34,867 research outputs found
Unstable manifolds and Schroedinger dynamics of Ginzburg-Landau vortices
The time evolution of several interacting Ginzburg-Landau vortices according
to an equation of Schroedinger type is approximated by motion on a
finite-dimensional manifold. That manifold is defined as an unstable manifold
of an auxiliary dynamical system, namely the gradient flow of the
Ginzburg-Landau energy functional. For two vortices the relevant unstable
manifold is constructed numerically and the induced dynamics is computed. The
resulting model provides a complete picture of the vortex motion for arbitrary
vortex separation, including well-separated and nearly coincident vortices.Comment: 23 pages amslatex, 5 eps figures, minor typos correcte
Identification and Characterization of the Corazonin Receptor and Possible Physiological Roles of the Corazonin-Signaling Pathway in Rhodnius prolixus.
Neuropeptides control many physiological and endocrinological processes in animals, acting as neuroactive chemicals within the central and peripheral nervous systems. Corazonin (CRZ) is one such neuropeptide that has a variety of physiological roles associated with control of heartbeat, ecdysis behavior initiation, and cuticle coloration. These physiological effects are mediated by the CRZ receptor (CRZR). In order to understand the role of the CRZ-signaling pathway in Rhodnius prolixus, the cDNA sequence encoding the Rhopr-CRZR was isolated and cloned revealing two splice variants (Rhopr-CRZR-α and β). Sequence analysis revealed characteristics of rhodopsin-like GPCRs. Rhopr-CRZR-α and β were dose-dependently activated by Rhopr-CRZ with EC50 values of 2.7 and 1 nM, respectively, when tested in a functional receptor assay using CHOKI-aeq cells. Neither receptors were activated by the evolutionarily-related peptides, Rhopr-AKH, or Rhopr-ACP. For 5th instars, qPCR revealed expression of Rhopr-CRZR transcript in the CNS, the dorsal vessel, abdominal dorsal epidermis, and prothoracic glands with associated fat body. Interestingly, transcript expression was also found in the female and male reproductive tissues. Rhopr-CRZR transcript was reduced after injection of dsCRZR into adult R. prolixus. In these insects, the basal heartbeat rate was reduced in vivo, and the increase in heartbeat frequency normally produced by CRZ on dorsal vessel in vitro was much reduced. No effect of dsCRZR injection was seen on ecdysis or coloration of the cuticle
Surface anchoring on layers of grafted liquid-crystalline chain molecules: A computer simulation
By Monte Carlo simulations of a soft ellipsoid model for liquid crystals, we
study whether a layer of grafted liquid-crystalline chain molecules can induce
tilt in a nematic fluid. The chains are fairly short (four monomers) and made
of the same particles as the solvent. They are attached to a substrate which
favors parallel (planar) alignment. At low grafting densities, the substrate
dominates and we observe planar alignment. On increasing the grafting density,
we find a first order transition from planar to tilted alignment. Beyond the
transition, the tilt angle with respect to the surface normal decreases
continuously. The range of accessible anchoring angles is quite large.Comment: To appear in J. Chem. Phy
An investigation of the suitability of white rats for sub-orbital studies of behavior in a gravity field
Suitability of white rats for suborbital studies of behavior in gravity field
The application of Floquet theory to the computation of small orbital perturbations over long time intervals using the Tschauner- Hempel equations
Calculation of path deviation of satellite from reference trajectory - perturbation theor
Planck pre-launch status: HFI ground calibration
Context. The Planck satellite was successfully launched on May 14th 2009. We have completed the pre-launch calibration measurements of the High Frequency Instrument (HFI) on board Planck and their processing.
Aims. We present the results of the pre-launch calibration of HFI in which we have multiple objectives. First, we determine instrumental parameters that cannot be measured in-flight and predict parameters that can. Second, we take the opportunity to operate and understand the instrument under a wide range of anticipated operating conditions. Finally, we estimate the performance of the instrument built.
Methods. We obtained our pre-launch calibration results by characterising the component and subsystems, then by calibrating the focal plane at IAS (Orsay) in the Saturne simulator, and later from the tests at the satellite level carried out in the CSL (Liège) cryogenic vacuum chamber. We developed models to estimate the instrument pre-launch parameters when no measurement could be performed.
Results. We reliably measure the Planck-HFI instrument characteristics and behaviour, and determine the flight nominal setting of all parameters. The expected in-flight performance exceeds the requirements and is close or superior to the goal specifications
Form Factors from Light-Cone Sum Rules with B-Meson Distribution Amplitudes
New sum rules for and form factors are derived
from the correlation functions expanded near the light-cone in terms of B-meson
distribution amplitudes. The contributions of quark-antiquark and
quark-antiquark-gluon components in the B meson are taken into account. Models
for the B-meson three-particle distribution amplitudes are suggested, based on
QCD sum rules in HQET. Employing the new light-cone sum rules we calculate the
form factors at small momentum transfers, including violation
effects. The results agree with the predictions of the conventional light-cone
sum rules.Comment: 32 pages, 7 figures, the discussion of numerical results extended,
two references added, version to be published in Phys.Rev.
On the engineering portion of a research program to develop a zero-g, drag-free satellite and to perform a gyro test of general relativity in a satellite Fourth semiannual status report
Zero gravity satellite concept feasibility and control system design evaluation using air cushion vehicl
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