Theoretical Study Research Articles

A theoretical study on behaviours of H2 on Fe(100) surface under environmental pressure and temperature

In order to investigate the behaviour of H2 molecules on Fe surface, the interaction between Fe and H atoms was characterized by molecular dynamics using the Reactive Force Field (ReaxFF) in atomistic simulations. The impact of environmental hydrogen pressure on H2 adsorption and H atom absorption on Fe(100) surface is researched at different temperatures. The analysis is done with variant methods to explore the relationship among binding energy, bond lengths, charge transfer and bond breaking under variant hydrogen pressures and temperatures.

The initial sticking of high velocity water onto graphite under non-equilibrium supersonic flow conditions.

In this paper, we present a combined experimental and theoretical study that explored the initial sticking of water on cooled surfaces. Specifically, these ultra-high vacuum gas-surface scattering experiments utilized supersonic molecular beam techniques in conjunction with a cryogenically cooled highly oriented pyrolytic graphite crystal, giving control over incident kinematic conditions. The D2O translational energy spanning 300-750meV, the relative D2O flux, and the incident angle could all be varied independently. Three different experimental measurements were made. One involved measuring the total amount of D2O scattering as a function of surface temperature to determine the onset of sticking under non-equilibrium gas-surface collision conditions. Another measurement used He specular scattering to assess structural and coverage information for the interface during D2O adsorption. Finally, we used time-of-flight (TOF) measurements of the scattered D2O to determine how energy is exchanged with the graphite surface at surface temperatures above and near the conditions needed for gaseous condensation. For comparison and elaboration of the roles that internal degrees of freedom play in this process, we also did similar TOF measurements using another mass 20 incident particle, atomic neon. Enriching this study are precise molecular dynamics simulations that elaborate on gas-surface energy transfer and the roles of molecular degrees of freedom in gas-surface collisional energy exchange processes. This study furthers our fundamental understanding of energy exchange and the onset of sticking and ultimately gaseous condensation for gas-surface encounters occurring under high-velocity flows.

Experimental and theoretical studies on the compatibility of DNTF and typical hydrocarbon polymer binders.

3,4-bis(3-nitrofurazan-4-yl) furoxan (DNTF) is one of the third-generation energetic compounds with excellent comprehensive properties, which can be added to polymer bonded explosive (PBX) to improve energy levels and regulate sensitivity, so the compatibility of DNTF with other components in PBX, especially the binder, is the first question. Herein, two typical hydrocarbon polymers commonly used in PBX, which are hydroxyl-terminated polybutadiene (HTPB) and polyisobutylene (PIB), were selected as the binder, and the compatibility of HTPB and PIB with DNTF was investigated by differential scanning calorimetry (DSC), the vacuum stability test (VST), and in situ infrared spectroscopy (in situ IR). The results of compatibility experiments were verified by using the binding energy and solubility parameter criteria in molecular dynamics (MD). Experimental and MD simulation results showed that DNTF could be compatible with PIB but incompatible with HTPB. The frontier molecular orbital theory in quantum chemistry (QC) was adopted to explore the frontier orbital electron distribution and energy levels of DNTF/HTPB and DNTF/PIB composite systems to better understand the microscopic compatibility mechanism. The compatibility results of the two composite systems were explained from the perspective of electron transfer. All these can deduce that a hydrocarbon polymer binder with a saturated carbon-hydrogen bond at the end of the molecular chain has good compatibility with DNTF, compared with a hydroxyl group, which has bad compatibility with DNTF.

Polymorphism and the Red Queen: The Selective Maintenance of Allelic Variation in a Deteriorating Environment.

Although allelic variation is ubiquitous in natural populations, our theoretical models are poor at predicting the existence and properties of these observed polymorphisms. Here, inspired by Van Valen's Red Queen hypothesis, we modelled the effect of viability selection in a deteriorating environment on the properties of allelic variation in populations subject to recurrent mutation. In Monte Carlo simulations, we found that levels of polymorphism consistently built up over time. We censused the simulated populations after 10,000 generations of mutation and selection, revealing that, compared to models assuming a constant environment, the mean number of alleles was greater, as was the range of allele numbers. These results were qualitatively robust to the addition of genetic drift and to relaxing the assumption that the viabilities of phenogenotypes containing a new mutation are independent of each other (i.e., incorporating a model of generalized dominance). The broad range of allele numbers realized in the simulated populations - from monomorphisms to highly polymorphic populations - more closely corresponds to the observed range from numerous surveys of natural populations than previously found in theoretical studies. This match suggests that, contrary to the views of some writers, selection may actively maintain genetic variation in natural populations, particularly if the selective environment is gradually becoming harsher. Our simulations also generated many populations with heterozygote advantage, a mismatch with real data that implies that this selective property must arise extremely rarely in natural populations.

