Simulating rotating fluid bodies: When is vorticity generation via density-stratification important?

NASA Astrophysics Data System (ADS)

Evonuk, M.; Samuel, H.

2012-02-01

Differential rotation is one of the key components needed to maintain a magnetic dynamo, therefore it is important to understand the processes that generate differential rotation in rotating bodies. In a rotating density-stratified fluid, local vorticity generation occurs as fluid parcels move radially, expanding or contracting with respect to the background density stratification. The convergence of this vorticity forms zonal flow structures as a function of the radius and the slope of the background density profile. While this effect is thought to be of importance in bodies that are quickly rotating and highly turbulent with large density stratifications such as Jupiter, it is generally neglected in bodies such as the Earth's outer core, where the density change is small. Simulations of thermal convection in the 2D rotating equatorial plane are conducted to determine the parameter regime where local vorticity generation plays a significant role in organizing the fluid flow. Three regimes are found: a dipolar flow regime, where the flow is not organized by the rotation, a transitional flow regime, and a differential flow regime, where the flow is strongly organized into differential rotation with multiple jets. A scaling law is determined based on the convective Rossby number and the density contrast across the equatorial plane, providing a simple way to determine in which regime a given body lies. While a giant planet such as Jupiter lies firmly in the differential flow regime as expected, the Earth's outer core is also found to lie in the differential flow regime indicating that, even in the Earth's outer core, where the density contrast is small, vorticity contributions via fluid movement through the density stratificationmay be non-negligible.

Spatial and Temporal Trends in the Density Stratification of Long Island Sound

NASA Astrophysics Data System (ADS)

Marchese, P.

2017-12-01

The density structure of Long Island Sound (LIS) was studied using historical hydrographic data. Like many estuaries, LIS suffers from hypoxia during the summer months; a result of the density stratification caused by surface warming and weak wind conditions. In summer, the water column is stratified at both ends (east and west) with a vertically well mixed region near the middle. During these months, the western side of LIS experiences low bottom dissolved from the higher nutrient influx and the resulting oxygen demand. Eastern LIS does not experience hypoxia despite sometimes being more highly stratified than the west because these bottom water are regularly ventilated by incoming higher DO water from outside. Topography and density gradients prevent the low DO water from encroaching to the eastern basin. In the fall, changing atmospheric conditions weakens the density stratification throughout LIS, although in some regions the vertical gradient will persist, sometimes until January.

Secular rotational motions and the mechanical structure of a dynamical viscoelastic earth

NASA Technical Reports Server (NTRS)

Yuen, D. A.; Sabadini, R.

1984-01-01

A survey is presented of analytical methods for computing the linear responses of the rotational axis of a layered viscoelastic earth to surface loading. Theoretical research in this area is first summarized, and the differences between the mechanical boundary conditions to be applied at the interface separating the upper and lower mantles for an adiabatically and chemically stratified mantle are discussed. Some examples of polar wander and secular variation of the spin rate from glacial excitation are presented for various types of chemical and viscosity stratifications. The effects of an artificial density jump at the base of the lithosphere in models are examined, and certain issues concerning the fluid tidal Love number for different types of density stratification are addressed. The meaning of effective plate thickness over geological time scales for rotational dynamics is discussed.

Eddy-driven stratification initiates North Atlantic spring phytoplankton blooms.

PubMed

Mahadevan, Amala; D'Asaro, Eric; Lee, Craig; Perry, Mary Jane

2012-07-06

Springtime phytoplankton blooms photosynthetically fix carbon and export it from the surface ocean at globally important rates. These blooms are triggered by increased light exposure of the phytoplankton due to both seasonal light increase and the development of a near-surface vertical density gradient (stratification) that inhibits vertical mixing of the phytoplankton. Classically and in current climate models, that stratification is ascribed to a springtime warming of the sea surface. Here, using observations from the subpolar North Atlantic and a three-dimensional biophysical model, we show that the initial stratification and resulting bloom are instead caused by eddy-driven slumping of the basin-scale north-south density gradient, resulting in a patchy bloom beginning 20 to 30 days earlier than would occur by warming.

DNS of helicity-induced stratified turbulent flow

NASA Astrophysics Data System (ADS)

Chandy, Abhilash J.; Rahimi, Abbas

2013-11-01

Helical flows undergoing density stratification have wide applications in meteorological phenomena such as dust devils, tornadoes, and hurricanes due to the complexity and disasters caused by them. Direct numerical simulations (DNS) of transition to turbulence in a stably stratified Boussinesq fluid are presented for different rotation and stratification intensities. In order to understand the effect of velocity on the energy cascade, comparisons are made between helicity initiated and non-helical flows. Results show that stratification decelerates the helicity decay and causes velocity and vorticity to align with each other. With respect to the helical and non-helical flow comparisons, the total energy in the presence of stratification decays faster with helicity. In addition, the behavior of length scales were examined by comparing temporal variations of the vertical shearing of velocities. Results showed a growing asymmetry with time in the case of helical flow, while non-helical flow stayed close to begin symmetric.

Eigenmode resonance in a two-layer stratification

NASA Astrophysics Data System (ADS)

Kanda, Isao; Linden, P. F.

2002-06-01

In this paper, we study the velocity field at the density interface of a two-layer stratification system when the flow is forced at the mid-depth of the lower layer by the source sink forcing method. It is known that, in a sufficiently strong linear stratification, the source sink forcing in certain configurations produces a single-vortex pattern which corresponds to the lowest eigenmode of the Helmholtz equation (Kanda & Linden 2001). Two types of forcing configuration are used for the two-layer experiments: one that leads to a steady single-vortex pattern in a linear stratification, and one that results in an unsteady irregular state. Strong single-vortex patterns appear intermittently for the former configurations despite the absence of stratification at the forcing height. When the single-vortex pattern occurs at the density interface, a similar flow field extends down to the forcing height. The behaviour is explained as the coupling of the resonant eigenmode at the interface with the horizontal component of the forcing jets. The results show that stratification can organise a flow, even though it is forced by an apparently random three-dimensional forcing.

How we compute N matters to estimates of mixing in stratified flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arthur, Robert S.; Venayagamoorthy, Subhas K.; Koseff, Jeffrey R.

We know that most commonly used models for turbulent mixing in the ocean rely on a background stratification against which turbulence must work to stir the fluid. While this background stratification is typically well defined in idealized numerical models, it is more difficult to capture in observations. Here, a potential discrepancy in ocean mixing estimates due to the chosen calculation of the background stratification is explored using direct numerical simulation data of breaking internal waves on slopes. There are two different methods for computing the buoyancy frequencymore » $N$$, one based on a three-dimensionally sorted density field (often used in numerical models) and the other based on locally sorted vertical density profiles (often used in the field), are used to quantify the effect of$$N$$on turbulence quantities. It is shown that how$$N$$is calculated changes not only the flux Richardson number$$R_{f}$$, which is often used to parameterize turbulent mixing, but also the turbulence activity number or the Gibson number$$Gi$$, leading to potential errors in estimates of the mixing efficiency using$$Gi$-based parameterizations.« less

How we compute N matters to estimates of mixing in stratified flows

DOE PAGES

Arthur, Robert S.; Venayagamoorthy, Subhas K.; Koseff, Jeffrey R.; ...

2017-10-13

We know that most commonly used models for turbulent mixing in the ocean rely on a background stratification against which turbulence must work to stir the fluid. While this background stratification is typically well defined in idealized numerical models, it is more difficult to capture in observations. Here, a potential discrepancy in ocean mixing estimates due to the chosen calculation of the background stratification is explored using direct numerical simulation data of breaking internal waves on slopes. There are two different methods for computing the buoyancy frequencymore » $N$$, one based on a three-dimensionally sorted density field (often used in numerical models) and the other based on locally sorted vertical density profiles (often used in the field), are used to quantify the effect of$$N$$on turbulence quantities. It is shown that how$$N$$is calculated changes not only the flux Richardson number$$R_{f}$$, which is often used to parameterize turbulent mixing, but also the turbulence activity number or the Gibson number$$Gi$$, leading to potential errors in estimates of the mixing efficiency using$$Gi$-based parameterizations.« less

Stratification of a two-phase monodisperse system in a plane laminar flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fedoseev, V. B., E-mail: vbfedoseev@yandex.ru

2016-05-15

A thermodynamic approach is used to describe the distribution of particles of a disperse phase in a plane laminar flow. The effect of the density, shape, and velocity of disperse particles in the flow is considered. Conditions are described under which various modes of stratification of the flow (near-wall, central, intermediate, and multilayer modes) arise. The equilibrium distributions obtained are self-similar; this allows one to compare the behavior of colloidal, highly disperse, coarsely disperse, and coarse-grain systems for various shear velocities and flow widths.

Laboratory-Scale Internal Wave Apparatus for Studying Copepod Behavior

NASA Astrophysics Data System (ADS)

Jung, S.; Webster, D. R.; Haas, K. A.; Yen, J.

2016-02-01

Internal waves are ubiquitous features in coastal marine environments and have been observed to mediate vertical distributions of zooplankton in situ. Internal waves create fine-scale hydrodynamic cues that copepods and other zooplankton are known to sense, such as fluid density gradients and velocity gradients (quantified as shear deformation rate). The role of copepod behavior in response to cues associated with internal waves is largely unknown. The objective is to provide insight to the bio-physical interaction and the role of biological versus physical forcing in mediating organism distributions. We constructed a laboratory-scale internal wave apparatus to facilitate fine-scale observations of copepod behavior in flows that replicate in situ conditions of internal waves in two-layer stratification. Two cases were chosen with density jump of 1 and 1.5 sigma-t units. Analytical analysis of the two-layer system provided guidance to the target forcing frequency needed to generate a standing internal wave with a single dominate frequency of oscillation. Flow visualization and signal processing of the interface location were used to quantify the wave characteristics. The results show a close match to the target wave parameters. Marine copepod (mixed population of Acartia tonsa, Temora longicornis, and Eurytemora affinis) behavior assays were conducted for three different physical arrangements: (1) no density stratification, (2) stagnant two-layer density stratification, and (3) two-layer density stratification with internal wave motion. Digitized trajectories of copepod swimming behavior indicate that in the control (case 1) the animals showed no preferential motion in terms of direction. In the stagnant density jump treatment (case 2) copepods preferentially moved horizontally, parallel to the density interface. In the internal wave treatment (case 3) copepods demonstrated orbital trajectories near the density interface.

Ionic Size Effects: Generalized Boltzmann Distributions, Counterion Stratification, and Modified Debye Length.

PubMed

Liu, Bo; Liu, Pei; Xu, Zhenli; Zhou, Shenggao

2013-10-01

Near a charged surface, counterions of different valences and sizes cluster; and their concentration profiles stratify. At a distance from such a surface larger than the Debye length, the electric field is screened by counterions. Recent studies by a variational mean-field approach that includes ionic size effects and by Monte Carlo simulations both suggest that the counterion stratification is determined by the ionic valence-to-volume ratios. Central in the mean-field approach is a free-energy functional of ionic concentrations in which the ionic size effects are included through the entropic effect of solvent molecules. The corresponding equilibrium conditions define the generalized Boltzmann distributions relating the ionic concentrations to the electrostatic potential. This paper presents a detailed analysis and numerical calculations of such a free-energy functional to understand the dependence of the ionic charge density on the electrostatic potential through the generalized Boltzmann distributions, the role of ionic valence-to-volume ratios in the counterion stratification, and the modification of Debye length due to the effect of ionic sizes.

Ionic Size Effects: Generalized Boltzmann Distributions, Counterion Stratification, and Modified Debye Length

PubMed Central

Liu, Bo; Liu, Pei; Xu, Zhenli; Zhou, Shenggao

2013-01-01

Near a charged surface, counterions of different valences and sizes cluster; and their concentration profiles stratify. At a distance from such a surface larger than the Debye length, the electric field is screened by counterions. Recent studies by a variational mean-field approach that includes ionic size effects and by Monte Carlo simulations both suggest that the counterion stratification is determined by the ionic valence-to-volume ratios. Central in the mean-field approach is a free-energy functional of ionic concentrations in which the ionic size effects are included through the entropic effect of solvent molecules. The corresponding equilibrium conditions define the generalized Boltzmann distributions relating the ionic concentrations to the electrostatic potential. This paper presents a detailed analysis and numerical calculations of such a free-energy functional to understand the dependence of the ionic charge density on the electrostatic potential through the generalized Boltzmann distributions, the role of ionic valence-to-volume ratios in the counterion stratification, and the modification of Debye length due to the effect of ionic sizes. PMID:24465094

An ecology of prestige in New York City: Examining the relationships among population density, socio-economic status, group identity, and residential canopy cover

Treesearch

J. Morgan Grove; Dexter H. Locke; Jarlath P.M. O' Neil-Dunne

2014-01-01

Several social theories have been proposed to explain the uneven distribution of vegetation in urban residential areas: population density, social stratification, luxury effect, and ecology of prestige. We evaluate these theories using a combination of demographic and socio-economic predictors of vegetative cover on all residential lands in New York City. We use...

Elliptical instability in stably stratified fluid interiors

NASA Astrophysics Data System (ADS)

Vidal, J.; Hollerbach, R.; Schaeffer, N.; Cebron, D.

2016-12-01

Self-sustained magnetic fields in celestial bodies (planets, moons, stars) are due to flows in internal electrically conducting fluids. These fluid motions are often attributed to convection, as it is the case for the Earth's liquid core and the Sun. However some past or present liquid cores may be stably stratified. Alternative mechanisms may thus be needed to understand the dynamo process in these celestial objects. Turbulent flows driven by mechanical forcings, such as tides or precession, seem very promising since they are dynamo capable. However the effect of density stratification is not clear, because it can stabilize or destabilize mechanically-driven flows.To mimic an elliptical distortion due to tidal forcing in spherical geometry (full sphere and shell), we consider a theoretical base flow with elliptical streamlines and an associated density profile. It allows to keep the numerical efficiency of spectral methods in this geometry. The flow satisfies the stress-free boundary condition. We perform the stability analysis of the base state using three-dimensional simulations to study both the linear and nonlinear regimes. Stable and unstable density profiles are considered. A complementary local stability analysis (WKB) is also performed. We show that elliptical instability can still grow upon a stable stratification. We also study the mixing of the stratification by the elliptical instability. Finally we look at the dynamo capability of these flows.

Momentum and buoyancy transfer in atmospheric turbulent boundary layer over wavy water surface - Part 1: Harmonic wave

NASA Astrophysics Data System (ADS)

Troitskaya, Yu. I.; Ezhova, E. V.; Zilitinkevich, S. S.

2013-10-01

The surface-drag and mass-transfer coefficients are determined within a self-consistent problem of wave-induced perturbations and mean fields of velocity and density in the air, using a quasi-linear model based on the Reynolds equations with down-gradient turbulence closure. Investigation of a harmonic wave propagating along the wind has disclosed that the surface drag is generally larger for shorter waves. This effect is more pronounced in the unstable and neutral stratification. The stable stratification suppresses turbulence, which leads to weakening of the momentum and mass transfer.

Low-Reynolds-number swimming at pycnoclines.

PubMed

Doostmohammadi, Amin; Stocker, Roman; Ardekani, Arezoo M

2012-03-06

Microorganisms play pivotal functions in the trophic dynamics and biogeochemistry of aquatic ecosystems. Their concentrations and activities often peak at localized hotspots, an important example of which are pycnoclines, where water density increases sharply with depth due to gradients in temperature or salinity. At pycnoclines organisms are exposed to different environmental conditions compared to the bulk water column, including reduced turbulence, slow mass transfer, and high particle and predator concentrations. Here we show that, at an even more fundamental level, the density stratification itself can affect microbial ecology at pycnoclines, by quenching the flow signature, increasing the energetic expenditure, and stifling the nutrient uptake of motile organisms. We demonstrate this through numerical simulations of an archetypal low-Reynolds-number swimmer, the "squirmer." We identify the Richardson number--the ratio of buoyancy forces to viscous forces--as the fundamental parameter that quantifies the effects of stratification. These results demonstrate an unexpected effect of buoyancy on low-Reynolds-number swimming, potentially affecting a broad range of abundant organisms living at pycnoclines in oceans and lakes.

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake

NASA Astrophysics Data System (ADS)

Nixdorf, E.; Boehrer, B.

2015-11-01

Lake stratification controls the cycling of dissolved matter within the water body. This is of particular interest in the case of meromictic lakes, where permanent density stratification of the deep water limits vertical transport, and a chemically different (reducing) milieu can be established. As a consequence, the geochemical setting and the mixing regime of a lake can stabilize each other mutually. We attempt a quantitative approach to the contribution of chemical reactions sustaining the density stratification. As an example, we chose the prominent case of iron meromixis in Waldsee near Doebern, a small lake that originated from near-surface underground mining of lignite. From a data set covering 4 years of monthly measured electrical conductivity profiles, we calculated summed conductivity as a quantitative variable reflecting the amount of electro-active substances in the entire lake. Seasonal variations followed the changing of the chemocline height. Coinciding changes of electrical conductivities in the monimolimnion indicated that a considerable share of substances, precipitated by the advancing oxygenated epilimnion, re-dissolved in the remaining anoxic deep waters and contributed considerably to the density stratification. In addition, we designed a lab experiment, in which we removed iron compounds and organic material from monimolimnetic waters by introducing air bubbles. Precipitates could be identified by visual inspection. Eventually, the remaining solutes in the aerated water layer looked similar to mixolimnetic Waldsee water. Due to its reduced concentration of solutes, this water became less dense and remained floating on nearly unchanged monimolimnetic water. In conclusion, iron meromixis as seen in Waldsee did not require two different sources of incoming waters, but the inflow of iron-rich deep groundwater and the aeration through the lake surface were fully sufficient for the formation of iron meromixis.

Breast cancer screening in the era of density notification legislation: summary of 2014 Massachusetts experience and suggestion of an evidence-based management algorithm by multi-disciplinary expert panel.

PubMed

Freer, Phoebe E; Slanetz, Priscilla J; Haas, Jennifer S; Tung, Nadine M; Hughes, Kevin S; Armstrong, Katrina; Semine, A Alan; Troyan, Susan L; Birdwell, Robyn L

2015-09-01

Stemming from breast density notification legislation in Massachusetts effective 2015, we sought to develop a collaborative evidence-based approach to density notification that could be used by practitioners across the state. Our goal was to develop an evidence-based consensus management algorithm to help patients and health care providers follow best practices to implement a coordinated, evidence-based, cost-effective, sustainable practice and to standardize care in recommendations for supplemental screening. We formed the Massachusetts Breast Risk Education and Assessment Task Force (MA-BREAST) a multi-institutional, multi-disciplinary panel of expert radiologists, surgeons, primary care physicians, and oncologists to develop a collaborative approach to density notification legislation. Using evidence-based data from the Institute for Clinical and Economic Review, the Cochrane review, National Comprehensive Cancer Network guidelines, American Cancer Society recommendations, and American College of Radiology appropriateness criteria, the group collaboratively developed an evidence-based best-practices algorithm. The expert consensus algorithm uses breast density as one element in the risk stratification to determine the need for supplemental screening. Women with dense breasts and otherwise low risk (<15% lifetime risk), do not routinely require supplemental screening per the expert consensus. Women of high risk (>20% lifetime) should consider supplemental screening MRI in addition to routine mammography regardless of breast density. We report the development of the multi-disciplinary collaborative approach to density notification. We propose a risk stratification algorithm to assess personal level of risk to determine the need for supplemental screening for an individual woman.

Dendritic brushes under theta and poor solvent conditions

NASA Astrophysics Data System (ADS)

Gergidis, Leonidas N.; Kalogirou, Andreas; Charalambopoulos, Antonios; Vlahos, Costas

2013-07-01

The effects of solvent quality on the internal stratification of polymer brushes formed by dendron polymers up to third generation were studied by means of molecular dynamics simulations with Langevin thermostat. The distributions of polymer units, of the free ends, the radii of gyration, and the back folding probabilities of the dendritic spacers were studied at the macroscopic states of theta and poor solvent. For high grafting densities we observed a small decrease in the height of the brush as the solvent quality decreases. The internal stratification in theta solvent was similar to the one we found in good solvent, with two and in some cases three kinds of populations containing short dendrons with weakly extended spacers, intermediate-height dendrons, and tall dendrons with highly stretched spacers. The differences increase as the grafting density decreases and single dendron populations were evident in theta and poor solvent. In poor solvent at low grafting densities, solvent micelles, polymeric pinned lamellae, spherical and single chain collapsed micelles were observed. The scaling dependence of the height of the dendritic brush at high density brushes for both solvents was found to be in agreement with existing analytical results.

Evaluation of Quantra Hologic Volumetric Computerized Breast Density Software in Comparison With Manual Interpretation in a Diverse Population.

PubMed

Richard-Davis, Gloria; Whittemore, Brianna; Disher, Anthony; Rice, Valerie Montgomery; Lenin, Rathinasamy B; Dollins, Camille; Siegel, Eric R; Eswaran, Hari

2018-01-01

Increased mammographic breast density is a well-established risk factor for breast cancer development, regardless of age or ethnic background. The current gold standard for categorizing breast density consists of a radiologist estimation of percent density according to the American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) criteria. This study compares paired qualitative interpretations of breast density on digital mammograms with quantitative measurement of density using Hologic's Food and Drug Administration-approved R2 Quantra volumetric breast density assessment tool. Our goal was to find the best cutoff value of Quantra-calculated breast density for stratifying patients accurately into high-risk and low-risk breast density categories. Screening digital mammograms from 385 subjects, aged 18 to 64 years, were evaluated. These mammograms were interpreted by a radiologist using the ACR's BI-RADS density method, and had quantitative density measured using the R2 Quantra breast density assessment tool. The appropriate cutoff for breast density-based risk stratification using Quantra software was calculated using manually determined BI-RADS scores as a gold standard, in which scores of D3/D4 denoted high-risk densities and D1/D2 denoted low-risk densities. The best cutoff value for risk stratification using Quantra-calculated breast density was found to be 14.0%, yielding a sensitivity of 65%, specificity of 77%, and positive and negative predictive values of 75% and 69%, respectively. Under bootstrap analysis, the best cutoff value had a mean ± SD of 13.70% ± 0.89%. Our study is the first to publish on a North American population that assesses the accuracy of the R2 Quantra system at breast density stratification. Quantitative breast density measures will improve accuracy and reliability of density determination, assisting future researchers to accurately calculate breast cancer risks associated with density increase.

Particle dispersion in a stably stratified channel flow

NASA Astrophysics Data System (ADS)

Pasquero, C.; Armenio, V.

2003-04-01

The motion of particles in a stably stratified channel flow is relevant in geophysic and environmental applications. In the present research this problem has been studied numerically using a mixed Lagrangian-Eulerian technique (Lagrangian motion of an ensemble of particles in an Eulerian field) by means of large eddy simulation. A stratified channel flows can be decomposed into a buoyancy affected region, with a strong turbulent activity, close to the walls, and into a buoyancy dominated region, where turbulence is strongly inhibited, in the center of the channel. For strong stratifications, counter gradient heat fluxes steepen the density gradient moving hot fluid up and cold fluid down. The stratification in the central region of the channel becomes extremely stable. However, the vertical turbulent energy, defined as the difference between the total vertical kinetic energy and its temporal average, is very strong. Particle statistics have shown that this can be related to the presence of high frequency internal waves, that do not contribute to dispersion because of their highly coherent behavior. Vertical stratification is shown to reduce or increase the decorrelation time for vertical motion, depending on the Richardson number. When stratification is increased there are two competing effects: Structures have a smaller vertical scale (acting to reduce the decorrelation time) and vertical velocities are smaller (acting to increase the decorrelation time, since particles stay for a longer time into a given structure in the flow). It has been shown that for low stratification the first mechanism dominates, while for large stratification the second effect is more important. The research is in progress and results for both fluid and inertial particles will be presented at the conference.

Evaluation of Quantra Hologic Volumetric Computerized Breast Density Software in Comparison With Manual Interpretation in a Diverse Population

PubMed Central

Richard-Davis, Gloria; Whittemore, Brianna; Disher, Anthony; Rice, Valerie Montgomery; Lenin, Rathinasamy B; Dollins, Camille; Siegel, Eric R; Eswaran, Hari

2018-01-01

Objective: Increased mammographic breast density is a well-established risk factor for breast cancer development, regardless of age or ethnic background. The current gold standard for categorizing breast density consists of a radiologist estimation of percent density according to the American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) criteria. This study compares paired qualitative interpretations of breast density on digital mammograms with quantitative measurement of density using Hologic’s Food and Drug Administration–approved R2 Quantra volumetric breast density assessment tool. Our goal was to find the best cutoff value of Quantra-calculated breast density for stratifying patients accurately into high-risk and low-risk breast density categories. Methods: Screening digital mammograms from 385 subjects, aged 18 to 64 years, were evaluated. These mammograms were interpreted by a radiologist using the ACR’s BI-RADS density method, and had quantitative density measured using the R2 Quantra breast density assessment tool. The appropriate cutoff for breast density–based risk stratification using Quantra software was calculated using manually determined BI-RADS scores as a gold standard, in which scores of D3/D4 denoted high-risk densities and D1/D2 denoted low-risk densities. Results: The best cutoff value for risk stratification using Quantra-calculated breast density was found to be 14.0%, yielding a sensitivity of 65%, specificity of 77%, and positive and negative predictive values of 75% and 69%, respectively. Under bootstrap analysis, the best cutoff value had a mean ± SD of 13.70% ± 0.89%. Conclusions: Our study is the first to publish on a North American population that assesses the accuracy of the R2 Quantra system at breast density stratification. Quantitative breast density measures will improve accuracy and reliability of density determination, assisting future researchers to accurately calculate breast cancer risks associated with density increase. PMID:29511356

Short-term thermal stratification and partial overturning events in a warm polymictic reservoir: effects on distribution of phytoplankton community.

PubMed

Santos, R M; Saggio, A A; Silva, T L R; Negreiros, N F; Rocha, O

2015-01-01

In lentic freshwater ecosystems, patterns of thermal stratification play a considerable part in determining the population dynamics of phytoplankton. In this study we investigated how these thermal patterns and the associated hydrodynamic processes affect the vertical distribution of phytoplankton during two consecutive diel cycles in a warm polymictic urban reservoir in the metropolitan region of São Paulo, Brazil. Water samples were taken and physical, chemical and biological data collected at half-meter intervals of depth along a water column at a fixed site, every 3 hours throughout the 48-hour period. Two events of stratification, followed by deepening of the thermocline occurred during the study period and led to changes in the vertical distribution of phytoplankton populations. Aphanocapsa delicatissima Nägeli was the single dominant species throughout the 48-hour period. In the second diel cycle, the density gradient induced by temperature differences avoided the sedimentation of Mougeotia sp. C. Agardh to the deepest layers. On the other hand, Pseudanabaena galeata Böcher remained in the 4.0-5.5 m deep layer. The thermal structure of the water was directly affected by two meteorological factors: air temperature and wind speed. Changes in the cell density and vertical distribution of the phytoplankton were controlled by the thermal and hydrodynamic events.

Breast Cancer Screening in the Era of Density Notification Legislation: Summary of 2014 Massachusetts Experience and Suggestion of An Evidence-Based Management Algorithm by Multi-disciplinary Expert Panel

PubMed Central

Freer, Phoebe E.; Slanetz, Priscilla J.; Haas, Jennifer S.; Tung, Nadine M.; Hughes, Kevin S.; Armstrong, Katrina; Semine, A. Alan; Troyan, Susan L.; Birdwell, Robyn L.

2015-01-01

Purpose Stemming from breast density notification legislation in Massachusetts effective 2015, we sought to develop a collaborative evidence-based approach to density notification that could be used by practitioners across the state. Our goal was to develop an evidence-based consensus management algorithm to help patients and health care providers follow best practices to implement a coordinated, evidence-based, cost-effective, sustainable practice and to standardize care in recommendations for supplemental screening. Methods We formed the Massachusetts Breast Risk Education and Assessment Task Force (MA-BREAST) a multi-institutional, multi-disciplinary panel of expert radiologists, surgeons, primary care physicians, and oncologists to develop a collaborative approach to density notification legislation. Using evidence-based data from the Institute for Clinical and Economic Review (ICER), the Cochrane review, National Comprehensive Cancer Network (NCCN) guidelines, American Cancer Society (ACS) recommendations, and American College of Radiology (ACR) appropriateness criteria, the group collaboratively developed an evidence-based best-practices algorithm. Results The expert consensus algorithm uses breast density as one element in the risk stratification to determine the need for supplemental screening. Women with dense breasts and otherwise low risk (<15% lifetime risk), do not routinely require supplemental screening per the expert consensus. Women of high risk (>20% lifetime) should consider supplemental screening MRI in addition to routine mammography regardless of breast density. Conclusion We report the development of the multi-disciplinary collaborative approach to density notification. We propose a risk stratification algorithm to assess personal level of risk to determine the need for supplemental screening for an individual woman. PMID:26290416

Observations of Tidal Straining Within Two Different Ocean Environments in the East China Sea: Stratification and Near-Bottom Turbulence

NASA Astrophysics Data System (ADS)

Yang, Wei; Wei, Hao; Zhao, Liang

2017-11-01

Tidal straining describes the straining effect induced by the vertical shear of oscillatory tidal currents that act on horizontal density gradients. It tends to create tidal periodic stratification and modulate the turbulence in the bottom boundary layer (BBL). Here, we present observations of current, hydrology and turbulence obtained at two mooring stations that are characterized by two typical hydrological environments in the East China Sea (ECS). One is located adjacent to the Changjiang River's mouth, and the other is located over a sloping shelf which is far from the freshwater sources. Tidal straining induces a semidiurnal switching between stable and unstable stratification at both stations. Near-bottom high-frequency velocity measurements further reveal that the dissipation rate of turbulent kinetic energy (TKE) is highly elevated during periods when unstable stratification occurs. A comparison between the TKE dissipation rate (ɛ) and the shear production (P) further reveals that the near-bottom mixing is locally shear-induced most of the time except during the unstable stratification period. Within this period, the magnitude of dissipation exceeds the expected value based on the law of the wall by an order of magnitude. The buoyancy flux that calculated by the balance method is too small to compensate for the existing discrepancy between the dissipation and shear production. Another plausible candidate is the advection of TKE, which may play an important role in the TKE budget during the unstable stratification period.

Interaction of lateral baroclinic forcing and turbulence in an estuary

USGS Publications Warehouse

Lacy, J.R.; Stacey, M.T.; Burau, J.R.; Monismith, Stephen G.

2003-01-01

Observations of density and velocity in a channel in northern San Francisco Bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross-channel baroclinic pressure gradient and vertical mixing due to turbulence. Profiles of velocity, salinity, temperature, and suspended sediment concentration were measured in transects across Suisun Cutoff, in northern San Francisco Bay, on two days over the 12.5-hour tidal cycle. During flood tides an axial density front developed between fresher water flowing from the shallows of Grizzly Bay into the northern side of Suisun Cutoff and saltier water flowing up the channel. North of the front, transverse currents were driven by the lateral salinity gradient, with a top-to-bottom velocity difference greater than 30 cm/s. South of the front, the secondary circulation was weak, and along-channel velocities were greater than to the north. The gradient Richardson number shows that stratification was stable north of the front, while the water column was turbulently mixed south of the front. Time-series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle. In estuaries, longitudinal dynamics predict less stratification during flood than ebb tides. These data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry.

Instability of a shear layer between multicomponent fluids at supercritical pressure

NASA Astrophysics Data System (ADS)

Fu, Qing-fei; Zhang, Yun-xiao; Mo, Chao-jie; Yang, Li-jun

2018-04-01

The temporal instability of a thin shear layer lying between streams of two components of fluids has been studied. The effects of density profile of the layer on the instability behavior were mainly considered. The detailed density profile was obtained through Linear Gradient Theory. The eigenvalue problem was calculated, and the temporal instability curves were obtained for the thermodynamic parameters, e.g. pressure and temperature. The results show that, increase of pressure leads to the increase of the maximum growth rate. However, increasing pressure has opposite effects on the disturbances with small and large wave length. The increase of temperature causes the decrease of disturbance growth rate. The instability behavior of the shear layers was determined mainly by the interval between the inflections of the velocity and density profiles, and the maximum density gradient. The total effects, determined by coupling density stratification, and interval between the inflections of the velocity and density profiles, were quite distinct for different ranges of temperature and pressure.

Gravitational circulation in a tidal strait

USGS Publications Warehouse

Smith, P.E.; Cheng, R.T.; Burau, J.R.; Simpson, M.R.; ,

1991-01-01

Eight months of continuous measurements of tidal current profiles with an acoustic Doppler current profiler (ADCP) were made in Carquinez Strait, California, during 1988 for the purpose of estimating long-term variations in vertical profiles of Eulerian residual currents. Salinity stratification near the ADCP deployment site also was analyzed. The strength of density-driven gravitational circulation and the amount of salinity stratification in the strait varied significantly over the spring-neap tidal cycle. Density currents and stratification were greater during neap tides when vertical mixing from the tide is at a minimum. Landward residual currents along the bottom were observed only during neap tides. Simulations made with a three-dimensional model to supplement the field measurements show a significant, tidally induced lateral variation in residual currents across the strait. The Stokes drift of 1-2 cm/s in the strait is small relative to the speed of gravitational currents.

Transport of magnetohydrodynamic nanomaterial in a stratified medium considering gyrotactic microorganisms

NASA Astrophysics Data System (ADS)

Waqas, M.; Hayat, T.; Shehzad, S. A.; Alsaedi, A.

2018-01-01

Impact of gyrotactic microorganisms on two-dimensional (2D) stratified flow of an Oldroyd-B nanomaterial is highlighted. Applied magnetic field along with mixed convection is considered in the formulation. Theory of microorganisms is utilized just to stabilize the suspended nanoparticles through bioconvection induced by combined effects of buoyancy forces and magnetic field. Convergent series solutions for the obtained nonlinear differential systems are derived. Impacts of different emerging parameters on velocity, temperature, concentration, motile microorganisms density, density number of motile microorganisms and local Nusselt and Sherwood numbers are graphically addressed. It is observed that thermal, concentration and motile density stratification parameters result in reduction of temperature, concentration and motile microorganisms density distributions respectively.

Prediction of the effects of thermal stratification on pressure and temperature response of the Apollo supercritical oxygen tank

NASA Technical Reports Server (NTRS)

Chen, I. M.; Anderson, R. E.

1971-01-01

A semiempirical design-oriented model has been developed for the prediction of the effects of thermal stratification on tank pressure and heater temperature response for the Apollo supercritical oxygen tank. The heat transfer formulation describes laminar free convection at low-g and takes into account the radiation and conduction processes occurring in the tank. The nonequilibrium thermodynamic behavior of the system due to localized heating of the stored fluid is represented by the characteristics of a discrete number of fluid regions and thermal nodes. Solutions to the time dependent variable fluid property problem are obtained through the use of a reference temperature procedure. A criterion which establishes the reference temperature as a function of the fluid density ratio is derived. The analytical results are compared with the flight data.

Vertically migrating swimmers generate aggregation-scale eddies in a stratified column.

PubMed

Houghton, Isabel A; Koseff, Jeffrey R; Monismith, Stephen G; Dabiri, John O

2018-04-01

Biologically generated turbulence has been proposed as an important contributor to nutrient transport and ocean mixing 1-3 . However, to produce non-negligible transport and mixing, such turbulence must produce eddies at scales comparable to the length scales of stratification in the ocean. It has previously been argued that biologically generated turbulence is limited to the scale of the individual animals involved 4 , which would make turbulence created by highly abundant centimetre-scale zooplankton such as krill irrelevant to ocean mixing. Their small size notwithstanding, zooplankton form dense aggregations tens of metres in vertical extent as they undergo diurnal vertical migration over hundreds of metres 3,5,6 . This behaviour potentially introduces additional length scales-such as the scale of the aggregation-that are of relevance to animal interactions with the surrounding water column. Here we show that the collective vertical migration of centimetre-scale swimmers-as represented by the brine shrimp Artemia salina-generates aggregation-scale eddies that mix a stable density stratification, resulting in an effective turbulent diffusivity up to three orders of magnitude larger than the molecular diffusivity of salt. These observed large-scale mixing eddies are the result of flow in the wakes of the individual organisms coalescing to form a large-scale downward jet during upward swimming, even in the presence of a strong density stratification relative to typical values observed in the ocean. The results illustrate the potential for marine zooplankton to considerably alter the physical and biogeochemical structure of the water column, with potentially widespread effects owing to their high abundance in climatically important regions of the ocean 7 .

The growth and breakdown of a vortex-pair in a stably stratified fluid

NASA Astrophysics Data System (ADS)

Advaith, S.; Tinaikar, Aashay; Manu, K. V.; Basu, Saptarshi

2017-11-01

Vortex interaction with density stratification is ubiquitous in nature and applied to various engineering applications. Present study have characterized the spatial and temporal dynamics of the interaction between a vortex and a density stratified interface. The present work is prompted by our research on single tank Thermal Energy Storage (TES) system used in concentrated solar power (CSP) plants where hot and cold fluids are separated by means of density stratification. Rigorous qualitative (High speed Shadowgraph) and quantitative (high speed PIV) studies enable us to have great understanding about vortex formation, propagation, interaction dynamics with density stratified interface, resulted plume characteristics and so on. We have categorized this interaction phenomena in to three different cases based on its nature as non-penetrative, partial penetrative and extensively penetrative. Along with that we have proposed a regime map consisting non-dimensional parameters like Reynolds, Richardson and Atwood numbers which predicts the occurrence above mentioned cases.

Understanding Transition to Turbulence in Shear Layers.

DTIC Science & Technology

1983-05-01

Imperfect bifurcations ; circular Couette flow 24 0.02.06 Interpretations of experiments on Poiseuille flow 26 ( a ) Absence of turbulence far Re > Re 27 (b...instability of the shear layer. This is a very effective com- bination, which fuels most flow-conditioned acoustic resonances, includ- ing organ pipes and...variable density as encountered in aeronautics are *confined to Appendix A , Sections A .07, A .08, A .10- A .15, and Chapter 10. Effects of stratification as

The Impact of Internal Wave Seasonality on the Continental Shelf Energy Budget

NASA Astrophysics Data System (ADS)

Wihsgott, Juliane U.; Sharples, Jonathan; Hopkins, Joanne; Palmer, Matthew R.; Mattias Green, J. A.

2017-04-01

Heating-stirring models are widely used to simulate the timing and strength of stratification in continental shelf environments. Such models are based on bulk potential energy (PE) budgets: the loss of PE due to thermal stratification is balanced by wind and tidal mixing. The model often fails to accurately predict the observed vertical structure, as it only considers forces acting on the surface and bottom boundary of the water column. This highlights the need for additional internal energy sources to close this budget, and produce an accurate seasonal cycle of stratification. We present new results that test the impact of boundary layer and internal wave forcing on stratification and vertical density structure in continental shelves. A new series of continuous measurements of full water depth vertical structure, dynamics and meteorological data spanning 17 months (March'14-July'15) provide unprecedented coverage over a full seasonal cycle at a station 120 km north-east from the continental shelf break. We observe a highly variable but energetic internal wave field from the onset of stratification that suggests a continuous supply of internal PE. The heating-stirring model reproduces bulk characteristics of the seasonal cycle. While it accurately predicts the timing of the onset in spring and peak stratification in late summer there is a persistent 20 J m-3 positive offset between the model and observations throughout this period. By including a source of internal energy in the model we improve the prediction for the strength of stratification and the vertical distribution of heat. Yet a constant source of PE seems to result in a seasonal discrepancy resulting in too little mixing during strong stratification and too much mixing during transient periods. The discrepancy seen in the model is consistent with the seasonality observed in the internal wave field. We will establish the role that changing stratification (N2) exerts on the internal wave field and vice versa. Ultimately, we will demonstrate how the strength and vertical range of shear varies seasonally and what effect it has on supplying PE to midwater mixing.

Internal waves and rectification in a linearly stratified fluid

NASA Astrophysics Data System (ADS)

Pérenne, Nicolas; Renouard, Dominique P.

Laboratory experiments were performed in a 13-m diameter rotating tank equipped with a continuous shelf break geometry and a central piston-like plunger. The fluid density was linearly stratified. The amplitude and period of the plunger, the rotation rate of the platform and the stratification are the parameters of the problem. The density fluctuations at six stations above and at mid-depth of the slope, along with dye visualization of the flow, were recorded. A limited set of experiments showed that a barotropic periodical forcing generated a first mode baroclinic wave which initially appears at the slope and propagates offshore. The likely presence of internal energy rays either slightly above, or immediately along the slope, is in agreement with previous analytical, laboratory and selected oceanic observations. In the former case, the stratification was such that the slope flow at mid-depth was supercritical while in the latter case, slope flow at mid-depth was critical. Rotation tended to decrease the amplitude of the generated internal wave. Also, non-linear processes were likely to act upon these waves for their normalized amplitude tended to decrease as the forcing increased (for similar forcing period, rotation rate and stratification). After the internal wave reflected from the plunger reaches the slope, there is a complex non-stationary regime with an occurrence of internal wave breaking in the vicinity of the slope. Thus there was an appearance of localized patches of turbulence and mixing. These events appeared both in dye visualization and in density fluctuations records. The subsequent mixing, or else the combined effect of topographical rectification and mixing, led to the appearance of a distinct Lagrangian transport, localized in the first few centimeters above the slope and oriented so as to leave the shallow waters on the right of its displacement.

Counterintuitive effect of fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

NASA Astrophysics Data System (ADS)

Fawcett, S. E.; Lomas, M. W.; Ward, B. B.; Sigman, D. M.

2012-12-01

The Sargasso Sea is characterized by a short period of deep vertical mixing in the late winter and early spring, followed by strong thermal stratification during the summer. Stratification persists into the fall, impeding the upward flux of nitrate from depth so that recycled forms of nitrogen (N) such as ammonium are thought to support most primary production. We collected particles from surface waters during March, July, October, and December, used flow cytometry to separate the prokaryotic and eukaryotic phytoplankton, and analyzed their respective 15N/14N. In all months, the 15N/14N of the prokaryotic genera, Prochlorococcus and Synechococcus, was low, indicative of reliance on recycled N throughout the year. In July, the 15N/14N of eukaryotic phytoplankton was variable but consistently higher than that of the prokaryotes, reflecting eukaryotic consumption of subsurface nitrate. Two eukaryotic profiles from October and December were similar to those from July. In three other fall profiles, the eukaryotes had a 15N/14N similar to that of the prokaryotes, suggesting a switch toward greater reliance on recycled N. This change in the dominant N source supporting eukaryotic production appears to be driven by the density structure of the upper water column. The very shallow low-density surface "mixed layer" (≤20 m) that develops in early-to-mid summer does not contribute to stratification at the base of the euphotic zone, and subsurface nitrate can mix up into the lower euphotic zone, facilitating continued production. The deepening of the mixed layer into the fall, typically taken as an indication of weaker overall stratification, actually strengthens the isolation of the euphotic zone as a whole, reducing the upward supply of nitrate to the photosynthetically active layer. The same counterintuitive dynamic explains the latitudinal patterns in a set of three October depth profiles. Two northern stations (32°N and 27°N) were characterized by a thick, low-density surface layer, and the 15N/14N of all phytoplankton was low, consistent with assimilation of recycled N. The southernmost station (23°N) had a shallower mixed layer, and eukaryote 15N/14N reflects growth on nitrate. In the subtropics, evidence for the direct supply of nitrate into surface waters in the face of the strong upper ocean stratification has long been sought. Our N isotope results suggest a mechanism by which subsurface nitrate is imported into shallow waters. This interpretation offers a new perspective on the relationship between euphotic zone stratification and nitrate assimilation, implying that significant new production occurs under conditions previously assumed to drive oligotrophy.

Effects of enhanced stratification on equatorward dynamo wave propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Käpylä, Petri J.; Mantere, Maarit J.; Cole, Elizabeth

We present results from simulations of rotating magnetized turbulent convection in spherical wedge geometry representing parts of the latitudinal and longitudinal extents of a star. Here we consider a set of runs for which the density stratification is varied, keeping the Reynolds and Coriolis numbers at similar values. In the case of weak stratification, we find quasi-steady dynamo solutions for moderate rotation and oscillatory ones with poleward migration of activity belts for more rapid rotation. For stronger stratification, the growth rate tends to become smaller. Furthermore, a transition from quasi-steady to oscillatory dynamos is found as the Coriolis number ismore » increased, but now there is an equatorward migrating branch near the equator. The breakpoint where this happens corresponds to a rotation rate that is about three to seven times the solar value. The phase relation of the magnetic field is such that the toroidal field lags behind the radial field by about π/2, which can be explained by an oscillatory α{sup 2} dynamo caused by the sign change of the α-effect about the equator. We test the domain size dependence of our results for a rapidly rotating run with equatorward migration by varying the longitudinal extent of our wedge. The energy of the axisymmetric mean magnetic field decreases as the domain size increases and we find that an m = 1 mode is excited for a full 2π azimuthal extent, reminiscent of the field configurations deduced from observations of rapidly rotating late-type stars.« less

Stratification and sample selection for multicrop experiments. [Arkansas, Kentucky, Michigan, Missouri, Mississippi, Ohio, Wisconsin, Illinois, Indiana, Minnesota, Iowa, Louisiana, Nebraska, South Dakota, and North Dakota

NASA Technical Reports Server (NTRS)

Landgrebe, D. A. (Principal Investigator); Hixson, M. M.; Davis, B. J.; Bauer, M. E.

1978-01-01

The author has identified the following significant results. A stratification was performed and sample segments were selected for an initial investigation of multicrop problems in order to support development and evaluation of procedures for using LACIE and other technologies for the classification of corn and soybeans, to identify factors likely to affect classification performance, and to evaluate problems encountered and techniques which are applicable to the crop estimation problem in foreign countries. Two types of samples, low density and high density, supporting these requirements were selected as research data set for an initial evaluation of technical issues. Looking at the geographic location of the strata, the system appears to be logical and the various segments seem to represent different conditions. This result is supportive not only of the variables and the methodology employed in the stratification, but also of the validity of the data sets employed.

Convection in an ideal gas at high Rayleigh numbers.

PubMed

Tilgner, A

2011-08-01

Numerical simulations of convection in a layer filled with ideal gas are presented. The control parameters are chosen such that there is a significant variation of density of the gas in going from the bottom to the top of the layer. The relations between the Rayleigh, Peclet, and Nusselt numbers depend on the density stratification. It is proposed to use a data reduction which accounts for the variable density by introducing into the scaling laws an effective density. The relevant density is the geometric mean of the maximum and minimum densities in the layer. A good fit to the data is then obtained with power laws with the same exponent as for fluids in the Boussinesq limit. Two relations connect the top and bottom boundary layers: The kinetic energy densities computed from free fall velocities are equal at the top and bottom, and the products of free fall velocities and maximum horizontal velocities are equal for both boundaries.

On the rising motion of a drop in stratified fluids

NASA Astrophysics Data System (ADS)

Bayareh, M.; Doostmohammadi, A.; Dabiri, S.; Ardekani, A. M.

2013-10-01

The rising dynamics of a deformable drop in a linearly stratified fluid is numerically obtained using a finite-volume/front-tracking method. Our results show that the drag coefficient of a spherical drop in a stratified fluid enhances as C_{d,s}/C_{d,h}-1˜ Fr_d^{-2.86} for drop Froude numbers in the range of 4 < Frd < 16. The role of the deformability of the drop on the temporal evolution of the motion is investigated along with stratification and inertial effects. We also present the important role of stratification on the transient rising motion of the drop. It is shown that a drop can levitate in the presence of a vertical density gradient. The drop undergoes a fading oscillatory motion around its neutrally buoyant position except for high viscosity ratio drops where the oscillation occurs around a density level lighter than the neutral buoyancy level. In addition, a detailed characterization of the flow signature of a rising drop in a linearly stratified fluid including the buoyancy induced vortices and the resultant buoyant jet is presented.

Tidal asymmetries of velocity and stratification over a bathymetric depression in a tropical inlet

NASA Astrophysics Data System (ADS)

Waterhouse, Amy F.; Valle-Levinson, Arnoldo; Morales Pérez, Rubén A.

2012-10-01

Observations of current velocity, sea surface elevation and vertical profiles of density were obtained in a tropical inlet to determine the effect of a bathymetric depression (hollow) on the tidal flows. Surveys measuring velocity profiles were conducted over a diurnal tidal cycle with mixed spring tides during dry and wet seasons. Depth-averaged tidal velocities during ebb and flood tides behaved according to Bernoulli dynamics, as expected. The dynamic balance of depth-averaged quantities in the along-channel direction was governed by along-channel advection and pressure gradients with baroclinic pressure gradients only being important during the wet season. The vertical structure of the along-channel flow during flood tides exhibited a mid-depth maximum with lateral shear enhanced during the dry season as a result of decreased vertical stratification. During ebb tides, along-channel velocities in the vicinity of the hollow were vertically sheared with a weak return flow at depth due to choking of the flow on the seaward slope of the hollow. The potential energy anomaly, a measure of the amount of energy required to fully mix the water column, showed two peaks in stratification associated with ebb tide and a third peak occurring at the beginning of flood. After the first mid-ebb peak in stratification, ebb flows were constricted on the seaward slope of the hollow resulting in a bottom return flow. The sinking of surface waters and enhanced mixing on the seaward slope of the hollow reduced the potential energy anomaly after maximum ebb. The third peak in stratification during early flood occurred as a result of denser water entering the inlet at mid-depth. This dense water mixed with ambient deep waters increasing the stratification. Lateral shear in the along-channel flow across the hollow allowed trapping of less dense water in the surface layers further increasing stratification.

Comprehensive numerical methodology for direct numerical simulations of compressible Rayleigh-Taylor instability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reckinger, Scott James; Livescu, Daniel; Vasilyev, Oleg V.

A comprehensive numerical methodology has been developed that handles the challenges introduced by considering the compressive nature of Rayleigh-Taylor instability (RTI) systems, which include sharp interfacial density gradients on strongly stratified background states, acoustic wave generation and removal at computational boundaries, and stratification-dependent vorticity production. The computational framework is used to simulate two-dimensional single-mode RTI to extreme late-times for a wide range of flow compressibility and variable density effects. The results show that flow compressibility acts to reduce the growth of RTI for low Atwood numbers, as predicted from linear stability analysis.

Magnetohydrodynamic effects in liquid metal batteries

NASA Astrophysics Data System (ADS)

Stefani, F.; Galindo, V.; Kasprzyk, C.; Landgraf, S.; Seilmayer, M.; Starace, M.; Weber, N.; Weier, T.

2016-07-01

Liquid metal batteries (LMBs) consist of two liquid metal electrodes and a molten salt ionic conductor sandwiched between them. The density ratios allow for a stable stratification of the three layers. LMBs were already considered as part of energy conversion systems in the 1960s and have recently received renewed interest for economical large-scale energy storage. In this paper, we concentrate on the magnetohydrodynamic aspects of this cell type with special focus on electro-vortex flows and possible effects of the Tayler instability.

Effect of the radial buoyancy on a circular Couette flow

NASA Astrophysics Data System (ADS)

Meyer, Antoine; Yoshikawa, Harunori N.; Mutabazi, Innocent

2015-11-01

The effect of a radial temperature gradient on the stability of a circular Couette flow is investigated when the gravitational acceleration is neglected. The induced radial stratification of the fluid density coupled with the centrifugal acceleration generates radial buoyancy which is centrifugal for inward heating and centripetal for outward heating. This radial buoyancy modifies the Rayleigh discriminant and induces the asymmetry between inward heating and outward heating in flow behavior. The critical modes are axisymmetric and stationary for inward heating while for outward heating, they can be oscillatory axisymmetric or nonaxisymmetric depending on fluid diffusion properties, i.e., on the Prandtl number Pr. The dependence of the critical modes on Pr is explored for different values of the radius ratio of the annulus. The power input of the radial buoyancy is compared with other power terms. The critical frequency of the oscillatory axisymmetric modes is linked to the Brunt-Väisälä frequency due to the density stratification in the radial gravity field induced by the rotation. These modes are associated with inertial waves. The dispersion relation of the oscillatory axisymmetric modes is derived in the vicinity of the critical conditions. A weakly nonlinear amplitude equation with a forcing term is proposed to explain the domination of these axisymmetric oscillatory modes over the stationary centrifugal mode.

Assessing factors affecting the thermal properties of a passive thermal refuge using three-dimensional hydrodynamic flow and transport modeling

USGS Publications Warehouse

Decker, Jeremy D.; Swain, Eric D.; Stith, Bradley M.; Langtimm, Catherine A.

2013-01-01

Everglades restoration activities may cause changes to temperature and salinity stratification at the Port of the Islands (POI) marina, which could affect its suitability as a cold weather refuge for manatees. To better understand how the Picayune Strand Restoration Project (PSRP) may alter this important resource in Collier County in southwestern Florida, the USGS has developed a three-dimensional hydrodynamic model for the marina and canal system at POI. Empirical data suggest that manatees aggregate at the site during winter because of thermal inversions that provide warmer water near the bottom that appears to only occur in the presence of salinity stratification. To study these phenomena, the environmental fluid dynamics code simulator was used to represent temperature and salinity transport within POI. Boundary inputs were generated using a larger two-dimensional model constructed with the flow and transport in a linked overland-aquifer density-dependent system simulator. Model results for a representative winter period match observed trends in salinity and temperature fluctuations and produce temperature inversions similar to observed values. Modified boundary conditions, representing proposed PSRP alterations, were also tested to examine the possible effect on the salinity stratification and temperature inversion within POI. Results show that during some periods, salinity stratification is reduced resulting in a subsequent reduction in temperature inversion compared with the existing conditions simulation. This may have an effect on POI’s suitability as a passive thermal refuge for manatees and other temperature-sensitive species. Additional testing was completed to determine the important physical relationships affecting POI’s suitability as a refuge.

Stable density stratification solar pond

NASA Technical Reports Server (NTRS)

Lansing, F. L. (Inventor)

1985-01-01

A stable density-stratification solar pond for use in the collection and storage of solar thermal energy including a container having a first section characterized by an internal wall of a substantially cylindrical configuration and a second section having an internal wall of a substantially truncated conical configuration surmounting the first section in coaxial alignment therewith, the second section of said container being characterized by a base of a diameter substantially equal to the diameter of the first section and a truncated apex defining a solar energy acceptance opening is discussed. A body of immiscible liquids is disposed within the container and comprises a lower portion substantially filling the first section of the container and an upper portion substantially filling the second section of the container, said lower portion being an aqueous based liquid of a darker color than the upper portion and of a greater density. A protective cover plate is removably provided for covering the acceptance opening.

New Methods for the Analysis of Heartbeat Behavior in Risk Stratification

PubMed Central

Glass, Leon; Lerma, Claudia; Shrier, Alvin

2011-01-01

Developing better methods for risk stratification for tachyarrhythmic sudden cardiac remains a major challenge for physicians and scientists. Since the transition from sinus rhythm to ventricular tachycardia/fibrillation happens by different mechanisms in different people, it is unrealistic to think that a single measure will be adequate to provide a good index for risk stratification. We analyze the dynamical properties of ventricular premature complexes over 24 h in an effort to understand the underlying mechanisms of ventricular arrhythmias and to better understand the arrhythmias that occur in individual patients. Two dimensional density plots, called heartprints, correlate characteristic features of the dynamics of premature ventricular complexes and the sinus rate. Heartprints show distinctive characteristics in individual patients. Based on a better understanding of the natures of transitions from sinus rhythm to sudden cardiac and the mechanisms of arrhythmia prior to cardiac arrest, it should be possible to develop better methods for risk stratification. PMID:22144963

Physical and biogeochemical controls on polymictic behavior in Sierra Nevada stream pools

NASA Astrophysics Data System (ADS)

Lucas, R. G.; Conklin, M. H.; Tyler, S. W.; Suarez, F. I.; Moran, J. E.; Esser, B. K.

2011-12-01

We observed polymictic behavior in stream pools in a low gradient montane meadow in the southern Sierra Nevada mountains, California. Thermal stratification in stream pools has been observed in various environments; stratification generally persists where the buoyancy forces created by a variation in water density, as a function of water temperature, are able to overcome turbulent forces resulting from stream flow. Because the density gradient creates a relatively weak buoyancy force, low flow conditions are generally required in order to overcome the turbulent forces. In some studies, a cold water source in to the pool bottoms can help to increase the density gradient and perpetuate thermal stratification. Our study took place in Long Meadow, Sequoia National Park, California. Long Meadow lies in the Wolverton Creek watershed and is part of the Southern Sierra Critical Zone Observatory. The 1-4 m diameter and 1-2 m deep pools in our study stratified thermally during the day and mixed completely at night. The low gradient of the meadow provided low stream flows. Piezometers in the meadow indicated groundwater discharge into the meadow in the months during which stratification was observed. Radon 222 activity measured in the pools also indicated groundwater influx to the pool bottoms. We used Fluent, a computational fluid dynamics equation solver, to construct a model of one of the observed pools. Initially we attempted to model the physical mechanisms controlling thermal stratification in the pool including stream flow, groundwater discharge, solar radiation, wind speed, and air, stream and ground water temperatures. Ultimately we found the model best agreed with our observed pool temperatures when we considered the light attenuation coefficients as a function of the dissolve organic carbon (DOC) concentration. Elevated DOC concentrations are expected in low stream flow regimes associated with highly organic soils such as a montane meadow. DOC concentrations measured in samples collected from the meadow stream, pools, and ground water wells ranged from 3.09 to 5.25 mg/L. We used a power equation taken from the literature to vary the visible light attenuation with DOC values measured in the meadow system. Light attenuation coefficients determined from measured DOC concentrations ranged from 0.507 m-1 to 0.899 m-1. The results from our modeling efforts indicate that in low flow streams and rivers elevated concentrations of DOC can increase the potential for thermal stratification in stream pools.

Review of factors affecting recovery of freshwater stored in saline aquifers

USGS Publications Warehouse

Merritt, Michael L.

1989-01-01

A simulation analysis reported previously, and summarized herein, identified the effects of various geohydrologic and operational factors on recoverability of the injected water. Buoyancy stratification, downgradient advection, and hydrodynamic dispersion are the principal natural processes that reduce the amount of injected water that can be recovered. Buoyancy stratification is shown to depend on injection-zone permeability and the density contrast between injected and saline native water. Downgradient advection occurs as a result of natural or induced hydraulic gradients in the aquifer. Hydrodynamic dispersion reduces recovery efficiency by mixing some of the injected water with native saline aquifer water. In computer simulations, the relation of recovery efficiency to volume injected and its improvement during successive injection-recovery cycles was shown to depend on changes in the degree of hydrodynamic dispersion that occurs. Additional aspects of the subject are discussed.

Lake Stability and Winter-Spring Transitions: Decoupled Ice Duration and Winter Stratification

NASA Astrophysics Data System (ADS)

Daly, J.; Dana, S.; Neal, B.

2016-12-01

Ice-out is an important historical record demonstrating the impact of warmer air temperatures on lake ice. To better understand regional differences in ice-out trends, to characterize the thermal dynamics of smaller mountain lakes, and to develop baseline data for Maine's high elevations landscapes, sub-hourly water temperatures have been collected in over a dozen of Maine's mountain lakes since 2010. Both surface water and hypolimnion temperature data are recorded year-round, facilitating the determination of ice-in, ice-out, and the duration of winter stratification. The multi-year record from sites across as 250 km transect allows us to compare spatial variability related to lake morphometry and location with inter-annual variability related to local weather. All of the study lakes are large enough to stratify during the summer and mix extensively during the fall. Most years, our data show that the onset of winter stratification is nearly synchronous across the study area and is associated with cold air temperatures. Winter stratification can begin days to weeks before ice-in; the timing of ice-in shows more variability, with both elevation and basin aspect influencing the timing. Ice-out shows both the anticipated spatial and interannual variability; some years there is strong coherence between locations while other years show high variability, possibly a function of differences in snowpack. Ice-out is not always immediately followed by the end of winter stratification, there is sometimes a lag of days to weeks before the lakes mix. If the warm temperatures that lead to ice-out are followed by calm days without significant wind, the surface of some lakes begins to warm quickly maintaining the density difference and prolonging winter stratification. The longer the lag time, the stronger the density difference becomes which may also result in a very brief period of mixing in the spring prior to set-up of summer stratification. This year's El Niño event resulted in very late ice-in, leading to an unusually short ice duration period at most sites. However, ice-out for these sites was within the range observed previous years and there may not be a significant impact on summer water temperatures.

Dynamical consequences of compositional and thermal density stratification beneath spreading centers

NASA Technical Reports Server (NTRS)

Sotin, C.; Parmentier, E. M.

