126,531 research outputs found
An alternative approach to solving the Hamiltonian constraint
Solving Einstein's constraint equations for the construction of black hole
initial data requires handling the black hole singularity. Typically, this is
done either with the excision method, in which the black hole interior is
excised from the numerical grid, or with the puncture method, in which the
singular part of the conformal factor is expressed in terms of an analytical
background solution, and the Hamiltonian constraint is then solved for a
correction to the background solution that, usually, is assumed to be regular
everywhere. We discuss an alternative approach in which the Hamiltonian
constraint is solved for an inverse power of the conformal factor. This new
function remains finite everywhere, so that this approach requires neither
excision nor a split into background and correction. In particular, this method
can be used without modification even when the correction to the conformal
factor is singular itself. We demonstrate this feature for rotating black holes
in the trumpet topology.Comment: 5 pages, 4 figures, matches version published in PR
Insects Associated with Michigan Bumblebees (\u3ci\u3eBombus\u3c/i\u3e Spp.)
(excerpt)
Studies of insect associates of bumblebees are not new. For example, Tuck (1896, 1897) reported over 50 species of insects associated with nests of British bumblebees. Sladen (1912) discussed nest associates and parasites of European bumblebees, and Plath (1934) published similar data for American bumblebees. Postner (1952) published more detailed data. He listed over 60 taxa of insects associated with bumblebees near Erlangen, Germany
The First Moments of Nucleon Generalized Parton Distributions
We extrapolate the first moments of the generalized parton distributions
using heavy baryon chiral perturbation theory. The calculation is based on the
one loop level with the finite range regularization. The description of the
lattice data is satisfactory and the extrapolated moments at physical pion mass
are consistent with the results obtained with dimensional regularization,
although the extrapolation in the momentum transfer to does show
sensitivity to form factor effects which lie outside the realm of chiral
perturbation theory. We discuss the significance of the results in the light of
modern experiments as well as QCD inspired models.Comment: 14 pages, 9 figure
On the Interpretation of the NA51 Experiment
We study the Drell-Yan asymmetry, recently measured by the NA51
collaboration, and conclude that the value quoted by their experiment only sets
a lower limit on the asymmetry of the proton sea. In particular, we notice that
charge symmetry breaking between the proton and the neutron may produce
corrections which should be taken into account.Comment: To appear in Phys. Lett.
Quark structure and nuclear effective forces
We formulate the quark meson coupling model as a many-body effective
Hamiltonian. This leads naturally to the appearance of many-body forces. We
investigate the zero range limit of the model and compare its Hartree-Fock
Hamiltonian to that corresponding to the Skyrme effective force. By fixing the
three parameters of the model to reproduce the binding and symmetry energy of
nuclear matter, we find that it allows a very satisfactory interpretation of
the Skyrme force.Comment: 4 pages, 1tabl
Induction of Cytokinin-Independent Tobacco Tissues by Substituted Fluorenes
Two morphactins and three aminofluorenes initiated the formation of compact tissue nodules in hormone-dependent tobacco callus cultures. These nodules, upon subculture, behaved like partially transformed plant tumors. They grew on cytokinin-free media, while control callus and nonnodule tissue still required an exogenous cytokinin source. The data indicate that substituted fluorenes, including carcinogenic aminofluorenes, can cause a neoplastic growth response in cultured tobacco tissues. Of particular interest in this study is the finding that a directed and heritable cellular change is induced in tobacco tissue in which a specific (the endogenous cytokinin) biosynthetic system is regularly and persistently activated
Preferences of Indian Meal Moth Larvae for Different Dog Foods
Indian meal moths (IMM), Plodiainterpuntella, are persistent pests to our foods (Fasulo et al.1998; Plunkett’s Pest Control 2018). When IMMs infest a a food product the resulting value loss is the result of contamination by larvae that leave droppings and silken webs in grain and grain products (Jacob and Calvin 2001). The IMM is an important pest of high-value dog foods and the grain components of these food may influence their infestation. Experiments were conducted with eggs of the IMM to determine if moth larvae would choose and infest the grain-based dog food in comparison to dog foods with a higher meat content. IMM laboratory rearing diet was included for comparison. No-choice and choice tests confirmed the IMM diet to be the most preferred and best for larval development. Forced infestation of 50 IMM eggs on the four different dog foods found difference among them. In two-choice test that require newly hatched larvae to walk to and infest either lab diet or a dog food, the highest proportion of larvae selecting any of the dog foods was on product C, which was a medium quality, grain-free food. These results suggest that IMM infestations in warehouses or consumer’s homes could be prevalent on some dog foods more than others
- …