Showing papers by "University of Stuttgart published in 1968"

Quantum theory of light propagation in a fluctuating laser-active medium

Abstract: The basic equations are derived which describe the propagation of an electromagnetic field in a fluctuating laser-active medium. The well-known methods of Langevinequations and master-equation for a few discrete modes are generalized to meet also the case of a radiation field with continuous spectrum. The medium is described by two-level atoms which are embedded in a merely passive solid matrix and homogeneously distributed over space. They have an inversion which is kept constant by an externally applied pump. The atomic line may be homogeneously or inhomogeneously broadened. We obtain a complete set of partial differential equations for the field operators with damping terms and fluctuating forces homogeneously distributed over the material. The telegraph equation with a fluctuating force occurs as a special case. After the exact elimination of the atomic variables we obtain a nonlinear field equation for the radiation field alone. By means of a pseudo-Hamiltonian and by a simple one-dimensional example we show that in a certain sense there exists a close formal analogy between the present theory and the theory of an interacting Bose gas. The characteristic differences between the two theories are also discussed. We find, that there occurs a phase transition of the radiation field because above a certain threshold of the pump the photons condense into a single mode and establish an “offdiagonal-long-range order”. The amplitude fluctuations and the phase fluctuations, which restore the broken phase symmetry, are calculated in detail. A new condition for the occurrence of undamped spiking (pulse formation) for a continuum of modes is derived.

The quantum fluctuations of the optical parametric oscillator. i.

Abstract: Our treatment is based on a microscopically correct Hamiltonian which contains the Bose-operators of the light modes and the Fermi-operators of the optically active electrons in the medium. The coupling between modes and atoms is taken from quantum-electrodynamics. Besides that, the light modes may interact with external “heat baths” like the mirrors, scattering centers etc., while the atoms interact with lattice vibrations, incoherent light fields etc. Using recently developed methods the effect of these heatbaths is taken into account in a quantum mechanically consistent fashion. In the present paper we apply quantum mechanical Langevin equations for the field and electron operators which contain dissipation and fluctuation terms. The elimination of the electron operators by an iteration procedure finally leaves us with a set of coupled nonlinear field equations which are shown to be quantum mechanically consistent. They are solved in the Heisenberg picture below threshold by linearization and well above threshold by quantum mechanical quasi-linearization. The solutions show that the line width of the signal mode below threshold is due to the vacuum fluctuations in the idler and vice versa, whereas the thermal noise of the resonator and the spontaneous emission noise of the medium may be neglected. Above threshold the linewidth is caused by the undamped diffusion of the phase difference between signal and idler, to which the vacuum fluctuations of both modes contribute in equal parts. The phase sum of both modes adiabatically follows the slow phase diffusion of the external pump light, produced by a laser, and therefore contributes to the linewidth too. Well above threshold the amplitudes are stable. Correlation and cross-correlation functions of their small residual fluctuations are calculated.

Energy Transfer in Organic Molecular Crystals: A Survey of Experiments

Abstract: Publisher Summary This chapter deals with some current problems of luminescence and energy transfer in organic molecular crystals. The quenching of energy transfer in anthracene crystals at low temperatures is caused by a competition between energy transfer to the guest molecules and to shallow traps that give rise to the emission from impurities or disturbed exciton states at low temperatures. The fluorescence of an anthracene crystal containing small traces of tetracene is measured. The result is that the fluorescence intensity of tetracene is relatively much stronger than the anthracene emission. The tetracene molecules act as traps for the electronic excitation energy, which is traveling in the anthracene crystal. To measure and separate the host and guest quantum yields, one has to measure the total fluorescence spectrum with good resolution. Only in this way is it possible to separate unambiguously the individual contributions from host, guest, and traps to the total emission.

Fehler im Flußliniengitter von Supraleitern zweiter Art

Abstract: Das Flusliniengitter von Supraleitern zweiter Art enthalt Gitterfehler, wie sie aus der Kristallphysik bekannt sind, namlich Versetzungen, Stapelfehler, “Punkt” fehler usw. Auserdem treten starke elastische Verzerrungen und Gitterkrummungen auf. Die verschiedenen Gitterfehler werden an Hand von Beispielen, die durch direkte Beobachtung gewonnen wurden, beschrieben und klassifiziert. The lattice of flux lines in typ II superconductors contains lattice defects, as known from crystal physics, namely dislocations, stacking faults, “point” defects, e.t.c. Moreover strong elastic distortions and lattice bendings occur. By examples, obtained by direct observations, the various lattice defects are described and classified.

