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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.
- Itemstress generation modulus as a counterpart of the stress relaxation modulus(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Brückner, Rolf; Hessenkemper, Heiko; Habeck, Andreas; Yue, YuanzhengIn order to measure the time dependence of the stress relaxation modulus, E, a stress-strain deformation has to precede which induces a stress within the viscoelastic sample from which the sample relaxes. The generation of stress is characterized by a strain rate-dependent and relaxation rate-dependent portion which exhibits a maximum value, E_max, which is called "stress generation modulus". E_max was called the "maximum stress relaxation modulus" in earlier papers. Meanwhile, however, it turned out that a better verbal distinction should be made in future by the new term "stress generation modulus" because E_max is about one order of magnitude larger than E.
- ItemZerstörungskennlinien für Verbundsicherheitsglasscheiben(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2001) Mayrhofer, Christoph; Kranzer, CarolineFür die Bewertung des Tragverhaltens von Bauteilen bei Explosionsereignissen sind sogenannte „Druck-Impuls-Diagramme" erforderlich. Diese geben in Abhängigkeit vom Druck und dem Impuls der Belastung an, für welche Wertepaare Zerstörung eintritt und welchen Belastungswerten das betrachtete Bauteil standhält. Derartige Zerstörungskennlinien sind am Fraunhofer EMI für eine Vielzahl von Werkstoffen entwickelt worden. Den Zerstörungskennlinien liegt das Rechenmodell des Ein-Massen-Schwingers zugrunde. Voraussetzungen für seine Anwendbarkeit sind Biegetragmechanismen, Bruch- bzw. Zerstörungskriterien (z.B. Grenzdurchbiegung) und die Kenntnis des statischen Last-Verformungsverhaltens. Untersuchungen ergaben, daß Verbundsicherheitsglasscheiben die Voraussetzungen für die Erstellung von Zerstörungskennlinien erfüllen. Es wird eine Näherungsmethode zur Erfassung des statischen Tragverformungsverhaltens unter Berücksichtigung von Membranspannungszuständen dargestellt. Am Beispiel anderer Werkstoffe wird die prinzipielle Vorgehensweise erläutert, da für Verbundsicherheitsscheiben bisher noch keine Bruchkriterien zur Verfügung stehen.
- ItemCollaborative study into the analysis of total selenium and selenium valence states in glass - a general method by hydride generation atomic absorption spectrometry and photometry : Report of the International Commission on Glass (ICG) Technical Committee 2 "Chemical Durability and Analysis"(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Guadagnino, Emanuel; Çorumluoğlu, OrhanWhilst the determination of total selenium in glass is of great relevance to environmental purposes, the measurement of the oxidation states of selenium which may arise under different redox conditions may contribute to clarify the mechanisms of colour formation. In the proposed method, the determination of total selenium is carried out by hydride generation atomic absorption spectrometry (HGAAS) on three different glasses covering the range of selenium content between 10 and 130 mg/kg of glass. To prevent losses during the decomposition step, selenium is converted into a nonvolatile form as selenate (Se6+). When the sample is decomposed, the HCl Solution (c(HC1) = 10 mol/l) is made and selenium is pre-reduced to Se4+ by heating for 2 h at 80 °C. The determination of selenium oxidation states requires a stepwise approach. The measurement of Se0 is based on its insolubility in HF. After the sample is decomposed, Se0 is filtered off, dissolved from the filter with a HBr-Br2 mixture and finally measured by HGAAS. Se4+ and Se6+ are recovered in the filtrate of the same sample and determined together after conversion of Se4+ into Se6+. Se4+ is determined in the same filtrate by photometry with o-phenylenediamine (OPDA).
- ItemAdvanced oxygen burner for the glass industry(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Legiret, Thierry; Philippe, Louis; Tsiava, Remi; Marié, Bruno[no abstract available]
- ItemThermodynamic calculations of chemical solubilities of gases in oxide melts and glasses(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Pelton, Arthur D.The Reddy-Blander thermodynamic model for calculating sulfide solubilities in oxide melts and glasses has been modified and extended to predict a priori solubilities of sulfide, sulfate, phosphate, carbonate and halides in multicomponent oxide melts and glasses, from a knowledge of the thermodynamic activities of the basic component oxides (SiO₂, Na₂O, K₂O, CaO, etc.), in most cases with no adjustable parameters. Agreement with measured solubilities is within or nearly within experimental uncertainties over wide ranges of composition in two-, three-, four- and five-component melts and glasses. Particularly good agreement is obtained for the dissolution of sulfur, SO₂ and SO₃ as sulfate. The oxide activities used in the computations are calculated from a database of model parameters obtained by optimizing thermodynamic and phase equilibrium data for oxide Systems. Sulfide, sulfate, phosphate, carbonate and halides as solutes have now been included in this database. Software for Gibbs energy minimization with automatic access to this and other databases permits the calculation of solubilides in multicomponent oxide melts and glasses in equilibrium with other phases such as gases, molten salts, solids and metals, and can be useful to model evaporation processes and bubble formation.