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Minerals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 98
Author(s):  
Jordi Ibáñez-Insa

The crystal structures of newly found minerals are routinely determined using single-crystal techniques. However, many rare minerals usually form micrometer-sized aggregates that are difficult to study with conventional structural methods. This is the case for numerous platinum-group minerals (PGMs) such as, for instance, zaccariniite (RhNiAs), the crystal structure of which was first obtained by studying synthetic samples. The aim of the present work is to explore the usefulness of USPEX, a powerful crystal structure prediction method, as an alternative means of determining the crystal structure of minerals such as zaccariniite, with a relatively simple crystal structure and chemical formula. We show that fixed composition USPEX searches with a variable number of formula units, using the ideal formula of the mineral as the only starting point, successfully predict the tetragonal structure of a mineral. Density functional theory (DFT) calculations can then be performed in order to more tightly relax the structure of the mineral and calculate different fundamental properties, such as the frequency of zone-center Raman-active phonons, or even their pressure behavior. These theoretical data can be subsequently compared to experimental results, which, in the case of newly found minerals, would allow one to confirm the correctness of the crystal structure predicted by the USPEX code.


Author(s):  
Shanmugapriya V ◽  
Bharathi S ◽  
Esakkinaveen D ◽  
Arunpandiyan S ◽  
Selvakumar B ◽  
...  

Abstract The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.


Author(s):  
Hua Liang

Abstract The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.


2022 ◽  
Vol 2022 ◽  
pp. 1-5
Author(s):  
Malik Bader Alazzam ◽  
Fahima Hajjej ◽  
Ahmed S AlGhamdi ◽  
Sarra Ayouni ◽  
Md Adnan Rahman

The thermal characteristics of polymathic methacrylate combined with unsaturated polyester were determined by numerical and experimental research. Models for numerically investigating the parameters of thermal conductivity, specific heat capacity, and thermal diffusivity were developed using COMSOL Multiphysics. The numerical data were then compared to experimental results for the same material using the same measurements to ensure that they were correct. By comparing the thermal conductivity data to two sets of theoretical data, the results were confirmed. The COMSOL models were quite close to the experimental data, with just minor differences between the three models. One set of theoretical data coincided with the mean of the other data, while the second set revealed a significant departure below the other data.


2022 ◽  
Author(s):  
Mike J. Newland ◽  
Camille Mouchel-Vallon ◽  
Richard Valorso ◽  
Bernard Aumont ◽  
Luc Vereecken ◽  
...  

Abstract. Reaction with ozone is an important atmospheric removal process for alkenes. The ozonolysis reaction produces carbonyls, and carbonyl oxides (Criegee intermediates, CI), which can rapidly decompose to yield a range of closed shell and radical products, including OH radicals. Consequently, it is essential to accurately represent the complex chemistry of Criegee intermediates in atmospheric models in order to fully understand the impact of alkene ozonolysis on atmospheric composition. A mechanism construction protocol is presented which is suitable for use in automatic mechanism generation. The protocol defines the critical parameters for describing the chemistry following the initial reaction, namely: the primary carbonyl / CI yields from the primary ozonide fragmentation; the amount of stabilisation of the excited CI (CI*); the unimolecular decomposition pathways, rates and products of the CI; the bimolecular rates and products of atmospherically important reactions of the stabilised CI (SCI). This analysis implicitly predicts the yield of OH from the alkene-ozone reaction. A comprehensive database of experimental OH, SCI and carbonyl yields has been collated using reported values in the literature and used to assess the reliability of the protocol. The protocol provides estimates OH, SCI and carbonyl yields with a root mean square error of 0.13 and 0.12 and 0.14, respectively. Areas where new experimental and theoretical data would improve the protocol and its assessment are identified and discussed.


2022 ◽  
pp. 268-278
Author(s):  
Khalida Akbar

The recovery period post acquired brain injury (ABI) results in individuals becoming vastly dependent on family support and caregivers. Theoretical data and findings suggest that there is a lack of awareness and family support structures surrounding those affected by ABI. The empirical data indicated the need for further research and development aimed at improving conditions for recovery for individuals who are recovering from acquired brain injury. This chapter is aimed at creating awareness of assistive technology that can be used in conjunction with existing family support structures for people who are affected by ABI. The findings of this study have the potential to significantly contribute to practices and policies in society through research by providing a local country-contextual theoretical understanding of what needs to be done for persons with ABI and how AT can be used as a recovery tool within family support structures during the recovery process.


