Rubber Indusrty of West Africa

The rubber industry began in West Africa by native exploitation of the wild rubber sources found in the tropical rain forests. The best quality of rubber was obtained from the tree, Funtumia elastica Stapf. and the vines Landolphia ovariensis Beauv. and Clitandra cymulosa Benth. The tapping methods were usually destructive and eventually new areas were difficult to find. As plantations of Manihot glaziovii Muell. Arg., the para rubber tree, and Hevea brasiliensis (H. B. K.) Muell. Arg., the para rubber tree, were established the wild rubber became less important. The yields from Manihot proved to be much lower than Hevea and the latter became the only important plantation rubber tree in West Africa. The discovery of rubber and the interesting story of how the rubber tree finally reached Africa is worth reviewing

Nitrogen and Potassium Interact to Shape a Yield Response Surface

In a field experiment with banana, fertilizer variables were applied systematically in strips across the blocks so that N increased gradually from none to large quantities in one direction, while K increased gradually perpendicular to the N fertilizer. An aerial view of the blocks and a plot of banana yields as influenced by the variables illustrate the interaction of the nutrients applied

Vegetation and Agriculture of Liberia and Adjacent West Africa

This paper treats agriculture in its broadest sense, including the useful plant products of the native vegetation as well as those which are actually cultivated by the native peoples. The vegetation, climate, and geography, as well as the agriculture of Liberia, are intimately related to that of the whole West Africa. For this reason the discussion, although chiefly concerned with Liberia, is not confined to its narrow boundaries. As the native vegetation is considered, the natural products from it are discussed

Room-temperature exciton-polaritons with two-dimensional WS2

Two-dimensional transition metal dichalcogenides exhibit strong optical transitions with significant potential for optoelectronic devices. In particular they are suited for cavity quantum electrodynamics in which strong coupling leads to polariton formation as a root to realisation of inversionless lasing, polariton condensationand superfluidity. Demonstrations of such strongly correlated phenomena to date have often relied on cryogenic temperatures, high excitation densities and were frequently impaired by strong material disorder. At room-temperature, experiments approaching the strong coupling regime with transition metal dichalcogenides have been reported, but well resolved exciton-polaritons have yet to be achieved. Here we report a study of monolayer WS$_2$ coupled to an open Fabry-Perot cavity at room-temperature, in which polariton eigenstates are unambiguously displayed. In-situ tunability of the cavity length results in a maximal Rabi splitting of $\hbar \Omega_{\rm{Rabi}} = 70$ meV, exceeding the exciton linewidth. Our data are well described by a transfer matrix model appropriate for the large linewidth regime. This work provides a platform towards observing strongly correlated polariton phenomena in compact photonic devices for ambient temperature applications.Comment: 12 pages, 6 figure

Integrated economic hydrologic model for groundwater basin management, An

May 1994.Also listed online under Open file reports list as no. 7.Revision of Faisal's thesis (Ph. D.--Colorado State University, 1994).Includes bibliographical references (pages 151-156).Financed in part by the U.S. Dept. of the Interior, Geological Survey, grant no. 14-08-0001-G2008/2 09

Strain Hardening of Polymer Glasses: Entanglements, Energetics, and Plasticity

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are pulled taut between entanglements rather than a change in entropy. A weak entropic stress is only observed in shape recovery of deformed samples when heated above the glass transition. While short chains do not form an entangled network, they exhibit partial shape recovery, orientation, and strain hardening. Stresses for all chain lengths collapse when plotted against a microscopic measure of chain stretching rather than the macroscopic stretch. The thermal contribution to the stress is directly proportional to the rate of plasticity as measured by breaking and reforming of interchain bonds. These observations suggest that the correct microscopic theory of strain hardening should be based on glassy state physics rather than rubber elasticity.Comment: 15 pages, 12 figures: significant revision