Spectral responses of gyrotropic chiral sculptured thin films to obliquely incident plane waves

Gyrotropic chiral sculptured thin films (STFs) exhibit optical activity due to their structural chirality, local anisotropy, and magneto-optic gyrotropy. We adapted two algorithms for nongyrotopic chiral STFs to investigate the circular-polarization-sensitivity of gyrotropic chiral STFs to incident plane waves. The impacts of gyrotropy and oblique angles of incidence on the reflectances and the transmittances were examined, and several conclusions drawn. In particular, we found that the incorporation of gyrotropy results in a blueshift of the Bragg regime.     

Computational design of multifunctional materials

We propose a general scheme for the computational design of new materials using density functional theory. We then apply the scheme to two classes of materials; ferromagnetic ferroelectrics and half-metallic antiferromagnets. Our first “designer” ferromagnetic ferroelectric has subsequently been synthesized and the predicted properties verified. Our computations on half-metallic antiferromagnets have stimulated experimental study but the phenomenon remains unconfirmed.     

Solar Fuels: Photoelectrosynthesis of CO from CO2 at p‐Type Si using Fe Porphyrin Electrocatalysts

Photoelectrocatalytic conversion of CO₂ to CO can be driven at a boron‐doped, hydrogen terminated, p‐type silicon electrode using a meso‐tetraphenylporphyrin Fe^III chloride in the presence of CF₃CH₂OH as a proton source and 0.1 M [NBu₄][BF₄]/MeCN/5 % DMF (v/v) as the electrolyte. Under illumination with polychromatic light, the photoelectrocatalysis operates with a photovoltage of about 650 mV positive of that for the dark reaction. Carbon monoxide is produced with a current efficiency >90 % and with a high selectivity over H₂ formation. Photoelectrochemical current densities of 3 mA cm^?2 at ?1.1 V versus SCE are typical, and 175 turnovers have been attained over a 6 h period. Cyclic voltammetric data are consistent with a turnover frequency of ${k{{{\rm Si}\hfill \atop {\rm obs}\hfill}}}$ =0.24×10⁴ s^?1 for the photoelectrocatalysis at p‐type Si at ?1.2 V versus SCE this compares with ${k{{{\rm C}\hfill \atop {\rm obs}\hfill}}}$ =1.03×10⁴ s^?1 for the electrocatalysis in the dark on vitreous carbon at a potential of ?1.85 V versus SCE.     

Reproducibility of Florida weathering data

We have investigated the consistency and reproducibility of Florida outdoor weathering data for aromatic engineering thermoplastics. Weather and broadband (295–385 nm) UV dose data for the 14-year period from 1989 to 2002 show that considerable variability is expected for exposures with duration < 1 year, but that standard deviations for UV exposure and temperature are approximately 7% of the mean at 1 year and <5% at 2 years and greater. Only rainfall shows significant long-term variability. Weathering data on pigmented aromatic engineering thermoplastics were consistent with these expectations. Overall trends and rates of color and gloss shifts were generally reproduced for samples exposed at different times. Color shift data were generally reproducible within a ΔE of 2 and 60° gloss loss within 10 units for samples beginning exposure 6 months apart. However, very large differences in absolute values for properties can occur for data taken near periods of rapid change, especially for gloss loss. Surprisingly, considering the data as a function of broadband UV dose rather than exposure time did not seem to reduce scatter. This emphasizes the problem of comparing results between data sets for exposure times < 1 year. We conclude that Florida data do provide a useful benchmark when rates and general trends are compared, but not for absolute values at arbitrary times.     

The role of CN and CO ligands in the vibrational relaxation dynamics of model compounds of the [FeFe]-hydrogenase enzyme

The vibrational dynamics of (μ-propanedithiolate)Fe(2)(CO)(4)(CN)(2)(2-), a model compound of the active site of the [FeFe]-hydrogenase enzyme, have been examined via ultrafast 2D-IR spectroscopy. The results indicate that the vibrational coupling between the stretching modes of the CO and CN ligands is small and restricted to certain modes but the slow growth of off-diagonal peaks is assigned to population transfer processes occurring between these modes on timescales of 30-40 ps. Analysis of the dynamics in concert with anharmonic density functional theory simulations shows that the presence of CN ligands alters the vibrational relaxation dynamics of the CO modes in comparison to all-carbonyl model systems and suggests that the presence of these ligands in the enzyme may be an important feature in terms of directing the vibrational relaxation mechanism.     

