48,190 research outputs found
Propagation of Love waves in layers with irregular boundaries
Propagation of Love waves in layers with irregular boundaries studied by earth model in which half space is elasti
Viking lander camera geometry calibration report. Volume 1: Test methods and data reduction techniques
The determination and removal of instrument signature from Viking Lander camera geometric data are described. All tests conducted as well as a listing of the final database (calibration constants) used to remove instrument signature from Viking Lander flight images are included. The theory of the geometric aberrations inherent in the Viking Lander camera is explored
PEO/CHCl3: Crystallinity of the polymer and vapor pressure of the solvent - Equilibrium and non-equilibrium phenomena -
Vapor pressures were measured for the system chloroform/polyethylene oxide
(peo, weight average molar mass = 1000 kg/mol) at 25 degrees centigrade as a
function of the weight fraction w of the polymer by means of a combination of
head space sampling and gas chromatography. The establishment of thermodynamic
equilibria was assisted by employing thin polymer films. The degrees of
crystallinity alpha of the pure peo and of the solid polymer contained in the
mixtures were determined via dsc. An analogous degree of polymer insolubility,
beta, was calculated from the vapor pressures measured in this composition
range. The experiments demonstrate that both quantities and their concentration
dependence are markedly affected by the particular mode of film preparation.
These non-equilibrium phenomena are discussed in terms of frozen local and
temporal equilibria, where differences between alpha and beta are attributed to
the occlusion of amorphous material within crystalline domains. Equilibrium
information was obtained from two sources, namely from the vapor pressures in
the absence of crystalline material (gas/liquid) and from the saturation
concentration of peo (liquid/solid). The thermodynamic consistency of these
data is demonstrated using a new approach that enables the modeling of
composition dependent interaction parameters by means of two adjustable
parameters only
Averting the magnetic braking catastrophe on small scales: disk formation due to Ohmic dissipation
We perform axisymmetric resistive MHD calculations that demonstrate that
centrifugal disks can indeed form around Class 0 objects despite magnetic
braking. We follow the evolution of a prestellar core all the way to
near-stellar densities and stellar radii. Under flux-freezing, the core is
braked and disk formation is inhibited, while Ohmic dissipation renders
magnetic braking ineffective within the first core. In agreement with
observations that do not show evidence for large disks around Class 0 objects,
the resultant disk forms in close proximity to the second core and has a radius
of only early on. Disk formation does not require
enhanced resistivity. We speculate that the disks can grow to the sizes
observed around Class II stars over time under the influence of both Ohmic
dissipation and ambipolar diffusion, as well as internal angular momentum
redistribution.Comment: 4 pages, 3 figures, accepted by A&A Letter
The antigenic index: a novel algorithm for predicting antigenic determinants
In this paper, we introduce a computer algorithm which can
be used to predict the topological features of a protein directly
from its primary amino acid sequence. The computer program
generates values for surface accessibility parameters and combines
these values with those obtained for regional backbone
flexibility and predicted secondary structure. The output of this
algorithm, the antigenic index, is used to create a linear surface
contour profile of the protein. Because most, if not all,
antigenic sites are located within surface exposed regions of
a protein, the program offers a reliable means of predicting
potential antigenic determinants. We have tested the ability of
this program to generate accurate surface contour profiles and
predict antigenic sites from the linear amino acid sequences
of well-characterized proteins and found a strong correlation
between the predictions of the antigenic index and known structural
and biological data
Action Potential Onset Dynamics and the Response Speed of Neuronal Populations
The result of computational operations performed at the single cell level are
coded into sequences of action potentials (APs). In the cerebral cortex, due to
its columnar organization, large number of neurons are involved in any
individual processing task. It is therefore important to understand how the
properties of coding at the level of neuronal populations are determined by the
dynamics of single neuron AP generation. Here we analyze how the AP generating
mechanism determines the speed with which an ensemble of neurons can represent
transient stochastic input signals. We analyze a generalization of the
-neuron, the normal form of the dynamics of Type-I excitable membranes.
Using a novel sparse matrix representation of the Fokker-Planck equation, which
describes the ensemble dynamics, we calculate the transmission functions for
small modulations of the mean current and noise noise amplitude. In the
high-frequency limit the transmission function decays as ,
where surprisingly depends on the phase at which APs are
emitted. In a physiologically plausible regime up to 1kHz the typical response
speed is, however, independent of the high-frequency limit and is set by the
rapidness of the AP onset, as revealed by the full transmission function. In
this regime modulations of the noise amplitude can be transmitted faithfully up
to much higher frequencies than modulations in the mean input current. We
finally show that the linear response approach used is valid for a large regime
of stimulus amplitudes.Comment: Submitted to the Journal of Computational Neuroscienc
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