Theoretical study of the hydrolysis mechanism of β-lactam antibiotics catalysed by a Zn(II) dinuclear biomimetic organometallic complex

The degradation and metabolism of antibiotics have attracted the scientific community's attention due to the environmental problems caused by the inappropriate use and disposal of these drugs. Therefore, it is crucial to understand the reaction mechanism involved in the degradation of these compounds. We studied the hydrolysis of nitrocefin and benzylpenicillin, two β-lactam ring antibiotics, mediated by an enzymatic mimetic Zn organometallic compound, using DFT methods. The electronic effects of functional groups adjacent to the β-lactam ring were analysed and good agreement between experimental and theoretical results was found. The reaction involves the nucleophilic attack of the bridging hydroxide group on the Zn atoms towards the β-lactam ring. A stepwise mechanism was found to agree with the experimental results. Chemical hardness profiles were affected by the solvent and reaction synchronicity. Geometric rearrangements dominated the activation barrier, and both antibiotics exhibited late transition states.

Theoretical study on the structure and properties of energetic salts with catenated N11 cation

Theoretical study on the structure and properties of energetic salts with catenated N11 cation

Theoretical study on photoelectric properties of ferroelectric photovoltaic perovskite CsGeBr3 based on first-principle calculations

Ferroelectric photovoltaic materials have attracted great attention because of their unique photoelectric conversion mechanism, high photo-generated voltage, and adjustable polarization intensity. Traditional ferroelectric oxide perovskites such as BaTiO3, BiFeO3, and Pb(ZrTi)O3 have attracted much attention but they are not suitable as light absorbing layers in solar cells, due to the large optical bandgap, low light absorption rate, and small photogenerated current. Therefore, it is necessary to seek prominent materials with both ferroelectric and suitable band gaps. Recently, the evidence of ferroelectricity in the typical three-dimensional all-inorganic halide perovskites CsGeX3, with band gaps of 1.6 eV to 2.3 eV has been confirmed. However, the spontaneous polarization of ferroelectric perovskite CsGeX3 is ∼10 to 20 μc cm−2 which is weaker than that of ABO3 (∼26 to 75 μc cm−2). Strain engineering has a significant influence on the properties of semiconductor materials by controlling the lattice scaling and the internal atomic spacing. Hence, in this work, strain engineering is introduced to adjust the ferroelectric polarization and the photoelectric properties of ferroelectric perovskite CsGeBr3. The calculated results show that when the applied compressive strain increases from 0% to −4%, the spontaneous polarization of ferroelectric perovskite CsGeBr3 increases from 14.23 μc cm−2 to 51.61 μc cm−2, and the band gap reduces from 2.3631 eV to 1.5310 eV. The effective mass of electrons and holes gradually reduces, exciton binding energies decrease from 48 meV to 5 meV, and the optical absorption coefficient is strongly enhanced from 3 × 105 cm−1 to 5 × 105 cm−1 in the visible range. Besides, the power conversion efficiency(PCE) of CsGeBr3 is significantly increased from 16.95% to 26.77%. Therefore, the results indicate that the application of compressive strain can increase the ferroelectric polarization and enhance the original photovoltaic performance of ferroelectric perovskite CsGeBr3. Our theoretical calculations can provide useful insights and beneficial guidance into experimental studies of ferroelectric perovskites in photoelectric applications.

Teaching Quality Care for Healthcare Professionals: Delphi Consensus on Designing Drama

Purpose: This study aimed to design drama for teaching quality care for healthcare professionals based on the newest evidence for continuous professional development and confront challenges for teaching healthcare professionals through multimedia that shift the trend in education from instructive to constructivist learning. Methodology: This study was conducted through a three-round stepwise Delphi consensus on a judgmental sample of expert panelists. The researchers identified the expert panelists' demographic and professional characteristics, studied the views and expectations of designing drama for teaching quality care, and appraised the designed drama with a self-administered structured questionnaire and a scale, respectively. Findings: Study results revealed that expert panelists achieved consensus on several items concerning the drama's content and design. The expert panelists' appraisals of the internal validity and consistency of the designed drama were (p≤0.05) and (0.767) as measured by the Pearson correlation test and Cronbach α, respectively. Unique Contribution to Theory, Practice, and Policy: The researchers conclude that expert panelists recommend applying drama in teaching, and with in-depth discussion, they verbalize how drama can improve educational outcomes. The researchers recommend adopting and disseminating the designed drama for teaching healthcare professionals’ quality care and instilling drama in teaching curricula to address the gap between theoretical study and what is faced in real fields.

