Long-range order, bosonic fluctuations, and pseudogap in strongly correlated electron systems

This thesis deals with the Hubbard model as prototypical model to describe the physics of electrons in the two-dimensional copper-oxide planes of high-$T_c$ cuprates. To get approximate solutions, we employ functional renormalization group (fRG) and dynamical mean-field theory (DMFT) methods. We deal with the problem of identifying bosonic fluctuations in the vertex function, exhibiting an intricate dependence on momenta and frequencies already at moderate coupling. In the normal, paramagnetic phase, the goal is achieved by employing the recently introduced single-boson exchange decomposition. In the symmetry-broken phases, we reformulate the previously introduced combination of fRG with mean-field theory by explicitly introducing a bosonic field. A widely discussed and challenging problem is the emergence of a pseudogap in the Hubbard model. In this thesis we assume this phase to be characterized by strong magnetic fluctuations. Following previous works, we fractionalize the electron in a chargon, carrying the electron's charge, and a charge neutral spinon, which represents local fluctuations of the spin orientation. The chargons undergo N\'eel or spiral magnetic order below a density-dependent transition temperature $T^*$. We compute DC charge transport coefficients for the chargons, and obtain a pronounced drop in the charge carrier density across the magnetic-to-paramagnetic transition. Directional fluctuations of the spin orientation are described by a non-linear sigma model and prevent long-range ordering of the electrons at any finite temperature. The phase where the chargon degrees of freedom are magnetically ordered shares many features with the pseudogap regime observed in high-$T_c$ cuprates: a strong reduction of the charge carrier density, a spin gap, Fermi arcs, and electronic nematicity.Comment: PhD thesis, Universit\"at Stuttgar

Quantum Effects in the Aubry Transition

The Aubry transition between sliding and pinned phases, driven by the competition between two incommensurate length scales, represents a paradigm that is applicable to a large variety of microscopically distinct systems. Despite previous theoretical studies, it remains an open question to what extent quantum effects modify the transition, or are experimentally observable. An experimental platform that can potentially reach the quantum regime has recently become available in the form of trapped laser-cooled ions subject to a periodic optical potential [A. Bylinskii, D. Gangloff, I. Counts, and V. Vuletic, Nature Materials 15, 717 (2016)]. Using Path-Integral Monte Carlo (PIMC) simulation methods, we analyze the impact of quantum tunneling on the sliding-to-pinned transition in this system, and determine the phase diagram in terms of incommensuration and potential strength. We propose new signatures of the quantum Aubry transition that are robust against thermal and finite-size effects, and that can be observed in future experiments.Comment: 10 pages, 7 figure

Identification of Sclerostin as a Putative New Myokine Involved in the Muscle-to-Bone Crosstalk

