Solution of the Bogoliubov-deGennes Equations at Zero Temperature Throughout the BCS-BEC Crossover: Josephson and Related Effects

The BCS-BEC crossover has received much attention lately, owing especially to its experimental realization with trapped ultracold Fermi atoms. Theoretically, the two limiting situations, of paired fermions described by BCS theory in weak coupling and of composite bosons undergoing BoseEinstein condensation (BEC) in strong coupling, can be connected with continuity throughout the crossover. This evolution encompasses the unitary limit at intermediate values of the coupling, where the scattering length for two-fermion scattering diverges. Several quantities have been measured experimentally and calculated theoretically in this context over the last several years, with the notable exception of the Josephson and related effects. This is in spite of the fact that the Josephson effect is intimately associated with the spontaneous breaking of the phase of the complex order parameter which unifies superconductivity and superfluidity. In the present paper, we aim at filling (at least partially) this gap and investigate the evolution of the Josephson and related effects throughout the BCSBEC crossover, by performing a systematic numerical solution of the (time-independent) Bogoliubovde Gennes (BdG) equations at zero temperature in a fully self-consistent fashion. We consider a stationary and uniform current flowing in the presence of a three-dimensional barrier with a slab geometry. This extended geometry is specifically required to reach the BEC limit of the crossover, where the formation of composite bosons in terms of their fermionic constituents requires consideration of wave vectors with components along all three dimensions. In addition, we regard the fermionic attraction to extend unmodified over the barrier region, a situation that typically applies to ultracold Fermi atoms. The fully selfconsistent solution of the BdG equations in such an extended geometry and coupling range represents a non-trivial numerical calculation. The numerical strategies and algorithms we have adopted will therefore be described in detail, with the aim of easing further independent studies. Several results are obtained by the present calculation. The profiles of the magnitude and phase of the gap parameter across the barrier are determined under a variety of conditions. We find that the Josephson current is considerably enhanced at about unitarity for all barriers we have considered. A related enhancement is also found in the contribution to the total current from the Andreev bound states, which stem from the depression of the gap profile about the barrier. The Josephson currentphase characteristics (relating the total current J to the phase difference across the barrier) turn out to evolve from the standard J / sin relation to J / cos , when the height of the barrier is decreased at fixed coupling or the coupling is decreased for a given barrier. For vanishing barrier height, we find that the critical Josephson current approaches the limiting value predicted by the Landau criterion, which is determined by either pair-breaking or soundmode excitations depending on the coupling value. In the BCS limit, we reveal the presence of Friedel oscillations in the oscillatory modulations of the gap and density profiles. In this limit, we also emphasize the special role played by the Andreev bound state in determining the critical Josephson current in the presence of a barrier. Finally, the stability of the two branches, out of which the Josephson characteristics are composed, is analyzed by calculating the energy required to produce a given spatial profile of the gap parameter

DC Josephson Effect with Fermi gases in the Bose-Einstein regime

We show that the DC Josephson effect with ultracold fermionic gases in the BEC regime of composite molecules can be described by a nonlinear Schrodinger equation (NLSE). By comparing our results with Bogoliubov-de Gennes calculations [Phys. Rev. Lett. 99, 040401 (2007)] we find that our superfluid NLSE, which generalizes the Gross-Pitaevskii equation taking into account the correct equation of state, is reliable in the BEC regime of the BCS-BEC crossover up to the limit of very large (positive) scattering length. We also predict that the Josephson current displays relevant beyond mean-field effects.Comment: 9 pages, 6 figures. In the new version added one figure and some paragraph

Rapid referral for headache management from emergency department to headache centre. four years data

