Fluorescence characteristics of thermo-altered exinites (sporinites)

Fluorescence spectra of heat-treated exinites (sporinites) vary systematically with increasing temperatures of treatment. The wavelength of the fluorescence maximum, λ_max, shifts toward the longer wavelength as a result of thermal alteration. The maxima shift from 560 nm in untreated lignite to 640 nm in lignite after heating to 350 °C. Numerical values, such as fluorescence maximum, λ_max, and spectral quotient, $\text{Q}{}_{\mathrm{S}}\text{=}\text{I}{}_{650}{}_{\mathrm{I}}\text{500}$, can be used as rank parameters of coals. The technique can also be used as a tool to monitor thermal reactions of coals at relatively moderate temperatures. The method can distinguish certain resinites from exinites.     

Geochemical implications of trace elements and sulfur in the saturate, aromatic and resin fractions of crude oil from the Mara and Mara Oeste fields, Venezuela

Ten trace elements (Cr, Zn, Fe, Mn, Cu, Co, Ni, Mo, V and Sr) and sulfur were determined in the saturate, aromatic and resin fractions of 15 crude oils from Mara (DM) and Mara Oeste (DMO) fields of the Maracaibo Basin, Venezuela. The oils studied are classified as unaltered or altered by biodegradation. In the altered oil, the depletion of n-alkanes, the absence of isoprenoids and the presence of steranes and hopanes unaltered by biodegradation are indicative of moderate biodegradation. The elements Zn, Fe, Mn, Cu, Ni, and Sr were detected in the saturated hydrocarbon fraction; Cr and V were detected in the aromatic fraction in addition to the above elements; whereas the elements detected for the resin fraction were Cr, Zn, Fe, Cu, Ni, Mo, V, and Sr. Co was not detected in any fractions of the oils analyzed. Sulfur was found in all fractions of the oils studied. It was proposed that Fe, Zn, Sr, and Mn could have entered the oil during migration or Fe, Zn and Mn as pollutants during oil extraction. Cr and Cu may be of biological origin and Mo could be incorporated into the reservoir through bacteria. Only S, V, and Ni in the resin fractions can be used as indicators of the origin and correlation of Mara and Mara Oeste oils. Based on the results obtained in this work, it can be established that the V/(V+Ni) ratio in the resin fraction can be used as a correlation parameter, for these oils.     

Host Sex Discrimination by an Egg Parasitoid on Brassica Leaves

Egg parasitoids are able to find their hosts by exploiting their chemical footprints as host location cues. In nature, the apolar epicuticular wax layer of plants that consists of several classes of hydrocarbons serves as the substrate that retains these contact kairomones. However, experiments on chemical footprints generally have used filter paper as substrate to study insect behavior. Here, we explored the ability of Trissolcus basalis (Scelionidae) females to discriminate between footprint cues left by male and female Nezara viridula (Pentatomidae) on leaves of their host plant Brassica oleracea (broccoli). Furthermore, we analyzed the chemical composition of the outermost wax layer of broccoli leaves to evaluate the degree of overlap in insect and plant cuticular hydrocarbons that could lead to masking effects in the detection of footprint cues. Our results showed that B. oleracea epicuticular wax retains the chemical footprints of adult bugs and allows T. basalis females to differentiate hosts of different sex. Traces of female bugs elicited more extensive searching behavior in egg parasitoids than traces of males. The application of n-nonadecane, a compound specific to male N. viridula, on the tarsi of female bugs prevented parasitoid females from distinguishing between host male and host female footprints. Analyses of B. oleracea leaves revealed that epicuticular waxes were mainly composed of linear alkanes, ketones, and secondary alcohols. Alkanes were dominated by n-nonacosane (nC29) and n-hentriacontane (nC31), while male-specific n-nonadecane (nC19) was absent. The ecological significance of these results for parasitoid host location behavior is discussed.     

Synthesis of layered MCM-22(P) in the presence of hexamethonium cations and its transformation into EUO- and MWW-type zeolites

Layered MCM-22(P) was synthesized in the presence of hexamethonium (HM) cations. Compared to zeolite EU-1 (EUO-type structure), which crystallizes in similar conditions, its formation is favored at high HM concentrations (HM/SiO₂ ≥ 0.3) and in the absence of Na₂O. HM-containing MCM-22(P) was used as starting material for zeolite formation. Upon hydrothermal treatment, HM-MCM-22(P) transforms into zeolite EU-1 and upon calcination into a MWW-type zeolite. Transformation mechanisms were studied by standard characterization techniques such as XRD, SEM and TEM. Catalytic properties of the MWW-type zeolite obtained from this precursor were evaluated in a m-xylene isomerization reaction. Compared to zeolite MCM-22 prepared with hexamethyleneimine, a higher catalytic activity and an increased isomerization selectivity were observed and discussed.     

