The phase diagram of quantum systems: Heisenberg antiferromagnets

A novel approach for studying phase transitions in systems with quantum degrees of freedom is discussed. Starting from the microscopic hamiltonian of a quantum model, we first derive a set of exact differential equations for the free energy and the correlation functions describing the effects of fluctuations on the thermodynamics of the system. These equations reproduce the full renormalization group structure in the neighborhood of a critical point keeping, at the same time, full information on the non universal properties of the model. As a concrete application we investigate the phase diagram of a Heisenberg antiferromagnet in a staggered external magnetic field. At long wavelengths the known relationship to the Quantum Non Linear Sigma Model naturally emerges from our approach. By representing the two point function in an approximate analytical form, we obtain a closed partial differential equation which is then solved numerically. The results in three dimensions are in good agreement with available Quantum Monte Carlo simulations and series expansions. More refined approximations to the general framework presented here and few applications to other models are briefly discussed.Comment: 17 pages, 7 figure

Lattice Pseudospin Model for ν=1\nu=1 Quantum Hall Bilayers

We present a new theoretical approach to the study of $\nu=1$ quantum Hall bilayer that is based on a systematic mapping of the microscopic Hamiltonian to an anisotropic SU(4) spin model on a lattice. To study the properties of this model we generalize the Heisenberg model Schwinger boson mean field theory (SBMFT) of Arovas and Auerbach to spin models with anisotropy. We calculate the temperature dependence of experimentally observable quantities, including the spin magnetization, and the differential interlayer capacitance. Our theory represents a substantial improvement over the conventional Hartree-Fock picture which neglects quantum and thermal fluctuations, and has advantages over long-wavelength effective models that fail to capture important microscopic physics at all realistic layer separations. The formalism we develop can be generalized to treat quantum Hall bilayers at filling factor $\nu=2$.Comment: 26 pages, 10 figures. The final version, to appear in PR

High-temperature deformation behavior of a gamma TiAl alloy-microstructural evolution and mechanisms

The present investigation was carried out in the context of the internal-variable theory of inelastic deformation and the dynamic-materials model (DMM), to shed light on the high-temperature deformation mechanisms in TiAl. A series of load-relaxation tests and tensile tests were conducted on a fine-grained duplex gamma TiAl alloy at temperatures ranging from 800 degreesC to 1050 degreesC. Results of the load-relaxation tests, in which the deformation took place at an infinitesimal level (epsilon congruent to 0.05), showed that the deformation behavior of the alloy was well described by the sum of dislocation-glide and dislocation-climb processes. To investigate the deformation behavior of the fine-grained duplex gamma TiAl alloy at a finite strain level, processing maps were constructed on the basis of a DMM. For this purpose, compression tests were carried out at temperatures ranging from 800 degreesC to 1250 degreesC using strain rates ranging from 10 to 10(-4)/s. Two domains were identified and characterized in the processing maps obtained at finite strain levels (0.2 and 0.6). One domain was found in the region of 980 degreesC and 10(-3)/s with a peak efficiency (maximum efficiency of power dissipation) of 48 pct and was identified as a domain of dynamic recrystallization (DRx) from microstructural observations. Another domain with a peak efficiency of 64 pct was located in the region of 1250 degreesC and 10(-4)/s and was considered to be a domain of superplasticity.ope

