What is Model: Definition and 1000 Discussions

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. nomadreid

    Classic model relation versus the Kripke model relation

    Looking at an exposition of Kripke semantics, the relationship ||- in a Kripke model is obviously supposed to be similar to the model relation |= . A possible world (a node) looks suspiciously like a model for second-order formulas. But of course it cannot be this simple. What is the connection...
  2. thegirl

    Rutherford Scattering model geometry

    Hi, I was just wondering if someone could help clarify how pi - theta = phi? That is the link to the youtube video I was watching, the guys pretty good check him out if you want to learn how to derive the differential scattering cross section.
  3. Quarlep

    Calculating Surface Density of the Universe Using the Shell Model

    You know friedmann equations derived from kinetic energy and potantial energy conservation.I found these shell model for universe.Here I am curious about something. This shell is like a surface of sphere isn't it.I mean it has only surface and that surface mass is m.And we made our equations...
  4. PrincessIceFall

    How to find the depth of immersion of this boat model?

    So I am trying to find the depth of immersion of this particular boat model, which has curvilinear edges (subparabolic edges) on each side. The figure of the pontoon is shown below So now when I place this pontoon in water, the height of the water that rises, called the depth of immersion is...
  5. K

    Population Dynamics: Logistic Model (Differential Equations)

    Homework Statement Population Dynamics: Logistic model. Suppose the environmental carrying capacity of the population is 100000 and the growth rate a t=0 is 5%. . If the population starts at 10000, how long does it take for the population to reach half the carrying capacity? dp/dt = A P...
  6. R

    Lotka-Volterra model Euler's Method

    Homework Statement *I am not sure if this should be in the computer science section or here? I am trying to graph the densities, of the Lotka-Volterra prey and predator model, as a function of time, i.e. ##p(t)## vs ##t## and ##q(t)## vs ##t##. Also, the phase space, i.e. ##p## vs ##q##, but...
  7. G

    C/C++ VCSEL, spin-flip model, c or c++ code?

    Is there any c or c++ written spin-flip model for simulation of dynamics in VCSELs available? Thanks.
  8. Breo

    Basic question on the pertubative Standard Model

    Dear all, how to 100% know if a process is allowed in standard model? And when a process is allowed, how to know what diagrams contribute, and what of those are the dominant ones? Thank you in advance.
  9. G

    Is there a minimal model for ZC that includes Gödel constructible elements?

    Is there a meta-mathematical model of ZC (Zermelo Set Theory with specification scheme and axiom of choice but not remplacement and) that includes a minimun quantity of Gödel constructible elements of L hierarchy with all the ordinals until ω⋅2 and that it "lives" in all the meta-mathematical...
  10. wolram

    Is There an Age Problem in the LCDM Cosmological Model?

    From what i have read, right or wrong, there seems to be an universe (age) problem for modern cosmologists, This is the best paper i have found on the subject. http://arxiv.org/pdf/1402.6433v3.pdf Abstract Many dark energy models fail to pass the cosmic age test. In this paper, we investigate...
  11. B

    HMM Homework: Calculate Pr(S,π) with aRG=aGR=1/4, aRR=aGG=3/4

    Homework Statement Consider an HMM with two possible states, “R” and “G” (for “regulatory” and “gene” sequences respectively). Each state emits one character, chosen from the alphabet {A,C,G,T}. The transition probabilities of this HMM are: aRG = aGR = 1/4 aRR = aGG = 3/4 The emission...
  12. G

    ¿Is there a minimal standard model for ZFC?

    ¿Is there a minimal standard methamatematical model for Zermelo set theory in the sense that the other models contains this model ?
  13. R

    4 parameter logistic model for fitting PCR data

    I have a question about the logistic fit they used on this paper: http://online.liebertpub.com/doi/pdf/10.1089/cmb.2005.12.1047. Its PDF page 5, or journal page 1051. They define all the variables and then say x0 and b define the shape of the model. If I am fitting 30 cycles of PCR data how am I...
  14. K

    Engineering Drawing the DC Model of a Circuit

    Homework Statement [Picture of Problem](http://i.imgur.com/7q4yj8O.png) Homework Equations [/B] * It is dealing with drawing the DC model of a circuit * Now i know when drawing a DC Model, all capacitors are open (or ground) and AC sources are grounded as well. * In this specific problem, i...
  15. sk1105

    Nuclear Shell Model - pp bound states?

