Distinguishing impurity concentrations in GaAs and AlGaAs, using very shallow undoped heterostructures

We demonstrate a method of making a very shallow, gateable, undoped 2-dimensional electron gas. We have developed a method of making very low resistivity contacts to these structures and systematically studied the evolution of the mobility as a function of the depth of the 2DEG (from 300nm to 30nm). We demonstrate a way of extracting quantitative information about the background impurity concentration in GaAs and AlGaAs, the interface roughness and the charge in the surface states from the data. This information is very useful from the perspective of molecular beam epitaxy (MBE) growth. It is difficult to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to have a large enough spacer layer to reduce scattering and switching noise from remote ionsied dopants.Comment: 4 pages, 5 eps figure

Causal Bulk Viscous Dissipative Isotropic Cosmologies with Variable Gravitational and Cosmological Constants

We consider the evolution of a flat Friedmann-Robertson-Walker Universe, filled with a causal bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The basic equation for the Hubble parameter, generalizing the evolution equation in the case of constant gravitational coupling and cosmological term, is derived, under the supplementary assumption that the total energy of the Universe is conserved. By assuming that the cosmological constant is proportional to the square of the Hubble parameter and a power law dependence of the bulk viscosity coefficient, temperature and relaxation time on the energy density of the cosmological fluid, two classes of exact solutions of the field equations are obtained. In the first class of solutions the Universe ends in an inflationary era, while in the second class of solutions the expansion of the Universe is non-inflationary for all times. In both models the cosmological "constant" is a decreasing function of time, while the gravitational "constant" increases in the early period of evolution of the Universe, tending in the large time limit to a constant value.Comment: 14 pages, 15 figure

Performance of Kedah-Kelantan Cattle Fed Palm Kernel Cake

An experiment involving a completely randomized design was conducted to compare the effect of PKC-S-B and PKC-S-F on the performance of Kedah-KeLantan bulls. No significant difference exists between the PKC-S-B and PKC-S-F treatment groups. Kedah-Kelantan bulls when fed an average daily feed of 3. 824 kg PKC-S for a period of 175 days could achieve an average daily gain of 0.583 kg. The feed efficiency obtained was 6.559. The income over feed cost l head/day obtained was M$1.096

Dynamically reconfigurable resource-aware component framework: architecture and concepts

Applications executed on a shared distributed platform compete for resources provided by the platform. In case these applications have highly fluctuating resource demands, a software architecture is required that provides support for runtime resource management. In position paper [1], we have proposed such architecture and have introduced its key concepts and entities. In this paper, we introduce a metamodel that captures the key concepts and we identify lifecycle models for both applications and individual components. A set of dynamic reconfiguration strategies is introduced and their relationship to the stages of the application lifecycle is given. Keywords: Component framework – networked services – resource management – dynamic reconfiguration – application lifecycle – component lifecycl

CVaR minimization by the SRA algorithm

Using the risk measure CV aR in �nancial analysis has become more and more popular recently. In this paper we apply CV aR for portfolio optimization. The problem is formulated as a two-stage stochastic programming model, and the SRA algorithm, a recently developed heuristic algorithm, is applied for minimizing CV aR

Performance of Hereford Crossbred and Kedah-Kelantan Cattle fed a Palm Kernel Cake-based Ration

In a feeding experiment involving the use of a PKC-based ration for·105 days, the average daily feed intake of 3.11 and 3.31 kg in Hereford crossbred and Kedah-Kelantan cattle respectively, was found to be not significant. Hereford crossbred cattle had an average daily gain of O.712 kg which was significantly higher (P < 0.05) than that of Kedah-Kelantan cattle (0.586 kg). Similarly Hereford crossbred cattle had a significantly better (P < 0.01) feed efficiericy (4.37) compared to that of Kedah-Kelantan cattle (5.71). The income overfeed cost per animal per day was $1.344 and$0.514 in Hereford crossbred and Kedah-Kelantan cattle respectively

Renormalization Group Approach to Causal Viscous Cosmological Models

The renormalization group method is applied to the study of homogeneous and flat Friedmann-Robertson-Walker type Universes, filled with a causal bulk viscous cosmological fluid. The starting point of the study is the consideration of the scaling properties of the gravitational field equations, of the causal evolution equation of the bulk viscous pressure and of the equations of state. The requirement of scale invariance imposes strong constraints on the temporal evolution of the bulk viscosity coefficient, temperature and relaxation time, thus leading to the possibility of obtaining the bulk viscosity coefficient-energy density dependence. For a cosmological model with bulk viscosity coefficient proportional to the Hubble parameter, we perform the analysis of the renormalization group flow around the scale invariant fixed point, therefore obtaining the long time behavior of the scale factor.Comment: 19 pages. RevTeX4. Revised version. Accepted in Classical and Quantum Gravit

Gap solitons in a model of a hollow optical fiber

We introduce a models for two coupled waves propagating in a hollow-core fiber: a linear dispersionless core mode, and a dispersive nonlinear quasi-surface one. The linear coupling between them may open a bandgap, through the mechanism of the avoidance of crossing between dispersion curves. The third-order dispersion of the quasi-surface mode is necessary for the existence of the gap. Numerical investigation reveals that the entire bandgap is filled with solitons, and they all are stable in direct simulations. The gap-soliton (GS) family is extended to include pulses moving relative to the given reference frame, up to limit values of the corresponding boost $\delta$, beyond which the solitons do not exists. The limit values are nonsymmetric for $\delta >0$ and $\delta <0$. The extended gap is also entirely filled with the GSs, all of which are stable in simulations. Recently observed solitons in hollow-core photonic-crystal fibers may belong to this GS family.Comment: 5 pages, 5 figure