15,684 research outputs found
Time delay occultation data of the Helios spacecraft for probing the electron density distribution in the solar corona
S-band time delay measurements were collected from the spacecraft Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 earth radius in terms of range, Doppler frequency shift, and electron content. Characteristic features of measurement and data processing are described. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound-K-coronagraph measurements. Using a weighted least squares estimation, parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities at r = 3, 65, 215 earth radius. Transient phenomena are discussed and a velocity of propagation v is nearly equal to 900 km/s is determined for plasma ejecta from a solar flare observed during an extraordinary set of Helios B electron content measurements
Electrostatic fluctuations in cavities within polar liquids and thermodynamics of polar solvation
We present the results of numerical simulations of fluctuations of the
electrostatic potential and electric field inside cavities created in the fluid
of dipolar hard spheres. We found that the thermodynamics of polar solvation
dramatically changes its regime when the cavity size becomes about 4-5 times
larger than the size of the liquid particle. The range of small cavities can be
reasonably understood within the framework of current solvation models. On the
contrary, the regime of large cavities is characterized by a significant
softening of the cavity interface resulting in a decay of the fluctuation
variances with the cavity size much faster than anticipated by both the
continuum electrostatics and microscopic theories. For instance, the variance
of potential decays with the cavity size approximately as
instead of the scaling expected from standard electrostatics. Our
results suggest that cores of non-polar molecular assemblies in polar liquids
lose solvation strength much faster than is traditionally anticipated.Comment: 10 pp, 10 fig
Solvated dissipative electro-elastic network model of hydrated proteins
Elastic netwok models coarse grain proteins into a network of residue beads
connected by springs. We add dissipative dynamics to this mechanical system by
applying overdamped Langevin equations of motion to normal-mode vibrations of
the network. In addition, the network is made heterogeneous and softened at the
protein surface by accounting for hydration of the ionized residues. Solvation
changes the network Hessian in two ways. Diagonal solvation terms soften the
spring constants and off-diagonal dipole-dipole terms correlate displacements
of the ionized residues. The model is used to formulate the response functions
of the electrostatic potential and electric field appearing in theories of
redox reactions and spectroscopy. We also formulate the dielectric response of
the protein and find that solvation of the surface ionized residues leads to a
slow relaxation peak in the dielectric loss spectrum, about two orders of
magnitude slower than the main peak of protein relaxation. Finally, the
solvated network is used to formulate the allosteric response of the protein to
ion binding. The global thermodynamics of ion binding is not strongly affected
by the network solvation, but it dramatically enhances conformational changes
in response to placing a charge at the active site of the protein
Helical structure of longitudinal vortices embedded in turbulent wall-bounded flow
Embedded vortices in turbulent wall-bounded flow over a flat plate, generated
by a passive rectangular vane-type vortex generator with variable angle
to the incoming flow in a low-Reynolds number flow ( based on the
inlet grid mesh size m and free stream velocity m s) have been studied with respect to helical symmetry. The
studies were carried out in a low-speed closed-circuit wind tunnel utilizing
Stereoscopic Particle Image Velocimetry (SPIV). The vortices have been shown to
possess helical symmetry, allowing the flow to be described in a simple
fashion. Iso-contour maps of axial vorticity revealed a dominant primary vortex
and a weaker secondary one for . For
angles outside of this range, the helical symmetry was impaired due to the
emergence of additional flow effects. A model describing the flow has been
utilized, showing strong concurrence with the measurements, even though the
model is decoupled from external flow processes that could perturb the helical
symmetry. The pitch, vortex core size, circulation and the advection velocity
of the vortex all vary linearly with the device angle . This is
important for flow control, since one thereby can determine the axial velocity
induced by the helical vortex as well as the swirl redistributing the axial
velocity component for a given device angle . This also simplifies
theoretical studies, \eg to understand and predict the stability of the vortex
and to model the flow numerically
Message passing for vertex covers
Constructing a minimal vertex cover of a graph can be seen as a prototype for
a combinatorial optimization problem under hard constraints. In this paper, we
develop and analyze message passing techniques, namely warning and survey
propagation, which serve as efficient heuristic algorithms for solving these
computational hard problems. We show also, how previously obtained results on
the typical-case behavior of vertex covers of random graphs can be recovered
starting from the message passing equations, and how they can be extended.Comment: 25 pages, 9 figures - version accepted for publication in PR
First-Pass Meconium Samples from Healthy Term Vaginally-Delivered Neonates : An Analysis of the Microbiota
Acknowledgments The authors would like to thank the parents who consented to provide samples with limited notice at an emotional and stressful time. This work was supported entirely from personal donations to the neonatal endowments fund at Aberdeen Maternity Hospital and we thank families for their continued generosity, year-on-year. The Rowett Institute of Nutrition and Health receives funding from the Scottish Government (SG-RESAS). Funding: This work was funded from NHS Grampian Neonatal Endowments. The Rowett Institute receives funding from the Rural and Environmental Science and Analytical Services programme of the Scottish Government. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
Intersubband Electron Interaction in 1D-2D Junctions
We have shown that the electron transport through junctions of
one-dimensional and two-dimensional systems, as well as through quantum point
contacts, is considerably affected by the interaction of electrons of different
subbands. The interaction mechanism is caused by Friedel oscillations, which
are produced by electrons of the closed subbands even in smooth junctions.
Because of the interaction with these oscillations, electrons of the open
subbands experience a backscattering. The electron reflection coefficient,
which describes the backscattering, has a sharp peak at the energy equal to the
Fermi energy and may be as high as about 0.1. This result allows one to explain
a number of available experimental facts.Comment: 5 pages, 3 figure
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