The impact of balsamo (Myroxylon balsamum L. Harms) on coffee yield and household income in El Balsamar, El Salvador

El Balsamar is a community that relies upon coffee trees intercropped with the balsamo tree (Myroxylon balsamum L. Harms) for a substantial portion of household income. The balsamo tree is valued for its resin which is used as medicine in the community and sold commercially. Farmers believe that the shade from the balsamo tree decreases coffee yield compared to the shade from non balsamo species. Thirty coffee farms were studied, each set up as a paired plot. When cover type was balsamo, coffee yield was more likely to decrease. Plots with higher basal area were more likely to be balsamo cover type. As basal area increased, coffee yield decreased. Although coffee yield is lower under balsamo cover type, farmers still continue to plant and manage coffee under this cover type. Farmers accept a lower coffee yield because balsamo resin provides an important income source. Farmers rely on the community cooperative to provide them work to support their households. The cooperative relies on the farmers to provide the labor needed to harvest coffee and extract balsamo resin.

STRUCTURAL CONTROL OF A SMALL-SCALE TEST-BED SHAKER STRUCTURE USING A SPONGE-TYPE MAGNETO-RHEOLOGICAL FLUID DAMPER

Semi-active damping devices have been shown to be effective in mitigating unwanted vibrations in civil structures. These devices impart force indirectly through real-time alterations to structural properties. Simulating the complex behavior of these devices for laboratory-scale experiments is a major challenge. Commercial devices for seismic applications typically operate in the 2-10 kN range; this force is too high for small-scale testing applications where requirements typically range from 0-10 N. Several challenges must be overcome to produce damping forces at this level. In this study, a small-scale magneto-rheological (MR) damper utilizing a fluid absorbent metal foam matrix is developed and tested to accomplish this goal. This matrix allows magneto-rheological (MR) fluid to be extracted upon magnetic excitation in order to produce MR-fluid shear stresses and viscosity effects between an electromagnetic piston, the foam, and the damper housing. Dampers for uniaxial seismic excitation are traditionally positioned in the horizontal orientation allowing MR-fluid to gather in the lower part of the damper housing when partially filled. Thus, the absorbent matrix is placed in the bottom of the housing relieving the need to fill the entire device with MR-fluid, a practice that requires seals that add significant unwanted friction to the desired low-force device. The damper, once constructed, can be used in feedback control applications to reduce seismic vibrations and to test structural control algorithms and wireless command devices. To validate this device, a parametric study was performed utilizing force and acceleration measurements to characterize damper performance and controllability for this actuator. A discussion of the results is presented to demonstrate the attainment of the damper design objectives.