485 research outputs found
Enlarging and cooling the N\'eel state in an optical lattice
We propose an experimental scheme to favor both the realization and the
detection of the N\'eel state in a two-component gas of ultracold fermions in a
three-dimensional simple-cubic optical lattice. By adding three compensating
Gaussian laser beams to the standard three pairs of retroreflected lattice
beams, and adjusting the relative waists and intensities of the beams, one can
significantly enhance the size of the N\'eel state in the trap, thus increasing
the signal of optical Bragg scattering. Furthermore, the additional beams
provide for adjustment of the local chemical potential and the possibility to
evaporatively cool the gas while in the lattice. Our proposals are relevant to
other attempts to realize many-body quantum phases in optical lattices.Comment: 8 pages, 10 figures (significantly revised text and figures
Trimers, molecules and polarons in imbalanced atomic Fermi gases
We consider the ground state of a single "spin-down" impurity atom
interacting attractively with a "spin-up" atomic Fermi gas. By constructing
variational wave functions for polarons, molecules and trimers, we perform a
detailed study of the transitions between each of these dressed bound states as
a function of mass ratio and interaction strength.
We find that the presence of a Fermi sea enhances the stability of the -wave
trimer, which can be viewed as a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)
molecule that has bound an additional majority atom. For sufficiently large
, we find that the transitions lie outside the region of phase separation in
imbalanced Fermi gases and should thus be observable in experiment, unlike the
well-studied equal-mass case.Comment: 5 pages, 2 figure
Cross-Layer Peer-to-Peer Track Identification and Optimization Based on Active Networking
P2P applications appear to emerge as ultimate killer applications due to their ability to construct highly dynamic overlay topologies with rapidly-varying and unpredictable traffic dynamics, which can constitute a serious challenge even for significantly over-provisioned IP networks. As a result, ISPs are facing new, severe network management problems that are not guaranteed to be addressed by statically deployed network engineering mechanisms. As a first step to a more complete solution to these problems, this paper proposes a P2P measurement, identification and optimisation architecture, designed to cope with the dynamicity and unpredictability of existing, well-known and future, unknown P2P systems. The purpose of this architecture is to provide to the ISPs an effective and scalable approach to control and optimise the traffic produced by P2P applications in their networks. This can be achieved through a combination of different application and network-level programmable techniques, leading to a crosslayer identification and optimisation process. These techniques can be applied using Active Networking platforms, which are able to quickly and easily deploy architectural components on demand. This flexibility of the optimisation architecture is essential to address the rapid development of new P2P protocols and the variation of known protocols
Phase separation and collapse in Bose-Fermi mixtures with a Feshbach resonance
We consider a mixture of single-component bosonic and fermionic atoms with an
interspecies interaction that is varied using a Feshbach resonance. By
performing a mean-field analysis of a two-channel model, which describes both
narrow and broad Feshbach resonances, we find an unexpectedly rich phase
diagram at zero temperature: Bose-condensed and non-Bose-condensed phases form
a variety of phase-separated states that are accompanied by both critical and
tricritical points. We discuss the implications of our results for the
experimentally observed collapse of Bose-Fermi mixtures on the attractive side
of the Feshbach resonance, and we make predictions for future experiments on
Bose-Fermi mixtures close to a Feshbach resonance.Comment: 7 pages, 3 figures. Extended versio
Maximizing the Neel temperature of fermions in a simple-cubic optical lattice
For a simple-cubic optical lattice with lattice spacing d, occupied by two
species of fermionic atoms of mass m that interact repulsively, we ask what
conditions maximize the Neel temperature in the Mott insulating phase at
density one atom per site, with equal numbers of the two species. This maximum
occurs near the edge of the regime where the system is well-approximated by the
usual Hubbard model. The correction to the Hubbard-model approximation that
produces a "direct" ferromagnetic interaction between atoms in nearest-neighbor
Wannier orbitals is the leading term that limits how high the Neel temperature
can be made.Comment: 4 pages, 3 figures, minor changes. A new paper, arXiv:0903.0108,
expands on this paper and contains most of its result
Search for weak M1 transitions in Ca with inelastic proton scattering
The spinflip M1 resonance in the doubly magic nucleus Ca, dominated by
a single transition, serves as a reference case for the quenching of
spin-isospin modes in nuclei. The aim of the present work is a search for weak
M1 transitions in Ca with a high-resolution (p,p') experiment at 295 MeV
and forward angles including 0 degree and a comparison to results from a
similar study using backward-angle electron scattering at low momentum
transfers in order to estimate their contribution to the total B(M1) strength.
