Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Element Method

Negatively buoyant jets consist in a dense fluid injected vertically upward into a lighter ambient fluid. The numerical simulation of this kind of buoyancy‐driven flows is challenging as it involves multiple fluids with different physical properties. In the case of immiscible fluids, it requires, in addition, to track the motion of the interface between fluids and accurately represent the discontinuities of the flow variables. In this paper, we investigate numerically the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid using the Particle Finite Element Method and compare the two‐dimensional numerical results with experiments on the injection of a jet of dyed water through a nozzle in the base of a cylindrical tank containing rapeseed oil. In both simulations and experiments, the fountain inlet flow velocity and nozzle diameter have been varied to cover a wide range of Froude Fr and Reynolds Re numbers ( 0.1 < Fr < 30, 8 < Re < 1350), reproducing both weak and strong laminar fountains. The flow behaviors observed for the different numerical simulations fit in the regime map based on the Re and Fr values of the experiments, and the maximum fountain height is in good agreement with the experimental observations, suggesting that particle finite element method is a useful tool for the study of immiscible two‐fluid systems

Fluoride Dentifrice Overcomes the Lower Resistance of Fluorotic Enamel to Demineralization

We evaluated if the low resistance of fluorotic enamel to demineralization could be overcome by fluoride dentifrice (FD) treatment. Paired enamel slabs of sound and fluorotic enamel (n = 20/group) from human teeth presenting Thylstrup and Fejerskov index (TF) scores from 0 to 4 were obtained. Half of the anatomic surface of the enamel slabs was isolated and used as a control (baseline) regarding enamel mineralization and fluoride concentration. The slabs were submitted to a pH-cycling model simulating a high cariogenic challenge, and 2×/day they were treated with placebo dentifrice (PD) or FD (1,100 µg F/g, as NaF). After 10 days, the slabs were cut into two halves. Enamel demineralization was evaluated by cross-sectional microhardness in one half, and the fluoride formed (FF) concentration was determined in the other half. For statistical analysis, the data on net demineralization area (ΔΔS) and FF (µg F/g) were grouped into TF0, TF1–2, and TF3–4, and analyzed by two-way ANOVA followed by Tukey’s test (α = 5%). The factors studied were TF (0, 1–2, and 3–4) and dentifrice treatment (PD or FD). The effect of the factors was statistically significant for ΔΔS and FF (p TF1–2 > TF0 (p 0.05) when FD was used. Regarding FF, the groups treated with PD did not differ (p > 0.05), but the greatest (p < 0.05) FF concentration was found in group TF3–4 treated with FD. These findings suggest that the higher susceptibility of fluorotic enamel to demineralization lesions is decreased by the use of FD

Arcanobacterium hemolyticum: identification and susceptibility to nine antimicrobial agents

AbstractObjective To evaluate the in vitro spectrum and activity of linezolid, a recent oxazolidinone, according to well-controlled surveillance data from 42 medical centers in 13 countries throughout Europe.Methods Participants tested the susceptibility of 125 clinical strains of enterococcal and staphylococcal species against 13 drugs using reference broth microdilution trays or the standardized disk diffusion method of the National Committee for Clinical Laboratory Standards (NCCLS). Streptococcal species (n = 25 at each center) were tested against six drugs using E test (AB BIODISK, Solna, Sweden). Quality assurance testing was conducted using NCCLS-recommended strains and verification of resistance to linezolid and other selected agents was performed by retesting strains at the regional (Europe) and international (USA) monitor sites.Results A total of 5598 strains from throughout Europe (91% compliance) were tested. Vancomycin resistance was reported in only 0.6 and 3.0% of Enterococcus faecalis and E. faecium, respectively. Penicillin resistance occurred in 25.1% of Streptococcus pneumoniae; 4.9% at the high-level (≥2 mg/L). The MIC90 for linezolid was 1 mg/L for streptococci and 2 mg/L for enterococci and staphylococci. Using the US FDA- and EUCAST-recommended susceptible breakpoints for linezolid, there were no confirmed reports of linezolid resistance [minimum inhibitory concentration (MIC), ≥8mg/L]. The distribution of linezolid MIC values was unimodal and varied between 0.25 and 1 mg/L for streptococci (≥90% of isolates), and between 1 and 2 mg/L for staphylococci (≥90%) and enterococci (≥95%). There were no differences in linezolid susceptibility in the vancomycin-, oxacillin-, or penicillin-resistant subsets of strains when compared to susceptible organism populations.Conclusions Compared to the North American component of this study, there was substantially less vancomycin resistance among E. faecium isolates (Europe 3.0% vs. North America 63.4%). While the occurrence of penicillin-resistant S. pneumoniae in Europe and North America was similar (25.1% vs. 29.7%), the recovery of high-level penicillin-resistant strains was nearly three-fold higher in North America (4.9% vs. 13.2%). Only linezolid was universally active against all the tested Gram-positive isolates at ≤4mg/L

