749 research outputs found
What is the limit of quantum theory ?
An analysis is made of the relation between quantum theory and classical
mechanics, in the context of the limit . Several ways in which
this limit may be performed are considered. It is shown that Schr\"odinger's
equation for a single particle moving in an external potential does not,
except in special cases, lead, in this limit, to Newton's equation of motion
for the particle. This shows that classical mechanics cannot be regarded as
emerging from quantum mechanics-at least in this sense-upon straightforward
application of the limit .Comment: 12 pages, no figure
Berry phase, topology, and diabolicity in quantum nano-magnets
A topological theory of the diabolical points (degeneracies) of quantum
magnets is presented. Diabolical points are characterized by their diabolicity
index, for which topological sum rules are derived. The paradox of the the
missing diabolical points for Fe8 molecular magnets is clarified. A new method
is also developed to provide a simple interpretation, in terms of destructive
interferences due to the Berry phase, of the complete set of diabolical points
found in biaxial systems such as Fe8.Comment: 4 pages, 3 figure
Relationship between brachycephalic airway syndrome and gastrointestinal signs in three breeds of dog
Objectives: To assess the breed-specific prevalence of, and effects of corrective airway surgery on, gastrointestinal signs in French bulldogs, English bulldogs and pugs presenting with brachycephalic airway syndrome to a referral teaching hospital.
Materials and Methods: In this retrospective study, ptyalism, regurgitation and vomiting were graded at presentation using a previously established scoring system. Staphylectomy and nares resection were performed on all dogs. Gastrointestinal signs were re-assessed via telephone follow-up at least 6 weeks after surgery.
Results: Ninety-eight dogs were included: French bulldogs (n=43), English bulldogs (n=12) and pugs (n=43). Overall population prevalence of all gastrointestinal signs was 56%. Breed-specific prevalence for French bulldogs was 93%, English bulldogs 58% and pugs 16%. There was post-surgical clinical improvement in gastrointestinal signs for the whole study population, especially in French bulldogs.
Clinical Significance: The prevalence of gastrointestinal signs in dogs presenting with brachycephalic airway syndrome and improvement in these clinical signs following corrective surgery may vary between breeds
Number-of-particle fluctuations in systems with Bose-Einstein condensate
Fluctuations of the number of particles for the dilute interacting gas with
Bose-Einstein condensate are considered. It is shown that in the Bogolubov
theory these fluctuations are normal. The fluctuations of condensed as well as
noncondensed particles are also normal both in canonical and grand canonical
ensembles.Comment: Latex file, 12 page
Spectroscopy on two coupled flux qubits
We have performed spectroscopy measurements on two coupled flux qubits. The
qubits are coupled inductively, which results in a
interaction. By applying microwave radiation, we observe resonances due to
transitions from the ground state to the first two excited states. From the
position of these resonances as a function of the magnetic field applied we
observe the coupling of the qubits. The coupling strength agrees well with
calculations of the mutual inductance
Optimal trap shape for a Bose gas with attractive interactions
Dilute Bose gas with attractive interactions is considered at zero
temperature, when practically all atoms are in Bose-Einstein condensate. The
problem is addressed aiming at answering the question: What is the optimal trap
shape allowing for the condensation of the maximal number of atoms with
negative scattering lengths? Simple and accurate analytical formulas are
derived allowing for an easy analysis of the optimal trap shapes. These
analytical formulas are the main result of the paper.Comment: Latex file, 21 page
Spin superfluidity and spin-orbit gauge symmetry fixing
The Hamiltonian describing 2D electron gas, in a spin-orbit active medium,
can be cast into a consistent non-Abelian gauge field theory leading to a
proper definition of the spin current. The generally advocated gauge symmetric
version of the theory results in current densities that are gauge covariant, a
fact that poses severe concerns on their physical nature. We show that in fact
the problem demands gauge fixing, leaving no room to ambiguity in the
definition of physical spin currents. Gauge fixing also allows for polarized
edge excitations not present in the gauge symmetric case. The scenario here is
analogous to that of superconductivity gauge theory. We develop a variational
formulation that accounts for the constraints between U(1) physical fields and
SU(2) gauge fields and show that gauge fixing renders a physical matter and
radiation currents and derive the particular consequences for the Rashba SO
interaction.Comment: to appear in EP
Multilinear Wavelets: A Statistical Shape Space for Human Faces
We present a statistical model for D human faces in varying expression,
which decomposes the surface of the face using a wavelet transform, and learns
many localized, decorrelated multilinear models on the resulting coefficients.
Using this model we are able to reconstruct faces from noisy and occluded D
face scans, and facial motion sequences. Accurate reconstruction of face shape
is important for applications such as tele-presence and gaming. The localized
and multi-scale nature of our model allows for recovery of fine-scale detail
while retaining robustness to severe noise and occlusion, and is
computationally efficient and scalable. We validate these properties
experimentally on challenging data in the form of static scans and motion
sequences. We show that in comparison to a global multilinear model, our model
better preserves fine detail and is computationally faster, while in comparison
to a localized PCA model, our model better handles variation in expression, is
faster, and allows us to fix identity parameters for a given subject.Comment: 10 pages, 7 figures; accepted to ECCV 201
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