Conserving elastic turbulence numerically using artificial diffusivity.

To simulate elastic turbulence, where viscoelasticity dominates, numerical solvers introduce an artificial stress diffusivity term to handle the steep polymer stress gradients that ensue. This has recently been shown [A. Gupta and D. Vincenzi, J. Fluid Mech. 870, 405 (2019)0022-112010.1017/jfm.2019.224; V. Dzanic et al., J. Fluid Mech. 937, A31 (2022)0022-112010.1017/jfm.2022.103] to introduce unphysical artifacts with a detrimental impact on simulations. In this Letter, we propose that artificial diffusion is limited to regions where stress gradients are steep instead of seeking the zero-diffusivity limit. Through the cellular forcing and four-roll mill problem, we demonstrate that this modified artificial diffusivity is devoid of unphysical artifacts, allowing all features of elastic turbulence to be retained. Results are found to conform with direct simulations, reducing the impact of artificial diffusivity from a qualitative scale to a quantitative scale while only requiring a fraction of the numerical resolution.

Application of high-order lattice Boltzmann pseudopotential models.

Higher-order lattice Boltzmann (LB) pseudopotential models have great potential for solving complex fluid dynamics in various areas of modern science. The discreteness of the lattice discretization makes these models an attractive choice due to their flexibility, capacity to capture hydrodynamic details, and inherent adaptability to parallel computations. Despite those advantages, the discreteness makes high-order LB models difficult to apply due to the larger lattice structure, for which basic fundamental properties, namely diffusion coefficient and contact angle, remain unknown. This work addresses this by providing general continuum solutions for those two basic properties and demonstrating these solutions to compare favorably against known theory. Various high-order LB models are shown to reproduce the sinusoidal decay of a binary miscible mixture accurately and consistently. Furthermore, these models are shown to reproduce neutral, hydrophobic, and hydrophilic contact angles. Discrete differences are shown to exist, which are captured at the discrete level and confirmed through droplet shape analysis. This work provides practical tools that allow for high-order LB pseudopotential models to be used to simulate multicomponent flows.

Interaction pressure tensor on high-order lattice Boltzmann models for nonideal fluids.

In this work we address the application of pseudopotentials directly on high-order lattice Boltzmann models. We derive a general expression for the pressure tensor on high-order lattices considering all nonideal interactions, including intra- and intermolecular interactions, following the discrete lattice theory introduced by X. Shan [Phys. Rev. E 77, 066702 (2008)PLEEE81539-375510.1103/PhysRevE.77.066702]. From the derived expression, a generalized continuum approximation, truncated at fourth-order isotropy, is obtained that is readily applicable to high-order lattices. With this, we demonstrate that high-order lattice models with pseudopotentials can satisfy thermodynamic consistency. The derived generalized expression and continuum approximation are validated for the case of a flat interface and compared against the standard definition available from the literature. The generalized expression is also shown to accurately reproduce the Laplace experiment for a variety of high-order lattice structures. This work sets the preliminary steps towards the application of high-order lattice models for simulating nonideal fluid mixtures.

Incidence of surgically treated osteoarthritis in the hip and knee in male construction workers.

