The role of initial state and final quench temperature on the aging properties in phase-ordering kinetics

We study numerically the two-dimensional Ising model with non-conserved dynamics quenched from an initial equilibrium state at the temperature $T_i\ge T_c$ to a final temperature $T_f$ below the critical one. By considering processes initiating both from a disordered state at infinite temperature $T_i=\infty$ and from the critical configurations at $T_i=T_c$ and spanning the range of final temperatures $T_f\in [0,T_c[$ we elucidate the role played by $T_i$ and $T_f$ on the aging properties and, in particular, on the behavior of the autocorrelation $C$ and of the integrated response function $\chi$. Our results show that for any choice of $T_f$, while the autocorrelation function exponent $\lambda _C$ takes a markedly different value for $T_i=\infty$ [$\lambda _C(T_i=\infty)\simeq 5/4$] or $T_i=T_c$ [$\lambda _C(T_i=T_c)\simeq 1/8$] the response function exponents are unchanged. Supported by the outcome of the analytical solution of the solvable spherical model we interpret this fact as due to the different contributions provided to autocorrelation and response by the large-scale properties of the system. As changing $T_f$ is considered, although this is expected to play no role in the large-scale/long-time properties of the system, we show important effects on the quantitative behavior of $\chi$. In particular, data for quenches to $T_f=0$ are consistent with a value of the response function exponent $\lambda _\chi=\frac{1}{2}\lambda _C(T_i=\infty)=5/8$ different from the one [$\lambda _\chi \in (0.5-0.56)$] found in a wealth of previous numerical determinations in quenches to finite final temperatures. This is interpreted as due to important pre-asymptotic corrections associated to $T_f>0$.Comment: 25 pages, 15 figures. To appear on Phys. Rev.

Multivariate Approach of End-Member Contributions to Streamflow in the Critical Zone. Case Study: Valles Caldera, New Mexico

Multivariable End-member Mixing Analysis (EMMA) that incorporates principal component analysis (PCA) is a widely utilized tool to identify the sources of water that generate streamflow in catchment hydrology. In this study, we investigated how different combinations of principal components (PC) allow assessing the importance that potential end-members have to surface waters. We evaluated mixing spaces of different dimensions in order to justify the number of end-members needed to generate streamflow. Furthermore, this multidimensional approach provided further evidence of the hydrologic processes that dominate in the headwaters at the Jemez River Basin Critical Zone Observatory (JRB-CZO). Our results showed that the U-mixing spaces of three dimensions of the La Jara and Upper Jaramillo catchments highlight the contributions of deep groundwater that the two-dimensional mixing space neglected. Conversely, in the History Grove catchment, a two-dimensional U-mixing space was enough to explain streamflow generation. Groundwater, snowmelt, rainfall and soil water are the end-members identified in each catchment. The geomorphology (e.g. aspect, topography, and geology) of each watershed and climate variability, however, influence the contribution of these source waters in each system. Groundwater contributions dominate streamflow generation in the JRB-CZO. Moreover, increments of snowmelt, rainfall and soil water contributions are observed specifically during base-flow conditions. We argue that the contributions of these end-members do not correspond specifically to overland flow, but rather contributions of shallow groundwater and subsurface lateral flow that possess the chemical signature of these source waters

Characterization of ENSO in a stratosphere-resolving version of the EC-EARTH model: comparison with observations and with the low-top version

Màster de Meteorologia, Facultat de Física, Universitat de Barcelona, Curs: 2019-2020, Tutors: Ileana Bladé Mendoza, Javier García SerranoA stratosphere-resolving configuration (HIGH-TOP) of the EC-EARTH global climate model (GCM) is used to characterize the El Ni~no-Southern Oscillation (ENSO) and compare it to observations. Despite the state of the art stratosphere, HIGH-TOP still presents some biases in the seasonal cycle and in the ENSO spatial pattern common to other GCMs. The interannual peak in the Ni~no3.4 index power spectrum is broadly captured, but the model is biased towards lower frequencies. To assess the effects of a well-resolved stratosphere in the tropical Pacific and, in particular, on ENSO, HIGH-TOP is compared with a low-top version of the model (LOW-TOP). HIGH-TOP displays systematic and statistically significant higher interannual variability in the central-eastern Pacific, along with an improvement in the ENSO pattern of sea surface temperature (SST) anomalies. The comparison of the ENSO-induced tropospheric circulation anomalies reveals a strengthening of the eastern Pacifc intertropical convergence zone (ITCZ) in HIGH-TOP with respect to LOW-TOP. Additionally, in the equatorial eastern Pacific, HIGH-TOP correctly simulates anomalous upward motion, while LOW-TOP simulates anomalous downward motion that enhances the climatological Walker circulation. The stronger ITCZ and the anomalous ascent in the eastern equatorial Pacific in HIGH-TOP are consistent with the higher total interannual variability in SST and precipitation in HIGH-TOP. Hence, incorporating a well-resolved stratosphere in the EC-EARTH model yields a more realistic representation of the variability in the central-eastern Pacific and tropical ENSO pattern

