Brownian regime of finite- N corrections to particle motion in the XY Hamiltonian mean field model

International audienceWe study the dynamics of the N-particle system evolving in the XY hamiltonian mean field (HMF) model for a repulsive potential, when no phase transition occurs. Starting from a homogeneous distribution, particles evolve in a mean field created by the interaction with all others. This interaction does not change the homogeneous state of the system, and particle motion is approximately ballistic with small corrections. For initial particle data approaching a waterbag, it is explicitly proved that corrections to the ballistic velocities are in the form of independent brownian noises over a time scale diverging not slower than N^(2/5) as N → ∞, which proves the propagation of molecular chaos. Molecular dynamics simulations of the XY-HMF model confirm our analytical findings

Renormalization-Group Theory of 1D quasiperiodic lattice models with commensurate approximants

We develop a renormalization group (RG) description of the localization properties of onedimensional (1D) quasiperiodic lattice models. The RG flow is induced by increasing the unit cell of subsequent commensurate approximants. Phases of quasiperiodic systems are characterized by RG fixed points associated with renormalized single-band models. We identify fixed-points that include many previously reported exactly solvable quasiperiodic models. By classifying relevant and irrelevant perturbations, we show that phase boundaries of more generic models can be determined with exponential accuracy in the approximant's unit cell size, and in some cases analytically. Our findings provide a unified understanding of widely different classes of 1D quasiperiodic systems

Incommensurability-Induced Enhancement of Superconductivity in One Dimensional Critical Systems

We show that incommensurability can enhance superconductivity in one dimensional quasiperiodic systems with s-wave pairing. As a parent model, we use a generalized Aubry-Andr\'e model that includes quasiperiodic modulations both in the potential and in the hoppings. In the absence of interactions, the model contains extended, critical and localized phases for incommensurate modulations. Our results reveal that in a substantial region inside the parent critical phase, there is a significant increase of the superconducting critical temperature compared to the extended phase and the uniform limit without quasiperiodic modulations. We also analyse the results for commensurate modulations with period close to the selected incommensurate one. We find that while in the commensurate case, the scaling of the critical temperature with interaction strength follows the exponentially small weak-coupling BCS prediction for a large enough system size, it scales algebraically in the incommensurate case within the critical and localized parent phases. These qualitatively distinct behaviors lead to a significant incommensurability-induced enhancement of the critical temperature in the weak and intermediate coupling regimes, accompanied by an increase in the superconducting order parameter at zero temperature.Comment: 8 pages, 4 figure

Short-range interactions are irrelevant at the quasiperiodic-driven Luttinger Liquid to Anderson Glass transition

We show that short-range interactions are irrelevant around gapless ground-state delocalization-localization transitions driven by quasiperiodicity in interacting fermionic chains. In the presence of interactions, these transitions separate Luttinger Liquid and Anderson glass phases. Remarkably, close to criticality, we find that excitations become effectively non-interacting. By formulating a many-body generalization of a recently developed method to obtain single-particle localization phase diagrams, we carry out precise calculations of critical points between Luttinger Liquid and Anderson glass phases and find that the correlation length critical exponent takes the value $\nu = 1.001 \pm 0.007$, compatible with $\nu=1$ known exactly at the non-interacting critical point. We also show that other critical exponents, such as the dynamical exponent $z$ and a many-body analog of the fractal dimension are compatible with the exponents obtained at the non-interacting critical point. Noteworthy, we find that the transitions are accompanied by the emergence of a many-body generalization of previously found single-particle hidden dualities. Finally, we show that in the limit of vanishing interaction strength, all finite range interactions are irrelevant at the non-interacting critical point

FORMACIÓN EN NANOTECNOLOGÍA PARA LA EDUCACIÓN SECUNDARIA: ACCIONES Y PERSPECTIVAS DEL PROYECTO LIFENANO-IFSP

En el medio de los desafíos e iniciativas encaminadas para mejorar la enseñanza en diversas áreas del conocimiento en la educación básica, está el perfeccionamiento de la formación docente. Esto viene siendo debatido tanto por el gobierno federal brasileño como por la comunidad académica. Los enfoques metodológicos innovadores orientados a temas de ciencia contemporáneos y las propuestas para la introducción sistemática de conceptos de nanociencia y nanotecnología son aún muy incipientes. Esa situación no se limita a Brasil; se presenta también en otros países iberoamericanos. En este panorama es necesario el uso de estrategias colaborativas con el fin de establecer acciones de difusión y formación en nano-ciencia y nanotecnología. En este trabajo se presentan acciones y perspectivas de un laboratorio para capacitación inter-disciplinar de educadores en nanociencia y nanotecnología en el interior del estado de São Paulo, en Brasil. También se muestra como el laboratorio interactúa con un programa de becas de iniciación a la enseñanza financiado por el gobierno federal brasileño. Finalmente, se discuten las motivaciones de los estudiantes participantes y las potenciales contribuciones del laboratorio para una red internacional orientada a la difusión y a la capacitación en nanociencia y nanotecnología.Among the challenges and initiatives aiming the improvement of teaching in several areas of knowledge in basic education, the enhancement of the formation of teachers plays a key role. Both the Brazilian government and the academic community have debated about this. Innovative methodological approaches devoted to contemporary topics of science are still incipient. This occurs in Brazil as well as in other Iberian American countries. In these conditions, the use of collaborative strategies is necessary towards the diffusion and the education in nanoscience and nanotechnology. This work presents actions and perspectives of the laboratory for the interdisciplinary formation of teachers in nanoscience and nanotechnology in the countryside of the State of São Paulo, in Brazil. It has been shown how this laboratory interacts with an institutional program of fellowships for teaching apprenticeship that is supported by the Brazilian Federal Government. Finally, the motivations of the participating students and the contributions of the laboratory to an international network devoted to the diffusion and education in nanoscience and nanotechnology are discussed

