embed within HTML emails, text emails, landing pages
Comment: This is not quite right - AMPScript also has the ability to handle API calls and manipulate Data Extension, etc.  It is actually the more recommended language to use in all aspects of SFMC. SSJS is generally slower processing and although a bit more robust, most of its 'extra' functions can be accomplished via SOAP/REST calls in AMPScript.  The best reason for using SSJS instead of AMPscript is JSON handling. (Albeit there are exceptions to the above - but they are specific use cases)
Comment: @A R
Thank you very much for your response.
Comment: @Faheem test Welcome

Difference between AMPscript and SSJS


How can I get all of the messages in the Datapad?

Question: In the Mass Effect 3 Datapad, messages appear as you progress through Mass Effect 3. Some seem to appear just from progressing through the main quest line, but others seem to depend on sidequests, and possibly other things. What do I have to do to get all of the messages?
Comment: Have you seen the iOS app? http://www.dayonepatch.com/index.php?/topic/47660-ios-mass-effect-3-datapad-is-out/
Comment: @William That's the app I'm asking the question about
Comment: Oops, my bad. Sorry! :)
Answer: This would require reverse engineering the source of these messages; they could either be stored in the application, stored in the Mass Effect 3 client or been sent from their server. But that could be considered illegal to some extent, so the best alternative is either by completing the whole game or by collaboratively collecting a full list of them into a Wiki. I would guess that if you can find others with a Datapad, it could be interesting to compose a Community Wiki here.
Completion of the game in this case doesn't mean to just finish the game, but you would have to do all possible (inter)actions under all conditions to trigger the various messages. This would require quite some replays to get all messages, depending on the amount of messages there are...


Why buy an expensive manual focus lens?

Question: What are the benefits of (expensive brand new) manual focus lenses?  Why did you, for example, buy a manual focus Carl Zeiss 85/1.4 rather than an auto-focus Nikon 85/1.4?  I'm not concerned with these two lenses in particular.  I'm curious about the reasons for buying expensive brand new manual focus lenses in general.
Comment: I think the question boils down to: 1) why use a manual focus lens and 2) what are the features to look for when buying manual focus lens. I'd be interested in these answers too :)
Comment: Every lens is a compromise.  I want to know what people look for in manual focus lenses that they don't find in auto focus lenses, i.e. which features they trade auto focus for.  Eruditass brings up interesting points so I've accepted his/her answer.  If other people have additional or different reasons for choosing auto focus lenses, I'm still interested in their opinions.
Answer: While you can obviously manual focus with an autofocus lens, manual focus lenses are catered towards manual focus users.  Some possibilities:

Longer focus throw (Autofocus lenses typically have short focus throws in order to focus faster.)
More distance markings or depth of field markings (DoF markings are particularly useful)
Wider focus ring
Better feel, such as smoother or more dampened and resistant focus ring.
Higher quality grip
Lower weight since there is no AF motor
No chance of AF motor failing (which could lock up the focus ring on certain lenses)

In addition, it could have been bought for its optical quality, bokeh, size, weight, build, prestige of Zeiss, and other qualities not intrinsic to simply being a manual focus lens.
Comment: Video also doesn't allow for autofocus; another good reason to use a manual focus lens.
Comment: This comment was written in 2010; with the advent of Canon's new STM lenses, video & auto-focus are friendlier now, right?
Answer: Because auto-focus doesn't work for what you do, or simply because you don't use it. Then you can get a better quality lens for the same money.
Auto-focus works fine when some part of the image is exactly in focus, but if you for example want to put the focus between two objects so that they end up at the front and back edge of the DOF, auto-focus is useless.
Example:
Easy to get one or three batteries sharp with autofocus, but not two:
Comment: Unless you autofocus on the floor inbetween :)

One area I always use MF is landscapes.  Thank goodness for DoF guides.
Comment: Manual focus certainly has its uses.  What I'm curious about is the particular reasons that make you use the phrase "better quality lens".  Obviously this differs from lens to lens.  I'm looking for questions to ask when shopping lenses rather than advice on a particular lens.
Answer: Simply because usually* you would want to spend as much money as possible on the actual glass.
Usually* you would want the fastest lens, with the best glass. In this case you would lose the auto focus because:
a. the awesome glass you want doesn't come in AF
b. the same awesome lens with AF is just too expensive.
Not all lenses are made equal, you just can't judge a lens solely by it's specifications.
*I say "usually because obviously different people have different priorities.
Answer: Don't forget that not all DSLR cameras are easy to use with manual focusing. Semi-professional cameras have dimmer viewfinder making the manual focusing process almost impossible, because you can't be sure you've focused right.
Comment: This doesn't really answer the question.  But yes, the dimmer viewfinder will hinder but certainly not make it "almost impossible." There is AF-confirm, trap-AF, distance markings, DoF guides.  LiveView with magnification also makes it incredibly easy with static scenes. Then there are split-image focus screens and viewfinder magnifiers, both quite popular with MFers.
Comment: But a good warning for the guy not to throw away some money.
BTW, do you know, for example, that AF-confirm on Canon 400D can miss for a half of DoF and it's okay for this cameras niche? So, AF-confirm on Canon 400D will NOT do any magic for you. So as a dim viewfinder. So, be careful before diving into manual focusing! Make sure your camera is from professional line (NOT from semi-professional)

Why buy an expensive manual focus lens?


OpenLayers 3 Print Example

Question: This example http://openlayers.org/en/v3.5.0/examples/export-map.html on OpenLayers 3 does not work if you add more than two layers. I'm reading my layers from MapServer and the error is Uncaught DOMException: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported. Can you assist
Answer: For security reasons, your local drive is declared to be "other-domain" and will taint the canvas.
(That's because your most sensitive info is likely on your local drive!).
While testing try these workarounds:

Put all page related files (.html, .jpg, .js, .css, etc) on your desktop (not in sub-folders).
Post your images to a site that supports cross-domain sharing (like dropbox.com).  Be sure you put your images in dropbox's public folder and also set the cross origin flag when downloading the image (var img=new Image(); img.crossOrigin="anonymous" ...)
Install a webserver on your development computer (IIS and PHP web servers both have free editions that work nicely on a local computer).

