Добірка наукової літератури з теми "Matter models"

I review the construction of simplified models for dark matter searches. After discussing the philosophy and some simple examples, I turn the attention to the aspect of the theoretical consistency and to the implications of the necessary extensions of these models.

Inspired by soliton models, we propose a description of static particles in terms of Riemannian 4-manifolds with self-dual Weyl tensor. For electrically charged particles, the 4-manifolds are non-compact and asymptotically fibred by circles over physical 3-space. This is akin to the Kaluza–Klein description of electromagnetism, except that we exchange the roles of magnetic and electric fields, and only assume the bundle structure asymptotically, away from the core of the particle in question. We identify the Chern class of the circle bundle at infinity with minus the electric charge and, at least provisionally, the signature of the 4-manifold with the baryon number. Electrically neutral particles are described by compact 4-manifolds. We illustrate our approach by studying the Taub–Newman, Unti, Tamburino (Taub–NUT) manifold as a model for the electron, the Atiyah–Hitchin manifold as a model for the proton, with the Fubini–Study metric as a model for the neutron and S 4 with its standard metric as a model for the neutrino.

Revealing the nature of the dark matter is among the most puzzling issues of today particle physics, astrophysics and cosmology. Given the striking evidences for dark matter at all astrophysical scales, starting from galactic and going to cosmological scales, a widespread and well motivated assumption on the nature of the dark matter is that it is made by a new particle that extends the Standard Models of Particle Physics. Indirect detection of dark matter, which annihilates in over-dense regions like the galactic centre, is an important probe of a possible dark matter interaction with the Standard Model particles. It could provide insights both to the underlying production mechanism of dark matter in the early Universe, on the annihilation properties at present time in galactic halos and on the underlying particle physics model. In this master thesis project we will focus on simplified leptophilic models for dark matter. These models feature an massive boson, called for instance Z', and a Dirac dark matter candidate, that complement the Standard Model of particle physics. We will study the annihilation of dark matter into leptons, focusing in particular on neutrino lines and box-shaped energy spectra. These tow signals are smoking gun signature to discover the dark matter properties. We will perform a numerical analysis using the dark matter software MadDM to predict the expected flux from the galactic centre, by performing scans in the model parameter space. We will implement the constrains from the Fermi-LAT telescope and the XENON1T experiment. Finally we will use the predictions of those models to assess the reach of the future KM3NeT neutrino telescope.

Diffusion-weighted MRI (DW-MRI) is a powerful in vivo imaging technique that is particularly sensitive to the underlying microstructure of white matter tissue in the brain. Many models of the DW-MRI signal exist that allow us to relate the signals we measure to various aspects of the tissue structure, including measures of diffusivity, cellularity and even axon size. From histology, we know that many of these microstructure measures display distinct patterns of variation on length scales greater than the average voxel size. However very few methods exist that use this spatial coherence to inform and guide parameter estimation. Instead, most techniques treat each voxel of data independently. This is particularly problematic when estimating parameters such as axon radius which only weakly influence the signal, as the resulting estimates are noisy. Several methods have been proposed that spatially smooth parameter estimates after fitting the model in each voxel. However if the parameter estimates are very noisy, the underlying trend is likely to be obscured. These methods are also unable to account for spatial coupling that may exist between the various parameters. This thesis introduces a novel framework, the Regional Variation Model (RVM), which exploits the underlying spatial coherence within white matter tracts to estimate trends of microstructure variation across large regions of interest. We fit curves describing parameter variation directly to the diffusion-weighted signals which should capture spatial changes in a more natural way as well as reducing the effects of noise. This allows for more precise estimates of a range of microstructure indices, including axon radius. The resulting curves, which show how microstructure parameters vary spatially through white matter regions, can also be used to detect groupwise differences with potentially greater power than traditional methods.

