Extern
Refine
Has Fulltext
- yes (1029) (remove)
Year of publication
- 2024 (28)
- 2023 (123)
- 2022 (33)
- 2021 (20)
- 2020 (26)
- 2019 (2)
- 2018 (1)
- 2017 (23)
- 2016 (1)
- 2014 (16)
- 2013 (72)
- 2012 (27)
- 2011 (18)
- 2010 (17)
- 2009 (6)
- 2008 (47)
- 2007 (79)
- 2006 (85)
- 2005 (45)
- 2004 (40)
- 2003 (37)
- 2002 (34)
- 2001 (46)
- 2000 (76)
- 1999 (28)
- 1998 (29)
- 1997 (25)
- 1996 (6)
- 1995 (8)
- 1994 (13)
- 1993 (2)
- 1992 (2)
- 1990 (1)
- 1989 (1)
- 1988 (1)
- 1987 (2)
- 1986 (2)
- 1984 (3)
- 1983 (2)
- 1982 (1)
- 1958 (1)
Document Type
- Article (512)
- Postprint (185)
- Review (140)
- Conference Proceeding (128)
- Monograph/Edited Volume (18)
- Part of a Book (15)
- Part of Periodical (15)
- Working Paper (8)
- Doctoral Thesis (4)
- Other (3)
Is part of the Bibliography
- no (1029) (remove)
Keywords
- Philosophie (17)
- philosophy (17)
- Lehrkräftebildung (11)
- Reflexion (8)
- Reflexionskompetenz (8)
- United States (8)
- Germany (7)
- USA (7)
- Anthropologie (6)
- Low German (6)
Institute
- Extern (1029) (remove)
This paper outlines a newly-developed method to include the effects of time variability in the radiative transfer code CMFGEN. It is shown that the flow timescale is often large compared to the variability timescale of LBVs. Thus, time-dependent effects significantly change the velocity law and density structure of the wind, affecting the derivation of the mass-loss rate, volume filling factor, wind terminal velocity, and luminosity. The results of this work are directly applicable to all active LBVs in the Galaxy and in the LMC, such as AG Car, HR Car, S Dor and R 127, and could result in a revision of stellar and wind parameters. The massloss rate evolution of AG Car during the last 20 years is presented, highlighting the need for time-dependent models to correctly interpret the evolution of LBVs.
We discuss the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is $\sim 1/5 Z_\odot$. We were able to detect and follow numerous small-scale wind-embedded inhomogeneities in all observed stars. The general properties of the moving features, such as their velocity dispersions, emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.
The influence of the wind to the total continuum of OB supergiants is discussed. For wind velocity distributions with β > 1.0, the wind can have strong influence to the total continuum emission, even at optical wavelengths. Comparing the continuum emission of clumped and unclumped winds, especially for stars with high β values, delivers flux differences of up to 30% with maximum in the near-IR. Continuum observations at these wavelengths are therefore an ideal tool to discriminate between clumped and unclumped winds of OB supergiants.
Massive stars usually form groups such as OB associations. Their fast stellar winds sweep up collectively the surrounding insterstellar medium (ISM) to generate superbubbles. Observations suggest that superbubble evolution on the surrounding ISM can be very irregular. Numerical simulations considering these conditions could help to understand the evolution of these superbubbles and to clarify the dynamics of these objects as well as the difference between observed X-ray luminosities and the predicted ones by the standard model (Weaver et al. 1977).
We present the latest results on the observational dependence of the mass-loss rate in stellar winds of O and early-B stars on the metal content of their atmospheres, and compare these with predictions. Absolute empirical rates for the mass loss of stars brighter than 10$^{5.2} L_{\odot}$, based on H$\alpha$ and ultraviolet (UV) wind lines, are found to be about a factor of two higher than predictions. If this difference is attributed to inhomogeneities in the wind this would imply that luminous O and early-B stars have clumping factors in their H$\alpha$ and UV line forming regime of about a factor of 3--5. The investigated stars cover a metallicity range $Z$ from 0.2 to 1 $Z_{\odot}$. We find a hint towards smaller clumping factors for lower $Z$. The derived clumping factors, however, presuppose that clumping does not impact the predictions of the mass-loss rate. We discuss this assumption and explain how we intend to investigate its validity in more detail.
We report on new mass-loss rate estimates for O stars in six massive binaries using the amplitude of orbital-phase dependent, linear-polarimetric variability caused by electron scattering off free electrons in the winds. Our estimated mass-loss rates for luminous O stars are independent of clumping. They suggest similar clumping corrections as for WR stars and do not support the recently proposed reduction in mass-loss rates of O stars by one or two orders of magnitude.
Clumping in O-star winds
(2007)
We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with Hα data. We have achieved an excellent match of the P V λλ1118, 1128 resonance doublet and N IV λ1718, as well as He II λ4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.