OpenLayers 3 Print Example


Web parts that react to displayed content

Question: So, imagine I have a wiki library. That library has had columns added to contain other interesting information, e.g. lookups to related items in the same list or lookups to parent lists.  How would I be able to include just that data on the wiki page itself, i.e. show all related items for the currently viewed page?  I'm thinking about OOTB solutions (Foundation where possible), I understand I could code a custom part but I'm trying to KISS.
Answer: You could do a number of things without custom code.  You could make site columns that populate field controls on a page with a filter web part sending a peice of data that populates the controls.
Or you could use a web part page with CQWP's to display the data you want from your central library.  An even more elegenat approach is to place these CQWP's ina  page layout along with a single filter web part that is only viewable in edit mode which feeds all the other web parts.


Possible Calibration Equations [Misc]

Question: this is my first post so hopefully this topic is considered OK.
Background:
In class we were using a laser (mounted on a planar robot) to measure various profiles of a sample underneath. The system was already calibrated when I used it but I started wondering how this calibration would be performed (i.e. the math behind it). Here is what I came up with for a setup (simplified):

Setup:
Assume the calibration gauge is a flat plate (blue, at angle $\alpha$ from x-axis and angle $\beta$ from y-axis, ideally it would be parallel to the x-y plane), then there will be: some initial height offset at the robot's origin ($\vec{Z_0}$, unknown), the laser's position attached to the planar robot ($\vec{P}$, known), the laser's measurement vector ($\vec{D_m}$, |$\vec{D_m}|$ known), the "true" height directly below the laser/robot ($\vec{D_t}$, unknown), and the error between the two ($\vec{E}$, unknown).
Ideally, the laser is to be mounted such that the output beam is parallel to the z-axis but I'm sure there are some mounting angle errors (error angle $\phi$ from the z-axis in x-z plane and angle $\psi$ from the z-axis in the y-z plane).
$i$ is the point where the laser makes contact with the plate (x,y,z).
The "known" variables are |$\vec{D_m}$|, P_x, and P_y.
The unknown variables I need to "calibrate" the system (so I can calculate $\vec{D_t}$) are $\vec{Z_0}$ and the angles $\alpha, \beta, \phi$, and $\psi$.
My Attempt to Figure It Out:
First, I found where the laser would intersect the plate/plane based on the robot's (x,y) position:
$i = ( P_x + \Phi\frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi}, P_y + \Psi\frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi}, \frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi})$
where $A$ is the slope of the plane along the x-direction, $B$ is the slope of the plane along the y-direction, $\Phi$ is the slope of $\vec{D_m}$'s x-component along the z-direction, and $\Psi$ is the slope of $\vec{D_m}$'s y-component along the z-direction. Using these instead of the angles made the equations cleaner.
The measurement vector: $\vec{D_m} = (\Phi\frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi},\Psi\frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi}, \frac{AP_x + BP_y + Z_0}{1-A\Phi-B\Psi})$
The Calibration Equations (need 5)

Take measurements along x-axis, regress to find slope, set equal to $\frac{\partial|\vec{D_m}|}{\partial P_x}$.
Take measurements along y-axis, regress to find slope, set equal to $\frac{\partial|\vec{D_m}|}{\partial P_y}$.
Move to origin ($P_x = P_y = 0$ to eliminates variables), take measurement set equal to |$\vec{D_m}$|.
Have two points on the plane ($p_1, p_2$) with a known distance between them ($\Delta$). Move the robot so that the laser dot hits the first point, save ($P_{x1}, P_{y1}$), move the laser to the second point, save that position information. Use $P_{x1}, P_{y1}, P_{x2}, P_{y2}$ in the equation: $\Delta = |i(P_{x1}, P_{y1}) - i(P_{x2}, P_{y2})|$.
...? I'm stuck.

Final Thoughts
I thought this was pretty interesting and not being able to solve it has been bugging me. :) I have no idea how the system was actually calibrated but this is how I set it up. If there is a far easier way or if someone knows how these types of systems are actually calibrated please let me know (it would be an interesting read) but I would also like to figure out that fifth equation using my way. I'm not a math major so I figured this would be the place to go!
Thanks!
Answer: First, a remark: if $\vec Z_0$ is indeed an unknown vector, then you have $7$ unknown scalars in the problem: $(\vec Z_0)_x,(\vec Z_0)_y,(\vec Z_0)_z,\alpha,\beta,\phi,\psi$, which means you'd need $7$ scalar equations, not five.
But suppose that $\vec Z_0$ is perfectly vertical, so only $(\vec Z_0)_z$ is unknown. And suppose even that we somehow know $\alpha=\beta=\phi=0$. Even in this situation we cannot determine $(\vec Z_0)_z$ and $\psi$ from any measurements of $|\vec D_m|$. Indeed, no matter where we move the robot by changing $P_x$ and $P_y$, the measurement is always $|\vec D_m|=|(\vec Z_0)_z|/\cos \psi$. A robot with $|(\vec Z_0)_z|=2$, $\psi=0$ will always give the same measurement as a robot with $|(\vec Z_0)_z|=1$, $\psi=\pi/3$.
Perhaps your robot actually measures something in addition (or instead of) $|\vec D_m|$.
Comment: Wow, I hadn't even noticed someone had answered; thanks for the response. Yes, it could very well be measuring something else (all I saw was the profile data but I was curious on how the system was calibrated to correct for various angle misalignments). I will ask my professor to see if he has any idea and update my post with any new info. Thanks again.

Possible Calibration Equations [Misc]


