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排序方式: 共有103条查询结果,搜索用时 15 毫秒
1.
The warmup rate of the165Ho-enhanced nuclear spins in a HoVO4 single crystal in contact with dilute3He is shown to be dominated by the Kapitza resistanceR
K at low bath temperature (T
b
<100 mK). This result is obtained from an analysis of the NMR signal during the warmup, following a demagnetization which cools the sample to a temperature of about 5 mK. The temperature variation ofR
K (T
b<
/–3
) is consistent with the acoustic mismatch model, but the magnitude is 40 times smaller than the theoretical predictions for a solid-liquid interface. The spin-lattice relaxation is also estimated, and found to be in agreement with the results of other authors. 相似文献
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Sergey N. Semenov Alar Ainla Ekaterina V. Skorb Sjoerd G. J. Postma 《Israel journal of chemistry》2018,58(6-7):781-786
This paper describes a four-variable model for an enzymatic oscillator based on trypsin. Variables in this model are concentrations of the essential proteins (trypsin and trypsinogen) and small molecules (masked and active inhibitors of trypsin) within the network. Importantly, to simplify the model, non-essential side reactions are neglected and essential reactions are assumed to follow first or second order kinetics. Numerical solutions of this reduced model semi-quantitatively reproduce experimentally determined periods, amplitudes, and phase shifts of oscillations in the concentrations of several species in the network. Moreover, linear stability analysis shows that oscillations in the trypsin oscillator emerge and disappear through Hopf bifurcation. The model will be helpful in situations where simplicity is necessary such as detailed analysis of dynamics and modeling of reaction-diffusion systems. 相似文献
4.
R Chen V Hatzimanikatis WM Yap PW Postma JE Bailey 《Canadian Metallurgical Quarterly》1997,13(6):768-775
E. coli strain PPA305, which has a wild-type PTS system, and PPA316, which utilizes a proton-galactose symport system for glucose uptake, were used as host strains to harbor a phenylalanine overproduction plasmid pSY130-14 and to study the effects of using different glucose uptake systems on phenylalanine production. The non-PTS strain (PPA316/pSY130-14) produced much less phenylalanine, ranging from 0 to 67% of that produced by the PTS strain (PPA305/pSY130-14) depending on cultivation conditions used. The non-PTS strain PPA316/pSY130-14 had an intracellular PEP concentration only one-sixth that of the PTS strain, PPA305/pSY130-14. Additionally, PPA316/pSY130-14 had a substantially lower energy state in terms of the size of the pool of high-energy phosphate compounds and the magnitude of the pH difference across the cytoplasmic membrane. The non-PTS strain consumed oxygen at a higher rate, attained lower biomass concentration, and produced no acetate and phenylalanine during fermentation, suggesting more carbon was oxidized to CO2, most likely through the TCA cycle. Analysis of intracellular fluxes through the central carbon pathways was performed for each strain utilizing exponential phase data on extracellular components and assuming quasi-steady state for intermediate metabolites. The non-PTS strain had a higher flux through pyruvate kinase (PYK) and TCA cycle which, in agreement with the observed higher oxygen uptake rate, suggests that more carbon was oxidized to CO2 through the TCA cycle. Further analysis using rate expression data for PYK and NMR data for the intracellular metabolites identified the regulatory properties of PYK as the probable cause for lower intracellular PEP levels in PPA316/pSY130-14. 相似文献
5.
Jiwei Cui Yajun Wang Almar Postma Jingcheng Hao Leticia Hosta‐Rigau Frank Caruso 《Advanced functional materials》2010,20(10):1625-1631
The preparation of monodisperse polymer (polydopamine, PDA) capsules by a one‐step interfacial polymerization of dopamine onto dimethyldiethoxysilane (DMDES) emulsion droplets and removal of the DMDES templates with ethanol is reported. The diameters of the PDA capsules can be tailored from 400 nm to 2.4 µm by varying either the DMDES emulsion condensation time or the emulsion concentration used for templating. Further, capsules with defined nanometer‐scale shell thicknesses (ranging from ~10 to 30 nm) can be prepared by adjusting the emulsion concentration. This shell thickness can be increased by repeated interfacial polymerization of dopamine, with three cycles yielding capsules with a shell thickness of up to 140 nm (for a 0.6% v/v suspension). Functional substances, such as organically stabilized magnetic (Fe3O4) nanoparticles, quantum dots (CdSe/CdS), and hydrophobic drugs (thiocoraline), can be preloaded in the emulsion droplets, and following PDA coating and DMDES removal, these materials remain encapsulated in the polymer capsules. All of the unloaded and loaded PDA capsules are monodisperse and do not aggregate. This work provides new avenues for the preparation of polymer capsules with defined size and shell thickness and for the encapsulation of a range of hydrophobic substances. 相似文献
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K van Dam N Jansen P Postma P Richard G Ruijter M Rutgers HP Smits B Teusink J van der Vlag M Walsh 《Canadian Metallurgical Quarterly》1993,63(3-4):315-321
The control of enzymes and substrates on the flux through microbial metabolic pathways can be quantified in terms of flux control coefficients. In pathways involving group transfer, the summation theorem for flux control by the enzymes has to be modified: the sum of control by all enzymes is between 1 and 2. The phosphoenolpyruvate:glucose phosphotransferase system is such a pathway. Experimental determination of the control by the enzymes in this pathway is under way. The control of the enzymes on the glycolytic flux in yeast is low, with the possible exception of the uptake step. In Klebsiella pneumoniae potassium and ammonium ions can simultaneously be 'limiting', (i.e. have significant control on growth) at pH6, but not at pH8. This may be due to the fact that at pH8 the high-affinity potassium uptake system is absent. 相似文献