Optimization of the dimensions of an Yb(3+):ZBLANP optical fiber sample for laser cooling of solids

We propose a theoretical model for an optimized fiber structure for use in anti-Stokes laser cooling of solids. The sample is an optical fiber fabricated from a fluorozirconate glass ZBLANP with a core doped with Yb(3+) ions. The diameter of the fiber core is optimized to achieve the largest temperature change in the sample. It is shown that for each value of the pump power there is an optimized diameter of the fiber core, which permits the largest drop in the temperature of the sample.     

Fabrication of buried waveguides in planar silica films using a direct CW laser writing technique

A CW CO₂ laser ablation technique is used to form buried waveguides in planar silica films. It is shown that the refractive index of a silica thin film is reduced sufficiently adjacent to the laser processed region to allow the fabrication of low loss waveguides. The refractive index distribution of these structures is measured using the reflectance of a focussed spot from the surface of the films. The change in refractive index is measured to be of the order of the core cladding refractive index difference of typical single mode waveguides. The spatial resolution of the reflectance technique is 1.3 μm with a refractive index resolution of ±5 × 10^?4. Devices such as 1 × 2 and 1 × 4 multi-mode interference (MMI) splitters have also been demonstrated and shown to exhibit low transmission losses.     

Application of metal free aromatization to total synthesis of perlolyrin,flazin, eudistomin U and harmane

Application of our recently reported metal free reaction conditions to the total synthesis of the four different and selective biologically interesting β-carboline natural products is reported. Using this simple methodology, flazin, perlolyrine, eudistomin U and harmane containing heteroaryl and alkyl substituents at C1 position were synthesized in good yields.

     

Impact of surface adaptation and Acacia nilotica biofiller on static and dynamic properties of sisal fiber composite

Nowadays, the awareness of the public along with strict legitimate forces over the use of polymers, the manufacturing and automotive industries started using the renewable materials. Since, natural fiber reinforced composites play vital role in developing lightweight structural materials, this study focuses on utilizing sisal fiber as reinforcement in polyester matrix along with natural filler. The influence of fiber length and fiber volume fraction on the mechanical properties of sisal fiber was studied initially. Test results revealed that the composite with 20?mm fiber length and 20-volume fraction composite has better mechanical properties. Furthermore, the effect of fiber surface modification has been analyzed using various chemical solutions such as NaOH, KMnO₄, stearic acid, and maleic acid. Of these, NaOH treatment enhances the mechanical properties of composite compared to all other cases. Finally, the influence of Acacia nilotica, a natural filler addition into the alkali-treated sisal fiber composite has been evaluated by mechanical and dynamic mechanical properties. It is found that the addition of natural filler and surface treatment has enhanced the properties of composites due to their synergetic effect. This effect improves the adhesion and uniform stress transfer among the reinforcements. The fiber surface morphology was evaluated using micrographs obtained from scanning electron microscope.     

Helix forming tendency of valine substituted poly-alanine: a molecular dynamics investigation

In this study, classical molecular dynamics simulations have been carried out on the valine (guest) substituted poly alanine (host) using the host-guest peptide approach to understand the role of valine in the formation and stabilization of helix. Valine has been substituted in the host peptide starting from N terminal to C terminal. Various structural parameters have been obtained from the molecular dynamics simulation to understand the tolerance of helical motif to valine. Depending on the position of valine in the host peptide, it stabilizes (or destabilizes) the formation of the helical structure. The substitution of valine in the poly alanine at some positions has no effect on the helix formation (deformation). It is interesting to observe the coexistence of 3 10 and alpha-helix in the peptides due to the dynamical nature of the hydrogen bonding interaction and sterical interactions.     

Designing,Structural Elucidation and Comparison of the Cleavage Ability of Metal Complexes Containing Tetradentate Schiff Bases 1

New N₂O₂ donor type Schiff bases have been designed and synthesized by condensing acetylaceto-4-aminoantipyrine/acetoacetanilido-4-aminoantipyrine with 2-amino benzoic acid in ethanol. Solid metal complexes of the Schiff bases with Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(IV), Hg(II) and Cd(II) metal ions were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conduction, FAB Mass, IR, UV-Vis., ¹H NMR, and ESR spectral studies. The data show that the complexes have a composition of the ML type. The UV-Vis., magnetic susceptibility, and ESR spectral data of the complexes suggest a square planar geometry around the central metal ion, except for VO(IV) complexes, which have square-pyramidal geometry. The redox behavior of copper and vanadyl complexes has been studied by cyclic voltammetry. The nuclease activity of the above metal complexes shows that the complexes cleave DNA through redox chemistry. In the presence of H₂O₂, all the complexes are capable of cleaving calf thymus DNA plasmids, in order to compare the cleavage efficiency of all metal complexes in the two different ligand environments. In this assay, Cu(II), Ni(II), Co(II), and Zn(II) exhibit more cleavage efficiency than other metal ions. This article was submitted by the authors in English.     

