116 research outputs found
Antihyperon potentials in nuclei via exclusive antiproton-nucleus reactions
The exclusive production of hyperon-antihyperon pairs close to their
production threshold in antiproton - nucleus collisions offers a unique and
hitherto unexplored opportunity to elucidate the behaviour of antihyperons in
nuclei. For the first time we analyse these reactions in a microscopic
transport model using the the Gie\ss en Boltzmann-Uehling-Uhlenbeck transport
model. The calculation take the delicate interplay between the strong
absorption of antihyperons, their rescattering and refraction at the nuclear
surface as well as the Fermi motion of the struck nucleon into account. We find
a substantial sensitivity of transverse momentum correlations of coincident
-pairs to the assumed depth of the
-potential. Because of the high cross section for this
process and the simplicity of the experimental method our results are highly
relevant for future activities at the international Facility for Antiproton and
Ion Research (FAIR)
Optimal Cerebral Perfusion Pressure During Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage
OBJECTIVES: The recommendation of induced hypertension for delayed cerebral ischemia treatment after aneurysmal subarachnoid hemorrhage has been challenged recently and ideal pressure targets are missing. A new concept advocates an individual cerebral perfusion pressure where cerebral autoregulation functions best to ensure optimal global perfusion. We characterized optimal cerebral perfusion pressure at time of delayed cerebral ischemia and tested the conformity of induced hypertension with this target value. DESIGN: Retrospective analysis of prospectively collected data. SETTING: University hospital neurocritical care unit. PATIENTS: Thirty-nine aneurysmal subarachnoid hemorrhage patients with invasive neuromonitoring (20 with delayed cerebral ischemia, 19 without delayed cerebral ischemia). INTERVENTIONS: Induced hypertension greater than 180 mm Hg systolic blood pressure. MEASUREMENTS AND MAIN RESULTS: Changepoint analysis was used to calculate significant changes in cerebral perfusion pressure, optimal cerebral perfusion pressure, and the difference of cerebral perfusion pressure and optimal cerebral perfusion pressure 48 hours before delayed cerebral ischemia diagnosis. Optimal cerebral perfusion pressure increased 30 hours before the onset of delayed cerebral ischemia from 82.8 +/- 12.5 to 86.3 +/- 11.4 mm Hg (p < 0.05). Three hours before delayed cerebral ischemia, a changepoint was also found in the difference of cerebral perfusion pressure and optimal cerebral perfusion pressure (decrease from -0.2 +/- 11.2 to -7.7 +/- 7.6 mm Hg; p < 0.05) with a corresponding increase in pressure reactivity index (0.09 +/- 0.33 to 0.19 +/- 0.37; p < 0.05). Cerebral perfusion pressure at time of delayed cerebral ischemia was lower than in patients without delayed cerebral ischemia in a comparable time frame (cerebral perfusion pressure delayed cerebral ischemia 81.4 +/- 8.3 mm Hg, no delayed cerebral ischemia 90.4 +/- 10.5 mm Hg; p < 0.05). Inducing hypertension resulted in a cerebral perfusion pressure above optimal cerebral perfusion pressure (+12.4 +/- 8.3 mm Hg; p < 0.0001). Treatment response (improvement of delayed cerebral ischemia: induced hypertension(+) [n = 15] or progression of delayed cerebral ischemia: induced hypertension(-) [n = 5]) did not correlate to either absolute values of cerebral perfusion pressure or optimal cerebral perfusion pressure, nor the resulting difference (cerebral perfusion pressure [p = 0.69]; optimal cerebral perfusion pressure [p = 0.97]; and the difference of cerebral perfusion pressure and optimal cerebral perfusion pressure [p = 0.51]). CONCLUSIONS: At the time of delayed cerebral ischemia occurrence, there is a significant discrepancy between cerebral perfusion pressure and optimal cerebral perfusion pressure with worsening of autoregulation, implying inadequate but identifiable individual perfusion. Standardized induction of hypertension resulted in cerebral perfusion pressures that exceeded individual optimal cerebral perfusion pressure in delayed cerebral ischemia patients. The potential benefit of individual blood pressure management guided by autoregulation-based optimal cerebral perfusion pressure should be explored in future intervention studies
High accuracy synchrotron radiation interferometry with relativistic electrons
A high-precision hypernuclear experiment has been performed at the Mainz
Microtron (MAMI) to determine the hypertriton {\Lambda} binding energy via
decay-pion spectroscopy. A key element of this measurement is an accurate
calibration of the magnetic spectrometers with the MAMI beam. For such an
absolute calibration with small statistical and systematic uncertainties the
undulator light interference method will be applied. In this contribution the
basic principle of this method is discussed and the analysis status of the
measured synchrotron radiation spectra is presentedComment: The 13th Biennial Conference on Classical and Quantum Relativistic
Dynamics of Particles and Fields (IARD22
Feasibility studies of time-like proton electromagnetic form factors at PANDA at FAIR
Simulation results for future measurements of electromagnetic proton form
factors at \PANDA (FAIR) within the PandaRoot software framework are reported.
The statistical precision with which the proton form factors can be determined
is estimated. The signal channel is studied on the basis
of two different but consistent procedures. The suppression of the main
background channel, , is studied.
Furthermore, the background versus signal efficiency, statistical and
systematical uncertainties on the extracted proton form factors are evaluated
using two different procedures. The results are consistent with those of a
previous simulation study using an older, simplified framework. However, a
slightly better precision is achieved in the PandaRoot study in a large range
of momentum transfer, assuming the nominal beam conditions and detector
performance
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