Models Definition and 400 Threads

In case anyone wants to comment, I thought I'd start a thread on it. http://arxiv.org/abs/0908.3683 Early Universe models from Noncommutative Geometry Matilde Marcolli (Caltech), Elena Pierpaoli (USC) 49 pages, 26 figures (Submitted on 25 Aug 2009) "We investigate cosmological predictions on...

I am currently preparing for a few wind tunnel tests on a NACA 2412 airfoil. The lab technician told me that before I can use the tunnel, I need to provide solid proof that the models will be able to hold up in the wind tunnel (up to speeds of 110 mph (30 psf)). In the technician's own words...

Homework Statement According to classical physics, a charge e moving with an acceleration a radiates at a rate dE/dt = - (e2a2)/(6pi epsilon c3) a) Show that an electron in a classical hydrogen atom spirals into the nucleus at a rate dr/dt = - e4/ (12pi^2 epsilon^2 r^2 me^2c3) b) Find...

I've never really understood how electron taking the form of a standing wave in the orbit of a nucleus can have particle characteristics (ex. momentum based on the formula p = h/lambda). Also I could never grasp with the idea of something being both a particle and a wave at the same time and...

I like to play and abuse RC car models like this: However, when making big jumps or high-speed crashes (they can even reach 90mph), even steel parts gets damaged and needs to be substituted. See these damaged/broken parts for example: http://img169.imageshack.us/img169/4286/cimg1700.jpg...

I know that answers to the following can sometimes be subjective and biased... but still... What are the most 'promising' models in string theory, judged by the potential realization of a realistic SS standard model? Also, in particular, how do Intersecting Brane Models (since their...

When using the Friedmann equation (flat space, no cosmological constant): H = sqrt (8 pi G / 3 ) * rho, if we use rho in mass/volume, H is in (time)^-1 like it should. Now for some inflation models, we use: H = sqrt (8 pi G / 3 ) * V(Phi). It seems that V(Phi) should also be able to be...

Following are some descriptions of Inflationary Model(s) of the Universe which are quite different than I have read elsewhere. My own view, I now believe, was likely a bit myopic. These comments reflect Paul Steinhardt and Neil Turoks' descriptions in their book ENDLESS UNIVERSE where they...

I am not sure if I am reading well the following article about KT phase transition in spin systems. http://www.itp.uzh.ch/~llucas/projects/proseminar.pdf Page 5 quotes a theory regarding the Helmholtz free energy function. The curve surrounding a spin site or an atom looks like everyone's best...

Hello. I use P-Spice student version and I regret that standard librairies offer very few number of models, especially for Op-Amp's. Is there sites where I can download more components models.

1. Homework Statement The transient behaviour of a capacitor has been studied by measuring the voltage from across the device as a function of time. The following data has been obtained. Time (s)/Voltage (v) 0 / 10 1 / 6.1 2 / 3.7 3 / 2.2 4 / 1.4 5 / 0.8 6 / 0.5 7 / 0.3 8 / 0.2 9...

1) "Simple linear regression model: Y = β0 + β1X + ε E(Y) = β0 + β1X A linear model means that it is linear in β's, and not necessarily a linear function of X. The independent variable X could be W2 or ln(W), and so on, for some other independent variable W." I have some trouble...

1) "Simple linear regression model: Yi = β0 + β1Xi + εi , i=1,...,n where n is the number of data points, εi is random error We want to estimate β0 and β1 based on our observed data. The estimates of β0 and β1 are denoted by b0 and b1, respectively." I don't understand the difference...

1) "In regression models, there are two types of variables: X = independent variable Y = dependent variable Y is modeled as random. X is sometimes modeled as random and sometimes it has fixed value for each observation." I don't understand the meaning of the last line. When is X random...

If you have a data set which consists of n variables and m factors which are essentially randomly correlated and you construct a single factor model, you usually get a very good fit (small chi-square statistic and a p-value which indicates that the hypothesis of perfect fit cannot be rejected)...

