Simulations of binary hard-sphere crystal-melt interfaces: Interface between a one-component fcc crystal and a binary fluid mixture

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/116/8/10.1063/1.1436078The crystal-melt interfaces of a binary hard-sphere fluid mixture in coexistence with a single-component hard-sphere crystal is investigated using molecular-dynamics simulation. In the system under study, the fluid phase consists of a two-component mixture of hard spheres of differing size, with a size ratio α=0.414. At low pressures this fluid coexists with a pure fcc crystal of the larger particles in which the small particles are immiscible. For two interfacial orientations, [100] and [111], the structure and dynamics within the interfacial region is studied and compared with previous simulations on single component hard-sphere interfaces. Among a variety of novel properties, it is observed that as the interface is traversed from fluid to crystal the diffusion constant of the larger particle vanishes before that of the small particle, defining a region of the interface where the large particles are frozen in their crystal lattice, but the small particles exhibit significant mobility. This behavior was not seen in previous binary hard-sphere interface simulations with less asymmetric diameters

Structure of a soft-sphere fluid at a soft repulsive wall: A comparison of weighted density-functional theories

This is the publisher's version, also available electronically from http://journals.aps.org/pre/abstract/10.1103/PhysRevE.69.051502.Density-functional theory is used to investigate the structure of a soft-sphere fluid at a soft wall. The fluid is modeled by an inverse sixth–power repulsive pair potential and the fluid particles interact with a flat stationary wall defined by an inverse-twelth power repulsive external potential. For comparison we examine results using three weighted density approximations (WDA), namely those due to Curtin and Ashcroft [Phys. Rev. A 32, 2909 (1985)], Denton and Ashcroft [Phys. Rev. A 39, 426 (1989)], and the partitioned WDA of Kol and Laird [Mol. Phys. 90, 951 (1997)]. The degree to which each of these approximations can accurately predict the structure of the fluid at the wall is evaluated for several densities through comparison with Monte Carlo simulation data

Simulations of binary hard-sphere crystal-melt interfaces: Interface between a one- component fcc crystal and a binary fluid mixture

The crystal-melt interfaces of a binary hard-sphere fluid mixture in coexistence with a single-component hard-sphere crystal is investigated using molecular-dynamics simulation. In the system under study, the fluid phase consists of a two-component mixture of hard spheres of differing size, with a size ratio $\alpha=0.414$. At low pressures this fluid coexists with a pure fcc crystal of the larger particles in which the small particles are immiscible. For two interfacial orientations, [100] and [111], the structure and dynamics within the interfacial region is studied and compared with previous simulations on single component hard-sphere interfaces. Among a variety of novel properties, it is observed that as the interface is traversed from fluid to crystal the diffusion constant of the larger particle vanishes before that of the small particle defining a region of the interface where the large particles are frozen in their crystal lattice, but the small particles exhibit significant mobility. This behavior was not seen in previous binary hard-sphere interface simulations with less asymmetric diameters

Structure and dynamics of the interface between a binary hard-sphere crystal of NaCl type and its coexisting binary fluid

This is the publisher's version, also available electronically from http://journals.aps.org/prb/abstract/10.1103/PhysRevB.66.144106.Molecular-dynamics simulations are performed to study the [100] and [111] orientations of the crystal-melt interface between an ordered two-component hard sphere with an NaCl structure and its coexisting binary hard-sphere fluid. The diameter ratio of the two types of hard spheres making up the mixture is α=0.414. This work complements our earlier interface simulations [J. Chem. Phys. 116, 3410 (2002)] for the same diameter ratio at lower pressures where the smaller component is immiscible in the solid and the fluid mixture coexists with a pure fcc crystal of large particles. Density profiles and diffusion coefficient profiles are presented for the AB interfacial system. We find that for this system, the transition from crystallike to fluidlike behavior of both the density and diffusion constant profiles occurs over a narrower region than that seen in our previous studies of the fcc/binary fluid system. But similar to what was found in the fcc/binary fluid interface the transition region for the large particle diffusion constant is shifted about 1.0σA toward the fluid phase relative to that for the small particles

Structure and dynamics of the interface between a binary hard-sphere crystal of NaCl type and its coexisting binary fluid

