6,133 research outputs found
Spin-Peierls transition with strong structural fluctuations in the vanadium oxide VOSbO
We report on the magnetic susceptibility and electron spin resonance
measurements on polycrystalline samples of the vanadium oxide
VOSbO, a quasi-one dimensional S=1/2 Heisenberg system. We show
that the susceptibility vanishes at zero temperature, as in a gapped system,
and we argue that this is due to a spin-Peierls transition with strong
structural fluctuations.Comment: 5 pages, 4 figure
Inviscid Large deviation principle and the 2D Navier Stokes equations with a free boundary condition
Using a weak convergence approach, we prove a LPD for the solution of 2D
stochastic Navier Stokes equations when the viscosity converges to 0 and the
noise intensity is multiplied by the square root of the viscosity. Unlike
previous results on LDP for hydrodynamical models, the weak convergence is
proven by tightness properties of the distribution of the solution in
appropriate functional spaces
Low Voltage Totally Free Flexible RF MEMS Switch With Anti-Stiction System
This paper concerns a new design of RF MEMS switch combined with an
innovative process which enable low actuation voltage (<5V) and avoid stiction.
First, the structure described with principal design issues, the corresponding
anti-stiction system is presented and FEM simulations are done. Then, a short
description of the process flow based on two non polymer sacrificial layers.
Finally, RF measurements are presented and preliminary experimental protocol
and results of anti-stiction validation is detailed. Resulting RF performances
are -30dB of isolation and -0.45dB of insertion loss at 10 GHz.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Unusual magnetic properties of the low-dimensional quantum magnet Na2V3O7
We report the results of low-temperature measurements of the specific heat
Cp(T), ac susceptibility chi(T) and 23Na nuclear magnetic resonance NMR of
Na2V3O7. At liquid He temperatures Cp(T)/T exhibits broad field-dependent
maxima, which shift to higher temperatures upon increasing the applied magnetic
field H. Below 1.5 K the ac magnetic susceptibility chi(T) follows a
Curie-Weiss law and exhibits a cusp at 0.086 mK which indicates a phase
transition at very low temperatures. These results support the previous
conjecture that Na2V3O7 is close to a quantum critical point (QCP) at mu_{0}H =
0 T. The entire data set, including results of measurements of the NMR
spin-lattice relaxation 1/T1(T), reveals a complex magnetic behavior at low
temperatures. We argue that it is due to a distribution of singlet-triplet
energy gaps of dimerized V moments. The dimerization process evolves over a
rather broad temperature range around and below 100 K. At the lowest
temperatures the magnetic properties are dominated by the response of only a
minor fraction of the V moments.Comment: 10.5 pages, 15 figures. Submitted to Phys. Rev.
Oxygen Uptake Kinetics Is Slower in Swimming Than Arm Cranking and Cycling during Heavy Intensity.
Oxygen uptake ([Formula: see text]) kinetics has been reported to be influenced by the activity mode. However, only few studies have compared [Formula: see text]O2 kinetics between activities in the same subjects in which they were equally trained. Therefore, this study compared the [Formula: see text]O2 kinetics response to swimming, arm cranking, and cycling within the same group of subjects within the heavy exercise intensity domain. Ten trained male triathletes (age 23.2 ± 4.5 years; height 180.8 ± 8.3 cm; weight 72.3 ± 6.6 kg) completed an incremental test to exhaustion and a 6-min heavy constant-load test in the three exercise modes in random order. Gas exchange was measured by a breath-by-breath analyzer and the on-transient [Formula: see text]O2 kinetics was modeled using bi-exponential functions. [Formula: see text]O2peak was higher in cycling (65.6 ± 4.0 ml·kg(-1)·min(-1)) than in arm cranking or swimming (48.7 ± 8.0 and 53.0 ± 6.7 ml·kg(-1)·min(-1); P < 0.01), but the [Formula: see text]O2 kinetics were slower in swimming (τ1 = 31.7 ± 6.2 s) than in arm cranking (19.3 ± 4.2 s; P = 0.001) and cycling (12.4 ± 3.7 s; P = 0.001). The amplitude of the primary component was lower in both arm cranking and swimming (21.9 ± 4.7 and 28.4 ± 5.1 ml·kg(-1)·min(-1)) compared with cycling (39.4 ± 4.1 ml·kg(-1)·min(-1); P = 0.001). Although the gain of the primary component was higher in arm cranking compared with cycling (15.3 ± 4.2 and 10.7 ± 1.3 ml·min(-1)·W(-1); P = 0.02), the slow component amplitude, in both absolute and relative terms, did not differ between exercise modes. The slower [Formula: see text]O2 kinetics during heavy-intensity swimming is exercise-mode dependent. Besides differences in muscle mass and greater type II muscle fibers recruitment, the horizontal position adopted and the involvement of trunk and lower-body stabilizing muscles could be additional mechanisms that explain the differences between exercise modalities
Ground state of the Kagome-like S=1/2 antiferromagnet, Volborthite Cu3V2O7(OH)2.2H2O
Volborthite compound is one of the very few realizations of S=1/2 quantum
spins on a highly frustrated kagome-like lattice. Low-T SQUID measurements
reveal a broad magnetic transition below 2K which is further confirmed by a
peak in the 51V nuclear spin relaxation rate (1/T1) at 1.4K0.2K. Through
51V NMR, the ground state (GS) appears to be a mixture of different spin
configurations, among which 20% correspond to a well defined short range order,
possibly of the type. While the freezing involve all
the Cu spins, only 40% of the copper moment is actually frozen which
suggests that quantum fluctuations strongly renormalize the GS.Comment: 4 pages, 4 figures, to appear in PR
Infrared study of spin-Peierls compound alpha'-NaV2O5
Infrared reflectance of alpha'-NaV2O5 single crystals in the frequency range
from 50 cm-1 to 10000 cm-1 was studied for a, b and c-polarisations. In
addition to phonon modes identification, for the a-polarised spectrum a broad
continuum absorption in the range of 1D magnetic excitation energies was found.
The strong near-IR absorption band at 0.8 eV shows a strong anisotropy with
vanishing intensity in c-polarisation. Activation of new phonons due to the
lattice dimerisation were detected below 35K as well as pretransitional
structural fluctuations up to 65K.Comment: 3 pages, 2 figures, 1 table. Contributed paper for the SCES'98 (15-18
July 1998, Paris). To be published in Physica
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