Characterization of qubit chains by Feynman probes

We address the characterization of qubit chains and assess the performances of local measurements compared to those provided by Feynman probes, i.e. nonlocal measurements realized by coupling a single qubit regis- ter to the chain. We show that local measurements are suitable to estimate small values of the coupling and that a Bayesian strategy may be successfully exploited to achieve optimal precision. For larger values of the coupling Bayesian local strategies do not lead to a consistent estimate. In this regime, Feynman probes may be exploited to build a consistent Bayesian estimator that saturates the Cram\'er-Rao bound, thus providing an effective characterization of the chain. Finally, we show that ultimate bounds to precision, i.e. saturation of the quantum Cram\'er-Rao bound, may be achieved by a two-step scheme employing Feynman probes followed by local measurements.Comment: 8 pages, 5 figure

Dynamics of quantum correlations in colored environments

We address the dynamics of entanglement and quantum discord for two non interacting qubits initially prepared in a maximally entangled state and then subjected to a classical colored noise, i.e. coupled with an external environment characterized by a noise spectrum of the form $1/f^{\alpha}$. More specifically, we address systems where the Gaussian approximation fails, i.e. the sole knowledge of the spectrum is not enough to determine the dynamics of quantum correlations. We thus investigate the dynamics for two different configurations of the environment: in the first case the noise spectrum is due to the interaction of each qubit with a single bistable fluctuator with an undetermined switching rate, whereas in the second case we consider a collection of classical fluctuators with fixed switching rates. In both cases we found analytical expressions for the time dependence of entanglement and quantum discord, which may be also extended to a collection of flcutuators with random switching rates. The environmental noise is introduced by means of stochastic time-dependent terms in the Hamiltonian and this allows us to describe the effects of both separate and common environments. We show that the non-Gaussian character of the noise may lead to significant effects, e.g. environments with the same power spectrum, but different configurations, give raise to opposite behavior for the quantum correlations. In particular, depending on the characteristics of the environmental noise considered, both entanglement and discord display either a monotonic decay or the phenomena of sudden death and revivals. Our results show that the microscopic structure of environment, besides its noise spectrum, is relevant for the dynamics of quantum correlations, and may be a valid starting point for the engineering of non-Gaussian colored environments.Comment: 8 pages, 3 figure

Statistical evaluation of the critical distance in the finite life fatigue regime

The procedure to evaluate the critical distance with an optimized V-notched specimen is initially reviewed in the paper. This procedure was devised by the authors, and another numerical methodology was recently proposed to evaluate the uncertainty of the critical distance assessment. The input of the analysis is the combination of the statistical distribution of the fatigue properties from which the critical distance is deduced. After assuming the specimen fatigue strengths as Gaussian (normal) distributions, the critical distance turns out to be well represented by a Skew-normal distribution. This statistical assessment is extended to the finite fatigue life, in the present paper, showing experimental results for the aluminium alloy 7075-T6 at two load ratios. The fatigue strength of other specimens are finally evaluated, reconsidering the critical distance deviation, thus providing a complete uncertainty analysis of the critical distance assessment, and a successful comparison with the experimental scatter is obtained

Statistical significance of notch fatigue prognoses based on the strain-energy-density method: Application to conventionally and additively manufactured materials

The inverse search determination of the strain-energy–density (SED) control radius R1 devised in Benedetti et al. Int J Fatigue 2019;126:306–318 and based on the knowledge of the notch fatigue factor estimated using an optimal V-notch specimen geometry is here reformulated to take into account the statistical properties of the input fatigue properties. It was found that R1 exhibits a non-symmetric probability density function that is well represented by a skew-normal distribution. The uncertainty in R1 can be attributed to the uncertainty in the inverse search procedure and to the material variability in notch sensitivity. By applying the devised procedure to real experimental data, it was found that the former contribution is preponderant in the assessment of very sharp notches, while the latter dictates the fatigue strength of blunt notches, especially in the case of intrinsically flawed materials, such as those additively manufactured

Combinatorial Hopf algebra of superclass functions of type DD

We provide a Hopf algebra structure on the space of superclass functions on the unipotent upper triangular group of type D over a finite field based on a supercharacter theory constructed by Andr\'e and Neto. Also, we make further comments with respect to types B and C. Type A was explores by M. Aguiar et. al (2010), thus this paper is a contribution to understand combinatorially the supercharacter theory of the other classical Lie types.Comment: Last section modified. Recent development added and correction with respect to previous version state

Atividade respiratória, produção de etileno e vida útil de repolho (Brassica oleracea, var. capitata) minimamente processado em atmosfera controlada.

