In this paper, we analyzed 3 years of carbon flux data from continuous eddy covariance measurements to investigate how soil moisture, rain pulses, and growth alter the response of ecosystem respiration to temperature. The data were acquired over an annual grassland and from the grass understory of an oak/grass savanna ecosystem in California. We observed that ecosystem respiration was an exponential function of soil temperature during the winter wet season and a jump in ecosystem respiration occurred, at comparable temperatures, during the spring growth period. The depletion of the moisture from the soil reservoir, during spring, limited ecosystem respiration after its volumetric water content dropped below a threshold of 0.15 m 3 m −3 . The senescence of grass during the summer switched the source of ecosystem respiration to heterotrophic bacteria and fungi. During the summer, respiration proceeded at a low basal rate (about 0.10 to 0.3 g C m −2 d −1 ), except when summer rain events stimulated large dynamic pulses in heterotrophic respiration. Peak respiratory pulses were on the order of 60–80 times baseline and could not be explained by functions that depend on mean soil moisture and temperature. We found that the magnitude of the respiratory pulses was inversely related to its prerain value and that the time constant, describing the exponential decay of the respiratory pulses after the rain event, was a function of the amount of rainfall. The amount of carbon lost, in association with a few summer rain events, was greater at the site with higher primary productivity and soil carbon content.
Studies the chaotic dynamics observed from a widely used second-order phase-locked loops (PLLs) operating as a frequency modulated demodulator. The authors apply Melnikov's method to high-damping PLLs to obtain the parameter range where there exist homoclinic points. This implies the PLL is chaotic in such a parameter range in view of the Smale-Birkhoff theorem. In particular, since the current PLL used in practice has a triangular phase detector as its nonlinearity (i.e., a periodic triangular shaped function), one can use piecewise-linear methods to derive the Melnikov integral analytically even for the practical high-damping (hence, high dissipation) case. The advantage of this method compared to the previous numerical integration method is that all integrations are made analytically, and therefore reliable results can be obtained for all parameter values. The authors have obtained many boundary curves for homoclinic tangency for a wide range of damping coefficients. As a result, some inaccuracies in previous numerical integration results have been detected.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Review: 264 refs.
A model for the elastic–plastic response of solids is formulated on the basis of the concept of a materially uniform Cosserat continuum. Plastic deformation and rotation tensors are defined in terms of invertible mappings of a local archetypal state, encoding the constitutive response of the material, to a neighborhood of a material point in an assigned reference configuration. The archetype is mapped to a neighborhood of this material point in a current configuration by corresponding elastic kinematic descriptors. These in turn furnish the arguments of a strain-energy function that describes the response of the archetype. In the specialization to hemitropic solids, the plastic rotation is effectively eliminated from the theory by exploiting the degree of freedom afforded by material symmetry. An appropriate version of Eshelby’s tensor is identified as the driving force for dissipation and used in the construction of a yield criterion and associated flow rule for plastic evolution. In a further specialization to decoupled strain-energy functions, the force and torque balances are found to be coupled solely by the plastic deformation. Moreover, in this case, a model of kinematic hardening emerges as a natural outcome of the theory. The present work is offered as a framework for the prediction of texture development due to local grain reorientation accompanying plastic deformation in polycrystalline metals.
