I Going Away. I Going Home. : Austin Clarke\u27s Leaving this Island Place

Austin Clarke’s “Leaving This Island Place” is one of scores of Caribbean autobiographical works that focus on a bright, young, lower-class islander leaving his/her small island place and setting out on “Eldorado voyages.” The narrative of that journey away from home to Europe or Canada or the United States and the later efforts to return may be said to be the Caribbean story, as suggested in the subtitle of Wilfred Cartey’s study of Caribbean literature, Whispers from the Caribbean: I Going Away, I Going Home, which argues that while in Caribbean literature there is much movement away, there is also a body of literature in which “the notion of ‘away’ and images of movement out are replaced by images of return” (xvi). Traditionally, however, the first autobiographical works, such as George Lamming’s In the Castle of My Skin, V. S. Naipaul’s A House for Mr. Biswas, Merle Hodge’s Crick Crack, Monkey, Jamaica Kincaid’s Annie John, Michelle Cliff’s No Telephone to Heaven, Edwidge Danticat’s Breath, Eyes, Memory, and Elizabeth Nunez’s Beyond the Limbo Silence, have focused on the childhood in the Caribbean and the journey away—or at least the preparation for that journey. Such is the case with Clarke’s “Leaving This Island Place.

Mantle Pb paradoxes : the sulfide solution

Author Posting. © Springer, 2006. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Contributions to Mineralogy and Petrology 152 (2006): 295-308, doi:10.1007/s00410-006-0108-1.There is growing evidence that the budget of Pb in mantle peridotites is largely contained in sulfide, and that Pb partitions strongly into sulfide relative to silicate melt. In addition, there is evidence to suggest that diffusion rates of Pb in sulfide (solid or melt) are very fast. Given the possibility that sulfide melt ‘wets’ sub-solidus mantle silicates, and has very low viscosity, the implications for Pb behavior during mantle melting are profound. There is only sparse experimental data relating to Pb partitioning between sulfide and silicate, and no data on Pb diffusion rates in sulfides. A full understanding of Pb behavior in sulfide may hold the key to several long-standing and important Pb paradoxes and enigmas. The classical Pb isotope paradox arises from the fact that all known mantle reservoirs lie to the right of the Geochron, with no consensus as to the identity of the “balancing” reservoir. We propose that long-term segregation of sulfide (containing Pb) to the core may resolve this paradox. Another Pb paradox arises from the fact that the Ce/Pb ratio of both OIB and MORB is greater than bulk earth, and constant at a value of 25. The constancy of this “canonical ratio” implies similar partition coefficients for Ce and Pb during magmatic processes (Hofmann et al. 1986), whereas most experimental studies show that Pb is more incompatible in silicates than Ce. Retention of Pb in residual mantle sulfide during melting has the potential to bring the bulk partitioning of Ce into equality with Pb if the sulfide melt/silicate melt partition coefficient for Pb has a value of ~ 14. Modeling shows that the Ce/Pb (or Nd/Pb) of such melts will still accurately reflect that of the source, thus enforcing the paradox that OIB and MORB mantles have markedly higher Ce/Pb (and Nd/Pb) than the bulk silicate earth. This implies large deficiencies of Pb in the mantle sources for these basalts. Sulfide may play other important roles during magmagenesis: 1). advective/diffusive sulfide networks may form potent metasomatic agents (in both introducing and obliterating Pb isotopic heterogeneities in the mantle); 2). silicate melt networks may easily exchange Pb with ambient mantle sulfides (by diffusion or assimilation), thus ‘sampling’ Pb in isotopically heterogeneous mantle domains differently from the silicate-controlled isotope tracer systems (Sr, Nd, Hf), with an apparent ‘de-coupling’ of these systems.Our intemperance should not be blamed on the support we gratefully acknowledge from NSF: EAR- 0125917 to SRH and OCE-0118198 to GAG

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

Chlorine and sulfur are of paramount importance for supporting the transport and deposition of ore metals at magmatic–hydrothermal systems such as the Coroccohuayco Fe–Cu–Au porphyry–skarn deposit, Peru. Here, we used recent partitioning models to determine the Cl and S concentration of the melts from the Coroccohuayco magmatic suite using apatite and amphibole chemical analyses. The pre-mineralization gabbrodiorite complex hosts S-poor apatite, while the syn- and post-ore dacitic porphyries host S-rich apatite. Our apatite data on the Coroccohuayco magmatic suite are consistent with an increasing oxygen fugacity (from the gabbrodiorite complex to the porphyries) causing the dominant sulfur species to shift from S2− to S6+ at upper crustal pressure where the magmas were emplaced. We suggest that this change in sulfur speciation could have favored S degassing, rather than its sequestration in magmatic sulfides. Using available partitioning models for apatite from the porphyries, pre-degassing S melt concentration was 20–200 ppm. Estimates of absolute magmatic Cl concentrations using amphibole and apatite gave highly contrasting results. Cl melt concentrations obtained from apatite (0.60 wt% for the gabbrodiorite complex; 0.2–0.3 wt% for the porphyries) seems much more reasonable than those obtained from amphibole which are very low (0.37 wt% for the gabbrodiorite complex; 0.10 wt% for the porphyries). In turn, relative variations of the Cl melt concentrations obtained from amphibole during magma cooling are compatible with previous petrological constraints on the Coroccohuayco magmatic suite. This confirms that the gabbrodioritic magma was initially fluid undersaturated upon emplacement, and that magmatic fluid exsolution of the gabbrodiorite and the pluton rooting the porphyry stocks and dikes were emplaced and degassed at 100–200 MPa. Finally, mass balance constraints on S, Cu and Cl were used to estimate the minimum volume of magma required to form the Coroccohuayco deposit. These three estimates are remarkably consistent among each other (ca. 100 km3) and suggest that the Cl melt concentration is at least as critical as that of Cu and S to form an economic mineralization

