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The presence of distributed generation (DG) in a power distribution network can cause difficulties in managing the voltage, power flow and fault level as the network was designed for supplying passive loads. This study focuses on the control of a back-to-back (B2B) voltage source converter operated as a synchronverter and a soft open point (SOP) between adjacent feeders to mitigate the voltage fluctuation caused by DG and to increase the reliability of the supply without increasing the fault level. Better reliability is achieved as the B2B converter can continue to supply the loads when a loss of mains occurs on one side. The proposed control of the two DC–AC converters, which also needs to regulate the DC link voltage and adapts the synchronverter algorithm to the new application requirements, so that events will cause minimum disruption. Simulation shows that the B2B-synchronverter is capable of regulating the load voltage under normal mains connected condition, and also limiting the fault current and supplying the loads within its rating during islanding, providing seamless transition to the islanded mode.

Synchronverters are inverters that mimic the behavior of synchronous generators. In this paper, we propose five modifications to the synchronverter algorithm from the paper “Synchronverters: Inverters that mimic synchronous generators,” ( IEEE Trans. Ind. Electron. , vol. 58, no. 4, pp. 1259–1267, Apr. 2011), to improve its stability and performance. These modifications are implemented in software and do not require any changes in the inverter hardware. The first two modifications concern the control of the virtual field current in the synchronverter so that it is more robust to faults. We prove the stability of the grid-connected synchronverter with this improved field current controller. The third modification is to increase the effective size of the filter inductors virtually. This is motivated using results from the stability analysis of a constant field current synchronous generator connected to an ac power grid and also by practical considerations. Simulations and experiments show that this leads to a much better response to changes in grid frequency, voltage, or to imbalance in the grid. The fourth modification is to change the formula for the (virtual) nominal active mechanical torque to take into account the (virtual) losses in the output impedance of the converter. This makes the tracking of the desired active power much more accurate. The fifth modification is to introduce virtual capacitors in series with the inverter outputs to filter spurious dc components from the current supplied to the grid.

We present a research of a possibility of constructing a photovoltaic DC to AC inverter based on a synchronverter operation principle. A possible area of an application for this inverter is in a photovoltaic power plant that is connected to the low voltage grid. We give a brief explanation about a theoretical control algorithm that governs an operation of the inverter including Maximum Power Point Tracking (MPPT). A Simulink average model verifies the performance of the algorithm. We also present a brief explanation of the experiments that are in progress in Smart Grid Interoperability Laboratory of the European Commission Joint Research Center in Ispra, Italy. The main goal of these experiments is to verify a performance of the control algorithm by using an external PCB uploaded with the control algorithm and connected to the Real Time Digital Simulator (RTDS).

The virtual infinite capacitor (VIC) is a nonlinear active capacitor for DC voltage filtering. It can replace large and unreliable electrolytic capacitors and is intended for DC systems where random fluctuations of the DC bus voltage may occur. In this paper, we investigate the use of a VIC for stabilizing the DC bus voltage in an electric vehicle (EV) charger. In order to solve the intrinsic problem of the second harmonic ripple power in a single-phase AC/DC converter, a plug-and-play VIC is used to replace the bulky DC-link capacitor for voltage filtering.

We define the virtual infinite capacitor (VIC) as a nonlinear capacitor that has the property that for an interval of the charge Q (the operating range), the voltage V remains constant. We propose a lossless approximate realization for the VIC using a switched power converter and capacitors. This circuit is simple but it requires a complex control algorithm that we describe. There are two controllers needed to operate a VIC: the voltage controller acts fast to maintain the desired terminal voltage, while the charge controller acts more slowly and maintains the charge Q in the desired operating range by influencing the incoming current. The VIC is useful as a filter capacitor for various applications, for example power factor compensators (PFC), as we describe. In spite of using small capacitors, the VIC can replace a very large capacitor in applications that do not require substantial energy storage. We give simulation results for a PFC working in critical conduction mode with a VIC for output voltage filtering.

Permanent-magnet synchronous motors (PMSMs) are widely used as high-performance variable-speed drives. Ripple in the electric torque of such motors is often a source of vibration and tracking errors, especially at low speeds. We study the torque characteristics of PMSMs and propose a method to minimize the torque ripple. First, we establish a detailed model for the motor and present a Fourier analysis of the torque ripple, caused by the non-sinusoidal back electro-motive force (BEMF) and the cogging torque, where the main conclusion is that the frequencies present in the torque disturbance are integer multiples of six times the electric frequency. The resulting model is highly nonlinear. We propose an adaptive controller based on the internal model principle, where the resonant frequencies of the controller and the associated gains change according to the motor speed. This is achieved by replacing the time variable by the motor angle, which simplifies the nonlinear model. Our approach is passivity based a...

