Highly anisotropic and tunable charge carrier of monolayer phosphorus allotropes by bi-axial strain

The complex variation of electronic properties and carrier mobility of four typical allotropes of phosphorus are investigated using first-principles calculations of bi-axial strain. Our study shows that the electronic properties and carrier mobility of single-layer α-, β-, γ- and δ-P are sensitive to bi-axial strain, and that the carrier mobility can even be increased by several orders of magnitude under specific tensile or compressive strain. Moreover, the anisotropy of their mobility in the two-dimensional plane shows different changes according to the variation of the bi-axial strain. In particular, the electron mobility of α-P (γ-P) along the two main axis directions is reversed when the bi-axial strain increased by 5% (−4%). This transformation is mainly caused by changes in the effective mass anisotropy due to alterations in band dispersion under external strain, as illustrated by the distribution of effective mass anisotropy and the corresponding changes of electronic properties under strain.     

On the regular holonomic character of theS-matrix and microlocal analysis of unitarity-type integrals

The previously proved results that every analytically renormalized Feynman integral is a regular holonomic function suggests that theS-matrix should be locally expressible as an infinite sum of regular holonomic functions. A regularity propertyR is formulated that expresses the condition that theS-matrix be locally expressible near each physical pointp as a convergent sum of regular holonomic functions, with each term enjoying some of the regularity properties of a corresponding Feynman integral. This propertyR holds at every physical pointp that has yet been analyzed by the methods of axiomatic field theory orS-matrix theory. Some analyticity properties of unitarity-type integrals are then examined under the assumption that theS-matrix satisfies propertyR and a weak integrability condition. These results rest heavily on some recently proved properties of regular holonomic functions.     

Even and odd qs-coherent states and their photon-statistical properties

We construct explicitly even and odd qs-coherent states (qs-CSs), which are proved to form a representation of the quantum Heisenberg-Weyl algebra, and use the numerical method to study the influences of q and s deformations on photon-statistical properties of even and odd qs-CSs. It is shown that nonclassical properties of the even and odd qs-CSs are very different from those of the usual even and odd coherent states (CSs). It is found that the squeezing and antibunching effects appear for both even and odd qs-CSs in some range of the parameters q, s and r. The smaller the q (q < 1) and s, the larger the difference between the even and odd qs-CSs and the usual even and odd CSs.     

Time delay in nuclear reactions

The time delays involved under different circumstances in nuclear reactions, e.g., isolated or overlapping resonances, are analysed from the unified point of view of unitarity and of the statistical and analytical properties of theS-matrix. A general theorem is proved which says that the average over then open channels of the time delay of a wave packet covering many resonances (whose average separation isD) is given by?/(nD). The case of an incoherent superposition of monochromatic beams is also studied and the corresponding time delay is evaluated in the statistical model of Ericson.     

Physical properties of Ima2-BN under pressure: First principles calculations

A fully orthorhombic boron nitride (BN) polymorph with an orthorhombic symmetry (Ima2-BN, space group: Ima2) was investigated by first-principles calculations. The Ima2-BN under 30 GPa is both mechanically and dynamically stable via elastic constants and phonon spectra. The anisotropic and electronic properties of Ima2-BN under different pressure are investigated in this work. The anisotropic properties calculations show that the Young's modulus of Ima2-BN in (001) plane exhibits the greatest anisotropy under ambient pressure, while in (111) plane it is the greatest when P > 20 GPa, while the (010) plane has always exhibited the minimal anisotropy whether under ambient pressure or high pressure. Ima2-BN is an indirect wider band gap semiconductor material under ambient pressure, and the band gap of Ima2-BN decreases with the increasing pressure. The minimum thermal conductivities κ_min of Ima2-BN is 1.85 W/(cmK), it is slightly higher than of B₄N₄-I and c-BN.     

Ultrasound and microwave assisted synthesis of dihydroxyacetophenone derivatives with or without 1,2-diazine skeleton

A thorough study concerning O-alkylation and α-bromination of dihydroxyacetophenone (DA) and N-alkylation of 1,2-diazine, under ultrasound (US) and microwave (MW) irradiation as well as under conventional thermal heating (TH) is presented. Under US and MW irradiation the yields are higher, the amount of used solvent decreases substantially, the reaction time decreases considerable (from hours or days to minutes) and the consumed energy decreases, consequently the O-alkylation, α-bromination and N-alkylation methods could be considered environmentally friendly. A selective and efficient way to either bis-O-alkylation or mono-O-alkylation of DA has been found, the relative position of the two hydroxyl groups on the phenyl moiety being compulsory. A selective and efficient way for α-bromination in heterogeneous catalysis of DA derivatives under US irradiation is presented. The N-alkylation reaction of DA under US and MW irradiation proved to be the most convenient setup procedure for these types of reactions. Overall, the use of US proved to be more efficient than MW or TH.     

