44,948 research outputs found
City-regionalism as a politics of collective provision : regional transport infrastructure in Denver, USA
The rise of the city-region concept has focused attention on the nature of territorial politics underpinning city-regionalism. This paper investigates the relationship between territorial politics, city-regionalism and the collective provision of mass transport infrastructure in the USA. It deploys a case study of the Denver region, examining the state and governance structures driving forward FasTracks, a long-term project to expand the Denver Regional Transportation District’s light and commuter rail system. FasTracks represents a programme to retrofit the Denver city-region for integrated mass transit but its funding has fostered tensions around new regionalist governance arrangements. The paper uses the findings of the case study to reflect upon the balance of bottom–up versus top–down geopolitical forces shaping the landscape of city-regionalism in the USA. It emphasises the variety of ways in which struggles around infrastructure provision shape the emergence of new city-regionalist structures inside the competition state
Boson stars in the centre of galaxies?
We investigate the possible gravitational redshift values for boson stars
with a self-interaction, studying a wide range of possible masses. We find a
limiting value of z_lim \simeq 0.687 for stable boson star configurations. We
can exclude the direct observation of boson stars. X-ray spectroscopy is
perhaps the most interesting possibility
On reduction of differential inclusions and Lyapunov stability
In this paper, locally Lipschitz, regular functions are utilized to identify
and remove infeasible directions from set-valued maps that define differential
inclusions. The resulting reduced set-valued map is point-wise smaller (in the
sense of set containment) than the original set-valued map. The corresponding
reduced differential inclusion, defined by the reduced set-valued map, is
utilized to develop a generalized notion of a derivative for locally Lipschitz
candidate Lyapunov functions in the direction(s) of a set-valued map. The
developed generalized derivative yields less conservative statements of
Lyapunov stability theorems, invariance theorems, invariance-like results, and
Matrosov theorems for differential inclusions. Included illustrative examples
demonstrate the utility of the developed theory
Two-channel Kondo physics in odd impurity chains
We study odd-membered chains of spin-(1/2) impurities, with each end
connected to its own metallic lead. For antiferromagnetic exchange coupling,
universal two-channel Kondo (2CK) physics is shown to arise at low energies.
Two overscreening mechanisms are found to occur depending on coupling strength,
with distinct signatures in physical properties. For strong inter-impurity
coupling, a residual chain spin-(1/2) moment experiences a renormalized
effective coupling to the leads; while in the weak-coupling regime, Kondo
coupling is mediated via incipient single-channel Kondo singlet formation. We
also investigate models where the leads are tunnel-coupled to the impurity
chain, permitting variable dot filling under applied gate voltages. Effective
low-energy models for each regime of filling are derived, and for even-fillings
where the chain ground state is a spin singlet, an orbital 2CK effect is found
to be operative. Provided mirror symmetry is preserved, 2CK physics is shown to
be wholly robust to variable dot filling; in particular the single-particle
spectrum at the Fermi level, and hence the low-temperature zero-bias
conductance, is always pinned to half-unitarity. We derive a Friedel-Luttinger
sum rule and from it show that, in contrast to a Fermi liquid, the Luttinger
integral is non-zero and determined solely by the `excess' dot charge as
controlled by gate voltage. The relevance of the work to real quantum dot
devices, where inter-lead charge-transfer processes fatal to 2CK physics are
present, is also discussed. Physical arguments and numerical renormalization
group techniques are used to obtain a detailed understanding of these problems.Comment: 21 pages, 19 figure
Commensurability oscillations due to pinned and drifting orbits in a two-dimensional lateral surface superlattice
We have simulated conduction in a two-dimensional electron gas subject to a
weak two-dimensional periodic potential, . The usual commensurability oscillations in are seen with
alone. An increase of suppresses these oscillations, rather than
introducing the additional oscillations in expected from
previous perturbation theories. We show that this behavior arises from drift of
the guiding center of cyclotron motion along contours of an effective
potential. Periodic modulation in the magnetic field can be treated in the same
way.Comment: 3 pages text, 4 eps figures, revte
The Near Infrared and Multiwavelength Afterglow of GRB 000301c
We present near-infrared observations of the counterpart of GRB 000301c. The
K' filter (2.1 micron) light curve shows a well-sampled break in the decay
slope at t=3.5 days post-burst. The early time slope is very shallow (~ -0.1),
while the late time slope is steep (-2.2). Comparison with the optical (R band)
light curve shows marginally significant differences, especially in the early
time decay slope (which is steeper in the optical) and the break time (which
occurs later in the optical). This is contrary to the general expectation that
light curve breaks should either be achromatic (e.g., for breaks due to
collimation effects) or should occur later at longer wavelengths (for most
other breaks). The observed color variations might be intrinsic to the
afterglow, or might indicate systematic errors of > 0.08 magnitude in all
fluxes. Even if the break is achromatic, we argue that its sharpness poses
difficulties for explanations that depend on collimated ejecta. The R light
curve shows further signs of fairly rapid variability (a bump, steep drop, and
plateau) that are not apparent in the K' light curve. In addition, by combining
the IR-optical-UV data with millimeter and radio fluxes, we are able to
constrain the locations of the self-absorption break and cooling break and to
infer the location of the spectral peak at t=3 days: f_nu = 3.4 mJy at nu=1e12
Hz. Using the multiwavelength spectral energy distribution, we are able to
constrain the blast wave energy, which was E > 3e53 erg if the explosion was
isotropic. This implies a maximum gamma ray production efficiency of ~ 0.15 for
GRB 000301C.Comment: Accepted to The Astrophysical Journal. 24 pages, 4 figures, 3 tables;
uses AASTeX 5 macros. This version includes a new figure (R-K' color vs.
time), a better sampled R band light curve, and more extensive discussion of
the optical data and error analysi
Fish -- More Than Just Another Commodity
This brief highlights the contribution of wild capture fisheries to nutritional security in fish dependent developing countries. It is intended to stimulate debate around two broad themes: (1) when should the focus of fisheries policies be on local food security and human well-being as opposed to revenue generation, and (2) how does the current research agenda, with its emphasis on environmental and economic issues, assist or impair decision making processes
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