2,940 research outputs found
Lindblad dynamics of the quantum spherical model
The purely relaxational non-equilibrium dynamics of the quantum spherical
model as described through a Lindblad equation is analysed. It is shown that
the phenomenological requirements of reproducing the exact quantum equilibrium
state as stationary solution and the associated classical Langevin equation in
the classical limit fix the form of the Lindblad dissipators, up to an
overall time-scale. In the semi-classical limit, the models' behaviour become
effectively the one of the classical analogue, with a dynamical exponent ,
and an effective temperature , renormalised by the quantum
coupling . A distinctive behaviour is found for a quantum quench, at zero
temperature, deep into the ordered phase , for dimensions.
Only for dimensions, a simple scaling behaviour holds true, with a
dynamical exponent , while for dimensions , logarithmic
corrections to scaling arise. The spin-spin correlator, the growing length
scale and the time-dependent susceptibility show the existence of several
logarithmically different length scales.Comment: 61 pages, 14 figure
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
Kinetics of the long-range spherical model
The kinetic spherical model with long-range interactions is studied after a
quench to or to . For the two-time response and correlation
functions of the order-parameter as well as for composite fields such as the
energy density, the ageing exponents and the corresponding scaling functions
are derived. The results are compared to the predictions which follow from
local scale-invariance.Comment: added "fluctuation-dissipation ratios"; fixed typo
Ammonia in the hot core W51-IRS2: 12 new maser lines and a maser component with a velocity drift
With the 100-m telescope at Effelsberg, 19 ammonia (NH3) maser lines have
been detected toward the prominent massive star forming region W51-IRS2. Eleven
of these inversion lines, the (J,K) = (6,2), (5,3), (7,4), (8,5), (7,6), (7,7),
(9,7), (10,7), (9,9), (10,9), and (12,12) transitions, are classified as masers
for the first time in outer space. All detected masers are related to highly
excited inversion doublets. The (5,4) maser originates from an inversion
doublet 340 K above the ground state, while the (12,12) transition, at 1450 K,
is the most highly excited NH3 maser line so far known. Strong variability is
seen not only in ortho- but also in para-NH3 transitions. Bright narrow
emission features are observed, for the first time, in (mostly) ortho-ammonia
transitions, at V ~ 45 km/s, well separated from the quasi-thermal emission
near 60 km/s. These features were absent 25 years ago and show a velocity drift
of about +0.2 km/s/yr. The component is likely related to the SiO maser source
in W51-IRS2 and a possible scenario explaining the velocity drift is outlined.
The 57 km/s component of the (9,6) maser line is found to be strongly linearly
polarized. Maser emission in the (J,K) to (J+1,K) inversion doublets is
strictly forbidden by selection rules for electric dipole transitions in the
ground vibrational state. However, such pairs (and even triplets with (J+2,K))
are common toward W51-IRS2. Similarities in line widths and velocities indicate
that such groups of maser lines arise from the same regions, which can be
explained by pumping through vibrational excitation. The large number of NH3
maser lines in W51-IRS2 is most likely related to the exceptionally high
kinetic temperature and NH3 column density of this young massive star forming
region.Comment: Accepted for publication in Astronomy & Astrophysics, 11 pages, 12
postscript figures, 1 tabl
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
Is local scale invariance a generic property of ageing phenomena ?
In contrast to recent claims by Enss, Henkel, Picone, and Schollwoeck [J.
Phys. A 37, 10479] it is shown that the critical autoresponse function of the
1+1-dimensional contact process is not in agreement with the predictions of
local scale invariance.Comment: 7 pages, 3 figures, final form, c++ source code on reques
Molecular gas and dust in NGC4550: A galaxy with two counterrotating stellar disks
We report the detection of 1 10^7 M_sun of molecular gas in the central region of the S0/E7 galaxy NGC4550, inferred from observations of CO(1-0) emission. Dust is detected in HST WFPC2 images and found to be asymmetrically distributed around the nucleus, only extending to a galactocentric distance of 7'' (600 pc). The shape of the CO emission profile is consistent with a molecular gas distribution following the dust. The distribution of the dust and gas in the center could be the result of an m=1 instability, which is the fastest growing unstable mode in counterrotating stellar disks. On a global scale the molecular gas in NGC4550 is stable against gravitational collapse but nevertheless star formation appears to be ongoing with normal star formation efficiency and gas consumption time scales. The stellar velocity dispersion in NGC4550 resembles that of elliptical galaxies. It is therefore likely that a hot X-ray emitting plasma limits the lifetime of the molecular gas, that must arise from a recent (<1 Gyr) accretion event
- …