French Optical Telegraphy, 1793-1855: Hardware, Software, Administration

The relatively stable contribution of technological change to aggregate growth masks technological trajectories which are, at the sectoral level, often highly discontinuous. For decades, even centuries, the capabilities used to produce a particular good or service may continue essentially unchanged or with relatively minor evolutionary modifications. Sometimes without much warning a breakthrough innovation will create a new technological paradigm, along with an accompanying gale of creative destruction, which is then followed by a period of consolidation within a maturing framework

Gamma-ray spectrometry in the field: Radioactive heat production in the Central Slovakian Volcanic Zone

We report 62 sets of measurements from central-southern Slovakia, obtained using a modern portable gamma-ray spectrometer, which reveal the radioactive heat production in intrusive and extrusive igneous rocks of the Late Cenozoic Central Slovakian Volcanic Zone. Sites in granodiorite of the Štiavnica pluton are thus shown to have heat production in the range ~ 2.2–4.9 μW m− 3, this variability being primarily a reflection of variations in content of the trace element uranium. Sites in dioritic parts of this pluton have a lower, but overlapping, range of values, ~ 2.1–4.4 μW m− 3. Sites that have been interpreted in adjoining minor dioritic intrusions of similar age have heat production in the range ~ 1.4–3.3 μW m− 3. The main Štiavnica pluton has zoned composition, with potassium and uranium content and radioactive heat production typically increasing inward from its margins, reflecting variations observed in other granodioritic plutons elsewhere. It is indeed possible that the adjoining dioritic rocks, hitherto assigned to other minor intrusions of similar age, located around the periphery of the Štiavnica pluton, in reality provide further evidence for zonation of the same pluton. The vicinity of this pluton is associated with surface heat flow ~ 40 mW m− 2 above the regional background. On the basis of our heat production measurements, we thus infer that the pluton has a substantial vertical extent, our preferred estimate for the scale depth for its downward decrease in radioactive heat production being ~ 8 km. Nonetheless, this pluton lacks any significant negative Bouguer gravity anomaly. We attribute this to the effect of the surrounding volcanic caldera, filled with relatively low-density lavas, ‘masking’ the pluton's own gravity anomaly. We envisage that emplacement occurred when the pluton was much hotter, and thus of lower density, than at present, its continued uplift, evident from the local geomorphology, being the isostatic consequence of localized erosion. The heat production in this intrusion evidently plays a significant role, hitherto unrecognized, in the regional geothermics

Coding Theory and Algebraic Combinatorics

This chapter introduces and elaborates on the fruitful interplay of coding theory and algebraic combinatorics, with most of the focus on the interaction of codes with combinatorial designs, finite geometries, simple groups, sphere packings, kissing numbers, lattices, and association schemes. In particular, special interest is devoted to the relationship between codes and combinatorial designs. We describe and recapitulate important results in the development of the state of the art. In addition, we give illustrative examples and constructions, and highlight recent advances. Finally, we provide a collection of significant open problems and challenges concerning future research.Comment: 33 pages; handbook chapter, to appear in: "Selected Topics in Information and Coding Theory", ed. by I. Woungang et al., World Scientific, Singapore, 201

The late quaternary palaeoenvironments of a subalpine wetland in Cathedral Peak, KwaZulu-Natal Drakensberg.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.In contrast to the wealth of palaeoenvironmental research stemming from the eastern Afromontane archipelago, the southern Afromontane component, which comprises largely of the Drakensberg, remains understudied. The Drakensberg constitute an area of significant biodiversity, cultural and economic importance. Suitable sites for palaeoenvironmental research are rare in South Africa due to general arid climatic conditions over much of the country. The KwaZulu-Natal Drakensberg offers a unique opportunity for palaeoenvironmental research through its increased rainfall and higher altitudes, which enable the development of wetlands that have the potential for polliniferous accumulation to occur. Catchment Six in Cathedral Peak is one such wetland that has provided an opportunity to research palaeoenvironmental conditions of the southern Afromontane archipelago component. A 371 cm sediment core was extracted from a subalpine wetland in Catchment Six and analysed using multiple proxies including; pollen, charcoal and geochemistry (carbon and nitrogen stable isotopes). A chronological framework for the core was established based on accelerated mass spectrometry radiocarbon dating of eight bulk sediment samples. A basal date of 15,100 ± 445 cal yr BP was determined at a depth of 298 cm. Poor pollen preservation of the basal portion of the core limited palaeoenvironmental inference for the late Pleistocene section of the record. The multiproxy record provides high chronological resolution for the early to late Holocene. Multi-proxy data indicate that the Holocene period in the Drakensberg was characterised by variable climatic conditions. Charcoal data indicate periods of increased regional fires in the last ca. 400 cal yr BP. Palaeoenvironmental inferences from the Catchment Six record are broadly in agreement with regional climatic indications based on existing literature

Biodiversity, management and utilization of West African fishes

Biodiversity, Nature conservation, Fishery management, Fishery resources, Fish, WorldFish Center Contrib. No. 1718, Africa, west,

Hydrothermal Crystal Growth of Tetravalent and Pentavalent Metal Oxides

Over the past two hundred years synthetic growth of crystals has become vital to the technological advancement of our society. A variety of crystal growth techniques have been developed during this time, with each having its own nuances. These differences have enabled the growth of a wide spectrum of crystalline materials that can be used for many applications which include solid state lasers, semiconductors, and communication devices. Despite these techniques there are entire classes of materials which have thus far proved quite difficult to prepare as single crystals. In particular, crystal growth of the tetravalent and pentavalent metal oxides has been a great challenge due to their high melting points. The extreme temperatures (2000-3400oC) needed to melt many of these materials have proved difficult for the classical melt based techniques. This dissertation utilizes the hydrothermal technique to provide a low temperature synthesis alternative to access single crystals of the tetravalent and pentavalent metal oxides. The materials that were explored can be characterized into three categories which include applications in the fields of nonlinear optics, dielectrics, and refractory oxides. This study initially began with the growth of the nonlinear materials fresnoite, Ba2TiOSi2O7, and KNbO3. While not extremely high melting members of the tetravalent and pentavalent metal oxides, growth of these materials at relatively low temperatures established a sound basis to proceed with the exploration of the refractory oxides. These included the monoclinic and stabilized cubic form of ZrO2 and HfO2 as well as ThO2. It was quickly discovered that these materials required higher synthesis temperatures than previously employed in this lab. However after a redesign of the heating system, hydrothermal growth of these materials was achieved at 750oC, which is still relatively low compared to their synthesis by other techniques. The new temperature regime also enabled the exploration of the Group IV transition metal perovskites structures with their high melting points and exceptional dielectric properties. With successes in these areas, basic exploratory work of the tetravalent and pentavalent metals provided many novel structures of alkali thorium silicates and barium titanium tantalates. The formation of these novel materials and the crystallization of the refractory oxides in this work demonstrate the versatility of the hydrothermal technique