Relaxation kinetics of photoconductivity in <Emphasis Type="Italic">р</Emphasis>-silicon compensated by phosphorus atoms

The relaxation kinetics of photoconductivity in neutron-doped silicon (NDS) of the p-type is discussed. It is found that the relaxation process in the compensated p-Si<B, P> differs from that in the reference p-Si<B> sample. The difference is explained on the basis of concept of different micrononuniformity of the material conductivity. A method based on studying the dependences of charge-carrier mobility on annealing time is developed for determining thermal annealing of structural defects.     

Astrophysical <Emphasis Type="Italic">S</Emphasis>-factor of the <Emphasis Type="Italic">p</Emphasis><Superscript>9</Superscript>Be → <Superscript>10</Superscript>Bγ radiative capture

The S-factor of the p ⁹Be → ¹⁰Bγ radiative capture is considered at astrophysical energies in the potential cluster model where orbital states are classified by the Young schemes.     

On the Uniqueness of Gravitational Centre

The dual volume of order α of a convex body A in R ⁿ is a function which assigns to every a ∈ A the mean value of α-power of distances of a from the boundary of A with respect to all directions. We prove that this function is strictly convex for α > n or α < 0 and strictly concave for 0 < α < n (for α = 0 and for α = n the function is constant). It implies that the dual volume of a convex body has the unique minimizer for α > n or α < 0 and has the unique maximizer for 0 < α < n. The gravitational centre of a convex body in R³ coincides with the maximizer of dual volume of order 2, thus it is unique.      

Photoluminescence of fluoroacrylate polymers impregnated with Eu(bta)<Subscript>3</Subscript> using supercritical CO<Subscript>2</Subscript>

Optical properties (photoluminescence and absorption) of Eu(bta)₃(B) _n (B = H₂O or 1,10-phenanthroline) polycrystalline powders and fluoroacrylate polymers (FAPs) impregnated with these compounds using supercritical CO₂ (SC CO₂) were investigated. It was established that impregnation of Eu(bta)₃phen into the FAPs using an SC CO₂ solution was difficult to achieve. The type of B (ancillary ligand) and the polymer matrix were shown to influence the temperature quenching of photoluminescence of Eu³⁺ ions in the range 25–100°C. A comparative analysis of quantum yields (λ_ex = 300 and 380 nm) and photoluminescence decay times (λ_ex = 337.1 nm) for Eu(bta)₃B _n and for Eu(bta)₃B _n -doped FAPs was performed.     

Spectrophotometric determination of ofloxacin in pharmaceuticals by redox reaction

Two simple spectrophotometric methods have been developed to analyze ofloxacin (OFX) in pharmaceuticals. The methods are based on the oxidation of OFX by a measured excess of cerium(IV) sulfate in H₂SO₄ medium. This was followed by the determination of the unreacted oxidant by reacting it with either p-toluidine (p-TD) and measuring the absorbance at 525 nm (method A) or o-dianisidine (o-DA) and measuring the absorbance at 470 nm (method B). In both methods, the amount of cerium(IV) sulfate reacted corresponds to the amount of OFX. Calibration graphs were linear over the ranges of 0–120 and 0–4 g/ml OFX for methods A and B, respectively. The calculated molar absorptivity (2.34⋅10³ and 5.99⋅10⁴), Sandell sensitivity, and limit of quantification for the methods are reported. The intra-day precision (%RSD) and accuracy (%RE) were < 8.0 and ≤ 4.0%, respectively, and the inter-day RSD and RE values were within 5 and 4.0%, respectively. The applicability of the methods was demonstrated by determining OFX in tablets with an accuracy (%RE) of < 3% and precision (%RSD) of ≤2.65%. The accuracy of the methods was further ascertained by recovery experiments via a standard-addition procedure.     