Molecular dynamics simulations are performed to study the [100] and [111] orientations of the crystal-melt interface between an ordered two-component hard sphere with a NaCl structure and its coexisting binary hard-sphere fluid. The diameter ratio of the two types of hard spheres making up the mixture is taken to be 0.414. This work complements our earlier interface simulations [J. Chem. Phys.116, 3410] for the same diameter ratio at lower pressures where the smaller component is immiscible in the solid and the fluid mixture coexists with a pure FCC crystal of large particles. Density profiles and diffusion coefficient profiles are presented for the AB interfacial system. We find that for this system, the transition from crystal-like to fluid-like behavior of both the density and diffusion constant profiles occurs over a narrower region than that seen in our previous studies [J. Chem. Phys. 116, 3410] of the FCC/binary fluid system. But similar to what was found in the FCC/binary fluid interface the transition region for the large particle diffusion constant is shifted about the size of the large particles toward the fluid phase relative to that for the small particles.Comment: 8 page

Fabrication of a 3D Printed Porous Junction for Ag|AgCl|gel-KCl Reference Electrode

Fused filament fabrication (FFF) is a 3D printing method that is attracting increased interest in the development of miniaturized electrochemical sensor systems due to its versatility, low cost, reproducibility, and capability for rapid prototyping. A key component of miniaturized electrochemical systems is the reference electrode (RE). However, reports of the fabrication of a true 3D-printed RE that exhibits stability to variations in the sample matrix remain limited. In this work, we report the development and characterization of a 3D-printed Ag|AgCl|gel-KCl reference electrode (3D-RE). The RE was constructed using a Ag|AgCl wire and agar-KCl layer housed in a watertight 3D-printed acrylonitrile butadiene styrene (ABS) casing. The novel feature of our electrode is a 3D-printed porous junction that protects the gel electrolyte layer from chloride ion leakage and test sample contamination while maintaining electrical contact with the sample solution. By tuning the 3D printing filament extrusion ratio (k), the porosity of the junction was adjusted to balance the reference electrode potential stability and impedance. The resulting 3D-RE demonstrated a stable potential, with a potential drift of 4.55 ± 0.46 mV over a 12-h period of continuous immersion in 0.1 M KCl, and a low impedance of 0.50 ± 0.11 kΩ. The 3D-RE was also insensitive to variations in the sample matrix and maintained a stable potential for at least 30 days under proper storage in 3 M KCl. We demonstrate the application of this 3D-RE in cyclic voltammetry and in pH sensing coupled with electrodeposited iridium oxide on a gold electrode. Our method offers a viable strategy for 3D printing a customizable true reference electrode that can be readily fabricated on demand and integrated into 3D-printed miniaturized electrochemical sensor systems

Sex-dependent diversity in ventral tegmental dopaminergic neurons and developmental programing: a molecular, cellular and behavioral analysis

The knowledge that diverse populations of dopaminergic neurons within the ventral tegmental area (VTA) can be distinguished in terms of their molecular, electrophysiological and functional properties, as well as their differential projections to cortical and subcortical regions has significance for key brain functions, such as the regulation of motivation, working memory and sensorimotor control. Almost without exception, this understanding has evolved from landmark studies performed in the male sex. However, converging evidence from both clinical and pre-clinical studies illustrates that the structure and functioning of the VTA dopaminergic systems are intrinsically different in males and females. This may be driven by sex differences in the hormonal environment during adulthood ('activational' effects) and development (perinatal and/or pubertal 'organizational' effects), as well as genetic factors, especially the SRY gene on the Y chromosome in males, which is expressed in a sub-population of adult midbrain dopaminergic neurons. Stress and stress hormones, especially glucocorticoids, are important factors which interact with the VTA dopaminergic systems in order to achieve behavioral adaptation and enable the individual to cope with environmental change. Here, also, there is male/female diversity not only during adulthood, but also in early life when neurobiological programing by stress or glucocorticoid exposure differentially impacts dopaminergic developmental trajectories in male and female brains. This may have enduring consequences for individual resilience or susceptibility to pathophysiological change induced by stressors in later life, with potential translational significance for sex bias commonly found in disorders involving dysfunction of the mesocorticolimbic dopaminergic systems. These findings highlight the urgent need for a better understanding of the sexual dimorphism in the VTA if we are to improve strategies for the prevention and treatment of debilitating conditions which differentially affect men and women in their prevalence and nature, including schizophrenia, attention/deficit hyperactivity disorder, autism spectrum disorders, anxiety, depression and addiction

General anaesthetic and airway management practice for obstetric surgery in England: a prospective, multi-centre observational study

