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Axmacher N.,University of Bonn | Henseler M.M.,University of Bonn | Henseler M.M.,University of Applied Science Koblenz | Jensen O.,Fc Donders Center For Cognitive Neuroimaging | And 3 more authors.
Proceedings of the National Academy of Sciences of the United States of America | Year: 2010

Recent findings indicate that the hippocampus supports not only long-term memory encoding but also plays a role inworking memory (WM) maintenance ofmultiple items; however, the neuralmechanism underlying multi-item maintenance is still unclear. Theoretical work suggests that multiple items are being maintained by neural assemblies synchronized in thegammafrequency range(25-100 Hz) that are locked to consecutive phase ranges of oscillatory activity in the theta frequency range (4-8 Hz). Indeed, cross-frequency coupling of the amplitude of high-frequency activity to the phase of slower oscillations has been described both in animals and in humans, but has never been linked to a theoretical model of a cognitive process. Herewe used intracranial EEG recordings in human epilepsy patients to test pivotal predictions from theoretical work. First,we show that simultaneous maintenance of multiple items in WM is accompanied by cross-frequency coupling of oscillatory activity in the hippocampus,which is recruited during multi-item WM. Second, maintenance of an increasing number of items is associated with modulation of beta/gamma amplitude with theta band activity of lower frequency, consistent with the idea that longer cycles are required for an increased number of representations by gamma cycles. This effect cannot be explained by a difference in theta or beta/ gamma power. Third,we describe howthe precision of cross-frequency coupling predicts individual WM performance. These data support the idea that working memory in humans depends on a neural code using phase information.

Oberlander K.D.,German Sport University Cologne | Bruggemann G.-P.,German Sport University Cologne | Hoher J.,Clinic for Sports Traumatology at Merheim Medical Center | Karamanidis K.,German Sport University Cologne | Karamanidis K.,University of Applied Science Koblenz
Medicine and Science in Sports and Exercise | Year: 2013

PURPOSE: This longitudinal study aimed to examine whether patients with anterior cruciate ligament (ACL) reconstruction show a similar landing strategy during the single-leg hop test (SLHT) postsurgery analog to that previously identified when ACL deficient. It is hypothesized that ACL-reconstructed patients demonstrate greater trunk flexion to reduce knee joint moments at the cost of postural dynamic stability at their involved leg compared to their uninvolved leg. METHODS: Ten ACL-reconstructed patients performed a bilateral SLHT 6 and 12 months after surgery. Landing mechanics were determined by means of a soft tissue artifact optimized, rigid, full-body model, and the margin of stability was quantified using an inverted pendulum approach. Knee extensor muscular strength (KS) was assessed during isometric maximal voluntary knee extension contractions. RESULTS: ACL-reconstructed patients showed similar landing strategies as previously reported in their ACL-deficient state. By flexing their trunk, patients repositioned the ground reaction force vector more anteriorly in relation to the joints of the lower extremity (P < 0.05) and, in doing so, were able to transfer joint moments from the knee to the adjacent joints (P < 0.05). This upper body strategy reduced the margin of stability in the ACL-reconstructed leg during landing (P < 0.05). Twelve months after surgery, the ACL-reconstructed leg showed lower KS compared to the uninvolved leg (P < 0.05), and knee joint moment output during landing was significantly correlated to KS. CONCLUSIONS: The results highlight the important role of KS on the interaction between trunk angle, joint kinetics, and postural dynamic stability during landing and show that ACL-reconstructed patients use an analogous feedforward strategy (e.g., more flexed trunk) to that used in their ACL-deficient state, aiming to compensate for KS deficits and thereby sacrificing postural dynamic stability and increasing the risk of loss of balance during landing maneuvers. Copyright © 2013 by the American College of Sports Medicine.

Kahm M.,University of Applied Science Koblenz | Hasenbrink G.,University of Bonn | Lichtenberg-Frate H.,University of Bonn | Ludwig J.,University of Bonn | Kschischo M.,University of Applied Science Koblenz
Journal of Statistical Software | Year: 2010

The grofit package was developed to fit many growth curves obtained under different conditions in order to derive a conclusive dose-response curve, for instance for a compound that potentially affects growth. grofit fits data to different parametric models and in addition provides a model free spline method to circumvent systematic errors that might occur within application of parametric methods. This amendment increases the reliability of the characteristic parameters (e.g.,lag phase, maximal growth rate, stationary phase) derived from a single growth curve. By relating obtained parameters to the respective condition (e.g.,concentration of a compound) a dose response curve can be derived that enables the calculation of descriptive pharma-/toxicological values like half maximum effective concentration (EC50). Bootstrap and cross-validation techniques are used for estimating confidence intervals of all derived parameters.

