9,005 research outputs found
Lost Directions: U.S. Foreign Assistance Policy Since New Directions
International Development,
Angular distribution in two-photon double ionization of helium by intense attosecond soft X-ray pulses
We investigate two-photon double ionization of helium by intense () ultrashort ( as) soft X-ray pulses (E = 91.6 eV). The
time-dependent two-electron Schr\"odinger equation is solved using a coupled
channel method. We show that for ultrashort pulses the angular distribution of
ejected electrons depends on the pulse duration and provides novel insights
into the role of electron correlations in the two-electron photoemission
process. The angular distribution at energies near the ``independent electron''
peaks is close to dipolar while it acquires in the ``valley'' of correlated
emission a significant quadrupolar component within a few hundred attoseconds.Comment: 17 pages, 6 fig
Many-body system with a four-parameter family of point interactions in one dimension
We consider a four-parameter family of point interactions in one dimension.
This family is a generalization of the usual -function potential. We
examine a system consisting of many particles of equal masses that are
interacting pairwise through such a generalized point interaction. We follow
McGuire who obtained exact solutions for the system when the interaction is the
-function potential. We find exact bound states with the four-parameter
family. For the scattering problem, however, we have not been so successful.
This is because, as we point out, the condition of no diffraction that is
crucial in McGuire's method is not satisfied except when the four-parameter
family is essentially reduced to the -function potential.Comment: 8 pages, 4 figure
The composition of corotating energetic particle streams
The relative abundances of 1.5 to 23 MeV/nucleon ions in corotating nucleon streams were compared with ion abundances in particle events associated with solar flares and with solar and solar wind abundances. He/O and C/O ratios were found to be a factor of the order two to three times greater in corotating streams than in flare associated events. The distribution of H/He ratios in corotating streams was found to be much narrower and of lower average value than in flare associated events. H/He in corotating energetic particle streams compared favorably both in lack of variability and numerical value to H/He in high speed solar wind plasma streams. This comparison suggested that the source population for the corotating energetic particles was the solar wind
Structural and physical properties of layered oxy-arsenides LnRuAsO (Ln = La, Nd, Sm, Gd)
Polycrystalline samples of LaRuAsO, NdRuAsO, SmRuAsO, and GdRuAsO have been
synthesized and studied using powder x-ray diffraction, electrical transport,
magnetization, and heat capacity measurements. Variations in structural
properties across the series reveal a trend toward more ideal tetrahedral
coordination around Ru as the size of the rare earth element is reduced. The
lattice parameters of these Ru compounds show a more anisotropic response to
variation in Ln than their Fe analogues, and significant anisotropy in thermal
expansion is also observed. Transport measurements show metallic behavior, and
carrier concentrations near 10^21 - 10^22 electrons per cm^3 are inferred from
simple analysis of Hall effect measurements. Anomalies in resistivity,
magnetization, and heat capacity indicate antiferromagnetic ordering of rare
earth moments at 5 K for GdRuAsO, 4.5 K for SmRuAsO, and <2 K for NdRuAsO.
Magnetization measurements on LaRuAsO show no evidence of a magnetic moment on
Ru. Observed behaviors are compared to those reported for similar Fe and Ru
compounds
Is There a Democracy–Civil Society Paradox in Global Environmental Governance?
Civil society is commonly assumed to have a positive effect on international cooperation. This paper sheds light on one important facet of this assumption: we examine the impact of environmental non-governmental organizations (ENGOs) on ratification behavior of countries vis-à-vis international environmental agreements (IEAs). The main argument of the paper focuses on a “democracy-civil society paradox”: although ENGOs have a positive effect on ratification of IEAs on average, this effect decreases with increasing levels of democracy. This argument is counter-intuitive and appears paradoxical because democracy is generally associated both with a more active civil society and more international cooperation. The reasons for this hypothesized effect pertain to public demand for environmental public goods provision, government incentives, and problems of collective action among ENGOs. To test the net effect of ENGOs on countries' ratification behavior, the paper uses a new dataset on ENGOs in the time-period 1973–2006. The results offer strong support for the presumed democracy–civil society paradox. </jats:p
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