1989-01-01

Dynamical consequences of compositional buoyancy and the combined effects of compositional and thermal buoyancy on mantle flow and crustal production are explored. The results show that for a low enough mantle viscosity, buoyant upwelling can significantly enhance the crustal thickness relative to that which would be produced by plate spreading alone, while for a mantle viscosity of 10 to the 22nd Pa s, upwelling due to plate spreading is dominant and crustal thickness is predicted to be a function of spreading rate. The results indicate that thermal and compositional density variations result in opposing buoyancy forces that can cause time-dependent upwelling.

On the Single-Layer Hydraulics Model for Flows and Ventilation over Unban Areas in Stable Stratification

NASA Astrophysics Data System (ADS)

Liu, C. H.

2015-12-01

Atmospheric stability has substantial effects on the flows and heat/mass transport processes. While extensive studies have been conducted for neutral and unstable stabilities, rather limited studies have been devoted to stable stratification. Major technical reason is the demanding spatio-temporal resolution required to solve the small scales in stratified turbulent flows. Instead of continuous density variation, we use the single-layer hydraulics model (analogous to shallow water equations for global dynamics), to simulate the stratified flows and turbulence structure over hypothetical urban areas. An array of identical ribs in cross flows is used to model an idealized urban surface and the aerodynamic resistance is controlled by the separation among the ribs. Two immiscible fluids (water and air) with a large density difference (three order of magnitude) are used to simulate the stratification. The key assumption is that the density in the (lower) single layer is uniform. As a result, the stratification is measured by the Froude number Fr (= U/(gH)1/2; where U is the flow speed, g the gravitational acceleration and H the single-layer depth). One of the characteristics of single-layer hydraulics model is hydraulic jump which occurs when the flows are slowing down from Fr > 1 (high-speed flows over smoother surfaces) to Fr < 1 (lower-speed flows over rougher surfaces). It is noteworthy that kinetic energy does not conserve across hydraulic jump that, unavoidably, cascades to turbulent kinetic energy (TKE). We thus hypotheses that the elevated TKE could modify the street-level ventilation mechanism in the stratified flows across an abrupt change in surface roughness entering urban areas. Large-eddy simulation and laboratory-scale water channel experiments are sought to improve our understanding of the occurrence of hydraulic jump and the associated street-level ventilation mechanism in the stratified flows over urban areas. Preliminary results, by comparing the dynamics at Fr = 2.4 and Fr = 2.8, demonstrate the notable changes in ventilation performance in the first several rows of ribs of urban areas. Substantial changes in the mean and fluctuating velocities are observed that contribute to the different street-level ventilation mechanism. Detailed results will be reported in the upcoming AGU fall meeting.

Maintenance of Coastal Surface Blooms by Surface Temperature Stratification and Wind Drift

PubMed Central

Ruiz-de la Torre, Mary Carmen; Maske, Helmut; Ochoa, José; Almeda-Jauregui, César O.

2013-01-01

Algae blooms are an increasingly recurrent phenomenon of potentially socio-economic impact in coastal waters globally and in the coastal upwelling region off northern Baja California, Mexico. In coastal upwelling areas the diurnal wind pattern is directed towards the coast during the day. We regularly found positive Near Surface Temperature Stratification (NSTS), the resulting density stratification is expected to reduce the frictional coupling of the surface layer from deeper waters and allow for its more efficient wind transport. We propose that the net transport of the top layer of approximately 2.7 kilometers per day towards the coast helps maintain surface blooms of slow growing dinoflagellate such as Lingulodinium polyedrum. We measured: near surface stratification with a free-rising CTD profiler, trajectories of drifter buoys with attached thermographs, wind speed and direction, velocity profiles via an Acoustic Doppler Current Profiler, Chlorophyll and cell concentration from water samples and vertical migration using sediment traps. The ADCP and drifter data agree and show noticeable current shear within the first meters of the surface where temperature stratification and high cell densities of L. polyedrum were found during the day. Drifters with 1m depth drogue moved towards the shore, whereas drifters at 3 and 5 m depth showed trajectories parallel or away from shore. A small part of the surface population migrated down to the sea floor during night thus reducing horizontal dispersion. The persistent transport of the surface bloom population towards shore should help maintain the bloom in favorable environmental conditions with high nutrients, but also increasing the potential socioeconomic impact of the blooms. The coast wise transport is not limited to blooms but includes all dissolved and particulate constituents in surface waters. PMID:23593127

Maintenance of coastal surface blooms by surface temperature stratification and wind drift.

PubMed

Ruiz-de la Torre, Mary Carmen; Maske, Helmut; Ochoa, José; Almeda-Jauregui, César O

2013-01-01

Algae blooms are an increasingly recurrent phenomenon of potentially socio-economic impact in coastal waters globally and in the coastal upwelling region off northern Baja California, Mexico. In coastal upwelling areas the diurnal wind pattern is directed towards the coast during the day. We regularly found positive Near Surface Temperature Stratification (NSTS), the resulting density stratification is expected to reduce the frictional coupling of the surface layer from deeper waters and allow for its more efficient wind transport. We propose that the net transport of the top layer of approximately 2.7 kilometers per day towards the coast helps maintain surface blooms of slow growing dinoflagellate such as Lingulodinium polyedrum. We measured: near surface stratification with a free-rising CTD profiler, trajectories of drifter buoys with attached thermographs, wind speed and direction, velocity profiles via an Acoustic Doppler Current Profiler, Chlorophyll and cell concentration from water samples and vertical migration using sediment traps. The ADCP and drifter data agree and show noticeable current shear within the first meters of the surface where temperature stratification and high cell densities of L. polyedrum were found during the day. Drifters with 1m depth drogue moved towards the shore, whereas drifters at 3 and 5 m depth showed trajectories parallel or away from shore. A small part of the surface population migrated down to the sea floor during night thus reducing horizontal dispersion. The persistent transport of the surface bloom population towards shore should help maintain the bloom in favorable environmental conditions with high nutrients, but also increasing the potential socioeconomic impact of the blooms. The coast wise transport is not limited to blooms but includes all dissolved and particulate constituents in surface waters.

Modelling the distribution of chickens, ducks, and geese in China

USGS Publications Warehouse

Prosser, Diann J.; Wu, Junxi; Ellis, Erie C.; Gale, Fred; Van Boeckel, Thomas P.; Wint, William; Robinson, Tim; Xiao, Xiangming; Gilbert, Marius

2011-01-01

Global concerns over the emergence of zoonotic pandemics emphasize the need for high-resolution population distribution mapping and spatial modelling. Ongoing efforts to model disease risk in China have been hindered by a lack of available species level distribution maps for poultry. The goal of this study was to develop 1 km resolution population density models for China's chickens, ducks, and geese. We used an information theoretic approach to predict poultry densities based on statistical relationships between poultry census data and high-resolution agro-ecological predictor variables. Model predictions were validated by comparing goodness of fit measures (root mean square error and correlation coefficient) for observed and predicted values for 1/4 of the sample data which were not used for model training. Final output included mean and coefficient of variation maps for each species. We tested the quality of models produced using three predictor datasets and 4 regional stratification methods. For predictor variables, a combination of traditional predictors for livestock mapping and land use predictors produced the best goodness of fit scores. Comparison of regional stratifications indicated that for chickens and ducks, a stratification based on livestock production systems produced the best results; for geese, an agro-ecological stratification produced best results. However, for all species, each method of regional stratification produced significantly better goodness of fit scores than the global model. Here we provide descriptive methods, analytical comparisons, and model output for China's first high resolution, species level poultry distribution maps. Output will be made available to the scientific and public community for use in a wide range of applications from epidemiological studies to livestock policy and management initiatives.

Modelling the distribution of chickens, ducks, and geese in China

PubMed Central

Prosser, Diann J.; Wu, Junxi; Ellis, Erle C.; Gale, Fred; Van Boeckel, Thomas P.; Wint, William; Robinson, Tim; Xiao, Xiangming; Gilbert, Marius

2011-01-01

Global concerns over the emergence of zoonotic pandemics emphasize the need for high-resolution population distribution mapping and spatial modelling. Ongoing efforts to model disease risk in China have been hindered by a lack of available species level distribution maps for poultry. The goal of this study was to develop 1 km resolution population density models for China’s chickens, ducks, and geese. We used an information theoretic approach to predict poultry densities based on statistical relationships between poultry census data and high-resolution agro-ecological predictor variables. Model predictions were validated by comparing goodness of fit measures (root mean square error and correlation coefficient) for observed and predicted values for ¼ of the sample data which was not used for model training. Final output included mean and coefficient of variation maps for each species. We tested the quality of models produced using three predictor datasets and 4 regional stratification methods. For predictor variables, a combination of traditional predictors for livestock mapping and land use predictors produced the best goodness of fit scores. Comparison of regional stratifications indicated that for chickens and ducks, a stratification based on livestock production systems produced the best results; for geese, an agro-ecological stratification produced best results. However, for all species, each method of regional stratification produced significantly better goodness of fit scores than the global model. Here we provide descriptive methods, analytical comparisons, and model output for China’s first high resolution, species level poultry distribution maps. Output will be made available to the scientific and public community for use in a wide range of applications from epidemiological studies to livestock policy and management initiatives. PMID:21765567

Effect of sample stratification on dairy GWAS results

PubMed Central

2012-01-01

Background Artificial insemination and genetic selection are major factors contributing to population stratification in dairy cattle. In this study, we analyzed the effect of sample stratification and the effect of stratification correction on results of a dairy genome-wide association study (GWAS). Three methods for stratification correction were used: the efficient mixed-model association expedited (EMMAX) method accounting for correlation among all individuals, a generalized least squares (GLS) method based on half-sib intraclass correlation, and a principal component analysis (PCA) approach. Results Historical pedigree data revealed that the 1,654 contemporary cows in the GWAS were all related when traced through approximately 10–15 generations of ancestors. Genome and phenotype stratifications had a striking overlap with the half-sib structure. A large elite half-sib family of cows contributed to the detection of favorable alleles that had low frequencies in the general population and high frequencies in the elite cows and contributed to the detection of X chromosome effects. All three methods for stratification correction reduced the number of significant effects. EMMAX method had the most severe reduction in the number of significant effects, and the PCA method using 20 principal components and GLS had similar significance levels. Removal of the elite cows from the analysis without using stratification correction removed many effects that were also removed by the three methods for stratification correction, indicating that stratification correction could have removed some true effects due to the elite cows. SNP effects with good consensus between different methods and effect size distributions from USDA’s Holstein genomic evaluation included the DGAT1-NIBP region of BTA14 for production traits, a SNP 45kb upstream from PIGY on BTA6 and two SNPs in NIBP on BTA14 for protein percentage. However, most of these consensus effects had similar frequencies in the elite and average cows. Conclusions Genetic selection and extensive use of artificial insemination contributed to overlapped genome, pedigree and phenotype stratifications. The presence of an elite cluster of cows was related to the detection of rare favorable alleles that had high frequencies in the elite cluster and low frequencies in the remaining cows. Methods for stratification correction could have removed some true effects associated with genetic selection. PMID:23039970

Stratified sampling design based on data mining.

PubMed

Kim, Yeonkook J; Oh, Yoonhwan; Park, Sunghoon; Cho, Sungzoon; Park, Hayoung

2013-09-01

To explore classification rules based on data mining methodologies which are to be used in defining strata in stratified sampling of healthcare providers with improved sampling efficiency. We performed k-means clustering to group providers with similar characteristics, then, constructed decision trees on cluster labels to generate stratification rules. We assessed the variance explained by the stratification proposed in this study and by conventional stratification to evaluate the performance of the sampling design. We constructed a study database from health insurance claims data and providers' profile data made available to this study by the Health Insurance Review and Assessment Service of South Korea, and population data from Statistics Korea. From our database, we used the data for single specialty clinics or hospitals in two specialties, general surgery and ophthalmology, for the year 2011 in this study. Data mining resulted in five strata in general surgery with two stratification variables, the number of inpatients per specialist and population density of provider location, and five strata in ophthalmology with two stratification variables, the number of inpatients per specialist and number of beds. The percentages of variance in annual changes in the productivity of specialists explained by the stratification in general surgery and ophthalmology were 22% and 8%, respectively, whereas conventional stratification by the type of provider location and number of beds explained 2% and 0.2% of variance, respectively. This study demonstrated that data mining methods can be used in designing efficient stratified sampling with variables readily available to the insurer and government; it offers an alternative to the existing stratification method that is widely used in healthcare provider surveys in South Korea.

Tsunami Speed Variations in Density-stratified Compressible Global Oceans

NASA Astrophysics Data System (ADS)

Watada, S.

2013-12-01

Recent tsunami observations in the deep ocean have accumulated unequivocal evidence that tsunami traveltime delays compared with the linear long-wave tsunami simulations occur during tsunami propagation in the deep ocean. The delay is up to 2% of the tsunami traveltime. Watada et al. [2013] investigated the cause of the delay using the normal mode theory of tsunamis and attributed the delay to the compressibility of seawater, the elasticity of the solid earth, and the gravitational potential change associated with mass motion during the passage of tsunamis. Tsunami speed variations in the deep ocean caused by seawater density stratification is investigated using a newly developed propagator matrix method that is applicable to seawater with depth-variable sound speeds and density gradients. For a 4-km deep ocean, the total tsunami speed reduction is 0.45% compared with incompressible homogeneous seawater; two thirds of the reduction is due to elastic energy stored in the water and one third is due to water density stratification mainly by hydrostatic compression. Tsunami speeds are computed for global ocean density and sound speed profiles and characteristic structures are discussed. Tsunami speed reductions are proportional to ocean depth with small variations, except for in warm Mediterranean seas. The impacts of seawater compressibility and the elasticity effect of the solid earth on tsunami traveltime should be included for precise modeling of trans-oceanic tsunamis. Data locations where a vertical ocean profile deeper than 2500 m is available in World Ocean Atlas 2009. The dark gray area indicates the Pacific Ocean defined in WOA09. a) Tsunami speed variations. Red, gray and black bars represent global, Pacific, and Mediterranean Sea, respectively. b) Regression lines of the tsunami velocity reduction for all oceans. c)Vertical ocean profiles at grid points indicated by the stars in Figure 1.

Internal wave energy flux from density perturbations in nonlinear stratifications

NASA Astrophysics Data System (ADS)

Lee, Frank M.; Allshouse, Michael R.; Swinney, Harry L.; Morrison, P. J.

2017-11-01

Tidal flow over the topography at the bottom of the ocean, whose density varies with depth, generates internal gravity waves that have a significant impact on the energy budget of the ocean. Thus, understanding the energy flux (J = p v) is important, but it is difficult to measure simultaneously the pressure and velocity perturbation fields, p and v . In a previous work, a Green's-function-based method was developed to calculate the instantaneous p, v , and thus J , given a density perturbation field for a constant buoyancy frequency N. Here we extend the previous analytic Green's function work to include nonuniform N profiles, namely the tanh-shaped and linear cases, because background density stratifications that occur in the ocean and some experiments are nonlinear. In addition, we present a finite-difference method for the general case where N has an arbitrary profile. Each method is validated against numerical simulations. The methods we present can be applied to measured density perturbation data by using our MATLAB graphical user interface EnergyFlux. PJM was supported by the U.S. Department of Energy Contract DE-FG05-80ET-53088. HLS and MRA were supported by ONR Grant No. N000141110701.

Stratified Sampling Design Based on Data Mining

PubMed Central

Kim, Yeonkook J.; Oh, Yoonhwan; Park, Sunghoon; Cho, Sungzoon

2013-01-01

Objectives To explore classification rules based on data mining methodologies which are to be used in defining strata in stratified sampling of healthcare providers with improved sampling efficiency. Methods We performed k-means clustering to group providers with similar characteristics, then, constructed decision trees on cluster labels to generate stratification rules. We assessed the variance explained by the stratification proposed in this study and by conventional stratification to evaluate the performance of the sampling design. We constructed a study database from health insurance claims data and providers' profile data made available to this study by the Health Insurance Review and Assessment Service of South Korea, and population data from Statistics Korea. From our database, we used the data for single specialty clinics or hospitals in two specialties, general surgery and ophthalmology, for the year 2011 in this study. Results Data mining resulted in five strata in general surgery with two stratification variables, the number of inpatients per specialist and population density of provider location, and five strata in ophthalmology with two stratification variables, the number of inpatients per specialist and number of beds. The percentages of variance in annual changes in the productivity of specialists explained by the stratification in general surgery and ophthalmology were 22% and 8%, respectively, whereas conventional stratification by the type of provider location and number of beds explained 2% and 0.2% of variance, respectively. Conclusions This study demonstrated that data mining methods can be used in designing efficient stratified sampling with variables readily available to the insurer and government; it offers an alternative to the existing stratification method that is widely used in healthcare provider surveys in South Korea. PMID:24175117

The influence of atmospheric stratification on scatterometer data

NASA Technical Reports Server (NTRS)

Louis, Jean-Francois; Hoffman, Ross N.

1989-01-01

The effects of atmospheric stratification and the stability of the atmospheric stratification on the scatterometer data measuring surface winds over the ocean were investigated using the boundary layer model developed by Louis (1979). A variational analysis method is proposed, which allows direct assimilation of scatterometer data. It is shown that the effect of the stability of atmospheric stratification on the wind increment is relatively small. However, it is a systematic effect, and neglecting it would consistently underestimate the winds in stable regions.

Observations and analysis of a stratification-destratification event in a tropical estuary

NASA Astrophysics Data System (ADS)

Uncles, R. J.; Ong, J. E.; Gong, W. K.

1990-11-01

A data set comprising 31 continuous tidal cycles was collected in the Sungai Merbok Estuary, Malaysia, in June 1987 as part of an ecological study of nutrient fluxes from a tropical mangrove estuary. Currents, salinity and salinity stratification at a deep-channel (15 m) station near the mouth of the Merbok Estuary showed a pronounced spring-neap variability. The slow currents and weak vertical mixing at neap tides favoured the formation of a stratified water column and generated a neap-spring cycle of water column stabilization and destabilization. A strong stratification event occurred during the period of observations. This was partly driven by a modest freshwater spate which coincided with neap tides. An eddy viscosity-diffusivity model of the stratification, which assumed a constant, longitudinal salinity gradient, demonstrated a pronounced stratification-destratification cycle due to neap-spring variations in vertical mixing. Larger and more realistic stratification was modelled when the estimated, time-varying longitudinal salinity gradient was incorporated. This gradient maximized in response to the peak in freshwater runoff. The measured and modelled density-driven circulations showed qualitative similarities and were of the order of 10 cm s -1 at neap tides. The circulation was weaker during spring tides. The tidally-filtered salt transport due to vertical shear was directed up-estuary and was an order of magnitude smaller during spring tides. The results are discussed in terms of their relevance to mangrove system oceanography.

High-resolution mapping of forest carbon stocks in the Colombian Amazon

NASA Astrophysics Data System (ADS)

Asner, G. P.; Clark, J. K.; Mascaro, J.; Galindo García, G. A.; Chadwick, K. D.; Navarrete Encinales, D. A.; Paez-Acosta, G.; Cabrera Montenegro, E.; Kennedy-Bowdoin, T.; Duque, Á.; Balaji, A.; von Hildebrand, P.; Maatoug, L.; Bernal, J. F. Phillips; Yepes Quintero, A. P.; Knapp, D. E.; García Dávila, M. C.; Jacobson, J.; Ordóñez, M. F.

2012-07-01

High-resolution mapping of tropical forest carbon stocks can assist forest management and improve implementation of large-scale carbon retention and enhancement programs. Previous high-resolution approaches have relied on field plot and/or light detection and ranging (LiDAR) samples of aboveground carbon density, which are typically upscaled to larger geographic areas using stratification maps. Such efforts often rely on detailed vegetation maps to stratify the region for sampling, but existing tropical forest maps are often too coarse and field plots too sparse for high-resolution carbon assessments. We developed a top-down approach for high-resolution carbon mapping in a 16.5 million ha region (> 40%) of the Colombian Amazon - a remote landscape seldom documented. We report on three advances for large-scale carbon mapping: (i) employing a universal approach to airborne LiDAR-calibration with limited field data; (ii) quantifying environmental controls over carbon densities; and (iii) developing stratification- and regression-based approaches for scaling up to regions outside of LiDAR coverage. We found that carbon stocks are predicted by a combination of satellite-derived elevation, fractional canopy cover and terrain ruggedness, allowing upscaling of the LiDAR samples to the full 16.5 million ha region. LiDAR-derived carbon maps have 14% uncertainty at 1 ha resolution, and the regional map based on stratification has 28% uncertainty in any given hectare. High-resolution approaches with quantifiable pixel-scale uncertainties will provide the most confidence for monitoring changes in tropical forest carbon stocks. Improved confidence will allow resource managers and decision makers to more rapidly and effectively implement actions that better conserve and utilize forests in tropical regions.

High-resolution Mapping of Forest Carbon Stocks in the Colombian Amazon

NASA Astrophysics Data System (ADS)

Asner, G. P.; Clark, J. K.; Mascaro, J.; Galindo García, G. A.; Chadwick, K. D.; Navarrete Encinales, D. A.; Paez-Acosta, G.; Cabrera Montenegro, E.; Kennedy-Bowdoin, T.; Duque, Á.; Balaji, A.; von Hildebrand, P.; Maatoug, L.; Bernal, J. F. Phillips; Knapp, D. E.; García Dávila, M. C.; Jacobson, J.; Ordóñez, M. F.

2012-03-01

High-resolution mapping of tropical forest carbon stocks can assist forest management and improve implementation of large-scale carbon retention and enhancement programs. Previous high-resolution approaches have relied on field plot and/or Light Detection and Ranging (LiDAR) samples of aboveground carbon density, which are typically upscaled to larger geographic areas using stratification maps. Such efforts often rely on detailed vegetation maps to stratify the region for sampling, but existing tropical forest maps are often too coarse and field plots too sparse for high resolution carbon assessments. We developed a top-down approach for high-resolution carbon mapping in a 16.5 million ha region (>40 %) of the Colombian Amazon - a remote landscape seldom documented. We report on three advances for large-scale carbon mapping: (i) employing a universal approach to airborne LiDAR-calibration with limited field data; (ii) quantifying environmental controls over carbon densities; and (iii) developing stratification- and regression-based approaches for scaling up to regions outside of LiDAR coverage. We found that carbon stocks are predicted by a combination of satellite-derived elevation, fractional canopy cover and terrain ruggedness, allowing upscaling of the LiDAR samples to the full 16.5 million ha region. LiDAR-derived carbon mapping samples had 14.6 % uncertainty at 1 ha resolution, and regional maps based on stratification and regression approaches had 25.6 % and 29.6 % uncertainty, respectively, in any given hectare. High-resolution approaches with reported local-scale uncertainties will provide the most confidence for monitoring changes in tropical forest carbon stocks. Improved confidence will allow resource managers and decision-makers to more rapidly and effectively implement actions that better conserve and utilize forests in tropical regions.

Development of experimental facilities for processing metallic crystals in orbit

NASA Technical Reports Server (NTRS)

Duncan, Bill J.

1990-01-01

This paper discusses the evolution, current status, and planning for facilities to exploit the microgravity environment of earth orbit in applied metallic materials science. Space-Shuttle based facilities and some precursor flight programs are reviewed. Current facility development programs and planned Space Station furnace capabilities are described. The reduced gravity levels available in earth orbit allow the processing of metallic materials without the disturbing influence of gravitationally induced thermal convection, stratification due to density differences in sample components, or the effects of hydrostatic pressure.

Magnetized stratified rotating shear waves.

PubMed

Salhi, A; Lehner, T; Godeferd, F; Cambon, C

2012-02-01

We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity Ω), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k(1) = 0, axisymmetric disturbances) and a finite one (k(1) ≠ 0, nonaxisymmetric disturbances). In the former case (k(1) = 0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k(1) ≠ 0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the stability of the solution at infinite vertical wavelength (k(3) = 0): There is an oscillatory behavior for τ > 1+|K(2)/k(1)|, where τ = St is a dimensionless time and K(2) is the radial component of the wave vector at τ = 0. The model is suitable to describe instabilities leading to turbulence by the bypass mechanism that can be relevant for the analysis of magnetized stratified Keplerian disks with a purely azimuthal field. For initial isotropic conditions, the time evolution of the spectral density of total energy (kinetic + magnetic + potential) is considered. At k(3) = 0, the vertical motion is purely oscillatory, and the sum of the vertical (kinetic + magnetic) energy plus the potential energy does not evolve with time and remains equal to its initial value. The horizontal motion can induce a rapid transient growth provided K(2)/k(1)>1. This rapid growth is due to the aperiodic velocity vortex mode that behaves like K(h)/k(h) where k(h)(τ)=[k(1)(2) + (K(2) - k(1)τ)(2)](1/2) and K(h) =k(h)(0). After the leading phase (τ > K(2)/k(1)>1), the horizontal magnetic energy and the horizontal kinetic energy exhibit a similar (oscillatory) behavior yielding a high level of total energy. The contribution to energies coming from the modes k(1) = 0 and k(3) = 0 is addressed by investigating the one-dimensional spectra for an initial Gaussian dense spectrum. For a magnetized Keplerian disk with a purely vertical field, it is found that an important contribution to magnetic and kinetic energies comes from the region near k(1) = 0. The limit at k(1) = 0 of the streamwise one-dimensional spectra of energies, or equivalently, the streamwise two-dimensional (2D) energy, is then computed. The comparison of the ratios of these 2D quantities with their three-dimensional counterparts provided by previous direct numerical simulations shows a quantitative agreement.

Near-surface Stratification and Submesoscale Fronts in the north Bay of Bengal during Summer Monsoon of 2014 and 2015.

NASA Astrophysics Data System (ADS)

Sengupta, D.; Jarugula, S. L.; D'Asaro, E. A.; Chaudhuri, D.; S, S.; Tandon, A.; M, R.; Lucas, A.; Simmons, H. L.

2016-02-01

The north bay of Bengal is characterised by a shallow layer of fresh water from monsoon rainfall and river discharge, with very strong stratification at its base, and a warm subsurface layer. The thermodynamic structure of the ocean has significant influence on air-sea interaction. We conducted two research cruises of ORV Sagar Nidhi in August-September 2014 and 2015, to study the physical processes that maintain the shallow fresh layer. We collected a total of about 4000 kilometers of underway Conductivity-Temperature-Depth (uCTD) and Acoustic Doppler Current Profiler (ADCP) data. The vertical resolution of the data is 1-2 m; at ship speeds of 4-5 knots, the horizontal resolution is 300-1500 m, sufficient to resolve submesoscale (1-20 km) features. It is known that dynamical instability of submesoscale fronts can lead to slumping of heavier water under lighter water, enhancing vertical stratification. We identified 35 major salinity-dominated near-surface density fronts along the ship track, with surface density gradient exceeding 0.03 kg/m3 per kilometer, and density difference exceeding 0.3 kg/m3. The largest gradients in the open ocean, between fresh water of riverine origin and ambient seawater, exceeded 10 psu in 40 km and 6 psu in 50 km; the spatial scales of the other fronts range from 1 to 25 km. At several submesoscale fronts, the surface mixed layer is shallower directly under the front than on either side, suggesting active restratification. ADCP observations reveal a region of confluence and narrow jets associated with some fronts, consistent with frontal slumping. In addition, wind-driven Ekman transport can enhance near-surface stratification by carrying lighter water over denser water. We discuss the relevance of these two mechanisms in observations and model simulations.

Hydraulic effects in a radiative atmosphere with ionization

NASA Astrophysics Data System (ADS)

Bhat, P.; Brandenburg, A.

2016-03-01

Context. In his 1978 paper, Eugene Parker postulated the need for hydraulic downward motion to explain magnetic flux concentrations at the solar surface. A similar process has also recently been seen in simplified (e.g., isothermal) models of flux concentrations from the negative effective magnetic pressure instability (NEMPI). Aims: We study the effects of partial ionization near the radiative surface on the formation of these magnetic flux concentrations. Methods: We first obtain one-dimensional (1D) equilibrium solutions using either a Kramers-like opacity or the H- opacity. The resulting atmospheres are then used as initial conditions in two-dimensional (2D) models where flows are driven by an imposed gradient force that resembles a localized negative pressure in the form of a blob. To isolate the effects of partial ionization and radiation, we ignore turbulence and convection. Results: Because of partial ionization, an unstable stratification always forms near the surface. We show that the extrema in the specific entropy profiles correspond to the extrema in the degree of ionization. In the 2D models without partial ionization, strong flux concentrations form just above the height where the blob is placed. Interestingly, in models with partial ionization, such flux concentrations always form at the surface well above the blob. This is due to the corresponding negative gradient in specific entropy. Owing to the absence of turbulence, the downflows reach transonic speeds. Conclusions: We demonstrate that, together with density stratification, the imposed source of negative pressure drives the formation of flux concentrations. We find that the inclusion of partial ionization affects the entropy profile dramatically, causing strong flux concentrations to form closer to the surface. We speculate that turbulence effects are needed to limit the strength of flux concentrations and homogenize the specific entropy to a stratification that is close to marginal.

Modal density of rectangular structures in a wide frequency range

NASA Astrophysics Data System (ADS)

Parrinello, A.; Ghiringhelli, G. L.

2018-04-01

A novel approach to investigate the modal density of a rectangular structure in a wide frequency range is presented. First, the modal density is derived, in the whole frequency range of interest, on the basis of sound transmission through the infinite counterpart of the structure; then, it is corrected by means of the low-frequency modal behavior of the structure, taking into account actual size and boundary conditions. A statistical analysis reveals the connection between the modal density of the structure and the transmission of sound through its thickness. A transfer matrix approach is used to compute the required acoustic parameters, making it possible to deal with structures having arbitrary stratifications of different layers. A finite element method is applied on coarse grids to derive the first few eigenfrequencies required to correct the modal density. Both the transfer matrix approach and the coarse grids involved in the finite element analysis grant high efficiency. Comparison with alternative formulations demonstrates the effectiveness of the proposed methodology.

An inversion of the estuarine circulation by sluice water discharge and its impact on suspended sediment transport

NASA Astrophysics Data System (ADS)

Schulz, Kirstin; Gerkema, Theo

2018-01-01

The Wadden Sea is characterized by a complex topography of branching channels and intertidal flats, in which the interplay between fresh water discharges, wind forcing and the tidal current causes sediment transport rates and direction to be highly variable in space and time. During three field campaigns, indications of a negative estuarine circulation have been found in a channel adjacent to the coast in the Western Dutch Wadden Sea. Contrary to the classical picture of estuarine circulation, a periodic density stratification was observed that builds up during flood and breaks down during ebb. This can be related to a large freshwater source at the mouth of the channel, the sluice in Kornwerderzand. In this study, observations of this phenomenon are presented, and with the help of a numerical model the different drivers for residual suspended matter transport in this area, namely tidal asymmetries in the current velocity and the above mentioned periodic stratification, are investigated. It is found that the residual current in the area of interest points in ebb direction, caused by both the elongated ebb flow phase and the periodic stratification. On the contrary, the stronger flood currents cause a transport of suspended matter in flood direction. This transport is counteracted and therefore diminished by the effects of the sluice discharge.

Large-eddy simulation study of oil/gas plumes in stratified fluid with cross current

NASA Astrophysics Data System (ADS)

Yang, Di; Xiao, Shuolin; Chen, Bicheng; Chamecki, Marcelo; Meneveau, Charles

2017-11-01

Dynamics of the oil/gas plume from a subsea blowout are strongly affected by the seawater stratification and cross current. The buoyant plume entrains ambient seawater and lifts it up to higher elevations. During the rising process, the continuously increasing density difference between the entrained and ambient seawater caused by the stable stratification eventually results in a detrainment of the entrained seawater and small oil droplets at a height of maximum rise (peel height), forming a downward plume outside the rising inner plume. The presence of a cross current breaks the plume's axisymmetry and causes the outer plume to fall along the downstream side of the inner plume. The detrained seawater and oil eventually fall to a neutral buoyancy level (trap height), and disperse horizontally to form an intrusion layer. In this study, the complex plume dynamics is investigated using large-eddy simulation (LES). Various laboratory and field scale cases are simulated to explore the effect of cross current and stratification on the plume dynamics. Based on the LES data, various turbulence statistics of the plume are systematically quantified, leading to some useful insights for modeling the mean plume dynamics using integral plume models. This research is made possible by a RFP-V Grant from The Gulf of Mexico Research Initiative.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhaoqing; Wang, Taiping

A three-dimensional coastal ocean model with a tidal turbine module was used in this paper to study the effects of tidal energy extraction on temperature and salinity stratification and density driven two-layer estuarine circulation. Numerical experiments with various turbine array configurations were carried out to investigate the changes in tidally mean temperature, salinity and velocity profiles in an idealized stratified estuary that connects to coastal water through a narrow tidal channel. The model was driven by tides, river inflow and sea surface heat flux. To represent the realistic size of commercial tidal farms, model simulations were conducted based on amore » small percentage of the total number of turbines that would generate the maximum extractable energy in the system. Model results indicated that extraction of tidal energy will increase the vertical mixing and decrease the stratification in the estuary. Extraction of tidal energy has stronger impact on the tidally-averaged salinity, temperature and velocity in the surface layer than the bottom. Energy extraction also weakens the two-layer estuarine circulation, especially during neap tides when tidal mixing the weakest and energy extraction is the smallest. Model results also show that energy generation can be much more efficient with higher hub height with relatively small changes in stratification and two-layer estuarine circulation.« less

Pumping bottom water to prevent Korean red tide damage caused by Cochlodinium polykrikoides Margalef.

PubMed

Cho, Eun Seob; Moon, Seong Yong; Shu, Young Sang; Hwang, Jae Dong; Youn, Seok Hyun

2015-09-01

Cochlodinium polykrikoides Margalef produces annual massive blooms in Korean coastal waters which cause great damage to aquaculture and fisheries. Although various methods have been developed to remove the red tide of C. polykrikoides, release of yellow loess has been regarded as the most desirable technique for mitigation for over 10 years. Each August, strong irradiation generates water column stratification separating warm surface from colder bottom waters. Water from a distance of 0 (St. 1), 5 (St. 2), 10 (St. 3), and 15 m (St. 4) was pumped by running a pump for 0, 10, 30 and 90 min and characterized water temperature, salinity collected, suspended solids, Chl-a, and phytoplankton including C. polykrikoides. After running for 30 min, was temperature and salinity in surface water was similar to those of bottom water, and water column stratification completely reversed after 90 min. Likewise, suspended solids, Chl-a, and total phytoplankton cell density decreased after 30 min, but C. polykrikoides did not show strong removal because of low cell density during sampling. However, the number of C. polykrikoides was significantly diluted (80%) after 90 min. These results suggested that pumping device was as an environmentally-friendly method convenient to be install in fish cages and effective to remove C. polykrikoides stratified water column conditions.

Comments: Should Principal Stratification Be Used to Study Mediational Processes?

ERIC Educational Resources Information Center

VanderWeele, Tyler J.

2012-01-01

Principal stratification provides an approach to study the effect of an exposure on an outcome within strata defined by the effect of the exposure on some third, posttreatment, variable (Frangakis & Rubin, 2002). There has been more recent interest in using principal stratification to study the extent to which the effect of an exposure on an…

Postimpoundment survey of water-quality characteristics of Raystown Lake, Huntingdon and Bedford Counties, Pennsylvania

USGS Publications Warehouse

Williams, Donald R.

1978-01-01

Water-quality data, collected from May 1974 to September 1976 at thirteen sites within Raystown Lake and in the inflow and outflow channels, define the water-quality characteristics of the lake water and the effects of impoundment on the quality of the lake outflow. Depth-profile measurements show Raystown Lake to be dimictic. Thermal stratification is well developed during the summer. Generally high concentrations of dissolved oxygen throughout the hypolimnion during thermal stratification, low phytoplankton concentrations, and small diel fluctuations of dissolved oxygen, pH, and specific conductance indicate that the lake is low in nutrients, or oligotrophic. Algal assays of surface samples indicate that orthophosphate was a growth-limiting nutrient. The diatoms (Chrysophyta) were the dominant phytoplankton group found through-out the study period. The lake waters contained very low populations of zooplankton. Fecal coliform and fecal streptococcus densities measured throughout the lake indicated no potentially dangerous areas of water-contact recreation. The most apparent effect that the impoundment had on water quality was the removal of nutrients, particularly orthophosphate, through phytoplankton uptake and sediment deposition.

Wind farm density and harvested power in very large wind farms: A low-order model

NASA Astrophysics Data System (ADS)

Cortina, G.; Sharma, V.; Calaf, M.

2017-07-01

In this work we create new understanding of wind turbine wakes recovery process as a function of wind farm density using large-eddy simulations of an atmospheric boundary layer diurnal cycle. Simulations are forced with a constant geostrophic wind and a time varying surface temperature extracted from a selected period of the Cooperative Atmospheric Surface Exchange Study field experiment. Wind turbines are represented using the actuator disk model with rotation and yaw alignment. A control volume analysis around each turbine has been used to evaluate wind turbine wake recovery and corresponding harvested power. Results confirm the existence of two dominant recovery mechanisms, advection and flux of mean kinetic energy, which are modulated by the background thermal stratification. For the low-density arrangements advection dominates, while for the highly loaded wind farms the mean kinetic energy recovers through fluxes of mean kinetic energy. For those cases in between, a smooth balance of both mechanisms exists. From the results, a low-order model for the wind farms' harvested power as a function of thermal stratification and wind farm density has been developed, which has the potential to be used as an order-of-magnitude assessment tool.

Distribution and exploitation of Nile perch Lates niloticus in relation to stratification in Lake Victoria, East Africa

USGS Publications Warehouse

Taabu-Munyaho, A.; Kayanda, Robert J.; Everson, Inigo; Grabowski, Timothy B.; Marteinsdóttir, Gudrún

2013-01-01

Stratification restricts habitable areas forcing fish to balance between favourable temperature and minimum dissolved oxygen requirements. Acoustic surveys conducted during the stratified and isothermal periods on tropical Lake Victoria indicated that stratification of temperature and dissolved oxygen (DO) affected vertical distribution of Nile perch. There was higher mean temperature (25.6 ± 0.5 °C) and lower DO (6.4 ± 1.8 mg/l) during stratified period compared to the isothermal period (mean temperature 24.9 ± 0.3 °C; mean DO 7.3 ± 0.6 mg/l). Higher mean densities of Nile perch were recorded in the coastal (0.44 ± 0.03) and deep (0.27 ± 0.02 g/m3) strata during the stratified compared to the isothermal season (coastal: 0.24 ± 0.01; deep: 0.12 ± 0.02 g/m3). In addition, Nile perch density in the upper 0–40 m depth layers in the coastal and deep strata increased by over 50% from the isothermal to the stratified season. Daily landings from 65 motorised fishing boats between October 2008 and September 2010 show higher mean catch (26.29 ± 0.17 kg/boat/day) during stratified compared to the isothermal (23.59 ± 0.15) season. Thermal stratification apparently compresses the habitat available to Nile perch and can potentially result in higher exploitation. Managers should evaluate the potential benefits of instituting closed seasons during the stratified period, and stock assessment models should take into account the seasonal niche compression.

A Mechanism for Stratifying Lava Flows

NASA Astrophysics Data System (ADS)

Rice, A.

2005-12-01

Relict lava flows (e.g., komatiites) are often reported to be zoned in the vertical, each zone separated by a sharp contact. Such stratifications in igneous flows, both intrusive and extrusive, can be treated as analogues of suspended loads of sediments in rivers and streams, and hence amenable to quantitative treatment derived for the hydraulic environment as long as dynamic similitude is assured. Situations typically encountered in the hydraulic environment are streams carrying a bed load at the bottom of the stream, the bed load separated by a sharp horizon from a sediment load carried above it. This sediment load may be topped by others of decreasing density as one moves to the surface of the flow, with perhaps the uppermost layer clear of any suspended matter. Rules exist for estimating the thickness D of these loads: one of them is given by D ~ 4.4V3/rgcvs where V is the shear velocity or average velocity of the flow, r = (ρs - ρl)/ρl where ρs is the density of the suspended solid matter, ρl the density of the fluid, g the acceleration of gravity, c the concentration of the particulate content and vs the settling velocity. The settling velocity is secured through Stoke's Law and the velocity of the flow is given by V = R2/3S1/2/n where R is the hydraulic radius, S the gradient along which the fluid flows and n is the Manning Coefficient. In the igneous case, the bed load would be composed of primocrysts, i.e., of the first crystals to come out of solution as the flow cools along its run. This would leave the upper portions of the flow more evolved except perhaps for a quenched crust riding atop the flow. As the viscosity of the flow is dependent not only on temperature but on composition and crystal content, the mean velocity of each layer will be different from the layer above and below it. This requires shear at the interface of adjoining stratifications, which brings into play another mechanism: dispersive pressure (the Bagnold effect). Dispersive pressure will drive primocrysts into boundary layers such as that attending the bottom of the flow and at those separating stratifications. For instance, if the primocrysts were spinals, then a Cr high might be expected at the interfaces separating stratifications. Since the melt throughout is evolving as it moves down stream, compositional variations along strike (as well is in the vertical) might be expected. Application of the above notions falls within the confines of field observation.

The warmer the ocean surface, the shallower the mixed layer. How much of this is true?

PubMed Central

González‐Pola, C.; Fernández‐Diaz, J.

2017-01-01

Abstract Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near‐surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at midlatitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at midlatitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10 m  decade−1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long‐term hydrographic time‐series, ocean reanalysis, and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability involves a subtle interplay between circulation and atmospheric forcing at midlatitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing. PMID:29201584

The warmer the ocean surface, the shallower the mixed layer. How much of this is true?

PubMed

Somavilla, R; González-Pola, C; Fernández-Diaz, J

2017-09-01

Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near-surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at midlatitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at midlatitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10 m  decade-1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long-term hydrographic time-series, ocean reanalysis, and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability involves a subtle interplay between circulation and atmospheric forcing at midlatitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing.

Unsteady Shear Disturbances Within a Two Dimensional Stratified Flow

NASA Technical Reports Server (NTRS)

Yokota, Jeffrey W.

1992-01-01

The origin and evolution of shear disturbances within a stratified, inviscid, incompressible flow are investigated numerically by a Clebsch/Weber decomposition based scheme. In contrast to homogeneous flows, within which vorticity can be redistributed but not generated, the presence of a density stratification can render an otherwise irrotational flow vortical. In this work, a kinematic decomposition of the unsteady Euler equations separates the unsteady velocity field into rotational and irrotational components. The subsequent evolution of these components is used to study the influence various velocity disturbances have on both stratified and homogeneous flows. In particular, the flow within a two-dimensional channel is used to investigate the evolution of rotational disturbances, generated or convected, downstream from an unsteady inflow condition. Contrasting simulations of both stratified and homogeneous flows are used to distinguish between redistributed inflow vorticity and that which is generated by a density stratification.

Stratification in Al and Cu foils exploded in vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baksht, R. B.; Electrical Discharge and Plasma Laboratory, Tel Aviv University, Tel Aviv 6997801; Rousskikh, A. G.

2015-10-15

An experiment with exploding foils was carried out at a current density of 0.7 × 10{sup 8} A/cm{sup 2} through the foil with a current density rise rate of about 10{sup 15} A/cm{sup 2} s. To record the strata arising during the foil explosions, a two-frame radiographic system was used that allowed tracing the dynamics of strata formation within one shot. The original striation wavelength was 20–26 μm. It was observed that as the energy deposition to a foil stopped, the striation wavelength increased at a rate of ∼(5–9) × 10{sup 3} cm/s. It is supposed that the most probable reason for the stratification is the thermal instabilitymore » that develops due to an increase in the resistivity of the metal with temperature.« less

Changes in oxidative patterns during dormancy break by warm and cold stratification in seeds of an edible fruit tree.

PubMed

Shalimu, Dilinuer; Sun, Jia; Baskin, Carol C; Baskin, Jerry M; Sun, Liwei; Liu, Yujun

2016-01-01

The transition from seed dormancy to germination is triggered by environmental factors, and in pomegranate (Punica granatum) seeds higher germination percentages are achieved by warm + cold stratification rather than by cold stratification alone. Our objective was to define the pattern of internal oxidative changes in pomegranate seeds as dormancy was being broken by warm + cold stratification and by cold stratification alone. Embryos isolated from seeds after 1-42 days of warm stratification, after 56 days of warm stratification + 7, 28 or 56 days of cold stratification, and after 1-84 days of cold stratification alone, were used in biochemical tests. Hydrogen peroxide (H2O2), nitric oxide (NO), proline, lipid peroxidation, protein carbonylation, and activities of the scavenging enzymes superoxide dismutase (SOD), hydrogen peroxide enzyme and peroxidase in the embryos were assessed by colorimetric methods. Our results indicated that warm + cold stratification had a stronger dormancy-breaking effect than cold stratification (85% versus 50% germination), which may be attributed to a higher yield of H2O2, NO, lipid peroxidation and protein carbonylation in warm + cold stratification. Furthermore, warm + cold stratification-induced H2O2 change led to greater changes (elevation followed by attenuation) in activities of the scavenging enzymes than that induced by cold stratification alone. These results indicated that restriction of the level of reactive oxygen species change within a positive and safe range by such enzymes promoted seed germination. In addition, a relatively strong elevation of proline during warm + cold stratification also contributed to dormancy breakage and subsequent germination. In conclusion, the strong dormancy alleviating effect of warm + cold stratification on pomegranate seeds may be attributed to the corresponding active oxidative change via H2O2, NO, proline, malondialdehyde, protein carbonylation and scavenging enzymes. Published by Oxford University Press on behalf of the Annals of Botany Company.

Changes in oxidative patterns during dormancy break by warm and cold stratification in seeds of an edible fruit tree

PubMed Central

Shalimu, Dilinuer; Sun, Jia; Baskin, Carol C.; Baskin, Jerry M.; Sun, Liwei; Liu, Yujun

2016-01-01

The transition from seed dormancy to germination is triggered by environmental factors, and in pomegranate (Punica granatum) seeds higher germination percentages are achieved by warm + cold stratification rather than by cold stratification alone. Our objective was to define the pattern of internal oxidative changes in pomegranate seeds as dormancy was being broken by warm + cold stratification and by cold stratification alone. Embryos isolated from seeds after 1–42 days of warm stratification, after 56 days of warm stratification + 7, 28 or 56 days of cold stratification, and after 1–84 days of cold stratification alone, were used in biochemical tests. Hydrogen peroxide (H2O2), nitric oxide (NO), proline, lipid peroxidation, protein carbonylation, and activities of the scavenging enzymes superoxide dismutase (SOD), hydrogen peroxide enzyme and peroxidase in the embryos were assessed by colorimetric methods. Our results indicated that warm + cold stratification had a stronger dormancy-breaking effect than cold stratification (85% versus 50% germination), which may be attributed to a higher yield of H2O2, NO, lipid peroxidation and protein carbonylation in warm + cold stratification. Furthermore, warm + cold stratification-induced H2O2 change led to greater changes (elevation followed by attenuation) in activities of the scavenging enzymes than that induced by cold stratification alone. These results indicated that restriction of the level of reactive oxygen species change within a positive and safe range by such enzymes promoted seed germination. In addition, a relatively strong elevation of proline during warm + cold stratification also contributed to dormancy breakage and subsequent germination. In conclusion, the strong dormancy alleviating effect of warm + cold stratification on pomegranate seeds may be attributed to the corresponding active oxidative change via H2O2, NO, proline, malondialdehyde, protein carbonylation and scavenging enzymes. PMID:27154624

Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake

NASA Astrophysics Data System (ADS)

Yang, Yichen; Wang, Yongwei; Zhang, Zhen; Wang, Wei; Ren, Xia; Gao, Yaqi; Liu, Shoudong; Lee, Xuhui

2018-04-01

Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here, the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient, the maximum of which exceeds 5°C m-1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s-1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer.

Quantitative description of the effect of stratification on dormancy release of grape seeds in response to various temperatures and water contents

PubMed Central

Wang, W. Q.; Song, S. Q.; Li, S. H.; Gan, Y. Y.; Wu, J. H.; Cheng, H. Y.

2009-01-01

The effect of stratification on dormancy release of grape seeds crossing from the sub- to the supraoptimal range of temperatures and water contents was analysed by modified threshold models. The stratification impacted on dormancy release in three different ways: (i) dormancy was consistently released with prolonged stratification time when stratified at temperatures of <15 °C; (ii) at 15 °C and 20 °C, the stratification effect initially increased, and then decreased with extended time; and (iii) stratification at 25 °C only reduced germinable seeds. These behaviours indicated that stratification could not only release primary dormancy but also induce secondary dormancy in grape seed. The rate of dormancy release changed linearly in two phases, while induction increased exponentially with increasing temperature. The thermal time approaches effectively quantified dormancy release only at suboptimal temperature, but a quantitative method to integrate the occurrence of dormancy release and induction at the same time could describe it well at either sub- or supraoptimal temperatures. The regression with the percentage of germinable seeds versus stratification temperature or water content within both the sub- and supraoptimal range revealed how the optimal temperature (Tso) and water content (Wso) for stratification changed. The Tso moved from 10.6 °C to 5.3 °C with prolonged time, while Wso declined from >0.40 g H2O g DW−1 at 5 °C to ∼0.23 g H2O g DW−1 at 30 °C. Dormancy release in grape seeds can occur across a very wide range of conditions, which has important implications for their ability to adapt to a changeable environment in the wild. PMID:19491305

Response of water temperatures and stratification to changing climate in three lakes with different morphometry

NASA Astrophysics Data System (ADS)

Magee, Madeline R.; Wu, Chin H.

2017-12-01

Water temperatures and stratification are important drivers for ecological and water quality processes within lake systems, and changes in these with increases in air temperature and changes to wind speeds may have significant ecological consequences. To properly manage these systems under changing climate, it is important to understand the effects of increasing air temperatures and wind speed changes in lakes of different depths and surface areas. In this study, we simulate three lakes that vary in depth and surface area to elucidate the effects of the observed increasing air temperatures and decreasing wind speeds on lake thermal variables (water temperature, stratification dates, strength of stratification, and surface heat fluxes) over a century (1911-2014). For all three lakes, simulations showed that epilimnetic temperatures increased, hypolimnetic temperatures decreased, the length of the stratified season increased due to earlier stratification onset and later fall overturn, stability increased, and longwave and sensible heat fluxes at the surface increased. Overall, lake depth influences the presence of stratification, Schmidt stability, and differences in surface heat flux, while lake surface area influences differences in hypolimnion temperature, hypolimnetic heating, variability of Schmidt stability, and stratification onset and fall overturn dates. Larger surface area lakes have greater wind mixing due to increased surface momentum. Climate perturbations indicate that our larger study lakes have more variability in temperature and stratification variables than the smaller lakes, and this variability increases with larger wind speeds. For all study lakes, Pearson correlations and climate perturbation scenarios indicate that wind speed has a large effect on temperature and stratification variables, sometimes greater than changes in air temperature, and wind can act to either amplify or mitigate the effect of warmer air temperatures on lake thermal structure depending on the direction of local wind speed changes.

Salt tracer experiments in wetland ponds: will density stratification spoil the outcome?

NASA Astrophysics Data System (ADS)

Schmid, Bernhard H.; Hengl, Michael A.

2017-04-01

Wetland ponds are among the treatment options for peatland flows prior to their discharge into a receiving ambient water course or water body. The removal efficiency and effectiveness of wetland ponds (free water surface or FWS wetlands) is considered to be strongly related to the residence time or travel time distribution in the pond, with a narrow distribution (close to plug flow) being preferable to a wider one. This travel time distribution is, in turn, reflected by a breakthrough curve of an ideal tracer injected instantaneously into the flow (entering the wetland). As the term 'ideal tracer' suggests, such a substance, in real world cases, does not exist and can, at best, be approximated by a real tracer. Among the tracer groups in most widespread use, salt has the advantage of low cost, straightforward detection and analysis as well as low related environmental risk. In contrast, use of radioactive artificial tracers may meet with resistance from authorities and public, and fluorescent dyes are not necessarily devoid of problems, either (as recently discovered, there are two structural isomers of Rhodamin WT, the mixture of which may compromise the validity of breakthrough data analyses). From previous work by the authors it is known that density stratification may result from the injection of a salt tracer into a low Reynolds number free surface flow, which is a frequent characteristic of wetland ponds. As the formation of density layers in the course of a tracer experiment is highly undesirable, it may be useful to judge prior to beginning of the field work, if stratification is to be expected (and the experimental design should, consequently, be adapted suitably). The current work reported here employs an energy argument to extend existing criteria for density stratification in turbulent free surface flows. Vertical mixing is assumed to be sustained by a fraction of the frictional energy loss (expressed by Manning's law, but this can easily be adapted to other friction laws such as Darcy-Weisbach's). Experimental data obtained by the authors in the course of the PRIMROSE project (Contract no. EVK1-CT-2000-00065) were used to calibrate the criterion with respect to the actual percentage of the friction loss that fuels the vertical mixing. The distance x (m) needed for (full) vertical mixing of the salt tracer (NaCl or KBr) is finally derived as: C0 ṡ(0.802- 0.002ṡTw) ṡh R4h/3 x =----0.0694-ṡρw----ṡ(n-ṡu)2 (1) with C = -M0-- 0 Q ṡΔt0 (2) and M0 the tracer mass (g), Q the flow rate (m3/s), Δt0 the injection pulse duration (s), Rh (m) the hydraulic radius (= flow cross-sectional area divided by wetted perimeter), Tw the water temperature (˚ C), ρw water mass density (g/m3), Manning's n in SI-units (s/m1/3) and cross-sectionally averaged flow velocity u (m/s). Tracer concentration C0, as obtained from Eq.(2), is to be expressed in mg/l or g/m3 for use in Eq.(1).

Stratification and salt-wedge in the Seomjin river estuary under the idealized tidal influence

NASA Astrophysics Data System (ADS)

Hwang, Jin Hwan; Jang, Dongmin; Kim, Yong Hoon

2017-12-01

Advection, straining, and vertical mixing play primary roles in the process of estuarine stratification. Estuaries can be classified as salt-wedge, partially-mixed or well-mixed depending on the vertical density structure determined by the balancing of advection, mixing and straining. In particular, straining plays a major role in the stratification of the estuarine water body along the estuarine channel. Also, the behavior of a salt wedge with a halocline shape in a stratified channel can be controlled by the competition between straining and mixing induced by buoyancy from the riverine source and tidal forcing. The present study uses Finite Volume Coastal Ocean Model (FVCOM) to show that straining and vertical mixing play major roles in controlling along-channel flow and stratification structures in the Seomjin river estuary (SRE) under idealized conditions. The Potential Energy Anomaly (PEA) dynamic equation quantifies the governing processes thereby enabling the determination of the stratification type. By comparing terms in the equation, we examined how the relative strengths of straining and mixing alter the stratification types in the SRE due to changes in river discharge and the depth resulting from dredging activities. SRE under idealized tidal forcing tends to be partially-mixed based on an analysis of the balance between terms and the vertical structure of salinity, and the morphological and hydrological change in SRE results in the shift of stratification type. While the depth affects the mixing, the freshwater discharge mainly controls the straining, and the balance between mixing and straining determines the final state of the stratification in an estuarine channel. As a result, the development and location of a salt wedge along the channel in a partially mixed and highly stratified condition is also determined by the ratio of straining to mixing. Finally, our findings confirm that the contributions of mixing and straining can be assessed by using the conventional non-dimensional parameters with respect to salt-wedge behavior.

Saturn Dynamo Model (Invited)

NASA Astrophysics Data System (ADS)

Glatzmaier, G. A.

2010-12-01

There has been considerable interest during the past few years about the banded zonal winds and global magnetic field on Saturn (and Jupiter). Questions regarding the depth to which the intense winds extend below the surface and the role they play in maintaining the dynamo continue to be debated. The types of computer models employed to address these questions fall into two main classes: general circulation models (GCMs) based on hydrostatic shallow-water assumptions from the atmospheric and ocean modeling communities and global non-hydrostatic deep convection models from the geodynamo and solar dynamo communities. The latter class can be further divided into Boussinesq models, which do not account for density stratification, and anelastic models, which do. Recent efforts to convert GCMs to deep circulation anelastic models have succeeded in producing fluid flows similar to those obtained from the original deep convection anelastic models. We describe results from one of the original anelastic convective dynamo simulations and compare them to a recent anelastic dynamo benchmark for giant gas planets. This benchmark is based on a polytropic reference state that spans five density scale heights with a radius and rotation rate similar to those of our solar system gas giants. The resulting magnetic Reynolds number is about 3000. Better spatial resolution will be required to produce more realistic predictions that capture the effects of both the density and electrical conductivity stratifications and include enough of the turbulent kinetic energy spectrum. Important additional physics may also be needed in the models. However, the basic models used in all simulation studies of the global dynamics of giant planets will hopefully first be validated by doing these simpler benchmarks.

Retinal ganglion cells in the eastern newt Notophthalmus viridescens: topography, morphology, and diversity.

PubMed

Pushchin, Igor I; Karetin, Yuriy A

2009-10-20

The topography and morphology of retinal ganglion cells (RGCs) in the eastern newt were studied. Cells were retrogradely labeled with tetramethylrhodamine-conjugated dextran amines or horseradish peroxidase and examined in retinal wholemounts. Their total number was 18,025 +/- 3,602 (mean +/- SEM). The spatial density of RGCs varied from 2,100 cells/mm(2) in the retinal periphery to 4,500 cells/mm(2) in the dorsotemporal retina. No prominent retinal specializations were found. The spatial resolution estimated from the spatial density of RGCs varied from 1.4 cycles per degree in the periphery to 1.95 cycles per degree in the region of the peak RGC density. A sample of 68 cells was camera lucida drawn and subjected to quantitative analysis. A total of 21 parameters related to RGC morphology and stratification in the retina were estimated. Partitionings obtained by using different clustering algorithms combined with automatic variable weighting and dimensionality reduction techniques were compared, and an effective solution was found by using silhouette analysis. A total of seven clusters were identified and associated with potential cell types. Kruskal-Wallis ANOVA-on-Ranks with post hoc Mann-Whitney U tests showed significant pairwise between-cluster differences in one or more of the clustering variables. The average silhouette values of the clusters were reasonably high, ranging from 0.52 to 0.79. Cells assigned to the same cluster displayed similar morphology and stratification in the retina. The advantages and limitations of the methodology adopted are discussed. The present classification is compared with known morphological and physiological RGC classifications in other salamanders.

Turbulence in Supercritical O2/H2 and C7H16/N2 Mixing Layers

NASA Technical Reports Server (NTRS)

Bellan, Josette; Harstad, Kenneth; Okong'o, Nora

2003-01-01

This report presents a study of numerical simulations of mixing layers developing between opposing flows of paired fluids under supercritical conditions, the purpose of the study being to elucidate chemical-species-specific aspects of turbulence. The simulations were performed for two different fluid pairs O2/H2 and C7H16/N2 at similar reduced initial pressures (reduced pressure is defined as pressure divided by critical pressure). Thermodynamically, O2/H2 behaves more nearly like an ideal mixture and has greater solubility, relative to C7H16/N2, which departs strongly from ideality. Because of a specified smaller initial density stratification, the C7H16/N2 layers exhibited greater levels of growth, global molecular mixing, and turbulence. However, smaller density gradients at the transitional state for the O2/H2 system were interpreted as indicating that locally, this system exhibits enhanced mixing as a consequence of its greater solubility and closer approach to ideality. These thermodynamic features were shown to affect entropy dissipation, which was found to be larger for O2/H2 and concentrated in high-density-gradient-magnitude regions that are distortions of the initial density-stratification boundary. In C7H16/N2, the regions of largest dissipation were found to lie in high-density-gradient-magnitude regions that result from mixing of the two fluids.

Stratification at the Earth's largest hyperacidic lake and its consequences

NASA Astrophysics Data System (ADS)

Caudron, Corentin; Campion, Robin; Rouwet, Dmitri; Lecocq, Thomas; Capaccioni, Bruno; Syahbana, Devy; Suparjan; Purwanto, Bambang Heri; Bernard, Alain

2017-02-01

Volcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases. Volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions. If acidic and hot, these lakes are usually considered to be too convective to allow any stratification within their waters. Kawah Ijen volcano, featuring the largest hyperacidic lake on Earth (volume of 27 million m3), is less homogeneous than previously thought. Hourly temperature measurements reveal the development of a stagnant layer of cold waters (<30 °C), overlying warmer and denser water (generally above 30 °C and density ∼1.083 kg/m3). Examination of 20 yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons. The yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn, i.e. limnic eruption, and a resonance of the lake, i.e. a seiche, highlighting a new hazard for these extreme reservoirs. A minor non-volcanic event, such as a heavy rainfall or an earthquake, may act as a trigger. The density driven overturn requires specific salinity-temperature conditions for the colder and less saline top water layer to sink into the hot saline water. Spectacular degassing occurs when the dissolved gases, progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer, are suddenly released. These findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups.

