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We present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human distribution on Holocene regional, vegetation, feature that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past.
The Tibetan Plateau is a region that is highly sensitive to recent global warming, but the complexity and heterogeneity of its mountainous landscape can result in variable responses. In addition, the scarcity and brevity of regional instrumental and palaeoecological records still hamper our understanding of past and present patterns of environmental change. To investigate how the remote, high-alpine environments of the Nianbaoyeze Mountains, eastern Tibetan Plateau, are affected by climate change and human activity over the last similar to 600 years, we compared regional tree-ring studies with pollen and diatom remains archived in the dated sediments of Dongerwuka Lake (33.22A degrees N, 101.12A degrees E, 4,307 m a.s.l.). In agreement with previous studies from the eastern Tibetan Plateau, a strong coherence between our two juniper-based tree-ring chronologies from the Nianbaoyeze and the Anemaqin Mountains was observed, with pronounced cyclical variations in summer temperature reconstructions. A positive directional trend to warmer summer temperatures in the most recent decades, was, however, not observed in the tree-ring record. Likewise, our pollen and diatom spectra showed minimal change over the investigated time period. Although modest, the most notable change in the diatom relative abundances was a subtle decrease in the dominant planktonic Cyclotella ocellata and a concurrent increase in small, benthic fragilarioid taxa in the similar to 1820s, suggesting higher ecosystem variability. The pollen record subtly indicates three periods of increased cattle grazing activity (similar to 1400-1480 AD, similar to 1630-1760 AD, after 1850 AD), but shows generally no significant vegetation changes during past similar to 600 years. The minimal changes observed in the tree-ring, diatom and pollen records are consistent with the presence of localised cooling centres that are evident in instrumental and tree-ring data within the southeastern and eastern Tibetan Plateau. Given the minor changes in regional temperature records, our complacent palaeoecological profiles suggest that climatically induced ecological thresholds have not yet been crossed in the Nianbaoyeze Mountains region.
(Paleo-)climatologists are challenged to identify mechanisms that cause the observed abrupt Holocene monsoon events despite the fact that monsoonal circulation is assumed to be driven by gradual insolation changes. Here we provide proxy and model evidence to show that moisture-advection feedback can lead to a non-linear relationship between sea-surface and continental temperatures and monsoonal precipitation. A pollen record from Lake Ximencuo (Nianbaoyeze Mountains) indicates that vegetation from the eastern margin of the Tibetan Plateau was characterized by alpine deserts and glacial flora after the Last Glacial Maximum (LGM) (21-15.5 cal kyr BP), by alpine meadows during the Late Glacial (15.5-10.4 cal kyr BP) and second half of the Holocene (5.0 cal kyr BP to present) and by mixed forests during the first half of the Holocene (10.4-5.0 cal kyr BP). The application of pollen-based transfer functions yields an abrupt temperature increase at 10.4 cal kyr BP and a decrease at 5.0 cal kyr BP of about 3 degrees C. By applying endmember modeling to grain-size data from the same sediment core we infer that frequent fluvial events (probably originating from high-magnitude precipitation events) were more common in the early and mid Holocene. We assign the inferred exceptional strong monsoonal circulation to the initiation of moisture-advection feedback, a result supported by a simple model that reproduces this feedback pattern over the same time period. (C) 2014 Published by Elsevier B.V.
Lacustrine sediments have been widely used to investigate past climatic and environmental changes on millennial to seasonal time scales. Sedimentary archives of lakes in mountainous regions may also record non-climatic events such as earthquakes. We argue herein that a set of 64 annual laminae couplets reconciles a stratigraphically inconsistent accelerator mass spectrometry (AMS) C-14 chronology in a similar to 4-m-long sediment core from Lake Mengda, in the north-eastern Tibetan Plateau. The laminations suggest the lake was formed by a large landslide, triggered by the 1927 Gulang earthquake (M = 8.0). The lake sediment sequence can be separated into three units based on lithologic, sedimentary, and isotopic characteristics. Starting from the bottom of the sequence, these are: (1) unweathered, coarse, sandy valley-floor deposits or landslide debris that pre-date the lake, (2) landslide-induced, fine-grained soil or reworked landslide debris with a high organic content, and (3) lacustrine sediments with low organic content and laminations. These annual laminations provide a high-resolution record of anthropogenic and environmental changes during the twentieth century, recording enhanced sediment input associated with two phases of construction activities. The high mean sedimentation rates of up to 4.8 mm year(-1) underscore the potential for reconstructing such distinct sediment pulses in remote, forested, and seemingly undisturbed mountain catchments.
