6,825 research outputs found
Galileo dust data from the jovian system: 2000 to 2003
The Galileo spacecraft was orbiting Jupiter between Dec 1995 and Sep 2003.
The Galileo dust detector monitored the jovian dust environment between about 2
and 370 R_J (jovian radius R_J = 71492 km). We present data from the Galileo
dust instrument for the period January 2000 to September 2003. We report on the
data of 5389 particles measured between 2000 and the end of the mission in
2003. The majority of the 21250 particles for which the full set of measured
impact parameters (impact time, impact direction, charge rise times, charge
amplitudes, etc.) was transmitted to Earth were tiny grains (about 10 nm in
radius), most of them originating from Jupiter's innermost Galilean moon Io.
Their impact rates frequently exceeded 10 min^-1. Surprisingly large impact
rates up to 100 min^-1 occurred in Aug/Sep 2000 when Galileo was at about 280
R_J from Jupiter. This peak in dust emission appears to coincide with strong
changes in the release of neutral gas from the Io torus. Strong variability in
the Io dust flux was measured on timescales of days to weeks, indicating large
variations in the dust release from Io or the Io torus or both on such short
timescales. Galileo has detected a large number of bigger micron-sized
particles mostly in the region between the Galilean moons. A surprisingly large
number of such bigger grains was measured in March 2003 within a 4-day interval
when Galileo was outside Jupiter's magnetosphere at approximately 350 R_J
jovicentric distance. Two passages of Jupiter's gossamer rings in 2002 and 2003
provided the first actual comparison of in-situ dust data from a planetary ring
with the results inferred from inverting optical images.Comment: 59 pages, 13 figures, 6 tables, submitted to Planetary and Space
Scienc
Pacifying the Fermi-liquid: battling the devious fermion signs
The fermion sign problem is studied in the path integral formalism. The
standard picture of Fermi liquids is first critically analyzed, pointing out
some of its rather peculiar properties. The insightful work of Ceperley in
constructing fermionic path integrals in terms of constrained world-lines is
then reviewed. In this representation, the minus signs associated with
Fermi-Dirac statistics are self consistently translated into a geometrical
constraint structure (the {\em nodal hypersurface}) acting on an effective
bosonic dynamics. As an illustrative example we use this formalism to study
1+1-dimensional systems, where statistics are irrelevant, and hence the sign
problem can be circumvented. In this low-dimensional example, the structure of
the nodal constraints leads to a lucid picture of the entropic interaction
essential to one-dimensional physics. Working with the path integral in
momentum space, we then show that the Fermi gas can be understood by analogy to
a Mott insulator in a harmonic trap. Going back to real space, we discuss the
topological properties of the nodal cells, and suggest a new holographic
conjecture relating Fermi liquids in higher dimensions to soft-core bosons in
one dimension. We also discuss some possible connections between mixed
Bose/Fermi systems and supersymmetry.Comment: 28 pages, 5 figure
Oscillations and instabilities of fast and differentially rotating relativistic stars
We study non-axisymmetric oscillations of rapidly and differentially rotating
relativistic stars in the Cowling approximation. Our equilibrium models are
sequences of relativistic polytropes, where the differential rotation is
described by the relativistic -constant law. We show that a small degree of
differential rotation raises the critical rotation value for which the
quadrupolar f-mode becomes prone to the CFS instability, while the critical
value of at the mass-shedding limit is raised even more. For softer
equations of state these effects are even more pronounced. When increasing
differential rotation further to a high degree, the neutral point of the CFS
instability first reaches a local maximum and is lowered afterwards. For stars
with a rather high compactness we find that for a high degree of differential
rotation the absolute value of the critical is below the corresponding
value for rigid rotation. We conclude that the parameter space where the CFS
instability is able to drive the neutron star unstable is increased for a small
degree of differential rotation and for a large degree at least in stars with a
higher compactness.Comment: 16 pages, 11 figures; paper accepted for publication in Phys. Rev. D
(81.084019
Phase diagram of the frustrated, spatially anisotropic S=1 antiferromagnet on a square lattice
We study the S=1 square lattice Heisenberg antiferromagnet with spatially
anisotropic nearest neighbor couplings , frustrated by a
next-nearest neighbor coupling numerically using the density-matrix
renormalization group (DMRG) method and analytically employing the
Schwinger-Boson mean-field theory (SBMFT). Up to relatively strong values of
the anisotropy, within both methods we find quantum fluctuations to stabilize
the N\'{e}el ordered state above the classically stable region. Whereas SBMFT
suggests a fluctuation-induced first order transition between the N\'{e}el
state and a stripe antiferromagnet for and an
intermediate paramagnetic region opening only for very strong anisotropy, the
DMRG results clearly demonstrate that the two magnetically ordered phases are
separated by a quantum disordered region for all values of the anisotropy with
the remarkable implication that the quantum paramagnetic phase of the spatially
isotropic - model is continuously connected to the limit of
decoupled Haldane spin chains. Our findings indicate that for S=1 quantum
fluctuations in strongly frustrated antiferromagnets are crucial and not
correctly treated on the semiclassical level.Comment: 10 pages, 10 figure
On-chip high-speed sorting of micron-sized particles for high-throughput analysis
A new design of particle sorting chip is presented. The device employs a dielectrophoretic gate that deflects particles into one of two microfluidic channels at high speed. The device operates by focussing particles into the central streamline of the main flow channel using dielectrophoretic focussing. At the sorting junction (T- or Y-junction) two sets of electrodes produce a small dielectrophoretic force that pushes the particle into one or other of the outlet channels, where they are carried under the pressure-driven fluid flow to the outlet. For a 40mm wide and high channel, it is shown that 6micron diameter particles can be deflected at a rate of 300particles/s. The principle of a fully automated sorting device is demonstrated by separating fluorescent from non-fluorescent latex beads
A dynamic density functional theory for particles in a flowing solvent
We present a dynamic density functional theory (dDFT) which takes into accou
nt the advection of the particles by a flowing solvent. For potential flows we
can use the same closure as in the absence of solvent flow. The structure of
the resulting advected dDFT suggests that it could be used for non-potential
flows as well. We apply this dDFT to Brownian particles (e.g., polymer coils)
in a solvent flowing around a spherical obstacle (e.g., a colloid) and compare
the results with direct simulations of the underlying Brownian dynamics.