Energy loss from Doppler effect

Question: The energy of electromagnetic radiation is related to frequency; higher the frequency, higher the energy level. If electromagnetic waves have lower frequency when they arrive on Earth than originally emitted due to the Doppler effect, where, according to the conservation of energy, does the excess energy go?
Comment: The answer by Steve Linton is not correct, I'm afraid. The answer by ACascarino is closer to the truth. The correct answer — that energy conservation doesn't apply in an expanding Universe — is explained very well in [this article by Tamara Davis](https://www.scientificamerican.com/article/is-the-universe-leaking-energy/). It's behind a paywall, unfortunately, but can be found online if you google for it.
Comment: Recommend also looking at: https://physics.stackexchange.com/questions/15279/conservation-of-energy-and-doppler-effect
Comment: @pela Are you saying that a police Doppler radar gun depends on the expansion of the Universe to operate?
Comment: @pela so I can't read the article because I don't have access, but that argument somehow makes the most sense per my other comment below. Thank you
Comment: Whether or not energy is conserved in an expanding (or contracting!) universe is somewhat immaterial - as the article you reference even quotes, "[...] the galaxy's redshift can be interpreted as the result of relative motion, rather than of the expansion of space. Therefore, no energy is lost." when motion is viewed relative to the particle's motion
through spacetime; it reduces again down to the fact that conservation of energy is meaningless if you start switching between reference frames without applying the correct transformations.
Comment: @user71659 No no, not at all. The question mentions photons arriving on Earth, so I interpret it as asking about cosmologically redshifted photons, which is actually different from Doppler-shifted police photons.
Answer: It's spread out in time. If a source emits a 1W pule of energy lasting 1 second and the receiver is receding so fast that it is Doppler shifted to a frequency which means the power is just 0.5W, then the pulse will take 2seconds to arrive (since the end of it had further to travel).
Comment: I think this is wrong.  What happens if the source emits one photon (with a given energy)?  If the receiver is retreating so fast that the photon energy is red-shifted to one half, the receiver still only receives one photon.  Where has the rest of the energy gone?
Comment: Yes, I think you are all right. My mistake.
Comment: We've all done it most likely, even the people giving answers can learn from this forum!
Comment: Yes, this doesn't seem right. A previous post from @bilkokuya was helpful, but to say that "conservation of energy doesn't apply between changing reference frames" feels unsatisfactory when dealing with the 1 photon case. Especially considering if, say, all light in the universe experienced this loss of energy; how could the overall energy in the universe remain constant?
Comment: Even without relativistic corrections, if a machine gun fires some bullets into a receding target,  the rate that bullets arrive is reduced by the target motion, and the energy per bullet is reduced even more.  One is not caused by the other, they are two separate effects of the motion.  Similarly, the change in intensity of a light source is separate from the change in frequency, one does not explain the other.
Answer: Completely ignoring relativistic effects, it depends on which reference frame you are using; the "missing" energy is seen as kinetic energy in either the emitting or receiving atom as recoil depending on which one you view as moving. Energy is not conserved between reference frames.
If I am travelling at a velocity away from you, and I emit a photon at you which I observe to have a frequency f, then I will assume that photon has an energy E = hf, where h is the Planck constant. I will never observe a different energy for that photon - in my reference frame, energy is conserved.
You, however, will observe a different frequency f, and therefore a different energy E. This energy remains constant for you - energy is conserved in your reference frame - but the energy I observe and the energy you observe differ - energy is not conserved between our reference frames; that is to say, the energy is conserved but not invariant
Consider - I drive past stationary you in a car and throw a tennis ball at you. In my perspective, the tennis ball has greater kinetic energy (it is moving at my speed, plus the speed of the ball) than in your perspective. Energy is not invariant in this circumstance either!
Comment: A simpler demonstration that KE isn't invariant is to just look at you in your car and forget the tennis ball altogether. In your frame, you're stationary and you have zero KE; in my frame, you're whizzing by and have a bunch of it.
Answer: Conservation of energy doesn't apply to this situation because the energy you measure when at rest with respect to the source and the energy you measure when moving with respect to the source are in different reference frames. Energy is not conserved between different reference frames; in other words, if you're going to use conservation of energy, you have to make all your measurements without changing velocity.
For more information, have a look at https://physics.stackexchange.com/questions/1368/is-kinetic-energy-a-relative-quantity-will-it-make-inconsistent-equations-when-a.
varbatim from David Z's answer for a question on physics SE

Energy loss from Doppler effect


Catalytic Converter self-service

Question: Can I remove catalytic converter, remove loose fragments, then put it back on without harming vehicle?  I have a 2003 Ford Windstar.
Comment: Welcome to Motor Vehicle Maintenance and Repair!
Answer: You can, and it won't "harm" the vehicle, but it won't get much better either.
If the catalyst honeycomb is breaking down, the catalyst element is shot, and needs to be replaced.  It will continue to break down and result in more "fragments".
Additionally, if the breakdown occurs inside the honeycomb, those fragments cannot be removed without destroying the catalyst entirely.  You will have additional backpressure and poor exhaust flow.
Also, think of it this way:  Other than the cost of a new cat (aftermarket can probably be had for less than $200) you are already doing the labor to remove the fragments - might as well just install a new cat.
I've completely removed the catalyst part in the past, but this is illegal on a street vehicle in many places and certainly affects emissions.
Comment: Couple of years ago while on a trip we had our engine light on and the engine delivering very little power. We had an emergency visit on a small repair shop and since they had no spare parts we had to remove the catalyst, cut open and completely remove the honey comb from inside and re-weld it in place, in order to continue our trip. It stopped the lambda sensor engine warning. The casing was cluttered with these "needles". Still illegal and quite noisy, it had to be replaced when we got back. All these needles are also quite toxic and given the choice any contact with them should be avoided.
Answer: I would say it would be a waste of time there are filters in a cat that need to be there.  Your just better off replacing the cat if you have it off.
Answer: Replacing it is the best option, but if the honeycomb inside looks like it is NOT badly damaged. Then watch this video. Here

Catalytic Converter self-service


How can i get the most air from a jump?