The feasibility of thermal and compositional convection in Earth's inner core

NASA Astrophysics Data System (ADS)

Lythgoe, Karen H.; Rudge, John F.; Neufeld, Jerome A.; Deuss, Arwen

2015-05-01

Inner core convection, and the corresponding variations in grain size and alignment, has been proposed to explain the complex seismic structure of the inner core, including its anisotropy, lateral variations and the F-layer at the base of the outer core. We develop a parametrized convection model to investigate the possibility of convection in the inner core, focusing on the dominance of the plume mode of convection versus the translation mode. We investigate thermal and compositional convection separately so as to study the end-members of the system. In the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core, the magnitude of which is poorly constrained. Furthermore recent estimates of a large core thermal conductivity result in stable thermal stratification, hindering convection. However, an unstable density stratification may arise due to the pressure dependant partition coefficient of certain light elements. We show that this unstable stratification leads to compositionally driven convection, and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity. The style of convection resulting from a combination of both thermal and compositional effects is not easy to understand. For reasonable parameter estimates, the stabilizing thermal buoyancy is greater than the destabilizing compositional buoyancy. However we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities.

The Feasibility of Thermal and Compositional Convection in Earth's Inner Core

NASA Astrophysics Data System (ADS)

Lythgoe, K.; Rudge, J. F.; Neufeld, J. A.; Deuss, A. F.

2014-12-01

Inner core convection, and the corresponding variations in grain size and alignment, has been proposed to explain the complex seismic structure of the inner core, including its anisotropy, lateral variations and the F-layer at the base of the outer core. We develop a parameterised convection model to investigate the possibility of convection in the inner core, focusing on the dominance of the plume mode of convection versus the translation mode. We investigate thermal and compositional convection separately so as to study the end-members of the system. In the thermal case the dominant mode of convection is strongly dependent on the viscosity of the inner core, the magnitude of which is poorly constrained. Furthermore recent estimates of a large core thermal conductivity result in stable thermal stratification, hindering convection. However, an unstable density stratification may arise due to the pressure dependant partition coefficient of certain light elements. We show that this unstable stratification leads to compositionally driven convection, and that inner core translation is likely to be the dominant convective mode due to the low compositional diffusivity. The style of convection resulting from a combination of both thermal and compositional effects is not easy to understand. The stabilising thermal buoyancy is greater than the destabilising compositional buoyancy, however we anticipate complex double diffusive processes to occur given the very different thermal and compositional diffusivities and more work is needed to understand these processes.

Impacts of backwashing on granular activated carbon filters for advanced wastewater treatment.

PubMed

Frank, Joshua; Ruhl, Aki Sebastian; Jekel, Martin

2015-12-15

The use of granular activated carbon (GAC) in fixed bed filters is a promising option for the removal of organic micropollutants (OMP) from wastewater treatment plant effluents. Frequent backwashing of the filter bed is inevitable, but its effect on potential filter stratification is not well understood yet and thus has been evaluated in the present study for two commercial GAC products. Backwashing of GAC filters was simulated with 10 or 100 filter bed expansions of 20 or 100% at backwash velocities of 12 and 40 m/h, respectively. Five vertical fractions were extracted and revealed a vertical stratification according to grain sizes and material densities. Sieve analyses indicated increasing grain sizes towards the bottom for one GAC while grain sizes of the other GAC were more homogeneously distributed throughout the filter bed. The apparent densities of the top sections were significantly lower than that of the bottom sections of both products. Comparative long term fixed bed adsorption experiments with the top and bottom sections of the stratified GAC showed remarkable differences in breakthrough curves of dissolved organic carbon, UV light absorption at 254 nm wavelength (UVA254) and OMP. GAC from the upper section showed constantly better removal efficiencies than GAC from the bottom section, especially for weakly adsorbing OMP such as sulfamethoxazole. Furthermore correlations between UVA254 reductions and OMP removals were found. Copyright © 2015 Elsevier Ltd. All rights reserved.

Turbidity Currents In The Ocean; Are They Stably Stratified?

NASA Astrophysics Data System (ADS)

Kneller, B. C.; Nasr-Azadani, M.; Meiburg, E. H.

2013-12-01

A large proportion of the sediment generated by erosion of the continents is ultimately delivered to the deep ocean to form submarine fans, being carried to the margins of these fans by turbidity currents that flow through submarine channels that may be hundreds or even thousands of kilometers long. The persistence of these flows over extremely long distances with gradients that may be 10-4 or less, while maintaining sediment as coarse as fine-grained sand in suspension, is enigmatic, given the drag that one would expect to be experienced by such flows, and the effects of progressive dilution by entrainment of ambient seawater. The commonly-held view of the flow structure of turbidity currents, based on many laboratory and numerical simulations and rare observations in the ocean, is that of a vertical profile of time-averaged horizontal velocity with a maximum value close the bed, largely due to much higher drag on the upper boundary than on the lower. This upper boundary drag is related to Kelvin-Helmholtz (K-H) instabilities generated by shear between the current and the ambient seawater. K-H instabilities result when fluid shear dominates over density stratification within the turbidity current; the dimensionless ratio of these two influences is the gradient Richardson number. When this exceeds a value of 0.25 the stratification is stable, and no K-H instabilities will form, eliminating much of the drag and entrainment. The majority of the entrainment of ambient seawater into the turbidity current also occurs via the K-H instabilities. Analysis by Birman et al. (2009) suggests that there may be little or no entrainment of ambient fluid in turbidity currents flowing over low gradients, implying that K-H instabilities may be absent under these conditions. We examine the case of flows on the extremely low gradients of the ocean floor, and suggest some conditions that may lead to stably-stratified currents, with dramatically reduced drag, and a fundamentally different mean and turbulent velocity structure. We report preliminary results of direct numerical simulations that may help to constrain the conditions under which such currents may form. In order to model accurately the potentially stabilizing effect of significant density gradients within such currents, it may be useful to abandon the Boussinesq approximation (under which density variations appear only in the buoyancy term), and explicitly model the influence of density variations. Experiments reported by Sequeiros at al. (2010) show the type of velocity profiles expected in flows without K-H instabilities, which they relate to Froude-subcritical flow. We suggest that the presence of stable density stratification is far more representative of the structure of turbidity currents in long fan channels than are the more familiar profiles commonly reported. Birman, V.K., Meiburg, E. & Kneller, B., 2009. J. Fluid Mech., 619, 367-376. Sequeiros, O. E.; Spinewine, B., Beaubouef, R.T., Sun, T. García, M.H. & Parker, G. 2010. J. Hydr. Eng, 136, 412-433

The Effect of Barotropic and Baroclinic Tides on Coastal Stratification and Mixing

NASA Astrophysics Data System (ADS)

Suanda, S. H.; Feddersen, F.; Kumar, N.

2017-12-01

The effects of barotropic and baroclinic tides on subtidal stratification and vertical mixing are examined with high-resolution, three-dimensional numerical simulations of the Central Californian coastal upwelling region. A base simulation with realistic atmospheric and regional-scale boundary forcing but no tides (NT) is compared to two simulations with the addition of predominantly barotropic local tides (LT) and with combined barotropic and remotely generated, baroclinic tides (WT) with ≈ 100 W m-1 onshore baroclinic energy flux. During a 10 day period of coastal upwelling when the domain volume-averaged temperature is similar in all three simulations, LT has little difference in subtidal temperature and stratification compared to NT. In contrast, the addition of remote baroclinic tides (WT) reduces the subtidal continental shelf stratification up to 50% relative to NT. Idealized simulations to isolate barotropic and baroclinic effects demonstrate that within a parameter space of typical U.S. West Coast continental shelf slopes, barotropic tidal currents, incident energy flux, and subtidal stratification, the dissipating baroclinic tide destroys stratification an order of magnitude faster than barotropic tides. In WT, the modeled vertical temperature diffusivity at the top (base) of the bottom (surface) boundary layer is increased up to 20 times relative to NT. Therefore, the width of the inner-shelf (region of surface and bottom boundary layer overlap) is increased approximately 4 times relative to NT. The change in stratification due to dissipating baroclinic tides is comparable to the magnitude of the observed seasonal cycle of stratification.

Improved Phase Corrections for Transoceanic Tsunami Data in Spatial and Temporal Source Estimation: Application to the 2011 Tohoku Earthquake

NASA Astrophysics Data System (ADS)

Ho, Tung-Cheng; Satake, Kenji; Watada, Shingo

2017-12-01

Systemic travel time delays of up to 15 min relative to the linear long waves for transoceanic tsunamis have been reported. A phase correction method, which converts the linear long waves into dispersive waves, was previously proposed to consider seawater compressibility, the elasticity of the Earth, and gravitational potential change associated with tsunami motion. In the present study, we improved this method by incorporating the effects of ocean density stratification, actual tsunami raypath, and actual bathymetry. The previously considered effects amounted to approximately 74% for correction of the travel time delay, while the ocean density stratification, actual raypath, and actual bathymetry, contributed to approximately 13%, 4%, and 9% on average, respectively. The improved phase correction method accounted for almost all the travel time delay at far-field stations. We performed single and multiple time window inversions for the 2011 Tohoku tsunami using the far-field data (>3 h travel time) to investigate the initial sea surface displacement. The inversion result from only far-field data was similar to but smoother than that from near-field data and all stations, including a large sea surface rise increasing toward the trench followed by a migration northward along the trench. For the forward simulation, our results showed good agreement between the observed and computed waveforms at both near-field and far-field tsunami gauges, as well as with satellite altimeter data. The present study demonstrates that the improved method provides a more accurate estimate for the waveform inversion and forward prediction of far-field data.

Understanding PSA and its derivatives in prediction of tumor volume: Addressing health disparities in prostate cancer risk stratification.

PubMed

Chinea, Felix M; Lyapichev, Kirill; Epstein, Jonathan I; Kwon, Deukwoo; Smith, Paul Taylor; Pollack, Alan; Cote, Richard J; Kryvenko, Oleksandr N

2017-03-28

To address health disparities in risk stratification of U.S. Hispanic/Latino men by characterizing influences of prostate weight, body mass index, and race/ethnicity on the correlation of PSA derivatives with Gleason score 6 (Grade Group 1) tumor volume in a diverse cohort. Using published PSA density and PSA mass density cutoff values, men with higher body mass indices and prostate weights were less likely to have a tumor volume <0.5 cm3. Variability across race/ethnicity was found in the univariable analysis for all PSA derivatives when predicting for tumor volume. In receiver operator characteristic analysis, area under the curve values for all PSA derivatives varied across race/ethnicity with lower optimal cutoff values for Hispanic/Latino (PSA=2.79, PSA density=0.06, PSA mass=0.37, PSA mass density=0.011) and Non-Hispanic Black (PSA=3.75, PSA density=0.07, PSA mass=0.46, PSA mass density=0.008) compared to Non-Hispanic White men (PSA=4.20, PSA density=0.11 PSA mass=0.53, PSA mass density=0.014). We retrospectively analyzed 589 patients with low-risk prostate cancer at radical prostatectomy. Pre-operative PSA, patient height, body weight, and prostate weight were used to calculate all PSA derivatives. Receiver operating characteristic curves were constructed for each PSA derivative per racial/ethnic group to establish optimal cutoff values predicting for tumor volume ≥0.5 cm3. Increasing prostate weight and body mass index negatively influence PSA derivatives for predicting tumor volume. PSA derivatives' ability to predict tumor volume varies significantly across race/ethnicity. Hispanic/Latino and Non-Hispanic Black men have lower optimal cutoff values for all PSA derivatives, which may impact risk assessment for prostate cancer.

Vertical patterns of ichthyoplankton at the interface between a temperate estuary and adjacent coastal waters: Seasonal relation to diel and tidal cycles

NASA Astrophysics Data System (ADS)

Primo, Ana Lígia; Azeiteiro, Ulisses M.; Marques, Sónia C.; Ré, Pedro; Pardal, Miguel A.

2012-07-01

Vertical distribution and migration pattern of ichthyoplankton assemblage in the Mondego estuary were investigated in relation to diel and tidal cycle. Summer and winter communities were sampled, at surface and bottom, over a diel cycle during spring and neap tides at a fixed station at the mouth of the estuary. Summer presented higher larvae density mainly of Pomatoschistus spp., Gobius niger and Parablennius pilicornis. Main species in winter assemblages were Pomatoschistus spp. and Sardina pilchardus. There were no differences between depth stratums across diel or tide cycle. Nevertheless, main species larval densities showed significant periodic variation associated with tide (M2) and diel (K1) cycles presenting generally, higher density at night and around low tide. Conversely, vertical patterns observed could not be related with diel or tidal cycle. Tough, main species presented some extent of vertical migration. Vertical patterns observed appear to be related to seasonal stratification and river flow, increasing amplitude during periods of less stratification and lower water currents. Present study provides a better understanding of ichthyoplankton vertical movement patterns and of small scale dynamics at the interface of two coastal European systems.

Simulation of Layered Magma Chambers.

ERIC Educational Resources Information Center

Cawthorn, Richard Grant

1991-01-01

The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

A new class of g-modes in neutron stars

NASA Technical Reports Server (NTRS)

Reisenegger, Andreas; Goldreich, Peter

1992-01-01

Because a neutron star is born hot, its internal composition is close to chemical equilibrium. In the fluid core, this implies that the ratio of the number densities of charged particles (protons and electrons) to neutrons is an increasing function of the mass density. This composition gradient stably stratifies the matter giving rise to a Brunt-Vaisala frequency N of about 500/s. Consequently, a neutron star core provides a cavity that supports gravity modes (g-modes). These g-modes are distinct from those previously identified with the thermal stratification of the surface layers and the chemical stratification of the crust. We compute the lowest-order, quadrupolar, g-modes for cold, Newtonian, neutron star models with M/solar M = 0.581 and M/solar M = 1.405, and show that the crustal and core g-modes have similar periods. We also discuss damping mechanisms and estimate damping rates for the core g-modes. Particular attention is paid to damping due to the emission of gravitational radiation.

Near-critical density filling of the SF6 fluid cell for the ALI-R-DECLIC experiment in weightlessness

NASA Astrophysics Data System (ADS)

Lecoutre, C.; Marre, S.; Garrabos, Y.; Beysens, D.; Hahn, I.

2018-05-01

Analyses of ground-based experiments on near-critical fluids to precisely determine their density can be hampered by several effects, especially the density stratification of the sample, the liquid wetting behavior at the cell walls, and a possible singular curvature of the "rectilinear" diameter of the density coexisting curve. For the latter effect, theoretical efforts have been made to understand the amplitude and shape of the critical hook of the density diameter, which depart from predictions from the so-called ideal lattice-gas model of the uniaxial 3D-Ising universality class. In order to optimize the observation of these subtle effects on the position and shape of the liquid-vapor meniscus in the particular case of SF6, we have designed and filled a cell that is highly symmetrized with respect to any median plane of the total fluid volume. In such a viewed quasi-perfect symmetrical fluid volume, the precise detection of the meniscus position and shape for different orientations of the cell with respect to the Earth's gravity acceleration field becomes a sensitive probe to estimate the cell mean density filling and to test the singular diameter effects. After integration of this cell in the ALI-R insert, we take benefit of the high optical and thermal performances of the DECLIC Engineering Model. Here we present the sensitive imaging method providing the precise ground-based SF6 benchmark data. From these data analysis it is found that the temperature dependence of the meniscus position does not reflect the expected critical hook in the rectilinear density diameter. Therefore the off-density criticality of the cell is accurately estimated, before near future experiments using the same ALI-R insert in the DECLIC facility already on-board the International Space Station.

Principal Stratification — Uses and Limitations

PubMed Central

VanderWeele, Tyler J

2011-01-01

Pearl (2011) asked for the causal inference community to clarify the role of the principal stratification framework in the analysis of causal effects. Here, I argue that the notion of principal stratification has shed light on problems of non-compliance, censoring-by-death, and the analysis of post-infection outcomes; that it may be of use in considering problems of surrogacy but further development is needed; that it is of some use in assessing “direct effects”; but that it is not the appropriate tool for assessing “mediation.” There is nothing within the principal stratification framework that corresponds to a measure of an “indirect” or “mediated” effect. PMID:21841939

A reconceptualization of age stratification in China.

PubMed

Yin, P; Lai, K H

1983-09-01

Using the concepts of age stratification theory--age effect, cohort effect, and subcohort differences--this paper provides a new perspective on age stratification in China. Currently, the literature suggests that the status of elderly people declined after the Communist Revolution and will further decline with modernization. We discuss the problems with this perspective and argue, instead, that the status of elderly adults did not decline for the majority of the aged during the Maoist years. Rather, the most important change in the age stratification system during the Maoist years was the change in the criterion of age stratification--from age differences to cohort and subcohort differences. Furthermore, the subcohort of elderly adults who suffered the most status decline during the Maoist years--the bourgeoisie--may actually enjoy an increase in status with the recent modernization impetus. Research suggestions from this new perspective are discussed.

Aspects of Supercritical Turbulence: Direct Numerical Simulation of O2/H2 and C7H16/N2 Temporal Mixing Layers

NASA Technical Reports Server (NTRS)

Bellan, J.; Okongo, N. A.; Harstad, K. G.; Hutt, John (Technical Monitor)

2002-01-01

Results from Direct Numerical Simulations of temporal, supercritical mixing layers for two species systems are analyzed to elucidate species-specific turbulence aspects. The two species systems, O2/H2 and C7HG16/N2, have different thermodynamic characteristics; thus, although the simulations are performed at similar reduced pressure (ratio of the pressure to the critical pressure), the former system is dose to mixture ideality and has a relatively high solubility with respect to the latter, which exhibits strong departures from mixture ideality Due to the specified, smaller initial density stratification, the C7H16/N2 layers display higher growth and increased global molecular mixing as well as larger turbulence levels. However, smaller density gradients at the transitional state for the O2/H2 system indicate that on a local basis, the layer exhibits an enhanced mixing, this being attributed to the increased solubility and to mixture ideality. These thermodynamic features are shown to affect the irreversible entropy production (i.e. the dissipation), which is larger for the O2/H2 layer and is primarily concentrated in high density-gradient magnitude regions that are distortions of the initial density stratification boundary. In contrast, the regions of largest dissipation in the C7H16/N2 layer are located in high density-gradient magnitude regions resulting from the mixing of the two fluids.

Principal Stratification — a Goal or a Tool?

PubMed Central

Pearl, Judea

2011-01-01

Principal stratification has recently become a popular tool to address certain causal inference questions, particularly in dealing with post-randomization factors in randomized trials. Here, we analyze the conceptual basis for this framework and invite response to clarify the value of principal stratification in estimating causal effects of interest. PMID:21556288

Marginal Mean Weighting through Stratification: Adjustment for Selection Bias in Multilevel Data

ERIC Educational Resources Information Center

Hong, Guanglei

2010-01-01

Defining causal effects as comparisons between marginal population means, this article introduces marginal mean weighting through stratification (MMW-S) to adjust for selection bias in multilevel educational data. The article formally shows the inherent connections among the MMW-S method, propensity score stratification, and…

[Physiological and biochemical changes of seeds of Coptis chinensis Franch. in stratification and the effect of ABA treatment].

PubMed

Li, X; Chen, Y; Zhan, J

1997-05-01

The seeds of Coptis chinensis need stratification to break dormancy. In this paper the changes of enzyme activities DNA contents and protein contents in stratification under refrigeration and outdoor temperature conditions, as well as the influence of ABA treatment were studied.

Flow resistance and suspended load in sand-bed rivers: Simplified stratification model

USGS Publications Warehouse

Wright, S.; Parker, G.

2004-01-01

New methods are presented for the prediction of the flow depth, grain-size specific near-bed concentration, and bed-material suspended sediment transport rate in sand-bed rivers. The salient improvements delineated here all relate to the need to modify existing formulations in order to encompass the full range of sand-bed rivers, and in particular large, low-slope sand-bed rivers. They can be summarized as follows: (1) the inclusion of density stratification effects in a simplified manner, which have been shown in the companion paper to be particularly relevant for large, low-slope, sand-bed rivers; (2) a new predictor for near-bed entrainment rate into suspension which extends a previous relation to the range of large, low-slope sand-bed rivers; and (3) a new predictor for form drag which again extends a previous relation to include large, low-slope sand-bed rivers. Finally, every attempt has been made to cast the relations in the simplest form possible, including the development of software, so that practicing engineers may easily use the methods. ?? ASCE.

Experimental study of mixing mechanisms in stably stratified Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Augier, Pierre; Caulfield, Colm-Cille; Dalziel, Stuart

2014-11-01

We consider experimentally the mechanisms of mixing in stably stratified Taylor-Couette (TC) flow in a TC apparatus for which both cylinders can rotate independently. In the case for which only the inner cylinder rotates, centrifugal instability rapidly splits an initially linear density profile into an array of thin nearly homogeneous layers. Shadowgraph, PIV and density profiles measured by a moving conductivity probe allow us to characterise this process and the resulting flow. In particular, we observe turbulent intrusions of mixed fluid propagating relatively slowly around the tank at the interfaces between the layers, leading to a time-dependent variation in the sharpness and turbulent activity at these interfaces, whose period scales with (but is much larger than) the rotation period. Interestingly, the turbulent intrusions are anti-correlated between adjacent interfaces leading to snake-skin-like patterns in the spatio-temporal diagrams of the density profiles. We also explore how the presence of a density stratification modifies end effects at the top and bottom of the cylinders, in both the presence and absence of primary centrifugal instability.

An Improved Model of Cryogenic Propellant Stratification in a Rotating, Reduced Gravity Environment

NASA Technical Reports Server (NTRS)

Oliveira, Justin; Kirk, Daniel R.; Schallhorn, Paul A.; Piquero, Jorge L.; Campbell, Mike; Chase, Sukhdeep

2007-01-01

This paper builds on a series of analytical literature models used to predict thermal stratification within rocket propellant tanks. The primary contribution to the literature is to add the effect of tank rotation and to demonstrate the influence of rotation on stratification times and temperatures. This work also looks levels of thermal stratification for generic propellant tanks (cylindrical shapes) over a parametric range of upper-stage coast times, heating levels, rotation rates, and gravity levels.

Adaptive scaling model of the main pycnocline and the associated overturning circulation

NASA Astrophysics Data System (ADS)

Fuckar, Neven-Stjepan

This thesis examines a number of crucial factors and processes that control the structure of the main pycnocline and the associated overturning circulation that maintains the ocean stratification. We construct an adaptive scaling model: a semi-empirical low-order theory based on the total transformation balance that linearly superimposes parameterized transformation rate terms of various mechanisms that participate in the water-mass conversion between the warm water sphere and the cold water sphere. The depth of the main pycnocline separates the light-water domain from the dense-water domain beneath the surface, hence we introduce a new definition in an integral form that is dynamically based on the large-scale potential vorticity (i.e., vertical density gradient is selected for the kernel function of the normalized vertical integral). We exclude the abyssal pycnocline from our consideration and limit our domain of interest to the top 2 km of water column. The goal is to understand the controlling mechanisms, and analytically predict and describe a wide spectrum of ocean steady states in terms of key large-scale indices relevant for understanding the ocean's role in climate. A devised polynomial equation uses the average depth of the main pycnocline as a single unknown (the key vertical scale of the upper ocean stratification) and gives us an estimate for the northern hemisphere deep water production and export across the equator from the parts of this equation. The adaptive scaling model aims to elucidate the roles of a limited number of dominant processes that determine some key upper ocean circulation and stratification properties. Additionally, we use a general circulation model in a series of simplified single-basin ocean configurations and surface forcing fields to confirm the usefulness of our analytical model and further clarify several aspects of the upper ocean structure. An idealized numerical setup, containing all the relevant physical and dynamical properties, is key to obtaining a clear understanding, uncomplicated by the effect of the real world geometry or intricacy of realistic surface radiative and turbulent fluxes. We show that wind-driven transformation processes can be decomposed into two terms separately driven by the mid-latitude westerlies and the low-latitude easterlies. Our analytical model smoothly connects all the classical limits describing different ocean regimes in a single-basin single-hemisphere geometry. The adjective "adaptive" refers to a simple and quantitatively successful adjustment to the description of a single-basin two-hemisphere ocean, with and without a circumpolar channel under the hemispherically symmetric surface buoyancy. For example, our water-mass conversion framework, unifying wind-driven and thermohaline processes, provides us with further insight into the "Drake Passage effect without Drake Passage". The modification of different transformation pathways in the Southern Hemisphere results in the equivalent net conversion changes. The introduction of hemispheric asymmetry in the surface density can lead to significant hemispheric differences in the main pycnocline structure. This demonstrates the limitations of our analytical model based on only one key vertical scale. Also, we show a strong influence of the northern hemisphere surface density change in high latitudes on the southern hemisphere stratification and circumpolar transport.

Propagation of 3D internal gravity wave beams in a slowly varying stratification

NASA Astrophysics Data System (ADS)

Fan, Boyu; Akylas, T. R.

2017-11-01

The time-mean flows induced by internal gravity wave beams (IGWB) with 3D variations have been shown to have dramatic implications for long-term IGWB dynamics. While uniform stratifications are convenient both theoretically and in the laboratory, stratifications in the ocean can vary by more than an order of magnitude over the ocean depth. Here, in view of this fact, we study the propagation of a 3D IGWB in a slowly varying stratification. We assume that the stratification varies slowly relative to the local variations in the wave profile. In the 2D case, the IGWB bends in response to the changing stratification, but nonlinear effects are minor even in the finite amplitude regime. For a 3D IGWB, in addition to bending, we find that nonlinearity results in the transfer of energy from waves to a large-scale time-mean flow associated with the mean potential vorticity, similar to IGWB behavior in a uniform stratification. In a weakly nonlinear setting, we derive coupled evolution equations that govern this process. We also use these equations to determine the stability properties of 2D IGWB to 3D perturbations. These findings indicate that 3D effects may be relevant and possibly fundamental to IGWB dynamics in nature. Supported by NSF Grant DMS-1512925.

Numerical modeling of flows and pollutant dispersion within and above urban street canyons under unstable thermal stratification by large-eddy simulation

NASA Astrophysics Data System (ADS)

Chan, Ming-Chung; Liu, Chun-Ho

2013-04-01

Recently, with the ever increasing urban areas in developing countries, the problem of air pollution due to vehicular exhaust arouses the concern of different groups of people. Understanding how different factors, such as urban morphology, meteorological conditions and human activities, affect the characteristics of street canyon ventilation, pollutant dispersion above urban areas and pollutant re-entrainment from the shear layer can help us improve air pollution control strategies. Among the factors mentioned above, thermal stratification is a significant one determining the pollutant transport behaviors in certain situation, e.g. when the urban surface is heated by strong solar radiation, which, however, is still not widely explored. The objective of this study is to gain an in-depth understanding of the effects of unstable thermal stratification on the flows and pollutant dispersion within and above urban street canyons through numerical modeling using large-eddy simulation (LES). In this study, LES equipped with one-equation subgrid-scale (SGS) model is employed to model the flows and pollutant dispersion within and above two-dimensional (2D) urban street canyons (flanked by idealized buildings, which are square solid bars in these models) under different intensities of unstable thermal stratifications. Three building-height-to-street-width (aspect) ratios, 0.5, 1 and 2, are included in this study as a representation of different building densities. The prevailing wind flow above the urban canopy is driven by background pressure gradient, which is perpendicular to the street axis, while the condition of unstable thermal stratification is induced by applying a higher uniform temperature on the no-slip urban surface. The relative importance between stratification and background wind is characterized by the Richardson number, with zero value as a neutral case and negative value as an unstable case. The buoyancy force is modeled by Boussinesq approximation and the intensity of stratification is controlled by the gravitational acceleration. The urban characteristic is modeled by periodic boundary conditions at the domain inlet-outlet and spanwise extent, so as to simulate the infinitely long and wide urban area. Pollutant dispersion is modeled by scalar transport with the pollutant area source on the ground of the first street canyon and by open boundary condition at the domain outlet. The numerical models are solved with incremental time steps until it reaches the pseudo steady-state. Afterwards, a set of data is collected for each model such that the temporal averages of mean and fluctuating field variables do not vary significantly if more time steps are included. It is found that the ventilation performance is improved and the plume dispersion in shear layer is enhanced when the stratification is more unstable. The mean flows, turbulent transports of pollutant and momentum, pollutant concentration fields in different unstable stratifications will be discussed with profile and contour plots. The ventilation performance of a street canyon evaluated by air exchange rate (ACH) and pollutant exchange rate (PCH) at roof level and the plume dispersion characterized by the mean plume height and dispersion coefficient in shear layer will also be discussed.

Quantitative spectroscopy of extreme helium stars Model atmospheres and a non-LTE abundance analysis of BD+10°2179

NASA Astrophysics Data System (ADS)

Kupfer, T.; Przybilla, N.; Heber, U.; Jeffery, C. S.; Behara, N. T.; Butler, K.

2017-10-01

Extreme helium stars (EHe stars) are hydrogen-deficient supergiants of spectral type A and B. They are believed to result from mergers in double degenerate systems. In this paper, we present a detailed quantitative non-LTE spectral analysis for BD+10°2179, a prototype of this rare class of stars, using UV-Visual Echelle Spectrograph and Fiber-fed Extended Range Optical Spectrograph spectra covering the range from ˜3100 to 10 000 Å. Atmosphere model computations were improved in two ways. First, since the UV metal line blanketing has a strong impact on the temperature-density stratification, we used the atlas12 code. Additionally, We tested atlas12 against the benchmark code sterne3, and found only small differences in the temperature and density stratifications, and good agreement with the spectral energy distributions. Secondly, 12 chemical species were treated in non-LTE. Pronounced non-LTE effects occur in individual spectral lines but, for the majority, the effects are moderate to small. The spectroscopic parameters give Teff =17 300±300 K and log g = 2.80±0.10, and an evolutionary mass of 0.55±0.05 M⊙. The star is thus slightly hotter, more compact and less massive than found in previous studies. The kinematic properties imply a thick-disc membership, which is consistent with the metallicity [Fe/H] ≈ -1 and α-enhancement. The refined light-element abundances are consistent with the white dwarf merger scenario. We further discuss the observed helium spectrum in an appendix, detecting dipole-allowed transitions from about 150 multiplets plus the most comprehensive set of known/predicted isolated forbidden components to date. Moreover, a so far unreported series of pronounced forbidden He I components is detected in the optical-UV.

Effects of storm runoff on the thermal regime and water quality of a deep, stratified reservoir in a temperate monsoon zone, in Northwest China.

PubMed

Huang, Tinglin; Li, Xuan; Rijnaarts, Huub; Grotenhuis, Tim; Ma, Weixing; Sun, Xin; Xu, Jinlan

2014-07-01

Jinpen Reservoir is a deep, stratified reservoir in Shaanxi province, located in a warm temperate zone of Northwest China. Influenced by a temperate monsoon climate, more than 60% of the annual precipitation is concentrated from late summer to autumn (July-September). In recent years, extreme rainfall events occurred more frequently and strongly affected the thermal structure, mixing layer depth and evolution of stratification of Jinpen Reservoir. The reservoir's inflow volume increased sharply after heavy rainfall during the flooding season. Large volumes of inflow induced mixing of stratified water zones in early autumn and disturbed the stratification significantly. A temporary positive effect of such disturbance was the oxygenation of the water close to the bottom of the reservoir, leading to inhibition of the release of nutrients from sediments, especially phosphate. However, the massive inflow induced by storm runoff with increased oxygen-consuming substances led to an increase of the oxygen consumption rate. After the bottom water became anaerobic again, the bottom water quality would deteriorate due to the release of pollutants from sediments. Heavy rainfall events could lead to very high nutrient input into the reservoir due to massive erosion from the surrounding uninhabited steep mountains, and the particulate matter contributed to most nutrient inputs. Reasonably releasing density flow is an effective way to reduce the amounts of particulate associated pollutants entering the reservoir. Significant turbid density flow always followed high rainfall events in Jinpen Reservoir, which not only affected the reservoir water quality but also increased costs of the drinking water treatment plant. Understanding the effects of the storm runoff on the vertical distributions of water quality indicators could help water managers to select the proper position of the intake for the water plant in order to avoid high turbidity outflow. Copyright © 2014 Elsevier B.V. All rights reserved.

Near-Surface Effects of Free Atmosphere Stratification in Free Convection

NASA Astrophysics Data System (ADS)

Mellado, Juan Pedro; van Heerwaarden, Chiel C.; Garcia, Jade Rachele

2016-04-01

The effect of a linear stratification in the free atmosphere on near-surface properties in a free convective boundary layer (CBL) is investigated by means of direct numerical simulation. We consider two regimes: a neutral stratification regime, which represents a CBL that grows into a residual layer, and a strong stratification regime, which represents the equilibrium (quasi-steady) entrainment regime. We find that the mean buoyancy varies as z^{-1/3}, in agreement with classical similarity theory. However, the root-mean-square (r.m.s.) of the buoyancy fluctuation and the r.m.s. of the vertical velocity vary as z^{-0.45} and ln z, respectively, both in disagreement with theory. These scaling laws are independent of the stratification regime, but the depth over which they are valid depends on the stratification. In the strong stratification regime, this depth is about 20 to 25 % of the CBL depth instead of the commonly used 10 %, which we only observe under neutral conditions. In both regimes, the near-surface flow structure can be interpreted as a hierarchy of circulations attached to the surface. Based on this structure, we define a new near-surface layer in free convection, the plume-merging layer, that is conceptually different from the constant-flux layer. The varying depth of the plume-merging layer depending on the stratification accounts for the varying depth of validity of the scaling laws. These findings imply that the buoyancy transfer law needed in mixed-layer and single-column models is well described by the classical similarity theory, independent of the stratification in the free atmosphere, even though other near-surface properties, such as the r.m.s. of the buoyancy fluctuation and the r.m.s. of the vertical velocity, are inconsistent with that theory.

A Basin-Wide Examination of the Arctic Ocean's Double-Diffusive Staircase

NASA Astrophysics Data System (ADS)

Shibley, N.; Timmermans, M. L.; Carpenter, J. R.; Toole, J. M.

2016-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure above the Atlantic Water Layer consisting of multiple mixed layers of order 1-m in height separated by sharp interfaces. This double-diffusive staircase structure is characterized across the entire Arctic Ocean through a detailed analysis of Ice-Tethered Profiler measurements acquired between 2004 and 2013. Staircase properties (mixed layer thicknesses and temperature-salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio for 50-m spanning the staircase stratification. It is shown that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (on the Eurasian side) and higher density ratio (on the Canadian side). We find that the diffusive staircase in the Eurasian Basin is characterized by fewer, thinner mixed layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin staircase mixed layers. Using a double-diffusive 4/3 flux law parameterization, the distribution of vertical heat fluxes through the staircase is estimated across the Arctic; it is found that heat fluxes in the Eurasian Basin [O(1) W/m^2] are generally an order of magnitude larger than those in the Canadian Basin [O(0.1) W/m^2].

Effect of Linkage Disequilibrium on the Identification of Functional Variants

PubMed Central

Thomas, Alun; Abel, Haley J; Di, Yanming; Faye, Laura L; Jin, Jing; Liu, Jin; Wu, Zheyan; Paterson, Andrew D

2011-01-01

We summarize the contributions of Group 9 of Genetic Analysis Workshop 17. This group addressed the problems of linkage disequilibrium and other longer range forms of allelic association when evaluating the effects of genotypes on phenotypes. Issues raised by long-range associations, whether a result of selection, stratification, possible technical errors, or chance, were less expected but proved to be important. Most contributors focused on regression methods of various types to illustrate problematic issues or to develop adaptations for dealing with high-density genotype assays. Study design was also considered, as was graphical modeling. Although no method emerged as uniformly successful, most succeeded in reducing false-positive results either by considering clusters of loci within genes or by applying smoothing metrics that required results from adjacent loci to be similar. Two unexpected results that questioned our assumptions of what is required to model linkage disequilibrium were observed. The first was that correlations between loci separated by large genetic distances can greatly inflate single-locus test statistics, and, whether the result of selection, stratification, possible technical errors, or chance, these correlations seem overabundant. The second unexpected result was that applying principal components analysis to genome-wide genotype data can apparently control not only for population structure but also for linkage disequilibrium. PMID:22128051

A probabilistic topic model for clinical risk stratification from electronic health records.

PubMed

Huang, Zhengxing; Dong, Wei; Duan, Huilong

2015-12-01

Risk stratification aims to provide physicians with the accurate assessment of a patient's clinical risk such that an individualized prevention or management strategy can be developed and delivered. Existing risk stratification techniques mainly focus on predicting the overall risk of an individual patient in a supervised manner, and, at the cohort level, often offer little insight beyond a flat score-based segmentation from the labeled clinical dataset. To this end, in this paper, we propose a new approach for risk stratification by exploring a large volume of electronic health records (EHRs) in an unsupervised fashion. Along this line, this paper proposes a novel probabilistic topic modeling framework called probabilistic risk stratification model (PRSM) based on Latent Dirichlet Allocation (LDA). The proposed PRSM recognizes a patient clinical state as a probabilistic combination of latent sub-profiles, and generates sub-profile-specific risk tiers of patients from their EHRs in a fully unsupervised fashion. The achieved stratification results can be easily recognized as high-, medium- and low-risk, respectively. In addition, we present an extension of PRSM, called weakly supervised PRSM (WS-PRSM) by incorporating minimum prior information into the model, in order to improve the risk stratification accuracy, and to make our models highly portable to risk stratification tasks of various diseases. We verify the effectiveness of the proposed approach on a clinical dataset containing 3463 coronary heart disease (CHD) patient instances. Both PRSM and WS-PRSM were compared with two established supervised risk stratification algorithms, i.e., logistic regression and support vector machine, and showed the effectiveness of our models in risk stratification of CHD in terms of the Area Under the receiver operating characteristic Curve (AUC) analysis. As well, in comparison with PRSM, WS-PRSM has over 2% performance gain, on the experimental dataset, demonstrating that incorporating risk scoring knowledge as prior information can improve the performance in risk stratification. Experimental results reveal that our models achieve competitive performance in risk stratification in comparison with existing supervised approaches. In addition, the unsupervised nature of our models makes them highly portable to the risk stratification tasks of various diseases. Moreover, patient sub-profiles and sub-profile-specific risk tiers generated by our models are coherent and informative, and provide significant potential to be explored for the further tasks, such as patient cohort analysis. We hypothesize that the proposed framework can readily meet the demand for risk stratification from a large volume of EHRs in an open-ended fashion. Copyright © 2015 Elsevier Inc. All rights reserved.

Experimental investigation on thermo-magnetic convection inside cavities.

PubMed

Gontijo, R G; Cunha, F R

2012-12-01

This paper presents experimental results on thermo-magnetic convection inside cavities. We examine the flow induced by convective currents inside a cavity with aspect ratio near the unity and the heat transfer rates measurements inside a thin cavity with aspect ratio equal to twelve. The convective unstable currents are formed when a magnetic suspension is subjected to a temperature gradient combined with a gradient of an externally imposed magnetic field. Under these conditions, stratifications in the suspension density and susceptibility are both important effects to the convective motion. We show a comparison between flow patterns of magnetic and gravitational convections. The impact of the presence of a magnetic field on the amount of heat extracted from the system when magnetic and gravitational effects are combined inside the test cell is evaluated. The convection state is largely affected by new instability modes produced by stratification in susceptibility. The experiments reveal that magnetic field enhances the instability in the convective flow leading to a more effective mixing and consequently to a more statistically homogenous temperature distribution inside the test cell. The experimental results allow the validation of the scaling law proposed in a previous theoretical work that has predicted that the Nusselt number scales with the magnetic Rayleigh number to the power of 1/3, in the limit in which magnetic force balances viscous force in the convective flow.

Reduction of MRI-targeted biopsies in men with low-risk prostate cancer on active surveillance by stratifying to PI-RADS and PSA-density, with different thresholds for significant disease.

PubMed

Schoots, Ivo G; Osses, Daniel F; Drost, Frank-Jan H; Verbeek, Jan F M; Remmers, Sebastiaan; van Leenders, Geert J L H; Bangma, Chris H; Roobol, Monique J

2018-02-01

The fear of undergrading prostate cancer (PCa) in men on active surveillance (AS) have led to strict criteria for monitoring, which have resulted in good long-term cancer-specific survival, proving the safety of this approach. Reducing undergrading, MRI-targeted biopsies are increasingly used in men with low-risk disease despite their undefined role yet. The objective of this study is to investigate the rate of upgrading using MRI-targeted biopsies in men with low-risk disease on AS, stratified on the basis of PI-RADS and PSA-density, with the aim to reduce potential unnecessary repeat biopsy procedures. A total of 331 men were prospectively enrolled following the MRI-PRIAS protocol. MR imaging was according to Prostate Imaging Reporting and Data System (PI-RADSv2) guidelines. Suspicious MRI lesions (PI-RADS 3-5) were additionally targeted by MRI-TRUS fusion biopsies. Outcome measure was upgrading to Gleason score (GS) ≥3+4 with MRI-targeted biopsies, stratified for PI-RADS and PSA-density. In total, 25% (82/331) of men on AS showed upgrading from GS 3+3. Only 3% (11/331) was upgraded to GS ≥8. In 60% (198/331) a suspicious MRI lesion was identified, but in only 41% (82/198) of men upgrading was confirmed. PI-RADS 3, 4 and 5 categorized index lesions, showed upgrading in 30%, 34% and 66% of men, respectively. Stratification to PI-RADS 4-5, instead of PI-RADS 3-5, would have missed a small number of high volume Gleason 4 PCa in PI-RADS 3 category. However, further stratification into PI-RADS 3 lesions and PSA-density <0.15 ng/mL 2 could result in a safe targeted biopsy reduction of 36% in this category, without missing any upgrades. Stratification with the combination of PI-RADS and PSA-density may reduce unnecessary additional MRI biopsy testing. Overall, the high rate of detected upgrading in men on AS may result in an unintended tightening of continuing in AS. Since patients, included under current AS criteria showed extremely favorable outcome, there might be no need to further restrict continuing on AS with MRI and targeted biopsies.

3D Numerical Simulation of Turbulent Buoyant Flow and Heat Transport in a Curved Open Channel

USDA-ARS?s Scientific Manuscript database

A three-dimensional buoyancy-extended version of kappa-epsilon turbulence model was developed for simulating the turbulent flow and heat transport in a curved open channel. The density- induced buoyant force was included in the model, and the influence of temperature stratification on flow field was...

Double hydrophilic block copolymer controlled growth and self-assembly of CaCO3 multilayered structures at the air/water interface.

PubMed

Gao, Yun-Xiang; Yu, Shu-Hong; Guo, Xiao-Hui

2006-07-04

Double hydrophilic block copolymers PEG-b-PEI-linear with different PEI block lengths have been examined for CaCO3 mineralization at the air/water interface. The results demonstrated that either PEI length or the solution acidity had a significant influence on the morphogenesis of vaterite crystals at the air/water interface. A possible mechanism for the stratification of CaCO3 vaterite crystals has been proposed. Increasing either PEI length or the initial pH value of the solution will decrease the density of the PEG block anchored on the binding interface and result in exposing more space as binding interface to solution and favoring the subnucleation and stratification growth on the polymer-CaCO3 interface. In contrast, higher density of PEG blocks will stabilize the growing crystals more efficiently and inhibit subnucleation on the polymer-CaCO3 interface, and thus prevent the formation of stratified structures. This study provides an example that it is possible to access morphogenesis of calcium carbonate structures by a combination of a block copolymer with the air/water interface.

Understanding PSA and its derivatives in prediction of tumor volume: addressing health disparities in prostate cancer risk stratification

PubMed Central

Chinea, Felix M; Lyapichev, Kirill; Epstein, Jonathan I; Kwon, Deukwoo; Smith, Paul Taylor; Pollack, Alan; Cote, Richard J; Kryvenko, Oleksandr N

2017-01-01

Objectives To address health disparities in risk stratification of U.S. Hispanic/Latino men by characterizing influences of prostate weight, body mass index, and race/ethnicity on the correlation of PSA derivatives with Gleason score 6 (Grade Group 1) tumor volume in a diverse cohort. Results Using published PSA density and PSA mass density cutoff values, men with higher body mass indices and prostate weights were less likely to have a tumor volume <0.5 cm3. Variability across race/ethnicity was found in the univariable analysis for all PSA derivatives when predicting for tumor volume. In receiver operator characteristic analysis, area under the curve values for all PSA derivatives varied across race/ethnicity with lower optimal cutoff values for Hispanic/Latino (PSA=2.79, PSA density=0.06, PSA mass=0.37, PSA mass density=0.011) and Non-Hispanic Black (PSA=3.75, PSA density=0.07, PSA mass=0.46, PSA mass density=0.008) compared to Non-Hispanic White men (PSA=4.20, PSA density=0.11 PSA mass=0.53, PSA mass density=0.014). Materials and Methods We retrospectively analyzed 589 patients with low-risk prostate cancer at radical prostatectomy. Pre-operative PSA, patient height, body weight, and prostate weight were used to calculate all PSA derivatives. Receiver operating characteristic curves were constructed for each PSA derivative per racial/ethnic group to establish optimal cutoff values predicting for tumor volume ≥0.5 cm3. Conclusions Increasing prostate weight and body mass index negatively influence PSA derivatives for predicting tumor volume. PSA derivatives’ ability to predict tumor volume varies significantly across race/ethnicity. Hispanic/Latino and Non-Hispanic Black men have lower optimal cutoff values for all PSA derivatives, which may impact risk assessment for prostate cancer. PMID:28160549

Seed flotation and germination of salt marsh plants: The effects of stratification, salinity, and/or inundation regime

USGS Publications Warehouse

Elsey-Quirk, T.; Middleton, B.A.; Proffitt, C.E.

2009-01-01

We examined the effects of cold stratification and salinity on seed flotation of eight salt marsh species. Four of the eight species were tested for germination success under different stratification, salinity, and flooding conditions. Species were separated into two groups, four species received wet stratification and four dry stratification and fresh seeds of all species were tested for flotation and germination. Fresh seeds of seven out of eight species had flotation times independent of salinity, six of which had average flotation times of at least 50 d. Seeds of Spartina alterniflora and Spartina patens had the shortest flotation times, averaging 24 and 26 d, respectively. Following wet stratification, the flotation time of S. alterniflora seeds in higher salinity water (15 and 36 ppt) was reduced by over 75% and germination declined by more than 90%. Wet stratification reduced the flotation time of Distichlis spicata seeds in fresh water but increased seed germination from 2 to 16% in a fluctuating inundation regime. Fresh seeds of Iva frutescens and S. alternflora were capable of germination and therefore are non-dormant during dispersal. Fresh seeds of I. frutescens had similar germination to dry stratified seeds ranging 25-30%. Salinity reduced seed germination for all species except for S. alterniflora. A fluctuating inundation regime was important for seed germination of the low marsh species and for germination following cold stratification. The conditions that resulted in seeds sinking faster were similar to the conditions that resulted in higher germination for two of four species. ?? 2009 Elsevier B.V.

Submesoscale-selective compensation of fronts in a salinity-stratified ocean.

PubMed

Spiro Jaeger, Gualtiero; Mahadevan, Amala

2018-02-01

Salinity, rather than temperature, is the leading influence on density in some regions of the world's upper oceans. In the Bay of Bengal, heavy monsoonal rains and runoff generate strong salinity gradients that define density fronts and stratification in the upper ~50 m. Ship-based observations made in winter reveal that fronts exist over a wide range of length scales, but at O(1)-km scales, horizontal salinity gradients are compensated by temperature to alleviate about half the cross-front density gradient. Using a process study ocean model, we show that scale-selective compensation occurs because of surface cooling. Submesoscale instabilities cause density fronts to slump, enhancing stratification along-front. Specifically for salinity fronts, the surface mixed layer (SML) shoals on the less saline side, correlating sea surface salinity (SSS) with SML depth at O(1)-km scales. When losing heat to the atmosphere, the shallower and less saline SML experiences a larger drop in temperature compared to the adjacent deeper SML on the salty side of the front, thus correlating sea surface temperature (SST) with SSS at the submesoscale. This compensation of submesoscale fronts can diminish their strength and thwart the forward cascade of energy to smaller scales. During winter, salinity fronts that are dynamically submesoscale experience larger temperature drops, appearing in satellite-derived SST as cold filaments. In freshwater-influenced regions, cold filaments can mark surface-trapped layers insulated from deeper nutrient-rich waters, unlike in other regions, where they indicate upwelling of nutrient-rich water and enhanced surface biological productivity.

Alcohol outlet densities and alcohol price: the British Columbia experiment in the partial privatization of alcohol sales off-premise.

PubMed

Treno, Andrew J; Ponicki, William R; Stockwell, Tim; Macdonald, Scott; Gruenewald, Paul J; Zhao, Jinhui; Martin, Gina; Greer, Alissa

2013-05-01

Alcohol beverage prices or taxes have been shown to be related to alcohol sales and use and related problems. What is not clear are the mechanisms underlying these relationships. This study examines the relationship between alcohol outlet density under conditions of the partial privatization of off-premise consumption in British Columbia (BC) occurring over the past decade. Two hypotheses are tested. First, reflecting basic supply-demand principles, greater geographic densities of alcohol outlets will be directly related to reductions in beverage prices in response to greater competition. Second, reflecting the effects of niche marketing and resulting market stratification, increased densities of private liquor stores will be especially related to reductions in beverage prices within this outlet category. Data were collected from: (i) a survey of BC private store prices and practices, (ii) alcohol outlet location information, and (iii) data on demographic characteristics. Multilevel models examine the relationships between prices at individual private liquor stores and the densities of government liquor stores, private liquor stores, bars, and restaurants, controlling for background demographics and geographic unit level effects. Spatial dependencies were also examined. Increased densities of private liquor stores were associated with lower mean prices of beer and all alcohol aggregated across brands at the store level. There appeared to be no outlet level effect on discounting patterns, however, with the mean price differences apparently reflecting differences in the quality of brands carried rather than unequal prices for any given brand. Increased densities of private off-sale alcohol outlets appear to result in lower prices charged at said establishments independently of other types of alcohol outlets suggesting that they represent an emerging marketing niche in the context of off-sale outlet privatization. Copyright © 2012 by the Research Society on Alcoholism.

Microbial stratification structure within cathodic biofilm of the microbial fuel cell using the freezing microtome method.

PubMed

Li, Xiao; Lu, Yaobin; Luo, Haiping; Liu, Guangli; Zhang, Renduo

2017-10-01

The aim of this study was to investigate the microbial stratification structure within cathodic biofilm of the microbial fuel cell (MFC) using the freezing microtome method. Experiments were conducted in a single-chamber air-cathode MFC with 0.8g/L maltodextrin as substrate for ∼30d operation. The maximum power density was 945±10mW/m 2 in the MFC. Maltodextrin resulted in the relative abundance of Candidatus Saccharibacteria of 37.0% in the anodic biofilm. Different bacterial communities were identified in different layers within the cathodic biofilm. The relative abundance of Enterococcus was 3.7%, 10.5%, and 1.6% in the top (100-150μm), middle (50-100μm), and bottom (0-50μm) layers, respectively. Higher bacterial viability was observed within the top and bottom layers of the cathodic biofilm. Understanding the stratification of bacterial community in cathodic biofilm should be important to control the cathodic biofilm in the MFC. Copyright © 2017 Elsevier Ltd. All rights reserved.

Stratified turbulent Bunsen flames: flame surface analysis and flame surface density modelling

NASA Astrophysics Data System (ADS)

Ramaekers, W. J. S.; van Oijen, J. A.; de Goey, L. P. H.

2012-12-01

In this paper it is investigated whether the Flame Surface Density (FSD) model, developed for turbulent premixed combustion, is also applicable to stratified flames. Direct Numerical Simulations (DNS) of turbulent stratified Bunsen flames have been carried out, using the Flamelet Generated Manifold (FGM) reduction method for reaction kinetics. Before examining the suitability of the FSD model, flame surfaces are characterized in terms of thickness, curvature and stratification. All flames are in the Thin Reaction Zones regime, and the maximum equivalence ratio range covers 0.1⩽φ⩽1.3. For all flames, local flame thicknesses correspond very well to those observed in stretchless, steady premixed flamelets. Extracted curvature radii and mixing length scales are significantly larger than the flame thickness, implying that the stratified flames all burn in a premixed mode. The remaining challenge is accounting for the large variation in (subfilter) mass burning rate. In this contribution, the FSD model is proven to be applicable for Large Eddy Simulations (LES) of stratified flames for the equivalence ratio range 0.1⩽φ⩽1.3. Subfilter mass burning rate variations are taken into account by a subfilter Probability Density Function (PDF) for the mixture fraction, on which the mass burning rate directly depends. A priori analysis point out that for small stratifications (0.4⩽φ⩽1.0), the replacement of the subfilter PDF (obtained from DNS data) by the corresponding Dirac function is appropriate. Integration of the Dirac function with the mass burning rate m=m(φ), can then adequately model the filtered mass burning rate obtained from filtered DNS data. For a larger stratification (0.1⩽φ⩽1.3), and filter widths up to ten flame thicknesses, a β-function for the subfilter PDF yields substantially better predictions than a Dirac function. Finally, inclusion of a simple algebraic model for the FSD resulted only in small additional deviations from DNS data, thereby rendering this approach promising for application in LES.

Principal Stratification: A Tool for Understanding Variation in Program Effects across Endogenous Subgroups

ERIC Educational Resources Information Center

Page, Lindsay C.; Feller, Avi; Grindal, Todd; Miratrix, Luke; Somers, Marie-Andree

2015-01-01

Increasingly, researchers are interested in questions regarding treatment-effect variation across partially or fully latent subgroups defined not by pretreatment characteristics but by postrandomization actions. One promising approach to address such questions is principal stratification. Under this framework, a researcher defines endogenous…

Effects of viscosity and conductivity stratification on the linear stability and transient growth within compressible Couette flow

NASA Astrophysics Data System (ADS)

Saikia, Bijaylakshmi; Ramachandran, Ashwin; Sinha, Krishnendu; Govindarajan, Rama

2017-02-01

Accurate prediction of laminar to turbulent transition in compressible flows is a challenging task, as it can be affected by a combination of factors. Compressibility causes large variations in thermodynamic as well as transport properties of a gas, which in turn are known to affect flow stability. We study the stratification of individual transport properties and their combined behavior. We also examine the effect of a change in the magnitude of viscosity and conductivity on flow stability. The Couette flow of a perfect gas is our model problem and both modal and non-modal analyses are carried out. We notice a large destabilizing role of the increase in the conductivity value and a dramatic stabilizing effect of mean viscosity stratification, over a range of free-stream Mach number, Reynolds number, Prandtl number, and disturbance wavenumber. In the combined case, viscosity stratification plays a dominant role. We find this to be the case for finite-time transient growth in the parameter regime below linear instability as well as asymptotically at large time. A budget of the transient growth energy amplification is also shown to identify the effects of transport properties on the constituents of perturbation energy. The extensive results presented in this paper, we believe should motivate those studying more realistic flows to examine how these contrasting effects of stratification come together.

Density profiles around A+B→C reaction-diffusion fronts in partially miscible systems: A general classification.

PubMed

Loodts, V; Trevelyan, P M J; Rongy, L; De Wit, A

2016-10-01

Various spatial density profiles can develop in partially miscible stratifications when a phase A dissolves with a finite solubility into a host phase containing a dissolved reactant B. We investigate theoretically the impact of an A+B→C reaction on such density profiles in the host phase and classify them in a parameter space spanned by the ratios of relative contributions to density and diffusion coefficients of the chemical species. While the density profile is either monotonically increasing or decreasing in the nonreactive case, reactions combined with differential diffusivity can create eight different types of density profiles featuring up to two extrema in density, at the reaction front or below it. We use this framework to predict various possible hydrodynamic instability scenarios inducing buoyancy-driven convection around such reaction fronts when they propagate parallel to the gravity field.

Exploring a new bilateral focal density asymmetry based image marker to predict breast cancer risk

NASA Astrophysics Data System (ADS)

Aghaei, Faranak; Mirniaharikandehei, Seyedehnafiseh; Hollingsworth, Alan B.; Wang, Yunzhi; Qiu, Yuchen; Liu, Hong; Zheng, Bin

2017-03-01

Although breast density has been widely considered an important breast cancer risk factor, it is not very effective to predict risk of developing breast cancer in a short-term or harboring cancer in mammograms. Based on our recent studies to build short-term breast cancer risk stratification models based on bilateral mammographic density asymmetry, we in this study explored a new quantitative image marker based on bilateral focal density asymmetry to predict the risk of harboring cancers in mammograms. For this purpose, we assembled a testing dataset involving 100 positive and 100 negative cases. In each of positive case, no any solid masses are visible on mammograms. We developed a computer-aided detection (CAD) scheme to automatically detect focal dense regions depicting on two bilateral mammograms of left and right breasts. CAD selects one focal dense region with the maximum size on each image and computes its asymmetrical ratio. We used this focal density asymmetry as a new imaging marker to divide testing cases into two groups of higher and lower focal density asymmetry. The first group included 70 cases in which 62.9% are positive, while the second group included 130 cases in which 43.1% are positive. The odds ratio is 2.24. As a result, this preliminary study supported the feasibility of applying a new focal density asymmetry based imaging marker to predict the risk of having mammography-occult cancers. The goal is to assist radiologists more effectively and accurately detect early subtle cancers using mammography and/or other adjunctive imaging modalities in the future.

Shaped Goals: Teaching Undergraduates the Effects of Social Stratification on the Formulation of Goals

ERIC Educational Resources Information Center

Touzard, Giselle

2009-01-01

This article describes an in-class activity that helps undergraduate students to understand the effects of their socio-economic position on the formulation, pursuit, and achievement of goals. Social stratification and inequality have an initial impact on the formulation of goals. Through this exercise students will perceive the effects of having a…

Effects of treatment and seed source on germination of eastern redcedar seed

Treesearch

David F. Van Haverbeke; C. W. Comer

1985-01-01

Germination of eastern redcedar (Juniperus virginiana L.) seeds was best with a 96-hour soak in citric acid (10,000 ppm), with 6 weeks of moist-warm (24° C) stratification, and 10 weeks of moist-cold (5° C) stratification. Geographic seed sources responded differently to treatment. Use of fresh seeds could reduce the time in moist-warm stratification, would improve...

Effects of moist cold stratification on germination, plant growth regulators, metabolites and embryo ultrastructure in seeds of Acer morrisonense (Sapindaceae).

PubMed

Chen, Shun-Ying; Chou, Shih-Han; Tsai, Ching-Chu; Hsu, Wen-Yu; Baskin, Carol C; Baskin, Jerry M; Chien, Ching-Te; Kuo-Huang, Ling-Long

2015-09-01

Breaking of seed dormancy by moist cold stratification involves complex interactions in cells. To assess the effect of moist cold stratification on dormancy break in seeds of Acer morrisonense, we monitored percentages and rates of germination and changes in plant growth regulators, sugars, amino acids and embryo ultrastructure after various periods of cold stratification. Fresh seeds incubated at 25/15 °C for 24 weeks germinated to 61%, while those cold stratified at 5 °C for 12 weeks germinated to 87% in 1 week. Neither exogenous GA3 nor GA4 pretreatment significantly increased final seed germination percentage. Total ABA content of seeds cold stratified for 12 weeks was reduced about 3.3-fold, to a concentration similar to that in germinated seeds (radicle emergence). Endogenous GA3 and GA7 were detected in 8-week and 12-week cold stratified seeds but not in fresh seeds. Numerous protein and lipid bodies were present in the plumule, first true leaves and cotyledons of fresh seeds. Protein and lipid bodies decreased greatly during cold stratification, and concentrations of total soluble sugars and amino acids increased. The major non-polar sugars in fresh seeds were sucrose and fructose, but sucrose increased and fructose decreased significantly during cold stratification. The major free amino acids were proline and tryptophan in fresh seeds, and proline increased and tryptophan decreased during cold stratification. Thus, as dormancy break occurs during cold stratification seeds of A. morrisonense undergo changes in plant growth regulators, proteins, lipids, sugars, amino acids and cell ultrastructure. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Jet-mixing of initially-stratified liquid-liquid pipe flows: experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Wright, Stuart; Ibarra-Hernandes, Roberto; Xie, Zhihua; Markides, Christos; Matar, Omar

2016-11-01

Low pipeline velocities lead to stratification and so-called 'phase slip' in horizontal liquid-liquid flows due to differences in liquid densities and viscosities. Stratified flows have no suitable single point for sampling, from which average phase properties (e.g. fractions) can be established. Inline mixing, achieved by static mixers or jets in cross-flow (JICF), is often used to overcome liquid-liquid stratification by establishing unstable two-phase dispersions for sampling. Achieving dispersions in liquid-liquid pipeline flows using JICF is the subject of this experimental and modelling work. The experimental facility involves a matched refractive index liquid-liquid-solid system, featuring an ETFE test section, and experimental liquids which are silicone oil and a 51-wt% glycerol solution. The matching then allows the dispersed fluid phase fractions and velocity fields to be established through advanced optical techniques, namely PLIF (for phase) and PTV or PIV (for velocity fields). CFD codes using the volume of a fluid (VOF) method are then used to demonstrate JICF breakup and dispersion in stratified pipeline flows. A number of simple jet configurations are described and their dispersion effectiveness is compared with the experimental results. Funding from Cameron for Ph.D. studentship (SW) gratefully acknowledged.

