Analysis of a new power electronics interface with approximatelysinusoidal 3-phase utility currents and a regulated DC output

A three phase rectification scheme that draws line currents with reduced distortion and provides a regulated DC output voltage is analyzed. The scheme employs two boost DC-DC converters to modulate the DC link currents. The modulation current is injected into the AC side through an impedance network consisting of series tuned L-C branches. The theoretical analysis and the basic simulation results, which can be used to carry out the design of a system based on this approach, are presented     

Simulation of power electronic and motion control systems-anoverview

This paper presents a users' perspective of simulation in power electronic and motion control systems. The rationale for simulation in research, education and in the design process, and the details of how simulation is carried out are discussed. Characteristics of a reliable simulation program are outlined and the hierarchical approach to simulation is stressed. Numerical solution issues in the simulation of “stiff” systems such as power electronics and motion control are discussed in general terms. A brief overview of the widely used simulation programs is provided along with the challenges in modeling the semiconductor devices. In conclusion, observations are made with respect to the future role and nature of computer simulations     

Selectively meshed surface representation

Surface rendering is an important technique for volume visualization. Any surface rendering algorithm has two phases—surface generation and rendering. We present a new surface rendering algorithm, which focuses on constructing the surface in a manner that speeds up the rendering phase. The motivation behind this is to reduce the response time for surface manipulations such as interactive rotations. We utilize a MC-like (Marching Cubes) approach to calculate the intersection points and their normals for each cube. But we dynamically link the intersection points to form triangles within the cube according to the locations of the last and the next visited neighboring cubes so that a good meshed surface can be generated. The difficulty with such an approach is that thousands of special cases need to be considered. But, we have found that the occurrence of five specific configurations out of the 14 basic MC cube configurations account for over 95% of all the cubes intersected by the iso-surface in most data sets. We process cubes belonging to these five configurations in a mesh mode, and the rest are processed in a non-mesh mode. As a result, the number of special cases are reduced substantially. Then a very careful analysis of the five configurations for mesh processing leads to just 136 cases, which makes the algorithm very simple. Test results show that the rendering time is almost halved compared to the time required for the rendering of a non-meshed surface generated by MC.     

Clinical, virologic and immunologic responses of children with advanced human immunodeficiency virus type 1 disease treated with protease inhibitors

OBJECTIVE: To determine the effects of combination antiretroviral therapy including a protease inhibitor (PI combination therapy) in children with advanced HIV-1 disease. STUDY DESIGN: An observational study of HIV-1 plasma RNA, lymphocyte subsets, delayed type hypersensitivity and physical growth after initiation of PI combination therapy. RESULTS: In nine children the median HIV-1 plasma RNA decreased 1.7 log10 (mean, 1.57; range, 0.7 to 2.2) following PI combination therapy and CD4 cells increased a median of 499 (mean, 528; range, 9 to 1088) cells/microl. A rebound of RNA, associated with the development of resistance to the PI, occurred in three subjects. Three of six children were no longer anergic and all nine achieved normal weight-growth velocities. Ritonavir was well-tolerated, despite its bitter taste; however, four of five children treated with indinavir developed renal complications. CONCLUSIONS: PI combination therapy in children with advanced HIV-1 disease was associated with a decrease in HIV-1 RNA, improved immunologic measures and normal or better weight gain. Of concern was the rebound in plasma HIV-1 associated with resistance to the PI observed in one-third of patients. This emphasizes the need for larger studies to define optimal PI containing regimens with long term efficacy in children.     

Insulin-like growth factor binding protein production in bovine retinal endothelial cells

Retinopathy is the most frequent microangiopathic complication in diabetes. Many circulating hormones and locally produced mitogenic factors have been involved. Bovine retinal endothelial cells (BRECs) were cultured to investigate if insulin, insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs), and a chronic high-glucose condition could control endothelial cell growth. Specific IGF-I receptors with two binding sites with high (Kd 0.03 nmol/L) and low (Kd 1.3 nmol/L) affinity were found when analyzing families of displacement curves between IGF-I versus IGF-I and IGF-I versus insulin. However, IGFs failed to be mitogenic factors in these cells. This could be explained by an inhibitory effect due to the presence of specific IGFBPs with a molecular weight between 24 and 43 kd. Using Western blot and immunoblot analysis, Northern blot study, and specific radioimmunoassay (RIA), these IGFBPs have been identified as IGFBP-3, -2, -5, and -4. Insulin, which does not bind to IGFBPs, was a potent mitogenic factor in these cells at a high concentration (10 nmol/L), suggesting a cross-reaction to IGF-I receptor. These IGFBPs, except the 24-kd form (IGFBP-4), were modulated by both IGF-I and IGF-II, with a maximum effect at 100 and 10 nmol/L, respectively. This regulation on IGFBPs was IGF-I receptor-independent. In fact, (1) IGFBP mRNA levels were not modified after stimulation with 100 nmol/L IGF-I, (2) 100 nmol/L IGF plus an equimolar concentration of alpha IR3 did not affect IGFBP production, (3) Des(1-3)IGF-I had no effect on IGFBP modulation, whereas at 10 nmol/L it enhanced BREC thymidine cell incorporation, and (4) 100 nmol/L insulin, which at this concentration can cross-react with the IGF-I receptor, did not modify the IGFBP pattern. Chronic exposure (4 weeks) of BRECs to 25 mmol/L glucose had no effect on cell growth. However, after 3 weeks, we observed a decreased IGFBP detection, and addition of 100 nmol/L IGF-I did not change IGFBP levels and did not modify cell growth. Conversely, BRECs grown in regular medium for 4 weeks showed increased IGFBP production. In conclusion, we showed that conditions mimicking hyperinsulinemia, rather than high levels of IGFs, could regulate BREC growth and that the IGF-I analog, Des(1-3), even with reduced affinity for IGFBPs but in part capable of binding to IGFBP-3, significantly stimulated BRECs growth only at 10 nmol/L. IGF actions are modulated by locally produced endothelial IGFBPs, and in turn, these endothelial IGFBPs are regulated, via in IGF-I receptor-independent mechanism, by the presence of IGFs. The autoregulatory IGF system together with the direct glucose modulation of IGFBPs could contribute in diabetic subjects to the retinal endothelial cell growth and metabolism through local changes in IGF bioavailability.     

Studies on laser-induced irreversible surface softening in a thermoset polymer of allyl diglycol carbonate (CR-39)

It is shown that controlled irreversible surface softening can be obtained in thermoset polymer of allyl diglycol carbonate (CR-39) without degrading its bulk properties on treating it with a cw-CO₂ laser. An average value of the threshold fluence for the onset of softening is found to be about 9 J/cm², which changes slightly with the interaction time and power density of the laser beam. Beyond this threshold the hardness of the treated surface decreases on increasing the power density and/or the interaction time till the onset of volatile decomposition in this polymer, which takes place at the laser fluence of 25 J/cm². Thereafter, the hardness tends to saturate at nearly 60% of its original value for the untreated surface. Formation of a new heterogenous interlinked porous microstructure has been observed in the laser softened polymer surface. Solution of the 1-dimensional heat flow equation incorporating the temperature-dependent decomposition energy of CR-39 has shown that at 9 J/cm² the surface attains the maximum temperature of about 280°C and then cools at a rate of about 10³°C/s. The starting value of the surface cooling rate increases with the fluence. A part of the absorbed energy goes in for the depolymerization, which is found to increase from about 0.004 to 4.5 J/cm² when the laser fluence is increased from 9 to 25 J/cm². The laser-induced depolymerization and subsequent rapid cooling of the surface explain the observed effects.