scholarly journals Structure-Dependent Doppler Broadening Using a Generalized Thermal Scattering Law

2021 ◽  
Vol 2 (2) ◽  
pp. 124-131
Author(s):  
Nina C. Fleming ◽  
Ayman I. Hawari
Keyword(s):  
Structural Information ◽  
Lattice Structure ◽  
Boltzmann Distribution ◽  
Material Structure ◽  
Doppler Broadening ◽  
Bonded Materials ◽  
Low Energies ◽  
Thermal Scattering ◽  
Energy Dependent ◽  
True Structure

The thermal scattering law (TSL), i.e., S(α,β), represents the momentum and energy exchange phase space for a material. The incoherent and coherent components of the TSL correlate an atom’s trajectory with itself and/or with other atoms in the lattice structure. This structural information is especially important for low energies where the wavelength of neutrons is on the order of the lattice interatomic spacing. Both thermal neutron scattering as well as low energy resonance broadening involve processes where incoming neutron responses are lattice dependent. Traditionally, Doppler broadening for absorption resonances approximates these interactions by assuming a Maxwell–Boltzmann distribution for the neutron velocity. For high energies and high temperatures, this approximation is reasonable. However, for low temperatures or low energies, the lattice structure binding effects will influence the velocity distribution. Using the TSL to determine the Doppler broadening directly introduces the material structure into the calculation to most accurately capture the momentum and energy space. Typically, the TSL is derived assuming cubic lattice symmetry. This approximation collapses the directional lattice information, including the polarization vectors and associated energies, into an energy-dependent function called the density of states. The cubic approximation, while valid for highly symmetric and uniformly bonded materials, is insufficient to capture the true structure. In this work, generalized formulation for the exact, lattice-dependent TSL is implemented within the Full Law Analysis Scattering System Hub (FLASSH) using polarization vectors and associated energies as fundamental input. These capabilities are utilized to perform the generalized structure Doppler broadening analysis for UO2.

scholarly journals Computational design, engineering and manufacturing of a material-efficient 3D printed lattice structure

2020 ◽  
Vol 18 (4) ◽  
pp. 404-423
Author(s):  
Roberto Naboni ◽  
Anja Kunic ◽  
Luca Breseghello
Keyword(s):  
Lattice Structure ◽  
Computational Design ◽  
Material Structure ◽  
Fused Deposition Modelling ◽  
Design Engineering ◽  
Design Development ◽  
Fused Deposition ◽  
Construction Methods ◽  
3D Printed ◽  
Scarcity Of Resources

Building with additive manufacturing is an increasingly relevant research topic in the field of Construction 4.0, where designers are seeking higher levels of automation, complexity and precision compared to conventional construction methods. As an answer to the increasing problem of scarcity of resources, the presented research exploits the potential of Fused Deposition Modelling in the production of a lightweight load-responsive cellular lattice structure at the architectural scale. The article offers an extensive insight into the computational processes involved in the design, engineering, analysis, optimization and fabrication of a material-efficient, fully 3D printed, lattice structure. Material, structure and manufacturing features are integrated within the design development in a comprehensive computational workflow. The article presents methods and results while discussing the project as a material-efficient approach to complex structures.

scholarly journals Structure of archaerhodopsin-2 at 1.8 Å resolution

2014 ◽  
Vol 70 (10) ◽  
pp. 2692-2701 ◽  
Author(s):  
Tsutomu Kouyama ◽  
Ryudo Fujii ◽  
Soun Kanada ◽  
Taichi Nakanishi ◽  
Siu Kit Chan ◽  
...  
Keyword(s):  
Structural Information ◽  
Lattice Structure ◽  
Hexagonal Lattice ◽  
Structural Features ◽  
Proton Pumping ◽  
Tryptophan Residue ◽  
Order Structure ◽  
Proton Release ◽  
Decay Kinetics ◽  
Release Channel

Archaerhodopsin-2 (aR2), the sole protein found in the claret membrane ofHalorubrumsp. Aus-2, functions as a light-driven proton pump. In this study, structural analysis of aR2 was performed using a novel three-dimensional crystal prepared by the successive fusion of claret membranes. The crystal is made up of stacked membranes, in each of which aR2 trimers are arranged on a hexagonal lattice. This lattice structure resembles that found in the purple membrane ofH. salinarum, except that lipid molecules trapped within the trimeric structure are not distributed with perfect threefold symmetry. Nonetheless, diffraction data at 1.8 Å resolution provide accurate structural information about functionally important residues. It is shown that two glutamates in the proton-release channel form a paired structure that is maintained by a low-barrier hydrogen bond. Although the structure of the proton-release pathway is highly conserved among proton-pumping archaeal rhodopsins, aR2 possesses the following peculiar structural features: (i) the motional freedom of the tryptophan residue that makes contact with the C13 methyl group of retinal is restricted, affecting the formation/decay kinetics of the L state, and (ii) the N-terminal polypeptide folds into an Ω-loop, which may play a role in organizing the higher-order structure.

