9,820 research outputs found
New structures in the proton-antiproton system
In the most recent measurements of the reaction
by the BABAR collaboration, new structures have been found with unknown origin.
We examine a possible relation of the most distinct peak to the recently
observed . Alternatively, we analyse possible explanations due to
the nucleon and thresholds. The latter
could explain a periodicity found in the data
Theoretical Constraints and Systematic Effects in the Determination of the Proton Form Factors
We calculate the two-photon exchange corrections to electron-proton
scattering with nucleon and intermediate states. The results show a
dependence on the elastic nucleon and nucleon--transition form factors
used as input which leads to significant changes compared to previous
calculations. We discuss the relevance of these corrections and apply them to
the most recent and precise data set and world data from electron-proton
scattering. Using this, we show how the form factor extraction from these data
is influenced by the subsequent inclusion of physical constraints. The
determination of the proton charge radius from scattering data is shown to be
dominated by the enforcement of a realistic spectral function. Additionally,
the third Zemach moment from the resulting form factors is calculated. The
obtained radius and Zemach moment are shown to be consistent with Lamb shift
measurements in muonic hydrogen.Comment: minor changes, added references, version to appear in PR
Josephson Junctions defined by a Nano-Plough
We define superconducting constrictions by ploughing a deposited Aluminum
film with a scanning probe microscope. The microscope tip is modified by
electron beam deposition to form a nano-plough of diamond-like hardness, what
allows the definition of highly transparent Josephson junctions. Additionally a
dc-SQUID is fabricated to verify appropriate functioning of the junctions. The
devices are easily integrated in mesoscopic devices as local radiation sources
and can be used as tunable on-chip millimeter wave sources
Impact of strong disorder on the static magnetic properties of the spin-chain compound BaCu2SiGeO7
The disordered quasi-1D magnet BaCu2SiGeO7 is considered as one of the best
physical realizations of the random Heisenberg chain model, which features an
irregular distribution of the exchange parameters and whose ground state is
predicted to be the scarcely investigated random-singlet state (RSS). Based on
extensive 29Si NMR and magnetization studies of BaCu2SiGeO7, combined with
numerical Quantum Monte Carlo simulations, we obtain remarkable quantitative
agreement with theoretical predictions of the random Heisenberg chain model and
strong indications for the formation of a random-singlet state at low
temperatures in this compound. As a local probe, NMR is a well-adapted
technique for studying the magnetism of disordered systems. In this case it
also reveals an additional local transverse staggered field (LTSF), which
affects the low-temperature properties of the RSS. The proposed model
Hamiltonian satisfactorily accounts for the temperature dependence of the NMR
line shapes.Comment: 10 pages, 7 figure
A feasibility study of hand kinematics for EVA analysis using magnetic resonance imaging
A new method of analyzing the kinematics of joint motion is developed. Magnetic Resonance Imaging (MRI) offers several distinct advantages. Past methods of studying anatomic joint motion have usually centered on four approaches. These methods are x-ray projection, goniometric linkage analysis, sonic digitization, and landmark measurement of photogrammetry. Of these four, only x-ray is applicable for in vivo studies. The remaining three methods utilize other types of projections of inter-joint measurements, which can cause various types of error. MRI offers accuracy in measurement due to its tomographic nature (as opposed to projection) without the problems associated with x-ray dosage. Once the data acquisition of MR images was complete, the images were processed using a 3D volume rendering workstation. The metacarpalphalangeal (MCP) joint of the left index finger was selected and reconstructed into a three-dimensional graphic display. From the reconstructed volumetric images, measurements of the angles of movement of the applicable bones were obtained and processed by analyzing the screw motion of the MCP joint. Landmark positions were chosen at distinctive locations of the joint at fixed image threshold intensity levels to ensure repeatability. The primarily two dimensional planar motion of this joint was then studied using a method of constructing coordinate systems using three (or more) points. A transformation matrix based on a world coordinate system described the location and orientation of a local target coordinate system. Future research involving volume rendering of MRI data focusing on the internal kinematics of the hand's individual ligaments, cartilage, tendons, etc. will follow. Its findings will show the applicability of MRI to joint kinematics for gaining further knowledge of the hand-glove (power assisted) design for extravehicular activity (EVA)
Ricci Collineations of the Bianchi Type II, VIII, and IX Space-times
Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX
space-times, associated with the vector fields of the form (i) one component of
is different from zero and (ii) two components of are
different from zero, for , are presented. In subcase (i.b), which
is , some known solutions are found, and in subcase
(i.d), which is , choosing ,
the Bianchi type II, VIII, and IX space-times is reduced to the
Robertson-Walker metric.Comment: 12 Pages, LaTeX, 1 Table, no figure
Mott-Hubbard exciton in the optical conductivity of YTiO3 and SmTiO3
In the Mott-Hubbard insulators YTiO3 and SmTiO3 we study optical excitations
from the lower to the upper Hubbard band, d^1d^1 -> d^0d^2. The multi-peak
structure observed in the optical conductivity reflects the multiplet structure
of the upper Hubbard band in a multi-orbital system. Absorption bands at 2.55
and 4.15 eV in the ferromagnet YTiO3 correspond to final states with a triplet
d^2 configuration, whereas a peak at 3.7 eV in the antiferromagnet SmTiO3 is
attributed to a singlet d^2 final state. A strongly temperature-dependent peak
at 1.95 eV in YTiO3 and 1.8 eV in SmTiO3 is interpreted in terms of a Hubbard
exciton, i.e., a charge-neutral (quasi-)bound state of a hole in the lower
Hubbard band and a double occupancy in the upper one. The binding to such a
Hubbard exciton may arise both due to Coulomb attraction between
nearest-neighbor sites and due to a lowering of the kinetic energy in a system
with magnetic and/or orbital correlations. Furthermore, we observe anomalies of
the spectral weight in the vicinity of the magnetic ordering transitions, both
in YTiO3 and SmTiO3. In the G-type antiferromagnet SmTiO3, the sign of the
change of the spectral weight at T_N depends on the polarization. This
demonstrates that the temperature dependence of the spectral weight is not
dominated by the spin-spin correlations, but rather reflects small changes of
the orbital occupation.Comment: Strongly extended version; new data of SmTiO3 included; detailed
discussion of temperature dependence include
Direct control of the tunnel splitting in a one-electron double quantum dot
Quasi-static transport measurements are employed on a laterally defined
tunnel-coupled double quantum dot. A nearby quantum point contact allows us to
track the charge as added to the device. If charged with only up to one
electron, the low-energy spectrum of the double quantum dot is characterized by
its quantum mechanical interdot tunnel splitting. We directly measure its
magnitude by utilizing particular anticrossing features in the stability
diagram at finite source-drain bias. By modification of gate voltages defining
the confinement potential as well as by variation of a perpendicular magnetic
field we demonstrate the tunability of the coherent tunnel coupling.Comment: High resolution pdf file available at
http://www2.nano.physik.uni-muenchen.de/~huettel/research/anticrossing.pd
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