Semiconductor optical fibres: progress and opportunities

This paper reviews recent progress in the nascent field of semiconductor optical fibres, from the fundamentals through to device demonstration. The incorporation of semiconductor materials into both the step‐index and microstructured fibre geometries provides a route to introducing new optoelectronic functionality into existing glass fibre technologies. Herein, the various fabrication methods that have been developed as of to date are described, and their compatibility with the different semiconductor materials and fibre designs discussed. Results will be presented on the optical transmission properties of several fibre types, with particular attention being paid to the observation of nonlinear propagation in silicon core fibres. Finally, some speculation regarding the future prospects and applications of this new class of fibre will be provided.     

Application of NMR Spectroscopy and Imaging in Heterogeneous Biocatalysis

Heterogeneously catalyzed enzymatic glucose isomerization was considered as a model process to extend the application of nuclear magnetic resonance (NMR) and magnetic resonance imaging techniques to the studies of biocatalytic processes and heterogeneous biocatalysts. It has been demonstrated that the T ₂ times of glucose are different for its aqueous solution in the pores of an unmodified porous support and in a heterogeneous biocatalyst, comprising bacterial cells immobilized on the same support. This observation has been used to map the spatial distribution of the active component within a packed bed of biocatalyst in a model reactor. ¹³C NMR spectroscopy was applied to follow the progress of glucose isomerization catalyzed by the heterogeneous biocatalyst in a batch reactor. The utilization of proton spin decoupling and nuclear Overhauser effect was shown to be necessary to obtain high signal-to-noise ratio in the natural abundance ¹³C NMR spectra of a glucose–fructose syrup present in the packed bed of biocatalyst. The spectra thus obtained were suitable for the quantification of the glucose-to-fructose ratio achieved in the biocatalytic reaction.     

Action Spectroscopy on Dense Samples of Photosynthetic Reaction Centers of Rhodobacter sphaeroides WT Based on Nanosecond Laser-Flash 13C Photo-CIDNP MAS NMR

Photochemically induced dynamic nuclear polarization magic-angle spinning nuclear magnetic resonance (photo-CIDNP MAS NMR) allows for the investigation of the electronic structure of the photochemical machinery of photosynthetic reaction centers (RCs) at atomic resolution. For such experiments, either continuous radiation from white xenon lamps or green laser pulses are applied to optically dense samples. In order to explore their optical properties, optically thick samples of isolated and quinone-removed RCs of the purple bacteria of Rhodobacter sphaeroides wild type are studied by nanosecond laser-flash ¹³C photo-CIDNP MAS NMR using excitation wavelengths between 720 and 940 nm. Action spectra of both the transient nuclear polarization as well as the nuclear hyperpolarization, remaining in the electronic ground state at the end of the photocycle, are obtained. It is shown that the signal intensity is limited by the amount of accessible RCs and that the different mechanisms of the photo-CIDNP production rely on the same photophysical origin, which is the photocycle induced by one single photon.     

AgGaS2- and Al-doped GaSe Crystals for IR Applications

We report a systematic study of AgGaS₂- and Al-doped GaSe crystals in comparison with pure GaSe and S-doped GaSe crystals. AgGaS₂-doped GaSe (GaSe:AgGaS₂) crystal was grown by Bridgman technique from the melt of GaSe:AgGaS₂ (10.6 wt.%). Its real composition was identified as GaSe:S (2 wt.%). Al-doped GaSe (GaSe:Al) crystals were grown from the melt of GaSe and 0.01, 0.05, 0.1, 0.5, 1, 2 mass % of aluminium. Al content in the grown crystals is too small to be measured. The hardness of GaSe:S (2 wt.%) crystal grown from the melt of GaSe:AgGaS₂ is 25% higher than that of GaSe:S (2 wt.%) crystal grown by a conventional S-doping technique and 1.5- to 1.9-times higher than that of pure GaSe. GaSe:Al crystals are characterized by 2.5- to 3-times higher hardness than that of pure GaSe and by extremely low conductivity of ≤ 10^− 7 Om^− 1 cm^− 1. A comparative experiment on SHG in AgGaS₂-, Al-, S-doped GaSe and pure GaSe is carried out under the pumps of 2.12-2.9 μm fs OPA and 9.2−10.8 μm ns CO₂ laser. It was found that GaSe:S crystals possess the best physical properties for mid-IR applications among these doped GaSe crystals. GaSe:Al crystals have relatively low conductivity which have strong potential for THz application.     

