633 research outputs found
Inequalities in Taxation of Farm Lands and City Property Due to Scope and Method of Assessment.
28 p
An Agricultural Economic Survey of Rockwall County, Texas : A Typical Blackland Cotton Farming Area.
165 p
Forward projection of transient signals obtained from a fiber-optic pressure sensor
An analytical/experimental approach is presented to reconstruct the spaceâtime pressure field in a plane and forward project the resultant spaceâtime pressure field using tomographic and wave vector time-domain methods. Transient pressure signals from an underwater ultrasonic planar transducer are first measured using a line fiber-optic pressure sensor which is scanned across a plane at a fixed distance z0 from the transducer. The resulting spatial line integrals in the plane are time-dependent signals which are first used to reconstruct the spaceâtime pressure field in the plane via simply implemented tomographic methods. These signals are then used to forward project the spaceâtime pressure field to arbitrary planes employing a wave vector time-domain method. Verification of the method is first presented using synthetic signals and the impulse response approach. An experimental verification of the approach is then presented using an ultrasonic planar transducer. The results of the projected and experimental fields are compared at various distances for synthetic signals and experimental data. Good correlation is found between the calculated, projected, and experimental data
Increasing Liana Abundance and Basal Area in a Tropical Forest: The Contribution of Longâdistance Clonal Colonization
Recent evidence suggests that liana abundance and biomass are increasing in Neotropical forests, representing a major structural change to tropical ecosystems. Explanations for these increases, however, remain largely untested. Over an 8âyr period (1999â2007), we censused lianas in nine, 24 Ă 36 m permanent plots in oldâgrowth and selectively logged forest at La Selva Biological Station, Costa Rica to test whether: (1) liana abundance and basal area are increasing in this forest; (2) the increase is being driven by increased recruitment, decreased mortality, or both; and (3) longâdistance clonal colonization explains the increase in liana abundance and basal area. We defined longâdistance clonal colonization as lianas that entered and rooted in the plots as vegetative propagules of stems that originated from outside or above the plot, and were present in 2007, but not in 1999 or 2002. Our hypotheses were supported in the oldâgrowth forest: mean liana abundance and BA (â„1 cm diameter) increased 15 and 20 percent, respectively, and clonal colonization from outside of the plots contributed 19 and 60 percent (respectively) to these increases. Lianas colonized clonally by falling vertically from the forest canopy above or growing horizontally along the forest floor and reârootingâcommon forms of colonization for many liana species. In the selectively logged forest, liana abundance and BA did not change, and thus the pattern of increasing lianas may be restricted to oldâgrowth forests. In summary, our data support the hypothesis that lianas are increasing in oldâgrowth forests, and that longâdistance clonal colonization is a major contributor
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