Search results for "selection"
showing 10 items of 1940 documents
NATURAL SELECTION AND THE ORGAN-SPECIFIC DIFFERENTIATION OF HIV-1 V3 HYPERVARIABLE REGION
2004
The existence of organ-specific HIV-1 populations within infected hosts has been studied for many years; nonetheless results reported by different authors are somewhat discrepant. To tackle this problem, we used a population genetics approach to analyze previously published data from the V3 hypervariable region of the envelope env gene. Our results are compatible with a population subdivision by organs in 95% of individuals analyzed at autopsy. In addition, populations infecting the nervous system and testicles clearly appear as differentiated subsets of the so-called macrophage-tropic variants. Liver and kidney may harbor differentiated populations as well. Although it is widely accepted t…
The fitness effects of synonymous mutations in DNA and RNA viruses.
2011
Despite being silent with respect to protein sequence, synonymous nucleotide substitutions can be targeted by natural selection directly at the DNA or RNA level. However, there has been no systematic assessment of how frequent this type of selection is. Here, we have constructed 53 single random synonymous substitution mutants of the bacteriophages Qb and UX174 by site-directed mutagenesis and assayed their fitness. Analysis of this mutant collection and of previous studies undertaken with a variety of single-stranded (ss) viruses demonstrates that selection at synonymous sites is stronger in RNA viruses than in DNA viruses. We estimate that this type of selection contributes approximately …
Propagation pattern analysis during atrial fibrillation based on sparse modeling.
2012
In this study, sparse modeling is introduced for the estimation of propagation patterns in intracardiac atrial fibrillation (AF) signals. The estimation is based on the partial directed coherence function, derived from fitting a multivariate autoregressive model to the observed signal using least-squares (LS) estimation. The propagation pattern analysis incorporates prior information on sparse coupling as well as the distance between the recording sites. Two optimization methods are employed for estimation of the model parameters, namely, the adaptive group least absolute selection and shrinkage operator (aLASSO), and a novel method named the distance-adaptive group LASSO (dLASSO). Using si…
Notice of Violation of IEEE Publication Principles<BR>An adaptive routing mechanism for P2P resource discovery
2005
The key to the usability of large-scale decentralize peer-to-peer (P2P) systems, and one of the most challenge design aspects, is efficient mechanism for distributed resource discovery. Unstructured P2P networks are very attractive because they do not suffer the limitations of centralized systems an the drawbacks of highly structured approaches. However the search algorithms are usually based on simple flooding scheme generating large loads on the network participants. In this paper to address this major limitation, we present the design an evaluation of an innovative searching protocol in unstructured P2P networks. The approach aims at dynamically adapting the network topology to peers' in…
Deployment of the ATLAS High-Level Trigger
2006
The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS High-Level Trigger (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests with the full detector in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.
Site selection for the new generation of giant neutrino detectors
2012
The main findings of the LAGUNA Design Study are briefly discussed. Construction of giant underground detectors is technically feasible at several sites. Physics factors will dominate in the site selection.
isotracer: An R package for the analysis of tracer addition experiments
2021
AbstractTracer addition experiments, particularly using isotopic tracers, are becoming increasingly important in a variety of studies aiming at characterizing the flows of molecules or nutrients at different levels of biological organization, from the cellular and tissue levels, to the organismal and ecosystem levels.We present an approach based on Hidden Markov Models (HMM) to estimate nutrient flow parameters across a network, and its implementation in the R package isotracer.The isotracer package is capable of handling a variety of tracer study designs, including continuous tracer drips, pulse experiments, and pulse-chase experiments. It can also take into account tracer decay when radio…
How social network sites and other online intermediaries increase exposure to news
2020
Research has prominently assumed that social media and web portals that aggregate news restrict the diversity of content that users are exposed to by tailoring news diets toward the users’ preferences. In our empirical test of this argument, we apply a random-effects within–between model to two large representative datasets of individual web browsing histories. This approach allows us to better encapsulate the effects of social media and other intermediaries on news exposure. We find strong evidence that intermediaries foster more varied online news diets. The results call into question fears about the vanishing potential for incidental news exposure in digital media environments.
Sex Loss in Monogonont Rotifers
2009
Monogonont rotifers are small, aquatic invertebrates capable of asexual and sexual reproduction. Sexual reproduction is required to produce diapausing eggs, which are able to survive adverse periods that typically occur every year. Their cyclically parthenogenetic life-cycle is believed to retain the advantages of recombination while minimizing the cost of sex. However, this life cycle is also thought to be unstable due to periodic loss of sexual reproduction by directional selection. Explaining the evolutionary dynamics of the monogonont rotifer life cycle is important for understanding how cyclical parthenogenesis is maintained, and for comparing monogononts with their close relatives, th…
Selection Correction in Panel Data Models: An Application to Labour Supply and Wages
2000
In recent years a number of panel estimators have been suggested for sample selection models, where both the selection equation and the equation of interest contain individual effects which are correlated with the explanatory variables. We review and compare some of these estimators, and apply them to estimating the return to actual labour market experience for females, using a panel of twelve years. All these estimators rely on the assumption of strict exogeneity of regressors in the equation of interest, conditional on individual specific effects and the selection mechanism. This assumption is likely to be violated in many applications. Also, life history variables are often measured with…