Table of contents

The recent discovery of borophene, a two-dimensional allotrope of boron, raises many questions about its structure and its chemical and physical properties. Boron has a high chemical affinity to oxygen but little is known about the oxidation behaviour of borophene. Here we use first principles calculations to study the phase diagram of free-standing, two-dimensional B_1−xO_x for compositions ranging from x = 0 to x = 0.6, which correspond to borophene and ${{\rm{B}}}_{2}{{\rm{O}}}_{3}$ sheets, respectively. Our results indicate that no stable compounds except borophene and ${{\rm{B}}}_{2}{{\rm{O}}}_{3}$ sheets exist. Intermediate compositions are heterogeneous mixtures of borophene and ${{\rm{B}}}_{2}{{\rm{O}}}_{3}$. Other hypothetical crystals such as ${{\rm{B}}}_{2}{\rm{O}}$ are unfavorable and some of them underwent spontaneous disproportionation into borophene and ${{\rm{B}}}_{2}{{\rm{O}}}_{3}$. It is also shown that oxidizing borophene inside the flakes is thermodynamically unfavorable over forming ${{\rm{B}}}_{2}{{\rm{O}}}_{3}$ at the edges. All findings can be rationalized by oxygen's preference of two-fold coordination which is incompatible with higher in-plane coordination numbers preferred by boron. These results agree well with recent experiments and pave the way to better understand the process of oxidation of borophene and other two-dimensional materials.

Ni-based composite ceramic coatings with good comprehensive performance are obtained by a supersonic plasma spraying process. A ceramic powder is added to a Ni60/WC powder to make the surface of the sprayed sample more uniform and compact. Pores are present on the surface of the two composite ceramic coatings prepared by NiWT(Ni60/WC + TiO₂) and NiWA(Ni60/WC + Al₂O₃), as well as five phase components. In the microscopic morphology of the two composite ceramic coatings, the surface composition of the NiWT coating is relatively uniform and the surface of NiWA exhibits a cluster structure with more pits than NiWT. The friction coefficient of the NiWT coating at 200 r min⁻¹ is between 0.40 and 0.43 and that of the NiWA coating is between 0.35 and 0.38. Simultaneously, the abrasion width and wear volume of the NiWT and NiWA coatings are small compared with the substrate, while the abrasion width and volume of the NiWT coating are smaller. The composite ceramic coatings prepared by the addition of two kinds of oxidized ceramics, through comparative analysis of the experiment, showed that NiWT had an improved surface micro-morphology and wear resistance than NiWA. The wear morphology of NiWT showed a wear mechanism of abrasive particles and the wear morphology of NiWA showed a fatigue wear mechanism.

Systems like the Morse oscillator with potential energies that have a minimum and states that are both bounded and extended are considered in this study in the microcanonical statistical ensemble. In the binding region, the entropy becomes a growing function of the internal energy and has a well-defined inflection point corresponding to a temperature maximum. Consequently, the specific heat supports negative and positive values around this region. Moreover, focusing on this inflection point allows to define the critical energy and temperature, both evaluated analytically and numerically. Specifically, the existence of this point is the signature of a phase transition, and latent heat dynamics occur to accomplish the transition. The conditions established below apply to a large variety of potentials, including molecular ones, and have relevance for physics, chemistry, and engineering sciences. As a specific application, we show that the inflection point for the H₂ molecule occurs at −1.26 [eV].

Wave functions for terms with the same orbital angular momentum L and spin angular momentum S, but different parents can be written as a linear combination of the pure parentage wave functions. These wavefunctions are important because various spectroscopic quantities e.g. energy and transition probability can be calculated with the help of these wavefunctions. In this study we present 46 wavefunctions of seventeen terms (²P,²D, ²F, ²G, ²H, ²I, ²K, ²L, ⁴S, ⁴D, ⁴F, ⁴G, ⁴I,( ²D, ²F, ²G, ²H) are repeated terms, all terms have seniorty number 3 except ²F whose seniorty number is 1) of $4{f}^{3}6{s}^{2}\,$configuration of Pr I, with seven parents (¹S, ¹D, ¹G, ¹I, ³P, ³F, ³H) belonging to ${f}^{2}.$ Some of the wavefunctions are non-orthogonal as they belong to same term symbol, having different seniority number. Gram-Schmidt procedure was used to make them orthogonal.

