An Experi mental Study on Wave-Induced Dynamic Stresses in Seabed

1 .IntroductionEvery year ,Taiwanis subjectedtotwo or three typhoonintrusions in average which always causedisasters . Most of the disasters which occur around the coastal zone are due to seabed instability andcoastal structure destruction caused bytyphoo…     

UDEC modeling of a field explosion test

A field explosion test is conducted to investigate the blast wave characteristics and propagation in jointed rock mass. A hybrid AUTODYN and UDEC scheme is used to predict the rock mass response due to the explosion. The original prediction is then modified by involving the actual test conditions and dynamic equation of state of the rock material. Correlating the prediction results with the field explosion test results shows that the hybrid AUTODYN and UDEC scheme is capable of modeling explosion problems with high reliability. It is observed that the modified prediction result agrees better with the field test result than the original prediction result, which implies that involving dynamic parameters in the modeling is very important to produce reliable prediction results.     

Cosmic microwave background polarization due to scattering in clusters

Scattering of the cosmic microwave background (CMB) in clusters of galaxies polarizes the radiation. We explore several polarization components which have their origin in the kinematic quadrupole moments induced by the motion of the scattering electrons, either directed or random. Polarization levels and patterns are determined in a cluster simulated by the hydrodynamical enzo code. We find that polarization signals can be as high as  ∼1 μK  , a level that may be detectable by upcoming CMB experiments.     

Biological influences on modern sulfates: Textures and composition of gypsum deposits from Guerrero Negro,Baja California Sur,Mexico

Gypsum (CaSO₄·2H₂O) deposits from a range of sedimentary environments at Guerrero Negro, Baja California Sur, Mexico were investigated for microscale texture and composition in order to differentiate features formed under substantial microbial influence from those for which microbial effects were relatively minor or absent. Gypsum deposits were classified according to their sedimentary environment, textures, crystal habit, brine composition and other geochemical factors. The environments studied included subaqueous sediments in anchialine pools and in solar salterns, as well as subsurface sediments of mudflats and saltpans. Gypsum that developed in the apparent absence of biofilms included crystals precipitated in the water column and subsedimentary discs that precipitated from phreatic brines. Subsedimentary gypsum developed in sabkha environments exhibited a sinuous microtexture and poikilitically enclosed detrital particles. Water column precipitates had euhedral prismatic habits and extensive penetrative twinning. Gypsum deposits influenced by biofilms included bottom nucleated crusts and gypsolites developing in anchialine pools and saltern ponds. Gypsum precipitating within benthic biofilms, and in biofilms within subaerial sediment surfaces provided compelling evidence of biological influences on crystal textures and habits. This evidence included irregular, high relief surface textures, accessory minerals (S°, Ca-carbonate, Sr/Ca-sulfate and Mg-hydroxide) and distinctive crystal habits such as equant forms and crystals having distorted prism faces.     

A 20cm 2 CCD mosaic camera for a dark matter search part II : Electronics,data acquisition and performance

Conclusion To summarize, the readout and the control system of the CCD mosaic camera are running since December 1991 at the La Silla Observatory (ESO). The overall performance of the camera has been good. About 12000 pictures (data and flat-fields) have been successfully registered up to now. We will report in the near future preliminary scientific results of the EROS experiment.     

Formation of chlorite rims and the impact of pore-lining chlorite on reservoir quality: a case study from Shiqianfeng sandstones in upper Permian of Dongpu Depression,Bohai Bay Basin,eastern China

The source material, precursor and formation processes of chlorite rims, and impact of pore-lining chlorite on reservoir quality of the Shiqianfeng sandstones, Dongpu Depression, Bohai Bay Basin, China, are studied using an integrated approach, including core observation, point-count analysis of thin-sections, scanning electron microscopy, electron microprobe analysis and cathode luminescence. The petrographic analysis shows that chlorite rims consist of grain-coating chlorite, poorly crystalline pore-lining chlorite and euhedral-crystallised pore-lining chlorite. The chemical composition shows that pore-lining chlorite is mainly Fe-rich with an average of 0.785 for Fe/(Fe+Mg) ratio. Petrographic analysis shows a large amount of volcanic dust (3.0～16.0 vol%, average of 7.93 vol%) in Shiqianfeng sandstones, which determines the formation of poorly crystalline pore-lining chlorite. Transformation of volcanic dust to smectite rims started with shallow burial depth at an early diagenetic stage, followed by in situ alteration of the smectite rims to poorly crystalline chlorite rims. Euhedral-crystallised chlorite mainly develops in sandstones with high porosity, high permeability and open flow systems. Pore-lining chlorite can inhibit quartz overgrowth but cannot effectively prevent pore-filling of authigenic quartz, carbonate and kaolinite cements, and therefore cannot prevent porosity destruction. However, the occurrence of pore-lining chlorite is a barometer of good reservoir quality and intense hydrodynamic conditions.     

Correlation of spectroscopic properties and substitutional sites of Cr3+ in aluminosilicates: II. Andalusite and sillimanite

This paper is an extension of the earlier one dealing with kyanite in which the best fitting value of the oxygen ligand distance for Cr³⁺ is adopted to study the spectroscopic properties of Cr³⁺ ions doped at the two possible Al sites in the other two polymorphs of the aluminosilicate group (Al₂O₃ · SiO₂), namely, andalusite and sillimanite. The superposition model and the crystal field analysis package recently developed for 3d ions doped at arbitrary low symmetry sites in crystals are used to predict energy levels and statevectors within the whole 3d ³ configuration. Then the values of the ground state zerofield splitting for Cr³⁺ ions at each Al sites in the two crystals are obtained. The splittings of the lower excited states ² E and ⁴ T ₂ as well as the admixture of ⁴ T ₂ into ² E have also been predicted. Comparison of our results with the available experimental data enable us to correlate the optical and EPR Spectroscopic properties with the substitutional Cr³⁺ sites. The conclusion is that in andalusite and sillimanite only the Al sites with nearly-octahedral six-fold coordination seem to be occupied by Cr³⁺ ions.     

