5,127 research outputs found
Konventionalisierungsfalle? was tun?
Der Öko-Landbau schrieb in den letzten Jahren Erfolgsgeschichte: Der Biosektor und seine Akteure scheinen in ihren Strukturen, Funktions- und Handlungsweisen der konventionellen Landwirtschaft immer ähnlicher zu werden. Während die einen Werte- und Sinnverlust beklagen, begrüßen die anderen Wachstum und öffentliche Anerkennung. Maßnahmen zur Überwindung dieses Spannungsfeldes wurden im März 2005 auf der Wissenschaftstagung zum Ökologischen Landbau im Rahmen eines Symposiums erörtert
Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams
The well-known Bragg-Kleeman rule RCSDA = A dot E0p has become a pioneer work
in radiation physics of charged particles and is still a useful tool to
estimate the range RCSDA of approximately monoenergetic protons with initial
energy E0 in a homogeneous medium. The rule is based on the
continuous-slowing-down-approximation (CSDA). It results from a generalized
(nonrelativistic) Langevin equation and a modification of the phenomenological
friction term. The complete integration of this equation provides information
about the residual energy E(z) and dE(z)/dz at each position z (0 <= z <=
RCSDA). A relativistic extension of the generalized Langevin equation yields
the formula RCSDA = A dot (E0 +E02/2M dot c2)p. The initial energy of
therapeutic protons satisfies E0 << 2M dot c2 (M dot c2 = 938.276 MeV), which
enables us to consider the relativistic contributions as correction terms.
Besides this phenomenological starting-point, a complete integration of the
Bethe-Bloch equation (BBE) is developed, which also provides the determination
of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE
itself (i.e., without further empirical parameters like modification of
friction). The results obtained in the context of the aforementioned methods
are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is
also used with regard to further topics such as lateral scatter, nuclear
interactions, and buildup effects. In the framework of the CSDA, the energy
transfer from protons to environmental atomic electrons does not account for
local fluctuations.Comment: 97 pages review pape
Comparison of the properties of two fossil groups of galaxies with the normal group NGC 6034 based on multiband imaging and optical spectroscopy
We collected multiband imaging and spectroscopy for two fossil groups (RX
J1119.7+2126 and 1RXS J235814.4+150524) and one normal group (NGC 6034). We
computed photometric redshifts in the central zones of each group, combining
previous data with the SDSS five-band data. For each group we investigated the
red sequence (RS) of the color-magnitude relation and computed the luminosity
functions, stellar population ages and distributions of the group members.
Spectroscopy allowed us to investigate the large-scale surroundings of these
groups and the substructure levels in 1RXS J235814.4+150524 and NGC 6034. The
large-scale environment of 1RXS J235814.4+150524 is poor, though its galaxy
density map shows a clear signature of the surrounding cosmic web. RX
J1119.7+2126 appears to be very isolated, while the cosmic environment of NGC
6034 is very rich. At the group scale, 1RXS J235814.4+150524 shows no
substructure. Galaxies with recent stellar populations seem preferentially
located in the group outskirts. A RS is discernable for all three groups in a
color-magnitude diagram. The luminosity functions based on photometric redshift
selection and on statistical background subtraction have comparable shapes, and
agree with the few points obtained from spectroscopic redshifts. These
luminosity functions show the expected dip between first and second brightest
galaxies for the fossil groups only. Their shape is also regular and relatively
flat at faint magnitudes down to the completeness level for RX J1119.7+2126 and
NGC 6034, while there is a clear lack of faint galaxies for 1RXS
J235814.4+150524. RX J1119.7+2126 is definitely classified as a fossil group;
1RXS J235814.4+150524 also has properties very close to those of a fossil
group, while we confirm that NGC 6034 is a normal group.Comment: Accepted in A&A, english-improved, 5 jpeg figures, and shortened
abstrac