Una enorme quantità di evidenze sperimentali sulla esistenza di una forma di materia non luminosa nell'Universo, si sono accumulate nel corso di circa un secolo. Chiarire la sua natura è diventata una delle sfide più eccitanti ed urgenti negli sforzi per capire il nostro Universo. In questo lavoro presento uno studio su un approccio per scoprire la Materia Oscura interpretata come particella elementare e sulla possibilità di produrla e rilevarla negli acceleratori. Nella parte introduttiva presento una breve storia delle evidenze astrofisiche e astronomiche che hanno portato alla ipotesi della esistenza di Materia Oscura. Assumendo che la Materia Oscura sia costituita da una particella elementare ulteriore a quelle predette dal Modello Standard, delineo poi i tre principali metodi di rilevazione utilizzati attualmente per identificarla. Nella seconda parte discuto come si possono costruire teorie nelle quali sia possibile interpretare le ricerche attuali ed i risultati corrispondenti. Eseguo un confronto tra approcci diversi, partendo da modelli completi fino a quelli che utilizzano teorie di campo effettive. In particolare, discuto i loro lati positivi e negativi, motivando l'utilizzo di uno schema intermedio, il cosiddetto approccio con modelli semplificati, caratterizzati da un numero limitato di nuovi stati e parametri e che supera le limitazioni intrinseche delle teorie effettive nel contesto delle ricerche negli acceleratori. Nell'ultima parte fornisco una esaustiva classificazione dei modelli semplificati nel canale t, che non sono ancora stati analizzati sistematicamente nella letteratura. Per ciascuno di essi presento un possibile completamento UV e i segnali più promettenti ad LHC. Per questa ragione tutti i modelli considerati sono stati implementati in strumenti Monte Carlo, validati nel confronto con risultati analitici, studiati in dettaglio e resi pronti per un rilascio pubblico per la comunità fenomenologica e sperimentale di LHC.

Condensed matter physics is the study of the macroscopic and microscopic properties of condensed phases of matter. For quite some time, Landau’s symmetry breaking theory was believed to describe and explain the nature of any phase transition. However, since the late 1980s, it has become apparent that it is necessary to introduce some new kind of order, named topological order, that transcends the traditional symmetry description. In this thesis we will study the Kitaev model, which is a Hamiltonian lattice model that allows one to incorporate the concept of topological order, as well as the corresponding operators and algebras. First, we consider the model on an infinite lattice, and show how to relate local and global degrees of freedom of the anyons/quasi-particles living on sites to the ribbon operators. Afterwards, we introduce holes and an external boundary to the lattice, and examine the ramifications of this generalization in terms of the ground state degeneracy. Lastly, we verify that the algebra formed by boundary site operators has the structure of a quasi-Hopf algebra.

This thesis uses theory and simulation to elucidate the principles and mechanisms that govern the thermodynamics, material science, and rheology of biological anisotropic soft matter that are involved in growth/self-assembly/material processing in plant cell walls, a multi-functional biological fibrous composite. The plant cell wall can be considered as a reinforced biological membrane consisting of cellulose microfibrils (CMFs) of high tensile strength embedded in a polysaccharide matrix. These CMFs in the extracellular matrix are oriented instrategic directions and generate commonly observed textures such as line, ring, helix, crossed helix and helicoids. The orientation of CMFs governs the physical properties of wood, controls the shape of the cell and contributes to themorphology at the tissue and organ level. Two models are used in this thesis, depending on the concentration of CMFs.At concentration of CMFs below Onsager critical limit, we develop an integrated mechanical model that describes nematic liquid crystalline self-assembly of rigid fibers on an arbitrarily curved 2D fluid membrane to demonstrate the possibility of the CMF orientation imparted by the interaction between membrane curvature and embedded fiber order. This curvature driven planar self assembly model can predict and explain the observed line, ring and helical cell wall textures. These predictions are partially validated through available experimental observations. An integrated shape and nematic order equation developed in this thesis gives a complete model whose solution describes the coupled membraneshape and fiber order state. The validated model is then used to analyze the structure and mechanics of biological and biomimetic fiber-laden membranes of variable curvature. The statics of anisotropic fiber-laden membranes developed inthis model is integrated with the planar nematodynamics of fibers and the dynamics of isotropic membranes to formulate a viscoelastic model to study dynamic remodeling of plant cell wall during growth and morphogenesis. The novel coupling between in-plane fiber orientation and order and membrane curvature formulated this thesis has the potential to open up a novel venue to control two dimensional anisotropic soft matter with tailored functionalities. When the concentration of the CMFs exceeds Onsager's critical fiber concentration threshold, the interaction between these CMFs results in theiralignment in a specific direction as an attempt to minimize the excluded volume of the CMFs. A mathematical model based on the Landau–de Gennes theory of liquid crystals is used to simulate defect textures arising in the domain of chiralself-assembly due to the presence of secondary phases such as pit canal and cell lumens. In addition to providing information on material properties and length scales that cannot be experimentally measured in vivo, the simulated transient defect pattern confirms for first time the long postulated formation mechanism of helicoidal plywoods through liquid crystalline self-assembly. The model is further extended to investigate defect textures and liquid crystalline (LC) phases observed in polygonal arrangement of cylindrical particles embedded in a cholesteric liquid crystal matrix. These validated findings provide a comprehensive set of trends and mechanisms that contribute to the evolving understanding of biological plywoods and serve as a platform for future biomimetic applications.The integration of soft matter physics theories and models with actual biological data for plant cell walls provides a foundation for understanding growth, form, and function and a platform for biomimetic innovation.
