278 research outputs found
Algebraic varieties with automorphism groups of maximal rank
We confirm, to some extent, the belief that a projective variety X has the
largest number (relative to the dimension of X) of independent commuting
automorphisms of positive entropy only when X is birational to a complex torus
or a quotient of a torus. We also include an addendum to an early paper though
it is not used in the present paper.Comment: Mathematische Annalen (to appear
The photometric properties of a vast stellar substructure in the outskirts of M33
We have surveyed sq.degrees surrounding M33 with CFHT MegaCam in the
g and i filters, as part of the Pan-Andromeda Archaeological Survey. Our
observations are deep enough to resolve the top 4mags of the red giant branch
population in this galaxy. We have previously shown that the disk of M33 is
surrounded by a large, irregular, low-surface brightness substructure. Here, we
quantify the stellar populations and structure of this feature using the PAndAS
data. We show that the stellar populations of this feature are consistent with
an old population with dex and an interquartile range in
metallicity of dex. We construct a surface brightness map of M33 that
traces this feature to mags\,arcsec. At these low surface
brightness levels, the structure extends to projected radii of kpc from
the center of M33 in both the north-west and south-east quadrants of the
galaxy. Overall, the structure has an "S-shaped" appearance that broadly aligns
with the orientation of the HI disk warp. We calculate a lower limit to the
integrated luminosity of the structure of mags, comparable to a
bright dwarf galaxy such as Fornax or AndII and slightly less than $1\$ of the
total luminosity of M33. Further, we show that there is tentative evidence for
a distortion in the distribution of young stars near the edge of the HI disk
that occurs at similar azimuth to the warp in HI. The data also hint at a
low-level, extended stellar component at larger radius that may be a M33 halo
component. We revisit studies of M33 and its stellar populations in light of
these new results, and we discuss possible formation scenarios for the vast
stellar structure. Our favored model is that of the tidal disruption of M33 in
its orbit around M31.Comment: Accepted for publication in ApJ. 17 figures. ApJ preprint forma
PCN99 The Cost-Effectiveness of Bendamustine Versus Fludarabine for the First-Line Treatment of Chronic Lymphocytic Leukemia (CLL) in Mexico
The voice of COVID-19: acoustic correlates of infection in sustained vowels
COVID-19 is a global health crisis that has been affecting many aspects of
our daily lives throughout the past year. The symptomatology of COVID-19 is
heterogeneous with a severity continuum. A considerable proportion of symptoms
are related to pathological changes in the vocal system, leading to the
assumption that COVID-19 may also affect voice production. For the very first
time, the present study aims to investigate voice acoustic correlates of an
infection with COVID-19 on the basis of a comprehensive acoustic parameter set.
We compare 88 acoustic features extracted from recordings of the vowels /i:/,
/e:/, /o:/, /u:/, and /a:/ produced by 11 symptomatic COVID-19 positive and 11
COVID-19 negative German-speaking participants. We employ the Mann-Whitney U
test and calculate effect sizes to identify features with the most prominent
group differences. The mean voiced segment length and the number of voiced
segments per second yield the most important differences across all vowels
indicating discontinuities in the pulmonic airstream during phonation in
COVID-19 positive participants. Group differences in the front vowels /i:/ and
/e:/ are additionally reflected in the variation of the fundamental frequency
and the harmonics-to-noise ratio, group differences in back vowels /o:/ and
/u:/ in statistics of the Mel-frequency cepstral coefficients and the spectral
slope. Findings of this study can be considered an important proof-of-concept
contribution for a potential future voice-based identification of individuals
infected with COVID-19.Comment: 8 page
Magnetic-field dependence of the critical currents in a periodic coplanar array of narrow superconducting strip
We calculate the magnetic-field dependence of the critical current due to
both geometrical edge barriers and bulk pinning in a periodic coplanar array of
narrow superconducting strips. We find that in zero or low applied magnetic
fields the critical current can be considerably enhanced by the edge barriers,
but in modest applied magnetic fields the critical current reduces to that due
to bulk pinning alone.Comment: 23 pages, 7 figure
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