1,956 research outputs found
The role of C-terminal amidation in the membrane interactions of the anionic antimicrobial peptide, maximin H5
Maximin H5 is an anionic antimicrobial peptide from amphibians, which carries a C-terminal amide moiety, and was found to be moderately haemolytic (20%). The α-helicity of the peptide was 42% in the presence of lipid mimics of erythrocyte membranes and was found able to penetrate (10.8mNm(-1)) and lyse these model membranes (64 %). In contrast, the deaminated peptide exhibited lower levels of haemolysis (12%) and α-helicity (16%) along with a reduced ability to penetrate (7.8mNm(-1)) and lyse (55%) lipid mimics of erythrocyte membranes. Taken with molecular dynamic simulations and theoretical analysis, these data suggest that native maximin H5 primarily exerts its haemolytic action via the formation of an oblique orientated α-helical structure and tilted membrane insertion. However, the C-terminal deamination of maximin H5 induces a loss of tilted α-helical structure, which abolishes the ability of the peptide's N-terminal and C-terminal regions to H-bond and leads to a loss in haemolytic ability. Taken in combination, these observations strongly suggest that the C-terminal amide moiety carried by maximin H5 is required to stabilise the adoption of membrane interactive tilted structure by the peptide. Consistent with previous reports, these data show that the efficacy of interaction and specificity of maximin H5 for membranes can be attenuated by sequence modification and may assist in the development of variants of the peptide with the potential to serve as anti-infective
The Sizes of 1720 MHz OH Masers: VLBA and MERLIN Observations of the Supernova Remnants W44 and W28
We have used the NRAO Very Long Baseline Array (VLBA) to image OH(1720 MHz)
masers in the supernova remnants W28 and W44 at a resolution of 40 mas. We also
used MERLIN to observe the same OH(1720 MHz) masers in W44 at a resolution of
290 x 165 mas. All the masers are resolved by these VLBA and MERLIN
observations. The measured sizes range from 50 to 180 mas and yield brightness
temperature estimates from 0.3--20 x 10**8 K. We investigate whether these
measured angular sizes are intrinsic and hence originate as a result of the
physical conditions in the supernova remnant shock, or whether they are scatter
broadened sizes produced by the turbulent ionized gas along the line of sight.
While the current data on the temporal and angular broadening of pulsars,
masers and extragalactic soures toward W44 and W28 can be understood in terms
of scattering, we cannot rule out that these large sizes are intrinsic. Recent
theoretical modeling by Lockett et al. suggests that the physical parameters in
the shocked region are indicative of densities and OH abundances which lead to
estimates of sizes as large as what we measure. If the sizes and structure are
intrinsic, then the OH(1720 MHz) masrs may be more like the OH(1612 MHz) masers
in circumstellar shells than OH masers associated with HII regions. At two
locations in W28 we observe the classical S-shapes in the Stokes V profiles
caused by Zeeman splitting and use it to infer magnetic fields of order 2
milliGauss.Comment: 24 pages, 6 figures, accepted by Ap
An Spectrometer for Investigating the Spectral Momentum Density of Thin Films
An (e, 2e) spectrometer has been constructed for detecting scattered and recoiling electrons from a thin solid film. The cross section for observing the two electrons in coincidence is proportional to the spectral momentum density of the target. In this spectrometer the energy of the incident electron beam is 25 keV and the beam current is approximately 40 μA. The energy resolution (FWHM) is ≤4 eV. The momentum resolution (FWHM) can be varied from 0.2 to 1.0 Å−1. Preliminary coincidence data from an amorphous carbon film are presented
Charge Storage Measuremens of Resistivity for Dielectric Samples from the CRRES Internal Discharge Monitor
Experimentally Derived Resistivity for Dielectric Samples From the CRRES Internal Discharge Monitor
Resistivity values were experimentally determined using charge storage methods for six samples remaining from the construction of the Internal Discharge Monitor (IDM) flown on the Combined Release and Radiation Effects Satellite (CRRES). Three tests were performed over a period of four to five weeks each in a vacuum of ~5×10-6 torr with an average temperature of ~25 ºC to simulate a space environment. Samples tested included FR4, PTFE, and alumina with copper electrodes attached to one or more of the sample surfaces. FR4 circuit board material was found to have a dark current resistivity of ~1×1018 Ω-cm and a moderately high polarization current. Fiber filled PTFE exhibited little polarization current and a dark current resistivity of ~3×1020 Ω-cm. Alumina had a measured dark current resistivity of ~3·1017 Ω-cm, with a very large and more rapid polarization. Experimentally determined resistivity values were two to three orders of magnitude more than found using standard ASTM test methods. The one minute wait time suggested for the standard ASTM tests is much shorter than the measured polarization current decay times for each sample indicating that the primary currents used to determine ASTM resistivity are caused by the polarization of molecules in the applied electric field rather than charge transport through the bulk of the dielectric. Testing over much longer periods of time in vacuum is required to allow this polarization current to decay away and to allow the observation of charged particles transport through a dielectric material. Application of a simple physics-based model allows separation of the polarization current and dark current components from long duration measurements of resistivity over day- to month-long time scales. Model parameters are directly related to the magnitude of charge transfer and storage and the rate of charge transport
On the Enhanced Interstellar Scattering Toward B1849+005
(Abridged) This paper reports new Very Large Array (VLA) and Very Long
Baseline Array (VLBA) observations of the extragalactic source B1849+005 at
frequencies between 0.33 and 15 GHz and the re-analysis of archival VLA
observations at 0.33, 1.5, and 4.9 GHz. The structure of this source is complex
but interstellar scattering dominates the structure of the central component at
least to 15 GHz. An analysis of the phase structure functions of the
interferometric visibilities shows the density fluctuations along this line of
sight to be anisotropic (axial ratio = 1.3) with a frequency-independent
position angle, and having an inner scale of roughly a few hundred kilometers.
