320 research outputs found
Magneto-infrared modes in InAs-AlSb-GaSb coupled quantum wells
We have studied a series of InAs/GaSb coupled quantum wells using
magneto-infrared spectroscopy for high magnetic fields up to 33T within
temperatures ranging from 4K to 45K in both Faraday and tilted field
geometries. This type of coupled quantum wells consists of an electron layer in
the InAs quantum well and a hole layer in the GaSb quantum well, forming the
so-called two dimensional electron-hole bilayer system. Unlike the samples
studied in the past, the hybridization of the electron and hole subbands in our
samples is largely reduced by having narrower wells and an AlSb barrier layer
interposed between the InAs and the GaSb quantum wells, rendering them weakly
hybridized. Previous studies have revealed multiple absorption modes near the
electron cyclotron resonance of the InAs layer in moderately and strongly
hybridized samples, while only a single absorption mode was observed in the
weakly hybridized samples. We have observed a pair of absorption modes
occurring only at magnetic fields higher than 14T, which exhibited several
interesting phenomena. Among which we found two unique types of behavior that
distinguishes this work from the ones reported in the literature. This pair of
modes is very robust against rising thermal excitations and increasing magnetic
fields alligned parallel to the heterostructures. While the previous results
were aptly explained by the antilevel crossing gap due to the hybridization of
the electron and hole wavefunctions, i.e. conduction-valence Landau level
mixing, the unique features reported in this paper cannot be explained within
the same concept. The unusual properties found in this study and their
connection to the known models for InAs/GaSb heterostructures will be
disccused; in addition, several alternative ideas will be proposed in this
paper and it appears that a spontaneous phase separation can account for most
of the observed features
One more neighbor: The first brown dwarf in the VVV survey
Context. The discovery of brown dwarfs (BDs) in the solar neighborhood and
young star clusters has helped to constraint the low-mass end of the stellar
mass function and the initial mass function. We use data of the Vista Variables
in the V\'ia L\'actea (VVV), a near-infrared (NIR) multiwavelength (Z Y J H Ks)
multi-epoch (Ks) ESO Public Survey mapping the Milky Way bulge and southern
Galactic plane to search for nearby BDs.
Aims. The ultimate aim of the project is to improve the completeness of the
census of nearby stellar and substellar objects towards the Galactic bulge and
inner disk regions.
Methods. Taking advantage of the homogeneous sample of VVV multi-epoch data,
we identified stars with high proper motion (> 0.1"/yr), and then selected
low-mass objects using NIR colors. We searched for a possible parallax
signature using the all available Ks band epochs. We set some constraints on
the month-to-year scale Ks band variability of our candidates, and even
searched for possible transiting companions. We obtained NIR spectra to
properly classify spectral type and then the physical properties of the final
list of candidates.
Results. We report the discovery of VVV BD001, a new member of the local
volume-limited sample (within 20pc from the sun) with well defined proper
motion, distance, and luminosity. The spectral type of this new object is an
L5+-1, unusually blue dwarf. The proper motion for this BD is
PM(\alpha)=-0.5455+-0.004 "/yr, PM(\delta)=-0.3255+-0.004 "/yr, and it has a
parallax of 57+-4 mas which translates into a distance of 17.5 +- 1.1 pc. VVV
BD001 shows no evidence of variability (\Delta Ks <0.05mag) over two years,
especially constrained on a six month scale during the year 2012.Comment: 5 pages, 4 figures, 1 table, Accepted for publication in Astronomy
and Astrophysics Letter
The Three-Point Correlation Function of Luminous Red Galaxies in the Sloan Digital Sky Survey
We present measurements of the redshift-space three-point correlation
function of 50,967 Luminous Red Galaxies (LRGs) from Data Release 3 (DR3) of
the Sloan Digital Sky Survey (SDSS). We have studied the shape dependence of
the reduced three-point correlation function (Qz(s,q,theta)) on three different
scales, s=4, 7 and 10 h-1 Mpc, and over the range of 1 < q < 3 and 0 < theta <
180. On small scales (s=4 h-1 Mpc), Qz is nearly constant, with little change
as a function of q and theta. However, there is evidence for a shallow U-shaped
behaviour (with theta) which is expected from theoretical modeling of Qz . On
larger scales (s=7 and 10 h-1 Mpc), the U-shaped anisotropy in Qz (with theta)
is more clearly detected. We compare this shape-dependence in Qz(s,q,theta)
with that seen in mock galaxy catalogues which were generated by populating the
dark matter halos in large N-body simulations with mock galaxies using various
Halo Occupation Distributions (HOD). We find that the combination of the