We report on the recent advances regarding the source code optimization of Reverse Monte Carlo modelling used in scattering data analysis of an amorphous molecular solid which has recently attracted attention as a new brilliant white light emitter if irradiated by a simple infrared laser diode. The algorithm used for generating random molecular starting configurations without overlapping molecules in a box with periodic boundary conditions has been accelerated by a factor of roughly 400 in a 54k atom case. The resulting bigger independent starting configurations are used to gain further insight into previously presented x-ray scattering data. New improved scattering data have been obtained, revealing new structural features in the lower Q range.

We report on the electrical transport properties of new graphene/blue phosphorene heterostructure devices by density functional theory (DFT) within the non-equilibrium Green's function (NEGF) approach. From the results, it is found that the devices with different length of contacts layers show semiconducting nature. The integrated contacted length of graphene/blue phosphorene two-layer device shows the best conductivity under a bias voltage. The negative differential resistance effect (NDR) is also found in the current-voltage curve of all the graphene/blue phosphorene devices. Transport characteristics can be explained by the eigenvalues of self-consistent Hamiltonian (MPSH). The results show that the device is fabricated from graphene/blue phosphorous and has good electrical conductivity. These interesting features will be useful for future electronic products.

We report on the growth of isotopically enriched ²⁸Si epitaxial films with precisely controlled enrichment levels, ranging from natural abundance ratio of 92.2% all the way to 99.99987% (0.832 × 10⁻⁶ mol mol^{−1 29}Si). Isotopically enriched ²⁸Si is regarded as an ideal host material for semiconducting quantum computing due to the lack of ²⁹Si nuclear spins. However, the detailed mechanisms for quantum decoherence and the exact level of enrichment needed for quantum computing remain unknown. Here we use hyperthermal energy ion beam deposition with silane gas to deposit epitaxial ²⁸Si. We switch the mass selective magnetic field periodically to control the ²⁹Si concentration. We develop a model to predict the residual ²⁹Si isotope fraction based on deposition parameters and measure the deposited film using secondary ion mass spectrometry (SIMS). The measured ²⁹Si concentrations show excellent agreement with the prediction, deviating on average by only 10%.

Time-dependent variational principle (TDVP) provides powerful methods in solving the time-dependent Schröinger equation. As such Kan developed a TDVP (Kan 1981 Phys. Rev. A 24, 2831) and found that there is no Legendre transformation in quantum variational principle, suggesting that there is no place for the Maupertuis reduced action to appear in quantum dynamics. This claim is puzzling for the study of quantum–classical correspondence, since the Maupertuis least action principle practically sets the very basic foundation of classical mechanics. Zambrini showed within the theory of stochastic calculus of variations that the Maupertuis least action principle can lead to the Nelson stochastic quantization theory (Zambrini 1984 J. Math. Phys.25, 1314). We here revisit the basic aspect of TDVP and reveal the hidden roles of Maupertuis-Hamilton least action in the Schrödinger wavepacket dynamics. On this basis we propose a dual least (stationary) action principle, which is composed of two variational functionals; one responsible for 'energy related dynamics' and the other for 'dynamics of wave-flow'. The former is mainly a manifestation of particle nature in wave-particle duality, while the latter represents that of matter wave. It is also shown that by representing the TDVP in terms of these inseparably linked variational functionals the problem of singularity, which is inherent to the standard TDVPs, is resolved. The structure and properties of this TDVP are also discussed.

We present a study of the magnetoresistivity of thin film MnSi in high magnetic fields. We establish that the magnetoresistivity can be understood in terms of spin fluctuation theory, allowing us to compare our data to studies of bulk material. Despite of a close qualitative resemblance of bulk and thin film data, there are clear quantitative differences. We propose that these reflect a difference of the spin fluctuation spectra in thin film and bulk material MnSi, and discuss possible causes.

