1,130 research outputs found
Exact infinite-time statistics of the Loschmidt echo for a quantum quench
The equilibration dynamics of a closed quantum system is encoded in the
long-time distribution function of generic observables. In this paper we
consider the Loschmidt echo generalized to finite temperature, and show that we
can obtain an exact expression for its long-time distribution for a closed
system described by a quantum XY chain following a sudden quench. In the
thermodynamic limit the logarithm of the Loschmidt echo becomes normally
distributed, whereas for small quenches in the opposite, quasi-critical regime,
the distribution function acquires a universal double-peaked form indicating
poor equilibration. These findings, obtained by a central limit theorem-type
result, extend to completely general models in the small-quench regime.Comment: 4 pages, 2 figure
123I MIBG: Are There Any Additional Roles in Clinical Practice of Heart Failure?
Since the advent of 123I-meta-iodobenzylguanidine(MIBG)in 1990s, it has been widely used in clinical practice in Japan. Based on the wide range of clinical applications, 123I MIBG is now incorporated in Japanese Circulation Society)s guidelines of nuclear cardiology. The major role of 123I MIBG has been in determination of severity and prognostic evaluation of heart failure. In addition, assessment of the treatment by various types of medications has been the second major role of 123 I MIBG imaging. Compared with the conventional clinical parameters of heart failure, additive values of 123I MIBG depend on how it reflects the patient condition more accurately, and how it relates to improvement in the patient outcome. 123 I MIBG is also now available for cardiac imaging in the USA and Europe. Unified methodology and further studies focusing on clinical decision-making are the next required steps to document MIBG utility
Stable Topologies of Event Horizon
In our previous work, it was shown that the topology of an event horizon (EH)
is determined by the past endpoints of the EH. A torus EH (the collision of two
EH) is caused by the two-dimensional (one-dimensional) set of the endpoints. In
the present article, we examine the stability of the topology of the EH. We see
that a simple case of a single spherical EH is unstable. Furthermore, in
general, an EH with handles (a torus, a double torus, ...) is structurally
stable in the sense of catastrophe theory.Comment: 21 pages, revtex, five figures containe
A Pooled Analysis of Multicenter Cohort Studies of 123I-mIBG Imaging of Sympathetic Innervation for Assessment of Long-Term Prognosis in Heart Failure
ObjectivesThe study objectives were to create a cardiac metaiodobenzylguanidine (mIBG) database using multiple prospective cohort studies and to determine the quantitative iodine-123–labeled mIBG indices for identifying patients with chronic heart failure (HF) at greatest and lowest risk of lethal events.BackgroundAlthough the prognostic value of cardiac mIBG imaging in patients with HF has been shown, clinical use of this procedure has been limited. It is required to define universally accepted quantitative thresholds for high and low risk that could be used as an aid to therapeutic decision-making using a large cohort database.MethodsSix prospective HF cohort studies were updated, and the individual datasets were combined for the present patient-level analysis. The database consisted of 1,322 patients with HF followed up for a mean interval of 78 months. Heart-to-mediastinum ratio (HMR) and washout rate of cardiac mIBG activity were the primary cardiac innervation markers. The primary outcome analyzed was all-cause death.ResultsLethal events were observed in 326 patients, and the population mortality rate was 5.6%, 11.3%, and 19.7% at 1, 2, and 5 years, respectively. Multivariate Cox proportional hazard model analysis for all-cause mortality identified age (p < 0.0001), New York Heart Association (NYHA) functional class (p < 0.0001), late HMR of cardiac mIBG activity (p < 0.0001), and left ventricular ejection fraction (LVEF) (p = 0.0029) as significant independent predictors. Analysis of the 512-patient subpopulation with B-type natriuretic peptide (BNP) results showed BNP (p < 0.0001), greater NYHA functional class (p = 0.0002), and late HMR (p = 0.0011) as significant predictors, but LVEF was not. The receiver-operating characteristic–determined threshold of HMR (1.68) identified patients at significantly increased risk in any LVEF category. Survival rates decreased progressively with decreasing HMR, with 5-year all-cause mortality rates >7% annually for HMR <1.25, and <2% annually for HMR ≥1.95. Addition of HMR to clinical information resulted in a significant net reclassification improvement of 0.175 (p < 0.0001).ConclusionsPooled analyses of independent cohort studies confirmed the long-term prognostic value of cardiac mIBG uptake in patients with HF independently of other markers, such as NYHA functional class, BNP, and LVEF, and demonstrated that categoric assessments could be used to define meaningful thresholds for lethal event risk
Influence of the coorbital resonance on the rotation of the Trojan satellites of Saturn
The Cassini spacecraft collects high resolution images of the saturnian
satellites and reveals the surface of these new worlds. The shape and rotation
of the satellites can be determined from the Cassini Imaging Science Subsystem
data, employing limb coordinates and stereogrammetric control points. This is
the case for Epimetheus (Tiscareno et al. 2009) that opens elaboration of new
rotational models (Tiscareno et al. 2009; Noyelles 2010; Robutel et al. 2011).
