Preparation of glucose oxidase immobilized in different carriers using radiation polymerization

Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry     

Dielectric and crystallization properties of massive amorphous selenium

The dielectric constant of amorphous selenium at 330kHz has been measured under vacuum as a function of time on different isothermsT _a. After a normal heating period, depending onT _a, the value of increases abruptly from 5.8 to a maximum (9.6 to 11) followed by a decrease to reach a constant value. The behaviour of the curves=f(t) is discussed in terms of the structural transformation in the amorphous matrix. The morphological changes during the spherulite growth of selenium are also discussed. The dielectric loss tan has been calculated during the crystallization stages using the mesurements of time-dependence of resistivityr(t). The crystallization kinetic parameters have also been computed from the variation of during the growth stage. A value of 1.2eV is obtained for the activation energy of the radial growth of selenium in the temperature range 90 to 140° C.     

A technical framework for light- handed regulation of cognitive radios - [Topics in radio communications]

Light-handed regulation is discussed often in policy circles, but what it should mean technically has always been a bit vague. For cognitive radios to succeed in reducing the regulatory overhead, this has to change. For us, light-handed regulation means minimizing the mandates to be met at radio certification and relying instead on incentives to deter bad behavior. We put forth a specific technical framework in which the certification mandates are minimal - radios must modulate their transmitted waveform to embed an identity fingerprint, and radios must obey certain go-to-jail commands directed toward their identities. More specifically, the identity is represented by a temporal profile of taboo time slots in which transmission is impossible. The fraction of taboo slots represents the overhead of this approach and determines how reliably harmful interference can be attributed to the culprit(s) responsible. Meanwhile, the fraction of time that innocent radios spend in jail is the overhead for the punishment system. The analysis is carried out in the context of a real-time spectrum market, but is also applicable to opportunistic use.     

Analysis of multiple-arm conical log-spiral antennas

AnN-arm log-spiral antenna may be excited inN - 1orthogonal modes ofN-tuple input. A rigorous solution to the spiral antenna of more than two arms is obtained by numerical solution of the integral equations. Results for a four-arm spiral, including current distribution, half-power beamwidth, beam orientation, and gain and phase centers, are presented. The propagation constant of the current waves along each spiral arm is found to be approximately the speed of light. An approximatek-betadiagram is given which may be used to estimate the size of the antenna for each mode of operation.     

Synthesis and characterization of binary copolymers of methyl methacrylate with glycidyl methacrylate and 2‐hydroxy ethyl methacrylate as carriers for cellulase

Cellulase was immobilized directly on methyl methacrylate‐glycidyl methacrylate copolymer (MMA‐co‐GMA) and methyl methacrylate‐2‐hydroxy ethyl methacrylate copolymer (MMA‐co‐HEMA) by covalent attachment and crosslinking methods. The properties of the immobilized cellulase were investigated and compared with those of the free one. For the assays carried out through crosslinking method at 25°C and pH 7, the retained activities were found to be 91.92% and 74.63%, respectively, for MMA‐co‐GMA and MMA‐co‐HEMA crosslinked with 0.1% of 1‐cyclohexyl‐3‐(2‐morpholino‐ethyl) carbodiimide metho‐p‐toluenesulfonate (CMCT), respectively. The immobilized cellulase had better stability and higher retained activities with respect to pH, temperature, and storage stability than the free one. In the repeated use experiments, the immobilized cellulase using (MMA‐co‐GMA)‐CMCT (0.1%) and (MMA‐co‐HEMA)‐CMCT (0.1%) did not change after 10 and eight times of repeated use and maintained 67% and 62% from their original activities after 25 times, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

添加超滤牛乳的拉斯干酪特性

拉斯干酪添加有超滤牛乳制得,该牛乳中乳固形物质量分数分别为对照样(纯牛乳)的1.4、1.6和2.0倍,成熟3个月.拉斯干酪显示了比对照样更高的干酪得率,其水分、脂肪质量分数和pH值与对照样的相似,在成熟期均呈下降趋势,但氮质量分数等均呈上升趋势,且以牛乳中乳固形物质量分数提高到对照样的1.6倍时最高.结果表明,乳固形物质量分数为对照样1.6倍时牛乳制得的拉斯干酪其感官特性最佳.     

