On the relation between the fermi energies in the presence and absence of magnetic quantization in degenerate semiconductors having non-parabolic energy bands

An investigation is made of the influence of band non-parabolicity on the relation between the Fermi energies in the presence and absence of magnetic quantization in degenerate semi-conductors through derivation of a simplified form of the relation.On leave of absence from theDept. of Physics, B. N. College, Patna University, Patna 800004.     

Influence of alloy composition on the diffusivity-mobility ratio in n-channel inversion layers on ternary semiconductors

An expression is derived for the diffusivity-mobility ratio of the carriers in n-channel inversion layers on semiconductors like the ternary compounds which have strongly non-parabolic energy bands. The dependence of the ratio on alloy composition is also studied under the weak-field limit taking n-channel Hg_1–xCd_x.Te as an example.On leave of absence fromthe Department of Physics, Patna University, Patna, India.     

Prolongation structure of a new integrable system

We have obtained the inverse scattering equations associated with a new pair of coupled nonlinear evolution equations in two dimensions. The spectral parameter is introduced by invoking the invariance of the equation set, and imposing those on the Lax pair.     

On hydromagnetic turbulent shear flow between moving parallel planes

Hydromagnetic turbulent shear flow of viscous, incompressible, electrically conducting fluid between two infinite uniformly porous moving parallel planes in the presence of axial and transverse magnetic field has been studied by the semi-empirical method. The expressions for the mean distributions for velocity and magnetic field for turbulent shear flow have been obtained for both the cases. As particular cases, the results have been obtained if the planes are fixed. The solutions obtained when the magnetic field is axial have been shown graphically for turbulent and laminar flows.     

Stress in polycrystalline GaN films prepared by r.f sputtering

Undoped, Be-doped and Si-doped polycrystalline GaN films were deposited by R.F. sputtering onto fused silica substrates. The films were deposited at various deposition temperatures ranging from 300 K to 623 K and characterized by optical measurements while the microstructural information was obtained from SEM and XRD studies. The compositional study for the GaN film was carried out using SIMS. Residual stresses in these films were evaluated from the band tail of the absorption spectra as well as from direct measurements of hardness by commercially available depth sensing indentometer. It was observed that undoped GaN films had the highest hardness followed by that for Be-doped and Si-doped films. The values of hardness obtained form the above optical measurement tallied quite well with those obtained from direct indentation measurement.     

Intracellular transport of single-headed molecular motors KIF1A

Motivated by experiments on single-headed kinesin KIF1A, we develop a model of intracellular transport by interacting molecular motors. It captures explicitly not only the effects of adenosine triphosphate hydrolysis, but also the ratchet mechanism which drives individual motors. Our model accounts for the experimentally observed single-molecule properties in the low-density limit and also predicts a phase diagram that shows the influence of hydrolysis and Langmuir kinetics on the collective spatiotemporal organization of the motors. Finally, we provide experimental evidence for the existence of domain walls in our in vitro experiment with fluorescently labeled KIF1A.     

Numerical simulation of polymer nanocomposites using self-consistent mean-field model

Clay-containing polymeric nanocomposites (PNC) are mixtures of dispersed clay platelets in a polymeric matrix. These materials show enhancement of physical properties, such as modulus, strength, and dimensional stability, as well as a reduction of gas permeability and flammability. The performance is related to the degree of clay dispersion (i.e., intercalation or exfoliation) and the bonding between the clay and the matrix. The main goal of this work has been to map the degree of dispersion as a function of independent variables (viz., magnitude of the interaction parameters, molecular weights, composition, etc.). In this paper, we present the results of the numerical analysis of the equilibrium thermodynamic miscibility using one- and two-dimensional (1D and 2D) models based on the self-consistent mean-field theory. In the limit, the 2D model reproduced the 1D model published results. The adopted 2D model considers the presence of four PNC components: solid clay platelets, low molecular weight intercalant, polymeric matrix, and end-functionalized compatibilizer. The simulations, with realistic values of the binary interaction parameters, were analyzed for potential exfoliation of PNC with a polyolefin as the matrix. The simulation results show that intercalation and exfoliation is expected within limited ranges of the independent variables. The presence of a bare clay surface (e.g., generated by thermal decomposition of intercalant or extraction by molten polymer) has a strong negative effect on the dispersion process. The simulation successfully identified the most influential factors, e.g., optimum ranges of the compatibilizer and the intercalant concentration.     

Does Solvent Influence the Ground-state Tautomeric Population of Hypericin?¶

Nuclear magnetic resonance measurements indicate that hypericin exists in the same "normal" tautomeric form irrespective of whether the solvent is dimethyl sulfoxide or tetrahydrofuran. This result is discussed in the context of previous experimental and theoretical work. It is concluded that solvent perturbations cannot induce tautomerization in hypericin.     

Figure of merit for near-velocity-matched traveling-wave modulators

We derive a relationship between the bandwidth and active length and a figure of merit for velocity- and near-velocity-matched lithium niobate traveling-wave electro-optic modulators. The figure of merit is given by the bandwidth per unit drive voltage squared and is independent of the length of the device. Alternatively, this figure of merit can be described by its inverse, which is proportional to the device's switching energy.     

Observation of the transverse optical plasmon in SmLa0.8Sr0.2CuO4-delta

We present microwave and infrared measurements on SmLa0.8Sr0.2CuO4-delta, which are direct evidence for the existence of a transverse optical plasma mode, observed as a peak in the c-axis optical conductivity. This mode appears as a consequence of the existence of two different intrinsic Josephson couplings between the CuO2 layers, one with a Sm2O2 block layer, and the other one with a (La,Sr)2O2-delta block layer. From the frequencies and the intensities of the collective modes we determine the value of the compressibility of the two dimensional electron fluid in the copper oxygen planes.