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51.
Julia Ertl Dr. Maria Elena Ortiz-Soto Thien Anh Le Julian Bechold Junwen Shan Dr. Jörg Teßmar Prof. Bernd Engels Prof. Jürgen Seibel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6533-6541
Selective chemical modification of proteins plays a pivotal role for the rational design of enzymes with novel and specific functionalities. In this study, a strategic combination of genetic and chemical engineering paves the way for systematic construction of biocatalysts by tuning the product spectrum of a levansucrase from Bacillus megaterium (Bm-LS), which typically produces small levan-like oligosaccharides. The implementation of site-directed mutagenesis followed by a tyrosine-specific modification enabled control of the product synthesis: depending on the position, the modification provoked either enrichment of short oligosaccharides (up to 800 % in some cases) or triggered the formation of high molecular weight polymer. The chemical modification can recover polymerization ability in variants with defective oligosaccharide binding motifs. Molecular dynamic (MD) simulations provided insights into the effect of modifying non-native tyrosine residues on product specificity. 相似文献
52.
Journal of Statistical Physics - In this paper, we will study the long time behavior of the simple symmetric exclusion process in the “channel” $$varLambda _N=[1,N]cap mathbb {N}$$... 相似文献
53.
G. Pozina C.G. Hemmingsson J.P. Bergman D. Trinh L. Hultman B. Monemar 《Superlattices and Microstructures》2008,43(5-6):605
Freestanding GaN layers of various thicknesses grown by HVPE have been studied by time-resolved spectroscopy combined with structural and electrical measurements. We have observed an increase of the PL lifetime with increasing layer thickness; however, a saturation of the recombination times has been detected for the GaN layers thicker than 400 μm. We explain the observed thickness-dependent behavior of the decay times by competition of two nonradiative mechanisms; namely, for layers with thickness less than 400 μm the main nonradiative channel is related to the structural defects, while in thicker layers the recombination decay time is limited by impurities and/or vacancies. 相似文献
54.
Nguyen Van Hieu Nguyen Van Duy Pham Thanh Huy Nguyen Duc Chien 《Physica E: Low-dimensional Systems and Nanostructures》2008,40(9):2950-2958
Nb-Pt co-doped TiO2 and the hybrid SWCNTs/Nb-Pt co-doped TiO2 thin films have been prepared by the sol–gel spin-coating process for gas-sensor fabrication. Field emission scanning electron microscope (FE-SEM, TEM and X-ray diffraction (XRD) characterizations indicated that the SWCNTs inclusion did not affect the morphology of the TiO2 thin film and the particle size. Additionally, the SWCNTs were well embedded in the TiO2 matrix. The gas-sensing properties of Nb–Pt co-doped TiO2 thin films with and without SWCNTs inclusion were investigated. The hybrid sensors with the inclusion of different SWCNTs contents are examined to elucidate the effect of SWCNTs content on the gas-sensing properties. Experimental results revealed that the responses to ethanol of Nb–Pt co-doped TiO2 sensors with SWNCTs inclusion increase by factors of 2–5 depending on the operating temperature and the ethanol concentration, compared to that of the sensor without SWCNTs inclusion. Moreover, all hybrid sensors can operate with high sensitivity and stability at a relatively low operating temperature (<335 °C). The responses of the hybrid sensors are greatly affected by SWCNTs content inclusion. The optimized SWCNTs content of 0.01% by weight was obtained for our experiment. The improved gas-sensing performance should be attributed to the additional formation of the p/n junction between SWCNTs (p-type) and TiO2 (n-type). 相似文献
55.
An investigation of the internal flow field for a drop at the antinode of a standing wave has been carried out. The main difference from the solid sphere case is the inclusion of the shear stress and velocity continuity conditions at the liquid-gas interface. To the leading order of calculation, the internal flow field was found to be quite weak. Also, this order being fully time dependent has a zero mean flow. At the next higher order, steady internal flows are predicted and, as in the case of a solid sphere, there is a recirculating layer consisting of closed streamlines near the surface. In the case of a liquid drop, however, the behavior of this recirculating Stokes layer is quite interesting. It is predicted that the layer ceases to have recirculation when [formula: see text], where [symbol: see text] is the liquid viscosity, mu is the exterior gas-phase viscosity, and M is the dimensionless frequency parameter for the gas phase, defined by M = i omega a2 rho/mu, with a being the drop radius. Thorough experimental confirmation of this interesting new development needs to be conducted. Although it seems to agree with many experiments with levitated drops where no recirculating layer has been clearly observed, a new set of experiments for specifically testing this interesting development need to be carried out. 相似文献
56.
