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71.
Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers 总被引:4,自引:0,他引:4
Controlled chemical modification of enzymes, targeting groups not involved
in the active site, can lead to modified catalysts that are intrinsically
more efficient and resistant to heat and denaturing agents. Bovine
pancreatic trypsin was covalently modified up to 75-85% with monomeric
glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and
oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in
activity occurred upon modification. Temperature optima of trypsin shifts
from 45-76 degrees C and T50 from 54-76 degrees C for the best modified
sample made with OSP. The efficiency of the modifiers in stabilization was
ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T >
Sucrose-T. Half-life of modified enzymes also followed the same trend. Both
stabilization factor and t1/2 decreased with increasing temperatures. The
free energy of activation for inactivation delta(deltaG*) varies from 12-20
kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin
by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin
by urea is less noticeable. The character of the two-step inactivation
process of trypsin changes with the degree of stabilization in that the
duration of phase I one increased noticeably as stabilization increases.
Native trypsin fluoresces less intensely showing a red shift under the
influence of denaturation. Such a fluorescence change is not so obvious for
the modified enzymes indicating conformational stability acquired by
modification.
相似文献
72.
Shahram Emami Venkatesh Meda Robert T. Tyler 《International Journal of Food Science & Technology》2011,46(2):421-428
The effect of micronisation (high‐intensity infrared heating) and microwave radiation of normal barley (NB), high‐amylose barley (HAB) and waxy barley (WB) on the physical and mechanical properties was studied. Samples were tempered to 42–45% moisture content and then subjected to infrared or microwave radiation to reduce the moisture content to approximately 10%. The grain surface temperature during radiation was maintained at 100 °C. The changes in physical and mechanical properties were compared with unprocessed samples. Thermal radiation increased slightly the volume of the kernels because of the diffusion of water vapour from inside to the outer surface. These changes resulted in a decrease in particle and bulk densities. Thermal radiation affected the Hunter colour values, as well. The mechanical properties including bio‐yield point, modulus of elasticity and breakage susceptibility were affected by micronisation and microwave heating. 相似文献
73.
Suddhasattwa Ghosh S. Vandarkuzhali Nibedita Gogoi P. Venkatesh G. Seenivasan B. Prabhakara Reddy K. Nagarajan 《Electrochimica acta》2011,(24):8204
The anodic dissolution of U and Zr metal was studied in LiCl–KCl–UCl3 and LiCl–KCl–ZrCl4, respectively, at 773 K by cyclic voltammetry and compared with their respective dissolution behaviour in blank LiCl–KCl eutectic. The anodic dissolution of U–Zr alloy in LiCl–KCl–UCl3 was also studied at 773 K to compare with the dissolution of U and Zr. The transfer coefficients evaluated by Tafel analysis and the method of Allen–Hickling for U and Zr dissolution were found to be in fair agreement with each other. U dissolution in LiCl–KCl–UCl3 and Zr dissolution LiCl–KCl–ZrCl4 were also studied by chronoamperometry and the diffusion coefficient value of U3+ was calculated to be in the range of 2.9 × 10−5 to 3.3 × 10−5 cm2 s−1 which is in agreement with those reported in literature. Convolution voltammetric analysis of Zr4+/Zr2+ redox couple in LiCl–KCl–ZrCl4 was carried out for the first time to have a comprehensive understanding of the electrode kinetics. 相似文献
74.
Chemical mechanical polishing (CMP) of copper in ammonium hydroxide based slurry in the presence of hydrogen peroxide was
investigated. The polishing trend was found to be similar to that exhibited by other slurries containing hydrogen peroxide
and various complexing agents used for Cu CMP. When the hydrogen peroxide concentration is increased, the polish rate increases,
reaches a maximum and then decreases. The location and the magnitude of the maximum depend on the ammonium hydroxide concentration.
The dissolution of copper in the NH4OH–hydrogen peroxide solution was probed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)
experiments. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to determine the mechanistic
reaction pathway of Cu dissolution in NH4OH–hydrogen peroxide system. Based on the RMA analysis, a four step catalytic mechanism with two adsorbed intermediate species
is proposed. 相似文献
75.
