Weak decays of medium and heavy Lambda-hypernuclei

We have made a new evaluation of the Lambda decay width in nuclear matter within the Propagator Method. Through the Local Density Approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the N-N and Lambda-N short range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths in a wide range of mass numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure

The NASA/MSFC global reference atmospheric model: MOD 3 (with spherical harmonic wind model)

Improvements to the global reference atmospheric model are described. The basic model includes monthly mean values of pressure, density, temperature, and geostrophic winds, as well as quasi-biennial and small and large scale random perturbations. A spherical harmonic wind model for the 25 to 90 km height range is included. Below 25 km and above 90 km, the GRAM program uses the geostrophic wind equations and pressure data to compute the mean wind. In the altitudes where the geostrophic wind relations are used, an interpolation scheme is employed for estimating winds at low latitudes where the geostrophic wind relations being to mesh down. Several sample wind profiles are given, as computed by the spherical harmonic model. User and programmer manuals are presented

Glitches in Southern Pulsars

Timing observations of 40 mostly young pulsars using the ATNF Parkes radio telescope between 1990 January and 1998 December are reported. In total, 20 previously unreported glitches and ten other glitches were detected in 11 pulsars. These included 12 glitches in PSR J1341$-$6220, corresponding to a glitch rate of 1.5 glitches per year. We also detected the largest known glitch, in PSR J1614$-$5047, with $\Delta\nu_g/\nu \approx 6.5 \times 10^{-6}$ where $\nu = 1/P$ is the pulse frequency. Glitch parameters were determined both by extrapolating timing solutions to inter-glitch intervals and by phase-coherent timing fits across the glitch(es). Analysis of glitch parameters, both from this work and from previously published results, shows that most glitches have a fractional amplitude $\Delta\nu_g/\nu$ of between $10^{-8}$ and $10^{-6}$. There is no consistent relationship between glitch amplitude and the time since the previous glitch or the time to the following glitch, either for the ensemble or for individual pulsars. As previously recognised, the largest glitch activity is seen in pulsars with ages of order 10$^4$ years, but for about 30 per cent of such pulsars, no glitches were detected in the 8-year data span. There is some evidence for a new type of timing irregularity in which there is a significant increase in pulse frequency over a few days, accompanied by a decrease in the magnitude of the slowdown rate. Fits of an exponential recovery to post-glitch data show that for most older pulsars, only a small fraction of the glitch decays. In some younger pulsars, a large fraction of the glitch decays, but in others, there is very little decay.Comment: 19 pages, 20 figures. Accepted for publication in MNRA

The Use of Gamma-ray Bursts as Direction and Time Markers in SETI Strategies

When transmitting a signal over a large distance it is more efficient to send a brief beamed signal than a continuous omni-directional transmission but this requires that the receiver knows where and when to look for the transmission. For SETI, the use of various natural phenomena has previously been suggested to achieve the desired synchronization. Here it is proposed that gamma-ray bursts may well the best ``synchronizers'' of all currently known phenomena due to their large intrinsic luminosities, high occurrence rate, isotropic sky distribution, large distance from the Galaxy, short duration, and easy detectability. For targeted searches, precise positions for gamma-ray bursts are required together with precise distance measurements to a target star. The required burst position determinations are now starting to be obtained, aided in large part by the discovery of optical afterglows. Good distance measurements are currently available from Hipparcos and even better measurements should be provided by spacecraft now being developed. For non-targeted searches, positional accuracies simply better than a detector's field of view may suffice but the time delay between the detection of a gamma-ray burst and the reception of the transmitted signal cannot be predicted in an obvious way.Comment: 8 pages, accepted for publication in PAS

Emission of neutron-proton and proton-proton pairs in electron scattering induced by meson-exchange currents

We use a relativistic model of meson-exchange currents to compute the proton-neutron and proton-proton yields in $(e,e')$ scattering from $^{12}$C in the 2p-2h channel. We compute the response functions and cross section with the relativistic Fermi gas model for a range of kinematics from intermediate to high momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the $\Delta$ isobar current. We also analyze the effect of the exchange contribution and show that the direct/exchange interference strongly affects the determination of the np/pp ratio.Comment: 5 pages, 6 figure

Nuclear dependence of the 2p2h electroweak response in the Relativistic Fermi Gas model

We present the results of a recent study of meson-exchange two-body currents in lepton-nucleus inclusive scattering at various kinematics and for different nuclei within the Relativistic Fermi Gas model. We show that the associated nuclear response functions at their peaks scale as $A k_F^2$, for Fermi momentum $k_F$ going from 200 to 300 MeV/c and momentum transfer $q$ from $2k_F$ to 2 GeV/c. This behavior is different from what is found for the quasielastic response, which scales as $A/k_F$. This result can be valuable in the analyses of long-baseline neutrino oscillation experiments, which need to implement these nuclear effects in Monte Carlo simulations for different kinematics and nuclear targets.Comment: 11 pages, 6 figures, Proccedings of the Workshop "Advanced Aspects in Nuclear Structure and Reactions at Different Energy Scales", 25-28 April 2017, Arbanasi, Bulgari

Decay rates of medium-heavy Lambda-hypernuclei within the Propagator Method

The Lambda decay rates in nuclei has been calculated in ref. 1 using the Propagator Method in Local Density Approximation. We have studied the dependence of the widths (including the one for the two-body induced process Lambda NN -> NNN) on the N-N and Lambda-N short range correlations. Using a reasonable parametrization of these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths from medium to heavy hypernuclei.Comment: 8 pages, 1 figure. Talk given at the APCTP Workshop Strangeness Nuclear Physics, Seoul National University, Seoul, Korea, 19-22 February 199

E-nose Development for Safety Monitoring Applications in Refinery Environment

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Density dependence of 2p-2h meson-exchange currents

We analyze the density dependence of the contribution of meson-exchange currents to the lepton-nucleus inclusive cross section in the two-particle two-hole channel. The model is based on the Relativistic Fermi Gas, where each nucleus is characterized by its Fermi momentum $k_F$. We find that the 2p-2h nuclear response functions at their peaks scale as $A k_F^2$ for Fermi momentum going from 200 to 300 MeV/c and momentum transfer $q$ from $2k_F$ to 2 GeV/c. This behavior is different from what is found for the quasielastic response, which scales as $A/k_F$. Additionally, the deep scaling region is also discussed and there the usual scaling behavior is found to be preferable.Comment: 9 pages, 8 figure