Comparative study of the recovery of silver(I) from aqueous solutions with different chelating resins derived from glycidyl methacrylate

Glycidyl methacrylate (GMA) was polymerized in the presence of divinylbenzene (DVB). The GMA/DVB resin was immobilized with different chelating moieties containing nitrogen or sulfur donor atoms. The resins obtained [an amino‐bearing resin (RI), an amino/thiocarbamate‐bearing resin (RII), a triazole‐bearing resin (RIII), and an amino/thiol‐bearing resin (RIV)] were tested toward the recovery of Ag(I) from its aqueous solutions. The adsorption behavior of Ag(I) and the resin regeneration were studied. The sulfur‐containing resins showed higher uptake and lower elution efficiency than those containing nitrogen. The maximum uptake values were 1.20, 1.33, 1.40, and 2.86 mmol/g for RI, RII, RIII, and RIV, respectively. The mechanism of interaction between Ag(I) and the resins is also suggested. Regeneration was achieved with a 0.5N thiourea solution, acidified thiourea, or 0.5N H₂SO₄, where the resins were stable over five cycles. Elution efficiencies of 94–96 and 90–93% were achieved for the nitrogen‐ and sulfur‐containing resins, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 806–812, 2005     

Immobilization of β‐amylase using polyacrylamide polymer derivatives

Barley β‐amlyase was immobilized on two polymeric materials; poly(acrylamide–acrylic acid) resin [P(AM‐AAc)] and poly(acrylamide–acrylic acid–diallylamine–HCl) resin [P(P(AM‐AAc‐DAA‐HCl) using two different methods: covalent and cross‐linking immobilization. Thionyl chloride, used to activate the polymers for covalent immobilization, has the advantage that it is able to react with a number of surface groups of protein under very mild conditions. Cross‐linking with glutaraldehyde gave a higher coupling yield (approximately 70%) than covalent immobilization (approximately 20%). The activity and stability of the resulting biopolymers have been compared with those of free β‐amylase. The specific activity of the immobilized enzyme was significantly influenced by the amount of enzyme loaded onto the polymers, the optimal level being 3.5 mg g^?1 polymer. It was found that the immobilized β‐amylase stored at 4°C retained approximately 90% of its original activity after 30 days, whereas free β‐amylase stored in solution at 4°C retained only 47% of its activity after same period. The difference in long term stability was more significant when the enzyme was stored at room temperature; the immobilized enzyme maintained 40% of its activity after 30 days, whereas the residual activity of free enzyme was only 10%. Copyright © 2003 Society of Chemical Industry     

Review of Intelligent Grinding and Dressing Operations

With the increased use of advanced materials, grinding processes become a popular means in the processing of parts, particularly in fabricating products from brittle materials such as ceramics and composites. At present grinding appears to be the only practical and economical means of shaping the parts into the final products with fine surface finish, acceptable surface integrity, and high geometric accuracy (Kovach, J. (1987). Improved grinding of ceramic components. In: Proceedings of the Department of Defence, Machine Tool/Manufacturing Development Conference. AFWAL-TR-4137, Vol. 7, 72-100). In the machining of conventional materials, grinding is also usually used as a finishing operation when high accuracy and surface finish is required, and usually determines the major portion of the processing cost. Despite this importance and popularity, grinding still remains as one of the most difficult to control processes. Unlike machining processes where cutting is performed by a defined single/multiple cutting edge(s), grinding is performed by a number of abrasive grits, which are randomly oriented within a grinding wheel. Therefore, it is impossible to maintain or control the shape of these hard grits, which are active in the cutting process (Malkin, S. (1989). Grinding Technology, Theory and Applications of Machining with Abrasives, Chister, England: Ellis Horwood Limited; Okafor, A. C., Marcus, M., Tipirneni, R. (1990). Multiple sensor integration via neural networks for estimating surface roughness and bore tolerance in circular end milling. Transaction of NAMRI/SME 128-136). Grinding is a very complicated process, consisting of complex interactions between a large numbers of variables. These variables can be grouped into four major categories: (a) machine tool, (b) workpiece material, (c) grinding wheel, and (d) operating parameters (Allor, R. L. Whalen, T. J., Baer, J. R., Kumar, K. V. (1993). Machining of silicon nitride: experimental determination of process/property relationships. In: Proceedings of the International Conference on Machining of Advanced Materials. Washington, DC, 223-234; Lezanski, P., Rafalowicz, J., Jedrzejewski, J. (1993). An intelligent monitoring system for cylindrical grinding. Annals of the CIRP 42(1):393-396; Li, K., Liao, T. W. (1997). Modelling of ceramic grinding processes, number of cutting points and grinding forces per grit. Journal of Materials Processing Technology 65(1-3):1-10). The dressing and truing processes used to prepare the wheel have an important effect on the grinding wheel variables and consequently on the output of the grinding process. To achieve this understanding, many researchers focused on the modeling of grinding processes. Some of these models are completely theoretical, and others are practical with theoretical explanations and empirical equations. The aim of this research was to find the relationship between the process variables, the process parameters, and workpiece quality. This review presents the theoretical and experimental models used, process design algorithms, expert systems, artificial intelligent algorithms, fuzzy logic and neural network algorithms, process monitoring and control, and in particular artificial intelligence control systems.