Magnetoresistivity and acoustoelectronic effects in a tilted magnetic field in <Emphasis Type="Italic">p</Emphasis>-Si/SiGe/Si structures with an anisotropic <Emphasis Type="Italic">g</Emphasis> factor

Magnetoresistivity ρ _xx and ρ _xy and the acoustoelectronic effects are measured in p-Si/SiGe/Si with an impurity concentration p = 1.99 × 10¹¹ cm⁻² in the temperature range 0.3–2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt θ to the normal to the plane of a two-dimensional p-Si/SiGe/Si channel is determined. A first-order ferromagnet-paramagnet phase transition is observed in the magnetic fields corresponding to a filling factor ν = 2 at θ ≈ 59°–60°.     

Synthesis of silver and lithium sub-micro- and nanoparticles coated with derivatives of <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butyl thiacalix[4]arenes

The effect of solvent nature and temperature on the formation of 3D-dimensional SAM (self-assembled monolayers on nanoparticles) based on synthetically available stereoisomers of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by pyrrolidide and octylamide groups (cone, partial cone, and 1,3-alternate) with lithium and silver nanoparticles were determined by dynamic light-scattering and transmission electron microscopy. It was found that the variation of the temperature of the system and the nature of the solvent leads to the formation discrete or extended particles (CH₂Cl₂) (98–110 nm), nanostructures (CH₃CN) (120–295 nm) or three-dimensional SAM (DMF) (1–13 nm; 46–622 nm).     

The emission spectrum of <Emphasis Type="Italic">p</Emphasis>-AlGaAs/GaAsP/<Emphasis Type="Italic">n</Emphasis>-AlGaAs diodes under uniaxial compression

New experimental data are presented on the effects of uniaxial compression of up to 4 kbar along the [110] and [1$ \bar 1 $ \bar 1 0] crystallographic directions on the spectra of electroluminescence and the current-voltage characteristics of diodes based on n-Al _x Ga_{1 − x} As/GaAs _y P_{1 − y} /p-Al _x Ga_{1 − x} As (y = 0.84) heterostructures that were designed for injection lasers. With increasing pressure, the spectra show a shift to shorter wavelengths, reaching 25 meV at 3 kbar; the intensity increases 2–3 times as well. Numerical calculations were carried out on the band structure of the investigated heterostructures under compression along the [110] axis, which indicate the increase in the effective band gap in the quantum well (QW) GaAs _y P_{1 − y} , with a pressure coefficient of about 8.5 meV/kbar and reduction of the barrier height at the boundaries of the QW. The calculations predict the possibility that light and heavy holes crossover at pressures above 4.5–5 kbar. The increase in the effective band gap completely describes the experimental data on the shift of the electroluminescence spectra. The mixing of light and heavy holes when approaching the band crosspoint is the probable cause of an increase in the intensity of radiation under uniaxial compression.     

Estimation of the deformation-potential constant for <Emphasis Type="Italic">p</Emphasis>-type isotropic polycrystalline silicon through the deformation potential of a <Emphasis Type="Italic">p</Emphasis>-type silicon single crystal

A method of calculating the effective deformation-potential constant E ₁ for holes and longitudinal acoustic phonons in isotropic polycrystalline silicon is suggested. The deformation-potential constant E ₁ is estimated through the deformation potentials a, b, and d of the silicon single crystal. The procedure of averaging of the squared modulus of the hole and acoustic phonon interaction Hamiltonian written in the plane wave basis over the polycrystal ensemble provides the basis for calculation of the constant E ₁ . It is demonstrated that for T = 200–600 K, hole concentration p = (5.0–10.0)∙10¹⁹ cm^–3, and crystallite size d = 300–3000 ?, the deformationpotential constant E ₁ is independent of the hole concentration p, temperature T, and crystallite size d.     

