Showing papers by "University of Bremen published in 2004"

Extending collostructional analysis: A corpus-based perspective on `alternations'

Abstract: This paper introduces an extension of distinctive-collocate analysis that takes into account grammatical structure and is specifically geared to investigating pairs of semantically similar grammatical constructions and the lexemes that occur in them. The method, referred to as `distinctive-collexeme analysis', identifies lexemes that exhibit a strong preference for one member of the pair as opposed to the other, and thus makes it possible to identify subtle distributional differences between the members of such a pair. The method can be applied in the context of what is sometimes referred to as `grammatical alternation' (e.g. the dative alternation), but it can also be applied to other choices provided by the grammar (such as the two future tense constructions in English). The method has two main applications. First, it can reveal subtle differences between seemingly synonymous constructions, many of which are difficult to identify on the basis of more traditional approaches. Second, it can be used to investigate the very notion of `alternation'; we show that many alternations are much more restricted than has hitherto been assumed, and thus confirm the claims of recent, non-derivational views of grammar.

Drive-thru Internet: IEEE 802.11b for "automobile" users

Abstract: This paper reports on measurement results for the use of IEEE 802.11 networks in drive-thru scenarios: we have measured transmission characteristics for sending and receiving high data volumes using UDP and TCP in vehicles moving at different speeds that pass one or more IEEE 802.11 access points at the roadside. We discuss possibilities and limitations for the use of scattered WLAN cells by devices in fast moving vehicles and provide an analysis of the performance that can he expected for the communication in such scenarios. Based on these observations, we discuss implications for higher-layer protocols and applications.

Intact polar membrane lipids in prokaryotes and sediments deciphered by high-performance liquid chromatography/electrospray ionization multistage mass spectrometry--new biomarkers for biogeochemistry and microbial ecology.

Abstract: Lipids from prokaryotic cell membranes can serve as sources of information on the biogeochemistry and microbial ecology of natural ecosystems. Traditionally, apolar derivatives of the intact polar membrane molecules, e.g., fatty acids, have been the major target of lipid-based biogeochemical studies. However, when still intact, i.e., as glycerol esters and ethers with attached polar headgroups, membrane lipids are diagnostic for living prokaryotes, which makes them excellent biomarkers for the study of in situ microbial processes in geological systems such as sediments or soils. Intact polar lipids (IPLs) are attractive analytical targets because they are taxonomically more specific than their apolar derivatives and avoid exclusion of signals from prokaryotes that primarily build their membranes with ether-bound lipids such as archaea and some bacteria. Here we report results from analyses of IPLs in pure cultures of biogeochemically relevant prokaryotes and marine sediments by high-performance liquid chromatography/electrospray ionization ion-trap mass spectrometry (HPLC/ESI-IT-MSn). This technique is suitable for screening of biomass and environmental samples for distinctive taxonomic structural features such as distribution of polar lipid headgroups, types of bonds between alkyl moiety and glycerol backbone, and the chain length and degree of unsaturation in the alkyl moieties. We present analytical protocols to decipher structural information from mass spectral data. The IPL contents in selected archaeal and bacterial species are diverse and qualify as molecular fingerprints. Applied to marine sediments, the approach provided detailed information on the dominant microbial groups. The IPLs from bacterial members of anaerobic methanotrophic communities in surface sediments at Hydrate Ridge resemble those found in Desulfosarcina variabilis. The presence of dietherglycerophospholipids, however, suggests the presence of other bacteria possibly affiliated with the deepest phylogenetic branches in the tree of life. Sediments from approximately 90 m below the seafloor on the Peruvian continental margin are dominated by intact archaeal tetraethers with glycosidically bound hexoses as headgroups, consistent with a significant fraction of the community being archaea. Additional calditol-based tetraethers imply that the sedimentary archaea are taxonomically linked to the crenarchaeal Sulfolobales.

