Bayesian Linear Regression with Conditional Heteroskedasticity

In this paper we consider adaptive Bayesian semiparametric analysis of the linear regression model in the presence of conditional heteroskedasticity. The distribution of the error term on predictors are modelled by a normal distribution with covariate-dependent variance. We show that a rate-adaptive procedure for all smoothness levels of this standard deviation function is performed if the prior is properly chosen. More specifically, we derive adaptive posterior distribution rate up to a logarithm factor for the conditional standard deviation based on a transformation of hierarchical Gaussian spline prior and log-spline prior respectively

Dynamic Behavior of Headspace Gases in Modified Atmosphere Packaging for Meat.

Headspace gas composition in food packaging undergoes dynamic changes as a result of film permeability, postmortem metabolic activity, CO\sb2 absorption in water and lipid, and bacteria growth and respiration. A methodology to study dynamic behavior of headspace CO\sb2 was developed and used to identify the significant factors influencing CO\sb2 behavior within modified atmosphere packaging (MAP) systems for beef. Additionally, a mathematical structure suitable for modeling microbial growth in MAP systems was presented. A combined analytical and experimental method was developed to investigate headspace CO\sb2 changes during isothermal storage. The ideal gas law was used as a theoretical basis, and a gas impermeable and constant volume chamber was constructed to evaluate the theoretical derivation. Changes in headspace pressure caused by dynamic interactions between beef and MAP atmospheres were monitored to predict concentration changes of CO\sb2 within the chamber. Two sets of independent experiments were conducted to evaluate the effects of initial packaging/product parameters and storage conditions on headspace CO\sb2 changes. The proposed methodology for measuring CO\sb2 concentration changes was confirmed by gas analysis and proved valid for prediction of headspace CO\sb2 concentration changes in MAP atmosphere within the range of initial gas composition 20% to 100% CO\sb2 balanced with N\sb2, temperature 3\sp\circ to 13\sp\circC, and initial headspace pressure 111 to 155 kPa. Headspace-to-meat volume ratio was the most significant packaging parameter affecting headspace CO\sb2 changes, and surface area and volume of meat sample also influenced headspace CO\sb2 changes. Decreased storage temperature reduced CO\sb2 concentration remaining in headspace. Higher initial CO\sb2 concentration resulted in more pronounced CO\sb2 concentration changes. Higher headspace gas pressures caused increased rates of CO\sb2 change. Biological factors of meat also affected headspace CO\sb2 changes. Two mathematical descriptions based on (1) a modified and additive Arrhenius equation and (2) a modified Arrhenius temperature characteristic equation were developed to describe the combined effects of temperature and initial gas composition of modified atmosphere storage on the population growth rate coefficients of Listeria monocytogenes and Pseudomonas fluorescens. The mathematical descriptions were shown applicable for oxygen concentration from 0% to 20.99% and carbon dioxide concentration from 0.03% to 80%

R&D offshoring and technology learning in emerging economies: Firm-level evidence from the ICT industry

This paper studies the impact of the R&D offshoring of multinational enterprises on the firms in host emerging economies. We develop a two-stage non-cooperative game to analyze the strategic interaction between multinational and host country enterprises engaged in R&D investment. An empirical analysis of 12,309 manufacturing firms in the ICT industry in China shows that R&D offshoring has a positive effect on the intensity of the R&D of host country firms. However, the magnitude of the impact depends on both the technological and geographical distance between the multinational and host country firms. The policy implications of these findings are that the governments of host country should be cautious about allowing advanced multinational R&D investment in under-developed sectors, but they should encourage such investment in developed sectors; and that local governments should be involved in R&D policy making because the positive impact of multinational R&D offshoring diminishes as the geographical distance between the multinational and host country firms increases.Research and Development, Offshoring, Spillovers, Emerging Economies

Envelope theorem in dynamic economic models with recursive utility

This paper investigates the first-order differentiability properties of the value function in dynamic economic models with recursive preferences where the optimal policy may lie at the boundary of the feasible set under several regular assumptions originating from the static optimization theory plus, an additional asymptotic conditionSupport from the Ministerio de Economía y Competitividad (Spain), grants ECO 2014-56384-P, MDM 2014-0431, and Comunidad de Madrid, MadEco-CM S2015/HUM-3444 is gratefully acknowledge

