population Definition and 278 Threads

Population is the term typically used to refer to the number of people in a single area. Governments conduct a census to quantify the size of a resident population within a given jurisdiction. The term is also applied to animals, microorganisms, and plants, and has specific uses within such fields as ecology and genetics.

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  1. B

    Maximum population for 2000 Kcal per day

    Dear physics, I'm new to the site. I found it reading this topic: https://www.physicsforums.com/showthread.php?t=145043 I wonder if we could manage to answer, if some not critical precision, the question of: How many people can live confortably, eating only potatos, in earth? As of...
  2. C

    Deriving Expression for Population Fraction (Statistical Mechanics)

    Homework Statement A quasi-3 level solid-state laser gain medium consists of a ground state manifold containing two energy levels within which a single electron can be promoted, with the second energy 10meV above that of the lowest level. A. Where the gain medium is not optically pumped...
  3. R

    How Can We Estimate Sampling Probability from Sales Data?

    In my research I am working on some data (let’s call it sales data), however we almost have no information on the original sample. My goal is to come up with possible explanations on how it could be sampled by consistency arguments. In more detail, the data provided is composed of sales...
  4. Drakkith

    Population III Stars Metallicity

    Early Population III stars in the universe were very metal poor if not metal free and were apparently required to be much larger than todays stars, up to hundreds of solar masses, to form. What does the metallicity have to do with this?
  5. M

    MHB Estimating a Population from Sampling with Imperfect Detection

    Hello All, thanks for looking at my post and question. I have jumped into deep statistical and probability waters which have outstripped my current state of knowledge so any help you can render would be greatly appreciated. Here is my question: I am trying to get an estimate of the original...
  6. A

    Exponential distribution/hydra population

    Hi, Somebody asked me for some help with his calc II homework, and this was one of the questions: "A hydra is a small freshwater animal and studies have shown that its probability of dying does not increase with the passage of time. The lack of influence of age on mortality rates for this...
  7. H

    How Do You Calculate Bacterial Growth Using Exponential Equations?

    Homework Statement The count in a bateria culture was 200 after 15 minutes and 1500 after 40 minutes. Find the population after 120 minutes. Homework Equations A=Pe^(rt) The Attempt at a Solution I did P=60e^(.0806 x 120) P= 952023.0848 (answer is wrong)
  8. A

    IVP involving Eigenvalues and Population Dynamics

    Homework Statement Consider the interaction of two species of animals in a habitat. We are told that the change of the populations and can be modeled by the equations \frac{dx}{dt}= 0.1x-0.8y \frac{dy}{dt}=-0.2x+0.7y Find the solution to the above equations with initial values x(0)=9 and...
  9. B

    Travel patterns distributions of a sample representative of a population?

    Travel patterns distributions of a sample representative of a population?? Hi, I was hoping that somebody might be in a position to advise me on a problem that I have. I am recording the travel patterns of a car for 80 different families for 2 years. Specifically I am recording the...
  10. C

    How small population can maintain contemporary technology level

    I'm interested in that question not for novel purpose, but for pen and paper RPG scenario. Assumptions: 1) It was possible (though under cost of becoming clearly a soft SF ;) ) of transporting a big group of people to a far away habitable planet with contemporary tech. 2) Such transfer...
  11. I

    Bacteria population formula reach 1 million?

    Homework Statement dP/dt = (3000)/(1+0.25t) This gives the rate population changes at We also know P is 1000 when t is 0 (days) The Attempt at a Solution The anti derivative 12 000 x Ln(1 + 0.25t) + c Do I just make this equation equal to one million?
  12. C

    Modeling Population Growth with Constraints: A Scientific Approach

    Homework Statement I'm trying to model how a population would grow wrt the following constraints: 1. Number of people within the population 2. How many people each person of the population informs 3. Probability of each person of the population informing a member outside the population...
  13. N

    Difference between sample standard deviation and population standard deviation?

    Homework Statement Just as the title suggests, although this is more to do with the formula. I know that for a sample, it implies it's a subset of a population. Why in the formula do you divide by n-1, whereas for calculating standard deviation for a population you divide by the total amount...
  14. M

    Using e to determine population growth?

    Homework Statement A population started at 10,000 in 1900. The population doubles every 50 years. What was the population in 2000? Homework Equations Q(time) = Q(initial)*e(rate)(time) The Attempt at a Solution I was able to come up with the answer using the standard growth...
  15. R

    Advice on same sizes vs population.

    Hello, I have a survey where there will be a known population and a number of people sampled from within the survey population. What I'd like to know is what sample size I should use to receive a certain margin of error which will be set at a constant 5% with 95% confidence. I would...
  16. F

    Approximation of Gaussian integral arising in population genetics

    The following problem arises in the context of a paper on population genetics (Kimura 1962, p. 717). I have posted it here because its solution should demand only straightforward applications of tools from analysis and algebra. However, I cannot figure it out. Homework Statement Let z = 4...
  17. T

    Differences between population lifetime and dipole moment lifetime

    Reading a book about atomic transitions i really don't understand physically what the book means when it talks about differences between the population lifetime and the dipole lifetime that appear in the coerence part of the density matrix of a 2 or a 3 level system. I imagine that the...
  18. B

    More human population = greater mass?

