Nuevos esquemas para el procesado de señales tensoriales = New schemes for tensor signal processing

Programa doctorado: Cibernética y Telecomunicación (2002/2004)

Diffusivity and enzymatic activity control the exchange of carbonyl sulfide (COS) between soils and the atmosphere

Carbonylsulfid (COS) ist eines der stabilsten reduzierten schwefelhaltigen Spurengase in der Atmosphäre. In der gut durchmischten Troposphäre bewegt sich seine Konzentration um 500 ppt. COS spielt eine wichtige Rolle in der Produktion von stratosphärischem Aerosol und im Ozon Zyklus. Dieses Spurengas hat eine Vielfalt an natürlichen und anthropogenen Quellen, denen gleichstarke Senken, darunter die dominanten wie Vegetation und Boden, gegenüber stehen. Die Stärke der Senken ist trotz langjähriger Forschungen immer noch Gegenstand der Diskussionen. Daher ist es wichtig die kontrollierenden Parameter zu charakterisieren. Alle Austauschmessungen vor 1990 vermuteten Böden als Quelle von COS, was aber durch Castro and Galloway (1991) klar widerlegt wurde. Heute werden Böden in Ergänzung zur Vegetation grundsätzlich als Senke betrachtet. Vor diesem Hintergrund wurden Bodenproben auf den Austausch von Carbonylsulfid mit der Atmosphäre unter verschiedenen Umgebungsbedingungen untersucht. Drei Ackerböden aus Deutschland, China und Finnland und zwei Waldböden aus Sibirien und Surinam konnten parametrisiert werden in Relation zur atmosphärischen Umgebungskonzentration, Temperatur und Bodenfeuchte (WC). Neben Umgebungskonzentration und Bodenfeuchte, scheinen Bodenstruktur und enzymatische Aktivität die Richtung und Größe des Austauschflusses zu kontrollieren. Die übereinstimmenden Optima für boreale Böden in Relation zum wassergefüllten Porenvolumen des Bodens (WFPS) und die Linearität zwischen Depositionsgeschwindigkeit (Vd) und Bulk density lassen auf eine Dominanz der Abhängigkeit der COS-Aufnahme von der durch WFPS bestimmten Diffusionsfähigkeit schließen. WFPS ist abhängig von WC, Bodenstruktur und Bodenporosität. In Ergänzung zu diesen eher physikalischen Parametern konnte die Carboanhydrase (CA) als kontrollierendes Enzym in Böden identifiziert werden. Erste Versuche zur direkten Bestimmung der CA in den untersuchten Böden erlaubten eine erste, aber noch sehr ungenaue Abschätzung der Enzymaktivität.

Cosmological predictions for a scalar tensor dark energy model by a dedicated Einstein-Boltzmann code

We have extended the Boltzmann code CLASS and studied a specific scalar tensor dark energy model: Induced Gravity

Black hole evaporation and stress tensor correlations

General Relativity is one of the greatest scientific achievementes of the 20th century along with quantum theory. These two theories are extremely beautiful and they are well verified by experiments, but they are apparently incompatible. Hints towards understanding these problems can be derived studying Black Holes, some the most puzzling solutions of General Relativity. The main topic of this Master Thesis is the study of Black Holes, in particular the Physics of Hawking Radiation. After a short review of General Relativity, I study in detail the Schwarzschild solution with particular emphasis on the coordinates systems used and the mathematical proof of the classical laws of Black Hole "Thermodynamics". Then I introduce the theory of Quantum Fields in Curved Spacetime, from Bogolubov transformations to the Schwinger-De Witt expansion, useful for the renormalization of the stress energy tensor. After that I introduce a 2D model of gravitational collapse to study the Hawking radiation phenomenon. Particular emphasis is given to the analysis of the quantum states, from correlations to the physical implication of this quantum effect (e.g. Information Paradox, Black Hole Thermodynamics). Then I introduce the renormalized stress energy tensor. Using the Schwinger-De Witt expansion I renormalize this object and I compute it analytically in the various quantum states of interest. Moreover, I study the correlations between these objects. They are interesting because they are linked to the Hawking radiation experimental search in acoustic Black Hole models. In particular I find that there is a characteristic peak in correlations between points inside and outside the Black Hole region, which correpsonds to entangled excitations inside and outside the Black Hole. These peaks hopefully will be measurable soon in supersonic BEC.

