Bondi-Sachs metrics and Photon Rockets

We study the Bondi-Sachs rockets with nonzero cosmological constant. We observe that the acceleration of the systems arises naturally in the asymptotic symmetries of (anti-) de Sitter spacetimes. Assuming the validity of the concepts of energy and mass previously introduced in asymptotically flat spacetimes, we find that the emission of pure radiation energy balances the loss of the Bondi mass in certain special families of the Bondi-Sachs rockets, so in these there is no gravitational radiation.Comment: 12 pages, to appear in General Relativity and Gravitatio

Fatigue Damage Analysis of an Asphalt Mixture Based on Pseudostiffness

The fatigue damage characteristics of an asphalt mixture were analyzed, a new fatigue damage model was constructed based on the Schapery pseudovariable theory and continuum damage mechanics. According to the Schapery theory and the generalized elastic-viscoelastic correspondence principle, the experimental stress–strain curves of the asphalt mixture are transformed into the stress vs. pseudostrain curves. The relation between stress and pseudostrain is shown to be linear, which eliminates the viscoelastic hysteresis effect of the asphalt mixture and its time dependence.Выполнен анализ характеристик усталостного повреждения битумной смеси. Построена новая модель усталостного повреждения на основании псевдопараметрической теории Шапери и механики повреждения сплошных сред. В соответствии с теорией Шапери и обобщенным принципом соответствия между упругими и вязкоупругими деформациями экспериментальные кривые напряжение–деформация для битумной смеси преобразуются в кривые напряжение–псевдодеформация. Показано, что последняя линейна, что устраняет вязкоупругий эффект гистерезиса битумной смеси и его временную зависимость

Creep Lifetime Assessment of Pressure-Tight PE100 Pipes Based on a Slow Fatigue Crack Growth

Polyethylene pipes are widely used in water supply, gas, and sewage systems due to their excellent mechanical properties. A slow crack growth is the primary fracture mechanism for the pipes under long-term internal pressures. If the creep loading is treated as a special case of fatigue loading, the slow crack growth kinetics of polyethylene is defined in fatigue fracture tests at different stress ratios and extrapolated to creep crack kinetics. Linear elastic fracture mechanics concepts became the basis for predicting the creep lifetime of pressure-tight pipes subjected to various hoop stresses from extrapolated (synthetic) creep crack growth curves, and the prediction is in good agreement with the standard extrapolation, in accordance with ISO 9080.Полиэтиленовые трубы широко применяются в водоснабжении, системах газоснабжения и канализации благодаря их высоким механическим свойствам. Медленный рост трещин является основным механизмом разрушения полиэтиленовых труб под длительным внутренним давлением. Рассматривая нагружение при ползучести как особый случай усталостного нагружения, кинетика медленного роста трещин в полиэтиленовом материале определяется путем испытаний на усталостное разрушение при различных коэффициентах асимметрии цикла напряжений и экстраполируется на кинетику трещин ползучести. Исходя из теории линейноупругой механики разрушения долговечность при ползучести полиэтиленовой трубы под давлением, подверженной действию различных окружных напряжений, прогнозируется на основе синтетической кривой роста трещин ползучести, и прогнозы хорошо согласуются со стандартной экстрополяцией в соответствии с ISO 9080

A Measurement of Psi(2S) Resonance Parameters

Cross sections for e+e- to hadons, pi+pi- J/Psi, and mu+mu- have been measured in the vicinity of the Psi(2S) resonance using the BESII detector operated at the BEPC. The Psi(2S) total width; partial widths to hadrons, pi+pi- J/Psi, muons; and corresponding branching fractions have been determined to be Gamma(total)= (264+-27) keV; Gamma(hadron)= (258+-26) keV, Gamma(mu)= (2.44+-0.21) keV, and Gamma(pi+pi- J/Psi)= (85+-8.7) keV; and Br(hadron)= (97.79+-0.15)%, Br(pi+pi- J/Psi)= (32+-1.4)%, Br(mu)= (0.93+-0.08)%, respectively.Comment: 8 pages, 6 figure

Measurements of the Mass and Full-Width of the ηc\eta_c Meson

In a sample of 58 million $J/\psi$ events collected with the BES II detector, the process J/$\psi\to\gamma\eta_c$ is observed in five different decay channels: $\gamma K^+K^-\pi^+\pi^-$, $\gamma\pi^+\pi^-\pi^+\pi^-$, $\gamma K^\pm K^0_S \pi^\mp$ (with $K^0_S\to\pi^+\pi^-$), $\gamma \phi\phi$ (with $\phi\to K^+K^-$) and $\gamma p\bar{p}$. From a combined fit of all five channels, we determine the mass and full-width of $\eta_c$ to be $m_{\eta_c}=2977.5\pm1.0 ({stat.})\pm1.2 ({syst.})$ MeV/$c^2$ and $\Gamma_{\eta_c} = 17.0\pm3.7 ({stat.})\pm7.4 ({syst.})$ MeV/$c^2$.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.

