20,038 research outputs found
Scaling Green-Kubo relation and application to three aging systems
The Green-Kubo formula relates the spatial diffusion coefficient to the
stationary velocity autocorrelation function. We derive a generalization of the
Green-Kubo formula valid for systems with long-range or nonstationary
correlations for which the standard approach is no longer valid. For the
systems under consideration, the velocity autocorrelation function asymptotically exhibits a certain scaling behavior and
the diffusion is anomalous . We
show how both the anomalous diffusion coefficient and exponent
can be extracted from this scaling form. Our scaling Green-Kubo relation thus
extends an important relation between transport properties and correlation
functions to generic systems with scale invariant dynamics. This includes
stationary systems with slowly decaying power law correlations as well as aging
systems, whose properties depend on the the age of the system. Even for systems
that are stationary in the long time limit, we find that the long time
diffusive behavior can strongly depend on the initial preparation of the
system. In these cases, the diffusivity is not unique and we
determine its values for a stationary respectively nonstationary initial state.
We discuss three applications of the scaling Green-Kubo relation: Free
diffusion with nonlinear friction corresponding to cold atoms diffusing in
optical lattices, the fractional Langevin equation with external noise recently
suggested to model active transport in cells and the L\'evy walk with numerous
applications, in particular blinking quantum dots. These examples underline the
wide applicability of our approach, which is able to treat very different
mechanisms of anomalous diffusion.Comment: 16 pages, 6 figures, 1 tabl
Infrared 3D Observations of Nearby Active Galaxies
We present multi-wavelength imaging observations of three nearby and famous
active galaxies obtained with NICMOS, ISOCAM and the MPE near-IR integral field
spectrometer. The data reveal a variety of features and properties that are
missed in optical studies and in traditional IR monodimensional spectroscopy.Comment: 6 pages, to appear in "Imaging the Universe in Three Dimensions:
Astrophysics with Advanced Multi-Wavelength Imaging Devices", eds. W. van
Breugel and J. Bland-Hawthorn, needs pasp3D.st
The nature and evolution of Ultraluminous Infrared Galaxies: A mid-infrared spectroscopic survey
We report the first results of a low resolution mid-infrared spectroscopic
survey of an unbiased, far-infrared selected sample of 60 ultraluminous
infrared galaxies, using ISOPHOT-S on board ISO. We use the ratio of the 7.7um
`PAH' emission feature to the local continuum as a discriminator between
starburst and AGN activity. About 80% of all the ULIRGs are found to be
predominantly powered by star formation but the fraction of AGN powered objects
increases with luminosity.
Observed ratios of the PAH features in ULIRGs differ slightly from those in
lower luminosity starbursts. This can be plausibly explained by the higher
extinction and/or different physical conditions in the interstellar medium of
ULIRGs. The PAH feature-to-continuum ratio is anticorrelated with the ratio of
feature-free 5.9um continuum to the IRAS 60um continuum, confirming suggestions
that strong mid-IR continuum is a prime AGN signature. The location of
starburst-dominated ULIRGs in such a diagram is consistent with previous
ISO-SWS spectroscopy which implies significant extinction even in the
mid-infrared.
We have searched for indications that ULIRGs which are advanced mergers might
be more AGN-like, as postulated by the classical evolutionary scenario. No such
trend has been found amongst those objects for which near infrared images are
available to assess their likely merger status.Comment: aastex, 4 eps figures. Revised version, accepted by ApJ (Letters
CHEMICALLY MODIFIED PHOTOSYNTHETIC BACTERIAL REACTION CENTERS: CIRCULAR DICHROISM, RAMAN RESONANCE, LOW TEMPERATURE ABSORPTION, FLUORESCENCE AND ODMR SPECTRA AND POLYPEPTIDE COMPOSITION OF BOROHYDRIDE TREATED REACTION CENTERS FROM Rhodobacter sphaeroides R26
Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta 766, 623 (1984)], and investigated spectroscopically and by gel electrophoresis.
(1) Low temperature (1.2 K) absorption, fluorescence, absorption- and fluorescence-detected ODMR, and microwave-induced singlet-triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the ‘additional’ bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (TP870).
(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm-1 region, the removed pigment is assigned to BchlM, e.g. the "extra" Bchl on the "inactive" M-branch.
(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band-shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.
(4) The modification is accompanied by partial proteolytic cleavage of the M-subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous
Polynomial conjunctive query rewriting under unary inclusion dependencies
Ontology-based data access (OBDA) is widely accepted as an important ingredient of the new generation of information systems. In the OBDA paradigm, potentially incomplete relational data is enriched by means of ontologies, representing intensional knowledge of the application domain. We consider the problem of conjunctive query answering in OBDA. Certain ontology languages have been identified as FO-rewritable (e.g., DL-Lite and sticky-join sets of TGDs), which means that the ontology can be incorporated into the user's query, thus reducing OBDA to standard relational query evaluation. However, all known query rewriting techniques produce queries that are exponentially large in the size of the user's query, which can be a serious issue for standard relational database engines. In this paper, we present a polynomial query rewriting for conjunctive queries under unary inclusion dependencies. On
the other hand, we show that binary inclusion dependencies do not admit
polynomial query rewriting algorithms
The structure of N(1535) in the aspect of chiral symmetry
The structure of N(1535) is discussed in dynamical and symmetry aspects based
on chiral symmetry. We find that the N(1535) in chiral unitary model has
implicitly some components other than meson-baryon one. We also discuss the
N(1535) in the chiral doublet picture.Comment: 4 pages, no figure, talk given at Workshop on Chiral Symmetry in
Hadron and Nuclear Physics: Chiral07, Osaka, Japan, 13-16 Nov 200
- …