Hydrographic data from R/V endeavor cruise #90

The final cruise of the NSF sponsored Warm Core Rings Program studied a Warm Core Ring (WCR) in the Fall of 1982 as it formed from a large northward meander of the Gulf Stream. This ring, known as 82-H or the eighth ring identified in 1982, formed over the New England Seamounts near 39.5 deg N, 65 deg W. Surveys using Expendable Bathythermographs, Conductivity-Temperature-Depth-Oxygen stations and Doppler Current Profiling provide a look at the genesis of a WCR. These measurements reveal that WCR 82-H separated from the Gulf Stream sometime between October 2-5. This ring was a typical WCR with a diameter of about 200 km and speeds in the high velocity core of the 175 cm/sec. Satellite imagery of 82-H following the cruise showed that it drifted WSW in the Slope Water region at almost 9 km/day, had at least one interaction with the Gulf Stream and was last observed on February 8, 1983 at 39 deg N, 72 deg W

Water sample and expendable bathythermograph (XBT) data from R/V Atlantis II cruise 107 : Leg X

This report summarizes in graphical and tabular form the continuous conductivity-temperature-pressure-dissolved-oxygen (CTD0 2) data collected during the R/V ATLANTIS II Cruise 107, Leg X. These data were collected in the austral winter of 1980 as part of the International Southern Ocean Studies (ISOS) to evaluate and test various Antarctic Intermediate Water formation and circulation mechanisms.Prepared for the National Science Foundation - Office of International Decade of Ocean Exploration under Grant OCE-78-22223

Disorder Effect on the Vortex Pinning by the Cooling Process Control in the Organic Superconductor κ\kappa-(BEDT-TTF)2_2Cu[N(CN)2_2]Br

We investigate the influence of disorders in terminal ethylene groups of BEDT-TTF molecules (ethylene-disorders) on the vortex pinning of the organic superconductor $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br. Magnetization measurements are performed under different cooling-processes. The second peak in the magnetization hysteresis curve is observed for all samples studied, and the hysteresis width of the magnetization becomes narrower by cooling faster. In contradiction to the simple pinning effect of disorder, this result shows the suppression of the vortex pinning force by introducing more ethylene-disorders. The ethylene-disorder domain model is proposed for explaining the observed result. In the case of the system containing a moderate number of the ethylene-disorders, the disordered molecules form a domain structure and it works as an effective pinning site. On the contrary, an excess number of the ethylene-disorders may weaken the effect of the domain structure, which results in the less effective pinning force on the vortices.Comment: 6 pages, 6 figure

First tests of wavefront sensing with a constellation of laser guide beacons

Adaptive optics to correct current telescopes over wide fields, or future very large telescopes over even narrow fields, will require real-time wavefront measurements made with a constellation of laser beacons. Here we report the first such measurements, made at the 6.5 m MMT with five Rayleigh beacons in a 2 arcmin pentagon. Each beacon is made with a pulsed beam at 532 nm, of 4 W at the exit pupil of the projector. The return is range-gated from 20-29 km and recorded at 53 Hz by a 36-element Shack-Hartmann sensor. Wavefronts derived from the beacons are compared with simultaneous wavefronts obtained for individual natural stars within or near the constellation. Observations were made in seeing averaging 1.0 arcsec with 2/3 of the aberration measured to be from a ground layer of mean height 380 m. Under these conditions, subtraction of the simple instantaneous average of the five beacon wavefronts from the stellar wavefronts yielded a 40% rms reduction in the measured modes of the distortion over a 2 arcmin field. We discuss the use of multiple Rayleigh beacons as an alternative to single sodium beacons on 8 m telescopes, and the impact of the new work on the design of a multi-sodium beacon system for the 25 m Giant Magellan Telescope.Comment: 25 pages, 7 figures, uses aastex.cls, to be published in the Astrophys.

A comparison of methods for the determination of dissolved oxygen in seawater

An intercalibration of dissolved oxygen methods was conducted at 2 stations in the Sargasso Sea between April 28 and May 3, 1990. The experiment compared three techniques using automated endpoint detection with the manual Winkler method using a starch endpoint. Institutions participating in the intercomparison were the Bedford Institute of Oceanography (automated photometric titration), the University of Delaware (automated amperometric titration), the Scripps Institution of Oceanography (manual titration), and the Woods Hole Oceanographic Institution (automated amperometric titration). Differences in measured oxygen concentrations between institutions were encouragingly small. However, small, systematic differences in dissolved oxygen between institutions did exist. The range between the highest and lowest oxygen values reported by the 4 institutions never exceeded 0.6% over the entire concentration range studied (3.4 to 6.2 mlj1). The good agreement is probably due to the use of the essentials of Carpenter's (1965) modification of the Winkler method by all institutions. The intercalibration revealed several aspects of dissolved oxygen measurements that require further research: (1) the intercalibration should be extended to very low oxygen concentrations; (2) procedures for measur ing and applying corrections for the seawater blank need to be formalized; (3) a simple procedure to measure the temperature of seawater at the time of sampling needs to be developed; and (4) the solubility of atmospheric oxygen in the Winkler reagents must be measured as a function of temperature. The intercalibration also revealed that analytical techniques required for precise and accurate volumetric measurements were often not applied, even by experienced analysts. It was found that uncalibrated pipets were used to dispense standards, that the volumes of oxygen flasks were not corrected for buoyancy, and that corrections for the thermal expansion of aqueous solutions were often not applied.This research was supported by National Science Foundation Grants OCE 88- 22542 and OCE 88-21977 and OCE 89-07815. Preparation and distribution of this report by the WHP Office, Woods Hole Oceanographic Institution, Woods Hole, MA. 02543 USA, was supported by NSF Grant OCE 89-07815

