GePEToS : A Geant4 Monte Carlo simulation package for Positron Emission Tomography

GePEToS is a simulation framework developed over the last few years for assessing the instrumental performance of future PET scanners. It is based on Geant4, written in Object-Oriented C++ and runs on Linux platforms. The validity of GePEToS has been tested on the well-known Siemens ECAT EXACT HR+ camera. The results of two application examples are presented : the design optimization of a liquid Xe micro-PET camera dedicated to small animal imaging as well as the evaluation of the effect of a strong axial magnetic field on the image resolution of a Concorde P4 micro-PET camera.Comment: 5 pages, 12 figures, submitted to IEEE Transactions on Nuclear Scienc

Non-volatile molecular memory elements based on ambipolar nanotube field effect transistors

We have fabricated air-stable n-type, ambipolar carbon nanotube field effect transistors (CNFETs), and used them in nanoscale memory cells. N-type transistors are achieved by annealing of nanotubes in hydrogen gas and contacting them by cobalt electrodes. Scanning gate microscopy reveals that the bulk response of these devices is similar to gold-contacted p-CNFETs, confirming that Schottky barrier formation at the contact interface determines accessibility of electron and hole transport regimes. The transfer characteristics and Coulomb Blockade (CB) spectroscopy in ambipolar devices show strongly enhanced gate coupling, most likely due to reduction of defect density at the silicon/silicon-dioxide interface during hydrogen anneal. The CB data in the ``on''-state indicates that these CNFETs are nearly ballistic conductors at high electrostatic doping. Due to their nanoscale capacitance, CNFETs are extremely sensitive to presence of individual charge around the channel. We demonstrate that this property can be harnessed to construct data storage elements that operate at the few-electron level.Comment: 6 pages text, 3 figures and 1 table of content graphic; available as NanoLetters ASAP article on the we

Experimental study of a liquid Xenon PET prototype module

A detector using liquid Xenon in the scintillation mode is studied for Positron Emission Tomography (PET). The specific design aims at taking full advantage of the liquid Xenon properties. It does feature a promising insensitive to any parallax effect. This work reports on the performances of the first LXe prototype module, equipped with a position sensitive PMT operating in the VUV range (178 nm).Comment: Proc. of the 7th International Workshops on Radiation Imaging Detectors (IWORID-7), Grenoble, France 4-7 July 200

Principal Component Analysis of the Time- and Position-Dependent Point Spread Function of the Advanced Camera for Surveys

We describe the time- and position-dependent point spread function (PSF) variation of the Wide Field Channel (WFC) of the Advanced Camera for Surveys (ACS) with the principal component analysis (PCA) technique. The time-dependent change is caused by the temporal variation of the $HST$ focus whereas the position-dependent PSF variation in ACS/WFC at a given focus is mainly the result of changes in aberrations and charge diffusion across the detector, which appear as position-dependent changes in elongation of the astigmatic core and blurring of the PSF, respectively. Using >400 archival images of star cluster fields, we construct a ACS PSF library covering diverse environments of the $HST$ observations (e.g., focus values). We find that interpolation of a small number ($\sim20$) of principal components or ``eigen-PSFs'' per exposure can robustly reproduce the observed variation of the ellipticity and size of the PSF. Our primary interest in this investigation is the application of this PSF library to precision weak-lensing analyses, where accurate knowledge of the instrument's PSF is crucial. However, the high-fidelity of the model judged from the nice agreement with observed PSFs suggests that the model is potentially also useful in other applications such as crowded field stellar photometry, galaxy profile fitting, AGN studies, etc., which similarly demand a fair knowledge of the PSFs at objects' locations. Our PSF models, applicable to any WFC image rectified with the Lanczos3 kernel, are publicly available.Comment: Accepted to PASP. To appear in December issue. Figures are degraded to meet the size limit. High-resolution version can be downloaded at http://acs.pha.jhu.edu/~mkjee/acs_psf/acspsf.pd