Chiral symmetry and functional integral

The change in the fermionic functional integral measure under chiral rotations is analyzed. Using the ζ-function method, the evaluation of chiral Jacobians to theories including nonhermitian Dirac operators D, can be extended in a natural way. (This being of interest, for example, in connection with the Weinberg-Salam model or with the relativistic string theory.) Results are compared with those obtained following other approaches, the possible discrepancies are analyzed and the equivalence of the different methods under certain conditions on D is proved. Also shown is how to compute the Jacobian for the case of a finite chiral transformation and this result is used to develop a sort of path-integral version of bosonization in d = 2 space-time dimensions. This result is used to solve in a very simple and economical way relevant d = 2 fermionic models. Furthermore, some interesting features in connection with the θ-vacuum in d = 2,4 gauge theories are discussed.     

Intra-center energy transfer dynamics in Cd1−xMnxTe semi magnetic semiconductors

Intra-center luminescence of Cd_1?xMn_xTe semi magnetic semiconductors under low excitation density was investigated both experimentally and by Monte-Carlo simulation. Experimental time-resolved spectra of 2 eV-band under different photon energy for excitation were used. The approach revealed that Mn²⁺–Mn²⁺excitation energy transfers take place by means of resonant dipole–dipole interaction. Besides energy transfer dynamics is strongly influenced by hopping-assisted quenching. Having been intra-center excitation selective-, mixed- and non-selective types of excitation are proved to occur if photon energy for excitation is increased. This is originated from overlapping of ⁴T₁- and ⁴T₂-states. Under inter-band excitation it was established that Mn²⁺-ion excitation takes place with the aid of excitonic energy transfer, with excitation energy being centered at exciton energy. Under temperature rise the transfer rate vigorously enhances due to great increase of overlap integral of Mn²⁺- ions' side-bands. The quenching is proved to be limited in accordance with existing theory. Inhomogeneous broadening diminishes as a result of fast fluctuation rate of excited ions' energy.     

Quantization of the conservation laws in the supersymmetric sine-Gordon model

The supersymmetric sine-Gordon model is quantized and proved to be superrenormalizable. The quantum version of the non-trivial conservation laws is obtained and it is proved (at different levels of rigour) that the equations ?_jp_jⁿ = 0 (n = 1, 3, 5, …) are not spoiled by the quantum anomalies.     

Dielectric relaxation in alkali silicate glasses: A new intepretation

The electric and dielectric properties of a ternary alkali sillicate glass (0.14 Na₂0?0.11 Mg0?0.75 SiO₂) have been studied as a function of temperature (350 K ? 600 K) and frequency (1 Hz ? 100 khz) using the impedance spectroscopy. It is proved that dispersion arises from the motion of sodium ions. Experimental data are interpreted with the helo of the CTRW, Continuous Time Random Walk, formalism developed by Scher and Lax which assumes that all the alkali ions are mobile but with different mobilities.     

Electron paramagnetic resonance of amorphous hydrogenated carbon grown under different conditions of deposition

Results from electron paramagnetic resonance (EPR) studies of amorphous hydrogenated carbon (a-C:H) obtained on a quartz substrate under different conditions of deposition E/p (where E is the electric field intensity between the electrodes, and p is the pressure of the gas mix in the capacitive chamber) and temperature of the substrate are presented. Correlations between the EPR line amplitude, spin density, and g-factor, and the optical, electrical, and mechanical properties of a-C:H are found.     

Thermostatistics of the multi-dimensional q-deformed fermionic Newton oscillators

The algebraic and representative properties of the multi-dimensional q-deformed fermionic Newton oscillator algebra are discussed. This algebra is covariant under the undeformed group U(n). The high- and low-temperature thermostatistical properties of a gas of the multi-dimensional q-deformed fermionic Newton oscillators are obtained.     

NEMD study for supercavitation mechanism with underwater object

An open system model was introduced for Non-Equilibrium Molecular Dynamics (NEMD) simulation for studying flow phenomenon surrounding different underwater object. Cavitation number σ criterion was proved to be applicable in predicting local cavitation mechanism. An interesting phenomenon was found that low σ areas and actual cavities were spatially separated in molecular scale, and stable supercavitation would require a large enough low σ area to sustain. Effects of cavitator shape and flow velocity were compared with macro scale flow under similar σ, providing a new computational method to study the molecular scale mechanism of this phenomenon     

Structural features of hydroxyapatite and carbonated apatite formed under the influence of ultrasound and microwave radiation and their effect on the bioactivity of the nanomaterials

