600 research outputs found
Evaluating Emerging CXL-enabled Memory Pooling for HPC Systems
Current HPC systems provide memory resources that are statically configured
and tightly coupled with compute nodes. However, workloads on HPC systems are
evolving. Diverse workloads lead to a need for configurable memory resources to
achieve high performance and utilization. In this study, we evaluate a memory
subsystem design leveraging CXL-enabled memory pooling. Two promising use cases
of composable memory subsystems are studied -- fine-grained capacity
provisioning and scalable bandwidth provisioning. We developed an emulator to
explore the performance impact of various memory compositions. We also provide
a profiler to identify the memory usage patterns in applications and their
optimization opportunities. Seven scientific and six graph applications are
evaluated on various emulated memory configurations. Three out of seven
scientific applications had less than 10% performance impact when the pooled
memory backed 75% of their memory footprint. The results also show that a
dynamically configured high-bandwidth system can effectively support
bandwidth-intensive unstructured mesh-based applications like OpenFOAM.
Finally, we identify interference through shared memory pools as a practical
challenge for adoption on HPC systems.Comment: 10 pages, 13 figures. Accepted for publication in Workshop on Memory
Centric High Performance Computing (MCHPC'22) at SC2
Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages
We have investigated asymptotic behavior of normal tunnel junctions at
voltages where even the best ohmic environments start to look like RC
transmission lines. In the experiments, this is manifested by an exceedingly
slow approach to the linear behavior above the Coulomb gap. As expected on the
basis of the quantum theory taking into account interaction with the
environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V-
dependence for the asymptote. These results agree with the horizon picture if
the frequency-dependent phase velocity is employed instead of the speed of
light in order to determine the extent of the surroundings seen by the
junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.
The Unusual S Star Binary HD 191589
Recently, we discovered with International Ultraviolet Explorer (IUE) an F0-F2 IV-V companion to the T(sub c)-deficient S star HD 191589. If the magnitude difference is (delta)V=3.7, as indicated by several arguments, and E(B-V) = 0.0, we obtain a value of M(sub v)= - 1.5 +/- 0.4 for the Peculiar Red Giant (PRG), too faint for it to be a thermally-pulsing asymptotic giant branch star. According to the binary mass-transfer hypothesis for T(sub c)-deficient PRG's, a white dwarf must be the source of the s-process enhancement of the current primary star, but it cannot be seen because of the presence of the secondary. If such is the case, the F-star companion may also have been contaminated by s-process material. High-dispersion IUE observations indicate an enhancement of Zr II in the photosphere of the F-star as well. Thus, HD 191589 is likely a triple system, where what was once the most massive component of the system has polluted both of its companions with s-process material. One of these is the current S star, while the other is the companion still near the main sequence
High Mass Triple Systems: The Classical Cepheid Y Car
We have obtained an HST STIS ultraviolet high dispersion Echelle mode
spectrum the binary companion of the double mode classical Cepheid Y Car. The
velocity measured for the hot companion from this spectrum is very different
from reasonable predictions for binary motion, implying that the companion is
itself a short period binary. The measured velocity changed by 7 km/ s during
the 4 days between two segments of the observation confirming this
interpretation. We summarize "binary" Cepheids which are in fact members of
triple system and find at least 44% are triples. The summary of information on
Cepheids with orbits makes it likely that the fraction is under-estimated.Comment: accepted by A
Comparative Modelling of the Spectra of Cool Giants
Our ability to extract information from the spectra of stars depends on
reliable models of stellar atmospheres and appropriate techniques for spectral
synthesis. Various model codes and strategies for the analysis of stellar
spectra are available today. We aim to compare the results of deriving stellar
parameters using different atmosphere models and different analysis strategies.
The focus is set on high-resolution spectroscopy of cool giant stars. Spectra
representing four cool giant stars were made available to various groups and
individuals working in the area of spectral synthesis, asking them to derive
stellar parameters from the data provided. The results were discussed at a
workshop in Vienna in 2010. Most of the major codes currently used in the
astronomical community for analyses of stellar spectra were included in this
experiment. We present the results from the different groups, as well as an
additional experiment comparing the synthetic spectra produced by various codes
for a given set of stellar parameters. Similarities and differences of the
results are discussed. Several valid approaches to analyze a given spectrum of
a star result in quite a wide range of solutions. The main causes for the
differences in parameters derived by different groups seem to lie in the
physical input data and in the details of the analysis method. This clearly
shows how far from a definitive abundance analysis we still are.Comment: accepted for publication in A&A. This version includes also the
online tables. Reference spectra will later be available via the CD
Rosette-Disrupting Effect of an Anti-Plasmodial Compound for the Potential Treatment of Plasmodium falciparum Malaria Complications
The spread of artemisinin-resistant parasites could lead to
higher incidence of patients with malaria complications.