The anisotropies occur on length scales of order 10^{15} cm (D/5 kpc), which
within the context of certain magnetohydrodynamic turbulence theories indicates
the length scale on which the kinetic and magnetic energy densities are
comparable. A conservative upper limit on the velocity of the scattering
material is 1800 km/s. In the 0.33 GHz field of view, there are a number of
other sources that might also be heavily scattered. Both B1849+005 and PSR
B1849+00 are highly scattered, and they are separated by only 13'. If the lines
of sight are affected by the same ``clump'' of scattering material, it must be
at least 2.3 kpc distant. However, a detailed attempt to account for the
scattering observables toward these sources does not produce a self-consistent
set of parameters for such a clump. A clump of H\alpha emission, possibly
associated with the H II region G33.418-0.004, lies between these two lines of
sight, but it seems unable to account for all of the required excess
scattering.Comment: 23 pages, LaTeX2e AASTeX, 13 figures in 14 PostScript files, accepted
for publication in Ap
Primary Carcinoma of the Gallbladder
Carcinoma of the gallbladder is a relatively rare malignancy which is difficult to diagnose. The advent of
improved imaging methods and the expansion of interventional radiology however, combined with
advances in surgical technique, has produced a change in attitude towards this tumour. The available
world literature since 1960 has been reviewed and is presented in this article. However, whilst the
outlook for diagnosis and treatment is improving, clearly the association with cholelithiasis (between
45% and 100%), is a cause for concern particularly with the advent of treatments (lithotripsy,
percutaneous gallstone extraction) which leave gall bladder mucosa and residual fragments of stone in situ
The Wisconsin H-Alpha Mapper Northern Sky Survey
The Wisconsin H-Alpha Mapper (WHAM) has surveyed the distribution and
kinematics of ionized gas in the Galaxy above declination -30 degrees. The WHAM
Northern Sky Survey (WHAM-NSS) has an angular resolution of one degree and
provides the first absolutely-calibrated, kinematically-resolved map of the
H-Alpha emission from the Warm Ionized Medium (WIM) within ~ +/-100 km/s of the
Local Standard of Rest. Leveraging WHAM's 12 km/s spectral resolution, we have
modeled and removed atmospheric emission and zodiacal absorption features from
each of the 37,565 spectra. The resulting H-Alpha profiles reveal ionized gas
detected in nearly every direction on the sky with a sensitivity of 0.15 R (3
sigma). Complex distributions of ionized gas are revealed in the nearby spiral
arms up to 1-2 kpc away from the Galactic plane. Toward the inner Galaxy, the
WHAM-NSS provides information about the WIM out to the tangent point down to a
few degrees from the plane. Ionized gas is also detected toward many
intermediate velocity clouds at high latitudes. Several new H II regions are
revealed around early B-stars and evolved stellar cores (sdB/O). This work
presents the details of the instrument, the survey, and the data reduction
techniques. The WHAM-NSS is also presented and analyzed for its gross
properties. Finally, some general conclusions are presented about the nature of
the WIM as revealed by the WHAM-NSS.Comment: 42 pages, 14 figures (Fig 6-9 & 14 are full color); accepted for
publication in 2003, ApJ, 149; Original quality figures (as well as data for
the survey) are available at http://www.astro.wisc.edu/wham
A Simple Family of Analytical Trumpet Slices of the Schwarzschild Spacetime
We describe a simple family of analytical coordinate systems for the
Schwarzschild spacetime. The coordinates penetrate the horizon smoothly and are
spatially isotropic. Spatial slices of constant coordinate time feature a
trumpet geometry with an asymptotically cylindrical end inside the horizon at a
prescribed areal radius (with ) that serves as the free
parameter for the family. The slices also have an asymptotically flat end at
spatial infinity. In the limit the spatial slices lose their trumpet
geometry and become flat -- in this limit, our coordinates reduce to
Painlev\'e-Gullstrand coordinates.Comment: 7 pages, 3 figure
- …