266 research outputs found
Novae Ejecta as Colliding Shells
Following on our initial absorption-line analysis of fifteen novae spectra we
present additional evidence for the existence of two distinct components of
novae ejecta having different origins. As argued in Paper I one component is
the rapidly expanding gas ejected from the outer layers of the white dwarf by
the outburst. The second component is pre-existing outer, more slowly expanding
circumbinary gas that represents ejecta from the secondary star or accretion
disk. We present measurements of the emission-line widths that show them to be
significantly narrower than the broad P Cygni profiles that immediately precede
them. The emission profiles of novae in the nebular phase are distinctly
rectangular, i.e., strongly suggestive of emission from a relatively thin,
roughly spherical shell. We thus interpret novae spectral evolution in terms of
the collision between the two components of ejecta, which converts the early
absorption spectrum to an emission-line spectrum within weeks of the outburst.
The narrow emission widths require the outer circumbinary gas to be much more
massive than the white dwarf ejecta, thereby slowing the latter's expansion
upon collision. The presence of a large reservoir of circumbinary gas at the
time of outburst is suggestive that novae outbursts may sometime be triggered
by collapse of gas onto the white dwarf, as occurs for dwarf novae, rather than
steady mass transfer through the inner Lagrangian point.Comment: 12 pages, 3 figures; Revised manuscript; Accepted for publication in
Astrophysics & Space Scienc
Synthesis and characterization of novel oxazines and demonstration that they specifically target cyclooxygenase 2
In the present study, we used solution combustion synthesis-bismuth oxide (Bi2O3) as catalyst for the simple and efficient synthesis of 1,2-oxazine based derivatives of 6-fluoro-3-(piperidin-4-yl)benzo[d]isoxazoles, 1-arylpiperazine and carbazoles. (4aR,8aR)-4-(4-Methoxyphenyl)-3-((4-(4-methoxyphenyl)piperazin-1-yl)methyl)-4a,5,6,7,8,8a-hexahydro-4H-benzo[e][1,2]oxazine was found to be the most potent compound with a high degree of selectivity in inhibition towards COX2 (1.7 μM) over COX1 (40.4 μM) demonstrating the significance of 1,2-oxazine derivatives in developing COX2 specific inhibitors. Molecular docking analyses demonstrated that an isoleucine residue in the active site of COX1 is responsible for lower affinity to COX1 and increased potency towards COX2. Overall, our study reveals that the new 1,2-oxazine-based small molecules qualify as lead structures in developing COX2-specific inhibitors for anti-inflammatory therapy
Like-minded sources on Facebook are prevalent but not polarizing
Many critics raise concerns about the prevalence of ‘echo chambers’ on social media and their potential role in increasing political polarization. However, the lack of available data and the challenges of conducting large-scale field experiments have made it difficult to assess the scope of the problem 1,2. Here we present data from 2020 for the entire population of active adult Facebook users in the USA showing that content from ‘like-minded’ sources constitutes the majority of what people see on the platform, although political information and news represent only a small fraction of these exposures. To evaluate a potential response to concerns about the effects of echo chambers, we conducted a multi-wave field experiment on Facebook among 23,377 users for whom we reduced exposure to content from like-minded sources during the 2020 US presidential election by about one-third. We found that the intervention increased their exposure to content from cross-cutting sources and decreased exposure to uncivil language, but had no measurable effects on eight preregistered attitudinal measures such as affective polarization, ideological extremity, candidate evaluations and belief in false claims. These precisely estimated results suggest that although exposure to content from like-minded sources on social media is common, reducing its prevalence during the 2020 US presidential election did not correspondingly reduce polarization in beliefs or attitudes
Delimitation of Neonectria and Cylindrocarpon (Nectriaceae, Hypocreales, Ascomycota) and related genera with Cylindrocarpon-like anamorphs
Neonectria is a cosmopolitan genus and it is, in part, defined by
its link to the anamorph genus Cylindrocarpon. Neonectria
has been divided into informal groups on the basis of combined morphology of
anamorph and teleomorph. Previously, Cylindrocarpon was divided into
four groups defined by presence or absence of microconidia and chlamydospores.
Molecular phylogenetic analyses have indicated that Neonectria
sensu stricto and Cylindrocarpon sensu stricto are
phylogenetically congeneric. In addition, morphological and molecular data
accumulated over several years have indicated that Neonectria sensu
lato and Cylindrocarpon sensu lato do not form a
monophyletic group and that the respective informal groups may represent
distinct genera. In the present work, a multilocus analysis (act,
ITS, LSU, rpb1, tef1, tub) was applied to representatives of
the informal groups to determine their level of phylogenetic support as a
first step towards taxonomic revision of Neonectria sensu
lato. Results show five distinct highly supported clades that correspond
to some extent with the informal Neonectria and
Cylindrocarpon groups that are here recognised as genera: (1) N.
coccinea-group and Cylindrocarpon groups 1 & 4
(Neonectria/Cylindrocarpon sensu stricto); (2) N.
rugulosa-group (Rugonectria gen. nov.); (3) N.
mammoidea/N. veuillotiana-groups and Cylindrocarpon group 2
(Thelonectria gen. nov.); (4) N. radicicola-group and
Cylindrocarpon group 3 (Ilyonectria gen. nov.); and (5)
anamorph genus Campylocarpon. Characteristics of the anamorphs and
teleomorphs correlate with the five genera, three of which are newly
described. New combinations are made for species where their classification is
confirmed by phylogenetic data
Multiple β− decaying states in 194 Re: Shape evolution in neutron-rich osmium isotopes
β decays from heavy, neutron-rich nuclei with A∼190 have been investigated following their production via the relativistic projectile fragmentation of an E/A=1 GeV 208Pb primary beam on a ∼2.5 g/cm2 9Be target. The reaction products were separated a
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
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