Photostimulated discharge in electret polymers: an alternative approach for investigating deep traps

The stability of space charge in electrets such as polytetrafluoroethylene (PTFE), polyethylene terephthalate (PETP) and polypropylene (PP) under ultraviolet irradiation has been investigated using photostimulated discharge spectroscopy. While only weak discharge currents were observed in PTFE coated with semitransparent gold electrodes, up to 15 pA/cm/sup 2/ were found in PETP around the UV absorption edge near 310 nm. Space charge profiles obtained with the piezoelectrically generated pressure step method indicate that near-surface charges were almost completely removed. In PP foam, recent findings of a UV-reduced d/sub 33/ coefficient were confirmed for exposure times of up to 3.5 h, and a discharge peak at 200 nm could be assigned to the charges stored on the surfaces of the voids. The unique morphology and the (quasi-)piezoelectric properties of cellular PP make it a role model for the future investigation of charge storage in electrets.     

异步电机直接转矩控制模糊DSVM控制策略

针对传统异步电机直接转矩控制系统低速转矩脉动大、电流畸变严重、磁链轨迹内陷以及开关频率不固定等问题,基于离散空间电压矢量调制(DSVM)技术和模糊控制技术,提出了一种改善低速性能的控制策略.利用DSVM技术合成19种电压矢量,使低速区可供选择的电压矢量数目增加,提高了转矩调节器的控制精确度,采用模糊控制器选择电压工作矢量,明显抑制了转矩脉动.仿真结果表明,改进的DSVM控制策略及模糊控制算法的应用,在保证开关频率恒定的前提下,明显克服了低速磁链轨迹内陷、转矩脉动大、电流畸变严重等缺点,有效地改善了直接转矩控制的低速运行性能.     

Modeling the pull‐in behavior of electrostatically actuated micro beams by an approximate finite element method

We establish the deflection functions of electrostatically actuated micro beams by an approximate finite element method (AFEM), in which the beam and the electrostatic load are discretized. The beam is replaced with a series of beam elements by traditional FEM. Using the total differential of the distributed electrostatic force, we represent such a force with the nodal forces on the beam elements. We calculate the deformation curve of the beam by gradually loading voltage in small increments, and pull‐in behavior is identified when the convergence of the deflection iteration cannot be achieved after voltage increment. The proposed method considers the effect of deformation on stiffness by establishing a new equivalent stiffness matrix for each voltage step based on of the results of previous steps. Through this approach, we prevent the approximate errors of the stiffness matrix from accumulating. The AFEM results on micro beams with different geometries indicate good agreement with those obtained by other studies and those derived using commercial FE software. Copyright © 2013 John Wiley & Sons, Ltd.     

A large generator's bids in an electricity supply auction: Uniform pricing versus pay‐as‐bid pricing

A pay‐as‐bid auction has been adopted in a balancing market under New Electricity Trading Arrangements in England and Wales since 2001 instead of a uniform price auction previously used in a day‐ahead pool market. In contrast, a spot market in Japan, where a general electric utility would be the main supplier, plans to employ a uniform price auction. In this paper we model an electricity spot market in which one large generator competes with many fringe generators to supply electricity, analyze how this large generator bids to maximize its profits, and report some implications for the design of this market. Three types of auction are analyzed: a highest‐winning‐bid pricing (HWB) uniform price auction, a lowest‐losing‐bid pricing (LLB) uniform price auction, and a pay‐as‐bid auction. It is shown that the slope of the bid curve, which is obtained by plotting the large generator's bidding prices against its generation costs, are steeper in an LLB uniform price auction and flatter in a pay‐as‐bid auction than those in an HWB uniform price auction. This implies that an LLB uniform price auction or a pay‐as‐bid auction would make room for the fringe generators to win an auction. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 41–48, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20420     

Charge and mass flux in the radial electric field of an evaporatingcharged water droplet: an experimental analysis

In the electrostatic application of pesticide sprays, charge retention by evaporating droplets in transit to deposit surfaces is a limiting problem. The possible charge loss via evaporative mass transfer and the possible alteration of evaporation rate caused by the presence of the droplet surface charge were experimentally investigated. For studies of evaporation from a charged 3 mm diameter water droplet conducted as a function of droplet potential (-1, -2, and -3 kV) and atmospheric relative humidity (22, 64, and 100%), the current flowing in the radial electric field of the charged evaporating was compared with that flowing in the radial field of a nonevaporating metal sphere to determine if the departing water vapor was electrified. It is concluded that electric charge on evaporating liquid droplets comprising agricultural chemical sprays neither alters the mass transfer rate nor is dissipated by the evaporation     

Quantitative accuracy of attenuation correction in the Philips Ingenuity TF whole-body PET/MR system: a direct comparison with transmission-based attenuation correction

Objective

Evaluation of the quantitative accuracy of MR-based attenuation correction (MRAC) in the Philips Ingenuity TF whole-body PET/MR.

