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. Q

    Fine Structure Constant appears to vary across the distant sky

    I guess I don't have much to say about this other than it's pretty amazing if it's true and I wanted to bring it to everyone's attention here. http://www.sciencedaily.com/releases/2010/09/100909004112.htm http://arxiv.org/abs/1008.3907
  2. R

    Question about alpha, the fine structure constant

    I understand that it's been determined to have a very small value. At the same time, it is also true that gravity is incredibly weak compared to the other fundamental forces. What I'm wondering whether there might be some relationship between them?
  3. T

    Exploring the Use of Topology in DNA Structure and Function

    I was wondering if topology has ever been utilized on the structure of DNA and how that applies to its functions? I am assuming that it has as this is one of the most obsessed over molecules in the 21st century. I am interested in this area of topology if it exists. Also I have no previous...
  4. quasar987

    Uniqueness of smooth structure

    How does one prove that the smooth structure on 2-manifolds is unique? Source? Thx!
  5. S

    The Entropy of Black Holes: Exploring the Structure of Matter

    I read recently that the entropy of a black hole is proportional to the surface area of its event horizon. Being that surface area is a two dimensional measurement, only requiring length and breadth, what does that say about the structure of matter contained in the event horizon? I'm not sure...
  6. bcrowell

    Fine structure constant probably doesn't vary with direction in space

    The thread "Fine Structure Constant Varies With Direction in Space!" was locked because it didn't cite papers published in refereed journals. Actually all of this stuff has been published in refereed journals. The list of references below is cut and pasted from...
  7. E

    Structure & bonding questions

    Homework Statement A) Potassium Methoxide, KOCH3 has both covalent & ionic bonds...Which are which? B) Why do you suppose no one has created a stable cyclopentyne molecule? C) How many electrons does a positively charged Carbon atom in a carbocation (C+H3) have? Why is it trigonal...
  8. S

    Fine Structure Constant Varies With Direction in Space

    Here's something profoundly earth-shaking: Thursday, August 26, 2010 http://www.technologyreview.com/blog/arxiv/25673/ A spatial variation in the fine structure constant has profound implications for cosmology -- What is going to have to be revised as a result of this discovery? What are the...
  9. W

    Fine structure constant increase with energy?

    Hi! Hope someone can help, I am currently studying an Open University course and I am a little confused by a statement in one of the textbooks. It says that the value of the fine structure constant increases with collision energy (in Electron/Positron annihilation). I am probably being...
  10. A

    Medical Which is the correct base structure of Penicillin?

    Hi, I have done quite a bit of looking about and I'm aware that there are many forms of penicillin... While looking at the base structure of penicillin i have found two different kinds... At a guess i'd say one is synthetic and one is natural form? Could someone possibly clear this up for...
  11. B

    Extending Trivializations and Structure Groups

    Hi, Everyone: LetB: E-->X be a line bundle, with scructure group G and X has a CW -decomposition. I am trying to understand why/how, if the structure group G of B is connected, then any trivialization over the 0-skeleton of X can be extended to a trivialization of the...
  12. D

    Protein structure, saccharides and fats

    Hi, Just need to clear up any misunderstanding about protein structure. Do all proteins have at least three levels of structure? If a protein has a quaternary structure, does it mean it also has primary, secondary and tertiary structures? I was wondering what separates a polysaccharide from...
  13. M

    Example of a differentiable structure on R

    Consider the manifold of the real-line R with a differentiable structure generated by the map x^3 : M \rightarrow \mathbb{R} . This example is given in a textbook I'm looking at, but I don't really understand how this can work. The inverse map is clearly not smooth at x=0. Do they mean that...
  14. abrogard

    How To Check A Simple Structure Design?

    I'd like to know how you check that some simple structure's design is adequate. I know that's bound to be a baby question for you engineers but, believe me, the answer isn't easy to get out there in the world for us non-engineers. If I, for instance, draw something like the frame of a...
  15. T

    Atomic Structure: Is It Necessary to Assume Orbits Are Circular?

    Please help me in clearing my basic doubt We all know that positive charges are concentrated at the centre of the atom , known as nucleus and electrons revolves around the nucleus in orbits. Is it necessary to assume that orbits are circular ?
  16. D

    MATLAB Troubleshooting: Passing String Inputs in Matlab's Structure Field Function

    For some reason, when I try to use this function it has a problem passing along the fname input. For example, I'd type something like : Field(S, 'names') ------------------------------ This returns an error: ? Reference to non-existent field 'fname'. Error in ==>...
  17. T

    X-ray structure analysis question

    Hello everyone! I have met such a curious thing: When chemists tried to synthesize CaCl by reducing CaCl2 with H2 they got CaClH instead, but the structure of a compound was determined using X-ray structure analysis which is not suitable for determining the position of light elemnts like...
  18. N

    Predicting Buckling Load for Thin-Walled Structures Using ANSYS/Nastran

    Homework Statement Finding the critical buckling load of a really short column with wide cross section (is it still considered a column?) E = 22 GPa Yield: 300 MPa Load: 28N thickness: 0.226 mm I = 670706.51 mm^4 (is this right?) Load Applied Area (as indicated by white arrows)...
  19. D

