Culture and Commerce

Illustrates the possibilities and challenges of making partnerships between economic development agencies and traditional arts organizations work. Examines the outcome of eight collaborations that were formed as part of a partnership funding initiative

Electron-electron interactions in decoupled graphene layers

Multi-layer graphene on the carbon face of silicon carbide is an intriguing electronic system which typically consists of a stack of ten or more layers. Rotational stacking faults in this system dramatically reduce inter-layer coherence. In this article we report on the influence of inter-layer interactions, which remain strong even when coherence is negligible, on the Fermi liquid properties of charged graphene layers. We find that inter-layer interactions increase the magnitudes of correlation energies and decrease quasiparticle velocities, even when remote-layer carrier densities are small, and that they lessen the influence of exchange and correlation on the distribution of carriers across layers.Comment: 8 pages, 4 figures, submitte

Phase Diagram of the Bose-Hubbard Model with T_3 symmetry

In this paper we study the quantum phase transition between the insulating and the globally coherent superfluid phases in the Bose-Hubbard model with T_3 structure, the "dice lattice". Even in the absence of any frustration the superfluid phase is characterized by modulation of the order parameter on the different sublattices of the T_3 structure. The zero-temperature critical point as a function of a magnetic field shows the characteristic "butterfly" form. At fully frustration the superfluid region is strongly suppressed. In addition, due to the existence of the Aharonov-Bohm cages at f=1/2, we find evidence for the existence of an intermediate insulating phase characterized by a zero superfluid stiffness but finite compressibility. In this intermediate phase bosons are localized due to the external frustration and the topology of the T_3 lattice. We name this new phase the Aharonov-Bohm (AB) insulator. In the presence of charge frustration the phase diagram acquires the typical lobe-structure. The form and hierarchy of the Mott insulating states with fractional fillings, is dictated by the particular topology of the T_3 lattice. The results presented in this paper were obtained by a variety of analytical methods: mean-field and variational techniques to approach the phase boundary from the superconducting side, and a strongly coupled expansion appropriate for the Mott insulating region. In addition we performed Quantum Monte Carlo simulations of the corresponding (2+1)D XY model to corroborate the analytical calculations with a more accurate quantitative analysis. We finally discuss experimental realization of the T_3 lattice both with optical lattices and with Josephson junction arrays.Comment: 16 pages, 17 figure

Cosmic downsizing of powerful radio galaxies to low radio luminosities

At bright radio powers ($P_{\rm 1.4 GHz} > 10^{25}$ W/Hz) the space density of the most powerful sources peaks at higher redshift than that of their weaker counterparts. This paper establishes whether this luminosity-dependent evolution persists for sources an order of magnitude fainter than those previously studied, by measuring the steep--spectrum radio luminosity function (RLF) across the range $10^{24} < P_{\rm 1.4 GHz} < 10^{28}$ W/Hz, out to high redshift. A grid-based modelling method is used, in which no assumptions are made about the RLF shape and high-redshift behaviour. The inputs to the model are the same as in Rigby et al. (2011): redshift distributions from radio source samples, together with source counts and determinations of the local luminosity function. However, to improve coverage of the radio power vs. redshift plane at the lowest radio powers, a new faint radio sample is introduced. This covers 0.8 sq. deg., in the Subaru/XMM-Newton Deep Field, to a 1.4 GHz flux density limit of $S_{\rm 1.4 GHz} \geq 100~\mu$Jy, with 99% redshift completeness. The modelling results show that the previously seen high-redshift declines in space density persist to $P_{\rm 1.4 GHz} < 10^{25}$ W/Hz. At $P_{\rm 1.4 GHz} > 10^{26}$ W/Hz the redshift of the peak space density increases with luminosity, whilst at lower radio luminosities the position of the peak remains constant within the uncertainties. This `cosmic downsizing' behaviour is found to be similar to that seen at optical wavelengths for quasars, and is interpreted as representing the transition from radiatively efficient to inefficient accretion modes in the steep-spectrum population. This conclusion is supported by constructing simple models for the space density evolution of these two different radio galaxy classes; these are able to successfully reproduce the observed variation in peak redshift.Comment: 7 pages, 6 figures; accepted for publication in Astronomy & Astrophysic

The quantum optical Josephson interferometer

The interplay between coherent tunnel coupling and on-site interactions in dissipation-free bosonic systems has lead to many spectacular observations, ranging from the demonstration of number-phase uncertainty relation to quantum phase transitions. To explore the effect of dissipation and coherent drive on tunnel coupled interacting bosonic systems, we propose a device that is the quantum optical analog of a Josephson interferometer. It consists of two coherently driven linear optical cavities connected via a central cavity with a single-photon nonlinearity. The Josephson-like oscillations in the light emitted from the central cavity as a function of the phase difference between two pumping fields can be suppressed by increasing the strength of the nonlinear coupling. Remarkably, we find that in the limit of ultra-strong interactions in the center-cavity, the coupled system maps on to an effective Jaynes-Cummings system with a nonlinearity determined by the tunnel coupling strength. In the limit of a single nonlinear cavity coupled to two linear waveguides, the degree of photon antibunching from the nonlinear cavity provides an excellent measure of the transition to the nonlinear regime where Josephson oscillations are suppressed.Comment: 9 pages, 7 figure

