The windmill topology

A widely used 18-pulse clean power converter with windmill transformer topology is presented and analyzed. It provides a more economical solution to achieve harmonicmitigation in electric power systems when compared with some of the earlier methods. With the proliferation of nonlinear loads in industrial power systems, the advent of IEEE 519-1992 [1], and the increasing demand by utilities for power factor improvement, the specification of harmonic mitigation has become common [2], [3]. In the past 14 years, several patented 18-pulse converter methods have been accepted in the marketplace and are successfully applied in a variety of practical applications such as water management, oil field installations, etc., where adjustable speed drive (ASD) and harmonic mitigation are required. A threeto nine-phase unity-gain autotransformer topology with a ±20° phase shift between output voltages is first proposed in [4]. The step-up and step-down 18-pulse autotransformer topologies with a 40° phase shift between the output voltages are discussed in [5]?[9]. The winding current looping and sharing problems in early days have already been solved [10]. The challenging design problem becomes one of economics [11].     

Cortical Spreading Depression in Rats

Cortical spreading depression (CSD) is an important neurophysiological phenomenon, which was first discovered more than 60 years ago [1]. As it is associated with migraine and focal cerebral ischemia, CSD has attracted intensive attention [2]?[5]. Various methodologies including positron emission tomography [6], magnetic resonance imaging (MRI) [7], laser Doppler flowmetry (LDF) [8], and autoradiography have been used to investigate CSD. Optical intrinsic signal imaging (OISI) is a neuroimaging technique that can monitor a large region of the cortex with both higher temporal and spatial resolution [9]?[11].     

Electromagnetic interference risk analysis

Electromagnetic interference (EMI), whether intentional or not, causes a wide spectrum of difficulties including momentary, minor inconveniences to system failures in electronic devices [7], [26]. Within a hospital environment, electronic devices must reliably perform or fail gracefully, including telecommunications infrastructure through basic instrumentation [1]. Lack of comprehensive EMI risk data has caused some facilities to ban wireless devices altogether for reducing risk from inadvertent emitters and yet relinquishing the possible lifesaving benefits [2], [3]. Often, the bans rely heavily on good-faith compliance with minimal or no detection and mitigation strategy. With increasing reliance on electronic medical records, timely access to patients' treatments, medications, and allergens, and timely communications with medical personnel can be critical, especially during disaster events [3].     

RFID Transponders

adio frequency identification (RFID) or auto-identification (ID) is a contactless data transmission and reception technique between the data carrying device, called a transmitter responder (transponder) or an RFID tag, and an interrogator, which is also known as an RFID reader. A more abstract approach to defining Auto-ID reveals that Auto-ID involves the automated extraction of the identity of an object [1], [2]. The contactless ID system relies on data transmission via radio frequency electromagnetic (EM) signals, and consequently, the whole operation is line-of-sight and weather independent [3]. These advantages overcome the limitations of optical barcodes, which are line-of-sight and weather dependent and need manual operation.     

High-voltage, electric field-driven micro/nanofabrication for polymeric drug delivery systems

One of the major challenges in drug delivery is to provide an appropriate dosage of therapeutic agents at the right time to the right location. The therapeutic agents include small molecules, macromolecules, nanoparticles, and cells, whose sizes range from less than 0.5 nm to 20 mum. Major noninvasive routes of administration include oral, pulmonary, and transdermal drug delivery. Transport barriers associated with these drug delivery routes prevent the delivery of appropriate dosage of therapeutic agents to the right location. Size is one of the determining factors for drug delivery systems. Polymeric microstructured or nanostructured systems show a great potential to stabilize therapeutic agents and overcome transport barriers by controlling the size and surface properties. A high-voltage electric field can be imposed on a polymer liquid to form microcapsules, to produce nanoparticles through electrospray or electrostatic assembly and to fabricate nanofibers through electrospinning. The addition of an electric field results in charging the components of the system and the resulting electrostatic interactions. Because electrostatic forces become meaningful at the nanoscale, electrostatic technologies attractmuch attention in microfabrication or nanofabrication [1]. There are several recent review articles available for microencapsulation [2], [3], electrospray [4], and electrospinning [5]-[9]. However, very few have investigated connections among all these processes. The major objectives of this article are to discuss mechanisms behind these electrostatic processes and explore connections among these techniques that can lead to the design and fabrication of specific drug delivery systems using an electrostatic generator.     

