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排序方式: 共有729条查询结果,搜索用时 62 毫秒
81.
82.
Nils C. Hildebrandt Julia Soldat Roland Marschall 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(17):2051-2057
The (111)‐layered perovskite materials Ba5Ta4O15, Ba5Ta2Nb2O15 and Ba5Nb4O15 are prepared with nanofiber morphology via electrospinning for the first time. The nanofibers are built up from small single crystals, with up to several micrometers length even after calcination. The formation mechanism is investigated in detail, revealing an intermediate formation of amorphous barium carbonate strengthening the nanofiber morphology for high temperature treatment. All nanofiber compounds are able to generate hydrogen without any co‐catalyst in photocatalytic reformation of methanol. After photodeposition of Rh‐Cr2O3 co‐catalysts, the nanofibers show better activity in overall water splitting compared to sol–gel‐derived powders. 相似文献
83.
Nicholas R. Haase Samuel Shian Kenneth H. Sandhage Nils Kröger 《Advanced functional materials》2011,21(22):4243-4251
Recent insight into the molecular mechanisms of biological mineral formation (biomineralization) has enabled biomimetic approaches for the synthesis of functional organic‐inorganic hybrid materials under mild reaction conditions. Here we describe a novel method for enzyme immobilization in thin (nanoscale) conformal mineral coatings using biomimetic layer‐by‐layer (LbL) mineralization. The method utilizes a multifunctional molecule comprised of a naturally‐occurring peptide, protamine (PA), covalently bound to the redox enzyme Glucose oxidase (GOx). PA mimics the mineralizing properties of biomolecules involved in silica biomineralization in diatoms, and its covalent attachment to GOx does not interfere with the catalytic activity. Highly efficient and stable incorporation of this modified enzyme (GOx‐PA) into nanoscale layers (~5–7 nm thickness) of Ti‐O and Si‐O is accomplished during protamine‐enabled LbL mineralization on silica spheres. Depending on the layer location of the enzyme and the type of mineral (silica or titania) within which the enzyme is incorporated, the resulting multilayer biocatalytic hybrid materials exhibit between 20–100% of the activity of the free enzyme in solution. Analyses of kinetic properties (Vmax, KM) of the immobilized enzyme, coupled with characterization of physical properties of the mineral‐bearing layers (thickness, porosity, pore size distribution), indicates that the catalytic activities of the synthesized hybrid nanoscale coatings are largely determined by substrate diffusion rather than enzyme functionality. The GOx‐PA immobilized in these nanoscale layers is substantially stabilized against heat‐induced denaturation and largely protected from proteolytic attack. The method for enzyme immobilization described here enables, for the first time, the high yield immobilization and stabilization of enzymes within continuous, conformal, and nanoscale coatings through biomimetic LbL mineralization. This approach will likely be applicable to a wide variety of surfaces and functional biomolecules. The ability to synthesize thin (nanoscale) conformal enzyme‐loaded layers is of interest for numerous applications, including enzyme‐based biofuel cells and biosensors. 相似文献
84.
Polylactide‐block‐Polypeptide‐block‐Polylactide Copolymer Nanoparticles with Tunable Cleavage and Controlled Drug Release 下载免费PDF全文
Robert Dorresteijn Nils Billecke Mischa Schwendy Sabine Pütz Mischa Bonn Sapun H. Parekh Markus Klapper Klaus Müllen 《Advanced functional materials》2014,24(26):4026-4033
A versatile nanoparticle system is presented in which drug release is triggered by enzymatic polymer cleavage, resulting in a physicochemical change of the carrier. The polylactide‐block‐peptide‐block‐polylactide triblock copolymer is generated by initiation of the ring‐opening polymerization of L‐lactide with a complex bifunctional peptide having an enzymatic recognition and cleavage site (Pro‐Leu‐Gly‐Leu‐Ala‐Gly). This triblock copolymer is specifically bisected by matrix metalloproteinase‐2 (MMP‐2), an enzyme overexpressed in tumor tissues. Triblock copolymer nanoparticles formed by nonaqueous emulsion polymerization are readily transferred into aqueous media without aggregation, even in the presence of blood serum. Cleavage of the triblock copolymer leads to a significant decrease of the glass transition temperature (Tg) from 39 °C to 31 °C, likely mediating cargo release under physiological conditions. Selective drug targeting is demonstrated by hampered mitosis and increased cell death resulting from drug release via MMP‐2 specific cleavage of triblock copolymer carrier. On the contrary, nanocarriers having a scrambled (non‐recognizable) peptide sequence do not cause enhanced cytotoxicity, demonstrating the enzyme‐specific cleavage and subsequent drug release. The unique physicochemical properties, cleavage‐dependent cargo release, and tunability of carrier bioactivity by simple peptide exchange highlight the potential of this polymer‐nanoparticle concept as platform for custom‐designed carrier systems. 相似文献
85.
