Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. I. Characterized by thermal-fractionation technique

In this article, the polydispersity of the ethylene sequence length (ESL) in ethylene/alpha-olefin copolymers was studied by atomic force microscopy (AFM) and the thermal-fractionation technique. The crystal morphology observation by AFM showed that morphology changed gradually with decreasing average ESL from complete lamellae over shorter and more curved lamellae to a granular-like morphology, and the mixed morphology was observed after stepwise crystallization from phase-separated melt. This result indicated that the ethylene sequence with different lengths crystallized into a crystalline phase with a different size and stability at the copolymer systems. The thermal-fractionation technique was used to characterize the polydispersity of ESL. Three of the following statistical terms were introduced to describe the distribution of ESL and the lamellar thickness: the arithmetic mean (L) over bar (n), the weight mean (L) over bar (w), and the broadness index I = (L) over bar (w)/(L) over bar (n). It was concluded that the polydispersity of ESL could be quantitatively characterized by the thermal-fractionation technique. The effects of temperature range, temperature-dependent specific heat capacity C-p of copolymer, and the molecular weight on the results of thermal fractionation were discussed,

High PL quantum efficiency of poly(phenylene vinylene) systems through exciton confinement

Photoluminescence (PL) quantum efficiency is a key issue in designing successful light-emitting polymer systems. Exciton relaxation is strongly affected by exciton quenching at nonradiative trapping centers and the formation of excimers. These factors reduce the PL quantum yield of light-emitting polymers. In this work, we have systematically investigated the effects of exciton confinement on the PL quantum yield of an oligomer, polymer, and alternating block copolymer (ABC) PPV system. Time-resolved and temperature-dependent luminescence studies have been performed. The ABC design effectively confine photoexcitations within the chromophores, preventing exciton migration and excimer formation. An unusually high (PL) quantum yield (above 90%) in the solid state is reported for the alternating block copolymer PPV, as compared to that of similar to 30% of the polymer and oligomer model compounds. (C) 2000 Elsevier Science S.A. All rights reserved.

Synthesis and thermotropic liquid crystalline behaviour of novel poly(aryl ether ketone)s with a lateral methoxy group

Novel poly(aryl ether ketone)s containing a lateral methoxy group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and methoxyhydroquinone with 1,4-bis(4-fluorobenzoyl)benzene in a sulfolane solvent in the presence of anhydrous potassium carbonate. Their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques, e.g. differential scanning calorimetry (DSC), polarized light microscopy and temperature-dependent FTIR. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 30-80 mol-% mexthoxyhydroquinone. Both melting (T-m) and isotropization (T-i) transitions appeared in the DSC curves. The polarized light microscopy study of the liquid crystalline copolymers suggested their ordered smectic structures. As expected, the copolymers had lower melting transitions than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer methoxyhydroquinone.

Charge transport in a blue-emitting alternating block copolymer with a small spacer to conjugated segment length ratio

We analyze current versus voltage data obtained using single carrier injection in several metal/polymer/metal sandwich structures. The polymer used in each case is a soluble blue-emitting alternating block copolymer. Our experimental results demonstrate that the electron transport is space-charge limited by the high density of traps having an exponential energy distribution (temperature dependent characteristic energy) in the copolymer. The electron mobility of 8x10(-10) cm(2)/V s is directly determined using space-charge-limited current analytical expressions. Hole transport is also space-charge limited, with a mobility of 2x10(-6) cm(2)/V s. A hole trap with energy 0.17 eV is observed. We compare these results with those obtained for related block copolymers with different spacer and conjugated segment lengths and discuss the influence of spacer length and conjugated segment length on the charge transport properties. (C) 2000 American Institute of Physics. [S0021-8979(00)04501-1].

Phase structure and transitions in a poly(methyloctadecylsilane) oligomer

A poly(methyloctadecylsilane) oligomer was synthesized by a typical Wurtz coupling reaction. Upon cooling, three transitions were observed at temperatures of 39.9, 37.5 and 33.9 degreesC at a rate of 2.5 degreesC/min in differential scanning calorimetry (DSC). The first transition, with enthalpy change of 0.47 kT/mol and supercooling of 0.2 degreesC, was characteristic of the conformational change in the Si-Si backbone into an all-trans conformation, which was detected by temperature-dependent Fourier transform infrared (FT-FR) spectroscopy. The second and the third transitions with large supercooling were identified as the formation of two-dimensional hexagonal crystal packing and three-dimensional two-chain orthorhombic crystal packing, respectively. The crystal structure was determined by the combination of WAXD and transmission electron microscopy (TEM) experiments. (C) 2000 Elsevier Science Ltd. All rights reserved.