    Hi everyone! This is my first post on this forum so please, if I have missed something please let me know! I have a lot of questions to ask but this is the main/first question in my mind right now! As I understand things, everything in the universe has mass (or anti-mass) and everything that...
  19. B

    Help me Diff Equation population model

    Homework Statement The population x of a certain city satisfies the logistic law dx/dt = x/100 - x^2/10^8 where time t is measured in years.given that the population of this city is 100000 in 1980,determine the population as a function of this for t>1980 .In particular,answer the...
  20. C

    Occupational Distribution Of Population

    Homework Statement Help! I just came across this question: A review of occupational distribution of population from time to time help help us to know the A. rate at which the population grows B. number of people that make up the labour force C. effciency of the working population D...
  21. Y

    Population Ecology Homework: Solving for N After Year One

    Homework Statement A flock of 10 Kolea birds going back to its mating grounds in Alaska from Hawaii gets blown off course and lands on a small island in the Aleutian (with no other Kolea birds) that is 25 km2 and has tundra habitat. The birds are known to have an intrinsic growth rate of 1.8...
  22. J

    Chromosphere population inversion?

    Assuming you could put two mirrors (one half-silvered) into the chromosphere, stationary, without them vaporizing/warping..., could they form a resonant chamber and produce laser radiation?
  23. S

    Cubic Population Model with steady states

    Cubic Population Model with steady states ! I am unsure as what this question means: Consider the cubic population model: dN/dt = cN(N-k)(1-N) where c>0 and 0<k<1 If the the initial populations is N_0 describe without proof the future of the population, distinguish the various cases on...
  24. G

    Method of characteristics for population balance equation

    Homework Statement The PDE: ∂n/∂t + G∂n/∂L=0 The initial condition: n(0,L)=ns The boundary condition: n(t,0)=B/G The parameter B and G above are dependent upon process conditions and change at each time. They can be calculated with adequate experimental data. Homework Equations...
  25. M

    Which Factor Does Not Change Homozygous and Heterozygous Frequencies?

    Homework Statement Which of the following is not a factor that causes changes in the frequency of homozygous and heterozygous individuals in a population? a. mutations b. migration c. random mating d. genetic drift The Attempt at a Solution I know that mutations is a factor, so cross...
  26. R

    Variance of a weighted population

    Homework Statement Homework Equations The Attempt at a Solution Was able to get the population mean of 5.3 with 4*.2 + 5*.4 + 6*.3 + 7*.1 But for some reason I'm drawing blank for the variance (which i guess is .81)
  27. M

    MHB Calculating probablity that random subset of population contains duplicates

    Hi, Apologies that this is basic question but I have to start somewhere! (-: The problem is succinctly stated in the msg title but, in greater detail; I'm working with some biological data from which samples have been taken. The sampling should have been at random. The samples include...
  28. 9

    Sample statistics vs population statistics

    Homework Statement My task is to explain why the sample statistics I have obtained differ from the population statistics I have obtained from some data - using "concepts taught in class, if they exist". I have calculated x̄ and s, as well as σ and µ. Homework Equations First of all, the...
  29. A

    How can I test the difference between two sample means from SAME population?

    Here is the scenario: Let's say that two sets of samples (SET 1 and SET 2) are from the same population (N=1000). SET 1 and SET 2 has the same sample size (n=500). SET 1 is composed of doctors only, and their average (mean) price that they are willing to pay for a certain product (a new drug) is...
  30. T

    Linear Algebra, Urban population dynamics Author: Bernard Kolman

    Homework Statement Linear Algebra Project : Urban Population Dynamics This project is about population modeling and how linear algebra tools may be used to study it. Background Population modeling is useful from different perspectives : 1. planners at the city, state, and national level...
  31. S

    How Does the Alligator Population Change Over Time in a Swamp?

    This has been posted before but i didn't understand the answer Suppose the number x(t) (with t in months) of alligators in a swamp satisfies the differential equation dp/dt = 0.0001x^2 - 0.01x (a) If there are initially 25 alligators in the swamp, solve this differential equation to...
  32. MathWarrior

    Population Growth Differential Equations

    Homework Statement A biologist prepares a culture. After 1 day of growth the biologist counts 1000 cells. After 2 days he counts 3000. Assuming a Malthusian model what is the reproduction rate and how many cells were present initially. Homework Equations P(t) = Ce^{rt} The...
  33. S

    Deriving Logistic Population Model (ODE question)

    Homework Statement Solve the logistic population model: dP/dt=rP(1-P/C); P(0)=P_{0} 2. The attempt at a solution First, I separated variables to get: \int \! \frac{1}{P(1-P/C)} \, \mathrm{d}P = \int \! r \, \mathrm{d}t Then, I took the left hand side and split into partial fractions: (1) -...
  34. G

    Understanding the Impact of Fishing on Fish Population Growth

    Hey everyone, I'm new here and wanted to see if I've gotten this question right, thanks in advance. 1. Consider a lake that is stocked with walleye pike and the population of pike is governed by the logistic equation: P' = 0.1P(1-P/10) where time is measured in days and P in thousands of...
  35. M

    How are error margins determined without using an integer for population?

