1,101 research outputs found
Runtime Distributions and Criteria for Restarts
Randomized algorithms sometimes employ a restart strategy. After a certain
number of steps, the current computation is aborted and restarted with a new,
independent random seed. In some cases, this results in an improved overall
expected runtime. This work introduces properties of the underlying runtime
distribution which determine whether restarts are advantageous. The most
commonly used probability distributions admit the use of a scale and a location
parameter. Location parameters shift the density function to the right, while
scale parameters affect the spread of the distribution. It is shown that for
all distributions scale parameters do not influence the usefulness of restarts
and that location parameters only have a limited influence. This result
simplifies the analysis of the usefulness of restarts. The most important
runtime probability distributions are the log-normal, the Weibull, and the
Pareto distribution. In this work, these distributions are analyzed for the
usefulness of restarts. Secondly, a condition for the optimal restart time (if
it exists) is provided. The log-normal, the Weibull, and the generalized Pareto
distribution are analyzed in this respect. Moreover, it is shown that the
optimal restart time is also not influenced by scale parameters and that the
influence of location parameters is only linear
Análise da resistência externa e da atividade eletromiográfica do movimento de extensão de quadril realizado segundo o método Pilates
Camparison of the Hanbury Brown-Twiss effect for bosons and fermions
Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in
light emitted by a chaotic source, highlighting the importance of two-photon
correlations and stimulating the development of modern quantum optics . The
quantum interpretation of bunching relies upon the constructive interference
between amplitudes involving two indistinguishable photons, and its additive
character is intimately linked to the Bose nature of photons. Advances in atom
cooling and detection have led to the observation and full characterisation of
the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions
should reveal an antibunching effect, i.e., a tendency to avoid each other.
Antibunching of fermions is associated with destructive two-particle
interference and is related to the Pauli principle forbidding more than one
identical fermion to occupy the same quantum state. Here we report an
experimental comparison of the fermion and the boson HBT effects realised in
the same apparatus with two different isotopes of helium, 3He (a fermion) and
4He (a boson). Ordinary attractive or repulsive interactions between atoms are
negligible, and the contrasting bunching and antibunching behaviours can be
fully attributed to the different quantum statistics. Our result shows how
atom-atom correlation measurements can be used not only for revealing details
in the spatial density, or momentum correlations in an atomic ensemble, but
also to directly observe phase effects linked to the quantum statistics in a
many body system. It may thus find applications to study more exotic situations
>.Comment: Nature 445, 402 (2007). V2 includes the supplementary informatio
Ab-initio prediction of the electronic and optical excitations in polythiophene: isolated chains versus bulk polymer
We calculate the electronic and optical excitations of polythiophene using
the GW approximation for the electronic self-energy, and include excitonic
effects by solving the electron-hole Bethe-Salpeter equation. Two different
situations are studied: excitations on isolated chains and excitations on
chains in crystalline polythiophene. The dielectric tensor for the crystalline
situation is obtained by modeling the polymer chains as polarizable line
objects, with a long-wavelength polarizability tensor obtained from the
ab-initio polarizability function of the isolated chain. With this model
dielectric tensor we construct a screened interaction for the crystalline case,
including both intra- and interchain screening. In the crystalline situation
both the quasi-particle band gap and the exciton binding energies are
drastically reduced in comparison with the isolated chain. However, the optical
gap is hardly affected. We expect this result to be relevant for conjugated
polymers in general.Comment: 15 pages including 4 figures; to appear in Phys. Rev. B, 6/15/200
In-situ formation characteristic, tribological characterization and anti-corrosion properties of quaternary composites films
Improvements of wear and corrosion properties are essential characteristic in engineering application. A study was made
on the structure, electro-oxidation and properties of fabricated Z
Electric Field-Tuned Topological Phase Transition in Ultra-Thin Na3Bi - Towards a Topological Transistor
The electric field induced quantum phase transition from topological to
conventional insulator has been proposed as the basis of a topological field
effect transistor [1-4]. In this scheme an electric field can switch 'on' the
ballistic flow of charge and spin along dissipationless edges of the