Solubility, diffusivity and permeability of gases in glassy polymers

Gas separation membranes of high CO2 permeability and selectivity have great potential in both natural gas sweetening and carbon dioxide capture. Many modified PIM membranes results permselectivity above Robinson upper bound. The big problem that should be solved for these polymers to be commercialized is their aging through time. In high glassy polymeric membrane such as PIM-1 and its modifications, solubility selectivity has more contribution towards permselectivity than diffusivity selectivity. So in this thesis work pure and mixed gas sorption behavior of carbon dioxide and methane in three PIM-based membranes (PIM-1, TZPIM-1 and AO-PIM-1) and Polynonene membrane is rigorously studied. Sorption experiment is performed at different temperatures and molar fraction. Sorption isotherms found from the experiment shows that there is a decrease of solubility as the temperature of the experiment increases for both gases in all polymers. There is also a decrease of solubility due to the presence of the other gas in the system in the mixed gas experiments due to competitive sorption effect. Variation of solubility is more visible in methane sorption than carbon dioxide, which will make the mixed gas solubility selectivity higher than that of pure gas solubility selectivity. Modeling of the system using NELF and Dual mode sorption model estimates the experimental results correctly Sorption of gases in heat treated and untreated membranes show that the sorption isotherms don’t vary due to the application of heat treatment for both carbon dioxide and methane. But there is decrease in the diffusivity coefficient and permeability of pure gases due to heat treatment. Both diffusivity coefficient and permeability decreases with increasing of heat treatment temperature. Diffusivity coefficient calculated from transient sorption experiment and steady state permeability experiment is also compared in this thesis work. The results reveal that transient diffusivity coefficient is higher than steady state diffusivity selectivity.

Machine Learning applicato al Web Semantico: Statistical Relational Learning vs Tensor Factorization

Obiettivo della tesi è analizzare e testare i principali approcci di Machine Learning applicabili in contesti semantici, partendo da algoritmi di Statistical Relational Learning, quali Relational Probability Trees, Relational Bayesian Classifiers e Relational Dependency Networks, per poi passare ad approcci basati su fattorizzazione tensori, in particolare CANDECOMP/PARAFAC, Tucker e RESCAL.

String inflationary models with non-monotonic slow-roll and detectable tensor modes

The first chapter of this work has the aim to provide a brief overview of the history of our Universe, in the context of string theory and considering inflation as its possible application to cosmological problems. We then discuss type IIB string compactifications, introducing the study of the inflaton, a scalar field candidated to describe the inflation theory. The Large Volume Scenario (LVS) is studied in the second chapter paying particular attention to the stabilisation of the Kähler moduli which are four-dimensional gravitationally coupled scalar fields which parameterise the size of the extra dimensions. Moduli stabilisation is the process through which these particles acquire a mass and can become promising inflaton candidates. The third chapter is devoted to the study of Fibre Inflation which is an interesting inflationary model derived within the context of LVS compactifications. The fourth chapter tries to extend the zone of slow-roll of the scalar potential by taking larger values of the field φ. Everything is done with the purpose of studying in detail deviations of the cosmological observables, which can better reproduce current experimental data. Finally, we present a slight modification of Fibre Inflation based on a different compactification manifold. This new model produces larger tensor modes with a spectral index in good agreement with the date released in February 2015 by the Planck satellite.

