A laboratory plasma experiment for studying magnetic dynamics of accretion discs and jets     

S. C. Hsu  P. M. Bellan 《Monthly notices of the Royal Astronomical Society》2002,334(2):257-261

This work describes a laboratory plasma experiment and initial results which should give insight into the magnetic dynamics of accretion discs and jets. A high-speed multiple-frame CCD camera reveals images of the formation and helical instability of a collimated plasma, similar to MHD models of disc jets, and also plasma detachment associated with spheromak formation, which may have relevance to disc winds and flares. The plasmas are produced by a planar magnetized coaxial gun. The resulting magnetic topology is dependent on the details of magnetic helicity injection, namely the force-free state eigenvalue α _gun imposed by the coaxial gun.  相似文献   

Distinct influential mechanisms of the warm pool Madden–Julian Oscillation on persistent extreme cold events in Northeast China          下载免费PDF全文

Yitian Qian  Pang-Chi Hsu  Huijun Wang  Mingkeng Duan 《大气和海洋科学快报》2022,15(5):100226

This study investigates whether and how the Madden–Julian Oscillation (MJO) influences persistent extreme cold events (PECEs), a major type of natural disaster in boreal winter, over Northeast China. Significantly increased occurrence probabilities of PECEs over Northeast China are observed in phases 3 and 5 of the MJO, when MJO-related convection is located over the eastern Indian Ocean and the western Pacific, respectively. Using the temperature tendency equation, it is found that the physical processes resulting in the cooling effects required for the occurrence of PECEs are distinct in the two phases of the MJO when MJO-related convection is consistently located over the warm pool area. The PECEs in phase 3 of the MJO mainly occur as a result of adiabatic cooling associated with ascending motion of the low-pressure anomaly over Northeast Asia. The cooling effect associated with phase 5 is stronger and longer than that in phase 3. The PECEs associated with phase 5 of the MJO are linked with the northwesterly cold advection of a cyclonic anomaly, which is part of the subtropical Rossby wave train induced by MJO-related convection in the tropical western Pacific.摘要 本文利用高分辨率气温数据和热带季节内振荡 (MJO) 实时指数, 研究了1979–2015年冬季MJO活动对中国东北持续性极端低温事件 (PECE) 的影响特征和机理.结果表明:当MJO对流分别位于暖池地区的东印度洋 (位相3) 和西太平洋 (位相5) 时, 中国东北PECE的发生频率显著增加.利用温度方程诊断分析发现MJO两个位相所导致的冷却过程不同: 当 MJO处于位相3时, 中国东北地区为低压异常, 上升运动引起绝热冷却作用; 而位相5所形成的气旋性环流为中国东北地区带来西北风冷平流, 降温过程更强且持续更长时间.  相似文献   

Multivariate hydrologic time series analysis     

C.T. Hsu  K. Adamowski 《Advances in water resources》1981,4(2):83-95

The objective of this study is to establish a multivariate watershed hydrologic system model involving meteorological data as the input and river flow as the output of the system. Monthly hydrological time series of runoff, temperature and precipitation were selected for analysis. A first-order autoregressive-moving average (ARMA) transfer function model was found adequate to describe the multivariate watershed hydrologic system for the monthly runoff and meteorological time series. The results also indicated that the coordinated use of the meteorological and hydrometric data would enhance the accuracy of estimation of runoff characteristics.  相似文献   

A RATIONAL METHOD OF DELIMITING STUDY AREAS FOR UNEVENLY DISTRIBUTED POINT PHENOMENA     

Shin-yi Hsu  Clifford E. Tiedemann 《The Professional geographer》1968,20(6):376-381

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On the Type Species of Chusenella     

Y. C. HSU  GENUS Chusenella LEE 《地质学报》1942,(Z2):175-176

正 DIAGNOSIS: Test fusiform, slightly rounded at the ends; about 11.2 mm. long, 3.7 mm. wide, giving an axial ratio of about 1:3; whorl 9 to 10, the first three or four volutions closely coiled thence gradually evolute; spiral wall increases in thickness as the test grows, being 0.016 mm. in the firs  相似文献   

Model test of the surface and submerged vehicles with the micro-bubble drag reduction     

Sheng-Ju Wu  Cheng-Hsing Hsu  Tsung-Te Lin 《Ocean Engineering》2007,34(1):83-93

This study is based on the effective experiment observation and measuring technology to discuss the interaction influence between liquid turbulent boundary layer and a crowded group micro-bubbles. It is in order to understand and quantify the micro-bubbles clouds inside the turbulent boundary layer to eliminate the capacity of skin friction drag. Whenever the micro-bubbles are over supplied, pile up effect happened which makes micro-bubbles to integrate to each other as a large-size air film. Although they still have the drag reduction effect, the efficiency of drag reduction slowed down at this transition period. In the experiment of vertical type circulating water tunnel, when 1 μm porous medium is at 7 m/s flow speed, the C_v value at 0.056 has the best drag reduction efficiency of 26%. While 10 μm porous medium is at the same flow speed, the drag reduction efficiency is only around 23%.  相似文献   