We study the optimal control for the maximization of profit in a grid-connected energy storage system. The changing price of electricity is assumed to be known in advance over the optimization horizon. The system has a storage device (such as a battery) which we model as a capacitor-type device, with natural constraints on its voltage and current. We prove the existence of an optimal control and the fact that a bang-off-bang type policy is optimal. The proof uses Filippov's theorem and the Pontryagin minimum principle.

We study the stability of the feedback interconnection\ud of two impedance passive linear time-invariant systems,\ud of which one is finite-dimensional. The closed-loop system is well known to be impedance passive, but no stability properties follow from this alone. We are interested in two main issues: (1)\ud the strong stability of the operator semigroup associated with the closed-loop system, (2) the input-output stability (meaning transfer function in H∞) of the closed-loop system. Our results are illustrated with the system obtained from the non-uniform SCOLE (NASA Spacecraft Control Laboratory Experiment) model representing a vertical beam clamped at the bottom, with a rigid body having a large mass on top, connected with a trolley\ud mounted on top of the rigid body, via a spring and a damper. Such an arrangement called a tuned mass damper (TMD), is used to stabilize tall buildings. We show that the SCOLE-TMD system is strongly stable on the energy state space and that the system is input-output stable from the horizontal force input to the horizontal velocity output.

We propose a plug-and-play realization of the virtual infinite capacitor (VIC), which is an electronic circuit recently proposed in the literature for DC voltage filtering. The VIC is meant to replace large, expensive and unreliable electrolytic capacitors, and is mainly intended for applications where random fluctuations of the DC bus voltage may occur (i.e., the VIC is not tuned to one particular ripple frequerncy). Connecting a VIC into a larger circuit, such as a power supply based on a power factor compensator (PFC) is relatively complicated, because the VIC charge controller needs access to the voltage control loop of the power source (e.g., the PFC). The plug-and-play realization of the VIC, proposed in this paper, can be connected directly to the DC bus like a usual filtering capacitor, no extra connections are needed. This is achieved by automatically adjusting the reference voltage of the VIC so that it will be equal to the equilibrium voltage of the DC bus (i.e., the constant DC bus voltage at which current supply and current demand are equal). We investigate carefully the output impedance of the plug-and-play VIC. This impedance must behave like a relatively small capacitor both at very low and at very high frequencies, but must be very small (ideally, zero) at an intermediate range of frequencies (the range where the ripple is expected). For the stability of complex interconnected systems, it is recommended that the output impedance of the plug-and-play VIC should be positive-real. We discuss how to achieve these properties by very careful choice of controllers and filters. The results are tested by simulation and experiment using a 300V demo system with a 270W load.

We evaluate the flying capacitor multilevel converter (FCMC) with one switched-capacitor cell under asymmetric working condition, as a highly efficient hardware realization for the virtual infinite capacitor (VIC). The VIC is a type of electronic circuit, recently introduced to replace large, expensive and unreliable electrolytic capacitors, mainly intended for smoothing random fluctuations of a DC bus voltage V. By the proposed novel control algorithm, the pulsating power that the VIC takes away from the DC bus is shared among the main buffering and the flying capacitors, with the proportion set by a prescribed value. This facilitates to reduce the physical size of the converter, and hence achieve higher power density. This flying capacitor converter operates in an unconventional way, as the flying capacitor voltage is highly variable and hence the converter works under an asymmetric scenario. An average model of this specific working mode is presented, with the design of a linearized current controller. To improve the capacitance reduction ratio, the average value the of flying capacitor voltage is regulated to a relatively high value, instead of V/2. This is achieved by adjusting the phase shift of the PWM carriers. Both continuous and discontinuous conduction modes are investigated, and verified by simulation.

We experimentally show the performance of a Virtual Infinite Capacitor (VIC) in suppressing the voltage ripple. VIC mainly uses a bi-directional DC-DC converter with only two small capacitors inside to mimic the filtering process of a large capacitor by applying suitable control algorithms. It was firstly proposed in [1], [2] and then improved in [3] in both control algorithms and circuit designs. Based on VIC's control algorithm in, [3] we injected the DC voltage together with a 50Hz, 85V (peak-to-peak) sinusoidal ripple to the VIC, and we achieved outstanding filtering performance in both the simulation and experiment. The 85V voltage ripple is eliminated and the DC voltage is extracted with no visible 50Hz ripples.

Summary This paper proposes three near-optimal (to a desired degree) deterministic charge and discharge policies for the maximization of profit in a grid-connected storage system. The changing price of electricity is assumed to be known in advance. Three near-optimal algorithms are developed for the following three versions of this optimization problem: (1) The system has supercapacitor type storage, controlled in continuous time. (2) The system has supercapacitor or battery type storage, and it is controlled in discrete time (i.e., it must give constant power during each sampling period). A battery type storage model takes into account the diffusion of charges. (3) The system has battery type storage, controlled in continuous time. We give algorithms for the approximate solution of these problems using dynamic programming, and we compare the resulting optimal charge/discharge policies. We have proved that in case 1 a bang off bang type policy is optimal. This new result allows the use of more efficient optimal control algorithms in case 1. We discuss the advantages of using a battery model and give simulation and experimental results. Copyright © 2014 John Wiley & Sons, Ltd.

