2,366 research outputs found
Hypernuclear Physics at PANDA
Hypernuclear research will be one of the main topics addressed by the PANDA
experiment at the planned Facility for Anti-proton and Ion Research FAIR at
Darmstadt, Germany. A copious production of Xi-hyperons at a dedicated internal
target in the stored anti-proton beam is expected, which will enable the
high-precision gamma-spectroscopy of double strange systems for the first time.
In addition to the general purpose PANDA setup, the hypernuclear experiments
require an active secondary target of silicon layers and absorber material as
well as high purity germanium (HPGe) crystals as gamma-detectors. The design of
the setup and the development of these detectors is progressing: a first HPGe
crystal with a new electromechanical cooling system was prepared and the
properties of a silicon strip detector as a prototype to be used in the
secondary target were studied. Simultaneously to the hardware projects,
detailed Monte Carlo simulations were performed to predict the yield of
particle stable hypernuclei. With the help of the Monte Carlo a procedure for
Lambda-Lambda-hypernuclei identification by the detection and correlation of
the weak decay pions was developed.Comment: prepared for the International Conference on Exotic Atoms and Related
Topics (EXA2011), Vienna, Sept. 5-9, 201
The double torus as a 2D cosmos: groups, geometry and closed geodesics
The double torus provides a relativistic model for a closed 2D cosmos with
topology of genus 2 and constant negative curvature. Its unfolding into an
octagon extends to an octagonal tessellation of its universal covering, the
hyperbolic space H^2. The tessellation is analysed with tools from hyperbolic
crystallography. Actions on H^2 of groups/subgroups are identified for SU(1,
1), for a hyperbolic Coxeter group acting also on SU(1, 1), and for the
homotopy group \Phi_2 whose extension is normal in the Coxeter group. Closed
geodesics arise from links on H^2 between octagon centres. The direction and
length of the shortest closed geodesics is computed.Comment: Latex, 27 pages, 5 figures (late submission to arxiv.org
Detector developments for the hypernuclear programme at PANDA
The technical design of the PANDA experiment at the future FAIR facility next
to GSI is progressing. At the proposed anti-proton storage ring the
spectroscopy of double Lambda hypernuclei is one of the four main topics which
will be addressed by the Collaboration. The hypernuclear experiments require
(i) a dedicated internal target, (ii) an active secondary target of alternating
silicon and absorber material layers, (iii) high purity germanium (HPGe)
detectors, and (iv) a good particle identification system for low momentum
kaons. All systems need to operate in the presence of a high magnetic field and
a large hadronic background. The status of the detector developments for this
programme is summarized.Comment: Contributed to 2008 IEEE Nuclear Science Symposium, 19-25 October
2008, Dresden, German
Creating pseudo Kondo-resonances by field-induced diffusion of atomic hydrogen
In low temperature scanning tunneling microscopy (STM) experiments a cerium
adatom on Ag(100) possesses two discrete states with significantly different
apparent heights. These atomic switches also exhibit a Kondo-like feature in
spectroscopy experiments. By extensive theoretical simulations we find that
this behavior is due to diffusion of hydrogen from the surface onto the Ce
adatom in the presence of the STM tip field. The cerium adatom possesses
vibrational modes of very low energy (3-4meV) and very high efficiency (> 20%),
which are due to the large changes of Ce-states in the presence of hydrogen.
The atomic vibrations lead to a Kondo-like feature at very low bias voltages.
We predict that the same low-frequency/high-efficiency modes can also be
observed at lanthanum adatoms.Comment: five pages and four figure
Surface embedding, topology and dualization for spin networks
Spin networks are graphs derived from 3nj symbols of angular momentum. The
surface embedding, the topology and dualization of these networks are
considered. Embeddings into compact surfaces include the orientable sphere S^2
and the torus T, and the not orientable projective space P^2 and Klein's bottle
K. Two families of 3nj graphs admit embeddings of minimal genus into S^2 and
P^2. Their dual 2-skeletons are shown to be triangulations of these surfaces.Comment: LaTeX 17 pages, 6 eps figures (late submission to arxiv.org
Kinematic assessment of subject personification of human body models (THUMS)
The goal of this study was to quantify the effect of improving the geometry of a human body model on the accuracy of the predicted kinematics for 4 post-mortem human subject sled tests. Three modifications to the computational human body model THUMS were carried out to evaluate if subject personification can increase the agreement between predicted and measured kinematics of post-mortem human subjects in full frontal and nearside oblique impacts. The modifications consisted of: adjusting the human body model mass to the actual subject mass, morphing it to the actual anthropometry of each subject and finally adjustment of the model initial position to the measured position in selected post-mortem human subject tests. A quantitative assessment of the agreement between predicted and measured response was carried out by means of CORA analysis by comparing the displacement of selected anatomical landmarks (head CoG, T1 and T8 vertebre and H-Point). For all three scenarios, the more similar the human body model was to the anthropometry and posture of the sled tested post-mortem human subject, the more similar the predictions were to the measured responses of the post-mortem human subject, resulting in higher CORA score
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