Low noise wide bandgap SiC based IMPATT diodes at sub-millimeter wave frequencies and at high temperature

We have presented a comparative account of the high frequency prospective as well as noise behaviors of wide-bandgap 4H-SiC and 6H-SiC based on different structures of IMPATT diodes at sub-millimeter-wave frequencies up to 2.18 THz. The computer simulation study establishes the feasibility of the SiC based IMPATT diode as a high power density terahertz source. The most significant feature lies in the noise behavior of the SiC IMPATT diodes. It is noticed that the 6H-SiC DDR diode shows the least noise measure of 26.1 dB as compared to that of other structures. Further, it is noticed that the noise measure of the SiC IMPATT diode is less at a higher operating frequency compared to that at a lower operating frequency.     

Shear waves in a fluid saturated elastic plate

In the present context, we consider the propagation of shear waves in the transverse isotropic fluid saturated porous plate. The frequency spectrum for SH-modes in the plate has been studied. It is observed that the frequency of the propagation is damped due to the two-phase character of the porous medium. The dimensionless phase velocities of the shear waves have also been calculated and presented graphically. It is interesting to note that the frequency and phase velocity of shear waves in porous media differ significantly in comparison to that in isotropic elastic media.     

Wavelet fuzzy combined approach for fault classification of a series-compensated transmission line

Series capacitor protected by metal-oxide varistor and air-gap arrangement imposes problems to line protection and other online decisions. Discrete wavelet transform integrated with a fuzzy logic system is designed for fault classification of a transmission line possessing a series capacitor at the midpoint. The approach uses information obtained from the wavelet decomposition of current signals for faulty phase selection and section identification. Two different FLSs are designed for the two classification objectives in this paper.     

Chronic phenytoin induced impairment of learning and memory with associated changes in brain acetylcholine esterase activity and monoamine levels

Groups of adult, male, Wistar rats were administered phenytoin (DPH) at 5, 12.5, 25, 50, or 75 mg/kg i.p. for 21 days. The learning and memory of these rats were assessed using the T-maze and passive avoidance tests. The plasma DPH levels, acetylcholine esterase (AChE) activity in different brain regions, and the levels of monoamines in the hippocampus were measured. The results indicate that DPH below the therapeutic plasma level did not significantly impair learning and memory. Correspondingly, no changes were noted in the brain 5-HT or AChE activity. However, DPH, at therapeutic plasma concentrations (i.e., 10.5 micrograms/ml in the dosage range of 50 and 75 mg/kg, respectively), significantly impaired learning and memory in rats. The impaired learning and memory functions were associated with increased 5-HT levels and decreased AChE activity in the hippocampus. With a dose of 75 mg/kg DPH, there was a reduction in the AChE activity in the striatum, in addition to hippocampus. It is conjectured that the neurochemical changes brought about by DPH at therapeutic plasma levels may account for the impairment of learning, memory, and cognitive functions in epilepsy.     

Kinetics of alkylation of phenol with methanol over Ce-exchanged NaX zeolite

The alkylation of phenol with methanol was investigated in vapor phase over a series of cerium-exchanged NaX zeolite with Ce loadings ranging from 0 to 10.43 wt%. The catalyst MX-4 with 8.86 wt% cerium was found to be the best one with total cresols selectivity of 72% at a temperature of 573 K and MeOH to phenol mole ratio of 4:1. The catalyst was also found to be quite stable in the operating range investigated. It was established that the stronger acid sties are required for C-alkylation compared to O-alkylation. From the study of the effects of various parameters, the optimum operating condition for highest cresols selectivity were determined as: MeOH to phenol mole ratio, 4:1; temperature, 623 K; space-time, 10.2 kg h/kgmole under atmospheric pressure. From the kinetic analysis of the experimental data, the apparent activation energy for the reaction was determined as 57.2 kJ/mole.     

Shape forming of ceramics via gelcasting of aqueous particulate slurries

Gelcasting is a promising technique for shape forming of bulk dense or porous ceramic, metal structures. The process offers a number of advantages over processes such as slip casting, injection molding in forming complex ceramic shapes. It is shown here that the optimization of slurry rheology, choice of mold material, mold design and the drying conditions have a significant role in the overall success of the process. In this process, components of simple or complex shapes can be produced to near net shape by direct casting. If required complex shapes can also be produced by machining the green gelcast bodies. The process of gelcasting also has a lot of potential in forming highly porous ceramic shapes.     

