4,437 research outputs found
On the dc Magnetization, Spontaneous Vortex State and Specific Heat in the superconducting state of the weakly ferromagnetic superconductor RuSrGdCuO
Magnetic-field changes 0.2 Oe over the scan length in magnetometers that
necessitate sample movement are enough to create artifacts in the dc
magnetization measurements of the weakly ferromagnetic superconductor
RuSrGdCuO (Ru1212) below the superconducting transition
temperature 30 K. The observed features depend on the specific
magnetic-field profile in the sample chamber and this explains the variety of
reported behaviors for this compound below . An experimental procedure
that combines improvement of the magnetic-field homogeneity with very small
scan lengths and leads to artifact-free measurements similar to those on a
stationary sample has been developed. This procedure was used to measure the
mass magnetization of Ru1212 as a function of the applied magnetic field H (-20
Oe H 20 Oe) at and discuss, in conjunction with
resistance and ac susceptibility measurements, the possibility of a spontaneous
vortex state (SVS) for this compound. Although the existence of a SVS can not
be excluded, an alternative interpretation of the results based on the granular
nature of the investigated sample is also possible. Specific-heat measurements
of SrGdRuO (Sr2116), the precursor for the preparation of Ru1212
and thus a possible impurity phase, show that it is unlikely that Sr2116 is
responsible for the specific-heat features observed for Ru1212 at .Comment: 17 pages, 6 figure
Time--Evolving Statistics of Chaotic Orbits of Conservative Maps in the Context of the Central Limit Theorem
We study chaotic orbits of conservative low--dimensional maps and present
numerical results showing that the probability density functions (pdfs) of the
sum of iterates in the large limit exhibit very interesting
time-evolving statistics. In some cases where the chaotic layers are thin and
the (positive) maximal Lyapunov exponent is small, long--lasting
quasi--stationary states (QSS) are found, whose pdfs appear to converge to
--Gaussians associated with nonextensive statistical mechanics. More
generally, however, as increases, the pdfs describe a sequence of QSS that
pass from a --Gaussian to an exponential shape and ultimately tend to a true
Gaussian, as orbits diffuse to larger chaotic domains and the phase space
dynamics becomes more uniformly ergodic.Comment: 15 pages, 14 figures, accepted for publication as a Regular Paper in
the International Journal of Bifurcation and Chaos, on Jun 21, 201
Noise induced state transitions, intermittency and universality in the noisy Kuramoto-Sivashinsky equation
We analyze the effect of pure additive noise on the long-time dynamics of the
noisy Kuramoto-Sivashinsky (KS) equation in a regime close to the instability
onset. We show that when the noise is highly degenerate, in the sense that it
acts only on the first stable mode, the solution of the KS equation undergoes
several transitions between different states, including a critical on-off
intermittent state that is eventually stabilized as the noise strength is
increased. Such noise-induced transitions can be completely characterized
through critical exponents, obtaining that both the KS and the noisy Burgers
equation belong to the same universality class. The results of our numerical
investigations are explained rigorously using multiscale techniques.Comment: 4 pages, 4 figure
Microwave saturation of the Rydberg states of electrons on helium
We present measurements of the resonant microwave excitation of the Rydberg
energy levels of surface state electrons on superfluid helium. The temperature
dependent linewidth agrees well with theoretical predictions and is very small
below 300 mK. Absorption saturation and power broadening were observed as the
fraction of electrons in the first excited state was increased to 0.49, close
to the thermal excitation limit of 0.5. The Rabi frequency was determined as a
function of microwave power. The high values of the ratio of the Rabi frequency
to linewidth confirm this system as an excellent candidate for creating qubits.Comment: 4 pages, 4 figure
Multifunctional Biocomposites Based on Polyhydroxyalkanoate and Graphene/Carbon Nanofiber Hybrids for Electrical and Thermal Applications
Most polymers are long-lasting and produced from monomers derived from fossil
fuel sources. Bio-based and/or biodegradable plastics have been proposed as a
sustainable alternative. Amongst those available, polyhydroxyalkanoate (PHA)
shows great potential across a large variety of applications but is currently
limited to packaging, cosmetics and tissue engineering due to its relatively
poor physical properties. An expansion of its uses can be accomplished by
developing nanocomposites where PHAs are used as the polymer matrix. Herein, a
PHA biopolyester was melt blended with graphene nanoplatelets (GNPs) or with a
1:1 hybrid mixture of GNPs and carbon nanofibers (CNFs). The resulting
nanocomposites exhibited enhanced thermal stability while their Young's modulus
roughly doubled compared to pure PHA. The hybrid nanocomposites percolated
electrically at lower nanofiller loadings compared to the GNP-PHA system. The
electrical conductivity at 15 wt.% loading was ~ 6 times higher than the
GNP-based sample. As a result, the electromagnetic interference shielding
performance of the hybrid material was around 50% better than the pure GNPs
nanocomposites, exhibiting shielding effectiveness above 20 dB, which is the
threshold for common commercial applications. The thermal conductivity
increased significantly for both types of bio-nanocomposites and reached values
around 5 W K-1 m-1 with the hybrid-based material displaying the best
performance. Considering the solvent-free and industrially compatible
production method, the proposed multifunctional materials are promising to
expand the range of application of PHAs and increase the environmental
sustainability of the plastic and plastic electronics industry.Comment: 26 page
Construction of Integrals of Higher-Order Mappings
We find that certain higher-order mappings arise as reductions of the
integrable discrete A-type KP (AKP) and B-type KP (BKP) equations. We find
conservation laws for the AKP and BKP equations, then we use these conservation
laws to derive integrals of the associated reduced maps.Comment: appear to Journal of the Physical Society of Japa
Calibration of the Herschel SPIRE Fourier Transform Spectrometer
The Herschel SPIRE instrument consists of an imaging photometric camera and
an imaging Fourier Transform Spectrometer (FTS), both operating over a
frequency range of 450-1550 GHz. In this paper, we briefly review the FTS
design, operation, and data reduction, and describe in detail the approach
taken to relative calibration (removal of instrument signatures) and absolute
calibration against standard astronomical sources. The calibration scheme
assumes a spatially extended source and uses the Herschel telescope as primary
calibrator. Conversion from extended to point-source calibration is carried out
using observations of the planet Uranus. The model of the telescope emission is
shown to be accurate to within 6% and repeatable to better than 0.06% and, by
comparison with models of Mars and Neptune, the Uranus model is shown to be
accurate to within 3%. Multiple observations of a number of point-like sources
show that the repeatability of the calibration is better than 1%, if the
effects of the satellite absolute pointing error (APE) are corrected. The
satellite APE leads to a decrement in the derived flux, which can be up to ~10%
(1 sigma) at the high-frequency end of the SPIRE range in the first part of the
mission, and ~4% after Herschel operational day 1011. The lower frequency range
of the SPIRE band is unaffected by this pointing error due to the larger beam
size. Overall, for well-pointed, point-like sources, the absolute flux
calibration is better than 6%, and for extended sources where mapping is
required it is better than 7%.Comment: 20 pages, 18 figures, accepted for publication in MNRA
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