The Hall Instability of Weakly Ionized, Radially Stratified, Rotating Disks

NASA Astrophysics Data System (ADS)

Liverts, Edward; Mond, Michael; Chernin, Arthur D.

2007-09-01

Cool weakly ionized gaseous rotating disks are considered by many models to be the origin of the evolution of protoplanetary clouds. Instabilities against perturbations in such disks play an important role in the theory of the formation of stars and planets. Thus, a hierarchy of successive fragmentations into smaller and smaller pieces as a part of the Kant-Laplace theory of formation of the planetary system remains valid also for contemporary cosmogony. Traditionally, axisymmetric magnetohydrodynamic (MHD) and, recently, Hall-MHD instabilities have been thoroughly studied as providers of an efficient mechanism for radial transfer of angular momentum and of radial density stratification. In the current work, the Hall instability against nonaxisymmetric perturbations in compressible rotating fluid in external magnetic field is proposed as a viable mechanism for the azimuthal fragmentation of the protoplanetary disk and, thus, perhaps initiates the road to planet formation. The Hall instability is excited due to the combined effect of the radial stratification of the disk and the Hall electric field, and its growth rate is of the order of the rotation period. This family of instabilities is introduced here for the first time in an astrophysical context.

Near-surface energy transfers from internal tide beams to smaller vertical scale motions

NASA Astrophysics Data System (ADS)

Chou, S.; Staquet, C.; Carter, G. S.; Luther, D. S.

2016-02-01

Mechanical energy capable of causing diapycnal mixing in the ocean is transferred to the internal wave field when barotropic tides pass over underwater topography and generate internal tides. The resulting internal tide energy is confined in vertically limited structures, or beams. As internal tide beams (ITBs) propagate through regions of non-uniform stratification in the upper ocean, wave energy can be scattered through multiple reflections and refractions, be vertically trapped, or transferred to non-tidal frequencies through different nonlinear processes. Various observations have shown that ITBs are no longer detectable in horizontal kinetic energy beyond the first surface reflection. Importantly, this implies that some of the internal tide energy no longer propagates in to the abyssal ocean and consequently will not be available to maintain the density stratification. Using the NHM, a nonlinear and nonhydrostatic model based on the MITgcm, simulations of an ITB propagating up to the sea surface are examined in order to quantify the transformation of ITB energy to other motions. We compare and contrast the transformations enabled by idealized, smoothly-varying stratification with transformations enabled by realistic stratification containing a broad-band vertical wavenumber spectrum of variations. Preliminary two-dimensional results show that scattering due to small-scale structure in realistic stratification profiles from Hawaii can lead to energy being vertically trapped near the surface. Idealized simulations of "locally" generated internal solitary waves are analyzed in terms of energy flux transfers from the ITB to solitary waves, higher harmonics, and mean flow. The amount of internal tide energy which propagates back down after near-surface reflection of the ITB in different environments is quantified.

Potential for Waste Stratification from Back-Dilution in Tank 241-SY-101

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antoniak, Z.I.; Meyer, P.A.

Since late 1997, the floating crust layer in Hanford Tank 241-SY-101 (SY-101) has grown about two meters by gas accumulation. To reverse crust growth and reduce its retained gas volume, the waste in SY-101 will be diluted by transferring at least 300,000 gal of waste out of the tank and replacing it with water. In the fall of 1999, approximately 100,000 gal of this waste will be transferred into Tank SY-102; within a few days of that initial transfer, approximately 100,000 gal of water will be added to SY-101. This initial back-dilution is being planned to ensure that the basemore » of the floating crust layer will be lifted away from the mixer pump inlet with minimal effect on the crust itself. The concern is that the added water will pool under the crust, so the resulting fluid mixture will be too light to lift the crust away from the mixer pump and dissolution at the crust base could cause unwanted gas release. To ensure sufficient mixing to prevent such stratification, water will be added near the tank bottom either through an existing sparge ring on the base of the mixer pump or through the dilution line at the inlet of the transfer pump. A number of simulations using the TEMPEST code showed that the mixing of the water and waste by this method is rapid, and the water does not pool under the crust. Although a density gradient is present, its magnitude is small compared with the difference between the slurry and water density. The result is essentially the same whether water is introduced at the base of the mixer pump or at the transfer pump. There is little effect of water flowrate up to the 500 gpm studied. In all cases, the minimum density remained above that required to float the crust and well above the density of saturated liquid. This indicates that the base of the crust will rise during back-dilution and there will be little or no dissolution of the crust base because the water will be close to saturation from the dissolution of solids in the mixed slurry.« less

Guidance for Subaqueous Dredged Material Capping.

DTIC Science & Technology

1998-06-01

from Ambrose Channel , over the contaminated sediments. At least two intermediate sur- veys and additional capping were required before capping was...organisms to a given bioturbation depth; reducing contami- nant flux rates to achieve specific sediment, pore water, or water column target...bathymetry, bottom slopes, cur- rents, water depths, water column density stratification, erosion/accretion trends, proximity to navigation channels

Hydrographic survey in the dying Aral Sea

NASA Astrophysics Data System (ADS)

Zavialov, P. O.; Kostianoy, A. G.; Emelianov, S. V.; Ni, A. A.; Ishniyazov, D.; Khan, V. M.; Kudyshkin, T. V.

2003-07-01

We report the results of a hydrographic survey conducted in November, 2002, in the Uzbekistan part of the western basin of the dying Aral Sea. There were very few hydrographic measurements in this region since at least early 1990s. The salinity in the western deep basin of the Aral Sea varied from about 82 psu at the surface to over 94 psu at the bottom. The absolute lake surface level was about 30.5 m. Hence, the observed salinity values were much higher, and the level much lower, than expected according to earlier predictions. The density in the western basin exhibited an extremely strong stratification of ~11 kg/m3 per ~20 m in the bottom layer. The picnocline was accompanied by a temperature inversion whose magnitude was ~4°C. The observed density stratification effectively isolating the lower part of the water column from surface exchanges may be responsible for the increase of summer SSTs and evaporation rates reported in previous studies. We discovered the hydrogen sulphide contamination in the bottom layer whose upper limit was at the depth of approximately 22 m. Estimates suggest that the western basin salinization occurs not only because of the local evaporation, but also because of the assimilation of the saltier eastern basin water in the course of the interbasin exchange through the connecting channel. The satellite imagery analysis, in particular the Maximum Cross-Correlation method, suggests that the circulation pattern in the Aral Sea in its present limits is cyclonic under the eastern winds that are predominant in the region throughout the year.

Response of soft-bottom macrobenthic assemblages to artisanal trawling fisheries in a subtropical estuary

NASA Astrophysics Data System (ADS)

Ortega, Ileana; Colling, Leonir André; Dumont, Luiz Felipe Cestari

2018-07-01

Bottom trawling is one of the most harmful and widespread activities affecting benthic habitats and fauna. In this study, we analyzed the impact of shrimp trawling fisheries on the densities, assemblage structure and vertical stratification of the benthic macrofauna in shallow mudflats of the Patos Lagoon Estuary (Brazil). Experimental trawls of different intensities were performed during three shrimp fishing seasons (2015-2017), comparing macrofauna among before and after trawling, and a control zone. The changes in macrofaunal assemblages were more consistently related to natural variability than to trawling impact, being mostly influenced by sediment structure and salinity variation. The trawling impact was mainly detected in the area with higher percentages of fine sediments, with different macrofaunal responses in each month and stratum. Some non-significant decreases on total densities after trawling were observed, mainly on the superficial stratum, and signs of burial activities. The response to trawling disturbance of each species was different and it highly depended on their natural variability. Only five species showed significant variation to the trawling treatment (Erodona mactroides, Heleobia australis, H. charruana, Heteromastus similis and Laeonereis acuta), with temporally different responses. Decreasing densities were more related to the high impact treatment. In some seasons, decreases on the abundance of Monokalliapseudes schubarti after high impact trawls were up to 60% of the seasonal mean densities. Trawling fisheries may reduce macrobenthic densities but not their vertical stratification. The impact of trawling on key species may compromise the ecosystem function, as benthic macrofauna provide food sources for many aquatic resources. This study highlights trawling impacts in an estuarine nursery area, which should be fully considered since they may be reflected in the trophic webs.

Crystalline heterogeneities and instabilities in thermally convecting magma chamber

NASA Astrophysics Data System (ADS)

Culha, C.; Suckale, J.; Qin, Z.

2016-12-01

A volcanic vent can supply different densities of crystals over an eruption time period. This has been seen in Hawai'i's Kilauea Iki 1959 eruption; however it is not common for all Kilauea or basaltic eruptions. We ask the question: Under what conditions can homogenous magma chamber cultivate crystalline heterogeneities? In some laboratory experiments and numerical simulations, a horizontal variation is observed. The region where crystals reside is identified as a retention zone: convection velocity balances settling velocity. Simulations and experiments that observe retention zones assume crystals do not alter the convection in the fluid. However, a comparison of experiments and simulations of convecting magma with crystals suggest that large crystal volume densities and crystal sizes alter fluid flow considerably. We introduce a computational method that fully resolves the crystalline phase. To simulate basaltic magma chambers in thermal convection, we built a numerical solver of the Navier-Stoke's equation, continuity equation, and energy equation. The modeled magma is assumed to be a viscous, incompressible fluid with a liquid and solid phase. Crystals are spherical, rigid bodies. We create Rayleigh-Taylor instability through a cool top layer and hot bottom layer and update magma density while keeping crystal temperature and size constant. Our method provides a detailed picture of magma chambers, which we compare to other models and experiments to identify when and how crystals alter magma chamber convection. Alterations include stratification, differential settling and instabilities. These characteristics are dependent on viscosity, convection vigor, crystal volume density and crystal characteristics. We reveal that a volumetric crystal density variation may occur over an eruption time period, if right conditions are met to form stratifications and instabilities in magma chambers. These conditions are realistic for Kilauea Iki's 1959 eruption.

Recommendations on breast cancer screening and prevention in the context of implementing risk stratification: impending changes to current policies

PubMed Central

Gagnon, J.; Lévesque, E.; Borduas, F.; Chiquette, J.; Diorio, C.; Duchesne, N.; Dumais, M.; Eloy, L.; Foulkes, W.; Gervais, N.; Lalonde, L.; L’Espérance, B.; Meterissian, S.; Provencher, L.; Richard, J.; Savard, C.; Trop, I.; Wong, N.; Knoppers, B.M.; Simard, J.

2016-01-01

In recent years, risk stratification has sparked interest as an innovative approach to disease screening and prevention. The approach effectively personalizes individual risk, opening the way to screening and prevention interventions that are adapted to subpopulations. The international perspective project, which is developing risk stratification for breast cancer, aims to support the integration of its screening approach into clinical practice through comprehensive tool-building. Policies and guidelines for risk stratification—unlike those for population screening programs, which are currently well regulated—are still under development. Indeed, the development of guidelines for risk stratification reflects the translational aspects of perspective. Here, we describe the risk stratification process that was devised in the context of perspective, and we then explain the consensus-based method used to develop recommendations for breast cancer screening and prevention in a risk-stratification approach. Lastly, we discuss how the recommendations might affect current screening policies. PMID:28050152

On the mechanism of self gravitating Rossby interfacial waves in proto-stellar accretion discs

NASA Astrophysics Data System (ADS)

Yellin-Bergovoy, Ron; Heifetz, Eyal; Umurhan, Orkan M.

2016-05-01

The dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. The fluid in basic state is prescribed to rotate with a Keplerian profile ? modified by some additional azimuthal sheared flow. A linear analysis shows that there are two azimuthally propagating edge waves, kin to the familiar Rossby waves and surface gravity waves in terrestrial studies, which move opposite to one another with respect to the local basic state rotation rate at the interface. Instability only occurs if the radial pressure gradient is opposite to that of the density jump (unstably stratified) where self-gravity acts as a wave stabiliser irrespective of the stratification of the system. The propagation properties of the waves are discussed in detail in the language of vorticity edge waves. The roles of both Boussinesq and non-Boussinesq effects upon the stability and propagation of these waves with and without the inclusion of self-gravity are then quantified. The dynamics involved with self-gravity non-Boussinesq effect is shown to be a source of vorticity production where there is a jump in the basic state density In addition, self-gravity also alters the dynamics via the radial main pressure gradient, which is a Boussinesq effect. Further applications of these mechanical insights are presented in the conclusion including the ways in which multiple density jumps or gaps may or may not be stable.

The Effect of an Isogrid on Cryogenic Propellant Behavior and Thermal Stratification

NASA Technical Reports Server (NTRS)

Oliveira, Justin; Kirk, Daniel R.; Chintalapati, Sunil; Schallhorn, Paul A.; Piquero, Jorge L.; Campbell, Mike; Chase, Sukhdeep

2007-01-01

All models for thermal stratification available in the presentation are derived using smooth, flat plate laminar and turbulent boundary layer models. This study examines the effect of isogrid (roughness elements) on the surface of internal tank walls to mimic the effects of weight-saving isogrid, which is located on the inside of many rocket propellant tanks. Computational Fluid Dynamics (CFD) is used to study the momentum and thermal boundary layer thickness for free convection flows over a wall with generic roughness elements. This presentation makes no mention of actual isogrid sizes or of any specific tank geometry. The magnitude of thermal stratification is compared for smooth and isogrid-lined walls.

Effect of stable stratification on dispersion within urban street canyons: A large-eddy simulation

NASA Astrophysics Data System (ADS)

Li, Xian-Xiang; Britter, Rex; Norford, Leslie K.

2016-11-01

This study employs a validated large-eddy simulation (LES) code with high tempo-spatial resolution to investigate the effect of a stably stratified roughness sublayer (RSL) on scalar transport within an urban street canyon. The major effect of stable stratification on the flow and turbulence inside the street canyon is that the flow slows down in both streamwise and vertical directions, a stagnant area near the street level emerges, and the vertical transport of momentum is weakened. Consequently, the transfer of heat between the street canyon and overlying atmosphere also gets weaker. The pollutant emitted from the street level 'pools' within the lower street canyon, and more pollutant accumulates within the street canyon with increasing stability. Under stable stratification, the dominant mechanism for pollutant transport within the street canyon has changed from ejections (flow carries high-concentration pollutant upward) to unorganized motions (flow carries high-concentration pollutant downward), which is responsible for the much lower dispersion efficiency under stable stratifications.

Change and Stability in Educational Stratification.

ERIC Educational Resources Information Center

Mare, Robert D.

1981-01-01

Using statistical models, discusses educational stratification with respect to socioeconomic origins. Describes the effects of social background on grade progression change across cohorts born during the 20th century and the consequences of these changes. (JW)

Numerical solution of chemically reactive non-Newtonian fluid flow: Dual stratification

NASA Astrophysics Data System (ADS)

Rehman, Khalil Ur; Malik, M. Y.; Khan, Abid Ali; Zehra, Iffat; Zahri, Mostafa; Tahir, M.

2017-12-01

We have found that only a few attempts are available in the literature relatively to the tangent hyperbolic fluid flow induced by stretching cylindrical surfaces. In particular, temperature and concentration stratification effects have not been investigated until now with respect to the tangent hyperbolic fluid model. Therefore, we have considered the tangent hyperbolic fluid flow induced by an acutely inclined cylindrical surface in the presence of both temperature and concentration stratification effects. To be more specific, the fluid flow is attained with the no slip condition, which implies that the bulk motion of the fluid particles is the same as the stretching velocity of a cylindrical surface. Additionally, the flow field situation is manifested with heat generation, mixed convection and chemical reaction effects. The flow partial differential equations give a complete description of the present problem. Therefore, to trace out the solution, a set of suitable transformations is introduced to convert these equations into ordinary differential equations. In addition, a self-coded computational algorithm is executed to inspect the numerical solution of these reduced equations. The effect logs of the involved parameters are provided graphically. Furthermore, the variations of the physical quantities are examined and given with the aid of tables. It is observed that the fluid temperature is a decreasing function of the thermal stratification parameter and a similar trend is noticed for the concentration via the solutal stratification parameter.

Decomposing Inequalities in Performance Scores: The Role of Student Background, Peer Effects and School Characteristics

ERIC Educational Resources Information Center

Mostafa, Tarek

2010-01-01

This paper analyses the mechanisms of stratification and inequalities in educational achievements. The main objective is to determine how stratification leads to unequal educational outcomes and how inequalities are channelled through student characteristics, school characteristics and peer effects. This analysis is undertaken in five countries…

Mixing of two solutions combined by gravity drainage.

PubMed

Leuptow, R M; Smith, K; Mockros, L F

1995-01-01

A variety of medical therapies require the mixing of solutions from two separate bags before use. One scenario for the mixing is to drain the solution from one bag into the other by gravity through a short connecting tube. The degree of mixing in the lower bag depends on the relative densities of the two solutions, the geometry of the two bags and the connecting tube, and the placement of the connecting tube. Solutions with densities differing by as much as 12% were mixed by draining the solution from an upper bag into a lower bag for a particular geometric configuration. The two solutions had different electrical conductivities, and the conductivity of the combined solution as it exited from the lower bag was used as a measure of the effectiveness of mixing. When the more dense solution was drained from the upper bag into the less dense solution in a lower bag, mixing was very effective. The incoming jet of high density solution entrained the low density solution. Flow visualization indicated that the incoming jet penetrated to the bottom of the lower bag, and resulting large vortical structures enhanced mixing. When the less dense solution was drained from the upper bag into the more dense solution in the lower bag mixing was less effective. The buoyancy force reduced the momentum of the incoming jet such that it did not penetrate to the bottom of the lower bag, resulting in stratification of the solutions.

M2 tidal effects in greater cook strait, New Zealand

NASA Astrophysics Data System (ADS)

Kibblewhite, Alick C.; Ash, David E.

1980-05-01

The application of a M2 nonlinear numerical tidal model to the shelf seas of central New Zealand (~38.500 km2 area) is described. It has provided a preliminary assessment of tidal and residual currents, bottom stress, energy dissipation, and the stratification index. The existence of a permanent, tidally driven mesoscale eddy (~75 km diameter) is predicted nort of D'Urville Island. Large spatial gradients in bottom stress qualitatively agree with many features of the surficial sediment distribution. A comparison of all available bulk stratification data with the h/u3 stratification index clearly demonstrates the dominance of tidal versus wind mixing over the control of summer stratification. A potential application of the model to fisheries science is suggested through a comparison of the stratification index contour map and some observations of squid fishing vessel locations.

M 2 tidal effects in greater Cook Strait, New Zealand

NASA Astrophysics Data System (ADS)

Bowman, Malcolm J.; Kibblewhite, Alick C.; Ash, David E.

1980-05-01

The application of an M2 nonlinear numerical tidal model to the shelf seas of central New Zealand (˜38,500 km2 area) is described. It has provided a preliminary assessment of tidal and residual currents, bottom stress, energy dissipation, and the stratification index. The existence of a permanent, tidally driven mesoscale eddy (˜75 km diameter) is predicted north of D'Urville Island. Large spatial gradients in bottom stress qualitatively agree with many features of the surficial sediment distribution. A comparison of all available bulk stratification data with the h/u3 stratification index clearly demonstrates the dominance of tidal versus wind mixing over the control of summer stratification. A potential application of the model to fisheries science is suggested through a comparison of the stratification index contour map and some observations of squid fishing vessel locations.

Design of fluidized-bed fermentors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, G.F.; Przezdziecki, J.

1986-06-01

Designing a fluidized-bed bioreactor requires choosing the best support particle (if any). Effectiveness factors (proportional to reactor volumetric productivity) are derived for flocs, solid spherical supports, porous supports, and adsorbent supports. The derivation demonstrates a mathematical procedure for reducing the diffusion/uptake equations for many components (substrates and inhibitory products) to a single equation, and for identifying the limiting component. With solid supports there exists a film thickness that maximizes the effectiveness, and the design objective is to keep the film near this optimum throughout the bed. This involves consideration of the effect of support particle density and film growth onmore » bed stratification. Other considerations in packing support particles are obtaining reasonable values for bed height and diameter, minimizing mass transfer resistance between liquid and biomass, and preventing surface shear from stripping off the biomass. 20 references.« less

Submesoscale-selective compensation of fronts in a salinity-stratified ocean

PubMed Central

Spiro Jaeger, Gualtiero; Mahadevan, Amala

2018-01-01

Salinity, rather than temperature, is the leading influence on density in some regions of the world’s upper oceans. In the Bay of Bengal, heavy monsoonal rains and runoff generate strong salinity gradients that define density fronts and stratification in the upper ~50 m. Ship-based observations made in winter reveal that fronts exist over a wide range of length scales, but at O(1)-km scales, horizontal salinity gradients are compensated by temperature to alleviate about half the cross-front density gradient. Using a process study ocean model, we show that scale-selective compensation occurs because of surface cooling. Submesoscale instabilities cause density fronts to slump, enhancing stratification along-front. Specifically for salinity fronts, the surface mixed layer (SML) shoals on the less saline side, correlating sea surface salinity (SSS) with SML depth at O(1)-km scales. When losing heat to the atmosphere, the shallower and less saline SML experiences a larger drop in temperature compared to the adjacent deeper SML on the salty side of the front, thus correlating sea surface temperature (SST) with SSS at the submesoscale. This compensation of submesoscale fronts can diminish their strength and thwart the forward cascade of energy to smaller scales. During winter, salinity fronts that are dynamically submesoscale experience larger temperature drops, appearing in satellite-derived SST as cold filaments. In freshwater-influenced regions, cold filaments can mark surface-trapped layers insulated from deeper nutrient-rich waters, unlike in other regions, where they indicate upwelling of nutrient-rich water and enhanced surface biological productivity. PMID:29507874

Possible effects of insulin-like growth factor-I, IGF-binding protein-3 and IGF-1/IGFBP-3 molar ratio on mammographic density: a cross-sectional study.

PubMed

Meggiorini, M L; Cipolla, V; Borgoni, G; Nofroni, I; Pala, A; de Felice, C

2012-01-01

The purpose of this study was to examine the possible effects of IGF-1, IGFBP-3 and IGF-1/IGFBP-3 molar ratio on mammographic density and assess whether this relationship was similar in subgroups of pre- and postmenopausal women. A group of 341 Italian women of childbearing age or naturally postmenopausal who had performed mammographic examination at the section of radiology of our department a maximum three months prior to recruitment were enrolled. A blood sample was drawn for determination of IGF-1, IGFBP-3 levels and IGF-1/IGFBP-3 molar ratio was calculated. On the basis of recent mammograms the women were divided into two groups: dense breast (DB) and non-dense breast (NDB). To assess the association between mammographic density and IGF-1, IGFBP-3 and Molar ratio Student's t-test was employed before and after stratified by menopausal status. The analysis of the relationship between mammographic density and plasma levels of IGF-1, IGFBP-3 and IGF-1/IGFBP-3 molar ratio showed that IGF-1 levels and molar ratio varied in the two groups resulting in higher mean values in the DB group whereas IGFBP-3 showed similar values in both groups (DB and NDB). After stratification of the study population by menopausal status, no association was found. Our study provides strong evidence of a crude association between breast density, and plasma levels of IGF-1 and molar ratio. IGF-1 and molar ratio might increase mammographic density and thus the risk of developing breast cancer.

Effects of the Relaxation of Upwelling-Favorable Winds on the Diurnal and Semidiurnal Water Temperature Fluctuations in the Santa Barbara Channel, California

NASA Astrophysics Data System (ADS)

Aristizábal, María. F.; Fewings, Melanie R.; Washburn, Libe

2017-10-01

In the Santa Barbara Channel, California, and around the Northern Channel Islands, water temperature fluctuations in the diurnal and semidiurnal frequency bands are intermittent, with amplitudes that vary on time scales of days to weeks. The cause of this intermittency is not well understood. We studied the effects of the barotropic tide, vertical stratification, propagation of coastal-trapped waves, regional wind relaxations, and diurnal-band winds on the intermittency of the temperature fluctuations during 1992-2015. We used temperature data from 43 moorings in 10-200 m water depth and wind data from two buoys and one land station. Subtidal-frequency changes in vertical stratification explain 20-40% of the intermittency in diurnal and semidiurnal temperature fluctuations at time scales of days to weeks. Along the mainland north of Point Conception and at the Northern Channel Islands, the relaxation of upwelling-favorable winds substantially increases vertical stratification, accounting for up to 55% of the subtidal-frequency variability in stratification. As a result of the enhanced stratification, wind relaxations enhance the diurnal and semidiurnal temperature fluctuations at those sites, even though the diurnal-band wind forcing decreases during wind relaxation. A linear model where the background stratification is advected vertically explains a substantial fraction of the temperature fluctuations at most sites. The increase of vertical stratification and subsequent increase in diurnal and semidiurnal temperature fluctuations during wind relaxation is a mechanism that can supply nutrients to the euphotic zone and kelp forests in the Channel in summer when upwelling is weak.

A new risk stratification algorithm for the management of patients with adrenal incidentalomas.

PubMed

Birsen, Onur; Akyuz, Muhammet; Dural, Cem; Aksoy, Erol; Aliyev, Shamil; Mitchell, Jamie; Siperstein, Allan; Berber, Eren

2014-10-01

Although adrenal incidentalomas (AI) are detected in ≤5% of patients undergoing chest and abdominal computed tomography (CT), their management is challenging. The current guidelines include recommendations from the National Institutes of Health, the American Association of Endocrine Surgeons (AAES), and the American Association for Cancer Education (AACE). The aim of this study was to develop a new risk stratification model and compare its performance against the existing guidelines for managing AI. A risk stratification model was designed by assigning points for adrenal size (1, 2, or 3 points for tumors <4, 4-6, or >6 cm, respectively) and Hounsfield unit (HU) density on noncontrast CT (1, 2, or 3 points for HU <10, 10-20, or >20, respectively). This model was applied retrospectively to 157 patients with AI managed in an endocrine surgery clinic to assign a score to each tumor. The utility of this model versus the AAES/AACE guidelines was assessed. Of the 157 patients, 54 (34%), had tumors <4 cm with HU <10 (a score of 2). One third of these were hormonally active on biochemical workup and underwent adrenalectomy. The remaining two thirds were nonsecretory lesions and have been followed conservatively with annual testing. In 103 patients (66%), the adrenal mass was >4 cm and/or had indeterminate features on noncontrast CT (HU >10, irregular borders, heterogeneity), and adrenalectomy was performed after hormonal evaluation was completed (10 were hormonally active on biochemical testing). Seven of these patients (7%) had adrenocortical cancer on final pathology with tumor size <4 cm in 0, 4-6 cm in 1, and >6 cm in 5 patients. Of the hormonally inactive patients, 32% had a score of 3, 38% 4, and 30% 5 or 6. The incidence of adrenocortical cancer in these subgroups was 0, 0, and 25%, respectively. This study shows that an algorithm that utilizes the hormonal activity at the first decision step followed by a consolidated risk stratification, based on tumor size and HU density, has a potential to spare a substantial number of patients from unnecessary "diagnostic" surgery for AI. Copyright © 2014 Elsevier Inc. All rights reserved.

Does the Sverdrup critical depth model explain bloom dynamics in estuaries?

USGS Publications Warehouse

Lucas, L.V.; Cloern, J.E.; Koseff, Jeffrey R.; Monismith, Stephen G.; Thompson, J.K.

1998-01-01

In this paper we use numerical models of coupled biological-hydrodynamic processes to search for general principles of bloom regulation in estuarine waters. We address three questions: what are the dynamics of stratification in coastal systems as influenced by variable freshwater input and tidal stirring? How does phytoplankton growth respond to these dynamics? Can the classical Sverdrup Critical Depth Model (SCDM) be used to predict the timing of bloom events in shallow coastal domains such as estuaries? We present results of simulation experiments which assume that vertical transport and net phytoplankton growth rates are horizontally homogeneous. In the present approach the temporally and spatially varying turbulent diffusivities for various stratification scenarios are calculated using a hydrodynamic code that includes the Mellor-Yamada 2.5 turbulence closure model. These diffusivities are then used in a time- and depth-dependent advection-diffusion equation, incorporating sources and sinks, for the phytoplankton biomass. Our modeling results show that, whereas persistent stratification greatly increases the probability of a bloom, semidiurnal periodic stratification does not increase the likelihood of a phytoplankton bloom over that of a constantly unstratified water column. Thus, for phytoplankton blooms, the physical regime of periodic stratification is closer to complete mixing than to persistent stratification. Furthermore, the details of persistent stratification are important: surface layer depth, thickness of the pycnocline, vertical density difference, and tidal current speed all weigh heavily in producing conditions which promote the onset of phytoplankton blooms. Our model results for shallow tidal systems do not conform to the classical concepts of stratification and blooms in deep pelagic systems. First, earlier studies (Riley, 1942, for example) suggest a monotonic increase in surface layer production as the surface layer shallows. Our model results suggest, however, a nonmonotonic relationship between phytoplankton population growth and surface layer depth, which results from a balance between several 'competing' processes, including the interaction of sinking with turbulent mixing and average net growth occurring within the surface layer. Second, we show that the traditional SCDM must be refined for application to energetic shallow systems or for systems in which surface layer mixing is not strong enough to counteract the sinking loss of phytoplankton. This need for refinement arises because of the leakage of phytoplankton from the surface layer by turbulent diffusion and sinking, processes not considered in the classical SCDM. Our model shows that, even for low sinking rates and small turbulent diffusivities, a significant % of the phytoplankton biomass produced in the surface layer can be lost by these processes.

On total turbulent energy and the passive and active role of buoyancy in turbulent momentum and mass transfer.

PubMed

de Nijs, Michel A J; Pietrzak, Julie D

Measurements of turbulent fluctuations of horizontal and vertical components of velocity, salinity and suspended particulate matter are presented. Turbulent Prandtl numbers are found to increase with stratification and to become larger than 1. Consequently, the vertical turbulent mass transport is suppressed by buoyancy forces, before the turbulent kinetic energy (TKE) and vertical turbulent momentum exchange are inhibited. With increasing stratification, the buoyancy fluxes do not cease, instead they become countergradient. We find that buoyantly driven motions play an active role in the transfer of mass. This is in agreement with trends derived from Monin-Obukhov scaling. For positive Richardson flux numbers (Ri f ), the log velocity profile in the near-bed layer requires correction with a drag reduction. For negative Ri f , the log velocity profile should be corrected with a drag increase, with increasing |Ri f |. This highlights the active role played by buoyancy in momentum transfer and the production of TKE. However, the data do not appear to entirely follow Monin-Obukhov scaling. This is consistent with the notion that the turbulence field is not in equilibrium. The large stratification results in the decay of turbulence and countergradient buoyancy fluxes act to restore equilibrium in the energy budget. This implies that there is a finite adjustment timescale of the turbulence field to changes in velocity shear and density stratification. The energy transfers associated with the source and sink function of the buoyancy flux can be modeled with the concept of total turbulent energy.

Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

DOE PAGES

Squire, J.; Bhattacharjee, A.

2015-11-02

Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is nomore » strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.« less

Changes in Bottom Water Physical Properties Above the Mid-Atlantic Ridge Flank in the Brazil Basin

NASA Astrophysics Data System (ADS)

Zhao, Jian; Thurnherr, Andreas M.

2018-01-01

Warming of abyssal waters in recent decades has been widely documented around the global ocean. Here repeat hydrographic data collected in 1997 and 2014 near a deep fracture zone canyon in the eastern Brazil Basin are used to quantify the long-term change. Significant changes are found in the Antarctic Bottom Water (AABW) within the canyon. The AABW in 2014 was warmer (0.08 ± 0.06°C), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 kg m-3) than in 1997. In contrast, the change in the North Atlantic Deep Water has complicated spatial structure and is almost indistinguishable from zero at 95% confidence. The resulting divergence in vertical displacement of the isopycnals modifies the local density stratification. At its peak, the local squared buoyancy frequency (N2) near the canyon is reduced by about 20% from 1997 to 2014. Similar reduction is found in the basinwide averaged profiles over the Mid-Atlantic Ridge flank along 25°W in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation.

Biogeochemical processes controlling density stratification in an iron-meromictic lake

NASA Astrophysics Data System (ADS)

Nixdorf, E.; Boehrer, B.

2015-06-01

Biogeochemical processes and mixing regime of a lake can control each other mutually. The prominent case of iron meromixis is investigated in Waldsee near Doebern, a small lake that originated from surface mining of lignite. From a four years data set of monthly measured electrical conductivity profiles, we calculated summed conductivity as a quantitative variable reflecting the amount of electro-active substances in the entire lake. Seasonal variations followed changing chemocline height. Coinciding changes of electrical conductivities in the monimolimnion indicated that a considerable share of substances, precipitated by the advancing oxygenated epilimnion, re-dissolved in the remaining anoxic deep waters and contributed considerably to the density stratification. In addition, we constructed a lab experiment, in which aeration of monimolimnetic waters removed iron compounds and organic material. Precipitates could be identified by visual inspection. Introduced air bubbles ascended through the water column and formed a water mass similar to the mixolimnetic Waldsee water. The remaining less dense water remained floating on the nearly unchanged monimolimnetic water. In conclusion, iron meromixis as seen in Waldsee did not require two different sources of incoming waters, but the inflow of iron rich deep groundwater and the aeration through the lake surface were fully sufficient.

Investigation of Methods to Predict Thermal Stratification and Its Effect on Solar Energy System Performance.

DTIC Science & Technology

1980-05-01

International Conference, Vol 1, Dhahran, Saudi Arabia (November 1975), pp 508-510. + C. W. J. Van Koppen, L. S. Fischer, and A. Dijkmans ...S. Fischer, and A. Dijkmans , "Stratification Effects in te Short and Long Term Storage of Solar Heat," Proceed- ings, 1978 meeting of Amercan Sec

On the nonlinear interfacial instability of rotating core-annular flow

NASA Technical Reports Server (NTRS)

Coward, Aidrian V.; Hall, Philip

1993-01-01

The interfacial stability of rotating core-annular flows is investigated. The linear and nonlinear effects are considered for the case when the annular region is very thin. Both asymptotic and numerical methods are used to solve the flow in the core and film regions which are coupled by a difference in viscosity and density. The long-term behavior of the fluid-fluid interface is determined by deriving its nonlinear evolution in the form of a modified Kuramoto-Sivashinsky equation. We obtain a generalization of this equation to three dimensions. The flows considered are applicable to a wide array of physical problems where liquid films are used to lubricate higher or lower viscosity core fluids, for which a concentric arrangement is desired. Linearized solutions show that the effects of density and viscosity stratification are crucial to the stability of the interface. Rotation generally destabilizes non-axisymmetric disturbances to the interface, whereas the centripetal forces tend to stabilize flows in which the film contains the heavier fluid. Nonlinear affects allow finite amplitude helically travelling waves to exist when the fluids have different viscosities.

Characterizing Urban Household Waste Generation and Metabolism Considering Community Stratification in a Rapid Urbanizing Area of China.

PubMed

Xiao, Lishan; Lin, Tao; Chen, Shaohua; Zhang, Guoqin; Ye, Zhilong; Yu, Zhaowu

2015-01-01

The relationship between social stratification and municipal solid waste generation remains uncertain under current rapid urbanization. Based on a multi-object spatial sampling technique, we selected 191 households in a rapidly urbanizing area of Xiamen, China. The selected communities were classified into three types: work-unit, transitional, and commercial communities in the context of housing policy reform in China. Field survey data were used to characterize household waste generation patterns considering community stratification. Our results revealed a disparity in waste generation profiles among different households. The three community types differed with respect to family income, living area, religious affiliation, and homeowner occupation. Income, family structure, and lifestyle caused significant differences in waste generation among work-unit, transitional, and commercial communities, respectively. Urban waste generation patterns are expected to evolve due to accelerating urbanization and associated community transition. A multi-scale integrated analysis of societal and ecosystem metabolism approach was applied to waste metabolism linking it to particular socioeconomic conditions that influence material flows and their evolution. Waste metabolism, both pace and density, was highest for family structure driven patterns, followed by lifestyle and income driven. The results will guide community-specific management policies in rapidly urbanizing areas.

Principal stratification in causal inference.

PubMed

Frangakis, Constantine E; Rubin, Donald B

2002-03-01

Many scientific problems require that treatment comparisons be adjusted for posttreatment variables, but the estimands underlying standard methods are not causal effects. To address this deficiency, we propose a general framework for comparing treatments adjusting for posttreatment variables that yields principal effects based on principal stratification. Principal stratification with respect to a posttreatment variable is a cross-classification of subjects defined by the joint potential values of that posttreatment variable tinder each of the treatments being compared. Principal effects are causal effects within a principal stratum. The key property of principal strata is that they are not affected by treatment assignment and therefore can be used just as any pretreatment covariate. such as age category. As a result, the central property of our principal effects is that they are always causal effects and do not suffer from the complications of standard posttreatment-adjusted estimands. We discuss briefly that such principal causal effects are the link between three recent applications with adjustment for posttreatment variables: (i) treatment noncompliance, (ii) missing outcomes (dropout) following treatment noncompliance. and (iii) censoring by death. We then attack the problem of surrogate or biomarker endpoints, where we show, using principal causal effects, that all current definitions of surrogacy, even when perfectly true, do not generally have the desired interpretation as causal effects of treatment on outcome. We go on to forrmulate estimands based on principal stratification and principal causal effects and show their superiority.

Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

NASA Astrophysics Data System (ADS)

Bandriyana, B.; Utaja

2010-06-01

Thermal stratification introduces thermal shock effect which results in local stress and fatique problems that must be considered in the design of nuclear power plant components. Local stress and fatique calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343° C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

Molecular aspect ratio and anchoring strength effects in a confined Gay-Berne liquid crystal

NASA Astrophysics Data System (ADS)

Cañeda-Guzmán, E.; Moreno-Razo, J. A.; Díaz-Herrera, E.; Sambriski, E. J.

2014-04-01

Phase diagrams for Gay-Berne (GB) fluids were obtained from molecular dynamics simulations for GB(2, 5, 1, 2) (i.e. short mesogens) and GB(3, 5, 1, 2) (i.e. long mesogens), which yield isotropic, nematic, and smectic-B phases. The long-mesogen fluid also yields the smectic-A phase. Ordered phases of the long-mesogen fluid form at higher temperatures and lower densities when compared to those of the short-mesogen fluid. The effect of confinement under weak and strong substrate couplings in slab geometry was investigated. Compared to the bulk, the isotropic-nematic transition does not shift in temprature significantly for the weakly coupled substrate in either mesogen fluid. However, the strongly coupled substrate shifts the transition to lower temperature. Confinement induces marked stratification in the short-mesogen fluid. This effect diminishes with distance from the substrate, yielding bulk-like behaviour in the slab central region. Fluid stratification is very weak for the long-mesogen fluid, but the strongly coupled substrate induces 'smectisation', an ordering effect that decays with distance. Orientation of the fluid on the substrate depends on the mesogen. There is no preferred orientation in a plane parallel to the substrate for the weakly coupled case. In the strongly coupled case, the mesogen orientation mimics that of adjacent fluid layers. Planar anchoring is observed with a broad distribution of orientations in the weakly coupled case. In the strongly coupled case, the distribution leans toward planar orientations for the short-mesogen fluid, while a marginal preference for tilting persists in the long-mesogen fluid.

Contribution to the thermodynamic description of the corium - The U-Zr-O system

NASA Astrophysics Data System (ADS)

Quaini, A.; Guéneau, C.; Gossé, S.; Dupin, N.; Sundman, B.; Brackx, E.; Domenger, R.; Kurata, M.; Hodaj, F.

2018-04-01

In order to understand the stratification process that may occur in the late phase of the fuel degradation during a severe accident in a PWR, the thermodynamic knowledge of the U-Zr-O system is crucial. The presence of a miscibility gap in the U-Zr-O liquid phase may lead to a stratified configuration, which will impact the accidental scenario management. The aim of this work was to obtain new experimental data in the U-Zr-O liquid miscibility gap. New tie-line data were provided at 2567 ± 25 K. The related thermodynamic models were reassessed using present data and literature values. The reassessed model will be implemented in the TAF-ID international database. The composition and density of phases potentially formed during stratification will be predicted by coupling current thermodynamic model with thermal-hydraulics codes.

A novel method to create high density stratification with matching refractive index for optical flow investigations

NASA Astrophysics Data System (ADS)

Krohn, Benedikt; Manera, Annalisa; Petrov, Victor

2018-04-01

Turbulent mixing in stratified environments represents a challenging task in experimental turbulence research, especially when large density gradients are desired. When optical measurement techniques like particle image velocimetry (PIV) are applied to stratified liquids, it is common practice to combine two aqueous solutions with different density but equal refractive index, to suppress particle image deflections. While refractive image matching (RIM) has been developed in the late 1970s, the achieved limit of 4% density ratio was not rivalled up to day. In the present work, we report a methodology, based on the behavior of excess properties and their change in a multicomponent system while mixing, that allows RIM for solutions with higher density differences. The methodology is then successfully demonstrated using a ternary combination of water, isopropanol and glycerol, for which RIM in presence of a density ratio of 8.6% has been achieved. Qualitative PIV results of a turbulent buoyant jet with 8.6% density ratio are shown.

Global Characteristics of Porosity and Density Stratification Within the Lunar Crust from GRAIL Gravity and Lunar Orbiter Laser Altimeter Topography Data

NASA Technical Reports Server (NTRS)

Han, Shin-Chan; Schmerr, Nicholas; Neumann, Gregory; Holmes, Simon

2014-01-01

The Gravity Recovery and Interior Laboratory (GRAIL) mission is providing unprecedentedly high-resolution gravity data. The gravity signal in relation to topography decreases from 100 km to 30 km wavelength, equivalent to a uniform crustal density of 2450 kg/cu m that is 100 kg/cu m smaller than the density required at 100 km. To explain such frequency-dependent behavior, we introduce rock compaction models under lithostatic pressure that yield radially stratified porosity (and thus density) and examine the depth extent of porosity. Our modeling and analysis support the assertion that the crustal density must vary from surface to deep crust by up to 500 kg/cu m. We found that the surface density of mega regolith is around 2400 kg/cu m with an initial porosity of 10-20%, and this porosity is eliminated at 10-20 km depth due to lithostatic overburden pressure. Our stratified density models provide improved fits to both GRAIL primary and extended mission data.

Thermal advection and stratification effects on surface winds and the low level meridional mass transport

NASA Technical Reports Server (NTRS)

Levy, Gad; Tiu, Felice S.

1990-01-01

Statistical tests are performed on the Seasat scatterometer observations to examine if and to what degree thermal advection and stratification effects manifest themselves in these remotely sensed measurements of mean wind and wind stress over the ocean. On the basis of a two layer baroclinic boundary layer model which is presented, it is shown that the thermal advection and stratification of the entire boundary layer as well as the geostrophic forcing influence the modeled near surface wind and wind stress profiles. Evidence of diurnal variation in the stratification under barotropic conditions is found in the data, with the daytime marine boundary layer being more convective than its nighttime counterpart. The temporal and spacial sampling pattern of the satellite makes it impossible to recover the full diurnal cycle, however. The observed effects of the thermal advection are shown to be statistically significant during the day (and presumed more convective) hours, causing a systematic increase in the poleward transport of mass and heat. The statistical results are in a qualitative agreement with the model simulations and cannot be reproduced in randomized control tests.

Temperature Stratification in a Cryogenic Fuel Tank

NASA Technical Reports Server (NTRS)

Daigle, Matthew John; Smelyanskiy, Vadim; Boschee, Jacob; Foygel, Michael Gregory

2013-01-01

A reduced dynamical model describing temperature stratification effects driven by natural convection in a liquid hydrogen cryogenic fuel tank has been developed. It accounts for cryogenic propellant loading, storage, and unloading in the conditions of normal, increased, and micro- gravity. The model involves multiple horizontal control volumes in both liquid and ullage spaces. Temperature and velocity boundary layers at the tank walls are taken into account by using correlation relations. Heat exchange involving the tank wall is considered by means of the lumped-parameter method. By employing basic conservation laws, the model takes into consideration the major multi-phase mass and energy exchange processes involved, such as condensation-evaporation of the hydrogen, as well as flows of hydrogen liquid and vapor in the presence of pressurizing helium gas. The model involves a liquid hydrogen feed line and a tank ullage vent valve for pressure control. The temperature stratification effects are investigated, including in the presence of vent valve oscillations. A simulation of temperature stratification effects in a generic cryogenic tank has been implemented in Matlab and results are presented for various tank conditions.

A comparison of stratification effectiveness between the National Land Cover Data set and photointerpretation in western Oregon

Treesearch

Paul Dunham; Dale Weyermann; Dale Azuma

2002-01-01

Stratifications developed from National Land Cover Data (NLCD) and from photointerpretation (PI) were tested for effectiveness in reducing sampling error associated with estimates of timberland area and volume from FIA plots in western Oregon. Strata were created from NLCD through the aggregation of cover classes and the creation of 'edge' strata by...

Superiority of delayed risk stratification in differentiated thyroid cancer after total thyroidectomy and radioactive iodine ablation.

PubMed

Hong, Chae Moon; Lee, Won Kee; Jeong, Shin Young; Lee, Sang-Woo; Ahn, Byeong-Cheol; Lee, Jaetae

2014-11-01

The aim of this study was to validate the effectiveness of delayed risk stratification (DRS) in predicting structural progression and compare the predictive value of American Thyroid Association (ATA) risk stratification with that of DRS in patients with differentiated thyroid cancer (DTC). A total of 398 patients with DTC who underwent surgery followed by radioactive iodine ablation were enrolled. Patients were categorized as having excellent response, acceptable response, biochemical incomplete response, or structural incomplete response at 8-15 months' evaluation after radioactive iodine ablation for DRS. Effectiveness of DRS was evaluated according to structural progression-free survival (PFS; median follow-up, 10.7 years). A total of 229 patients (57.5%) were classified as having excellent response, 78 (19.6%) as having acceptable response, 62 (15.6%) as having biochemical incomplete response, and 29 patients (7.3%) as having structural incomplete response. After DRS, 60.2% of intermediate-risk patients and 20.5% of high-risk patients were shifted to the excellent response category. Sixty-nine patients (17.3%) showed structural progression. DRS showed statistical difference in PFS (hazard ratio, 4.268; 95% confidence interval, 3.258-5.477; P<0.001). In multivariate analysis of ATA risk stratification and DRS, DRS was significantly associated with PFS (hazard ratio, 4.383; 95% confidence interval, 3.250-5.912; P<0.001), but ATA risk stratification was not. There was no significant difference in deviances between the use of DRS alone and the use of both DRS and ATA risk stratification (χ=0.103, d.f.=1, P=0.748). DRS is superior to ATA risk stratification in predicting structural disease progression for DTC patients.

The effects of soak temperature on sugar maple seed germination

Treesearch

Carol A. Janerette

1978-01-01

The temperature at which sugar maple seeds were soaked before stratification significantly influenced their germination. Maximal germination was obtained when seeds were soaked at 4?C, but if seeds were soaked at 25?C, germination decreased and the stratification requirement increased.

Cross-diffusion-driven hydrodynamic instabilities in a double-layer system: General classification and nonlinear simulations

NASA Astrophysics Data System (ADS)

Budroni, M. A.

2015-12-01

Cross diffusion, whereby a flux of a given species entrains the diffusive transport of another species, can trigger buoyancy-driven hydrodynamic instabilities at the interface of initially stable stratifications. Starting from a simple three-component case, we introduce a theoretical framework to classify cross-diffusion-induced hydrodynamic phenomena in two-layer stratifications under the action of the gravitational field. A cross-diffusion-convection (CDC) model is derived by coupling the fickian diffusion formalism to Stokes equations. In order to isolate the effect of cross-diffusion in the convective destabilization of a double-layer system, we impose a starting concentration jump of one species in the bottom layer while the other one is homogeneously distributed over the spatial domain. This initial configuration avoids the concurrence of classic Rayleigh-Taylor or differential-diffusion convective instabilities, and it also allows us to activate selectively the cross-diffusion feedback by which the heterogeneously distributed species influences the diffusive transport of the other species. We identify two types of hydrodynamic modes [the negative cross-diffusion-driven convection (NCC) and the positive cross-diffusion-driven convection (PCC)], corresponding to the sign of this operational cross-diffusion term. By studying the space-time density profiles along the gravitational axis we obtain analytical conditions for the onset of convection in terms of two important parameters only: the operational cross-diffusivity and the buoyancy ratio, giving the relative contribution of the two species to the global density. The general classification of the NCC and PCC scenarios in such parameter space is supported by numerical simulations of the fully nonlinear CDC problem. The resulting convective patterns compare favorably with recent experimental results found in microemulsion systems.

Abundance stratification in the atmospheres of blue horizontal-branch stars

NASA Astrophysics Data System (ADS)

LeBlanc, F.

2013-12-01

Horizontal-branch stars with effective temperatures larger than approximately 11 500 K show abundance anomalies as well as other peculiar observational properties believed to be due to atomic diffusion in their atmosphere. These stars possess low rotational velocities that makes it possible for atomic diffusion to come into play and are therefore of great interest with respect to diffusion theory. Observational anomalies of blue horizontal-branch stars found in globular clusters such as photometric jumps and gaps are reviewed. Recent detections of vertical stratification of elements are also discussed. These results are compared to predictions of atmospheric modeling while including vertical stratification of the elements. The atmospheric structure of these models is calculated self-consistently while taking into account vertical stratification of the elements.

Large Area Crop Inventory Experiment (LACIE). Second-generation sampling strategy evaluation report. [Kansas, North Dakota, and U.S.S.R.

NASA Technical Reports Server (NTRS)

Basu, J. P. (Principal Investigator); Dragich, S. M.; Mcguigan, D. P.

1978-01-01

The author has identified the following significant results. The stratification procedure in the new sampling strategy for LACIE included: (1) correlation test results indicating that an agrophysical stratum may be homogeneous with respect to agricultural density, but not with respect to wheat density; and (2) agrophysical unit homogeneity test results indicating that with respect to agricultural density many agrophysical units are not homogeneous, but removal of one or more refined strata from any such current agrophysical unit can make the strata homogeneous. The apportioning procedure results indicated that the current procedure is not performing well and that the apportioned estimates of refined strata wheat area are often unreliable.

Vertical Mixing in the Dead Sea

NASA Astrophysics Data System (ADS)

Gertman, Isaac; Ozer, Tal; Katsenelson, Boris; Lensky, Nadav

2015-04-01

For hundreds of years, the Dead Sea was characterized by a stable haline stratification, supported by runoff. The penetration of the winter convection was limited to an upper mixed layer (UML) of about 30-50 m. Below the UML, a stable halocline prevented the mixing. As a result of the runoff reduction, the UML salinity increased and the gravitational stability diminished. During the winter of 1978-1979, the sea water overturned, ending the long-term stable hydrological regime. Since 1979, the haline stratification structure reoccurred twice after extremely rainy winters, in 1980-82 and 1992-1995. In other years, the sea was entirely mixed by winter thermal convection ( which occurs from November to March ) and had a seasonal pycnocline beneath the UML during summer. Profiles of temperature and quasi-salinity (density anomaly from 1000 kg/m3 for the chosen reference temperature of 32° C) during the last 19 years, show the formation of summer ``overturning halocline'' beneath the UML, and the thermocline that supports the stable stratification. Another warm and saline layer is formed also during the summer period near the bottom. This layer spreads from the southern part of the sea, where end-brine is discharged to the sea from the Israeli and Jordanian salt plants' evaporation ponds. The end-brine has extremely high salinity (˜ 350 g/kg) and, in spite of the high temperatures ( ˜ 45° C), high density (1350 kg/m^3), it therefore spreads as a gravitational current in the Dead Sea deep basin. Estimation of the density ratio (Rρ) for the Dead Sea water (where measurements of water salinity is quite difficult) was done using quasi-salinity (σ32) and potential temperature (θ): Rρ= [α(partialθ/partial z)]/[β(partial σ32/partial z)], where α and β are temperature expansion and quasi-salinity contraction coefficients respectively. The values of α and β for the Dead Sea water were defined from water samples collected during 2008. The Rρ values confirm that the summer Dead Sea thermohaline structure is appropriate for double diffusion mixing. A salt fingers regime beneath the UML (1.3< Rρ

MULTIGENERATIONAL ASPECTS OF SOCIAL STRATIFICATION: ISSUES FOR FURTHER RESEARCH.

PubMed

Mare, Robert D

2014-03-01

The articles in this special issue show the vitality and progress of research on multigenerational aspects of social mobility, stratification, and inequality. The effects of the characteristics and behavior of grandparents and other kin on the statuses, resources, and positions of their descendants are best viewed in a demographic context. Intergenerational effects work through both the intergenerational associations of socioeconomic characteristics and also differential fertility and mortality. A combined socioeconomic and demographic framework informs a research agenda which addresses the following issues: how generational effects combine with variation in age, period, and cohort within each generation; distinguishing causal relationships across generations from statistical associations; how multigenerational effects vary across socioeconomic hierarchies, including the possibility of stronger effects at the extreme top and bottom; distinguishing between endowments and investments in intergenerational effects; multigenerational effects on associated demographic behaviors and outcomes (especially fertility and mortality); optimal tradeoffs among diverse types of data on multigenerational processes; and the variability across time and place in how kin, education, and other institutions affect stratification.

MULTIGENERATIONAL ASPECTS OF SOCIAL STRATIFICATION: ISSUES FOR FURTHER RESEARCH

PubMed Central

Mare, Robert D.

2014-01-01

The articles in this special issue show the vitality and progress of research on multigenerational aspects of social mobility, stratification, and inequality. The effects of the characteristics and behavior of grandparents and other kin on the statuses, resources, and positions of their descendants are best viewed in a demographic context. Intergenerational effects work through both the intergenerational associations of socioeconomic characteristics and also differential fertility and mortality. A combined socioeconomic and demographic framework informs a research agenda which addresses the following issues: how generational effects combine with variation in age, period, and cohort within each generation; distinguishing causal relationships across generations from statistical associations; how multigenerational effects vary across socioeconomic hierarchies, including the possibility of stronger effects at the extreme top and bottom; distinguishing between endowments and investments in intergenerational effects; multigenerational effects on associated demographic behaviors and outcomes (especially fertility and mortality); optimal tradeoffs among diverse types of data on multigenerational processes; and the variability across time and place in how kin, education, and other institutions affect stratification. PMID:24748709

Effects of stratification and temperature on seed germination speed and uniformity in central Oregon ponderosa pine (Pinus ponderosa Dougl. ex Laws.).

Treesearch

John C. Weber; Frank C. Sorensen

1990-01-01

Effects of stratification period and incubation temperature on seed germination speed and uniformity were investigated in a bulked seed lot of 200 ponderosa pine trees (Pinus ponderosa Dougl. ex Laws.) sampled from 149 locations in central Oregon. Mean rate of embryo development towards germination (l/days to 50 percent germination) and standard...

Germination of dimorphic seeds of Suaeda aralocaspica in response to light and salinity conditions during and after cold stratification

PubMed Central

Wang, Hong-Ling; Tian, Chang-Yan

2017-01-01

Cold stratification is a requirement for seed dormancy breaking in many species, and thus it is one of the important factors for the regulation of timing of germination. However, few studies have examined the influence of various environmental conditions during cold stratification on subsequent germination, and no study has compared such effects on the performance of dormant versus non-dormant seeds. Seeds of halophytes in the cold desert might experience different light and salinity conditions during and after cold stratification. As such, dimorphic seeds (non-dormant brown seeds and black seeds with non-deep physiological dormancy) of Suaeda aralocaspica were cold stratified under different light (12 h light–12 h darkness photoperiod or continuous darkness) or salinity (0, 200 or 1,000 mmol L-1 NaCl) conditions for 20 or 40 days. Then stratified seeds were incubated under different light or salinity conditions at daily (12/12 h) temperature regime of 10:25 °C for 20 days. For brown seeds, cold stratification was also part of the germination period. In contrast, almost no black seeds germinated during cold stratification. The longer the cold stratification, the better the subsequent germination of black seeds, regardless of light or salinity conditions. Light did not influence germination of brown seeds. Germination of cold-stratified black seeds was inhibited by darkness, especially when they were stratified in darkness. With an increase in salinity at the stage of cold stratification or germination, germination percentages of both seed morphs decreased. Combinational pre-treatments of cold stratification and salinity did not increase salt tolerance of dimorphic seeds in germination phase. Thus, light and salinity conditions during cold stratification partly interact with these conditions during germination stage and differentially affect germination of dimorphic seeds of S. aralocaspica. PMID:28828266

Thermal relaxation and critical instability of near-critical fluid microchannel flow.

PubMed

Chen, Lin; Zhang, Xin-Rong; Okajima, Junnosuke; Maruyama, Shigenao

2013-04-01

We present two-dimensional numerical investigations of the temperature and velocity evolution of a pure near-critical fluid confined in microchannels. The fluid is subjected to two sides heating after it reached isothermal steady state. We focus on the abnormal behaviors of the near-critical fluid in response to the sudden imposed heat flux. New thermal-mechanical effects dominated by fluid instability originating from the boundary and local equilibrium process are reported. Near the microchannel boundaries, the instability grows very quickly and an unexpected vortex formation mode is identified when near-critical thermal-mechanical effect is interacting with the microchannel shear flow. The mechanism of the new kind of Kelvin-Helmholtz instability induced by boundary expansion and density stratification processes is also discussed in detail. This mechanism may bring about innovations in the field of microengineering.

Thermal relaxation and critical instability of near-critical fluid microchannel flow

NASA Astrophysics Data System (ADS)

Chen, Lin; Zhang, Xin-Rong; Okajima, Junnosuke; Maruyama, Shigenao

2013-04-01

We present two-dimensional numerical investigations of the temperature and velocity evolution of a pure near-critical fluid confined in microchannels. The fluid is subjected to two sides heating after it reached isothermal steady state. We focus on the abnormal behaviors of the near-critical fluid in response to the sudden imposed heat flux. New thermal-mechanical effects dominated by fluid instability originating from the boundary and local equilibrium process are reported. Near the microchannel boundaries, the instability grows very quickly and an unexpected vortex formation mode is identified when near-critical thermal-mechanical effect is interacting with the microchannel shear flow. The mechanism of the new kind of Kelvin-Helmholtz instability induced by boundary expansion and density stratification processes is also discussed in detail. This mechanism may bring about innovations in the field of microengineering.

Investigating Summer Thermal Stratification in Lake Ontario

NASA Astrophysics Data System (ADS)

James, S. C.; Arifin, R. R.; Craig, P. M.; Hamlet, A. F.

2017-12-01

Seasonal temperature variations establish strong vertical density gradients (thermoclines) between the epilimnion and hypolimnion. Accurate simulation of vertical mixing and seasonal stratification of large lakes is a crucial element of the thermodynamic coupling between lakes and the atmosphere in integrated models. Time-varying thermal stratification patterns can be accurately simulated with the versatile Environmental Fluid Dynamics Code (EFDC). Lake Ontario bathymetry was interpolated onto a 2-km-resolution curvilinear grid with vertical layering using a new approach in EFDC+, the so-called "sigma-zed" coordinate system which allows the number of vertical layers to be varied based on water depth. Inflow from the Niagara River and outflow to the St. Lawrence River in conjunction with hourly meteorological data from seven local weather stations plus three-hourly data from the North American Regional Reanalysis govern the hydrodynamic and thermodynamic responses of the Lake. EFDC+'s evaporation algorithm was updated to more accurately simulate net surface heat fluxes. A new vertical mixing scheme from Vinçon-Leite that implements different eddy diffusivity formulations above and below the thermocline was compared to results from the original Mellor-Yamada vertical mixing scheme. The model was calibrated by adjusting solar-radiation absorption coefficients in addition to background horizontal and vertical mixing parameters. Model skill was evaluated by comparing measured and simulated vertical temperature profiles at shallow (20 m) and deep (180 m) locations on the Lake. These model improvements, especially the new sigma-zed vertical discretization, accurately capture thermal-stratification patterns with low root-mean-squared errors when using the Vinçon-Leite vertical mixing scheme.

Magnetically Induced Rotating Rayleigh-Taylor Instability.