Cette thèse utilise la théorie et la simulation pour élucider les principes et mécanismes qui gouverne la hermodynamique, la science des matériaux, et la rhéologie de la matière biologique molle anisotropique qui est impliquée dans ledéveloppement/auto-assemblage/la transformation des parois cellulaires de plantes, un composite biologique fibreux multifonctionnel. Les parois cellulaires de plantes peuvent être considérées comme des membranes biologiques renforcées consistant en des microfibres de cellulose (CMFs) de hautes ténacités contenues dans une matrice de polysaccaride. Ces CMFs dans la matrice extracellulaire sont orientés dans une direction stratégique hélices et des hélicoïdes. L'orientation des CMFs gouverne les propriétés physiques du bois et contrôle la forme des cellules. Deux modèles sont employés dans cette thèse dépendamment de la concentration en CMFs. A la concentration de CMFs dessous la limite critique de Onsager, nous développons un modèle mécanique intégré qui décrit un auto-assemblage de fibres rigides de type cristal liquide nématique sur une membrane courbée bidimensionnelle arbitraire afin de démontrer la possibilité de l'orientation des CMFs indue par les interactions entre la courbature de la membrane et l'organisation fibrillaire intrinsèque. Cette auto-assemblage planaire indus par la courbature peut prédire et expliquer les lignes, annaux et textures hélicoïdales observées dans les parois cellulaires. Ces prédictions sont partiellement validées au travers d'observations expérimentales publiés. Une équation décrivant l'ordre nématique et la forme intégrée qui a été développé dans cette thèse fournis un modèle complet dont la solution décrit le couplage entre l'alignement des fibres et la forme de la membrane. Le model validé est par la suite utilisé à fin d'analyser la structure et la mécanique de membrane fibreuses biologiques et biomimétiques de courbatures variables. La statique des membranes fibreuses anisotropes développés dans ce modèle est intégrée avec la némato-dynamique planaire des fibres et la dynamique des membranes isotropes afin de formuler un modèle viscoélastique pour étudier le remodelage dynamique des CMF durant leur développement et morphogénèse. Le nouveau couplage entre l'orientation fibrillaire planaire et l'ordre ainsi que la courbature de la membrane formulé dans cette thèse à le potentiel d'ouvrir de nouvelles avenues pour contrôler l'ordre bidimensionnel de matière molle selon des propriétés bien définies. Quand la concentration en CMFs excède la limite critique en fibre de Onsager, l'interaction entre les CMFs résulte en un alignement dans une direction spécifique qui tente de minimiser le volume exclu de CMFs. Un modèle mathématique basé sur la théorie de Landau de Gennes des cristaux liquides est utilisé pour simuler les textures de défauts survenant dans un chirale d'auto assemblage du à la présence de phases secondaires tel que les lumens cellulaires. En plus de fournir de l'information sur les propriétés matériels et les ordres de grandeurs qui ne peuvent être mesuré expérimentalement in vivo, les motifs des défauts transitoires simulés confirment pour la première fois le mécanisme de formation des assemblages hélicoïdaux. Le modèle est de plus étendu pour investiguer les textures de défauts et les phases liquides cristallines (LC) observées dans les arrangements polygonaux de particules cylindriques inclus dans des matrices de cristaux liquide cholestériques. Ces découvertes validées fournissent un ensemble de mécanismes qui contribues à faire évoluer la compréhension des assemblages lamellaires biologiques et servent de plateforme pour de futur développement d'applications biomimétiques. L'intégration des théories et des modèles de la matière molle avec des données biologique concrète pour les parois cellulaires fournissent des fondement pour la compréhension du développement, de formation et fonctionnalité ainsi qu'une plateforme pour l'innovation biomimétique