I discuss observational evidence – independent of the direct spectral diagnostics of stellar winds themselves – suggesting that mass-loss rates for O stars need to be revised downward by roughly a factor of three or more, in line with recent observed mass-loss rates for clumped winds. These independent constraints include the large observed mass-loss rates in LBV eruptions, the large masses of evolved massive stars like LBVs and WNH stars, WR stars in lower metallicity environments, observed rotation rates of massive stars at different metallicity, supernovae that seem to defy expectations of high mass-loss rates in stellar evolution, and other clues. I pay particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too soon, and therefore making higher rates appear highly implausible. Some of these arguments by themselves may have more than one interpretation, but together they paint a consistent picture that steady line-driven winds of O-type stars have lower mass-loss rates and are significantly clumped.
The P v λλ1118, 1128 resonance doublet is an extraordinarily useful diagnostic of O-star winds, because it bypasses the traditional problems associated with determining mass-loss rates from UV resonance lines. We discuss critically the assumptions and uncertainties involved with using P v to diagnose mass-loss rates, and conclude that the large discrepancies between massloss rates determined from P v and the rates determined from “density squared” emission processes pose a significant challenge to the “standard model” of hot-star winds. The disparate measurements can be reconciled if the winds of O-type stars are strongly clumped on small spatial scales, which in turn implies that mass-loss rates based on Hα or radio emission are too large by up to an order of magnitude.
Significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the hypothesis that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells which are deficient in polyunsaturated fatty acids (PUFAs), and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50% reduction of the postmetamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha lead to irreversible effects for postmetamorphic animals, and is related to inferior competitive abilities.
In the old days (pre ∼1990) hot stellar winds were assumed to be smooth, which made life fairly easy and bothered no one. Then after suspicious behaviour had been revealed, e.g. stochastic temporal variability in broadband polarimetry of single hot stars, it took the emerging CCD technology developed in the preceding decades (∼1970-80’s) to reveal that these winds were far from smooth. It was mainly high-S/N, time-dependent spectroscopy of strong optical recombination emission lines in WR, and also a few OB and other stars with strong hot winds, that indicated all hot stellar winds likely to be pervaded by thousands of multiscale (compressible supersonic turbulent?) structures, whose driver is probably some kind of radiative instability. Quantitative estimates of clumping-independent mass-loss rates came from various fronts, mainly dependent directly on density (e.g. electron-scattering wings of emission lines, UV spectroscopy of weak resonance lines, and binary-star properties including orbital-period changes, electron-scattering, and X-ray fluxes from colliding winds) rather than the more common, easier-to-obtain but clumping-dependent density-squared diagnostics (e.g. free-free emission in the IR/radio and recombination lines, of which the favourite has always been Hα). Many big questions still remain, such as: What do the clumps really look like? Do clumping properties change as one recedes from the mother star? Is clumping universal? Does the relative clumping correction depend on $\dot{M}$ itself?
Mass loss is a very important aspect of the life of massive stars. After briefly reviewing its importance, we discuss the impact of the recently proposed downward revision of mass loss rates due to clumping (difficulty to form Wolf-Rayet stars and production of critically rotating stars). Although a small reduction might be allowed, large reduction factors around ten are disfavoured. We then discuss the possibility of significant mass loss at very low metallicity due to stars reaching break-up velocities and especially due to the metal enrichment of the surface of the star via rotational and convective mixing. This significant mass loss may help the first very massive stars avoid the fate of pair-creation supernova, the chemical signature of which is not observed in extremely metal poor stars. The chemical composition of the very low metallicity winds is very similar to that of the most metal poor star known to date, HE1327-2326 and offer an interesting explanation for the origin of the metals in this star. We also discuss the importance of mass loss in the context of long and soft gamma-ray bursts and pair-creation supernovae. Finally, we would like to stress that mass loss in cooler parts of the HR-diagram (luminous blue variable and yellow and red supergiant stages) are much more uncertain than in the hot part. More work needs to be done in these areas to better constrain the evolution of the most massive stars.
