49 research outputs found
Study of local structure and magnetism in high-T(sub c) copper oxide superconductors
The muon spin rotation (MUSR) study of local magnetism of Sr-doped La2CuO4 is reviewed. Emphasis is placed on magnetic order as detected by local and bulk probes with local atomic environments studied by x ray absorption fine structure (XAFS). Correlations between the MUSR study of local magnetic ordering and the bulk magnetization study are presented along with a discussion of the dependence upon oxygen stoichiometry. Results are presented for both superconducting phases and magnetic phases. Recent data which reveals the existence of local magnetic ordering in the hydrogen-doped YBa2Cu3O7 system are also discussed
Oscillatory biquadratic coupling in Fe/Cr/Fe(001)
Copyright © 1997 The American Physical SocietyPolar Kerr measurements have been used to measure the dependence of the biquadratic coupling strength B12 on Cr thickness in an Fe/Cr/Fe trilayer. The overall behavior, which consists of a maximum coupling strength at dCr=5 Å (3.5 ML) with a falloff at greater Cr thicknesses, is found to be consistent with in-plane Kerr and Brillouin light-scattering measurements performed on the same sample. The polar Kerr measurements suggest additionally that B12 increases from zero near zero Cr thickness, and that it oscillates in magnitude after the first peak, with a second peak in B12 occurring at about dCr=12 Å (8.3 ML). The positions and heights of the first and second biquadratic coupling maxima, in relation to the first bilinear coupling maximum, show excellent agreement with previous measurements by Köbler et al. of the biquadratic coupling behavior in Fe/Cr/Fe, and also show good agreement with the predictions of an intrinsic biquadratic coupling mechanism due to Edwards et al
Thermophysical and chemical properties of perennial energy crops depending on harvest period
This paper presents analyses of the
thermophysical and chemical properties of eleven perennial crop
species harvested in one-year rotation cycles. The crops included
four species grown for biomass in the form of straw, five species
producing semi-wood biomass, and two species yielding wood
biomass. The research comprised three consecutive crop harvests.
In each harvesting season, biomass samples for analyses were
taken on six dates at one-month intervals. Thermophysical and
chemical properties of the biomass were significantly differentiated
within the main experimental factors and their interactions.
The biomass produced by Virginia mallow had the best quality
parameters as solid fuel. In fact, it achieved the lowest water content
and the highest lower heating value during all of the analyzed
seasons and harvest dates. The biomass of the species yielding
straw or semi-wood products attained better quality as solid fuel on
later harvest dates. In turn, the quality of willow biomass remained
practically unchanged between the harvest dates
New hippocampal neurons are not obligatory for memory formation; cyclin D2 knockout mice with no adult brain neurogenesis show learning
The role of adult brain neurogenesis (generating new neurons) in learning and memory appears to be quite firmly established in spite of some criticism and lack of understanding of what the new neurons serve the brain for. Also, the few experiments showing that blocking adult neurogenesis causes learning deficits used irradiation and various drugs known for their side effects and the results obtained vary greatly. We used a novel approach, cyclin D2 knockout mice (D2 KO mice), specifically lacking adult brain neurogenesis to verify its importance in learning and memory. D2 KO mice and their wild-type siblings were tested in several behavioral paradigms, including those in which the role of adult neurogenesis has been postulated. D2 KO mice showed no impairment in sensorimotor tests, with only sensory impairment in an olfaction-dependent task. However, D2 KO mice showed proper procedural learning as well as learning in context (including remote memory), cue, and trace fear conditioning, Morris water maze, novel object recognition test, and in a multifunctional behavioral system-IntelliCages. D2 KO mice also demonstrated correct reversal learning. Our results suggest that adult brain neurogenesis is not obligatory in learning, including the kinds of learning where the role of adult neurogenesis has previously been strongly suggested