Versuche mit markierten Atomen über den Mechanismus der Vermehrung von Tabakmosaikvirus in Nicotiana tabacum

Zusammenfassung Tabakmosaikvirus hoher spezifischer Aktivität, das am Phosphor und/oder Kohlenstoff markiert war, wurde biosynthetisch hergestellt. Damit wurde jeweils ein Blatt einer Pflanze von Nicotiana tabacum infiziert und der etwaige Transport von intaktem Virus durch das Leitungssystem der Pflanzen dadurch weitgehend unterbunden, daß die Leitgefäße des behandelten Blattes durchtrennt wurden.Das aus den unbehandelten Blättern der Pflanze nach 17 1/2, 48 und 72 Stdn. isolierte Virus wies im Vergleich zum eingesetzten TMV einen viel geringeren Anteil an Gesamtradiokohlenstoff im Protein auf. Dies deutet darauf hin, daß das Virus der unbehandelten Blätter höchstens zu einem sehr geringen Teil aus intakt transportiertem TMV bestehen könnte.Die nicht im TMV enthaltenen Polynukleotide der unbehandelten Blätter enthalten 7 Stdn. nach der Infektion verhältnismäßig viel³²P, doch tritt derselbe innerhalb 70 Stdn. zum allergrößten Teil in niedermolekulare Verbindungen über.Die in Puffer unlöslichen Polynukleotide der unbehandelten Blätter (Blattnukleinsäure) weisen ein mit der Zeit abnehmendes Verhältnis von³²P/¹⁴C auf. Auch innerhalb der Nukleinsäure (NS) des TMV dieser Blätter nimmt dieses Verhältnis zunächst ab, steigt aber später wieder an.Die angeführten Ergebnisse stehen mit der Vorstellung im Einklang, daß das Virus NS abspaltet und sowohl die systemische Infektion der Pflanze wie auch die Virusvermehrung mindestens zum Teil durch diese freie NS bewirkt wird. Die aus dem Virus stammende freie NS unterliegt zum großen Teil lebhaftem Abbau, wobei ihre Komponenten wahrscheinlich dem Aufbau normaler Blattbestandteile dienen.Mit 3 Abbildungen     

Canonical connections with an algebraic curvature tensor field on naturally reductive spaces

We study Ambrose-Singer connections with an algebraic curvature tensor on simply connected manifolds carrying a homogeneous Riemannian structure of class ₃ in the classification given by F. Tricerri and L. Vanhecke.This work was partially supported by MURST.     

Besov-Morrey spaces: Function space theory and applications to non-linear PDE

This paper is devoted to the analysis of function spaces modeled on Besov spaces and their applications to non-linear partial differential equations, with emphasis on the incompressible, isotropic Navier-Stokes system and semi-linear heat equations. Specifically, we consider the class, introduced by Hideo Kozono and Masao Yamazaki, of Besov spaces based on Morrey spaces, which we call Besov-Morrey or BM spaces. We obtain equivalent representations in terms of the Weierstrass semigroup and wavelets, and various embeddings in classical spaces. We then establish pseudo-differential and para-differential estimates. Our results cover non-regular and exotic symbols. Although the heat semigroup is not strongly continuous on Morrey spaces, we show that its action defines an equivalent norm. In particular, homogeneous BM spaces belong to a larger class constructed by Grzegorz Karch to analyze scaling in parabolic equations. We compare Karch's results with those of Kozono and Yamazaki and generalize them by obtaining short-time existence and uniqueness of solutions for arbitrary data with subcritical regularity. We exploit pseudo-differential calculus to extend the analysis to compact, smooth, boundaryless, Riemannian manifolds. BM spaces are defined by means of partitions of unity and coordinate patches, and intrinsically in terms of functions of the Laplace operator.

     

A priori bounds in weighted spaces

In unbounded domains we state some a priori bounds for solutions of the Dirichlet problem for linear second order elliptic differential equations in nondivergence form with discontinuous coefficients in weighted spaces. The weight function is related to the distance function from a fixed subset S of ∂Ω.     

Collision Avoidance in Bi-Directional AGV Systems

The use of a bi-directional, as opposed to a one-way, transportation system, can increase the operational efficiency of automated guided vehicles in both manufacturing and warehousing environments. However, the full potential will only be realized if the routeing algorithms pay particular attention to the problem of collision avoidance. This paper is concerned with the development of such an algorithm. The method is based on the use of delays and deviations to avoid collisions that could arise when using the shortest routes for each vehicle, and is applicable to any transportation system which can be represented as a network with known travel times.