Polarization transfer in 4He(\vec{e},e'\vec{p}) and 16O(\vec{e},e'\vec{p}) in a relativistic Glauber model
Polarization-transfer components for 4He(\vec{e},e'\vec{p})3H and
16O(\vec{e},e'\vec{p})15N are computed within the relativistic
multiple-scattering Glauber approximation (RMSGA). The RMSGA framework adopts
relativistic single-particle wave functions and electron-nucleon couplings. The
predictions closely match those of a relativistic plane-wave model indicating
the smallness of the final-state interactions for polarization-transfer
components. Also short-range correlations play a modest role for the studied
observables, as long as small proton missing-momenta are probed in
quasi-elastic kinematics. The predictions with free and various
parameterizations for the medium-modified electromagnetic form factors are
compared to the world data.Comment: 24 pages, 11 figure
Single fraction radiosurgery using Rapid Arc for treatment of intracranial targets
<p>Abstract</p> <p>Background</p> <p>Stereotactic-Radio-Surgery (SRS) using Conformal-Arc-Therapy (CAT) is a well established irradiation technique for treatment of intracranial targets. Although small safety margins are required because of very high accuracy of patient positioning and exact online localisation, there are still disadvantages like long treatment time, high number of monitor units (MU) and covering of noncircular targets. This planning study analysed whether Rapid Arc (RA) with stereotactic localisation for single-fraction SRS can solve these problems.</p> <p>Methods</p> <p>Ten consecutive patients were treated with Linac-based SRS. Eight patients had one or more brain metastases. The other patients presented a symptomatic vestibularis schwannoma and an atypic meningeoma. For all patients, two plans (CAT/RA) were calculated and analysed.</p> <p>Results</p> <p>Conformity was higher for RA with additional larger low-dose areas. Furthermore, RA reduced the number of MU and the treatment time for all patients. Dose to organs at risk were equal or slightly higher using RA in comparison to CAT.</p> <p>Conclusions</p> <p>RA provides a new alternative for single-fraction SRS irradiation combining advantages of short treatment time with lower number of MU and better conformity in addition to accuracy of stereotactic localisation in selected cases with uncomplicated clinical realization.</p
Influenza nucleoprotein delivered with aluminium salts protects mice from an influenza virus that expresses an altered nucleoprotein sequence
Influenza virus poses a difficult challenge for protective immunity. This virus is adept at altering its surface proteins, the proteins that are the targets of neutralizing antibody. Consequently, each year a new vaccine must be developed to combat the current recirculating strains. A universal influenza vaccine that primes specific memory cells that recognise conserved parts of the virus could prove to be effective against both annual influenza variants and newly emergent potentially pandemic strains. Such a vaccine will have to contain a safe and effective adjuvant that can be used in individuals of all ages. We examine protection from viral challenge in mice vaccinated with the nucleoprotein from the PR8 strain of influenza A, a protein that is highly conserved across viral subtypes. Vaccination with nucleoprotein delivered with a universally used and safe adjuvant, composed of insoluble aluminium salts, provides protection against viruses that either express the same or an altered version of nucleoprotein. This protection correlated with the presence of nucleoprotein specific CD8 T cells in the lungs of infected animals at early time points after infection. In contrast, immunization with NP delivered with alum and the detoxified LPS adjuvant, monophosphoryl lipid A, provided some protection to the homologous viral strain but no protection against infection by influenza expressing a variant nucleoprotein. Together, these data point towards a vaccine solution for all influenza A subtypes
The Quasielastic 3He(e,e'p)d Reaction at Q^2 = 1.5 GeV^2 for Recoil Momenta up to 1 GeV/c
We have studied the quasielastic 3He(e,e'p)d reaction in perpendicular
coplanar kinematics, with the energy and momentum transferred by the electron
fixed at 840 MeV and 1502 MeV/c, respectively. The 3He(e,e'p)d cross section
