Mixing Strength Research Articles

Impact of uncertainties in atmospheric mixing on simulated UTLS composition and related radiative effects

The upper troposphere/lower stratosphere (UTLS) region plays an important role in the climate system. Changes in the structure and chemical composition of this region result in particularly large changes in radiative forcings of the atmosphere. Quantifying the processes that control UTLS composition (e.g., stratosphere‐troposphere exchange) therefore represents a crucial task. We assess the influence of uncertainties in the atmospheric mixing strength on global UTLS distributions of greenhouse gases (water vapor, ozone, methane, and nitrous oxide) and associated radiative effects. The study is based on multiannual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by ERA‐Interim meteorological data and on a state‐of‐the‐art radiance code. Mixing, the irreversible part of transport, is controlled by the local horizontal strain and vertical shear of the atmospheric flow. We find that simulated radiative effects of water vapor and ozone, both characterized by steep gradients in the UTLS, are particularly sensitive to uncertainties of the atmospheric mixing strength. Globally averaged radiative effects are about 0.72 and 0.17 W/m2for water vapor and ozone, respectively. For ozone, the largest impact of mixing uncertainties is observed in the extra‐tropical lower stratosphere.

Effects of 3-D channel blockage and turbulent wake mixing on the limit of power extraction by tidal turbines

Three-dimensional incompressible Reynolds-averaged Navier–Stokes (RANS) computations are performed for water flow past an actuator disk model (representing a tidal turbine) placed in a rectangular channel of various blockages and aspect ratios. The study focuses on the effects of turbulent mixing behind the disk, as well as on the effects of channel blockage and aspect ratio on the prediction of the hydrodynamic limit of power extraction. To qualitatively account for the effect of turbulence generated by the turbine (rather than by the shear flow behind the turbine), we propose a new approach, called a blade-induced turbulence model, which does not use any additional model coefficients other than those used in the original RANS turbulence model. Results demonstrate that the power removed from the mean flow by the disk increases as the strength of turbulent mixing behind the disk increases, being consistent with the turbulent shear stress on the interface between the bypass and core flow passages acting in such a way as to decelerate the bypass flow and accelerate the core flow. The channel aspect ratio also affects the flow downstream of the disk but has less influence upstream of the disk; hence its effect on the limit of power extraction is relatively minor compared to that of the channel blockage, which is shown to be significant but satisfactorily estimated using one-dimensional inviscid theory previously reported in the literature.

Effects of tides on freshwater and volume transports in the Changjiang River plume

Effects of tides on the Changjiang River plume are investigated using a numerical model of the East China and Yellow Seas. In the absence of tides, the buoyancy‐driven coastal current downstream of the river mouth is a surface‐trapped plume attached to the coast. In the presence of tides, however, the plume shifts away from the coast and features a bottom boundary layer. The freshwater transport by the coastal current accounts for only 35% of the Changjiang River discharge without tides but increases to 80% with tides. Tidal currents stabilize the plume bulge near the river mouth and force the plume water to move in the direction of tidal currents, thus increasing the downstream freshwater transport. In contrast, tidal residual currents are weak and make little contributions to the total freshwater transport. Tidal mixing reduces the plume's buoyancy but increases its thickness so that the freshwater transport is insensitive to the strength of turbulent mixing. Volume transport in the tidal‐affected buoyancy coastal current exceeds the river discharge by 4 to 12 times, as opposed to 2–3 fold amplification in the plume without tides. Tidal mixing between the plume and ambient shelf waters produces higher salinity classes in the plume so that the volume flux in the downstream coastal current increases to discharge the freshwater released from the Changjiang River.