The factors that determine the efficiency of energy transfer in aquatic food webs have been investigated for many decades. The plant-animal interface is the most variable and least predictable of all levels in the food web. In order to study determinants of food quality in a large lake and to test the recently proposed central importance of the long-chained eicosapentaenoic acid (EPA) at the pelagic producer-grazer interface, we tested the importance of polyunsaturated fatty acids (PUFAs) at the pelagic producerconsumer interface by correlating sestonic food parameters with somatic growth rates of a clone of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments spanning one season with Daphnia feeding on natural seston from Lake Constance, a large pre-alpine lake. Somatic growth rates were fitted to sestonic parameters by using a saturation function. A moderate amount of variation was explained when the model included the elemental parameters carbon (r2 = 0.6) and nitrogen (r2 = 0.71). A tighter fit was obtained when sestonic phosphorus was incorporated (r2 = 0.86). The nonlinear regression with EPA was relatively weak (r2 = 0.77), whereas the highest degree of variance was explained by three C18-PUFAs. The best (r2 = 0.95), and only significant, correlation of Daphnia's growth was found with the C18-PUFA α-linolenic acid (α-LA; C18:3n-3). This correlation was weakest in late August when C:P values increased to 300, suggesting that mineral and PUFA-limitation of Daphnia's growth changed seasonally. Sestonic phosphorus and some PUFAs showed not only tight correlations with growth, but also with sestonic α-LA content. We computed Monte Carlo simulations to test whether the observed effects of α-LA on growth could be accounted for by EPA, phosphorus, or one of the two C18-PUFAs, stearidonic acid (C18:4n-3) and linoleic acid (C18:2n-6). With >99 % probability, the correlation of growth with α-LA could not be explained by any of these parameters. In order to test for EPA limitation of Daphnia's growth, in parallel with experiments on pure seston, growth was determined on seston supplemented with chemostat-grown, P-limited Stephanodiscus hantzschii, which is rich in EPA. Although supplementation increased the EPA content 80-800x, no significant changes in the nonlinear regression of the growth rates with α-LA were found, indicating that growth of Daphnia on pure seston was not EPA limited. This indicates that the two fatty acids, EPA and α-LA, were not mutually substitutable biochemical resources and points to different physiological functions of these two PUFAs. These results support the PUFA-limitation hypothesis for sestonic C:P < 300 but are contrary to the hypothesis of a general importance of EPA, since no evidence for EPA limitation was found. It is suggested that the resource ratios of EPA and α-LA rather than the absolute concentrations determine which of the two resources is limiting growth.
4-Phenylphenoxazinones were isolated after biomimetic oxidation, using diphenoloxidases of insect cuticle, mushroom tyrosinase, or after autoxidation of N-acetyldopamine (Image ) in the presence of β-alanine, β-alanine methyl ester or N-acetyl-L-lysine. They are formed presumably by addition of 2-aminoalkyl-5-alkylphenols to the o-quinone of biphenyltetrol which, in turn, arises from oxidative coupling of. The structures of present the first examples for the assembly of reasonably stable intermediates in the rather complex process of chemical modifications of aliphatic amino acid residues by o-quinones.
Amphiphilic derivatives of octadiene and docosadiene were investigated in monolayers and Langmuir-Blodgett multilayers, with respect to their self-organization and their polymerization behavior. All amphiphiles investigated form monolayers. However, only acid and alcohol derivatives were able to build up multilayers. Those multilayers are rapidly photopolymerized in the layers via a two-step process: Irradiation with long-wavelength UV light yields soluble polymers, whereas additional irradiation with sfiort-wavelength UV light produces insoluble and presumably cross-linked polymers. The reaction meclianism is discussed according to the polymer characterization by UV spectroscopy, small-angle X-ray scattering, NMR spectroscopy, and gel permeation chromatography. All multilayers undergo structural changes during the polymerization; substantial changes result in defects in the polymerized layers as observed by scanning electron microscopy. In contrast to the acids and alcohols, the deposition of monolayers of the aldehyde derivatives did not yield well-ordered multilayers, but rather amorphous films. In this different film structure, the photopolymerization process differs from the one observed in multilayers.
Aus dem Inhalt: Die Juvenilhormone 1a-c werden im Blut von Insekten enzymatisch zu den biologisch inaktiven Sluren hydrolysiert. Bei der Hydrolyse von racemischem 1c im Blut der Wanderheuschrecke Locusta migratoria wird ein Umsatz von 40-60% erreicht. Das unumgesetzte Edukt enthällt einen Überschuß an natürlich konfiguriertem (10R)-1c (e.e. 47.2%). Wir konnten zeigen, daß das in der Hämolymphe vorhandene Hormon-Bindungsprotein bevorzugt mit (10R)- 1c assoziiert.
The topography of first-order catchments in a region of western Amazonia was found to exhibit distinctive, recurrent features: a steep, straight lower side slope, a flat or nearly flat terrace at an intermediate elevation between valley floor and interfluve, and an upper side slope connecting interfluve and intermediate terrace. A detailed survey of soil-saturated hydraulic conductivity (K sat)-depth relationships, involving 740 undisturbed soil cores, was conducted in a 0.75-ha first-order catchment. The sampling approach was stratified with respect to the above slope units. Exploratory data analysis suggested fourth-root transformation of batches from the 0–0.1 m depth interval, log transformation of batches from the subsequent 0.1 m depth increments, and the use of robust estimators of location and scale. The K sat of the steep lower side slope decreased from 46 to 0.1 mm/h over the overall sampling depth of 0.4 m. The corresponding decrease was from 46 to 0.1 mm/h on the intermediate terrace, from 335 to 0.01 mm/h on the upper side slope, and from 550 to 0.015 mm/h on the interfluve. A depthwise comparison of these slope units led to the formulation of several hypotheses concerning the link between K sat and topography.
Rainfall erosivities as defined by the R factor from the universal soil loss equation were determined for all events during a two-year period at the station La Cuenca in western Amazonia. Three methods based on a power relationship between rainfall amount and erosivity were then applied to estimate event and daily rainfall erosivities from the respective rainfall amounts. A test of the resulting regression equations against an independent data set proved all three methods equally adequate in predicting rainfall erosivity from daily rainfall amount. We recommend the Richardson model for testing in the Amazon Basin, and its use with the coefficient from La Cuenca in western Amazonia.
Previous hydrometric studies demonstrated the prevalence of overland flow as a hydrological pathway in the tropical rain forest catchment of South Creek, northeast Queensland. The purpose of this study was to consider this information in a mixing analysis with the aim of identifying sources of, and of estimating their contribution to, storm flow during two events in February 1993. K and acid-neutralizing capacity (ANC) were used as tracers because they provided the best separation of the potential sources, saturation overland flow, soil water from depths of 0.3, 0.6, and 1.2 m, and hillslope groundwater in a two-dimensional mixing plot. It was necessary to distinguish between saturation overland flow, generated at the soil surface and following unchanneled pathways, and overland flow in incised pathways. This latter type of overland flow was a mixture of saturation overland flow (event water) with high concentrations of K and a low ANC, soil water (preevent water) with low concentrations of K and a low ANC, and groundwater (preevent water) with low concentrations of K and a high ANC. The same sources explained the streamwater chemistry during the two events with strongly differing rainfall and antecedent moisture conditions. The contribution of saturation overland flow dominated the storm flow during the first, high-intensity, 178-mm event, while the contribution of soil water reached 50% during peak flow of the second, low-intensity, 44-mm event 5 days later. This latter result is remarkably similar to soil water contributions to storm flow in mountainous forested catchments of the southeastern United States. In terms of event and preevent water the storm flow hydrograph of the high-intensity event is dominated by event water and that of the low-intensity event by preevent water. This study highlights the problems of applying mixing analyses to overland flow-dominated catchments and soil environments with a poorly developed vertical chemical zonation and emphasizes the need for independent hydrometric information for a complete characterization of watershed hydrology and chemistry.
Chemical fingerprints of hydrological compartments and flow paths at La Cuenca, western Amazonia
(1995)
A forested first-order catchment in western Amazonia was monitored for 2 years to determine the chemical fingerprints of precipitation, throughfall, overland flow, pipe flow, soil water, groundwater, and streamflow. We used five tracers (hydrogen, calcium, magnesium, potassium, and silica) to distinguish “fast” flow paths mainly influenced by the biological subsystem from “slow” flow paths in the geochemical subsystem. The former comprise throughfall, overland flow, and pipe flow and are characterized by a high potassium/silica ratio; the latter are represented by soil water and groundwater, which have a low potassium/silica ratio. Soil water and groundwater differ with respect to calcium and magnesium. The groundwater-controlled streamflow chemistry is strongly modified by contributions from fast flow paths during precipitation events. The high potassium/silica ratio of these flow paths suggests that the storm flow response at La Cuenca is dominated by event water.
Earlier investigations at South Creek in northeastern Queensland established the importance of overland flow as a hydrologic pathway in this tropical rainforest environment. Since this pathway is ‘fast’, transmitting presumably ‘new’ water, its importance should be reflected in the stormflow chemistry of South Creek: the greater the volumentric contribution to the stormflow hydrograph, the more similarity between the chemical composition of streamwater and of overland flow is to be expected. Water samples were taken during two storm events in an ephemeral gully (gully A), an intermittent gully (gully B) and at the South Creek catchment outlet; additional spot checks were made in several poorly defined rills. The chemical composition of ‘old’ water was determined from 45 baseflow samples collected throughout February. The two events differed considerably in their magnitudes, intensities and antecedent moisture conditions. In both events, the stormflow chemistry in South Creek was characterized by a sharp decrease in Ca, Mg, Na, Si, Cl, EC, ANC, alkalinity and total inorganic carbon. pH remained nearly constant with discharge, whereas K increased sharply, as did sulfate in an ill-defined manner. In event 1, this South Creek stormflow pattern was closely matched by the pattern in gully A, implying a dominant contribution of ‘new’ water. This match was confirmed by the spot samples from rills. Gully B behaved like South Creek itself, but with a dampened ‘new’ water signal, indicating less overland flow generation in its subcatchment. In event 2, which occurred five days later, the initial ‘new’ water signal in gully A was rapidly overwhelmed by a different signal which is attributed to rapid drainage from a perched water table. This study shows that stormflow in this rainforest catchment consists predominantly of ‘new’ water which reaches the stream channel via ‘fast’ pathways. Where the ephemeral gullies delivering overland flow are incised deeply enough to intersect a perched water table, a delayed, ‘old’ water-like signal may be transmitted.
