1,707 research outputs found
Weighted norm inequalities for polynomial expansions associated to some measures with mass points
Fourier series in orthogonal polynomials with respect to a measure on
are studied when is a linear combination of a generalized Jacobi
weight and finitely many Dirac deltas in . We prove some weighted norm
inequalities for the partial sum operators , their maximal operator
and the commutator , where denotes the operator of pointwise
multiplication by b \in \BMO. We also prove some norm inequalities for
when is a sum of a Laguerre weight on and a positive mass on
Multiple imputation approach for interval-censored time to HIV RNA viral rebound within a mixed effects Cox model
This is the peer reviewed version of the following article: âAlarcĂłn-Soto, Y, Langohr K., FehĂ©r, C., GarcĂa, F., and GĂłmez, G. (2018) Multiple imputation approach for interval-censored time to HIV RNA viral rebound within a mixed effects Cox Model.Biometrical journal, December 13th âwhich has been published in final form at [doi: 10.1002/bimj.201700291]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.We present a method to fit a mixed effects Cox model with interval-censored data. Our proposal is based on a multiple imputation approach that uses the truncated Weibull distribution to replace the interval-censored data by imputed survival times and then uses established mixed effects Cox methods for right-censored data. Interval-censored data were encountered in a database corresponding to a recompilation of retrospective data from eight analytical treatment interruption (ATI) studies in 158 human immunodeficiency virus (HIV) positive combination antiretroviral treatment (cART) suppressed individuals. The main variable of interest is the time to viral rebound, which is defined as the increase of serum viral load (VL) to detectable levels in a patient with previously undetectable VL, as a consequence of the interruption of cART. Another aspect of interest of the analysis is to consider the fact that the data come from different studies based on different grounds and that we have several assessments on the same patient. In order to handle this extra variability, we frame the problem into a mixed effects Cox model that considers a random intercept per subject as well as correlated random intercept and slope for pre-cART VL per study. Our procedure has been implemented in R using two packages: truncdist and coxme, and can be applied to any data set that presents both interval-censored survival times and a grouped data structure that could be treated as a random effect in a regression model. The properties of the parameter estimators obtained with our proposed method are addressed through a simulation study.Peer ReviewedPostprint (author's final draft
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Placebo Tests for Causal Inference
Placebo tests are increasingly common in applied social science research, but the methodological literature has not previously offered a comprehensive account of what we learn from them. We define placebo tests as tools for assessing the plausibility of the assumptions underlying a research design relative to some departure from those assumptions. We offer a typology of tests defined by the aspect of the research design that is altered to produce it (outcome, treatment, or population) and the type of assumption that is tested (bias assumptions or distributional assumptions). Our formal framework clarifies the extra assumptions necessary for informative placebo tests; these assumptions can be strong, and in some cases similar assumptions would justify a different procedure allowing the researcher to relax the research design's assumptions rather than test them. Properly designed and interpreted, placebo tests can be an important device for assessing the credibility of empirical research designs
Corporate information transparency on the Internet by listed companies in Spain (IBEX35) and Mexico (IPYC)
Financial and non-financial disclosure play a central role in the functioning of capital markets. In this context, the Internet has been adopted as an effective mechanism for large companies to disseminate corporate information. The institutional theory approach has been applied to identify both formal (fundamentally legal and economic) and informal factors that significantly influence listed companiesâ level of corporate transparency on the Internet. Our work aims to build on existing study by focusing on two main objectives. Firstly, to make a comparative study of the corporate transparency of listed companies from Mexico and Spain by creating an index of corporate transparency on the Internet (e-CTI). And secondly, to identify the factors that affect this index using multiple regression analysis. Our study population is comprised of 70 companies, of which 35 belong to the Mexican Price and Quotations Index (IPyC) and 35 to the Spanish IBEX 35 index. The descriptive analysis reveals significant differences in the level of information disclosure between the two countries. The companies listed in Mexico obtain an e-CTI of 59%, while the Spanish ones register 80%, i.e. more importance is assigned to the disclosure of corporate governance data in Spain than in Mexico. Furthermore, this analysis shows that the factors most telling with regards to corporate transparency are the strength and application of law, GDP per capita, inflation and firm-level variables such as ownership concentration and Chairman of the Board-Chief Executive Officer (COB-CEO) duality. However, other variables such as board size and composition, profitability, leverage and firm size are not significant for the purposes of this analysis. Our work is of great relevance today, since most studies have focused on developed countries, mainly in the U.S. and Europe, with few comparisons being made between developed and developing countries, such as Spain and Mexico
