Computer analysis of effects of altering jet fuel properties on refinery costs and yields

This study was undertaken to evaluate the adequacy of future U.S. jet fuel supplies, the potential for large increases in the cost of jet fuel, and to what extent a relaxation in jet fuel properties would remedy these potential problems. The results of the study indicate that refiners should be able to meet jet fuel output requirements in all regions of the country within the current Jet A specifications during the 1990-2010 period. The results also indicate that it will be more difficult to meet Jet A specifications on the West Coast, because the feedstock quality is worse and the required jet fuel yield (jet fuel/crude refined) is higher than in the East. The results show that jet fuel production costs could be reduced by relaxing fuel properties. Potential cost savings in the East (PADDs I-IV) through property relaxation were found to be about 1.3 cents/liter (5 cents/gallon) in January 1, 1981 dollars between 1990 and 2010. However, the savings from property relaxation were all obtained within the range of current Jet A specifications, so there is no financial incentive to relax Jet A fuel specifications in the East. In the West (PADD V) the potential cost savings from lowering fuel quality were considerably greater than in the East. Cost savings from 2.7 to 3.7 cents/liter (10-14 cents/gallon) were found. In contrast to the East, on the West Coast a significant part of the savings was obtained through relaxation of the current Jet A fuel specifications

14-Bit and 2GS/s Low Power Digitizing Boards for Physics Experiments

International audienceThe trend in data acquisition systems for modern physics experiments is to digitize analog signals closer and closer to the detector. The digitization systems have followed the progress of commercial analog to digital converters. The state of the art for these devices is currently 200 MSample/s for a 14-bit range. The new boards, described in this paper, have been designed to improve these performances by more than an order of magnitude. This board mainly includes 4 channels sampling analog data up to 2 GSamples/s with an analog bandwidth of 300 MHz, and digitizing it with a 14-bit dynamic range. It is based on the custom-designed MATACQ chip. The latter's innovative design permits reaching these performances with power consumption smaller than 1W, thus allowing a total consumption below 20W for the whole board. The board is triggerable either by internal or external signals and several boards are easily synchronizable. The board integrates USB, GPIB and VME interfaces that permit a readout speed of up to 500 events/s with the whole memory depth of the 4 channels read

Stability and Fairness in Models with a Multiple Membership

This article studies a model of coalition formation for the joint production (and finance) of public projects, in which agents may belong to multiple coalitions. We show that, if projects are divisible, there always exists a stable (secession-proof) structure, i.e., a structure in which no coalition would reject a proposed arrangement. When projects are indivisible, stable allocations may fail to exist and, for those cases, we resort to the least core in order to estimate the degree of instability. We also examine the compatibility of stability and fairness in metric environments with indivisible projects, where we also explore the performance of well-known solutions, such as the Shapley value and the nucleolus.Stability, Fairness, Membership, Coalition Formation

Stability and fairness in models with a multiple membership

This article studies a model of coalition formation for the joint production (and finance) of public projects, in which agents may belong to multiple coalitions. We show that, if projects are divisible, there always exists a stable (secession-proof) structure, i.e., a structure in which no coalition would reject a proposed arrangement. When projects are in- divisible, stable allocations may fail to exist and, for those cases, we resort to the least core in order to estimate the degree of instability. We also examine the compatibility of stability and fairness on metric environments with indivisible projects. To do so, we explore, among other things, the performance of several well-known solutions (such as the Shapley value, the nucleolus, or the Dutta-Ray value) in these environments.stability, fairness, membership, coalition formation

Generating Gowdy cosmological models

Using the analogy with stationary axisymmetric solutions, we present a method to generate new analytic cosmological solutions of Einstein's equation belonging to the class of $T^3$ Gowdy cosmological models. We show that the solutions can be generated from their data at the initial singularity and present the formal general solution for arbitrary initial data. We exemplify the method by constructing the Kantowski-Sachs cosmological model and a generalization of it that corresponds to an unpolarized $T^3$ Gowdy model.Comment: Latex, 15 pages, no figure

Monte Carlo tomographic reconstruction in SPECT impact of bootstrapping and number of generated events

In Single Photon Emission Computed Tomography (SPECT), 3D images usually reconstructed by performing a set of bidimensional (2D) analytical or iterative reconstructions can also be reconstructed using an iterative reconstruction algorithm involving a 3D projector. Accurate Monte Carlo (MC) simulations modeling all the physical effects that affect the imaging process can be used to estimate this projector. However, the accuracy of the projector is affected by the stochastic nature of MC simulations. In this paper, we study the accuracy of the reconstructed images with respect to the number of simulated histories used to estimate the MC projector. Furthermore, we study the impact of applying the bootstrapping technique when estimating the projectorComment: 15 pages, 9 figures, 2 table

