The Structure and Evolution of a Two-Dimensional H2/O2/Ar Cellular Detonation

This paper reports on two-dimensional numerical simulation of cellular detonation wave in a / / mixture with low initial pressure using a detailed chemical reaction model and high order WENO scheme. Before the final equilibrium structure is produced, a fairly regular but still non-equilibrium mode is observed during the early stage of structure formation process. The numerically tracked detonation cells show that the cell size always adapts to the channel height such that the cell ratio is fairly independent of the grid sizes and initial and boundary conditions. During the structural evolution in a detonation cell, even as the simulated detonation wave characteristics suggest the presence of an ordinary detonation, the evolving instantaneous detonation state indicates a mainly underdriven state. As a considerable region of the gas mixture in a cell is observed to be ignited by the incident wave and transverse wave, it is further suggested that these two said waves play an essential role in the detonation propagation.

Step Structure in Cold-Rolled Deformed Nanocrystalline Nickel

The microstructure characteristic of the cold-rolled deformed nanocrystalline nickel metal is studied by transmission electron microscopy. The results show that there are step structures nearby the grain boundary (GB), and the contrast of stress field in front of the step corresponds to the step in the shape. It is indicated that the interaction between twins and dislocations is not a necessary condition to realizing the deformation. In the later stage of the deformation when the grain size becomes about 100nm, the deformation can depend upon the moving of the boundary of the stack faults (SFs) which result from the partial dislocations emitted from GBs. However, when the size of SFs grows up, the local internal stress which is in front of the step gradually becomes higher. When this stress reaches a critical value which stops the gliding of the partial dislocations, the SFs will stop to grow up and leave a step structure behind.

The nuclear matrix of Euglena gracilis (Euglenophyta): A stage of nuclear matrix evolution?

Euglena gracilis cell was extracted sequentially with CSK-Triton buffer, RSB-Magik solution and DNase-As solution. DGD embedment-free electron microscopy showed that in the extracted nucleus there was a residual non-chromatin fibrous network. That it could not be removed by hot trichloroacetic acid further supported the idea that it was a non-histone, non-chromatin fibrous protein network, and should be the internal network of the nuclear matrix. After the sequential extraction, the nuclear membrane was removed, leaving behind a layer of lamina; the chromatin was digested and eluted from the dense chromosomes and residual chromosomal structures that should be chromosomal scaffold were revealed. Western blot analysis with antiserum against rat lamins showed that nuclear lamina of the cell possessed two positive polypeptides, a major one and a minor one, which had molecular masses similar to lamin B and lamin A, respectively. Comparing these data with those of the most primitive eukaryote Archezoa and of higher eukaryotes, it was suggested that the lower unicellular eukaryote E. gracillis already had the nuclear matrix structure, and its nuclear matrix (especially the lamina) might represent a stage of evolutionary history of the nuclear matrix. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

Primary succession of algal community structure in desert soil

The microbiotic crust study is among new focuses in investigating on the desertification control. Based on determination of algal crusts with different successive ages (4-, 8-, 17-, 34-, 42-year-old) and unconsolidated sand in the desert area, species composition and clustering analyses were carried out in this study. Results on successional orientation revealed that (1) the abundance of Cyanophyta, specially of Scytonema javanicum gradually decreased; (2) the abundance of Chlorophyta, Bacillariophyta and a species of Cyanophyta, Phormidium tenue increased; (3) the biodiversity increased gradually with the community succession; and (4) biomass of microalgae increased at the early stage, but decreased at the later stage due to the abundance of lichens and mosses. But, the speed of natural succession was so slow that the community-building species was still the first dominant species after 42 years, except that its dominant degree decreased just slightly. However, successive speed and trend were affected by water, vegetation coverage, terrain, time and soil physico-chemical properties as well, especially Mn content in the soil appeared to have a threshold effect.

The compact microcrystalline Si thin film with structure uniformity in the growth direction by hydrogen dilution profile

The hydrogen dilution profiling (HDP) technique has been developed to improve the quality and the crystalline uniformity in the growth direction of mu c-Si:H thin films prepared by hot-wire chemical-vapor deposition. The high H dilution in the initial growth stage reduces the amorphous transition layer from 30-50 to less than 10 nm. The uniformity of crystalline content X-c in the growth direction was much improved by the proper design of hydrogen dilution profiling which effectively controls the nonuniform transition region of Xc from 300 to less than 30 nm. Furthermore, the HDP approach restrains the formation of microvoids in mu c-Si: H thin films with a high Xc and enhances the compactness of the film. As a result the stability of mu c-Si: H thin films by HDP against the oxygen diffusion, as well as the electrical property, is much improved. (c) 2005 American Institute of Physics.

