Effects of hyperbaric (6 ATA) pressure on voluntary and evoked skeletal muscle contractile properties

The objective of this study was to investigate the effect of 6 atmospheres of pressure (ATA) on plantar flexors' (PF) voluntary force and activation, force-frequency characteristics, and rate of torque development (RTD). Eight subjects performed PF isometric contractions. Muscle activation was monitored by electromyographic (EMG) activity (PF and dorsiflexors) and the interpolated twitch technique (ITT). Maximal evoked contractions of the PF were elicited at 1, 2, 3, 5, 10, 20, and 40 Hz. PF RTD was calculated with maximal voluntary, 1 and 40 Hz contractions. Hyperbaric pressures significantly decreased PF voluntary torque; 6.2%, ITT activation; 2.8% with a trend for a 19.1% decrease in EMG (p = 0.1). There were no significant differences in the dorsiflexors/PF EMG ratio. One Hz torque was potentiated 15.7% with an increased absolute RTD of 12.8%, but no change in relative RTD. The results suggested hyperbaric-induced decreases in PF activation contributed to voluntary torque loss. A lack of torque reduction with higher frequency tetanic stimulation (2-40 Hz) suggested that 6 ATA does not impair myofilament kinetics, whereas twitch potentiation may include changes in excitation-contraction coupling.

Development of Physics-based Models and Design Optimization of Power Electronic Conversion Systems

The main objective for physics based modeling of the power converter components is to design the whole converter with respect to physical and operational constraints. Therefore, all the elements and components of the energy conversion system are modeled numerically and combined together to achieve the whole system behavioral model. Previously proposed high frequency (HF) models of power converters are based on circuit models that are only related to the parasitic inner parameters of the power devices and the connections between the components. This dissertation aims to obtain appropriate physics-based models for power conversion systems, which not only can represent the steady state behavior of the components, but also can predict their high frequency characteristics. The developed physics-based model would represent the physical device with a high level of accuracy in predicting its operating condition. The proposed physics-based model enables us to accurately develop components such as; effective EMI filters, switching algorithms and circuit topologies [7]. One of the applications of the developed modeling technique is design of new sets of topologies for high-frequency, high efficiency converters for variable speed drives. The main advantage of the modeling method, presented in this dissertation, is the practical design of an inverter for high power applications with the ability to overcome the blocking voltage limitations of available power semiconductor devices. Another advantage is selection of the best matching topology with inherent reduction of switching losses which can be utilized to improve the overall efficiency. The physics-based modeling approach, in this dissertation, makes it possible to design any power electronic conversion system to meet electromagnetic standards and design constraints. This includes physical characteristics such as; decreasing the size and weight of the package, optimized interactions with the neighboring components and higher power density. In addition, the electromagnetic behaviors and signatures can be evaluated including the study of conducted and radiated EMI interactions in addition to the design of attenuation measures and enclosures.

Diversity of LFPs Activated in Different Target Regions by a Common CA3 Input

Identifying the pathways contributing to local field potential (LFP) events and oscillations is essential to determine whether synchronous interregional patterns indicate functional connectivity. Here, we studied experimentally and numerically how different target structures receiving input from a common population shape their LFPs. We focused on the bilateral CA3 that sends gamma-paced excitatory packages to the bilateral CA1, the lateral septum, and itself (recurrent input). The CA3-specific contribution was isolated from multisite LFPs in target regions using spatial discrimination techniques. We found strong modulation of LFPs by target-specific features, including the morphology and population arrangement of cells, the timing of CA3 inputs, volume conduction from nearby targets, and co-activated inhibition. Jointly they greatly affect the LFP amplitude, profile, and frequency characteristics. For instance, ipsilateral (Schaffer) LFPs occluded contralateral ones, and septal LFPs arise mostly from remote sources while local contribution from CA3 input was minor. In the CA3 itself, gamma waves have dual origin from local networks: in-phase excitatory and nearly antiphase inhibitory. Also, waves may have different duration and varying phase in different targets. These results indicate that to explore the cellular basis of LFPs and the functional connectivity between structures, besides identifying the origin population/s, target modifiers should be considered.

Characteristics of the interfacial capacitance in thin film Ba0.5Sr0.5TiO3 capacitors with SrRuO3 and (La, Sr)CoO3 bottom electrodes

Thin film Ba0.5Sr0.5TiO3 (BST) capacitors of thickness similar to75 nm to similar to1200 nm, with Au top electrodes and SrRuO 3 (SRO) or (La, Sr)CoO3 (LSCO) bottom electrodes were fabricated using Pulsed Laser Deposition. Implementing the "series capacitor model," bulk and interfacial capacitance properties were extracted as a function of temperature and frequency. 'Bulk' properties demonstrated typical ceramic behaviour, displaying little frequency dependence and a permittivity and loss peak at 250 K and 150 K respectively. The interfacial component was found to be relatively temperature and frequency independent for the LSCO/BST capacitors, but for the SRO/BST configuration the interfacial capacitance demonstrated moderate frequency and little temperature dependence below T similar to 300 K but a relatively strong frequency and temperature dependence above T similar to3 00 K. This was attributed to the thermal activation of a space charge component combined with a thermally independent background. The activation energy for the space charge was found to be E-A similar to 0.6 eV suggesting de-trapping of electrons from shallow level traps associated with a thin interfacial layer of oxygen vacancies, parallel to the electrodes.

