Joint modelling of longitudinal and survival data for dynamic prediction in credit-related applications

Lenders monitor their borrowers over time, allowing them to dynamically predict the probability of an event of interest, such as default. The widely used survival models focus on when the event happens and can handle time-varying covariates (TVCs) and censored observations. However, an issue little addressed in the literature is that the model specification and the predictive framework depend on the type of TVC included. TVCs can be either exogenous or endogenous to the survival time. Exogenous are those whose future paths are not affected by the event’s occurrence, such as macroeconomic variables. Endogenous, on the contrary, are those whose paths are influenced by the survival status. An example of the latter would be the unpaid principal balance when the event is the default. This thesis explores new mathematical models in credit-related applications, known as joint models of longitudinal and survival data. Initially developed in medical research, these models, in their standard version, are formed by two sub-models, one for the survival process and the other for the endogenous TVC (also named longitudinal outcome in this context). A latent structure links the sub-models, commonly in the form of random effects. Joint models have two advantages compared to survival models. First, they allow us to handle possible endogeneities in the TVCs. Second, by jointly modelling both processes, they offer us a dynamic prediction framework that incorporates their mutual evolution. We propose a series of innovations to make the approach appropriate to creditrelated applications. These innovations relate to the nature of survival time, the specific evolution of the TVCs, ways to scale the technique to large datasets and how to leverage the available data in the modelling framework. In concrete, we adapt the formulation of the joint models and their performance metrics to the discrete nature of the loan data. In addition, we include autoregressive terms in the TVC specification to address observed serial correlation and enhance predictive capability. Moreover, we can study more complex specifications with larger datasets by reformulating the approach within the INLA framework, a fast and accurate algorithm for Bayesian inference. Among these specifications are the joint models with more than one TVC and the joint model that leverages geographical information to include spatial and spatio-temporal effects in the hazard function. We also introduce a more accurate way to estimate individual survival predictions using the Laplace method. Finally, to compare different models, we propose a computationally efficient implementation of the cross-entropy estimate of the posterior predictive conditional density that uses the estimates obtained in the inference step. We apply joint models to predict the time to credit events in the following three settings: default in US mortgages, full prepayment in a German consumer loan portfolio, and full prepayment in US mortgages. The main empirical results show that the autoregressive terms in the joint model let us achieve better discrimination performance, the predictive ability is significantly enhanced compared to survival models when more TVCs are considered, and the inclusion of spatial effects consistently leads to better data representation

Two electron entanglement enhancement by an inelastic scattering process

In order to assess inelastic effects on two fermion entanglement production, we address an exactly solvable two-particle scattering problem where the target is an excitable scatterer. Useful entanglement, as measured by the two particle concurrence, is obtained from post-selection of oppositely scattered particle states. The $S$ matrix formalism is generalized in order to address non-unitary evolution in the propagating channels. We find the striking result that inelasticity can actually increase concurrence as compared to the elastic case by increasing the uncertainty of the single particle subspace. Concurrence zeros are controlled by either single particle resonance energies or total reflection conditions that ascertain precisely one of the electron states. Concurrence minima also occur and are controlled by entangled resonance situations were the electron becomes entangled with the scatterer, and thus does not give up full information of its state. In this model, exciting the scatterer can never fully destroy phase coherence due to an intrinsic limit to the probability of inelastic events.Comment: 8 pages, to appear in Phys. Rev

Spermatozoa Obtained From Alpaca vas deferens. Effects of Seminal Plasma Added at Post-thawing

The viscous seminal plasma (SP) is currently a major impediment to the handling of ejaculate and the development of some biotechnologies in South American camelids. The vas deferens-collected spermatozoa of alpacas is a useful technique to avoid this problem. On the other hand, SP contains a large protein component that has been implicated in the function of spermatozoa within the female reproductive tract. In this sense, the low fertility achieved using transcervical insemination with frozen-thawed spermatozoa in alpacas could be improved by adding SP. This study aimed to evaluate the effect of the whole SP on some in vitro parameters of alpaca spermatozoa after the freezing-thawing-process and the fertility after artificial insemination. It would contribute to a better understanding of the interaction between thawed sperm cells and SP. Spermatozoa were obtained by surgically diverted vas deferens. The samples were diluted with a Tris-based extender, packaged in straws, and frozen. At thawing, each straw was divided into two post-thawing conditions: with the addition of 10% of PBS (control) or with 10% SP (treatment). The sperm cells were evaluated using dynamic parameters, sperm cell morphology, and morphometry. Fertility was assessed by an artificial insemination trial. All in vitro parameters were analyzed by ANOVA. A heterogeneity test was scheduled for the fertility trial. After the freezing-thawing process, motility and plasma membrane functionality was improved when SP was added. No differences were found for post-thaw viability between the control and treatment samples. The percentage of normal cells was higher with SP at post-thawing, and a decrease of the presence of bent tailed spermatozoa with a droplet in the SP group was observed. The length of the head spermatozoa was 3.4% higher in the samples with PBS compared to those in which SP was added. Females pregnant at day 25 post-insemination were 0/12 (with SP inside the straw) and 1/10 (without SP inside the straw). In conclusion, the presence of 10% SP at post-thawing improves sperm cells' motility, functionality, and morphology, indicating that it would be beneficial to improve the frozen-thawed alpaca's physiology spermatozoa. More fertility trials must be developed to increase this knowledge