A lossless switching technique for smart grid applications

Smart grid is an upgrade of the existing electricity infrastructure in which integration of non conventional energy sources are an integral part. This leads to the introduction of harmonics and increased switching losses in the system. Thus there is a need of loss less switching techniques for smart grid applications. Switched mode power supplies (SMPSs) are being extensively used in most power processes [1]. Developments were carried out centered on hard switched converters, where switching frequency is limited to 10 s of kHz [2]. The uses of soft switching techniques, [3], [4], [5], [6] zero voltage switching (ZVS) or zero current switching (ZCS), is an attempt to substantially reduce the switching losses and hence attain high efficiency at increased switching frequency. The soft-switching topologies belong to families namely resonant load converters [3], resonant switch converters [2], [4], resonant transition converters [5], [6], and most recently active clamped PWM converters [7], [8], [9]. The active clamp topology adds an active clamp network, consisting of a small auxiliary switch in series with a capacitance plus the associated drive circuitry to the traditional hard switch converters. The proposed paper basically deals with the design, modeling and simulation of a ZVS–PWM active clamp/reset forward converter having features like zero switching power losses, constant frequency and PWM operation, Soft-switching for all devices and Low voltage stresses on active devices due to clamping action.     

Assessing experiences of international students in Haiti and Benin

The past two decades have seen an increase in international experiences for engineering students focused on service and research in developing countries. Motivation for these programs reflects the growing recognition that there is a need for creating engineers with greater global awareness [18] who are familiar with the need for integrating solutions to complex problems through interdisciplinary approaches [12]. Of particular interest have been programs in humanitarian engineering that address these needs while at the same time contributing to the attractiveness of engineering, helping to bridge the gender gap that has challenged engineering education, and providing new opportunities to see engineering in a broader global/ethical realm [3], [11], [12], [14], [16], [30].     

Public health information infrastructure

The public health infrastructure is a set of agencies and organizations whose mission is to create the environment in which we can be healthy. This broadest of definitions includes state and local health departments, selected federal agencies, and a wide range of other governmental, nonprofit, and for-profit agencies and organizations [1], [2]. This report will limit itself to state and local health departments and the federal Centers for Disease Control and Prevention (CDC), the nation's foremost public health agency. With numerous exceptions, this public health infrastructure is in a state of crisis, incapable of meeting our collective needs for public health protections and services, and likely to get worse in the near-term future.     

Cellular/Tissue Engineering

Self-repair capacity of the adult skeletal muscle is deficient in its ability to restore significant tissue loss caused by traumatic injury, congenital defects, tumor ablation, prolonged denervation, or functional damage due to a variety of myopathies [1], [2]. Conventional surgical treatments including local or distant autologous muscle transposition yield a limited degree of success [2]. Alternatively, transplantation of exogenous myogenic cells (satellite cells and myoblasts) has been proposed to increase the regenerative capacity of skeletal muscle [3]. However, the clinical outcomes from intramuscular injection of allogeneic myoblasts were compromised by numerous limitations, including poor cell retention and survival, as well as immunorejection [3], [4]. Studies of other muscle-derived stem cells [5] and genetically modified myoblasts [6] are currently in progress, for their ability to overcome these limitations and improve therapeutic efficacy.     

Validation of the earth resistance formulae using computational and experimental methods for gas insulated sub-station (GIS)

This paper shows the mathematical formulas involved in obtaining the earth resistance value of a gas insulated sub-station (GIS) of 275/132 kV systems. It involves resistivity measurements and then interpretation as two layers of soil [1], [2], [3], [4], [5], [6], [7], [8]. This study compares the formulas available in previously published work and the results obtained for the field site [1], [2], [3], [8], which has not been attempted before. All of these formulas are only considered for 2 layers, which may be adequate for the design of earthing systems. Some considerations of the initial design of the earthing systems are also presented in this paper.     

Multiscale modeling of respiration

To distinguish mechanisms of impaired muscle oxygen delivery and oxidative metabolism in response to exercise, we need to evaluate how these factors affect muscle oxygen utilization (UO2m), which represents cellular respiration. During human or animal exercise experiments, direct in vivo measurement of UO2m is not feasible. Instead, pulmonary oxygen uptake (VO2p), which represents external respiration, is measured noninvasively at the mouth as an indirect indicator of metabolic processes that control cellular respiration in the working skeletal muscles [1]. Factors that contribute to the differences between the dynamic responses of UO2m and VO2p are circulatory dynamics [2], ventilation, oxygen stored in blood and muscle [3], and oxygen exchange across membranes. Therefore, using VO2p as an indicator of metabolic processes may be misleading in the presence of various disease states. In chronic obstructive pulmonary disease [4], diabetes [5], [6], or chronic heart failure [7], the dynamic response of VO2p to exercise is abnormally slow. In type 2 diabetes, low muscle blood flow may impair oxygen delivery to the working muscle. Clinically, these diseases may impair the mitochondrial oxidative metabolism as well [8].     

