International Journal of Modern Physics B

In this paper, we propose an algorithm for one-way hash function construction based on the chaotic look-up table with changeable parameter. First, the original message with padding is divided into block messages as groups and then further broken into sub-block messages, which are translated into corresponding ASCII codes by groups. Then the group ASCII codes are successively inputted into the chaotic look-up table updated by changeable parameter to permute corresponding values. Finally, based on the calculation of the values, 128-bit hash value is generated. Performance analysis indicates that our proposed algorithm satisfies sensitive requirements and can resist all kinds of attacks.

Ge-doped (Cu_0.5Tl_0.5)Ba₂Ca₃(Cu_4-yGe_y)O_12-δ (y = 0, 0.3, 0.6 and 0.9) superconductors have been synthesized at normal pressure through solid state reaction method. Ge has been doped in the CuO₂ planes constituting the superconducting block of these structures. In the as-prepared samples, a suppression of the critical temperature is observed with increased Ge concentration. The suppression of the critical temperature can be attributed to the decreased number of carriers due to their localization at Ge⁴⁺ ions. Ge-doped post-annealed samples have shown enhancement in the critical temperature as well as magnitude of diamagnetism. Oxygen annealing seems to have replenished the charge carries through the process of hole doping in CuO₂/GeO₂ planes, thereby bringing the carrier density closer to the optimum level. Oxygen related phonon modes have also been investigated. A shift in peak positions of the apical and planar oxygen related modes have been observed while modes associated with O_δ oxygen atoms seem stable in both cases of Ge doping and oxygen annealing.

Near-ideal n-SnO₂/n-Si heterojunction band edge lineup has been investigated with aid of I–V and C–V measurements. The heterojunction was manufactured by rapid thermal oxidation of Sn metal films prepared by thermal evaporation technique on monocrystalline n-type silicon. The experimental data of the conduction band offset ΔEc and valence band offset ΔEc were compared with theoretical values. The band offset ΔEc = 0.55 eV and ΔEv = 1.8 eV obtained at 300 K. The energy band diagram of n-SnO₂/n-Si HJ was constructed. C–V measurements depict that the junction was an abrupt type and the built-in voltage was determined from 1/C²–V plot.

The effect of gate voltage on electronic transport properties in single C₆₀ molecular device is investigated by a first-principles method based on density functional theory and nonequilibrium Green's function formalism. The calculated results show that the variation of the equilibrium conductance with gate voltage strongly corresponds with the variation of transmission eigenvalues and depends on the shift of molecular orbitals. The positive gate voltage can enhance the device's electronic transport, while negative gate voltage weaken it, which shows a gate-controlled molecular current switch. More importantly, the negative differential resistance behavior is observed and can be modulated by the gate potential. A detailed explanations for these phenomena are given.

Al³⁺-doped Ni–Zn ferrites with composition of Ni_0.5Zn_0.5(Fe_1-xAl_x)₂ O₄ (where x = 0, 0.012, 0.023, 0.035 and 0.045) were prepared by a method named "one-step synthesis." The magnetic and dielectric properties of the as-prepared Ni–Zn ferrites were investigated. X-ray diffraction data indicated that all the ferrite samples had a single-phase spinel structure. The addition of Al³⁺ resulted in a reduction of the grain size, lattice constant, density, shrinkage and saturation magnetization of the as-prepared samples. The Curie temperatures, however, raised first and reduced later with increasing contents of Al³⁺ in the samples, but still kept high values. Both the real and imaginary parts of permeability of ferrites decreased with increasing amount of Al³⁺ doped before they reached peak value. As the applied frequency increased to higher than about 10 MHz, the real part of permeability of non-doped ferrite had already become lower than those of ferrites doped with Al³⁺. Moreover, the doping of Al³⁺ made their utility of magnetic permeability move to much higher frequency. The observed decreases in dielectric constants and dielectric loss tangent could be attributed to the decreased electron conductivity by substituting Fe³⁺ with Al³⁺ in the samples. The as-prepared high-performance soft magnetic materials prepared using such a simple and low-cost method will be much promising in high-frequency applications and industrialization.

The impulsive synchronization of two chaotic Chen–Lee systems was investigated in this paper. Based on Lyapunov's direct method, sufficient conditions for the global exponential synchronization and global asymptotical synchronization were derived. Further, the theoretical results were verified by a numerical simulation. In addition, the impulsive synchronization of two chaotic Chen–Lee systems was also implemented using an electronic circuit.