Bone and muscle have been recognized as endocrine organs since they produce and secrete “hormone-like factors” that can mutually influence each other and other tissues, giving rise to a “bone–muscle crosstalk”. In our study, we made use of myogenic (C2C12 cells) and osteogenic (2T3 cells) cell lines to investigate the effects of muscle cell-produced factors on the maturation process of osteoblasts. We found that the myogenic medium has inhibitory effects on bone cell differentiation and we identified sclerostin as one of the myokines produced by muscle cells. Sclerostin is a secreted glycoprotein reportedly expressed by bone/cartilage cells and is considered a negative regulator of bone growth due to its role as an antagonist of the Wnt/β-catenin pathway. Given the inhibitory role of sclerostin in bone, we analyzed its expression by muscle cells and how it affects bone formation and homeostasis. Firstly, we characterized and quantified sclerostin synthesis by a myoblast cell line (C2C12) and by murine primary muscle cells by Western blotting, real-time PCR, immunofluorescence, and ELISA assay. Next, we investigated in vivo production of sclerostin in distinct muscle groups with different metabolic and mechanical loading characteristics. This analysis was done in mice of different ages (6 weeks, 5 and 18 months after birth) and revealed that sclerostin expression is dynamically modulated in a muscle-specific way during the lifespan. Finally, we transiently expressed sclerostin in the hind limb muscles of young mice (2 weeks of age) via in vivo electro-transfer of a plasmid containing the SOST gene in order to investigate the effects of muscle-specific overproduction of the protein. Our data disclosed an inhibitory role of the muscular sclerostin on the bones adjacent to the electroporated muscles. This observation suggests that sclerostin released by skeletal muscle might synergistically interact with osseous sclerostin and potentiate negative regulation of osteogenesis possibly by acting in a paracrine/local fashion. Our data point out a role for muscle as a new source of sclerostin.Bone and muscle have been recognized as endocrine organs since they produce and secrete “hormone-like factors” that can mutually influence each other and other tissues, giving rise to a “bone–muscle crosstalk”. In our study, we made use of myogenic (C2C12 cells) and osteogenic (2T3 cells) cell lines to investigate the effects of muscle cell-produced factors on the maturation process of osteoblasts. We found that the myogenic medium has inhibitory effects on bone cell differentiation and we identified sclerostin as one of the myokines produced by muscle cells. Sclerostin is a secreted glycoprotein reportedly expressed by bone/cartilage cells and is considered a negative regulator of bone growth due to its role as an antagonist of the Wnt/β-catenin pathway. Given the inhibitory role of sclerostin in bone, we analyzed its expression by muscle cells and how it affects bone formation and homeostasis. Firstly, we characterized and quantified sclerostin synthesis by a myoblast cell line (C2C12) and by murine primary muscle cells by Western blotting, real-time PCR, immunofluorescence, and ELISA assay. Next, we investigated in vivo production of sclerostin in distinct muscle groups with different metabolic and mechanical loading characteristics. This analysis was done in mice of different ages (6 weeks, 5 and 18 months after birth) and revealed that sclerostin expression is dynamically modulated in a muscle-specific way during the lifespan. Finally, we transiently expressed sclerostin in the hind limb muscles of young mice (2 weeks of age) via in vivo electro-transfer of a plasmid containing the SOST gene in order to investigate the effects of muscle-specific overproduction of the protein. Our data disclosed an inhibitory role of the muscular sclerostin on the bones adjacent to the electroporated muscles. This observation suggests that sclerostin released by skeletal muscle might synergistically interact with osseous sclerostin and potentiate negative regulation of osteogenesis possibly by acting in a paracrine/local fashion. Our data point out a role for muscle as a new source of sclerostin

Opinion, knowledge, and clinical experience with functional neurological disorders among Italian neurologists: results from an online survey

Background: Functional neurological disorders (FND) are disabling medical conditions commonly seen in neurological practice. Neurologists play an essential role in managing FND, from establishing a diagnosis to coordination of multidisciplinary team-based treatment for patients. With this study, we investigated the knowledge and the clinical experience of Italian neurologists in managing patients with FND. Methods: Members of the Italian Society of Neurology were invited via e-mail to participate in this ad hoc online survey; 492 questionnaires were returned completed. Results: The term "Functional neurological disorders" in reference to FND was used more frequently than other psychological (e.g., psychogenic or conversion), or descriptive terms (e.g., non-organic or stress-related). When speaking with patients, the respondents stated that they preferred explaining symptoms based on abnormal functioning of the nervous system than discussing mental illness and that they would refer their patient to a psychologist rather than to a psychiatrist. Few considered that physiotherapy and psychiatric interventions are useful approaches to treating FND. Some believed that patients simulate their symptoms. Conclusions: Overall, the responses suggest that knowledge about scientific advances in FND is somewhat sparse. A psychiatric-centered view of FND opens the way to an approach in which neurobiological and psychological aspects constitute essential factors of the condition. In this context, professional education could improve understanding of FND and optimize patient management

Local-Field Dielectric Theory of the BEC-BCS Crossover

The aim of the present thesis is to explore the crossover in a quantum atomic gas of attractively-interacting fermions from a Bardeen-Cooper-Schrieffer (BCS) superfluid state (BCS) [1] to a Bose-Einstein condensate (BEC) of composite bosons. The BCS-BEC crossover is a powerful concept, in that while the attraction strength is progressively increased and all the fundamental quantities smoothly interpolate between the two limiting regimes, the ground-state firmly maintains the same kind of spontaneous symmetry-breaking. BCS superfluidity is a state of matter in which a whatever weak attractive interaction produces pairing of fermions in momentum-space, i.e. of fermions located at opposite sides in the Fermi surface with different possible symmetries of the spin-part of the wave-function. These (Cooper) pairs have large size on the scale of the average inter-particle distance and strongly overlapping in real-space, while occupying the lowest quantum state. A minimum threshold energy is required to break them up, that shows up as an energy gap in the collective excitation spectrum. On the other side, BEC superfluidity is a quantum degenerate state in which all the fermion pairs can be considered as very small-size objects, say point-like composite bosons with given binding energy, that then may Bose-Einstein condense in the lowest quantum state. In the crossover, the Pauli principle is thus preserved while the pairing evolves from occurring in momentum to real space, and the chemical potential correspondingly evolves from the Fermi-energy value in the BCS limit to half-the binding energy of the composite boson in the BEC regime. In all cases, this process leads to the formation of a coherent state characterised by well-established phase coherence of the many-body wave function: this produces at the same time the macroscopic occupation of the lowest quantum state, that is the condensate fraction, and a new stiffness against transverse perturbations, that is the superfluid fraction, the former mainly influenced by the interaction strength and the latter by the system geometry

