Determinants of serum leptin levels in Cushing's syndrome

Corticosteroids and insulin increase leptin expression in vivo and in vitro. To investigate whether increased serum cortisol influences serum leptin concentrations in humans, we analyzed fasting serum leptin and insulin levels in 50 patients with Cushing's syndrome [34 female patients: 27 with the pituitary form and 7 with the adrenal form; age, 41.6 +/- 2.7 yr; body mass index (BMI), 29.6 +/- 1.2 kg/m2; 16 male patients all with the pituitary form; age, 39.2 +/- 3.1 yr; BMI, 26.3 +/- 2.3 kg/m2] and in controls matched for BMI, age, and gender. Serum leptin levels were higher in female than in male patients in both the Cushing (P < 0.01) and control (P < 0.001) groups. Disease-specific differences in serum leptin levels were only detected in male (106 vs. 67 pmol/L; Cushing's syndrome vs. control, P < 0.05), not female, patients. Multiple stepwise regression analysis of both patient groups revealed insulin as the best predictor of serum leptin concentrations, accounting for 37% of the variance in serum leptin levels, in contrast to BMI or mean serum cortisol (as measured by sampling in 10-min intervals over 24 h). In the subgroup of patients (n = 9) with pituitary adenoma, serum leptin levels were reduced after tumor resection, with concurrent decreases in serum cortisol, insulin, and BMI. In conclusion, chronic hypercortisolemia in Cushing's syndrome appears not to directly affect serum leptin concentrations, but to have an indirect effect via the associated hyperinsulinemia and/or impaired insulin sensitivity.     

Intestinal parasite infections after extended use of chloroquine or primaquine for malaria prevention

Comparative results of baseline and endpoint screening for intestinal parasites are reported from Javanese men enrolled in a year-long, placebo-controlled malaria prophylaxis trial in Irian Jaya. The objective was to detect nontarget qualitative changes that may have resulted from prolonged chloroquine (300 mg base weekly) or primaquine (0.5 mg base/kg daily) prophylaxis. Fresh fecal specimens were examined (blinded trial) for parasites and ova using a modified Kato-Katz thick smear method. More than 88% (94/106) of the baseline population was infected by 1 or more parasite species of which hookworm and Blastocystis hominis were dominant. Paired comparison between baseline and endpoint revealed no significant changes within the primaquine or chloroquine groups with regard to the variety of species found, the mean number of species or ova/subject, the relative proportion of infections caused by these species, or the occurrence of parasite-free, single, and multiple infections. Relative to placebo, there was a significantly greater proportion of infections by Entamoeba histolytica/dispar and a lower mean hookworm egg count in the chloroquine group. The endpoint proportion of new or increased infections in the primaquine group was significantly lower than that of the chloroquine group but comparable to that of the placebo. Despite the dosage employed, the frequency and duration of use, and excretion primarily through the bowels as the active parent compound, primaquine appeared to have little or no significant effect against a variety of common intestinal parasites. These largely negative results lend support for the safety and acceptability of primaquine as a daily malaria prophylactic in a population frequently at risk of intestinal helminth infections.     

Electrorheological and Magnetorheological Duct Flow in Shear-Flow Mode Using Herschel-Bulkley Constitutive Model

A quasi-steady duct flow through a parallel plate model for electrorheological (ER) and magnetorheological (MR) fluids under shear-flow mode is investigated mathematically. To do so Herschel-Bulkley power law constitutive model for ER and MR fluid is adopted to account for postyield shear thinning or shear thickening conditions as indicated in recent research. This approach is selected in order to obtain a more flexible representation of ER or MR postyield behavior rather than using the mostly adopted Bingham plastic model. This will lead to developing a theoretical method for prediction of ER or MR force characteristics.     

Failure mode analysis of oxide VCSELs in high humidity and high temperature

High-speed fiber-optic transceiver modules using parallel optics require that oxide-confined vertical-cavity surface-emitting lasers (VCSELs) be moisture resistant in a non-hermetic package. We have found that the conventional storage 85/85 (85/spl deg/C/85% relative humidity) test does not adequately characterize oxide VCSELs moisture resistance. We have identified three failure modes in the oxide VCSELs under operating conditions in high humidity. In this paper, we discuss the failure mechanisms including dislocation growth, semiconductor cracks, and aperture surface degradation, all associated with operation under high relative humidity. Understanding of these failure modes has led to more appropriate qualification standards and environmentally robust oxide VCSELs.     

Performance issues in VC-merge capable switches for multiprotocollabel switching

In a multiprotocol label switching (MPLS) domain, ATM label-switching routers (LSRs) are potentially capable of providing the highest forwarding capacity in the backbone network. Virtual circuit (VC) merging is a mechanism in an ATM-LSR that allows many IP routes to be mapped to the same VC label and provides a scalable mapping method that can support thousands of destinations. VC merging requires reassembly buffers so that cells belonging to different packets intended for the same destination do not interleave with each other. In this paper, the impact of VC merging on the buffering requirement for the reassembly buffers is investigated. We propose a realistic architecture that supports VC merging. We study the performance of this architecture using an analytic approach and using simulation driven by empirical Internet packet-size distribution. At the cell level, our main finding indicates that VC merging incurs a minimal overhead compared to non-VC merging, in terms of additional buffering. Moreover, the overhead decreases as utilization increases or as the traffic becomes more bursty with longer dependence. The finding has important practical consequences since routers and switches are dimensioned for high utilization and stressful traffic conditions. At the packet level, VC merging generally achieves a higher goodput than non-VC merging with EPD for the same buffer size. We also study the delay performance and find that the additional delay due to VC merging is insignificant at high speed     

Oxidation of methane over Pd/mixed oxides for catalytic combustion

Palladium catalysts supported on mixed oxides (Pd/Al₂O₃–MO_x; M=Co, Cr, Cu, Fe, Mn, and Ni) were investigated for the low-temperature catalytic combustion of methane. Although the surface area decreased with increasing NiO in Pd/mAl₂O₃–nNiO, Pd/Al₂O₃–36NiO demonstrated an excellent activity due to the small particle size of palladium. Also, the catalytic activity strongly depended on the composition of the support. Temperature-programmed desorption of oxygen revealed that the catalytic activity in the low-temperature region depends on the adsorption state of oxygen on palladium. The activity was enhanced when the amount of adsorbed oxygen increased. In-situ XRD analysis indicated that the PdO phase was thermally stabilized on Pd/Al₂O₃–36NiO.     

Switching dynamics of IGBTs in soft-switching converters

Next generation of power semiconductor devices will be designed and optimized to meet the specific application requirements. Mixed-mode simulations are used to study the carrier dynamics in punch-through and nonpunch-through Insulated Gate Bipolar Transistor (IGBT) structures during soft- and hard-switching conditions. The simulation results are shown to qualitatively predict the measured bump in the tail current with varying output dv/dt conditions and excessive forward conduction voltage under varying di/dt conditions. A new physical effect termed “conductivity modulation lag” is shown to occur during turn-on under soft-switching conditions. This mechanism is caused by the fact that minority carrier injection into the base of the bipolar transistor significantly lags behind the rate at which drift region conductivity can be modulated. The proposed phenomenon leads to an inductive effect that results in dynamic voltage saturation during turn-on and causes excessive forward voltage drop     

IP router using optical address recognition with second-harmonic generator

A novel optical header address recognition using a second-harmonic generator cascaded with optical correlator is proposed as a cost-effective way of realising routing in optical networks. The second-harmonic generator is used for minimising optical loss due to wavelength mismatch, while the optical correlator performs address recognition.