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排序方式: 共有1194条查询结果,搜索用时 15 毫秒
31.
Formation and growth of neutral SO2 clusters is investigated in an adiabatic-expansion setup by means of sulfur 2p (S2p) photoelectron spectroscopy and theoretical modeling. The shift in S2p ionization energy between the cluster and a single molecule, i.e., IE(cluster)-IE(monomer), is recorded and used to monitor the mean cluster size over a wide range of expansion conditions. The produced clusters were shown to fall into two different size regimes. Comparison between theoretical simulations and experimental observations suggests that while the smallest clusters belong to the ultrafine particle mode and have a liquid-like structure, the larger clusters belong to the accumulation mode of fine particles and possibly have a frozen cluster core. The transition between the two size/structure regimes occurs over a narrow interval in expansion conditions and may possibly reflect a change in growth mechanism from monomer addition to growth by cluster-cluster collisions.(c) Jarle Harnes, Mahmoud Abu-Samha, Mathias Winkler, and Knut J. Børve 相似文献
32.
Jolanta Lisowiec-Wąchnicka Mathias B. Danielsen Eugenie Abi Nader Per T. Jørgensen Jesper Wengel Anna Pasternak 《Chembiochem : a European journal of chemical biology》2022,23(15):e202200168
We analyzed the effect of modified nucleotides within gapmer antisense oligonucleotides on RNase H mediated gene silencing. Additionally, short hairpins were introduced into antisense oligonucleotides as structural motifs, and their influence on biological and physicochemical properties of pre-structured gapmers was investigated for the first time. The results indicate that two LNA residues in specified positions of the gap flanking regions are sufficient and favorable for efficient knock-down of the β-actin gene. Furthermore, the introduction of other modified nucleotides, i. e. glycyl-amino-LNA−T, 2′-O-propagyluridine, polyamine functionalized uridine, and UNA, in specified positions, also increases the inhibition of β-actin expression. Importantly, the presence of hairpins within the gapmers improves their silencing properties. 相似文献
33.
Mathias Herrmann Jan RäthelSören Höhn Jens EichlerAlexander Michaelis 《Journal of the European Ceramic Society》2011,31(13):2401-2406
Hexagonal boron nitride/titanium diboride composites are widely used as evaporation boats for aluminium deposition to produce functional and decorative layers on different target materials. The lifetime of such a material is limited mainly by the interaction of the metal with the ceramic substrate, but the corrosion mechanism has still not yet been thoroughly investigated and understood. In this article the corrosion mechanism for the evaporation boats used was investigated using thermodynamic calculations, FESEM, EDX and XRD phase analysis. The analysis showed that hexagonal boron nitride (hBN), which is thermodynamically less stable than TiB2, is passivated during the application process through the formation of AlN surface layers, whereas the thermodynamically more stable TiB2 phase dissolves and Ti-rich components precipitate in cooler regions of the evaporation boats. 相似文献
34.
35.
M. Hossein Alaei Puneet Mahajan Mathias Brieu Djimedo Kondo S. Javed Ahmed Rizvi Sandeep Kumar Naresh Bhatnagar 《Iranian Polymer Journal》2013,22(11):853-863
Particulate composite materials (PCM) consisting of a matrix reinforced by micro to nano-sized dispersed phase are receiving the attention of designers as a promising futuristic materials. This study unearths the thermal and mechanical behavior of maleic anhydride grafted polypropylene/silica (MA-g-PP/silica) composites for reinforcement ranging from micro- to nano-size. The monodisperse silica spherical particles were used in all the formulations of composites. Further the volume fraction was kept the same in all the compounded thermoplastic composites ranging from 100 nm to 130 μm in a co-rotating conical twin-screw micro-compounder. The micrographs were obtained from transmission electron microscopy (TEM) and the scanning electron microscopy (SEM). The SEM and TEM results revealed a good dispersion of the silica spheres within the MA-g-PP matrix. The compounded composite materials were injection molded to fabricate tensile test specimens (ASTM D638 type V) and tested for tensile properties. In order to investigate the effect of particle size on crystallite structure of the matrix, the composites were tested on differential scanning calorimeter and X-ray diffraction (WAXD). The thermal stability and degradation kinetics were studied via thermogravimetric analysis. The results show increase in crystallization rate, crystallinity percentage, Young’s modulus, strength and thermal stability of MA-g-PP by addition of the silica particles. Further it was observed that the small-sized dispersed phase had better overall thermal and mechanical behavior than its larger sized counterpart. 相似文献
36.
