Die "Netzgeneration". Empirische Untersuchungen zur Mediennutzung bei Jugendlichen

In diesem Kapitel wird das Konzept der "Netzgeneration" vorgestellt und kritisch beleuchtet. Im ersten Abschnitt werden die zentralen Aussagen der Verfechterinnen und Verfechter einer "Netzgeneration" dargelegt. Im zweiten Abschnitt wird die Kritik an diesem Konzept aufgeführt, mit dem zentralen Ergebnis, dass die Behauptung der Existenz einer "Netzgeneration" einer wissenschaftlichen Überprüfung nicht standhält. Das Bild der "Netzgeneration" oder sogenannter "Digitaler Eingeborener" als Bezeichnung für die heutigen Kinder und Jugendlichen wurde zwar breit rezipiert und hat den Diskurs um neue Lern- und Lehrformen stark beeinflusst, muss in seiner verallgemeinert-pauschalen Form aber als Mythos bezeichnet werden. Ein Überblick über zentrale Ergebnisse empirischer Studien zum Medien(nutzungs)verhalten von Kindern und Jugendlichen im dritten Abschnitt liefert entsprechend ein sehr viel differenzierteres Bild. Im vierten Abschnitt wird aufgezeigt, welche Konsequenzen diese Ergebnisse für das Bildungssystem allgemein und für das Lehren und Lernen mit Technologien im Besonderen haben, jenseits der Pauschalforderungen der Propagandisten und Propagandistinnen einer "Netzgeneration". Eine Aufzählung zentraler Erkenntnisse im fünften Abschnitt rundet das Kapitel ab. (DIPF/Orig.

Effects of Oxymethylene Ether in a Commercial Diesel Engine

Oxymethylen Ether (OME) is a promising alternative fuel for diesel engines. It can be produced sustainably, and its combustion is clean and efficient. This study investigates the effects of different OME$_{3-5}$ mixtures on emissions and combustion. The measurements were done on a four-cylinder common rail commercial diesel engine equipped with an exhaust gas recirculation system (EGR). Five different blends of OME$_{3-5}$ and B7 diesel were applied with 0, 7, 15, 25 and 45 vol% OME$_{3-5}$content at four loads. The NO$_{x}$–PM trade-off was investigated at 11 EGR rates for each mixture at each load. Increasing OME$_{3-5}$ mixing ratio reduced the PM emission, improved the NO$_{x}$–PM trade-off, and increased the brake thermal efficiency. The maximum achieved PM emission reduction was 86.8% for high loads. However, NO$_{x}$ emission increased, and also low heat capacity and viscosity can be a problem for real applications

Cross-Cultural Variations in Identifying Embedded Figures : Comparisons from the United States, Germany, Russia, and Malaysia

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Previous studies have found cross-cultural variation in field dependence. In this study, cross-cultural differences were expected depending on the degree of individualism or collectivism of the respective cultures. Samples were taken from two prototypically individualist cultures, the United States and Germany, and two collectivist cultures, Russia and Malaysia. As predicted, field dependence did not differ between those samples that represented the same type of culture, either collectivist or individualist. However, a clear difference could be found between the two types of cultures; that is, U.S. and German participants were more field independent than were Russian and Malaysian participants

Suppressing the aromatic cycle of the dimethyl ether to hydrocarbons reaction on zeolites

The influence of the zeolite framework type on the conversion of dimethyl ether (DME) to hydrocarbons (DTH) was investigated for *MRE, MFI and TON zeolite catalysts. Remarkable differences in the catalytic performance of the materials were observed. In particular, the *MRE zeolite showed an exceptionally high yield of olefins (90%) with a substantial ratio of products in the chain length range C$_5$-C$_{11}$. Additionally, the longevity of the *MRE zeolite clearly exceeded previously reported data. The comparison of mechanistic parameters (Hydrogen-Transfer-Index HTI$_{Ci}$ and C$_3$/C$_2$ ratio) demonstrated for this zeolite, that the formation of aromatics in the reaction network can be almost completely suppressed under suitable reaction conditions. By varying the reaction parameters temperature, DME partial pressure and weight hourly space velocity (WHSV), it was possible to identify the optimal combination of selectivity and deactivation resistance for each material. The olefin-rich DTH product of the *MRE zeolite offers manifold possibilities for further conversion to valuable renewably produced low-emission fuels like gasoline or jet fuel

Can the energy dependence of elliptic flow reveal the QGP phase transition?

