The role sol–gel process for nuclear fuels-an overview

The paper reviews the sol–gel methods used for the preparation of nuclear fuel materials in the form of microspheres. It also discusses how these microspheres can be fabricated into nuclear fuels for reactors such as High Temperature Gas Cooled Reactors and Fast Reactors. The performance of these microsphere-based fuels is reviewed. More recent applications, such as the transmutation of minor actinides, (Np, Am and Cm) and hydrogen production, are also briefly covered.     

Competition between hydrogen bonding and dispersion interactions in the indole···pyridine dimer and (indole)2···pyridine trimer studied in a supersonic jet

Structures of the indole···pyridine dimer and (indole)2···pyridine trimer have been investigated in a supersonic jet using resonant two-photon ionization (R2PI) and IR-UV double resonance spectroscopic techniques combined with quantum chemistry calculations. R2PI spectra of the dimer and the trimer recorded by electronic excitation of the indole moiety show that the red-shift in the band origin of the dimer with respect to the 0(0)(0) band of the monomer is larger compared to that of the trimer. The presence of only one conformer in the case of both the dimer and the trimer has been confirmed from IR-UV hole-burning spectroscopy. The structures of the dimer and the trimer have been determined from resonant ion dip infrared (RIDIR) spectra combined with ab initio as well as DFT/M05-2X and DFT/M06-2X calculations. It has been found that the dimer, observed in the experiment, has a V-shaped geometry stabilized by N–H···N and C–H···N hydrogen bonding interactions, as well as C–H···π and π···π dispersion interactions. The geometry of the trimer has been found to be a cyclic one stabilized by N–H···N, N–H···π, C–H···π, and C–H···N interactions. The most important finding of this current study is the observation of the mixed dimer and trimer, which are stabilized by hydrogen bonding as well as dispersion interactions.     

Influence of momentum-dependent interactions on balance energy and mass dependence⋆

We aim to understand the role of momentum-dependent interactions in transverse flow as well as in its disappearance. For the present study, central collisions involving masses between 24 and 394 are considered. We find that the momentum-dependent interactions have different impact in lighter colliding nuclei compared to heavier colliding nuclei. In lighter nuclei, the contribution of the mean field towards flow is smaller compared to heavier nuclei where binary nucleon-nucleon collisions dominate the scene. The inclusion of momentum-dependent interactions also explains the energy of the vanishing flow in the ¹²C + ¹²C reaction which otherwise was not possible with the static hard equation of state. An excellent agreement of our theoretical attempt is found for balance energy with experimental data throughout the periodic table.     

Competitive Multi-period Pricing for Perishable Products: A Robust Optimization Approach

We study a multi-period oligopolistic market for a single perishable product with fixed inventory. Our goal is to address the competitive aspect of the problem together with demand uncertainty using ideas from robust optimization and variational inequalities. The demand function for each seller has some associated uncertainty and we assume that the sellers would like to adopt a policy that is robust to adverse uncertain circumstances. We believe this is the first paper that uses robust optimization for dynamic pricing under competition. In particular, starting with a given fixed inventory, each seller competes over a multi-period time horizon in the market by setting prices and protection levels for each period at the beginning of the time horizon. Any unsold inventory at the end of the horizon is worthless. The sellers do not have the option of periodically reviewing and replenishing their inventory. We study non-cooperative Nash equilibrium policies for sellers under such a model. This kind of a setup can be used to model pricing of air fares, hotel reservations, bandwidth in communication networks, etc. In this paper we demonstrate our results through some numerical examples.     

Measurement of angular distribution of M shell fluorescent X-rays excited by 5·95 keV photons in thorium

The differential cross-sections for the emission of M shell fluorescent X-rays from Th by 5·95 keV photons at eight angles ranging from 50° to 120° have been measured. The differential cross-section is found to decrease with increase in the emission angle showing anisotropic spatial distribution of M shell fluorescent X-rays. The present results contradict the predictions of the calculations of Cooper and Zare [1] that the atomic inner shell vacancy states produced in photoionization are not aligned but confirm those of Fluggeet al [2] and Scofield [3] that the vacancy states withJ > 1/2 are aligned. The integral M shell fluorescent emission cross sections have been determined from the measured angular distribution coefficients and compared with theoretical integral cross-sections calculated by using theoretical values of M subshell photoionization cross-sections, fluorescence yields and coster kronig transition probabilities available in literature. The experimental and theoretical values of integral crosssections show a reasonable agreement.     

Pulsed laser heating calculations incorporating vapourization

We present a scheme for solution of the heat flow equation in one-dimension incorporating melting and vapourization produced under pulsed laser irradiation. The method can be applied to pure materials as well as multilayered structures such as deposited films. The variation of physical properties with temperature can be easily taken into account. Results of calculation are presented for aluminium and for chromium and antimony layers deposited on aluminium. As a consequence of excessive vapourization at high energy densities, the melt depth and the melt duration do not increase beyond a certain limit. The resolidification front velocity is strongly dependent on energy density and can be controlled in an experiment by a careful choice of laser parameters. Some recent experimental data on laser treated chromium films are discussed in light of our calculations.     

GeneralizedM-diffusion model of molecular rotations

The widely usedM-model of rotational diffusion of molecules in fluid phases is generalized. The ordinaryM-model assumes that intermolecular collisions causeinstantaneous changes in the orientation of an otherwise free rotor. The present scheme takes cognizance of the ubiquitous intermolecular torques which should make the molecular orientation a continuously variable random function of time. It is assumed here that the component of the angular velocity, which is conjugate to the angle specifying the orientation of the molecule, is a stationary Gaussian-Markov process. The ordinaryM-model emerges then as a special case of the more general treatment presented here. The results derived for the dipole correlation function of a linear rotor on the basis of the generalized scheme are applied to a series of infrared data. The observed agreement is highly satisfactory. The present analysis affords a justification for the Gordon scheme which generalizes theM-model by assigning to the mean rate of collision anad-hoc dependence on the angular speed of the rotor. It is argued also that the model treated here incorporates certain memory effects which are ignored in the ordinaryM-model, and may yield, in some cases, results which are similar to those based on certain memory function formalisms.