Now showing 1 - 10 of 377
- ItemAerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn(Copenhagen : Blackwell Munksgaard, 1996) Covert, D.S.; Wiedensohler, A.; Aalto, P.; Heintzenberg, J.; Mcmurry, P.H.; Leck, C.Aerosol physics measurements made onboard the Swedish icebreaker Oden in the late Summer and early Autumn of 1991 during the International Arctic Ocean Expedition (IAOE-91) have provided the first data on the size distribution of particles in the Arctic marine boundary layer (MBL) that cover both the number and mass modes of the size range from 3 to 500 nm diameter. These measurements were made in conjunction with atmospheric gas and condensed phase chemistry measurements in an effort to understand a part of the ocean-atmosphere sulfur cycle. Analysis of the particle physics data showed that there were three distinct number modes in the submicrometric aerosol in the Arctic MBL. These modes had geometric mean diameters of around 170 nm. 45 nm and 14 nm referred to as accumulation, Aitken and ultrafine modes, respectively. There were clear minima in number concentrations between the modes that appeared at 20 to 30 nm and at 80 to 100 nm. The total number concentration was most frequently between 30 and 60 particles cm-3 with a mean value of around 100 particles cm-3, but the hourly average concentration varied over two to three orders of magnitude during the 70 days of the expedition. On average, the highest concentration was in the accumulation mode that contained about 45% of the total number, while the Aitken mode contained about 40%. The greatest variability was in the ultrafine mode concentration which is indicative of active, earby sources (nucleation from the gas phase) and sinks; the Aitken and accumulation mode concentrations were much less variable. The ultrafine mode was observed about two thirds of the time and was dominant 10% of the time. A detailed description and statistical analysis of the modal aerosol parameters is presented here.
- ItemGravitational lensing in astronomy(Berlin : Springer, 1998) Wambsganss, J.Deflection of light by gravity was predicted by General Relativity and observationally confirmed in 1919. In the following decades, various aspects of the gravitational lens effect were explored theoretically. Among them were: the possibility of multiple or ring-like images of background sources, the use of lensing as a gravitational telescope on very faint and distant objects, and the possibility of determining Hubble's constant with lensing. It is only relatively recently, (after the discovery of the first doubly imaged quasar in 1979), that gravitational lensing has became an observational science. Today lensing is a booming part of astrophysics. In addition to multiply-imaged quasars, a number of other aspects of lensing have been discovered: For example, giant luminous arcs, quasar microlensing, Einstein rings, galactic microlensing events, arclets, and weak gravitational lensing. At present, literally hundreds of individual gravitational lens phenomena are known. Although still in its childhood, lensing has established itself as a very useful astrophysical tool with some remarkable successes. It has contributed significant new results in areas as different as the cosmological distance scale, the large scale matter distribution in the universe, mass and mass distribution of galaxy clusters, the physics of quasars, dark matter in galaxy halos, and galaxy structure. Looking at these successes in the recent past we predict an even more luminous future for gravitational lensing.
- ItemResonance Raman and optical dephasing study of HITCI(Routledge : Taylor and Francis Inc., 1999) Kummrow, A.; Ashworth, S.H.; Lenz, K.Line shape analysis based on resonance Raman spectra of HITCI is used to determine the details of the vibrational part of the line broadening function. Forced Light Scattering with 20 fs pulses from a Ti: sapphire laser measured optical dephasing probing with an Ar+ laser. The observed response is well described by the line broadening function derived from the fluorescence line shape.
- ItemMolecular dynamics investigated by temporally two-dimensional coherent Raman spectroscopy(Routledge : Taylor and Francis Inc., 1999) Lau, A.; Pfeiffer, M.; Kozich, V.; Kummrow, A.A six-wave set-up is described to determine molecular dynamics in the condensed phase. Applying two independent time delays between excitation and probe pulses additional information on the dynamics should be obtainable. We show experimentally that such investigations can be carried out with noisy light having intensity fluctuations in the femtosecond region. As first result we found a fast relaxation time in neat nitrobenzene of 100 fs, becoming even faster in mixtures with low viscosity liquids. Switching on a Raman resonance yields a longer relaxation time, which could be explained by an additional contribution by that vibration.
- ItemSelf-stabilization of the biosphere under global change: A tutorial geophysiological approach(Abingdon : Taylor and Francis Ltd., 1997) Von Bloh, W.; Block, A.; Schellnhuber, H.J.A 2-dimensional extension of the simple Lovelock-Watson model for geosphere-biosphere feed-back is introduced and discussed. Our enriched version also takes into account various pertinent physical, biological, and civilisatory processes like lateral heat transport, species competition, mutation, germination, and habitat fragmentation. The model is used as a caricature of the Earth System, which allows potential response mechanisms of the biosphere to environmental stress (as generated, e.g., by global warming or anthropogenic land-cover change) to be investigated qualitatively. Based on a cellular automaton representation of the system, extensive calculations are performed. They reveal a number of remarkable and, partially, counter-intuitive phenomena: our model biosphere is able to control almost perfectly the geophysical conditions for its own existence. If the environmental stress exceeds certain thresholds, however, life breaks down on the artificial planet via a first-order phase transition, i.e., in a non-reversible way. There is a close connection between self-stabilizing capacity, biodiversity and geometry of habitat fragmentation. It turns out, in particular, that unrestricted Darwinian competition, which reduces the number of co-existing species, is the best guarantee for survival of the artificial ecosphere as a whole.
