Stress tests of ODP Site 131-808 sediments

Sediments undergoing accretion in trench-forearc systems are subjected to conditions of large lateral thrusting. This stress regime controls the mechanism of faulting as well as the yield and strength properties of the sediment. Understanding them is therefore crucial for the construction of quantitative models of sediment dynamics in convergent margin settings. For this purpose triaxial and oedometer tests were performed on six whole-round core samples recovered from Site 808 from depths between 173 and 705 mbsf. Samples from five depth intervals were subjected to a triaxial test program that was primarily designed to define yield and strength behavior. Test specimens were cut parallel and normal to the core axis. Additional five oedometer tests with similarly prepared specimens were performed on samples from four depth intervals to evaluate the directional state and degree of sediment compaction. Test results show that the degree of sediment compaction is higher than expected from overburden. This overcompaction increases with depth. A well-developed mechanical anisotropy is evident in all samples tested, regardless of their depth and lithology. Values of yield limit, stiffness, and shear strength are up to 40% higher in the horizontal direction compared to the vertical direction. In addition the test data demonstrate that the axis of the volumetric yield loci have rotated into extensional stress field. This verifies that the mechanical state of sediment in the accretionary wedge is controlled by in-situ stress conditions of extensional nature. The coefficients of lateral stress inferred suggest that the extensional stress regime becomes increasingly effective with depth.

Mineralogical-sedimentological and chemical investigation of sediments from Cross Bank off Florida

The sediments of a core of.1.55 m length taken on the windward side of the Cross Bank, Florida Bay, are clearly subdivided into two portions, as shown by grain size analysis: silt-sized particles predominate in the relatively homogeneous lower two thirds of the core. This is succeeded abruptly by a thin layer of sand, containing fragments of Halimeda. They indicate a catastrophic event in the Florida Bay region, because Halimeda does not grow within Florida Bay. Above this layer, the amount of sand decreases at first and then continuously increases right to the present sediment-water-interface. The median and skewness increase simultaneously with the increase in the sand and granule portion. We assume that the changing grain size distribution was determined chiefly by the density of the marine flora: during the deposition of the lower two thirds of the core a dense grass cover acted as a sediment catcher for the fine-grained detritus washed out of the shallow basins of the Florida Bay, and simultaneously prohibited renewed reworking. Similar processes go on today on the surface of most mud banks of Florida Bay. The catastrophic event indicated by the sand layer probably changed the morphology of the bank to such an extent that the sampling point was shifted more to the windward side of the bank. This side is characterized by less dense plant growth. Therefore, less detritus could be caught and the material deposited could be reworked. The pronounced increase in skewness in the upper third of the core certainly indicates a strong washing out of the smaller-sized particles. The sediments are predominantly made up of carbonates, averagely 88.14 percent. The average CaCO3-content is 83.87 percent and the average MgCO3-content amounts to 4.27 percent. The chief carbonate mineral is aragonite making up 60.1 percent of the carbonate portion in the average, followed by high-magnesian calcite (33.8 percent) and calcite (6.1 percent). With increasing grain size the aragonite clearly increases at the cost of high-magnesian calcite in the upper third of the core. Chemically, this is shown by an increase of the CaCO3 : MgCO3-ratio. This increase is mainly caused by the more common occurrence of aragonitic fragments of mollusks in the coarse grain fractions. The bulk of the carbonates is made up of mollusks, foraminifera, ostracods, and - to a much lesser extent - of corals, worm-tubes, coccolithophorids, and calcareous algae, as shown by microscopic investigations. The total amount of the carbonate in the sediments is biogenic detritus with the possible exception of a very small amount of aragonite needles in the clay and fine silt fraction. The individual carbonate components of the gravel and sand fraction can be relatively easy identified as members of a particular animal or plant group. This becomes very difficult in the silt and clay fraction. Brownish aggregates are very common in the coarse and medium silt fraction. It was not always possible to clarify their origin (biogenic detritus, faecal pellets or carbonate particles cemented by carbonates or organic slime, etc.). Organic matter (plant fragments, rootlets), quartz, opal (siliceous sponge needles), and feldspar also occur in the sediments, besides carbonates. The lowermost part of the core has an age of 1365 +/- 90 years, as shown by 14C analysis.

