Generating potentials via difference equations

The condition for pressure isotropy, for spherically symmetric gravitational fields with charged and uncharged matter, is reduced to a recurrence equation with variable, rational coefficients. This difference equation is solved in general using mathematical induction leading to an exact solution to the Einstein field equations which extends the isotropic model of John and Maharaj. The metric functions, energy density and pressure are well behaved which suggests that this model could be used to describe a relativistic sphere. The model admits a barotropic equation of state which approximates a polytrope close to the stellar centre.Comment: 11 pages, To appear in Math. Meth. Appl. Sc

Fuel Cell Auxiliary Power Study Volume 1: RASER Task Order 5

This study evaluated the feasibility of a hybrid solid oxide fuel cell (SOFC) auxiliary power unit (APU) and the impact in a 90-passenger More-Electric Regional Jet application. The study established realistic hybrid SOFC APU system weight and system efficiencies, and evaluated the impact on the aircraft total weight, fuel burn, and emissions from the main engine and the APU during cruise, landing and take-off (LTO) cycle, and at the gate. Although the SOFC APU may be heavier than the current conventional APU, its weight disadvantage can be offset by fuel savings in the higher SOFC APU system efficiencies against the main engine bleed and extraction during cruise. The higher SOFC APU system efficiency compared to the conventional APU on the ground can also provide considerable fuel saving and emissions reduction, particularly at the gate, but is limited by the fuel cell stack thermal fatigue characteristic

Towards the Design of Resilient Large-scale Engineering Systems

Resilience has mostly been thought of as the ability to recover from adversity. However, it is now increasingly recognised that resilience should not only serve as a means for organisations to survive hardship, but also to thrive and prosper. For large-scale engineering systems, such as telecommunications networks and power grids, this is vital due to relatively long life cycles leading to large uncertainties, and also due to the significant investments involved. Exactly how this and thus resilience should be designed into such systems, however, is less well defined. Here, the term resilience is explored through engineering, organisational and ecological literature to understand differing perspectives from select domains before distilling these into the three engineering design lifecycle properties: robustness, adaptability and flexibility. In particular, a distinction is highlighted between adaptability and flexibility following findings in literature. These properties and the concept of resilience are discussed with reference to system performance in order to serve as requirements for designing large-scale resilient engineering systems

Towards the Design of Resilient Large-scale Engineering Systems

Resilience has mostly been thought of as the ability to recover from adversity. However, it is now increasingly recognised that resilience should not only serve as a means for organisations to survive hardship, but also to thrive and prosper. For large-scale engineering systems, such as telecommunications networks and power grids, this is vital due to relatively long life cycles leading to large uncertainties, and also due to the significant investments involved. Exactly how this and thus resilience should be designed into such systems, however, is less well defined. Here, the term resilience is explored through engineering, organisational and ecological literature to understand differing perspectives from select domains before distilling these into the three engineering design lifecycle properties: robustness, adaptability and flexibility. In particular, a distinction is highlighted between adaptability and flexibility following findings in literature. These properties and the concept of resilience are discussed with reference to system performance in order to serve as requirements for designing large-scale resilient engineering systems

Supercontinuum generation in the vacuum ultraviolet through dispersive-wave and soliton-plasma interaction in noble-gas-filled hollow-core photonic crystal fiber

We report on the generation of a three-octave-wide supercontinuum extending from the vacuum ultraviolet (VUV) to the near-infrared, spanning at least 113 to 1000 nm (i.e., 11 to 1.2 eV), in He-filled hollow-core kagome-style photonic crystal fiber. Numerical simulations confirm that the main mechanism is a novel and previously undiscovered interaction between dispersive-wave emission and plasma-induced blueshifted soliton recompression around the fiber zero dispersion frequency. The VUV part of the supercontinuum, which modeling shows to be coherent and possess a simple phase structure, has sufficient bandwidth to support single-cycle pulses of 500 attosecond duration. We also demonstrate, in the same system, the generation of narrower-band VUV pulses, through dispersive-wave emission, tunable from 120 to 200 nm with efficiencies exceeding 1% and VUV pulse energies in excess of 50 nJ.Comment: 7 pages, 5 figure

END SPLICE ASSEMBLY FOR BOX-BEAM GUARDRAIL AND TERMINAL SYSTEMIS

An end splice assembly for a box-beam guardrail and terminal system having a first stage rail element and a second stage rail element. The assembly has two major connecting components. Upper and lower bent plate channels and upper and lower channel splice plates. The channels and plates have side walls which extend laterally to one another when the two rail elements are mated. The channels and plates are fastened together to provide moment strength to the splice within the system

ENERGY ABSORBING GUARDRAIL SYSTEM

A highway crash attenuation system having W - beam rail elements attached to a plurality of vertical posts . An impact terminal with a feeder chute guides one or more of the W - beam rail elements through the impact terminal . The feeder chute has an impact shield extending along a traffic facing side of the chute from an upstream - most end to a downstream - most end of the chute closing the traffic - facing side of the chute . The system also has an anchor cable release mechanism for releasing the cable downstream of the first vertical post and an improved first breakaway post