Structural phase stability studies on MBeH3 (M = Li, Na, K, Rb, Cs) from density functional calculations

Density functional theory calculations within the generalized-gradient approximation are used to establish the ground-state structure, equilibrium structural parameters, and electronic structure for MBeH(3) phases. From the 24 structural arrangements used as inputs for structural optimization calculations, the ground-state crystal structures of MBeH(3) phases have been predicted. At ambient conditions, LiBeH(3) and NaBeH(3) crystallize with perovskite-related orthorhombic and cubic structures, respectively. The remaining phases KBeH(3), RbBeH(3), and CsBeH(3) crystalize in a monoclinic structure. In the predicted phases one can store up to 15.93 wt % of hydrogen. The formation energy for the MBeH(3) phases have been investigated along different reaction pathways. The electronic structures reveal that all these phases are insulators with estimated band gaps varying between 1.79 and 3.44 eV.     

An optimal asymptotic-numerical method for convection dominated systems having exponential boundary layers

The convection dominated diffusion problems are studied. Higher order accurate numerical methods are presented for problems in one and two dimensions. The underlying technique utilizes a superposition of given problem into two independent problems. The first one is the reduced problem that refers to the outer or smooth solution. Stretching transformation is used to obtain the second problem for inner layer solution. The method considered for outer or degenerate problems are based on higher order Runge–Kutta methods and upwind finite differences. However, inner problem is solved analytically or asymptotically. The schemes presented are proved to be consistent and stable. Possible extensions to delay differential equations and to nonlinear problems are outlined. Numerical results for several test examples are illustrated and a comparative analysis is presented. It is observed that the method presented is highly accurate and easy to implement. Moreover, the numerical results obtained are not only comparable with the exact solution but also in agreement with the theoretical estimates.     

Fluorescence properties and photophysics of the sulfoindocyanine Cy3 linked covalently to DNA

The sulfoindocyanine Cy3 is one of the most commonly used fluorescent dyes in the investigation of the structure and dynamics of nucleic acids by means of fluorescence methods. In this work, we report the fluorescence and photophysical properties of Cy3 attached covalently to single-stranded and duplex DNA. Steady-state and time-resolved fluorescence techniques were used to determine fluorescence quantum yields, emission lifetimes, and fluorescence anisotropy decays. The existence of a transient photoisomer was investigated by means of transient absorption techniques. The fluorescence quantum yield of Cy3 is highest when attached to the 5' terminus of single-stranded DNA (Cy3-5' ssDNA), and decreases by a factor of 2.4 when the complementary strand is annealed to form duplex DNA (Cy3-5' dsDNA). Substantial differences were also observed between the 5'-modified strands and strands modified through an internal amino-modified deoxy uridine. The fluorescence decay of Cy3 became multiexponential upon conjugation to DNA. The longest lifetime was observed for Cy3-5' ssDNA, where about 50% of the decay is dominated by a 2.0-ns lifetime. This value is more than 10 times larger than the fluorescence lifetime of the free dye in solution. These observations are interpreted in terms of a model where the molecule undergoes a trans-cis isomerization reaction from the first excited state. We observed that the activation energy for photoisomerization depends strongly on the microenvironment in which the dye is located. The unusually high activation energy measured for Cy3-5' ssDNA is an indication of dye-ssDNA interactions. In fact, the time-resolved fluorescence anisotropy decay of this sample is dominated by a 2.5-ns rotational correlation time, which evidences the lack of rotational freedom of the dye around the linker that separates it from the terminal 5' phosphate. The remarkable variations in the photophysical properties of Cy3-DNA constructs demonstrate that caution should be used when Cy3 is used in studies employing DNA conjugates.     

Effect of beta-cyclodextrin nanocavity confinement on the photophysics of robinetin

We have studied the confinement of robinetin, a therapeutically active plant flavonol, in cyclodextrin (CDx) nanocavities, using steady state and time resolved fluorescence spectroscopy. Enhanced tautomer emission (arising from excited state intramolecular proton transfer (ESIPT)) as well as dramatically blue shifted (approximately 10 nm in beta-CDx and approximately 33 nm in SHP beta-CDx) normal fluorescence observed upon addition of the beta-CDxs indicate that robinetin readily enters the doughnut-shaped hydrophobic cavity of beta-CDx where the chromone moiety is well shielded from external hydrogen bonding perturbations. Detailed analyses of the fluorescence data (emission profile, anisotropy, decay times) indicate that robinetin forms 1:1 inclusion complexes with both natural and chemically modified beta-cyclodextrins (beta-CDx and SHP beta-CDx) with affinity constant values K=195+/-17 M(-1) and 1055+/-48 M(-1) respectively, indicating the prospective utility of SHP beta-CDx in particular as an effective drug carrier. Unlike beta-CDxs, alpha-CDxs do not form inclusion complexes with robinetin. To further characterize the robinetin/beta-CDxs complexes, circular dichroism (CD) spectroscopic studies have been performed, which reveal that incorporation of robinetin molecules in the chiral environment of the beta-CDxs strongly affects the electronic transitions of robinetin leading to the occurrence of positive induced circular dichroism (ICD) bands in the near ultra-violet (UV) region. Molecular mechanics calculations show that the inclusion complex with the chromone ring inserted into the beta-CDx cavity is most favorable, in agreement with our spectroscopic data.     