However, there are no current treatments that directly dislodge
sequestered parasites from the microvasculature. We show that
four common antiplasmodial drugs do not disperse rosettes
(erythrocyte clusters formed by malaria parasites) and therefore
develop a cell-based high-throughput assay to identify potential
rosette-disrupting compounds. A pilot screen of 2693 compounds
identified Malaria Box compound MMV006764 as a potential
candidate. Although it reduced rosetting by a modest 20%,
MMV006764 was validated to be similarly effective against both
blood group O and A rosettes of three laboratory parasite lines.
Coupled with its antiplasmodial activity and drug-likeness,
MMV006764 represents the first small-molecule compound that
disrupts rosetting and could potentially be used in a
resource-limited setting to treat patients deteriorating rapidly
from malaria complications. Such dual-action drugs that
simultaneously restore microcirculation and reduce parasite load
could significantly reduce malaria morbidity and mortality
Strong dust processing in circumstellar discs around 6 RV Tauri stars. Are dusty RV Tauri stars all binaries?
We present extended Spectral Energy Distributions (SEDs) of seven classical
RV Tauri stars, using newly obtained submillimetre continuum measurements and
Geneva optical photometry supplemented with literature data. The broad-band
SEDs show a large IR excess with a black-body slope at long wavelengths in six
of the seven stars, R Sct being the noticeable exception. This long wavelength
slope is best explained assuming the presence of a dust component of large
grains in the circumstellar material. We show that the most likely distribution
of the circumstellar dust around the six systems is that the dust resides in a
disc. Moreover, very small outflow velocities are needed to explain the
presence of dust near the sublimation temperature and we speculate that the
discs are Keplerian. The structure and evolution of these compact discs are as
yet not understood but a likely prerequisite for their formation is that the
dusty RV Tauri stars are binaries.Comment: 10 pages, will be published in A&
Randomized assessment of imatinib in patients with acute ischaemic stroke treated with intravenous thrombolysis
BackgroundImatinib, a tyrosine kinase inhibitor, has been shown to restore bloodâ brain barrier integrity and reduce infarct size, haemorrhagic transformation and cerebral oedema in stroke models treated with tissue plasminogen activator. We evaluated the safety of imatinib, based on clinical and neuroradiological data, and its potential influence on neurological and functional outcomes.MethodsA phase II randomized trial was performed in patients with acute ischaemic stroke treated with intravenous thrombolysis. A total of 60 patients were randomly assigned to four groups [3 (active): 1 (control)]; the active treatment groups received oral imatinib for 6 days at three dose levels (400, 600 and 800 mg). Primary outcome was any adverse event; secondary outcomes were haemorrhagic transformation, cerebral oedema, neurological severity on the National Institutes of Health Stroke Scale (NIHSS) at 7 days and at 3 months and functional outcomes on the modified Rankin scale (mRS).ResultsFour serious adverse events were reported, which resulted in three deaths (one in the control group and two in the 400â mg dose group; one patient in the latter group did not receive active treatment and the other received two doses). Nonserious adverse events were mostly mild, resulting in full recovery. Imatinib ameliorated neurological outcomes with an improvement of 0.6 NIHSS points per 100 mg imatinib (P = 0.02). For the 800â mg group, the mean unadjusted and adjusted NIHSS improvements were 4 (P = 0.037) and 5 points (P = 0.012), respectively, versus controls. Functional independence (mRS 0â 2) increased by 18% versus controls (61 vs. 79; P = 0.296).ConclusionThis phase II study showed that imatinib is safe and tolerable and may reduce neurological disability in patients treated with intravenous thrombolysis after ischaemic stroke. A confirmatory randomized trial is currently underway.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136298/1/joim12576_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136298/2/joim12576.pd
Numerical analysis of the radio-frequency single-electron transistor operation
We have analyzed numerically the response and noise-limited charge
sensitivity of a radio-frequency single-electron transistor (RF-SET) in a
non-superconducting state using the orthodox theory. In particular, we have
studied the performance dependence on the quality factor Q of the tank circuit
for Q both below and above the value corresponding to the impedance matching
between the coaxial cable and SET.Comment: 14 page
CRIRES-POP: A library of high resolution spectra in the near-infrared
New instrumental capabilities and the wealth of astrophysical information
extractable from the near-infrared wavelength region have led to a growing
interest in the field of high resolution spectroscopy at 1-5 mu. We aim to
provide a library of observed high-resolution and high signal-to-noise-ratio
near-infrared spectra of stars of various types throughout the
Hertzsprung-Russell diagram. This is needed for the exploration of spectral
features in this wavelength range and for comparison of reference targets with
observations and models.
High quality spectra were obtained using the CRIRES near-infrared
spectrograph at ESO's VLT covering the range from 0.97 to 5.3 mu at high
spectral resolution. Accurate wavelength calibration and correction for of
telluric lines were performed by fitting synthetic transmission spectra for the
Earth's atmosphere to each spectrum individually. We describe the observational
strategy and the current status and content of the library which includes 13
objects. The first examples of finally reduced spectra are presented. This
publication will serve as a reference paper to introduce the library to the
community and explore the extensive amount of material.Comment: accepted for publication in A&A; see also the project webpage
http://www.univie.ac.at/crirespo
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