What is Structure: Definition and 1000 Discussions

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. E

    Internal forces in members of structure

    what are the internal force in the hinged member 1-4?
  2. T

    Sn1 Reactions: Substrate structure vs leaving group stabilit

    Homework Statement Let's say I have two compounds in an identical solvent. The compounds are also identical except for the following: One has a Br bonded to a tertiary carbon, and the other has an I bonded to a secondary carbon. Which would react first in an Sn1 nucleophilic reaction...
  3. S

    My Proof of Structure Theorem for Finite Abelian Groups

    Hello! If anybody has a minute, I'd appreciate a quick look-through of my proof that a finite abelian group can be decomposed into a direct product of cyclic subgroups. I'm new to formal writing (as well as Latex) and all feedback is greatly appreciated! Thanks in advance for your time...
  4. H

    Does (R × Z,+, ·) Form a Ring Without a Multiplicative Identity?

    Homework Statement Let (R,+, ·) be an algebraic object that satisfies all the axioms for a ring except for the multiplicative identity. Define addition and multiplication in R × Z by (a, n) + (b,m) = (a + b, n + m) and (a, n) · (b,m) = (ab + ma + nb, nm). Show that (R × Z,+, ·) is a...
  5. T

    How to draw Lewis structure of molecules with N

    Many times, I find it hard to draw correct Lewis structure of molecules with nitrogen. For instance: the Lewis structure of H2CNN. I thought it should be double bond between C and N and single bond between N and N, like this: But actually it's not. I have done many problems like this wrong...
  6. Saitama

    Solving for Volume of 3-D Structures

    Homework Statement (see attachment) Homework Equations The Attempt at a Solution How the equation ##x^2+y^2-x=0## is that of a cylinder? That looks to me an equation of a circle. I haven't learned about the different 3-D structures so I tried solving this using graphs. I tried to...
  7. M

    Calculating Torque to Uprighten Structure: A Beginner's Guide

    Homework Statement Hi All, I am new to this forum and have a question for which I need some assistance. My knowledge about this subject is limited, but I need te following: For a project we need to specify the torque required to uprighten a structure when rotated to a certain angle. The...
  8. Safinaz

    What are the SU(3) structure constants and how can they be calculated?

    Hi, How can I calculate such terms d^Aae d^ebD f^AaE f^EbD d^Aae d^EbD f^AaE f^ebD Cheers, Safinaz
  9. P

    Largest structure in the universe discovered so far

    Just saw this http://www.space.com/19220-universe-largest-structure-discovered.htmlarticle about a quasar group that's 4 Gly long. Not to speculate too much, but any thoughts on how much of an impact this could have on our current models and understanding of the formation of the universe? The...
  10. D

    Exploring the Darwin Term in Hydrogen Fine Structure

    I'm trying to do a HW involving the Darwin Term in the fine structure of hydrogen. I'm given that the perturbation from the Darwin term is equal to (times a constant factor which I'll ignore), V_D = [p_i,[p_i, \frac{e^2}{r}]] = e^2\vec{p}^2\frac{1}{r} -2e^2\vec{p}\frac{1}{r}\vec{p} +...
  11. S

    Upper limit to size of Air Supported Structure?

    Upper limit to size of Air Supported Structure?? Hey yall! I am new here, and I'd like to ask a question I can't seem to get an answer to anywhere else, so why not get it here! I'll get right to it! The question is...What is the upper limit of an air supported structure, and what is the maximum...
  12. E

    Crystal Structure: rc/ra = 1, <.23, >1

    What would be the structure of the crystal if rc/ra=1? hexagonal closed packed or anything else? What would be the structure of the crystal if rc/ra< .23 ? What would be the structure of the crystal if rc/ra>1 ?
  13. H

    Band structure and electric field

    Suppose an electron in a crystal(periodic potential) has the Bloch wave function \psi (k_0,x) at t=0. Applying a constant electric field E(at t=0), the electron would still have Bloch-type wave function at any time t with k(t)=-(1/\hbar) eEt+k_0. Now According to this formula for k(t), one can...
  14. O

    Half-edge data structure in 3D?

