1,983 research outputs found
Arp 220 - IC 4553/4: understanding the system and diagnosing the ISM
Arp220 is a nearby system in final stages of galaxy merger with powerful
ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected
in HI absorption and OH Megamaser emission and later recognized as the nearest
ultra-luminous infrared galaxy also showing powerful molecular and X-ray
emissions. In this paper we review the available radio and mm-wave
observational data of Arp 220 in order to obtain an integrated picture of the
dense interstellar medium that forms the location of the powerful
star-formation at the two nuclei.Comment: 9 pages, 4 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
Two-time autocorrelation function in phase-ordering kinetics from local scale-invariance
The time-dependent scaling of the two-time autocorrelation function of spin
systems without disorder undergoing phase-ordering kinetics is considered. Its
form is shown to be determined by an extension of dynamical scaling to a local
scale-invariance which turns out to be a new version of conformal invariance.
The predicted autocorrelator is in agreement with Monte-Carlo data on the
autocorrelation function of the 2D kinetic Ising model with Glauber dynamics
quenched to a temperature below criticality.Comment: Latex2e, 7 pages with 2 figures, with epl macro, final from, to
appear in EP
Local scale invariance as dynamical space-time symmetry in phase-ordering kinetics
The scaling of the spatio-temporal response of coarsening systems is studied
through simulations of the 2D and 3D Ising model with Glauber dynamics. The
scaling functions agree with the prediction of local scale invariance,
extending dynamical scaling to a space-time dynamical symmetry.Comment: Latex, 4 pages, 4 figure
Dynamic Package Interfaces - Extended Version
A hallmark of object-oriented programming is the ability to perform
computation through a set of interacting objects. A common manifestation of
this style is the notion of a package, which groups a set of commonly used
classes together. A challenge in using a package is to ensure that a client
follows the implicit protocol of the package when calling its methods.
Violations of the protocol can cause a runtime error or latent invariant
violations. These protocols can extend across different, potentially
unboundedly many, objects, and are specified informally in the documentation.
As a result, ensuring that a client does not violate the protocol is hard.
We introduce dynamic package interfaces (DPI), a formalism to explicitly
capture the protocol of a package. The DPI of a package is a finite set of
rules that together specify how any set of interacting objects of the package
can evolve through method calls and under what conditions an error can happen.
We have developed a dynamic tool that automatically computes an approximation
of the DPI of a package, given a set of abstraction predicates. A key property
of DPI is that the unbounded number of configurations of objects of a package
are summarized finitely in an abstract domain. This uses the observation that
many packages behave monotonically: the semantics of a method call over a
configuration does not essentially change if more objects are added to the
configuration. We have exploited monotonicity and have devised heuristics to
obtain succinct yet general DPIs. We have used our tool to compute DPIs for
several commonly used Java packages with complex protocols, such as JDBC,
HashSet, and ArrayList.Comment: The only changes compared to v1 are improvements to the Abstract and
Introductio
[CI], [CII] and CO emission lines as a probe for alpha variations at low and high redshifts
The offsets between the radial velocities of the rotational transitions of
carbon monoxide and the fine structure transitions of neutral and singly
ionized carbon are used to test the hypothetical variation of the fine
structure constant, alpha. From the analysis of the [CI] and [CII] fine
structure lines and low J rotational lines of 12CO and 13CO, emitted by the
dark cloud L1599B in the Milky Way disk, we find no evidence for fractional
changes in alpha at the level of || < 3*10^-7. For the
neighbour galaxy M33 a stringent limit on Delta alpha/alpha is set from
observations of three HII zones in [CII] and CO emission lines: || < 4*10^-7. Five systems over the redshift interval z = 5.7-6.4,
showing CO J=6-5, J=7-6 and [CII] emission, yield a limit on || < 1.3*10^-5. Thus, a combination of the [CI], [CII], and CO
emission lines turns out to be a powerful tool for probing the stability of the
fundamental physical constants over a wide range of redshifts not accessible to
optical spectral measurements.Comment: 10 pages, 3 figures, 5 tables. Accepted for publication in MNRA
Hyperuniversality of Fully Anisotropic Three-Dimensional Ising Model
For the fully anisotropic simple-cubic Ising lattice, the critical
finite-size scaling amplitudes of both the spin-spin and energy-energy inverse
correlation lengths and the singular part of the reduced free-energy density
are calculated by the transfer-matrix method and a finite-size scaling for
cyclic L x L x oo clusters with L=3 and 4. Analysis of the data obtained shows
that the ratios and the directional geometric means of above amplitudes are
universal.Comment: RevTeX 3.0, 24 pages, 2 figures upon request, accepted for
publication in Phys. Rev.
On the predictive power of Local Scale Invariance
Local Scale Invariance (LSI) is a theory for anisotropic critical phenomena
designed in the spirit of conformal invariance. For a given representation of
its generators it makes non-trivial predictions about the form of universal
scaling functions. In the past decade several representations have been
identified and the corresponding predictions were confirmed for various
anisotropic critical systems. Such tests are usually based on a comparison of
two-point quantities such as autocorrelation and response functions. The
present work highlights a potential problem of the theory in the sense that it
may predict any type of two-point function. More specifically, it is argued
that for a given two-point correlator it is possible to construct a
representation of the generators which exactly reproduces this particular
correlator. This observation calls for a critical examination of the predictive
content of the theory.Comment: 17 pages, 2 eps figure
Universal amplitudes in the FSS of three-dimensional spin models
In a MC study using a cluster update algorithm we investigate the finite-size
scaling (FSS) of the correlation lengths of several representatives of the
class of three-dimensional classical O(n) symmetric spin models on a column
geometry. For all considered models we find strong evidence for a linear
relation between FSS amplitudes and scaling dimensions when applying
antiperiodic instead of periodic boundary conditions across the torus. The
considered type of scaling relation can be proven analytically for systems on
two-dimensional strips with periodic bc using conformal field theoryComment: 4 pages, RevTex, uses amsfonts.sty, 3 Figure
Local scale invariance and strongly anisotropic equilibrium critical systems
A new set of infinitesimal transformations generalizing scale invariance for
strongly anisotropic critical systems is considered. It is shown that such a
generalization is possible if the anisotropy exponent \theta =2/N, with N=1,2,3
... Differential equations for the two-point function are derived and
explicitly solved for all values of N. Known special cases are conformal
invariance (N=2) and Schr\"odinger invariance (N=1). For N=4 and N=6, the
results contain as special cases the exactly known scaling forms obtained for
the spin-spin correlation function in the axial next nearest neighbor spherical
(ANNNS) model at its Lifshitz points of first and second order.Comment: 4 pages Revtex, no figures, with file multicol.sty, to appear in PR
Transfer-matrix DMRG for stochastic models: The Domany-Kinzel cellular automaton
We apply the transfer-matrix DMRG (TMRG) to a stochastic model, the
Domany-Kinzel cellular automaton, which exhibits a non-equilibrium phase
transition in the directed percolation universality class. Estimates for the
stochastic time evolution, phase boundaries and critical exponents can be
obtained with high precision. This is possible using only modest numerical
effort since the thermodynamic limit can be taken analytically in our approach.
We also point out further advantages of the TMRG over other numerical
approaches, such as classical DMRG or Monte-Carlo simulations.Comment: 9 pages, 9 figures, uses IOP styl
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