Abnormally expressed low-voltage-activated calcium channels in beta-cells from NOD mice and a related clonal cell line

A macroscopic low-voltage-activated (LVA) inward current was found in pancreatic beta-cells isolated from NOD mice. However, this current was not present in nondiabetic prone mouse (e.g., Swiss-Webster) pancreatic beta-cells. We performed pharmacological analyses on this current in NOD insulinoma tumor cells (NIT-1). This cell line was developed from pancreatic beta-cells of a transgenic NOD mouse. The sodium-channel blocker, tetrodotoxin (TTX; 2 micromol/l) had no effect on this LVA current. The amplitudes of currents elicited by a -20 mV test pulse retained similarity when the extracellular sodium concentration was increased from 0 to 115 mmol/l; when the extracellular calcium concentration was decreased from 10 to 2 mmol/l, there was an approximate 50% reduction of this current elicited by a -30 mV test pulse. Neither the L-type calcium-channel blocker, nifedipine (3 micromol/l), nor the N-type calcium-channel blocker, omega-CgTx-GVIA (1 micromol/l), at -30 mV produced an appreciable effect. The T-type calcium-channel blockers, nickel (3 micromol/l) and amiloride (250 micromol/l), effectively reduced the peak of this current. In 2 mmol/l calcium external solution, the threshold of voltage-dependent activation of this calcium current was approximately -65 mV, and the peak current occurred at -20 mV. Half-maximum steady-state inactivation was around -43 mV. The mean time constant of slow deactivating tail currents generated by a preceding 20 mV pulse was 2.53 ms. The intracellular free calcium concentration was two- to threefold higher in NOD mouse pancreatic beta-cells compared with Swiss-Webster pancreatic beta-cells. We concluded that there are LVA calcium channels abnormally expressed in NOD mouse beta-cells. This LVA calcium channel may be factorial to the high cytosolic free calcium concentration observed in these cells, and thereby may contribute to the pathogenesis of NOD mouse beta-cells.     

Characterization of the maize prolamin box-binding factor-1 (PBF-1) and its role in the developmental regulation of the zein multigene family

Voltage-dependent Ca2+ channels (VCCs) represent one of the main routes of Ca2+ entry into neuronal cells. Changes in intracellular Ca2+ dynamics and homeostasis can cause long-lasting cellular changes via activation of different Ca2+ dependent signalling pathways. We have investigated the properties of VCCs in human hippocampal dentate granule cells (DGCs) using the whole-cell configuration of the patch-clamp method. Classical high-threshold Ca2+ currents were composed mainly of omega-CgTx-sensitive N-type and nifedipine-sensitive L-type currents that were present in similar proportions. In addition, a Ca2+ current component that was sensitive to low concentrations of Ni2+, but not to nifedipine or omega-conotoxin GVIA (omega-CgTx GVIA) was present. This latter component showed a half-maximal inactivation at more hyperpolarized potentials than high-threshold currents and a more rapid time-dependent inactivation. This current was termed T-type Ca2+ current. Current components with similar pharmacological and kinetic characteristics could be elicited in acutely isolated control rat DGCs. The current density of high threshold and T-type Ca2+ components was significantly larger in human DGCs and in the kainate model compared to DGCs isolated from adult control rats. These differences in current density were not accompanied by parallel differences in the voltage-dependence of VCCs. Taken together, these data suggest that an up-regulation of Ca2+ current density may occur in hippocampal epileptogenesis without consistent changes in Ca2+ current properties.     

Utility of the injury severity score: a confirmation

When a strand of the rabbit sinoatrial node tissue was shortened by ligation, the spatial decay of electrotonic potential decreased and the input impedance increased. In a piece of the tissue 0.2-0.3 mm in diameter apparently uniform current spread was obtained. Action potentials recorded from three different sites in this small piece occurred simultaneously and were superimposable. In voltage clamp experiments using the double microelectrode method, the membrane potential was usually held at -30 to -40 mV, where no net current flowed. When membrane potential was suddenly changed from the holding potential, the sign and the time course of the ionic current varied with membrane potential. Hyperpolarization gave an inward current which increased with time. Depolarization gave a transient inward current followed by sustained outward current, and repolarization gave an outward current tail which exponentially subsided with a time constant of 0.37 s. The membrane time constant was 12.0 ms. When the specific membrane capacitance was assumed to be 1 muF/cm2, the specific membrane resistance at the resting potential was 12 Komega cm2. The peak of the transient inward current on depolarization was 1.3 X 10(-5) A/cm2.     

