Swelling-activated anion channels are essential for volume regulation of mouse thymocytes

Channel-mediated trans-membrane chloride movement is a key process in the active cell volume regulation under osmotic stress in most cells. However, thymocytes were hypothesized to regulate their volume by activating a coupled K-Cl cotransport mechanism. Under the patch-clamp, we found that osmotic swelling activates two types of macroscopic anion conductance with different voltage-dependence and pharmacology. At the single-channel level, we identified two types of events: one corresponded to the maxi-anion channel, and the other one had characteristics of the volume-sensitive outwardly rectifying (VSOR) chloride channel of intermediate conductance. A VSOR inhibitor, phloretin, significantly suppressed both macroscopic VSOR-type conductance and single-channel activity of intermediate amplitude. The maxi-anion channel activity was largely suppressed by Gd(3+) ions but not by phloretin. Surprisingly, [(dihydroindenyl)oxy] alkanoic acid (DIOA), a known antagonist of K-Cl cotransporter, was found to significantly suppress the activity of the VSOR-type single-channel events with no effect on the maxi-anion channels at 10 μM. The regulatory volume decrease (RVD) phase of cellular response to hypotonicity was mildly suppressed by Gd(3+) ions and was completely abolished by phloretin suggesting a major impact of the VSOR chloride channel and modulatory role of the maxi-anion channel. The inhibitory effect of DIOA was also strong, and, most likely, it occurred via blocking the VSOR Cl(-) channels.     

No Influence of Exogenous Hyaluronan on the Behavior of Human Cancer Cells or Endothelial Cell Capillary Formation

Hyaluronan (HA), a type of glycosaminoglycan used to construct the extracellular matrix, is involved in the proliferation and motility of cells, including cancer cells. The aim of this study was to determine whether exogenous HA has an influence on cancer in vitro and in vivo. High‐molecular‐weight HA (900 kDa) and low‐molecular‐weight HA (10 kDa) were added to several types of cancer cell lines in vitro, and proliferation and invasion were assessed. The effect of HA on capillary formation by human umbilical vein endothelial cells was also analyzed. The results showed that both types of HA had no apparent effect on cellular proliferation, invasion, or capillary formation. In an animal study, the 2 types of HA were orally administered to tumor‐bearing mice at a dosage of 200 mg/kg/d for 4 wk. Analysis using an in vivo imaging system revealed that tumor proliferation and metastasis were not greatly altered by HA administration. Furthermore, CD31 immunohistochemical staining revealed no obvious change in tumor microvessels. Taken together, these results demonstrate that exogenously administered HA has little effect on cancer. This study may support the safety of various forms of HA administration, including oral intake.     

Current distribution in parallel-connected YBCO high-temperature superconducting elements with different critical currents

A high-temperature superconductor is investigated for application to a fault-current limiter. However, the current-carrying capacity of a single element is too low for practical use. This parallel connection of superconducting elements is required to increase the current capacity. This paper discusses an ac current distribution between two YBa₂Cu₃O_7-x superconducting elements connected in parallel that differ in electrical aspects such as a critical current level and voltage-current characteristic. As the instantaneous value of the current rises from zero to peak, the following processes are observed: (1) the transition from superconducting to normal conducting state is initiated in the element with the smaller critical current; (2) the current value in the element is kept constant until the other element with the larger critical current level becomes normal conducting state; and (3) only when the instantaneous value of the ac current exceeds the summation of the individual critical current values of each element does the voltage across parallel-connected elements appear. These results are caused by the quick recovery characteristic of YBCO superconductors from the normal conducting state to the superconducting state.     

DC voltage control and harmonic current suppression in a single‐phase PFC converter

This paper presents a DC voltage control scheme for a single‐phase PFC converter which can realize both the harmonic suppression of the input current and the fast dynamic response to the DC voltage. Instead of using a constant DC voltage reference, the controller calculates a fluctuating DC voltage reference, having the frequency at twice the source frequency. In the calculation of the DC voltage reference, the circuit parameters are used. Since the parameter errors may cause an error in the DC voltage reference, parameter identification is also described. The effectiveness of the proposed control algorithm has been verified experimentally. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 54–64, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10060     

Experimental studies of the improvement of power system stability by superconducting fault current limiters

With increasing demands for electric power, the electric power system is becoming more and more complicated, and the stable, highly reliable delivery of electric power is encountering two major problems, namely, large fault currents and power system instability. In particular, the fault currents occurring in power systems are tending to increase. To solve this problem, superconducting fault current limiters (SCFCLs) have been developed, and it is hoped that they will also solve the problem of power system stability. This paper describes the results of experiments on the improvement of power system stability and the suppression of fault currents with SCFCLs, performed with power transmission simulators. An experiment using an R‐type SCFCL in a power system was performed. An R‐type SCFCL was simulated by using a resistor and an electromagnetic contactor with thyristors. It was found that the inclusion of an SCFCL in the electric power system gives improved suppression of fault currents and improved power system transient stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 41–52, 2000     

Improvement of Mechanical and Electrical Properties of Scandia-Doped Zirconia Ceramics by Post-Sintering with Hot Isostatic Pressing

Significant improvement in the fracture strength, accompanied by an enhancement in the electrical conductivity, of zirconia polycrystals that were doped with 3–7 mol% Sc₂O₃ was obtained by sintering at 1300°C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300° and 1450°C for 1.5 h in an argon-gas atmosphere. Dense bodies (with an average grain size of <0.5 μm) that were doped with 3.5 mol% of Sc₂O₃ showed the highest average fracture strength up to 1770 MPa and an electrical conductivity of 0.08 S/cm at 1000°C. The present zirconia ceramics, which consisted of submicrometer-sized grains of tetragonal phases and were stabilized with 5 and 6 mol% of Sc₂O₃, exhibited high strength (1330 and 1140 MPa, respectively) and good conductivity (0.15 and 0.18 S/cm, respectively); values for both properties were greater than those previously reported. The present HIPed zirconia ceramics, which have excellent properties, are candidates for an electrolyte of planar-type solid oxide fuel cells.     

Suppression of Rhombohedral-Phase Appearance and Low-Temperature Sintering of Scandia-Doped Cubic-Zirconia

Inhibition of cubic-rhombohedral phase transformation and low-temperature sintering at 1000°C were achieved for 10-mol%-Sc₂O₃-doped cubic-ZrO₂ by the presence of 1 mol% Bi₂O₃. The powders of 1-mol%-Bi₂O₃–10-mol%-Sc₂O₃-doped ZrO₂ were prepared using a hydrolysis and homogeneous precipitation technique. No trace of rhombohedral-ZrO₂ phase could be detected, even after sintering at 1000°–1400°C. The average grain size of the ZrO₂ sintered at 1200°C was >2 μm because of grain growth in the presence of Bi³⁺. Cubic, stabilized Bi-Sc-doped ZrO₂ sintered at 1200°C had sufficient conductivity at 1000°C (0.33 S/cm) to be used as an electrolyte for a solid-oxide fuel cell (SOFC) and at 800°C (0.12 S/cm) for an intermediate-temperature SOFC.