Caracterización varietal del chile habanero (Capsicum chinense Jacq.) var. Rosita

Objective: Characterize the Rosita variety of habanero pepper (Capsicum chinense Jacq.) as a variant landrace of the traditional habanero for conservation and genetic improvement purposes. Design/methodology/approach: Fruits were collected from ten production units in 2015, reproducing and characterizing them. The varietal characterization was carried out ex situ under greenhouse and fertigation conditions based on the IPGRI guide (1995), characterizing the seedling in nursery and the plant to transplant: leaves, stem, flower, fruit and seed. The fertilization was carried out applying every third day a gram of triple fertilizer 19 (N-P-K) dissolved in water, from the appearance of the first true leaves, after the transplant the formula 100-100-100 (N-P-K) was applied by fertigation. With the data obtained and the use of descriptive statistics, averages and standard deviations were obtained for the quantitative characteristics. The qualitative characteristics gave value to a certain characteristic from its highest absolute frequency. Results: The distinguishing characteristics found were: hypocotyl with anthocyanins and pubescence; plant with semi-perennial cycle; habit of prostrate growth; anthocyanins in the knots; height greater than 85 cm; color of greenish yellow corolla; two or more flowers per armpit acampa breadfruit; transverse wrinkling of the fruit and medium-sized rough seed. Limitations on study/implications: The presence of some pests was treated with chemicals for whitefly, such as CalypsoÒ (Thiacloprid), ActaraÒ (Thiamethoxam), EvisectÒ (Tiocyclam hydrogenoxalate), and AplaudÒ (Buprofezin). Findings/conclusions: The distinctive morphological characteristics of habanero pepper Rosita were found in seedlings, flowering plants, fruits and seeds, which differentiate it from traditional habanero peppers.Objetivo: Caracterizar la variedad Rosita de chile habanero (Capsicum chinense Jacq.) como una variante de uso común del habanero tradicional con fines de conservación y mejoramiento genético. Diseño/metodología/aproximación: Fueron recolectados frutos de diez unidades de producción, reproduciéndolas para su caracterización ex situ en condiciones de invernadero y fertirriego con base a la guía del IPGRI (1995), caracterizando la plántula en vivero y la planta al trasplante: hojas, tallo, flor, fruto y semilla. La fertilización de realizó aplicando cada tercer día un gramo de fertilizante triple 19 (N-P-K) disuelto en agua, a partir de la aparición de las primeras hojas verdaderas, después del trasplante se aplicó mediante fertirriego la fórmula 100-100-100 (N-P-K). Con los datos obtenidos y el uso de estadística descriptiva se obtuvieron promedios y desviación estándar para las características cuantitativas. Las características cualitativas dieron valor a una determinada característica a partir de su mayor frecuencia absoluta. Resultados: Las características distintivas fueron: hipocotilo con antocianinas y pubescencia; planta con ciclo semi-perenne; hábito de crecimiento postrado; antocianinas en los nudos; altura mayor de 85 cm; color de la corola amarillo verdosa; dos o más flores por axila fruto acampanulado; arrugamiento trasversal del fruto y semilla rugosa de tamaño medio. Limitaciones del estudio/implicaciones: La presencia de algunas organismos plaga fueron combatidos con CalypsoÒ (Thiacloprid), ActaraÒ (Tiametoxam), EvisectÒ (Tiocyclam hidrogenoxalato), y AplaudÒ (Buprofezin). Hallazgos/conclusiones: Las características morfológicas distintivas del chile habanero Rosita se encontraron en plántula, planta flor, fruto y semilla, que lo diferencian del chile habanero tradicional

Isolation and characterization of mercury resistant trichoderma strains from soil with high levels of mercury and its effects on Arabidopsis thaliana mercury uptake

"Traditional mining activities are usually correlated with high levels of soil pollution, which is a major environmental concern. Extensive mining activities have taken place in the San Joaquin region in the State of Querétaro, México resulting in high levels of mercury soil pollution (up to 1532 ± 300 mg/kg). We isolated mercury-resistant fungal strains from the San Joaquin region soils and identified them through morphologic characteristics and ITS rDNA region sequence analysis. We determined that fungi isolated belong to the genus Trichoderma. All the isolates selected showed the ability to catalyze the volatilization of Hg. For air sampling, an active sampling device was constructed and using acid KMnO4 as an absorbent, the concentration of mercury in solution was determined through the cold vapor atomic absorption method. The results show mercury volatilization from the fungal species assay, with a maximum of 213.04 ± 32.6 µg/m3 while mycelium accumulation ranged from less than 17.5 ± 2.9 to 20.0 ± 3.4 µg/g. The fungal isolates were also evaluated for their ability to reduce mercury uptake in Arabidopsis thaliana. These observations suggest the utility of Trichoderma for the mobilization of mercury in those contaminated soils.