BEBIG Ruthenium-106 ophthalmic plaques have been used for treatment of uveal melanoma, retinoblastoma, melanoma of the iris and other special applications for more than 30 years. The plaques consist of a thin film of Ru-106, a beta emitter encapsulated in pure silver. Simulations of small concave applicators CCA and CCB, manufactured by Bebig, were performed using Monte Carlo MCNP4C code which allows for description of the applicator (geometry and materials) in detail. Electrons are emitted from the ¹⁰⁶Ru nuclei isotropically with initial energy randomly sampled from the corresponding Fermi spectra and with initial positions uniformly distributed on the radioactive layer. In this work, relative doses were calculated in soft tissue phantom near the active layer. Isodose curves for CCA and CCB eye applicators were determined. Our calculated data agrees well with the measured phantom data reported in literature.

Ground-state structural properties of alkali metal selenides and tellurides (M₂X) [M: Li, Na, K, Rb; X: Se, Te] have been studied in the framework of density functional theory for the first time using local density approximation, Perdew–Burke–Ernzerhof generalized gradient approximation (GGA) and Wu–Cohen (WC) GGA parameterization schemes. Also structural properties of alkali metal oxides and sulfides (M₂X) [M: Li, Na, K, Rb; X: O, S] have been reinvestigated using WC GGA. Electronic band structures of alkali metal chalcogenide compounds have been calculated using the aforementioned schemes as well as the modified GGA proposed by Engel and Vosko. The calculated structural parameters for all 16 materials have been compared with earlier theoretical and experimental results, and certain trends are discussed. Furthermore, electronic density of states for these compounds has also been presented herein and behavior in electronic properties analyzed. Li, K and Rb chalcogenides have been found to have indirect bandgap, whereas Na chalcogenides appear to have direct bandgap.

In this paper, we present a theoretical study of a Bose–Einstein condensate of interacting bosons in a quartic trap in one-, two- and three-dimensions. Using Thomas–Fermi approximation, suitably complemented by numerical solutions of the Gross–Pitaevskii equation, we study the ground-state condensate density profiles, the chemical potential, the effects of cross-terms in the quartic potential, temporal evolution of various energy components of the condensate and width oscillations of the condensate. Results obtained are compared with corresponding results for a bose condensate in a harmonic confinement.

Wide band gap diamond-like carbon films (DLCs) are deposited on silicon (1 0 0) substrates using capacitive coupled radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) technique. The deposition of films is carried out at a constant pressure (~5×10^-2mbar) using acetylene precursor diluted with argon at constant R.F. power of 5 W. Raman spectroscopy of deposited DLC films shows broad G peak near 1550 cm^-1 and a weak D peak near 1320 cm¹. FTIR plot of DLC films shows a peak near 2900 cm^-1 corresponding to C–H stretching mode and peaks below 2000 cm^-1 corresponding to C–C modes and C–H bending modes. Maximum hardness of the deposited films is found to be ~15 GPa. Band gap of the DLC films is ~3.5 eV. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures show that the deposited films are amorphous. Deposition mechanism of wide band gap DLC film is explained on the basis of subplantation model.

In this paper, based on the idea of nonlinear observer, lag synchronization of chaotic fractional system with commensurate and incommensurate order is studied by the stability theorem of linear fractional-order systems. The theoretical analysis of fractional-order systems in this paper is a systematic method. This technique is applied to achieve the lag synchronization of fractional-order Rössler's system, verified by numerical simulation.

Beam-type nano-electromechanical system (NEMS) is one of the most components in constructing nano-devices. Herein, a distributed parameter model is used to study the influence of van der Waals (vdW) attraction on the pull-in performance of the cantilever NEMS. Homotopy perturbation method (HPM) is applied to solve the nonlinear governing equation of the actuators in the form of convergent series. Moreover, analytical results are compared with those of numerical method as well as a lumped parameter model. The pull-in voltage and critical cantilever tip deflection of NEMS are determined. Results depict that vdW attraction decreases the pull-in deflection and voltage of the NEMS. On the other hand, the fringing field increases the pull-in deflection while decreases the pull-in voltage of the system. The analytical results have good agreement with numerical results and those available in the literature.

Coherence resonance at a saddle-node bifurcation point and the corresponding stochastic firing patterns are simulated in a theoretical neuronal model. The characteristics of noise-induced neural firing pattern, such as exponential decay in histogram of interspike interval (ISI) series, independence and stochasticity within ISI series are identified. Firing pattern similar to the simulated results was discovered in biological experiment on a neural pacemaker. The difference between this firing and integer multiple firing generated at a Hopf bifurcation point is also given. The results not only revealed the stochastic dynamics near a saddle-node bifurcation, but also gave practical approaches to identify the saddle-node bifurcation and to distinguish it from the Hopf bifurcation in neuronal system. In addition, many previously observed firing patterns can be attribute to stochastic firing pattern near such a saddle-node bifurcation.