Stability and Fairness in Models with a Multiple Membership

This article studies a model of coalition formation for the joint production (and finance) of public projects, in which agents may belong to multiple coalitions. We show that, if projects are divisible, there always exists a stable (secession-proof) structure, i.e., a structure in which no coalition would reject a proposed arrangement. When projects are indivisible, stable allocations may fail to exist and, for those cases, we resort to the least core in order to estimate the degree of instability. We also examine the compatibility of stability and fairness in metric environments with indivisible projects, where we also explore the performance of well-known solutions, such as the Shapley value and the nucleolus.Stability, Fairness, Membership, Coalition Formation

WISDOM: A Grid-Enabled Drug Discovery Initiative Against Malaria

The goal of this chapter is to present the WISDOM initiative, which is one of the main accomplishments in the use of grids for biomedical sciences achieved on grid infrastructures in Europe. Researchers in life sciences are among the most active scientifi c communities on the EGEE infrastructure. As a consequence, the biomedical virtual organization stands fourth in terms of resources consumed in 2007, with an average of 7000 jobs submitted every day to the grid and more than 4 million hours of CPU consumed in the last 12 months. Only three experiments on the CERN Large Hadron Collider have used more resources. Compared to particle physics, the use of resources is much less centralized as about 40 different scientifi c applications are now currently deployed on EGEE. Each of them requires an amount of CPU which ranges from a few to a few hundred CPU years. Thanks to the 20,000 processors available to the users of the biomedical virtual organization, crunching factors in the hundreds are witnessed routinely. Such performances were already achieved on supercomputers but at the cost of reservation and long delays in the access to resources. On the contrary, grid infrastructures are constantly open to the user communities. Such changes in the scale of the computing resources made continuously available to the researchers in biomedical sciences open opportunities for exploring new fi elds or changing the approach to existing challenges. In this chapter, we would like to show the potential impact of grids in the fi eld of drug discovery through the example of the WISDOM initiative

Picosecond time measurement using ultra fast analog memories

International audienceThe currently existing electronics dedicated to precise time measurement is mainly based on the use of constant fraction discriminators (CFD) associated with Time to Digital Converters (TDC). The constant fraction technique minimizes the time walk effect (dependency of timing on the pulse amplitude). Several attempts have been made to integrate CFD in multi-channel ASICs. But the time resolution measured on the most advanced one is of the order of 30 ps rms. Two main techniques are used for the TDC architectures. The first one makes use of a voltage ramp started or stopped by the digital pulse. The obtained voltage is converted into digital data using an Analog to Digital Converter (ADC). The timing resolution of such a system is excellent (5 ps rms). But this technique is limited by its large dead time which can be unacceptable for the future high rate experiments. Another popular technique associates a coarse measurement performed by a digital counter with a fine measurement (interpolation) using Delay Line Loop. Such a system can integrate several (8-16) channels on an FPGA or an ASIC. The most advanced DLL-based TDC ASIC exhibits a timing resolution of 25 ps, but only after a careful calibration. It should be noticed that the overall timing resolution is given by the quadratic sum of the discriminator and of the TDC. In the meantime, alternative methods based on digital treatment of the analogue sampled then digitized detector signal have been developed. Such methods permit achieving a timing resolution far better than the sampling frequency. For example, 100ps rms resolution has been reported for a signal sampled at only 100MHz. Digitization systems have followed the progress of commercial ADCs, which currently offer a rate of 500 MHz over 12 bits. Their main drawbacks are the huge output data rate and power consumption. Their packaging, cooling, and tricky clock requirements also makes them very hard to implement. Conversely, high speed analog memories now offer sampling rates far above 1GHz at low cost and with low power consumption. The new USB-WaveCatcher board has been designed to provide high performances over a short time window. It houses on a small surface two 12-bit 500-MHz-bandwidth digitizers sampling between 400 MS/s and 3.2 GS/s. It is based on the patented SAM chip, an analog circular memory of 256 cells per channel. Its innovative matrix design permits reaching these performances, yet in a cheap pure CMOS 0.35µm technology, while consuming only 300 mW. Raw sampling precision is as good as 15ps rms. In an embodiment where the clock is directly sent to the SAM chip, thus limiting the usable sampling frequency to 3.2GHz, and after a calibration of the fixed pattern time distribution, a reproducible time precision of a few ps has been demonstrated. The board also offers various functionalities. Its input offset is tunable over a range of 2 V. It can be triggered either internally or externally and several boards can easily be synchronized. Trigger rates counters are implemented. Both channels can also be used for reflectometry thanks to their internal pulser. The precision obtained for cable length measurements is as good as 2mm. Charge measurement mode is also provided, through integrating on the fly over a programmable time window the signal coming for instance from photo-multipliers. Power consumption is only 2.5 W which permits powering with the sole USB. Signal connectors can be BNC, SMA or LEMO. The board houses a USB 12 Mbits/s interface permitting a dual-channel readout speed of 500 events/s. Faster readout modes are also available. In charge measurement mode, the sustained trigger rate can reach a few tens kHz. A 480Mbits/s version will soon be available. Various evolutions of the SAM chip are under study, targeting either higher precision time measurements or longer time window. The USB-WaveCatcher can thus replace oscilloscopes for a much lower cost in most high-precision short-window applications. Moreover, it opens new doors into the domain of very high precision time measurements