Pt and Nb species on various supports: An alternative to current materials for NOx removal

Meso- or micro/mesoporous supports (NbMCM-41 and NaY + NbMCM-41, respectively) were tested for Pt loading. The effects of the support structure and composition on the metal oxidation and on nitrate storage properties were pointed out in the SCR for NO_x removal. Nitrate species were found directly related to the catalytic performance of Pt. Niobium from NbMCM-41 matrix in Pt/NbMCM-41 play the role of NO_x storage species, whereas in the presence of NaY in the support, sodium cations act as storage for NO_x.     

Operando systems for the evaluation of the catalytic performance of NOx storage and reduction materials

Operando measurements were carried out in a quartz reactor to evaluate the catalytic performance of NO_x storage and reduction materials containing Pt and Ba supported on Al₂O₃. Carbonates present on the surface after activation were removed after the first exposure of the sample to the nitration flow. Nitrite species bound to barium were observed at low temperatures. Barium nitrates are the predominant species in the studied temperature range under wet and dry conditions. These species are not stable at temperatures above 723 K. The presence of water inhibits the formation of alumina nitrates favoring the coordination of nitrates with the barium sites.     

Aligning Text and Phonemes for Speech Technology Applications Using an EM-Like Algorithm

A common requirement in speech technology is to align two different symbolic representations of the same linguistic ‘message’. For instance, we often need to align letters of words listed in a dictionary with the corresponding phonemes specifying their pronunciation. As dictionaries become ever bigger, manual alignment becomes less and less tenable yet automatic alignment is a hard problem for a language like English. In this paper, we describe the use of a form of the expectation-maximization (EM) algorithm to learn alignments of English text and phonemes, starting from a variety of initializations. We use the British English Example Pronunciation (BEEP) dictionary of almost 200,000 words in this work. The quality of alignment is difficult to determine quantitatively since no ‘gold standard’ correct alignment exists. We evaluate the success of our algorithm indirectly from the performance of a pronunciation by analogy system using the aligned dictionary data as a knowledge base for inferring pronunciations. We find excellent performance—the best so far reported in the literature. There is very little dependence on the start point for alignment, indicating that the EM search space is strongly convex. Since the aligned BEEP dictionary is a potentially valuable resource, it is made freely available for research use.     

Requirements for synthetic diamond devices for radiotherapy dosimetry applications

CVD diamond is a remarkable material for the fabrication of radiation detectors. Radiation hardness, chemical resistance and high-temperature operation capabilities of diamond motivate its use for fabrication of devices operating in hostile environments such as that encountered in nuclear industry and high energy physics. Its potentialities for such applications have been well documented and recent studies have led to the developments of a few applications that are addressing specific industrial needs.One particular interest of diamond stands in the fact that its atomic number is close to that of human tissues. This implies that the response of a diamond device to radiation is close to that received by the human body. Its thus enables the straightforward measurement of the dose for radiotherapy applications. However, this requires high reproducibility and linearity. It is widely observed that radiation exposure is modifying the initial performances of diamond detectors and priming devices is therefore required to obtain the required linearity. However, the nature of defects in the material strongly influences the type of priming required. This paper will address this problem from the study of trapping levels and their influence on the device response. We present here the current status of the development of polycrystalline diamond for this type of application, and propose new techniques of improving the material characteristics toward the optimisation of ionisation chamber performances as well as that of thermoluminescent dosimeters for the particular field of radiotherapy applications.     

