ALBERT

Notes: Low frequency Raman spectra (5–50 cm−1) show very obvious effects of disorder in the glass, and of the changes in the system which occur at the liquid–glass transition. Yet this frequency range has been considered in only very few glass formers. Here we report on this frequency range for the glass former system GeSBr2 which constitutes a statistically interrupted network. The temperature range studied was from far below the glass transition temperature (Tg=−30 °C) to well above it (T=−168 °C to +71 °C). In the glass, the loss of q conservation for phonon observation (due to static disorder) leads to a broad inelastic scattering peak around 10–15 cm−1, the so-called boson peak. The Raman spectrum is interpreted in terms of a correlation length Rc of phonon propagation and of phonon–photon-coupling; Rc is a measure of intermediate range order and amounts to ∼10 A(ring), independent of temperature. As T is raised, the minimum between this peak and the elastic peak is gradually filled up due to fast dynamic processes which increase rapidly above Tg. This scattering is interpreted in terms of fast dynamical processes, and the connection is made to the dynamical aspects of the liquid–glass transition. The strength and the time constants of fast processes are discussed in terms of two phenomenological models; both models describe the observed spectra well using a small number of parameters. The relaxation time found for the fast dynamical process (10−11–10−12 s) is in rough agreement with the value found independently in Brillouin scattering.

Notes: The two possible causes of depth inhomogeneities of the microstructure of porous silicon are changes in the HF concentration with depth and a varying chemical etching rate of the porous silicon layer. During anodization chemical etching will become important for microporous silicon — e.g. p-porous silicon — due to the large internal surface area, especially at long etching times. On the other hand, a considerable decrease of the HF concentration will occur during etching with high current densities to produce p+-porous silicon with high porosities. We have investigated the depth inhomogeneity of porous silicon layers by spectroscopic ellipsometry, Raman spectroscopy and photoluminescence measurements. From a line shape analysis of the Raman signal a size distribution of nanocrystals is deduced. For p-porous silicon smaller nanocrystals are found near the surface of the layer; for p+-porous silicon etched with high current densities smaller nanocrystals are found near the porous silicon/substrate interface. © 1996 American Institute of Physics.

Notes: Electron-electron scattering of ballistic electrons in a two-dimensional electron gas was studied as a function of the electron excess energy above the Fermi energy and of temperature. At low temperatures of 1.4 K it is found that for excess energies of approximately 30% of the Fermi energy the electrons in a ballistic electron beam are already scattered significantly due to electron-electron interaction. A very good agreement between our experimental data and theory was found, when the measured data were compared with numerical calculations based on a theory of Giuliani and Quinn [Phys. Rev. B 26, 4421 (1982)], while the agreement was only poor for the analytical approximation of the electron-electron scattering rate. © 1995 American Institute of Physics.

Notes: We have investigated the electron heating in metallic diffusive wires of varying length at liquid-helium temperature by measuring the electric noise. The local increase of the electron temperature can be essential already for small currents and is well described by a heat-diffusion equation for the electrons. Depending on the electron thermal conductance and the electron–phonon coupling in the wire, different length regimes are identified. The quantitative knowledge of the electron temperature is important for analysis of nonequilibrium effects involving current heating in mesoscopic wires. © 1997 American Institute of Physics.

Notes: We explore the electric-field effect of carbon nanotubes (NTs) in electrolytes. Due to the large gate capacitance, Fermi energy (EF) shifts of order ±1 V can be induced, enabling to tune NTs from p to n-type. Consequently, large resistance changes are measured. At zero gate voltage, the NTs are hole-doped in air with |EF|(approximate)0.3–0.5 eV, corresponding to a doping level of (approximate)1013 cm−2. Hole-doping increases in the electrolyte. © 2001 American Institute of Physics.

