Structure Definition and 1000 Threads

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

    Lowest fine structure energy transitions

    Hi, I would like to know what atoms have the lowest fine-structure energy transitions with their wavelengths. Also I want to know what molecules have the lowest rotational energy transitions with their wavelengths. Is there a database where one can find them? Thank you
  2. L

    A Structure preserved by strong equivalence of metrics?

    Let ##d_1## and ##d_2## be two metrics on the same set ##X##. We say that ##d_1## and ##d_2## are equivalent if the identity map from ##(X,d_1)## to ##(X,d_2)## and its inverse are continuous. We say that they’re uniformly equivalent if the identity map and its inverse are uniformly...
  3. L

    Is cast iron a Body and Face Centered Cube structure?

    Homework Statement is cast irion body and face centenerd cube structure? wasnt quiet sure, i thought it was both because it can solidify different temperatures one of them Homework Equations mululpe different cast irons The Attempt at a Solution
  4. I

    I Center of inversion of cubic diamond structure?

    I'm having hard time finding the center of inversion of cubic diamond structure. At first I thought (2,2,2) would be the center of inversion, but (1,1,3), (3,3,3), (1,3,1), (3,1,1) (i.e. four atoms inside the cube) are not centrosymmetric about (2,2,2).
  5. M

    A Fine structure and fixed points

    I apologize for creating a new thread which has significant overlap with two other ongoing threads ("Quantization isn't fundamental", "Atiyah's arithmetic physics"). But both those threads discuss theories or paradigms of extreme breadth, whereas here I want to focus on a very specific bundle of...
  6. coolul007

    Magnetism and atomic structure

    Does atomic structure require a magnetic force? I understand that in the world of people it is most appreciated, however, it doesn't seem to have a purpose in the atomic structure.
  7. Vishesh Jain

    Distance to 3rd and 5th nearest ion to S2- in ZnS structure

    Hey folks ZnS has a ccp structure with S2- ions forming FCC lattice with Zn2+ ions at half the tetrahedral voids Attached is a table showing no. of nearest neighbours and their distance for an S2- ion 'a' is edge length of the unit cell I want to know how the distance to the 3rd & 5th...
  8. cianfa72

    I Differential structure on a half-cone

    Hi, consider an "half-cone" represented in Euclidean space ##R^3## in cartesian coordinates ##(x,y,z)## by: $$(x,y,\sqrt {x^2+y^2})$$ It does exist an homeomorphism with ##R^2## through, for instance, the projection ##p## of the half-cone on the ##R^2## plane. You can use ##p^{-1}## to get a...
  9. DarMM

    A Structure of Matter in Quantum Field Theory

    This is a topic I've mentioned a few times before. Essentially the structure of matter in quantum gauge field theories is unclear to me. I have no clear question here, just some initial discussion points. So at the first level, it seems a particle based view of quantum field theory is difficult...
  10. X

    Column buckling in a pin jointed structure

    << Mentor Note -- thread moved from the schoolwork forums to the ME forum because it's more of a general question >> Hi, in these column bucking notes (photo attached below) it says that bar BC will buckle first out of all the other bars in compression, but it does not explain why. I know it...
  11. Navin

    What is the structural level of fibrous proteins: secondary or tertiary?

    My question is if fibrous proteins posess secandory or if they posess tertiary structure There is a fiery debate between me and one smart dude from my class.I believe(firmly) that proteins posess secandory structure while he is of that school of thought that believes fibrous proteins have a...
  12. F

    A Silicon band structure for both ibrav 0 and ibrav 2

    Silicon Band Structure for both ibrav 0 and ibrav 2 I did scf and bands for silicon using both ibrav=0 and ibrav 2 After running the two bands separately I noticed that the band structures for the two (ibrav 0 and ibrav 2) were totally difference but in literature i read that the two (both ibrav...
  13. W

    A Defining a Contact Structure Globally -- Obstructions?

