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. shounakbhatta

    Magnetic monopoles, fine structure and String theory

    Hello, Can anybody please explain me how magnetic monopoles, fine structure constant and string theory are related to each other? Thanks
  2. hunc

    Understanding Galilean structure

    I just start to read Mathematical Methods of Classical Mechanics by Arnold. And I am sort of very puzzled by all the notion. Firstly, if the universe is seen as a 4D affine space, why is time a mapping from R^4→R? I mean this kind of 4D contains time, right? Secondly, I thought the kernel of...
  3. C

    Help me identify this mystery structure in my SEM image?

    Hey all, As the title suggests, I've found some recurring structure on an SEM image and I can't for the life of me figure out what it is. I took the image this morning. Here she is: http://i.imgur.com/nFuBsW2.png Here's a larger, more zoomed out and higher res version. A few more of...
  4. gfd43tg

    MATLAB Mastering Structure Arrays in Matlab: Confusion and Exam Preparation

    Hello, I am preparing for the exam for my Matlab class, and have run into some confusion with Structure arrays. I have a hard time keeping all the concepts straight in my head. I am working on an old exam problem, where this is the structure array, which I will use as an example to demonstrate...
  5. Z

    Books or references for nuclear structure?

    Although I am a newer publishing thread here, I notice this forums for a long time. And I hope someone could help me. I am doing some nuclear reaction research and want to shift myself to the nuclear structure area. I can find some references for some special topic. While I think I...
  6. P

    Does Magnetic Field Affect Positronium States? Exploring the Fine Structure

    Hi all, I'm trying to compute the effect that a magnetic field has on the singlet and triplet states of positronium. I know that the positron has a charge and magnetic moment opposite that of the electron, so I'm tempted to write the interaction as: \vec{B} \cdot (\vec{M}_{1}+\vec{M}_{2})=...
  7. marellasunny

    Using the prop shaft tunnel as ''backbone'' for body structure

    In regards to the Lotus Elan from 1962, my book H-point says that Colin Chapman used the prop shaft tunnel as ''backbone'' to the body structure. Can someone please elaborate on this? Does this mean that the structure of the prop shaft tunnel acted like a stiffener for the entire body...
  8. S

    Optical tweezers for manipulating atoms together to form new structure

    I am trying to figure out a method for using optical tweezers to manipulate individual atoms into new meta-material structures. I understand this would require a very complicated process. I thought of some general steps this process might use. This is roughly what I think it might require...
  9. nicolauslamsiu

    How can the bond angle of a molecule be determined using its formula?

    How to determine the bond angle based on the formula of molecules?
  10. M

    Effect of Cooling on Molecular Structure

    I am interested in knowing whether what changes would happen at the molecular and atomic level, to a material subjected to Cooling. 1. Does the minimum temperature that can be achieved has limit? 2. Is it Zero Kelvin? 3. If so, is it a global standard for minimum temperature for any material...
  11. H

    Optimizing structure for toppling

    Hi! everyone... I'm a building a standing frame for disabled children, the structure in elemental form is shown in picture. https://drive.google.com/file/d/0B60ALttRvwKmdzRGc0pGWlN5Z3c/edit?usp=sharing link to picture -...
  12. S

    Structure of galaxy and the laws behind it

    dear sir, i want to know the structure of the galaxies. the process that caused it happen.and finally some peculiar and intersting about galaxy.
  13. M

    Platform Structure material thickness

    I'm building a 6'x12' steel platform that will be 3' elevated from the ground. How can I determine what load bearing weight will be if I use 2" Square Tubing, 1/4" wall thickness and then use 1/4" angle iron for the platform structure? I was going to use 2" Sq tube, 3/8" thick, but most local...
  14. M

    Turbulence and Structure Functions

    Hey PF! I was wondering if any of you were familiar with structure functions and how they relate to turbulence? Do you know of any good articles to research? Structure functions may be defined as $$S_{ij}(\vec{R}) = \mathbb{E} \Big[ \big( u_i(\vec{x}+\vec{R}) - u_i(\vec{x}) \big) \big(...
  15. berkeman

    What is this antenna structure? (vertical bow tie)

    I saw this antenna on a residential rooftop yesterday (in the US). I'm guessing it is a over-the-air Digital TV antenna, but I don't recognize the vertical bow tie structure. The antenna is about half a meter tall. Any ideas?
  16. T

    Stainless steel crystal structure

    Hi, I'm looking for a simple s.s crystal unit cell structure and can't find it anywhere. I understand that stainless steel is a very general word and takes many forms and has many different types, but isn't there a standard type that people use in the industry and ususlay talk about when they...
  17. S

    Structure of Nucleus: Proton & Neutron Arrangement

    dear sir, I am curious to know the way protons and neutron are arranged in the nucleus and movement of protons and neutrons in the nucleus.please guide me.
  18. M

    Understanding the Structure Function for Velocity in Two Directions

    Hello again pf! i was wondering if any of you could help me with the intuition for the following structure function: $$S_{xy}(R) = \overline{\big[v_x (x + R) - v_x(x)\big] \big[v_y(x+R) - v_y(x) \big]}$$ where ##v_i## is the velocity in the ##i## direction, ##x## is distance, and ##R## is a...
  19. A

    How does this structure exist?

