Anomalous temperature dependence of elastic constant c44 in V, Nb, Ta, Pd, and Pt

The anomalous temperature dependence of elastic constant c₄₄ for elements V, Nb, Ta, Pd, and Pt, has been calculated using first-principles theory. It is shown that the variation of elastic constant for simple elements can be approximated as the sum of thermal expansion and electronic components. The thermal expansion contributes the normal linearly decreasing effect to the elastic constant with temperature, while electronic contribution is determined by the unique character of electronic structure of elements and leads to the anomalous effect to the elastic constant with temperature.     

Electrical and magnetic properties of Ni-Cu-Si heterojunction prepared by the liquid phase epitaxy technique

Ni-Cu-Si heterojunction was prepared by the liquid phase epitaxy (LPE) technique. Two growth solutions containing Indium (In) with Cu pieces and In with Ni pieces were employed during the fabrication process. The as-formed junction was directly characterized by different techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and thin film X-ray diffraction (XRD) measurements. The current-voltage (I-V) characteristics of the Au/Ni/Cu/Si diode were found to be nonlinear, asymmetric, having a good rectification behavior with a very small leakage current of 0.003 μA at a reverse bias voltage of 2.0 V. The value of turn on voltage was located at 0.2 V. The magnetic properties were also evaluated at room temperature with a vibrating sample magnetometer. Systematic study of junction fabrication and characterization of such a heterosystem, comparison of the behavior of flat silicon and nanoporous silicon as substrates are presented and thoroughly discussed.     

Dielectric, thermal and optical study of an unusually shaped liquid crystal

Dielectric measurements have been carried out for the determination of real and imaginary parts of the permittivity of a newly synthesized, unusually shaped liquid crystal. The sample has been investigated in the frequency range from 100 Hz to 10 MHz within a temperature range 80-130 °C. The dielectric measurements in the smectic A phase indicate a Cole-Cole type of dispersion, and the activation energy was found to be 5.5 meV by using the Arrhenius plot of relaxation time. In addition to this, thermal and optical transmittance studies have also been conducted in the above mentioned temperature range, and the temperature dependence of these parameters has been discussed in detail. The phase transition temperature obtained from a differential scanning calorimetry (DSC) study matches within 2 °C that was obtained from an optical transmittance study. The dielectric and optical behavior of the unusually shaped liquid crystal has been explained on the basis of a proposed theoretical model in which a sample possesses two different conformers having induced polarizations in opposite directions.     

Enhancing electrical properties of high-Curie temperature piezoelectric ceramics BNT-PZT and their mechanism

Due to the urgent demands for high-Curie temperature (T_C/T_m) piezoelectric materials in geothermal exploration, aerospace and related fields, high-T_C/T_m ferroelectrics have attracted booming research attention. The high-T_m 0.25Bi(Ni_1/2Ti_1/2)O₃-0.75 Pb(Zr_1/2Ti_1/2)O₃ (0.25BNT-0.75PZT) ceramics were prepared by solid-state sintering method and via partial oxalate route, where the 0.25BNT-0.75PZT ceramics prepared via the partial oxalate route exhibit better electrical properties (T_m = 232 °C (10 kHz), ε_m = 10963, P_r = 26.14 μC/cm², E_c = 15.61 kV/cm, d₃₃ = 521 pC/N, d₃₃* = 553.3 pm/V, K_p = 47.1%, and Q_m = 21.6). The nano-scale domain configuration of the ceramics was revealed by piezoelectric force microscopy (PFM), and the relationship between the micro-structure and macro-electrical properties was analyzed. The ferroelectric phase transition mechanism was studied by temperature dependent Raman spectroscopy. The reduction of energy barrier of lattice distortion and polarization deflection is caused by nanometer-sized domain structure, low symmetric polar nano-regions and/or coexistence of multi-ferroelectric phases, contributing to the excellent electrical properties of the 0.25BNT-0.75PZT ceramics prepared via the partial oxalate route.     

Uniqueness results for nonlocal Hamilton-Jacobi equations

We are interested in nonlocal eikonal equations describing the evolution of interfaces moving with a nonlocal, non-monotone velocity. For these equations, only the existence of global-in-time weak solutions is available in some particular cases. In this paper, we propose a new approach for proving uniqueness of the solution when the front is expanding. This approach simplifies and extends existing results for dislocation dynamics. It also provides the first uniqueness result for a Fitzhugh-Nagumo system. The key ingredients are some new perimeter estimates for the evolving fronts as well as some uniform interior cone property for these fronts.     

First-principles calculation of structural and electronic properties of pyrochlore Lu2Sn2O7

A Density functional theory method within generalized gradient approximation has been performed to obtain the static lattice parameters, oxygen positional parameter, bond length and bond angle and electronic properties of ideal Lu₂Sn₂O₇ pyrochlore. The results are in excellent agreement with available experimental measurements. Density of states (DOS) of this compound was presented and analysed. We also notice the presence of the hybridization between oxygen and Lu metal. The band structure calculations show that the compound has direct band gap of 2.67 eV at the Γ point in the Brillouin zone and this indicates that the material has a semi-conducting feature.     

