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Showing papers by "Leibniz Association published in 2004"


Journal ArticleDOI
TL;DR: In this paper, the maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100-80 ka),(3) the Middle Weichsellian (60-50 ka), and (4) the late Weichselsian (25-15 ka) based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic and sediment core data.

1,426 citations


Journal ArticleDOI
TL;DR: In this article, the authors apply a new conditional fixed-effect ordinal estimator to their measure of life satisfaction using data from the German Socio-economic Panel (GSOEP).
Abstract: One of the most prominent political and economic events of recent decades was the falling of the Berlin Wall on November 9, 1989, which was quickly followed by the reunification of the formerly separate entities of East and West Germany. It is well acknowledged that the falling of the wall was widely unanticipated in Germany (Stefan Bach and Harold Trabold, 2000), and thus it provides some useful exogenous variation with which we can more firmly establish causality in empirical analyses. In this paper, we aim to contribute to the growing economics literature on the determinants of life satisfaction (or happiness) by investigating how life satisfaction in East Germany changed over the decade following reunification. We are particularly interested in identifying the contribution that the substantial increase in real household income in East Germany in the post-reunification years (i.e., around 60 percent between 1990 and 2001) made to reported levels of life satisfaction. In order to achieve this aim, we apply a new conditional fixed-effect ordinal estimator to our measure of life satisfaction using data from the German Socio-Economic Panel (GSOEP). The estimates from this new model are then decomposed, using a new causal technique, in order to identify the factors that drove average changes in life satisfaction in East Germany following reunification. Our methodology exploits the fact that the GSOEP is an evolving panel, allowing us to make a distinction among changes in variables affecting everyone, changes in the aggregate unobserved fixed individual characteristics of the panel due to new entrants (who are also mostly younger cohorts), and panel attrition. In Section I, we briefly review the literature and describe our data. In Section II, we present the fixed-effect methodology and the causal decomposition approach that we adopt. Section III presents the results. Finally, Section IV concludes.

642 citations


Journal ArticleDOI
TL;DR: It is shown that nestin is abundant in ES-derived progenitor cells that have the potential to develop into neuroectodermal, endodermal and mesodermal lineages and suggested that its presence in cells may indicate multi-potentiality and regenerative potential.
Abstract: Tissue-specific progenitor cells are characterized by proliferation and differentiation, but, in contrast to embryonic stem (ES) cells, have limited capacities for self-renewal and no tumourigenic potential. These latter traits make progenitor cells an ideal source for regenerative cell therapies. In this review, we describe what is currently known about nestin, an intermediate filament first identified in neuroepithelial stem cells. During embryogenesis, nestin is expressed in migrating and proliferating cells, whereas in adult tissues, nestin is mainly restricted to areas of regeneration. We show that nestin is abundant in ES-derived progenitor cells that have the potential to develop into neuroectodermal, endodermal and mesodermal lineages. Although it remains unclear what factors regulate in vitro and in vivo expression of nestin, we conclude that nestin represents a characteristic marker of multi-lineage progenitor cells and suggest that its presence in cells may indicate multi-potentiality and regenerative potential.

637 citations


Journal ArticleDOI
01 Dec 2004-Polymer
TL;DR: In this paper, a series of composites of polycarbonate (PC) with 23 different contents of multiwalled carbon nanotubes (MWNT) was produced by melt mixing using the masterbatch dilution method.

634 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed a variety of factors that might enhance firms' propensity to implement cleaner products and production technologies instead of end-of-pipe technologies and found that regulatory measures and the stringency of environmental policies are positively correlated with clean production, while cost savings, general management systems, and specific environmental management tools tend to favor clean production.
Abstract: While both fundamental types of abatement measures mitigate the adverse environmental impacts of production, cleaner production technologies are frequently more advantageous than end-of-pipe technologies for environmental and economic reasons. This paper analyzes a variety of factors that might enhance firms' propensity to implement cleaner products and production technologies instead of end-of-pipe technologies. On the basis of a unique facility-level data set derived from a recent OECD survey, we find a clear dominance of cleaner production in seven OECD countries: Surprisingly, 76.8% of the facilities report that they invest predominantly in cleaner production technologies. With regard to environmental product innovations, the large majority of facilities reports that the measures they have undertaken to reduce environmental impacts were geared at production processes and not so much at products. Our estimation results are based on multinomial logit models which indicate that regulatory measures and the stringency of environmental policies are positively correlated with end-of-pipe technologies, while cost savings, general management systems, and specific environmental management tools tend to favor clean production. We conclude that improvements towards cleaner products and production may be reached by the continuous development and wider diffusion of these management tools. Improvements may also be stimulated by widening the cost gap between the two types of technologies, for instance, by additionally charging for waste and energy use.

