585 research outputs found
Biomolecule surface patterning may enhance membrane association
Under dehydration conditions, amphipathic Late Embryogenesis Abundant (LEA)
proteins fold spontaneously from a random conformation into alpha-helical
structures and this transition is promoted by the presence of membranes. To
gain insight into the thermodynamics of membrane association we model the
resulting alpha-helical structures as infinite rigid cylinders patterned with
hydrophobic and hydrophilic stripes oriented parallel to their axis.
Statistical thermodynamic calculations using Single Chain Mean Field (SCMF)
theory show that the relative thickness of the stripes controls the free energy
of interaction of the alpha-helices with a phospholipid bilayer, as does the
bilayer structure and the depth of the equilibrium penetration of the cylinders
into the bilayer. The results may suggest the optimal thickness of the stripes
to mimic the association of such protein with membranes.Comment: Published in ACS Nano http://pubs.acs.org/doi/pdf/10.1021/nn204736
Spectropolarimetric Observations of Herbig Ae/Be Stars. II. Comparison of Spectropolarimetric Surveys: HAeBe, Be and Other Emission-Line Stars
The polarization of light across individual spectral lines contains
information about the circumstellar environment on very small spatial scales.
We have obtained a large number of high precision, high resolution
spectropolarimetric observations of Herbig Ae/Be, Classical Be and other
emission-line stars collected on 117 nights of observations with the HiVIS
spectropolarimeter at a resolution of R=13000 on the 3.67m AEOS telescope. We
also have many observations from the ESPaDOnS spectropolarimeter at a
resolution of R=68000 on the 3.6m CFH telescope. In roughly ~2/3 of the
so-called "windy" or "disky" Herbig Ae/Be stars, the detected H-alpha linear
polarization varies from our typical detection threshold near 0.1% to over 2%.
In all but one HAe/Be star the detected polarization effect is not coincident
with the H-alpha emission peak but is detected in and around the obvious
absorptive part of the line profile. The qu-loops are dominated by the
polarization in this absorptive region. In several stars the polarization
varies in time mostly in the absorptive component and is not necessarily tied
to corresponding variations in intensity. This is a new result not seen at
lower resolution. In the Be and emission-line stars, 10 out of a sample of 30
show a typical broad depolarization effect but 4 of these 10 show weaker
effects only visible at high resolution. Another 5 of 30 show smaller
amplitude, more complex signatures. Six stars of alternate classification
showed large amplitude (1-3%) absorptive polarization effects. These detections
are largely inconsistent with the traditional disk-scattering and
depolarization models.Comment: Published in ApJS 180. 47 pages, 34 figures. Small corrections made
to tex
Accurate magnetic field measurements of Vega-like stars and Herbig Ae/Be stars
We have obtained accurate circular spectropolarimetric observations for a
sample of Vega-like and Herbig Ae/Be stars with FORS1 at the VLT in an attempt
to detect their magnetic fields. No magnetic field could be diagnosed in any
Vega-like star. The most accurate determination of a magnetic field, at 2.6
sigma level, has been performed for the Vega-like star iota Cen for which we
have measured = -77+-30 G. In the prototype of Vega-like stars, the star
beta Pictoris, which shows conspicuous signs of chromospheric activity, a
longitudinal magnetic field is measured only at ~1.5 sigma level. We diagnose
for the first time a longitudinal magnetic field at a level larger than 3 sigma
for the two Herbig Ae stars HD31648 and HD144432 and we confirm the previous
detection of a magnetic field in a third Herbig Ae star, HD139614. Finally, we
discuss the discovery of distinctive Zeeman features in the unusual Herbig Ae
star HD190073 where the Ca II doublet displays several components in both H and
K lines. From the measurement of circular polarization in all Balmer lines from
H_beta to H_8 we obtain = +26+-34 G. However, using for the measurement
of circular polarization only the Ca II H and K lines, we are able to diagnose
a longitudinal magnetic field at 2.8 sigma level, = +84+-30 G.Comment: 7 pages, 3 figures, accepted for publication in A&
Saturation effect for dependence of the electrical conductivity of planar oriented nematic liquid crystal 6CB on the concentration of Cu7PS6 nanoparticles
The influence of Cu7PS6 nanoparticles with the average size 117 nm on the dielectric properties of planar oriented nematic liquid crystal 6CB has been investigated within the frequency range 10(1) ...10(6) Hz and at the temperature 293 K. It has been shown that when changing the concentration of nanoparticles within the range 0 to 1 wt.%, the conductivity of the liquid crystal changes stronger than its dielectric permittivity. It has been shown that the electrical conductivity increases monotonously with increasing the concentration of nanoparticles. However, for this dependence a saturation effect is observed. The mechanism of this effect was proposed.info:eu-repo/semantics/publishedVersio
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