Elevated radionuclide concentrations in heavy mineral-rich beach sands in the Cox's Bazar region, Bangladesh and related possible radiological effects

The study focuses on elevated levels of environmental radioactivity present in heavy mineral deposits located along a 120-km coastal section of Cox's Bazar on the eastern panhandle of Bangladesh. The deposits are situated in or at sand dunes located on the recent beach (foredune area) or in attached paleo-beach areas (backdune area). This study investigates activity concentrations in bulk beach sands (six representative samples) and in five mineral fractions separated from the beach sands in order to assess potential radio-ecological effects and the possible use of the mineral deposits as a source for uranium and thorium. The bulk beach sands and individual mineral fractions were analysed by gamma-ray spectroscopy. The activity concentrations of U-238, U-235, Th-232 and K-40 in the bulk beach sand samples were found to be considerably high and positively correlated to the concentration of heavy minerals in the sand. In the mineral fractions, the highest activity concentrations were found in the zircon fraction followed by garnet, rutile, ilmenite and magnetite. The determination of (i) the radium activity, (ii) several radiation hazard indices and (iii) adsorbed and effective gamma doses allowed to assess the related exposure of the environment and the local population to elevated radioactivity. It becomes evident from the present data that (1) if raw sands or mineral fractions mined in the study area are used for building purposes or industrial use, their activity concentrations have to be considered from a radio-ecological perspective and (2) if mining and processing of the minerals is being considered, uranium and thorium may become strategically significant by-products.     

Effects of Hall current on unsteady MHD flows of a second grade fluid

The aim of this present paper is to construct exact solutions corresponding to the motion of magnetohydrodynamic (MHD) fluid in the presence of Hall current, due to cosine and sine oscillations of a rigid plate as well as those induced by an oscillating pressure gradient. A uniform magnetic field is applied transversely to the flow. By using Fourier sine transform steady state and transient solutions are presented. These solutions satisfy the governing equations and all associated initial and boundary conditions. The results for a hydrodynamic second grade fluid can be obtained as a limiting case when B ₀ → 0 and for a Newtonian fluid when α ₁ → 0.     

Sodium borohydride reduction of aromatic carboxylic acids via methyl esters

A number of important aromatic carboxylic acids precursors, or intermediates in the syntheses of natural products, are converted into methyl esters and reduced to the corresponding primary alcohols using a sodium borohydride-THF-methanol system. The alcohols are obtained in 70–92% yields in 2–5 hours, in a pure state. This two-step procedure not only provides a better alternative to aluminum hydride reduction of acids but also allows the selective reduction of esters in presence of acids, amides, nitriles or nitro functions which are not affected under these conditions.     

Isomeric yield ratios for the natNd(γ, xn) 139m,g; 141m,gNd reactions in the bremsstrahlung energy region from 45 to 60 MeV

The independent isomeric yield ratios (IR) for the ^139m,gNd and the ^141m,gNd isomeric pairs produced from the ^natNd(γ, xn) reactions were determined by the activation and the off-line γ-ray spectrometric technique at the end-point bremsstrahlung energies of 45, 50, 55, and 60 MeV in the 100 MeV electron Linac of the Pohang accelerator laboratory, Korea. The present IR for the ^141m,gNd isomeric pair were compared with those from the literature measured by the bremsstrahlung and the neutron to examine the role of excitation energy. The obtained IR for the ^139m,gNd and the ^141m,gNd isomeric pairs from ^natNd(γ, xn) reactions were compared with those from the ¹⁴¹Pr(p, x), the ^natCe(³He, x), and the ¹³⁶Ce(α, n) reactions to examine the role of parameters in entrance channel i.e. excitation energy and the effect of the input angular momentum. The present IR of ^139m,gNd and ^141m,gNd were compared with those calculated by using the TALYS 1.4 code as well as those from the literature data of above mentioned reactions.     

Measurement of isomeric yield ratios of the 104m,g,106m,gAg in the 45- and 55-MeV bremsstrahlung induced reactions of natural silver

The isomeric yield ratios for the ^natAg(γ,xn)^{104m,g,106m,g}Ag reactions with the end-point bremsstrahlung energies of 45- and 55-MeV have been determined by the off-line γ-ray spectrometric technique using 100 MeV electron linac at Pohang accelerator laboratory, Korea. The present data were compared with literature data in comparable compound nucleus from the ^natAg(γ,xn), ^natPd(p,xn), and ¹⁰³Rh(α,xn) reactions to examine the effects of an excitation energy and an input angular momentum. It is observed that the isomeric yield ratios of ^104,106Ag in ^natAg(γ,xn), ^natPd(p,xn) and ¹⁰³Rh(α,xn) reactions increase with the end-point bremsstrahlung energy, proton and alpha energy, which indicate the role of excitation energy. It is also found that for the similar compound nucleus at same excitation energy, the isomeric yield ratio of ^104m,gAg is higher in the ^natPd(p,xn) and ¹⁰³Rh(α,xn) reactions than those in ^natAg(γ,xn) reaction, which indicate the effect of an input angular momentum.     

