2,064 research outputs found
From Bare Metal to Virtual: Lessons Learned when a Supercomputing Institute Deploys its First Cloud
As primary provider for research computing services at the University of
Minnesota, the Minnesota Supercomputing Institute (MSI) has long been
responsible for serving the needs of a user-base numbering in the thousands.
In recent years, MSI---like many other HPC centers---has observed a growing
need for self-service, on-demand, data-intensive research, as well as the
emergence of many new controlled-access datasets for research purposes. In
light of this, MSI constructed a new on-premise cloud service, named Stratus,
which is architected from the ground up to easily satisfy data-use agreements
and fill four gaps left by traditional HPC. The resulting OpenStack cloud,
constructed from HPC-specific compute nodes and backed by Ceph storage, is
designed to fully comply with controls set forth by the NIH Genomic Data
Sharing Policy.
Herein, we present twelve lessons learned during the ambitious sprint to take
Stratus from inception and into production in less than 18 months. Important,
and often overlooked, components of this timeline included the development of
new leadership roles, staff and user training, and user support documentation.
Along the way, the lessons learned extended well beyond the technical
challenges often associated with acquiring, configuring, and maintaining
large-scale systems.Comment: 8 pages, 5 figures, PEARC '18: Practice and Experience in Advanced
Research Computing, July 22--26, 2018, Pittsburgh, PA, US
Nimodipine vs. Milrinone – Equal or Complementary Use? A Retrospective Analysis
Background: Cerebral vasospasm (CVS) continues to account for high morbidity and
mortality in patients surviving the initial aneurysmal subarachnoid hemorrhage (SAH).
Nimodipine is the only drug known to reduce delayed cerebral ischemia (DCI), but it
is believed not to affect large vessel CVS. Milrinone has emerged as a promising option.
Our retrospective study focused on the effectiveness of the intra-arterial application of
both drugs in monotherapy and combined therapy.
Methods: We searched for patients with aneurysmal SAH, angiographically confirmed
CVS, and at least one intra-arterial pharmacological angioplasty. Ten defined vessel
sections on angiograms were assessed before and after vasodilator infusion. The
improvement in vessel diameters was compared to the frequency of DCI-related cerebral
infarction before hospital discharge and functional outcome reported as the modified
Rankin Scale (mRS) score after 6 months.
Results: Between 2014 and 2021, 132 intra-arterial interventions (144 vascular
territories, 12 bilaterally) in 30 patients were analyzed for this study. The vasodilating
effect of nimodipine was superior to milrinone in all intradural segments. There was
no significant intergroup difference concerning outcome in mRS (p = 0.217). Only
nimodipine or the combined approach could prevent DCI-related infarction (both 57.1%),
not milrinone alone (87.5%). Both drugs induced a doubled vasopressor demand due to
blood pressure decrease, but milrinone alone induced tachycardia.
Conclusions: The monotherapy with intra-arterial nimodipine was superior to milrinone.
Nimodipine and milrinone may be used complementary in an escalation scheme with the
administration of nimodipine first, complemented by milrinone in cases of severe CVS.
Milrinone monotherapy is not recommended
Code Vectors: Understanding Programs Through Embedded Abstracted Symbolic Traces
With the rise of machine learning, there is a great deal of interest in
treating programs as data to be fed to learning algorithms. However, programs
do not start off in a form that is immediately amenable to most off-the-shelf
learning techniques. Instead, it is necessary to transform the program to a
suitable representation before a learning technique can be applied.
In this paper, we use abstractions of traces obtained from symbolic execution
of a program as a representation for learning word embeddings. We trained a
variety of word embeddings under hundreds of parameterizations, and evaluated
each learned embedding on a suite of different tasks. In our evaluation, we
obtain 93% top-1 accuracy on a benchmark consisting of over 19,000 API-usage
analogies extracted from the Linux kernel. In addition, we show that embeddings
learned from (mainly) semantic abstractions provide nearly triple the accuracy
of those learned from (mainly) syntactic abstractions
Electron-Positron Pair Production in Relativistic Heavy Ion Collisions
In recent years, a large number of papers have appeared that dealt with
\EPEM pair production in heavy ion collisions at high energies. To a large
extent these studies were motivated by the existence of relativistic heavy ion
accelerators all over the world. There pair production can be studied in so
called ``ultra-peripheral collisions'', where the ions do not come close enough
to interact strongly with each other. Various different methods have been used
and it is the purpose of this review to present a unified picture of the
present status of the field.Comment: 51 pages, 16 figures, submitted to Physics Report
Postglacial species arrival and diversity buildup of northern ecosystems took millennia
What drives ecosystem buildup, diversity, and stability? We assess species arrival and ecosystem changes across 16 millennia by combining regional-scale plant sedimentary ancient DNA from Fennoscandia with near-complete DNA and trait databases. We show that postglacial arrival time varies within and between plant growth forms. Further, arrival times were mainly predicted by adaptation to temperature, disturbance, and light. Major break points in ecological trait diversity were seen between 13.9 and 10.8 calibrated thousand years before the present (cal ka BP), as well as break point in functional diversity at 12.0 cal ka BP, shifting from a state of ecosystem buildup to a state where most habitat types and biotic ecosystem components were in place. Trait and functional diversity stabilized around 8 cal ka BP, after which both remained stable, although changes in climate took place and species inflow continued. Our ecosystem reconstruction indicates a millennial-scale time phase of formation to reach stable and resilient levels of diversity and functioning.publishedVersio
The first determination of Generalized Polarizabilities of the proton by a Virtual Compton Scattering experiment
Absolute differential cross sections for the reaction (e+p -> e+p+gamma) have
been measured at a four-momentum transfer with virtuality Q^2=0.33 GeV^2 and
polarization \epsilon = 0.62 in the range 33.6 to 111.5 MeV/c for the momentum
of the outgoing photon in the photon-proton center of mass frame. The
experiment has been performed with the high resolution spectrometers at the
Mainz Microtron MAMI. From the photon angular distributions, two structure
functions which are a linear combination of the generalized polarizabilities
have been determined for the first time.Comment: 4 pages, 3 figure
- …