This paper discusses reliability issues in torsional MEMS varactor. Self-actuation due to high ac signals is analyzed, and solutions are proposed. The mode of failure at high actuation voltages is analyzed and established through experiments. Issues like stiction due to high voltages and effect of high residual stress are studied experimentally. 相似文献
76.
Learning pattern classification-a survey 总被引:3,自引:0,他引:3
Kulkarni S.R. Lugosi G. Venkatesh S.S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1998,44(6):2178-2206
Classical and recent results in statistical pattern recognition and learning theory are reviewed in a two-class pattern classification setting. This basic model best illustrates intuition and analysis techniques while still containing the essential features and serving as a prototype for many applications. Topics discussed include nearest neighbor, kernel, and histogram methods, Vapnik-Chervonenkis theory, and neural networks. The presentation and the large (though nonexhaustive) list of references is geared to provide a useful overview of this field for both specialists and nonspecialists 相似文献
77.
Fire Endurance of High Strength Concrete Columns 总被引:5,自引:0,他引:5
In buildings, fire represents one of the most severe environmental conditions, and therefore, should be properly accounted for in the design of high strength concrete (HSC) structural members. The increased use of HSC in buildings has raised concerns regarding the behavior of such concrete in fire. In particular, spalling at elevated temperatures, as identified in studies by a number of laboratories, is a main concern.In this paper, results from an experimental program on the fire resistance of HSC columns are presented. The factors that influence the thermal and structural behavior of HSC concrete columns under fire conditions are discussed. Data from this study indicate that the type of aggregate, concrete strength, load intensity, and detailing and spacing of ties have an influence on the fire resistance performance of HSC columns. Further, the test results show that tie configuration (bending of ties at 135°, ties and provision of cross ties) and closer tie spacing has a significantly beneficial effect on the fire resistance of HSC columns. The results presented will generate data on the fire resistance of HSC columns, and contribute to identifying the factors that influence the behavior of HSC columns. 相似文献
78.
The parameterized feedback vertex (arc) set problem is to find whether there are k vertices (arcs) in a given graph whose removal makes the graph acyclic. The parameterized complexity of this problem in general directed graphs is a long standing open problem. We investigate the problems on tournaments, a well studied class of directed graphs. We consider both weighted and unweighted versions. 相似文献
79.
The preparation and dielectric properties of potassium niobate tantalate (KTN) have been investigated with the aim of exploring the material's potential for ferroelectric tunable applications. The samples were prepared both by conventional sintering in air and by uniaxial hot pressing. A relative average density greater than 92% was obtained with both methods. An inhomogeneous Nb/Ta distribution was found in the samples prepared by both methods, but the inhomogeneity extent was lower in the hot-pressed samples. While both sintering processes resulted in ceramics of lower transition temperatures in comparison with the reported results on single crystals, a relative up shift of the temperature ( T max ) at which the dielectric constant is maximum was found for hot-pressed samples compared with that of samples sintered in air. All the samples exhibited strong frequency dispersion in dielectric properties. The effect of DC bias at room temperature was measured and modeled using the Landau–Devonshire model. It was found that the nonlinear coefficient β of KTN, which is important for tunable applications, is comparable with the value reported on KNbO3 and SrTiO3 single crystals. A dielectric tunability of 16% and 42% at room temperature was demonstrated under 20 kV/cm for the sintered and hot-pressed ceramics, respectively. The loss tangent, low at megahertz frequencies, was augmented to 9%–17% at low gigahertz frequencies. This is believed to be related to the frequency dispersion observed in the ceramics because of charged defects. 相似文献
80.
Long Range Self‐Assembly of Polythiophene Breath Figures: Optical and Morphological Characterization
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Prahlad K. Routh Dmytro Nykypanchuk T. A. Venkatesh Mircea Cotlet 《Advanced functional materials》2015,25(37):5902-5909
Large‐area, device relevant sized microporous thin films are formed with commercially available polythiophenes by the breath figure technique, a water‐assisted micropatterning method, with such semitransparent thin films exhibiting periodicity and uniformity dictated by the length of the polymer side chain. Compared to drop‐casted thin films, the microporous thin films exhibit increased crystallinity due to stronger packing of the polymer inside the honeycomb frame. 相似文献