Co-, Ni-, and Mn-doped BiFeO3 (BFO) ceramics were synthesized herein through a solid-state reaction. All doped BFO samples exhibit visible-light response, and the Co- and Ni-doped BFO samples present enhanced ferromagnetic order at room temperature. All doped samples show secondary phases in minor quantities. Optical spectra reveal two absorptions bands, indicating multiple electron transitions for BFO and its secondary phases. M − H hysteresis loops suggest enhanced ferromagnetism in the Co- and Ni-doped BFO samples because of magnetic spinel CFP and NFO phases, respectively, whereas changes in oxygen vacancies and Fe–O–Fe bond angle play minor roles in the ferromagnetic behavior.
The world’s population suffers a COVID-19 pandemic. By September 2020 nearly 1 million people had died. These are official numbers. The real cases might be much higher, due to under-reporting in many countries. Different strategies were adopted by national governments. Neglecting what was defined by sanitarian authorities, some politicians, at the beginning of the pandemic, declared that it would be a little flu, without consequences, lighter than seasonal flues. Some politicians propagated medicines with no scientific support. In many countries and regions, people became confused. The population’s reactions to these political positions may facilitate or block the virus spread. In this paper, we propose a model connecting the spreading of opinions with the propagation of a pandemic. We discuss how conflicting opinions can diffuse in the pandemic environment and the influence it has on the population’s behavior; how it may cause a greater or smaller number of infected individuals.
The number of COVID-19 infected people in each country is a crucial factor to determine public policies. It guides the governments to strengthen movement restrictions of people or to relieve it. The number of infected people is very important to forecast the needs of the health systems, which are collapsing in many countries. Thus, underreporting of infected people is a huge problem, since authorities do not know the real problem and act in darkness. In the present work, we discuss this subject for the Brazilian case. We take the time series of acute respiratory syndromes reported in the health public system in the last ten years and estimated the number for March/20 when the COVID-19 appeared in Brazil. Our results show a 7.7:1 rate of underreporting, meaning that the real cases in Brazil should be, at least, seven times the publicized number.
Este artigo examina o contexto e as implicações da pandemia por Covid-19 na cidade de Belo Horizonte (BH) nos primeiros 80 dias da doença. Utilizamos um recorte analítico descritivo para mensurar a evolução dos casos, o excesso de óbitos, a taxa de transmissibilidade do vírus e a pressão da doença sobre o sistema de saúde de BH e região, através da taxa de ocupação hospitalar nos leitos públicos. Além disso, identificamos as principais políticas de contenção adotadas pelas autoridades locais, bem como as implicações da redução do distanciamento social. Nossos resultados demonstram que o Sistema Único de Saúde (SUS), bem gerido, é fundamental para o enfrentamento da pandemia e a mitigação de suas consequências para a população. O processo de flexibilização que se inicia tem imposto novos desafios que requererão monitoramento atento das autoridades e da sociedade.
We investigate theoretically, through of first-principles calculations, the effect of the application of large in-plane uniaxial stress on single-layer of MoS2, MoSe2, and MoSSe alloys. For stress applied along the zigzag direction, we predict an anomalous behavior near the point fracture. This behavior is characterized by the reorientation of the MoS2 structure along the applied stress from zigzag to armchair due to the formation of transient square-lattice regions in the crystal, with an apparent (although not real) crystal rotation of 30 degrees. After reorientation, a large plastic deformation √3-1 remains after the stress is removed. This behavior is also observed in MoSe2 and in MoSSe alloys. This phenomenon is observed both in stress-constrained geometry optimizations and in ab initio molecular dynamics simulations at finite temperature and applied stress.
The direct bonding between a thiazolo[5,4-d]thiazole and two 1,3,4-oxadiazole units allowed us to create a new and versatile rigid core for luminescent liquid crystal, which showed interesting and variable mesomorphic and photophysical properties. From the 5-bis(5-phenyl-1,3,4-oxadiazol-2-yl)thiazolo[5,4-d]thiazole new core, three molecules with different number of alkoxy chains were synthesized and had their properties correlated with the molecular structure. The molecule with two chains showed a smectic C mesophase, while the mesogens with four and six chains presented hexagonal columnar mesomorphism, which was confirmed by POM and XRD measurements. In addition, the molecule with six chains presented liquid crystalline behavior close to room temperature. In solution, the molecules presented strong photoluminescence ranging from blue to yellow, with quantum yields higher than 0.6. Excited state lifetimes allowed to correlate the fluorescence component associated to the different emitting species to the molecular organization in spin coated films. The molecular energy levels, together with thermal stability and possible charge carrier transport due to molecular packing, suggest that these molecules are promising for optoelectronic applications. Overall, this work contributes to the development of the use of thiazolo[5,4-d]thiazole in liquid crystals, demonstrating its great efficiency and versatility.
Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO2/Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp3-containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4-6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to ≈ 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (≈ 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surface-to-bulk phase transition mechanism that gives hint of diamondene formation.
Generalized uncertainty principles (GUP) and, independently, Lorentz symmetry violations are two common features in many candidate theories of quantum gravity. Despite that, the overlap between both has received limited attention so far. In this brief paper, we carry out further investigations on this topic. At the nonrelativistic level and in the realm of commutative spacetime coordinates, a large class of both isotropic and anisotropic GUP models is shown to produce signals experimentally indistinguishable from those predicted by the Standard Model Extension (SME), the common framework for studying Lorentz-violating phenomena beyond the Standard Model. This identification is used to constrain GUP models using current limits on SME coefficients. In particular, bounds on isotropic GUP models are improved by a factor of $10^7$ compared to current spectroscopic bounds and anisotropic models are constrained for the first time.
Abstract Research in hybrid and flexible natural fiber-reinforced polymer composites has included advances in innovative and environmentally sustainable devices. However, in practice, controversies still exist regarding the relationship between electrical and materials performance targets in a system design context. This work aimed to investigate the alternating conductivity of a novel pressure sensor based on semiconducting polyaniline (PANI)-coated vegetable fiber (VF, Euterpe oleracea Mart., Acai) in silicone polydimethylsiloxane (PDMS) rubber. We used alternating electrical conductivity measurements, σ*(ω) ∝ ωs (frequency range—ω from 1 Hz to 10 MHz; s 0.6), to adjust the optimal operating frequency region to enhance the pressure sensing performance of the PDMS-PANI-VF composites. A generalized effective-medium approach to the pressure-induced conductivity in terms of loading pressure, percolation regime, and the interpolation between Bruggeman's symmetric and asymmetric media theories was obtained. We have found a solution for inducing percolation in composites with a low concentration of fiber inclusions by uniaxial pressure (P), characterized by the expression σ ∝ (P−P0)t (0 ≤ t ≤ 4.0, 0 ≤ P0 ≤ 250 kPa). The sensor demonstrates maximum sensitivity of 1.5 Pa−1 in the operating electrical frequency from 1 to 100 Hz, and a wide linearity range from 0 to 250 kPa. The result provides new insight into the AC universality, s, and t behaviors of natural fiber-reinforced polymer composites to enhance pressure sensitivity of a new concept and technology for resource-efficiency optimization of sustainable environmental devices.
In this work we apply first principles calculations to investigate the stability trends of mixed boron, nitrogen and carbon diamondol-like compounds. Several distinct geometric models are tested by varying the stoichiometry and position of boron and nitrogen dopants. We verify the special stability of a complete boron nitride compound – the bonitrol –, and we show that carbon substitutions in the bonitrol structure may also lead to stable systems. The electronic characterization of the resulting compounds indicates a rich phenomenology, with metallic, semimetallic, half-metallic and semiconducting behaviors.