OBJECTIVE: Occupational workload has been associated with an increased risk of osteoarthritis. The objective was to further examine the association between workload and occurrence of osteoarthritis and in particular to study whether heavy workload has similar importance as a causative factor for osteoarthritis of the hip and knee. METHODS: In a cohort study, the authors investigated the incidence of surgically treated osteoarthritis in the hip and knee among men employed in the Swedish construction industry (n = 204 741). Incident cases were found by linkage with the Swedish hospital discharge register between 1987 and 1998. Incidence rates adjusted for age and BMI were compared between different occupational groups. RESULTS: The incidence rates for osteoarthritis in hip and knee were positively correlated (r = 0.62; p = 0.01). There was a significantly increased risk of surgically treated osteoarthritis in the knee among floor layers, asphalt workers, sheet-metal workers, rock workers, plumbers, brick layers, wood workers and concrete workers. Even if there was a trend towards increased relative risks for osteoarthritis in the hip in floor layers, asphalt workers, wood workers and concrete workers they were not statistically significant. The relative risk for surgically treated osteoarthritis of the knee was 4.7 (95% CI 1.8 to 12.3) among floor layers, indicating an attributable fraction for work factors of 79%. CONCLUSIONS: This study shows that some work-related factors seem to be risk factors for osteoarthritis both in the knee and hip. However, the risk factors seem to be of greater importance for osteoarthritis in the knee compared with the hip. This study indicates that at least 50% of the cases of severe osteoarthritis of the knee can be prevented through decreasing occupational risk factors in some occupational groups.

Cytotoxicity in Bacillus mojavensis is abolished following loss of surfactin synthesis: implications for assessment of toxicity and food poisoning potential.

Bacillus subtilis and the closely related species Bacillus pumilus and Bacillus licheniformis have periodically been suggested to play a role in the aetiology of food poisoning despite the fact that the organisms do not possess the genes associated with enteropathogenicity in Bacillus cereus. We show here that Bacillus mojavensis, an organism closely related to B. subtilis, is able to produce toxic components which identify as a complex of three different surfactin analogues. These cyclic lipopeptides were soluble in methanol, heat stable after treatment in a boiling water bath for 10 min, resistant to enzymatic degradation by pepsin, trypsin, endoprotease V8 and proteinase K and formed pores in planar lipid bilayers. They were cytotoxic when tested in a series of commonly used laboratory cytotoxicity assays, namely, lactate dehydrogenase release, haemolysis, inhibition of both protein synthesis in Vero cells and motility in boar sperm. We show that such in vitro markers of enterotoxicity are due entirely to production of cyclic lipopeptides since deletion of sfp, a gene essential for surfactin synthesis which abolished the cytotoxicity to Vero cells, boar sperm motility and haemolytic activity. Thus, the relevance of cyclic lipopeptides as food poisoning toxins needs to be evaluated in assays other than the cell cytotoxicity assays in common use.

Cytotoxic Bacillus spp. belonging to the B. cereus and B. subtilis groups in Norwegian surface waters.

AIMS: To investigate the presence and numbers of Bacillus spp. spores in surface waters and examine isolates belonging to the B. cereus and B. subtilis groups for cytotoxicity, and to discuss the presence of cytotoxic Bacillus spp. in surface water as hazard identification in a risk assessment approach in the food industry. METHODS AND RESULTS: Samples from eight different rivers with variable degree of faecal pollution, and two drinking water sources, were heat shocked and examined for the presence of Bacillus spp. spores using membrane filtration followed by cultivation on bovine blood agar plates. Bacillus spp. was present in all samples. The numbers varied from 15 to 1400 CFU 100 ml(-1). Pure cultures of 86 Bacillus spp. isolates representing all sampling sites were characterized using colony morphology, atmospheric requirements, spore and sporangium morphology, and API 50 CHB and API 20E. Bacillus spp. representing the B. cereus and B. subtilis groups were isolated from all samples. Twenty-one isolates belonging to the B. cereus and B. subtilis groups, representing eight samples, were screened for cytotoxicity. Nine strains of B. cereus and five strains belonging to the B. subtilis group were cytotoxic. CONCLUSIONS: The presence of cytotoxic Bacillus spp. in surface water represents a possible source for food contamination. Filtration and chlorination of surface water, the most common drinking water treatment in Norway, do not remove Bacillus spores efficiently. This was confirmed by isolation of spores from tap water samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Contamination of food with water containing low numbers of Bacillus spores implies a risk for bacterial growth in foods. Consequently, high numbers of Bacillus spp. may occur after growth in some products. High numbers of cytotoxic Bacillus spp. in foods may represent a risk for food poisoning.