    Hi, Let ##M^3## be a 3-manifold embedded in ##\mathbb R^3## and consider a 2-plane field ( i.e. a Contact Structure) assigned at each tangent space ##T_p##. I am trying to understand obstructions to defining the plane field as a 1-form ( Whose kernel is the plane field/ Contact Structure) Given...
  14. BillTre

    Detailed Structure of the Fruit Fly Brain

    A group of scientists have assembled transmission electron microscopic (EM) images from the serially sectioned brain of a female fruit fly (Drosophila melangaster, a model research organism) to make a database of the detailed structure of its brain. Z. Zheng et al., “A complete electron...
  15. M

    I SR Time Dilation in Rigid Structure Clocks

    Special relativity says that all clocks will show same time dilation, irrespective of clock mechanism. But Time period of a clock is a formula that must continue to hold even if time dilates. Let us look at a tuning fork clock. Here time period depends on the dimensions of the vibrating...
  16. N

    I What time structure supports info moving backward in time?

    This of course is speculative, but IF faster-than-light travel (or wormhole tunneling or some other exotic means) was found to be able to communicate information from the future to the present, what would that indicate about the structure of time? Some might argue that indicates a block-type of...
  17. mrspeedybob

    Stronger tubes using internal structure?

    On the topic of structural tubing... It is my understanding that round tubing is stronger than square tubing, or conversely that, that round tubing is lighter for a tube of the same strength. Does it necessarily follow that the best possible use of material when making a tube, is to use it all...
  18. LesterTU

    How to evaluate the effective mass tensor (band structure)

    Homework Statement The energy-band dispersion for a 3D crystal is given by $$E(\mathbf k) = E_0 - Acos(k_xa) - Bcos(k_yb) - Ccos(k_zc)$$ What is the value of the effective mass tensor at ## \mathbf k = 0 ##? Homework Equations The effective mass tensor is given by $$ \left( \frac{1}{m^*}...
  19. Admiller

    I List of hyperfine structure of the elements?

    If caesium 133 frequency for its hyperfine structure is 9 192 631 770, and hydrogen is 1 420 405 751.7667 what are the frequencies for the other elements and their isotopes? Is there a list on line some were because this would be a long list. Any help on where to look on line would be...
  20. B

    The crystal structure for Ba2TiO explained with symmetries

    Hello! I would love to get help on this particular question that I find extremely difficult to answer. -"Bariumtitanate can under a certain set of conditions crystallize in the given structure. With the help of the compounds symmetries, explain how it is possible for it to achieve such a...
  21. G

    What is responsible for the structure of magnetic fields?

    Both the gravitational and electric fields associated with matter are centered on the matter itself. However, for a bar magnet, the magnetic field seems to be emanate from discrete loops, only part of which pass through the matter of the magnet. What causes a magnetic field to have this...
  22. R

    Help Identifying AESA Antenna Structure Type found in the F-35 aircraft

    This is the AN/APG-81 AESA Radar antenna by Northrop Grumman currently found in the F-35 (photo from wikipedia article). It seems to have a very different structure than past AESA/PESA antennas. For example the APG-68 from the F-16 looks a lot like stacked, slotted wave guides to me. So...
  23. pairofstrings

    Mathematical Structure and Mathematical Space Hierarchies

    Hi. I am trying to understand the images that I have posted below. Each layer of Mathematical Structure Hierarchy in the image in this post and Mathematical Space Hierarchy in the image in this post are: statements. 1. What do these statements of each layer of these hierarchies in the...
  24. rxy152

    Atomic Structure problem regarding interatomic spacing

    Homework Statement In a gas of hydrogen under normal conditions, the interatomic spacing is 1.56 × 10^−8 m . Assume the gas is made of atomic, not molecular, hydrogen. For what n-value of the hydrogen atoms is the size of the atom comparable to the interatomic spacing?The value of h bar is...
  25. rxy152

    Atomic Structure- Energy diff between levels

    Homework Statement Consider the NaCl molecule, in which the atomic weights of Na and Cl are 23 and 37, respectively. The internuclear separation is 0.236 nm, and the ”spring constant” for vibrations is k = Mred ω^2 = 1 × 10^9 J/m^2 . Calculate the energy difference between adjacent vibrational...
  26. thomassmith235