two-dimensional (2D) quantum spin Hall insulator [5-9], and when 'off' is a
conventional insulator with no conductive channels. Such as topological
transistor is promising for low-energy logic circuits [4], which would
necessitate electric field-switched materials with conventional and topological
bandgaps much greater than room temperature, significantly greater than
proposed to date [6-8]. Topological Dirac semimetals(TDS) are promising systems
in which to look for topological field-effect switching, as they lie at the
boundary between conventional and topological phases [3,10-16]. Here we use
scanning probe microscopy/spectroscopy (STM/STS) and angle-resolved
photoelectron spectroscopy (ARPES) to show that mono- and bilayer films of TDS
Na3Bi [3,17] are 2D topological insulators with bulk bandgaps >400 meV in the
absence of electric field. Upon application of electric field by doping with
potassium or by close approach of the STM tip, the bandgap can be completely
closed then re-opened with conventional gap greater than 100 meV. The large
bandgaps in both the conventional and quantum spin Hall phases, much greater
than the thermal energy kT = 25 meV at room temperature, suggest that ultrathin
Na3Bi is suitable for room temperature topological transistor operation
Reoperação de tromboendarterectomia pulmonar em recidiva de tromboembolismo pulmonar crônico hipertensivo
Artificial graphene as a tunable Dirac material
Artificial honeycomb lattices offer a tunable platform to study massless
Dirac quasiparticles and their topological and correlated phases. Here we
review recent progress in the design and fabrication of such synthetic
structures focusing on nanopatterning of two-dimensional electron gases in
semiconductors, molecule-by-molecule assembly by scanning probe methods, and
optical trapping of ultracold atoms in crystals of light. We also discuss
photonic crystals with Dirac cone dispersion and topologically protected edge
states. We emphasize how the interplay between single-particle band structure
engineering and cooperative effects leads to spectacular manifestations in
tunneling and optical spectroscopies.Comment: Review article, 14 pages, 5 figures, 112 Reference
Microcrystalline Tyrosine (MCT®): A Depot Adjuvant in Licensed Allergy Immunotherapy Offers New Opportunities in Malaria
Microcrystalline Tyrosine (MCT®) is a widely used proprietary depot excipient in specific immunotherapy for allergy. In the current study we assessed the potential of MCT to serve as an adjuvant in the development of a vaccine against malaria. To this end, we formulated the circumsporozoite protein (CSP) of P. vivax in MCT and compared the induced immune responses to CSP formulated in PBS or Alum. Both MCT and Alum strongly increased immunogenicity of CSP compared to PBS in both C57BL/6 and BALB/c mice. Challenge studies in mice using a chimeric P. bergei expressing CSP of P. vivax demonstrated clinically improved symptoms of malaria with CSP formulated in both MCT and Alum; protection was, however, more pronounced if CSP was formulated in MCT. Hence, MCT may be an attractive biodegradable adjuvant useful for the development of novel prophylactic vaccines
Ganglionopatia como manifestação inicial de neoplasia pulmonar: relato de caso
Ganglionopathy is a rare condition defined by an injury to the sensory neurons in the dorsal root ganglion. This disease belongs to a group of peripheral polyneuropathies with an exclusively sensory and axonal pattern and its diagnoses can be made by an electromyoneurographic study. The association between ganglionopathy and other underlying pathologies, such as some types of cancer, autoimmune diseases, and celiac disease is often mentioned in published studies. The purpose of this report was to describe the case of a patient suffering from ganglionopathy including a detailed discussion of the electromyoneurographic study that led the attending physician to a diagnosis of neoplastic lung disease. The conclusion therefore was that it is important for the neurophysiology specialist to keep in mind the possible causes of ganglionopathy and, through this diagnosis, to help the attending physician in making an early and full workup of the patient.A ganglionopatia é uma entidade rara que consiste na afecção dos neurônios sensitivos da raiz dorsal, fazendo parte do grupo das polineuropatias periféricas do tipo exclusivamente sensitivo com comprometimento axonal e tendo seu diagnóstico feito através de estudo eletroneuromiográfico. A associação entre a ganglionopatia e outras patologias como neoplasias, doenças autoimunes, doença celíaca, entre outras é amplamente citada na literatura. O objetivo deste trabalho é descrever o caso clínico de um paciente com diagnóstico de neoplasia pulmonar cuja manifestação inicial foi a ganglionopatia, incluindo a descrição detalhada do exame eletroneuromiográfico que auxiliou no processo diagnóstico do médico assistente. Concluímos ser importante que o médico neurofisiologista tenha em mente as possíveis causas da ganglionopatia e saiba apontar o médico assistente para que a investigação possa ser realizada de maneira completa e precoce
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