Background: Headache is one of the most common reason for medical consultation to emergency department (ED). The inappropriate use of ED for non-emergency conditions is a problem in terms of overcrowding of emergency facilities, unnecessary testing and treatment, increased medical costs, burden on medical service providers and weaker relationships between patient and primary care provider. The aim of this study was to analyze the different stages of ED management of headache to identify those deficiencies that can be overcome by a fast referral to a headache clinic. Methods: The study is a retrospective analysis of the electronic medical records of patients discharged from an academic ED between January 1, 2015 and December 31, 2018 and referred to the tertiary level headache centre of the same hospital. We analyzed all aspects related to the permanence in ED and also assessed whether there was a match between the diagnosis made in ED and ours. Results: Among our sample of 244 patients, 76.2% were admitted as "green tag", 75% underwent a head computed tomography, 19.3% received a neurological consultation, 43% did not receive any pharmacological treatment and 62.7% still had headache at discharge. The length of stay in ED was associated with reporting the first aura ever (p = 0.014) and whether patients received consultations (p < 0.001). The concordance analysis shown a significant moderate agreement only for the diagnosis of migraine and only between triage and headache centre. Conclusions: Most patients who went to ED complaining of headache received the same treatment regardless of their diagnosis and in many cases the headache had not yet resolved at the time of discharge. Given the many shortcomings in headache management in ED, rapid referral to the headache centre is of paramount importance to help the patient achieve a definiteve diagnosis and appropriate treatment

The Josephson effect throughout the BCS-BEC crossover

We study the stationary Josephson effect for neutral fermions across the BCS-BEC crossover, by solving numerically the Bogoliubov-de Gennes equations at zero temperature. The Josephson current is found to be considerably enhanced for all barriers at about unitarity. For vanishing barrier, the Josephson critical current approaches the Landau limiting value which, depending on the coupling, is determined by either pair-breaking or sound-mode excitations. In the coupling range from the BCS limit to unitarity, a procedure is proposed to extract the pairing gap from the Landau limiting current.Comment: 4 pages, 3 figures; improved version to appear in Phys. Rev. Let

Recurrent COVID-19 pneumonia in the course of chemotherapy: consequence of a weakened immune system?

Letter to the Editor - We report a case of recurrent COVID‐19 pneumonia in a vulnerable patien

Using INTERCheck® to Evaluate the Incidence of Adverse Events and Drug–Drug Interactions in Out- and Inpatients Exposed to Polypharmacy

Background: Polypharmacy exposes patients with comorbidities (particularly elderly patients) to an increased risk of drug-specific adverse events and drug–drug interactions. These adverse events could be avoided with the use of a computerized prescription support system in the primary care setting. The INTERCheck® software is a prescription support system developed with the aim of balancing the risks and benefits of polytherapy and examining drug–drug interactions. Objectives: This observational study used the INTERCheck® software to evaluate the incidence of adverse events and of drug–drug interactions in outpatients and inpatients receiving multiple medications. Methods: Patients were randomly enrolled from the outpatient department (n = 98) and internal medicine ward (n = 46) of S. Andrea Hospital of Rome. Polypharmacological treatment was analyzed using INTERCheck® software, and the prevalence of risk indicators and adverse events was compared between the two groups. Results: Polypharmacy (use of five or more drugs) applied to all except three cases among outpatients and one case among inpatients. A significant positive correlation was found between the number of medications and the INTERCheck® score (ρ = 0.67; p < 0.000001), and a significant negative correlation was found between the drug-related anticholinergic burden and cognitive impairment (r = − 0.30 p = 0.01). Based on the INTERCheck® analysis, inpatients had a higher score for class D (contraindicated drug combination should be avoided) than did outpatients (p = 0.01). The potential class D drug–drug interactions were associated with adverse events that caused hospitalization (χ2 = 7.428, p = 0.01). Conclusions: INTERCheck® analysis indicated that inpatients had a high risk of drug–drug interactions and a high percentage of related adverse drug events. Further prospective studies are necessary to evaluate whether the INTERCheck® software may help reduce polypharmacy-related adverse events when used in a primary care setting and thus potentially avoid related hospitalization and severe complications such as physical and cognitive decline