Zooplankton carcasses are ubiquitous in marine and freshwater systems, implicating the importance of non-predatory mortality, but both are often overlooked in ecological studies compared with predatory mortality. The development of several microscopic methods allows the distinction between live and dead zooplankton in field samples, and the reported percentages of dead zooplankton average 11.6 (minimum) to 59.8 (maximum) in marine environments, and 7.4 (minimum) to 47.6 (maximum) in fresh and inland waters. Common causes of non-predatory mortality among zooplankton include senescence, temperature change, physical and chemical stresses, parasitism and food-related factors. Carcasses resulting from non-predatory mortality may undergo decomposition leading to an increase in microbial production and a shift in microbial composition in the water column. Alternatively, sinking carcasses may contribute significantly to vertical carbon flux especially outside the phytoplankton growth seasons, and become a food source for the benthos. Global climate change is already altering freshwater ecosystems on multiple levels, and likely will have significant positive or negative effects on zooplankton non-predatory mortality. Better spatial and temporal studies of zooplankton carcasses and non-predatory mortality rates will improve our understanding of this important but under-appreciated topic.
Zooplankton support distinct bacterial communities in high concentrations relative to the surrounding water, but little is known about how the compositions and functionalities of these bacterial communities change through time in relation to environmental conditions. We conducted a year-long field study of bacterial communities associated with common zooplankton groups as well as free-living bacterial communities in the York River, a tributary of Chesapeake Bay. Bacterial community genetic fingerprints and their carbon substrate usage were examined by denaturing gradient gel electrophoresis (DGGE) of amplified 16S rDNA and by Biolog EcoPlates, respectively. Zooplankton-associated communities were genetically distinct from free-living bacterial communities but utilized a similar array of carbon substrates. On average, bacteria associated with different zooplankton groups were genetically more similar to each other within each month (65.4% similarity) than to bacterial communities of the same zooplankton group from different months (28 to 30% similarity), which suggests the importance of ambient environmental conditions in shaping resident zooplankton-associated bacterial communities. Monthly changes in carbon substrate utilization were less variable for zooplankton-associated bacteria than for free-living bacteria, suggesting that the zooplankton microhabitat is more stable than the surrounding water and supports specific bacterial groups in the otherwise unfavorable conditions in the water column.
The widely reported paradox of methane oversaturation in oxygenated water challenges the prevailing paradigm that microbial methanogenesis only occurs under anoxic conditions. Using a combination of field sampling, incubation experiments, and modeling, we show that the recurring mid-water methane peak in Lake Stechlin, northeast Germany, was not dependent on methane input from the littoral zone or bottom sediment or on the presence of known micro-anoxic zones. The methane peak repeatedly overlapped with oxygen oversaturation in the seasonal thermocline. Incubation experiments and isotope analysis indicated active methane production, which was likely linked to photosynthesis and/or nitrogen fixation within the oxygenated water, whereas lessening of methane oxidation by light allowed accumulation of methane in the oxygen-rich upper layer. Estimated methane efflux from the surface water was up to 5 mmol m(-2) d(-1). Mid-water methane oversaturation was also observed in nine other lakes that collectively showed a strongly negative gradient of methane concentration within 0-20% dissolved oxygen (DO) in the bottom water, and a positive gradient within >= 20% DO in the upper water column. Further investigation into the responsible organisms and biochemical pathways will help improve our understanding of the global methane cycle.
A new concept for shortening hard X-ray pulses emitted from a third-generation synchrotron source down to few picoseconds is presented. The device, called the PicoSwitch, exploits the dynamics of coherent acoustic phonons in a photo-excited thin film. A characterization of the structure demonstrates switching times of <= 5 ps and a peak reflectivity of similar to 10(-3). The device is tested in a real synchrotron-based pump-probe experiment and reveals features of coherent phonon propagation in a second thin film sample, thus demonstrating the potential to significantly improve the temporal resolution at existing synchrotron facilities.
