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. A

    What is the unit cell and coordinates for wurtzite crystal structure?

    As far as I understand wurtzite is the name given to the crystal structure defined by the stacking sequence ABABABAB.. However, I am having a hard time understanding what the unit cell is of wurtzite. From what I know the unit cell is the smallest repetitive unit and in it you specify the...
  2. A

    Understanding the Unit Cell of Wurtzite Crystal Structure: A Brief Overview

    My teacher wrote down something to day which I wish I had written down myself. It was about the crystal structure of wurtzite, which is an ABABABAB stacking of hexagonal lattices. What he wrote was two different specifications of the unit cell of wurtzite depending on which groups of elements in...
  3. locksmithdon

    Weight supporting structure. Help needed.

    Hello all. I need to build a weight supporting structure with the following requirements. At this point, I'm still in learning mode and need help understanding the appropriate terms and formulas to search for. Of course solutions are awesome too, but any direction forward would be most...
  4. Q

    N2O5 Lewis Structure and Bond Angle Analysis | 40 Valence Electrons

    Homework Statement Draw the best LS for N2O5, which studies show a) has a N-O-N central atom skeleton and b) Has a central atom bond angle of 180 degrees. Comment on the unexpected bond angle of 180 degrees around the central atom. Homework Equations There are 40 valence electrons...
  5. Math Amateur

    MHB Structure of R[X] and an exercise on ring adjunction

    I am reading R.Y. Sharp's book "Steps in Commutative Algebra" At the moment I am trying to achieve a full understanding of the mechanics and nature of LEMMA 1.11 and am reflecting on Exercise 1.12 which follows it. LEMMA 1.11 reads as follows: (see attachment)...
  6. Crazymechanic

    Why Do Identical Cast Iron Crankshafts Emit Different Pitch Sounds?

    Hi there , I have two cast iron crankshafts for an engine I'm building , now even though they are similar in every way , made ofr the same engine etc etc, there is one thing I noticed different and it got my attention , I took a stainless steel screwdriver and hit each one of the cranks at...
  7. Sudharaka

    MHB How Is the Structure Tensor Computed for Triangular 2x2 Matrices?

    Hi everyone, :) Here's is a question I have trouble understanding. Hope you can help me out. :) Specifically what is meant by the structure tensor and how is it computed when given a \(2\times 2\) triangular matrix? Problem: Write the structure tensor for the algebra \(A\) of traingular...
  8. mathbalarka

    MHB Semigroup Structure: Exploiting Non-Finitely Generated Monoids

    What are the best ways to exploit the structures of a given non-finitely generated cancellative commutative monoid? This is not the best way to put together a question, I admit, as what I am asking is very general, but I think it is best to put in here rather than the Chat Room. Also, is the...
  9. C

    Protein Secondary Structure Question

    Homework Statement 15) How is it possible that many different linear sequences of amino acids can form the same secondary structure (alpha helices, beta sheets, random coils, etc.)? I understand that alpha-helices, beta-sheets, etc. appear in tons of proteins and peptides, but I do not...
  10. V

    Preservation of Poisson Bracket Structure upon quantization?

    When (canonically) quantizing a classical system we promote the Poisson brackets to (anti-)commutators. Now I was wondering how much of Poisson bracket structure is preserved. For example for a classical (continuous) system we have $$ \lbrace \phi(z), f(\Pi(y)) \rbrace = \frac{\delta...
  11. U

    Where is the center of mass of this structure?

    Homework Statement So I'm taking the safe side by posting this question as a h/w problem, since even though its just to satisfy my curiosity, I don't want to take the risk of being penalized for putting a specific case like this one on another forum. Please look at...
  12. J

    Good books on practical molecular electronic structure theory?

    Does anyone know of a good code-oriented book on molecular electronic structure theory? I've been looking for a good modern book that teaches how to write SCF code to solve simple cases of the kind of problem that standard quantum chemistry packages (e.g. Gaussian, Orca) are used for without...
  13. A

    Are Moments Treated Differently than Forces in Beam Analysis?

    I am always wondering, when we are analysing beam structure where many externally applied moments are added on, why we can sum up all the externally applied moments and write equilibrium equations according to that. Because these moments are actually along different axes. Is it because in...
  14. Primroses

    Structure constants in Lie algebra

    I am studying QFT and got stuck on one question which may be simple. Why is structure constants (in Lie algebra) real and independent on representations? Can you give me a detailed proof? Thanks!
  15. LarryS

    Molecules Structure as Planar Graphs?

