1,956 research outputs found
Volatility distribution in the S&P500 Stock Index
We study the volatility of the S&P500 stock index from 1984 to 1996 and find
that the volatility distribution can be very well described by a log-normal
function. Further, using detrended fluctuation analysis we show that the
volatility is power-law correlated with Hurst exponent .Comment: 6 pages, 5 figure
Network resilience
Many systems on our planet are known to shift abruptly and irreversibly from
one state to another when they are forced across a "tipping point," such as
mass extinctions in ecological networks, cascading failures in infrastructure
systems, and social convention changes in human and animal networks. Such a
regime shift demonstrates a system's resilience that characterizes the ability
of a system to adjust its activity to retain its basic functionality in the
face of internal disturbances or external environmental changes. In the past 50
years, attention was almost exclusively given to low dimensional systems and
calibration of their resilience functions and indicators of early warning
signals without considerations for the interactions between the components.
Only in recent years, taking advantages of the network theory and lavish real
data sets, network scientists have directed their interest to the real-world
complex networked multidimensional systems and their resilience function and
early warning indicators. This report is devoted to a comprehensive review of
resilience function and regime shift of complex systems in different domains,
such as ecology, biology, social systems and infrastructure. We cover the
related research about empirical observations, experimental studies,
mathematical modeling, and theoretical analysis. We also discuss some ambiguous
definitions, such as robustness, resilience, and stability.Comment: Review chapter
Effect of nonstationarities on detrended fluctuation analysis
Detrended fluctuation analysis (DFA) is a scaling analysis method used to
quantify long-range power-law correlations in signals. Many physical and
biological signals are ``noisy'', heterogeneous and exhibit different types of
nonstationarities, which can affect the correlation properties of these
signals. We systematically study the effects of three types of
nonstationarities often encountered in real data. Specifically, we consider
nonstationary sequences formed in three ways: (i) stitching together segments
of data obtained from discontinuous experimental recordings, or removing some
noisy and unreliable parts from continuous recordings and stitching together
the remaining parts -- a ``cutting'' procedure commonly used in preparing data
prior to signal analysis; (ii) adding to a signal with known correlations a
tunable concentration of random outliers or spikes with different amplitude,
and (iii) generating a signal comprised of segments with different properties
-- e.g. different standard deviations or different correlation exponents. We
compare the difference between the scaling results obtained for stationary
correlated signals and correlated signals with these three types of
nonstationarities.Comment: 17 pages, 10 figures, corrected some typos, added one referenc
Statistical Properties of Share Volume Traded in Financial Markets
We quantitatively investigate the ideas behind the often-expressed adage `it
takes volume to move stock prices', and study the statistical properties of the
number of shares traded for a given stock in a fixed time
interval . We analyze transaction data for the largest 1000 stocks
for the two-year period 1994-95, using a database that records every
transaction for all securities in three major US stock markets. We find that
the distribution displays a power-law decay, and that the
time correlations in display long-range persistence. Further, we
investigate the relation between and the number of transactions
in a time interval , and find that the long-range
correlations in are largely due to those of . Our
results are consistent with the interpretation that the large equal-time
correlation previously found between and the absolute value of
price change (related to volatility) are largely due to
.Comment: 4 pages, two-column format, four figure
Immune Gene Expression Profiles in High Grade Urothelial Carcinoma of the Bladder: A NanoString Study
Can immune markers help identify fast relapse in patients with muscle invasive bladder cancer?
Major urban transport expenditure initiatives: where are the returns likely to be strongest and how significant is social exclusion in making the case?
This paper explores whether the benefits from major urban transport spending increases are likely to differ greatly, depending on whether that spending prioritises light rail, a mode with growing interest and several new services recently developed in Australia, major road network improvement or provision of additional bus services. It does this through a series of case studies based on Sydney, using MetroScan, an integrated transport and land use strategic model system. MetroScan is the most sophisticated strategic integrated land use, transport and economic system evaluation model in Australia, with the capability of exploring dynamic interactions between transport improvements, residential locations and job locations, among other things. We specifically focus on the impacts of major transport initiatives on reducing risks that people will be socially excluded because of poor mobility opportunities
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