    Hello Everyone I'm currently working on a unstructured quadrilateral mesh for a discontinuous galerkin free surface flow model. I use the half-edge data structure in the two dimensional code. Does something like a half-edge or "half-face" three dimensional data structure exist. Otherwise...
  15. Greg Bernhardt

    March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure

    Author: Jerry March, Michael B. Smith Title: March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure Amazon Link: https://www.amazon.com/dp/0471720917/?tag=pfamazon01-20 Prerequisities: High-School Chemistry Contents: User comments...
  16. N

    K41 Kolmogorov scaling relation and structure functions (turbulence)

    Hi there. I am having trouble interpreting the Kolmogorov K41 scaling relation for homogeneous and isotropic turbulence: S_{p}(l) = <\delta u(l)^{p}> = <|u(r+l) - u(r)|^{p}> \propto (\epsilon l)^{p/3} where l is the length of displacement between two points under consideration in the...
  17. T

    Thought this would be interesting - largest structure in Universe Discovered

    Largest Structure in Universe Discovered By Mike Wall | SPACE.com Astronomers have discovered the largest known structure in the universe, a clump of active galactic cores that stretches 4 billion light-years from end to end. The structure is a large quasar group (LQG), a collection of...
  18. S

    Establishing a smooth differential structure on the ellipsoid

    Homework Statement Construct a C∞ natural differential structure on the ellipsoid \left\{(x_{1}, x_{2}, x_{3})\in E | \frac{x_{1}^{2}}{a^{2}}+\frac{x_{2}^{2}}{b^{2}}+ \frac{x_{3}^{2}}{c^{2}}=1\right\} Is this diffeomorphic to S2? Explain. Homework Equations Do I need to prove...
  19. L

    Using magnetism to control the structure of concrete

    So this is my idea: make concrete using iron sand, preferably one with a decent ferromagnetic interaction. As the concrete sets, apply a magnetic field. The ferromagnetic particles align to the field creating a structure within the concrete. Possible to coat the iron sand in a retarding...
  20. F

    Diffeomorphisms, Differential Structure, ETC.

    I'm trying to understand the difference between diffeomorphisms, diffeomorphism invariance, reparameterization invariance, and differential structures and how each of these terms relate to physics. Perhaps there's a book out there that explains the differences between these constructs and the...
  21. pairofstrings

    Dynamic memory allocation and structure fields

    Please take a look at my program. Please help. I want to allocate memory dynamically for one field in structure. I tried to write the code but it has error. I posting a paint document for you to see. Help me please. Please tell me why is my code not working properly and what needs to be done...
  22. edguy99

    Does oxygen in water have an sp3 orbital structure?

    The angle of the water H2O molecule is 104.5°, the angle of ammonia H3N is 107°. The angle between 2 p-orbitals is 90°, the angle between 2 sp3 hybrid orbitals is 109°28', the tetrahedral angle. Why is it assumed that water is a "greatly" expanded p-orbital angle, rather then a "slightly"...
  23. S

    First direct image of DNA showing the Double-Helix structure

    The Daily Mail Even as a novice in biology, I found this amazing and had to post it here.
  24. A

    Why Do SO2 and XeO4 Form Different Types of Bonds?

