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排序方式: 共有666条查询结果,搜索用时 31 毫秒
1.
Gerhard Ströhmer 《Journal of Mathematical Fluid Mechanics》2006,8(1):36-63
This paper is concerned with the question of linear stability of motionless, spherically symmetric equilibrium states of viscous,
barotropic, self-gravitating fluids. We prove the linear asymptotic stability of such equilibria with respect to perturbations
which leave the angular momentum, momentum, mass and the position of the center of gravity unchanged. We also give some decay
estimates for such perturbations, which we derive from resolvent estimates by means of analytic semigroup theory. 相似文献
2.
Jessica Strömbro Peter Gudmundson 《International Journal of Solids and Structures》2008,45(22-23):5765-5787
In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strömbro, J., Gudmundson, P., 2008. Mechano-sorptive creep under compressive loading – a micromechanical model. International Journal of Solids and Structures 45 (9), 2420–2450.]. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined. 相似文献
3.
4.
The strain energies and through-space distances between the two bridgehead E atoms of a selection of 1,3-dimethyl-1,3-ditetrelbicyclo[1.1.1]pentanes
(tetrel E = Si, Ge or Sn) were examined by quantum chemical calculations at MP2 and B3LYP levels. The aim is to identify which
bridges lead to short through-space E,E distances, and simultaneously, to as low strain as possible. A short E,E distance
should improve through-space interaction, and a low strain should promote the thermal stability and possibly also facilitate
their synthesis. The bridges examined included CH2, CMe2, CtBu2, C(CH2)n (n = 2–4), O, NMe, S, PMe, SiMe2, GeMe2, and SnMe2. The calculations indicate that the phospha bridge is a good compromise providing reasonably low strain as well as E,E through-space
distances which are only longer than normal E–E single bonds by factors of 1.06–1.10.
This paper is dedicated to Professor Mitsuo Kira in recognition of his stimulating Si chemistry and his 2005 Wacker Award. 相似文献
5.
Veronica?StigssonEmail author G?ran?Kloow Ulf?Germg?rd Niclas?Andersson 《Cellulose (London, England)》2005,12(4):395-401
Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose
(CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst
for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted
in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in
the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage.
It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity. 相似文献
6.
The conduction mechanism in microcrystalline cellulose (MCC) tablets at varying relative humidity (RH) has been investigated by using the techniques of low frequency dielectric spectroscopy and transient current analysis at room temperature. The dependence on RH on the measured conductivity and charge carrier density indicates that a high-power-law-exponent percolation process of cations being conducted on water molecules occupying available 6-OH units on the cellulose chains is the dominating dc conduction mechanism at RH below 3 wt % of moisture content. The experimentally observed decrease in charge carrier mobility with increasing moisture content shows that protons and H3O+ ions that are being blocked at empty 6-OH sites also contribute to the charge transport process in cellulose at low moisture contents. 相似文献
7.
Two new zinc ion dependent oligonucleotide based artificial nucleases (OBAN's) have been synthesized. These consist of 2'-O-methyl modified RNA oligomers conjugated to 5-amino-2,9-dimethylphenanthroline (neocuproine)via a urea linker. OBAN 4 carries the catalytic group on a linker extending from the C-4 of an internal cytosine moiety. OBAN 5 has two neocuproine units attached, each to linkers extending from the C-5 position of uridine moieties, one placed internally and the other at the at the 5'-end of the oligonucleotide. The key step in the synthesis of the OBAN systems is conjugation of the catalytic group to the respective amino linkers of the modified oligonucleotides. This is achieved by first converting the 5-amino-2,9-dimethylphenanthroline to the phenylcarbamate. The reaction of this neocuproine phenylcarbamate with the oligonucleotide carrying one or two primary aliphatic amines in aqueous buffer (at pH 8.5) leads to nearly quantitative formation of the urea-linked conjugates. Both OBAN systems were found to cleave RNA in the bulged out regions formed from the non-complementary part of the target sequences, in the presence of Zn(II) ions. Differences in efficiency between these and previously reported systems are discussed. 相似文献
8.
Carola Griehl Dieter Ströhl Hans Jeschkeit Erich Kleinpeter 《Monatshefte für Chemie / Chemical Monthly》1992,123(6-7):647-654
Summary During the addition of amines to maleylamino acids in general -amino derivatives are formed. In order to change the reactivity within the vinylogous maleyl system we introduced the -benzylester group into the starting compound N-(cis--carboxyacryloyl)-phenylalanine methylester1. The obtained benzylester2 is adding benzylamine in -position yielding N-benzyl--aspartyl(-benzyl)-phenylalanine methylester4. The addition reaction was investigated by1H-NMR-spectroscopy. The structures of the compounds have been confirmed by elemental analysis, IR,1H-NMR and13C-NMR spectroscopy. 相似文献
9.
G. Strübel V. Rzepka-Glinder K. H. Grobecker K. Jarrar 《Fresenius' Journal of Analytical Chemistry》1990,337(3):316-319
Summary Heavy metals are incorporated in human urinary calculi during a complex pathological process. The trace metals cadmium, lead, chromium, nickel and mercury are determined with regard to significance in pathogenesis and therapy. The amounts of cadmium, lead and chromium were determined as well directly in the solid sample as after chemical digestion by Zeeman-GFAAS. Both analyzing techniques show corresponding results. Nickel could be determined after chemical digestion only, while mercury was determined by a solid sampling technique. The evaluation of the results of trace metal analysis in the pilot study of 11 urinary calculi showed increased amounts of lead and cadmium compared to the results of tartar and salivary calculi. 相似文献
10.
Strübing A Wittstock G Szargan R Werner G 《Analytical and bioanalytical chemistry》1996,356(3-4):274-278
Bismuth modified platinum electrodes are used for constant-potential amperometric determination of carbohydrates in flow systems. The monitored response is stable and reproducible over more than two days. An attempt is made to gain more detailed information about the characteristics of the modified layer by electrochemical methods and X-ray photoelectron spectroscopy. The response proved to be linear over the investigated concentration range (1.1–1200 mol/L) and detection limits for glucose and fructose were found to be 1.1 mol/L. 相似文献