Analysis of delay mean and variance of collision-free WDM rings with segment recirculation of blocked traffic

In Tunable-Transmitter Fixed-Receiver (TT-FR)-based Wavelength Division Multiplexed (WDM) ring topologies, each node is provided with a dedicated wavelength (home channel) for reception, which must be shared by the upstream nodes willing to communicate with it. Thus, to avoid channel collisions, it is necessary to define a Medium Access Control (MAC) mechanism that arbitrates access to a given destination wavelength. This work proposes and analyses a simple MAC mechanism that avoids channel collisions by recirculating traffic on the upstream ring segment where congestion was detected. Essentially, whenever a given node has got any traffic to transmit, it must first block access to in-transit traffic, which is reflected back to the upstream node over a second optical fibre. Such blocked traffic is given a second chance to pass through the congested node after a round segment delay, thus making use of the ring topology as buffering units. This work analyses the performance operation of such a MAC protocol under two policies applied to recirculated traffic: (1) recirculation bypass and (2) recirculation store-and-forward.     

Modeling of the radiation field in a parabolic trough solar photocatalytic reactor

We calculate the distribution of absorbed radiation inside a solar photocatalytic reactor, by means of radiative transfer theory. The reactor configuration is that of a glass tube illuminated by a parabolic trough collector, where the catalyst consists of titanium dioxide micro-particles suspended in water. The calculations are made within the framework of the P1 approximation, which allows to solve analytically the radiative transfer equations. The obtained solution is used to study the effect of catalyst concentration on the degradation of pollutants, by means of a general kinetic model. The results obtained display the main features which are observed in experiments reported in the literature.     

Measuring and interpreting the lifetime of silicon wafers

The carrier lifetime is the most important electronic property of semiconductor materials for solar cells. In this paper we discuss traditional and novel methods for its experimental determination. Among the latter, the Quasi-steady-state photoconductance is particularly powerful since it permits measuring the injection level dependence of the lifetime. The analysis and interpretation of this dependence yields a wealth of information on the physical mechanisms that limit the performance of silicon solar cells. The effect of the surfaces of the silicon wafers, the emitter saturation current density and the Shockley–Read–Hall and Auger recombination mechanisms are explained and their possible determination from lifetime measurements discussed.     

Degradation processes in Al/SiCp/MgAl2O4 composites prepared from recycled aluminum with fly ash and rice hull ash

The degradation characteristics of Al/SiC_p/spinel composites prepared with fly ash (FA) and rice hull ash (RHA) under environmental conditions were investigated. Composite specimens were prepared with recycled aluminum via reactive infiltration in the temperature range 1050–1150 °C for 50–70 min and, in argon atmosphere at a pressure slightly above that of the atmospheric pressure. Results reveal that although both FA and RHA help in preventing SiC_p dissolution and the subsequent chemical degradation of the composites, due to the interaction of native carbon in FA with liquid aluminum, FA‐composites are susceptible to corrosion via Al₄C₃. Moreover, this phase accelerates the degradation process and increases the damage severity. The primary corrosion mechanism in both types of composites is attributed to microgalvanic coupling between the intermetallic Mg₂Si and the matrix. Accordingly, an appropriate control of the Si/(Si + Mg) molar ratio in the aluminum alloy hinders the Mg₂Si corrosion mechanism in both types of composites and a proper FA calcination prevents chemical degradation in FA composites.     

Morphogenesis of the Drosophila fusome and its implications for oocyte specification

The Drosophila oocyte develops within a cyst of 16 germline cells interconnected by ring canals. Polarized, microtubule-based transport of unknown determinants is required for oocyte formation, but whether polarity is established during or after cyst formation is not clear. We have analyzed how polarity develops in stem cells and dividing cysts by following the growth of the fusome, a vesiculated cytoplasmic organelle. Our studies show that the fusome grows by a regular, polarized process throughout the stem cell and cyst cell cycles. Each polarization cycle begins in mitosis, when the fusome segregates to a single daughter cell of each pair. Following mitosis, a 'plug' of fusomal material forms in each nascent ring canal and gradually fuses with the pre-existing fusome. In stem cells, the ring canal is transient and closes down after the fusome is partitioned through it. In dividing cysts, as the fusome plugs move toward the pre-existing fusome, their associated ring canals also move, changing the geometry of the cyst. At the end of each cycle of cyst growth, the fusome remains asymmetrically distributed within the cyst; one of the two cells with four ring canals retains a bigger piece of fusome than any other cell, including the other cell with four ring canals. Based on these observations, we argue that the oocyte is specified at the first cyst division.     

