Corotational damping of discoseismic c modes in black hole accretion discs     

David Tsang  Dong Lai 《Monthly notices of the Royal Astronomical Society》2009,393(3):992-998

Discoseismic c modes in accretion discs have been invoked to explain low-frequency variabilities observed in black hole X-ray binaries. These modes are trapped in the innermost region of the disc and have frequencies much lower than the rotation frequency at the disc inner radius. We show that because the trapped waves can tunnel through the evanescent barrier to the corotational wave zone, the c modes are damped due to wave absorption at the corotation resonance. We calculate the corotational damping rates of various c modes using the Wentzel-Kramers-Brillouin (WKB) approximation. The damping rate varies widely depending on the mode frequency, the black hole spin parameter and the disc sound speed, and is generally much less than 10 per cent of the mode frequency. A sufficiently strong excitation mechanism is needed to overcome this corotational damping and make the mode observable.  相似文献   

水文地质研究新动向     

TSang  CF 《地学前缘》1996,3(1):43-48

由于日益增长的社会发展的需要，水文地质研究正在产生巨大变化。人们对各种工农业活动所产生的诸多环境污染问题的关注，以及对“高放”放射性废物和毒性液体的地下深层埋设的安全评价需求，致使水文地质研究产生许多新的生长点。无论是在水文地质研究的学科发展领域，还是在解决重大社会问题方向，水文地质学家均面临着巨大的挑战和机遇。  相似文献   

Natural and industrial analogues for leakage of CO2 from storage reservoirs: identification of features, events, and processes and lessons learned     

Jennifer L. Lewicki  Jens Birkholzer  Chin-Fu Tsang 《Environmental Geology》2007,52(3):457-467

Instances of gas leakage from naturally occurring CO₂ reservoirs and natural gas storage sites serve as analogues for the potential release of CO₂ from geologic storage sites. This paper summarizes and compares the features, events, and processes that can be identified from these analogues, which include both naturally occurring releases and those associated with industrial processes. The following conclusions are drawn: (1) carbon dioxide can accumulate beneath, and be released from, primary and secondary shallower reservoirs with capping units located at a wide range of depths; (2) many natural releases of CO₂ are correlated with a specific event that triggered the release; (3) unsealed fault and fracture zones may act as conduits for CO₂ flow from depth to the surface; (4) improperly constructed or abandoned wells can rapidly release large quantities of CO₂; (5) the types of CO₂ release at the surface vary widely between and within different leakage sites; (6) the hazard to human health was small in most cases, possibly because of implementation of post-leakage public education and monitoring programs; (7) while changes in groundwater chemistry were related to CO₂ leakage, waters often remained potable. Lessons learned for risk assessment associated with geologic carbon sequestration are discussed. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.  相似文献   

Apparent flow-dimension approach to the study of heterogeneous fracture network systems     

Sharma  Kunwar Mrityunjai  Dessirier  Benoit  Tsang  Chin-Fu  Niemi  Auli 《Hydrogeology Journal》2023,31(4):873-891

Hydrogeology Journal - The generalized radial flow (GRF) model in well-test analysis employs noninteger flow dimensions to represent the variation in flow area with respect to radial distance from...  相似文献   

A Zoneless Approach for Probabilistic Seismic Hazard Analysis     

Hing-Ho Tsang 《华南地震》2009,(Z1):50-59

-Conventional Probabilistic Seismic Hazard Analysis(PSHA) is difficult to apply in regions lacking sufficient information of the geological setting,active faults,and so forth.Also,for a site-specific PSHA,site effects arising from both crustal rock and overlying soil sediments are generally not assessed rigorously.This is of particular importance for those metropolitan cities having a significant proportion of reclaimed land,because the site-to-site variability of such site effects can be very large.The objective of this paper is to demonstrate an alternative procedure for constructing site-specific uniform hazard response spectra(UHS),extended from a recently-developed Direct Amplitude-Based(DAB) approach.The method has a number of important advantages compared with conventional PSHA.Using the proposed approach,response spectral values have been computed for the whole period range of engineering interest,to form a set of site-specific UHS.  相似文献   

Ionospheric photoelectrons: Comparing Venus, Earth, Mars and Titan     

A.J. Coates  S.M.E. Tsang  A. Wellbrock  R.A. Frahm  S. Barabash  D.T. Young 《Planetary and Space Science》2011,59(10):1019-1027

