5,913 research outputs found
The Magnus representation and higher-order Alexander invariants for homology cobordisms of surfaces
The set of homology cobordisms from a surface to itself with markings of
their boundaries has a natural monoid structure. To investigate the structure
of this monoid, we define and study its Magnus representation and Reidemeister
torsion invariants by generalizing Kirk-Livingston-Wang's argument over the
Gassner representation of string links. Moreover, by applying Cochran and
Harvey's framework of higher-order (non-commutative) Alexander invariants to
them, we extract several pieces of information about the monoid and related
objects.Comment: 28 pages. The whole paper has been rewritten, and the title has been
change
Predicting death and readmission after intensive care discharge
Background: Despite initial recovery from critical illness, many patients deteriorate after discharge from the intensive care unit (ICU). We examined prospectively collected data in an attempt to identify patients at risk of readmission or death after intensive care discharge. Methods: This was a secondary analysis of clinical audit data from patients discharged alive from a mixed medical and surgical (non-cardiac) ICU. Results: Four hundred and seventy-five patients (11.2%) died in hospital after discharge from the ICU. Increasing age, time in hospital before intensive care admission, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, and discharge Therapeutic Intervention Scoring System (TISS) score were independent risk factors for death after intensive care discharge. Three hundred and eighty-five patients (8.8%) were readmitted to intensive care during the same hospital admission. Increasing age, time in hospital before intensive care, APACHE II score, and discharge to a high dependency unit were independent risk factors for readmission. One hundred and forty-three patients (3.3%) were readmitted within 48 h of intensive care discharge. APACHE II scores and discharge to a high dependency or other ICU were independent risk factors for early readmission. The overall discriminant ability of our models was moderate with only marginal benefit over the APACHE II scores alone. Conclusions: We identified risk factors associated with death and readmission to intensive care. It was not possible to produce a definitive model based on these risk factors for predicting death or readmission in an individual patient.Not peer reviewedAuthor versio
HI Observations of the Ca II absorbing galaxies Mrk 1456 and SDSS J211701.26-002633.7
In an effort to study Damped Lyman Alpha galaxies at low redshift, we have
been using the Sloan Digital Sky Survey to identify galaxies projected onto QSO
sightlines and to characterize their optical properties. For low redshift
galaxies, the HI 21cm emission line can be used as an alternate tool for
identifying possible DLA galaxies, since HI emitting galaxies typically exhibit
HI columns that are larger than the classical DLA limit. Here we report on
follow-up HI 21 cm emission line observations of two DLA candidates that are
both low-redshift spiral galaxies, Mrk 1456 and SDSS J211701.26-002633.7. The
observations were made using the Green Bank and Arecibo Telescopes,
respectively. Analysis of their HI properties reveal the galaxies to be about
one and two M_HI* galaxies, respectively, and to have average HI mass,
gas-richness, and gas mass fraction for their morphological types. We consider
Mrk 1456 and SDSS J211701.26-002633.7 to be candidate DLA systems based upon
the strength of the CaII absorption lines they cause in their QSO's spectra,
and impact parameters to the QSO that are smaller than the stellar disk.
Compared to the small numbers of other HI-detected DLA and candidate DLA
galaxies, Mrk 1456 and SDSS J211701.26-002633.7 have high HI masses. When
compared with the expected properties of low-z DLAs from an HI-detected sample
of galaxies, Mrk 1456 and SDSS J211701.26-002633.7 fall within the ranges for
impact parameter and B-band absolute magnitude; and the HI mass distribution
for the HI-detected DLAs agrees with that of the expected HI mass distribution
for low-z DLAs. Our observations support galaxy-evolution models in which high
mass galaxies make up an increasing contribution to the DLA cross-section at
lower redshifts. [abridged]Comment: 12 pages, 5 figures, 5 tables; to be published in The Astronomical
Journa
Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies
We have used the Spitzer Space Telescope to study the dust properties of a
sample of star-forming dwarf galaxies. The differences in the mid-infrared
spectral energy distributions for these galaxies which, in general, are low
metallicity systems, indicate differences in the physical properties, heating,
and/or distribution of the dust. Specifically, these galaxies have more hot
dust and/or very small grains and less PAH emission than either spiral or
higher luminosity starburst galaxies. As has been shown in previous studies,
there is a gradual decrease in PAH emission as a function of metallicity.