    The S molecule of SO2 forms a double bond with one O and dative covalent bond with another O Meanwhile,XeO4 is a molecule which Xe forms a double bond with each O I have a question here Why doesn't that S forms 2 double bonds with O to extend its octet structure? Similarly,why doesn't that...
  25. E

    Determining a statically indeterminate structure

    Is this structure statically indeterminate? I'm thinking it actually statically determinate, since there are three unknowns (Ax, Bx, By) and three equations. The external loading Px, Py are known. I also solved for the forces in the members of the truss and they seem to work out, but my...
  26. Telemachus

    Understanding the Lewis Structure for NSF: N≡S-F and Formal Charges Explained

    Hi there. I have to determine the Lewis structure for NSF. So first I thought of something like this: N=S-F, with the nitrogen with four free electrons, the sulfur with two, and the fluorine with six. The formal charges gives -1 for Nitrogen, +1 For sulfur, and 0 for Fluorine. But the...
  27. aphirst

    1D Finite Planar Photonic Structure - Transfer Matrix Method

    Homework Statement I'm implementing the transfer matrix method (manually) for an EM wave through a 1D layered structure. Basically I'm just considering a plane wave in the positive-x direction, conserving E and H across each material interface, and constructing interface matrices, the...
  28. X

    Real-Life Aerospace Structure Buckling Example Needed

    Can someone give me a real-life example of an aerospace structure buckling? I need a real example to discuss column buckling theory..etc. I couldn't find any online. Thanks.
  29. P

    Stellar structure - Helium burning

    1. The problem statement. Calculate the energy generated per unit mass, if helium burning produces equal amounts (mass fractions) of carbon and oxygen. mH = 1.672621581 x 10^-27 kg 2. The attempt at a solution Helium burning produces carbon according to the following reaction: 3He -> C...
  30. P

    Lewis dot structure of nitrate ion

    I'm wondering if anyone can help me with the reasoning for what follows, I'm thinking I must just be missing something quite obvious but I can't seem to see what that is at the moment! :redface: I understand how to get the structure by starting from a 'skeleton structure' and just filling in...
  31. B

    Physics as an interface to underlying structure

    I have put down https://dl.dropbox.com/u/6040582/CategoricalPhysicsAug26_2012.pdf on how we can start to see physics as an interface to underlying "structure". "Structure" is posed without its normal qualifier "Causal" and it will become more clear why I am doing this if you read the paper. Does...
  32. C

    Is the Hydrogen Energy Level Formula Truly Degenerate in j?

    Griffiths writes that the formula for the hydrogen energy levels taking fine structure into account "breaks the degeneracy in l" but "still preserves degeneracy in j." I'm confused by this, because the formula he gives (Eq. 6.67 in the textbook) depends on j. How can the system be degenerate...
  33. C

    Can this truss structure be statically indeterminate?

    I have designed this truss but I'm reading on the internet that this equation, 2j = m + r IS NOT enough to determine whether a structure is statically determinate. It has to do with the arrangement of the members as well? How can I tell beyond the equation I guess is my question? Also...
  34. R

    Crystal Structure & Metallic Bond: What Comes First?

    For metals for instance, is the metallic bond that determines the crystal structure(i.e. FCC (face centered cubic), HCP (hexagonal close packed)) or is the crystal structure that determines the type of bond? In other words, if someone were to ask me what kind of bond an element with an FCC...
  35. S

    What are the different ways bonds can be represented?

    In the following link http://en.wikipedia.org/wiki/File:Silicon-tetrafluoride-2D-dimensions.png the bonds are represented pictorially in different ways(like the black triangle). Do these just show the physical structure of the bonds or do they show the different types of bonds?
  36. S

    Interpreting an Answer to Graph Structure Function

    Homework Statement This isn't a homework question. I'm working through my book's exercises and am having difficulty interpreting an answer. Any guidance will be very much appreciated. The problem is to come up with a structure function for a graph (image attached with this post). The answer is...
  37. S

    Could a universal Oort cloud structure cause expansive acceleration?

    Could a universal "Oort cloud" structure cause expansive acceleration? Could there be a giant sphere of invisible non-reactive matter (neutrinos?), left over from the big bang, so massive that it's gravity is pulling galaxies outward? I know the Oort cloud doesn't pull planets outward, but...
  38. soothsayer

    How Does String Theory's Concept of Finite Strings Impact Quantum Field Theory?

