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排序方式: 共有361条查询结果,搜索用时 15 毫秒
1.
Victor Chabanenko Roman Puźniak Adam Nabiałek Sergei Vasiliev Vladimir Rusakov Loh Huanqian Ritta Szymczak Henryk Szymczak Jan Jun Janusz Karpiński Vitaly Finkel 《Journal of Low Temperature Physics》2003,130(3-4):175-191
We present a study of magneto-thermal instabilities in polycrystalline MgB2 superconductor, by magnetic hysteresis loop measurements and by investigations of magnetic flux dynamics with a miniature Hall probe. Temperature and magnetic field ranges where the flux jumps may be observed have been determined. On the basis of measurements of the magnetic flux dynamics, an average magnetic diffusivity describing the process of the flux jump is estimated. This parameter is compared with the thermal and magnetic diffusivities calculated on the basis of available data for thermal conductivity, heat capacity and resistivity. It is shown that the estimated value of the field of the first flux jump is influenced significantly by the field dependence of specific heat. In order to explain the observed phenomenon, the temperature reached by the sample during the flux jump at different magnetic fields is calculated. 相似文献
2.
The diffusion coefficient of the cationic dye Anilana Red BL in the anionically modified polyester fiber Dilana has been calculated regarding a general diffusion-immobilization model. In the model the mobile species are distinguished from the immobilized ones. In computations of Sand's equation and experimentally determined sorption isotherm of the dye in the fiber, the rate-of-dyeing curve and the concentration profiles of the dye in the same fiber were employed. The diffusion coefficient of the mobile species of Anilana Red BL in the fiber is two orders of magnitude higher than the average diffusion coefficient obtained from Hill's equation and the apparent diffusion coefficient calculated by the Boltzmann–Matano method. 相似文献
3.
Andrzej Malag Jacek Ratajczak Jerzy Gazecki 《Materials Science and Engineering: B》1993,20(3):332-338
Selective wet chemical etching of the AlxGa1−xAs/GaAs system has been applied to heterostructure characterization. Samples of LPE grown AlGaAs/GaAs laser double-heterostructures and separate confinement heterostructures as well as antiresonant reflecting optical waveguides heterostructures were treated with “I2 solution” (I2:KI:H2O) and hydrochloric acid. These compounds selectively etch the ternary AlxGa1−xAs layers, but with different “threshold composition” xth values (the x value is that above which the etching rate of a given compound increases sharply). Selectively etched samples have been examined by SEM. The experimental dependence of etching rate on the x value for I2 solution has been derived. From this dependence, the x composition of any ternary layer can be estimated simply. Observations were made of the “microscopic” properties of the heterostructure, such as the smoothness of the interfaces and the uniformity of layers. All imperfections resulting from the growth process, such as interface perturbations or compositional nonuniformity of layers, are clearly seen. An additional advantage of this etching technique is its simplicity. It allows quick examination of grown heterostructure for the selection of wafers for further processing. 相似文献
4.
Anna Michalska Alicja Ceglińska Henryk Zieliński 《European Food Research and Technology》2007,225(3-4):545-551
Rye flours with extraction rate of 100% (wholemeal flour), 95% (brown flour), 90% (brown flour) and 70% (light flour) were
prepared in order to study the relation between flour extraction rates and content of bioactive compounds. The following compounds
were analysed: total phenolic compounds (TPC), total flavonoids (TF), inositol hexaphosphate (IP6), reduced (GSH) and oxidized
(GSSG) glutathione, tocopherols (T) and tocotrienols (T3). The reduced/oxidized glutathione status (GSH/GSSG) of the flours
was examined as a potential index of flour resistance against oxidative stress. The following observations were made in relation
to the flour extraction rates and bioactive compounds contents: (a) milling process caused decrease in content in TPC, TF,
IP6, GSH and GSSG, T and T3, (b) the most resistant against oxidation processes were suggested a brown flours, then light
and finally wholemeal flour, (c) the ratio of tocotrienols to tocopherols (T3/T) was the highest in rye flours with extraction
rate of 100–90% whereas light flour was the poorest source of tocopherols and tocotrienols. The provided data support current
trend to increase number of rye products from wholemeal or brown flours. 相似文献
5.
MZ Ratajczak J Ratajczak DA Kregenow W Marlicz B Machalinski M Simon S Luger AM Gewirtz 《Canadian Metallurgical Quarterly》1997,2(2):5-11
Forty-one patients for whose direct care at least one machine was used and 33 registered nurses from the same five non-critical care units as the patients and from one related unit, participated in a semistructured tape-recorded interview to identify the core categories of the human-machine interface in clinical nursing practice and the relationships between them. Constant comparative analysis was used to organize and process the data. Patients perceived the machines as neutral because of their view of health care and because nurses were the interface between them and the machines. Nurses perceived the machines as either positive or negative, depending on their effect on the nurses' professional competence and the extent to which they worked directly with them. 相似文献
6.
