6,954 research outputs found
Private Governance Responses to Climate Change: The Case of Global Civil Aviation
This Article explores how private governance can reduce the climate effects of global civil aviation. The civil aviation sector is a major contributor to climate change, accounting for emissions comparable to a top ten emitting country. National and international governmental bodies have taken important steps to address civil aviation, but the measures adopted to date are widely acknowledged to be inadequate. Civil aviation poses particularly difficult challenges for government climate mitigation efforts. Many civil aviation firms operate globally, emissions often occur outside of national boundaries, nations differ on their respective responsibilities, and demand is growing rapidly. Although promising new technologies are emerging, they will take time to develop and adopt. This Article argues that private initiatives can overcome many of these barriers. Private initiatives can motivate civil aviation firms to act absent government pressure at the national level and can create pressure for mitigation that transcends national boundaries. The Article argues that it is time to develop a private climate governance agenda for civil aviation and identifies examples of the types of existing and new initiatives that could be included in the effort. If public and private policymakers can overcome the tendency to focus almost exclusively on public governance, private initiatives can yield large and prompt emissions reductions from global civil aviation, buy time for more comprehensive government measures, and complement the government measures when they occur
The Merger of Small and Large Black Holes
We present simulations of binary black holes mergers in which, after the
common outer horizon has formed, the marginally outer trapped surfaces (MOTSs)
corresponding to the individual black holes continue to approach and eventually
penetrate each other. This has very interesting consequences according to
recent results in the theory of MOTSs. Uniqueness and stability theorems imply
that two MOTSs which touch with a common outer normal must be identical. This
suggests a possible dramatic consequence of the collision between a small and
large black hole. If the penetration were to continue to completion then the
two MOTSs would have to coalesce, by some combination of the small one growing
and the big one shrinking. Here we explore the relationship between theory and
numerical simulations, in which a small black hole has halfway penetrated a
large one.Comment: 17 pages, 11 figure
Comment on "Mechanical analog of temperature for the description of force distribution in static granular packings"
It has been proposed by Ngan [Phys. Rev. E 68, 011301 (2003)] that the
granular contact force distribution may be analytically derived by minimizing
the analog of a thermodynamic free energy, in this case consisting of the total
potential energy stored in the compressed contacts minus a particular form of
entropy weighted by a parameter. The parameter is identified as a mechanical
temperature. I argue that the particular form of entropy cannot be correct and
as a result the proposed method produces increasingly errant results for
increasing grain rigidity. This trend is evidenced in Ngan's published results
and in other numerical simulations and experiments.Comment: 4 pages, 1 figure, minor editorial correction
Private Governance Responses to Climate Change: The Case of Global Civil Aviation
This Article explores how private governance can reduce the climate effects of global civil aviation. The civil aviation sector is a major contributor to climate change, accounting for emissions comparable to a top ten emitting country. National and international governmental bodies have taken important steps to address civil aviation, but the measures adopted to date are widely acknowledged to be inadequate. Civil aviation poses particularly difficult challenges for government climate mitigation efforts. Many civil aviation firms operate globally, emissions often occur outside of national boundaries, nations differ on their respective responsibilities, and demand is growing rapidly. Although promising new technologies are emerging, they will take time to develop and adopt. This Article argues that private initiatives can overcome many of these barriers. Private initiatives can motivate civil aviation firms to act absent government pressure at the national level and can create pressure for mitigation that transcends national boundaries. The Article argues that it is time to develop a private climate governance agenda for civil aviation and identifies examples of the types of existing and new initiatives that could be included in the effort. If public and private policymakers can overcome the tendency to focus almost exclusively on public governance, private initiatives can yield large and prompt emissions reductions from global civil aviation, buy time for more comprehensive government measures, and complement the government measures when they occur
Leonardo's rule, self-similarity and wind-induced stresses in trees
Examining botanical trees, Leonardo da Vinci noted that the total
