1,214 research outputs found
Fusion-Fission of 16O+197Au at Sub-Barrier Energies
The recent discovery of heavy-ion fusion hindrance at far sub-barrier
energies has focused much attention on both experimental and theoretical
studies of this phenomenon. Most of the experimental evidence comes from
medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system
decays primarily by charged-particle evaporation. In order to study heavier
systems, it is, however, necessary to measure also the fraction of the decay
that goes into fission fragments. In the present work we have, therefore,
measured the fission cross section of 16O+197Au down to unprecedented far
sub-barrier energies using a large position sensitive PPAC placed at backward
angles. The preliminary cross sections will be discussed and compared to
earlier studies at near-barrier energies. No conclusive evidence for
sub-barrier hindrance was found, probably because the measurements were not
extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure
at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5
pages, 4 figure
Associations between Measures of Structural Morphometry and Sensorimotor Performance in Individuals with Nonspecific Low Back Pain
ABSTRACT BACKGROUND AND PURPOSE: To date, most structural brain imaging studies in individuals with nonspecific low back pain have evaluated volumetric changes. These alterations are particularly found in sensorimotor-related areas. Although it is suggested that specific measures, such as cortical surface area and cortical thickness, reflect different underlying neural architectures, the literature regarding these different measures in individuals with nonspecific low back pain is limited. Therefore, the current study was designed to investigate the association between the performance on a sensorimotor task, more specifically the sit-to-stand-to-sit task, and cortical surface area and cortical thickness in individuals with nonspecific low back pain and healthy controls
Direct current control of three magnon scattering processes in spin-valve nanocontacts
We have investigated the generation of spin waves in the free layer of an
extended spin-valve structure with a nano-scaled point contact driven by both
microwave and direct electric current using Brillouin light scattering
microscopy. Simultaneously with the directly excited spin waves, strong
nonlinear effects are observed, namely the generation of eigenmodes with
integer multiple frequencies (2 \emph{f}, 3 \emph{f}, 4 \emph{f}) and modes
with non-integer factors (0.5 \emph{f}, 1.5 \emph{f}) with respect to the
excitation frequency \emph{f}. The origin of these nonlinear modes is traced
back to three magnon scattering processes. The direct current influence on the
generation of the fundamental mode at frequency \emph{f} can be related to the
spin-transfer torque, while the efficiency of three-magnon-scattering processes
is controlled by the Oersted field as an additional effect of the direct
current
Decay modes of 250No
The Fragment Mass Analyzer at the ATLAS facility has been used to
unambiguously identify the mass number associated with different decay modes of
the nobelium isotopes produced via 204Pb(48Ca,xn)(252-x)No reactions.
Isotopically pure (>99.7%) 204Pb targets were used to reduce background from
more favored reactions on heavier lead isotopes. Two spontaneous fission
half-lives (t_1/2 = 3.7+1.1-0.8 us and 43+22-15 us) were deduced from a total
of 158 fission events. Both decays originate from 250No rather than from
neighboring isotopes as previously suggested. The longer activity most likely
corresponds to a K-isomer in this nucleus. No conclusive evidence for an alpha
branch was observed, resulting in upper limits of 2.1% for the shorter lifetime
and 3.4% for the longer activity.Comment: RevTex4, 10 pages, 5 figures, submitted to PR
Measurement of the Beam-Recoil Polarization in Low-Energy Virtual Compton Scattering from the Proton
Double-polarization observables in the reaction have been measured at . The experiment
was performed at the spectrometer setup of the A1 Collaboration using the 855
MeV polarized electron beam provided by the Mainz Microtron (MAMI) and a recoil
proton polarimeter. From the double-polarization observables the structure
function is extracted for the first time, with the value , using the low-energy theorem
for Virtual Compton Sattering. This structure function provides a hitherto
unmeasured linear combination of the generalized polarizabilities of the
proton
Characterizing Interdisciplinarity of Researchers and Research Topics Using Web Search Engines
Researchers' networks have been subject to active modeling and analysis.
Earlier literature mostly focused on citation or co-authorship networks
reconstructed from annotated scientific publication databases, which have
several limitations. Recently, general-purpose web search engines have also
been utilized to collect information about social networks. Here we
reconstructed, using web search engines, a network representing the relatedness
of researchers to their peers as well as to various research topics.
Relatedness between researchers and research topics was characterized by
visibility boost-increase of a researcher's visibility by focusing on a
particular topic. It was observed that researchers who had high visibility
boosts by the same research topic tended to be close to each other in their
network. We calculated correlations between visibility boosts by research
topics and researchers' interdisciplinarity at individual level (diversity of
topics related to the researcher) and at social level (his/her centrality in
the researchers' network). We found that visibility boosts by certain research
topics were positively correlated with researchers' individual-level
interdisciplinarity despite their negative correlations with the general
popularity of researchers. It was also found that visibility boosts by
network-related topics had positive correlations with researchers' social-level
interdisciplinarity. Research topics' correlations with researchers'
individual- and social-level interdisciplinarities were found to be nearly
independent from each other. These findings suggest that the notion of
"interdisciplinarity" of a researcher should be understood as a
multi-dimensional concept that should be evaluated using multiple assessment
means.Comment: 20 pages, 7 figures. Accepted for publication in PLoS On
Hindrance of Heavy-ion Fusion at Extreme Sub-Barrier Energies in Open-shell Colliding Systems
The excitation function for the fusion-evaporation reaction 64Ni+100Mo has
been measured down to a cross-section of ~5 nb. Extensive coupled-channels
calculations have been performed, which cannot reproduce the steep fall-off of
the excitation function at extreme sub-barrier energies. Thus, this system
exhibits a hindrance for fusion, a phenomenon that has been discovered only
recently. In the S-factor representation introduced to quantify the hindrance,
a maximum is observed at E_s=120.6 MeV, which corresponds to 90% of the
reference energy E_s^ref, a value expected from systematics of closed-shell
systems. A systematic analysis of Ni-induced fusion reactions leading to
compound nuclei with mass A=100-200 is presented in order to explore a possible
dependence of the fusion hindrance on nuclear structure.Comment: 10 pages, 9 figures, Submitted to Phys. Rev.
A new measurement of the structure functions and in virtual Compton scattering at 0.33 (GeV/c)
The cross section of the reaction has been measured at
(GeV/c). The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions P_LL}-P_{TT}/epsilon and which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same . This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial -evolution of the generalized polarizabilities and
call for more measurements in the low- region ( 1 (GeV/c)).Comment: 9 pages, 10 figures. EPJA version. slight revisions in the text and
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