Interaction of linear waves with an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth

The linear water wave scattering and radiation by an array of infinitely long horizontal circular cylinders in a two-layer fluid of infinite depth is investigated by use of the multipole expansion method. The diffracted and radiated potentials are expressed as a linear combination of infinite multipoles placed at the centre of each cylinder with unknown coefficients to be determined by the cylinder boundary conditions. Analytical expressions for wave forces, hydrodynamic coefficients, reflection and transmission coefficients and energies are derived. Comparisons are made between the present analytical results and those obtained by the boundary element method, and some examples are presented to illustrate the hydrodynamic behavior of multiple horizontal circular cylinders in a two-layer fluid. It is found that for two submerged circular cylinders the influence of the fluid density ratio on internal-mode wave forces is more appreciable than surface-mode wave forces, and the periodic oscillations of hydrodynamic results occur with the increase of the distance between two cylinders; for four submerged circular cylinders the influence of adding two cylinders on the wave forces of the former cylinders is small in low and high wave frequencies, but the influence is appreciable in intermediate wave frequencies.     

New P–T constraints on the Tamayen glaucophane‐bearing rocks,eastern Taiwan: Perple_X modelling results and geodynamic implications

New pseudosection modelling was applied to better constrain the P–T conditions and evolution of glaucophane‐bearing rocks in the Tamayen block of the Yuli belt, recognized as the world's youngest known blueschist complex. Based on the predominant clinoamphibole, textural relationships, and mineral compositions, these glaucophane‐bearing high‐P rocks can be divided into four types. We focused on the three containing garnet. The chief phase assemblages are (in decreasing mode): amphibole + quartz + epidote + garnet + chlorite + rutile/titanite (Type‐I), phengite + amphibole + quartz + garnet + chlorite + epidote + titanite + biotite + magnetite (Type‐II), and amphibole + quartz + albite + epidote + garnet + rutile + hematite + titanite (Type‐III). Amphibole exhibits compositional zoning from core to rim as follows: glaucophane → pargasitic amphibole → actinolite (Type‐I), barroisite → Mg‐katophorite/taramite → Fe‐glaucophane (Type‐II), glaucophane → winchite (Type‐III). Using petrographic data, mineral compositions and Perple_X modelling (pseudosections and superimposed isopleths), peak P–T conditions were determined as 13 ± 1 kbar and 550 ± 40 °C for Type‐I, 10.5 ± 0.5 kbar and 560 ± 30 °C for Type‐II (thermal peak) and 11 ± 1 kbar and 530 ± 30 °C for Type‐III. The calculations yield higher pressures and temperatures than previously thought; the difference is ~1–6 kbar and 50–200 °C. The three rock types record similar P–T retrograde paths with clockwise trajectories; all rocks followed trajectories with substantial pressure decrease under near‐isothermal conditions (Type‐I and Type‐III), with the probable exception of Type‐II where decompression followed colder geotherms. The P–T paths suggest a tectonic environment in which the rocks were exhumed from maximum depths of ~45 km within a subduction channel along a relative cold geothermal gradient of ~11–14 °C km^?1.     

Diagenesis impact on a deeply buried sandstone reservoir (Es1 Member) of the Shahejie Formation,Nanpu Sag,Bohai Bay Basin,East China

Diagenesis has a significant impact on reservoir quality in deeply buried formations. Sandstone units of the Shahejie Formation (Es₁ Member) of Nanpu Sag, Bohai Bay Basin, East China is a typical deeply buried sandstone with large hydrocarbon accumulations. The methodology includes core observations and thin section studies, using fluorescence, scanning electron microscope (SEM), cathodoluminescence (CL), fluid inclusion and isotope and electron probing analysis as well as the numerical determination of reservoir characteristics. The sandstones consist of medium to coarse-grained, slight to moderate sorted lithic arkose and feldspathic litharenite. Porosity and permeability values range from 0.5 to 30% and 0.006 to 7000 mD, respectively. The diagenetic history reveals mixed episodes of diagenesis and deep burial followed by uplift. The main diagenetic events include compaction, cementation alteration, dissolution of unstable minerals and grain fracturing. Compaction resulted in densification and significantly reduced the primary porosity. Quartz, calcite and clay are the dominant pore-occluding cement and occur as euhedral to subhedral crystals. Alteration and dissolution of volcanic lithic fragments and pressure solution of feldspar grains were the key sources of quartz cement whereas carbonate cement is derived from an external source. Clay minerals resulted from the alteration of feldspar and volcanic lithic fragments. Porosity and permeability data predict a good inverse relationship with cementation whereas leaching of metastable grains, dissolution of cement and in some places formation of pore-lining chlorite enhanced the reservoir quality. The best reservoir is thicker sandstone bodies that are medium to coarse-grained, well-sorted sandstone with low primary ductile grains with a minor amount of calcite cement. The present study shows several diagenetic stages in the Es₁ Member, but the overall reservoir quality is preserved.