T.A. Stolarski 《Ceramics International》1992,18(6):379-384
The results of studies on the parameters controlling the rate of material removal from the surface of silicon nitride balls are presented. They indicate that the rotational speed and the lubricating fluid used as a medium to introduce abrasive particles into the contact zone are the most important parameters controlling the rate of grinding. Load and contact configuration, although playing some role in the process of material removal, are of less importance. The results obtained could have some significance for surface finish of engineering elements made of ceramics. 相似文献
37.
An investigation into the wear process of five polymers tested under different contact conditions is presented. Polymer pin on metal plate and metal pin on polymer plate configurations were used. The metal pin on polymer plate configuration gave significantly lower wear rates compared to that observed for the polymer pin on metal plate configuration. The results are discussed in terms of morphology of wear debris generated. 相似文献
38.
In spite of its great importance for the dry classification of fine powders, the processes in deflector wheel classifiers are to a large extent unknown. Therefore, in the present work a commercial available classifier was modified to gain an optical access to the deflector wheel. For the first time, the obtained photographs enable an observation of the gas flow and the particle motion between the blades of the deflector wheel. Especially the importance of particle‐particle‐ and particle‐blade‐collisions could be shown. 相似文献
39.
Joseph X. Kugbe Fosu Mathias Tamene L. Desta Manfred Denich Paul L. G. Vlek 《Nutrient Cycling in Agroecosystems》2012,93(3):265-284
This study has assessed the seasonal occurrence of annual vegetation fires and defined inter-seasonally burned area for the different vegetation cover types across Ghana and the northern region of Ghana using 10-year (2001?C2010) remote sensing data. These values were used with fire induced elemental losses to estimate greenhouse gas emissions and net plant nutrient loss due to gross bush fire nutrient transfers and annual atmospheric nutrient depositions. About 21, 68, 10 and 1?% of annual burns across the northern region of Ghana take place in the months of November, December, January and February respectively. As much as 68?±?4 thousand km2 (25?C32?%) and 37?±?2.6 thousand km2 (46?C60?%) of dry land are annually burned across Ghana and the northern region of Ghana respectively, with 53?C56?% of the total annual burns across the country taking place in the northern region. About 10,100?C28,400 Gg of C, comprising 215?C4,700 thousand Gg of CO2 equivalent (CO2, CH4) potential global warming green house gases and 48?C324 thousand Gg of local pollutants (CO, NOx) are estimated to be released annually through bush fire occurrence across Ghana. Net negative balance for P between fire-induced nutrient transfers and, annual wet and dry nutrient deposits is of concern given the high P-sorbing mineral content of the soils. The temporal loss of P suggest an input source than wet and dry atmospheric P depositions for the sustenance of the ecosystem or predict a long term threat to regional food production. 相似文献
40.
Kylie B. Manning Nicholas Wyatt Lindsey Hughes Adam Cook Nicholas H. Giron Estevan Martinez Christopher G. Campbell Mathias C. Celina 《大分子材料与工程》2019,304(3)
The use of self‐assembling, pre‐polymer materials in 3D printing is rare, due to difficulties of facilitating printing with low molecular weight species and preserving their reactivity and/or functions on the macroscale. Akin to 3D printing of small molecules, examples of extrusion‐based printing of pre‐polymer thermosets are uncommon, arising from their limited rheological tuneability and slow reactions kinetics. The direct ink write (DIW) 3D printing of a two‐part resin, Epon 828 and Jeffamine D230, using a self‐assembly approach is reported. Through the addition of self‐assembling, ureidopyrimidinone‐modified Jeffamine D230 and nanoclay filler, suitable viscoelastic properties are obtained, enabling 3D printing of the epoxy–amine pre‐polymer resin. A significant increase in viscosity is observed, with an infinite shear rate viscosity of approximately two orders of magnitude higher than control resins, in addition to, an increase in yield strength and thixotropic behavior. Printing of simple geometries is demonstrated with parts showing excellent interlayer adhesion, unachievable using control resins. 相似文献