SUMMARY This paper proposes a control method for a doubly fed induction generator (DFIG) driven by a wind turbine, whose rotor is connected to the power grid via two back-to-back pulse-width modulation power converters. First, we design a rotor current controller for this system using the linear matrix inequality based approach to linear parameter varying systems, which takes into account the nonlinear dynamics of the system. We propose a two-loop hierarchical control structure. The inner-loop current controller, which considers the synchronous speed and the generator rotor speed as the components of the parameter vector, achieves tracking of the rotor current reference signals. The outer-loop electrical torque controller aims for wind energy capture maximization and also grid frequency support, and it generates the reference rotor current. We perform a controller reduction for the inner-loop linear parameter varying controller, which is not doable by conventional model-reduction techniques, because the controller is parameter dependent. In simulation, the reduced-order controller has been tested on a nonlinear fourth-order DFIG model with a two-mass model for the drive train. Stability and high performance have been achieved over the entire operating range of the DFIG in the wind turbine. Simulation results have demonstrated the capability of the proposed two-loop control system to implement also grid frequency support. Copyright © 2013 John Wiley & Sons, Ltd.

Synchronous generators are an essential component of the electric grid. Recently, the stability of the electric grid has become an area of high interest and intensive research. We discuss the stability of a single generator connected to an infinite bus, and show that certain reduced models fail to predict the behavior of this system.

The modular multilevel converter (MMC) is now very popular in high power high voltage applications. However, the bulky capacitor employed in each submodule (SM) accounts for more than half of the total volume and weight of the entire system. This prohibits further system level integration due to space and weight restrictions. To tackle this issue, a virtual infinite capacitor (VIC)-based active SM (VIC-SM) configuration is presented in this paper. Special attention is given to the charge control of an MMC with a low number of SMs. The concept is verified in the MATLAB/Simulink environment with a downscaled case study of a 50W 400VDC/110VAC 11 levels single phase MMC. We show that the VIC-SM can reduce the SM capacitance by 60% with sufficient safety margin.

We demonstrate that deterministic sea wave prediction (DSWP) combined with constrained optimal control can dramatically improve the efficiency of sea wave energy converters (WECs), while maintaining their safe operation. We focus on a point absorber WEC employing a hydraulic/electric power take-off system. Maximizing energy take-off while minimizing the risk of damage is formulated as an optimal control problem with a disturbance input (the sea elevation) and with both state and input constraints. This optimal control problem is non-convex, which prevents us from using quadratic programming algorithms for the optimal solution. We demonstrate that the optimum can be achieved by bang–bang control. This paves the way to adopt a dynamic programming (DP) algorithm to resolve the on-line optimization problem efficiently. Simulation results show that this approach is very effective, yielding at least a two-fold increase in energy output as compared with control schemes which do not exploit DSWP. This level of improvement is possible even using relatively low precision DSWP over short time horizons. A key finding is that only about 1 second of prediction horizon is required, however, the technical difficulties involved in obtaining good estimates necessitate a DSWP system capable of prediction over tens of seconds.

This study was designed to develop a descriptive profile of parents and caregivers who bring their children to the emergency department (ED) for nonurgent issues and to explore the reasons for presenting to an urban hospital pediatric ED for nonurgent conditions. Such work is necessary to develop effective interventions.A total of 106 parents/caregivers whose child was triaged with a nonemergent/urgent condition completed a 15- to 20-minute computerized survey (English and Spanish) in an urban pediatric ED.Most respondents described themselves as Latino (76%) and foreign born (62%). About one half (49%) reported having an annual income of less than $20,000, and 43% of respondents did not have health insurance for themselves. Almost all (95%) of the index children had a primary care physician and health insurance. Despite being triaged as nonurgent, more than one half (63%) described their child's condition as "very" or "extremely" urgent. About one half of the respondents reported not receiving basic information on childhood illnesses from their child's physician. Reasons for nonurgent visits seemed to revolve around issues of convenience and perception of quality of care.Interventions should focus on health literacy and ensure that parents are provided relevant and accurate education on pediatric illnesses and common safety concerns; by increasing parental education on pediatric health, parents may be better able to assess acuity of their child's health issues.

In this paper, the idea of operating an inverter to mimic a synchronous generator (SG) is motivated and developed. We call the inverters that are operated in this way synchronverters. Using synchronverters, the well-established theory/algorithms used to control SGs can still be used in power systems where a significant proportion of the generating capacity is inverter-based. We describe the dynamics, implementation, and operation of synchronverters. The real and reactive power delivered by synchronverters connected in parallel and operated as generators can be automatically shared using the well-known frequency- and voltage-drooping mechanisms. Synchronverters can be easily operated also in island mode, and hence, they provide an ideal solution for microgrids or smart grids. Both simulation and experimental results are given to verify the idea.