Measurement of Branching Ratios for ηc\eta_c Hadronic Decays

In a sample of 58 million $J/\psi$ events collected with the BES II detector, the process J/$\psi\to\gamma\eta_c$ is observed in five decay channels: $\eta_c \to K^+K^-\pi^+\pi^-$, $\pi^+\pi^-\pi^+\pi^-$, $K^\pm K^0_S \pi^\mp$ (with $K^0_S\to\pi^+\pi^-$), $\phi\phi$ (with $\phi\to K^+K^-$) and $p\bar{p}$. From these signals, we determine $Br(J/\psi\to\gamma\eta_c)\times Br(\eta_c\to K^+K^-\pi^+\pi^-)$ $=(1.5\pm0.2\pm0.2)\times10^{-4}$, $Br(J/\psi\to\gamma\eta_c)\times Br(\eta_c\to \pi^+\pi^-\pi^+\pi^-)$ $=(1.3\pm0.2\pm0.4)\times10^{-4}$, $Br(J/\psi\to\gamma\eta_c)\times Br(\eta_c\to K^\pm K_{S}^{0}\pi^\mp)$ $=(2.2\pm0.3\pm0.5)\times10^{-4}$, $Br(J/\psi\to\gamma\eta_c)\times Br(\eta_c\to \phi\phi)$ $=(3.3\pm0.6\pm0.6)\times10^{-5}$ and $Br(J/\psi\to\gamma\eta_c)\times Br(\eta_c\to p\bar{p})$ $=(1.9\pm0.3\pm0.3)\times10^{-5}$.Comment: 8 pages, 1 figures and 4 table. Submitted to Phys. Lett.

Measurements of J/psi --> p \bar{p}

The process J/\psi --> p \bar{p} is studied using 57.7 X 10^6 J/\psi events collected with the BESII detector at the Beijing Electron Positron Collider. The branching ratio is determined to be Br(J/\psi --> p \bar{p})=(2.26 +- 0.01 +- 0.14) X 10^{-3}, and the angular distribution is well described by \frac{dN}{d cos\theta_p}=1+\alpha\cos^2\theta_p with \alpha = 0.676 +- 0.036 +- 0.042, where \theta_p is the angle between the proton and beam directions. The value of \alpha obtained is in good agreement with the predictions of first-order QCD.Comment: 6 pages, 2 figures, RevTex4, Submitted to Phys.Lett.

Search for K_S K_S in J/psi and psi(2S) decays

The CP violating processes J/psi-->K_S K_S and psi(2S)-->K_S K_S are searched for using samples of 58 million J/psi and 14 million psi(2S) events collected with the Beijing Spectrometer at the Beijing Electron Positron Collider. No signal is observed, and upper limits on the decay branching ratios are determined to be BR(J/psi-->K_S K_S) K_S K_S) < 4.6x10^{-6} at the 95% confidence level.Comment: 6 pages, 4 figures, submitted to Phys. Lett.

A Study of J/psi-->gamma gamma V(rho,phi) Decays with the BESII Detector

Using a sample of $58\times 10^6$ $J/\psi$ events collected with the BESII detector, radiative decays $J/\psi\to\gamma\gamma V$, where $V=\rho$ or $\phi$, are studied. A resonance around 1420 MeV/c$^2$ (X(1424)) is observed in the $\gamma\rho$ mass spectrum. Its mass and width are measured to be $1424\pm 10(stat)\pm 11(sys)$ MeV/c$^2$ and $101.0\pm 8.8 \pm 8.8$ MeV/c$^2$, respectively, and its branching ratio $B(J/\psi\to \gamma X(1424)\to \gamma \gamma \rho)$ is determined to be $(1.07\pm0.17 \pm 0.11)\times 10^{-4}$. A search for $X(1424)\to \gamma\phi$ yields a 95% C.L. upper limit $B(J/\psi\to \gamma X(1424)\to \gamma\gamma \phi) < 0.82 \times 10^{-4}$.Comment: 10 pages, 5 figures, submitted to PL