Early Stopping of a Neural Network via the Receiver Operating Curve.

This thesis presents the area under the ROC (Receiver Operating Characteristics) curve, or abbreviated AUC, as an alternate measure for evaluating the predictive performance of ANNs (Artificial Neural Networks) classifiers. Conventionally, neural networks are trained to have total error converge to zero which may give rise to over-fitting problems. To ensure that they do not over fit the training data and then fail to generalize well in new data, it appears effective to stop training as early as possible once getting AUC sufficiently large via integrating ROC/AUC analysis into the training process. In order to reduce learning costs involving the imbalanced data set of the uneven class distribution, random sampling and k-means clustering are implemented to draw a smaller subset of representatives from the original training data set. Finally, the confidence interval for the AUC is estimated in a non-parametric approach

Statistical Contributions to Operational Risk Modeling

In this dissertation, we focus on statistical aspects of operational risk modeling. Specifically, we are interested in understanding the effects of model uncertainty on capital reserves due to data truncation and in developing better model selection tools for truncated and shifted parametric distributions. We first investigate the model uncertainty question which has been unanswered for many years because researchers, practitioners, and regulators could not agree on how to treat the data collection threshold in operational risk modeling. There are several approaches under consideration—the empirical approach, the “naive” approach, the shifted approach, and the truncated approach—for fitting the loss severity distribution. Since each approach is based on a different set of assumptions, different probability models emerge. Thus, model uncertainty arises. When possible we investigate such model uncertainty analytically using asymptotic theorems of mathematical statistics and several parametric distributions commonly used for operational risk modeling, otherwise we rely on Monte Carlo simulations. The effect of model uncertainty on risk measurements is quantified by evaluating the probability of each approach producing conservative capital allocations based on the value-at-risk measure. These explorations are further illustrated using a real data set for legal losses in a business unit. After clarifying some prevailing misconceptions around the model uncertainty issue in operational risk modeling, we then employ standard (Akaike Information Criterion, AIC, and Bayesian Information Criterion, BIC) and introduce new model selection tools for truncated and shifted parametric models. We find that the new criteria, which are based on information complexity and asymptotic mean curvature of the model likelihood, are more effective at distinguishing between the competing models than AIC and BIC

The governance-production nexus of eco-efficiency in Chinese resource-based cities:A two-stage network DEA approach

For decades, resource-based cities in China have significantly contributed to China's socio-economic development. The heavy resource dependence of resource-based cities inevitably leads to a series of environmental problems. Mitigating environmental impacts in an unthinking manner might be disruptive for economic development. Improving eco-efficiency has been a crucial solution for protecting the environment while mitigating its negative economic impact. However, the method commonly used to evaluate the eco-efficiency – that is, the black-box data envelopment analysis (DEA) – cannot examine the inefficiencies of the internal structure, and as a result, the underlying management defects are unclear. To open the black box, this study presents a two-stage network DEA framework incorporating government and industrial sectors and measures the eco-efficiency of 84 resource-based cities during the post-financial crisis period (2007–2015). The results indicate that the average eco-efficiency of China's resource-based cities shows a promising increase, and there is a positive relationship between governance efficiency and production efficiency. The decreasing trend of governance efficiency in the Central, Western, and Northeast regions after 2014 shows the low quality of the government sector in the usage of fiscal income. Proactive disclosure of how the government sector conducts public business and spends taxpayers' money should be made to increase transparency, attract more entrepreneurial resources to carry out production activities, and further improve sustainability. The two-stage network DEA framework helps obtain more insights into the internal management defects of the government and industrial sectors and enhance their cooperation to improve the eco-efficiency precisely