We investigate models of composite dark matter in which the dark matter candidate arises naturally as an accidentally stable bound state of a confining dynamics and with observable signatures in a wide variety of experiments. In the first part of the thesis we introduce and explore a new class of models with dark fermions in the adjoint repre- sentation of the confining gauge group. The low energy dynamics and the cosmological history are peculiar and provide a dark matter candidate with properties much different from that of a canonical WIMP. The dark matter is heavy but has a large interaction range and can be tested primarily with indirect searches. In the second part of the thesis we classify and study models of composite dark matter with a strongly interacting chiral dark sector, in which all the mass scales are generated dynamically. In this case the candidate is a SM singlet dark pion with a thermal abundance whose low energy phenomenology can be thoroughly studied through chiral lagrangian techniques. We present an analysis of the low energy phenomenology, compute the radiatively generated masses of the light states and study the cosmological history of the model. The presence of partner states interacting with the SM offers the opportunity to test the model at colliders. In the last part of the thesis we present the phenomenological signatures of the models previously introduced and determine the current bounds. In doing so we also present a strategy to derive a limit on the lifetime of dark matter particles in generic models of particle dark matter from the observation of the 21 cm cosmological signal.

At present, the best model for the Universe as a whole is given by the so called ``Hot Big Bang'', which describes an expanding universe in which the density and temperature of matter and radiation are followed in time. The value of the parameters characterizing the observed universe is summarized by the concordance $\Lambda$CDM model, where CDM stands for Cold Dark Matter (the main matter component), and $\Lambda$ is the cosmological constant (some kind of unknown energy, with an anti-gravitational effect). According to this model, the universe is spatially flat (i.e. the density parameter $\Omega$ equals one), and 75\% of its energy balance is assigned to dark energy, about 20\% to dark matter and about 5\% to ordinary (baryonic) matter; the expansion speed assumes a value $H_{0}=70.5$ Km/s/Mpc (the Hubble parameter). The present dissertation focuses on the distribution of dark matter into virialized structures, called dark matter haloes. According to structure formation theory, cosmic structures originates from the amplification of quantum fluctuations during an early stage of accelerated expansion (cosmic inflation); these perturbations grow by self-gravity until they collapse and originate virialized structures. In the linear regime (when fluctuations are small), this process is well understood by the Jeans' theory. The non linear regime is much harder to describe; erlier attempts assumed a simple spherical simmetry, where the collapse is driven only by the internal density (e.g. Peebles, 1980); more recently (White \& Silk 1979; Bond \& Myers 1996) this hypothesis has been relaxed, and a more complex model was proposed in which proto-structures are described by triaxial ellipsoids, governed by their internal density and shape. Using the results coming from the dynamical analysis of the spherical collapse, and exploiting the statistical ``excursion sets formalism'', it is possible to obtain analytical information about the mass distribution of dark matter haloes. In this approach, for each particle in the universe, the trajectory describing the density evolution of a sphere of matter built around that particle is modeled as a random walk as a function of the mass $M$ within that sphere. When a trajectory crosses some pre-defined threshold, one assumes that a virialized structure of mass $M$ has formed. By considering all the particles in the universe one obtains analytical forms for the global mass function, and for the progenitor and descendant mass functions. From these it is possible to calculate other quantities, like the (instantaneous and integrated) rates of creation and destruction of dark matter haloes. In the 1990's the ellipsoidal collapse was first tried in order to find a better match with numerical