Functionalized carbon nanocones performance in water harvesting.

In this work, we investigate the water capture process for functionalized carbon nanocones (CNCs) through molecular dynamic simulations in the following three scenarios: a single CNC in contact with a reservoir containing liquid water, a single CNC in contact with a water vapor reservoir, and a combination of more than one CNC in contact with vapor. We found that water flows through the nanocones when in contact with the liquid reservoir if the nanocone tip presents hydrophilic functionalization. In contact with steam, we observed the formation of droplets at the base of the nanocone only when hydrophilic functionalization is present. Then, water flows through in a linear manner, a process that is more efficient than that in the liquid reservoir regime. The scalability of the process is tested by analyzing the water flow through more than one nanocone. The results suggest that the distance between the nanocones is a fundamental ingredient for the efficiency of water harvesting.

Androcentrism in the scientific field: Brazilian systems of graduate studies, science and technology as a case study.

This article performs an analysis of female participation in science, in the Brazilian system of graduate studies and scientific research as a case study. This is relevant because science is a central supporting structure for modern societies and, therefore, a detailed analysis of the scientific power structure behind academic policy creation can reveal aspects of androcentrism in scientific activity. The main goal of this work is to identify the process of misogyny in science by describing its reproductive pattern. Our results show that women are around 50% of the undergraduate and graduate students when all fields are taken into consideration, but only 37% of the researchers in the CNPq system. We also observe a significant increase in female percentage within scientific activities at the initial and intermediary levels, except for the most prestigious areas as hard science. However, a scissor effect is identified between the initial level and the more prominent positions. This unbalanced participation reveals that female occupations in science are mostly as lower workforce since women are quite far from the social decision-making circles in this career.

Structure and dynamics of nanoconfined water and aqueous solutions.

This review is devoted to discussing recent progress on the structure, thermodynamic, reactivity, and dynamics of water and aqueous systems confined within different types of nanopores, synthetic and biological. Currently, this is a branch of water science that has attracted enormous attention of researchers from different fields interested to extend the understanding of the anomalous properties of bulk water to the nanoscopic domain. From a fundamental perspective, the interactions of water and solutes with a confining surface dramatically modify the liquid's structure and, consequently, both its thermodynamical and dynamical behaviors, breaking the validity of the classical thermodynamic and phenomenological description of the transport properties of aqueous systems. Additionally, man-made nanopores and porous materials have emerged as promising solutions to challenging problems such as water purification, biosensing, nanofluidic logic and gating, and energy storage and conversion, while aquaporin, ion channels, and nuclear pore complex nanopores regulate many biological functions such as the conduction of water, the generation of action potentials, and the storage of genetic material. In this work, the more recent experimental and molecular simulations advances in this exciting and rapidly evolving field will be reported and critically discussed.

Water mobility in MoS2 nanopores: effects of the dipole-dipole interaction on the physics of fluid transport.

Use of nanoscale materials is a promising desalination technology. While fast water flow in nanotubes is well understood, this is not the case for water permeability in single-layer membranes. The advances in nanofluidics have opened up the possibility to shift the permeability-selectivity tradeoff. The physical-chemical balance between nanopore size, shape, and charge might be the answer. In this work, we investigate the role of the MoS2 nanopore charge distribution in water mobility by tuning its strength. We shed light on the competition between charge and nanopore size. The strong dipole interaction between water and the MoS2 nanopore is responsible for adding a constraint to the water angular orientation possibilities to travel through the nanopore, but this effect also depends on the nanopore size.

Molecular fluid flow in MoS2 nanoporous membranes and hydrodynamics interactions.

We study the impact of the induced pressure fields on the water flow and salt rejection in nanopores produced in MoS2 membranes. We observe that the water permeability and the salt rejection are not impacted by the distance between the pores. This result contradicts the continuous fluid mechanics calculations in microfilters, which indicates the existence of hydrodynamic interactions between adjacent pores that increase the water mobility. Our results suggest that at this nanoscale, the hydrodynamic interactions do not affect the water mobility through nanopores.