Simple Time-to-Failure Estimation Techniques for Reliability and Maintenance of Equipment

In 1979, MIT produced a report on maintenance with a focus on tribology. They estimated that $200 billion US dollars were spent on the direct costs associated with reliability and maintenance (R&M) [1]. At the time it was also estimated that over 14% of the 1979 gross domestic product (GDP) was lost opportunity due to improper R&M practices [2]. This level continued to increase as the industrial infrastructure aged, as well as other reliability-based reasons, to over 20% of the US GDP, or over $2.5 trillion in lost business opportunity [3]. This is greater than all but the top three economies in the world! At this time it is estimated that the R&M industry is approximately $1.2 trillion in size with up to $750 billion being the direct cost of breakdown maintenance (reactive) or generally poor, incorrect or excessive practices [4].The primary cause of the loss is that over 60% of maintenance programs are reactive, and the number is growing [2], which includes those programs which were initiated and later failed due to "maintenance entropy," or collapsing successful programs where the significant paybacks are no longer seen. At this time over 90% of maintenance initiatives fail, 57% of computerized maintenance management system (CMMS) applications fail, and over 93% of motor management programs fail [4]. The primary reason is that the present business mindset calls for immediate improvements, whereas it normally takes 12 to 24 months for a supported program to take hold and begin to show results?a rule of thumb that applies to all business practices.     

C-Sight Visual Prostheses for the Blind

Visual prostheses based on a stimulating microelectrode array to restore vision offer a promising approach for the blind and has become a rapidly growing scientific field in neurorehabilitation engineering [1]. A number of research groups from major developed countries lead the research activities in this field [1]?[12]. The goal of the C-Sight Project is to develop an implantable microelectronic medical device that will restore useful vision to blind patients. Retinitis pigmentosa (RP) and age-related macular degeneration are the two leading causes for blindness, for which there have been no effective treatments, both surgically and biologically, until now. In 1968, Brindley and Lewin [2] demonstrated that electrical stimulation of the visual cortex of blind patients could elicit phosphene. Since then, several groups [3]?[12] have been doing research on investigating the possibility of using artificial prostheses based on electrical stimulation to restore vision, and the successful development and application of cochlear implants in the deaf has enhanced the researchers? confidence.     

Good computing

Explicit attention to computer ethics began with Norbert Weiner's (1950) groundbreaking book, The Human Use of Human Beings [33]. The teaching of computer ethics arguably started in the 1970s with the distribution of Walter Maner's Starter Kit in Computer Ethics and the publication of Deborah Johnson's seminal text Computer Ethics [18], [19] (see Bynum [4] for a short history). Since that time, many excellent scholars have entered the field and much work has been done. Work on the philosophical groundwork for computing ethics [9], [31], the policy diffi culties associated with computing [22], [24], [30], and professional ethics in computing [10], [11] has multiplied and borne much fruit.     

Robust Mapping for Mobile Robot Based on Immobile Area Grid Map Considering Potential Moving Objects

Mobile robots need Simultaneous Localization and Mapping (SLAM) for autonomous movement in human living environments. The occupancy grid map used in SLAM is a conventional method which makes a map by an occupancy probability in each grid. This method renews a map based on whether an object is observed or not. In order to remove moving objects from a map, an additional method is required. However, conventional methods deal only with actually moving objects, and potential moving objects (e.g., standing humans) are mapped as static objects. Furthermore, only binary states, used or not used, are given to each object in map updating. This paper proposes the immobility area grid map to represent a map by an immobility probability in each grid. The proposed method renews a map based on the identification of observed objects by a robot's sensors, in addition to whether an object is observed or not. We introduce the map update parameter, which is set adaptively from the certainty of identification result of the object. Observed objects can take continuous states, truly static—unknown—truly moving, according to the parameter value. Potential moving objects are not mapped if the parameter takes values corresponding to moving objects. The experimental results show robust mapping in dynamic environments including potential moving objects.     

