En esta tesis se estudian carteras de inversión compuestas únicamente por fondos de inversión cotizados (ETF), los que utilizan un activo índice como benchmark y buscan replicar sus resultados con diversificación a bajos costos y mínimas inversiones de capital. En el caso de un inversor argentino, cuyo mercado y economía tienen un alto grado de volatilidad, con elevada inflación y permanente devaluación de la moneda, restricciones en la compra de divisas, así como también falta de estabilidad en las políticas macroeconómicas de largo plazo, podría encontrar en activos de otras economías una respuesta a todos estos inconvenientes, manteniendo el valor real de sus inversiones en el tiempo. En este trabajo se hace énfasis en ETF de diferentes mercados del mundo, asociados a activos de distinta naturaleza, los cuales son cotizados en moneda dólar estadounidense, cuya tenencia en sí misma ya puede considerarse un refugio de valor en el contexto actual. A su vez, se pretende obtener rendimientos que puedan superar la inflación anualmente en dicha moneda y generar un flujo positivo a largo plazo mediante una gestión pasiva de la misma, es decir sin una necesidad permanente de rearmado de la cartera. Metodológicamente, la investigación presenta un abordaje cuantitativo, de índole empírica con alcance correlacional, trabajando a partir de información secundaria histórica sobre los ETF seleccionados en ventanas temporales de 5 y 10 años y su comparación con la situación con Covid-19 durante el primer semestre de 2020. Sobre los datos se calculan rendimientos, volatilidades y ratios de Sharpe de las carteras para diferentes problemas de optimización. A partir de los análisis realizados se puede argumentar que para el período de análisis resulta redundante la inclusión de más de un ETF de grandes grupos de acciones, como lo son los que representan al “S&P500” (SPY), las empresas en crecimiento de pequeña capitalización (VBK), el índice russell 2000 de empresas pequeñas (IWV) y el índice que replica prácticamente la totalidad del mercado de acciones estadounidense (VTI), ya que los mismos encuentran en un índice de acciones de base tecnológica (QQQ) una cartera dominante que no da lugar a otros grupos de ETF de renta variable, solo presentándose beneficios de la diversificación en el ORO y la renta fija, con GLD y VCIT (bonos corporativos) respectivamente. En relación a los mercados internacionales emergentes y otros desarrollados no norteamericanos, el resultado es idéntico, ya que el desempeño de los ETF incluidos en este trabajo no justifica su incorporación para el rango de los últimos 5 años, siendo sus métricas de rendimiento claramente inferiores a las del mercado norteamericano. Desde el punto de vista de un inversor argentino se puede determinar que el uso de instrumentos internacionales permite una disminución considerable del riesgo de su cartera aplicando la optimización del precio del riesgo, así como también en caso de que el perfil de la persona lo amerite, un mayor rendimiento igualando la volatilidad obtenida por un portafolio integrado únicamente por activos argentinos. / In this thesis, investment portfolios composed only of listed Exchange-traded funds (ETF) are studied, those that use an asset or index as a benchmark and seek to replicate their results with diversification at low costs and minimal capital investments. In the case of an Argentine investor, whose market and economy have a high degree of volatility, with high inflation and permanent devaluation of the currency, restrictions on the purchase of foreign currency, as well as lack of stability in long-term macroeconomic policies, you could find an answer to all these inconveniences in assets from other economies, maintaining the real value of your investments over time. In this paper, emphasis is placed on ETF from different markets around the world, associated with assets of different nature, which are quoted in US dollar currency. Holding in US dollars can already be considered a refuge of value in the current context. In turn, the aim is to obtain returns that can exceed inflation annually in said currency and generate a long-term positive flow through passive management of the same. Methodologically, the research presents a quantitative approach, of an empirical nature with a correlational scope, working from secondary historical information on the ETF selected. The time windows are 5 and 10 years and their comparison with the Covid-19 situation in the first semester of 2020. Portfolio returns, volatilities and Sharpe ratios are calculated on the data for different optimization problems. Based on the analyzes carried out, it can be argued that for the period of analysis the inclusion of more than one ETF of large groups of stocks is redundant. Index representing the “S&P500” (SPY), small growth companies capitalization (VBK), the russell 2000 index of small companies (IWV) and the index that tracks practically the entire US stock market (VTI), find in a technology-based equity index (QQQ) a dominant portfolio. It does not give rise to other groups of variable income ETF, only presenting benefits from diversification in GOLD and fixed income, with GLD and VCIT (corporate bonds) respectively. In relation to emerging international markets and other non-North American developed markets, the result is identical, since the performance of the ETF included in this study does not justify their incorporation. For the range of the last 5 years, their performance metrics was clearly lower than those of the North American market. From the point of view of an Argentine investor, it can be determined that the use of international instruments allows a considerable reduction of the risk of their portfolio by applying the optimization of the risk price, as well as in case the profile of the person warrants it, a higher return equaling the volatility obtained by a portfolio made up solely of Argentine assets.