612 citations


Journal ArticleDOI
01 Jan 2004-Carbon
TL;DR: In this paper, a volume production of a single carbon nanofiber type which can be used in a wide range of systems beyond, but not restricted to polymer composites is discussed.

490 citations


Journal ArticleDOI
TL;DR: In this article, a consistent explanation for the generation of these radar echoes has been developed based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region.
Abstract: . Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is effectively determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition for monostatic radars; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the neutral gas turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e., 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like neutral temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.

407 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that significant systematic biases exist in the reporting of fund performance, and that these biases depend on the degree of accounting conservatism and the strength of the legal environment in a country, and on proxies for the degreeof information asymmetry between institutional investors and private equity fund managers.
Abstract: To obtain more funds from the institutional investors, private equity fund managers may report inflated valuations of private investee companies that are not yet sold. However, such overvaluations may result in a reputational cost when those investments are realized. Using evidence from 39 countries, we show that significant systematic biases exist in the reporting of fund performance, and that these biases depend on the degree of accounting conservatism and the strength of the legal environment in a country, and on proxies for the degree of information asymmetry between institutional investors and private equity fund managers.

398 citations


Journal ArticleDOI
TL;DR: This work shows that the chromodomain of CMT3 can directly interact with the N‐terminal tail of histone H3, but only when it is simultaneously methylated at both the H3K9 and H3k27 positions, and suggests a model in which H 3K9 methylation by KYP, and H2K27 methylationby an unknown enzyme provide a combinatorial histone code for the recruitment of C MT3 to silent loci.
Abstract: Both DNA methylation and post-translational histone modifications contribute to gene silencing, but the mechanistic relationship between these epigenetic marks is unclear. Mutations in two Arabidopsis genes, the KRYPTONITE (KYP) histone H3 lysine 9 (H3K9) methyltransferase and the CHROMOMETHYLASE3 (CMT3) DNA methyltransferase, cause a reduction of CNG DNA methylation, suggesting that H3K9 methylation controls CNG DNA methylation. Here we show that the chromodomain of CMT3 can directly interact with the N-terminal tail of histone H3, but only when it is simultaneously methylated at both the H3K9 and H3K27 positions. Furthermore, using chromatin immunoprecipitation analysis and immunohistolocalization experiments, we found that H3K27 methylation colocalizes with H3K9 methylation at CMT3-controlled loci. The H3K27 methylation present at heterochromatin was not affected by mutations in KYP or in several Arabidopsis PcG related genes including the Enhancer of Zeste homologs, suggesting that a novel pathway controls heterochromatic H3K27 methylation. Our results suggest a model in which H3K9 methylation by KYP, and H3K27 methylation by an unknown enzyme provide a combinatorial histone code for the recruitment of CMT3 to silent loci.

372 citations


Journal ArticleDOI
TL;DR: The FRU gene is a mediator in induction of iron mobilization responses in Arabidopsis, indicating that regulation of iron uptake is conserved in dicot species.

338 citations


Journal ArticleDOI
TL;DR: An overview is given on proteome studies performed to analyze whole plants or specific tissues with particular emphasis on important physiological processes such as germination and the use of proteome approaches to investigate the interaction of plants with pathogens or with symbiotic organisms.
Abstract: Proteome analysis is becoming a powerful tool in the functional characterization of plants. Due to the availability of vast nucleotide sequence information and based on the progress achieved in sensitive and rapid protein identification by mass spectrometry, proteome approaches open up new perspectives to analyze the complex functions of model plants and crop species at different levels. In this review, an overview is given on proteome studies performed to analyze whole plants or specific tissues with particular emphasis on important physiological processes such as germination. The chapter on subcellular proteome analysis of plants focuses on the progress achieved for plastids and mitochondria but also mentions the difficulties associated with membrane-bound proteins of these organelles. Separate chapters are dedicated to the challenging analysis of woody plants and to the use of proteome approaches to investigate the interaction of plants with pathogens or with symbiotic organisms. Limitations of current techniques and recent conceptual and technological perspectives for plant proteomics are briefly discussed in the final chapter.

