This is an archive of past discussions with User:Crowsnest. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
Sure. Regarding non-dimensional and dimensionless: that is just the same and can stay as it is.
Regarding Abdul Ahad: he is not-notable, nor his constant. Peer-reviewed scientific articles (as required for such a scientific term) are lacking. Even if one or two existed, that still would not be enough since that would give this insignificant material an undue weight in the articles. Abdul Ahad himself being not notable enough for inclusion in WP, certainly is not a famous astronomer. -- Crowsnest (talk) 22:54, 22 February 2009 (UTC)
Dimensionless it is then :)
I don't buy that this guy is not notable for wikipedia; He's published for one thing, has had massive amounts of publicity in third party sources covering radio, TV and newspapers, has had his books reviewed in independent sources, etc. There are many, many people listed in thousands of articles strewn across Wikipedia that are redlinked on whom you may not get a single reliable source. So I struggle to understand why he is being singled out and attacked in this way. The Ahad's constant is a fundamental scientific phenomenon measuring the universe's background light flux [1] incident upon the earth - named after him - that's out across the internet. It is the constant of electromagnetic flux incident upon the earth when one excludes the solar constant. To refuse him a position here seems to me a pity considering his achievements as both an author and a budding astronomer. Constructive editor (talk) 23:09, 22 February 2009 (UTC)
Your ref to http://www.astroscience.org is just his own website, so a primary instead of a secondary source, see WP:PSTS. I would expect a renowned astronomer to have published several papers in peer-reviewed scientific articles. Also have a look at WP:ACADEMIC for notability requirements regarding scientists. Best regards, Crowsnest (talk) 23:17, 22 February 2009 (UTC)
With respect to Ahad's constant in Apparent magnitude: it is not a celestial object, as what is the subject of the list.
With respect to Scientific phenomena named after people: a significant amount of reliable secondary sources (peer-reviewed scientific articles) by others than Ahad himself should refer to Ahad's constant, before it is notable enough to be considered one of the "scientific phenomena named after people" in this list. This is not the case. -- Crowsnest (talk) 00:46, 23 February 2009 (UTC)
First thanks for tagging that bunch of articles for WikiProject Physics and its Fluid dynamics taskforce. Just a reminder to please give them class and importance ratings, it really helps our effort to keep track of the quality of articles in our projects. (I gave them ratings, if you disagree with them, simply change them).
Second, since you've tagged a bunch of fluids dynamics-related articles, I'll have to ask you if you happen to know anything about fluid dynamics? There's a big gap at the physics project when it comes to fluid-dynamics, most people seem to have a background in particle physics and QM. If you are, we'd all really appreciate it if you joined us and the Fluid dynamics taskforce (which is almost completely inactive due to lack of experts). If you know of other people interest in physics and fluid dynamics (in and out of wikipedia), could you let them know about the physics project and fluid dynamics taskforce?
Hello Headbomb! Thank you for assessing all these thousands of physics articles the last half year! In reply, using your numbering:
I will do that in the future. The reason, why I did not give them a rating, is that I created or heavily edited a significant portion of the articles I tagged. That made me reluctant.
Yes, I have a background in fluid dynamics. I will contact some more WP editors who know about the subject and see if they are willing to participate. If there is interest by some others as well, I am willing to help revive the fluid-dynamics task force.
No, I have not considered nominating them as good or featured articles. Although I see that such a review process has its strong merits, I do not think that is what I would like to do at Wikipedia. It would easily give me too much stress. -- Crowsnest (talk) 09:34, 23 February 2009 (UTC)
Fluid Dynamics Taskforce
Hi Crowsnest, thank you for inviting me to join the Fluid Dynamics Taskforce. I will be glad to join the task force and do whatever I can do to improve the fluid dynamics related articles. Salih(talk)16:42, 3 March 2009 (UTC)
No, I just did a simple Google Books and Google Scholar search, and had a look at some of the references that came up and seemed worthwhile. I have no further direct affinity with, or knowledge of, the subject (more with Hamiltonian mechanics, as far as Hamilton is concerned). Thanks for removing the garbage! -- Crowsnest (talk) 23:54, 4 March 2009 (UTC)
Thanks for the post submission editing as well as the pre...
I had trouble finding what {refbegin} and {refend} did. Is the only thing it does is change the size of the font? Zipity11 (talk) 11:24, 13 March 2009 (UTC)
Yes. It makes the same font size, in between the tags {{refbegin}} and {{refend}}, as used in the footnotes. If you do not like, you can just remove it. -- Crowsnest (talk) 11:28, 13 March 2009 (UTC)
New article
Hi Crowsnest...
Oh, the disadvantages of your being so helpful...here I come again with hand outstretched.
I have created a new article on a local garden. You can find it on my user's page 'Alternative Sandbox'. I think I did okay [said with a muted tone of exhuberent hubris in the voice].
I would appreciate anything that you can say about it.
Just that it is really beautiful (both the garden and the article). Seems a very well done article to me, ready for article mainspace. Best regards, Crowsnest (talk) 23:58, 19 March 2009 (UTC)
The article on Sally Mann has been rated a Start-Class, and the one on Bedrock Gardens a (gasp) Stub! While I can understand that BG's importance is low, I am unclear about the quality scale. It doesn't seem to me that the BG article "Provides very little meaningful content; may be little more than a dictionary definition", and the Mann article "Provides some meaningful content, but the majority of readers will need more."
What would have made these articles better? Was the documentation inadequate? Was there not enough material? More photographs? More analysis and less facts? Visa Versa?
Strange. Personally (I have made some assessments), I would qualify them as B (or at worst C). As far as I can see, the B criteria are fullfilled, see WP:QUALITY.
Another possibility is to ask for a peer review, say first for the Sally Mann article. Then you can see what experienced editors think of it, and they may have valuable advice on possible improvements. Further I changed the tags to B-class. -- Crowsnest (talk) 07:57, 24 March 2009 (UTC)
Yes, because there were no indications of notability. I searched the web (e.g. this news search), but did not find reliable sources to back up his notability. However, the company is notable (I added a reference to the article), so the administrator (Bettia) who handled the speedy deletion request turned the page into a redirect to "Bevolo Gas and Electric Lights".
P.S. The custom is to add new sections to the bottom of the talk page. This is done automatically for you, if you click the "new section" tab, which is visible on the top of talk pages (not on articles).