was measured for missing momenta up to 1000 MeV/c, while the A_TL asymmetry was
extracted for missing momenta up to 660 MeV/c. For missing momenta up to 150
MeV/c, the measured cross section is described well by calculations that use a
variational ground-state wave function of the 3He nucleus derived from a
potential that includes three-body forces. For missing momenta from 150 to 750
MeV/c, strong final-state interaction effects are observed. Near 1000 MeV/c,
the experimental cross section is more than an order of magnitude larger than
predicted by available theories. The A_TL asymmetry displays characteristic
features of broken factorization, and is described reasonably well by available
models.Comment: 5 pages, 3 figures, submitted to Physical Review Letters, v3: changed
conten
Measurement of the 3He(e,e'p)pn reaction at high missing energies and momenta
Results of the Jefferson Lab Hall A quasielastic 3He(e,e'p)pn measurements
are presented. These measurements were performed at fixed transferred momentum
and energy, q = 1502 MeV/c and omega = 840 MeV, respectively, for missing
momenta p_m up to 1 GeV/c and missing energies in the continuum region, up to
pion threshold; this kinematic coverage is much more extensive than that of any
previous experiment. The cross section data are presented along with the
effective momentum density distribution and compared to theoretical models.Comment: 5 pages, 3 figures, updated to reflect published paper: minor text
changes from previous version along with updated and added reference
The reaction dynamics of the 16O(e,e'p) cross section at high missing energies
We measured the cross section and response functions (R_L, R_T, and R_LT) for
the 16O(e,e'p) reaction in quasielastic kinematics for missing energies 25 <=
E_miss <= 120 MeV at various missing momenta P_miss <= 340 MeV/c. For 25 <
E_miss < 50 MeV and P_miss \approx 60 MeV/c, the reaction is dominated by
single-nucleon knockout from the 1s1/2-state. At larger P_miss, the
single-particle aspects are increasingly masked by more complicated processes.
For E_miss > 60 MeV and P_miss > 200 MeV/c, the cross section is relatively
constant. Calculations which include contributions from pion exchange currents,
isobar currents and short-range correlations account for the shape and the
transversity but only for half of the magnitude of the measured cross section.Comment: 6 pages, 4 figures, submitted to Phys Rev Lett, formatting error
fixe
Recoil Polarization Measurements for Neutral Pion Electroproduction at Q^2=1 (GeV/c)^2 Near the Delta Resonance
We measured angular distributions of differential cross section, beam
analyzing power, and recoil polarization for neutral pion electroproduction at
Q^2 = 1.0 (GeV/c)^2 in 10 bins of W across the Delta resonance. A total of 16
independent response functions were extracted, of which 12 were observed for
the first time. Comparisons with recent model calculations show that response
functions governed by real parts of interference products are determined
relatively well near 1.232 GeV, but variations among models is large for
response functions governed by imaginary parts and for both increases rapidly
with W. We performed a nearly model-independent multipole analysis that adjusts
complex multipoles with high partial waves constrained by baseline models.
Parabolic fits to the W dependence of the multipole analysis around the Delta
mass gives values for SMR = (-6.61 +/- 0.18)% and EMR = (-2.87 +/- 0.19)% that
are distinctly larger than those from Legendre analysis of the same data.
Similarly, the multipole analysis gives Re(S0+/M1+) = (+7.1 +/- 0.8)% at
W=1.232 GeV, consistent with recent models, while the traditional Legendre
analysis gives the opposite sign because its truncation errors are quite
severe. Finally, using a unitary isobar model (UIM), we find that excitation of
the Roper resonance is dominantly longitudinal with S1/2 = (0.05 +/- 0.01)
GeV^(-1/2) at Q^2=1. The ReS0+ and ReE0+ multipoles favor pseudovector coupling
over pseudoscalar coupling or a recently proposed mixed-coupling scheme, but
the UIM does not reproduce the imaginary parts of 0+ multipoles well.Comment: 60 pages, 54 figure
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