Superconducting Mechanism through direct and redox layer doping in Pnictides

The mechanism of superconductivity in pnictides is discussed through direct doping in superconducting FeAs and also in charge reservoir REO layers. The un-doped SmFeAsO is charge neutral SDW (Spin Density Wave) compound with magnetic ordering below 150 K. The Superconducting FeAs layers are doped with Co and Ni at Fe site, whereas REO layers are doped with F at O site. The electron doping in SmFeAsO through Co results in superconductivity with transition temperature (Tc) maximum up to 15 K, whereas F doping results in Tc upto 47 K in SmFeAsO. All these REFe/Co/NiAsO/F compounds are iso-structural to ZrCuSiAs structure. The samples are crystallized in a tetragonal structure with space group P4/nmm. Variation of Tc with different doping routes shows the versatility of the structure and mechanism of occurrence of superconductivity. It seems doping in redox layer is more effective than direct doping in superconducting FeAs layer.Comment: 4 Pages text + Figs: ([email protected]

Dynamic range of nanotube- and nanowire-based electromechanical systems

Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [[proportional]dsqrt((d/L)[sup 5])] of the dynamic range on aspect ratio

Non-singular inflationary universe from polymer matter

We consider a polymer quantization of a free massless scalar field in a homogeneous and isotropic cosmological spacetime. This quantization method assumes that field translations are fundamentally discrete, and is related to but distinct from that used in loop quantum gravity. The semi-classical Friedman equation yields a universe that is non-singular and non-bouncing, without quantum gravity. The model has an early de Sitter-like inflationary phase with sufficient expansion to resolve the horizon and entropy problems, and a built in mechanism for a graceful exit from inflation.Comment: 4 pages, 1 figure; v2 clarifications added, reference update

Scalar field collapse in three-dimensional AdS spacetime

We describe results of a numerical calculation of circularly symmetric scalar field collapse in three spacetime dimensions with negative cosmological constant. The procedure uses a double null formulation of the Einstein-scalar equations. We see evidence of black hole formation on first implosion of a scalar pulse if the initial pulse amplitude $A$ is greater than a critical value $A_*$. Sufficiently near criticality the apparent horizon radius $r_{AH}$ grows with pulse amplitude according to the formula $r_{AH} \sim (A-A_*)^{0.81}$.Comment: 10 pages, 1 figure; references added, to appear in CQG(L

A two-dimensional representation of four-dimensional gravitational waves

The Einstein equation in D dimensions, if restricted to the class of space-times possessing n = D - 2 commuting hypersurface-orthogonal Killing vectors, can be equivalently written as metric-dilaton gravity in 2 dimensions with n scalar fields. For n = 2, this results reduces to the known reduction of certain 4-dimensional metrics which include gravitational waves. Here, we give such a representation which leads to a new proof of the Birkhoff theorem for plane-symmetric space--times, and which leads to an explanation, in which sense two (spin zero-) scalar fields in 2 dimensions may incorporate the (spin two-) gravitational waves in 4 dimensions. (This result should not be mixed up with well--known analogous statements where, however, the 4-dimensional space-time is supposed to be spherically symmetric, and then, of course, the equivalent 2-dimensional picture cannot mimic any gravitational waves.) Finally, remarks on hidden symmetries in 2 dimensions are made.Comment: 12 pages, LaTeX, no figures, Int. J. Mod. Phys. D in prin

Semiclassical states for quantum cosmology

In a metric variable based Hamiltonian quantization, we give a prescription for constructing semiclassical matter-geometry states for homogeneous and isotropic cosmological models. These "collective" states arise as infinite linear combinations of fundamental excitations in an unconventional "polymer" quantization. They satisfy a number of properties characteristic of semiclassicality, such as peaking on classical phase space configurations. We describe how these states can be used to determine quantum corrections to the classical evolution equations, and to compute the initial state of the universe by a backward time evolution.Comment: 13 page

Constants of motion for vacuum general relativity

The 3+1 Hamiltonian Einstein equations, reduced by imposing two commuting spacelike Killing vector fields, may be written as the equations of the $SL(2,R)$ principal chiral model with certain `source' terms. Using this formulation, we give a procedure for generating an infinite number of non-local constants of motion for this sector of the Einstein equations. The constants of motion arise as explicit functionals on the phase space of Einstein gravity, and are labelled by sl(2,R) indices.Comment: 10 pages, latex, version to appear in Phys. Rev. D

Basins of attraction of a nonlinear nanomechanical resonator

We present an experiment that systematically probes the basins of attraction of two fixed points of a nonlinear nanomechanical resonator and maps them out with high resolution. We observe a separatrix which progressively alters shape for varying drive strength and changes the relative areas of the two basins of attraction. The observed separatrix is blurred due to ambient fluctuations, including residual noise in the drive system, which cause uncertainty in the preparation of an initial state close to the separatrix. We find a good agreement between the experimentally mapped and theoretically calculated basins of attraction

Nanowire-based very-high-frequency electromechanical resonator

Fabrication and readout of devices with progressively smaller size, ultimately down to the molecular scale, is critical for the development of very-high-frequency nanoelectromechanical systems (NEMS). Nanomaterials, such as carbon nanotubes or nanowires, offer immense prospects as active elements for these applications. We report the fabrication and measurement of a platinum nanowire resonator, 43 nm in diameter and 1.3 µm in length. This device, among the smallest NEMS reported, has a fundamental vibration frequency of 105.3 MHz, with a quality factor of 8500 at 4 K. Its resonant motion is transduced by a technique that is well suited to ultrasmall mechanical structures

New Solution for ICT/ELV Infrastructure Project Reporting Using Datalink Technique System

In infrastructure project, a failure on reliable project reporting will lead to Variation Order (VO) and Project Delay issues. It is now a normal phenomenon, which leads to many negative effects such as lawsuits, claims, loss of productivity and revenue, which may also lead to contract termination. Hence, the research aims to develop a new solution system program, called Datalink Technique System (DTS) to solve the problems that occur in an infrastructure project. The objective is to eliminate the loss and reduce the project cost. However, it is not limited to that as in future it can also be applied to others. DTS introduces the new advanced technologies system solution and reliable, yet it is still consistent with the current approach to manage the project. The program produces data/information correctly and precisely