Open Access Publications with Article Processing Charge (APC) Payment: a Brazilian Scenario Analysis.

The expansion of open access publications has been correlated with specific government policies in many countries. The evolution in these cases is understandable within the framework of funding regulations. However, this is not the case for Brazil, where no regulation is currently in place. The unusually high percentage of open access publications in the Brazilian scientific community is analyzed here toward understanding which factors influence this growth and how similar effects may also impact other countries, particularly developing nations. We found that from 2012 to 2019 the Brazilian scientific community drifted to international open access journals. This transition is discussed in the framework of mega journals.

Misogyny in Brazilian Federal Government Agencies for Science and High-Education.

The transformation of women's role in society has been systematically studied. Numerous authors point out that among the factors of extreme relevance to this fact, the main is the increased presence of women in the formal job market. Researches also reveal that the increase in quantity is not reflected equally in all productive sectors nor the egalitarian occupation of high hierarchical positions. The present study aimed to analyze how the presence of women, especially in leadership positions, has evolved at the Brazilian Federal Agency for the Support and Evaluation of Postgraduate Education (CAPES) and the National Council for Scientific and Technological Development (CNPq) over the last 20 years. For these analyzes, surveys were conducted in the people management systems of the Brazilian Federal Public Administration. The initial hypothesis was that female attendance had increased in both the total number of female servants and in management and auxiliary positions, known as DAS in Brazil; however, evidence shows that women reduced overall agency presence, especially in the number of female Analysts occupying DAS positions. These results indicate that the misogyny observed in the academic sphere of the Brazilian National Postgraduate and Science, Technology, and Innovation systems are replicated in the politic-bureaucratic sphere that manages and sponsors these systems.

Salt parameterization can drastically affect the results from classical atomistic simulations of water desalination by MoS2 nanopores.

Water scarcity is a reality in our world, and scenarios predicted by leading scientists in this area indicate that it will worsen in the next decades. However, new technologies based on low-cost seawater desalination can prevent the worst scenarios, providing fresh water for humanity. With this goal, membranes based on nanoporous materials have been suggested in recent years. One of the materials suggested is MoS2, and classical Molecular Dynamics (MD) simulation is one of the most powerful tools to explore these nanomaterials. However, distinct force fields employed in MD simulations are parameterized based on distinct experimental quantities. In this paper, we compare two models of salt that were built based on distinct properties of water-salt mixtures. One model fits the hydration free energy and lattice properties, and the second fits the crystal density and the density and the dielectric constant of water and salt mixtures. To compare the models, MD simulations for salty water flow through nanopores of two sizes were used - one pore big enough to accommodate hydrated ions, and one smaller in which the ion has to dehydrate to enter - and two rigid water models from the TIP4P family - TIP4P/2005 and TIP4P/ε. Our results indicate that the water permeability and salt rejection by the membrane are more influenced by the salt model than by the water model, especially for the narrow pore. In fact, completely distinct mechanisms were observed, and they are related to the characteristics employed in the ion model parameterization. The results show that not only can the water model influence the outcomes, but the ion model plays a crucial role when the pore is small enough.

Correction: Salt parameterization can drastically affect the results from classical atomistic simulations of water desalination by MoS2 nanopores.

Correction for 'Salt parameterization can drastically affect the results from classical atomistic simulations of water desalination by MoS2 nanopores' by João P. K. Abal et al., Phys. Chem. Chem. Phys., 2020, 22, 11053-11061, DOI: 10.1039/d0cp00484g.

Water diffusion in rough carbon nanotubes.

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of deformation at 300 K. We found that the number of hydrogen bonds that water forms depends on nanotube topology, leading to enhancement or suppression of water diffusion. The simulation results reveal that more realistic nanotubes should be considered to understand the confined water diffusion behavior, at least for the narrowest nanotubes, when the interaction between water molecules and carbon atoms is relevant.

Water diffusion in carbon nanotubes: Interplay between confinement, surface deformation, and temperature.

