Quantitative test of thermal field theory for Bose-Einstein condensates

We present numerical results from a full second order quantum field theory of Bose-Einstein condensates applied to the 1997 JILA experiment [D. S. Jin et al., Phys. Rev. Lett. Vol. 78, 764 (1997)]. Good agreement is found for the energies and decay rates for both the lowest-energy m = 2 and m = 0 modes. The anomalous behaviour of the m = 0 mode is due to experimental perturbation of the non-condensate. The theory includes the coupled dynamics of the condensate and thermal cloud, the anomalous pair average and all relevant finite size effects.Comment: 4 pages, 3 figures. Uses revtex4, amsmath, amssymb and psfra

Should You Be Allowed to Use Your Cellular Phone While Driving?

Regulation of the use of cellular phones by individuals while driving is now commonplace outside the United States and has been proposed in a number of jurisdictions in the United States. There is growing concern that using cellular phones while driving leads to increases in accidents and fatalities. This paper provides an economic analysis of regulatory options for addressing cellular phone usage by drivers of vehicles. While large uncertainties surrounding both benefits and costs exist, a key conclusion is that banning drivers from using cellular phones is a bad idea. Our best estimate is that the costs of a ban are likely to exceed benefits by about $20 billion annually. Less intrusive regulation, such as requiring the use of a hands-free device that would allow a driver to use both hands for steering also is not likely to be economically justified.

Nucleosynthesis in the early history of the solar system

Nucleosynthesis in early history of solar syste

EPA's Arsenic Rule: The Benefits of the Standard Do Not Justify the Costs

The U.S. Environmental Protection Agency recently finalized a rule that would reduce the maximum allowable level of arsenic in drinking water by 80 percent. While arsenic is thought to be essential for the human body at low levels, it can cause cancer when consumed at higher concentrations for extended periods of time. This regulatory analysis evaluates the benefits and costs of the EPA's rule. On the basis of currently available information, we find that the EPA's standard cannot be justified on economic grounds. We estimate that the costs of the final rule will exceed the benefits by about $190 million annually. We also find that the rule probably will result in a net loss of life. We find that the rule probably will result in a net loss of life. The direct effect of the rule will be to save about ten lives annually in the future. After taking into account the indirect impacts of the cost of the rule on items like health care expenditures, however, we find that the rule is likely to result in a net loss of about ten lives annually. A question that the rule does not examine carefully is whether other regulatory alternatives could result in positive net benefits. We explore the option of targeting specific water systems and find that this strategy is unlikely to be very helpful. Instead of regulating more stringently now, the agency should wait until more information becomes available over the next few years. Such a strategy would have the advantage of avoiding large capital expenditures until the time that evidence suggests that risks posed by arsenic in drinking water are significant.

Excitations of Bose-Einstein condensates in optical lattices

In this paper we examine the excitations observable in atoms confined in an optical lattice around the superfluid-insulator transition. We use increases in the number variance of atoms, subsequent to tilting the lattice as the primary diagnostic of excitations in the lattice. We show that this locally determined quantity should be a robust indicator of coherence changes in the atoms observed in recent experiments. This was found to hold for commensurate or non-commensurate fillings of the lattice, implying our results will hold for a wide range of physical cases. Our results are in good agreement with the quantitative factors of recent experiments. We do, howevers, find extra features in the excitation spectra. The variation of the spectra with the duration of the perturbation also turns out to be an interesting diagnostic of atom dynamics.Comment: 6 pages, 7 figures, using Revtex4; changes to version 2: new data and substantial revision of tex

A general variational principle for spherically symmetric perturbations in diffeomorphism covariant theories

We present a general method for the analysis of the stability of static, spherically symmetric solutions to spherically symmetric perturbations in an arbitrary diffeomorphism covariant Lagrangian field theory. Our method involves fixing the gauge and solving the linearized gravitational field equations to eliminate the metric perturbation variable in terms of the matter variables. In a wide class of cases--which include f(R) gravity, the Einstein-aether theory of Jacobson and Mattingly, and Bekenstein's TeVeS theory--the remaining perturbation equations for the matter fields are second order in time. We show how the symplectic current arising from the original Lagrangian gives rise to a symmetric bilinear form on the variables of the reduced theory. If this bilinear form is positive definite, it provides an inner product that puts the equations of motion of the reduced theory into a self-adjoint form. A variational principle can then be written down immediately, from which stability can be tested readily. We illustrate our method in the case of Einstein's equation with perfect fluid matter, thereby re-deriving, in a systematic manner, Chandrasekhar's variational principle for radial oscillations of spherically symmetric stars. In a subsequent paper, we will apply our analysis to f(R) gravity, the Einstein-aether theory, and Bekenstein's TeVeS theory.Comment: 13 pages; submitted to Phys. Rev. D. v2: changed formatting, added conclusion, corrected sign convention

Creation of macroscopic superposition states from arrays of Bose-Einstein condensates

We consider how macroscopic quantum superpositions may be created from arrays of Bose-Einstein condensates. We study a system of three condensates in Fock states, all with the same number of atoms and show that this has the form of a highly entangled superposition of different quasi-momenta. We then show how, by partially releasing these condensates and detecting an interference pattern where they overlap, it is possible to create a macroscopic superposition of different relative phases for the remaining portions of the condensates. We discuss methods for confirming these superpositions.Comment: 7 pages, 5 figure

Simultaneous dual-element analyses of refractory metals in naturally occurring matrices using resonance ionization of sputtered atoms

The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed