Size effects on dynamics of nanodroplets in binary head-on collisions

Head-on collision dynamics of 10, 50 and 100 nm droplets are investigated in vacuum by molecular dynamics, involving 35,858, 4,506,410 and 36,051,466 molecules, respectively. A variety of droplet collision dynamics are observed, such as coalescence, hole formation and shattering, as a function of the Weber number. It is found for the first time that the collision and reflexive separation can occur in the nanodroplet regime when the droplet diameter reaches 100 nm but not for 10 or 50 nm droplets. The size effect in droplet collisions is studied based on the analysis of stretching factors, energy dissipation and collision outcomes for droplets of different diameters. The kinetic energy dissipation due to the atomic interactions at nanoscales is identified to significantly influence the occurrence or otherwise of reflexive separation. Through quantitative analysis of the evolution of the internal structure of the 100 nm nanodroplets collision at the Weber number of 277, it is revealed for the first time that molecules from both parent nanodroplets have penetrated the full length of the merged nanodroplet in the direction of collision, due to a combination of molecular mixing and internal currents. Consequently, all three child nanodroplets have molecules from both parent nanodroplets, contrary to the perception gained from common imaging techniques. The results show that the dynamics, outcomes and mechanisms of nanodroplet collisions have both similarities and differences compared with their micro- and macro-counterparts

A molecular dynamics simulation on the oxidation of core-shell aluminum nanoparticles in oxygen and water environments

The oxidation mechanisms of core-shell aluminum nanoparticles (ANPs) in high-temperature steam and oxygen are investigated by ReaxFF molecular dynamics (MD) simulation. The details concerning reaction heat release, heat transfer, atomic diffusion process, and ANP structure evolution are studied by examining the temporal variations of temperature, energy, atoms concentration distributions and particle structure, respectively. The atomic-level heat and mass transfer processes reveal that for both ANP/H2O and ANP/O2 systems, at the initial stage of oxidation, the heat transfer between ANP and environmental oxidizer is dominant. Thereafter, the reaction plays an increasingly significant role. The heat transfer efficiency of ANP/H2O is higher than that of ANP/O2, while the reaction exotherm of ANP/H2O is lower than ANP/O2. The final particle temperature for ANP/O2 system is much higher than that of ANP/H2O. The diameter of the former is also larger. During the oxidation of ANP, the core Al atoms diffuse outward into the oxide shell, which pushes the shell Al atoms outward and results in the expansion of ANP. The shell O atoms diffuse inward and left a vacant lattice site, through which the ambient H and O atoms diffuse into the oxide shell

Recursos educacionais online como parte essencial do processo de aprendizagem da língua Inglesa

The article discusses the use of educational web resources in the process of learning English. The authors present different web resources to teach English which have proved to be an effective source in second language acquisition. Web resources help to improve the foreign language perception, to study grammar rules and correct pronunciation, to get acquainted to the culture of the target language and to heighten the interest of learning a foreign language. The advantage of using web resources lies behind the didactic principle of visibility. Visual representation of material proves to be the most important tool to better perceive information and to overall motivate children to stay focused on the task, while creating a natural language environment. As a result of this analysis the authors strongly agree on the benefits of using authentic web resources in teaching English. The analysis has also shown a complete correlation between the use of Internet technologies and course content mastering.El artículo analiza el uso de recursos web educativos en el proceso de aprendizaje del idioma inglés. Los autores presentaron diferentes recursos web para la enseñanza del idioma inglés que resultan ser una fuente eficaz en la adquisición de un segundo idioma. Los recursos web ayudan a mejorar la percepción del idioma extranjero, estudian las reglas gramaticales, enseñan la pronunciación correcta, se familiarizan con la cultura del idioma de destino y aumentan el interés en aprender un idioma extranjero. La ventaja de utilizar recursos web radica en el principio didáctico de visibilidad. La representación visual del material demuestra ser la más importante y necesaria para una mejor percepción de la información y, en general, para motivar a los niños a mantenerse enfocados en la tarea creando un entorno de lenguaje natural. Como resultado de este análisis, los autores obtuvieron una impresión completa sobre el uso de recursos web auténticos en la enseñanza del idioma inglés. El análisis también ha mostrado una correlación completa entre el uso de tecnologías de Internet y el dominio del contenido del curso.O artigo discute o uso de recursos educacionais online no processo de aprendizagem da língua inglesa. Os autores apresentam diversos recursos online para o ensino da língua inglesa que se revelam uma fonte eficaz na aquisição de uma segunda língua. Os recursos ajudam a melhorar a percepção da língua estrangeira, estudar regras gramaticais, ensinar a pronúncia correta, a se familiarizar com a cultura da língua-alvo e aumentar o interesse em aprender uma língua estrangeira. A vantagem de usar tais recursos tem por princípio a didática da visibilidade. A representação visual do material prova ser a mais importante e necessária para uma melhor percepção da informação – motivando as crianças a permanecerem focadas na tarefa ao criar um ambiente de linguagem natural. Como resultado desta análise, os autores tiveram uma visão ampla sobre o uso de recursos autênticos da web no ensino da língua inglesa. A análise também mostrou uma correlação completa entre o uso de tecnologias da Internet e o domínio do conteúdo do curso