We investigate the thermoelastic response of a nanolayered sample composed of a metallic SrRuO3 electrode sandwiched between a ferroelectric Pb(Zr0.2Ti0.8)O-3 film with negative thermal expansion and a SrTiO3 substrate. SrRuO3 is rapidly heated by fs-laser pulses with 208 kHz repetition rate. Diffraction of X-ray pulses derived from a synchrotron measures the transient out-of-plane lattice constant c of all three materials simultaneously from 120 ps to 5 mu s with a relative accuracy up to Delta c/c = 10(-6). The in-plane propagation of sound is essential for understanding the delayed out-of-plane compression of Pb(Zr0.2Ti0.8)O-3.
During this work I built a four wave mixing setup for the time-resolved femtosecond spectroscopy of Raman-active lattice modes. This setup enables to study the selective excitation of phonon polaritons. These quasi-particles arise from the coupling of electro-magnetic waves and transverse optical lattice modes, the so-called phonons. The phonon polaritons were investigated in the optically non-linear, ferroelectric crystals LiNbO₃ and LiTaO₃.
The direct observation of the frequency shift of the scattered narrow bandwidth probe pulses proofs the role of the Raman interaction during the probe and excitation process of phonon polaritons. I compare this experimental method with the measurement where ultra-short laser pulses are used. The frequency shift remains obscured by the relative broad bandwidth of these laser pulses. In an experiment with narrow bandwidth probe pulses, the Stokes and anti-Stokes intensities are spectrally separated. They are assigned to the corresponding counter-propagating wavepackets of phonon polaritons. Thus, the dynamics of these wavepackets was separately studied. Based on these findings, I develop the mathematical description of the so-called homodyne detection of light for the case of light scattering from counter propagating phonon polaritons.
Further, I modified the broad bandwidth of the ultra-short pump pulses using bandpass filters to generate two pump pulses with non-overlapping spectra. This enables the frequency-selective excitation of polariton modes in the sample, which allows me to observe even very weak polariton modes in LiNbO₃ or LiTaO₃ that belong to the higher branches of the dispersion relation of phonon polaritons. The experimentally determined dispersion relation of the phonon polaritons could therefore be extended and compared to theoretical models. In addition, I determined the frequency-dependent damping of phonon polaritons.
Using ultrafast X-ray diffraction, we study the coherent picosecond lattice dynamics of photoexcited thin films in the two limiting cases, where the photoinduced stress profile decays on a length scale larger and smaller than the film thickness. We solve a unifying analytical model of the strain propagation for acoustic impedance-matched opaque films on a semi-infinite transparent substrate, showing that the lattice dynamics essentially depend on two parameters: One for the spatial profile and one for the amplitude of the strain. We illustrate the results by comparison with high-quality ultrafast X-ray diffraction data of SrRuO3 films on SrTiO3 substrates. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
Herein, a facile method is presented to integrate large gold nanoflowers (similar to 80 nm) and small gold nanoparticles (2-4 nm) into a single entity, exhibiting both surface-enhanced Raman scattering (SERS) and catalytic activity. The as-prepared gold nanoflowers were coated by a gelatin layer, in which the gold precursor was adsorbed and in situ reduced into small gold nanoparticles. The thickness of the gelatin shell is controlled to less than 10 nm, ensuring that the small gold nanoparticles are still in a SERS-active range of the inner Au core. Therefore, the reaction catalyzed by these nanocomposites can be monitored in situ using label-free SERS spectroscopy. In addition, these bifunctional nanocomposites are also attractive candidates for application in SERS monitoring of bioreactions because of their excellent biocompatibility.
