On the use of curvature estimates in quasi- Newton methods

AbstractIn previous work, Ford and Ghandhari (1989) considered the use of nonlinear gradient models for quasi-Newton methods. By means of such models, values of the objective function (in addition to values of the gradient) were utilised in updating formulae. Numerical experiments provided evidence that such an approach could yield gains, in terms of the evaluations required, but at the cost of the solution of a nonlinear equation at each iteration. In a subsequent paper, Ford and Ghandhari (to appear) have developed alternative models which enable the parameter to be determined explicitly. In this paper, we shall consider further models (of the general type introduced in the latter paper) which determine the parameter explicitly by employing estimates of the curvature of the objective function, thus following a technique first introduced by Biggs (1971, 1973). We conclude by presenting the results of numerical tests on the new methods

Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems

High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied

Taking Liberties: The Personal Jurisdiction of Military Commissions

On September 11, 2001, Al Qaeda operatives attacked civilian and military targets on US territory, causing thousands of deaths and billions of dollars of economic loss. The next day, the United Nations Security Council unanimously adopted Resolution 1368 characterizing the attack by Al Qaeda as a threat to international peace and security and recognizing the right of states to use armed force in self defense

Investigating the Interplay of Emotional Intelligence and Interlanguage Pragmatic Competence in Iranian Lower-Intermediate EFL Learners

Despite the significant role of emotions in any aspect of language learning, including its pragmatic aspect, there have been few research studies on this topic. As a stride toward narrowing this research niche, the objectives of this research were threefold. Firstly, it aimed to examine the two face-threatening speech acts of request and apology as indicators of learners’‎ interlanguage pragmatic competence (ILP) and its relationships with learners’ Emotional Quotient (EQ). Secondly, it sought to investigate ‎whether gender as an intervening variable would have any significant relationship with ILP and EQ, and thirdly whether EQ could predict ILP ‎development. To this end, 72 (50 females and 22 males) Iranian lower-intermediate level learners ranging ‎in age from 17 to 25 from two universities took part in this research. A multiple-choice discourse completion test ‎‎(MDCT) (Liu, 2004) and Bar-Onʼs ‎(1997) EQ scale were used and correlation analysis was done to search for any linkage between ILP and EQ. The Pearson product-moment correlation outcomes ‎revealed no significant relationship between EQ and ILP. However, a significant relation was found between Independence as a component of EQ and ‎EFL learners’ ILP competence. The independent samples t-test outcomes indicated ‎that female participants had a higher level of (ILP) competence than male participants; however, male and female participants did not differ significantly regarding their EQ level. The findings indicate that ‎EQ, in general, is not influential in EFL learners’ ILP competence. The paper concludes by providing pedagogical implications for EFL learners and instructors

Is facet tropism associated with increased risk of disc herniation in the lumbar spine?

Study Design: Retrospective case control study. Purpose: In current study, we compared the incidence of facet tropism (FT) in patients with lumbar disc herniation and normal controls. Overview of Literature: It has been suggested that FT can be associated with increased risk of lumbar disc herniation. Methods: A total of 66 and 63 patients with L4/L5 and L5/S1 disc herniation, respectively, were evaluated in the present study. The control group comprised 61 normal subjects. Facet joint angle was measured using axial magnetic resonance images. The FT was defined as a difference of > 10° between the right and left facet joints. The incidence of FT was compared between patients and controls. We also investigated the relationship between facet orientation (sagittal or coronal) and side of disc herniation. Results: The incidence of FT at the L4/L5 level was significantly higher in patients with disc herniation (48.5 vs. 26.2, p =0.01), while it was found to be the same at the L5/S1 level in patients and controls (50.8 vs. 36, p =0.098). Among the 64 patients with FT, intervertebral disc herniation occurred significantly toward the more sagittally oriented facet joint in 41 patients (p < 0.05). Conclusions: FT is associated with increased risk of L4/L5 intervertebral disc herniation, but not at the L5/S1 level. In addition, disc herniation occurred toward the more sagittally oriented facet joint. © 2018 by Korean Society of Spine Surgery

The Role of Routine Preoperative Magnetic Resonance Imaging in Idiopathic Scoliosis: A Ten Years Review