Purpose. This study investigated human immunodeficiency virus (HIV) testing and risk behaviors in a longitudinal sample of young men who have sex with men (YMSM). Design. Data came from the Healthy Young Men's study, comprising five waves of nonexperimental survey data collection every 6 months between February 2005 and January 2008. Setting. Participants were recruited from public venues in Los Angeles County in which YMSM spend time. Subjects. A total of 526 participants (24% African-American, 37% white, 39% Latino; mean age, 20.14 years; range, 18–24 years) were enrolled. Retention was 93%. Measures. Testing recency was assessed with a four-point ordinal scale. HIV risk behaviors were operationalized as binary measures of unprotected anal intercourse with multiple partners or partners with unknown or discordant serostatus, club drug use, and illicit drug use over the prior 3 months. Analysis. Correlations, Cochran's Q tests, and repeated-measures analysis of variance (ANOVA) were performed in SPSS. Analyses included all data available at each wave. Results. No significant correlations emerged between testing recency and sex risk at any wave. Repeated-measures ANOVA showed significant positive, linear change in HIV testing recency over time, but no significant changes emerged for sex risk or drug use. Conclusion. Although participation in testing increased, there was no corresponding change in HIV risk behavior. Initiatives may need to target risk behavior separately and specifically to reduce these behaviors among YMSM. (Am J Health Promot 2011;25[4]:244–247.)

We propose the parallel virtual infinite capacitor (PVIC) concept, which refers to two virtual infinite capacitors (VIC) connected to the same DC link and sharing one capacitor, one tuned to low frequencies (LF) and one tuned to high frequencies (HF). A PVIC can suppress voltage variations (ripple) in a wider frequency range than a usual VIC. The LF-VIC is controlled by a sliding mode controller to regulate the low-frequency component of the voltage to its reference value, and by a proportional-integral (PI) controller to maintain its state of charge within the desired operating range and achieve the ‘plug-and-play’ pattern of PVIC. The HF-VIC is controlled by another sliding mode controller to limit the high-frequency ripples and also to keep its state of charge within a reasonable operating interval. As our main application, we use the PVIC to replace a DC-link capacitor for voltage filtering on the DC link of a doubly fed induction generator (DFIG), which is driven by a WindPact (WP) 1.5-MW wind turbine under different grid conditions with turbulent wind input. The simulation study indicates that the PVIC provides much better voltage stabilisation than a DC-link capacitor with the same capacitance, especially in the low frequency range.

SUMMARY This paper investigates the stability of a variable-speed wind turbine operating under low to medium wind speed. The turbine is controlled to capture as much wind energy as possible. We concentrate on the mechanical level of the turbine system, more precisely on the drive-train with the standard quadratic generator torque controller. We consider both the one-mass and the two-mass models for the drive-train, with the inputs being the deviation of the active torque from an arbitrary positive nominal value and the tracking error of the generator torque. We show that the turbine system is input-to-state stable for the one-mass model and integral input-to-state stable for the two-mass model. Copyright c ∞ 2008 John Wiley & Sons, Ltd.

Recruiting a scientifically sound cohort of young men who have sex with men (YMSM) is an enduring research challenge. The few cohort studies that have been conducted to date on YMSM have relied on non-probability sampling methods to construct their cohorts. While these studies have provided valuable information about HIV risk behaviors among YMSM, their generalizability to broader YMSM populations is limited.In this paper the authors describe a venue-based sampling methodology used to recruit a large and diverse cohort of YMSM from public venues in Los Angeles County. Venue-based sampling is a multi-stage, probability sampling design that uses standard outreach techniques and standard survey methods to systematically enumerate, sample, and survey hard-to-reach populations. The study design allowed the authors to estimate individual, familial and interpersonal psychosocial factors associated with HIV risk and health seeking behaviors for a cohort of YMSM with known properties. Study participants completed an extensive baseline survey and over a two year period will complete four follow-up surveys at six-month intervals. The baseline survey was administered in both English and Spanish.

Permanent magnet synchronous motors (PMSMs) are widely used as high-performance variable-speed drives. Ripple in the electric torque of such motors is often a source of vibration and tracking errors, especially at low speeds. In this paper we study the torque characteristics of PMSMs and propose a method to minimize the torque ripple. First, we establish a model for the motor to cover all dynamics without any assumptions on the signals. Next, we present a Fourier analysis of the torque ripple, caused by non-sinusoidal EMF and cogging torque. We propose a controller based on the internal model principle, and we prove the stability of the (non-linear) closed-loop, based on the passivity of the motor model. Finally, simulation results are given to verify the concept.