Just and Carpenter (1980) presented a theory of reading based on eye fixations wherein their "psycholinguistic" variables accounted for 72% of the variance in word gaze durations. This comment raises some statistical and theoretical problems with their use of simultaneous regression analysis of gaze duration measures and with the resulting theory of reading. A major problem was the confounding of perceptual with psycholinguistic factors. New eye fixation data are presented to support these criticisms. Analysis of fixations within words revealed that most gaze duration variance was contributed by number of fixations rather than by fixation duration.
The synthesis of galactose clusters that are linked to a steroid moiety by a peptide-like spacer unit is described. The galactose cluster is obtained by Koenigs-Knorr glycosylation of TRIS-Gly-Fmoc (2b) under Helferich conditions. Peptide and ester bonds are formed after activation of carboxylic acids as diphenylthiophene dioxide (TDO) esters. 6a is synthesized in a convergent way by coupling of (Ac4Gal)3-TRIS-Gly (3e) with cholesteryl TDO succinate (5b). Coupling of (Ac4Gal)3-TRIS-Gly hydrogen succinate (3f) with Gly-O-Chol (5d) by means of EEDQ yields 6d. Reaction of (Ac4Gal)3-TRIS-Gly-SUCC-O-TDO (3g) with 25-hydroxycholesterol leads in a linear sequence to the oxysterol derivative 6f. Selective cleavage of the acetyl groups from galactose units yields the known compound 6b and the new derivatives 6e and 6g.
The complement fragments C3a and C5a were purified from zymosan-activated human serum by column chromatographic procedures after the bulk of the proteins had been removed by acidic polyethylene glycol precipitation. In the isolated in situ perfused rat liver C3a increased glucose and lactate output and reduced flow. Its effects were enhanced in the presence of the carboxypeptidase inhibitor DL-mercaptomethyl-3-guanidinoethylthio-propanoic acid (MERGETPA) and abolished by preincubation of the anaphylatoxin with carboxypeptidase B or with Fab fragments of an anti-C3a monoclonal antibody. The C3a effects were partially inhibited by the thromboxane antagonist BM13505. C5a had no effect. It is concluded that locally but not systemically produced C3a may play an important role in the regulation of local metabolism and hemodynamics during inflammatory processes in the liver.
In the isolated rat liver perfused in situ stimulation of the nerve bundles around the portal vein and the hepatic artery caused an increase of urate formation that was inhibited by the α1-blocker prazosine and the xanthine oxidase inhibitor allopurinol. Moreover, nerve stimulation increased glucose and lactate output and decreased perfusion flow. Infusion of noradrenaline had similar effects. Compared to nerve stimulation infusion of glucagon led to a less pronounced increase of urate formation and a twice as large increase in glucose output but a decrease in lactate release without affecting the flow rate. Insulin had no effect on any of the parameters studied.
Increase in prostanoid formation in rat liver macrophages (Kupffer cells) by human anaphylatoxin C3a
(1993)
Human anaphylatoxin C3a increases glycogenolysis in perfused rat liver. This action is inhibited by prostanoid synthesis inhibitors and prostanoid antagonists. Because prostanoids but not anaphylatoxin C3a can increase glycogenolysis in hepatocytes, it has been proposed that prostanoid formation in nonparenchymal cells represents an important step in the C3a-dependent increase in hepatic glycogenolysis. This study shows that (a) human anaphylatoxin C3a (0.1 to 10 mug/ml) dose-dependently increased prostaglandin D2, thromboxane B, and prostaglandin F2alpha formation in rat liver macrophages (Kupffer cells); (b) the C3a-mediated increase in prostanoid formation was maximal after 2 min and showed tachyphylaxis; and (c) the C3a-elicited prostanoid formation could be inhibited specifically by preincubation of C3a with carboxypeptidase B to remove the essential C-terminal arginine or by preincubation of C3a with Fab fragments of a neutralizing monoclonal antibody. These data support the hypothesis that the C3a-dependent activation of hepatic glycogenolysis is mediated by way of a C3a-induced prostanoid production in Kupffer cells.
"Considerons une particule mobile se mouvant aleatoirement sur la droite (ou sur un segment de droite). Supposons qu'il existe une probabilite F(x,y;s,t) bien definie pour que la particule se trouvant a l'instant s dans la position x se trouve a l'instant t (> s) a gauche de y, probabilite independante du mouvement anterieur de la particule...." Mit diesen Worten beginnt eines der berühmtesten mathematischen Manuskripte des letzten Jahrhunderts. Es stammt vom Soldaten Wolfgang Döblin, Sohn des deutschen Schriftstellers Alfred Döblin, und trägt den Titel "Sur l'equation de Kolmogoroff". Seine Veröffentlichung verbindet sich mit einer unglaublichen Geschichte. Wolfgang Döblin, stationiert mit seiner Einheit in den Ardennen im Winter 1939/1940, arbeitete an diesem Manuskript. Er entschloss sich, es als versiegeltes Manuskript an die Academie des Sciences in Paris zu schicken. Aber er kehrte nie aus diesem Krieg zurück. Sein Manuskript blieb 60 Jahre unter Verschluss im Archiv, und wurde erst im Jahre 2000 geöffnet. Wie weit Döblin damit seiner Zeit voraus war, wurde erkannt, nachdem es von Bernard Bru und Marc Yor ausgewertet worden war. Im ersten Satz umschreibt W. Döblin gleichzeitig das Programm des Manuskripts: "Wir betrachten ein bewegliches Teilchen, das sich zufällig auf der Geraden (oder einem Teil davon) bewegt." Er widmet sich damit der Aufgabe, die Fundamente eines Gebiets zu legen, das wir heute als stochastische Analysis bezeichnen.