Question: I'd like to know what technique/s to use to get both the most height, and the most distance from a dirt jump. The stock image below is the kind of dirt jump I'm referring to.
Comment: By pushing the bike down, the body will rise.  Timed just before the brow/crest of the rise will mean your Center of Mass is moving up faster.
Imagine there's no bike and you were running on the same track... you'd put your last foot down and push upwards.  That's pretty much what you want to do with the bike.
Comment: I suspect it will be some combination of  "go faster", and push off more just before the lip,
Comment: That picture is typcial what you get when beginners try to clear a jump by aiming all for speed, but not pushing off as Criggie says. I really cannot properly explain how to do it, but it is basically pushing the bike against the transition using your knees - and doing it pretty early i.e. well before you're at the lip. The effect is you push the bike more in front of you, so it's pointing more upwards, and then you let it follw through that motion resulting in the bike and yourself going up.
Comment: @Criggie how does one 'push off more'?
Comment: sounds logical. should there be a lot of pulling up on the handle bars? and can you add this as an answer?
Answer: Regarding the picture: in the comment I said the rider isn't going high because of not trying hard enough, but on second thought the main reason for not being able to get proper air from such jump is that the lip is not steep enough; in fact the entire transition of that jump is rather mellow and not suited for height, you'd almost have to bunny hop out of it to go higher. The second jump on the pic seems better in that regard though it is hard to tell. For reference, something like this will launch you in the air no matter what:
(sidenote: it takes a lot of practice to be able to build jumps like that, almost as much as it takes practice to be able to ride them:)
Now, the optimium between height and length can probably mathematically be derived but I don't know how. I do know in the end it is irrelevant: once you practiced enough sometimes you'll just want to flow through lines without going particularily high while other times you'll try to really boost it. Another thing to realize is that pure distance at itself is almost never the aim: you'll rather want the perfect distance to nicely clear the jump. And not much further than that or you'll land too deep into the transition of the landing which makes it hard to maintain speed.
As for the actual answer (finally): as said I cannot explain it very well, but to go heigh (on jumps as pictured above) you basically push the bike against the transition, somewhere in the center so well before the lip, using mainly (at least for me) legs and arms. Doing that pushes the bike somewhat in more in front of you and forces it to follow the an upwards direction of the jump, and your body follows that. I don't think there is any pulling up on the handle bars until you are airborne. On the contrary, pushing the bike into the transition means extending limbs. This is a pretty good illustration you can also check the rest of the explanation there:
Final note: I rode/ride quite some dirt and met many people and when talking about it is usually in rather vague terms like 'push the bike' etc. It is just hard to break down all steps because they happen so fast and as a consequence it is hard to explain it to others. Best thing you can do is watch fellow riders or watch films, eventually in slow motion to see what exactly happens. But even if you do that you'll need practice, practice and then some more practice and one day you'll realize you suddenly know how to do it. If you can then explain exactly why, please report back here!
Comment: great answer thanks @stijn! It kind of sounds like 'pumping' when riding a skateboard on a half pipe to develop speed, except without the change in direction. now to give it a go!
Comment: Yes, it is exactly the same principle as pumping in a transition with a board (or bike, or skates, or...)
Answer: That last photo from @stijn is a good illustration. See how the rider is crouched at the bottom of the transition with legs and arms bent. As he takes off his legs and arms are extended. That means that his centre of mass is moving more steeply up than the transition itself, and he pulls the whole bike up with him.
If he were speed jumping it he would be doing the opposite: his legs and arms would be straighter at the bottom of the transition, bending to absorb the jump as he went up the face, giving a much flatter trajectory.
You want to be careful of pulling up too hard in a jerky motion and stalling in the air. You need enough speed to get the distance, and then use the whole height of the takeoff to launch your whole body − don't just pull on the bars.
Skilled riders don't need a big takeoff to get height. Watch how someone like Danny Macaskill can use a small stone or tiny kicker to launch onto high ledges, etc. It's kind of a bunny-hop with a boost.
Distance is more dependant on the speed of the rider and the shape of the takeoff. My memories of school physics tell me that a launch angle of 45° gives the greatest distance, but launching a bike from a dirt takeoff involves so many variables that I wouldn't dwell too much on that number. As @stijn says, you'll usually just want to aim for the sweet spot in the landing, whatever distance that may be.
(Relating to your other question about building dirt jumps: look at those shovels! Nice long handles, smooth curved backs, and see how that guy is using it on the face of that jump to compact it and smooth it at the same time.)

How can i get the most air from a jump?


How can I set up a Local Area Network without a router?

Question: I have a reliance bandwidth connection and I want to set a local area network without using a router. How can I do this?
Comment: What is your goal?  Do you want to share internet access or just files and folders or other?
Answer: You can do it with an ethernet switch, it will be more work than with a router.
See http://compnetworking.about.com/od/homenetworkhardware/f/routervsswitch.htm and this http://www.duxcw.com/faq/ics/diffrout.htm for more info.
Answer: You could use a token ring configuration, but then you would need a media access unit which performs the same basic function as a router. If you want Ethernet, you would need a switch as bryan said, which again, performs the same basic function as a router. In any case, if you want more than two devices to be connected, then you need some sort of device to route the packets. You may be able to find some sort of esoteric network topology that allows several devices to be connected directly, but I doubt it since that would cause problems if any one of them has a problem, is shut down, etc; that is why you need a separate device.
If you only need two, then you can connect them directly with a patch-cable like Kevin suggested, a direct-cable connection like with a serial Interlink cable, or special USB cables.
Answer: A crossover ethernet cable will allow two machines to send IP packets to one another without the need for a router, a hub, or a switch between them, but ethernet over twisted pair is strictly point to point, so you can't do something weird like wire together a couple of sockets and pretend that it is a hub.
Maybe being in India you can still get 10b2 coax network cards, and if so then you can set up a relatively slow LAN by daisy chaining the coax cable from one machine to the next, but as I remember it coax was extremely time consuming to troubleshoot.  A break anywhere in the daisy chain could knock out a large percentage of the network and tracking down the problem meant crawling under every desk to determine whether or not the ethernet carrier was making it to that machine.
To get a couple of additional machines connected you could use additional network cards and configure your computer to route packets between the ports.  On the whole though I'd recommend against it; routers, switches, and hubs are by far the easiest and fastest way to set up a LAN.


Our two year anniversary is coming up, how should we celebrate?

Question: February 7, 2013 marks our second anniversary since day 1 of the private beta.  Should we celebrate this event somehow? If so, how?
Comment: Um...award 10,000 points to all active participants as party gifts? :)
Comment: We'll double everyone's points, then divide them in half, and repeat the process until everyone is above 10,000. ;D Sorry, bad joke.
Answer: PMI grants CPE/PDU for blogging on their site.  I wonder who we'd need to contact to arrange credit for answering questions here.
Comment: Good idea. Maybe there's a point of contact for Internet marketing?  Mark Phillips might know the answer to that as I think he might be an active PMI member.
Answer: I think we should summarize the achievements of this website, such as:

Membership growth
Reputation growth
# of questions asked vs # of accepted answers
Range of pm topics covered
Range of pm tools covered

One possibility is to blog about this and share it on social media as well so that more people may have a chance to discover the site and participate.
I volunteer to write up the first draft, although I don't have a clue how to get the data for 1 to 3 yet.
Comment: Hi Ashok, this is a great suggestion. Many of these stats are available in [Area 51](http://area51.stackexchange.com/proposals/10947/project-management).  Also, you can see snapshots of where we were a year ago in [this PMSE Meta post](http://meta.pm.stackexchange.com/q/555/34).
Answer: Second Anniversary Blog – Draft
As promised, I have written a draft of the second Anniversary Blog. I am new around here. I suggest that one of the senior members should publish this blog. Please feel free to edit it, as needed.

Excellent Q&A Site; Got to Reach More Project Management Practitioners
February 7, 2013 marks the  second anniversary of The Project Management Q&A Site on Stack Exchange (PMSE). It is rated "Excellent" even by the very demanding standards of Stack Exchange.