PubMed

Scase, Matthew M; Baldwin, Kyle A; Hill, Richard J A

2017-03-03

Classical techniques for investigating the Rayleigh-Taylor instability include using compressed gasses 1 , rocketry 2 or linear electric motors 3 to reverse the effective direction of gravity, and accelerate the lighter fluid toward the denser fluid. Other authors e.g. 4 , 5 , 6 have separated a gravitationally unstable stratification with a barrier that is removed to initiate the flow. However, the parabolic initial interface in the case of a rotating stratification imposes significant technical difficulties experimentally. We wish to be able to spin-up the stratification into solid-body rotation and only then initiate the flow in order to investigate the effects of rotation upon the Rayleigh-Taylor instability. The approach we have adopted here is to use the magnetic field of a superconducting magnet to manipulate the effective weight of the two liquids to initiate the flow. We create a gravitationally stable two-layer stratification using standard flotation techniques. The upper layer is less dense than the lower layer and so the system is Rayleigh-Taylor stable. This stratification is then spun-up until both layers are in solid-body rotation and a parabolic interface is observed. These experiments use fluids with low magnetic susceptibility, |χ| ~ 10 -6 - 10 -5 , compared to a ferrofluids. The dominant effect of the magnetic field applies a body-force to each layer changing the effective weight. The upper layer is weakly paramagnetic while the lower layer is weakly diamagnetic. When the magnetic field is applied, the lower layer is repelled from the magnet while the upper layer is attracted towards the magnet. A Rayleigh-Taylor instability is achieved with application of a high gradient magnetic field. We further observed that increasing the dynamic viscosity of the fluid in each layer, increases the length-scale of the instability.

High resolution monitoring of episodic stratification events in an enclosed marine system

NASA Astrophysics Data System (ADS)

Sullivan, Timothy; Broszeit, Stefanie; O'Sullivan, Keith P. A.; McAllen, Rob; Davenport, John; Regan, Fiona

2013-05-01

While hypoxic and anoxic environments have existed throughout geological time, their frequency of occurrence in shallow coastal and estuarine areas appears to be increasing. However, few data are available on the physicochemical conditions at the boundary between anoxic and normoxic layers, including the conditions required for both formation and dissipation of stratification. Advances in autonomous environmental sensing technology have produced robust sensors capable of detailed measurements under inhospitable conditions created in such environments. In this study, an autonomous sensor approach was used to compare water column properties above and below the stratification before during and after dissipation of the stratification. Further, an investigation into the effect of the stratification on sedimentation rates of organic and inorganic matter and current speeds is reported here. Lough Hyne, a seasonally stratified temperate marine lake provided favourable conditions for this study. It was shown that temperatures dropped rapidly above the oxy-thermocline while increasing rapidly below the stratification, leading to a mixing of the complete water column. This was reflected in oxygen measurements below the stratification, which rose from anoxia to normoxic conditions over the same time period. During summer, the thermocline formed a barrier to organic matter sedimentation, reducing it significantly when present, while inorganic matter sedimentation was unaffected by the presence of thermocline. It also caused a reduction in current speeds below the thermocline.

Characterization and modeling of turbidity density plume induced into stratified reservoir by flood runoffs.

PubMed

Chung, S W; Lee, H S

2009-01-01

In monsoon climate area, turbidity flows typically induced by flood runoffs cause numerous environmental impacts such as impairment of fish habitat and river attraction, and degradation of water supply efficiency. This study was aimed to characterize the physical dynamics of turbidity plume induced into a stratified reservoir using field monitoring and numerical simulations, and to assess the effect of different withdrawal scenarios on the control of downstream water quality. Three different turbidity models (RUN1, RUN2, RUN3) were developed based on a two-dimensional laterally averaged hydrodynamic and transport model, and validated against field data. RUN1 assumed constant settling velocity of suspended sediment, while RUN2 estimated the settling velocity as a function of particle size, density, and water temperature to consider vertical stratification. RUN3 included a lumped first-order turbidity attenuation rate taking into account the effects of particles aggregation and degradable organic particles. RUN3 showed best performance in replicating the observed variations of in-reservoir and release turbidity. Numerical experiments implemented to assess the effectiveness of different withdrawal depths showed that the alterations of withdrawal depth can modify the pathway and flow regimes of the turbidity plume, but its effect on the control of release water quality could be trivial.

Horizontal convection with mechanical stirring

NASA Astrophysics Data System (ADS)

Griffiths, Ross; Stewart, Kial; Hughes, Graham

2012-11-01

The effects of turbulent mixing on convective circulation forced by a horizontal gradient of buoyancy at the surface is examined using laboratory experiments in which a salt flux is introduced at the surface, at one end of a box, and a freshwater buoyancy condition is applied over the rest of the surface. Horizontal rods are oscillated and yo-yoed continuously through the water column, providing a diffusivity that can be calibrated. The convection reaches a stationary state having zero net salt flux. We find that for small stirring rates the small but finite volume flux from the dense source is significant and a virtual source correction is required to take this into account. The density stratification and overturning volume transport are consistent with a theoretical model for high Rayleigh numbers: the transport ψ increases with diffusivity κ (ψg ~ gκ 1 / 4) . The results show that vertical mixing in the boundary layer is important, particularly in setting the density of the interior and the overturning rate. However, interior mixing is unimportant, which raises an interesting question over whether abyssal mixing rates in the ocean play any significant role in setting the abyssal ocean density or the transport in the Meridional Overturning Circulation.

Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

USGS Publications Warehouse

Cloern, James E.; Cole, Brian E.; Hager, Stephen W.

1994-01-01

Discrete red patches of water were observed in South San Francisco Bay (USA) on 30 April 1993, and examination of live samples showed that this red tide was caused by surface accumulations of the pigmented ciliate Mesodinium rubrum . Vertical profiles showed strong salinity and temperature stratification in the upper 5 m, peak chlorophyll fluorescence in the upper meter, and differences in the small-scale density structure and fluorescence distribution among red patches. Events preceding this Mesodinium red tide included: (i) heavy precipitation and run-off, allowing for strong salinity stratification; (ii) a spring diatom bloom where the chlorophyll a concentration reached 50 mg m −3 ; (ii) depletions of dissolved inorganic N and Si in the photic zone; and (iv) several days of rapid warming and stabilization of the upper surface layer. These conditions may be general prerequisites for M.rubrum blooms in temperate estuaries.

Plasma ion stratification by weak planar shocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simakov, Andrei N.; Keenan, Brett D.; Taitano, William T.

We derive fluid equations for describing steady-state planar shocks of a moderate strength (0 < M - 1 ≲ 1 with M the shock Mach number) propagating through an unmagnetized quasineutral collisional plasma comprising two separate ion species. In addition to the standard fluid shock quantities, such as the total mass density, mass-flow velocity, and electron and average ion temperatures, the equations describe shock stratification in terms of variations in the relative concentrations and temperatures of the two ion species along the shock propagation direction. We have solved these equations analytically for weak shocks (0 < M - 1 <

Plasma Ion Stratification by Weak Planar Shocks

NASA Astrophysics Data System (ADS)

Simakov, A. N.; Keenan, B. D.; Taitano, W. T.; Chacón, L.

2017-10-01

We derive fluid equations for describing steady-state planar shocks of a moderate strength (0

Plasma ion stratification by weak planar shocks

NASA Astrophysics Data System (ADS)

Simakov, Andrei N.; Keenan, Brett D.; Taitano, William T.; Chacón, Luis

2017-09-01

We derive fluid equations for describing steady-state planar shocks of a moderate strength ( 0

Plasma ion stratification by weak planar shocks

DOE PAGES

Simakov, Andrei N.; Keenan, Brett D.; Taitano, William T.; ...

2017-08-01

We derive fluid equations for describing steady-state planar shocks of a moderate strength (0 < M - 1 ≲ 1 with M the shock Mach number) propagating through an unmagnetized quasineutral collisional plasma comprising two separate ion species. In addition to the standard fluid shock quantities, such as the total mass density, mass-flow velocity, and electron and average ion temperatures, the equations describe shock stratification in terms of variations in the relative concentrations and temperatures of the two ion species along the shock propagation direction. We have solved these equations analytically for weak shocks (0 < M - 1 <

Effects of warm water inflows on the dispersion of pollutants in small reservoirs.

PubMed

Palancar, María C; Aragón, José M; Sánchez, Fernando; Gil, Roberto

2006-11-01

The effects of the warm water discharged by a nuclear power plant (NPP) into a small reservoir are studied. A case study is presented (José Cabrera NPP-Zorita Hidráulica Reservoir) with experimental data of the reservoir stratification and predicted data of the dispersion of radioactive pollutants from operative or accidental releases. The vertical and longitudinal temperature profiles, electrical conductivity and transparency of the reservoir water were measured for an annual cycle. The results indicate that the continuous warm water discharge from the NPP causes permanent and artificial reservoir stratification. The stratification is significant within 1500 m upstream and 1000 m downstream from the warm water outfall. The pollutant dispersion has been predicted by using a flow model based on N(T) perfect-mixing compartments in series with feedback. The model parameter, N(T), is calculated from the longitudinal diffusion coefficient. The prediction of pollutant dispersion by means of this model shows that the stratification slows down the vertical mixing in the whole water body, and reduces the reservoir volume that is effective for the dilution and dispersion of pollutants. This means that, in the case of a radioactive pollutant release, the reservoir radioactivity level could increase significantly.

Detection of Oil in Water Column, Final Report: Detection Prototype Tests

DTIC Science & Technology

2014-07-01

first phase of the project involved initial development and testing of three technologies to address the detection problem . This second phase...important oceanic phenomena such as density stratification and naturally occurring particulate matter, which will affect the performance of sensors in the ...2 UNCLAS//Public | CG-926 RDC | M. Fitzpatrick, et al.| Public July 2014 spills of submerged oil is far more complex due to the problems

Sediment Transport at Density Fronts in Shallow Water

DTIC Science & Technology

2014-07-16

June 2009 on the Skagit Tidal flats in Puget Sound, coordinated with other researchers in the Tidal Flats DRI. Focused observations of the shallow...on wind correlation length scales and implications for coastal ocean modeling (Raubenheimer et al., 2013). We also worked on applying to the model...From the Skagit model results, we found that the rate of change of stratification, quantified as the integrated potential energy anomaly O (Simpson

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keren, Y.; Bemporad, G.A.; Rubin, H.

This paper concerns an experimental evaluation of the basic aspects of operation of the advanced solar pond (ASP). Experiments wee carried out in a laboratory test section in order to assess the feasibility of the density gradient maintenance in stratified flowing layers. The density stratification was caused by a non uniform distribution of temperatures in the flow field. Results of the experiments are reported and analyzed in the paper. Experimental data were used in order to calibrate the numerical model able to simulate heat and momentum transfer in the ASP. The numerical results confirmed the validity of the numerical modelmore » adopted, and proved the latter applicability for the simulation of the ASP performance.« less

Cyanobacterial blooms in stratified and destratified eutrophic reservoirs in semi-arid region of Brazil.

PubMed

Dantas, Enio W; Moura, Ariadne N; Bittencourt-Oliveira, Maria do Carmo

2011-12-01

This study investigated the dynamics of cyanobacteria in two deep, eutrophic reservoirs in a semi-arid region of Brazil during periods of stratification and destratification. Four collections were carried out at each reservoir at two depths at three-month intervals. The following abiotic variables were analyzed: water temperature, dissolved oxygen, pH, turbidity, water transparency, total phosphorus, total dissolved phosphorus, orthophosphate and total nitrogen. Phytoplankton density was quantified for the determination of the biomass of cyanobacteria. The data were analyzed using CCA. Higher mean phytoplankton biomass values (29.8 mm(3).L(-1)) occurred in the period of thermal stratification. A greater similarity in the phytoplankton communities also occurred in this period and was related to the development of cyanobacteria, mainly Cylindrospermopsis raciborskii (>3.9 mm(3).L(-1)). During the period of thermal destratification, this species co-dominated the environment with Planktothrix agardhii, Geitlerinema amphibium, Microcystis aeruginosa and Merismopedia tenuissima, as well as with diatoms and phytoflagellates. Environmental instability and competition among algae hindered the establishment of blooms more during the mixture period than during the stratification period. Thermal changes in the water column caused by climatologic events altered other physiochemical conditions of the water, leading to changes in the composition and biomass of the cyanobacterial community in tropical reservoirs.

Characterisation of the Subaquatic Groundwater Discharge That Maintains the Permanent Stratification within Lake Kivu; East Africa

PubMed Central

Ross, Kelly Ann; Gashugi, Elisée; Gafasi, Augustin; Wüest, Alfred; Schmid, Martin

2015-01-01

Warm and cold subaquatic groundwater discharge into Lake Kivu forms the large-scale density gradients presently observed in the lake. This structure is pertinent to maintaining the stratification that locks the high volume of gases in the deepwater. Our research presents the first characterisation of these inflows. Temperature and conductivity profiling was conducted from January 2010 to March 2013 to map the locations of groundwater discharge. Water samples were obtained within the lake at the locations of the greatest temperature anomalies observed from the background lake-profile. The isotopic and chemical signatures of the groundwater were applied to assess how these inflows contribute to the overall stratification. It is inferred that Lake Kivu’s deepwater has not been completely recharged by the groundwater inflows since its turnover that is speculated to have occurred within the last ~1000 yrs. Given a recent salinity increase in the lake constrained to within months of seismic activity measured beneath the basin, it is plausible that increased hydrothermal-groundwater inflows into the deep basin are correlated with episodic geologic events. These results invalidate the simple two-component end-member mixing regime that has been postulated up to now, and indicate the importance of monitoring this potentially explosive lake. PMID:25799098

Characterizing Urban Household Waste Generation and Metabolism Considering Community Stratification in a Rapid Urbanizing Area of China

PubMed Central

Xiao, Lishan; Lin, Tao; Chen, Shaohua; Zhang, Guoqin; Ye, Zhilong; Yu, Zhaowu

2015-01-01

The relationship between social stratification and municipal solid waste generation remains uncertain under current rapid urbanization. Based on a multi-object spatial sampling technique, we selected 191 households in a rapidly urbanizing area of Xiamen, China. The selected communities were classified into three types: work-unit, transitional, and commercial communities in the context of housing policy reform in China. Field survey data were used to characterize household waste generation patterns considering community stratification. Our results revealed a disparity in waste generation profiles among different households. The three community types differed with respect to family income, living area, religious affiliation, and homeowner occupation. Income, family structure, and lifestyle caused significant differences in waste generation among work-unit, transitional, and commercial communities, respectively. Urban waste generation patterns are expected to evolve due to accelerating urbanization and associated community transition. A multi-scale integrated analysis of societal and ecosystem metabolism approach was applied to waste metabolism linking it to particular socioeconomic conditions that influence material flows and their evolution. Waste metabolism, both pace and density, was highest for family structure driven patterns, followed by lifestyle and income driven. The results will guide community-specific management policies in rapidly urbanizing areas. PMID:26690056

Cryogenic formation of brine and sedimentary mirabilite in submergent coastal lake basins, Canadian Arctic

NASA Astrophysics Data System (ADS)

Grasby, Stephen E.; Rod Smith, I.; Bell, Trevor; Forbes, Donald L.

2013-06-01

Two informally named basins (Mirabilite Basins 1 and 2) along a submergent coastline on Banks Island, Canadian Arctic Archipelago, host up to 1 m-thick accumulations of mirabilite (Na2SO4·10H2O) underlying stratified water bodies with basal anoxic brines. Unlike isostatically uplifting coastlines that trap seawater in coastal basins, these basins formed from freshwater lakes that were transgressed by seawater. The depth of the sill that separates the basins from the sea is shallow (1.15 m), such that seasonal sea ice formation down to 1.6 m isolates the basins from open water exchange through the winter. Freezing of seawater excludes salts, generating dense brines that sink to the basin bottom. Progressive freezing increases salinity of residual brines to the point of mirabilite saturation, and as a result sedimentary deposits of mirabilite accumulate on the basin floors. Brine formation also leads to density stratification and bottom water anoxia. We propose a model whereby summer melt of the ice cover forms a temporary freshwater lens, and rather than mixing with the underlying brines, it is exchanged with seawater once the ice plug that separates the basins from the open sea melts. This permits progressive brine development and density stratification within the basins.

Effect of stratification and geometrical spreading on sonic boom rise time

NASA Technical Reports Server (NTRS)

Cleveland, Robin O.; Hamilton, Mark F.; Blackstock, David T.

1994-01-01

The purpose of our investigation is to determine the effect of unsteadiness (not associated with turbulence) on rise time. The unsteadiness considered here is due to (1) geometrical spreading, (2) stratification, which includes variation in density, temperature, and relative humidity, and (3) N shaped waveform. A very general Burgers equation, which includes all these effects, is the propagation model for our study. The equation is solved by a new computational algorithm in which all the calculations are done in the time domain. The present paper is a progress report in which some of the factors contributing to unsteadiness are studied, namely geometrical spreading and variation in relative humidity. The work of Pierce and Kang, which motivated our study, is first reviewed. We proceed with a discussion of the Burgers equation model and the algorithm for solving the equation. Some comparison tests to establish the validity of the algorithm are presented. The algorithm is then used to determine the distance required for a steady-state shock, on encountering an abrupt change in relative humidity, to reach a new steady state based on the new humidity. It is found that the transition distance for plane shocks of amplitude 70 Pa is about 4 km when the change in relative humidity is 10 percent. Shocks of amplitude 140 Pa require less distance. The effect of spherical and cylindrical spreading is also considered. We demonstrate that a spreading shock wave never reaches steady state and that its rise time will be less than the equivalent steady state shock. Finally we show that an N wave has a slightly shorter rise time than a step shock of the same amplitude.

Zeno: Critical Fluid Light Scattering Experiment

NASA Technical Reports Server (NTRS)

Gammon, Robert W.; Shaumeyer, J. N.; Briggs, Matthew E.; Boukari, Hacene; Gent, David A.; Wilkinson, R. Allen

1996-01-01

The Zeno (Critical Fluid Light Scattering) experiment is the culmination of a long history of critical fluid light scattering in liquid-vapor systems. The major limitation to making accurate measurements closer to the critical point was the density stratification which occurs in these extremely compressible fluids. Zeno was to determine the critical density fluctuation decay rates at a pair of supplementary angles in the temperature range 100 mK to 100 (mu)K from T(sub c) in a sample of xenon accurately loaded to the critical density. This paper gives some highlights from operating the instrument on two flights March, 1994 on STS-62 and February, 1996 on STS-75. More detail of the experiment Science Requirements, the personnel, apparatus, and results are displayed on the Web homepage at http://www.zeno.umd.edu.

Modeling lateral circulation and its influence on the along-channel flow in a branched estuary

NASA Astrophysics Data System (ADS)

Zhu, Lei; He, Qing; Shen, Jian

2018-02-01

A numerical modeling study of the influence of the lateral flow on the estuarine exchange flow was conducted in the north passage of the Changjiang estuary. The lateral flows show substantial variabilities within a flood-ebb tidal cycle. The strong lateral flow occurring during flood tide is caused primarily by the unique cross-shoal flow that induces a strong northward (looking upstream) barotropic force near the surface and advects saltier water toward the northern part of the channel, resulting in a southward baroclinic force caused by the lateral density gradient. Thus, a two-layer structure of lateral flows is produced during the flood tide. The lateral flows are vigorous near the flood slack and the magnitude can exceed that of the along-channel tidal flow during that period. The strong vertical shear of the lateral flows and the salinity gradient in lateral direction generate lateral tidal straining, which are out of phase with the along-channel tidal straining. Consequently, stratification is enhanced at the early stage of the ebb tide. In contrast, strong along-channel straining is apparent during the late ebb tide. The vertical mixing disrupts the vertical density gradient, thus suppressing stratification. The impact of lateral straining on stratification during spring tide is more pronounced than that of along-channel straining during late flood and early ebb tides. The momentum balance along the estuary suggests that lateral flow can augment the residual exchange flow. The advection of lateral flows brings low-energy water from the shoal to the deep channel during the flood tide, whereas the energetic water is moved to the shoal via lateral advection during the ebb tide. The impact of lateral flow on estuarine circulation of this multiple-channel estuary is different from single-channel estuary. A model simulation by blocking the cross-shoal flow shows that the magnitudes of lateral flows and tidal straining are reduced. Moreover, the reduced lateral tidal straining results in a decrease in vertical stratification from the late flood to early ebb tides during the spring tide. By contrast, the along-channel tidal straining becomes dominant. The model results illustrate the important dynamic linkage between lateral flows and estuarine dynamics in the Changjiang estuary.

The Dynamics of Social Stratification in Contemporary Asian Societies. Asian Studies Module.

ERIC Educational Resources Information Center

Inyang, Ambrose

This curriculum module is designed to provide potential users with access to pedagogic techniques and scholarly works on the subject of social stratification in contemporary Asian societies that can be effectively integrated into appropriate sociology and other relevant courses. First, a set of goals and learning objectives is presented in an…

Stratification, Elaboration and Formalisation of Design Documents: Effects on the Production of Instructional Materials

ERIC Educational Resources Information Center

Boot, Eddy W.; Nelson, Jon; van Merrienboer, Jeroen J. G.; Gibbons, Andrew S.

2007-01-01

Designers and producers of instructional materials lack a common design language. As a result, producers have difficulties translating design documents into technical specifications. The 3D-model is introduced to improve the stratification, elaboration and formalisation of design documents. It is hypothesised that producers working with improved…

USA Stratified Monopoly: A Simulation Game about Social Class Stratification

ERIC Educational Resources Information Center

Fisher, Edith M.

2008-01-01

Effectively teaching college students about social class stratification is a difficult challenge. Explanations for this difficulty tend to focus on the students who often react with resistance, paralysis, or rage. Sociologists have been using games and simulations as alternative methods for several decades to teach about these sensitive subjects.…

Sycamore Seed Germination: The Effects of Provenance, Stratification, Temperature, and Parent Tree

Treesearch

Charles D. Webb; Robert E. Farmer

1968-01-01

Various stratification periods and germination temperatures were applied to sycamore seed collected along the Chattahoochee River from north Georgia to west Florida. Results showed that percent and speed of germination were greater for seed from southern than from northern provenances. Percent and speed of germination increased as temperature increased. The...

[Comparing the Application of Hema-Obs RSS to 250 Pregnancies from Obstetrics/Hematology Consultation in Centro Hospitalar São João, Portugal with the Application of Galit Sarig RSS to 90 Pregnancies from Rambam Health Care Campus, Israel].

PubMed

Salselas, Ana; Pestana, Inês; Bischoff, Francisco; Guimarães, Mariana; Andrade, Joaquim Aguiar

2015-01-01

Pregnant women with thromboembolic diseases, previous thrombotic episodes or thrombophilia family history were supervised in a multidisciplinary Obstetrics/ Hematology consultation in Centro Hospitalar São João EPE, Porto, Portugal. For the evaluation and medication of these women, a risk stratification scale was used. The aim of this study was to validate a Risk Stratification Scale and thromboprophylaxis protocol by means of comparing it with a similar scale, developed and published by Sarig. We have compared: The distribution, by risk groups, obtained through the application of the two scales on pregnant women followed at Centro Hospitalar São João, Porto, Portugal, consultation; the sensibility and specificity for each one of the scales (DeLong scale, applied to Receiver Operating Characteristic) curves; the outcomes in pregnancies followed in Hospital São João, Porto, PortugalResults: According to our Hema-Obs risk stratification scale, 29% were allocated to low-risk, 47% to high-risk and 24% to very-high-risk groups. According to Galit Sarig risk stratification scale, 24% were considered low-risk, 53% moderate, 16% high-risk and 7% as very high-risk group. In our study we observed 9% of spontaneous abortions, in comparison with 18% in the Galit Sarig cohort. From the application of Receiver Operating Characteristic curve to both risk stratification scales, the results of the calculated areas were 58,8% to our Hema-Obs risk stratification scale and 38,7% to Galit Sarig risk stratification scale, with a Delong test significancie of p = 0.0006. We concluded that Hema-Obs risk stratification scale is an effective support for clinical monitoring of therapeutic strategies.

Dissolved oxygen stratification and response to thermal structure and long-term climate change in a large and deep subtropical reservoir (Lake Qiandaohu, China).

PubMed

Zhang, Yunlin; Wu, Zhixu; Liu, Mingliang; He, Jianbo; Shi, Kun; Zhou, Yongqiang; Wang, Mingzhu; Liu, Xiaohan

2015-05-15

From January 2010 to March 2014, detailed depth profiles of water temperature, dissolved oxygen (DO), and chromophoric dissolved organic matter (CDOM) were collected at three sites in Lake Qiandaohu, a large, deep subtropical reservoir in China. Additionally, we assessed the changes in DO stratification over the past 61 years (1953-2013) based on our empirical models and long-term air temperature and transparency data. The DO concentration never fell below 2 mg/L, the critical value for anoxia, and the DO depth profiles were closely linked to the water temperature depth profiles. In the stable stratification period in summer and autumn, the significant increase in CDOM in the metalimnion explained the decrease in DO due to the oxygen consumed by CDOM. Well-developed oxygen stratification was detected at the three sites in spring, summer and autumn and was associated with thermal stratification. Oxycline depth was significantly negatively correlated with daily air temperature and thermocline thickness but significantly positively correlated with thermocline depth during the stratification weakness period (July-February). However, there were no significant correlations among these parameters during the stratification formation period (March-June). The increase of 1.67 °C in yearly average daily air temperature between 1980 and 2013 and the decrease of 0.78 m in Secchi disk depth caused a decrease of 1.65 m and 2.78 m in oxycline depth, respectively, facilitating oxygen stratification and decreasing water quality. Therefore, climate warming has had a substantial effect on water quality through changing the DO regime in Lake Qiandaohu. Copyright © 2015 Elsevier Ltd. All rights reserved.

Stratification strategy for evaluating the influence of diabetes complication severity index on the risk of hospitalization: a record linkage data in Western Australia.

PubMed

Ha, Ninh Thi; Harris, Mark; Robinson, Suzanne; Preen, David; Moorin, Rachael

2017-07-01

This study aimed to develop a risk stratification strategy for evaluating the relationship between complications of diabetes and the risk of diabetic-related hospitalization to accurately classify diabetes severity. The study used administrative health records for 40,624 individuals with diabetes aged ≥18years in Western Australian. The adapted Diabetes Complication Severity Index (DCSI), socio-demographic and clinical characteristics were used in random effects negative binomial and threshold effect models to determine the optimal stratification strategy for diabetes severity based on the homogeneity of the risk of hospitalization in response to variation of the DCSI. The optimal stratification of people with diabetes was specified by four sub-populations. The first sub-population was no complications with an inverse association with the risk of hospitalizations (coefficient-0.247, SE 0.03). Further three sub-populations with DCSI at one (coefficient 0.289, SE 0.01), two (coefficient 0.339, SE 0.01) and three or more (coefficient 0.381, SE 0.01) were used to accurately describe the impact of DCSI on the risk of hospitalization. A stratification into four subpopulations based on the homogeneous impact of diabetes DCSI on the risk of hospitalization may be more suitable for evaluating health care interventions and planning health care provision. Copyright © 2017 Elsevier Inc. All rights reserved.

Spatial variability of the Arctic Ocean's double-diffusive staircase

NASA Astrophysics Data System (ADS)

Shibley, N. C.; Timmermans, M.-L.; Carpenter, J. R.; Toole, J. M.

2017-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure overlying the Atlantic Water Layer that can be attributed to the diffusive form of double-diffusive convection. The staircase consists of multiple layers of O(1) m in thickness separated by sharp interfaces, across which temperature and salinity change abruptly. Through a detailed analysis of Ice-Tethered Profiler measurements from 2004 to 2013, the double-diffusive staircase structure is characterized across the entire Arctic Ocean. We demonstrate how the large-scale Arctic Ocean circulation influences the small-scale staircase properties. These staircase properties (layer thicknesses and temperature and salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio spanning the staircase stratification. We show that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (approximately 3-4) on the Eurasian side and higher density ratio (approximately 6-7) on the Canadian side. We find that the Eurasian Basin staircase is characterized by fewer, thinner layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin layers and the absence of a well-defined staircase. A double-diffusive 4/3 flux law parametrization is used to estimate vertical heat fluxes in the Canadian Basin to be O(0.1) W m-2. It is shown that the 4/3 flux law may not be an appropriate representation of heat fluxes through the Eurasian Basin staircase. Here molecular heat fluxes are estimated to be between O(0.01) and O(0.1) W m-2. However, many uncertainties remain about the exact nature of these fluxes.

Reaction-space analysis of homogeneous charge compression ignition combustion with varying levels of fuel stratification under positive and negative valve overlap conditions

DOE PAGES

Kodavasal, Janardhan; Lavoie, George A.; Assanis, Dennis N.; ...

2015-10-26

Full-cycle computational fluid dynamics simulations with gasoline chemical kinetics were performed to determine the impact of breathing and fuel injection strategies on thermal and compositional stratification, combustion and emissions during homogeneous charge compression ignition combustion. The simulations examined positive valve overlap and negative valve overlap strategies, along with fueling by port fuel injection and direct injection. The resulting charge mass distributions were analyzed prior to ignition using ignition delay as a reactivity metric. The reactivity stratification arising from differences in the distributions of fuel–oxygen equivalence ratio (Φ FO), oxygen molar fraction (χ O2) and temperature (T) was determined for threemore » parametric studies. In the first study, the reactivity stratification and burn duration for positive valve overlap valve events with port fuel injection and early direct injection were nearly identical and were dominated by wall-driven thermal stratification. nitrogen oxide (NO) and carbon monoxide (CO) emissions were negligible for both injection strategies. In the second study, which examined negative valve overlap valve events with direct injection and port fuel injection, reactivity stratification increased for direct injection as the Φ FO and T distributions associated with direct fuel injection into the hot residual gas were positively correlated; however, the latent heat absorbed from the hot residual gas by the evaporating direct injection fuel jet reduced the overall thermal and reactivity stratification. These stratification effects were offsetting, resulting in similar reactivity stratification and burn durations for the two injection strategies. The higher local burned gas temperatures with direct injection resulted in an order of magnitude increase in NO, while incomplete combustion of locally over-lean regions led to a sevenfold increase in CO emissions compared to port fuel injection. The final study evaluated positive valve overlap and negative valve overlap valve events with direct injection. Furthermore, relative to positive valve overlap, the negative valve overlap condition had a wider reactivity stratification, a longer burn duration and higher NO and CO emissions associated with reduced fuel–air mixing.« less

Using Multiple-hierarchy Stratification and Life Course Approaches to Understand Health Inequalities: The Intersecting Consequences of Race, Gender, SES, and Age.

PubMed

Brown, Tyson H; Richardson, Liana J; Hargrove, Taylor W; Thomas, Courtney S

2016-06-01

This study examines how the intersecting consequences of race-ethnicity, gender, socioeconomics status (SES), and age influence health inequality. We draw on multiple-hierarchy stratification and life course perspectives to address two main research questions. First, does racial-ethnic stratification of health vary by gender and/or SES? More specifically, are the joint health consequences of racial-ethnic, gender, and socioeconomic stratification additive or multiplicative? Second, does this combined inequality in health decrease, remain stable, or increase between middle and late life? We use panel data from the Health and Retirement Study (N = 12,976) to investigate between- and within-group differences in in self-rated health among whites, blacks, and Mexican Americans. Findings indicate that the effects of racial-ethnic, gender, and SES stratification are interactive, resulting in the greatest racial-ethnic inequalities in health among women and those with higher levels of SES. Furthermore, racial-ethnic/gender/SES inequalities in health tend to decline with age. These results are broadly consistent with intersectionality and aging-as-leveler hypotheses. © American Sociological Association 2016.

The effect of stratification on premixed swirl-flame flashback by using porous center-body injection

NASA Astrophysics Data System (ADS)

McCaslin, Andrew; Ranjan, Rakesh; Clemens, Noel

2016-11-01

Boundary layer flashback must be prevented in order to stably operate stationary gas turbines. One strategy to avoid flashback is to create equivalence-ratio stratification, such as by reducing the fuel/air ratio in the boundary layer below the flammability limit. Typically, stratification is achieved by using radially non-uniform fuel injection. The goal of the current study is to reduce the propensity of flashback in a premixed annular swirl combustor that uses a premix section with center-body. A porous metal center-body (10 micron pore size) is used to bleed air directly into the boundary layer and thus locally reduce the equivalence ratio. Planar laser-induced fluorescence imaging of anisole-seeded flow is carried out to assess the stratification in the flow. Time-resolved PIV and chemiluminescence imaging are used to investigate flashback at atmospheric pressure conditions. A comparative study between fully premixed and stratified flame flashback is conducted to determine how stratification influences flashback physics. This work was sponsored by the DOE NETL under Grant DEFC2611-FE0007107. This source of funding is gratefully acknowledged.

Using Multiple-hierarchy Stratification and Life Course Approaches to Understand Health Inequalities: The Intersecting Consequences of Race, Gender, SES, and Age

PubMed Central

Brown, Tyson H.; Richardson, Liana J.; Hargrove, Taylor W.; Thomas, Courtney S.

2016-01-01

This study examines how the intersecting consequences of race-ethnicity, gender, socioeconomics status (SES), and age influence health inequality. We draw on multiple-hierarchy stratification and life course perspectives to address two main research questions. First, does racial-ethnic stratification of health vary by gender and/or SES? More specifically, are the joint health consequences of racial-ethnic, gender, and socioeconomic stratification additive or multiplicative? Second, does this combined inequality in health decrease, remain stable, or increase between middle and late life? We use panel data from the Health and Retirement Study (N = 12,976) to investigate between- and within-group differences in in self-rated health among whites, blacks, and Mexican Americans. Findings indicate that the effects of racial-ethnic, gender, and SES stratification are interactive, resulting in the greatest racial-ethnic inequalities in health among women and those with higher levels of SES. Furthermore, racial-ethnic/gender/SES inequalities in health tend to decline with age. These results are broadly consistent with intersectionality and aging-as-leveler hypotheses. PMID:27284076

Global warming-induced upper-ocean freshening and the intensification of super typhoons

PubMed Central

Balaguru, Karthik; Foltz, Gregory R.; Leung, L. Ruby; Emanuel, Kerry A.

2016-01-01

Super typhoons (STYs), intense tropical cyclones of the western North Pacific, rank among the most destructive natural hazards globally. The violent winds of these storms induce deep mixing of the upper ocean, resulting in strong sea surface cooling and making STYs highly sensitive to ocean density stratification. Although a few studies examined the potential impacts of changes in ocean thermal structure on future tropical cyclones, they did not take into account changes in near-surface salinity. Here, using a combination of observations and coupled climate model simulations, we show that freshening of the upper ocean, caused by greater rainfall in places where typhoons form, tends to intensify STYs by reducing their ability to cool the upper ocean. We further demonstrate that the strengthening effect of this freshening over the period 1961–2008 is ∼53% stronger than the suppressive effect of temperature, whereas under twenty-first century projections, the positive effect of salinity is about half of the negative effect of ocean temperature changes. PMID:27886199

Global warming-induced upper-ocean freshening and the intensification of super typhoons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balaguru, Karthik; Foltz, Gregory R.; Leung, L. Ruby

Here, super typhoons (STYs), intense tropical cyclones of the western North Pacific, rank among the most destructive natural hazards globally. The violent winds of these storms induce deep mixing of the upper ocean, resulting in strong sea surface cooling and making STYs highly sensitive to ocean density stratification. Although a few studies examined the potential impacts of changes in ocean thermal structure on future tropical cyclones, they did not take into account changes in near-surface salinity. Here, using a combination of observations and coupled climate model simulations, we show that freshening of the upper ocean, caused by greater rainfall inmore » places where typhoons form, tends to intensify STYs by reducing their ability to cool the upper ocean. We further demonstrate that the strengthening effect of this freshening over the period 1961–2008 is ~53% stronger than the suppressive effect of temperature, whereas under twenty-first century projections, the positive effect of salinity is about half of the negative effect of ocean temperature changes.« less

Global warming-induced upper-ocean freshening and the intensification of super typhoons.

PubMed

Balaguru, Karthik; Foltz, Gregory R; Leung, L Ruby; Emanuel, Kerry A

2016-11-25

Super typhoons (STYs), intense tropical cyclones of the western North Pacific, rank among the most destructive natural hazards globally. The violent winds of these storms induce deep mixing of the upper ocean, resulting in strong sea surface cooling and making STYs highly sensitive to ocean density stratification. Although a few studies examined the potential impacts of changes in ocean thermal structure on future tropical cyclones, they did not take into account changes in near-surface salinity. Here, using a combination of observations and coupled climate model simulations, we show that freshening of the upper ocean, caused by greater rainfall in places where typhoons form, tends to intensify STYs by reducing their ability to cool the upper ocean. We further demonstrate that the strengthening effect of this freshening over the period 1961-2008 is ∼53% stronger than the suppressive effect of temperature, whereas under twenty-first century projections, the positive effect of salinity is about half of the negative effect of ocean temperature changes.

Global warming-induced upper-ocean freshening and the intensification of super typhoons

DOE PAGES

Balaguru, Karthik; Foltz, Gregory R.; Leung, L. Ruby; ...

2016-11-25

Here, super typhoons (STYs), intense tropical cyclones of the western North Pacific, rank among the most destructive natural hazards globally. The violent winds of these storms induce deep mixing of the upper ocean, resulting in strong sea surface cooling and making STYs highly sensitive to ocean density stratification. Although a few studies examined the potential impacts of changes in ocean thermal structure on future tropical cyclones, they did not take into account changes in near-surface salinity. Here, using a combination of observations and coupled climate model simulations, we show that freshening of the upper ocean, caused by greater rainfall inmore » places where typhoons form, tends to intensify STYs by reducing their ability to cool the upper ocean. We further demonstrate that the strengthening effect of this freshening over the period 1961–2008 is ~53% stronger than the suppressive effect of temperature, whereas under twenty-first century projections, the positive effect of salinity is about half of the negative effect of ocean temperature changes.« less

The Stagger-grid: A grid of 3D stellar atmosphere models. II. Horizontal and temporal averaging and spectral line formation

NASA Astrophysics Data System (ADS)

Magic, Z.; Collet, R.; Hayek, W.; Asplund, M.

2013-12-01

Aims: We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as ⟨3D⟩) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from ⟨3D⟩ averages. Methods: We explored methods for computing mean ⟨3D⟩ stratifications from the Stagger-grid time-dependent 3D radiative hydrodynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigated the influence of alternative averages (logarithmic, enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we computed curves of growth for Fe i and Fe ii lines in LTE. Results: The resulting ⟨3D⟩ stratifications for the four reference depth scales can be very different. We typically find that in the upper atmosphere and in the superadiabatic region just below the optical surface, where the temperature and density fluctuations are highest, the differences become considerable and increase for higher Teff, lower log g, and lower [Fe / H]. The differential comparison of spectral line formation shows distinctive differences depending on which ⟨3D⟩ model is applied. The averages over layers of constant column-mass density yield the best mean ⟨3D⟩ representation of the full 3D models for LTE line formation, while the averages on layers at constant geometrical height are the least appropriate. Unexpectedly, the usually preferred averages over layers of constant optical depth are prone to increasing interference by reversed granulation towards higher effective temperature, in particular at low metallicity. Appendix A is available in electronic form at http://www.aanda.orgMean ⟨3D⟩ models are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A8 as well as at http://www.stagger-stars.net

Turbulence suppression at water density interfaces: observations under moderate wind forcing.

NASA Astrophysics Data System (ADS)

Marcello Falcieri, Francesco; Kanth, Lakshmi H.; Benetazzo, Alvise; Bergamasco, Andrea; Bonaldo, Davide; Barbariol, Francesco; Malačič, Vlado; Sclavo, Mauro; Carniel, Sandro

2016-04-01

Water column stratification has a strong influence on the behaviour of turbulence kinetic energy (TKE) dissipation rates. Density gradient interfaces, due to thermohaline characteristics and to suspended sediment concentration, can act as a barrier and significantly damp TKE. Between January 30th - February 4th 2014 (CARPET2014 oceanographic campaign on R/V URANIA) we collected the very first turbulence data in the Gulf of Trieste (a small bay located in the North-eartern part of the Adriatic Sea). Observation consisted of 38 CTD casts and 478 microstructure profiles (145 ensembles) collected with a free-falling probe (MSS90L). Among those 48 were grouped in three sets of yoyo casts, each lasting for about 12 consecutive hours. The meteorological conditions during the campaign were of moderate wind (average wind speed 10 m s-1) and heat flux (net negative heat flux ranging from 150 to 400 W m-2). The water column characteristics in the Gulf during the campaign evolved from well-mixed to stratified conditions with waters intruding from the Adriatic Sea at the bottom. Two types of water intrusions were found during yoyo casts: one coming from the Adriatic Sea northern coast (i.e. warmer, saltier and more turbid) and one coming from the open sea in front of the Po Delta (i.e. cooler, fresher and less turbid). Our observations show that under moderate wind forcing, the GOT was not completely mixed due to the interfaces created by the bottom waters intruding from the open sea. The comparison of microstructure profiles collected during well mixed and stratified conditions permitted us to highlight the effect of different stratification on TKE dissipation rates. While during well mixed condition TKE profiles are governed just by their forcing, the two intrusions showed different impacts on TKE dissipation rate profiles. The coastal one, with high turbidity, acted as a barrier to surface driven turbulence dumping it of almost two order of magnitude, while the one coming from the open sea, with low sediment concentrations and a smaller vertical density gradient, was not able to suppress downward penetration of turbulence from the surface.

A case-control study to assess the impact of mammographic density on breast cancer risk in women aged 40-49 at intermediate familial risk.

PubMed

Assi, Valentina; Massat, Nathalie J; Thomas, Susan; MacKay, James; Warwick, Jane; Kataoka, Masako; Warsi, Iqbal; Brentnall, Adam; Warren, Ruth; Duffy, Stephen W

2015-05-15

Mammographic density is a strong risk factor for breast cancer, but its potential application in risk management is not clear, partly due to uncertainties about its interaction with other breast cancer risk factors. We aimed to quantify the impact of mammographic density on breast cancer risk in women aged 40-49 at intermediate familial risk of breast cancer (average lifetime risk of 23%), in particular in premenopausal women, and to investigate its relationship with other breast cancer risk factors in this population. We present the results from a case-control study nested with the FH01 cohort study of 6,710 women mostly aged 40-49 at intermediate familial risk of breast cancer. One hundred and three cases of breast cancer were age-matched to one or two controls. Density was measured by semiautomated interactive thresholding. Absolute density, but not percent density, was a significant risk factor for breast cancer in this population after adjusting for area of nondense tissue (OR per 10 cm(2) = 1.07, 95% CI 1.00-1.15, p = 0.04). The effect was stronger in premenopausal women, who made up the majority of the study population. Absolute density remained a significant predictor of breast cancer risk after adjusting for age at menarche, age at first live birth, parity, past or present hormone replacement therapy, and the Tyrer-Cuzick 10-year relative risk estimate of breast cancer. Absolute density can improve breast cancer risk stratification and delineation of high-risk groups alongside the Tyrer-Cuzick 10-year relative risk estimate. © 2014 UICC.

Water-Column Stratification Observed along an AUV-Tracked Isotherm

NASA Astrophysics Data System (ADS)

Zhang, Y.; Messié, M.; Ryan, J. P.; Kieft, B.; Stanway, M. J.; Hobson, B.; O'Reilly, T. C.; Raanan, B. Y.; Smith, J. M.; Chavez, F.

2016-02-01

Studies of marine physical, chemical and microbiological processes benefit from observing in a Lagrangian frame of reference, i.e. drifting with ambient water. Because these processes can be organized relative to specific density or temperature ranges, maintaining observing platforms within targeted environmental ranges is an important observing strategy. We have developed a novel method to enable a Tethys-class long-range autonomous underwater vehicle (AUV) (which has a propeller and a buoyancy engine) to track a target isotherm in buoyancy-controlled drift mode. In this mode, the vehicle shuts off its propeller and autonomously detects the isotherm and stays with it by actively controlling the vehicle's buoyancy. In the June 2015 CANON (Controlled, Agile, and Novel Observing Network) Experiment in Monterey Bay, California, AUV Makai tracked a target isotherm for 13 hours to study the coastal upwelling system. The tracked isotherm started from 33 m depth, shoaled to 10 m, and then deepened to 29 m. The thickness of the tracked isotherm layer (within 0.3°C error from the target temperature) increased over this duration, reflecting weakened stratification around the isotherm. During Makai's isotherm tracking, another long-range AUV, Daphne, acoustically tracked Makai on a circular yo-yo trajectory, measuring water-column profiles in Makai's vicinity. A wave glider also acoustically tracked Makai, providing sea surface measurements on the track. The presented method is a new approach for studying water-column stratification, but requires careful analysis of the temporal and spatial variations mingled in the vehicles' measurements. We will present a synthesis of the water column's stratification in relation to the upwelling conditions, based on the in situ measurements by the mobile platforms, as well as remote sensing and mooring data.

Vertical stratification of forest canopy for segmentation of understory trees within small-footprint airborne LiDAR point clouds

NASA Astrophysics Data System (ADS)

Hamraz, Hamid; Contreras, Marco A.; Zhang, Jun

2017-08-01

Airborne LiDAR point cloud representing a forest contains 3D data, from which vertical stand structure even of understory layers can be derived. This paper presents a tree segmentation approach for multi-story stands that stratifies the point cloud to canopy layers and segments individual tree crowns within each layer using a digital surface model based tree segmentation method. The novelty of the approach is the stratification procedure that separates the point cloud to an overstory and multiple understory tree canopy layers by analyzing vertical distributions of LiDAR points within overlapping locales. The procedure does not make a priori assumptions about the shape and size of the tree crowns and can, independent of the tree segmentation method, be utilized to vertically stratify tree crowns of forest canopies. We applied the proposed approach to the University of Kentucky Robinson Forest - a natural deciduous forest with complex and highly variable terrain and vegetation structure. The segmentation results showed that using the stratification procedure strongly improved detecting understory trees (from 46% to 68%) at the cost of introducing a fair number of over-segmented understory trees (increased from 1% to 16%), while barely affecting the overall segmentation quality of overstory trees. Results of vertical stratification of the canopy showed that the point density of understory canopy layers were suboptimal for performing a reasonable tree segmentation, suggesting that acquiring denser LiDAR point clouds would allow more improvements in segmenting understory trees. As shown by inspecting correlations of the results with forest structure, the segmentation approach is applicable to a variety of forest types.

Stratification Learning: Detecting Mixed Density and Dimensionality in High Dimensional Point Clouds (PREPRINT)

DTIC Science & Technology

2006-09-01

Medioni, [11], estimates the local dimension using tensor voting . These recent works have clearly shown the necessity to go beyond manifold learning, into...2005. [11] P. Mordohai and G. Medioni. Unsupervised dimensionality estimation and manifold learning in high-dimensional spaces by tensor voting . In...walking, jumping, and arms waving. The whole run took 361 seconds in Matlab , while the classification time (PMM) can be neglected compared to the kNN

Surface Structure of Liquid Li and Na: An ab initio Molecular Dynamics Study

NASA Astrophysics Data System (ADS)

González, D. J.; González, L. E.; Stott, M. J.

2004-02-01

Molecular dynamics simulations of the liquid-vapor interfaces of liquid metals have been performed using first principles methods. Results are presented for liquid lithium and sodium near their respective triple points, for samples of 2000 particles in a slab geometry. The atomic density profiles show a pronounced stratification extending several atomic diameters into the bulk, which is similar to that already experimentally observed in liquid K, Ga, In, and Hg.

Risk Stratification of Stress Fractures and Prediction of Return to Duty

DTIC Science & Technology

2015-12-01

enrollment. In study Task 1 we aim to determine the sex- and race -ethnicity-specific bone traits that may contribute to stress fracture risk in military...SUBJECT TERMS bone microarchitecture, HRpQCT, race , gender, sex, bone mineral density, vBMD, bone geometry, stress fracture 16. SECURITY...sectional study aimed at identifying the bone properties that may be related to the well-known sex and race /ethnicity differences in risk for stress

Buoyancy Driven Coolant Mixing Studies of Natural Circulation Flows at the ROCOM Test Facility Using ANSYS CFX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hohne, Thomas; Kliem, Soren; Rohde, Ulrich

2006-07-01

Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shiftedmore » towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. From the test matrix experiments with 0 resp. 2% density difference between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a higher order Reynolds stress turbulence model was employed and a mesh consisting of 6.4 million hybrid elements was utilized. Only the experiments and CFD calculations with modeled density differences show a stratification in the downcomer. Depending on the degree of density differences the less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core. The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities. (authors)« less

Effects of Climate Change on Stratification-Destratification Cycles and Resulting Cyanobacterial Blooms in Shallow Lakes of the North Temperate Zone

NASA Astrophysics Data System (ADS)

King, A. T.; Schaffner, L. R.; Gilman, B.; Gronwall, T. R.; Gronwall, D.; Dietz, E. R.; Hairston, N., Jr.

2016-12-01

"Harmful Algal Blooms" of cyanobacteria (cyanoHABs) have become more frequent and larger in extent for inland waters across the globe. Honeoye Lake, the shallowest of the New York State Finger Lakes (9 m max depth, 7 km long), has experienced recent problematic blooms. We use this lake as a model system for understanding the effects of climate change on cyanoHABs in shallow lakes. Cyanobacteria thrive in warm waters with high phosphorus concentrations. While high P is often caused by external nutrient loading via surface runoff, it can also result from internal loading when P-rich sediment is exposed to anoxic/reducing conditions in a lake's hypolimnion after prolonged stratification. In deep lakes, hypolimnetic water remains isolated from the epilimnion throughout the summer with the dissolved P separated from illuminated surface water; in very shallow lakes where the entire water column remains oxygenated/oxidizing, P is bound in insoluble inorganic complexes. However, in lakes of intermediate depth, hypolimnetic water high in soluble reactive P may mix into the photic zone if sufficiently strong winds occur, stimulating a cyanoHAB. We suggest that repeated cycles of stratification, hypolimnetic anoxia, and subsequent mixing may result in "phosphorus pumping" with recurrent cyanoHABs throughout summer. Climate change is causing stronger thermal stratification in lakes through increased surface warming but also causing more frequent storms that can break down stratification in a shallow lake. We use Honeoye Lake as a model system for understanding the extent to which P-pumping occurs and the likely effects of climate change on cyanoHABs. Field data collected in summer 2016 were used to calibrate the publically available General Lake Model (GLM) to predict Honeoye's discontinuous polymictic pattern of stratification punctuated by overturn events and spikes in epilimnetic P and cyanobacterial biomass. We use the calibrated model to determine cyanoHAB incidence as a function of lake morphometry, summer temperature, and summer storm frequency and intensity. This allows projection of the effects of different climate change scenarios on the incidence of cyanoHABs for this lake and for lakes along a continuum of length-depth morphometries across the North Temperate Zone.

Incorporating Stroke and Bleeding Risk Stratification Tools into Atrial Fibrillation Management Making Sense of the Alphabet Soup.

PubMed

Deering, Thomas F

2017-01-01

Atrial fibrillation (AF) is a common arrhythmia managed by many physicians in a variety of clinical settings. One of the most important clinical decisions related to effective AF management centers upon the need to perform accurate thromboembolic risk stratification followed by effective management decisions that align with established guidelines. This manuscript will review the present state of the art and provide guidance to physicians to enhance patient outcomes.

MODFLOW 2.0: A program for predicting moderator flow patterns

NASA Astrophysics Data System (ADS)

Peterson, P. F.; Paik, I. K.

1991-07-01

Sudden changes in the temperature of flowing liquids can result in transient buoyancy forces which strongly impact the flow hydrodynamics via flow stratification. These effects have been studied for the case of potential flow of stratified liquids to line sinks, but not for moderator flow in SRS reactors. Standard codes, such as TRAC and COMMIX, do not have the capability to capture the stratification effect, due to strong numerical diffusion which smears away the hot/cold fluid interface. A related problem with standard codes is the inability to track plumes injected into the liquid flow, again due to numerical diffusion. The combined effects of buoyant stratification and plume dispersion have been identified as being important in the operation of the Supplementary Safety System which injects neutron-poison ink into SRS reactors to provide safe shutdown in the event of safety rod failure. The MODFLOW code discussed here provides transient moderator flow pattern information with stratification effects, and tracks the location of ink plumes in the reactor. The code, written in Fortran, is compiled for Macintosh II computers, and includes subroutines for interactive control and graphical output. Removing the graphics capabilities, the code can also be compiled on other computers. With graphics, in addition to the capability to perform safety related computations, MODFLOW also provides an easy tool for becoming familiar with flow distributions in SRS reactors.

Forest/Nonforest Classification of Landsat TM Data For Annual Inventory Phase One Stratification

Treesearch

Jim Rack

2001-01-01

Launch of Landsat 7 creates the opportunity to use relatively inexpensive and regularly acquired land cover data as an alternative to high altitude aerial photography. Creating a forest/nonforest mask from satellite imagery may offer a cost-effective alternative to interpretation of aerial photography for Phase One stratification of annual inventory plots. This paper...

Boiling water scarification plus stratification improves germination of Iliamna rivularis (Malvaceae) seeds

Treesearch

Katri Himanen; Markku Nygren; R. Kasten Dumroese

2012-01-01

Scarification with boiling water plus stratification was most effective in improving germination of Iliamna rivularis (Douglas ex Hook.) Greene (Malvaceae) in an experiment that compared 3 treatments. Seeds from 15 sites representing 5 western US states were used in the experiment. Initial response of the seedlots to the treatments was similar, apart from one seedlot....

Results of Sustained Observations from SABSOON

NASA Astrophysics Data System (ADS)

Seim, H.; Nelson, J.

2001-12-01

A variety of meteorological and oceanographic data being collected on the continental shelf off Georgia by the South Atlantic Bight Synoptic Offshore Observational Network (SABSOON) permit an examination of episodic and seasonal phenomena operative on the shelf. Data are collected at offshore platforms and transmitted to shore in near-real time and made available on the project website. Examples of data collected since 1999 are presented that illustrate some of processes being addressed using the network. Maximum winds occur during remarkably energetic downbursts observed in spring and summer, associated with the passage of squalls over the coastal ocean. Peak wind speed at 50 m height exceed 40 ms and air temperature drops by 4 oC or more in less than 6 minutes, often accompanied by large changes in humidity and heavy rainfall, suggesting down draft of air from aloft. These events may play an important role in the offshore transport of continentally-derived material. Continuous ADCP measurements are being used to examine the seasonality of cross-shelf exchange and its relationship to the cross-shelf density gradient. The low-frequency cross-shelf circulation changes sign when the cross-shelf density gradient changes sign. Vertical stratification is surprisingly episodic, and maximum stratification has occurred in the winter and spring associated with appearance of long-salinity surface lens and may be associated with baroclinic instabilities. Strong stratification has also been observed in summer during Gulf Stream-derived intrusions onto the shelf, during which time the upper and lower layers become largely decoupled. Continuous optical measurements of above-water and in-water irradiance (PAR) show the mid-shelf surface sediments are often in the euphotic zone. Chlorophyll fluorescence (stimulated) shows strong light-dependent diurnal variability in near-surface waters and evidence of resuspension of benthic diatoms during storm events, particularly in the early fall. >http://www.skio.peachnet.edu/projects/sabsoon.html

Advanced techniques to prepare seed to sow

Treesearch

Robert P. Karrfalt

2013-01-01

This paper reviews research on improving the basic technique of cold stratification for tree and shrub seeds. Advanced stratification techniques include long stratification, stratification re-dry, or multiple cycles of warm-cold stratification. Research demonstrates that careful regulation of moisture levels and lengthening the stratification period have produced a...

A comparison of five methods of measuring mammographic density: a case-control study.

PubMed

Astley, Susan M; Harkness, Elaine F; Sergeant, Jamie C; Warwick, Jane; Stavrinos, Paula; Warren, Ruth; Wilson, Mary; Beetles, Ursula; Gadde, Soujanya; Lim, Yit; Jain, Anil; Bundred, Sara; Barr, Nicola; Reece, Valerie; Brentnall, Adam R; Cuzick, Jack; Howell, Tony; Evans, D Gareth

2018-02-05

High mammographic density is associated with both risk of cancers being missed at mammography, and increased risk of developing breast cancer. Stratification of breast cancer prevention and screening requires mammographic density measures predictive of cancer. This study compares five mammographic density measures to determine the association with subsequent diagnosis of breast cancer and the presence of breast cancer at screening. Women participating in the "Predicting Risk Of Cancer At Screening" (PROCAS) study, a study of cancer risk, completed questionnaires to provide personal information to enable computation of the Tyrer-Cuzick risk score. Mammographic density was assessed by visual analogue scale (VAS), thresholding (Cumulus) and fully-automated methods (Densitas, Quantra, Volpara) in contralateral breasts of 366 women with unilateral breast cancer (cases) detected at screening on entry to the study (Cumulus 311/366) and in 338 women with cancer detected subsequently. Three controls per case were matched using age, body mass index category, hormone replacement therapy use and menopausal status. Odds ratios (OR) between the highest and lowest quintile, based on the density distribution in controls, for each density measure were estimated by conditional logistic regression, adjusting for classic risk factors. The strongest predictor of screen-detected cancer at study entry was VAS, OR 4.37 (95% CI 2.72-7.03) in the highest vs lowest quintile of percent density after adjustment for classical risk factors. Volpara, Densitas and Cumulus gave ORs for the highest vs lowest quintile of 2.42 (95% CI 1.56-3.78), 2.17 (95% CI 1.41-3.33) and 2.12 (95% CI 1.30-3.45), respectively. Quantra was not significantly associated with breast cancer (OR 1.02, 95% CI 0.67-1.54). Similar results were found for subsequent cancers, with ORs of 4.48 (95% CI 2.79-7.18), 2.87 (95% CI 1.77-4.64) and 2.34 (95% CI 1.50-3.68) in highest vs lowest quintiles of VAS, Volpara and Densitas, respectively. Quantra gave an OR in the highest vs lowest quintile of 1.32 (95% CI 0.85-2.05). Visual density assessment demonstrated a strong relationship with cancer, despite known inter-observer variability; however, it is impractical for population-based screening. Percentage density measured by Volpara and Densitas also had a strong association with breast cancer risk, amongst the automated measures evaluated, providing practical automated methods for risk stratification.

A parameterization of the passive layer of a quasigeostrophic flow in a continuously-stratified ocean

NASA Astrophysics Data System (ADS)

Benilov, E. S.

2018-05-01

This paper examines quasigeostrophic flows in an ocean that can be subdivided into an upper active layer (AL) and a lower passive layer (PL), with the flow and density stratification mainly confined to the former. Under this assumption, an asymptotic model is derived parameterizing the effect of the PL on the AL. The model depends only on the PL's depth, whereas its Väisälä-Brunt frequency turns out to be unimportant (as long as it is small). Under an additional assumption-that the potential vorticity field in the PL is well-diffused and, thus, uniform-the derived model reduces to a simple boundary condition. This condition is to be applied at the AL/PL interface, after which the PL can be excluded from consideration.

Turbulence and wave particle interactions in solar-terrestrial plasmas

NASA Technical Reports Server (NTRS)

Dulk, G. A.; Goldman, M. V.; Toomre, J.

1985-01-01

Activities in the following study areas are reported: (1) particle and wave processes in solar flares; (2) solar convection zone turbulence; and (3) solar radiation emission. To investigate the amplification of cyclotron maser radiation in solar flares, a radio frequency. (RF) heating model was developed for the corona surrounding the energy release site. Then nonlinear simulations of compressible convection display prominent penetration by plumes into regions of stable stratification at the base of the solar convection zone, leading to the excitation of internal gravity waves there. Lastly, linear saturation of electron-beam-driven Langmuir waves by ambient density fluctuations, nonlinear saturation by strong turbulence processes, and radiation emission mechanisms are examined. An additional section discusses solar magnetic fields and hydromagnetic waves in inhomogeneous media, and the effect of magnetic fields on stellar oscillation.

Measuring the Densities of Aqueous Glasses at Cryogenic Temperatures.

PubMed

Shen, Chen; Julius, Ethan F; Tyree, Timothy J; Dan, Ritwik; Moreau, David W; Thorne, Robert

2017-06-28

We demonstrate a method for determining the vitreous phase cryogenic temperature densities of aqueous mixtures, and other samples that require rapid cooling, to prepare the desired cryogenic temperature phase. Microliter to picoliter size drops are cooled by projection into a liquid nitrogen-argon (N2-Ar) mixture. The cryogenic temperature phase of the drop is evaluated using a visual assay that correlates with X-ray diffraction measurements. The density of the liquid N2-Ar mixture is adjusted by adding N2 or Ar until the drop becomes neutrally buoyant. The density of this mixture and thus of the drop is determined using a test mass and Archimedes principle. With appropriate care in drop preparation, management of gas above the liquid cryogen mixture to minimize icing, and regular mixing of the cryogenic mixture to prevent density stratification and phase separation, densities accurate to <0.5% of drops as small as 50 pL can readily be determined. Measurements on aqueous cryoprotectant mixtures provide insight into cryoprotectant action, and provide quantitative data to facilitate thermal contraction matching in biological cryopreservation.

