24,120 research outputs found
Frustrated Polyelectrolyte Bundles and T=0 Josephson-Junction Arrays
We establish a one-to-one mapping between a model for hexagonal
polyelectrolyte bundles and a model for two-dimensional, frustrated
Josephson-junction arrays. We find that the T=0 insulator-to-superconductor
transition of the {\it quantum} system corresponds to a continuous
liquid-to-solid transition of the condensed charge in the finite temperature
{\it classical} system. We find that the role of the vector potential in the
quantum system is played by elastic strain in the classical system. Exploiting
this correspondence we show that the transition is accompanied by a spontaneous
breaking of chiral symmetry and that at the transition the polyelectrolyte
bundle adopts a universal response to shear.Comment: 4 pages, 2 figures, 1 table minor changes to text, reference adde
Evaluating incentive mechanisms for conserving habitat
Private lands have an important role in the success of the Endangered Species Act (ESA). The current command-andcontrol approach to protecting species on private land has resulted in disincentives to the landowner, which have decreased the ability of the ESA to protect many of our endangered and threatened species. Herein we define and evaluate, from an economic perspective, eight incentive mechanisms, including the status quo, for protecting species on private land. We highlight the strengths and weaknesses and compare and contrast the incentive mechanisms according to a distinct set of biological, landowner, and government criteria. Our discussion indicates that market instruments, such as tradable permits or taxes, which have been successful in controlling air pollution, are not as effective for habitat protection. Alternatively, voluntary incentive mechanisms can be designed such that landowners view habitat as an asset and are willing participants in protecting habitat. The incentive mechanism best suited for conserving habitat in a given region depends on many factors, including government funding, land values, quantity and quality of habitat, and the region's developmental pressure.Incentives, Conservation, TDRs, Subsidies, Zoning, conservation Easements, mitigation banking, impact fees
How Hot is the Wind from TW Hydrae?
It has recently been suggested that the winds from Classical T Tauri stars in
general, and the wind from TW Hya in particular, reaches temperatures of at
least 300,000 K while maintaing a mass loss rate of \Msol
yr or larger. If confirmed, this would place strong new requirements on
wind launching and heating models. We therefore re-examine spectra from the
Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope and
spectra from the Far Ultraviolet Spectroscopic Explorer satellite in an effort
to better constrain the maximum temperature in the wind of TW Hya. We find
clear evidence for a wind in the \ion{C}{2} doublet at 1037 \AA and in the
\ion{C}{2} multiplet at 1335 \AA. We find no wind absorption in the \ion{C}{4}
1550 \AA doublet observed at the same time as the \ion{C}{2} 1335 \AA line or
in observations of \ion{O}{6} observed simultaneously with the \ion{C}{2} 1037
\AA line. The presence or absence of \ion{C}{3} wind absorption is ambiguous.
The clear lack of a wind in the \ion{C}{4} line argues that the wind from TW
Hya does not reach the 100,000 K characteristic formation temperature of this
line. We therefore argue that the available evidence suggests that the wind
from TW Hya, and probably all classical T Tauri stars, reaches a maximum
temperature in the range of 10,000 -- 30,000 K.Comment: 17 pages, 3 figures, Figure 1 in 2nd version fixes a small velocity
scaling error and new revision adds a reference to an additional paper
recently foun
Efficient diagnosis of multiprocessor systems under probabilistic models
The problem of fault diagnosis in multiprocessor systems is considered under a probabilistic fault model. The focus is on minimizing the number of tests that must be conducted in order to correctly diagnose the state of every processor in the system with high probability. A diagnosis algorithm that can correctly diagnose the state of every processor with probability approaching one in a class of systems performing slightly greater than a linear number of tests is presented. A nearly matching lower bound on the number of tests required to achieve correct diagnosis in arbitrary systems is also proven. Lower and upper bounds on the number of tests required for regular systems are also presented. A class of regular systems which includes hypercubes is shown to be correctly diagnosable with high probability. In all cases, the number of tests required under this probabilistic model is shown to be significantly less than under a bounded-size fault set model. Because the number of tests that must be conducted is a measure of the diagnosis overhead, these results represent a dramatic improvement in the performance of system-level diagnosis techniques
Tradable Set-Aside Requirements (TSARs): Conserving Spatially Dependent Environmental Amenities
In the lab, we examine the effectiveness of two land use conservation policies: a tradable set aside requirements (TSARs), and the TSARs combined with an agglomeration bonus. Evaluated by bioeconomic efficiency, our experimental results suggest: 1) TSARs is a cost-effective land conservation tool; and 2) combining TSARS with the agglomeration bonus increases habitat connectivity but at a price—lower economic efficiency.Conservation, tradable development rights, spatial conservation, market instruments