Journal ArticleDOI
TL;DR: In drd1 mutants, RNA-induced non-CpG methylation is almost eliminated at a target promoter, resulting in reactivation, whereas methylation of centromeric and rDNA repeats is unaffected, so DRD1 is not a global regulator of cytosine methylation.

Journal ArticleDOI
TL;DR: A few species of arthropoda can de novo synthesize cyanogenic glucosides and some of these species are able to sequester them from their host plant (Zygaenidae).

Journal ArticleDOI
01 Jan 2004-Carbon
TL;DR: In this article, composites of polycarbonate (PC) having different amounts of multiwalled carbon nanotubes (MWNT) were prepared by diluting a masterbatch of PC with 15 wt% MWNT using melt mixing in a DACA-Micro Compounder.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed deep-sea cores from the central Arctic Ocean, the Fram Strait, and the Yermak Plateau to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200,000 years.

Journal ArticleDOI
TL;DR: In this paper, the state of dispersion of MWNTs in polycarbonate (PC) matrix was investigated using TEM and AFM micrographs, and it was found that the nanotubes dispersed uniformly through the matrix showing no significant agglomeration in the compositions studied.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the vanadia particles exhibit very similar morphology on both supports but differ in the extent of particle-support interactions, which strongly affect the CO adsorption behavior of the particles.

Journal ArticleDOI
TL;DR: Results emphasise the promising non-toxic antifouling properties of microtextured surfaces and highlight the role of surface microtopography in marine defence systems.
Abstract: Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (<500 mum) of different marine organisms, such as Cancer pagurus , Mytilus edulis , Ophiura texturata and the eggcase of Scyliorhinus canicula , has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising non-toxic antifouling properties of microtextured surfaces

Posted Content
TL;DR: In this article, the authors analyze the impact of cross-country differences in legality, including legal origin and accounting standards, on the governance structure of investments in the VC industry: better laws facilitate faster deal screening and deal origination, a higher probability of syndication and a lower probability of potentially harmful co-investment, and facilitate investor board representation of the investor.
Abstract: We analyze governance with a new dataset on investments of venture capitalists in 3848 portfolio firms in 39 countries from North and South America, Europe and Asia spanning 1971-2003. We provide evidence that cross-country differences in legality, including legal origin and accounting standards, have a significant impact on the governance structure of investments in the VC industry: better laws facilitate faster deal screening and deal origination, a higher probability of syndication and a lower probability of potentially harmful co-investment, and facilitate investor board representation of the investor and the use of securities that do not require periodic cash flows prior to exit. We also show country-specific differences exist apart from legal and economic development.

Journal ArticleDOI
TL;DR: In this paper, the authors used a recursive bivariate probit model that explicitly takes into account that a facility's decision on innovation activities is correlated with the decision on environmental management systems certification.
Abstract: It is frequently hypothesized that environmental management systems (EMSs) may improve a firm's environmental performance. Whether or not this hypothesis is true is as important from the perspective of environmental policy as questions relating to the relevant incentives for (1) a firm's voluntary adoption of an EMS and (2) its environmental innovation behavior. Based on ample empirical evidence for German manufacturing, this paper addresses these issues on the basis of a recursive bivariate probit model that explicitly takes into account that a facility's decision on innovation activities is correlated with the decision on EMS certification. Our empirical results indicate that environmental innovation activities are not associated with EMS certification nor any other single policy instrument. Rather, innovation behavior seems to be correlated to the stringency of environmental policy.

Journal ArticleDOI
TL;DR: Chemical analysis showed a time-dependent decline of BPA during semistatic exposure, indicating that BPA is taken up and metabolized to some extent by tadpoles, and clear evidence that B PA induces feminization in X. laevis tadpole is shown, revealing an estrogenic potency of B PA that influences sexual development in amphibians.

