3,026 research outputs found
Inclusive deuteron-induced reactions and final neutron states
We present in this paper a formalism for deuteron-induced inclusive
reactions. We disentangle direct elastic breakup contributions from other
processes (which we generically call non-elastic breakup) implying a capture of
the neutron both above and below the neutron emission threshold. The reaction
is described as a two step process, namely the breakup of the deuteron followed
by the propagation of the neutron-target system driven by an optical potential.
The final state interaction between the neutron and the target can eventually
form an excited compound nucleus. Within this context, the direct neutron
transfer to a sharp bound state is a limiting case of the present formalism.Comment: To appear in the proceedings of the 14th International Conference on
Nuclear Reaction Mechanisms, Varenna, Ital
Estimating the Effects of U.S. Distortions in the Ethanol Market Using a Partial Equilibrium Trade Model
In this paper we assess the impact of the elimination of trade distortions on imports from Brazil to the U.S. For this purpose, we estimate a partial equilibrium trade model an ethanol export supply function for Brazil and an ethanol import demand function for the U.S.-, based on annual data from 1975 to 2006, and use the results to compute a back-of-the-envelope measure of the deadweight loss derived from those trade distortions as well as one derived from producing the 35 billion gallons proposed in the Twenty in Ten 2007 State of the Union Policy Initiative assuming the distortions are not eliminated. Two-stage least squares is used to estimate both functions, the world price of ethanol being treated as endogenous. This paper supports the idea that the U.S. and Brazil would reap gains from trade if trade distortions were eliminated.Resource /Energy Economics and Policy,
Absorption-Fluctuation Theorem for Nuclear Reactions: Brink-Axel, Incomplete Fusion and All That
We discuss the connection between absorption, averages and fluctuations in
nuclear reactions. The fluctuations in the entrance channel result in the
compound nucleus, Hauser-Feshbach, cross section, the fluctuations in the
intermediate channels, result in modifications of multistep reaction cross
sections, while the fluctuations in the final channel result in hybrid cross
sections that can be used to describe incomplete fusion reactions. We discuss
the latter in details and comment on the validity of the assumptions used in
the develpoment of the Surrogate method. We also discuss the theory of
multistep reactions with regards to intermediate state fluctuations and the
energy dependence and non-locality of the intermediate channels optical
potentials.Comment: 9 pages. Contribution to the International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*2007), October 22-26,
2007, Fish Camp, California. To be published in AIP Proceedings (Editor Jutta
Escher
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No Evidence of Short-Term Exchange of Meat for Sex among Chimpanzees
The meat-for-sex hypothesis posits that male chimpanzees (Pan troglodytes) trade meat with estrous females in exchange for short-term mating access. This notion is widely cited in the anthropological literature and has been used to construct scenarios about human evolution. Here we review the theoretical and empirical basis for the meat-for-sex hypothesis. We argue that chimpanzee behavioral ecology does not favor the evolution of such exchanges because 1) female chimpanzees show low mate selectivity and require little or no material incentive to mate, violating existing models of meat-for-sex exchange; and 2) meat-for-sex exchanges are unlikely to provide reproductive benefits to either partner. We also present new analyses of 28 years of data from two East African chimpanzee study sites (Gombe National Park, Tanzania; Kanyawara, Kibale National Park, Uganda) and discuss the results of previously published studies. In at least three chimpanzee communities, 1) the presence of sexually receptive females did not increase hunting probability; 2) males did not share preferentially with sexually receptive females and 3) sharing with females did not increase a male’s short-term mating success. We acknowledge that systematic meat-sharing by male chimpanzees in expectation of or as reward for immediate copulations might be discovered in future studies of chimpanzees. However current data indicate that such exchanges are so rare in studied populations, and are so different in nature from exchanges among humans, that with respect to chimpanzees, sexual bartering in humans should be regarded as a derived trait with no known antecedents in the behavior of wild chimpanzees.Human Evolutionary Biolog
GaN directional couplers for integrated quantum photonics
Large cross-section GaN waveguides are proposed as a suitable architecture to
achieve integrated quantum photonic circuits. Directional couplers with this
geometry have been designed with aid of the beam propagation method and
fabricated using inductively coupled plasma etching. Scanning electron
microscopy inspection shows high quality facets for end coupling and a well
defined gap between rib pairs in the coupling region. Optical characterization
at 800 nm shows single-mode operation and coupling-length-dependent splitting
ratios. Two photon interference of degenerate photon pairs has been observed in
the directional coupler by measurement of the Hong-Ou-Mandel dip with 96%
visibility.Comment: 4 pages, 5 figure
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