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Search Results: 1 - 10 of 6159 matches for " Matthias Hunger "
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Longitudinal beta regression models for analyzing health-related quality of life scores over time
Hunger Matthias,D?ring Angela,Holle Rolf
BMC Medical Research Methodology , 2012, DOI: 10.1186/1471-2288-12-144
Abstract: Background Health-related quality of life (HRQL) has become an increasingly important outcome parameter in clinical trials and epidemiological research. HRQL scores are typically bounded at both ends of the scale and often highly skewed. Several regression techniques have been proposed to model such data in cross-sectional studies, however, methods applicable in longitudinal research are less well researched. This study examined the use of beta regression models for analyzing longitudinal HRQL data using two empirical examples with distributional features typically encountered in practice. Methods We used SF-6D utility data from a German older age cohort study and stroke-specific HRQL data from a randomized controlled trial. We described the conceptual differences between mixed and marginal beta regression models and compared both models to the commonly used linear mixed model in terms of overall fit and predictive accuracy. Results At any measurement time, the beta distribution fitted the SF-6D utility data and stroke-specific HRQL data better than the normal distribution. The mixed beta model showed better likelihood-based fit statistics than the linear mixed model and respected the boundedness of the outcome variable. However, it tended to underestimate the true mean at the upper part of the distribution. Adjusted group means from marginal beta model and linear mixed model were nearly identical but differences could be observed with respect to standard errors. Conclusions Understanding the conceptual differences between mixed and marginal beta regression models is important for their proper use in the analysis of longitudinal HRQL data. Beta regression fits the typical distribution of HRQL data better than linear mixed models, however, if focus is on estimating group mean scores rather than making individual predictions, the two methods might not differ substantially.
Official statistics and claims data records indicate non-response and recall bias within survey-based estimates of health care utilization in the older population
Hunger Matthias,Schwarzkopf Larissa,Heier Margit,Peters Annette
BMC Health Services Research , 2013, DOI: 10.1186/1472-6963-13-1
Abstract: Background The validity of survey-based health care utilization estimates in the older population has been poorly researched. Owing to data protection legislation and a great number of different health care insurance providers, the assessment of recall and non-response bias is challenging to impossible in many countries. The objective of our study was to compare estimates from a population-based study in older German adults with external secondary data. Methods We used data from the German KORA-Age study, which included 4,127 people aged 65–94 years. Self-report questions covered the utilization of long-term care services, inpatient services, outpatient services, and pharmaceuticals. We calculated age- and sex-standardized mean utilization rates in each domain and compared them with the corresponding estimates derived from official statistics and independent statutory health insurance data. Results The KORA-Age study underestimated the use of long-term care services ( 52%), in-hospital days ( 21%) and physician visits ( 70%). In contrast, the assessment of drug consumption by postal self-report questionnaires yielded similar estimates to the analysis of insurance claims data ( 9%). Conclusion Survey estimates based on self-report tend to underestimate true health care utilization in the older population. Direct validation studies are needed to disentangle the impact of recall and non-response bias.
A Scanning Cavity Microscope
Matthias Mader,Jakob Reichel,Theodor W. H?nsch,David Hunger
Physics , 2014, DOI: 10.1038/ncomms8249
Abstract: Imaging of the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information. However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available. Here we use signal enhancement in a scanning optical microcavity to demonstrate ultra-sensitive imaging. Harnessing multiple interactions of probe light with a sample within an optical resonator, we achieve a 1700-fold signal enhancement compared to diffraction-limited microscopy. We demonstrate quantitative imaging of the extinction cross section of gold nanoparticles with a sensitivity below 1 nm2, we show a method to improve spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods. The demonstrated simultaneous enhancement of absorptive and dispersive signals promises intriguing potential for optical studies of nanomaterials, molecules, and biological nanosystems.
Intense Long-Lived Fluorescence of 1,6-Diphenyl-1,3,5-Hexatriene: Emission from the S1-State Competes with Formation of O2 Contact Charge Transfer Complex  [PDF]
Katharina Hunger, Karl Kleinermanns
Open Journal of Physical Chemistry (OJPC) , 2013, DOI: 10.4236/ojpc.2013.31008
Abstract:

The fluorescence kinetics of 1,6-diphenyl-1,3,5-hexatriene (DPH) dissolved in cyclohexane was investigated as a function of temperature, concentration and 355 nm excitation pulse energy. At concentrations above 2.5 μM and excitation energies above 1 mJ a long-lived, very intense emission, which appears within less than 5 ns and lasts up to 70 ns, is observed. During the first 50 ns the decay does not follow an exponential but rather a linear behaviour. In oxygen saturated solutions the long-lived emission is suppressed and solely short-lived fluorescence with τ < 5 ns can be detected. A kinetic simulation was performed, based on a model whereupon the long-lived emission originates from the S1-state and competes with the formation of DPH-O2 contact charge-transfer complexes and intersystem crossing which both quench the fluorescence. Our investigations show that even the small amount of oxygen dissolved in nitrogen saturated solutions has a distinct influence on the fluorescence kinetics of DPH.