Fabrication of Au@Pt multibranched nanoparticles and their application to in situ SERS monitoring
(2014)
Here, we present an Au@Pt core-shell multibranched nanoparticle as a new substrate capable of in situ surface-enhanced Raman scattering (SERS), thereby enabling monitoring of the catalytic reaction on the active surface. By careful control of the amount of Pt deposited bimetallic Au@Pt, nanoparticles with moderate performance both for SERS and catalytic activity were obtained. The Pt-catalyzed reduction of 4-nitrothiophenol by borohydride was chosen as the model reaction. The intermediate during the reaction was captured and clearly identified via SERS spectroscopy. We established in situ SERS spectroscopy as a promising and powerful technique to investigate in situ reactions taking place in heterogeneous catalysis.
Protein-metal coordination complexes are well known as active centers in enzymatic catalysis, and to contribute to signal transduction, gas transport, and to hormone function. Additionally, they are now known to contribute as load-bearing cross-links to the mechanical properties of several biological materials, including the jaws of Nereis worms and the byssal threads of marine mussels. The primary aim of this thesis work is to better understand the role of protein-metal cross-links in the mechanical properties of biological materials, using the mussel byssus as a model system. Specifically, the focus is on histidine-metal cross-links as sacrificial bonds in the fibrous core of the byssal thread (Chapter 4) and L-3,4-dihydroxyphenylalanine (DOPA)-metal bonds in the protective thread cuticle (Chapter 5).
Byssal threads are protein fibers, which mussels use to attach to various substrates at the seashore. These relatively stiff fibers have the ability to extend up to about 100 % strain, dissipating large amounts of mechanical energy from crashing waves, for example. Remarkably, following damage from cyclic loading, initial mechanical properties are subsequently recovered by a material-intrinsic self-healing capability. Histidine residues coordinated to transition metal ions in the proteins comprising the fibrous thread core have been suggested as reversible sacrificial bonds that contribute to self-healing; however, this remains to be substantiated in situ. In the first part of this thesis, the role of metal coordination bonds in the thread core was investigated using several spectroscopic methods. In particular, X-ray absorption spectroscopy (XAS) was applied to probe the coordination environment of zinc in Mytilus californianus threads at various stages during stretching and subsequent healing. Analysis of the extended X-ray absorption fine structure (EXAFS) suggests that tensile deformation of threads is correlated with the rupture of Zn-coordination bonds and that self-healing is connected with the reorganization of Zn-coordination bond topologies rather than the mere reformation of Zn-coordination bonds. These findings have interesting implications for the design of self-healing metallopolymers.
The byssus cuticle is a protective coating surrounding the fibrous thread core that is both as hard as an epoxy and extensible up to 100 % strain before cracking. It was shown previously that cuticle stiffness and hardness largely depend on the presence of Fe-DOPA coordination bonds. However, the byssus is known to concentrate a large variety of metals from seawater, some of which are also capable of binding DOPA (e.g. V). Therefore, the question arises whether natural variation of metal composition can affect the mechanical performance of the byssal thread cuticle. To investigate this hypothesis, nanoindentation and confocal Raman spectroscopy were applied to the cuticle of native threads, threads with metals removed (EDTA treated), and threads in which the metal ions in the native tissue were replaced by either Fe or V. Interestingly, replacement of metal ions with either Fe or V leads to the full recovery of native mechanical properties with no statistical difference between each other or the native properties. This likely indicates that a fixed number of metal coordination sites are maintained within the byssal thread cuticle – possibly achieved during thread formation – which may provide an evolutionarily relevant mechanism for maintaining reliable mechanics in an unpredictable environment.
While the dynamic exchange of bonds plays a vital role in the mechanical behavior and self-healing in the thread core by allowing them to act as reversible sacrificial bonds, the compatibility of DOPA with other metals allows an inherent adaptability of the thread cuticle to changing circumstances. The requirements to both of these materials can be met by the dynamic nature of the protein-metal cross-links, whereas covalent cross-linking would fail to provide the adaptability of the cuticle and the self-healing of the core. In summary, these studies of the thread core and the thread cuticle serve to underline the important and dynamic roles of protein-metal coordination in the mechanical function of load-bearing protein fibers, such as the mussel byssus.