In this article, we investigate, through molecular dynamics simulations, the diffusion behavior of the TIP4P/2005 water confined in pristine and deformed carbon nanotubes (armchair and zigzag). To analyze different diffusive mechanisms, the water temperature was varied as 210 ≤ T ≤ 380 K. The results of our simulations reveal that water presents a non-Arrhenius to Arrhenius diffusion crossover. The confinement shifts the diffusion transition to higher temperatures when compared with the bulk system. In addition, for narrower nanotubes, water diffuses in a single line, which leads to its mobility independent of the activation energy.

2D nanoporous membrane for cation removal from water: Effects of ionic valence, membrane hydrophobicity, and pore size.

Using molecular dynamic simulations, we show that single-layers of molybdenum disulfide (MoS2) and graphene can effectively reject ions and allow high water permeability. Solutions of water and three cations with different valencies (Na+, Zn2+, and Fe3+) were investigated in the presence of the two types of membranes, and the results indicate a high dependence of the ion rejection on the cation charge. The associative characteristic of ferric chloride leads to a high rate of ion rejection by both nanopores, while the monovalent sodium chloride induces lower rejection rates. Particularly, MoS2 shows 100% of Fe3+ rejection for all pore sizes and applied pressures. On the other hand, the water permeation does not vary with the cation valence, having dependence only with the nanopore geometric and chemical characteristics. This study helps us to understand the fluid transport through a nanoporous membrane, essential for the development of new technologies for the removal of pollutants from water.

Geographic and Gender Diversity in the Brazilian Academy of Sciences.

Recent studies have shown that diversity in race and gender is important to improve competitiveness, creativity and innovation. However, many studies have shown that the universe of science is not diverse in none of these criteria. In this work, we quantify the gender and geographic diversity in the Brazilian science. We study in detail the profile of the titular members of the most prestigious academic institution of Brazil, the Brazilian Academy of Sciences (ABC). Our analysis shows that the members of the ABC concentrates 80% in the Southeast region and that the overwhelming majority is composed by men. We show that female and male researchers have roughly the same amount of publication per year but women produce more human resources. Using the Brazilian Researchers' Fellowship databank we show that the gender and diversity both in gender and in geography decreases along the researchers' career.

Breakdown of the Stokes-Einstein water transport through narrow hydrophobic nanotubes.

In this paper the transport properties of water confined inside hydrophobic and hydrophilic nanotubes are compared for different nanotube radii and densities. While for wider nanotubes the nature of the wall plays no relevant role in the water mobility, for small nanotubes the hydrophobic confinement presents a peculiar behavior. As the density is increased the viscosity shows a huge increase associated with a small increase in the diffusion coefficient. This breakdown in the Stokes-Einstein relation for diffusion and viscosity was observed in the hydrophobic, but not in the hydrophilic nanotubes. The mechanism underlying this behavior is explained in terms of the structure of water under confinement. This result indicates that some of the features observed for water inside hydrophobic carbon nanotubes cannot be observed in other nanopores.

Structure and mobility of water confined in AlPO4-54 nanotubes.

We performed molecular dynamics simulations of water confined within AlPO4-54 nanotubes. AlPO4-54 is an artificial material made of AlO4 and of PO4 in tetrahedra arranged in a periodic structure forming pores of approximately 1.3 nm in diameter. This makes AlPO4-54 an excellent candidate for practical applications, such as for water filtration and desalination. In this work, the structural and dynamical properties of the confined water are analyzed for various temperatures and water loadings. We find that the water structure is controlled by the heterogeneity of the nanopore surface with the water molecules located preferentially next to the surface of oxygens of AlPO4-54; consequently, at very low densities, water forms helicoidal structures in string-like arrangements.

Scientometric indicators for Brazilian research on High Energy Physics, 1983-2013.