Near-maximum-likelihood detection of MIMO systems using MMSE-based lattice reduction

Abstract: In recent publications the use of lattice-reduction for signal detection in multiple antenna systems has been proposed. In this paper, we adopt these lattice-reduction-aided schemes to the MMSE criterion. We show that an obvious way to do this is infeasible and propose an alternative method based on an extended system model, which in conjunction with simple successive interference cancellation nearly reaches the performance of maximum-likelihood detection. Furthermore, we demonstrate that, a sorted QR decomposition can significantly reduce the computational effort associated with lattice-reduction. Thus, the new algorithm clearly outperforms existing methods with comparable complexity.

Himalayan-type indenter-escape tectonics model for the southern part of the late Neoproterozoic–early Paleozoic East African– Antarctic orogen

Abstract: The East African–Antarctic orogen is one of the largest orogenic belts on the planet. It resulted from the collision of various parts of proto–East and West Gondwana during late Neoproterozoic–early Paleozoic time (between 650 and 500 Ma). We propose that the southern part of this Himalayan-type orogen can be interpreted in terms of a lateral-escape tectonic model. Modern Gondwana reconstructions show that the southern part of the East African– Antarctic orogen can best be reassembled when a number of microplates (the Falkland, Ellsworth-Haag, and Filchner blocks) are positioned between southern Africa and East Antarctica. This microplate assemblage is unusual. The microplates probably represent shear-zone–bounded blocks, produced by tectonic translation during lateral escape, similar to those currently evolving in Southeast Asia. One of the escape-related shear zones is exposed as the 20-km-wide Heimefront transpression zone in western Dronning Maud Land. Coats Land, a crustal block within the orogen, probably represents a block of older crust that was not subjected to tectonometamorphic reworking ca. 500 Ma by lateral tectonic escape. The southern part of the orogen is also typified by very large volumes of late-tectonic A2-type granitoids, intruded ca. 530–490 Ma, probably as a consequence of delamination of the orogenic root and the subsequent influx of hot asthenospheric mantle during tectonic escape. Erosional unroofing of the orogen is documented by the remnants of originally massive areas covered by Cambrian– Ordovician molasse-type sedimentary rocks throughout Africa, Arabia, and Antarctica, testifying to the past extent and size of this largest of orogens.

Ethical principles and standards for the conduct of human and animal biological rhythm research.

Abstract: Most research papers published in Chronobiology International report the findings of investigations conducted on laboratory animals and human beings. The Journal, its editors and the publication committee endorse the compliance of investigators to the principles of the Declaration of Helsinki of the World Medical Association relating to the conduct of ethical research on human beings and the Guide for the Care and Use of Laboratory Animals of the Institute for Laboratory Animal Research of the National Research Council relating to the conduct of ethical research on laboratory and other animals. Chronobiology International requires that submitted manuscripts reporting the findings of human and animal research conform to the respective policy and mandates of the Declaration of Helsinki and the Guide for the Care and Use of Laboratory Animals. The peer review of manuscripts will thus include judgment of whether or not the involved research methods conform to the standards of good research practice. This article outlines the basic expectations for the methods of human and animal biological rhythm research, both from the perspective of the fundamental criteria necessary for quality chronobiology investigation and from the perspective of humane and ethical research on human beings and animals.

Increased seasonality in Middle East temperatures during the last interglacial period

Abstract: The last interglacial period (about 125,000 years ago) is thought to have been at least as warm as the present climate. Owing to changes in the Earth's orbit around the Sun, it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales, which would have led to corresponding changes in the seasonal temperature cycle. Here we present seasonally resolved proxy records using corals from the northernmost Red Sea, which record climate during the last interglacial period, the late Holocene epoch and the present. We find an increased seasonality in the temperature recorded in the last interglacial coral. Today, climate in the northern Red Sea is sensitive to the North Atlantic Oscillation, a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region. From our coral records and simulations with a coupled atmosphere-ocean circulation model, we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period, which is consistent with European proxy records, contributed to the larger amplitude of the seasonal cycle in the Middle East.

