Direct numerical simulation of open-channel flow over smooth-to-rough and rough-to-smooth step changes

Direct numerical simulations (DNS) are reported for open-channel flow over streamwise-alternating patches of smooth and fully rough walls. The rough patch is a three-dimensional sinusoidal surface. Owing to the streamwise periodicity, the flow configuration consists of a step change from smooth to rough, and a step change from rough to smooth. The friction Reynolds number varies from 437 over the smooth patch to 704 over the rough patch. Through the fully resolved DNS dataset it is possible to explore many detailed aspects of this flow. Two aspects motivate this work. The first one is the equilibrium assumption that has been widely used in both experiments and computations. However, it is not clear where this assumption is valid. The detailed DNS data reveal a significant departure from equilibrium, in particular over the smooth patch. Over this patch, the mean velocity is recovered up to the beginning of the log layer after a fetch of five times the channel height. However, over the rough patch, the same recovery level is reached after a fetch of two times the channel height. This conclusion is arrived at by assuming that an error of up to 5 % is acceptable and the log layer, classically, starts from 30 wall units above the wall. The second aspect is the reported internal boundary-layer (IBL) growth rates in the literature, which are inconsistent with each other. This is conjectured to be partly caused by the diverse IBL definitions. Five common definitions are applied for the same DNS dataset. The resulting IBL thicknesses are different by 100 %, and their apparent power-law exponents are different by 50 %. The IBL concept, as a layer within which the flow feels the surface underneath, is taken as the basis to search for the proper definition. The definition based on the logarithmic slope of the velocity profile, as proposed by Elliot (Trans. Am. Geophys. Union, vol. 39, 1958, pp. 1048–1054), yields better consistency with this concept based on turbulence characteristics

Dynamic subfilter-scale stress model for large-eddy simulations

We present a modification of the integral length-scale approximation (ILSA) model originally proposed by Piomelli et al. [Piomelli et al., J. Fluid Mech. 766, 499 (2015)] and apply it to plane channel flow and a backward-facing step. In the ILSA models the length scale is expressed in terms of the integral length scale of turbulence and is determined by the flow characteristics, decoupled from the simulation grid. In the original formulation the model coefficient was constant, determined by requiring a desired global contribution of the unresolved subfilter scales (SFSs) to the dissipation rate, known as SFS activity; its value was found by a set of coarse-grid calculations. Here we develop two modifications. We de-fine a measure of SFS activity (based on turbulent stresses), which adds to the robustness of the model, particularly at high Reynolds numbers, and removes the need for the prior coarse-grid calculations: The model coefficient can be computed dynamically and adapt to large-scale unsteadiness. Furthermore, the desired level of SFS activity is now enforced locally (and not integrated over the entire volume, as in the original model), providing better control over model activity and also improving the near-wall behavior of the model. Application of the local ILSA to channel flow and a backward-facing step and comparison with the original ILSA and with the dynamic model of Germano et al. [Germano et al., Phys. Fluids A 3, 1760 (1991)] show better control over the model contribution in the local ILSA, while the positive properties of the original formulation (including its higher accuracy compared to the dynamic model on coarse grids) are maintained. The backward-facing step also highlights the advantage of the decoupling of the model length scale from the mesh

Accuracy control for large-eddy simulation of turbulent mixing - Integral length-scale approach

Turbulent flow at high Reynolds numbers is currently not accessible on the basis of direct numerical simulation (DNS) of the Navier-Stokes equations - the computational complexity is too high to allow DNS in most realistic flow conditions. Instead, Large-Eddy Simulation (LES) offers an alternative in which the focus is on capturing the larger dynamic scales of a problem. However, the fundamental closure problem in LES induced by spatial filtering of nonlinear terms, and the role of discretization errors in the numerical treatment of the LES equations, induce a principal uncertainty in any LES prediction. This uncertainty requires quantification and control. We investigate error control capabilities of the Integral Length-Scale Approximation (ILSA) and apply this modeling to transitional and turbulent mixing, focussing on the achieved reliability of LES as function of the grid resolution and ‘sub-filter activity’.</p

Variable DNA methylation of transposable elements: The case study of mouse Early Transposons

Phenotypic variation stems from both genetic and epigenetic differences between individuals. In order to elucidate how phenotypes are determined, it is necessary to understand the forces that generate variation in genome sequence as well as its epigenetic state. In both contexts, transposable elements (TEs) may play an important role. It is well established that TE activity is a major generator of genetic variation, but recent research also suggests that TEs contribute to epigenetic variation. Stochastic epigenetic silencing of some TE insertions in mice has been shown to cause phenotypic variability between individuals. However, the prevalence of this phenomenon has never been evaluated. Here, we use 18 insertions of a mouse Endogenous Retrovirus (ERV) family, the Early Transposons (ETns), to detect insertion-dependent determinants of DNA methylation levels and variability between both cells and individuals. We show that the structure and age of insertions influence methylation levels and variability, resulting in a subgroup of loci that displays unexpectedly high variability in methylation and suggesting stochastic events during methylation establishment. Despite variation in methylation according to the age and structure of each locus, homologous CpG sites show similar tendencies in methylation levels across loci, emphasizing the role of the insertion's sequence in methylation determination. Our results show that differences in methylation of ETns between individuals is not a sporadic phenomenon and support the hypothesis that ERVs contribute to phenotypic variability through their stochastic silencing

