291 research outputs found
On asymptotic constants related to products of Bernoulli numbers and factorials
We discuss the asymptotic expansions of certain products of Bernoulli numbers
and factorials, e.g., for
integers and . Our main interest is to determine exact
expressions, in terms of known constants, for the asymptotic constants of these
expansions and to show some relations among them.Comment: 22 pages, final revised versio
Progress toward scalable tomography of quantum maps using twirling-based methods and information hierarchies
We present in a unified manner the existing methods for scalable partial
quantum process tomography. We focus on two main approaches: the one presented
in Bendersky et al. [Phys. Rev. Lett. 100, 190403 (2008)], and the ones
described, respectively, in Emerson et al. [Science 317, 1893 (2007)] and
L\'{o}pez et al. [Phys. Rev. A 79, 042328 (2009)], which can be combined
together. The methods share an essential feature: They are based on the idea
that the tomography of a quantum map can be efficiently performed by studying
certain properties of a twirling of such a map. From this perspective, in this
paper we present extensions, improvements and comparative analyses of the
scalable methods for partial quantum process tomography. We also clarify the
significance of the extracted information, and we introduce interesting and
useful properties of the -matrix representation of quantum maps that can
be used to establish a clearer path toward achieving full tomography of quantum
processes in a scalable way.Comment: Replaced with published version (only minor changes respect to the
first version
Hamiltonian Determination with Restricted Access in Transverse Field Ising Chain
We propose a method to evaluate parameters in the Hamiltonian of the Ising
chain under site-dependent transverse fields, with a proviso that we can
control and measure one of the edge spins only. We evaluate the eigenvalues of
the Hamiltonian and the time-evoultion operator exactly for a 3-spin chain,
from which we obtain the expectation values of of the first spin.
The parameters are found from the peak positions of the Fourier transform of
the expectation value. There are four assumptions in our method, which are mild
enough to be satisfied in many physical systems.Comment: 15pages, 4 figure
Competition and Selection Among Conventions
In many domains, a latent competition among different conventions determines
which one will come to dominate. One sees such effects in the success of
community jargon, of competing frames in political rhetoric, or of terminology
in technical contexts. These effects have become widespread in the online
domain, where the data offers the potential to study competition among
conventions at a fine-grained level.
In analyzing the dynamics of conventions over time, however, even with
detailed on-line data, one encounters two significant challenges. First, as
conventions evolve, the underlying substance of their meaning tends to change
as well; and such substantive changes confound investigations of social
effects. Second, the selection of a convention takes place through the complex
interactions of individuals within a community, and contention between the
users of competing conventions plays a key role in the convention's evolution.
Any analysis must take place in the presence of these two issues.
In this work we study a setting in which we can cleanly track the competition
among conventions. Our analysis is based on the spread of low-level authoring
conventions in the eprint arXiv over 24 years: by tracking the spread of macros
and other author-defined conventions, we are able to study conventions that
vary even as the underlying meaning remains constant. We find that the
interaction among co-authors over time plays a crucial role in the selection of
them; the distinction between more and less experienced members of the
community, and the distinction between conventions with visible versus
invisible effects, are both central to the underlying processes. Through our
analysis we make predictions at the population level about the ultimate success
of different synonymous conventions over time--and at the individual level
about the outcome of "fights" between people over convention choices.Comment: To appear in Proceedings of WWW 2017, data at
https://github.com/CornellNLP/Macro
