5,870 research outputs found
Living Standards, Scarce Resources and Immigration: An Interview With Labor Economist Vernon M. Briggs, Jr.
[Excerpt] Immigration reformers are drawn to the issue by myriad paths. Some arrive with a burning concern over the prospect of a billion person nation in a lifetime. The wildlife and natural heritage of the nation will be irretrievably altered by this expansive footprint. Others are motivated by present concerns over dwindling water reserves, energy, pauperized soils, solid waste, urban sprawl, congestion, and maybe just because our national parks are being loved to death.
Vernon Briggs, Ph.D., a liberal Democrat, comes to immigration reform through an interest in labor economics. He responds to an interest in the underprivileged American citizen. His compassion runs deep.
As revealed in this interview, exposure to John F. Kennedy during college days placed a claim upon his conscience. He has not escaped from this claim during the past 4.5 decades. His support of the underprivileged citizenry has found prolific expression in countless academic journals.
His interest in conferring dignity upon labor is more than academic. It is a passion. And his passion endures.
In this issue, The Social Contract honors the integrity, compassion, resourcefulness, and genius of Professor Briggs of Cornell University
Improved radiative corrections for (e,e'p) experiments: Beyond the peaking approximation and implications of the soft-photon approximation
Analysing (e,e'p) experimental data involves corrections for radiative
effects which change the interaction kinematics and which have to be carefully
considered in order to obtain the desired accuracy. Missing momentum and energy
due to bremsstrahlung have so far always been calculated using the peaking
approximation which assumes that all bremsstrahlung is emitted in the direction
of the radiating particle. In this article we introduce a full angular Monte
Carlo simulation method which overcomes this approximation. The angular
distribution of the bremsstrahlung photons is reconstructed from H(e,e'p) data.
Its width is found to be underestimated by the peaking approximation and
described much better by the approach developed in this work.Comment: 11 pages, 13 figure
Improved radiative corrections for (e, e'p) experiments: Beyond the peaking approximation and implications of the soft-photon approximation
Abstract.: Analyzing (e, e'p) experimental data involves corrections for radiative effects which change the interaction kinematics and which have to be carefully considered in order to obtain the desired accuracy. Missing momentum and energy due to bremsstrahlung have so far often been incorporated into the simulations and the experimental analyses using the peaking approximation. It assumes that all bremsstrahlung is emitted in the direction of the radiating particle. In this article we introduce a full angular Monte Carlo simulation method which overcomes this approximation. As a test, the angular distribution of the bremsstrahlung photons is reconstructed from H(e, e'p) data. Its width is found to be underestimated by the peaking approximation and described much better by the approach developed in this work. The impact of the soft-photon approximation on the photon angular distribution is found to be minor as compared to the impact of the peaking approximatio
Reduction of Tc due to Impurities in Cuprate Superconductors
In order to explain how impurities affect the unconventional
superconductivity, we study non-magnetic impurity effect on the transition
temperature using on-site U Hubbard model within a fluctuation exchange (FLEX)
approximation. We find that in appearance, the reduction of Tc roughly
coincides with the well-known Abrikosov-Gor'kov formula. This coincidence
results from the cancellation between two effects; one is the reduction of
attractive force due to randomness, and another is the reduction of the damping
rate of quasi-particle arising from electron interaction. As another problem,
we also study impurity effect on underdoped cuprate as the system showing
pseudogap phenomena. To the aim, we adopt the pairing scenario for the
pseudogap and discuss how pseudogap phenomena affect the reduction of Tc by
impurities. We find that 'pseudogap breaking' by impurities plays the essential
role in underdoped cuprate and suppresses the Tc reduction due to the
superconducting (SC) fluctuation.Comment: 14 pages, 28 figures To be published in JPS
Extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
Nucleon electromagnetic form factor data (including recent data) is fitted
with models that respect the confinement and asymptotic freedom properties of
QCD. Gari-Krumpelmann (GK) type models, which include the major vector meson
pole contributions and at high momentum transfer conform to the predictions of
perturbative QCD, are combined with Hohler-Pietarinen (HP) models, which also
include the width of the rho meson and the addition of higher mass vector meson
exchanges, but do not evolve into the explicit form of PQCD at high momentum
transfer. Different parameterizations of the GK model's hadronic form factors,
the effect of including the width of the rho meson and the addition of the next
(in mass) isospin 1 vector meson are considered. The quality of fit and the
consistency of the parameters select three of the combined HP/GK type models.
