Performance improvement of a PGNAA setup due to change in moderator design: A Monte Carlo study

Effect of neutron source-moderator geometry has been studied on the performance of a thermal neutron capture-based prompt gamma neutron activation analysis (PGNAA) setup. In the study prompt gamma-ray and thermal neutron yield was calculated for various positions of the neutron source inside 3–10 cm long high density polyethylene moderators. The study has been carried out for a Portland cement sample using Monte Carlo calculations. The maximum yields of the thermal neutrons and prompt gamma-rays have been observed for a neutron source at a distance of 1 cm from the sample. The maximum yield of the 1.94 and 6.42 MeV prompt gamma-ray from a Portland cement sample has been observed for moderators having length equal to or greater than 7 cm. The yield of both gamma rays is 2.57 times higher than the previously reported value for a PGNAA setup with the source placed outside a 5 cm thick moderator. The higher yield of gamma rays will result in higher sensitivity of the PGNAA setup.     

Some results on the internal finite‐time stabilization of vibrating strings with interior mass

In this paper, the problem of internal finite‐time stabilization for 1‐D coupled wave equations with interior point mass is handled. The nonlinear stabilizing feedback law leads, in closed‐loop, to nonlinear evolution equations where Kato theory is used to prove the well‐posedness. In addition, it is showed that in some cases, the solution of this hybrid system is constant in finite‐time if we use Neumann boundary conditions. This result can be improved (in complete finite‐time stability sense) if we change the above feedback.     

Chemistry of 2-Amino-3-cyanopyridines

This review presents a systematic and comprehensive survey of the method of preparation and the chemical reactivity of 2-amino-3-cyanopyridines. The target compounds are important intermediates for the synthesis of a variety of synthetically useful and novel heterocyclic systems.     

Synthesis,biological evaluation,and docking studies of various β-substituted porphyrin conjugates embedded with N-containing heterocycles

A new methodology for the synthesis of some new β-porphyrin heterocyclic compounds containing nitrogen derivatives 10 , 12 , 13 , 15 , 17 , 19 , 21 , 22 , 25 , 27 , and 29 was screened for their cytotoxic activities. Both elemental and spectral analyses were used to confirm the structures of new compounds. Compounds 22 , 27 , and 21 exhibited very strong activity against the HepG2 cell line. Investigation of the binding between porphyrin 22 and the binding site of telomerase was performed by molecular docking.     

A Silica Bilayer Supported on Ru(0001): Following the Crystalline‐to Vitreous Transformation in Real Time with Spectro‐microscopy

The crystalline‐to‐vitreous phase transformation of a SiO₂ bilayer supported on Ru(0001) was studied by time‐dependent LEED, local XPS, and DFT calculations. The silica bilayer system has parallels to 3D silica glass and can be used to understand the mechanism of the disorder transition. DFT simulations show that the formation of a Stone–Wales‐type of defect follows a complex mechanism, where the two layers show decoupled behavior in terms of chemical bond rearrangements. The calculated activation energy of the rate‐determining step for the formation of a Stone—Wales‐type of defect (4.3 eV) agrees with the experimental value. Charge transfer between SiO₂ bilayer and Ru(0001) support lowers the activation energy for breaking the Si?O bond compared to the unsupported film. Pre‐exponential factors obtained in UHV and in O₂ atmospheres differ significantly, suggesting that the interfacial ORu underneath the SiO₂ bilayer plays a role on how the disordering propagates within the film.     

Laplace transforms and American options

Laplace transform methods are used to study the valuation of American call and put options with constant dividend yield, and to derive integral equations giving the location of the optimal exercise boundary. In each case studied, the main result of this paper is a nonlinear Fredholm-type integral equation for the location of the free boundary. The equations differ depending on whether the dividend yield is less than or exceeds the risk-free rate. These integral equations contain a transform variable, so the solution of the equations would involve finding the free boundary that satisfies the equations for all values of this transform variable. Expressions are also given for the transform of the value of the option in terms of this free boundary.     

Synthesis and Acaricidal Activity of Some New 1,2,4‐Triazine Derivatives

A new series of 1,2,4‐triazine derivatives were designed, synthesized, and identified on the basis of IR, ¹H‐NMR, ¹³C‐NMR, and EI‐MS spectral data. The potent acaricidal activity of 1,2,4‐triazine derivatives against eggs and adult female of Tetranychus urticae (Koch) was assessed compared with pyridaben under laboratory conditions. Structure acaricidal activity relationships of the promising 1,2,4‐triazine derivatives were analyzed for eggs and adult female; the nature and position of the substituents were important in demonstration of the activities.     

Cellulosic-based hydrogel from biomass material for removal of metals from waste water

Abstract

Cellulose and carboxymethyl cellulose (CMC), prepared from rice straw, were used for hydrogel preparation, separately or in a mixture of both of them in a ratios of 1:1, 1:4, 1:9, 2:3 and 3:7 (by weight).They were polymerized with partially neutralized acrylic acid (AA) in the presence of potassium persulphate, as initiator, and vinylsulphone (VS), as cross-linker. Moreover, glutaraldehyde, N,N-methylene bis acrylamide (MBA) and Epichlorohydrin (ECH) were used as cross-linker for the mixture of 1:1 of Cellulose: CMC. The mechanism of the polymerization was studied and the resulted hydrogels were characterized for their appearances, yields percentage, and water absorbencies. The Fourier transform infrared spectroscopy (FT-IR) and XRD analysis were also investigated for the hydrogel samples. Since the textile industry produces large volumes of wastewaters which contain hazardous compounds such as dyes, heavy metals like Cu(II), and surfactants, so we aimed in this research to use the hydrogel samples for Cu²⁺ absorption that can be presented in the wastewater. The FT-IR spectrum, before and after absorption, indicated that the prepared hydrogels were able to absorb the Cu²⁺. The Cu²⁺ ions can be recovered and dried to be reused again as well as the hydrogel samples can be available again for reuse.     

Epoxidation and bis-hydroxylation of C-phenyl-delta(2,3)-glycopyranosides

Epoxidation and cis-hydroxylation of C-phenyl-delta(2,3)-glycopyranosides have been carried out with a view to developing C-aryl glycoside synthesis. Epoxidation of (2,3- and (6-O-tert-butyldimethylsilyl-2,3-dideoxy-D-erythro-hex-2-enopyranosyl)benzenedideoxy-D-erythro-hex-2-enopyranosyl)benzene gave predominantly the allo-adducts whatever the configuration at the anomeric center. Epoxidation of (4,6-di-O-tert-butyl-dimethylsilyl-2,3-dideoxy-D-erythro-hex-2-enopyranosyl)benzene gave the manno- and allo-adducts in a 89:11 and 40:60 ratios for the alpha- and beta-anomers, respectively.Hydroxylation of alpha-C-phenyl-(2,3)-glycopyranosides using OsO4 afforded the manno-adduct only, whatever the substituents at positions 4 and 6, whereas hydroxylation of (2,3-dideoxy-beta-D-erythro-hex-2-enopyranosyl)benzene and (4,6-di-O-tert-butyldimethylsilyl-2,3-dideoxy- beta-D-erythro-hex-2-enopyranosyl)benzene gave the manno- and allo-adducts in 25:75 and 80:20 ratios, respectively.