52,581 research outputs found
On the equivalence of Lambda(t) and gravitationally induced particle production cosmologies
The correspondence between cosmological models powered by a decaying vacuum
energy density and gravitationally induced particle production is investigated.
Although being physically different in the physics behind them we show that
both classes of cosmologies under certain conditions can exhibit the same
dynamic and thermodynamic behavior. Our method is applied to obtain three
specific models that may be described either as Lambda(t)CDM or gravitationally
induced particle creation cosmologies. In the point of view of particle
production models, the later class of cosmologies can be interpreted as a kind
of one-component unification of the dark sector. By using current type Ia
supernovae data, recent estimates of the cosmic microwave background shift
parameter and baryon acoustic oscillations measurements we also perform a
statistical analysis to test the observational viability within the two
equivalent classes of models and we obtain the best-fit of the free parameters.
By adopting the Akaike information criterion we also determine the rank of the
models considered here. Finally, the particle production cosmologies (and the
associated decaying Lambda(t)-models) are modeled in the framework of field
theory by a phenomenological scalar field model.Comment: 9 pages, 3 figures, new comments and 8 references added. Accepted for
publication in Physics Letters
Mass, angular-momentum, and charge inequalities for axisymmetric initial data
We present the key elements of the proof of an upper bound for
angular-momentum and charge in terms of the mass for electro-vacuum
asymptotically flat axisymmetric initial data sets with simply connected orbit
space
Coleman meets Schwinger
It is well known that spherical D-branes are nucleated in the presence of an
external RR electric field. Using the description of D-branes as solitons of
the tachyon field on non-BPS D-branes, we show that the brane nucleation
process can be seen as the decay of the tachyon false vacuum. This process can
describe the decay of flux-branes in string theory or the decay of quintessence
potentials arising in flux compactifications.Comment: 5 pages, 2 figure
Insetos daninhos a cultura do tomateiro (Lycopersicon esculentum, Mill) na Transamazônica - Pará.
bitstream/item/57570/1/Altamira-ComTec1.pd
Avaliação regional de cultivares de caupi de porte ereto e ramador na Transamazônica-Pará.
bitstream/item/61326/1/Altamira-CirTec5.pd
Predicting Intermediate Storage Performance for Workflow Applications
Configuring a storage system to better serve an application is a challenging
task complicated by a multidimensional, discrete configuration space and the
high cost of space exploration (e.g., by running the application with different
storage configurations). To enable selecting the best configuration in a
reasonable time, we design an end-to-end performance prediction mechanism that
estimates the turn-around time of an application using storage system under a
given configuration. This approach focuses on a generic object-based storage
system design, supports exploring the impact of optimizations targeting
workflow applications (e.g., various data placement schemes) in addition to
other, more traditional, configuration knobs (e.g., stripe size or replication
level), and models the system operation at data-chunk and control message
level.
This paper presents our experience to date with designing and using this
prediction mechanism. We evaluate this mechanism using micro- as well as
synthetic benchmarks mimicking real workflow applications, and a real
application.. A preliminary evaluation shows that we are on a good track to
meet our objectives: it can scale to model a workflow application run on an
entire cluster while offering an over 200x speedup factor (normalized by
resource) compared to running the actual application, and can achieve, in the
limited number of scenarios we study, a prediction accuracy that enables
identifying the best storage system configuration
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