Three-phase four-wire inverters, with either three-leg or four-leg topology, are useful for interfacing distributed generation to networks of unbalanced loads, but neither of the available circuit topologies is ideal. The split-link three-leg topology (with six switches) suffers from poor DC voltage utilization compared with the four-leg topology (with eight switches). The four-leg topology has an electromagnetic compatibility (EMC) difficulty because it imposes large-amplitude high-frequency voltages between the DC-link busbars and ground. To obtain both good dc voltage utilization and good EMC performance, it is proposed to use a split-link inverter with an active balancing circuit (also eight switches). The balancing circuit is used to modulate the DC busbar offset voltage to make better use of the available DC-link voltage. The optimum voltage term is established to be a third harmonic term, and the DC voltage utilization is improved. A deadbeat controller supplemented with a repetitive controller is designed to give good tracking and good disturbance rejection for the busbar offset voltage. System performance is studied through an experimental test rig.

Young men who have sex with men (MSM) in urban areas of the United States continue to be vulnerable to HIV infection. Qualitative data collected with participants in a community level HIV intervention in West Hollywood and Orange County, California, suggest that space—both actual physical space and the concept of having space—should be an integral part of an HIV prevention intervention for young MSM. Having such spaces appears to contribute to youth sense of empowerment and efficacy and foster community building, all important components of an effective HIV prevention. Data were drawn from a qualitative research sample of 73. Through narratives, young men describe specific characteristics of the space necessary for effective HIV intervention, including mentoring and supportive staff, tolerant and like–minded peers, information exchange, opportunities for strengthening self-esteem, and a sense of collaborative community invested in social change.

Geographic information system (GIS) analysis is an emerging tool for public health intervention planning. Connect to Protect, a researcher–community collaboration working in 15 cities to reduce HIV infection among youths, developed GIS databases of local health, crime, and demographic data to evaluate the geographic epidemiology of sexually transmitted infections and HIV risk among adolescents. We describe the process and problems of data acquisition, analysis, and mapping in the development of structural interventions, demonstrating how program planners can use this technology to inform and improve planning decisions. The Connect to Protect project’s experience suggests strategies for incorporating public data and GIS technology into the next generation of public health interventions.

Introduction:Mildly injured and “worried well” patients can have profound effects on the management of a mass-casualty incident. The objective of this study is to describe the characteristics and lessons learned from an event that occurred on 28 August 2005 near the central bus station in Beer-Sheva, Israel. The unique profile of injuries allows for the examination of the medical and operational aspects of the management of mild casualties.Methods:Data were collected during and after the event, using patient records and formal debriefings.They were processed focusing on the characteristics of patient complaints, medical response, and the dynamics of admission.Results:A total of 64 patients presented to the local emergency department, including two critical casualties. The remaining 62 patients were mildly injured or suffered from stress. Patient presentation to the emergency department was bi-phasic; during the first two hours following the attack (i.e., early phase), the rate of arrival was high (one patient every three minutes), and anxiety was the most frequent chief complaint.During the second phase, the rate of arrival was lower (one patient every 27 minutes), and the typical chief complaint was somatic. Additionally, tinnitus and complaints related to minor trauma also were recorded frequently.Psychiatric consultation was obtained for 58 (91%) of the patients. Social services were involved in the care of 47 of the patients (73%).Otolaryngology and surgery consultations were obtained for 45% and 44%, respectively. The need for some medical specialties (e.g., surgery and orthopedics) mainly was during the first phase, whereas others, mainly psychiatry and otolaryngology, were needed during both phases. Only 13 patients (20%) needed a consultation from internal medicine.Conclusions:Following a terrorist attack, a large number of mildly injured victims and those experiencing stress are to be expected, without a direct relation to the effectiveness of the attack. Mildly injured patients tend to appear in two phases. In the first phase, the rate of admission is expected to be higher. Due to the high incidence of anxiety and other stress-related phenomena, many mildly injured patients will require psychiatric evaluation. In the case of a bombing attack, many of the victims must be evaluated by an otolaryngologist.

Background In recent years, the World Health Organization in general, and Israel in particular, have dealt with mass casualty events (MCEs) resulting from terrorism. Children are the casualties in many of these events—a reality that forces hospitals to prepare to deal with such a scenario. A literature review designed to identify unique recommendations regarding pediatric MCEs highlights both a lack of existing training programs and uncertainty on the part of health care staff when dealing with these events. Objectives The purpose of the study was to examine the preparedness level of emergency department staff to deal with MCEs involving pediatric casualties. The study included 104 physicians and nurses working in, or responding to, the emergency department at a hospital in Israel. Method The study included a 41-item questionnaire examining perception, approaches, and staff knowledge regarding dealing with pediatric MCEs versus those involving adults. The reliability of all sections of the questionnaire ranged between Chronbach's α coefficient 0.6 α-0.94. Results The preparedness levels for MCEs involving children were found to be low. Study participants ranked the likelihood of a pediatric MCE lower than one involving adults, while ranking significantly higher ( P = .000) their ability to cope mentally and the knowledge and skills required when treating adults involved in MCEs. While nurses ranked higher than physicians regarding their knowledge and skills in dealing with pediatric MCE casualties, the level of knowledge for MCEs involving children was low in all subjects. Staff agreement for the parent of an MCE victim to be present during treatment was medium-low. Implications On the basis of these findings, additional research involving a larger number of individuals and hospitals is indicated to determine if these results are consistent throughout the region.

