Water Gas Shift Reaction： A Monte Carlo Simulation

The water gas shift （WGS） reaction is reacts with water on a catalytic surface a process of industrial importance to form CO2 and H2. We study this In this reaction carbon monoxide reaction with thermal （Langmuir- Hinshelwood） and non-thermal （precursor and Eley-Rideal） reaction mechanisms using the techniques of Monte Carlo computer simulation. The details of surface coverages and production rates are given as a function of CO partial pressure. The diffusion of species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system have been drawn to observe the behaviour of reacting species on the surface. The study reveals that the production rates are higher for non-thermal precursor mechanism and are in agreement with the experimental finding.

Formation of Charged Particle Tracks in Solids

A criterion for formation of etchable tracks in solids is suggested using the well-known concepts of ionization and thermal spikes, diffusion process with useful and justified assumptions, and present or published experimental and theoretical investigations on the same subject. The suggested criterion is useful for a wide spectrum of researchers including development and applications of track recording materials, ions implantation, sputtering and other areas, which include interactions of charged particles with solids.

Monte Carlo Study of CO-NO Catalytic Surface Reaction Including CO-CO Repulsion

The CO-NO reaction on a catalytic surface is studied by using Langmuir-Hinshclwood thermal mechanism with Monte Carlo computer simulation. In this model, a novel concept of CO CO repulsion is introduced, which has experimental evidence due to the formation of dipoles when these molecules are chemisorbed on the surface. The system is investigated by applying two approaches of NO dissociation. In the first ca.se, NO always decomposes into N and O before adsorption on the surface, In the second case, NO adsorbs on the surface molecularly and then dissociates into N and O if a vacancy is present in its adjacent neighbourhood. The steady state reactive window （i.e. the continuous production of CO2 and N2） is obtained only with the diffusion of N-atoms on the surface, which extends with CO-CO repulsion in the first, case. Itowever, in the second case, reactive window is obtained with CO-CO repulsion alone, The reactive window width in this case is reasonably large. The first-order phase transition is eliminated in both the cases with CO-CO repulsion.

Re-estimation of absolute gamma ray intensities of ^(56)Mn using k_0-standardization

The thermal neutron capture gamma ray facility at Pakistan Research Reactor (PARR-1) is being used forthe re-estimation of various properties like capture cross-sections, resonance integral, absolute gamma intensities, etc.of different isotopes. The data for gamma ray transitions from the capture of thermal neutrons by 55Mn are not ingood agreement specifically below 2 MeV. So there is a need to re-estimate its intensities with better accuracy. Analyticalgrade MnCl2 powder and high purity Mn metal pieces were used in this study. Standard 152Eu and 60Co radioactivesources as well as thermal neutron capture γ-rays in chlorine were chosen for efficiency calibration. The k0standardization technique was applied for these measurements to eliminate systematic errors in efficiencies. Chlorinealso acted as a comparator in k0- factor calculations. The results have been tabulated for the main gamma rays from56Mn in the low as well as in the medium energy regions. The absolute intensities are in good agreement with most ofthe reported values.

Annihilation of Antiprotons in Light Nuclei

CR-39 detectors have been exposed to a 5.9-MeV antiproton beam using the low energy antiproton ring （LEAR） facility at CERN. At this energy, tracks of antiprotons appear in a CR-39 detector after 135 rain of etching in 6M NaOH at 70℃. Fluence of the antiproton beam has been determined using track density. We have also found tracks in the etched CR-39 detector at different depths （250-500μm）. These tracks have resulted from the annihilation of antiprotons with the constituents （H, C and O） of the CR-39 detector. The goal of the experiment is to develop a simple and low-cost method to study properties of antiparticles and those formed after annihilation of these particles with the target matter.

Synthesis and study the influence of yttrium doping on band structure,optical,non-linear optical and dielectric results for Ca_(12)Al_(14)O_(33) (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method

Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)single crystals were grown by using the traveling-solvent floating zone(TSFZ)method.The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material.We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface.The structures of both Ca_(12)Al_(14)O_(33)(C12A7)and Y_(0.02)Ca_(11.98)Al_(14)O_(33)(Y-C12A7)were studied by using x-ray diffraction(XRD).Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap(Eg),refractive index n,oscillating energy(Eo),dispersion energy(Ed),volume energy loss function(VELF),and surface energy loss function(SELF).Finally,a new result for these samples is that the third-order nonlinear optical susceptibility(χ(3))was determined.The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.

