1,857 research outputs found
Spin-Peierls instability in a quantum spin chain with Dzyaloshinskii-Moriya interaction
We analysed the ground state energy of some dimerized spin-1/2 transverse XX
and Heisenberg chains with Dzyaloshinskii-Moriya (DM) interaction to study the
influence of the latter interaction on the spin-Peierls instability. We found
that DM interaction may act either in favour of the dimerization or against it.
The actual result depends on the dependence of DM interaction on the distortion
amplitude in comparison with such dependence for the isotropic exchange
interaction.Comment: 12 pages, latex, 3 figure
Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study
We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAlO and MnAlO using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAlO, macroscopic measurements evidence a "cusp" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAlO. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} factor points towards orbital contributions from Fe.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAlO, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAlO. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
-site spinels which have predominant short-range spin correlations
reminiscent of the "spin liquid" state.Comment: 10 pages, 10 figures, double-column, accepted in Phys. Rev. B, 201
Quantifying the Re-identification Risk of Event Logs for Process Mining
Event logs recorded during the execution of business processes constitute a
valuable source of information. Applying process mining techniques to them,
event logs may reveal the actual process execution and enable reasoning on
quantitative or qualitative process properties. However, event logs often
contain sensitive information that could be related to individual process
stakeholders through background information and cross-correlation. We therefore
argue that, when publishing event logs, the risk of such re-identification
attacks must be considered. In this paper, we show how to quantify the
re-identification risk with measures for the individual uniqueness in event
logs. We also report on a large-scale study that explored the individual
uniqueness in a collection of publicly available event logs. Our results
suggest that potentially up to all of the cases in an event log may be
re-identified, which highlights the importance of privacy-preserving techniques
in process mining.Comment: Accepted to CAiSE-202
Sheep can be used as animal model of regional myocardial remodeling and controllable work
Background: Pacing the right heart has been shown to induce reversible conduction delay and subsequent asymmetric remodeling of the left ventricle (LV) in dogs and pigs. Both species have disadvantages in animal experiments. Therefore the aim of this study was to develop a more feasible and easy-to-use animal model in sheep.
Methods: Dual-chamber (DDD) pacemakers with epicardial leads on the right atrium and right ventricular free wall were implanted in 13 sheep. All animals underwent 8 weeks of chronic rapid pacing at 180 bpm. Reported observations were made at 110 bpm.
Results: DDD pacing acutely induced a left bundle branch block (LBBB) — like pattern with almost doubling in QRS width and the appearance of a septal flash, indicating mechanical dyssynchrony. Atrial pacing (AAI) resulted in normal ventricular conduction and function. During 8 weeks of rapid DDD pacing, animals developed LV remodeling (confirmed with histology) with septal wall thinning (–30%, p < 0.05), lateral wall thickening (+22%, p < 0.05), LV volume increase (+32%, p < 0.05), decrease of LV ejection fraction (–31%, p < 0.05), and functional mitral regurgitation. After 8 weeks, segmental pressure-strain-loops, representing regional myocardial work, were recorded. Switching from AAI to DDD pacing decreased immediately work in the septum and increased it in the lateral wall (–69 and +41%, respectively, p < 0.05). Global LV stroke work and dP/dtmax decreased (–27% and -25%, respectively, p < 0.05).
Conclusions: This study presents the development a new sheep model with an asymmetrically remodeled LV. Simple pacemaker programing allows direct modulation of regional myocardial function and work. This animal model provides a new and valuable alternative for canine or porcine models and has the potential to become instrumental for investigating regional function and loading conditions on regional LV remodeling
Continuity of the Maximum-Entropy Inference
We study the inverse problem of inferring the state of a finite-level quantum
system from expected values of a fixed set of observables, by maximizing a
continuous ranking function. We have proved earlier that the maximum-entropy
inference can be a discontinuous map from the convex set of expected values to
the convex set of states because the image contains states of reduced support,
while this map restricts to a smooth parametrization of a Gibbsian family of
fully supported states. Here we prove for arbitrary ranking functions that the
inference is continuous up to boundary points. This follows from a continuity
condition in terms of the openness of the restricted linear map from states to
their expected values. The openness condition shows also that ranking functions
with a discontinuous inference are typical. Moreover it shows that the
inference is continuous in the restriction to any polytope which implies that a
discontinuity belongs to the quantum domain of non-commutative observables and
that a geodesic closure of a Gibbsian family equals the set of maximum-entropy
states. We discuss eight descriptions of the set of maximum-entropy states with
proofs of accuracy and an analysis of deviations.Comment: 34 pages, 1 figur
Trends in the elastic response of binary early transition metal nitrides
