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- ItemSporadic Ca and Ca+ layers at mid-latitudes: Simultaneous observations and implications for their formation(München : European Geopyhsical Union, 2001) Gerding, M.; Alpers, M.; Höffner, J.; von Zahn, U.We report on the observations of 188 sporadic layers of either Ca atoms and/or Ca ions that we have observed during 112 nights of lidar soundings of Ca, and 58 nights of Ca+ soundings, at Kühlungsborn, Germany (54° N, 12° E). The Ca+ soundings have been performed simultaneously and in a common volume with the Ca soundings by two separate lidars. Correlations between sporadic neutral and ionized metal layers are demonstrated through four case studies. A systematic study of the variations of occurrence of sporadic Ca and Ca+ layers reveals that neutral and ionized Ca layers are not as closely correlated as expected earlier: (a) The altitude distribution shows the simultaneous occurrence of both sporadic Ca and Ca+ layers to be most likely only in the narrow altitude range between 90 and 95 km. Above that region, in the lower thermosphere, the sporadic ion layers are much more frequent than atom layers. Below 90 km only very few sporadic layers have been observed; (b) The seasonal variation of sporadic Ca layers exhibits a minimum of occurrence in summer, while sporadic Ca+ layers do not show a significant seasonal variation (only the dense Ca+ layers appear to have a maximum in summer). At mid-latitudes sporadic Ca layers are more frequent than sporadic layers of other atmospheric metals like Na or K. For the explanation of our observations new formation mechanisms are discussed.
- ItemOn the longitudinal structure of the transient day-to-day variation of the semidiurnal tide in the mid-latitude lower thermosphere - I. Winter season(München : European Geopyhsical Union, 2001) Merzlyakov, E.G.; Portnyagin, Yu.I.; Jacobi, C.; Mitchell, N.J.; Muller, H.G.; Manson, A.H.; Fachrutdinova, A.N.; Singer, W.; Hoffmann, P.The longitudinal structure of the day-to-day variations of semidiurnal tide amplitudes is analysed based on coordinated mesosphere/lower thermosphere wind measurements at several stations during three winter campaigns. Possible excitation sources of these variations are discussed. Special attention is given to a nonlinear interaction between the semidiurnal tide and the day-to-day mean wind variations. Data processing includes the S-transform analysis which takes into account transient behaviour of secondary waves. It is shown that strong tidal modulations appear during a stratospheric warming and may be caused by aperiodic mean wind variations during this event.
- 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.
- 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.
- 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.
- ItemShort Communication: the Influence of Air-Abrasive Trimming on the Current Noise of Thick Film Resistors(London [u.a.] : Gordon & Breach, 1984) Wolf, M.[No abstract available]
- ItemOn Experimental Data of the Tcr of Tfrs and Their Relation to Theoretical Models of Conduction Mechanism(London [u.a.] : Gordon & Breach, 1985) Storbeck, I.; Wolf, M.Any theory of electrical conduction in TFRs encounters mainly two problems: (i) explanation of the dependence of R□ on properties of conducting component (volume fraction, grain size, resistivity), (ii) explanation of the temperature dependence of R□ taking into account (i). In order to achieve this one has to fit some microscopic parameters to experimental R□-and TCR-values, and to check if they are reasonable or not. The aim of the following discussion is to show, that such a fitting by means of experimental TCR-values is not correct. This is due to the fact that TCR-behaviour, as is well known, is determined also by the dependence of resistivity on strain. But any theoretical model neglects strains, also those who are induced by thermal strains. By means of published experiments concerning the strain dependence of resistance, the magnitude is estimated by which the TCR-values have to be corrected for the described fit.
- ItemMagnetic holes in the solar wind between 0.3 AU and 17 AU(Göttingen : Copernicus GmbH, 2000) Sperveslage, K.; Neubauer, F.M.; Baumgärtel, K.; Ness, N.F.Magnetic holes (MHs) are depressions of the magnetic field magnitude. Turner et al. (1977) identified the first MHs in the solar wind and determined an occurrence rate of 1.5 MHs/d. Winterhalter et al. (1994) developed an automatic identification criterion to search for MHs in Ulysses data in the solar wind between 1 AU and 5.4 AU. We adopt their criterion to expand the search to the heliocentric distances down to 0.3 AU using data from Helios 1 and 2 and up to 17 AU using data from Voyager 2. We relate our observations to two theoretical approaches which describe the so-called linear MHs in which the magnetic vector varies in magnitude rather than direction. Therefore we focus on such linear MHs with a directional change less than 10°. With our observations of about 850 MHs we present the following results: Approximately 30% of all the identified MHs are linear. The maximum angle between the initial magnetic field vector and any vector inside the MH is 20°in average and shows a weak relation to the depth of the MHs. The angle between the initial magnetic field and the minimum variance direction of those structures is large and very probably close to 90°. The MHs are placed in a high β environment even though the average solar wind shows a smaller β. The widths decrease from about 50 proton inertial length in a region between 0.3 AU and 0.4 AU heliocentric distance to about 15 proton inertial length at distances larger than 10 AU. This quantity is correlated with the β of the MH environments with respect to the heliocentric distance. There is a clear preference for the occurrence of depressions instead of compressions. We discuss these results with regard to the main theories of MHs, the mirror instability and the alternative soliton approach. Although our observational results are more consistent with the soliton theory we favor a combination of both. MHs might be the remnants of initial mirror mode structures which can be described as solitons during the main part of their lifetime.
- ItemKernmagnetische Ordnung in Metallen mit starker Hyperfeinwechselwirkung : Schlussbericht(Dresden : Forschungszentrum Dresden-Rossendorf, 2000) Pobell, Frank[no abstract available]
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