Questions answered: 90% answered is healthy. We are at 100% answered, which is excellent.
Every site needs a solid group of core users to assist in moderating the site. Stack Exchange recommends a minimum number of users with certain reputation levels. We currently exceed all these, which is excellent. Minimum of 150 users with a reputation score of 200+; we are currently at 214 users. Minimum of 10 users with a reputation score of 2,000+; we are currently at 17 users. Minimum of 5 users with a reputation score of 3,000+; we are currently at 12 users.
Answers per question: 2.5 answers per question is good. We are at 4, which is excellent.
Visits per day: 1,500 visits per day is good. We are at 1849, which is excellent.

A variety of questions get answered here:

On a range of project management processes: From traditional project management to CMMI to Earned Value Management (EVM) as well as from Waterfall to RUP to Agile/Scrum/Kanban/Extreme Programming (XP).
In a range of industries:  Construction, software development, aerospace, defense and others.
About a range of tools and solutions: Desktop and web-based Project Management tools such as MS Project/Project Server, Agile/Scrum tools such as Rally and other commercial tools as well as open source tools such as Redmine and Trac.

Also we have tripled the site traffic over the last one year from just an okay level of about 600 visits per day to an excellent level of about 1800 visits per day. Do we rest on our laurels saying we have done a great job?
To get a broader understanding of what percentage of PM users we are reaching, let us look at some stats. We have currently about 5000 users. The 2011 Annual Report of the Project Management Institute (PMI) reports "more than 600,000 PMI members and credential holders in more than 184 countries". Some of the open source project management tools have been downloaded a few million times. Among commercial tools, Microsoft claims to have 20 million users for Project and Project Server. This is not counting other project management tools and solutions.
So, it is clear that we have just scratched the surface of the user base. Here is a great Q&A site where you pop the question that is blocking you from managing your project better and you are guaranteed to get a satisfactory resolution. But the vast majority of project management professionals as well as casual users seem to be totally unaware of that.
Let us spread the word. On this second anniversary we are asking everyone's help to get the message out. Please share the link to this blog with your professional contacts. Send an email, put it on your web site or curate it. Share it on FaceBook, Twitter, LinkedIn and other social media sites. And they will thank you when their next Project Management problem gets resolved or, even better, when they are able to help resolve another user's problem.
Comment: Hi Ashok, thanks for putting this together. If you have a blog, you could publish this yourself. Otherwise, maybe one of our PMSE users could publish you as a guest author on their blog?  One suggestion, in the 2nd to last paragraph, I suggest focusing on the fact that this is *not* a forum but instead is a Q&A site. Sometimes this does trip people up a bit when they first visit. :)
Comment: I have changed the Forum to Q&A site. I don't have a blog. I am open to going the guest blog route.
Comment: Hi @jmort253, Tomorrow being Feb 7, let me know whether I should be publishing the blog. If so, appreciate any guidance you can provide in advance for the guest blog.
Comment: Hi Ashok, in terms of publishing this post, it's all up to you and whomever would be interested in posting this to a blog they're affiliated with. I'll drop a link to this in our [chat] to see if anyone else bites. Good luck, and thank you for putting this together! :)
Comment: I published the blog on my hobby site here: http://smb-soft.com/blog
Comment: Awesome! Thanks again for putting this together. :)
Comment: Great post, Ashok! Thanks for putting it together.
Comment: @MarkPhillips - Hi Mark! :) Can you take a look at this?  http://meta.pm.stackexchange.com/a/582/34


What is the difference between Communism and Anarchism?

Question: Can anybody please explain me, in brief, the difference between Communists and Anarchists?
Comment: Welcome to Philosophy! :) So this is at least two separate concerns, with not very much context or motivation. Is there any chance you could narrow this down to a single question (and maybe indicate what might have made this an interesting or important problem for you in your study of philosophy?)
Comment: To the people voting as "too broad": this is exactly the kind of question political theory is for!
Comment: A brief explanation is not possible.  For one thing, there are many varieties of anarchism, ranging from an idealistic "everyone will voluntarily become communist) to Ayn Randian anarcho-capitalism to civilization collapsed and everyone has to arm themselves to fight off everyone else.  But as an attempt at brevity, consider that anarchism is defined as not having government, while no communist state has ever existed with out a strong, if not absolutely tyrannical, central government.  So in the real world, communist is the antithesis of anarchist.
Comment: Wait! This so does not belong here. It belongs to the _Politics_ stack.
Comment: Actually I am an Engineer. I came across Marxism at a very early age due to my socio-political milieu. Unfortunately, I never came across the philosophy of Anarchism. I used to think that anyone who doesn't believe in the prevailing order is an Anarchist. Few month back I decided to prepare for civil services examination. I have opted Sociology as my optional paper. Marx was there in my syllabus. But I was not convinced with Marx on some points. When I discussed my doubts with my professor he said that I am an Anarchist. I thought that the term "Anarchism" has a negative connotation but I was
Comment: Now I am curious about Anarchism but it is not there in our syllabus. Hence, it is an irrelevant topic for my class but very interesting topic for me. Please help.
Comment: @user17997: Check out https://libcom.org/files/1345266991261.pdf - it is "Chomsky on Anarchism"
Comment: "This question does not show any research effort."
Comment: Anarchism is the broader definition. Communism (read: anarcho-communism) is a specific variety of anarchism that does not use any capital or wage labour based economy, as well as private property (which is different from personal property) as opposed to collective ownership (specifically the means of production). The defining trait in any anarchist school of thought is non-authority or total egalitarianism (eg stateless). Curiosity: Anarchists don't like Marx (that includes anarchists contemporary with him), and the Communist manifesto has little to nothing to do with philosophical communism.
Answer: Communist's and Anarchist's motives are quite similar, however their politics are informed by different assumptions.
Communists who agree with what Lenin wrote in "The State and Revolution" and what Marx and Engels wrote, believe that the state will "wither away" when what Lenin calls "class antagonisms" vanish. The state emerged as a tool for class control, and they believe it will fade away as there is no class to dominate or be dominated by another.
"Class" in this sense is defined by a persons relation to production (a laborer or a proprietor.)
Anarchists, however believe that class antagonisms can be quelled without the need of a state apparatus, and because of this decry all states.
Communists think the state will wither away as the proletariat (workers) become the only remaining class.
Anarchism and Other Essays is a good book by Emma Goldman to explain Anarchism.
The Principles of Communism by Engels is a good short pamphlet explaining the goals of communism.
The Communist Manifesto is arguably the most important book for understanding Marxist communism, being the first consolidation of his thought.
The State and Revolution by Vladimir Lenin well explains the function of the communist state and when it will vanish.
Anarchism Or Socialism ? by J. V. Stalin is a text where Stalin explains the differences between Marxist and Anarchist positions.
Comment: Welcome to Politics.SE. Once you get more reputation through upvotes, please consider adding some links to your answer to make it even better.
Answer: Both anarchism and communism are political philosophies which reject the linkages of capitalism and government.  However, they are significantly different in what they reject.
History
Anarchism and socialism have overlapping histories, which accounts for their similarities. Although there were historical antecedents, the modern forms of communism and anarchism were both created in the mid-to-late 19th century in Europe as a response to the problems brewing in industrial, capitalist society. While the anarchists would blame government for their social problems, communists would come to blame capitalism (via industrialization).
There are two incredibly notable publications in this period:

1840: Proudhon publishes What is Property?, one of the most influential anarchist texts. Proudhon is notable for being the first person to call himself an anarchist, and his work would inspire significant intellectual discussion on the topic.
1848: Karl Marx publishes the Communist Manifesto, espousing the general aims of a group of socialists and communists in Europe. Later, he would publish the academic version which more thoroughly argued for their ideas: Capital

Anarchism: Rejection of the State
One of the basic questions of political theory is, "What is the value of a government?".  There are generally two answers. Statists maintain that the government is good, while anarchists argue that the state is bad. What "good" and "bad" mean will vary greatly depending on what author you are reading.
The role of capitalism is a contentious issue among anarchists. It's also a non-trivial: once anarchists abolish the state, do they need to abolish private property? Or employee-employer relations?  Because the answer to these questions may overlap with communism (or Marxism) a person may be an anarcho-capitalist (who supports capitalism, but not the state), an anarcho-communist (who supports neither capitalism nor the state).
Communism: Rejection of Capitalism
Marxist philosophy is dense, with a lot of variation in terminology between different authors. Generally, communism is a near-utopian society which exists after the state is no longer necessary.
That may sound a lot like anarchism. You'd be right - it's a rejection of the state. However, all Marxist thought is based on materialism: the idea that everything can be reduced down to physical things. In social terms, everything about our society can be reduced to the physical objects we need, which makes the state fundamentally an economic problem. Once we reject capitalism, the state will wither away and die, paving the way for communism.
Whether or not a communist is an anarchist will depend on what exactly they think. Mark himself suggested that, although he didn't know what communism would look like exactly, it would be a state-less world. Others say that under communism some amount of government will be necessary, but since it will exist without the influence of capitalism everything will be fine.
Answer: Communism in contrast to Anarchism does not dismiss the governing role of the state.  Here is a link to a possibly helpful text by Judith Suissa, Anarchism and Education: a Philosophical Perspective - Routledge Pub., New-York, 2006:
http://rebels-library.org/files/anarchismandeducation.pdf
Comment: @SVilcans: It may be impossible to define an exact boundary. Anarchism is defined by its rejection of centralized power, but this generally is not an absolute and unconditional rejection. Communism is far more focused on centralized power, but again practical arguments restrict how much of that you can have.
Comment: Well, there are also libertarian communism that is quite close to anarchism. The main difference is that libertarian communists use a Marxist analysis of history, while anarchists may or may not do that.
Comment: Many would disagree with that answer. This is evidenced by the first paragraph on the Wikipedia article on Communism, which lays it out as a (quote) "socioeconomic order structured upon the common ownership of the means of production and the **absence of social classes, money, and the state**" The situation with a state you might refer to is the route to communism via Marxism.
Answer: I think it is a mistake to think of anarchism as being essentially related to communism, or even being essentially left wing at all. Communism in practice (if you accept that countries such as the Soviet Union, China, North Korea, etc., are genuinely communist) involves very strong centralised control by the state, usually at the expense of the individual liberties of its citizens. Anarchism on the other hand is motivated by the belief that government of any kind is bad: we should either not have it at all, or to the extent that it is a necessary evil, keep it to a minimum.
Some anarchists have certainly been strongly left wing and have advocated abandoning the right of property, for example, but on the other side there are some who are motivated by classical liberalism, and who are opposed to government precisely because it infringes on liberties such as the right of property. One can hardly call these people right wing, because that term usually implies being conservative, and people of this persuasion are often far from conservative, but they are certainly not left wing.
Comment: I think it is misleading to try to fit all political views into a single spectrum running from left to right. Reality is not bipolar. Also, the fact that one holds views that are not mainstream does not mean that one has no role to play. Some laissez-faire anarchists run for political office under the banner of libertarianism. As to what they believe in, there's quite a mix of different views, but one political text you might care to consult is Anarchy, State and Utopia by Robert Nozick. It advocates a minimal "night watchman" state.
Comment: Does this mean that Anarchists have no role to play in today's political arena? Are they out of the political spectrum? If they are not left or right then what do they believe in?
Comment: You say "in practice", and indeed we know they failed disastrously. As with other answers in question, you rather describe systems that took the route to communism which arose after Marxist theories. But this then doesn't provide an answer to the question how the ideology differs from the Anarchist one. The first paragraph on the Wikipedia article on Communism lays it out as a (quote) "socioeconomic order structured upon the common ownership of the means of production and the **absence of social classes, money, and the state.**"
Answer: There are many different Marxisms and Communisms and many different Anarchisms. At least parts of the new left use the terms interchangably. So the question is not nail down one possible definition for each and then list the differences, but to find a few interesting trains of political thought and actions.
If you come from a Marxist direction (though you didn't state which Marxism), I'd look at these:

Syndicalism
Crimethinc's Days of War Nights of Love is a good start on an anarchism that puts a high value on subjectivity and adventure.
The Invisible Comitees The Coming Insurrection -  the word Anarchism shows up no where in the text but the emphasis on solidarity and action puts it near classical anarchist thoughts

(Must add links and expand later)
Answer: Marx was for centralizing most power in the hands of the state as a step on the way to a workers paradise. Anarchists believe that centralization is where things will fail, because special interests always hijack centralized power, which is why democracy is a revolutionary cycle.
Answer: People think Karl Marx and his friend Engels are communists. ( Although they claimed they were ). Unfortunately, they did not leave clear image of what the exact form of the "Communism" would be. Only slight mentionings about their image of the "coming world" remain.
For example,

while in communist society, where nobody has one exclusive sphere of activity but each can become accomplished in any branch he wishes, society regulates the general production and thus makes it possible for me to do one thing today and another tomorrow, to hunt in the morning, to fish in the afternoon, rear cattle in the evening,criticize after dinner, just as I have in mind, without ever becoming hunter, fisherman, shepherd or critic.