M1 cross sections of individual peaks in the spectra are deduced with a
multipole decomposition analysis. The corresponding reduced B(M1) transition
strengths are extracted following the approach outlined in J. Birkhan et al.,
Phys. Rev. C 93, 041302(R) (2016). In total, 29 peaks containing a M1
contribution are found in the excitation energy region 7 - 13 MeV. The
resulting B(M1) strength distribution compares well to the electron scattering
results considering different factors limiting the sensitivity in both
experiments and the enhanced importance of mechanisms breaking the
proportionality of nuclear cross sections and electromagnetic matrix elements
for weak transitions as studied here. The total strength of 1.19(6)
deduced assuming a non-quenched isoscalar part of the (p,p') cross sections
agrees with the (e,e') result of 1.21(13) . A binwise analysis above
10 MeV provides an upper limit of 1.62(23) . The present results
confirm that weak transitions contribute about 25% to the total B(M1) strength
in Ca and the quenching factors of GT and spin-M1 strength are
comparable in fp-shell nuclei. Thus, the role of of meson exchange currents
seems to be neglible, in contrast to sd-shell nuclei.Comment: 11 pages, 9 figures, revised analysis with oxygen contamination
remove
Defect mediated melting and the breaking of quantum double symmetries
In this paper, we apply the method of breaking quantum double symmetries to
some cases of defect mediated melting. The formalism allows for a systematic
classification of possible defect condensates and the subsequent confinement
and/or liberation of other degrees of freedom. We also show that the breaking
of a double symmetry may well involve a (partial) restoration of an original
symmetry. A detailed analysis of a number of simple but representative examples
is given, where we focus on systems with global internal and external (space)
symmetries. We start by rephrasing some of the well known cases involving an
Abelian defect condensate, such as the Kosterlitz-Thouless transition and
one-dimensional melting, in our language. Then we proceed to the non-Abelian
case of a hexagonal crystal, where the hexatic phase is realized if
translational defects condense in a particular rotationally invariant state.
Other conceivable phases are also described in our framework.Comment: 10 pages, 4 figures, updated reference
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Quantum Flutter: Signatures and Robustness
We investigate the motion of an impurity particle injected with finite velocity into an interacting one-dimensional quantum gas. Using large-scale numerical simulations based on matrix product states, we observe and quantitatively analyze long-lived oscillations of the impurity momentum around a nonzero saturation value, called quantum flutter. We show that the quantum flutter frequency is equal to the energy difference between two branches of collective excitations of the model. We propose an explanation of the finite saturation momentum of the impurity based on the properties of the edge of the excitation spectrum. Our results indicate that quantum flutter exists away from integrability and provide parameter regions in which it could be observed in experiments with ultracold atoms using currently available technology.Physic
French translation and validation of the Jefferson Scale of Empathy - Health Professions Student version
Background: Background: Jefferson Scale of Empathy is one of the most widely used tools worldwide to assess empathy.
The extended version for Health Professions Students (JSE HPS) has not yet been translated into French. Objective:
The aim of our study was to translate the JSE HPS into French and assess the psychometric properties of this new
version (JSE HPS Fr). Methods: The JSE HPS was translated according to international recommendations. The main
psychometric qualities (test-retest reliability, internal consistency, floor and ceiling effects and construct validity) were studied in a sample of physiotherapy students. Participants provided general information (age, gender, year of study) and completed the JSE HPS Fr and the Questionnaire of Cognitive and Affective Empathy (QCAE). Participants were also asked to complete the JSE-HPS-Fr again one week later to assess its test-retest reliability. Results: 408 students (161 males and 247 females; mean age: 21.3 years) participated. The JSE HPS Fr demonstrated good test-retest reliability for the total score (ICC=0.81) and good internal consistency (α Cronbach: 0.79). The JSE HPS also showed good convergent validity with the QCAE questionnaire (r=0.41, p<0.05). No floor or ceiling effects were observed. Conclusions: The results indicate that the JSE HPS Fr is a valid and reliable tool to assess the level of empathy of French-speaking physiotherapy students
Inactivation of α2-Macroglobulin by Activated Human Polymorphonuclear Leukocytes
The proteolytic activity of trypsin releases the dye Remazol
Brilliant Blue from its high molecular weight substrate, the skin
powder (Hide Powder Azure, Sigma), with an increase in absorbance at
595 nm. Active α2- macroglobulin (80 μg/ml) totally inhibits the
proteolytic activity of trypsin (14 μg/ml) by trapping this
protease. But after a 20 min incubation of α2-macroglobulin at 37°C
with 2 × 106 human polymorphonuclear leukocytes activated by
N-formyl-L-methionyl-L-leucyl-L-phenylalanine
(10−7 M) and cytochalasin B (10−8 M), 100% of trypsin
activity was recovered, indicating a total inactivation of
α2-macroglobuHn. Incubation with granulocyte myeloperoxidase also
inactivates α2-macroglobulin. Hypochlorous acid, a by-product of
myeloperoxidase activity, at a concentration of 10−7 M also
inactivates α2-macroglobulin, which indicates that an important
cause of α2-macroglobulin inactivation by activated
polymorphonuclear leukocytes could be the activity of myeloperoxidase
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