Destruction of Superconductivity by Impurities in the Attractive Hubbard Model

We study the effect of U=0 impurities on the superconducting and thermodynamic properties of the attractive Hubbard model on a square lattice. Removal of the interaction on a critical fraction of $f_{\rm crit} \approx 0.30$ of the sites results in the destruction of off-diagonal long range order in the ground state. This critical fraction is roughly independent of filling in the range $0.75 < \rho < 1.00$, although our data suggest that $f_{\rm crit}$ might be somewhat larger below half-filling than at $\rho=1$. We also find that the two peak structure in the specific heat is present at $f$ both below and above the value which destroys long range pairing order. It is expected that the high $T$ peak associated with local pair formation should be robust, but apparently local pairing fluctuations are sufficient to generate a low temperature peak

The role of control region mitochondrial DNA mutations in cardiovascular disease : stroke and myocardial infarction

Recent studies associated certain type of cardiovascular disease (CVD) with specific mitochondrial DNA (mtDNA) defects, mainly driven by the central role of mitochondria in cellular metabolism. Considering the importance of the control region (CR) on the regulation of the mtDNA gene expression, the aim of the present study was to investigate the role of mtDNA CR mutations in two CVDs: stroke and myocardial infarction (MI). MtDNA CR mutations (both fixed and in heteroplasmy) were analysed in two demographically-matched case-control samples, using 154 stroke cases, 211 MI cases and their corresponding control individuals. Significant differences were found, reporting mutations m.16145 G > A and m.16311 T > C as potential genetic risk factors for stroke (conditional logistic regression: p = 0.038 and p = 0.018, respectively), whereas the m.72 T > C, m.73 A > G and m.16356 T > C mutations could act as possible beneficial genetic factors for MI (conditional logistic regression: p = 0.001, p = 0.009 and p = 0.016, respectively). Furthermore, our findings also showed a high percentage of point heteroplasmy in MI controls (logistic regression: p = 0.046; OR = 0.209, 95% CI [0.045-0.972]). These results demonstrate the possible role of mtDNA mutations in the CR on the pathogenesis of stroke and MI, and show the importance of including this regulatory region in genetic association studies

Structural and electrical properties of Zr-doped K0.48 Na 0.52 NbO 3 ceramics: “Hard” lead-free piezoelectric

The structural and electrical properties of K0.48Na0.52Nb1−xZrxO3−δ (x = 0–0.04) ceramics prepared by the conventional solid-state reaction method were studied. Pellets with composition x ≤ 0.03 sintered at 1125 °C for 2 h showed single-phase of potassium sodium niobate (KNN) perovskite structure. Based on X-ray diffraction and Raman results, a mixture of orthorhombic and monoclinic phases was observed in intermediate compositions. The addition of Zr improved the sinterability and the “hard” piezoelectric properties of KNN, increasing the Ec and Qm values. The composition with x = 0.03 presented the highest permittivity at room temperature, ɛr′ = 363 and the lowest dielectric losses, tan δ = 0.027. Moreover, it was the sample with the highest Qm and d33 values, with Qm = 1781 and d33 = 82 pC/N. It was therefore the best compositions to obtain a “hard” piezoelectric material based on Zr-doped KNN, which makes it promising candidate for use as “hard” lead-free piezoelectric material for high power applications

Overall survival analyses of female malignancies in Southern Brazil during 2008–2017: A closer look at breast, cervical and ovarian cancer

Background: The aim of this study was to report the overall survival and baseline factors associated with OS for breast, cervical and ovarian cancer in Florianópolis, Southern Brazil, a region with quality-of-life indicators comparable to high-income countries. Methods: Cohort study was performed from probabilistic record linkage of the Mortality Information System and the Population-based cancer registry of Florianópolis. It was included breasts, cervical and ovarian cancer diagnosis during the period of 2008–2012 with a follow up of 60 months. Cox regression and Kaplan-Meier method were used for associations with overall survival and risk factors. Findings: 1857 cases of the three malignancies were included in the analysis. We identified 202 deaths in breast cancer subjects, 53 for cervical cancer and 51 for ovarian cancer. Metastatic disease at diagnosis was present in 31%, 9.6%, and 55% of the cases, respectively. Overall survival was statistically correlated with age, educational level and stage for breast cancer; age and stage for cervical cancer; age and stage for ovarian cancer. Interpretation: Metastatic disease and age are the main prognostic factors for the malignancies studied, as they were associated with both overall survival and risk of death. Better screening and preventive tests for early diagnosis are needed. Funding: Support of Research and Innovation in the State of Santa Catarina, Research Program for the Unified Health System (FAPESC/MS-DECIT/CNPQ/SES-SC-PPSUS); the Brazilian National Research Council (CNPq); and the Coordination for the Improvement of Higher Education Personnel (CAPES)

Multiscale modelling approach for simulating low velocity impact tests of aramid-epoxy composite with nanofillers

The addition of nanofillers to composites has attracted great attention since it adds multifunctional potential. However, the presence of nanofillers inside a composite may cause a more complex response in many situations, e.g. damage accumulation processes, and this response poses extra challenges in the development of reliable numerical approaches. In this work, a three-step multiscale modelling strategy was used to investigate the mechanical properties and damage accumulation of plain-weave aramid-epoxy composites with hybrid nanofillers (carbon nanotubes and graphene nanoplatelets). First, the mean-field method was employed in a microscale model to provide the elastic modulus of the matrix with nanofillers inside. The mechanical properties of such a matrix were then used to predict the global mechanical properties of aramid-epoxy composite using mesoscale models. Finally, those predictions were added as input to a homogeneous material model used to replicate a more complex loading condition (low-velocity tests), for which the direct use of the mesoscale approach is not feasible. In the latter, the mechanical properties of aramid-epoxy composite with nanofillers have been modelled using MAT_162 in LS-DYNA. The agreement between the experiments and simulations with regards to the loading curves and damage phenomena can thus validate the presented approach. In addition, the effect of nanofillers on the mechanical properties and damage evolution of the woven composites in low-velocity impact has been discussed. Finally, the present work can be helpful to improve the awareness in the design of innovative materials by means of predictive modelling approaches

Interplay of quantum and classical fluctuations near quantum critical points

For a system near a quantum critical point (QCP), above its lower critical dimension $d_L$, there is in general a critical line of second order phase transitions that separates the broken symmetry phase at finite temperatures from the disordered phase. The phase transitions along this line are governed by thermal critical exponents that are different from those associated with the quantum critical point. We point out that, if the effective dimension of the QCP, $d_{eff}=d+z$ ($d$ is the Euclidean dimension of the system and $z$ the dynamic quantum critical exponent) is above its upper critical dimension $d_C$, there is an intermingle of classical (thermal) and quantum critical fluctuations near the QCP. This is due to the breakdown of the generalized scaling relation $\psi=\nu z$ between the shift exponent $\psi$ of the critical line and the crossover exponent $\nu z$, for $d+z>d_C$ by a \textit{dangerous irrelevant interaction}. This phenomenon has clear experimental consequences, like the suppression of the amplitude of classical critical fluctuations near the line of finite temperature phase transitions as the critical temperature is reduced approaching the QCP.Comment: 10 pages, 6 figures, to be published in Brazilian Journal of Physic