15,490 research outputs found
A new measurement of thermal conductivity of amorphous ice and its implications for the thermal evolution of comets
Very slowly deposited amorphous ice has a thermal conductivity about four orders of magnitude or more smaller than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the properties of amorphous ice leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters
Anomalous elasticity of nematic elastomers
We study the anomalous elasticity of nematic elastomers by employing the
powers of renormalized field theory. Using general arguments of symmetry and
relevance, we introduce a minimal Landau-Ginzburg-Wilson elastic energy for
nematic elastomers. Performing a diagrammatic low temperature expansion, we
analyze the fluctuations of the displacement fields at and below the upper
critical dimension 3. Our analysis reveals an anomaly of certain elastic moduli
in the sense that they depend on the length scale. In this dependence
is logarithmic and below it is of power law type with anomalous scaling
exponents. One of the 4 relevant shear moduli vanishes at long length scales
whereas the only relevant bending modulus diverges.Comment: 4 page
Initiation and Early Kinematic Evolution of Solar Eruptions
We investigate the initiation and early evolution of 12 solar eruptions,
including six active region hot channel and six quiescent filament eruptions,
which were well observed by the \textsl{Solar Dynamics Observatory}, as well as
by the \textsl{Solar TErrestrial RElations Observatory} for the latter. The
sample includes one failed eruption and 11 coronal mass ejections, with
velocities ranging from 493 to 2140~km~s. A detailed analysis of the
eruption kinematics yields the following main results. (1) The early evolution
of all events consists of a slow-rise phase followed by a main-acceleration
phase, the height-time profiles of which differ markedly and can be best fit,
respectively, by a linear and an exponential function. This indicates that
different physical processes dominate in these phases, which is at variance
with models that involve a single process. (2) The kinematic evolution of the
eruptions tends to be synchronized with the flare light curve in both phases.
The synchronization is often but not always close. A delayed onset of the
impulsive flare phase is found in the majority of the filament eruptions (5 out
of 6). This delay, and its trend to be larger for slower eruptions, favor ideal
MHD instability models. (3) The average decay index at the onset heights of the
main acceleration is close to the threshold of the torus instability for both
groups of events (although based on a tentative coronal field model for the hot
channels), suggesting that this instability initiates and possibly drives the
main acceleration.Comment: Accepted for publication in ApJ; 24 pages, 12 figures, 3 table
On Optimizing Distributed Tucker Decomposition for Dense Tensors
The Tucker decomposition expresses a given tensor as the product of a small
core tensor and a set of factor matrices. Apart from providing data
compression, the construction is useful in performing analysis such as
principal component analysis (PCA)and finds applications in diverse domains
such as signal processing, computer vision and text analytics. Our objective is
to develop an efficient distributed implementation for the case of dense
tensors. The implementation is based on the HOOI (Higher Order Orthogonal
Iterator) procedure, wherein the tensor-times-matrix product forms the core
routine. Prior work have proposed heuristics for reducing the computational
load and communication volume incurred by the routine. We study the two metrics
in a formal and systematic manner, and design strategies that are optimal under
the two fundamental metrics. Our experimental evaluation on a large benchmark
of tensors shows that the optimal strategies provide significant reduction in
load and volume compared to prior heuristics, and provide up to 7x speed-up in
the overall running time.Comment: Preliminary version of the paper appears in the proceedings of
IPDPS'1
Investigation On The Interaction Analysis Of Beam-Nonlinear Isolator With Low And High Stiffness Support
This paper presents the study of the interaction between a beam and a nonlinear isolator for low and high supporting stiffness. The system consists of an elastic beam- like structure and a geometrically nonlinear isolation system in which a horizontal degree provides a physical approach for realising the required horizontal force. The generalised dynamic equations of the system are derived and the modal summation method is used to analyse the beam. The dynamic interaction mechanism between the nonlinear isolation system and the elastic structure is revealed. The beam- nonlinear isolator design for low stiffness support and high stiffness support is discussed. It is found that the beam provides additional mass, stiffness and force to the nonlinear vibration isolator and the requirement to perform ground vibration test whereby the rigid mode of the beam must be less than one third of the first elastic natural frequency of the free-free beam has been satisfied. The condition to achieve high stiffness support has also been satisfied. Nonlinear dynamical behaviour of the beam-nonlinear isolator indicates that period doubling bifurcation occurs when the excitation force is 1 and excitation frequency is 0.5Hz. Poincare’ maps reveals that the system form closed loops and no chaotic behaviour is observed. Perfomance analysis in terms of force transmissibility of the nonlinear isolator shows that the nonlinear isolator performs better than a linear isolator and also performs better than a hardening HSLDS mount
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Can the Lepton Flavor Mixing Matrix Be Symmetric?
Current neutrino oscillation data indicate that the 3x3 lepton flavor mixing
matrix V is likely to be symmetric about its V_{e3}-V_{\mu 2}-V_{\tau 1} axis.
This off-diagonal symmetry corresponds to three pairs of {\it congruent}
unitarity triangles in the complex plane. Terrestrial matter effects can
substantially modify the genuine CP-violating parameter and off-diagonal
asymmetries of V in realistic long-baseline experiments of neutrino
oscillations.Comment: RexTex 14 pages (4 PS figures). More discussions adde
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