Dynamic Nuclear Polarization in III–V Semiconductors

We report on electron spin resonance, nuclear magnetic resonance and Overhauser shift experiments on two of the most commonly used III–V semiconductors, GaAs and InP. Localized electron centers in these semiconductors have extended wavefunctions and exhibit strong electron–nuclear hyperfine coupling with the nuclei in their vicinity. These interactions not only play a critical role in electron and nuclear spin relaxation mechanisms, but also result in transfer of spin polarization from the electron spin system to the nuclear spin system. This transfer of polarization, known as dynamic nuclear polarization (DNP), may result in an enhancement of the nuclear spin polarization by several orders of magnitude under suitable conditions. We determine the critical range of doping concentration and temperature conducive to DNP effects by studying these semiconductors with varying doping concentration in a wide temperature range. We show that the electron spin system in undoped InP exhibits electric current-induced spin polarization. This is consistent with model predictions in zinc-blende semiconductors with strong spin–orbit effects.     

Tissue-specific and neural activity-regulated expression of human BDNF gene in BAC transgenic mice

Background  

Brain-derived neurotrophic factor (BDNF) is a small secreted protein that has important roles in the developing and adult nervous system. Altered expression or changes in the regulation of the BDNF gene have been implicated in a variety of human nervous system disorders. Although regulation of the rodent BDNF gene has been extensively investigated, in vivo studies regarding the human BDNF gene are largely limited to postmortem analysis. Bacterial artificial chromosome (BAC) transgenic mice harboring the human BDNF gene and its regulatory flanking sequences constitute a useful tool for studying human BDNF gene regulation and for identification of therapeutic compounds modulating BDNF expression.     

Stopping power contribution due to target and projectile excitation/ionization: a comparative study

A comparative study of stopping power codes for different ions in compounds has been made by comparing the computed stopping power values using different codes with the corresponding experimental data. Two computer codes, semiempirical SRIM2006.02 and theoretical CasP3.2 have been used to evaluate and compare the stopping powers of different compounds for protons (125 KeV), helium (500 KeV) and lithium ion (175 KeV) projectiles. The energy behaviour of stopping power of various compounds for helium ion in the energy range (0.3–2.0 MeV) has been studied. The merits and demerits of the adopted formulations are highlighted. It has been observed that the calculation based on SRIM2006.02 provides the best agreement with the experimental data as compared to CasP3.2 code. The stopping power contribution due to target and projectile excitation/ionization at low energies has been evaluated and discussed with reference to CasP3.2 code. From these comparative studies it has been concluded that the target and projectile excitation-ionization increases the stopping power (>20%) at lower energies.     

Rapidity distribution as a probe for elliptical flow at intermediate energies

The interplay between spectator and participant matter in heavy-ion collisions is investigated within the isospin-dependent quantum molecular dynamics (IQMD) model in terms of the rapidity distribution of light charged particles. The effect of different types and sizes of rapidity distributions is studied in elliptical flow. The elliptical-flow patterns show the important role of nearby spectator matter on the participant zone. This role is further explained on the basis of the passing time of the spectator and the expansion time of the participant zone. The transition from in-plane to out-of-plane emission is observed only when the mid-rapidity region is included into the rapidity bin. Otherwise no transition occurs. The transition energy is found to be highly sensitive to the size of the rapidity bin, while it is only weakly dependent on the type of the rapidity distribution. These theoretical findings are found to be in agreement with experimental results.     

Static and dynamic properties of KCN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cl<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>

An extended three-body force shell model (ETSM) has been applied to investigate the static and dynamic properties of KCN _x Cl_1−x for the compositionx = 0.56 and 1.0 at 300 K. The phonon dispersion curves computed by us are compared with the single crystal neutron diffraction data. The unusual features of these curves are the upward curvature seen in some of the acoustic branches. This is a result ofK-dependent softening of the phonon due to translation-rotation coupling. The transverse acoustic branch is more soft near the zone centre.     

