An analysis of multiple parallel coupled quasi-tem transmission lines

A theoretical analysis of general multiple parallel coupled transmission lines in an inhomogeneous medium is presented. The analysis is based on the generalized telegraphists' equation. It is relatively simple and has the advantage of giving explicit solutions for the properties of the coupled-line system. Considerations are also given to a coupled-line structure whose lines have the same characteristic impedance. Results for two and three coupled lines are found in agreement with those published previously.     

X gene and precore region mutations in the hepatitis B virus genome in persons positive for antibody to hepatitis B e antigen: comparison between asymptomatic "healthy" carriers and patients with severe chronic active hepatitis

Hepatitis B virus (HBV) carriers with antibody to hepatitis e antigen comprise asymptomatic carriers (ASCs), who have low replication levels of HBV, and patients with chronic active hepatitis (CAH), who have high levels of viral replication. To investigate whether defects in the X protein might be responsible for this difference in the level of viral replication, nucleotide sequences of X and precore gene regions in serum HBV were analyzed in 19 ASCs and 9 CAH patients. All patients had a point mutation creating a stop codon in the precore region. Seventeen ASCs (87.3%) had identical mutations consisting of 4 noncontiguous 1-bp deletions or an 8-bp deletion, both of which truncate the normal X protein, whereas no CAH patient had an X gene mutation (P < .001). Thus, deletion of the X protein might be responsible for the low levels of viral replication in ASCs.     

Prolongation and enhancement of postischemic c-fos expression after fasting

BACKGROUND AND PURPOSE: A rapid but transient expression of c-fos after cerebral ischemia has been extensively documented. However, the mechanism of this induction and whether induction of c-fos is neuroprotective or detrimental to the brain after ischemia is presently not clear. Fasting before transient cerebral ischemia has been shown to reduce delayed neuronal necrosis and infarct volume. The purpose of the present study was to examine the effect of preischemic fasting for 24 hours on the expression of c-fos after transient focal cerebral ischemia. METHODS: Focal cerebral ischemia was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries for 60 minutes. Male Long-Evans rats weighting 250 to 300 g were randomly divided into two groups: fed (control group) and food deprived for 24 hours (fasted group) before ischemic surgery. Infarct volumes were measured on the basis of triphenyltetrazolium chloride-delineated infarct areas, and plasma glucose levels were determined by the glucose oxidase method. Temporal and spatial expression of c-fos was assessed by Northern blot analysis, in situ hybridization, and immunohistochemistry. RESULTS: Fasting for 24 hours before 60 minutes of ischemia resulted in a 26.6% decrease in preischemic plasma glucose levels and a 74.5% reduction in infarct volumes in the fasted group compared with the control group. A rapid but transient induction of c-fos mRNA was observed in the ischemic cortex in control animals after 60 minutes of ischemia. Fasting not only prolonged but also enhanced the intensity of c-fos expression in the ischemic cortex. Regional c-fos expression was also different between these two groups. CONCLUSIONS: The results support the contention that c-fos expression may be compatible with its purported neuroprotective role in selected experimental paradigms. The signaling mechanisms underlying the effect of fasting and subsequent lowering of plasma glucose levels on postischemic c-fos expression remain to be explored.     

应用线性相关分析方法探讨国土卫片几何畸变纠正的精度

我国卫星影像具有空间分辫率高，比例尺适中的特点。由于国土片是全.景成像比例尺变化大，用它来编绘专业地图，给精度衡蚤带来很大困难，需要对国土片进行几何校正。本文试图用线性相关分析方法，分析经过AR月尧卜n图像处理系统刘正的国土片几何精度。以便为分析专题图精度提供依据，同时也为分析遥感影像几何精度介绍一种方法。     

Development of Online Ultrasound Instructional Module and Comparison to Traditional Teaching Methods

A Web‐based teaching device was constructed to deliver information on fundamentals of ultrasound imaging to approximately one‐half the students in an undergraduate medical imaging course, while the remaining students were taught the same material via traditional lectures and typed notes. The students participating in this study were separated randomly but in such a manner that prior achievement was statistically equivalent for the two groups. After approximately two weeks of instruction, an ultrasound imaging exam was administered. Results indicated no statistically significant difference in scores on homework assigned during the instructional period between the traditional and online groups. Similarly, there was no statistically significant difference in the average exam scores of students in the two groups. The traditional group required significantly more time on learning activities than did the online group. These results indicated that level of understanding was not affected by use of the online device, while efficiency of learning improved dramatically. Reasons reported by the students for the improved efficiency of the online method included flexibility in time usage and ability to cater to the individual, which came with the added responsibility of self‐discipline. The traditional teaching method, meanwhile, allowed interaction with and instant feedback from a professor and other students. In this study we have demonstrated that the nature of an online device yields a higher level of efficiency than traditional lectures, despite the inherent drawbacks of the approach. The effectiveness of this device could potentially be improved by implementing enhancements to increase the level of interaction for the user and to help with discipline and time management.     

Ion implantation doping of OMCVD grown GaN

Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have indicated a redistribution in the measured profiles of Mg due to annealing.     

On the Direct Addition of Amine N–H to Ch≡C Triple Bonds with Late Transition Metal Catalysts

The kinetics of the transition metal-catalysed direct addition of amine NH bonds to carbon--carbon multiple bonds (hydroamination) has been explored by in situ spectroscopic techniques. From an open mass balance it was concluded that an intermediate species was formed during the cyclisation of 6-aminohex-1-yne. This species was identified as the enamine 2-methylene-piperidine, which is the primary hydroamination product.     

Fast‐scale bifurcation in power‐factor‐correction buck‐boost converters and effects of incompatible periodicities

In this paper, we derive the discrete‐time model for the power‐factor‐correction (PFC) buck‐boost converter in terms of a stroboscopic switching map. Fast‐scale instability is analysed through a fold diagram, which exposes the periodicity of the operation as well as the locations of the critical phase angles of the line voltage at which instability begins to occur along a half‐line cycle. The asymmetrical locations of the critical phase angles along a half‐line cycle is explained in terms of ‘under‐developed’ bifurcation. Border collision bifurcations are observed and analysed in detail. Copyright © 2006 John Wiley & Sons, Ltd.     

New compact wideband bandpass filter using three parallel-coupledlines

A new miniature bandpass filter, comprising three-conductor short-circuited spurline resonators of approximately a quarter-wavelength long, with a very wide bandwidth approaching multioctaves is reported for the first time. The chain matrix of the filter resonator is derived. The new filter has been developed using microstrip line with less than 1 dB insertion loss over a passband from 2 to 8 GHz. Reasonably good agreement between the measured and calculated results is observed     

Structure and Magnetic Properties of LaCo_(13-X)M_X Intermetallic Compounds

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