Exploration of Artificial Multiferroic Thin-Film Heterostructures using Composition Spreads
We have fabricated a series of composition spreads consisting of ferroelectric BaTiO3 and piezomagnetic CoFe2O4 layers of varying thicknesses modulated at nanometer level in order to explore artificial magnetoelectricthin-film heterostructures. Scanning microwavemicroscopy and scanning superconducting quantum interference device microscopy were used to map the dielectric and magnetic properties as a function of continuously changing average composition across the spreads, respectively. Compositions in the middle of the spreads were found to exhibit ferromagnetism while displaying a dielectric constant as high as ≈120
Exact Eigenstates of Tight-Binding Hamiltonians on the Penrose Tiling
We investigate exact eigenstates of tight-binding models on the planar
rhombic Penrose tiling. We consider a vertex model with hopping along the edges
and the diagonals of the rhombi. For the wave functions, we employ an ansatz,
first introduced by Sutherland, which is based on the arrow decoration that
encodes the matching rules of the tiling. Exact eigenstates are constructed for
particular values of the hopping parameters and the eigenenergy. By a
generalized ansatz that exploits the inflation symmetry of the tiling, we show
that the corresponding eigenenergies are infinitely degenerate. Generalizations
and applications to other systems are outlined.Comment: 24 pages, REVTeX, 13 PostScript figures include
Tunable Multiferroic Properties in Nanocomposite PbTiO\u3csub\u3e3\u3c/sub\u3e-CoFe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e Epitaxial Thin Films
We report on the synthesis of PbTiO3–CoFe2O4 multiferroic nanocomposites and continuous tuning of their ferroelectric and magnetic properties as a function of the average composition on thin-film composition spreads. The highest dielectric constant and nonlinear dielectric signal was observed at (PbTiO3)85–(CoFe2O4)15, where robust magnetism was also observed. Transmission electron microscopy revealed a pancake-shaped epitaxial nanostructure of PbTiO3 on the order of 30 nm embedded in the matrix of CoFe2O4 at this composition. Composition dependent ferroics properties observed here indicate that there is considerable interdiffusion of cations into each other
Energy spectra, wavefunctions and quantum diffusion for quasiperiodic systems
We study energy spectra, eigenstates and quantum diffusion for one- and
two-dimensional quasiperiodic tight-binding models. As our one-dimensional
model system we choose the silver mean or `octonacci' chain. The
two-dimensional labyrinth tiling, which is related to the octagonal tiling, is
derived from a product of two octonacci chains. This makes it possible to treat
rather large systems numerically. For the octonacci chain, one finds singular
continuous energy spectra and critical eigenstates which is the typical
behaviour for one-dimensional Schr"odinger operators based on substitution
sequences. The energy spectra for the labyrinth tiling can, depending on the
strength of the quasiperiodic modulation, be either band-like or fractal-like.
However, the eigenstates are multifractal. The temporal spreading of a
wavepacket is described in terms of the autocorrelation function C(t) and the
mean square displacement d(t). In all cases, we observe power laws for C(t) and
d(t) with exponents -delta and beta, respectively. For the octonacci chain,
0<delta<1, whereas for the labyrinth tiling a crossover is observed from
delta=1 to 0<delta<1 with increasing modulation strength. Corresponding to the
multifractal eigenstates, we obtain anomalous diffusion with 0<beta<1 for both
systems. Moreover, we find that the behaviour of C(t) and d(t) is independent
of the shape and the location of the initial wavepacket. We use our results to
check several relations between the diffusion exponent beta and the fractal
dimensions of energy spectra and eigenstates that were proposed in the
literature.Comment: 24 pages, REVTeX, 10 PostScript figures included, major revision, new
results adde
Magnetic Photon Splitting: the S-Matrix Formulation in the Landau Representation
Calculations of reaction rates for the third-order QED process of photon
splitting in strong magnetic fields traditionally have employed either the
effective Lagrangian method or variants of Schwinger's proper-time technique.
