15,674 research outputs found
Overcoming ambiguities in classical and quantum correlation measures
We identify ambiguities in the available frameworks for defining quantum,
classical, and total correlations as measured by discordlike quantifiers. More
specifically, we determine situations for which either classical or quantum
correlations are not uniquely defined due to degeneracies arising from the
optimization procedure over the state space. In order to remove such
degeneracies, we introduce a general approach where correlations are
independently defined, escaping therefore from a degenerate subspace. As an
illustration, we analyze the trace-norm geometric quantum discord for two-qubit
Bell-diagonal states.Comment: 5 pages, 2 figures. v2: Minor corrections. Published versio
A grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis
In this work we present a grid of LTE and non-LTE synthetic spectra of hot DA
white dwarfs (WDs). In addition to its usefulness for the determination of
fundamental stellar parameters of isolated WDs and in binaries, this grid will
be of interest for the construction of theoretical libraries for stellar
studies from integrated light. The spectral grid covers both a wide temperature
and gravity range, with 17,000 K <= T_eff <= 100,000 K and 7.0 <= log(g) <=
9.5. The stellar models are built for pure hydrogen and the spectra cover a
wavelength range from 900 A to 2.5 microns. Additionally, we derive synthetic
HST/ACS, HST/WFC3, Bessel UBVRI and SDSS magnitudes. The grid was also used to
model integrated spectral energy distributions of simple stellar populations
and our modeling suggests that DAs might be detectable in ultraviolet bands for
populations older than ~8 Gyr.Comment: to be published in The Astrophysical Journal Supplement Serie
Geometric classical and total correlations via trace distance
We introduce the concepts of geometric classical and total correlations
through Schatten 1-norm (trace norm), which is the only Schatten p-norm able to
ensure a well-defined geometric measure of correlations. In particular, we
derive the analytical expressions for the case of two-qubit Bell-diagonal
states, discussing the superadditivity of geometric correlations. As an
illustration, we compare our results with the entropic correlations, discussing
both their hierarchy and monotonicity properties. Moreover, we apply the
geometric correlations to investigate the ground state of spin chains in the
thermodynamic limit. In contrast to the entropic quantifiers, we show that the
classical correlation is the only source of 1-norm geometric correlation that
is able to signaling an infinite-order quantum phase transition.Comment: v2: published versio
Angular Correlation Function from sample covariance with BOSS and eBOSS LRG
The Baryon Acoustic Oscillations (BAO) are one of the most used probes to
understand the accelerated expansion of the Universe. Traditional methods rely
on fiducial model information within their statistical analysis, which may be a
problem when constraining different families of models. The aim of this work is
to provide a method that constrains through a model-independent
and compare parameter estimation of the angular correlation function polynomial
approach, using the covariance matrix from the galaxy sample from thin redshift
bins, with the usual mock sample covariance matrix. We proposed a different
approach to finding the BAO angular feature revisiting previous work in the
literature, we take the bias between the correlation function between the bins
and the whole sample. We used widths of separation for all
samples as the basis for a sample covariance matrix weighted by the statistical
importance of the redshift bin. We propose a different weighting scheme based
only on random pair counting. We also propose an alternate shift parameter
based only on the data. Each sample belongs to the Sloan Digital Sky Survey
Luminous Red Galaxies (LRG): BOSS1, BOSS2, and eBOSS, with effective redshift
: 0.35, 0.51, 0.71, respectively, and different numbers of bins with
50, 100, and 200 respectively. In addition, we correct the angular separation
from the polynomial fit () that encodes the BAO feature with a
bias function obtained by comparing each bin correlation function with the
correlation function of the whole set. We also tested the same correction
choosing the bin at and found that for eBOSS is in agreement with the Planck 18 model. BOSS1 and BOSS2
agreed in with the Pantheon+ & SES FlatCDM model, in
tension with Planck 18.Comment: 18 page
O uso da argumentação na montagem de um modelo
Trabalhos recentes na área de Ensino de ciência têm tratado a argumentação como parte imprescindÃvel das aulas de ciência, pois argumentar seria uma das caracterÃsticas da ciência. A forma de análise recorrente em tais trabalhos é o padrão criado por Toulmin, que permite uma divisão do argumento e a identificação de seus elementos constituintes. Foi analisada uma seqüência didática com as turmas de 3º ano da escola de Aplicação da Universidade de São Paulo que culminou na montagem de um modelo de DNA. Tal montagem foi feita em grupos e as discussões ocorridas durante a tarefa foram gravadas e transcritas. A análise dos discursos mostrou argumentos simples compostos basicamente por dados e conclusão. A atividade se mostra diferente da ciência já que não são defendidos pontos de vista sobre uma questão aberta, mas sim opiniões sobre algo já estabelecido
Observations of the SW Sextantis star DW Ursae Majoris with the Far Ultraviolet Spectroscopic Explorer
We present an analysis of the first far-ultraviolet observations of the SW
Sextantis-type cataclysmic variable DW Ursae Majoris, obtained in November 2001
with the Far Ultraviolet Spectroscopic Explorer. The time-averaged spectrum of
DW UMa shows a rich assortment of emission lines (plus some contamination from
interstellar absorption lines including molecular hydrogen). Accretion disk
model spectra do not provide an adequate fit to the far-ultraviolet spectrum of
DW UMa. We constructed a light curve by summing far-ultraviolet spectra
extracted in 60-sec bins; this shows a modulation on the orbital period, with a
maximum near photometric phase 0.93 and a minimum half an orbit later. No other
periodic variability was found in the light curve data. We also extracted
spectra in bins spanning 0.1 in orbital phase; these show substantial variation
in the profile shapes and velocity shifts of the emission lines during an
orbital cycle of DW UMa. Finally, we discuss possible physical models that can
qualitatively account for the observed far-ultraviolet behavior of DW UMa, in
the context of recent observational evidence for the presence of a
self-occulting disk in DW UMa and the possibility that the SW Sex stars may be
the intermediate polars with the highest mass transfer rates and/or weakest
magnetic fields.Comment: accepted by the Astronomical Journal; 36 pages, including 12 figures
and 4 table
- …