simulations. However, partly due to the analytical complexity of the model, until now one can still not find in the literature analytical forms for e.g. the descendant and merger rate distributions (see Table \ref{tab:scec}). The main goal of this work is to provide such expressions for a number of statistics related to the mass distributions of dark matter haloes, striving to obtain simple and accurate formulas. In order to do so, we start from the statistical considerations by Sheth, Mo e Tormen (2001), who introduced the dynamical effects of the ellipsoidal collapse into the excursion sets formalism just by modifying the shape of the density threshold. Sheth and Tormen (2002) further suggested an new expression for the ellipsoidal global mass function, using a Taylor expansion series for the barrier: this expression allows one to also derive analytical formulas for the conditional mass functions. We obtain a set of models changing the order of this Taylor expansion, and considering the normalization of the distribution as a free parameter; we then compare these equations with the results of the cosmological simulation Gif2 (Gao et al. 2004) and, in some cases, with the Millennium Simulation (Springel et al. 2005). For the global and conditional mass functions the match between models and simulations is estimated using a $\chi ^2$-method. For the merger rates we compare the results qualitatively, whereas for the creation rates we only derived analytical results. We especially focus on the cases providing the simplest analytical expressions: the zero-order and the infinite-orders Taylor series. In the last part of the dissertation we propose a new statistical method that can overcome two inconvenients of $\chi ^2$-methods: (i) data binning and (ii) neglect of field particles (dust) in simulations. Concerning point (i), different bin-sizes can lead to small differences in the $\chi ^2$-results. As for point (ii), particles that are not bound to haloes are usually considered only for computing the normalization. By using a maximum likelihood analysis we can treat unbinned data, as well as take into account dust in the determination of the best parameters of the mass function. Our tests are performed by comparing a two-parameter mass function with results of Monte Carlo simulations. Our work naturally settles within the systematic search of analytical expressions associated to the ellipsoidal collapse of dark matter haloes. Since haloes are thought to be the sites where baryons can condense and form stars, galaxies and other luminous objects, the expression we derive can be used for a number of applications, ranging from unveiling the nature of dark matter through self-annihilation, to the understanding of the mechanisms leading to galaxy formation. Furthermore, the description of galaxy evolution requires knowledge on the hosting haloes: semi-analytical models of galaxy formation depend on the global mass function of the dark matter haloes, and the corrisponding merger-trees are based on the progenitor mass functions. The rates of creation and destruction are useful to compute the abundances of objects like Active Galactic Nuclei (AGNs) and Super Massive Black Holes (SMBHs). Many other examples can be found in the literature for the use of dark matter distributions in studies of galaxy formation. The structure of the dissertation is as follows: {\bf Chapters 1} justifies the need of dark matter. In {\bf Chapters 2} we present the concordance cosmological model, its geometry and thermal history. We also introduce the linear and non-linear models for the formation of dark matter haloes. {\bf Chapter 3} describes the excursion sets approach in the framework of the spherical collapse. The extension of this method to the ellipsoidal collapse is given in {\bf Chapter 4}, where the firsts analytical results are derived. In {\bf Chapter 5} we compare our analytical predictions to a number of results from numerical simulations. {\bf Chapter 6} is devoted to the new maximum likelihood tests with unbinned data and dust particles. We finally draw our {\bf Conclusions}, followed by one {\bf Appendix} where the numerical simulations are described.
