Local dynamical lattice instabilities: Prerequisites for resonant pairing superconductivity

Fluctuating local diamagnetic pairs of electrons, embedded in a Fermi sea, are candidates for non-phonon-mediated superconductors without the stringent conditions on Tc which arise in phonon-mediated BCS classical low-Tc superconductors. The local accumulations of charge, from which such diamagnetic fluctuations originate, are irrevocably coupled to local dynamical lattice instabilities and form composite charge-lattice excitations of the system. For a superconducting phase to be realized, such excitations must be itinerant spatially phase-coherent modes. This can be achieved by resonant pair tunneling in and out of polaronic cation-ligand sites. Materials in which superconductivity driven by such local lattice instability can be expected, have a Tc which is controlled by the phase stiffness rather than the amplitude of the diamagnetic pair fluctuations. Above Tc, a pseudogap phase will be maintained up to a T*, where this pairing amplitude disappears. We discuss the characteristic local charge and lattice properties which characterize this pseudogap phase and which form the prerequisites for establishing a phase-coherent macroscopic superconducting state.Comment: 15 pages, 13 figure

Resonant pairing isotope effect in polaronic systems

The intermediate coupling regime in polaronic systems, situated between the adiabatic and the anti-adiabatic limit, is characterized by resonant pairing between quasi-free electrons which is induced by an exchange interaction with localized bipolarons. The onset of this resonant pairing takes place below a characteristic temperature T* and is manifest in the opening of a pseudogap in the density of states of the electrons. The variation of T* is examined here as a function of (i) the typical frequency \omega_0 of the local lattice modes, which determines the binding energy of the bipolarons, and (ii) the doping, which amounts to a relative change of the bipolaron concentration n_B to that of the free electrons n_F. We concentrate on a doping regime, where small changes in doping give rise to a large change in T*, which is the case when n_B is small (< 0.1 per site). For finite values of n_B we find negative and practically doping independent values of the isotope coefficient \alpha^* which characterizes the formation of resonating electron pairs. Upon decreasing the total particle density such that n_B becomes exponentially small, we find a rapid change in sign of \alpha^*. This is related to the fact that the system approaches a state which is more BCS-like, where electron pairing occurs via virtual excitations into bipolaronic states and where T* coincides with the onset of superconductivity.Comment: 7 pages, 6 figures, enlarged discussion on the limits of validity of the model, to be published in Phys. Rev.

Spin-orbital coupling in a triplet superconductor-ferromagnet junction

We study a novel type of coupling between spin and orbital degrees of freedom which appears at triplet superconductor-ferromagnet interfaces. Using a self-consistent spatially-dependent mean-field theory, we show that increasing the angle between the ferromagnetic moment and the triplet vector order parameter enhances or suppresses the p-wave gap close to the interface, according as the gap antinodes are parallel or perpendicular to the boundary, respectively. The associated change in condensation energy establishes an orbitally-dependent preferred orientation for the magnetization. When both gap components are present, as in a chiral superconductor, we observe a first-order transition between different moment orientations as a function of the exchange field strength.Comment: 5 pages, 4 figures and Supplemental Material (3 pages

Multiparametric Investigation of Dynamics in Fetal Heart Rate Signals

In the field of electronic fetal health monitoring, computerized analysis of fetal heart rate (FHR) signals has emerged as a valid decision-support tool in the assessment of fetal wellbeing. Despite the availability of several approaches to analyze the variability of FHR signals (namely the FHRV), there are still shadows hindering a comprehensive understanding of how linear and nonlinear dynamics are involved in the control of the fetal heart rhythm. In this study, we propose a straightforward processing and modeling route for a deeper understanding of the relationships between the characteristics of the FHR signal. A multiparametric modeling and investigation of the factors influencing the FHR accelerations, chosen as major indicator of fetal wellbeing, is carried out by means of linear and nonlinear techniques, blockwise dimension reduction, and artificial neural networks. The obtained results show that linear features are more influential compared to nonlinear ones in the modeling of HRV in healthy fetuses. In addition, the results suggest that the investigation of nonlinear dynamics and the use of predictive tools in the field of FHRV should be undertaken carefully and limited to defined pregnancy periods and FHR mean values to provide interpretable and reliable information to clinicians and researchers

Resonating bipolarons

Electrons coupled to local lattice deformations end up in selftrapped localized molecular states involving their binding into bipolarons when the coupling is stronger than a certain critical value. Below that value they exist as essentially itinerant electrons. We propose that the abrupt crossover between the two regimes can be described by resonant pairing similar to the Feshbach resonance in binary atomic collision processes. Given the intrinsically local nature of the exchange of pairs of itinerant electrons and localized bipolarons, we demonstrate the occurrence of such a resonance on a finite-size cluster made out of metallic atoms surrounding a polaronic ligand center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter

A hybrid approach for the analysis of complex categorical data structures: assessment of latent distance learning perception in higher education

