Advanced Concepts for Automatic Differentiation based on Operator Overloading

Mit Hilfe der Technik des Automatischen Differenzierens (AD) lassen sich für Funktionen, die als Programmquellcode gegeben sind, Ableitungsinformationen rechentechnisch effizient und mit geringem Aufwand für den Nutzer bereitstellen. Eine Variante der Implementierung von AD basiert auf der Überladung von Operatoren und Funktionen, die von vielen modernen Programmiersprachen ermöglicht wird. Durch Ausnutzung des Konzepts der Überladung wird eine interne Funktions-Repräsentation (Tape) generiert, die anschließend für die Ableitungsberechnung herangezogen wird. In der Dissertation werden neue Techniken erarbeitet, die eine effizientere Tape-Erstellung und die parallele Tape-Auswertung ermöglichen. Anhand von Laufzeituntersuchungen für numerische Beispiele werden die Möglichkeiten der neuen Techniken verdeutlicht.Using the technique of Automatic Differentiation (AD), derivative information can be computed efficiently for any function that is given as source code in a supported programming languages. One basic implementation strategy is based on the concept of operator overloading that is available for many programming languages. Due the overloading of operators, an internal representation of the function can be generated at runtime. This so-called tape can then be used for computing derivatives. In the thesis, new techniques are introduced that allow a more efficient tape creation and the parallel evaluation of tapes. Advantages of the new techniques are demonstrated by means of runtime analyses for numerical examples

Antenna radiation in the presence of a chiral sphere

The radiation emitted by electromagnetic sources placed both inside and outside of a homogeneous sphere of chiral media is studied using an exact formulation. For both cases, dyadic Green’s functions are found in terms of spherical vector wave functions. The radiated fields and radiation resistance are examined for a dipole located at the center of the chiral sphere. For this case, it is shown that by choosing the sphere’s size and material parameters properly, purely circular polarization can be achieved in the far field. It is also demonstrated that the radiation resistance of the dipole can be increased

Electromagnetic Waves in Faraday Chiral Media

Plane wave propagation in two kinds of Faraday chiral media, where Faraday rotation is combined with optical activity, is studied to examine methods of controlling chirality. The two types of media studied are magnetically biased chiroplasmas and chiroferrites. For propagation along the biasing magnetic field, four wavenumbers and two wave impedances are found which are dependent on the strength of the biasing field. Dispersion diagrams for the chiroplasma case are plotted. Propagation at the plasma frequency of the chiroplasma is also investigated

Surface wave generation and propagation on metallic subwavelength structures measured by far-field interferometry

Transmission spectra of metallic films or membranes perforated by arrays of subwavelength slits or holes have been widely interpreted as resonance absorption by surface plasmon polaritons (SPPs). Alternative interpretations involving evanescent waves diffracted on the surface have also been proposed. These two approaches lead to divergent predictions for some surface wave properties. Using far-field interferometry, we have carried out a series of measurements on elementary one-dimensional (1-D) subwavelength structures with the aim of testing key properties of the surface waves and comparing them to predictions of these two points of view

Flo8 – A versatile regulator for improving recombinant protein production in Pichia pastoris

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Periodic Chiral Structures

The electromagnetic properties of a structure that is both chiral and periodic are investigated using coupled-mode equations. The chirality is characterized by the constitutive relations D = εE + iXicB and H = iXicE+B/µ, where Xic is the chiral admittance. The periodicity is described by a sinusoidal perturbation of the permittivity, permeability and chiral admittance. The coupled-mode equations are derived from physical considerations. The coupled-mode equations are used to examine bandgap structure and reflected and transmitted fields. Chirality is observed predominantly in transmission while periodicity is present in both reflection and transmission

Late Quaternary vegetation history of central North Island, New Zealand

23 sites in the central North Island of Otiran and Aranuian age (Last Glaciation and post-glacial) were pollen analysed. Three regions were examined in detail: Taranaki, Taupo-Tongariro and Bay of Plenty. For most of the Otiran period (c. 70 000 BP-14 000 BP) the central North Island was covered with scrub-grassland communities. Forest was scarce and scattered. Within this period two major interstadials are recognized. During an early Otiran interstadial, which reached its maximum at about an estimated 60 000 BP, both podocarp-hardwood forest and Nothofagus forest were abundant. Although perhaps 2°C cooler than present, the climate seems to have been mild and moist during this period. A second interstadial lasted from about 45 000 BP to 25 000 BP. It was a time of diverse vegetation and climates. Although scrub was the dominant vegetation over most of the region, there were substantial areas of podocarp-hardwood forest, Nothofagus forest and also some grassland. In some localities it appears that all these vegetation types co-existed. Forest was most abundant from 32 - 27 000 BP. The climate was considerably cooler than that of today with mean annual temperatures up to 4°C lower. Rainfall was lower than at present, but still adequate for podocarp forest growth in some regions. From after 25 000 BP until 14 000 BP grassland/scrubland associations were almost totally dominant. Some forest survived throughout this period, but mainly in hilly and mountainous regions. The grassland/scrubland associations appear to have been very uniform throughout, and there is no evidence for better developed vegetation in the northern regions. The climate was much cooler than today, perhaps 5°C cooler but, more importantly, appears to have been harsh and variable. Rainfall was much lower than at present, especially in the east. In Taranaki, forest dominated by podocarpus spicatus replaced grassland between 13 000 and 12 000 BP. At about 10 000 BP Dacrydium cupressinum and Ascarina lucida became abundant and remained so until about 5000 BP. After this date Ascarina declined while Knightia excels and Dacrydium colensoi spread. After 3000 BP D. colensoi became scarce and today is no longer found in the region. In Hawkes Bay Podocarpus spicatus/totara forest replaced the previous grass and scrub communities by 10 000 BP, but probably not much earlier. These forests remained dominant with only minor changes until the Polynesian burnings of the last millenium. The early Aranuian (14 000 - 10 000 BP) was drier than present, but rainfall was adequate to support podocarp forest in most places, except the drier east coast districts. Increase in rainfall, rather than the well-attested Aranuian warming, was the main reason for the spread of forest. The period from 10 000 BP to 5000 BP was the mildest and wettest of the last 70 000 years. Since 5000 BP there has been a drift to a cooler, droughtier climate