Recently, Mentzel, Berg and Wunner (1994) presented an alternative derivation
via an S-matrix formulation in the Landau representation. Advantages of such a
formulation include the ability to compute rates near pair resonances above
pair threshold. This paper presents new developments of the Landau
representation formalism as applied to photon splitting, providing significant
advances beyond the work of Mentzel et al. by summing over the spin quantum
numbers of the electron propagators, and analytically integrating over the
component of momentum of the intermediate states that is parallel to field. The
ensuing tractable expressions for the scattering amplitudes are satisfyingly
compact, and of an appearance familiar to S-matrix theory applications. Such
developments can facilitate numerical computations of splitting considerably
both below and above pair threshold. Specializations to two regimes of interest
are obtained, namely the limit of highly supercritical fields and the domain
where photon energies are far inferior to that for the threshold of
single-photon pair creation. In particular, for the first time the
low-frequency amplitudes are simply expressed in terms of the Gamma function,
its integral and its derivatives. In addition, the equivalence of the
asymptotic forms in these two domains to extant results from effective
Lagrangian/proper-time formulations is demonstrated.Comment: 19 pages, 3 figures, REVTeX; accepted for publication in Phys. Rev.
Prevalence of Fabry Disease in Young Patients with Stroke in Argentina.
Background: Fabry disease (FD) is an underdiagnosed cause of stroke in youngadults, but the frequency of this association is largely unknown. We estimatedthe prevalence of FD in a nationwide cohort of young adults who had stroke andtransient ischemic attack (TIA) in Argentina. Methods: This was a prospective, multicenterstudy of stroke and FD in young adults (18-55 years) conducted in Argentinabetween 2011 and 2015. Patients were enrolled if they had had a TIA or an ischemicor hemorrhagic stroke within the previous 180 days. FD was diagnosed bymeasuring α-galactosidase A activity (males) and through genetic studies (females).Results: We enrolled 311 patients (54% men, mean age: 41 years). Ischemic eventsoccurred in 89% of patients (80% infarcts, 9% TIA) and hemorrhagic strokes in11%. One female (.3% of the total group, 1% of the cryptogenic ischemic strokes)had the pathogenic mutation c.888G>A/p.Met296Ile /Exon 6 on the GAL gene.Her only other manifestation of FD was angiokeratoma. Eighteen females hadnonpathogenic intronic variations: c.-10C>T, c.-12G>A, or both. Two patients hadthe nonpathogenic mutation D313Y, while a third had the likely benign mutationS126G. Conclusions: FD was identified in 1 patient (.3%) in this first LatinAmerican study. The patient presented with a late-onset oligo-symptomatic formof the disease. A large number of nonpathogenic mutations were present in ourcohort, and it is essential that they not be mistaken for pathogenic mutations to avoid unnecessary enzyme replacement treatment.Fil: Reisin, Ricardo C.. Hospital Británico de Buenos Aires; ArgentinaFil: Mazziotti, Julieta. Hospital Británico de Buenos Aires; ArgentinaFil: León Cejas, Luciana. Hospital Británico de Buenos Aires; ArgentinaFil: Zinnerman, Alberto. Hospital Posadas; ArgentinaFil: Bonardo, Pablo. Hospital Británico de Buenos Aires; ArgentinaFil: Fernandez Pardal, M.. Hospital Británico de Buenos Aires; ArgentinaFil: Martinez, A.. Hospital Posadas; ArgentinaFil: Riccio, Patricia. Fundación Favaloro; ArgentinaFil: Ameriso, Sebastián. Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia; ArgentinaFil: Bendersky, Eduardo. INAREPS; ArgentinaFil: Nofal, Pedro. Sanatorio Parque Tucumán; ArgentinaFil: Cairola, Patricia. CEMIC; ArgentinaFil: Jure, Lorena. Sanatorio Parque Rosario; ArgentinaFil: Sotelo, Andrea. Sanatorio Adventista del Plata; ArgentinaFil: Rozenfeld, Paula Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Estudios Inmunológicos y Fisiopatológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Estudios Inmunológicos y Fisiopatológicos; ArgentinaFil: Ceci, Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Estudios Inmunológicos y Fisiopatológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Estudios Inmunológicos y Fisiopatológicos; ArgentinaFil: Casas Parera, Ignacio Faustino. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Sánchez Luceros, Analía Gabriela. Academia de Medicina; Argentin
- …