Sedimentology on profile Co1202 from Lake Ohrid

Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between ca. 97.6 and 81.7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake. Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods, high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean.

Mineralogy and petrology of Black Sea Basin sediments

The origin and modes of transportation and deposition of inorganic sedimentary material of the Black Sea were studied in approximately 60 piston, gravity, and Kasten cores. The investigation showed that the sediment derived from the north and northwest (especially from the Danube) has a low calcite-dolomite ratio and a high quartz-feldspar ratio. Rock fragments are generally not abundant; garnet is the principal heavy mineral and illite is the predominant clay mineral. This sedimentary material differs markedly from that carried by Anatolian rivers, which is characterized by a high calcite-dolomite ratio and a low quartz-feldspar ratio. Rock fragments are abundant; pyroxene is the principal heavy mineral and montmorillonite is the predominant clay mineral. In generel, the clay fraction is large in all sediments (27.6-86.9 percent), and the lateral distributian indicates an increase in clay consent from the coasts toward two centers in the western and eastern Black Sea basin. Illite is the most common clay mineral in the Black Sea sediments. The lateral changes in composition of the clay mineral can easily be traced to the petrologic character of northern (rich in illite) and southern (rich in montmorillonite) source areas. In almost all cores, a rhythmic change of the montmorillonite-illite ratio with depth was observed. These changes may be related to the changing influence of the two provinces during the Holocene and late Pleistocene. Higher montmorillonite content seems to indicate climctic changes, probably stages of glaciation end permafrost in the northern area, at which time the illite supply was diminished to a large extent. The composition of the sand fraction is relatad to the different petrologic and morphologic characteristics of two major source provimces: (1) a northern province (rich in quartz, feldspars, and garnet) characterized by a low elevation, comprising the Danube basin area and the rivers draining the Russian platform; and (2) a southern province (rich in pyroxene and volcanic and metamorphic rocks) in the mountainous region of Anatolia and the Caucasus, characterized by small but extremely erosive rivers. The textural properties (graded bedding) of the deep-sea send layers clearly suggest deposition from turbidity currents. The carbonate content of the contemporary sediments ranges from 5 to 65 percent. It increases from the coast to a maximum in two centers in the western and eastern basin. This pattern reflects the distribution of the <2-µm fraction. The contemporary mud sedimentation is governed by two important factors: (1) the deposition of terrigenous allochthonous material of low carbonate content originating from the surrounding hinterland (northern and southern source areas), and (2) the autochthonous production of large quantities of biogenic calcite by coccolithophores during the last period of about 3,000-4,000 years.

SYNTHESIS AND X-RAY CRYSTAL-STRUCTURE OF A MONOPENTAMETHYLCYCLOPENTADIENYL DERIVATIVE OF GADOLINIUM (NA(MU-2-THF)[(C5ME5)GD(THF)]2(MU-2-CL)3(MU-3-CL)2)2.6THF

The reaction of GdCl3 with 1 equiv of NaC5Me5 generates a neutral complex C5Me5GdCl2(THF)3 and a novel complex {Na(mu-2-THF)[(C5Me5)Gd(THF)]2(mu-2-Cl)3(mu-3-Cl)2}2.6THF whixh recrystallizes from THF in triclinic, the space group P1BAR with unit cell dimentions of a 12.183(4), b 13.638(6), c 17.883(7) angstrom, alpha-110.38(3), beta-94.04(3), gamma-99.44(3)-degrees, V 2721.20 angstrom-3 and D(calc) 1.43 g cm-3 for Z = 1. Least-squares refinement of 2170 observed reflections led to a final R value of 0.047. The title complex consists of two Na(mu-2-THF)[(C5Me5)Gd(THF)]2(mu-3-Cl)3(mu-3-Cl)2 units bridged together via two mu-2-THF to Na coordination. Each Gd ion is surrounded by one C5Me5 ligand, two mu-3-Cl, two mu-2-Cl and one THF in a distorted octahedral arrangement with average Gd-C(ring) 2.686(33), Gd-mu-2-Cl 2.724(7), Gd-mu-3-Cl 2.832(8) and Gd-O 2.407(11) angstrom. The sodium ion coordinates to two bridging THF, two mu-2-Cl and two mu-3-Cl to form a distorted octahedron with average Na-mu-2-O, Na-mu-2-Cl and Na-mu-3-Cl of 2.411(21), 2.807(15) and 2.845(12) angstrom, respectively.

