# 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. ### I Shell structure topological defects as substitute for dark matter

Recently a paper was published 'The binding of cosmological structures by massless topological defects' which proposes how 'massless' shells can bind galaxies in lieu of dark matter. There are a few basic technical details I am looking to clarify: 1. It is mentioned in the paper that an...
2. ### I Status of the X17 search with the MEG II apparatus

Status of the X17 search with the MEG II apparatus The MEGII experiment at PSI July 2024 pdf here https://indico.cern.ch/event/1291157/contributions/5887844/attachments/2900132/5085565/MEGII_X17_ICHEP2024_AP.pdf could an experimental physicist explains the data and results ? also included...
3. ### Reproduce band structure Kagome Fermi-Hubbard using Python

We need to define a high symmetry point path in the Brillouin zone, we can choose: Gamma-K-M-Gamma My attempt: import numpy as np import matplotlib.pyplot as plt # lattice vectors a1 = np.array([1, 0]) a2 = np.array([-1/2, np.sqrt(3)/2]) a3 = -(a1 + a2) a = [a1,a2,a3] #high symmetry points...
4. ### I How Do Quantum Fluctuations Shape Cosmic Structures?

How do quantum fluctuations affect the formation and evolution of structures in the universe on large scales?
5. ### Debunking the Hypervalence Theory: The Truth About Bonds in HClO4

In HClO4 Cl forms one single bond with an oxygen and three dative bonds with the other 3 oxygen atoms. However, according to VB theory, Cl is hybridized and forms double bonds instead of dative bonds. Then, the structural formula of the molecule never shows arrows as it would if there were...
6. ### I Effects of gravity on planetary core structure

Hello everyone! I joined this forum to reach out to people much smarter than me. After searching the matter, i realize this subject has been beaten to death for a VERY long time. But, as of yet, I have not stumbled upon a definitive answer to my question. Flipping through my news feed...
7. ### I can't figure out why isomers change their structure...

I'm new to chemistry, I'm looking at isomers, chiral topics, but I can't figure out why isomers change their structure, why chirals want to change in polarized light, why cis and trans do not remain constant but produce two different structures and which of these is the real structure, where do...
8. ### I Can we now explain the Fine Structure Constant?

In this video Dirac talks about the Fine Structure Constant 1/137. Can we now explain why this is?
9. ### A New paper claims there is evidence of suppression of structure growth

A paper by Nhat-Minh Nguyen, Dragan Huterer, Yuewei Wen titled "Evidence for suppression of structure growth in the concordance cosmological model" https://arxiv.org/abs/2302.01331 The abstract says: We present evidence for a suppressed growth rate of large-scale structure during the...
10. ### Definition of angular frequency in nuclear structure

Hi all I am a little bit confused about the definition of angular frequency in the context of nuclear rotation, some times its defined in the regular way as $$E=\hbar \omega$$ and other time from the rigid rotor formula $$E=\frac{\hbar^{2}}{2I} J(J+1)$$ where ##I## is the moment of inertia...
11. ### A Empirical tight-binding sp3s* band structure of semiconductors

I'm simulating on code the tight-binding sp3s* bandstructure of certain semiconductors, such as GaAs, AlP, InP, ZnSe, etc. with spin-orbit coupling at a temperature of T = 0 K but I'm having trouble at finding the corresponding spin-orbit splitting parameters. For example, I've found in this...
12. ### B What is a photon's structure composed of?

I read that a photon is an electromagnetic field but how could that be since electromagnetic fields are based on electronic and thermodynamics.
13. ### Engineering Calculating the safe load of a glued structure with given shear stress

I have tried to calculate the safe load with the equation of maximum shear stress, A = 4*6*10^-4, and the given shear stress 5MPa, but I couldn't seem to get the right answer which is 18kN.
14. ### Integration of structure function F2 to calculate quark momentum

I study particle physics with “Particles and Nuclei” / Povh et al. and “Modern particle physics” / Mark Thomson and I am currently at “Deep-Inelastic scattering”. After introducing several scattering equations, such as Rosenbluth, that all include terms for electric AND magnetic scattering, i.e...
15. ### I Does a set of matrices form a ring? Or what is the algebraic structure?

Square matrices are closed under addition and their own form of multiplication, but in general do not commute. What algebraic structure then describes this, along with polynomials of matrices and allows us to amend with other operations, such as differentiation or integration defined on these...

