Nonbonded interactions in membrane active cyclic biopolymers. II. Ion binding by valinomycin

A possible mode for the capture of a cation by the carrier molecule valinomycin has been simulated. The intramolecular nonbonded energy and the binding energy for a centrally located potassium ion at different stages in the capture process have been evaluated using a method proposed earlier. Contrary to intuitive expectations the open conformation of valinomycin is also found to have a strong affinity for K⁺. There appears to be a rather high potential barrier between the open and closed symmetric conformations.     

Study of degraded neutron spectra through metal matrix composites using CR-39 films

Considerable interest has grown in the last decade in the use of CR-39 films in routine neutron monitoring and dosimetry. In addition, work in neutron spectrometry has been undertaken by various workers (Decossas et al., 1984; Faermann et al., 1983; Fews et al., 1984; Turner et al., 1984). In the present study metal matrix composites (MMC) samples of Pb-Li, Pb-Cd, Al-Li and Al-B₄C were prepared by using powder metallurgy and alloying elements techniques. The density was obtained for these MMC samples in the range of 80-90% of the metal density. Degraded neutron spectra were obtained by exposing these samples to a ²⁵²Cf source housed in a camera and the detector used was CR-39 films covered with a 1 mm PE radiator. These spectra have also been validated through Monte Carlo Neutron and Photon Transport Code (1983).     

Effect of MgO nanoparticles on ionic conductivity and electrochemical properties of nanocomposite polymer electrolyte

This paper analyzes the comparison between the performances and morphologies of the PMMA gel and composite electrolyte membrane with nanosized MgO particles. These polymer electrolytes were studied in detailed using XRD, DSC, SEM and AC impedance analysis. The conductivity enhancement has been attributed to the addition of ceramic filler that yields a significant increase of surface to volume ratio related to the decrease in glass transition temperature values in the composite polymer electrolyte. Good interfacial stability at the electrode/electrolyte interface resulted on account of the improved ion dissociation by ceramic filler and a rise in the room temperature conductivity (8.14 × 10⁻³ S cm⁻¹) due to the iono-covalent or Lewis acid–base bonds to the ions and ether oxygen base groups was also observed. Further enhancement of conductivity has been observed on MgO surface, as Lewis-acidic sites interact with both PMMA and ClO₄⁻ ions. The percentage of swelling was found to increase with increasing soaking periods upto 12 h. Beyond that soaking period, it was found that there was a negligible increase in the % of swelling.     

Weyl multipliers for invariant Sobelev spaces

A concrete characterization for theL ^P -multipliers (1<p<∞) for the Weyl transform is obtained. This is used to study the Weyl multipliers for Laguerre Sobolev spacesW ^m,p (? ⁿ ). A dual space characterization is obtained for the Weyl multiplier classM _W (W _L ^m,1 (? ⁿ )).     

Automatic acoustic synthesis of human-like laughter

A technique to synthesize laughter based on time-domain behavior of real instances of human laughter is presented. In the speech synthesis community, interest in improving the expressive quality of synthetic speech has grown considerably. While the focus has been on the linguistic aspects, such as precise control of speech intonation to achieve desired expressiveness, inclusion of nonlinguistic cues could further enhance the expressive quality of synthetic speech. Laughter is one such cue used for communicating, say, a happy or amusing context. It can be generated in many varieties and qualities: from a short exhalation to a long full-blown episode. Laughter is modeled at two levels, the overall episode level and at the local call level. The first attempts to capture the overall temporal behavior in a parametric model based on the equations that govern the simple harmonic motion of a mass-spring system is presented. By changing a set of easily available parameters, the authors are able to synthesize a variety of laughter. At the call level, the authors relied on a standard linear prediction based analysis-synthesis model. Results of subjective tests to assess the acceptability and naturalness of the synthetic laughter relative to real human laughter samples are presented.     

A new intramolecular charge transfer receptor as a selective ratiometric ‘off-on’ sensor for Zn

A new intramolecular charge transfer (ICT) probe 3 is found to display a highly selective photophysical response in the presence of Zn²⁺, among various biologically significant metal ions examined. The absorption band of 3 is red shifted by 84 nm and the fluorescence intensity increases 13-fold in the presence of Zn²⁺. The binding interaction follows the order Zn²⁺ > Cd²⁺ > Mg²⁺ > Ba²⁺ > Ca²⁺ > K⁺ ≅ Na⁺ ≅ Li⁺ and the stability constant for 3 + Zn²⁺ is over an order of magnitude higher compared to biologically competing Ca²⁺ and Mg²⁺.     