Multimorbidity and health-related quality of life in the older population: results from the German KORA-Age study
Matthias Hunger, Barbara Thorand, Michaela Schunk, Angela D?ring, Petra Menn, Annette Peters, Rolf Holle
Health and Quality of Life Outcomes , 2011, DOI: 10.1186/1477-7525-9-53
Abstract: The EQ-5D was administered in the population-based KORA-Age study of 4,565 Germans aged 65 years or older. A generalised additive regression model was used to assess the effects of chronic conditions on HRQL and to account for the nonlinear associations with age and body mass index (BMI). Disease interactions were identified by a forward variable selection method.The conditions with the greatest negative impact on the EQ-5D index were the history of a stroke (regression coefficient -11.3, p < 0.0001) and chronic bronchitis (regression coefficient -8.1, p < 0.0001). Patients with both diabetes and coronary disorders showed more impaired HRQL than could be expected from their separate effects (coefficient of interaction term -8.1, p < 0.0001). A synergistic effect on HRQL was also found for the combination of coronary disorders and stroke. The effect of BMI on the mean EQ-5D index was inverse U-shaped with a maximum at around 24.8 kg/m2.There are important interactions between coronary problems, diabetes mellitus, and the history of a stroke that negatively affect HRQL in the older German population. Not only high but also low BMI is associated with impairments in health status.Multimorbidity, defined as the coexistence of two or more chronic conditions, is a common phenomenon among the older population worldwide: two recent population-based studies indicated that the prevalence of multimorbidity ranges between 40% and 56% in the general population aged 65 years and older [1,2]. Multimorbidity is known to negatively affect health outcomes including mortality, hospitalisation, and readmission [3].Health-related quality of life (HRQL) is a health outcome measure which is increasingly used to assess the medical effectiveness of interventions and to support allocation decisions in the health care sector. Generic HRQL instruments like the EQ-5D are appropriate for non-disease-specific analyses and allow comparisons between patient groups with different medical conditions [
Spectroscopy of mechanical dissipation in micro-mechanical membranes
Andreas J?ckel,Matthew T. Rakher,Maria Korppi,Stephan Camerer,David Hunger,Matthias Mader,Philipp Treutlein
Physics , 2011, DOI: 10.1063/1.3646914
Abstract: We measure the frequency dependence of the mechanical quality factor (Q) of SiN membrane oscillators and observe a resonant variation of Q by more than two orders of magnitude. The frequency of the fundamental mechanical mode is tuned reversibly by up to 40% through local heating with a laser. Several distinct resonances in Q are observed that can be explained by coupling to membrane frame modes. Away from the resonances, the background Q is independent of frequency and temperature in the measured range.
Spurensuche einer Rezeptionsgeschichte Alexander von Humboldt und Johann Gottfried Herder
Bernhard Hunger
HiN. Alexander von Humboldt im Netz , 2009,
Abstract: Article in German, Abstracts in English, German and Spanish.Alexander von Humboldt's work displays traces of Johann Gottfried Herder which are as multifaceted as the references to the latter are scarce. In light of this aspect, the present essay focuses on Humboldt's Physiognomy of Plants (1806), in which he explicitly mentions Herder for the first time in a publication. Two years later, the text is incorporated within Aspects of Nature (1808 ff.). In the third edition of Aspects (1849), Herder's name is curiously omitted. This omission is incomprehensible both in form and content. The historical context characterising the years between 1805 and 1808 suggests that Humboldt's references to Herder must have been made very deliberately. Humboldt's correspondence with the historian Johannes von M ller and other sources shows that Humboldt carefully studied Herder's writings. As the publisher of Herder's complete works, Johannes von M ller, who was Humboldtís friend and neighbour at the time, even considered Humboldt to be a direct descendant of the Herder school.
Psarros, Nikos: "Die Chemie und ihre Methoden. Eine philosophische Betrachtung" (Weinheim 1999) (book review)
Johannes Hunger
Hyle : International Journal for Philosophy of Chemistry , 2001,
Abstract: book review of Psarros, Nikos: "Die Chemie und ihre Methoden. Eine philosophische Betrachtung" (Weinheim 1999)
The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture by Francesca Rochberg
Hermann Hunger
Aestimatio : Critical Reviews in the History of Science , 2004,
Abstract:
Transverse-mode coupling and diffraction loss in tunable Fabry-Pérot microcavities
Julia Benedikter,Thomas Hümmer,Matthias Mader,Benedikt Schlederer,Jakob Reichel,Theodor W. H?nsch,David Hunger
Physics , 2015,
Abstract: We report on measurements and modeling of the mode structure of tunable Fabry-P\'erot optical microcavities with imperfect mirrors. We find that non-spherical mirror shape and finite mirror size lead to loss, mode deformation, and shifted resonance frequencies at particular mirror separations. For small mirror diameters, the useful cavity length is limited to values significantly below the expected stability range. We explain the observations by resonant coupling between different transverse modes of the cavity and mode-dependent diffraction loss. A model based on resonant state expansion that takes into account the measured mirror profile can reproduce the measurements and identify the parameter regime where detrimental effects of mode mixing are avoided.
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