Electron impact excitation of 2p and 3p states of hydrogen at intermediate energies

The recent theoretical work by Bartlett et al. [J. Phys. B 38, L95 (2005)] and the latest measurements on the reduced Stokes parameters , and for 54.4 eV electron impact excitation of the 2p state atomic hydrogen by Williams and Mikosza [J. Phys. B 39, 4113 (2006)] has motivated the present work. A coupled-channel-optical calculation with 9 and 12 atomic states supplemented with the continuum optical potentials for the stronger coupling channels has been performed. The calculated n = 2 and n = 3 differential cross sections and the reduced Stokes parameters are comparable with the state-of-the art calculations. There is closer agreement between the present calculations and the experimental measurements for the reduced Stokes parameters and in the n = 2p excitation at 54.4 eV. The present CCO calculations also display good accord with the limited experimental data for the reduced Stokes parameters in the n=3p excitation.     

Rational Conformal Field Theories and Complex Multiplication

We study the geometric interpretation of two dimensional rational conformal field theories, corresponding to sigma models on Calabi-Yau manifolds. We perform a detailed study of RCFTs corresponding to the T² target and identify the Cardy branes with geometric branes. The T²s leading to RCFTs admit complex multiplication which characterizes Cardy branes as specific D0-branes. We propose a condition for the conformal sigma model to be RCFT for arbitrary Calabi-Yau n-folds, which agrees with the known cases. Together with recent conjectures by mathematicians it appears that rational conformal theories are not dense in the space of all conformal theories, and sometimes appear to be finite in number for Calabi-Yau n-folds for n>2. RCFTs on K3 may be dense. We speculate about the meaning of these special points in the moduli spaces of Calabi-Yau n-folds in connection with freezing geometric moduli.     

One-step conversion of Mg2Si into hydrogen-terminated porous silicon nanostructures

A simple, fast, and low-cost acid-treatment method is proposed for the conversion of magnesium silicide (Mg₂Si) into hydrogen-terminated mesoporous silicon nanostructured material (M-pSi). The formation of porosity in M-pSi is attributed to the generation of gas species during the acid treatment, providing a large number of active sites. The adsorption and the photocatalytic performances of M-pSi toward the degradation of methyl orange are investigated. It is found that the mesoporous Si material exhibits an unusual and high photocatalytic ability toward the dye degradation in acidic conditions, outperforming the performance of commercially available Si nanoparticles. This unusual photocatalytic performance is related to the presence of hydrogen-terminated silicon nanostructures with a high surface area of 203 m²/g. The article proposes an alternative way of producing porous silicon materials with enhanced photocatalytic activity.     

Cochlear Synaptopathy Following Noise Exposure in Guinea Pigs: Its Electrophysiological and Histological Assessments

Exposure to high level of noise, may cause the permanent cochlear synaptic degeneration. In present study, a model of noise induced cochlear synaptopathy was established and the electrophysiological and histological metrics for its assessment was designed. 6 guinea pigs were subjected to a synaptopathic noise (octave band of 4 kHz at 104 dB SPL, for 2-h). The amplitude growth curve of Auditory Brainstem Response (ABR) wave-I and wave-III latency shift in presence of noise were calculated. These indexes were considered in pre-exposure, 1 day post exposure (1DPE), 1 week post exposure (1WPE) and 1 month post exposure (1MPE) to noise. Finally, the samples were histologically analyzed. ABR wave-I amplitude was different between pre and 1DPE (p-value ≤ 0.05). However, at 1WPE, it was recovered at low intensities but at 70 dB SPL and above, the differences persisted even till 1MPE. In masked ABR, the latency shift of wave-III was different between pre and 3 post exposure assessments (p-value ≤ 0.05). Electro-microscopic analysis confirmed the synaptic degeneration, as the ribbons were larger than normal, hollow inside, and spherical and irregular in shape, also, the post synaptic density was abnormally thick and missed its flat orientation. These data revealed that noise at level below that can produce permanent hearing loss, can incur synaptic injury. So, noise is considered to be more damaging than previously thought. Accordingly, designing tools for clinical assessment of synaptopathy is beneficial in comprehensive auditory evaluation of those with history of noise exposure and also in hearing protection planning.     

DFT investigation for NH3 adsorption behavior on Fe,Ru, and Os-embedded graphitic carbon nitride: promising candidates for ammonia adsorbent

Journal of the Iranian Chemical Society - The adsorption of NH3 molecules on the pristine graphitic carbon nitride (gCN) and TM-embedded gCN systems (TM = Fe, Ru, and Os atoms) was...     

Ce-promoted Mn/Na2WO4/SiO2 catalyst for oxidative coupling of methane at atmospheric pressure

A series of Ce-promoted Mn-Na2WO4/SiO2 catalysts were prepared by incipient wetness impregnation method, and their catalytic performance for oxidative coupling of methane (OCM) was investigated at atmospheric pressure in a micro-quartz-tube reactor. The catalysts were characterized by X-ray diffraction (XRD), temperature program reduction (TPR) and BET surface area. Ce promoter increased surface area and Na2WO4 species dispersion, which enriched the amount of the surface species. In addition, Ce promoter in...     

Thermokinetic study on the phase evolution of mechanically alloyed Ni–B powders

A combination of differential thermal analysis and detailed X-ray diffraction (XRD) analyses were used for the thermokinetic study of phase evolution during heating–cooling of the mechanically alloyed (MA-ed) Ni–15 wt% B. According to the results obtained, different phase transition sequences led to the formation of nanocrystalline Ni–B alloys comprising of Ni₂B + o-Ni₄B₃ and Ni₂B + m-Ni₄B₃ + B. Using the XRD studies, it was found that the Ni₂B is the most stable intermetallic compound in the Ni–B binary phase diagram, and its nanocrystalline nature retained unchanged even after annealing up to temperatures near the melting point. In addition, average enthalpy as well as activation energy of occurred reactions was calculated; the latter was estimated using two well-known Kissinger and Augis & Bennett methods.     

Filament-induced breakdown remote spectroscopy in a polar environment

We demonstrate the feasibility of filament-induced breakdown spectroscopy (FIBS) for remote sensing of solid samples in a polar environment. FIBS spectra from an aluminum target induced by 800-nm laser pulses propagating in air were probed. The air visibility in an open winter field was as low as 3.2 km fluctuating with precipitation, pressure and relative humidity. Under such polar condition, clean spectral Al I lines from an aluminum target located at a distance of 60 m were obtained. This shows the technique FIBS could be potentially useful for sensing remote targets in a variety of polar environments.     

Synthesis of polysubstituted 2-azetidinones via in situ generation of a vanillinyl ketene and electrocyclic reaction of the corresponding zwitterionic intermediate

Research on Chemical Intermediates - Highly stereoselective synthesis of polyfunctionalized 2-azetidinones was achieved starting from vanillin as an available natural product. Our approach to these...