Search Results - (Author, Cooperation:S. M. Thompson)

2016-05-05

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1089-7550

AIP Digital Archive

Physics

A new technique is presented for studying spin dependent transport properties in mesoscopic magnetic structures which exploits the magnetorefractive effect (MRE). A Fourier transform infrared spectrometer was used to measure the MRE of CoAg granular films deposited on thinned Si(001) substrates. Infrared transmission spectra were recorded over a wavelength range from 2.5 to 18.2 μm in an applied magnetic field up to 1.5 kOe. The resulting relative transmission curves have a minimum at approximately 7 μm which deepens if the applied magnetic field is increased. This behavior can be described by model calculations in the self-averaging limit from which the scattering rates can be extracted when fitted to the experimental spectra. The field dependent behavior of the MRE reproduces the magnetoresistance behavior measured using a conventional four-point probe demonstrating the capability of the MRE to study magnetotransport without making electrical contacts. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A mechanism is described which considers the effect of small magnetic particles on the spin diffusion length in a granular giant magnetoresistive material. Spin depolarization occurs by precession of the spin orientation of the carrier due to the s–d exchange interaction within a magnetic particle. Numerical simulation of this jitterbug effect is found to generate a temperature and field dependence of the distance a carrier may travel within the sample without losing its spin memory. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Co–Ag granular films are prepared by molecular-beam epitaxy to enable a detailed structural study to be conducted in conjunction with magnetotransport properties. It is demonstrated that the shape, size, location, and segregation of the magnetic Co grains and the morphology of the surface depend on the growth temperature. Detailed transmission electron microscopy reveals inherent differences between samples prepared at room temperature and those prepared at high temperature. Small clusters of only a few atoms are found to be present in the matrix of the low-temperature samples significantly affecting the spin diffusion length. Well-crystallized regions of both Co and Ag are found in the high-temperature samples, however, the Co grains remain relatively small in size even at the highest growth temperatures. © 1996 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The presence of perpendicular anisotropy in Co/Pt multilayers is often attributed to an enhanced orbital magnetization at the surface or interfaces of the multilayers. By the application of the 〈Lz/Sz〉 sum rule to magnetic x-ray circular dichroism spectra it is possible to probe directly the orbital to spin ratio. In this study a comparison has been made of this ratio between Co/Pt multilayers with different anisotropies and also with single films of Co with and without Pt. The multilayers were prepared in high vacuum by evaporation on Si substrates with a 2.4 nm Pt buffer and a 1.2 nm Pt capping layers, characterized by x-ray diffraction and magneto-optic Kerr effect. The magnetic circular dichroism experiments were carried out at Daresbury laboratory in 75% polarization in ±1 T perpendicular applied fields as a function of temperature from 25 to 300 K. We find that the 〈Lz/Sz〉 ratio is enhanced for a multilayer with perpendicular anisotropy compared to a similar multilayer with in-plane anisotropy.© 1997 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A correlation is found between the room temperature giant magnetoresistive (GMR) behavior and the direction of the easy axis of the magnetization in molecular beam epitaxy grown CoAg granular films. Samples containing between 15 and 50 at. % Co were prepared by co-evaporation at temperatures ranging from 0 to 600 °C. GMR curves are recorded with the current in the film plane and the external field either parallel or perpendicular to the film. Out-of-plane torque magnetometry has been used to determine the anisotropy energies and carry out a full directional analysis. Below Co concentrations of 30 at. %, the GMR curve for the field perpendicular to the plane always decreases more rapidly than for the field parallel to the plane. In contrast, for higher Co concentrations, the in-plane GMR decreases more rapidly at low fields and then crosses over the out-of-plane GMR curve. Thus, the maximum GMR is always observed when the field is perpendicular to the plane. Torque measurements show that for all growth temperatures, the direction of the easy axis of magnetization changes from out-of-plane to in-plane with increasing Co concentration. This crossover shifts to lower Co concentrations as the growth temperature increases. The maximum anisotropy energy density is larger in the case where the easy axis lies in the film plane. Unexpectedly, for all growth temperatures two uniaxial anisotropy contributions are found to coexist in films containing 20 at. % of Co. We attribute our findings to the shape anisotropy of the magnetic grains, which is dominated by columnar growth at low and thin film like behavior at high Co concentrations, respectively.© 1997 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The molecular dynamics method is used to study the liquid–vapor interface of the Stockmayer fluid. We compare our results for the singlet density-orientation distribution function and surface tension with the predictions of integral equation and perturbation theory. We find that at low temperature and high moment conditions, dipolar orientations in the interfacial region parallel to the surface are more probable. The pressure tensor, mean squared force, and mean squared torque are also determined as functions of position with respect to the interface. Directional anisotropy in the mobility of particles in the vicinity of the surface is found by decomposing the mean squared displacements into components parallel and perpendicular to the interfacial plane.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The structure and surface tension of the liquid–vapor interface of a polar fluid are investigated using integral equation and perturbation theories. A recently introduced integro-differential equation and a perturbation theory are employed to determine the extent to which purely multipolar anisotropies in the pair potential induce orientational ordering. Both of these theories agree that orientational ordering can be induced at the liquid–vapor interface by purely multipolar anisotropies in the intermolecular potential. The Yvon–Born–Green equation and the virial equation for the surface tension are written in terms of the spherical harmonic coefficients of the one and two particle distributions, and simple expressions are obtained for the density profile and the anisotropic contribution to the surface tension for molecular models of multipolar symmetry. The density profiles, density-orientation profiles, surface thickness, and surface tension are calculated for the Stockmayer fluid for a range of temperatures and dipole moments.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Giant magnetoresistance of 7.7% at 5 K is observed in bulk mechanically alloyed Co30Ag70. Our recently defined δ(Δρ/ρ) technique used to determine the predominant interactions within the system indicated that negative interactions dominate between the particles. Exchange anisotropy and metastable magnetization processes characterized by large Barkhausen jumps are observed at low temperatures on a small volume of the sample.

