914 research outputs found
Long-term polarimetric observations of OH127.8+0.0
OH 1612 and 1667 MHz masers from the well known object OH127.8+0.0 were mon-
itored in full-polarization mode over a period of 6.5 years and mapped with
MERLIN at one epoch. The OH variability pattern of the star is typical of
extremely long- period AGB stars. The distance determined from the 1612 MHz
light curve and a new measurement of the angular radius is 3.87 (0.28) kpc. At
both frequencies, the flux of polarized emission tightly follows the total flux
variations while, the degrees of circu- lar and linear polarization are
constant within measurement accuracy.. There is net polarization at both lines.
The magnetic field strength estimated from a likely Zeeman pair is -0.6 mG at
the distance of 5400 au from the star.At the near and far sides of the
envelope, the polarization vectors are well aligned implying a regular
structure of the magnetic field. The polarization characteristics of the OH
maser emission suggest a radial magnetic field which is frozen in the stellar
wind.Comment: 12 pages, 9 figure
Stretching of proteins in a uniform flow
Stretching of a protein by a fluid flow is compared to that in a force-clamp
apparatus. The comparison is made within a simple topology-based dynamical
model of a protein in which the effects of the flow are implemented using
Langevin dynamics. We demonstrate that unfolding induced by a uniform flow
shows a richer behavior than that in the force clamp. The dynamics of unfolding
is found to depend strongly on the selection of the amino acid, usually one of
the termini, which is anchored. These features offer potentially wider
diagnostic tools to investigate structure of proteins compared to experiments
based on the atomic force microscopy.Comment: J. Chem. Phys. (in press
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Instabilities in the dissolution of a porous matrix
A reactive fluid dissolving the surrounding rock matrix can trigger an
instability in the dissolution front, leading to spontaneous formation of
pronounced channels or wormholes. Theoretical investigations of this
instability have typically focused on a steadily propagating dissolution front
that separates regions of high and low porosity. In this paper we show that
this is not the only possible dissolutional instability in porous rocks; there
is another instability that operates instantaneously on any initial porosity
field, including an entirely uniform one. The relative importance of the two
mechanisms depends on the ratio of the porosity increase to the initial
porosity. We show that the "inlet" instability is likely to be important in
limestone formations where the initial porosity is small and there is the
possibility of a large increase in permeability. In quartz-rich sandstones,
where the proportion of easily soluble material (e.g. carbonate cements) is
small, the instability in the steady-state equations is dominant.Comment: to be published in Geophysical Research Letter
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