257 research outputs found
Three-body analysis of incoherent -photoproduction on the deuteron in the near threshold region
A three-body calculation of the reaction in the energy
region from threshold up to 30 MeV above has been performed. The primary goal
of this study is to assess the importance of the three-body aspects in the
hadronic sector of this reaction. Results are presented for the -meson
spectrum as well as for the total cross section. The three-body results differ
significantly from those predicted by a simple rescattering model in which only
first-order - and -interactions in the final state are considered.
The major features of the experimental data are well reproduced although right
at threshold the rather large total cross section could not be explained.Comment: 6 pages revtex including 3 figure
Rescattering effects in coherent eta-photoproduction on the deuteron
Rescattering effects in coherent eta photoproduction on the deuteron are
studied in the region of the S_11(1535) resonance. For the elementary reaction
mechanism on the nucleon, an effective isobar model with inclusion of
resonances and Born terms is used. The resonance parameters are fixed by
considering pion photoproduction only. For the coherent eta production on the
deuteron we have considered the impulse approximation taking into account the
P_11(1440), D_13(1520), and S_11(1535) resonances, rescattering, and meson
exchange currents. For the rescattering mechanism a coupled channel model
including the dominant S_11(1535) resonance is used.Comment: 8 pages LaTeX using revtex, 6 postscript figures (using epsf.sty
Do we understand the interaction from the near threshold photoproduction on the deuteron?
The effects of final state interaction in incoherent photoproduction
on deuteron are studied within a three-body approach including a realistic
potential. The results are compared with available data, and differences with
other theoretical predictions are analyzed. The role of the
interaction and the possibility of extracting the scattering
parameters from this reaction are discussed.Comment: 9 pages revtex including 6 ps-figure
eta-photoproduction in the resonance energy region
The production in the nucleon resonance energy region is studied
within the unitary coupled-channels effective Lagrangian approach of the
Giessen model. We demonstrate that the second peak recently observed in the
cross section of photoproduction on the neutron at =1.66 GeV
can be explained in terms of coupled-channel effects due to and
resonance excitations
The -system at low energy within a three-body approach
The role of the -interaction is studied in the low energy regime in
-deuteron reactions as well as in coherent and incoherent
-photoproduction on the deuteron using a three-body model with separable
two-body interactions. The three-body approach turns out to be quite essential
in the most important lowest partial wave. Results are presented for
differential and total cross sections as well as for the -meson spectrum.
They differ significantly from those predicted by a simple rescattering model
in which only first-order - and -interactions in the final state
are considered. The major features of the experimental data of
-photoproduction in the near-threshold region are well reproduced.Comment: 20 pages revtex including 10 figures, revised version accepted for
publication in Nucl. Phys.
The Complexity of Computing Minimal Unidirectional Covering Sets
Given a binary dominance relation on a set of alternatives, a common thread
in the social sciences is to identify subsets of alternatives that satisfy
certain notions of stability. Examples can be found in areas as diverse as
voting theory, game theory, and argumentation theory. Brandt and Fischer [BF08]
proved that it is NP-hard to decide whether an alternative is contained in some
inclusion-minimal upward or downward covering set. For both problems, we raise
this lower bound to the Theta_{2}^{p} level of the polynomial hierarchy and
provide a Sigma_{2}^{p} upper bound. Relatedly, we show that a variety of other
natural problems regarding minimal or minimum-size covering sets are hard or
complete for either of NP, coNP, and Theta_{2}^{p}. An important consequence of
our results is that neither minimal upward nor minimal downward covering sets
(even when guaranteed to exist) can be computed in polynomial time unless P=NP.