Nonlinear theory of multimode action in loss modulated lasers

Abstract: A set of cavity modes which are coupled together by an externally synchronous driven loss modulator is considered. The nonlinear polarization of the material is taken into account, and the mode coupling for the case when many modes are coupled together is treated nearly exactly. The formulas for the pulse shape and pulse width are explicitly derived for the case of a homogeneously broadened line. They show the dependence of these quantities on the system's parameters, such as pump power, modulator driving strength, detuning between modulator frequency, frequency spacing of the cavity modes, etc. Several configurations for the locked modes which have higher pulse widths are possible. This last result in particular seems to be completely new.

Die embryogenese des gehirns paurometaboler insekten untersuchungen an Carausius morosus und Periplaneta americana

Abstract: The origin of the neuroblasts and their further development is investigated as to the arrangement and formation of functional groups. These groups are visible mainly in the protocerebrum with its highly developed centers. Moreover the development of brain-parts and -structures is described. These researches finally allow some remarks concerning head segmentation.

[Synthesis of 5'-modified adenosine derivatives].

Abstract: Es werden neue und einfache Verfahren zur Synthese von Adenosin-5′-carbonsaure (2), 5′-O-Tosyl-adenosin (3), 5′-O-Tosyl-adenosin-5′.5′-d2 (11) und 5′-Amino-5′-desoxy-adenosin (4) ausgehend von 2′.3′-O-Isopropyliden-adenosin beschrieben.

Vacancies, divacancies, and self‐diffusion in platinum

Abstract: Thin wires of high-purity platinum are quenched from high temperatures by means of the helium-II technique. After quenching from about 1000 °C the electrical resistivity is found to recover between 380 and 520 °C with an activation energy of (1.33±0.05) eV. After quenching from near the melting point the recovery occures between 200 and 460°C and can be decomposed into two second-order processes with activation energies of 1.0 and 1.34 eV, respectively. The self-diffusion data are re-analysed allowing for the contribution of both mono- and divacancies. This analysis is compared critically with the results of the present quenching experiments and with previous work. A consistent set of vacany parameters is proposed for Pt. Hochreines Platin in Form dunner Drahte wurde mit Hilfe der He-II-Methode von hohen Temperaturen abgeschreckt. In Proben, die von etwa 1000 °C abgeschreckt worden waren, erholte sich der elektrische Widerstand zwischen 380 und 520 °C mit einer Aktivierungsenergie von (1,33 ± 0,05) eV. Nach Abschrecken von der Nahe des Schmelzpunktes erfolgte die Erholung zwischen 200 und 460 °C und konnte in zwei Prozesse zweiter Ordnung mit Aktivierungsenergien von 1,0 bzw. 1,34 eV zerlegt werden. Die Selbstdiffusionsdaten werden erneut ausgewertet unter Berucksichtigung gleichzeitiger Beitrage von Einfach- und Doppelleerstellen. Die Ergebnisse werden kritisch mit denjenigen der vorliegenden Abschreckmessungen und mit fruheren Arbeiten verglichen. Ein in sich konsistenter Satz von Leerstellen-(bzw. Doppelleerstellen)-Eigenschaften wird vorgeschlagen.

Die kritische Schubspannung mit zweiwertigen Kationen dotierter Alkalihalogenide I. Nicht‐agglomerierte Fremdion‐Leerstellen‐Paare

Abstract: Es wird gezeigt, das bei Alkalihalogeniden, welche zweiwertige Kationen in Form von Fremdion-Kationleerstellen-Paaren (elastischen Dipolen) enthalten, die kritische Schubspannung τ0 durch die elastische Wechselwirkung dieser Dipole mit den Versetzungen verursacht wird. Unterhalb Raumtemperatur ist τ0 durch das thermisch aktivierte Vorbeigleiten von Versetzungen an Dipolen in der Nahe der Gleitebenen bestimmt, wahrend oberhalb Raumtemperatur der induzierte Snoek-Effekt der Dipole im Spannungsfeld der Versetzungen τ0 entscheidend beeinflust. An einen temperaturunabhangigen Bereich oberhalb Raumtemperatur schliest sich ein Hochtemperaturabfall von τ0 an, zu dem neben dem induzierten Snoek-Effekt der Zerfall der Dipole in zweiwertige Kationen und Kation-Leerstellen beitragt. It is shown that in alkali halides containing divalent cations which form elastic dipoles by associating with cation vacancies the critical shear stress τ0 is determined by the elastic interactions between these dipoles and the dislocations. Below room temperature τ0 arises from the thermally activated passing of dislocations near dipoles which are located close to the slip planes. Above room temperature the induced Snoek effect of dipoles in the stress fields of dislocations determines τ0. The temperature-independent region just above room temperature is continued by a regime in which τ0 decreases rapidly. In this high-temperature region the breaking-up of dipoles into divalent cations and cation vacancies plays a decisive role in addition to the induced Snoek effect.