The structural characterization and hydroformylation activity of the tri-rhodium complex [Rh-3(mu(2)-dppm)(2)(mu(2)-CO)(3)(K-1-CO)(3)]BF4

Rh-2(cod)(2)(mu(2)-dppm)(mu(2)-Cl)]BF4 (1) rearranges under carbon monoxide to give [Rh-3(mu(2)-dppm)(2)-(mu(2)-CO)(3)(K-1-CO)(3)]BF4 (2). Complex 2 has been structurally characterized by single crystal X-ray crystallography. The hydroformylation activities of 1 and 2 were compared for substrates styrene and 1-hexene and the activity of 2 found to be unexpectedly high.

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum wells with higher indium content grown by molecular-beam expitaxy

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum well (QW) samples with higher (42.5%) indium content were successfully grown by molecular-beam epitaxy. The cross-sectional transmission electron microscopy measurements reveal that there are no structural defects in such high indium content QWs. The room-temperature photoluminescence peak intensity of the GaIn0.425NAs/GaAs (6 nm/20 nm) 3QW is higher than, and the full width at half maximum is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality caused by strain compensation effect of introducing N to the high indium content InGaAs epilayer. (C) 2005 American Institute of Physics.

Design and analysis of 1.3 mu m GaAs-based quantum dot vertical-cavity surface-emitting lasers

A theoretical study on 1.3 mu m GaAs-based quantum dot vertical-cavity surface-emitting lasers (VCSELs) was made. Investigation of the influence of VCSELs on the optical confinement factors and the optical loss and the calculation of the material gain of the assembled InGaAs/GaAs quantum dots. Analysis of the threshold characteristic was made and the multi-wavelength cavity and multilayer quantum-dot stack structure is found to be more suitable for quantum dot VCSELs.

Optimization of GaInNAs(Sb)/GaAs quantum wells at 1.3-1.55 mu m grown by molecular beam epitaxy

The InGaNAs(Sb)/(GaNAs)/GaAs quantum wells (QWs) emitting at 1.3-1.55 mu m have been grown by molecular beam epitaxy (MBE). The parameters of the radio frequency (RF) such as RF power and flow rate are optimized to reduce the damages from the ions or energetic species. The growth temperature is carefully controlled to prevent the phase segregation and strain relaxation. The effects of Sb on the wavelength and quality are investigated. The GaNAs barrier is used to extend the wavelength and reduce the strain. A 1.5865 mu m InGaNAs(Sb)/GaNAs SQW edge emitting laser lasing at room temperature at continuous wave operation mode is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.

Application of rapid thermal annealing on 1.3-1.55 mu m GaInNAs(Sb) lasers grown by molecular beam epitaxy

Rapid thermal annealing (RTA) has been demonstrated as an effective way to improve the crystal quality of GaInNAs(Sb) quantum wells (QWs). However, few investigations have been made into its application in laser growth and fabrication. We have fabricated 1.3 mu m GaInNAs lasers, both as -grown and with post-growth RTA. Enhanced photoluminescence (PL) intensity and decreased threshold current are obtained with RTA, but the characteristic temperature T-o and slope efficiency deteriorate. Furthermore, T-o has an abnormal dependence on the cavity length. We attribute these problems to the deterioration of the wafer's surface. RTA with deposition Of SiO2 was performed to avoid this deterioration, T-o was improved over the samples that underwent RTA without SiO2. Post-growth and in situ annealing were also investigated in a 1.55 mu m GaInNAsSb system. Finally, continuous operation at room temperature of a GaAs-based dilute nitride laser with a wavelength over 1.55 mu m was realized by introducing an in situ annealing process. (c) 2007 Elsevier B.V. All rights reserved.