    I was looking at this problem. It says I should write appropriate resonance structures. But, even with resonance, I do not see how a carbon cannot fill its octet. Why does the carbon in the middle have a positive charge. Is that not unstable?
  20. miraiw

    Preservation of protein structure in electroblotting

    Hello, I am reading about the Western blot technique, and I am looking for clarification of the transfer step described in the wikipedia article and in this video walkthrough. It is not clear to me why the proteins should keep their shape needed for the probing step rather than breaking or...
  21. C

    Uniqueness of smooth structure

    I'm looking to prove the Global Frobenius theorem, however in order to do so I need to prove the following lemma: If ##D## is an involutive distribution and and ##\left\{N_\alpha\right\}## is collection of integral manifolds of ##D## with a point in common, then ##N = \cup_\alpha...
  22. M

    What do you think would be the best way to structure a math course?

    What do you think is the best way to structure a maths course in general? Be it algebra, calculus, analysis, probability, geometry, etc. What I mean by structure is number of exams, their percentages, type of exams, and timing of exams. I am looking for a structure that best helps students...
  23. Islam Hassan

    "Implausibly Large Structure" in the Universe

    How much of a threat is this assembly/structure of quasars (400 billion light years long) to the homogeneity hypothesis of the universe? Is it being taken seriously in academis circles or are researchers shrugging it off for the moment? IH
  24. E

    Relation of fine structure constant to splitting of spectral li

    Homework Statement Estimate the magnitude of the fine structure splitting in H-α in THzHomework Equations Rydberg -- R_y \left(\frac{1}{n_f^2}-\frac{1}{n_i^2}\right) = \Delta E The Attempt at a Solution This isn't really a request for solution help, and more a justification. I know that if...
  25. A

    Sulfur Dioxide (SO2) Lewis Structure

    Hi, I drew the lewis structure of SO2. The one with 0 formal charges gives me two double bonds. But, I see on the web that one single bond and another double bond is an acceptable resonance structure. What do they mean? Sulfur can expand its octet. Having 0 formal charge is much more...
  26. S

    Can One Electron Make Two Transitions in a Row?

    Homework Statement Three photons coming from excited atomic hydrogen sample are picked up. Their energies are 12.1 eV, 10.2 eV and 1.9 eV. These photons must come from? A)two or three atoms B)single atom C)three atoms D)two atoms The Attempt at a Solution By solving it i got single...
  27. D

    Terminology in structure generating

    I am very mixed-up with the terms perturbation, anisotropy and ripple. What is the relation or difference between them?
  28. T

    Question about the atomic structure of insulators

    I'm an apprentice electrician taking night courses. My question isn't a specific mathematical problem. It's a query about a concept. Please let me know if there's a better way/place I can ask it. My text say that atoms can have a max of 32 electrons per shell, with 1-3 being ideal for...
  29. S

    Information on large scale structure?

    Can anyone recommend some usufull links,pdf,... for information on large scale structure? I want to fully understand how in the cold dark matter model the the hierarchical formation of matter occurs and the role of the initial perturbations in the evolution of the universe. Thank you.
  30. C

    MATLAB Stellar structure equations in Matlab?

    Does anyone have a Matlab file for solving the stellar structure equations that they wouldn't mind passing along? I'm trying to settle an argument with a friend that they can't really be used to describe nuetron stars and I don't have much programming experience. Thanks, Alex
  31. T

    Questions about the structure of the universe

    In general, what's a good way to understand the structure of the universe? I'm especially curious about the nature of the edge of the universe. Relativistic concepts dealing with the expanding universe confuse me greatly. Thanks for your time!
  32. E

    A problem in sections method in analyzing structure

    Homework Statement Determine the force in members BF, BG, and AB, and state if the members are in tension or compression. Homework Equations Method of sections The Attempt at a Solution Now I cut the sections FB, BG and BA... I took the lower end. I now have three unknowns. I...
  33. carllacan

    Older nuclear structure models.

