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排序方式: 共有597条查询结果,搜索用时 15 毫秒
51.
Several studies have been carried out on the grinding characteristic of three species of common wheat (Triticum aestivum, ssp. vulgare). The three-day germinated kernels were pulverized in a micro hammer mill equipped with a changeable screen. The moisture of samples was 12% (w.b.). The results showed that the sprouting of wheat had a significant influence on the grinding process. The average particle size of the pulverized material obtained from the sprouted kernels was almost always significantly lower than those from the sound kernels. The highest changes were observed in the increase of the fraction of particles below a size of 200 μm, caused by sprouting. The sprouting caused a decrease in the value of specific grinding energy in all cultivars. Based on the parameters of screen openings and cultivar, the values of specific grinding energy ranged from 35.5 to 141.6 kJ kg−1 and from 41.4 to 164.3 kJ kg−1 for the sprouted and sound kernels, respectively. In addition, the other values of grinding energy indices confirmed that sprouting significantly reduced the grinding energy requirements. The average value of the grinding ability index was 3.9 and 4.8 kJ m−2 for the sprouted and sound wheat, respectively. Whereas, sprouting caused a decrease in the average value of the grinding index from 71.2 to 58.0 kJ kg−1 mm0.5. 相似文献
52.
Bielinski Dariusz Wrobel Aleksander M. Walkiewicz-Pietrzykowska Agnieszka 《Tribology Letters》2002,13(2):71-76
Silicon carbonitride (a-Si:N:C) films produced by remote plasma chemical vapor deposition (RP-CVD) were investigated. Tetramethyldisilazane as a single-source precursor and (H2+N2) upstream gas mixture for plasma generation were used. The influence of the upstream gas composition on the structure, density, mechanical and tribological properties of the films deposited on p-type Si (001) wafers (both heated—T
s
=300°C and unheated—T
s
=30°C) are reported. The H2 RP-CVD process was found to result in the formation of outstanding low friction (0.04) and high hardness (H=27-31 GPa) a-Si:N:C films exhibiting promisingly high H/E values. 相似文献
53.
Williams SM Brodbelt JS Marchand AP Cal D Mlinaric-Majerski K 《Analytical chemistry》2002,74(17):4423-4433
In the present study, electrospray ionization mass spectrometry is used to evaluate the metal-binding selectivities of an array of novel caged macrocycles for mercury(II), lead(II), cadmium(II), and zinc(II) ions. In homogeneous methanol/chloroform solutions as well as extractions of metals from aqueous solution by macrocycles in chloroform, it is found that the type of heteroatom (S, O, N), cavity size, and presence of other substituents influence the metal selectivities. Several of the macrocycles in this study bind mercury ion very selectively and efficiently in the presence of many other metal ions and have an avidity toward mercury that was tunable by the size and combination of heteroatoms in the macrocycle ring and the number of cage groups attached. The extraction mechanism was further investigated by determining the variation in extraction selectivity as a function of the counterions of the mercury salts. 相似文献
54.
Using Koopman's approach to classical dynamical systems we show that classical damping may be interpreted as the appearance of resonant states of the corresponding Koopman's operator. It turns out that simple classical damped systems give rise to discrete complex spectra. Therefore, the corresponding generalized eigenvectors may be interpreted as classical resonant states. 相似文献
55.
Hans‐Peter Heim 《大分子材料与工程》2002,287(11):773-783
Plastics processing companies can only meet up to present‐day quality requirements if they adopt systematic methods. This holds particularly true for the extremely stringent demands that are now placed on injection molding technology. Working on from a sound experimental basis, it is possible to define cause/effect correlations for two sets of empirical data (the current process conditions and the molded part attributes) for each quality variable by using a statistical process model. The process model enables the processor to calculate the effect of each individual combination of parameters in the experimental area and to perform an optimization. If it proves possible to describe the cause/effect correlation between the fluctuations in the molded part attributes and those in the process parameters by means of a statistical process model, then this can be used for the continuous monitoring of production. The statistical experimentation method and continuous process monitoring are grouped together to form the so‐called CPC concept, permitting traceable, gap‐free documentation of the quality data for a production chain. Three examples are set out to illustrate the possibilities for use of the CPC concept; these are then assessed on the basis of the benefit observed.
56.