No / Two novel reduced-size, printed spiral antennas are proposed for use in personal communications mobile terminals exploiting the “big low earth orbit” (Big-LEO) satellite system (uplink 1.61–1.63 GHz; downlink 2.48–2.5 GHz). The two proposed antenna give 3.12―6.25% bandwidth at lower resonant mode of 1600MHz, while at the higher resonant mode of 2450MHz a bandwidth of around 6% is obtained. The experimental and simulated return losses of the proposed antennas show good agreement. The computed and measured gains, and axial ratios are presented, showing that the performance of the proposed two antennas meets typical specifications for the intended applications.

Yes / This paper presents the results of laboratory experiments and numerical simulations to investigate the effect of different piggyback pipeline configuration on the morphology of local seabed scour subject to steady currents. Piggyback pipeline configuration investigated includes the commonly used piggyback pipeline, namely a small pipe attached on the top of large pipe and new form of piggyback pipeline proposed in this study in which a small pipe is attached to the large pipe on the upstream and downstream side, respectively. Pressure gradient, drag coefficient, lift coefficient and scour extent around pipelines are measured and analyzed for a range of pipelines and current conditions. Results show that the vortex strength downstream of the commonly used piggyback pipeline is larger than that for a single as well as the new piggyback pipeline under the same condition. This new type piggyback pipeline can effectively reduce the depth and width of the scour hole. In particular, when the ratio of the small pipe diameter over the large pipe diameter is greater than 0.3, little scour under this new type piggyback pipeline occurs for the test conditions. The bed topography downstream of the pipe has also been altered to favor the backfill. / National Natural Science Foundation of China (No. 51279189).

Nutrient accumulation in vegetable crops is declining. New varieties, selected for high yield, may be subject to a dilution effect of nutrient concentration. Alternatively, soil fertility may be to blame. Here, we investigate how nitrogen fertilization can enhance or suppress calcium and potassium content in two lettuce varieties already known to accumulate high or low amounts of these nutrients. Effects of varying the ammonium:nitrate ratio and effects of calcium carbonate buffering on plant growth by mass and on uptake and accumulation of potassium and calcium in two lettuce (Lactuca sativa L.) cultivars, Two Star and Red Deer Tongue, were investigated in three greenhouse hydroponic experiments in which ammonium supplied none, 6%, 12%, 25%, 50%, 75% or all of the nitrogen. Ammonium, supplied as the sole nitrogen source (15 mM), was toxic under buffered or unbuffered conditions. It limited growth and concentrations of potassium and calcium in lettuce leaves. Proportions of ammonium-N greater than 50% of total N nutrition severely curtailed growth and nutrient accumulation for both cultivars. For both cultivars, optima for all three variables occurred in treatments that contained less than 50% NH4+-N in the total N supply. Application of calcium carbonate buffer did not result in improved maxima for growth and shoot potassium or shoot calcium concentrations compared to the best responses in unbuffered solutions. However, supplying calcium carbonate buffer did raise the minima for growth and shoot potassium and shoot calcium concentration. Both cultivars in buffered solutions compared to unbuffered solutions had significantly greater values for growth and for shoot potassium or shoot calcium concentration in treatments that contained 50% ammonium-N or greater in the total N supply. Although buffering relieved symptoms of ammonium toxicity, it did not eliminate symptoms, confirming the work of other researchers that ammonium toxicity is not due solely to acidification of the root-zone and that buffering has an effect on the capacity of plants to tolerate ammonium nutrition. Supplying nitrogen with ammonium:nitrate ratios in which nitrate predominates enhances yield and accumulation of calcium and potassium in lettuce. Two Star, the modern variety, is more ammonium-sensitive than Red Deer Tongue, the heirloom variety, if calcium carbonate buffering is not provided.

