274 research outputs found
TaskInsight: Understanding Task Schedules Effects on Memory and Performance
Recent scheduling heuristics for task-based applications have managed to improve their by taking into account memory-related properties such as data locality and cache sharing. However, there is still a general lack of tools that can provide insights into why, and where, different schedulers improve memory behavior, and how this is related to the applications' performance.
To address this, we present TaskInsight, a technique to characterize the memory behavior of different task schedulers through the analysis of data reuse between tasks. TaskInsight provides high-level, quantitative information that can be correlated with tasks' performance variation over time to understand data reuse through the caches due to scheduling choices. TaskInsight is useful to diagnose and identify which scheduling decisions affected performance, when were they taken, and why the performance changed, both in single and multi-threaded executions.
We demonstrate how TaskInsight can diagnose examples where poor scheduling caused over 10% difference in performance for tasks of the same type, due to changes in the tasks' data reuse through the private and shared caches, in single and multi-threaded executions of the same application. This flexible insight is key for optimization in many contexts, including data locality, throughput, memory footprint or even energy efficiency.We thank the reviewers for their feedback. This work was supported by the Swedish Research Council, the Swedish Foundation for Strategic Research project FFL12-0051 and carried out within the Linnaeus Centre of Excellence UPMARC, Uppsala Programming for Multicore Architectures Research Center. This paper
was also published with the support of the HiPEAC network that received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 687698.Peer ReviewedPostprint (published version
Cavity cooling of a levitated nanosphere by coherent scattering
We report three-dimensional cooling of a levitated nanoparticle inside an
optical cavity. The cooling mechanism is provided by cavity-enhanced coherent
scattering off an optical tweezer. The observed 3D dynamics and cooling rates
are as theoretically expected from the presence of both linear and quadratic
terms in the interaction between the particle motion and the cavity field. By
achieving nanometer-level control over the particle location we optimize the
position-dependent coupling and demonstrate axial cooling by two orders of
magnitude at background pressures as high as mbar. We also
estimate a significant ( dB) suppression of laser phase noise, and hence
of residual heating, which is a specific feature of the coherent scattering
scheme. The observed performance implies that quantum ground state cavity
cooling of levitated nanoparticles can be achieved for background pressures
below mbar
Cavity cooling of an optically levitated nanoparticle
The ability to trap and to manipulate individual atoms is at the heart of
current implementations of quantum simulations, quantum computing, and
long-distance quantum communication. Controlling the motion of larger particles
opens up yet new avenues for quantum science, both for the study of fundamental
quantum phenomena in the context of matter wave interference, and for new
sensing and transduction applications in the context of quantum optomechanics.
Specifically, it has been suggested that cavity cooling of a single
nanoparticle in high vacuum allows for the generation of quantum states of
motion in a room-temperature environment as well as for unprecedented force
sensitivity. Here, we take the first steps into this regime. We demonstrate
cavity cooling of an optically levitated nanoparticle consisting of
approximately 10e9 atoms. The particle is trapped at modest vacuum levels of a
few millibar in the standing-wave field of an optical cavity and is cooled
through coherent scattering into the modes of the same cavity. We estimate that
our cooling rates are sufficient for ground-state cooling, provided that
optical trapping at a vacuum level of 10e-7 millibar can be realized in the
future, e.g., by employing additional active-feedback schemes to stabilize the
optical trap in three dimensions. This paves the way for a new light-matter
interface enabling room-temperature quantum experiments with mesoscopic
mechanical systems.Comment: 14 pages, 6 figure
Non-destructive Three-dimensional Imaging of Artificially Degraded CdS Paints by Pump-probe Microscopy
Cadmium sulfide (CdS) pigments have degraded in several well-known paintings,
but the mechanisms of degradation have yet to be fully understood. Traditional
non-destructive analysis techniques primarily focus on macroscopic degradation,
whereas microscopic information is typically obtained with invasive techniques
that require sample removal. Here, we demonstrate the use of pump-probe
microscopy to nondestructively visualize the three-dimensional structure and
degradation progress of CdS pigments in oil paints. CdS pigments, reproduced
following historical synthesis methods, were artificially aged by exposure to
high relative humidity (RH) and ultraviolet (UV) light. Pump-probe microscopy
was applied to track the degradation progress in single grains, and volumetric
imaging revealed early CdS degradation of small particles and on the surface of
large particles. This indicates that the particle dimension influences the
extent and evolution of degradation of historical CdS. In addition, the
pump-probe signal decrease in degraded CdS is observable before visible changes
to the eye, demonstrating that pump-probe microscopy is a promising tool to
detect early-stage degradation in artworks. The observed degradation by
pump-probe microscopy occurred through the conversion from CdS into CdSO4.xH2O,
verified by both FTIR (Fourier-transform infrared) and XPS (X-ray photoelectron
spectroscopy) experiment
Nonequilibrium control of thermal and mechanical changes in a levitated system
Fluctuation theorems are fundamental extensions of the second law of
thermodynamics for small nonequilibrium systems. While work and heat are
equally important forms of energy exchange, fluctuation relations have not been
experimentally assessed for the generic situation of simultaneous mechanical
and thermal changes. Thermal driving is indeed generally slow and more
difficult to realize than mechanical driving. We here use feedback cooling
techniques to implement fast and controlled temperature variations of an
underdamped levitated microparticle that are one order of magnitude faster than
the equilibration time. Combining mechanical and thermal control, we verify the
validity of a fluctuation theorem that accounts for both contributions, well
beyond the range of linear response theory. Our system allows the investigation
of general far-from-equilibrium processes in microscopic systems that involve
fast mechanical and thermal changes at the same time
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