Quantum phase transitions in one-dimensional nanostructures: a comparison between DFT and DMRG methodologies

In the realm of quantum chemistry, the accurate prediction of electronic structure and properties of nanostructures remains a formidable challenge. Density Functional Theory (DFT) and Density Matrix Renormalization Group (DMRG) have emerged as two powerful computational methods for addressing electronic correlation effects in diverse molecular systems. We compare ground-state energies ($e_0$), density profiles ($n$) and average entanglement entropies ($\bar S$) in metals, insulators and at the transition from metal to insulator, in homogeneous, superlattices and harmonically confined chains described by the fermionic one-dimensional Hubbard model. While for the homogeneous systems there is a clear hierarchy between the deviations, $D\%(\bar S)<D\%(e_0)< \bar D\%(n)$, and all the deviations decrease with the chain size; for superlattices and harmonical confinement the relation among the deviations is less trivial and strongly dependent on the superlattice structure and the confinement strength considered. For the superlattices, in general increasing the number of impurities in the unit cell represents less precision on the DFT calculations. For the confined chains, DFT performs better for metallic phases, while the highest deviations appear for the Mott and band-insulator phases. This work provides a comprehensive comparative analysis of these methodologies, shedding light on their respective strengths, limitations, and applications

Silagem de soja no enriquecimento de dietas compostas por silagem de ponta de cana-de-açúcar. 1 - Consumo de nutrientes.

Conduziu-se o estudo com o objetivo de avaliar o desempenho de ovinos alimentados com dietas compostas por silagem da ponta de cana-de-açúcar enriquecida com silagem de soja. Foram utilizados 24 cordeiros da raça Morada Nova com idade média de 75 dias e peso vivo médio de 16,98 kg ± 2,62 kg. Avaliaram-se as seguintes dietas: T1= 20% de silagem da ponta de cana + 80% de concentrado; T2= 20% de silagem da ponta de cana + 30% de silagem de soja + 50% de concentrado; T3= 20% de silagem da ponta de cana + 60% de silagem de soja + 20% de concentrado. O delineamento experimental foi o de blocos completos casualizados, com oito repetições. Foram avaliados os consumos de matéria seca, proteína bruta, nitrogênio contido na fibra em detergente neutro (nFDN) e na fibra em detergente ácido (nFDA). Dietas compostas por silagem de ponta de cana-de-açúcar enriquecida com silagem de soja + concentrado proporcionam maior consumo de nutrientes. A utilização de silagem de soja para enriquecer o teor protéico de dietas compostas por silagem de ponta de cana-de-açúcar fica na dependência do custo para aquisição de concentrado protéico ou produção de proteína na propriedade por meio da ensilagem da planta de soja

Association between lowering restriction levels during the coronavirus outbreak and physical activity among adults: a longitudinal observational study in Brazil

OBJECTIVE The COVID-19 pandemic has had significant consequences on public health and lifestyle and has negatively affected mental health and the level of physical activity worldwide. This study examined the impact of reopening fitness centers and nonessential services and introducing flexible measures to ensure social distancing on physical activity and mental health. MATERIALS AND METHODS This was a longitudinal study. A self-administered questionnaire, including personal, behavioral, physical activity, perception of health, and mood state disorder information, was answered by 128 Brazilians in June 2020 (during severe restrictive measures) and again in April 2021 (after fitness centers and nonessential services were reopened). RESULTS The restriction level adopted in April 2021 was significantly lower than that in June 2020 (p<0.001). The level of physical activity (p<0.001) and health status perception (p<0.001) decreased from June 2020 to April 2021. The median values for depression and anxiety did not differ across the study period. CONCLUSIONS The level of physical activity was reduced during the COVID-19 pandemic, and anxiety and depression were not improved following less restrictive social distancing measures and the reopening of fitness centers. Thus, the return to a prepandemic level of physical activity and mental health status may not be automatic. The results presented herein suggest that the decrease in physical activity observed in the population may be challenging in the postpandemic period