scholarly journals Repositioning septins within the core particle

2019 ◽  
Author(s):  
Deborah C. Mendonça ◽  
Joci N. Macedo ◽  
Rosangela Itri ◽  
Samuel L. Guimaraes ◽  
Fernando L. Barroso da Silva ◽  
...  
Keyword(s):  
Lipid Bilayers ◽  
Self Assembly ◽  
Binding Proteins ◽  
Structural Information ◽  
Core Particle ◽  
Affinity Tag ◽  
The Core ◽  
Gtp Binding ◽  
True Structure ◽  
Core Particles

AbstractSeptins are GTP binding proteins considered to be a novel component of the cytoskeleton. They polymerize into filaments based on hetero-oligomeric core particles which, in humans, are either hexamers or octamers composed of two copies each of either three or four different septins from the 13 available. Not all combinations are possible as it is believed that these must obey substitution rules which determine that different septins must be derived from four distinct and well-established sub-groups. Here, we have purified and characterized one such combinations, SEPT5-SEPT6-SEPT7, and used TEM to derive the first structural information concerning its assembly. The full complex was purified using an affinity tag attached to only one of its components (SEPT7) and was able to bind to and perturb lipid bilayers. Although the complex assembled into elongated hexameric particles, the position of SEPT5 was incompatible with that predicted by the reported structure of SEPT2-SEPT6-SEPT7 based on the substitution rules. MBP-fusion constructs for SEPT5 and SEPT2 and immuno-staining clearly show that these septins occupy the terminal positions of the SEPT5-SEPT6-SEPT7 and SEPT2-SEPT6-SEPT7 hexamers, respectively. In so doing they expose a so-called NC interface which we show to be more susceptible to perturbation at high salt concentrations. Our results show that the true structure of the hexamer is inverted with respect to that described previously and, as such, is more compatible with that reported for yeast. Taken together, our results suggest that the mechanisms involved in spontaneous self-assembly of septin core particles and their filaments deserve further reflection.

scholarly journals 4U 1909+07: a Hidden Pearl

10.14311/1326 ◽  
2011 ◽  
Vol 51 (1) ◽  
Author(s):  
I. Kreykenbohm ◽  
F. Fürst ◽  
L. Barrágan ◽  
J. Wilms ◽  
R. E. Rothschild ◽  
...  
Keyword(s):  
Timing Analysis ◽  
High Mass ◽  
Folding Energy ◽  
Pulse Profile ◽  
Spectral Parameters ◽  
Phase Dependence ◽  
X Ray ◽  
Low Energies ◽  
Fluorescence Line ◽  
Energy Dependent

We present a detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U1909+07 is a persistent accreting X-ray pulsar with a period of approximately 605 s. The period changes erratically consistent with a random walk expected for a wind accreting system. INTEGRAL detects the source with an average of 2.4 cps (corresponding to 15mCrab), but sometimes exhibits flaring activity up to 50 cps (i.e. 300mCrab). The strongly energy dependent pulse profile shows a double peaked structure at low energies and only a single narrow peak at energies above 20 keV. The phase averaged spectrum is well described by a powerlaw modified at higher energies by an exponential cutoff and photoelectric absorption at low energies. In addition at 6.4 keV a strong iron fluorescence line and at lower energies a blackbody component are present. We performed phase resolved spectroscopy to study the pulse phase dependence of the spectral parameters: while most spectral parameters are constant within uncertainties, the blackbody normalization and the cutoff folding energy vary strongly with phase.

scholarly journals Degradation processes influencing bonded joins

2009 ◽  
Vol 55 (No. 1) ◽  
pp. 29-34 ◽  
Author(s):  
M. Müller ◽  
R. Chotěborský ◽  
P. Hrabě
Keyword(s):  
Laboratory Experiments ◽  
Adhesive Bond ◽  
Strength Properties ◽  
Climatic Changes ◽  
Economic Losses ◽  
Material Structure ◽  
Bonded Materials ◽  
Degradation Processes ◽  
Specific Degradation ◽  
Adhesive Materials