Control Of Flexible Load Deformations And Environment Contact Forces In Dual-Arm Manipulation

. A pseudo-inverse-Jacobian scheme to control deformations of a flexible load while attaining contact force goals with an external environment is discussed in this paper. The flexible load is manipulated by two arms. A kinematic description of the flexible load is obtained from a lumped-parameter model. Coordinated motion of the arms is achieved through kinematic redundancy resolution at the differential kinematic level. The strategy proposed here uses load flexibility to accommodate for position errors that would result in the build-up of internal forces in a rigid-load case. Simulation results are presented that illustrate the success of the method. Keywords. multiple-arm coordination; flexible materials; redundancy resolution; differential inverse kinematics. 1. INTRODUCTION A variety of assembly operations involve the manipulation of flexible parts. Sometimes, demanding operations like part mating of flexible componenents are required. For part mating to take place, it might be de..

Modelling and Control of Interaction Forces in Nonlinear-Stiffness Types of Contact

This paper analyses a force control scheme used for interactions between a manipulator and a nonlinearly stiff environment. Initially, a nonlinear model for the contact stiffness is developed, and the idea of using an accommodation law in controlling force is introduced. Accommodation is the inverse of damping, and corresponds to a force input/velocity output mapping. The stability of the scheme is analysed using the second method of Lyapunov. The analysis is new since it takes into account the variation in stiffness caused by changes in the deformation of the load (or environment). The results are applicable to many types of contact that can be described by nonlinear stiffness models. Such models are more general than the linear ones which have been the base for the results available in the literature. 1 Introduction This paper presents stability proofs for a taskspace accommodation force controller in the presence of environments with non-linear stiffness properties. The motivation ..

Controlling Dual-Arm Manipulation of Flexible Loads in Surface-Following Tasks

The control of a dual-arm robotic system in a manipulation task involving a flexible load is considered in this paper. The task consists of following an environment surface without loss of contact. In contrast to other schemes for control of environment interaction, the method used here is purely kinematic, taking advantage of load flexibility for keeping contact with the surface. A kinematic description of the load is obtained from a lumped-parameter model. The control scheme adopted uses the pseudoinverse of the Jacobian from the tip of the load to the generalized coordinates that describe the system. The main issue with the control strategy is the use of configuration redundancy to accomplish task requirements. A method for translating task requirements into control specifications is presented, which extends existing results in pseudo-inversion techniques to constrained robotic systems. 1 Introduction There are many tasks in industrial manufacturing processes for which a single robo..

Minimum-Time Control For The Transport Of Flexible Loads By Two Manipulators

The minimum-time pointwise motion of two manipulators grasping the same flexible object is examined in this paper. We model the object as a spring with an associated damping factor. The coordinated motion is accomplished through the specification of the trajectory for the mid-point between the two manipulators. The separate trajectories for each manipulator are not relevant per se, since they only need to preserve the desired motion of the mid-point. This freedom in the motion together with the presence of the flexible material causes the minimum time to be less than the minimum time required to move two manipulators with a rigid link between them. This result shows the advantage of exploiting the flexibility of the material being worked by two manipulators. Keywords: Multirobot systems; flexible materials; minimum-time trajectory planning and control; linear systems. 1 Introduction Flexibility is normally seen as a complicating factor in robotics. The amount of literature dedicated ..

Force Fields in the Manipulation of Flexible Materials

Assembly operations that involve flexible parts differ greatly from rigid-part assembly due to the capacity of the parts to comply with motions of the manipulators by yielding to the contact forces. This natural compliance can be exploited in the design of tasks involving the manipulation of flexible loads. Namely, using knowledge about the force vector field generated by conservative restoring forces of the load, a trajectory for the manipulator end-effector can be specified. The idea is illustrated through two case studies: an analysis of the problem of bending a flexible sheet, and experiments on an insertion task where a flexible beam has to be inserted in a hole with friction in the direction of insertion. 1 Introduction Robotic manipulation of flexible loads has only recently become part of the robotics literature, despite the fact that there are many industrial tasks that involve the assembly of flexible parts. Examples of such tasks include the plastic or rubber molding of car..

Case Studies in the Manipulation of Flexible Parts Using a Hybrid Position/Force Approach

A unified method for the planning and control of tasks involving flexible parts is applied to two case studies: the bending of sheet metal and the insertion of a beam into a hole with friction. The method is formulated on a hybrid position/force framework so as to exploit the advantages brought about by load elasticity. The unifying design guideline is the maintainance of deformations on the load so that a region of reduced stiffness is presented to the force controller. The main focus of this paper is the experimental results obtained from the implementation of the tasks. 1 Introduction Many industrial processes involve the manipulation of flexible parts. Some examples include the assembly of car bodies, bending of sheet metal, manipulation of large metalic structures in space, and molding of car interiors. The importance of such industrial applications has turned the robotic manipulation of flexible loads into an active part of the robotics literature. The objective of this paper is..