FRACTURE-TOUGHNESS OF PHENOLPHTHALEIN POLYETHER KETONE

The static and impact fracture toughness of phenolphthalein polyether ketone (PEK-C) were studied at different temperatures. The static fracture toughness of PEK-C was evaluated via the linear elastic fracture mechanics (LEFM) and the J-integral analysis. Impact fracture toughness was also analyzed using the LEFM approach. Temperature and strain rate effects on the fracture toughness were also studied. The enhancement in static fracture toughness at 70 degrees C was thought to be caused by plastic crack tip blunting. The increase in impact fracture toughness with temperature was attributed two different mechanisms, namely, the relaxation process in a relatively low temperature and thermal blunting of the crack tip at higher temperature. The temperature-dependent fracture toughness data obtained in static tests could be horizontally shifted to match roughly the data for impact tests, indicating the existence of a time-temperature equivalence relationship. (C) 1995 John Wiley & Sons, Inc.

A preliminary genetic linkage map of the pacific abalone Haliotis discus hannai Ino

Preliminary genetic linkage maps were constructed for the Pacific abalone (Haliotis discus hannai Ino) using amplified fragment length polymorphism (AFLP), randomly amplified polymorphic DNA (RAPD), and microsatellite markers segregating in a F, family. Nine microsatellite loci, 41 RAPD, and 2688 AFLP markers were genotyped in the parents and 86 progeny of the mapping family. Among the 2738 markers, 384 (including 365 AFLP markers, 10 RAPD markers, and 9 microsatellite loci) were polymorphic and segregated in one or both parents: 241 in the female and 146 in the male. The majority of these markers, 232 in the female and 134 in the male, segregated according to the expected 1:1 Mendelian ratio (alpha = 0.05). Two genetic linkage maps were constructed using markers segregating in the female or the male parent. The female framework map consisted of 119 markers in 22 linkage groups, covering 1773.6 cM with an average intermarker space of 18.3 cM. The male framework map contained 94 markers in 19 linkage groups, spanning 1365.9 cM with an average intermarker space of 18.2 cM. The sex determination locus was mapped to the male map but not to the female map, suggesting a XY-male determination mechanism. Distorted markers showing excess of homozygotes were mapped in clusters, probably because of their linkage to a gene that is incompatible between two parental populations.

CO2H2O and energy exchange of an Inner Mongolia steppe ecosystem during a dry and wet year

We used an eddy covariance technique to measure evapotranspiration and carbon flux over two very different growing seasons for a typical steppe on the Inner Mongolia Plateau, China. The rainfall during the 2004 growing season (344.7 mm) was close to the annual average (350.43 mm). In contrast, precipitation during the 2005 growing season was significantly lower than average (only 126 mm). The wet 2004 growing season had a higher peak evapotranspiration (4 mm day(-1)) than did the dry 2005 growing season (3.3 mm day(-1)). In 2004, latent heat flux was mainly a consumption resource for net radiation, accounting for similar to 46% of net radiation. However, sensible heat flux dominated the energy budget over the whole growing season in 2005, accounting for 60% of net radiation. The evaporative rate (LE/R-n) dropped by a factor of four from the non-soil stress to soil water limiting conditions. Maximum half-hourly CO2 uptake was -0.68 mg m(-2) s(-1) and maximum ecosystem exchange was 4.3 g CO2 m(-2) day(-1) in 2004. The 2005 drought growing stage had a maximum CO2 exchange value of only -0.22 mg m(-2) s(-1) and a continuous positive integrated-daily CO2 flux over the entire growing season, i.e. the ecosystem became a net carbon source. Soil respiration was temperature dependent when the soil was under non-limiting soil moisture conditions, but this response declined with soil water stress. Water availability and a high vapor pressure deficit severely limited carbon fixing of this ecosystem; thus, during the growing season, the capacity to fix CO2 was closely related to both timing and frequency of rainfall events. (c) 2007 Published by Elsevier Masson SAS.

