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. J

    Indeterminate beam structures

    Homework Statement In the enclosed picture is a loaded beam and strut, what I need to do is determine the reactions at the supports. The problem is that I think the beam is indeterminable because there are more than three reactions? Homework Equations I do no the three equations of...
  2. E

    What are resonance structures and how can I understand them better?

    My teacher is explaining resonance structures in class, but I don't understand it that well. Can someone please help? (:
  3. S

    Algebraic Structures on Sets?

    I just found out that the words "algebraic structure" have a precise definition and that this notion is not just common language! Then below this definition they give another (equivalent) definition: So based on this I have three questions: 1: How is this concept explained in terms of...
  4. J

    Confirming Glycine Structures at pH's 1,6,13

    Structures of Glycine at pH's 1, 5.97 and 13, just wondering if anyone can confirm these, been a while since molecular bio. pH 1 pH 6 pH 13 Regards, Andrew Johnson
  5. F

    How to find a number in a matrix efficiently?

    Hi guys, was wondering if someone could help me with a homework problem. The problem: The input is an N x N matrix of numbers that is already in memory. Each individual row is increasing from left to right. Each individual column is increasing from top to bottom. Give an O(N) worst-case...
  6. Simfish

    Are double bonds/resonance structures more nucleophilic?

    I'm only talking about carbon-carbon double/triple bonds here. A nucleophilic atom is one that would donate electrons to an electrophile (often a highly electronegative atom like oxygen or a halogen). Anyways, what about carbon-carbon double bonds? I'm inclined to think that they're less...
  7. J

    C programming Q: initializing an array of structures

    I am writing a program in C (vanilla, non-C++/C#) and I am having trouble figuring out why my initialization of my array of structures isn't working. I have tried a number of things without any luck. I still get a compiler error: "conflicting types for 'cardInfo' " I am writing a simple...
  8. D

    Resonance/energy levels contributing structures

    I'm working my way through The Art of Writing Reasonable Organic Reaction Mechanisms by Robert B. Grossman (excellent book, by the way), but the way he describes resonance is confusing me. I feel like the more I think about it, the more confusing it gets. Consider a carbon-carbon double...
  9. P

    Algebra - Number of Nonisomorphic Binary Structures

    Homework Statement (Fraleigh's Algebra, 2003, p. 36) There are 16 possible binary structures on the set {a, b} of two elements. How many nonisomorphic (that is, structurally different) structures are there among these 16? Phrased more precisely in terms of the isomorphism equivalence...
  10. W

    Equivalence Relation (discrete structures)

    Homework Statement Let A be a set prove relation R, defined as R : = {<c,d> \in A x A | T } is an equivalence relation on A. What's the quotient A / R ? 2. Relevant Info the x in A x A means the Cartesian product T means "always true" set theory briefly covered in class The Attempt...
  11. M

    Isomorphism and Binary Structures

    Let J be a set of all linear functions. Consider the set R^2 in the Euclidean plane. Define a binary operation * on R^2 in such a way that the two binary structures <J, +> and <R^2, *> will be isomorphic. Any thoughts? If something is not clear please ask. Thank you.
  12. N

    Explore Unusual DNA Structures: Hoogsteen Pairs, Hairpin Structures & More!

    i have to fill in the blanks for the following questions using the following choices (some will be used once, others more than once, and others not at all) : z-dna, cruciform structure, mirror repeat, hairpin structure, g-tetraplex, triplex dna, hoogsteen pairs, a-dna, duplex dna, inverted...
  13. S

    Crystall structures of Cu, Al, and Fe at different temperatures.

    I was wondering if someone could tell me (in pedestrian terms) what are the crystal structures of aluminum, copper and iron as a function of the temperature. I just read the chapter on crystalline arrays of Callister's Materials Ecience & Eng. but the book just says that Cu and Al have a FCC...
  14. L

    How to Determine Bonding in Lewis Structures for Oxoacids

    When drawing a Lewis structure for a compound how do you know what bonds to what? For example, with H2SO4, how does one know whether the H bond to O or to S?
  15. S

    What is the Best Data Structures Book for Learning Computer Science?

    Hello I have used Data Abstraction and Problem solving in Java Walls and mirrors, for my 1st data structures course I found i didn't use it that much at all, it pretty wordy and quite boring to read. Can anyone recommend me a good book for data structures? Basically in the course we...
  16. S

    Biology on cells structures etc

    Homework Statement The maximum size to which a cell may grow is limited by the cell's ? Homework Equations NIL The Attempt at a Solution It's a multiple-choice question... so i picked nucleus. My argument is that the nucleus controls the internal functions of the cell. However...
  17. W

    Medical Identifying structures in brain MRI

    Hello all, experts and otherwise. I'm looking for some links to software and documentation for selecting Regions of Interest (ROI) in MRI data of the human brain. Saving ROIs is a must. Any tips also appreciated. Thank you!
  18. R

    Differentiable structures and diffeomorphisms

    The definition of having multiple differentiable structures is that given two atlases, {(U_i ,\phi_i)} and {(V_j,\psi_j)} (where the open sets are the first entry and the homeomorphisms to an open subset of Rn are the second entry), that the union {(U_i,V_j;\phi_i,\psi_j)} is not necessarily...
  19. K

    Which structures can constitute the foundations of mathematics?

