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  • 1
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Excitatory amino acids have been proposed to play a critical role in the development and maintenance of epileptic seizures and in the development of neuronal damage. Previous animal studies of glutamate during seizures, however, have often failed to measure any rise in glutamate. We have overcome many of the problems of these studies by using an animal model in which epileptic afterdischarges are induced by stimulation of the perforant path, and glutamate and ascorbate are measured using a newly developed microdialysis electrode that combines the advantages of microdialysis and in vivo electrochemistry. We have successfully shown (1) a rise in glutamate after an epileptic afterdischarge, (2) a concomitant initial fall and then a later rise in ascorbate, and (3) progressive dwindling of this effect when afterdischarges are repeated within minutes, despite similar electroencephalographic responses. The possible mechanisms of these effects are discussed and include ascorbate/glutamate heteroexchange, reversal of the glutamate uptake mechanism, and augmentation of glutamate uptake after a seizure.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6546-6547 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results for the temperature and magnetic-field dependence of melt-spun Cu87Co13 are presented and discussed. The magnetoresistance of the as-spun sample exhibits superparamagnetic behavior with a magnetoresistance of 18% at 0.4 K and in a field of 80 kOe. The magnetic-field dependence of the magnetoresistance is approximately proportional to the Langevin function. The microstructure of the sample was investigated by transmission electron microscopy and it appears that the giant magnetoresistance is due to the presence of small Co precipitates with an approximate mean diameter of 12 A(ring) and a mean separation of 35 A(ring).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An initial study of the field dependence of 59Co nuclear magnetic resonance (NMR) has been undertaken for two Co/Cu(111) multilayer films grown by molecular beam epitaxy. The multilayer structure of the films was nominally identical, [Co(15 A(ring))/Cu(7 A(ring))]×20, however by growing the multilayers with similar structures on different buffer layers, Cu(200 A(ring)) and Au(10 A(ring)), saturation magnetoresistances ΔR/R of 4% and 22%, respectively, were obtained. The NMR signal in ferromagnetic materials arises due to the enhancement effect from the electronic magnetization. This enhancement effect is therefore a function of the domain structure and any external magnetic field. By applying a simple model of how the NMR enhancement factor varies with applied field, in the absence of a domain structure, the anisotropy fields at the interfaces and in the bulk were determined separately at T=4.2 K. These were then compared with the coercive field obtained from magnetization measurements. Our results show that at low temperature the anisotropy field at the interfaces is approximately equal to the coercivity obtained from magnetization measurements (260 Oe), while in the bulk the anisotropy field was found to be ∼550 Oe for the low magnetoresistance sample with ΔR/R=4%, and ∼1230 Oe for the high magnetoresistance sample with ΔR/R=22%.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    International journal of cosmetic science 8 (1986), S. 0 
    ISSN: 1468-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The in vitro permeability of human and some common laboratory animals'skin has been measured to two chemicals with different physico-chemical properties: [3H] water, a small polar molecule and [14C]paraquat dichloride (the ion), a fully ionised divalent cation. All the skins examined had similar permeabilities to [3H]water: relative to human skin the greatest difference (x4.8) was measured through guinea pig skin. However, relative to human skin, all the animals were much more permeable to [14C]paraquat, with factors of difference ranging between 40 (haired rat) and 1460 (hairless mouse). The in vitro technique allows the permeability of human and animal skin to be compared, facilitating extrapolation to Man of effects seen in animals during dermal exposure studies. Comparaison de la permeabilite in vitro de la peau humaine et de la peau de certains animaux de laboratoire
