20,317 research outputs found
High-velocity gas towards the LMC resides in the Milky Way halo
To explore the origin of high-velocity gas in the direction of the Large
Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum
of a Galactic halo star that is located in front of the LMC at d=9.2 kpc
distance. We study the velocity-component structure of low and intermediate
metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic
Origins Spectrograph (COS) onboard HST, and measure equivalent widths and
column densities for these ions. We supplement our COS data with a
Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59
and with HI 21cm data from the Leiden-Argentina-Bonn (LAB) survey. Metal
absorption towards RXJ0439.8-6809 is unambiguously detected in three different
velocity components near v_LSR=0,+60, and +150 km/s. The presence of absorption
proves that all three gas components are situated in front of the star, thus
being located in the disk and inner halo of the Milky Way. For the
high-velocity cloud (HVC) at v_LSR=+150 km/s we derive an oxygen abundance of
[O/H]=-0.63 (~0.2 solar) from the neighbouring Sk-69 59 sightline, in
accordance with previous abundance measurements for this HVC. From the observed
kinematics we infer that the HVC hardly participates in the Galactic rotation.
Our study shows that the HVC towards the LMC represents a Milky Way halo cloud
that traces low-column density gas with relatively low metallicity. It rules
out scenarios in which the HVC represents material close to the LMC that stems
from a LMC outflow.Comment: 4 pages, 3 figures; submitted to A&A Letter
Explorer Satellite Electronics
A discussion is presented of the design restrictions and the philosophy which enabled the Explorer satellites to be first during the IGY to reveal the presence of a belt of intense cosmic radiation encircling the earth's equator. In addition, an indication of the amount and momentum of cosmic dust in the solar system was obtained from the Explorers. Methods used to obtain reliability in the transducing and communications system are described, together with interpretations of space-environment information as deduced from the narrow-band telemetry
Implementation of liquid culture for tuberculosis diagnosis in a remote setting: lessons learned.
Although sputum smear microscopy is the primary method for tuberculosis (TB) diagnosis in low-resource settings, it has low sensitivity. The World Health Organization recommends the use of liquid culture techniques for TB diagnosis and drug susceptibility testing in low- and middle-income countries. An evaluation of samples from southern Sudan found that culture was able to detect cases of active pulmonary TB and extra-pulmonary TB missed by conventional smear microscopy. However, the long delays involved in obtaining culture results meant that they were usually not clinically useful, and high rates of non-tuberculous mycobacteria isolation made interpretation of results difficult. Improvements in diagnostic capacity and rapid speciation facilities, either on-site or through a local reference laboratory, are crucial
Machine learning classification: case of Higgs boson CP state in H to tau tau decay at LHC
Machine Learning (ML) techniques are rapidly finding a place among the
methods of High Energy Physics data analysis. Different approaches are explored
concerning how much effort should be put into building high-level variables
based on physics insight into the problem, and when it is enough to rely on
low-level ones, allowing ML methods to find patterns without explicit physics
model.
In this paper we continue the discussion of previous publications on the CP
state of the Higgs boson measurement of the H to tau tau decay channel with the
consecutive tau^pm to rho^pm nu; rho^pm to pi^pm pi^0 and tau^pm to a_1^pm nu;
a_1^pm to rho^0 pi^pm to 3 pi^pm cascade decays. The discrimination of the
Higgs boson CP state is studied as a binary classification problem between
CP-even (scalar) and CP-odd (pseudoscalar), using Deep Neural Network (DNN).
Improvements on the classification from the constraints on directly
non-measurable outgoing neutrinos are discussed. We find, that once added, they
enhance the sensitivity sizably, even if only imperfect information is
provided. In addition to DNN we also evaluate and compare other ML methods:
Boosted Trees (BT), Random Forest (RF) and Support Vector Machine (SVN).Comment: 1+20 pages, 9 figures, 6 tables, extended content and improved
readabilit
Linear independence of localized magnon states
At the magnetic saturation field, certain frustrated lattices have a class of
states known as "localized multi-magnon states" as exact ground states. The
number of these states scales exponentially with the number of spins and
hence they have a finite entropy also in the thermodynamic limit
provided they are sufficiently linearly independent. In this article we present
rigorous results concerning the linear dependence or independence of localized
magnon states and investigate special examples. For large classes of spin
lattices including what we called the orthogonal type and the isolated type as
well as the kagom\'{e}, the checkerboard and the star lattice we have proven
linear independence of all localized multi-magnon states. On the other hand the
pyrochlore lattice provides an example of a spin lattice having localized
multi-magnon states with considerable linear dependence.Comment: 23 pages, 6 figure
ORFEUS II echelle spectra: Absorption by H_2 in the LMC
We present the first detection of molecular hydrogen (H_2) UV absorption
profiles on the line of sight to the LMC. The star LH 10:3120 in the LMC was
measured with the ORFEUS telescope and the Tuebingen echelle spectrograph
during the space shuttle mission of Nov./Dec. 1996. 16 absorption lines from
the Lyman band are used to derive the column densities of H_2 for the lowest 5
rotational states in the LMC gas. For these states we find a total column
density of N(H_2)=6.6 x 10^18$ cm^-2 on this individual line of sight. We
obtain equivalent excitation temperatures of T < 50 K for the rotational ground
state and T = 470 K for 0 < J < 6 by fitting the population densities of the
rotational states to theoretical Boltzmann distributions. We conclude that UV
pumping dominates the population of the higher rotational levels, as known from
the H_2 gas in the Milky Way. (Research supported in part by the DARA)Comment: Astronomy & Astrophysics, Letter, in pres
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