The Urban and Historical Geography of Kirkwall and Stromness, Orkney

Settlements which have developed over a long period of time inevitably reflect the environmental and historical factors which have shaped their physical and socio-economic identity. It is the purpose of this thesis to trace the influence of such factors on the development of Kirkwall and Stromness and, in addition, to examine the elements of townscape which, in view of possible economic changes within the island group, may require careful consideration if the unusual character of these burghs is not to be lost by ill-considered development. Although lying only 8 miles from the north coast of Scotland, the Orkney Islands came under Norse influence during the earliest period of major settlement. The earldom which was created in the ninth century brought about the rationalisation of agricultural holdings throughout the isles and the foundation of an administrative capital adjacent to a sheltered lagoon towards the centre of the Orkney Mainland. Under successive earls Kirkwall developed in two distinct sections : the earl's town, a development of the shoreside fishing settlement, and the Laverock or bishop's town to the south around St. Magnus Cathedral and the Bishop's Palace. With impignoration of the islands in 1468 the Norse culture was superseded by that of the Scots. By a series of charters King James III gained control of both earldom and bishopric properties and in 1486 established Kirkwall as a royal burgh. Fluctuations in the power of the Scottish earls and bishops affected the development of the Orcadian capital and produced repercussions throughout the landward areas and islands. Further burgh expansion occurred, however, during the following two centuries ; the diversification of the economy attracting immigrants from the outlying islands - a trend that continues at the present time. Improvements in land and sea communications increased Kirkwall's sphere of influence and encouraged both a consolidation of the administrative function of the burgh and the development of service industries. With such socio-economic changes residential development was forced into the surrounding farm land while the former dwellings of merchant lairds and ecclesiastics along the main street were converted to commercial premises. In contrast no urban development had occurred around Hamna Voe in the West Mainland prior to 1590. However, in the early years of the following century a few artisans seised plots of land from the bishopric on the steeply sloping ground to the west of the bay, and the trading settlement of Stromness became established. During the eighteenth and nineteenth centuries the economy flourished as a result of contacts with the 'New World' via the rice trade, the whaling ships and the Hudson's Bay Company. The increase in wealth in the community in turn attracted a considerable number of immigrants particularly from Northern Scotland and the South Isles, the maximum population being reached in 1821. Following the decline in overseas trading the economy became oriented towards home-based industry such as spinning, straw-plaiting, boat-building and fishing. The characteristic townscape of the settlement developed during this period : shore-line dwellings being constructed with their long axis to the sea, partially on individual stone wharves to maximise the use of building land and access to the harbour. During the present century many changes have been wrought both in the socio-economic structure and the townscape of the two burghs. The functions of Kirkwall and Stromness tend, at the present time, to be complementary and reflect local and National Government policies for development of what are essentially rural areas. However, economic expansion associated with the North Sea oil exploration is imminent - an expansion which may rapidly obliterate the historical character of both the burghs and submerge the Orcadian identity. It is obvious that the historical factors, mentioned in the thesis, have at various times had a considerable effect on the development of both burghs. Yet detailed studies of the present state, and particularly the townscape elements, of Kirkwall and Stromness indicate that the character of the settlements is the result not only of the periods of economic expansion but also those of economic and social decline. For this reason it is necessary to trace the influence of each factor and show how the possibly detrimental effects of further economic growth and urban renewal may be limited so that the character of the Orcadian burghs may be retained for future generations

Annealing-induced reduction in nanoscale heterogeneity of thermally evaporated amorphous As2S3 films

The morphology and structural order of thermally deposited and annealed amorphous As2S3 films have been investigated using high resolution transmission electron microscopy. It was found that both the as-deposited and annealed films contained sparsely distributed nanocrystallites of the orpiment As2S3 crystalline phase. However, from selected area electron diffraction both films appeared amorphous. Fluctuation electron microscopy revealed that the as-deposited film contained greater nanoscale inhomogeneity. Low temperature annealing reduced the nanoscale inhomogeneity and resulted in a more homogeneous and energetically favorable network. The reduction in nanoscale inhomogeneity upon low temperature annealing was accompanied by the appearance of a first sharp diffraction peak in the diffraction pattern. This first-sharp diffraction peak has been attributed to chemical ordering of interstitial voids. Our measurements suggest that this chemical short-range ordering is associated with the dissolution of the energetically unfavorable larger correlated structures that contribute to the inhomogeneity of the as-deposited film

Low loss high index contrast nanoimprinted polysiloxane waveguides

Nanoimprint lithography is gaining rapid acceptance in fields as diverse as microelectronics and microfluidics due to its simplicity high resolution and low cost. These properties are critically important for the fabrication of photonic devices, where cost is often the major inhibiting deployment factor for high volume applications. We report here on the use of nanoimprint technology to fabricate low loss broadband high index contrast waveguides in a Polysiloxane polymer system for the first time

Laser-induced microexplosion confined in a bulk of silica: formation of nanovoids