Contributions to Bayesian nonparametrics

This dissertation focuses on the frequentist properties of Bayesian procedures in a broad spectrum of infinite-dimensional statistical models via Bayesian nonparametric approaches. Three essays concern the asymptotic aspects of posterior distribution in various statistical models presented in the subsequent three chapters. In the context of multivariate density estimation discussed in Chapter 2, a Bernstein-Dirichlet prior is constructed in the space of multivariate densities on hypercube and the corresponding posterior contraction rate is obtained. We implement this model through a novel sampling algorithm based on a slice sampling scheme for the simulated and real data. In Chapter 3, we consider a Bayesian semiparametric approach for a linear regression model with conditional moment restrictions. The error variable follows a Gaussian distribution whose variance depends on the predictors. An adaptive Bayesian procedure is performed when the priors on the conditional standard deviation function are carefully constructed. Chapter 4 is devoted to the issue of posterior convergence rate for a broad range of priors. Motivated by the boundary support estimation problems where any constructed prior could not meet the usual criteria for large sample analysis of the posterior distribution, we develop a new yardstick that allows flexible prior selections to counteract these problems by the stronger model conditions and meanwhile the rate optimality property is maintained.Esta tesis se centra en las propiedades frecuentistas de los procedimientos Bayesianos dentro de un amplio espectro de modelos estadísticos de dimensión infinita a través de métodos no paramétricos Bayesianos. Se presentan tres ensayos sobre los aspectos asintóicos de la distribución a posteriori en varios modelos estadísticos introducidos en tres capítulos. En el Capítulo 2, dentro de un contexto de estimación Bayesiana de densidades, se construye una distribución a priori del tipo Berstein-Dirichlet en el espacio de densidades multivariantes en hipercubo unidad y se obtiene la tasa de convengencia de la distribución a posteriori correspondiente. Se desarrolla un nuevo algoritmo de muestreo para este modelo basado en métodos de “slice sampling” y se ilustra mediante datos simulados y reales. En el Capítulo 3, se considera un enfoque semiparamétrico Bayesiano para un modelo de regresión lineal con restricciones de momentos condicionales. La variable de error sigue una distribución Gaussiana cuya varianza depende de los predictores. Se desarrolla un procedimiento Bayesiano adaptativo en el que las distribuciones a priori sobre la función de desviación estándar condicional se construyen cuidadosamente. El Capítulo 4 está dedicado a la cuestión de la tasa de convergencia de la distribución a posteriori en una amplia gama de modelos a priori. Teniendo en cuenta los problemas de estimación en la frontera del soporte donde ning ´un modelo a priori puede cumplir los criterios habituales para el análisis de la distribucióon a posteriori en muestras grandes, se desarrolla un nuevo criterio que permite la selección de modelos a priori flexibles para contrarrestar estos problemas con condiciones del modelo más fuertes, manteniendo además la propiedad de tasa óptima.Programa Oficial de Doctorado en Ingeniería MatemáticaPresidente: Juan Miguel Marín Diazaraque.- Secretario: Nuria Torrado Robles.- Vocal: Fabrizio Leise

High Ozone (O3) Affects the Fitness Associated with the Microbial Composition and Abundance of Q Biotype Bemisia tabaci

Abstract Ozone (O3) affects the fitness of an insect, such as its development, reproduction and protection against fungal pathogens, but the mechanism by which it does so remains unclear. Here, we compared the fitness (i.e., the growth and development time, reproduction and protection against Beauveria bassiana (B. bassiana) of Q biotype whiteflies fumigated under hO3 (280 ± 20 ppb) and control O3 (50 ± 10 ppb) concentrations. Moreover, we determined that gene expression was related to development, reproduction and immunity to B. bassiana and examined the abundance and composition of bacteria and fungi inside of the body and on the surface of the Q biotype whitefly. We observed a significantly enhanced number of eggs that were laid by a female, shortened developmental time, prolonged adult lifespan, decreased weight of one eclosion, and reduced immunity to B. bassiana in whiteflies under hO3, but hO3 did not significantly affect the expression of genes related to development, reproduction and immunity. However, hO3 obviously changed the composition of the bacterial communities inside of the body and on the surface of the whiteflies, significantly reducing Rickettsia and enhancing Candidatus_Cardinium. Similarly, hO3 significantly enhanced Thysanophora penicillioides from the Trichocomaceae family and reduced Dothideomycetes (at the class level) inside of the body. Furthermore, positive correlations were found between the abundance of Candidatus_Cardinium and the female whitefly ratio and the fecundity of a single female, and positive correlations were found between the abundance of Rickettsia and the weight of adult whiteflies just after eclosion and immunity to B. bassiana. We conclude that hO3 enhances whitefly development and reproduction but impairs immunity to B. bassiana, and our results also suggest that the changes to the microbial environments inside of the body and on the surface could be crucial factors that alter whitefly fitness under hO3. Key words: Bemisia tabaci, high ozone (hO3), fitness, microbial communities, inside of the body, on the surfac

