269 research outputs found

    Waste Minimization by Reuse and Recycling

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    Recently, pollution prevention directs attention towards the elimination or reduction of undesired by- products within the production process itself before treatment. On the long term, pollution prevention through waste minimization and cleaner production is more cost-effective and environmentally sound than traditional pollution control methods. The objective of this work was to carry out a feasibility study to define and implement an integrated pollution prevention and control measure in order to minimize waste and therefore to achieve compliance with the Romanian Environmental law

    Path integral Monte Carlo simulation of charged particles in traps

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    This chapter is devoted to the computation of equilibrium (thermodynamic) properties of quantum systems. In particular, we will be interested in the situation where the interaction between particles is so strong that it cannot be treated as a small perturbation. For weakly coupled systems many efficient theoretical and computational techniques do exist. However, for strongly interacting systems such as nonideal gases or plasmas, strongly correlated electrons and so on, perturbation methods fail and alternative approaches are needed. Among them, an extremely successful one is the Monte Carlo (MC) method which we are going to consider in this chapter.Comment: 18 pages, based on talks on Hareaus school on computational methods, Greifswald, September 200

    Interaction potential between dynamic dipoles: polarized excitons in strong magnetic fields

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    The interaction potential of a two-dimensional system of excitons with spatially separated electron-hole layers is considered in the strong magnetic field limit. The excitons are assumed to have free dynamics in the xx-yy plane, while being constrained or `polarized' in the zz direction. The model simulates semiconductor double layer systems under strong magnetic field normal to the layers. The {\em residual} interaction between excitons exhibits interesting features, arising from the coupling of the center-of-mass and internal degrees of freedom of the exciton in the magnetic field. This coupling induces a dynamical dipole moment proportional to the center-of-mass magnetic moment of the exciton. We show the explicit dependence of the inter-exciton potential matrix elements, and discuss the underlying physics. The unusual features of the interaction potential would be reflected in the collective response and non-equilibrium properties of such system.Comment: REVTEX - 11 pages - 1 fi

    New pathway to bypass the 15O waiting point

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    We propose the sequential reaction process 15^{15}O(pp,γ)(β+\gamma)(\beta^{+})16^{16}O as a new pathway to bypass of the 15^{15}O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 1010^{10} times higher than the 15^{15}O(pp,β+\beta^{+})16^{16}O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound 16^{16}F low lying states, obtained using the H(15^{15}O,p)15^{15}O reaction. The large (p,γ)(β+)(p,\gamma)(\beta^{+}) cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte

    Experimental investigation of the effect of ionization on the 51V(p,n)51Cr reaction

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    The investigation of the effects of average atomic ionization on nuclear reactions is of prime importance for nuclear astrophysics. No direct experimental measurement using a plasma target has been done yet. In this regard, we measured for the first time the neutron production of a (p,n) reaction in different states of ionization. The studied nuclear reaction was 51V(p,n)51Cr. We measured a significantly lower neutron production than expected when the target was ionized, even when taking into account existing electron screening theory or the effect of the stopping power in the target on the injected proton beam. This experiment is a first step in the process to characterize the influence of ionization at astrophysically relevant energies.Comment: 20 pages, 10 figures, submitted to EP

    Probing Nuclear forces beyond the drip-line using the mirror nuclei 16^{16}N and 16^{16}F

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    Radioactive beams of 14^{14}O and 15^{15}O were used to populate the resonant states 1/2+^+, 5/2+^+ and 0,1,20^-,1^-,2^- in the unbound 15^{15}F and 16^{16}F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in 16^{16}F can be viewed as a core of 14^{14}O plus a proton in the 2s1/2_{1/2} or 1d5/2_{5/2} shell and a neutron in 1p1/2_{1/2}. Experimental energies were used to derive the strength of the 2s1/2_{1/2}-1p1/2_{1/2} and 1d5/2_{5/2}-1p1/2_{1/2} proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus 16^{16}N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an =0\ell=0 proton configuration.Comment: 6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review

    Spectroscopy of 28^{28}Na: shell evolution toward the drip line

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    Excited states in 28^{28}Na have been studied using the β\beta-decay of implanted 28^{28}Ne ions at GANIL/LISE as well as the in-beam γ\gamma-ray spectroscopy at the NSCL/S800 facility. New states of positive (Jπ^{\pi}=3,4+^+) and negative (Jπ^{\pi}=1-5^-) parity are proposed. The former arise from the coupling between 0d_5/2\_{5/2} protons and a 0d_3/2\_{3/2} neutron, while the latter are due to couplings with 1p_3/2\_{3/2} or 0f_7/2\_{7/2} neutrons. While the relative energies between the Jπ^{\pi}=1-4+^+ states are well reproduced with the USDA interaction in the N=17 isotones, a progressive shift in the ground state binding energy (by about 500 keV) is observed between 26^{26}F and 30^{30}Al. This points to a possible change in the proton-neutron 0d_5/2\_{5/2}-0d_3/2\_{3/2} effective interaction when moving from stability to the drip line. The presence of Jπ^{\pi}=1-4^- negative parity states around 1.5 MeV as well as of a candidate for a Jπ^{\pi}=5^- state around 2.5 MeV give further support to the collapse of the N=20 gap and to the inversion between the 0f_7/2\_{7/2} and 1p_3/2\_{3/2} levels below Z=12. These features are discussed in the framework of Shell Model and EDF calculations, leading to predicted negative parity states in the low energy spectra of the 26^{26}F and 25^{25}O nuclei.Comment: Exp\'erience GANIL/LISE et NSCL/S80

    Initial State Dependence of the Breakup of Weakly Bound Carbon Isotopes

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    The one-neutron nuclear breakup from the Carbon isotopes 19^{19}C and 17^{17}C, is calculated as an example of application of the theory of transfer to the continuum reactions in the formulation which includes spin coupling. The effect of the energy sharing between the parallel and transverse neutron momentum distributions is taken into account thus resulting in a theory which is more general than sudden eikonal approaches. Both effects are necessary to understand properly the breakup from not too weakly bound li>1l_i>1 orbitals. Breakup which leaves the core into an excited state below particle threshold is also considered. The core-target interaction is treated in the smooth cut-off approximation. By comparing to presently available experimental data we show how to make some hypothesis on the quantum numbers and occupancy of the neutron initial state. Possible ambiguities in the interpretation of inclusive cross sections are discussed.Comment: 22 RevTeX pages,3 ps figures. Phys. Rev. C, accepte
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