P.P.S. If you create a new article, it is handier to use "copy and paste" instead of the move of your user page. This move changed your user page, as well as your talk page, into a redirect. That made the messages I — well actually the tool I used when proposing the speedy delete — left on your talk page invisible until I removed the redirect. You can create a new article in article space by typing the desired page name in the search box at the left and pressing the Go button. If it not already exists, a search page pops up containing a red link "Create the page", which you can press to create the page (surprisingly). And just copy your text there.
I have a question. What's the difference between a reference and an external link, and how can you decide a link is one or the other? Thanks. Jackroven (talk) 21:07, 24 March 2009 (UTC)
Hello Jackroven. The references (and notes) are to support the material presented in the article (the reliable sources and additional sources). They can be anything: newspaper articles, books, scientific papers, etc. Not necessarily available online, but verifiable. While the external links are specifically links to web sites, for further reading. There is more on this in the Manual of Style: MOS:APPENDIX. Regards, Crowsnest (talk) 23:15, 24 March 2009 (UTC)
Many thanks for the improvements you have made to several of the articles that I have written. I was wondering, where or how did you find the references to the original introduction of the Orr--Sommerfeld equation by Messers Orr and Sommerfeld? Are they available anywhere? The Royal Irish Acadamy only has recent copies of their proceedings online.
You can get them through a university library service. I found them in the standard textbooks on hydrodynamic stability, e.g. Drazin & Reid (1981) "Hydrodynamic stability" and Lin (1966) "The theory of hydrodynamic stability". -- Crowsnest (talk) 22:53, 24 March 2009 (UTC)
Momentum - lift relationship
Is this correct, for potential flow theory? :
Sectional Lift = - dPy/dt
where P is the limit of the total momentum (double integral of momentum over the region) enclosed by a circular region with some part of the wing at its center, as the radius of the circle goes to infinity.
If so, then I understand what the articles mean when they refer to the change in vertical momentum of "the air" associated with lift.
Basically, "the air" would mean "all the air". The use of the limit would make the derivative into a finite quantity, even though the total momentum of the air is infinite. Mark.camp (talk) 20:49, 17 March 2009 (UTC)
The problem is, that the momentum change as you depict it: the rate of change of the vertical momentum in a fixed region R, in a frame of reference moving with the wing, is zero! The vertical momentum in the region is:
Since in this reference frame ρ and vy are time-independent, while also the region R is time-independent, the result is that Py is time independent: dPy/dt=0. The problem is due to the fact, that the boundaries of the region are not closed: vertical momentum can be transported through the boundary of the region. In front of the wing (the side where the air is coming from, in this reference frame) this is not a problem, since there vy is zero (assuming that the x-axis corresponds with the incoming flow direction). But at the back, the outflow side, the wing has induced a downwash (downward directed vy). And this vertical momentum ρvy is transported out of region R with velocity vn (which is the velocity component normal to the boundary ∂R of R). So there is a flux of vertical momentum out of the region R, with boundary ∂R, equal to
which is balanced by the lift. The Landau & Lifshitz reference in lift (force) does this, relating the lift to the flux of vertical momentum through a vertical boundary behind the wing (then vn=vx. This all has to do with the difference between Lagrangian and Eulerian coordinate systems in fluid dynamics. The form of Newton's 2nd law you depict is valid in a Lagrangian frame of reference (with a region Ř(t) and its boundaries moving with the flow). While in the Eulerian frame of reference (a fixed region w.r.t. the wing) the approach is as sketched above. See also Reynolds transport theorem. I hope this does not confuse you even more. -- Crowsnest (talk) 23:55, 18 March 2009 (UTC)
Thanks much. Yes, it's obvious now to me that in this frame, the momentum in any finite region doesn't change wrt time. I will study the rest of your note and then see if I can understand it. Mark.camp (talk) 02:13, 20 March 2009 (UTC)
I realize that I didn't describe the momentum I was thinking of clearly. I refer to the limit of the momentum Pyn in a body of air which at time t0 is enclosed by a region Rn, where R1,2,...n is an infinite series of successively larger regions. The boundary of this body changes in time, regardless of choice of Lagrangian or Eulerian frame. I think that this dPy/dt might be non-zero, and identical in either frame.
Yes, it is the vertical component of momentum of this "body of air", moving with the flow, that is increasing. And then it does not matter whether you talk about and Eulerian or Lagrangian frame of reference. Or whether the air is flowing around the airfoil, or the airfoil flying through air at rest (far from the airplane). This body of air has to be large (many chord lengths in diameter, say five or more), for the effects of the airfoil on the boundary to be small enough to be negligible (from a practical point of view; a case which not satisfies this is the ground effect where the boundary influences the kinematics and forces). -- Crowsnest (talk) 11:21, 28 March 2009 (UTC)
This is a great help, thanks. My next difficulty is this: how does one link the momentum of this body of air to it's interaction with the wing?
I find it difficult enough when considering just the differential volumes which are actually exerting a force on the wing, that is, those which are in contact with the wing. The wing is transferring vertical momentum to these parcels on two levels--macroscopic (dependent on the change in momentum of the parcel as a whole) and microscopic (dependent on the static pressure, and occurring even when the wing is at rest--irrelevant at rest when all static pressures are the same, but not with the wing in motion).
Not only that, but the vertical momentum change of a parcel in contact with the wing is NOT due only to the force of the wing, which is only one contributor to that momentum change. The parcels above, aft, and ahead are also involved.
But more perplexing is this. How does one relate the change in momentum of a parcel 5 chords above and 3 chords in front of the wing to the wing itself? There is no direct interaction with the wing, and yet it is contributing the momentum of the body of air which is determining the lift on the wing.
Information, including momentum and pressure, is transferred from one parcel to its neighbours with the speed of sound (like Newton's cradle, but more complex ). At low Mach numbers, there is plenty of time for an exchange of momentum with parcels several chord lengths away from the wing. In the mathematical model of this, incompressible potential flow satisfying Laplace's equation, the speed of sound is even infinite (due to the incompressibility) and information on a flow change is available everywhere instantaneously (so this is mathematics, not real physics; although often giving reasonable estimates on lift).-- Crowsnest (talk) 22:23, 28 March 2009 (UTC)
I didn't express my questions well. They have nothing to do with ability of information to flow within a certain amount of time to the wing. In fact, they apply to potential flow theory, where density variations and transmission of energy and pressure changes by sound are ignored.
Part of my problem is that the body of air in question is not isolated. It is subject to pressure not only from the wing, but by the air outside the boundary of the body. Therefore, Newton's law for the force between it and the wing doesn't apply, at least not directly.
