Scanning system for high-energy electron diffractometry

1999 ◽  
Vol 32 (6) ◽  
pp. 1033-1038 ◽  
Author(s):  
A. S. Avilov ◽  
A. K. Kuligin ◽  
U. Pietsch ◽  
J. C. H. Spence ◽  
V. G. Tsirelson ◽  
...  
Keyword(s):  
High Energy ◽  
Scanning System ◽  
Registration System ◽  
Hartree Fock ◽  
Intensity Measurements ◽  
Structure Factors ◽  
Additional Control ◽  
Thin Polycrystalline ◽  
The Stability ◽  
Electron Diffractometry

A new electron diffractometer with a diffraction-pattern scanning system in front of a fixed counter has been developed. Significant improvement was achieved in the measured diffraction intensities by using fast electronics and additional control of the stability of the electron beam. The measurement of and accounting for the gear-frequency characteristic of the registration system was performed, and the signal accumulation mode for intensity measurements together with advanced statistical data processing were employed. Good agreement between the experimental and Hartree–Fock structure factors for LiF, NaF and MgO was achieved (to avoid strong extinction effects, rather thin polycrystalline films were used as samples).

Theoretical study on six-fold coordinated silicon in silicophosphate compounds

2006 ◽  
Vol 84 (8) ◽  
pp. 1024-1030 ◽  
Author(s):  
Hassan Rabaâ ◽  
Fatima Bkiri
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
High Energy ◽  
Functional Theory ◽  
Model Cluster ◽  
Hartree Fock ◽  
Ir Frequencies ◽  
The Stability ◽  
Remarkable Agreement ◽  
Cluster 2

Extended Hückel tight-binding (EHTB) calculations were performed on silicophosphate compounds with six-coordinated silicon. Speculative structures related to silicon coordination in SiP2O7 are reported. To account for the particular structural distortion caused by the presence of SiO6 in the silicon pyrophosphate, it is important to examine how the stability and the band gap of the extended structure of SiP2O7 are affected. Different theoretical tools are used (EHTB, ab initio Hartree–Fock, and density functional theory DFT-B3LYP). To obtain detailed descriptions of the incorporation of hexacoordinated silicon in this material, the band structures in SiP2O7 and [P2O7]4– were analyzed. It seems that the diffuse orbitals of silicon and the high energy of the Si 3p orbital lead to higher energy coordination and contribute to the breaking of the P-O-P bridge and the forming of a Si-O-P entity in this material. In addition, to provide more evidence of the existence of the octahedral silicon coordination in SiP2O7 (1), two model clusters [P4Si2O23H18] (2) and [P4Si2O19H10] (3) involving silicon atoms in octahedral and tetrahedral sites were investigated using Hartree–Fock and DFT theories. A remarkable agreement between calculated and experimental bond lengths for Si—O and P—O is obtained using the DFT calculation. The model cluster 2 corroborates the structural change in the Si-O-P and P-O-P fragments seen in 1. The IR vibrational frequencies are calculated for both model clusters and are predicted to shift towards lower frequencies in the octahedral Si sites, which is consistent with experimental data.Key words: silicophosphate, SiO6, band structure, tight-binding calculations, Hartree-Fock, DFT, B3LYP, model cluster, IR frequencies.

scholarly journals Carbon Substitution on N24Cages: Crossover between Triangular and Hexagonal Structures

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Carrie Sanders ◽  
Douglas L. Strout
Keyword(s):  
Theoretical Calculations ◽  
High Energy ◽  
Energy Materials ◽  
Cylindrical Structures ◽  
High Energy Materials ◽  
Energy Applications ◽  
Carbon Substitution ◽  
Complex Forms ◽  
The Stability ◽  
Carbon Inclusion

Complex forms of nitrogen are of interest for their potential as high-energy materials, but many all-nitrogen systems lack the stability for practical high-energy applications. Inclusion of carbon atoms in an otherwise all-nitrogen structure can increase stability. Nitrogen cages are known for energetically preferring cylindrical structures with triangular endcaps, but carbon cages prefer the pentagon-hexagon structure of the fullerenes. Previous calculations on N22C2have shown that carbon inclusion narrows the gap between triangular and fullerene-like structures. In the current study, three isomers of N24are used as frameworks for carbon substitution. Theoretical calculations are carried out on isomers of N20C4, N18C6, and N16C8, with the goal of determining what level of carbon substitution causes the carbon fullerene-like structures to become energetically preferred.

Electrochemical lithium recovery with lithium iron phosphate: What causes performance degradation and how can we improve the stability?

2021 ◽  
Author(s):  
Lei Wang ◽  
Kathleen C Frisella ◽  
Pattarachai Srimuk ◽  
Oliver Janka ◽  
Guido Kickelbick ◽  
...  
Keyword(s):  
Energy Efficiency ◽  
Manganese Oxide ◽  
Lithium Iron Phosphate ◽  
Iron Phosphate ◽  
High Energy ◽  
Performance Degradation ◽  
Electrochemical Processes ◽  
High Energy Efficiency ◽  
The Stability

Electrochemical processes enable fast lithium extraction, for example, from brines, with high energy efficiency and stability. Lithium iron phosphate (LiFePO4) and manganese oxide (λ-MnO2) have usually been employed as the...

scholarly journals Global predictions for astrophysics applications

2020 ◽  
Vol 13 ◽  
pp. 18
Author(s):  
P. Demetriou
Keyword(s):  
Nuclear Reaction ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Nuclear Astrophysics ◽  
Reaction Network ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Hartree Fock ◽  
Microscopic Models ◽  
The Stability