Peculiar behavior of structure rearrangement in nanofiber of intermetallic Ni<Subscript>3</Subscript>Al,containing long-period paired thermal anti-phase boundaries,under high-rate tensile uniaxial loading along <001>

Using molecular dynamics simulations, peculiarities of structure rearrangement in nanofiber of intermetallic Ni₃Al containing long-period, paired, thermal (nonconservative) anti-phase boundarties (APBs is investigated in the course of high-rate, tensile uniaxial loading along <001>. Four main deformation stages are determined (quasi-elastic, plastic, material flow and rupture), with each stage revealing particular features of structure transformations and energy transfer. The presence of periodic thermal planar defects in the long-period nanostructure (combined thermal anti-phase boundaries) significantly affects the onset of plastic deformation. A change in the type of thermal APBs in the long-period structure in turn affects the time to total rupture of nanofiber under plastic deformation condition. For the thermal AA 1/2 < 110 > {001}APBs, the time to total nanofiber rupture is slightly decreased, while that for the thermal AB 1/2 < 110 > {001} APBs is considerably increased.     

Vortex pinning in YBa2Cu3O7?x films

Evidence that pinning on linear or planar defects dominates the vortex dynamics in YBa₂Cu₃O_7−x (YBCO) films is provided by complex impedance measurements at temperature 8 K<T<T _c and magnetic field 0<B<6 T. Below the vortex lattice melting transition B_g(T) but above a threshold field B_p≈8(1-T/T _c ) T, the inductance of vortices increases as B², much less rapidly than predicted for collective pinning of vortices by point defects. Above the vortex melting line, critical scaling persists over the region B_g(T<B<B^*(T) where the vortex correlation length ξ exceeds a characteristic length scale ξ^*≡ξ(B=B^*)≈450?. The value of ξ^* is not sensitive to Al-doping in the Cu sites in the lattice and is close to the size of twin domains in the film. The nature of the observed crossovers is discussed in terms of available theoretical models for a glass-liquid transition at B_g.     

Optical properties of nonlinear solid solution GaSe<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> (0 < <Emphasis Type="Italic">x</Emphasis> ≤ 0.4) crystals

Transmission spectra and phase matching conditions for second harmonic generation in GaSe_1–x S _x (0 < x ≤ 0.4) solid solution crystals are experimentally investigated. An algorithm is suggested and dispersion equations are derived that allow the phase matching angles describing best the available experimental data to be estimated as a function of the mixing ratio x. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 80–85, October, 2008.     

Synthesis and characterization of electron beam evaporated LiCoO<Subscript>2</Subscript> thin films

LiCoO₂ thin films were prepared by electron beam evaporation technique using LiCoO₂ target with Li/Co ratio 1.1 in an oxygen partial pressure of 5 × 10⁻⁴ mbar. The films prepared at substrate temperature T _s < 573 K were amorphous in nature, and the films prepared at T _s > 573 K exhibited well defined (104), (101), and (003) peaks among which the (104) orientation predominates. The X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) data revealed that the films prepared in the substrate temperature range 673–773 K are nearly stoichiometric. The grain size increases with an increase of substrate temperature. The Co–e_g absorption bands, are empty and their peak position lies at around 1.7 eV above the top to the Co–t_2g bands. The fundamental absorption edge was observed at 2.32 eV. The films annealed at 1,023 K in a controlled oxygen environment exhibit (104) out plane texture with large grains. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006     

Collisional processes near the CH B 2Σ- v′=0,1 predissociation limit in laser-induced fluorescence flame diagnostics

Excitation and dispersed laser-induced fluorescence spectra of CH B ²Σ^-v^′=0,1 in methane flames are analyzed using rotational relaxation models to investigate their applicability for flame diagnostics. The existence of non-predissociative and highly predissociative rotational levels in the same vibrational state provides a unique scenario to test the effects of rotational relaxation in laser-induced fluorescence measurements. Using a statistical power gap law for rotational relaxation modeling, we find that the levels with collision-free lifetimes as short as 100 ps have apparent fluorescence yields larger than expected because of the extent of rotational relaxation at atmospheric pressure. Also, vibrational (v^′=1 to v^′=0) and electronic energy transfer (B ²Σ^-v^′=1 to A ²Δ) are competitive, and together are half the value for the total collisional removal rate from CH B ²Σ^-v^′=0. The measured electronic energy transfer branching ratio into A (v^′=0-3) depends on the initial rotational level pumped, and energy gap considerations can be used to explain these propensities. The combination of measurements and model calculations finds the excitation of the CH B ²Σ^- v^′=1,N^′=8 level a good candidate for laser-induced fluorescence quantitative measurements in flames at atmospheric pressure. Received: 24 September 1999 / Published online: 7 June 2000     

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.     

