2,296 research outputs found
Clustering of discretely observed diffusion processes
In this paper a new dissimilarity measure to identify groups of assets
dynamics is proposed. The underlying generating process is assumed to be a
diffusion process solution of stochastic differential equations and observed at
discrete time. The mesh of observations is not required to shrink to zero. As
distance between two observed paths, the quadratic distance of the
corresponding estimated Markov operators is considered. Analysis of both
synthetic data and real financial data from NYSE/NASDAQ stocks, give evidence
that this distance seems capable to catch differences in both the drift and
diffusion coefficients contrary to other commonly used metrics
Empirical -distance test statistics for ergodic diffusions
The aim of this paper is to introduce a new type of test statistic for simple
null hypothesis on one-dimensional ergodic diffusion processes sampled at
discrete times. We deal with a quasi-likelihood approach for stochastic
differential equations (i.e. local gaussian approximation of the transition
functions) and define a test statistic by means of the empirical -distance
between quasi-likelihoods. We prove that the introduced test statistic is
asymptotically distribution free; namely it weakly converges to a
random variable. Furthermore, we study the power under local alternatives of
the parametric test. We show by the Monte Carlo analysis that, in the small
sample case, the introduced test seems to perform better than other tests
proposed in literature
Nonparametric methods for volatility density estimation
Stochastic volatility modelling of financial processes has become
increasingly popular. The proposed models usually contain a stationary
volatility process. We will motivate and review several nonparametric methods
for estimation of the density of the volatility process. Both models based on
discretely sampled continuous time processes and discrete time models will be
discussed.
The key insight for the analysis is a transformation of the volatility
density estimation problem to a deconvolution model for which standard methods
exist. Three type of nonparametric density estimators are reviewed: the
Fourier-type deconvolution kernel density estimator, a wavelet deconvolution
density estimator and a penalized projection estimator. The performance of
these estimators will be compared. Key words: stochastic volatility models,
deconvolution, density estimation, kernel estimator, wavelets, minimum contrast
estimation, mixin
Direct observations of nucleation in a nondilute multicomponent alloy
The chemical pathways leading to gamma-prime(L1_2)-nucleation from nondilute
Ni-5.2 Al-14.2 Cr at.%, gamma(f.c.c.), at 873 K are followed with radial
distribution functions and isoconcentration surface analyses of direct-space
atom-probe tomographic images. Although Cr atoms initially are randomly
distributed, a distribution of congruent Ni3Al short-range order domains (SRO),
=0.6 nm, results from Al diffusion during quenching. Domain site occupancy
develops as their number density increases leading to Al-rich phase separation
by gamma-prime-nucleation, =0.75 nm, after SRO occurs.Comment: 5 pages, 4 figure
Volatility forecasting
Volatility has been one of the most active and successful areas of research in time series econometrics and economic forecasting in recent decades. This chapter provides a selective survey of the most important theoretical developments and empirical insights to emerge from this burgeoning literature, with a distinct focus on forecasting applications. Volatility is inherently latent, and Section 1 begins with a brief intuitive account of various key volatility concepts. Section 2 then discusses a series of different economic situations in which volatility plays a crucial role, ranging from the use of volatility forecasts in portfolio allocation to density forecasting in risk management. Sections 3, 4 and 5 present a variety of alternative procedures for univariate volatility modeling and forecasting based on the GARCH, stochastic volatility and realized volatility paradigms, respectively. Section 6 extends the discussion to the multivariate problem of forecasting conditional covariances and correlations, and Section 7 discusses volatility forecast evaluation methods in both univariate and multivariate cases. Section 8 concludes briefly. JEL Klassifikation: C10, C53, G1
X-ray Emission of Baryonic Gas in the Universe: Luminosity-Temperature Relationship and Soft-Band Background
We study the X-ray emission of baryon fluid in the universe using the WIGEON
cosmological hydrodynamic simulations. It has been revealed that cosmic baryon
fluid in the nonlinear regime behaves like Burgers turbulence, i.e. the fluid
field consists of shocks. Like turbulence in incompressible fluid, the Burgers
turbulence plays an important role in converting the kinetic energy of the
fluid to thermal energy and heats the gas. We show that the simulation sample
of the CDM model without adding extra heating sources can fit well the
observed distributions of X-ray luminosity versus temperature ( vs.
) of galaxy groups and is also consistent with the distributions of X-ray
luminosity versus velocity dispersion ( vs. ). Because the
baryonic gas is multiphase, the and
distributions are significantly scattered. If we describe the relationships by
power laws and , we find and . The
X-ray background in the soft keV band emitted by the baryonic gas in
the temperature range K has also been calculated. We show that of
the total background, (1) no more than 2% comes from the region with
temperature less than K, and (2) no more than 7% is from the region
of dark matter with mass density . The
region of is generally clustered and
discretely distributed. Therefore, almost all of the soft X-ray background
comes from clustered sources, and the contribution from truly diffuse gas is
probably negligible. This point agrees with current X-ray observations.Comment: 32 pages including 14 figures and 2 tables. Final version for
publication in Ap
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