A Computer Vision Inspired Automatic Acoustic Material Tagging System for Virtual Environments

This paper presents the ongoing work on an approach to material information retrieval in virtual environments (VEs). Our approach uses convolutional neural networks to classify materials by performing semantic segmentation on images captured in the VE. Class maps obtained are then re-projected onto the environment. We use transfer learning and fine-tune a pretrained segmentation model on images captured in our VEs. The geometry and semantic information can then be used to create mappings between objects in the VE and acoustic absorption coefficients. This can then be input for physically-based audio renderers, allowing a significant reduction in manual material tagging

Essays in financial economics

This thesis comprises three essays investigating the role of connections and personal experiences on firms’ and individuals’ decisions. In the first two chapters, I investigate how governance networks affect the transmission of information among competitors and their implications on product market outcomes. The third chapter contributes to the literature on the effects of personal experiences on individuals’ patience and savings behavior

Causality and black holes in spacetimes with a preferred foliation

We develop a framework that facilitates the study of the causal structure of spacetimes with a causally preferred foliation. Such spacetimes may arise as solutions of Lorentz-violating theories, e.g. Hořava gravity. Our framework allows us to rigorously define concepts such as black/white holes and to formalize the notion of a ‘universal horizon’, that has been previously introduced in the simpler setting of static and spherically symmetric geometries. We also touch upon the issue of development and prove that universal horizons are Cauchy horizons when evolution depends on boundary data or asymptotic conditions. We establish a local characterisation of universal horizons in stationary configurations. Finally, under the additional assumption of axisymmetry, we examine under which conditions these horizons are cloaked by Killing horizons, which can act like usual event horizons for low-energy excitations

Aspects of Lorentz violating theories of gravity

Lorentz symmetry is arguably the most fundamental symmetry of physics, at least in its modern conception. On the other hand, some of the issues that plague the currently accepted theory of gravitation could be solved by breaking such symmetry. The theory proposed by Petr Horava in 2009 brings forward exactly this aspect. The theory, dubbed Horava gravity, is a UV complete theory of gravity that is also renormalisable. It represents therefore a good candidate for a quantum theory of gravity. There are some issues though, which typically arise in any theory which explicitely violates Lorentz symmetry. In this thesis we will be concerned with two of these issues, in particular the matter problem and the existence of black holes. The first issue mentioned arises every time we try to couple matter to a Lorentz violating theory of gravity. Indeed, in the matter sector Lorentz symmetry is extremely well constrained, and therefore we need to find a way to avoid the percolation of Lorentz violations to the matter sector through higher order operators. One possible solution based on the separation of scales was proposed in the last few years (Pospelov et al.,2010). While studying the proposed mechanism though, the authors uncovered a naturalness problem in the vector sector of the theory. The solutions they proposed relies on the use of some higher derivative terms that are not normally present in the ``traditional'' Horava theory. It is unclear then what impact this type of terms can have on the whole theory. In our work we precisely addressed this question. We analysed the perturbations around Minkowski of the most generic theory extended to these type of terms, both from the point of view of the stability of the theory and of the renormalisability. What we found is that the theory retains its renormalisability, but some instabilities occur in the scalar sector. More work is hence required in order to understand whether such instabilities could be tamed, or if the mixed derivatives should be abandoned in favour of some alternative solution, not presently available. The second theme we concentrated on is that of the existence of black holes. The definition of black hole in general relativity rely strongly on the causal structure dictated by Lorentz symmetry. As soon as Lorentz symmetry is broken it is therefore unclear whether black holes will still exist. Surprisingly enough black holes have been shown to exist in Lorentz breaking theories, but a rigorous definition was still to be found. In our work we developed the mathematically rigorous definitions for the causal structure of foliated spacetimes and we defined for the first time black holes in such spacetimes. We also uncovered a number of interesting properties of this objects and we developed a local characterisation that allows one to locate horizons without the knowledge of the whole structure of the complete spacetime. Finally we developed the Initial Value Problem for these types of theory in the hope that new simulations of gravitational collapse will be performed using our analysis as a starting point. The thesis is organised as follows. In the first Chapter we give an introduction on gravity and the problems with its renormalization. We also introduce some of the theories that have been proposed to solve this difficulties. In the second Chapter we start discussing Lorentz violations and we provide a proof of the power-counting renormalizability of a toy model of a Lorentz violationg scalar field theory. We also introduce the theories that we will be studying throughout the thesis. In the third Chapter we discuss the mixed derivative extension to Horava gravity and we discuss the consequences of the new terms that occur in the theory. In the fourth and fifth Chapters we introduce the causal structure of spacetimes which violate Lorentz symmetry by means of a preferred foliation, we discuss the notion of black holes and horizons and we formalise some results present in the literature adapting them to our framework. In the sixth Chapter we then discuss the Initial Value Problem for such spacetimes, with some attention to the process of gravitational collapse leading to the formation of black holes. Finally in the last Chapter we draw some conclusions and discuss some ideas for future work