The influence of mixing methods and disinfectant on the physical properties of alginate impression materials

The aims of this in vitro study were to quantify the effect of manual versus automatic mixing and of using a disinfectant on mechanical properties of three different alginate impression materials. Two of the three alginates tested were especially developed for orthodontic use: Orthotrace® and Orthofine® while the third was a conventional alginate CA37FS®. Alginates were mixed by hand or automatically using a Cavex alginate mixer II®. Mixing was performed at room temperature using tap water. The material was allowed to set in a water bath at 35°C (±1°C), simulating intra-oral setting conditions, and half of the samples were disinfected before testing. For each tested material, 10 standardized samples were used. The disinfectant used was the CavexImpreSafe® that has a bactericide, virucide, and fungicide function. The specimens were exposed for 3 minutes in a 3% solution and were then tested according to the ISO 1563: 1990 (E) standard specifications. Descriptive statistics and three-way analysis of variance were performed, and a 5% significance level was used for statistical analysis. Evaluation of tensile strength and elastic recovery of different alginate samples, hand versus automatical mixing or disinfected versus not disinfected, resulted in significant differences for all materials except for Orthofine®. Considering detail reproduction, all three alginates evaluated reproduced the 50-μm line successfully without interruption. The mixing method can significantly affect the elastic recovery and tensile strength of the alginates tested while the effect of using a disinfectant is less explicit.

The Role of Advection, Straining, and Mixing on the Tidal Variability of Estuarine Stratification

Abstract Data from the Hudson River estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along-channel tidal straining. These observations result from three additional processes not accounted for in the traditional tidal straining model: 1) along-channel and 2) lateral advection of horizontal gradients in the vertical salinity gradient and 3) tidal asymmetries in the strength of vertical mixing. As a result, cross-sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb. Only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood. These observations highlight the three-dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters, even when direct turbulent mixing through the pycnocline is prohibited by strong stratification.

Flow topology and scalar mixing in spatially heterogeneous flow fields

Scalar mixing plays a significant role for transport in geophysical flows because it controls dilution and is a main driver for many chemical reactions. Here we study the local scale flow mechanisms that lead to enhanced scalar mixing, and how they impact on the global mixing behavior. Mixing is quantified in terms of the entropy of the scalar distribution. It is shown that the evolution of entropy is directly linked to the flow topology in terms of the Okubo‐Weiss parameter Θ. Dominant shear and stretching deformation (Θ > 0) leads to a strong increase of local mixing strength, while dominant vorticity (Θ < 0) has only a minor impact. This allows to delineate regions of increased scalar mixing potential by mapping out the spatial distribution of Θ(x), and to relate global scalar mixing to an areal averaged effective Okubo‐Weiss measure.

Interfacial configurations and mixing performances of fluids in staggered curved-channel micromixers

A parallel laminar micromixer with staggered curved channels is designed and fabricated in our study. The split-and-recombination (SAR) structures of the flow channels result in the reduction of the diffusion distance of two fluids. Furthermore, the impinging effects increase the mixing strength whereas one stream is injected into the other. The particles trajectories are utilized to numerically examine the mixing and fluidic behaviors inside the staggered curved microchannel with tapered structures. The effects of various Reynolds numbers and channel configurations on mixing performances are investigated in terms of the experimental mixing indices and the computational interfacial patterns.

Experimental investigation and feasibility study on stabilized compacted earth block using local resources

Investigation is carried out mainly to find out a suitable mix proportion to blend locally available materials such as soil, sand, clay, grits, jute, etc. with cement for making compacted earth block for construction of affordable residential buildings. The local soil and clay in and around Jalpaiguri town of West Bengal was mixed with the local sand, and stone grits to make a composite good soil of gravel 15 percent, Sand 50 percent, Silt and Clay 35 percent, for compacted stabilized earth blocks (CSEB).1 Blocks of 254 mm x 127 mm x 76 mm size, were prepared with varying percent of Ordinary Portland Cement (5.0 percent, 7.5 percent, and 10.0 percent) and jute fibre of size 2.5 cm and compacting manually to the standard proctor density. Jute size of 2.5cm was chosen as it was found best option from earlier investigation by the same author 8 compared to other sizes from mixing and compressive strength point of view. The blocks were cured and tested for compressive strength, water absorption and density. Based on the results, it has been concluded that the compacted cement stabilized earth blocks both with or without jute fibre may be a cost effective and environment friendly alternative to the burnt clay bricks in lightly loaded building (rural areas) where stability is not a governing factor.