Diurnal, seasonal and annual variation in net ecosystem CO2 exchange of an alpine shrubland on Qinghai-Tibetan plateau

Thus far, grassland ecosystem research has mainly been focused on low-lying grassland areas, whereas research on high-altitude grassland areas, especially on the carbon budget of remote areas like the Qinghai-Tibetan plateau is insufficient. To address this issue, flux of CO2 were measured over an alpine shrubland ecosystem (37 degrees 36'N, 101 degrees 18'E; 325 above sea level [a. s. l.]) on the Qinghai-Tibetan Plateau, China, for 2 years (2003 and 2004) with the eddy covariance method. The vegetation is dominated by formation Potentilla fruticosa L. The soil is Mol-Cryic Cambisols. To interpret the biotic and abiotic factors that modulate CO2 flux over the course of a year we decomposed net ecosystem CO2 exchange (NEE) into its constituent components, and ecosystem respiration (R-eco). Results showed that seasonal trends of annual total biomass and NEE followed closely the change in leaf area index. Integrated NEE were -58.5 and -75.5 g C m(-2), respectively, for the 2003 and 2004 years. Carbon uptake was mainly attributed from June, July, August, and September of the growing season. In July, NEE reached seasonal peaks of similar magnitude (4-5 g C m(-2) day(-1)) each of the 2 years. Also, the integrated night-time NEE reached comparable peak values (1.5-2 g C m(-2) day(-1)) in the 2 years of study. Despite the large difference in time between carbon uptake and release (carbon uptake time < release time), the alpine shrubland was carbon sink. This is probably because the ecosystem respiration at our site was confined significantly by low temperature and small biomass and large day/night temperature difference and usually soil moisture was not limiting factor for carbon uptake. In general, R-eco was an exponential function of soil temperature, but with season-dependent values of Q(10). The temperature-dependent respiration model failed immediately after rain events, when large pulses of R-eco were observed. Thus, for this alpine shrubland in Qinghai-Tibetan plateau, the timing of rain events had more impact than the total amount of precipitation on ecosystem R-eco and NEE.

地幔对流理论及其在解释地球物理观测的应用

With the improving of mantle convection theory, the developing of computing method and increasing of the measurement data, we can numerically simulate more clearly about the effects on some geophysical observed phenomenons such as the global heat flow and global lithospheric stress field in the Earth's surface caused by mantle convection, which is the primary mechanism for the transport of heat from the Earth's deep interior to its surface and the underlying force mechanism of dynamics in the Earth.Chapter 1 reviews the historical background and present research state of mantle convection theory.In Chapter 2, the basic conception of thermal convection and the basic theory about mantle flow.The effects on generation and distribution of global lithospheric stres s field induced by mantle flow are the subject of Chapter 3. Mantle convection causes normal stress and tangential stresses at the bottom of the lithosphere, and then the sublithospheric stress field induces the lithospheric deformation as sixrface force and results in the stress field within the lithosphere. The simulation shows that the agreement between predictions and observations is good in most regions. Most of subduction zones and continental collisions are under compressive. While ocean ridges, such as the east Pacific ridge, the Atlantic ridge and the east African rift valley, are under tensile. And most of the hotspots preferentially occur in regions where calculated stress is tensile. The calculated directions of the most compressive principal horizontal stress are largely in accord with that of the observation except for some regions such as the NW-Pacifie subduction zone and Qinghai-Tibet Plateau, in which the directions of the most compressive principal horizontal stress are different. It shows that the mantel flow plays an important role in causing or affecting the large-scale stress field within the lithosphere.The global heat flow simulation based on a kinematic model of mantle convection is given in Chapter 4. Mantle convection velocities are calculated based on the internal loading theory at first, the velocity field is used as the input to solve the thermal problem. Results show that calculated depth derivatives of the near surface temperature are closely correlated to the observed surface heat flow pattern. Higher heat flow values around midocean ridge systems can be reproduced very well. The predicted average temperature as a function of function of depth reveals that there are two thermal boundary layers, one is close to the surface and another is close to the core-mantle boundary, the rest of the mantle is nearly isothermal. Although, in most of the mantle, advection dominates the heat transfer, the conductive heat transfer is still locally important in the boundary layers and plays an important role for the surface heat flow pattern. The existence of surface plates is responsible for the long wavelength surface heat flow pattern.In Chapter 5, the effects on present-day crustal movement in the China Mainland resulted from the mantle convection are introduced. Using a dynamic method, we present a quantitative model for the present-day crustal movement in China. We consider not only the effect of the India-Eurasia collision, the gravitational potential energy difference of the Tibet Plateau, but also the contribution of the shear traction on the bottom of the lithosphere induced by the global mantle convection. The comparison between our results and the velocity field obtained from the GPS observation shows that our model satisfactorily reproduces the general picture of crustal deformation in China. Numerical modeling results reveal that the stress field on the base of the lithosphere induced by the mantle flow is probably a considerable factor that causes the movement and deformation of the lithosphere in continental China with its eflfcet focuing on the Eastern China A numerical research on the small-scale convection with variable viscosity in the upper mantle is introduced in Chapter 6. Based on a two-dimensional model, small-scale convection in the mantle-lithosphere system with variable viscosity is researched by using of finite element method. Variation of viscosity in exponential form with temperature is considered in this paper The results show that if viscosity is strongly temperature-dependent, the upper part of the system does not take a share in the convection and a stagnant lid, which is identified as lithosphere, is formed on the top of system because of low temperature and high viscosity. The calculated surface heat flow, topography and gravity anomaly are associated well with the convection pattern, namely, the regions with high heat flow and uplift correspond to the upwelling flow, and vice versa.In Chapter 7, we give a brief of future research subject: The inversion of lateral density heterogeneity in the mantle by minimizing the viscous dissipation.

