Flashover voltage characteristics of contaminated station insulators under temporary ac overvoltages in the ac system connected with a frequency converter station

According to the recent analysis results of temporary ac overvoltage in the ac system connected with a frequency converter station, large-magnitude over-voltages were confirmed to occur under some special system conditions. Most of the station insulators currently used cannot withstand such overvoltages according to an evaluation based on the data obtained earlier. The necessity of tests to be done to evaluate such performance more accurately was recognized. Both power frequency and switching impulse overvoltage flashover tests were made on contaminated insulators by the method well simulating the natural wetting condition. Switching impulse flashover voltage with the waveshape having a long wavefront time of 2 ms can be well correlated with the flashover voltage characteristics of temporary ac overvoltage. Higher flashover voltage characteristics were obtained by a clean fog test method compared with those obtained by equivalent fog test method.     

A new method for power generation planning and problems of uncertainty

This paper presents a new method for power system planning which considers uncertainties of various system parameters as a part of the criterion function. The criterion function involves both the expected values of total system costs and the cost variances of different power plants. Previously, the authors proposed that these cost variances be evaluated from the existing power system plans in the form of the solutions to the inverse optimization problem, and then applied this procedure to the planning of power systems in Japan. However, because of the correlation between fuel and facility costs, the cost variances could not be determined as specific values. Here, to overcome this difficulty, the authors now introduce hydropower plants into the model as the so-called nonrisky elements and focus on the expenditure shares rather than the plant capacity shares. As a result, more reasonable results are obtained. This improved methodology is applied and the derived cost variances are shown. Further, using the resultant cost variances, the authors make Pareto-optimal power generation plans and demonstrate also the robustness of the method to price fluctuations.     

Some experimental findings in compression-after-impact (CAI) tests of CF/PEEK (APC-2) and conventional CF/epoxy flat plates

Compression-after-impact (CAI) tests have been conducted for quasi-isotropic thick plates with 48 plies by using the NASA method and on plates with 32 plies by using the SACMA method. Specimens are made of CF/PEEK (APC-2) and conventional CF/epoxy for the NASA plates and CF/epoxy for the SACMA plates. In the NASA CAI tests, the sequence of delamination buckling and its propagation is clearly revealed through various experimental techniques. One major technique is moiré topography, and the other is thermo-mechanical stress analysis with a high-accuracy infrared sensor. The arrest of delamination propagation just before catastrophic failure due to high fracture toughness is clearly captured by the moiré camera. This behavior provides good CAI values of CF/PEEK. The initial buckling properties of the delaminated region by the impact are then extensively discussed. Numerical predictions of initial buckling stress have been obtained by modelled geometry of the delaminated region simplified from its precise structure clarified by ultrasonic C-scanning. They agree fairly well with the experimental results. The in-plane stress distribution in the delaminated region before initial buckling is measured by an infrared stress graphic system. This compared favorably with finite element predictions. Two types of symmetric buckling modes with respect to the central plate surface, twin and single peak ones, are experimentally captured.     

Molecular analysis of p21 and p27 genes in human pituitary adenomas

OBJECTIVES: To determine the prevalence of thyroid dysfunction in institutionalised elderly people in Cape Town and to assess the usefulness of an abnormal thyroid-stimulating hormone (TSH) concentration as a screening test in this group. DESIGN: Cross-sectional survey. SETTING: Four old-age homes in Cape Town. SUBJECTS: Old-age home residents aged 60 years and over. OUTCOME MEASURES: Serum concentrations of TSH, free thyroxine and free tri-iodothyronine. RESULTS: Serum TSH estimations were performed on 658 participants, and were abnormal in 103 (15.6%)-41 (6.2%) being elevated (> 5.0 microU/ml) and 62 (9.4%) being low (> 0.4 microU/ml). There were 3 newly diagnosed cases of hyperthyroidism and 7 of hypothyroidism. Subclinical disease was diagnosed in 40 subjects. The overall prevalence of thyroid dysfunction in this population was 11.2%. In 22 (3.4%) this had previously been recognised, while in 50 (7.8%) the dysfunction was newly diagnosed by the current survey. The positive predictive value of a TSH concentration > 20 microU/ml in predicting hypothyroidism is 67%, while it will predict 100% of cases of subclinical hypothyroidism. A TSH concentration < 0.1 microU/ml will predict 23% of cases of hyperthyroidism, but 81% of cases of subclinical disease. CONCLUSIONS: The prevalence of thyroid dysfunction in institutionalised elderly people in Cape Town is similar to that reported for elderly people in other centres. Thyroid dysfunction had not previously been recognised in approximately two-thirds of the subjects in this study. The serum TSH concentration is a reliable screening test for thyroid dysfunction in the elderly, but is less useful if used to identify biochemical thyroid disease. An elevated TSH concentration is a better predictor of thyroid dysfunction in the elderly than a depressed TSH concentration.     