Eosinophilic lung disease associated with Candida albicans allergy

PURPOSE: We evaluate the effect of the provision of postgraduate educational material on improving practitioner knowledge base during a 3-year period. MATERIALS AND METHODS: A total of 210 urologists were provided 67 monographs in a 2-year period. They were given a pretest before and posttest 1 year after receipt of all monographs. RESULTS: There was significant improvement in posttest scores for the group as a whole. Improvement correlated with years post-training and number of monographs read. Multivariate analysis revealed the number of monographs read was the only independent predictor of outcome. CONCLUSIONS: Although the improvement in test scores was significant and did correlate with the postgraduate educational material read, it was modest. This finding raises significant concerns about the usefulness of this format for graduate medical education.     

Cross-cultural differences in the perception of the emotional content of speech: A study of the development of sensitivity in Canadian and Mexican children.

Examined and compared the ability of Canadian and Mexican children to identify the emotional content of vocal expressions. Ss were 10 males from each country at each age 6-11 yrs. 10 male Canadian and 10 male Mexican undergraduates also served as Ss. Canadian and Mexican actresses, speaking any words they wished in their respective languages, simulated the emotions of happiness, sadness, love, and anger. After the initial recording, speech samples were arranged in random order and then rendered unintelligible by means of an electronic filtering device (which removed semantic content while leaving intact the tonal qualities of speech). When the filtered vocal expressions were played to Ss, a progressive increase with age in ability to identify correctly the emotions expressed was found. Further, the Mexican Ss overall were significantly more sensitive than the Canadian Ss. However, Ss from both countries judged the speech samples from Mexican actresses more accurately than those from Canadian actresses. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Moderately doped NMOS (M-LDD)-hot electron and current driveoptimization

Short-channel NMOS transistors with moderately doped drain (10¹⁴ cm^-2), and variable sidewall oxide spacer thickness were fabricated and studied. The sensitivities of hot carrier degradation, current drive capability, and other device parameters to the sidewall spacer thickness were measured and evaluated. The results clearly indicate that a moderately doped drain (M-LDD) provides a stable and well-optimized device, compared to a conventional LDD transistor with substantially lower implant dose. A simple model, explaining the observations, is proposed and discussed     

Influence of risk factors and pharmacological treatment on mortality in patients with essential hypertension

BACKGROUND: The V JNC consensus stated that although new antihypertensive agents, such as angiotensin converting enzyme inhibitors and calcium channel blockers, are considered safer drugs, there is no firm evidence from large controlled trials that these drugs are associated with a lower cardiovascular mortality. AIM: To study the association between cardiovascular risk factors, blood pressure levels, pharmacological treatment and mortality in a group of hypertensive patients followed at an hypertension outpatient clinic. PATIENTS AND METHODS: Patients with essential hypertension were treated with different antihypertensive medications, according to physicians criteria, and controlled until death or loss from follow up. Causes of death were obtained from hospital records and death certificates. Survival was analyzed using life tables, comparisons between groups of patients were done using chi square or a Cox's proportional hazards model. RESULTS: Three hundred thirty-nine hypertensive patients aged 33 to 80 years old were followed for a mean period of 9.8 +/- 4.9 years. Eighty-six were treated with beta blockers, 64 with diuretics, 133 with calcium antagonists and 56 with ACE inhibitors. Blood pressure dropped similarly with all medications. During follow up, 79 patients died. Life table analysis showed that patients with a history of angina, diabetes or myocardial infarction had higher mortality rates. Similarly, patients treated with beta blockers and diuretics had higher mortality than patients treated with calcium antagonists or angiotensin converting enzyme inhibitors. The proportional hazards model showed that the effect of treatment modality persisted after correction for the other risk factors for mortality. CONCLUSIONS: In this series of hypertensive patients, those treated with beta blockers or diuretics had higher mortality rates than those receiving calcium channel antagonists or angiotensin converting enzyme inhibitors.