Geodesic motion in the neighbourhood of submanifolds embedded in warped product spaces

We study the classical geodesic motions of nonzero rest mass test particles and photons in (3 + 1 + n)- dimensional warped product spaces. An important feature of these spaces is that they allow a natural decoupling between the motions in the (3 + 1)-dimensional spacetime and those in the extra n dimensions. Using this decoupling and employing phase space analysis we investigate the conditions for confinement of particles and photons to the (3 + 1)- spacetime submanifold. In addition to providing information regarding the motion of photons, we also show that these motions are not constrained by the value of the extrinsic curvature. We obtain the general conditions for the confinement of geodesics in the case of pseudo-Riemannian manifolds as well as establishing the conditions for the stability of such confinement. These results also generalise a recent result of the authors concerning the embeddings of hypersurfaces with codimension one.     

Carpet oscillator: A new megastable nonlinear oscillator with infinite islands of self-excited and hidden attractors

Polarisation of the particle spin can be an important problem for different plasmas. In this article, the contribution of the electron spin on the growth rate of the temperature anisotropy of electromagnetic instabilities has been investigated. Results show that polarisation of the electron spin will restrict the instability growth rate while instability can survive due to the spin-depolarised electrons even when the requested temperature anisotropy is vanished. Instability can reach the damping state exponentially due to the spin-polarised electrons while it can grow linearly due to the spin-depolarised (the semi-classical) electrons.     

The electronic transport properties of defected bilayer sliding armchair graphene nanoribbons

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, we investigate and compare the electronic transport properties of perfect and defected bilayer armchair graphene nanoribbons (BAGNRs) under finite bias. Two typical defects which are placed in the middle of top layer (i.e. single vacancy (SV) and stone wale (SW) defects) are examined. The results reveal that in both perfect and defected bilayers, the maximum current refers to β-AB, AA and α-AB stacking orders, respectively, since the intermolecular interactions are stronger in them. Moreover it is observed that a SV decreases the current in all stacking orders, but the effects of a SW defect is nearly unpredictable. Besides, we introduced a sequential switching behavior and the effects of defects on the switching performance is studied as well. We found that a SW defect can significantly improve the switching behavior of a bilayer system. Transmission spectrum, band structure, molecular energy spectrum and molecular projected self-consistent Hamiltonian (MPSH) are analyzed subsequently to understand the electronic transport properties of these bilayer devices which can be used in developing nano-scale bilayer systems.     

Modified grating-based external cavity diode laser for simultaneous dual-wavelengths operation

We have reported a modified V-shaped external cavity, which is constructed around a commercial diode laser operating at a center wavelength of λ=785 nm by adding a new coated glass plate with about 50% reflectivity to the cavity. This allows simultaneous dual-wavelengths operation in the vicinity of Δν_min=0.18 THz to Δν_max=0.22 THz, which can be used as laser source for terahertz generation either for semiconductor devices or nonlinear schemes.     

Gold-surface binding of molecular switches studied by M?ssbauer spectroscopy

The nonanuclear coordination compound [Mo^IV{(CN)Fe^III(3-methyl-saldptn)}₈]Cl₄ exhibits multiple spin transitions (3-methyl-saldptn = N,N′-bis(3′′-methyl-2′′-hydroxy-benzyliden)-1,7-diamino-4-azaheptane). This spin crossover cluster is bound via a self-assembled monolayer onto a two dimensional array gold surface. M?ssbauer spectroscopy indicates that the thermally and optically induced spin crossover of the compound is maintained. Thereby, the foundation for its potential practical application (e.g. in the field of information storage) was laid.     

Pulsed electron-electron double resonance (PELDOR) distance measurements in detergent micelles

Pulsed electron-electron double resonance (PELDOR) spectroscopy is a powerful tool for measuring nanometer distances in spin-labeled systems. A common approach is doubly covalent spin-labeling of a macromolecule and measurement of the inter-spin distance, or to use singly-labeled components of a system that forms aggregates or oligomers. This situation has been described as a spin-cluster. The PELDOR signal, however, does not only contain the desired dipolar coupling between the spin-labels of the molecule or cluster under study. In samples of finite concentration the dipolar coupling between the spin-labels of the randomly distributed molecules or spin-clusters also contributes significantly. In homogeneous frozen solutions or lipid vesicle membranes this second contribution can be considered to be an exponential or stretched exponential decay, respectively. In this study, we show that this assumption is not valid in detergent micelles. Spin-labeled fatty acids that are randomly partitioned into different detergent micelles give rise to PELDOR time traces which clearly deviate from stretched exponential decays. The obtained signals can be modeled quantitatively based on the size of the micelles, their aggregation number, the spin-label concentration and the degree of spin-labeling. As a main conclusion a PELDOR signal deviating from a stretched exponential decay does not necessarily prove the observation of specific distance information on the molecule or cluster. These results are important for the interpretation of PELDOR experiments on membrane proteins or lipophilic peptides solubilized in detergent micelles or small vesicles, which often do not show pronounced dipolar oscillations in their time traces.     

Fabrication and characterization of Zn1−xAlxO nanoparticles by DC arc plasma

In this paper we have introduced a simple method for the fabrication of aluminum doped zinc oxide (AZO) nanoparticles. The Zn_1−xAl_xO nanoparticles with different concentrations of Al (x=0.01, 0.03, 0.06, 0.09, 0.12) were fabricated successfully by this method. The samples were analyzed by the use of several techniques such as SEM, EDX, XRD, PL and UV-vis spectroscopy. The SEM images showed that the fabricated nanoparticles had spherical shapes. The XRD patterns of the samples indicated that the Al atoms substituted in the Zn positions in the crystal lattice of ZnO and there were some changes in the lattice parameters. A blue shift in the λ_max of the absorption and a red shift in the λ_max of the emission were observed. The results also indicated that the amount of shifts had a direct relationship with the changes in the lattice parameters.     

Influences of substrate temperature on microstructure and corrosion behavior of APS Ni_(50)Ti_(25)Al_(25) inter-metallic coating

In the present investigation, Ni_(50)Ti_(25)Al_(25)(at.%) mechanically alloyed powder is deposited on carbon steel substrate.Before the coating process, the substrate is heated to temperature ranging from room temperature to 400℃. The microstructure, porosity, microhardness, adhesion strength, and corrosion behavior of the coating are investigated at different substrate temperatures. Results show that coating porosity is lower on high temperature surface. Microhardness and adhesion strength of the deposition layer on the substrate without preheating have lower values than with preheating. The polarization test result shows that corrosion performance of the coating is dependent on micro cracks and porosities and the increasing of substrate temperature can improve the quality of coating and corrosion performance.     

Dust acoustic solitary and shock waves in strongly coupled dusty plasmas with nonthermal ions

The Korteweg-de Vries-Burgers (KdV-Burgers) equation and modified Korteweg-de Vries-Burgers equation are derived in strongly coupled dusty plasmas containing nonthermal ions and Boltzmann distributed electrons. It is found that solitary waves and shock waves can be produced in this medium. The effects of important parameters such as ion nonthermal parameter, temperature, density and velocity on the properties of shock waves and solitary waves are discussed.