Eye movement and diffusion tensor imaging analysis of treatment effects in a Niemann-Pick Type C patient

New treatment options for Niemann-Pick Type C (NPC) have recently become available. To assess the efficiency and efficacy of these new treatment markers for disease status and progression are needed. Both the diagnosis and the monitoring of disease progression are challenging and mostly rely on clinical impression and functional testing of horizontal eye movements. Diffusion tensor imaging (DTI) provides information about the microintegrity especially of white matter. We show here in a case report how DTI and measures derived from this imaging method can serve as adjunct quantitative markers for disease management in Niemann-Pick Type C. Two approaches are taken--first, we compare the fractional anisotropy (FA) in the white matter globally between a 29-year-old NPC patient and 18 healthy age-matched controls and show the remarkable difference in FA relatively early in the course of the disease. Second, a voxelwise comparison of FA values reveals where white matter integrity is compromised locally and demonstrate an individualized analysis of FA changes before and after 1year of treatment with Miglustat. This method might be useful in future treatment trials for NPC to assess treatment effects.

Forensic application of postmortem diffusion-weighted and diffusion tensor MR imaging of the human brain in situ

DWI and DTI of the brain have proved to be useful in many neurologic disorders and in traumatic brain injury. This prospective study aimed at the evaluation of the influence of the PMI and the cause of death on the ADC and FA for the application of DWI and DTI in forensic radiology.

Groups Acting on Tensor Products

Groups preserving a distributive product are encountered often in algebra. Examples include automorphism groups of associative and nonassociative rings, classical groups, and automorphism groups of p-groups. While the great variety of such products precludes any realistic hope of describing the general structure of the groups that preserve them, it is reasonable to expect that insight may be gained from an examination of the universal distributive products: tensor products. We give a detailed description of the groups preserving tensor products over semisimple and semiprimary rings, and present effective algorithms to construct generators for these groups. We also discuss applications of our methods to algorithmic problems for which all currently known methods require an exponential amount of work. (C) 2013 Elsevier B.V. All rights reserved.

Diffusion tensor imaging in episodic cluster headache

Cluster headache (CH) is a rare headache disorder with severe unilateral headache bouts and autonomic symptoms. The pathophysiology of CH is not completely understood. Using a voxel-based morphometric paradigm or functional imaging, a key role of the hypothalamus and the pain matrix could be demonstrated during CH episodes. However, there are no diffusion tensor imaging (DTI) data investigating the white matter microstructure of the brain in patients with CH. Therefore, we used DTI to delineate microstructural changes in patients with CH in a headache-free state.

Optic radiation fiber tracking using anteriorly angulated diffusion tensor imaging: a tested algorithm for quick application

Fiber tracking (FT) of the optic pathways (OPs) is difficult because there is no standard for the parameters of diffusion tensor imaging (DTI), placement of seed volumes, or interpreting the results.

Cortico-cortical white matter motor pathway microstructure is related to psychomotor retardation in major depressive disorder

Alterations of brain structure and function have been associated with psychomotor retardation in major depressive disorder (MDD). However, the association of motor behaviour and white matter integrity of motor pathways in MDD is unclear. The aim of the present study was to first investigate structural connectivity of white matter motor pathways in MDD. Second, we explore the relation of objectively measured motor activity and white matter integrity of motor pathways in MDD. Therefore, 21 patients with MDD and 21 healthy controls matched for age, gender, education and body mass index underwent diffusion tensor imaging and 24 hour actigraphy (measure of the activity level) the same day. Applying a probabilistic fibre tracking approach we extracted connection pathways between the dorsolateral prefrontal cortex (dlPFC), the rostral anterior cingulate cortex (rACC), the pre-supplementary motor area (pre-SMA), the SMA-proper, the primary motor cortex (M1), the caudate nucleus, the putamen, the pallidum and the thalamus. Patients had lower activity levels and demonstrated increased mean diffusivity (MD) in pathways linking left pre-SMA and SMA-proper, and right SMA-proper and M1. Exploratory analyses point to a positive association of activity level and mean-fractional anisotropy in the right rACC-pre-SMA connection in MDD. Only MDD patients with low activity levels had a negative linear association of activity level and mean-MD in the left dlPFC-pre-SMA connection. Our results point to structural alterations of cortico-cortical white matter motor pathways in MDD. Altered white matter organisation of rACC-pre-SMA and dlPFC-pre-SMA pathways may contribute to movement initiation in MDD.