Mass Transfer： a Deciding Factor for the Multiplicity of an Event in Deep Inelastic Collisions

Intermediate stage of the three and four-pronged events is investigated in the reaction ^208Pb＋^197Au at beam energy 11.67 MeV/u. Multiprong events are analysed numerically using an empirical mass-dependent velocityrauge relation. Using the measured three-dimensional coordinates of correlated tracks, it is possible to determine the quantities such as mass transfer and total kinetic energy loss. These quantities are then used to study the intermediate stage of the reaction. It has been observed that mass transfer and total kinetic energy loss at the first step of the reaction decides the multiplicity of an event at the second stage of the sequential fission process.

Electroconductive Composites Containing Nanocellulose,Nanopolypyrrole,and Silver Nanoparticles

In this work,conducting composites of nanocellulose(NC)/polypyrrole nanoparticles(NPPy)and silver nanoparticles(AgNPs),i.e.,NC/NPPyAg,were synthesized for the first time,to the best of our knowledge,via in situ emulsion polymerization of pyrrole in the presence of surfactant dopants.The AgNPs acted as an oxidizing agent to simultaneously incorporate nanoparticles into the prepared composites.The structures and morphologies of the prepared composites were studied using Fourier transform infrared(FTIR)spectroscopy,X-ray diffraction(XRD),UV-Vis Spectra,thermogravimetric analysis(TGA),and scanning and transmission electron microscopy(SEM and TEM)techniques.Additionally,the prepared composites were characterized by their conductivities,and the dielectric constants(e΄),dielectric losses(e˝),and AC conductivities were studied for the prepared composites with an increasing NPPy content as a function of the frequency.

Effect of SrO on the Structure of Apatite and Wollastonite Phases of Na₂O-CaO-SiO₂-P₂O₅Glass System

Glasses in the system 24.5Na2O·24.5CaO·6P2O5·xSrO·(45-x)SiO2 have been studied in the composition region of x = 0 - 15 mol%. The as prepared glasses are transparent and have an amorphous network structure. On the otherhand, heat treated glasses are transformed to opaque white glass ceramic characterized by their highly crystalline network structure. Crystalline apatite (calcium phosphate, Ca3(PO4)2, wollastonite (calcium silicate, CaSiO3), and strontium calcium phosphate Ca2Sr(PO4)2 are the main well-formed crystalline species played the major role in material bioactivity. Increasing SrO leads to enhancing material crystallite and enhances the hardness of the host glass matrix. The change of XRD spectra, 31P NMR chemical shift and hardness number upon increasing SrO are considered due to modification of the apatit Ca(PO3)2 to involve Sr ions inducing Ca2Sr (PO4)2 apatite one. Such species play the role in enhancing material properties and hardness.

Cross Section of Heavy Ion Reaction （14.5 MeV/u） ^132Xe ＋ Bi

We investigate the cross section of the heavy ion reaction （14.5 MeV/u） ^132Xe ＋ Bi by using a CR-39 plastic track detector. The target-detector assembly is exposed at UNILAC beam facility of GSI, Germany. After etching under appropriate etching conditions, the detector is scanned for multipronged events produced as a result of interactions of projectile ions with target atoms. The elastic events are separated from binary events and used for the determination of the quarter-point angle. The quarter-point angle obtained is used to determine the total reaction cross section. The total experimental reaction cross section is determined by using statistics of inelastic events of two-pronged and higher multiplicity events. The experimental reaction cross sections determined by using elastic and inelastic data observed in the reaction under study are found to be in good agreement with the theoretically calculated value of reaction cross section using a sharp cutoff model.

