Bianchi type II cosmology in Hořava–Lifshitz gravity

In this work a Bianchi type II space-time within the framework of projectable Horava Lifshitz gravity was investigated; the resulting field equations in the infrared limit λ = 1 were analyzed qualitatively. We have found the analytical solutions for a toy model in which only the higher curvature terms cubic in the spatial Ricci tensor are considered. The resulting behavior is still described by a transition among two Kasner epochs, but we have found a different transformation law of the Kasner exponents with respect to the one of Einstein's general relativity.

Percezione depth guidata mediante proiezione virtuale di pattern

L’utilizzo di informazioni di profondità è oggi di fondamentale utilità per molteplici settori applicativi come la robotica, la guida autonoma o assistita, la realtà aumentata e il monitoraggio ambientale. I sensori di profondità disponibili possono essere divisi in attivi e passivi, dove i sensori passivi ricavano le informazioni di profondità dall'ambiente senza emettere segnali, bensì utilizzando i segnali provenienti dall'ambiente (e.g., luce solare). Nei sensori depth passivi stereo è richiesto un algoritmo per elaborare le immagini delle due camere: la tecnica di stereo matching viene utilizzata appunto per stimare la profondità di una scena. Di recente la ricerca si è occupata anche della sinergia con sensori attivi al fine di migliorare la stima della depth ottenuta da un sensore stereo: si utilizzano i punti affidabili generati dal sensore attivo per guidare l'algoritmo di stereo matching verso la soluzione corretta. In questa tesi si è deciso di affrontare questa tematica da un punto di vista nuovo, utilizzando un sistema di proiezione virtuale di punti corrispondenti in immagini stereo: i pixel delle immagini vengono alterati per guidare l'algoritmo ottimizzando i costi. Un altro vantaggio della strategia proposta è la possibilità di iterare il processo, andando a cambiare il pattern in ogni passo: aggregando i passi in un unico risultato, è possibile migliorare il risultato finale. I punti affidabili sono ottenuti mediante sensori attivi (e.g. LiDAR, ToF), oppure direttamente dalle immagini, stimando la confidenza delle mappe prodotte dal medesimo sistema stereo: la confidenza permette di classificare la bontà di un punto fornito dall'algoritmo di matching. Nel corso della tesi sono stati utilizzati sensori attivi per verificare l'efficacia della proiezione virtuale, ma sono state anche effettuate analisi sulle misure di confidenza: lo scopo è verificare se le misure di confidenza possono rimpiazzare o assistere i sensori attivi.

A Phase Space Box-counting based Method for Arrhythmia Prediction from Electrocardiogram Time Series

Arrhythmia is one kind of cardiovascular diseases that give rise to the number of deaths and potentially yields immedicable danger. Arrhythmia is a life threatening condition originating from disorganized propagation of electrical signals in heart resulting in desynchronization among different chambers of the heart. Fundamentally, the synchronization process means that the phase relationship of electrical activities between the chambers remains coherent, maintaining a constant phase difference over time. If desynchronization occurs due to arrhythmia, the coherent phase relationship breaks down resulting in chaotic rhythm affecting the regular pumping mechanism of heart. This phenomenon was explored by using the phase space reconstruction technique which is a standard analysis technique of time series data generated from nonlinear dynamical system. In this project a novel index is presented for predicting the onset of ventricular arrhythmias. Analysis of continuously captured long-term ECG data recordings was conducted up to the onset of arrhythmia by the phase space reconstruction method, obtaining 2-dimensional images, analysed by the box counting method. The method was tested using the ECG data set of three different kinds including normal (NR), Ventricular Tachycardia (VT), Ventricular Fibrillation (VF), extracted from the Physionet ECG database. Statistical measures like mean (μ), standard deviation (σ) and coefficient of variation (σ/μ) for the box-counting in phase space diagrams are derived for a sliding window of 10 beats of ECG signal. From the results of these statistical analyses, a threshold was derived as an upper bound of Coefficient of Variation (CV) for box-counting of ECG phase portraits which is capable of reliably predicting the impeding arrhythmia long before its actual occurrence. As future work of research, it was planned to validate this prediction tool over a wider population of patients affected by different kind of arrhythmia, like atrial fibrillation, bundle and brunch block, and set different thresholds for them, in order to confirm its clinical applicability.

Ecological distribution of semi-demersal fishes in space and time on the shelf of Antalya Gulf

In this study we provide a baseline data on semidemersal fish assemblages and biology in a heterogeneous and yet less studied portion of the shelf of Antalya Gulf. The distribution of fish abundance in three transects subjected to different fisheries regulations (fishery vs non fishery areas), and including depths of 10, 25, 75, 125, 200 m, was studied between May 2014 and February 2015 in representative months of winter, spring, summer and autumn seasons. A total of 76 fish species belonging to 40 families was collected and semidemersal species distribution was analyzed in comparison with the whole community. Spatial distribution of fish was driven mainly by depth and two main assemblages were observed: shallow waters (10-25; 75 m) and deep waters (125-200 m). Significant differences among transects were found for the whole community but not for the semidemersal species. Analysis showed that this was due to a strong relation of these species with local environmental characteristics rather than to a different fishing pressure over transects. Firstly all species distribute according to the bathymetrical gradient and secondly to the bottom type structure. Semidemersal species were then found more related to zooplankton and suspended matter availability. The main morphological characteristics, sex and size distribution of the target semidemersal species Spicara smaris (Linnaeus, 1758), Saurida undosquamis (Richardson, 1848), Pagellus acarne (Risso, 1827) were also investigated.