High resolution polar Kerr magnetometer for nanomagnetism and nanospintronics

A new high resolution polar magneto-optical (MO) Kerr magnetometer, devoted to the study of nanometer sized elements with perpendicular magnetic anisotropy, is described. The unique performances of this setup in terms of sensitivity (1.2x10(-15) emu), stability (lateral drift +/-35 nm over 3 h), and resolution (laser spot full width at half maximum down to 470 nm) are demonstrated, and illustrated by Kerr hysteresis loop measurements on a unique ultrathin magnetic nanodot, and over small segments of ultranarrow magnetic tracks. Large scanning MO Kerr microscopy images were also obtained with the same performances.     

Tuning quantum corrections and magnetoresistance in ZnO nanowires by ion implantation

Using ion implantation, the electrical as well as the magnetotransport properties of individual ZnO nanowires (NWs) can be tuned. The virgin NWs are configured as field-effect transistors which are in the enhancement mode. Al-implanted NWs reveal a three-dimensional metallic-like behavior, for which the magnetoresistance is well described by a semiempirical model that takes into account the presence of doping induced local magnetic moments and of two conduction bands. On the other hand, one-dimensional electron transport is observed in Co-implanted NWs. At low magnetic fields, the anisotropic magnetoresistance can be described in the framework of weak electron localization in the presence of strong spin-orbit scattering. From the weak localization, a large phase coherence length is inferred that reaches up to 800 nm at 2.5 K. The temperature-dependent dephasing is shown to result from a one-dimensional Nyquist noise-related mechanism. At the lowest temperatures, the phase coherence length becomes limited by magnetic scattering.     

Zinc impregnation of the anodic oxidation layer of 1050 and 2024 aluminium alloys

The porous oxide layer obtained by phosphoric anodic oxidation (PAO) of 1050 and 2024T3 aluminium alloys is modified by impregnation with zinc under alternating voltage. The resulting current against applied voltage relationship shows that a threshold voltage is required to deposit the zinc. Beyond a low critical voltage, V _{c L}, zinc electrocrystallization starts near the barrier layer and grows with time through the porous oxide layer whatever the alloy used as substrate. For the 2024T3 alloy, beyond a high critical voltage V _{c H}, S.I.M.S. analysis shows that zinc is also present on top of the oxide layer. The distribution of zinc particles depends on the porous layer morphology: formation of zinc needles in a columnar form (1050 alloy) and dispersion of zinc particles in a disorganized structure (2024T3 alloy). The polarization curves obtained in a 3 wt % NaCl solution show a decrease in anodic and cathodic currents indicating a protective effect of zinc impregnation, confirmed by electrochemical impedance analysis.     

The fracture behavior of tungsten wire reinforced superalloy composites during isothermal forging

The isothermal forging behavior of a wire reinforced superalloy powder composite has been examined. The material consisted of a Mar-M200 matrix containing 40 pct by volume of tungsten wire and was prepared by hot isostatic pressing. Specimens were deformed by uniaxial compression at constant temperature in the range 1050 °C to 1180 °C, and at constant true strain rates between 10^-5 s^-1 and 10^-1 s^-1. Loading was normal to the direction of wire alignment. Microstructural defects existing in the as-pressed composites are compared with defects in the forged materials. An upper bound forming limit occurs when fibers come into contact. However, microstructural damage occurs at lower strains which depends on temperature and strain rate. Observed and calculated values of peak flow stress are used to define practical forming conditions for the material which should avoid the formation of internal damage at low strains. Formerly with Mechanical and Aeronautical Engineering Department, Carleton University, Ottawa, Ontario, Canada, K1S 5B6.     

Experimental Study of Ozone Action on Glycine

A first order reaction has been found for glycine oxidation when ozone is applied in a buffered solution. By-products have been studied and apparent rate constants determined.     

AN EXPERIMENTAL STUDY OF PARTICLE FLOW VELOCITIES IN SOLID-LIQUID FOOD MIXTURES

The design of equipment to sterilise solid-liquid food mixtures continuously requires that the flow properties of such mixtures be understood. Little information is available on food flows, which can consist of high solids fractions of particles of a range of densities in non-Newtonian and viscous liquids. A metal detection system which can log two types of particle in the same experiment has been constructed and used in a loop flow rig to study flows of single particles and carrot-water mixtures. Results can be correlated using the particle Froude number; some preliminary analysis is presented to suggest that data can be correlated against 1/Fr_p. The effect of solids fraction on particle flow velocity has been investigated; greatest variations in the particle velocity appear for stratified flows for solids fractions between 10-20%.     

An assessment of veering wind effects on scatterometry from the sea surface

To characterize scatterometer returns from the sea surface near meteorological fronts, we investigated microwave scattering from seas in which long waves are at oblique angles to short waves. We simulate the effects of veering winds on C- and K_u-band scatterometers by using models in which the short waves align with the wind friction velocity u_? , but the long waves are at oblique angles to the u_? direction. The analysis reveals two main effects due to the rotation of the long wave slope probability density distribution. Azimuthally averaged normalized radar cross-section a _o decreases as the oblique angle increases. Additionally, two regimes exist. In the small angle regime, azimuthal scans of normalized radar cross-section σ^o exhibit features similar to the classic double-maxima pattern for non-veering wind conditions, but the axis of σ^o maxima is rotated toward the long-wave axis. In the large angle regime, more than two maxima are apparent in azimuthal scans. Therefore it may be inappropriate to use standard three term Fourier cosine models for some veering wind conditions.     

Gangliosides from rat cerebellum: Demonstration of considerable heterogeneity using a new solvent for thin layer chromatography

Using a new solvent (methyl acetate/n-propanol/chloroform/methanol/0.25% aqueous KCl, 25∶20∶20∶20∶17, v/v) and high performance silica gel thin layer chromatographic plates, all common gangliosides found in brain can be easily separated with 1 hr. This system is reproducible and “tailing” is negligible compared with previous solvents. When such a system is applied to separate the gangliosides found during the development of the rat cerebellum, a considerable heterogeneity is observed. Data are presented (using rechromatography experiments, fractionation on DEAE-Sephadex, treatment with neuraminidase or alkaline medium and carbohydrate analysis) suggesting that the complex profiles obtained with this chromatographic system are not due to chromatographic artifacts but result from the high resolving power of the system. After separation by ion-exchange chromatography, 28 gangliosides can be detected.