Synthesis of Poly(ϵ-caprolactone) Grafted Poly(2-hydroxyethyl methacrylate) Functionalized Hydroxyapatite by RAFT and ROP

Poly(?-caprolactone) grafted poly(2-hydroxyethyl methacrylate) functionalized hydroxyapatite (HAP@PHEMA-g-PCL) nanocomposites were synthesized by the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). The RAFT agent was anchored on the surface of hydroxyapatite nanocrystals (HAPs) through the silane condensation process of 3-chloropropyltrimethoxysilane followed by reaction with potassium xanthogenate. Poly(2-hydroxyethyl methacrylate) (PHEMA) was covalently functionalized on the surface of HAPs by RAFT polymerization. Then, poly(?-caprolactone) (PCL) was grafted on HAPs by ROP based on the hydroxyl groups of PHEMA to afford HAP@PHEMA-g-PCL. The structure and composition of HAP@PHEMA-g-PCL nanocomposites were characterized by FT-IR, XRD, and TGA analyses. The morphology and formation of the polymer encapsulating HAPs were demonstrated from SEM and TEM images, while the ¹H MNR analysis of the cleaved PHEMA-g-PCL confirmed the grafting.     

Improvements of Tolerance to Stress Conditions by Genetic Engineering in Saccharomyces Cerevisiae during Ethanol Production

Saccharomyces cerevisiae, industrial yeast isolate, has been of great interest in recent years for fuel ethanol production. The ethanol yield and productivity depend on many inhibitory factors during the fermentation process such as temperature, ethanol, compounds released as the result of pretreatment procedures, and osmotic stress. An ideal strain should be able to grow under different stress conditions occurred at different fermentation steps. Development of tolerant yeast strains can be achieved by reprogramming pathways supporting the ethanol metabolism by regulating the energy balance and detoxicification processes. Complex gene interactions should be solved for an in-depth comprehension of the yeast stress tolerance mechanism. Genetic engineering as a powerful biotechnological tool is required to design new strategies for increasing the ethanol fermentation performance. Upregulation of stress tolerance genes by recombinant DNA technology can be a useful approach to overcome inhibitory situations. This review presents the application of several genetic engineering strategies to increase ethanol yield under different stress conditions including inhibitor tolerance, ethanol tolerance, thermotolerance, and osmotolerance.     

Design of aromatic copolyesters for use in microelectronic devices

The next generation of microelectronic devices will require design of new kinds of polymers which are tailored to display a dielectric constant as low as 2.0, a coefficient of thermal expansion (CTE) which matches the metal circuitry as well as the silicon substrate, moisture and chemical resistance, and dimensional stability at processing temperatures of 300-400°C which are required to form an adhesive bond between laminates. In our program, we have made significant progress in all of these areas through the use of liquid crystalline copolyesters (LCP's) laminated with a newly developed crosslinkable copolyester. In this paper, data are presented which illustrate how films and coatings of either system can be made to adhere in the solid state by interchain transesterification reactions (ITR) at the interface. Ability to foam the crosslinkable copolyester films provides direct control over the dielectric constant. The effect of pore size and distribution on the dielectric constant will be discussed. The potential to dramatically increase the melting point of the LCP's through high temperature annealing is also discussed.     

Crystal structure and computational studies of (E)-1-(benzo[b]thiophen-3-yl)-N-(4-ethoxyphenyl)methanimine

Crystallography Reports - The title compound, C17H15NOS, crystallizes in the orthorhombic sp. gr. Pca21. Two molecules in the asymmetric unit have similar structure. Crystal structure contains weak...     

Dynamic role of the correlation effect revealed in the exceptionally slow autodetachment rates of the vibrational Feshbach resonances in the dipole-bound state