Isomeric yield ratios of 148Pm from the natSm(γ, x) and the natNd(p,xn) reactions

The independent isomeric yield ratios of ¹⁴⁸Pm from the ^natSm(γ, x) reaction at the end-point bremsstrahlung energy of 45–64 MeV have been determined using an off-line γ-ray spectrometric technique at the 100 MeV electron linac of Pohang accelerator laboratory, Pohang, Korea. We also have determined the isomeric yield ratios of ¹⁴⁸Pm from the ^natNd(p,xn) reactions in the proton energy of 5.08–44.72 MeV by a stacked-foil activation and an off-line γ-ray spectrometric techniques at the MC-50 cyclotron of the Korean Institute of Radiological and Medical Sciences, Korea. The determined isomeric yield ratios of ¹⁴⁸Pm were compared with literature data and theoretical values estimated by the TALYS 1.4. The present data along with the similar data from literature at other energies shows that the isomeric yield ratio of ¹⁴⁸Pm increases with the excitation energy both in the ^natSm(γ, x) and the ^natNd(p, xn) reactions. The isomeric yield ratios of ¹⁴⁸Pm from the ^natNd(p, xn) reactions are always higher than those from the ^natSm(γ, x) reactions at the same excitation energy, which indicate the role of input angular momentum besides excitation energy.     

Reaction of Dimethyl Sulfoxide with 4-Acyloxycoumarins

Dimethyl sulfoxide converts 4-acetoxycoumarin (1) exclusively to 2-(2-hydroxybenzoyl)-2-[(methylthio)methyl]-2,3-dihydro-4 H-furo[3,2-c]chromen-4-one (3) at 180°C under a nitrogen atmosphere, but in the absence of nitrogen, the products obtained are dicoumarol and its dehydrative cyclization products 7 H-bis[1]benzopyrano[4,3-b: 3′,4′-c]pyran-6,8-dione (9) and (3). Under similar conditions, 4-benzoyloxycoumarin (1a) affords benzoic acid, 4-hydroxy-3-({2-[(methylthio)methyl]-3-oxo-2,3-dihydro-1-benzofuran-2-yl}methyl)-2H-chromen-2-one (7), and 3-(2-hydroxybenzoyl)-3,4-dihydro-2H,5H-pyrano[2,3-b] chromen-5-one (8).     

Metal–Organic Framework‐Derived Carbon Nanorods Encapsulating Bismuth Oxides for Rapid and Selective CO2 Electroreduction to Formate

Carbon dioxide (CO₂) conversion is promising in alleviating the excessive CO₂ level and simultaneously producing valuables. This work reports the preparation of carbon nanorods encapsulated bismuth oxides for the efficient CO₂ electroconversion toward formate production. This resultant catalyst exhibits a small onset potential of ?0.28 V vs. RHE and partial current density of over 200 mA cm^?2 with a stable and high Faradaic efficiency of 93 % for formate generation in a flow cell configuration. Electrochemical results demonstrate the synergistic effect in the Bi₂O₃@C promotes the rapid and selective CO₂ reduction in which the Bi₂O₃ is beneficial for improving the reaction kinetics and formate selectivity, while the carbon matrix would be helpful for enhancing the activity and current density of formate production. This work provides effective bismuth‐based MOF derivatives for efficient formate production and offers insights in promoting practical CO₂ conversion technology.     

Substituent effects on novel diaminovinylidenes by DFT

Research on Chemical Intermediates - Electronic and steric effects on singlet and triplet symmetric 2,4-diX-vinylidenes with acyclic, cyclic-saturated, and cyclic-unsaturated structures are...     

Velocity measurements in jets with application to noise source modeling

This paper describes an experimental investigation of the statistical properties of turbulent velocity fluctuations in an axisymmetric jet. The focus is on those properties that are relevant to the prediction of noise. Measurements are performed using two single hot-wire anemometers as well as a two-component anemometer. Two-point cross correlations of the axial velocity fluctuations and of the fluctuations in the square of the axial velocity fluctuations are presented. Several reference locations in the jet are used including points on the jet lip and centerline. The scales of the turbulence and the convection velocity are determined, both in an overall sense as well as a function of frequency. The relationship between the second and fourth order correlations is developed and compared with the experimental data. The implications of the use of dimensional as well as non-dimensional correlations are considered. Finally, a comparison is made between the length scales deduced from the flow measurements and a RANS CFD calculation.