Projections are made to the higher momentum transfers which are relevant to
electron-deuteron experiments. The projections vary little for the preferred
models, removing much of the ambiguity in electron-nucleus scattering
predictions.Comment: 18pp, 7 figures, using RevTeX with BoxedEPS macros; 1 new figure,
minor textual changes; email correspondence to [email protected]
NEOTROPICAL CARNIVORES: a data set on carnivore distribution in the Neotropics
Incluye contenido parcial de los autoresAbstract.Mammalian carnivores are considered a key group in maintaining ecologicalhealth and can indicate potential ecological integrity in landscapes where they occur. Carni-vores also hold high conservation value and their habitat requirements can guide managementand conservation plans. The order Carnivora has 84 species from 8 families in the Neotropicalregion: Canidae; Felidae; Mephitidae; Mustelidae; Otariidae; Phocidae; Procyonidae; andUrsidae. Herein, we include published and unpublished data on native terrestrial Neotropicalcarnivores (Canidae; Felidae; Mephitidae; Mustelidae; Procyonidae; and Ursidae). NEOTRO-PICAL CARNIVORES is a publicly available data set that includes 99,605 data entries from35,511 unique georeferenced coordinates. Detection/non-detection and quantitative data wereobtained from 1818 to 2018 by researchers, governmental agencies, non-governmental organi-zations, and private consultants. Data were collected using several methods including cameratrapping, museum collections, roadkill, line transect, and opportunistic records. Literature(peer-reviewed and grey literature) from Portuguese, Spanish and English were incorporated inthis compilation. Most of the data set consists of detection data entries (n=79,343; 79.7%) butalso includes non-detection data (n=20,262; 20.3%). Of those, 43.3% also include count data(n=43,151). The information available in NEOTROPICAL CARNIVORES will contribute tomacroecological, ecological, and conservation questions in multiple spatio-temporal perspec-tives. As carnivores play key roles in trophic interactions, a better understanding of their distri-bution and habitat requirements are essential to establish conservation management plans andsafeguard the future ecological health of Neotropical ecosystems. Our data paper, combinedwith other large-scale data sets, has great potential to clarify species distribution and relatedecological processes within the Neotropics. There are no copyright restrictions and no restric-tion for using data from this data paper, as long as the data paper is cited as the source of theinformation used. We also request that users inform us of how they intend to use the data
Correlated Strength in Nuclear Spectral Function
We have carried out an (e,e'p) experiment at high momentum transfer and in
parallel kinematics to measure the strength of the nuclear spectral function
S(k,E) at high nucleon momenta k and large removal energies E. This strength is
related to the presence of short-range and tensor correlations, and was known
hitherto only indirectly and with considerable uncertainty from the lack of
strength in the independent-particle region. This experiment confirms by direct
measurement the correlated strength predicted by theory.Comment: 4 pages, 2 figures, accepted by Phys. Rev. Let
Effect of recent R_p and R_n measurements on extended Gari-Krumpelmann model fits to nucleon electromagnetic form factors
The Gari-Krumpelmann (GK) models of nucleon electromagnetic form factors, in
which the rho, omega, and phi vector meson pole contributions evolve at high
momentum transfer to conform to the predictions of perturbative QCD (pQCD), was
recently extended to include the width of the rho meson by substituting the
result of dispersion relations for the pole and the addition of rho' (1450)
isovector vector meson pole. This extended model was shown to produce a good
overall fit to all the available nucleon electromagnetic form factor (emff)
data. Since then new polarization data shows that the electric to magnetic
ratios R_p and R_n obtained are not consistent with the older G_{Ep} and G_{En}
data in their range of momentum transfer. The model is further extended to
include the omega' (1419) isoscalar vector meson pole. It is found that while
this GKex cannot simultaneously fit the new R_p and the old G_{En} data, it can
fit the new R_p and R_n well simultaneously. An excellent fit to all the
remaining data is obtained when the inconsistent G_{Ep} and G_{En} is omitted.
The model predictions are shown up to momentum transfer squared, Q^2, of 8
GeV^2/c^2.Comment: 14 pages, 8 figures, using RevTeX4; email correspondence to
[email protected] ; minor typos corrected, figures added, conclusions
extende
Nuclear transparency and effective kaon-nucleon cross section from the A(e, e'K+) reaction
We have determined the transparency of the nuclear medium to kaons from
measurements on C, Cu, and Au targets.
The measurements were performed at the Jefferson Laboratory and span a range in
four-momentum-transfer squared Q=1.1 -- 3.0 GeV. The nuclear
transparency was defined as the ratio of measured kaon electroproduction cross
sections with respect to deuterium, (). We further
extracted the atomic number () dependence of the transparency as
parametrized by and, within a simple model assumption,
the in-medium effective kaon-nucleon cross sections. The effective cross
sections extracted from the electroproduction data are found to be smaller than
the free cross sections determined from kaon-nucleon scattering experiments,
and the parameter was found to be significantly larger than those
obtained from kaon-nucleus scattering. We have included similar comparisons
between pion- and proton-nucleon effective cross sections as determined from
electron scattering experiments, and pion-nucleus and proton-nucleus scattering
data.Comment: 7 pages, 5 figure
Study of the A(e,e') Reaction on H, H, C, Al, Cu and Au
Cross sections for the p()n process on H, H, C,
Al, Cu and Au targets were measured at the Thomas
Jefferson National Accelerator Facility (Jefferson Lab) in order to extract the
nuclear transparencies. Data were taken for four-momentum transfers ranging
from =1.1 to 4.8 GeV for a fixed center of mass energy of =2.14
GeV. The ratio of and was extracted from the measured
cross sections for H, H, C and Cu targets at = 2.15
and 4.0 GeV allowing for additional studies of the reaction mechanism. The
experimental setup and the analysis of the data are described in detail
including systematic studies needed to obtain the results. The results for the
nuclear transparency and the differential cross sections as a function of the
pion momentum at the different values of are presented. Global features
of the data are discussed and the data are compared with the results of model
calculations for the p()n reaction from nuclear targets.Comment: 28 pages, 19 figures, submited to PR
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