Garching bei München, Germany
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Elsayed S.,Technical University Mnchen | Elsayed S.,Menoufia University | Mistele B.,Technical University Mnchen | Schmidhalter U.,Technical University Mnchen
Functional Plant Biology | Year: 2011

Leaf water potential (LWP) is an important indicator of plant water status. However, its determination via classical pressure-chamber measurements is tedious and time-consuming. Moreover, such methods cannot easily account for rapid changes in this parameter arising from changes in environmental conditions. Spectrometric measurements, by contrast, have the potential for fast and non-destructive measurements of plant water status, but are not unproblematic. Spectral characteristics of plants vary across plant development stages and are also influenced by environmental factors. Thus, it remains unclear whether changes in leaf water potential per se can reliably be detected spectrometrically or whether such measurements also reflect autocorrelated changes in the leaf water content (LWC) or the aerial plant biomass. We tested the accuracy of spectrometric measurements in this context under controlled climate chamber conditions in series of six experiments that minimised perturbing influences but allowed for significant changes in the LWP. Short-term exposure of dense stands of plants to increasing or decreasing artificial light intensities in a growth chamber more markedly decreased LWP than LWC in both wheat and maize. Significant relationships (R 2-values 0.74-0.92) between LWP and new spectral indices ((R 940/R 960)/NDVI; R 940/R 960) were detected with or without significant changes in LWC of both crop species. The exact relationships found, however, were influenced strongly by the date of measurement or water stress induced. Thus, global spectral relationships measuring LWP probably cannot be established across plant development stages. Even so, spectrometric measurements supplemented by a reduced calibration dataset from pressure chamber measurements might still prove to be a fast and accurate method for screening large numbers of diverse lines. © CSIRO 2011.

Tiso P.,Technical University of Delft | Rixen D.J.,Technical University Mnchen
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2013

Model Order Reduction (MOR) in nonlinear structural analysis problems in usually carried out by a Galerkin projection of the primary variables on a sensibly smaller space. However, the cost of computing the nonlinear terms is still of the order of the full system. The Discrete Empirical Interpolation Method is an effective algorithm to reduce the computational of the nonlinear term. However, its efficiency is diminished when applied to a Finite Element (FE) framework. We present here an alternative formulation of the DEIM that suits an FE formulation and preserves the efficiency of the method. © The Society for Experimental Mechanics Inc. 2013.

Dannohl C.,BMW AG | Muller S.,University of Kaiserslautern | Ulbrich H.,Technical University Mnchen
Vehicle System Dynamics | Year: 2012

Electric power steering (EPS) is more and more in use for passenger cars. Compared with hydraulic steering systems there are many advantages, such as reduced CO 2 emissions and the possibility to use the EPS motor torque for advanced driver assistance systems. One task of the steering system is to give the driver an adequate steering feel. This includes providing road feedback and the right level of assistance torque. This article describes the steering torque control of a rack-assisted EPS. The controller's task is to follow a reference steering torque quickly and accurately. First, a mechanical model of the EPS is shown. Then, an H ∞-controller is designed, implemented and compared with other steering torque controllers. As steering torque discontinuities are a topic when looking at new control algorithms, the phenomenon and its cause are analysed using a detailed mechanical model. The results of this analysis are considered in the controller design. © 2012 Copyright Taylor and Francis Group, LLC.

Zhang X.,Tsinghua University | Zhang X.,China University of Petroleum - Beijing | Shi H.,Tsinghua University | Shi H.,Technical University Mnchen | Xu B.-Q.,Tsinghua University
Journal of Catalysis | Year: 2011

Hydrogenation of 1,3-butadiene over Au/ZrO2 catalysts with different gold loadings and calcination temperatures was reported. The catalysts were characterized in depth to understand their structure-property relationship. Gold oxidation states and surface hydroxyl groups, which were found to be sensitive to the gold loading, calcination temperature, and treatment with water, were shown to play vital roles in the hydrogenation activity of Au/ZrO2. Continued activity decrease was seen when the density of surface hydroxyl groups was lowered by elevating the pre-calcination temperature of ZrO2. Fully dehydroxylated Au/ZrO2 was essentially inactive, but became very active after partial regeneration of the hydroxyl groups by water treatment. Moreover, the activity of Au/ZrO2 increased with increasing Au3+/Au0 ratio. Isolated Au3+ ions at the support surface showed up to two orders of magnitude higher activity than Au0 atoms on Au particles. Several models are proposed to address the structural features of active sites for H2 activation in Au/ZrO2 catalysts. © 2011 Elsevier Inc. All rights reserved.

Adhikari S.,University of Kiel | Jansen S.,University of Kiel | Kuschnerov M.,ADVA Optical Networking | Inan B.,Technical University Mnchen | And 2 more authors.
Optics Express | Year: 2012

DFTS-OFDM has been proposed recently as an alternative to coherent optical OFDM due to its improved transmission performance. This paper proposes spectral shaping for DFTS-OFDM which reduces the PAPR leading to further improvement in nonlinear tolerance. It is shown that for both SSMF and LEAF, the optimized spectrally shaped DFTS-OFDM outperforms DFTS-OFDM for dispersion managed and unmanaged links by ~10.8% and ~6.8%, respectively. The number of bands and the excess bandwidth parameters are also investigated to optimize the transmission performance. © 2012 Optical Society of America.