Thermodynamic calculations for molecules with asymmetric internal rotors. II. Application to the 1,2-dihaloethanes

The thermodynamic properties of three halocarbon molecules relevant in atmospheric and public health applications are presented from ab initio calculations. Our technique makes use of a reaction path-like Hamiltonian to couple all the vibrational modes to a large-amplitude torsion for 1,2-difluoroethane, 1,2-dichloroethane, and 1,2-dibromoethane, each of which possesses a heavy asymmetric rotor. Optimized ab initio energies and Hessians were calculated at the CCSD(T) and MP2 levels of theory, respectively. In addition, to investigate the contribution of electronically excited states to thermodynamic properties, several excited singlet and triplet states for each of the halocarbons were computed at the CASSCF/MRCI level. Using the resulting potentials and projected frequencies, the couplings of all the vibrational modes to the large-amplitude torsion are calculated using the new STAR-P 2.4.0 software platform that automatically parallelizes our codes with distributed memory via a familiar MATLAB interface. Utilizing the efficient parallelization scheme of STAR-P, we obtain thermodynamic properties for each of the halocarbons, with temperatures ranging from 298.15 to 1000 K. We propose that the free energies, entropies, and heat capacities obtained from our methods be used to supplement theoretical and experimental values found in current thermodynamic tables.     

Design, synthesis, spectroscopic characterization, biological screening, and DNA nuclease activity of transition metal complexes derived from a tridentate Schiff base

A new series of transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Cd(II), Hg(II), and VO(IV) have been designed and synthesized from the Schiff base derived from cinnamidene-4-aminoantipyrine and 2-aminophenol by involving the carbonyl group of 4-aminoantipyrine. The structural features have been arrived from their elemental analyses, magnetic susceptibility, molar conduction, FAB mass, IR, UV-Vis, ¹H NMR and ESR spectral studies. The data show that the complexes have composition of the ML₂ type. The UV-Vis, magnetic susceptibility, and ESR spectral data of the complexes suggest an octahedral geometry around the central metal ion except the VO(IV) complex, which has a square-pyramidal geometry. The redox behavior of the copper and vanadyl complexes has been studied by cyclic voltammetry. The antimicrobial activity of the ligand and its complexes has been extensively studied on microorganisms such as Salmonella typhi, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Aspergillus niger, and Rhizoctonia bataicola. It has been found that most of the complexes have higher activities than that of the free ligand. The nuclease activity of the above metal complexes shows that the complexes cleave DNA through redox chemistry. In the presence of H₂O₂, the complexes are capable of cleaving calf thymus DNA. The text was submitted by the authors in English.     

Predicted reaction rates of H(x)N(y)O(z) intermediates in the oxidation of hydroxylamine by aqueous nitric acid

This work reports computed rate coefficients of 90 reactions important in the autocatalytic oxidation of hydroxylamine in aqueous nitric acid. Rate coefficients were calculated using four approaches: Smoluchowski (Stokes-Einstein) diffusion, a solution-phase incarnation of transition state theory based on quantum chemistry calculations, simple Marcus theory for electron-transfer reactions, and a variational TST approach for dissociative isomerization reactions that occur in the solvent cage. Available experimental data were used to test the accuracy of the computations. There were significant discrepancies between the computed and experimental values for some key parameters, indicating a need for improvements in computational methodology. Nonetheless, the 90-reaction mechanism showed the ability to reproduce many of the trends seen in experimental studies of this very complicated kinetic system. This work highlights reactions that may govern the system evolution and branching behavior critical to the stability of the system. We hope that this analysis will guide experimental investigations to reduce the uncertainties in the critical rate coefficients and thermochemistry, allowing an unambiguous determination of the dominant reaction pathways in the system. Advances in efficient and accurate solvation models that effectively separate entropic and enthalpic contributions will most directly benefit solution-phase modeling efforts. Methods for more accurately estimating activity coefficients, including at infinite dilution in multicomponent mixtures, are needed for modeling high ionic strength aqueous systems. A detailed derivation of the solution-phase equilibrium and transition state theory rate expressions in solution is included in the Supporting Information.     

Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 × 10¹² s⁻¹ in benzonitrile through 8.3 × 10¹¹ s⁻¹ in MTBE, around 1.6 × 10¹¹ s⁻¹ in dibutylether and toluene and to 3.8 × 10⁹ s⁻¹ in n-hexane.