Urbanism(s) and informality(ies) in Rio de Janeiro, Brazil

This article examines urbanisms and informalities intertwined with Brazilian popular culture, in the light of a theoretical and empirical study of two examples from the city of Rio de Janeiro, Brazil. The primary conclusions underscore a tension between formal urbanism, which attempts to propagate a uniform way of urban existence, and the exuberance of life in the urbe. This highlights that urbanism is inherently multifaceted and requires the incorporation of multiple urban existences within global south cities while considering their distinctions.

A mathematical expression to predict a laser pulse shape

A mathematical expression to predict the shape of a laser pulse is obtained. It is compatible with an experimental one published elsewhere. Comparative computations with other published trials that follow the same trend are made. As a result, our trial is recommended for forthcoming theoretical studies to be published in the field of pulsed laser heating.

Modeling Density Waves and Circulations in Vertical Cross-Section in Adhesive Contacts

This work continues the study of the process of friction between a steel spherical indenter and a soft elastic elastomer previously published in our paper. It is done in the context of our previous experimental results obtained on systems with strongly pronounced adhesive interaction between the surfaces of contacting bodies during the process of friction between a steel spherical indenter and a soft elastic elastomer. In the present paper, we concentrate on the theoretical study of the processes developing in a vertical cross-section of the system. For continuity, here the case of indenter motion at a low speed at different indentation depths is considered as before. The analysis of the evolution of normal and tangential contact forces, mean normal pressure, tangential stresses, as well as the size of the contact area is performed. Despite its relative simplicity, a numerical two-dimensional (2D = 1 + 1) model, which is used here, satisfactorily reproduces experimentally observed effects. Furthermore, it allows direct visualization of the motion in the vertical cross-section of the system, which is currently invisible experimentally. Partially, it recalls two-dimensional (2D = 1 + 1) models recently proposed to describe the “turbulent” shear flow of solids under torsion and in cellular materials. The observations extracted from the model help us to understand better the adhesive processes that underlie the experimental results.

A theoretical study of electronic, magnetic, magnetocaloric and thermoelectric of perovskite LaCoO 3 compound with high spin

A theoretical study of electronic, magnetic, magnetocaloric and thermoelectric of perovskite LaCoO ₃ compound with high spin

Theoretical study of the nonlinear magnon-phonon coupling in CoF2.

The coupling and interplay between magnon and phonon are important topics for spintronics and magnonics. In this work we studied the nonlinear magnon-phonon coupling in CoF2. First-principles calculations demonstrate that the antiferromagnetic resonance magnon drives a phonon with B1g character; the oscillating driving force has a frequency twice of that of the magnon. Comparing with similar materials indicates a strong correlation between the strength of nonlinear magnon-phonon coupling and the orbital magnetic moment of the magnetic ion. This work pave the way for theoretical study of nonlinear magnon-phonon coupling.&#xD.

Theoretical Study of the Adsorption of Some Azoles on the Graphene Surface

Theoretical Study of the Adsorption of Some Azoles on the Graphene Surface

Band Engineering of Perovskite Quantum Dot Solids for High-Performance Solar Cells.

CsPbI3 perovskite quantum dot (PQD) shows high potential for next-generation photovoltaics due to their tunable surface chemistry, good solution-processability and unique photophysical properties. However, the remained long-chain ligand attached to the PQD surface significantly impedes the charge carrier transport within the PQD solids, thereby predominantly influencing the charge extraction of PQD solar cells (PQDSCs). Herein, a ligand-induced energy level modulation is reported for band engineering of PQD solids to improve the charge extraction of PQDSCs. Detailed theoretical calculations and systemic experimental studies are performed to comprehensively understand the photophysical properties of the PQD solids dominated by the surface ligands of PQDs. The results reveal that 4-nitrobenzenethiol and 4-methoxybenzenethiol molecules with different dipole moments could firmly anchor to the PQD surface thoroughly the thiol group to modulate the energy levels of PQDs, and a gradient band structure within the PQD solid is subsequently realized. Consequently, the band-engineered PQDSC delivers an efficiency of up to 16.44%, which is one of the highest efficiencies of CsPbI3 PQDSCs. This work provides a feasible avenue for the band engineering of PQD solids by tuning the surface chemistry of PQDs for high-performing solar cells or other optoelectronic devices. This article is protected by copyright. All rights reserved.

Мultiple regression analysis of indicators influencing the sports result in sprinting

Given the slogan "Faster, Higher, Stronger", which inspires athletes to win and set new records, unfortunately, today it is impossible without data and figures. Therefore, the article presents the results of theoretical and experimental studies aimed at finding and analyzing the factors that most affect the final sports result of athletes in sprinting. Based on the world ranking as of 2023, 3000 records were selected and analyzed. The authors have created a unique dataset of 7 attributes. In the paper, the authors emphasize the need to prepare the obtained records for mathematical analysis. It was found that out of 3000 records, 1278 were valid, which became the basis for the application of multiple linear regression. It is emphasized that it was the use of regression that made it possible to identify the contribution of each independent variable to the variation of the dependent variable. The author concludes that there is a need for further search for factors that have a much greater impact on the final sports result.

