A Tutorial on the Expectation-Maximization Algorithm Including Maximum-Likelihood Estimation and EM Training of Probabilistic Context-Free Grammars

The paper gives a brief review of the expectation-maximization algorithm (Dempster 1977) in the comprehensible framework of discrete mathematics. In Section 2, two prominent estimation methods, the relative-frequency estimation and the maximum-likelihood estimation are presented. Section 3 is dedicated to the expectation-maximization algorithm and a simpler variant, the generalized expectation-maximization algorithm. In Section 4, two loaded dice are rolled. A more interesting example is presented in Section 5: The estimation of probabilistic context-free grammars.Comment: Presented at the 15th European Summer School in Logic, Language and Information (ESSLLI 2003). Example 5 extended (and partially corrected

Using a Probabilistic Class-Based Lexicon for Lexical Ambiguity Resolution

This paper presents the use of probabilistic class-based lexica for disambiguation in target-word selection. Our method employs minimal but precise contextual information for disambiguation. That is, only information provided by the target-verb, enriched by the condensed information of a probabilistic class-based lexicon, is used. Induction of classes and fine-tuning to verbal arguments is done in an unsupervised manner by EM-based clustering techniques. The method shows promising results in an evaluation on real-world translations.Comment: 7 pages, uses colacl.st

RAP2.4c and RAP2.4d in the regulation of cold stress and cold priming in Arabidopsis thaliana

Cold stress is a major factor restricting plant performance and fitness. Depending on the length and intensity of the cold stimulus, plants respond to the stress event by alleviating immediately occurring adverse effects of cold stress and by inducing cold acclimation. In the case of a timely limited cold stimulus, Arabidopsis thaliana responds with the formation of a cold memory that modifies its response to a future cold stimulus, a phenomenon which is called priming. Short-term cold priming was previously shown to attenuate chloroplast to nucleus signalling in the regulation of cold-induced ZAT10 expression. In the present study, this effect was mimicked by transient overexpression of tAPX, but not of sAPX at 20 °C, while counteracting priming-induced tAPX accumulation during the lag-phase abolished the priming effect. This demonstrated that cold priming is mediated at the thylakoid membrane and is regulated by post-priming tAPX expression. Electrolyte leakage assays demonstrated that the AP2/ERF-Ib transcription factors RAP2.4c and RAP2.4d, that have been proposed to regulate chloroplast APX gene expression, negatively regulate the direct cold response and cold acclimation. RNAseq analysis of rap2.4c and rap2.4d KO plants one hour after transfer to 4 °C revealed stronger induction of genes that are involved in JA/ET, JA and SA signalling pathways than in wild type Col-0 pants. Subsequent analyses did not show differences in hormone contents and in sensitivity to hormone signals in rap2.4c and rap2.4d plants, demonstrating that misregulation of gene expression in the knock-out lines is independent of hormone availability and sensing. Transient overexpression of RAP2.4c and RAP2.4d also did not influence hormone-related transcript levels. Additionally, the lack of RAP2.4c and RAP2.4d did not affect cold priming-dependent attenuation of ZAT10 regulation. The similarities of the expression patterns of rap2.4c and rap2.4d with that of an npr1 mutant in the cold indicate an upstream function of both transcription factors in NPR1-mediated gene expression regulation. A putative target is TRXH5, which is involved in quaternary structure regulation and, consequently, nuclear translocation of NPR1. This gene was strongly upregulated in the rap2.4d line. Besides a DRE-motif, which is a known RAP2.4d binding site, the TRXH5 promoter contains a RAP2.4d binding motif, which was identified in the present study based on a Yeast-One-Hybrid screen with RAP2.4d and random genomic DNA fragments of Arabidopsis thaliana. The present study highlights RAP2.4d, and to a lesser extent RAP2.4c, as cold-inducible inhibitors of TRXH5 expression attenuating the NPR1-mediated induction of JA/ET, JA and SA responses in the early cold response

Seed orchards - genetic considerations on function, management and seed procurement

Seed orchards are a cost-efficient way to increase future forest production. This thesis summarizes and discusses the results of eleven studies developing models and evaluating real seed orchard data to improve seed orchard management in Pinus sylvestris L. and Picea abies (L.) Karst. When establishing a new seed orchard, not much emphasis should be put on selecting clones with high fertility, since variation in female fertility was found to be rather low and difficult to forecast. For considering active life time of a seed orchard, the possible genetic improvement is an important factor, but there are other factors such as seed production and seed harvest cost that have to be considered as well. The age at which replacement is justified seems to be 30 years for Pinus sylvestris, and 40 years for Picea abies. The age becomes shorter if forest owners are willing to pay more for genetically better reproductive material. It is suggested that advanced-generation seed orchards in Sweden should contain 20-25 tested clones, with ramets deployed linearly with respect to breeding value, for an effective number of 15-18 clones. Even considering the complication that outcrossing pollen is more effective than selfing; the linear deployment concept is close to optimal. The linear deployment algorithm was applied to genetic thinning of two orchards, combining desires for high gain and conservation of gene diversity. The harvesting of cones can often be started as soon as significant amounts of cones develop (typically by age eight in Pinus sylvestris), but if contaminating pollen changes the adaptability of the harvested seed, harvest may be postponed until levels of orchard pollen increase or the use of the seeds modified. Around one quarter of the seed production occurred in the top level of the crown, half in the middle, and one quarter in the bottom. A yield of 9 kg seed per hectare is possible in Pinus sylvestris seed orchards. The cone harvest is a dominating cost which has consequences for management, e.g., orchards should be pruned in order to reduce tree height and thus lower harvesting costs

Inducing a Semantically Annotated Lexicon via EM-Based Clustering

We present a technique for automatic induction of slot annotations for subcategorization frames, based on induction of hidden classes in the EM framework of statistical estimation. The models are empirically evalutated by a general decision test. Induction of slot labeling for subcategorization frames is accomplished by a further application of EM, and applied experimentally on frame observations derived from parsing large corpora. We outline an interpretation of the learned representations as theoretical-linguistic decompositional lexical entries.Comment: 8 pages, uses colacl.sty. Proceedings of the 37th Annual Meeting of the ACL, 199

Journey With a Purpose

The modern church is in bondage from years of trauma rooted in the Post-Christendom decline. As the church has responded to the trauma it is enduring, it has responded by becoming stagnant as it seeks to maintain any relevance it still has. What the modern church is going through has strong parallels with the Hebrew people who were in bondage in Egypt and were delivered through the wilderness into the promised land of Canaan. Following this example, this dissertation walks church leadership through an understanding of the traumatized church and presents a what a modern-day Exodus journey could look like in creating space for the church to reclaim its identity, process through its trauma, and reclaim its relevance in a hurting world