Probing the turbulent mixing strength in protoplanetary disks across the stellar mass range: no significant variations

Dust settling and grain growth are the first steps in the planet-formation process in protoplanetary disks. These disks are observed around stars with different spectral types, and there are indications that the disks around lower mass stars are significantly flatter, which could indicate that they settle and evolve faster, or in a different way. We aim to test this assumption by modeling the median spectral energy distributions (SEDs) of three samples of protoplanetary disks: around Herbig stars, T Tauri stars and brown dwarfs. We focus on the turbulent mixing strength to avoid a strong observational bias from disk and stellar properties that depend on stellar mass. We generated SEDs with the radiative transfer code MCMax, using a hydrostatic disk structure and settling the dust in a self-consistent way with the alpha-prescription to probe the turbulent mixing strength. We are able to fit all three samples with a disk with the same input parameters, scaling the inner edge to the dust evaporation radius and disk mass to millimeter photometry. The Herbig stars require a special treatment for the inner rim regions, while the T-Tauri stars require viscous heating, and the brown dwarfs lack a good estimate of the disk mass because only few millimeter detections exist. We find that the turbulent mixing strength does not vary across the stellar mass range for a fixed grain size distribution and gas-to-dust ratio. Regions with the same temperature have a self-similar vertical structure independent of stellar mass, but regions at the same distance from the central star appear more settled in disks around lower mass stars. We find a relatively low turbulent mixing strength of alpha = 10^(-4) for a standard grain size distribution, but our results are also consistent with alpha = 0.01 for a grain size distribution with fewer small grains or a lower gas-to-dust ratio.

Sterile neutrinos, coherent scattering, and oscillometry measurements with low-temperature bolometers

Coherent neutrino-nucleon scattering offers a unique approach in the search for physics beyond the standard model. When used in conjunction with monoenergetic neutrino sources, the technique can be sensitive to the existence of light sterile neutrinos. The ability to utilize such reactions has been limited in the past due to the extremely low-energy threshold (10--50 eV) needed for detection. In this paper, we discuss an optimization of cryogenic solid-state bolometers that enables reaching extremely low kinetic energy thresholds. We investigate the sensitivity of an array of such detectors to neutrino oscillations to sterile states. A recent analysis of available reactor data appears to favor the existence of such a sterile neutrino with a mass splitting of $|\ensuremath{\Delta}{m}_{\mathrm{sterile}}{|}^{2}\ensuremath{\ge}1.5\text{ }\text{ }{\mathrm{eV}}^{2}$ and mixing strength of ${sin}^{2}2{\ensuremath{\theta}}_{\mathrm{sterile}}=0.17\ifmmode\pm\else\textpm\fi{}0.08$ at 95% confidence level. An array of such low-threshold detectors would be able to make a definitive statement as to the validity of the interpretation.

