14,725 research outputs found
Convergence of adaptive mixtures of importance sampling schemes
In the design of efficient simulation algorithms, one is often beset with a
poor choice of proposal distributions. Although the performance of a given
simulation kernel can clarify a posteriori how adequate this kernel is for the
problem at hand, a permanent on-line modification of kernels causes concerns
about the validity of the resulting algorithm. While the issue is most often
intractable for MCMC algorithms, the equivalent version for importance sampling
algorithms can be validated quite precisely. We derive sufficient convergence
conditions for adaptive mixtures of population Monte Carlo algorithms and show
that Rao--Blackwellized versions asymptotically achieve an optimum in terms of
a Kullback divergence criterion, while more rudimentary versions do not benefit
from repeated updating.Comment: Published at http://dx.doi.org/10.1214/009053606000001154 in the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification
We report on the optical spectroscopic analysis of a sample of 99
low-luminosity quasi-stellar objects (LLQSOs) at base the
Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility
of studying the faint end of the QSO population at smaller cosmological
distances and, therefore, in greater detail. A small number of our LLQSO
present no broad component. Two sources show double broad components, whereas
six comply with the classic NLS1 requirements. As expected in NLR of broad line
AGNs, the [S{\sc{ii}}]based electron density values range between 100 and
1000 N/cm. Using the optical characteristics of Populations A and
B, we find that 50\% of our sources with H broad emission are consistent
with the radio-quiet sources definition. The remaining sources could be
interpreted as low-luminosity radio-loud quasar. The BPT-based classification
renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources,
the possible star burst contribution might control the LINER and HII
classification. Finally, we discuss the aperture effect as responsible for the
differences found between data sets, although variability in the BLR could play
a significant role as well.Comment: 22 pages; 5 tables; 17 figures; in press with A&
Entropy of vortex cores on the border of the superconductor-to-insulator transition in an underdoped cuprate
We present a study of Nernst effect in underdoped in
magnetic fields as high as 28T. At high fields, a sizeable Nernst signal was
found to persist in presence of a field-induced non-metallic resistivity. By
simultaneously measuring resistivity and the Nernst coefficient, we extract the
entropy of vortex cores in the vicinity of this field-induced
superconductor-insulator transition. Moreover, the temperature dependence of
the thermo-electric Hall angle provides strong constraints on the possible
origins of the finite Nernst signal above , as recently discovered by Xu
et al.Comment: 5 Pages inculding 4 figure
Exploiting the layer-by-layer nanoarchitectonics for the fabrication of polymer capsules : A toolbox to provide multifunctional properties to target complex pathologies
Polymer capsules fabricated via the layer-by-layer (LbL) approach have attracted a great deal of attention for biomedical applications thanks to their tunable architecture. Compared to alternative methods, in which the precise control over the final properties of the systems is usually limited, the intrinsic versatility of the LbL approach allows the functionalization of all the constituents of the polymeric capsules following relatively simple protocols. In fact, the final properties of the capsules can be adjusted from the inner cavity to the outer layer through the polymeric shell, resulting in therapeutic, diagnostic, or theranostic (i.e., combination of therapeutic and diagnostic) agents that can be adapted to the particular characteristics of the patient and face the challenges encountered in complex pathologies. The biomedical industry demands novel biomaterials capable of targeting several mechanisms and/or cellular pathways simultaneously while being tracked by minimally invasive tech-niques, thus highlighting the need to shift from monofunctional to multifunctional polymer capsules. In the present review, those strategies that permit the advanced functionalization of polymer capsules are accordingly introduced. Each of the constituents of the capsule (i.e., cavity, multilayer membrane and outer layer) is thor-oughly analyzed and a final overview of the combination of all the strategies toward the fabrication of multi-functional capsules is presented. Special emphasis is given to the potential biomedical applications of these multifunctional capsules, including particular examples of the performed in vitro and in vivo validation studies. Finally, the challenges in the fabrication process and the future perspective for their safe translation into the clinic are summarized.Peer reviewe
Corrigendum: Initiating Change of People With Criminal Justice Involvement Through Participation in a Drama Project: An Exploratory Study
Author proofs are not yet ready for revisio
Parallel transport modeling of linear divertor simulators with fundamental ion cyclotron heating
The Material Plasma Exposure eXperiment (MPEX) is a steady state linear
device with the goal to perform plasma material interaction (PMI) studies at
future fusion reactor relevant conditions. A prototype of MPEX referred as
Porto-MPEX is designed to carry out research and development related to source,
heating and transport concepts on the planned full MPEX device. The auxiliary
heating schemes in MPEX are based on cyclotron resonance heating with radio
frequency (RF) waves. Ion cyclotron heating (ICH) and electron cyclotron
heating (ECH) in MPEX are used to independently heat the ions and electrons and
provide fusion divertor conditions ranging from sheath-limited to fully
detached divertor regimes at a material target. A Hybrid Particle-In-Cell code-
PICOS++ is developed and applied to understand the plasma parallel transport
during ICH heating in MPEX Proto-MPEX to the target. With this tool, evolution
of the distribution function of MPEX/Proto-MPEX ions is modeled in the presence
of (1) Coulomb collisions, (2) volumetric particle sources and (3) quasi-linear
RF-based ICH. The code is benchmarked against experimental data from Proto-MPEX
and simulation data from B2.5 EIRENE. The experimental observation of
density-drop near the target in Proto-MPEX and MPEX during ICH heating is
demonstrated and explained via physics-based arguments using PICOS++ modeling.
In fact, the density drops at the target during ICH in Proto-MPEX/MPEX to
conserve the flux and to compensate for the increased flow during ICH.
Furthermore, sensitivity scans of various plasma parameters with respect to ICH
power are performed for MPEX to investigate its role on plasma transport and
particle and energy fluxes at the target. Finally, we discuss the pathway to
model ECH in MPEX using the Hybrid PIC formulation herein presented for kinetic
electrons and fluid ions
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