835 research outputs found
Metabolic Activity of the Epiphytic Community Associated with Spartina alterniflora
Primary production and respiration rates were determined for two epiphytic communities associated with Spartina alternifloraLoisel., in the southwestern Barataria Bay area of Louisiana. The communities studied were: (1) a shoreline community and (2) a community 1.5 meters inland from the shoreline site. Annual mean net production and respiration rates for the shoreline community were 25.8 and -19.6 mg C • (m2 substrate area)-1 • h-1 respectively;whereas the inland community showed corresponding rates of -3.3 and -12.5 mg C • (m2 substrate area)-1 • h-1, respectively. Thus, the shoreline community was a net contributor to system production; the inland community was an energy sink. The inland community was elevated 15 to 20 cm above the shoreline community, lacked the conspicuous filamentous algal growth common at the shoreline location, and had a significantly smaller diatom population. The role of epiphytes is speculated to be one of quality rather than quantity production
Metabolic Activity of the Epiphytic Community Associated with Spartina alterniflora
Primary production and respiration rates were determined for two epiphytic communities associated with Spartina alternifloraLoisel., in the southwestern Barataria Bay area of Louisiana. The communities studied were: (1) a shoreline community and (2) a community 1.5 meters inland from the shoreline site. Annual mean net production and respiration rates for the shoreline community were 25.8 and -19.6 mg C • (m2 substrate area)-1 • h-1 respectively;whereas the inland community showed corresponding rates of -3.3 and -12.5 mg C • (m2 substrate area)-1 • h-1, respectively. Thus, the shoreline community was a net contributor to system production; the inland community was an energy sink. The inland community was elevated 15 to 20 cm above the shoreline community, lacked the conspicuous filamentous algal growth common at the shoreline location, and had a significantly smaller diatom population. The role of epiphytes is speculated to be one of quality rather than quantity production
Signatures of four-particle correlations associated with exciton-carrier interactions in coherent spectroscopy on bulk GaAs
Transient four-wave mixing studies of bulk GaAs under conditions of broad
bandwidth excitation of primarily interband transitions have enabled
four-particle correlations tied to degenerate (exciton-exciton) and
nondegenerate (exciton-carrier) interactions to be studied. Real
two-dimensional Fourier-transform spectroscopy (2DFTS) spectra reveal a complex
response at the heavy-hole exciton emission energy that varies with the
absorption energy, ranging from dispersive on the diagonal, through absorptive
for low-energy interband transitions to dispersive with the opposite sign for
interband transitions high above band gap. Simulations using a multilevel model
augmented by many-body effects provide excellent agreement with the 2DFTS
experiments and indicate that excitation-induced dephasing (EID) and
excitation-induced shift (EIS) affect degenerate and nondegenerate interactions
equivalently, with stronger exciton-carrier coupling relative to
exciton-exciton coupling by approximately an order of magnitude. These
simulations also indicate that EID effects are three times stronger than EIS in
contributing to the coherent response of the semiconductor
The inversion, part-whole, and composite effects reflect distinct perceptual mechanisms with varied relationships to face recognition
Face recognition is thought to rely on specific mechanisms underlying a perceptual bias toward processing faces as undecomposable wholes. This face-specific "holistic processing" is commonly quantified using 3 measures: the inversion, part-whole, and composite effects. Consequently, many researchers assume that these 3 effects measure the same cognitive mechanism(s) and these mechanisms contribute to the wide range of individual differences seen in face recognition ability. We test these assumptions in a large sample (N = 282), with individual face recognition abilities measured by the well-validated Cambridge Face Perception Test. Our results provide little support for either assumption. The small to nonexistent correlations among inversion, part-whole, and composite effects (correlations between -.03 and .28) fail to support the first assumption. As for the second assumption, only the inversion effect moderately predicts face recognition (r = .42); face recognition was weakly correlated with the part-whole effect (r = .25) and not correlated with the composite effect (r = .04). We rule out multiple artifactual explanations for our results by using valid tasks that produce standard effects at the group level, demonstrating that our tasks exhibit psychometric properties suitable for individual differences studies, and demonstrating that other predicted correlations (e.g., between face perception measures) are robust. Our results show that inversion, part-whole, and composite effects reflect distinct perceptual mechanisms, and we argue against the use of the single, generic term holistic processing when referring to these effects. Our results also question the contribution of these mechanisms to individual differences in face recognition
Environmental services in agricultural landscapes: scale-dependent effects and households adaptive capability interactions.
A Bi-Directional Refinement Algorithm for the Calculus of (Co)Inductive Constructions
The paper describes the refinement algorithm for the Calculus of
(Co)Inductive Constructions (CIC) implemented in the interactive theorem prover
Matita. The refinement algorithm is in charge of giving a meaning to the terms,
types and proof terms directly written by the user or generated by using
tactics, decision procedures or general automation. The terms are written in an
"external syntax" meant to be user friendly that allows omission of
information, untyped binders and a certain liberal use of user defined
sub-typing. The refiner modifies the terms to obtain related well typed terms
in the internal syntax understood by the kernel of the ITP. In particular, it
acts as a type inference algorithm when all the binders are untyped. The
proposed algorithm is bi-directional: given a term in external syntax and a
type expected for the term, it propagates as much typing information as
possible towards the leaves of the term. Traditional mono-directional
algorithms, instead, proceed in a bottom-up way by inferring the type of a
sub-term and comparing (unifying) it with the type expected by its context only
at the end. We propose some novel bi-directional rules for CIC that are
particularly effective. Among the benefits of bi-directionality we have better
error message reporting and better inference of dependent types. Moreover,
thanks to bi-directionality, the coercion system for sub-typing is more
effective and type inference generates simpler unification problems that are
more likely to be solved by the inherently incomplete higher order unification
algorithms implemented. Finally we introduce in the external syntax the notion
of vector of placeholders that enables to omit at once an arbitrary number of
arguments. Vectors of placeholders allow a trivial implementation of implicit
arguments and greatly simplify the implementation of primitive and simple
tactics
Recent Decisions
Comments on recent decisions by Wilmer A. McLaughlin, Robert C. Enburg, Robert A. Layden, Lenton G. Sculthorp, Joseph T. Helling, John L. Globensky, Maurice J. Moriarty, Robert J. Affeldt, Louis J. Mustico, Donald John Tufts, Sidney Baker, and Edward J. VanTassel
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