    I have read that the structure of almost all organic molecules can be represented visually as Planar Graphs, i.e. 2-dimensional lattice-like structures consisting of nodes (points) connected by lines in which no lines cross. From the perspective of Physical Chemistry, does anybody know why this...
  16. F

    Pin-jointed structure - Mechanics of Solids

    Homework Statement "A force F of magnitude 90 kN is applied at point C at an angle of 45°. The pin-joint B may be assumed to be resting on frictionless rollers. Determine the reaction forces at A and B" Image of the diagram here: http://i.imgur.com/jUL0rJe.jpg?1 Homework Equations two...
  17. M

    Statically Indeterminate Structure Advantages

    Hello, I was wondering why it might be advantageous in some applications to create a structure that is statically indeterminate? Thanks
  18. Q

    Lewis Structure; Non-bonding pair missing

    Homework Statement http://i.minus.com/jxoYt94CAd9LY.png Homework Equations The total number of valence electrons in SOCl2 is 6 + 6 + 7(2) or 26 valence electrons. Dividing by 8, this implies a total of three bonds formed with the central atom (the least electronegative atom, or...
  19. D

    Worst load cases lattice structure

    Introduction Dear all, I'm working on an assignment to model a ship-to-shore crane for a FEM design course. Having modeled the crane, I now need to apply the load of the trolley (which is hoisting the container) on the boom (which in my case is a lattice structure made up of beam elements)...
  20. B

    About the mathematical structure of wave functions

    Hello everybody Two questions concerning the notion of wave function. 1. Every quantum mechanics book describes the space of wave functions (or more generally of quantum states) of a given system as a Hilbert space. But correct me if I'm wrong QM also says that two elements of such a...
  21. M

    Determining internal force with section cut on structure

    Homework Statement Homework Equations The Attempt at a Solution Hello, my problem seems to be that I have two values that are possible for the Force FG, but I also am not considering the internal forces F_DE and F_FE. I'm not sure how to go about finding those if they are important for...
  22. S

    Magnetic Structure: Distinguishing Neutron Diffraction Data

    How we can distinguish between different type of magnetic structures by simply looking at neutron diffraction data??
  23. E

    Flat sheet-like structure approaching a massive object

    I'm thinking about a flat sheet-like structure approaching a massive object (maybe a black hole?). If it were to approach with the plane of the object tangent to the mass, it seems to me that eventually, with enough gravity, the sheet would end up looking much like those hokey "bowling ball...
  24. M

    Structural Forces and Unknowns: Solving for Reaction Forces in a Complex System

    My problem here seems that I can't figure out how to solve for my unknowns. I have 3 equations for force, and I'm not sure if that equation I have for the moment around the origin counts as 3 new independent equations if I split them up into i, j, and k components. If that is allowed, then I...
  25. M

    Reaction forces on a structure

    Homework Statement Problem 4.36 http://xps2pdf.co.uk/4c82ad8dcb91d5507169e0a18804ea30bf81d592/4.36.pdf Homework Equations The Attempt at a Solution I am not sure if I am doing this correctly..there is a lot of information that I am not using to solve the problem (i.e. all the different...
  26. Hyo X

    Order and Disorder in Liquid Water: Investigating the Structure of H2O Molecules

    Does liquid water have ordered structure? I.e., are there significant domains of ordered H2O molecules that maintain crystallinity - translational symmetry - in liquid water at room temperature? I guess this is essentially a hydrogen bonded network - How big are these domains? Or are they...
  27. J

    CH3CH3 tetrahedral VSEPR structure

    Homework Statement Draw the VSEPR structures. CH3CH3 Homework Equations The Attempt at a Solution This is throwing me off because there are basically 2 tetrahedral. So, that is what I did. I drew a tetrahedral VSEPR structure and I connected another one to it upside down. Is...
  28. M

    Experimental status of stellar structure

    A naive question from someone who knows nothing about the subject: I was wondering how much we can tell experimentally about what's going on inside a star. Can we determine, say, how the temperature or pressure vary as a function of the radius? Thanks in advance.
  29. Hyo X

    Ordered lattice necessary for band structure?

    Is it possible for a disordered or amorphous structure to have band structure? I understand derivation of bands from Kronig-Penney model. E.g. does amorphous silicon have a band structure? While amorphous silicon oxide does not have a band structure?
  30. S

    What is the difference between structure and enum?.

    or else what is the difference between structure,union and enum. can anyone please provide the exact information about them.
  31. L

    The Structure of Galilean Space

    A Galilean transformation is defined as a transformation that preserves the structure of Galilean space, namely: 1. time intervals; 2. spatial distances between any two simultaneous events; 3. rectilinear motions. Can anyone give a short argument for the fact that only measuring the...
  32. N

    Symplectic Structure of Thermodynamics and the Hamiltonian

    (inspired partially by this blog post: http://johncarlosbaez.wordpress.com/2012/01/19/classical-mechanics-versus-thermodynamics-part-1/ To my understanding, the thermodynamic configuration space has a nice symplectic structure. For example, using the language of classical mechanics, starting...
  33. A

    Simulating opposing rotational forces at different points on structure

    Hi, I am trying to simulate a tangential force acting on a point on a structure and the corresponding opposing force caused by the moment of inertia of a mass at a different position. In this image the structure rotates around point c and there is a vector out of mass m opposing the...
  34. S