Structures, C-13 chemical shifts, and the occupation quotients of anti-bonding pi* and bonding pi orbitals of the C C triple bond along a series of push-pull alkynes (p)X-C6H4 C(O)-C C-NH-C6H4-Y(P) (X,Y= H, Me, OMe, NMe2, NO2, COMe, COOMe, F, Cl, Br) were computed at the DFT level (B3LYP/6-311G**) of theory. Both the stereochemistry (cis/trans-isomers) by steric twist and the push-pull character by both C-13 chemical shift differences (Delta delta(C C)) and the occupation quotient (pi(C C)/pi(C C)) were studied; the latter two parameters can be readily employed to precisely quantify the push-pull effect in alkynes. (C) 2014 Elsevier B.V. All rights reserved.
Changes in performance parameters over four consecutive maximal incremental cycling tests were investigated to determine how many tests can be performed within one single day without negatively affecting performance. Sixteen male and female subjects (eight trained (T): 25 +/- 3 yr, BMI 22.6 +/- 2.5 kg center dot m(-2), maximal power output (P-max) 4.6 +/- 0.5 W center dot kg(-1); eight untrained (UT): 27 +/- 3 yr, BMI 22.3 +/- 1.2 kg center dot m(-2), P-max 2.9 +/- 0.3 W center dot kg(-1)) performed four successive maximal incremental cycling tests separated by 1.5 h of passive rest. Individual energy requirements were covered by standardised meals between trials. Maximal oxygen uptake (VO2max) remained unchanged over the four tests in both groups (P = 0.20 and P = 0.33, respectively). P-max did not change in the T group (P = 0.32), but decreased from the third test in the UT group (P < 0.01). Heart rate responses to submaximal exercise were elevated from the third test in the T group and from the second test in the UT group (P < 0.05). The increase in blood lactate shifted rightward over the four tests in both groups (P < 0.001 and P < 0.01, respectively). Exercise-induced net increases in epinephrine and norepinephrine were not different between the tests in either group (P 0.15). If VO2max is the main parameter of interest, trained and untrained individuals can perform at least four maximal incremental cycling tests per day. However, because other parameters changed after the first and second test, respectively, no more than one test per day should be performed if parameters other than VO2max are the prime focus.
Restricted rotation about the N-S partial double bonds in a bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane derivative 1 has been frozen at low temperature (Delta G* = 11.6 kcal mol(-1)), and the existence of all four rotamers about the two N-S bonds, 3-in, 8-in, 3-in, 8-out, 3-out, 8-in, and 3-out, 8-out, respectively, proved experimentally by NMR spectroscopy and theoretically by DFT and MP2 calculations. Copyright (C) 2014 John Wiley & Sons, Ltd.
We sought to investigate the effects of wearing a mobile respiratory gas analysis system during a treadmill test on blood lactate (bLa) concentrations and commonly applied bLa thresholds. A total of 16 recreational athletes (31 +/- 3 years, V0205: 58 6 ml min(-1)-kg(-1)) performed one multistage treadmill test with and one without gas exchange measurements (GEM and noGEM). The whole bLa curve, the lactate threshold (LT), the individual anaerobic thresholds according to Stegmann(IAT(sr)) and Dickhuth (IAT(Di)), and a fixed bLa concentration of 4 mmob.l(-1) (OBLA) were evaluated. The bLa curve was shifted slightly leftward in GEM compared to noGEM (P<0.05), whereas the heart rate response was not different between conditions (P= 0.89). There was no difference between GEM and noGEM for LT (2.61 +/- 0.34 vs. 2.64 +/- 0.39 m(-1) s(-1) P=0.49) and IAT(st) (3.47 +/- 0.42 vs. 3.55 +/- 0.47m-s(-1), P=0.12). However, IATD(Di) (3.57 +/- 0.39 vs. 3.66 +/- 0.44m-s(-1), P<0.01) and OBLA (3.85 +/- 0.46 vs. 3.96 +/- 0.47m-s-1, P<0.01) occurred at slower running velocities in GEM. The bLa response to treadmill tests is mildly affected by wearing a mobile gas analysis system. This also applies to bLa thresholds located at higher exercise intensities. While the magnitude of the effects is of little importance for recreational athletes, it might be relevant for elite athletes and scientific studies.