Progress in South America Dendrochronology

South America extends from 11°N to 62°S. Major boundaries such as the Andes on the western side of the continent and the land mass in the tropics create north-south and west-east variations in climate and ecosystems. Tropical forest covers 44% of the total land surface. Between 36 and 56°S, a temperate forest composed of high longevity trees dominates. The northern and central highlands are covered by small trees, shrubs and grasses. The central western part (Peru, Chile, the Andes, western Argentina and eastern Patagonia) is composed of deserts. These diverse climatic zones and ecosystems offer various potential sites for dendrochronological studies. The ideal conditions for paleoclimatic reconstructions using tree-rings are those that support the existence of long-living trees required to develop long chronologies, and/or the presence of subfossil woods. Over the last decade, the search for areas with some of these conditions has been one of the major goals of dendroclimatological studies in South America.Fil: Boninsegna, Jose Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Sparse learning of stochastic dynamic equations

With the rapid increase of available data for complex systems, there is great interest in the extraction of physically relevant information from massive datasets. Recently, a framework called Sparse Identification of Nonlinear Dynamics (SINDy) has been introduced to identify the governing equations of dynamical systems from simulation data. In this study, we extend SINDy to stochastic dynamical systems, which are frequently used to model biophysical processes. We prove the asymptotic correctness of stochastics SINDy in the infinite data limit, both in the original and projected variables. We discuss algorithms to solve the sparse regression problem arising from the practical implementation of SINDy, and show that cross validation is an essential tool to determine the right level of sparsity. We demonstrate the proposed methodology on two test systems, namely, the diffusion in a one-dimensional potential, and the projected dynamics of a two-dimensional diffusion process

The assessment of present, past and future climatic variability in the americas from tree-line environments

In this note we introduce one of 14 Collaborative Research Networks (CRN) funded by the Inter-American Institute for Global Change Research. It was established in 1999 and involves 15 principal investigators from 13 institutions in Canada, USA, Mexico, Bolivia, Chile and Argentina. The primary goals of the project are (i) to develop a network of tree-ring chronologies from climatically-sensitive treeline sites in the western American Cordillera and (ii) to use these data to reconstruct and compare regional interannual to decadal climate variability along the PEP-1 transect from Alaska to Tierra del Fuego. The project also seeks to enhance the development and utilization of dendrochronology for tropical mountain tree species and expand collaboration, training and the application of paleoenvironmental science within Latin America to address the issues of climate variability and change.Fil: Luckman, Brian H.. University of Western Ontario; CanadáFil: Boninsegna, Jose Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Arrangiamenti di sfere: stime sul "kissing number".

La tesi ha lo scopo di iniziare, in quanto non lo esaurisce completamente, a riordinare il percorso fatto nella stima del kissing number

Problems of ranking and dynamics of complex bipartite networks

openA recent new line of research that aims to couple network theory and economics has grown in the last decade, thanks to its ability to capture information from large datasets of exports and cast it into human-readable measures to rank nations and commodities. With Economic Complexity, we aim to infer as much as possible meaningful information about the nodes of the network of worldwide exports and, possibly, use this information to deduce the future topology of the economic network. In this thesis, we will present a new algorithm to measure the complexity of nations and the ubiquity of products, based on a self-consistent use of the Shannon entropy function that makes full use of the exports dataset information. We will discuss how these new entropic measures differ from the usually used complexity measures in the economic complexity framework, such as Fitness and Economic Complexity Index (ECI), highlighting the improvements. An original discussion about the dynamics of the measure will be presented, constructing an entropy-income plane by coupling the entropic complexity measure to some macroeconomic monetary indicator. A coarse-grained analysis of the plane will unveil a flow structure, individuating a laminar dynamics region thanks to the entropic dimension of nations. Moreover, we will observe how entropy and economic stability are strongly correlated. Finally, we will use the dynamical information of the entropy-income plane to predict Gross Domestic Product (GDP) growth at five years. We will use an algorithm developed in the context of Fitness, the selective predictability scheme bootstrap. This algorithm is an example of the method of analogues, firstly developed in the context of atmospheric prediction, as we will look at historical dynamics of nations with comparable entropy and GDP, hence at the analogues, to infer future growth. However, in the original formulation of the algorithm the problem to choose the right ”comparable” nations’ dynamics was not addressed. We will individuate and solve this problem using a statistical learning approach to historical data, combined with an update of the algorithm towards kernel regression. The use of the maximum information available in the dataset of exports, their stability against noisy data, the relevant dynamical information, and the improvement in accuracy of a 20% with respect to the International Monetary Fund prediction of growth make this measure an excellent candidate to rank nations and products according to their relevance in the trade market

