Constraint Damping in First-Order Evolution Systems for Numerical Relativity

A new constraint suppressing formulation of the Einstein evolution equations is presented, generalizing the five-parameter first-order system due to Kidder, Scheel and Teukolsky (KST). The auxiliary fields, introduced to make the KST system first-order, are given modified evolution equations designed to drive constraint violations toward zero. The algebraic structure of the new system is investigated, showing that the modifications preserve the hyperbolicity of the fundamental and constraint evolution equations. The evolution of the constraints for pertubations of flat spacetime is completely analyzed, and all finite-wavelength constraint modes are shown to decay exponentially when certain adjustable parameters satisfy appropriate inequalities. Numerical simulations of a single Schwarzschild black hole are presented, demonstrating the effectiveness of the new constraint-damping modifications.Comment: 11 pages, 5 figure

Rare earth element deposition in pelagic sediment at the Cenomanian‐Turonian Boundary, Exmouth Plateau

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95314/1/grl8050.pd

The role of genes, stress, and dopamine in the development of schizophrenia

The dopamine hypothesis is the longest standing pathoetiologic theory of schizophrenia. Because it was initially based on indirect evidence and findings in patients with established schizophrenia, it was unclear what role dopamine played in the onset of the disorder. However, recent studies in people at risk of schizophrenia have found elevated striatal dopamine synthesis capacity and increased dopamine release to stress. Furthermore, striatal dopamine changes have been linked to altered cortical function during cognitive tasks, in line with preclinical evidence that a circuit involving cortical projections to the striatum and midbrain may underlie the striatal dopamine changes. Other studies have shown that a number of environmental risk factors for schizophrenia, such as social isolation and childhood trauma, also affect presynaptic dopaminergic function. Advances in preclinical work and genetics have begun to unravel the molecular architecture linking dopamine, psychosis, and psychosocial stress. Included among the many genes associated with risk of schizophrenia are the gene encoding the dopamine D2 receptor and those involved in the upstream regulation of dopaminergic synthesis, through glutamatergic and gamma-aminobutyric acidergic pathways. A number of these pathways are also linked to the stress response. We review these new lines of evidence and present a model of how genes and environmental factors may sensitize the dopamine system so that it is vulnerable to acute stress, leading to progressive dysregulation and the onset of psychosis. Finally, we consider the implications for rational drug development, in particular regionally selective dopaminergic modulation, and the potential of genetic factors to stratify patients

Late Tertiary history of hydrothermal deposition at the East Pacific Rise, 19°S: Correlation to volcano‐tectonic events

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95132/1/grl3614.pd

Geochemistry of rare earth elements in pacific hydrothermal sediments

The concentrations and mass accumulation rates of rare earth elements (REE) in hydrothermal sediments from two Pacific sites support earlier predictions that hydrothermal REE inputs are significant to the overall marine REE mass balance. Although REE are enriched in hydrothermal vent fluids, they are rapidly and extensively scavenged from the water column by Fe oxyhydroxides and undergo some degree of fractionation prior to removal. Evidence for significant light REE (LREE) hydrothermal inputs tends to be masked by the fact that the LREE patterns and inter-element ratios of both proximal and distal hydrothermal precipitates are similar to those of seawater. However, the heavy REE (HREE) patterns clearly reflect a basaltic source and the HREE ratios from both sites are similar to each other but distinct from their seawater analogs. This suggests HREE ratios potentialy could be used as proxy indicators in our attempts to reconstruct the history of seafloor hydrothermal activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27113/1/0000105.pd

REE/Fe variations in hydrothermal sediments: Implications for the REE content of seawater

Seafloor hydrothermal vent solutions exhibit rare earth element (REE) enrichments ranging between one to three orders of magnitude greater than average seawater. To assess the impact of these hydrothermal inputs on ocean chemistry, we have examined the behavior of REEs for hydrothermal sediments collected adjacent to two Pacific spreading ridge sites: the East Pacific Rise at 19[deg]S, and the Southern Juan de Fuca Ridge at 4S[deg]N. In general, the REE/Fe ratios for both proximal and distal hydrothermal sediments are greater than vent solutions by a factor of 2 to 500, and these ratios increase with increasing distance away from the ridge axis. An evaluation of these results in the context of previous models of REE behavior indicates that, in fact, seawater experiences a net depletion in REEs as a result of hydrothermal activity. This is due primarily to the large scavenging capacity of iron oxyhydroxides which precipitate from these solutions. Such an interpretation explains why the REE content of seawater collected in the vicinity of hydrothermal vents is anomalously lower than "normal" seawater sampled from a comparable depth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28043/1/0000482.pd

The europium anomaly of seawater: implications for fluvial versus hydrothermal REE inputs to the oceans

Seafloor hydrothermal vent fluids are characterized by rare earth element (REE) enrichments and large positive Eu anomalies; however, this input is not recorded by seawater. Hydrothermal sediments from the southeast Pacific (DSDP Site 598) were examined to address this discrepancy between the observed and predicted REE pattern of seawater. "Scavenging indices", which reflect long-term REE scavenging by iron-rich hydrothermal precipitates, were calculated for each of eight REE's. Comparisons between these indices and the REE content of seawater indicate that the intensity of REE scavenging by hydrothermal precipitates is proportional to the concentration of REE's in the fluid phase. We predict that REE's are rapidly scavenged from hydrothermal solutions, and that Eu is removed disproportionately faster relative to its neighbors. Eu-anomaly values for Site 598 and other hydrothermal sediments support this prediction: a vent signature is recorded in sediments closest to the ridge axis and the Eu-anomaly values become more seawater-like with increasing distance and scavenging. This implies that the REE content of seawater cannot be used to constrain hydrothermal versus fluvial fluxes to the oceans.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29082/1/0000117.pd