    My first post on these forums, was referred here by a friend of mine. Thanks in advance! Mind that this question is coming from a BA in psych's worth of understanding: If I understand correctly, estimations of error margins are based on the relationship between a population and a sample of...
  36. G

    Harvesting Fish: Examining Population Models

    Homework Statement I only need help with problem 16 but included problem 15 because it is referenced in problem 16. 16. Suppose that the growth-rate parameter k = 0.3 and the carrrying capacity N = 2500 in the logistic population model of Excercise 15. Suppose p(0) = 2500. (a) If 100...
  37. D

    How to Calculate Population Change in the United States?

    Homework Statement Let b(t) be the number of births in the United States at the end of year t, and let d(t) represent the number of deaths in the United States at the end of year t. If p(t) is the population of the United States at the beginning of year t, write a function c(t) that...
  38. S

    Differential Equations - Population Growth

    Would anyone be able to go through some of the steps for these problems? 1. The birth rate in a state is 2% per year and the death rate is 1.3% per year. The current population of the state is 8,000,000. a) Write a differential equation which models the population of the state. Be sure to...
  39. K

    News Can Shifting Dietary Patterns Reduce Global Hunger?

    Most of the world consumes non vegetarian food significantly. http://en.wikipedia.org/wiki/Virtual_water#Agricultural_products" compares the virtual water requirements of various food products :- I am showing the water requirements just as an example. But even land required to produce 1 kg...
  40. D

    Boltzmann Distribution Relative Population of 2 atomic states

    Homework Statement The relative population of two atomic population states in equilibrium is given by Boltzmann Distribution: n1/n0 (proportional to) e^(-ε/(κT)) , where ε is the energy difference between the two states, T is the temperature and κ is the Boltzmann constant = (1.38 x...
  41. M

    News How big should the US population be?

    I was listening to the news today, and the issue touched briefly on population size. And, for fun, I was just wondering how big people in the US think their population size should be. This is meant to be informal, just imagine how you would like your country to look a century from now.
  42. P

    Simple population growth problem

    Homework Statement At the beginning of the Gold Rush, the population of Coyote Gulch, Arizona was 365. From then on, the population would have grown by a factor of e each year, except for the high rate of "accidental" death, amounting to one victim per day among every 100 citizens. By solving...
  43. micromass

    IQ-test: only 12% of the population can solve this

    [PLAIN]http://chzmemebase.files.wordpress.com/2011/09/memes-quickly-now1.gif
  44. J

    Population growth carrying capacity on a logistic model

    Homework Statement Here is the equation I am given. I'm supposed to find the carrying capacity. dp/dt=.05P-6.6666667e-5P^2 I know the general solution is rp-rp^2/k with k=carrying capacity, but the addition of the middle term has thrown me off. The Attempt at a Solution I tried...
  45. 1

    Rate of change of fish population.

    Homework Statement The population of a species of fish is given by the equation below. Where t is time in years. What is the rate of change of the fish population after 5 years? Homework Equations P(t)= 1.2 x 10^8(1+0.02t)^ -2 where t is time in years The Attempt at a Solution...
  46. C

    Population mean help, Statistics

    Homework Statement Assume that the population is normal with some unknown mean and standard deviation of 25. A sample size 400 is taken. The resultant sample mean is 67. a.) What is your best estimate for the value of the population mean? b.) What is the value of the standard error...
  47. T

    Statistical Thermodinamics: how many ways to make a set of population?

    Hi everyone! Here's my problem of the day: Let's take a box containing 3 identical (but distinguishable) particles A B C. Let this be a canonical ensamble. Suppose that A has energy \varepsilon_0 and both B and C have energy \varepsilon_1. We thereforre have 2 energy level, n_0,n_1...
  48. T

    How many ways to realize a set of population?

    Hi everyone! Here's my problem of the day: Let's take a box containing 3 identical (but distinguishable) particles A B C. Let this be a canonical ensamble. Suppose that A has energy \varepsilon_0 and both B and C have energy \varepsilon_1. We thereforre have 2 energy level, n_0,n_1. Take the...
  49. N

    High school math (population & exponents)

    Homework Statement 7. Between 1950 and 1989, the world’s population grew by 1.85%/a. (a) Determine the doubling time for this example. (b) If the population in 1950 was 2.5 billion, what was it in 1989? Homework Equations dt = 72%/growth rate The Attempt at a Solution a. dt =...
  50. S

    Can Intense Laser Pumping Induce Lasing in a Two-Level System?

    Homework Statement Assume a two-energy-level system with energetic separation between the two levels of 10000 cm-1 (as you can easily see, λ = 1 μm equals 1/λ = 10000 cm-1, and E ∝ 1/λ, i.e. the unit [cm-1] defines an energy). a) What is the thermal population in the upper level? b) If you pump...
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