The sunlit portion of planetary ionospheres is sustained by photoionization. This was first confirmed using measurements and modelling at Earth, but recently the Mars Express, Venus Express and Cassini-Huygens missions have revealed the importance of this process at Mars, Venus and Titan, respectively. The primary neutral atmospheric constituents involved (O and CO₂ in the case of Venus and Mars, O and N₂ in the case of Earth and N₂ in the case of Titan) are ionized at each object by EUV solar photons. This process produces photoelectrons with particular spectral characteristics. The electron spectrometers on Venus Express and Mars Express (part of ASPERA-3 and 4, respectively) were designed with excellent energy resolution (ΔE/E=8%) specifically in order to examine the photoelectron spectrum. In addition, the Cassini CAPS electron spectrometer at Saturn also has adequate resolution (ΔE/E=16.7%) to study this population at Titan. At Earth, photoelectrons are well established by in situ measurements, and are even seen in the magnetosphere at up to 7R_E. At Mars, photoelectrons are seen in situ in the ionosphere, but also in the tail at distances out to the Mars Express apoapsis (∼3R_M). At both Venus and Titan, photoelectrons are seen in situ in the ionosphere and in the tail (at up to 1.45R_V and 6.8R_T, respectively). Here, we compare photoelectron measurements at Earth, Venus, Mars and Titan, and in particular show examples of their observation at remote locations from their production point in the dayside ionosphere. This process is found to be common between magnetized and unmagnetized objects. We discuss the role of photoelectrons as tracers of the magnetic connection to the dayside ionosphere, and their possible role in enhancing ion escape.  相似文献   

Effects of alumina refinery wastewater and signature metal constituents at the upper thermal tolerance of: 1. The tropical diatom Nitzschia closterium     

Harford AJ  Hogan AC  Tsang JJ  Parry DL  Negri AP  Adams MS  Stauber JL  van Dam RA 《Marine pollution bulletin》2011,62(3):466-473

Ecotoxicological studies, using the tropical marine diatom, Nitzschia closterium (72-h growth rate), were undertaken to assess potential issues relating to the discharge from an alumina refinery in northern Australia. The studies assessed: (i) the species’ upper thermal tolerance; (ii) the effects of three signature metals, aluminium (Al), vanadium (V) and gallium (Ga) (at 32 °C); and (iii) the effects of wastewater (at 27 and 32 °C). The critical thermal maximum and median inhibition temperature for N. closterium were 32.7 °C and 33.1 °C, respectively. Single metal toxicity tests found that N. closterium was more sensitive to Al compared to Ga and V, with IC₅₀s (95% confidence limits) of 190 (140-280), 19,640 (11,600-25,200) and 42,000 (32,770-56,000) μg L⁻¹, respectively. The undiluted wastewater samples were of low toxicity to N. closterium (IC₅₀s > 100% wastewater). Environmental chemistry data suggested that the key metals and discharge are a very low risk to this species.  相似文献   

A new site classification approach based on neural networks     

Saman Yaghmaei-Sabegh  Hing-Ho Tsang 《Soil Dynamics and Earthquake Engineering》2011

Site classification is an important procedure for a reliable site-specific seismic hazard assessment. On the other hand, the site conditions at strong-motion stations are essential for accurate interpretation and analysis of the recorded ground motion data obtained from different regions of the world. For some countries with insufficient data on the subsurface geological settings, the required site condition information is not available. This paper presents a new and efficient approach for site classification based on artificial neural networks (ANN) along with a selected set of representative horizontal to vertical spectral ratio (HVSR) curves for four site classes. The nonlinear nature of ANN and their ability to learn in a complex environment make it highly suitable for function approximation and solving complicated engineering problems. Two types of radial basis function (RBF) neural networks, namely, probabilistic neural networks (PNN) and generalized regression neural networks (GRNN) were chosen in this study, as no separate training phase is required, rendering them particularly suitable for site classification. The proposed approach has been tested using data of the Chi-Chi, Taiwan, earthquake (Mw=7.6) recorded from 87 stations at which the site conditions are known. Analyses show that both the PNN and the GRNN perform very well with similar accuracy in estimating site conditions, with successful rates of 78% and 75%, respectively.  相似文献   

Analysis of landslide dam geometries   总被引：2，自引：1，他引：1  

Yu-Shu Kuo  Yun-Chung Tsang  Kun-Ting Chen  Chjeng-Lun Shieh 《山地科学学报》2011,8(4):544-550

The geometry of a landslide dam is an important component of evaluating dam stability. However, the geometry of a natural dam commonly cannot be obtained immediately with field investigations due to their remote locations. A rapid evaluation model is presented to estimate the geometries of natural dams based on the slope of the stream, volume of landslides, and the properties of the deposit. The proposed model uses high resolution satellite images to determine the geometry of the landside dam. These satellite images are the basic information to a preliminary stability analysis of a natural dam. This study applies the proposed method to two case studies in Taiwan. One is the earthquake-induced Lung-Chung landslide dam in Taitung, and the second is the rainfall-induced Shih-Wun landslide dam in Pingtung.  相似文献   

Corotational instability of inertial-acoustic modes in black hole accretion discs and quasi-periodic oscillations     

Dong Lai  David Tsang 《Monthly notices of the Royal Astronomical Society》2009,393(3):979-991

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