1,354,361 research outputs found
Estimation of the treatment effect variance in a difference-in-differences framework
No full textWe compare two regression-based estimators of treatment/policy effects in a standard difference-in-differences setting without additional covariates. These two estimators, deriving from what we term the piled and unpiled regression models, produce identical finite-sample estimates, thus sharing the same theoretical variance. However, they are not equivalent with regard to the estimation of such a variance. We show that under the assumed model the piled approach should be preferred
since it results in a more efficient variance estimator, thereby returning more reliable standard errors for the treatment effect. We further show that this result holds even when the normality assumption for the regression error terms is violated
Amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD)
No full textThere is increasing clinical, imaging and neurophatological evidence that Amyotrophic lateral sclerosis (ALS) represents a multisystem neurodegenerative disease. Neurodegeneration is not restricted to motor neurons, but also includes parts of the brain other than the motor cortex, especially the prefrontal and/or anterior temporal lobe, that contribute to the clinical syndrome. In some cases an evident dementia that resembles frontotemporal degeneration (FTD) was observed. It is now suggested that ALS and FTD are closely related conditions with overlapping clinical, pathological, radiological, and genetic characteristics. The presence of a frontal dementia in ALS has also crucial practical consequences for management of the patients, whose disorder requires critical life decisions for enteral nutrition and respiratory complications. It is our intent to provide a brief overview of the relationships between ALS and FTD
Mediation analysis with case–control sampling : identification and estimation in the presence of a binary mediator
No full textWith reference to a stratified case–control (CC) procedure based on a binary variable of primary interest, we derive the expression of the distortion induced by the sampling design on the parameters of the logistic model of a secondary variable. This is particularly relevant when performing mediation analysis (possibly in a causal framework) with stratified case–control (SCC) data in settings where both the outcome and the mediator are binary. Despite being designed for parametric identification, our strategy is general and can be used also in a nonparametric context. With reference to parametric estimation, we derive the maximum likelihood (ML) estimator and the M-estimator of the joint outcome–mediator parameter vector. We then conduct a simulation study focusing on the main causal mediation quantities (i.e., natural effects) and comparing M- and ML estimation to existing methods, based on weighting. As an illustrative example, we reanalyze a German CC data set in order to investigate whether the effect of reduced immunocompetency on listeriosis onset is mediated by the intake of gastric acid suppressors
Missing Data: A Unified Taxonomy Guided by Conditional Independence
No full textRecent work (Seaman et al., 2013; Mealli & Rubin, 2015) attempts to clarify the not always well-understood difference between realised and everywhere definitions of missing at random (MAR) and missing completely at random. Another branch of the literature (Mohan et al., 2013; Pearl & Mohan, 2013) exploits always-observed covariates to give variable-based definitions of MAR and missing completely at random. In this paper, we develop a unified taxonomy encompassing all approaches. In this taxonomy, the new concept of ‘complementary MAR’ is introduced, and its relationship with the concept of data observed at random is discussed. All relationships among these definitions are analysed and represented graphically. Conditional independence, both at the random variable and at the event level, is the formal language we adopt to connect all these definitions. Our paper covers both the univariate and the multivariate case, where attention is paid to monotone missingness and to the concept of sequential MAR. Specifically, for monotone missingness, we propose a sequential MAR definition that might be more appropriate than both everywhere and variable-based MAR to model dropout in certain contexts
Statistical assessment of public health care services: a multilevel Markov model
No full textIn this work, a multilevel Latent Markov model is proposed to study the evolution of the health status of elderly patients hosted in different nursing homes. A dataset is considered which is gathered from the Long Term Care Facilities programme, a longitudinal study carried on in Umbria (Italy). The data at hand cover the years 2012 and 2013. The final goal of our analysis is to rank the nursing homes according to their performance in retaining patients in the best health conditions. Our results show significantly different nursing home performances
Experimental investigation into two-phase flow patterns inside a herringbone microfin tube
No full textDuring in-tube microfinned enhanced tubes show a heat transfer enhancement, as compared to
equivalent smooth tubes under the same operating conditions, that is partly due to the mere increase
in the effective exchange area and additionally to the turbulence induced in the liquid film by the
micro fins and to the surface tension effect on the liquid drainage.
Furthermore there is agreement in the literature that the mechanisms of heat transfer and pressure
drop are intimately linked with the prevailing two-phase flow regime.