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness

The genetic architecture of the human cerebral cortex

INTRODUCTION The cerebral cortex underlies our complex cognitive capabilities. Variations in human cortical surface area and thickness are associated with neurological, psychological, and behavioral traits and can be measured in vivo by magnetic resonance imaging (MRI). Studies in model organisms have identified genes that influence cortical structure, but little is known about common genetic variants that affect human cortical structure. RATIONALE To identify genetic variants associated with human cortical structure at both global and regional levels, we conducted a genome-wide association meta-analysis of brain MRI data from 51,665 individuals across 60 cohorts. We analyzed the surface area and average thickness of the whole cortex and 34 cortical regions with known functional specializations. RESULTS We identified 306 nominally genome-wide significant loci (P < 5 × 10−8) associated with cortical structure in a discovery sample of 33,992 participants of European ancestry. Of the 299 loci for which replication data were available, 241 loci influencing surface area and 14 influencing thickness remained significant after replication, with 199 loci passing multiple testing correction (P < 8.3 × 10−10; 187 influencing surface area and 12 influencing thickness). Common genetic variants explained 34% (SE = 3%) of the variation in total surface area and 26% (SE = 2%) in average thickness; surface area and thickness showed a negative genetic correlation (rG = −0.32, SE = 0.05, P = 6.5 × 10−12), which suggests that genetic influences have opposing effects on surface area and thickness. Bioinformatic analyses showed that total surface area is influenced by genetic variants that alter gene regulatory activity in neural progenitor cells during fetal development. By contrast, average thickness is influenced by active regulatory elements in adult brain samples, which may reflect processes that occur after mid-fetal development, such as myelination, branching, or pruning. When considered together, these results support the radial unit hypothesis that different developmental mechanisms promote surface area expansion and increases in thickness. To identify specific genetic influences on individual cortical regions, we controlled for global measures (total surface area or average thickness) in the regional analyses. After multiple testing correction, we identified 175 loci that influence regional surface area and 10 that influence regional thickness. Loci that affect regional surface area cluster near genes involved in the Wnt signaling pathway, which is known to influence areal identity. We observed significant positive genetic correlations and evidence of bidirectional causation of total surface area with both general cognitive functioning and educational attainment. We found additional positive genetic correlations between total surface area and Parkinson’s disease but did not find evidence of causation. Negative genetic correlations were evident between total surface area and insomnia, attention deficit hyperactivity disorder, depressive symptoms, major depressive disorder, and neuroticism. CONCLUSION This large-scale collaborative work enhances our understanding of the genetic architecture of the human cerebral cortex and its regional patterning. The highly polygenic architecture of the cortex suggests that distinct genes are involved in the development of specific cortical areas. Moreover, we find evidence that brain structure is a key phenotype along the causal pathway that leads from genetic variation to differences in general cognitive function

Outcomes After Transcatheter Edge-to-Edge Mitral Valve Repair According to Mitral Regurgitation Etiology and Cardiac Remodeling

BACKGROUND Transcatheter edge-to-edge repair (TEER) has been increasingly used for selected patients with mitral regurgitation (MR), but limited data are available regarding clinical outcomes in patients with varied etiology and mechanism of MR.OBJECTIVES The aim of this study was to evaluate the outcomes of TEER according to etiology and left ventricular (LV) and left atrial remodeling.METHODS Consecutive patients who underwent TEER between 2007 and 2020 were included in the analysis. Among patients with functional MR (FMR), those with predominant LV remodeling were classified as having ventricular FMR (v-FMR), whereas those without LV remodeling but predominant left atrial remodeling were classified as having atrial FMR (a-FMR). The primary outcome was a composite of all-cause mortality and heart failure hospitalization at 2 years and was compared among patients with degenerative MR (DMR), a-FMR, and v-FMR.RESULTS A total of 1,044 patients (11% with a-FMR, 48% with v-FMR, and 41% with DMR) with a mean Society of Thoracic Surgeons score of 8.6 +/- 7.8 underwent TEER. Patients with a-FMR had higher rates of atrial fibrillation and severe tricuspid regurgitation with larger left and right atria, whereas patients with v-FMR had lower LV ejection fractions with larger LV dimensions. Residual MR more than moderate at discharge was not significantly different among the 3 groups (5.2% vs 3.2% vs 2.6%; P = 0.37). Compared with patients with DMR, 2-year event rates of the primary outcome were significantly higher in patients with a-FMR and v-FMR (21.6% vs 31.5% vs 42.3%; log-rank P < 0.001).CONCLUSIONS Despite excellent procedural outcomes, patients with a-FMR and v-FMR had worse clinical outcomes compared with those with DMR. (c) 2022 by the American College of Cardiology Foundation

Prognostic Value of Increased Mitral Valve Gradient After Transcatheter Edge-to-Edge Repair for Primary Mitral Regurgitation

