14,734 research outputs found
Future Spin Physics at JLab; 12 GeV and Beyond
The project to upgrade the CEBAF accelerator at Jefferson Lab to 12 GeV is
presented. Most of the research program supporting that upgrade, will require a
highly polarized beam, as will be illustrated by a few selected examples. To
carry out that research program will require an extensively upgraded
instrumentation in two of the existing experimental halls and the addition of a
fourth hall. The plans for a high-luminosity electron-ion collider are briefly
discussed.Comment: 6 pages; 2 figures; submitted to the Proceedings of SPIN200
Nucleon Electromagnetic Form Factors
A review of data on the nucleon electromagnetic form factors in the
space-like region is presented. Recent results from experiments using polarized
beams and polarized targets or nucleon recoil polarimeters have yielded a
significant improvement on the precision of the data obtained with the
traditional Rosenbluth separation. Future plans for extended measurements are
outlined.Comment: 12 pages, 6 figures, Talk presented at the Bates25 Symposiu
Nucleon Form Factor Experiments and the Pion Cloud
The experimental and theoretical status of elastic electron scattering from
the nucleon is reviewed. A wealth of new data of unprecedented precision,
especially at small values of the momentum transfer, in parallel to new
theoretical insights, has allowed sensitive tests of the influence of the
pionic cloud surrounding the nucleon.Comment: 9 pages; 4 figures; submitted to the Proceedings of the Shape of the
Nucleo
On the origin of the Korteweg-de Vries equation
The Korteweg-de Vries equation has a central place in a model for waves on
shallow water and it is an example of the propagation of weakly dispersive and
weakly nonlinear waves. Its history spans a period of about sixty years,
starting with experiments of Scott Russell in 1834, followed by theoretical
investigations of, among others, Lord Rayleigh and Boussinesq in 1871 and,
finally, Korteweg and De Vries in 1895.
In this essay we compare the work of Boussinesq and Korteweg-de Vries,
stressing essential differences and some interesting connections. Although
there exist a number of articles, reviewing the origin and birth of the
Korteweg-de Vries equations, connections and differences, not generally known,
are reported.Comment: minor corrections; 25 pages, 3 figure
Estimating the birth period of pulsars through GLAST/LAT observations of their wind nebulae
In this paper we show that the high energy -ray flux in the GeV
domain from mature pulsar wind nebulae (PWN) scales as the change in rotational
kinetic energy since birth, rather than the present
day spindown power . This finding holds as long as the
lifetime of inverse Compton emitting electrons exceeds the age of the system.
For a typical electron spectrum, the predicted flux depends
mostly on the pulsar birth period, conversion efficiency of spindown power to
relativistic electrons and distance to the PWN, so that first order estimates
of the birth period can be assessed from {\it GLAST/LAT} observations of PWN.
For this purpose we derive an analytical expression. The associated
(``uncooled'') photon spectral index in the GeV domain is expected to cluster
around , which is bounded at low energies by an intrinsic spectral
break, and at higher energies by a second spectral break where the photon index
steepens to due to radiation losses. Mature PWN are expected to have
expanded to sizes larger than currently known PWN, resulting in relatively low
magnetic energy densities and hence survival of GeV inverse Compton emitting
electrons. Whereas such a PWN may be radio and X-ray quiet in synchrotron
radiation, it may still be detectable as a {\it GLAST/LAT} source as a result
of the relic electrons in the PWN.Comment: 10 pages, no figures. To appear in Astrophysical Journal Letter
The Development of Regulatory Standards for Gene Therapy in the European Union
This note examines the EU\u27s efforts to regulate gene therapy, considering the Union\u27s resolve to establish scientifically, economically, and morally sound parameters acceptable to its varied constituency. This includes discussion of legal and ethical considerations, biotechnology goals in the EU, and EU-wide uniform regulations
Probing the Nature of the Vela X Cocoon
Vela X is a pulsar wind nebula (PWN) associated with the active pulsar
B0833-45 and contained within the Vela supernova remnant (SNR). A collimated
X-ray filament ("cocoon") extends south-southwest from the pulsar to the center
of Vela X. VLA observations uncovered radio emission coincident with the
eastern edge of the cocoon and H.E.S.S. has detected TeV -ray emission
from this region as well. Using XMM-\textit{Newton} archival data, covering the
southern portion of this feature, we analyze the X-ray properties of the
cocoon. The X-ray data are best fit by an absorbed nonequilibrium plasma model
with a powerlaw component. Our analysis of the thermal emission shows enhanced
abundances of O, Ne, and Mg within the cocoon, indicating the presence of
ejecta-rich material from the propagation of the SNR reverse shock, consistent
with Vela X being a disrupted PWN. We investigate the physical processes that
excite the electrons in the PWN to emit in the radio, X-ray and -ray
bands. The radio and non-thermal X-ray emission can be explained by synchrotron
emission. We model the -ray emission by Inverse Compton scattering of
electrons off of cosmic microwave background (CMB) photons. We use a
3-component broken power law to model the synchrotron emission, finding an
intrinsic break in the electron spectrum at keV and a
cooling break at 5.5 keV. This cooling break along with
a magnetic field strength of 5 G indicate that the synchrotron
break occurs at 1 keV.Comment: accepted for publication to ApJ
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