Mixing of a split and recombine micromixer with tapered curved microchannels

We demonstrate a novel parallel laminar micromixer with two-dimensional staggered curved channels with tapered structures. Dean vortex flows are produced in curved rectangular channels by centrifugal forces. The split structures of the tapered channels result in the uneven split of the main stream and the reduction of the diffusion distance of two fluids. Furthermore, when one stream is injected into the other the impingement effects increase the mixing strength. Cross-sectional concentration distributions and particle trajectories are utilized to examine the flow characteristics inside the curved microchannel numerically. To evaluate the mixing performance of the designed micromixer, four different designs of a curved channel micromixer are introduced for the purpose of comparison. The mixing index of the staggered curved-channel mixer with a tapered channel is 20% higher than those of the other curved-channel mixers: i.e., the staggered curved-channel mixer with sudden contracted channels, the staggered curved-channel mixer with uniform channel width and the continuous curved-channel mixer. However, a comparison of the pressure drop penalty for the mixing is also reported. The pressure drop of the staggered curved-channel mixer with a tapered channel is about 50% higher than those of the other two staggered curved-channel mixers. The effects of various Reynolds numbers (Re) and channel configurations on mixing performances are investigated in terms of the experimental mixing indices and the computational interfacial patterns. It appears that the Dean vortex and split and recombine (SAR) effects provide improved mixing when the Re is increased above 5. At the Re of 50, the channel length necessary for mixing to be achieved is 5 times shorter compared to the case where the Re equals 1. The comparison between the experimental data and numerical results shows a very similar trend.

An improved lake model for climate simulations: Model structure, evaluation, and sensitivity analyses in CESM1

Lakes can influence regional climate, yet most general circulation models have, at best, simple and largely untested representations of lakes. We developed the Lake, Ice, Snow, and Sediment Simulator (LISSS) for inclusion in the land‐surface component (CLM4) of an earth system model (CESM1). The existing CLM4 lake model performed poorly at all sites tested; for temperate lakes, summer surface water temperature predictions were 10–25°C lower than observations. CLM4‐LISSS modifies the existing model by including (1) a treatment of snow; (2) freezing, melting, and ice physics; (3) a sediment thermal submodel; (4) spatially variable prescribed lake depth; (5) improved parameterizations of lake surface properties; (6) increased mixing under ice and in deep lakes; and (7) correction of previous errors. We evaluated the lake model predictions of water temperature and surface fluxes at three small temperate and boreal lakes where extensive observational data was available. We also evaluated the predicted water temperature and/or ice and snow thicknesses for ten other lakes where less comprehensive forcing observations were available. CLM4‐LISSS performed very well compared to observations for shallow to medium‐depth small lakes. For large, deep lakes, the under‐prediction of mixing was improved by increasing the lake eddy diffusivity by a factor of 10, consistent with previous published analyses. Surface temperature and surface flux predictions were improved when the aerodynamic roughness lengths were calculated as a function of friction velocity, rather than using a constant value of 1 mm or greater. We evaluated the sensitivity of surface energy fluxes to modeled lake processes and parameters. Large changes in monthly‐averaged surface fluxes (up to 30 W m−2) were found when excluding snow insulation or phase change physics and when varying the opacity, depth, albedo of melting lake ice, and mixing strength across ranges commonly found in real lakes. Typical variation among model parameterization choices can therefore cause persistent local surface flux changes much larger than expected changes in greenhouse forcing. We conclude that CLM4‐LISSS adequately simulates lake water temperature and surface energy fluxes, with errors comparable in magnitude to those resulting from uncertainty in global lake properties, and is suitable for inclusion in global and regional climate studies.

Effect of Rice Straw Amount Portion on Physical Properties of Adding Admixtures Hollow Block

This study presents the impact of rice straw as additive material on physical properties of hollow block as compressive, flexural strength and water absorption, Softening coefficient. Through testing the hollow block physical properties, the of rice straw additive was studied. When the rice straw amount portion was 0~15%, with rice straw amount portion increased, compressive, flexural strength and water resistance effect of adding one kind of early strength agent and mixing Al2(SO4)3, CaCl2 early strength agent hollow block decreased gradually. When the rice straw amount portion was 10%, adding early strength agent Al2(SO4)3, CaCl2 ，the 28d compressive strength of hollow block was minimum, 3.5MPa; while mixing CaCl2, Al2(SO4)3 early strength agent, the hollow block softening coefficient was 0.76, water absorption rate was 3.9%, meet the requirements of national standard of common concrete hollow block. Through the experiment, the conclusion is mixing early strength agent Al2(SO4)3, CaCl2, Obviously superior to adding one kind of —early strength agent—Al2(SO4)3 or CaCl2 on the physical properties of hollow block.