Network formation and swelling behavior of photosensitive poly(vinyl alcohol) gels prepared by photogenerated crosslinking

Poly (vinyl alcohol) with pendent styrylpyridinium groups (SbQ) is insolubilized by photoirradiation. An association takes place in SbQ groups. The association of polymer chains becomes marked with increasing the number of SbQ groups. Mainly intermolecular crosslinks were formed. Transparent and homogeneous macrogels consisting of several intermolecular crosslinks are obtained. The proportion of the free water to the bound water in PVA-SbQ gels was 3.3?2.9 despite of the large change in conversion of photodimerization of SbQ groups, x=0.27?0.58. The water uptake after swelling of the gels in water increased 6–27 times compared to the original weight at pH=7. The higher the degree of photocrosslinking, the lower was the degree of swelling. The water diffusion coefficients, D, were (2.2?5.8) × 10^?5 cm² S^?1 for a 88% saponified PVA with 1 . 3 mol% SbQ groups. The volume of the gel increased discontinuously about 10-fold for the 99% saponified PVA with 0 . 096 mol% SbQ and 51% water (49% acetone). The acetone concentration at the transition decreased with increasing the degree of saponification of the PVA.     

分子束外延CdTe（211）B／GaAs（211）B的特性研究

ＣｄＴｅ／ＧａＡｓ是ＨｇＣｄＴｅ分子束外延的重要替代衬底材料。用Ｘ双晶衍射和光致发光测试研究了分子束外延生长的ＣｄＴｅ（２１１）Ｂ／ＧａＡｓ（２１１）Ｂ的晶体结构质量，表明外延膜晶体结构完整，具有很高的质量。用高分辨率的透射电镜研究其界面特性，观察到ＣｄＴｅ（２１１）Ｂ相对于ＧａＡｓ（２１１）Ｂ向着［１１１］方向倾斜一个小角度（约３°），界面的四面体键网发生扭曲，由于晶格失配，在界面存在很高的失配位错密度。用二次离子质谱分析仪分析了ＧａＡｓ衬底中的Ｇａ和Ａｓ向ＣｄＴｅ外扩散的情况。结果表明：如果要在ＧａＡｓ衬底上生长ＨｇＣｄＴｅ外延膜，必须先生长一层具有一定厚度的ＣｄＴｅ来阻止Ｇａ和Ａｓ向ＨｇＣｄＴｅ的外扩散和失配位错的延伸。     

A Unified Approach to Submicron DC MOS Transistor Modeling for Low-Voltage ICs

A unified single-equation approach for the MOS transistordrain current modeling for energy-efficient submicron MOS circuitsis presented. Instead of three sets of separate equations forthe triode, saturation, and weak inversion regions, only a continuousexpression which is valid to describe the behavior of drain currentand the derivatives in all operation regions can be realizedby using a combination of hyperbola, sigmoid, and interpolationmethods. The model expression can predict accurate results forthe current, output conductance, and transconductance with continuousand smooth characteristics. The simulation results agree wellwith experimental data.     

Dirac Cone Spin Polarization of Graphene by Magnetic Insulator Proximity Effect Probed with Outermost Surface Spin Spectroscopy

The effects of the proximity contact with magnetic insulator on the spin‐dependent electronic structure of graphene are explored for the heterostructure of single‐layer graphene (SLG) and yttrium iron garnet Y₃Fe₅O₁₂ (YIG) by means of outermost surface spin spectroscopy using a spin‐polarized metastable He atom beam. In the SLG/YIG heterostructure, the Dirac cone electrons of graphene are found to be negatively spin polarized in parallel to the minority spins of YIG with a large polarization degree, without giving rise to significant changes in the π band structure. Theoretical calculations reveal the electrostatic interfacial interactions providing a strong physical adhesion and the indirect exchange interaction causing the spin polarization of SLG at the interface with YIG. The Hall device of the SLG/YIG heterostructure exhibits a nonlinear Hall resistance attributable to the anomalous Hall effect, implying the extrinsic spin–orbit interactions as another manifestation of the proximity effect.     

8—12μm量子阱超晶格红外探测器材料与器件

介绍了近年来迅速发展的8～12μmGaAs-GaAlAs多量子阱红外探测器、InAsSb和InAs-Ga_(1-x)In_xSb应变超晶格材料和器件以及HgTe-CdTe超晶格材料的简单原理、特点及国外最新动态。预计在90年代它们将与HgCdTe材料和器件同样受到人们的关注与重视。     

Low-Temperature Physical Properties of Ba8Ni x Ge46?x (x?=?3,?4,?6)

Polycrystalline samples of type?I clathrate Ba₈Ni _x Ge_46?x (x?=?3, 4, 6) have been synthesized using a radio-frequency (RF) induction furnace. Ba₈Ni _x Ge_46?x samples show metallic-like behavior (d??/dT?>?0) with high resistivity at room temperature, and diamagnetic susceptibility at 2?K and 300?K. The charge carriers vary from n type to p type depending on the Ni stoichiometry. The carrier concentrations at 300?K are calculated to be 5.84(3)?e^?/cell for x?=?3, 2.29(1)?e^?/cell for x?=?4, and 3.29(1)?h⁺/cell for x?=?6. The deviation of the carrier concentrations from the values expected based on 4-bonded Ni suggests that vacancies may play a very important role in the electronic states. The effective carrier masses are estimated from the low-temperature heat capacity data.