observed number density of LRGs, the (redshift-space) two-point correlation
function and Qz provides a strong constraint on the allowed HOD parameters
(M_min, M_1, alpha) and breaks key degeneracies between these parameters. For
example, our observed Qz disfavors mock catalogues that overpopulate massive
dark matter halos with many LRG satellites. We also estimate the linear bias of
LRGs to be b=1.87+/-0.07 in excellent agreement with other measurements.Comment: 14 pages. Accepted for publication to the MNRAS. Data accompanying
paper can be found at http://www.dsg.port.ac.uk/~nicholb/3pt/kulkarni
Campus source to sink wastewater surveillance of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)
Wastewater-based surveillance (WBS) offers an aggregate, and cost-effective approach for tracking infectious disease outbreak prevalence within communities, that provides data on community health complementary to individual clinical testing. This study reports on a 16-month WBS initiative on a university campus in England, UK, assessing the presence of SARS-CoV-2 in sewers from large buildings, downstream sewer locations, raw wastewater, partially treated and treated effluents. Key findings include the detection of the Alpha (B.1.1.7) variant in wastewater, with 70 % of confirmed campus cases correlating with positive wastewater samples. Notably, ammonium nitrogen (NH4-N) levels showed a positive correlation (Ï = 0.543, p < 0.01) with virus levels at the large building scale, a relationship not observed at the sewer or wastewater treatment works (WWTW) levels due to dilution. The WWTW was compliant to wastewater standards, but the secondary treatment processes were not efficient for virus removal as SARS-CoV-2 was consistently detected in treated discharges. Tools developed through WBS can also be used to enhance traditional environmental monitoring of aquatic systems. This study provides a detailed source-to-sink evaluation, emphasizing the critical need for the widespread application and improvement of WBS. It showcases WBS utility and reinforces the ongoing challenges posed by viruses to receiving water quality
VVV High proper motion stars I. The catalogue of bright Ks stars
The final, definitive version of this paper has been published in Monthly Notices of the Royal Astronomical Society, Vol. 464(1): 1247-1258, January 2017, DOI: 10.1093/mnras/stw2357, first published on line September 16, 2016, published by Oxford University Press on behalf of MNRAS.Knowledge of the stellar content near the Sun is important for a broad range of topics ranging from the search for planets to the study of Milky Way structure. The most powerful method for identifying potentially nearby stars is proper motion (PM) surveys. All old optical surveys avoid, or are at least substantially incomplete, near the Galactic plane. The depth and breadth of the "Vista Variables in Via Lactea" (VVV) near-IR survey significantly improves this situation. Taking advantage of the VVV survey database, we have measured PMs in the densest regions of the MW bulge and southern plane in order to complete the census of nearby objects. We have developed a custom PM pipeline based on VVV catalogues from the Cambridge Astronomy Survey Unit (CASU), by comparing the first epoch of JHKs with the multi-epoch Ks-bands acquired later. Taking advantage of the large time baseline between the 2MASS and the VVV observations, we also obtained 2MASS-VVV PMs. We present a near-IR proper motion catalogue for the whole area of the VVV survey, which includes 3003 moving stellar sources. All of these have been visually inspected and are real PM objects. Our catalogue is in very good agreement with the proper motion data supplied in IR catalogues outside the densest zone of the MW. The majority of the PM objects in our catalogue are nearby M-dwarfs, as expected. This new database allow us to identify 57 common proper motion binary candidates, among which are two new systems within ~30pc of the Sun.Peer reviewe
Oscillatory Shear Flow-Induced Alignment of Lamellar Melts of Hydrogen-Bonded Comb Copolymer Supramolecules
In this work we present the orientational behavior of comb copolymer-like supramolecules P4VP(PDP)1.0, obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol, during large-amplitude oscillatory shear flow experiments over a broad range of frequencies (0.001-10 Hz). The alignment diagram, presenting the macroscopic alignment in T/TODT vs Ï/Ïc, contains three regions of parallel alignment separated by a region of perpendicular alignment. For our material, the order-disorder temperature TODT = 67 °C and Ïc, the frequency above which the distortion of the chain conformation dominates the materialsâ viscoelasticity, is around 0.1 Hz at 61 °C. For the first time flipping from a pure transverse alignment via biaxial transverse/perpendicular alignment to a perpendicular alignment as a function of the strain amplitude was found.