The embryonic development of the brain in paurometabolic insects a study on carausius morosus and periplaneta americana

Abstract: The origin of the neuroblasts and their further development is investigated as to the arrangement and formation of functional groups. These groups are visible mainly in the protocerebrum with its highly developed centers. Moreover the development of brain-parts and -structures is described. These researches finally allow some remarks concerning head segmentation.

Orthoamide, VIII Über die Umsetzung aktivierter Methylgruppen an substituierten Toluolen und Heterocyclen mit Aminal‐tert.‐butylester zu Enaminen

Abstract: Aktivierte Methylgruppen an substituierten Toluolen und Heterocyclen lassen sich mit dem Aminal-tert.-butylester 3 zu Enaminen umsetzen; einige dieser Enamine konnten durch saure Hydrolyse in die entsprechend substituierten Aldehyde oder deren Dinitrophenylhydrazone ubergefuhrt werden.

Photon statistics of the optical parametric oscillator including the threshold region

Abstract: Starting from an effective Hamiltonian the derivation of a set of classical Langevin equations for the amplitudes of signal, idler, and pump is briefly reconsidered. From these equations all variables except those describing the signal mode are eliminated with the help of an adiabatic approximation and certain others, which are valid in the threshold region and somewhat above (i.e. photonumbers ≪ 1014). The signal mode amplitude then satisfies a van der Pol equation in the rotating wave approximation and is driven by a fluctuating force.

Die Embryogenese des Gehirns paurometaboler Insekten

Abstract: The origin of the neuroblasts and their further development is investigated as to the arrangement and formation of functional groups. These groups are visible mainly in the protocerebrum with its highly developed centers. Moreover the development of brain-parts and -structures is described. These researches finally allow some remarks concerning head segmentation.

Thermally activated dislocation motion in a solid containing a multiple spectrum of dislocation obstacles

Abstract: A theoretical treatment is given of the thermally activated motion of dislocations in the presence of dislocation obstacles with different hardness. The hardness of an obstacle is allowed to depend on an arbitrary number of characteristic parameters (multiple obstacle spectrum). It is shown that even under these conditions the slip rate ȧ obeys an Arrhenius equation mean free activation enthalpy. The general theory is applied to the case of plastic flow in neutron-irradiated copper. In this case the dislocation obstacles are vacancy dislocation loops of different sizes, different orientations, and different distances from the slip planes of the mobile dislocations (triple spectrum).

Die elastischen Moduln von Eis-Einkristallen

Abstract: Mit zwei voneinander unabhangigen Ultraschall-Impulsmethoden wurden die Schallgeschwindigkeiten in Eis vom Schmelzpunkt bis −140°C gemessen. Aus diesen Werten wurde fur den genannten Temperaturbereich der vollstandige Satz der funf elastischen Moduln berechnet. Ferner wird das Modell eines Alterungsprozesses vorgeschlagen, durch den unterschiedliche Ergebnisse beim Piezoeffekt, der Dichte und den elastischen Moduln geklart werden konnen.

Elektronenmikroskopische Untersuchungen zur Sporenentwicklung von Henneguya pinnae Schubert (Sporozoa, Myxosporidea, Myxobolidae)

Abstract: Das Plasmodium von Henneguya pinnae wird vom Wirt (Ctenopoma kingsleyae) durch ein Epitheloid abgeschlossen. Feinstruktur des Epitheloids, des Plasmodiums und der Sporenbildungsstadien bis zur reifen Spore werden beschrieben. Von den beiden Zellen des Zweizellstadiums entwickelt sich eine zu Hullzellen, die andere zu den eigentlichen Sporen. Die Schalenzellen entwickeln sich unter Verlust der meisten Zellorganellen zur Sporenschale. Die Entwicklung der Polkapselzellen konnte bis fast zur reifen Polkapsel verfolgt werden. Im Amoboidkeim sind kugelige Korper, die wahrscheinlich Reservestoffe enthalten, und sehr eigenartig geformte Mitochondrien nachweisbar.

