357 research outputs found
Does urbanization mean bigger governments?
This paper proposes urbanization as a determinant of government size. As people move to cities, their demand for a more de ned set of regulations, but also for basic health, education, and income standards rises. Our theoretical framework determines how the regional distribution of the population a ects government size. We test this theory on panel data of 175 countries from 1960 to 2010 and two state-level samples from Colombia and Germany. Results demonstrate a strong positive e ect from urbanization on government spending, with a 1 percent increase in the amount of urban citizens leading to a 0.2 percent rise in public expenditure. Our ndings indicate that public sectors may become more important as worldwide urbanization is progressing. This result underlines why government e ectiveness and the quality of public goods provision will be even more important in the future
Multivariate Anisotropic Interpolation on the Torus
We investigate the error of periodic interpolation, when sampling a function
on an arbitrary pattern on the torus. We generalize the periodic Strang-Fix
conditions to an anisotropic setting and provide an upper bound for the error
of interpolation. These conditions and the investigation of the error
especially take different levels of smoothness along certain directions into
account
Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials
The sensitivity of nucleon-nucleus elastic scattering to the off-shell
behavior of realistic nucleon-nucleon interactions is investigated when
on-shell equivalent nucleon-nucleon potentials are used. The study is based on
applications of the full-folding optical model potential for an explicit
treatment of the off-shell behavior of the nucleon-nucleon effective
interaction. Applications were made at beam energies between 40 and 500 MeV for
proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris
potential and its local on-shell equivalent as obtained with the
Gelfand-Levitan and Marchenko inversion formalism for the two nucleon
Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering
show small fluctuations in the corresponding observables. This implies that
off-shell features of the NN interaction cannot be unambiguously identified
with these processes. Inversion potentials were also constructed directly from
NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in
proton-nucleus scattering above 200 MeV provide a superior description of the
observables relative to those obtained from current realistic NN potentials.
Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.
Exploring the nuclear pion dispersion relation through the anomalous coupling of photon to photon and neutral pion
We investigate the possibility of measuring the pion dispersion relation in
nuclear matter through the anomalous coupling in the reaction \gamma - \gamma'
\pi_0. It is shown that this reaction permits the study of pionic modes for
space-like momenta. If the pion is softened in nuclear matter due to mixing
with the delta-hole state, significant strength for this reaction is expected
to move into the space-like region. Competing background processes are
evaluated, and it is concluded that useful insight can be obtained
experimentally, but only through a difficult exclusive measurement
The digital data processing concepts of the LOFT mission
The Large Observatory for X-ray Timing (LOFT) is one of the five mission
candidates that were considered by ESA for an M3 mission (with a launch
opportunity in 2022 - 2024). LOFT features two instruments: the Large Area
Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m 2 -class
instrument with approximately 15 times the collecting area of the largest
timing mission so far (RXTE) for the first time combined with CCD-class
spectral resolution. The WFM will continuously monitor the sky and recognise
changes in source states, detect transient and bursting phenomena and will
allow the mission to respond to this. Observing the brightest X-ray sources
with the effective area of the LAD leads to enormous data rates that need to be
processed on several levels, filtered and compressed in real-time already on
board. The WFM data processing on the other hand puts rather low constraints on
the data rate but requires algorithms to find the photon interaction location
on the detector and then to deconvolve the detector image in order to obtain
the sky coordinates of observed transient sources. In the following, we want to
give an overview of the data handling concepts that were developed during the
study phase.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
The influence of negative-energy states on proton-proton bremsstrahlung
We investigate the effect of negative-energy states on proton-proton
bremsstrahlung using a manifestly covariant amplitude based on a T-matrix
constructed in a spectator model. We show that there is a large cancellation
among the zeroth-order, single- and double-scattering diagrams involving
negative-energy nucleonic currents. We thus conclude that it is essential to
include all these diagrams when studying effects of negative-energy states.Comment: 12 pages revtex and 3 figure
Efficient single-photon emission from electrically driven InP quantum dots epitaxially grown on Si(001)
The heteroepitaxy of III-V semiconductors on silicon is a promising approach
for making silicon a photonic platform for on-chip optical interconnects and
quantum optical applications. Monolithic integration of both material systems
is a long-time challenge, since different material properties lead to high
defect densities in the epitaxial layers. In recent years, nanostructures
however have shown to be suitable for successfully realising light emitters on
silicon, taking advantage of their geometry. Facet edges and sidewalls can
minimise or eliminate the formation of dislocations, and due to the reduced
contact area, nanostructures are little affected by dislocation networks. Here
we demonstrate the potential of indium phosphide quantum dots as efficient
light emitters on CMOS-compatible silicon substrates, with luminescence
characteristics comparable to mature devices realised on III-V substrates. For
the first time, electrically driven single-photon emission on silicon is
presented, meeting the wavelength range of silicon avalanche photo diodes'
highest detection efficiency
Tuning emission energy and fine structure splitting in quantum dots emitting in the telecom O-band
We report on optical investigations of MOVPE-grown InGaAs/GaAs quantum dots emitting at the telecom O-band that were integrated onto uniaxial piezoelectric actuators. This promising technique, which does not degrade the emission brightness of the quantum emitters, enables us to tune the quantum dot emission wavelengths and their fine-structure splitting. By spectrally analyzing the emitted light with respect to its polarization, we are able to demonstrate the cancelation of the fine structure splitting within the experimental resolution limit. This work represents an important step towards the high-yield generation of entangled photon pairs at telecommunication wavelength, together with the capability to precisely tune the emission to target wavelengths
Delta--Excitation and Exchange Corrections for NN--Bremsstrahlung
The role of the relativistic amplitudes for a number of
processes usually neglected in potential model calculations of
NN--bremsstrahlung is investigated. In particular, we consider the
--excitation pole contributions related to the one--pion and one--rho
exchange and in addition include the exchange contributions induced by the
radiative decays. The contributions are
calculated from relativistic Born amplitudes fitted to --production and
absorption data in the energy range up to 1 GeV and then used to supplement
potential model and soft photon calculations for nucleon--nucleon
bremsstrahlung. The effects on --observables, although moderate in
general, are found to be important in some kinematic domains.Comment: 15 pages in LaTex, using Revtex, 6 figures as uufile'd, compressed
Postscript file included, TRIUMF preprint TRI-PP-94-9
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