1,140 research outputs found
[All]-S,S-dioxide Oligo-Thienylenevinylenes: Synthesis and Structural/Electronic Shapes from Their Molecular Force Fields
Oligo-S,S-dioxothienylenevinylenes have been
prepared by transferring oxygen atoms to the sulfur
atoms using the HOF·CH3CN complex. Their photophysical
properties are presented in comparison with their thio phenevinylene congeners. Together with their vibrational
properties and molecular force fields, this study allows for
the interpretation of the alteration of aromaticity and
inter-ring exocyclic p-conjugation in this series
A new L-dwarf member of the moderately metal-poor triple system HD 221356
We report on the discovery of a fourth component in the HD 221356 star
system, previously known to be formed by an F8V, slightly metal-poor primary
([Fe/H]=-0.26), and a distant M8V+L3V pair. In our ongoing common proper motion
search based on VISTA Hemisphere Survey (VHS) and 2MASS catalogues, we have
detected a faint (J=13.76+/-0.04 mag) co-moving companion of the F8 star
located at angular separation of 12.13+/-0.18 arcsec (position angle of
221.8+/-1.7), corresponding to a projected distance of ~312 AU at 26 pc.
Near-infrared spectroscopy of the new companion, covering the 1.5-2.4 micron
wavelength range with a resolving power of R~600, indicates an L1+/-1 spectral
type. Using evolutionary models the mass of the new companion is estimated at
~0.08 solar masses, which places the object close to the stellar-substellar
borderline. This multiple system provides an interesting example of objects
with masses slightly above and below the hydrogen burning mass limit. The low
mass companions of HD 221356 have slightly bluer colours than field dwarfs with
similar spectral type, which is likely a consequence of the sub-solar
metallicity of the system.Comment: 7 pages, 4 figures, accepted for publication in MNRA
Cosmic-ray searches with the MATHUSLA detector
The performance of the proposed MATHUSLA detector as an instrument for
studying the physics of cosmic rays by measuring extensive air showers is
presented. The MATHUSLA detector is designed to observe and study the decay of
long-lived particles produced at the pp interaction point of the CMS detector
at CERN during the HL-LHC data-taking period. The proposed MATHUSLA detector
will be composed of many layers of long scintillating bars that cannot measure
more than one hit per bar and correctly report the hit coordinate in case of
multiple hits. This study shows that adding a layer of RPC detectors with both
analogue and digital readout significantly enhances the capabilities of
MATHUSLA to measure the local densities and arrival times of charged particles
at the front of air showers. We discuss open issues in cosmic-ray physics that
the proposed MATHUSLA detector with an additional layer of RPC detectors could
address and conclude by comparing with other air-shower facilities that measure
cosmic rays in the PeV energy range.Comment: 64 pages, 58 figure
Pyropyga julietafierroae sp. nov. (Coleoptera: Lampyridae): Un ejemplo de participación ciudadana en la ciencia
Se presenta la descripción de Pyropyga julietafierroae sp. nov., incluyendo los genitales de la hembra, de modo que es la primera vez que se describen estas estructuras para una hembra del género Pyropyga Motschulsky, 1852. La especie nueva fue descubierta en un ambiente urbanizado de Ciudad Universitaria en la Ciudad de México, lo que aumenta a 13 especies el género Pyropyga, de las cuales ocho se registran en México. Se muestra un mapa de distribución de las especies mexicanas. Además, se comenta sobre la participación de la ciudadanía para la propuesta y elección del nombre científico con la temática “Mujeres Mexicanas Ilustres”, este ejercicio se realiza por primera vez para nombrar una especie de luciérnaga en nuestro país.We present the description of Pyropyga julietafierroae sp. nov., including the female genitalia, so that it is the first time that these structures are described for a female of the genus Pyropyga Motschulsky, 1852. The new species was recovered from the urbanized environment of Ciudad Universitaria, Mexico City. The total number of species for the genus increases to 13, of which, eight are recorded from Mexico. A distribution map of Mexican species is included. Moreover, herein we comment on the citizen involvement for the proposal and choice of the scientific name with the theme “Illustrious Mexican Women”, this is the first time that a dynamic like this is carried out for naming a firefly species in our country
VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l.
in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design,
construction techniques and data acquisition system of the HAWC observatory.
HAWC is an air-shower array currently under construction at the same site of
VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water
Cherenkov detectors and two different data acquisition systems. It was in
operation between October 2011 and May 2012 with an average live time of 30%.
