3,249 research outputs found
On the stability of a superspinar
The superspinar proposed by Gimon and Horava is a rapidly rotating compact
entity whose exterior is described by the over-spinning Kerr geometry. The
compact entity itself is expected to be governed by superstringy effects, and
in astrophysical scenarios it can give rise to interesting observable
phenomena. Earlier it was suggested that the superspinar may not be stable but
we point out here that this does not necessarily follow from earlier studies.
We show, by analytically treating the Teukolsky equations by Detwiler's method,
that in fact there are infinitely many boundary conditions that make the
superspinar stable, and that the modes will decay in time. It follows that we
need to know more on the physical nature of the superspinar in order to decide
on its stability in physical reality.Comment: 5 page
Auto-Surprise: An Automated Recommender-System (AutoRecSys) Library with Tree of Parzens Estimator (TPE) Optimization
We introduce Auto-Surprise, an Automated Recommender System library.
Auto-Surprise is an extension of the Surprise recommender system library and
eases the algorithm selection and configuration process. Compared to
out-of-the-box Surprise library, Auto-Surprise performs better when evaluated
with MovieLens, Book Crossing and Jester Datasets. It may also result in the
selection of an algorithm with significantly lower runtime. Compared to
Surprise's grid search, Auto-Surprise performs equally well or slightly better
in terms of RMSE, and is notably faster in finding the optimum hyperparameters.Comment: To be presented at RecSys '20 Fourteenth ACM Conference on
Recommender Systems, September 21-26, 2020, Virtual Even
Development of a model of ischemic heart disease using cardiomyocytes differentiated from human induced pluripotent stem cells
Ischemic heart disease remains the largest cause of death worldwide. Accordingly, many researchers have sought curative options, often using laboratory animal models such as rodents. However, the physiology of the human heart differs significantly from that of the rodent heart. In this study, we developed a model of ischemic heart disease using cardiomyocytes differentiated from human induced pluripotent stem cells (hiPS-CMs). After optimizing the conditions of ischemia, including the concentration of oxygen and duration of application, we evaluated the consequent damage to hiPS-CMs. Notably, exposure to 2% oxygen, 0 mg/ml glucose, and 0% fetal bovine serum increased the percentage of nuclei stained with propidium iodide, an indicator of membrane damage, and decreased cellular viability. These conditions also decreased the contractility of hiPS-CMs. Furthermore, ischemic conditioning increased the mRNA expression of IL-8, consistent with observed conditions in the in vivo heart. Taken together, these findings suggest that our hiPS-CM-based model can provide a useful platform for human ischemic heart disease research
Quantifying the Performance Benefits of Partitioned Communication in MPI
Partitioned communication was introduced in MPI 4.0 as a user-friendly
interface to support pipelined communication patterns, particularly common in
the context of MPI+threads. It provides the user with the ability to divide a
global buffer into smaller independent chunks, called partitions, which can
then be communicated independently. In this work we first model the performance
gain that can be expected when using partitioned communication. Next, we
describe the improvements we made to \mpich{} to enable those gains and provide
a high-quality implementation of MPI partitioned communication. We then
evaluate partitioned communication in various common use cases and assess the
performance in comparison with other MPI point-to-point and one-sided
approaches. Specifically, we first investigate two scenarios commonly
encountered for small partition sizes in a multithreaded environment: thread
contention and overhead of using many partitions. We propose two solutions to
alleviate the measured penalty and demonstrate their use. We then focus on
large messages and the gain obtained when exploiting the delay resulting from
computations or load imbalance. We conclude with our perspectives on the
benefits of partitioned communication and the various results obtained
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