cross-section of branches is conserved across branching nodes. In this Letter,
it is proposed that this rule is a consequence of the tree skeleton having a
self-similar structure and the branch diameters being adjusted to resist
wind-induced loads
Effects of Spacecraft Landings on the Moon
The rocket exhaust of spacecraft landing on the Moon causes a number of observable effects that need to be quantified, including: disturbance of the regolith and volatiles at the landing site; damage to surrounding hardware such as the historic Apollo sites through the impingement of high-velocity ejecta; and levitation of dust after engine cutoff through as-yet unconfirmed mechanisms. While often harmful, these effects also beneficially provide insight into lunar geology and physics. Research results from the past 10 years is summarized and reviewed here
Compensatory transâregulatory alleles minimizing variation in TDH3 expression are common within Saccharomyces cerevisiae
Heritable variation in gene expression is common within species. Much of this variation is due to genetic differences outside of the gene with altered expression and is transâacting. This transâregulatory variation is often polygenic, with individual variants typically having small effects, making the genetic architecture and evolution of transâregulatory variation challenging to study. Consequently, key questions about transâregulatory variation remain, including the variability of transâregulatory variation within a species, how selection affects transâregulatory variation, and how transâregulatory variants are distributed throughout the genome and within a species. To address these questions, we isolated and measured transâregulatory differences affecting TDH3 promoter activity among 56 strains of Saccharomyces cerevisiae, finding that transâregulatory backgrounds varied approximately twofold in their effects on TDH3 promoter activity. Comparing this variation to neutral models of transâregulatory evolution based on empirical measures of mutational effects revealed that despite this variability in the effects of transâregulatory backgrounds, stabilizing selection has constrained transâregulatory differences within this species. Using a powerful quantitative trait locus mapping method, we identified âŒ100 transâacting expression quantitative trait locus in each of three crosses to a common reference strain, indicating that regulatory variation is more polygenic than previous studies have suggested. Loci altering expression were located throughout the genome, and many loci were strain specific. This distribution and prevalence of alleles is consistent with recent theories about the genetic architecture of complex traits. In all mapping experiments, the nonreference strain alleles increased and decreased TDH3 promoter activity with similar frequencies, suggesting that stabilizing selection maintained many transâacting variants with opposing effects. This variation may provide the raw material for compensatory evolution and larger scale regulatory rewiring observed in developmental systems drift among species.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151914/1/evl3137_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151914/2/evl3137.pd
Ballistics Model for Particles on a Horizontal Plane in a Vacuum Propelled by a Vertically Impinging Gas Jet
A simple trajectory model has been developed and is presented. The particle trajectory path is estimated by computing the vertical position as a function of the horizontal position using a constant horizontal velocity and a vertical acceleration approximated as a power law. The vertical particle position is then found by solving the differential equation of motion using a double integral of vertical acceleration divided by the square of the horizontal velocity, integrated over the horizontal position. The input parameters are: x(sub 0) and y(sub 0), the initial particle starting point; the derivative of the trajectory at x(sub 0) and y(sub 0), s(sub 0) = s(x(sub 0))= dx(y)/dy conditional expectation y = y((sub 0); and b where bx(sub 0)/y(sub 0) is the final trajectory angle before gravity pulls the particle down. The final parameter v(sub 0) is an approximation to a constant horizontal velocity. This model is time independent, providing vertical position x as a function of horizontal distance y: x(y) = (x(sub 0) + s(sub 0) (y-y(sub 0))) + bx(sub 0) -(s(sub 0)y(sub 0) ((y - y(sub 0)/y(sub 0) - ln((y/y(sub 0)))-((g(y-y(sub 0)(exp 2))/ 2((v(sub 0)(exp 2). The first term on the right in the above equation is due to simple ballistics and a spherically expanding gas so that the trajectory is a straight line intersecting (0,0), which is the point at the center of the gas impingement on the surface. The second term on the right is due to vertical acceleration, which may be positive or negative. The last term on the right is the gravity term, which for a particle with velocities less than escape velocity will eventually bring the particle back to the ground. The parameters b, s(sub 0), and in some cases v(sub 0), are taken from an interpolation of similar parameters determined from a CFD simulation matrix, coupled with complete particle trajectory simulations
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