Long-range molecular resonances in a cold Rydberg gas

We present evidence for molecular resonances in a cold dense gas of rubidium Rydberg atoms. Single UV photon excitation from the 5s ground state to np Rydberg states (n=50-90) reveals resonances at energies corresponding to excited atom pairs (n-1)d+ns. We attribute these normally forbidden transitions to avoided crossings between the long-range molecular potentials of two Rydberg atoms. These strong van der Waals interactions result in avoided crossings at extremely long range, e.g., approximately 58 000 times the Bohr radius (a(0)) for n=70.     

An Improved Hybrid Adjoint Method in External Aerodynamics Using Variational Technique for the Boundary Integral Based Optimal Objective Function Gradient

An improved hybrid adjoint method to the viscous, compressible Reynold-Averaged Navier-Stokes Equation (RANS) is developed for the computation of objective function gradient and demonstrated for external aerodynamic design optimization. In this paper, the main idea is to extend the previous coupling of the discrete and continuous adjoint method by the grid-node coordinates variation technique for the computation of the variation in the gradients of flow variables. This approach in combination with the Jacobian matrices of flow fluxes refrained the objective function from field integrals and coordinate transformation matrix. Thus, it opens up the possibility of employing the hybrid adjoint method to evaluate the subsequent objective function gradient analogous to many shape parameters, comprises of only boundary integrals. This avoids the grid regeneration in the geometry for every surface perturbation in a structured and unstructured grid. Hence, this viable technique reduces the overall CPU cost. Moreover, the new hybrid adjoint method has been successfully applied to the computation of accurate sensitivity derivatives. Finally, for the investigation of the presented numerical method, simulations are carried out on NACA0012 airfoil in a transonic regime and its accuracy and effectiveness related to the new gradient equation have been verified with the Finite Difference Method (FDM). The analysis reveals that the presented methodology for the optimization provides the designer with an indispensable CPU-cost effective tool to reshape the complex geometry airfoil surfaces, useful relative to the state-of-the-art, in a less computing time.     

Core-shell microgel stabilized silver nanoparticles for catalytic reduction of aryl nitro compounds

Silver nanoparticles loaded into shell of poly (styrene-N-isopropylmethacrylamide-co-acrylic acid) core shell [P (SNA-CS)] gel particles were synthesized and analyzed by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), ultraviolet–visible spectroscopy (UV–vis) and dynamic light scattering (DLS). Catalytic activity of Ag@P (SNA-CS) particles was investigated by reducing p-nitroaniline (p-NA) into p-aminoaniline (p-AA) in the presence of sodium borohydride (NaBH₄) reductant. Molecules of the substrate adsorbed on the surface of silver nanoparticles interact with borohydride ions (BH₄⁻) to form p-AA. Other nitroarenes like o-nitroaniline (o-NA), p-nitrophenol (p-NP) o-nitrophenol (o-NP), 2,4-dinitrophenol(2,4-DNP) were also reduced into their corresponding aryl amines using Ag@P (SNA-CS) composite microgels as catalyst. Reported catalyst efficiently reduced the nitro aromatic compounds individually as well as simultaneously at ambient temperature. Effect of different reaction conditions (catalyst dose, concentration of NaBH₄ and concentration of p-NA) on reaction completion time, value of apparent rate constant (k_app) and reduction efficiency of the catalyst for reduction of p-NA was also demonstrated. Ag@P (SNA-CS) catalyst was found to be able to retain activity up to four cycles.     

Structure elucidation,DNA binding,DFT, molecular docking and cytotoxic activity studies on novel single crystal (E)-1-(2-fluorobenzylidene)thiosemicarbazide

Compound 3 {(E)-1-(2-fluorobenzylidene)thiosemicarbazide} – a new Schiff base of thiosemicarbazide has been synthesized, characterized and reported for crystal structure. Planer side chain in the crystal structure was observed co-planer with aromatic ring plane and molecules were connected into centrosymmetric dimmers via intermolecular hydrogen bonding. DFT geometry optimization and the relevant quantum parameters indicated unstable and reactive nature of compound 3. Experimental and theoretical findings for DNA binding by UV–visible, cyclic voltammetry and molecular docking studies showed consistency in kinetic (K_b) and thermodynamic (ΔG) parameters and that compound 3 significantly interacted with DNA via intercalation. Viscometric analysis further comprehended intercalation as possible binding mode of the compound with DNA and non-denaturing of DNA in the presence of 10% aqueous DMSO. Docked parameters further assured the drug like characteristics of the investigated compound as fit in Lipinski’s criteria. Dose dependant cytotoxic activity of compound 3 against human Huh-7 cell line indicated its anti-cancer potential at 100?µg/ml concentration.     