From German Ideology around at the bottom of page 12.
Here I see no difference between "Communism" and "Anarchism". It does not even need to ponder if all of the people on the planet can do one thing today and another tomorrow, to hunt in the morning, to fish in the afternoon, rear cattle in the evening,criticize after dinner, as Marx says. Who makes the arrows for hunting for "them" ( whoever they are ) to play it? Who makes the hut or house to "criticize after dinner" for them? Here, we see the division of labor is inevitable. So I think many people tend to connect Communism with Marx, Engels,I can not agree on it, he did not mention crystal clearly what "Communism" would be.
Now when it comes to "Anarchism", we can not forget about Michail Bakunin.
Since I have never thoroughly read Bakunin's books, only the citation through Marx ( Engels' ) activities, I would like to quote from the internet.
For example,

Political Freedom without economic equality is a pretense, a fraud, a lie; and the workers want no lying.

What is this? It sounds more like a country whose means of production is collective and distribution is through rationing and even if you look at his quotes I have no idea whatsoever Bakunin had any coherent idea about "anarchism."
Conclusion
Marx, to me, is in no way the communist but a hyper capitalist. ( because in order for us to conquer his idea of "refication", we have to "exchange the labor" through which we confirm we are the Nature, by without any form visible ( such as money ) and which is impossible. )
Bakunin
Such as

The freedom of all is essential to my freedom.

Sounds like his idea of anarchism ( when you read other his sayings ), there is no States, which is enemy to human beings, thus we must be free from anything, and if the condition that all men are equal is a must to accomplish for an individual to be free, then there would be no freedom at all, since A's freedom hinders other's freedom ( whatever that would mean. )
Answer: Communism, as a ideology, is a more radical form of Socialism and in it itself a economic model, to be true.
Anarchism, as a ideology, is a revolutionary form of Authority where all forms of illegitimate form of authority has been done away.
So in this way Communism is on the horizontal economic axis (left-right axis) and Anarchism is on the vertical authority axis (authoritarian-anarchist axis). These ideology can't be compared in the traditional sense as both them address different problem.
But for this sake, lets compare using the communist way of establishing a Communist society.
So,
Communism (in Marx's term) demands a revolution whereby Socialism would be established and this Socialist reign will be used to establish and form a class-less, state-less society.
But in Anarchism, a revolution is required for the people to unite and destroy illegitimate forms of institutions. Anarchism don't necessary demands a state-less society, if the one can legitimize the presence of state
The basic difference with Communism and Anarchism is in the relation towards state and hierarchy. Both of them want a bottom-up non-hierarchical approach of governance, but in communism, one must finally do away with state and other "incompatible" ideology, especially Capitalism. But in case of Anarchism only authorities that can't be legitimized to the people must be done away, and demands to be replaced by horizontal non-hierarchical democratic free associations.
Hope I made it clear. Anarchism, in its purest form doesn't exists. It's mostly coupled with Communism (Anarco-Communism) or Socialism (Libertarian-Socialism) or Capitalism (Anarco-Capitalism) and has mostly developed as a answer to the authoritarian ideologies like Leninism, Maoism, Authoritarian Capitalism.
Comment: This answer should reference existing bodies of theory. Currently, this reads a lot like your own formulation or opinion of anarchism/communism. Can you back any of this up?
Answer: Anarchy is essentially apolitical. It is counter-political in the strongest of senses. It is the very negation of politics of whatever kind.

Anarchy = no authority.
Politics = The art of leading a state ("being about statesmanship").
State implies authority/government

There can be not only no state (communists want to achieve this, too), but no human community at all if anarchy is meant seriously. What most anarchists do not see is that they in fact mean communism as a form of organisation of human communities. Or, one may assume, they practice anarchy to overthrow the present political system only in order to instate a communist society.
On the other side, like the answer of @bumble shows, totalitarian socialist regimes claim to be communists. But they aren't (see here).
Conclusion: Anarchists may be anarchists only insofar as they are against the present political system, but at the same time communists insofar as they endorse the idea of communist society.
Disclaimer: I know most hate Wiki-links, but these terms are well stated.


Use something that slower than light in Michelson–Morley experiment

Question: Follow by the Michelson–Morley experiment, What happen if we use something that has a speed lower than light instead of light in Michelson–Morley experiment? How about the result?
Comment: It's not about the speed as such. It is about the relationship between the observed speed of the wave and speed of the observer relative the *medium of propagation* (if any). The expectation for (say) sound in air is exactly what MM calculated as the assumed result of their experiment before they started. Only you don't need an interferometer to observe this effect in air, you can do it with a car horn because you can travel at multiple percent of the speed of sound very easily.
Answer: The aim of the Michelson–Morley experiment was to measure how fast the aether is moving relative to Earth, and to do this you need some phenomenon that propagates as a disturbance in the aether. Light was the only phenomenon believed (incorrectly of course :-) to propagate as a disturbance in the aether. That's why light was used.
As dmckee says in his comment, if you use something like sound you aren't measuring the speed of the aether because sound propagates as disturbances in air not in the aether. Using sound would measure how fast the air is moving relative to your equipment. This would work fine, though there are easier ways to measure wind speed.
Answer: Interesting question. Mathematically the apparatus using the Vl (velocity of light) and Ve (velocity of the aether) can not prove anything except  Vl+Ve (1st leg) Vl (2nd leg) + Vl (3rd leg) +Vl-Ve (4th leg) = 4Vl which really demonstrates nothing. it will only show a difference in the fringes when accelerated.
the apparatus can not get past the Doppler like condition of what goes in one dimension V+v also returns in the same dimension V-v.


Master degree business administration vs. Project Management Professional (PMP) to become project manager in Programming Inc. and why

Question: I want to be project manager; now my job is .net/web developer . What is the best way to become a project manager and what are  the minimum years of experience needed?
pmp
Comment: Possible duplicate of [Career path in project management](http://pm.stackexchange.com/questions/2165/career-path-in-project-management)
Answer: My suggestion would be for you to review the current job description requirements at the companies for which you want to apply for the project manager role.
Many companies are not necessarily looking for candidates with a master's degree for this role. Some companies ask for professional organization credentials and others do not. Some companies will have different levels of project managers with different education, credential and experience requirements.
If you think that your education and experience currently qualifies you for the project manager role, large companies often have human resources professionals that assist employees with promoting to roles within the organization. Have you considered applying for the role at your current company?
If you do not think that your education and experience currently qualifies you for the project manager role, the same human resources employees at the company that could help you promote can help you identify your training deficiencies and even enroll you in training programs to help you promote.


