380 research outputs found

    Public Policy for Suburban Integration...The Case for New Communities

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    In this Article we examine the integration experience of one type of suburban community - new communities developed from the ground up - to determine whether integration has been beneficial to blacks and low- and moderate-income households, whether it is acceptable to the affluent white majority, and whether new community development is a desirable means of fostering integration

    Coherence control for qubits

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    We study the influence of an external driving field on the coherence properties of a qubit under the influence of bit-flip noise. In the presence of driving, two paradigmatic cases are considered: (i) a field that results for a suitable choice of the parameters in so-called coherent destruction of tunneling and (ii) one that commutes with the static qubit Hamiltonian. In each case, we give for high-frequency driving a lower bound for the coherence time. This reveals the conditions under which the external fields can be used for coherence stabilization.Comment: 15 pages, 1 figur

    Temperature effects on zoeal morphometric traits and intraspecific variability in the hairy crab Cancer setosus across latitude

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    International audiencePhenotypic plasticity is an important but often ignored ability that enables organisms, within species-specific physiological limits, to respond to gradual or sudden extrinsic changes in their environment. In the marine realm, the early ontogeny of decapod crustaceans is among the best known examples to demonstrate a temperature-dependent phenotypic response. Here, we present morphometric results of larvae of the hairy crab , the embryonic development of which took place at different temperatures at two different sites (Antofagasta, 23°45′ S; Puerto Montt, 41°44′ S) along the Chilean Coast. Zoea I larvae from Puerto Montt were significantly larger than those from Antofagasta, when considering embryonic development at the same temperature. Larvae from Puerto Montt reared at 12 and 16°C did not differ morphometrically, but sizes of larvae from Antofagasta kept at 16 and 20°C did, being larger at the colder temperature. Zoea II larvae reared in Antofagasta at three temperatures (16, 20, and 24°C) showed the same pattern, with larger larvae at colder temperatures. Furthermore, larvae reared at 24°C, showed deformations, suggesting that 24°C, which coincides with temperatures found during strong EL Niño events, is indicative of the upper larval thermal tolerance limit.   is exposed to a wide temperature range across its distribution range of about 40° of latitude. Phenotypic plasticity in larval offspring does furthermore enable this species to locally respond to the inter-decadal warming induced by El Niño. Morphological plasticity in this species does support previously reported energetic trade-offs with temperature throughout early ontogeny of this species, indicating that plasticity may be a key to a species' success to occupy a wide distribution range and/or to thrive under highly variable habitat conditions

    The barycentric motion of exoplanet host stars: tests of solar spin-orbit coupling

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    Empirical evidence suggests a tantalising but unproven link between various indicators of solar activity and the barycentric motion of the Sun. The latter is exemplified by transitions between regular and more disordered motion modulated by the motions of the giant planets, and rare periods of retrograde motion with negative orbital angular momentum. An examination of the barycentric motion of exoplanet host stars, and their stellar activity cycles, has the potential of proving or disproving the Sun's motion as an underlying factor in the complex patterns of short- and long-term solar variability indices, by establishing whether such correlations exist in other planetary systems. A variety of complex patterns of barycentric motions of exoplanet host stars is demonstrated, depending on the number, masses and orbits of the planets. Each of the behavioural types proposed to correlate with solar activity are also evident in exoplanet host stars: repetitive patterns influenced by massive multiple planets, epochs of rapid change in orbital angular momentum, and intervals of negative orbital angular momentum. The study provides the basis for independent investigations of the widely-studied but unproven suggestion that the Sun's motion is somehow linked to various indicators of solar activity. We show that, because of the nature of their barycentric motions, the host stars HD168443 and HD74156 offer particularly powerful tests of this hypothesis.Comment: 7 pages, 3 figures. Accepted for publication in A&

    Molecular and atomic line surveys of galaxies I: the dense, star-forming phase as a beacon

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    We predict the space density of molecular gas reservoirs in the Universe, and place a lower limit on the number counts of carbon monoxide (CO), hydrogen cyanide (HCN) molecular and [CII] atomic emission lines in blind redshift surveys in the submillimeter-centimeter spectral regime. Our model uses: (a) recently available HCN Spectral Line Energy Distributions (SLEDs) of local Luminous Infrared Galaxies (LIRGs, L_IR>10^11 L_sun), (b) a value for epsilon=SFR/M_dense(H_2) provided by new developments in the study of star formation feedback on the interstellar medium and (c) a model for the evolution of the infrared luminosity density. Minimal 'emergent' CO SLEDs from the dense gas reservoirs expected in all star-forming systems in the Universe are then computed from the HCN SLEDs since warm, HCN-bright gas will necessarily be CO-bright, with the dense star-forming gas phase setting an obvious minimum to the total molecular gas mass of any star-forming galaxy. We include [CII] as the most important of the far-infrared cooling lines. Optimal blind surveys with the Atacama Large Millimeter Array (ALMA) could potentially detect very distant (z~10-12) [CII] emitters in the >ULIRG galaxy class at a rate of ~0.1-1 per hour (although this prediction is strongly dependent on the star formation and enrichment history at this early epoch), whereas the (high-frequency) Square Kilometer Array (SKA) will be capable of blindly detecting z>3 low-J CO emitters at a rate of ~40-70 per hour. The [CII] line holds special promise for the detection of metal-poor systems with extensive reservoirs of CO-dark molecular gas where detection rates with ALMA can reach up to 2-7 per hour in Bands 4-6.Comment: 16 pages, 9 figures, accepted for publication in Ap

    Phase diffusion as a model for coherent suppression of tunneling in the presence of noise

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    We study the stabilization of coherent suppression of tunneling in a driven double-well system subject to random periodic δ−\delta-function ``kicks''. We model dissipation due to this stochastic process as a phase diffusion process for an effective two-level system and derive a corresponding set of Bloch equations with phase damping terms that agree with the periodically kicked system at discrete times. We demonstrate that the ability of noise to localize the system on either side of the double-well potenital arises from overdamping of the phase of oscillation and not from any cooperative effect between the noise and the driving field. The model is investigated with a square wave drive, which has qualitatively similar features to the widely studied cosinusoidal drive, but has the additional advantage of allowing one to derive exact analytic expressions.Comment: 17 pages, 4 figures, submitted to Phys. Rev.
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