939 research outputs found
Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy
The ferromagnetism of a thin GaMnAs layer with a perpendicular easy
anisotropy axis is investigated by means of several techniques, that yield a
consistent set of data on the magnetic properties and the domain structure of
this diluted ferromagnetic semiconductor. The magnetic layer was grown under
tensile strain on a relaxed GaInAs buffer layer using a procedure that limits
the density of threading dislocations. Magnetometry, magneto-transport and
polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality
of this layer, in particular through its high Curie temperature (130 K) and
well-defined magnetic anisotropy. We show that magnetization reversal is
initiated from a limited number of nucleation centers and develops by easy
domain wall propagation. Furthermore, MOKE microscopy allowed us to
characterize in detail the magnetic domain structure. In particular we show
that domain shape and wall motion are very sensitive to some defects, which
prevents a periodic arrangement of the domains. We ascribed these defects to
threading dislocations emerging in the magnetic layer, inherent to the growth
mode on a relaxed buffer
Evaluation of Serum 1,5 Anhydroglucitol Levels as a Clinical Test to Differentiate Subtypes of Diabetes
OBJECTIVE: Assignment of the correct molecular diagnosis in diabetes is necessary for informed decisions regarding treatment and prognosis. Better clinical markers would facilitate discrimination and prioritization for genetic testing between diabetes subtypes. Serum 1,5 anhydroglucitol (1,5AG) levels were reported to differentiate maturity-onset diabetes of the young due to HNF1A mutations (HNF1A-MODY) from type 2 diabetes, but this requires further validation. We evaluated serum 1,5AG in a range of diabetes subtypes as an adjunct for defining diabetes etiology. RESEARCH DESIGN AND METHODS: 1,5AG was measured in U.K. subjects with: HNF1A-MODY (n = 23), MODY due to glucokinase mutations (GCK-MODY, n = 23), type 1 diabetes (n = 29), latent autoimmune diabetes in adults (LADA, n = 42), and type 2 diabetes (n = 206). Receiver operating characteristic curve analysis was performed to assess discriminative accuracy of 1,5AG for diabetes etiology. RESULTS: Mean (SD range) 1,5AG levels were: GCK-MODY 13.06 microg/ml (5.74-29.74), HNF1A-MODY 4.23 microg/ml (2.12-8.44), type 1 diabetes 3.09 microg/ml (1.45-6.57), LADA 3.46 microg/ml (1.42-8.45), and type 2 diabetes 5.43 (2.12-13.23). Levels in GCK-MODY were higher than in other groups (P < 10(-4) vs. each group). HNF1A-MODY subjects showed no difference in unadjusted 1,5AG levels from type 2 diabetes, type 1 diabetes, and LADA. Adjusting for A1C revealed a difference between HNF1A-MODY and type 2 diabetes (P = 0.001). The discriminative accuracy of unadjusted 1,5AG levels was 0.79 for GCK-MODY versus type 2 diabetes and 0.86 for GCK-MODY versus HNF1A-MODY but was only 0.60 for HNF1A-MODY versus type 2 diabetes. CONCLUSIONS: In our dataset, serum 1,5AG performed well in discriminating GCK-MODY from other diabetes subtypes, particularly HNF1A-MODY. Measurement of 1,5AG levels could inform decisions regarding MODY diagnostic testing
Strong fields induce ultrafast rearrangement of H-atoms in HO
H-atoms in HO are rearranged by strong optical fields generated by
intense, 10 fs laser pulses to form H, against prevailing wisdom that
strong fields inevitably lead to multiple molecular ionization and the
subsequent Coulomb explosion into fragments. This atomic rearrangement is shown
to occur within a single 10 fs pulse. Comparison with results obtained with
300-attosecond long strong fields generated using fast Si ions
helps establish thresholds for field strength and time required for such
rearrangements. Quantum-chemical calculations reveal that H originates in
the A state of HO when the O-H bond elongates to 1.15 a.u. and
the H-O-H angle becomes 120. Bond formation on the ultrafast timescale of
molecular vibrations (10 fs for H) has hitherto not been reported.Comment: Submitted to Physical Review Lotter
Thermal Effects in the dynamics of disordered elastic systems
Many seemingly different macroscopic systems (magnets, ferroelectrics, CDW,
vortices,..) can be described as generic disordered elastic systems.
