Etching of silicon nanowires on Ag(1 1 0) by atomic hydrogen

Scanning Tunnelling Microscopy, High Resolution Electron Energy Loss Spectroscopy and High Resolution X-Ray Photoelectron Spectroscopy have been used to study the adsorption of atomic hydrogen onto Si nanowires grown on Ag(1 1 0). We demonstrate that the hydrogen strongly interacts with the Si nanowires modifying their structural and electronic properties. Hydrogen atoms etch the Si nanowires and eventually lead to their complete removal from the Ag(1 1 0) surface.     

One-dimensional organic nanostructures: A novel approach based on the selective adsorption of organic molecules on silicon nanowires

Scanning tunneling microscopy (STM) is used to investigate the formation of one-dimensional organic nanostructures by chemisorption of specific molecules on silicon nanowires. STM data demonstrate that depending on the molecular functional groups, the molecules adsorb either randomly on the substrate or preferentially on the nanowires. In the latter case, chemisorption of suitable organic molecules on the nanowires leads to a well-defined one-dimensional aggregation and changes the metallic character of the nanowires to a semi-conducting one.     

Development and validation of an LCMS method to determine the pharmacokinetic profiles of caffeic acid phenethyl amide and caffeic acid phenethyl ester in male Sprague–Dawley rats

A validated LCMS method was developed for the quantitative determination of caffeic acid phenethyl amide (CAPA) and caffeic acid phenethyl ester (CAPE) from rat plasma. Separation was achieved using a reverse‐phase C₁₂ HPLC column (150 × 2.00 mm, 4 µm) with gradient elution running water (A) and acetonitrile (B). Mass spectrometry was performed with electrospray ionization in negative mode. This method was used to determine the pharmacokinetic profiles of CAPA and CAPE in male Sprague–Dawley rats following intravenous bolus administration of 5, 10 and 20 mg/kg of CAPA and 20 mg/kg of CAPE. The pharmacokinetic analysis suggests the lack of dose proportionality in the dose range of 5–20 mg/kg of CAPA. Total clearance values for CAPA ranged from 45 to 156 mL/min and decreased with increasing dose of CAPA. The volume of distribution for CAPA ranged from 17,750 to 52,420 mL, decreasing with increasing dose. The elimination half‐life for CAPA ranged from 243.1 to 295.8 min and no statistically significant differences were observed between dose groups in the range of 5–20 mg/kg (p > 0.05). The elimination half‐life for CAPE was found to be 92.26 min. Copyright © 2013 John Wiley & Sons, Ltd.     

Temperature dependence of the Isomer Shift and electric field gradient of181Ta in Re-metal

The 6.2-keV Mössbauer transition of¹⁸¹Ta was used to study both the Isomer-Shift (IS) and the quadrupole interaction in Re-single crystal host in the temperature range of 77 K to 517 K. Spectra were obtained for the¹⁸¹W diffused into Re-single crystal source using a single line Ta-metal absorber. The temperature change for the IS, δS/δT, is 55(1)×10^?4 mm/s·deg, which is of the order of ?24 times the second-order Doppler shift. The temperature change of the electric field gradient follows the T^3/2 relation. The relative smaller change of the EFG with respect to the IS change with temperature, reflects the strong role of the change of the s-electron density (s-d electron transfer) with temperature over other parameters.     

ULTRAVIOLET AND γ-RAY-INDUCED REACTIONS OF NUCLEIC ACID CONSTITUENTS. REACTIONS OF PURINES WITH AMINES

Abstract— Photochemical and γ-ray-induced reactions of purines with amines are described. These lead to the appropriate 8-substituted purines. The photoproducts were obtained in yields of up to 100% by the use of a variety of photosensitizers, including peroxides. A free radical mechanism is proposed for these reactions.
Such reactions may be relevant to the problem of the nature of DNA-protein cross-links induced by ultraviolet radiation.     

Investigation of sub-Doppler cooling effects in a cesium magneto-optical trap

We present an investigation of sub-Doppler effects in a cesium magneto-optical trap. First, a simple one-dimensional theoretical model of the trap is developed for aJ _g = 1 J _e = 2 transition. This model predicts the size of the trapped atom cloud and temperature as a function of laser intensity and detuning. In the limit of small magnetic field gradients, the trap temperature is found to be equal to the molasses temperature and a minimum size for the trap is calculated. We then describe several experiments performed in a three-dimensional cesium trap to measure the trap parameters, spring constant, friction coefficient, temperature and density. Whilst the temperature of the trapped atoms is found to be equal to the molasses temperature, in agreement with theory, the trap spring constant is found to be two orders of magnitude smaller than the one-dimensional prediction, a value close to that predicted by Doppler models. The maximum density is found to be on the order of 10¹² atoms/cm³ or one atom per optical wavelength on average. When the number of trapped atoms becomes large, the temperature begins to increase dramatically. This excess temperature depends in a very simple way on the atom number, laser intensity and detuning, suggesting that its origin lies in multiple photon scattering within the trap.     