Purpose To describe the range of health and mental health problems for which young men who have sex with men (YMSM) may be at risk. Methods An audio-computer-assisted survey was administered to a large, ethnically diverse sample of 526 YMSM (aged 18–24 years) recruited from bars, clubs, and other social venues using a venue-based probability sampling method. Results Subjects reported a range of health and mental health problems, and involvement in health-compromising behaviors, such as overweight/obesity, depression, and suicidal thoughts/attempts, and many were found to have high rates of sexually transmitted infections. Moreover, many reported not having insurance coverage and/or limited access to care. Conclusions Many of the health concerns and risks reported by these young men are preventable and can be addressed by any number of sectors, including health care and social service providers, religious organizations, schools, and employers.

There is growing behavioral and epidemiological evidence to suggest that young men who have sex with men (YMSM) are at high risk for becoming HIV-infected. Unfortunately, relatively little research has been conducted to examine the range of individual, social, and community-level factors that put these young men at increased risk. To address existing gaps in the literature, the Healthy Young Men's (HYM) Study was launched in Los Angeles to examine the range of factors associated with HIV risk and protective behaviors within an ethnically diverse sample of 526 YMSM recruited using a venue-based stratified probability sampling design. In this paper we present findings that demonstrate that YMSM who experience residential instability, who have been forced to leave their home because of their sexuality, and/or who are precariously housed are at significantly greater risk for drug use and involvement in HIV risk-related behaviors.

Little is known about young men who have sex with men's use of club drugs and the risk factors associated with such use. A structured survey was administered in 2005 to 496 young men who were 18-22 years old (40% were 18-19 years old); self-identified as with a same-sex sexuality (83%), bisexual (16%), and/or had had sex with a man (97%); Caucasian (35%), African American (24%), and Latino of Mexican descent (40%). Subjects were recruited from gay-identified venues in Los Angeles, California using a venue-based probability sampling design. Descriptive statistics revealed a high prevalence of drug and club drug use. Regression analyses revealed risk factors associated with recent club drug use, including place of residence, religiosity, disclosure of sexuality to family, frequency of attendance at bars/clubs, and involvement in sexual exchange and the street economy. Limitations and implications of this research are discussed.

We define the virtual infinite capacitor (VIC) as a nonlinear capacitor that has the property that for an interval of the charge Q (the operating range), the voltage V remains constant. We propose a lossless zero-voltage switching realization for the VIC using a switched power converter and capacitors. This circuit is simple but it requires a complex control algorithm that we describe. There are two controllers needed to operate a VIC: the voltage controller acts fast to maintain the desired terminal voltage, while the charge controller acts more slowly and maintains the charge Q in the desired operating range by influencing the incoming current. The VIC is useful as a filter capacitor for various applications, for example power factor compensators (PFC), as we describe. In spite of using small capacitors, the VIC can replace a very large capacitor in applications that do not require substantial energy storage. We give simulation results for a PFC working in critical conduction mode with a VIC for output voltage filtering.

This article describes an interdisciplinary and theory-based radio campaign that has been developed to counteract, and sensitize citizens to hate speech in the Democratic Republic of the Congo (DRC). The article provides a brief overview of the instrumentalization of hate speech and the violent effects it has had in the Great Lakes region of Africa. A summary of the most recent events in the DRC is given. Here, hate speech was used in the presidential election campaigns in 2006, contributing to a polarization of the country and giving the campaign an ethnic underpinning. A radio program developed to counteract hate speech during the election campaigns is described. Its theoretical basis, the application of Staub’s (1989) theory of the evolution of mass violence to hate speech, is presented. Based on this and other relevant psychological concepts, characteristics and psychological aspects of hate speech are summarized, and markers and guidelines are provided that allow listeners to detect and counteract hate speech.

This study describes the perceived influence of group-level HIV interventions on persons living with HIV in Los Angeles, California. Funded by the Centers for Disease Control and Prevention and developed by a broad range of community organizations, group-level interventions ranged from small skills-building workshops to large educational forums and to intensive weekend gatherings. Recognizing the relationship between psychosocial factors and HIV-related risk taking, these interventions were designed not only to provide HIV prevention education and develop risk reduction skills but also to bring people together to facilitate the formation of supportive relationships. The formative data presented here are based on 35 qualitative interviews conducted with a sample of intervention participants. Interviews highlight the experiential opportunities that group interventions offer with respect to HIV knowledge, social support, HIV disclosure skills, and HIV risk reductions. Participants talked highly of their experiences in group-level interventions, suggesting that they should be considered an important prevention strategy for people living with HIV.

