Modern Physics Letters B

We have studied fluctuations on the electrical conductivity of granular compounds of Er_1-xTb_xBa₂Cu₃O_7-δ(0 ≤ x ≤ 0.10) superconductors. From the temperature derivative of the resistivity, we have found that the transition proceeds in two intragranular–intergranular stages, with intergranular character accentuated for higher concentrations of terbium (x ≅ 0.10). The data also revealed the occurrence of critical regimes, as well as fluctuation regimes beyond 3D-XY. However, for higher concentrations of terbium, it was not possible to observe fluctuation regimes beyond 3D-XY, probably because TbBa₂Cu₃O_7-δ is a metastable phase. Below T_C, on approaching the zero resistance state, our results showed a power-law behavior with critical exponents consistent with a phase transition from a paracoherent to a coherent state of the granular array.

With the development of information technology, networks become a crucial part in modern society. Therefore, the improvement in routing strategy of networks is of great importance and significance. For the purpose of improving the efficiency of network traffic, we propose a new routing strategy with two tunable parameters based on local information of network. In our strategy, we include the static information, node degree, and dynamic information, buffer queue length, to guide the selection of the next transmission node. Since the importing of buffer queue length information, packets can be distributed more evenly in the network, which can reduce the congestion possibility of network. In addition, for the sake of evaluation of a routing strategy, we propose four criterions to assess the performance of network. Based on the four criterions, we first compare the experimental results of our strategy with the original strategy only including node degree information and then give some insights of our new strategy according to the simulation results.

In this paper, we study the ultracold atoms in optical lattice with a weak random external potential by an extended Bose–Hubbard model. When the on-site interaction is strong enough, the model can be mapped to the XXZ model. Then the mean-field theory is applied and we get the zero- and finite-temperature phase diagrams in different optical parameters. The differences between the systems with and without disorder were found, and the Bose-glass phase may exist in the system with disorder.

Spike synchrony of the neural system is thought to have very dichotomous roles. On the one hand, it is ubiquitously present in the healthy brain and is thought to underlie feature binding during information processing. On the other hand, large scale synchronization is an underlying mechanism of epileptic seizures. In this paper, we investigate the spike synchrony of Hindmarsh–Rose (HR) neural networks. Our focus is the influence of the network connections on the spike synchrony of the neural networks. The simulations show that desynchronization in the nearest-neighbor coupled network evolves into accurate synchronization with connection-rewiring probability p increasing. We uncover a phenomenon of enhancement of spike synchrony by randomly rewiring connections. With connection strength c and average connection number m increasing spike synchrony is enhanced but it is not the whole story. Furthermore, the possible mechanism behind such synchronization is also addressed.

The local structures and the spin Hamiltonian parameters (zero-field splittings D and E and the anisotropic g factors g_x, g_y and g_z) for the rhombic Ni²⁺ centers in AgX (X = Cl, Br) are theoretically studied from the perturbation formulas of these parameters for a 3d⁸ ion under rhombically distorted octahedra. In these formulas, the ligand p- and s-orbital and spin-orbit coupling contributions are included on the basis of the cluster approach. The rhombic centers are attributed to the impurity Ni²⁺ associated with one nearest-neighbor silver vacancy V_Ag along the [110] direction as charge compensation. Based on the calculations, Ni²⁺ is found to suffer an off-center displacement 0.092 Å (or 0.335 Å) for AgCl (or AgBr) towards the V_Ag along the [110] axis, while the ligands closest to the V_Ag undergo a small shift 0.065 Å (or 0.006 Å) away from (or towards) the V_Ag. The theoretical spin Hamiltonian parameters based on the above defect structures show good agreement with the experimental data.

This paper presents a novel architecture for a bio-detection system to reuse magnetoresistive sensors and improve its repeatability. The architecture is composed of two fixed magnetoresistive sensors, a movable biochip, a microfluidic device and two current straps. On the action of a magnetic field gradient generated by current strap, functional magnetic particles pass along the channel. Some particles are bound by a special reaction to the biochip surface, and magnetoresistive sensors on the two ends measure the number of particles of original state and subsequencial state. The signal difference of two magnetoresistive sensors reflect the number of the depletion magnetic particles captured by the biochip.