Hello, I'm a student from Lithuania. I have found in one forum topic your discussion about non-linear equation convertion into a linear form.. I have some problem with that...Could you help me, please? :) For, example, I have two non-linear models: 1. y = a [1/(1+b/(c+x))]*exp(-d*x) 2. y =...

In my high school Honors Chemistry course today, we performed a simulation (along with several real labs) of chemical (dynamic) equilibriums. I'll briefly outline the simulation: 1. Place 42 pennies on the reactants side and 0 on the products side. 2. In the first round, move 1/3 of the...

Homework Statement The radius of the orbit of an electron in a hydrogen atom is 0.05 nm. Using the planetary model, calculate the orbital velocity needed by the electron to avoid being pulled into the nucleus by electrostatic attraction. Round up your answer to the nearest tenth...

Can someone explain what's Z2 symmetry ? Is it necessary to have it in a model, even SM ?

This video is worth watching. http://pirsa.org/08120001/ Quantum Nature of the Big bang in Simple Models. Abhay Ashtekar Perimeter video with slides PDF 3 December 2008 "According to general relativity, space-time ends at singularities and classical physics just stops. In particular, the big...

arXiv:0811.4129 (cross-list from gr-qc) [ps, pdf, other] Title: Consistent Loop Quantum Cosmology Authors: Martin Bojowald Comments: 13 pages Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph); High Energy Physics - Theory (hep-th) A consistent...

1. Given Information/Objectives The following system for "stable competition": dx/dt=(2-2x-y)x dy/dt=(2-x-2y)y Find the equilibrium points for the system. Using the Jacobian matrix, linearize the system about the equilibrium that has both species present. Classify this equilibrium...

Hello, I am studing polytropes and I found something intersting here: http://astronomy.sussex.ac.uk/~pd48/Polytropes.ppt I got a problem at slide 5 where she says that the polytropic index n is equal to 0 for a homogenous gas sphere. I am not able to figure out why. From the polytropic...

A rocket is fired vertically and ascends with constant acceleration a=100m/s^2 for 1min. At that point, the rocket motor shuts off and the rocket continues upward under the influence of gravity. a) Find the maximum altitude acquired by the rocket b) The total time elapsed from the...

I'm wondering if anyone is aware of any computational/theoretical work on solving the problem of describing the motion of a biological macromolecule in a cellular microdomain? This would have to mean setting up and solving a stochastic partial differential equation with boundary conditions...

I'm looking at different topics for my masters thesis and one of them that has a lot of potential is a heat transfer model for a piston in an internal combustion engine. Apparently the auto industry has never directly addressed this problem and use a trial and error method when it comes to...

What are the acceptable models to eplain how the big bang is expanding the space of our visible universe? Are these the choices? 1) An expanding infinity 2) local expansion with an area of non-expansion beyond our range of observation 3) local expansion with an an area of non expansion in...

http://www.alexisparkinn.com/weird_aviation_videos.htm scroll down to bottom of page for video. Are these models? impressive looking.

I am taking a project this year. As the title suggests this project is a maths project but I was wondering if anyone can direct me to some science field in which I could use stochastic models. I have very limited knowladge in science so something theoretical would be nice. Any books would be...

I'm about to buy a refurbished laptop because there cheap, I've been using a refurbished gateway for a year no now significant problems i just want better hardware. Now one model is INTEL and one model is AMD. So if anyone wants to look at these two models and give there unbiased opinion that...

Hi, I'm interessed in using GridMathematica for parallel computing of cellular automata models. I know using mathematica so the syntax shouldn't be a problem. however, I wonder if there's here someone who has worked with it since I would like to know if the program is worth the cost etc...

Hello, I'm a computer science student in desperate need for help. In the process of writing my master's thesis I've successfully developed a traffic simulation using a model I've found in the traffic research literature, the IDM, to be precise. This model seems straight-forward and is easy to...

