Structure Definition and 1000 Threads

A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as biological organisms, minerals and chemicals. Abstract structures include data structures in computer science and musical form. Types of structure include a hierarchy (a cascade of one-to-many relationships), a network featuring many-to-many links, or a lattice featuring connections between components that are neighbors in space.

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  1. T

    Galactic Structure: Do Astrophysicists See Stars Where They Are Now?

    when astrophysicists study the structure and rotation of galaxies do they take into account that we are seeing the stars in it where they were at different times, we aren't seeing them where they actually are now? Say stars on the closest edge are 100,000 light years away but stars on the...
  2. G

    GaP Band Structure: Find Paper & Reference

    Hi again, first of all i want to thanks the replies to my previous posts. Second... I'm looking for a paper about the GaP band structure. Actually i only need the band structure tu compare it with mine but i need the reference to that paper, can you help me?? sorry for my bad english by the way...
  3. L

    What Determines the Secondary Structure of a Protein?

    [SOLVED] Secondary structure of protein. 1. What determines the secondary structure of a protein? 2. I do not fully understand this question, does it mean the two general types of secondary structure a-helices and b-pleated sheets. Or does it mean by how we determine them DSSP code. And...
  4. N

    Quark Structure of Particles & Antiparticles: Rules & Order

    I am asking this question because I did not get it clarified in any of the books I have read. What is the rule for having the quark structure of an antiparticle given the structure of the particle?Is it always OK to put bar on the quark symbols of the corresponding particle? Specifically,I...
  5. S

    How many atoms are in the unit cell of graphite?

    Homework Statement How many atoms are there in the unit cell of graphite? 2. The attempt at a solution I know graphite is hexagonal crystal structure. hcp also know that hcp has basis of hexagonal lattice which as 2 basis atoms. is there some other info i need because the answer...
  6. C

    Cesium Chloride Crystal Structure

    I am working this problem... http://www.fiu.edu/~saulj/Teaching/Physics2/01-Electric_Force/CrystalStructure.html I got the answer to a as 0, but don't understand b.
  7. G

    Are These Two Structures Resonance Forms?

    Homework Statement Are these two structures resonance? if not why not? Homework Equations The Attempt at a Solution I drew these resonance forms myself, but the answer book didnt' have this resonance structure in its answer and i wanted to know if this indeed is a...
  8. C

    Truss Structure Dilemma: Determining Compression and Tension Forces

    Homework Statement I spent a few hours trying out this question, so I probably need help. This is a seven pin-jointed structure mounted on the wall, with the following information given: 1) S1 and S2 are wall supports, but S2 is assumed to have no friction with the wall i.e. no vertical...
  9. N

    Action vs Structure: Can Life Be Categorised?

    Do you think that it maybe possible to categorise life by actions rather than by structure?
  10. R

    Why Might a Program Incorrectly Represent Resonance Structures?

    [SOLVED] Resonance Structure #3 Homework Statement Can't seem to figure this one out either...I think the program may have the charges messed up...usually if i post the same exact problem as the answer, it tells me that the answer is the same as the original problem...but with this...
  11. R

    Solve Lowest Energy Resonance Structure

    [SOLVED] Resonance Structure Draw the lowest energy alternative http://img87.imageshack.us/my.php?image=82956480uh8.jpg I can't figure out what I am doing wrong, but I've tried everything..any help?
  12. B

    Genetic Structure: Does Age Affect It?

    Does your genetic structure change as you get older? I guess it's just the levels of NFKappa and things iike that that change?
  13. E

    Math behind tipping/toppling a column or vertical structure

    I want to know where to look for information relating to toppling. I have looked at stability of equilibrium but the real question is: If say for arguments sake, there is a column 2m high and 1/4m wide - it would be easy, if we knew the weight of the column, to establish the force required...
  14. A

    What Might the Atomic Structures and Properties of Atoms 117 & 119 Be?

    what would the atomic structures of atoms 117 & 119 look like and what properties would these elements have?
  15. D

    Chemistry Differences in Structure of Steroid, Phospholipid & Fat Molecules

    Homework Statement what is the difference between a steroid molecule, phopholipid, and fat molecule?Homework Equations discuss the general difference in their structuresThe Attempt at a Solutionphospholipids are asymetrical with a hydrophilic head and a hydrophobic tail and the other two are...
  16. P

    Bismuth Bulk-electronic structure

    hi all as known, Bismuth is a semi-metal. the question is: What is the characteristic of the electronic structure of this family (Semi-metal).
  17. S

    Geometrical Structure: Uncovering the Mysteries of Matter?

    Would a geometrical structure following a single set of simple rules when it tessellates that: 1) Predicts the mass ratio of the electron to the proton 2) Derives and explains the fine structure constant 3) Explains the reason for only 3 generations of matter 4) Predicts the electron...
  18. E

    How Do Electron Spin and Proton Movement Influence Hydrogen Atom's Structure?

