Toward a practical performance index for predicting voltagecollapse in electric power systems

Voltage collapse is generally caused by either of two types of power system disturbances: load variations; and contingencies. A number of performance indices intended to measure the severity of the voltage collapse problem have been proposed in the literature. However, few of these performance indices can answer questions such as: “can the system withstand another 100 MVar increase on bus 11?” This paper presents a new performance index that provides a direct relationship between its value and the amount of load demand that the system can withstand before collapse. One of the features that distinguishes the proposed performance is its development in the load-demand space and its ability to answer questions such as: “can the system withstand a simultaneous increase of 70 MW on bus 2 and 50 MVAr on bus 6?” This feature makes the performance index readily interpretable to operators. Moreover, the computation involved in the proposed performance index is relatively inexpensive in comparison with those required in existing solutions. Simulation results on the IEEE 39-bus system and a 234-bus power system are presented with promising results     

A Radix-4 New Svobota-Tung Divider with Constant Timing Complexity for Prescaling

A new floating-point division architecture that complies with the IEEE 754-1985 standard is proposed in this paper. This architecture is based on the New Svoboda-Tung (NST) division algorithm and the radix-4 MROR (maximally redundant maximally recoded) signed digit number system. In NST division, the divisor and dividend must be prescaled. We summarize a general systematic method to accomplish the prescaling, and we also propose a hardware scheme such that the timing complexity is constant regardless of the bit length of the divisor. For the divider implementation, a new MROR signed digit adder with carry free characteristic is proposed for addition and subtraction, and this adder can improve the cycle time significantly. A 32-b/32-b radix-4 divider is thus designed in Verilog HDL; the simulation results show that this architecture is implementable using currently available libraries. The hardware complexity and performance of this divider is competitive with conventional SRT dividers.     

Blood lead levels in Taiwanese adults: distribution and influencing factors

Five-thousand nine-hundred thirteen Taiwanese adults were selected by multistage sampling methods to investigate environmental lead exposure in Taiwan. The blood specimens were distributed to six laboratories for blood lead levels (BLL) measurement. The mean BLL of the 5913 Taiwanese adults was 8.28 ± 5.39 μg/dl, with a maximum level of 57.6 μg/dl. The median was 7.0 μg/dl and 90th percentile was 15.0 μg/dl. BLLs were associated with gender, ethnic group, education level, smoking, alcohol consumption, herbal drug consumption, milk consumption, sources of drinking water, level of urbanization, and occupational lead exposure. These results showed that BLLs in Taiwanese adults were stable during the 2-year study. Most of the influencing factors were consistent with other studies, while local risk factors, such as Chinese herbal drug consumption are important ways of preventing the general population from overexposure to lead.     

Predictors of systemic embolism in patients with mitral stenosis. A prospective study

BACKGROUND: Most studies of the predictors of systemic embolism in patients with mitral stenosis have been retrospective. OBJECTIVE: To prospectively study factors associated with systemic embolism in mitral stenosis. DESIGN: Prospective cohort study. SETTING: University-affiliated medical institution with 3000 beds. PATIENTS: 534 consecutive patients with a mitral valve area of 2.0 cm2 or less; 132 patients were in sinus rhythm, and 402 were in atrial fibrillation. MEASUREMENTS: Nine clinical and 10 echocardiographic variables were assessed for prediction of systemic embolism over a mean (+/- SD) follow-up of 36.9 +/- 22.5 months. Diagnosis of systemic embolism was based on symptoms and signs (sudden onset of peripheral arterial ischemic or neurologic manifestations without prodromes) and on findings on computed tomography, angiography, and surgery. RESULTS: For patients in sinus rhythm, age (relative risk [RR], 1.12 [95% CI, 1.04 to 1.21]), the presence of a left atrial thrombus (RR, 37.1 [CI, 2.82 to 487.8]), mitral valve area (RR, 16.9 [CI, 1.53 to 187.0]), and the presence of significant aortic regurgitation (RR, 22.4 [CI, 2.72 to 184.8]) were positively associated with embolism. For patients in atrial fibrillation, previous embolism (RR, 3.11 [CI, 1.66 to 5.85]) was positively associated with embolism; percutaneous balloon mitral commissurotomy (RR, 0.37 [CI, 0.18 to 0.79]) was a negative predictor. CONCLUSIONS: It may be prudent to give anticoagulants not only to patients in atrial fibrillation and patients with previous systemic embolism but also to those showing a left atrial thrombus or significant aortic regurgitation on echocardiography. Early percutaneous balloon mitral commissurotomy may also help prevent systemic embolism in patients with mitral stenosis.     