Real-time autodetachment dynamics of the loosely bound excess electron from the vibrational Feshbach resonances of the dipole-bound states (DBS) of 4-bromophonoxide (4-BrPhO⁻) and 4-chlorophenoxide (4-ClPhO⁻) anions have been thoroughly investigated. The state-specific autodetachment rate measurements obtained by the picosecond time-resolved pump-probe method on the cryogenically cooled anions exhibit an exceptionally long lifetime (τ) of ∼823 ± 156 ps for the 11′¹ vibrational mode of the 4-BrPhO⁻ DBS. Strong mode-dependency in the wide dynamic range has also been found, giving τ ∼ 5.3 ps for the 10′¹ mode, for instance. Though it is nontrivial to get the state-specific rates for the 4-ClPhO⁻ DBS, the average autodetachment lifetime of the 19′¹20′¹/11′¹ mode has been estimated to be ∼548 ± 108 ps. Observation of these exceptionally slow autodetachment rates of vibrational Feshbach resonances strongly indicates that the correlation effect may play a significant role in the DBS photodetachment dynamics. Fermi''s golden rule has been invoked so that the correlation effect is taken into account in the form of the interaction between the charge and the induced dipole where the latter is given by the polarizable counterparts of the electron-rich halogenated compound and the diffuse non-valence electron. This report suggests that one may measure, from the real-time autodetachment dynamics, the extent of the correlation effect contribution to the stabilization and/or dynamics of the excess non-valence electron among many different types of long-range interactions of the DBS.

Exceptionally slow autodetachment dynamics of the vibrational Feshbach resonances found in the dipole-bound state of 4-bromophonoxide (4-BrPhO⁻) or 4-chlorophenoxide (4-ClPhO⁻) anions reveals the associated dynamic role of the correlation effect.     

Stable atomic structure and magnetism of Pt–Cr binary surface alloys on Pt(0 0 1): First-principle calculations

The possibility of Pt–Cr surface alloys formation on Pt(0 0 1) was investigated and their magnetism was calculated by the full-potential linearized augmented plane wave (FLAPW) method with eight different atomic configurations. The most stable structure was calculated to be the Pt-segregated L1₂ ferromagnetic surface alloy. A₃B types (L1₂ or D0₂₂) were more stable compared to AB types (L1₀). It implies that the A₃B type surface alloys may be formed when depositing a monolayer of Cr on Pt(0 0 1). It was found from the total energy calculations that there exists a strong tendency of the Pt segregation. The segregation further stabilizes the surface alloy significantly. The work function of the most stable surface alloy was calculated to be 6.02 eV and the magnetic moment of the surface Cr was much enhanced to 3.3 μ_B. It is a quite interesting finding that the coupling between Cr and Pt atoms on the surface plane is ferromagnetic in the Pt-segregated L1₂ ferromagnetic surface alloy, while the coupling is antiferromagnetic in the bulk.     

The charge structure and interaction mechanism on In-doped sulphur spinel

The charge structure and interaction mechanism on In-doped sulphur spinel FeIn_xCr_2−xS₄ are studied. The temperature dependence of magnetization μ_B, measured from 60 K to room temperature, suggests that FeIn_xCr_2−xS₄ (x=0.1$x=0.1$, 0.3) are ferrimagnetic. The Néel temperature is decreased with increasing non-magnetic In substitution as consequence of reduction of superexchange interaction for increased lattice parameter. FeIn_xCr_2−xS₄ is investigated by Mössbauer spectra from 4.2 K to room temperature. The asymmetric line broadening is observed for the sample FeIn_xCr_2−xS₄ and considered to be dynamic Jahn–Teller relaxation. The charge state of Fe ions is ferrous in character.     

Theoretical investigation of controlled generation of a dense attosecond relativistic electron bunch from the interaction of an ultrashort laser pulse with a nanofilm

For controllable generation of an isolated attosecond relativistic electron bunch [relativistic electron mirror (REM)] with nearly solid-state density, we propose using a solid nanofilm illuminated normally by an ultraintense femtosecond laser pulse having a sharp rising edge. With two-dimensional (2D) particle-in-cell (PIC) simulations, we show that, in spite of Coulomb forces, all of the electrons in the laser spot can be accelerated synchronously, and the REM keeps its surface charge density during evolution. We also developed a self-consistent 1D theory, which takes into account Coulomb forces, radiation of the electrons, and laser amplitude depletion. This theory allows us to predict the REM parameters and shows a good agreement with the 2D PIC simulations.     

Analysis of High Power Millimeter Wave Waveguide Mode Converters with Input Mode Mixture

Based on the coupled mode theory, this paper presents the study on the influence of input mode mixture in circular oversized waveguide mode converters. Three kinds of commonly used waveguide mode converters, including the waveguide mode converters with varying wall radius or small axis perturbations, and the waveguide mode converters with bent structures, are taken as the examples. The results show that the spurious input modes do not simply superimpose onto the output modes, and in some cases they may deteriorate the conversion efficiency for the main output mode. Methods for transforming such spurious input mode mixture simultaneously into the main output mode are also presented in this paper.