    Finding Unknown Forces on a Beam Structure

    Homework Statement I've been trying to find the unknown forces for this beam so I can complete an FEA analysis. Homework Equations ∑mz=0, ∑fx=0,∑fy=0 The Attempt at a Solution Attempt is attached
  27. S

    A Causal Structure of Metric Prop.: Matrix Size Differs

    Proposition: Consider an ##n + 1##-dimensional metric with the following product structure: $$ g=\underbrace{g_{rr}(t,r)\mathrm{d}r^2+2g_{rt}(t,r)\mathrm{d}t\mathrm{d}r+g_{tt}(t,r)\mathrm{d}t^2}_{:=^2g}+\underbrace{h_{AB}(t,r,x^A)\mathrm{d}x^A\mathrm{d}x^B}_{:=h} $$ where ##h## is a Riemannian...
  28. P

    I Calculating the fine structure constant in Feynman diagrams

    Griffith's Introduction to Elementary Particles, if I understand it correctly, states that in QED, the fine structure constant contributes less and less to the strength of the EM interaction as we add more and more vertices since the constant is so small (1/137). However, in QCD, since the...
  29. Physics345

    Drawing Lewis structure and structural formula

    Homework Statement Draw the Lewis structure and structural formula for: a) HCN b) SO3 2- Homework Equations none The Attempt at a Solution Did I do these correctly? Thanks!
  30. Physics345

    Electronegativity / predicting structure / ranking order

    Homework Statement a) Calculate the differences in electronegativity between the elements in each of these compounds. I)CaBr2 II) Na3N III) CH4 b) Predict whether each of these compounds would be an ionic or a molecular compound and justify each prediction. c) Rank the bonds in these compounds...
  31. V

    Why Does Diamond/Silicon Have 8 Bands in Its Band Structure?

    Homework Statement I am asked to discuss the band structure of diamond. I saw the band structure of diamond has 4 filled valence bands and then 4 conduction bands. Silicon, the same. Homework Equations --- The Attempt at a Solution I'm feeling really silly because I don't understand why it is...
  32. A

    Stiffness matrix for a symmetric structure

    Good day All While trying to solve the following exercice, I was stucked by a couple of issues for the first part in which we have to find the simplest configuration ( symmetry) according to my basic understanding Symmetry must be : geometry load support here I don t have the third...
  33. M

    Why does a frozen balloon have this structure?

    Hi, I forgot a water-filled balloon in my backyard last fall. When my kid brought the frozen balloon in and removed the rubber, we were surprised to see the beautiful structure inside the ball of glass. I remember that glass paperweights used to have similar designs inside them. I used to think...
  34. J

    Can You Construct a Functional Building Using Car Tires?

    Would it be possible to build a small 20' X 20' or 30' X 30' building using car tires using maybe one layer tires then black plastic to keep rain out then another layer of tires? If you just stack them vertical for the wall how would you build roof? Stacking them like great pyramids would look...
  35. DaveC426913

    Optimum shape for a pressurized structure in a pressure gradient

    I came across this pie-in-the-sea concept: (Obviously, the pictured structure would be extremely susceptible to complete catastrophic failure, having no apparent internal means of water-tight seals to prevent complete implosion. Which is why you'd more logically build a city in tube-and pod...
  36. Ventrella

    A Examples of fractal structure in prime partition numbers?