The quantum optical Josephson interferometer

The interplay between coherent tunnel coupling and on-site interactions in dissipation-free bosonic systems has lead to many spectacular observations, ranging from the demonstration of number-phase uncertainty relation to quantum phase transitions. To explore the effect of dissipation and coherent drive on tunnel coupled interacting bosonic systems, we propose a device that is the quantum optical analog of a Josephson interferometer. It consists of two coherently driven linear optical cavities connected via a central cavity with a single-photon nonlinearity. The Josephson-like oscillations in the light emitted from the central cavity as a function of the phase difference between two pumping fields can be suppressed by increasing the strength of the nonlinear coupling. Remarkably, we find that in the limit of ultra-strong interactions in the center-cavity, the coupled system maps on to an effective Jaynes-Cummings system with a nonlinearity determined by the tunnel coupling strength. In the limit of a single nonlinear cavity coupled to two linear waveguides, the degree of photon antibunching from the nonlinear cavity provides an excellent measure of the transition to the nonlinear regime where Josephson oscillations are suppressed.Comment: 9 pages, 7 figure

Matrix Product State representation for Slater Determinants and Configuration Interaction States

Slater determinants are product states of filled quantum fermionic orbitals. When they are expressed in a configuration space basis chosen a priori, their entanglement is bound and controlled. This suggests that an exact representation of Slater determinants as finitely-correlated states is possible. In this paper we analyze this issue and provide an exact Matrix Product representation for Slater determinant states. We also argue possible meaningful extensions that embed more complex configuration interaction states into the description.Comment: 16 pages, 4 figures. Published in IJMPB, focus issue on "Classical vs. Quantum Correlations in Composite Systems

Fuzzy Inference System for VOLT/VAR control in distribution substations in isolated power systems

This paper presents a fuzzy inference system for voltage/reactive power control in distribution substations. The purpose is go forward to automation distribution and its implementation in isolated power systems where control capabilities are limited and it is common using the same applications as in continental power systems. This means that lot of functionalities do not apply and computational burden generates high response times. A fuzzy controller, with logic guidelines embedded based upon heuristic rules resulting from operators at dispatch control center past experience, has been designed. Working as an on-line tool, it has been tested under real conditions and it has managed the operation during a whole day in a distribution substation. Within the limits of control capabilities of the system, the controller maintained successfully an acceptable voltage profile, power factor values over 0,98 and it has ostensibly improved the performance given by an optimal power flow based automation system

Application of a portable FTIR for measuring on-road emissions

The objective of this work was the development of an onroad in-vehicle emissions measurement technique utilizing a relatively new, commercial, portable Fourier Transform Infra-Red (FTIR) Spectrometer capable of identifying and measuring (at approximately 3 second intervals) up to 51 different compounds. The FTIR was installed in a medium class EURO1 spark ignition passenger vehicle in order to measure on-road emissions. The vehicle was also instrumented to allow the logging of engine speed, road speed, global position, throttle position, air-fuel ratio, air flow and fuel flow in addition to engine, exhaust and catalyst temperatures. This instrumentation allowed the calculation of massbased emissions from the volume-based concentrations measured by the FTIR. To validate the FTIR data, the instrument was used to measure emissions from an engine subjected to a real-world drive cycle using an AC dynamometer. Standard analyzers were operated simultaneously for comparison with the FTIR and the standard analyzer results showed that most pollutants (NOx, CO2, CO) were within ~10% of a standard analyzer during steady state conditions and within 20% during transients. The exception to this was total HC which was generally 50% or less than actual total HC, but this was due to the limited number of hydrocarbons measured by the FTIR. In addition to the regulated emissions, five toxic hydrocarbon species were analyzed and found to be sensitive to cold starts in varying proportions. Finally, FTIR data was compared to results from a commercially available on-road measurement system (Horiba OBS- 1000), and there was good agreement

Spatially Resolved Stellar Populations of Eight GOODS-South Active Galactic Nuclei at z ~ 1

We present a pilot study of the stellar populations of eight active galactic nucleus (AGN) hosts at z ~ 1 and compare with (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the Great Observatories Origins Deep Survey South field obtained with the laser guide star adaptive optics system at Keck Observatory. We combine these K' data with B, V, i, and z imaging from the Advanced Camera for Surveys on Hubble Space Telescope to give multicolor photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGNs as inferred from their high X-ray luminosities (LX > 10^42 erg s^–1) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [O III] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there are only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR spectral energy distributions of the strong Type II AGNs indicate that they are excited to Luminous InfraRed Galaxy (LIRG) status via galactic starbursting, while the strong Type I AGNs are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGNs at z ~ 1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are by-products of this starbursting