Orthoamide, VII Synthese vinyloger Amidacetale, Aminalester und Amidaminale

Abstract: Vinyloge N.N-disubstituierte Saureamide bilden mit Dialkylsulfaten Addukte, die sich mit Alkoholat in vinyloge Saureamidacetale, mit primaren Aminen in vinyloge N.N.N′ -trisubstituierte und mit sekundaren Aminen in vinyloge N.N.N′.N′-tetrasubstituierte Amidinium-methylsulfate uberfuhren lassen. Aus letzteren entstehen mit Alkoholaten vinyloge Aminalester und mit Metalldialkylamiden vinyloge Amidaminale.

Der direkte Nachweis von Flußlinienbewegungen in stromdurchflossenen Supraleitern

Abstract: Supraleitende Bleifolien mit einer Dicke d ≤ 0,05 mm zeigen unter der Wirkung eines transversalen Magnetfeldes eine magnetische Struktur, die aus Makrofluslinien mit ca. 50 Fluxoidquanten pro Fluslinie besteht. Schickt man durch die Folien einen hinreichend hohen Transportstrom senkrecht zur Feldrichtung, so bewegen sich die Fluslinien in diskreten Bahnen unter einem Hallwinkel α durch die Proben. Durch Versetzungen und Korngrenzen wird die Fluslinienbewegung erheblich beeinflust. Under the influence of a transversal magnetic field superconductive lead foils with a thickness of d ≤ 0.05 mm show a magnetic structure which consists of macro flux lines with about 50 fluxoid quanta per flux line. If a sufficiently high transport current is driven through the foil normally to the field orientation, the flux lines move in discrete paths under a Hall angle α. Dislocations and grain boundaries considerably influence the movement of the flux lines.

Präparative und spektroskopische Studien an Dialkylgalliumfluoriden

Abstract: Dimethyl- und Diathylgalliumfluorid wurden aus den entsprechenden Trialkylgalliumatheraten und Trimethylzinnfluorid oder Bortrifluorid-atherat in guten Ausbeuten dargestellt. Nach analytischen und spektroskopischen Untersuchungen liegen in den flussigen Verbindungen und in ihren Losungen trimere Molekule vor, denen ein planares sechsgliedriges Ringsystem aus drei vierbindigen Galliumatomen und drei zweibindigen Fluoratomen zugrunde liegt.

Investigation of lattice dynamics by means of vibronic spectra

Abstract: Electronic transitions at a foreign probe ion in a lattice exhibit vibrational sidebands. They may be used as a new tool to investigate lattice dynamics. To make this too effective the theory of vibronic spectra has been refined. The principal refinement is that of a partial Born-Oppenheimer approximation which establishes a rigid coupling of the electronic wavefunctions of the foreign ion to its own nucleus. The structural form of the one-phonon sideband is given as a projection of the classical Greens' function (imaginary part) onto single multipole-fields in lattice space. Employing a variety of electronic transitions and by careful group-theoretical analysis a complete irreducible sequence of projections can be extracted from the experiments. These functional forms depend sensibly on the eigenvectors of the lattice modes, whence they contain information, which cannot be received from neutron scattering. Moreover, the spectra related to the higher multipoles give insight into the disturbed (local) dynamics, whereas the lower type spectra concern the undisturbed (ideal) one. Systems, where the foreign probe ion has high symmetry, are most suitable for the new method. For systems of low local symmetry approximations are suggested by the low-frequency behaviour of the measured one-phonon band. Because of the high resolution of optical measurements, the information from vibronic spectra is comparable or even superior in detailed richness to neutron scattering data.

Die kritische Schubspannung mit zweiwertigen Kationen dotierter Alkalihalogenide II. Fremdion‐Leerstellen‐Dipol‐Agglomerate und fremdionenreiche Ausscheidungen