Fluorescent Carbon Dots Capped with PEG<Subscript>200</Subscript> and Mercaptosuccinic Acid

The synthesis and functionalization of carbon nanoparticles with PEG₂₀₀ and mercaptosuccinic acid, rendering fluorescent carbon dots, is described. Fluorescent carbon dots (maximum excitation and emission at 320 and 430 nm, respectively) with average dimension 267 nm were obtained. The lifetime decay of the functionalized carbon dots is complex and a three component decay time model originated a good fit with the following lifetimes: τ ₁ = 2.71 ns; τ ₂ = 7.36 ns; τ ₃ = 0.38 ns. The fluorescence intensity of the carbon dots is affected by the solvent, pH (apparent pK _a of 7.4 ± 0.2) and iodide (Stern-Volmer constant of 78 ± 2 M⁻¹).     

TEM and photoluminescence characterization of porous-silicon layers from <111>-oriented p + silicon substrates

Summary A first structural investigation, carried out by transmission electron microscopy on porous-silicon samples fromp ⁺, <111>-oriented substrates is presented. The samples, which show intense visible room temperature luminescence, are composed by an interconnected network of crystalline nanostructures. Evidences of the pores propagation along the <100> directions are provided. The optical and morphological characteristics of the investigated samples are found to be much similar to those of samples coming fromp-type, non-degenerate, <100>-oriented substrates rather than those obtained from <100> substrates with comparable resistivity. This striking effect is explained by invoking different etch-limiting mechanisms during pore formation. Their relative weights are proposed to depend on the crystallographic orientation of the silicon specimen subjected to etching. Paper presented at the III INSEL (Incontro Nazionale sul Silicio Emettitore di Luce), Torino, 12–13 October 1995.     

Anomalous dynamics in reaction-diffusion systems

Summary We review recent developments in the study of the diffusion reaction systems of the type A+B→C in which the reactants are initially separated. We consider the case where the A and B particles are initially placed uniformly in Euclidean space atx>0 andx<0, respectively. We find that whereas ford≥2 the mean-field exponent characterizes the width of the reaction zone, fluctuations are relevant in the one-dimensional system. We also presented analytical and numerical results for the reaction rate on fractals and percolation systems. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Structure,thermal properties,conductivity and electrochemical stability of di-urethanesil hybrids doped with LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript>

Variable chain length di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks were prepared by application of a sol-gel strategy. These materials, designated as di-urethanesils (represented as d-Ut(Y′), where Y′ indicates the average molecular weight of the polymer segment), were doped with lithium triflate (LiCF₃SO₃). The two host hybrid matrices used, d-Ut(300) and d-Ut(600), incorporate POE chains with approximately 6 and 13 (OCH₂CH₂) repeat units, respectively. All the samples studied, with compositions ∞ > n ≥ 1 (where n is the molar ratio of (OCH₂CH₂) repeat units per Li⁺), are entirely amorphous. The di-urethanesils are thermally stable up to at least 200 °C. At room temperature the conductivity maxima of the d-Ut(300)- and d-Ut(600)-based di-urethanesil families are located at n = 1 (approximately 2.0 × 10⁻⁶ and 7.4 × 10⁻⁵ Scm⁻¹, respectively). At about 100 °C, both these samples also exhibit the highest conductivity of the two electrolyte systems (approximately 1.6 × 10⁻⁴ and 1.0 × 10⁻³ Scm⁻¹, respectively). The d-Ut(600)-based xerogel with n = 1 displays excellent redox stability.     

