Self-Consistent Cosmological Simulations of DGP Braneworld Gravity

We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati braneworld model, by solving the full non-linear equations of motion for the scalar degree of freedom in this model, the brane bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes non-linear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to General Relativity. The code uses a multi-grid relaxation scheme to solve the non-linear field equation in the quasi-static approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane bending mode. This allows us to isolate the effects of the non-linear self-couplings of the field which are noticeable already on quasi-linear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane bending mode within cosmological structure formation. We find that, independently of CMB constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.Comment: 21 pages; 10 figures. Revised version matching published versio

Paleoseismic and Slip-Rate Observations along the Honey Lake Fault Zone, Northeastern California, USA

The Honey Lake fault is a major strike-slip fault in northeastern California that accommodates northwest-directed right-lateral shear in the northern Walker Lane. We reexamine the fault’s paleoseismic history and slip rate by evaluating a natural stream bank exposure of the fault and offset terrace riser. Structural and stratigraphic relations within the modern stream cut, radiocarbon ages, and a detailed topographic survey of the offset terrace riser are used to estimate a Holocene fault slip rate of 1.7–0.6 mm/yr or more. We also interpret the occurrence of at least four surface-rupturing earthquakes during the last 7025 calendar years before present (B.P.). Three of the surface-rupturing earthquakes occurred prior to 4670 calendar years B.P. and have interevent times that range between 730 and 990 yr. The stratigraphic record is limited after ~4670 calendar years B.P., and records evidence for at least one more subsequent surface-rupturing earthquake

The Reciprocal Enforcement of Support Act in Montana

The Reciprocal Enforcement of Support Act in Montan

Carry-Over Effects and Plumage Polymorphism in Swainson's Hawks

The maintenance of genetic diversity in the face of forces such as genetic drift and natural selection has intrigued scientists for decades. Such processes should seemingly oppose diversity in a stable environment. However, environments are rarely stable in natural systems and processes can be complex. We investigate how a plumage polymorphism is maintained in a population of Swainson's Hawks (Buteo swainsoni) in northern California, USA. Swainson's Hawks are highly polymorphic in the belly, flanks and underwing coverts ranging from white to dark brown and seemingly everything in between. Generally, these morphs can be grouped into 3 general classes; light, intermediate and dark. We first examined potential fitness differences among morph classes. Specifically we examined two primary hypotheses of heterosis (i.e., heterozygote advantage) and apostatic (i.e., frequency dependant) selection. Both mechanisms have been cited before in predator populations as potential mechanisms to maintain a polymorphism. However, we found no evidence of differences in any fitness parameter between the morph classes including; nest success, nest productivity, recruitment of offspring or lifetime reproductive success. There was marginal evidence of differences in survival between morph classes with dark individuals having a slightly higher adult survival compared to intermediate and dark morph. We also examined sexual selection in this population. Individuals did not appear to mate assortatively (i.e. there was no preference for a mate based on one's own mate class). For females, there was similarly no evidence for imprinting. In contrast, males chose mates that consistently matched the maternal morph. Further, males selected mates more consistently than we expect by chance. Finally, males that were not able to select mates with the same morph class as their mother had a lower lifetime reproductive success. This result indicates that these males may not have invested as heavily in reproduction, or were lower quality males that could not attract a mate of the correct morph. This sexual selection of the males may aid in the maintenance of the polymorphism over time.We also examined carry-over effects, processes and events in one season that affect an individual or population in another. Carry-over effects are garnering greater attention in studies of migratory species. Part of this newfound interest stems from tools and techniques allowing researchers to follow individuals or glean greater insights about foraging locations in different times of the year. We used feathers as indices of body condition from both the wintering grounds in Argentina and the breeding area. Specifically, we used the average daily growth of the feather, the level of corticosterone in the feather, and number of fault bars in the retrices and remiges of breeding hawks. We used deuterium levels in feathers to determine where each feather was grown to ensure that indices of condition came from a known location. Average daily growth was correlated with mass adjusted for body size, but corticosterone in feathers and fault bars were not. For males, average daily growth of feathers grown in Argentina and number of fault bars on worn feathers were correlated with nest success demonstrating carry-over effects and that individual in good body condition on their wintering grounds had higher reproductive performance. In contrast, measures of feather condition in females were not correlated with nest success. Corticosterone in feathers was higher in breeding males, but not in females. As males are the primary providers of prey for both the female and young nestlings their condition may drive the ability of a nesting attempt to succeed because an individual in poor condition may not be able to effectively provision the female or offspring