(not so random un-indent)
Perhaps easiest is to imagine an airfoil propagating through a large "body of air" which is initially at rest. Once the airfoil is well inside this body of air (by several chord lengths, say 5 or more), the rate of vertical momentum change of this body of air is equal to the lift. Or more precise: the reaction force of the wing on the air (minus the lift force). At the edges of this body of air, far from the airfoil, nothing is happening.
Small air parcels are subject to three laws:
mass conservation: the mass of a parcel is constant. Its position, volume and shape may change.
Newton's laws: the 2nd law states that the rate of change of momentum is equal to the net force on the parcel. The 3rd law states that the force by one parcel on its neighbour is equal to minus the force by that neighbour on that particular parcel.
A force model: if incompressible flow is assumed, the pressure distribution at the edge of the parcel is such that its volume does not change (but its position and shape may change). In case of a compressible fluid, pressure and volume are related through some thermodynamic equation of state (since the parcel mass is constant, a volume change implies a density change) .
These three act together. In general the influence of the airfoil diminished with the distance from it, since the effect of the displaced volume by the moving airfoil is largest in its neighbourhood. Hope this gives some clues to pinpoint where the crux of your problem is. -- Crowsnest (talk) 21:57, 29 March 2009 (UTC)
This seems to be exactly the well-defined scenario I've been looking for. Thanks much.
As a start, I am picturing this mass as square of side n, n>>chord, with vertical sides. I'm beginning not quite as you recommended, (with vertical momentum of the body very near its steady state) but rather with the wing approaching the right boundary. I think that the derivative of total vertical momentum of the large mass starts at zero and gradually goes positive (upwash) , and then at some point after wing has entered the mass (maybe halfway) goes negative, and then asymptotically reaches a final negative value after the wing has passed. Before I think any further, is this much correct?
Yes, that is correct, as far as I can see. Note that the initial straight boundary of the "body of air" deforms as the wing approaches and passes (a phenomenon associated with the so-called "Darwin drift", no WP article on it yet, and related to Stokes drift in water waves; with interesting dynamical consequences; see also here or File:Karman trefftz.gif). -- Crowsnest (talk) 22:36, 31 March 2009 (UTC)
I use Matlab for the computations, as well as generating and writing the individual images in the animation. Subsequently, I transform the individual images to GIF-format (and often reduce them in size: I get better quality this way than by letting Matlab producing them at the desired final size). Finally I use gifsicle to glue the images together to an animated GIF. Both in Matlab, as well as for the other stages, I write scripts to accomplish the desired manipulations. I hope this is the answer to your question . Best regards, Crowsnest (talk) 09:39, 28 March 2009 (UTC)
It does, thanks. Your images are great work, they really add the articles. I'll have to try making a few myself. --Odie5533 (talk) 11:05, 28 March 2009 (UTC)
Hi Crowsnest. The opening sentence of Lift (force) begins In the context of … Use of the word context appears to be rare in Wikipedia. (I am not actually aware of any other article that uses the word in this way.) It is not a word in common useage so I am concerned that young readers, and readers who are new to the English language, may be deterred from proceeding further because they are unfamiliar with the meaning of context.
In Wikipedia, it is much more common for an article to begin by specifying the field or subject in which the article is relevant. That is why my proposed text on my sandbox begins In aeronautics and fluid dynamics … …
I am keen to repair the opening sentence to eliminate the word context. What do you think of the following?
In aeronautics and fluid dynamics the lift force is the component of the aerodynamic force that is perpendicular to the oncoming flow direction.
I can't thank you enough for helping me out with the equations in this article. They look absolutely beautiful !!!!!! -- logger9 (talk) 05:53, 13 April 2009 (UTC)
Hi, I had a few thoughts about the air parcel article you deleted/merged recently. I wrote it obviously, and I don't really care if you remove it. The thing is, I think it's valid to have a separate article on air parcels specifically as used in meteorology. I don't know what your background discipline is, but I come from an atmospheric science background, and we often use the notion of air parcels in introductory texts. I taught an undergraduate class in atmospheric science recently, and when we were discussing convective cloud development in an act of shameless self-promotion I pulled up my article on air parcels, which I found to fit well with the material even though I had written it several years ago. In summary, you can edit it all you want, but for the field of meteorology, I think it should be separate, and it should mention how meteorologists usually view convective clouds as air parcels. Your fluid dynamics article is great, but please consider putting a separate article back for meteorology. Darrenvc (talk) 06:21, 15 April 2009 (UTC)
Hello Darrenvc. I removed it because I could not find references for this use of the concept "air parcel": verifiability is essential to Wikipedia. If you have reliable secondary sources — which should be peer-reviewed articles or reliable science books in case of science subjects — in support of your material, please feel free to re-insert it into the article, or elsewhere. The proof is with the editor who is inserting material. Good luck and best regards, Crowsnest (talk) 11:21, 15 April 2009 (UTC).
On April 25, 2009, Did you know? was updated with a fact from the article Cnoidal wave, which you created or substantially expanded. If you know of another interesting fact from a recently created article, then please suggest it on the Did you know? talk page.
Hi Woz2. MOS:LAYOUT talks about the possible section headings: Notes, Footnotes, or References (Notes and references, or References and notes, is also often used). And it was References, containing two subsections (the MOS isn't talking about that). So for article stability there is no reason to change that.
But my main problem was that the inline citations are real references, e.g. to the original papers by Kramers and Kronig, and putting them in a separate section Notes creates a distinction with the other references which I thought a bit artificial. Now they are all under the same heading References.
But it is not a matter of life and death to me, so if you think your way the better, please undo my reversal. Best regards, Crowsnest (talk) 15:07, 14 May 2009 (UTC)
The image here seems to imply that inline and general refs should be under their own separate sections (not subsections). I haven't seen any other article laid out the way this one is presently. Anyone else have an opinion? Woz2 (talk) 16:18, 14 May 2009 (UTC)
Just clicking a few of the featured articles in physics gave me e.g. Europa (moon).
