Models Definition and 400 Threads

A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin modulus, a measure.
Representational models can be broadly divided into the concrete (e.g. physical form) and the abstract (e.g. behavioural patterns, especially as expressed in mathematical form). Of particular importance in the modern context, conceptual models are central to philosophy of science, as almost every scientific theory effectively embeds some kind of model of the physical or human sphere.
In commerce, a model might instead reference a specific version or configuration of a product offering, rather than functioning as a representation of something else.
In taxonomic settings (e.g. biology, architecture, art) a model is sometimes a particular instance of a set of related entities (species, built structures, artistic compositions) chosen as a convenient reference point around which to build discourse; such a model is almost always chosen to typify some central tendency of the group, exemplify the group's defining characteristic, or reify the group's historical lineage.
Kinds of models include:

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  1. marcus

    Marcolli Pierpaoli: Early Universe models from Noncommutative Geometry

    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...
  2. W

    How Can I Stress Test My NACA 2412 Airfoil Models for Wind Tunnel Use?

    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...
  3. D

    How Quickly Does an Electron Spiral into the Nucleus in Classical Physics?

    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...
  4. R

    What is the relationship between quantum bits and classical measurements?

    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...
  5. I

    What's the best/strongest material for RC car models?

    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...
  6. C

    Leading models for building realistic SM from Strings.

    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...
  7. E

    Chaotic Inflation Models & Equations

    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...
  8. N

    Inflationary Models: A Dead End?

    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...
  9. G

    Mexican hat potential around spin site (TOPIC: spin models)

    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...
  10. R

    Where can I find more PSpice models for Op-Amps?

    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.
  11. M

    Solving Models: Deriving Expressions for Transient Capacitor Voltage

    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...
  12. K

    Examples of Multiple Linear Regression Models

    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...
  13. K

    What is the difference between random error and residual?

    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...
  14. K

    What is the difference between E(Y|X) and E(Y|X=x) in linear regression models?

    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...
  15. E

    Problems with single factor models

    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)...
  16. D

    Linerization of non-linear models

    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 =...
  17. jacksonpeeble

    Mathematical Models for Equilibrium Simulation

    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...
  18. S

    What is the Orbital Velocity of an Electron in a Hydrogen Atom?

    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...
  19. T

    Understanding Z2 Symmetry in Models

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

    Quantum Nature of the Big bang in Simple Models (Ashtekar@Perimeter)

    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...
  21. wolram

    Large class of models ruled out.

    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...
  22. T

    Systems of Differential Equations- Two models of interacting species

    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...
  23. G

    Polytropic Models: Solving Problem at Slide 5

    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...
  24. rocomath

    Calculating Altitude and Time of a Fired Rocket

    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...
  25. Cincinnatus

    Models of the diffusion of biological macromolecules

    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...
  26. Topher925

    Trying to find info about ICE piston heat models.

    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...
  27. P

    Exploring Models of the Big Bang Expansion

    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...
  28. wolram

    Weird Aviation Videos: Models or Something More?

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

    Exploring Stochastic Models in a New Scientific Field

    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...
  30. B

    Help with comparing laptop models

    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...
  31. J

    Mathematica GridMathematica for parallel computing of cellular automata models

    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...
  32. A

    Car Following Models: Explaining Older Models

    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...
  33. Z

    Does the Capernican Principle Apply to Pre-Big Bang Models?

    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...
  34. Nabeshin

    Big Bang v. Cyclic Universe models

    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...
  35. J

    Kinematic GR models of expansion

    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...
  36. Cincinnatus

    Insight from invertebrate models

    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...
  37. E

    How close is LQG/SF to Wen's lattice spin models

    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...
  38. N

    Independent and interacting electron models

    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.
  39. A

    Stability of cosmological models

    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...
  40. E

    Do New Spinfoam Models Have a Good Semiclassical Limit?

    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.
  41. C

    Simple Calculus Word Problem (using derivatives to anaylze function models)

    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? ** * * <<<...
  42. D

    Nonstandard Analysis models using non-well-founded sets

    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?
  43. J

    Observations About Global Circulation Models

    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...
  44. S

    Exploring Kinetic Models of Liquids and Gases

    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...
  45. B

    Understanding Photon: Models from Classical Physics to Quantum Field Theory

    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...
  46. P

    Integrable models and the frontiers of physics?

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

    Are there cosmological models in which Planck's constant varies?

    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...
  48. L

    Exploring Nikola Tesla: Models & Presentations

    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
  49. Peter Morgan

    Classical interacting random field models

    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...
  50. robphy

    Forbidden LEGO: Building Unconventional Models

    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
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