Transport, atom blockade and output coupling in a Tonks-Girardeau gas

Recent experiments have demonstrated how quantum-mechanical impurities can be created within strongly correlated quantum gases and used to probe the coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M. K\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a phenomenological model to simulate such an output coupler for a Tonks-Girardeau gas that shows qualitative agreement with the experimental results for atom transport and output coupling. Our model allows us to explore nonequilibrium transport phenomena in ultracold quantum gases and leads us to predict a regime of atom blockade, where the impurity component becomes localized in the parent cloud despite the presence of gravity. We show that this provides a stable mixed-species quantum gas in the strongly correlated limit

Structural Estimation and Solution of International Trade Models with Heterogeneous Firms

We present an empirical implementation of a general-equilibrium model of international trade with heterogeneous manufacturing firms. The theory underlying our model is consistent with Melitz (2003). A nonlinear structural estimation procedure identifies a set of core parameters and unobserved firm-level trade frictions that best fit the geographic pattern of trade. Once the parameters are identified, we utilize a decomposition technique for computing general-equilibrium counterfactuals. We illustrate this technique using trade and protection data from the Global Trade Analysis Project (GTAP). We first assess the economic effects of reductions in measured tariffs. Taking the simple-average welfare change across regions the Melitz structure indicates welfare gains from liberalization that are nearly four times larger than in a standard policy simulation model. Furthermore, when we compare the economic impact of tariffs with reductions in estimated fixed trade costs we find that policy measures affecting the fixed costs of firmentry are of greater importance than conventional tariff barriers.

Structural Estimation and Solution of International Trade Models with Heterogeneous Firms

We present an empirical implementation of a general-equilibrium model of international trade with heterogeneous manufacturing firms. The theory underlying our model is consistent with Melitz (2003). A nonlinear structural estimation procedure identifies a set of core parameters and unobserved firm-level trade frictions that best fit the geographic pattern of trade. Once the parameters are identified, we utilize a decomposition technique for computing general-equilibrium counterfactuals. We first assess the economic effects of reductions in measured tariffs. Taking the simple-average welfare change across regions the Melitz structure indicates welfare gains from liberalization that are nearly four times larger than in a standard trade policy simulation. Furthermore, when we compare the economic impact of tariff reductions with reductions in estimated fixed trade costs we find that policy measures affecting the fixed costs are of greater importance than tariff barriers

Trade and Welfare: Does Industrial Organization Matter?

Many contemporary theoretic studies of trade over geography reduce to an ex- amination of constant-elasticity reactions to changes in iceberg trade costs. These impacts are readily analyzed in simple constant-returns models based on the Arm- ington (1969) assumption of regionally differentiated goods. Following the line of reasoning suggested by Arkolakis et al. (2008) one can reach the surprising conclu- sion that industrial organization does not matter. In the present paper, we show that this finding is fragile, and with a minor elaboration of their model, the rich industrial-organization features of the popular Melitz (2003) model do, in fact, gen- erate important differences for trade and welfare.Variety effects, Heterogeneous firms, Gains from trade

Modeling services liberalization : the case of Kenya

This paper employs a 55 sector small open economy computable general equilibrium model of the Kenyan economy to assess the impact of the liberalization of regulatory barriers against foreign and domestic business service providers in Kenya. The model incorporates productivity effects in both goods and services markets endogenously, through a Dixit-Stiglitz framework. It estimates the ad valorem equivalent of barriers to foreign direct investment based on detailed questionnaires completed by specialists in Kenya. The authors estimate that Kenya will gain about 11 percent of the value of Kenyan consumption in the medium run (or about 10 percent of gross domestic product) from a full reform package that also includes uniform tariffs. The estimated gains increase to 77 percent of consumption in the long-run steady-state model, where the impact on the accumulation of capital from an improvement in the productivity of capital is taken into account. Decomposition exercises reveal that the largest gains to Kenya will derive from liberalization of costly regulatory barriers that are non-discriminatory in their impacts between Kenyan and multinational service providers.Transport Economics Policy&Planning,Economic Theory&Research,Banks&Banking Reform,Emerging Markets,Debt Markets

Modelling Harvester-Forwarder System Performance in a Selection Harvest

A harvester - forwarder system was studied in a selection harvest operation conducted in an interior forest stand composed of Douglas fir (Pseudotsuga menziesii), Ponderosa pine (Pinus ponderosa), and Grand fir (Abies grandis). A time-study analysis was used to develop models for predicting individual machine productivity over time for both the harvester and forwarder involved in the study. Analysis indicates that harvester productivity (13.85 m3 per SMH) closely matched forwarder production (14.10 m3 per SMH) during the study. Further analysis yielded models that can be used to predict system productivity across the range of stand values observed during the study. The results suggest that system productivity is balanced when operating in stands averaging 15 to 25 cm DBH. In stands of larger or smaller average diameter, productivity for the system becomes unbalanced and affects machine operation, particularly the forwarder. Further research is suggested to improve the developed predictor models and allow for prediction of system performance over a broad range of stand and site conditions

Doppler cooling of gallium atoms: 2. Simulation in complex multilevel systems

This paper derives a general procedure for the numerical solution of the Lindblad equations that govern the coherences arising from multicoloured light interacting with a multilevel system. A systematic approach to finding the conservative and dissipative terms is derived and applied to the laser cooling of gallium. An improved numerical method is developed to solve the time-dependent master equation and results are presented for transient cooling processes. The method is significantly more robust, efficient and accurate than the standard method and can be applied to a broad range of atomic and molecular systems. Radiation pressure forces and the formation of dynamic dark-states are studied in the gallium isotope 66Ga.Comment: 15 pages, 8 figure

The Impact of Border Carbon Adjustments under Alternative Producer Responses

Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/)Border carbon adjustments (BCAs) have been proposed to address leakage and competitiveness concerns. In traditional assessments, firms regard BCAs as output taxes rather than implicit emissions taxes. Using a stylized energy-economic model, we analyze the impact of BCAs for alternative producer responses. When firms view BCAs as an implicit emissions tax, the outcome depends on whether or not firms can differentiate production across destination markets. If firms are able to produce a low-emissions variety for regions imposing BCAs, results are similar to when firms regard BCAs as an output tax. If firms produce a single variety for all markets, BCAs result in larger leakage reductions than in standard approaches. We also find that BCAs are less effective at addressing competitive concerns in scenarios that result in larger leakage reductions.This study received support from the MIT Joint Program on the Science and Policy of Global Change, which is funded by a consortium of government, industry and foundation sponsors

Knizhnik-Zamolodchikov equations and the Calogero-Sutherland-Moser integrable models with exchange terms

It is shown that from some solutions of generalized Knizhnik-Zamolodchikov equations one can construct eigenfunctions of the Calogero-Sutherland-Moser Hamiltonians with exchange terms, which are characterized by any given permutational symmetry under particle exchange. This generalizes some results previously derived by Matsuo and Cherednik for the ordinary Calogero-Sutherland-Moser Hamiltonians.Comment: 13 pages, LaTeX, no figures, to be published in J. Phys.