Ultrasonic attenuation as an indicator of fatigue life of graphite/epoxy fiber composite

The narrow band ultrasonic longitudinal wave velocity and attenuation were measured as a function of the transfiber compression-compression fatigue of unidirectional graphite/epoxy composites. No change in velocity was detected at any point in fatigue life. For specimens fatigued at 80% of static strength, there was generally a 5% to 10% increase in attenuation, however, this increase does not appear to be a satisfactory indicator of fatigue life. On the other hand, there appears to be a correlation between initial attenuation (measured prior to cycling) and cycles to fracture. Initial attenuation as measured at 1.5 MHz and 2.0 MHz appears to be a good indicator of relative fatigue life

Quantum Annealing: A New Method for Minimizing Multidimensional Functions

Quantum annealing is a new method for finding extrema of multidimensional functions. Based on an extension of classical, simulated annealing, this approach appears robust with respect to avoiding local minima. Further, unlike some of its predecessors, it does not require an approximation to a wavefunction. In this paper, we apply the technique to the problem of finding the lowest energy configurations of Lennard-Jones clusters of up to 19 particles (roughly 10$^5$ local minima). This early success suggests that this method may complement the widely implemented technique of simulated annealing

Measurements of the τ mass and the mass difference of the τ^+ and τ^- at BABAR

We present the result from a precision measurement of the mass of the τ lepton, M_τ, based on 423  fb^(-1) of data recorded at the Υ(4S) resonance with the BABAR detector. Using a pseudomass endpoint method, we determine the mass to be 1776.68±0.12(stat)±0.41(syst)  MeV. We also measure the mass difference between the τ^+ and τ^-, and obtain (M_(τ+)-M_(τ-))/M_(AVG)^τ=(-3.4±1.3(stat)±0.3(syst))×10^(-4), where M^τ_(AVG) is the average value of M_(τ+) and M_(τ-)

Search for B^+→ℓ^+ν_ℓ recoiling against B^-→D^0ℓ^-ν̅ X

We present a search for the decay B^+→ℓ^+ν_ℓ(ℓ=τ, μ, or  e) in (458.9±5.1)×10^6 BB̅ pairs recorded with the BABAR detector at the PEP-II B-factory. We search for these B decays in a sample of B^+B^- events where one B-meson is reconstructed as B^-→D^0ℓ^-ν̅ X. Using the method of Feldman and Cousins, we obtain B(B^+→τ^+ν_τ)=(1.7±0.8±0.2)×10^(-4), which excludes zero at 2.3σ. We interpret the central value in the context of the standard model and find the B meson decay constant to be f_B^2=(62±31)×10^3   MeV^2. We find no evidence for B^+→e^+ν_e and B^+→μ^+ν_μ and set upper limits at the 90% C.L. B(B^+→e^+ν_e)<0.8×10^(-5) and B(B^+→μ^+ν_μ)<1.1×10^(-5)

Measurements of the semileptonic decays B[overbar]→Dℓν[overbar] and B[overbar]→D^*ℓν[overbar] using a global fit to DXℓν[overbar] final states

Semileptonic B[overbar] decays to DXℓν[overbar](ℓ=e or μ) are selected by reconstructing D^0ℓ and D^+ℓ combinations from a sample of 230×10^6 Υ(4S)→BB[overbar] decays recorded with the BABAR detector at the PEP-II e^+e^- collider at SLAC. A global fit to these samples in a three-dimensional space of kinematic variables is used to determine the branching fractions B(B^-→D^0ℓν[overbar])=(2.34±0.03±0.13)% and B(B^-→D^(*0)ℓν[overbar])=(5.40±0.02±0.21)% where the errors are statistical and systematic, respectively. The fit also determines form-factor parameters in a parametrization based on heavy quark effective theory, resulting in ρ_D^2=1.20±0.04±0.07 for B[overbar]→Dℓν[overbar] and ρ_(D*)^2=1.22±0.02±0.07 for B[overbar]→D^*ℓν[overbar]. These values are used to obtain the product of the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)| times the form factor at the zero recoil point for both B[overbar]→Dℓν[overbar] decays, G(1)|V_(cb)|=(43.1±0.8±2.3)×10^(-3), and for B[overbar]→D^*ℓν[overbar] decays, F(1)|V_(cb)|=(35.9±0.2±1.2)×10^(-3)

Ground-state properties of rutile: electron-correlation effects

Electron-correlation effects on cohesive energy, lattice constant and bulk compressibility of rutile are calculated using an ab-initio scheme. A competition between the two groups of partially covalent Ti-O bonds is the reason that the correlation energy does not change linearly with deviations from the equilibrium geometry, but is dominated by quadratic terms instead. As a consequence, the Hartree-Fock lattice constants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.Comment: 1 figure to appear in Phys. Rev.