Fundamental equations of the theory of spatially reinforced media with a matrix reinforced by spherical particles are proposed on the basis of a linearly reinforced layer and tl.e hypothesis of a longitudinal state. For an arbitrary orientation of the fibers, the generalized elasticity equation for composites was found to contain 21 elastic constants and approximate formulas were derived for their determination.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga. Latvia (October, 1995).Communication 1. see preceding article.A. A. Blagonravov Institute of Mechanical Engineering. Russian Academy of Sciences, Moscow. Russian. Translated from Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 306–316, May–June, 1996. 相似文献
57.
In this note, we prove that if N is a compact totally geodesic submanifold of a complete Riemannian manifold M, g whose sectional curvature K satisfies the relation K ≥ k > 0, then
for any point m ∈ M. In the case where dim M = 2, the Gaussian curvature K satisfies the relation K ≥ k ≥ 0, and γ is of length l, we get Vol (M, g) ≤
if k ≠ 0 and Vol (M, g ≤ 2ldiam (M) if k = 0.__________Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 56, No. 11, pp. 1576–1583, November, 2004. 相似文献
58.
The problem of steady streaming around a rigid isolated sphere in a plane standing acoustic field is considered. Existing results in the literature have been generalized to allow for noncompactness of the sphere, and the influence of fluid compressibility on the streaming behavior has been included. It is found that in the high-frequency limit of interest for which the streaming is strongest, the effective steady slip velocity at the edge of the inner boundary layer region that is responsible for driving the steady streaming in the bulk of the fluid in the outer region, has a complex variation over the surface of the sphere that depends on (i) the sphere position (with respect to the node/antinode of the acoustic field), (ii) the extent of sphere compactness, and (iii) on a well-defined function (representing compressibility effects) of the fluid Prandtl number and its ratio of specific heats. Not surprisingly, the contribution from this function is negligible when the host fluid is a liquid. The steady streaming behavior around the sphere is demonstrated with the help of flow streamlines for various cases in the diffusive limit of weak outer flow for low streaming Reynolds numbers. 相似文献
59.
Tran Duc Thiep Truong Thi An Nguyen The Vinh Phan Viet Cuong A. G. Belov O. D. Maslov Trinh Thi Thu My 《Physics of Particles and Nuclei Letters》2007,4(5):397-402
We have carried out the study on the isomeric ratios in (γ,p) photonuclear reactions with isotopes
40
92
Zr and
74
183
W in the giant dipole resonance (GDR) region. The targets were irradiated with bremsstrahlungs produced by electron accelerator
Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, Russia. Spectra
of the irradiated samples were measured with a spectroscopic system consisting of 8192-channel analyzer CANBERRA and high-energy
resolution semiconductor detector CANBERRA. The results were discussed and compared with those of other authors.
The text was submitted by the authors in English. 相似文献
60.
This study is directed towards investigating the role of the surface treatment of clay particles on the rheological and thermomechanical
behaviour of clay-epoxy blends. Nanocomposites were prepared by mixing small amounts (5–10 mass %) of commercial organoclays
or raw clays with an epoxy system commonly used in civil engineering. Rheological characterisations in the liquid state revealed
a pronounced thixotropic character of the organoclay-based systems, which all exhibited a shear-thinning behaviour above a
critical stress threshold (yield stress), depending on both the intensity of interfacial interactions and the degree of filler
dispersion. On the other hand, systems based on raw clay particles behaved like Newtonian fluids, in the same way as the unreinforced
polymer matrix. Complementary dynamic mechanical analyses (DMA) performed on the cured cross-linked nanocomposites also showed
significant changes in the viscoelastic behaviour of the epoxy matrix due to the introduction of organoclays, whereas only
minor variations were observed following the introduction of raw fillers. These results were consistent with nanoscale morphological
characterisations performed by conventional X-ray diffraction (XRD) on the various hybrid systems. In this context, rheology
and DMA appear as attractive alternative methods for assessing the filler dispersion at a macroscopic (and possibly more relevant)
scale. This research is of practical interest for civil engineers, since clay reinforced-epoxies could in the future be used
as coating materials with enhanced barrier performances, in order to protect infrastructures against environmental ageing
or corrosion. 相似文献