Anisotropy of amorphous nanogranular composites CoNbTa-SiO<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> and CoFeB-SiO<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

A comparative investigation of the magnetic properties of amorphous nanogranular composites (Co₄₁Fe₃₉B₂₀) _x (SiO _n )_{100 − x} and (Co₈₆Nb₁₂Ta₂) _x (SiO _n )_{100 − x} has been performed in the subpercolation region at temperatures in the range 4.2–300 K. The thermomagnetic dependences in the range 4.2–300 K and the processes of magnetization reversal and remanent magnetization relaxation at liquid-helium temperatures have been studied. It has been established that the average anisotropy constants of amorphous nanograins are equal to 3.6–7.0 kJ/m³ for the (Co₄₁Fe₃₉B₂₀) _x (SiO _n )_{100 − x} composites and 5–8 kJ/m³ for the (Co₈₆Nb₁₂Ta₂) _x (SiO _n )_{100 − x} composites. The fundamental differences in the concentration dependences of the anisotropy constant K _eff and the coercive force H _C have been revealed for the two systems under investigation. It has been demonstrated that, as the concentration of the metal phase increases, the quantities K _eff and H _C increase for the (Co₈₆Nb₁₂Ta₂) _x (SiO _n )_{100 − x} composites and decrease for the (Co₄₁Fe₃₉B₂₀) _x (SiO _n )_{100 − x} composites.     

Rapid extra-/intracellular biosynthesis of gold nanoparticles by the fungus <Emphasis Type="Italic">Penicillium</Emphasis> sp.

In this work, the fungus Penicillium was used for rapid extra-/intracellular biosynthesis of gold nanoparticles. AuCl₄ ⁻ ions reacted with the cell filtrate of Penicillium sp. resulting in extracellular biosynthesis of gold nanoparticles within 1 min. Intracellular biosynthesis of gold nanoparticles was obtained by incubating AuCl₄ ⁻ solution with fungal biomass for 8 h. The gold nanoparticles were characterized by means of visual observation, UV–Vis absorption spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The extracellular nanoparticles exhibited maximum absorbance at 545 nm in UV–Vis spectroscopy. The XRD spectrum showed Bragg reflections corresponding to the gold nanocrystals. TEM exhibited the formed spherical gold nanoparticles in the size range from 30 to 50 nm with an average size of 45 nm. SEM and TEM revealed that the intracellular gold nanoparticles were well dispersed on the cell wall and within the cell, and they are mostly spherical in shape with an average diameter of 50 nm. The presence of gold was confirmed by EDX analysis.     

Recent high-<Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> results from STAR

We present selected recent results of multi-hadron correlation measurements in azimuth and pseudorapidity at intermediate and high p _T in Au+Au collisions at , from the STAR experiment at RHIC. At intermediate p _T , measurements are presented that attempt to determine the origin of the associated near-side (small Δφ) yield at large pseudo-rapidity difference Δη that is found to be present in heavy ion collisions. In addition, results are reported on new multi-hadron correlation measures at high-p _T that use di-hadron triggers and multi-hadron cluster triggers with the goal to constrain the underlying jet kinematics better than in the existing measurements of inclusive spectra and di-hadron correlations.     

Effects of <Emphasis Type="Italic">d</Emphasis>-wave pairing in <Emphasis Type="Italic">n</Emphasis>-type high-temperature superconductors with anisotropic impurity scattering

The temperature dependences of the resistivity of single-crystal films of the Nd_{2 − x} Ce _x CuO_{4 + δ} n-type superconductors with x = 0.14 (underdoped region) and x = 0.15 (optimal doping region) and different degrees of disorder δ have been investigated in various magnetic fields (B ‖ c, J ‖ ab) in the temperature range 0.4–300 K. It has been demonstrated that there are differences in the behavior of the dependences of the slope of the upper critical field $ (dB_{c2} /dT)_{T \to T_c } $ (dB_{c2} /dT)_{T \to T_c } on the disorder parameter for the underdoped samples (x = 0.14) and the samples with the optimal doping (x = 0.15). The study of the dependence of the slope of the upper critical field on the degree of disorder has made it possible to discriminate experimentally between the superconductors with the d pairing and anisotropic s pairing. It has been revealed that the relative stability of the n-type superconductor with the optimal doping with respect to disordering is possibly due to the strong anisotropy of impurity scattering with symmetry of the d type.     