    It is a well known view that mathematical logic together with set theory can be used as a foundation for the whole the rest of mathematics. Category theory also has been mentioned as a candidate for this, as an alternative of set theory. But recently I heard (from a non-mathematician) a view...
  20. icystrike

    Understanding OCH- Lewis Structures

    Homework Statement Assign formal charges to the possible lewis structures of the following and decide which structure is the most important: OCH^{-}Homework Equations The Attempt at a Solution Most important I'm wondering how can i come up with all possiblities..
  21. A

    Materials and their use in structures

    A cable has an unstretched length of 12.0m and is stretched by 1.2 x 10^(-4)m when a 6.4 x 10^(8) Pa stress is applied. What is the strain per unit volume in the cable in J m^(-3), when this stress is applied? Any help would be very nice. I don't understand what to do.
  22. O

    How do vortices help astronomical structures to form?

    I often watch tongues of cold mist spreading over a high plain ahead of an approaching cold front. Their upper surfaces are characteristically corrugated by whorls of mist rotating about a horizontal axis, which form and dissolve as a slab of cold air slides under the warmer upper air. Meshed...
  23. D

    Castiglianos second theorem for indeterminate structures

    in the following question it is known that the rod BD has only axial internal forces, (which i called Q) if AL2=10*I, find the reaction at C and the internal force Q. Assume that the energy of normal forces is negligible compared to moment where there are both. instead of using L/4 i...
  24. D

    How to Prove the Even Permutations in Sn Form a Group?

    Homework Statement Prove that the set of even permutations in Sn (i.e, An) is a group. List the elements of A4 Homework Equations How do I even try to prove these The Attempt at a Solution I have started a new course and am finding the problems very difficult. Is there any books...
  25. V

    Concrete Structures Notes & Resources | Get Help Now

    Hey, sorry this isn't really a homework question, wasn't too sure where to put it. At the moment I'm taking a concrete structures course. I ordered the textbook online but it's not here yet. I have an assignment due on friday, and really need somewhere to start. So my question is: Does...
  26. J

    Solids and Structures - Vector question

    Homework Statement The rope BC exerts an 800 N force F on the bar AB at B. Determine the vector components of F parallel to the bar. Homework Equations I already know how to complete dot product (e.g. a.b), cross product (e.g. axb) and understand the basic principles of these...
  27. P

    How long do structures continue shaking after quake?

    I live in northern California and there was a substantial earthquake here yesterday. To me, it seemed as though the shaking continued for somewhere between 30 seconds and 60 seconds, but one newspaper article stated the ground shook for 10 seconds. Does anyone know how long structures such...
  28. S

    Question about a Discrete Structures class

    I'm in a bit of a hairy situation right now. Spring 2010 will be my last semester at my current school studying Forensic Science, and in the fall I'll be transferring to a physics program at another school. I'm trying to get some classes in that will help me in th fall before I leave but there's...
  29. W

    Logical distinction between sets and algebraic structures

    Let's say we have a set S, and a function f : S -> S. Now let S be endowed with a binary operation, forming a group G. Is it correct to write f : G - > G? Up to now I have been operating on the assumption that yes, although G is not technically a set, there is little harm in being sloppy and...
  30. Rasalhague

    Defining algebraic structures as n-tuples

    Bowen & Wang, in Introduction to Vectors and Tensors often define some algebraic structure as an n-tuple, e.g. "A semigroup is a pair (G,*) consisting of a nonsempty set G with an associative binary operation: (a*b)*c=a*(b*c) for all a,b,c in G." For more complicated structures, they use this...
  31. P

    Chemistry Lewis dot structures of complex molecules

    Homework Statement determine the electron dot structure of molecules a and b http://session.masteringchemistry.com/problemAsset/1144353/2/MMAt.05.067.jpgHomework Equations The Attempt at a Solution A) ::O: H | | H-C=N-HB) H | .. H-C-N=C=O:: | H I am not at all sure...
  32. O

    Chemistry Wedge-and-dash Molecular Structures in 2-dimensions

    Homework Statement I'm having trouble drawing a wedge-and-dash, 2 dimensional molecular structure for Vitamin C (ascorbic acid). All of the diagrams I've looked at (on the Wikipedia page, and some .edu websites) are incomplete: they either don't include the carbon and/or hydrogens molecules, or...
  33. A

    Distortion of Zr2Cu crystal structures?

