2,244 research outputs found
Second Thessalonians: Two Early Medieval Apocalyptic Commentaries
Apocalyptic speculation, in one form or another, is as persistent at the turn of this millennium as it was at the last. The commentaries of Haimo of Auxerre and Thietland of Einsiedeln offer glimpses of two links in [the] unbroken chain of the apocalyptic tradition.https://scholarworks.wmich.edu/mip_teamscs/1011/thumbnail.jp
Microplastics in the Antarctic marine system: An emerging area of research
It was thought that the Southern Ocean was relatively free of microplastic contamination; however, recent studies and citizen science projects in the Southern Ocean have reported microplastics in deep-sea sediments and surface waters. Here we reviewed available information on microplastics (including macroplastics as a source of microplastics) in the Southern Ocean. We estimated primary microplastic concentrations from personal care products and laundry, and identified potential sources and routes of transmission into the region. Estimates showed the levels of microplastic pollution released into the region from ships and scientific research stations were likely to be negligible at the scale of the Southern Ocean, but may be significant on a local scale. This was demonstrated by the detection of the first microplastics in shallow benthic sediments close to a number of research stations on King George Island. Furthermore, our predictions of primary microplastic concentrations from local sources were five orders of magnitude lower than levels reported in published sampling surveys (assuming an even dispersal at the ocean surface). Sea surface transfer from lower latitudes may contribute, at an as yet unknown level, to Southern Ocean plastic concentrations. Acknowledging the lack of data describing microplastic origins, concentrations, distribution and impacts in the Southern Ocean, we highlight the urgent need for research, and call for routine, standardised monitoring in the Antarctic marine system
Dynamical Wasserstein Barycenters for Time-series Modeling
Many time series can be modeled as a sequence of segments representing
high-level discrete states, such as running and walking in a human activity
application. Flexible models should describe the system state and observations
in stationary "pure-state" periods as well as transition periods between
adjacent segments, such as a gradual slowdown between running and walking.
However, most prior work assumes instantaneous transitions between pure
discrete states. We propose a dynamical Wasserstein barycentric (DWB) model
that estimates the system state over time as well as the data-generating
distributions of pure states in an unsupervised manner. Our model assumes each
pure state generates data from a multivariate normal distribution, and
characterizes transitions between states via displacement-interpolation
specified by the Wasserstein barycenter. The system state is represented by a
barycentric weight vector which evolves over time via a random walk on the
simplex. Parameter learning leverages the natural Riemannian geometry of
Gaussian distributions under the Wasserstein distance, which leads to improved
convergence speeds. Experiments on several human activity datasets show that
our proposed DWB model accurately learns the generating distribution of pure
states while improving state estimation for transition periods compared to the
commonly used linear interpolation mixture models.Comment: To appear at Neurips 202
Non-Parametric and Regularized Dynamical Wasserstein Barycenters for Time-Series Analysis
We consider probabilistic time-series models for systems that gradually
transition among a finite number of states. We are particularly motivated by
applications such as human activity analysis where the observed time-series
contains segments representing distinct activities such as running or walking
as well as segments characterized by continuous transition among these states.
Accordingly, the dynamical Wasserstein barycenter (DWB) model introduced in
Cheng et al. in 2021 [1] associates with each state, which we call a pure
state, its own probability distribution, and models these continuous
transitions with the dynamics of the barycentric weights that combine the pure
state distributions via the Wasserstein barycenter. Here, focusing on the
univariate case where Wasserstein distances and barycenters can be computed in
closed form, we extend [1] by discussing two challenges associated with
learning a DWB model and two improvements. First, we highlight the issue of
uniqueness in identifying the model parameters. Secondly, we discuss the
challenge of estimating a dynamically evolving distribution given a limited
number of samples. The uncertainty associated with this estimation may cause a
model's learned dynamics to not reflect the gradual transitions characteristic
of the system. The first improvement introduces a regularization framework that
addresses this uncertainty by imposing temporal smoothness on the dynamics of
the barycentric weights while leveraging the understanding of the
non-uniqueness of the problem. This is done without defining an entire
stochastic model for the dynamics of the system as in [1]. Our second
improvement lifts the Gaussian assumption on the pure states distributions in
[1] by proposing a quantile-based non-parametric representation. We pose model
estimation in a variational framework and propose a finite approximation to the
infinite dimensional problem
Perioperative morbidity and mortality after transmyocardial laser revascularization: incidence and risk factors for adverse events
AbstractOBJECTIVESThe purpose of this study was to describe the incidence and spectrum of perioperative cardiac and noncardiac morbidity and mortality after transmyocardial laser revascularization (TMR) and to identify predictors of these adverse clinical events.BACKGROUNDClinical studies have demonstrated the efficacy of TMR for relieving angina pectoris, although no study to date has specifically addressed the associated perioperative morbidity and mortality.METHODSBetween October 1995 and August 1997, 34 consecutive patients with end-stage coronary artery disease (CAD) underwent isolated TMR. The majority of patients (94%) had class III or IV angina pectoris, and two patients (6%) had unstable symptoms preoperatively. Patient records were reviewed for fatal and nonfatal adverse cardiac and noncardiac events.RESULTSPerioperative death occurred in two patients (5.9%) due to cardiogenic shock complicating acute myocardial infarction. Perioperative cardiac morbidity occurred in 16 patients (47.1%); noncardiac morbidity was seen in 12 patients (35.3%). Preoperative unstable angina was the only variable predictive of perioperative death (p = 0.005). Cardiac (p = 0.005) and noncardiac (p < 0.001) morbidity rates were significantly higher for the initial 15 patients undergoing the procedure. Other predictors of perioperative complications included lack of postoperative treatment with a furosemide infusion (p ≤ 0.04) and preoperative unstable angina (p = 0.05).CONCLUSIONSPerioperative mortality in patients undergoing isolated TMR is low. Transmyocardial laser revascularization patients are at higher risk for adverse perioperative cardiac and noncardiac events, likely reflecting the lack of immediate benefit from the procedure in the setting of severe CAD. These patients merit vigilant surveillance for adverse events and aggressive medical management in the perioperative period
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