1,269 research outputs found
Possibility of valence-fluctuation mediated superconductivity in Cd-doped CeIrIn probed by In-NQR
We report on a pressure-induced evolution of exotic superconductivity and
spin correlations in CeIr(InCd) by means of
In-Nuclear-Quadrupole-Resonance (NQR) studies. Measurements of an NQR spectrum
and nuclear-spin-lattice-relaxation rate have revealed that
antiferromagnetism induced by the Cd-doping emerges locally around Cd dopants,
but superconductivity is suddenly induced at = 0.7 and 0.9 K at 2.34 and
2.75 GPa, respectively. The unique superconducting characteristics with a large
fraction of the residual density of state at the Fermi level that increases
with differ from those for anisotropic superconductivity mediated by
antiferromagnetic correlations. By incorporating the pressure dependence of the
NQR frequency pointing to the valence change of Ce, we suggest that
unconventional superconductivity in the CeIr(InCd) system may
be mediated by valence fluctuations.Comment: Accepted for publication in Physical Review Letter
Comparison of Control Modes of a Hand-Held Robot for Laparoscopic Surgery
Teleoperated robots for minimally invasive surgery make surgeons loose direct contact with the patient. We are developing a handheld, dexterous surgical robot that can be controlled with one hand only, while standing at the operating table. The instrument is composed of a master part (the handle) and a slave part (the tip). This work compares the performance of different control modes, i.e. different ways to map the degrees of freedom of the handle to those of the tip. We ask users to drive the tip along complex trajectories in a virtual environment, using
the real master to drive a simulated slave, and assess their performance. Results show that, concerning time, users with no training in laparoscopy prefer a direct mapping of position and orientation, like in free hand motion. However, users trained in laparoscopy perform equally fast with our hand-held robot and, concerning precision, make a smaller number of errors
Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?
It is demonstrated that present and DIS ep data on the structure of
the virtual photon can be understood entirely in terms of the standard `naive'
quark--parton model box approach. Thus the QCD renormalization group (RG)
improved parton distributions of virtual photons, in particular their gluonic
component, have not yet been observed. The appropriate kinematical regions for
their future observation are pointed out as well as suitable measurements which
may demonstrate their relevance.Comment: 24 pages, LaTeX, 5 figure
Moments of the Virtual Photon Structure Function
The photon structure function is a useful testing ground for QCD. It is
perturbatively computable apart from a contribution from what is usually called
the hadronic component of the photon. There have been many proposals for this
nonperturbative part of the real photon structure function. By studying moments
of the virtual photon structure function, we explore the extent to which these
proposed nonperturbative contributions can be identified experimentally.Comment: LaTeX, 16 pages + 14 compressed and uuencoded postscript figures,
UMN-TH-1111/9
A fabrication guide for planar silicon quantum dot heterostructures
We describe important considerations to create top-down fabricated planar
quantum dots in silicon, often not discussed in detail in literature. The
subtle interplay between intrinsic material properties, interfaces and
fabrication processes plays a crucial role in the formation of
electrostatically defined quantum dots. Processes such as oxidation, physical
vapor deposition and atomic-layer deposition must be tailored in order to
prevent unwanted side effects such as defects, disorder and dewetting. In two
directly related manuscripts written in parallel we use techniques described in
this work to create depletion-mode quantum dots in intrinsic silicon, and
low-disorder silicon quantum dots defined with palladium gates. While we
discuss three different planar gate structures, the general principles also
apply to 0D and 1D systems, such as self-assembled islands and nanowires.Comment: Accepted for publication in Nanotechnology. 31 pages, 12 figure
Adaptive Optimization of Wave Functions for Fermion Lattice Models
We present a simulation algorithm for Hamiltonian fermion lattice models. A
guiding trial wave function is adaptively optimized during Monte Carlo
evolution. We apply the method to the two dimensional Gross-Neveu model and
analyze systematc errors in the study of ground state properties. We show that
accurate measurements can be achieved by a proper extrapolation in the
algorithm free parameters.Comment: 4 pages, 6 figures (Encapsulated PostScript
Generating All Wigner Functions
In the context of phase-space quantization, matrix elements and observables
result from integration of c-number functions over phase space, with Wigner
functions serving as the quasi-probability measure. The complete sets of Wigner
functions necessary to expand all phase-space functions include off-diagonal
Wigner functions, which may appear technically involved. Nevertheless, it is
shown here that suitable generating functions of these complete sets can often
be constructed, which are relatively simple, and lead to compact evaluations of
matrix elements. New features of such generating functions are detailed and
explored for integer-indexed sets, such as for the harmonic oscillator, as well
as continuously indexed ones, such as for the linear potential and the
Liouville potential. The utility of such generating functions is illustrated in
the computation of star functions, spectra, and perturbation theory in phase
space.Comment: LaTex2e, 21 page
Lambda Polarization in Polarized Proton-Proton Collisions at RHIC
We discuss Lambda polarization in semi-inclusive proton-proton collisions,
with one of the protons longitudinally polarized. The hyperfine interaction
responsible for the - and - mass splittings gives
rise to flavor asymmetric fragmentation functions and to sizable polarized
non-strange fragmentation functions. We predict large positive Lambda
polarization in polarized proton-proton collisions at large rapidities of the
produced Lambda, while other models, based on SU(3) flavor symmetric
fragmentation functions, predict zero or negative Lambda polarization. The
effect of and decays is also discussed. Forthcoming
experiments at RHIC will be able to differentiate between these predictions.Comment: 18 pages, 5 figure
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