The effect of moderate rates of nitrogen deposition on ground floor vegetation is poorly predicted by uncontrolled surveys or fertilization experiments using high rates of nitrogen (N) addition. We compared the temporal trends of ground floor vegetation in permanent plots with moderate (7–13 kg ha−1 year−1) and lower bulk N deposition (4–6 kg ha−1 year−1) in southern Sweden during 1982–1998. We examined whether trends differed between growth forms (vascular plants and bryophytes) and vegetation types (three types of coniferous forest, deciduous forest, and bog). Trends of site-standardized cover and richness varied among growth forms, vegetation types, and deposition regions. Cover in spruce forests decreased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs cover decreased faster with low deposition. Cover of bryophytes in spruce forests increased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs and deciduous forests there was a strong non-linear increase with moderate deposition. The trend of number of vascular plants was constant with moderate and decreased with low deposition. We found no trend in the number of bryophyte species. We propose that the decrease of cover and number with low deposition was related to normal ecosystem development (increased shading), suggesting that N deposition maintained or increased the competitiveness of some species in the moderate-deposition region. Deposition had no consistent negative effect on vegetation suggesting that it is less important than normal successional processes.
Recent research has shown that the early lexical representations children establish in their second year of life already seem to be phonologically detailed enough to allow differentiation from very similar forms. In contrast to these findings children with specific language impairment show problems in discriminating phonologically similar word forms up to school age. In our study we investigated the question whether there would be differences in the processing of phonological details in normally developing and in children with low language performance in the second year of life. This was done by a retrospective study in which in the processing of phonological details was tested by a preferential looking experiment when the children were 19 months old. At the age of 30 months children were tested with a standardized German test of language comprehension and production (SETK2). The preferential looking data at 19 months revealed an opposite reaction pattern for the two groups: while the children scoring normally in the SETK2 increase their fixations of a pictured object only when it was named with the correct word, children with later low language performance did so only when presented with a phonologically slightly deviant mispronunciation. We suggest that this pattern does not point to a specific deficit in processing phonological information in these children but might be related to an instability of early phonological representations, and/or a generalized problem of information processing as compared to typically developing children.
Recent work has shown that English-learning 18-month-olds can detect the relationship between discontinuous morphemes such as is and -ing in Grandma is always running (Gomez, 2002; Santelmann & Jusczyk, 1998) but only at a maximum of 3 intervening syllables. In this article we examine the tracking of discontinuous dependencies in children acquiring German. Due to freer word order, German allows for greater distances between dependent elements and a greater syntactic variety of the intervening elements than English does. The aim of this study was to investigate whether factors other than distance may influence the child’s capacity to recognize discontinuous elements. Our findings provide evidence that children’s recognition capacities are affected not only by distance but also by their ability to linguistically analyze the material intervening between the dependent elements. We speculate that this result supports the existence of processing mechanisms that reduce a discontinuous relation to a local one based on subcategorization relations.
How do children determine the syntactic category of novel words? In this article we present the results of 2 experiments that investigated whether German children between 12 and 16 months of age can use distributional knowledge that determiners precede nouns and subject pronouns precede verbs to syntactically categorize adjacent novel words. Evidence from the head-turn preference paradigm shows that, although 12- to 13-month-olds cannot do this, 14- to 16-month-olds are able to use a determiner to categorize a following novel word as a noun. In contrast, no categorization effect was found for a novel word following a subject pronoun. To understand this difference we analyzed adult child-directed speech. This analysis showed that there are in fact stronger co-occurrence relations between determiners and nouns than between subject pronouns and verbs. Thus, in German determiners may be more reliable cues to the syntactic category of an adjacent novel word than are subject pronouns. We propose that the capacity to syntactically categorize novel words, demonstrated here for the first time in children this young, mediates between the recognition of the specific morphosyntactic frame in which a novel word appears and the word-to-world mapping that is needed to build up a semantic representation for the novel word.
