356 research outputs found
Generalized Fluctuation-Dissipation Relation and Effective Temperature upon Heating a Deeply Supercooled Liquid
We show that a generalized fluctuation-dissipation relation applies upon
instantaneously increasing the temperature of a deeply supercooled liquid. This
has the same two-step shape of the relation found upon cooling the liquid, but
with opposite violation, indicating an effective temperature that is lower than
bath temperature. We show that the effective temperature exhibits some sensible
time-dependence and that it retains its connection with the partitioned phase
space visited in ageing. We underline the potential relevance of our numerical
results for experimental studies of the fluctuation-dissipation relation in
glassy systems.Comment: 5 pages, 4 figure
Space Time MUSIC: Consistent Signal Subspace Estimation for Wide-band Sensor Arrays
Wide-band Direction of Arrival (DOA) estimation with sensor arrays is an
essential task in sonar, radar, acoustics, biomedical and multimedia
applications. Many state of the art wide-band DOA estimators coherently process
frequency binned array outputs by approximate Maximum Likelihood, Weighted
Subspace Fitting or focusing techniques. This paper shows that bin signals
obtained by filter-bank approaches do not obey the finite rank narrow-band
array model, because spectral leakage and the change of the array response with
frequency within the bin create \emph{ghost sources} dependent on the
particular realization of the source process. Therefore, existing DOA
estimators based on binning cannot claim consistency even with the perfect
knowledge of the array response. In this work, a more realistic array model
with a finite length of the sensor impulse responses is assumed, which still
has finite rank under a space-time formulation. It is shown that signal
subspaces at arbitrary frequencies can be consistently recovered under mild
conditions by applying MUSIC-type (ST-MUSIC) estimators to the dominant
eigenvectors of the wide-band space-time sensor cross-correlation matrix. A
novel Maximum Likelihood based ST-MUSIC subspace estimate is developed in order
to recover consistency. The number of sources active at each frequency are
estimated by Information Theoretic Criteria. The sample ST-MUSIC subspaces can
be fed to any subspace fitting DOA estimator at single or multiple frequencies.
Simulations confirm that the new technique clearly outperforms binning
approaches at sufficiently high signal to noise ratio, when model mismatches
exceed the noise floor.Comment: 15 pages, 10 figures. Accepted in a revised form by the IEEE Trans.
on Signal Processing on 12 February 1918. @IEEE201
Donor/Acceptor Heterojunction Organic Solar Cells
The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF ≈ 50%, an external quantum efficiency (electrons/s over incident photons/s) EQE ≈ 5% and a power conversion efficiency of about 0.5%. Measurements of the photoelectrical characteristics with time are also reported, confirming that non encapsulated organic solar cells have limited stability in ambient atmosphere
Interface Energy in the Edwards-Anderson model
We numerically investigate the spin glass energy interface problem in three
dimensions. We analyze the energy cost of changing the overlap from -1 to +1 at
one boundary of two coupled systems (in the other boundary the overlap is kept
fixed to +1). We implement a parallel tempering algorithm that simulate finite
temperature systems and work with both cubic lattices and parallelepiped with
fixed aspect ratio. We find results consistent with a lower critical dimension
. The results show a good agreement with the mean field theory
predictions.Comment: 5 pages; 7 figures; corrected typos; to appear in JS
Optimization of Parallel Computations on Heterogeneous GPU-Based Systems
In this master thesis, we design and implement MultiStream: a solution that extends the existing data parallel skeleton library SkePU with NVIDIA CUDA Streams to overlap main memory – device memory data transfers with CUDA Kernel executions.
We show the benefits of this approach using a task-parallel framework, FastFlow, on-top of SkePU.
Finally, we compare the MultiStream extended SkePU to an ad-hoc solution to discuss the tradeoffs between the level of abstraction and the maximum achievable performance
Claude Calame, Mythe et histoire dans l’Antiquité grecque. La création symbolique d’une colonie
https://scholarlycommons.pacific.edu/pacific-review/1134/thumbnail.jp
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