Influence of reactive gas and temperature on structural properties of magnetron sputtered CrSiN coatings

CrSiN coatings were deposited on stainless steel (Grade: SA304) and silicon Si(1 0 0) substrates, with varying argon-nitrogen gas proportions and deposition temperature, using reactive magnetron sputtering technique in the present work. The influence of sputtering (Ar) and reactive gas proportions (N₂) and temperature on the structural properties of the CrSiN coating was investigated. A small amount of silicon content (3.67 at.% Si) plays a crucial role in addition to the nitrogen content for the formation of different phases in the CrSiN coatings as observed in the present work. For example, the coating with comparatively low nitrogen content, 40% N₂, during deposition, formed a crystalline structure consisting of nano-crystalline CrN which is separated by an amorphous SiN phase, as evident from X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of CrN(1 1 1) and Cr₂N(1 1 1) phases has occurred at 30% N₂ with 3.67% Si content, which transformed in to CrN(1 1 1) and CrN(2 0 0) with increase in N₂ content but with same Si content. The surface topography and morphology of the coatings were analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM), respectively. A less columnar growth is observed in CrSiN coatings deposited at low argon content, Ar:N₂ (20:80), and with 3.67 at.% Si in the coatings. However, it becomes dense with increase in nitrogen content and temperature. The XRD analysis showed that the intensity of a dominating peak (1 1 1) is decreasing from (80:20) to (60:40) argon:nitrogen environment. With a further increase of nitrogen content, from (60:40), in the sputtering gas mixture, to (40:60) argon-nitrogen, there is a sudden increase in (1 1 1) peak and above (40:60), the peak reduction rate is very slow than the previous one. The (1 1 1) and (2 0 0) peak intensity variations are very limited due to high nitrogen content, above 50%, and considerable amount of Si atoms, 3.67 at.%, present in the CrN coatings.     

Finite size effect on Gd doped CoGdxFe2−xO4 (0.0≤x≤0.5) particles

Nanoparticles of CoGd_xFe_2−xO₄ (where x=0.0, 0.1, 0.3, 0.5) series have been prepared by chemical co-precipitation. The effect of Gd³⁺ ion concentration on crystalline phase, crystallinity, crystallite size, molecular vibrations and magnetic resonance has been investigated in detail. The crystallinity decreases with an increase in Gd³⁺ ion concentration and changes the structural parameters. The spin lattice relaxation has been correlated with the doping ion concentration. Similarly, the superparamagnetic behavior of these particles has been observed with EPR spectroscopy.     

Structural analysis of trypanosomal sirtuin: an insight for selective drug design

The infectious disease burden imposed by trypanosomatidae family continues to create burden in countries that are least equipped to bring new medicines to the clinic. For sickness caused by this family of parasites (African trypanosomiasis, Chagas disease, and leishmaniasis) no vaccines are available, and currently available drugs suffer from insufficient efficacy, excessive toxicity, and steady loss of effectiveness due to resistance. Availability of the genome sequence of pathogens of this family offers a unique avenue for the identification of novel common drug targets for all three pathogens. Sirtuin family of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases are remarkably conserved throughout evolution from archaebacteria to eukaryotes and plays an important role in trypanosomatidae biology and virulence. In order to gain insight for selective drug design, three-dimensional (3D) models of L. major, L. infantum, T. brucie, and T. cruzi sirtuin were constructed by homology modeling and compared with human sirtuin. The molecular electrostatic potentials and cavity depth analysis of these models suggest that the inhibitor binding catalytic domain has various minor structural differences in the active site of trypanosomal and human sirtuin, regardless of sequence similarity. These studies have implications for designing effective strategies to identify inhibitors that can be developed as novel broad-spectrum antitrypanosomal drugs.     

Effect of cation doping on low-temperature specific heat of LaMnO3 manganite

We have investigated the thermodynamic properties of perovskite manganite LaMnO₃, the parent compound of colossal magnetoresistive manganites, with the Ca²⁺ doping at the A-site. As strong electron-phonon interactions are present in these compounds, the lattice part of the specific heat deserves proper attention. We have described the temperature dependence of the lattice contribution to the specific heat at constant volume (C_v(lattice)) of La_1−xCa_xMnO₃ (x=0.125, 0.175, 0.25, 0.35, 0.50, 0.67, 0.75) as a function of temperature (1 K–20 K) by means of a rigid ion model (RIM).The trends of specific heat variations with temperature are almost similar at all the composition. The Debye temperatures obtained from the lattice contributions are found to be in somewhat closer agreement with the experimental data. The specific heat values revealed by using RIM are in closer agreement with the available experimental data, particularly at low temperatures for some concentrations (x) of La_1−xCa_xMnO₃. The theoretical results at higher temperatures can be improved by including the effects of the charge ordering, van der Waals attraction and anharmonicity in the framework of RIM.