209 research outputs found
Electroless Nickel Deposition:An Alternative for Graphene Contacting
We report the first investigation into the potential of electroless nickel deposition to form ohmic contacts on single layer graphene. To minimize the contact resistance on graphene, a statistical model was used to improve metal purity, surface roughness, and coverage of the deposited film by controlling the nickel bath parameters (pH and temperature). The metalized graphene layers were patterned using photolithography and contacts deposited at temperatures as low as 60 °C. The contact resistance was 215 ± 23 ω over a contact area of 200 μm × 200 μm, which improved upon rapid annealing to 107 ± 9 ω. This method shows promise toward low-cost and large-scale graphene integration into functional devices such as flexible sensors and printed electronics
Surfactant protein D increases fusion of Mycobacterium tuberculosis- containing phagosomes with lysosomes in human macrophages
Lung surfactant protein D (SP-D) binds to Mycobacterium tuberculosis surface lipoarabinomannan and results in bacterial agglutination, reduced uptake, and inhibition of growth in human macrophages. Here we show that SP-D limits the intracellular growth of bacilli in macrophages by increasing phagosome-lysosome fusion but not by generating a respiratory burst
The GALAH survey: Properties of the Galactic disc(s) in the solar neighbourhood
Using data from the GALAH pilot survey, we determine properties of the Galactic thin and thick discs near the solar neighbourhood. The data cover a small range of Galactocentric radius (7.9 RGC 9.5 kpc), but extend up to 4 kpc in height from the Galactic plane, and several kpc in the direction of Galactic anti-rotation (at longitude 260◦ ≤ ≤ 280◦). This allows us to reliably measure the vertical density and abundance profiles of the chemically and
kinematically defined ‘thick’ and ‘thin’ discs of the Galaxy. The thin disc (low-α population) exhibits a steep negative vertical metallicity gradient, at d[M/H]/dz = −0.18 ± 0.01 dex kpc−1, which is broadly consistent with previous studies. In contrast, its vertical α-abundance profile is almost flat, with a gradient of d[α/M]/dz = 0.008 ± 0.002 dex kpc−1. The steep vertical metallicity gradient of the low-α population is in agreement with models where radial
migration has a major role in the evolution of the thin disc. The thick disc (high-α population) has a weaker vertical metallicity gradient d[M/H]/dz = −0.058 ± 0.003 dex kpc−1. The αabundance of the thick disc is nearly constant with height, d[α/M]/dz = 0.007 ± 0.002 dex kpc−1. The negative gradient in metallicity and the small gradient in [α/M] indicate that the high-α population experienced a settling phase, but also formed prior to the onset of major
Type Ia supernova enrichment. We explore the implications of the distinct α-enrichments and narrow [α/M] range of the sub-populations in the context of thick disc formation.LD and MA acknowledge funding from the Australian Government through ARC Laureate Fellowship FL110100012. LD, KCF, and RFGW acknowledge
support from ARC grant DP160103747. LC gratefully acknowledges support from the Australian Research Council (grants
DP150100250, FT160100402). DMN was supported by the Allan C. and Dorothy H. Davis Fellowship. DS is the recipient of
an Australian Research Council Future Fellowship (project number
FT1400147). TZ acknowledges financial support from the Slovenian Research Agency (research core funding No. P1-0188). Part of
this research was supported by the Munich Institute for Astro- and
Particle Physics (MIAPP) of the DFG cluster of excellence ‘Origin
and Structure of the Universe’
The GALAH survey: Milky Way disc metallicity and alpha-abundance trends in combined APOGEE-GALAH catalogues
GALAH and APOGEE are two high resolution multi object spectroscopic surveys
that provide fundamental stellar parameters and multiple elemental abundance
estimates for 400,000 stars in the Milky Way. They are complimentary in
both sky coverage and wavelength regime. Thus combining the two surveys will
provide us a large sample to investigate the disc metallicity and alpha
abundance trends. We use the Cannon data-driven approach selecting training
sets from among 20,000 stars in common for the two surveys to predict the
GALAH scaled stellar parameters from APOGEE spectra as well as APOGEE scaled
stellar parameters from GALAH spectra. We provide two combined catalogues with
GALAH scaled and APOGEE scaled stellar parameters each having 500,000
stars after quality cuts. With 470,000 stars that are common in both
these catalogues, we compare the GALAH scaled and APOGEE scaled metallicity
distribution functions (MDF), radial and vertical metallicity gradients as well
as the variation of [/Fe] vs [Fe/H] trends along and away from the
Galactic mid plane. We find mean metallicities of APOGEE scaled sample to be
higher compared to that for the GALAH scaled sample. We find similar
[/Fe] vs [Fe/H] trends using both samples consistent with previous
observational as well as simulation based studies. Radial and vertical
metallicity gradients derived using the two survey scaled samples are
consistent except in the inner and outer Galactocentric radius bins. Our
gradient estimates in the solar neighborhood are also consistent with previous
studies and are backed by larger sample size compared to previous works.Comment: 21 pages, 19 figures, submitted to MNRA
The GALAH Survey: Chemical Clocks
Previous studies have found that the elemental abundances of a star correlate
directly with its age and metallicity. Using this knowledge, we derive ages for
a sample of 250,000 stars taken from GALAH DR3 using only their overall
metallicity and chemical abundances. Stellar ages are estimated via the machine
learning algorithm , using main sequence turnoff stars with precise
ages as our input training set. We find that the stellar ages for the bulk of
the GALAH DR3 sample are accurate to 1-2 Gyr using this method. With these
ages, we replicate many recent results on the age-kinematic trends of the
nearby disk, including the age-velocity dispersion relationship of the solar
neighborhood and the larger global velocity dispersion relations of the disk
found using and GALAH. The fact that chemical abundances alone can be
used to determine a reliable age for a star have profound implications for the
future study of the Galaxy as well as upcoming spectroscopic surveys. These
results show that the chemical abundance variation at a given birth radius is
quite small, and imply that strong chemical tagging of stars directly to birth
clusters may prove difficult with our current elemental abundance precision.