    The 'Huge-LQG' quasar 'structure' does not violate homogeneity

    There was some excitement a few months ago about the discovery of the Huge-LQG quasar structure, claimed to be the "largest structure in the Universe", which was said to violate the cosmological principle and the assumption of homogeneity of the Universe. Some previous threads on this topic on...
  35. S

    Atomic Structure of Wet Oxidized Silicon

    Hello everyone, I would like to buy some Si wafer with SiO2 layer on it. The manufacturer told me that they obtain the SiO2 with a wet oxidation process. My question is, would this layer be amorphous or crystalline or polycrystalline? Thanks!
  36. P

    Use the Jacobi identity to show Lie algebra structure constant id.

    Homework Statement Use the Jacobi identity in the form $$ \left[e_i, \left[e_j,e_k\right]\right] + \left[e_j, \left[e_k,e_i\right]\right] + \left[e_k, \left[e_i,e_j\right]\right] $$ and ## \left[e_i,e_j\right] = c^k_{ij}e_k ## to show that the structure constants ## c^k_{ij} ## satisfy the...
  37. W

    Why is the fine structure constant what it is?

    This question occurred to me while working through some textbooks. Since it is dimensionless, its value can't be explained away saying it's because of the way we chose the units. Well it turns out I'm a 100 years late to this game. I found it's even more serious than I had realized. (And it...
  38. SSGD

    Crystal Structure of Metals at Absolute Zero, Waves

    I have been trying to find information on the crystal structure or phase of solid elemental metals at temperatures close to absolute zero, but I can only find information on there ambient structures. Does anyone know of any sources that would have thermodynamic tables for solid metals at low...
  39. X

    Basic physics confusion in my structure

    My physics core is a little bit weak, and this one question confuses me. Homework Statement A 3kg box sits on top of a 7 kg box. The object accelerates at 1 m/s^2. Find the force applied on the bottom block; if there are no forces besides this one. Homework Equations F= ma The...
  40. D

    How to analyze band structure and the density of states?

    Hello! I'm having my materialphysics exam in a few days, and looking some of the older exams I saw that there are many times questions about band structure and density of states. More specifically there might be a picture of some band structure plus the density of states, like this. Then...
  41. J

    How Do I Complete This Lewis Structure?

    Homework Statement Draw the best Lewis Dot Structures the following species: ClF4+Homework Equations none The Attempt at a Solution I calculated that there should be a total of 34 e- in the Lewis structure": 7 (1 chlorine atom) + 28 ( 7 from each of the four fluorine atoms) - 1(b/c the atom...
  42. M

    What is the Correct Crystal Lattice Structure?

    what is this answer choices: a. Primitive cubic with an octahedral hole b. Body centered cubic with an octahedral hole c. Face centered cubic with an octahedral hole d. None of the above e. Not enough information to determine We didn't talk about this in class, and this was a question...
  43. P

    Structure beam question engineering help

    Homework Statement Hello could someone please help me on how to work this question out I have attached a photo so you can see the question. The equation i think you use is the equation of equilibrium. thanks if someone could please help me! you would be my life saver! Homework Equations...
  44. Rlam90

    Neutrinos to probe nuclear structure?

    Do you think it would be possible to use a beam of neutrinos to probe the structure of atomic nuclei? Since they do not interact electronically, they would be useful to study the structure of both neutrons and protons, either through gravitational deflection or weak interactions. Could this...
  45. michael879

    Fermion Mass Structure: Explaining the Reversal of Up/Down Quarks

    I was taking a look at the SM particle table and I noticed that the up/down quarks seem to be "reversed" from the usual structure. Neglecting those two quarks, the "up" family is the most massive, then the "down" family, then the "electron" family, then the "neutrino" family. However for some...
  46. M

    Biochemical structure of dominant vs recessive gene

    Most all familiar with the terms dominant and recessive trait in a general way. I have seen little on the biochemical difference. Assume 1. Gene codes for characteristic 2. Variance in characteristic due to sequence within gene How does the structure of an allele differ from an...
  47. M

    How would you structure high school physics?

    If you were the mister of education or whatever, how would you structure high school physics? Would you make it more math heavy, would you put an emphasis on critical thinking and understanding or would you increase rote-learning or decrease it? Would you make it so that it prepares students...
  48. T

    Band structure and diffraction intensity

    Hello, Is there an established relationship between the diffraction intensity that a sample produces with its band structure? Thanks
  49. V

    A few simple questions about band structure and conduction

    Hi! I'm reading about band structure and conduction in regular crystals and semiconductors, and I've hit a few confusing points my book doesn't explain well enough for me. In one part, they're explaining conduction in a 1D crystal with lattice spacing a (and therefore reciprocal lattice...
  50. A

    What Factors Influence the Band Gap in Band Structures?

    What are the parameters affects the band gap in a band structure?
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