Materials and methods

In 13 patients, PET emission data from the PET/MR were reconstructed using two different methods for attenuation correction. In the first reconstruction, the vendor-provided standard MRAC was used. In the second reconstruction, a coregistered transmission-based attenuation map from a second immediately preceding investigation with a stand-alone Siemens ECAT EXACT HR⁺ PET scanner was used (TRAC). The two attenuation maps were compared regarding occurrence of segmentation artifacts in the MRAC procedure. Standard uptake values (SUVs) of multiple VOIs (liver, cerebellum, hot focal structures at various locations in the trunk) were compared between both reconstructed data sets. Furthermore, a voxel-wise intensity correlation analysis of both data sets in the lung and trunk was performed.

Results

VOI averaged SUV differences between MRAC and TRAC were as follows (relative differences, mean ± standard deviation): (+12 ± 6) % cerebellum, (?4 ± 9) % liver, (?2 ± 11) % hot focal structures. The fitted slopes of the voxel-wise correlations in the lung and trunk were 0.87 ± 0.17 and 0.95 ± 0.10 with averaged adjusted R ² values of 0.96 and 0.98, respectively. These figures include two instances with partially erroneous lung segmentation due to artifacts in the underlying MR images.

Conclusion

The MR-based attenuation correction implemented on the Philips Ingenuity PET/MR provides reasonable quantitative accuracy. On average, deviations from TRAC-based results are small (on the order of 10 %  or below) across the trunk, but due to interindividual variability of the segmentation quality, deviations of more than 20 %  can occur. Future improvement of the segmentation quality would help to increase the quantitation accuracy further and to reduce the inter-subject variability.     

Magnetic resonance imaging and67ga scan versus computed tomography in the staging and in the monitoring of mediastinal malignant lymphoma: a prospective pilot study

Purpose: To assess the potential value of magnetic resonance imaging (MRI) combined with⁶⁷Ga single-photon emission computed tomography (SPECT) versus computed tomography (CT) in the staging and in the monitoring of mediastinal malignant lymphoma. Materials and methods: Twenty-three patients, referred to our institute for the evaluation of lymphoma, underwent CT,⁶⁷Ga scan, and MRI between April 1993 and February 1996 at sequential intervals. The tests studied (MRI,^67Ga, and CT) were performed according to the following schedule: 1) before start of therapy; 2) after four courses of chemotherapy; and 3) 2, 6, 12, and 18 months after the end of treatment. Results: All patients studied at the time of diagnosis had abnormal gallium accumulation in the mediastinum as well as pathologic CT and pathologic signal intensity at MRI. Six months after the end of treatment full consistency was found between the results of MRI and SPECT, whereas during treatment and 2 months after the end of therapy MRI and⁶⁷Ga scan were not in agreement in nine patients. In the 23 patients in follow-up, in CT there were nine false-positive and three false-negative findings; in SPECT three false negatives; in MRI one false positive and one false negative. Conclusion: MRI can give morphologic information similar to CT, even superior due to multiplanarity and with major precision in the distinction between fibrosis and active disease. MRI is thus an alternative to CT. The association with SPECT allows a great diagnostic accuracy in the positive and negative predictive value.     

Role of magnetic resonance methods in the evaluation of prostate cancer: an Indian perspective

The challenges in detection, localization, and staging of prostate cancer have prompted the investigation of the role of various magnetic resonance (MR) methodologies in a large cohort of men prior to biopsy. The identification of suspicious areas of malignancy was carried out using magnetic resonance imaging (MRI), magnetic resonance spectroscopic imaging (MRSI) and diffusion-weighted imaging (DWI). Our data shows that apparent diffusion coefficient (ADC) may be a reliable marker to differentiate normal, benign, and malignant prostate tissues similar to the metabolite ratio. Also, the combined use of MRSI and DWI improves the diagnosis of prostate cancer. In this review, we present our experience on the use of MRI, MRSI and DWI methods in the assessment of prostate cancer in Indian men. Further, analysis of the comparison of the ADC and the metabolite ratio values reported in the literature across various patient populations are presented. An erratum to this article can be found at     

KIRCHHOFF: an educational software for learning the basicprinciples and methodology in electrical circuits modeling

An interactive courseware package designed to be used as an auxiliary instructional tool by lower division students is described. The pedagogical goal of KIRCHHOFF is to foster mastery of basic methodological skills in the study of lumped electrical circuits. For a given circuit layout, proposed by the teacher, this is verified when the circuit has been systematically labeled and when a correct, complete and nonredundant set of algebraic and integro-differential equations has been written down by the student. KIRCHHOFF, a symbolic exercising tool, provides graphic guidance in such a process and, when needed, gives the learner suitable corrective explanations     