La miglior descrizione dell'Universo, di cui si dispone al momento, è il modello del ``Big Bang Caldo'', che contempla un universo in espansione nel quale viene seguita l'evoluzione temporale della densità e della temperatura della materia e della radiazione. I parametri che caratterizzano l'Universo osservato sono riassunti in un modello chiamato $\Lambda$CDM di concordanza: CDM sta per Cold Dark Matter (la componente dominante della materia), e $\Lambda$ è la costante cosmologica (una sorta di energia oscura, con effetto anti-gravitazionale). Secondo questo modello, l'universo è spazialmente piatto (cioè il parametro di densità $\Omega$ è uguale a uno), e il $75\%$ del suo bilancio energetico è assegnato all'energia oscura, circa il $20\%$ alla materia oscura e circa il $5\%$ alla materia ordinaria (barioni); la velocità dell'espansione assume il valore $70.5$ Km/s/Mpc (parametro di Hubble). Questa tesi si sofferma sulla distribuzione della materia oscura in strutture virializzate, chiamate aloni di materia oscura. Secondo la teoria di formazione delle strutture, le strutture cosmiche hanno origine dall'amplificazione di fluttuazione quantistiche durante un periodo iniziale di espansione accelerata (inflazione cosmica); queste perturbazioni crescono per effetto dell'autogravità fino al collasso, creando delle strutture virializzate. Durante il regime lineare (quando le fluttuazioni sono piccole), questo processo è ben descritto dalla teoria di Jeans. Il regime non lineare è molto più difficile da descrivere; i primi tentativi assumono una simmetria sferica, per la quale il collasso è descritto solo dalla densità interna (es. Peebles, 1980); più recentemente (White \& Silk 1979; Bond \& Myers 1996) questa ipotesi è stata rilassata, ed è stato proposto un modello più complesso nel quale le protostrutture sono descritte da ellissoidi triassiali, regolati dalla loro densità interna e dalla loro forma. Utilizzando i risultati ottenuti dall'analisi dinamica del collasso sferico e sfruttando il formalismo statistico degli ``excursion set'', è possibile ottenere informazioni analitiche in merito alla distribuzione di massa degli aloni di materia oscura. In questo approccio, per ogni particella nell'universo, la traiettoria che descrive l'evoluzione della densità della sfera di materia costruita attorno a quella particella viene modellata come un cammino browniano come funzione della massa $M$ all'interno della sfera. Quando una traiettoria interseca una pre-definita soglia, si assume che venga a formarsi una struttura virializzata di massa $M$. Considerando tutte le particelle dell'universo, si ottengono forme analitiche per la funzione di massa globale, e per le funzioni di massa dei progenitori e dei figli. Da queste, è possibile calcolare altre quantità, come i tassi di creazione e distruzione (istantanei e integrati). Negli anni '90, il collasso ellissoidale è stato utilizzato per trovare un miglior accordo con le simulazioni numeriche. Tuttavia, in parte a causa della complessità analitica del modello, fino ad ora non è stato ancora possibile trovare in letteratura forme analitiche per esempio per la funzione dei figli o per i tassi di distruzione (vedi Tabella \ref{tab:scec}). l'obiettivo principale di questo lavoro è di fornire tali espressioni per una serie di funzioni legate alle distribuzione di massa degli aloni di materia oscura, aspirando ad ottenere delle formule semplici ed accurate. Per farlo, siamo partiti dalle considerazioni statistiche di Sheth, Mo e Tormen (2001) che introducono gli effetti dinamici del collasso ellissoidale nel formalismo excursion sets, modificando la forma della soglia di densità. Sheth e Tormen (2002), inoltre, propongono una nuova espressione per la funzione di massa globale ellissoidale, usando uno sviluppo in serie di Taylor per la barriera: questa espressione permette di derivare forme analitiche anche per le funzioni di massa condizionali. Abbiamo ottenuto un set di modelli cambiando l'ordine di questo sviluppo di Taylo, e considerando la normalizzazione delle distribuzioni come un parametro libero; abbiamo poi confrontato queste equazioni con i risultati della simulazione cosmologica Gif2 (Gao et al. 2004) e, in alcuni casi, con la Millennium Simulation (Springel et al. 2005). Per le funzioni di massa globale e condizionali, l'accordo tra modelli e simulazioni è stimato usando un metodo $\chi ^2$. Per i merger rates abbiamo confronti qualitativi, mentre per i tassi di creazione abbiamo derivato le sole equazioni analitiche. Ci siamo soffermati specialmente sui casi che forniscono le espressioni analiticamente più semplici: le serie di Taylor con zero ordini e con infiniti ordini. Nell'ultima parte della tesi, proponiamo un nuovo metodo statistico che può scartare gli inconvenienti dei metodi $\chi ^2$: (i) la divisione in intervalli dei dati e (ii) il trascurare le particelle di