Ideal hydrodynamic simulations are performed to compute the evolution with collision energy of hadron spectra and elliptic flow between AGS and LHC energies. We argue that viscous effects should decrease with increasing energy, improving the applicability of ideal fluid dynamics at higher energies. We show that the increasing radial flow at higher energies pushes the elliptic flow to larger transverse momenta, leading to a peaking and subsequent decrease of the elliptic flow at fixed p_T with increasing collision energy, independent of whether or not there is a phase transition in the equation of state.Comment: Final version, to appear in the proceedings of Quark Matter 2009: 21th International Conference on Ultra-Relativistic Nucleus Nucleus Collisions (QM 2009), Knoxville, TN, Mar.30 - Apr.4, 2009. This version 2 uses larger fonts in Fig. 1c; no other change

Continuous Synthesis of Oxymethylene Ether Fuels from Dimethyl Ether in a Heterogeneously Catalyzed Liquid Phase Process

Oxymethylene ethers (OME) are an attractive alternative to fossil diesel fuel due to strongly reduced harmful emissions. An anhydrous, liquid phase production process based on dimethyl ether (DME) has been elaborated, which offers high selectivity and economic advantages. A catalyst screening for the reaction of DME with trioxane has been carried out. Highly active catalysts could be identified and further insight into the relationship between catalyst properties and catalytic performance could be gained. Furthermore, production in a continuous process could be realized, disclosing the influence of kinetics on OME formation and enabling a better understanding of the reaction mechanism

Comparison of empirical noise models for GRACE Follow-On derived with the Celestial Mechanics Approach

A key component of any model is the accurate specification of its quality. In gravity field modelling from satellite data, as it is done with the observation collected by GRACE Follow-On, usually least-squares adjustments are performed to obtain a monthly solution of the Earth's gravity field. However, the jointly estimated formal errors usually do not reflect the error level that could be expected but provides much lower error estimates. We take the Celestial Mechanics Approach (CMA), developed at the Astronomical Institute, University of Bern (AIUB), and extend it by an empirical modelling of the noise based on the post-fit residuals between the final GRACE Follow-On orbits, that are co-estimated together with the gravity field, and the observations, expressed in position residuals to the kinematic positions and in K-band range-rate residuals. We compare and validate the solutions that employ empirical modelling with solutions that do not contain sophisticated noise modelling by examining the stochastic behaviour of the respective post-fit residuals, by investigating areas where a low noise is expected and by inspecting the mass trend estimates in certain areas of global interest. Finally, we investigate the influence of the empirically weighted solutions in a combination of monthly gravity fields based on other approaches as it is done in the COST-G framework

Variance component estimation for co-estimated noise parameters in GRACE Follow-On gravity field recovery

Temporal gravity field modelling from GRACE Follow-On has to cope with several noise sources contaminating not only the observations but also the observation equations via mis-modellings in the underlying background force models. One way to deal with such deficiencies is to extend the parameter space by additional quantities, such as pseudo-stochastic parameters, which are co-estimated in the Least-Squares Adjustment (LSA). These parameters are meant to absorb any kind of noise while retaining the signal in the gravity field and orbit parameters. In the Celestial Mechanics Approach (CMA) such pseudo-stochastic parameters are typically set-up as Piece-wise Constant Accelerations (PCA) in regular intervals of e.g., 15 min. The stochastic behaviour of these parameters is unknown because they reflect an accumulation of a variety of noise sources. In the CMA fictitious artificial zero-observations are appended to the vector of observations together with an empirically determined variance to introduce a stochastic model for the PCAs. In order to also co-estimate a stochastic model for the pseudo-stochastic parameters in the LSA we use Variance Component Estimation (VCE) as a well established tool to assign variance components to individual groups of observation. In the simplest case the magnitude of the constraints of the pseudo-stochastic parameters can be determined fully automatically. We present results for GRACE Follow-On gravity field recovery when extending the CMA by stochastic models for the piece-wise constant accelerations computed with VCE and provide noise and signal assessment applying the quality control tools routinely used in the frame of the Combination Service for Time-variable gravity fields (COST-G)

Time-variable gravity field determination from GRACE Follow-On data usingthe Celestial Mechanics Approach extended by empirical noise modelling

We study gravity field determination from GRACE Follow-On satellite-to-satellite tracking using the inter-satellite K-band link and kinematic positions of the satellites as observations and pseudo- observations respectively. A key component of any model is the accurate specification of its quality. In the case of gravity field modelling from satellite data with the Celestial Mechanics Approach (CMA) a least-squares adjustment is performed to obtain a monthly solution of the Earthâ?Ts gravity field. However, the jointly estimated formal errors usually do not reflect the error level that could be expected but provides much lower error estimates. We present gravity field solutions computed with the CMA and extend it by an empirical modelling of the noise based on the post-fit residuals between the final GRACE Follow-On orbits, that are co-estimated together with the gravity field, and the observations, expressed in position residuals to the kinematic positions and in K-band range-rate residuals. We compare and validate the solutions that use empirical modelling with solutions from the operational GRACE Follow-On processing at AIUB by examining the stochastic behaviour of the respective post-fit residuals, by investigating areas where a low noise is expected and by inspecting the mass trend estimates in certain areas of global interest. Finally, we investigate the influence of the empirically weighted solutions in a combination of monthly gravity fields based on other approaches as it is done by the Combination Service for Time-variable Gravity fields (COST-G) and make use of noise and signal assessment applying the quality control tools routinely used in the frame of COST-G