    A couple of discrete structure questions

    1. Explain how to find a shortest path between any given pair of vertices, given the length of edges connecting the vertices and the shortest distance between vertices (after doing the shortest-path calculation) So I am given a two matrices, as said one with length of edges connecting and the...
  20. J

    Quark Structure of Baryons: Sigma & Lambda

    Hi this isn't actually a homework question more my own curiosity/confusion. They have the same quark constituents and http://en.wikipedia.org/wiki/File:Baryon_octet.png" for both but mass and decay rate are different, please explain. (if the lambda is an excited state of the sigma why isn't it...
  21. 6

    Building a Submarine-Like Structure: Materials & Thickness for a Given Volume

    I´m trying to find approx. numbers or formulas for a submarine like structure to mantain a constant volume. For a given volume, which materials and to what thickness should the container be?
  22. V

    Fine structure diagrams-drawing program

    hey I was trying to draw some fine structure diagrams like this one but it is too slow and unflexible with normal graphic softwares. Does anyone know a good graphing software *expecifically* designed for atom structure diagrams like the above one? Thanks, valleyman
  23. C

    Calculating Iodine Number and Structure of Oil

    Hi, I understand that the iodine number is the number of moles of iodine reacting with one mole of fat/oil which indicates the number of double bonds present in the fat/oil molecule. However I am having trouble calculating them. Can someone show me how to solve the following question...
  24. H

    MEMS spring structure analysis

    Homework Statement I am trying to analyze this structure to find its resonant frequency when activated with a electrostatic comb drive for a lab report. I know how to find electrostatic force but what I'm not so sure on what models to use for the semi circular spring. Homework Equations...
  25. E

    What is the packing fraction for a body centred packed structure?

    What is the packing fraction for a body centred packed structure?
  26. H

    Transmission Electron Microscopy - Crystal Structure

    Hi I have a tutorial problem involving determining the ideal methods for identifying material properties of a layered semiconductor structure. The problem states to use either scanning or transmission electron microscopy. THe structure consists of several monolayers (around 5nm) of AlGaAs...
  27. M

    Torque required to rotate a composite structure

    Hi everyone I posted this in the classical physics forum but maybe it is more suitable for this forum. I'm currently trying to select 2 hydraulic motors to rotate a relatively sizeable structure, I'm hoping to rotate it through .5pi radians over a period of 30 mins (0.052 RPM), I'm hoping...
  28. C

    Solving Structure Factors for Cesium Chloride & X-Ray Diffraction

    Homework Statement I have the ionic compound cesium chloride and have been asked to use the equation p(k) = (sum over j) exp(-iK.r)f(k) to find the structure factor for x-ray diffraction from cesium and explain why it can take two values. It also asks how you would expect the intensities...
  29. M

    Rotating 306 ton Structure with 0.052 RPM - Help Appreciated

    Hi everyone just wondering if someone could help me with a problem I'm having on a piece of work atm, I'm currently trying to select 2 hydraulic motors to rotate a relatively sizeable structure, I'm hoping to rotate it through .5pi radians over a period of 30 mins (0.052 RPM), I'm hoping...
  30. N

    Complete Analysis of Rotating 2-arm structure

    Hey Guys, I have a dynamics problem I've been working on for a few days and I'm not quite sure that the results I've gotten are correct, or even if the way I'm approaching it is. The problem consists of 2 arms connected to each other by a movable pivot. However, the whole structure cannot...
  31. V

    Answer: Find Order of A, J, N and Subgroup of Each Possible Order

    I have a problem a group consists of following element A,B,C,D,F,G,H,J,K,L,M,N.How can we find the order of elements A,J,N? state the possible orders of the proper subgroups? Here is the group table ... A B C D F G H J K L M N A . C G J M B K A D N F H L B . F H L K A M B N D C G J C ...
  32. E

    Lewis structure, hybridization and VSEPR

    Homework Statement Consider the related molecules POF2- and POF3. Choose all the following statements that are correct for both molecules. Homework Equations A) P atom is sp3-hybridised B) The F-P-F bond angle will be approximately 109.5 degrees C) Geometry around he P centre is...
  33. E

    Inorganic crystal structure theory for linear birefringence

    There is a crystal structure relationship for circular birefringence which can tell you if a crystal structure will have circular birefringence and its handedness (left,right) (e.g. "On the origin of optical activity in crystal structures" J. Appl. Cryst. 1986. 19, 108-122, A. M. Glazer and K...
  34. E

    Inorganic crystal structure theory for linear birefringenc

    There is a crystal structure relationship for circular birefringence which can tell you if a crystal structure will have circular birefringence and its handedness (left,right) (e.g. "On the origin of optical activity in crystal structures" J. Appl. Cryst. 1986. 19, 108-122, A. M. Glazer and K...
  35. L

    Particle or Structure Physics: Which Career Path is Best for You?