    Hello I need your help! Using XRD, I detected single crystals (single peak) on the surface of a bulk specimen. My guess is that the structure is most probably Zr2Cu, but a distorted one. I know that Zr2Cu structure is MoSi2 type, spacing group of I4/mmm, tetragonal. I want to ask 1)...
  34. P

    Largest and smallest structures

    Will we ever be able to find the smallest or the largest structures of the universe or is that not possible in the way infinitesimals and the number line never end.
  35. G

    Indeterminate Structures and Stress

    Homework Statement A tunnel of length L = 141 m, height H = 6.9 m high, and width 6.0 m (with a flat roof) is to be constructed at distance d = 60 m beneath the ground. The tunnel roof is to be supported entirely by square steel columns, each with a cross-sectional area of 960 cm2. The mass of...
  36. T

    Resonant Structure of Nitrate Ion in AgNO3: Draw a Possible Solution

    Homework Statement Draw at least one resonant structure of the nitrate ion in AgNO_{3}. The Attempt at a Solution Is this a possible resonant structure of the nitrate ion?
  37. D

    Analysis of Structures: Finding Reactions & Forces in Trusses

    I have a question on setting up a problem to find the reactions and forces in members of trusses. So initially I find the reactions at the pins using a free body diagram, I get that. However, when I need to find the forces of the particular members am I supposed to take an initial guess as...
  38. C

    Structures and Materials problem - stress and strain

    Homework Statement A 4000 kg car traveling at 160 km/h crashes into a concrete post. If all the kinetic energy of the car is used to crush the low alloy steel at the front of the car, how many kg of steel will be crushed before the car stops? Properties of low alloy steel from a table of...
  39. B

    Need answers on tubular structures

    Ok so I have been looking over the internet on reading material on structures of tube. From experience I know this happens with items like straws (see illustration below). Is there an actual name of the phenomenon that happens (maybe a few formulas) If you don't understand the picture...
  40. S

    My Airframe Structures exam.

    Hello everybody. Well, I failed my airframe structures exam in May, and now have to resit it. I have been attempting to do some exercises to get back into it, but it all looks foreign to me. I'm struggling A LOT, and another fail would mean that I have to resit the year (even though I...
  41. O

    How to compare two similar structures?

    I am doing some simulation like recrystallizaiton, crystal A-amorphous-crystal B. This crystal B is different from A and experimentally proved that B is more like crystal C. Even though the recrystallizaiton is not obvious. As far as I have done, the bond lengths and radial distribution...
  42. P

    Piezo-electricity, can it be applied to large structures

    I'm new to electrical engineering so this is probably a stupid question. But after reading about piezo-electricity, can it be applied to large structures, like a bridge, to generate electricity when traffic travels over it ?
  43. H

    Understanding Lewis Structures: When to Form Double Bonds

    Is this how you tell when to form double bonds when drawing lewis structures, such as with CO2?
  44. C

    Structures & Materials - Cranes and Steel Cable

    Homework Statement A crane consists of a crane arm which is held in place and moved by strong steel cables. The crane arm is a truss structure, which is a rigid framework of quite thin steel beams welded together, forming many triangles. The cables are made of steel and they are not one...
  45. J

    First principle calculation of lattice structures

    Hi Well I have been thinking of this quite sometime, but i really dint know anyone who could answer my question. We all know that may elements exist in the form of crystals e.g. Si, Cu etc. And they have very specific crystal structure like Diamond for Si and face centered for Cu. Can we...
  46. N

    What is the Correct Way to Initialize a Character in C Programming?

    the foolowing program is to read inputed data and display them all at once but when i run it it asks for the first information and then runs the total program without asking for the input of other information.after that it doesn't respond and closes immediatelly. can someone help me and tells...
  47. F

    MATLAB Help with matlab, structures and movies

    Hi, I made an m-file which which outputs movies at the end. The movie frames are made from images of a 200 by 200 matrix. I wanted to input the movies into a second program which then analyzes each frame. The problem is the frames are structure files and I don't know how to convert the frame...
  48. S

    Using Radioactive Dating to Determine Ancient Structures' Ages

    Hello my smart fellows, I was wondering why scientists say that when an ancient civilization constructs a structure, they can tell the date that the structure was built with radioactive dating methods? Surely the materials used to make the structure already HAD an age, so how would they be able...
  49. C

    Best Stability of Structures Textbooks/Resources?

    Hi, I am a student pursuing an MS in Aerospace Engineering with a concentration in Aerospace Structures. I am currently taking a course in Stability of Structures. The "required" textbook is Guide to Stability Design Criteria for Metal Structures (ISBN 0471127426), and the other recommended text...
  50. D

    Crystal structures and Friction

    Hello, I have this ongoing argument with my professor. I read in a paper (friction and wear) that the crystal structure can affect friction. HCP crystal structures having lower friction coefficients. I have two papers that mention this in passing one, linking FCC crystal structures to have...
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