High aspect-ratio flying wing configurations designed for high altitude, long endurance missions are characterized by high flexibility, leading to significant static aeroelastic deformation in flight, and coupling between aeroelasticity and flight dynamics. As a result of this coupling, an integrated model of the aeroelasticity and flight dynamics has to be used to accurately model the dynamics of the flexible flying wing. Such an integrated model of the flight dynamics and the aeroelasticity developed by Patil and Hodges is reviewed in this dissertation and is used for studying the unique flight dynamics of high aspect-ratio flexible flying wings. It was found that a rigid body configuration that accounted for the static aeroelastic deformation at trim captured the predominant flight dynamic characteristics shown by the flexible flying wing. Moreover, this rigid body configuration was found to predict the onset of dynamic instability in the flight dynamics seen in the integrated model. Using the concept of the mean axis, a six degree-of-freedom reduced order model of the flight dynamics is constructed that minimizes the coupling between rigid body modes and structural dynamics while accounting for the nonlinear static aeroelastic deformation of the flying wing. Multi-step nonlinear dynamic inversion applied to this reduced order model is coupled with a nonlinear guidance law to design a flight controller for path following. The controls computed by this flight controller are used as inputs to a time-marching simulation of the integrated model of aeroelasticity and flight dynamics. Simulation results presented in this dissertation show that the controller is able to successfully follow both straight line and curved ground paths while maintaining the desired altitude. The controller is also shown to be able to handle an abrupt change in payload mass while path-following. Finally, the equations of motion of the integrated model were non-dimensionalized to identify aeroelastic parameters for optimization and design of high aspect-ratio flying wings. / Ph. D.

Whether the quality of a firm's reported earnings affects investors' ability to predict future earnings and stock returns is still a subject of much debate among accounting researchers. Lev (1989) suggests that low quality earnings may be causing the relatively low correlation between reported earnings and stock returns (or the market's evaluation of future earnings). This dissertation used the valuation model described in Ohlson (1995) and Feltham and Ohlson (1995) to explore the possible links between accounting method choices and the ability of investors to use reported earnings to predict future earnings. The results demonstrate that prior researchers' assumptions regarding which accounting methods are generally conservative or liberal are reasonably accurate over large numbers of firms. The results also show that one group of analysts (Value Line Investment Survey) is able to predict future earnings more accurately over medium-term and long-term forecast horizons for firms using generally conservative accounting methods than those firms employing generally liberal accounting methods. This research adds to the prior "quality of earnings" research by showing that analysts can predict earnings more accurately for certain classes of firms (i.e., firms using conservative accounting methods), thus increasing our knowledge of what constitutes high-quality earnings. The research also explores the effects of growth on the quality of earnings question, the effects of firm size, leverage, and industry membership on the relationship, and the robustness of the Feltham and Ohlson Model to alternative definitions of key components of the model. / Ph. D.

The open bin packing problem (OBPP) is a new variant of the well-known bin packing problem. In the OBPP, items are packed into bins so that the total content before the last item in each bin is strictly less than the bin capacity. The objective is to minimize the number of bins used. The applications of the OBPP can be found in the subway station systems in Hong Kong and Taipei and the scheduling in manufacturing industries. We show that the OBPP is NP-hard and propose two heuristic algorithms instead of solving the problem to optimality. We propose two offline algorithms in which the information of the items is known in advance. First, we consider the First Fit Decreasing (FFD) which is a good approximation algorithm for the bin packing problem. We prove that its asymptotic worst-case performance ratio is no more than 3/2. We observe that its performance for the OBPP is worse than that of the BPP. Consequently, we modify it by adding the algorithm that the set of largest items is the set of last items in each bin. Then, we propose the Modified First Fit Decreasing (MFFD) as an alternative and prove that its asymptotic worst-case performance ratio is no more than 91/80. We conduct empirical tests to show their average-case performance. The results show that in general, the FFD and MFFD algorithms use no more than 33% and 1% of the number of bins than that of optimal packing, respectively. In addition, the MFFD is asymptotically optimal when the sizes of items are (0,1) uniformly distributed. / Ph. D.

