Torque analysis on a double rotor electrical variable transmission with hybrid excitation

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q- and d-axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d-axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d-axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine

Measuring market risk using extreme value theory

The adoption of Basel II standards by the Bangko Sentral ng Pilipinas initiates financial institutions to develop value-at-risk (VaR) models to measure market risk. In this paper, two VaR models are considered using the peaks-over-threshold (POT) approach of the extreme value theory: (1) static EVT model which is the straightforward application of POT to the bond benchmark rates; and (2) dynamic EVT model which applies POT to the residuals of the fitted AR-GARCH model. The results are compared with traditional VaR methods such as RiskMetrics and AR-GARCH-type models. The relative size, accuracy and efficiency of the models are assessed using mean relative bias, backtesting, likelihood ratio tests, loss function, mean relative scaled bias and computation of market risk charge. Findings show that the dynamic EVT model can capture market risk conservatively, accurately and efficiently. It is also practical to use because it has the potential to lower a bank’s capital requirements. Comparing the two EVT models, the dynamic model is better than static as the former can address some issues in risk measurement and effectively capture market risks.extreme value theory, peaks-over-threshold, value-at-risk, market risk, risk management

A Propensity-Matched Analysis of Outcomes for Patients With M2 Branch Occlusions at Endovascular Stroke Centers

Introduction: Endovascular therapy (EVT) for Emergent Large Vessel Occlusion (ELVO) is recommended for patients with acute proximal MCA (M1 segment) occlusions (Class I, level A evidence), but the benefits of EVT are uncertain in patients with M2 and more distal occlusions. The purpose of this study was to compare the efficacy and outcomes of EVT-treated M2 ELVOs with EVT-treated M1 ELVOs, and to examine the outcomes of EVT-treated M2 ELVO patients with those whose M2 ELVOs were not treated. Methods: Data were obtained from a multi-hospital system of patients from January 2014 and May 2018. Two propensity score (PS)-based nearest-neighbor matching analyses were used to match similar patients who had 1) EVT-treated M1 vs EVT-treated M2 ELVOs and 2) EVT-treated vs non-EVT-treated M2 ELVOs. Outcomes included length of stay (LOS), rate of successful reperfusion, discharge disposition, symptomatic intracranial hemorrhage (sICH), and discharge mRS. Chi-squared, Fisher’s exact, and Mann-Whitney U tests were used to compare matched patients. Results: Overall, 160 patients with EVT-treated M2 ELVOs, 350 with EVT-treated M1 ELVOs, and 113 with non-EVT-treated M2 ELVOs were included. Propensity score analyses resulted in 118 matched patients with EVT-treated M2 and EVT-treated M1 occlusions and 70 matched patients with EVT-treated and non-EVT-treated M2 ELVOs. M2 ELVOs made up 20% of all LVO patients. Treated M1 and M2 ELVOs were similar with respect to baseline NIHSS and outcomes. When attempted,intra-arterial reperfusion of M2 ELVOs was achieved at comparable rates to M1 ELVOs with equal rates of sICH (1.7%). Higher NIHSS was associated with EVT of M2 ELVOs (15.00[8.50,21.00] vs 7.00[4.00,17.75]; p\u3c0.001). Rates of mortality trended more favorably in treated M2 ELVOs (12.9% vs 20), which was not statistically significant (p=0.362). Conclusions: EVT for M2 ELVOs is as safe and effective as EVT for M1 vessel ELVOs. Rates of successful reperfusion, discharge mRS, LOS, sICH, discharge disposition and mortality are similar among EVT treated M2 and EVT treated M1 ELVOs. Though not statistically significant, EVT for patients with M2 ELVOs resulted in favorable trends toward higher survival rates of potential clinical significance

Endovascular Treatment With or Without Prior Intravenous Alteplase for Acute Ischemic Stroke

Background It is unclear whether intravenous thrombolysis ( IVT ) with alteplase before endovascular treatment ( EVT ) is beneficial for patients with acute ischemic stroke caused by a large vessel occlusion. We compared clinical and procedural outcomes, safety, and workflow between patients treated with both IVT and EVT and those treated with EVT alone in routine clinical practice. Methods and Results Using multivariable regression, we evaluated the association of IVT + EVT with 90-day functional outcome (modified Rankin Scale), mortality, reperfusion, first-pass effect, and symptomatic intracranial hemorrhage in the MR CLEAN (Multicenter Randomised Controlled Trial of Endovascular Treatment for Acute Ischemic Stroke in The Netherlands) Registry. Of 1485 patients, 1161 (78%) were treated with IVT + EVT , and 324 (22%) with EVT alone. Patients treated with IVT + EVT had atrial fibrillation less often (16% versus 44%) and had better pre-stroke modified Rankin Scale scores (pre-stroke modified Rankin Scale 0: 73% versus 52%) than those treated with EVT alone. Procedure time was shorter in the IVT + EVT group (median 62 versus 68 minutes). Nontransferred IVT + EVT patients had longer door-to-groin-puncture times (median 105 versus 94 minutes). IVT + EVT was associated with better functional outcome (adjusted common odds ratio 1.47; 95% CI : 1.10-1.96) and lower mortality (adjusted odds ratio 0.58; 95% CI : 0.40-0.82). Successful reperfusion, first-pass effect, and symptomatic intracranial hemorrhage did not differ between groups. Conclusions In this observational study, patients treated with IVT + EVT had better clinical outcomes than patients who received EVT alone. This finding may demonstrate a true benefit of IVT before EVT , but its interpretation is hampered by the possibility of residual confounding and selection bias. Randomized trials are required to properly assess the effect of IVT before EVT .</p

