11,704 research outputs found
Volatility Comovement: A Multifrequency Approach
We implement a multifrequency volatility decomposition of three exchange rates and show that components with similar durations are strongly correlated across series. This motivates a bivariate extension of the Markov-Switching Multifractal (MSM) introduced in Calvet and Fisher (2001, 2004). Bivariate MSM is a stochastic volatility model with a closed-form likelihood. Estimation can proceed by ML for state spaces of moderate size, and by simulated likelihood via a particle filter in high-dimensional cases. We estimate the model and confirm its main assumptions in likelihood ratio tests. Bivariate MSM compares favorably to a standard multivariate GARCH both in- and out-of-sample. We extend the model to multivariate settings with a potentially large number of assets by proposing a parsimonious multifrequency factor structure.
Measurement-based Run-to-run Optimization of a Batch Reaction-distillation System
Measurement-based optimization schemes have been developed to deal with uncertainty and process variations. One of the methods therein, labeled NCO tracking, relies on appropriate parameterization of the input profiles and adjusts the corresponding input parameters using measurements so as to satisfy the necessary conditions of optimality (NCO). The applicability of NCO-tracking schemes has been demonstrated on several academic-size examples. The goal of this paper is to show that it can be applied with similar ease to more complex real-life systems. Run-to-run optimization of a batch reaction-separation system with propylene glycol is used for illustration
Why is the Schwarzschild Solution Independent of the Spatial Stresses?
The following paradox is raised and resolved: Both the energy density T_(00) and the spatial stresses T_(kl) are (independent) sources of the tensor gravitational field in general relativity. Yet the general Schwarzschild exterior solution depends only on one parameter m, related to T_(00), so that no properties of T_(ij) “propagate” to affect an outside observer
Energy Spectra of Superfluid Turbulence in He
In superfluid He turbulence is carried predominantly by the superfluid
component. To explore the statistical properties of this quantum turbulence and
its differences from the classical counterpart we adopt the time-honored
approach of shell models. Using this approach we provide numerical simulations
of a Sabra-shell model that allows us to uncover the nature of the energy
spectrum in the relevant hydrodynamic regimes. These results are in qualitative
agreement with analytical expressions for the superfluid turbulent energy
spectra that were found using a differential approximation for the energy flux
Canonical analysis of the BCEA topological matter model coupled to gravitation in (2+1) dimensions
We consider a topological field theory derived from the Chern - Simons action
in (2+1) dimensions with the I(ISO(2,1)) group,and we investigate in detail the
canonical structure of this theory.Originally developed as a topological theory
of Einstein gravity minimally coupled to topological matter fields in (2+1)
dimensions, it admits a BTZ black-hole solutions, and can be generalized to
arbitrary dimensions.In this paper, we further study the canonical structure of
the theory in (2+1) dimensions, by identifying all the distinct gauge
equivalence classes of solutions as they result from holonomy considerations.
The equivalence classes are discussed in detail, and examples of solutions
representative of each class are constructed or identified.Comment: 17 pages, no figure
Critical Casimir forces in colloidal suspensions on chemically patterned surfaces
We investigate the behavior of colloidal particles immersed in a binary
liquid mixture of water and 2,6-lutidine in the presence of a chemically
patterned substrate. Close to the critical point of the mixture, the particles
are subjected to critical Casimir interactions with force components normal and
parallel to the surface. Because the strength and sign of these interactions
can be tuned by variations in the surface properties and the mixtures
temperature, critical Casimir forces allow the formation of highly ordered
monolayers but also extend the use of colloids as model systems.Comment: 4 papges, 4 figures, accepted at Phys. Rev. Let
Spectral decomposition of starbursts and AGNs in 5-8 micron Spitzer IRS spectra of local ULIRGs
We present an analysis of the 5-8 micron Spitzer-IRS spectra of a sample of
68 local Ultraluminous Infrared Galaxies (ULIRGs). Our diagnostic technique
allows a clear separation of the active galactic nucleus (AGN) and starburst
(SB) components in the observed mid-IR emission, and a simple analytic model
provides a quantitative estimate of the AGN/starburst contribution to the
bolometric luminosity. We show that AGNs are ~30 times brighter at 6 micron
than starbursts with the same bolometric luminosity, so that even faint AGNs
can be detected. Star formation events are confirmed as the dominant power
source for extreme infrared activity, since ~85% of ULIRG luminosity arises
from the SB component. Nonetheless an AGN is present in the majority (46/68) of
our sources.Comment: 5 Pages, 3 figures. MNRAS Letters, Accepte
Thurston equivalence of topological polynomials
We answer Hubbard's question on determining the Thurston equivalence class of
``twisted rabbits'', i.e. images of the ``rabbit'' polynomial under n-th powers
of the Dehn twists about its ears.
The answer is expressed in terms of the 4-adic expansion of n. We also answer
the equivalent question for the other two families of degree-2 topological
polynomials with three post-critical points.
In the process, we rephrase the questions in group-theoretical language, in
terms of wreath recursions.Comment: 40 pages, lots of figure
Fast Forwarding with Network Processors
Forwarding is a mechanism found in many network operations. Although a regular workstation is able to perform forwarding operations it still suffers from poor performances when compared to dedicated hardware machines. In this paper we study the possibility of using Network Processors (NPs) to improve the capability of regular workstations to forward data. We present a simple model and an experimental study demonstrating that even though NPs are less powerful than Host Processors (HPs) they can forward data more efficiently than HPs in some specific cases
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