Augmented reality-assisted ultrasound breast biopsy

Breast cancer is the most prevalent cancer in the world and the fifth-leading cause of cancer-related death. Treatment is effective in the early stages. Thus, a need to screen considerable portions of the population is crucial. When the screening procedure uncovers a suspect lesion, a biopsy is performed to assess its potential for malignancy. This procedure is usually performed using real-time Ultrasound (US) imaging. This work proposes a visualization system for US breast biopsy. It consists of an application running on AR glasses that interact with a computer application. The AR glasses track the position of QR codes mounted on an US probe and a biopsy needle. US images are shown in the user’s field of view with enhanced lesion visualization and needle trajectory. To validate the system, latency of the transmission of US images was evaluated. Usability assessment compared our proposed prototype with a traditional approach with different users. It showed that needle alignment was more precise, with 92.67 ± 2.32° in our prototype versus 89.99 ± 37.49° in a traditional system. The users also reached the lesion more accurately. Overall, the proposed solution presents promising results, and the use of AR glasses as a tracking and visualization device exhibited good performance.This work was funded by the projects “NORTE-01-0145-FEDER-000045” and “NORTE-01- 0145-FEDER-000059", supported by Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (FEDER). It was also funded by national funds, through the FCT (Fundação para a Ciência e a Tecnologia) and FCT/MCTES in the scope of the project UIDB/05549/2020, UIDP/05549/2020 and LASI-LA/P/0104/2020. The authors also acknowledge FCT, Portugal and the European Social Found, European Union, for funding support through the “Programa Operacional Capital Humano” (POCH) in the scope of the PhD grants SFRH/BD/136721/2018 (Oliveira B.) and SFRH/BD/136670 (Torres H. R.)

Efeito da hidroxiapatita bovina no período inicial de formação óssea

PURPOSE: This study aimed to characterize the effect of bovine hydroxyapatite particles (HA) on the early stages of bone repairing in a rat femur defect model. METHODS: A non-critical 2 mm diameter bone defect was made in both femurs of 25 male albino Wistar rats. The left femurs defects were filled with HA and the right femurs defects were just let to fill with blood. Five animals were sacrificed at the 1st, 3rd, 5th, 7th or 14th post-surgery day and bone tissue sections were stained with hematoxylin and eosin for comparison of inflammatory response by light microscopy. Histomorphometrical analysis of the newly formed bone was evaluated at the three last periods, using independent t-student test to compare both groups at each period (a=0.05). RESULTS: Histological analyses showed same standard of bone repair on first and third day; however, from the fifth post-surgery day there was a higher deposit of collagen fibers surrounding the hydroxyapatite particles and a greater thickness of the opposite side periosteum. There was no significant histomorphometrical difference between groups at all periods. CONCLUSION: It can be concluded that hydroxyapatite does not accelerate the early-stage of bone repairing, despite of induction of a higher deposit of collagen fibers.OBJETIVO: O objetivo deste estudo foi caracterizar o efeito das partículas de hidroxiapatita bovina (HA) nos estágios iniciais da reparação óssea em modelo de defeito ósseo em fêmur de ratos. METDOLOGIA: Defeito ósseo não crítico de 2 mm de diâmetro foi feito em cada fêmur de 25 ratos Wistar albinos. O defeito do fêmur esquerdo foi preenchido com HA enquanto a cavidade direita foi preenchida apenas com sangue. Cinco animais foram sacrificados no 1º, 3º, 5º, 7º e 14º dia pós-cirúrgico. Os cortes histológicos do tecido ósseo foram corados com hematoxicilina e eosina para comparação da resposta inflamatória por microscopia óptica. Análise histomorfométrica do tecido ósseo neoformado foi avaliado nos três últimos períodos utilizando o teste t de Student para comparação de ambos os grupos em cada período de avaliação (a=0,05). RESULTADOS: A análise histológica mostrou o mesmo padrão de reparação óssea no 1º e 3º dia; entretanto, no 5º dia pós-cirúrgico houve um maior depósito de fibras de colágeno ao redor dos cristais de hidroxiapatita e uma maior espessura do perióstio oposto. Não houve diferença histomorfométrica significativa entre os grupos em todos os períodos avaliados. CONCLUSÃO: Pode ser concluído que a hidroxiapatita não acelera os estágios inicias da reparação óssea, apesar de induzir a um maior depósito de fibras de colágeno