Nuclear reaction rates play a crucial role in nuclear astrophysics. In the last decades there has been an enormous effort to measure reaction cross sections and extensive experimental databases have been compiled as a result. In spite of these efforts, most nuclear reaction network calculations still have to rely on theoretical predic- tions of experimentally unknown rates. In particular, in astrophysics applications such as the s-, r- and p-process nucleosynthesis involving a large number of nuclei and nuclear reactions (thousands). Moreover, most of the ingredients of the cal- culations of reaction rates have to be extrapolated to energy and/or mass regions that cannot be explored experimentally. For this reason it is important to develop global microscopic or semi-microscopic models of nuclear properties that give an accurate description of existing data and are reliable for predictions far away from the stability line. The need for more microscopic input parameters has led to new devel- opments within the Hartree-Fock-Bogoliubov method, some of which are presented in this paper.

scholarly journals Charged projectile spectrometry using solid-state nuclear track detector of the PM-355 type

Nukleonika ◽  
2015 ◽  
Vol 60 (3) ◽  
pp. 591-596 ◽  
Author(s):  
Aneta Malinowska ◽  
Marian Jaskóła ◽  
Andrzej Korman ◽  
Adam Szydłowski ◽  
Karol Malinowski ◽  
...  
Keyword(s):  
Solid State ◽  
Detection Efficiency ◽  
Radiation Detector ◽  
High Energy ◽  
High Energy Resolution ◽  
Projectile Energy ◽  
Scanning System ◽  
Nuclear Track Detector ◽  
Temperature Plasma ◽  
Wide Range

Abstract To use effectively any radiation detector in high-temperature plasma experiments, it must have a lot of benefits and fulfill a number of requirements. The most important are: a high energy resolution, linearity over a wide range of recorded particle energy, high detection efficiency for these particles, a long lifetime and resistance to harsh conditions existing in plasma experiments and so on. Solid-state nuclear track detectors have been used in our laboratory in plasma experiments for many years, but recently we have made an attempt to use these detectors in spectroscopic measurements performed on some plasma facilities. This paper presents a method that we used to elaborate etched track diameters to evaluate the incident projectile energy magnitude. The method is based on the data obtained from a semiautomatic track scanning system that selects tracks according to two parameters, track diameter and its mean gray level.

scholarly journals A CHARGE FORM FACTOR (CFF) OF 5He NUCLEUS

2019 ◽  
Vol 14 (2) ◽  
Author(s):  
Piyush Sinha ◽  
Neelam Sinha
Keyword(s):  
Electron Scattering ◽  
Fourier Transforms ◽  
Form Factors ◽  
High Energy ◽  
Energy Electron ◽  
High Energy Electron ◽  
Structure Factors ◽  
Transition Matrix Elements ◽  
Current Densities ◽  
A Charge

High energy electron scattering is a very powerful tool for studying geometrical details of nuclear structure. The studies provide information on static distribution of charge and magnetization in nuclei. As the interaction is relatively weak so that in the scattering process the internal structure of the target nucleus is not significantly disturbed. Using electrons as projectile, we can study how transition matrix elements vary with q2 and map out the Fourier transforms of the transition charge and current densities called Form Factors or Structure factors. In the high energy electron scattering we can know the details of the spatial distribution of transition charge and current density. In this paper we have formulated CFF for 5He nucleus

scholarly journals Likelihood weighting of partial structure factors using spline coefficients

2005 ◽  
Vol 38 (1) ◽  
pp. 193-198 ◽  
Author(s):  
Kevin Cowtan
Keyword(s):  
Spline Functions ◽  
Partial Structure ◽  
Structure Factors ◽  
The Stability ◽  
Smooth Spline

A method for the weighting of structure factors from an incomplete and inaccurate model is described which relies on the fitting of smooth spline functions of resolution. The use of smooth spline functions avoids the problems of discontinuities introduced when performing calculations in resolution shells. The complexity of the functions to be fit may be varied by changing the number of spline parameters. This approach is used to investigate the stability of the problem when data are limited.

scholarly journals Study on the Fracture Law of Inclined Hard Roof and Surrounding Rock Control of Mining Roadway in Longwall Mining Face

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5344
Author(s):  
Feng Cui ◽  
Shuai Dong ◽  
Xingping Lai ◽  
Jianqiang Chen ◽  
Chong Jia ◽  
...  
Keyword(s):  
Energy Release ◽  
Longwall Mining ◽  
Coal Pillar ◽  
High Energy ◽  
Mechanical Analysis ◽  
Engineering Practice ◽  
Analysis Model ◽  
Hard Roof ◽  
Working Face ◽  
The Stability

In the inclination direction, the fracture law of a longwall face roof is very important for roadway control. Based on the W1123 working face mining of Kuangou coal mine, the roof structure, stress and energy characteristics of W1123 were studied by using mechanical analysis, model testing and engineering practice. The results show that when the width of W1123 is less than 162 m, the roof forms a rock beam structure in the inclined direction, the floor pressure is lower, the energy and frequency of microseismic (MS) events are at a low level, and the stability of the section coal pillar is better. When the width of W1123 increases to 172 m, the roof breaks along the inclined direction, forming a double-hinged structure, the floor pressure is increased, and the frequency and energy of MS events also increases. The roof gathers elastic energy release, and combined with the MS energy release speed it can be considered that the stability of the section coal pillar is better. As the width of W1123 increases to 184 m, the roof in the inclined direction breaks again, forming a multi-hinged stress arch structure, and the floor pressure increases again. MS high-energy events occur frequently, and are not conducive to the stability of the section coal pillar. Finally, through engineering practice we verified the stability of the section coal pillar when the width of W1123 was 172 m, which provides a basis for determining the width of the working face and section coal pillar under similar conditions.

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