Modelling the post-failure stage of rainfall-induced landslides of the flow type
The geomechanical modeling of failure and post failure stages of rainfall induced shallow landslides represents a fundamental issue to properly assess the failure conditions and recognize the potential for long travel distances of the failed soil masses
Footprints of an exhalative smoker activity lithified at the sulfide horizon of Cerdeirinha ore body, Caminha, northern Portugal
Na mina da Cerdeirinha ocorrem minĂ©rios de tungstĂ©nio, que embora relacionĂĄveis com metassomatismo, na sua origem primordial, tiveram a actividade vulcanogĂ©nica SilĂșrica. Existem evidĂȘncias texturais restĂticas e assinaturas mineralĂłgicas e geoquĂmicas que sugerem a importĂąncia de uma descarga metalĂfera, exalativa e primordial. No
Talude Sul da Corta da Cerdeirinha estĂŁo litificados alguns dispositivos estruturais correlacionĂĄveis com anatomias fumarolianas - tubos de sulfato/sulfureto equivalentes a âsmokers pelo menos do ponto de vista funcional - numa transição litolĂłgica entre sulfureto maciço e ârocha verdeâ siliciosa. Aqui, predominam os sulfuretos de Fe, sulfatos de Ca, apatite, anfĂbola e mineralizaçÔes polimetĂĄlicas de W, Fe, As, Bi > (Au), Te, Zn, Cu, Pb. A scheelite Ă© ubĂqua e por vezes num intervalo espacial curto, alterna entre paragĂ©neses formadas em condiçÔes oxidantes, com ilmenite, e
outras formadas em condiçÔes redutoras, com sulfuretos intersticiais. Os critérios adoptados parecem conjugar-se no sentido da identificação de uma interface SEDEX com polaridade exalativa normal.At Cerdeirinha mine, tungsten mineralization, although related to metassomatism, may be considered partially related to Silurian volcanic activity. There are resthitic textures and mineralogical and geochemical signatures suggesting the importance of an initial metal discharge of exhalative type. At the southern slope of Cerdeirinha open pit, several smoker
anatomies are lithified at the lithologic transition between massive sulphide and green silica rock. Iron sulphides are the main constituents plus anhydrite, amphibole and polimetallic mineralization of W, Fe, As, Bi > (Au), Te, Zn, Cu, Pb. Scheelite is ubiquitous, and sometimes, in a narrow space and time interval, its association oscillates between, oxidative
assemblages with typomorphic ilmenite and, reductive assemblages with interstitial sulphides. The adopted criteria are consistent with the definition here of a SEDEX interface with normal exhalative polarity
Acoustoelastic Pure-Displacement Elements Based on Biot's Poromechanics Theory
From the elastic energy contained in a displacement based porous material the general form of the stiffness and mass matrices are obtained. If both fields can be expanded with equal order polynomials the general form is further simplified and it is shown that the coupling stiffness reduces to the one arising to compute volume changes in an elastic medium. A plane beam and a four node tetrahedron are developed. To avoid spurious rotational modes appearance in the tetrahedron fluid a penalty formulation is used. The effect of the penalty factor in matrix conditioning is analysed. Elements dynamic behaviour is compared
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Complete Genomes of Symbiotic Cyanobacteria Clarify the Evolution of Vanadium-Nitrogenase.
Plant endosymbiosis with nitrogen-fixing cyanobacteria has independently evolved in diverse plant lineages, offering a unique window to study the evolution and genetics of plant-microbe interaction. However, very few complete genomes exist for plant cyanobionts, and therefore little is known about their genomic and functional diversity. Here, we present four complete genomes of cyanobacteria isolated from bryophytes. Nanopore long-read sequencing allowed us to obtain circular contigs for all the main chromosomes and most of the plasmids. We found that despite having a low 16S rRNA sequence divergence, the four isolates exhibit considerable genome reorganizations and variation in gene content. Furthermore, three of the four isolates possess genes encoding vanadium (V)-nitrogenase (vnf), which is uncommon among diazotrophs and has not been previously reported in plant cyanobionts. In two cases, the vnf genes were found on plasmids, implying possible plasmid-mediated horizontal gene transfers. Comparative genomic analysis of vnf-containing cyanobacteria further identified a conserved gene cluster. Many genes in this cluster have not been functionally characterized and would be promising candidates for future studies to elucidate V-nitrogenase function and regulation
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