2,321 research outputs found
Experimental determination of a nonclassical Glauber-Sudarshan P function
A quantum state is nonclassical if its Glauber-Sudarshan P function fails to
be interpreted as a probability density. This quantity is often highly
singular, so that its reconstruction is a demanding task. Here we present the
experimental determination of a well-behaved P function showing negativities
for a single-photon-added thermal state. This is a direct visualization of the
original definition of nonclassicality. The method can be useful under
conditions for which many other signatures of nonclassicality would not
persist.Comment: 4 pages, 4 figure
Cosmological Neutrino Entanglement and Quantum Pressure
Context: The widespread view that cosmological neutrinos, even if massive,
are well described since the decoupling redshift z~10^10 down to the present
epoch by an almost perfectly collisionless fluid of classical point particles
is re-examined. Aims: In view of the likely sub-eV rest mass of neutrinos, the
main effects due to their fermionic nature are studied. Methods: By numerical
means we calculate the accurate entropy, fugacity and pressure of cosmological
neutrinos in the Universe expansion. By solving the Schroedinger equation we
derive how and how fast semi-degenerate identical free fermions become
entangled. Results: We find that for sub-eV neutrinos the exchange degeneracy
has significantly increased during the relativistic to non-relativistic
transition epoch at z~10^4-10^5. At all times neutrinos become entangled in
less than 10^-6 s, much faster than any plausible decoherence time. The total
pressure is increased by quantum effect from 5% at high redshifts to 68% at low
redshifts with respect to a collisionless classical fluid. Conclusions: The
quantum overpressure has no dynamical consequences in the homogeneous regime at
high redshifts, but must be significant for neutrino clustering during the
non-linear structure formation epoch at low redshifts.Comment: 11 pages, 7 figures, accepted version to Astronomy & Astrophysics (no
change, correct wrong TeX rendering
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Efficient risk allocation within a non-life insurance group under Solvency II Regime
Intra-group transfers are risk management tools that are usually widely used to optimise the risk position of an insurance group. In this paper, it is shown that premium and liability transfers could be optimally made in such a way as to reduce the amount of Technical Provisions and Minimum Capital Requirement for the entire insurance conglomerate. These levels of required capital represent the minimal amount that needs to be held by the insurance group without regulator intervention, according to the Solvency II regulation. We assume that only proportional risk transfers are feasible, since such transfers are not difficult to administer for a large scaled insurance group, as is always the case. In addition, any risk shifting should be made for commercial purposes in order to be considered acceptable by the local regulators that impose restrictions on how much the assets within an insurance group are fungible. Our numerical examples illustrate the efficiency of the optimal proportional risk transfers which can easily be implemented, in terms of computation, in any well-known solver even for an insurance conglomerate with many subsidiaries. We found that our proposed optimal proportional allocations are more beneficial for large insurance group, since the relative reduction in capital requirement tends to be small, whereas the gain in absolute terms is quite significant for large scaled insurance group
FSH prevents depletion of the resting follicle pool by promoting follicular number and morphology in fresh and cryopreserved primate ovarian tissues following xenografting
Background: Cryopreservation and transplantation of ovarian tissue is one option for re-establishing ovarian function, but optimal conditions for graft sustainment and follicular survival are still considered experimental. The present study aims to analyze the effect of FSH treatment on the resting follicle pool in fresh and cryopreserved primate ovarian tissues following xenografting.
Methods: Ovarian tissues from adult marmosets were grafted freshly or following cryopreservation to ovarectomized nude mice treated with FSH 25 IU twice daily post transplantation or left untreated as controls. Grafts were retrieved 2 or 4 weeks after transplantation to evaluate the number and morphological appearance of follicles.
Results: Early start of FSH treatment within 1 week following transplantation partly prevents primordial follicle loss in fresh and frozen-thawed tissues, whereas after a 3 weeks time interval this effect is present only in fresh tissues. A similar positive effect of early, but not later FSH treatment on primary follicles is seen in fresh tissues compared to only marginal effects in frozen-thawed tissues. The percentage of morphologically normal follicles is generally increased in FSH treated tissues, whereas the percentage of primary follicles over all primordial and primary follicles is increased by FSH only in freshly-grafted tissues.
