What is Structures: Definition and 350 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. N

    Are Our Scientific Models Direct Representations of Reality?

    When we see structures like DNA for example is it to be understood that if we had a microscope powerful enough to see detail at the level of a DNA molecule we would see the double helix structure? Or are our structures simply models to help explain experimental results? Either way, at what...
  2. J

    Structures. column theory, Buckling

    Homework Statement the question is in the picture. the rectangular steel bar shown supports a concentric load of 13000lbf. Both ends are fixed. If te modulus of elasticity is 29x10^6 lbf/in^2, what is the maximum length the rod can be without experiencing buckling failure? Homework...
  3. D

    Stress and strain in crystal structures

    Are there stress and strain graphs for different crystal structures?
  4. Z

    Algebraic structures (a subgroups proof)

    Homework Statement Let n>1 be an integer, and let a be a fixed integer, prove or disprove that the set E will stand for is an element of H = {xEZ| ax = (mod n) is a subgroup under addition. The Attempt at a Solution I recognized that ax = a + a + a... + a. I figured this might help...
  5. D

    Chemistry Chemistry, how do i draw the lewis structures for these molecules?

    chemistry, how do i draw the lewis structures for these molecules? i have tried all sorts of ways but keep on geting stuck with atoms which i can't connect, don't have enough non paired valence electrons to join em all up H_{5}IO_{6} TeF_{6} IF_{7} SF_{4} BrCL_{3}
  6. D

    Are these the correct lewis structures

    are these the correct lewis structures for these molecules?? http://picasaweb.google.com/devanlevin/DropBox?authkey=sbH95pBl_D8#5275619652409681410 also, if i have an ion for example Al^{3+} what is its lewis structure, this ion is like noble gas Ne as far as valent electrons, so is its...
  7. S

    Cayley Tables and algebraic structures

    I have a question regarding Cayley tables, specifically using the composition operator for this particular problem. I had to miss class the other week and was just now sitting down to catch up on my homework for this class when I was hit with the algebraic structures section. They have a...
  8. K

    Lewis Structures and Valence Electrons?

    Hi there! I was wondering if anyone could help me. With Lewis Structures and Valence electrons, do the valence electrons have to go in a certain order around the element symbol? ie: four dots around each side of carbon, or two on the left side and two on the right side? How would you do...
  9. quasar987

    Question about differentiable structures

    If M is a topological manifold, a smooth structure A (or maximal atlas) on M is a set of smoothly compatible charts of M that is maximal in the sense that if we consider any chart that is not in A, then there is some chart in A with whom it is not smoothly compatible. Now, it is a fact that...
  10. D

    Crystal Structures: Finding Positions Per Unit Cell

    Hey All.. I'm having some problems trying to understand the tetrahedral and octahedral sites in face centered cubic (fcc) and body centered cubic (bcc). It is hard to visualise the structures in 3D.. I wanted to know how to find out the positions per unit cell for the tetrahedral and...
  11. D

    What are the key atomic structures that make an atom metal or nonmetal?

    Just wondering.
  12. D

    Tight binding (FCC structures)

    I'm reading my lectures on TBM and I don't understand the following thing: \omega(\overrightarrow k)=\omega_0-4t\cdot[\cos(k_xa/2)\cos(k_ya/2)+...] It's related to FCC structures, in which the number of Nearest Neighbors (Z) of an atom is equal to 12. Basically the three dots at the end...
  13. B

    How does one draw Lewis structures on the computer?

    Homework Statement Is there some sort of Latex that allows one to draw Lewis structures on the computer? The Attempt at a Solution The following code works in Textify: http://www.texify.com/links.php but not here, apparently. Anyway, I can make 1D Lewis structures (every element in a...
  14. P

    Chem question on dash-wedge structures

    Homework Statement how would you draw this structure in 3d using dash-wedge representation? HN=C=CH2 From my guess, I drew the N=C=C as being parallel, and the two hydrogens coming off the second C without having any dashes or wedges, but curving at 120 degrees from the carbon. For the...
  15. F

    Simple Discrete Structures problem

    OK this is the first assignment I have in this class and I can't figure out how to negate and simplify the logical structure of W <--> S (bi-conditional implication) I got this so far: ~[(W --> S) ^ (S --> W)] by Definition ~(W --> S) v ~(S --> W) by DeMorgan's Law ~(~W v S) v ~(~S v W)...
  16. phoenixthoth

    Piecing together structures: question

    Is it possible to form or "glue together" somehow a structure out of other (not necessarily identical to one another) structures such that each of the other structures is elementarily embeddable within the formed structure? With ultraproduct formulation and Los's theorem, it appears that only...
  17. A

    Lewis Structures and Resonance

    1. I need to be able to draw K C2H3O2 and any resonance structures. SO far I have drawn four and I can think of at least four more to draw... does anyone know if there are more than four and if so, could you please submit a pdf of the resonance structures?
  18. K

    How Does Tree Height Evolve in Disjoint Set Structures?

