Fast Cross-Validation via Sequential Testing

With the increasing size of today's data sets, finding the right parameter configuration in model selection via cross-validation can be an extremely time-consuming task. In this paper we propose an improved cross-validation procedure which uses nonparametric testing coupled with sequential analysis to determine the best parameter set on linearly increasing subsets of the data. By eliminating underperforming candidates quickly and keeping promising candidates as long as possible, the method speeds up the computation while preserving the capability of the full cross-validation. Theoretical considerations underline the statistical power of our procedure. The experimental evaluation shows that our method reduces the computation time by a factor of up to 120 compared to a full cross-validation with a negligible impact on the accuracy

Estimating Local Function Complexity via Mixture of Gaussian Processes

Real world data often exhibit inhomogeneity, e.g., the noise level, the sampling distribution or the complexity of the target function may change over the input space. In this paper, we try to isolate local function complexity in a practical, robust way. This is achieved by first estimating the locally optimal kernel bandwidth as a functional relationship. Specifically, we propose Spatially Adaptive Bandwidth Estimation in Regression (SABER), which employs the mixture of experts consisting of multinomial kernel logistic regression as a gate and Gaussian process regression models as experts. Using the locally optimal kernel bandwidths, we deduce an estimate to the local function complexity by drawing parallels to the theory of locally linear smoothing. We demonstrate the usefulness of local function complexity for model interpretation and active learning in quantum chemistry experiments and fluid dynamics simulations.Comment: 19 pages, 16 figure

Die Welt der Gründe Hiob und die Theodizee: Warum gibt es Leid auf Erden?

Das Buch Hiob ist eine einzigartige theologische und philosophische Reflexion auf die Frage nach Gerechtigkeit und die Begründung von Leid. Im Unglück Hiobs verdichten sich überzeitliche, allgemeinmenschliche Erfahrungen der Gottessuche und der Möglichkeit von Sinngebung angesichts von Schicksalsschlägen, die sich dem Gerechtigkeitsempfinden und dem Verstehensanspruch widersetzen. Das Buch Hiob beantwortet und problematisiert die Theodizee, die Frage nach der Rechtfertigung Gottes in Anbetracht des menschlichen Leids, mit konkurrierenden Begründungskonzepten. Der Vortrag zeigt, wie die philosophische und theologische Substanz des Textes an ausgewählten Textstellen im Schulunterricht erarbeitet werden kann. Dazu wird ein Konzept vorgestellt, das die philosophischen Methoden nach Martens und Rohbeck mit den Verfahren der sogenannten Handlungs- und Produktionsorientierung kombiniert. In ganzheitlicher Ausrichtung eröffnen sie nicht nur kognitive, sondern auch affektive, soziale und motorische Lernwege. Mit ihrer Hilfe werden, wie die Ausführungen darlegen, den Lernenden Sinn- und Identitätsangebote ermöglicht, die Muster zur Krisenbewältigung bieten und verdeutlichen, dass die Erfahrung von vermeintlich unbegründetem Leid aufs Engste mit dem Leben zusammenhäng

Capacity of different cell types to stimulate cytotoxic T lymphocyte precursor cells in the presence of interleukin 2

Plastic-adherent cells enriched for dendritic cells (AC) were found to be among the most potent stimulator cells for the activation of cytotoxic T lymphocytes (CTL) in vitro in the presence of interleukin 2 (IL 2) and a constant second set of allogeneic stimulator cells. Concanavalin A-activated nylon wool-nonadherent spleen cells ( CNWT ), concanavalin A-activated unfractionated spleen cells ( Cspl ), and some variants of the ESb T lymphoma line were equally effective as stimulator cells, however, and provoked a substantial cytotoxic response at concentrations of 10(4) cells per culture or less. In contrast, nonactivated nylon wool-nonadherent spleen cells ( NWT ) or unfractionated spleen cells (Spl) and cells of the P815 mastocytoma, the Meth A fibrosarcoma, and the T cell lymphomas Ly 5178 Eb and ESb did not stimulate cytotoxic responses at these cell concentrations. The strong stimulatory potential of the Cspl preparation was reduced by treatment with anti-Thy-1 antibody plus complement, whereas the stimulatory activity of the AC preparation was resistant to this treatment. All cell types tested expressed class I major histocompatibility antigens. Nonactivated NWT cells, in contrast to the CNWT preparation, showed no detectable staining with anti-I-E or anti-I-A antibodies and also a slightly weaker staining with class I antisera. Experiments with the tumor cell lines revealed, however, that there was no strict correlation between stimulatory potential and density of class I alloantigens or the expression of I-E determinants. Experiments on primary cytotoxic responses in vivo gave similar results. Experiments in cultures with a single set of stimulator cells and I region-compatible responder cells indicated that AC and Cspl or CNWT also have a markedly stronger capacity than NWT to induce IL 2-dependent DNA synthesis

