39 research outputs found

    Photonuclear Reactions of Three-Nucleon Systems

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    We discuss the available data for the differential and the total cross section for the photodisintegration of 3^3He and 3^3H and the corresponding inverse reactions below Eγ=100E_\gamma = 100 MeV by comparing with our calculations using realistic NNNN interactions. The theoretical results agree within the errorbars with the data for the total cross sections. Excellent agreement is achieved for the angular distribution in case of 3^3He, whereas for 3^3H a discrepancy between theory and experiment is found.Comment: 11 pages (twocolumn), 12 postscript figures included, uses psfig, RevTe

    Influence of Gamma-Ray Emission on the Isotopic Composition of Clouds in the Interstellar Medium

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    We investigate one mechanism of the change in the isotopic composition of cosmologically distant clouds of interstellar gas whose matter was subjected only slightly to star formation processes. According to the standard cosmological model, the isotopic composition of the gas in such clouds was formed at the epoch of Big Bang nucleosynthesis and is determined only by the baryon density in the Universe. The dispersion in the available cloud composition observations exceeds the errors of individual measurements. This may indicate that there are mechanisms of the change in the composition of matter in the Universe after the completion of Big Bang nucleosynthesis. We have calculated the destruction and production rates of light isotopes (D, 3He, 4He) under the influence of photonuclear reactions triggered by the gamma-ray emission from active galactic nuclei (AGNs). We investigate the destruction and production of light elements depending on the spectral characteristics of the gamma-ray emission. We show that in comparison with previous works, taking into account the influence of spectral hardness on the photonuclear reaction rates can increase the characteristic radii of influence of the gamma-ray emission from AGNs by a factor of 2-8. The high gamma-ray luminosities of AGNs observed in recent years increase the previous estimates of the characteristic radii by two orders of magnitude. This may suggest that the influence of the emission from AGNs on the change in the composition of the medium in the immediate neighborhood (the host galaxy) has been underestimated.Comment: 13 pages, 13 figures, 3 table

    Photodisintegration of the triton with realistic potentials

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    The process γ+tn+d\gamma + t \to n + d is treated by means of three-body integral equations employing in their kernel the W-Matrix representation of the subsystem amplitudes. As compared to the plane wave (Born) approximation the full solution of the integral equations, which takes into account the final state interaction, shows at low energies a 24% enhancement. The calculations are based on the semirealistic Malfliet-Tjon and the realistic Paris and Bonn B potentials. For comparison with earlier calculations we also present results for the Yamaguchi potential. In the low-energy region a remarkable potential dependence is observed, which vanishes at higher energies.Comment: 16 pages REVTeX, 8 postscript figures included, uses epsfig.st

    Triton photodisintegration in three-dimensional approach

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    Two- and three- particles photodisintegration of the triton is investigated in a three-dimensional (3D) Faddeev approach. For this purpose the Jacobi momentum vectors for three particles system and spin-isospin quantum numbers of the individual nucleons are considered. Based on this picture the three-nucleon Faddeev integral equations with the two-nucleon interaction are formulated without employing the partial wave decomposition. The single nucleon current as well as π\pi- and ρ\rho- like exchange currents are used in an appropriate form to be employed in 3D approach. The exchange currents are derived from AV18 NN force. The two-body t-matrix, Deuteron and Triton wave functions are calculated in the 3D approach by using AV18 potential. Benchmarks are presented to compare the total cross section for the two- and three- particles photodisintegration in the range of Eγ<30MeVE_{\gamma}<30 MeV. The 3D Faddeev approach shows promising results

    Radiative capture of protons by deuterons

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    The differential cross section for radiative capture of protons by deuterons is calculated using different realistic NN interactions. We compare our results with the available experimental data below Ex=20MeVE_x = 20 MeV. Excellent agreement is found when taking into account meson exchange currents, dipole and quadrupole contributions, and the full initial state interaction. There is only a small difference between the magnitudes of the cross sections for the different potentials considered. The angular distributions, however, are practically potential independent.Comment: 4 pages (twocolumn), 4 postscript figures included, submitted for publication, revised versio

    Exploring the value of a cyber threat intelligence function in an organization

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    Organizations can struggle to cope with the rapidly advancing threat landscape. A cyber threat intelligence (CTI) function broadly aims to understand how threats operate to better protect the organization from future attacks. This seems like a natural step to take in hardening security. However, CTI is understood and experienced differently across organizations. To explore the value of this function this study used a qualitative method, guided by the Socio-Technical Framework, to understand how the CTI function is interpreted by organizations in South Africa. Thematic analysis was used to provide an in-depth view of how each organization implemented its CTI function and what benefits and challenges they’ve experienced. Findings show that CTI tasks tend to be more manual and resource-intensive, but these challenges can be resolved through automation. It was noted that only larger organizations seem to have the budget and resources available to implement the CTI function, whereas smaller organizations put more reliance on tools. It was observed that skills for the CTI function can be learned on the job, but that formal education provides a good foundation. The findings illustrate the value the CTI function can provide an organization but also the challenges, thereby enabling other organizations to improve preparation before such a function is adopted

    Determination of Omega_b From Big Bang Nucleosynthesis in the Presence of Regions of Antimatter

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    Production of regions of antimatter in the early universe is predicted in many baryogenesis models. Small scale antimatter regions would annihilate during or soon after nucleosynthesis, affecting the abundances of the light elements. In this paper we study how the acceptable range in Omega_b changes in the presence of antimatter regions, as compared to the standard big bang nucleosynthesis. It turns out that it is possible to produce at the same time both a low 4He value (Y_p < 0.240) and a low D/H value (D/H < 4e-5), but overproduction of 7Li is unavoidable at large Omega_b.Comment: 9 pages, PRD version, ref. 6 correcte

    Antimatter Regions in the Early Universe and Big Bang Nucleosynthesis

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    We have studied big bang nucleosynthesis in the presence of regions of antimatter. Depending on the distance scale of the antimatter region, and thus the epoch of their annihilation, the amount of antimatter in the early universe is constrained by the observed abundances. Small regions, which annihilate after weak freezeout but before nucleosynthesis, lead to a reduction in the 4He yield, because of neutron annihilation. Large regions, which annihilate after nucleosynthesis, lead to an increased 3He yield. Deuterium production is also affected but not as much. The three most important production mechanisms of 3He are 1) photodisintegration of 4He by the annihilation radiation, 2) pbar-4He annihilation, and 3) nbar-4He annihilation by "secondary" antineutrons produced in anti-4He annihilation. Although pbar-4He annihilation produces more 3He than the secondary nbar-4He annihilation, the products of the latter survive later annihilation much better, since they are distributed further away from the annihilation zone.Comment: 15 pages, 9 figures. Minor changes to match the PRD versio

    Circadian control of oviposition activity in Ostrinia nubilalis

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