    Homework Statement I am trying to see if I understand these corrections to the hydrogen atom: To explain the fine structure correction, we go to the electrons frame of reference, in which the proton is moving with velocity v. This produces a magnetic field according to Maxwell's equations the...
  19. C

    Good computer for running electronic structure calculations?

    Hi- We're thinking of purchasing Gaussian 03 for electronic structure calculations. I think the basic license only allows for it to be run on a single processor. Can anyone recommend a decent desktop <1500 dollars that will do a decent job at running electronic-structure? I suspect that...
  20. A

    Crystal Lattice/crystaline structure

    Hi, I've got a question, I recently got interested in piezoelectricity. I almost no nothing about it tho. From the wiki artcile I gathered that when a force acts upon a piezoelectric material and deforms its shape, an electrical potential is created. I know that it has many applications in...
  21. H

    What Is the Significance of the Fine Structure Constant 1/137?

    The dimensionless pure number 1/137 obtained from the bohr theory (e^2/2hc epsilon_0) is given a particular name 'The Fine Structure Constant'. What is the significance of this number? Why has this value a name?
  22. M

    Least amount of structure for vector space.

    Hello all. Back to basics again. When defining a set of geometric vectors for a vector space of n dimensions how can we define such a set without a certain amount of structure already defined upon the n dimensional space. We presumably need some concept of direction to determine linear...
  23. S

    Materials Engineering (Crystal Structure) - C/A Ratio?

    Hi there, This may be a very basic question, but I have almost no knowledge of chemistry, unfortunately! Homework Statement Beryllium (Be) is a HCP metal with an atomic weight of 9, an atomic radius of 0.112nm and a density of 1850kg/m^3. Calculate its c/a ratio given that Avogadro's Number...
  24. L

    What Is the Fine Structure Constant in Physics?

    Recently I read about element 137 (feynmanium / Untriseptium ), the element which would theoretically have its electrons moving faster than light (if I understood it the right way). I know that if you involve relativity in the analysis, the problem occurs in element 139, but that's kind of...
  25. S

    Electronic structure of the atoms

    I'm a little confused about something very simple. From a chemistry perspective I am told about how many electrons fit into each type of orbital. For instance, 1s and 2s can only have two each, the 2p orbitals total 6. It is composed of the Px, Py, and Pz and only two can be in each set, while...
  26. K

    The dimension of the fine structure constant

    Everyone "knows" that the fine structure constant (alpha) is a dimensionless number, but I am troubled by the fact that the Planck unit of resistance must be one - if that is true - and that strikes me as suspicious. I wonder if anyone can shed any light on this. I present the complete...
  27. A

    The modern Large-Scale Structure of Spacetime book

    The modern "Large-Scale Structure of Spacetime" book Ever since I started reading Hawking's classic "Large-Scale Structure of Spacetime", written in 1973, I always wished that there was a more up-to-date book on general relativity that uses the book's level of mathematical rigour. But every...
  28. L

    Help with Questions on Membrane Structure, Proteins & Vitamin E

    I have some questions that i am not sure...can u guys help me out ? 1. Which of the following is the best phrase to describe the modern view of membrane structure? a. Membranes are lipid-lipid bilayers. b. Membranes are lipid-lipid bilayers with associated proteins. c. Membranes are...
  29. T

    Unifying M-Theory & Quantum Mechanics for Structure of Universe

    I am a Sophomore (not the college type) and I know next to nothing about the math that is involved here. But this is my career goal, so I am studying it as much as I possibly can. Now what I want to know is how to unify the M-Theory and Quantum Mechanics models of universe formation and...
  30. H

    Diamond Structure: Obtaining X-Ray Reflection Planes

    Hi everybody... I have a question and i hope u could help me. Consider the diamond structure as simple cubic with 8 basis atoms. obtain the first two planes contributing to x-ray reflection from the diamond structure.
  31. I

    Structure of Matter Homework: Find the Solution

    Homework Statement http://img528.imageshack.us/img528/6569/tempwv3.png Homework Equations unknown The Attempt at a Solution unsufficient amount of knowledge. Originally I thought this might've been a coefficient of friction problem with K as Kinetic energy and v as velocity... but that...
  32. L

    X ray diffraction For crystal structure Analysis

    1. Find the crystal structure , the lattice parameter of the metal. Known 2\theta of the peaks 17 21 28 33 35 41 45 46 2. bragg's law \lambda=2 d_{h,k,l} /b]sin^{2}(\theta) Also, the cubic interplanes distance d_{h,k,l} = a0/(squr(h^{2}+k^{2}+l^{2}) [b]3. The Attempt at a Solution ...
  33. S

    Structure R^k and midpoints of vectors (rudin's PMA chapter 1 problem 16)