This paper proposes a new block encryption algorithm. The chaotic trajectories are computed by weighting. Then the result is used to mask the plaintext. Multiple blocks of plaintext are encrypted at the same time and this decreases the chaotic iterations. So the encryption speed is improved to some extent. The proposed algorithm is flexible. When the number of weights is increased, the number of the encrypted plaintext block at the same time is increased and the encryption speed is improved. The simulation result shows that the proposed algorithm has fast encryption speed and fine security.

The numerical calculations of the standard Eliashberg–Nambu strong coupling theory and a formula of isotope effect derived in this paper provide direct evidences that an-harmonic vibrations of lattice enhance isotope effect with anomalous coefficient α>1/2. The results in this paper explain very well the wide distributed α values for the samples with different ratios of substitutions of ¹²C by ¹³C of fulleride superconductor Rb₃C₆₀. The calculations of isotope effects indicate that the intra-molecule radial modes have more important contributions to superconductivity than the intra-molecule tangential modes with higher phonon frequencies.

In the present work we theoretically develop a k⋅π model to calculate the carrier electronic structure for both n- and p-type SnTe. Here π is the momentum operator in the presence of the spin–orbit interaction. The work is an extension of the theory developed for n- and p-PbTe earlier by one of the authors to evaluate the Fermi energy and the density of states (DOS). We consider a six-level energy basis for SnTe, as proposed by Bernick and Kleinman. One set of calculations was done by diagonalizing the k⋅π Hamiltonian matrix for the band-edge states and treating the far bands using perturbation theory. In the second set we have rediagonalized the k⋅π Hamiltonian matrix for the band edge states, treating the first diagonalization as the basis. The far bands are, as usual, included through perturbation. We have compared the results of both the sets. Results obtained for n- and p-type SnTe are also compared with that of n- and p-type PbTe. The similarities and contrasts are discussed. An indirect comparison with the DOS of the metallic tin suggests that the calculations are fairly reasonable. The results are also compared with some recent results for SnTe.

In this paper, we have considered a generalized coupled higher-order nonlinear Schrödinger equations. We applied multiple scales method to coupled higher-order nonlinear Schrödinger equations to derive the coupled KdV equation. Then, the extended tanh method is applied to derived coupled KdV equation for exact solutions. The obtained results include solitary wave solutions.

In this study, density-functional theory plane-wave pseudopotential method was employed to investigate several oxygen vacancies on TiO₂ anatase (101) surface. At first, a suitable defect-free slab model has been established by analyzing the surface energies and the atomic relaxations influenced by different technical parameters. The formation energies of different kinds of oxygen vacancies in the outermost layer have also been compared as well as the atomic displacement of the defective surfaces. It was found that the presence of bridging oxygen vacancy is more energetically favored and causes larger atomic displacement than other types of surface oxygen vacancies. The reactivity of oxygen vacancies has also been tested by both molecular and dissociated oxygen adsorption. Furthermore, we discussed the configurations and the electronic properties of O₂-adsorbed surface, and found that the appearance of oxygen adsorbate-induced states in the band gap can make the surface sensitive to visible light.

Layer-by-Layer (LBL) self-assembled films of rose bengal (RB) have been fabricated onto quartz substrate by the alternative adsorption of polycation poly (amine hydrochloride) (PAH) and RB. UV–Vis absorption studies reveal the formation of RB dimmer in PAH-RB LbL films. Scanning Electron Micrograph (SEM) picture confirms the aggregation of RB molecules in LbL films. Almost 15 min is required to complete the interaction between RB and PAH molecules in the 1 bilayer LbL film. The dye (RB) was found to come off the film during the subsequent poly cation (PAH) deposition. As an alternative approach RB was anchored to the polycation PAH via physiadsorption and controlling the concentration of the combination of RB and PAH was used as polycation and poly (acrylic acid) (PAA) as polyanion for film deposition. The absorption spectra after each deposition showed that there was no material loss during layer depositions via second method.

Combining the modified analytic embedded atom method (MAEAM) with lattice dynamics theory, the phonon dispersion along five symmetry directions have been calculated for three transition metals V, Nb and Ta. A good agreement between calculations and experiments along three high symmetry directions [q00], [qqq] and [qq0] implies that the predicted phonon dispersion along the other two directions [1qq] and are well behaved. Along each direction, the phonon frequency decreases for V, Nb and Ta successively may be related to the ratio of the cohesive energy to atomic mass.