Inhibition of myocardial L- and T-type Ca2+ currents by efonidipine: possible mechanism for its chronotropic effect

Effects of efonidipine, a dihydropyridine phosphonate Ca2+ channel antagonist, on the guinea-pig heart were compared with those of nifedipine. In the sino-atrial node, 1 microM efonidipine produced increase in cycle length accompanied by prolongation of the phase 4 depolarization which was not prominent with 0.1 microM nifedipine. In ventricular myocytes, both efonidipine and nifedipine produced inhibition of the L-type Ca2+ current, nifedipine being tenfold more potent than efonidipine. Efonidipine also inhibited the T-type Ca2+ current at higher concentrations but nifedipine did not. Both Ca2+ channel antagonists had no or only a weak effect on K+ currents. In addition, 40 microM Ni2+, which selectively inhibited the T-type Ca2+ current, had no effect on myocardial Ca2+ transients and contractile force. In conclusion, efonidipine was shown to have inhibitory effects on both L- and T-type Ca2+ currents, which may contribute to its high negative chronotropic potency.     

Contrasting biophysical and pharmacological properties of T-type and R-type calcium channels

In contrast to other kinds of voltage-gated Ca2+ channels, the underlying molecular basis of T-type and R-type channels is not well-understood. To facilitate comparisons with cloned Ca2+ channel subunits, we have carried out a systematic analysis of the properties of T-type currents in undifferentiated NG108-15 cells and R-type currents in cerebellar granule neurons. Marked differences were found in their biophysical and pharmacological features under identical recording conditions. T-type channels became activated at potentials approximately 25 mV more negative than R-type channels; however, T-type channels required potentials approximately 15 mV less negative than R-type channels to be available. Accordingly, T-type channels display a much larger overlap between the curves describing inactivation and activation, making them more suitable for generating sustained Ca2+ entry in support of secretion or pacemaker activity. In contrast, R-type channels are not equipped to provide a steady current, but are very capable of supplying transient surges of Ca2+ influx. In response to a series of increasingly strong depolarizations T-type and R-type Ca2+ channels gave rise to very different kinetic patterns. T-type current records crossed each other in a characteristic pattern not found for R-type currents. These biophysical distinctions were independent of absolute membrane potential and were, therefore, complementary to the conventional categorization of T- and R-type Ca2+ channels as low- and high-voltage activated. R-type channels deactivated approximately eight-fold more quickly than T-type channels, with clear consequences for the generation of divalent cation influx during simulated action potentials. Pharmacological comparisons revealed additional contrasts. R-type current was responsive to block by omega-Aga IIIA but not nimodipine, while the opposite was true for T-type current. Both channel types were potently inhibited by the non-dihydropyridine compound mibefradil. In all respects examined, R-type currents were similar to currents derived from expression of the alpha1E subunit whereas T-type currents were not.     

Dynamics and control of solidification of molten metal flows

A solidified layer on the inside of a cooled flow channel can be used to control the flow rate of molten material through that channel. This concept can be used for flow rate control of molten furnace products in the metallurgical industry. In this study, internal solidification of molten metal flows has been modeled mathematically for both steady-state and dynamic cases. The model predicted solidified layer thickness and metal flow rate. Experimental verification of the mathematical model was obtained using molten tin. Novel design features of the experimental apparatus included the use of boiling heat transfer and the vertical mounting of the cooling section. Engineering knowledge regarding the design, operation, and control of a pilot scale (24 kg/s) molten metal circuit was obtained during the construction, commissioning, and operation of the experimental apparatus. Experimental results for tin flow rate from the experimental apparatus were within experimental error of the predictions of the mathematical model.     

螺旋弹簧多目标稳健优化设计

以螺旋弹簧的给定刚度变化最小、自振频率最大和质量最小为设计目标,综合考虑优化设计中的随机因素,建立了基于稳健性的多目标优化模型,并在科学计算语言MATLAB中编程求解.通过液压阀螺旋弹簧设计实例的分析说明,多目标稳健优化设计提高了设计目标的稳健性,一定程度上提升了液压阀的动态响应特性.     

用于计算机辅助设计的晶闸管模型

本文讨论了用于功率电子电路的晶闸管模型的建立方法。给出了一个适用于计算机辅助设计的非线性集中参数的晶闸管等效电路模型。
模型的建立是基于对器件内部载流子运动的物理过程进行模拟,分析了器件的少数载流子注入;空间电荷区内部载流子的产生与复合;雪崩倍增效应;基区宽度调制效应及电荷存贮效应。将反映这些物理过程的数学公式用非线性电路元件表示,组成了由非线性电阻、电容及受控电流源所构成的晶闸管模型。
利用这个模型可以分析晶闸管开关过程的动态非线性特性。     

A G protein is involved in the angiotensin AT2 receptor inhibition of the T-type calcium current in non-differentiated NG108-15 cells