There are no current descriptions of general anaesthesia characteristics for obstetric surgery, despite recent changes to patient baseline characteristics and airway management guidelines. This analysis of data from the direct reporting of awareness in maternity patients' (DREAMY) study of accidental awareness during obstetric anaesthesia aimed to describe practice for obstetric general anaesthesia in England and compare with earlier surveys and best-practice recommendations. Consenting patients who received general anaesthesia for obstetric surgery in 72 hospitals from May 2017 to August 2018 were included. Baseline characteristics, airway management, anaesthetic techniques and major complications were collected. Descriptive analysis, binary logistic regression modelling and comparisons with earlier data were conducted. Data were collected from 3117 procedures, including 2554 (81.9%) caesarean deliveries. Thiopental was the induction drug in 1649 (52.9%) patients, compared with propofol in 1419 (45.5%). Suxamethonium was the neuromuscular blocking drug for tracheal intubation in 2631 (86.1%), compared with rocuronium in 367 (11.8%). Difficult tracheal intubation was reported in 1 in 19 (95%CI 1 in 16-22) and failed intubation in 1 in 312 (95%CI 1 in 169-667). Obese patients were over-represented compared with national baselines and associated with difficult, but not failed intubation. There was more evidence of change in practice for induction drugs (increased use of propofol) than neuromuscular blocking drugs (suxamethonium remains the most popular). There was evidence of improvement in practice, with increased monitoring and reversal of neuromuscular blockade (although this remains suboptimal). Despite a high risk of difficult intubation in this population, videolaryngoscopy was rarely used (1.9%)

Design and fabrication of a multi-stationary phase thin-layer chromatography system for the rapid chemometric fingerprinting of B. balsamifera and V. negundo

Despite rising consumer demand for herbal medicinal products in the Philippines, the growth in the industry has been limited by the supply of quality raw plant materials for processing into finished products. One of the major factors contributing to this limited supply is the lack of accessible technology for quality control at the farmer-supplier level, which leads to high rates of supply rejection. This study aimed to address the lack of accessible quality assessment tools by developing a field-ready thin-layer chromatography (TLC) method coupled with chemometric fingerprinting that can identify common concerns such as incorrect plant variety, contamination, plant quality degradation, or sample mishandling or mislabeling. To ensure the adoptability of the method for field use, a novel multi-stationary phase(MSP) TLC plate was designed and fabricated for the one-step multiple development of ethanolic plant extracts with a 60:40 (v/v) ethanol-water mobile phase. This approach minimizes the use of volatile organic solvents typically used in TLC protocols, while varying the selectivity of chromatographic separation by using multiple phenylandoctyl-modified stationary phases printed on a silica gel TLC plate. The method was applied to B. balsamifera and V. negundo ethanolic extracts as model systems, and was coupled with image analysis and one-class soft independent modeling of class analogy (SIMCA) to classify samples as within-specifications (WS) or off-specifications(OS) based on their MSP-TLC profiles. WS samples used in this study were pure plant samples of known processing history that passed the Pharmacopeia acceptance criteria, whereas OS samples used in this study were samples that did not pass the acceptance criteria and/or were intentionally degraded or contaminated. The optimized SIMCA model for B. balsamifera demonstrated 75.0% and 95.7% sensitivity and specificity, respectively. The increased specificity of the method is an improvement over the Pharmacopeia method which is subject to misclassification of adulterations as high as 50% (w/w). The optimized SIMCA model for V. negundo, meanwhile, demonstrated 83.3% and 78.6% sensitivity and specificity, respectively. However, the model could only correctly detect contaminations as low as 30% (w/w), which is nonetheless a significant improvement over the Pharmacopeia method which can potentially misclassify samples up to 80% (w/w) adulteration. The lower sensitivity of the classification models, on the other hand, may be due to the greater responsiveness of the method to unusual features in the profiles compared to the Pharmacopeia acceptance criteria. Overall, this study serves as a proof-of-concept demonstration of the use of a general one-step multiple development TLC method that when coupled with image analysis and chemometric fingerprinting, has greater specificity with respect to contaminations compared to the standard Pharmacopeia method. The proposed method can serve as a promising field-ready quality assessment tool that is user-friendly, robust, portable, reliable, and safe for end-users such as farmers and processors

Learning Grit and the Intervening Effects of MOOCs in Learning the English Language among College Students

Learning a foreign language such as English usually takes a considerable amount of effort on the part of non-native speakers. The English language as the modern-day lingua franca in almost all aspects of global communications spanning from business to the academe requires that students should be adept of it after they finished their tertiary education. The Southeast Asian Region in which the Philippines belong, is trying to catch-up with the global productivity index that must produce college graduates that are adept in using the English language in order to be competitive. Learning English in college through the use of traditional teaching methods makes students disinterested and disengaged in their course works. The advent of technology specifically the Internet has offered an alternative method to learn English in a more interesting and engaging way through synchronous and asynchronous learning methods such as the massive open online courses (MOOCs). This learning modality has eased the tension of acquiring the necessary English language proficiency among college students. This study is anchored on the structural equation modelling about the effects of MOOCs in learning the English language along with their learning grit from the vantage point of Filipino college students