Bayesian optimization of the PC algorithm for learning Gaussian Bayesian networks

The PC algorithm is a popular method for learning the structure of Gaussian Bayesian networks. It carries out statistical tests to determine absent edges in the network. It is hence governed by two parameters: (i) The type of test, and (ii) its significance level. These parameters are usually set to values recommended by an expert. Nevertheless, such an approach can suffer from human bias, leading to suboptimal reconstruction results. In this paper we consider a more principled approach for choosing these parameters in an automatic way. For this we optimize a reconstruction score evaluated on a set of different Gaussian Bayesian networks. This objective is expensive to evaluate and lacks a closed-form expression, which means that Bayesian optimization (BO) is a natural choice. BO methods use a model to guide the search and are hence able to exploit smoothness properties of the objective surface. We show that the parameters found by a BO method outperform those found by a random search strategy and the expert recommendation. Importantly, we have found that an often overlooked statistical test provides the best over-all reconstruction results

G93-1145 Management of the Army Cutworm and Pale Western Cutworm

This NebGuide describes the life cycle of the army cutworm and pale western cutworm, and provides recommendations for management.The army cutworm, Euxoa auxiliaris, and the pale western cutworm, Agrotis orthogonia, are sporadic pests that are distributed throughout the Great Plains. The army cutworm can be found throughout Nebraska, but is more common in the western half of the state. Because of the drier environment, the pale western cutworm is found only in the western third of Nebraska. Both cutworms can feed on a vast array of crops and weeds. Their major economic impact is limited to winter wheat and alfalfa, because these are the vulnerable crops growing in the early spring when larval feeding activity occurs. However, they can also cause substantial damage to early spring row crops (sugarbeets and corn), especially in areas where winter cereal cover crops are used

G93-1145 Management of the Army Cutworm and Pale Western Cutworm

This NebGuide describes the life cycle of the army cutworm and pale western cutworm, and provides recommendations for management.The army cutworm, Euxoa auxiliaris, and the pale western cutworm, Agrotis orthogonia, are sporadic pests that are distributed throughout the Great Plains. The army cutworm can be found throughout Nebraska, but is more common in the western half of the state. Because of the drier environment, the pale western cutworm is found only in the western third of Nebraska. Both cutworms can feed on a vast array of crops and weeds. Their major economic impact is limited to winter wheat and alfalfa, because these are the vulnerable crops growing in the early spring when larval feeding activity occurs. However, they can also cause substantial damage to early spring row crops (sugarbeets and corn), especially in areas where winter cereal cover crops are used

EC03-1568 Grasshopper Identification Guide for Rangeland and Pasture Summer Feeding Species

Many kinds of summer-feeding grasshoppers are found in Nebraska rangeland and pastures. Of these, the six species listed in this guide are most likely to be numerous during outbreak years. These species overwinter as eggs and hatch through much of May and June. When abundant they can cause severe damage to rangeland and pastures, especially when dry conditions limit grass growth. Identification of the species present is important because some have greater potential for damage than others

Uniform random generation of large acyclic digraphs

Directed acyclic graphs are the basic representation of the structure underlying Bayesian networks, which represent multivariate probability distributions. In many practical applications, such as the reverse engineering of gene regulatory networks, not only the estimation of model parameters but the reconstruction of the structure itself is of great interest. As well as for the assessment of different structure learning algorithms in simulation studies, a uniform sample from the space of directed acyclic graphs is required to evaluate the prevalence of certain structural features. Here we analyse how to sample acyclic digraphs uniformly at random through recursive enumeration, an approach previously thought too computationally involved. Based on complexity considerations, we discuss in particular how the enumeration directly provides an exact method, which avoids the convergence issues of the alternative Markov chain methods and is actually computationally much faster. The limiting behaviour of the distribution of acyclic digraphs then allows us to sample arbitrarily large graphs. Building on the ideas of recursive enumeration based sampling we also introduce a novel hybrid Markov chain with much faster convergence than current alternatives while still being easy to adapt to various restrictions. Finally we discuss how to include such restrictions in the combinatorial enumeration and the new hybrid Markov chain method for efficient uniform sampling of the corresponding graphs.Comment: 15 pages, 2 figures. To appear in Statistics and Computin

Experimental identification and validation of models in micro and macro plasticity

For micro-macro approaches to finite plasticity, one needs experimental results on both scales, the engineering scale (macro scale) and the crystal scale (micro scale). Since we know that a monocrystal behaves different from a crystallite embedded in a polycrystal, one is also interested in data obtained on the micro scale of a polycrystal. Such data is needed not only for the identification of the material parameters like hardening variables, but also for the validation of these models. In this paper, experiments on both scales and, in parallel, FEM-simulations are presented, in order to compare the results of both approaches. The specimens stem from a rolled sheet of the deep-drawing steel DC04. On the micro scale indenter tests have been performed and the orientation changes in the volume below the indent have been measured using micron-resolution 3D x-ray microscopy (Larson et al., 2004, 2008). On the macro scale the usual tension tests and additional shear tests in different directions (Bouvier etal.,2006) have been performed. In corresponding simulations, the micro-macro transition is performed by a full constrained Taylor-model and, in order to overcome the drawbacks of the Taylor-model, the RVE technique has been applied

Single Superfield Representation for Mixed Retarded and Advanced Correlators in Disordered Systems

We propose a new single superfield representation for mixed retarded and advanced correlators for noninteracting disordered systems. The method is tested in the simpler context of Random Matrix theory, by comparing with well known universal behavior for level spacing correlations. Our method is general and could be especially interesting to study localization properties encoded in the mixed correlators of Quantum Hall systems.Comment: 13 pages including two figures, RevTex4. Improved version. Figures changed. To appear in Journal of Physics

Hospital variation in missed nursing care

Quality of nursing care across hospitals is variable, and this variation can result in poor patient outcomes. One aspect of quality nursing care is the amount of necessary care that is omitted. This article reports on the extent and type of nursing care missed and the reasons for missed care. The MISSCARE Survey was administered to nursing staff (n = 4086) who provide direct patient care in 10 acute care hospitals. Missed nursing care patterns as well as reasons for missing care (labor resources, material resources, and communication) were common across all hospitals. Job title (ie, registered nurse vs nursing assistant), shift worked, absenteeism, perceived staffing adequacy, and patient work loads were significantly associated with missed care. The data from this study can inform quality improvement efforts to reduce missed nursing care and promote favorable patient outcomes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94115/1/Hospital variation in missed nursing care.pd