This study is aimed at the development of high-temperature superconducting (HTS) magnets for application in a fusion experimental device next to the Large Helical Device (LHD). By applying the features of an HTS, high current density and high stability can be balanced. As a candidate conductor, REBCO tapes and pure aluminum sheets are laminated and placed in the groove of an aluminum alloy jacket with a circular cross-section, after joining a lid to the jacket using friction stir welding, and twisting the conductor to homogenize its electrical and mechanical properties. The FAIR conductor derives its name from the processes and materials used in its development: Friction stir welding, an Aluminum alloy jacket, Indirect cooling, and REBCO tapes. Initially, the degradation of the critical current of the FAIR conductor is observed, which was eventually resolved. The development status of the FAIR conductor has been reported.

Motivated by recent data on high-quality MgB₂ thin films implying that the smaller energy gap has l = 6 (i-wave) symmetry, we consider a simple model for an all-MgB₂ symmetric Josephson Junction (JJ). The model assumes an arbitrary-strength delta-function barrier and one-dimensional current conduction. It is shown that in this context a nodal energy gap with i-wave symmetry acts as an isotropic energy gap (s-wave) with an amplitude modified by the energy-gap misalignment-angle with respect to the crystal principal axes. The corresponding exact Green's function in momentum space is derived employing a novel approach. The ensuing current-phase relations in the strong and weak barrier-strengths limits are calculated and found to confirm known results, e.g., the Ambegaokar-Baratoff current-phase relation. Inspired by an HTS experiment that established the d-wave energy-gap symmetry, we propose a JJ-related experiment with a MgB₂ bicrystal to confirm our premise that the smaller energy has i-wave symmetry.

The electron kinetics in nanowire-based hot-carrier solar cells is studied, where both relaxation and extraction are considered concurrently. Our kinetics is formulated in the many-particle basis of the interacting system. Detailed comparison with simplified calculations based on product states shows that this includes the Coulomb interaction both in lowest and higher orders. While relaxation rates of 1 ps are obtained, if lowest order processes are available, timescales of tens of ps arise if these are not allowed for particular designs and initial conditions. Based on these calculations we quantify the second order effects and discuss the extraction efficiency, which remains low unless an energy filter by resonant tunnelling is applied.

In this paper, the energy-extraction efficiencies of the electron beam are studied for several cases of free-electron laser (FEL). For an initially cold electron beam, the optimal initial detuning for the maximum energy-extraction efficiency and the corresponding saturation length are given. A scheme of the 'top up' is proposed to enhance the efficiency: after the electron energy being modulated somewhat, a phase shift and a step-down of the phase bucket are introduced, so that all electrons are located near the upper separatrix of the bucket in the phase space. Finally, the energy-extraction efficiency can be increased by 30% compared with that of the normal undulator case. For a linear tapering undulator with an initially cold electron beam, the simple scaling laws for the maximum energy-extraction efficiency and the corresponding optical power gain are obtained. For a tapered undulator with the pre-bunched electron beam, our analysis gives that the energy-extraction efficiency reaches the maximum when the phase bucket height of the tapered undulator is equal to the amplitude of the detuning modulation. The numerical results validated this reasoning and show that the efficiency has a large increase compared with the case of the unbunched electron beam. The single stair-step undulator is investigated, the optimal step and the corresponding saturation power and saturation length are given by analysis, they agree well with the numerical simulation results.

This paper proposes a novel method for modeling retinal cone distribution in humans. It is based on Blue-noise sampling algorithms being strongly related with the mosaic sampling performed by cone photoreceptors in the human retina. Here we present the method together with a series of examples of various real retinal patches. The same samples have also been created with alternative algorithms and compared with plots of the center of the inner segments of cone photoreceptors from imaged retinas. Results are evaluated with different distance measure used in the field, like nearest-neighbor analysis and pair correlation function. The proposed method can effectively describe features of a human retinal cone distribution by allowing to create samples similar to the available data. For this reason, we believe that the proposed algorithm may be a promising solution when modeling local patches of retina.