2021 ◽  
Vol 7 (12) ◽  
pp. 117054-117072
Author(s):  
Cristiane de Oliveira Vieira Souza ◽  
Marta Batista de Souza Neta ◽  
Marcela Maria de Sena ◽  
Ângelo Angell Almeida ◽  
Mariana Guimarães dos Santos ◽  
...  

Psychological assessment is a practical application of professional psychologists working in different areas of health, education, safety, traffic and so on. as well as it can be applied in different contexts and at different moments of human development. Given the above, this article aimed to conduct a literature review to understand the paths built by psychological assessment in their contexts, ramifications and future possibilities, through a search in sources such as books, articles published in journals indexed in the main scientific databases from Brazil and the world, in order to promote a compilation of the main findings of science on the subject, in the light of different views and areas of psychology, education science and human health in general. To this end, a literature review was carried out, from scientific sources such as books, articles, dissertations, theses and monographs, in specialized websites and in scientific databases such as Scielo, Scopus, Lilacs, among others. Inclusion and exclusion criteria were used, filtering texts in Portuguese or English that were relevant to the theme. Theoretical data were analyzed and discussed between the authors and their views. Based on the research, it is possible to conclude that psychological assessment is a tool that directs the psychologist's therapeutics and praxis in educational, clinical, criminal contexts, among others. It is understood from the data in the literature that psychological assessment needs theoretical and practical knowledge, aligning and directing the procedure and guiding the correct diagnosis. Being the psychologist's responsibility, psychological assessment needs ethical procedures based on the professional psychologist's code of ethics, for collective and individual well-being in professional practice.


2021 ◽  
pp. 118-125
Author(s):  
V. Ternovsky ◽  
A. Svinarenko ◽  
Yu. Dubrovskaya

Theoretical studying spectrum of the excited states for the ytterbium atom is carried out within the relativistic many-body perturbation theory with ab initio zeroth approximation and generalized relativistic energy approach.  The zeroth approximation of the relativistic perturbation theory is provided by the optimized Dirac-Kohn-Sham ones. Optimization has been fulfilled by means of introduction of the parameter to the Kohn-Sham exchange potentials and further minimization of the gauge-non-invariant contributions into radiation width of atomic levels with using relativistic orbital set, generated by the corresponding zeroth approximation Hamiltonian. The obtained theoretical data on energies E and widths W of the ytterbium excited states are compared with alternative theoretical results (the Dirac-Fock, relativistic Hartree-Fock, perturbation  theories) and available experimental data. Analysis shows that the theoretical and experimental values ​​of energies are in good agreement with each other, however, the values ​​of widths differ significantly. In our opinion, this fact is explained by insufficiently accurate estimates of the radial integrals, the use of unoptimized bases, and some other approximations of the calculation.


2021 ◽  
pp. 126-133
Author(s):  
P. Zaichko ◽  
A. Kuznetsova ◽  
A. Tsudik ◽  
V. Mansarliysky

We present the results of relativistic calculation of the radiative transition probabilities and excited states lifetimes for a heavy Rydberg atomic systems in a black-body (thermal) radiation field on example of the rubidium. As theoretical approach we apply the combined generalized relativistic energy approach and relativistic many-body perturbation theory with ab initio Dirac zeroth  approximation. There are obtained the calculational data for the radiative transition probabilities and excited states lifetimes, in particular, the rubidium atom in the Rydberg states with principal quantum number n=10-100. It is carried out the comparison of obtained theoretical data on the effective lifetime for the group of Rydberg  nS states of the rubidium atom at a temperature of T = 300K with experimental data as well as data of alternative theoretical calculation based on the improved quasiclassical model.  It is shown that the  accuracy of the theoretical data on the radiative transition probabilities and excited states lifetimes is provided by a correctness of the corresponding relativistic wave functions and accounting for the exchange-correlation effects.


2021 ◽  
pp. 94-101
Author(s):  
A. Chernyshev ◽  
E. Efimova ◽  
V. Buyadzhi ◽  
I. Nikola

The energy parameters of the Auger transitions for the xenon atomic system are calculated within the combined relativistic energy approach and relativistic many-body perturbation theory with the zeroth order density functional approximation. The results are compared with reported experimental data as well as with those obtained by semiempirical method. The important point is linked with an accurate accounting for the complex exchange-correlation (polarization) effect contributions and using the optimized one-quasiparticle representation in the relativistic many-body perturbation theory zeroth order that significantly provides a physically reasonable agreement between theory and experiment.


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