Noncommutative electromagnetism as a large <Emphasis Type="Italic">N</Emphasis> gauge theory

We map noncommutative (NC) U(1) gauge theory on ℝ _C ^d ×ℝ _NC ²ⁿ to U(N→∞) Yang–Mills theory on ℝ _C ^d , where ℝ _C ^d is a d-dimensional commutative spacetime while ℝ _NC ²ⁿ is a 2n-dimensional NC space. The resulting U(N) Yang–Mills theory on ℝ _C ^d is equivalent to that obtained by the dimensional reduction of (d+2n)-dimensional U(N) Yang–Mills theory onto ℝ _C ^d . We show that the gauge-Higgs system (A _μ ,Φ ^a ) in the U(N→∞) Yang–Mills theory on ℝ _C ^d leads to an emergent geometry in the (d+2n)-dimensional spacetime whose metric was determined by Ward a long time ago. In particular, the 10-dimensional gravity for d=4 and n=3 corresponds to the emergent geometry arising from the 4-dimensional N=4{\mathcal{N}}=4 vector multiplet in the AdS/CFT duality. We further elucidate the emergent gravity by showing that the gauge-Higgs system (A _μ ,Φ ^a ) in half-BPS configurations describes self-dual Einstein gravity.     

Dielectron widths of the <Emphasis Type="Italic">S</Emphasis>-, <Emphasis Type="Italic">D</Emphasis>-vector bottomonium states

The dielectron widths of Y(nS)(n = 1, …, 7) and vector decay constants are calculated using the relativistic string Hamiltonian with a universal interaction. For Y(nS) (n = 1, 2, 3) the dielectron widths and their ratios are obtained in full agreement with the latest CLEO data. For Y(10580) and Y(11020) a good agreement with experiment is reached only if the 4S-3D mixing (with a mixing angle θ = 27°± 4°) and 6S-5D mixing (with θ = 40°±5°) are taken into account. The possibility to observe higher “mixed D-wave” resonances, $ \tilde \Upsilon $ \tilde \Upsilon (n ³ D ₁) with n = 3, 4, 5 is discussed. In particular, $ \tilde \Upsilon $ \tilde \Upsilon (≈11120), originating from the pure 5³ D ₁ state, can acquire a rather large dielectron width, ∼130 eV, so that this resonance may become manifest in the e ⁺ e ⁻ experiments. On the contrary, the widths of pure D-wave states are very small, Γ _ee (n ³ D ₁)≤ 2 eV.     

A rapid and highly sensitive spectrofluorimetric method for the determination of venlafaxine by charge transfer complexation reaction with <Emphasis Type="Italic">p</Emphasis>-bromanil and <Emphasis Type="Italic">p</Emphasis>-chloranil

Simple, rapid and highly sensitive spectrofluorimetric methods were developed for the determination of venlafaxine in pure and pharmaceutical preparations. The proposed methods were based on the reaction of venlafaxine as n-electron donor with π-acceptors namely, p-bromanil and p-chloranil. The method for the determination of venlafaxine over a concentration range of 5–100 and 5–150 ng/mL, for p-bromanil and p-chloranil methods, respectively. The intra- and inter-day precisions were satisfactory, the relative standard deviations did not exceed 1.69%. The proposed method was successfully applied to the determination of venlafaxine in its pharmaceutical preparations with good accuracy; the mean recovery percentages were 99.80%. The results were compared favorably with those of the reference method.     

Fragmentation of sputtered Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>O<Stack><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript><Superscript>+</Superscript></Stack> clusters: Release kinetic and dissociation energies

The spectra of kinetic energies of positive Si _n O _m ⁺ cluster ions (n = 2–5, m = 2–7) have been measured using a double focusing ion microanalyzer with reverse geometry at instants 10⁻⁵ to 10⁻⁴ s after emission. The dissociation energies have been determined within the evaporative ensemble model and the theory of unimolecular decay reactions. The results obtained are compared with the binding energies of neutral Si _n O _m clusters.     