Faktorer av betydelse för predationstakten på älg hos skandinaviska vargar

Winter wolf (Canis lupus) kill rates on moose (Alces alces) on the Scandinavian Peninsula are high and subject to strong variation, compared to other boreal wolf-moose systems. A more detailed understanding of factors influencing this variation is crucial for management and conservation of the Scandinavian wolf population. Although functional response models explain the relationship between prey density and kill rates, few studies quantify and investigate the predator-prey characteristics shaping the mechanisms of predation at a finer scale. I analysed 18 605 hourly GPS locations from 13 wolf packs during 2001-2010. There were 182 usable moose predation events from 17 winter study periods during this time span. With the GPS data I assessed patterns of wolf activity detecting consecutive killsites and reconstructing wolf hunting paths between predation events. I estimated two components of kill rate i.e., searching time (Ts) which is the time spent to detect, chase, and kill prey, and handling time (Th), i.e., the time used to consume and process the prey for each predation event. I tested the difference between two different methods used for defining spatial criteria and evaluated a set of models to test factors potentially affecting Ts and Th. These factors included prey age, pack size, winter period, moose density, and wolf density at two functional levels of scale. I demonstrate that the method used for defining Ts and Th influenced their estimates and model selection. The majority of moose kills occurred during night time and wolves spent 75% of their total time away (>1km) from kill-sites. Wolf search time decreased with an increase in local moose density and pack size. At the pack level, Th increased with pack size and decreased with the number of neighbouring packs highlighting the influence of territoriality and social interactions among wolf packs. Age of moose, i.e., calf ( 2 year) moose, was an important variable for explaining variation in both Ts and Th. This study shows the potential of a research approach using GPS data in time-to-event models and the effectiveness of these models to quantify mechanisms of predation and factors influencing wolf kill rates on moose

DaMiRseq—an R/Bioconductor package for data mining of RNA-Seq data: normalization, feature selection and classification

Abstract Summary RNA-Seq is becoming the technique of choice for high-throughput transcriptome profiling, which, besides class comparison for differential expression, promises to be an effective and powerful tool for biomarker discovery. However, a systematic analysis of high-dimensional genomic data is a demanding task for such a purpose. DaMiRseq offers an organized, flexible and convenient framework to remove noise and bias, select the most informative features and perform accurate classification. Availability and implementation DaMiRseq is developed for the R environment (R ≥ 3.4) and is released under GPL (≥2) License. The package runs on Windows, Linux and Macintosh operating systems and is freely available to non-commercial users at the Bioconductor open-source, open-development software project repository (https://bioconductor.org/packages/DaMiRseq/). In compliance with Bioconductor standards, the authors ensure stable package maintenance through software and documentation updates. Supplementary information Supplementary data are available at Bioinformatics online