    First this is NOT a homework problem. I am undertaking a self-study of mathematical analysis by following Rudin's Principles of Mathematical analysis. I have done a course in analysis before but this is a high-powered review of sorts. So I'm currently on the first chapter's problem set and...
  34. S

    Structure R^k and midpoints of vectors

    First this is NOT a homework problem. I am undertaking a self-study of mathematical analysis by following Rudin's Principles of Mathematical analysis. I have done a course in analysis before but this is a high-powered review of sorts. So I'm currently on the first chapter's problem set and...
  35. marcus

    Three video-talks on the CMB and structure of universe

    Joao Magueijo. Cosmologist at London Imperial, and Perimeter Institute. Three introductory lectures on the CMB observation and interpretation The first talk is a light intro to the technology, the software that does the mapping, and the analysis that derives the power spectrum (what...
  36. L

    How Does Electron Energy Affect Atomic and Nuclear Dimensions?

    I need help with these two questions: 1. Electron diffraction can be used to investigate both the arrangement of atoms and the dimensions of nuclei. Explain how changing the energy of the electrons can be used to achieve this. And... 2. Uranium has atomic number 92. Two of its common...
  37. B

    Understanding the field structure for A_5 and more

    Something I've been reflecting about: Question 1: Given any degree 5 polynomial f over the rationals, what are the conditions on the roots of f if I want its Galois group to be isomorphic to the alternating group A_5? I know that if f is an irreducible degree 5 polynomial with 3 real...
  38. B

    Electronic structure - Outer shell

    Can someone tell me how the outer shell structure is determined from the electronic structure. I know i can look this up but I'd like to know how it is derived and are there any rules I should follow so i can determine them myself?
  39. T

    Smilga paper, in which he derives an estimate to the fine structure constant

    I've been trying to figure out this paper by W. Smilga: Spin foams, causal links, and geometry-induced interactions I don't have the knowledge and background to be able to determine whether his derivation of an estimate to the fine structure constant is interesting, or just a trick. I am...
  40. jal

    An experiment showing a structure from 10^-18

    The Ashoori group is claiming to have a picture of the ACTUAL energy density. (NOT the "wavefunction" associated with the particle). Something does not add up. We should not be able to “see” the energy density of something as small as 10^-18. -------------...
  41. J

    Dispersion relations in diamond crystal structure

    I know acoustic and optical phonons can interact with one another. Also, longitudinal and transverse phonons can interact with one another. I am wondering can a longitudinal phonon in one plane act with a transverse phonon from another plane to create a third phonon? Or, do these...
  42. C

    Galilean structure, inertial system and two bodies

    Say I have two bodies, idealized as points with mass, in Galilean spacetime A^4. When thinking about the 2-body problem (just two bodies with interaction forces in the entire universe), one usually goes from the 3-dim. to the 2-dimensional problem using some special idea. I read the following...
  43. C

    Analysis of Truss Structure: Horizontal Component at Hinge?

    If the loads are all vertical in a truss, will there be horizontal component on the hinge of the given truss? Does the presence of the horizontal component depends on the design of the truss?
  44. J

    Symplectic structure vs. metric structure

    Symplectic structure vs. metric structure A question about the relationship between the phase space of the Hamiltonian formulation of classical mechanics and of the Lagrangian formulation; that is, between the cotangent bundle of configuration space, T*Q, which has a natural symplectic...
  45. J

    Mathematica Can Quantum Mechanics Be Expressed as a Specific Mathematical Structure?

    My question is: can we say that QM can be expressed as a given mathematical structure? More precisely, GR can be understood easily as "something to do" with differential geometry (even though some authors, like Weinberg, prefer not even to talk about DG when talking about GR). You have your...
  46. N

    Forces on an unusual supporting structure

    Homework Statement The frame must support a weight of 10kg, approximately 0.5m above the floor. The weight is suspended from the top of a vertical elipse shape, of which 1 side is missing. The bottom of the half elipse rests on a base. It looks like a slightly straighter "C" with the weight...
  47. Z

    Atomic structure and classification studies

    Kindly give me a link to some place I can study about Atomic Structure and Periodicity/Classification for IIT-JEE
  48. M

    What is the structure of NaN3? Why is N2 gas, and P solid at STP?

    Here are the two questions: 1)What is the structure of NaN3? 2)Why is nitreogen gas whereas phosphorus is solid? Keep Smiling Malay
  49. S

    Aircraft structure (thin walled closed section beam)

    Figure shows the cross section of a single cell, thin walled beam with the horizontal axis of symmetry. The direct stresses are carried by the booms B1 to B4, while the walls are effective only in carrying shear stresses. Assuming that the basic theory of bending is applicable, calculate the...
  50. S

    Problem 9.17 aircraft structure, Megson

    does anyone know the solution of problem 9.17 of the book Aircraft structures for engineering students or help me with how to approach to solve the problem. regards,
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