JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 128.235.251.160 on SunAbstract. A nonlinear function general enough to include the effects of feeding saturation and intraspecific consumer interference is used to represent the transfer of material or energy from one trophic level to another. The function agrees with some recent experimental data on feeding rates. A model using this feeding rate function is subjected to equilibrium and stability analyses to ascertain its mathematical implications. The analyses lead to several observations; for example, increases in maximum feeding rate may, under certain circumstances, result in decreases in consumer population and mutual interference between consumers is a major stabilizing factor in a nonlinear system. The analyses also suggest that realistic classes of consumer-resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable.
Induced pluripotent stem (iPS) cells are human somatic cells that have been reprogrammed to a pluripotent state. There are several hurdles to be overcome before iPS cells can be considered as a potential patient-specific cell therapy, and it will be crucial to characterize the developmental potential of human iPS cell lines. As a research tool, iPS-cell technology provides opportunities to study normal development and to understand reprogramming. iPS cells can have an immediate impact as models for human diseases, including cancer
The International Society for Stem Cell Research (ISSCR) task force that developed new Guidelines for the Clinical Translation of Stem Cells discusses core principles that should guide the responsible transition of basic stem cell research into appropriate clinical applications.
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The discrepancy between estimates of net terrestrial CO2 emissions derived from (1) inverse modeling of the ocean/atmosphere system and (2) modeling of land use change, better known as the "missing" CO2 sink, suggests that some changing environmental factor, such as CO2, anthropogenic N emissions, or climate, has fertilized terrestrial ecosystems. To address this question, we herein describe and apply GLOCO, a global carbon cycle model. GLOCO's ocean submodel combines a box diffusion model with representations of chemical equilibria and biological processes to simulate the distributions and cycling of inorganic and organic carbon, phosphate, and alkalinity. The terrestrial submodel divides the biosphere into seven natural biomes with dynamic carbon and nitrogen cycling in both vegetation and soils. Anthropogenic influences on the functioning of the carbon and nitrogen cycles, such as fossil fuel combustion, forestry, and agricultural development, are also incorporated in the model. Our analysis confirms previous suggestions that because temperate and boreal forests are N limited, CO2 fertilization of these forests is less than predicted by short-term CO2 response factors. Modeling of temperate/boreal forest fertilization by anthropogenic N deposition suggests that CO2 is initially sequestered at a C:N ratio of --100, rather than the steady state value for the ecosystem of-30. If N deposition is to account for the 40-70% of the fertilization of the terrestrial biosphere not explainable by CO2 fertilization and temperature increases, then we estimate that 26-30 Tg N yr-1 of anthropogenic deposition in the temperate and boreal zones would be required. Recent anthropogenic NOx and NH3 deposition fluxes at northern temperate latitudes have been estimated to be 20-28 Tg N yr-1. Thus fertilization by anthropogenic N emissions likely constitutes a significant portion of the missing CO2 sink. HUDSON ET AL.' MODELING THE GLOBAL CARBON CYCLE Z•tC + AOc + Z•Bc = I EFossil fuel dt or expressed in terms of rates of change d/dt dAc dOc dBc • + + -EFossil fuel dt dt dt (la) (lb) The rate of change in atmospheric CO2 is the best quantified term in the mass balance at 3.2_+0.2 Pg C yr 4 for the period 1980-1989 [Keeling, 1990]. Fossil fuel emissions are also well quantified at 5.4_+0.5 Pg C yr-• for the same period [Marland, 1990; Marland and Rotty, 1984]. The change in carbon storage in the oceans, assumed to arise primarily from increased absorption of atmospheric CO2, can be modeled by &convolution of the atmospheric CO2 record (reconstructing oceanic uptake using models and historical atmospheric CO2 partial pressure Pco2). By considering the results of a number of such studies, Siegenthaler and Sarmiento [1993] argue that the perturbation in oceanic uptake (~dOc/dt) is 2.0_+0.6 Pg C yr-• for the 1980s. Analysis of measured surface ocean Pco2 values and the distributions, sources, and sinks of atmospheric CO2 using an atmospheric transport model lead Tans et al. [1990] to suggest that the perturbation in oceanic uptake was les...
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