Calculation of nonadiabatic couplings in density-functional theory

This paper proposes methods for calculating the derivative couplings between adiabatic states in density-functional theory (DFT) and compares them with each other and with multiconfigurational self-consistent field calculations. They are shown to be accurate and, as expected, the costs of their calculation scale more favorably with system size than post-Hartree-Fock calculations. The proposed methods are based on single-particle excitations and the associated Slater transition-state densities to overcome the problem of the unavailability of multielectron states in DFT which precludes a straightforward calculation of the matrix elements of the nuclear gradient operator. An iterative scheme employing linear-response theory was found to offer the best trade-off between accuracy and efficiency. The algorithms presented here have been implemented for doublet-doublet excitations within a plane-wave-basis and pseudopotential framework but are easily generalizable to other excitations and basis sets. Owing to their fundamental importance in cases where the Born-Oppenheimer separation of motions is not valid, these derivative couplings can facilitate, for example, the treatment of nonadiabatic charge transfers, of electron-phonon couplings, and of radiationless electronic transitions in DFT.     

Autophosphorylation, electrophoretic mobility and immunoreaction of oat phototropin 1 under UV and blue Light

Phototropins are UV-A/blue light photoreceptors containing two flavin mononucleotide (FMN)-binding domains, light, oxygen and voltage (LOV)1 and LOV2, of which LOV2 is more sensitive toward light and more important for the physiological response compared with LOV1. Some physiological responses are plant phototropism, chloroplast migration and stomatal opening. Oat phototropin 1 together with light-dependent autophosphorylation shows a reduced electrophoretic mobility and reduced immunoreaction against a heterologous antiserum; both effects were suggested to be caused by phosphorylation at the same sites (M. Salomon, E. Knieb, T. von Zeppelin and W. Rudiger [2003] Biochemistry 42, 4217-4225). In this study, we show that both effects can be separated from each other: at low temperature, reduced immunoreaction preceded the mobility shift, and irradiation with UV-C light led to the mobility shift without the loss of immunoreactivity. We demonstrated that UV-C light at 280 nm, which does not match any absorption maximum of FMN, leads to autophosphorylation of phototropin. It is hypothesized that UV-C light causes differential activation of the LOV domains via energy transfer from aromatic amino acids.     

Conductance of solutions of lithium bis(trifluoromethanesulfone)imide in water,propylene carbonate,acetonitrile and methyl formate at 25°C

Conductance data for lithium bis(trifluoromethanesulfone)imide, LiN(CF ₃ SO ₂ ) ₂ , are reported for the solvents water, propylene carbonate, acetonitrile and methyl formate at 25°C. Limiting molar conductivitiesA ₀, association constants K _A , and triple ion formation constants K _t are reported where applicable. These data are compared with literature data for the commonly studied lithium salts LiClO ₄ and LiAsF ₆ . Non-coulombic energy contributions to ion pair formation are evaluated and discussed in terms of ion-ion and ion-solvent interactions.     

Conductivities of 1∶1 salts in 2-cyanopyridine

Electrolytic conductivities of eight simple 11 electrolytes have been measured in dilute solutions of 2-cyanopyridine (2CNP) at 30°. Infinite dilution mobilities and association constants were calculated using the Fuoss-Hsia equation. With the exception of LiCF₃SO₃ all salts show very little association, consistent with the very high dielectric constant of 2CNP. The weak association which does occur is attributed to weak ion-solvent interactions. No evidence was found for triple ion formation. Conductivities of concentrated solutions of LiAsF₆ in 2CNP increase slowly with concentration reaching a maximum at a concentration of around 0.65 mol-dm^–3. These conductances are slightly lower than those in propylene carbonate which has a lower dielectric constant and a higher viscosity. Conductivities of concentrated LiAsF₆ solutions in 2CNP mixtures with acetonitrile vary monotonically, consistent with solution viscosities, and show no sign of the maximum commonly observed in mixed organic solvents.