Modern Physics Letters B

Recent advances in single molecule experiments have made it possible to investigate the mechanical anisotropy of protein stability in greater detail. It has been found that proteins can exhibit a diverse range of responses when pulled in different directions. We review some of the experimental and numerical work related to the study of the resistance of proteins to force-induced mechanical unfolding. Based on model studies in the framework of statistical mechanics, we discuss the possible molecular origin of the anisotropy of protein resistance to unfolding.

This article deals with quantum hydrodynamic models (QHD) for electronic transport in semiconductor devices. Numerical simulation of ballistic diode and resonant tunneling diode is discussed. Based on overall results, it can be concluded that the considered QHD models have remarkable abilities to express the refinements of electronic transport in nanodevices.

We propose a scheme to realize the economical 1 → M phase-covariant quantum cloning in 2-dimension with M Λ-type three-level atoms in an optical cavity. In our scheme, we do not require addressing and exactly manipulating on every atoms, never so much as controlling the time of interaction between atoms and photon. The success or failure of cloning can be determined simply by detecting the polarization of the photon leaking out of the cavity. With the use of an automatic feedback, the success probability of the scheme can be made to approach unity. And the desired output state is a superposition of different combination of two grounds states and thus is free from decoherence caused by spontaneous emission.

We have investigated the effect of Tb substitution for Y in both YBa₂Cu₃O_7-δ and the more stabilized YSr₂Cu_2.7Mo_0.3O_7-δ systems. Adding Mo has been shown to stabilize the Tb-doped systems. The samples of Y_1-xTb_xBa₂Cu₃O_7-δ with x=0.0, 0.1, 0.15, 0.2, 0.3, 0.35, 0.4, 0.5, 0.55, and 0.6, and of Y_1-xTb_xSr₂Cu_2.7Mo_0.3O_7-δ with x=0.0, 0.2, 0.4, 0.6, and 0.8 have been prepared by the standard solid-state reaction technique. The superconducting transition occurs only with x=0–0.5 for the Ba-based samples, and with x=0–0.8 for the Sr-based samples. The structural parameter identification and phase determination of the samples have been carried out by the Rietveld analysis of the X-ray diffraction patterns, which indicates that Tb does not enter in the structure of the Ba-based 123 phase, while in the Sr-based 123 structure Tb enters in the structure and substitutes for Y. In the Y_1-xTb_xBa₂Cu₃O_7-δ samples, a new secondary TbBaO₃ phase forms; and by increasing the amount of Tb, the secondary phase increases as the Y123 phase decreases. But, for the Y_1-xTb_xSr₂Cu_2.7Mo_0.3O_7-δ samples, by increasing the amount of Tb doping, no impurity phase is detected in the XRD patterns. For both groups of samples, by increasing the amount of Tb, the normal resistivity increases, and the metallic behavior of the resistivity changes to semiconducting behavior. The magnetoresistance of Y_1-xTb_xBa₂Cu₃O_7-δ was measured in different magnetic fields. The width of transition for the same values of magnetic field increases with the increase of Tb doping, indicating that with the increase of Tb, grains link weaker due to the increase in the amount of the secondary TbBaO₃ phase. The pinning energy has also been evaluated based on the thermally activated phase creep model.

A quantum rotation can be divided into M pieces and teleported from a sender onto M distant receivers via the control of N agents in a quantum network. We utilize the entanglement property of a (2M + N + 1)-qubit Einstein–Podolsky–Rosen (EPR) — Greenberger–Horne–Zeilinger (GHZ) state to design a theoretical scheme for implementing these rotations remotely with unit fidelity and unit probability. The feature of the scheme is that, apart from a sender and M receivers, N agents are included in the process as controllers. Should any one of the N agents not cooperate, the receivers could not gain the original rotations. This scheme can be used to sender-encoded quantum secret sharing. It definitely has the strong security.

The structure and electrical-magnetic transport properties of (La_0.7Ca_0.3MnO₃)_1-x/(Bi₂O₃)_x has been investigated systematically by conventional solid-state reaction method. The composite samples were obtained by pure La_0.7Ca_0.3MnO₃ (LCMO) and Bi₂O₃ powders and sintered at different temperature (T_s) 800°C and 1300°C for 2 h. For T_s=800°C samples, the results of X-ray diffraction (XRD) and scanning electronic microscopy (SEM) indicate that Bi₂O₃ and LCMO coexist in the composites and Bi₂O₃ mainly segregates at the grain boundaries or grain surface of LCMO, and double peaks related to the metal-to-insulator (M–I) transition have been observed. Corresponding to the two M–I transition peaks, the curves of magnetoresistance (MR) against temperature also showed two peaks for all composites. But for T_s = 1300°C samples, Bi³⁺ ions mainly enter into the lattice of LCMO to form reaction products layer La_0.7-xBi_x Ca_0.3MnO₃, only one peak occurs around the M–I transition temperature and the MR around T_P has been enhanced. The results also indicate that the added Bi₂O₃ has an important effect on the LFMR. These phenomena can be explained by the double exchange (DE) mechanism, the grain boundary effect and the intrinsic transport properties together. And the grain surface state of the particles is a key factor influencing the magnetoresistance effects.

