Search results for "Spline"

ANALISI GIS E MODELLI STATISTICI PER LA VALUTAZIONE DELLA SUSCETTIBILITÀ DA FRANA A SCALA DI BACINO: IL CASO STUDIO DEL BACINO DEL TORRENTE MARVELLO

Lo studio condotto nel presente lavoro di tesi ha affrontato il tema della valutazione, a scala di bacino idrografico, della suscettibilità ai fenomeni di tipo colamento, attraverso l’applicazione di modelli statistici e tecniche di analisi spaziale GIS. La fase iniziale della preparazione di un modello di suscettibilità da frana prevede la realizzazione di un inventario degli eventi verificatesi nell’area di studio. Questo passo è di fondamentale importanza, considerando che proprio attraverso l’archivio frane è possibile analizzare ed individuare le condizioni che in passato hanno favorito l’innesco dei movimenti di versante. L’identificazione di queste condizioni, infatti, consente di pr…

Functional principal component analysis of quantile curves

2017

Literature on functional data analysis is mainly focused on estimation of individuals curves and characterization of average dynamics. The idea underlying this proposal is to focus attention on other particular features of the distribution of the observed data, moving from mean functions towards functional quantiles. The motivating examples are functional data sets that are collections of high frequency data recorded along time. As quantiles provide information on various aspects of a time series, we propose a modelling framework for the joint estimation of functional quantiles, varying along time, and functional principal components, summarizing some common dynamics shared by the functiona…

A comparison of different methods for speleothem age modelling

2012

Abstract Speleothems, such as stalagmites and flowstones, can be dated with unprecedented precision in the range of the last 650,000 a by the 230Th/U-method, which is considered as one of their major advantages as climate archives. However, a standard approach for the construction of speleothem age models and the estimation of the corresponding uncertainty has not been established yet. Here we apply five age modelling approaches ( StalAge , OxCal, a finite positive growth rate model and two spline-based models) to a synthetic speleothem growth model and two natural samples. All data sets contain problematic features such as outliers, age inversions, large and abrupt changes in growth rate a…

Growth curves of sorghum roots via quantile regression with P-splines

2014

Plant roots are a major pool of total carbon in the planet and their dynamics are directly relevant to greenhouse gas balance. Composted wastes are increasingly used in agriculture for environmental and economic reasons and their role as a substitute for traditional fertilizers needs to be tested on all plant components. Here we propose a regression quantile approach based on P-splines to assess, quantify and compare the root growth patterns in two treatment groups respectively undergoing compost and traditional fertilization.

Fast Computation by Subdivision of Multidimensional Splines and Their Applications

2016

We present theory and algorithms for fast explicit computations of uni- and multi-dimensional periodic splines of arbitrary order at triadic rational points and of splines of even order at diadic rational points. The algorithms use the forward and the inverse Fast Fourier transform (FFT). The implementation is as fast as FFT computation. The algorithms are based on binary and ternary subdivision of splines. Interpolating and smoothing splines are used for a sample rate convertor such as resolution upsampling of discrete-time signals and digital images and restoration of decimated images that were contaminated by noise. The performance of the rate conversion based spline is compared with the…

ON SOME GENERALIZATION OF SMOOTHING PROBLEMS

2015

The paper deals with the generalized smoothing problem in abstract Hilbert spaces. This generalized problem involves particular cases such as the interpolating problem, the smoothing problem with weights, the smoothing problem with obstacles, the problem on splines in convex sets and others. The theorem on the existence and characterization of a solution of the generalized problem is proved. It is shown how the theorem gives already known theorems in special cases as well as some new results.

Local cubic splines on non-uniform grids and real-time computation of wavelet transform

2017

In this paper, local cubic quasi-interpolating splines on non-uniform grids are described. The splines are designed by fast computational algorithms that utilize the relation between splines and cubic interpolation polynomials. These splines provide an efficient tool for real-time signal processing. As an input, the splines use either clean or noised arbitrarily-spaced samples. Formulas for the spline’s extrapolation beyond the sampling interval are established. Sharp estimations of the approximation errors are presented. The capability to adapt the grid to the structure of an object and to have minimal requirements to the operating memory are of great advantages for offline processing of s…

Automatic detection of lung nodules in CT datasets based on stable 3D mass–spring models

2012

We propose a computer-aided detection (CAD) system which can detect small-sized (from 3 mm) pulmonary nodules in spiral CT scans. A pulmonary nodule is a small lesion in the lungs, round-shaped (parenchymal nodule) or worm-shaped (juxtapleural nodule). Both kinds of lesions have a radio-density greater than lung parenchyma, thus appearing white on the images. Lung nodules might indicate a lung cancer and their early stage detection arguably improves the patient survival rate. CT is considered to be the most accurate imaging modality for nodule detection. However, the large amount of data per examination makes the full analysis difficult, leading to omission of nodules by the radiologist. We…

Snapshot Spectral Imaging

2018

This chapter describes an application of the spline-based wavelet frames to the spectral imaging. It presents a method that enables to convert a regular digital camera into a snapshot spectral imager by equipping the camera with a dispersive diffuser and with a compressed sensing-based algorithm for digital processing. The method relies on the assumption that typical images can be sparsely represented in the frame domain. The solution is found from the constrained \(l_{1}\) minimization of a functional by Bregman iterations. Results of optical experiments are reported. The chapter is based on the paper (Golub et al., Appl. Opt. 55, 432–443, (2016), [11]).

Landslide susceptibility zonation by exploiting GIS tools and two statistical methods: binary logistic regression and multivariate adaptive regressio…

2013

In the recent years advanced statistical methods and GIS tools have been frequently used to assess landslide susceptibility. The latter is estimated by establishing statistical relationships between landscape characteristics and spatial distribution of past slope-failures. These are mapped mainly by recognizing changes on slope morphology produced by gravity. Despite of this, most of the researches on landslide susceptibility do not consider that slope-failures modify topography and associate high probability of landsliding with topographic characteristics that differ from those that led slope-failures. In this research we analyzed landslide susceptibility in the basin of the Malvello river…