Average extinction curves and relative abundances for quasi-stellar object absorption-line systems at 1 ≤z_abs < 2     

Donald G. York  Pushpa Khare  Daniel Vanden Berk  Varsha P. Kulkarni  Arlin P. S. Crotts  James T. Lauroesch  Gordon T. Richards  Donald P. Schneider  Daniel E. Welty  Yusra Alsayyad  Abhishek Kumar  Britt Lundgren  Natela Shanidze  Tristan Smith  Johnny Vanlandingham  Britt Baugher  Patrick B. Hall  Edward B. Jenkins  Brice Menard  Sandhya Rao  Jason Tumlinson  David Turnshek  Ching-Wa Yip  Jon Brinkmann 《Monthly notices of the Royal Astronomical Society》2006,367(3):945-978

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An investigation into the correlations among GNSS observations and their impact on height and zenith wet delay estimation for medium and long baselines     

Johnny LO  Ahmed EL-MOWAFY 《地球空间信息科学学报》2013,16(4):219-228

Most stochastic modelling techniques neglect the correlations among the raw un-differenced observations when forming the variance–covariance matrix of the Global Navigation Satellite System (GNSS) observations. Some methods were developed to model these correlations. One such method is the Minimum Norm Quadratic Unbiased Estimator (MINQUE). Studies have shown that MINQUE improves ambiguity resolution, and ultimately, the positioning solution in short baselines. However, its effect in cases of processing with longer baselines and on the estimation of zenith wet delay (ZWD) is somewhat unknown. In this paper, a comparison between the impact of neglecting the correlations among the observations using an elevation-angle-dependent model (EADM) and modelling the correlations using MINQUE on height determination and ZWD for medium and long baselines is carried out. The initial testing was carried out across two Australian GNSS stations with a medium-length baseline throughout a three-week campaign. The results showed that using MINQUE did not resolve the coordinate, height and wet delay components as accurately as the EADM. The results were further verified with two long-baseline campaigns whereby EADM was also able to provide better wet delay estimates. The coordinate results were, however, mixed. Overall, the study concluded that the inclusion of the correlations among the observations, in general, do not improve the resolution of the coordinate and wet delay estimates.  相似文献   

一株脂肽产生菌发酵参数的响应曲面法优化          下载免费PDF全文

单大鹏  李旭  产竹华  刘洋  邵宗泽 《海洋科学进展》2012,30(4)

从渤海污染土壤中分离的表面活性剂产生菌,经鉴定为Bacillus sp.BO2,该菌在对数生长期产生表面活性剂,至稳定期后可将发酵液的表面张力降低至31.0 mN·m1.初步分析发现其表面活性剂成分为环脂肽,该脂肽在不同温度、盐度、pH条件下有较好的稳定性.进一步采用响应曲面法(RSM),以乳化系数作为响应值来优化菌株BO2产生物表面活性剂培养条件.还通过实验确定碳源(液体石蜡)、NH4NO3、KH2PO4为3个影响表面活性剂产量的显著因素,再进行发酵培养基优化,获得最佳培养基配方.获得的发酵参数为利用该菌株发酵生产生物表面活性剂提供数据,为石油降解菌的应用开发提供了有价值的信息.  相似文献   

Water vapor sources associated with the early summer precipitation over China     

K. C. Chow  Hang-Wai Tong  Johnny C. L. Chan 《Climate Dynamics》2008,30(5):497-517

This study investigates the water vapor sources for the early summer precipitation over China in association with the Asian summer monsoon, based on the sensitivity experiments performed by a regional climate model for the year 1998. It is found that the northern South China Sea (NSCS) is an important region for the early summer precipitation over China, particularly the south China region. The evaporative water vapor flux or sea surface temperature over the NSCS could significantly affect the southwesterly water vapor transport towards the NSCS. This in turn may significantly change the water vapor transport from the NSCS to China and so changes the precipitation there. The results of the experiments also show that the precipitation over China does not particularly depend on the water vapor transports from some distant sources by the large-scale flows. Most of the required water vapor could be obtained from the ocean within the monsoon region. The results suggest that the water vapor transport over China is basically a combination of the southeasterly water vapor transport associated with the north Western Pacific subtropical high and the southwesterly water vapor transport associated with the Indian summer monsoon. Without the latter, the early summer precipitation over China could be reduced by up to half of the original amount.  相似文献   

Improving the Analyses and Forecasts of a Tropical Squall Line Using Upper Tropospheric Infrared Satellite Observations     

Man-Yau CHAN  Xingchao CHEN 《大气科学进展》2022,39(5):733-746

The advent of modern geostationary satellite infrared radiance observations has noticeably improved numerical weather forecasts and analyses.However,compared to midlatitude weather systems and tropical cyclones,research into using infrared radiance observations for numerically predicting and analyzing tropical mesoscale convective systems remain mostly fallow.Since tropical mesoscale convective systems play a crucial role in regional and global weather,this deficit should be addressed.This study is the first of its kind to examine the potential impacts of assimilating all-sky upper tropospheric infrared radiance observations on the prediction of a tropical squall line.Even though these all-sky infrared radiance observations are not directly affected by lower-tropospheric winds,the high-frequency assimilation of these all-sky infrared radiance observations improved the analyses of the tropical squall line’s outflow position.Aside from that,the assimilation of all-sky infrared radiance observations improved the analyses and prediction of the squall line’s cloud field.Finally,reducing the frequency of assimilating these all-sky infrared radiance observations weakened these improvements to the analyzed outflow position,as well as the analyses and predictions of cloud fields.  相似文献   