A reduced‐order approach for optimal control of fluids using proper orthogonal decomposition

In this article, a reduced‐order modeling approach, suitable for active control of fluid dynamical systems, based on proper orthogonal decomposition (POD) is presented. The rationale behind the reduced‐order modeling is that numerical simulation of Navier–Stokes equations is still too costly for the purpose of optimization and control of unsteady flows. The possibility of obtaining reduced‐order models that reduce the computational complexity associated with the Navier–Stokes equations is examined while capturing the essential dynamics by using the POD. The POD allows the extraction of a reduced set of basis functions, perhaps just a few, from a computational or experimental database through an eigenvalue analysis. The solution is then obtained as a linear combination of this reduced set of basis functions by means of Galerkin projection. This makes it attractive for optimal control and estimation of systems governed by partial differential equations (PDEs). It is used here in active control of fluid flows governed by the Navier–Stokes equations. In particular, flow over a backward‐facing step is considered. Reduced‐order models/low‐dimensional dynamical models for this system are obtained using POD basis functions (global) from the finite element discretizations of the Navier–Stokes equations. Their effectiveness in flow control applications is shown on a recirculation control problem using blowing on the channel boundary. Implementational issues are discussed and numerical experiments are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Ground-state properties of neutron magic nuclei

A systematic study of the ground-state properties of the entire chains of even–even neutron magic nuclei represented by isotones of traditional neutron magic numbers N = 8, 20, 40, 50, 82, and 126 has been carried out using relativistic mean-field plus Bardeen–Cooper–Schrieffer approach. Our present investigation includes deformation, binding energy, two-proton separation energy, single-particle energy, rms radii along with proton and neutron density profiles, etc. Several of these results are compared with the results calculated using nonrelativistic approach (Skyrme–Hartree–Fock method) along with available experimental data and indeed they are found with excellent agreement. In addition, the possible locations of the proton and neutron drip-lines, the (Z, N) values for the new shell closures, disappearance of traditional shell closures as suggested by the detailed analyzes of results are also discussed in detail.     

Disposition Kinetics of Amitraz in Lactating Does

Amitraz, a member of the formamidine pesticide family, commonly used for ectoparasite control, is applied as a dip or low-pressure hand spray to cattle and swine, and the neck collar on dogs. Data on amitraz were generated mainly on laboratory animals, hens, dogs, and baboons. The data on the toxicity and disposition of amitraz in animals and its residues in the milk are inadequate. Therefore, the present study was intended to analyze the disposition kinetics of amitraz and its pattern of elimination in the milk of lactating does after a single dermal application at a concentration of 0.25%. Blood at predetermined time intervals and milk twice daily were collected for eight days post application. The drug concentration was assayed by high-performance liquid chromatography (HPLC). Amitraz was detected in whole blood as early as 0.5 h, which attained a peak concentration at 12 ± 5 h, followed by a steady decline; however, detection persisted until 168 h. Amitraz was present in the blood at its 50% C_max even after 48 h, and was still detectable after 7 days. The disposition after a single dermal application was best described non-compartmentally. The mean terminal half-life (t_1/2), mean residence time (MRT), and area under the curve (AUC_0–t) were 111 ± 31 h, 168 ± 39 h, and 539 ± 211 µg/mL/h, respectively. The apparent volume of distribution (Vd_area) was 92 ± 36 mL/g with an observed clearance (Cl) of 0.57 ± 0.33 mL/kg/h. Thus, the drug was well absorbed, widely distributed and slowly eliminated from the animal body. Amitraz achieved milk concentration approximating 0.2 per cent of the total dose after a single exposure and the steady-state elimination of amitraz in milk above the recommended maximum residue limit (MRL) of 0.01 mg/kg can act as a source of public health concern when applied on lactating animals.     

Modulation of the PGE2-Mediated Pathway in the Eclosion Blocking Effect of Flumethrin and Terpenoid Subfraction Isolated from Artemesia nilagirica in Rhipicephalus annulatus

Prostaglandins are a group of important cell-signaling molecules involved in the regulation of ovarian maturation, oocyte development, egg laying and associated behaviors in invertebrates. However, the presence of prostaglandin E₂ (PGE₂), the key enzymes for PGE₂ biosynthesis and its interference by drugs were not investigated previously in the ovary of ticks. The present study was undertaken to assess the modulation of the PGE₂-mediated pathway in the eclosion blocking effect of flumethrin and terpenoid subfraction isolated from Artemisia nilagirica in Rhipicephalus annulatus ticks. The acaricidal activities and chemical profiling of the terpenoid subfraction were performed. The localization of the cyclooxygenase1 (COX1) and prostaglandin E synthase (PGES) enzymes and the quantification of PGE₂ in the ovaries of the ticks treated with methanol (control), flumethrin and terpenoid subfraction were also undertaken. In addition, the vitellogenin concentration in hemolymph was also assayed. Both flumethrin and the terpenoid subfraction of A. nilagirica elicited a concentration-dependent inhibition of fecundity and blocking of hatching of the eggs. The COX1 could not be detected in the ovaries of treated and control ticks, while there was no significant difference observed in the concentration of vitellogenin (Vg) in them. The presence of PGES in the oocytes of control ticks was confirmed while the immunoreactivities against PGES were absent in the vitellogenic oocytes of ticks treated with flumethrin and terpenoid subfraction. The levels of PGE₂ were below the detection limit in the ovaries of the flumethrin-treated ticks, while it was significantly lower in the ovaries of the terpenoid subfraction-treated ticks. Hence, the prostaglandin E synthase and PGE₂ were identified as very important mediators for the signaling pathway for ovarian maturation and oviposition in ticks. In addition, the key enzyme for prostaglandin biosynthesis, PGES and the receptors for PGE₂ can be exploited as potential drug targets for tick control. The detection of PGES by immunohistochemistry and quantification of PGE₂ by LC-MSMS can be employed as valuable tools for screening newer compounds for their eclosion blocking acaricidal effects.     

Working group report: Quantum chromodynamics sub-group

This is the report of the QCD working sub-group at the Tenth Workshop on High Energy Physics Phenomenology (WHEPP-X).