    Regarding the recent discovery by Ken Ono and colleagues of the fractal structure of partition numbers for primes: a great lever of intuition would be to see a diagram, or any presentation of the numbers that reveals this fractal structure. Perhaps the fractal structure is somehow hidden in a...
  37. N

    How is this diagram of the structure of diamond correct?

    see this diagram of the structure of diamond given in my textbook- I have read in my textbook that each carbon atom in a Diamond crystal is attached to four other carbon atoms by strong covalent bonds.But, in the diagram above I can see that some of the carbon atoms are not attached to 4...
  38. M

    Statics of structure, distributed load

    Homework Statement All data are in the image uploaded Homework Equations I don't know how to deal with two confounded loads The Attempt at a Solution I really need fast replies thnak for your attempt
  39. T

    Determining reaction of indeterminate beam structure

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] As this is an indeterminate structure with degree of redundancy 2, I have released support B & C. I then draw the BMD M0 of the Primary structure as well as BMD m1 and m2 of unit load system acting on B & C as follow: I...
  40. ohwilleke

    I Is there a fine structure constant running anomaly?

    Background The chart above, via Lubos Motl's blog which is standard in any textbook talking about supersymmetry, illustrates the running of the the inverse of the Standard Model (SM) and Minimal Supersymmetric Model (MSSM) coupling constants with energy scale for the electromagnetic force...
  41. T

    How does pH affect secondary structure of proteins?

    I understand that pH affect the tertiary structure as it will change the ionic interactions between the COO- and NH3+ groups, however, as the secondary structure is caused by hydrogen bonds, how does pH affect it? Is it because the change in tertiary structure will alter the shape of the protein...
  42. J

    MHB Proof & Structure: Solve (¬ p V q) ↔ ( p Λ ¬ q) - John

    Dear ALL, Today, I am really struggling to complete...an important Assignment on time? In particular, this Question has ...Frazzled me, re Truth Tables etc etc...? Any good advice, by close of business - greatly appreciated...
  43. J

    MHB Is the Converse of the Given Statement True for Any Positive Integer n?

    if n is a positive integer greater than 2 and m the smallest integer greater than or = n, that is a perfect square. Let a = m-n. Show that if n is prime, then a is not a perfect square. Also, is the converse of above true, for any integer n? any guidance, will be much appreciated? Thanks
  44. H Tomasz Grzybowski

    A Mechanism of α decay - truth about structure of nuclei

    α decay probably implies that heavy enough nuclei which undergo this decay, consist relatively loosely bound α particles and extra neutrons. I haven't found any theory which views nuclei in this way. I value truth in science, and would like to know it, also regarding stucture of nuclei and...
  45. C

    Electron dot structure, Lewis structure

    Which is more correct, teaching the first two valence electrons as paired in the electron dot structure or teaching them as not pairing until forced.
  46. D

    How do I draw Lewis Structure Diagrams? +1 More

    Homework Statement : 2 Questions, sorry about this if It adds confusion. 1) How do I go about drawing Lewis Structure Diagrams? I've searched the web, but all I can find, even when they say it's a "Lewis structure" diagram is lewis dot diagrams. My teacher wants it in the specific form where...
  47. T

    I Is the fine structure constant the biggest myth ever?

    The fine structure constant ##\alpha## is commonly cited as a very important quantity, because it gives the strengh coupling of the electromagnetic force. But it seems that the fine structure constant is not actually constant. It rather changes with the momentum of the (mediating?) particle and...
  48. D

    Taylor expansion fine structure

    I have to do a Taylor expansion of the energy levels of Dirac's equation with a coulombian potential in orders of (αZ/n)^2 , but the derivatives I get are just too large, I guess there is another approach maybe? This is the expression of the energy levels And i know it has to end like this:
  49. alphaj

    Organic chem: draw this in line angle structure

    Homework Statement Draw this formula in line angle structure. CH3CH2OC(O)CH2CC(CH2)3CH(CN)CHO. Homework Equations None. The Attempt at a Solution I'm confused with the CC(CH2)3 part of the condensed formula. I knew I got it wrong the first time I drew it because I couldn't just tag three...
  50. D

    I How Does Rubidium's Electron Spin Affect Its Energy Levels?

    Hello everybody, while I tried to understand the Rubidium level scheme, I realized that I have some issues concerning the energy levels in general... If in addition to the orbital Momentum the spin momentum of an electron is considered for example the p level splits to the 2P1/2-level and the...
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