Bielefeld University

About: Bielefeld University is a education organization based out in Bielefeld, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Quantum chromodynamics. The organization has 10123 authors who have published 26576 publications receiving 728250 citations. The organization is also known as: University of Bielefeld & UNIVERSITAET BIELEFELD.

Nested by design: model fitting and interpretation in a mixed model era

Abstract: 1. Nested data structures are ubiquitous in the study of ecology and evolution, and such structures need to be modelled appropriately. Mixed-effects models offer a powerful framework to do so.Nested effects can usually be fitted using the syntax for crossed effects in mixed models, provided that the coding reflects implicit nesting. But the experimental design (either nested or crossed) affects the interpretation of the results. 2. The key difference between nested and crossed effects in mixed models is the estimation and interpretation of the interaction variance. With nested data structures, the interaction variance is pooled with the main effect variance of the nested factor. Crossed designs are required to separate the two components. This difference between nested and crossed data is determined by the experimental design (thus by the nature of data sets) and not by the coding of the statistical model. 3. Data can be nested by design in the sense that it would have been technically feasible and biologically relevant to collect the data in a crossed design. In such cases, the pooling of the variances needs to be clearly acknowledged. In other situations, it might be impractical or even irrelevant to apply a crossed design. We call such situations naturally nested, a case in which the pooling of the interaction variance will be less of an issue. 4. The interpretation of results should reflect the fact that the interaction variance inflates the main effect variance when dealing with nested data structures. Whether or not this distinction is critical depends on the research question and the system under study. 5. We present mixed models as a particularly useful tool for analysing nested designs, and we highlight the value of the estimated random variance as a quantity of biological interest. Important insights can be gained if random-effect variances are appropriately interpreted. We hope that our paper facilitates the transition from classical ANOVAs to mixed models in dealing with categorical data.

Oxidative stress and ozone: perception, signalling and response

Abstract: The primary site of ozone interaction with plant cells is the extracellular matrix where ozone challenges the antioxidant protection of the cells. Accordingly, ozone sensitivity generally correlates with the ascorbate status of the apoplast, which is an important signal initiation point. In addition, ozone sensing takes place by covalent modification of redox-sensitive components of the plasma membrane, for example ion channels like the plasma membrane Ca2+-channels. Subsequent intracellular signal transduction is an intriguing network of hormone, Ca2+ and MAPK signalling pathways, significantly overlapping with oxidative burst-induced pathogen signalling. Comparison of recent transcriptome analysis revealed that in addition to genes generally induced by all kinds of oxidative stress, for example, transcripts for PR-proteins and most antioxidant enzymes, approximately one-third of the responsive transcripts are ozone specific, indicating jasmonic acid, salicylic acid and ethylene-independent redox signalling triggered by extracellular redox sensing.

Heavy-ion collisions at the LHC-Last call for predictions

Abstract: This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.