コンクリートのトレーサビリティ確保のためのICタグの活用技術

In this paper, the basic experiments aiming at the technical establishment utilizing IC-tags which performs information management of concrete were shown, when the IC-tags were thrown into the fresh concrete at mixing process. The durability of IC-tags against the mixing, agitating, and compressive strength of concrete were examined by the tests which we extracted as the most fundamental experiment. It was clarified that the IC-tags, which do not assume supplying to concrete, beard the various external force at the mixing and agitating process of concrete. Moreover, the result that compressive strength did not decreased was obtained when an IC-tag was installed inside concrete specimen.

Effect of Rice Straw Amount Portion on Physical Properties of Adding Admixtures Hollow Block

This study presents the impact of rice straw as additive material on physical properties of hollow block as compressive, flexural strength and water absorption, Softening coefficient. Through testing the hollow block physical properties, the of rice straw additive was studied. When the rice straw amount portion was 0~15%, with rice straw amount portion increased, compressive, flexural strength and water resistance effect of adding one kind of early strength agent and mixing Al2(SO4)3, CaCl2 early strength agent hollow block decreased gradually. When the rice straw amount portion was 10%, adding early strength agent Al2(SO4)3, CaCl2 ，the 28d compressive strength of hollow block was minimum, 3.5MPa; while mixing CaCl2, Al2(SO4)3 early strength agent, the hollow block softening coefficient was 0.76, water absorption rate was 3.9%, meet the requirements of national standard of common concrete hollow block. Through the experiment, the conclusion is mixing early strength agent Al2(SO4)3, CaCl2, Obviously superior to adding one kind of —early strength agent—Al2(SO4)3 or CaCl2 on the physical properties of hollow block.

Tidal mixing around Indonesia and the Maritime continent: Implications for paleoclimate simulations

[1] Tidal mixing provides an important source of mechanical energy for the ocean circulation and as such is being incorporated into state-of-the-art climate models. Calculation of the tidal energy flux depends on high-resolution topographic datasets, not available for paleoclimate simulations. In this study we demonstrate that changes in the tidal mixing may have significant impacts on ocean circulation, sea surface temperatures, and hence climate. Using a coupled climate model, we test the system's sensitivity to perturbations in the tidal mixing surrounding the Maritime continent and show that an increase in such mixing could cause significant changes in the ocean thermal structure, including a ∼1°C warming of the ocean surface in the eastern equatorial Pacific and a similar cooling in the west. The mechanism of these changes involves mixing the relatively cold waters of the Equatorial undercurrent with warmer surface waters. The reduction of the zonal temperature gradient is amplified by ocean–atmosphere interactions associated with a weakening of the atmospheric Walker circulation. Potential implications of this study concern the Pliocene (an epoch characterized by a reduced zonal temperature contrast along the equator) and other past climates. While the actual strength of tidal mixing during the Pliocene is uncertain, our study assesses the bounds on how much tidal mixing may have contributed to maintaining its climate state. We conclude that, on geological timescales, changes in tidal mixing may be an important dynamical factor together with ocean bathymetry and continental configuration.

Resolving the reactor neutrino anomaly with the KATRIN neutrino experiment

The KArlsruhe TRItium Neutrino experiment (KATRIN) combines an ultra-luminous molecular tritium source with an integrating high-resolution spectrometer to gain sensitivity to the absolute mass scale of neutrinos. The projected sensitivity of the experiment on the electron neutrino mass is 200 meV at 90% C.L. With such unprecedented resolution, the experiment is also sensitive to physics beyond the Standard Model, particularly to the existence of additional sterile neutrinos at the eV mass scale. A recent analysis of available reactor data appears to favor the existence of such a sterile neutrino with a mass splitting of |Δmsterile|2⩾1.5 eV2 and mixing strength of sin22θsterile=0.17±0.08 at 95% C.L. Upcoming tritium beta decay experiments should be able to rule out or confirm the presence of the new phenomenon for a substantial fraction of the allowed parameter space.