Spinal Cord Diffusion-Tensor Imaging and Motor-evoked Potentials in Multiple Sclerosis Patients: Microstructural and Functional Asymmetry

Purpose: To assess possible association between intrinsic structural damage and clinical disability by correlating spinal cord diffusion-tensor (DT) imaging data with electrophysiological parameters in patients with a diagnosis of multiple sclerosis (MS). Materials and Methods: This study was approved by the local ethical committee according to the declaration of Helsinki and written informed consent was obtained. DT images and T1- and T2-weighted images of the spinal cord were acquired in 28 healthy volunteers and 41 MS patients. Fractional anisotropy (FA) and apparent diffusion coefficients were evaluated in normal-appearing white matter (NAWM) at the cervical level and were correlated with motor-evoked potentials (n = 34). Asymmetry index was calculated for FA values with corresponding left and right regions of interest as percentage of the absolute difference between these values relative to the sum of the respective FA values. Statistical analysis included Spearman rank correlations, Mann-Whitney test, and reliability analysis. Results: Healthy volunteers had low asymmetry index (1.5%-2.2%). In MS patients, structural abnormalities were reflected by asymmetric decrease of FA (asymmetry index: 3.6%; P = .15). Frequently asymmetrically affected among MS patients was left and right central motor conduction time (CMCT) to abductor digiti minimi muscle (ADMM) (asymmetry index, 15%-16%) and tibialis anterior muscle (TAM) (asymmetry index, 9.5%-14.1%). Statistically significant correlations of functional (ie, electrophysiological) and structural (ie, DT imaging) asymmetries were found (P = .005 for CMCT to ADMM; P = .007 for CMCT to TAM) for the cervical lateral funiculi, which comprise the crossed pyramidal tract. Interobserver reliability for DT imaging measurements was excellent (78%-87%). Conclusion: DT imaging revealed asymmetric anatomic changes in spinal cord NAWM, which corresponded to asymmetric electrophysiological deficits for both arms and legs, and reflected a specific structure-function relationship in the human spinal cord. © RSNA, 2013.

Examining the gateway to the limbic system with diffusion tensor imaging: the perforant pathway in dementia

Current treatments for Alzheimer's disease (AD) are only able to slow the progression of mental deterioration, making early and reliable diagnosis an essential part of any promising therapeutic strategy. In the initial stages of AD, the first neuropathological alterations occur in the perforant pathway (PP), a large neuronal fiber tract located at the entrance to the limbic system. However, to date, there is no sensitive diagnostic tool for performing in vivo assessments of this structure. In the present bimodal magnetic resonance imaging (MRI) study, we examined 10 elderly controls, 10 subjects suffering from mild cognitive impairment (MCI), and 10 AD patients in order to evaluate the sensitivity of diffusion tensor imaging (DTI), a new MRI technique, for detecting changes in the PP. Furthermore, the diagnostic explanatory power of DTI data of the PP should be compared to high-resolution MRI volumetry and intervoxel coherences (COH) of the hippocampus and the entorhinal cortex, two limbic regions also involved in the pathophysiology of early AD. DTI revealed a marked decrease in COH values in the PP region of MCI (right side: 26%, left side: 29%, as compared to controls) and AD patients (right side: 37%, left side: 43%, as compared to controls). Reductions in COH values of the PP region were significantly correlated with cognitive impairment. DTI data of the PP zone were the only parameter differing significantly between control subjects and MCI patients, while the volumetric measures and the COH values of the hippocampus and the entorhinal cortex did not. DTI of medial temporal brain regions is a promising non-invasive tool for the in vivo diagnosis of the early/preclinical stages of AD.