This paper proposes a voltage controller design method for DC-AC converters supplying power to a microgrid, which is also connected to the power grid. This converter is meant to operate in conjunction with a small power generating unit. The design of the output voltage controller is based on H/sup /spl infin// and repetitive control techniques. This leads to a very low harmonic distortion of the output voltage, even in the presence of nonlinear loads and/or grid distortions. The output voltage controller contains an infinite-dimensional internal model, which enables it to reject all periodic disturbances which have the same period as the grid voltage, and whose highest frequency components are up to approximately 1.5 kHz.

We demonstrate how adding synchronverters to a power grid can help stabilize the system. By using fast communication between two synchronverters in separate areas, we can create virtual friction between their virtual rotors. We show by simulations that this virtual friction is an effective way to suppress inter-area oscillations.

We investigate the strong stabilisation of a wind turbine tower model in the plane of the turbine blades, which comprises a nonuniform NASA Spacecraft Control Laboratory Experiment (SCOLE) system and a two-mass drive-train model (with gearbox). The control input is the torque created by the electrical generator. Using a strong stabilisation theorem for a class of impedance passive linear systems with bounded control and observation operators, we show that the wind turbine tower model can be strongly stabilised. The control is by static output feedback from the angular velocities of the nacelle and the generator rotor.

In many engineering problems, periodic signals which should be either tracked (reference signals) or rejected (disturbances) occur. A successful way of solving such problems is repetitive control, a well-known technique based on the internal model principle. Here, we extend repetitive control theory to plants with several outputs, of which only some have to track reference signals. The other outputs are used to supply additional information to the controller. We analyze stability, robustness and give estimates of the size of the error in such a feedback system. Our approach to this analysis is new, based on the recent theory of regular linear systems. We introduce a correction to the amount of delay used in the internal model and this leads to a significant improvement in performance (i.e., to a smaller error).

Objectives. We investigated the roles of House membership and the influence of social and sexual network members on the sexual risk behavior of men in the Los Angeles House and Ball community. Methods. From February 2009 to January 2010, male participants (n = 233) completed interviewer-assisted surveys during a House meeting or Ball event. We used logistic regression to model the effects of sexual network size, influence of sexual network members, House membership status, and their interactions on high-risk sex. Results. Significant predictors of high-risk sex included number of sexual partners in the nominated social network, multiethnicity, and previous diagnosis of sexually transmitted infection. House membership was protective against high-risk sex. Additionally, a 3-way interaction emerged between number of sexual partners in the network, influence, and network members’ House membership. Conclusions. Future research should assess network members’ attitudes and behavior in detail to provide a greater understanding of the dynamics of social influence and to identify additional avenues for intervention.

African American young men who have sex with men (AAYMSM) represent the largest proportion of new HIV infections among MSM. While evidence-based interventions are lacking, all too often HIV interventions are implemented in a community without thoroughly understanding its needs, risks and assets. AAYMSM are not homogenous; subgroups exist that may require different approaches to be effective. The House and Ball communities represent one such subgroup. A community-engaged, mixed-methods approach was used. Participant observations, qualitative interviews (N = 26), and a survey at House/Ball events (N = 252) were completed. Survey data broadly describe the community. For example: 69 % of survey respondents identify as gay; 25 % as bisexual; 13 % reported recent use of ecstasy and 11 % recently participated in sex exchange. The depth of qualitative data is key for intervention development. For example, while the survey provides broad descriptions of respondents' involvement in the House and Ball communities, leaders provided in-depth descriptions of the structure of the House and Ball scene-something vital to the development of HIV prevention programs within these communities. This kind of rigorous study is recommended prior to implementing an intervention. Findings are discussed in relation to leveraging the communities' supportive aspects to design culturally relevant HIV prevention programs.

This study was undertaken to determine whether present regulations for discarding milk from cows treated with sulfadimethoxine (SDM) can be supported by modern analytical methodology. Two groups of milking cows (10 in first group; 11 in the second) were treated orally with SDM at the recommended dose levels for 5 days. The SDM concentration in the milk was determined with 4 methods (Charm Inhibition Assay [CIA], Charm II, enzyme linked immunosorbent assay, and liquid chromatography) during the treatment and the subsequent withdrawal periods. The results of the 4 assays were compared.

This paper proposes near optimal (to a desired degree) deterministic charge/discharge policies for the maximization of profit in a grid-connected storage system. The changing price of electricity is assumed to be known. We give algorithms for the approximate solution using dynamic programming. We prove that a bang off bang (BOB) type policy is optimal if the storage device is a supercapacitor. The advantages of using a battery model that takes into account the diffusion of charges are discussed and both simulation and experimental results are shown.