Generating High-Precision Force Fields for Molecular Dynamics Simulations to Study Chemical Reaction Mechanisms Using Molecular Configuration Transformer.

Theoretical studies on chemical reaction mechanisms have been crucial in organic chemistry. Traditionally, calculating the manually constructed molecular conformations of transition states for chemical reactions using quantum chemical calculations is the most commonly used method. However, this way is heavily dependent on individual experience and chemical intuition. In our previous study, we proposed a research paradigm that used enhanced sampling in molecular dynamics simulations to study chemical reactions. This approach can directly simulate the entire process of a chemical reaction. However, the computational speed limited the use of high-precision potential energy functions for simulations. To address this issue, we presented a scheme for training high-precision force fields for molecular modeling using a previously developed graph-neural-network-based molecular model, molecular configuration transformer. This potential energy function allowed for highly accurate simulations at a low computational cost, leading to more precise calculations of the mechanism of chemical reactions. We applied this approach to study a Claisen rearrangement reaction and a carbonyl insertion reaction catalyzed by manganese.

Theoretical study on the mechanism of alcohol photooxidation on Nb2O5 surface.

Theoretical modeling of the solid-state photocatalysis is one of the important issues as various useful photocatalysts have been developed to date. In this work, we investigated the mechanism of the alcohol photooxidation on niobium oxide (Nb2O5) which was experimentally developed, using the density functional theory (DFT)/time-dependent (TD)DFT calculations based on the cluster model. The alcohol adsorption and the first hydrogen transfer from hydroxy group to surface occur in the ground state, while the second hydrogen transfer from CH proceeds in the excited states during the photoirradiation of UV or visible light. The spin crossing was identified and the low-lying triplet states were solved for the reaction pathway. The photoabsorption in the visible light region was characterized as the charge transfer transition from O 2p of alcohol to Nb 4d of the Nb2O5 surface. The spin density and the natural population analysis indicated the generation of spin density in the moiety of carbonyl compound and its dissipation to the interface of the surface, which partly explains the electron paramagnetic resonance measurement. It was confirmed that the rate determining step is the desorption of carbonyl compound and water molecule in agreement with the experimental rate equation analysis. The present findings with the theoretical modeling will provide useful information for the further studies of the solid-state photocatalysis.

Non-Linear Creep-Relaxation Constitutive Damage Model for Aging Concrete

A thermodynamic constitutive damage model for plain concrete, and other quasi-brittle aging materials, under creep relaxation is developed. The model accounts for the anisotropic damage induced through a second-order tensor damage variable. The aging viscoelasticity of the material is considered through the theory of solidification for aging solidifying materials. The material is considered a viscoelastic-damageable material. The Helmholtz free energy, utilized in the formulation, is treated based on the representation theorem of coupled damage strain tensors and Volterra integral equations. The model can analyze time-dependent damage (tertiary creep) under constant loading and can account for damage due to cyclic creep. Theoretical case studies are considered to illustrate the applicability of the model. The determination of the functions and constants, representing the material behavior, as well as any experimental companion is proposed for further research.

Influence of coupled water and thermal treatments on the fracture characteristics of a typical sandstone

Understanding the fracture behavior of rock after coupled water and thermal environment is important for many geotechnical projects. This study examines the influence of coupled water and thermal treatments on the fracture toughness and characteristics of a typical sandstone under mode I and mode II loading conditions. Notched deep beam (NDB) specimens were utilized and subjected to soaking treatments at various water temperatures (23 °C, 60 °C, and 99 °C). The experimental results indicate a significant reduction in both mode I and mode II fracture toughness values, with reductions ranging from 15.4% to 13.2% for mode I and 26.1% to 8.9% for mode II respectively. As the water temperatures increase, a slightly rising trend is observed in both mode I and mode II fracture toughness within the examined temperature range. Sandstone specimens displayed typical brittle fracture characteristics at lower soaking temperatures. For mode I specimens, an increase in ductility was evident with higher soaking temperatures, while the ductile behavior is less pronounced in the mode II specimens. Based on the Maximum Tangential Stress (MTS) criterion and the Generalized Maximum Tangential Stress (GMTS) criterion, the predicted values of mode II fracture toughness and the fracture process zone (FPZ) were discussed. The results show that both the GMTS and MTS criteria exhibit inaccuracies in predicting the mode II fracture toughness of sandstone treated at different soaking water temperatures. However, the GMTS criterion, which incorporates T-stress, demonstrates smaller errors compared to the MTS criterion. The study shows that the radius r0 of the fracture process zone is not a constant under both mode I and mode II loading conditions. The calculation of the fracture process zone radius r0 in the GMTS criterion requires further theoretical and experimental study.