Motivated by an increasing demand for coherent data that can be used for
selecting materials with properties tailored for specific application
requirements, we studied elastic response of nine binary early transition metal
nitrides (ScN, TiN, VN, YN, ZrN, NbN, LaN, HfN, and TaN) and AlN. In
particular, single crystal elastic constants, Young's modulus in different
crystallographic directions, polycrystalline values of shear and Young's
moduli, and the elastic anisotropy factor were calculated. Additionally, we
provide estimates of the third order elastic constants for the ten binary
nitrides.Comment: 10 pages, 7 figure
Late Maastrichtian carbon isotope stratigraphy and cyclostratigraphy of the Newfoundland Margin (Site U1403, IODP Expedition 342)
Earth’s climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma4051 to Ma4057) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary. A high-resolution carbon-isotope record from bulk carbonates allows us to identify global trends in the late Maastrichtian carbon cycle. Low-amplitude variations (up to 0.4‰) in carbon isotopes at Site U1403 match similar scale variability in records from Tethyan and Pacific open-ocean sites. Comparison between Site U1403 and the hemipelagic restricted basin of the Zumaia section (northern Spain), with its own well-established independent cyclostratigraphic framework, is more complex. Whereas the pre-K/Pg oscillations and the negative values of the Mid-Maastrichtian Event (MME) can be readily discerned in both the Zumaia and U1403 records, patterns diverge during a ~ 1 Myr period in the late Maastrichtian (67.8–66.8 Ma), with Site U1403 more reliably reflecting global carbon cycling. Our new carbon isotope record and cyclostratigraphy offer promise for Site U1403 to serve as a future reference section for high-resolution studies of late Maastrichtian paleoclimatic change
Constraining interactions mediated by axion-like particles with ultracold neutrons
We report a new limit on a possible short range spin-dependent interaction
from the precise measurement of the ratio of Larmor precession frequencies of
stored ultracold neutrons and Hg atoms confined in the same volume. The
measurement was performed in a 1 T vertical magnetic holding field
with the apparatus searching for a permanent electric dipole moment of the
neutron at the Paul Scherrer Institute. A possible coupling between freely
precessing polarized neutron spins and unpolarized nucleons of the wall
material can be investigated by searching for a tiny change of the precession
frequencies of neutron and mercury spins. Such a frequency change can be
interpreted as a consequence of a short range spin-dependent interaction that
could possibly be mediated by axions or axion-like particles. The interaction
strength is proportional to the CP violating product of scalar and pseudoscalar
coupling constants . Our result confirms limits from complementary
experiments with spin-polarized nuclei in a model-independent way. Limits from
other neutron experiments are improved by up to two orders of magnitude in the
interaction range of m
Typical equilibrium state of an embedded quantum system
We consider an arbitrary quantum system coupled non perturbatively to a large
arbitrary and fully quantum environment. In [G. Ithier and F. Benaych-Georges,
Phys. Rev. A 96, 012108 (2017)] the typicality of the dynamics of such an
embedded quantum system was established for several classes of random
interactions. In other words, the time evolution of its quantum state does not
depend on the microscopic details of the interaction. Focusing at the long time
regime, we use this property to calculate analytically a new partition function
characterizing the stationary state and involving the overlaps between
eigenvectors of a bare and a dressed Hamiltonian. This partition function
provides a new thermodynamical ensemble which includes the microcanonical and
canonical ensembles as particular cases. We check our predictions with
numerical simulations.Comment: 1 figure, 5 pages. This article supersedes the part on the
equilibrium state in arXiv:1510.0435
Extended Smoothed Boundary Method for Solving Partial Differential Equations with General Boundary Conditions on Complex Boundaries
In this article, we describe an approach for solving partial differential
equations with general boundary conditions imposed on arbitrarily shaped
boundaries. A continuous function, the domain parameter, is used to modify the
original differential equations such that the equations are solved in the
region where a domain parameter takes a specified value while boundary
conditions are imposed on the region where the value of the domain parameter
varies smoothly across a short distance. The mathematical derivations are
straightforward and generically applicable to a wide variety of partial
differential equations. To demonstrate the general applicability of the
approach, we provide four examples herein: (1) the diffusion equation with both
Neumann and Dirichlet boundary conditions; (2) the diffusion equation with both
surface diffusion and reaction; (3) the mechanical equilibrium equation; and
(4) the equation for phase transformation with the presence of additional
boundaries. The solutions for several of these cases are validated against
corresponding analytical and semi-analytical solutions. The potential of the
approach is demonstrated with five applications: surface-reaction-diffusion
kinetics with a complex geometry, Kirkendall-effect-induced deformation,
thermal stress in a complex geometry, phase transformations affected by
substrate surfaces, and a self-propelled droplet.Comment: This document is the revised version of arXiv:0912.1288v
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