Influence of size effects on <Emphasis Type="Italic">para</Emphasis>-dichlorobenzene lattice dynamics

We have obtained experimental low-frequency Raman spectra for light scattering by nanoparticles of para-dichlorobenzene of size ∼300–70 nm. As their sizes decrease, the line frequencies decrease. The size of the nanoparticles was determined using an electron microscope. We found that in the lattice vibrational spectrum of nanoparticles of size 300–70 nm, a summed spectrum appears from α-para-dichlorobenzene and β-para-ichlorobenzene. This is consistent with molecular dynamics calculations of the structure of the nanoparticle and calculations of the histograms for the lattice vibrational spectra by the Dean method.     

Reconstruction of <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">T</Emphasis>) gravity according to holographic dark energy

We develop the reconstruction of the f(T) gravity model according to the holographic dark energy. T is the torsion scalar and its initial value from the teleparallel gravity is imposed for fitting the initial value of the function f(T). The evolutionary nature of the holographic dark energy is essentially based on two important parameters, Ω _V  and ω _V , respectively, the dimensionless dark energy and the parameter of the equation of state, related to the holographic dark energy. The result shows a polynomial function for f(T), and we also observe that, when Ω _V →1 at the future time, ω _V may cross −1 for some values of the input parameter b. Another interesting aspect of the obtained model is that it provides a unification scenario of dark matter with dark energy.     

Density functional theory study on the structural and electronic properties of Ag-adsorbed (MgO)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clusters

Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO) _n (n = 1–8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for exchange-correlation functional. The results show that hollow site is energetically preferred for n⩾4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies and electron affinities show that the Ag(MgO)₄ and Ag(MgO)₆ are the most stable among studied clusters. Supported by the Startup Fund of High-level Personal for Shihezi University (Grant No. RCZX200747)     

Generation of reactive oxygen species and oxidative stress in <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> by a novel semiconductor catalyst

The objective of this study was to investigate antimicrobial mechanisms of a new catalytic material (charge transfer auto oxidation–reduction type catalyst, CT catalyst) that may have great potential for application in water/wastewater treatment. Generation of reactive oxygen species (ROS) in bacteria-free solution, induction of ROS and oxidative damage in bacteria (including E. coli and S. aureus) were examined for the CT catalyst. The results showed that significantly higher (p < 0.05, via t-test) amount of hydroxyl radicals was generated by the CT catalyst compared with the control, particularly after 6 h of contact time that more than twice of the amount of the control was produced. The generation of ROS in the bacteria was greater under higher pH and temperature levels, which closely related with the oxidative damage in cells. The results indicated that CT catalyst induced oxidative damage in the bacteria might serve as an important mechanism interpreting the anti-microbial function of the CT catalyst.     

Colossal resistive switching behavior and its physical mechanism of Pt/<Emphasis Type="Italic">p</Emphasis>-NiO/<Emphasis Type="Italic">n</Emphasis>-Mg<Subscript>0.6</Subscript>Zn<Subscript>0.4</Subscript>O/Pt thin films

A heterojunction structure of p-NiO/n-Mg_0.6Zn_0.4O with an aim to tuning or improving the resistive switching properties was fabricated on Pt/TiO₂/SiO₂/Si substrates by the sol-gel spin-coating technique. The Pt/NiO/Mg_0.6Zn_0.4O/Pt heterojunction thin-film device shows excellent resistive switching properties, such as a reduced threshold current of 1 μA for device initiation, a small dispersion of reset voltage ranging from 0.54 to 0.62 V, long retention time and a high resistance ratio of high-resistance state to low-resistance state about six orders of magnitude. These results indicate that the resistive switching properties can be greatly improved by constructing the p-NiO/n-Mg_0.6Zn_0.4O heterojunction for nonvolatile memory applications. The physical mechanism responsible for colossal resistive switching properties of the heterojunction was analyzed based on interfacial defect effect and formation and rapture of conductive filaments.     