黄土高原全新世风成沉积的岩石磁学性质

Chinese eolian deposits are especially suitable for the studies of paleoclimatic changes, environmental magnetism and remanence acquisition mechanisms. In the past two decades, many studies have documented their magnetic properties. However, some important problems, such as the origin of magnetic minerals, the mechanisms for enhancing magnetic susceptibility and the lock-in effect, remain debatable. Therefore, it is essential to detail the rock-magnetic properties of the eolian deposits. This study shows thermomagnetic analyses, petrographic measurements and soil chemistry methods can be combined to obtain a better understanding of the sequence of magnetic mineral alterations during thermal treatment and of the pedogenic mechanism responsible for the susceptibility enhancement. This helps to further develop the interpretation of paleoclimate records in the Holocene eolian deposits along a NW-SE transect of the loess plateau. A partial heating/cooling method and X-ray diffraction (XRD) analysis were performed on representative samples of the present-day loess, in order to investigate mineralogical changes during thermal treatment. The temperature-dependent susceptibility (TDS) and XRD results show complex alteration of magnetic phases during heating and cooling. The 300 ℃ susceptibility hump in heating curves might be due to the production of maghemite from less magnetic lepidocrocite during heating. Goethite is transformed into hematite when heating to above 300 ℃. The susceptibility decrease from 300 ℃ to 450 ℃ can be interpreted as the conversion of maghemite to hematite. This thermal instability makes it possible to quantatively estimate the maghemite contribution to the pedogenically-enhanced susceptibility in loess or paleosols. Minor occurrence of thermally-stable maghemite in the present-day loess is possible; nevertheless, the TDS measurements show that the degree of the thermally-induced alteration is closely related to pedogenesis. The TDS measurement and XRD analysis results demonstrate that although magnetite and hematite both exist in the Holocene loess eolian deposits and their modern source area, magnetite is the predominant contributor to magnetic susceptibility. Both magnetite and hematite are the primary carriers of the remanent magnetization. Fine-grained maghemite, mainly produced by pedogenesis, is significantly responsible for enhancement of the magnetic susceptibility in the Chinese loess and paleosols. Since the degree of oxidation of magnetite grains depends on climate, the presence of maghemite has paleoclimatic significance, and variations in climate could be reflected as variations in the amount of low-temperature oxidation. If that is the case, the TDS curves can be used to compare the effects of climate at different sampling sites. The TDS results along the studied NW-SE transect suggest that stronger pedogenesis results in higher content of maghemite and greater susceptibility decrease during thermal treatment. This behavior seems to indicate that the final product of pedogenic magnetite in Chinese loess and paleosols is maghemite, which makes significant contributions to the enhanced magnetic susceptibility of Chinese eolian deposits. It is interesting to note that the 510 ℃ Hopkinson/alteration peak is larger in the present-day loess than in the black loam for each section. Obiviously, the Hopkinson/alteration peak of the Holocene eolian deposits is closely related to the degree of pedogenesis, which is a function of climate, and thus the peak itself could be a useful climate indicator. There are three effects that may be important in producing this trend. First, low-temperature oxidation preferentially affects the finer single-domain magnetites responsible for the Hopkinson peak, which is therefore suppressed in the more oxidized loams. Second, the possible production of uniaxial magnetite with shape anisotropy can also lead to a relatively muted Hopkinson peak. There is, additionally, a third alternative, and the one preferred here, that the natural alteration processes involved in pedogenic susceptibility enhancement have probably depleted the supply of iron-bearing precursor phases, so that less new magnetite is formed on heating. In summary, the TDS method is very reliable and highly sensitive in detecting magnetic phase changes in eolian deposits during thermal treatment, which are closely related to pedogenic processes. Thus, the studied NW-SE transect clearly exhibits paleoclimatically-induced mineral- and rock-magnetic variations. It is suggested that TDS can be used as a new method for the analysis of pedogenesis and climatic change.

