5,254 research outputs found
The structure of frontoparallel haptic space is task dependent
In three experiments, we investigated the structure of frontoparallel haptic space. In the first experiment, we asked blindfolded participants to rotate a matching bar so that it felt parallel to the reference bar, the bars could be at various positions in the frontoparallel plane. Large systematic errors were observed, in which orientations that were perceived to be parallel were not physically parallel. In two subsequent experiments, we investigated the origin of these errors. In Experiment 2, we asked participants to verbally report the orientation of haptically presented bars. In this task, participants made errors that were considerably smaller than those made in Experiment 1. In Experiment 3, we asked participants to set bars in a verbally instructed orientation, and they also made errors significantly smaller than those observed in Experiment 1. The data suggest that the errors in the matching task originate from the transfer of the reference orientation to the matching-bar position
Approximations for many-body Green's functions: insights from the fundamental equations
Several widely used methods for the calculation of band structures and photo
emission spectra, such as the GW approximation, rely on Many-Body Perturbation
Theory. They can be obtained by iterating a set of functional differential
equations relating the one-particle Green's function to its functional
derivative with respect to an external perturbing potential. In the present
work we apply a linear response expansion in order to obtain insights in
various approximations for Green's functions calculations. The expansion leads
to an effective screening, while keeping the effects of the interaction to all
orders. In order to study various aspects of the resulting equations we
discretize them, and retain only one point in space, spin, and time for all
variables. Within this one-point model we obtain an explicit solution for the
Green's function, which allows us to explore the structure of the general
family of solutions, and to determine the specific solution that corresponds to
the physical one. Moreover we analyze the performances of established
approaches like over the whole range of interaction strength, and we
explore alternative approximations. Finally we link certain approximations for
the exact solution to the corresponding manipulations for the differential
equation which produce them. This link is crucial in view of a generalization
of our findings to the real (multidimensional functional) case where only the
differential equation is known.Comment: 17 pages, 7 figure
Observation of Feshbach resonances between two different atomic species
We have observed three Feshbach resonances in collisions between lithium-6
and sodium-23 atoms. The resonances were identified as narrow loss features
when the magnetic field was varied. The molecular states causing these
resonances have been identified, and additional lithium-sodium resonances are
predicted. These resonances will allow the study of degenerate Bose-Fermi
mixtures with adjustable interactions, and could be used to generate ultracold
heteronuclear molecules
Formation Time of a Fermion Pair Condensate
The formation time of a condensate of fermionic atom pairs close to a
Feshbach resonance was studied. This was done using a phase-shift method in
which the delayed response of the many-body system to a modulation of the
interaction strength was recorded. The observable was the fraction of condensed
molecules in the cloud after a rapid magnetic field ramp across the Feshbach
resonance. The measured response time was slow compared to the rapid ramp,
which provides final proof that the molecular condensates reflect the presence
of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure
Dimensional Crossover of Dilute Neon inside Infinitely Long Single-Walled Carbon Nanotubes Viewed from Specific Heats
A simple formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and the potential of neon (Ne)
inside an infinitely long SWNT is analytically derived under the assumption of
pair-wise Lennard-Jones potential between Ne and carbon atoms. Specific heats
of dilute Ne inside infinitely long (5, 5), (10, 10), (15, 15) and (20, 20)
SWNT's are calculated at different temperatures. It is found that Ne inside
four kinds of nanotubes exhibits 3-dimensional (3D) gas behavior at high
temperature but different behaviors at low temperature: Ne inside (5, 5)
nanotube behaves as 1D gas but inside (10, 10), (15, 15), and (20, 20)
nanotubes behaves as 2D gas. Furthermore, at ultra low temperature, Ne inside
(5, 5) nanotube still displays 1D behavior but inside (10, 10), (15, 15), and
(20, 20) nanotubes behaves as lattice gas.Comment: 10 pages, 5 figure
Conductor-backed coplanar waveguide resonators of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O on LaAlO3
Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from Tl-Ba-Ca-O (TBCCO) and Y-Ba-Cu-O (YBCO) thin films on LaAlO3. The resonators consist of a coplanar waveguide (CPW) patterned on the superconducting film side of the LaAlO3 substrate with a gold ground plane coated on the opposite side. These resonators were tested in the temperature range from 14 to 106 K. At 77 K, the best of our TBCCO and YBCO resonators have an unloaded quality factor (Qo) 7 and 4 times, respectively, larger than that of a similar all-gold resonator. In this study, the Qo's of the TBCCO resonators were larger than those of their YBCO counterparts throughout the aforementioned temperature range
Rectification by charging -- the physics of contact-induced current asymmetry in molecular conductors
We outline the qualitatively different physics behind charging-induced
current asymmetries in molecular conductors operating in the weakly interacting
self-consistent field (SCF) and the strongly interacting Coulomb Blockade (CB)
regimes. A conductance asymmetry arises in SCF because of the unequal
mean-field potentials that shift a closed-shell conducting level differently
for positive and negative bias. A very different current asymmetry arises for
CB due to the unequal number of open-shell excitation channels at opposite bias
voltages. The CB regime, dominated by single charge effects, typically requires
a computationally demanding many-electron or Fock space description. However,
our analysis of molecular Coulomb Blockade measurements reveals that many novel
signatures can be explained using a {{simpler}} orthodox model that involves an
incoherent sum of Fock space excitations and {\it{hence treats the molecule as
a metallic dot or an island}}. This also reduces the complexity of the Fock
space description by just including various charge configurations only, thus
partially underscoring the importance of electronic structure, while retaining
the essence of the single charge nature of the transport process. We finally
point out, however, that the inclusion of electronic structure and hence
well-resolved Fock space excitations is crucial in some notable examples.Comment: 12 pages, 10 figure
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