If not stated otherwise in the MOS, it is permitted, and then it should not be altered unless there are strong reasons to do so (which I have not heard yet). The picture above appears to be an illustrative example: the text of WP:Layout and WP:CITE clearly states this section or group of sections may go under different names. -- Crowsnest (talk) 04:35, 15 May 2009 (UTC)
I saw some recent mergings of Yaw Axis, etc. made by User:Juansempere and I think it's created a lot of error. I'd like to just revert the lot of it. I'm bold, but not bold enough to do such a thing without concurrence from "bigger heads" (you guys and others you think should be consulted). I also don't know if I know how to do it properly anyway. I made a few edits myself before I realized how much chaos and error had been created, those edits should be reverted too of course. Could you guys take a look at it and see if you agree that it should just all be reverted? (With kindness toward User:Juansempere of course.)
I already undid my edits to Aircraft principal axes to get the ball rolling (and also because I don't want to be associated with this article and the long slow slog up the hill to correctness it would need). --Gummer85 (talk) 05:43, 19 May 2009 (UTC)
I am afraid I am cannot be of much help here. I do not know about the conventions used with respect to these axes. One expects these to be able to find them in text books on the subject. -- Crowsnest (talk) 11:24, 19 May 2009 (UTC)
Laplace operator
Hi Crowsnest, you has a query about the delta sign being used as laplace operator. To be honest, I never saw that operator in any of my uni subjects, neither in my maths degree, nor in my mechanical engineering degree. The unambiguity of the grad² operator is great, it can only mean one thing. On the other hand, the Delta has meaning in differential calculus to do with non-infinitesimal (finite) differences. So it might happen that some people use Delta but I feel that grad² should be preferred in most places. Jdpipe (talk) 12:22, 1 June 2009 (UTC)
Hello Jdpipe. Sure it is your good right to use ∇2, given your background. Which is apparently different from mine, being used to Δ as the Laplace operator. But, as indicated in Laplace operator, both notations are used, just as is used for the D'Alembert operator, By the way, formally also ∇2 is not an unambiguous notation, since it can also imply a tensor product instead of the inner product As already said on your talk page, I have no problems with this, if you do it as carefully as you did on potential flow, also referring to the other notation. Best regards, Crowsnest (talk) 12:53, 1 June 2009 (UTC)
Question about the Ursell number
hello Crowsnest
I need to include something about Ursell's number in my thesis corrections: in particular the limit for which lineaer wave theroy applies. In the wikpedia page it's down as 3 / (32 π2). I went back to the reference [ref 1]
and it seems to come from ka << (kh) 3, which gives the linearity limit of 8 π2.
Could you tell me if I have got this right? This is my first time inside Wikipedia so please excuse me if I'm not adhering to any of the rules!
Hi Crowsnest. The reason I changed the article on "group velocity" is because I disagree with the fact that it speaks about "the group velocity of a wave". The group velocity is defined for pulses (a wave's envelope) and a wave's velocity can be defined in many ways (phase and group velocities).
Furthermore, if the wave propagates throughout a non-linear dispersive material, there is no such thing as the "group velocity of a wave" because the pulses are distorted. This is clearly stated in the "Note" in the "Definition" section and I found it contradictory with the first paragraph of the article.
The current definition (in the Wikipedia article) is in agreement with the traditional definition of "group velocity" but recent discoveries (see "The speed of information in a 'fast light' optical medium", Nature 425, 665 (2003)) encourage to realize that group velocity only makes sense when defined for modulated pulses. Avalcarce (talk) 14:46, 31 July 2009 (UTC) —Preceding unsigned comment added by 194.80.219.17 (talk) 12:47, 30 July 2009 (UTC)
Hi Avalcarce. "The group velocity of a wave" is indeed imprecise. For slowly-modulated waves (i.e. narrow-band carrier waves) however, there are ways to define the group velocity as a local property everywhere – provided the local wave amplitude is non-zero – also for non-linear waves, see e.g. the article by Hayes (1973) Proc.R.Soc.Lond.A 332:199–221, or the book by Whitham (1974) Linear and nonlinear waves. For linear media, the group velocity can be defined for each Fourier component, which can for instance be used to describe the evolution of power spectra for waves propagating in mildly-inhomogeneous media (example: wind wave model). In this respect I also disagree with the 'Note' in the 'Definition' section: group velocity is also a valuable concept for other signals than pulses, provided they are localised in frequency space (and not necessarily in real space). So also for instance for a beat signal, as in the animation.
Apart from solitons (and some special periodic envelope shapes of constant form) and in non-dispersive media, pulses never travel with undistorted envelope. Where it should be remarked that e.g. the soliton for the (focussing) nonlinear Schrödinger equation are pulses in a non-linear medium.
Further I did not read the Nature article you mentioned, but I assume that near the wave front in a 'fast light' medium the assumption of slow modulation is no longer valid. -- Crowsnest (talk) 22:36, 3 August 2009 (UTC)
An editor has nominated one or more articles which you have created or worked on, for deletion. The nominated article is Ronnie Nelson. We appreciate your contributions, but the nominator doesn't believe that the article satisfies Wikipedia's criteria for inclusion and has explained why in his/her nomination (see also Wikipedia:Notability and "What Wikipedia is not").
Your opinions on whether the article meets inclusion criteria and what should be done with the article are welcome; please participate in the discussion(s) by adding your comments to Wikipedia:Articles for deletion/Ronnie Nelson. Please be sure to sign your comments with four tildes (~~~~).
You may also edit the article during the discussion to improve it but should not remove the articles for deletion template from the top of the article; such removal will not end the deletion debate.
Please note: This is an automatic notification by a bot. I have nothing to do with this article or the deletion nomination, and can't do anything about it. --Erwin85Bot (talk) 01:13, 3 February 2010 (UTC)
Spamming links
Hello,
I saw nanohub links already present on other wikipedia topic pages before I added. Nanohub has many good resources that Wikipedia can benefit from. Further more it is a non commercial web site.
There seems a fine line between advertisement and adding external resource links in my opinion.
Pls let me know your thoughts.
Hello Beatnik8983, see also my question on your talk page. I was triggered into this because the nanohub.org addition to WKB approximation was of rather poor quality, to my personal opinion. I saw a "recipe" to the WKB approach without a thorough motivation and derivation, as in the "Modern references" section, e.g. Ravazy. Thereafter I observed your systematic approach to adding nanohub.org links to articles, which is in general an undesirable practice on Wikipedia, see e.g. WP:SPAMLINKS (independent of nanohub.org being a non-commercial site and having many good resources). I stopped removing the links, because I became curious into your motivation. Best regards, Crowsnest (talk) 22:25, 19 May 2010 (UTC)
Nanohub links
Hello,
I am developer of some free to use online tools at nanohub. It has lot of good tutorials and resources contributed by
reputed researchers/professors in the area of nanoelectronics.