If one has some sort of bounce scenario for BB, with preceding contraction, then for say 1 sec or 10 sec after BB, one has a certain Hubble parameter and temperture, and associated quantum description. Then for 1 or 10 sec before the BB, would it seem most likely to have the same Hubble...

I had the pleasure of attending a lecture given by Paul Steinhardt, a Princeton professor, regarding the big bang and cyclic universe models at Fermilab this evening. Steinhardt, having written a book called The Endless Universe, is obviously a fan of the cyclic universe camp and the main focus...

M. Chodorowski argues in his http://arxiv.org/abs/astro-ph/0610590v3" that the concept of "expansion of space" is not necessary to explain the expansion of the universe, and therefore Occam's Razor tells us that we should consider discarding the concept entirely. He says that expansion is...

Has anyone in this forum worked on translating findings from invertebrates to mammals? I'm wondering how successful this tends to be. How often are actual gene sequences conserved? When the genes are conserved, how often do they have the same function across systems? Or is the most valuable...

Wen's papers purport to show that given a 3D extended lattice spin model, the emergence of light, electrons, gravitons and others should work well. How similar is what he is doing with what LQG and SF have done? How hard would it be to construct a verion of LQG/SF that reproduces all of Wen's...

Why is it that we can treat electrons as independent and non-interacting in solid state physics? What is the difference between mean-field theory and density functional theory? In lame terms please.

to those experts in the field of cosmology i was wondering if " large scale structures can be formed in stable cosmological models" or should i say that " large scale structures cannot be formed in those cosmological models that are stable with respect to gravitational or other curvature...

Does the new spinfoam models have a good semiclassical low energy large volume limit? By new I mean the new connections Rovelli have discussed as spinfoam 4d now talks to LQG.

Hello, new here, first post. Just need some help with homework. Question One Homework Statement This norman window is made up of a semicircle and a rectangle. The total perimeter of the window is 16 cm. What is the maximum area? ** * * <<<...

I've been told that non-well-founded sets can be used to model nonstandard analysis, but I can't find any literature on the subject. Does anyone know where I can find it?

I want to post some interesting quotes about global circulation models. Well, I believe they have potential I believe that the application of the theory is often misapplied. http://www.climateaudit.org/?p=483#comment-208656 http://www.climateaudit.org/?p=483#comment-209256...

sorry to ask this stupid question... can anyone tell me exactly the difference between liquid and gas based on kinetic model? most textbooks give that in liquids inter molecular spaces are lesser than gases ,etc & etc but if compress the gas to much ,still it doesn't get converted into...

I believe, nobody knows exactly what photon is. Instead we have several MODELS of photon. Let us summarize these models. 1. Classical Physics. There is NO photon in classical physics. There reason is that there is NO QUANTIZATION of field in classical physics. However there is an...

How important is the role of integrable models in today's and future development of theories of fundamental physics? Any examples?

If we take Planck's constant to be a measure of quantum fluctuations, which seems natural in the world-view of https://www.physicsforums.com/showthread.php?t=204567", then it also seems natural to ask whether Planck's constant might vary over cosmological scales, just as temperature is a measure...

1. The problem is that I have to create a two-minute presentation on Nikola Tesla and I'm not sure what I can show that is of interest (i.e. model, etc.) I've tried making powerpoints but I have found that they aren't as interesting as models etc. Thanks

This is an announcement, in the Physics Forums context, of my "Lie fields revisited", http://arxiv.org/abs/0704.3420" , which has recently been accepted by J. Math. Phys., and an attempt to elaborate on why you might read it and to elicit critiques. For a little over ten years, I have been...

http://www.foxnews.com/story/0,2933,316734,00.html http://nostarch.com/frameset.php?startat=flego_extras Forbidden LEGO Build the Models Your Parents Warned You Against by Ulrik Pilegaard and Mike Dooley http://www.tinker.tv/downloads/forbidden_lego_gun.jpg