38. ### MATLAB Graphene band structure Matlab code

I have this code for 3D band structure of graphene but i can't understand why while graphene first brillouin zone is hexagonal but here a rectangle form of first brillouin zone is used?E0 = 0; % coloumb integral V = -2.7; % hopping integral [eV] acc = 1.41; % c-c bond length [Angstrom] lattice =...
39. ### Should I consider internal forces for this hinged structure?

Summary:: A hinged structure applied with a load, should the structure totally been calculated in order to find the resultant force? Hello, Two situations, the first is a simple structure with a 20 N load at point C. The moment-equation is composed next to it. Second situation: A hinged...
40. ### Riemann curvature coefficients using Cartan structure equation

To calculate the Riemann coefficient for a metric ##g##, one can employ the second Cartan's structure equation: $$\frac{1}{2} \Omega_{ab} (\theta^a \wedge \theta^b) = -\frac{1}{4} R_{ijkl} (dx^i \wedge dx^j)(dx^k \wedge dx^l)$$ and using the tetrad formalism to compute the coefficients of the...
41. ### Solid-state Physics: Fermi surface and necks in an FCC structure

Does anyone have some bibliography about necks in FCC structure Fermi surface? I have to solve this problem and I have no idea how to start. Thanks.
42. ### Working out Plane Structure via Powder X-ray Diffraction Multiplicand

Below is the measured values for the Debye rings I obtained. I have to multiply the ratio (which is (sin^2(theta_n))/(sin^2(theta_min))) by a multiplicand until I get an integer. However for the multiplicand and the values I measured I get 1, 3, 13, ??, 4, 8, ??. These should either correspond...
43. ### Exploring the Structure of the Poisson Equation

Theorem 1: There exists at most one solution ##u\in C^2(\bar{\Omega})## of the Dirichlet boundary value problem. Proof: (1) We assume there is a second solution ##\tilde{u}## of the Dirichlet boundary value problem. We compute \Delta v=\Delta (u-\tilde{u})\Rightarrow -\Delta u + \Delta...
44. ### I How to work in the |F,m_F> states in hyperfine structure

Suppose that we have two atoms with one proton one electron each, and these electrons interact with each other. The states for the electrons are the singlet(S=0) and the triplet states(S=1). My question is if i have to keep the nuclear spin of the protons parallel when i write the states, for...
45. ### Chemistry Drawing the structure of 1,3,5 - trimethylphenol

The picture above is the correct answer, but I do not understand why. I thought that the OH group on the top has to be prioritized and be numbered 1. But then, the structure would have to be named 2,4,6-trimethylphenol, not 1,3,5-trimethylphenol. For example, 4-chloroaniline structure looks...
46. ### Chemistry Drawing resonance structure for this O-CH2 ion

ion shown: My answer: the following is the answer of the question: I identified the major contributor correctly, but the resonance structures, but the second resonance I drew is missing in the answer sheet. Can anyone tell me why the second resonance structure is not part of the answer...
47. ### Chemistry Drawing resonance structure for SO42

I was told that there are six resonance structures for SO42-, as shown below. I am wondering why this structure with single bonds is not one of the possible resonance. I understand that it is unfavorable as the formal charges are spread out over all four atoms, but shouldn't is still be a...
48. ### I What kx/ky Values Are Used for Graphene Band Structure Plots?

Hello, https://www.researchgate.net/figure/Top-Graphene-nanoribbons-with-zigzag-left-and-armchair-right-edges-with-disordered_fig1_258105786 With what kx/ky values are these band structures plotted? The energy dispersion of graphene is given by this , yet I am confused to what kx/ky value...
49. ### Tension force of a thread in a complex structure of six masless rods

At first I tried solving the problemteh following way: Due to symmetry let the rods connected to the green rod have tension forces in magnitde T1 => mg = 2T1cos(a), where a is half the angle formed by the two rods. From tere I got an expression from the longer rods in the force projected by them...
50. ### Internal Structure of SARS-CoV-2 virus

Homework Statement:: Does Sars-cov-2 Virus have Reverse Transcriptase enzyme for its replication purpose? Relevant Equations:: None I surfed Google for a relevant answer to my query but failed to find one.I just want to confirm whether Sars-cov-2 has the Reverse Transcriptase or...