Er³⁺and Er³⁺/Yb³⁺Ions Embedded in Nano-Structure BaTi_0.9Sn_0.1O₃: Structure, Morphology and Dielectric Properties

Barium titanate tin oxides BaTi0.9Sn0.1O3 referred to as (BTSO) doped with 0.5Er3+ and co-doped with (0.75 and 1) Yb3+ ions, were prepared using a modified sol-gel method and calcinated at 1050?C in the air for 4 h. The influence of the selected rare earth element on the structure morphology, dielectric properties behavior was investigated. From TEM micrographs, it has appeared that the particles have a spherical shape with a small size in nanoscale. The average particle size is determined both by TEM and XRD diffraction was found to be in agreement and within the range between 45.9 and 57.7 nm. The effects of Lanthanide incorporation on the evolution of these nano-crystalline structures were followed by XRD and (FTIR). The XRD patterns give rise to a single perovskite phase, while the tetragonality was found to decrease gradually with Er3+ and Er3+/Yb3+ ions, respectively. FTIR results showed enhancement of the crystallinity and the absence of carbonates upon increasing Yb3+ ions concentration from 0.75 up to 1 mol%. The dielectric and conductivity properties were found to be enhanced by the nature and the concentration of the lanthanide element (Er3+, Yb3+) in the BTSO host lattice. The Curie temperature (Tc) shifted to a lower value from 117 for BTSO: 0.5Er to 93 for BTSO: 0.5Er/1Yb and the permittivity ε’ increased from 3972 to 6071, so BTSO: 0.5Er/1Yb good crystalline material candidate for capacitors application due to its higher permittivity.

Selectivity of CO_(2)reduction reaction to CO on the graphitic edge active sites of Fe-single-atom and dual-atom catalysts:A combined DFT and microkinetic modeling

We study the carbon dioxide reduction reaction(CO_(2)RR)activity and selectivity of Fe single-atom catalyst(Fe-SAC)and Fe dual-atom catalyst(Fe-DAC)active sites at the interior of graphene and the edges of graphitic nanopore by using a combination of DFT calculations and microkinetic simulations.The trend of limiting potentials for CO_(2)RR to produce CO can be described by using either the adsorption energy of COOH,CO,or their combination.CO_(2)RR process with reasonable reaction rates can be achieved only on the active site configurations with weak tendencies toward CO poisoning.The efficiency of CO_(2)RR on a catalyst depends on its ability to suppress the parasitic hydrogen evolution reaction(HER),which is directly related to the behavior of H adsorption on the catalyst’s active site.We find that the edges of the graphitic nanopore can act as potential adsorption sites for an H atom,and in some cases,the edge site can bind the H atom much stronger than the main Fe site.The linear scaling between CO and H adsorptions is broken if this condition is met.This condition also allows some edge active site configurations to have their CO_(2)RR limiting potential lower than the HER process favoring CO production over H2 production.

Structural and dielectric properties of prepared PbS and PbTe nanomaterials

In this work, PbS and PbTe nanomaterials with various morphologies were synthesized by a hydrothermal method. The structural properties were investigated by using X-ray diffraction(XRD) and corresponding scanning electron microscopy together with their EDX analysis. Both the PbS and PbTe nanomaterials possess good polycrystalline structure. The crystallite size, determined from the XRD data, of PbS is 5 nm whereas the corresponding value of PbTe is 2.69 nm. SEM micrographs reveal that the prepared PbS nanomaterial has starshaped structures, micro-flowers, some cubes, and semi-dendrites, whereas PbTe has semi-flower structures. Additionally, the dielectric properties have been studied in a broad frequency range from 0.1 Hz up to 1 MHz at temperatures from 298-423 K. The real and imaginary parts of the complex dielectric constant ε' and ε" of PbTe are comparatively higher than those of PbS. Moreover, the dielectric data were analyzed on the basis of the electric modulus.

Fabrication,electrical and photovoltaic characteristics of CuInGeSe4/n-Si diode

The CuInGeSe_4 thin film was deposited onto n-type single crystal silicon wafers by the electron beam deposition technique. The Au/CuInGeSe_4/n-Si/Al heterojunction device has been fabricated. The structure of the CuInGeSe_4 thin film was characterized by X-ray diffraction(XRD), scanning electron microscope(SEM), and energy dispersive X-ray analysis(EDX). The dark current-voltage characteristics of the Au/CuInGeSe_4/n-Si/Al heterojunction diode have been studied at a temperature range of 303-383 K. Also, the photovoltaic properties were examined at different illumination intensities. The capacitance-voltage characteristics of the CuInGeSe_4/n-Si heterojunction were studied at different temperatures in the dark.