Besides the scientific verification purposes, the eight months of data were
used to obtain the results presented in this paper: the detector response to
the Forbush decrease of March 2012, and the analysis of possible emission, at
energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages,
10 figures). Corresponding authors: A.Marinelli and D.Zaboro
New isolated planetary mass objects and the stellar and substellar mass function of the sigma Orionis cluster
We report on our analysis of the VISTA Orion ZYJHKs photometric data
(completeness magnitudes Z=22.6 and J=21.0mag) focusing on a circular area of
2798.4 arcmin^2 around the young sigma Orionis star cluster (~3Myr, ~352pc,
solar metallicity). The combination of the VISTA photometry with optical, WISE
and Spitzer data allows us to identify a total of 210 cluster member candidates
with masses in the interval 0.25-0.004Msun, 23 of which are new planetary-mass
object findings. These discoveries double the number of cluster planetary-mass
candidates known so far. One object has colors compatible with a T spectral
type. The cluster harbors about as many brown dwarfs (69, 0.072-0.012Msun) and
planetary-mass objects (37, 0.012-0.004Msun) as very low-mass stars (104,
0.25-0.072Msun). Based on Spitzer data, we derive a disk frequency of ~40% for
very low-mass stars, brown dwarfs, and planetary mass objects in sigma Orionis.
The radial density distributions of these three mass intervals are alike: all
are spatially concentrated within an effective radius of 12arcmin (1.2pc)
around the multiple star sigma Ori, and no obvious segregation between
disk-bearing and diskless objects is observed. Using the VISTA data and the
Mayrit catalog, we derive the cluster mass spectrum (DeltaN/DeltaM ~
M^{-alpha}) from ~19 to 0.006Msun (VISTA ZJ completeness), which is reasonably
described by two power-law expressions with indices of alpha=1.7+/-0.2 for
M>0.35Msun, and alpha=0.6+/-0.2 for M<0.35Msun. The sigma Orionis mass spectrum
smoothly extends into the planetary-mass regime down to 0.004Msun. Our findings
of T-type sources (<0.004Msun) in the VISTA sigma Orionis exploration appear to
be smaller than what is predicted by the extrapolation of the cluster mass
spectrum down to the survey J-band completeness.Comment: Accepted for publication in ApJ. 69 pages, 15 figure
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at , 2.76 and 7 TeV
Measurements of the sphericity of primary charged particles in minimum bias
proton--proton collisions at , 2.76 and 7 TeV with the ALICE
detector at the LHC are presented. The observable is linearized to be collinear
safe and is measured in the plane perpendicular to the beam direction using
primary charged tracks with GeV/c in . The
mean sphericity as a function of the charged particle multiplicity at
mid-rapidity () is reported for events with different
scales ("soft" and "hard") defined by the transverse momentum of the leading
particle. In addition, the mean charged particle transverse momentum versus
multiplicity is presented for the different event classes, and the sphericity
distributions in bins of multiplicity are presented. The data are compared with
calculations of standard Monte Carlo event generators. The transverse
sphericity is found to grow with multiplicity at all collision energies, with a
steeper rise at low , whereas the event generators show the
opposite tendency. The combined study of the sphericity and the mean with multiplicity indicates that most of the tested event generators
produce events with higher multiplicity by generating more back-to-back jets
resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with
tune PERUGIA-2011 exhibits a noticeable improvement in describing the data,
compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16,
published version, figures from
http://aliceinfo.cern.ch/ArtSubmission/node/308
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
Measurement of charm production at central rapidity in proton-proton collisions at TeV
The -differential production cross sections of the prompt (B
feed-down subtracted) charmed mesons D, D, and D in the rapidity
range , and for transverse momentum GeV/, were
measured in proton-proton collisions at TeV with the ALICE
detector at the Large Hadron Collider. The analysis exploited the hadronic
decays DK, DK, DD, and their charge conjugates, and was performed on a
nb event sample collected in 2011 with a
minimum-bias trigger. The total charm production cross section at TeV and at 7 TeV was evaluated by extrapolating to the full phase space
the -differential production cross sections at TeV
and our previous measurements at TeV. The results were compared
to existing measurements and to perturbative-QCD calculations. The fraction of
cdbar D mesons produced in a vector state was also determined.Comment: 20 pages, 5 captioned figures, 4 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/307
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