Algorithmic construction of static perfect fluid spheres

Perfect fluid spheres, both Newtonian and relativistic, have attracted considerable attention as the first step in developing realistic stellar models (or models for fluid planets). Whereas there have been some early hints on how one might find general solutions to the perfect fluid constraint in the absence of a specific equation of state, explicit and fully general solutions of the perfect fluid constraint have only very recently been developed. In this article we present a version of Lake's algorithm [Phys. Rev. D 67 (2003) 104015; gr-qc/0209104] wherein: (1) we re-cast the algorithm in terms of variables with a clear physical meaning -- the average density and the locally measured acceleration due to gravity, (2) we present explicit and fully general formulae for the mass profile and pressure profile, and (3) we present an explicit closed-form expression for the central pressure. Furthermore we can then use the formalism to easily understand the pattern of inter-relationships among many of the previously known exact solutions, and generate several new exact solutions.Comment: Uses revtex4. V2: Minor clarifications, plus an additional section on how to turn the algorithm into a solution generalization technique. This version accepted for publication in Physical Review D. Now 7 page

High-Tc ramp-type Josephson junctions on MgO substrates for Terahertz applications

The authors successfully fabricated high-Tc ramp-type junctions with PrBa2Cu3-xGaxO7-δ (PBCGO: x=0.1, 0.4) barriers on MgO substrates. The junctions showed resistively shunted Josephson junction (RSJ)-like I-V curves with thermally and voltage activated conductivity. The IcRn products for these junctions scaled very well with the Ga-doping. Maximum response of the junctions for 100-GHz millimeter-wave irradiation could be observed up to 12 mV corresponding to 6 THz. Using far infrared laser radiation, we confirmed a terahertz (THz) response of these junctions. These results show promise for THz-wave applications of ramp-type Josephson junctions

The Third Way for the Third Sector: Using Design to Transfer Knowledge and Improve Service in a Voluntary Community Sector Organisation

This paper describes a two-year Knowledge Transfer Partnership that concluded in September 2011. Knowledge Transfer Partnerships (KTP) is a UK-wide activity that helps organisations to improve their competitiveness and productivity by making better use of knowledge, technology and skills within universities, colleges and research organisations. This paper details the outcome of a KTP between Age UK Newcastle and Northumbria University’s School of Design that aimed to use Design approaches to improve the charity’s services. This paper will describe the recent context for organisations operating in the Voluntary Community Sector and discuss the relevance of a Design approach to both the improvement of customer services in this circumstance, as well as the transfer of knowledge to a capacity-starved organisation. It will also document how Design was used to achieve both of these aims, and the resulting impact of this engagement on the organisation and stakeholders

Quadratic eigenproblems are no problem

High-dimensional eigenproblems often arise in the solution of scientific problems involving stability or wave modeling. In this article we present results for a quadratic eigenproblem that we encountered in solving an acoustics problem, specifically in modeling the propagation of waves in a room in which one wall was constructed of sound-absorbing material. Efficient algorithms are known for the standard linear eigenproblem, Ax = x where A is a real or complex-valued square matrix of order n. Generalized eigenproblems of the form Ax = Bx, which occur in nite element formulations, are usually reduced to the standard problem, in a form such as B Ax = x. The reduction requires an expensive inversion operation for one of the matrices involved. Higher-order polynomial eigenproblems are also usually transformed into standard eigenproblems. We discuss here the second-degree (i.e., quadratic) eigenproblem 2C2 + C1 + C0 x = 0 in which the matrices Ci are square matrices

Numerical Analysis of Ca2+ Depletion in the Transverse Tubular System of Mammalian Muscle

AbstractCalcium currents were recorded in contracting and actively shortening mammalian muscle fibers. In order to characterize the influence of extracellular calcium concentration changes in the small unstirred lumina of the transverse tubular system (TTS) on the time course of the slow L-type calcium current (ICa), we have combined experimental measurements of ICa with quantitative numerical simulations of Ca2+ depletion. ICa was recorded both in calcium-buffered and unbuffered external solutions using the two-microelectrode voltage clamp technique (2-MVC) on short murine toe muscle fibers. A simulation program based on a distributed TTS model was used to calculate the effect of ion depletion in the TTS. The experimental data obtained in a solution where ion depletion is suppressed by a high amount of a calcium buffering agent were used as input data for the simulation. The simulation output was then compared with experimental data from the same fiber obtained in unbuffered solution. Taking this approach, we could quantitatively show that the calculated Ca2+ depletion in the transverse tubular system of contracting mammalian muscle fibers significantly affects the time-dependent decline of Ca2+ currents. From our findings, we conclude that ion depletion in the tubular system may be one of the major effects for the ICa decline measured in isotonic physiological solution under voltage clamp conditions