Cardiovascular and cortisol reactions to acute psychological stress and cognitive ability in the Dutch Famine Birth Cohort Study

Objective: Recently, in analyses of data from a large community sample, negative cross-sectional and prospective associations between cardiac stress reactivity and obesity were observed. The present study re-examined the association between cardiovascular reactivity and adiposity in the Dutch Famine Birth Cohort, with the additional aim of examining the association between cortisol reactivity and adiposity. Methods: Blood pressure, heart rate, and salivary cortisol were measured at rest and in response to standard laboratory stress tasks in 725 adults. Height, weight, waist and hip circumference, and skin fold thickness were measured. Four to seven years later 460 participants reported current height and weight. Obesity was defined as a BMI > 30kg/m2. Results: Cross-sectional analyses revealed negative associations between all measures of adiposity and heart rate reactivity; those with a greater BMI (ß = -0.39 bpm), waist-hip ratio (ß = -0.15 bpm), and triceps and subscapular skin fold thicknesses (ß = -1.0 bpm and -1.8 bpm), or categorized as obese (-3.9 bpm) displayed smaller cardiac reactions to acute stress (all p <.001). With the exception of waist-hip ratio, the same negative associations emerged for cortisol reactivity (all p ≤ .01). In prospective analyses, low cardiac reactivity was associated with an increased likelihood of becoming or remaining obese in the subsequent 4-7 years (OR 1.03, p = .01). All associations withstood adjustment for a range of possible confounders. Conclusions: The present analyses provide additional support for the hypothesis that it is low not high cardiac and cortisol stress reactivity that is related to adiposity

Extraction of Fragmentation Functions from Charged Kaon and Pion Production at COMPASS

Quark helicity distributions can be accessed by measuring spin asymmetries in polarised deep-inelastic scattering, but for a full flavour separation the precise knowledge of quark fragmentation functions is essential. Those can only be inferred from experimental data, and are still poorly determined today. The few existing parametrisations of fragmentation functions are derived from world data (mainly on electron-positron annihilation), and often differ considerably, most notably for strange quarks. This thesis presents an independent evaluation of fragmentation functions from deep-inelastic scattering data recorded at the COMPASS experiment. A method of extraction was developed, based on the relation between hadron multiplicities, rh(x, z), unpolarised parton distribution functions, q(x), and quark fragmentation functions into hadrons, Dqh(z). (In this work x stands for the Bjorken scaling variable, and z for the fraction of the quark momentum that is transferred to the produced hadron.) Multiplicities for charged kaons and pions from 2004 data extracted by the COMPASS collaboration and two sets of unpolarised parton distribution functions from global parametrisations (CTEQ6 and MSTW) were used as input for a system of equations, and five different fragmentation functions (Dfav, Dunf for pions and Dstr, Dfav, Dunf for kaons) were extracted in four z bins. To evaluate the stability of the results a number of tests was performed, among them limiting the x range of the multiplicities and unpolarised parton distribution functions used for the analysis, and comparing them to results derived with a set of artificial multiplicities generated with the particle physics event generator PYTHIA. Four of the five extracted fragmentation functions - Dfav and Dunf for both pions and kaons - are quite stable with regard to the parton distribution used as well as to the x range in which the analysis was performed, and agree with an earlier evaluation by the EMC collaboration. The fifth fragmentation function, Dstr for charged kaons, shows incompatible results for the different x intervals of the multiplicities used in the analysis, and also differs considerably for the two parametrisations of unpolarised parton distribution functions. The extracted values for Dstr are often negative - and therefore physically impossible, and do not agree with predictions from parametrisations.Helizitätsverteilungen von Quarks im Nukleon lassen sich durch die Messung von Spin-Asymmetrien in polarisierter tiefinelastischer Streuung erforschen, doch für eine komplette Flavourzerlegung ist die genaue Kenntnis von Quark-Fragmentationsfunktionen unerlässlich. Diese können nur aus experimentellen Daten erschlossen werden, und sind noch immer schlecht bestimmt. Die existierenden Parametrisierungen von Fragmentationsfunktionen beruhen größtenteils auf Elektron-Positron-Annihilations-Daten, und unterscheiden sich zum Teil stark voneinander, insbesondere für Strange-Quarks. In der vorliegenden Arbeit wird eine unabhängige Bestimmung von Fragmentationsfunktionen präsentiert, die auf Daten über tiefinelastische Streuung des COMPASS-Experiments beruht. Es wurde eine Extraktionsmethode entwickelt, die die Beziehung zwischen Hadronmultiplizitäten, rh(x,z), unpolarisierten Partondistributionsfunktionen, q(x), und Fragmentationsfunktionen Dqh(z), ausnutzt. (Hierbei steht x für die Bjorken Skalenvariable, und z für den Impulsbruchteil, der vom Quark auf das produzierte Hadron übertragen wird.) Ein Gleichungssystem wurde entwickelt, in dem von der COMPASS-Kollaboration aus 2004er Daten extrahierte Multiplizitäten für geladene Kaonen und Pionen, sowie zwei Parametrisierungen unpolarisierter Partondistributionsfunktionen (CTEQ6 und MSTW) als Eingabedaten verwendet wurden. Es konnten fünf verschiedene Fragmentationsfunktionen (Dfav, Dunf für Pionen und Dstr, Dfav, Dunf für Kaonen) in vier z-Intervallen extrahiert werden. Die Stabilität der Ergebnisse wurde überprüft, unter anderem durch Einschränkung des x-Bereichs der in der Analyse verwendeten Multiplizitäten und Partondistributionsfunktionen. Als weiterer Test wurden die experimentellen Multiplizitäten durch künstliche ersetzt, die mit Hilfe des Elementarteilchen-Physik-Generators PYTHIA erstellt wurden, und die Ergebnisse der beiden Extraktionen verglichen. Die Ergebnisse für vier der fünf extrahierten Fragmentationsfunktionen - Dfav und Dunf für sowohl Pionen als auch Kaonen - sind stabil in Hinsicht auf die verwendeten Partondistributionsfunktionen, und ebenso für die unterschiedlichen x-Bereiche, in denen die Analyse durchgeführt wurde. Sie stimmen überein mit den Ergebnissen einer früheren Extraktion, die von der EMC-Kollaboration durchgeführt wurde. Die extrahierten Werte für die fünfte Fragmentationsfunktion, Dstr für geladene Kaonen, sind stark von der verwendeten Parametrisierung der Partondistributionsfunktionen abhängig, und die Ergebnisse für verschiedene x-Intervalle sind nicht miteinander vereinbar. Die Werte für Dstr sind in mehreren Fällen negativ - und damit physikalisch unmöglich, und widersprechen den vorhandenen Parametrisierungen