Structural Evaluation and Maintenance of Brooks Aqueduct Historic Site

Brooks Aqueduct in Alberta, Canada is one of the largest and most sophisticated reinforced concrete aqueducts in the world. Now a national historic site, Brooks Aqueduct was built in 1914. The structure suffers from cracking and degradation in certain locations. To find out the possible main causes of potential overstress and damage in the different areas of the structure, it was evaluated by site inspections, some laboratory tests and analyzed numerically using Abaqus finite element software. Results of the numerical analysis are compared with the inspection and testing results and conclusions are made about the causes of deterioration and ways to conserve and repair the structure

Distribution of zooplankton in the southern Caspian Sea

The zooplanktons were studied in spring, autumn and winter in the southern Caspian Sea in 1996. Sampling carried out in four season. In each season, 180 specimens were identified and their frequency calculated per m^3. 55 species of zooplanktons were identified including 55% Cladocera, 15% Copepoda and 11 % Rotatoria, 9% other groups such as meroplanktons. The maximum species diversity was observed for Cladocera and the maximum frequency were observed for Copepoda. The Copepoda affected on abundance of zooplanktons as this frequency included in spring, summer, autumn and winter that were 38% to 97%, 22% to 92%, 71 % to 99% and 31 % to 92%, respectively. In summer, the Copepoda and lamellibranchiata larvae had main role in formation of zooplankton population in western region of the southern Caspian Sea, but in autumn, 70% of zooplankton population were copepods. The frequency of zooplanktons in spring, summer, autumn and winter were calculated 4081 to 20143; 7812 to 65741; 10850 to 34406 and 4510 to 20576 inch/m^3, respectively. The maximum biomass was observed during summer with 200 mg/m^3

Solubility isotope effects in aqueous solutions of methane

The isotope effect on the Henry's law coefficients of methane in aqueous solution (H/D and C-12/C-13 substitution) are interpreted using the statistical mechanical theory of condensed phase isotope effects. The missing spectroscopic data needed for the implementation of the theory were obtained either experimentally (infrared measurements), by computer simulation (molecular dynamics technique), or estimated using the Wilson's GF matrix method. The order of magnitude and sign of both solute isotope effects can be predicted by the theory. Even a crude estimation based on data from previous vapor pressure isotope effect studies of pure methane at low temperature can explain the inverse effect found for the solubility of deuterated methane in water. (C) 2002 American Institute of Physics

An examination of the cryptocurrency pump-and-dump ecosystem

The recent introduction of thousands of cryptocurrencies in an unregulated environment has created many opportunities for unscrupulous traders to profit from price manipulation. We quantify the scope of one widespread tactic, the “pump and dump”, in which actors coordinate to bid up the price of coins before selling at a profit. We joined all relevant channels on two popular group-messaging platforms, Telegram and Discord, and identified thousands of different pumps targeting hundreds of coins. We find that pumps are modestly successful in driving short-term price rises, but that this effect has diminished over time. We also find that the most successful pumps are those that are most transparent about their intentions. Combined with evidence of concentration among a small number of channels, we conclude that regulators have an opportunity to effectively crack down on this illicit activity that threatens broader adoption of blockchain technologies

Analyzing Target-Based Cryptocurrency Pump and Dump Schemes

As the number of cryptocurrencies has exploded in recent years, so too has the fraud. One popular strategy is when actors promote coordinated purchases of coins in hopes of temporarily driving up prices. Prior work investigating such pump and dump schemes has focused on the immediate impact to prices following pump signals, which were largely interpreted as following the same strategy. The reality, as with most cybercrimes, is that the operators of the schemes try out a much more heterogeneous mix of tactics. From a population of 12,252 pump signals observed between July 2017 and January 2019, we identify and examine 3,683 so-called target-based pump signals that announce promoted coins alongside buy and sell targets, but without a coordinated purchase time. We develop a strategy to measure the success of target pumps over longer time horizons. We find that around half of these pumps reach at least one of their sell targets, and that reaching their peak price often takes days, as opposed to the seconds or minutes required in pumps studied previously. We also examine the various groups promoting coins and present evidence that groups try a variety of distinct strategies and experience varying success. We find that the most successful groups promote many coins and issue many pumps, but not for the same coins. As decentralized finance becomes more popular, a deeper understanding of price manipulation techniques like target pumps is needed to combat fraud

Responding to physical and psychological health impacts of disasters: Case study of the Iranian disaster rehabilitation plan Agir en réponse aux conséquences physiques et psychologiques des catastrophes naturelles: �tude de cas du plan de relèvement post-catastrophe en Iran

This paper describes the process of developing a national pre-disaster plan for physical health and psychological rehabilitation of disaster-stricken communities. Data gathered from a literature review and expert panel discussions informed the process of drawing up unified definitions of physical and psychological health rehabilitation, carrying out stakeholder and STEEP-V analyses, and assigning the responsible organization and the collaborative organizations for each task. The Ministry of Health and the Welfare Organization were selected as the two responsible organizations. Integrated management at all levels, and sharing information, education and funding, were identified as ways to improve stakeholders� participation and collaboration. A system is needed for evaluating the implementation of the disaster rehabilitation plan, using valid and reliable indicators. © 2016, World Health Organization. All rights reserved