Simulating the Formation of the Local Galaxy Population
We simulate the formation and evolution of the local galaxy population
starting from initial conditions with a smoothed linear density field which
matches that derived from the IRAS 1.2 Jy galaxy survey. Our simulations track
the formation and evolution of all dark matter haloes more massive than 10e+11
solar masses out to a distance of 8000 km/s from the Milky Way. We implement
prescriptions similar to those of Kauffmann et al. (1999) to follow the
assembly and evolution of the galaxies within these haloes. We focus on two
variants of the CDM cosmology: an LCDM and a tCDM model. Galaxy formation in
each is adjusted to reproduce the I-band Tully-Fisher relation of Giovanelli et
al. (1997). We compare the present-day luminosity functions, colours,
morphology and spatial distribution of our simulated galaxies with those of the
real local population, in particular with the Updated Zwicky Catalog, with the
IRAS PSCz redshift survey, and with individual local clusters such as Coma,
Virgo and Perseus. We also use the simulations to study the clustering bias
between the dark matter and galaxies of differing type. Although some
significant discrepancies remain, our simulations recover the observed
intrinsic properties and the observed spatial distribution of local galaxies
reasonably well. They can thus be used to calibrate methods which use the
observed local galaxy population to estimate the cosmic density parameter or to
draw conclusions about the mechanisms of galaxy formation. To facilitate such
work, we publically release our z=0 galaxy catalogues, together with the
underlying mass distribution.Comment: 25 pages, 20 figures, submitted to MNRAS. High resolution copies of
figures 1 and 3, halo and galaxy catalogues can be found at
http://www.mpa-garching.mpg.de/NumCos/CR/index.htm
Spectroscopic signatures of youth in low-mass kinematic candidates of young moving groups
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 by the Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present a study of age-related spectral signatures observed in 25 young low-mass objects that we have previously determined as possible kinematic members of five young moving groups: the Local Association (Pleiades moving group, age = 20â150âMyr), the Ursa Major group (Sirius supercluster, age = 300âMyr), the Hyades supercluster (age = 600âMyr), IC 2391 supercluster (age = 35â55âMyr) and the Castor moving group (age = 200âMyr). In this paper we characterize the spectral properties of observed high- or low-resolution spectra of our kinematic members by fitting theoretical spectral distributions. We study signatures of youth, such as lithium I 6708Ă
, Hα emission and other age-sensitive spectroscopic signatures in order to confirm the kinematic memberships through age constraints. We find that 21 (84 per cent) targets show spectroscopic signatures of youth in agreement with the age ranges of the moving group to which membership is implied. For two further objects, age-related constraints remain difficult to determine from our analysis. In addition, we confirm two moving group kinematic candidates as brown dwarfs.Peer reviewe
Spatial clustering in the ESO-Sculptor Survey: two-point correlation functions by galaxy type at redshifts 0.1 - 0.5
We calculate the spatial two-point auto and cross-correlation functions for
the 765 galaxies with Rc<21.5 and 0.1<z<0.51 in the ESO-Sculptor survey, and
explore the segregation effects among the populations of giant (early-type,
late spiral) and dwarf (dE, dI) galaxies. At separation of 0.3 h^-1 Mpc, pairs
of early-type galaxies dominate the clustering over all the other types of
pairs. At intermediate scales, 0.3-5 h^-1 Mpc, mixed pairs of dwarf and giant
galaxies contribute equally as pairs of giant galaxies, whereas the latter
dominate at ~10 h^-1 Mpc. We detect the signature of the transition between the
1-halo and 2-halo regimes which is expected in the scenario of galaxy formation
by hierarchical merging of dark matter halos. The early-type galaxies largely
outdo the late spiral galaxies in their 1-halo component, whereas the 2-halo
components of both giant populations are comparable. The dwarf galaxies have an
intermediate 1-halo component between the 2 giant galaxy types, and their
2-halo component is weak and consistent with null clustering. The present
analysis indicates that the early-type galaxies are preferentially located near
the centers of the most massive halos, whereas late spiral galaxies tend to
occupy their outskirts or the centers of less massive halos. This analysis also
unveils new results on the spatial distribution of dwarf galaxies: at the scale
at which they significantly cluster inside the halos (<0.3 h^-1 Mpc), they are
poorly mixed with the late spiral galaxies, and appear preferentially as
satellites of early-type galaxies.Comment: Astronomy & Astrophysics, in press. 29 pages, 15 color figures, 3
table
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
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