Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance

Low energy $\beta$-detected nuclear magnetic resonance ($\beta$-NMR) was used to investigate the spatial dependence of the hyperfine magnetic fields induced by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001) magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag layer shows dramatic broadening compared to intrinsic Ag. This broadening is attributed to large induced magnetic fields in this layer by the magnetic Fe layer. We find that the induced hyperfine field in the Ag follows a power law decay away from the Ag/Fe interface with power $-1.93(8)$, and a field extrapolated to $0.23(5)$ T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.

β\beta-NMR of Isolated 8^{8}Li+^{+} Implanted into a Thin Copper Film

Depth-controlled $\beta$-NMR was used to study highly spin-polarized $^8$Li in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive Knight Shifts and spin relaxation data show that $^8$Li occupies two sites at low temperatures, assigned to be the substitutional ($S$) and octahedral ($O$) interstitial sites. Between 50 to 100 K, there is a site change from $O$ to $S$. The temperature dependence of the Knight shifts and spin-lattice relaxation rates at high temperatures, i.e. when all the Li are in the $S$ site, is consistent with the Korringa Law for a simple metal.Comment: Accepted for publication in Phys. Rev.

Kinks Dynamics in One-Dimensional Coupled Map Lattices

We examine the problem of the dynamics of interfaces in a one-dimensional space-time discrete dynamical system. Two different regimes are studied : the non-propagating and the propagating one. In the first case, after proving the existence of such solutions, we show how they can be described using Taylor expansions. The second situation deals with the assumption of a travelling wave to follow the kink propagation. Then a comparison with the corresponding continuous model is proposed. We find that these methods are useful in simple dynamical situations but their application to complex dynamical behaviour is not yet understood.Comment: 17pages, LaTex,3 fig available on cpt.univ-mrs.fr directory pub/preprints/94/dynamical-systems/94-P.307

Persistent Spin Dynamics in the S=1/2S=1/2 V15_{15} Molecular Nano-Magnet

We present muon spin lattice relaxation measurements in the V15 spin 1/2 molecular nano-magnet. We find that the relaxation rate in low magnetic fields (<5 kG) is temperature independent below ~10 K, implying that the molecular spin is dynamically fluctuating down to 12 mK. These measurements show that the fluctuation time increases as the temperature is decreased and saturates at a value of ~6 nsec at low temperatures. The fluctuations are attributed to V15 molecular spin dynamics perpendicular to the applied magnetic field direction, induced by coupling between the molecular spin and nuclear spin bath in the system.Comment: Accepted for publication in Phys. Rev. B, 5 pages, 5 figur

Extraction of the πNN\pi NN coupling constant from NN scattering data

We reexamine Chew's method for extracting the $\pi NN$ coupling constant from np differential cross section measurements. Values for this coupling are extracted below 350 MeV, in the potential model region, and up to 1 GeV. The analyses to 1~GeV have utilized 55 data sets. We compare these results to those obtained via $\chi^2$ mapping techniques. We find that these two methods give consistent results which are in agreement with previous Nijmegen determinations.Comment: 12 pages of text plus 2 figures. Revtex file and postscript figures available via anonymous FTP at ftp://clsaid.phys.vt.edu/pub/n

Effect of noise on coupled chaotic systems

Effect of noise in inducing order on various chaotically evolving systems is reviewed, with special emphasis on systems consisting of coupled chaotic elements. In many situations it is observed that the uncoupled elements when driven by identical noise, show synchronization phenomena where chaotic trajectories exponentially converge towards a single noisy trajectory, independent of the initial conditions. In a random neural network, with infinite range coupling, chaos is suppressed due to noise and the system evolves towards a fixed point. Spatiotemporal stochastic resonance phenomenon has been observed in a square array of coupled threshold devices where a temporal characteristic of the system resonates at a given noise strength. In a chaotically evolving coupled map lattice with logistic map as local dynamics and driven by identical noise at each site, we report that the number of structures (a structure is a group of neighbouring lattice sites for whom values of the variable follow certain predefined pattern) follow a power-law decay with the length of the structure. An interesting phenomenon, which we call stochastic coherence, is also reported in which the abundance and lifetimes of these structures show characteristic peaks at some intermediate noise strength.Comment: 21 page LaTeX file for text, 5 Postscript files for figure

A new derivation of Luscher F-term and fluctuations around the giant magnon

15 pages, no figures; v2: added assumption on diagonal scattering and a section on generalizations; v3: minor changes, version accepted for publication in JHEPIn this paper we give a new derivation of the generalized Luscher F-term formula from a summation over quadratic fluctuations around a given soliton. The result is very general providing that S-matrix is diagonal and is valid for arbitrary dispersion relation. We then apply this formalism to compute the leading finite size corrections to the giant magnon dispersion relation coming from quantum fluctuations.Peer reviewe

An intensive multi-site pilot study investigating atmospheric mercury in Broward County, Florida

An intensive multi-site pilot study of atmospheric Hg was conducted in Broward County, Florida in August and September of 1993. Broward County, which contains the city of Fort Lauderdale, is located in southeastern Florida. The county borders the Florida Everglades on the west and the Atlantic Ocean on the east. A network of four sampling sites was set up for 20 days throughout Broward County to measure Hg in both the vapor phase and the particle phase as well as Hg in precipitation. The mean concentrations of total vapor phase Hg measured at two inland sites were found to be significantly higher (3.3 and 2.8 ng/m 3 ) than that measured at a site located on the Atlantic shore (1.8 ng/m 3 ). The mean concentrations of particle phase Hg collected at the two inland sites (51 and 49 pg/m 3 ) were found to be 50% greater than that measured at the coastal site (34 pg/m 3 ). In addition, event precipitation samples were collected at four sampling sites over the 20 day study period and were analyzed for both reactive and total Hg. The mean concentration of total Hg in the precipitation samples was found to be 44 ng/L, with a range of 14 to 130 ng/L. It was determined that further meteorological analysis and a more complete characterization of the aerosol and precipitation composition are needed to identify the probable source(s) contributing to the increased deposition of Hg.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43910/1/11270_2005_Article_BF01189665.pd

Local Magnetic Properties of a Monolayer of Mn12 Single Molecule Magnets

The magnetic properties of a monolayer of Mn12 single molecule magnets grafted onto a Si substrate have been investigated using depth-controlled $\beta$-detected nuclear magnetic resonance. A low energy beam of spin polarized radioactive 8Li was used to probe the local static magnetic field distribution near the Mn12 monolayer in the Si substrate. The resonance linewidth varies strongly as a function of implantation depth as a result of the magnetic dipolar fields generated by the Mn12 electronic magnetic moments. The temperature dependence of the linewidth indicates that the magnetic properties of the Mn12 moments in this low dimensional configuration differ from bulk Mn12.Comment: 6 pages, 4 figure

Space Flight Qualification on a Multi-Fiber Ribbon Cable and Array Connector Assembly

NASA's Goddard Space Flight Center (GSFC) cooperatively with Sandia National Laboratories completed a series of tests on three separate configurations of multi-fiber ribbon cable and MTP connector assemblies. These tests simulate the aging process of components during launch and long-term space environmental exposure. The multi-fiber ribbon cable assembly was constructed of non-outgassing materials, with radiation-hardened, graded index 100/140-micron optical fiber. The results of this characterization presented here include vibration testing, thermal vacuum monitoring, and extended radiation exposure testing data