Optimization of Inorganic Ceramic Membrane Filtration Process for Tea Enzymes

In order to enhance the clarity of tea enzymes while maximizing the preservation of their functional components during the clarification process, this experiment utilized tea enzymes derived from summer and autumn tea fermentation as the primary material. Through both single-factor and response surface experiments, the effects of inorganic ceramic membrane pore size, transmembrane power, transmembrane pressure, and transmembrane temperature on the content of functional components, membrane flux, transmittance, and soluble solids content of the enzyme solution after membrane filtration were examined. The objective was to determine the optimal conditions for ceramic membrane filtration of tea enzymes. The results showed that, the ideal conditions for ceramic membrane filtration of tea enzymes were as follows: Membrane pore size of 400 nm, transmembrane power of 47 Hz, transmembrane pressure of 0.28±0.02 MPa, and transmembrane temperature of 15±2 ℃. Under these conditions, the retention rates of tea polyphenols, theanine, zinc, selenium, and soluble solids content in tea enzymes were 95.28%, 82.91%, 90.48%, 91.67%, and 84.46% respectively. The transmittance reached 85.10%±0.12% with 2.5-fold improvement compared to before membrane filtration. Additionally, the membrane flux achieved 123.25±2.68 m3/(m2·h). These optimal conditions not only maximized the retention of functional components in tea enzymes, but also ensured their transparency and uniformity. Therefore, employing these conditions for the filtration and clarification of tea enzymes was a viable approach

Model Uncertainty in Operational Risk Modeling Due to Data Truncation: A Single Risk Case

Over the last decade, researchers, practitioners, and regulators have had intense debates about how to treat the data collection threshold in operational risk modeling. Several approaches have been employed to fit the loss severity distribution: the empirical approach, the “naive” approach, the shifted approach, and the truncated approach. Since each approach is based on a different set of assumptions, different probability models emerge. Thus, model uncertainty arises. The main objective of this paper is to understand the impact of model uncertainty on the value-at-risk (VaR) estimators. To accomplish that, we take the bank’s perspective and study a single risk. Under this simplified scenario, we can solve the problem analytically (when the underlying distribution is exponential) and show that it uncovers similar patterns among VaR estimates to those based on the simulation approach (when data follow a Lomax distribution). We demonstrate that for a fixed probability distribution, the choice of the truncated approach yields the lowest VaR estimates, which may be viewed as beneficial to the bank, whilst the “naive” and shifted approaches lead to higher estimates of VaR. The advantages and disadvantages of each approach and the probability distributions under study are further investigated using a real data set for legal losses in a business unit (Cruz 2002)

Model Uncertainty and Selection of Risk Models for Left-Truncated and Right-Censored Loss Data

Insurance loss data are usually in the form of left-truncation and right-censoring due to deductibles and policy limits, respectively. This paper investigates the model uncertainty and selection procedure when various parametric models are constructed to accommodate such left-truncated and right-censored data. The joint asymptotic properties of the estimators have been established using the Delta method along with Maximum Likelihood Estimation when the model is specified. We conduct the simulation studies using Fisk, Lognormal, Lomax, Paralogistic, and Weibull distributions with various proportions of loss data below deductibles and above policy limits. A variety of graphic tools, hypothesis tests, and penalized likelihood criteria are employed to validate the models, and their performances on the model selection are evaluated through the probability of each parent distribution being correctly selected. The effectiveness of each tool on model selection is also illustrated using well-studied data that represent Wisconsin property losses in the United States from 2007 to 2010

ADSORPTION AND DISSOCIATION OF O/O2 ON FLAT AND STEPPED PALLADIUM SURFACES

The 5-parameter Morse potential (5-MP) of an O–Pd system and the improved extended LEPS potential of an O2–Pd system were constructed. The adsorption and dissociation of oxygen atoms and oxygen molecules on flat and stepped palladium single crystal surfaces were studied detailedly, and the data of adsorption sites, adsorption geometry, binding energy, eigenvibration, dissociative mechanism, etc. were obtained. Theoretical results show that the high-symmetry sites are the preferred adsorption sites for tilted adsorption of oxygen molecules, and the tilted angle depends on the number of atoms per unit surface area. Meanwhile, a variety of dissociation pathways are analyzed in detail related to the O2–Pd(111) system. These results show that the adsorptive dissociation of oxygen molecules on the Pd(111) hollow site is precursor-mediated, on the Pd(111) bridge site is direct dissociation and on the Pd(111) top site is not only depended on the translational energy, but also depended on the vibrational energy. Moreover, the role of the step defect for oxygen atoms and oxygen molecules is also discussed related to flat surface. Theoretical results are in good agreement with the experimental results, and explain well the divergence [N. Salanov and V. N. Bibin, Surf. Sci. 441 (1999) 399; P. D. Nolan, B. R. Lutz, P. L. Tanaka and C. B. Mullins, Surf. Sci. 419 (1998) L107] related to the O2 dissociation mechanism.Oxygen, palladium, pair-potential, 5-MP, LEPS