Na-23, Si-29, and C-13 MAS NMR investigation of glass-forming reactions between Na2CO3 and SiO2

Winter, Rudolf; Jones, A.R.; Greaves, G.N.; Smith, I.H., (2005) 'Na-23, Si-29, and C-13 MAS NMR investigation of glass-forming reactions between Na2CO3 and SiO2', Journal of Physical Chemistry B 109(49) pp.23154-23161 RAE2008

Li+ Diffusion and its Structural Basis in the Nanocrystalline and Amorphous Forms of Two-dimensionally Ion-conducting LixTiS2

Winter, Rudolf; Heitjans, P., (2001) 'Li+ Diffusion and its Structural Basis in the Nanocrystalline and Amorphous Forms of Two-dimensionally Ion-conducting LixTiS2', Journal of Physical Chemistry B 105(26) pp.6108-6115 RAE2008

Latest development of the combinatorial model of nuclear level densities

The combinatorial model of nuclear level densities has now reached a level of accuracy comparable to that of the best global analytical expressions without suffering from the limits imposed by the statistical hypothesis on which the latter expressions rely. In particular, it provides, naturally, non-Gaussian spin distribution as well as non-equipartition of parities which are known to have an impact on cross section predictions at low energies [1, 2, 3]. Our previous global models developed in Refs. [1, 2] suffered from deficiencies, in particular in the way the collective effects - both vibrational and rotational - were treated. We have recently improved this treatment using simultaneously the single-particle levels and collective properties predicted by a newly derived Gogny interaction [4], therefore enabling a microscopic description of energy-dependent shell, pairing and deformation effects. In addition for deformed nuclei, the transition to sphericity is coherently taken into account on the basis of a temperature-dependent Hartree-Fock calculation which provides at each temperature the structure properties needed to build the level densities. This new method is described and shown to give promising results with respect to available experimental data.

Pseudomonas aeruginosa vesicles associate with and are internalized by human lung epithelial cells.

BACKGROUND: Pseudomonas aeruginosa is the major pathogen associated with chronic and ultimately fatal lung infections in patients with cystic fibrosis (CF). To investigate how P. aeruginosa-derived vesicles may contribute to lung disease, we explored their ability to associate with human lung cells. RESULTS: Purified vesicles associated with lung cells and were internalized in a time- and dose-dependent manner. Vesicles from a CF isolate exhibited a 3- to 4-fold greater association with lung cells than vesicles from the lab strain PAO1. Vesicle internalization was temperature-dependent and was inhibited by hypertonic sucrose and cyclodextrins. Surface-bound vesicles rarely colocalized with clathrin. Internalized vesicles colocalized with the endoplasmic reticulum (ER) marker, TRAPalpha, as well as with ER-localized pools of cholera toxin and transferrin. CF isolates of P. aeruginosa abundantly secrete PaAP (PA2939), an aminopeptidase that associates with the surface of vesicles. Vesicles from a PaAP knockout strain exhibited a 40% decrease in cell association. Likewise, vesicles from PAO1 overexpressing PaAP displayed a significant increase in cell association. CONCLUSION: These data reveal that PaAP promotes the association of vesicles with lung cells. Taken together, these results suggest that P. aeruginosa vesicles can interact with and be internalized by lung epithelial cells and contribute to the inflammatory response during infection.