40,225 research outputs found
Dynamic models of residential segregation: brief review, analytical resolution and study of the introduction of coordination
In his 1971's Dynamic Models of Segregation paper, the economist Thomas C.
Schelling showed that a small preference for one's neighbors to be of the same
color could lead to total segregation, even if total segregation does not
correspond to individual preferences and to a residential configuration
maximizing the collective utility.
The present work is aimed at deepening the understanding of the properties of
dynamic models of segregation based on Schelling's hypotheses. Its main
contributions are (i) to offer a comprehensive and up-to-date review of this
family of models; (ii) to provide an analytical solution to the most general
form of this model under rather general assumptions; to the best of our
knowledge, such a solution did not exist so far; (iii) to analyse the effect of
two devices aimed at decreasing segregation in such a model.Comment: 52 pages, 21 figures, working pape
High quality epitaxial ZnSe and the relationship between electron mobility and photoluminescence characteristics
High quality epitaxial layers of nominally undoped ZnSe have been grown by metalorganic chemical vapor deposition at low temperature (325 °C) and pressure (30 Torr), using dimethylzinc and hydrogen selenide. All layers were unintentionally doped n type with net carrier concentrations of 6.4×10^(14)–1.5×10^(16) cm^(−3) and exhibited very high mobility at room temperature (up to 500 cm2/V s) as well as at 77 K, where the measured value of 9250 cm^2/V s is the highest so far reported for vapor phase growth. Additional evidence for the high quality of the material is provided by photoluminescence. Experimental results indicate a correlation between the photoluminescence characteristics and the electrical properties that may be useful in assessing the quality of ZnSe films
Conformal field theory correlations in the Abelian sandpile mode
We calculate all multipoint correlation functions of all local bond
modifications in the two-dimensional Abelian sandpile model, both at the
critical point, and in the model with dissipation. The set of local bond
modifications includes, as the most physically interesting case, all weakly
allowed cluster variables. The correlation functions show that all local bond
modifications have scaling dimension two, and can be written as linear
combinations of operators in the central charge -2 logarithmic conformal field
theory, in agreement with a form conjectured earlier by Mahieu and Ruelle in
Phys. Rev. E 64, 066130 (2001). We find closed form expressions for the
coefficients of the operators, and describe methods that allow their rapid
calculation. We determine the fields associated with adding or removing bonds,
both in the bulk, and along open and closed boundaries; some bond defects have
scaling dimension two, while others have scaling dimension four. We also
determine the corrections to bulk probabilities for local bond modifications
near open and closed boundaries.Comment: 13 pages, 5 figures; referee comments incorporated; Accepted by Phys.
Rev.
One Dimensional Nonequilibrium Kinetic Ising Models with Branching Annihilating Random Walk
Nonequilibrium kinetic Ising models evolving under the competing effect of
spin flips at zero temperature and nearest neighbour spin exchanges at
are investigated numerically from the point of view of a phase
transition. Branching annihilating random walk of the ferromagnetic domain
boundaries determines the steady state of the system for a range of parameters
of the model. Critical exponents obtained by simulation are found to agree,
within error, with those in Grassberger's cellular automata.Comment: 10 pages, Latex, figures upon request, SZFKI 05/9
Tracking and data systems support for the Helios project. Volume 3: DSN support of Project Helios May 1976 - June 1977
Spacecraft extended mission coverage does not generally carry a high priority, but Helios was fortunate in that a combination of separated viewperiods and unique utilization of the STDN Goldstone antenna have provided a considerable amount of additional science data return, particularly at key times such a perihelion and/or solar occultation
Carbon incorporation in ZnSe grown by metalorganic chemical vapor deposition
Carbon incorporation in ZnSe films grown by metalorganic chemical vapor deposition is reported. Secondary‐ion mass spectrometry measurements in ZnSe films grown from methylallylselenide and dimethylzinc show an enhanced carbon accumulation at the interface between ZnSe and GaAs. The carbon incorporation in the bulk ZnSe increases with the VI/II ratio and for a value of VI/II=3–4, the amount of incorporated carbon abruptly jumps to concentrations of 10^(21) cm^(−3), whereupon the films become polycrystalline. A new shallow peak I^C at 2.7920 eV dominates the near‐band‐edge low‐temperature photoluminescence spectra of all carbon‐contaminated ZnSe films. The intensity and linewidth of I^C increase with the VI/II ratio in a similar manner to the carbon concentration. This peak is proposed to be due to the radiative decay of excitons bound to a complex defect, which is associated with the presence of carbon in the films
Nonuniversal Critical Spreading in Two Dimensions
Continuous phase transitions are studied in a two dimensional nonequilibrium
model with an infinite number of absorbing configurations. Spreading from a
localized source is characterized by nonuniversal critical exponents, which
vary continuously with the density phi in the surrounding region. The exponent
delta changes by more than an order of magnitude, and eta changes sign. The
location of the critical point also depends on phi, which has important
implications for scaling. As expected on the basis of universality, the static
critical behavior belongs to the directed percolation class.Comment: 21 pages, REVTeX, figures available upon reques
The Successful Operation of Hole-type Gaseous Detectors at Cryogenic Temperatures
We have demonstrated that hole-type gaseous detectors, GEMs and capillary
plates, can operate up to 77 K. For example, a single capillary plate can
operate at gains of above 10E3 in the entire temperature interval between 300
until 77 K. The same capillary plate combined with CsI photocathodes could
operate perfectly well at gains (depending on gas mixtures) of 100-1000.
Obtained results may open new fields of applications for capillary plates as
detectors of UV light and charge particles at cryogenic temperatures: noble
liquid TPCs, WIMP detectors or LXe scintillating calorimeters and cryogenic
PETs.Comment: Presented at the IEEE Nuclear Science Symposium, Roma, 200
Dynamic Critical approach to Self-Organized Criticality
A dynamic scaling Ansatz for the approach to the Self-Organized Critical
(SOC) regime is proposed and tested by means of extensive simulations applied
to the Bak-Sneppen model (BS), which exhibits robust SOC behavior. Considering
the short-time scaling behavior of the density of sites () below the
critical value, it is shown that i) starting the dynamics with configurations
such that one observes an {\it initial increase} of the
density with exponent ; ii) using initial configurations with
, the density decays with exponent . It is
also shown that he temporal autocorrelation decays with exponent . Using these, dynamically determined, critical exponents and suitable
scaling relationships, all known exponents of the BS model can be obtained,
e.g. the dynamical exponent , the mass dimension exponent , and the exponent of all returns of the activity , in excellent agreement with values already accepted and obtained
within the SOC regime.Comment: Rapid Communication Physical Review E in press (4 pages, 5 figures
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