545 research outputs found
(D-Ser2)Oxm[Lys38-γ-glu-PAL] improves hippocampal gene expression and cognitionin a mouse model of type 1 diabetes
A novel peptide isolated from Aphonopelma chalcodes tarantula venom with benefits on pancreatic islet function and appetite control
The micrometeoroid complex and evolution of the lunar regolith
The interaction of the micrometeoroid complex with the lunar surface is evidenced by numerous glass-lined microcraters on virtually every lunar surface exposed to space. Such craters range in size from less than .1 micron to approximately 2 sq cm diameter. Using small scale laboratory cratering experiments for calibration, the observed crater-sized frequency distributions may be converted into micrometeoroid mass distributions. These lunar mass distributions are in essential agreement with satellite data. Some physical properties of micrometeoroids may be deduced by comparing lunar crater geometries with those obtained in laboratory experiments. The proponderance of circular outlines of lunar microcraters necessitates equidimensional, if not spherical, micrometeoroids
Scalable Substrate Development for Aqueous Biological Samples for Atom Probe Tomography
Reliable and consistent preparation of atom probe tomography (APT) specimens
from aqueous and hydrated biological specimens remains a significant challenge.
One particularly difficult process step is the use of a focused ion beam (FIB)
instrument for preparing the required needle-shaped specimen, typically
involving a "lift-out" procedure of a small sample of material. Here, two
alternative substrate designs are introduced that enable using FIB only for
sharpening, along with example APT datasets. The first design is a laser-cut
FIB-style half-grid close to those used for transmission-electron microscopy,
that can be used in a grid holder compatible with APT pucks. The second design
is a larger, standalone self-supporting substrate called a "crown", with
several specimen positions that self-aligns in APT pucks, prepared by
electrical discharge machining (EDM). Both designs are made nanoporous, to
provide strength to the liquid-substrate interface, using chemical and vacuum
dealloying. We select alpha brass a simple, widely available, lower-cost
alternative to previously proposed substrates. We present the resulting
designs, APT data, and provide suggestions to help drive wider community
adoption
Microstructural evolution during ageing of Al-Cu-Li-x alloys
In this study, atom probe tomography was used to investigate the microstructure of the alloy AA2198 (Al–1.35 Cu–3.55 Li–0.29 Mg–0.08 Ag) over a range of ageing conditions to examine the evolution of phases in the alloy, in particular aiming to reveal the nucleation mechanism of the strengthening T1 phase. T1 precursor phases were observed from early ageing, most of which were connected to dislocations enriched with Mg and Ag. This Mg solute segregation on the dislocations was subsequently observed to develop into S-like phases. Ag and Mg segregation to T1 interfaces was systematically observed when the plates were oriented perpendicular to the probing direction. The matrix solute content was followed during the course of T1 precipitation. It was found that the evolution of Cu, Li, Mg and Ag was similar, giving additional evidence for their co-precipitation
Nanoporous gold thin films as substrates to analyze liquids by cryo-atom probe tomography
Cryogenic atom probe tomography (cryo-APT) is being developed to enable
nanoscale compositional analyses of frozen liquids. Yet, the availability of
readily available substrates that allow for the fixation of liquids while
providing sufficient strength to their interface, is still an issue. Here we
propose the use of 1-2 microns thick binary alloy film of gold-silver (AuAg)
sputtered onto flat silicon, with sufficient adhesion without an additional
layer. Through chemical dealloying, we successfully fabricate a nanoporous
substrate, with open-pore structure, which is mounted on a microarray of Si
posts by lift out in the focused-ion beam, allowing for cryogenic fixation of
liquids. We present cryo-APT results obtained after cryogenic sharpening,
vacuum cryo-transfer and analysis of pure water on top and inside the
nanoporous film. We demonstrate that this new substrate has the requisite
characteristics for facilitating cryo-APT of frozen liquids, with a relatively
lower volume of precious metals. This complete workflow represents an improved
approach for frozen liquid analysis, from preparation of the films to the
successful fixation of the liquid in the porous network, to cryo-atom probe
tomography
The micrometeoroid complex and evolution of the lunar regolith
Monte Carlo-based computer calculations, as well as analytical approaches utilizing probabilistic arguments, were applied to gain insight into the principal regolith impact processes and their resulting kinetics. Craters 10 to 1500 m in diameter are largely responsible for the overall growth of the regolith. As a consequence the regolith has to be envisioned as a complex sequence of discrete ejecta blankets. Such blankets constitute first-order discontinuities in the evolving debris layer. The micrometeoroid complex then operates intensely on these fresh ejecta blankets and accomplishes only in an uppermost layer of approximately 1-mm thickness. The absolute flux of micrometeoroids based on lunar rock analyses averaged over the past few 10 to the 6th power years is approximately an order of magnitude lower than presentday satellite fluxes; however, there is indication that the flux increased in the past 10 to the 4th power years to become compatible with the satellite data. Furthermore, there is detailed evidence that the micrometeoroid complex existed throughout geologic time
A mass spectrometry-based approach to distinguish annular and specific lipid binding to membrane proteins
Membrane proteins engage in a variety of contacts with theirsurrounding lipids, but distinguishing between specifically boundlipids, and non-specific annular interactionsis a challenging problem. Applying native mass spectrometry to three membrane protein complexes with different lipid binding properties, we explore the ability of detergents to compete with lipids bound in different environments. We show that lipids in annular positions on the Presenilin Homologue protease are subject to constant exchange with detergent. Bycontrast,detergent-resistantlipids bound at the dimer interface in the Leucine transportershowdecreased koffrates in molecular dynamics simulations.Turning tothe lipid flippase MurJ, we findthat addition of the natural substrate lipid-II results in the formation of a 1:1 protein-lipid complex, where the lipid cannot be displaced by detergentfromthe highly protected active site.In summary, we distinguish annular from non-annular lipids based on their exchange rates in solution. [Abstract copyright: © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
QUBIC: The QU Bolometric Interferometer for Cosmology
One of the major challenges of modern cosmology is the detection of B-mode
polarization anisotropies in the CMB. These originate from tensor fluctuations
of the metric produced during the inflationary phase. Their detection would
therefore constitute a major step towards understanding the primordial
Universe. The expected level of these anisotropies is however so small that it
requires a new generation of instruments with high sensitivity and extremely
good control of systematic effects. We propose the QUBIC instrument based on
the novel concept of bolometric interferometry, bringing together the
sensitivity advantages of bolometric detectors with the systematics effects
advantages of interferometry. Methods: The instrument will directly observe the
sky through an array of entry horns whose signals will be combined together
using an optical combiner. The whole set-up is located inside a cryostat.
Polarization modulation will be achieved using a rotating half-wave plate and
interference fringes will be imaged on two focal planes (separated by a
polarizing grid) tiled with bolometers. We show that QUBIC can be considered as
a synthetic imager, exactly similar to a usual imager but with a synthesized
beam formed by the array of entry horns. Scanning the sky provides an
additional modulation of the signal and improve the sky coverage shape. The
usual techniques of map-making and power spectrum estimation can then be
applied. We show that the sensitivity of such an instrument is comparable with
that of an imager with the same number of horns. We anticipate a low level of
beam-related systematics thanks to the fact that the synthesized beam is
determined by the location of the primary horns. Other systematics should be
under good control thanks to an autocalibration technique, specific to our
concept, that will permit the accurate determination of most of the systematics
parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic
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