Teaching elliptical excision skills to novice medical students: a randomized controlled study comparing low- and high-fidelity bench models

Background: The search for alternative and effective forms of training simulation is needed due to ethical and medico-legal aspects involved in training surgical skills on living patients, human cadavers and living animals. Aims : To evaluate if the bench model fidelity interferes in the acquisition of elliptical excision skills by novice medical students. Materials and Methods: Forty novice medical students were randomly assigned to 5 practice conditions with instructor-directed elliptical excision skills' training (n = 8): didactic materials (control); organic bench model (low-fidelity); ethylene-vinyl acetate bench model (low-fidelity); chicken legs' skin bench model (high-fidelity); or pig foot skin bench model (high-fidelity). Pre- and post-tests were applied. Global rating scale, effect size, and self-perceived confidence based on Likert scale were used to evaluate all elliptical excision performances. Results : The analysis showed that after training, the students practicing on bench models had better performance based on Global rating scale (all P < 0.0000) and felt more confident to perform elliptical excision skills (all P < 0.0000) when compared to the control. There was no significant difference (all P > 0.05) between the groups that trained on bench models. The magnitude of the effect (basic cutaneous surgery skills' training) was considered large (>0.80) in all measurements. Conclusion : The acquisition of elliptical excision skills after instructor-directed training on low-fidelity bench models was similar to the training on high-fidelity bench models; and there was a more substantial increase in elliptical excision performances of students that trained on all simulators compared to the learning on didactic materials.

Assessment of variance components in nonlinear mixed-effects elliptical models

The issue of assessing variance components is essential in deciding on the inclusion of random effects in the context of mixed models. In this work we discuss this problem by supposing nonlinear elliptical models for correlated data by using the score-type test proposed in Silvapulle and Silvapulle (1995). Being asymptotically equivalent to the likelihood ratio test and only requiring the estimation under the null hypothesis, this test provides a fairly easy computable alternative for assessing one-sided hypotheses in the context of the marginal model. Taking into account the possible non-normal distribution, we assume that the joint distribution of the response variable and the random effects lies in the elliptical class, which includes light-tailed and heavy-tailed distributions such as Student-t, power exponential, logistic, generalized Student-t, generalized logistic, contaminated normal, and the normal itself, among others. We compare the sensitivity of the score-type test under normal, Student-t and power exponential models for the kinetics data set discussed in Vonesh and Carter (1992) and fitted using the model presented in Russo et al. (2009). Also, a simulation study is performed to analyze the consequences of the kurtosis misspecification.

Influence diagnostics in heteroscedastic and/or autoregressive nonlinear elliptical models for correlated data

In this paper, we propose nonlinear elliptical models for correlated data with heteroscedastic and/or autoregressive structures. Our aim is to extend the models proposed by Russo et al. [22] by considering a more sophisticated scale structure to deal with variations in data dispersion and/or a possible autocorrelation among measurements taken throughout the same experimental unit. Moreover, to avoid the possible influence of outlying observations or to take into account the non-normal symmetric tails of the data, we assume elliptical contours for the joint distribution of random effects and errors, which allows us to attribute different weights to the observations. We propose an iterative algorithm to obtain the maximum-likelihood estimates for the parameters and derive the local influence curvatures for some specific perturbation schemes. The motivation for this work comes from a pharmacokinetic indomethacin data set, which was analysed previously by Bocheng and Xuping [1] under normality.

Influence diagnostics for elliptical semiparametric mixed models

In this paper we extend semiparametric mixed linear models with normal errors to elliptical errors in order to permit distributions with heavier and lighter tails than the normal ones. Penalized likelihood equations are applied to derive the maximum penalized likelihood estimates (MPLEs) which appear to be robust against outlying observations in the sense of the Mahalanobis distance. A reweighed iterative process based on the back-fitting method is proposed for the parameter estimation and the local influence curvatures are derived under some usual perturbation schemes to study the sensitivity of the MPLEs. Two motivating examples preliminarily analyzed under normal errors are reanalyzed considering some appropriate elliptical errors. The local influence approach is used to compare the sensitivity of the model estimates.

