2005年7月台湾海峡西南部海域的上升流与冲淡水观测

根据2005年7月台湾海峡西南部海域CTD观测数据,绘制出相关温盐分布图,分析了调查期间该海域的温盐分布特征.结果表明,调查期间东山海域、南澳海域以及台湾浅滩东南侧海域存在明显的上升流现象;在近岸上层,一股较强的冲淡水从西南部进入该海域并影响至台湾浅滩.     

Dynamical evolution properties of debris flows controlled by different mesh-sized flexible net barriers

Because the flexible net barrier is a gradually developed open-type debris-flow counter-measure, there are still uncertainties in its design criterion. By using several small-scale experimental flume model tests, the dynamical evolution properties of debris flows controlled by large and small mesh-sized (equal to D₉₀ and D₅₀, respectively) flexible net barriers are studied, including the debris flow behaviors, segregation, and permeability of sediments, as well as the energy absorption rates and potential overtopping occurring when debris flows impact the small mesh-sized one. Experimental results reveal that (a) two sediment deposition patterns are observed depending on variations in debris flow textures and mesh sizes; (b) the aggregation against flexible net barriers is dominated by flow dynamics; (c) the segregation and permeable functions of the barrier are determined by the mesh size, concentration, and flow dynamics; and (d) the smaller mesh-sized flexible net barrier tends to be more efficient in restraining more turbulent debris flows and can absorb greater rate of kinematic energy, and finally, the great kinematic energy dissipation that occurs when secondary debris flows interact with the post-deposits in front of the small mesh-sized flexible net barrier is believed to cause the failure of overtopping phenomenon. The mesh size is concluded to be the decisive parameter that should be associated with debris flow textures to design the control functions of flexible net barriers.     

Thin accretion disc with a corona in a central magnetic field

We study the steady-state structure of an accretion disc with a corona surrounding a central, rotating, magnetized star. We assume that the magneto-rotational instability is the dominant mechanism of angular momentum transport inside the disc and is responsible for producing magnetic tubes above the disc. In our model, a fraction of the dissipated energy inside the disc is transported to the corona via these magnetic tubes. This energy exchange from the disc to the corona which depends on the disc physical properties is modified because of the magnetic interaction between the stellar magnetic field and the accretion disc. According to our fully analytical solutions for such a system, the existence of a corona not only increases the surface density but reduces the temperature of the accretion disc. Also, the presence of a corona enhances the ratio of gas pressure to the total pressure. Our solutions show that when the strength of the magnetic field of the central neutron star is large or the star is rotating fast enough, profiles of the physical variables of the disc significantly modify due to the existence of a corona.     

Precursor times of abnormal <Emphasis Type="Italic">b</Emphasis>-values prior to mainshocks

Seismic observations exhibit the presence of abnormal b-values prior to numerous earthquakes. The time interval from the appearance of abnormal b-values to the occurrence of mainshock is called the precursor time. There are two kinds of precursor times in use: the first one denoted by T is the time interval from the moment when the b-value starts to increase from the normal one to the abnormal one to the occurrence time of the forthcoming mainshock, and the second one denoted by T _p is the time interval from the moment when the abnormal b-value reaches the peak one to the occurrence time of the forthcoming mainshock. Let T* be the waiting time from the moment when the abnormal b-value returned to the normal one to the occurrence time of the forthcoming mainshock. The precursor time, T (usually in days), has been found to be related to the magnitude, M, of the mainshock expected in a linear form as log(T)?=?q?+?rM where q and r are the coefficient and slope, respectively. In this study, the values of T, T _p , and T* of 45 earthquakes with 3?≤?M?≤?9 occurred in various tectonic regions are compiled from or measured from the temporal variations in b-values given in numerous source materials. The relationships of T and T _p , respectively, versus M are inferred from compiled data. The difference between the values of T and T _p decreases with increasing M. In addition, the plots of T*/T versus M, T* versus T, and T* versus T-T* will be made and related equations between two quantities will be inferred from given data.     

Radioactive anomalies associated with the graphite-bearing metasediments,Wadi Umm Gheig area,Central Eastern Desert,Egypt

The study area is located in the central part of the Eastern Desert of Egypt and is mainly covered by different varieties of Precambrian basement rocks represented mainly by younger and older granites, metadiorite, metavolcanics, and metasediments. The analysis and interpretation of airborne gamma-ray spectrometric survey data are essentially based on the computation of the three radioelements (U, Th, and K) favorability indices, estimation of uranium migration rate percentage, variation of eU with eTh and eU/eTh ratio, and the construction of the contour map of the (eU-eTh/3.5) in the different rock units. The highest percent of uranium migration- out or leaching rate is connected with the red and pink granites of Gebel Kadabora El-hamra, metadiorite, and red and pink granites of G. Umm Rakham (??20.8%, ??18.57%, and ??8.45% respectively), which indicates that they could represent a major U-source bodies in the area. It was observed that the metasediments and associated graphite-bearing schists west and northwest of G. Kadabora El-hamra reflect more precipitation than the other locations around the pluton (the uranium migration rates varies between 2.59 and 30%) which mean that the graphite may have acted as a reducing agent for uranium carried in oxidizing fluids (surface meteoric water) and resulted in its precipitation. In the light of the availability of uranium source, its mobility, and graphite-bearing metasediments, the area has a good potential for the possible occurrence of uranium mineralization.     

Diatoms grow faster using ammonium in rapidly flushed eutrophic Dokai Bay,Japan

The importance of the nitrogen source for phytoplankton growth in a highly eutrophic embayment, Dokai Bay, was investigated. The DIN concentration often exceeded 100 μM of which 40–70% was NH₄ ⁺. During two incubation experiments, the natural assemblage of mainly diatoms took up NH₄ ⁺ instead of NO₃ ⁻. The growth of two Skeletonema species isolated in Dokai Bay were significantly faster on NH₄ ⁺ (1.86 and 1.27 div. d⁻¹ respectively) than on NO₃ ⁻ (1.55 and 1.04 div. d⁻¹ respectively). Our results indicated that these diatoms could grow faster by using NH₄ ⁺ compared to NO₃ ⁻ in this eutrophic bay.     

Peierls dislocation modelling in perovskite (CaTiO<Subscript>3</Subscript>): comparison with tausonite (SrTiO<Subscript>3</Subscript>) and MgSiO<Subscript>3</Subscript> perovskite

We present here a numerical modelling study of dislocations in perovskite CaTiO₃. The dislocation core structures and properties are calculated through the Peierls–Nabarro model using the generalized stacking fault (GSF) results as a starting model. The GSF are determined from first-principles calculations using the VASP code. The dislocation properties such as collinear, planar core spreading and Peierls stresses are determined for the following slip systems: [100](010), [100](001), [010](100), [010](001), [001](100), [001](010), and All dislocations exhibit lattice friction, but glide appears to be easier for [100](010) and [010](100). [001](010) and [001](100) exhibit collinear dissociation. Comparing Peierls stresses among tausonite (SrTiO₃), perovskite (CaTiO₃) and MgSiO₃ perovskite demonstrates the strong influence of orthorhombic distortions on lattice friction. However, and despite some quantitative differences, CaTiO₃ appears to be a satisfactory analogue material for MgSiO₃ perovskite as far as dislocation glide is concerned.     

Detection of the Long Period Long Duration (LPLD) Events in Time-and Frequency-Domain

Long Period Long Duration (LPLD) signals are unusual seismic events that can be observed during hydraulic fracturing. These events are very similar in appearance to tectonic tremors sequences, which were first observed in subduction zones. Their nature is not well known. LPLD might be related to the productivity of the reservoir. Different methods of the LPLD events’ detection recorded during hydraulic fracturing are presented. The author applied two methods for LPLD detection–Butterworth filtering and Continuous Wavelet Transform (CWT). Additionally, a new approach to LPLD events detection–instantaneous seismic attributes–was used, common in a classical seismic interpretation but not in microseismic monitoring.     

A reinterpretation of two chertbreccias from the Proterozoic basins of India

Several horizons of a unique lithotype called “chertbreccia” are interbedded within the Proterozoic platform sediments of the Peninsular India. These cherty rocks with brecciated texture appearing as blocky masses were earlier diversely interpreted as being products of disparate processes such as fault-zone breccias, collapse breccias, and so on. Two of these horizons, one from the Kaladgi Basin (Dharwar Craton) and the other from the Dhar Forest Inlier of the Vindhyanchal Basin (Bundelkhand — Aravalli Craton) are compared in context of their geological setting, field relations and petrological constitution. A model of the mode of development of these peculiar rocks is reconstructed, taking into account their characters and limitations of previous interpretations. They are interpreted as transported debris deposits of syntectonogenic material released during the episodic activity of the growth faults of the Kaladgi and Vindhyanchal Basins that was diagenetically silicified.     

The effect of seafloor topography in the Southern Ocean on tabular iceberg drifting and grounding

Antarctic tabular icebergs are important active components in the ice sheet-ice shelf-ocean system. Seafloor topography is the key factor that affects the drifting and grounding of icebergs, but it has not been fully investigated. This study analyzes the impact of seafloor topography on the drifting and grounding of Antarctic tabular icebergs using Bedmap-2 datasets and iceberg route tracking data from Brigham Young University. The results highlight the following points. (1) The quantitative distributions of iceberg grounding events and the tracking points of grounded icebergs are mainly affected by iceberg draft and reach their peak values in sea water with depths between 200 m and 300 m. The peak tracking point number and linear velocity of free-drifting icebergs are found in the Antarctic Slope Front (water depth of approximately 500 m). (2) The area of possible grounding regions of small-scale icebergs calved from ice shelf fronts accounts for 28% of the sea area at water depths less than 2000 m outside the Antarctic coastline periphery (3.62 million km²). Their spatial distribution is mainly around East Antarctica and the Antarctic Peninsula. The area of possible grounding regions of large tabular icebergs with long axes larger than 18.5 km (in water depths of less than 800 m) accounts for 74% of the sea area. (3) The iceberg drifting velocity is positively correlated with ocean depth in areas where the depth is less than 2000 m (R=0.85, P<0.01). This result confirms the effect of water depth variations induced by seafloor topography fluctuations on iceberg drifting velocity.