It seemed a good idea for me to link to some wikipedia topics . I don't intend to add nanohub links indefinitely,
rather I am stopping now.
Nanohub.org is a non commercial website (funded by NSF) which offers free to use simulation tools/resources.
Hello Beatnik8983, thank you very much for your answer. I wholeheartedly am positive towards the idea behind nanohub, but I think that the motivation for adding links to nanohub on an article should be driven from the question whether this particular link really adds something to the article at hand.
I will also stop removing the links you provided, and leave it to others whether they find them useful or not (since I am not an expert on many of these subjects). Thanks again, and I hope I did not discourage you to contribute to Wikipedia in the future. Best regards, Crowsnest (talk) 22:36, 19 May 2010 (UTC)
Nanohub links
Hello,
Let me relook at the resources I added. I will try to check for relevance before
adding. I agree with you for WKB may be the nanohub resource is not that apt.
Hello Beatnik8983, with regard to the addition of nanohub resources: as you may have noticed in WP:Conflict of interest, this may be a bit delicate in your case (with respect to additions directly linking to nanohub, or on the Nanohub article). The procedure you use on Talk:Schrödinger equation is fine.
Further, you can sign your posts on talk pages with four tildes: ~~~~; which will be replaced by your signature and a time stamp. More on the use of discussion pages can be found on WP:TALK. Best regards, Crowsnest (talk) 23:13, 19 May 2010 (UTC)
Esso Languedoc v. rouge wave
Hi,
You undid my addition to the page on rouge waves.
I saw a report from PBS about these waves, and it included the story of the Esso Languedoc. I wanted to confirm the story and searched Wikipedia, only to find no info. So I searched a bit more, and added the info, in a proper format, and included references that showed the existence of the ship and cited the event, including photos.
You removed all of that because you didn't like the references.
Why didn't you remove the references and leave the added information with a 'needs reference' note? A little googling would have shown you that not only was my addition in good faith, but that it was as accurate as can be expected for an event from 30 years ago of an unconfirmed deep ocean phenomenon. I don't see how removing information from an encyclopedia can be viewed as a 'contribution' when it deletes info that the public might use. Nor can deleted information be updated by someone who is more knowledgeable - like, for example, someone who knows the French Wikipedia page for the Esso Languedoc, or a French language media report about the first mate.
I have wasted another hour of my time trying to find a reliable source - I hope PBS (See the Crow's Nest, http://www.pbs.org/wnet/savageseas/neptune-main.html), the BBC, and the ESA are OK by you - and trying to get the reference to work appropriately.
I am not a pro at this, I just saw a missing piece of information that people might want to know about. If I don't measure up to your standards of wave knowledge and editing accumen, why don't you do it better yourself, instead of just obliterating it?
BTW: one of the other examples in that section was of a 30 meter lighthouse being washed over by a 48m wave ... how do you suppose that was measured? Well, we can't know because that reference is only accessible by subscription to a commercial site.
Incidentally, your blanket undo also removed a few things I edited to improve other people's shoddy updates.
thank you so much for your contributions ! I am particularly fascinated by the File:Karman_trefftz.gif simulation. Could you please tell us what software you used to produce such an animation? I would love to experiment further with it.
I don't think this image is replaceable, because :
1 - The work of Charles W Bartlett is absolutely not elevant in terms of surf art depiction. He's not featured on any major surf art website, nor his work inspiring actual surf artists. He is not considered as a surf artist at all, this painting is only showing people surfing and therefore is relevant, but in a surf history article. And even if it was, you can't replace an oil painting with a woodcut. This painting is also used in other pages, such as surf culture, and wind wave.
2 - The picture is in sufficiently low resolution (622p)
Hi! I undid your most recent edit to Shear stress, as it introduced an unnecessary comma, and made that equation different from the earlier ones. I also don't believe the edits made by User:202.185.32.6 were actually vandalism, though they weren't helpful (and also broke the parallel structure of the equation layout). Argyriou(talk)15:45, 13 October 2010 (UTC)
Hi, I saw the link on your main page to a BibTex to Wikitext conveter, which looks very handy. However, the link appears to be broken (http://en.norro.de/Wikipedia/BibTeX2Wp/). I was wondering if you know of a working link to it? I couldn't find anything equivalent on Google. Thanks! --Charlesreid1 (talk) 04:57, 6 November 2010 (UTC)
Hi Charlesreid1, yes, that was a very handy tool. Unfortunately it is broken for a year or so, and I have not found a replacement yet. If you stumble upon one, please let me know . Best regards, Crowsnest (talk) 05:03, 6 November 2010 (UTC)
Glad you liked the reshuffle- one of many. I hate it when there's just a mass of words on the screen. A few sub-headings makes a lot of difference to the readability of an article. Even the folk that wrote the Bible had cottoned on to that.
Plucas58 (talk) 19:21, 14 December 2010 (UTC)
Hello Crowsnest! In Airfoil#Introduction, at the end of the fourth paragraph, is the following sentence: For intermediate Reynolds numbers already before maximum thickness boundary layer separation occurs for a circular shape, thus the curvature is reduced going from front to back and the typical wing shape is retrieved.
The quality and meaning of this sentence have been challenged. See Talk:Airfoil#Translation required. Are you able to re-word this sentence so that it is more meaningful? Alternatively, are you able to explain the likely meaning behind the sentence so that others can have a go at re-wording it? If we can’t improve it in the short term the sentence should be removed.
No offence taken. It's all O.K., since I don't generaly welcome band or blocked users. Thanks for letting me know he was banned. Good luck.--Wipsenade (talk) 11:09, 11 January 2011 (UTC)
Welcome
Welcome!