Experimental study on Carbon FRP-confined elliptical concrete columns

It is well recognized that the technique of strengthening reinforced concrete (RC) using fiber-reinforced polymer (FRP) jackets is more effective for circular sections, but less effective for rectangular sections. Indeed the presence of angular corners does not permit a uniform confinement to be provided by the FRP jackets to the columns. While rounded corners can enhance the effectiveness of FRP confinement, it will be more efficient to modify the rectangular section into an elliptical section. In addition to the better confinement effectiveness, from an aesthetical point of view, the shape modification would be a surprise to the built environment. This paper presents an experimental study on the behavior of FRP-confined concrete columns with elliptical section. Thirty-two short columns, divided in eight batches, were tested under axial compression. Each batch presents four specimens with different elliptical sections, determined by the aspect ratio a/b, that is the ratio between the minor and mayor axis. By varying this value from 1.0 to 2.0 (1.0, 1.3., 1.7, 2.0), the section becomes more and more elliptical starting from a circular shape. In this way it is possible to study the trend of effectiveness of FRP confinement for different section geometries. It is also interesting to study how the confinement effectiveness may vary by changing the cylinder strength of concrete and the number of the layers of CFRP. For this reason, a cylinder strength of concrete of 25 and 45 MPa have been used for the present research work, and half of the specimens were wrapped by one layer of CFRP, while the remaining specimens were wrapped with two layers. A simple analysis of the results has been carried out for evaluating the experimental work described in the present document. Further studies and analysis on this work should help to achieve a new and more accurate stress-strain model for CFRP-confined concrete columns with an elliptical section.

Dynamical properties and mass-luminosity relation of elliptical galaxies

In questo elaborato abbiamo analizzato un campione di 22 galssie early-type. Utilizzando una tecnica di cross-correlazione, abbiamo ottenuto profili radiali di rotazione e di dis- persione di velocitá. Questi dati ci hanno permesso di investigare molte delle proprietá dinamiche delle nostre galassie. Abbiamo ottenuto indizi sull’anisotropia orbitale e stimato le masse e il rapporto M/L del campione. Le masse misurate variano da 1010 a 1012 M , mentre i valori degli M/L, per cui abbiamo trovato una dipendenza del tipo Log M/L ∝ 0.28 Log L , sono dell’ordine dell’unitá. Abbiamo anche riprodotto le famose relazioni di scala e abbi- amo utlizzato un set di dati sugli indici di Lick/IDS per ricercare relazioni tra le proprietá chimiche e quelle dinamiche. In particolare, abbiamo riscontrato una correlazione tra molti degli indici dipendenti dalla metallicitá e la profonditá della buca di potenziale. Tali indici sembrano correlare anche con il M/L. La rotazione e la forma del profilo di dispersione di velocitá sembrano essere ininfluenti sulle proprietá chimiche. In ultima analisi, abbiamo considerato le implicazioni delle nostre misure riguardo la natura della popolazione stellare e dell’emissione X delle nostre galassie. L’indice di colore e il M/L sembrano indicare che la popolazione stellare delle nostre galassie é dominata da stelle appartenenti alle classi spettrali late-G e early-K. Sembra inoltre esserci una correlazione tra l’emissione X degli elementi del nostro campione e la profonditá della loro buca di potenziale.

Origin of cold gas and dust in massive elliptical galaxies

The recent availability of multi-wavelength data revealed the presence of large reservoirs of warm and cold gas and dust in the innermost regions of the majority of massive elliptical galaxies. To prove an internal origin of cold and warm gas, the investigation of the spatially distributed cooling process which occurs because of non-linear density perturbations and subsequent thermal instabilities is of crucial importance. The first goal of this work of thesis is to investigate the internal origin of warm and cold phases. Numerical simulations are the powerful tool of analysis. The way in which a spatially distributed cooling process originates has been examined and the off-centre amount of gas mass which cools when different and differently characterized AGN feedback mechanisms operate has been quantified. This thesis demonstrates that the aforementioned non-linear density perturbations originate and develop from AGN feedback mechanisms in a natural fashion. An internal origin of the warm phase from the once hot gas is shown to be possible. Computed velocity dispersions of ionized and hot gas are similar. The cold gas as well can originate from the cooling process: indeed, it has been estimated that the surrounding stellar radiation, which is one of the most feasible sources of ionization of the warm gas, does not manage to keep ionized all the gas at 10^4 K. Therefore, cooled gas does undergo a further cooling which can lead the warm phase to lower temperatures. However, the gas which has cooled from the hot phase is expected to be dustless; nonetheless, a large fraction of early type galaxies has detectable dust in their cores, both concentrated in filamentary and disky structures and spread over larger regions. Therefore a regularly rotating disk of cold and dusty gas has been included in the simulations. A new quantitative investigation of the spatially distributed cooling process has therefore been essential: the contribution of the included amount of dust which is embedded in the cold gas does have a role in promoting and enhancing the cooling. The fate of dust which was at first embedded in cold gas has been investigated. The role of AGN feedback mechanisms in dragging (if able) cold and dusty gas from the core of massive ellipticals up to large radii has been studied.

Main characteristics of the emission from elliptical galaxies

Elliptical galaxies are one of the most characteristic objects we can find in the sky. In order to unveil their properties, such as their structure or chemical composition, one must study their spectral emission. In fact they seem to behave rather differently when observed with different eyes. This is because their light is mainly brought by two different components: optical radiation arises from its stars, while the X emission is primarly due to a halo of extremely hot gas in which ellipticals seem to be embedded. After a brief classification, the two main processes linked to these phenomena will be described, together with the informations we can collect thanks to them. Eventually, we will take a quick look at the other regions of the electromagnetic spectrum.