Especially, Epimetheus is characterized by its horseshoe shape orbit and the
presence of the swap is essential to introduce explicitly into rotational
models. During its journey in the saturnian system, Cassini spacecraft
accumulates the observational data of the other satellites and it will be
possible to determine the rotational parameters of several of them. To prepare
these future observations, we built rotational models of the coorbital (also
called Trojan) satellites Telesto, Calypso, Helene, and Polydeuces, in addition
to Janus and Epimetheus. Indeed, Telesto and Calypso orbit around the L_4 and
L_5 Lagrange points of Saturn-Tethys while Helene and Polydeuces are coorbital
of Dione. The goal of this study is to understand how the departure from the
Keplerian motion induced by the perturbations of the coorbital body, influences
the rotation of these satellites. To this aim, we introduce explicitly the
perturbation in the rotational equations by using the formalism developed by
Erdi (1977) to represent the coorbital motions, and so we describe the
rotational motion of the coorbitals, Janus and Epimetheus included, in compact
form
Nambu Quantum Mechanics: A Nonlinear Generalization of Geometric Quantum Mechanics
We propose a generalization of the standard geometric formulation of quantum
mechanics, based on the classical Nambu dynamics of free Euler tops. This
extended quantum mechanics has in lieu of the standard exponential time
evolution, a nonlinear temporal evolution given by Jacobi elliptic functions.
In the limit where latter's moduli parameters are set to zero, the usual
geometric formulation of quantum mechanics, based on the Kahler structure of a
complex projective Hilbert space, is recovered. We point out various novel
features of this extended quantum mechanics, including its geometric aspects.
Our approach sheds a new light on the problem of quantization of Nambu
dynamics. Finally, we argue that the structure of this nonlinear quantum
mechanics is natural from the point of view of string theory.Comment: 15 pages, LaTeX, typos correcte
Time evolution and observables in constrained systems
The discussion is limited to first-class parametrized systems, where the
definition of time evolution and observables is not trivial, and to finite
dimensional systems in order that technicalities do not obscure the conceptual
framework. The existence of reasonable true, or physical, degrees of freedom is
rigorously defined and called {\em local reducibility}. A proof is given that
any locally reducible system admits a complete set of perennials. For locally
reducible systems, the most general construction of time evolution in the
Schroedinger and Heisenberg form that uses only geometry of the phase space is
described. The time shifts are not required to be 1symmetries. A relation
between perennials and observables of the Schroedinger or Heisenberg type
results: such observables can be identified with certain classes of perennials
and the structure of the classes depends on the time evolution. The time
evolution between two non-global transversal surfaces is studied. The problem
is posed and solved within the framework of the ordinary quantum mechanics. The
resulting non-unitarity is different from that known in the field theory
(Hawking effect): state norms need not be preserved so that the system can be
lost during the evolution of this kind.Comment: 31 pages, Latex fil
Peeling back the layers: Deconstructing information literacy discourse in higher education
The discourses of information literacy practice create epistemological assumptions about how the practice should happen, who should be responsible and under what conditions instruction should be given. Analysis of a wide range of documents and texts emerging from the Higher Education (HE) sector suggest that information literacy (IL) is shaped by two competing and incongruent narratives. The outward facing narrative of information literacy (located in information literacy standards and guidelines) positions information literacy as an empowering practice that arms students with the knowledge and skills to battle the complexity of the modern information world. In contrast, the inward facing narrative (located in information literacy texts) positions students as lacking appropriate knowledge, skills and agency. This deficit perception, which has the capacity to influence pedagogical practice, is at odds with constructivist and action-oriented views that are espoused within information literacy instructional pedagogy. This presentation represents the first paper in a research programme that interrogates the epistemological premises and discourses of information literacy within HE
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