Hadron structure on the back of an envelope

In order to remove a little of the mysticism surrounding the issue of strangeness in the nucleon, we present simple, physically transparent estimates of both the strange magnetic moment and charge radius of the proton. Although simple, the estimates are in quite good agreement with sophisticated calculations using the latest input from lattice QCD. We further explore the possible size of systematic uncertainties associated with charge symmetry violation (CSV) in the recent precise determination of the strange magnetic moment of the proton. We find that CSV acts to increase the error estimate by 0.003 \mu_N such that G_M^s = -0.046 +/- 0.022 \mu_N.Comment: 9 pages, 1 figure, Invited talk at First Workshop on Quark-Hadron Duality and the Transition to pQCD, Frascati, June 6-8 200

Considerations on the Role of Fall-Back Discs in the Final Stages of the Common Envelope Binary Interaction

The common envelope interaction is thought to be the gateway to all evolved compact binaries and mergers. Hydrodynamic simulations of the common envelope interaction between giant stars and their companions are restricted to the dynamical, fast, in-spiral phase. They find that the giant envelope is lifted during this phase, but remains mostly bound to the system. At the same time, the orbital separation is greatly reduced, but in most simulations it levels off? at values larger than measured from observations. We conjectured that during the post-in-spiral phase the bound envelope gas will return to the system. Using hydrodynamic simulations, we generate initial conditions for our simulation that result in a fall-back disk with total mass and angular momentum in line with quantities from the simulations of Passy et al. We find that the simulated fall-back event reduces the orbital separation efficiently, but fails to unbind the gas before the separation levels off once again. We also find that more massive fall-back disks reduce the orbital separation more efficiently, but the efficiency of unbinding remains invariably very low. From these results we deduce that unless a further energy source contributes to unbinding the envelope (such as was recently tested by Nandez et al.), all common envelope interactions would result in mergers. On the other hand, additional energy sources are unlikely to help, on their own, to reduce the orbital separation. We conclude by discussing our dynamical fall-back event in the context of a thermally-regulated post-common envelope phase.Comment: 12 pages, 12 pages, Accepted to MNRA

Dynamic Scoring: A Back-of-the-Envelope Guide

This paper uses the neoclassical growth model to examine the extent to which a tax cut pays for itself through higher economic growth. The model yields simple expressions for the steady-state feedback effect of a tax cut. The feedback is surprisingly large: for standard parameter values, half of a capital tax cut is self-financing. The paper considers various generalizations of the basic model, including elastic labor supply, departures from infinite horizons, and non-neoclassical production settings. It also examines how the steady-state results are modified when one considers the transition path to the steady state.

Properties of Gamma-Ray Burst Progenitor Stars

We determine some basic properties of stars that produce spectacular gamma-ray bursts at the end of their life. We assume that accretion of the outer portion of the stellar core by a central black hole fuels the prompt emission, and that fall-back and accretion of the stellar envelope later produces the plateau in the X-ray light curve seen in some bursts. Using X-ray data for three bursts we estimate the radius of the stellar core to be ~ 1-3 x 10^10 cm, and that of the stellar envelope to be ~ 1-2 x 10^11 cm. The density profile in the envelope is fairly shallow, with \rho ~ r^-2. The rotation speeds of the core and envelope are ~ 0.05 and ~ 0.2 of the local Keplerian speed, respectively.Comment: Science in pres

Back of the envelope estimates of environmental damage costs in Mexico

For developing countries, budget constraints help set the agenda on mitigating environmental damage, one of the indelible marks of our era. Political considerations often dictate the measures taken. There are no firm analytical formulas to help even environmentally conscious policymakers rank needs and remedies. A developing country such as Mexico - the focus of this paper - cannot afford an in-depth study of every environmental issue. Policymakers need to be provided with rough,"back-of-the envelope"estimates of the economic costs of various environmental problems. This allows them to rank the issues and act. In this paper the author applied existing methods to estimate the costs stemming from different environmental problems in Mexico. Although the examples are from Mexico, the method can be useful in other developing countries as well. The author how creative use of U.S. and other data can help provide simple estimates of the likely costs of soil erosion, air pollution, mining of underground waters, and estimates of the health effects of water and solid waste pollution, lack of sanitation, and the ingestion of food contaminated by polluted irrigation. The assumptions underlying all calculations are conservative. Some environmental damage issues, such as loss of biodiversity, were too complex to permit quantification.Water Conservation,Economic Theory&Research,Health Monitoring&Evaluation,Environmental Economics&Policies,Pollution Management&Control