Variational bounds on the energy dissipation rate in body-forced shear flow

A new variational problem for upper bounds on the rate of energy dissipation in body-forced shear flows is formulated by including a balance parameter in the derivation from the Navier-Stokes equations. The resulting min-max problem is investigated computationally, producing new estimates that quantitatively improve previously obtained rigorous bounds. The results are compared with data from direct numerical simulations.Comment: 15 pages, 7 figure

"Ultimate state" of two-dimensional Rayleigh-Benard convection between free-slip fixed temperature boundaries

Rigorous upper limits on the vertical heat transport in two dimensional Rayleigh-Benard convection between stress-free isothermal boundaries are derived from the Boussinesq approximation of the Navier-Stokes equations. The Nusselt number Nu is bounded in terms of the Rayleigh number Ra according to $Nu \leq 0.2295 Ra^{5/12}$ uniformly in the Prandtl number Pr. This Nusselt number scaling challenges some theoretical arguments regarding the asymptotic high Rayleigh number heat transport by turbulent convection.Comment: 4 page

Micromagnetic simulations of the magnetization precession induced by a spin polarized current in a point contact geometry

This paper is devoted to numerical simulations of the magnetization dynamics driven by a spin-polarized current in extended ferromagnetic multilayers when a point-contact setup is used. We present (i) detailed analysis of methodological problems arising by such simulations and (ii) physical results obtained on a system similar to that studied in Rippard et al., Phys. Rev. Lett., v. 92, 027201 (2004). We demonstrate that the usage of a standard Slonczewski formalism for the phenomenological treatment of a spin-induced torque leads to a qualitative disagreement between simulation results and experimental observations and discuss possible reasons for this discrepancy.Comment: Invited paper on MMM2005 (San Jose); accepted for publication in J. Applied Physic

Near-Infrared Photometric Survey of Herbig Ae/Be Candidate Stars

We report near-infrared photometric measurements of 35 Herbig Ae/Be candidate stars obtained with direct imaging and aperture photometry. Observations were made through the broadband J, H, and K' filters, with each source imaged in at least one of the wavebands. We achieved subarcsecond angular resolution for all observations, providing us with the opportunity to search for close binary candidates and extended structure. The imaging revealed five newly identified binary candidates and one previously resolved T Tauri binary among the target sources with separations of <~2.5". Separate photometry is provided for each of the binary candidate stars. We detect one extended source that has been identified as a protoplanetary nebula. Comparing our magnitudes to past measurements yields significant differences for some sources, possibly indicating photometric variability. H-band finding charts for all of our sources are provided to aid follow-up high-resolution imaging.Comment: 22 pages, 1 figure, accepted for publication in A

The Evolution of the Rationale for Government Involvement in Agriculture

Agricultural and Food Policy, Q18, Q10,

Building Community Resiliency Against Disasters

Disasters impact people in many different places around the world. The impact to communities by disasters is shaped by their constructed vulnerability. The goal of this research project was to better understand how the vulnerability and resiliency of different communities was shaped at six different sites across the U.S. and to construct a collection of best practices to raise the resiliency of populations and locations in the face of many different forms of possible disasters in the future. These concepts and conclusions were drawn from internet research of the chosen sites. Phase 1 of the research determined noteworthy sites and gathered details and data on each site to guide recommendations. Phase 2 gathered information by interviewing individuals with credible and meaningful insights to add to the research data. The sites chosen had disaster events that happened recently or were still occurring during the research in order to better understand the current issues disasters pose and to generate more creative and applicable solutions to these issues. Researching these sites provided a better understanding regarding the best ways to interact with vulnerable communities and raise their resiliency against disasters. It was found that if vulnerable communities had better access to resources, infrastructure, and decision-making agency, and locations had sustainable electricity sources that could operate through extreme weather, they would be more resilient to disasters. Politics plays a large role in shaping vulnerability and resiliency, particularly in how policies determine who has access to resources, power distribution, what disaster response occurs, and how disasters are perceived, showing that these specific areas of resiliency are important to focus on, but to be effective, they need support from the political realm. If these proposed recommendations are implemented, communities will be better able to withstand disruptive forces from the environment and mitigate harm, or possibly even fully prevent disasters from occurring

RNA interference screening reveals host CaMK4 as a regulator of cryptococcal uptake and pathogenesis

ABSTRACT Cryptococcus neoformans , the causative agent of cryptococcosis, is an opportunistic fungal pathogen that kills over 200,000 individuals annually. This yeast may grow freely in body fluids, but it also flourishes within host cells. Despite extensive research on cryptococcal pathogenesis, host genes involved in the initial engulfment of fungi and subsequent stages of infection are woefully understudied. To address this issue, we combined short interfering RNA silencing and a high-throughput imaging assay to identify host regulators that specifically influence cryptococcal uptake. Of 868 phosphatase and kinase genes assayed, we discovered 79 whose silencing significantly affected cryptococcal engulfment. For 25 of these, the effects were fungus specific, as opposed to general alterations in phagocytosis. Four members of this group significantly and specifically altered cryptococcal uptake; one of them encoded CaMK4, a calcium/calmodulin-dependent protein kinase. Pharmacological inhibition of CaMK4 recapitulated the observed defects in phagocytosis. Furthermore, mice deficient in CaMK4 showed increased survival compared to wild-type mice upon infection with C. neoformans . This increase in survival correlated with decreased expression of pattern recognition receptors on host phagocytes known to recognize C. neoformans . Altogether, we have identified a kinase that is involved in C. neoformans internalization by host cells and in host resistance to this deadly infection. </jats:p