    I have looked around for help with this, including on existing threads, but I can't quite find what I'm looking for. I know that in the nuclear shell model we fill the shells in the same way as with electrons, so 2 protons in the first and 6 in the second etc, with the same being true for...
  16. I

    Engineering Analyzing diode circuit with Constant Voltage Drop model

    Homework Statement Homework Equations Whenever assuming a diode is "on", replace that diode with a 0.7 voltage source. Whenever assuming a diode is "off", replace that diode with an open circuit. The Attempt at a Solution The problem is pretty straightforward but the format of the circuit...
  17. A

    Ising Model and Partition FUnction

    Hi all This is probably a naïve question to ask, but I am puzzled by it and need an answer. The first time I encountered the term 'partition function' that was in context of Boltzmann distribution. But the same formulas of manipulating a partition function ( to obtain free energy, temperature...
  18. U

    Nearly free electron model - band gap

    For a wavefunction at the Brillouin boundary we have: \langle k|H|k\rangle = \epsilon_0 (\vec k) \langle k'|H|k'\rangle = \epsilon_0 (\vec k+\vec G) \langle k'|H|k\rangle = V_G = \frac{1}{L^3} \int e^{i(\vec k - \vec k') \cdot \vec r} V(r) d\vec r \langle k|H|k'\rangle = V_G^* Using...
  19. J

    Has Anyone Experienced Challenges with the Weber-Davis Solar Wind Model?

    Hi, I was wondering if anyone here had any experience (preferably intimate) with the Weber-Davis solar wind model, i.e. ...
  20. D

    Problem integrating gamma ray absorption model

    Homework Statement In this lab various thicknesses of a few materials are placed between a source of gamma radiation and a couple different detectors. It is reasonable to assume that some small change in the thickness of the shielding would produce a proportional change in the intensity of the...
  21. matteo137

    Simulating the driven-dissipative Bose-Hubbard model

    I'm trying to simulate with Mathematica the driven-dissipative Bose-Hubbard model, and I would like to know what is the most convenient way of doing it. The Hamiltonian of the system is the following: H= \Delta \sum_j a^\dagger_j a_j + U \sum_j a^\dagger_j a^\dagger_j a_j a_j + J \sum_{\langle...
  22. BonesSheppard

    Why buy new model rocket engines?

    Hi I was wondering why are model rocket engines disposable after one use? Is it because it is more economically feasible to buy a new model rocket engine than to repair a used one because the process of using a model rocket engine always ruins it? Also, if it is the case that model rocket...
  23. M

    Modeling the Kinematics of a Tennis Serve

    Hey Guys, I know its an Odd Question but i have an assignment where i should be doing a tennis serve and taking a video of it, importing it on laptop and draw graphs and make conclusions about its position with time and compare my results with theories, so any suggestions on how to do that, in...
  24. J

    Do I Need a License for Horizontal Thrust Rocket Tests?

    If your rocket is of a certain power range you need a certain license. My question is of you need these license's if you are only doing horizontal thrusts tests and never actually launching it vertically into the air?
  25. R

    Particle Model of Thermal Energy questions

    Homework Statement a) Assume that a substance in a closed container is at thermal equilibrium with about half of its molecules in the gas phase and half of its molecules in the liquid phase. How could you use the Particle Model of Thermal Energy to explain which molecules are moving faster, on...
  26. F

    What is responsible for force in the standard model?

    It is touted that modern physics has discovered what is actually responsible for force which are particles. Yet, the force responsible for EM is "virtual" particles and then you have the "W" particle in Electroweak. So it seems the issue is not all that clear. I know how the math works, but I am...
  27. C

    Statistical Mechanics Mean Field Model

    I don't think I've fully grasped the underlying ideas of this class, so at the moment I'm just sort of flailing for equations to plug stuff into... Homework Statement Show that in the mean field model, M is proportional to H1/3 at T=Tc and that at H=0, M is proportional to (Tc - T)1/2...
  28. Kevin Bacon

    PFR model with n order reactions

    I have this problem for my reactor design course and I need some help wrapping my head around it. We have to design a plug flow reactor (PFR), which can be modeled as five equal volume CSTR's in series. The PFR has an inlet volumetric flow rate of ##q_{in}## which contains species ##A_i, i =...
  29. resurgance2001

    Derivation of standard model lagrangian

    What's the simplest, most direct way to derive the lagrangian of the SM? I saw earlier today: L[S M] = L[Dirac] + L[mass] + L[Gauge] + L[Gauge/psi] That seems like a good starting point. I like it because it says the SM Lagrangian is simply the sum of four lagrangians. The next step...
  30. L

    CC Problem Beyond the Standard Model

    Which of the following do you prefer as possible solution to the cosmological constant problem or why QFT computes vacuum energy density that is 120 magnitude more than from observational data? Sometimes I think the metric (1.a) needs to change, but on other days I think QFT needs to change...
  31. J

    Max Scattering Angle from Thompson Plum Pudding Model

    1. Problem Statement: Consider the scattering of an alpha particle from the positively charged part of the Thomson plum-pudding model. Let the kinetic energy of the α particle be K (nonrelativistic) and let the atomic radius be R. (a) Assuming that the maximum transverse Coulomb force acts on...
  32. nearc

    Gravitational equations used in model of orbiting bodies

    In practice I’ve found that a valid gravitational model of orbiting bodies only works when the force is computed with only the other mass and not both masses. Thus, the original equation does not work but the modified one does. Is using one mass ok or am I doing something wrong? thanks. [also...
  33. H

    Can the Lorentz Oscillator Model be Modified to Include Radiation Force?