Thermal and mechanical properties of polypropylene/wood‐flour composites

In this research, polypropylene/wood‐flour composites (WPCs) were blended with different contents of wood and/or maleated polypropylene (MAPP) and clay. We found that the addition of MAPP or clay in the formulation greatly improved the dispersion of the wood fibers in the composite; this suggested that MAPP or clay may have played the role of an adhesion promoter in the WPCs. The results obtained with clay indicate that it also acted as a flame retardant. The thermal tests carried out with the produced samples showed an increased crystallization temperature (T_c), crystallinity, and melting temperature (T_m) with wood loading. The increase of the two former parameters was explained by the incorporation of wood flour, which played the role of nucleating agent and induced the crystallization of the matrix polymer. On the other hand, the T_m increase was ascribed to the insulating properties of wood, which hindered the movement of heat conduction. The effects of UV irradiation on T_m and T_c were also examined. T_c increased with UV exposure time; this implied that UV degradation generated short chains with low molecular weight that could move easily in the bulk of the sample and, thus, catalyze early crystallization. The flexural strength and modulus increased with increasing wood‐flour content. In contrast, the impact strength and tensile strength and strain decreased with increasing wood‐flour content. All of these changes were related to the level of dispersion of the wood flour in the polymeric matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nonlinear gain coefficients in semiconductor quantum-well lasers:effects of carrier diffusion, capture, and escape

Effective nonlinear gain coefficients due to the effects of carrier diffusion, capture, and escape are derived from the carrier transport equations. The quantum capture and escape processes between the confined states and the unconfined states are calculated from first principles by evaluating the carrier-polar longitudinal optical phonon interactions. The dc and ac capture times and escape times are derived from evaluating the net capture current of carriers. The differences in capture and escape times between dc and ac operating conditions are numerically investigated. We find that both dc and ac escape times are strongly dependent on the quantum well structure. This differs from the dc and ac capture times that are not sensitive to the quantum well structure. We also find that the dc escape time predicted by the classical thermionic emission theory will no longer be valid for narrow or shallow quantum wells. We show that both dc and ac capture and escape time ratios will increase as the carrier temperature and the carrier density in the quantum well increase. Therefore, we suggest that the possible cause of the resonant frequency degradation and dramatic increase in the damping rate results from the increase of the ac capture to escape time ratio by the effects of carrier heating. Two theoretical models (2N and 3N models) were used to study the effects of carrier diffusion-capture-escape on the modulation response of quantum-well lasers and a distributed model of carrier transport in quantum-well lasers is proposed. Their implications in designing high-speed quantum-well lasers are discussed     

The nanostructure and dewetting of block copolymer thin films annealed in different neutral solvents

The morphology of polystyrene‐b‐poly(2‐vinyl pyridine) thin films annealed under various neutral solvents was investigated. The morphological transition depends on the vapor pressure of the solvent, the quantity of the solvent in the film, and annealing time. We introduced the volume fraction of solvent in a film (Q) to correlate these factors to the morphology. At low Q, the amount of solvent that penetrates into the film is limited and it cannot induce enough chain mobility. Thus, thin film shows short stripes or a worm‐like structure. At high Q, the great diffusion of solvent into the film facilitates polymer mobility, leading to an ordered structure. Our results also suggested that the dewetting mechanism of thin film depends on Q. At low Q, dewetting develops via the nucleation and growth. At high Q, the condensation of solvent on the surface removes some polymer and dewetting is dominated by spinodal mechanism. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

两层浆砌块模型房屋动力特性试验研究

本文介绍两层免浆砌块房屋模型动力特性试验情况及测试数据分析结果。为模型地震反应试验并判定结构减震性能提供试验依据。     

Potential Effect of CD271 on Human Mesenchymal Stromal Cell Proliferation and Differentiation

The Low-Affinity Nerve Growth Factor Receptor (LNGFR), also known as CD271, is a member of the tumor necrosis factor receptor superfamily. The CD271 cell surface marker defines a subset of multipotential mesenchymal stromal cells and may be used to isolate and enrich cells derived from bone marrow aspirate. In this study, we compare the proliferative and differentiation potentials of CD271⁺ and CD271⁻ mesenchymal stromal cells. Mesenchymal stromal cells were isolated from bone marrow aspirate and adipose tissue by plastic adherence and positive selection. The proliferation and differentiation potentials of CD271⁺ and CD271⁻ mesenchymal stromal cells were assessed by inducing osteogenic, adipogenic and chondrogenic in vitro differentiation. Compared to CD271⁺, CD271⁻ mesenchymal stromal cells showed a lower proliferation rate and a decreased ability to give rise to osteocytes, adipocytes and chondrocytes. Furthermore, we observed that CD271⁺ mesenchymal stromal cells isolated from adipose tissue displayed a higher efficiency of proliferation and trilineage differentiation compared to CD271⁺ mesenchymal stromal cells isolated from bone marrow samples, although the CD271 expression levels were comparable. In conclusion, these data show that both the presence of CD271 antigen and the source of mesenchymal stromal cells represent important factors in determining the ability of the cells to proliferate and differentiate.