Hello, Crowsnest, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are some pages that you might find helpful:
I hope you enjoy editing here and being a Wikipedian! Please sign your messages on discussion pages using four tildes (~~~~); this will automatically insert your username and the date. If you need help, check out Wikipedia:Questions, ask me on my talk page, or ask your question on this page and then place {{help me}} before the question. Again, welcome! --Wipsenade (talk) 11:09, 11 January 2011 (UTC)
May I ask where you looked to find ISBN's for Youvan's ebooks? Did you find the math book's ISBN to be missing, too? In the USA, ISBN's originate from Browker. It is possible they take some time to propogate. OoZeus (talk) 23:41, 26 January 2011 (UTC)
http://www.bookwire.com is the first to have Browker-purchased ISBN numbers in the USA, and both Youvan's e-books are there. I was mistaken too, because I initially looked at the US Library of Congress. So, rather humorously, may I suggest that errors in a mathematics e-book are far more harmful than "errors" in a metaphysics book - if that is even possible to do. So, if you would please put the metaphysics book back up, we might be able to move onto something more constructive. Alternatively, we could collaborate on setting standards for all references to e-books from wikipedia biographies via external links. I doubt that will go over very big with the commmunity because it is very time consuming and it will be argued that no two cases are the same. If you are steadfast in your position, my response would be to wait until other references are made to the ebook. I am not willing or able to argue with you as a new editor. OoZeus (talk) 20:09, 27 January 2011 (UTC)
Both books have not been reviewed in reliable sources; whether they have an isbn-number or not is not so important. However, the math book is at least once referenced in a scientific paper [2], which is why I did not delete it form the external links. I do question however if one reference to a book makes it notable in the WP sense. Further, discussions on the in- or exclusion of material should go on Talk:Douglas Youvan. -- Crowsnest (talk) 08:55, 28 January 2011 (UTC)
This may seem to be an esoteric point, but in my view the merge of Foil (Fluid Mechanics) and Airfoil shouldnt have taken place. Specifically, there are foils operating in fluids that do not conform at all to the model of a "hydrofoil" as the term is commonly used and as represented on the page of the same name. Surfboard fins are one, but I would argue that their natural analogue (and original model), the fins of sea animals and mammals are *certainly* also "hydrofoils," according to the lifting physics of their operation. Surfboard fins of certain design and configuration most definitely are. In the vast majority of cases, they are not designed to lift the hull clear of the water surface in any way, in fact the opposite is true, and they work much the same way as wings do in applying lift to the water surface and near-surface, albeit with very different effects on the hull theyre attached to (than wings). They are a unique type of foil, a merge of air- and hydro- foil, and the existence of this (and animal fins) necessitates a fluid foil page. As to "verifiability," the content and edits to a restored page on Foil (Fluid Mechanics) should be as verifiable as possible with regard to the most well-understood general characteristics of foils seen operating in all media. The air-, hydro-, and fin areas should be represented, as well as, I would argue, the spoilers of cars and race cars and other applications I am sure I'm forgetting or not aware of. The problem of coherence is simply one that Wikipedia works through with constant flux. The best it can be is the best it can be. Please consider restoring this page to cover the overarching thing and let the fluid understanding process. — Preceding unsigned comment added by 99.88.232.255 (talk) 15:15, 5 June 2011 (UTC) EDIT: I would add that keels are shaped to effectively deflect fluid and provide lift too (from "Sailboat keels" : In sailboats, keels use the forward motion of the boat to generate lift to counteract the leeward force of the wind. The rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion." These are obviously doing the work of LIFT: deflecting flow, in this case water, and yet are obviously not "hydrofoils," as given on the page of that name, nor "airfoils," as per that page. The broader page on the subject "Foils (Fluid Mechanics)" should be restored. — Preceding unsigned comment added by 99.88.232.255 (talk) 22:20, 5 June 2011 (UTC) I would also add Propellors to the list of foils acting underwater without lifting a hull clear of the surface as represented on the "hydro" foil page. http://en.wiki.x.io/wiki/Propeller. Why this didnt occur to me before as a clear example of a hydrofoil I dont know. The US Navy has used the term "hydrofoil" for submerged foiled control surfaces here: http://www.navysbir.com/n09_2/N092-143.htm . And consider the laughable confusion of terms here: http://www.docstoc.com/docs/68702716/CONTROL-SURFACE-AND-ACTUATOR-DESIGN-FOR-A-LOW-DRAG--LAMINAR-FLOW-AUV . Clearly the "Hydrofoil" page is totally incomplete, at a minimum. EDIT: After studying the pages on Aerodynamics (ref: "Aerodynamics is a branch of dynamics concerned with studying the motion of AIR" - emphasis added to highlight the relatively uniform viscosity of the subject medium vs the highly variable viscosity of ALL fluids, plasma, gases, liquids, air, etc), vs Fluid Dynamics, and Fluid Mechanics, it is impossible to not feel, yes, aggrieved that the subject of Foils (Fluid Mechanics) was evaporated willy-nilly into "AIRfoil."
99.101.212.165 (talk) 04:08, 9 June 2011 (UTC)
Hello, the discussion on the content of Wikipedia articles takes place on the talk page of the concerning article. In this case that is on Talk:Airfoil, so that other editors can give their opinion, in order to reach consensus. It would be best if you bring up your concerns there, in a new section. If you wish so, I can copy this section to Talk:Airfoil. I myself am working on other subjects at the moment. Best regards, Crowsnest (talk) 10:49, 9 June 2011 (UTC)
Please do copy this to Airfoils Talk. My apologies. The Foils page I'm referring to above is a matter of passionate interest to me (everybody's got something) but you won't see me elsewhere most likely--but I won't rest until the Foils (Fluid Mechanics) page is restored. Merging it with Airfoils was a huge mistake for all the above-cited reasons. — Preceding unsigned comment added by 206.16.109.32 (talk) 15:35, 9 June 2011 (UTC)
rename/merge accounts?
Hi! Thank you for welcoming me.
Actually I am quite an old contributor in French (contrib:Cgay).
In English, I never managed to have the same login as in French. Don't know why.
So I have done a few edits under Cypgay for several years contrib:Cypgay.
The other day, I couldn't get my password again: the new one I requested was probably sent to an old email address. Maybe I could send privately to an administrator my previous email addresses so that they can check that Cypgay is recorded with one of them? But maybe that wouldn't help.
Anyway, because of that I created the present account the other day and made a few edits contrib:Cygay.
So I have a request, in case you can help me. I see that Cgay is not used in English (no contribs and no UserPage). However, I can neither (i) create this login or (ii) connect to it using my French password. Ideally, I would like the two accounts to be merged and renamed to Cgay so I have a unified account that includes English. Anyhow, I'd like to know what I can do. Any ideas? Thanks!