Abstract: Bei Alkalihalogeniden, welchen genugende Mengen zweiwertiger Kationen zugesetzt sind, fuhrt hinreichend langsames Abkuhlen zur Ausscheidung fremdionenreicher Partikel. Sind die Ausscheidungen klein, so stellen sie Agglomerate von Fremdion-Kationleerstellen-Paaren dar. Es wird gezeigt, das die kritische Schubspannung τ0 solcher Proben dadurch bestimmt ist, das diese Partikel die Versetzungsbewegung behindern. Aus der Temperaturabhangigkeit von τ0 sowie aus seiner Abhangigkeit vom Fremdionengehalt werden quantitative Schlusse uber die mittlere Zahl zweiwertiger Kationen pro Ausscheidung gezogen. Es stellt sich heraus, das die kleinsten Agglomerate drei Fremdion-Kationleerstellen-Paare enthalten. Lediglich in NaCl:Ca2+ treten auch Doppelpaare auf. Andererseits enthalten die Ausscheidungen in langsam abgekuhltem LiF:Mg2+ einige hundert Mg2+-Ionen. Die Untersuchungen dieser Arbeit erlauben eine qualitative Deutung der Abschreckver- und -entfestigung, welche bei mit zweiwertigen Kationen dotierten Alkalihalogeniden auftreten. In alkali halides containing a sufficient amount of divalent cation impurities slow cooling leads to the precipitation of impurity-rich particles. If these precipitates are small, they consist of associated impurity-cation vacancy pairs. It is shown that the critical shear stress τ0 of such specimens is controlled by the impeding of the dislocation motion by these particles. The average number of divalent cations per precipitate is derived from the dependencies of τ0 on the deformation temperature and on the impurity content. It is concluded that the smallest aggregates consist of three impurity-cation vacancy pairs with the exception of NaCl:Ca2+ where double pairs appear to be stable, too. On the other hand, precipitates in slowly cooled LiF:Mg2+ contain some hundreds of Mg2+ ions. The investigations presented in this paper permit a qualitative understanding of the phenomena of quench-hardening and quench-softening in alkali halide crystals doped with divalent cations.

Zur Chemie cyclischer π‐Elektronensysteme, IV. Stabile Chinotropilidene

Abstract: Tropon reagiert mit Phosgen unter milden Bedingungen zu Chlortropyliumchlorid (6). Dessen Umsetzung mit Anthron fuhrt zum 10-Tropyliden-anthron (12). Als weiteres stabiles Chinotropiliden wurde das 2.6-Di-tert.-butyl-4-tropyliden-cyclohexadien-(2.5)-on-(1) (15) erhalten. Benzanellierte Chinotropilidene entstehen aus Benzotroponen und Anthron.

Aminobenzole, IV. N‐Persubstituierte 3.5‐Diamino‐phenole und 1.3.5‐Triamino‐benzole

Abstract: Die Synthese von 3.5-Bis-dialkylamino-phenolen 2 und 1.3.5-Tris-dialkylamino-benzolen 3 gelingt durch Erhitzen von Phloroglucin (1) mit sek. Aminen im Autoklaven. Die UV- und insbesondere die 1H-NMR-Spektren bestatigen die aus Mesomeriebetrachtungen und einfachen HMO-Berechnungen in der Literatur abgeleiteten besonderen elektronischen Verhaltnisse in diesen Verbindungen.

Hyperfine and Quadrupole Interactions of the F-Centre in KCl as Measured by ENDOR

Abstract: The isotropic and anisotropic hyperfine constants of the nuclei surrounding the F-centre in KCl were newly determined by electron nuclear double resonance (ENDOR) in a region within the distance of three lattice constants around the centre (up to nuclei 003). Quadrupole interactions of nuclei 002, 102, and 112 could be measured.

Synthesen in der heterocyclischen Reihe, XI. Synthesen von Pyrido[2.3‐d]‐ und Pyrimido[4.5‐d]pyrimidinen. Über eine Ketimin‐Enamin‐Tautomerie

Abstract: 4-Imino-1.3-dimethyl-5-methylaminomethylen-dihydrouracil (1) reagiert mit nucleophilen Agentien (Phenylhydrazin, Hydroxylamin und CH-aciden Verbindungen) an der CH-Gruppe am C-5 zu den 4-Imino-5-aminomethylen-Verbindungen 2, 3 bzw. unter Ringschlus zu Pyrido[2.3-d]pyrimidinen 4, 5, 6, und mit elektrophilen Agentien (Phenylisocyanat, Phenyl-senfol) zu Pyrimido[4.5-d]pyrimidinen 7, 8, — Bei vorsichtiger Benzoylierung von 1 entstehen zwei Tautomere 9a und 9b, die durch Umkristallisation ineinander ubergefuhrt werden konen. Mit uberschussigem Benzoylchlorid/Pyridin erfolgt in der Warme Ringschlus zum Pyrimido[4.5-d]pyrimidin 12.