Crystallization of amorphous SiCN matrix of carbon fiber reinforced SiCN matrix composite (C/SiCN) under vacuum and tensile creep stress was investigated. The phase and microstructure evolution of amorphous SiCN matrix were examined by X-ray diffraction and transmission electron microscopy, respectively. The crystallization behavior of the as-received and 1900°C-annealed C/SiCN during tensile creep test conducted at 1500°C was analyzed. The results indicate that crystallization takes place after annealing at 1900°C for 0.5 h, and the phases formed are β-SiC and α-SiC. Decomposition of amorphous SiCN produces gaseous species such as SiO and CO, and vapor reaction between them and carbon induces SiC nucleation. Local atomic (Si-, C-, N-) rearrangement due to SiCN degradation also yields a large number of Si-C-enriched regions which gradually induces SiC nucleation. The annealing treatment of C/SiCN shows stabilization effect to some extent on the SiCN matrix, but is not sufficient to get a thorough stable phase.

Thermal entanglement of a two-qubit Heisenberg XXZ chain in the presence of different Dzyaloshinskii–Moriya (DM) anisotropic antisymmetric interactions and entanglement teleportation using two independent Heisenberg chains as quantum channel are investigated. It is found that the anisotropic coupling coefficient J_z (z-component exchange constant) and DM interactions can excite the entanglement, and x-component DM interaction D_x has a more remarkable influence than the z-axis DM interaction D_z for exchange constant J > 0 (antiferromagnetic) case, which is contrary to coupling coefficient J < 0 (ferromagnetic) case. The output entanglement and fidelity increase with increasing z-axis coupling parameter J_z for both the antiferromagnetic J > 0 case and ferromagnetic J < 0 case. By introducing the different DM interactions, it is superior to teleportate initial state by using the D_z interaction in the model for J > 0 case. But for J < 0 case, the D_x interaction is better, and the output concurrence and fidelity can reach the maximum value 1 with suitable D_x.

Nanosized La₂O₃:Sm³⁺ and La₂O₃:Sm³⁺, Bi³⁺ phosphor powders were prepared via combustion synthesis. The structures and morphology were examined using powder X-ray diffraction and transmission electron microscope, respectively. The photoluminescence spectra were investigated at different doping concentrations of Sm³⁺ and Bi³⁺ ions. The results indicate that La₂O₃:Sm³⁺ (Bi³⁺) exhibited good crystallinity and spherical-like particles. All phosphors give emission bands centered at 564, 608 and 650 nm corresponding to ⁴G_5/2→⁶H_J (J=5/2, 7/2 and 9/2) transitions of Sm³⁺ ions, respectively. Interestingly, the emission intensity of Sm³⁺ ions is significantly enhanced with the addition of Bi³⁺ ions to La₂O₃:Sm³⁺ and the maximum occurs at a Bi³⁺ concentration of 0.8 mol%. The La₂O₃:Sm³⁺, Bi³⁺ phosphor with highly enhanced luminescence is very encouraging for applications in display and tunable solid lasers.

An experiment was conducted in a wind-tunnel to study the internal acoustic field and flow oscillations inside rectangular-box cavities. The length-to-depth ratio of the cavities was 8. The data presented herein was obtained over a Mach number of 1.5 at a Reynolds number of 2.26×10⁷ per meter with different boundary-layer thicknesses of approximately 24 mm and 5.5 mm. The experimental angle of attack, yawing and rolling angles were 0°. The rules were revealed as governing the effects of boundary-layer thickness on flow oscillations and unsteady characteristics by comparing the experimental results with flow oscillation modes predicated by Rossiter's and Heller's modified equation. The results indicate that a decrease in the ratio of boundary-layer thickness to cavity-depth (δ/D) induces flow oscillations amplification, peak oscillation frequency splitting and shifting phenomena of open cavity tones in the low-frequency region.

A series of Hf, Er co-doped LiNbO₃ crystals were grown by Czochralski technique with 1 mol% of Er₂O₃ and with 2, 4, 6 and 8 mol% of HfO₂, respectively. The optical damage resistance of Hf:Er:LiNbO₃ crystals was studied by the transmitted beam pattern distortion method. The optical damage resistance of Hf (6 mol%): Er:LiNbO₃ crystals is about two orders of magnitude higher than that in Hf:Er:LiNbO₃. The X-ray power diffraction, the ultraviolet-visible absorption spectra and the infrared absorption spectrum were measured and discussed in terms of the spectrometric characterization and the defect structure of crystals. The results showed that with mild co-doping with HfO₂, Er³⁺ substitutes Nb⁵⁺, whereas with heavy co-doping, a part of Er³⁺ substitutes Li⁺. The structure defects were discussed in this paper to explain the improvement of the optical damage resistance in the Hf:Er:LiNbO₃.

In this paper, we propose a new robust stability analysis method for uncertain cellular neural networks with time-varying delay. The proposed stability criterion is based on the Lyapunov function with sector bounded nonlinear function. The sufficient condition for the stability is derived in terms of LMI (linear matrix inequality). Numerical examples show the effectiveness of the proposed method.