Frahm G.,University of Cologne | Jaekel U.,University of Applied Science Koblenz
Computational Statistics and Data Analysis | Year: 2010

Many different robust estimation approaches for the covariance or shape matrix of multivariate data have been established. Tyler's M-estimator has been recognized as the 'most robust' M-estimator for the shape matrix of elliptically symmetric distributed data. Tyler's M-estimators for location and shape are generalized by taking account of incomplete data. It is shown that the shape matrix estimator remains distribution-free under the class of generalized elliptical distributions. Its asymptotic distribution is also derived and a fast algorithm, which works well even for high-dimensional data, is presented. A simulation study with clean and contaminated data covers the complete-data as well as the incomplete-data case, where the missing data are assumed to be MCAR, MAR, and NMAR. © 2009 Elsevier B.V. All rights reserved.

Thomas N.W.,University of Applied Science Koblenz
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2011

A fast Fourier transform algorithm is introduced into the method recently defined for calculating powder diffraction patterns by means of the Debye scattering equation (DSE) [Thomas (2010). Acta Cryst. A66, 64-77]. For this purpose, conventionally used histograms of interatomic distances are replaced by compound transmittance functions. These may be Fourier transformed to partial diffraction patterns, which sum to give the complete diffraction pattern. They also lead to an alternative analytical expression for the DSE sum, which reveals its convergence behaviour. A means of embedding the DSE approach within the reciprocal-lattice-structure-factor method is indicated, with interpolation methods for deriving the peak profiles of nanocrystalline materials outlined. Efficient calculation of transmittance functions for larger crystallites requires the Patterson group symmetry of the crystals to be taken into account, as shown for - and Β-quartz. The capability of the transmittance functions to accommodate stacking disorder is demonstrated by reference to kaolinite, with a fully analytical treatment of disorder described. Areas of future work brought about by these developments are discussed, specifically the handling of anisotropic atomic displacement parameters, inverse Fourier transformation and the incorporation of instrumental (diffractometer) parameters. © International Union of Crystallography Printed in Singapore - all rights reserved.

Thomas N.W.,University of Applied Science Koblenz
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

A new method is defined for the calculation of X-ray and neutron powder diffraction patterns from the Debye scattering equation (DSE). Pairwise atomic interactions are split into two contributions, the first from lattice-pair vectors and the second from cell-pair vectors. Since the frequencies of lattice-pair vectors can be directly related to crystallite size, application of the DSE is thereby extended to crystallites of lengths up to ~200 nm. The input data correspond to unit-cell parameters, atomic coordinates and displacement factors. The calculated diffraction patterns are characterized by full backgrounds as well as complete reflection profiles. Four illustrative systems are considered: sodium chloride (NaCl), -quartz, monoclinic lead zirconate titanate (PZT) and kaolinite. The effects of varying crystallite size on diffraction patterns are calculated for NaCl, quartz and kaolinite, and a method of modelling static structural disorder is defined for kaolinite. The idea of partial diffraction patterns is introduced and a treatment of atomic displacement parameters is included. Although the method uses pair distribution functions as an intermediate stage, it is anticipated that further progress in reducing computational times will be made by proceeding directly from crystal structure to diffraction pattern. © 2010 International Union of Crystallography.

Beck I.R.,University of Basel | Schmid N.S.,University of Basel | Berres M.,University of Applied Science Koblenz | Monsch A.U.,University of Basel
International Journal of Geriatric Psychiatry | Year: 2014