Electronic Resource

1432-1106

Pretectal complex ; Thalamic lateral dorsal nucleus ; Cat

Springer Online Journal Archives 1860-2000

Medicine

Summary The subcortical projections to the lateral dorsal nucleus (LD) of the cat thalamus were studied with retrograde transport techniques. Deposits of horseradish peroxidase (HRP) or fluorescent tracers were placed unilaterally in LD of adult cats, using electrophoretic or pressure injection techniques. Following post-injection survival periods of 1, 2 or 3 days, HRP retrogradely labeled cells were identified in sections reacted with benzidine dihydrochloride; fluorescent labeled cells were identified by fluorescent microscopy. Injections in LD result in retrogradely labeled neurons in all nuclei of the pretectal complex, including the nucleus of the optic tract (NTO), the posterior pretectal nucleus (NPP), the anterior pretectal nucleus (NPA), the pretectal olivary nucleus (NOL), and the medial pretectal nucleus (NPM). Small electrophoretic injections of HRP were used to investigate a possible topographic organization of the pretectal projections. Results from a variety of injection sites indicate only a subtle rostral-caudal gradient. That is, small injection sites in rostral LD result in retrograde labeling of neuron somata in the rostral parts of NTO, NPA and NPP, and throughout NPM. Injections in caudal LD result in labeled cells more caudally situated in NTO, NPA, NPP, and throughout NPM. Injections in the pulvinar (Pul) also result in retrogradely labeled cells in the pretectal complex, particularly NTO, NPP, and NOL. Experiments with injections of distinguishable fluorescent tracers in LD and Pul reveal that many more cells project to Pul than to LD. These experiments also reveal that while neurons that project to LD are intermingled with neurons that project to Pul, the two projections originate from separate sub-populations of cells. These results are discussed in regard to phylogenetic comparison of pretectal projections and subcortical pathways of sensory input to the limbic system.

