7,174 research outputs found
Transient dynamics and structure of optimal excitations in thermocapillary spreading: Precursor film model
Linearized modal stability theory has shown that the thermocapillary spreading of a liquid film on a homogeneous, completely wetting surface can produce a rivulet instability at the advancing front due to formation of a capillary ridge. Mechanisms that drain fluid from the ridge can stabilize the flow against rivulet formation. Numerical predictions from this analysis for the film speed, shape, and most unstable wavelength agree remarkably well with experimental measurements even though the linearized disturbance operator is non-normal, which allows transient growth of perturbations. Our previous studies using a more generalized nonmodal stability analysis for contact lines models describing partially wetting liquids (i.e., either boundary slip or van der Waals interactions) have shown that the transient amplification is not sufficient to affect the predictions of eigenvalue analysis. In this work we complete examination of the various contact line models by studying the influence of an infinite and flat precursor film, which is the most commonly employed contact line model for completely wetting films. The maximum amplification of arbitrary disturbances and the optimal initial excitations that elicit the maximum growth over a specified time, which quantify the sensitivity of the film to perturbations of different structure, are presented. While the modal results for the three different contact line models are essentially indistinguishable, the transient dynamics and maximum possible amplification differ, which suggests different transient dynamics for completely and partially wetting films. These differences are explained by the structure of the computed optimal excitations, which provides further basis for understanding the agreement between experiment and predictions of conventional modal analysis
Comment on "Absence of Compressible Edge Channel Rings in Quantum Antidots"
In a recent article, Karakurt et al. [I. Karakurt et al., Phys. Rev. Lett.
89, 226803 (2002)] reported the absence of compressible regions around antidots
in the quantum Hall regime. We wish to point out a significant flaw in their
analysis, which invalidates their claim.Comment: 1 page 1 figure, to be published in Phys. Rev. Let
Dynamics and High Energy Emission of the Flaring HST-1 Knot in the M 87 Jet
Stimulated by recent observations of a radio-to-X-ray synchrotron flare from
HST-1, the innermost knot of the M 87 jet, as well as by a detection of a very
high energy gamma-ray emission from M 87, we investigated the dynamics and
multiwavelength emission of the HST-1 region. We study thermal pressure of the
hot interstellar medium in M 87 and argue for a presence of a gaseous
condensation in its central parts. Interaction of the jet with such a feature
is likely to result in formation of a converging reconfinement shock in the
innermost parts of the M 87 jet. We show that for a realistic set of the
outflow parameters, a stationary and a flaring part of the HST-1 knot located
\~100 pc away from the active center can be associated with the decelerated
portion of the jet matter placed immediately downstream of the point where the
reconfinement shock reaches the jet axis. We discuss a possible scenario
explaining a broad-band brightening of the HST-1 region related to the variable
activity of the central core. We show that assuming a previous epoch of the
high central black hole activity resulting in ejection of excess particles and
photons down along the jet, one may first expect a high-energy flare of HST-1
due to inverse-Comptonisation of the nuclear radiation, followed after a few
years by an increase in the synchrotron continuum of this region. If this is
the case, then the recently observed increase in the knot luminosity in all
spectral bands could be regarded as an unusual echo of the outburst that had
happened previously in the active core of the M 87 radio galaxy.Comment: 30 pages, 7 figures included. Accepted for publication in MNRA
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Conjugative transfer of a Streptomyces plasmid, pSN22
pSN22, an 11 kb multicopy conjugative plasmid from Streptomyces nigrifaciens, promotes chromosome recombination in Streptomyces lividans. Five genes have been identified to be involved in plasmid transfer and pock formation: traB is essential for plasmid transfer; traA for pock formation; spdA and spdB are concerned with pock size; and traR, which corresponds to a kor gene in a kil-kor system, encodes a repressor of traR itself and the traA-traB-spdB (tra) operon. Studies on the interaction of TraR with promoter regions suggest that the negative regulation of transfer-related genes by TraR is achieved by two mechanisms, i.e. promoter hiding and roadblock. The predicted ATPase activity and the membrane localization of TraB suggest that the protein plays a direct role in ATP-driven DNA translocation. TraB is also thought to be involved in intra- and intermycelial transfers of pSN22.ArticleActinomycetologica. 10(1):12-22 (1996)journal articl
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