Com o objetivo de avaliar a atividade respiratória e a produção de etileno do repolho inteiro e minimamente processado e a vida útil do repolho mimimamente processado em atmosfera controlada, realizaram-se dois experimentos em etapas seqüenciais. Na primeira etapa, avaliaram-se a atividade respiratória e a produção de etileno do repolho inteiro e minimamente processado, em sistema fechado, nas temperaturas de 5 ºC e 10 ºC. Na segunda etapa, avaliou-se a vida útil do repolho minimamente processado em atmosfera controlada. O produto foi submetido a fluxo contínuo de misturas gasosas ternárias, com concentrações de 2% a 10% de O2 e de 3% a 10% de CO2, previamente umidificadas, na temperatura de 5 ºC por 10 dias. Como controle, foi utilizado o ar atmosférico. A atividade respiratória do repolho inteiro e minimamente processado, armazenado a 5 ºC, foi significativamente menor que a do armazenado a 10 ºC, sendo que, em ambas as temperaturas, o repolho minimamente processado foi o que obteve a maior atividade respiratória com relação ao repolho inteiro. Não foi detectada a produção de etileno pelo método de análise utilizado. A atmosfera controlada não prolongou a vida útil do repolho minimamente processado nas concentrações de 2% a 10% de oxigênio e de 3% a 10% de dióxido de carbono

Inverse determination of the fatigue Strain Energy Density control radius for conventionally and additively manufactured rounded V-notches

The Strain Energy Density (SED) fatigue criterion is based on a material control radius. The value of this length is therefore required for an accurate assessment of the fatigue strength of any, especially severely, notched components. The singularity-based control radius is initially obtained by considering the hypothetical perfectly sharp V-notched specimen. The effect of the notch radius on the inverse search is then investigated with numerical simulations, and a new analytical procedure is introduced for the determination of the (actual) control radius. This procedure is applied to the experimental data of three metal alloys with different load ratios and manufacturing conditions

optimal notched specimen parameters for accurate fatigue critical distance determination

Abstract The critical distance value should theoretically be determined from the plain specimen fatigue limit and the threshold stress intensity factor, though usually ordinary notch geometries are considered. In this paper, we proposed an optimized sharp notch with the aims of simple and reliable manufacture and, more importantly, a local strong stress gradient able to minimize the sensitivity on the deduced critical distance value. A numerical procedure is proposed to find the critical distance from the fatigue strength of the notched specimen, by implementing the line method with simple formulas based on dimensionless equations and specific coefficients derived from accurate FE analyses. A definition of the boundaries for a valid critical distance evaluation is also introduced and discussed. Finally, an application example is provided on a quenched and tempered steel also comparing the obtained critical distances with the threshold derived values

sensibility analysis of the fatigue critical distance values assessed by combining plain and notched cylindrical specimens

Abstract The material critical distance is often deduced from plain and notched specimens, instead of experimentally measuring the (long) crack threshold, which is a challenging task and not adequate in some cases. A dedicated V-notched specimen was proposed along with a dimensionless numerical procedure to derive the critical distance from the fatigue stress concentration factor, by implementing both the line and the point methods. An experimental validation activity is provided here on 42CrMo4+QT steel, focusing on how the critical distance result is sensitive to the actual local radius, the specimen sharpness, and the choice between the line or the point method. The determination of the critical distance with the point method systematically provides higher values than the line method. However, these length discrepancies do not produce large effects in terms of the component strength assessment if the same method for the fatigue limit evaluation is used. By alternatively considering the specimen not involved in the critical distance determination, as a potential design component, the prediction accuracy was evaluated. This analysis confirmed that a small notch radius is recommended for the fatigue strength assessment of larger radius notches or even of a crack, whereas by deducing the critical distance from a blunt notch, a noticeable inaccuracy can be found on smaller radius and crack threshold

Determination of the fatigue critical distance according to the Line and the Point Methods with rounded V-notched specimen

The critical distance length should in principle be deduced from the plain specimen fatigue limit and the threshold stress intensity factor range. However, the threshold range is difficult to measure experimentally, hence this length is usually obtained by means of a notched specimen. The critical distance inverse search, both according to the Line and the Point Methods, is presented in this paper referring to a relatively sharp V-notched specimen. Precise indications about the geometry parameters are given along with a complete analytical procedure to easily obtain the critical distance. A sensitivity analysis is discussed, providing evidence of a critical distance range for a well-posed inversion problem