Schechita und Kaschrut
(2007)
Many methods have been proposed for the simulation of constrained mechanical systems. The most obvious of these have mild instabilities and drift problems. Consequently, stabilization techniques have been proposed A popular stabilization method is Baumgarte's technique, but the choice of parameters to make it robust has been unclear in practice. Some of the simulation methods that have been proposed and used in computations are reviewed here, from a stability point of view. This involves concepts of differential-algebraic equation (DAE) and ordinary differential equation (ODE) invariants. An explanation of the difficulties that may be encountered using Baumgarte's method is given, and a discussion of why a further quest for better parameter values for this method will always remain frustrating is presented. It is then shown how Baumgarte's method can be improved. An efficient stabilization technique is proposed, which may employ explicit ODE solvers in case of nonstiff or highly oscillatory problems and which relates to coordinate projection methods. Examples of a two-link planar robotic arm and a squeezing mechanism illustrate the effectiveness of this new stabilization method.
A Hamiltonian system in potential form (formula in the original abstract) subject to smooth constraints on q can be viewed as a Hamiltonian system on a manifold, but numerical computations must be performed in Rn. In this paper methods which reduce "Hamiltonian differential algebraic equations" to ODEs in Euclidean space are examined. The authors study the construction of canonical parameterizations or local charts as well as methods based on the construction of ODE systems in the space in which the constraint manifold is embedded which preserve the constraint manifold as an invariant manifold. In each case, a Hamiltonian system of ordinary differential equations is produced. The stability of the constraint invariants and the behavior of the original Hamiltonian along solutions are investigated both numerically and analytically.
Many methods have been proposed for the stabilization of higher index differential-algebraic equations (DAEs). Such methods often involve constraint differentiation and problem stabilization, thus obtaining a stabilized index reduction. A popular method is Baumgarte stabilization, but the choice of parameters to make it robust is unclear in practice. Here we explain why the Baumgarte method may run into trouble. We then show how to improve it. We further develop a unifying theory for stabilization methods which includes many of the various techniques proposed in the literature. Our approach is to (i) consider stabilization of ODEs with invariants, (ii) discretize the stabilizing term in a simple way, generally different from the ODE discretization, and (iii) use orthogonal projections whenever possible. The best methods thus obtained are related to methods of coordinate projection. We discuss them and make concrete algorithmic suggestions.
During the last few years there was a tremendous growth of scientific activities in the fields related to both Physics and Control theory: nonlinear dynamics, micro- and nanotechnologies, self-organization and complexity, etc. New horizons were opened and new exciting applications emerged. Experts with different backgrounds starting to work together need more opportunities for information exchange to improve mutual understanding and cooperation. The Conference "Physics and Control 2007" is the third international conference focusing on the borderland between Physics and Control with emphasis on both theory and applications. With its 2007 address at Potsdam, Germany, the conference is located for the first time outside of Russia. The major goal of the Conference is to bring together researchers from different scientific communities and to gain some general and unified perspectives in the studies of controlled systems in physics, engineering, chemistry, biology and other natural sciences. We hope that the Conference helps experts in control theory to get acquainted with new interesting problems, and helps experts in physics and related fields to know more about ideas and tools from the modern control theory.
Es gibt aus unserer Sicht eine Reihe von Gründen, sich in der gewerkschaftlichen Bildungsarbeit von der Dominanz des Lehrplans abzuwenden und sich an Stelle dessen dem Lernenden in einer Weise zuzuwenden, die seine Deutungen, seine Handlungsmotive und seine Lerninteressen in den Vordergrund stellt. Für den Bildungspraktiker ergeben sich Gründe vor allem aus der wiederholten Erfahrung von Diskrepanzen. Erstens die Diskrepanzen, die zwischen der Definition von Lehrzielen und ihrem Erreichen in der Erwachsenenbildung bestehen. Zweitens die Diskrepanzen, die zwischen dem tatsächlich erlernten Wissen und seiner Umsetzung und Anwendung in der Praxis sich auftun. (aus dem Inhalt)
Im vorliegenden Beitrag wird an Hand dreier Beispiele der Einsatz von optischer Sensorik zur Produktcharakterisierung dargestellt, nämlich Untersuchungen zum O2-Gehalt in Fruchtsäften, zur Isotopiesignatur von CO2 in Mineralwässern und zu Lichtstreueigenschaften eines Sonnenschutzmittels. Inhalt: Bestimmung von O2 mit Lumineszenzsonden Isotopenselektive Bestimmung von CO2 mit TDLAS Optische Charakterisierung stark streuender Materialien mit Photonendichtewellen
An approach to the development of fluorescent probes to follow polymerizations in situ using fluorinated cross-conjugated enediynes (Y-enynes) is reported. Different substitution patterns in the Y-enynes result in distinct solvatochromic behavior. β,β-Bis(phenylethynyl)pentafluorostyrene 7, which bears no donor substituents and only fluorine at the styrene moiety, shows no solvatochromism. Donor substituted β,β-bis(3,4,5-trimethoxyphenylethynyl) pentafluorostyrene 8 and β,β-bis(4-butyl-2,3,5,6-tetrafluorophenylethynyl)-3,4,5-trimethoxystyrene 9 exhibit solvatochromism upon change of solvent polarity. Y-enyne 8 showed the largest solvatochromic shift (94 nm bathochromic shift) upon changing solvent from cyclohexane to acetonitrile. A smaller solvatochromic response (44 nm bathochromic shift) was observed for 9. Lippert–Mataga treatment of 8 and 9 yields slopes of -10,800 and -6,400 cm -1, respectively. This corresponds to a change in dipole moment of 9.6 and 6.9 D, respectively. The solvatochromic behavior in 8 and 9 supports the formation of an intramolecular charge transfer (ICT) state. The low fluorescence quantum yields are caused by competitive double bond rotation. The fluorescence decay time of 9 decreases in methyltetrahydrofuran from 2.1 ns at 77 K to 0.11 ns at 200 K. Efficient single bond rotation in 9 was frozen at -50 °C in a configuration in which the trimethoxyphenyl ring is perpendicular to the fluorinated rings. 7–9 are photostable compounds. The X-ray structure of 7 shows it is not planar and that its conjugation is distorted. Y-enyne 7 stacks in the solid state showing coulombic, actetylene–arene, and fluorine–π interactions.