Choix multicritère de procédés d'épuration des eaux usées municipales

Les stations d'épuration des eaux usées municipales du Québec, comme ailleurs au Canada et aux États Unis, sont en général peu efficaces sur le plan énergétique. Il est donc possible de concevoir des hypothèses de chaînes épuratoires améliorées au plan de leur efficacité énergétique et de leur performance globale en y introduisant, d'une part, diverses MEEE et, d'autre part, certains procédés unitaires améliorant l'épuration. Cependant, le problème de choisir, parmi ces hypothèses de chaînes d'épuration, celle correspondant au procédé le plus adéquat pour prendre en charge une situation donnée, demeure entier. Cet article analyse ce problème de choix pour les stations d'épuration de capacité comprise entre 5,000 m3/d (≈ 5000 personnes) et 100,000 m3/d (≈ 100,000 personnes). En faisant l'hypothèse, d'un côté, que l'ajout des mesures d'efficacité énergétique peut améliorer la consommation énergétique d'une chaîne d'épuration, et d'un autre côté, que l'insertion de segments de procédés peut contribuer à améliorer leur performance globale, nous avons élaboré, à partir des stations d'épuration de types Biofiltration, Physico-chimique, Réacteurs Biologiques séquentiels (deux variantes), Boues activées et Étangs aérés, six (6) hypothèses de chaînes épuratoires (chaînes 1 à 6) respectant les exigences opérationnelles et épuratoires et nous les avons comparées entre elles, sur la base d'une analyse multicritère d'aide à la décision, en vue d'en déterminer les plus performantes. Cette analyse multicritère intègre les aspects techniques, énergétiques, économiques, etc. et prend en compte les préférences du(des) décideur(s) dans le processus de choix. Les résultats obtenus montrent que, parmi les six hypothèses de chaînes étudiées, les trois premières positions sont occupées par les chaînes 3, 1 et 4 respectivement. Ce type d'analyse pourrait jouer un rôle complémentaire à une étude technico-économique visant le choix de technologies d'épuration.Quebec municipal wastewater treatment facilities, like those elsewhere in Canada and the United States, generally are low efficiency energy consumers (ELECTRIC POWER RESEARCH INSTITUTE (EPRI), 1993; OWEN, 1982; ONTARIO-HYDRO, 1993; METCALF and EDDY, INC., 1992, SASSEVILLE et al., 1995). The work of METCALF and EDDY, INC. (1992) and of EPRI (1993) concluded that it would be possible to substantially reduce electricity demand and to improve the utilization of electrical energy in the municipal wastewater treatment processes by introducing Electricity Saving Measures (ESMs) in the processes and their management.In the province of Quebec, given the potential savings linked to the reduction of electricity consumption in municipal wastewater treatment facilities, and the progressive expansion of the province's wastewater treatment facilities, the adoption of energetically efficient wastewater treatment technologies is particularly timely. SASSEVILLE et al. (1995) estimated that it would be possible to save 5 M $at the present level of wastewater treatment, based on a cost of about 24 M$ for the 400 GWh of electricity annually consumed in the municipal wastewater treatment facilities. This saving would come solely from the implementation of appropriate energy-saving measures.In hypothesizing on one hand that adding energy-saving measures can improve the energy consumption of a wastewater treatment chain, and on the other hand that the introduction of segments of processes can contribute in improving overall performance, we have elaborated from existing wastewater treatment facilities six hypotheses of liquid treatment chains that respect operational and regulation requirements, on the basis of the experience developed in the operation of municipal wastewater treatment facilities. The six hypothetical treatment chains were elaborated from facilities of the following types: biofiltration (chain 1), physico-chemical (chain 2), sequencing biological (batch) reactors system A (chain 3), sequencing biological (batch) reactors system B (chain 4), activated sludge (chain 5) and aerated lagoons (chain 6). The energy-saving measures utilized in the elaboration of these hypothetical treatment chains were chosen on the basis of a conjunctive analysis (KIBI et al., 1997). However, the problem of choosing among these treatment chains the one corresponding to the most adequate process for a particular situation is still present. The present article analyzes this choice for wastewater treatment facilities of a capacity between 5 000 m3/d (≈ 5 000 persons) and 100 000 m3/d (≈ 100 000 persons).How then to choose the most efficient of these hypothetical municipal wastewater treatment chains?Generally, the choice of the treatment technologies is done on the basis of single-criterion mathematical models: for example, the reduction of construction costs, or of exploitation and maintenance costs (ECKENFELDER, 1982; PINEAU et al., 1985; WANG and WANG, 1979; TYTECA et al., 1977). There are other approaches based on dynamic simulation models or on technological and econometric analyses (HYDRO-QUÉBEC, 1993; MACRAE 1989; LESSARD, 1989; BROCKTON, 1987; HOLDREN, 1987; FOSBERG and MUKHOPADHYAY, 1981; REID, CROWTHER and PARTNERS, 1978; KLEMETSON and GRENNEY, 1976).These different approaches are often insufficient to distinguish the real value of the different technological options. Furthermore, they do not take into account many important factors (technological, economic, financial and environmental, ergonomic and socio-political) that affect their implementation and should be considered in identifying an acceptable and viable solution.The multicriteria approach of decision-making advocated in this article can mitigate this difficulty. It will take into account key factors in the conception and operation of treatment technologies, especially energy and environmental factors, likely to give rise to efficient treatment facilities from both an energy and a treatment point of view. However the analysis of decisional factors to consider in this multicriteria analysis gives rise to a particular problem. They affect the decision that can be appreciated by deterministic relationships, offering a high level of certainty as to its evaluation, while others have a non-deterministic nature (uncertainty and imprecision). Research using the multicriteria analysis approach has been performed in similar situations over the last twenty years, in some cases applied to the environmental and energy sectors (e.g. KEENEY and NAIR 1977; ROY and VINCKE 1981; TEGHEM and KUNSCH 1985; SIMOS 1990; HANSON 1991; ROUSSEAU and MARTEL 1994). Here again, these approaches have limits since the cases were treated either in a situation of certainty or a situation of uncertainty and imprecision. The proposed model deals with the case of certainty and uncertainty at the same time, therefore improving the applicability of the multicriteria approach in the situation under study. The solution retained consists of applying this type of modelling in order to classify from the best to the worst, the six hypothetical treatment chains. This approach utilizes in the modelling process, fourteen evaluation criteria, various criteria weights, quantitative and qualitative evaluations, as well as the indifference, preference and veto thresholds. The main steps of the model are the construction of evaluated outclass relationships and the exploitation of these outclass relationships. The multicriteria aggregation procedure utilizes an elaborated mathematical model based upon the methods of ELECTRE III (Roy, 1978) and PROMETHEE II (BRANS et al., 1984), as well as the works of DÉROT et al. (1994). The ranking of these treatment chain hypotheses, elaborated on an empirical level in consultation with the operators and others involved in wastewater treatment and obtained on the basis of this procedure, can discriminate among their overall performance characteristics rather well. It also emphasizes their energy efficiency, since the energy criteria have on average in the analysis a weight that is 28% higher than the other evaluation criteria. The results obtained show that the hypothetical chain 3 is ranked first, chain 1 occupies the second rank, whereas chain 4 is in the third rank. The last three ranks are occupied respectively by chains 6, 5 and 2.In a decisional and strategic approach, the first three treatment chain hypotheses can be considered overall as being the highest achievers. This result signifies that in the scope of investments related to the expansion of treatment facilities and the construction of facilities with a flow rate contained within the considered range, these three treatment chains (when considering different modification hypotheses), should be preferred over the other chains when the emphasis is on their overall performance including energy efficiency. However, other analyses would be necessary in the case of the construction of a new wastewater treatment facility with a flow rate above the level considered in this study.Generally, the results of this analysis can assist in discriminating among the behaviors of the technologies considered, and in judging their relative performance in the investments of the construction of new wastewater treatment facilities, in addition to a technico-economic analysis. Overall, the multicriteria model described in this study identified a compromise solution between evaluations of a different and conflicting nature. This result demonstrates that this type of analysis is appropriate for tackling multidimensional problems