Degradation processes cause huge material and economic losses all over the world. On one hand, in today’s globalised society, various climatic changes occur affecting products in different ways. On the other hand, different specific degradation media exist in specific branches of the human activity. Due to the influence of the degradation environment (media), destruction can set in. The aim of the laboratory experiments was to evaluate the influence of the degradation environment occurring mainly in agriculture. The adhesive bond strength properties as well as the influence on adhesive bonded materials were evaluated. For the degrading environment tested, a natural and an artificial fertilisers, machine oil, and water were selected. Also, the influence of corrosion was tested on the bonded material. The surfaces of adhesive materials debased by corrosion inevitably stop fulfilling their functions. The degree of the corrosion effect depends mainly on the type, the material structure, and of course, on the corrosion environment.

scholarly journals Energy-dependent Ps-He momentum-transfer cross section at low energies

2008 ◽  
Vol 77 (1) ◽  
Author(s):  
J. J. Engbrecht ◽  
M. J. Erickson ◽  
C. P. Johnson ◽  
A. J. Kolan ◽  
A. E. Legard ◽  
...  
Keyword(s):  
Momentum Transfer ◽  
Cross Section ◽  
Low Energies ◽  
Energy Dependent ◽  
Momentum Transfer Cross Section

Réaction séquentielle : influence de différents paramètres

1973 ◽  
Vol 51 (21) ◽  
pp. 2233-2241 ◽  
Author(s):  
Gisèle Goulard
Keyword(s):  
Cross Section ◽  
Relative Motion ◽  
Final State ◽  
Sequential Reaction ◽  
Absolute Value ◽  
Low Energies ◽  
Cross Section Formula ◽  
The Absolute ◽  
Energy Dependent

Given a sequential reaction at low energies A + B → C* → D + G* → D + E + F, we previously derived a cross-section formula which corresponds to the detection of two final-state particles. In this expression of σL some energy-dependent terms appear which are related to the relative motion of D–G* and E–F. In this paper, we study their influence on the absolute value of σL for the special reaction 11B + p → 3α at incident energies of 2.65 MeV and 163 keV and also the variations of σL with the parameters of α–α scattering.

scholarly journals String Phase in an Artificial Spin Ice

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaoyu Zhang ◽  
Ayhan Duzgun ◽  
Yuyang Lao ◽  
Shayaan Subzwari ◽  
Nicholas S. Bingham ◽  
...  
Keyword(s):  
Lattice Structure ◽  
Boltzmann Distribution ◽  
Energy Scale ◽  
Magnetic Interactions ◽  
Dynamic State ◽  
Santa Fe ◽  
Spin Ice ◽  
Artificial Spin Ice ◽  
Topological Quantum ◽  
Ice Lattice

AbstractOne-dimensional strings of local excitations are a fascinating feature of the physical behavior of strongly correlated topological quantum matter. Here we study strings of local excitations in a classical system of interacting nanomagnets, the Santa Fe Ice geometry of artificial spin ice. We measured the moment configuration of the nanomagnets, both after annealing near the ferromagnetic Curie point and in a thermally dynamic state. While the Santa Fe Ice lattice structure is complex, we demonstrate that its disordered magnetic state is naturally described within a framework of emergent strings. We show experimentally that the string length follows a simple Boltzmann distribution with an energy scale that is associated with the system’s magnetic interactions and is consistent with theoretical predictions. The results demonstrate that string descriptions and associated topological characteristics are not unique to quantum models but can also provide a simplifying description of complex classical systems with non-trivial frustration.

scholarly journals ASSESSMENT OF PARTICLE PACKING CHARACTERISTICS AT INTERFACES BY SPACE SYSTEM

2011 ◽  
Vol 19 (2) ◽  
pp. 85 ◽  
Author(s):  
Piet Stroeven ◽  
Martijn Stroeven
Keyword(s):  
Structural Information ◽  
Particle Interaction ◽  
Particle Packing ◽  
Material Structure ◽  
Evolution System ◽  
Compositional Evolution ◽  
Natural Processes ◽  
Structure Sensitive ◽  
Random Generators ◽  
Cementitious Systems

Interest in material structure has been raised by upgrading of cementitious systems. Computer-simulation of material structure has been pursued so far by using random generators. Such systems were successfully applied for estimating global properties. Realistic estimation of structure-sensitive properties, however requires a more appropriate simulation of material structure. The SPACE (Software Package for the Assessment of Compositional Evolution) system has been developed for that purpose. It incorporates particle interaction and gravitational influences, which are typical for the 'natural' processes underlying the formation of material structure in the production stage. The capabilities are discussed of the two computersimulation methods for generating structural information relevant for either structure-insensitive, or structure-sensitive properties in bulk and in the interfacial transition zone (ITZ). The structural information will deal with composition and configuration of the material, respectively. The use of random generatorbased (RG) systems is demonstrated not justified when dealing with structure-sensitive problems.

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