Sloshing instability and electrolyte layer rupture in liquid metal batteries

NASA Astrophysics Data System (ADS)

Weber, Norbert; Beckstein, Pascal; Herreman, Wietze; Horstmann, Gerrit Maik; Nore, Caroline; Stefani, Frank; Weier, Tom

2017-05-01

Liquid metal batteries (LMBs) are discussed today as a cheap grid scale energy storage, as required for the deployment of fluctuating renewable energies. Built as stable density stratification of two liquid metals separated by a thin molten salt layer, LMBs are susceptible to short-circuit by fluid flows. Using direct numerical simulation, we study a sloshing long wave interface instability in cylindrical cells, which is already known from aluminium reduction cells. After characterising the instability mechanism, we investigate the influence of cell current, layer thickness, density, viscosity, conductivity and magnetic background field. Finally we study the shape of the interface and give a dimensionless parameter for the onset of sloshing as well as for the short-circuit.

A theoretical study of topographic effects on coastal upwelling and cross-shore exchange

NASA Astrophysics Data System (ADS)

Song, Y. Tony; Chao, Yi

The effects of topographic variations on coastal upwelling and cross-shore exchange are examined with a theoretical, continuously stratified, three-dimensional coastal ocean model. The model takes into account topographic variations in both alongshore and cross-shore directions and allows analytical solutions with an Ekman surface layer that faithfully represents the physical nature of the coastal upwelling system. Theoretical solutions with any analytical form of alongshore-varying topography can be solved based on the perturbation method of Killworth [J. Phys. Oceanogr. 8 (1978) 188]. Analyses of the model solutions lead to the following conclusions: The variation of upwelling fronts and currents is shown to be caused by the combined effect of topography and stratification. Topographic variation causes uneven upwelling distribution and leads to density variation, which results in a varying horizontal pressure gradient field that causes the meandering currents. The variation index is dependent upon a bilinear function of their physical parameters--the ratio of the topographic variation depth to the total depth and Burger's number of stratification. Cross-shore slope is found to play a role in maintaining the meandering structure of the alongshore currents. The anticyclonic circulations can further induce downwelling on the offshore side of the current, while the cyclonic circulations enhance upwelling and form upwelling centers on the inshore side of the current. Alongshore topography does not change the total upwelled water, i.e., the total Ekman pumping is conserved. However, it increases cross-exchange of water masses by transporting inshore (offshore) water near topographic features far offshore (inshore) from the mean position of the front. The applicability and limitations of the theory are also discussed.

Stratification by cyanobacteria in lakes: a dynamic buoyancy model indicates size limitations met by Planktothrix rubescens filaments.

PubMed

Walsby, Anthony E

2005-11-01

The ability of the Planktothrix rubescens to stratify in Lake Zürich is related to the size and shape of the cyanobacterial filaments. Detailed measurements made in the lake are used in a dynamic computer model of buoyancy regulation to investigate the vertical movements of filaments tracking the depth at which the irradiance would support neutral buoyancy. The movement of the filament lags behind the constantly changing target depth owing to (a) the time taken for the filament to respond to the irradiance by changing its density and (b) the time it takes to move by sinking down or floating up through the water column. The model simulates the stratification depth over a 5-month period of the summer from the continuous measurements of irradiance and weekly measurements of light attenuation and temperature, without any further adjustment over the period. Models using filaments of the size observed in Lake Zürich explain several details of the observed depth changes: smaller planktonic cyanobacteria (e.g. Limnothrix sp.) are unable to migrate fast enough and larger ones (e.g. Anabaena spp.) will overshoot and become entrained in the epilimnion. The model can be used to simulate recruitment of Planktothrix filaments from different depths after vernal stratification. Recruitment of filaments from depths down to 45 m will contribute to the metalimnetic population increase in early July.

Rollover in volcanic crater lakes: a possible cause for Lake Nyos type disasters

NASA Astrophysics Data System (ADS)

Rice, A.

2000-04-01

Seemingly stably stratified fluids, that is a heavier layer of fluid underlying an upper layer of lighter fluid, can overturn if there is a heat flux through the system. Such events are termed ;rollover; in the engineering literature (occurring for instance in liquid natural gas tanks). They take place as well in lakes and ponds. In all such cases, the stratification starts off with the heavier, more dense fluid underlying lighter. Convection driven mixing at the stratification interface (due to the heat flux) as well as other processes serves to minimize with time the stabilizing density differences, which may eventually cause the stratification to invert. If gas has been contained under pressure in the lower layer, this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard. These processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles. Provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids. These calculations suggest rollover could occur in volcanic lakes. The August 1986 gas release at Lake Nyos is employed as an example. These estimates were made taking note that water is commonly supersaturated in CO2

Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jurisa, Joseph T.; Nash, Jonathan D.; Moum, James N.

Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate ..epsilon.. and mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ..epsilon.. as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ..epsilon.. over a range of tidal and river discharge forcings. Observedmore » ..epsilon.. is found to be characterized by Kunze et al.'s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, ..epsilon.. scaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric. The Kunze et al. ..epsilon.. parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.« less

Competitive Adsorption and Ordered Packing of Counterions near Highly Charged Surfaces: From Mean-Field Theory to Monte Carlo Simulations

PubMed Central

Wen, Jiayi; Zhou, Shenggao; Xu, Zhenli; Li, Bo

2013-01-01

Competitive adsorption of counterions of multiple species to charged surfaces is studied by a size-effect included mean-field theory and Monte Carlo (MC) simulations. The mean-field electrostatic free-energy functional of ionic concentrations, constrained by Poisson’s equation, is numerically minimized by an augmented Lagrangian multiplier method. Unrestricted primitive models and canonical ensemble MC simulations with the Metropolis criterion are used to predict the ionic distributions around a charged surface. It is found that, for a low surface charge density, the adsorption of ions with a higher valence is preferable, agreeing with existing studies. For a highly charged surface, both of the mean-field theory and MC simulations demonstrate that the counterions bind tightly around the charged surface, resulting in a stratification of counterions of different species. The competition between mixed entropy and electrostatic energetics leads to a compromise that the ionic species with a higher valence-to-volume ratio has a larger probability to form the first layer of stratification. In particular, the MC simulations confirm the crucial role of ionic valence-to-volume ratios in the competitive adsorption to charged surfaces that had been previously predicted by the mean-field theory. The charge inversion for ionic systems with salt is predicted by the MC simulations but not by the mean-field theory. This work provides a better understanding of competitive adsorption of counterions to charged surfaces and calls for further studies on the ionic size effect with application to large-scale biomolecular modeling. PMID:22680474

Competitive adsorption and ordered packing of counterions near highly charged surfaces: From mean-field theory to Monte Carlo simulations.

PubMed

Wen, Jiayi; Zhou, Shenggao; Xu, Zhenli; Li, Bo

2012-04-01

Competitive adsorption of counterions of multiple species to charged surfaces is studied by a size-effect-included mean-field theory and Monte Carlo (MC) simulations. The mean-field electrostatic free-energy functional of ionic concentrations, constrained by Poisson's equation, is numerically minimized by an augmented Lagrangian multiplier method. Unrestricted primitive models and canonical ensemble MC simulations with the Metropolis criterion are used to predict the ionic distributions around a charged surface. It is found that, for a low surface charge density, the adsorption of ions with a higher valence is preferable, agreeing with existing studies. For a highly charged surface, both the mean-field theory and the MC simulations demonstrate that the counterions bind tightly around the charged surface, resulting in a stratification of counterions of different species. The competition between mixed entropy and electrostatic energetics leads to a compromise that the ionic species with a higher valence-to-volume ratio has a larger probability to form the first layer of stratification. In particular, the MC simulations confirm the crucial role of ionic valence-to-volume ratios in the competitive adsorption to charged surfaces that had been previously predicted by the mean-field theory. The charge inversion for ionic systems with salt is predicted by the MC simulations but not by the mean-field theory. This work provides a better understanding of competitive adsorption of counterions to charged surfaces and calls for further studies on the ionic size effect with application to large-scale biomolecular modeling.

Turbidity current with a roof: Direct numerical simulation of self-stratified turbulent channel flow driven by suspended sediment

NASA Astrophysics Data System (ADS)

Cantero, Mariano I.; Balachandar, S.; Cantelli, Alessandro; Pirmez, Carlos; Parker, Gary

2009-03-01

In this work we present direct numerical simulations (DNS) of sediment-laden channel flows. In contrast to previous studies, where the flow has been driven by a constant, uniform pressure gradient, our flows are driven by the excess density imposed by suspended sediment. This configuration provides a simplified model of a turbidity current and is thus called the turbidity current with a roof configuration. Our calculations elucidate with DNS for the first time several fascinating features of sediment-laden flows, which may be summarized as follows. First, the presence of sediment breaks the symmetry of the flow because of a tendency to self-stratify. More specifically, this self-stratification is manifested in terms of a Reynolds-averaged suspended sediment concentration that declines in the upward normal direction and a Reynolds-averaged velocity profile with a maximum that is below the channel centerline. Second, this self-stratification damps the turbulence, particularly near the bottom wall. Two regimes are observed, one in which the flow remains turbulent but the level of turbulence is reduced and another in which the flow relaminarizes in a region near the bottom wall, i.e., bed. Third, the analysis allows the determination of a criterion for the break between these two regimes in terms of an appropriately defined dimensionless settling velocity. The results provide guidance for the improvement of Reynolds-averaged closures for turbulent flow in regard to stratification effects. Although the analysis reported here is not performed at the scale of large oceanic turbidity currents, which have sufficiently large Reynolds numbers to be inaccessible via DNS at this time, the implication of flow relaminarization is of considerable importance. Even a swift oceanic turbidity current which at some point crosses the threshold into the regime of relaminarization may lose the capacity to reentrain sediment that settles on the bed and thus may quickly die as it loses its driving force.

The effect of stratification and topography on high-frequency internal waves in a continental shelf sea

NASA Astrophysics Data System (ADS)

Domina, Anastasiia; Palmer, Matthew; Vlasenko, Vasil; Sharples, Jonathan; Green, Mattias; Stashchuk, Nataliya

2017-04-01

Internal gravity waves (IWs) have been recognised as one of the main drivers of climate controlling circulation, sustaining fisheries in shelf seas and CO2-pump system. High frequency IWs are particularly important to internal mixing in the shelf seas, where they contain an enhanced fraction of the available baroclinic energy. The origin, generation mechanism, propagation and spatial distribution of these waves are unfortunately still poorly understood since they are difficult to measure and simulate, and are therefore not represented in the vast majority of ocean and climate models. In this study we aim to increase our understanding of high frequency IWs dynamics in shelf seas through a combination of observational (from moorings and ocean gliders) and modelling methods (MITgcm), and test the hypothesis that "Solitary waves are responsible for driving a large fraction of the vertical diffusivity at the shelf edge and adjacent shelf region". A new high-resolution (50m horizontal) MITgcm configuration is employed to identify the generation and propagation of IWs in a regional shelf sea and subsequently identify internal wave generation hotspots by using calculated Froude number and body force maps. We assess the likely impact of changing seasonal and climate forcing on IWs with a range of different density structures. Our model suggests that under increasing stratification, the IW field becomes more energetic at all frequencies, however the increase in energy is not evenly distributed. While energy in the dominant low frequency IWs increase by 20-40%, energy associated with high frequency waves increases by as much as 90%. These model results are compared to varying stratification scenarios from observations made during 2012 and 2013 to interpret the impact on continental shelf sea IW generation and propagation. We use the results from a turbulence enabled ocean glider to assess the impact that this varying wavefield has on internal mixing, and discuss the implications this might have on future climate scenarios.

Planktonic events may cause polymictic-dimictic regime shifts in temperate lakes

PubMed Central

Shatwell, Tom; Adrian, Rita; Kirillin, Georgiy

2016-01-01

Water transparency affects the thermal structure of lakes, and within certain lake depth ranges, it can determine whether a lake mixes regularly (polymictic regime) or stratifies continuously (dimictic regime) from spring through summer. Phytoplankton biomass can influence transparency but the effect of its seasonal pattern on stratification is unknown. Therefore we analysed long term field data from two lakes of similar depth, transparency and climate but one polymictic and one dimictic, and simulated a conceptual lake with a hydrodynamic model. Transparency in the study lakes was typically low during spring and summer blooms and high in between during the clear water phase (CWP), caused when zooplankton graze the spring bloom. The effect of variability of transparency on thermal structure was stronger at intermediate transparency and stronger during a critical window in spring when the rate of lake warming is highest. Whereas the spring bloom strengthened stratification in spring, the CWP weakened it in summer. The presence or absence of the CWP influenced stratification duration and under some conditions determined the mixing regime. Therefore seasonal plankton dynamics, including biotic interactions that suppress the CWP, can influence lake temperatures, stratification duration, and potentially also the mixing regime. PMID:27074883

Numerical study of a thermally stratified flow of a tangent hyperbolic fluid induced by a stretching cylindrical surface

NASA Astrophysics Data System (ADS)

Ur Rehman, Khali; Ali Khan, Abid; Malik, M. Y.; Hussain, Arif

2017-09-01

The effects of temperature stratification on a tangent hyperbolic fluid flow over a stretching cylindrical surface are studied. The fluid flow is achieved by taking the no-slip condition into account. The mathematical modelling of the physical problem yields a nonlinear set of partial differential equations. These obtained partial differential equations are converted in terms of ordinary differential equations. Numerical investigation is done to identify the effects of the involved physical parameters on the dimensionless velocity and temperature profiles. In the presence of temperature stratification it is noticed that the curvature parameter makes both the fluid velocity and fluid temperature increase. In addition, positive variations in the thermal stratification parameter produce retardation with respect to the fluid flow, as a result the fluid temperature drops. The skin friction coefficient shows a decreasing nature for increasing value of both power law index and Weissenberg number, whereas the local Nusselt number is an increasing function of the Prandtl number, but opposite trends are found with respect to the thermal stratification parameter. The obtained results are validated by making a comparison with the existing literature which brings support to the presently developed model.

Planktonic events may cause polymictic-dimictic regime shifts in temperate lakes.

PubMed

Shatwell, Tom; Adrian, Rita; Kirillin, Georgiy

2016-04-14

Water transparency affects the thermal structure of lakes, and within certain lake depth ranges, it can determine whether a lake mixes regularly (polymictic regime) or stratifies continuously (dimictic regime) from spring through summer. Phytoplankton biomass can influence transparency but the effect of its seasonal pattern on stratification is unknown. Therefore we analysed long term field data from two lakes of similar depth, transparency and climate but one polymictic and one dimictic, and simulated a conceptual lake with a hydrodynamic model. Transparency in the study lakes was typically low during spring and summer blooms and high in between during the clear water phase (CWP), caused when zooplankton graze the spring bloom. The effect of variability of transparency on thermal structure was stronger at intermediate transparency and stronger during a critical window in spring when the rate of lake warming is highest. Whereas the spring bloom strengthened stratification in spring, the CWP weakened it in summer. The presence or absence of the CWP influenced stratification duration and under some conditions determined the mixing regime. Therefore seasonal plankton dynamics, including biotic interactions that suppress the CWP, can influence lake temperatures, stratification duration, and potentially also the mixing regime.

Natural sampling strategy

NASA Technical Reports Server (NTRS)

Hallum, C. R.; Basu, J. P. (Principal Investigator)

1979-01-01

A natural stratum-based sampling scheme and the aggregation procedures for estimating wheat area, yield, and production and their associated prediction error estimates are described. The methodology utilizes LANDSAT imagery and agrophysical data to permit an improved stratification in foreign areas by ignoring political boundaries and restratifying along boundaries that are more homogeneous with respect to the distribution of agricultural density, soil characteristics, and average climatic conditions. A summary of test results is given including a discussion of the various problems encountered.

Mobile Bay river plume mixing in the inner shelf

NASA Astrophysics Data System (ADS)

Parra, S. M.; Book, J. W.; Warner, S. J.; Moum, J.

2017-12-01

The microtidal region (0.5 m spring tides) of the inner shelf outside Mobile Bay presented a complex circulation pattern driven by the pulsed river discharge and winds. Currents, salinity, temperature, and turbulence profiles were measured for up to three weeks in April 2016 at six moorings outside Mobile Bay. Currents varied between locations and with depth. During neap and spring tides the currents were reliably >0.4 and <0.4 m/s, respectively. The outflow from Mobile Bay generated a complex density circulation, where two to three layers were normally present. Multiple density layers included a thicker brackish middle layer (5-10 m thickness), and a salty bottom layer (5-10 m thickness), with a thin ( 1-3 m) freshwater surface layer found intermittently. The multilayer currents were strongest at neap tides (>0.5 m/s) and toward deeper waters, concurrent with the strongest stratification. The possible flow drivers considered include tides, winds, inertial oscillations, waves, and stratification. Turbulent kinetic energy production and dissipation were calculated with multiple methods using data from bottom-mounted, upward-looking acoustic Doppler current profilers sampling at 1 Hz, and using data from line-moored chi-pod turbulent temperature microstructure instruments sampling at 100 Hz. This work explores different forcing mechanisms involved in modulating the circulation and turbulence in a multi-layered pulsed-river inner shelf region in the Gulf of Mexico.

Water-quality reconnaissance of the Pascagoula and Escatawpa Rivers, Jackson County, Mississippi, May 1974 to July 1978

USGS Publications Warehouse

Faye, Robert E.

1980-01-01

Short-term, water-quality reconnaissances along the downstream reaches of the Pascagoula and Escatawpa Rivers in Jackson County , Miss., indicate that stream quality during the period May 1974 to July 1978 was affected by wastewater discharges as well as river discharge and the extent of tidal intrusion. Specific conductances on the Pascagoula River ranged from less than 100 to more than 40,000 micromhos per centimeter and increased downstream. Specific conductance also increased with depth at downstram sites, indicating density stratification. Dissolved-oxygen concentrations were also affected by density stratification but were generally greater than 4.0 milligrams per liter in both rivers. Analyses of 5-day biochemical oxygen demand and nutrient concentrations indicate that oxidation of both carbonaceous and nitrogenous materials significantly affected the waste assimilative capacity of the rivers. Concentrations of pesticides and most trace elements in both the water column and the bottom sediments were zero or very small. Titanium concentrations were less than 220 micrograms per liter in the water column and 6,500 micrograms per gram in bottom sediments. Small concentrations of oil and grease, PCB's, and phenols were also detected. Fecal coliform and fecal streptococcal bacteria concentrations were generally greater in the Escatawpa River and ranged from about 10 to 18,000 colonies per 100 milliliters of water. (USGS)

Instability of two-layer film flows due to the interacting effects of surfactants, inertia, and gravity

NASA Astrophysics Data System (ADS)

Kalogirou, Anna

2018-03-01

We consider a two-fluid shear flow where the interface between the two fluids is coated with an insoluble surfactant. An asymptotic model is derived in the thin-layer approximation, consisting of a set of nonlinear partial differential equations describing the evolution of the film and surfactant disturbances at the interface. The model includes important physical effects such as Marangoni forces (caused by the presence of surfactant), inertial forces arising in the thick fluid layer, as well as gravitational forces. The aim of this study is to investigate the effect of density stratification or gravity—represented through the Bond number Bo—on the flow stability and the interplay between the different (de)stabilisation mechanisms. It is found that gravity can either stabilise or destabilise the interface (depending on fluid properties) but not always as intuitively anticipated. Different traveling-wave branches are presented for varying Bo, and the destabilising mechanism associated with the Marangoni forces is discussed.

A Review on Automatic Mammographic Density and Parenchymal Segmentation

PubMed Central

He, Wenda; Juette, Arne; Denton, Erika R. E.; Oliver, Arnau

2015-01-01

Breast cancer is the most frequently diagnosed cancer in women. However, the exact cause(s) of breast cancer still remains unknown. Early detection, precise identification of women at risk, and application of appropriate disease prevention measures are by far the most effective way to tackle breast cancer. There are more than 70 common genetic susceptibility factors included in the current non-image-based risk prediction models (e.g., the Gail and the Tyrer-Cuzick models). Image-based risk factors, such as mammographic densities and parenchymal patterns, have been established as biomarkers but have not been fully incorporated in the risk prediction models used for risk stratification in screening and/or measuring responsiveness to preventive approaches. Within computer aided mammography, automatic mammographic tissue segmentation methods have been developed for estimation of breast tissue composition to facilitate mammographic risk assessment. This paper presents a comprehensive review of automatic mammographic tissue segmentation methodologies developed over the past two decades and the evidence for risk assessment/density classification using segmentation. The aim of this review is to analyse how engineering advances have progressed and the impact automatic mammographic tissue segmentation has in a clinical environment, as well as to understand the current research gaps with respect to the incorporation of image-based risk factors in non-image-based risk prediction models. PMID:26171249

Correction of Population Stratification in Large Multi-Ethnic Association Studies

PubMed Central

Serre, David; Montpetit, Alexandre; Paré, Guillaume; Engert, James C.; Yusuf, Salim; Keavney, Bernard; Hudson, Thomas J.; Anand, Sonia

2008-01-01

Background The vast majority of genetic risk factors for complex diseases have, taken individually, a small effect on the end phenotype. Population-based association studies therefore need very large sample sizes to detect significant differences between affected and non-affected individuals. Including thousands of affected individuals in a study requires recruitment in numerous centers, possibly from different geographic regions. Unfortunately such a recruitment strategy is likely to complicate the study design and to generate concerns regarding population stratification. Methodology/Principal Findings We analyzed 9,751 individuals representing three main ethnic groups - Europeans, Arabs and South Asians - that had been enrolled from 154 centers involving 52 countries for a global case/control study of acute myocardial infarction. All individuals were genotyped at 103 candidate genes using 1,536 SNPs selected with a tagging strategy that captures most of the genetic diversity in different populations. We show that relying solely on self-reported ethnicity is not sufficient to exclude population stratification and we present additional methods to identify and correct for stratification. Conclusions/Significance Our results highlight the importance of carefully addressing population stratification and of carefully “cleaning” the sample prior to analyses to obtain stronger signals of association and to avoid spurious results. PMID:18196181

Free Falling in Stratified Fluids

NASA Astrophysics Data System (ADS)

Lam, Try; Vincent, Lionel; Kanso, Eva

2017-11-01

Leaves falling in air and discs falling in water are examples of unsteady descents due to complex interaction between gravitational and aerodynamic forces. Understanding these descent modes is relevant to many branches of engineering and science such as estimating the behavior of re-entry space vehicles to studying biomechanics of seed dispersion. For regularly shaped objects falling in homogenous fluids, the motion is relatively well understood. However, less is known about how density stratification of the fluid medium affects the falling behavior. Here, we experimentally investigate the descent of discs in both pure water and in stable linearly stratified fluids for Froude numbers Fr 1 and Reynolds numbers Re between 1000 -2000. We found that stable stratification (1) enhances the radial dispersion of the disc at landing, (2) increases the descent time, (3) decreases the inclination (or nutation) angle, and (4) decreases the fluttering amplitude while falling. We conclude by commenting on how the corresponding information can be used as a predictive model for objects free falling in stratified fluids.

Development of a depth-integrated sample arm (DISA) to reduce solids stratification bias in stormwater sampling

USGS Publications Warehouse

Selbig, William R.; ,; Roger T. Bannerman,

2011-01-01

A new depth-integrated sample arm (DISA) was developed to improve the representation of solids in stormwater, both organic and inorganic, by collecting a water quality sample from multiple points in the water column. Data from this study demonstrate the idea of vertical stratification of solids in storm sewer runoff. Concentrations of suspended sediment in runoff were statistically greater using a fixed rather than multipoint collection system. Median suspended sediment concentrations measured at the fixed location (near the pipe invert) were approximately double those collected using the DISA. In general, concentrations and size distributions of suspended sediment decreased with increasing vertical distance from the storm sewer invert. Coarser particles tended to dominate the distribution of solids near the storm sewer invert as discharge increased. In contrast to concentration and particle size, organic material, to some extent, was distributed homogenously throughout the water column, likely the result of its low specific density, which allows for thorough mixing in less turbulent water.

Development of a depth-integrated sample arm to reduce solids stratification bias in stormwater sampling.

PubMed

Selbig, William R; Bannerman, Roger T

2011-04-01

A new depth-integrated sample arm (DISA) was developed to improve the representation of solids in stormwater, both organic and inorganic, by collecting a water quality sample from multiple points in the water column. Data from this study demonstrate the idea of vertical stratification of solids in storm sewer runoff. Concentrations of suspended sediment in runoff were statistically greater using a fixed rather than multipoint collection system. Median suspended sediment concentrations measured at the fixed location (near the pipe invert) were approximately double those collected using the DISA. In general, concentrations and size distributions of suspended sediment decreased with increasing vertical distance from the storm sewer invert. Coarser particles tended to dominate the distribution of solids near the storm sewer invert as discharge increased. In contrast to concentration and particle size, organic material, to some extent, was distributed homogenously throughout the water column, likely the result of its low specific density, which allows for thorough mixing in less turbulent water.

Development of a depth-integrated sample arm to reduce solids stratification bias in stormwater sampling

USGS Publications Warehouse

Selbig, W.R.; Bannerman, R.T.

2011-01-01

A new depth-integrated sample arm (DISA) was developed to improve the representation of solids in stormwater, both organic and inorganic, by collecting a water quality sample from multiple points in the water column. Data from this study demonstrate the idea of vertical stratification of solids in storm sewer runoff. Concentrations of suspended sediment in runoff were statistically greater using a fixed rather than multipoint collection system. Median suspended sediment concentrations measured at the fixed location (near the pipe invert) were approximately double those collected using the DISA. In general, concentrations and size distributions of suspended sediment decreased with increasing vertical distance from the storm sewer invert. Coarser particles tended to dominate the distribution of solids near the storm sewer invert as discharge increased. In contrast to concentration and particle size, organic material, to some extent, was distributed homogenously throughout the water column, likely the result of its low specific density, which allows for thorough mixing in less turbulent water. ?? 2010 Publishing Technology.

Chromosome 9p21 In Ischemic Stroke: Population Structure and Meta-Analysis

PubMed Central

Anderson, CD; Biffi, A; Rost, NS; Cortellini, L; Furie, KL; Rosand, J

2011-01-01

Background and Purpose Sequence variants on chromosome 9p21.3 are implicated in coronary artery disease (CAD) and myocardial infarction (MI), but studies in ischemic stroke have produced inconsistent results. We investigated whether these conflicting findings were due to false positive studies confounded by population stratification, or false negative studies that failed to account for effects specific to certain stroke subtypes. Methods After assessing for population stratification at 9p21.3 using genome-wide data, we meta-analyzed 8 ischemic stroke studies. This analysis focused on two single nucleotide polymorphisms (SNPs), rs1537378 and rs10757278, as these variants are in strong linkage disequilibrium with most SNPs analyzed in prior studies of the region. Results Principal component analysis of the genome-wide data showed no evidence of population stratification at that locus. Meta-analysis confirmed that both rs1537378 and rs10757278 are risk factors for ischemic stroke (odds ratios 1.09, [p = 0.0014], and 1.11, [p = 0.001] respectively). Subtype analysis revealed a substantial increase in the effect of each SNP for risk of large artery (LA) stroke, achieving an effect size similar to that seen in CAD/MI. Conclusions Variants on 9p21.3 are associated with ischemic stroke, and restriction of analysis to LA stroke increases effect size towards that observed in prior association studies of CAD/MI. Previous inconsistent findings are best explained by this subtype-specificity rather than any unmeasured confounding by population stratification. PMID:20395606

The effect of thermal stratification on microbial community diversity and structure in a temperate reservoir

NASA Astrophysics Data System (ADS)

Qu, Jiangqi; Jia, Chengxia; Zhao, Meng; Li, Wentong; Liu, Pan; Yang, Mu; Zhang, Qingjing

2018-02-01

Miyun reservoir is a typical temperate deep reservoir located in the northeast of Beijing, China. In order to explore the effect of thermal stratification on microbial community diversity, structure and its influencing environmental factors, stratified sampling at three sites was conducted during the summer period. Field observations indicate that the water temperature and dissolved oxygen concentrations dropped to 11.9 °C and 1.57 mg/L, respectively, leading to the development of anoxia in the hypolimnetic layer. The Illumina Miseq sequencing results showed that microbial communities from different thermal stratification showed obvious differences, the highest microbial diversity and richness in the hypolimnion samples. RDA ordination analysis suggested that the microbial communities in the epilimnion and metalimnion were mainly affected by water temperature, pH and dissolved oxygen, while total nitrogen was the key environmental factor which shaped the microbial structure in hypolimnion.

Acoustic sounding of wind velocity profiles in a stratified moving atmosphere.

PubMed

Ostashev, V E; Georges, T M; Clifford, S F; Goedecke, G H

2001-06-01

The paper deals with analytical and numerical studies of the effects of atmospheric stratification on acoustic remote sensing of wind velocity profiles by sodars. Both bistatic and monostatic schemes are considered. Formulas for the Doppler shift of an acoustic echo signal scattered by atmospheric turbulence advected with the mean wind in a stratified moving atmosphere are derived. Numerical studies of these formulas show that errors in retrieving wind velocity can be of the order of 1 m/s if atmospheric stratification is ignored. Formulas for the height at which wind velocity is retrieved are also derived. Approaches are proposed which allow one to take into account the effects of atmospheric stratification when restoring the wind velocity profile from measured values of the Doppler shift and the time interval of acoustic impulse propagation from a sodar to the scattering volume and back to the ground.

Enthalpy-Based Thermal Evolution of Loops: II. Improvements to the Model

NASA Technical Reports Server (NTRS)

Cargill, P. J.; Bradshaw, S. J.; Klimchuk, J. A.

2011-01-01

This paper further develops the zero-dimensional (0D) hydrodynamic coronal loop model "Enthalpy-based Thermal Evolution of Loops" (EBTEL) originally proposed by Klimchuk et al (2008), which studies the plasma response to evolving coronal heating. It has typically been applied to impulsive heating events. The basis of EBTEL is the modelling of mass exchange between the corona and transition region and chromosphere in response to heating variations, with the key parameter being the ratio of transition region to coronal radiation. We develop new models for this parameter that now include gravitational stratification and a physically motivated approach to radiative cooling. A number of examples are presented, including nanoflares in short and long loops, and a small flare. It is found that while the evolution of the loop temperature is rather insensitive to the details of the model, accurate tracking of the density requires the inclusion of our new features. In particular, we are able to now obtain highly over-dense loops in the late cooling phase and decreases to the coronal density arising due to stratification. The 0D results are compared to a 1D hydro code (Hydrad). The agreement is acceptable, with the exception of the flare case where some versions of Hydrad can give significantly lower densities. This is attributed to the method used to model the chromosphere in a flare. EBTEL is suitable for general use as a tool for (a) quick-look results of loop evolution in response to a given heating function and (b) situations where the modelling of hundreds or thousands of elemental loops is needed. A single run takes a few seconds on a contemporary laptop.

Infiltration of diametrically polarized macrophages predicts overall survival of patients with gastric cancer after surgical resection.

PubMed

Zhang, Heng; Wang, Xuefei; Shen, Zhenbin; Xu, Jiejie; Qin, Jing; Sun, Yihong

2015-10-01

Tumor-associated macrophages (TAMs), the most predominant tumor-infiltrating immune cells, are emerging prognostic factors and therapeutic targets for personalized therapy against malignant neoplasms. We aimed to evaluate the prognostic significance of diametrically polarized TAMs in gastric cancer and generate a predictive nomogram to refine a risk stratification system. We evaluated polarized functional status of infiltrated TAMs by immunohistochemical staining of CD68, CD11c, and CD206 in 180 consecutive gastric cancer patients from Zhongshan Hospital, Shanghai, China. Prognostic values were assessed in these patients. We created a predictive nomogram by integrating polarized TAMs with the TNM staging system for overall survival of gastric cancer patients. CD68(+) TAMs display polarized programs comprising CD11c(+) proinflammatory macrophages (M1) and CD206(+) immunosuppressive macrophages (M2) that configure versatile infiltration files in gastric cancer. CD11c(+) TAMs negatively correlated with lymph node metastasis (p = 0.012), whereas CD206(+) TAMs correlated with the Lauren classification (p = 0.031). No prognostic difference was observed for overall survival for CD68 density (high vs low, p = 0.1031), whereas high versus low CD11c density (p < 0.0001) and low vs high CD206 density (p = 0.0105) indicate better overall survival. Multivariate Cox regression analysis identified CD11c and CD206 as independent prognostic factors (p < 0.001 and p = 0.030, respectively), which could be integrated with the TNM staging system to generate a predictive nomogram for patient outcomes. Infiltration of polarized TAMs, a novel identified independent prognostic factor, could be combined with the TNM stage to refine a risk stratification system and better stratify patients with different prognosis. Tipping TAMs to an antitumoral phenotype might be a promising therapeutic target for postoperative treatment.

Fresh clouds: A parameterized updraft method for calculating cloud densities in one-dimensional models

NASA Astrophysics Data System (ADS)

Wong, Michael H.; Atreya, Sushil K.; Kuhn, William R.; Romani, Paul N.; Mihalka, Kristen M.

2015-01-01

Models of cloud condensation under thermodynamic equilibrium in planetary atmospheres are useful for several reasons. These equilibrium cloud condensation models (ECCMs) calculate the wet adiabatic lapse rate, determine saturation-limited mixing ratios of condensing species, calculate the stabilizing effect of latent heat release and molecular weight stratification, and locate cloud base levels. Many ECCMs trace their heritage to Lewis (Lewis, J.S. [1969]. Icarus 10, 365-378) and Weidenschilling and Lewis (Weidenschilling, S.J., Lewis, J.S. [1973]. Icarus 20, 465-476). Calculation of atmospheric structure and gas mixing ratios are correct in these models. We resolve errors affecting the cloud density calculation in these models by first calculating a cloud density rate: the change in cloud density with updraft length scale. The updraft length scale parameterizes the strength of the cloud-forming updraft, and converts the cloud density rate from the ECCM into cloud density. The method is validated by comparison with terrestrial cloud data. Our parameterized updraft method gives a first-order prediction of cloud densities in a “fresh” cloud, where condensation is the dominant microphysical process. Older evolved clouds may be better approximated by another 1-D method, the diffusive-precipitative Ackerman and Marley (Ackerman, A.S., Marley, M.S. [2001]. Astrophys. J. 556, 872-884) model, which represents a steady-state equilibrium between precipitation and condensation of vapor delivered by turbulent diffusion. We re-evaluate observed cloud densities in the Galileo Probe entry site (Ragent, B. et al. [1998]. J. Geophys. Res. 103, 22891-22910), and show that the upper and lower observed clouds at ∼0.5 and ∼3 bars are consistent with weak (cirrus-like) updrafts under conditions of saturated ammonia and water vapor, respectively. The densest observed cloud, near 1.3 bar, requires unexpectedly strong updraft conditions, or higher cloud density rates. The cloud density rate in this layer may be augmented by a composition with non-NH4SH components (possibly including adsorbed NH3).

On the Asymptotic Regimes and the Strongly Stratified Limit of Rotating Boussinesq Equations

NASA Technical Reports Server (NTRS)

Babin, A.; Mahalov, A.; Nicolaenko, B.; Zhou, Y.

1997-01-01

Asymptotic regimes of geophysical dynamics are described for different Burger number limits. Rotating Boussinesq equations are analyzed in the asymptotic limit, of strong stratification in the Burger number of order one situation as well as in the asymptotic regime of strong stratification and weak rotation. It is shown that in both regimes horizontally averaged buoyancy variable is an adiabatic invariant for the full Boussinesq system. Spectral phase shift corrections to the buoyancy time scale associated with vertical shearing of this invariant are deduced. Statistical dephasing effects induced by turbulent processes on inertial-gravity waves are evidenced. The 'split' of the energy transfer of the vortical and the wave components is established in the Craya-Herring cyclic basis. As the Burger number increases from zero to infinity, we demonstrate gradual unfreezing of energy cascades for ageostrophic dynamics. The energy spectrum and the anisotropic spectral eddy viscosity are deduced with an explicit dependence on the anisotropic rotation/stratification time scale which depends on the vertical aspect ratio parameter. Intermediate asymptotic regime corresponding to strong stratification and weak rotation is analyzed where the effects of weak rotation are accounted for by an asymptotic expansion with full control (saturation) of vertical shearing. The regularizing effect of weak rotation differs from regularizations based on vertical viscosity. Two scalar prognostic equations for ageostrophic components (divergent velocity potential and geostrophic departure ) are obtained.

Stratification period and germination of Douglas-fir seed from Oregon seed orchards: two case studies.

Treesearch

Frank C. Sorenson

1991-01-01

Effect of stratification period (S) and incubation temperature (T) on germination be- havior were tested by using two groups of Douglas-fir orchard seedlots that had given low germination percentages in standard tests. One group of seedlots that had experienced different cone-drying regimes, but otherwise were treated comparably, were germinated at T = 15 and 25 °C...

Wind-Wave Effects on Vertical Mixing in Chesapeake Bay, USA: comparing observations to second-moment closure predictions.

NASA Astrophysics Data System (ADS)

Fisher, A. W.; Sanford, L. P.; Scully, M. E.

2016-12-01

Coherent wave-driven turbulence generated through wave breaking or nonlinear wave-current interactions, e.g. Langmuir turbulence (LT), can significantly enhance the downward transfer of momentum, kinetic energy, and dissolved gases in the oceanic surface layer. There are few observations of these processes in the estuarine or coastal environments, where wind-driven mixing may co-occur with energetic tidal mixing and strong density stratification. This presents a major challenge for evaluating vertical mixing parameterizations used in modeling estuarine and coastal dynamics. We carried out a large, multi-investigator study of wind-driven estuarine dynamics in the middle reaches of Chesapeake Bay, USA, during 2012-2013. The center of the observational array was an instrumented turbulence tower with both atmospheric and marine turbulence sensors as well as rapidly sampled temperature and conductivity sensors. For this paper, we examined the impacts of surface gravity waves on vertical profiles of turbulent mixing and compared our results to second-moment turbulence closure predictions. Wave and turbulence measurements collected from the vertical array of Acoustic Doppler Velocimeters (ADVs) provided direct estimates of the dominant terms in the TKE budget and the surface wave field. Observed dissipation rates, TKE levels, and turbulent length scales are compared to published scaling relations and used in the calculation of second-moment nonequilibrium stability functions. Results indicate that in the surface layer of the estuary, where elevated dissipation is balanced by vertical divergence in TKE flux, existing nonequilibrium stability functions underpredict observed eddy viscosities. The influences of wave breaking and coherent wave-driven turbulence on modeled and observed stability functions will be discussed further in the context of turbulent length scales, TKE and dissipation profiles, and the depth at which the wave-dominated turbulent transport layer transitions to a turbulent log layer. The influences of fetch-limited wind waves, density stratification, and surface buoyancy fluxes will also be discussed.

Gender and cultural differences in the association between family roles, social stratification, and alcohol use: a European cross-cultural analysis.

PubMed

Kuntsche, Sandra; Gmel, Gerhard; Knibbe, Ronald A; Kuendig, Hervé; Bloomfield, Kim; Kramer, Stephanie; Grittner, Ulrike

2006-01-01

First, this paper investigates (i) gender differences in associations of social stratification, family roles, and heavy drinking, and (ii) country differences in these associations. Second, it seeks to explain country differences in the associations of social stratification and family roles with alcohol consumption by societal level variables. Survey data of 25 to 49-years-old from eight European countries were used. Logistic regressions were used to analyse gender differences in the association between family roles (marriage, having children), social stratification (education, employment), and heavy drinking (>20 g/day for women; 30 g/day for men). Gender differences were tested by means of interactions between gender and social stratification/family roles. Structural measures of work desirability, social welfare, and gender equity were used to explain differences in associations across countries. The associations between social stratification, family roles, and heavy drinking varied across gender and countries. A country's social welfare system was associated with heavy drinking only among women. Women in countries with a strong social welfare system, such as Nordic countries, tended to drink more heavily if employed, having lower formal education, and a non-traditional family role. In countries with weak social welfare systems or work desirability, heavy drinking was associated with high education, while effects of family roles and employment were small. It appeared that the social welfare system and gender equity of a country determines to a large extent how education, employment, and family roles are associated with heavy drinking.

The Sexual Stratification Hypothesis: Is the Decision to Arrest Influenced by the Victim/Suspect Racial/Ethnic Dyad?

PubMed

O'Neal, Eryn Nicole; Beckman, Laura O; Spohn, Cassia

2016-05-24

The sexual stratification hypothesis suggests that criminal justice responses to sexual victimization will differ depending on the victim/suspect racial/ethnic dyad. Previous research examining the sexual stratification hypothesis has primarily focused on court processes, and the small body of literature examining arrest decisions is dated. There remains substantial opportunity for testing the sexual stratification hypothesis at response stages apart from the court level (i.e., arrest). Using quantitative data on 655 sexual assault complaints that were reported to the Los Angeles County Sherriff's Department (LASD) and the Los Angeles Police Department (LAPD) in 2008, this study examines the effect of the victim/suspect racial/ethnic dyad on the decision to arrest. Findings suggest that police consider the victim/suspect racial/ethnic dyad when making arrest decisions. In addition, victim characteristics, strength of evidence indicators, and measures of case factors predict the police decision to make an arrest. © The Author(s) 2016.

Dynamics of a vertical turbulent plume in a stratification typical of Greenland fjords: an idealized model of subglacial discharge

NASA Astrophysics Data System (ADS)

Stenberg, Erik; Ezhova, Ekaterina; Cenedese, Claudia; Brandt, Luca

2017-04-01

We the report results of large eddy simulations of a turbulent buoyant plume in a configuration providing an idealized model of subglacial discharge from a submarine glacier in stratifications typical of Greenland Fjords. We neglect a horizontal momentum of the plume and assume that its influence on the plume dynamics is small and important only close to the source. Moreover, idealized models have considered the plume adjacent to the glacier as a half-conical plume (e.g., [1]). Thus, to compare the results for such plume with the classical plume theory, developed for free plumes entraining ambient fluid from all directions, it is convenient to add the second half-conical part and consider a free plume with double the total discharge as a model. Given the estimate of the total subglacial discharge for Helheim Glacier in Sermilik Fjord [2], we perform simulations with double the total discharge in order to investigate the dynamics of the flow in typical winter and summer stratifications in Greenland fjords [3]. The plume is discharged from a round source of various diameters. In winter, when the stratification is similar to an idealised two-layers case, turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two-layer stratification. In summer, instead, the stratification is more complex and turbulent entrainment is significantly reduced. The subsurface layer in summer is characterized by a strong density gradient and the oscillating plume generates non-linear internal waves which are able to mix this layer even if the plume does not penetrate to the surface. The classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions of the plume parameters in the weakly stratified lower layer up to the pycnocline. [1] Mankoff, K. D., F. Straneo, C. Cenedese, S. B. Das, C. D. Richards, and H. Singh, 2016: Structure and dynamics of a subglacial discharge plume in a Greenland Fjord. J. Geophys. Res., 121, doi:10.1002/2016JC011764. [2] Sciascia, R., F. Straneo, C. Cenedese, and P. Heimbach, 2013: Seasonal variability of submarine melt rate and circulation in an East Greenland fjord. J. Geophys. Res., 118, 2492-2506. [3] Straneo, F., R. Curry, D. Sutherland, G. Hamilton, C. Cenedese, K. Vage, and L. Stearns, 2011: Impact of fjord dynamics and glacial runoff on the circulation near Helheim Glacier. Nature Geosci., 4, 322-327.

Evaluating analytical approaches for estimating pelagic fish biomass using simulated fish communities

USGS Publications Warehouse

Yule, Daniel L.; Adams, Jean V.; Warner, David M.; Hrabik, Thomas R.; Kocovsky, Patrick M.; Weidel, Brian C.; Rudstam, Lars G.; Sullivan, Patrick J.

2013-01-01

Pelagic fish assessments often combine large amounts of acoustic-based fish density data and limited midwater trawl information to estimate species-specific biomass density. We compared the accuracy of five apportionment methods for estimating pelagic fish biomass density using simulated communities with known fish numbers that mimic Lakes Superior, Michigan, and Ontario, representing a range of fish community complexities. Across all apportionment methods, the error in the estimated biomass generally declined with increasing effort, but methods that accounted for community composition changes with water column depth performed best. Correlations between trawl catch and the true species composition were highest when more fish were caught, highlighting the benefits of targeted trawling in locations of high fish density. Pelagic fish surveys should incorporate geographic and water column depth stratification in the survey design, use apportionment methods that account for species-specific depth differences, target midwater trawling effort in areas of high fish density, and include at least 15 midwater trawls. With relatively basic biological information, simulations of fish communities and sampling programs can optimize effort allocation and reduce error in biomass estimates.

Environmental and Cultural Impact. Proposed Tennessee Colony Reservoir, Trinity River, Texas. Volume II. Appendices A, B and C.

DTIC Science & Technology

1972-01-01

in a considerable increase in the water salinity . Density stratification of the water is possible, the denser saline water forming the lower water...layer in the lake basin which causes anaerobic, toxic conditions. Salinity causes also an increase in flocculation and sedi- mentation of clay minerals...increased salin - ity of the lake water. Excessive water seepage in the fault zone intersecting the northern most part of the reservoir will probably

Shear Thinning in Xenon

NASA Technical Reports Server (NTRS)

Bergm Robert F.; Moldover, Michael R.; Yao, Minwu; Zimmerli, Gregory A.

2009-01-01

We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids such as molten plastics or ketchup, near the critical point of xenon. The data span a wide range of dimensionless shear rate: the product of the shear rate and the relaxation time of critical fluctuations was greater than 0.001 and was less than 700. As predicted by theory, shear thinning occurred when this product was greater than 1. The measurements were conducted aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity.

Secondary Circulation Asymmetry in a Meandering, Partially Stratified Estuary

NASA Astrophysics Data System (ADS)

Pein, J.; Valle-Levinson, A.; Stanev, E. V.

2018-03-01

Numerical model experiments are used to study the effects of multiple channel bends on estuarine dynamics and, in particular, on secondary flows. These effects are demonstrated by comparing experiments with two different idealized trumpet-shaped estuaries, one straight and another one with a ˜8 km meandering section in the middle of the estuary. Meanders complicate the flow field by introducing secondary processes. For instance, meanders increase turbulence and associated mixing locally within the water column, as well as outside the meandering portion. Furthermore, meanders transform up to 30% of the along-channel momentum into secondary circulation. Production of turbulence and secondary currents is different at flood and ebb tidal phases. At flood, meanders lead to unstable stratification and increased turbulence. At ebb, the flow develops a helical pattern and adjusts to the channel curvature with minimal decrease in density stability. The secondary circulation asymmetry is caused by an interplay between the across-channel baroclinic pressure gradient force and the centrifugal force. During ebb both forces enhance each other, whereas they oppose during flood. As a consequence of this interaction between baroclinic forcing and curving morphology, ebb flows and horizontal buoyancy fluxes increase relative to flood. The enhanced ebb dominance shifts a density front toward the mouth of the estuary, thus reducing salt intrusion.

AN ANALYTIC MODEL OF DUSTY, STRATIFIED, SPHERICAL H ii REGIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodríguez-Ramírez, J. C.; Raga, A. C.; Lora, V.

2016-12-20

We study analytically the effect of radiation pressure (associated with photoionization processes and with dust absorption) on spherical, hydrostatic H ii regions. We consider two basic equations, one for the hydrostatic balance between the radiation-pressure components and the gas pressure, and another for the balance among the recombination rate, the dust absorption, and the ionizing photon rate. Based on appropriate mathematical approximations, we find a simple analytic solution for the density stratification of the nebula, which is defined by specifying the radius of the external boundary, the cross section of dust absorption, and the luminosity of the central star. Wemore » compare the analytic solution with numerical integrations of the model equations of Draine, and find a wide range of the physical parameters for which the analytic solution is accurate.« less

Effect of date of cone collection and stratification period on germination and growth of Douglas-fir seeds and seedlings.

Treesearch

Frank C. Sorensen

1980-01-01

Low-elevation seeds collected 6 and 2 weeks before assumed natural seed fall were stratified 1, 2, 4, 8, 16, 32, 64, and 123 days and germinated in the laboratory. Germinated seeds from all stratification periods were sown at the same time in the nursery bed. Germination and seedling measurements were taken over two growing seasons.Early collection gave...

[The stratification of moisture content and its dynamics in co-composting of sewage sludge and pig manure].

PubMed

Luo, Wei; Chen, Tong-bin; Gao, Ding; Zheng, Yu-qi; Zheng, Guo-di

2004-03-01

The experiment of co-composting of sewage sludge and pig manure was studied. The moisture contents were 50.82%-60.87% at the stage of temperature rising and 38.7%-52.17% at the stage of thermophilic fermentation, and the stratification of moisture content were not obvious for both stages because the door, the internal wall and the depth of the composting bay had little effect on the stratification. At the stage of cooling, the moisture content was 24.54%-49.39%, and the stratification of moisture content was remarkable as the door, the internal wall and the depth of the composting bay had great influence on it. At the stage of maturity, the moisture content was 19.18%-49.34%, and the stratification of moisture weakened, for which the door and the internal wall were mainly responsible. At the different composting stage, the degree of difference of moisture content on the profiles of the pile was of the order: maturity stage > cooling stage > thermophilic stage = temperature rising stage, and the moisture content in the pile was as follows: the lower > the middle > the upper. The relation between moisture content and composting time meeted with two-order kinetics equation.

Options for refractive index and viscosity matching to study variable density flows

NASA Astrophysics Data System (ADS)

Clément, Simon A.; Guillemain, Anaïs; McCleney, Amy B.; Bardet, Philippe M.

2018-02-01

Variable density flows are often studied by mixing two miscible aqueous solutions of different densities. To perform optical diagnostics in such environments, the refractive index of the fluids must be matched, which can be achieved by carefully choosing the two solutes and the concentration of the solutions. To separate the effects of buoyancy forces and viscosity variations, it is desirable to match the viscosity of the two solutions in addition to their refractive index. In this manuscript, several pairs of index matched fluids are compared in terms of viscosity matching, monetary cost, and practical use. Two fluid pairs are studied in detail, with two aqueous solutions (binary solutions of water and a salt or alcohol) mixed into a ternary solution. In each case: an aqueous solution of isopropanol mixed with an aqueous solution of sodium chloride (NaCl) and an aqueous solution of glycerol mixed with an aqueous solution of sodium sulfate (Na_2SO_4). The first fluid pair allows reaching high-density differences at low cost, but brings a large difference in dynamic viscosity. The second allows matching dynamic viscosity and refractive index simultaneously, at reasonable cost. For each of these four solutes, the density, kinematic viscosity, and refractive index are measured versus concentration and temperature, as well as wavelength for the refractive index. To investigate non-linear effects when two index-matched, binary solutions are mixed, the ternary solutions formed are also analyzed. Results show that density and refractive index follow a linear variation with concentration. However, the viscosity of the isopropanol and NaCl pair deviates from the linear law and has to be considered. Empirical correlations and their coefficients are given to create index-matched fluids at a chosen temperature and wavelength. Finally, the effectiveness of the refractive index matching is illustrated with particle image velocimetry measurements performed for a buoyant jet in a linearly stratified environment. The creation of the index-matched solutions and linear stratification in a large-scale experimental facility are detailed, as well as the practical challenges to obtain precise refractive index matching.

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton-bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

NASA Astrophysics Data System (ADS)

Carrillo, P.; Medina-Sánchez, J. M.; Durán, C.; Herrera, G.; Villafañe, V. E.; Helbling, E. W.

2015-02-01

An indirect effect of global warming is a reduction in the depth of the upper mixed layer (UML) causing organisms to be exposed to higher levels of ultraviolet (UVR, 280-400 nm) and photosynthetically active radiation (PAR, 400-700 nm). This can affect primary and bacterial production as well as the commensalistic phytoplankton-bacteria relationship. The combined effects of UVR and reduction in the depth of the UML were assessed on variables related to the metabolism of phytoplankton and bacteria, during in situ experiments performed with natural pico- and nanoplankton communities from two oligotrophic lakes with contrasting UVR transparency (high-UVR versus low-UVR waters) of southern Spain. The negative UVR effects on epilimnetic primary production (PP) and on heterotrophic bacterial production (HBP), intensified under increased stratification, were higher in the low-UVR than in the high-UVR lake, and stronger on the phytoplanktonic than on the heterotrophic bacterial communities. Under UVR and increased stratification, the commensalistic phytoplankton-bacteria relationship was strengthened in the high-UVR lake where excretion of organic carbon (EOC) rates exceeded the bacterial carbon demand (BCD; i.e., BCD : EOC(%) ratio < 100). This did not occur in the low-UVR lake (i.e., BCD : EOC(%) ratio > 100). The greater UVR damage to phytoplankton and bacteria and the weakening of their commensalistic interaction found in the low-UVR lake indicates that these ecosystems would be especially vulnerable to UVR and increased stratification as stressors related to global climate change. Thus, our findings may have important implications for the carbon cycle in oligotrophic lakes of the Mediterranean region.

Case finding with incomplete administrative data: observations on playing with less than a full deck.

PubMed

Holmes, Ann M; Ackermann, Ronald T; Katz, Barry P; Downs, Stephen M; Inui, Thomas S

2010-12-01

Capacity constraints and efficiency considerations require that disease management programs identify patients most likely to benefit from intervention. Predictive modeling with available administrative data has been used as a strategy to match patients with appropriate interventions. Administrative data, however, can be plagued by problems of incompleteness and delays in processing. In this article, we examine the effects of these problems on the effectiveness of using administrative data to identify suitable candidates for disease management, and we evaluate various proposed solutions. We build prospective models using regression analysis and evaluate the resulting stratification algorithms using R² statistics, areas under receiver operator characteristic curves, and cost concentration ratios. We find delays in receipt of data reduce the effectiveness of the stratification algorithm, but the degree of compromise depends on what proportion of the population is targeted for intervention. Surprisingly, we find that supplementing partial data with a longer panel of more outdated data produces algorithms that are inferior to algorithms based on a shorter window of more recent data. Demographic data add little to algorithms that include prior claims data, and are an inadequate substitute when claims data are unavailable. Supplementing demographic data with additional information on self-reported health status improves the stratification performance only slightly and only when disease management is targeted to the highest risk patients. We conclude that the extra costs associated with surveying patients for health status information or retrieving older claims data cannot be justified given the lack of evidence that either improves the effectiveness of the stratification algorithm.

Revealing the timing of ocean stratification using remotely-sensed ocean fronts: links with marine predators

NASA Astrophysics Data System (ADS)

Miller, P. I.; Loveday, B. R.

2016-02-01

Stratification is of critical importance to the mixing and productivity of the ocean, though currently it can only be measured using in situ sampling, profiling buoys or underwater autonomous vehicles. Stratification is understood to affect the surface aggregation of pelagic fish and hence the foraging behaviour and distribution of their predators such as seabirds and cetaceans. Satellite Earth observation sensors cannot directly detect stratification, but can observe surface features related to the presence of stratification, for example shelf-sea fronts that separate tidally-mixed water from seasonally stratified water. This presentation describes a novel algorithm that accumulates evidence for stratification from a sequence of oceanic front maps, and in certain regions can reveal the timing of the seasonal onset and breakdown of stratification. Initial comparisons will be made with seabird locations acquired through GPS tagging. If successful, a remotely-sensed stratification timing index would augment the ocean front metrics already developed at PML, that have been applied in over 20 journal articles relating marine predators to ocean fronts. The figure below shows a preliminary remotely-sensed 'stratification' index, for 25-31 Jul. 2010, where red indicates water with stronger evidence for stratification.

Understanding the destabilizing role for surface tension in planar shear flows in terms of wave interaction

NASA Astrophysics Data System (ADS)

Biancofiore, L.; Heifetz, E.; Hoepffner, J.; Gallaire, F.

2017-10-01

Both surface tension and buoyancy force in stable stratification act to restore perturbed interfaces back to their initial positions. Hence, both are intuitively considered as stabilizing agents. Nevertheless, the Taylor-Caulfield instability is a counterexample in which the presence of buoyancy forces in stable stratification destabilize shear flows. An explanation for this instability lies in the fact that stable stratification supports the existence of gravity waves. When two vertically separated gravity waves propagate horizontally against the shear, they may become phase locked and amplify each other to form a resonance instability. Surface tension is similar to buoyancy but its restoring mechanism is more efficient at small wavelengths. Here, we show how a modification of the Taylor-Caulfield configuration, including two interfaces between three stably stratified immiscible fluids, supports interfacial capillary gravity whose interaction yields resonance instability. Furthermore, when the three fluids have the same density, an instability arises solely due to a pure counterpropagating capillary wave resonance. The linear stability analysis predicts a maximum growth rate of the pure capillary wave instability for an intermediate value of surface tension corresponding to We-1=5 , where We denotes the Weber number. We perform direct numerical nonlinear simulation of this flow and find nonlinear destabilization when 2 ≤We-1≤10 , in good agreement with the linear stability analysis. The instability is present also when viscosity is introduced, although it is gradually damped and eventually quenched.

An assessment of long term ecosystem research activities across European socio-ecological gradients.

PubMed

Metzger, M J; Bunce, R G H; van Eupen, M; Mirtl, M

2010-06-01

Integration of European long term ecosystem research (LTER) would provide important support for the management of the pan-European environment and ecosystems, as well as international policy commitments. This does require appropriate coverage of Europe and standardised frameworks and research methods between countries. Emerging interest in socio-ecological systems prompted the present assessment of the distribution of LTER activities across European socio-ecological gradients. This paper presents a European stratification with a 1 km(2) resolution, delineating 48 broad socio-ecological regions. The dataset is based on an existing biogeophysical stratification constructed using multivariate clustering of mainly climatic variables and a newly developed socio-economic stratification based on an economic density indicator. The coverage of European LTER facilities across the socio-ecological gradients is tested using this dataset. The analysis shows two strong biases in the present LTER effort. Firstly, urban and disturbed regions are consistently under-represented, illustrating a bias for traditional ecological research away from human activity. Secondly, the Mediterranean, for which some of the most extreme global change impacts are projected, is receiving comparatively little attention. Both findings can help guide future investment in the European LTER network - and especially in a Long Term Socio-Ecological Research (LTSER) component- to provide a more balanced coverage. This will provide better scientific understanding of pan-European environmental concerns and support the management of natural resources and international policy commitments in the European Union. (c) 2010 Elsevier Ltd. All rights reserved.

A stratification approach using logit-based models for confounder adjustment in the study of continuous outcomes.

PubMed

Tan, Chuen Seng; Støer, Nathalie C; Chen, Ying; Andersson, Marielle; Ning, Yilin; Wee, Hwee-Lin; Khoo, Eric Yin Hao; Tai, E-Shyong; Kao, Shih Ling; Reilly, Marie

2017-01-01

The control of confounding is an area of extensive epidemiological research, especially in the field of causal inference for observational studies. Matched cohort and case-control study designs are commonly implemented to control for confounding effects without specifying the functional form of the relationship between the outcome and confounders. This paper extends the commonly used regression models in matched designs for binary and survival outcomes (i.e. conditional logistic and stratified Cox proportional hazards) to studies of continuous outcomes through a novel interpretation and application of logit-based regression models from the econometrics and marketing research literature. We compare the performance of the maximum likelihood estimators using simulated data and propose a heuristic argument for obtaining the residuals for model diagnostics. We illustrate our proposed approach with two real data applications. Our simulation studies demonstrate that our stratification approach is robust to model misspecification and that the distribution of the estimated residuals provides a useful diagnostic when the strata are of moderate size. In our applications to real data, we demonstrate that parity and menopausal status are associated with percent mammographic density, and that the mean level and variability of inpatient blood glucose readings vary between medical and surgical wards within a national tertiary hospital. Our work highlights how the same class of regression models, available in most statistical software, can be used to adjust for confounding in the study of binary, time-to-event and continuous outcomes.

The fluid dynamics of deep-sea mining

NASA Astrophysics Data System (ADS)

Peacock, Thomas; Rzeznik, Andrew

2017-11-01

With vast mineral deposits on the ocean floor, deep-sea nodule mining operations are expected to commence in the next decade. Among several fundamental fluid dynamics problems, this could involve plans for dewatering plumes to be released into the water column by surface processing vessels. To study this scenario, we consider the effects of non-uniform, realistic stratifications on forced compressible plumes with finite initial size. The classical plume model is developed to take into account the influence of thermal conduction through the dewatering pipe and also compressibility effects, for which a dimensionless number is introduced to determine their importance compared to the background stratification. Among other things, our results show that small-scale features of a realistic stratification can have a large effect on plume dynamics compared to smoothed profiles and that for any given set of environmental parameters there is a discharge flow rate that minimizes the plume vertical extent. Our findings are put in the context of nodule mining plumes for which the rapid and efficient re-sedimentation of waste material has important environmental consequences.

