A modified wire clamp system for thirty-liter Niskin bottles

A modified clamping system for 30-liter Niskin bottles, consisting of a wire stop, a socket block, and a toggle clamp, has been designed and has been tested at sea. The modified system makes deployment and recovery of the Niskin bottles considerably easier than it is with the standard clamps .Funding was provided by the National Science Foundation under grant Number OCE 84-17910, and by the United States Department of Energy under contract Number DE-AC02-76EV03566

Critical properties of S=1/2 Heisenberg ladders in magnetic fields

The critical properties of the $S=1/2$ Heisenberg two-leg ladders are investigated in a magnetic field. Combining the exact diagonalization method and the finite-size-scaling analysis based on conformal field theory, we calculate the critical exponents of spin correlation functions numerically. For a strong interchain coupling, magnetization dependence of the critical exponents shows characteristic behavior depending on the sign of the interchain coupling. We also calculate the critical exponents for the $S=1/2$ Heisenberg two-leg ladder with a diagonal interaction, which is thought as a model Hamiltonian of the organic spin ladder compound ${Cu}_2({1,4-diazacycloheptane})_2{Cl}_4$. Numerical results are compared with experimental results of temperature dependence of the NMR relaxation rate $1/T_1$.Comment: REVTeX, 10 pages, 8 figures, accepted for Phys. Rev.

Diffuse transport and spin accumulation in a Rashba two-dimensional electron gas

The Rashba Hamiltonian describes the splitting of the conduction band as a result of spin-orbit coupling in the presence of an asymmetric confinement potential and is commonly used to model the electronic structure of confined narrow-gap semiconductors. Due to the mixing of spin states some care has to be exercised in the calculation of transport properties. We derive the diffusive conductance tensor for a disordered two-dimensional electron gas with spin-orbit interaction and show that the applied bias induces a spin accumulation, but that the electric current is not spin-polarized.Comment: REVTeX4 format, 5 page

Spin Hall effect transistor

Spin transistors and spin Hall effects have been two separate leading directions of research in semiconductor spintronics which seeks new paradigms for information processing technologies. We have brought the two directions together to realize an all-semiconductor spin Hall effect transistor. Our scheme circumvents semiconductor-ferromagnet interface problems of the original Datta-Das spin transistor concept and demonstrates the utility of the spin Hall effects in microelectronics. The devices use diffusive transport and operate without electrical current, i.e., without Joule heating in the active part of the transistor. We demonstrate a spin AND logic function in a semiconductor channel with two gates. Our experimental study is complemented by numerical Monte Carlo simulations of spin-diffusion through the transistor channel.Comment: 11 pages, 3 figure

A low-dimensional spin S = 1/2 system at the quantum critical limit: Na2V2O7

We report the results of measurements of the dc-susceptibility and the 23Na-NMR response of Na2V2O7, a recently synthesized, non metallic low dimensional spin system. Our results indicate that upon reducing the temperature to below 100 K, the V^{4+} moments are gradually quenched, leaving only one moment out of 9 active. The NMR data reveal a phase transition at very low temperatures. With decreasing applied field H, the critical temperature shifts towards T = 0 K, suggesting that Na2V2O7 may be regarded as an insulator reaching a quantum critical point at H = 0.Comment: 4 pages, 5 figure

Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field

The T=0 dynamical properties of the one-dimensional (1D) $s=1/2$ Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe ansatz for cyclic chains of $N$ sites. The ground state at magnetization $0<M_z<N/2$, which can be interpreted as a state with $2M_z$ spinons or as a state of $M_z$ magnons, is reconfigured here as the vacuum for a different species of quasiparticles, the {\em psinons} and {\em antipsinons}. We investigate three kinds of quantum fluctuations, namely the spin fluctuations parallel and perpendicular to the direction of the applied magnetic field and the dimer fluctuations. The dynamically dominant excitation spectra are found to be sets of collective excitations composed of two quasiparticles excited from the psinon vacuum in different configurations. The Bethe ansatz provides a framework for (i) the characterization of the new quasiparticles in relation to the more familiar spinons and magnons, (ii) the calculation of spectral boundaries and densities of states for each continuum, (iii) the calculation of transition rates between the ground state and the dynamically dominant collective excitations, (iv) the prediction of lineshapes for dynamic structure factors relevant for experiments performed on a variety of quasi-1D antiferromagnetic compounds, including KCuF$_3$, Cu(C$_4$H$_4$N$_2)(NO_3)_2$, and CuGeO$_3$.Comment: 13 pages, 12 figure

Statistical design and monitoring of the Carotene and Retinol Efficacy Trial (CARET).

CARET is a chemoprevention trial of beta-carotene and vitamin A with lung cancer as the primary outcome. Participants at high risk for lung cancer are drawn from two populations: asbestos-exposed workers and heavy smokers. The intervention is a daily combination of 30 mg beta-carotene and 25,000 IU vitamin A as retinyl palmitate. Nearly 18,000 participants will be followed for a mean 6 years, yielding over 100,000 person-years of follow-up. We project that this sample size will have 80% power to detect a 23% decrease in the incidence of lung cancer cases. The purpose of this paper is to present the values of the key sample size parameters of CARET; our schemes for monitoring CARET for sample size adequacy, incidence of side effects, and efficacy of the study vitamins; an overview of the data collected; and plans for the primary, secondary, and ancillary analyses to be performed at the end of the trial. These approaches to the design, monitoring, and analysis of CARET are applicable for many other prevention trials

Neutron Scattering Study of Magnetic Ordering and Excitations in the Doped Spin Gap System Tl(Cu1−x_{1-x}Mgx_x)Cl3_3

Neutron elastic and inelastic scattering measurements have been performed in order to investigate the spin structure and the magnetic excitations in the impurity-induced antiferromagnetic ordered phase of the doped spin gap system Tl(Cu$_{1-x}$Mg$_x$)Cl$_3$ with $x=0.03$. The magnetic Bragg reflections indicative of the ordering were observed at ${\pmb Q}=(h, 0, l)$ with integer $h$ and odd $l$ below $T_{\rm N}=3.45$ K. It was found that the spin structure of the impurity-induced antiferromagnetic ordered phase on average in Tl(Cu$_{1-x}$Mg$_x$)Cl$_3$ with $x=0.03$ is the same as that of the field-induced magnetic ordered phase for ${\pmb H} \parallel b$ in the parent compound TlCuCl$_3$. The triplet magnetic excitation was clearly observed in the $a^*$-$c^*$ plane and the dispersion relations of the triplet excitation were determined along four different directions. The lowest triplet excitation corresponding to the spin gap was observed at ${\pmb Q}=(h, 0, l)$ with integer $h$ and odd $l$, as observed in TlCuCl$_3$. It was also found that the spin gap increases steeply below $T_{\rm N}$ upon decreasing temperature. This strongly indicates that the impurity-induced antiferromagnetic ordering coexists with the spin gap state in Tl(Cu$_{1-x}$Mg$_x$)Cl$_3$ with $x=0.03$.Comment: 24 pages, 7 figures, 11 eps files, revtex style, will appear in Phys. Rev.