    Quantum mechanics tells us that particles have a wave-like nature: their position, momentum and energy are not absolutely defined, and obey the Uncertainty principle. One thing that strikes me as peculiar in String Theory is how much internal structure string appear to have at the Planck...
  39. M

    Discovering a Protein's Primary Structure: Methods and Strategies

    hello! what are the available methods to determine the sequence (primary structure) of a protein? from where one can start (what info he can gather) and how he can deduce the primary structure? thanks!
  40. H

    Where did Epsilon go in the Fine Structure Constant Equation?

    Homework Statement e is charge epsilon is permittivity Homework Equations e^2 = 4\pi \epsilon GM^2 The Attempt at a Solution This is just a question really because I am a bit confused about something. Was reading up on the fine structure constant and apparently the fine...
  41. S

    What is a High Gradient RF Structure

    Can anyone tell me what a high gradient RF structure is? I think it is referring to the strength of say an electric field in a structure oscillating at radio frequency but I am not sure. I would appreciate any explanation.
  42. E

    Structure of Dolphin Brain and Comparison to Primates?

    Dolphins have larger brains than humans. So, why aren't they smarter than humans... or, are they? Are those sneaky Dolphins playing dumb? j/k It's my (very limited) understanding that the cortex is responsible for the higher levels of what we think of as intelligence. So, what's different...
  43. K

    Phonon Band Structure Quantum Atempt

    I found a lecture on the internet where a LCAO assumptions are used to calculate the phonon band structure. In this lecture (Here) we can find that the true Hamiltonian: H = \frac{p^2}{2m}+V_0(x) where V_0(x)=V_0(x+a) is replaced with the following aproximate hamiltonian: H\cong \sum_n...
  44. T

    Software/database for simple crystal structure design?

    Hello, Does anyone know any (free) software for generating simple crystal structures like forms of SiO2 or TiO2? It must be a really common problem. My current strategy is to search the web for hours until I get lucky. There are online databases which have really complicated structures from...
  45. D

    Structure of the Phonon Free Propagator

    Hey Everyone, I've a quick a question regarding the make-up of bosonic Green's functions, taking the free propagator for phonons as example. According to Mahan, 3rd ed. it is given by: D(q, \lambda, t-t')=-i\langle0|TA_{q}(t)A_{-q}(t')|0\rangle with A_{q}=a_{q}+a^{+}_{q} [ Eqs...
  46. M

    Understanding Group Structures: A Scientist's Perspective

    What does it mean to give a group structure? I'm working on a problem and part of it asks for the structure of the group. The law of composition and generators seem to be given already (and an expression that says that a^2 = 1 for any elt a of the group). Is there anything to do other than...
  47. L

    Change in fine structure constant

    What would be the consequences of slightly changing the fine structure constant, i.e. changing the strength of the electromagnetic interaction - but not changing gravitation or the strong force? In the everyday world? You might imagine that the strength of chemical forces etc. would change...
  48. A

    Viscous fingering and structure of space

    Everytime I see a picture of the large scale structure of space with matter arranged in a web like form, I come to think of the fenomenon of viscous fingering in fluids between to surfaces when they are moved apart. Since space is expanding as well, maybee these structures have something to do...
  49. B

    Super Structure - Evidence for Handedness Spiral Galaxies

    There is observational evidence for preferred alignment of spiral galaxies with alignment to the so called axis of evil in the CMB (cosmic microwave backgound 2.75K) data. http://arxiv.org/ftp/arxiv/papers/0707/0707.3793.pdf http://arxiv.org/ftp/arxiv/papers/1104/1104.2815.pdf
  50. S

    Understanding Crystal Structure Basics: Q&A with the Experts

    Hello experts! Q#1) Write down the family members of {110} plane in a cubic crystal. Attempted Answer) According to my study the this family has 6 members. But what are they? Are these the members (110),(101),(011),(-1-10),(-10-1),(0-1-1)? Q#2) Describe the method to construct the...
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