An optimal under-frequency load shedding strategy considering distributed generators and load static characteristics

The well-established under-frequency load shedding (UFLS) is deemed to be the last of effective remedial measures against a severe frequency decline of a power system. With the ever-increasing size of power systems and the extensive penetration of distributed generators (DGs) in power systems, the problem of developing an optimal UFLS strategy is facing some new challenges. Given this background, an optimal UFLS strategy for a distribution system with DGs and load static characteristics taken into consideration is developed. Based on the frequency and the rate of change of frequency, the presented strategy consists of several basic rounds and a special round. In the basic round, the frequency emergency can be alleviated by quickly shedding some loads. In the special round, the frequency security can be maintained, and the operating parameters of the distribution system can be optimized by adjusting the output powers of DGs and some loads. The modified IEEE 37-node test feeder is employed to demonstrate the essential features of the developed optimal UFLS strategy in the MATLAB/SIMULINK environment.

Optical emission characteristics and mode transitions in low-frequency inductively coupled plasmas

An attempt was made to investigate the optical emission spectra of atomic, molecular, and ionic species in low-frequency, high-density ICP discharges in pure nitrogen, ar con gases, and gas mixtures Ar+H2, N2+Ar, and N2+H2. The excited species were identified by in situ optical emission intensity (OEI) measurements in the discharge chamber. In general, significant results were obtained.

Impacts of wind power integration on small signal stability and low frequency oscillation characteristics of interconnected power systems

为研究风电并网对互联系统低频振荡的影响,基于完整的双馈风电机组模型,定性分析了两区域互联系统在风电机组并网前后阻尼特性的变化情况.从双馈风电机组并网输送距离、并网容量、互联系统联络线传送功率、是否加装电力系统稳定器等多个方面,多角度分析了风电场并网对互联系统小干扰稳定及低频振荡特性的影响.之后,以两个包括两个区域的电力系统为例,进行了系统的计算分析和比较.结果表明,有双馈风电机组接入的互联电力系统,在不同运行模式下,双馈风电机组的并网输送距离、出力水平、联络线传送功率对低频振荡模式的影响在趋势和程度上均有显著差异,这样在对风电场进行入网规划、设计和运行时就需要综合考虑这些因素的影响.

Low loss and frequency (1 kHz-1 MHz) independent dielectric characteristics of 3BaO-3TiO(2)-B2O3 glasses

X-ray powder diffraction along with differential thermal analysis carried out on the as-quenched samples in the 3BaO-3TiO(2)-B2O3 system confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 1 kHz-1 MHz frequency range were measured as a function of temperature (323-748 K). The dielectric constant and loss were found to be frequency independent in the 323-473 K temperature range. The temperature coefficient of dielectric constant was estimated using Havinga's formula and found to be 16 ppm K-1. The electrical relaxation was rationalized using the electric modulus formalism. The dielectric constant and loss were 17 +/- 0.5 and 0.005 +/- 0.001, respectively at 323 K in the 1 kHz-1 MHz frequency range which may be of considerable interest to capacitor industry.

Negative differential capacitance in n-GaN/p-Si heterojunctions

Negative differential capacitance (NDC) has been observed in n-GaN/p-Si heterojunctions grown by plasma assisted molecular beam epitaxy (PAMBE). The NDC is observed at low frequencies 1 and 10 kilohertz (kHz) and disappeared at a higher testing frequency of 100 kHz. The NDC is also studied with temperature and found that it has disappeared above 323 degrees C. Current-Voltage (I-V) characteristics of n-GaN /p-Si heterojunction were measured at different temperatures and are attributed to the space-charge-limited current (SCLC). A simple model involving two quantum states is proposed to explain the observed NDC behavior. (C) 2010 Elsevier Ltd. All rights reserved.

Low loss and frequency (1 kHz–1 MHz) independent dielectric characteristics of 3BaO–3TiO2–B2O3 glasses

X-ray powder diffraction along with differential thermal analysis carried out on the as-quenched samples in the 3BaO–3TiO2–B2O3 system confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 1 kHz–1 MHz frequency range were measured as a function of temperature (323–748 K). The dielectric constant and loss were found to be frequency independent in the 323–473 K temperature range. The temperature coefficient of dielectric constant was estimated using Havinga’s formula and found to be 16 ppm K−1. The electrical relaxation was rationalized using the electric modulus formalism. The dielectric constant and loss were 17±0.5 and 0.005±0.001, respectively at 323 K in the 1 kHz–1 MHz frequency range which may be of considerable interest to capacitor industry.

Estimation of Series Capacitance of a Transformer Winding Based on Frequency-Response Data: An Indirect Measurement Approach

A novel procedure to determine the series capacitance of a transformer winding, based on frequency-response measurements, is reported. It is based on converting the measured driving-point impedance magnitude response into a rational function and thereafter exploiting the ratio of a specific coefficient in the numerator and denominator polynomial, which leads to the direct estimation of series capacitance. The theoretical formulations are derived for a mutually coupled ladder-network model, followed by sample calculations. The results obtained are accurate and its feasibility is demonstrated by experiments on model-coil and on actual, single, isolated transformer windings (layered, continuous disc, and interleaved disc). The authors believe that the proposed method is the closest one can get to indirectly measuring series capacitance.

Estimation of Series Capacitance for a Three-Phase Transformer Winding From Its Measured Frequency Response

Recently, authors published a method to indirectly measure series capacitance (C-s) of a single, isolated, uniformly wound transformer winding, from its measured frequency response. The next step was to implement it on an actual three-phase transformer. This task is not as straightforward as it might appear at first glance, since the measured frequency response on a three-phase transformer is influenced by nontested windings and their terminal connections, core, tank, etc. To extract the correct value of C-s from this composite frequency response, the formulation has to be reworked to first identify all significant influences and then include their effects. Initially, the modified method and experimental results on a three-phase transformer (4 MVA, 33 kV/433 V) are presented along with results on the winding considered in isolation (for cross validation). Later, the method is directly implemented on another three-phase unit (3.5 MVA, 13.8 kV/765 V) to show repeatability.