236 research outputs found
Crossover in Growth Law and Violation of Superuniversality in the Random Field Ising Model
We study the nonconserved phase ordering dynamics of the d = 2, 3 random
field Ising model, quenched to below the critical temperature. Motivated by the
puzzling results of previous work in two and three di- mensions, reporting a
crossover from power-law to logarithmic growth, together with superuniversal
behavior of the correlation function, we have undertaken a careful
investigation of both the domain growth law and the autocorrelation function.
Our main results are as follows: We confirm the crossover to asymptotic
logarithmic behavior in the growth law, but, at variance with previous
findings, the exponent in the preasymptotic power law is disorder-dependent,
rather than being the one of the pure system. Furthermore, we find that the
autocorre- lation function does not display superuniversal behavior. This
restores consistency with previous results for the d = 1 system, and fits
nicely into the unifying scaling scheme we have recently proposed in the study
of the random bond Ising model.Comment: To be published in Physical Review
Test of Local Scale Invariance from the direct measurement of the response function in the Ising model quenched to and to below
In order to check on a recent suggestion that local scale invariance
[M.Henkel et al. Phys.Rev.Lett. {\bf 87}, 265701 (2001)] might hold when the
dynamics is of Gaussian nature, we have carried out the measurement of the
response function in the kinetic Ising model with Glauber dynamics quenched to
in , where Gaussian behavior is expected to apply, and in the two
other cases of the model quenched to and to below , where
instead deviations from Gaussian behavior are expected to appear. We find that
in the case there is an excellent agreement between the numerical data,
the local scale invariance prediction and the analytical Gaussian
approximation. No logarithmic corrections are numerically detected. Conversely,
in the cases, both in the quench to and to below , sizable
deviations of the local scale invariance behavior from the numerical data are
observed. These results do support the idea that local scale invariance might
miss to capture the non Gaussian features of the dynamics. The considerable
precision needed for the comparison has been achieved through the use of a fast
new algorithm for the measurement of the response function without applying the
external field. From these high quality data we obtain for
the scaling exponent of the response function in the Ising model quenched
to below , in agreement with previous results.Comment: 24 pages, 6 figures. Resubmitted version with improved discussions
and figure
Nonlinear response and fluctuation dissipation relations
A unified derivation of the off equilibrium fluctuation dissipation relations
(FDR) is given for Ising and continous spins to arbitrary order, within the
framework of Markovian stochastic dynamics. Knowledge of the FDR allows to
develop zero field algorithms for the efficient numerical computation of the
response functions. Two applications are presented. In the first one, the
problem of probing for the existence of a growing cooperative length scale is
considered in those cases, like in glassy systems, where the linear FDR is of
no use. The effectiveness of an appropriate second order FDR is illustrated in
the test case of the Edwards-Anderson spin glass in one and two dimensions. In
the second one, the important problem of the definition of an off equilibrium
effective temperature through the nonlinear FDR is considered. It is shown
that, in the case of coarsening systems, the effective temperature derived from
the second order FDR is consistent with the one obtained from the linear FDR.Comment: 24 pages, 6 figure
Does the Presence of an Iliac Aneurysm Affect Outcome of Endoluminal AAA Repair? An Analysis of 336 Cases
AbstractObjective: to determine whether the presence of an iliac aneurysm compromises outcome of endovascular exclusion of AAA and to ascertain the fate of the iliac aneurysmal sac.Patients and methods: between April 1997 and March 2001, data on 336 consecutive patients undergoing endovascular repair for AAA were entered in a prospective database. Suitability for endovascular repair was assessed by preoperative contrast-enhanced computed tomography. A maximum common iliac artery (CIA) diameter ≥20mm was defined as iliac aneurysm. Patients with and without iliac aneurysms were compared to early (immediate conversion or perioperative death) and late failure (increase in aneurysm diameter or persisting graft-related