P Wlodarski M Wasik MZ Ratajczak C Sevignani G Hoser J Kawiak AM Gewirtz B Calabretta T Skorski 《Canadian Metallurgical Quarterly》1998,91(8):2998-3006
Prompt reconstitution of hematopoiesis after cytoreductive therapy is essential for patient recovery and may have a positive impact on long-term prognosis. We examined the role of the p53 tumor suppressor gene in hematopoietic recovery in vivo after treatment with the cytotoxic drug 5-fluorouracil (5-FU). We used p53 knock-out (p53-/-) and wild-type (p53+/+) mice injected with 5-FU as the experimental model. Analysis of the repopulation ability and clonogenic activity of hematopoietic stem cells (HSCs) and their lineage-committed descendants showed a greater number of HSCs responsible for reconstitution of lethally irradiated recipients in p53-/- bone marrow cells (BMCs) recovering after 5-FU treatment than in the corresponding p53+/+ BMCs. In post-5-FU recovering BMCs, the percentage of HSC-enriched Lin- Sca-1(+) c-Kit+ cells was about threefold higher in p53-/- than in p53+/+ cells. Although the percentage of the most primitive HSCs (Lin- Sca-1(+) c-Kit+ CD34(low/-)) did not depend on p53, the percentage of multipotential HSCs and committed progenitors (Lin- Sca-1(+) c-Kit+ CD34(high/+)) was almost fourfold higher in post-5-FU recovering p53-/- BMCs than in their p53+/+ counterparts. The pool of HSCs from 5-FU-treated p53-/- BMCs was exhausted more slowly than that from the p53+/+ population as shown in vivo using pre-spleen colony-forming unit (CFU-S) assay and in vitro using long-term culture-initiating cells (LTC-ICs) and methylcellulose replating assays. Clonogenic activity of various lineage-specific descendants was significantly higher in post-5-FU regenerating p53-/- BMCs than in p53+/+ BMCs, probably because of their increased sensitivity to growth factors. Despite all these changes and the dramatic difference in sensitivity of p53-/- and p53+/+ BMCs to 5-FU-induced apoptosis, lineage commitment and differentiation of hematopoietic progenitors appeared to be independent of p53 status. These studies suggest that suppression of p53 function facilitates hematopoietic reconstitution after cytoreductive therapy by: (1) delaying the exhaustion of the most primitive HSC pool, (2) stimulating the production of multipotential HSCs, (3) increasing the sensitivity of hematopoietic cells to growth factors, and (4) decreasing the sensitivity to apoptosis. 相似文献
7.
A new method of preparation of carboxyl cation exchangers directly from methacrylic acid and divinylbenzene is described. A suspension technique with a concentrated aqueous calcium chloride solution as the water phase was used. n-Octane and toluene were inert diluents of the monomers. The copolymers obtained have high ion-exchange capacity (9.6–10.6 mequ./g) and porous structure. 相似文献
8.
The stereologic analysis of a solid grain has been applied for determination of its porosity. The investigations were carried out on a natural hematite grain reduced to magnetite at 723 K. Stereologic analysis enabled the porosity of this material to be determined on the basis of independently measured grain contours and volume fractions of grain components: hematite, magnetite and pores. A conformity criterion has been formulated, regarding determination of grain volume on the basis of known densities of components and their measured volume fractions in the grain, and on the basis of weight and apparent grain density measurements. The volume increase accompanying reduction of hematite to magnetite, determined from these independent measurements, was in the range 7–19%. By measuring Ferets diameter, the volume of the convex envelope of the grain increased as a result of phase transformation by about 11%. Simultaneously, the volume of the solid phase was found to decrease by 1.5%. The total porosity of the reduced grain, determined by stereologic analysis amounted to 17.5%; 7.7% of which was related to cracks and large pores, and 9.8% to small pores in the magnetite phase. The porosity value determined by the classical mercury method was approximately the same. 相似文献
9.
Brice T. Hughes Jordan M. Berg Darryl L. James Akif Ibraguimov Shaorong Liu Henryk Temkin 《Microfluidics and nanofluidics》2008,5(6):761-774
This paper presents a numerical steady-state model of ion transport in micro- and nanofluidic devices with widely varying
geometric scale, such as transitions between micro- and nanochannels. Finite element or finite volume simulation of such problems
is challenging, due to the number of elements needed to produce a satisfactory mesh. Here, only the lengthwise channel dimension
is meshed; standard analytical approximations are used to incorporate cross-channel properties. Singularly perturbed cases
are built up by continuation. The method is shown to reproduce our previously reported measurements of electric double-layer
effects on conductivity, ion concentration, and ion enhancement and depletion. Comparison with 2-D simulations reported in
the literature shows that effects on accuracy due to the 1-D approximation are small. The model incorporates analytical models
of surface charge density taken from the literature. This enables predictive simulation with reasonable accuracy using published
parameter values, or these values may be tuned based on experiment to give improved results. Use of the model for iterative
design and parameter estimation is demonstrated. 相似文献
10.
Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038–0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840–1200 °C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed. 相似文献