Observation of the χ_(c2)(2P) meson in the reaction γγ→DD at BABAR

A search for the Z(3930) resonance in γγ production of the DD system has been performed using a data sample corresponding to an integrated luminosity of 384  fb^(-1) recorded by the BABAR experiment at the PEP-II asymmetric-energy electron-positron collider. The DD invariant mass distribution shows clear evidence of the Z(3930) state with a significance of 5.8σ. We determine mass and width values of (3926.7±2.7±1.1)  MeV/c^2 and (21.3±6.8±3.6)  MeV, respectively. A decay angular analysis provides evidence that the Z(3930) is a tensor state with positive parity and C parity (J^(PC)=2^(++)); therefore we identify the Z(3930) state as the χ_(c2)(2P) meson. The value of the partial width Γ_(γγ)×B(Z(3930)→DD) is found to be (0.24±0.05±0.04)  keV

Moments of spectral functions: Monte Carlo evaluation and verification

The subject of the present study is the Monte Carlo path-integral evaluation of the moments of spectral functions. Such moments can be computed by formal differentiation of certain estimating functionals that are infinitely-differentiable against time whenever the potential function is arbitrarily smooth. Here, I demonstrate that the numerical differentiation of the estimating functionals can be more successfully implemented by means of pseudospectral methods (e.g., exact differentiation of a Chebyshev polynomial interpolant), which utilize information from the entire interval $(-\beta \hbar / 2, \beta \hbar/2)$. The algorithmic detail that leads to robust numerical approximations is the fact that the path integral action and not the actual estimating functional are interpolated. Although the resulting approximation to the estimating functional is non-linear, the derivatives can be computed from it in a fast and stable way by contour integration in the complex plane, with the help of the Cauchy integral formula (e.g., by Lyness' method). An interesting aspect of the present development is that Hamburger's conditions for a finite sequence of numbers to be a moment sequence provide the necessary and sufficient criteria for the computed data to be compatible with the existence of an inversion algorithm. Finally, the issue of appearance of the sign problem in the computation of moments, albeit in a milder form than for other quantities, is addressed.Comment: 13 pages, 2 figure

Study of B → πlν and B → ρlν decays and determination of |V_(ub)|

We present an analysis of exclusive charmless semileptonic B-meson decays based on 377 × 10^6 BB̅ pairs recorded with the BABAR detector at the Υ(4S) resonance. We select four event samples corresponding to the decay modes B^0 → π^-ℓ^+ν, B^+ → π^0ℓ^+ν, B^0 → ρ^-ℓ^+ν, and B^+ → ρ^0ℓ^+ν and find the measured branching fractions to be consistent with isospin symmetry. Assuming isospin symmetry, we combine the two B → πℓν samples, and similarly the two B → ρℓν samples, and measure the branching fractions B(B^0→π^-ℓ^+ν)=(1.41 ± 0.05 ± 0.07) × 10^(-4) and B(B^0 → ρ^-ℓ^+ν)=(1.75 ± 0.15 ± 0.27) × 10^(-4), where the errors are statistical and systematic. We compare the measured distribution in q^2, the momentum transfer squared, with predictions for the form factors from QCD calculations and determine the Cabibbo-Kobayashi-Maskawa matrix element |V_(ub)|. Based on the measured partial branching fraction for B → πℓν in the range q^2 < 12  GeV^2 and the most recent QCD light-cone sum-rule calculations, we obtain |V_(ub)|=(3.78 ± 0.13^(+0.55)_(-0.40)) × 10^(-3), where the errors refer to the experimental and theoretical uncertainties. From a simultaneous fit to the data over the full q^2 range and the FNAL/MILC lattice QCD results, we obtain |V_(ub)|=(2.95 ± 0.31) × 10^(-3) from B → πℓν, where the error is the combined experimental and theoretical uncertainty