Size effects in statistical fracture

We review statistical theories and numerical methods employed to consider the sample size dependence of the failure strength distribution of disordered materials. We first overview the analytical predictions of extreme value statistics and fiber bundle models and discuss their limitations. Next, we review energetic and geometric approaches to fracture size effects for specimens with a flaw. Finally, we overview the numerical simulations of lattice models and compare with theoretical models.Comment: review article 19 pages, 5 figure

On the Relationship Between Complex Potentials and Strings of Projection Operators

It is of interest in a variety of contexts, and in particular in the arrival time problem, to consider the quantum state obtained through unitary evolution of an initial state regularly interspersed with periodic projections onto the positive $x$-axis (pulsed measurements). Echanobe, del Campo and Muga have given a compelling but heuristic argument that the state thus obtained is approximately equivalent to the state obtained by evolving in the presence of a certain complex potential of step-function form. In this paper, with the help of the path decomposition expansion of the associated propagators, we give a detailed derivation of this approximate equivalence. The propagator for the complex potential is known so the bulk of the derivation consists of an approximate evaluation of the propagator for the free particle interspersed with periodic position projections. This approximate equivalence may be used to show that to produce significant reflection, the projections must act at time spacing less than 1/E, where E is the energy scale of the initial state.Comment: 29 pages, LaTex, 4 figures. Substantial revision

Fully Interactive and Refined Resolution Simulations of the Martian Dust Cycle by the MarsWRF Model

Acknowledgments: First of all, our warmest thanks go to the PlanetWRF development team for providing the MarsWRF model free of charge to us and their proactive attitude in general. We thank Andy Heaps, National Centre for Atmospheric Science (NCAS), Department of Meteorology, University of Reading, UK, for his helpful advice regarding the data visualization using cf‐Python. We would also like to thank Michael Mischna, Alexandre Kling, and the Associate Editor Claire Newman for their several detailed and insightful comments and suggestions that helped to significantly improve the quality of the paper. M. P. Z. acknowledges the partial support by the Spanish State Research Agency (AEI) project MDM‐2017‐0737 Centro de Astrobiología (CSIC‐INTA), Unidad de Excelencia María de Maeztu. Internally, we would like to express our greatest thanks to the High‐Performance Computing, Division of Information Technology, United Arab Emirates University. Our particular thanks go to Asma AlNeyadi, Anil Thomas, and Nithin Damodaran for their intensive and continuous support in technically demanding questions. Also, we would like to thank the Digitization Unit, UAEU Libraries, for the digitization of auxiliary data on the observational record of the atmospheric T15 temperature and vertical weighting functions of Viking/IRTM. In addition, we thank UAEU Libraries for their assistance in making supporting data of this article available online. In particular, we are grateful to Digitization Technician Shireen M. Wolied, Fadl M. Musa/Digital Library Service, and Student Muhammad Abdul Rahim Sami Ullah. Funding Information: United Arab Emirates University (UAEU). Grant Number: 21R033‐NSS Center 7‐2017 Spanish State Research Agency (AEI). Grant Number: MDM‐2017‐0737Peer reviewedPublisher PD