Our results highlight the need of spectroscopic surveys to deliver precision
abundances for as many nucleosynthetic production sites as possible in order to
estimate reliable ages for stars directly from their chemical abundances.
Applying the methods outlined in this paper opens a new door into studies of
the kinematic structure and evolution of the disk, as ages may potentially be
estimated for a large fraction of stars in existing spectroscopic surveys. This
would yield a sample of millions of stars with reliable age determinations, and
allow precise constraints to be put on various kinematic processes in the disk,
such as the efficiency and timescales of radial migration.Comment: 13 pages, 15 figures, submitted to MNRA
The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and eDR3
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stab3504Since the advent of astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, -Sausage-Enceladus (GSE), appears to be an early "building block" given its virial mass at infall (). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low- abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] vs. [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including , we can characterise an unprecedented 24 abundances of this structure with GALAH+ DR3. Our chemical selection allows us to prevent circular reasoning and characterise the dynamical properties of the GSE, for example mean . We find only of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way.Peer reviewedFinal Accepted Versio
The GALAH survey: tracing the Galactic disk with Open Clusters
Open clusters are unique tracers of the history of our own Galaxy's disk.
According to our membership analysis based on \textit{Gaia} astrometry, out of
the 226 potential clusters falling in the footprint of GALAH or APOGEE, we find
that 205 have secure members that were observed by at least one of the survey.
Furthermore, members of 134 clusters have high-quality spectroscopic data that
we use to determine their chemical composition. We leverage this information to
study the chemical distribution throughout the Galactic disk of 21 elements,
from C to Eu. The radial metallicity gradient obtained from our analysis is
0.0760.009 dex kpc, which is in agreement with previous works
based on smaller samples. Furthermore, the gradient in the [Fe/H] - guiding
radius (r) plane is 0.0730.008 dex kpc. We show
consistently that open clusters trace the distribution of chemical elements
throughout the Galactic disk differently than field stars. In particular, at
given radius, open clusters show an age-metallicity relation that has less
scatter than field stars. As such scatter is often interpreted as an effect of
radial migration, we suggest that these differences are due to the physical
selection effect imposed by our Galaxy: clusters that would have migrated
significantly also had higher chances to get destroyed. Finally, our results
reveal trends in the [X/Fe]rage space, which are important
to understand production rates of different elements as a function of space and
time.Comment: 18 pages, 10 figures, accepted for publication MNRA
Treatment of breast cancer cells with DNA demethylating agents leads to a release of Pol II stalling at genes with DNA-hypermethylated regions upstream of TSS
Inactivation of tumor suppressor genes plays an important role in tumorigenesis, and epigenetic modifications such as DNA methylation are frequently associated with transcriptional repression. Here, we show that gene silencing at selected genes with signs of DNA hypermethylation in breast cancer cells involves Pol II stalling. We studied several repressed genes with DNA hypermethylation within a region 1-kb upstream of the transcriptional start site that were upregulated after treatment with DNA demethylating agents, such as Azacytidine and several natural products. All those selected genes had stalled Pol II at their transcriptional start site and showed enhanced ser2 phosphorylated Pol II and elevated transcripts after drug treatment indicating successful elongation. In addition, a decrease of the epigenetic regulator LSH in a breast cancer cell line by siRNA treatment reduced DNA methylation and overcame Pol II stalling, whereas overexpression of LSH in a normal breast epithelial cell line increased DNA methylation and resulted in repression. Decrease of LSH was associated with reduced DNMT3b binding to promoter sequences, and depletion of DNMT3b by siRNA could release Pol II suggesting that DNMT3b is functionally involved. The release of paused Pol II was accompanied by a dynamic switch from repressive to active chromatin marks. Thus release of Pol II stalling can act as a mechanism for gene reactivation at specific target genes after DNA demethylating treatment in cancer cells
- …