90 research outputs found

    Time to Die?

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    The issue of when life begins has inspired heated debate in this country for nearly half of a century. The importance of this issue cannot be overstated; it has played a pivotal role in elections of public officials and in confirmation hearings of federal judges and justices and has dominated legal, political, economic, religious and ethical discussions. While the issue is far from resolved, it will be joined by another contentious issue in the near future. With our society rapidly getting older, and with the rapidly rising cost of health care, including the extremely high cost of end-of-life care, Americans will soon be confronted with the difficult question of when to die. In fact, the issue of when life ends has the potential to be even more controversial than the abortion issue. Some terminally-ill patients feel that the option of physician assisted suicide (PAS) should be available to them. Two states, Oregon and Washington, have legislation allowing terminally-ill, mentally competent adults to request the medical means to end their lives. Rhode Island currently has legislation making it illegal for anyone to assist another person in the act of committing suicide. This paper will thoroughly examine all sides of the issue from a variety of disciplines. Relying on both extensive research and several interviews with members of the academic and legal communities, this paper will closely look at PAS in both theory and practice. The implementation of the Oregon and Washington laws will be discussed in detail. It will also discuss the potential implications of physician assisted suicide legislation on both a national and a state level in an effort to determine the appropriate response to end of life concerns in the state of Rhode Island

    The Tribal Blues

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    A poe

    Sex allocation and the emergence of helping in cooperatively breeding species.

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    In cooperative breeding systems individuals invest in the reproductive success of others. In this paper, we study the emergence of cooperative breeding systems in which reproductively active breeders receive investment from reproductively non-active helpers. Our goal is to understand how the division of an investment between male and female components of breeder fitness (i.e. the helper sex-allocation strategy) influences the emergence of cooperative breeding itself. Using mathematical models, we arrive at expressions for the inclusive-fitness advantage of helpful behaviour that generalize previous work. These expressions assume an ecologically stable environment, and that breeders make evolutionarily stable sex-allocation decisions. We find that, when breeders are extremely resource limited, the sex-allocation strategy used by a helper can be a key determinant in the success of helpful alleles. This finding, however, is restricted to cases in which helpers have access to intermediate levels of resources. Surprisingly, when helpers can make only a small investment in a recipient the division of the investment matters only very little to advantage of help. By contrast when resources are extremely abundant, we obtain the unsurprising result that the manner in which resources are allocated has little influence on the emergence of help. When breeders have access to intermediate levels of resources we find increasing relatedness can, in certain cases, inhibit the emergence of help. We also find that increasing the amount of resources available to a breeder can impede help as well. Both of these counter-intuitive results are mediated by evolutionary responses in breeder sex allocation

    Feshbach Resonance Cooling of Trapped Atom Pairs

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    Spectroscopic studies of few-body systems at ultracold temperatures provide valuable information that often cannot be extracted in a hot environment. Considering a pair of atoms, we propose a cooling mechanism that makes use of a scattering Feshbach resonance. Application of a series of time-dependent magnetic field ramps results in the situation in which either zero, one, or two atoms remain trapped. If two atoms remain in the trap after the field ramps are completed, then they have been cooled. Application of the proposed cooling mechanism to optical traps or lattices is considered.Comment: 5 pages, 3 figures; v.2: major conceptual change

    Atom-Molecule Laser Fed by Stimulated Three-Body Recombination

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    Using three-body recombination as the underlying process, we propose a method of coherently driving an atomic Bose-Einstein condensate (BEC) into a molecular BEC. Superradiant-like stimulation favors atom-to-molecule transitions when two atomic BECs collide at a resonant kinetic energy, the result being two molecular BEC clouds moving with well defined velocities. Potential applications include the construction of a molecule laser.Comment: 4 pgs, 3 figs, RevTeX4, submitted to PRL; Corrected numerical example

    Kinisi:Bayesian analysis of mass transport from molecular dynamics simulations

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    kinisi is a Python package for estimating transport coefficients—e.g., self-diffusion coefficients, ∗—and their corresponding uncertainties from molecular dynamics simulation data. It includes an implementation of the approximate Bayesian regression scheme described in McCluskey etal. (2023), wherein the mean-squared displacement (MSD) of mobile atoms is modelled as a multivariate normal distribution that is parametrised from the input simulation data. kinisi uses Markov-chain Monte Carlo (Foreman-Mackey et al., 2019; Goodman &amp; Weare, 2010) to sample this model multivariate normal distribution to give a posterior distribution of linear model ensemble MSDs that are compatible with the observed simulation data. For each linear ensemble MSD, x(), a corresponding estimate of the diffusion coefficient, ̂∗ is given via the Einstein relation, ̂∗ =1d x() / 6 d where is time. The posterior distribution of compatible model ensemble MSDs calculated by kinisi gives a point estimate for the most probable value of ∗ , given the observed simulation data, and an estimate of the corresponding uncertainty in ̂∗. kinisi also provides equivalent functionality for estimating collective transport coefficients, i.e., jump-diffusion coefficients and ionic conductivities<br/

    Coherent Quantum Engineering of Free-Space Laser Cooling

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    We perform a quantitative analysis of the cooling dynamics of three-level atomic systems interacting with two distinct lasers. Employing sparse-matrix techniques, we find numerical solutions to the fully quantized master equation in steady state. Our method allows straightforward determination of laser-cooling temperatures without the ambiguity often accompanied by semiclassical calculations, and more quickly than non-sparse techniques. Our calculations allow us to develop an understanding of the regimes of cooling, as well as a qualitative picture of the mechanism, related to the phenomenon of electromagnetically induced transparency. Effects of the induced asymmetric Fano-type lineshapes affect the detunings required for optimum cooling, as well as the predicted minimum temperatures which can be lower than the Doppler limit for either transition.Comment: 5 pages, 3 figure
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