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排序方式: 共有643条查询结果,搜索用时 31 毫秒
631.
632.
633.
This article considers the problem of mixed convection stagnation-point flow towards a vertical plate embedded in a porous
medium with prescribed surface heat flux. It is assumed that the free stream velocity and the surface heat flux vary linearly
from the stagnation point. Using a similarity transformation, the governing system of partial differential equations is transformed
into a system of ordinary differential equations, before being solved numerically by a finite-difference method. The features
of the flow and the heat transfer characteristics are analyzed and discussed. It is found that dual solutions exist for both
buoyancy assisting and opposing flows. 相似文献
634.
The physico-chemical property data for l-glutamic acid in aqueous NaCl solutions were obtained at 0, 0.5, 1.0 and 2.0 mol·kg?1 NaCl and amino acid molalities from 0 to 0.0669 mol·kg?1 between 293.15 and 323.15 K. The influence of NaCl addition on the volumetric and viscometric properties of the amino acid has been studied. From the experimental densities, the apparent molar volumes and transfer volumes of l-glutamic acid in aqueous electrolyte solutions have been calculated. The viscosity data in the studied domain of amino acid molalities have led to the evaluation of the Falkenhagen and Jones–Dole viscosity coefficients of l-glutamic acid in NaCl aqueous solutions. The results have been discussed in terms of interactions occurring in the systems. 相似文献
635.
Wangsa Tirta Ismaya Khomaini Hasan Idar Kardi Amalia Zainuri Rinrin Irma Rahmawaty Satyawisnu Permanahadi Baiq Vera El Viera Gunawan Harinanto Shabarni Gaffar Dessy Natalia Toto Subroto Soetijoso Soemitro 《Applied biochemistry and biotechnology》2013,170(1):44-57
α-Amylase catalyzes hydrolysis of starch to oligosaccharides, which are further degraded to simple sugars. The enzyme has been widely used in food and textile industries and recently, in generation of renewable energy. An α-amylase from yeast Saccharomycopsis fibuligera R64 (Sfamy) is active at 50 °C and capable of degrading raw starch, making it attractive for the aforementioned applications. To improve its characteristics as well as to provide information for structural study ab initio, the enzyme was chemically modified by acid anhydrides (nonpolar groups), glyoxylic acid (GA) (polar group), dimethyl adipimidate (DMA) (cross-linking), and polyethylene glycol (PEG) (hydrophilization). Introduction of nonpolar groups increased enzyme stability up to 18 times, while modification by a cross-linking agent resulted in protection of the calcium ion, which is essential for enzyme activity and integrity. The hydrophilization with PEG resulted in protection against tryptic digestion. The chemical modification of Sfamy by various modifiers has thereby resulted in improvement of its characteristics and provided systematic information beneficial for structural study of the enzyme. An in silico structural study of the enzyme improved the interpretation of the results. 相似文献
636.
D. Dadarlat M. N. Pop O. Onija M. Streza M. M. Pop S. Longuemart M. Depriester A. H. Sahraoui V. Simon 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1129-1132
The front photopyroelectric configuration was applied to measure the thermal effusivity of some composite materials, inserted as backing layers in the detection cell. The technique is based on the scanning procedure of the coupling fluid’s thickness (TWRC method). Two particular composite materials were selected for investigation: (i) a liquid one: water based nanofluids with gold nanoparticles and (ii) a solid one: urea—fumaric acid (1:1) cocrystal. The thermal effusivity was found independent on the size and concentration of gold particles. Concerning the urea—fumaric acid cocrystal, the thermal effusivity value of the compound is different from the pure starting materials, indicating the formation of the compound. 相似文献
637.