In non-differentiated NG108-15 cells, both angiotensin II (Ang II) (100 nM) and CGP 42112 (100 nM) decreased the T-type calcium current amplitude by 24 +/- 2% and 21 +/- 3%, respectively. cGMP is not a mediator of the Ang II effect, since loading of cells with 50 microM cGMP did not prevent the inhibitory effects of Ang II. The effects of Ang II involves a non-identified GTPase activity since incubation with GDP beta S (3 mM) completely reversed the inhibitory effect of Ang II while GTP gamma S mimicked its effect. However, Ang II binding was not affected by GTP gamma S, and the effect of Ang II was not modified in pertussis toxin-treated cells. The inhibitory effect of Ang II on the T-type Ca2+ current involves a phosphotyrosine phosphatase activity since sodium orthovanadate prevented the effects of Ang II, although microcystin-LR, a selective Ser/Thr phosphatase 1 and 2A inhibitor, did not modify the effect of Ang II. These results provide the first evidence of a modulation of membrane conductance by Ang II through the AT2 receptor and demonstrate the involvement of a phosphotyrosine phosphatase and a G protein in the AT2 transduction mechanism in NG108-15 cells. Moreover, our data suggest that phosphotyrosine phosphatase activation is proximal to receptor occupation, since sodium orthovanadate inhibits both GTPase activity and T-type current blockage induced by Ang II or CGP 42112, while GTP gamma S inhibition of the T-type calcium current is not impaired.     

Modeling and Control of Oxygen Transfer in High Purity Oxygen Activated Sludge Process

A dynamic mathematical model for the high purity oxygen activated sludge process, which incorporates structured biomass, gas–liquid interactions and control systems, was developed. The model was calibrated using pilot plant data associated with the development of the West Point Treatment Plant near Seattle, Wash. The calibrated model was used to simulate oxygen transfer rates for various operating conditions. Simulations showed that an optimal control system can reduce aerator power by 33% as compared to a conventional design, and reduce average oxygen feed gas by as much as 18%. Vent gas purity control dramatically reduced the peak aerator horsepower required to maintain set point dissolved oxygen concentration during high loadings. Step feed operation reduced the stag-to-stage variation in aerator horsepower and also reduced the required peak power. Predicted power savings for a 605,000?m3/day plant were $500,000 per year at current power costs.     

直线运动轴承优化设计及试验研究

对振动台上的液体静压轴承装置进行研究,对其相关结构进行数值模拟及优化设计。在理论分析过程中,首先建立了油膜及压力场分布的数学模型,在提出了一系列假设的前提下,得到了油膜间隙中液体流动的控制方程即简化的纳维尔-斯托克斯方程及边界条件;然后采用有限元分析软件ANSYS对油膜的流场进行了计算、流体力学数值模拟以及优化设计,解出油膜的压力分布、速度分布、承载能力、流量和最优解。以数值模拟分析为基础,重点进行了试验研究以及相关问题的分析。运用计算得出的最优解,进行了一系列试验。从得到的测试数据中,分析了各种参数对油膜性能的影响规律。     

A model for determining the current yield during electrodeposition of zinc from sulfate solutions

A hypothesis on the existence of two mechanisms of the cathode reaction is formulated. A mathematical model of the current yield on the cathode during the electrodeposition of zinc from sulfate solutions is developed. This model can be used for the design and technological calculations of the process parameters of hydrometallurgical obtaining of zinc. The results of modeling are analyzed to evaluate the influence that concentrations of components of the solution and current density have on the process characteristics. The region of parameters characterized by a high current yield is selected.     

Mathematical modelling of unsteady-state transport of metal ions through supported liquid membrane

In this study, a mathematical model for unsteady-state transport of metal ions from aqueous solution through supported liquid membrane containing carrier is presented. For a transport process using supported liquid membrane, the three resistances to consider are the membrane resistance and the aqueous boundary layer resistances at the side of feed and stripping phases. The transport of species in the feed, the membrane and the stripping phases is modelled by Fick's second law. Time-dependent boundary conditions for the feed, the membrane and the stripping phases are obtained by means of kinetics of chemical reaction in the feed–membrane and the membrane–stripping interface. Partial differential equations obtained for the feed, the membrane and the stripping phases are analytically solved by using Duhamel's Theorem. Concentration distribution within the aqueous film layers and membrane as a function of position and time was derived from models obtained. The obtained model is checked against experimental data corresponding to the transport of copper ions from aqueous solution through supported liquid membrane by LIX 984.     