The samples of hydroxyapatite and carbonate substituted hydroxyapatite (CHA) were obtained under the influence of physical factors, namely ultrasound (US) and microwave (MW) radiations. The results of Fourier transform infrared spectroscopy and X-ray diffraction analysis have proved the formation of the calcium deficient hydroxyapatite and B-type CHA with the Ca/P ratio in the ranges 1.62–1.87. In vitro studies have showed the increased bioactivity of the samples, synthesized under the influence of physical factors as compared to the standard ones. The samples of both groups, synthesized under the influence of 600 W MW, have shown the greatest stability in biological environment. In vivo tests confirm that obtained under US and MW radiations hydroxyapatite-based biomaterials are biocompatible, non-toxic and exhibit osteoconductive properties. The usage of US and MW radiations can significantly shorten the time (up to 5–20 min) of obtaining of calcium deficient hydroxyapatite and B-type CHA in nanopowder form, close in structure and composition to the biological hydroxyapatite.     

Quantization on a two-dimensional phase space with a constant curvature tensor

Some properties of the star product of the Weyl type (i.e., associated with the Weyl ordering) are proved. Fedosov construction of the *-product on a two-dimensional phase space with a constant curvature tensor is presented. Eigenvalue equations for momentum p and position q on a two-dimensional phase space with constant curvature tensors are solved.     

Comparative investigations of the P-V-T relationship of NaCl at high pressure and temperature

Two different potential models of molecular dynamics (MD) simulations have been applied to investigate the pressure-volume-temperature (P-V-T) relationship and lattice parameter of NaCl under high pressure and temperature. The first one is the shell model (SM) potentials in which due to the short-range interaction pairs of ions are moved together as is the case in polarization of a crystal due to the motion of the positive and negative ions, and the second one is the two-body rigid-ion Born-Mayer-Huggins-Fumi-Tosi (BMHFT) potentials with full treatment of long-range Coulomb forces. The P-V relationship at 300 K, T-V relationship at zero pressure, and lattice parameter a, have been obtained and compared with the available experimental data and other theoretical results. Compared with SM potentials, the MD simulation with BMHFT potentials is very successful in reproducing accurately the measured volumes of NaCl. At an extended pressure and temperature ranges, P-V relationship under different isotherms at selected temperatures, T-V relationship under different pressures, and lattice parameter a have also been predicted. The properties of NaCl are summarized in the pressure range 0-30 GPa and the temperature up to 2000 K.     

Application of spherical tensors and Wigner 3-j-symbols to the calculation of relative intensities of rotational lines in Raman bands of molecular gases

Spherical tensors, Wigner 3-j-symbols, and matrices for finite rotations have been used in order to derive closed formulas for the rotational line strength of lth order. The Placzek-Teller coefficients b_J′k′^Jk, are given in a closed form and relations among these coefficients are proved to follow from symmetry and orthogonality properties of the 3-j-symbols. Intensity sum rules for Raman scattering transitions have been derived in a simpler way than before.     

Weighted Graph Colorings

We study two weighted graph coloring problems, in which one assigns q colors to the vertices of a graph such that adjacent vertices have different colors, with a vertex weighting w that either disfavors or favors a given color. We exhibit a weighted chromatic polynomial Ph(G,q,w) associated with this problem that generalizes the chromatic polynomial P(G,q). General properties of this polynomial are proved, and illustrative calculations for various families of graphs are presented. We show that the weighted chromatic polynomial is able to distinguish between certain graphs that yield the same chromatic polynomial. We give a general structural formula for Ph(G,q,w) for lattice strip graphs G with periodic longitudinal boundary conditions. The zeros of Ph(G,q,w) in the q and w planes and their accumulation sets in the limit of infinitely many vertices of G are analyzed. Finally, some related weighted graph coloring problems are mentioned.     

Electronic properties of single-walled V2O5 nanotubes

Atomistic models of quasi-one-dimensional vanadium pentoxide nanostructures—single-walled nanotubes formed by rolling (010) layers of V₂O₅ are constructed and their electronic properties and bond indices are studied using the tight-binding band method. We show that all zigzag (n,0)- and armchair (n,n)-like nanotubes are uniformly semiconducting, and the band gap trends to vanish as the tube diameters decrease. The V-O covalent bonds were found to be the strongest interactions in V₂O₅ tubes, whereas V-V bonds proved to be much weaker.     

Bounded perturbations of the P(ϕ)2 theory

As a perturbation to the P(?)₂ theory we consider interaction densities of the form V(?(x)), where ?(x) is a scalar hermitian boson field and V(α) is a bounded real continuous function. It is proved that the asymptotic fields exist and are equal to the asymptotic fields of the P(?)₂ theory. The connection with non-polynomial theories of rational type is indicated. Furthermore the consequences of a bounded perturbation for the S-matrix and the spectral properties are discussed.