Objective The diagnosis of mild cognitive impairment (MCI) and dementia requires detailed neuropsychological examinations. These examinations typically yield a large number of outcome variables, which may complicate the interpretation and communication of results. The purposes of this study were the following: (i) to reduce a large data set of interrelated neuropsychological variables to a smaller number of cognitive dimensions; (ii) to create a common metric for these dimensions (z-scores); and (iii) to study the ability of the cognitive dimensions to distinguish between groups of patients with different types of cognitive impairment. Methods We tested 1646 patients with different forms of dementia or with a major depression with a standard (n = 632) or, if cognitively less affected, a challenging neuropsychological battery (n = 1014). To identify the underlying cognitive dimensions of the two test batteries, maximum likelihood factor analyses with a promax rotation were conducted. To interpret the sum scores of the factors as standard scores, we divided them by the standard deviation of a cognitively healthy sample (n = 1145). Results The factor analyses yielded seven factors for each test battery. The cognitive dimensions in both test batteries distinguished patients with different forms of dementia (MCI, Alzheimer's dementia or frontotemporal dementia) and patients with major depression. Furthermore, patients with stable MCI could be separated from patients with progressing MCI. Discriminant analyses with an independent new sample of patients (n = 306) revealed that the new dimension scores distinguished new samples of patients with MCI from patients with Alzheimer's dementia with high accuracy. Conclusion These findings suggest that these cognitive dimensions may benefit neuropsychological diagnostics. © 2013 The Authors International Journal of Geriatric Psychiatry Published by John Wiley & Sons Ltd. © 2013 The Authors International Journal of Geriatric Psychiatry Published by John Wiley & Sons Ltd.

Hubert W.,University of Applied Science Koblenz | Ankerhold G.,University of Applied Science Koblenz
Analytical and Bioanalytical Chemistry | Year: 2011

In this work, the Stark effect is shown to be mainly responsible for wrong elemental allocation by automated laser-induced breakdown spectroscopy (LIBS) software solutions. Due to broadening and shift of an elemental emission line affected by the Stark effect, its measured spectral position might interfere with the line position of several other elements. The micro-plasma is generated by focusing a frequency-doubled 200 mJ pulsed Nd/YAG laser on an aluminum target and furthermore on a brass sample in air at atmospheric pressure. After laser pulse excitation, we have measured the temporal evolution of the Al(II) ion line at 281.6 nm (4s 1 S-3p 1 P) during the decay of the laser-induced plasma. Depending on laser pulse power, the center of the measured line is red-shifted by 130 pm (490 GHz) with respect to the exact line position. In this case, the well-known spectral line positions of two moderate and strong lines of other elements coincide with the actual shifted position of the Al(II) line. Consequently, a time-resolving software analysis can lead to an elemental misinterpretation. To avoid a wrong interpretation of LIBS spectra in automated analysis software for a given LIBS system, we recommend using larger gate delays incorporating Stark broadening parameters and using a range of tolerance, which is non-symmetric around the measured line center. These suggestions may help to improve time-resolving LIBS software promising a smaller probability of wrong elemental identification and making LIBS more attractive for industrial applications. [Figure not available: see fulltext.] © 2011 Springer-Verlag.

Kschischo M.,University of Applied Science Koblenz
European Physical Journal: Special Topics | Year: 2010

Reaction networks in thermodynamic equilibrium under isothermal and isobaric conditions minimize the Gibbs free energy, but chemical reactions in living organisms operate typically far from equilibrium. Currently, there is no general optimization principle for nonequilibrium systems which can be used in the analysis of biochemical networks. Motivated by the avalailabity of whole genome reconstructions of metabolic reactions, the thermodynamics of biochemical stoichiometric networks has made significant progress in the last decade. These include the consistent formulation of conservation conditions resembling Kirchhoff's law for electrical networks. In addition, Beard and Qian suggested that the flow force relationship Δμ = RT log(J+/J-) between the forward and backward fluxes J+ and J- and the chemical potential difference of a chemical reaction can be extended from mass action kinetics to more general reactions schemes. In this tutorial review we summarize the recent literature on reaction network thermodynamics and discuss its implications to the analysis of large biochemical systems. In addition, we discuss some recent work on flow-force relationships and global variational principles characterizing nonequilibrium steady states of reaction networks. © 2010 EDP Sciences and Springer.

Jaekel U.,University of Applied Science Koblenz
Procedia Computer Science | Year: 2011

A direct Monte Carlo method for volume estimation of star-shaped or convex domains is presented, and is generalized to a Markov Chain Monte Carlo method for high-dimensional problems. The direct approach itself, which is closely related to a method proposed by Fok and Crevier, is already applicable to some moderately high-dimensional problems. The combination with a Markov Chain Monte Carlo method and nested sampling or thermodynamic integration extends its scope considerably. Applications to the volume estimation for high-dimensional polytopes are presented, and the method is tested using exact results for the first 10 Birkhoff polytopes. © 2011 Published by Elsevier Ltd.

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