Conclusions: FSH treatment alleviates depletion of the resting follicle pool and promotes normal follicular morphology both in freshly and frozen-thawed grafted tissues. In previously cryopreserved tissues, applying to most of the tissues intended for clinical use in fertility preservation attempts, its positive effect on primordial follicle numbers and potential graft sustainment is dependent on an early start of treatment within one week of transplantation
A Combined Patch-Clamp and Electrorotation Study of the Voltage- and Frequency-Dependent Membrane Capacitance Caused by Structurally Dissimilar Lipophilic Anions
Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPAâ), tetraphenylborate (TPBâ) and [W2(CO)10(S2CH)]â, the putative lipophilic anion
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\begin{document}\end{document} and three new heterocyclic W(CO)5 derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPAâ, TPBâ and \documentclass[12pt]{minimal}
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\begin{document}\end{document} increased and that of W(CO)5 derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPAâ and W(CO)5 derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPBâ and \documentclass[12pt]{minimal}
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\begin{document}\end{document} no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions
Camparison of the Hanbury Brown-Twiss effect for bosons and fermions
Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in
light emitted by a chaotic source, highlighting the importance of two-photon
correlations and stimulating the development of modern quantum optics . The
quantum interpretation of bunching relies upon the constructive interference
between amplitudes involving two indistinguishable photons, and its additive
character is intimately linked to the Bose nature of photons. Advances in atom
cooling and detection have led to the observation and full characterisation of
the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions
should reveal an antibunching effect, i.e., a tendency to avoid each other.
Antibunching of fermions is associated with destructive two-particle
interference and is related to the Pauli principle forbidding more than one
identical fermion to occupy the same quantum state. Here we report an
experimental comparison of the fermion and the boson HBT effects realised in
the same apparatus with two different isotopes of helium, 3He (a fermion) and
4He (a boson). Ordinary attractive or repulsive interactions between atoms are
negligible, and the contrasting bunching and antibunching behaviours can be
fully attributed to the different quantum statistics. Our result shows how
atom-atom correlation measurements can be used not only for revealing details
in the spatial density, or momentum correlations in an atomic ensemble, but
also to directly observe phase effects linked to the quantum statistics in a
many body system. It may thus find applications to study more exotic situations
>.Comment: Nature 445, 402 (2007). V2 includes the supplementary informatio
Theory of output coupling for trapped fermionic atoms
We develop a dynamic theory of output coupling, for fermionic atoms initially
confined in a magnetic trap. We consider an exactly soluble one-dimensional
model, with a spatially localized delta-type coupling between the atoms in the
trap and a continuum of free-particle external modes. Two important special
cases are considered for the confinement potential: the infinite box and the
harmonic oscillator. We establish that in both cases a bound state of the
coupled system appears for any value of the coupling constant, implying that
the trap population does not vanish in the infinite-time limit. For weak
coupling, the energy spectrum of the outgoing beam exhibits peaks corresponding
to the initially occupied energy levels in the trap; the height of these peaks
increases with the energy. As the coupling gets stronger, the energy spectrum
is displaced towards dressed energies of the fermions in the trap. The
corresponding dressed states result from the coupling between the unperturbed
fermionic states in the trap, mediated by the coupling between these states and
the continuum. In the strong-coupling limit, there is a reinforcement of the
lowest-energy dressed mode, which contributes to the energy spectrum of the
outgoing beam more strongly than the other modes. This effect is especially
pronounced for the one-dimensional box, which indicates that the efficiency of
the mode-reinforcement mechanism depends on the steepness of the confinement
potential. In this case, a quasi-monochromatic anti-bunched atomic beam is
obtained. Results for a bosonic sample are also shown for comparison.Comment: 16 pages, 7 figures, added discussion on time-dependent spectral
distribution and corresponding figur
The 3-Band Hubbard-Model versus the 1-Band Model for the high-Tc Cuprates: Pairing Dynamics, Superconductivity and the Ground-State Phase Diagram
One central challenge in high- superconductivity (SC) is to derive a
detailed understanding for the specific role of the - and
- orbital degrees of freedom. In most theoretical studies an
effective one-band Hubbard (1BH) or t-J model has been used. Here, the physics
is that of doping into a Mott-insulator, whereas the actual high- cuprates
are doped charge-transfer insulators. To shed light on the related question,
where the material-dependent physics enters, we compare the competing magnetic
and superconducting phases in the ground state, the single- and two-particle
excitations and, in particular, the pairing interaction and its dynamics in the
three-band Hubbard (3BH) and 1BH-models. Using a cluster embedding scheme, i.e.
the variational cluster approach (VCA), we find which frequencies are relevant
for pairing in the two models as a function of interaction strength and doping:
in the 3BH-models the interaction in the low- to optimal-doping regime is
dominated by retarded pairing due to low-energy spin fluctuations with
surprisingly little influence of inter-band (p-d charge) fluctuations. On the
other hand, in the 1BH-model, in addition a part comes from "high-energy"
excited states (Hubbard band), which may be identified with a non-retarded
contribution. We find these differences between a charge-transfer and a Mott
insulator to be renormalized away for the ground-state phase diagram of the
3BH- and 1BH-models, which are in close overall agreement, i.e. are
"universal". On the other hand, we expect the differences - and thus, the
material dependence to show up in the "non-universal" finite-T phase diagram
(-values).Comment: 17 pages, 9 figure
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