Modeling Longevity Risk using Extreme Value Theory: An Empirical Investigation using Portuguese and Spanish Population Data

Extreme value theory (EVT) provides a framework to formalize the study of behaviour in the tails of a distribution. In this paper we use EVT to model the statistical behaviour of mortality rates over a given high threshold age and to estimate the significance of rare longevity risk in a given population. We adopt a piecewise approach in estimating the optimal threshold age using an iterative algorithm of maximum likelihood estimation.that statistically determines the cut-off between the central (Gompertz) part of the distribution and the upper tail modelled using the generalized Pareto distribution. The model is empirically tested using the most recent period mortality data for the total, male and female populations of Portugal and Spain. We use some classical results from EVT to estimate the evolution of the theoretical maximum life span over time and to derive confidence intervals for the central estimates. We then use time series methods to forecast the highest attained age. We observe a good fit of the model in all populations and subperiods analysed and on the whole life span considered. We estimate an increase in the theoretical maximum life span over time for all populations, more significant in the male subpopulations

Endovascular Treatment With or Without Prior Intravenous Alteplase for Acute Ischemic Stroke

Background It is unclear whether intravenous thrombolysis ( IVT ) with alteplase before endovascular treatment ( EVT ) is beneficial for patients with acute ischemic stroke caused by a large vessel occlusion. We compared clinical and procedural outcomes, safety, and workflow between patients treated with both IVT and EVT and those treated with EVT alone in routine clinical practice. Methods and Results Using multivariable regression, we evaluated the association of IVT + EVT with 90-day functional outcome (modified Rankin Scale), mortality, reperfusion, first-pass effect, and symptomatic intracranial hemorrhage in the MR CLEAN (Multicenter Randomised Controlled Trial of Endovascular Treatment for Acute Ischemic Stroke in The Netherlands) Registry. Of 1485 patients, 1161 (78%) were treated with IVT + EVT , and 324 (22%) with EVT alone. Patients treated with IVT + EVT had atrial fibrillation less often (16% versus 44%) and had better pre-stroke modified Rankin Scale scores (pre-stroke modified Rankin Scale 0: 73% versus 52%) than those treated with EVT alone. Procedure time was shorter in the IVT + EVT group (median 62 versus 68 minutes). Nontransferred IVT + EVT patients had longer door-to-groin-puncture times (median 105 versus 94 minutes). IVT + EVT was associated with better functional outcome (adjusted common odds ratio 1.47; 95% CI : 1.10-1.96) and lower mortality (adjusted odds ratio 0.58; 95% CI : 0.40-0.82). Successful reperfusion, first-pass effect, and symptomatic intracranial hemorrhage did not differ between groups. Conclusions In this observational study, patients treated with IVT + EVT had better clinical outcomes than patients who received EVT alone. This finding may demonstrate a true benefit of IVT before EVT , but its interpretation is hampered by the possibility of residual confounding and selection bias. Randomized trials are required to properly assess the effect of IVT before EVT .</p

Endovascular Treatment for Acute Stroke Patients With a Pre-stroke Disability: An International Survey

Background: It is unclear what factors clinicians consider when deciding about endovascular thrombectomy (EVT) in acute ischemic stroke patients with a pre-existing disability. We aimed to explore international practice patterns and preferences for EVT in patients with a pre-stroke disability, defined as a modified Rankin score (mRS) ≥ 2. Methods: Electronic survey link was sent to principal investigators of five major EVT trials and members of a professional interventional neurology society. Results: Of the 81 survey-responding clinicians, 57% were neuro-interventionalists and 33% were non-interventional stroke clinicians. Overall, 64.2% would never or almost never consider EVT for a patient with pre-stroke mRS of 4-5, and 49.3% would always or almost always offer EVT for a patient with pre-stroke mRS 2-3. Perceived benefit of EVT (89%) and severity of baseline disability (83.5%) were identified as the most important clinician-level and patient-level factors that influence EVT decisions in these patients. Conclusion: In this survey of 80 respondents, we found that EVT practice for patients with pre-stroke disability across the world is heterogenous and depends upon patient characteristics. Individual clinician opinions substantially alter EVT decisions in pre-stroke disabled patients

Using Extreme Value Theory for Determining the Probability of Carrington-Like Solar Flares

Space weather events can negatively affect satellites, the electricity grid, satellite navigation systems and human health. As a consequence, extreme space weather has been added to the UK and other national risk registers. By their very nature, extreme space weather events occur rarely and, therefore, statistical methods are required to determine the probability of their occurrence. Space weather events can be characterised by a number of natural phenomena such as X-ray (solar) flares, solar energetic particle (SEP) fluxes, coronal mass ejections and various geophysical indices (Dst, Kp, F10.7). In this paper extreme value theory (EVT) is used to investigate the probability of extreme solar flares. Previous work has assumed that the distribution of solar flares follows a power law. However such an approach can lead to a poor estimation of the return times of such events due to uncertainties in the tails of the probability distribution function. Using EVT and GOES X-ray flux data it is shown that the expected 150-year return level is approximately an X60 flare whilst a Carrington-like flare is a one in a 100-year event. It is also shown that the EVT results are consistent with flare data from the Kepler space telescope mission.Comment: 13 pages, 4 figures; updated content following reviewer feedbac