Performance Evaluation of Sparse Matrix Multiplication Kernels on Intel Xeon Phi

Intel Xeon Phi is a recently released high-performance coprocessor which features 61 cores each supporting 4 hardware threads with 512-bit wide SIMD registers achieving a peak theoretical performance of 1Tflop/s in double precision. Many scientific applications involve operations on large sparse matrices such as linear solvers, eigensolver, and graph mining algorithms. The core of most of these applications involves the multiplication of a large, sparse matrix with a dense vector (SpMV). In this paper, we investigate the performance of the Xeon Phi coprocessor for SpMV. We first provide a comprehensive introduction to this new architecture and analyze its peak performance with a number of micro benchmarks. Although the design of a Xeon Phi core is not much different than those of the cores in modern processors, its large number of cores and hyperthreading capability allow many application to saturate the available memory bandwidth, which is not the case for many cutting-edge processors. Yet, our performance studies show that it is the memory latency not the bandwidth which creates a bottleneck for SpMV on this architecture. Finally, our experiments show that Xeon Phi's sparse kernel performance is very promising and even better than that of cutting-edge general purpose processors and GPUs

An Experimental Study of the Effects of Inequality and Relative Deprivation on Trusting Behavior

Several non-experimental studies report that income inequality and other forms of population-based heterogeneity reduce levels of trust in society. However, recent work by Glaeser et al. (2000) calls into question the reliability of widely used survey-based measures of trust. Specifically, survey responses regarding trust attitudes did not reflect subjects actual behavior in a trust game. In this paper, we conduct a novel experimental test of the effects of inequality on trust and trustworthiness. Our experimental design induces inequality by varying the show-up fees paid to subjects, in contrast to previous experiments that focus on broad cultural or national differences in trust. We do not find robust support for the hypothesis that inequality per se dampens trusting behavior among all subjects; however, we do find some evidence that trust and rustworthiness are influenced by an individuals relative position in the group. Finally, we confirm previous findings that common survey-based measures of social trust are not associated with actual trusting behavior.Trust, social capital, heterogeneity, inequality, experiment

Cauchy horizon singularity without mass inflation

A perturbed Reissner-Nordstr\"om-de Sitter solution is used to emphasize the nature of the singularity along the Cauchy horizon of a charged spherically symmetric black hole. For these solutions, conditions may prevail under which the mass function is bounded and yet the curvature scalar $R_{\alpha\beta\gamma\delta} R^{\alpha\beta\gamma\delta}$ diverges.Comment: typeset in RevTex, 13 page

An experimental investigation of the hypergolic ignition of some polymeric fuels with oxygen

Hypergolic ignition of polymeric fuels with oxyge

Increased surface flashover voltage in microfabricated devices

With the demand for improved performance in microfabricated devices, the necessity to apply greater electric fields and voltages becomes evident. When operating in vacuum, the voltage is typically limited by surface flashover forming along the surface of a dielectric. By modifying the fabrication process we have discovered it is possible to more than double the flashover voltage. Our finding has significant impact on the realization of next-generation micro- and nano-fabricated devices and for the fabrication of on-chip ion trap arrays for the realization of scalable ion quantum technology

Cosmic Censorship: As Strong As Ever

Spacetimes which have been considered counter-examples to strong cosmic censorship are revisited. We demonstrate the classical instability of the Cauchy horizon inside charged black holes embedded in de Sitter spacetime for all values of the physical parameters. The relevant modes which maintain the instability, in the regime which was previously considered stable, originate as outgoing modes near to the black hole event horizon. This same mechanism is also relevant for the instability of Cauchy horizons in other proposed counter-examples of strong cosmic censorship.Comment: 4 pages RevTeX style, 1 figure included using epsfi

Accumulation and distribution of doxorubicin in tumour spheroids: the influence of acidity and expression of P-glycoprotein

Purpose: The intra-tumour distribution of anticancer drugs remains an important, but often under-estimated, influence on drug efficacy. Tumour acidity and the presence of efflux pumps were examined for their influence on the distribution of doxorubicin in a solid tumour model. Methods: Anticancer drug distribution and overall accumulation was measured in tumour spheroids (TS) of varying sizes. The distribution profiles were examined in normoxic and hypoxic TS, the latter generating metabolic acidosis. Finally, the drug distribution profiles were related to efficacy using radial outgrowth assays. Results: In large tumour spheroids (TS) (d ∼500 μm), intracellular accumulation of doxorubicin was restricted to cells in the outermost layers and failed to accumulate within the viable cells in the intermediate hypoxic zone. A similar profile was obtained for another protonatable amine, 7-AAD. In contrast, the distribution of the non-ionisable drug (at physiological pH) BODIPY-Taxol was uniform throughout the TS. In order to independently model the hypoxic and normoxic zones of TS, we compared drug accumulation in small entirely normoxic TS (d ∼200 μm) with equivalent sized ones exposed to hypoxia in an anaerobic chamber. Exposure of TS to hypoxia caused a considerable reduction in the pH of the bathing medium and lower tissue accumulation of doxorubicin. Interstitial acidity reduces the proportion of doxorubicin in the non-ionised form. Conclusions: In TS, the accumulation and distribution of doxorubicin was influenced by both the expression of P-glycoprotein and hypoxia-induced acidity. Therefore, optimisation of doxorubicin chemotherapy for hypoxic tumours will require circumvention of both of these crucial pharmacokinetic determinants

Pair Creation of Black Holes by Domain Walls

In this paper we study the production of pairs of neutral and charged black holes by domain walls, finding classical solutions and calculating their classical actions. We find that neutral black holes whose creation is mediated by Euclidean instantons must be produced mutually at rest with respect to one another, but for charged black holes a new type of instanton is possible in which after formation the two black holes accelerate away from one another. These new types of instantons are not possible in Einstein-Maxwell theory with a cosmological constant. We also find that the creation of non-orientable black hole solutions can be mediated by Euclidean instantons and that in addition if one is prepared to consider entirely Lorentzian no-boundary type contributions to the path integral then mutually accelerating pairs may be created even in the neutral case. Finally we consider the production of Kaluza-Klein monopoles both by a standard cosmological term and in the presence of a domain wall. We find that compactification is accompanied by the production of pairs of Kaluza-Klein monopoles.Comment: 22 pages (REVTeX with AMS Symbols) with 5 postscript figures attached in a single uuencoded, g-zipped, tar file at end of tex fil