Impurity Effect on the In-plane Penetration Depth of the Organic Superconductors κ\kappa-(BEDT-TTF)2X_2X (XX = Cu(NCS)2_2 and Cu[N(CN)2_2]Br)

We report the in-plane penetration depth $\lambda_{\parallel}$ of single crystals $\kappa$-(BEDT-TTF)$_2X$ ($X=$ Cu(NCS)$_2$ and Cu[N(CN)$_2$]Br) by means of the reversible magnetization measurements under the control of cooling-rate. In $X$ = Cu(NCS)$_2$, $\lambda_{\parallel}(0)$ as an extrapolation toward $T$ = 0 K does not change by the cooling-rate within the experimental accuracy, while $T_{\textrm{c}}$ is slightly reduced. On the other hand, in $X$ = Cu[N(CN)$_2$]Br, $\lambda_{\parallel}(0)$ indicates a distinct increase by cooling faster. The different behavior of $\lambda_{\parallel}(0)$ on cooling-rate between the two salts is quantitatively explained in terms of the local-clean approximation (London model), considering that the former salt belongs to the very clean system and the later the moderate clean one. The good agreement with this model demonstrates that disorders of ethylene-group in BEDT-TTF introduced by cooling faster increase the electron(quasiparticle)-scattering, resulting in shorter mean free path.Comment: 8 pages, 9 figure

Real space imaging of the metal - insulator phase separation in the band width controlled organic Mott system κ\kappa-(BEDT-TTF)2_{2}Cu[N(CN)2_{2}]Br

Systematic investigation of the electronic phase separation on macroscopic scale is reported in the organic Mott system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br. Real space imaging of the phase separation is obtained by means of scanning micro-region infrared spectroscopy using the synchrotron radiation. The phase separation appears near the Mott boundary and changes its metal-insulator fraction with the substitution ratio $x$ in $\kappa$-[($h$-BEDT-TTF)$_{1-x}$($d$-BEDT-TTF)$_{x}$]$_{2}$Cu[N(CN)$_{2}$]Br, of which band width is controlled by the substitution ratio $x$ between the hydrogenated BEDT-TTF molecule ($h$-BEDT-TTF) and the deuterated one ($d$-BEDT-TTF). The phase separation phenomenon observed in this class of organics is considered on the basis of the strongly correlated electronic phase diagram with the first order Mott transition.Comment: 10 pages, 8 figure

Metal-insulator transition and charge ordering in the extended Hubbard model at one-quarter filling

We study with exact diagonalization the zero temperature properties of the quarter-filled extended Hubbard model on a square lattice. We find that increasing the ratio of the intersite Coulomb repulsion, $V$, to the band width drives the system from a metal to a charge ordered insulator. The evolution of the optical conductivity spectrum with increasing $V$ is compared to the observed optical conductivity of several layered molecular crystals with the theta and beta'' crystal structures.Comment: 5 pages, 3 figure

Evidence for structural and electronic instabilities at intermediate temperatures in κ\kappa-(BEDT-TTF)2_{2}X for X=Cu[N(CN)2_{2}]Cl, Cu[N(CN)2_{2}]Br and Cu(NCS)2_{2}: Implications for the phase diagram of these quasi-2D organic superconductors

We present high-resolution measurements of the coefficient of thermal expansion $\alpha (T)=\partial \ln l(T)/\partial T$ of the quasi-twodimensional (quasi-2D) salts $\kappa$-(BEDT-TTF)$_2$X with X = Cu(NCS)$_2$, Cu[N(CN)$_2$]Br and Cu[N(CN)$_2$]Cl. At intermediate temperatures (B), distinct anomalies reminiscent of second-order phase transitions have been found at $T^\ast = 38$ K and 45 K for the superconducting X = Cu(NCS)$_2$ and Cu[N(CN)$_2$]Br salts, respectively. Most interestingly, we find that the signs of the uniaxial pressure coefficients of $T^\ast$ are strictly anticorrelated with those of $T_c$. We propose that $T^\ast$ marks the transition to a spin-density-wave (SDW) state forming on minor, quasi-1D parts of the Fermi surface. Our results are compatible with two competing order parameters that form on disjunct portions of the Fermi surface. At elevated temperatures (C), all compounds show $\alpha (T)$ anomalies that can be identified with a kinetic, glass-like transition where, below a characteristic temperature $T_g$, disorder in the orientational degrees of freedom of the terminal ethylene groups becomes frozen in. We argue that the degree of disorder increases on going from the X = Cu(NCS)$_2$ to Cu[N(CN)$_2$]Br and the Cu[N(CN)$_2$]Cl salt. Our results provide a natural explanation for the unusual time- and cooling-rate dependencies of the ground-state properties in the hydrogenated and deuterated Cu[N(CN)$_2$]Br salts reported in the literature.Comment: 22 pages, 7 figure

Pairing Symmetry Competition in Organic Superconductors

A review is given on theoretical studies concerning the pairing symmetry in organic superconductors. In particular, we focus on (TMTSF)$_2$X and $\kappa$-(BEDT-TTF)$_2$X, in which the pairing symmetry has been extensively studied both experimentally and theoretically. Possibilities of various pairing symmetry candidates and their possible microscopic origin are discussed. Also some tests for determining the actual pairing symmtery are surveyed.Comment: 16 pages, 8 figures, to be published in J. Phys. Soc. Jpn., special issue on "Organic Conductors