Computational fluid dynamics

Variation in the individual airway geometry makes subject-specific models essential for the study of pulmonary air flow and drug delivery. Recent evidence also suggests that early exposure to environmental pollutants has chronic, adverse effects on lung development in children from the age of ten to 18 years [1]. Thus, the capability of predicting air flow and particle deposition in the subjectspecific breathing lungs is highly desirable for understanding the correlation between structure and function and for assessing individual differences in vulnerability to airborne pollutants. Furthermore, it has been demonstrated that a strong interaction exists between lung geometry and gas properties [2]. The interaction has major implications in determining gas delivery to and clearance from the lung periphery during ventilation imaging through X-ray computed tomography (CT) using xenon gas [3]-[5] or magnetic resonance imaging (MRI) using hyperpolarized helium gas [6]-[9]. Although there is a critical need to understand these geometry?property interactions, the current state of knowledge acquired from experiments is still far from revealing the true nature of their interplays. At the same time, three-dimensional (3-D) computational fluid dynamics (CFD) simulation of air flow for the entire lung geometry remains intractable because of constraints on imaging resolution and computational power. As a result, current 3-D CFD simulations of air flow are often restricted to a few generations of branching on a fixed mesh, and most studies are based on idealized Weibel airway models. With advances in imaging and computing technologies, anatomy coupled with functional measures (ventilation and perfusion) can now be obtained via CT imaging [10], [11]. These measures provide the detail needed to interrogate the utility of CFD in providing insights into subject-specific differences in regional lung function and the underlying mechanisms of pathologic developments     

Dynamic Contrast-Enhanced Magnetic Resonance Images of the Kidney

Magnetic resonance renography (MRR) is a dynamic MR examination method that provides the functional information of the kidney and renal transplant in terms of signal intensity changes of the renal parenchyma after gadolinium-diethylene triamine pentaacetic acid (Gd- DTPA) injection. With the successive perfusion of the contrast agents through the renal cortex and medulla, the intensity curve of MRR provides the filtration information of different structures. The high spatial resolution of the MR image allows the cortical and medullary structures to be separated, a feature that is not observed by scintigraphic techniques and that plays an important role in distinguishing disease processes affecting different parts of the kidney or renal transplant. Earlier reports have indicated the usefulness of MRR in discriminating disease and measuring kidney function through the investigation of renal perfusion [1], [2].     

Aufbau der Raumladung in einem betriebswarmen Gleichspannungskabel

Übersicht Es ist schon seit einiger Zeit bekannt, daß sich in einem durch Strom erwärmten und an Gleichspannung angelegten Kabel infolge der temperaturabhängigen Leitfähigkeit des Isolationsmaterials eine Raumladung ausbildet. Der Endwert dieser Raumladung ist bereits berechnet worden: [1], [2], [3], [4]. Messungen haben gezeigt, daß sich diese Raumladung sehr langsam ausbildet [5]. In der vorliegenden Arbeit wird der zeitliche Aufbau mit erlaubten Vereinfachungen berechnet.

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Contents It is well known that space-charges do appear in current-heated underground d.c.-cables while connected to high-voltage source. The space-charges are explained by the influence of temperature on the conductivity of insulating materials. Their final local distribution has already been calculated. [1...4] Measurements have shown that the formation of space-charges goes over a long period of time [5]. In the present paper space-charge-build up as function of time is calculated with some allowed simplifications.

     

Nanocomposites-a review of electrical treeing and breakdown

Polymer nanocomposites are composite materials having several wt% of inorganic particles of nanometer dimensions homogeneously dispersed into their polymer matrix. This new type of polymer composite has recently drawn considerable attention because nanocomposites or nanostructured polymers have the potential of improving the electrical, mechanical, and thermal properties as compared to the neat polymers [1]. Polymer nanocomposites are, among other applications, increasingly desirable as coatings, structural, and packaging materials in a wide range of automobile, civil, aerospace, and electrical engineering applications. Also, nanocomposites find applications in medical services, healthcare, and decorative coloring [2], [3]. These new materials show excellent mechanical properties such as high tensile strength, increased hardness and toughness, improved flexural strength modulus, and greater heat and chemical resistance. Polymer nanocomposites are characterized by an enormously large interfacial surface area between the inorganic particles and the polymer matrix into which they are embedded. This ratio is typically more than two orders of magnitude greater than that in traditional microcomposite materials. The percentage by weight of the nanoparticles is usually quite low because of the low nanoparticle percolation threshold, particularly for the commonly used platelet and nanotube particles [4]. However, when the nanoparticle content increases beyond the percolation threshold, the nanocomposite may loose its beneficial properties [5]. Various polymers such as polyamide (PA), polyethylene (PE), polypropylene (PP), ethylene vinyl acetate (EVA), epoxy resin (EP), and silicone rubber (SiR) can be combined with inorganic particles such as layered silicate (LS), silica (SiO2), titania (TiO2), alumina (Al2O3), and magnesia (MgO) [1], and there are a number of papers that describe the tests and the properties of the aforementioned combinations of materials [6]?[10].