Angular dependent characteristics of a 1.3-mu m GaInNAs/GaAs quantum-well resonant cavity enhanced photodetect

Characteristics of a 1.3-mum GaInNAs RCE PD with respect to the incident light angle were analyzed both in theoretical simulation and experiments. The results show the influence can be neglected when the light incidence angle is less than 3degrees. This is a requirement for the PD to be applied in WDM networks. (C) 2002 Wiley Periodicals, Inc.

High-speed and high-power 1.3 mu m InGaAsP/InP selective proton-bombarded buried crescent lasers with optical field attenuation regions

High-speed and high-power InGaAsP/lnP selective proton-bombarded buried crescent (SPB-BC) lasers with optical field attenuation regions were reported. The defect of proton bombardment can not affect the lifetime of the SPB-BC laser because the optical field attenuation region obstructs the growth and propagation of defects. A CW light output over 115 mW was achieved at room temperature using a 500 mu m long cavity SPB-BC laser. The 3 dB bandwidth was 8.5 GHz, and the lifetime was about 8.5 x 10(5) h. The capacitance of four kinds of current blocking structures was first measured in our experiment, and the results shown that the capacitance of proton-bombarded pnpn structure was not only less than that of pnpn current blocking structure, but also less than that of semi-insulating Fe-InP structure.

1.3 mu m GaInNAs/GaAs quantum well lasers and photodetectors

The growth of GalnNAs/GaAs quantum well (QW) has been investigated by solid-source molecular beam epitaxy (MBE). N was introduced by a dc-active plasma source. Highest N concentration of 2.6% in GaInNAs/GaAs QW was obtained, corresponding to the photoluminescence peak wavelength of 1.57 mum at 10K. The nitrogen incorporation behavior in MBE growth and the quality improvement of the QW have been studied in detail. 1.3 mum GaInNAs/GaAs SQW laser and MQW resonant-cavity enhanced photodetector have been achieved.

Dinuclear half-sandwich complexes containing bridging 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolato ligands. Molecular structures of Cp2Fe2(CO)(3)[mu-Se2C2(B10H10)], Cp2Ru2[mu-S2C2(B10H10)](2), and CP*Ru-2(2)(mu-Se)[mu-Se2C2(B10H10)].

Three prototypes of dinuclear complexes were obtained from the reactions of dilithium 1,2-dicarbacloso-dodecaborane-1,2-dichalcogenolates, (B10H10)C-2-(ELi)(2) (E = S, Se), with CpFe(CO)(2)Cl (1), CpRu(PPh3)(2)Cl (2), or [Cp*RuCl2](2) (3), respectively, and their structures have been determined by X-ray crystallography.

New half-sandwich heterobimetallic CpMPt (M=Rh, Ir) dithiolato bridged complexes

Cationic heterobimetallic complexes 5–7 [(PPh3)2Pt(μ-edt)MClCp′)]BF4 (edt=−S(CH2)2S−; 5: M=Rh and Cp′=η5-C5H5; 6: M=Rh and Cp′=η5-C5Me5 and 7: M=Ir and Cp′=η5-C5Me5) were prepared by reaction of [Pt(edt)(PPh3)2] with [Cp′ClM(μ-Cl)2MClCp′] in THF in the presence of two equivalents of AgBF4. The crystalline structure of 5 was determined by X-ray diffraction methods. Cationic heterobimetallic complexes [(PPh3)2Pt(μ-S(CH2)2S)MClCp′)]BF4 (M=Rh, Ir) were prepared. The crystalline structure of [(PPh3)2Pt(μ-edt)RhClCp)]BF4 was determined by X-ray diffraction methods.