-- Cygay (talk) 17:56, 15 November 2011 (UTC)
how does improving the understanding of a subject matter within the community of contributors do anything less than improve the concerning articles? — Preceding unsigned comment added by 203.79.68.185 (talk) 22:44, 16 November 2011 (UTC)
Blank lines around formula
In several of your recent edits you have added blank lines before and after LaTeX formulas citing WP:MOSMATH, e.g. this diff. I can't find where this is mentioned and if it is I'd disagree with it since it makes it difficult to identify paragraphs while editing. If it is mentioned and I just can't find it then please point it out, otherwise please stop since making large numbers of trivial changes can be disruptive.--RDBury (talk) 23:30, 21 November 2011 (UTC)
I didn't see you were fixing other problems as well; the additional lines made it hard to see what the other changes were. Apologies for the confusion.--RDBury (talk) 07:25, 23 November 2011 (UTC)
I see you have removed both Dexawave and Wavestar energymachines.
I really dont see why you have to do this, both projects are one of the leaders in this area.
These are the ones which troubles you because they are made by themself right ?
Arpedk, just take a look on it :)
Just wondering why you didnt remove "wavedragon" also, there is not even an link for that one. I can tell that the things
they say about the machine is correct but not in progress anymore. Its resting in Hanstholm harbour. — Preceding unsigned comment added by Arpedk (talk • contribs) 18:51, 29 December 2011 (UTC)
Hello Arpedk, information on Wikipedia should be verifiable an be based -- among others -- on reliable secondary sources, see WP:RS, WP:PSTS and WP:V. (At least) three of the four sources you give above are primary sources, and not usable to establish verifiability and notability. The burden of proof for providing these sources lies primarily with the person adding material to an article, see WP:BURDEN. Note that since Wikipedia is an encyclopedia, it also contains information on projects which are no longer being used (but have been notable in the past, see WP:N). Best regards, Crowsnest (talk) 14:07, 30 December 2011 (UTC)
I see, within a few months these projects should be public known in the whole world. It's just a matter of time :-)
At the moment, articles are only on danish. comment added by Arpedk (talk • contribs) 13:45, 31 December 2011 (UTC)
Did you remove the external link I inserted because it hooks to Amazon? (I am trying to learn the rules here, really!) I've been on the Special Page for ISBN look up, here. There are commercial sources for Yahoo and Google sales, but they must be manually clicked. I don't understand how we are suppose to get readers of Wikipedia to the source material if such links are not allowed. Can you explain this to me? For example, what would we do with a link that goes to Science magazine, and then run into a pay-per-view of that referenced article? That frequently happens on PubMed, and I don't know about Wikipedia.
Is the reference for an external link on Youvan now correct? I did not hyperlink the title to Amazon after you removed the entire reference, but I did link the ISBN to something. His book's ISBN is from Browker (I checked), and I have no idea how it gets from there to our Special Page with look ups. Should we suggest an addition of Browker and Amazon to that page where it already has links to Yahoo Shopping and Google Market Place?
Is this a topic that could be used as a Wikipedia fund-raising idea, or is it considered "dirty" to have any link that directs a reader to a money-charging site? I'm thinking in terms of a "lunch card", prepaid by readers, that would generate income for Wikipedia if one wants commercial links to function. It would be the reader, not the editor, that would make the decision to pay to click and take 10 cents off their card.
I do not want to inherit any of the problems between you and our favorite Creationist. (I'm Catholic.) You have seen that I have a temper after getting frustrated and having work removed. I am sorry about that, and it won't happen again. Noncanonical (talk) 17:51, 4 January 2012 (UTC)
Hello Noncanonical, I removed the link because it does not relate to where Doug Youvan is renowned for. These books are not reviewed in any reliable secondary source. My intent is to improve the quality of WikiPedia articles, and I have no problems with Douglas Youvan (or his beliefs and opinions). Best regards, Crowsnest (talk) 22:42, 4 January 2012 (UTC)
Wave Power - mod tech....why continued deletion?
Crowsnest,
I note that you have deleted the AquaGen Technologies entry twice - why are you doing this? Please re-post this entry or explain why it is being deleted.
Hello Chrisa72, additions to Wikipedia are required to be backed up by reliable sources, see WP:RS and WP:PSTS. The burden of proof for inclusion lies with the authors adding the material, not with the one who removes it, see WP:BURDEN. So if you can find enough reliable sources, and it is notable enough, you can add the material again. Happy editing, Crowsnest (talk) 10:58, 5 January 2012 (UTC)
Notice of discussion at the Administrators' Noticeboard
Hi. In your recent article edits, you've added some links pointing to disambiguation pages. Such links are almost always unintended, since a disambiguation page is merely a list of "Did you mean..." article titles. Read the FAQ • Join us at the DPL WikiProject.
Hi. In your recent article edits, you've added some links pointing to disambiguation pages. Such links are almost always unintended, since a disambiguation page is merely a list of "Did you mean..." article titles. Read the FAQ • Join us at the DPL WikiProject.
Hi. When you recently edited Wave flume, you added links pointing to the disambiguation pages Vector and Breakwater (check to confirm | fix with Dab solver). Such links are almost always unintended, since a disambiguation page is merely a list of "Did you mean..." article titles. Read the FAQ • Join us at the DPL WikiProject.
Hi. In your recent article edits, you've added some links pointing to disambiguation pages. Such links are almost always unintended, since a disambiguation page is merely a list of "Did you mean..." article titles. Read the FAQ • Join us at the DPL WikiProject.
Hello Crowsnest. I am just letting you know that I declined the speedy deletion of Brian Penny, a page you tagged for speedy deletion, because of the following concern: The article makes a credible assertion of importance or significance, sufficient to pass A7. Thank you. Reaper Eternal (talk) 18:19, 2 March 2012 (UTC)
Hi Reaper Eternal, thanks for informing me. I will see whether I want to put it to AfD, since it is quite far from my field of interest here. -- Crowsnest (talk) 20:45, 2 March 2012 (UTC)
Hi Crowsnet, regarding the mentioned page I wonder if there is an error in the last equation. I think the equation is for 'xi', not for 'mu', i.e. it should be
Hi Mariostorti, I do not have time now, but I will check out later. Thanks for your concern and interest. Best regards, Crowsnest (talk) 18:01, 10 March 2012 (UTC)
Hey F=q(E+v^B), no apologies needed. You did what you thought was needed, nobody had objected against the merger and you were just bold. Furthermore, it makes clear that something is missing in these articles about their interrelation. So in that respect there still is work to do. At this moment, I do not have time, but if nothing happens I can give it a try in a month or so. Or somebody else perhaps has the inspiration and time to do something about it. Regards, Crowsnest (talk) 12:25, 23 April 2012 (UTC)
Hi LittleWink, yes, I changed the redirect, since compressibility is physical and incompressibility is a mental construct to ease finding approximate solutions for fluid flows. But I did not notice the hatnotes, and you fortunately did :-) I do not have time now, but I will look into it within 4 days. Regards, Crowsnest (talk) 13:07, 16 May 2012 (UTC)
Dispersion Relation (Mathematics)
Hi Crownsnest. I was wondering if you could tell me how the page on the dispersion relation in mathematics I wrote is the same as the the Dispersion relation in optics. I am new to this and am just wondering where they are the same for future reference. I've looked over the page and the two (at least to me) seem to be only very loosely (and I mean extremely loosely) related. Thanks. k3thomps—Preceding undated comment added 01:58, 22 May 2012 (UTC).
