Boosting the concordance index for survival data - a unified framework to derive and evaluate biomarker combinations

The development of molecular signatures for the prediction of time-to-event outcomes is a methodologically challenging task in bioinformatics and biostatistics. Although there are numerous approaches for the derivation of marker combinations and their evaluation, the underlying methodology often suffers from the problem that different optimization criteria are mixed during the feature selection, estimation and evaluation steps. This might result in marker combinations that are only suboptimal regarding the evaluation criterion of interest. To address this issue, we propose a unified framework to derive and evaluate biomarker combinations. Our approach is based on the concordance index for time-to-event data, which is a non-parametric measure to quantify the discrimatory power of a prediction rule. Specifically, we propose a component-wise boosting algorithm that results in linear biomarker combinations that are optimal with respect to a smoothed version of the concordance index. We investigate the performance of our algorithm in a large-scale simulation study and in two molecular data sets for the prediction of survival in breast cancer patients. Our numerical results show that the new approach is not only methodologically sound but can also lead to a higher discriminatory power than traditional approaches for the derivation of gene signatures.Comment: revised manuscript - added simulation study, additional result

How nucleophilic are silyl enol ethers? Kinetics of the reactions of electron rich CC-double bonded systems with carbenium ions

Rate constants for the reactions of the bis(p-dimethylaminophenyl)carbenium ion 1 with silyl enol ethers, allyl silanes, and allyl stannanes show the reactivity order H2C=CR-CH2SiMe3 < H2C=CR-OSiMe3 < H2C=CR-CH2SnBu3

Phase Diagram of a Model for Diluted Magnetic Semiconductors Beyond Mean-Field Approximations

A lattice spin-fermion model for diluted magnetic semiconductors (DMS) is investigated numerically, improving on previously used mean-field (MF) approximations. Curie temperatures are obtained varying the Mn-spin x and hole n densities, and the impurity-hole exchange J in units of the hopping amplitude t. Optimal values are found in the subtle intermediate regime between itinerant and localized carriers. Our main result is the behavior of the Curie temperature at large J/t, where a "clustered" state is observed and ferromagnetism is suppressed. Formal analogies between DMS and manganites are also discussed.Comment: Revtex4, 4 pages, 4 figures. New figures, emphasis change

A Mobile Robot System for Ambient Intelligence

Over the last years, Ambient Intelligence (AmI) has been pointed out as an alternative to current practices in home care. AmI supports the concept of Ambient Assisted Living, which aims to allow older people to remain independent at their own homes for longer. The integration of a mobile robot into a database-centric platform for Ambient Assisted Living is described in this thesis. The robot serves as a rst-aid agent to respond to emergencies, such as a fall, detected by the intelligent environment. To accomplish that the robot must 1) be able to receive tasks from intelligent environment; 2) execute the task; 3) report the progress and the result of the task back to the intelligent environment. The system of the robot is built on top of the Robot Operating System, while the existing intelligent environment on a PostgreSQL database. To receive tasks from the intelligent environment, the robot maintains an active connection with the database and subscribes to specic tasks. A task, for example, is to nd a person in the environment, which includes asking if the person is doing well. To nd a person a map-based approach and a face recognition are used. The robot can interact with people in the environment using text-to-speech and speech recognition. The active connection with the database enables the robot to report back about the execution of a task and to receive new or abort tasks. As a conclusion, together with an AAL system, mobile robots can support people living alone. The system has been implemented and successfully tested at Halmstad University on a Turtlebot 2. The code is available on Github

Model-based Boosting in R: A Hands-on Tutorial Using the R Package mboost

We provide a detailed hands-on tutorial for the R add-on package mboost. The package implements boosting for optimizing general risk functions utilizing component-wise (penalized) least squares estimates as base-learners for fitting various kinds of generalized linear and generalized additive models to potentially high-dimensional data. We give a theoretical background and demonstrate how mboost can be used to fit interpretable models of different complexity. As an example we use mboost to predict the body fat based on anthropometric measurements throughout the tutorial

Nucleophilie- und Elektrophilieskalen als Ordnungsprinzipien polarer organischer und metallorganischer Reaktionen

Entgegen landläufiger Meinung ist es für zahlreiche Reaktionen der Organischen und Metallorganischen Chemie möglich, Nucleophilie- und Elektrophilieparameter zu definieren, die nicht vom jeweiligen Reaktionspartner abhängig sind. Dieses Phänomen, das Anfang der siebziger Jahre von Ritchie bei Reaktionen hochstabilisierter Carbenium- und Diazonium-Ionen mit n-Nucleophilen entdeckt wurde, tritt auch bei Reaktionen von Carbenium-Ionen mit aliphatischen und aromatischen -Elektronensystemen sowie bei Hydridübertragungen auf. Mit Hilfe der hier vorgestellten Nucleophilie- und Elektrophilieskalen, die über jeweils 18 Zehnerpotenzen reichen, gelingt die Voraussage, ob und wie rasch eine bestimmte C-C-Verknüpfung, eine ionische Reduktion oder eine Azokupplung abläuft. Eine Anknüpfung an die Reaktivitätsskalen von Ritchie und Sweigart/Kane-Maguire macht eine einheitliche Behandlung einer großen Zahl polarer Reaktionen möglich