Size-derived reaction mechanism of core-shell aluminum nanoparticle

To prompt the application of aluminum nanoparticles (ANPs) in combustion as the fuel additive and in chemical synthesis as the catalyst, this study examines the reaction dynamics of core-shell ANPs under an oxygen atmosphere via Transient Non-Equilibrium Reactive Molecular Dynamics simulations. Two distinct oxidation modes determined by the competition between the oxide shell melting and core reaction have been identified. One is the fast oxidation mode with a high reaction heat release rate, where core Al and ambient O atoms diffuse into each other to form a homogeneous alumina particle. The other is the moderate oxidation with lower heat release, where only core Al atoms diffuse into the oxide shell to form a hollow spherical structure. By modeling the shell melting and Al core reaction, a size-derived oxidation model has been proposed to conveniently but accurately predict the ANP reaction dynamics. This work also provides fundamental insight into the synthesis of ANPs that serve as a high energy density fuel and high-performance catalyst

Experimental and numerical investigation into hydraulic fracture and natural fracture interaction in shale formations

Two 0.3 m × 0.3 m × 0.3 m shale blocks, one representing a homogeneous sample while the other representing a naturally fractured sample, are modelled using the lattice based DEM code, XSite. The synthetic rock mass approach (SRM), which assigns the smooth joint contacts (SJM) to the weakness planes, is used to represent the natural fractures in shale block-2. Firstly, the developed models are compared with the findings of previously conducted true-triaxial hydraulic fracturing experiments with acoustic measurements, and their subsequent computed tomography (CT) and seismic velocity tomography results. The 3D model results confirmed the curved shape hydraulic fractures, which propagated perpendicular to the minimum stress directions in both shale blocks. Model results also captured the natural fracture (NF) and hydraulic fracture (HF) interaction, particularly the arrest, the dilation of major NFs, followed by crossing with offset mechanism, in shale block-2. Secondly, the parametric studies are carried out to investigate the role of fluid flow rate (q), and fluid viscosity (µ) on different NF/HF interaction mechanisms. The effects of q and µ are discussed based on the total stimulated area including the tensile and shear microcracks, the pipe apertures, and the pressure evolutions within NFs

Levinson's Theorem for Non-local Interactions in Two Dimensions

In the light of the Sturm-Liouville theorem, the Levinson theorem for the Schr\"{o}dinger equation with both local and non-local cylindrically symmetric potentials is studied. It is proved that the two-dimensional Levinson theorem holds for the case with both local and non-local cylindrically symmetric cutoff potentials, which is not necessarily separable. In addition, the problems related to the positive-energy bound states and the physically redundant state are also discussed in this paper.Comment: Latex 11 pages, no figure, submitted to J. Phys. A Email: [email protected], [email protected]

Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors

MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV–vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV–vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate

Heat Treated NiP–SiC Composite Coatings: Elaboration and Tribocorrosion Behaviour in NaCl Solution

Tribocorrosion behaviour of heat-treated NiP and NiP–SiC composite coatings was investigated in a 0.6 M NaCl solution. The tribocorrosion tests were performed in a linear sliding tribometer with an electrochemical cell interface. It was analyzed the influence of SiC particles dispersion in the NiP matrix on current density developed, on coefficient of friction and on wear volume loss. The results showed that NiP–SiC composite coatings had a lower wear volume loss compared to NiP coatings. However, the incorporation of SiC particles into the metallic matrix affects the current density developed by the system during the tribocorrosion test. It was verified that not only the volume of co-deposited particles (SiC vol.%) but also the number of SiC particles per coating area unit (and consequently the SiC particles size) have made influence on the tribocorrosion behaviour of NiP–SiC composite coatings

Hormonal regulation of ovarian bursa fluid in mice and involvement of aquaporins.

In rodent species, the ovary and the end of oviduct are encapsulated by a thin membrane called ovarian bursa. The biological functions of ovarian bursa remain unexplored despite its structural arrangement in facilitating oocytes transport into oviduct. In the present study, we observed a rapid fluid accumulation and reabsorption within the ovarian bursa after ovarian stimulation (PMSG-primed hCG injection), suggesting that the ovarian bursa might play an active role in regulating local fluid homeostasis around the timing of ovulation. We hypothesized that the aquaporin proteins, which are specialized channels for water transport, might be involved in this process. By screening the expression of aquaporin family members (Aqp1-9) in the ovarian tissue and isolated ovarian bursa (0, 1, 2 and 5 h after hCG injection), we found that AQP2 and AQP5 mRNA showed dynamic changes after hCG treatment, showing upregulation at 1-2 h followed by gradually decrease at 5 h, which is closely related with the intra-bursa fluid dynamics. Further immunofluorescence examinations of AQP2 and AQP5 in the ovarian bursa revealed that AQP2 is specifically localized in the outer layer (peritoneal side) while AQP5 localized in the inner layer (ovarian side) of the bursa, such cell type specific and spatial-temporal expressions of AQP2 and 5 support our hypothesis that they might be involved in efficient water transport through ovarian bursa under ovulation related hormonal regulation. The physiological significance of aquaporin-mediated water transport in the context of ovarian bursa still awaits further clarification