A comparison of simple analytical methods for determination of fluoride in microlitre-volume plasma samples

The aim was to compare potential methods for fluoride analysis in microlitre-volume plasma samples containing nano-gram amounts of fluoride. Methods: A group of 4 laboratories analysed a set of standardised biological samples as well as plasma to determine fluoride concentration using 3 methods. In Phase-1, fluoride analysis was carried out using the established hexamethyldisiloxane (HMDS)-diffusion method (1 mL-aliquot/analysis) to obtain preliminary measurement of agreement between the laboratories. In Phase-2, the laboratories analysed the same samples using a micro-diffusion method and known-addition technique with 200 µL-aliquot/analysis. Coefficients of Variation (CVs) and intra-class correlation coefficients (ICCs) were estimated using analysis of variance to evaluate the amount of variation within- and between-laboratories. Based on the results of the Phase-2 analysis, 20 human plasma samples were analysed and compared using the HMDS-diffusion method and known-addition technique in Phase-3. Results: Comparison of Phase-1 results showed no statistically significant difference among the laboratories for the overall data set. The mean between- and within-laboratory CVs and ICCs were < 0.13 and ≥0.99, respectively, indicating very low variability and excellent reliability. In Phase-2, the overall results for between-laboratory variability showed a poor CV (1.16) and ICC (0.44) for the micro-diffusion method, whereas with the known-addition technique the corresponding values were 0.49 and 0.83. Phase-3 results showed no statistically significant difference in fluoride concentrations of the plasma samples measured with HMDS-diffusion method and known- addition technique, with a mean (SE) difference of 0.002 (0.003) µg/mL. In conclusion, the known-addition technique could be a suitable alternative for the measurement of fluoride in plasma with microlitre-volume samples

Effect of toothbrushing duration and dentifrice quantity on enamel remineralisation: An in situ randomized clinical trial

Objectives The influence of toothbrushing duration and dentifrice quantity on fluoride efficacy against dental caries is poorly understood. This study investigated effects of these two oral hygiene factors on enamel remineralisation (measured as surface microhardness recovery [SMHR]), enamel fluoride uptake (EFU), and net acid resistance (NAR) post-remineralisation in a randomized clinical study using an in situ caries model. Methods Subjects (n = 63) wore their partial dentures holding partially demineralised human enamel specimens and brushed twice-daily for two weeks, following each of five regimens: brushing for 120 or 45 s with 1.5 g of 1150 ppm F (as NaF) dentifrice; for 120 or 45 s with 0.5 g of this dentifrice; and for 120 s with 1.5 g of 250 ppm F (NaF) dentifrice. Results Comparing brushing for 120 s against brushing for 45 s, SMHR and EFU increased by 20.0% and 26.9% respectively when 1.5 g dentifrice was used; and by 22.8% and 19.9% respectively when 0.5 g dentifrice was used. Comparing brushing with 1.5 g against brushing with 0.5 g dentifrice, SMHR and EFU increased by 35.3% and 51.3% respectively when brushing for 120 s, and by 38.4% and 43.0% respectively when brushing for 45 s. Increasing brushing duration and dentifrice quantity also increased the NAR value. The effects of these two oral hygiene factors on SMHR, EFU, and NAR were statistically significant (p < 0.05 in all cases). Conclusion Brushing duration and dentifrice quantity have the potential to influence the anti-caries effectiveness of fluoride dentifrices. Study NCT01563172 on ClinicalTrials.gov. Clinical significance The effect of two key oral hygiene regimen factors – toothbrushing duration and dentifrice quantity – on fluoride’s anticaries effectiveness is unclear. This 2-week home-use in situ remineralisation clinical study showed both these factors can influence fluoride bioactivity, and so can potentially affect fluoride’s ability to protect against caries