Modern Physics Letters B

We test a simplified, local version of the helix model¹ on two synthetic and two natural proteins, to study its efficiency in predicting the native secondary structure. The results we obtain are very good for the synthetic sequences, poorer for the two natural ones. This suggests that nonlocal terms play a fundamental role in determining the secondary structure, even if in some cases local terms alone may be sufficient.

A magnetic plane, exchange coupled to an electron gas, generates a spin polarization and in the nonlinear theory also a charge distribution. The corresponding electrostatic energy per unit surface is evaluated. For an electron gas at metallic densities this turns out to be negligible, while it must be taken into account in dilute degenerate semiconductors.

Direct numerial calculations reveal the fine-scale structures of the local Lyapunov exponent as a spatial function in the chaotic region of a three-dimensional volume-preserving flow.

The motion of Brownian particles in a spatial symmetric periodic potential is considered. In the absence of any external driving forces, when the potential profile fluctuates cyclically between three states, directed motion can be induced. For a cosine potential, the finite probability current is evaluated.

The influence of (non-magnetic and magnetic) impurities on the transition temperature of a d-wave superconductor is studied anew within the framework of BCS theory. Pairing interaction decreases linearly with the impurity concentration. Accordingly T_c suppression is proportional to the (potential or exchange) scattering rate, 1/τ, due to impurities. The initial slope versus 1/τ is found to depend on the superconductor contrary to Abrikosov–Gor'kov type theory. Near the critical impurity concentration T_c drops abruptly to zero. Because the potential scattering rate is generally much larger than the exchange scattering rate, magnetic impurities will also act as non-magnetic impurities as far as the T_c decrease is concerned. The implication for the impurity doping effect in high T_c superconductors is also discussed.

The sample Bi₂Sr₂YCu₂O_y prepared by solid state reaction method showed a single phase Bi-2212. DC resistivity measured in the temperature range 77.5–300 K showed M–I like transition. AC conductivity measurements were performed in the temperature range 80–473 K at different frequencies. The conduction is by Mott's Variable Range Hopping. Various parameters pertaining to the conduction process are evaluated. The value of dielectric constant ε increases with temperature and shows a very high value. For a given temperature the value is found to decrease with increase in frequency.

β, β″ and γ-Al₂O₃ samples were synthesized. The temperature dependence of the magnetic susceptibility has anomalous diamagnetic-paramagnetic transitions, like Meissner effect, around 80 K, and consequently high T_c superconducting like magnetic behavior.

X-ray absorption fine structure XAFS spectroscopy has been used to determine the valence system for the Fe atom in ilmenite, FeTiO₃. This is the first XAFS data in FeTiO₃ to our knowledge. The α-Fe₂O₃ data served as the standard in determining the ionization of the Fe atom in FeTiO₃. Observation of intensity and k-space are consistent. There was no evidence of mixed valence on comparing the FeTiO₃ near edge X-ray absorption spectrum with α-Fe₂O₃ data. The absorption spectra suggest that iron is in the trivalent state in ilmenite.

Boron carbon nitride coatings have been synthesized by the pulsed laser deposition method. Vickers micro-hardness and adhesion of the coatings were studied. A new model was applied to determine the hardness of the coatings which were too thin to be directly measured by the Vickers micro-hardness test. An intermediate layer of silicon was used to enhance the adhesion of the coatings on stainless steel, glass, and quartz substrates.

Diamond-like carbon films have been synthesized by the pulsed laser deposition under a magnetic field. The hardness of the films was increased considerably. However, due to the large compressive stress in the films, adhesion of the films became a serious problem. Two methods, i.e. laser irradiation of the silicon substrate surface and growing a composition-graded intermediate layer, were used to increase the adhesion. With the variations of the interface conditions, the change of the stress type from compressive stress to tensile stress was observed. By careful choosing the composition change of the intermediate layer, adherent diamond-like carbon films with a thickness of 1145 nm were successfully grown on silicon substrates at 80°C.