Perfect spin polarization in symmetric two-terminal mesoscopic rings

Spin-polarized transport through an Aharonov–Bohm (AB) semiconductor mesoscopic ring is investigated in the presence of both the Rashba spin–orbit interaction (RSOI) and the Dresselhaus spin–orbit interaction (DSOI). The ring symmetrically bridges two input and output electrodes. Based on tight-binding model and Green?s function formalism, we find that for AB fluxes other than integer or half-integer multiples of the flux quanta the ring acts as a spin selective device with unit efficiency only when the difference between strengths of RSOI and DSOI is nonzero and small. Results of this study can be used to design a nonmagnetic-material-based perfect spin filter.     

On solving continuous-time dynamic network flows

Temporal dynamics is a crucial feature of network flow problems occurring in many practical applications. Important characteristics of real-world networks such as arc capacities, transit times, transit and storage costs, demands and supplies etc. are subject to fluctuations over time. Consequently, also flow on arcs can change over time which leads to so-called dynamic network flows. While time is a continuous entity by nature, discrete-time models are often used for modeling dynamic network flows as the resulting problems are in general much easier to handle computationally. In this paper, we study a general class of dynamic network flow problems in the continuous-time model, where the input functions are assumed to be piecewise linear or piecewise constant. We give two discrete approximations of the problem by dividing the considered time range into intervals where all parameters are constant or linear. We then present two algorithms that compute, or at least converge to optimum solutions. Finally, we give an empirical analysis of the performance of both algorithms.     

Interactions of NO2 with amine-functionalized SBA-15: effects of synthesis route

SBA-15 mesoporous silica was modified using (3-aminopropyl)trimethoxysilane (APTMS) following co-condensation or grafting methods and then used as a NO(2) adsorbent at room temperature. The samples were characterized before and after exposure to NO(2) by SEM-EDX, N(2) adsorption at 77 K, potentiometric titration, thermal analysis, and FTIR spectroscopy. Even though, regardless of the synthesis route, the addition of propylamine groups leads to a significant enhancement in the amount of NO(2) adsorbed (from 21 to 124 mg(NO(2))/g), a higher retention of NO(2) and NO (released as a result of surface reactions) was measured on the grafted silica than on all of the co-condensed samples. In the case of the latter materials, improvements in both NO(2) adsorption capacity and NO retention were found for the samples treated with NaOH. This behavior is related to the higher reactivity of deprotonated propylamine groups (formed during NaOH treatment) with NO(2), the presence of silanol groups, and the residual amount of sodium present in the samples. The mechanism of NO(2) adsorption on propylamine groups involves the formation of nitramine and/or nitrosamine. Analysis of the spent materials indicates that the porosity of co-condensed materials is not affected to the same extent by adsorption of NO(2) as that of the grafted silica.     

A Self-Consistent Model for Positronium Formation from Helium Atoms

The differential and total cross sections for electron capture by positrons from helium atoms are calculated using a first-order distorted wave theory satisfying the Coulomb boundary conditions. In this formalism, a parametric potential is used to describe the electron screening in a consistent and realistic manner. The present procedure is self-consistent because (a) it satisfies the correct boundary conditions and post–prior symmetry, and (b) the potential and the electron binding energies appearing in the transition amplitude are consistent with the wave functions describing the collision system. The results are compared with the other theories and with the available experimental measurements. At the considered range of collision energies, the results agree reasonably well with recent experiments and theories.     

Time-division multiplexing of the orbital angular momentum of light

We present an optical setup for generating a sequence of light pulses in which the orbital angular momentum (OAM) degree of freedom is correlated with the temporal one. The setup is based on a single q plate within a ring optical resonator. By this approach, we demonstrate the generation of a train of pulses carrying increasing values of OAM, or, alternatively, of a controlled temporal sequence of pulses having prescribed OAM superposition states. Finally, we exhibit an "OAM-to-time conversion" apparatus that divides different input OAM states into different time bins. The latter application provides a simple approach to digital spiral spectroscopy of pulsed light.     

Lithium-7 NMR Study of Several Li+-Crown Ether Complexes in Binary Acetone-Nitrobenzene Mixtures

⁷Li NMR measurements were employed to monitor the stoichiometry andstability of Li⁺ ion complexes with 12-crown-4 (12C4), 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) l8-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6) in binary acetone-nitrobenzene mixtures of varying composition. In all cases studied, the variation of ⁷Li chemical shift with the crown/Li⁺ mole ratio indicated the formation of 1:1 complexes. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In all solvent mixtures used, the stabilities of the resulting 1:1 complexes varied in the order15C5 > B15C5 > DC18C6 > 18C6 > 12C4 >DB18C6. It was found that,in the case of all complexes, an increase in the percentage of acetone in thesolvent mixtures significantly decreased the stability of the complexes.     

Multi‐responses optimization of simultaneous adsorption of methylene blue and malachite green dyes in binary aqueous system onto Ni:FeO(OH)‐NWs‐AC using experimental design: derivative spectrophotometry method

In this research, response surface methodology (RSM) approach using Central Composite Design (CCD) coupled by derivative spectrophotometry method was applied to develop mathematical model and optimize process parameters for simultaneous adsorption of methylene blue (MB) and malachite green (MG) from aqueous solution using Ni:FeO(OH) ‐ NWs‐AC. The optimal conditions to adsorption of MB and MG in binary mixture solution from aqueous solution were found at pH 8.0, MB concentration 20 mg L^‐1, MG concentration 20 mg L^‐1, adsorbent dosage 0.033 g and contact time 40 min. At these conditions, high adsorption efficiency (99.39% and 100.0% for MB and MG, respectively) was achieved. Among experimental equilibrium, Langmuir isotherm model fitted well with maximum monolayer adsorption capacity of 28.6 and 29.8 mg g^‐1 for MB and MG, respectively. The adsorption kinetic data followed pseudo second‐order kinetics for MB and MG dyes.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Investigation of double-diffusive mixed convection effect on the particles dissolution in the shear flow using coupled SPM–LBM

Journal of Thermal Analysis and Calorimetry - In the present study, double-diffusive mixed convection related to the heat and mass transfer of the solid particles dissolution in a shear flow was...     

Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide

Hyperfine Interactions - Cement clinker is the main component of Portland cement. It is composed of four main phases. One of them is the brownmillerite or the ferrite phase of cement clinker. It is...