This paper is an application to Einstein's gravity (EG) of the mathematics developed in (Plastino and Rocca 2018 J. Phys. Commun.2, 115029). We will quantize EG by appeal to the most general quantization approach, the Schwinger-Feynman variational principle, which is more appropriate and rigorous that the functional integral method, when we are in the presence of derivative couplingsWe base our efforts on works by Suraj N. Gupta and Richard P. Feynman so as to undertake the construction of a Quantum Field Theory (QFT) of Einstein Gravity (EG). We explicitly use the Einstein Lagrangian elaborated by Gupta (Gupta, Proc. Pys. Soc. A, 65, 161) but choose a new constraint for the theory that differs from Gupta's one. In this way, we avoid the problem of lack of unitarity for the S matrix that afflicts the procedures of Gupta and Feynman. Simultaneously, we significantly simplify the handling of constraints. This eliminates the need to appeal to ghosts for guarantying the unitarity of the theory. Our ensuing approach is obviously non-renormalizable. However, this inconvenience can be overcome by appealing tho the mathematical theory developed by (Bollini et al Int. J. of Theor. Phys.38, 2315, Bollini and Rocca Int. J. of Theor. Phys.43, 1909, Bollini and Rocca Int. J. of Theor. Phys.43, 59, Bollini et al, Int. J. of Theor. Phys.46, 3030, Plastino and Rocca J. Phys. Commun.2, 115029) Such developments were founded in the works of Alexander Grothendieck (Grothendieck Mem. Amer. Math Soc.16 and in the theory of Ultradistributions of Jose Sebastiao e Silva Math. Ann.136, 38) (also known as Ultrahyperfunctions). Based on these works, we have constructed a mathematical edifice, in a lapse of about 25 years, that is able to quantize non-renormalizable Field Theories (FT). Here we specialize this mathematical theory to treat the quantum field theory of Einsteins's gravity (EG). Because we are using a Gupta-Feynman inspired EG Lagrangian, we are able to evade the intricacies of Yang-Mills theories.

Magnetostatic dipolar anisotropy energy and the total dipolar anisotropy constant, ${K}_{{total}}$, in periodic arrays of ferromagnetic nanowires have been calculated as a function of the nanowire radius, the interwall distance of the nanowires in the arrays and the geometry of the array (square or hexagonal), by using a realistic atomistic model and the Ewald method. The simulated nanowires have a radius size up to 175 Å that corresponds to 31 500 atoms, and the simulated nanowire arrays have interwall distances between 35 and 3000 Å. The dependence of total magnetostatic dipolar anisotropy constant on the nanowire radius, their interwall distance and the type of array symmetry has been analyzed. The total dipolar anisotropy constant, which is the sum of the intrananowire dipolar anisotropy constant, ${K}_{{intra}}$, due to the dipolar interactions inside an isolated nanowire and the main responsible of the shape anisotropy, and of the internanowire dipolar anisotropy constant, ${K}_{{inter}}$, due to the magnetostatic dipolar interactions among nanowires in the array, have been calculated and compared with the magnetocrystalline anisotropy constant for three nanowire compositions and their crystalline structures. The simulations of the nanowire arrays with large interwall distances have been used to calculate the intrananowire anisotropy constant, ${K}_{{intra}}$, and to analyze the competition between the intrananowire, internanowire and magnetocrystalline anisotropies. According to some magnetic theories, the ratio $| {K}_{{inter}}/{K}_{{intra}}|$ equals to the areal filling fraction of a nanowire array. Present calculations indicate that the equation for the areal filling fraction matches perfectly for any interwall distance and radius of Ni and Co nanowire arrays. This first equation is used to write a general equation that relates the radius and interwall distance of nanowire arrays with the intrananowire, internanowire and magnetocrystalline anisotropies. This general equation allows to design the geometry of nanowire arrays with the desired orientation of the easy magnetization axis.