Tetralin hydrogenation catalyzed by Mo2C/Al2O3 and WC/Al2O3 in the presence of H2S

Supported molybdenum and tungsten carbides were synthesized by temperature-programmed reactions. These materials were characterized by XRD, EDS analysis, HRTEM and CO chemisorption. Hydrogenation of tetralin was carried out at a total pressure of 4 MPa (3.06 MPa of H₂), at 573 K, without or with sulfur (200 ppm of sulfur as DMDS). The resulting activities were compared with those of MoS₂/Al₂O₃ and Pt (1% (w/w) metal loading) supported on Al₂O₃ or SiO₂. In the absence of sulfur, WC/Al₂O₃ showed an initial activity similar to that of Pt/SiO₂, higher than that of MoS₂/Al₂O₃ but lower than that of Pt/Al₂O₃. In the presence of H₂S, WC/Al₂O₃ showed a steady-state activity similar to that of Pt/Al₂O₃ (which suffered a marked deactivation). Post-reaction characterization did not show any sulfur poisoning of the supported carbides. Therefore the supported carbides are sulfur-tolerant and promising catalysts for the hydrogenation of aromatics in diesel fuels in the presence of small amounts of S-containing compounds.     

Stochastic analysis of a slotted FIFO communication channel

Messages arrive randomly at one end of a slotted communication channel. They are assigned to (packed in) packets of fixed duration which queue up for transmission in first-in-first-out order; the packets are sent one per time slot. In a stochastic setting, where message durations are also random, we analyze a model which yields statistics on message delays and the number of waiting messages, assuming that the assignment protocol is the well-known next-fit rule of one-dimensional bin packing. A stability condition is obtained as a function of general discrete message-length distributions. As a by-product, we contribute a new result to the literature on the probabilistic analysis of the static next-fit bin-packing rule, viz. the limiting expected bin occupancy for general discrete distributions. Specializations of the results to constant message lengths and to uniform message-length distributions are worked out in detail     

The giant organelles in beige and Chediak-Higashi fibroblasts are derived from late endosomes and mature lysosomes

Chediak-Higashi Syndrome (CHS) is an autosomal recessive disease affecting secretory granules and lysosomes-like organelles. In CHS fibroblasts, acidic organelles are abnormally large and clustered in the perinuclear area. We have analyzed fibroblast cell lines from a CHS patient and from the murine model for CHS, the beige mouse, to determine which lysosome-like compartments are affected. Uptake of neutral red showed that in both beige and CHS cell lines, the acidic organelles were markedly clustered in the perinuclear region of the cells. Giant organelles (> 4 microns) were observed in a fraction of the cells, and these were more dramatic in the beige fibroblasts than in the CHS fibroblasts. The total dye uptake of both mutant cell lines was similar to their respective wild type fibroblasts, suggesting that the overall volume of acidic compartments is unaffected by the disorder. Histochemistry and immunofluorescence showed that the giant organelles in both beige and CHS fibroblasts were positive for cathepsin D, lysosome-associated membrane protein (LAMP) 1, LAMP 2, and a 120-kD lysosomal glycoprotein, all marker proteins for late endosomes and lysosomes. The giant organelles were also negative for transferrin receptor and mannose-6-phosphate receptor, and most of them were also negative for rab 7. This distribution of marker proteins shows that the giant organelles in both beige and CHS are derived from late compartments of the endocytic pathway. This conclusion was confirmed using endocytic tracers. BSA was transported to the giant organelles, but only after long incubation times, and only at 37 degrees C. alpha 2-Macroglobulin was taken up and degraded at similar rates by CHS or beige cells and their respective wild type control cells. Taken together, our results indicate that the mutation in CHS specifically affects late endosomes and lysosomes, with little or no effect on early endosomes. Although the mutation clearly causes mislocalization of these organelles, it appears to have little effect on their endocytic and degradative functions.     

Rat antigen-induced arthritis: cartilage alterations assessed with iodine-123-antileukoproteinase

