There are no abnormal solutions of the Bethe−-Salpeter equation in the static model

The four-point Green's function of static QED, where a fermion and an antifermion are located at fixed space positions, is calculated in covariant gauges. The bound state spectrum does not display any abnormal state corresponding to excitations of the relative time. The equation that was established by Mugibayashi in this model and which has abnormal solutions does not coincide with the Bethe$-$Salpeter equation. Gauge transformation from the Coulomb gauge also confirms the absence of abnormal solutions in the Bethe$-$Salpeter equation.Comment: 11 pages, late

Isospin breaking corrections to low-energy pi-K scattering

We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and next-to-leading order. As a direct application the releveant combination of the S-wave scattering lengths involved in the pion-kaon atom lifetime is determined. We discuss the sensitivity of the results with respect to the input parameters.Comment: 33 pages, plain latex, 2 figure

Relativistic Calculation of the Meson Spectrum: a Fully Covariant Treatment Versus Standard Treatments

A large number of treatments of the meson spectrum have been tried that consider mesons as quark - anti quark bound states. Recently, we used relativistic quantum "constraint" mechanics to introduce a fully covariant treatment defined by two coupled Dirac equations. For field-theoretic interactions, this procedure functions as a "quantum mechanical transform of Bethe-Salpeter equation". Here, we test its spectral fits against those provided by an assortment of models: Wisconsin model, Iowa State model, Brayshaw model, and the popular semi-relativistic treatment of Godfrey and Isgur. We find that the fit provided by the two-body Dirac model for the entire meson spectrum competes with the best fits to partial spectra provided by the others and does so with the smallest number of interaction functions without additional cutoff parameters necessary to make other approaches numerically tractable. We discuss the distinguishing features of our model that may account for the relative overall success of its fits. Note especially that in our approach for QCD, the resulting pion mass and associated Goldstone behavior depend sensitively on the preservation of relativistic couplings that are crucial for its success when solved nonperturbatively for the analogous two-body bound-states of QED.Comment: 75 pages, 6 figures, revised content

Public opinion on energy crops in the landscape: considerations for the expansion of renewable energy from biomass

Public attitudes were assessed towards two dedicated biomass crops – Miscanthus and Short Rotation Coppice (SRC), particularly regarding their visual impacts in the landscape. Results are based on responses to photographic and computer-generated images as the crops are still relatively scarce in the landscape. A questionnaire survey indicated little public concern about potential landscape aesthetics but more concern about attendant built infrastructure. Focus group meetings and interviews indicated support for biomass end uses that bring direct benefits to local communities. Questions arise as to how well the imagery used was able to portray the true nature of these tall, dense, perennial plants but based on the responses obtained and given the caveat that there was limited personal experience of the crops, it appears unlikely that wide-scale planting of biomass crops will give rise to substantial public concern in relation to their visual impact in the landscape

First measurement of the π+π−\pi^+\pi^- atom lifetime

The goal of the DIRAC experiment at CERN (PS212) is to measure the $\pi^+\pi^-$ atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the $S$-wave $\pi\pi$ scattering lengths combination $|a_0-a_2|$. Based on part of the collected data we present a first result on the lifetime, $\tau=[2.91 ^{+0.49}_{-0.62}]\times 10^{-15}$ s, and discuss the major systematic errors. This lifetime corresponds to $|a_0-a_2|=0.264 ^{+0.033}_{-0.020} m_{\pi}^{-1}$.Comment: 18 pages, 6 figure

Detection of π+π−\pi^+\pi^-atoms with the DIRAC spectrometer at CERN

The goal of the DIRAC experiment at CERN is to measure with high precision the lifetime of the $\pi^+\pi^-$ atom ($A_{2\pi}$), which is of order $3\times10^{-15}$ s, and thus to determine the s-wave $\pi\pi$-scattering lengths difference $|a_{0}-a_{2}|$. $A_{2\pi}$ atoms are detected through the characteristic features of $\pi^+\pi^-$ pairs from the atom break-up (ionization) in the target. We report on a first high statistics atomic data sample obtained from p Ni interactions at 24 GeV/$c$ proton momentum and present the methods to separate the signal from the background.Comment: 19 pages, 12 figures, 1 tabl

In Vivo Methods to Study Uptake of Nanoparticles into the Brain

Several in vivo techniques have been developed to study and measure the uptake of CNS compounds into the brain. With these techniques, various parameters can be determined after drug administration, including the blood-to-brain influx constant (Kin), the permeability-surface area (PS) product, and the brain uptake index (BUI). These techniques have been mostly used for drugs that are expected to enter the brain via transmembrane diffusion or by carrier-mediated transcytosis. Drugs that have limitations in entering the brain via such pathways have been encapsulated in nanoparticles (based on lipids or synthetic polymers) to enhance brain uptake. Nanoparticles are different from CNS compounds in size, composition and uptake mechanisms. This has led to different methods and approaches to study brain uptake in vivo. Here we discuss the techniques generally used to measure nanoparticle uptake in addition to the techniques used for CNS compounds. Techniques include visualization methods, behavioral tests, and quantitative methods

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

An Effective Localization Method for Robot Navigation Through Combined Encoders Positioning and Retiming Visual Control

The paper presents an optimal mobile robot localization method through encoders' measurements and absolute localization using webcam data. This technique has been developed and implemented for the motion of the robot from an initial position towards another desired position, taking into account Kinematic constraints. The proposed method is a cheap technique, which deals with the problem of robot initial position as the visual system provides the origin absolute coordinates related to the reference system. First, we have developed an interface, which ensures the real-time localization of the mini robot Khepera II while tracking a virtual moving target. Secondly, we have carried out experimentations of both the relative localization method, which determines the speed values of each driving wheel, and absolute localization using webcam data, which determines the robot start position. Next, a correction of the mobile robot position has been realized by retiming points using webcam measures. The obtained results are compared and discussed through different trajectories

Statistical analysis of Post-HEVC encoded videos

International audienceThe Post-HEVC is the emerging video coding standard beyond the High Efficiency Video Coding (HEVC) standard. It is more complex in transformation and prediction steps but it offers the opportunity of 3D and 360° videos coding and compression. This paper presents different statistical analyzes of Post-HEVC encoded videos especially analysis on 1D and 2D transformation types and analysis on intra and inter prediction types of some test videos for different classes and resolutions. Analyzes are carried out at the decoder level where the coding decision has already been taken by the encoder. Results show that the choice of transformation (type and size) and the prediction type (intra or inter) depends on the nature of video: motion and texture. This work can be considered as a milestone for proposing intelligent algorithms based on video characteristics to perform fast decision in the Post-HEVC encoding process. © 2017 IEEE