Impacto del cambio climático en los oasis del oeste argentino

En Argentina, una de las regiones más vulnerables al Cambio Climático son los oasis productivos del centro-oeste. La actividad agrícola, industrial, la producción de hidroelectricidad y los asentamientos humanos dependen casi exclusivamente del agua proveniente de la fusión de la nieve y de los cuerpos de hielo que se encuentran en la Cordillera de los Andes. la variabilidad de las nevadas (y de los caudales de ríos) es  alta, con años de abundancia y de escasez, aunque para la región su tendencia es a disminuir. El aumento de la temperatura, observable en las series instrumentales, es coherente con el aumento pronosticado debido al incremento de la concentración de CO2 en la atmósfera. La disminución de las precipitaciones y el aumento de la temperatura originan el retroceso de los glaciares observado desde el siglo XIX, indicando una pérdida importante en reserva de agua. La variación de los caudales originada puede alterar la distribución del agua para riego y el manejo de las presas para generar hidroelectricidad. En la Cordillera de Mendoza y San Juan, la precipitación es fundamentalmente invernal. En cambio en los oasis, ubicados en el pedemonte, la lluvia ocurre durante el verano en forma de tormentas convectivas. Éstas han aumentado durante las últimas décadas en forma significativa y constituyen un aporte de agua que puede aliviar condiciones de sequía. la temperatura también muestra una tendencia positiva en esta región. Los estudios realizados mediante el uso de modelos regionales de circulación general han permitido construir hipótesis sobre el impacto del cambio climático, estimar la vulnerabilidad de la región y diseñar posibles medidas de adaptación.In Argentina, one of the most vulnerable regions to climate change is the central-west productive oases. All agricultural, industrial, hydropower production and human settlements depend almost exclusively on the melting water from the snow and ice bodies found in the Andes. The variability of the snowfall and stream-flow are very high, with years of abundance and years of scarcity, although in the region the number of abundant years is decreasing. The observed time series of temperature indicates a positive trend, consistent with the predicted increase due to the higher CO2 concentration in the atmosphere. The negative trend in rainfall and positive in temperature explain the glacier retreat observed since the 19th century indicating the loss of a major water reserve. This altered hydrograph can have a high impact on the distribution of water for irrigation and for the management of dams to generate hydroelectricity. In the Cordillera of Mendoza and San Juan, precipitation falls mainly in winter. In contrast, in the foothills oases, rainfall occurs during the summer in the form of convective storms. The summer precipitation has significantly increased in recent decades and represents a water contribution that to some extent could relieve drought conditions. The temperature also shows a positive trend in the region of cultivated oases. The use of regional general circulation models has permitted to build hypotheses about the expected impact of climate change. These studies are important to estimate the vulnerability to the changes and to design possible adaptation measures.Fil: Boninsegna, Jose Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Quantum Charge Transport and Conformational Dynamics of Macromolecules

We study the dynamics of quantum excitations inside macromolecules which can undergo conformational transitions. In the first part of the paper, we use the path integral formalism to rigorously derive a set of coupled equations of motion which simultaneously describe the molecular and quantum transport dynamics, and obey the fluctuation/dissipation relationship. We also introduce an algorithm which yields the most probable molecular and quantum transport pathways in rare, thermally-activated reactions. In the second part of the paper, we apply this formalism to simulate the propagation of a charge during the collapse of a polymer from an initial stretched conformation to a final globular state. We find that the charge dynamics is quenched when the chain reaches a molten globule state. Using random matrix theory we show that this transition is due to an increase of quantum localization driven by dynamical disorder.Comment: 11 pages, 2 figure

Definizione e validazione di uno strumento per la misurazione dell'impatto delle variabili redazionali di un item matematico sulla performance degli studenti

