Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas

In this article we study the two-dimensional (2D) ultracold Fermi gas with weak impurity in the framework of mean-field theory where the impurity is introduced through Gaussian fluctuations. We have investigated the role of the impurity by studying the experimentally accessible quantities such as condensate fraction and equation of state of the ultracold systems. Our analysis reveals that, at the crossover the disorder enhances superfluidity, which we attribute to the unique nature of the unitary region and to the dimensional effect.Comment: To appear in Int. J. Mod. Phys.

Does Copyright Piracy Pay? The Effects of U.S. International Copyright Laws on the Market for Books, 1790-1920

Does the lack of international copyrights benefit or harm developing countries? I examine the effects of U.S. copyright piracy during a period when the U.S. was itself a developing country. U.S. statutes since 1790 protected the copyrights of American citizens, but until 1891 deemed the works of foreign citizens to be in the public domain. In 1891, the laws were changed to allow foreigners to obtain copyright protection in the United States if certain conditions were met. Thus, this episode in American history provides us with a convenient way of investigating the consequences of international copyright piracy. My analysis is based on copyright registrations, information on authors, book titles and prices, financial data from the accounts of a major publishing company, and lawsuits regarding copyright questions. These data are used to investigate the welfare effects of widespread infringement of foreign works on American publishers, writers, and the public. The results suggest that the United States benefited from piracy and that the choice of copyright regime was endogenous to the level of economic development.

Technological Innovations and Endogenous Changes in U.S. Legal Institutions, 1790-1920

Recent scholarship highlights the importance of institutions to the processes of economic growth, but the precise nature of their relationship bears further examination. This paper considers how the evolution of legal institutions has contributed to, and in turn been affected by, major technological innovations. The first section of the paper examines the U.S. intellectual property system. Patent and copyright laws, and their interpretation and enforcement by the federal judiciary, certainly influenced the course of technical and cultural change, but it is clear that they did not develop independently of the state of technology and of the economy. Both the statutes and their interpretations altered in response to the introduction and diffusion of new technologies. The second section explores in more detail the impact of some of these technological innovations -- including steamboats, railroads, telegraphy, medical technologies, and automobiles -- on the common law, regulation and insurance. Such technological advances often led to institutional bottlenecks, which then required accommodations in legal rules and their enforcement. Although the common law had some capability for economizing on legal adjustment costs through 'adjudication by analogy', the socio-economic changes wrought by major innovations ultimately produced more fundamental change in legal institutions, such as shifts in the relative importance of state and federal policies, and in the degree of reliance on regulation by bureaucracy. In sum, the historical record of the evolution of legal rules and standards in the United States indicates a remarkable degree of flexibility as such institutions responded to changing economic circumstances.

The Dynamics of International R & D spillovers

Coe and Helpman (1995) among others report positive and equivalent R&D spillovers across groups of countries. However, the nature of their econometric tests does not address the heterogeneity of knowledge diffusion across countries. We empirically examine these issues in a sample of 10 OECD countries by extending both the time span and the coverage of R&D activities in the data set. We find that the elasticity of total factor productivity with respect to domestic and foreign R&D stocks is extremely heterogeneous across countries and that data cannot be pooled. Thus, panel estimates conceal important cross-country differences. The US appears to be a net loser in terms of international R&D spillovers. Our interpretation is that when competitors ‘catch-up’ technologically, they challenge US market shares and investments worldwide. This has implications for US productivity

Are international R&D spillovers costly for the US?

Coe and Helpman (1995) and others report positive and equivalent R&D spillovers across G7 countries. We argue that their homogeneity constraint on spillovers across G7 countries is inappropriate, and show that it is rejected by the data. Extending the data set and applying new empirical approaches, we find: (i) R&D spillovers are extremely heterogeneous across G7 countries; (ii) panel estimates do not correspond to country specific estimates and conceal important cross-country differences in knowledge diffusion; and (iii) the US is a net loser in terms of international R&D spillovers. Our interpretation is that when competitors ‘catch-up’ technologically, they challenge US market shares and investments worldwide and this has implications for US productivity

Investigating Dirty Crossover through Fidelity Susceptibility and Density of States

We investigate the BCS-BEC crossover in an ultracold atomic gas in the presence of disorder. The disorder is incorporated in the mean-field formalism through Gaussian fluctuations. We observe evolution to an asymmetric line-shape of fidelity susceptibility as a function of interaction coupling with increasing disorder strength which may point to an impending quantum phase transition. The asymmetric line-shape is further analyzed using the statistical tools of skewness and kurtosis. We extend our analysis to density of states (DOS) for a better understanding of the crossover in the disordered environment.Comment: 12 pages, 6 figures. To appear in Int. J. Mod. Phys.

Growth and Risk-Sharing with Private Information

We examine the impact of incomplete risk-sharing on growth and welfare. The source of market incompleteness in our economy is private information: a household's idiosyncratic productivity shock is not observable by others. Risk-sharing between households occurs through long-term contracts with intermediaries. We find that incomplete risk- sharing tends to reduce the rate of growth relative to the complete risk sharing benchmark. Numerical examples indicate the contracts are relatively efficient and that the growth effects of private information are small.growth, long-term contracts, risk-sharing

Costly technology adoption and capital accumulation

The authors develop a model of costly technology adoption where the cost is irrecoverable and fixed. Households must decide when to switch from an existing technology to a new, more productive technology. Using a recursive approach, the authors show that there is a unique threshold level of wealth above which households will adopt the new technology and below which they will not. This threshold is independent of preference parameters and depends only on technology parameters. Prior to adoption, households invest at increasing rates, but consumption growth is constant. The authors also show that richer households adopt sooner and that income inequality increases over time. Both these results are consistent with the evidence from the Green Revolution.Technology ; Wealth

Costly Technology Adoption and Capital Accumulation

We develop a model of costly technology adoption where the cost is irrecoverable and fixed. Households must decide when to switch from an existing technology to a new, more productive technology. Using a recursive approach, we show that there is a unique threshold level of wealth above which a household will adopt the new technology and below which it will not. This threshold is independent of preference parameters, and depends only on technological parameters. Prior to adoption, households invest at increasing rates but consumption growth is constant. We also show that richer households adopt sooner which is consistent with the evidence from the Green Revolution. Our results are robust to households having access to loans.