Are Large Physiological Reactions to Acute Psychological Stress Always Bad for Health?

How we react physiologically to stress has long been considered to have implications for our health. There is now persuasive evidence that individuals who show large cardiovascular reactions to stress are at increased risk of developing cardiovascular disease, particularly hypertension. By implication, low reactivity is protective or benign. However, there is recent evidence that low reactivity may predict elevated risk for a range of adverse health outcomes, such as depression, obesity, poor self-reported health, and compromised immunity. In addition, low cortisol and cardiovascular reactivity may be a characteristic of individuals with addictions to tobacco and alcohol, as well as those at risk of addiction and those who relapse from abstinence. Our ideas about reactivity may have to be revised in the light of such findings

Disordered eating behaviour is associated with blunted cortisol and cardiovascular reactions to acute psychological stress

Research suggests a potential dysregulation of the stress response in individuals with bulimia nervosa. This study measured both cardiovascular and cortisol reactions to a standardised laboratory stress task in individuals identified as showing disordered eating behaviour to determine whether dysregulation of the stress response is characteristic of the two branches of the stress response system. Female students (N = 455) were screened using two validated eating disorder questionnaires. Twelve women with disordered eating, including self-induced vomiting, and 12 healthy controls were selected for laboratory stress testing. Salivary cortisol and cardiovascular activity, via Doppler imaging and semi-automatic blood pressure monitoring, were measured at resting baseline and during and after exposure to a 10-min mental arithmetic stress task. Compared to controls the disordered eating group showed blunted cortisol, cardiac output, heart rate, and stroke volume reactions to the acute stress, as well as an attenuated vasodilatory reaction. These effects could not be accounted for in terms of group differences in stress task performance, subjective task impact/engagement, age, BMI, neuroticism, cardiorespiratory fitness, or co-morbid exercise dependence. Our findings suggest that disordered eating is characterised by a dysregulation of the autonomic stress-response system. As such, they add further weight to the general contention that blunted stress reactivity is characteristic of a number of maladaptive behaviours and states

Measurement of the Longitudinal Spin Transfer to Lambda and Anti-Lambda Hyperons in Polarised Muon DIS

The longitudinal polarisation transfer from muons to lambda and anti-lambda hyperons, D_LL, has been studied in deep inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to lambda and anti-lambda produced in the current fragmentation region exhibit different behaviours as a function of x and xF . The measured x and xF dependences of D^lambda_LL are compatible with zero, while D^anti-lambda_LL tends to increase with xF, reaching values of 0.4 - 0.5. The resulting average values are D^lambda_LL = -0.012 +- 0.047 +- 0.024 and D^anti-lambda_LL = 0.249 +- 0.056 +- 0.049. These results are discussed in the frame of recent model calculations.Comment: 13 pages, 7 figure