Al-Lahham A Rohde V Heim P Leuchter R Veeck J Wunderlich C Wolf K Zimmermann M 《Yeast (Chichester, England)》1999,15(5):385-396
By complementation screening of a cadmium-sensitive Schizosaccharomyces pombe mutant deficient in phytochelatin synthesis, but with 44% of the wild-type glutathione content, we cloned a DNA fragment involved in phytochelatin synthesis. Sequence analysis revealed that it encodes the second enzyme involved in glutathione (GSH) biosynthesis, glutathione synthetase (GSH2) (E.C.6.3.2.3, Wang and Oliver, 1997). The mutant allele shows a single base-pair exchange at the 3' end of the reading frame leading to a single amino acid change from glycine to aspartate. This mutation leads to a significant reduction of phytochelatin synthesis, whereas glutathione synthesis is impaired to a far lesser extent. Complementation with the Arabidopsis thaliana GSH2 cDNA led to a partial restoration of phytochelatin synthesis. These data strongly suggest that the GSH2 gene encodes a bifunctional enzyme that is able to catalyse both the synthesis of GSH by adding glycine to the dipeptide (gammaGlu-Cys) and the synthesis of phytochelatins. The sequence has been submitted to EMBL, Accession No. Y08414. 相似文献
57.
58.
The necessity of magnetically levitating a superconducting, current carrying ring without mechanical supports requires an electrical stabilizing system. The ring, when supported, has only one equilibrium position and this position is one of unstable equilibrium. The ring is free to move with up to six degrees of freedom. Two degrees are dictated by the ability of the ring to move in any direction in the plane of the ring. Additionally, the ring can be tilted requiring three more reference points to determine a new plane. The sixth degree of freedom is the ability of the ring to rotate upon its own axis, but because external forces tending to cause this rotation can, in principal, be eliminated, a restoring supply is not provided. Each of the five identical stabilizing supplies in this system has a feedback loop composed of the following segments. The position detector element is an optical head which sends a light beam across an optical edge on the ring, the reflection of which is sensed on a photo diode. This diode voltage signal, proportional to the ring position, is the input to an amplifier whose output is a signal proportional to position, velocity and ring acceleration. A 50 volt, 100 ampere, bidirectional dc transistor power supply is activated from this signal which in turn powers the appropriate stabilizing coil located near the floating current carrying ring. 相似文献
59.
We present an approach based on three-dimensional Monte Carlo radiative transfer simulations for estimating scattering error in measurements of light absorption by aquatic particles with a typical laboratory double-beam spectrophotometer. The scattering error is calculated by combining the weighting function describing the angular distribution of photon losses that are due to scattering on suspended particles with the volume scattering function of particles. We applied this method to absorption measurements made on marine phytoplankton, a diatom Thalassiosira pseudonana and a cyanobacterium Synechococcus. Assuming that the scattering phase function is described by the Henyey-Greenstein formula, we determined the backscatter probability of phytoplankton, which yields the best correction for scattering error at a light wavelength of 750 nm, where true absorption is null. The backscattering ratio estimated for both phytoplankton species is significantly higher than previously reported data based on Mie-scattering calculations for homogeneous spheres. Depending on the type of particles, the corrected absorption spectra obtained with our method may be similar or significantly different from spectra obtained with the null-point correction based on wavelength-independent scattering error. 相似文献
60.
The present methodological development and the primary application field originate from diffusion tensor imaging (DTI), a powerful nuclear magnetic resonance technique which enables the quantification of microscopical tissue properties. The current analysis framework of separate voxelwise regressions is reformulated as a 3D space-varying coefficient model (SVCM) for the entire set of diffusion tensor images recorded on a 3D voxel grid. The SVCM unifies the three-step cascade of standard data processing (voxelwise regression, smoothing, interpolation) into one framework based on B-spline basis functions. Thereby strength is borrowed from spatially correlated voxels to gain a regularization effect right at the estimation stage. Two SVCM variants are conceptualized: a full tensor product approach and a sequential approximation, rendering the SVCM numerically and computationally feasible even for the huge dimension of the joint model in a realistic setup. A simulation study shows that both approaches outperform the standard method of voxelwise regression with subsequent regularization. Application of the fast sequential method to real DTI data demonstrates the inherent ability to increase the grid resolution by evaluating the incorporated basis functions at intermediate points. The resulting continuous regularized tensor field may serve as basis for multiple applications, yet, ameloriation of local adaptivity is desirable. 相似文献