campo (polvere) delle simulazioni. Per quanto riguarda il punto (i), differenti ampiezze degli internalli di massa possono portare a piccole differenze nei risultati del $\chi^2$. Il punto (ii) si riferisce al fatto che le particelle che non sono legate in aloni sono di solito considerate solo per il calcolo della normalizzazione. Usando un'analisi di massima verosimiglianza, possiamo trattare dati non raggruppati in intervalli e considerare la polvere nella determinazione dei parametri migliori per la funzione di massa. I nostri tests sono condotti confrontando una funzione di massa a due parametri con i risultati di simulazioni Monte Carlo. Il nostro lavoro si inserisce naturalmente nella ricerca sistematica delle espressioni analitiche associate al collasso ellissoidale degli aloni di materia oscura. Poichè si pensa che gli aloni siano i siti ove i barioni possono concentrarsi e formare stelle, galassie ed altri oggetti luminosi, le espressioni che otteniamo possono essere usate in varie applicazioni, dallo svelare la natura della materia oscura attraverso l'auto annichilazione, fino alla comprensione dei meccanismi che portano alla formazione galattica. Inoltre, la descrizione dell'evoluzione galattica richiede la conoscenza dell'alone correlato: i modelli semi-analitici di formazione galattica dipendono dalla funzione di massa globale degli aloni di materia oscura, e i corrispondenti merger-trees sono basati sulle funzioni di massa dei progenitori. I tassi di creazione e distruzione sono utili per calcolare le abbondanze di oggetti come Nuclei Galattici Attivi (AGN) e Buchi Neri Super Massicci (SMBH). Altri esempi dell'utilizzo delle distribuzioni della materia oscura in studi di formazione galattica si possono trovare copiosi in letteratura.\\ L'elaborato si articola in questo modo: il {\bf Capitoli 1} giustifica la necessità della materia oscura. Nel {\bf Capitolo 2} presentiamo il modello cosmologico di concordanza, la sua geometria e la storia termica. Inoltre, introduciamo i modelli, lineare e non lineare, di formazione degli aloni di materia oscura. Il {\bf Capitolo 3} descrive l'approccio degli excursion sets nel contesto del collasso sferico. L'estensione di questo metodo al collasso ellissoidale è proposto nel {\bf Capitolo 4}, ove vengono esposti i primi risultati analitici. Nel {\bf Capitolo 5} confrontiamo le nostre predizioni analitiche con i risultati di due simulazioni numeriche. Il {\bf Capitolo 6} è dedicato all'esposizione dei test di un nuovo metodo di massima verosimiglianza con l'utilizzo di dati non raggruppati in intervalli e con le particelle di polvere. Infine tracciamo le nostre {\bf Conclusioni}, seguite da un'{\bf Appendice} ove sono descritte le simulazioni numeriche.

This thesis explores topics related to the formation and development of the large-scale structure in the Universe, with the focus being to compute properties of the evolved non-linear density field in an approximate way. The first three chapters form an introduction: Chapter 1 contains the theoretical basis of modern cosmology, Chapter 2 discusses the role of N-body simulations in the study of structure formation and Chapter 3 considers the phenomenological halo model. In Chapter 4 a novel method of computing the matter power spectrum is developed. This method uses the halo model directly to make accurate predictions for the matter spectrum. This is achieved by fitting parameters of the model to spectra from accurate simulations. The final predictions are good to 5% up to k = 10 hMpc-1 across a range of cosmological models at z = 0, however accuracy degrades at higher redshift and at quasi-linear scales. Chapter 5 is dedicated to a new method of rescaling a halo catalogue that has previously been generated from a simulation of a specific cosmological model to a different model; a gross rescaling of the simulation box size and redshift label takes place, then individual halo positions are modified in accord with the large scale displacement field and their internal structure is altered. The final power spectrum of haloes can be matched at the 5% level up to k = 1 hMpc-1, as can the spectrum of particles within haloes reconstituted directly from the rescaled catalogues. Chapter 6 applies the methods of the previous two chapters to modified gravity models. This is done in as general a way possible but tests are restricted to f(R) type models, which have a scale-dependent linear growth rate as well as having 'chameleon screening' - by which modifications to gravity are screened within some haloes. Taking these effects into account leads to predictions of the matter spectrum at the 5% level and rescaled halo distributions that are accurate to 5% in both real and redshift space. For the spectrum of halo particles it is demonstrated that accurate results may be obtained by taking the enhanced gravity in some haloes into account.