Prony's method: an efficient tool for the analysis of earth faultcurrents in Petersen-coil-protected networks

Prony's method is a technique for estimating the modal components present in a signal. Every modal component is defined by four parameters frequency, magnitude, phase, and damping. This method is used to analyse earth fault currents in Petersen-coil-protected 20 kV networks. The variations of Prony's parameters in terms of some of the power systems characteristics (distance between the busbar and the fault, fault resistance and capacitive current of the whole network) are presented. It is shown that some of the Prony's parameters relating to the fault current transient may be useful to determine what kind of fault occurred, and where it occurred     

Hyperammonemia and chronic hepatic encephalopathy: an in vivo PMRS study of the rat brain

The brain energy metabolism of rats affected by chronic hepatic encephalopathy due to portacaval shunting was monitored by in vivo³¹P-nuclear magnetic resonance spectroscopy before and after ammonium acetate administration. With respect to healthy unoperated and to sham operated controls, portacaval shunting decreased the levels of the nuclear magnetic resonance (NMR) visible brain phosphocreatine and nucleoside phosphates, and the intracellular [free Mg²⁺]. Ammonium acetate induced a further decrease of the levels of the NMR detectable phosphocreatine and nucleoside triphosphates and of the [free Mg²⁺], while the PMR spectra of the brain of non-shunted rats did not show any significant change even after treatment with ammonium acetate.     

Quantum energy-transport and drift-diffusion models for electron transport in graphene: an approach by the wigner function

Journal of Computational Electronics - The present work aims at formulating quantum energy-transport and drift-diffusion equations for charge transport in graphene from a quantum hydrodynamic model...     

The effect of diffusion gradient direction number on corticospinal tractography in the human brain: an along-tract analysis

Objectives

We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs).

Materials and methods

The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD.

Results

FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD.

Conclusions

Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.

     

e-Learning in Project Management Using Simulation Models: A Case Study Based on the Replication of an Experiment

Current e-learning systems are increasing their importance in higher education. However, the state of the art of e-learning applications, besides the state of the practice, does not achieve the level of interactivity that current learning theories advocate. In this paper, the possibility of enhancing e-learning systems to achieve deep learning has been studied by replicating an experiment in which students had to learn basic software engineering principles. One group learned these principles using a static approach, while the other group learned the same principles using a system-dynamics-based approach, which provided interactivity and feedback. The results show that, quantitatively, the latter group achieved a better understanding of the principles; furthermore, qualitatively, they enjoyed the learning experience     

Longitudinal sensitivity to change of MRI-based muscle cross-sectional area versus isometric strength analysis in osteoarthritic knees with and without structural progression: pilot data from the Osteoarthritis Initiative

Object

Biomechanical measurement of muscle strength represents established technology in evaluating limb function. Yet, analysis of longitudinal change suffers from relatively large between-measurement variability. Here, we determine the sensitivity to change of magnetic resonance imaging (MRI)-based measurement of thigh muscle anatomical cross sectional areas (ACSAs) versus isometric strength in limbs with and without structural progressive knee osteoarthritis (KOA), with focus on the quadriceps.

Materials and methods

Of 625 “Osteoarthritis Initiative” participants with radiographic KOA, 20 had MRI cartilage and radiographic joint space width loss in the right knee isometric muscle strength measurement and axial T1-weighted spin-echo acquisitions of the thigh. Muscle ACSAs were determined from manual segmentation at 33 % femoral length (distal to proximal).

Results

In progressor knees, the reduction in quadriceps ACSA between baseline and 2-year follow-up was ?2.8 ± 7.9 % (standardized response mean [SRM] = ?0.35), and it was ?1.8 ± 6.8 % (SRM = ?0.26) in matched, non-progressive KOA controls. The decline in extensor strength was more variable than that in ACSAs, both in progressors (?3.9 ± 20 %; SRM = ?0.20) and in non-progressive controls (?4.5 ± 28 %; SRM = ?0.16).

Conclusion

MRI-based analysis of quadriceps muscles ACSAs appears to be more sensitive to longitudinal change than isometric extensor strength and is suggestive of greater loss in limbs with structurally progressive KOA than in non-progressive controls.     

海外子公司网络学习的知识与效应研究——以东道国网络为例

为理解跨国公司海外子公司的网络学习行为,提高网络学习效果,通过对组织学习理论和跨国公司海外子公司理论进行回顾和展望,阐明了网络学习的内涵,以东道国网络为例,探讨了海外子公司网络学习的具体知识,分析了海外子公司嵌入网络的学习效应。