405 research outputs found
Carolina Forum: Beach Houses And Shifting Sands: An Interview With Dr. Orrin H. Pilkey; North Carolina Nature Conservancy: Conservation Through Private Action; Congress Revises Coastal Zone Management Act
This edition of Carolina Forum includes the following: BEACH HOUSES AND SHIFTING SANDS: AN INTERVIEW WITH DR. ORRIN H. PILKEY: One of the burning issues of coastal planning today is the subject of beach development. On one side are those who feel development is inevitable yet manageable through actions taken to alter the beach and protect the structures: protection of development is paramount. On the other side are those who feel beach preservation is the overriding concern. Their argument centers on the fact that actions taken to save the structures will only result in damage to the shoreline. They advocate beach development that recognizes the inevitable dynamism of the coastal ecosystem and does not interfere with that process. This, however, translates into development that is very different in concept and value from traditional notions of property ownership and enjoyment. In the thick of the controversy is Dr. Orrin H. Pilkey, who has been called "the man who wants to let the lighthouse fall in." His view, simply put, is that the beach is a dynamic system that will run its course regardless of what man does to change it. Whatever intrusion man makes into the system in order to save it is doomed; in the long run he will cause more harm that he tried to prevent. Dr. Pilkey's concern for beach preservation is explained at length in his 1979 book, The Beaches Are Moving, co-authored by Wallace Kaufman. It is the culmination of his many years as a passionate observer of coastal change and as Professor of Marine Geology at Duke University. Dr. Pilkey is also president-elect of the North Carolina Academy of Sciences. NORTH CAROLINA NATURE CONSERVANCY: CONSERVATION THROUGH PRIVATE ACTION: Until about four years ago, few people in North Carolina had ever heard of Carrot Island and Bird Shoal with the exception of Beaufort and Carteret County residents, naturalists, and those connected with the adjacent Duke University Marine Laboratory. Carrot Island and Bird Shoal, located directly across Taylors Creek from Beaufort's historic Front Street, have traditionally served as open space for the area's townspeople. Yet it took the threat of development and the publicity that followed for most people to realize just how special this area really is. CONGRESS REVISES COASTAL ZONE MANAGEMENT ACT: On October 1, 1980, Congress cleared and sent to the President the final bill HR 6979 containing a package of significant amendments to the Coastal Zone Management Act of 1972. The intended impact of the bill, according to the report of the full Committee on Merchant Marine and Fisheries, was to strengthen the Act; moreover, the bill aimed to signal to the States a continued commitment on the part of Congress to a program of support for states managing the valuable resources of the coastal areas
Measurement of the Target-Normal Single-Spin Asymmetry in Quasielastic Scattering from the Reaction \u3csup\u3e3\u3c/sup\u3eHe\u3csup\u3e↑\u3c/sup\u3e(\u3cem\u3ee\u3c/em\u3e,\u3cem\u3ee\u3c/em\u3e′ )
We report the first measurement of the target single-spin asymmetry, Ay, in quasielastic scattering from the inclusive reaction 3He↑(e,e′ ) on a 3He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A nonzero Ay can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the substructure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q2=0.13, 0.46, and 0.97 GeV2. These measurements demonstrate, for the first time, that the 3He asymmetry is clearly nonzero and negative at the 4σ–9σ level. Using measured proton-to-3He cross-section ratios and the effective polarization approximation, neutron asymmetries of −(1–3)% were obtained. The neutron asymmetry at high Q2 is related to moments of the generalized parton distributions (GPDs). Our measured neutron asymmetry at Q2=0.97 GeV2 agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions
New Measurement of Compton Scattering from the Deuteron and an Improved Extraction of the Neutron Electromagnetic Polarizabilities
The electromagnetic polarizabilities of the nucleon are fundamental
properties that describe its response to external electric and magnetic fields.
They can be extracted from Compton-scattering data --- and have been, with good
accuracy, in the case of the proton. In contradistinction, information for the
neutron requires the use of Compton scattering from nuclear targets. Here we
report a new measurement of elastic photon scattering from deuterium using
quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden.
