924 research outputs found
Polarization transfer in scattering using the Super BigBite Spectrometer
The effects of multi-photon-exchange and other higher-order QED corrections
on elastic electron-proton scattering have been a subject of high experimental
and theoretical interest since the polarization transfer measurements of the
proton electromagnetic form factor ratio at large momentum
transfer conclusively established the strong decrease of this ratio with
for GeV. This result is incompatible with previous
extractions of this quantity from cross section measurements using the
Rosenbluth Separation technique. Much experimental attention has been focused
on extracting the two-photon exchange (TPE) effect through the unpolarized
cross section ratio, but polarization transfer in polarized elastic
scattering can also reveal evidence of hard two-photon exchange. Furthermore,
it has a different sensitivity to the generalized TPE form factors, meaning
that measurements provide new information that cannot be gleaned from
unpolarized scattering alone. Both -dependence of polarization
transfer at fixed , and deviations between electron-proton and
positron-proton scattering are key signatures of hard TPE. A polarized positron
beam at Jefferson Lab would present a unique opportunity to make the first
measurement of positron polarization transfer, and comparison with
electron-scattering data would place valuable constraints on hard TPE. Here, we
propose a measurement program in Hall A that combines the Super BigBite
Spectrometer for measuring recoil proton polarization, with a non-magnetic
calorimetric detector for triggering on elastically scattered positrons. Though
the reduced beam current of the positron beam will restrict the kinematic
reach, this measurement will have very small systematic uncertainties, making
it a clean probe of TPE.Comment: 6 pages, 3 figures. Contribution to the EPJA topical issue, "An
Experimental Program with Positron Beams at Jefferson Lab." arXiv admin note:
substantial text overlap with arXiv:2007.15081, arXiv:1906.0941
Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance
Final analysis of proton form factor ratio data at Q(2)=4.0, 4.8, and 5.6 GeV2
Precise measurements of the proton electromagnetic form factor ratio R = mu(p)G(E)(p)/G(M)(p) using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of R with momentum transfer Q(2) for Q(2) greater than or similar to 1 GeV2, in strong disagreement with previous extractions of R from cross-section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab\u27s Hall A measured R at four Q(2) values in the range 3.5 GeV2 \u3c = Q(2) \u3c = 5.6 GeV2. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q(2) motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus, and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for R, improving the consistency of the polarization transfer data in the high-Q(2) region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis
Using the Conservation Planning Tool to Effectively Recover Northern Bobwhites: An Example for States to Effectively Step-Down the NBCI Plan
The National Bobwhite Conservation Initiative (NBCI) 2.0 provides a sound foundation for recovering northern bobwhites (Colinus virginianus) range-wide, regionally and, to some extent, even locally. However, the NBCI does not provide detailed guidance to states on how to step-down the plan for efficacious delivery of on-the-ground management actions prescribed via biologists within the plan itself. States often must incorporate multiple planning efforts (e.g., state wildlife action plans) and geospatial layers not directly included in the NBCI plan (see NBCI Appendix in these Proceedings) to make tenable decisions which best guide allocation of resources and benefit multiple species of greatest conservation concern. The Conservation Planning Tool (CPT), developed as part of NBCI 2.0, provides the infrastructure for states and conservation organizations to capture biologist information coalesced in the plan while incorporating other data (e.g., species emphasis areas, current CRP implementation, etc.) germane to conservation planning. We use 3 states (Kansas, Florida, and Virginia) to demonstrate the utility of the CPT and to develop a step-down implementation plan, via creation of a habitat prioritization model, for recovery of bobwhites in each state. We explore the implications associated with creation of focal areas with respect to high versus medium ranked areas and underscore the importance of inclusion of major land-use opportunities and constraints prescribed within the plan to garner successful bobwhite recovery. We propose a framework for the integration of monitoring efforts into the step-down model to assess bird response and evaluate NBCI success through estimating bobwhite population density
Microwave Assisted Synthesis of Py-Im Polyamides
Microwave synthesis was utilized to rapidly build Py-Im polyamides in high yields and purity using Boc-protection chemistry on Kaiser oxime resin. A representative polyamide targeting the 5′-WGWWCW-3′ (W = A or T) subset of the consensus Androgen and Glucocorticoid Response Elements was synthesized in 56% yield after 20 linear steps and HPLC purification. It was confirmed by Mosher amide derivatization of the polyamide that a chiral α-amino acid does not racemize after several additional coupling steps
Luminescent Ruthenium(II) Polypyridyl Functionalized Gold Nanoparticles; Their DNA Binding Abilities and Application As Cellular Imaging Agents
The synthesis and photophysical and biological
investigation of Ru(II)-polypyridyl stabilized watersoluble,
luminescent gold nanoparticles (AuNPs) are described.