ML in Finance: Portfolio Management via Side & Size Prediction on the Bonds Market

The rise in automation and utilization of algorithms in the last decades had been meaningful in several areas, finance, and portfolio management included. The present study combines two approaches to reach an integral optimized model. The first one is the traditional approach, which starting from forecasting the future bond yield curve, generates a decision to take: establish a long position (expecting a rise on the price) or a short one (expecting a fall on the price). Therefore, the output of this first model will be to determine the position side. The second approach is the application of the bet-sizing technique to optimize the resulting decisions from the traditional model by assigning them a probability of being correct: decisions with a low probability of generating profits will have a lower size, while decisions with a high probability of generating returns will have a bigger size. The algorithms used were the ARIMA regression for the traditional model and random forest for the bet-sizing model. Cross-validation and out-of-sample backtests were conducted to evaluate how the model would have performed and results show that employing the integrated optimized model exhibits higher Sharpe ratios than using only the traditional approach. The work demonstrates that the modern techniques used along with the traditional ones reach better efficiency on returns than when only traditional models are employed. Additionally, generalizations to other areas inside finance, both on asset management as well as on credit risk are discussed

Estudio cinético de la fotodegradación de nuevas dihidropiridinas antihipertensivas en sistemas homogéneos y en simulación de sistemas biológicos.

Tesis (Licenciado en Química)De los diversos fármacos terapéuticos disponibles en el mercado formal, un número considerable se ha visto directamente relacionado con efectos secundarios del tipo fototóxico o fotoalérgico. Un ejemplo de los efectos colaterales de estos fármacos son las 4-aril-1,4-dihidropiridinas, ampliamente utilizadas como antihipertensivos los cuales actúan como bloqueadores de canales de calcio. La gran mayoría de los fármacos comerciales usados para el tratamiento de la hipertensión presentan sustituyentes aceptores de electrones sobre el grupo 4-arilo de la dihidropiridina (Ej.: Nimodipino, Felodipino), se ha buscado estudiar los efectos de la presencia de diferentes grupos dadores de electrones (Ej.: grupo metoxi, grupo hidroxilo). Teniendo en cuenta estos antecedentes, este trabajo se ha enfocado en el análisis cinético del proceso de fotodegradación de 2 diferentes dihidropiridinas con grupos dadores de electrones sobre el grupo 4-arilo (Compuestos A y B), así como la identificación de los fotoproductos generados a partir de la degradación de estos compuestos. Se ha determinado además la capacidad de estos compuestos para producir una especie reactiva del oxígeno (oxígeno molecular singulete, O2(1g)), así también como su reactividad con esta especie transiente. Dada la alta lipofilicidad de estos compuestos, adicionalmente al análisis cinético de estas dihidropiridinas en distintos solventes (medio homogéneo) también se procedió a analizar la fotodegradación de estos compuestos incorporados a medios microheterogéneos (micelas iónicas y no iónicas), que permitan estimar el comportamiento de estos compuestos en medios biológicos

Electrostatic charging of non-polar colloids by reverse micelles

Colloids dispersed in a non-polar solvent become charged when reverse micelles are added. We study the charge of individual sterically-stabilized poly(methyl methacrylate) spheres dispersed in micellar solutions of the surfactants sodium bis(2-ethyl 1-hexyl) sulfosuccinate [AOT], zirconyl 2-ethyl hexanoate [Zr(Oct)$_{2}$], and a copolymer of poly(12-hydroxystearic acid)--poly(methyl methacrylate) [PHSA-PMMA]. Although the sign of the particle charge is positive for Zr(Oct)$_{2}$, negative for AOT, and essentially neutral for PHSA-PMMA the different micellar systems display a number of common features. In particular, we demonstrate that, over a wide range of concentrations, the colloid charge is independent of the number of micelles added and scales linearly with the colloid size. A simple thermodynamic model, in which the particle charge is generated by the competitive adsorption of both positive and negative micelles, is in good agreement with the experimental data

