29,462 research outputs found

    Probing Hadronic Structure with The Decay ΔNl+l\Delta\rightarrow Nl^+l^-

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    We compute the branching ratio for ΔNe+e\Delta\rightarrow Ne^+e^- and ΔNμ+μ\Delta\rightarrow N\mu^+\mu^- in chiral perturbation theory and find that both decays should be observable at CEBAF. With sufficiently low thresholds on the e+ee^+e^- invariant mass a branching ratio of 105\sim 10^{-5} may be observed for ΔNe+e\Delta\rightarrow Ne^+e^-. For the ΔNμ+μ\Delta\rightarrow N\mu^+\mu^- decay mode we predict a branching ratio of 3×1073\times 10^{-7}. The dependence of the M1 and E2 amplitudes on the momentum transfer will provide a useful test of chiral perturbation theory which predicts 20%\sim 20\% variation over the allowed kinematic range.Comment: 6 pages, 3 figures, UCSD/PTH 93-06, QUSTH-93-02, Duke-TH-93-4

    Microscopes and computers combined for analysis of chromosomes

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    Scanning machine CHLOE, developed for photographic use, is combined with a digital computer to obtain quantitative and statistically significant data on chromosome shapes, distribution, density, and pairing. CHLOE permits data acquisition about a chromosome complement to be obtained two times faster than by manual pairing

    The relational ethics of conflict and identity

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    The contemporary psychoanalytically inflected vocabulary of relational ethics centres on acknowledgement, witnessing and responsibility. It has become an important code for efforts to connect with otherness across fractures of hurt, oppression and suffering. One can see the deployment of this vocabulary to challenge patterns of exclusion and dehumanisation in zones of intense political conflict in many situations in which destructive hatred reigns. This paper traces some of the use of and disputes over this ‘acknowledgement-based’ relational ethics in the recent work of Jessica Benjamin and Judith Butler. The field of application is their response to Israel’s treatment of the Palestinians, given their position as Jews. The challenge of the acknowledgement agenda leads back to an issue of general concern – the degree to which relational ethics can prise open apparently closed and defensive psychosocial identities

    Comment on "Valence QCD: Connecting QCD to the Quark Model"

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    I criticize certain conclusions about the physics of hadrons drawn from a "valence QCD" approximation to QCD.Comment: 12 pages, 8 figures; some minor improvements made to the tex

    Features in the ion emission of Cu, Al, and C plasmas produced by ultrafast laser ablation

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    © 2015 AIP Publishing LLC. The bi-modal nature of charge integrated ion kinetic energy distributions, which result from ultrafast laser produced plasmas, is discussed in this paper. A negatively biased Faraday cup was used as a charge collector to measure ion distributions from three different solid targets that had been irradiated with an ultrafast laser in the fluence range 0.1-1 J/cm2. A bi-modal time of flight distribution is found for all three targets (C, Al, and Cu). In the case of the metallic targets (Al and Cu), high- and low-kinetic energy peaks exhibit quite different dependencies on laser fluence, whereas for the semi-metallic target (C), both peaks scale similarly with ultrafast laser fluence. The results are discussed within the framework of a one dimensional capacitor model resulting in ion acceleration

    Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation

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    We study the decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation. Our approach for unquenching the theory is based on the heavy baryon perturbation theory in which the axial couplings for baryon - meson and the meson-meson-photon couplings from the chiral perturbation theory are used together with the QM moment couplings. It also involves the introduction of a form factor characterizing the structure of baryons considered as composite particles. Using the parameters obtained from fitting the octet baryon magnetic moments, we predict the decuplet baryon magnetic moments. The Ω\Omega^- magnetic moment is found to be in good agreement with experiment: μΩ\mu_{\Omega^-} is predicted to be 1.97μN-1.97 \mu_N compared to the experimental result of (-2.02 ±\pm 0.05) μN\mu_N.Comment: 19 pages, 2 figure

    A site-specific standard for comparing dynamic solar ultraviolet protection characteristics of established tree canopies

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    A standardised procedure for making fair and comparable assessments of the ultraviolet protection of an established tree canopy that takes into account canopy movement and the changing position of the sun is presented for use by government, planning, and environmental health authorities. The technique utilises video image capture and replaces the need for measurement by ultraviolet radiometers for surveying shade quality characteristics of trees growing in public parks, playgrounds and urban settings. The technique improves upon tree shade assessments that may be based upon single measurements of the ultraviolet irradiance observed from a fixed point of view. The presented technique demonstrates how intelligent shade audits can be conducted without the need for specialist equipment, enabling the calculation of the Shade Protection Index (SPI) and Ultraviolet Protection Factor (UPF) for any discreet time interval and over a full calendar year

    Robust ecological pattern formation induced by demographic noise

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    We demonstrate that demographic noise can induce persistent spatial pattern formation and temporal oscillations in the Levin-Segel predator-prey model for plankton-herbivore population dynamics. Although the model exhibits a Turing instability in mean field theory, demographic noise greatly enlarges the region of parameter space where pattern formation occurs. To distinguish between patterns generated by fluctuations and those present at the mean field level in real ecosystems, we calculate the power spectrum in the noise-driven case and predict the presence of fat tails not present in the mean field case. These results may account for the prevalence of large-scale ecological patterns, beyond that expected from traditional non-stochastic approaches.Comment: Revised version. Supporting simulation at: http://guava.physics.uiuc.edu/~tom/Netlogo
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