Probing the optical conductivity of trapped charge-neutral quantum gases

We study a harmonically confined atomic gas which is subjected to an additional external potential such as an optical lattice. Using a linear response formulation, we determine the response of the gas to a small, time-dependent displacement of the harmonic trap and derive a simple exact relation showing that the centre-of-mass position of the atomic cloud is directly related to the global optical conductivity of the system. We demonstrate the usefulness of this approach by calculating the optical conductivity of bosonic atoms in an optical lattice. In the Mott insulating phase, there is clear evidence of an optical Mott gap, providing a proof-of-principle demonstration that the global optical conductivity gives high-quality information about the exci- tations of strongly-correlated quantum gases.Comment: 6 pages, 2 figures. Published versio

Optimal Design of Government Hierarchy for Ecosystem Service Provision

There is broad concern that humans are transforming our environment. This transformation has potential to impact humanity as we depend on the environment ecosystem services. According to the Millennium Assessment (2005), degradation and unsustainable exploitation presently threaten over 60% of ecosystem services with real implications for health and standards of living. Furthermore, both the exploitation of ecosystem services and the growth rate of that exploitation have been far higher in recent decades than ever before due to population growth and rising standards of living, i.e. consumption. Increasing pressure on ecosystem services has driven thinking on mitigation strategies. Payment for ecosystem services (PES) has emerged as a strategy to encourage provision of services or, often, to discourage activities that reduce provision. In economic terms, the inability of agents to capture the full rents of service provision results in divergent private and social values. By creating markets for these services, PES arrangements can correct this disincentive and bring provision closer to the socially optimal level. While private sector PES schemes have been envisioned and in some cases implemented, most large-scale PES programs to date have been implemented by governments. We consider optimal design of policy aimed at increasing the provision of services from private land. In particular, we examine on a theoretical level the possibility of optimal decision-making hierarchies among government agencies targeting ecosystem service provision. Should we have multiple agencies focusing on separate services or one agency coordinating efforts across services? Should policy be implemented nationally, regionally, or locally? Under what conditions and assumptions does one organizational structure stand out as optimal? To answer these questions, we adapt the model of hierarchy design developed by Hart and Moore (JPE, 2005). We develop a two period model of decision-making with n agencies and m assets. The assets are parcels available for targeting under PES schemes. Each agency is tasked with thinking about how to use a subset of the m assets to enhance service provision, according to its mission. Also associated with each agency is some probability of success in its task - i.e., the probability of thinking of a productive use for the assigned subset of assets - and a value generated for society if the task is completed. There is some rivality among assets; the use of an asset by one agency may preclude its use by another. Determination of seniority and assignment of tasks occur in period 0. In period 1, agencies with access to all assets they require carry out the tasks and generate value for society. Assets are unavailable if put to a conflicting use by a senior agency. Altering the hierarchy structure alters the set of completed tasks and thus the total value. We optimize across hierarchies by assigning tasks and seniority in period 0 to maximize total expected value in period 1. Following the development of the model, we explore implications and results. To demonstrate the driving intuition, we provide results in the two-agency, three-agency, and general case. Our results shed light on the optimal design of hierarchies, including the optimal relationship between coordinators (those considering how to use many assets simultaneously) and specialists (those considering a narrower subset of assets). The model relies on a number of assumptions - some of which are more restrictive than others - and we examine the implications for our results of relaxing assumptions. Two preliminary results stand out as generally applicable. First, in an optimal hierarchy an agency's seniority should be inversely related to its probability of success. So agencies with a low probability of having an idea about how to use the assets assigned to them should have high seniority. This seems counter-intuitive as the value of an idea is not considered, but it becomes clearer considering that tasks and seniority are assigned in period 0 to maximize period 1 total expected value. With this endogenized task selection, no agency would be assigned a task with low value and a low probability of success. Second, crisscross hierarchies are never optimal. This result, which states that agency a should never be senior to agency b on one asset and junior on another, is more intuitive. The central contribution of this paper is the adaptation of a theoretical model of hierarchy design to the context of programs targeting ecosystem services. The nature of interaction between various government entities involved in encouraging service provision necessitated an alternative representation of rivality between agencies. Assumptions were evaluated and revised based on their applicability to behavior in this context. Future research may involve further modification of the model to account for issues like threshold effects, joint production, and uncertainty.Environmental Economics and Policy,

Demonstration of a moving guide based atom interferometer for rotation sensing

We demonstrate area-enclosing atom interferometry based on a moving guide. Light pulses along the free propagation direction of a magnetic guide are applied to split and recombine the confined atomic matter-wave, while the atoms are translated back and forth along a second direction in 50 ms. The interferometer is estimated to resolve ten times the earth rotation rate per interferometry cycle. We demonstrate a ``folded figure 8'' interfering configuration for creating a compact, large-area atom gyroscope with multiple-turn interfering paths.Comment: Minor revisio

A dynamic Bayesian nonlinear mixed-effects model of HIV response incorporating medication adherence, drug resistance and covariates

HIV dynamic studies have contributed significantly to the understanding of HIV pathogenesis and antiviral treatment strategies for AIDS patients. Establishing the relationship of virologic responses with clinical factors and covariates during long-term antiretroviral (ARV) therapy is important to the development of effective treatments. Medication adherence is an important predictor of the effectiveness of ARV treatment, but an appropriate determinant of adherence rate based on medication event monitoring system (MEMS) data is critical to predict virologic outcomes. The primary objective of this paper is to investigate the effects of a number of summary determinants of MEMS adherence rates on virologic response measured repeatedly over time in HIV-infected patients. We developed a mechanism-based differential equation model with consideration of drug adherence, interacted by virus susceptibility to drug and baseline characteristics, to characterize the long-term virologic responses after initiation of therapy. This model fully integrates viral load, MEMS adherence, drug resistance and baseline covariates into the data analysis. In this study we employed the proposed model and associated Bayesian nonlinear mixed-effects modeling approach to assess how to efficiently use the MEMS adherence data for prediction of virologic response, and to evaluate the predicting power of each summary metric of the MEMS adherence rates.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS376 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Application of Sentiment Analysis and Machine Learning Techniques to Predict Daily Cryptocurrency Price Returns

This paper examines the effects of social media sentiment relating to Bitcoin on the daily price returns of Bitcoin and other popular cryptocurrencies by utilizing sentiment analysis and machine learning techniques to predict daily price returns. Many investors think that social media sentiment affects cryptocurrency prices. However, the results of this paper find that social media sentiment relating to Bitcoin does not add significant predictive value to forecasting daily price returns for each of the six cryptocurrencies used for analysis and that machine learning models that do not assume linearity between the current day price return and previous daily price returns combined with previous daily sentiment scores were more accurate than machine learning models that assume linearity

From mean-motion resonances to scattered planets: Producing the Solar System, eccentric exoplanets and Late Heavy Bombardments

We show that interaction with a gas disk may produce young planetary systems with closely-spaced orbits, stabilized by mean-motion resonances between neighbors. On longer timescales, after the gas is gone, interaction with a remnant planetesimal disk tends to pull these configurations apart, eventually inducing dynamical instability. We show that this can lead to a variety of outcomes; some cases resemble the Solar System, while others end up with high-eccentricity orbits reminiscent of the observed exoplanets. A similar mechanism has been previously suggested as the cause of the lunar Late Heavy Bombardment. Thus, it may be that a large-scale dynamical instability, with more or less cataclysmic results, is an evolutionary step common to many planetary systems, including our own.Comment: 12 pages, 7 figures, submitted to Ap