    Hello, The subject is disjoint set structures There's following pseudocode for merging sets, by representing every set as single rooted tree and merging is like merging trees. {h[] is array of heights of trees} Mege(a,b) if(h[a]==h[b]) set parent of b is a h[a]++...
  19. D

    Atomic Radius and Lattice Parameter Relationship in HCP Crystals?

    Hello, can anyone help me out the the relationship of the atomic radius R with the lattice parameter a for a Hexagonal close packed cystals (HCP) and how to prove the ratio of a:C is 1.633. Any information on this issues would be appreciated. Thanks
  20. J

    Temperature between Galactic Structures

    So I’m trying to understand a bit more about the structure of the universe and I keep running across all these “if you think that’s strange wait until you hear this” moments and they almost always cause me an almost painful paradigm shift (without a clutch). Here is the latest. I was always...
  21. M

    Formalizing 3D Structures of Adenine, Cytosine, Guanine, Uracil, and Thymine

    can one give me Formalise 3D for adinine , citozin , guoanine , urasil , timine
  22. C

    I need advice with my Discrete Structures class

    I need advice with my "Discrete Structures" class Hi everyone, I'm a sophomore undergraduate student at the Polytechnic University Of Puerto Rico, currently majoring in "Computer Engineering", for the record this university works by trimesters. I'm currently getting a bit frustrated with my...
  23. D

    Ultrafilters and Similar Structures

    M\equiv N means M and N are elementarily equivalent, that is, for any setence S in the language of M and N, M\models S \Leftrightarrow N\models S. An elementary embedding f:M->N is a mapping f:|M|->|N| between the underlying sets such that, for any formula t(x) and matching tuple y of elements...
  24. P

    Effective Mass & Its Effects on Crystalline Structures

    what is effective mass? and how does it effect both the electrical and optical properties of a crystaline structure?
  25. qspeechc

    Discrete Structures: Worth Studying for Maths Majors?

    Hi. I would be terribly grateful for your help. I am a second year student, and I am pretty sure I will major in Mathematics, and will probably (if I'm smart enough), do maths post-grad. I was looking through the faculty handbook, and saw that for 2nd year math they offered a module on...
  26. L

    Mathematic operations and structures in C

    Hello guys, I was wondering: say you have a structure: struct tag{ int a char b int b int c } how would you make int c equal to int a + int b for all variables of type struct tag? I have tried using pointers but it baffles me how you would make a global change in that all...
  27. H

    Data Structures and Algorithm Analysis

    Has anyone here taken this class before? I've been in this class for two weeks, and I still can't get a feel for how difficult or time consuming it may be. My instructor keeps mentioning discrete mathematics (which I haven't taken), although it wasn't a prerequisite for the course. Additionally...
  28. Shaun Culver

    Exploring the Link between Math Structures with Category Theory

    Does 'category theory' link different mathematical structures? Can you give a superficial example of how this has been done (eg. Name two mathematical structures and, with waving of hands, explain how they have been linked)? Could you direct me to a link where this has been done elegantly in...
  29. S

    Solving Resonance Structures of NH2OH Conjugate Base

    [SOLVED] Resonance Structures 1. Homework Statement [/b] Draw the major resonance contributors that show electron delocaliztion of the formal charge for the following ions, The conjugate base of .O .||... NH2 /..\ /...\\ / ...||...| ... \...//\ ....OH 3. The Attempt at a...
  30. R

    Organic Chem - Resonance Structures #2

    [SOLVED] Organic Chem - Resonance Structures #2 Homework Statement Trying to figure out this resonance structure...Draw the lowest energy alternative.. http://img162.imageshack.us/my.php?image=553562cu7.jpg The Attempt at a Solution ive been trying to move the upper double bond...
  31. S

    Energy levels in quantum well structures

    Does anyone knows how to solve the following eigenvalue equation using matlab? so as to obtain the energy levels in a quantum well structure.. or does anyone has the codes or knows where to find the codes to do so? Eigenvalue equation: tan(sq_root(2mE/hbar^2)*(d/2)) = sq_root((V-E)/E) for...
  32. S

    Energy levels in quantum well structures

    Does anyone knows how to solve the following eigenvalue equation using matlab? so as to obtain the energy levels in a quantum well structure.. or does anyone has the codes or knows where to find the codes to do so? Eigenvalue equation: tan(sq_root(2mE/hbar^2)*(d/2)) = sq_root((V-E)/E)...
  33. T

    Force Analysis of Structures and Machines

    Hey guys Im having problems figuring out this Statics question I feel like I can solve it, But it has been bugging me for weeks Here it is. and Here is a quick FBD and notes I posted from others Would Anyone let me know If the FBD is correct? Im not asking for the answer. I honestly just...
  34. A

    Help with Data Structures Assignment Needed

    "]Dear all; I have this assignment in data structures, and it needs for a lot time to solve it by myself really I'm buzy and I stick on it for A long time, I want it as soon as much anyone can:cry:[/FONT] Regards; LoLO:blushing:
  35. M

    Wood structures: story shear & unit shear question

    Homework Statement A rectangular two-story building with a wood roof and floor system and masonry walls is analyzed to determine seismic forces. Given: I=1, roof dead load D=15psf, floor load=25psf including partition load. Exterior wall dead load D=80 psf along both long and short walls...
  36. N

    Calculate Size of Column for 10 Storey Building

    Homework Statement A 10 storey building has columns spaced on a 8m by 10m grid. a) Calculate the reaction at the base of an internal column assuming a 300mm thick concrete floor slab and a live load of 3.0kPA (ignore self weight of column and assume concrete density 2.4t/m^3 b) Assuming...
  37. V

    Comp Sci C++ Binary Search Tree: Infix Exp. & Tree Traversal

    c++ data structures! please help! i want to write a c++ program that implements a binary search tree from an infix expression. the program should perform the following: -the expression should be saved and read from a file. -use a stack to check if the expression is well formed in terms of...
  38. K

    Resonance Structures and VSEPR

    Hi, I'm having trouble figuring out which of the following molecules can be described using three charge-minimized resonance structures. Does anyone have any idea which molecules this would include? a. SF4 b. SO3 c. SO32- d. HSO4- e. SO2+
  39. H

    Preparing for a Test: Struggling with Crystal Structures

    I have a test after a few days and I face agreat deal with some concepts. Really I don't understand the crystal structure? how we know the Bravias lattice and how we get the primitive vectors and how we know the cells that make the lattice Bravias if it not? I want very clear...
  40. K

    Organic Chemistry - Nomenclature Structures

    The question/direction is to: "Draw the structure of the following compound!" 2-methyl-4-(1-methylethyl)octane I tired several different ways of constructing this compound but the online homework program ACE Organic says that: I don't know what to do or what I am missing. If anyone can...
  41. M

    What determines the number of differentiable structures on a manifold?

    Another question: How do we define compatibility of atlases and a maximal atlas? why do we need to define them? How do we conclude for example sphere and circle have 1 differential structure? ( I said "another question but it turn out to be questions")
  42. G

    Electrostatics and band structures?

    Hi all, Recently got to thinking about electrostatics and electron densities and band structures. If you have an electrostatically charged piece of material, say for example, a metal, does the density of states of that metal change because of the depletion of electrons? Alternately, if...
  43. S

    Predicting Crystal Structures in Metals: Is There a Simple Explanation?

    Is there any way to predict what crystal structure a pure metal element will be? It seems that the simple 'electron sea' idea does not explain a lot of things. Thanks -scott
  44. jal

    Exploring Nuclear Structures

    What has mainstream decided is the arrangement of the protons and neutrons in the nucleus of the atom? Lattice or cluster structures or ? jal
  45. M

    Exploring CoIr Alloys: Crystal Structures & Lattice Parameters

    I am looking for informations about CoIr alloys. Who can tell me about crystal structure, lattice parameters of CoIr alloy? Please share me some references about this material. Thanks! :!)
  46. M

    Exploring My Arch Design Bridge: Physics of Spaghetti Structures

    I'm currently in my final year of high school, doing physics. We have been given an assingment about bridge structures. Basically, we build a bridge out of spaghetti, test it and discuss it. I'm thinking of things in which I can talk about. I've built an Arch Design Bridge. Mainly due to...
  47. O

    Resonance Structures of PO4 (3-)

    hi :biggrin: please help. thankyouuu :] Homework Statement i am studying for my apchem exam in may.and got stuckup on a question. it's just a little exercise.so the answers aren't there.but ok here it is; give the resonance structures of PO4 (3-) and there's supposed to be four Homework...
  48. A

    Civil Engineering - Structures

    I was curious if anyone has this as a job/major? I'm 100% sure I'm going into it. I haven't done any job shadowing =(. I really want to, but, I personally don't know anyone who does it. For those who do it: How are the working conditions? I heard you work with a lot of people also. I was...
  49. S

    Simple models of nanoscale carbon structures

    Hello - I am searching for some guidance, and I would greatly (greatly) appreciate any tips, pointers, etc. I am interested in the stability and geometry of nanoscale carbon structures, such as fullerenes and single-walled carbon nanotubes. I am wondering where to begin to develop - for my own...
  50. C

    Fortran Fortran Structures: What Are They?

    Hi - I expect this is quite a simple question. What are fortran structures? I'm trying to convert fortran code into MATLAB and I don't know what a structure / endstructure statement is. e.g. structure /pixel/ union map INTEGER*4 cl INTEGER*4 rw endmap map INTEGER*4 x INTEGER*4...
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