A parameter-uniform numerical method for a singularly perturbed two parameter elliptic problem

In this paper, a class of singularly perturbed elliptic partial differential equations posed on a rectangular domain is studied. The differential equation contains two singular perturbation parameters. The solutions of these singularly perturbed problems are decomposed into a sum of regular, boundary layer and corner layer components. Parameter-explicit bounds on the derivatives of each of these components are derived. A numerical algorithm based on an upwind finite difference operator and a tensor product of piecewise-uniform Shishkin meshes is analysed. Parameter-uniform asymptotic error bounds for the numerical approximations are established.     

Effects of temperature on the weathering lifetime of coated polycarbonate

The lifetime of polycarbonate (PC) coated with silicone hardcoats containing UV absorber is shorter at elevated temperatures. The activation energy (E_a) for delamination was found to be 18 ± 2 kJ/mol (4.3 ± 0.5 kcal/mol) at the 95% confidence level in this study. This E_a is the consequence of the sensitivity of the substrate and the UV absorber to temperature. The E_a for PC photodegradation was previously found to be 17-21 kJ/mol (4-5 kcal/mol). The E_a for loss of absorbance in the second-generation silicone hardcoat was found to be 28.5 ± 5.4 kJ/mol (6.8 ± 1.3 kcal/mol) at the 95% confidence level. Results are consistent with experimental findings when these activation energies are used in published predictive models. Since the E_a for coating delamination depends on the E_a of UV absorber loss, coating systems different from the one in this study will need to be investigated separately.     

Explicit construction of self-dual integral normal bases for the square-root of the inverse different

Let K be a finite extension of Qp, let L/K be a finite abelian Galois extension of odd degree and let OL be the valuation ring of L. We define AL/K to be the unique fractional OL-ideal with square equal to the inverse different of L/K. For p an odd prime and L/Qp contained in certain cyclotomic extensions, Erez has described integral normal bases for AL/Qp that are self-dual with respect to the trace form. Assuming K/Qp to be unramified we generate odd abelian weakly ramified extensions of K using Lubin-Tate formal groups. We then use Dwork's exponential power series to explicitly construct self-dual integral normal bases for the square-root of the inverse different in these extensions.     

Electron-hole symmetry and magnetic coupling in antiferromagnetic LaFeAsO

When either electron or hole doped at concentrations x approximately 0.1, the LaFeAsO family displays remarkably high temperature superconductivity with Tc up to 55 K. In the most energetically stable Q-->M=(pi,pi,0) antiferromagnetic (AFM) phase comprised of tetragonal-symmetry breaking alternating chains of aligned spins, there is a deep pseudogap in the Fe 3d states centered at the Fermi energy arising from light carriers (m* approximately 0.25-0.33), and very strong magnetophonon coupling is uncovered. Doping (of either sign) beyond x approximately 0.08 results in heavy carriers per Fe (by roughly an order of magnitude) with a large Fermi surface. Calculated Fe-Fe transverse exchange couplings Jij(R) reveal that exchange coupling is strongly dependent on both the AFM symmetry and on the Fe-As distance.     

The metabolism of methylarsine oxide and sulfide

Methylarsine oxide and sulfide are more toxic to Candida humicola than arsenite; the sulfide is rapidly metabolized to trimethylarsine (Me₃As) and methylarsine (MeAsH₂) and the oxide to dimethylarsinic acid [Me₂AsO(OH)]. Cell-free extracts of C. humicola also convert the oxide to Me₂AsO(OH). The glutathione (RSH) derivative Me₂AsSR is metabolized by C. humicola to Me₃As and Me₂AsH, but some other Me₂AsSR′ compounds are unaffected. Studies involving the interaction of the arsenic(III) compounds with natural ecosystems and other micro-organisms such as Scopulariopsis brevicaulis, Straptococcus sanguis, Escherichia coli, and Veillonella alcalescens are described.