3,220 research outputs found
Club Convergence of House Prices: Evidence from China's Ten Key Cities
The latest global financial tsunami and its follow-up global economic
recession has uncovered the crucial impact of housing markets on financial and
economic systems. The Chinese stock market experienced a markedly fall during
the global financial tsunami and China's economy has also slowed down by about
2\%-3\% when measured in GDP. Nevertheless, the housing markets in diverse
Chinese cities seemed to continue the almost nonstop mania for more than ten
years. However, the structure and dynamics of the Chinese housing market are
less studied. Here we perform an extensive study of the Chinese housing market
by analyzing ten representative key cities based on both linear and nonlinear
econophysical and econometric methods. We identify a common collective driving
force which accounts for 96.5\% of the house price growth, indicating very high
systemic risk in the Chinese housing market. The ten key cities can be
categorized into clubs and the house prices of the cities in the same club
exhibit an evident convergence. These findings from different methods are
basically consistent with each other. The identified city clubs are also
consistent with the conventional classification of city tiers. The house prices
of the first-tier cities grow the fastest, and those of the third- and
fourth-tier cities rise the slowest, which illustrates the possible presence of
a ripple effect in the diffusion of house prices in different cities.Comment: 16 Latex pages including 6 figures and 4 table
Graphic Method for Arbitrary -body Phase Space
In quantum field theory, the phase space integration is an essential part in
all theoretical calculations of cross sections and decay widths. It is also
needed for computing the imaginary part of a physical amplitude. A key problem
is to get the phase space formula expressed in terms of any chosen invariant
masses in an -body system. We propose a graphic method to quickly get the
phase space formula of any given invariant masses intuitively for an arbitrary
-body system in general -dimensional spacetime, with the involved momenta
in any reference frame. The method also greatly simplifies the phase space
calculation just as what Feynman diagrams do in calculating scattering
amplitudes.Comment: More explanations, generalization to the general spacetime dimensions
include
Decentralized Approximate Newton Methods for Convex Optimization on Networked Systems
In this paper, a class of Decentralized Approximate Newton (DEAN) methods for
addressing convex optimization on a networked system are developed, where nodes
in the networked system seek for a consensus that minimizes the sum of their
individual objective functions through local interactions only. The proposed
DEAN algorithms allow each node to repeatedly perform a local approximate
Newton update, which leverages tracking the global Newton direction and
dissipating the discrepancies among the nodes. Under less restrictive problem
assumptions in comparison with most existing second-order methods, the DEAN
algorithms enable the nodes to reach a consensus that can be arbitrarily close
to the optimum. Moreover, for a particular DEAN algorithm, the nodes linearly
converge to a common suboptimal solution with an explicit error bound. Finally,
simulations demonstrate the competitive performance of DEAN in convergence
speed, accuracy, and efficiency
A Smooth Double Proximal Primal-Dual Algorithm for a Class of Distributed Nonsmooth Optimization Problem
This technical note studies a class of distributed nonsmooth convex consensus
optimization problem. The cost function is a summation of local cost functions
which are convex but nonsmooth. Each of the local cost functions consists of a
twice differentiable convex function and two lower semi-continuous convex
functions. We call this problem as single-smooth plus double-nonsmooth (SSDN)
problem. Under mild conditions, we propose a distributed double proximal
primal-dual optimization algorithm. The double proximal operator is designed to
deal with the difficulty caused by the unproximable property of the summation
of those two nonsmooth functions. Besides, it can also guarantee that the
proposed algorithm is locally Lipschitz continuous. An auxiliary variable in
the double proximal operator is introduced to estimate the subgradient of the
second nonsmooth function. Theoretically, we conduct the convergence analysis
by employing Lyapunov stability theory. It shows that the proposed algorithm
can make the states achieve consensus at the optimal point. In the end,
nontrivial simulations are presented and the results demonstrate the
effectiveness of the proposed algorithm
Long GRBs as a Tool to Investigate Star Formation in Dark Matter Halos
First stars can only form in structures that are suitably dense, which can be
parametrized by the minimum dark matter halo mass .