These first new data in more than a decade effectively double the world
dataset. Their energy range overlaps with previous experiments and extends it
by 20 MeV to higher energies. An analysis using Chiral Effective Field Theory
with dynamical \Delta(1232) degrees of freedom shows the data are consistent
with and within the world dataset. After demonstrating that the fit is
consistent with the Baldin sum rule, extracting values for the isoscalar
nucleon polarizabilities and combining them with a recent result for the
proton, we obtain the neutron polarizabilities as \alpha_n = [11.55 +/-
1.25(stat) +/- 0.2(BSR) +/- 0.8(th)] X 10^{-4} fm^3 and \beta_n = [3.65 -/+
1.25(stat) +/- 0.2(BSR) -/+ 0.8(th)] X 10^{-4} fm3, with \chi^2 = 45.2 for 44
degrees of freedom.Comment: 6 pages, 3 figures, comments from Physical Review Letters Referees
addresse
First Measurement of Unpolarized Semi-Inclusive Deep-Inelastic Scattering Cross Sections From a He 3 Target
The unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in 3He(e,e′π±)X have been measured for the first time in Jefferson Lab experiment E06-010 with a 5.9GeV e- beam on a 3He gas target. The experiment focuses on the valence quark region, covering a kinematic range 0.12\u3cxbj\u3c0.45,1\u3cQ2\u3c4(GeV/c)2,0.45\u3czh\u3c0.65, and 0.05\u3cPt\u3c0.55GeV/c. The extracted SIDIS differential cross sections of π± production are compared with existing phenomenological models while the 3He nucleus approximated as two protons and one neutron in a plane-wave picture, in multidimensional bins. Within the experimental uncertainties, the azimuthal modulations of the cross sections are found to be consistent with zero. © 2017 American Physical Society
Quasi-free Compton Scattering and the Polarizabilities of the Neutron
Differential cross sections for quasi-free Compton scattering from the proton
and neutron bound in the deuteron have been measured using the Glasgow/Mainz
tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48
cm 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA
recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV
at . Liquid deuterium and hydrogen targets
allowed direct comparison of free and quasi-free scattering from the proton.
The neutron detection efficiency of the SENECA detector was measured via the
reaction . The "free" proton Compton scattering cross
sections extracted from the bound proton data are in reasonable agreement with
those for the free proton which gives confidence in the method to extract the
differential cross section for free scattering from quasi-free data.
Differential cross sections on the free neutron have been extracted and the
difference of the electromagnetic polarizabilities of the neutron have been
obtained to be
in units . In combination with the polarizability sum deduced from photoabsorption data, the neutron electric and
magnetic polarizabilities, and
are obtained. The backward spin polarizability of the neutron was determined to
be
Single Spin Asymmetries in Charged Kaon Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized He-3 Target
We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of0.1 \u3c xbj \u3c 0.4for K+ and K− production. While the Collins and Sivers moments for K+ are consistent with zero within the experimental uncertainties, both moments for K− favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the K+ Sivers moments are consistent with the prediction, the K− results differ from the prediction at the 2-sigma level
Double Spin Asymmetries of Inclusive Hadron Electroproduction From a Transversely Polarized \u3csup\u3e3\u3c/sup\u3eHe Target
We report the measurement of beam-target double spin asymmetries (ALT) in the inclusive production of identified hadrons, e⃗ + 3He↑→h+X, using a longitudinally polarized 5.9-GeV electron beam and a transversely polarized 3He target. Hadrons (π±,K±, and proton) were detected at 16∘ with an average momentum ⟨Ph⟩=2.35 GeV/c and a transverse momentum (pT) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the 3He target were observed to be nonzero for π± production when the target was polarized transversely in the horizontal plane. The π+ and π− asymmetries have opposite signs, analogous to the behavior of ALT in semi-inclusive deep-inelastic scattering
Single Spin Asymmetries in Charged Kaon Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized \u3csup\u3e3\u3c/sup\u3eHe Target
We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of 0.1\u3cxbj\u3c0.4 for K+ and K− production. While the Collins and Sivers moments for K+ are consistent with zero within the experimental uncertainties, both moments for K− favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the K+ Sivers moments are consistent with the prediction, the K− results differ from the prediction at the 2-sigma level
In-medium modifications of the interaction in photon-induced reactions
Differential cross sections of the reactions
and have been measured for several
nuclei (H,C, and Pb) at an incident-photon energy of
=400-460 MeV at the tagged-photon facility at MAMI-B using the TAPS
spectrometer. A significant nuclear-mass dependence of the
invariant-mass distribution is found in the channel. This
dependence is not observed in the channel and is
consistent with an in-medium modification of the interaction in the
==0 channel. The data are compared to -induced measurements and to
calculations within a chiral-unitary approach
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