Understanding their static and dynamics thus poses challenging problems both
from the point of view of fundamental physics and of practical applications.
Despite important progress many questions remain open. In particular the
temperature has drastic effects on the way these systems respond to an external
force. We address here the important question of the thermal effect close to
depinning, and whether these effects can be understood in the analogy with
standard critical phenomena, analogy so useful to understand the zero
temperature case. We show that close to the depinning force temperature leads
to a rounding of the depinning transition and compute the corresponding
exponent. In addition, using a novel algorithm it is possible to study
precisely the behavior close to depinning, and to show that the commonly
accepted analogy of the depinning with a critical phenomenon does not fully
hold, since no divergent lengthscale exists in the steady state properties of
the line below the depinning threshold.Comment: Proceedings of the International Workshop on Electronic Crystals,
Cargese(2008
Quantum Magnetic Deflagration in Mn12 Acetate
We report controlled ignition of magnetization reversal avalanches by surface
acoustic waves in a single crystal of Mn12 acetate. Our data show that the
speed of the avalanche exhibits maxima on the magnetic field at the tunneling
resonances of Mn12. Combined with the evidence of magnetic deflagration in Mn12
acetate (Suzuki et al., cond-mat/0506569) this suggests a novel physical
phenomenon: deflagration assisted by quantum tunneling.Comment: 4 figure
Spectral representation of the effective dielectric constant of graded composites
We generalize the Bergman-Milton spectral representation, originally derived
for a two-component composite, to extract the spectral density function for the
effective dielectric constant of a graded composite. This work has been
motivated by a recent study of the optical absorption spectrum of a graded
metallic film [Applied Physics Letters, 85, 94 (2004)] in which a broad
surface-plasmon absorption band has been shown to be responsible for enhanced
nonlinear optical response as well as an attractive figure of merit. It turns
out that, unlike in the case of homogeneous constituent components, the
characteristic function of a graded composite is a continuous function because
of the continuous variation of the dielectric function within the constituent
components. Analytic generalization to three dimensional graded composites is
discussed, and numerical calculations of multilayered composites are given as a
simple application.Comment: Physical Review E, submitted for publication
Domain structure in CoFeB thin films with perpendicular magnetic anisotropy
Domain structures in CoFeB-MgO thin films with a perpendicular easy
magnetization axis were observed by magneto-optic Kerr-effect microscopy at
various temperatures. The domain wall surface energy was obtained by analyzing
the spatial period of the stripe domains and fitting established domain models
to the period. In combination with SQUID measurements of magnetization and
anisotropy energy, this leads to an estimate of the exchange stiffness and
domain wall width in these films. These parameters are essential for
determining whether domain walls will form in patterned structures and devices
made of such materials
Spin Transfer Torques in MnSi at Ultra-low Current Densities
Spin manipulation using electric currents is one of the most promising
directions in the field of spintronics. We used neutron scattering to observe
the influence of an electric current on the magnetic structure in a bulk
material. In the skyrmion lattice of MnSi, where the spins form a lattice of
magnetic vortices similar to the vortex lattice in type II superconductors, we
observe the rotation of the diffraction pattern in response to currents which
are over five orders of magnitude smaller than those typically applied in
experimental studies on current-driven magnetization dynamics in
nanostructures. We attribute our observations to an extremely efficient
coupling of inhomogeneous spin currents to topologically stable knots in spin
structures
The Contribution of Under Leaves to Fruit Production in Calabacita (Cucurbita pepo L. cv GRAY ZUCCHINI)
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