Shahidine, a novel and highly labile oxazoline from Aegle marmelos: the parent compound of aegeline and related amides

A rare alkaloid, shahidine (1), having an unstable oxazoline core has been isolated as a major constituent from the fresh leaves of Aegle marmelos. It is moisture-sensitive, and found to be the parent compound of aegeline and other amides, however, it is stable in dimethyl sulfoxide. Its structure was established by spectroscopic analysis. Biogenetically, oxazolines may be considered as the precursor of hydroxy amides and oxazoles found in plants. Shahidine (1) showed activity against a few Gram-positive bacteria.     

Elemental characterization of airborne particulates at two Nigerian locations during the Harmattan season

Airborne particulate matter collected during the Harmattan season at Kano in the northern part, and Ile-Ife in the southern part of Nigeria was analyzed for about 30 elements by a combination of instrumental neutron activation analysis and X-ray fluorescence analysis. Although the total suspended particulate concentration (ng/m³) is much higher in Kano than Ife, the elemental composition at both locations is very similar and cluster analysis shows a strong correlation between the two, indicating a common origin for particulates. Particle-size distribution studies show that Kano dust is mainly coarse while Ife dust is mainly fine. The crustal-type elements are mainly concentrated in the coarse particles (3 m) at both locations while the conventional anthropogenic elements are hosted mainly by the fine particles (0.49 m and below).     

Usefulness of nuclear and atomic-based analysis techniques in air pollution studies in Nigeria

Three nuclear and atomic-based techniques for elemental analysis of air-particulate samples are discussed in terms of their usefulness in an environmental monitoring and impact assessment programme, supported by the European Economic Community, in Nigeria. Instrumental neutron activation analysis (INAA) and proton induced X-ray emission (PIXE) analysis are compared with respect to the number of elements detected and the detection limits obtained for air-particulate matrices. The latter is used in conjunction with Rutherford backscattering spectrometry (RBS) in order to correct for variations in matrix composition. A scanning electron microprobe (SEM) with analytical facilities is also employed mainly for characterization of the air-particulates through measurement of particle size and morphology. The value of carrying out statistical analysis for differentiating between collection sites or sources of pollution is emphasised. Reference to results obtained from the analysis of air-particulates collected during the Harmattan season at Kano and Ife, separated by about 1000 km place the problem in context and serve to illustrate the requirements.     

Temperature-Responsive Poly(N-Isopropylacrylamide-Acrylamide-Phenylboronic Acid) Microgels for Stabilization of Silver Nanoparticles

Poly(N-isopropylacrylamide-acrylamide-phenylboronic acid) [P(NIPAM-AAm-PBA)] microgels of uniform size were prepared by the chemical reaction of 3-aminophenylboronic acid with poly(N-isopropylacrylamide-acrylamide-acrylic acid) [P(NIPAM-AAm-AA)] microgels in aqueous medium in the presence of N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride catalyst via carbodiimide coupling. Silver (Ag) nanoparticles were prepared using seed-mediated growth method and stabilized in P(NIPAM-AAm-PBA)] microgels. Ag nanoparticles and hybrid microgels were characterized by transmission electron microscopy, UV–visible, and dynamic light scattering techniques. The temperature-responsive behavior of hybrid microgels was found to be similar to that of the pure microgels. The value of volume transition temperature of hybrid microgels was found to be slightly higher than that of pure microgels due to shielding effect of Ag nanoparticles present on the surface of microgel particle. The decrease in the size of hybrid microgels as compared to that of pure microgels in swollen state is due to physical cross-linking by Ag nanoparticles inside the network of microgels. The stable hybrid polymer microgel system has a potential to be used for different applications.