Review question / Objective: To assess the effects of particulate matter exposure during various periods of pregnancy on low birth weight and term low birth weight. Population:pregnant women and their singleton live-births; Exposure: maternal exposure to ambient PM2.5 and PM10 during the entire pregnancy or each trimesters were estimated based on ground-level atmospheric pollution monitoring stations or validated exposure models (μg/m3 ); Comparator(s): risk estimates were presented as hazard ratios (HRs) or odds ratios (ORs) and their 95% confidence intervals (95% CI) with per specific increment in PM2.5; Outcomes: term LBW(≥37weeks and<2500g) or LBW(<2500g)were defined as a dichotomous variables.

A major goal in Israeli and U.S. agroecosystems is to maximize nitrogen availability to crops while minimizing nitrogen losses to air and water resources. This goal has presented a significant challenge to global agronomists and scientists because crops require large inputs of nitrogen (N) fertilizer to maximize yield, but N fertilizers are easily lost to surrounding ecosystems where they contribute to water pollution and greenhouse gas concentrations. Determination of the optimum N fertilizer input is complex because the amount of N produced from soil organic matter varies with time, space and management. Indicators of soil N availability may help to guide requirements for N fertilizer inputs and are increasingly viewed as indicators of soil health To address these challenges and improve N availability indicators, project 4550 “Improving nitrogen availability indicators by emphasizing correlations between gross nitrogen mineralization and the quality and quantity of labile organic matter fractions” addressed the following objectives: Link the quantity and quality of labile soil organic matter fractions to indicators of soil fertility and environmental quality including: i) laboratory potential net N mineralization ii) in situ gross N mineralization iii) in situ N accumulation on ion exchange resins iv) crop uptake of N from mineralized soil organic matter sources (non-fertilizer N), and v) soil nitrate pool size. Evaluate and compare the potential for hot water extractable organic matter (HWEOM) and particulate organic matter quantity and quality to characterize soil N dynamics in biophysically variable Israeli and U.S. agroecosystems that are managed with different N fertility sources. Ultimately, we sought to determine if nitrogen availability indicators are the same for i) gross vs. potential net N mineralization processes, ii) diverse agroecosystems (Israel vs. US) and, iii) management strategies (organic vs. inorganic N fertility sources). Nitrogen availability indicators significantly differed for gross vs. potential N mineralization processes. These results highlight that different mechanisms control each process. Although most research on N availability indicators focuses on potential net N mineralization, new research highlights that gross N mineralization may better reflect plant N availability. Results from this project identify the use of ion exchange resin (IERs) beads as a potential technical advance to improve N mineralization assays and predictors of N availability. The IERs mimic the rhizosphere by protecting mineralized N from loss and immobilization. As a result, the IERs may save time and money by providing a measurement of N mineralization that is more similar to the costly and time consuming measurement of gross N mineralization. In further search of more accurate and cost-effective predictors of N dynamics, Excitation- Emission Matrix (EEM) spectroscopy analysis of HWEOM solution has the potential to provide reliable indicators for changes in HWEOM over time. These results demonstrated that conventional methods of labile soil organic matter quantity (HWEOM) coupled with new analyses (EEM) may be used to obtain more detailed information about N dynamics. Across Israeli and US soils with organic and inorganic based N fertility sources, multiple linear regression models were developed to predict gross and potential N mineralization. The use of N availability indicators is increasing as they are incorporated into soil health assessments and agroecosystem models that guide N inputs. Results from this project suggest that some soil variables can universally predict these important ecosystem process across diverse soils, climate and agronomic management. BARD Report - Project4550 Page 2 of 249

The need to control the risk that accompanies businesses in their day- to-day operations, and at the same time changing economic conditions make risk management an almost indispensable element of economic life. Selection of the main aspects of the selected phases of the risk management process: risk identification and risk assessment are related to their direct relationship with the subject matter (risk identification to be managed; risk analysis leading to the establishment of a risk hierarchy, and, consequently, the definition of risk control’ methods) and its purpose (bringing the risk to acceptable level). It is impossible to identify the basic patterns of development of the oil and gas industry without exploring the relationship between economic processes and enterprise risks. The latter are subject to simulation, and based on models it is possible to determine with certain probability whether there have been qualitative and quantitative changes in the processes, in their mutual influence on each other, etc. The work is devoted to exploring the possibilities of applying the Granger test to examine the causal relationship between the risks and obligations of oil and gas companies. The analysis is based on statistical tests and the use of linear regression models.