Electronic Resource

1432-1793

Springer Online Journal Archives 1860-2000

Biology

Abstract In two temperate reef fish, Pseudolabrus celidotus (Bloch and Schneider) and Tripterygion varium (Bloch and Schneider) studied near Leigh, New Zealand, most spawning activity was concentrated during the first 2 months of spawning seasons which lasted about 5 months. In P. celidotus, maturation and spawning of first-year females (0+) was delayed with respect to older (≥1+yr) females. Within the 0+ age class, the minimum size of maturation declined as the spawning season proceeded. However, in all females of T. varium, ripening and spawning took place over the same time ranges. Observations on the seasonal patterns of female aggression suggested that larger female P. celidotus were socially inhibiting the maturation of small females. The level of interaction was high compared to that in T. varium, and reached a peak over the onset of the spawning season. This hypothesis was tested by the removal of larger (≥1+yr) female P. celidotus from a field population. The remaining 0+ females increased in ovary weight and matured earlier than those in an undisturbed area. We argue from this experiment that it is of advantage for P. celidotus females to spawn early in the season and of advantage to inhibit other females from doing so. Two possible reasons are suggested, the first applying to sexchanging species such as P. celidotus, the second to temperate-water fishes in general.

Electronic Resource

1432-1793

Springer Online Journal Archives 1860-2000

Biology

Abstract Long-term behavioural studies were made of the blennioid fish Forsterygion varium and the wrasse Pseudolabrus celidotus in the Cape Rodney-Okakari Point Marine Reserve in New Zealand. Both male and female F. varium defended small 1 to 2 m2 territories from the wrasse all year round, althoughl aggressive encounters were most frequent from December to April. Only Large P. celidotus (≧180 mm standard length) were observed to dominate the blenny in interactions. Defence of nests, which were found only on the territories of males between May and October, did not explain the distribution of F. varium aggression between the sexes and seasons. An extensive overlap in the categories and size of prey eaten suggested that protection of food was a major function of F. varium territoriality. F. varium was most frequently aggressive toward P. celidotus of an intermediate size (110 to 160 mm SL) and exhibited greatest overlap in diet with wrasses in this size lange. This dnected the study toward examining the effect of F. varium on the feeding activity of P. celidotus. Within a shallow, Leterogeneous reef habitat, feeding pressure by P. celidotus (bites/are/time) was inversely related to the density of F. varium. Removal of F. varium from small 5x5 m quadrats resulted in large increases in wrasse feeding pressure, suggesting that the blenny influences the foraging of wrasses within their home ranges. When F. varium were removed from the entire home ranges of five 1+yr (110 to 130 mm SL) P. celidotus, these fish exhibited relative increases in both feeding rate and foraging time. The results suggest that P. celidotus grow through a period during which individuals compete with F. varium for food, adding support to the contention that territoriality in F. varium functions to preserve its food supply.

Electronic Resource

1432-1424

Springer Online Journal Archives 1860-2000

Biology

Chemistry and Pharmacology

Electronic Resource

1573-1995

Springer Online Journal Archives 1860-2000

Electrical Engineering, Measurement and Control Technology

Abstract Any project, programme or organisation, working in any environment with released information, managing its change, maintaining traceability, and ensuring results always meet expectations, needs configuration management. Software projects introduce additional complexities — multiple developers working on the same item at the same time, the need for compatibility with other products and systems, targeting releases for multiple platforms, and supporting multiple versions (for example development and released versions). This paper describes the configuration management processes that support and manage products through their entire life cycle as they change and evolve.

Electronic Resource

0142-2421

XPS ; AES ; CoAg granular film ; CoPt alloy ; magnetoresistance ; Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Physics

The chemical state of Co, Ag and Pt in giant magnetoresistive CoAg granular films sandwiched between Pt layers is studied using high-resolution x-ray photoelectron spectroscopy. Measurements were carried out as a function of depth for samples deposited at different temperatures and containing different amounts of Co. In all samples Ag is found to segregate at the surface to form an AgPt alloy. The depth profiles are consistent with the deposited Co concentration modified by preferential sputtering. No variation of the chemical state for Co or Ag in the CoAg layer is found for different deposition conditions. However, small amounts of Pt do affect the Co 3d electrons. © 1998 John Wiley & Sons, Ltd.

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Electronic Resource