3,718 research outputs found
A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau
In searches for low-mass companions to late-type stars, correlation between
radial velocity variations and line bisector slope changes indicates
contamination by large starspots. Two young stars demonstrate that this test is
not sufficient to rule out starspots as a cause of radial velocity variations.
As part of our survey for substellar companions to T Tauri stars, we identified
the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases,
visible light radial velocity modulation appears periodic and is uncorrelated
with line bisector span variations, suggesting close companions of several
M_Jup in these systems. However, high-resolution, infrared spectroscopy shows
that starspots cause the radial velocity variations. We also report unambiguous
results for V827 Tau, identified as a spotted star on the basis of both visible
light and infrared spectroscopy. Our results suggest that infrared follow up
observations are critical for determining the source of radial velocity
modulation in young, spotted stars.Comment: Accepted for publication in the Astrophysical Journal Letter
Entanglement and alpha entropies for a massive scalar field in two dimensions
We find the analytic expression of the trace of powers of the reduced density
matrix on an interval of length L, for a massive boson field in 1+1 dimensions.
This is given exactly (except for a non universal factor) in terms of a finite
sum of solutions of non linear differential equations of the Painlev\'e V type.
Our method is a generalization of one introduced by Myers and is based on the
explicit calculation of quantities related to the Green function on a plane,
where boundary conditions are imposed on a finite cut. It is shown that the
associated partition function is related to correlators of exponential
operators in the Sine-Gordon model in agreement with a result by Delfino et al.
We also compute the short and long distance leading terms of the entanglement
entropy. We find that the bosonic entropic c-function interpolates between the
Dirac and Majorana fermion ones given in a previous paper. Finally, we study
some universal terms for the entanglement entropy in arbitrary dimensions
which, in the case of free fields, can be expressed in terms of the two
dimensional entropy functions.Comment: 13 pages, 2 figure
Generalized Jordan-Wigner Transformations
We introduce a new spin-fermion mapping, for arbitrary spin generating
the SU(2) group algebra, that constitutes a natural generalization of the
Jordan-Wigner transformation for . The mapping, valid for regular
lattices in any spatial dimension , serves to unravel hidden symmetries in
one representation that are manifest in the other. We illustrate the power of
the transformation by finding exact solutions to lattice models previously
unsolved by standard techniques. We also present a proof of the existence of
the Haldane gap in 1 bilinear nearest-neighbors Heisenberg spin chains and
discuss the relevance of the mapping to models of strongly correlated
electrons. Moreover, we present a general spin-anyon mapping for the case .Comment: 5 pages, 1 psfigur
Mirror matter admixtures and isospin breaking in the \Delta I=1/2 rule in \Omega^- two body non-leptonic decays
We discuss a description of \Omega^- two body non-leptonic decays based on
possible, albeit tiny, admixtures of mirror matter in ordinary hadrons. The
\Delta I=1/2 rule enhancement is obtained as a result of isospin symmetry and,
more importantly, the rather large observed deviations from this rule result
from small isospin breaking. This analysis lends support to the possibility
that the enhancement phenomenon observed in low energy weak interactions may be
systematically described by mirror matter admixtures in ordinary hadrons.Comment: Changed conten
Contact tracing and epidemics control in social networks
A generalization of the standard susceptible-infectious-removed (SIR)
stochastic model for epidemics in sparse random networks is introduced which
incorporates contact tracing in addition to random screening. We propose a
deterministic mean-field description which yields quantitative agreement with
stochastic simulations on random graphs. We also analyze the role of contact
tracing in epidemics control in small-world networks and show that its
effectiveness grows as the rewiring probability is reduced.Comment: 4 pages, 4 figures, submitted to PR
Carbon nanofiber-supported tantalum oxides as durable catalyst for the oxygen evolution reaction in alkaline media
Active and durable electrocatalysts for the oxygen evolution reaction (OER), capable of replacing noble metal catalysts, are required to develop efficient and competitive devices within the frame of the water electrolysis technology for hydrogen production. In this work, we have investigated tantalum based catalysts supported on carbon nanofibers (CNF) for the first time. The effect of CNF characteristics and the catalyst annealing temperature on the electrochemical response for the OER have been analyzed in alkaline environment using a rotating ring disc electrode (RRDE). The best OER activity and oxygen efficiency were found with a highly graphitic CNF, despite its lower surface area, synthesized at 700 °C, and upon a catalyst annealing temperature of 800 °C. The ordering degree of carbon nanofibers favors the production of oxygen in combination with a low oxygen content in tantalum oxides. The most active catalyst exhibited also an excellent durability.The authors want to thank the Ministerio de Economía, Industria y Competitividad (MICINN) and FEDER for the received funding in the project of reference ENE2017-83976-C2-1-R, and to the Gobierno de Aragón (DGA) for the funding to Grupo de Investigación Conversión de Combustibles ( T06_17R ). J.C. Ruiz-Cornejo acknowledges DGA for his PhD grant. D. Sebastián acknowledges the MICINN for the Ramón y Cajal research contract (RyC-2016-20944
Pneumonic versus Nonpneumonic Exacerbations of Chronic Obstructive Pulmonary Disease.
Patients with chronic obstructive pulmonary disease (COPD) often suffer acute exacerbations (AECOPD) and community-acquired pneumonia (CAP), named nonpneumonic and pneumonic exacerbations of COPD, respectively. Abnormal host defense mechanisms may play a role in the specificity of the systemic inflammatory response. Given the association of this aspect to some biomarkers at admission (e.g., C-reactive protein), it can be used to help to discriminate AECOPD and CAP, especially in cases with doubtful infiltrates and advanced lung impairment. Fever, sputum purulence, chills, and pleuritic pain are typical clinical features of CAP in a patient with COPD, whereas isolated dyspnea at admission has been reported to predict AECOPD. Although CAP may have a worse outcome in terms of mortality (in hospital and short term), length of hospitalization, and early readmission rates, this has only been confirmed in a few prospective studies. There is a lack of methodologically sound research confirming the impact of severe AECOPD and COPD + CAP. Here, we review studies reporting head-to-head comparisons between AECOPD and CAP + COPD in hospitalized patients. We focus on the epidemiology, risk factors, systemic inflammatory response, clinical and microbiological characteristics, outcomes, and treatment approaches. Finally, we briefly discuss some proposals on how we should orient research in the future
Shear velocity structure of central Antarctica from teleseismic Rayleigh waves
第2回極域科学シンポジウム/第31回極域地学シンポジウム 11月16日(水) 国立国語研究
Quantum Algorithms for Fermionic Simulations
We investigate the simulation of fermionic systems on a quantum computer. We
show in detail how quantum computers avoid the dynamical sign problem present
in classical simulations of these systems, therefore reducing a problem
believed to be of exponential complexity into one of polynomial complexity. The
key to our demonstration is the spin-particle connection (or generalized
Jordan-Wigner transformation) that allows exact algebraic invertible mappings
of operators with different statistical properties. We give an explicit
implementation of a simple problem using a quantum computer based on standard
qubits.Comment: 38 pages, 2 psfigur
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