African-American young men who have sex with men and transgender persons are at elevated risk for HIV infection. House and Ball communities, networks of mostly African-American gay, bisexual, and transgender individuals who compete in modeling and dance, represent a prime venue for HIV prevention with these difficult-to-reach populations; however, little research exists on effective approaches to HIV prevention within these communities. Using a mixed-methods approach, the present study sought to document participation in HIV prevention activities of a sample from the Los Angeles House and Ball communities (n = 263) in order to inform future service development. While 80% of participants were tested for HIV within the past 6 months, only 26% report HIV prevention program attendance. House leaders recommend a holistic approach to HIV prevention, one that incorporates attention to social problems beyond HIV, including poverty, housing difficulties, and lack of job training.

This article describes a community-engaged study with the Los Angeles House and Ball scene in which the perspectives of the leaders of these communities are captured to better understand how the House and Ball communities may protect or increase its members' risks for HIV infection. Data were collected through in-depth interviews with House parents (N = 26). This study identified key features of both support (e.g., family and support, acceptance, and validation and recognition) and risk (e.g., members' struggles to maintain status in the Ballroom scene, sex work, substance use, danger of becoming too involved in the Ball community, and perception and stigma of the Ballroom scene within the larger gay community) within these communities. Findings are discussed in relation to framing how to leverage the supportive aspects of the House and Ball communities to design relevant HIV-prevention interventions.

We derive a model for a wind turbine tower in the plane of the turbine blades, consisting of a non-uniform SCOLE beam system coupled with a two-mass drive-train model (with gearbox). The control input of this wind turbine tower model is the torque created by the electrical generator. Using the theory of coupled linear systems developed by us recently, we show that this wind turbine tower model is well-posed and regular on either the energy state space Xc or the domain of its generator on Xc, denoted by X 1 c. We also show that generically, this model is exactly controllable on X 1 c in arbitrarily short time. More precisely, for every T > 0 we show that if we vary a certain parameter in the model, then exact controllability in time T holds for all except three values of the parameter.

We derive a model for a wind turbine tower in the plane of the turbine blades, that comprises a non-uniform SCOLE system and a two-mass drive-train model (with gearbox). The input of this model is the electric torque created by the electrical generator. We show the impedance passivity and well-posedness of this model in the natural state space. We also prove that generically, this system can be strongly stabilized by feedback using information about the angular velocity of the nacelle and the angular velocity of the generator rotor.

The Internet has opened many doors with its accessibility to information, entertainment and web-based communities. For young men who have sex with men (YMSM), the Internet can provide access to information on relevant sexual behavior and health information, stories from other men about relationship issues, and a venue for locating potential sexual and dating partners. Understanding YMSM’s motivations for going online for information, advice or sexual relationships, is important as the Internet becomes increasingly used not only as a space to find sexual partners, but also as a venue for HIV and STI interventions. Having an understanding of the risks associated with searching for partners online, and how and why YMSM use the Internet for a variety of purposes, can inform the development of more effective Internet-based risk reduction programs. This article presents qualitative and quantitative data from the Healthy Young Men’s Study, a longitudinal study of an ethnically diverse cohort of 526 YMSM. Qualitative interviews (N = 24) described not only the prevalence of using the Internet for finding sexual partners and the possible benefits and risks associated with that practice, but also the processes and perceptions of using this mechanism. Our data indicate that YMSM used the Internet to find information related to sex and sexuality, seek friendships, sexual partners as well as “hook-ups” or casual sex. Findings were presented in relation to how YMSM researchers and interventionists can identify how to most effectively reach YMSM through online methods.

A growing body of research has investigated the effectiveness of abstinence-only sexual education. There remains a dearth of research on the relevant sexual health information available to young men who have sex with men (YMSM). Drawing on a mixed-methods study with 526 YMSM, this study explores how and where YMSM receive relevant information on sexual health/behavior. Findings indicate that information related to gay men’s sexuality is not readily available from family, friends, or schools. At initiation of anal intercourse, respondents generally had limited information about HIV and sexually transmitted infections (STIs). In some cases, this resulted in the perception that activities such as unprotected sex were “low risk.” Many mentioned they first learned about anal sex during their sexual debut, describing painful and/or unpleasant experiences. Some relied on older/more experienced partners, the Internet, and pornography for information. Findings are discussed in relation to how providers can help YMSM build solid foundations of sexual education to protect them from STI and HIV infection.

In this paper, the idea of operating an inverter as a synchronous generator is developed after establishing a model for synchronous generators to cover all dynamics without any assumptions on the signals. The inverters which are operated in this way are called static synchronous generators (SSG). This means that the well-established theory/device for synchronous generators can still be used for inverters, which will dominate the power generation in the future because of the increasing share of distributed generation sources and renewable energy sources utilised. The power of an SSG can be regulated using the well-known frequency and voltage drooping mechanism. SSGs can also be easily operated in grid-connected mode or island mode. Simulation results are given to verify the idea.