Santos da Silva

Learn More
We describe a user study comparing a low cost VR system using a Head-Mounted-Display (HMD) to a desktop and another setup where the image is projected on a screen. Eighteen participants played the same game in the three platforms. Results show that users generally did not like the setup using a screen and the best performances were obtained with the desktop(More)
In this note we identify and illustrate some shortcomings of the poisson command in STATA. Specifically, we point out that the command fails to check for the existence of the estimates and show that it is very sensitive to numerical problems. While these are serious problems that may prevent users from obtaining estimates, or even produce spurious and(More)
Understanding and quantifying the determinants of the number of sectors or firms exporting in a given country is of relevance for the assessment of trade policies. Estimation of models for the number of sectors, however, poses a challenge because the dependent variable has both a lower and upper bound, implying that the partial effects of the explanatory(More)
We show that the quantile regression estimator is consistent and asymptotically normal when the error terms are correlated within clusters but independent across clusters. A consistent estimator of the covariance matrix of the asymptotic distribution is provided and we propose a specification test capable of detecting the presence of intra-cluster(More)
This paper describes a methodology for using neural networks in an inverse heat conduction problem. Three neural network (NN) models are used to determine the initial temperature profile on a slab with adiabatic boundary condition, given a transient temperature distribution at a given time. This is an ill-posed 1D parabolic inverse problem, where the(More)
This paper presents a comparison among mesh simplification methods performed through quality indices and a controlled experiment involving 32 observers. The simplification methods: OpenMesh, OpenMesh with a normal flipping criterion and QSlim, were compared at two simplification levels: 50% and 20% of the original number of faces. Results obtained using the(More)
The purpose of this study was to verify the effect of the microwave disinfection in denture base acrylic resins with Candida sp biofilm formation. Samples (n=90) of each resin were submitted to ethylene oxide sterilization, and then infected by inoculum of yeast (C. albicans, C. tropicalis and C. dubliniensis) with 200 μL of cultures adjusted to 108 CFU/mL,(More)
Godfrey (1996, Journal of Econometrics 72, 275}299) has shown that the Glejser test for heteroskedasticity is valid only under conditional symmetry. Here, modi"cations of the Glejser test are suggested. The proposed test statistics are asymptotically valid even when the disturbances are not symmetrically distributed and can be used to test for(More)