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We describe methods for measuring crystal orientation fabric with sonic waves in an ice core borehole, with special attention paid to vertical-girdle fabrics that are prevalent at the WAIS Divide. The speed of vertically propagating compressional waves in ice is influenced by vertical clustering of the ice crystal c-axes. Shear-wave speeds – particularly the speed separation between fast and slow shear polarizations – are sensitive to azimuthal anisotropy. Sonic data from the WAIS Divide complement thin-section measurements of fabric. Thin sections show a steady transition to strong girdle fabrics in the upper 2000 m of ice, followed by a transition to vertical-pole fabrics below 2500 m depth. Compressional-wave sonic data are inconclusive in the upper ice, due to noise, as well as the method's inherent insensitivity to girdle fabrics. Compared with available thin sections, sonic data provide better resolution of the transition to pole fabrics below 2500 m, notably including an abrupt increase in vertical clustering near 3000 m. Our compressional-wave measurements resolve fabric changes occurring over depth ranges of a few meters that cannot be inferred from available thin sections, but are sensitive only to zenithal anisotropy. Future logging tools should be designed to measure shear waves in addition to compressional waves, especially for logging in regions where ice flow patterns favor the development of girdle fabrics.
In this chapter, we address the biophysical impacts of climate change, and the consequent impacts on socio-economic systems. Modelling the impacts associated with future climate change provides important information for society’s mitigation and adaptation responses. It also presents significant challenges for Earth system science. We discuss the ways in which uncertainty in impact modelling arises and how it can be managed.
Changes in climate, including those arising as a consequence of anthropogenic perturbations of the climate system, can result in a wide variety of impacts on Earth’s ecosystems and the human activities that depend on them. There are two good practical reasons why it is important to understand the processes involved and assess the possible magnitudes of impacts.
First, an assessment of the extent to which continued anthropogenic climate change could inflict damage is needed in order that well-informed decisions can be made about the reduction of human influences on climate. Our understanding of Earth system behaviour alerts us to the fact that action to mitigate climate change through reductions in greenhouse-gas emissions is not without consequences; so decisions to pursue mitigation options need to be weighed up on the basis of reliable estimates of the costs, risks and benefits of different courses of action.
Secondly, the increase in atmospheric greenhouse-gas concentrations since the Industrial Revolution means that further climate change is inevitable even if greenhouse-gas emissions were to be reduced soon ( Figure 6.1 ). It is therefore necessary for society to adapt to unavoidable changes. Since adaptation action is also not without consequences, it is important that adaptive action addresses credible risks , and represents an efficient allocation of resources.
The low temperature (ca. 300°C) deposition of antimony films by low-pressure chemical vapor deposition (LPCVD) on glass substrates from tribenzylantimony, Bn3Sb, is described. The facile elimination of the benzyl ligands results in preferentially oriented antimony films with low carbon content. The pyrolysis, decomposition mechanism and precursor design strategies are discussed. In addition, the deposition of bismuth from tribenzylbismuth, Bn3Bi, is presented. The potential for alloy growth using these precursors is discussed. Resulting films were characterized by XRD, SEM, and AFM.
While geochemical analysis of obsidian artifacts is now widely applied around the world, both new instrumental methods and new research questions continue to be applied in archaeology. In the Mediterranean, many analytical methods have been employed and proven successful in distinguishing all of the island sources. In this study, results are presented from the virtually non-destructive, LA-ICP-MS multi-element analysis of 95 carefully selected obsidian artifacts from four neolithic period sites in southwestern Sardinia. The patterns of exploitation of specific Monte Arci obsidian subsources revealed in this study support a down-the-line model of obsidian trade during the neolithic period, but with chronological changes that are best explained by increased socioeconomic complexity.
Glazes found on ancient Nubian quartzite sculpture were characterized in a previous study by scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS). Now in the collection of the Museum of Fine Arts, Boston, these objects were excavated in the early 20th century by the joint Harvard University-Boston Museum of Fine Arts Expedition, in ancient Kerma, the capital of ancient Kush. The project presented here attempts to recreate the ancient technology used to glaze quartzite with compositions determined in the previous study. Raw and fritted experimental glazes were prepared, as well as an alkali paste mixed with a copper colorant. All of the samples were fired in modern kilns. After firing, samples of the glazes and their quartzite substrates were examined with SEM/EDS.
In this paper we present a technique for designing planar parallel
manipulators with platforms capable of reaching any number of desired poses. The
manipulator consists of a platform connected to ground by RPR chains. The set of
positions and orientations available to the end-effector of a general RPR chain
is mapped into the space of planar quaternions to obtain a quadratic manifold.
The coefficients of this constraint manifold are functions of the
locations of the base and platform R joints and the distance between
them. Evaluating the constraint manifold at each desired pose and defining the
limits on the extension of the P joint yields a set of equations.
Solutions of these equations determine chains that contain the desired poses as
part of their workspaces. Parallel manipulators that can reach the prescribed
workspace are assembled from these chains. An example shows the determination of
three RPR chains that form a manipulator able to reach a prescribed
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