endoleak, or late AAA rupture or conversion).Results: fifty-nine patients (18%) had iliac aneurysms, 19 were bilateral, for a total of 78 aneurysmal iliac arteries (median diameter 23mm; range 20–50mm). A distal seal was achieved by landing in 33 external iliac arteries, in 20 ectatic CIAs, and in 25 normal CIAs. Operating time differed significantly between patients with and without CIA aneurysms (153±71 vs 123±55min,p =0.0001), whereas no statistically significant differences were found with respect to early and late failure (2% vs 3%, p=0.5 and 14% vs 8%, p=0.11, respectively). There were no cases of buttock or colon necrosis. At a median follow-up of 14 months (range 0–46; i.q.r. 7–27 months) common iliac diameter decreased ≥2mm in 49 cases, remained stable in 25, and increased ≥2mm in 3.Conclusion: the presence of iliac aneurysm rendered endoluminal AAA repair more complex but did not affect feasibility and long-term outcome of the procedure. In our experience internal iliac exclusion was never associated with significant morbidity. These data may be useful when considering endovascular repair in high-risk patients with challenging anatomy
Role of Duplex Scan in Endoleak Detection After Endoluminal Abdominal Aortic Aneurysm Repair
AbstractObjective: to validate the role of duplex scan in endoleak detection in postoperative surveillance of endoluminal abdominal aneurysm repair (EAAR). Patients and methods between April 1997 and March 1999, 103 patients were eligible for duplex and computed tomography (CT) scan after EAAR. Mean follow-up was 8 months (range 1–24 months). The study protocol comprised concurrent examination with colour-duplex and CT scan at 1, 6, and 12 months after EAAR, for a total of 198 concurrent examinations. All duplex scan examinations were performed by two vascular surgeons with the same machine (ATL HDI 3000). Interobserver agreement in endoleak detection (κ=1) and in type of endoleak (κ=0.7) was evaluated in 50 random duplex examinations. Endoleak detection was examined comparatively in duplex and CT scan, the latter being the gold standard. Sensitivity and specificity tests together with negative- and positive-predictive values (NPV and PPV) were calculated. Results duplex scan was not feasible in one patient. On CT scan the endoleak rate was 4% at one month, 3% at 6 months, and 4% at one year. Overall, CT scan detected 12 endoleaks. With respect to endoleak detection, duplex scan revealed a great ability in ruling out false-negative results (sensitivity 91.7%, NPV 99.4%), but overestimated the presence of endoleak (specificity 98.4%, PPV 78.6%). Regarding type of endoleak, the ability of duplex scan to identify the source of endoleak was low (sensitivity 66.7%). Conclusions duplex scan, if validated, appears to be a reliable means for excluding the presence of endoleak after EAAR
Fluctuation-Dissipation relations far from Equilibrium
In this Article we review some recent progresses in the field of
non-equilibrium linear response theory. We show how a generalization of the
fluctuation-dissipation theorem can be derived for Markov processes, and
discuss the Cugliandolo-Kurchan \cite{Cugliandolo93} fluctuation dissipation
relation for aging systems and the theorem by Franz {\it et. al.}
\cite{Franz98} relating static and dynamic properties. We than specialize the
subject to phase-ordering systems examining the scaling properties of the
linear response function and how these are determined by the behavior of
topological defects. We discuss how the connection between statics and dynamics
can be violated in these systems at the lower critical dimension or as due to
stochastic instability.Comment: 18 pages, 10 figure
Effects of an external drive on the fluctuation-dissipation relation of phase-ordering systems
The relation between the autocorrelation and the integrated linear
response function is studied in the context of the large-N model
for phase-ordering systems subjected to a shear flow. In the high temperature
phase a non-equilibrium stationary state is entered which is
characterized by a non-trivial fluctuation-dissipation relation . For quenches below the splitting of the
order parameter field into two statistically independent components,
responsible for the stationary and aging part
of the autocorrelation function, can be explicitly exhibited in close analogy
with the undriven case. In the regime the same relation is found between the response and
, as for . The aging part of is
negligible for , as without drive, resulting in a flat in the aging regime .Comment: 8 pages, 2 figure
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