Self-magnetic insulation in plasma opening switches

The paper analyses the penetration of a magnetic field into the plasma bridge of nanosecond and microsecond opening switches. For switches with a conduction time of ~100 ns, simple formulae are derived to estimate the magnetic field velocity in collisionless and collisional plasmas. It is shown that in both cases this velocity is determined by the magnetic field rise rate to plasma density ratio raised to the power of 1/2. As the conduction time is increased to ~1 ${\rm \mu}$ s, the field velocity starts to depend on the plasma aggregation by a magnetic piston. At the same time, irrespective of the conduction time, the electron flow velocity is limited by the radial drift velocity in crossed magnetic and polarization electric fields. Such a limitation suppresses the current channel conductivity with respect to the Spitzer value by a factor equal to the electron magnetization parameter raised to one or another power. On completion of the conduction phase, the rate of rise of the switch resistance is proportional to the electron drift velocity. The peak switch voltage obtained in calculations is compared with its values recorded in experiments on mega-ampere current switching. A procedure is also presented for calculating the switch parameters to obtain the maximum possible voltage in the phase of current cutoff.

Improvement of protection of distribution of sectioned lines with distributed generation sources (DGS)

When powered from a backup source, the short-circuit currents in the protected area are much lower than the current cutoff insert installed at the sectioning point, therefore, in this case, the current cutoff is ineffective. In cases where the maximum current directional protection (MCDP) does not provide the required sensitivity, it is advisable to use distance protection with dependent exposure on sectioned lines and lines from distributed generation sources (DGS) in a significant decrease in voltage on the DGS buses during external short circuits through a relatively large reactance of small and medium power. Different modes of operation of sectioned lines from DGS are characterized by a change in the direction of flow of the load current and short-circuit current. Therefore, on such lines, maximum current directional protections can be applied, which provide selective action of adjacent sets of line protection in different modes of their operation. The use of definite time protection leads to the accumulation of a long time delay for the protection installed on the main switch (especially when several sectioning switches are installed on the line), which complicates the coordination of the protection of the main sections of the lines from the protection of the supply substations. The article deals with the problems of improving relay protection for distribution networks with distributed generation sources (DGS). Paying attention to the peculiarities of protection operation under different operating modes of such networks, namely: normal and post-emergency. The protection of lines from DGS must meet the general requirements for ensuring the necessary sensitivity, selectivity of action for different types of damage. Difficulties in ensuring the required sensitivity when using overcurrent protection and current cutoff in such networks are caused by the low level of short-circuit currents from backup sources. The features of the implementation of relay protection in sectioned networks when they are powered from the DGS are given. The expediency of using remote triggering devices for distance protection to increase the sensitivity of protection of sectioned lines from DGS has been substantiated.

Dilemma of Interpretation of High Sensitivity Troponin in Non-ST Elevated Myocardial Infarction

Background: Non-ST Elevated Myocardial Infarction (NSTEMI) diagnosis is dependent on elevation of high sensitivity troponin (hs-troponin). The current cutoff point for hs-troponin is highly sensitive but not specific for detecting obstructive myocardial infarction. Our aim is to better risk stratify patients by determining the significance of the current cut off point hs-troponin in determining obstructive myocardial infarction. Methods: We studied 202 patients. All patients were assessed for their demographics, clinical history, laboratory and imaging results. Using SPSS version 22, the pooled cohort of patients were analyzed at significant level <0.05 and the data were test for significant correlations between two predetermined groups; A and B. Group A included patients with positive coronary angiography (CAG) results who had obstructive coronary artery disease and required intervention, and group B included patients with negative CAG results who had normal or near normal coronary arteries that required no intervention. Results: Group A comprised 87.6% of the patients. Both groups had a median age of 53 years. In Group A, 91% were males, 54% were diabetics, 54% hypertensives and median hs-troponin was 145 ng/L. While in group B, 88% were males, 39% were diabetics, 60% hypertensives, and median hs-troponin was 54 ng/L. There is significant correlation between the two groups in the percentage of diabetes and median troponin level (p < 0.05). Conclusions: A ROC curve was generated and identified a level of 127 ng/dL as the best cutoff of hs-troponin in detecting obstructive myocardial infarction (p=0.03). Interestingly, 60% of patients in group B had alternative diagnosis.

The Use of Procalcitonin as a Sepsis Marker in a Community Hospital

Background Procalcitonin (PCT) is a biomarker that shows good sensitivity and specificity in identifying septic patients. Methods This study investigated the diagnostic accuracy of PCT in a community hospital setting and how it compared to that of lactic acid. It explored the impact on patient care before and after PCT implementation regarding costs and length of stay. Two comparative groups were analyzed using an exploratory descriptive case–control study with data from a 19-month period after PCT implementation and a retrospective quasi-experimental study using a control group of emergency department patients diagnosed with sepsis using data before PCT implementation. Results Post-procalcitonin implementation samples included 165 cases and pre-procalcitonin implementation sample included 69 cases. From the 165 sepsis cases who had positive blood cultures, PCT had a sensitivity of 89.7%. In comparison, lactic acid's sensitivity at the current cutoff of 18.02 mg/dL (2.0 mmol/L) was 64.9%. There was a 32% decrease in median cost before and after PCT implementation, even with the length of stay remaining at 5 days in both time periods. Conclusions There was a significant decrease after the implementation of PCT in cost of hospitalization compared to costs before implementation. This cost is highly correlated with length of stay; neither the hospital nor the intensive care unit length of stay showed a difference with before and after implementation. There was a positive correlation between lactic acid and PCT values. PCT values had a higher predictive usefulness than the lactic acid values.

Lowered obesity indicator cutoff points more effectively predict 5-year incidence of hypertension in premenopausal women

Objective To compare proposed new cutoff points for four obesity indicators—waist-to-height ratio (WHtR), waist circumference (WC), waist-to-hip ratio (WHR) and body mass index (BMI)—with their current cutoff points to determine which are better standards predicting 5-year incidence of hypertension (HT) and diabetes mellitus (DM) among premenopausal women. Design Data were obtained from the 2002 and 2007 Survey on the Prevalence of HT, Hyperglycemia and Hyperlipidemia in Taiwan conducted by the Ministry of Health and Welfare, Taiwan. Premenopausal women were grouped based on the proposed cutoff points versus reference cutoff points for obesity indicators. Participant A total of 1466 premenopausal women aged between 20 and 57 years old were recruited. Main outcome measure Five-year incidence of HT and DM. Results Our new obesity indicator cutoff points—WHtR 0.49, WC 74.7 cm, WHR 0.79 and BMI 22.3 kg/m2—were better predictors for 5-year HT incidence in premenopausal women compared with those of current standards, but were not significantly different for DM. Among the four obesity indicators, WHtR and WC were optimal for their 5-year predictive ability for HT and DM in premenopausal women. Conclusions To avoid too many cutoff points for practitioners to adopt and memorize, the proposed new cutoff points were recommended preferentially to prevent the incidence of HT and DM in premenopausal women.