The origin and control of the sources of AMR in (Ga,Mn)As devices

We present details of our experimental and theoretical study of the components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. We develop experimental methods to yield directly the non-crystalline and crystalline AMR components which are then independently analysed. These methods are used to explore the unusual phenomenology of the AMR in ultra thin (5 nm) (Ga,Mn)As layers and to demonstrate how the components of the AMR can be engineered through lithography induced local lattice relaxations. We expand on our previous [A.W. Rushforth, et al., Phys. Rev. Lett. 99 (2007) 147207] theoretical analysis and numerical calculations to present a simplified analytical model for the origin of the non-crystalline AMR. We find that the sign of the non-crystalline AMR is determined by the form of the spin-orbit coupling in the host band and by the relative strengths of the non-magnetic and magnetic contributions to the impurity potential.     

Oxygen difluoride

The preparation and chemical and physical properties of the oxygen fluorides (OF₂, OF, O₂F₂, OOF and O₄F₂) are reviewed. There has been speculation about the existence of other oxygen fluorides (O₃F₂, O₃F, OSF₂ and O₆F₂) but these have not been well-characterized. The first member, OF₂, is much more stable than the other oxygen fluorides, and is also less-reactive. In addition to acting as a fluorinating agent and oxidizer, OF₂ has been shown to be a source of the OF radical. Dioxygen difluoride is a powerful fluorinating agent, but if reacted under carefully controlled conditions, can be a source of the OOF radical.     

Generation of 0.4-keV femtosecond electron pulses using impulsively excited surface plasmons

We demonstrate the generation of 0.4-keV, sub-27 fs electron pulses using low-intensity laser pulses from a Ti:sapphire oscillator through the excitation of surface plasmon waves on a time scale within the plasmon lifetime. Modeling of the ponderomotive electron pulse acceleration yields electron energy spectra that are in excellent agreement with the observed ones. Our work opens a doorway for time-resolved experimentation using low-power, high-repetition rate laser pulses.     

Analysis of VX nerve agent hydrolysis products in wastewater effluents by ion chromatography with amperometric and conductivity detection

An analytical method, based on the use of ion chromatography, was developed to monitor the levels of three regulated VX hydrolysis products in the effluent from a biological wastewater treatment process--ethylmethylphosphonic acid, methylphosphonic acid and 2-(diisopropyl)aminoethanethiol. Previous methods have not been applied to wastewater matrices or 2-(diisopropyl)aminoethanethiol. Despite the specificity and sensitivity constraints of this method, it was possible to measure the compounds in bioreactor effluents down to a level substantially below the US Army discharge limit of 0.1% (w/v). Analytical data was confirmed by liquid chromatography-mass spectrometry (LC-MS) at an independent laboratory.     

New odourless protocols for efficient Pauson-Khand annulations

An inexpensive and commercially available odourless additive, dodecyl methyl sulfide, has been shown to be a highly effective promoter in the Pauson-Khand cyclisation of both intra- and intermolecular substrates, affording good to excellent yields of cyclopentenone products.     

Shell model calculations on the positive parity states in 20Ne

The results of an extended shell model calculation in the space spanned by the $\text{0}\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ orbital and the whole of the sd-shell for the nucleus ²⁰Ne are presented. The positions of the (4p-0h), (6p-2h) and (8p-4h) bands are located and the results are compared with recent experiments.     

Results of studies of potential light spectrum effects on human performance

Abstract— Sensitization of the phytochrome-mediated germination at 20°C of lettuce seeds (Lactuca sativa L. cv. Grand Rapids) by pretreatment at 4°C, 28°C, or on 1% ethanol, was studied. The 660 nm fiuence-response characteristics were similarly biphasic for all sensitizing treatments and displayed responses at very low fluences (VLFR) as well as responses characteristic of non-sensitized seeds at 10000-fold higher, low fluences (LFR). Maximum VLFR increased with the duration of sensitizing treatments. However, the fluence ranges required for the two types of responses remained relatively constant. These and additonal responses of sensitized seeds to 730 nm fluences were compared to simulations of a mechanism involving a receptor, X, and based on the dimeric structure of phytochrome in which each monomer is independently phototransformed from the inactive (P_r) to the active (P_fr) form. The fluence requirements for phytochrome photoconversion in seeds were determined to be similar to those of purified Avena phytochrome in vitro, on which photochemical parameters for the simulations were based. The analyses suggest that P_r:P_fr-Xand P_fr:P_fr-X are responsible, respectively, for the VLFR and the LFR, and that sensitization involves membrane influences on the activity of P_r:P_r-X. They also suggest the concentration of X to be about 0.001 that of total phytochrome dimer in this system.     

A high-yielding enantiospecific synthesis of (−)-7-deoxydaunomycinone

A comparison is made between two regiospecific modes of base-catalysed condensation of 4 (or 7)-methoxy-3-phenylsulfonyl phthalides with chiral bicyclic quinone monoketals, one of which occurs in 95% yield and forms the basis of the first enantiospecific total synthesis of (?)-7-deoxydaunomycinone (3).