Relaxation phenomena in ensembles of CoFe2O4 nanoparticles

Collective magnetic behavior of CoFe₂O₄ nanoparticles with diameters of 76, 16, 15 and 8 nm, respectively, prepared by different chemical methods has been investigated. Particle composition, size and structure have been characterized by inductive coupled plasma (ICP), transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). Basic magnetic properties have been determined from the temperature dependence of magnetization and magnetization isotherms measurements. The three samples exhibit characteristic of a superparamagnetic system with the presence of strong interparticle interactions. Magnetic relaxation phenomena have been examined via frequency-dependent ac susceptibility measurements and aging and memory effect experiments. For the particles coated with oleic acid, it has been demonstrated that the sample reveals all attributes of a super-spin glass (SSG) system with strong interparticle interactions.     

Synthesis, structural and magnetic properties of the nanocomposite Fe63B23Nd7Y3Nb3Cr1 magnets

The Fe₆₃B₂₃Nd₇Y₃Nb₃Cr₁ nanocomposite magnets in the form of sheets have been prepared by copper mold casting technique. The phase evolution, crystal structure, microstructural and magnetic properties have been investigated in the as-cast and annealed states. The as-cast sheets show magnetically soft behaviors which become magnetically hard by thermal annealing. The optimal annealed microstructure was composed of nanosize soft magnetic α-Fe (19-29 nm) and hard magnetic Nd₂Fe₁₄B (45-55 nm) grains. The best hard magnetic properties such as intrinsic coercivity, _jH_c of 1119 kA/m, remanence, B_r of 0.44 T, magnetic induction to saturation magnetization ratio, M_r/M_s=0.61 and maximum energy product, (BH)_max of 55 kJ/m³ was obtained after annealing at 680 °C for 15 min. The annealing treatment above 680 °C results in non-ideal phase grains growth, which degrade the magnetic properties.     

Electronic structure and half-metallicity in Heusler alloys Fe2YB (Y=Ti, V, Mn, Cr)

The electronic structure and magnetic properties of B-based Heusler alloys Fe₂YB (Y=Ti, V, Cr and Mn) have been studied theoretically. These alloys are all ferrimagnets except for Fe₂VB. The latter has 24 valence electrons and is a paramagnetic semimetal. Fe₂CrB is predicted to be half-metals at equilibrium lattice constant. The spin polarization of Fe₂MnB is also quite high. The calculated total moments are 1.00 μ_B for Fe₂CrB and 2.04 μ_B for Fe₂MnB. In Fe₂CrB and Fe₂MnB, the total moments are mainly determined by the partial moment of Cr or Mn. The Fe moment is relatively small and antiparallel to that of Cr or Mn. Under uniform lattice distortion, the half-metallicity of Fe₂CrB is more stable than Fe₂MnB, which is related to the detailed DOS structure of them near E_F.     

Effects of ultrasound on growth, bioconversion of isoflavones and probiotic properties of parent and subsequent passages of Lactobacillus fermentum BT 8633 in biotin-supplemented soymilk

This study aimed to evaluate the effects of ultrasound on Lactobacillus fermentum BT 8633 in parent and subsequent passages based on their growth and isoflavone bioconversion activities in biotin-supplemented soymilk. The treated cells were also assessed for impact of ultrasound on probiotic properties. The growth of ultrasonicated parent cells increased (P < 0.05) by 3.23-9.14% compared to that of the control during fermentation in biotin-soymilk. This was also associated with enhanced intracellular and extracellular (8.4-17.0% and 16.7-49.2%, respectively; P < 0.05) β-glucosidase specific activity, leading to increased bioconversion of isoflavones glucosides to aglycones during fermentation in biotin-soymilk compared to that of the control (P < 0.05). Such traits may be credited to the reversible permeabilized membrane of ultrasonicated parent cells that have facilitated the transport of molecules across the membrane. The growing characteristics of first, second and third passage of treated cells in biotin-soymilk were similar (P > 0.05) to that of the control, where their growth, enzyme and isoflavone bioconversion activities (P > 0.05) were comparable. This may be attributed to the temporary permeabilization in the membrane of treated cells. Ultrasound affected probiotic properties of parent L. fermentum, by reducing tolerance ability towards acid (pH 2) and bile; lowering inhibitory activities against selected pathogens and reducing adhesion ability compared to that of the control (P < 0.05). The first, second and third passage of treated cells did not exhibit such traits, with the exception of their bile tolerance ability which was inherited to the first passage (P < 0.05). Our results suggested that ultrasound could be used to increase bioactivity of biotin-soymilk via fermentation by probiotic L. fermentum FTDC 8633 for the development of functional food.