Notes: Abstract On Helgoland (North Sea), the imagines ofClunio emerge during two seasonal periods (late spring and summer) from water temperatures of 8°–18 °C. The temperature dependence of the known semilunar eclosion rhythm ofClunio (correlated in nature with the spring tides every 14–15 days) was tested in the laboratory. Between 15° and 23 °C the semilunar eclosion maxima varied by only one day within the artifical 15-day zeitgebercycle, below 15 °C they were delayed up to 8 days at 8 °C. However, the days of pupation were approximately independent of the temperature level. One can conclude the existence of a temperature-independent physiological switch inducing the pupation only within a few days of the semilunar zeitgeber-cycle. Moreover, a semilunar synchronized differentiation of the imaginal discs already starts in the preceding larval instar, indicating an additional physiological switch. A model is suggested in which the semilunar eclosion rhythm and its relatively slight temperature dependence is explained by the action of two physiological switches which are coupled with the endogenous temperature-compensated lunar timing mechanism on the same days of the 15-day zeitgeber-cycle. In the laboratory, the diurnal eclosion and its underlying circadian timing mechanism (correlated on Helgoland with the time of spring low water in the late afternoon) also proved to be temperature independent between 12° and 20 °C. A comparison of field and laboratory data showed very similar results at temperatures around 18 °C (summer swarming period). In contrast, the midges emerged on all days of the semimonthly cycle of springs and neaps during the spring swarming period. This lack of semilunar synchronization may be the consequence of fluctuating temperatures during the larval and pupal development in spring time due to a general rise in the water temperature (4°–8 °C) and to short temperature rises up to 18 °C during exposure of the intertidal habitat at about low tide. Since some higher parts of theClunio habitat suitable for egg deposition are exposed on almost every day of the semimonthly cycle, even such animals that undergo lunar unsynchronized metamorphosis can reproduce within the short imaginal life duration (ca 2 h) if they emerge just about the time of low water. In correspondence with the daily delay in the times of low water by about 50 min, the diurnal eclosion rhythm was in fact modified with the tides during the spring period resulting in shifts of the diurnal eclosion time of up to 12 hours within the semimonthly cycle of springs and neaps.

Notes: Abstract Branching ratios for the decay τ→ν+(n pions) withn≧2 are presented. The new data include all possible charge configurations of the pion system and, in particular, final states containing one or several neutral pions. The data are compared with predictions from CVC (even number of pions in final state) and current algebra (odd number of pions). They strongly support the standard coupling of the τ to the weak charged current.

Notes: Abstract The production of thef 0 in two photon collisions, with the subsequent decayf 0→π+π− has been observed in the CELLO detector at PETRA. Thef 0 peak was found to lie on a dipion continuum and to be shifted downwards in mass by ≃50 MeV/c2. The ππ mass spectrum from 0.8 to 1.5 GeV/c2 was well fitted by the model of Mennessier using only a unitarised Born amplitude and helicity 2f 0 amplitude. The previously observed mass shift and distortion of thef 0 peak are explained by strong interference between the Born andf 0 amplitudes. The only free parameter in the fit of the data to the model is the radiative widthΓ γγ(f 0). It was found that:Γ γγ(f 0)=2.5±0.1±0.5 keV where the first (second) quoted errors are statistical (systematic).

Notes: Zusammenfassung In einem Medium 1 befinde sich eine Kugelwellenstrahlungsquelle in endlichem Abstand von der Grenzebene gegen ein Medium 2. Es werden dann am elektro-dynamischen Beispiel unter Voraussetzung eines vertikalen Dipols exakte asymptotische Entwicklungen der Potentialfunktion in beiden Medien gegeben, in den Abschnitten 3, 4 für endlichen komplexen, in Abschnitt 5 für reellen Brechungsindex. Die Ergebnisse gelten für Entfernungen, welche groß sind gegen die Wellenlänge, für beliebigen endlichen Abstand der Strahlungsquelle von der Grenzebene und für beliebige Zenitdistanz des Aufpunktes. In dieser Allgemeinheit gelingt die Lösung des Problems mit Hilfe der Weylschen Methode der Transformation der komplexen Ausgangsdoppelintegrale. Durch Spezialisierung werden bisher vorliegende Lösungen wiedergewonnen und dabei durch Berücksichtigung einer von Weyl vernachlässigten Singularität bei komplexer Integration die Weylsche und die hinsichtlich der „Oberflächenwelle“ verbesserte Sommerfeldsche Theorie der Wellenausbreitung, welche im Ansatz übereinstimmen, auch in der Auswertung in völliger Übereinstimmung gefunden. Die Berücksichtigung der erwähnten Singularität liefert ferner mutatis mutandis die von O.v.Schmidt entdeckte elastische „Kopfwelle“.