11,884 research outputs found
Rethinking the Effective Sample Size
The effective sample size (ESS) is widely used in sample-based simulation
methods for assessing the quality of a Monte Carlo approximation of a given
distribution and of related integrals. In this paper, we revisit and complete
the approximation of the ESS in the specific context of importance sampling
(IS). The derivation of this approximation, that we will denote as
, is only partially available in Kong [1992]. This
approximation has been widely used in the last 25 years due to its simplicity
as a practical rule of thumb in a wide variety of importance sampling methods.
However, we show that the multiple assumptions and approximations in the
derivation of , makes it difficult to be considered even
as a reasonable approximation of the ESS. We extend the discussion of the ESS
in the multiple importance sampling (MIS) setting, and we display numerical
examples. This paper does not cover the use of ESS for MCMC algorithms
The solution space of metabolic networks: producibility, robustness and fluctuations
Flux analysis is a class of constraint-based approaches to the study of
biochemical reaction networks: they are based on determining the reaction flux
configurations compatible with given stoichiometric and thermodynamic
constraints. One of its main areas of application is the study of cellular
metabolic networks. We briefly and selectively review the main approaches to
this problem and then, building on recent work, we provide a characterization
of the productive capabilities of the metabolic network of the bacterium E.coli
in a specified growth medium in terms of the producible biochemical species.
While a robust and physiologically meaningful production profile clearly
emerges (including biomass components, biomass products, waste etc.), the
underlying constraints still allow for significant fluctuations even in key
metabolites like ATP and, as a consequence, apparently lay the ground for very
different growth scenarios.Comment: 10 pages, prepared for the Proceedings of the International Workshop
on Statistical-Mechanical Informatics, March 7-10, 2010, Kyoto, Japa
Neural Mechanisms Underlying Paradoxical Performance for Monetary Incentives Are Driven by Loss Aversion
Employers often make payment contingent on
performance in order to motivate workers. We used
fMRI with a novel incentivized skill task to examine
the neural processes underlying behavioral responses
to performance-based pay. We found that
individuals’ performance increased with increasing
incentives; however, very high incentive levels led
to the paradoxical consequence of worse performance.
Between initial incentive presentation and
task execution, striatal activity rapidly switched
between activation and deactivation in response
to increasing incentives. Critically, decrements in
performance and striatal deactivations were directly
predicted by an independent measure of behavioral
loss aversion. These results suggest that incentives
associated with successful task performance are
initially encoded as a potential gain; however, when
actually performing a task, individuals encode the
potential loss that would arise from failure
LoCuSS: Hydrostatic Mass Measurements of the High- Cluster Sample -- Cross-calibration of Chandra and XMM-Newton
We present a consistent analysis of Chandra and XMM-Newton observations of an
approximately mass-selected sample of 50 galaxy clusters at -- the
"LoCuSS High- Sample". We apply the same analysis methods to data from
both satellites, including newly developed analytic background models that
predict the spatial variation of the Chandra and XMM-Newton backgrounds to
and precision respectively. To verify the cross-calibration of
Chandra and XMM-Newton-based cluster mass measurements, we derive the mass
profiles of the 21 clusters that have been observed with both satellites,
extracting surface brightness and temperature profiles from identical regions
of the respective datasets. We obtain consistent results for the gas and total
hydrostatic cluster masses: the average ratio of Chandra- to XMM-Newton-based
measurements of and at are and
, respectively with an intrinsic scatter of for gas
masses and for hydrostatic masses. Comparison of our hydrostatic mass
measurements at with the latest LoCuSS weak-lensing results indicate
that the data are consistent with non-thermal pressure support at this radius
of . We also investigate the scaling relation between our hydrostatic
cluster masses and published integrated Compton parameter
measurements from the Sunyaev-Zel'dovich Array. We measure a scatter in mass at
fixed of at , which is consistent with
theoretical predictions of scatter.Comment: 21 pages, 11 figure
Integrating geomechanical surveys and remote sensing for sea cliff slope stability analysis: the Mt. Pucci case study (Italy)
Abstract. An integrated approach to the geomechanical characterization of coastal sea cliffs was applied at Mt. Pucci (Gargano promontory, Southern Italy) by performing field-based geomechanical investigations and remote geostructural investigations via a terrestrial laser scanner (TLS). The consistency of the integrated techniques allowed to achieve a comprehensive and affordable characterization of the main joint sets on the sea cliff slope. The observed joint sets were considered to evaluate the proneness of the slope to rock failures by attributing safety factor (SF) values to the topple- and wedge-prone rock blocks under three combined or independent triggering conditions: (a) hydrostatic water pressures within the joints, (b) seismic action, and (c) strength reduction due to weathering of the joint surfaces. The combined action of weathering and water pressures within the joints was also considered, resulting in a significant decrease in the stability. Furthermore, remote survey analyses via InfraRed Thermography (IRT) and Ground Based Synthetic Aperture Radar Interferometry (GBInSAR) were performed to evaluate the role of the surveyed joint sets in inducing instabilities in the Mt. Pucci sea cliff. The results from the remote surveys: (i) GBInSAR monitoring revealed permanent displacements coupled to cyclic daily displacements, these last ones detected in certain sectors of the cliff wall; (ii) the thermal images allowed us to identify anomalies that correspond well to the main joints and to the slope material released due to recent collapses
The role of the carbohydrates in plasmatic membrane.
In the following paper, authors describe glycans present on cell membranes as they affect the folding, the spatial arrangement, the behavior and the interaction with the substrate of some membrane proteins. Authors describe the synthesis and assembly of a glycan on a protein, the formation of N-glycans, the maturation of an N-glycan in different cellular compartments, the structure of the glycocalyx and how it interacts with any pathogens. The study of the E-cadherin and the potassium channel to demonstrate how glycans affect the spatial arrangement, the stability and activity of the glycoproteins on the membranes. Subsequently, authors analyze the correlation between disorder glycosylation and human health. Authors define glycosylation disorders as a genetic defect that alter the structure or biosynthesis of glycans (sugar chains) in one or more biosynthetic pathways. Human glycosylation disorders reflect the disruption of early steps in the pathways of glycan biosynthesis. More in details, authors analyze the role of glycoprotein in tumor cell adhesion, in particular, in cells MCF-7 and MDA-MB-231 on zeolite scaffold. In the same time, the role of metalloproteinase is described in the mobilization of cancer cells and in metastasis
HT Camelopardalis: The simplest intermediate polar spin pulse
The intermediate polar HT Cam is unusual in that it shows no evidence for
dense absorption in its spectrum. We analyse an XMM-Newton observation of this
star, which confirms the absence of absorption and shows that the X-ray
spin-pulse is energy independent. The modulation arises solely from occultation
effects and can be reproduced by a simple geometrical model in which the lower
accretion footprint is fainter than the upper one.
We suggest that the lack of opacity in the accretion columns of HT Cam, and
also of EX Hya and V1025 Cen, results from a low accretion rate owing to their
being below the cataclysmic variable period gap.Comment: 5 pages, 6 figures, accepted for publication in MNRA
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