These structures bind to DNA and undergo rapid
cellular uptake, being localized within the cell cytoplasm and
nucleus within 4 h
A precise extraction of the induced polarization in the 4He(e,e'p)3H reaction
We measured with unprecedented precision the induced polarization Py in
4He(e,e'p)3H at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2. The induced polarization
is indicative of reaction-mechanism effects beyond the impulse approximation.
Our results are in agreement with a relativistic distorted-wave impulse
approximation calculation but are over-estimated by a calculation with strong
charge-exchange effects. Our data are used to constrain the strength of the
spin independent charge-exchange term in the latter calculation.Comment: submitted to Physical Review Letter
2006 SQ372: A Likely Long-Period Comet from the Inner Oort Cloud
We report the discovery of a minor planet (2006 SQ372) on an orbit with a
perihelion of 24 AU and a semimajor axis of 796 AU. Dynamical simulations show
that this is a transient orbit and is unstable on a timescale of 200 Myrs.
Falling near the upper semimajor axis range of the scattered disk and the lower
semimajor axis range of the Oort Cloud, previous membership in either class is
possible. By modeling the production of similar orbits from the Oort Cloud as
well as from the scattered disk, we find that the Oort Cloud produces 16 times
as many objects on SQ372-like orbits as the scattered disk. Given this result,
we believe this to be the most distant long-period comet ever discovered.
Furthermore, our simulation results also indicate that 2000 OO67 has had a
similar dynamical history. Unaffected by the "Jupiter-Saturn Barrier," these
two objects are most likely long-period comets from the inner Oort Cloud
Somatostatin subtype-2 receptor-targeted metal-based anticancer complexes
Conjugates of a dicarba analogue of octreotide, a potent somatostatin agonist whose receptors are overexpressed on tumor cells, with [PtCl 2(dap)] (dap = 1-(carboxylic acid)-1,2-diaminoethane) (3), [(η 6-bip)Os(4-CO 2-pico)Cl] (bip = biphenyl, pico = picolinate) (4), [(η 6-p-cym)RuCl(dap)] + (p-cym = p-cymene) (5), and [(η 6-p-cym)RuCl(imidazole-CO 2H)(PPh 3)] + (6), were synthesized by using a solid-phase approach. Conjugates 3-5 readily underwent hydrolysis and DNA binding, whereas conjugate 6 was inert to ligand substitution. NMR spectroscopy and molecular dynamics calculations showed that conjugate formation does not perturb the overall peptide structure. Only 6 exhibited antiproliferative activity in human tumor cells (IC 50 = 63 ± 2 μ in MCF-7 cells and IC 50 = 26 ± 3 μ in DU-145 cells) with active participation of somatostatin receptors in cellular uptake. Similar cytotoxic activity was found in a normal cell line (IC 50 = 45 ± 2.6 μ in CHO cells), which can be attributed to a similar level of expression of somatostatin subtype-2 receptor. These studies provide new insights into the effect of receptor-binding peptide conjugation on the activity of metal-based anticancer drugs, and demonstrate the potential of such hybrid compounds to target tumor cells specifically. © 2012 American Chemical Society
Polarization Transfer in the 4He(e,e'p)3H Reaction at Q^2 = 0.8 and 1.3 (GeV/c)^2
Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H
reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision.
The polarization-transfer coefficients are found to differ from those of the
1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation,
and favoring either the inclusion of medium-modified proton form factors
predicted by the quark-meson coupling model or a spin-dependent charge-exchange
final-state interaction. For the first time, the polarization-transfer ratio is
studied as a function of the virtuality of the proton
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