Investigations with frequency domain photon density waves allow elucidation of absorption and scattering properties of turbid media. The temporal and spatial propagation of intensity modulated light with frequencies up to more than 1 GHz can be described by the P1 approximation to the Boltzmann transport equation. In this study, we establish requirements for the appropriate choice of turbid model media and characterize mixtures of isosulfan blue as absorber and polystyrene beads as scatterer. For these model media, the independent determination of absorption and reduced scattering coefficients over large absorber and scatterer concentration ranges is demonstrated with a frequency domain photon density wave spectrometer employing intensity and phase measurements at various modulation frequencies.
Die Anwendung von optischen Parametern zur Stoffcharakterisierung wird diskutiert. Dabei ist der Schwerpunkt der Diskussion auf absorptions- und fluoreszenzspektroskopische Methoden gesetzt. Beide Methoden können schnell und zuverlässig – auch im on-line Betrieb – eingesetzt werden. Der Beitrag soll einen Überblick über die grundlegenden Möglichkeiten der Anwendung beider Methoden geben.
I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae. I supplement my {3+1} GR hydrodynamic simulations with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on (1) the late postbounce gravitational wave emission owing to convective overturn, anisotropic neutrino emission and protoneutron star pulsations, and (2) on the gravitational wave signature of accretion-induced collapse of white dwarfs to neutron stars.
China ist auf dem Weg zu einer offeneren Gesellschaft mit zunehmender Partizipation, größerer rechtlicher Sicherheit und individueller Autonomie. Der Staat zog sich aus vielen Bereichen zurück, ökonomische Ziele bestimmen seine Prioritäten. Die Entwicklungserfolge brachten jedoch eine Legitimationskrise des Staates mit sich. Vier Dilemmata, die China heute konfrontieren, werden aufgezeigt und Hypothesen zur Charakterisierung des chinesischen party state diskutiert.
Chinas Wandel und die Welt
(2006)
Wie stellt sich das Verhältnis zwischen China und der Welt im 21. Jahrhundert dar? Die Autorin, Politikwissenschaftlerin aus Peking, verweist auf die aktuelle Debatte in China, in der das Primat der Innenpolitik, regionaler Multilateralismus und harmonische Weltordnung intensiv diskutiert werden. China habe nicht vor, das internationale System herauszufordern oder zu zerstören. Vielmehr sei es um stärkere Einbindung bemüht.
Der Artikel stellt grundlegende Aspekte der Steuerung von öffentlichen Unternehmen und damit verbundenen Herausforderungen dar. Zu diesem Zweck wird der zentrale Begriff der Untersteuerung sowie die Ursachen und Folgen betrachtet. Nachfolgend wird die Entwicklung privatwirtschaftlicher Unternehmen analysiert, um daraus Schlussfolgerungen für den öffentlichen Sektor zu ziehen. Inhalt: 1. Einleitung 2. Untersteuerung als Herausforderung kommunaler Corporate Governance 3. Public Corporate Governance 4. Eigentumsrechte als zentrales Element einer Public Corporate Governance 5. Zusammenfassung und Ausblick 6. Literatur
Der optimale Umfang staatlicher Aufgaben wird im Rahmen der normativen Theorie der Staatsaufgaben diskutiert. In diesem explorativen Beitrag wird vorgeschlagen, die Reputation der Marke des demokratischen Staates als wesentlichen Einflussfaktor bei der Bestimmung der Staatsaufgaben einzuführen. Inhalt: 1. Einleitung 2. Staatsaufgaben in der Diskussion verschiedener Disziplinen 3. Staatsaufgaben in der leistungstiefenpolitischen Betrachtung 4. Die Reputation der Marke des demokratischen Staates 5. Zusammenfassung 6. Literatur