Journal ArticleDOI
TL;DR: Property of broccoli and cauliflower which, when optimised to the tastes of the consumer, could boost their acceptability are identified.
Abstract: The objective of this study was to investigate the influence that the species, form or cultivar exerts on the glucosinolate spectrum for glucosinolates and free sugars in selected vegetable species of the Brassica genus (Brassica oleracea var. italica Plenck, Brassica rapa var. alboglabra and Brassica oleracea var. botrytis L.). The results showed significant differences amongst the cultivar groups for the glucosinolate proportions as well as the contents of health-promoting and flavour-influencing alkyl, alkenyl and indole glucosinolates. The clear differences in the proportions of glucosinolates amongst the groups were not significantly influenced by the weather, although the absolute glucosinolate contents were. Interestingly, the species, forms and cultivars diverged in their external and internal sensory attributes, for example, colour, taste properties such as bitter and sweet, flavour such as green/ grassy, spicy, broccoli-like, cabbage-like, cauliflower-like, kohlrabi-like, leek-like and mouth-feel pungent. Differences in the sensory attributes led to different consumer acceptability based on first impressions judged on colour, flavour and overall liking. Consumers were seen to prefer cultivars with a bright colour, a lower level of bitter tasting glucosinolates (alkenyl and indole glucosinolates) and a higher sucrose content. Significant correlations were determined between the compound concentrations, the descriptively determined sensory properties and the consumer scores. Here, we identified properties of broccoli and cauliflower which, when optimised to the tastes of the consumer, could boost their acceptability.

Journal ArticleDOI
TL;DR: A profiling approach that combines separation by capillary liquid chromatography with the high resolution, high sensitivity, and high mass accuracy of quadrupole time-of-flight mass spectrometry has the potential to significantly contribute to establishing the metabolome of Arabidopsis and other model systems.
Abstract: Large-scale metabolic profiling is expected to develop into an integral part of functional genomics and systems biology. The metabolome of a cell or an organism is chemically highly complex. Therefore, comprehensive biochemical phenotyping requires a multitude of analytical techniques. Here, we describe a profiling approach that combines separation by capillary liquid chromatography with the high resolution, high sensitivity, and high mass accuracy of quadrupole time-of-flight mass spectrometry. About 2,000 different mass signals can be detected in extracts of Arabidopsis roots and leaves. Many of these originate from Arabidopsis secondary metabolites. Detection based on retention times and exact masses is robust and reproducible. The dynamic range is sufficient for the quantification of metabolites. Assessment of the reproducibility of the analysis showed that biological variability exceeds technical variability. Tools were optimized or established for the automatic data deconvolution and data processing. Subtle differences between samples can be detected as tested with the chalcone synthase deficient tt4 mutant. The accuracy of time-of-flight mass analysis allows to calculate elemental compositions and to tentatively identify metabolites. In-source fragmentation and tandem mass spectrometry can be used to gain structural information. This approach has the potential to significantly contribute to establishing the metabolome of Arabidopsis and other model systems. The principles of separation and mass analysis of this technique, together with its sensitivity and resolving power, greatly expand the range of metabolic profiling.

Journal ArticleDOI
TL;DR: Analysis of the resulting double mutants revealed that in contrast to the JA-induced suppression of H(2)O(2)/superoxide-dependent cell death reported earlier, JA promotes singlet oxygen-mediated cell death in flu, whereas other oxylipins such as OPDA and dnOPDA antagonize this death-inducing activity of JA.
Abstract: Upon a dark/light shift the conditional flu mutant of Arabidopsis starts to generate singlet oxygen ((1)O(2)), a non-radical reactive oxygen species that is restricted to the plastid compartment. Immediately after the shift, plants stop growing and develop necrotic lesions. We have established a protoplast system, which allows detection and characterization of the death response in flu induced by the release of (1)O(2). Vitamin B6 that quenches (1)O(2) in fungi was able to protect flu protoplasts from cell death. Blocking ethylene production was sufficient to partially inhibit the death reaction. Similarly, flu mutant seedlings expressing transgenic NahG were partially protected from the death provoked by the release of (1)O(2), indicating a requirement for salicylic acid (SA) in this process, whereas in cells depleted of both, ethylene and SA, the extent of cell death was reduced to the wild-type level. The flu mutant was also crossed with the jasmonic acid (JA)-depleted mutant opr3, and with the JA, OPDA and dinor OPDA (dnOPDA)-depleted dde2-2 mutant. Analysis of the resulting double mutants revealed that in contrast to the JA-induced suppression of H(2)O(2)/superoxide-dependent cell death reported earlier, JA promotes singlet oxygen-mediated cell death in flu, whereas other oxylipins such as OPDA and dnOPDA antagonize this death-inducing activity of JA.