Experimental Economics and the Environment: Eliciting Values for Controversial Goods
We illustrate the experimental method by examining bidding behavior for controversial goods, i.e., goods in which bidders have positive and negative values. Our results suggest that bidding behavior differs across auction type. Bidders with positive induced values bid sincerely in a WTP auction. Bidders bid conservatively, however, in the WTA auction, foregoing profitable opportunities. Informing bidders of their optimal strategy serves to attenuate bidding discrepancies but does not eliminate them. Treating the WTP and WTA auctions as equivalent given positive and negative values could lead one to overstate the costs relative to the benefits of the controversial good.experiments, willingness to pay, willingness to accept, positive and negative induced values, Crop Production/Industries, Institutional and Behavioral Economics,
Quadratic Dynamical Decoupling with Non-Uniform Error Suppression
We analyze numerically the performance of the near-optimal quadratic
dynamical decoupling (QDD) single-qubit decoherence errors suppression method
[J. West et al., Phys. Rev. Lett. 104, 130501 (2010)]. The QDD sequence is
formed by nesting two optimal Uhrig dynamical decoupling sequences for two
orthogonal axes, comprising N1 and N2 pulses, respectively. Varying these
numbers, we study the decoherence suppression properties of QDD directly by
isolating the errors associated with each system basis operator present in the
system-bath interaction Hamiltonian. Each individual error scales with the
lowest order of the Dyson series, therefore immediately yielding the order of
decoherence suppression. We show that the error suppression properties of QDD
are dependent upon the parities of N1 and N2, and near-optimal performance is
achieved for general single-qubit interactions when N1=N2.Comment: 17 pages, 22 figure
Rotationally Modulated X-ray Emission from T Tauri Stars
We have modelled the rotational modulation of X-ray emission from T Tauri
stars assuming that they have isothermal, magnetically confined coronae. By
extrapolating surface magnetograms we find that T Tauri coronae are compact and
clumpy, such that rotational modulation arises from X-ray emitting regions
being eclipsed as the star rotates. Emitting regions are close to the stellar
surface and inhomogeneously distributed about the star. However some regions of
the stellar surface, which contain wind bearing open field lines, are dark in
X-rays. From simulated X-ray light curves, obtained using stellar parameters
from the Chandra Orion Ultradeep Project, we calculate X-ray periods and make
comparisons with optically determined rotation periods. We find that X-ray
periods are typically equal to, or are half of, the optical periods. Further,
we find that X-ray periods are dependent upon the stellar inclination, but that
the ratio of X-ray to optical period is independent of stellar mass and radius.Comment: 10 pages, 8 figures, accepted for publication in MNRA
On General Off-Shell Representations of Worldline (1D) Supersymmetry
Every finite-dimensional unitary representation of the N-extended worldline
supersymmetry without central charges may be obtained by a sequence of
differential transformations from a direct sum of minimal Adinkras, simple
supermultiplets that are identifiable with representations of the Clifford
algebra. The data specifying this procedure is a sequence of subspaces of the
direct sum of Adinkras, which then opens an avenue for classification of the
continuum of so constructed off-shell supermultiplets.Comment: 21 pages, 5 illustrations; references update
The magnetic fields of forming solar-like stars
Magnetic fields play a crucial role at all stages of the formation of low
mass stars and planetary systems. In the final stages, in particular, they
control the kinematics of in-falling gas from circumstellar discs, and the
launching and collimation of spectacular outflows. The magnetic coupling with
the disc is thought to influence the rotational evolution of the star, while
magnetised stellar winds control the braking of more evolved stars and may
influence the migration of planets. Magnetic reconnection events trigger
energetic flares which irradiate circumstellar discs with high energy particles
that influence the disc chemistry and set the initial conditions for planet
formation. However, it is only in the past few years that the current
generation of optical spectropolarimeters have allowed the magnetic fields of
forming solar-like stars to be probed in unprecedented detail. In order to do
justice to the recent extensive observational programs new theoretical models
are being developed that incorporate magnetic fields with an observed degree of
complexity. In this review we draw together disparate results from the
classical electromagnetism, molecular physics/chemistry, and the geophysics
literature, and demonstrate how they can be adapted to construct models of the
large scale magnetospheres of stars and planets. We conclude by examining how
the incorporation of multipolar magnetic fields into new theoretical models
will drive future progress in the field through the elucidation of several
observational conundrums.Comment: 55 pages, review article accepted for publication in Reports on
Progress in Physics. Astro-ph version includes additional appendice
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