    Hi people. I just read this somewhere and I can't get my head around it. How is the Uncertainty Relation uncompatible with the idea of a proton-electron nucleus? And can you explain why this model predicted those values for the nuclear spin? Thank you.
  34. M

    Solving Forces in Structures: Eliminating Members & Calculating Forces

    See attachment for question and diagrams. This problem is concerned with using the stiffness matrix method to find displacements and force in a structure. My problem is pre-eliminating the members. i have attached 2 diagrams. i would like help in trying to get from the first diagram, to the...
  35. B

    Can Charge and EM Energy Change Metal Structure

    Hello Everyone, This is my first post. Background: I am an audio guy and seek to understand how cables contribute to the sound of my stereo. Issue: Do audio cables such as power cords, interconnects, and speaker cables "break in" as they are used? Typically, with high-end cables, users...
  36. T

    How to write coupled mode equation of a given structure

    Recently I am reading the papers in the field of PT symmetry systems. What I am confused is that in these papers, authors directly write out the equations describe the dynamics of the given systems( For example, in this paper http://arxiv.org/ftp/arxiv/papers/1103/1103.3389.pdf , authors put...
  37. D

    Lewis dot structure, octet rule for a central atom

    As you can see, octet rule isn't satisfied for the central atom Xe, it has 2 more electrons attached to it. So does it mean, that you should first try to make sure octet rule works for any "side" atoms, and then you just put any remaining electrons to a central atom? (or central atoms?) And if...
  38. craigi

    Metal packing structure and curved space

    In flat space the atoms in a metal have regular packing structures. A slight curvature of space would mean this wasn't geometrically possible. As a consequence do we expect metals to have a significantly lower density with a slight curvature of space? Obviously, this doesn't just apply to...
  39. Q

    Determining forces in members of a structure

    Homework Statement I want to find the force in the vertical purple member. Assuming I know the forces in all the other members, there's a problem with working out the force in the purple member. (Bear in mind, I'm using the method where I assume equilibrium at each joint in the...
  40. B

    Understanding Hydrogen Fine Structure Validity and Field Discrepancies

    Homework Statement This is not homework, I am trying learn fine structure. This site is reliable : http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html, can you tell me if the content of "hydrogen fine structure" is still valid or dated?. Even if it were classical oudated model, I'd like to...
  41. Jalo

    Cristaline structure: simple solid state physics problem

    Homework Statement The atomic mass of Niquel is 58.7 amu (atomic mass unit), and it's density (at 90ºC) is 8.86 g/cm³. (a) Find the distance from one atom to the closest one from him.Homework Equations 1 amu = 1.66053*19⁻²⁷ The Attempt at a Solution I started by finding the number of atoms...
  42. F

    Stellar structure of stars problem

    Homework Statement Consider a star of radius R, with density p that is constant, composed of classical, nonrelativistic, idealg gas of fully ionized hydrogen. a. Solve the equations of stellar structure for the pressure profile, P(r) with the boundary condition P(R)=0 b. Find the temperature...
  43. S

    MHB Eigenvalue separation of a Block Matrix with a special structure

    Hi everyone, I have a square matrix J \in \mathbb{C}^{2n \times 2n} where, $J=\left(\begin{array}{cc}A&B\\\bar{B}&\bar{A}\end{array}\right)$ A \in \mathbb{C}^{n \times n} and its conjugate \bar{A} are diagonal.Assume the submatrices A,B \in \mathbb{C}^{n \times n} are constructed in a way...
  44. S

    Reactions of a redundant frame structure using Unit Load Method

    Homework Statement Hi, I am having trouble with the following problem and I can't seem to find any examples: I am trying to determine reactions at points A and D of the redundant structure below using the unit load method, there is a 10kN load at the top left point (B), all lengths are...
  45. curious bishal

    Why do solids compress more than liquids under pressure?

    Atoms in solid are more closedly packed as compared to liquid and gases. But we exert more force, some solid gets compressed but liquid doesn't, why? If atoms are loosely packed in liquid than solids, liquids should get compressed...
  46. N

    Confirming structure of aspartic acid at PH 4

    Homework Statement Draw the structure of aspartic acid at PH 4. I calculated the PI and based on that, drew the charged structure. If anyone can confirm that this is the correct structure. Homework Equations The Attempt at a Solution I attached the structure. Thanks for any assistance.
  47. H

    Strange reflectance from periodic structure

    Hi, last semester I did a project with two fellow students. We made a numerical model to calculate the reflectance from a periodic V-shaped structure of silicon similar to this: In the course of doing so, we came across something we could not explain. I have placed an image of it below...
  48. C

    Crystal Structure vector question

    Homework Statement Identify the [221] vector? A B C D E Homework Equations The Attempt at a Solution I reduce [221] to [1 1 0.5].BUT after getting the wrong answer, the feed back is as follows "Feedback: [221]: has a 0.5 component along the x-axis...
  49. R

    Statics - Pin & Slider Structure - Equilibrium

    Homework Statement Given force F (=5000N), find Moment on member 4. I have attempted to start solving this problem by drawing the following diagram: I added the letter 'A' to the support of member 2, and also put an angle of 7 degrees to the vertical at the support 1. I have...
  50. R

    Geometry of the atomic structure

    Hey guys, I was looking at both the time-dependent and time-independent schrodinger equations, and I notice that we often choose to solve these in spherical coordinates. I understand that we do this because they are convenient for problems with azimuthal symmetry. However, how do we know that...
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