High Performance Direct Gravitational N-body Simulations on Graphics Processing Units

We present the results of gravitational direct $N$-body simulations using the commercial graphics processing units (GPU) NVIDIA Quadro FX1400 and GeForce 8800GTX, and compare the results with GRAPE-6Af special purpose hardware. The force evaluation of the $N$-body problem was implemented in Cg using the GPU directly to speed-up the calculations. The integration of the equations of motions were, running on the host computer, implemented in C using the 4th order predictor-corrector Hermite integrator with block time steps. We find that for a large number of particles (N \apgt 10^4) modern graphics processing units offer an attractive low cost alternative to GRAPE special purpose hardware. A modern GPU continues to give a relatively flat scaling with the number of particles, comparable to that of the GRAPE. Using the same time step criterion the total energy of the $N$-body system was conserved better than to one in $10^6$ on the GPU, which is only about an order of magnitude worse than obtained with GRAPE. For N\apgt 10^6 the GeForce 8800GTX was about 20 times faster than the host computer. Though still about an order of magnitude slower than GRAPE, modern GPU's outperform GRAPE in their low cost, long mean time between failure and the much larger onboard memory; the GRAPE-6Af holds at most 256k particles whereas the GeForce 8800GTF can hold 9 million particles in memory.Comment: Submitted to New Astronom

In vitro metabolic studies of REV-ERB agonists SR9009 and SR9011

SR9009 and SR9011 are attractive as performance-enhancing substances due to their REV-ERB agonist effects and thus circadian rhythm modulation activity. Although no pharmaceutical preparations are available yet, illicit use of SR9009 and SR9011 for doping purposes can be anticipated, especially since SR9009 is marketed in illicit products. Therefore, the aim was to identify potential diagnostic metabolites via in vitro metabolic studies to ensure effective (doping) control. The presence of SR9009 could be demonstrated in a black market product purchased over the Internet. Via human liver microsomal metabolic assays, eight metabolites were detected for SR9009 and fourteen metabolites for SR9011 by liquid chromatography-high resolution mass spectrometry (LC-HRMS). Structure elucidation was performed for all metabolites by LC-HRMS product ion scans in both positive and negative ionization mode. Retrospective data analysis was applied to 1511 doping control samples previously analyzed by a full-scan LC-HRMS screening method to verify the presence of SR9009, SR9011 and their metabolites. So far, the presence of neither the parent compound nor the metabolites could be detected in routine urine samples. However, to further discourage use of these potentially harmful compounds, incorporation of SR9009 and SR9011 into screening methods is highly recommended

Generic Computing on a Graphics Processing Unit

With the increasing demand for better, more realistic and more detailed graphics, more and more effort and money is put into improving the Graphics Processing Unit (GPU) in a computer. As a result of this, the GPU has become a very powerful computing unit with its own programmable processor and a unique architecture. Unlike CPUs, GPUs are special purpose hardware, designed to perform tasks often encountered in computer graphics. While CPU manufacturers only just start using multiple cores in a CPU, parallelism is already in long use in GPUs. Though GPUs are designed for graphics computations, they can be used for more. This research project explores the application of GPUs both in graphics and in generic computing. The emphasis will be on the latter. We explain how the GPU can be used to build useful programs that can speed up simple cellular automata to over 50 times faster than on a conventional processor. We also show that complex computations like the gravitational N-body problem can be turned into a GPU based version to speed up computation. Acknowledgement

Criteria for energy efficient lighting in buildings

In order to assess the energy efficiency of an indoor lighting installation, a criterion for the installed electrical power is proposed which is broadly applicable and easy to use. Introducing target values for lamps and gear and taking into account some basic lighting comfort requirements, the maximum electrical power to be installed can be predicted for any kind of application. Herewith, one or more task areas with appropriate target illuminance values may be defined. The key parameter of the criterion is the analytical expression for the target utilance as a function of common lighting design parameters. Two practical examples illustrate the validity of the criterion. In a first example, a general case where the task area is coincident with a reference plane parallel with the floor has been studied. The values obtained converge to actual target values in current practice. In a second example, the lighting design of a store with many vertical task areas is explained. These cases illustrate the advantages of the criterion as compared to energy evaluation criteria based on the normalized power density. From 2010 on, the proposed criterion will be used in Flanders to assign grants for a re- or newlighting.status: publishe

Grants for re- and newlighting in Flanders: a new approach

For a long time, Flemish companies and local authorities which realize energy efficient lighting solutions have the opportunity to get grants from the Flemish government. However, the conditions and the amount of the grant have been changed substantially since January 2010. The new approach is proposed and illustrated by two practical examples.status: publishe