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排序方式: 共有678条查询结果,搜索用时 187 毫秒
91.
92.
H. Din C. J. Gray J. C. Ireson R. McDonald 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1991,50(2):181-189
T-Butyloxycarbonyl-α-aza-(4-aminophenyl)alanine phenyl ester (Fig. 1, III: R = NH2) has been synthesized. The rate of inhibition of trypsin (EC 3.4.21.4) by this compound (due to acylation followed by slower deacylation) shows a marked pH maximum at approximately 6. The shape of the pH—rate curve is discussed in terms of (i) the normal pH—activity curve of trypsin reacting with a charged substrate, i.e. the protonated form of the amino compound, (ii) the deprotonation of the 4-amino group with pKa 4·3, and (iii) the lower rate of reaction of the enzyme with the uncharged, deprotonated form of the ester. 相似文献
93.
The results of galvanostatic polarization experiments on four 17.3% Cr / 5.3% Ni stainless steels containing increasing amounts of Mn (upto 13.9%) are compared with those of an 18/8 stainless steel. All alloyes exhibit an initial step for the dissolution of Fe. A second arrest is recorded in dilute acid solutions and/or when applying high currents, and is related to the oxidation of the Cr. With an alloy containing traces of N2, a third arrest is observed in dilute acid solutions; it is attributed to the oxidation of Cr2N. The incorporation of Mn in CrNi steels is detrimental to their anti-corrosion characteristics. The content of this metal should be kept as low as feasible. 相似文献
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96.
We present in this letter a blind frame synchronization method based on a Maximum A Posteriori probability (MAP) approach. Applied to coded communication systems, this method is based on the calculation of the Log-likelihood Ratios (LLR) of the syndrome obtained according to the parity check matrix of the code. After presenting the proposed method, we compare it to an existing blind synchronization method previously introduced. Simulation results show that the proposed method outperforms the existing one and presents good performance when applied to codes having a sparse parity check matrix such as Low Density Parity Check (LDPC) codes and convolutional codes. 相似文献
97.
Z. Perić A. Jovanović O. Milanović V. Manojlović M. Dinčić 《Journal of Communications Technology and Electronics》2009,54(12):1384-1396
The logarithmic companding technique has shown to be extremely useful in speech quantization with rate of 8 bits/sample. However,
for lower bit rates it is not the ideal solution for high quality speech coding. Because of that, in this paper we establish
source coding scheme which enables better spectrum efficiency for input that has a large dynamic range. Since our wish is
also to improve signal quality in comparison with quality defined with standards G.711 and G.712, we opt for adaptive technique
application to the speech coding. Our research shows that proper design of forward gain-adaptive polar quantization can enable
compression of about 1 bit/sample as well as significantly better quality than in case of using coder designed according to
standard G.711. Furthermore, performances can be sustained over the whole speech dynamic range. Also, if the requisite speech
quality is not supposed to be lower than G.712 standard quality, the achieved compression can be almost 1.5 bits/sample. Besides,
we propose knew simple encoding rule which can additionally reduce bit rate for 0.1 bit/sample. 相似文献
98.
Adsorption of cationic polyacrylamide onto sepiolite 总被引:3,自引:0,他引:3
The adsorption of PAM onto sepiolite from aqueous solutions has been investigated systematically as a function of some parameters such as calcination temperature of sepiolite, pH, ionic strength and temperature. The adsorption of cationic polyacrylamide (PAM) increases with pH from 5.50 to 11.00, temperature from 25 to 55 degrees C and ionic strength from 0 to 0.1molL(-1). The sepiolite sample calcined at 200 degrees C has a higher adsorption capacity than the other calcined samples. Adsorption isotherms of PAM onto sepiolite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. The zeta potentials of sepiolite suspensions have been measured in aqueous solutions of NaCl and different PAM concentrations and pH. From the experimental results: (i) pH strongly alters the zeta potential of sepiolite, (ii) sepiolite has an isoelectric point at about pH 6.6 in water and about pH 8 in 250mgL(-1) PAM concentration, (iii) PAM changes the interface charge from negative to positive for sepiolite. Effect of temperature on adsorption has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy. The dimensionless separation factor (R(L)) has shown that sepiolite can be used for adsorption of PAM from aqueous solutions. 相似文献
99.
Zuhaib F. Bhat James D. Morton Susan L. Mason Alaa El‐Din A. Bekhit Hina F. Bhat 《Comprehensive Reviews in Food Science and Food Safety》2019,18(4):1192-1208
Defined as meat cultured in a laboratory within a bioreactor under controlled artificial conditions, in vitro meat is a relatively recent area that has opened a whole universe of possibilities and opportunities for the meat sector. With improved chemical and microbial safety and varied options, in vitro meat has been proposed as a green, healthy, environmentally friendly, and nutritionally better product that is free from animal suffering and death. Cell culture and tissue culture are the most probable technologies for the development of this futuristic muscle product. However, there are many challenges in the production of a suitable product at an industrial scale under a sustainable production system and a great body of research is required to fill the gaps in our knowledge. Many materials used in the product development are novel and untested within the food industry and demand urgent regulatory and safety assessment systems capable of managing any risks associated with the development of cultured meat. The future of this product will depend on the actions of governments and regulatory agencies. This article highlights emerging biotechnological options for the development of cultured meat and suggests ways to integrate these emerging technologies into meat research. It considers the problems and possibilities of developing cultured meat, opportunities, ethical issues as well as emerging safety and regulatory issues in this area. 相似文献
100.
Semiconductors - This paper presents a finite-element-based two-dimensional numerical simulation study of the vertical channel engineering approaches for controlling the short-channel effects... 相似文献