Because much of the energy from star formation in galaxies is re-radiated in
the mid-infrared, star-formation rate indicators based on both line and
continuum measurements in this wavelength range are coming into more common
usage. We show that the variations in the interstellar medium properties of
galaxies in our sample, as measured in the mid-infrared, result in over an
order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte
Gene surfing
Spatially resolved genetic data is increasingly used to reconstruct the
migrational history of species. To assist such inference, we study, by means of
simulations and analytical methods, the dynamics of neutral gene frequencies in
a population undergoing a continual range expansion in one dimension. During
such a colonization period, lineages can fix at the wave front by means of a
``surfing'' mechanism [Edmonds C.A., Lillie A.S. & Cavalli-Sforza L.L. (2004)
Proc Natl Acad Sci USA 101: 975-979]. We quantify this phenomenon in terms of
(i) the spatial distribution of lineages that reach fixation and, closely
related, (ii) the continual loss of genetic diversity (heterozygosity) at the
wave front, characterizing the approach to fixation. Our simulations show that
an effective population size can be assigned to the wave that controls the
(observable) gradient in heterozygosity left behind the colonization process.
This effective population size is markedly higher in pushed waves than in
pulled waves, and increases only sub-linearly with deme size. To explain these
and other findings, we develop a versatile analytical approach, based on the
physics of reaction-diffusion systems, that yields simple predictions for any
deterministic population dynamics
Adolescents and adults with Fontan circulation:insights from the PREpArE-Fontan registry
The Patient Registry for Adolescents and Adults with Stable Fontan Circulation aims to describe a contemporary cohort of Fontan patients who could be eligible for a clinical trial investigating macitentan, an endothelin receptor antagonist. This international, non-interventional, multicentre, cross-sectional, observational registry enrolled patients with “stable” Fontan circulation ≥10 years following extra-cardiac conduit or lateral tunnel procedure. Main exclusion criteria were NYHA functional class IV, reoperation of Fontan circulation, or signs of disease worsening. Patient characteristics at enrolment are described; available data were collected during a single registration visit. Of the 266 screened patients, 254 were included in this analysis. At enrolment, median (interquartile range) age was 24 (20;30) years, 37%/63% of patients were from the USA/Europe, 54% were male, 54%/47% had undergone extra-cardiac conduit/lateral tunnel procedures, and 95% were in NYHA functional class I or II. History of arrhythmia was more common in older patients and patients with lateral tunnel; overall prevalence was 19%. Most laboratory values were within the normal range but mean creatinine clearance was abnormally low (87.7 ml/min). Angiotensin-converting enzyme inhibitors were used by 48% of patients and their use was associated with creatinine clearance <90 ml/min (p = 0.007), as was Fontan completion at an older age (p = 0.007). 53.4% of patients had clinical characteristics that could potentially meet an endothelin receptor antagonist trial’s eligibility criteria. The PREpArE-Fontan registry describes a cohort of patients who could potentially participate in an endothelin receptor antagonist trial and identified early subtle signs of Fontan failure, even in “stable” patients
Conserved small RNAs govern replication and incompatibility of a diverse new plasmid family from marine bacteria
Plasmids are autonomously replicating extrachromosomal DNA molecules that often impart key phenotypes to their bacterial hosts. Plasmids are abundant in marine bacteria, but there is scant knowledge of the mechanisms that control their replication in these hosts. Here, we identified and characterized the factors governing replication of a new family of plasmids from marine bacteria, typified by the virulence-linked plasmid pB1067 of Vibrio nigripulchritudo. Members of this family are prevalent among, yet restricted to, the Vibrionaceae. Unlike almost all plasmid families characterized to date, the ori regions of these plasmids do not encode a Rep protein to initiate DNA replication; instead, the ori regions encode two partially complementary RNAs. The smaller, termed RNA I, is ∼68-nt long and functions as a negative regulator and the key determinant of plasmid incompatibility. This Marine RNA-based (MRB) plasmid family is the first characterized family of replicons derived from marine bacteria. Only one other plasmid family (the ColE1 family) has previously been reported to rely on RNA-mediated replication initiation. However, since the sequences and structures of MRB RNA I transcripts are not related to those of ColE1 replicons, these two families of RNA-dependent replicons likely arose by convergent evolution
Thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The composite orogenic system
The Himalayan orogen represents a ‘‘Composite Orogenic System’’ in which channel flow, wedge extrusion, and thrust stacking operate in separate ‘‘Orogenic Domains’’ with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >7008C to 550–6508C), to rigid wedge extrusion (Stage 2, 400–6008C) and duplexing (Stage 3, <280–4008C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems
41 GHz and 10.6 GHz low threshold and low noise InAs/InP quantum dash two-section mode-locked lasers in L band
International audienceThis paper reports recent results on InAs/InP quantum dash-based, two-section, passively mode- locked lasers pulsing at 41 GHz and 10.6 GHz and emitting at 1.59 lm at 20°C. The 41-GHz device (1 mm long) starts lasing at 25 mA under uniform injection and the 10.6 GHz (4 mm long) at 71 mA. Their output pulses are significantly chirped. The 41-GHz laser exhibits 7 ps pulses after propagation in 60 m of a single-mode fiber. The 10.6-GHz laser generates one picosecond pulses with 545 m of a single-mode fiber. Its single side-band phase noise does not exceed -80 dBc/Hz at 100 kHz offset, leading to an average timing jitter of 800 fs
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