According to a familiar objection to Davidson's causal theory of action, reasons are not causes qua reasons unless explanations of actions fit reason and action into a nomic nexus. The focus of this criticism should really be redirected to the issue of whether or not Davidson's theory provides an account of the explanatory force of explanations of actions.
We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator, Alligator mississippiensis. Detailed embryological studies by Westergaard and Ferguson (1986, 1987, 1990) have shown that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. Based on biological data we develop a dynamic patterning mechanism, which crucially includes domain growth. The mechanism can reproduce the spatial pattern development of the first seven teeth primordia in each half jaw (...) of A. mississippiensis. The results for the precise spatio-temporal sequence compare well with experiment. Simulation of the model also predicts that certain transplantations can alter the spatial sequence of teeth primordia initiation. (shrink)
Endothelial cells, when cultured on gelled basement membrane matrix exert forces of tension through which they deform the matrix and at the same time they aggregate into clusters. The cells eventually form a network of cord-like structures connecting cell aggregates. In this network, almost all of the matrix has been pulled underneath the cell cords and cell clusters. This phenomenon has been proposed as a possible model for the growth and development of planar vascular systems in vitro. Our hypothesis is (...) that the matrix is reorganized and the cellular networks form as a result of traction forces exerted by the cells on the matrix and the latter's elasticity. We construct and analyze a mathematical model based on this hypothesis and examine conditions necessary for the formation of the pattern. We show cell migration is not necessary for pattern formation and that isotropic, strain-stimulated traction is sufficient to form the observed patterns. (shrink)
In 2007, Massachusetts instituted a universal coverage health plan that requires all citizens to purchase insurance. I argue that there is nothing wrong in principle with the use of an individual mandate to force citizens to secure health insurance. I argue that state neutrality is not tenable on this issue. Then I proceed to show that even if state neutrality were viable, it is not a violation of state neutrality (thought of as neutrality of intent) to force citizens to insure (...) themselves with the primary purpose of securing the normative good of health. I adapt recent work on universal medical coverage to demonstrate that such a mandate is in keeping with several principles of fairness shared in liberal democratic societies. This argument not only applies to the Massachusetts plan but likely to any other health care coverage schemes using individual mandates in the US political context, including recently passed federal health care reform measures. However, even though the Massachusetts plan may provide increased access to health care for many, there are still legitimate worries that it currently places disproportionate financial burdens on the working poor and thus will need refinement. (shrink)
A philosophical approach to interracial dialogue in North America is based on moral and epistemological principles defended by James M. Jones, Lawrence Thomas, and Cornel West. The different perspectives of the racial majority and racial minorities give rise to different moral obligations.
Gliomas are diffuse and invasive brain tumors with the nefarious ability to evade even seemingly draconian treatment measures. Here we introduce a simple mathematical model for drug delivery of chemotherapeutic agents to treat such a tumor. The model predicts that heterogeneity in drug delivery related to variability in vascular density throughout the brain results in an apparent tumor reduction based on imaging studies despite continual spread beyond the resolution of the imaging modality. We discuss a clinical example for which the (...) model-predicted scenario is relevant. The analysis and results suggest an explanation for the clinical problem of the long-standing confounding observation of shrinkage of the lesion in certain areas of the brain with continued growth in other areas. (shrink)
Recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross-shore extent of active sediment transport. A simple morphodynamic instability arises from the feedback between wave-driven alongshore sediment flux and coastline shape. Coastline segments with different orientations experience different alongshore sediment fluxes, so that curvatures in coastline shape drive gradients in sediment flux, which can augment the shoreline curvatures. In a simple numerical model, this instability, and subsequent finite-amplitude interactions between pattern (...) elements, lead to a wide range of different rhythmic shapes and behaviours—ranging from symmetric cuspate capes and bays to alongshore migrating ‘flying spits’—depending on the characteristics of the input wave forcing. The scale of the pattern coarsens in some cases because of the merger of migrating coastline features, and in other cases because of non-local screening interactions between coastline protrusions, which affect the waves reaching other parts of the coastline. Features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies. Initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature. (shrink)