Atmospheric methane and carbon dioxide from SCIAMACHY satellite data: initial comparison with chemistry and transport models

Abstract: . The remote sensing of the atmospheric greenhouse gases methane (CH4) and carbon dioxide (CO2) in the troposphere from instrumentation aboard satellites is a new area of research. In this manuscript, results obtained from observations of the up-welling radiation in the near-infrared by SCIAMACHY on board ENVISAT are presented. Vertical columns of CH4, CO2 and oxygen (O2) have been retrieved and the (air or) O2-normalised CH4 and CO2 column amounts, the dry air column averaged mixing ratios XCH4 and XCO2 derived. In this manuscript the first results, obtained by using the version 0.4 of the Weighting Function Modified (WFM) DOAS retrieval algorithm applied to SCIAMACHY data, are described and compared with global models. For the set of individual cloud free measurements over land the standard deviation of the difference with respect to the models is in the range ~100–200 ppbv (5–10%) for XCH4 and ~14–32 ppmv (4–9%) for XCO2. The inter-hemispheric difference of the methane mixing ratio, as determined from single day data, is in the range 30–110 ppbv and in reasonable agreement with the corresponding model data (48–71 ppbv). The weak inter-hemispheric difference of the CO2 mixing ratio can also be detected with single day data. The spatiotemporal pattern of the measured and the modelled XCO2 are in reasonable agreement. However, the amplitude of the difference between the maximum and the minimum for SCIAMACHY XCO2 is about ±20 ppmv which is about a factor of four larger than the variability of the model data which is about ±5 ppmv. More studies are needed to explain the observed differences. The XCO2 model field shows low CO2 concentrations beginning of January 2003 over a spatially extended CO2 sink region located in southern tropical/sub-tropical Africa. The SCIAMACHY data also show low CO2 mixing ratios over this area. According to the model the sink region becomes a source region about six months later and exhibits higher mixing ratios. The SCIAMACHY and the model data over this region show a similar time dependence over the period from January to October 2003. These results indicate that for the first time a regional CO2 surface source/sink region has been detected by measurements from space. The interpretation of the SCIAMACHY CO2 and CH4 measurements is difficult, e.g., because the error analysis of the currently implemented retrieval algorithm indicates that the retrieval errors are on the same order as the small greenhouse gas mixing ratio changes that are to be detected.

SCIATRAN 2.0 - A new radiative transfer model for geophysical applications in the 175 - 2400 nm spectral region.

Abstract: A successor version of the SCIATRAN radiative transfer model (RTM) has been developed to perform radiative transfer modeling in any observation geometry appropriate to measurements of the scattered solar radiation in the Earth’s atmosphere. The model is designed to be used as a forward model in the retrieval of atmospheric constituents from measurements of scattered solar light by satellite, ground-based, or airborne instruments in UV–Vis–NIR spectral region. Furthermore, it can be used to calculate air mass factors or fluxes. The new generation of the SCIATRAN model comprises all features of the latest SCIATRAN 1.2 RTM supporting additionally radiative transfer calculations in a spherical atmosphere. The program is written in FORTRAN 95 and suitable for parallel execution using the OpenMP standard. The wavelength range covered by the radiative transfer model is extended to 175–2380 nm including Schuman-Runge and Herzberg absorption bands of oxygen. The SCIATRAN 2.0 model exhibits the following new capabilities: (i) modeling of the scattered solar radiation in limb viewing geometry as well as any kind of measurements of the scattered radiation within the atmosphere, (ii) corresponding quasi-analytical calculation of weighting functions of atmospheric parameters, (iii) airmass factor calculations for ground-based, space and airborne measurements including off-axis geometry, (v) accounting for photochemically active species, i.e., radiative transfer calculations can be performed using solar zenith angle dependent vertical distributions of atmospheric species, (iv) height resolved radiation fluxes, including actinic fluxes for photolysis rate calculations, (vi) inelastic rotational Raman scattering in any supported viewing geometry, (vii) new effective approximations for radiative transfer modeling in presence of clouds. The SCIATRAN model is freely available via the world wide web for non-commercial scientific applications.