OBJECTIVES This study sought to evaluate the prognostic value of an increased mean mitral valve pressure gradient (MVG) in patients with primary mitral regurgitation (MR) after transcatheter edge-to-edge repair (TEER).BACKGROUND Conflicting data exist regarding impact of increased mean MVG on outcomes after TEER.METHODS This study included 419 patients with primary MR (mean age 80.6 +/- 10.4 years; 40.6% female) who underwent TEER. Patients were divided into quartiles (Qs) based on discharge echocardiographic mean MVG. Primary outcome was the composite endpoint of all-cause mortality and heart failure hospitalization. Secondary outcomes included all-cause mortality and the secondary composite endpoint of all-cause mortality, heart failure hospitalization, and mitral valve reintervention.RESULTS The median number of MitraClips used was 2 per patient. MR reduction <= moderate was achieved in 407 (97.1%) patients. Mean MVG was 1.9 +/- 0.3 mm Hg, 3.0 +/- 0.1 mm Hg, 4.0 +/- 0.1 mm Hg, and 6.0 +/- 1.2 mm Hg in Q1, Q2, Q3, and Q4, respectively. There was no significant differences across quartiles in the primary outcome (15.4%, 19.6%, 22.0%, and 21.9% in Q1-Q4, respectively; P = 0.63), all-cause mortality (15.9% vs 18.6% vs 19.4% vs 17.1%, respectively; P = 0.91), and the secondary composite endpoint at 2 years (33.3% vs 29.5% vs 22.0% vs 31.6%, respectively; P = 0.37). After multivariate adjustment for baseline clinical and procedural variables, the mean MVG in Q4 compared with Q1 to Q3 was not independently associated with the primary outcome (HR: 1.22; 95% CI: 0.82-1.83; P = 0.33), allcause mortality, and the secondary composite endpoint.CONCLUSIONS Increased mean MVG was not independently associated with adverse events after TEER in patients with primary MR. (C) 2022 by the American College of Cardiology Foundation

Prognostic Value of Increased Mitral Valve Gradient After Transcatheter Edge-to-Edge Repair for Primary Mitral Regurgitation

OBJECTIVES This study sought to evaluate the prognostic value of an increased mean mitral valve pressure gradient (MVG) in patients with primary mitral regurgitation (MR) after transcatheter edge-to-edge repair (TEER).BACKGROUND Conflicting data exist regarding impact of increased mean MVG on outcomes after TEER.METHODS This study included 419 patients with primary MR (mean age 80.6 +/- 10.4 years; 40.6% female) who underwent TEER. Patients were divided into quartiles (Qs) based on discharge echocardiographic mean MVG. Primary outcome was the composite endpoint of all-cause mortality and heart failure hospitalization. Secondary outcomes included all-cause mortality and the secondary composite endpoint of all-cause mortality, heart failure hospitalization, and mitral valve reintervention.RESULTS The median number of MitraClips used was 2 per patient. MR reduction <= moderate was achieved in 407 (97.1%) patients. Mean MVG was 1.9 +/- 0.3 mm Hg, 3.0 +/- 0.1 mm Hg, 4.0 +/- 0.1 mm Hg, and 6.0 +/- 1.2 mm Hg in Q1, Q2, Q3, and Q4, respectively. There was no significant differences across quartiles in the primary outcome (15.4%, 19.6%, 22.0%, and 21.9% in Q1-Q4, respectively; P = 0.63), all-cause mortality (15.9% vs 18.6% vs 19.4% vs 17.1%, respectively; P = 0.91), and the secondary composite endpoint at 2 years (33.3% vs 29.5% vs 22.0% vs 31.6%, respectively; P = 0.37). After multivariate adjustment for baseline clinical and procedural variables, the mean MVG in Q4 compared with Q1 to Q3 was not independently associated with the primary outcome (HR: 1.22; 95% CI: 0.82-1.83; P = 0.33), allcause mortality, and the secondary composite endpoint.CONCLUSIONS Increased mean MVG was not independently associated with adverse events after TEER in patients with primary MR. (C) 2022 by the American College of Cardiology Foundation.Cardiolog