Goldenbaum M.,TU Berlin | Goldenbaum M.,Technical University Mnchen | Stanczak S.,TU Berlin | Stanczak S.,Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut
IEEE Transactions on Communications | Year: 2013

Wireless sensor network applications often involve the computation of pre-defined functions of the measurements such as for example the arithmetic mean or maximum value. Standard approaches to this problem separate communication from computation: digitized sensor readings are transmitted interference-free to a fusion center that reconstructs each sensor reading and subsequently computes the sought function value. Such separation-based computation schemes are generally highly inefficient as a complete reconstruction of individual sensor readings at the fusion center is not necessary to compute a function of them. In particular, if the mathematical structure of the channel is suitably matched (in some sense) to the function of interest, then channel collisions induced by concurrent transmissions of different nodes can be beneficially exploited for computation purposes. This paper proposes an analog computation scheme that allows for an efficient estimate of linear and nonlinear functions over the wireless multiple-access channel. A match between the channel and the function being evaluated is thereby achieved via some pre-processing on the sensor readings and post-processing on the superimposed signals observed by the fusion center. After analyzing the estimation error for two function examples, simulations are presented to show the potential for huge performance gains over time- and code-division multiple-access based computation schemes. © 1972-2012 IEEE.

V'lk F.,Technical University Mnchen
Acta Acustica united with Acustica | Year: 2015

The existing analytical expressions describing the frequency dependencies of critical bandwidth and equivalentrectangular bandwidth were derived from the results of different sets of listening experiments. As the corresponding band-rate scales are constructed by integrating the reciprocal bandwidth function over frequency, also the band-rate functions are based on the respectively selected experiments. The critical-bandwidth formula converges to 100 Hz at frequencies below about 500 Hz and the critical-band-rate function is not invertible in closed form, which complicates the application of the critical-band concept in modeling. In order to overcome these restrictions, the data used earlier to construct and validate the bandwidth functions were re-evaluated separately for the critical-band and the equivalent-rectangular-band concepts, and also combined. It is shown that the shape of a critical-bandwidth-frequency formula derived from a cochlear frequency-position function that results in an invertible critical-band-rate formula can be fitted to both data sets. Depending on frequency, the formulae predict about 1.53 to 1.55 times larger critical than equivalent-rectangular bandwidths. Low-frequency critical bandwidths, which are overestimated compared to the data by the earlier formula, are represented more accurately and at the same time suited better to avoid modeling artifacts. The determined functions are compared against each other and against the previously proposed bandwidth and band-rate formulae. The results indicate that a common function shape with a simple parameter variation is suited to account for the data used earlier to validate two different sets of formulae. © S. Hirzel Verlag • EAA.

Fischer M.K.,Technical University Mnchen | Rossmadl H.,Technical University Mnchen | Iglev H.,Technical University Mnchen
Journal of Chemical Physics | Year: 2011

We studied the photolysis of neat protonated and heavy water using pump-probe and pump-repump-probe spectroscopy. A novel recombination channel is reported leading to ultrafast quenching (0.7 0.1 ps) of almost one third of the initial number of photo-generated electrons. The efficiency and the recombination rate of this channel are lower in heavy water, 27 5 and (0.9 0.1 ps)-1, respectively. Comparison with similar data measured after photodetachment of aqueous hydroxide provides evidence for the formation of short-lived OH:e- (OD:e-) pairs after indirect photoionization of water at 9.2 eV. © 2011 American Institute of Physics.

Wiedenmann O.,Technical University Mnchen | Eibert T.F.,Technical University Mnchen
Proceedings - 2011 International Conference on Electromagnetics in Advanced Applications, ICEAA'11 | Year: 2011

The iterative solution of linear equation systems resulting from Method of Moments (MoM) discretizations of integral equations is of particular attractiveness because of the possibility to employ fast integral methods such as the Multilevel Fast Multipole Method (MLFMM). However, the robustness of the iterative solvers is often still not satisfying and the search for improved preconditioners is an ongoing process. In this paper, we concentrate on two classical near-zone preconditioning techniques: Gauss-Seidel smoothing and a special form of incomplete LU factorization. It is found that Gauss-Seidel smoothing is a relatively cheap preconditioner working well for fine meshes. Our special form of incomplete LU factorization gives reliable convergence for complex problems with very bad convergence behavior, regardless of mesh density but for the cost of increased memory requirements. © 2011 IEEE.

Matera S.,Fritz Haber Institute | Meskine H.,Fritz Haber Institute | Reuter K.,Fritz Haber Institute | Reuter K.,Technical University Mnchen
Journal of Chemical Physics | Year: 2011

Microkinetic modeling of surface chemical reactions still relies heavily on the mean-field based rate equation approach. This approach is expected to be most accurate for systems without appreciable lateral interactions among the adsorbed chemicals, and there in particular for the uniform adlayers resulting in poisoned regimes with predominant coverage of one species. Using first-principles kinetic Monte Carlo simulations and the CO oxidation at RuO2(110) as a showcase, we demonstrate that even in this limit mean-field rate equations fail to predict the catalytic activity by orders of magnitude. This deficiency is traced back to the inability to account for the vacancy pair formation that is kinetically driven by the ongoing reactions. © 2011 American Institute of Physics.

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