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.     

Applying Dynamic Training‐Subset Selection Methods Using Genetic Programming for Forecasting Implied Volatility

Volatility is a key variable in option pricing, trading, and hedging strategies. The purpose of this article is to improve the accuracy of forecasting implied volatility using an extension of genetic programming (GP) by means of dynamic training‐subset selection methods. These methods manipulate the training data in order to improve the out‐of‐sample patterns fitting. When applied with the static subset selection method using a single training data sample, GP could generate forecasting models, which are not adapted to some out‐of‐sample fitness cases. In order to improve the predictive accuracy of generated GP patterns, dynamic subset selection methods are introduced to the GP algorithm allowing a regular change of the training sample during evolution. Four dynamic training‐subset selection methods are proposed based on random, sequential, or adaptive subset selection. The latest approach uses an adaptive subset weight measuring the sample difficulty according to the fitness cases' errors. Using real data from S&P500 index options, these techniques are compared with the static subset selection method. Based on mean squared error total and percentage of non‐fitted observations, results show that the dynamic approach improves the forecasting performance of the generated GP models, especially those obtained from the adaptive‐random training‐subset selection method applied to the whole set of training samples.     

Selective Recovery of Cadmium,Cobalt, and Nickel from Spent Ni–Cd Batteries Using Adogen® 464 and Mesoporous Silica Derivatives

Spent Ni–Cd batteries are now considered an important source for many valuable metals. The recovery of cadmium, cobalt, and nickel from spent Ni–Cd Batteries has been performed in this study. The optimum leaching process was achieved using 20% H₂SO₄, solid/liquid (S/L) 1/5 at 80 °C for 6 h. The leaching efficiency of Fe, Cd, and Co was nearly 100%, whereas the leaching efficiency of Ni was 95%. The recovery of the concerned elements was attained using successive different separation techniques. Cd(II) ions were extracted by a solvent, namely, Adogen^® 464, and precipitated as CdS with 0.5% Na₂S solution at pH of 1.25 and room temperature. The extraction process corresponded to pseudo-2nd-order. The prepared PTU-MS silica was applied for adsorption of Co(II) ions from aqueous solution, while the desorption process was performed using 0.3 M H₂SO₄. Cobalt was precipitated at pH 9.0 as Co(OH)₂ using NH₄OH. The kinetic and thermodynamic parameters were also investigated. Nickel was directly precipitated at pH 8.25 using a 10% NaOH solution at ambient temperature. FTIR, SEM, and EDX confirm the structure of the products.     

Evaluating leakages through GMB/GCL composite liners considering random hole distributions in wrinkle networks

This paper presents a study on the development of a hydraulic connectivity analysis-based approach for evaluating leakage rates through geomembrane (GMB)-geosynthetic clay liner (GCL) composite liners considering random hole distributions in a GMB wrinkle network. An algorithm for hydraulic connectivity analysis was developed to find the hydraulically connected wrinkles from a wrinkle network, and an explicitly expressed criterion is proposed to define the hydraulic connection between wrinkles under the assumption that only one of the two adjacent wrinkles is possible to be damaged. A Monte Carlo simulation was used to evaluate the probability weighted average of the total leakage through multiple randomly distributed holes considering numerous possible combinations of locations of holes. The proposed approach was applied to typical examples reported in the literature and shows that it can objectively quantify the effect of the hydraulic properties of the liner and overburden pressure on the hydraulic connectivity between wrinkles in a wrinkle network. The proposed approach also allowed assessing the effect of different probabilities of various hole distributions on the calculated leakage, which was demonstrated to be non-negligible, especially when the hole frequency is small.     

Spray drying of drug-swellable dispersant suspensions for preparation of fast-dissolving,high drug-loaded,surfactant-free nanocomposites

Bioavailability of a poorly soluble drug can be improved by preparing a drug nanosuspension and subsequently drying it into nanocomposite microparticles (NCMPs). Unfortunately, drug nanoparticles aggregate during milling and drying, causing incomplete recovery and slow dissolution. The aim of this study is to investigate the impact of various classes of dispersants on drug dissolution from drug NCMPs, with the ultimate goal of enhancing the bioavailability of poorly water-soluble drugs via high drug nanoparticle loaded, surfactant-free NCMPs. Precursor suspensions of griseofulvin (GF, model drug) nanoparticles in the presence of various dispersants were prepared via wet stirred media milling and spray dried to form the NCMPs. Hydroxypropyl cellulose (HPC, polymer) alone and with sodium dodecyl sulfate (SDS, surfactant) was used as a base-line stabilizer/dispersant during milling. Two swellable crosslinked polymers, croscarmellose sodium (CCS) and sodium starch glycolate (SSG), and a conventional soluble matrix former, Mannitol, were used in addition to HPC. Besides being used as-received, CCS was also wet co-milled with GF for two different durations to examine the impact of CCS particle size. Laser diffraction, scanning electron microscopy, powder X-ray diffraction (XRD), UV spectroscopy, NCMP redispersion and dissolution tests were used for characterization. The results show that incorporation of CCS/SSG, preferably wet-milled to a wide particle size distribution, into the spray-dried NCMPs resulted in fast release and dispersion of drug nanoparticle clusters. The swellable dispersants were superior to Mannitol in dissolution enhancement, and could achieve fast release comparable to SDS, demonstrating the feasibility of spray drying to prepare high drug-loaded, surfactant-free nanocomposites.     

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.     

The Solutions on One-Dimensional Dirac Oscillator with Energy-Dependent Potentials and Their Effects on the Shannon and Fisher Quantities of Quantum Information Theory

Journal of Low Temperature Physics - In this paper, we focus, at first, on the exact solutions on the one-dimensional Dirac oscillator with the energy-dependent potentials. Then, the influence of...     

Optimal Heat Input for Estimating Luikov's Parameters in a Heat and Mass Transfer Problem

In this article, the problem of computing an optimal heat input in Luikov's heat and mass transfer problem is detailed and analyzed. The main objective is the establishment of an optimal time-dependent heat flux profile with the goal of maximizing the temperature and moisture sensitivities of some parameters to this excitation in a drying process. Such maximization makes the estimation of the desired parameters possible, easier, and with limited uncertainty intervals. It also helps to reduce the linearity dependence between the parameters of interest and the number of temperature and moisture sensors used. The estimation of the optimal heat input is obtained with Uzawa's algorithm, while the estimation of parameters is performed with Levenberg-Marquardt's method of minimization of the ordinary least-square criterion. The six dimensionless parameters characterizing Luikov's equations are estimated successfully with this optimal heat flux profile, which also helps to reduce the number of both temperature and moisture sensors needed in the estimation procedure. By doing so, the objective of estimating simultaneously the six parameters which appear in the formulation of Luikov's physical problem is reached by using a limited transient temperature and/or moisture measurements taken anywhere in the drying medium.