I'm no mathematician, but I was wondering the same thing. I had considered the redirect to dispersion relation, but it seemed that K3thomps' article was about a more purely mathematical concept than the physical concept defined in dispersion relation. It may well be that the mathematical concept describes the physical concept, but it appeared to be more broadly scoped than that. I'll admit that the original article was too brief, and written in an improper tone, but I think it could have been cleaned up with the proper attention from subject matter experts. WikiDan61ChatMe!ReadMe!!13:45, 22 May 2012 (UTC)
Hi. Thank you for your recent edits. Wikipedia appreciates your help. We noticed though that when you edited Flame supervision device, you added links pointing to the disambiguation pages Draught and Expansion valve (check to confirm | fix with Dab solver). Such links are almost always unintended, since a disambiguation page is merely a list of "Did you mean..." article titles. Read the FAQ • Join us at the DPL WikiProject.
Hi. No, I have no evidence supporting the idea that "drag constant" is Reynolds number. However, both the Reynolds number and Drag coefficient are "dimensionless quantities" that are not actually constants, but essentially scalar conversion factors that depend on the physical properties of the "solid" object in the fluid. So, it made sense for me to mention both in a disambiguation page rather than a redirect, but you can change it to a straight redirect with a see-also component stashed away in some obscure article if you'd like. Thanks. ~AH1(discuss!)20:16, 12 September 2012 (UTC)
Hi Maschen, there is nothing wrong with your editing pattern. I like it . And I like the nice articles you make. I am unfamiliar with relativistic quantum physics, but Bargmann–Wigner equations looks impressive. Best regards, -- Crowsnest (talk) 17:04, 18 September 2012 (UTC)
Thanks RockMagnetist, that was a nice discussion. At the moment I am working on something else, but I will put it on my "to do" list. Regards, Crowsnest (talk) 12:15, 30 September 2012 (UTC)
when i calculated the laplacian in kartezian coordinates i found that i get -K(0)^2*E(0) twice, once from x direction and once from y direction, can you explain me where im wrong ? — Preceding unsigned comment added by 87.69.192.171 (talk) 13:58, 10 November 2012 (UTC)
The wavenumber k0 of the carrier wave is a vector, with components (in case of three-dimensional wave propagation): k0,x, k0,y and k0,z. The length k0 of the wavenumber vector k0 is related to the components through k02 = |k0|2 = k0,x2 + k0,y2 + k0,z2. Hence when applying the Laplace operator k02 only appears once. Hope this helps, Crowsnest (talk) 16:34, 10 November 2012 (UTC)
Versteeg & Malalasekera (2007) is book on computational fluid dynamics (CFD). The word "non-dimensional" appears only five times in the whole book, and "dimensional analysis" 7 times, but never in the sense as indicated in the sentence they should support.
Patankar (1980) is also about CFD and does not seem to address dimensional analysis at all (cannot find it in the contents or index).
White (I have the 4th and 7th editions of this undergraduate course book for mechanical engineers) only talks about dimensional analysis in connection with experiments, not for partial differential equations as it is used for in the citation.
Especially the text in the section "Need for non-dimensionalization and scaling" is dubious, with all the talk about experiments in an article containing the Navier-Stokes eqs. in its title. The sentence footnoted with the Salvi citation (a non-peer-reviewed conference proceedings) claims that without heat transfer, the flow only depends on "the" Reynolds number (which length and velocity scales appear in this Reynolds number? Often there are several Reynolds numbers of importance in a flow). Which is not true since the flow and its effects may also depend on e.g. Froude number, Mach number, Weber number, (yet another) Euler number, etc. For the equations themselves (Eq. 2 has errors) references can be found, but the accompanying texts raise quite some doubts, or are in error. As one example: near the end it says "Similarly if Re → ∞ i.e. when the inertia forces dominates, the viscous force can be neglected ..." which has in the past lead to the long-time unresolved d'Alembert's paradox. -- Crowsnest (talk) 22:40, 1 December 2012 (UTC)
D'Alembert's paradox
Hello Crowsnest. Congratulations on all the good work you have been doing on D'Alembert's paradox. You have added the following three excellent images and they really improve the quality of the article:
You have added and clarified a lot of the text too and the article is now an excellent treatment of the subject. I have learned a lot about the paradox from reading this article. Congratulations! Dolphin(t)21:45, 10 December 2012 (UTC)
This message concerns the redirection of "wavetrain" to wave packet, which you wrote a few months ago. I have just written a new article on periodic travelling wave; it is my first contribution to wikipedia. In applied mathematics (which is my field), the term "wavetrain" is used as a synonym of periodic travelling wave. Therefore it would seem natural have redirection of some kind from wavetrain to my new page. Therefore I proposed a disambiguation of the term wavetrain, but it was declined. In response to my querying it, the reviewer said "I declined this because there wasn't enough context from just looking at the disambig page to know if it was necessary or not". Do you have any ideas as to how to proceed with this? (Also -- how confident are you about the use of wavetrain to mean wave packet -- I have no idea since I don't have any expertise in quantum mechanics).
Thanks
Jasherratt (talk) 14:28, 15 January 2013 (UTC)
In physics a wavetrain can be both a packet and a periodic wave of infinite extend, but most often it is modulated or of finite extend. See e.g. "light (physics)" in the Encyclopædia Brittanica: ... as a short “wave train” lasting from about 10−9 to 10−8 second ... I do not know about its use in mathematics. -- Crowsnest (talk) 16:42, 16 January 2013 (UTC)
. Best regards, Crowsnest (talk) 09:39, 28 March 2009 (UTC)
.-- Crowsnest (talk) 15:48, 13 April 2009 (UTC)
. Best regards, Crowsnest (talk) 05:03, 6 November 2010 (UTC)