Aspects of Lorentz violating theories of gravity

Lorentz symmetry is arguably the most fundamental symmetry of physics, at least in its modern conception. On the other hand, some of the issues that plague the currently accepted theory of gravitation could be solved by breaking such symmetry. The theory proposed by Petr Horava in 2009 brings forward exactly this aspect. The theory, dubbed Horava gravity, is a UV complete theory of gravity that is also renormalisable. It represents therefore a good candidate for a quantum theory of gravity. There are some issues though, which typically arise in any theory which explicitely violates Lorentz symmetry. In this thesis we will be concerned with two of these issues, in particular the matter problem and the existence of black holes. The first issue mentioned arises every time we try to couple matter to a Lorentz violating theory of gravity. Indeed, in the matter sector Lorentz symmetry is extremely well constrained, and therefore we need to find a way to avoid the percolation of Lorentz violations to the matter sector through higher order operators. One possible solution based on the separation of scales was proposed in the last few years (Pospelov et al.,2010). While studying the proposed mechanism though, the authors uncovered a naturalness problem in the vector sector of the theory. The solutions they proposed relies on the use of some higher derivative terms that are not normally present in the ``traditional'' Horava theory. It is unclear then what impact this type of terms can have on the whole theory. In our work we precisely addressed this question. We analysed the perturbations around Minkowski of the most generic theory extended to these type of terms, both from the point of view of the stability of the theory and of the renormalisability. What we found is that the theory retains its renormalisability, but some instabilities occur in the scalar sector. More work is hence required in order to understand whether such instabilities could be tamed, or if the mixed derivatives should be abandoned in favour of some alternative solution, not presently available. The second theme we concentrated on is that of the existence of black holes. The definition of black hole in general relativity rely strongly on the causal structure dictated by Lorentz symmetry. As soon as Lorentz symmetry is broken it is therefore unclear whether black holes will still exist. Surprisingly enough black holes have been shown to exist in Lorentz breaking theories, but a rigorous definition was still to be found. In our work we developed the mathematically rigorous definitions for the causal structure of foliated spacetimes and we defined for the first time black holes in such spacetimes. We also uncovered a number of interesting properties of this objects and we developed a local characterisation that allows one to locate horizons without the knowledge of the whole structure of the complete spacetime. Finally we developed the Initial Value Problem for these types of theory in the hope that new simulations of gravitational collapse will be performed using our analysis as a starting point. The thesis is organised as follows. In the first Chapter we give an introduction on gravity and the problems with its renormalization. We also introduce some of the theories that have been proposed to solve this difficulties. In the second Chapter we start discussing Lorentz violations and we provide a proof of the power-counting renormalizability of a toy model of a Lorentz violationg scalar field theory. We also introduce the theories that we will be studying throughout the thesis. In the third Chapter we discuss the mixed derivative extension to Horava gravity and we discuss the consequences of the new terms that occur in the theory. In the fourth and fifth Chapters we introduce the causal structure of spacetimes which violate Lorentz symmetry by means of a preferred foliation, we discuss the notion of black holes and horizons and we formalise some results present in the literature adapting them to our framework. In the sixth Chapter we then discuss the Initial Value Problem for such spacetimes, with some attention to the process of gravitational collapse leading to the formation of black holes. Finally in the last Chapter we draw some conclusions and discuss some ideas for future work

Uninvited guest in mixed derivative Hořava gravity

We revisit the mixed-derivative extension of Hořava gravity which was designed to address the naturalness problems of the standard theory in the presence of matter couplings. We consider the minimal theory with mixed-derivative terms that contain two spatial and two temporal derivatives. Including all terms compatible with the (modified) scaling rules and the foliation-preserving diffeomorphisms, we calculate the dispersion relations of propagating modes. We find that the theory contains four propagating degrees of freedom, as opposed to three in the standard Hořava gravity. The new degree of freedom is another scalar graviton, and it is unstable at low energies. Our result brings tension to the Lorentz-violation suppression mechanism that relies on separation of scales

Evolution and spherical collapse in Einstein-Æther theory and Hořava gravity

We compare the initial value formulation of the low-energy limit of (nonprojectable) Hořava gravity to that of Einstein-æther theory when the æther is assumed to be hypersurface orthogonal at the level of the field equations. This comparison clearly highlights a crucial difference in the causal structure of the two theories at the nonperturbative level: in Hořava gravity evolution equations include an elliptic equation that is not a constraint relating initial data but needs to be imposed on each slice of the foliation. This feature is absent in Einstein-æther theory. We discuss its physical significance in Hořava gravity. We also focus on spherical symmetry, and we revisit existing collapse simulations in Einstein-æther theory. We argue that they have likely already uncovered the dynamical formation of a universal horizon and that they can act as evidence that this horizon is indeed a Cauchy horizon in Hořava gravity