Factor analysis as a means of determining response to chemotherapy in patients with osteogenic sarcoma

The prognosis of localized osteogenic sarcoma (OS) has improved considerably since the introduction of neoadjuvant chemotherapy. However, there is a subset of patients who do not show full benefit from neoadjuvant chemotherapy because of chemoresistance. The early identification of poor responders to chemotherapy during neoadjuvant therapy remains difficult. In order to evaluate the role of bone scintigraphy we report our experience of dynamic technetium-99m hydroxymethylene diphosphonate bone scintigraphy in 19 cases of paediatric osteogenic sarcomas. Before the beginning of chemotherapy, a dynamic scan was recorded during 30 min followed by static images at 3 h. The procedure was repeated halfway through the course of chemotherapy (6th week). Histological grading of the response to chemotherapy was carried out in the 12th week, showing nine good responses and ten poor responses. Factor analysis of dynamic structures (FADS) applied to dynamic scans allowed us to identify three factors termed vascular, "soft tissue" and osseous factors. The effect of chemotherapy on each factor was evaluated. Using FADS we were able to detect all the poor histological responders with the combination of vascular and osseous factors. Six out of nine good histological responders were also classified as scintigraphic responders. FADS applied to dynamic bone scans allowed us to identify at an early stage all the poor histological responders to neoadjuvant chemotherapy. This method may have clinical relevance for the therapeutic strategy in patients with OS.     

On the molecular origin of supercapacitance in nanoporous carbon electrodes

Lightweight, low-cost supercapacitors with the capability of rapidly storing a large amount of electrical energy can contribute to meeting continuous energy demands and effectively levelling the cyclic nature of renewable energy sources. The excellent electrochemical performance of supercapacitors is due to a reversible ion adsorption in porous carbon electrodes. Recently, it was demonstrated that ions from the electrolyte could enter sub nanometre pores, greatly increasing the capacitance. However, the molecular mechanism of this enhancement remains poorly understood. Here we provide the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes. We show how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values (125 F g(-1)) than with simpler electrode geometries. The proposed mechanism opens the door for the design of materials with improved energy storage capabilities. It also sheds new light on situations where ion adsorption in porous structures or membranes plays a role.     

Complement-fixing elicited antibodies are a major component in the pathogenesis of xenograft rejection

Hamster to rat cardiac xenografts undergo delayed rejection as compared with the hyperacute rejection of discordant xenografts. Elicited xenoreactive Abs (EXA) are thought to initiate hamster to rat cardiac xenograft rejection. In this study, we demonstrate that following transplantation of a hamster heart, rats generated high levels of EXA. Adoptive transfer into naive recipients of purified IgM, IgG2b, or IgG2c, but not IgG1 or IgG2a EXA, induced xenograft rejection in a complement-dependent manner. Ability of EXA to cause rejection correlated with complement activation, platelet aggregation, and P-selectin expression in the xenograft endothelium. Cyclosporin A (CyA) administration, after transplantation, totally suppressed IgG1, IgG2a, IgG2b, and IgG2c EXA, and inhibited IgM EXA production, but failed to overcome rejection. Administration of cobra venom factor (CVF), 1 day before and at the time of transplantation, resulted in complement inhibition during 3 days after transplantation, which failed to overcome rejection. Combination of CyA and CVF, which we have previously shown to overcome rejection, resulted in suppression of IgG EXA production and in the return of IgM XNA to preimmunization serum levels, 3 to 7 days after xenotransplantation, while complement remained inhibited. Thus, under CyA/CVF treatment, complement activation by hamster cells was suppressed following xenotransplantation, and presumably for this reason xenograft rejection did not occur. In conclusion, our data demonstrate that EXA play a pivotal role in the pathogenesis of xenograft rejection and that CyA and CVF suppress xenograft rejection by preventing exposure of xenograft endothelial cells to complement activation by EXA.     

A low-cost laser range finder based on an FMCW-like method

The purpose of this paper is to present the prototype of a low-cost laser range finder. It belongs to the flight time measurement category. In this case, the time of flight is converted into a beat frequency proportional to the distance to be measured. This physical conversion is realized with an optical power modulation of the laser beam by a chirped wave. The experimental set-up is detailed with the main functional blocks. Experimental results are provided and the main possible improvements are discussed     

Editorial

Computing and Visualization in Science -