First-principles quantum simulations of dissociation of molecular condensates: Atom correlations in momentum space

We investigate the quantum many-body dynamics of dissociation of a Bose-Einstein condensate of molecular dimers into pairs of constituent bosonic atoms and analyze the resulting atom-atom correlations. The quantum fields of both the molecules and atoms are simulated from first principles in three dimensions using the positive-P representation method. This allows us to provide an exact treatment of the molecular field depletion and s-wave scattering interactions between the particles, as well as to extend the analysis to nonuniform systems. In the simplest uniform case, we find that the major source of atom-atom decorrelation is atom-atom recombination which produces molecules outside the initially occupied condensate mode. The unwanted molecules are formed from dissociated atom pairs with non-opposite momenta. The net effect of this process -- which becomes increasingly significant for dissociation durations corresponding to more than about 40% conversion -- is to reduce the atom-atom correlations. In addition, for nonuniform systems we find that mode-mixing due to inhomogeneity can result in further degradation of the correlation signal. We characterize the correlation strength via the degree of squeezing of particle number-difference fluctuations in a certain momentum-space volume and show that the correlation strength can be increased if the signals are binned into larger counting volumes.Comment: Final published version, with updated references and minor modification

Heavy Quark Fragmentation to Baryons Containing Two Heavy Quarks

We discuss the fragmentation of a heavy quark to a baryon containing two heavy quarks of mass $m_Q\gg\Lambda_{\rm QCD}$. In this limit the heavy quarks first combine perturbatively into a compact diquark with a radius small compared to $1/\Lambda_{\rm QCD}$, which interacts with the light hadronic degrees of freedom exactly as does a heavy antiquark. The subsequent evolution of this $QQ$ diquark to a $QQq$ baryon is identical to the fragmentation of a heavy antiquark to a meson. We apply this analysis to the production of baryons of the form $ccq$, $bbq$, and $bcq$.Comment: 9 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH 93-11, CALT-68-1868, SLAC-PUB-622

Calibration of the LIGO displacement actuators via laser frequency modulation

We present a frequency modulation technique for calibration of the displacement actuators of the LIGO 4-km-long interferometric gravitational-wave detectors. With the interferometer locked in a single-arm configuration, we modulate the frequency of the laser light, creating an effective length variation that we calibrate by measuring the amplitude of the frequency modulation. By simultaneously driving the voice coil actuators that control the length of the arm cavity, we calibrate the voice coil actuation coefficient with an estimated 1-sigma uncertainty of less than one percent. This technique enables a force-free, single-step actuator calibration using a displacement fiducial that is fundamentally different from those employed in other calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit

Do mergers benefit patients in underperforming administrations? Lessons from area health service amalgamation

© 2014 Economic Society of Australia. Evidence supporting the effects of mergers in healthcare markets on quality is mixed. In this study we exploit a government policy in NSW that imposed mergers on area health services (AHSs) to evaluate the effects of the merger on patient waiting times, an indicator of quality. We focus on the specific question of whether the merger had a larger impact on worse-performing AHSs. Our results show heterogeneous impacts, reducing waiting times for relatively urgent public patients but further delaying non-urgent patients. In addition, we find the merger reduced the waiting time gap between public and private patients

Discovering unhealthiness: Evidence from cluster analysis

Purpose: This study examines information on an array of health limitations, chronic conditions, treatments, and drug consumptions to reveal the prevalence and severity of unhealthiness that are not directly observed. Methods: Cluster analysis is applied to 265,468 individuals who participated in the 45 and Up Study in Australia. Results: Among the study participants, 8% of those age 45-54 years, 10% of those age 55-64, 13% of those age 65-74, and 17% of those age 75 and older were classified as unhealthy. For the youngest individuals, unhealthiness is characterized by moderate-to-high mental distress, a poor physical health score equivalent to the score associated with having four major limitations in physical functioning, teeth health less than good, and having been diagnosed with at least two chronic conditions. The oldest individuals also suffer from these limitations, as well as dependence on at least three different drug groups and two medical treatments, but they are in better mental health state. Conclusions: Understanding unhealthiness across population groups will result in more effective allocation of health resources. Older populations require more resources to be devoted to the management of physical health and chronic illnesses. © 2013 Elsevier Inc

Sources of advantageous selection: Evidence using actual health expenditure risk

In a market where insurers are not allowed to risk rate, we find evidence of advantageous selection using observed health expenditure risk. Selection is driven by income and optimism about the future. This may explain insurers' profitability, despite community rating. © 2012 Elsevier B.V