Journal ArticleDOI
TL;DR: In this article, the authors used ozone (O 3) to generate reactive oxygen species (ROS) in plants, which trigger the activation of signaling cascades such as the mitogen-activated protein kinase (MAPK) cascade and accumulation of plant hormones, jasmonic acid, salicylic acid (SA), and ethylene (ET).
Abstract: *† Summary Changing environmental conditions, atmospheric pollutants and resistance reactions to pathogens cause production of reactive oxygen species (ROS) in plants. ROS in turn trigger the activation of signaling cascades such as the mitogen-activated protein kinase (MAPK) cascade and accumulation of plant hormones, jasmonic acid, salicylic acid (SA), and ethylene (ET). We have used ozone (O 3) to generate ROS in the apoplast of wildtype Col-0 and hormonal signaling mutants of Arabidopsis thaliana and show that this treatment caused a transient activation of 43 and 45 kDa MAPKs. These were identified as AtMPK3 and AtMPK6. We also demonstrate that initial AtMPK3 and AtMPK6 activation in response to O 3 was not dependent on ET signaling, but that ET is likely to have secondary effects on AtMPK3 and AtMPK6 function, whereas functional SA signaling was needed for full-level AtMPK3 activation by O 3. In addition, we show that AtMPK3, but not AtMPK6, responded to O 3 transcriptionally and translationally during O3 exposure. Finally, we show in planta that activated AtMPK3 and AtMPK6 are translocated to the nucleus during the early stages of O 3 treatment. The use of O3 to induce apoplastic ROS formation offers a non-invasive in planta system amenable to reverse genetics that can be used for the study of stress-responsive MAPK signaling in plants.

Journal ArticleDOI
TL;DR: Since A. fusiformis mass developments are characteristic of alkaline-saline lakes, health risks to wildlife, especial the Arthrospira-consuming Lesser Flamingo, may be expected.
Abstract: For decades frequent mass mortalities of Lesser Flamingos (Phoeniconaias minor Geoffroy) have been observed at alkaline-saline Kenyan Rift Valley lakes. To estimate the potential influence of toxic cyanobacteria on these mass deaths, the phytoplankton communities were investigated in Lakes Bogoria, Nakuru and Elmenteita. Cyanobacterial toxins were analyzed both in the phytoplankton from the three lakes and in isolated monocyanobacterial strains of Arthrospira fussiformis, Anabaenopsis abjjatae, Spirulina subsalsa and Phormidium terebriformis. Lake Bogoria was dominated by the cyanobacterium A. fusiformis. In L. Nakuru and L. Elmenteita the phytoplankton mainly consisted of A. fusiformis, A. abjatae and Anabaenopsis arnoldii, and in L. Nakuru an unknown Anabaena sp. was also found. Furthermore, this is the first time A. abijatae and the unknown Anabaena sp. have been found in Kenyan lakes. Phytoplankton wet weight biomass was found to be high, reaching 777 mg L -1 in L. Bogoria, 104 mg L -1 in L. Nakuru and 202 mg L -1 in L. Elmenteita. Using HPLC, the cyanobacterial hepatotoxins microgstin-LR, -RR -γR, -LF and -LA and the neurotoxin anatoxin-a were detected in phytoplankton samples from L. Bogoria and L. Nakuru. Total microcystin concentrations amounted to 155 μg microcystin-LR equivalents g -1 DW in L. Bogoria, and 4593 μg microcystin-LR equivalents g -1 DW in L. Nakuru, with anatoxin-a concentrations at 9 μg g -1 DW in L. Bogoria and 223 μg g -1 DW in L. Nakuru. In L. Elmenteita phytoplankton, no cyanobacterial toxins were found. A. fusiformis was identified as one source of the toxins. The isolated strain of A. fusiformis from L. Bogoria was found to produce both microcystin-YR (15.0 μg g -1 DW) and anatoxin-a (10.4 μg g -1 DW), whilst the A. fusiformis strain from L. Nakuru was found to produce anatoxin-a (0.14 μg g -1 DW). Since A. fusiformis mass developments are characteristic of alkaline-saline lakes, health risks to wildlife, especial the Arthrospira-consuming Lesser Flamingo, may be expected.

Journal ArticleDOI
TL;DR: The Ifaty coral oxygen isotope record was used to investigate the natural variability of the western Indian Ocean subtropical SST dipole and ENSO as mentioned in this paper, and showed evidence that these variations are caused by changes in the regional hydrologic balance.

Journal ArticleDOI
TL;DR: In this article, polyphosphate (poly-P) was detected with the use of 31 P nuclear magnetic resonance (NMR) spectroscopy in sediments from a large variety of lakes with different trophic state and morphometry.
Abstract: Polyphosphate (poly-P) was detected with the use of 31 P nuclear magnetic resonance (NMR) spectroscopy in sediments from a large variety of lakes with different trophic state and morphometry. In the top 0.5 cm of sediment, poly-P was 1.5 to 11.4% of total P. Nonreactive phosphorus (NRP) in the NaOH fraction (often classified as organically bound phosphate) was up to 46% inorganic poly-P. In some surface sediments, the poly-P content equalled the iron-fixed phosphorus determined by chemical phosphorus fractionation. Sediments were probably supplied with poly-P by sedimentation because there were substantial amounts of poly-P in plankton and settling seston. As demonstrated with sediments of Lake Petersdorf, benthic organisms can also contribute to the formation of poly-P (up to 0.11 mg P [g dry weight] 21 ) under favorable aerobic conditions. Poly-P is more rapidly transformed into single orthophosphate during diagenesis than other inorganic and organic P species. The transformation of organic P compounds and poly-P can contribute significantly to the release of P during diagenesis and should be considered along with the reductive dissolution of P sorbed to iron oxihydroxides.

Journal ArticleDOI
TL;DR: The results suggest that cyclization of small peptides of an appropriate amino acid composition may serve as a promising strategy in the design of antimicrobial peptides.
Abstract: Arginine- and tryptophan-rich motifs have been identified in antimicrobial peptides with various secondary structures. We synthesized a set of linear hexapeptides derived from the sequence AcRRWWRF-NH(2) by substitution of tryptophan (W) by tyrosine (Y) or naphthylalanine (Nal) and by replacement of arginine (R) by lysine (K) to investigate the role of cationic charge and aromatic residues in membrane activity and selectivity. A second set of corresponding head-to-tail cyclic analogues was prepared to analyze the role of conformational constraints. The biological activity of the linear peptides followed the order Nal- >> W- > Y-containing compounds and slightly decreased upon R-K substitution. A pronounced activity-improving and bacterial selectivity-enhancing effect was found upon cyclization of the R- and W-bearing parent peptide, whereas the activity-modifying effect of cyclization of Y- and Nal-containing peptides was low. The analysis of the driving forces of peptide interaction with model membranes showed that the activities correlated with the partition coefficients and the depths of peptide insertion into neutral and negatively charged lipid bilayers. Spectroscopic studies, RP-HPLC, and titration calorimetry implied that the combination of cationic and aromatic amino acid composition and conformational rigidity afforded a membrane-active, amphipathic structure with a highly charged face opposed by a cluster of aromatic side chains. However, threshold values of low and high hydrophobicity seemed to exist beyond which the activity-enhancing effect of cyclization was negligible. The results suggest that cyclization of small peptides of an appropriate amino acid composition may serve as a promising strategy in the design of antimicrobial peptides.

Journal ArticleDOI
TL;DR: Using the extended tight-binding model that allows bond lengths and angles to vary, the optical transition energies in single-wall carbon nanotubes are calculated as a function of inverse tube diameter as discussed by the authors.
Abstract: Using the extended tight-binding model that allows bond lengths and angles to vary, the optical transition energies Eii in single-wall carbon nanotubes are calculated as a function of inverse tube diameter. After geometrical structure optimization, the 2n+m=constant family behavior observed in photoluminescence (PL) experiments is obtained, and detailed agreement between the calculations and PL experiments is achieved after including many-body corrections.