The gastrin-releasing peptide receptor is differentially coupled to adenylate cyclase and phospholipase C in different tissues

A magnetization-prepared sequence, T2-Prep-IR, exploits T1, T2, and chemical shift differences to suppress background tissues relative to arterial blood. The resulting flow-independent angiograms depict vessels with any orientation and flow velocity. No extrinsic contrast agent is required. Muscle is the dominant source of background signal in normal volunteers. However, long-T2 deep venous blood and nonvascular fluids such as edema also contribute background signal in some patients. Three sets of imaging parameters are described to address patient-specific contrast requirements. A rapid, spiral-based, three-dimensional readout is utilized to generate high-resolution angiograms of the lower extremities. Comparisons with x-ray angiography and two-dimensional time-of-flight angiography indicate that this flow-independent technique has unique capabilities to accurately depict stenoses and to visualize slow flow and in-plane vessels.     

Pharmacology and intracellular signaling mechanisms of the native human orphan receptor BRS-3 in lung cancer cells

Neither the native ligand nor the cell biology of the bombesin (Bn)-related orphan receptor subtype 3 (BRS-3) is known. In this study, we used RT-PCR to identify two human lung cancer lines that contain sufficient numbers of native hBRS-3 to allow study: NCI-N417 and NCI-H720. In both cell lines, [DPhe6,betaAla11,Phe13, Nle14]Bn(6-14) stimulates [3H]inositol phosphate. In NCI-N417 cells, binding of 125I-[DTyr6,betaAla11,Phe13,Nle14]Bn(6-14) was saturable and high-affinity. [DPhe6,betaAla11,Phe13,Nle14]Bn(6-14) stimulated phospholipase D activity and a concentration-dependent release of [3H]inositol phosphate (EC50 = 25 nM) and intracellular calcium (EC50 = 14 nM); the increases in intracellular calcium were primarily from intracellular stores. hBRS-3 activation was not coupled to changes in adenylate cyclase activity, [3H]-thymidine incorporation or cell proliferation. No naturally occurring Bn-related peptides bound or activated the hBRS-3 with high affinity. Four different bombesin receptor antagonists inhibited increases in [3H]inositol phosphate. Using cytosensor microphysiometry, we found that [DPhe6,betaAla11,Phe13, Nle14]Bn(6-14) caused concentration-dependent acidification. The results show that native hBRS-3 receptors couple to phospholipases C and D but not to adenylate cyclase and that they stimulate mobilization of intracellular calcium and increase metabolism but not growth. The discovery of human cell lines with native, functional BRS-3 receptors, of new leads for a more hBRS-3-specific antagonist and of the validity of microphysiometry as an assay has yielded important tools that can be used for the identification of a native ligand for hBRS-3 and for the characterization of BRS-3-mediated biological responses.     

Value of anterior chamber lenses in developing countries. Results of a clinical study

There are estimated to be 20 million people blinded by cataracts, 80-90% of whom live in rural areas of developing countries where expert surgical resources are scarce. The majority of all cataract operations are still intracapsular extractions (ICCE). Aphakic correction using spectacles is problematical in developing countries. This study was undertaken to evaluate the safety of multiflex open loop anterior chamber intraocular lenses (AC IOLs). METHODS: A total of 2000 people attending Lahan Eye Hospital, South-east Nepal, with bilateral cataract were randomly allocated to receive in their first eye either ICCE with AC IOL (AC IOL group) or ICCE with aphakic correction (control group). All operations were performed by two ophthalmologists using a standardized technology and 4.5 x operating loupe magnification. Functional and best corrected vision was recorded. The primary outcome measure was poor vision after surgery, which was defined as a visual acuity of less than 6/60 at 1 year follow-up (WHO definition for severe visual impairment and blindness). FINDINGS: The median time needed to perform ICCE was 4.1 min and to perform ICCE with AC IOL 6 min. Of all study patients 91% were examined after 1 year. Five percent of the AC IOL group and 5.4% of the control group had a functional visual acuity of less than 6/60. Causes of reduced vision in the AC IOL group versus the control group were: correctable refractive error (22 vs 29), uveitis/secondary glaucoma (13 vs 2), endophthalmitis (4 vs 7), pre-existing eye diseases (4 vs 5), retinal detachment (0 vs 4), and corneal decompensation (0 vs 1). Of the control group, 24 patients were found to be functionally blind in the operated eye (vision < 3/60) because they did not wear their aphakic spectacles. Normal vision (WHO definition: > or = 6/18) was achieved best corrected in 89.9% of the AC IOL group and 93.2% of the control group. Analysis of additional long-term follow-ups (2-5 years post-operatively) has not yet been completed. INTERPRETATION: This study provides evidence that in developing countries well-manufactured multiflex open loop AC IOLs can be implanted safely by experienced ophthalmologists after routine ICCE, avoiding the disadvantages of aphakic spectacle correction.