αs\alpha_s from τ\tau decays: contour-improved versus fixed-order summation in a new QCD perturbation expansion

We consider the determination of $\alpha_s$ from $\tau$ hadronic decays, by investigating the contour-improved (CI) and the fixed-order (FO) renormalization group summations in the frame of a new perturbation expansion of QCD, which incorporates in a systematic way the available information about the divergent character of the series. The new expansion functions, which replace the powers of the coupling, are defined by the analytic continuation in the Borel complex plane, achieved through an optimal conformal mapping. Using a physical model recently discussed by Beneke and Jamin, we show that the new CIPT approaches the true results with great precision when the perturbative order is increased, while the new FOPT gives a less accurate description in the regions where the imaginary logarithms present in the expansion of the running coupling are large. With the new expansions, the discrepancy of 0.024 in $\alpha_s(m_\tau^2)$ between the standard CI and FO summations is reduced to only 0.009. From the new CIPT we predict $\alpha_s(m_\tau^2)= 0.320 ^{+0.011}_{-0.009}$, which practically coincides with the result of the standard FOPT, but has a more solid theoretical basis

Modeling power corrections to the Bjorken sum rule for the neutrino structure function F_1

Direct measurements of the the structure functions F_1^{nu p} and F_1^{nu n} at a neutrino factory would allow for an accurate extraction of alpha_s from the Q^2-dependence of the Bjorken sum rule, complementing that based on the Gross-Llewellyn-Smith sum rule for F_3. We estimate the power (1/Q^2-) corrections to the Bjorken sum rule in the instanton vacuum model. For the reduced matrix element of the flavor-nonsinglet twist-4 operator ubar_g_Gdual_gamma_gamma5_u - (u -> d) we obtain a value of 0.18 GeV^2, in good agreement with the QCD sum rule calculations of Braun and Kolesnichenko. Our result allows to reduce the theoretical error in the determination of alpha_s.Comment: 3 pages, 1 figure, uses iopart.cls. Proceedings of the 4th NuFact'02 Workshop "Neutrino Factories based on Muon Storage Rings", Imperial College, London, July 1-6, 200

Four-loop beta function and mass anomalous dimension in Dimensional Reduction

Within the framework of QCD we compute renormalization constants for the strong coupling and the quark masses to four-loop order. We apply the DR-bar scheme and put special emphasis on the additional couplings which have to be taken into account. This concerns the epsilon-scalar--quark Yukawa coupling as well as the vertex containing four epsilon-scalars. For a supersymmetric Yang Mills theory, we find, in contrast to a previous claim, that the evanescent Yukawa coupling equals the strong coupling constant through three loops as required by supersymmetry.Comment: 15 pages, fixed typo in Eq. (18

КОМП’ЮТЕРНЕ МОДЕЛЮВАННЯ ВІБРАЦІЙ ВІДЦЕНТРОВОГО ПОЖЕЖНОГО НАСОСА

The paper deals with computer FE modelling of forced harmonic vibrations of centrifugal fire pumps PN-40UV. A 3D FE model of the pump is developed and a theoretical study of its vibration characteristics determination is carried out. Natural frequencies and coupled models are identified. Frecuency response functions (FRF) showing resonant vibration zones are calculated. A spatial mode of vibrations at the rated speed of the rotor is built. The biggest vibrations amplitude are observed at the upstream end.Робота присвячена комп’ютерному моделюванню вимушених гармонічних коливань відцентрових пожежних насосів ПН-40УВ. В роботі розроблено тривимірну модель скінчених елементів (СЕ) насоса, проведено теоретичні дослідження визначення його вібраційних характеристик. Визначені власні частоти та форми коливань. Розраховані амплітудно-частотні характеристики (АЧХ), які показують резонансні зони вібрацій. Побудовано просторову форму вібрацій на номінальній частоті обертання ротора. Визначено, що найбільші амплітуди вібрацій спостерігаються на вхідному патрубку насоса

Cultivating Resilience in Adolescence: How Educational Environments Can Support Positive Youth Development During Identity Exploration

Adolescence is a critical stage of human development, one that can be especially challenging for teens that are navigating certain vulnerabilities in their identity formation. With the World Health Organization stating that 14% of 10–19 year-olds experience mental health conditions, educational environments are increasingly needed to address mental concerns in their curriculums. This qualitative research project used a combination of art based inquiry and narrative analysis to answer the following question, “How can educational environments promote resilience and positive youth development during adolescent identity exploration?” Findings illuminated several emergent themes that culminated in the following four recommendations for educational environments; 1) Integrate opportunities for creative self-expression in general education spaces, 2) Professional development for educators to integrate Social Emotional Learning (SEL), 3) Create opportunities for social interactions between students and educators, 4) Create and support opportunities for social interactions between students, and 5) Ensure educational spaces include mental health support for students

Observation of a narrow baryon resonance with positive strangeness formed in K+K^+Xe collisions

The charge-exchange reaction K^+ Xe --> K^0 p Xe' is investigated using the data of the DIANA experiment. The distribution of the pK^0 effective mass shows a prominent enhancement near 1538 MeV formed by \sim 80 events above the background, whose width is consistent with being entirely due to the experimental resolution. Under the selections based on a simulation of K^+Xe collisions, the statistical significance of the signal reaches 5.5\sigma. We interpret this observation as strong evidence for formation of a pentaquark baryon with positive strangeness, \Theta^+(uudd\bar{s}), in the charge-exchange reaction K^+ n --> K^0 p on a bound neutron. The mass of the \Theta^+ baryon is measured as m(\Theta^+) = 1538+-2 MeV. Using the ratio between the numbers of resonant and non-resonant charge-exchange events in the peak region, the intrinsic width of this baryon resonance is determined as \Gamma(\Theta^+) = 0.34+-0.10 MeV.Comment: 19 pages, 8 figure

Spin-dependent twist-4 matrix elements from the instanton vacuum: Flavor-singlet and nonsinglet

We estimate the twist-4 spin-1 nucleon matrix element f_2 in an instanton-based description of the QCD vacuum. In addition to the flavor-nonsinglet we compute also the flavor-singlet matrix element, which appears in next-to-leading order of the (1/N_c)-expansion. The corresponding twist-3 spin-2 matrix elements d_2 are suppressed in the packing fraction of the instanton medium, (\bar \rho)/(\bar R) << 1. We use our results to estimate the leading (1/Q^2) power corrections to the first moment of the proton and neutron spin structure functions G_1, as well as the intrinsic charm contribution to the nucleon spin.Comment: 17 pages, 4 eps figures include