电子中心至市邮局模拟中继传输方式的改进

本文就现有微波传输电路及路由走向进行了最佳配置,并利用现有设备将电子中心至市邮局的模拟中继进行了数字化传输     

2-μm GaAs HBT工艺的L型网络分布式放大器

首先对分布式放大器中L型和T型网络的频率特性进行了研究.分析表明,L型网络比T型网络在设计中具有更好的频率特性.基于稳懋半导体的2-μm GaAs HBT工艺实现了一种L型网络的分布式放大器.测试结果表明,在3～18 GHz频率范围内其增益为5.5 dB,增益平坦度为±1 dB,体现了很好的带宽性能.此外,在设计的频率范围内反射损耗S11,S22均低于-10 dB.在5 GHz时的1 dB压缩点处输出功率为13.3 dBm.芯片面积为0.95 mm2,在3.5 V电源下功耗为95 mW.     

Mechanisms of stretch-induced changes in [Ca2+]i in rat atrial myocytes: role of increased troponin C affinity and stretch-activated ion channels

To study the effects of stretch on the function of rat left atrium, we recorded contraction force, calcium transients, and intracellular action potentials (APs) during stretch manipulations. The stretch of the atrium was controlled by intra-atrial pressure. The Frank-Starling behavior of the atrium was manifested as a biphasic increase of the contraction force after increasing the stretch level. The development of the contraction force after step increase of the stretch (intra-atrial pressure from 1 to 3 mm Hg) was accompanied by the increase in the amplitude of the calcium transients (P<0.05, n=4) and decrease in the time constant of the Ca2+ transient decay. The APs of the individual myocytes were also affected by stretch; the duration of the AP was decreased at positive voltages (AP duration at 15% repolarization level, P<0.001; n=13) and increased at negative voltages (AP duration at 90% repolarization level, P<0. 01; n=13). To study the mechanisms causing these changes we developed a mathematical model describing [Ca2+]i and electrical behavior of single rat atrial myocytes. Stretch was simulated in the model by increasing the troponin (TnC) sensitivity and/or applying a stretch-activated (SA) calcium influx. We mimicked the Ca2+ influx by introducing a nonselective cationic conductance, the SA channels, into the membrane. Neither of the 2 plausible mechanosensors (TnC or SA channels) alone could produce similar changes in the Ca2+ transients or APs as seen in the experiments. The model simulated the effects of stretch seen in experiments best when both the TnC affinity and the SA conductance activation were applied simultaneously. The SA channel activation led to gradual augmentation of Ca2+ transients, which modulated the APs through increased Na+/Ca2+-exchanger inward current. The role of TnC affinity change was to modulate the Ca2+ transients, stabilize the diastolic [Ca2+]i, and presumably to produce the immediate increase of the contraction force after stretch seen in experiments. Furthermore, we found that the same mechanism that caused the normal physiological responses to stretch could also generate arrhythmogenic afterpotentials at high stretch levels in the model.     

低噪声回波测距系统的电路设计与系统分析

描述了超声波脉冲回波测距系统的基本组成,重点研究了超声波测距系统中的低噪声问题,设计了分时和分区的开关隔离式超声波发射和接收电路,彻底切断了发射电路和其他电干扰信号对接收电路的影响.低噪声\     

Preparation and specificity of FITC-labeled immune serums against dermatophytes

The effect of ultraviolet radiation on the asymmetrical displacement currents in the membrane of the node of Ranvier was measured and compared with the ultraviolet blocking of the sodium current. Ultraviolet radiation irreversibly reduced the peak sodium current and the charge displaced during a depolarizing test pulse, the relative reduction being independent of potential. The ratio of the ultraviolet sensitivities of the sodium and the asymmetrical displacement currents is 2.3+/- 0.2. This result suggests two independent identical gating particles per sodium channel in the membrane of myelinated nerve.     

Improvement of the Parameterized Identification Model Using Quasi-Steady and Nonuniform Inflow Aerodynamic Model

Compared with those of a fixed-wing aircraft, the dynamics of a rotorcraft are significantly more complex. One of the major challenges in the design of an autonomous helicopter is the development of a flight dynamic model, which can be useful for simulation studies and for the design of control law and navigational aspects. There is always a trade-off from the accuracy of the mathematical model to the more simplified model required for a control design as far as the helicopter rotor/fuselage dynamics is concerned. Small-scale helicopters posses a higher bandwidth of dynamics; hence, models developed from the first principle alone do not fulfill the needs, and more-sophisticated mathematical models are thus required. The main objective of the present work is to improve the parameterized identification model by replacing it with a most-general flight dynamic model for a minihelicopter. This model includes the rotor blade flap dynamics, stabilizer bar dynamics, and vehicle dynamics, which will be applicable for a general maneuvering flight. A systematic study is undertaken to analyze the influence of inflow models and flap response on the helicopter trim. Stability of the minihelicopter is also analyzed; except for phugoid, all other modes are stable in hover and high forward flight conditions.