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 381-384 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A digital–analog integrator has been developed for use with inductive magnetic sensors in long-pulse tokamaks. Continuous compensation of input offsets is accomplished by alternating analog-to-digital convertor samples from the sensor and a dummy load, while a RC network provides passive integration between samples. Typically a sampling rate of 10 kHz is used. In operational tests on the DIII-D tokamak, digital and analog integration of tokamak data show good agreement. The output drift error during a 1200 s integration interval corresponds to a few percent of the anticipated signal for poloidal field probes in International Thermonuclear Experimental Reactor, and bench tests suggest that the error can be reduced further. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5840-5842 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A magnetic ink has been prepared which consists of a colloidal suspension of cobalt particles of ∼10-nm median diameter of the volume fraction. Gel filtration techniques have been used to separate the particles into a number of fractions of different particle size. Isothermal remanent magnetization (IRM) curves have been plotted for each fraction in the dried state. The maximum value of IR/IS (remanence/saturation magnetization) is 0.5 equal to a value for a distribution of uniaxial particles with easy axes randomly oriented. This value is well below the value of 0.8 expected for cobalt ferrite which has cubic crystalline anisotropy. All fractions, except for those containing the largest particles, have values of IR/IS 〈0.5 due to the presence of superparamagnetic particles. The experimental points on the IRM curves have been fitted to theoretical curves derived from a model by Chantrell et al.7 for a system of uniaxial particles with axes randomly oriented and containing a lognormal distribution of particle volume. Using a value of anisotropy constant K=1.8×105 J m−3 obtained from measurement of the decay of remanence with temperature, satisfactory agreement between particle size determined experimentally and that used in the model has been obtained.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of a giant magnetothermopower (GMT), giant magnetoresistance (GMR), and on magnetization measurements in Co/Cu[111] superlattices grown by molecular beam epitaxy. The maximum value of the GMT (at room temperature) was 14% for a Cu thickness of 9 A(ring) and the maximum GMR (at 4.2 K) was −26% at 7 A(ring) of Cu. Oscillations in the remnant magnetization and the saturation field as a function of Cu thickness with a period of about 10 A(ring) were observed. However, there were no oscillations in the GMT or the GMR. The maximum values of both the GMT and GMR are associated with saturation fields in excess of 40 kOe and with small remnant magnetizations. These results are consistent with the presence of antiferromagnetic coupling.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the magnetization reversal and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 and 27 A(ring)) trilayer structures prepared by MBE on a 500-A(ring) Ge/GaAs(110) epilayer. We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal MOKE measurements. For the samples examined, coherent rotation of the magnetization vector is observed when the magnetic field is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths. An absence of antiferromagnetic (AF) coupling has been observed previously [W. F. Egelhoff, Jr. and M. T. Kief, Phys. Rev. B 45, 7795 (1992)] in contrast to recent results, indicating that AF coupling [M. T. Johnson et al., Phys. Rev. Lett. 69, 969 (1992)] and GMR [D. Grieg et al., J. Magn. Magn. Mater. 110, L239 (1992)] can occur in Co/Cu(111)/Co structures grown by MBE, but these properties are sensitively dependent on growth conditions. The absence of coupling in our samples is attributed to the presence of a significant interface roughness induced by the Ge epilayer. The uniaxial anisotropies are assumed to arise from strain or defects induced in the film.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The 59Co NMR has been measured for superlattices of Co(15 A(ring))/Cu (7 or 18 A(ring)) grown with either a Au or Cu buffer layer between the substrate and the superlattice. As was reported earlier the Co (15 A(ring))/Cu (7 A(ring)) (Au) superlattice has the largest magnetoresistance (ΔR/R∼26%) known for a MBE grown Co/Cu multilayer. The NMR measurements show that the Au-based superlattices have very flat interfaces and (111) orientation, two features which were supposed to preclude a large value of ΔR/R, and that the average strain in the Co layers is greater for a Au than a Cu buffer layer.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4476-4478 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ability to grow high quality thin metallic layers has brought about the discovery of the giant magnetoresistance (GMR) in multilayers and equally the perpendicular anisotropy exhibited by certain ferromagnetic thin films such as Co. In this article, we will describe magnetoresistance and magneto-optical Kerr effect (MOKE) measurements of molecular beam epitaxy-grown multilayers of Co/Cu(111). It is demonstrated that by controlled doping of the interface between the Co and Cu with submonolayer amounts of Au we are able to increase the magnitude of the GMR. Analysis of MOKE data shows that there is an increase in the perpendicular anisotropy of the Au-doped samples compared to those without Au which can account for the increase in the GMR. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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