653 research outputs found
New Procedure for the Isolation of Membrane Vesicles of Bacillus subtilis and an Electron Microscopy Study of Their Ultrastructure
A rapid procedure for the isolation of membrane vesicles of Bacillus subtilis is described that minimizes the action of proteolytic enzymes, excreted by this organism, on the membrane proteins. The membrane vesicles obtained have, in addition to a low endogenous respiration rate, a low endogenous activity for transport of amino acids and carboxylic acids. In the presence of the electron donor, ascorbate-phenazine methosulfate, the transport activities for these compounds were comparable to the activities of intact cells. In addition, these activities were retained for a prolonged period of time. Electron microscopy examination of thin sections of the vesicles showed that the preparation consisted almost exclusively of membrane vesicles which were not contaminated with other cell components. The membrane vesicles, which are six to seven times smaller in diameter than protoplasts, often enclosed smaller vesicles. Freeze-etching of intact cells, protoplasts, and membrane vesicles showed that the orientation of the membrane of the vesicles was identical to the orientation of the plasma membrane in intact cells and protoplasts. This also held for the majority of the membranes of the enclosed vesicles, only 15% having the opposite orientation
New Procedure for the Isolation of Membrane Vesicles of Bacillus subtilis and an Electron Microscopy Study of Their Ultrastructure
Infrared spectroscopy of HCOOH in interstellar ice analogues
Context: HCOOH is one of the more common species in interstellar ices with
abundances of 1-5% with respect to solid H2O. Aims: This study aims at
characterizing the HCOOH spectral features in astrophysically relevant ice
mixtures in order to interpret astronomical data. Methods: The ices are grown
under high vacuum conditions and spectra are recorded in transmission using a
Fourier transform infrared spectrometer. Pure HCOOH ices deposited at 15 K and
145 K are studied, as well as binary and tertiary mixtures containing H2O, CO,
CO2 and CH3OH. The mixture concentrations are varied from 50:50% to ~10:90% for
HCOOH:H2O. Binary mixtures of HCOOH:X and tertiary mixtures of HCOOH:H2O:X with
X = CO, CO2, and CH3OH, are studied for concentrations of ~10:90% and
~7:67:26%, respectively. Results: Pure HCOOH ice spectra show broad bands which
split around 120 K due to the conversion of a dimer to a chain-structure. Broad
single component bands are found for mixtures with H2O. Additional spectral
components are present in mixtures with CO, CO2 and CH3OH. The resulting peak
position, full width at half maximum and band strength depend strongly on ice
structure, temperature, matrix constituents and the HCOOH concentration.
Comparison of the solid HCOOH 5.9, 7.2, and 8.1 micron features with
astronomical data toward the low mass source HH 46 and high mass source W 33A
shows that spectra of binary mixtures do not reproduce the observed ice
features. However, our tertiary mixtures especially with CH3OH match the
astronomical data very well. Thus interstellar HCOOH is most likely present in
tertiary or more complex mixtures with H2O, CH3OH and potentially also CO or
CO2, providing constraints on its formation.Comment: 11 pages, 10 figures, accepted by A&
A recent accretion burst in the low-mass protostar IRAS 15398-3359: ALMA imaging of its related chemistry
Low-mass protostars have been suggested to show highly variable accretion
rates through-out their evolution. Such changes in accretion, and related
heating of their ambient envelopes, may trigger significant chemical variations
on different spatial scales and from source-to-source. We present images of
emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar
IRAS 15398-3359 on 0.5" (75 AU diameter) scales with the Atacama Large
Millimeter/submillimeter Array (ALMA) at 340 GHz. The resolved images show that
the emission from H13CO+ is only present in a ring-like structure with a radius
of about 1-1.5" (150-200 AU) whereas the CO and other high dipole moment
molecules are centrally condensed toward the location of the central protostar.
We propose that HCO+ is destroyed by water vapor present on small scales. The
origin of this water vapor is likely an accretion burst during the last
100-1000 years increasing the luminosity of IRAS 15398-3359 by a factor of 100
above its current luminosity. Such a burst in luminosity can also explain the
centrally condensed CH3OH and extended warm carbon-chain chemistry observed in
this source and furthermore be reflected in the relative faintness of its
compact continuum emission compared to other protostars.Comment: Accepted for publication in ApJ Letters; 14 pages, 5 figure
New Procedure for the Isolation of Membrane Vesicles of Bacillus subtilis and an Electron Microscopy Study of Their Ultrastructure
Rational use of <sup>18</sup>F-FDG PET/CT in patients with advanced cutaneous melanoma:A systematic review
18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is increasingly used in patients with advanced melanoma. Immune checkpoint inhibitors and BRAF/MEK-targeted therapy have transformed the therapeutic landscape of metastatic melanoma. Consequently, a need for markers predicting (early) response to treatment and for monitoring treatment (toxicity) has arisen. This systematic review appraises the current literature evidence for rational use of 18F-FDG PET/CT scans in staging, clinical decision-making, treatment monitoring and follow-up in advanced melanoma. 18F-FDG PET/CT has high overall accuracy for detection of distant metastases and is, combined with cerebral MRI, the preferred imaging strategy for staging metastatic melanoma. In contrast, strong evidence supporting the standard use of 18F-FDG PET/CT for predicting and monitoring therapy response and toxicity is currently lacking. Essential for determining the position of 18F-FDG PET/CT during treatment course in advanced melanoma are well-designed studies with standardized scanning protocols, incorporation of clinical parameters and comparison with contrast-enhanced CT alone
A Comparison of Haptic and Auditory Feedback as a Warning Signal for Slip in Tele-Operation Scenarios
Slip feedback is an important cue in everyday object manipulation, but it is generally missing in tele-operation systems. To test the usefulness of simple, abstract types of feedback that warn the user about slip events, we tested the effect of auditory and haptic vibration feedback in a tele-operation task. Participants were asked to hold an object in a remote robot hand, and the force profiles that they exerted in response to slip events were measured. Haptic feedback did not significantly change the response characteristics, but auditory feedback did significantly improve response latency. A small but significant difference between haptic and auditory reaction times (60 ms) found in our control experiment might explain the difference between the feedback types
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