Active Microrheology of Networks Composed of Semiflexible Polymers I. Computer Simulation of Magnetic Tweezers

We have simulated the motion of a bead subjected to a constant force while embedded in a network of semiflexible polymers which can represent actin filaments. We find that the bead displacement obeys the power law x ~ t^alfa. After the initial stage characterized by the exponent alfa=0.75 we find a new regime with alfa=0.5. The response in this regime is linear in force and scales with the polymer concentration as c^(-1.4). We find that the polymers pile up ahead of the moving bead, while behind it the polymer density is reduced. We show that the force resisting the bead motion is due to steric repulsion exerted by the polymers on the front hemisphere of the bead.Comment: 35 pages with 10 figure

Multichannel heart scanner based on high-Tc SQUIDs

A 7-channel magnetometer for magnetocardiography based on high-T c SQUIDs has been realized. This magnetometer is used for test experiments in the development of a multichannel high-Tc SQUID based heart-scanner for clinical applications. The intrinsic noise level of the channels in the 7-channel system is typically 120 fT/¿(Hz) down to 1 Hz. Magnetocardiograms were recorded inside a magnetically shielded room. Introductory experiments were performed on the suppression of noise by combining magnetometers to form planar gradiometers. The noise suppression that can be established appeared to be limited by the imbalance of the gradiometric configuration, which is roughly 2%. This relatively poor balance of the system is caused by inaccuracies in the transfer functions of the individual SQUID magnetometers, and by deviations from the planar geometr

Analysis of the mechanical behaviour of a 11.5 T Nb3Sn LHC dipole magnet according to the ring collar concept

According to the CERN-LHC (Large Hadron Collider) reference design, 10-tesla twin-aperture NbTi dipoles will be built with split collars that enclose both apertures. As part of the development program towards an experimental 11.5-tesla Nb3Sn LHC dipole magnet, the mechanical implications of an alternative collar concept have been studied with a finite element analysis. In this concept ring shaped collars are shrunk on each finished single aperture coil, thus providing the necessary room-temperature prestress. This system results in a major improvement of the stress distribution in the collars. It is noted that introduction of friction at the sliding planes can cause reopening of the gap between the yoke halves during excitation. This depends strongly on the value of the friction coefficient

Beef Cattle Instance Segmentation Using Fully Convolutional Neural Network

In this paper we present a novel instance segmentation algorithm that extends a fully convolutional network to learn to label objects separately without prediction of regions of interest. We trained the new algorithm on a challenging CCTV recording of beef cattle, as well as benchmark MS COCO and Pascal VOC datasets. Extensive experimentation showed that our approach outperforms the state-of-the-art solutions by up to 8% on our data

Leaving the BPS bound: Tunneling of classically saturated solitons

We discuss quantum tunneling between classically BPS saturated solitons in two-dimensional theories with N=2 supersymmetry and a compact space dimension. Genuine BPS states form shortened multiplets of dimension two. In the models we consider there are two degenerate shortened multiplets at the classical level, but there is no obstruction to pairing up through quantum tunneling. The tunneling amplitude in the imaginary time is described by instantons. We find that the instanton is nothing but the 1/4 BPS saturated ``wall junction,'' considered previously in the literature in other contexts. Two central charges of the superalgebra allow us to calculate the instanton action without finding the explicit solution (it is checked, though, numerically, that the saturated solution does exist). We present a quantum-mechanical interpretation of the soliton tunneling.Comment: LaTeX, 22 pages, 9 figures (eps

AdS-Carroll Branes

Coset methods are used to determine the action of a co-dimension one brane (domain wall) embedded in (d+1)-dimensional AdS space in the Carroll limit in which the speed of light goes to zero. The action is invariant under the non-linearly realized symmetries of the AdS-Carroll spacetime. The Nambu-Goldstone field exhibits a static spatial distribution for the brane with a time varying momentum density related to the brane's spatial shape as well as the AdS-C geometry. The AdS-C vector field dual theory is obtained.Comment: 47 page

LPM effect as the origin of the jet fragmentation scaling in heavy ion collisions

We address a recent puzzling result from the LHC: the jet fragmentation functions measured in $PbPb$ and $pp$ collisions appear very similar in spite of a large medium-induced energy loss (we will call this "jet fragmentation scaling", JFS). To model the real-time non-perturbative effects in the propagation of a high energy jet through the strongly coupled QCD matter, we adopt an effective dimensionally reduced description in terms of the $(1+1)$ quasi-Abelian Schwinger theory. This theory is exactly soluble at any value of the coupling and shares with QCD the properties of dynamical generation of "mesons" with a finite mass and the screening of "quark" charge that are crucial for describing the transition of the jet into hadrons. We find that this approach describes quite well the vacuum jet fragmentation in $e^+e^-$ annihilation at $z\geq0.2$ at jet energies in the range of the LHC heavy ion measurements ($z$ is the ratio of hadron and jet momenta). In QCD medium, we find that the JFS is reproduced if the mean free path $\lambda$ of the jet is short, $\lambda \leq 0.3$ fm, which is in accord with the small shear viscosity inferred from the measurements of the collective flow. The JFS holds since at short mean free path the quantum interference (analogous to the Landau-Pomeranchuk-Migdal effect in QED) causes the produced mesons to have low momenta $p \sim m$, where $m \simeq 0.6$ GeV is the typical meson mass. Meanwhile the induced jet energy loss at short mean free path is much larger than naively expected in string models.Comment: 4 pages, 4 figure