Electronic excitations of fluoroethylenes

Several lowest-lying singlet electronic states of vinyl fluoride, trans-, cis-, and 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene were investigated by using symmetry-adapted cluster configuration interaction theory. Basis sets up to Dunning's aug-cc-pVTZ augmented with appropriate Rydberg functions were utilized for the calculations. Calculated excitation energies show a good agreement with the available experimental values. Even in the troublesome pi-->pi(*) transitions, the excitation energies obtained in the present study agree well with the experimental values except in one or two fluoroethylenes. Strong mixing between different states was noticed in a few fluoroethylenes; especially the mixing is very strong between pi-pi(*) and pi-3ppi states in trifluoroethylene. No pure pi-sigma(*) excited state was found in almost all the fluoroethylenes. Several assignments and reassignments of features in the experimental spectra were suggested. The present study does not support the existing argument that the interaction between the pi-pi(*) and sigma-sigma(*) states is the reason behind the blueshift of around 1.25 eV in the pi-pi(*) excitation energy of tetrafluoroethylene. Possible reasons, including structural changes, for this shift are discussed in detail. Several low-lying triplet excited states were also studied.     

Riesz transform and Riesz potentials for Dunkl transform

Analogues of Riesz potentials and Riesz transforms are defined and studied for the Dunkl transform associated with a family of weight functions that are invariant under a reflection group. The L^p$L^p$ boundedness of these operators is established in certain cases.     

Evolution of intermolecular structure and dynamics in supercritical carbon dioxide with pressure: an ab initio molecular dynamics study

The effect of pressure on supercritical carbon dioxide (scCO2) has been characterized by using Car-Parrinello molecular dynamics simulations. Structural and dynamical properties along an isotherm of 318.15 K and at pressures ranging from 190 to 5000 bar have been obtained. Intermolecular pair correlation functions and three-dimensional atomic probability density map calculations indicate that the local environment of a central CO2 molecule becomes more structured with increasing pressure. The closest neighbors are predominantly oriented in a distorted T-shaped geometry while neighbors separated by larger distances are likely oriented in a slipped parallel arrangement. The structure of scCO2 at high densities has been compared with that of crystalline CO2. The probability distributions of intramolecular distances narrow down with increasing pressure. A marginal but non-negligible effect of pressure on the instantaneous intramolecular OCO angle is observed, lending credence to the idea that intermolecular interactions between CO2 molecules in an inhomogeneous near neighbor environment could contribute to the observed instantaneous molecular dipole moment. The extent of deviation from a perfect linear geometry of the carbon dioxide molecule decreases with increasing pressure. Time constants derived from reorientational time correlation functions of the molecular backbone compare well with experimental data. Within the range of thermodynamic conditions explored here, no significant changes are observed in the frequencies of intramolecular vibrational modes. However, a blue shift is observed in the low-frequency cage rattling mode with increasing pressure.     

Optimal Control of Batch MMA Polymerization with Specified Time,Monomer Conversion,and Average Polymer Molecular Weights

Summary: In this paper, the optimal control policies are determined for the free-radical polymerization of methyl methacrylate (MMA) in a non-isothermal batch reactor. The temperature of the fluid inside reactor-jacket is used as the control function to realize four different optimal control objectives. Each objective is formulated to optimize a given variable simultaneously specifying another. The first two objectives target the maximization of monomer conversion in a specified operation time, and the minimization of operation time for a specified, final monomer conversion. The last two objectives target the maximization of monomer conversion for specified, final number- and weight-average polymer molecular weights. The realization of these objectives is expected to be very useful for the batch production of polymers. To meet the specification of an optimization variable other than time, the differential model of batch process is expressed and utilized in the range of specified variable. Equations are provided for Jacobian evaluations to help in the accurate solution of process model. A genetic algorithms-based optimal control method is applied to realize the four optimal control objectives. The results of this application show considerable improvements in the performance of batch MMA polymerization.