Spectrum analysis of strong motion earthquakes

The problem of the dynamic response of a structure to an earthquake has been formulated in a manner which permits separation of the characteristics of particular structures from the characteristics of the earthquake. The expression involving the characteristics of the earthquake is defined as the "spectrum" of the earthquake and it is shown that the spectrum is simply a plot of the response of a simple oscillator versus the period of the oscillator. Eighty-eight such spectra were computed by means of an electric analog computer and are presented in this report. It is found that damping is a very important parameter in the overall problem; relatively small amounts of damping reduce structural response sharply. It is shown that, when damping is considered, the spectra are consistent with the hypothesis of a distribution about a mean value. It is concluded that the concept of a "dominant ground period" is not valid for the purpose of aseismic structural design. Further research on damping in buildings is recommended, and it is proposed that the mean value of a damped spectrum be used as a quantitative measure of earthquake intensity

NIKEL: Electronics and data acquisition for kilopixels kinetic inductance camera

A prototype of digital frequency multiplexing electronics allowing the real time monitoring of microwave kinetic inductance detector (MKIDs) arrays for mm-wave astronomy has been developed. Thanks to the frequency multiplexing, it can monitor simultaneously 400 pixels over a 500 MHz bandwidth and requires only two coaxial cables for instrumenting such a large array. The chosen solution and the performances achieved are presented in this paper.Comment: 21 pages, 14 figure

Global well-posedness of the KP-I initial-value problem in the energy space

We prove that the KP-I initial value problem is globally well-posed in the natural energy space of the equation

Finite size effects near the onset of the oscillatory instability

A system of two complex Ginzburg - Landau equations is considered that applies at the onset of the oscillatory instability in spatial domains whose size is large (but finite) in one direction; the dependent variables are the slowly modulated complex amplitudes of two counterpropagating wavetrains. In order to obtain a well posed problem, four boundary conditions must be imposed at the boundaries. Two of them were already known, and the other two are first derived in this paper. In the generic case when the group velocity is of order unity, the resulting problem has terms that are not of the same order of magnitude. This fact allows us to consider two distinguished limits and to derive two associated (simpler) sub-models, that are briefly discussed. Our results predict quite a rich variety of complex dynamics that is due to both the modulational instability and finite size effects