Timing and nature of the deepening of the Tasmanian Gateway

Abstract: [1] Tectonic changes that produced a deep Tasmanian Gateway between Australia and Antarctica are widely invoked as the major mechanism for Antarctic cryosphere growth and Antarctic Circumpolar Current (ACC) development during the Eocene/Oligocene (E/O) transition (∼34–33 Ma). Ocean Drilling Program (ODP) Leg 189 recovered near-continuous marine sedimentary records across the E/O transition interval at four sites around Tasmania. These records are largely barren of calcareous microfossils but contain a rich record of siliceous- and organic-walled marine microfossils. In this study we integrate micropaleontological, sedimentological, geochemical, and paleomagnetic data from Site 1172 (East Tasman Plateau) to identify four distinct phases (A–D) in the E/O Tasmanian Gateway deepening that are correlative among ODP Leg 189 sites. Phase A, prior to ∼35.5 Ma: minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes. Phase B, ∼35.5–33.5 Ma: increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom-water currents. Phase C, ∼33.5–30.2 Ma: further deepening to bathyal depths, with episodic erosion by increasingly energetic bottom-water currents. Phase D, <30.2 Ma: establishment of stable, open-ocean, warm-temperate, oligotrophic settings characterized by siliceous-carbonate ooze deposition. Our combined evidence indicates that this early Oligocene Tasmanian Gateway deepening initially produced an eastward flow of relatively warm surface waters from the Australo-Antarctic Gulf into the southwestern Pacific Ocean. This “proto-Leeuwin” current fundamentally differs from previous regional reconstructions of eastward flowing cool water (e.g., a “proto-ACC”) during the early Oligocene and thereby represents an important new constraint for reconstructing regional- to global-scale dynamics for this major global change event.

Imatinib (STI571)-Mediated Changes in Glucose Metabolism in Human Leukemia BCR-ABL-Positive Cells

Abstract: The therapeutic efficacy of imatinib mesylate (Gleevec) is based on its specific inhibition of the BCR-ABL oncogene protein, a widely expressed tyrosine kinase in chronic myelogenous leukemia (CML) cells. The goal of this study was to evaluate glucose metabolism in BCR-ABL-positive cells that are sensitive to imatinib exposure. Two human BCR-ABL-positive cell lines (CML-T1 and K562) and one BCR-ABL-negative cell line (HC-1) were incubated with different imatinib concentrations for 96 hours. Magnetic resonance spectroscopy on cell acid extracts was performed to evaluate [1-13C]glucose metabolism, energy state, and changes in endogenous metabolites after incubation with imatinib. Imatinib induced a concentration-dependent inhibition of cell proliferation in CML-T1 (IC50, 0.69 +/- 0.06 micromol/L) and K562 cells (IC50, 0.47 +/- 0.04 micromol/L), but not in HC-1 cells. There were no metabolic changes in imatinib-treated HC-1 cells. In BCR-ABL-positive cells, the relevant therapeutic concentrations of imatinib (0.1-1.0 micromol/L) decreased glucose uptake from the media by suppressing glycolytic cell activity (C3-lactate at 0.25 mmol/L, 65% for K562 and 77% for CML-T1 versus control). Additionally, the activity of the mitochondrial Krebs cycle was increased (C4-glutamate at 0.25 micromol/L, 147% for K562 and 170% for CML-T1). The improvement in mitochondrial glucose metabolism resulted in an increased energy state (nucleoside triphosphate/nucleoside diphosphate at 0.25 micromol/L, 130% for K562 and 125% for CML-T1). Apoptosis was observed at higher concentrations. Unlike standard chemotherapeutics, imatinib, without cytocidal activity, reverses the Warburg effect in BCR-ABL-positive cells by switching from glycolysis to mitochondrial glucose metabolism, resulting in decreased glucose uptake and higher energy state.

Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry

Abstract: [1] Frost flowers grow on newly-formed sea ice from a saturated water vapour layer. They provide a large effective surface area and a reservoir of sea salt ions in the liquid phase with triple the ion concentration of sea water. Recently, frost flowers have been recognised as the dominant source of sea salt aerosol in the Antarctic, and it has been speculated that they could be involved in processes causing severe tropospheric ozone depletion events during the polar sunrise. These events can be explained by heterogeneous autocatalytic reactions taking place on salt-laden ice surfaces which exponentially increase the reactive gas phase bromine (‘‘bromine explosion’’). We analyzed tropospheric bromine monoxide (BrO) and the sea ice coverage both measured from satellite sensors. Our model based interpretation shows that young ice regions potentially covered with frost flowers seem to be the source of bromine found in bromine explosion events. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 1640 Global Change: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 3360 Meteorology and Atmospheric Dynamics: Remote sensing. Citation: Kaleschke, L., et al. (2004), Frost flowers on sea ice as a source of sea salt and their influence on tropospheric halogen chemistry, Geophys. Res. Lett., 31, L16114, doi:10.1029/ 2004GL020655.

MAX-DOAS measurements of atmospheric trace gases in Ny- ˚ Alesund - Radiative transfer studies and their application

Abstract: . A new approach to derive tropospheric concentrations of some atmospheric trace gases from ground-based UV/vis measurements is described. The instrument, referred to as the MAX-DOAS, is based on the well-known UV/vis instruments, which use the sunlight scattered in the zenith sky as the light source and the method of Differential Optical Absorption Spectroscopy (DOAS) to derive column amounts of absorbers like ozone and nitrogen dioxide. Substantial enhancements have been applied to this standard setup to use different lines of sight near to the horizon as additional light sources (MAX - multi axis). Results from measurements at Ny-Alesund (79° N, 12° E) are presented and interpreted with the full-spherical radiative transfer model SCIATRAN. In particular, measurements of the oxygen dimer O4 which has a known column and vertical distribution in the atmosphere are used to evaluate the sensitivity of the retrieval to parameters such as multiple scattering, solar azimuth, surface albedo and refraction in the atmosphere and also to validate the radiative transfer model. As a first application, measurements of NO2 emissions from a ship lying in Ny-Alesund harbour are presented. The results of this study demonstrate the feasibility of long term UV/vis multi axis measurement that can be used to derive not only column amounts of different trace gases but also some information on the vertical location of these absorbers.

Cadmium-induced apoptosis in C6 glioma cells: influence of oxidative stress.

Abstract: Cadmium has recently been shown to induce apoptosis in C6 glioma cells via disruption of the mitochondrial membrane potential and subsequent caspase 9-activation Here we show that both H2O2 and CdCl2 induced apoptotic DNA fragmentation in C6 cells The employment of glutathione as an antioxidant prevented the induction of apoptotic DNA fragmentation by cadmium completely and catalase strongly reduced cadmium-induced DNA fragmentation suggesting that cadmium exerts its apoptotic effects at least partly via the production of H2O2 Apoptosis may be induced by cadmium indirectly through formation of oxidative stress, eg, by inhibition of antioxidant enzymes After incubation of C6 cells with cadmium for short times (up to 4 h), we analyzed the formation of intracellular reactive oxygen species and cellular lipid peroxidation After 1 h of incubation with inreasing concentrations of CdCl2 (1-500 microM), no increase in dichlorofluorescein fluorescence was found At variance, lipid peroxidation was slightly elevated after 2 h incubation with cadmium (50-100 microM) Furthermore, we analyzed the modulation of markers for oxidative stress after prolonged (24 h) exposure to cadmium The intracellular glutathione content as measured using the fluorescent probe monobromobimane was decreased after incubation with CdCl2 (05-10 microM) for 24 h Furthermore, we measured the effect of cadmium on the level of oxidized DNA lesions (predominantly 8-hydroxyguanine) using the bacterial Fpg-DNA-repair protein After 24 h of incubation with 5 microM CdCl2 we found a sixfold increase in Fpg-sensitive DNA-lesions We conclude that short time incubations with cadmium (up to 4 h) caused only slight or insignificant effects on the generation of reactive oxygen species (formation of thiobarbituric acid reactive substances, fluorescence of dichlorofluorescein), whereas incubation with this heavy metal for 24 h lead to a decrease in intracellular glutathione concentration and an increase in oxidative DNA-lesions Our data demonstrate that cadmium as similar to H2O2 is a potent inducer of apoptosis in C6 cells Even if cadmium unlike Fenton-type metals can not produce reactive oxygen species directly, the apoptotic effects of cadmium at least in part are mediated via induction of oxidative stress Because both apoptosis and oxidative stress are thought to play important roles in neurodegenerative diseases, low concentrations of cadmium that initiate programmed cell death may lead to a selective cell death in distinct brain regions via generation of oxidative stress

