3,442 research outputs found
Stability of jammed packings I: the rigidity length scale
In 2005, Wyart et al. (Europhys. Lett., 72 (2005) 486) showed that the low
frequency vibrational properties of jammed amorphous sphere packings can be
understood in terms of a length scale, called l*, that diverges as the system
becomes marginally unstable. Despite the tremendous success of this theory, it
has been difficult to connect the counting argument that defines l* to other
length scales that diverge near the jamming transition. We present an alternate
derivation of l* based on the onset of rigidity. This phenomenological approach
reveals the physical mechanism underlying the length scale and is relevant to a
range of systems for which the original argument breaks down. It also allows us
to present the first direct numerical measurement of l*.Comment: 8 pages, 5 figure
Higher-Order Gravitational Lensing Reconstruction using Feynman Diagrams
We develop a method for calculating the correlation structure of the Cosmic
Microwave Background (CMB) using Feynman diagrams, when the CMB has been
modified by gravitational lensing, Faraday rotation, patchy reionization, or
other distorting effects. This method is used to calculate the bias of the
Hu-Okamoto quadratic estimator in reconstructing the lensing power spectrum up
to O(\phi^4) in the lensing potential . We consider both the diagonal
noise TTTT, EBEB, etc. and, for the first time, the off-diagonal noise TTTE,
TBEB, etc. The previously noted large O(\phi^4) term in the second order noise
is identified to come from a particular class of diagrams. It can be
significantly reduced by a reorganization of the expansion. These
improved estimators have almost no bias for the off-diagonal case involving
only one component of the CMB, such as EEEB.Comment: 17 pages, 17 figure
Gravitational Lensing of the CMB: a Feynman Diagram Approach
We develop a Feynman diagram approach to calculating correlations of the
Cosmic Microwave Background (CMB) in the presence of distortions. As one
application, we focus on CMB distortions due to gravitational lensing by Large
Scale Structure (LSS). We study the Hu-Okamoto quadratic estimator for
extracting lensing from the CMB and derive the noise of the estimator up to
in the lensing potential . The previously noted
large term can be significantly reduced by a
reorganization of the expansion. Our approach makes it simple to obtain
expressions for quadratic estimators based on any CMB channel. We briefly
discuss other applications to cosmology of this diagrammatic approach, such as
distortions of the CMB due to patchy reionization, or due to Faraday rotation
from primordial axion fields.Comment: 5 pages, 8 figures, v2: journal versio
Sheared force-networks: anisotropies, yielding and geometry
A scenario for yielding of granular matter is presented by considering the
ensemble of force networks for a given contact network and applied shear stress
. As is increased, the probability distribution of contact forces
becomes highly anisotropic, the difference between average contact forces along
minor and major axis grows, and the allowed networks span a shrinking subspace
of all force-networks. Eventually, contacts start to break, and at the yielding
shear stress, the packing becomes effectively isostatic. The size of the
allowed subspace exhibits simple scaling properties, which lead to a prediction
of the yield stress for packings of arbitrary contact number.Comment: 4 pages, 4 figure
The tail of the contact force distribution in static granular materials
We numerically study the distribution P(f) of contact forces in frictionless
bead packs, by averaging over the ensemble of all possible force network
configurations. We resort to umbrella sampling to resolve the asymptotic decay
of P(f) for large f, and determine P(f) down to values of order 10^{-45} for
ordered and disordered systems in two and three dimensions. Our findings
unambiguously show that, in the ensemble approach, the force distributions
decay much faster than exponentially: P(f) ~ exp(-f^{\alpha}), with alpha
\approx 2.0 for 2D systems, and alpha \approx 1.7 for 3D systems.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Liver microwave ablation:a systematic review of various FDA-approved systems
ObjectivesThe aim of the present study is to analyze preclinical and clinical data on the performance of the currently US Food and Drug Administration (FDA)-approved microwave ablation (MWA) systems.MethodsA review of the literature, published between January 1, 2005, and December 31, 2016, on seven FDA-approved MWA systems, was conducted. Ratio of ablation zone volume to applied energy R(AZ:E) and sphericity indices were calculated for ex vivo and in vivo experiments.ResultsThirty-four studies with ex vivo, in vivo, and clinical data were summarized. In total, 14 studies reporting data on ablation zone volume and applied energy were included for comparison R(AZ:E). A significant correlation between volume and energy was found for the ex vivo experiments (r=0.85,
Simulations of elementary processes in entangle wormlike micelles under tension : a kinetic pathway to Y-junctions and shear induced structures
The merging process of two amphiphilic cylindrical micelles has been simulated using a coarse grained model in which amphiphiles are represented as chains of one head particle and four tail particles. In our set-up with twisted boundary conditions, a ring-shaped worm is effectively entangled with itself. Upon stretching the box, putting the worms under tension, a fusion into an H-like structure is observed, which eventually transforms into an almost tensionless structure with two freely gliding Y-junctions. The tensions on the worms never reach the point where scission becomes an alternative to fusion. We end with a short discussion of the possible implications of these observations
Ensemble Theory for Force Networks in Hyperstatic Granular Matter
An ensemble approach for force networks in static granular packings is
developed. The framework is based on the separation of packing and force
scales, together with an a-priori flat measure in the force phase space under
the constraints that the contact forces are repulsive and balance on every
particle. In this paper we will give a general formulation of this force
network ensemble, and derive the general expression for the force distribution
. For small regular packings these probability densities are obtained in
closed form, while for larger packings we present a systematic numerical
analysis. Since technically the problem can be written as a non-invertible
matrix problem (where the matrix is determined by the contact geometry), we
study what happens if we perturb the packing matrix or replace it by a random
matrix. The resulting 's differ significantly from those of normal
packings, which touches upon the deep question of how network statistics is
related to the underlying network structure. Overall, the ensemble formulation
opens up a new perspective on force networks that is analytically accessible,
and which may find applications beyond granular matter.Comment: 17 pages, 17 figure
Insights from SONATA: Implementing and integrating a microservice-based NFV service platform with a DevOps methodology
Plate fixation of clavicle fractures:comparison between early and delayed surgery
Background: The optimal treatment strategy for clavicle fractures remains a topic of debate. We evaluated our step-wise treatment protocol for patients with clavicle fractures to determine our success rate of conservative treatment. In addition, we evaluated the incidence of complications after clavicle plate fixation in patients undergoing acute surgery vs. delayed surgery. Methods: This was a retrospective analysis in which we registered all patients aged 14 years or older with a clavicle fracture between January 2010 and May 2018 and at least 6 weeks' follow-up. Patients who underwent surgery were included from a prospectively maintained database. Functional outcomes were measured by Disabilities of the Arm, Shoulder and Hand and Constant-Murley scores 6 weeks after surgery. Results: Conservative treatment was successful in 1627 of 1748 patients (93%). Primary fixation was performed in 73 patients (61%) and delayed fixation in 48 (39%). In 8 patients (6.6%), radiologic widening of the acromioclavicular (AC) joint was present after surgery, suggestive of AC injury. The incidence of complications was significantly higher among patients who underwent delayed fixation vs. those who underwent primary fixation: 15 of 48 patients (31.3%) vs. 9 of 73 patients (12.3%). Conclusion: Most patients with clavicle fractures have an excellent outcome using conservative management. Acute surgery can be performed in high-demand patients, resulting in high performance scores. Delayed surgery is associated with a higher risk of complications, although the outcome is generally good. Associated AC joint dislocation found on postoperative radiographs does not influence outcomes. Shared decision making is key, and patients should be well aware of the potential risks and benefits of surgery
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