Chi-square degrees of freedom proof

Question: I need to prove why we have the following result:
When:
$Y_i=\beta_0+\epsilon_i$, then:
$\sum\frac{\epsilon_i^2}{\sigma^2}\sim \chi ^2(n-1)$
Thanks :)
Answer: You've omitted a fair amount of information.  If, as in many contexts in which this notation is used, $\varepsilon_1,\ldots,\varepsilon_n$ are normally distributed with expected value $0$ and variance $\sigma^2$, and are mutually independent, and $\beta_0$ is constant, i.e. not random, then the result is false.  In that case, you'd have
$$
\sum_{i=1}^n \frac{\varepsilon_i^2}{\sigma^2} \sim\chi^2_n. \tag{1}
$$
Now let $\hat\beta_0$ be the sample mean $(Y_1+\cdots+Y_n)/n$, as opposed to the population mean $\beta_0$, and let $\hat\varepsilon_i$ be the residual $\hat\varepsilon_i=Y_i-\hat\beta_0$, as opposed to the error $\varepsilon=Y_i-\beta_0$.  Then one has
$$
\sum_{i=1}^n \frac{\hat\varepsilon_i^2}{\sigma^2} \sim\chi^2_{n-1}. \tag{2}
$$
The reason for $(1)$ is that the $\chi^2_n$ distribution is the distribution of the sum of squares of $n$ independent random variables with a standard normal distribution.
The proof of $(2)$ is more involved: write
$$
\begin{bmatrix} Y_1 \\  \vdots \\  Y_n\end{bmatrix} = \hat\beta_0\begin{bmatrix} 1 \\  \vdots \\  1 \end{bmatrix} + \begin{bmatrix} Y_1-\hat\beta_0 \\  \vdots \\  Y_n-\hat\beta_0\end{bmatrix}.
$$
The vector on the left has a distribution that is rotationally symmetric.
The second vector in the sum on the right side of $(2)$ is constrained to lie in the space in which the sum of the components is $0$.  It is the orthogonal projection of the vector on the left side of $(2)$ onto that space.  It inherits the rotational symmetry, but it should be apparent that its expected value is the zero vector.
Since its distribution is rotationally symmetric and its in an $(n-1)$-dimensional subspace and has expected value $0$, the distribution of the sum of squares of its entries is the same as the distribution of the squares of the norms of $n-1$ independent random variables each normally distributed with expected value $0$ and variance $\sigma^2$, so the distribution you get is $\chi^2_{n-1}$.
That's a somewhat terse answer, but you should get clear about what the statement says and which statements are true and which are not before you try to understand why.
Comment: Thank you, this was all I needed.
Comment: @ChiGuy Plz read the comment just above this.

Chi-square degrees of freedom proof


Disappearing post to meta

Question: About 30 hours ago, I posted an item on meta that was not here 12 hours later.  What's going on?
Comment: @Skliwz: could you perhaps edit the link in your comment so that the title is not visible.
Comment: I can't verify it, but you should have been notified of the answer.
Comment: A message was sent off site immediately after deletion but apparently did not reach user Michael Hardy.
Comment: It's been [deleted](http://meta.mathoverflow.net/questions/252). See answer by the relevant mod.
Comment: @MichaelHardy If a moderator leaves a *comment* before deleting a post, the poster is guaranteed to be notified about it. This is one of the changes that came in with SE 2.0, and I let the moderator know so that they're better able to prevent confusion like this in the future.
Comment: @MichaelHardy there are six moderators for the site, this was also so before the change, you can find [the names of the moderators](http://meta.mathoverflow.net/users?tab=moderators) on various places on the site. The are marked by a diamond see François G. Dorais. But note that now there are also general network-wide moerators also marked by a diamond. But mainly the relevant ones for this site are those behind the link I give. you can contact them by email via writing to moderators "at" MO.net with MO expanded in the obvious way.
Comment: Was any attempt made to inform me of the deletion?  It didn't appear in notifications or elsewhere.
Comment: OK, I've found out that a notice was sent to an email address that I've recently looked at only every two or three days.  I don't know how moderation works on this site, other than the crowd-sourced forms of it.
Answer: Okay, my fault apparently.
I deleted the post and immediately contacted Michael to discuss it offline. I then hopped on a plane to Australia and missed the discussion here.
François recommended to me that I use the new 2.0 feature for contacting users through the site rather than by email. At this point I don't like the idea very much, but could be persuaded.
Our previous policy had been that if you don't provide identifying information in your profile (e.g. a real name or email address), you shouldn't expect particularly much patience from the moderators!
The new "internal" notification mechanism in fact makes it easier for users to remain pseudymous, which I think is a bad thing! I would prefer to stick to our old ways --- you're welcome to be pseudonymous or uncontactable, but only on your best behaviour!
Comment: The difficulty of getting a pseudonymous email address is so minimal that I would say regarding the difficulty of being pseudonymous it does not change anything, except if out of principle you would not write to such an address, which however was never said like this.
Comment: You're definitely welcome to use whatever moderation techniques you think work best for you guys, but I just want to note one advantage of using the internal messaging system - it leaves a record on the site that is easy to find and review later. This would come in handy if, say, more moderators joined the team down the road since they'd right away be aware of previous discussions with a user.
Comment: @FrançoisG.Dorais: thank you for the information/confirmation. Incidentally, to celebrate the upgrade, I finally added an email address in my profile (I assume visible to moderators, if not it'd be a bit unclear where to put it). So I take it I can now behave worse than before. ;-)
Comment: @quid, we noticed... >:)
Comment: We always wrote to whatever address was supplied, if any. The issue is mostly with users who do not supply contact info of any kind, or users who supply invalid contact info.
Comment: @FrançoisG.Dorais: while I just got into some complicated exchange, I did mean this behaving worse as a pure joke. I hope this was clear. (I am now sort of unsure in categorizing your final comment. The emoticon being a bit confusing.)
Comment: @quid: Sorry. Honestly, I don't know how to use emoticons. This one was suggested by a younger friend after I asked how to type an humoristic "evil grin" as a response. I shouldn't have tried so hard...
Comment: @Will: sending us an email is still the best way to reach us.
Comment: @FrançoisG.Dorais: me neither, and I had nobody to ask and the info on the internet was a bit inconclusive, yes I found  'evil' but then maybe this is rather also 'angry'. Completely inadvertently it seems I almost fulfilled my joke. Sorry! I will write a bit less in the days to come.
Comment: Much like the First Men of the North, one of the sayings passed from father to son in the MO moderators society is "Our way is the old way".

Disappearing post to meta