Testing the equality between two high-dimensional covariance matrices is challenging. As the most efficient way to measure evidential discrepancies in observed data, the likelihood ratio test is expected to be powerful when the null hypothesis is violated. However, when the data dimensionality becomes large and potentially exceeds the sample size by a substantial margin, likelihood ratio based approaches face practical and theoretical challenges. To solve this problem, this study proposes a method by which we first randomly project the original high-dimensional data into lower-dimensional space, and then apply the corrected likelihood ratio tests developed with random matrix theory. We show that testing with a single random projection is consistent under the null hypothesis. Through evaluating the power function, which is challenging in this context, we provide evidence that the test with a single random projection based on a random projection matrix with reasonable column sizes is more powerful when the two covariance matrices are unequal but component-wise discrepancy could be small -- a weak and dense signal setting. To more efficiently utilize this data information, we propose combined tests from multiple random projections from the class of meta-analyses. We establish the foundation of the combined tests from our theoretical analysis that the p-values from multiple random projections are asymptotically independent in the high-dimensional covariance matrices testing problem. Then, we show that combined tests from multiple random projections are consistent under the null hypothesis. In addition, our theory presents the merit of certain meta-analysis approaches over testing with a single random projection. Numerical evaluation of the power function of the combined tests from multiple random projections is also provided based on numerical evaluation of power function of testing with a single random projection. Extensive simulations and two real genetic data analyses confirm the merits and potential applications of our test. / Statistics

This paper investigates the role of artificial light as a tool for spread a political message, focusing on Brazilian political scenario. Given the recent context of the weakening of many democratic institutions around the world together with Covid-19 pandemic, new ways of protesting have been transforming the character of political demonstrations. The aim is to identify which tools are being used in Brazil for this purpose and to comprehend what is the future of light protests. First, an analysis of how light has been incorporated into political art is briefly described. Then, some recent political protests around the world in which light was used in different ways are presented. After an overview of the use of light in contemporaneity, the research focus on Brazilian protest scene using three light tools: drones, lasers and projectors.  The research methodology is conducted through case studies of works by five artists combined with interviews with artists, projection collectives and academic experts. The results show that the pandemic in Brazil along with political mismanagement, triggered a massive wave of projections throughout the country. What before the pandemic had already gained strength, after the year 2020 took on a larger dimension. As a result, projections became popular to the extent that workshops were held in low-income communities to teach people how to build projectors with flashlights and paper. Another aspect raised during the research is that lasers have taken hold and tend to become more popular in the coming years. There is no Brazilian national legislation for the use of lasers, projectors and drones in cities during protest situations, as the laws are in each individual state. Given this growth in the use of these lighting tools, a national law may be created.

The tropical Andes are one of the regions where climate change has been most evident. This is consistent with the notion that tropical high-elevation mountains will be more affected by warming. One of the main impacts of this warming is the retreat of glaciers; a process that may affect the availability of water for human consumption, irrigation and power production. This study presents results related to the most important changes in climate that might be expected in tropical South America, but especially in the tropical Andes, at the end of the 21st century. Results are provided by the comparison of two Regional Climate Model simulations based on the Hadley Center Regional Climate Modeling System, PRECIS. A medium-high CO2 emission scenario simulation for the period 2071-2100 (A2) is compared to a base-line mean climate state simulation for the 1961-1990 period. In addition, some results using a low-medium CO2 emission scenario (B2) are also presented for comparison. Results show a clear warming trend over South America reaching up to 8º C in northeastern South America. In this same place the largest decrease in precipitation and cloud cover are found. Along the Andes warming reaches up to 7º C in Cordillera Blanca in the A2 scenario and precipitation presents a mixed pattern of increases and decreases across the Cordillera. Warming is expected to be larger at higher elevations and significant changes in temperature variability are expected along both slopes of the Andes based on the A2 scenario. In addition both scenarios (B2 and A2) show an amplification of free tropospheric warming at higher altitudes. Finally, pressure-longitude cross-sections of zonal winds and vertical velocities at the latitudes of the Altiplano and the Cordillera Blanca show weakened mid- and upper tropospheric easterlies and strengthened westerlies in the A2 scenario. This change in the atmospheric circulation is conducive to a decrease in precipitation in those areas, and consequently may negatively impact glacier mass balance. In summary the obtained results reveal that anthropogenic climate change, as predicted with the A2 scenario, may constitute a serious threat to the survival of many tropical glaciers along the Andes Cordillera.

In recent years there has been an increasing interest in mathematics teaching and learning at undergraduate level. However, many fields are little explored; differential equations being one of these topics. In this study I use the theoretical framework of Coordination Classes to analyze how undergraduate mechanical engineering students apply their knowledge in the context of system dynamics and what resources and strategies they used; in this subject, students model dynamics systems based on Ordinary Differential Equations (ODEs). I applied three tasks in different contexts (Mechanical, Electrical and Fluid Systems) in order to identify what information was relevant for the students, readout strategies; what inferences students made with the relevant information, causal nets; and what strategies students used to apply their knowledge in those contexts, concept projections. I found that the core problem at projecting their knowledge relied on the causal nets, coinciding with diSessa and Wagner's conjecture (2005). I also identified and characterized three strategies or concept projections students used in solving the tasks: Diagram-based approach, Component-based approach and Equation-based approach.

<p> This dissertation consists of three essays that evaluate long-term agricultural projections. The first essay focus on evaluating Congressional Budget Office’s (CBO) baseline projection of United States Department of Agriculture (USDA) mandatory farm and nutrition programs. The second essay examine USDA soybean ending stock projections, and the third essay investigate impact of macroeconomic assumptions on USDA’s baseline farm income projections.  We use publicly available data from Congressional Budget Office (CBO) and United States Department of Agriculture (USDA)</p>

The global increase in demand for wood products, calls for a more sustainable management of forests to optimize both the production of wood and the conservation of forest biodiversity. In this paper, we evaluate the status and future trends of forest birds in Central European forests, assuming different forest management scenarios that to a varying degree respond to the demand for wood production. To this end, we use niche models (Boosted Regression Trees and Generalized Linear Models) to model the responses of 15 forest bird species to predictors related to forest stand (e.g., stand volume of specific tree species) and landscape structure (e.g., percentage cover), and to climate (bioclimatic variables). We then define five distinct forest management scenarios, ranging from set-aside to productivity-driven scenarios, project them 100 years into the future, and apply our niche models into these scenarios to assess the birds’ responses to different forest management alternatives. Our models show that the species’ responses to management vary reflecting differences in their ecological niches, and consequently, no single management practice can benefit all species if applied across the whole landscape. Thus, we conclude that in order to promote the overall forest bird species richness in the study region, it is necessary to manage the forests in a multi-functional way, e.g., by spatially optimizing the management practices in the landscape.

This thesis report deals with the meaning of dynamics in lighting in context of the current state oflighting technology and how certain aspects of those can be applied to a specific space.Former studies discovered that biophilic aspects in design can create great benefits for the usersof a space. Natural elements is what we humans most affiliate to. Based on those findings I implementedaspects of dynamics in lighting into my design proposal assuming to be able to give theusers of the MIDDLA space benefit by recreating some degree of ‘virtual biophilia’.MIDDLA is the laboratory of the Media Technology and Interaction Design department of KTH.Characteristics of these facilities are unique as it is located in the attic floor of the oldest buildingon campus which is rather restricted in terms of daylighting and room clearance. Focus is put onthe corridor to evolve into an extension of the laboratory itself as a study area.Future post-occupancy research could be worthwhile of being conducted in combination with furtherdevelopment of the lighting design.

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