Influence of transverse interdot coupling on transport properties of an Aharonov-Bohm structure composed by two dots and two reservoirs

We derive the modified rate equations for an Aharonov-Bohm (AB) ring with two transversely coupled quantum dots (QD's) embedded in two arms in the presence of a magnetic field. We find that the interdot coupling between the two QD's can cause a temporal oscillation in electron occupation at the initial stage of the quantum dynamics, while the source-drain current decays monotonically to a stationary value. On the other hand, the interdot coupling equivalently divides the AB ring into two coupled subrings. That also destroys the normal AB oscillations with a period of 2pi, and generates new and complex periodic oscillations with their periods varying in a linear manner as the ratio between two magnetic fluxes (each penetrates one AB subring) increases. Furthermore, the interference between two subrings is also evident from the observation of the perturbed fundamental AB oscillation.

Relating the molecular structure and crystallization behavior of polypropylene

The crystallization behavior of two polypropylene (PP) resins as used for biaxially oriented polypropylene (BOPP) and general injection mold applications, respectively, has been intensively investigated and compared by means of polarized light optical micrography (POM), differential scanning calorimetry (DSC), conventional transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). It is found that both molecular weight distribution and isotacticity of polypropylene strongly affect its crystallization characteristics, e.g., the number of crystal nuclei at the initial stage, crystallization dynamics, the morphology, size and perfection of crystals in the final product, and so on. The results indicate an appropriate molecular structure is vital in producing high-quality BOPP film.

Structure identification of a prenylflavonol glycoside from Epimedium koreanum by electrospray ionization tandem mass spectrometry

A novel prenylflavonol glycoside, named acetylicariin, has been isolated from the aerial parts of Epimedium koreanum Nakai. The structure has been identified by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn) and other chemical evidence, which has been elucidated as 8-prenylkaempferol-4'-methoxyl-3-O-alpha-L-rhamnopyranosyl-7-O-beta-D-(2''-O-acetyl)glucopyranoside.

Structure identification of five unknown dilipo-alkaloids extracted from processed tuber of Aconitum carmiechaeli by electrospray ionization tandem mass spectrometry

The alkaloids in processed aconite tuber of Aconitum Carmiechaeli were studied, and five novel alkaloids in extract from processed aconite tuber were found. The first step involved the use of electrospray ionization mass spectrometry (ESI-MS), and then multi-stage tandem mass spectrometry (MSn) was used to provide structural information. Based on their MSn spectra, the structures of the five novel compounds were elucidated to be C3,C8-difatty acid esters of mesaconitine, aconitine and 10-hydroxyaconitine.

In situ study of nanostructure and morphological development during the crystal-mesophase transition of poly(di-n-hexylsilane) and poly(di-n-butylsilane) by X-ray and hot-stage AFM

Nanostructure and morphology and their development of poly(di-n-hexylsilane) (PDHS) and poly(di-n-butylsilane) (PDBS) during the crystal-mesophase transition are investigated using small angle X-ray scattering (SAXS), wide angle X-ray diffraction and hot-stage atomic force microscopy. At room temperature, PDHS consists of stacks of lamellae separated by mesophase layers, which can be well accounted using an ideal two-phase model. During the crystal-mesophase transition, obvious morphological changes are observed due to the marked changes in main chain conformation and intermolecular distances between crystalline phase and mesophase. In contrast to PDHS, the lamellae in PDBS barely show anisotropy in dimensions at room temperature. The nonperiodic structure and rather small electronic density fluctuation in PDBS lead to the much weak SAXS. The nonperiodic structure is preserved during the crystal-mesophase transition because of the similarity of main chain conformation and intermolecular distances between crystalline phase and mesophase.

Synthesis, structure and ring-opening polymerization of phenolphthalein macrocyclic polyarylates

Phenolphthalein based polyarylate macrocyclic oligomers were selectively synthesized by an interfacial polycondensation reaction of o-phthaloyl dichloride with phenolphthalein. The high selectivity benefits from the role of phenolphthalein as a color indicator, an efficient phase transfer catalyst, acid a preferred conformation of the starting materials as indicated by analyzing a single-crystal X-ray structure of an analogous macrocycle. The melt ROP of phenolphthalein polyarylate cyclic dimer was studied using nucleophilic initiators, The molecular weight of the resulting polymers builds up very rapidly at the very early stage of polymerization but decreases with time. During the ROP of cyclic dimer, analogous macrocycles with higher degree of polymerization (n greater than or equal to 3) and linear oligomers were produced by backbiting reaction especially at later stage of polymerization. Conversion of cyclic dimer is very fast at the earlier stage of polymerization and then increases slowly with time as analyzed by gel permeation chromatography. However, the total amount of cyclic oligomers in the ROP system increases with time at the later stage of polymerization because of the formation of larger macrocycles. The resulting polymers are amorphous. Glass transition temperatures (T(g)s) of these polymers are influenced by the polymerization time, type of initiator, and initiator concentration.

Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus

Electrospray ionization (ESI) combined with multiple-stage tandem mass spectrometry (MSn) was used to directly analyze the glycolipid mixture from bacteria Bacillus pumilus without preliminary separation. Full scan ESI-MS revealed the composition of picomole quantities of glycerolglycolipid species containing C-14-C-19 fatty acids, some of which were monounsaturated, Two main components were identified from their molecular masses and fragmentation pathways. The fragmentation pathway of the known compound compared with the investigated compound verified the proposed structure as 1(3)-acyl-2-pentadecanoyl-3(1)-O-[beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl]-sn-glycerols. A comparison of the multiple tandem mass spectra of the different alkali-metal cation adducts indicates that the intensity of fragments and the dissociation pathways are dependent on the alkali-metal type, The basic structures of glycerolglycolipids were reflected clearly from the fragmentation patterns of the sodium cations, The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct ions. ESI-MSn spectra of [M + K](+) ions did not provide as much fragmentation as [M + Na](+) and [M + Li](+) adducts, but their spectra allow the position of glycerol acylation to be determined. On the basis of MS2 spectra of[M + K](+) ions, it was established that all components have a C-15:0 fatty acid at the sn-2 position of the glycerol backbone and C-14-C-19 acids at the sn-1 position of the glycerol backbone. Copyright (C) 1999 John Wiley & Sons, Ltd.

Multi-stage mass spectrometric studies of triterpenoid saponins in crude extracts from Acanthopanax senticosus harms

Three triterpenoid saponins in crude extracts from Acanthopanax senticosus Harms have been investigated by use of multi-stage mass spectrometry (MSn) combined with electrospray ionization (ESI), MSn spectra were applied to direct structure elucidation of these saponins in crude plant extracts, in positive and negative ion mode. The characteristic fragmentations of triterpenoid saponins are discussed. The method provides a means of rapid initial screening of crude plant extracts. Copyright (C) 1999 John Wiley & Sons, Ltd.

Molecular structure and expression patterns of flounder (Paralichthys olivaceus) Myf-5, a myogenic regulatory factor

Myf-5, a member of the myogenic regulatory factors (MRF), has been shown to be expressed in muscle precursors in early stage zebrafish embryos. The MRFs, including MyoD, Myf-5, Myogenin and MR-F4, belong to the basic Helix-Loop-Helix transcription factors that contain a conserved basic Helix-Loop-Helix (bHLH) domain. To better understand the role of Myf-5 in the development of fish muscles, we have isolated the Myf-5 genomic sequence and cDNA from Flounder (Paralichthys olivaceus), and analyzed its structures and patterns of expression. Promoter analysis identified several putative transcription factor binding sites such as an E-box, NF-Y sites that might confer muscle-specific expression. Myf-5 transcripts were first detected in the paraxial mesoderm that gives rise to slow muscles. During somitogenesis, Myf-5 expression was found in developing somites. Myf-5 expression decreased gradually in somites in the anterior region, but remained strong in the newly formed somites. In the hatching stage, the expression was also detected in other muscle cells such as head muscle and fin muscle. In the growing fish, RT-PCR results showed that Myf-5 was expressed in the skeletal muscle and intestine. (c) 2006 Elsevier Inc. All rights reserved.

The variation of upper ocean structure and paleoproductivity in the Kuroshio source region during the last 200 kyr

A core from the source region of the Kuroshio warm current (east of the Luzon Island) was analyzed using several proxies in order to study the variability of the Western Pacific Warm Pool (WPWP) during the last two glacial-interglacial cycles. Primary productivity (PP) variations were deduced from variations in the coccolith flora. Primary productivity was higher during glacial periods (the end of Marine Isotope Stage [MIS] 3, some periods in MIS 2 and 6), and decreased during interglacial periods (MIS 7, MIS Se and probably MIS 5c-5d), with the lowest PP in MIS 5e. variations in the delta C-13 difference in benthic and bulk carbonate, thus in the vertical gradient of delta C-13 in dissolved inorganic carbon (Delta delta C-13(c). (wuellerstorfi-N. dutertrei) and Delta delta C-13(c.) (wuellerstorfi-coccolith)) Coincided With the PP Changes, showing that export productivity was low during interglacial periods (MIS 7, MIS 5e and Holocene) and high during glacial periods (MIS 6, probably MIS 5c-5d, late MIS 4 and late MIS 3). Comparison of foraminiferal carbonate dissolution indicators and PP changes reveals that nannofossil assemblage in core Ph05-5 is not sensitive to carbonate dissolution intensity. The depth of the thermocline (DOT) was estimated from planktonic forminiferal assemblages, and was relatively greater during interglacial periods (MIS 7, MIS 5e, probably MIS 5c and Holocene) than during glacials (middle MIS 6, probably MIS 5b and 5d, some periods in MIS 4, MIS 3 and MIS 2). Good coherence between the paleoproductivity records and the DOT suggests that the DOT changes could be the primary control factor in changes of paleoproductivity, and the glacial high productivity in the Kuroshio source region could be associated with a global increase of nutrient concentration in the intermediate waters that upwelled into the photic zone. The low CO2 values derived for intervals of high productivity and a relatively shallow DOT suggest that the changes in biological productivity and DOT in the equatorial Pacific could have modified atmospheric CO2 concentrations. High Sea Surface Temperatures (SSTs) during the warm MIS 5e in combination with intensified monsoonal rain fall could have resulted in a more intense stratification of the upper waters, resulting in low nutrient supply to the surface waters and a resulting decrease in productivity. (C) 2010 Elsevier B.V. All rights reserved.