612 research outputs found
A Search for Candidate Light Echoes: Photometry of Supernova Environments
Supernova (SN) light echoes could be a powerful tool for determining
distances to galaxies geometrically, Sparks 1994. In this paper we present CCD
photometry of the environments of 64 historical supernovae, the first results
of a program designed to search for light echoes from these SNe. We commonly
find patches of optical emission at, or close to, the sites of the supernovae.
The color distribution of these patches is broad, and generally consistent with
stellar population colors, possibly with some reddening. However there are in
addition patches with both unusually red and unusually blue colors. We expect
light echoes to be blue, and while none of the objects are quite as blue in V-R
as the known light echo of SN1991T, there are features that are unusually blue
and we identify these as candidate light echoes for follow-on observations.Comment: 13 pages, Latex, 5 Postscript Tables, 42 Postscript figures, accepted
for publication in the A&AS. Figures 1 through 36 are available at the web
address: http://www.stsci.edu/~boffi
Application of crossflow ultrafiltration for scaling up the purification of a recombinant ferritin
Ferritin proteins are taking center stage as smart nanocarriers for drug delivery due to their hollow cage-like structures and their unique 24-meric assembly. Among all ferritins, the chimeric Archaeoglobus ferritin (HumFt) is able assemble/disassemble varying the ionic strength of the medium while recognizing human TfR1 receptor overexpressed in cancer cells. In this paper we present a highly efficient, large scale purification protocol mainly based on crossflow ultrafiltration, starting from fermented bacterial paste. This procedure allows one to obtain about 2 g of purified protein starting from 100 g of fermented bacterial paste. The current procedure can easily remove contaminant proteins as well as DNA molecules in the absence of expensive and time consuming chromatographic steps
Nucleon magnetic moments in an extended chiral constituent quark model
We present results for the nucleon magnetic moments in the context of an
extended chiral constituent quark model based on the mechanism of the Goldstone
boson exchange, as suggested by the spontaneous breaking of chiral symmetry in
QCD. The electromagnetic charge-current operator is consistently deduced from
the model Hamiltonian, which includes all force components for the
pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation
is satisfied for each piece of the interaction, avoiding the introduction of
any further parameter. A good agreement with experimental values is found. The
role of isoscalar two-body operators, not constrained by the continuity
equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B,
elsart.sty/elsart12.sty include
On the NN-final-state-interaction in the reaction
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in the reaction has been investigated.
Results for various kinematics are discussed. In general, the effect of
NN-FSI depends on kinematics and the chosen final state in the excitation
spectrum of .Comment: 12 pages Revtex including 4 postscript figure
NN correlations and final-state interactions in (e,e'NN) reactions
After a brief overview of relevant studies on one-nucleon knockout showing
the importance of quantitatively understanding the origin of the quenched
spectroscopic factors extracted from data, attention is focussed on two-nucleon
emission as a suitable tool to investigate nucleon-nucleon correlations inside
complex nuclei. In particular, direct (e,epp) and (e,epn) reactions are
discussed, and the role of final-state interactions is studied. The influence
of the mutual interaction between the two outgoing nucleons is shown to depend
on the kinematics and on the type of the considered reaction.Comment: 13 pages, 4 figures. Proceedings of 2nd Int. Conf. on Nuclear and
Particle Physics with CEBAF at Jefferson Lab, Dubrovnik, 26-31 May 2003, to
be published on Fyzika
On the treatment of the -contribution in electromagnetic -knockout reactions
The treatment of the -current and its contribution in the exclusive
OC and OC knockout reactions are
investigated in combination with the effects of correlations.
Different parametrizations of the effective -current and different
treatments of correlations in the two-nucleon overlap function are considered.
The results are presented and discussed for a suitable choice of kinematics. It
is found that the investigation of different mutually supplementing kinematics
is necessary to resolve the uncertainties in the theoretical ingredients and
extract clear and unambiguous information on correlations.Comment: 15 pages, 9 figures, EPJA styl
The NN-final-state-interaction in two-nucleon-knockout reactions
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from has
been investigated perturbatively. It turns out that the effect of NN-FSI
depends on the kinematics and on the type of reaction considered. In the
kinematics studied so far, the effect is larger in pp- than in pn-knockout and
in electron induced than in photoinduced reactions.Comment: 10 pages including 9 postscript figures, contribution to the 6th
workshop on "Electromagnetically Induced Two-Hadron Emission", Pavia,
September 24-27, 200
Extraction of the Compton Form Factor H from DVCS measurements at Jefferson Lab
In the framework of Generalised Parton Distributions, we study the
helicity-dependent and independent cross sections measured in Hall A and the
beam spin asymmetries measured in Hall B at Jefferson Laboratory. We perform a
global fit of these data and fits on each kinematical bin. We extract the real
and imaginary parts of the Compton Form Factor under the main
hypothesis of dominance of the Generalised Parton Distribution and twist 2
accuracy. We discuss our results and compare to previous extractions as well as
to the VGG model. We pay extra attention to the estimation of errors on the
extraction of .Comment: 24 pages, 8 figure
Electromagnetic proton-neutron knockout off 16O: new achievements in theory
Results for the cross sections of the exclusive 16O(e,e'pn)14N and
16O(gamma,pn)14N knockout reactions are presented and discussed in different
kinematics. In comparison with earlier work, a complete treatment of the
center-of-mass (CM) effects in the nuclear one-body current is considered in
connection with the problem of the lack of orthogonality between initial bound
and final scattering states. The effects due to CM and orthogonalization are
investigated in combination with different treatments of correlations in the
two-nucleon overlap function and for different parametrizations of the two-body
currents. The CM effects lead in super-parallel kinematics to a dramatic
increase of the 16O(e,e'pn) cross section to the 1_2^+ excited state (3.95 MeV)
of 14N. In all the situations considered the results are very sensitive to the
treatment of correlations. A crucial role is played by tensor correlations, but
also the contribution of long-range correlations is important.Comment: 13 pages, 10 figure
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