Prevalence of molar incisor hypomineralization among school children in Rome, Italy

Molar incisor hypomineralization (MIH) is a highly prevalent condition associated with increased caries experience, dental pain and treatment need. Aim of this study was to determine the prevalence and severity of MIH in a group of 7–8 years old primary school children living in Rome, Italy; and to assess the association with caries experience and possible perinatal risk factors. A survey has been conducted in the city of Rome, between April 2019 and March 2020 with a total of 49 primary schools and 176 2nd grade primary school classes and a total of 3611 children being involved. Of these, a subset of 346 children of 21 primary schools was selected for the epidemiological investigation. The prevalence of MIH was of 18.2%, with girls showing twice the probability of being subject to a mild-severe condition. Molar location was present in 71.4%, while location on both molar plus incisor was present in 28.6% of cases. The mean DMFT was 0.44 ± 0.78, “D” was 0.17 ± 0.58; the mean dmft was 1.7 ± 2.56, “d” was 1.32 ± 2.21. Female gender, caries experience, insufficient oral hygiene were risk factors. The incidence of MIH is increasing in the pediatric population. Knowledge about diagnosis and treatment options should be disseminated among dental professionals.publishedVersio

Grey solitons in a strongly interacting superfluid Fermi Gas

The Bardeen-Cooper-Schrieffer to Bose-Einstein condensate (BCS to BEC) crossover problem is solved for stationary grey solitons via the Boguliubov-de Gennes equations at zero temperature. These \emph{crossover solitons} exhibit a localized notch in the gap and a characteristic phase difference across the notch for all interaction strengths, from BEC to BCS regimes. However, they do not follow the well-known Josephson-like sinusoidal relationship between velocity and phase difference except in the far BEC limit: at unitary the velocity has a nearly linear dependence on phase difference over an extended range. For fixed phase difference the soliton is of nearly constant depth from the BEC limit to unitarity and then grows progressively shallower into the BCS limit, and on the BCS side Friedel oscillations are apparent in both gap amplitude and phase. The crossover soliton appears fundamentally in the gap; we show, however, that the density closely follows the gap, and the soliton is therefore observable. We develop an approximate power law relationship to express this fact: the density of grey crossover solitons varies as the square of the gap amplitude in the BEC limit and a power of about 1.5 at unitarity.Comment: 10 pages, 6 figures, part of New Journal of Physics focus issue "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas," in pres

Strongly Correlated Quantum Fluids: Ultracold Quantum Gases, Quantum Chromodynamic Plasmas, and Holographic Duality

Strongly correlated quantum fluids are phases of matter that are intrinsically quantum mechanical, and that do not have a simple description in terms of weakly interacting quasi-particles. Two systems that have recently attracted a great deal of interest are the quark-gluon plasma, a plasma of strongly interacting quarks and gluons produced in relativistic heavy ion collisions, and ultracold atomic Fermi gases, very dilute clouds of atomic gases confined in optical or magnetic traps. These systems differ by more than 20 orders of magnitude in temperature, but they were shown to exhibit very similar hydrodynamic flow. In particular, both fluids exhibit a robustly low shear viscosity to entropy density ratio which is characteristic of quantum fluids described by holographic duality, a mapping from strongly correlated quantum field theories to weakly curved higher dimensional classical gravity. This review explores the connection between these fields, and it also serves as an introduction to the Focus Issue of New Journal of Physics on Strongly Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas. The presentation is made accessible to the general physics reader and includes discussions of the latest research developments in all three areas.Comment: 138 pages, 25 figures, review associated with New Journal of Physics special issue "Focus on Strongly Correlated Quantum Fluids: from Ultracold Quantum Gases to QCD Plasmas" (http://iopscience.iop.org/1367-2630/focus/Focus%20on%20Strongly%20Correlated%20Quantum%20Fluids%20-%20from%20Ultracold%20Quantum%20Gases%20to%20QCD%20Plasmas