9,316 research outputs found
Club Efficiency and Lindahl Equilibrium with Semi-Public Goods
Limit core allocations are the ones that remain in the core of a replicated economy. An equivalent notion for economies with public goods is Schweizer's club efficiency. We extend this notion to economies with goods that have a semi-public nature. The notion encompasses purely private as well as purely public club goods as polar cases. We show that given certain conditions the equivalence of club efficient allocations and Lindahl equilibria holds for a wide range of economies with semi-public club goods. We also show that extension to a more general class of economies seems implausible.clubs;club efficiency;Lindahl equilibrium;limit cores
Lindahl Equilibrium and Schweitzer's Open Club Model Semi-Public Goods
Limit core allocations are the ones that remain in the core of a replicated economy.An equivalent notion for economies with public goods is Schweizer s concept of club e ciency under a variable number of economic agents.We extend this notion to economies with goods that have a semi-public nature.We show that given certain conditions the equivalence of club e cient allocations and Lindahl equilibria holds for a wide range of economies with semi-public club goods.We also show that extension to a more general class of economies seems implausible.general equilibrium;public goods;efficiency;allocation
A unified picture of ferromagnetism, quasi-long range order and criticality in random field models
By applying the recently developed nonperturbative functional renormalization
group (FRG) approach, we study the interplay between ferromagnetism, quasi-long
range order (QLRO) and criticality in the -dimensional random field O(N)
model in the whole (, ) diagram. Even though the "dimensional reduction"
property breaks down below some critical line, the topology of the phase
diagram is found similar to that of the pure O(N) model, with however no
equivalent of the Kosterlitz-Thouless transition. In addition, we obtain that
QLRO, namely a topologically ordered "Bragg glass" phase, is absent in the
3--dimensional random field XY model. The nonperturbative results are
supplemented by a perturbative FRG analysis to two loops around .Comment: 4 pages, 4 figure
Two-loop Functional Renormalization Group of the Random Field and Random Anisotropy O(N) Models
We study by the perturbative Functional Renormalization Group (FRG) the
Random Field and Random Anisotropy O(N) models near , the lower critical
dimension of ferromagnetism. The long-distance physics is controlled by
zero-temperature fixed points at which the renormalized effective action is
nonanalytic. We obtain the beta functions at 2-loop order, showing that despite
the nonanalytic character of the renormalized effective action, the theory is
perturbatively renormalizable at this order. The physical results obtained at
2-loop level, most notably concerning the breakdown of dimensional reduction at
the critical point and the stability of quasi-long range order in , are
shown to fit into the picture predicted by our recent non-perturbative FRG
approach.Comment: 19 pages, 20 figures. Minor correction
Why does wurtzite form in nanowires of III-V zinc-blende semiconductors?
We develop a nucleation-based model to explain the formation of the wurtzite
(WZ) crystalline phase during the vapor-liquid-solid growth of free-standing
nanowires of zinc-blende (ZB) semiconductors. We first show that, in nanowires,
nucleation generally occurs at the outer edge of the solid/liquid interface
(the triple phase line) rather than elsewhere at the solid/liquid interface. In
the present case, this entails major differences between ZB and WZ nuclei.
Depending on the pertinent interface energies, WZ nucleation is favored at high
liquid supersaturation. This explains our systematic observation of ZB during
the early stages of nanowire growth.Comment: 4 pages with 4 figures Submitted to Physical Review Letter
Spectral cutoffs in indirect dark matter searches
Indirect searches for dark matter annihilation or decay products in the
cosmic-ray spectrum are plagued by the question of how to disentangle a dark
matter signal from the omnipresent astrophysical background. One of the
practically background-free smoking-gun signatures for dark matter would be the
observation of a sharp cutoff or a pronounced bump in the gamma-ray energy
spectrum. Such features are generically produced in many dark matter models by
internal Bremsstrahlung, and they can be treated in a similar manner as the
traditionally looked-for gamma-ray lines. Here, we discuss prospects for seeing
such features with present and future Atmospheric Cherenkov Telescopes.Comment: 4 pages, 2 figures, 1 table; conference proceedings for TAUP 2011,
Munich 5-9 Se
Local deformations and incommensurability of high quality epitaxial graphene on a weakly interacting transition metal
We investigate the fine structure of graphene on iridium, which is a model
for graphene weakly interacting with a transition metal substrate. Even the
highest quality epitaxial graphene displays tiny imperfections, i.e. small
biaxial strains, ca. 0.3%, rotations, ca. 0.5^{\circ}, and shears over
distances of ca. 100 nm, and is found incommensurate, as revealed by X-ray
diffraction and scanning tunneling microscopy. These structural variations are
mostly induced by the increase of the lattice parameter mismatch when cooling
down the sample from the graphene preparation temperature to the measurement
temperature. Although graphene weakly interacts with iridium, its thermal
expansion is found positive, contrary to free-standing graphene. The structure
of graphene and its variations are very sensitive to the preparation
conditions. All these effects are consistent with initial growth and subsequent
pining of graphene at steps
Nonperturbative Functional Renormalization Group for Random Field Models. III: Superfield formalism and ground-state dominance
We reformulate the nonperturbative functional renormalization group for the
random field Ising model in a superfield formalism, extending the
supersymmetric description of the critical behavior of the system first
proposed by Parisi and Sourlas [Phys. Rev. Lett. 43, 744 (1979)]. We show that
the two crucial ingredients for this extension are the introduction of a
weighting factor, which accounts for ground-state dominance when multiple
metastable states are present, and of multiple copies of the original system,
which allows one to access the full functional dependence of the cumulants of
the renormalized disorder and to describe rare events. We then derive exact
renormalization group equations for the flow of the renormalized cumulants
associated with the effective average action.Comment: 28 page
Effects of environmental factors on development of Pyrenopeziza brassicae (light leaf spot) apothecia on oilseed rape debris
Publication no. P-2001-0221-01R. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2001The development of Pyrenopeziza brassicae (light leaf spot) apothecia was studied on petiole debris from artificially infected oilseed rape leaves incubated at temperatures from 6 to 22 degreesC under different wetness regimes and in 16 h light/8 h dark or continuous darkness. There was no significant difference between light treatments in numbers of apothecia that developed. Mature apothecia developed at temperatures from 5 to 18 degreesC but not at 22 degreesC. The rate of apothecial development decreased as temperature decreased from 18 to 5 degreesC; mature apothecia were first observed after 5 days at 18 degreesC and after 15 days at 6 degreesC. Models were fitted to estimates of the time (days) for 50% of the maximum number of apothecia to develop (t(1); model 1, t(1) = 7.6 + 55.8(0.839)(T)) and the time for 50% of the maximum number of apothecia to decay (t(2); model 2, t(2) = 24.2 + 387(0.730)(T)) at temperatures (T) from 6 to 18 degreesC. An interruption in wetness of the petiole debris for 4 days after 4, 7, or 10 days of wetness delayed the time to observation of the first mature apothecia for approximate to4 days and decreased the number of apothecia produced (by comparison with continuous wetness). A relationship was found between water content of pod debris and electrical resistance measured by a debris-wetness sensor. The differences between values of tl predicted by model 1 and observed values of t(1) were 1 to 9 days. Model 2 did not predict t(2); apothecia decayed more quickly under natural conditions than predicted by model 2.Peer reviewe
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