    Hi Guys, I'm looking into the Lorentz model Since the acceleration/de-acceleration of electron can cause radiation hence create force, can anyone tell me how to modify the above equation to include the term of radiation force? Thanks. jack
  34. O

    Simulating dark matter by assuming stable solution

    Hey, I've a short question. Is there any research attempting to constrain models of dark matter by assuming stable solution for the universe? I'm interested in knowing whether this gives any sensible constraints on the dark matter models. I'm still fairly new to studying dark matter but as I...
  35. P

    Graphene Superlattices & Kronig-Penney model

    Numerically, Kronig-Penney model in graphene superlattices (SL) is drastically different from those in semiconductor SL. In semiconductors, transverse momentum k// can be isolated from the longitudinal momentum q, even if the superlattices potential is complex. In graphene, however, k_y cannot...
  36. Qturtle

    Coupling to an electric field in a tight binding model

    Hi i'm looking for some references (prefer books) or explanations as to how one couple electrons so an EM field in a second quantized formalism tight binding model. from what i know, one need to replace the hopping parameter with the same parameter multiplied by an exponent of the line integral...
  37. E

    Heat conduction numerical model

    Hi Guys, I'm new on this forum, currently studying Aerospace Engineering and am trying to produce the model of a radioisotope thermoelectric generator using numerical methods to solve the heat conduction equation as part of my research. The way it works is that I have a radioisotope source in...
  38. P

    Σ Model, from not obvious to obvious?

    Georgi in his book, for reference: http://www.people.fas.harvard.edu/~hgeorgi/weak.pdf he says that it is not obvious that the form of $$\Sigma = \sigma + i\tau_a\pi_a$$ is preserved under (2.6.6) $$ \delta \Sigma = i \epsilon_L^aT_a \Sigma - i \Sigma \epsilon_R^aT_a$$ But then he said, "But it...
  39. N

    Gravity's reaction force in the relativist model?

    this is related to the following thread: https://www.physicsforums.com/threads/gravitys-reaction-force.28395/ (but it doesn't seem to accept more replies so i posted here) my cuestions are: - ¿if gravity depends on mass, how come we define a black hole as an object so massive that photons (mass...
  40. Gbl911

    Can a Model Rocket reach space?

    I was wondering if there is a way to build a model rocket that has the capabilities to reach space (not go into orbit though). It would seem to be very difficult to reach space from the ground, but if you launch it from a balloon some 30 miles up, would it be possible, if not, any easier?
  41. S

    How to simplify behavior of a field-effect transistor

    Are there simple governing equations for FETs like there are for BJTs, and if so, what are they? For example, in the BJT case we have IC = β×IB IE + IC + IB I'm sure it depends on the type - MOSFET, JFET, etc. - so anything anyone could contribute would be helpful. From what I understand, the...
  42. haael

    Can memristance be simulated using op-amps?

    Is it possible to model memristance using op-amps? I searched google but found nothing.
  43. T

    Einstein's heat capacity model .and law of corresponding

    Homework Statement B/c the textbook mentions that Einstein's heat capacity equation obeys a law of corresponding states...but, I don't really understand how this can be...I've tried to figure out, to no avail...so, any help would be welcome! Homework Equations Cv/NkB =...
  44. lfqm

    Where does the 1/√N factor in the Dicke model arise from?

    Hello colleagues, hope you can help me. The Dicke model describes a system of N two-level atoms cooperatively interacting with a single mode of an electromagnetic field as follows...
  45. 2

    Differential gravitational force causing tides model?

    Homework Statement Homework EquationsThe Attempt at a Solution For a), I initially tried to consider the component of the gravitational force of the moon acting normally to the Earth's surface. This would be F=F_0 cos(theta) where theta is the angle between a horizontal line going through A...
  46. J

    Understanding the Bohr Model and Electron Decay

    Hi, I'm really struggling to comprehend how the Bohr model solves the problem of accelerating electrons losing energy and decaying into the nucleus. I've read through a lot of discussions on line and on PF and all I keep on reading is stuff like, the quantization of energy levels leads to a...
  47. P

    What is the three-body potential and how does it affect the baryon spectrum?

    Homework Statement I have to study the effect of the three body potential given below on the baryon spectrum. Homework Equations V(rij,rjk)=∑i≠j≠k≠i -V0(exp[-mrij]/mrij)(exp[-mrjk]/mrjk) where V0>0. The Attempt at a Solution Where can I find a discussion about this potential? I have no idea...
  48. C

    Question about the Limitations of Physics

    Here is a question about the possible limitations of physics, specifically about whether a theory of everything can actually explain everything. Assume we have a theory of everything. Now, consider an electron e with all the relevant properties. Now, our theory of everything, being mathematical...
  49. L

    Difference between Hubbard and tJ model

    What is the difference between Hubbard and tJ model? Does anyone knows?
  50. Abscissas

    Solving a Model Rocket Launch Problem

    Hello loves, I know there are post very very similar to this, but I just needed some help understanding it. any help is truly appreciated. 1. Homework Statement A model rocket is launched straight upward with an initial speed of 50 m/s. It accelerates with a constant upward acceleration of 30...
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