A long tradition of analysing ordinal response data deals with parametric models, which started with the seminal approach of cumulative models. When data are collected by means of Likert scale survey questions in which several scored items measure one or more latent traits, one of the sore topics is how to deal with the ordered categories. A stacked ensemble (or hybrid) model is introduced in the proposal to tackle the limitations of summing up the items. In particular, multiple items responses are synthesised into a single meta-item, defined via a joint data reduction approach; the meta-item is then modelled according to regression approaches for ordered polytomous variables accounting for potential scaling effects. Finally, a recursive partitioning method yielding trees provides automatic variable selection. The performance of the method is evaluated empirically by using a survey on Distance Learning perception

Proximity effect between an unconventional superconductor and a ferromagnet with spin bandwidth asymmetry

We study the proximity effect within a junction made of an unconventional superconductor (US) and a ferromagnet (F) in the clean limit with high barrier transparency. Superconductivity in the US side is described by an extended Hubbard model with intersite attractive interaction, while metallic ferromagnetism in the F side is assumed to be originated by a relative change in the bandwidths of electrons with opposite spin. The effect of this mass-split mechanism is analyzed in conjunction with the usual Stoner-like one, where one band is rigidly shifted with respect to the other, due to the presence of a constant exchange field. Starting from the numerical solution of the Bogoliubov-de Gennes equations, we show that the two above mentioned mechanisms for ferromagnetism lead to different features as concerns the formation at the interface of dominant and subdominant superconducting components, as well as their propagation in the ferromagnetic side. This considerably affects the opening of gaplike structures in the local density of states for majority and minority spin electrons, leading to distinct effects as one moves toward the half-metallic regime, where the density of the minority carriers becomes vanishing

Risk Factors of Cholelithiasis Unrelated to Hematological Disorders in Pediatric Patients Undergoing Cholecystectomy

Background: Pediatric cholelithiasis unrelated to hematological disorders is an increasing disease. We analyzed our experience in the surgical treatment of these cases to evaluate risk factors, clinical presentation, intervention and follow-up. Methods: From January 2010 to December 2016, we retrospectively recorded all data (hematological study, familiarity, use of lithogenic drugs and parenteral nutrition) of cholecystectomies for cholelithiasis not related to hematological diseases. The body mass index (BMI) was calculated (obesity if &gt; 25), medical treatment, surgery and follow-up were evaluated. All patients underwent ultrasound for diagnosis and major biliary tract assessment prior to surgery. All patients had a 1-year follow-up. Results: There were twenty-four cases (eight males), with a median age of 11.2 years. Predisposing factors were familiarity in 19, use of lithogenic drugs in 5 and total parental nutrition (TPN) in 3. Median BMI was 19.8 kg/m2, with BMI &gt; 25 kg/m2 in eight cases. Regarding the clinical presentation, 14 had acute pain in the right upper quadrant, 5 had cholecystitis and 5 had non-specific abdominal pain. The medical treatment lasted 6 months in all, except for five (three operated after 2 months and two after 12 months). Preoperative ultrasound did not show stones in the biliary tract. MRI was performed in three cases for suspected malformation of the biliary tract (negative). Laparoscopic cholecystectomy was performed in all cases: mean intervention time was 95 min. A case of postcolecystectomy syndrome was found. At follow-up, all were asymptomatic, except two (recurrent abdominal pain). Conclusion: Main predisposing factors are familiarity and obesity. Preoperative ultrasound in our series replaced the intraoperative study of the biliary tract. Laparoscopic cholecystectomy is the gold standard

LIFE-THREATENING HYPOCALCEMIA IN A PATIENT WITH HIGHLY SUSPECTED OSTEOMALACIA: A CASE REPORT

ABSTRACT: Objective: Osteomalacia is a metabolic bone disease characterized by impaired mineralization with increased non-mineralized osteoid tissue, increased frailty, and reduced bone mineral density. A common cause of osteomalacia in adults and the elderly is severe deficiency of vitamin D, which leads to chronic hypocalcemia, hypophosphatemia, and secondary hyperparathyroidism. The objective of this case report is to describe an unusual clinical presentation of osteomalacia, consisting of life-threatening acute hypocalcemia.Methods: Clinical, laboratory, and imaging data are presented.Results: We report the case of a 65-year-old man that showed symptoms and signs of severe and prolonged hypocalcemia due to unrecognized vitamin D deficiency. He presented at the emergency room reporting abdominal pain and vomiting since the evening before. Blood tests showed increased levels of rhabdomyolysis markers, severe hypocalcemia, hypophosphatemia, hypomagnesemia, normal renal function, elevated levels of alkaline phosphatase, extremely high levels of parathyroid hormone, and hypovitaminosis D. Radiological skeletal features of bone demineralization and bone abnormalities suggestive of osteomalacia were additionally detected. Other secondary causes of hypocalcemia were excluded. Clinical and biochemical resolution were progressively obtained only after an intramuscular loading dose of cholecalciferol was added to the standard calcium intravenous replacement therapy.Conclusion: This case report shows that osteomalacia consequent to a severe vitamin D deficiency can present with acute symptoms and signs of severe hypocalcemia requiring hospital admission. In such cases, vitamin D administration, and not intensive calcium supplementation alone, is essential to achieve clinical resolution of symptoms and normalization of mineral metabolism parameters.Abbreviations: 25-OH-D 25-hydroxyvitamin D CT computed tomography IV intravenous PTH parathyroid hormon