Bayesian multivariate Bernstein polynomial density estimation

This paper introduces a new approach to Bayesian nonparametric inference for densities on the hypercube, based on the use of a multivariate Bernstein polynomial prior. Posterior convergence rates under the proposed prior are obtained. Furthermore, a novel sampling scheme, based on the use of slice sampling techniques, is proposed for estimation of the posterior predictive density. The approach is illustrated with both simulated and real data example

Analyses of m6A regulatory genes and subtype classification in atrial fibrillation

ObjectiveTo explore the role of m6A regulatory genes in atrial fibrillation (AF), we classified atrial fibrillation patients into subtypes by two genotyping methods associated with m6A regulatory genes and explored their clinical significance.MethodsWe downloaded datasets from the Gene Expression Omnibus (GEO) database. The m6A regulatory gene expression levels were extracted. We constructed and compared random forest (RF) and support vector machine (SVM) models. Feature genes were selected to develop a nomogram model with the superior model. We identified m6A subtypes based on significantly differentially expressed m6A regulatory genes and identified m6A gene subtypes based on m6A-related differentially expressed genes (DEGs). Comprehensive evaluation of the two m6A modification patterns was performed.ResultsThe data of 107 samples from three datasets, GSE115574, GSE14975 and GSE41177, were acquired from the GEO database for training models, comprising 65 AF samples and 42 sinus rhythm (SR) samples. The data of 26 samples from dataset GSE79768 comprising 14 AF samples and 12 SR samples were acquired from the GEO database for external validation. The expression levels of 23 regulatory genes of m6A were extracted. There were correlations among the m6A readers, erasers, and writers. Five feature m6A regulatory genes, ZC3H13, YTHDF1, HNRNPA2B1, IGFBP2, and IGFBP3, were determined (p < 0.05) to establish a nomogram model that can predict the incidence of atrial fibrillation with the RF model. We identified two m6A subtypes based on the five significant m6A regulatory genes (p < 0.05). Cluster B had a lower immune infiltration of immature dendritic cells than cluster A (p < 0.05). On the basis of six m6A-related DEGs between m6A subtypes (p < 0.05), two m6A gene subtypes were identified. Both cluster A and gene cluster A scored higher than the other clusters in terms of m6A score computed by principal component analysis (PCA) algorithms (p < 0.05). The m6A subtypes and m6A gene subtypes were highly consistent.ConclusionThe m6A regulatory genes play non-negligible roles in atrial fibrillation. A nomogram model developed by five feature m6A regulatory genes could be used to predict the incidence of atrial fibrillation. Two m6A modification patterns were identified and evaluated comprehensively, which may provide insights into the classification of atrial fibrillation patients and guide treatment

Wine Grape Pomace as Antioxidant Dietary Fiber for Enhancing Nutritional Value and Improving Storability of Yogurt and Salad Dressing

Wine grape pomace (WGP) as a source of antioxidant dietary fiber (ADF) was fortified in yogurt (Y), Italian (I) and Thousand Island (T) salad dressings. During the three weeks of storage at 4 °C, viscosity and pH of WGP-Y increased and decreased, respectively, but syneresis and lactic acid percentage of WGP-Y and pH of WGP-I and WGP-T were stable. Adding WGP resulted in 35-65% reduction of peroxide values in all samples. Dried whole pomace powder (WP) fortified products had dietary fiber content of 0.94-3.6% (w/w product), mainly insoluble fractions. Total phenolic content and DPPH radical scavenging activity were 958-1340 mg GAE/kg product and 710-936 mg AAE/kg product, respectively. The highest ADF were obtained in 3%WP-Y, 1%WP-I and 2%WP-T, while 1%WP-Y, 0.5%WP-I and 1%WP-T were mostly liked by consumers based on the sensory study. Study demonstrated that WGP may be used as a functional food ingredient for promoting human health and extending shelf-life of food products.Keywords: yogurt, antioxidant dietary fiber, wine grape pomace, salad dressing, storabilityKeywords: yogurt, antioxidant dietary fiber, wine grape pomace, salad dressing, storabilit

Structural roles of TiO2 in CaF2- SiO2-CaO-TiO2 submerged arc welding fluxes

A series of fused CaF2-SiO2-CaO-based fluxes geared towards submerged arc welding has been prepared with incremental TiO2 additions. Through systematic investigation on physical properties, quantitative relationship between TiO2 content and corresponding structural information has been established, and the roles played by TiO2 have been profiled. It is found that TiO2 has been introduced into the silicate network by acting as network-former, increasing the degree of polymerization while lowering the strength of the flux.The National Natural Science Foundation of China, Newton Advanced Fellowship by the Royal Society , Special Fund for Key Program of Science and Technology of Liaoning Province, Research Fund for Central Universities, Xingliao Talents Program and State Key Laboratory of Metal Material for Marine Equipment and Application.http://link.springer.com/journal/116632021-08-20am2021Materials Science and Metallurgical Engineerin