Is risk stratification ever the same as 'profiling'?

PubMed

Braithwaite, R Scott; Stevens, Elizabeth R; Caplan, Arthur

2016-05-01

Physicians engage in risk stratification as a normative part of their professional duties. Risk stratification has the potential to be beneficial in many ways, and implicit recognition of this potential benefit underlies its acceptance as a cornerstone of the medical profession. However, risk stratification also has the potential to be harmful. We argue that 'profiling' is a term that corresponds to risk stratification strategies in which there is concern that ethical harms exceed likely or proven benefits. In the case of risk stratification for health goals, this would occur most frequently if benefits were obtained by threats to justice, autonomy or privacy. We discuss implications of the potential overlap between risk stratification and profiling for researchers and for clinicians, and we consider whether there are salient characteristics that make a particular risk stratification algorithm more or less likely to overlap with profiling, such as whether the risk stratification algorithm is based on voluntary versus non-voluntary characteristics, based on causal versus non-causal characteristics, or based on signifiers of historical disadvantage. We also discuss the ethical challenges created when a risk stratification scheme helps all subgroups but some more than others, or when risk stratification harms some subgroups but benefits the aggregate group. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

Numerical simulations of the stratified oceanic bottom boundary layer

NASA Astrophysics Data System (ADS)

Taylor, John R.

Numerical simulations are used to consider several problems relevant to the turbulent oceanic bottom boundary layer. In the first study, stratified open channel flow is considered with thermal boundary conditions chosen to approximate a shallow sea. Specifically, a constant heat flux is applied at the free surface and the lower wall is assumed to be adiabatic. When the surface heat flux is strong, turbulent upwellings of low speed fluid from near the lower wall are inhibited by the stable stratification. Subsequent studies consider a stratified bottom Ekman layer over a non-sloping lower wall. The influence of the free surface is removed by using an open boundary condition at the top of the computational domain. Particular attention is paid to the influence of the outer layer stratification on the boundary layer structure. When the density field is initialized with a linear profile, a turbulent mixed layer forms near the wall, which is separated from the outer layer by a strongly stable pycnocline. It is found that the bottom stress is not strongly affected by the outer layer stratification. However, stratification reduces turbulent transport to the outer layer and strongly limits the boundary layer height. The mean shear at the top of the boundary layer is enhanced when the outer layer is stratified, and this shear is strong enough to cause intermittent instabilities above the pycnocline. Turbulence-generated internal gravity waves are observed in the outer layer with a relatively narrow frequency range. An explanation for frequency content of these waves is proposed, starting with an observed broad-banded turbulent spectrum and invoking linear viscous decay to explain the preferential damping of low and high frequency waves. During the course of this work, an open-source computational fluid dynamics code has been developed with a number of advanced features including scalar advection, subgrid-scale models for large-eddy simulation, and distributed memory parallelism.

Intrabreed Stratification Related to Divergent Selection Regimes in Purebred Dogs May Affect the Interpretation of Genetic Association Studies

PubMed Central

Chang, Melanie L.; Yokoyama, Jennifer S.; Branson, Nick; Dyer, Donna J.; Hitte, Christophe; Overall, Karen L.

2009-01-01

Until recently, canine genetic research has not focused on population structure within breeds, which may confound the results of case–control studies by introducing spurious correlations between phenotype and genotype that reflect population history. Intrabreed structure may exist when geographical origin or divergent selection regimes influence the choices of potential mates for breeding dogs. We present evidence for intrabreed stratification from a genome-wide marker survey in a sample of unrelated dogs. We genotyped 76 Border Collies, 49 Australian Shepherds, 17 German Shepherd Dogs, and 17 Portuguese Water Dogs for our primary analyses using Affymetrix Canine v2.0 single-nucleotide polymorphism (SNP) arrays. Subsets of autosomal markers were examined using clustering algorithms to facilitate assignment of individuals to populations and estimation of the number of populations represented in the sample. SNPs passing stringent quality control filters were employed for explicitly phylogenetic analyses reconstructing relationships between individuals using maximum parsimony and Bayesian methods. We used simulation studies to explore the possible effects of intrabreed stratification on genome-wide association studies. These analyses demonstrate significant stratification in at least one of our primary breeds of interest, the Border Collie. Demographic and pedigree data suggest that this population substructure may result from geographic isolation or divergent selection regimes practiced by breeders with different breeding program goals. Simulation studies indicate that such stratification could result in false discovery rates significant enough to confound genome-wide association analyses. Intrabreed stratification should be accounted for when designing and interpreting the results of case–control association studies using purebred dogs.

On the role of modeling choices in estimation of cerebral aneurysm wall tension.

PubMed

Ramachandran, Manasi; Laakso, Aki; Harbaugh, Robert E; Raghavan, Madhavan L

2012-11-15

To assess various approaches to estimating pressure-induced wall tension in intracranial aneurysms (IA) and their effect on the stratification of subjects in a study population. Three-dimensional models of 26 IAs (9 ruptured and 17 unruptured) were segmented from Computed Tomography Angiography (CTA) images. Wall tension distributions in these patient-specific geometric models were estimated based on various approaches such as differences in morphological detail utilized or modeling choices made. For all subjects in the study population, the peak wall tension was estimated using all investigated approaches and were compared to a reference approach-nonlinear finite element (FE) analysis using the Fung anisotropic model with regionally varying material fiber directions. Comparisons between approaches were focused toward assessing the similarity in stratification of IAs within the population based on peak wall tension. The stratification of IAs tension deviated to some extent from the reference approach as less geometric detail was incorporated. Interestingly, the size of the cerebral aneurysm as captured by a single size measure was the predominant determinant of peak wall tension-based stratification. Within FE approaches, simplifications to isotropy, material linearity and geometric linearity caused a gradual deviation from the reference estimates, but it was minimal and resulted in little to no impact on stratifications of IAs. Differences in modeling choices made without patient-specificity in parameters of such models had little impact on tension-based IA stratification in this population. Increasing morphological detail did impact the estimated peak wall tension, but size was the predominant determinant. Copyright © 2012 Elsevier Ltd. All rights reserved.

Depth investigation of rapid sand filters for drinking water production reveals strong stratification in nitrification biokinetic behavior.

PubMed

Tatari, K; Smets, B F; Albrechtsen, H-J

2016-09-15

The biokinetic behavior of NH4(+) removal was investigated at different depths of a rapid sand filter treating groundwater for drinking water preparation. Filter materials from the top, middle and bottom layers of a full-scale filter were exposed to various controlled NH4(+) loadings in a continuous-flow lab-scale assay. NH4(+) removal capacity, estimated from short term loading up-shifts, was at least 10 times higher in the top than in the middle and bottom filter layers, consistent with the stratification of Ammonium Oxidizing Bacteria (AOB). AOB density increased consistently with the NH4(+) removal rate, indicating their primarily role in nitrification under the imposed experimental conditions. The maximum AOB cell specific NH4(+) removal rate observed at the bottom was at least 3 times lower compared to the top and middle layers. Additionally, a significant up-shift capacity (4.6 and 3.5 times) was displayed from the top and middle layers, but not from the bottom layer at increased loading conditions. Hence, AOB with different physiological responses were active at the different depths. The biokinetic analysis predicted that despite the low NH4(+) removal capacity at the bottom layer, the entire filter is able to cope with a 4-fold instantaneous loading increase without compromising the effluent NH4(+). Ultimately, this filter up-shift capacity was limited by the density of AOB and their biokinetic behavior, both of which were strongly stratified. Copyright © 2016 Elsevier Ltd. All rights reserved.

Tidal variations of flow convergence, shear, and stratification at the Rio de la Plata estuary turbidity front

NASA Astrophysics Data System (ADS)

FramiñAn, Mariana B.; Valle-Levinson, Arnoldo; Sepúlveda, HéCtor H.; Brown, Otis B.

2008-08-01

Intratidal variability of density and velocity fields is investigated at the turbidity front of the Río de la Plata Estuary, South America. Current velocity and temperature-salinity profiles collected in August 1999 along a repeated transect crossing the front are analyzed. Horizontal and vertical gradients, stability of the front, convergence zones, and transverse flow associated to the frontal boundary are described. Strong horizontal convergence of the across-front velocity and build up of along-front velocity shear were observed at the front. In the proximity of the front, enhanced transverse (or along-front) flow created jet-like structures at the surface and near the bottom flowing in opposite directions. These structures persisted throughout the tidal cycle and were advected upstream (downstream) by the flood (ebb) current through a distance of ˜10 km. During peak flood, the upper layer flow reversed from its predominant downstream direction and upstreamflow occupied the entire water column; outside the peak flood, two-layer estuarine circulation dominated. Changes in density field were observed in response to tidal straining, tidal advection, and wind-induced mixing, but stratification remained throughout the tidal cycle. This work demonstrates the large spatial variability of the velocity field at the turbidity front; it provides evidence of enhanced transverse circulation along the frontal boundary; and reveals the importance of advective and frictional intratidal processes in the dynamics of the central part of the estuary.

Temperature profiles from Pos Crater Lake

NASA Astrophysics Data System (ADS)

Neshyba, Steve; Fernandez, Walter; Diaz-Andrade, José

In 1984, we took part in an expedition to measure the temperature field and bathymetry of the acid lake (Figure 1) that has formed in the crater of Poás volcano, Costa Rica, since its last eruption in 1953. Obtaining these data was the first step in a long-range study planned by researchers at the Center for Geophysical Research, University of Costa Rica (San Jose, Costa Rica), and the College of Oceanography, Oregon State University (Corvallis). The study will eventually consider all aspects of fluid behavior in a volcanic lake that is heated or otherwise convectively driven by energy injected at the lake bottom.Evidence of convection is clearly visible on the surface of the Poás lake most of the time. Fumarole activity has been continuous since 1953. Phreatic explosions are quite frequent, varying from weak to strong, and the height of the ejected column varies from 1 to more than 500 m. One immediately useful result of the research would be an estimate of the heat transfer from sources within the conduit to the overlying water column. As far as geophysical fluid behavior goes, we are interested in the turbulent and diffusive processes by which heat and chemical species are transferred. We are especially interested in the impact on the density stratification of the density changes that occur as particulates settle downward through the fluid column. The stratification would otherwise be controlled by the turbulent and diffusive processes driven by thermochemical factors.

Environmental regulation of dormancy loss in seeds of Lomatium dissectum (Apiaceae)

PubMed Central

Scholten, Melissa; Donahue, Jacklyn; Shaw, Nancy L.; Serpe, Marcelo D.

2009-01-01

Background and Aims Lomatium dissectum (Apiaceae) is a perennial, herbaceous plant of wide distribution in Western North America. At the time of dispersal, L. dissectum seeds are dormant and have under-developed embryos. The aims of this work were to determine the requirements for dormancy break and germination, to characterize the type of seed dormancy, and to determine the effect of dehydration after embryo growth on seed viability and secondary dormancy. Methods The temperature requirements for embryo growth and germination were investigated under growth chamber and field conditions. The effect of GA3 on embryo growth was also analysed to determine the specific type of seed dormancy. The effect of dehydration on seed viability and induction of secondary dormancy were tested in seeds where embryos had elongated about 4-fold their initial length. Most experiments examining the nature of seed dormancy were conducted with seeds collected at one site in two different years. To characterize the degree of variation in dormancy-breaking requirements among seed populations, the stratification requirements of seeds collected at eight different sites were compared. Key Results Embryo growth prior to and during germination occurred at temperatures between 3 and 6 °C and was negligible at stratification temperatures of 0·5 and 9·1 °C. Seeds buried in the field and exposed to natural winter conditions showed similar trends. Interruption of the cold stratification period by 8 weeks of dehydration decreased seed viability by about 30 % and induced secondary dormancy in the remaining viable seeds. Comparison of the cold stratification requirements of different seed populations indicates that seeds collected from moist habitats have longer cold stratification requirements that those from semiarid environments. Conclusions Seeds of L. dissectum have deep complex morphophysiological dormancy. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. PMID:19233890

Numerical investigation of the entrainment and mixing processes in neutral and stably-stratified mixing layers

NASA Astrophysics Data System (ADS)

Cortesi, A. B.; Smith, B. L.; Yadigaroglu, G.; Banerjee, S.

1999-01-01

The direct numerical simulation (DNS) of a temporally-growing mixing layer has been carried out, for a variety of initial conditions at various Richardson and Prandtl numbers, by means of a pseudo-spectral technique; the main objective being to elucidate how the entrainment and mixing processes in mixing-layer turbulence are altered under the combined influence of stable stratification and thermal conductivity. Stratification is seen to significantly modify the way by which entrainment and mixing occur by introducing highly-localized, convective instabilities, which in turn cause a substantially different three-dimensionalization of the flow compared to the unstratified situation. Fluid which was able to cross the braid region mainly undisturbed (unmixed) in the unstratified case, pumped by the action of rib pairs and giving rise to well-formed mushroom structures, is not available with stratified flow. This is because of the large number of ribs which efficiently mix the fluid crossing the braid region. More efficient entrainment and mixing has been noticed for high Prandtl number computations, where vorticity is significantly reinforced by the baroclinic torque. In liquid sodium, however, for which the Prandtl number is very low, the generation of vorticity is very effectively suppressed by the large thermal conduction, since only small temperature gradients, and thus negligible baroclinic vorticity reinforcement, are then available to counterbalance the effects of buoyancy. This is then reflected in less efficient entrainment and mixing. The influence of the stratification and the thermal conductivity can also be clearly identified from the calculated entrainment coefficients and turbulent Prandtl numbers, which were seen to accurately match experimental data. The turbulent Prandtl number increases rapidly with increasing stratification in liquid sodium, whereas for air and water the stratification effect is less significant. A general law for the entrainment coefficient as a function of the Richardson and Prandtl numbers is proposed, and critically assessed against experimental data.

Stratification Pattern of Static and Scale-Invariant Dynamic Measures of Heartbeat Fluctuations Across Sleep Stages in Young and Elderly

PubMed Central

Schmitt, Daniel T.; Stein, Phyllis K.; Ivanov, Plamen Ch.

2010-01-01

Cardiac dynamics exhibit complex variability characterized by scale-invariant and nonlinear temporal organization related to the mechanism of neuroautonomic control, which changes with physiologic states and pathologic conditions. Changes in sleep regulation during sleep stages are also related to fluctuations in autonomic nervous activity. However, the interaction between sleep regulation and cardiac autonomic control remains not well understood. Even less is known how this interaction changes with age, as aspects of both cardiac dynamics and sleep regulation differ in healthy elderly compared to young subjects. We hypothesize that because of the neuroautonomic responsiveness in young subjects, fractal and nonlinear features of cardiac dynamics exhibit a pronounced stratification pattern across sleep stages, while in elderly these features will remain unchanged due to age-related loss of cardiac variability and decline of neuroautonomic responsiveness. We analyze the variability and the temporal fractal organization of heartbeat fluctuations across sleep stages in both young and elderly. We find that independent linear and nonlinear measures of cardiac control consistently exhibit the same ordering in their values across sleep stages, forming a robust stratification pattern. Despite changes in sleep architecture and reduced heart rate variability in elderly subjects, this stratification surprisingly does not break down with advanced age. Moreover, the difference between sleep stages for some linear, fractal, and nonlinear measures exceeds the difference between young and elderly, suggesting that the effect of sleep regulation on cardiac dynamics is significantly stronger than the effect of healthy aging. Quantifying changes in this stratification pattern may provide insights into how alterations in sleep regulation contribute to increased cardiac risk. PMID:19203874

The interplay between crystallization, replenishment and hybridization in large felsic magma chambers

NASA Astrophysics Data System (ADS)

Bateman, R.

1995-09-01

While hybridized granitoid magmas are readily identifiable, the mechanisms of hybridization in large crustal magma chambers are so not clearly understood. Characteristic features of hybrid granitoids are (1) both the granitoid and included enclaves are commonly hybrids, as shown by mineralogy, geochemistry and isotopes; (2) mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early; (3) zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution; (4) mafic end-members in hybrids are commonly fractionated magmas and (5) stratification in subvolcanic granitoid magma chambers is not uncommon, and stratification has been identified in some deeper level plutons. Hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma. Experimental work with magma analogues and theoretical considerations reveal very severe thermal, rheological and dynamical limitations on mixing: only very similar (composition, temperature) magmas are likely to mix to homogeneity, and only moderately silicic hybrids are likely to be produced. However, "impossibly" silicic hybrids do exist. Synchronous, interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas, in the following manner. A mafic magma intrudes into the base of a stratified felsic magma and is cooled against it. Crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber. Subsequently, melt released by crystallization pf this, now-hybrid zone mixes with adjacent, more felsic zones. Thus, a suite of hybrid magmas are progressively formed. Density inhibitions are overcome by the generation of relatively low density residual melts. As crystallization proceeds, later injections are preserved as dykes and enclaves composed of hybrid magma. In this process, only physically adjacent and dynamically-thermally similar magmas directly interact, and so may mix to homogeneity. Finally, not simply felsic and mafic endmembers mix, but a whole suite of "intermediate" endmembers participate, ranging from relatively mafic through to felsic pairs of magmas. Direct mixing between the primary magmas only occurs at the beginning.

A perspective on the range of gasoline compression ignition combustion strategies for high engine efficiency and low NOx and soot emissions: Effects of in-cylinder fuel stratification

DOE PAGES

Dempsey, Adam B.; Curran, Scott J.; Wagner, Robert M.

2016-01-14

Many research studies have shown that low temperature combustion in compression ignition engines has the ability to yield ultra-low NOx and soot emissions while maintaining high thermal efficiency. To achieve low temperature combustion, sufficient mixing time between the fuel and air in a globally dilute environment is required, thereby avoiding fuel-rich regions and reducing peak combustion temperatures, which significantly reduces soot and NOx formation, respectively. It has been demonstrated that achieving low temperature combustion with diesel fuel over a wide range of conditions is difficult because of its properties, namely, low volatility and high chemical reactivity. On the contrary, gasolinemore » has a high volatility and low chemical reactivity, meaning it is easier to achieve the amount of premixing time required prior to autoignition to achieve low temperature combustion. In order to achieve low temperature combustion while meeting other constraints, such as low pressure rise rates and maintaining control over the timing of combustion, in-cylinder fuel stratification has been widely investigated for gasoline low temperature combustion engines. The level of fuel stratification is, in reality, a continuum ranging from fully premixed (i.e. homogeneous charge of fuel and air) to heavily stratified, heterogeneous operation, such as diesel combustion. However, to illustrate the impact of fuel stratification on gasoline compression ignition, the authors have identified three representative operating strategies: partial, moderate, and heavy fuel stratification. Thus, this article provides an overview and perspective of the current research efforts to develop engine operating strategies for achieving gasoline low temperature combustion in a compression ignition engine via fuel stratification. In this paper, computational fluid dynamics modeling of the in-cylinder processes during the closed valve portion of the cycle was used to illustrate the opportunities and challenges associated with the various fuel stratification levels.« less

A perspective on the range of gasoline compression ignition combustion strategies for high engine efficiency and low NOx and soot emissions: Effects of in-cylinder fuel stratification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dempsey, Adam B.; Curran, Scott J.; Wagner, Robert M.

Many research studies have shown that low temperature combustion in compression ignition engines has the ability to yield ultra-low NOx and soot emissions while maintaining high thermal efficiency. To achieve low temperature combustion, sufficient mixing time between the fuel and air in a globally dilute environment is required, thereby avoiding fuel-rich regions and reducing peak combustion temperatures, which significantly reduces soot and NOx formation, respectively. It has been demonstrated that achieving low temperature combustion with diesel fuel over a wide range of conditions is difficult because of its properties, namely, low volatility and high chemical reactivity. On the contrary, gasolinemore » has a high volatility and low chemical reactivity, meaning it is easier to achieve the amount of premixing time required prior to autoignition to achieve low temperature combustion. In order to achieve low temperature combustion while meeting other constraints, such as low pressure rise rates and maintaining control over the timing of combustion, in-cylinder fuel stratification has been widely investigated for gasoline low temperature combustion engines. The level of fuel stratification is, in reality, a continuum ranging from fully premixed (i.e. homogeneous charge of fuel and air) to heavily stratified, heterogeneous operation, such as diesel combustion. However, to illustrate the impact of fuel stratification on gasoline compression ignition, the authors have identified three representative operating strategies: partial, moderate, and heavy fuel stratification. Thus, this article provides an overview and perspective of the current research efforts to develop engine operating strategies for achieving gasoline low temperature combustion in a compression ignition engine via fuel stratification. In this paper, computational fluid dynamics modeling of the in-cylinder processes during the closed valve portion of the cycle was used to illustrate the opportunities and challenges associated with the various fuel stratification levels.« less

Understanding the Effect of Stratification on Vertical and Temporal Heterogenieties of Cyanobacteria Blooms in Lakes Using a Long Term in-situ Monitoring Station

NASA Astrophysics Data System (ADS)

Wilkinson, A.; Guala, M.; Hondzo, M.

2017-12-01

Harmful Algal Blooms (HAB) are made up of potentially toxic freshwater microorganisms called cyanobacteria, because of this they are a ecological and public health hazard. The occurrences of toxic HAB are unpredictable and highly spatially and temporary variable in freshwater ecosystems. To study the abiotic drivers for toxic HAB, a floating research station has been deployed in a hyper-eutrophic lake in Madison Lake, Minnesota, from June-October 2016. This research station provides full depth water quality (hourly) and meteorological monitoring (5 minutes). Water quality monitoring is performed by an autonomously traversed water quality sonde that provides chemical, physical and biological measurements; including phycocyanin, a photosynthetic pigment distinct to cyanobacteria. A bloom of cyanobacteria recorded in the epiliminion in mid-July was driven by prolonged strong thermal stratification in the water column, high surface water temperatures and high phosphate concentrations in the epiliminion. The high biovolume (BV) persisted until late September and was sustained below the surface after stratification weakened, when the thermocline did not confine cyanobacteria-rich layers any more, and cyanobacteria vertical heterogeneities decayed in the water column. High correlations among BV stratification, surface water temperature, and stratification stability informed the development of a quantitative relationship to determine how BV heterogeneities vary with thermal structure in the water column. The BV heterogeneity decreased with thermal stratification stability and surface water temperature, and the dynamic lake stability described by the Lake Number. Finally the location of maximum BV accumulation showed diurnal patterns ie. BV peaks were observed at 1 m depth during the day and deeper layers during the night, which followed patterns in light penetration and thermocline depth. These findings capture cyanobacteria vertical and temporal heterogeneities on a on full depth, seasonal scale and quantify BV distribution throughout the water column under different stratification conditions, which can be important for mitigating risks of contamination of drinking water and recreational exposure.

Copepod Behavior Response in an Internal Wave Apparatus

NASA Astrophysics Data System (ADS)

Webster, D. R.; Jung, S.; Haas, K. A.

2017-11-01

This study is motivated to understand the bio-physical forcing in zooplankton transport in and near internal waves, where high levels of zooplankton densities have been observed in situ. A laboratory-scale internal wave apparatus was designed to create a standing internal wave for various physical arrangements that mimic conditions observed in the field. A theoretical analysis of a standing internal wave inside a two-layer stratification system including non-linear wave effects was conducted to derive the expressions for the independent variables controlling the wave motion. Focusing on a case with a density jump of 1.0 σt, a standing internal wave was generated with a clean interface and minimal mixing across the pycnocline. Spatial and frequency domain measurements of the internal wave were evaluated in the context of the theoretical analysis. Behavioral assays with a mixed population of three marine copepods were conducted in control (stagnant homogeneous fluid), stagnant density jump interface, and internal wave flow configurations. In the internal wave treatment, the copepods showed an acrobatic, orbital-like motion in and around the internal wave region (bounded by the crests and the troughs of the waves). Trajectories of passive, neutrally-buoyant particles in the internal wave flow reveal that they generally oscillate back-and-forth along fixed paths. Thus, we conclude that the looping, orbital trajectories of copepods in the region near the internal wave interface are due to animal behavior rather than passive transport.

High efficiency stratification of apple cultivar Ligol seed dormancy by phytohormones, heat shock and pulsed radio frequency.

PubMed

Grzesik, Mieczysław; Górnik, Krzysztof; Janas, Regina; Lewandowki, Mariusz; Romanowska-Duda, Zdzislawa; Duijn, Bert van

2017-12-01

The aim of the study was to improve the effect of stratification of apple "Ligol" seeds by application of selected compounds, phytohormones, and physical methods For this purpose the seeds were stratified at 3°C in distilled water or in the presence of potassium nitrate (KNO 3 ), ethephon (ET), carbon monoxide (CO), hydrogen peroxide (H 2 O 2 ), a mixture of KNO 3 , ET, CO, H 2 O 2 , gibberellins (GA 3 ), 6-benzylaminopurine (BAP), jasmonic acid (JA), salicylic acid (SA) and a mixture of SA, GA 3 , BAP, JA, nitric oxide (NO), hydrogen chloride (HCL). Arranged protocols included various durations and combinations of selected compounds and phytohormones as well as laser and red light, heat shock - 2h heat shock (45°C) and Pulsed Radio Frequency (PRF) were investigated by germination tests and the activity of selected enzymes, gas exchange and index of chlorophyll in leaves. The obtained results showed the possibility to shorten more effectively the time of the apple 'Ligol' dormancy removal by treatments of the stratified seeds at 3°C with different biological and physical methods Selected compounds and phytohormones acted collectively as a regulatory complex controlling the course of release from dormancy. Physical methods (PRF and heat shock) additionally contributed to dormancy breakage. Duration of phytohormones or compounds impacts during stratification should be prolonged to minimum 7days to assure more balanced conditions of the regulatory complex for the acceleration of dormancy a removal. The most beneficial results were obtained after seed stratification for 7days on filter paper moistened in KNO 3 +Etephon+CO+H 2 O 2 at 3°C, and then on filter paper moistened in phytohormones (GA 3 +BAP+JA) till the end of seed germination (3°C). The application of this protocol could be a very useful tool in a shortening the apple breeding cycle since the period of removing dormancy was reduced by 38days in comparison to stratified in water. PRF has also the additive role in breaking dormancy of apple 'Ligol' seed. Positive effects of compounds and phytohormones applied during stratification remarkably accelerated the growth of developed from them seedlings. Further research is needed to optimize stratification methods with appropriate contents and concentrations of compounds and phytohormones combined with PRF exposure. Copyright © 2017 Elsevier GmbH. All rights reserved.

Spatial Holmboe instability

NASA Astrophysics Data System (ADS)

Ortiz, Sabine; Chomaz, Jean-Marc; Loiseleux, Thomas

2002-08-01

In mixing-layers between two parallel streams of different densities, shear and gravity effects interplay; buoyancy acts as a restoring force and the Kelvin-Helmholtz mode is known to be stabilized by the stratification. If the density interface is sharp enough, two new instability modes, known as Holmboe modes, appear, propagating in opposite directions. This mechanism has been studied in the temporal instability framework. The present paper analyzes the associated spatial instability problem. It considers, in the Boussinesq approximation, two immiscible inviscid fluids with a piecewise linear broken-line velocity profile. We show how the classical scenario for transition between absolute and convective instability should be modified due to the presence of propagating waves. In the convective region, the spatial theory is relevant and the slowest propagating wave is shown to be the most spatially amplified, as suggested by intuition. Predictions of spatial linear theory are compared with mixing-layer [C. G. Koop and F. K. Browand, J. Fluid Mech. 93, 135 (1979)] and exchange flow [G. Pawlak and L. Armi, J. Fluid Mech. 376, 1 (1999)] experiments. The physical mechanism for Holmboe mode destabilization is analyzed via an asymptotic expansion that predicts the absolute instability domain at large Richardson number.

Spatial Holmboe Instability

NASA Astrophysics Data System (ADS)

Sabine, Ortiz; Marc, Chomaz Jean; Thomas, Loiseleux

2001-11-01

In mixing layers between two parallel streams of different densities, shear and gravity effects interplay. When the Roosby number, which compares the nonlinear acceleration terms to the Coriolis forces, is large enough, buoyancy acts as a restoring force, the Kelvin-Helmholtz mode is known to be stabilized by the stratification. If the density interface is sharp enough, two new instability modes, known as Holmboe modes, propagating in opposite directions appear. This mechanism has been study in the temporal instability framework. We analyze the associated spatial instability problem, in the Boussinesq approximation, for two immiscible inviscid fluids with broken-line velocity profile. We show how the classical scenario for transition between absolute and convective instability should be modified due to the presence of propagating waves. In convective region, the spatial theory is relevant and the slowest propagative wave is shown to be the most spatially amplified, as suggested by the intuition. Spatial theory is compared with mixing layer experiments (C.G. Koop and Browand J. Fluid Mech. 93, part 1, 135 (1979)), and wedge flows (G. Pawlak and L. Armi J. Fluid Mech. 376, 1 (1999)). Physical mechanism for the Holmboe mode destabilization is analyzed via an asymptotic expansion that explains precisely the absolute instability domain at large Richardson number.

A propagator matrix method for the Rayleigh-Taylor instability of multiple layers: a case study on crustal delamination in the early Earth

NASA Astrophysics Data System (ADS)

Mondal, Puskar; Korenaga, Jun

2018-03-01

The dispersion relation of the Rayleigh-Taylor instability, a gravitational instability associated with unstable density stratification, is of profound importance in various geophysical contexts. When more than two layers are involved, a semi-analytical technique based on the biharmonic formulation of Stokes flow has been extensively used to obtain such dispersion relation. However, this technique may become cumbersome when applied to lithospheric dynamics, where a number of layers are necessary to represent the continuous variation of viscosity over many orders of magnitude. Here, we present an alternative and more efficient method based on the propagator matrix formulation of Stokes flow. With this approach, the original instability problem is reduced to a compact eigenvalue equation whose size is solely determined by the number of primary density contrasts. We apply this new technique to the stability of the early crust, and combined with the Monte Carlo sensitivity analysis, we derive an empirical formula to compute the growth rate of the Rayleigh-Taylor instability for this particular geophysical setting. Our analysis indicates that the likelihood of crustal delamination hinges critically on the effective viscosity of eclogite.

Violent storms within the sea: Dense water formation episodes in the Mediterranean.

NASA Astrophysics Data System (ADS)

Salat, J.

2009-09-01

The Mediterranean is a semi enclosed basin which receives surface water from the Atlantic Ocean. Most of this water is returned into the Ocean with higher density, spreading at more than 1000 m depth (the rest is transported by the atmosphere and the rivers to the Ocean surface). In terms of water budget, the Mediterranean is considered an evaporation basin, but the loss of water is neither the only process that increases the water density nor it is a steady or uniform process. The factors affecting the water density, temperature and salinity, are driven by mass and heat exchanges with the atmosphere. Those exchanges may be by direct contact or mediated by the land. Therefore, changes in water density depend on the water circulation and local weather conditions, both with seasonal and geographical constraints. As the compressibility of water is very low, stratification is expected and horizontal motion is the predominant in the sea interior. Among the few processes that may introduce a vertical component in the water motion are surface heat loss or evaporation that increase the surface water density triggering convective cells. Such processes will be enhanced by surface cooling or by dry continental winds, and counterbalanced by rain, river runoff, solar heating and condensation. Therefore dense water formation are more likely to occur when sea surface temperature is higher than the surface air temperature. There are several scales of convective motions in the ocean, starting from the formation of the surface mixed layer during summer, by night cooling, breezes, and occasional wind storms. During autumn and winter, the vertical scale of the mixing is increasing by steps, through wind storms and progressive cooling, to easily reach the bottom over the continental shelves, typically not deeper than 150 m. However, as the Gibraltar sill is relatively shallow (~350 m) in relation to the average Mediterranean basin (2000-3000 m), the stratification of the deeper layers is weak. Therefore, where and when the surface layer becomes well mixed, typically in winter, in the northern regions, conditions are given (pre-conditioning phase) to the occurrence of dense water formation episodes. Those episodes require the participation of strong cold and dry winds which force an intense evaporation. In the NW Mediterranean, such forcing may act over the continental shelves, like that of the Gulf of Lions, or over deep open seas, typically the central part east of Catalonia and south of Provence. Over the shelf, surface water is expected to be fresher because of the runoff (e.g. the Rhône). Along the continental margin the water circulation, geostrophically adapted, is cyclonic and the stratification in the centre is lower, then density reached may be higher in the central part than on the shelf. However, cooling will be more effective over the shelf as the heat content of the water column is lower because it is much shorter. Once density over the shelf is high enough, the bottom water overflows and violently sinks along the slope in relatively narrow areas through what has been called a cascading event. In the central part, dense water formed sinks almost vertically in funnels not larger than a few kilometres in diameter, and is accompanied by a compensating rise of water from great depth on all sides. In such open sea winter convection events, the dense water can sink some 800 m within a matter of hours and may reach the bottom level, >2500 m deep, within a couple of days. Such short and violent episodes, cascading or open sea convection, of a few days' duration supply enough water to feed the lower layer to compensate the outflow through the Strait of Gibraltar for several weeks. The repeated events in some few points across the Mediterranean, like those above mentioned, are maintaining the Mediterranean circulation and the water exchanges with the Ocean. The overall amount of dense water formed however is highly variable from one year to another according to the forcings involved and perturbations of the water circulation.

Revealing the timing of ocean stratification using remotely sensed ocean fronts

NASA Astrophysics Data System (ADS)

Miller, Peter I.; Loveday, Benjamin R.

2017-10-01

Stratification is of critical importance to the circulation, mixing and productivity of the ocean, and is expected to be modified by climate change. Stratification is also understood to affect the surface aggregation of pelagic fish and hence the foraging behaviour and distribution of their predators such as seabirds and cetaceans. Hence it would be prudent to monitor the stratification of the global ocean, though this is currently only possible using in situ sampling, profiling buoys or underwater autonomous vehicles. Earth observation (EO) sensors cannot directly detect stratification, but can observe surface features related to the presence of stratification, for example shelf-sea fronts that separate tidally-mixed water from seasonally stratified water. This paper describes a novel algorithm that accumulates evidence for stratification from a sequence of oceanic front maps, and discusses preliminary results in comparison with in situ data and simulations from 3D hydrodynamic models. In certain regions, this method can reveal the timing of the seasonal onset and breakdown of stratification.

Prospective Validation of ATA and ETA Sonographic Pattern Risk of Thyroid Nodules Selected for FNAC.

PubMed

Maino, Fabio; Forleo, Raffaella; Martinelli, Martina; Fralassi, Noemi; Barbato, Filomena; Pilli, Tania; Capezzone, Marco; Brilli, Lucia; Ciuoli, Cristina; Di Cairano, Giovanni; Nigi, Laura; Pacini, Furio; Castagna, Maria Grazia

2018-06-01

Recently, the American Thyroid Association (ATA) and the European Thyroid Association (ETA) have proposed that thyroid ultrasound (US) should be used to stratify the risk of malignancy in thyroid nodules and to aid decision-making about whether fine-needle aspiration cytology (FNAC) is indicated. To validate and to compare the ATA and ETA US risk stratification systems of thyroid nodules in a prospective series of thyroid nodules submitted to FNAC. We prospectively evaluated 432 thyroid nodules selected for FNAC from 340 patients. Cytology reports were based on the five categories according to the criteria of the British Thyroid Association. The proportion of Thy2 nodules decreased significantly, whereas the proportion of Thy4/Thy5 nodules significantly increased with increasing US risk class (P < 0.0001). The ability to identify benign and malignant nodules was similar between ATA and ETA systems. According to ATA and ETA US risk stratification systems, 23.7% and 56.0% nodules did not meet the criteria for FNAC, respectively. Considering only categories at lower risk of malignancy, the cumulative malignancy rate in these nodules was 1.2% for ATA and 1.7% for ETA US risk stratification systems. ETA and ATA US risk stratification systems provide effective malignancy risk stratification for thyroid nodules. In clinical practice, using this approach, we should be able to reduce the number of unnecessary FNAC without losing clinically relevant thyroid cancer.

Quantitative risk stratification in Markov chains with limiting conditional distributions.

PubMed

Chan, David C; Pollett, Philip K; Weinstein, Milton C

2009-01-01

Many clinical decisions require patient risk stratification. The authors introduce the concept of limiting conditional distributions, which describe the equilibrium proportion of surviving patients occupying each disease state in a Markov chain with death. Such distributions can quantitatively describe risk stratification. The authors first establish conditions for the existence of a positive limiting conditional distribution in a general Markov chain and describe a framework for risk stratification using the limiting conditional distribution. They then apply their framework to a clinical example of a treatment indicated for high-risk patients, first to infer the risk of patients selected for treatment in clinical trials and then to predict the outcomes of expanding treatment to other populations of risk. For the general chain, a positive limiting conditional distribution exists only if patients in the earliest state have the lowest combined risk of progression or death. The authors show that in their general framework, outcomes and population risk are interchangeable. For the clinical example, they estimate that previous clinical trials have selected the upper quintile of patient risk for this treatment, but they also show that expanded treatment would weakly dominate this degree of targeted treatment, and universal treatment may be cost-effective. Limiting conditional distributions exist in most Markov models of progressive diseases and are well suited to represent risk stratification quantitatively. This framework can characterize patient risk in clinical trials and predict outcomes for other populations of risk.

Elite formation under occupation: the internal stratification of palestinian elites in the West Bank and Gaza Strip.

PubMed

Mazawi, A E; Yogev, A

1999-09-01

This paper examines the internal stratification of Palestinian elites in the West Bank and Gaza Strip under Israeli occupation. Our general aim is to clarify the extent to which social and political subordination to outside rule influences the development of indigenous elites in stateless societies. In contrast to nation-state societies, such elites may be horizontally stratified into a wider range of institutional settings, and vertically stratified by anti-occupation activism alongside the attainment of occupational prestige. In addition, context-specific determinants of their stratification patterns, such as refugee status, regionality, and country in which educational credentials were acquired, should be considered. A secondary content analysis of interviews conducted by the Palestinian Panorama centre with 249 elite members reveals, that the vertical stratification of Palestinian elites along occupational attainment and anti-occupation activism constitutes two quite independent status dimensions. A multinomial logit regression shows that, horizontally, elite groups are embedded in four distinct types of institutional activity, further demonstrating the multi-faceted formation of Palestinian elites. Contextual resources, such as refugee versus non-refugee status, regionality, and the acquiring of Western credentials, have differential effects on the vertical and horizontal stratification of Palestinian elites. The implications of these findings for further research on elite formation in the post-Oslo Palestinian society and in other stateless societies are discussed in conclusion.

Estimating the palliative effect of percutaneous endoscopic gastrostomy in an observational registry using principal stratification and generalized propensity scores

PubMed Central

Mishra-Kalyani, Pallavi S.; Johnson, Brent A.; Glass, Jonathan D.; Long, Qi

2016-01-01

Clinical disease registries offer a rich collection of valuable patient information but also pose challenges that require special care and attention in statistical analyses. The goal of this paper is to propose a statistical framework that allows for estimating the effect of surgical insertion of a percutaneous endogastrostomy (PEG) tube for patients living with amyotrophic lateral sclerosis (ALS) using data from a clinical registry. Although all ALS patients are informed about PEG, only some patients agree to the procedure which, leads to the potential for selection bias. Assessing the effect of PEG is further complicated by the aggressively fatal disease, such that time to death competes directly with both the opportunity to receive PEG and clinical outcome measurements. Our proposed methodology handles the “censoring by death” phenomenon through principal stratification and selection bias for PEG treatment through generalized propensity scores. We develop a fully Bayesian modeling approach to estimate the survivor average causal effect (SACE) of PEG on BMI, a surrogate outcome measure of nutrition and quality of life. The use of propensity score methods within the principal stratification framework demonstrates a significant and positive effect of PEG treatment, particularly when time of treatment is included in the treatment definition. PMID:27640365

Estimating the palliative effect of percutaneous endoscopic gastrostomy in an observational registry using principal stratification and generalized propensity scores

NASA Astrophysics Data System (ADS)

Mishra-Kalyani, Pallavi S.; Johnson, Brent A.; Glass, Jonathan D.; Long, Qi

2016-09-01

Clinical disease registries offer a rich collection of valuable patient information but also pose challenges that require special care and attention in statistical analyses. The goal of this paper is to propose a statistical framework that allows for estimating the effect of surgical insertion of a percutaneous endogastrostomy (PEG) tube for patients living with amyotrophic lateral sclerosis (ALS) using data from a clinical registry. Although all ALS patients are informed about PEG, only some patients agree to the procedure which, leads to the potential for selection bias. Assessing the effect of PEG is further complicated by the aggressively fatal disease, such that time to death competes directly with both the opportunity to receive PEG and clinical outcome measurements. Our proposed methodology handles the “censoring by death” phenomenon through principal stratification and selection bias for PEG treatment through generalized propensity scores. We develop a fully Bayesian modeling approach to estimate the survivor average causal effect (SACE) of PEG on BMI, a surrogate outcome measure of nutrition and quality of life. The use of propensity score methods within the principal stratification framework demonstrates a significant and positive effect of PEG treatment, particularly when time of treatment is included in the treatment definition.

A numerical solution of the Navier-Stokes equations for supercritical fluid thermodynamic analysis

NASA Technical Reports Server (NTRS)

Heinmiller, P. J.

1971-01-01

An explicit numerical solution of the compressible Navier-Stokes equations is applied to the thermodynamic analysis of supercritical oxygen in the Apollo cryogenic storage system. The wave character is retained in the conservation equations which are written in the basic fluid variables for a two-dimensional Cartesian coordinate system. Control-volume cells are employed to simplify imposition of boundary conditions and to ensure strict observance of local and global conservation principles. Non-linear real-gas thermodynamic properties responsible for the pressure collapse phenomonon in supercritical fluids are represented by tabular and empirical functions relating pressure and temperature to density and internal energy. Wall boundary conditions are adjusted at one cell face to emit a prescribed mass flowrate. Scaling principles are invoked to achieve acceptable computer execution times for very low Mach number convection problems. Detailed simulations of thermal stratification and fluid mixing occurring under low acceleration in the Apollo 12 supercritical oxygen tank are presented which model the pressure decay associated with de-stratification induced by an ordinary vehicle maneuver and heater cycle operation.

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient.

PubMed

Orihuela, Rodrigo L L; Peres, Carlos A; Mendes, Gabriel; Jarenkow, João A; Tabarelli, Marcelo

2015-01-01

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide.

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient

PubMed Central

Orihuela, Rodrigo L. L.; Peres, Carlos A.; Mendes, Gabriel; Jarenkow, João A.; Tabarelli, Marcelo

2015-01-01

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide. PMID:26309252

The relationship between breast density and bone mineral density in postmenopausal women.

PubMed

Buist, Diana S M; Anderson, Melissa L; Taplin, Stephen H; LaCroix, Andrea Z

2004-11-01

It is not well understood whether breast density is a marker of cumulative exposure to estrogen or a marker of recent exposure to estrogen. The authors examined the relationship between bone mineral density (BMD; a marker of lifetime estrogen exposure) and breast density. The authors conducted a cross-sectional analysis among 1800 postmenopausal women > or = 54 years. BMD data were taken from two population-based studies conducted in 1992-1993 (n = 1055) and in 1998-1999 (n = 753). The authors linked BMD data with breast density information collected as part of a mammography screening program. They used linear regression to evaluate the density relationship, adjusted for age, hormone therapy use, body mass index (BMI), and reproductive covariates. There was a small but significant negative association between BMD and breast density. The negative correlation between density measures was not explained by hormone therapy or age, and BMI was the only covariate that notably influenced the relationship. Stratification by BMI only revealed the negative correlation between bone and breast densities in women with normal BMI. There was no relationship in overweight or obese women. The same relationship was seen for all women who had never used hormone therapy, but it was not significant once stratified by BMI. BMD and breast density were not positively associated although both are independently associated with estrogen exposure. It is likely that unique organ responses obscure the relationship between the two as indicators of cumulative estrogen exposure.

Experimental study of oil plume stability: Parametric dependences and optimization.

PubMed

Li, Haoshuai; Shen, Tiantian; Bao, Mutai

2016-10-15

Oil plume is known to interact with density layer in spilled oil. Previous studies mainly focused on tracking oil plumes and predicting their impact on marine environment. Here, simulated experiments are presented that investigated the conditions inducing the formation of oil plume, focusing especially on the effects of oil/water volume ratio, oil/dispersant volume rate, ambient stratification and optimal conditions of oil plume on determining whether a plume will trap or escape. Scenario simulations showed that OWR influences the residence time most, dispersants dosage comes second and salinity least. The optimum residence time starts from 2387s, occurred at approximately condition (OWR, 0.1, DOR, 25.53% and salinity, 32.38). No change in the relative distribution under the more scale tank was observed, indicating these provide the time evolution of the oil plumes. Copyright © 2016 Elsevier Ltd. All rights reserved.

Inference for Environmental Intervention Studies using Principal Stratification

PubMed Central

Hackstadt, A. J.; Butz, Arlene M.; Williams, D’Ann L.; Diette, Gregory B.; Breysse, Patrick N.; Matsui, Elizabeth C.; Peng, Roger D.

2014-01-01

Previous research has found evidence of an association between indoor air pollution and asthma morbidity in children. Environmental intervention studies have been performed to examine the role of household environmental interventions in altering indoor air pollution concentrations and improving health. Previous environmental intervention studies have found only modest effects on health outcomes and it is unclear if the health benefits provided by environmental modification are comparable to those provided by medication. Traditionally, the statistical analysis of environmental intervention studies has involved performing two intention-to-treat analyses that separately estimate the effect of the environmental intervention on health and the effect of the environmental intervention on indoor air pollution concentrations. We propose a principal stratification (PS) approach to examine the extent to which an environmental intervention’s effect on health outcomes coincides with its effect on indoor air pollution. We apply this approach to data from a randomized air cleaner intervention trial conducted in a population of asthmatic children living in Baltimore, Maryland, USA. We find that amongst children for whom the air cleaner reduced indoor particulate matter concentrations, the intervention resulted in a meaningful improvement of asthma symptoms with an effect generally larger than previous studies have shown. A key benefit of using principal stratification in environmental intervention studies is that it allows investigators to estimate causal effects of the intervention for sub-groups defined by changes in the indoor air pollution concentration. PMID:25164949

Inference for environmental intervention studies using principal stratification.

PubMed

Hackstadt, Amber J; Matsui, Elizabeth C; Williams, D'Ann L; Diette, Gregory B; Breysse, Patrick N; Butz, Arlene M; Peng, Roger D

2014-12-10

Previous research has found evidence of an association between indoor air pollution and asthma morbidity in children. Environmental intervention studies have been performed to examine the role of household environmental interventions in altering indoor air pollution concentrations and improving health. Previous environmental intervention studies have found only modest effects on health outcomes and it is unclear if the health benefits provided by environmental modification are comparable with those provided by medication. Traditionally, the statistical analysis of environmental intervention studies has involved performing two intention-to-treat analyses that separately estimate the effect of the environmental intervention on health and the effect of the environmental intervention on indoor air pollution concentrations. We propose a principal stratification approach to examine the extent to which an environmental intervention's effect on health outcomes coincides with its effect on indoor air pollution. We apply this approach to data from a randomized air cleaner intervention trial conducted in a population of asthmatic children living in Baltimore, Maryland, USA. We find that among children for whom the air cleaner reduced indoor particulate matter concentrations, the intervention resulted in a meaningful improvement of asthma symptoms with an effect generally larger than previous studies have shown. A key benefit of using principal stratification in environmental intervention studies is that it allows investigators to estimate causal effects of the intervention for sub-groups defined by changes in the indoor air pollution concentration. Copyright © 2014 John Wiley & Sons, Ltd.

Internal Waves in CVX

NASA Technical Reports Server (NTRS)

Berg, Robert F.

1996-01-01

Near the liquid-vapor critical point, density stratification supports internal gravity waves which affect 1-g viscosity measurements in the CVX (Critical Viscosity of Xenon) experiment. Two internal-wave modes were seen in the horizontal viscometer. The frequencies of the two modes had different temperature dependences: with decreasing temperature, the higher frequency increased monotonically from 0.7 to 2.8 Hz, but the lower frequency varied non-monotonically, with a maximum of 1.0 Hz at 20 mK above the critical temperature. The measured frequencies agree with independently calculated frequencies to within 15%.

Representing Reservoir Stratification in Land Surface and Earth System Models

NASA Astrophysics Data System (ADS)

Yigzaw, W.; Li, H. Y.; Leung, L. R.; Hejazi, M. I.; Voisin, N.; Payn, R. A.; Demissie, Y.

2017-12-01

A one-dimensional reservoir stratification modeling has been developed as part of Model for Scale Adaptive River Transport (MOSART), which is the river transport model used in the Accelerated Climate Modeling for Energy (ACME) and Community Earth System Model (CESM). Reservoirs play an important role in modulating the dynamic water, energy and biogeochemical cycles in the riverine system through nutrient sequestration and stratification. However, most earth system models include lake models that assume a simplified geometry featuring a constant depth and a constant surface area. As reservoir geometry has important effects on thermal stratification, we developed a new algorithm for deriving generic, stratified area-elevation-storage relationships that are applicable at regional and global scales using data from Global Reservoir and Dam database (GRanD). This new reservoir geometry dataset is then used to support the development of a reservoir stratification module within MOSART. The mixing of layers (energy and mass) in the reservoir is driven by eddy diffusion, vertical advection, and reservoir inflow and outflow. Upstream inflow into a reservoir is treated as an additional source/sink of energy, while downstream outflow represented a sink. Hourly atmospheric forcing from North American Land Assimilation System (NLDAS) Phase II and simulated daily runoff by ACME land component are used as inputs for the model over the contiguous United States for simulations between 2001-2010. The model is validated using selected observed temperature profile data in a number of reservoirs that are subject to various levels of regulation. The reservoir stratification module completes the representation of riverine mass and heat transfer in earth system models, which is a major step towards quantitative understanding of human influences on the terrestrial hydrological, ecological and biogeochemical cycles.

The Auckland Cataract Study II: Reducing Complications by Preoperative Risk Stratification and Case Allocation in a Teaching Hospital.

PubMed

Kim, Bia Z; Patel, Dipika V; McKelvie, James; Sherwin, Trevor; McGhee, Charles N J

2017-09-01

To assess the effect of preoperative risk stratification for phacoemulsification surgery on intraoperative complications in a teaching hospital. Prospective cohort study. Prospective assessment of consecutive phacoemulsification cases (N = 500) enabled calculation of a risk score (M-score of 0-8) using a risk stratification system. M-scores of >3 were allocated to senior surgeons. All surgeries were performed in a public teaching hospital setting, Auckland, New Zealand, in early 2016. Postoperatively, data were reviewed for complications and corrected distance visual acuity (CDVA). Results were compared to a prospective study (N = 500, phase 1) performed prior to formal introduction of risk stratification. Intraoperative complications increased with increasing M-scores (P = .044). Median M-score for complicated cases was higher (P = .022). Odds ratio (OR) for a complication increased 1.269 per unit increase in M-score (95% confidence interval [CI] 1.007-1.599, P = .043). Overall rate of any intraoperative complication was 5.0%. Intraoperative complication rates decreased from 8.4% to 5.0% (OR = 0.576, P = .043) comparing phase 1 and phase 2 (formal introduction of risk stratification). The severity of complications also reduced. A significant decrease in complications for M = 0 (ie, minimal risk cases) was also identified comparing the current study (3.1%) to phase 1 (7.2%), P = .034. There was no change in postoperative complication risks (OR 0.812, P = .434) or in mean postoperative CDVA (20/30, P = .484) comparing current with phase 1 outcomes. A simple preoperative risk stratification system, based on standard patient information gathered at preoperative consultation, appears to reduce intraoperative complications and support safer surgical training by appropriate allocation of higher-risk cases. Copyright © 2017 Elsevier Inc. All rights reserved.

Sensitivity of coronal loop sausage mode frequencies and decay rates to radial and longitudinal density inhomogeneities: a spectral approach

NASA Astrophysics Data System (ADS)

Cally, Paul S.; Xiong, Ming

2018-01-01

Fast sausage modes in solar magnetic coronal loops are only fully contained in unrealistically short dense loops. Otherwise they are leaky, losing energy to their surrounds as outgoing waves. This causes any oscillation to decay exponentially in time. Simultaneous observations of both period and decay rate therefore reveal the eigenfrequency of the observed mode, and potentially insight into the tubes’ nonuniform internal structure. In this article, a global spectral description of the oscillations is presented that results in an implicit matrix eigenvalue equation where the eigenvalues are associated predominantly with the diagonal terms of the matrix. The off-diagonal terms vanish identically if the tube is uniform. A linearized perturbation approach, applied with respect to a uniform reference model, is developed that makes the eigenvalues explicit. The implicit eigenvalue problem is easily solved numerically though, and it is shown that knowledge of the real and imaginary parts of the eigenfrequency is sufficient to determine the width and density contrast of a boundary layer over which the tubes’ enhanced internal densities drop to ambient values. Linearized density kernels are developed that show sensitivity only to the extreme outside of the loops for radial fundamental modes, especially for small density enhancements, with no sensitivity to the core. Higher radial harmonics do show some internal sensitivity, but these will be more difficult to observe. Only kink modes are sensitive to the tube centres. Variation in internal and external Alfvén speed along the loop is shown to have little effect on the fundamental dimensionless eigenfrequency, though the associated eigenfunction becomes more compact at the loop apex as stratification increases, or may even displace from the apex.

A Comparative Review of Stratification Texts and Readers

ERIC Educational Resources Information Center

Peoples, Clayton D.

2012-01-01

Social stratification is a core substantive area within sociology. There are a number of textbooks and readers available on the market that deal with this central topic. In this article, I conduct a comparative review of (a) four stratification textbooks and (b) four stratification readers. (Contains 2 tables.)

The effect of different biologic and biosynthetic wound covers on keratinocyte growth, stratification and differentiation in vitro

PubMed Central

Mestak, Ondrej

2014-01-01

The purpose of this study was to compare, by means of in vitro cultivation technique, five marketed brands of wound covers used in the treatment of burns and other skin defects (Biobrane®, Suprathel®, Veloderm®, Xe-Derma®, and Xenoderm®) for their ability to stimulate the keratinocyte growth, stratification, and differentiation. In three independent experiments, human keratinocytes were grown on the tested covers in organotypic cultures by the 3T3 feeder layer technique. Vertical paraffin sections of the wound covers with keratinocytes were processed using hematoxylin–eosin staining and immunostaining for involucrin. Keratinocyte populations on the dressings were assessed for (1) number of keratinocyte strata (primary variable), (2) quantitative growth, (3) thickness of the keratinocyte layer, and (4) cell differentiation. The Xe-Derma wound cover provided the best support to keratinocyte proliferation and stratification, with the number of keratinocyte strata significantly (p < 0.05) higher in comparison to all products studied, except Xenoderm. However, in contrast to Xe-Derma, Xenoderm did not significantly differ from the other dressings. The results of this in vitro study show that the brands based on porcine dermal matrix possess the strongest effect on keratinocyte proliferation and stratification. The distinctive position of Xe-Derma may be related to its composition, where natural dermal fibers form a smooth surface, similar to the basement membrane. Furthermore, the results indicate that in vitro evaluation of effects on epithelial growth may accelerate the development of new bio-engineering-based wound covers. PMID:25383177

Numerical Study of Wake Vortex Behavior in Turbulent Domains with Ambient Stratification

NASA Technical Reports Server (NTRS)

Switzer, George F.; Proctor, Fred H.

2000-01-01

A three-dimensional large eddy simulation model is used to investigate the sensitivity of ambient stratification with turbulence on the behavior of aircraft wake vortices. Modeled ambient turbulence levels range from very weak to moderate, and stratification levels range from strongly stable to unstable. The results of profound significance from this study are: 1) very little sensitivity between vortex linking time and the level of stratification, 2) the mean vortex separation remained nearly constant regardless of stratification and turbulence (at least prior to linking), 3) the wake vortices did not rise regardless of the level of stratification, and 4) for very strong stratification, the vortex stopped descending and quickly dissipated even before vortex linking could occur. These results are supported by experimental data and are contrary to conclusions from other numerical studies that assume laminar flow and/or relatively-low Reynolds numbers.

A refined model of sedimentary rock cover in the southeastern part of the Congo basin from GOCE gravity and vertical gravity gradient observations

NASA Astrophysics Data System (ADS)

Martinec, Zdeněk; Fullea, Javier

2015-03-01

We aim to interpret the vertical gravity and vertical gravity gradient of the GOCE-GRACE combined gravity model over the southeastern part of the Congo basin to refine the published model of sedimentary rock cover. We use the GOCO03S gravity model and evaluate its spherical harmonic representation at or near the Earth's surface. In this case, the gradiometry signals are enhanced as compared to the original measured GOCE gradients at satellite height and better emphasize the spatial pattern of sedimentary geology. To avoid aliasing, the omission error of the modelled gravity induced by the sedimentary rocks is adjusted to that of the GOCO03S gravity model. The mass-density Green's functions derived for the a priori structure of the sediments show a slightly greater sensitivity to the GOCO03S vertical gravity gradient than to the vertical gravity. Hence, the refinement of the sedimentary model is carried out for the vertical gravity gradient over the basin, such that a few anomalous values of the GOCO03S-derived vertical gravity gradient are adjusted by refining the model. We apply the 5-parameter Helmert's transformation, defined by 2 translations, 1 rotation and 2 scale parameters that are searched for by the steepest descent method. The refined sedimentary model is only slightly changed with respect to the original map, but it significantly improves the fit of the vertical gravity and vertical gravity gradient over the basin. However, there are still spatial features in the gravity and gradiometric data that remain unfitted by the refined model. These may be due to lateral density variation that is not contained in the model, a density contrast at the Moho discontinuity, lithospheric density stratifications or mantle convection. In a second step, the refined sedimentary model is used to find the vertical density stratification of sedimentary rocks. Although the gravity data can be interpreted by a constant sedimentary density, such a model does not correspond to the gravitational compaction of sedimentary rocks. Therefore, the density model is extended by including a linear increase in density with depth. Subsequent L2 and L∞ norm minimization procedures are applied to find the density parameters by adjusting both the vertical gravity and the vertical gravity gradient. We found that including the vertical gravity gradient in the interpretation of the GOCO03S-derived data reduces the non-uniqueness of the inverse gradiometric problem for density determination. The density structure of the sedimentary formations that provide the optimum predictions of the GOCO03S-derived gravity and vertical gradient of gravity consists of a surface density contrast with respect to surrounding rocks of 0.24-0.28 g/cm3 and its decrease with depth of 0.05-0.25 g/cm3 per 10 km. Moreover, the case where the sedimentary rocks are gravitationally completely compacted in the deepest parts of the basin is supported by L∞ norm minimization. However, this minimization also allows a remaining density contrast at the deepest parts of the sedimentary basin of about 0.1 g/cm3.

Changes in Serving Size, Calories, and Sodium Content in Processed Foods From 2009 to 2015.

PubMed

Clapp, Jenifer E; Niederman, Sarah A; Leonard, Elizabeth; Curtis, Christine J

2018-03-15

Approximately 60% of the American diet comes from processed foods, which makes improving their nutritional quality important for Americans' health. The objective of this study was to measure changes in serving sizes, calories, and sodium in top-selling processed foods that were on the market in 2009 and 2015. We analyzed products in the top 80% of sales in the 54 processed food categories with consistent serving sizes and sales metrics that were on the market in both 2009 and 2015. Mean serving size, calories (per serving and density), sodium (per serving and density), and sales were calculated for 2,979 branded processed food products. For each stratification of calorie density and sodium density (decreased, increased, or did not change), we calculated the mean serving size, calorie density, sodium density, and sales for each year. From 2009 to 2015, we found decreases in serving size (-2.3%, P < .001), calories per serving (-2.0%, P < .001), calorie density (-1.1%, P < .001), sodium per serving (-7.6%, P < .001), and sodium density (-6.0%, P < .001). A decrease in calorie density did not correspond to an increase in sodium density or vice versa. A decline in sales was observed regardless of whether calorie density or sodium density decreased, increased, or did not change. Reductions in calorie and sodium density occurred in tandem, suggesting that manufacturers reformulated for more than one health goal at the same time. Instead of unintended negative consequences of encouraging companies to reformulate for one nutrient, an overall net nutritional benefit occurred.

Dynamo Tests for Stratification Below the Core-Mantle Boundary

NASA Astrophysics Data System (ADS)

Olson, P.; Landeau, M.