This article presents an analysis of Brazilian research on High Energy Physics (HEP) indexed by Web of Science (WoS) from 1983 to 2013. Scientometric indicators for output, collaboration and impact were used to characterize the field under study. The results show that the Brazilian articles account for 3% of total HEP research worldwide and that the sharp rise in the scientific activity between 2009 and 2013 may have resulted from the consolidation of graduate programs, the increase of the funding and of the international collaboration as well as the implementation of the Rede Nacional de Física de Altas Energias (RENAFAE) in 2008. Our results also indicate that the collaboration patterns in terms of the authors, the institutions and the countries confirm the presence of Brazil in multinational Big Science experiments, which may also explain the prevalence of foreign citing documents (all types), emphasizing the international prestige and visibility of the output of Brazilian scientists. We concluded that the scientometric indicators suggested scientific maturity in the Brazilian HEP community due to its long history of experimental research.

Self-Assembly and Water-like Anomalies in Janus Nanoparticles.

We explore the pressure versus temperature phase diagram of a system of dimeric Janus nanoparticles using molecular dynamics simulations. Each nanoparticle is modeled as a dumbbell which has one monomer that interacts by a standard Lennard-Jones potential while the other monomer interacts by a core-softened potential. The systems composed by particles interacting only by core-softened potential exhibit the density and the diffusion anomalous behavior observed in water while if the particles interact only by the Lennard-Jones potential no anomaly is present. Here we explore if the anomalous behavior is present when half of the particles are modeled by a core-softened potential and half with Lennard-Jones potential. We show that the diffusion anomaly is preserve, while the density anomaly can disappear depending on the nonanomalous monomer characteristics. We also show that the self-assembly structures characteristics of the dumbbell systems are affected by the balance between core-softened and non-core-softened monomers.

The associating lattice gas in the presence of interacting solutes.

We have investigated the phase diagram of a statistical model for hydrogen-bonding solutions for polar solutes. The structured solvent is represented by an associating lattice gas, which presents anomalous density and liquid-liquid coexistence. Polar solute particles and solvent particles interact attractively, while the solvent-solvent interaction is made directional through bonding arms, which mimic hydrogen bonds. The model behavior is obtained via Monte Carlo simulations in the grand-canonical ensemble, for different sets of parameters. For small solute chemical potential and weak attraction between solute and solvent particles, addition of solute yields a shift in the transition lines of the pure solvent. This is the scenario explored by different authors, in the pursuit of stabilizing the water liquid-liquid coexistence line. However, as we show, in the case of larger solute chemical potentials, or of stronger solute-solvent attractions, new phases may arise.

Effects of confinement on anomalies and phase transitions of core-softened fluids.

We use molecular dynamics simulations to study how the confinement affects the dynamic, thermodynamic, and structural properties of a confined anomalous fluid. The fluid is modeled using an effective pair potential derived from the ST4 atomistic model for water. This system exhibits density, structural, and dynamical anomalies, and the vapor-liquid and liquid-liquid critical points similar to the quantities observed in bulk water. The confinement is modeled both by smooth and structured walls. The temperatures of extreme density and diffusion for the confined fluid show a shift to lower values while the pressures move to higher amounts for both smooth and structured confinements. In the case of smooth walls, the critical points and the limit between fluid and amorphous phases show a non-monotonic change in the temperatures and pressures when the nanopore size is increase. In the case of structured walls, the pressures and temperatures of the critical points varies monotonically with the pore size. Our results are explained on basis of the competition between the different length scales of the fluid and the wall-fluid interaction.

High pressure induced phase transition and superdiffusion in anomalous fluid confined in flexible nanopores.

The behavior of a confined spherical symmetric anomalous fluid under high external pressure was studied with Molecular Dynamics simulations. The fluid is modeled by a core-softened potential with two characteristic length scales, which in bulk reproduces the dynamical, thermodynamical, and structural anomalous behavior observed for water and other anomalous fluids. Our findings show that this system has a superdiffusion regime for sufficient high pressure and low temperature. As well, our results indicate that this superdiffusive regime is strongly related with the fluid structural properties and the superdiffusion to diffusion transition is a first order phase transition. We show how the simulation time and statistics are important to obtain the correct dynamical behavior of the confined fluid. Our results are discussed on the basis of the two length scales.