The transformation of <Emphasis Type="Italic">n</Emphasis>-alkanes on H-forms of zeolites under supercritical conditions

The skeleton isomerization of n-butane, n-hexane, and n-heptane was studied under supercritical conditions on H-forms of zeolites mordenite, beta, and ZSM-5 over the temperature and pressure ranges 260–450°C and 80–130 atm. The isomerization of n-hexane and n-heptane was accompanied by side processes such as oligomerization and cracking. The selectivity of formation of branched isomers of these hydrocarbons did not exceed 70 and 30%, respectively. The catalyst with the most stable operation was pentasil ZSM-5, but the selectivity of formation of branched isomers on it did not exceed 30% even at 260–280°C and decreased to 3% as the reaction temperature increased to 400–450°C. The fraction of aromatization products was then more than 15%. A study of the influence of C₆–C₇ n-alkane additives on the isomerization of n-pentane on mordenite in the H-form under supercritical conditions at 260°C and 120 atm showed that a gradual decrease in the activity of this catalyst in the isomerization of n-pentane was related to the formation of heavier hydrocarbons.     

Cluster Structure of Liquid Alcohols,Water, and <Emphasis Type="Italic">n</Emphasis>-Hexane

The processes of cluster formation in liquid alcohols, water, methanol, n-hexanol, and n-hexane have been investigated by the method of flicker-noise spectroscopy. Two types of clusters — clusters with a close-packed structure and clusters with a loose structure — have been detected. The energy of formation of different clusters in methanol and n-hexane ranges, respectively, from −250 to +250 J/mole and from −50 to +50 J/mole. The smallest clusters of methanol, n-hexanol, water, and n-hexane consist, respectively, of six, two, eleven, and two molecules, and their largest clusters represent oscillators consisting, respectively, of 50,400, 17,200, 93,500, and 33,150 molecules at 274 K. In methanol at 271 K, more than 44 types of clusters consisting of 6, 97, 152, 219, 297, 492, 1029, 1368, 1560, etc. molecules were detected. In n-hexanol at 273 K, 57 types of clusters were detected. Models of small clusters are proposed. In water, the content of close-packed clusters is maximum at 277 K. The energy of formation/decomposition of small clusters in water ranges from −0.4 to +0.4 kJ/mole and increases with increase in the water temperature. The hysteresis of transformation of the (H₂O)₂₈₀ cluster in the process of heating and cooling of water in the temperature range 273–280 K was detected. Series of energy spectra of clusters in liquids at different temperatures are presented and discussed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 305–312, May–June, 2005.     

Photoconductivity of poly-<Emphasis Type="Italic">p</Emphasis>-xylylene + CdS nanocomposite films over a wide temperature range

For poly-p-xylylene + CdS (PPX + CdS) nanocomposite films, the dependences of the photo-conductivity σ _ph (T) on the concentration C of CdS nanoparticles, intensity and wavelength of exciting light, and temperature T within 15–300 K are examined. An appreciable photocurrent appears at C ≥ 10 vol %, when a large percolation cluster of CdS nanoparticles is formed. The photocurrent spectrum is compared to the absorption spectrum of the film. The photocurrent I _ph (P) increases with the intensity of light flux P in a wavelength range near 435 nm according to the I _ph (P) ∼ P ⁿ power law, where n < 1. At 15 K, the photoconductivity of films with C ≈ 11.5 and 13.5 vol % is higher than that of a pure CdS film (C = 100 vol %) by factors of ≈100 and ≈30, respectively. For films with C > 11.5 vol %, the σ _ph (T) dependence at low T exhibits a metal-like character (σ _ph (T) decreases with increasing temperature). Atomic force microscopy is used to examine the surface topography of PPX + CdS films, which is found to be strongly dependent on the concentration of nanoparticles. The dark conductivity and photoconductivity of nanocomposite films arise due to the thermo- and photoexcitation transfer of electrons from the CdS nanoparticles to the PPX matrix with the formation of an electronic double layer at the PPX matrix-large percolation CdS cluster interface, a process that populates the phenyl rings of the adjacent PPX layer with excess electrons. As a result, various mechanisms of electron transfer in the polymer matrix can be realized: Mott’s hopping conduction mechanism with variable-range hopping in the matrix between CdS clusters and the metal-like behavior of the conductivity in the polymer shell of the large cluster at low temperatures. The polymer shell contains excess electrons on the phenyl rings -C₆H₄- in the composition of anion-resonances -C₆H₄⁻-.