Characterization of ramp-type YBa₂Cu₃O₇ junctions by AFM

We studied the morphology of ramps in REBa2Cu3O7 (REBCO) epitaxial films on SrTiO3 substrates, fabricated by RF magnetron sputter deposition and pulsed laser deposition (PLD), by Atomic Force Microscopy (AFM) and High Resolution Electron Microscopy (HREM). The ramps were fabricated by Ar ion beam etching using different masks of standard photoresist and TiN. AFM-studies on ramps in sputter deposited films show a strong dependence, i.e., formation of facets and ridges, on the angle of incidence of the ion beam with respect to the substrate surface as well as the rotation angle with respect to the crystal axes of the substrate. Ramps in pulsed laser deposited films did not show this dependence. Furthermore, we studied the effect of an anneal step prior to the deposition of barrier layers (i.e. PrBa2Cu3-xGaxO7) on the ramp. First results show a crystallization of the ramp surface, resulting in terraces and a non-homogeneous growth of the barrier material on top of it. The thickness variations, for thin layers of barrier material, can even become much larger than expected from the amount of deposited material and are dependent on the deposition and anneal conditions. HREM studies show a well-defined interface between barrier layer and electrodes. The angle of the ramp depends on the etch rate of the mask and REBCO and on the angle of incidence of the ion beam. Hard masks, like TIN, have a much lower etch rate compared to photoresist, resulting in an angle of the ramp comparable to the angle of incidence and, subsequently, in a low etching rate on the ram

Generic theory of colloidal transport

We discuss the motion of colloidal particles relative to a two component fluid consisting of solvent and solute. Particle motion can result from (i) net body forces on the particle due to external fields such as gravity; (ii) slip velocities on the particle surface due to surface dissipative phenomena. The perturbations of the hydrodynamic flow field exhibits characteristic differences in cases (i) and (ii) which reflect different patterns of momentum flux corresponding to the existence of net forces, force dipoles or force quadrupoles. In the absence of external fields, gradients of concentration or pressure do not generate net forces on a colloidal particle. Such gradients can nevertheless induce relative motion between particle and fluid. We present a generic description of surface dissipative phenomena based on the linear response of surface fluxes driven by conjugate surface forces. In this framework we discuss different transport scenarios including self-propulsion via surface slip that is induced by active processes on the particle surface. We clarify the nature of force balances in such situations.Comment: 22 pages, 1 figur

Collective Excitations and Ground State Correlations

A generalized RPA formalism is presented which treats pp and ph correlations on an equal footing. The effect of these correlations on the single-particle Green function is discussed and it is demonstrated that a self-consistent treatment of the single-particle Green function is required to obtain stable solutions. A simple approximation scheme is presented which incorporates for this self-consistency requirement and conserves the number of particles. Results of numerical calculations are given for $^{16}$O using a G-matrix interaction derived from a realistic One-Boson-Exchange potential.Comment: 16 Pages + 2 Figures (included at the end as uuencoded ps-files), TU-18089

Thermal Field Theory and Generalized Light Front Coordinates

The dependence of thermal field theory on the surface of quantization and on the velocity of the heat bath is investigated by working in general coordinates that are arbitrary linear combinations of the Minkowski coordinates. In the general coordinates the metric tensor $g_{\bar{\mu\nu}}$ is non-diagonal. The Kubo, Martin, Schwinger condition requires periodicity in thermal correlation functions when the temporal variable changes by an amount $-i\big/(T\sqrt{g_{\bar{00}}})$. Light front quantization fails since $g_{\bar{00}}=0$, however various related quantizations are possible.Comment: 10 page

Lattice QCD and the Schwarz alternating procedure

A numerical simulation algorithm for lattice QCD is described, in which the short- and long-distance effects of the sea quarks are treated separately. The algorithm can be regarded, to some extent, as an implementation at the quantum level of the classical Schwarz alternating procedure for the solution of elliptic partial differential equations. No numerical tests are reported here, but theoretical arguments suggest that the algorithm should work well also at small quark masses.Comment: Plain TeX source, 20 pages, figures include