695 research outputs found
Molecular Model of the Contractile Ring
We present a model for the actin contractile ring of adherent animal cells.
The model suggests that the actin concentration within the ring and
consequently the power that the ring exerts both increase during contraction.
We demonstrate the crucial role of actin polymerization and depolymerization
throughout cytokinesis, and the dominance of viscous dissipation in the
dynamics. The physical origin of two phases in cytokinesis dynamics ("biphasic
cytokinesis") follows from a limitation on the actin density. The model is
consistent with a wide range of measurements of the midzone of dividing animal
cells.Comment: PACS numbers: 87.16.Ka, 87.16.Ac
http://www.ncbi.nlm.nih.gov/pubmed/16197254
http://www.weizmann.ac.il/complex/tlusty/papers/PhysRevLett2005.pd
Normal-mode spectroscopy of a single bound atom-cavity system
The energy-level structure of a single atom strongly coupled to the mode of a
high-finesse optical cavity is investigated. The atom is stored in an
intracavity dipole trap and cavity cooling is used to compensate for inevitable
heating. Two well-resolved normal modes are observed both in the cavity
transmission and the trap lifetime. The experiment is in good agreement with a
Monte Carlo simulation, demonstrating our ability to localize the atom to
within at a cavity antinode.Comment: 4 pages, 4 figure
Trapping of single atoms in cavity QED
By integrating the techniques of laser cooling and trapping with those of
cavity quantum electrodynamics (QED), single Cesium atoms have been trapped
within the mode of a small, high finesse optical cavity in a regime of strong
coupling. The observed lifetime for individual atoms trapped within the cavity
mode is ms, and is limited by fluctuations of light forces
arising from the far-detuned intracavity field. This initial realization of
trapped atoms in cavity QED should enable diverse protocols in quantum
information science.Comment: 4 pages, 4 figure
Superlubricity mechanism of diamond-like carbon with glycerol. Coupling of experimental and simulation studies
We report a unique tribological system that produces superlubricity under boundary lubrication conditions with extremely little wear. This system is a thin coating of hydrogen-free amorphous Diamond-Like-Carbon (denoted as ta-C) at 353 K in a ta-C/ta-C friction pair lubricated with pure glycerol. To understand the mechanism of friction vanishing we performed ToF-SIMS experiments using deuterated glycerol and 13C glycerol. This was complemented by first-principles-based computer simulations using the ReaxFF reactive force field to create an atomistic model of ta-C. These simulations show that DLC with the experimental density of 3.24 g/cc leads to an atomistic structure consisting of a 3D percolating network of tetrahedral (sp3) carbons accounting for 71.5% of the total, in excellent agreement with the 70% deduced from our Auger spectroscopy and XANES experiments. The simulations show that the remaining carbons (with sp2 and sp1 character) attach in short chains of length 1 to 7. In sliding simulations including glycerol molecules, the surface atoms react readily to form a very smooth carbon surface containing OH-terminated groups. This agrees with our SIMS experiments. The simulations find that the OH atoms are mostly bound to surface sp1 atoms leading to very flexible elastic response to sliding. Both simulations and experiments suggest that the origin of the superlubricity arises from the formation of this OH-terminated surface
State determination in continuous measurement
The possibility of determining the state of a quantum system after a
continuous measurement of position is discussed in the framework of quantum
trajectory theory. Initial lack of knowledge of the system and external noises
are accounted for by considering the evolution of conditioned density matrices
under a stochastic master equation. It is shown that after a finite time the
state of the system is a pure state and can be inferred from the measurement
record alone. The relation to emerging possibilities for the continuous
experimental observation of single quanta, as for example in cavity quantum
electrodynamics, is discussed.Comment: 12 pages, 4 figures, Revte
Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality
A dense gas of cesium atoms at the crossover to two-dimensionality is
prepared in a highly anisotropic surface trap that is realized with two
evanescent light waves. Temperatures as low as 100nK are reached with 20.000
atoms at a phase-space density close to 0.1. The lowest quantum state in the
tightly confined direction is populated by more than 60%. The system offers
intriguing prospects for future experiments on degenerate quantum gases in two
dimensions
In Vitro Contraction of Cytokinetic Ring Depends on Myosin II but not on Actin Dynamics
10.1038/ncb2781Nature Cell Biology157853-859NCBI
Quantum state transfer and entanglement distribution among distant nodes in a quantum network
We propose a scheme to utilize photons for ideal quantum transmission between
atoms located at spatially-separated nodes of a quantum network. The
transmission protocol employs special laser pulses which excite an atom inside
an optical cavity at the sending node so that its state is mapped into a
time-symmetric photon wavepacket that will enter a cavity at the receiving node
and be absorbed by an atom there with unit probability. Implementation of our
scheme would enable reliable transfer or sharing of entanglement among
spatially distant atoms.Comment: 4 pages, 3 postscript figure
Stability conditions and positivity of invariants of fibrations
We study three methods that prove the positivity of a natural numerical
invariant associated to parameter families of polarized varieties. All
these methods involve different stability conditions. In dimension 2 we prove
that there is a natural connection between them, related to a yet another
stability condition, the linear stability. Finally we make some speculations
and prove new results in higher dimension.Comment: Final version, to appear in the Springer volume dedicated to Klaus
Hulek on the occasion of his 60-th birthda
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