在EBEX-2000实验资料中湍流谱和局地各向同性特征   总被引：10，自引：4，他引：6  

刘树华  李洁  刘和平  梁福明  王建华  Johnny C.L.CHAN  Andrew Y.S.CHENG  胡非  刘辉志 《大气科学》2005,29(2):213-224

采用2000年8月在美国加州棉花地两个高度上应用超声三分量仪、快速响应050206 温度和湿度仪进行的EBEX-2000 (International Energy Balance Experiment,2000,EBEX-2000)风速三分量、温度和湿度湍流实验观测数据,计算分析了湍流速度、温度和湿度谱在不同稳定度下的特征.对湍流的局地各向同性进行了讨论并与Kansas和长白山原始森林湍流实验得到的结果进行了比较,得到了一些湍流特征量在不同下垫面情况下的一些有意义的特征.  相似文献   

在EBEX-2000实验资料中的湍流宏观量特征   总被引：7，自引：1，他引：6  

刘树华  李洁  刘和平  梁福明  王建华  Johnny C. L. CHAN  Andrew Y. S. CHENG  胡非  刘辉志 《大气科学》2005,29(4):503-509

采用2000年8月在美国加州棉花地两个高度上应用超声三分量仪、快速响应温度和湿度仪进行的EBEX-2000 (International Energy Balance Experiment, 2000) 风速三分量、温度和湿度湍流实验观测数据, 计算分析了湍流宏观量(即 u*, T*, σu/u*, σv/u*, σw/u*和σT/T*等), 湍流动能和感热通量等的特征, 并与其他湍流实验得到的结果进行了比较.  相似文献   

Dependency of typhoon intensity and genesis locations on El Ni?o phase and SST shift over the western North Pacific     

Kyung-Ja Ha  Soon-Jo Yoon  Kyung-Sook Yun  Jong-Seong Kug  Yeon-Soo Jang  Johnny C. L. Chan 《Theoretical and Applied Climatology》2012,109(3-4):383-395

The effects of the El Ni?o-Southern Oscillation (ENSO) phase and the shifting of the ENSO sea surface temperature (SST) on the intensity of tropical cyclones (TC) have been extensively investigated in terms of TC genesis locations in the western North Pacific (WNP). To advance the hypothesis for a relation of genesis location–intensity that the TC formation location hints its intensity, two cases have been compared, which include the phase of the decaying El Ni?o turning over to La Ni?a (type I) and the phase that recovers to a neutral condition (type II). In addition, the shift of ENSO SST to the central Pacific warming (CPW) from the East Pacific warming (EPW) has been examined. The genesis potential index (GPI) and the accumulated cyclone energy have been applied to compare the differences between the ENSO phase and the TC formation location. It was apparent that ENSO influences the WNP typhoon formation location depending on the cycle of the ENSO phase. In addition, the typhoon activity was affected by the zonal shift of the El Ni?o SST. The CPW, which has maximum SST over the central Pacific, tends to have a persistently high GPI over the WNP in September–November and June–August, demonstrating that the formation locations of strong TCs significantly shift southeastward compared with the EPW having SST maximum over the eastern Pacific. CPW years revealed a distinguishable relationship between the TC formation location and the TC between the tropical depression (TD) + tropical storm (TS) and the intense typhoon of category 4?+?5.  相似文献   

Potential use of a regional climate model in seasonal tropical cyclone activity predictions in the western North Pacific     

Andie Y. M. Au-Yeung  Johnny C. L. Chan 《Climate Dynamics》2012,39(3-4):783-794

This study investigates the potential use of a regional climate model in forecasting seasonal tropical cyclone (TC) activity. A modified version of Regional Climate Model Version 3 (RegCM3) is used to examine the ability of the model to simulate TC genesis and landfalling TC tracks for the active TC season in the western North Pacific. In the model, a TC is identified as a vortex satisfying several conditions, including local maximum relative vorticity at 850?hPa with a value?≥450?×?10^?6?s^?1, and the temperature at 300?hPa being 1°C higher than the average temperature within 15° latitude radius from the TC center. Tracks are traced by following these found vortices. Six-month ensemble (8 members each) simulations are performed for each year from 1982 to 2001 so that the climatology of the model can be compared to the Joint Typhoon Warning Center (JTWC) observed best-track dataset. The 20-year ensemble experiments show that the RegCM3 can be used to simulate vortices with a wind structure and temperature profile similar to those of real TCs. The model also reproduces tracks very similar to those observed with features like genesis in the tropics, recurvature at higher latitudes and landfall/decay. The similarity of the 500-hPa geopotential height patterns between RegCM3 and the European Centre for Medium-Range Weather Forecasts 40 Year Re-analysis (ERA-40) shows that the model can simulate the subtropical high to a large extent. The simulated climatological monthly spatial distributions as well as the interannual variability of TC occurrence are also similar to the JTWC data. These results imply the possibility of producing seasonal forecasts of tropical cyclones using real-time global climate model predictions as boundary conditions for the RegCM3.  相似文献   

水下运载器系统快速开盖运动学研究          下载免费PDF全文

袁瑞  产斯志 《数字海洋与水下攻防》2022,5(2):157-161

水下运载器根据其使命,通常内部装载不同战斗载荷,其中上浮开盖过程是其作战流程中非常关键的一个动作过程,水下运载器在其工作过程中受到波浪力、火箭推力、重力、流体阻力等外界因素的影响,而开盖动作又使得水下运载器系统构件之间产生相对运动,其运动特性较为复杂.针对水下运载器系统,利用多刚体Kane方法建立了系统的动力学方程,利...  相似文献