J Kartus S Stener R Nilsén U Nilsson BI Eriksson J Karlsson 《Canadian Metallurgical Quarterly》1998,8(6):449-455
Dairy calves under 14 days of age with naturally occurring, uncomplicated diarrhea were treated for 3 days with a hypertonic oral electrolyte solution with (n = 15) or without (n = 12) psyllium. Clinical response and clinical pathology data were compared between the 2 groups. Glucose absorption was evaluated on days 1 and 3 by measurement of plasma glucose and lactate and serum insulin concentrations for 4 hours after formula administration. On day 1, glucose, lactate, and insulin concentrations were lower in psyllium-fed calves than in control calves, with significant differences noted in glucose and lactate concentrations at several time points (P < 0.05). Plasma lactate concentrations were higher at several times in both treatment groups on day 3 than on day 1 (P < 0.05). Fecal consistency was markedly different in psyllium-fed calves as compared with control calves within 24 hours of psyllium supplementation. Fecal percent dry matter content was lower in psyllium-fed calves than in control calves at least once a day during supplementation and on day 3 compared with day 0 in the psyllium-fed calves (P < 0.05). There were no significant differences in clinical performance scores, hydration status, arterial blood gas, serum anion gap, electrolyte, or total CO2 concentrations. Addition of psyllium to an oral electrolyte solution resulted in immediate alterations in glucose absorption without impairing rehydration in diarrheic calves, but differences were transient and did not affect clinical outcome. 相似文献
86.
The melting of secondary-phase particles—or, more precisely, the melting of such particles together with the surrounding matrix—in
two ternary Al-Mg-Si alloys has been studied. In the quasi-binary Al-Mg2Si alloy, one melting reaction is found. In the alloy with an Si content in excess of that necessary to form Mg2Si, three different melting reactions are observed. At upquenching temperatures above the eutectic temperature, the reaction
rates are very high, and it is assumed that they are controlled by diffusion of the alloying elements in the liquid. Melting
is also observed after prolonged annealing at temperatures below the eutectic temperature in these alloys, which is explained
by the different diffusion rates of Mg and Si. The rate of the melting reaction is in this case assumed to be controlled by
diffusion of the alloying elements in the solid α-Al phase. It is shown that calculation of the particle/matrix interface
composition, which determines when melting is possible, cannot be made solely on the basis of the phase diagram, but must
also include the rate of diffusion of Mg and Si. The melting temperatures observed differ somewhat from the accepted eutectic
temperatures for these alloys. On prolonged annealing, the liquid droplets formed dissolve into the surrounding matrix and
their chemical composition is found to change during dissolution. The resulting eutectic structure after quenching of a droplet
is explained by the phase diagram and the different diffusion rates of Mg and Si as well as by the nucleation conditions of
the constituents involved. 相似文献
87.
88.
Nils Kjellman Krister Kristiansson Lennart Malmqvist 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,235(1):193-197
A method has been worked out to identify lithium and boron in mineral samples by means of a solid state nuclear track detector technique. The samples have been irradiated with thermal neutrons which react with 10B and 6Li and give α-particles of different energies. The ranges of these α-particles in air are measured with the SSNTD-technique and found to be sufficiently different to make identification possible. A number of tests are made and the possibility for determining the distribution and the abundance of lithium and boron in a specific mineral in a rock sample is discussed. 相似文献
89.
The authors propose that volitional action is supported by intuitive affect regulation, defined as flexible, efficient, and nonrepressive control of own affective states. Intuitive affect regulation should be most apparent among action-oriented individuals under demanding conditions. Consistent with this, a demanding context led action-oriented individuals to down-regulate negative affect in self-reports (Study 1), in an affective Simon task (Study 2), and in a face discrimination task (Study 3). In line with the idea that intuitive affect regulation is guided by top-down self-regulation processes, intuitive affect regulation in a face discrimination task was mediated by increases in self-accessibility (Study 3). No parallel effects emerged among action-oriented participants in a nondemanding context or among state-oriented participants. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
90.
Lars-Olof Kihlstrm Nils Viklund David Bridgewater 《International Journal of Satellite Communications and Networking》1990,8(6):461-490
This paper discusses the systematization effort undertaken to generate an equipment specification of an extremely detailed and new nature for DCMEs in accordance with the INTELSAT specification IESS-501. The main areas of importance addressed are additional to what has already been defined within the IESS-501. A discussion of important aspects when introducing DCME into actual network conditions is also contained and results based on simulations of performance under simulated network environments are included. 相似文献