Analisi di sensitività al tasso di cambio: un’informazione utile per gli investitori?

Il lavoro analizza gli effetti dell’entrata in vigore dell’IFRS 7, emanato dallo IASB con lo scopo di aumentare l’informazione sull’esposizione delle imprese ai rischi di mercato. La nostra ricerca indaga l’utilità per gli investitori dell’analisi di sensitività al rischio di tasso di cambio fornita dalle società quotate italiane. I risultati mostrano che prima dell’introduzione dell’IFRS 7 il mercato stimava erroneamente l’esposizione al tasso di cambio, mentre successivamente la sensitività dei rendimenti al tasso di cambio sembra allinearsi con le esposizioni dichiarate. Dall’analisi, inoltre, emerge che l’informazione sull’esposizione riduce la sensitività dei volumi al tasso di cambio. I nostri risultati integrano la letteratura statunitense fornendo evidenze di come un’analisi di sensitività anche backward-looking sia utile al mercato.IFRS 7, rischio di tasso di cambio, rischio di mercato, analisi di sensitività, disclosure

Lesion volume predicts prostate cancer risk and aggressiveness: validation of its value alone and matched with prostate imaging reporting and data system score

Objective: To demonstrate the association between magnetic resonance imaging (MRI) estimated lesion volume (LV), prostate cancer detection and tumour clinical significance, evaluating this variable alone and matched with Prostate Imaging Reporting and Data System version 2 (PI-RADS v2) score. Patients and methods: We retrospectively analysed 157 consecutive patients, with at least one prior negative systematic prostatic biopsy, who underwent transperineal prostate MRI/ultrasonography fusion-targeted biopsy between January 2014 and February 2016. Suspicious lesions were delineated using a \u2018region of interest\u2019 and the system calculated prostate volume and LV. Patients were divided in groups considering LV ( 640.5, 0.5\u20131, 651 mL) and PI-RADS score (1\u20135). We considered clinically significant prostate cancer as all cancers with a Gleason score of 653 + 4 as suggested by PI-RADS v2. A direct comparison between MRI estimated LV (MRI LV) and histological tumour volume (HTV) was done in 23 patients who underwent radical prostatectomy during the study period. Differences between MRI LV and HTV were assessed using the paired sample t-test. MRI LV and HTV concordance was verified using a Bland\u2013Altman plot. The chi-squared test and logistic and ordinal regression models were used to evaluate difference in frequencies. Results: The MRI LV and PI-RADS score were associated both with prostate cancer detection (both P < 0.001) and with significant prostate cancer detection (P < 0.001 and P = 0.008, respectively). When the two variables were matched, increasing LV increased the risk within each PI-RADS group. Prostate cancer detection was 1.4-times higher for LVs of 0.5\u20131 mL and 1.8-times higher for LVs of 651 mL; significant prostate cancer detection was 2.6-times for LVs of 0.5\u20131 mL and 4-times for LVs of 651 mL. There was a positive correlation between MRI LV and HTV (r = 0.9876, P < 0.001). Finally, Bland\u2013Altman analysis showed that MRI LV was underestimated by 4.2% compared to HTV. Study limitations include its monocentric and retrospective design and the limited cohort. Conclusions: This study demonstrates that PI-RADS score and the MRI LV, independently and in combination, are associated with prostate cancer detection and with tumour clinical significance

External validation of a novel side-specific, multiparametric magnetic resonance imaging-based nomogram for the prediction of extracapsular extension of prostate cancer: preliminary outcomes on a series diagnosed with multiparametric magnetic resonance imaging-targeted plus systematic saturation biopsy

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