C. Haţiegan M. Răduca D. Frunzăverde E. Răduca N. Pop G. R. Gillich 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1217-1221
This paper presents the modeling and simulation of the thermal analysis on the hydrogenerator stator winding. The insulation aging is predetermined first by the insulation temperatures that, in turn, are influenced by the environmental conditions and second by the speed increase of the high temperature chemical reaction in materials. By increasing the temperature in the electro-insulated material, many molecules enter in chemical reaction accelerating the insulation aging. The heat transfer is a natural process, caused by inner energy, between bodies with high temperature and bodies with lower temperature. This process can also take place between parts of the same body that have different temperatures. The heat is transmitted by conduction, convection, and radiation. The heat transfer and especially the thermal conduction are a domain in which the finite element method is successfully applied. The thermal conduction problems will be solved by the finite elements method. The analysis of the thermal transfer process was made using the modeling and simulation program with finite elements ANSYS, and the results of the simulations were compared with measurement values. The analyzed stator winding is supplied with high voltage of 11 kV that is used for a high power hydrogenerator. To realize the thermal analysis of the winding stator, the coil will be supplied with 11 kV. The results of the analysis on a prototype model present the thermal transfer in coil–insulation–air system when the coil is hot. 相似文献
638.
Adriana Cecilia Csakvari Cristian Moisa Dana G. Radu Leonard M. Olariu Andreea I. Lupitu Anca Ofelia Panda Georgeta Pop Dorina Chambre Vlad Socoliuc Lucian Copolovici Dana Maria Copolovici 《Molecules (Basel, Switzerland)》2021,26(13)
Cannabis sativa L. (hemp) is a plant used in the textile industry and green building material industry, as well as for the phytoremediation of soil, medical treatments, and supplementary food products. The synergistic effect of terpenes, flavonoids, and cannabinoids in hemp extracts may mediate the biogenic synthesis of metal nanoparticles. In this study, the chemical composition of aqueous leaf extracts of three varieties of Romanian hemp (two monoecious, and one dioecious) have been determined by Fourier-Transformed Infrared spectroscopy (FT-IR), high-performance liquid chromatography, and mass spectrometry (UHPLC-DAD-MS). Then, their capability to mediate the green synthesis of silver nanoparticles (AgNPs) and their pottential antibacterial applications were evaluated. The average antioxidant capacity of the extracts had 18.4 ± 3.9% inhibition determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and 78.2 ± 4.1% determined by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS™) assays. The total polyphenolic content of the extracts was 1642 ± 32 mg gallic acid equivalent (GAE) L−1. After this, these extracts were reacted with an aqueous solution of AgNO3 resulting in AgNPs, which were characterized by UV−VIS spectroscopy, FT-IR, scanning electron microscopy (SEM-EDX), and dynamic light scattering (DLS). The results demonstrated obtaining spherical, stable AgNPs with a diameter of less than 69 nm and an absorbance peak at 435 nm. The mixture of extracts and AgNPs showed a superior antioxidant capacity of 2.3 ± 0.4% inhibition determined by the DPPH• assay, 88.5 ± 0.9% inhibition as determined by the ABTS•+ assay, and a good antibacterial activity against several human pathogens: Escherichia coli, Klebsiella pneumoniae, Pseudomonas fluorescens, and Staphylococcus aureus. 相似文献
639.
Heat transfer over a stretching surface with uniform or variable heat flux in micropolar fluids is investigated in this Letter. The boundary layer equations are transformed into ordinary differential equations, and then they are solved numerically by a finite-difference method. The effects of the material parameter K, Prandtl number Pr, velocity exponent parameter m, and heat flux exponent parameter n on the heat transfer characteristics are studied. It is found that the local Nusselt number is higher for micropolar fluids compared to Newtonian fluids. 相似文献
640.
A. P. Yal’ch I. E. Mitropol’skii V. S. Buksar L. M. Markovich S. S. Pop 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2008,2(4):577-581
The characteristics of optical radiation produced under bombardment by ions (1–15 keV) and electrons (100–1000 eV) of a ruby surface are studied. Two broad bands with maxima at 330 and 450 nm attributed to defects of the crystal lattice are discovered in the spectral region of 200 to 800 nm. Characteristic radiation related to radiative relaxation of excited Cr3+ ions in the near-surface region of the crystal is observed. The dependence of the radiation intensity on the energy and current density of the bombarding particles is obtained experimentally. The degree of radiation polarization is determined. 相似文献