Ab-initio approach to the stability and the structural, electronic and magnetic properties of the (001) Znfe₂O₄ surface terminations

We present a Density Functional Theory (DFT) based study of the structural and magnetic properties of the (001) surface of the semiconducting oxide Znfe₂O₄ (spinel structure). The calculations were performed using the DFT based ab initio plane wave and pseudopotential method as implemented in the Quantum Espresso code. The all electron Full-potential linearized-augmented-plane-wave method (FP-LAPW) was also employed to check the reproducibility of the plane wave method. In both calculations the DFT+U methodology was employed and different (001) surface terminations of Znfe₂O₄ were studied. We find that the surface terminated in Zn is the stable one. For all the (001) surface terminations our calculations predict that the Zn-Fe cationic inversion (antisites), which are defects in bulk Znfe₂O₄, becomes stable and an integral part of the surface. Also, a ferrimagnetic behavior is predicted for the case of anti-sites in the superficial layer. Our results for different properties of the surface of Znfe₂O₄ are compared with those obtained in bulk samples and those reported in the literature.Facultad de Ciencias ExactasInstituto de Física La Plat

When Are New Hippocampal Neurons, Born in the Adult Brain, Integrated into the Network That Processes Spatial Information?

Adult-born neurons in the dentate gyrus (DG) functionally integrate into the behaviorally relevant hippocampal networks, showing a specific Arc-expression response to spatial exploration when mature. However, it is not clear when, during the 4- to 6-week interval that is critical for survival and maturation of these neurons, this specific response develops. Therefore, we characterized Arc expression after spatial exploration or cage control conditions in adult-born neurons from rats that were injected with BrdU on one day and were sacrificed 1, 7, 15, 30, and 45 days post-BrdU injection (PBI). Triple immunostaining for NeuN, Arc, and BrdU was analyzed through the different DG layers. Arc protein expression in BrdU-positive cells was observed from day 1 to day 15 PBI but was not related to behavioral stimulation. The specific Arc-expression response to spatial exploration was observed from day 30 and 45 in about 5% of the BrdU-positive cell population. Most of the BrdU-positive neurons expressing Arc in response to spatial exploration (∼90%) were located in DG layer 1, and no Arc expression was observed in cells located in the subgranular zone (SGZ). Using the current data and that obtained previously, we propose a mathematical model suggesting that new neurons are unlikely to respond to exploration by expressing Arc after they are 301 days old, and also that in a 7-month-old rat the majority (60%) of the neurons that respond to exploration must have been born during adulthood; thus, suggesting that adult neurogenesis in the DG is highly relevant for spatial information processing

Biological processes, properties and molecular wiring diagrams of candidate low-penetrance breast cancer susceptibility genes

Background: Recent advances in whole-genome association studies (WGASs) for human cancer risk are beginning to provide the part lists of low-penetrance susceptibility genes. However, statistical analysis in these studies is complicated by the vast number of genetic variants examined and the weak effects observed, as a result of which constraints must be incorporated into the study design and analytical approach. In this scenario, biological attributes beyond the adjusted statistics generally receive little attention and, more importantly, the fundamental biological characteristics of low-penetrance susceptibility genes have yet to be determined. Methods: We applied an integrative approach for identifying candidate low-penetrance breast cancer susceptibility genes, their characteristics and molecular networks through the analysis of diverse sources of biological evidence. Results: First, examination of the distribution of Gene Ontology terms in ordered WGAS results identified asymmetrical distribution of Cell Communication and Cell Death processes linked to risk. Second, analysis of 11 different types of molecular or functional relationships in genomic and proteomic data sets defined the 'omic' properties of candidate genes: i/ differential expression in tumors relative to normal tissue; ii/ somatic genomic copy number changes correlating with gene expression levels; iii/ differentially expressed across age at diagnosis; and iv/ expression changes after BRCA1 perturbation. Finally, network modeling of the effects of variants on germline gene expression showed higher connectivity than expected by chance between novel candidates and with known susceptibility genes, which supports functional relationships and provides mechanistic hypotheses of risk. Conclusion: This study proposes that cell communication and cell death are major biological processes perturbed in risk of breast cancer conferred by low-penetrance variants, and defines the common omic properties, molecular interactions and possible functional effects of candidate genes and proteins