Aspects from condensed matter physics combined with recent advances on statistical physics and physics of complex systems related to critical phenomena have inspired the continuous experimental study of electromagnetic precursory phenomena. For example, during the last two decades anomalous electromagnetic signals have been repeatedly observed before big earthquakes. Since it has been independently found that weak electromagnetic fields can produce biological effects, the following possibility is forwarded in this paper: The finding that electromagnetic signals are emitted before earthquakes, may be the key for the explanation that anomalous animal behavior have been frequently observed in various countries before major events.

Here we report the investigations on Sm-substituted PZTFN (Pb_1-xSm_xZr_0.588Ti_0.392Fe_0.01Nb_0.01O₃) (where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) polycrystalline solid solutions fabricated by solid-state reaction method. XRD analysis shows all the samples to be single phase with tetragonal structure. Dielectric measurements were carried out in the temperature range 30°C–400°C at different frequencies in the range 100 Hz to 100 kHz. From the temperature variation of dielectric constant (ε), Curie temperature (T_C) was determined which was found to decrease with increasing x. The room temperature dielectric constant (ε_RT) initially increases with increasing x and then starts decreasing. Dielectric loss improves with Sm-doping.

Theoretical computation of the pressure dependence of superconducting state parameters of binary Mg₇₀Zn₃₀ is reported using model potential formalism. Explicit expressions have been derived for the volume dependence of the electron–phonon coupling strength λ and the Coulomb pseudopotential μ* considering the variation of Fermi momentum k_F and Debye temperature θ_D with volume. The well-known Ashcroft's empty core (EMC) model pseudopotential and five different types of the local field correction functions viz. Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) have been used for obtaining pressure dependence of transition temperature T_C and the logarithmic volume derivative Φ of the effective interaction strength N₀V for metallic glass. It has been observed that the μ* curve shows a linear nature and an elbow is formed in the Φ graph.

A simple geometrical method is used here for divergence determination of a TEA N₂ laser. Using beam cross-section (rectangle) monitoring on the fluorescence paper and geometrical method, the laser beam divergence is determined. Variations of the laser beam width (W) and height (H) with respect to the gap distance are investigated for propagation distances of 10, 30, and 50 cm from the laser aperture. For the 0.52 mm gap, the beam width (W) at a distance of 10 cm is about 2 cm and height is also 2 cm (H = 2 cm), while both increase to about W = 3.125 cm, and H = 2.4 cm at a distance of 50 cm. At 50 cm distance, for a gap distance range of 0.52 mm, W = 3.125, H = 2.4 cm, which increases to W = 18.5 cm, H = 3.6 cm for gap distances of 1.3 mm. Variations of the defined aspect ratio (H/W) as a function of electrode separation and beam propagation distance are also investigated. Variation of the divergence angle along the short and long side of the rectangular beam is investigated. The divergence angle along the long side for the 0.52 mm gap is about 0.0281 rad, and increases with gap value, and for the 1.3 mm gap is 0.284 rad, corresponding to an average divergence of 0.156 rad in this range. The average divergence in the short side is about 0.01 rad, which is much smaller than the divergence angle along the long side (0.156 rad). This study shows that the discharge gap distance, in addition to its important role in N₂ laser output power, it also plays an important role in the beam divergence, especially in the horizontal plane.

A formal investigation describing the failure limit of the spline aided solution technique has been carried out. The influence of spline width on trajectory assigning accuracy at different axial positions is discussed in detail. Additionally this influence has been investigated widely concerning the accuracy of aberration calculations for two different cases. In the first one, spline width was made variable for both trajectory and aberration calculations. The second one analyzed the case in which this width varies only for aberration determination. Results clearly show that spline width is the only parameter that affects calculations. Generally, the technique's accuracy is found to be proportional to the quadratic spline width and hence accurate results can be reached as long as the spline width is small.

Tantalum modified strontium bismuth titanate ceramic discs with general formula SrBi₄Ti_(4-5x)Ta_4xO₁₅ with x = 0, 0.1, 0.2 and 0.3 have been prepared through solid state reaction method. The samples are poled and dielectric constant, loss and AC conductivity measurements are done in the temperature region (30–600°C). Ta⁵⁺ doping brought out interesting changes in dielectric phase transition behavior of the samples. Dielectric loss and conductivity measurements indicate the presence of charged defects. The results indicate changes in the distortion of the lattice. The distortion is calculated from the changes in the Curie temperature. AC conductivity results are understood in terms of the unoccupied sites and oxygen vacancies that are present in the samples.