We report on the nanovoid formation inside synthetic silica, viosil, by single femtosecond pulses of 30–100nJ energy, 800nm wavelength, and 180fs duration. It is demonstrated that the void is formed as a result of shock and rarefaction waves at pulse power much lower than the threshold of self-focusing. The shock-compressed region around the nanovoid is demonstrated to have higher chemical reactivity. This was used to reveal the extent of the shock-compressed region by wet etching. Application potential of nanostructuring of dielectrics is discussed

Raman spectra of GexAsySe1−x−y glasses

Various Ge–As–Se glasses spanning a mean coordination number (MCN) from 2.2 to 2.94 have been investigated using differential scanning calorimetry and Raman spectroscopy. The glass transition temperature Tg was found to increase with increasing MCN, except for those glasses located within the nanoscale phase-separated region of the phase diagram. The evolution of Raman features at wavenumbers from 150 to 350 cm⁻¹ exhibits two transitionlike features. Merging of the 225 and 250 cm⁻¹ modes at MCN=2.5 is a symbol of the extinction of Se–Se bonds. Additionally, the appearance of two modes at 280–290 and 170 cm⁻¹ at MCN>2.7 come from the defect modes of ethanelike Ge₂Se₆/₂. The increase in the scattering from these defects is an important factor leading to enhanced optical loss in the glasses with high MCN.This research was partly supported by the Australian Research Council through its Centres of Excellence and Federation Fellow Programs

Thermal annealing of arsenic tri-sulphide thin film and its influence on device performance

Arsenic tri-sulphide (As₂S₃)thin filmwaveguides have been used successfully as nonlinear optical devices for all-optical signal processors. For such devices, low propagation loss is vital if high performance is to be obtained. In this study, thermal annealing was employed not only to stabilize the physical properties of the films, but also to reduce the sources of light attenuation in the as-deposited material. Here we investigated heat-induced changes to the microstructure and optical properties of As₂S₃thin films and, based on this information, determined the best annealing conditions. The refractive index of the films rises with annealing due to thermal densification and increased heteropolar bond density. The growth of surface roughness and thermal stress in the film, however, limits the annealing temperature to ∼130 °C. We fabricated and analyzed waveguides produced from as-deposited and annealedfilms and found that the propagation loss of the guides dropped by ∼0.2 dB/cm as a result of appropriate annealing.Rayleigh scattering and absorption from defects associated with phase separation, homopolar bonds, voids, and dangling bonds in the as-deposited film are shown to contribute to the higher light attenuation in unannealed films.This research was supported by the Australian Research Council through its Centre of Excellence program

Hydrogen contamination in Ge-doped SiO[sub 2] thin films prepared by helicon activated reactive evaporation

Germanium-doped silicon oxidethin films were deposited at low temperature by using an improved helicon plasma assisted reactive evaporation technique. The origins of hydrogen contamination in the film were investigated, and were found to be H incorporation during deposition and postdeposition water absorption. The H incorporation during deposition was avoided by using an effective method to eliminate the residual hydrogen present in the depositionsystem. The microstructure, chemical bonds, chemical etch rate, and optical index of the films were studied as a function of the deposition conditions. Granular microstructures were observed in low-density films, and were found to be the cause of postdeposition water absorption. The granular microstructure was eliminated and the film was densified by increasing the helicon plasma power and substrate bias during deposition. A high-density film was shown to have no postdeposition water absorption and no OH detected by using a Fourier-transform infrared spectrometer

Birth and decay of coherent optical phonons in femtosecond-laser-excited bismuth

The transient reflectivity of bismuth crystal excited by a 45 fs laser pulse in the near-infrared range has been recovered with an accuracy of 10-5, at initial sample temperatures ranging from 50 to 510 K, and at pump fluences from 2 mJ/ cm2 to 21 mJ/ cm2. The coherent phonon excitation and decay processes were imprinted into the time-dependent reflectivity and this allows us to uncover the temporal phonon history preceding the structural transformation of solid Bi. Analysis showed that the first coherent atomic displacement was produced by the polarization force and the electron pressure force during the laser pulse, and that manifests itself by a negative change in the reflectivity. The frequency of the subsequent reflectivity oscillations was chirped, redshifted from the initial value due to the lattice heating. The amplitude decreased gradually while electrons transferred their energy to the lattice. Heating and thermal expansion of the lattice transformed the initially coherent harmonic vibrations of atoms into strongly nonlinear chaotic motion that signifies the onset of disordering of the solid. This process was identified through measurement of the damping rate of the reflectivity oscillations and interpretation of this rate as the decay rate of an optical phonon into two acoustic phonons. The analysis of the reflectivity oscillations provides evidence that the overheated solid experiences only the onset of the solid-liquid phase transition but did not proceed into the liquid phase. General relations between the laser-exerted forces, the atomic motion, and the optical parameters were established. The proposed theory reproduces well the measured transient reflectivity across a wide range of crystal temperatures and laser excitation fluences

High-Q (>750,000) photonic crystal nanocavities fabricated from chalcogenide glass fully embedded in an index-matched cladding

We have fabricated a Ge11.5As24Se64.5 2-D photonic crystal containing a hetero-structure cavity fully embedded in a cladding with index of 1.44. Because of the low index contrast of this structure (≈1.2) we had to use a W0.54 defect waveguide to inhibi