11,797 research outputs found
Growth, Income Distribution, And well-Being In Transition Countries
In this paper we use several well-being measures that combine average income with a measure of inequality to undertake international and intertemporal well-being comparisons in transition countries. Our well-being measures drastically change the impression of levels and changes in well-being from a traditional reliance on income measures. They also significantly affect the ranking of countries, when compared to rankings based on real incomes. Due to low inequality and moderate income levels, socialist countries enjoyed relatively high levels of economic well-being. In the transition process, rising inequality and falling incomes have led to a dramatic decline in well-being in many transition countries, and a corresponding worsening in rank when compared to other countries. There is great variance in the income and inequality performance of transition countries. We find a close correlation between income losses and inequality increases suggesting the ability of appropriate policies to reduce the income losses and reduce rising inequality. While the political dimension of transformation remains largely successful, our indicators suggest that most transition countries have yet to reach the level of economic well-being enjoyed in the late 1980s.
Distributed Exact Shortest Paths in Sublinear Time
The distributed single-source shortest paths problem is one of the most
fundamental and central problems in the message-passing distributed computing.
Classical Bellman-Ford algorithm solves it in time, where is the
number of vertices in the input graph . Peleg and Rubinovich (FOCS'99)
showed a lower bound of for this problem, where
is the hop-diameter of .
Whether or not this problem can be solved in time when is
relatively small is a major notorious open question. Despite intensive research
\cite{LP13,N14,HKN15,EN16,BKKL16} that yielded near-optimal algorithms for the
approximate variant of this problem, no progress was reported for the original
problem.
In this paper we answer this question in the affirmative. We devise an
algorithm that requires time, for , and time, for larger . This
running time is sublinear in in almost the entire range of parameters,
specifically, for . For the all-pairs shortest paths
problem, our algorithm requires time, regardless of
the value of .
We also devise the first algorithm with non-trivial complexity guarantees for
computing exact shortest paths in the multipass semi-streaming model of
computation.
From the technical viewpoint, our algorithm computes a hopset of a
skeleton graph of without first computing itself. We then conduct
a Bellman-Ford exploration in , while computing the required edges
of on the fly. As a result, our algorithm computes exactly those edges of
that it really needs, rather than computing approximately the entire
Cooling and aggregation in wet granulates
Wet granular materials are characterized by a defined bond energy in their
particle interaction such that breaking a bond implies an irreversible loss of
a fixed amount of energy. Associated with the bond energy is a nonequilibrium
transition, setting in as the granular temperature falls below the bond energy.
The subsequent aggregation of particles into clusters is shown to be a
self-similar growth process with a cluster size distribution that obeys
scaling. In the early phase of aggregation the clusters are fractals with
D_f=2, for later times we observe gelation. We use simple scaling arguments to
derive the temperature decay in the early and late stages of cooling and verify
our results with event-driven simulations.Comment: 4 pages, 6 figures, suggestions of the referees implemented, EPAPS
supplementary material added:
http://netserver.aip.org/cgi-bin/epaps?ID=E-PRLTAO-102-00391
Bose-Glass Phases in Disordered Quantum Magnets
In disordered spin systems with antiferromagnetic Heisenberg exchange,
transitions into and out of a magnetic-field-induced ordered phase pass through
a unique regime. Using quantum Monte Carlo simulations to study the
zero-temperature behavior, these intermediate regions are determined to be a
Bose-Glass phase. The localization of field-induced triplons causes a finite
compressibility and hence glassiness in the disordered phase.Comment: 4 pages, 4 figure
High energy scattering in the saturation regime including running coupling and rare fluctuation effects
The analytic result for the -matrix in the saturation regime including the
running coupling is obtained. To get this result we solve the Balitsky and
Kovchegov-Weigert evolution equations in the saturation regime, which include
running coupling corrections. We study also the effect of rare fluctuations on
top of the running coupling. We find that the rare fluctuations are less
important in the running coupling case as compared to the fixed coupling case.Comment: 10 page
ac Stark shift and multiphoton-like resonances in low-frequency driven optical lattices
We suggest that Bose-Einstein condensates in optical lattices subjected to ac
forcing with a smooth envelope may provide detailed experimental access to
multiphoton-like transitions between ac-Stark-shifted Bloch bands. Such
transitions correspond to resonances described theoretically by avoided
quasienergy crossings. We show that the width of such anticrossings can be
inferred from measurements involving asymmetric pulses. We also introduce a
pulse tracking strategy for locating the particular driving amplitudes for
which resonances occur. Our numerical calculations refer to a currently
existing experimental set-up [Haller et al., PRL 104, 200403 (2010)].Comment: 5 pages, 6 figure
Dilute Wet Granulates: Nonequilibrium Dynamics and Structure Formation
We investigate a gas of wet granular particles, covered by a thin liquid
film. The dynamic evolution is governed by two-particle interactions, which are
mainly due to interfacial forces in contrast to dry granular gases. When two
wet grains collide, a capillary bridge is formed and stays intact up to a
certain distance of withdrawal when the bridge ruptures, dissipating a fixed
amount of energy. A freely cooling system is shown to undergo a nonequillibrium
dynamic phase transition from a state with mainly single particles and fast
cooling to a state with growing aggregates, such that bridge rupture becomes a
rare event and cooling is slow. In the early stage of cluster growth,
aggregation is a self-similar process with a fractal dimension of the
aggregates approximately equal to D_f ~ 2. At later times, a percolating
cluster is observed which ultimately absorbs all the particles. The final
cluster is compact on large length scales, but fractal with D_f ~ 2 on small
length scales.Comment: 14 pages, 20 figure
Fidelity approach to the disordered quantum XY model
We study the random XY spin chain in a transverse field by analyzing the
susceptibility of the ground state fidelity, numerically evaluated through a
standard mapping of the model onto quasi-free fermions. It is found that the
fidelity susceptibility and its scaling properties provide useful information
about the phase diagram. In particular it is possible to determine the Ising
critical line and the Griffiths phase regions, in agreement with previous
analytical and numerical results.Comment: 4 pages, 3 figures; references adde
Phase Diagram and Quantum Order by Disorder in the Kitaev - Honeycomb Magnet
We show that the topological Kitaev spin liquid on the honeycomb lattice is
extremely fragile against the second-neighbor Kitaev coupling , which has
recently been shown to be the dominant perturbation away from the
nearest-neighbor model in iridate NaIrO, and may also play a role in
-RuCl and LiIrO. This coupling naturally explains the
zigzag ordering (without introducing unrealistically large longer-range
Heisenberg exchange terms) and the special entanglement between real and spin
space observed recently in NaIrO. Moreover, the minimal -
model that we present here holds the unique property that the classical and
quantum phase diagrams and their respective order-by-disorder mechanisms are
qualitatively different due to the fundamentally different symmetries of the
classical and quantum counterparts.Comment: Published version (9+13 pages
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