International Journal of Modern Physics B

The microstructure and nonohmic properties of SnO₂–Ta₂O₅–ZnO based ceramics sintered at 1450°C for 2 h were investigated in accordance with TiO₂ content (0–8 mol%). Without TiO₂ the prepared sample is nonstoichiometric SnO₂ semiconductor with excessive oxygen; but for the samples doped with TiO₂, Sn_0.9Ti_0.1O₂ phase can be identified, and the incorporation of TiO₂ into the ternary system SnO₂–Ta₂O₅–ZnO ceramics can compensate the defects of Sn⁴⁺ ions loss, promote the sample densification, and facilitate the growth of SnO₂ grains. After 4.0 mol% of TiO₂ is doped, the samples present no precipitated substances residing in the grain juncture, resulting in varistors with maximum nonlinear exponent of 21, varistor voltage of about 1000 V/mm, and minimum leakage current of 100 μA/cm², which are promising in high-voltage applications. The improvement in nonohmic performance of the varistors after the doping of TiO₂ is mainly attributed to the increase in effective barrier height in grain boundary, which can be supported by the decrease in band gap caused by defects and impurities from periodic density function theory calculation.

In this paper, we discuss two problems on asymmetric quantum error-correcting codes (AQECCs). The first one is on the construction of a [[12, 1, 5/3]]₂ asymmetric quantum code, we show an impure [[12, 1, 5/3 ]]₂ exists. The second one is on the construction of AQECCs from binary cyclic codes, we construct many families of new asymmetric quantum codes with d_z> δ_max+1 from binary primitive cyclic codes of length n = 2^m-1, where δ_max = 2^⌈m/2⌉-1 is the maximal designed distance of dual containing narrow sense BCH code of length n = 2^m-1. A number of known codes are special cases of the codes given here. Some of these AQECCs have parameters better than the ones available in the literature.

This communication reports the successful fabrication and the comparative study of Langmuir and Langmuir–Blodgett (LB) films of nonamphiphilic phenanthrene derivative, 1, 10 phenanthroline (bathophenanthroline) (BATH), when incorporated to a long chain fatty acid viz. heptadecanoic acid and stearic acid. Measurements of compressibility modulus from the surface pressure versus area per molecule isotherm indicate that the mixed film of BATH and SA is harder than that with HA. The plot of area per molecule versus mole fraction is the indication of some repulsive interactions between binary components of the mixed monolayer which facilitates the formation of aggregates. UV–Vis absorption spectroscopy and steady-state fluorescence spectroscopy confirms the formation of microcrystalline aggregates in the mixed LB films. Scanning electron microscopic study supports this observation. The dependence of various LB parameters in the mixed films such as mole fraction, number of layers and surface pressure of lifting have also been investigated in the light of electronic absorption spectroscopy.

Synchronization of Coullet systems is investigated via back stepping method when parameters are unknown. A novel adaptive control scheme is presented, which contains a single controller. To achieve the synchronization of Coullet systems, sufficient conditions are derived and the unknown parameters are estimated. Finally, some numerical simulations are employed to verify the effectiveness of the proposed scheme.

In this paper, we present a selective image encryption system based on couple spatial chaotic systems, the cascade one-dimensional Logistic map and high-dimensional spatial chaotic system has been used to generate the adequate encryption sequence, then the selective gray-level image encryption is implemented with the sequence, which can greatly improve the encryption performance and efficiency. In addition, we also adopt an index array to control the generation of the secret key, a completely different cipher text will be obtained if a pixel's value is altered in the original image, which can resist the differential attack effectively.

Nanocrystalline Ni–Co alloys are electrodeposited by direct (DC) and pulse current (PC) in an electrolyte solution which consisted of nickel sulfate, cobalt sulfate and boric acid. Electrodeposition parameters including current density, electrolyte pH and pulse times in a single electrolyte bath were changed. XRD pattern showed that the structure of the alloys depends on Co content and the synthesis parameter and changed from single phase structure (fcc) to dual phase structure (fcc + hcp). The Co content in the deposited alloys declined from 70 at.% to 50 at.% by increasing in direct current from 70 mA/cm² to 115 mA/cm² and also decreased from 75 at.% to 33 at.% with decrease in pH values from 4 to 2. By applying PC the Co content changed from 76 at.% to 41 at.%. Magnetic properties measurements showed the saturation magnetization (M_s) increased with increasing the Co content. There was no significant effect on coercivity values (H_c) with change in Co content and about 40 Oe was obtained for all samples. The grain size of deposited alloys obtained between 24–58 nm and 15–21 nm by applying DC and PC, respectively.

Magnetic induction dependence of the dispersion of longitudinal magnetoplasmon in a two-dimensional electron gas with finite layer thickness under a static uniform magnetic field normal to the layer plane is calculated using the self-consistent linear response approximation. Two longitudinal magnetoplasmon modes are obtained. The calculated dispersion agrees with the experiment by Batke et al. [Phys. Rev. B34, 6951 (1986)].

Based on the first-principles plane wave ultra-soft pseudo potential (USP) method of density function theory pure N and Ce doped and Ce–N codoping anatase TiO₂ supercell models were established, respectively, and calculated their energy in this paper. The calculated results show that the three doping systems compared to the pure anatase TiO₂ band gap narrowed which results in red-shift of the optical absorption edges and Ce–N codoped anatase TiO₂ have the most obvious visible effect. Meanwhile, synergy is very effective for the separation of electron–hole pairs and the electrons have a better lifespan. Research found that the trend of the donor's movements at the shallow level of Ce–N codoped anatase TiO₂ is not obvious. This is due to its very thick shell, resulting in shielding effect of the outer layer of the Ce-4f.

First principle calculations on cesium chloride (CsCl) compound have been performed using state of the art full potential linearized augmented plane wave (FP-LAPW) method. Calculated structural parameters are found in excellent agreement to the experimental results. Band gap of the compound decreases with the increase of pressure. At 507GPa, electronic nature of the compound changed from the insulating to metallic. Changes are reported in the optical properties like real and imaginary parts of dielectric function, optical conductivity and reflectivity of CsCl on application of high pressure.