Quantitative trait loci influencing end-use quality traits of hard red spring wheat breeding lines

Wheat bread-making quality is influenced by a complex group of traits including dough visco-elastic characteristics. In this study, quantitative trait locus/loci (QTL) mapping and analysis were conducted for endosperm polymeric proteins together with dough mixing strength and bread-making properties in a population of 139 (MN98550 × MN99394) recombinant inbred lines that was evaluated at three environments in 2006. Eleven chromosome regions were associated with endosperm polymeric proteins, explaining 4.2–31.8% of the phenotypic variation. Most of these polymeric proteins QTL coincided with several QTL for dough-mixing strength and bread-making properties. Major QTL clusters were associated with the low-molecular weight glutenin gene Glu-A3, the two high-molecular weight glutenin genes Glu-B1 and Glu-D1, and two regions on chromosome 6D. Alleles at these QTL clusters have previously been proven useful for wheat quality except one of the 6D QTL clusters.

Using boundary layer equilibrium to reduce uncertainties in transport models and CO<sub>2</sub> flux inversions

Abstract. This paper reexamines evidence for systematic errors in atmospheric transport models, in terms of the diagnostics used to infer vertical mixing rates from models and observations. Different diagnostics support different conclusions about transport model errors that could imply either stronger or weaker northern terrestrial carbon sinks. Conventional mixing diagnostics are compared to analyzed vertical mixing rates using data from the US Southern Great Plains Atmospheric Radiation Measurement Climate Research Facility, the CarbonTracker data assimilation system based on Transport Model version 5 (TM5), and atmospheric reanalyses. The results demonstrate that diagnostics based on boundary layer depth and vertical concentration gradients do not always indicate the vertical mixing strength. Vertical mixing rates are anti-correlated with boundary layer depth at some sites, diminishing in summer when the boundary layer is deepest. Boundary layer equilibrium concepts predict an inverse proportionality between CO2 vertical gradients and vertical mixing strength, such that previously reported discrepancies between observations and models most likely reflect overestimated as opposed to underestimated vertical mixing. However, errors in seasonal concentration gradients can also result from errors in modeled surface fluxes. This study proposes using the timescale for approach to boundary layer equilibrium to diagnose vertical mixing independently of seasonal surface fluxes, with applications to observations and model simulations of CO2 or other conserved boundary layer tracers with surface sources and sinks. Results indicate that frequently cited discrepancies between observations and inverse estimates do not provide sufficient proof of systematic errors in atmospheric transport models. Some previously hypothesized transport model biases, if found and corrected, could cause inverse estimates to further diverge from carbon inventory estimates of terrestrial sinks.

LSND/MiniBooNe excess events and heavy neutrino fromμandKdecays

It has been recently shown that puzzling excess events observed by the LSND and MiniBooNE neutrino experiments could be interpreted as a signal from the radiative decay of a heavy sterile neutrino ($\nu_h$) of the mass from 40 to 80 MeV, with a muonic mixing strength $\mix \simeq 10^{-3} - 10^{-2}$, and the lifetime $10^{-11} < \tau_h < 10^{-9}$ s. We discuss bounds on $\mix$ obtained from the recent precision measurements with muons and show that they are consistent with the above limits. If the $\nu_h$ exists its admixture in the ordinary muon or kaon decay would result in the decay chain $\muhd$ or $\khd$, respectively. We propose a new experiment for a sensitive search for these processes in $\mu$ and $K$ decays at rest allowing to either definitively confirm or exclude the existence of the $\nu_h$. To our knowledge, no experiment has specifically searched for the signature of radiative decay of massive neutrinos from particles decays as proposed in this work. The search is complementary to the current experimental efforts to clarify the origin of the LSND and MiniBooNE anomalies.