must plays an important role in star formation. The connection of long
gamma-ray bursts (LGRBs) with the collapse of massive stars has provided a good
opportunity for probing star formation in dark matter halos. We place some
constraints on using the latest LGRB data. We
conservatively consider that LGRB rate is proportional to the cosmic star
formation rate (CSFR) and an additional evolution parametrized as
, where the CSFR model as a function of . Using
the statistic, the contour constraints on the -- plane show that at the confidence level, we have
from 118 LGRBs with redshift and
luminosity erg . We also find that
adding 12 high-\emph{z} LGRBs (consisting of 104 LGRBs with and
erg ) could result in much tighter
constraints on , for which, (). Through Monte Carlo simulations, we
estimate that future five years of Sino-French spacebased multiband
astronomical variable objects monitor (\emph{SVOM}) observations would tighten
these constraints to . The strong constraints on indicate that LGRBs are a
new promising tool for investigating star formation in dark matter halos.Comment: 23 pages, 6 figures, 1 table, accepted by Journal of High Energy
Astrophysic
Effects of temperature gradient on the interface microstructure and diffusion of diffusion couples: phase-field simulation
The temporal interface microstructure and diffusion in the diffusion couples
with the mutual interactions of temperature gradient, concentration difference
and initial aging time of the alloys were studied by phase-field simulation,
the diffusion couples are produced by the initial aged spinodal alloys with
different compositions. Temporal composition evolution and volume fraction of
the separated phase indicates the element diffusion direction through the
interface under the temperature gradient. The increased temperature gradient
induces a wide single-phase region at two sides of the interface. The uphill
diffusion proceeds through the interface, no matter the diffusion directions
are up or down to the temperature gradient. For an alloy with short initial
aging time, phase transformation accompanying the interdiffusion results in the
straight interface with the single-phase regions at both sides. Comparing with
the temperature gradient, composition difference of diffusion couple and
initial aging time of the alloy show greater effect on the diffusion and
interface microstructure.Comment: 18 pages,11 figure
Bounds and Constructions of Locally Repairable Codes: Parity-check Matrix Approach
A -ary locally repairable code (LRC) is an linear code
over such that every code symbol can be recovered by accessing
at most other code symbols. The well-known Singleton-like bound says that
and an LRC is said to be optimal if it attains
this bound. In this paper, we study the bounds and constructions of LRCs from
the view of parity-check matrices. Firstly, a simple and unified framework
based on parity-check matrix to analyze the bounds of LRCs is proposed. Several
useful structural properties on -ary optimal LRCs are obtained. We derive an
upper bound on the minimum distance of -ary optimal -LRCs in terms
of the field size . Then, we focus on constructions of optimal LRCs over
binary field. It is proved that there are only 5 classes of possible parameters
with which optimal binary -LRCs exist. Moreover, by employing the
proposed parity-check matrix approach, we completely enumerate all these 5
classes of possible optimal binary LRCs attaining the Singleton-like bound in
the sense of equivalence of linear codes.Comment: 18 page
Systemic risk and spatiotemporal dynamics of the US housing market
Housing markets play a crucial role in economies and the collapse of a
real-estate bubble usually destabilizes the financial system and causes
economic recessions. We investigate the systemic risk and spatiotemporal
dynamics of the US housing market (1975-2011) at the state level based on the
Random Matrix Theory (RMT). We identify rich economic information in the
largest eigenvalues deviating from RMT predictions and unveil that the
component signs of the eigenvectors contain either geographical information or
the extent of differences in house price growth rates or both. Our results show
that the US housing market experienced six different regimes, which is
consistent with the evolution of state clusters identified by the box
clustering algorithm and the consensus clustering algorithm on the partial
correlation matrices. Our analysis uncovers that dramatic increases in the
systemic risk are usually accompanied with regime shifts, which provides a
means of early detection of housing bubbles.Comment: 8 RevTex pages including 4 eps figure
Role of intensity fluctuations in third-order correlation double-slit interference of thermal light
A third-order double-slit interference experiment with pseudo-thermal light
source in the high-intensity limit has been performed by actually recording the
intensities in three optical paths. It is shown that not only can the visibil-
ity be dramatically enhanced compared to the second-order case as previously
theoretically predicted and shown experimentally, but also that the higher
visi- bility is a consequence of the contribution of third-order correlation
interaction terms, which is equal to the sum of all contributions from
second-order cor- relation. It is interesting that, when the two reference
detectors are scanned in opposite directions, negative values for the
third-order correlation term of the intensity fluctuations may appear. The
phenomenon can be completely explained by the theory of classical statistical
optics, and is the first concrete demonstration of the influence of the
third-order correlation terms.Comment: 10 pages,4figure
Low-rank Tensor Bandits
In recent years, multi-dimensional online decision making has been playing a
crucial role in many practical applications such as online recommendation and
digital marketing. To solve it, we introduce stochastic low-rank tensor
bandits, a class of bandits whose mean rewards can be represented as a low-rank
tensor. We propose two learning algorithms, tensor epoch-greedy and tensor
elimination, and develop finite-time regret bounds for them. We observe that
tensor elimination has an optimal dependency on the time horizon, while tensor
epoch-greedy has a sharper dependency on tensor dimensions. Numerical
experiments further back up these theoretical findings and show that our
algorithms outperform various state-of-the-art approaches that ignore the
tensor low-rank structure
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