- ItemCoherent motion of low frequency vibrations in ultrafast excited state proton transfer(Routledge : Taylor and Francis Inc., 1999) Pfeiffer, M.; Chudoba, C.; Lau, A.; Lenz, K.; Elsaesser, T.Photoexcitation of internal proton transfer in the tinuvin molecule causes the excitation of some low frequency vibrational modes which oscillate with high amplitudes in a coherent manner over 700 fs. Such effect is observed for the first time applying two color pump/probe measurement with 25 fs pulses. Based on resonance Raman spectra a normal coordinate analysis of the modes is performed. It is shown that the nuclear movement given by the normal vibration of one of the modes serves to open up a barrierfree proton transfer path.
- ItemThe role of spatial variability of soil moisture for modelling surface runoff generation at the small catchment scale(Göttingen : Copernicus GmbH, 1999) Bronstert, A.; Bárdossy, A.The effects of spatial variability of soil moisture on surface runoff generation at the hillslope and small catchment scale were studied. The model used is physically based accounting for the relevant hydrological processes during storm runoff periods. A case study investigating the effects on runoff generation in a loessy small catchment is presented. In this study the storm rainfall response was modelled using different distribution patterns of the initial soil moisture content, and where different initial soil moisture fields were generated by using both interpolation methods and stochastic simulation methods. It is shown that spatial variability of pre-event soil moisture results in an increase in runoff production compared to averaged values. It is of particular importance to note the combined organised/stochastic variability features, that is, the superposition of systematic and random features of soil moisture dominate local generation of surface runoff. In general one can say that the stronger the organised heterogeneity is, the more important is an adequate and refined interpolation technique which is capable of accounting for complex spatial trends. The effects of soil moisture variations are of particular importance for storms, where the produced runoff volume is just a small fraction of precipitation.
- ItemWirkung von Klimaänderungen auf Vegetation: Entwicklung eines allgemeinen Modells für die Klimafolgenforschung : Abschlußbericht(Potsdam : Potsdam-Institut für Klimaforschung, 1999) Cramer, Wolfgang[no abstract available]
- ItemReaktions-Diffusionsgleichungen in Heterostrukturen mit Anwendungen in der Halbleitertechnologie : Schlußbericht zu einem Vorhaben im BMBF-Förderprogramm Anwendungsorientierte Verbundvorhaben auf dem Gebiet der Mathematik(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 1997) Hünlich, Rolf; Glitzky, Annegret; Röpke, WilfriedIm Vorhaben wurden Beitraege zur Modellierung und Simulation relevanter Teilprozesse bei der Herstellung von Halbleiterbauelementen der Nanoelektronik geleistet. Behandelt wurden vorrangig Fragestellungen,die beim Verbundpartner, dem Institut fueur Halbleiterphysik Frankfurt (Oder), zur Entwicklung von SiGe--Heterojunction--Bipolartransistoren von Bedeutung waren. Schwerpunkte bildeten Fragen zur Diffusion von Fremdatomen in verspannten SiGe--Schichten sowie zu Feldeffekten bei der Diffusion elektrisch geladener Teilchen im Hochkonzentrationsfall. Gegenstand der analytischen und numerischen Untersuchungen waren verschiedene Klassen von Elektro-Reaktions-Diffusionsgleichungen in Heterostrukturen, die relevante Aufgaben aus der Halbleitertechnologie auf verschiedenen Niveaus modellieren. Hier wurden neue Aussagen zur globalen Existenz, Einzigkeit und zum asymptotischen Verhalten der Loesungen erhalten.Weiterhin wurden Diskretisierungsschemata, die Konvergenz von Naeherungsverfahren sowie die Reduktion der Modellgleichungen fuer singulaer gestoerte Faelle diskutiert.
- ItemCrystal structure of distrontium praseodym gallium pentaoxide, Sr2PrGaO5(München : R. Oldenbourg Verlag GmbH, 1999) Gesing, T.M.; Uecker, R.; Buhl, J.-C.GaO5PrSr2, tetragonal, I4/mcm (No. 140), a = 6.8441(2) Å, c = 11.2534(4) Å, V = 527.1 Å3, Z = 4, R(P) = 0.035, wR(P) = 0.052, R(I) = 0.038, T = 295 K. © by Oldenbourg Wissenschaftsverlag.