Questa tesi descrive la ricerca condotta tra l'autunno e l'inverno di quest'anno da un gruppo di ricercatori in didattica della matematica relativamente all'influenza che le variazioni redazionali di un quesito matematico hanno sulle performance degli studenti. Lo scopo della ricerca è quella di strutturare e validare una metodologia e uno strumento che permettano di individuare e quantificare l'influenza delle variazioni del testo sulle prestazioni dello studente. Si è sentita l'esigenza di condurre uno studio di questo tipo poichè è sempre più evidente il profondo legame tra il linguaggio e l'apprendimento della matematica. La messa a punto di questo strumento aprirebbe le porte a una serie di ricerche più approfondite sulle varie tipologie di variazioni numeriche e/o linguistiche finora individuate. Nel primo capitolo è presentato il quadro teorico di riferimento relativo agli studi condotti fino ad ora nell'ambito della didattica della matematica, dai quali emerge la grossa influenza che la componente linguistica ha sulla comprensione e la trasmissione della matematica. Si farà quindi riferimento alle ricerche passate volte all'individuazione e alla schematizzazione delle variazioni redazionali dei Word Problems. Nel secondo capitolo, invece si passerà alla descrizione teorica relativa allo strumento statistico utilizzato. Si tratta del modello di Rasch appartenente alla famiglia dei modelli statistici dell'Item Response Theory, particolarmente utilizzato nella ricerca in didattica. Il terzo capitolo sarà dedicato alla descrizione dettagliata della sperimentazione svolta. Il quarto capitolo sarà il cuore di questa tesi; in esso infatti verrà descritta e validata la nuova metodologia utilizzata. Nel quinto sarà eseguita un analisi puntuale di come lo strumento ha messo in evidenza le differenze per ogni item variato. Infine verranno tratte le conclusioni complessive dello studio condotto

Spectral Properties of Effective Dynamics from Conditional Expectations

The reduction of high-dimensional systems to effective models on a smaller set of variables is an essential task in many areas of science. For stochastic dynamics governed by diffusion processes, a general procedure to find effective equations is the conditioning approach. In this paper, we are interested in the spectrum of the generator of the resulting effective dynamics, and how it compares to the spectrum of the full generator. We prove a new relative error bound in terms of the eigenfunction approximation error for reversible systems. We also present numerical examples indicating that, if Kramers–Moyal (KM) type approximations are used to compute the spectrum of the reduced generator, it seems largely insensitive to the time window used for the KM estimators. We analyze the implications of these observations for systems driven by underdamped Langevin dynamics, and show how meaningful effective dynamics can be defined in this setting

The Computed Sinusoid

Hepatic sinusoids are lined with thin endothelial cells with transcellular pores, termed fenestrations. These fenestrations are open channels that connect the sinusoidal lumen to the underlying Space of Disse (SoD) and the hepatocytes of the liver parenchyma. Fenestrations range from 0.05 to 0.35 µm in diameter and cover 5–15% of the sinusoidal endothelial surface area, depending on their location along the sinusoids. The direct measurement of hemodynamic parameters, such as pressure and flow velocity, remains challenging within the narrow sinusoids. Such knowledge would increase our understanding of the physiology of the hepatic niche and possible implications in aging or diseases in which fenestrations are reduced or lost. Few simulations of liver blood flow focus on the level of the individual sinusoid, and fewer still include the transcellular pores (fenestrations) of the sinusoidal endothelium. Furthermore, none have included (i) a porosity gradient along the sinusoid wall, modeled using through-all pores rather than a porous medium, (ii) the presence of the SoD, or (iii) lymphatic drainage. Herein, computed fluid dynamics (CFD) simulations were performed using a numerical model with relevant anatomical characteristics (length, diameter, porosity, inlet/outlet pressure, and lymphatic outflow from the portal region of the SoD). The greatest contribution to luminal velocity magnitude and pressure was the overall shape of the vessel. Divergent-radius models yielded velocity magnitudes 1.5–2 times higher than constant-radius models, and pressures were 5–8% lower in the divergent-radius models compared to the constant-radius models. Porosity only modestly contributed to luminal pressure. The luminal velocity magnitude was largely unaffected by the presence or absence of lymphatic drainage. Velocity magnitudes through fenestrations were lower in higher-porosity models (20%) vs. lower-porosity models (5%) across all models (0.4–0.55-fold lower). Velocity magnitudes through the space of Disse were increased 3–4 times via the addition of lymphatic drainage to the models, while pressures were decreased by 6–12%. The flow velocity in the SoD was modified via differences in porosity, while the flow velocity in the lumens of the sinusoids was largely unaffected. The overall shape of the vessel is the single most important factor in the pressure flow behavior of the sinusoidal lumen. The flow rate over hepatocytes and the SoD is modestly affected by the distribution of porosity along the sinusoid and greatly affected by the lymphatic drainage, parameters that would be of interest for modeling the exchange of blood with the hepatic parenchyma