Many-body theory of carrier capture and relaxation in semiconductor quantum-dot lasers

Abstract: In quantum-dot laser devices containing a quasi-two-dimensional wetting layer, a pump process initially populates the wetting-layer states. The scattering of carriers from these spatially-extended quasi-two-dimensional states into the quantum-dot states as well as the relaxation of carriers between the quantum-dot levels are studied theoretically. Based on the wave functions for the coupled quantum-dot/wetting-layer system interaction matrix elements are calculated for carrier-carrier Coulomb interaction and carrier-phonon interaction. Scattering rates for various capture and relaxation processes are evaluated under quasiequilibrium conditions. For elevated carrier densities in the wetting layer, Coulomb scattering provides processes with capture (relaxation) times typically faster than $10\phantom{\rule{0.3em}{0ex}}\mathrm{ps}\phantom{\rule{0.3em}{0ex}}(1\phantom{\rule{0.3em}{0ex}}\mathrm{ps})$. When energy conservation allows for interaction with LO phonons, comparable rates are obtained.

Interlaboratory comparison study of Mg/Ca and Sr/Ca measurements in planktonic foraminifera for paleoceanographic research

Abstract: Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2–3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1–2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

Perceptual learning: a case for early selection.

Abstract: Perceptual learning is any relatively permanent change of perception as a result of experience. Visual learning leads to sometimes dramatic and quite fast improvements of performance in perceptual tasks, such as hyperacuity discriminations. The improvement often is very specific for the exact task trained, for the precise stimulus orientation, the stimulus position in the visual field, and the eye used during training. This specificity indicates location of the underlying changes in the nervous system at least partly on the level of the primary visual cortex. The dependence of learning on error feedback and on attention, on the other hand, proves the importance of top-down influences from higher cortical centers. In summary, perceptual learning seems to rely at least partly on changes on a relatively early level of cortical information processing (early selection), such as the primary visual cortex under the influence of top-down influences (selection and shaping). An alternative explanation based on late selection is discussed.

Toxicity of a mixture of dissimilarly acting substances to natural algal communities: predictive power and limitations of independent action and concentration addition.

Abstract: Predictive studies of chemical mixtures are typically based on experiments with single species. To study the applicability of the concepts of independent action (IA) and concentration addition (CA) on a multispecies level, the carbon fixation of natural algal communities under toxicant exposure was studied. The presented study focused on a mixture of six dissimilarly acting substances. Conceptual reasoning as well as empirical evidence from single-species tests suggest that IA is more appropriate for this type of mixture. Nonetheless, the potential of CA was also investigated, to assess whether this concept may be applicable as a reasonable worst case prediction of mixture toxicities also on a community level. IA predicted the experimental EC50 precisely. CA underestimated the EC50 by a factor of only 1.4, although the shape of the predicted concentration−response curve was clearly different from experimental data. Hence, it can be concluded that the applicability of the concepts is not restricted to the ...