This study examines intertemporal variation in the associations of accounting data with subsequent firm returns. A number of accounting research studies pool data indiscriminately across time and firms. Previous research has disclosed the nature and effects of cross-sectional dependencies in pooled data. On the other hand, intertemporal dependencies associated with real macroeconomic phenomena have not been widely researched. The objective of this study was to provide evidence as to whether accounting data's associations with subsequent firm returns systematically vary across recession-associated and expansion-associated valuation change periods. Eighty-two accounting ratios were examined for evidence of systematic variation in association across business cycle-associated valuation events. Analyses are conducted, using both simple and multiple regression. Business cycle effects on the predictive accuracy of regression models were also examined. / Ph. D.

The use of satellite and airborne remote sensing data to predict foliar macronutrients and pigments for a boreal mixedwood forest composed of black and white spruce, balsam fir, northern white cedar, white birch, and trembling aspen was investigated. Specifically, imaging spectroscopy (IS) and light detection and ranging (LiDAR) are used to model the foliar N:P ratio, macronutrients (N, P, K, Ca, Mg) and chlorophyll. Measurement of both foliar macronutrients and foliar chlorophyll provide critical information about plant physiological and nutritional status, stress, as well as ecosystem processes such as carbon (C) exchange (photosynthesis and net primary production), decomposition and nutrient cycling. Results show that airborne and spaceborne IS data explained approximately 70% of the variance in the canopy N:P ratio with predictions errors of less than 8% in two consecutive years. LiDAR models explained more than 50% of the variance in the canopy N:P ratio with similar predictions errors. Predictive models using spaceborne Hyperion IS data were developed with adjusted R2 values of 0.73, 0.72, 0.62, 0.25, and 0.67 for N, P, K, Ca and Mg, respectively. The LiDAR model explained 80% of the variance in canopy Ca concentration with an RMSE of less than 10%, suggesting strong correlations between forest height and Ca. Two IS derivative indices emerged as good predictors of chlorophyll across time and space. When the models of these two indices with the same parameters as generated from Hyperion data were applied to other years' data for chlorophyll concentration prediction, they could explain 71, 63 and 6% and 61, 54 and 8 % of the variation in chlorophyll concentration in 2002, 2004 and 2008, respectively with prediction errors ranging from 11.7% to 14.6%. Results demonstrate that the N:P ratio, N, P, K, Mg and chlorophyll can be modeled by spaceborne IS data and Ca can only be predicted by LiDAR data in the canopy of this forest. The ability to model the N:P ratio and macronutrients using spaceborne Hyperion data demonstrates the potential for mapping them at the canopy scale across larger geographic areas and being able to integrate them in future studies of ecosystem processes. / Ph. D.

yes / The coupling between natural convection and conduction within rectangular enclosure was investigated numerically. Three separate heat sources flush mounted on a vertical wall and an isoflux condition was applied at the back of heat sources. Continuity, momentum and energy conservation equations were solved by using control volume formulation and the coupling of velocity and pressure was treated by using the “SIMPLE” algorithm. The modified Rayleigh number and the substrate/fluid thermal conductivity ratio were used in the range 𝑹𝒂𝒍𝒛∗=𝟏𝟎^𝟒−𝟏𝟎^𝟕 and 𝑹𝒔=𝟏𝟎−𝟏𝟎𝟎𝟎 respectively. The investigation was extended to compare results of FC-77 with Air and also for high values of 𝑹𝒔>𝟏𝟎𝟎𝟎. The results illustrated that, when the modified Rayleigh number increases, dimensionless heat flux and local Nusselt number increases for both fluids. Opposite behaviour for the thermal spreading in the substrate and the dimensionless temperature 𝜽, they were decreased when 𝑹𝒂𝒍𝒛∗ is increased. Also with increasing the substrate/fluid thermal conductivity ratio for a given value of the modified Rayleigh number the thermal spreading in the substrate increased which is the reason of the decrease in the maximum temperature value. The present study concluded that, for high values of 𝑹𝒔>𝟏𝟓𝟎𝟎, the effect of the substrate is negligible.