In vitro direct conversion of somatic cells from the adult human brain into functional neurons by defined factors

Reprogramming of somatic cells into neurons provides a new approach toward cell-based therapy of neurodegenerative diseases. Conversion of postnatal astroglia from the cerebral cortex of mice into functional neurons in vitro can be achieved by forced expression of a single transcription factor. Also skin fibroblasts have been successfully reprogrammed into functional neurons yet through the synergistic action of several transcription factors. A major challenge for the translation of neuronal reprogramming into therapy concerns the feasibility of this approach in adult human tissues. This work demonstrates the potential of perivascular cells isolated from the adult human brain to serve as a substrate prompted to neuronal reprogramming by forced co-expression of neurogenic transcription factors, namely the SRY-related HMG box protein Sox2 and the basic helix loop helix (bHLH) mammalian homologue of achaete-schute-1 Mash1 (also known as Ascl1). The cells used in this study display characteristics of pericytes assessed by immunocytochemistry, fluorescence-activated cell sorting (FACS) and real time RT-PCR. The presence of neural progenitor cells was excluded by real time RT-PCR analysis of mRNAs typically expressed by these cell lineages. Upon expression of Sox2 and Mash1, these cells adopt a neuronal phenotype characterized by the expression of neuronal markers such us ßIII-Tubulin, MAP2, NeuN, GABA and calretinin. Electrophysiological recordings reveal the ability of these cells to fire repetitive action potentials and to integrate into neuronal networks when co-cultured with mouse embryonic neurons. The pericytic nature of the reprogrammed cells was further demonstrated by isolation of PDGFRß-positive cells from adult human brain cultures by FACS and monitoring the Mash1/Sox2-induced neuronal conversion by time-lapse video microscopy. Genetic fate-mapping in mice expressing an inducible Cre recombinase under the tissue non-specific alkaline phosphatase promoter corroborated that pericytes from the adult cerebral cortex can be expanded and reprogrammed in vitro into neurons by co-expression of Sox2 and Mash1. These results demonstrate the feasibility of an in vitro neuronal reprogramming approach on somatic cells isolated from the adult human cerebral cortex which could have important implications in the development of in vivo direct repair strategies in neurodegenerative diseases and brain injury

In vitro direct conversion of somatic cells from the adult human brain into functional neurons by defined factors

Reprogramming of somatic cells into neurons provides a new approach toward cell-based therapy of neurodegenerative diseases. Conversion of postnatal astroglia from the cerebral cortex of mice into functional neurons in vitro can be achieved by forced expression of a single transcription factor. Also skin fibroblasts have been successfully reprogrammed into functional neurons yet through the synergistic action of several transcription factors. A major challenge for the translation of neuronal reprogramming into therapy concerns the feasibility of this approach in adult human tissues. This work demonstrates the potential of perivascular cells isolated from the adult human brain to serve as a substrate prompted to neuronal reprogramming by forced co-expression of neurogenic transcription factors, namely the SRY-related HMG box protein Sox2 and the basic helix loop helix (bHLH) mammalian homologue of achaete-schute-1 Mash1 (also known as Ascl1). The cells used in this study display characteristics of pericytes assessed by immunocytochemistry, fluorescence-activated cell sorting (FACS) and real time RT-PCR. The presence of neural progenitor cells was excluded by real time RT-PCR analysis of mRNAs typically expressed by these cell lineages. Upon expression of Sox2 and Mash1, these cells adopt a neuronal phenotype characterized by the expression of neuronal markers such us ßIII-Tubulin, MAP2, NeuN, GABA and calretinin. Electrophysiological recordings reveal the ability of these cells to fire repetitive action potentials and to integrate into neuronal networks when co-cultured with mouse embryonic neurons. The pericytic nature of the reprogrammed cells was further demonstrated by isolation of PDGFRß-positive cells from adult human brain cultures by FACS and monitoring the Mash1/Sox2-induced neuronal conversion by time-lapse video microscopy. Genetic fate-mapping in mice expressing an inducible Cre recombinase under the tissue non-specific alkaline phosphatase promoter corroborated that pericytes from the adult cerebral cortex can be expanded and reprogrammed in vitro into neurons by co-expression of Sox2 and Mash1. These results demonstrate the feasibility of an in vitro neuronal reprogramming approach on somatic cells isolated from the adult human cerebral cortex which could have important implications in the development of in vivo direct repair strategies in neurodegenerative diseases and brain injury