Characterization of Ultrathin Dielectric Films With the Prism-Coupler Method

We demonstrate a technique of applying the prism-coupler method to the characterization of dielectric films that are too thin to support enough guided modes in air for the normal application of the method. The technique is based on applying suitable index-matching liquids on the surface of the thin film to increase the number of effective indexes available for the determination of the refractive index and the thickness of the film. With this technique, even thin films that do not support any guided modes in air can be characterized. We apply the technique to the characterization of polymer thin films as thin as 100-200 nm and discuss its performance and limitation     

Pharmacokinetic and pharmacodynamic evaluation of the potential drug interaction between venlafaxine and ethanol

Venlafaxine is a new antidepressant with a unique mode of action. Because many patients taking antidepressant therapy may self-medicate with ethanol, this study was undertaken to assess the possible pharmacokinetic and pharmacodynamic interactions between venlafaxine and ethanol. This randomized, double-blind, placebo-controlled, two-period crossover study was conducted with 16 healthy men. Multiple doses of venlafaxine (50 mg every 8 hours) or placebo were administered for 7 days. On days 5 and 7 a single dose of 0.5 g/kg of ethanol or a placebo solution was administered in a randomized fashion. Pharmacokinetic data indicated that ethanol administration did not affect the disposition of venlafaxine or O-desmethylvenlafaxine. Similarly, venlafaxine administration did not affect the pharmacokinetic disposition of ethanol. Ethanol produced its expected effects on the eight psychometric tests administered. Venlafaxine produced small effects on the results of the Digit Symbol Substitution Test, the Divided Attention Reaction Time, and the Profile of Mood States. No pharmacodynamic interaction was detected between venlafaxine and ethanol.     

Characterization of a peptide analog of a determinant of type II collagen that suppresses collagen-induced arthritis

Immunization of susceptible strains of mice with type II collagen (CII) elicits an autoimmune arthritis known as collagen-induced arthritis (CIA). One analogue peptide of the immunodominant T cell determinant, A9 (CII245-270 (I260-->A, A261-->B, F263-->N)), was previously shown to induce a profound suppression of CIA when coadministered at the time of immunization with CII. In the present study, A9 peptide was administered i.p., orally, intranasally, or i.v. 2 to 4 wk following CII immunization. We found that arthritis was significantly suppressed even when A9 was administered after disease was induced. To determine the mechanism of action of A9, cytokine responses to A9 and wild-type peptide A2 by CII-sensitized spleen cells were compared. An increase in IL-4 and IL-10, but not in IFN-gamma, was found in A9 culture supernatants. Additionally, cells obtained from A9-immunized mice produced higher amounts of IL-4 and IL-10 when cultured with CII compared with cells obtained from mice immunized with A2, which produced predominantly IFN-gamma. Suppression of arthritis could be transferred to naive mice using A9-immune splenocytes. Lastly, phosphorylation of TCRzeta was not altered in the immunoprecipitates from the lysates of cells exposed to analogue peptides (A9 and A10) together with wild-type A2 in a T cell line and two I-Aq-restricted, CII-specific T hybridomas. We conclude that analogue peptide A9 is effective in suppressing established CIA by inducing T cells to produce a Th2 cytokine pattern in response to CII.