Electronic transport in Mo/Ni superlattices

An experimental relationship between superconductivity, magnetism and localization is explored in short-wavelength (14Å ? ? ? 40Å) sputtered Mo/Ni superlattices. A crossover to a superconducting state is observed for ? < 9Å consistent with the observed paramagnetic behavior when the Ni strata are four atomic layers thick, or less. All samples show localization effects at helium temperatures and non-superconducting samples develop an unusual resistance plateau below T ? 0.5K.     

Variational approach to the Hamiltonian structure of a new hierarchy of nonlinear equations

We determine the symplectic Hamiltonian structure associated with the nonlinear evolution equations obtained from two new isospectral problems. We follow the method of variation with respect to the field variables. An explicit example is given to demonstrate the new class of equations that are generated.     

Generation of Exactly Solvable Non-Hermitian Potentials with Real Energies

Series of exactly solvable non-trivial complex potentials (possessing real spectra) are generated by applying the Darboux transformation to the excited eigenstates of a non-Hermitian potential V(x). This method yields an infinite number of non-trivial partner potentials, defined over the whole real line, whose spectra are nearly exactly identical to the original potential.     

Structural investigations of synthetic ferrihydrite nanoparticles doped with Si

X-ray diffraction (XRD), transmission electron microscopy (TEM), and photoacoustic/Fourier transform infrared spectroscopy (PA/FTIR) are employed to monitor the changes in the structural aspects of two-line ferrihydrite (FHYD) nanoparticles doped with silica viz. Si_xFe_1−xOOH·nH₂O for x=0, 0.02, 0.05, 0.10, 0.15, 0.20, 0.26, 0.40 and 0.50. In XRD, crystallinity decreases and d-spacings increase with increase in x. TEM studies show that the particle size increases systematically with increase in x, from 3.7 nm for x=0 to 5.7 nm for x=0.50. In PA/FTIR, two new bands appear, band F near 3700 cm⁻¹ identified with the surface Si-O-H group and band A near 900 cm⁻¹ identified with Si-O-Fe group, which shifts to higher wavenumbers with increase in x. These results are used to propose a model in which doped Si⁴⁺ ions do not displace Fe³⁺ ions but are chemisorbed on the FHYD surface making a shell of silica for higher doping. This model is consistent with the reported changes in the magnetic properties of FHYD with Si doping.     

Electron impact single and double ionization of argon

Stable two-mode, and three-mode oscillations due to the spatial hole burning effect were observed experimentally with the increase of the pump power ratio in a laser-diode pumped sub-nanosecond microchip Cr,Yb:YAG self-Q-switched multimode laser. The stability of the output pulse trains was attributed to the mode coupling through antiphase dynamics between different modes. Modified multimode rate equations including the spatial hole-burning effect in the active medium and the non-linear absorption of the saturable absorber were proposed. Numerical simulations of the antiphase dynamics of such a laser were in good agreement with the experimental data, and the antiphase dynamics were explained by the evolution of the inversion population and the bleaching and recovery of the inversion population of the saturable absorber.     

Total reflections,partial products,and hereditary factorizations

This paper shows that many, but not all, reflective subcategories of Top have a certain property, here called total reflectivity, hitherto studied in some special cases, such as for compactness. It is related to Pasynkov's partial topological products and to the stability of topological factorizations under pullback along open inclusions.     

Oriented growth of CdS nanoparticulate film with constant average particle size with thickness up to 1 μm

Oriented growth of hexagonal CdS nanoparticulate film with the C-axis perpendicular to the plane of the surface has been achieved up to a film thickness of 1 μm, using the combination of Langmuir–Blodgett (LB) and chemical bath deposition techniques. This combination is shown to eliminate the inherent limitation of the LB technique on the film thickness (up to300 Å). The average size of the particles has been found to be constant with the film thickness.     

Mechanical breakdown of trabecular bone: Dependence on microstructure

Experiment on mechanical strength of porous trabecular bone shows power law dependence on the density of the structure. Physical structure and mechanical properties of the trabecular network are modelled here with a fractal lattice network of elastic springs having a strain based fracture criteria. An analysis of the model system supports the power law and shows that lacunarity is an important parameter in differentiating the mechanical strength of trabecular bones of same density.     

Fractal flux jumps in an organic superconducting crystal

Angle dependant torque magnetization measurements have been carried out on the organic superconductor, κ-(ET)₂Cu(NCS)₂ at extremely low temperatures (25-300 mK). Magneto-thermal instabilities are observed in the form of abrupt magnetization (flux) jumps for magnetic field sweeps of 0-20 T. A fractal analysis of the flux jumps indicate that the instabilities do show a self similar structure with a fractal dimension of varying between 1.15 and 1.6. The fractal structure of the flux jumps in our sample shows a striking similarity to that of MgB₂ thin film samples, in which magneto-optical experiments have recently shown that the small flux jumps are due to the formation of dendritic flux structures. These smaller instabilities act to suppress the critical current density of the thin films. The similarity of the flux jump structure of our samples suggests that we may also observing the dendritic instability, but in a bulk sample rather than a thin film. If true, this is the first observation of the dendritic instability in a bulk superconducting sample, and is likely due to the layered nature of κ-(ET)₂Cu(NCS)₂, which results in a quasi-two dimensional flux structure over the majority it's mixed state phase diagram.