Nonlinear wave effect on the slow drift motion of a floating body   总被引：1，自引：0，他引：1  

Takumi Ohyama  John R. C. Hsu 《Applied Ocean Research》1995,17(6):349-362

The slow drift motion of a floating body in a two-dimensional wave field has been investigated using a time-domain, fully nonlinear numerical model with non-reflective open boundaries. Preliminary computations were conducted for incident bichromatic waves, in which wave theories with different orders were applied in generating the waves required. The results show that the use of low-order theories generates undesirable free waves, and that fourth-order terms contribute markedly to low-frequency input. The motion of a rectangular floating body in response to nonlinear bichromatic waves was computed. The numerical results for small-amplitude incident waves agree reasonably well with the second-order approximation for both the steady and difference-frequency (Δσ) components in the body's motion. For relatively large waves, however, the 2Δσ component becomes predominant compared with the Δσ component. The motion of the body in irregular waves with different wave parameters has also been presented in order to discuss the validity range of a second-order approximation.  相似文献   

Coastal erosion in Eastern Black Sea Region, Turkey, by Ö. Yüksek et al.: comments     

Richard Silvester  John R. C. Hsu 《Coastal Engineering》1997,30(3-4)

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Trends of precipitation extreme indices over a subtropical semi-arid area using PERSIANN-CDR     

Pari-Sima?Katiraie-BoroujerdyEmail author  Hamed?Ashouri  Kuo-lin?Hsu  Soroosh?Sorooshian 《Theoretical and Applied Climatology》2017,130(1-2):249-260

In this study, satellite-based daily precipitation estimation data from precipitation estimation from remotely sensed information using artificial neural networks (PERSIANN)-climate data record (CDR) are being evaluated in Iran. This dataset (0.25°, daily), which covers over three decades of continuous observation beginning in 1983, is evaluated using rain-gauge data for the period of 1998–2007. In addition to categorical statistics and mean annual amount and number of rainy days, ten standard extreme indices were calculated to observe the behavior of daily extremes. The results show that PERSIANN-CDR exhibits reasonable performance associated with the probability of detection and false-alarm ratio, but it overestimates precipitation in the area. Although PERSIANN-CDR mostly underestimates extreme indices, it shows relatively high correlations (between 0.6316–0.7797) for intensity indices. PERSIANN-CDR data are also used to calculate the trend in annual amounts of precipitation, the number of rainy days, and precipitation extremes over Iran covering the period of 1983–2012. Our analysis shows that, although annual precipitation decreased in the western and eastern regions of Iran, the annual number of rainy days increased in the northern and northwestern areas. Statistically significant negative trends are identified in the 90th percentile daily precipitation, as well as the mean daily precipitation from wet days in the northern part of the study area. The positive trends of the maximum annual number of consecutive dry days in the eastern regions indicate that the dry periods became longer in these arid areas.  相似文献   

Cymrite: new occurrence and stability   总被引：2，自引：0，他引：2  

L. C. Hsu 《Contributions to Mineralogy and Petrology》1994,118(3):314-320

The rare mineral cymrite, BaAl₂Si₂O₈·H₂O, was discovered in Nevada in a Cambrian bedded barite sequence that exhibits low-grade metamorphism. The mineral occurs exclusively in thin-bedded siliceous rock containing anhedral pyrite crystals up to 1 cm. Cymrite forms rectangular grains ca 40 m across, distributed throughout the chalcedonic quartz matrix. An SEM image of one such blocky grain shows that it is filled by tiny aggregates, instead of a single crystal of cymrite. This cymrite may have replaced a pre-existing rectangular mineral, most likely barite. The Nevada occurrence of cymrite prompted a restudy of its stability relations. Conventional hydrothermal techniques were adopted in the experimental work with run durations up to 7 months. The univariant curve for the dehydration reaction: BaA1₂Si₂O₈· H₂O -BaA1₂Si₂O₈ +H₂O passes the following reversed brackets: 300–315° C at 3 kbar, 290–300° C at a 2 kbar, 270–285° C at 1 kbar, and 240–270° C at 0.5 kbar. These results indicate that cymrite can be stable at much lower pressures than those previously reported. The replacement of barite by cymrite was experimentally demonstrated with an alkaline solution as depicted by the reaction: BaSO₄+2OH^-+A1₂O₃-2SiO₂=BaA1₂Si₂O₈·H₂O+SO ₄ ² Such replacement failed to take place when an acidic solution was used instead.  相似文献