In the recent open literature evidence is given to the effect of fins orientation on flow patterns in
herringbone tubes (Miyara et al., 2003). In particular, at the same operating conditions, it was
pointed out that when the fins convergences are positioned at the top and bottom of the tube
(dubbed here as Position-I), the occurring flow pattern can be completely different from the tube
arrangement with the fins convergences at both sides (Position-II). In a previous paper by the
present authors, the “Position-II” arrangement was investigated with three different refrigerants for
a saturation temperature of 40°C and mass velocities 100÷800 kg m-2s-1. In this paper the “Position-
I” arrangement is now investigated for the fluid R134a and a comparison with the available
visualization data for “Position-II” is presented.
In order to investigate the two phase flow pattern during condensation a specific test section was
built up. For the study of the main flow patterns, in particular focusing on the stratified/annular
mode transition, the visualisation experimental data are analysed with reference to the
dimensionless vapour velocity and the Martinelli parameter
An EKF-based observer for sensorless valve control in camless internal combustion engine
No full textCamless internal combustion engines offer improvements over traditional engines in terms of torque performance reduction of emissions, reduction of pumping losses, fuel economy. Theoretically, electromagnetic valve actuators offer the highest potentials for improving efficiency due to their control flexibility. Sensorless control is one of the most important issues with regard to real implementation of this new technology. This paper proposes an observer based on an extended Kalman filter to realize a sensorless control. Current is measured while position as well as velocity of the electromagnetic valve are estimated. Real data from a valve actuator prototype are used to show the effectiveness of the proposed method
Il Codice Rosa: un nuovo modello di presa in carico per le vittime di violenza. L'esperienza in Toscana
No full textThe dimension of gender-based violence is a phenomenon which, unfortunately, still does not emerge in its real extent: despite the great attention paid on at international and national levels, the available data are still partial and insufficient, due to different reasons: data are largely “submerged” and it is difficult to compare data and studies because they are not exhaustive enough. In this perspective the great work of local anti-violence networks, institutions and associations that have multiplied their efforts, tried to give tangible answers to needs, offering new ways of providing services. For these motivations, the role played in the healthcare system by the “Codice Rosa” model is particularly important. It is necessary to mention the experience of this model in the Tuscany Region, which has set itself the goal of a serious and effective fight against gender violence and has realized a new model for taking care of victims. Through the “Percorso Donna Codice Rosa”, this network activates a specific, direct and punctual intervention within the Emergency Department, which is then developed in a coordinated manner through the various local networks.La violenza di genere è un fenomeno la cui dimensione effettiva purtroppo ancora non emerge nella sua reale entità: nonostante la grande attenzione su di essa a livello internazionale e nazionale i dati disponibili risultano essere ancora parziali a causa sia di un ampio “sommerso”, sia per la difficoltà nel comparare dati e studi poco esaustivi. In questa ottica si inserisce il grande lavoro delle reti locali antiviolenza, delle istituzioni e delle associazioni che hanno moltiplicato i loro sforzi cercando di dare risposte concrete ai bisogni e offrendo nuove modalità di erogazione dei servizi. Di particolare rilevanza è il ruolo svolto sul versante sanitario dal modello “Codice Rosa” che, partendo dall’esperienza nella Regione Toscana, si è posto l’obiettivo di un serio ed efficace contrasto alla violenza di genere e come nuovo modello di presa in carico delle vittime. Tale rete attraverso il “Percorso Donna Codice Rosa” attiva un intervento specifico, diretto e tempestivo all’interno dei Pronto Soccorso, che si sviluppa poi in maniera coordinata attraverso le varie reti territoriali. 
Optimal trajectory generation for camless internal combustion engine valve control
No full textCamless internal combustion engines offer improvements over traditional engines in terms of torque performance, reduction of emissions, reduction of pumping losses and fuel economy. Theoretically, electromagnetic valve actuators offer the highest potentials for improving efficiency due to their control flexibility. For real applications, however, the valve actuators developed so far suffer from high power consumption and other control problems. One key point for the control is the design of the reference trajectory to be tracked by the closed loop controller. In this paper an optimal trajectory design technique aimed at minimizing power consumption is proposed. An optimization problem that explicitly considers the physical constraints of the system is formulated and a suboptimal solution is derived by exploiting local flatness of the system
Nanoparticulate Deposition During Cu-Water Nanofluid Pool Boiling on Roughened Copper Surfaces
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