This sharply contrasts with Brandt and Fischer's result that minimal
bidirectional covering sets (i.e., sets that are both minimal upward and
minimal downward covering sets) are polynomial-time computable.Comment: 27 pages, 7 figure
Considerations on rescattering effects for threshold photo- and electro-production of on deuteron
We show that for the S-state -production in processes and the rescattering effects due to the
transition: (or are cancelled
out due to the Pauli principle. The large values for these effects predicted in
the past may result from the fact that the spin structure of the corresponding
matrix element and the necessary antisymmetrization induced by the presence of
identical protons (or neutrons) in the intermediate state was not taken into
account accurately. One of the important consequences of these considerations
is that photo- and electro-production on deuteron near threshold can
bring direct information about elementary neutron amplitudes.Comment: Add a new sectio
Photoproduction of mesons from nuclei - In-medium properties of hadrons
Recent experimental results for the in-medium properties of hadrons obtained
with photoproduction of mesons from nuclei are discussed. The experiments were
done with the TAPS detector at the tagged photon beam of the MAMI accelerator
in Mainz. Measured were the final states , , , and
for C, Ca, Nb, and Pb up to the
second resonance region. The results were used for an investigation of the
in-medium properties of the P(1232), the P(1440), the
D(1520), and the S(1535) resonances. It was found that the cross
sections can be spilt into a component which originates from the low density
surface region of the nuclei and a component which scales like the nuclear
volume. The energy dependence of the surface component is strikingly similar to
the deuteron, it shows a clear signal for the second resonance peak. The volume
component is lacking this peak and shows an enhancement at intermediate
energies. Furthermore the measurement of coherent -photoproduction and
the final state from He is discussed in the context of the search
for -mesic nuclei.Comment: Proceedings of International School of Nuclear Physics, 26th Course,
Lepton Scattering and the Structure of Hadrons and Nuclei, Erice-Sicily,
Italy 16. - 24. September 2004, to be published in Prog. Part. Nucl. Phy
Clonal karyotype evolution involving ring chromosome 1 with myelodysplastic syndrome subtype RAEB-t progressing into acute leukemia
s Karyotypic evolution is a well-known phenomenon in patients with malignant hernatological disorders during disease progression. We describe a 50-year-old male patient who had originally presented with pancytopenia in October 1992. The diagnosis of a myelodysplastic syndrome (MDS) FAB subtype RAEB-t was established in April 1993 by histological bone marrow (BM) examination, and therapy with low-dose cytosine arabinoside was initiated. In a phase of partial hernatological remission, cytogenetic assessment in August 1993 revealed a ring chromosome 1 in 13 of 21 metaphases beside BM cells with normal karyotypes {[}46,XY,r(1)(p35q31)/46,XY]. One month later, the patient progressed to an acute myeloid leukemia (AML), subtype M4 with 40% BM blasts and cytogenetic examination showed clonal evolution by the appearance of additional numerical aberrations in addition to the ring chromosome{[}46,XY,r(1),+8,-21/45,XY,r(1),+8,-21,-22/46, XY]. Intensive chemotherapy and radiotherapy was applied to induce remission in preparation for allogeneic bone marrow transplantation (BMT) from the patient's HLA-compatible son. After BMT, complete remission was clinically, hematologically and cytogenetically (normal male karyotype) confirmed. A complete hematopoietic chimerism was demonstrated. A relapse in January 1997 was successfully treated using donor lymphocyte infusion and donor peripheral blood stem cells (PB-SC) in combination with GM-CSF as immunostimulating agent in April 1997, and the patient's clinical condition remained stable as of January 2005. This is an interesting case of a patient with AML secondary to MDS. With the ring chromosome 1 we also describe a rare cytogenetic abnormality that predicted the poor prognosis of the patient, but the patient could be cured by adoptive immunotherapy and the application of donor's PB-SC. This case confirms the value of cytogenetic analysis in characterizing the malignant clone in hernatological neoplasias, the importance of controlling the quality of an induced remission and of the detection of a progress of the disease. Copyright (c) 2006 S. Karger AG, Basel
Light Hadron Masses from Lattice QCD
This article reviews lattice QCD results for the light hadron spectrum. We
give an overview of different formulations of lattice QCD, with discussions on
the fermion doubling problem and improvement programs. We summarize recent
developments in algorithms and analysis techniques, that render calculations
with light, dynamical quarks feasible on present day computer resources.
Finally, we summarize spectrum results for ground state hadrons and resonances
using various actions.Comment: 53 pages, 24 figures, one table; Rev.Mod.Phys. (published version);
v2: corrected typ
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