Study DesignProspective study.PurposeTo determine the role of routine preoperative magnetic resonance imaging (MRI) to detect the incidence and risk factors for intraspinal anomalies in patients with idiopathic scoliosis.Overview of LiteratureThe incidence and risk factors for intraspinal anomalies in patients with idiopathic scoliosis are controversial, and the indications for preoperative MRI in these patients vary among centers.MethodsInformation on patients with idiopathic scoliosis who were surgical candidates over 10 years (age at presentation, sex, magnitude and apex of major curve, intraspinal anomalies detected by MRI, and neurological examination results) were recorded, the patients were grouped according to the intraspinal anomaly, and the data were analyzed.ResultsOf the 271 patients with idiopathic scoliosis, 27 had neuroaxial abnormalities (9.9%). Of these 27 patients, 14 (52%) underwent a neurosurgical procedure. Significant differences were observed in the frequency of early disease onset and male sex (p<0.05) between the group of patients with neuroaxial abnormalities on preoperative MRI and those who did not have a cord anomaly. No difference was detected in the magnitude or direction of the curve.ConclusionsNeuroaxial abnormalities in patients with idiopathic scoliosis and a normal neurological examination were highly frequent (9.9%). Missing these abnormalities before surgery could inflict catastrophic postoperative complications. The incidence of neuroaxial abnormalities was higher in male patients and in those with early onset disease. Thus, MRI is essential for all patients with idiopathic scoliosis who require medical intervention

Market Integration of HVDC Lines: Cost Savings from Loss Allocation and Redispatching

In the Nordic region, many interconnectors are formed by HVDC links, as Scandinavia, Continental Europe and the Baltic region are non-synchronous AC systems. This paper presents two cost benefit analyses on the utilization of HVDC interconnectors in the Nordic countries: in the first we investigate the utilization of HVDC interconnectors for reserve procurement and, in the second, we assess the implementation of implicit grid losses on HVDC interconnectors in the day-ahead market. The first analysis is motivated by real events in 2018 where the inertia of the Nordic system dropped below a critical level and the most critical generating unit, a nuclear power plant in Sweden, was redispatched to guarantee the security of the system. In order to guarantee system security while reducing the costs of preventive actions, in summer 2020 new frequency products were introduced in the Nordic system: the Fast Frequency Reserves (FFR). HVDC lines, however, can perform similar tasks at lower costs. In our analysis, we are, thus, investigating the cost savings of using HVDC lines for frequency support using their Emergency Power Control (EPC) functionality, instead of redispatching or FFR. The second analysis is based on the proposition of Nordic Transmission System Operators (TSOs) to introduce linear HVDC loss factors in the market clearing. With our analysis, we show that linear loss factors can unfairly penalize one HVDC line over the other, and this can reduce social benefits and jeopardize revenues of merchant HVDC lines. In this regard, we propose piecewise-linear loss factors: a simple-to-implement but highly-effective solution. Moreover, we demonstrate how the introduction of HVDC loss factors is a partial solution, since it disproportionally increases the AC losses. Our results show that the additional inclusion of AC loss factors can eliminate this problem.Comment: Submitted to "CIGRE Centennial Exhibition 2021" on December 15, 2020. arXiv admin note: text overlap with arXiv:1910.05607, arXiv:2001.0066

Comparison of Harrington rod and Cotrel-Dubousset devices in surgical correction of adolescent idiopathic scoliosis

Background: Since the time of Paul Harrington numerous implants have been introduced for correction of scoliosis, but none are ideal. Newer devices are very expensive, and in our country some patients cannot afford them. Objectives: The aim of this study was to compare the results of the Harrington rod (HR) device and the newer Cotrel-Dubousset (CD) device in treatment of adolescent idiopathic scoliosis (AIS). Materials and Methods: A retrospective review assessed patients with AIS admitted for spinal curve correction treated with HR (n = 120) and CD devices (n = 138) between October 1988 to April 2001 at the Shafa Yahyaeian Hospital, Tehran, Iran. We extracted information from the patient's file and radiographs before, after and two years post-operation. Results: The mean age of patients was 16.7 ± 2.5 years. There was no statistically significant difference between the two groups regarding gender, age, curve before surgery, and percentage of flexibility. The mean curvature was 70 ± 20.7 in the HR and 64.81 ± 19.4 in the CD group before surgery (P = 0.09); and the mean curvature was 40 ± 16.3 and 26.58 ± 15.37 in HR and CD groups respectively after surgery (P = 0.156). The mean curvature was 47.2 ± 15.9 in HR and 31.2 ± 15.4 in CD groups at two years follow-up (P = 0.156). Conclusions: Results of many studies have shown no significant impairment in long-term quality of life and function in patients treated with Harrington rods. According to previously performed studies and the current study, surgical correction with Harrington rods seem to be comparable with the newer more expensive CD device. Although there is no doubt that the preference is to use newer devices in view of some disadvantages of HR, but this does not preclude using it for patients that cannot afford the newer devices. Copyright © 2013, Trauma Research Center; Published by Kowsar Corp