8,615 research outputs found
Outbreaks of coinfections: the critical role of cooperativity
Modeling epidemic dynamics plays an important role in studying how diseases
spread, predicting their future course, and designing strategies to control
them. In this letter, we introduce a model of SIR
(susceptible-infected-removed) type which explicitly incorporates the effect of
{\it cooperative coinfection}. More precisely, each individual can get infected
by two different diseases, and an individual already infected with one disease
has an increased probability to get infected by the other. Depending on the
amount of this increase, we observe different threshold scenarios. Apart from
the standard continuous phase transition for single disease outbreaks, we
observe continuous transitions where both diseases must coexist, but also
discontinuous transitions are observed, where a finite fraction of the
population is already affected by both diseases at the threshold. All our
results are obtained in a mean field model using rate equations, but we argue
that they should hold also in more general frameworks.Comment: 5 pages, including 5 figure
Symmetry, Entropy, Diversity and (why not?) Quantum Statistics in Society
We describe society as a nonequilibrium probabilistic system: N individuals
occupy W resource states in it and produce entropy S over definite time
periods. Resulting thermodynamics is however unusual because a second entropy,
H, measures a typically social feature, inequality or diversity in the
distribution of available resources. A symmetry phase transition takes place at
Gini values 1/3, where realistic distributions become asymmetric. Four
constraints act on S: expectedly, N and W, and new ones, diversity and
interactions between individuals; the latter result from the two coordinates of
a single point in the data, the peak. The occupation number of a job is either
zero or one, suggesting Fermi-Dirac statistics for employment. Contrariwise, an
indefinite nujmber of individuals can occupy a state defined as a quantile of
income or of age, so Bose-Einstein statistics may be required.
Indistinguishability rather than anonymity of individuals and resources is thus
needed. Interactions between individuals define define classes of equivalence
that happen to coincide with acceptable definitions of social classes or
periods in human life. The entropy S is non-extensive and obtainable from data.
Theoretical laws are compared to data in four different cases of economical or
physiological diversity. Acceptable fits are found for all of them.Comment: 13 pages, 2 figure
Phase separation in the vicinity of "quantum critical" doping concentration: implications for high temperature superconductors
A general quantitative measure of the tendency towards phase separation is
introduced for systems exhibiting phase transitions or crossovers controlled by
charge carrier concentration. This measure is devised for the situations when
the quantitative knowledge of various contributions to free energy is
incomplete, and is applied to evaluate the chances of electronic phase
separation associated with the onset of antiferromagnetic correlations in
high-temperature cuprate superconductors. The experimental phenomenology of
lanthanum- and yittrium-based cuprates was used as input to this analysis. It
is also pointed out that Coulomb repulsion between charge carriers separated by
the distances of 1-3 lattice periods strengthens the tendency towards phase
separation by accelerating the decay of antiferromagnetic correlations with
doping. Overall, the present analysis indicates that cuprates are realistically
close to the threshold of phase separation -- nanoscale limited or even
macroscopic with charge density varying between adjacent crystal planes
Can Symmetry non-restoration solve the Monopole Problem?
We reexamine a recently proposed non-inflationary solution to the monopole
problem, based on the possibility that spontaneously broken Grand-Unified
symmetries do not get restored at high temperature. We go beyond leading order
by studying the self-consistent one-loop equations of the model. We find large
next-to-leading corrections that reverse the lowest order results and cause
symmetry restoration at high temperature.Comment: 17 pages plus three coded and compressed postscript files for figure
Stabilizing Consensus with Many Opinions
We consider the following distributed consensus problem: Each node in a
complete communication network of size initially holds an \emph{opinion},
which is chosen arbitrarily from a finite set . The system must
converge toward a consensus state in which all, or almost all nodes, hold the
same opinion. Moreover, this opinion should be \emph{valid}, i.e., it should be
one among those initially present in the system. This condition should be met
even in the presence of an adaptive, malicious adversary who can modify the
opinions of a bounded number of nodes in every round.
We consider the \emph{3-majority dynamics}: At every round, every node pulls
the opinion from three random neighbors and sets his new opinion to the
majority one (ties are broken arbitrarily). Let be the number of valid
opinions. We show that, if , where is a
suitable positive constant, the 3-majority dynamics converges in time
polynomial in and with high probability even in the presence of an
adversary who can affect up to nodes at each round.
Previously, the convergence of the 3-majority protocol was known for
only, with an argument that is robust to adversarial errors. On
the other hand, no anonymous, uniform-gossip protocol that is robust to
adversarial errors was known for
Solution of gauge theories induced by fundamental representation scalars
Gauge theories induced by scalars in the fundamental representation of the
group are investigated in the large
and limit. A master field is defined from bilinears of the scalar
field following an Eguchi-Kawai type reduction of spacetime. The density
function for the master field satisfies an integral equation that can be solved
exactly in two dimensions (D=2) and in a convergent series of approximations at
. While at D=2 the system is in the same phase at all ,
it undergoes a phase transition at a critical value, , for
.Comment: 12 pages, LaTe
Predictions from Quantum Cosmology
The world view suggested by quantum cosmology is that inflating universes
with all possible values of the fundamental constants are spontaneously created
out of nothing. I explore the consequences of the assumption that we are a
`typical' civilization living in this metauniverse. The conclusions include
inflation with an extremely flat potential and low thermalization temperature,
structure formation by topological defects, and an appreciable cosmological
constant.Comment: (revised version), 15 page
Partial Strategyproofness: Relaxing Strategyproofness for the Random Assignment Problem
We present partial strategyproofness, a new, relaxed notion of
strategyproofness for studying the incentive properties of non-strategyproof
assignment mechanisms. Informally, a mechanism is partially strategyproof if it
makes truthful reporting a dominant strategy for those agents whose preference
intensities differ sufficiently between any two objects. We demonstrate that
partial strategyproofness is axiomatically motivated and yields a parametric
measure for "how strategyproof" an assignment mechanism is. We apply this new
concept to derive novel insights about the incentive properties of the
probabilistic serial mechanism and different variants of the Boston mechanism.Comment: Working Pape
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