The coronal structure of Speedy Mic – I. A densely packed prominence system beyond corotation

We present new observations of the prominence system on the K3 dwarf Speedy Mic (BO Mic, HD 197890). Using an improved technique to track the absorption features in Hα we find a very active prominence system with approximately 10 prominences on the observable hemisphere per rotation. From a total of 25 prominences, we find an average axial distance of  (2.85 ± 0.54) R _*  which is twice the corotation radius above the stellar surface. We discuss the consequences of these observations on the nature of the supporting magnetic structures. Two consecutive nights, with complete phase coverage, combined with a further night after a three-night gap allow us to study the evolution of the prominence system on two different time-scales. Several of the prominences have counterparts at similar phases on consecutive nights. During this interval, many prominences show evidence for evolution in their heights and phases of observation. Five nights (13 rotation cycles) later, we recover many prominences at approximately the same phases. Whilst individual prominences change axial distances or appear/reappear from night-to-night, the underlying prominence supporting structures appear to be stable over as many as 13 stellar rotations.     

Lines formed in rotating and expanding atmospheres

Spectral lines formed in a rotating and expanding atmosphere have been computed in the frame of the observer at infinity. Two kinds of velocity laws are employed: (i) a uniform radial velocity of the gas and (ii) velocity increasing with radius (i.e. velocity gradients). The atmosphere has been assumed to be rotating with constant velocity. We have considered maximum radial and rotational velocities to be 10 and 3 mean thermal units respectively in an atmosphere whose geometrical thickness is 10 times the stellar radius. The total radial optical depth at line centre is taken to be about 100. In all cases, Doppler profile and a source function which is varying as 1/r ² have been used. Generally, the lines are broadened when rotation is introduced. However, when radial motion is also present, broadening becomes asymmetric and the red emission and blue absorption are enhanced.     

A One-Dimensional Relativistic Shock Model for the Light Curve of Gamma-ray Bursts

We investigate the forming of gamma-ray burst pulses with a simple one-dimensional relativistic shock model. The mechanism is that a "central engine" drives forward the nearby plasma inside the fireball to generate a series of pressure waves. We give a relativistic geometric recurrence formula that connects the time when the pressure waves are produced and the time when the corresponding shocks occurred. This relation enables us to relate the pulse magnitude with the observation time. Our analysis shows that the evolution of the pressure waves leads to a fast rise and an exponential decay pulses. In determining the width of the pulses, the acceleration time is more important than that of the deceleration.     

机载雷达技术在中小比例尺地形图中的应用研究

机载雷达技术已经广泛应用于各个领域,机载雷达能瞬间获得大量的采样点,采样点具有高密度、高精度的优势,本文阐述了机载雷达技术在中小比例尺地形图中的应用。     

Publications received by the Editor

Abstract

Temperature profiles (temperature as function of depth) can be used to derive vertical flow velocities or recharge rates. In many cases, solutions to the one-dimensional (1-D) heat transport equation are used, considering steady-state boundary conditions. Factors which can influence the derivation of the mean vertical flow velocity are studied here. Therefore, an explicit finite-difference approximation to the 1-D heat transport equation coupled with an inverse scheme was used to interpret temperature profiles. Measurement error (larger than 0.05°C) can result in important deviation of the derived mean flow velocity. Variation of vertical flow velocity as a function of time leads to asymmetric temperature envelopes. Yearly variation in vertical flow velocities, or temperature variations of the recharge water, also results in asymmetric temperature envelopes. Interpretation of these asymmetric envelopes leads to important differences between derived and actual mean vertical flow velocities.

Citation Vandenbohede, A. &; Lebbe, L. (2010) Vandenbohede, A. and Lebbe, L. 2010. Parameter estimation based on vertical heat transport in the surficial zone. Hydrogeol. J., 18 , 931–943,doi:10.1007/s10040-009–0557–5 [Google Scholar] Recharge assessment by means of vertical temperature profiles: analysis of possible influences. Hydrol. Sci. J. 55(5), 792–804.     

莱州湾河流表层沉积物中六溴环十二烷的含量水平、分布及组成特征

从莱州湾附近河流采集了36个表层沉积物样品,采用高效液相色谱耦合三重四极杆串联质谱的分析方法对沉积物中的六溴环十二烷（HBCDsl3种异构体进行了测定,目的是表征研究区域内HBCDs的污染水平和组成特征,并探讨其分布、来源及影响因素。结果表明,莱州湾河流沉积物中ZHBCDs的含量范围为0．03～20．17ng／gdw（均值是2．14ng／gdw）：较国内外其他河流,该研究区域HBCDs含量水平较低。HBCDs异构体组成各不相同,除1个站位外,其他站位样品中7-HBCD占主导地位（52．3％～97．3％,均值72．4％）,但是在农业区a-HBCD相对丰度较高。对HBCDs的分布特征及来源分析得出,含量较高的站点多集中在工业区,呈现出明显的点源特征：而远离工业区的采样点,HBCDs可能主要来自大气的传输和沉降,且HBCDs的含量与TOC含量呈现出较好的相关性,表明TOC是非工业区分布的一个控制因素。     

On the use of horizontal acoustic Doppler profilers for continuous bed shear stress monitoring

Continuous monitoring of bed shear stress in large river systems may serve to better estimate alluvial sediment transport to the coastal ocean.Here we explore the possibility of using a horizontally deployed acoustic Doppler current profiler(ADCP) to monitor bed shear stress,applying a prescribed boundary layer model,previously used for discharge estimation.The model parameters include the local roughness length and a dip correction factor to account for sidewall effects.Both these parameters depend on river stage and on the position in the cross-section, and were estimated from shipborne ADCP data.We applied the calibrated boundary layer model to obtain bed shear stress estimates over the measuring range of the HADCP.To validate the results,co-located coupled ADCPs were used to infer bed shear stress,both from Reynolds stress profiles and from mean velocity profiles. From HADCP data collected over a period of 1.5 years,a time series of width profiles of bed shear stress was obtained for a tidal reach of the Mahakam River,East Kalimantan,Indonesia.A smaller dataset covering 25 hours was used for comparison with results from the coupled ADCPs.The bed shear stress estimates derived from Reynolds stress profiles appeared to be strongly affected by local effects causing upflow and downflow,which are not included in the boundary layer model used to derive bed shear stress with the horizontal ADCP.Bed shear stresses from the coupled ADCP are representative of a much more localized flow,while those derived with the horizontal ADCP resemble the net effect of the flow over larger scales.Bed shear stresses obtained from mean velocity profiles from the coupled ADCPs show a good agreement between the two methods,and highlight the robustness of the method to uncertainty in the estimates of the roughness length.