Pseudogap and incommensurate magnetic fluctuations in YBa_2Cu_3O_{6. 6}

Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility, $\chi''(q,\omega)$, of a well characterized single crystal $YBa_2Cu_3O_{6.6}$ ($T_c=62.7$ K). We find that a pseudogap opens in the spin fluctuation spectrum at temperatures well above $T_c$. We speculate that the appearance of the low frequency incommensurate fluctuations is associated with the opening of the pseudogap. To within the error of the measurements, a gap in the spin fluctuation spectrum is found in the superconducting state.Comment: 6 pages, 3 ps figs, Proceedings of ICNS, Physica B, to be publishe

Macro- and micro-strain in GaN nanowires on Si(111)

We analyze the strain state of GaN nanowire ensembles by x-ray diffraction. The nanowires are grown by molecular beam epitaxy on a Si(111) substrate in a self-organized manner. On a macroscopic scale, the nanowires are found to be free of strain. However, coalescence of the nanowires results in micro-strain with a magnitude from +-0.015% to +-0.03%.This micro-strain contributes to the linewidth observed in low-temperature photoluminescence spectra

Access Pricing, Competition, and Incentives to Migrate From"Old" to "New" Technology - Harvard Kennedy School of Government RWP11-029

In this paper, we analyze the incentives of an incumbent and an entrant to migrate from an "old" technology to a "new" technology, and discuss how the terms of wholesale access affect this migration. We show that a higher access charge on the legacy network pushes the entrant firm to invest more, but has an ambiguous effect on the incumbent's investments, due to two conflicting effects: the wholesale revenue effect, and the business migration effect. If both the old and the new infrastructures are subject to ex-ante access regulation, we also find that the two access charges are positively correlate

Heisenberg Uncertainty Principle as Probe of Entanglement Entropy: Application to Superradiant Quantum Phase Transitions

Quantum phase transitions are often embodied by the critical behavior of purely quantum quantities such as entanglement or quantum fluctuations. In critical regions, we underline a general scaling relation between the entanglement entropy and one of the most fundamental and simplest measure of the quantum fluctuations, the Heisenberg uncertainty principle. Then, we show that the latter represents a sensitive probe of superradiant quantum phase transitions in standard models of photons such as the Dicke Hamiltonian, which embodies an ensemble of two-level systems interacting with one quadrature of a single and uniform bosonic field. We derive exact results in the thermodynamic limit and for a finite number N of two-level systems: as a reminiscence of the entanglement properties between light and the two-level systems, the product $\Delta x\Delta p$ diverges at the quantum critical point as $N^{1/6}$. We generalize our results to the double quadrature Dicke model where the two quadratures of the bosonic field are now coupled to two independent sets of two level systems. Our findings, which show that the entanglement properties between light and matter can be accessed through the Heisenberg uncertainty principle, can be tested using Bose-Einstein condensates in optical cavities and circuit quantum electrodynamicsComment: 7 pages, 3 figures. Published Versio

Copyright Law and Subject Matter Specificity: The Case of Computer Software

Drawing on recent work by Dan Burk and Mark Lemley in the patent context, this paper explores the extent to which courts have adapted pre-existing copyright doctrines to the special case of computer software. We argue that a number of courts have, as has been widely recognized, significantly adapted copyright doctrines to deal with special features of the computer software market. We further argue that these adaptations have, by and large, positively sought to strike a balance between the copyright act\u27s dual goals of incentive and access. Despite this general trend toward adaptation, however, we point to a handful of instances in which courts and legislatures have adopted a more wooden approach to software copyright questions. Given the nuanced nature of copyright law\u27s underlying goals, we contend that some level of flexibility and adaptation is critical in the software context, where network effects, interoperability, and functionality play a prominent role. We suggest that copyright law should-and indeed must-have some vehicle for considering these unique features of software markets, and we recommend a number of changes to maintain the more flexible, policy-lever approach to software copyright law

Access Pricing, Competition, and Incentives to Migrate From“Old” to “New” Technology - Harvard Kennedy School of Government RWP11-029

In this paper, we analyze the incentives of an incumbent and an entrant to migrate from an “old” technology to a “new” technology, and discuss how the terms of wholesale access affect this migration. We show that a higher access charge on the legacy network pushes the entrant firm to invest more, but has an ambiguous effect on the incumbent’s investments, due to two conflicting effects: the wholesale revenue effect, and the business migration effect. If both the old and the new infrastructures are subject to ex-ante access regulation, we also find that the two access charges are positively correlated

Access regulation and the transition from copper to fiber networks in telecoms

In this paper we study the impact of different forms of access obligations on firms’ incentives to migrate from the legacy copper network to ultra-fast broadband infrastructures. We analyze three different kinds of regulatory interventions: geographical regulation of access to copper networks–where access prices are differentiated depending on whether or not an alternative fiber network has been deployed; access obligations on fiber networks and its interplay with wholesale copper prices; and, finally, a mandatory switch-off of the legacy copper network–to foster the transition to the higher quality fiber networks. Trading-off the different static and dynamic goals, the paper provides guidelines and suggestions for policy makers’ decisions

Wheat Mill Stream Properties for Discrete Element Method Modeling

A discrete phase approach based on individual wheat kernel characteristics is needed to overcome the limitations of previous statistical models and accurately predict the milling behavior of wheat. As a first step to develop a discrete element method (DEM) model for the wheat milling process, this study determined the physical and mechanical properties of wheat mill streams (wheat kernels, break stream, and wheat flour) required as input parameters. The parameters measured were particle size and size distribution, bulk density, Young’s modulus, static and rolling coefficients of friction, and coefficient of restitution. The effect of moisture content (12% to 16% wet basis) on these properties was evaluated. The density, Young’s modulus, and coefficient of restitution tended to decrease while the coefficients of friction tended to increase with increasing moisture content of wheat kernels. The effect of moisture content on material properties was significant for break stream, but there was no significant (p > 0.05) material property change with moisture content for flour. It was concluded that moisture content had a greater significant effect on physical properties (bulk, true, and tapped densities and particle size) of the mill streams than it did on the mechanical properties (Young’s modulus, coefficients of static and rolling friction, and coefficient of restitution)