Bose-Einstein condensation of excitons in Cu2_2O

We present a parameter-free model which estimates the density of excitons in Cu$_2$O, related to experiments that have tried to create an excitonic Bose-Einstein condensate. Our study demonstrates that the triplet-state excitons move along adiabats and obey classical statistics, while the singlet-state excitons are a possible candidate for forming a Bose-Einstein condensate. Finally we show that the results of this study do not change qualitatively in a two-dimensional exciton gas, which can be realized in a quantum well.Comment: 6 pages, RevTex, 1 ps figur

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers II: Surface characterization and in vitro assessments

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), as well as heparin-coated glass beads and tubes were evaluated for the amounts and activities of surface-immobilized heparin. Because the amphiphilic copolymer system is thermodynanmcally predicted to demonstrate low-energy phase enrichment on the surfaces of aircast films, studies were also undertaken to understand the in vitro results. Solvent-cast copolymer films have a heterogeneous microphase-separated structure according to transmission electron micrographs. Wilhelmy plate contact angle analysis indicates significant surface restructuring occurs upon hydration. Attenuated total reflectance infrared spectroscopy studies of the desiccated and hydrated films at two different sampling depths show compositional heterogeneity as a function of depth, as well as near surface restructuring allowing surface enrichment of the high-energy segments following contact with water. Significant concentrations of heparin are detected on the surface of these coatings by toluidine blue assays. In addition, a portion of the surface-bound heparin maintains its original bioactivity as determined by recalification times, thrombin times, and Factor Xa assays. These substrates were also tested for platelet adhesion and activation reactions in vitro using polymer-coated beads in rabbit platelet-rich plasma. Heparinized polymers promoted low levels of platelet adhesion and serotonin release. Surface concentrations of heparin from bioactivity assays were then correlated with platelet adhesion and the extent of platelet release to assess the efficacy of this heparin-immobilized copolymer as a blood-compatible material or coating

Cloudbus Toolkit for Market-Oriented Cloud Computing

This keynote paper: (1) presents the 21st century vision of computing and identifies various IT paradigms promising to deliver computing as a utility; (2) defines the architecture for creating market-oriented Clouds and computing atmosphere by leveraging technologies such as virtual machines; (3) provides thoughts on market-based resource management strategies that encompass both customer-driven service management and computational risk management to sustain SLA-oriented resource allocation; (4) presents the work carried out as part of our new Cloud Computing initiative, called Cloudbus: (i) Aneka, a Platform as a Service software system containing SDK (Software Development Kit) for construction of Cloud applications and deployment on private or public Clouds, in addition to supporting market-oriented resource management; (ii) internetworking of Clouds for dynamic creation of federated computing environments for scaling of elastic applications; (iii) creation of 3rd party Cloud brokering services for building content delivery networks and e-Science applications and their deployment on capabilities of IaaS providers such as Amazon along with Grid mashups; (iv) CloudSim supporting modelling and simulation of Clouds for performance studies; (v) Energy Efficient Resource Allocation Mechanisms and Techniques for creation and management of Green Clouds; and (vi) pathways for future research.Comment: 21 pages, 6 figures, 2 tables, Conference pape

Structural Relaxation and Frequency Dependent Specific Heat in a Supercooled Liquid

We have studied the relation between the structural relaxation and the frequency dependent thermal response or the specific heat, $c_p(\omega)$, in a supercooled liquid. The Mode Coupling Theory (MCT) results are used to obtain $c_p(\omega)$ corresponding to different wavevectors. Due to the two-step relaxation process present in the MCT, an extra peak, in addition to the low frequency peak, is predicted in specific heat at high frequency.Comment: 14 pages, 13 Figure

A Detailed Monte-Carlo Simulation for the Belle TOF System

We have developed a detailed Monte Carlo simulation program for the Belle TOF system. Based on GEANT simulation, it takes account of all physics processes in the TOF scintillation counters and readout electronics. The simulation reproduces very well the performance of the Belle TOF system, including the dE/dx response, the time walk effect, the time resolution, and the hit efficiency due to beam background. In this report, we will describe the Belle TOF simulation program in detail.Comment: To be submitted to NI

Boundary Effects on Dynamic Behavior of Josephson-Junction Arrays

The boundary effects on the current-voltage characteristics in two-dimensional arrays of resistively shunted Josephson junctions are examined. In particular, we consider both the conventional boundary conditions (CBC) and the fluctuating twist boundary conditions (FTBC), and make comparison of the obtained results. It is observed that the CBC, which have been widely adopted in existing simulations, may give a problem in scaling, arising from rather large boundary effects; the FTBC in general turn out to be effective in reducing the finite-size effects, yielding results with good scaling behavior. To resolve the discrepancy between the two boundary conditions, we propose that the proper scaling in the CBC should be performed with the boundary data discarded: This is shown to give results which indeed scale well and are the same as those from the FTBC.Comment: RevTex, Final version to appear in Phys. Rev.

Dynamical modelling of the elliptical galaxy NGC 2974

In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\rm e}.$Comment: 7 figure

Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time

We present a model for structure formation, melting, and optical properties of gold/DNA nanocomposites. These composites consist of a collection of gold nanoparticles (of radius 50 nm or less) which are bound together by links made up of DNA strands. In our structural model, the nanocomposite forms from a series of Monte Carlo steps, each involving reaction-limited cluster-cluster aggregation (RLCA) followed by dehybridization of the DNA links. These links form with a probability $p_{eff}$ which depends on temperature and particle radius $a$. The final structure depends on the number of monomers (i. e. gold nanoparticles) $N_m$, $T$, and the relaxation time. At low temperature, the model results in an RLCA cluster. But after a long enough relaxation time, the nanocomposite reduces to a compact, non-fractal cluster. We calculate the optical properties of the resulting aggregates using the Discrete Dipole Approximation. Despite the restructuring, the melting transition (as seen in the extinction coefficient at wavelength 520 nm) remains sharp, and the melting temperature $T_M$ increases with increasing $a$ as found in our previous percolation model. However, restructuring increases the corresponding link fraction at melting to a value well above the percolation threshold. Our calculated extinction cross section agrees qualitatively with experiments on gold/DNA composites. It also shows a characteristic ``rebound effect,'' resulting from incomplete relaxation, which has also been seen in some experiments. We discuss briefly how our results relate to a possible sol-gel transition in these aggregates.Comment: 12 pages, 10 figure

NMR quantum computation with indirectly coupled gates

An NMR realization of a two-qubit quantum gate which processes quantum information indirectly via couplings to a spectator qubit is presented in the context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive NMR implementation of the Deutsch-Jozsa algorithm for functions with three argument bits and demonstrates a technique essential for multi-qubit quantum computation.Comment: 9 pages, 2 figures. 10 additional figures illustrating output spectr

Dynamic instabilities induced by asymmetric influence: Prisoners' dilemma game on small-world networks

A two-dimensional small-world type network, subject to spatial prisoners' dilemma dynamics and containing an influential node defined as a special node with a finite density of directed random links to the other nodes in the network, is numerically investigated. It is shown that the degree of cooperation does not remain at a steady state level but displays a punctuated equilibrium type behavior manifested by the existence of sudden breakdowns of cooperation. The breakdown of cooperation is linked to an imitation of a successful selfish strategy of the influential node. It is also found that while the breakdown of cooperation occurs suddenly, the recovery of it requires longer time. This recovery time may, depending on the degree of steady state cooperation, either increase or decrease with an increasing number of long range connections.Comment: 5 pages, 6 figure