Wavelength Dependant Quenching of 2,5-Diphenyloxazole Fluorescence by Nucleotides

The quenching of 2,5-diphenyloxazole (PPO) fluorescence by nucleotides has been investigated by electronic absorption and steady state fluorescence spectra. Five purine nucleotides AMP, ADP, ATP, GMP and dGMP, one pyrimidine nucleotide UMP and one dinucleotide NAD have been employed in the present study. Electronic absorption studies indicate that there is no ground state complexation between the nucleotides and PPO. The quenching of PPO fluorescence was investigated at two different wavelengths. When excited at 304 nm, the λ _max of PPO, the fluorescence spectra of PPO is quenched following Stern–Volmer kinetics. The quenching ability of nucleotides are in the order NAD > AMP > ADP > GMP > dGMP > UMP. The K _SV and k _q values obtained indicate that AMP is a better quencher of PPO fluorescence than GMP, which is contrary to commonly observed pattern. The quenching is found to be dynamic in nature. However, when excited at 260 nm, the absorption maximum of the nucleotides, the fluorescence intensity of PPO is reduced with increase in the concentration of the nucleotide. This is attributed to the primary inner filter effect arising due to the absorption of the incident radiation by the nucleotides. Thus the inner filter effect phenomenon can be employed to assay the non-fluorescent molecules by fluorimetry.     

Manifestly-covariant <Emphasis Type="Italic">p</Emphasis><Superscript>3</Superscript> calculation of nucleon Compton scattering

We compute the Compton scattering off the nucleons in the framework of manifestly covariant baryon chiral perturbation theory (BχPT). The results for observables differ substantially from the corresponding calculations in heavy-baryon chiral perturbation theory (HBχPT), most appreciably in the forward kinematics. We verify that the covariant p ³ result fulfills the forward-Compton-scattering sum rules. We also explore the effect of the Δ(1232) resonance at order p ⁴/Δ, with Δ ≈ 300 MeV, the resonance excitation energy. We find that the substantial effect of the Δ-excitation on the nucleon polarizabilities can naturally be accommodated in the manifestly covariant calculation. The article is published in the original.     

Estimation of applicability of perturbation theory to solution of the kinetic Boltzmann equation in calculations of charge-carrier relaxation time in isotropic polycrystalline <Emphasis Type="Italic">p-</Emphasis>silicon

A condition is formulated for application of perturbation theory to solution of the kinetic Boltzmann equation in calculations of charge-carrier relaxation time in an isotropic silicon polycrystal, where holes are scattered both by a disordered system of potential barriers formed on crystallite surfaces and by a disordered lattice of silicon atoms characterized by local ordering. The total specific resistance of p-type isotropic polycrystalline silicon is estimated for the grain size d = 230 ?, temperature T = 300 K, and hole concentration p = (5.0 – 10.0) ⋅ 10¹⁹ cm⁻³. The calculated specific resistances of p-type polycrystalline silicon are compared with the experimental data.     

Semilinear PDEs on Self-Similar Fractals

A Laplacian may be defined on self-similar fractal domains in terms of a suitable self-similar Dirichlet form, enabling discussion of elliptic PDEs on such domains. In this context it is shown that that semilinear equations such as Δu+u ^p = 0, with zero Dirichlet boundary conditions, have non-trivial non-negative solutions if 0<ν≤ 2 and p>1, or if ν >2 and 1<p< (ν+ 2)/(ν− 2), where ν is the “intrinsic dimension” or “spectral dimension” of the system. Thus the intrinsic dimension takes the r\^{o}le of the Euclidean dimension in the classical case in determining critical exponents of semilinear problems. Received: 11 December 1998 / Accepted: 22 March 1999     

Two-phase reaction mechanism during chemical lithium insertion into α-MoO<Subscript>3</Subscript>

The phase transition during chemical lithium insertion into α-MoO₃ was investigated by chemical analysis, X-ray diffraction (XRD) and electrochemical characterisation. The samples have been prepared by reaction of various amounts of water-free lithium iodide with fine-particulate orthorhombic molybdenum trioxide in n-hexane (non-aqueous media), which yielded materials with different Li/Mo ratio. XRD investigations of these materials proved that the crystal structure of the layered α-MoO₃ has been changed after the chemical lithiation. The phase transition ranged from 0.25 < x < 0.5 in Li _x MoO₃ upon chemical lithium insertion into α-MoO₃. The XRD lines of lithium inserted phase Li _x MoO₃ grew at the expense of the XRD lines of the pristine α-MoO₃ as lithium ions were chemically inserted until the disappearance of lines related to α-MoO₃. The electrochemical performance of the lithiated samples is improved in comparison with the starting material (non-lithiated α-MoO₃).