Imaging of cartilage alterations was attempted in joints of rats with chronic antigen-induced arthritis (AIA) using the cationic 123I-labeled serine proteinase inhibitor antileukoproteinase (123I-ALP; pI > 10), which selectively accumulates in normal cartilage, presumably through interaction with negatively charged proteoglycans. METHODS: Iodine-123-ALP or 123I-myoglobin, a control protein of comparable size but with different isoelectric point (pI=7.3) was injected intravenously into normal or AIA rats. Joint accumulation was followed by scintigraphy for 14 hr. Tissue radioactivity was assessed by well-counter measurements after dissection. The content of charged molecules in articular cartilage was determined by toluidine blue staining; the degree of joint destruction was assessed in parallel by x-ray, ex vivo MRI and histopathology. RESULTS: In intact articular cartilage, ALP accumulated to a significantly higher degree than myoglobin. This preferential accumulation was lost in rats with chronic AIA. The target-to-background ratio for 123I-ALP negatively correlated with the loss of toluidine blue staining in cartilage, which documents depletion of charged matrix molecules (r=-0.92, p < 0.01 at 4 hr; r=-0.97, p < 0.01 at 13 hr). ALP scintigraphy was sensitive in detecting cartilage alterations, even though the degree of joint destruction and inflammatory infiltration was mild, as demonstrated by x-ray, MRI and histopathology. CONCLUSION: In rat AIA, loss of ALP accumulation appears to document proteoglycan depletion in mildly altered arthritic cartilage. ALP scintigraphy may represent a functional assay for early, premorphological cartilage alterations in human arthritis as well.     

Analytic approximation of the jitter incurred by CBR traffics in IP networks

In this paper, an analytic approximation is derived for the end-to-end delay-jitter incurred by a periodic traffic with constant packet size. The single node case is considered first. It is assumed that the periodic traffic is multiplexed with a background packet stream under the FCFS service discipline. The processes governing the packet arrivals and the packet sizes of the background traffic are assumed to be general renewal processes. A very simple analytical approximation is derived and its accuracy is assessed by means of event-driven simulations. This approximation is then extended to the multiple node case yielding a simple analytical approximation of the end-to-end jitter. This approximation is shown to be fairly accurate in the light to moderate traffic conditions typically encountered in IP core networks.     

Precipitate formation contributing to sump screens clogging of a nuclear power plant during an accident

For many years, the French “Institut de Radioprotection et de Sûreté Nucléaire” has developed studies concerning chemical effects, which can occur during a loss of coolant accident (LOCA) on a nuclear power plant, due to precipitate formation leading to an increase of head loss to sump screens. This increase can cause the loss of emergency core cooling system (ECCS) and of the containment spray system (CSS), which are the two removal heat safety systems which ensure the accident mitigation.These precipitates are formed by recombination of mineral species, which are released due to corrosion of immersed debris (particles of concrete, glass fibre insulation, piece of paint…). PHREEQC software has been used to identify nature and mass of precipitates that can be formed during a LOCA.This report presents the results of sensitivity studies carried out with PHREEQC. Chemical precipitate formation is studied as a function of several physical parameters, such as temperature, pH, nature and debris concentration. The optimal conditions in order to reduce the formation of precipitates are drawn from these calculations.     

Delay Bounds for Voice over IP Calls Transported over Satellite Access Networks

Whether or not voice calls of traditional quality can be supported between two users connected to an IP backbone via satellite access systems depends largely on the mouth-to-ear delay, an important part of which is consumed by the satellite networks themselves. In this paper, a methodology is developed to calculate upper bounds for the latter delay component as a function of the used codec, the experienced packet loss ratio, the echo levels at both sides of the connection and the chosen voice packet size. Illustrations are provided.     

Contrast enhancement and distributed encoding by bipolar cells in the retina

Responses of bipolar cells, cone photoreceptors, and horizontal cells were recorded intracellularly in superfused eyecup preparations of the tiger salamander (Ambystoma tigrinum). Contrast flashes of positive and negative polarity were applied at the center of the receptive field while the entire retina was light adapted to a background field of 20 cd/m2. For small contrasts, many bipolar cells showed remarkably high contrast gain: up to 15-20% of the bipolar response was evoked by a contrast step of 1%. There was considerable variation from cell to cell but, on average, no striking differences in contrast gain were found between the depolarizing (Bd) and hyperpolarizing (Bh) bipolar cells. Quantitative comparisons of contrast/response measurements for cone photoreceptors and cone-driven bipolars suggest that the high contrast gain of bipolars is the consequence of a 5-10 x amplification of small signals across the cone-->bipolar synapse. Bipolar cells had a very restricted linear range of response and tended to saturate at stimulus levels that were within the linear range of the cone response. The contrast/response of horizontal cells was similar to that of cones and differed markedly from that of Bh cells. For steps of equal contrast, the latency of the Bh cells was approximately 20 ms shorter than that of the Bd cells regardless of the contrast magnitude. For both bipolar cells and cones, the effect of contrast polarity on latency seems largely due to the absolute value of the light step, delta L. In the large signal domain, properties of the contrast responses of bipolar cells varied appreciably, both within and between the Bd and Bh classes. Cells of either class could be positive- or negative-contrast dominant. These and additional results show that in the light-adapted retina, the bipolar population is functionally diverse and has the potential to provide a rich substrate for distributed encoding of visual images.