Although numerical limitations do not allow for an accurate quantitative
check of the advected dDFT both show the same qualitative features. In contrast
to previous works which neglected the deformation of the flow by the obstacle,
we find that the bow-wave in the density distribution of particles in front of
the obstacle as well as the wake behind it are reduced dramatically. As a
consequence the friction force exerted by the (polymer) particles on the
colloid can be reduced drastically.Comment: 7 pages, 5 figures, 2 tables, submitte
Stratosphere troposphere coupling: the influence of volcanic eruptions
Stratospheric sulfate aerosols produced by major volcanic eruptions modify the radiative and dynamical properties of the troposphere and stratosphere through their reflection of solar radiation and absorption of infrared radiation. At the Earth's surface, the primary consequence of a large eruption is cooling, however, it has long been known that major tropical eruptions tend to be followed by warmer than usual winters over the Northern Hemisphere (NH) continents. This volcanic "winter-warming" effect in the NH is understood to be the result of changes in atmospheric circulation patterns resulting from heating in the stratosphere, and is often described as positive anomalies of the Northern Annular Mode (NAM) that propagate downward from the stratosphere to the troposphere. In the southern hemisphere, climate models tend to also predict a positive Southern Annular Mode (SAM) response to volcanic eruptions, but this is generally inconsistent with post-eruption observations during the 20th century. We review present understanding of the influence of volcanic eruptions on the large scale modes of atmospheric variability in both the Northern and Southern Hemispheres. Using models of varying complexity, including an aerosol-climate model, an Earth system model, and CMIP5 simulations, we assess the ability of climate models to reproduce the observed post-eruption climatic and dynamical anomalies. We will also address the parametrization of volcanic eruptions in simulations of the past climate, and identify possibilities for improvemen
Magnetic fluctuations in n-type high- superconductors reveal breakdown of fermiology
By combining experimental measurements of the quasiparticle and dynamical
magnetic properties of optimally electron-doped PrLaCeCuO
with theoretical calculations we demonstrate that the conventional fermiology
approach cannot possibly account for the magnetic fluctuations in these
materials. In particular, we perform tunneling experiments on the very same
sample for which a dynamical magnetic resonance has been reported recently and
use photoemission data by others on a similar sample to characterize the
fermionic quasiparticle excitations in great detail. We subsequently use this
information to calculate the magnetic response within the conventional
fermiology framework as applied in a large body of work for the hole-doped
superconductors to find a profound disagreement between the theoretical
expectations and the measurements: this approach predicts a step-like feature
rather than a sharp resonance peak, it underestimates the intensity of the
resonance by an order of magnitude, it suggests an unreasonable temperature
dependence of the resonance, and most severely, it predicts that most of the
spectral weight resides in incommensurate wings which are a key feature of the
hole-doped cuprates but have never been observed in the electron-doped
counterparts. Our findings strongly suggest that the magnetic fluctuations
reflect the quantum-mechanical competition between antiferromagnetic and
superconducting orders.Comment: 10 pages, 9 figures, 1 tabl
Relativistic electronic dressing
We study the effects of the relativistic electronic dressing in
laser-assisted electron-hydrogen atom elastic collisions. We begin by
considering the case when no radiation is present. This is necessary in order
to check the consistency of our calculations and we then carry out the
calculations using the relativistic Dirac-Volkov states. It turns out that a
simple formal analogy links the analytical expressions of the differential
cross section without laser and the differential cross section in presence of a
laser field.Comment: 11 pages, 18 figures, Late
- …