    Hi everybody! I'm an italian student, I'm about to get my bachelor in physics, and naturally the next academic year I'm going to begin grad school. My problem is: starting with the fact that I'm with no doubt a theoretical physicist, i'd like to know if, as far as regards career, it will be...
  36. H

    Photon-to-baryon ratio from CMB structure details?

    Not sure if this is an easy question or not. The Wikipedia entry on the Big Bang, in its section on "Abundance of primordial elements," cites the 1988 book by Kolb and Turner (The Early Universe), in saying that the ratio of photons to baryons "can be calculated independently from the...
  37. S

    Estimating discharge at the outflow structure of a lake

    I am a fisheries biologist interested in manipulating a lake level by about six inches via a box cement outlet structure on a small lake. The outlet structure is currently governed by two adjacent 5ft by 0.5ft dam boards,which have historically been removed one at a time in the spring and...
  38. R

    Crystall Structure for Why Materials Tend to Fail in Tension

    why lot of materials tend to fail in tension rather then compression? please explain using crystall structure of material , suggest some pdf regarding to this topic
  39. D

    Band structure simulation using Snider program

    Does anyone have any experience using Gregory Snider's 1D Schrodinger/Poisson solver? I'm trying to do some simulations of a quantum well my group is studying, and I'm not sure if I'm doing something wrong or if the code is buggy or if I'm just interpreting the results incorrectly. Here's the...
  40. L

    Why Does the 'Sensor' Structure Cause Multiple Definition Errors in C?

    I'm actually getting pretty frustrated with this now. It makes no sense. I have this structure defined in detector.h //This structure contains all raw sensor data struct sensor_data { //ADC Values For Each Sensor int ADC_LOuter; //Outer Left Sensor int ADC_LInner; //Inner Left Sensor...
  41. L

    Fixing Syntax Error in C Structure for Robot IR Sensor Reading

    I have a function for my robot that reads multiple IR sensors, and I get a syntax error on the bolded lines. //Performs An ADC Reading On All RLS Channels //Reads left to right void ADC_All(void) { //Reads Left Outer Sensor SetChanADC(RLS_LOuter); ConvertADC(); while(BusyADC())...
  42. maverick280857

    Understanding Hadron Structure through Electron-Positron Collisions

    Hi, Halzen and Martin, on page 18 of their book, describe the resolution of hadron structure using virtual photons obtained by annihilating e+ and e- beams. In Figure 1.11(b), isn't the positron arrow shown wrongly? It seems to be moving forward in time. (Or maybe I'm just being picky...
  43. G

    Phase transitions: from the potential to the dynamical structure factor ?

    Hi everybody, I've just started studying phase transitions and symmetry breaking for my PhD and I've met something I'd like to understand better. When we study the local potential vs. the order parameter in a structural phase transition I see there are two limiting cases, the one in which the...
  44. D

    Solve the structure in the diagram below

    I have been asked to solve the structure in the diagram below where the arcs radius is R, and the force acting is P my question is whether this structure is at all stable?? surely the middle leg cannot resist and moment about about the joint at its top end and will fall (it only has a...
  45. D

    Is this another statically indeterminate structure?

    Is this another statically indeterminate structure? (urgent) Homework Statement [PLAIN]http://1.bp.blogspot.com/__d7SU8yZ6pk/S4JApel7HdI/AAAAAAAAAKo/NhmSNIOxNik/s1600-h/IBq4.jpghttp://1.bp.blogspot.com/__d7SU8yZ6pk/S4JApel7HdI/AAAAAAAAAKo/NhmSNIOxNik/s1600-h/IBq4.jpg Homework Equations...
  46. H

    Calculate the sparameters of a coplanar stripline structure

    how to calculate the sparameters of a coplanar stripline structure with 434microns breath 45microns height and 1950microns length fed with 1Win TE10 mode at 35GHz... can some one help me regards..
  47. M

    How to calculate the band structure?

    Hi, all, I want to calculate the band structure and there is example such like that: BandLinesScale pi/a %block BandLines # These are comments 1 0.000 0.000 0.000 \Gamma # Begin at Gamma 50 2.000 0.000 0.000 X # 25 points from Gamma to X 20 2.000...
  48. Loren Booda

    Extended structure of dark matter

    Since pure dark matter apparently does not have charge but has mass, might it be found in the galaxy's edge as something akin to uncharged black holes? Typically, pure dark matter is invoked as particles. Wouldn't they form aggregations under gravity? Extended (i.e., not particulate) dark...
  49. Z

    Chromosome Structure: Questions Answered

    I am in intro to genetics class and I am getting really confused with the terminology: -Is a chromosome made up of 2 sister chromatids? -are the 2 sister chromatids identiical? -what's the difference between chromatins and chromatids? and between the kinetochore and centromere? -gene...
  50. B

    Will My DIY Pipe Shelving Be Stable Enough?

    I plan on building shelving using 3/4" pipe and fittings. The general design is a 2 shelf system -180 degrees from each other around a center pole at different heights. I plan on bolting the center pole to a plywood base. Each shelf will hold between 5 and 100 lbs. I want to make sure its...
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