2017-12-01

Evidence from seismology, mineral physics, and core dynamics points to a layer with an overall stable stratification in the Earth's outer core, possibly thermal in origin, extending below the core-mantle boundary (CMB) for several hundred kilometers. In contrast, energetic deep mantle convection with elevated heat flux implies locally unstable thermal stratification below the CMB in places, consistent with interpretations of non-dipole geomagnetic field behavior that favor upwelling flows below the CMB. Here, we model the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux in order to rationalize this conflicting evidence. Strongly heterogeneous boundary heat flux generates localized convection beneath the CMB that coexists with an overall stable stratification there. Partially stratified dynamos have distinctive time average magnetic field structures. Without stratification or with stratification confined to a thin layer, the octupole component is small and the CMB magnetic field structure includes polar intensity minima. With more extensive stratification, the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions. Comparisons with the time-averaged geomagnetic field are generally favorable for partial stratification in a thin layer but unfavorable for stratification in a thick layer beneath the CMB.

Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia.

PubMed

Tokuda, Shinsaku; Kim, Young Hak; Matsumoto, Hisako; Muro, Shigeo; Hirai, Toyohiro; Mishima, Michiaki; Furuse, Mikio

2015-01-01

The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma.

Effects of Hydrostatic Pressure on Carcinogenic Properties of Epithelia

PubMed Central

Tokuda, Shinsaku; Kim, Young Hak; Matsumoto, Hisako; Muro, Shigeo; Hirai, Toyohiro; Mishima, Michiaki; Furuse, Mikio

2015-01-01

The relationship between chronic inflammation and cancer is well known. The inflammation increases the permeability of blood vessels and consequently elevates pressure in the interstitial tissues. However, there have been only a few reports on the effects of hydrostatic pressure on cultured cells, and the relationship between elevated hydrostatic pressure and cell properties related to malignant tumors is less well understood. Therefore, we investigated the effects of hydrostatic pressure on the cultured epithelial cells seeded on permeable filters. Surprisingly, hydrostatic pressure from basal to apical side induced epithelial stratification in Madin-Darby canine kidney (MDCK) I and Caco-2 cells, and cavities with microvilli and tight junctions around their surfaces were formed within the multi-layered epithelia. The hydrostatic pressure gradient also promoted cell proliferation, suppressed cell apoptosis, and increased transepithelial ion permeability. The inhibition of protein kinase A (PKA) promoted epithelial stratification by the hydrostatic pressure whereas the activation of PKA led to suppressed epithelial stratification. These results indicate the role of the hydrostatic pressure gradient in the regulation of various epithelial cell functions. The findings in this study may provide clues for the development of a novel strategy for the treatment of the carcinoma. PMID:26716691

Using multivariate generalizability theory to assess the effect of content stratification on the reliability of a performance assessment.

PubMed

Keller, Lisa A; Clauser, Brian E; Swanson, David B

2010-12-01

In recent years, demand for performance assessments has continued to grow. However, performance assessments are notorious for lower reliability, and in particular, low reliability resulting from task specificity. Since reliability analyses typically treat the performance tasks as randomly sampled from an infinite universe of tasks, these estimates of reliability may not be accurate. For tests built according to a table of specifications, tasks are randomly sampled from different strata (content domains, skill areas, etc.). If these strata remain fixed in the test construction process, ignoring this stratification in the reliability analysis results in an underestimate of "parallel forms" reliability, and an overestimate of the person-by-task component. This research explores the effect of representing and misrepresenting the stratification appropriately in estimation of reliability and the standard error of measurement. Both multivariate and univariate generalizability studies are reported. Results indicate that the proper specification of the analytic design is essential in yielding the proper information both about the generalizability of the assessment and the standard error of measurement. Further, illustrative D studies present the effect under a variety of situations and test designs. Additional benefits of multivariate generalizability theory in test design and evaluation are also discussed.

[Effects of atmospheric thermally stratified condition on sensible heat within forest canopy].

PubMed

Diao, Yi-Wei; Wang, An-Zhi; Guan, De-Xin; Jin, Chang-Jie; Pei, Tie-Fan

2010-01-01

By using Eulerian second-order closure model, this paper studied the source-sink distribution and flux characteristics of sensible heat within forest canopy under atmospheric thermally stratified condition. In the daytime, a notable feature for the atmospheric stratification of forest canopy was the unstable stratification above the canopy and the stable stratification under the canopy. The changes of temperature profile indicated there was a 'hot spot' at about 2/3 of canopy height. The counter-gradient fluxes within the canopy were discovered by modeling the heat flux under weak stable atmospheric condition. Simulations of the diurnal variation of sensible heat flux were consistent with the measurements (R2 = 0.9035, P < 0.01). Adding buoyancy in the sensible heat balance equation could increase the simulation accuracy of inversion model, and improve the simulation capability for heat flux balance.

Ecosystem variability along the estuarine salinity gradient: Examples from long-term study of San Francisco Bay

USGS Publications Warehouse

Cloern, James E.; Jassby, Alan D.; Schraga, Tara; Kress, Erica S.; Martin, Charles A.

2017-01-01

The salinity gradient of estuaries plays a unique and fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes. We use variability along the salinity gradient of San Francisco Bay to illustrate some lessons about the diversity of spatial structures in estuaries and their variability over time. Spatial patterns of dissolved constituents (e.g., silicate) can be linear or nonlinear, depending on the relative importance of river-ocean mixing and internal sinks (diatom uptake). Particles have different spatial patterns because they accumulate in estuarine turbidity maxima formed by the combination of sinking and estuarine circulation. Some constituents have weak or no mean spatial structure along the salinity gradient, reflecting spatially distributed sources along the estuary (nitrate) or atmospheric exchanges that buffer spatial variability of ecosystem metabolism (dissolved oxygen). The density difference between freshwater and seawater establishes stratification in estuaries stronger than the thermal stratification of lakes and oceans. Stratification is strongest around the center of the salinity gradient and when river discharge is high. Spatial distributions of motile organisms are shaped by species-specific adaptations to different salinity ranges (shrimp) and by behavioral responses to environmental variability (northern anchovy). Estuarine spatial patterns change over time scales of events (intrusions of upwelled ocean water), seasons (river inflow), years (annual weather anomalies), and between eras separated by ecosystem disturbances (a species introduction). Each of these lessons is a piece in the puzzle of how estuarine ecosystems are structured and how they differ from the river and ocean ecosystems they bridge.

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

PubMed Central

Andrei, Adrian-Ştefan; Robeson, Michael S; Baricz, Andreea; Coman, Cristian; Muntean, Vasile; Ionescu, Artur; Etiope, Giuseppe; Alexe, Mircea; Sicora, Cosmin Ionel; Podar, Mircea; Banciu, Horia Leonard

2015-01-01

Hypersaline meromictic lakes are extreme environments in which water stratification is associated with powerful physicochemical gradients and high salt concentrations. Furthermore, their physical stability coupled with vertical water column partitioning makes them important research model systems in microbial niche differentiation and biogeochemical cycling. Here, we compare the prokaryotic assemblages from Ursu and Fara Fund hypersaline meromictic lakes (Transylvanian Basin, Romania) in relation to their limnological factors and infer their role in elemental cycling by matching taxa to known taxon-specific biogeochemical functions. To assess the composition and structure of prokaryotic communities and the environmental factors that structure them, deep-coverage small subunit (SSU) ribosomal RNA (rDNA) amplicon sequencing, community domain-specific quantitative PCR and physicochemical analyses were performed on samples collected along depth profiles. The analyses showed that the lakes harbored multiple and diverse prokaryotic communities whose distribution mirrored the water stratification patterns. Ursu Lake was found to be dominated by Bacteria and to have a greater prokaryotic diversity than Fara Fund Lake that harbored an increased cell density and was populated mostly by Archaea within oxic strata. In spite of their contrasting diversity, the microbial populations indigenous to each lake pointed to similar physiological functions within carbon degradation and sulfate reduction. Furthermore, the taxonomy results coupled with methane detection and its stable C isotope composition indicated the presence of a yet-undescribed methanogenic group in the lakes' hypersaline monimolimnion. In addition, ultrasmall uncultivated archaeal lineages were detected in the chemocline of Fara Fund Lake, where the recently proposed Nanohaloarchaeota phylum was found to thrive. PMID:25932617

Influences of Ocean Thermohaline Stratification on Arctic Sea Ice

NASA Astrophysics Data System (ADS)

Toole, J. M.; Timmermans, M.-L.; Perovich, D. K.; Krishfield, R. A.; Proshutinsky, A.; Richter-Menge, J. A.

2009-04-01

The Arctic Ocean's surface mixed layer constitutes the dynamical and thermodynamical link between the sea ice and the underlying waters. Wind stress, acting directly on the surface mixed layer or via wind-forced ice motion, produce surface currents that can in turn drive deep ocean flow. Mixed layer temperature is intimately related to basal sea ice growth and melting. Heat fluxes into or out of the surface mixed layer can occur at both its upper and lower interfaces: the former via air-sea exchange at leads and conduction through the ice, the latter via turbulent mixing and entrainment at the layer base. Variations in Arctic Ocean mixed layer properties are documented based on more than 16,000 temperature and salinity profiles acquired by Ice-Tethered Profilers since summer 2004 and analyzed in conjunction with sea ice observations from Ice Mass Balance Buoys and atmospheric heat flux estimates. Guidance interpreting the observations is provided by a one-dimensional ocean mixed layer model. The study focuses attention on the very strong density stratification about the mixed layer base in the Arctic that, in regions of sea ice melting, is increasing with time. The intense stratification greatly impedes mixed layer deepening by vertical convection and shear mixing, and thus limits the flux of deep ocean heat to the surface that could influence sea ice growth/decay. Consistent with previous work, this study demonstrates that the Arctic sea ice is most sensitive to changes in ocean mixed layer heat resulting from fluxes across its upper (air-sea and/or ice-water) interface.

Interaction between the tidal and seasonal variability of the Gulf of Maine and Scotian Shelf region

NASA Astrophysics Data System (ADS)

Katavouta, Anna; Thompson, Keith; Lu, Youyu; Loder, John

2017-04-01

In the Gulf of Maine and Scotian Shelf (off the northeastern coast of North America) tides are large and can alter the local hydrographic properties, circulation, and sea surface height through processes such as tidal rectification, mixing, and horizontal advection. Furthermore, the stratification of the water column can influence tidal elevation and currents over the shelves (e.g., baroclinic tides). To investigate this interaction, a newly developed high resolution (1/36 degree) regional circulation model is used (GoMSS model). First, numerical experiments with and without density stratification are used to demonstrate the influence of stratification on the tides. GoMSS model is then used to interpret the physical mechanisms responsible for the largest seasonal variations in the M2 surface current which occur over, and to the north of, Georges Bank. An alternating pattern of highs and lows in the summer maximum M2 surface speed in the Gulf of Maine is identified, for the first time, in both the model output and observations by a high frequency coastal radar system. This pattern consists of extended striations in tidal speed aligned with the northern flank of Georges Bank that separates the Gulf of Maine from the North Atlantic. The striations are explained in terms of a linear superposition of the barotropic tide flowing across the northern flank of Georges Bank and the reflected, phase-locked baroclinic tide. The striations have amplitudes of about 0.1 m/s and longitudinal length scales of order 100 km, and are thus of practical significance.

Short-term variations in mesozooplankton, ichthyoplankton, and nutrients associated with semi-diurnal tides in a patagonian Gulf

NASA Astrophysics Data System (ADS)

Castro, L. R.; Cáceres, M. A.; Silva, N.; Muñoz, M. I.; León, R.; Landaeta, M. F.; Soto-Mendoza, S.

2011-03-01

The relationships between the distribution of different zooplankton and ichthyoplankton stages and physical and chemical variables were studied using samples and data (CTD profiles, ADCP and current meter measurements, nutrients, mesozooplankton, ichthyoplankton) obtained from different strata during two 24-h cycles at two oceanographic stations in a Chilean Patagonian gulf during the CIMAR 10-Fiordos cruise (November, 2004). A station located at the Chacao Channel was dominated by tidal mixing and small increments in surface stratification during high tides, leading to decreased nutrient availability. This agreed with short periods of increased phytoplankton abundance during slack waters at the end of flood currents. Increases in larval density for all zooplankton and ichthyoplankton taxa corresponded to the flooding phases of the tidal cycle. When the larval density data were fit to a sinusoidal model, the regression coefficients were high, suggesting that tides are important features that modulate short-term variations in plankton abundance. All larvae did not vary synchronously with the tidal phase; rather, time lags were observed among species. The abundances of older individuals of the copepodite Rhincalanus nasutus and all zoea stages of the squat lobster Munida gregaria increased during night flood tides, whereas younger stages increased during daytime flood tides. At a station located at the Queullin Pass, which was dominated by vertical stratification patterns, the variations in peak larval density were better fitted to the semi-diurnal sea level fluctuations. Other evidence indicated internal tides below the pycnocline, which could promote larval transport in deeper layers. In the overall picture that emerges from this study, planktonic organisms from different habitats and phylogenetic origins seem to respond to the local tidal regimes. In some cases, this response might be beneficial, transporting these individuals inshore to areas that are rich in food during the peak biological production season.

Density-stratified flow events in Great Salt Lake, Utah, USA: implications for mercury and salinity cycling

USGS Publications Warehouse

Naftz, David L.; Carling, Gregory T.; Angeroth, Cory; Freeman, Michael; Rowland, Ryan; Pazmiño, Eddy

2014-01-01

Density stratification in saline and hypersaline water bodies from throughout the world can have large impacts on the internal cycling and loading of salinity, nutrients, and trace elements. High temporal resolution hydroacoustic and physical/chemical data were collected at two sites in Great Salt Lake (GSL), a saline lake in the western USA, to understand how density stratification may influence salinity and mercury (Hg) distributions. The first study site was in a causeway breach where saline water from GSL exchanges with less saline water from a flow restricted bay. Near-surface-specific conductance values measured in water at the breach displayed a good relationship with both flow and wind direction. No diurnal variations in the concentration of dissolved (total and MeHg loadings was observed during periods of elevated salinity. The second study site was located on the bottom of GSL where movement of a high-salinity water layer, referred to as the deep brine layer (DBL), is restricted to a naturally occurring 1.5-km-wide “spillway” structure. During selected time periods in April/May, 2012, wind-induced flow reversals in a railroad causeway breach, separating Gunnison and Gilbert Bays, were coupled with high-velocity flow pulses (up to 55 cm/s) in the DBL at the spillway site. These flow pulses were likely driven by a pressure response of highly saline water from Gunnison Bay flowing into the north basin of Gilbert Bay. Short-term flow reversal events measured at the railroad causeway breach have the ability to move measurable amounts of salt and Hg from Gunnison Bay into the DBL. Future disturbance to the steady state conditions currently imposed by the railroad causeway infrastructure could result in changes to the existing chemical balance between Gunnison and Gilbert Bays. Monitoring instruments were installed at six additional sites in the DBL during October 2012 to assess impacts from any future modifications to the railroad causeway.

Effect of the physiognomy of Attalea butyracea (Arecoideae) on population density and age distribution of Rhodnius prolixus (Triatominae).

PubMed

Urbano, Plutarco; Poveda, Cristina; Molina, Jorge

2015-04-01

Rhodnius prolixus Stål, 1859 is one of the main vectors of Trypanosoma (Schyzotrypanum) cruzi Chagas, 1909. In its natural forest environment, this triatomine is mainly found in palm tree crowns, where it easily establishes and develops dense populations. The aim of this study was to evaluate the effect of the physiognomy and reproductive status of Attalea butyracea on the population relative density and age structure of R. prolixus and to determine the vector's population stratification according to the vertical and horizontal profile of an A. butyracea forest. Using live bait traps, 150 individuals of A. butyracea with different physiognomy and 40 individuals with similar physiognomy (crown size, number of leaves, palm tree height, diameter at breast height, reproductive status) were sampled for triatomines in Yopal, Casanare-Colombia. Temperature and relative humidity were measured in the crown of the palm tree. Entomological indices and natural infection rates were also determined. The relative population density of R. prolixus on natural A. butyracea groves is associated with the palm's height, number of leaves and crown volume. The young immature stages were present mostly at the crown's base and the advanced immature stages and adults were present mostly at the crown of the palm tree. This distribution correlates with the temperature stability and relative humidity in the base and the fluctuation of both environmental variables in the palm's crown. A higher density of R. prolixus was found as the palm tree height increased and as the distance of the palm with respect to the forest border decreased, especially towards anthropically intervened areas. A density index of 12.6 individuals per palm tree with an infestation index of 88.9% and a colonization index of 98.7% was observed. 85.2% was the infection index with T. cruzi. The physiognomy of palm trees affects the relative population density and the distribution of developmental stages of R. prolixus. Therefore, they constitute a risk factor for the potential migration of infected insects from wild environments towards residential environments and the subsequent epidemiological risk of transmission of T. cruzi to people.

Recruitment of Hexagenia mayfly nymphs in western Lake Erie linked to environmental variability

USGS Publications Warehouse

Bridgeman, Thomas B.; Schloesser, Don W.; Krause, Ann E.

2006-01-01

After a 40-year absence caused by pollution and eutrophication, burrowing mayflies (Hexagenia spp.) recolonized western Lake Erie in the mid 1990s as water quality improved. Mayflies are an important food resource for the economically valuable yellow perch fishery and are considered to be major indicator species of the ecological condition of the lake. Since their reappearance, however, mayfly populations have suffered occasional unexplained recruitment failures. In 2002, a failure of fall recruitment followed an unusually warm summer in which western Lake Erie became temporarily stratified, resulting in low dissolved oxygen levels near the lake floor. In the present study, we examined a possible link between Hexagenia recruitment and periods of intermittent stratification for the years 1997-2002. A simple model was developed using surface temperature, wind speed, and water column data from 2003 to predict stratification. The model was then used to detect episodes of stratification in past years for which water column data are unavailable. Low or undetectable mayfly recruitment occurred in 1997 and 2002, years in which there was frequent or extended stratification between June and September. Highest mayfly reproduction in 2000 corresponded to the fewest stratified periods. These results suggest that even relatively brief periods of stratification can result in loss of larval mayfly recruitment, probably through the effects of hypoxia. A trend toward increasing frequency of hot summers in the Great Lakes region could result in recurrent loss of mayfly larvae in western Lake Erie and other shallow areas in the Great Lakes.

Post-stratification sampling in small area estimation (SAE) model for unemployment rate estimation by Bayes approach

NASA Astrophysics Data System (ADS)

Hanike, Yusrianti; Sadik, Kusman; Kurnia, Anang

2016-02-01

This research implemented unemployment rate in Indonesia that based on Poisson distribution. It would be estimated by modified the post-stratification and Small Area Estimation (SAE) model. Post-stratification was one of technique sampling that stratified after collected survey data. It's used when the survey data didn't serve for estimating the interest area. Interest area here was the education of unemployment which separated in seven category. The data was obtained by Labour Employment National survey (Sakernas) that's collected by company survey in Indonesia, BPS, Statistic Indonesia. This company served the national survey that gave too small sample for level district. Model of SAE was one of alternative to solved it. According the problem above, we combined this post-stratification sampling and SAE model. This research gave two main model of post-stratification sampling. Model I defined the category of education was the dummy variable and model II defined the category of education was the area random effect. Two model has problem wasn't complied by Poisson assumption. Using Poisson-Gamma model, model I has over dispersion problem was 1.23 solved to 0.91 chi square/df and model II has under dispersion problem was 0.35 solved to 0.94 chi square/df. Empirical Bayes was applied to estimate the proportion of every category education of unemployment. Using Bayesian Information Criteria (BIC), Model I has smaller mean square error (MSE) than model II.

Cholesteryl Ester Transfer Protein Intimately Involved in Dyslipidemia-Related Susceptibility to Cognitive Deficits in Type 2 Diabetic Patients.

PubMed

Sun, Jie; Cai, Rongrong; Huang, Rong; Wang, Pin; Tian, Sai; Sun, Haixia; Xia, Wenqing; Wang, Shaohua

2016-08-01

Cholesteryl ester transfer protein (CETP) is involved in diabetic dyslipidemia. We aim to test the hypothesis that CETP might be of importance in mediating dyslipidemia-related susceptibility to cognitive deficits in diabetic patients. We recruited 190 type 2 diabetic patients and divided them into two groups according to the Montreal Cognitive Assessment (MoCA) score. The association between CETP and cognitive decline was analyzed with logistic regression and stratification. There were 110 diabetic patients with mild cognition impairment (MCI) and 80 healthy cognition subjects as controls. Dyslipidemia is more common among diabetic patients with MCI; they had a significant increase of serum CETP concentrations, which was negatively correlated with MoCA (r = -0.638; p < 0.001). Negative correlations were also found between the serum CETP concentration with the Auditory Verbal Learning Test (r = -0.266; p = 0.008), indicating memory deficit. Logistic regression analysis revealed that CETP concentration was an independent factor of diabetic MCI (p < 0.001). Further stratification study showed that high serum levels of CETP was an independent risk factor of MCI in diabetic patients with a low density lipoproteins level ≥2.59 mmol/L, or high density lipoproteins level ≤1.0 mmol/L for men and ≤1.3 mmol/L for women, or TG level ≥1.7 mmol/L, after adjusting for age, sex, education, and glucose control (all ps < 0.05). CETP was intimately involved in dyslipidemia-related susceptibility to cognitive decline, especially memory function in type 2 diabetic patients.

Experimental and Numerical Study of Wind and Turbulence in a Near-Field Dispersion Campaign at an Inhomogeneous Site

NASA Astrophysics Data System (ADS)

Wei, Xiao; Dupont, Eric; Gilbert, Eric; Musson-Genon, Luc; Carissimo, Bertrand

2016-09-01

We present a detailed experimental and numerical study of the local flow field for a pollutant dispersion experimental program conducted at SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique), a complex and intensively instrumented site in a southern suburb of Paris. Global analysis of continuous measurements over 2 years highlights the impact of terrain heterogeneity on wind and turbulence. It shows that the forest to the north of the experimental field induces strong directional shear and wind deceleration below the forest canopy height. This directional shear is stronger with decreasing height and decreasing distance from the forest edge. Numerical simulations are carried out using Code_Saturne, a computational fluid dynamics code, in Reynolds-averaged Navier-Stokes mode with a standard k{-}ɛ closure and a canopy model, in neutral and stable stratifications. These simulations are shown to reproduce globally well the characteristics of the mean flow, especially the directional wind shear in northeasterly and northwesterly cases and the turbulent kinetic energy increase induced by the forest. However, they slightly underestimate wind speed and the directional shear of the flow below the forest canopy height. Sensitivity studies are performed to investigate the influence of leaf area density, inlet stability condition, and roughness length. These studies show that the typical features of the canopy flow become more pronounced as canopy density increases. Performance statistics indicate that the impact of the forest and adequate inlet profiles are the most important factors in the accurate reproduction of flow at the site, especially under stable stratification.

An explicit asymptotic preserving low Froude scheme for the multilayer shallow water model with density stratification

NASA Astrophysics Data System (ADS)

Couderc, F.; Duran, A.; Vila, J.-P.

2017-08-01

We present an explicit scheme for a two-dimensional multilayer shallow water model with density stratification, for general meshes and collocated variables. The proposed strategy is based on a regularized model where the transport velocity in the advective fluxes is shifted proportionally to the pressure potential gradient. Using a similar strategy for the potential forces, we show the stability of the method in the sense of a discrete dissipation of the mechanical energy, in general multilayer and non-linear frames. These results are obtained at first-order in space and time and extended using a second-order MUSCL extension in space and a Heun's method in time. With the objective of minimizing the diffusive losses in realistic contexts, sufficient conditions are exhibited on the regularizing terms to ensure the scheme's linear stability at first and second-order in time and space. The other main result stands in the consistency with respect to the asymptotics reached at small and large time scales in low Froude regimes, which governs large-scale oceanic circulation. Additionally, robustness and well-balanced results for motionless steady states are also ensured. These stability properties tend to provide a very robust and efficient approach, easy to implement and particularly well suited for large-scale simulations. Some numerical experiments are proposed to highlight the scheme efficiency: an experiment of fast gravitational modes, a smooth surface wave propagation, an initial propagating surface water elevation jump considering a non-trivial topography, and a last experiment of slow Rossby modes simulating the displacement of a baroclinic vortex subject to the Coriolis force.

Low Tumor Infiltrating Mast Cell Density Confers Prognostic Benefit and Reflects Immunoactivation in Colorectal Cancer.

PubMed

Mao, Yihao; Feng, Qingyang; Zheng, Peng; Yang, Liangliang; Zhu, Dexiang; Chang, Wenju; Ji, Meiling; He, Guodong; Xu, Jianmin

2018-06-06

The role of mast cells (MCs) in colorectal cancer (CRC) progression was controversial. Thus, this study was designed to evaluate the prognostic value of MCs as well as their correlation with immune microenvironment. A retrospective cohort of CRC patients of stage I-IV was enrolled in this study. 854 consecutive patients were divided into training set (427 patients) and validation set (427 patients) randomly. The findings were further validated in a GEO cohort, GSE39582 (556 patients). The mast cell density (MCD) was measured by immunohistochemical staining of tryptase or by CIBERSORT algorithm. Low MCD predicted prolonged overall survival (OS) in training and validation set. Moreover, MCD was identified as an independent prognostic indicator in both sets. Better stratification for CRC prognosis can be achieved by building a MCD based nomogram. The prognostic role of MCD was further validated in GSE39582. In addition, MCD predicted improved survival in stage II and III CRC patients receiving adjuvant chemotherapy (ACT). Multiple immune pathways were enriched in low MCD group while cytokines/chemokines promoting anti-tumor immunity were highly expressed in such group. Furthermore, MCD was negatively correlated with CD8+ T cells infiltration. In conclusion, MCD was identified as an independent prognostic factor, as well as a potential biomarker for ACT benefit in stage II and III CRC. Better stratification of CRC prognosis could be achieved by building a MCD based nomogram. Moreover, immunoactivation in low MCD tumors may contributed to improved prognosis. This article is protected by copyright. All rights reserved. © 2018 UICC.

Meteorological drivers of hypolimnetic anoxia in a eutrophic, north temperate lake

USGS Publications Warehouse

Snortheim, Craig A.; Hanson, Paul C.; McMahon, Katherine D.; Read, Jordan S.; Carey, Cayelan C.; Dugan, Hilary

2017-01-01

Oxygen concentration is both an indicator and driver of water quality in lakes. Decreases in oxygen concentration leads to altered ecosystem function as well as harmful consequences for aquatic biota, such as fishes. The responses of oxygen dynamics in lakes to climate-related drivers, such as temperature and wind speed, are well documented for lake surface waters. However, much less is known about how the oxic environment of bottom waters, especially the timing and magnitude of anoxia in eutrophic lakes, responds to changes in climate drivers. Understanding how important ecosystem states, such as hypolimnetic anoxia, may respond to differing climate scenarios requires a model that couples physical-biological conditions and sufficiently captures the density stratification that leads to strong oxygen gradients. Here, we analyzed the effects of changes in three important meteorological drivers (air temperature, wind speed, and relative humidity) on hypolimnetic anoxia in a eutrophic, north temperate lake using the anoxic factor as an index that captures both the temporal and spatial extent of anoxia. Air temperature and relative humidity were found to have a positive correlation with anoxic factor, while wind speed had a negative correlation. Air temperature was found to have the greatest potential impact of the three drivers on the anoxic factor, followed by wind speed and then relative humidity. Across the scenarios of climate variability, variation in the simulated anoxic factor was primarily due to changes in the timing of onset and decay of stratification. Given the potential for future changes in climate, especially increases in air temperature, this study provides important insight into how these changes will alter lake water quality.

On electron bunching and stratification of glow discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Golubovskii, Yuri B.; Kolobov, Vladimir I.; Nekuchaev, Vladimir O.

2013-10-15

Plasma stratification and excitation of ionization waves is one of the fundamental problems in gas discharge physics. Significant progress in this field is associated with the name of Lev Tsendin. He advocated the need for the kinetic approach to this problem contrary to the traditional hydrodynamic approach, introduced the idea of electron bunching in spatially periodic electric fields, and developed a theory of kinetic resonances for analysis of moving striations in rare gases. The present paper shows how Tsendin's ideas have been further developed and applied for understanding the nature of the well-known S-, P-, and R-striations observed in glowmore » discharges of inert gases at low pressures and currents. We review numerical solutions of a Fokker-Planck kinetic equation in spatially periodic electric fields under the effects of elastic and inelastic collisions of electrons with atoms. We illustrate the formation of kinetic resonances at specific field periods for different shapes of injected Electron Distribution Functions (EDF). Computer simulations illustrate how self-organization of the EDFs occurs under nonlocal conditions and how Gaussian-like peaks moving along resonance trajectories are formed in a certain range of discharge conditions. The calculated EDFs agree well with the experimentally measured EDFs for the S, P, and R striations in noble gases. We discuss how kinetic resonances affect dispersion characteristics of moving striations and mention some non-linear effects associated with glow discharge stratification. We propose further studies of stratification phenomena combining physical kinetics and non-linear physics.« less

Lectin-like oxidized low-density lipoprotein receptor (LOX-1) in sickle cell disease vasculopathy

PubMed Central

Chen, Mingyi; Qiu, Hong; Lin, Xin; Nam, David; Ogbu-Nwobodo, Lucy; Archibald, Hannah; Joslin, Amelia; Wun, Ted; Sawamura, Tatsuya; Green, Ralph

2017-01-01

Lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1) is an endothelial receptor for oxidized LDL. Increased expression of LOX-1 has been demonstrated in atherosclerotic lesions and diabetic vasculopathy. In this study, we investigate the expression of LOX-1 receptor in sickle cell disease (SCD) vasculopathy. Expression of LOX-1 in brain vascular endothelium is markedly increased and LOX-1 gene expression is upregulated in cultured human brain microvascular endothelial cells by incubation with SCD erythrocytes. Also, the level of circulating soluble LOX-1 concentration is elevated in the plasma of SCD patients. Increased LOX-1 expression in endothelial cells is potentially involved in the pathogenesis of SCD vasculopathy. Soluble LOX-1 concentration in SCD may provide a novel biomarker for risk stratification of sickle cell vascular complications. PMID:27519944

Sharp magnetic structures from dynamos with density stratification

NASA Astrophysics Data System (ADS)

Jabbari, Sarah; Brandenburg, Axel; Kleeorin, Nathan; Rogachevskii, Igor

2017-05-01

Recent direct numerical simulations (DNS) of large-scale turbulent dynamos in strongly stratified layers have resulted in surprisingly sharp bipolar structures at the surface. Here, we present new DNS of helically and non-helically forced turbulence with and without rotation and compare with corresponding mean-field simulations (MFS) to show that these structures are a generic outcome of a broader class of dynamos in density-stratified layers. The MFS agree qualitatively with the DNS, but the period of oscillations tends to be longer in the DNS. In both DNS and MFS, the sharp structures are produced by converging flows at the surface and might be driven in non-linear stage of evolution by the Lorentz force associated with the large-scale dynamo-driven magnetic field if the dynamo number is at least 2.5 times supercritical.

CoAIMs: A Cost-Effective Panel of Ancestry Informative Markers for Determining Continental Origins

PubMed Central

Londin, Eric R.; Keller, Margaret A.; Maista, Cathleen; Smith, Gretchen; Mamounas, Laura A.; Zhang, Ran; Madore, Steven J.; Gwinn, Katrina; Corriveau, Roderick A.

2010-01-01

Background Genetic ancestry is known to impact outcomes of genotype-phenotype studies that are designed to identify risk for common diseases in human populations. Failure to control for population stratification due to genetic ancestry can significantly confound results of disease association studies. Moreover, ancestry is a critical factor in assessing lifetime risk of disease, and can play an important role in optimizing treatment. As modern medicine moves towards using personal genetic information for clinical applications, it is important to determine genetic ancestry in an accurate, cost-effective and efficient manner. Self-identified race is a common method used to track and control for population stratification; however, social constructs of race are not necessarily informative for genetic applications. The use of ancestry informative markers (AIMs) is a more accurate method for determining genetic ancestry for the purposes of population stratification. Methodology/Principal Findings Here we introduce a novel panel of 36 microsatellite (MSAT) AIMs that determines continental admixture proportions. This panel, which we have named Continental Ancestry Informative Markers or CoAIMs, consists of MSAT AIMs that were chosen based upon their measure of genetic variance (Fst), allele frequencies and their suitability for efficient genotyping. Genotype analysis using CoAIMs along with a Bayesian clustering method (STRUCTURE) is able to discern continental origins including Europe/Middle East (Caucasians), East Asia, Africa, Native America, and Oceania. In addition to determining continental ancestry for individuals without significant admixture, we applied CoAIMs to ascertain admixture proportions of individuals of self declared race. Conclusion/Significance CoAIMs can be used to efficiently and effectively determine continental admixture proportions in a sample set. The CoAIMs panel is a valuable resource for genetic researchers performing case-control genetic association studies, as it can control for the confounding effects of population stratification. The MSAT-based approach used here has potential for broad applicability as a cost effective tool toward determining admixture proportions. PMID:20976178

Prognostic factors and risk stratification in patients with castration-resistant prostate cancer receiving docetaxel-based chemotherapy.

PubMed

Yamashita, Shimpei; Kohjimoto, Yasuo; Iguchi, Takashi; Koike, Hiroyuki; Kusumoto, Hiroki; Iba, Akinori; Kikkawa, Kazuro; Kodama, Yoshiki; Matsumura, Nagahide; Hara, Isao

2016-03-22

While novel drugs have been developed, docetaxel remains one of the standard initial systemic therapies for castration-resistant prostate cancer (CRPC) patients. Despite the excellent anti-tumor effect of docetaxel, its severe adverse effects sometimes distress patients. Therefore, it would be very helpful to predict the efficacy of docetaxel before treatment. The aims of this study were to evaluate the potential value of patient characteristics in predicting overall survival (OS) and to develop a risk classification for CRPC patients treated with docetaxel-based chemotherapy. This study included 79 patients with CRPC treated with docetaxel. The variables, including patient characteristics at diagnosis and at the start of chemotherapy, were retrospectively collected. Prognostic factors predicting OS were analyzed using the Cox proportional hazard model. Risk stratification for overall survival was determined based on the results of multivariate analysis. PSA response ≥50 % was observed in 55 (69.6 %) of all patients, and the median OS was 22.5 months. The multivariate analysis showed that age, serum PSA level at the start of chemotherapy, and Hb were independent prognostic factors for OS. In addition, ECOG performance status (PS) and the CRP-to-albumin ratio were not significant but were considered possible predictors for OS. Risk stratification according to the number of these risk factors could effectively stratify CRPC patients treated with docetaxel in terms of OS. Age, serum PSA level at the start of chemotherapy, and Hb were identified as independent prognostic factors of OS. ECOG PS and the CRP-to-albumin ratio were not significant, but were considered possible predictors for OS in Japanese CRPC patients treated with docetaxel. Risk stratification based on these factors could be helpful for estimating overall survival.

Turbulent entrainment in a strongly stratified barrier layer

NASA Astrophysics Data System (ADS)

Pham, H. T.; Sarkar, S.

2017-06-01

Large-eddy simulation (LES) is used to investigate how turbulence in the wind-driven ocean mixed layer erodes the stratification of barrier layers. The model consists of a stratified Ekman layer that is driven by a surface wind. Simulations at a wide range of N0/f are performed to quantify the effect of turbulence and stratification on the entrainment rate. Here, N0 is the buoyancy frequency in the barrier layer and f is the Coriolis parameter. The evolution of the mixed layer follows two stages: a rapid initial deepening and a late-time growth at a considerably slower rate. During the first stage, the mixed layer thickens to the depth that is proportional to u∗/fN0 where u∗ is the frictional velocity. During the second stage, the turbulence in the mixed layer continues to deepen further into the barrier layer, and the turbulent length scale is shown to scale with u∗/N0, independent of f. The late-time entrainment rate E follows the law of E=0.035Ri∗-1/2 where Ri∗ is the Richardson number. The exponent of -1/2 is identical but the coefficient of 0.035 is much smaller relative to the value of 2-3/2 for the nonrotating boundary layer. Simulations using the KPP model (version applicable to this simple case without additional effects of Langmuir turbulence or surface buoyancy flux) also yield the entrainment scaling of E∝Ri∗-1/2; however, the proportionality coefficient varies with the stratification. The structure of the Ekman current is examined to illustrate the strong effect of stratification in the limit of large N0/f.

Analysis of the embryo proteome of sycamore (Acer pseudoplatanus L.) seeds reveals a distinct class of proteins regulating dormancy release.

PubMed

Pawłowski, Tomasz Andrzej; Staszak, Aleksandra Maria

2016-05-20

Acer pseudoplatanus seeds are characterized by a deep physiological embryo dormancy that requires a few weeks of cold stratification in order to promote germination. Understanding the function of proteins and their related metabolic pathways, in conjunction with the plant hormones implicated in the breaking of seed dormancy, would expand our knowledge pertaining to this process. In this study, a proteomic approach was used to analyze the changes occurring in seeds in response to cold stratification, which leads to dormancy release. In addition, the involvement of abscisic (ABA) and gibberellic acids (GA) was also examined. Fifty-three proteins showing significant changes were identified by mass spectrometry. An effect of ABA on protein variation was observed at the beginning of stratification, while the influence of GA on protein abundance was observed during the middle phase of stratification. The majority of proteins associated with dormancy breaking in the presence of only water, and also ABA or GA, were classified as being involved in metabolism and genetic information processing. For metabolic-related proteins, the effect of ABA on protein abundance was stimulatory for half of the proteins and inhibitory for half of the proteins. On the other hand, the effect on genetic information processing related proteins was stimulatory. GA was found to upregulate both metabolic-related and genetic information processing-related proteins. While seed dormancy breaking depends on proteins involved in a variety of processes, proteins associated with methionine metabolism (adenosine kinase, methionine synthase) and glycine-rich RNA binding proteins appear to be of particular importance. Copyright © 2016 Elsevier GmbH. All rights reserved.

Effects of reduced winter duration on seed dormancy and germination in six populations of the alpine herb Aciphyllya glacialis (Apiaceae)

PubMed Central

Hoyle, G. L.; Cordiner, H.; Good, R. B.; Nicotra, A. B.

2014-01-01

The life stages of seed germination and seedling establishment play a vital role in maintaining plant populations and determining range dynamics of species. Thus, it is not surprising that specific germination requirements and dormancy mechanisms have evolved in all major angiosperm clades. In a rapidly changing climate, we face growing pressure to manage, conserve and restore native plant species and communities. To achieve these aims, we require solid knowledge of whether and how seed germination requirements and dormancy status vary between different populations of a given species and how germination strategies may be affected by warming climatic conditions. We assessed the effect of decreasing durations of cold stratification (i.e. conditions representing a shortened winter as predicted under climate change) on germination and dormancy of the alpine herb Aciphylla glacialis. Our results confirmed previous research showing that A. glacialis seeds possess physiological dormancy that can be alleviated by cold stratification. In addition, the results demonstrated that A. glacialis seeds have underdeveloped embryos at dispersal; these grow to germinable size following 4–9 weeks at both constant 5°C and 10–5°C (day–night) temperatures. We conclude that A. glacialis exhibits morphophysiological dormancy. Furthermore, we found that the final percentage germination and dormancy status varied significantly among natural populations and that this variation did not correlate with elevation at the site of seed origin. Seeds germinated following 6–8 weeks of cold stratification, and seedlings showed no detrimental effects as a result of shorter stratification periods. Together, these results suggest that reduced duration of winter is unlikely to have direct negative impacts on germination or early seedling growth in A. glacialis. The causes and implications of the population variation in germination traits are discussed. PMID:27293636

Numerical simulation of idealized front motion in neutral and stratified atmosphere with a hyperbolic system of equations

NASA Astrophysics Data System (ADS)

Yudin, M. S.

2017-11-01

In the present paper, stratification effects on surface pressure in the propagation of an atmospheric gravity current (cold front) over flat terrain are estimated with a non-hydrostatic finite-difference model of atmospheric dynamics. Artificial compressibility is introduced into the model in order to make its equations hyperbolic. For comparison with available simulation data, the physical processes under study are assumed to be adiabatic. The influence of orography is also eliminated. The front surface is explicitly described by a special equation. A time filter is used to suppress the non-physical oscillations. The results of simulations of surface pressure under neutral and stable stratification are presented. Under stable stratification the front moves faster and shows an abrupt pressure jump at the point of observation. This fact is in accordance with observations and the present-day theory of atmospheric fronts.

Stratification calculations in a heated cryogenic oxygen storage tank at zero gravity

NASA Technical Reports Server (NTRS)

Shuttles, J. T.; Smith, G. L.

1971-01-01

A cylindrical one-dimensional model of the Apollo cyrogenic oxygen storage tank has been developed to study the effect of stratification in the tank. Zero gravity was assumed, and only the thermally induced motions were considered. The governing equations were derived from conservation laws and solved on a digital computer. Realistic thermodynamic and transport properties were used. Calculations were made for a wide range of conditions. The results show the fluid behavior to be dependent on the quantity in the tank or equivalently the bulk fluid temperature. For high quantities (low temperatures) the tank pressure rose rapidly with heat addition, the heater temperature remained low, and significant pressure drop potentials accrued. For low quantities the tank pressure rose more slowly with heat addition and the heater temperature became high. A high degree of stratification resulted for all conditions; however, the stratified region extended appreciably into the tank only for the lowest tank quantity.

1-D DSMC simulation of Io's atmospheric collapse and reformation during and after eclipse

NASA Astrophysics Data System (ADS)

Moore, C. H.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Stewart, B.

2009-06-01

A one-dimensional Direct Simulation Monte Carlo (DSMC) model is used to examine the effects of a non-condensable species on Io's sulfur dioxide sublimation atmosphere during eclipse and just after egress. Since the vapor pressure of SO 2 is extremely sensitive to temperature, the frost-supported dayside sublimation atmosphere had generally been expected to collapse during eclipse as the surface temperature dropped. For a pure SO 2 atmosphere, however, it was found that during the first 10 min of eclipse, essentially no change in the atmospheric properties occurs at altitudes above ˜100 km due to the finite ballistic/acoustic time. Hence immediately after ingress the auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. Furthermore, the collapse dynamics are found to be greatly altered by the presence of even a small amount of a non-condensable species which forms a diffusion layer near the surface that prevents rapid collapse. It is found that after 10 min essentially no collapse has occurred at altitudes above ˜20 km when a nominal mole fraction of non-condensable gas is present. Collapse near the surface occurs relatively quickly until a static diffusion layer many mean free paths thick of the non-condensable gas builds up which then retards further collapse of the SO 2 atmosphere. For example, for an initial surface temperature of 110 K and 35% non-condensable mole-fraction, the ratio of the SO 2 column density to the initial column density was found to be 0.73 after 10 min, 0.50 after 30 min, and 0.18 at the end of eclipse. However, real gas species (SO, O 2) may not be perfectly non-condensable at Io's surface temperatures. If the gas species was even weakly condensable (non-zero sticking/reaction coefficient) then the effect of the diffusion layer on the dynamics was dramatically reduced. In fact, if the sticking coefficient of the non-condensable exceeds ˜0.25, the collapse dynamics are effectively the same as if there were no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size, and the formation of an effective diffusion layer requires that the layer be stationary; this does not occur if the surface is a sink. Upon egress, vertical stratification of the condensable and non-condensable species occurs, with the non-condensable species being lifted (or pushed) to higher altitudes by the sublimating SO 2 after the sublimating atmosphere becomes collisional. Stratification should affect the morphology and intensity of auroral glows shortly after egress.

Microbial community structure and density under different tree species in an acid forest soil (Morvan, France).

PubMed

Lejon, David P H; Chaussod, Rémi; Ranger, Jacques; Ranjard, Lionel

2005-11-01

Overexploitation of forests to increase wood production has led to the replacement of native forest by large areas of monospecific tree plantations. In the present study, the effects of different monospecific tree cover plantations on density and composition of the indigenous soil microbial community are described. The experimental site of "Breuil-Chenue" in the Morvan (France) was the site of a comparison of a similar mineral soil under Norway spruce (Picea abies), Douglas fir (Pseudotuga menziesii), oak (Quercus sessiflora), and native forest [mixed stand dominated by oak and beech (Fagus sylvatica)]. Sampling was performed during winter (February) at three depths (0-5, 5-10, and 10-15 cm). Abundance of microorganisms was estimated via microbial biomass measurements, using the fumigation-extraction method. The genetic structure of microbial communities was investigated using the bacterial- and fungal-automated ribosomal intergenic spacer analysis (B-ARISA and F-ARISA, respectively) DNA fingerprint. Only small differences in microbial biomass were observed between tree species, the highest values being recorded under oak forest and the lowest under Douglas fir. B- and F-ARISA community profiles of the different tree covers clustered separately, but noticeable similarities were observed for soils under Douglas fir and oak. A significant stratification was revealed under each tree species by a decrease in microbial biomass with increasing depths and by distinct microbial communities for each soil layer. Differences in density and community composition according to tree species and depth were related to soil physicochemical characteristics and organic matter composition.

Progress Report on SAM Reduced-Order Model Development for Thermal Stratification and Mixing during Reactor Transients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, R.

This report documents the initial progress on the reduced-order flow model developments in SAM for thermal stratification and mixing modeling. Two different modeling approaches are pursued. The first one is based on one-dimensional fluid equations with additional terms accounting for the thermal mixing from both flow circulations and turbulent mixing. The second approach is based on three-dimensional coarse-grid CFD approach, in which the full three-dimensional fluid conservation equations are modeled with closure models to account for the effects of turbulence.

The role stratification on Indian ocean mixing under global warming

NASA Astrophysics Data System (ADS)

Praveen, V.; Valsala, V.; Ravindran, A. M.

2017-12-01

The impact of changes in Indian ocean stratification on mixing under global warming is examined. Previous studies on global warming and associated weakening of winds reported to increase the stratification of the world ocean leading to a reduction in mixing, increased acidity, reduced oxygen and there by a reduction in productivity. However this processes is not uniform and are also modulated by changes in wind pattern of the future. Our study evaluate the role of stratification and surface fluxes on mixing focusing northern Indian ocean. A dynamical downscaling study using Regional ocean Modelling system (ROMS) forced with stratification and surface fluxes from selected CMIP5 models are presented. Results from an extensive set of historical and Representative Concentration Pathways 8.5 (rcp8.5) scenario simulations are used to quantify the distinctive role of stratification on mixing.

Seasonal and Solar Activity Variations of f3 Layer and StF-4 F-Layer Quadruple Stratification) Near the Equatorial Region

NASA Astrophysics Data System (ADS)

Tardelli, A.; Fagundes, P. R.; Pezzopane, M.; Kavutarapu, V.

2016-12-01

The ionospheric F-layer shape and electron density peak variations depend on local time, latitude, longitude, season, solar cycle, geomagnetic activity, and electrodynamic conditions. In particular, the equatorial and low latitude F-layer may change its shape and peak height in a few minutes due to electric fields induced by propagation of medium-scale traveling ionospheric disturbances (MSTIDs) or thermospheric - ionospheric coupling. This F-layer electrodynamics feature characterizing the low latitudes is one of the most remarkable ionospheric physics research field. The study of multiple-stratification of the F-layer has the initial records in the mid of the 20th century. Since then, many studies were focused on F3 layer. The diurnal, seasonal and solar activity variations of the F3 layer characteristics have been investigated by several researchers. Recently, investigations on multiple-stratifications of F-layer received an important boost after the quadruple stratification (StF-4) was observed at Palmas (10.3°S, 48.3°W; dip latitude 5.5°S - near equatorial region), Brazil (Tardelli & Fagundes, JGR, 2015). This study present the latest findings related with the seasonal and solar activity characteristics of the F3 layer and StF-4 near the equatorial region during the period from 2002 to 2006. A significant connection between StF-4 and F3 layer has been noticed, since the StF-4 is always preceded and followed by an F3 layer appearance. However, the F3 layer and StF-4 present different seasonal and solar cycle variations. At a near equatorial station Palmas, the F3 layer shows the maximum and minimum occurrence during summer and winter seasons respectively. On the contrary, the StF-4 presents the maximum and minimum occurrence during winter and summer seasons respectively. While the F3 layer occurrence is not affected by solar cycle, the StF-4 appearance is instead more frequent during High Solar Activity (HSA).

Influence of precipitating light elements on stable stratification below the core/mantle boundary

NASA Astrophysics Data System (ADS)

O'Rourke, J. G.; Stevenson, D. J.

2017-12-01

Stable stratification below the core/mantle boundary is often invoked to explain anomalously low seismic velocities in this region. Diffusion of light elements like oxygen or, more slowly, silicon could create a stabilizing chemical gradient in the outermost core. Heat flow less than that conducted along the adiabatic gradient may also produce thermal stratification. However, reconciling either origin with the apparent longevity (>3.45 billion years) of Earth's magnetic field remains difficult. Sub-isentropic heat flow would not drive a dynamo by thermal convection before the nucleation of the inner core, which likely occurred less than one billion years ago and did not instantly change the heat flow. Moreover, an oxygen-enriched layer below the core/mantle boundary—the source of thermal buoyancy—could establish double-diffusive convection where motion in the bulk fluid is suppressed below a slowly advancing interface. Here we present new models that explain both stable stratification and a long-lived dynamo by considering ongoing precipitation of magnesium oxide and/or silicon dioxide from the core. Lithophile elements may partition into iron alloys under extreme pressure and temperature during Earth's formation, especially after giant impacts. Modest core/mantle heat flow then drives compositional convection—regardless of thermal conductivity—since their solubility is strongly temperature-dependent. Our models begin with bulk abundances for the mantle and core determined by the redox conditions during accretion. We then track equilibration between the core and a primordial basal magma ocean followed by downward diffusion of light elements. Precipitation begins at a depth that is most sensitive to temperature and oxygen abundance and then creates feedbacks with the radial thermal and chemical profiles. Successful models feature a stable layer with low seismic velocity (which mandates multi-component evolution since a single light element typically increases seismic velocity) growing to its present-day size while allowing enough precipitation to drive compositional convection below. Crucially, this modeling offers unique constrains on Earth's accretion and the light element composition of the core compared to degenerate estimates derived from bulk density and seismic measurements.

Changes in Serving Size, Calories, and Sodium Content in Processed Foods From 2009 to 2015

PubMed Central

Niederman, Sarah A.; Leonard, Elizabeth; Curtis, Christine J.

2018-01-01

Introduction Approximately 60% of the American diet comes from processed foods, which makes improving their nutritional quality important for Americans’ health. The objective of this study was to measure changes in serving sizes, calories, and sodium in top-selling processed foods that were on the market in 2009 and 2015. Methods We analyzed products in the top 80% of sales in the 54 processed food categories with consistent serving sizes and sales metrics that were on the market in both 2009 and 2015. Mean serving size, calories (per serving and density), sodium (per serving and density), and sales were calculated for 2,979 branded processed food products. For each stratification of calorie density and sodium density (decreased, increased, or did not change), we calculated the mean serving size, calorie density, sodium density, and sales for each year. Results From 2009 to 2015, we found decreases in serving size (−2.3%, P < .001), calories per serving (−2.0%, P < .001), calorie density (−1.1%, P < .001), sodium per serving (−7.6%, P < .001), and sodium density (−6.0%, P < .001). A decrease in calorie density did not correspond to an increase in sodium density or vice versa. A decline in sales was observed regardless of whether calorie density or sodium density decreased, increased, or did not change. Conclusion Reductions in calorie and sodium density occurred in tandem, suggesting that manufacturers reformulated for more than one health goal at the same time. Instead of unintended negative consequences of encouraging companies to reformulate for one nutrient, an overall net nutritional benefit occurred. PMID:29543584

What causes the buoyancy reversal in compressible convection?

NASA Technical Reports Server (NTRS)

Chan, K. L.

1983-01-01

The problem posed by the existence of a negative buoyancy work region at the top of cellular type convection in a deeply stratified superadiabatic layer (Massaguer and Zahn, 1980) is addressed. It is approached by studying two-dimensional cellular compressible convection with different physical parameters. The results suggest that a large viscosity, together with density stratification, is responsible for the buoyancy reversal. The numerical results obtained are analyzed. It is pointed out, however, that in an astrophysical situation a fluid involved in convection will generally have very small viscosity. It is therefore thought unlikely that buoyancy reversal occurs in this way.

Relevance of magnetic resonance imaging for early detection and diagnosis of Alzheimer disease.

PubMed

Teipel, Stefan J; Grothe, Michel; Lista, Simone; Toschi, Nicola; Garaci, Francesco G; Hampel, Harald

2013-05-01

Hippocampus volumetry currently is the best-established imaging biomarker for AD. However, the effect of multicenter acquisition on measurements of hippocampus volume needs to be explicitly considered when it is applied in large clinical trials, for example by using mixed-effects models to take the clustering of data within centers into account. The marker needs further validation in respect of the underlying neurobiological substrate and potential confounds such as vascular disease, inflammation, hydrocephalus, and alcoholism, and with regard to clinical outcomes such as cognition but also to demographic and socioeconomic outcomes such as mortality and institutionalization. The use of hippocampus volumetry for risk stratification of predementia study samples will further increase with the availability of automated measurement approaches. An important step in this respect will be the development of a standard hippocampus tracing protocol that harmonizes the large range of presently available manual protocols. In the near future, regionally differentiated automated methods will become available together with an appropriate statistical model, such as multivariate analysis of deformation fields, or techniques such as cortical-thickness measurements that yield a meaningful metrics for the detection of treatment effects. More advanced imaging protocols, including DTI, DSI, and functional MRI, are presently being used in monocenter and first multicenter studies. In the future these techniques will be relevant for the risk stratification in phase IIa type studies (small proof-of-concept trials). By contrast, the application of the broader established structural imaging biomarkers, such as hippocampus volume, for risk stratification and as surrogate end point is already today part of many clinical trial protocols. However, clinical care will also be affected by these new technologies. Radiologic expert centers already offer “dementia screening” for well-off middle-aged people who undergo an MRI scan with subsequent automated, typically VBM-based analysis, and determination of z-score deviation from a matched control cohort. Next-generation scanner software will likely include radiologic expert systems for automated segmentation, deformation-based morphometry, and multivariate analysis of anatomic MRI scans for the detection of a typical AD pattern. As these developments will start to change medical practice, first for selected subject groups that can afford this type of screening but later eventually also for other cohorts, clinicians must become aware of the potentials and limitations of these technologies. It is decidedly unclear to date how a middle-aged cognitively intact subject with a seemingly AD-positive MRI scan should be clinically advised. There is no evidence for individual risk prediction and even less for specific treatments. Thus, the development of preclinical diagnostic imaging poses not only technical but also ethical problems that must be critically discussed on the basis of profound knowledge. From a neurobiological point of view, the main determinants of cognitive impairment in AD are the density of synapses and neurons in distributed cortical and subcortical networks. MRI-based measures of regional gray matter volume and associated multivariate analysis techniques of regional interactions of gray matter densities provide insight into the onset and temporal dynamics of cortical atrophy as a close proxy for regional neuronal loss and a basis of functional impairment in specific neuronal networks. From the clinical point of view, clinicians must bear in mind that patients do not suffer from hippocampus atrophy or disconnection but from memory impairment, and that dementia screening in asymptomatic subjects should not be used outside of clinical studies. Copyright © 2013 Elsevier Inc. All rights reserved.

Gender-dependent association of a β(2)-adrenergic gene variant with obesity parameters in Malaysian Malays.

PubMed

Apalasamy, Yamunah Devi; Ming, Moy Foong; Rampal, Sanjay; Bulgiba, Awang; Mohamed, Zahurin

2015-03-01

Recent findings have shown that the rs1042714 (Gln27Glu) single-nucleotide polymorphism (SNP) on the β2-adrenoceptor gene may predispose to obesity. The findings from other studies carried on different populations, however, have been inconsistent. The authors investigated the association between the rs1042714 SNP with obesity-related parameters. DNA of 672 Malaysian Malays was analyzed using real-time polymerase chain reaction. Univariate and multivariate linear regression analyses revealed significant associations between rs1042714 and diastolic blood pressure in the pooled Malaysian Malay subjects under additive and recessive models. After gender stratification, however, a significant association was found between the rs1042714 and triglyceride and the rs1042714 and log-transformed high-density lipoprotein cholesterol levels in Malaysian Malay men. No significant association was found between the SNP and log-transformed body mass index. This polymorphism may have an important role in the development of obesity-related traits in Malaysian Malays. Gender is an effect modifier for the effect of the rs1042714 polymorphism on obesity-related traits in Malaysian Malays. © 2011 APJPH.

The integration of two health systems: social stratification, work and health in East and West Germany.

PubMed

Lüschen, G; Niemann, S; Apelt, P

1997-03-01

This is an analysis of system integration, social stratification and work for health status and health care in East and West Germany. It is based on aggregate data and representative survey data of random samples of 2554 adults in both subsystems. Findings show that there were marked differences in life-expectancy prior to unification. The integration of the two systems, which occurred almost totally with regard to terms of West German health care organization, shows adjustment problems in the East for the public Health-Care-Funds and few if any for ambulatory care. The work situation has an impact on health, but there are no significant differences for East versus West. Social stratification variables show an influence on subjective health status for education (East) and for income, social status (West), while physician utilization (despite a preference of specialists by those with higher status) is not significantly determined by stratification variables in either East or West Germany. Beyond the central focus on work and stratification determinants a major finding pertains to a comparatively worse health situation for the aged and for women in what was the former East Germany. System models of Capitalism versus Socialism fit the results and recent history of the two systems to only a limited degree, as the West German corporate health system shows clear limits in following free market principles. The East German system, regardless of its centralized organization and move towards a socialist system, never fully abandoned the traditional model of German health care. Unlike the East German health system, that of West Germany, with its general expansion to 92% of the population, shows an increasing effect for social redistribution. The latter may be a reason why standard indicators of social stratification show less of an impact on health and health care than expected, while conditions at work clearly determine the health of people-the latter being the case in both the former East and West Germany.

Optimal energy growth in a stably stratified shear flow

NASA Astrophysics Data System (ADS)

Jose, Sharath; Roy, Anubhab; Bale, Rahul; Iyer, Krithika; Govindarajan, Rama

2018-02-01

Transient growth of perturbations by a linear non-modal evolution is studied here in a stably stratified bounded Couette flow. The density stratification is linear. Classical inviscid stability theory states that a parallel shear flow is stable to exponentially growing disturbances if the Richardson number (Ri) is greater than 1/4 everywhere in the flow. Experiments and numerical simulations at higher Ri show however that algebraically growing disturbances can lead to transient amplification. The complexity of a stably stratified shear flow stems from its ability to combine this transient amplification with propagating internal gravity waves (IGWs). The optimal perturbations associated with maximum energy amplification are numerically obtained at intermediate Reynolds numbers. It is shown that in this wall-bounded flow, the three-dimensional optimal perturbations are oblique, unlike in unstratified flow. A partitioning of energy into kinetic and potential helps in understanding the exchange of energies and how it modifies the transient growth. We show that the apportionment between potential and kinetic energy depends, in an interesting manner, on the Richardson number, and on time, as the transient growth proceeds from an optimal perturbation. The oft-quoted stabilizing role of stratification is also probed in the non-diffusive limit in the context of disturbance energy amplification.

Subsurface storage of freshwater in South Florida; a digital analysis of recoverability

USGS Publications Warehouse

Merritt, Michael L.

1983-01-01

As part of a feasibility study of cyclic freshwater injection, digital models were implemented to analyze the relation of recovery efficiency to various hydrogeologic conditions which could prevail in brackish aquifers and to various management regimes. The analyses implemented an approach in which the control for sensitivity testing was a hypothetical aquifer representative of potential injection zones in south Florida, and parameter variations in sensitivity tests represented possible variations in aquifer conditions in the area. The permeability of the aquifer determined whether buoyancy stratification could reduce recovery efficiency. The range of permeability leading to buoyancy stratification became lower as resident fluid salinity increased. Thus, recovery efficiency was optimized by both low permeability and low resident fluid density. High levels of simulated hydrodynamic dispersion led to the lowest estimates of recovery efficiency. Advection by regional flow within the artesian injection zone could significantly affect recovery efficiency, depending upon the storage period, the volume injected, and site-specific hydraulic characteristics. Recovery efficiency was unrelated to the rate of injection or withdrawal or to the degree of penetration of permeable layers, and improved with successive cycles of injection and recovery. (USGS)

Liver Enzymes and Bone Mineral Density in the General Population.

PubMed

Breitling, Lutz Philipp

2015-10-01

Liver enzyme serum levels within and just above the normal range are strong predictors of incident morbidity and mortality in the general population. However, despite the close links between hepatic pathology and impaired bone health, the association of liver enzymes with osteoporosis has hardly been investigated. The aim of the present study was to clarify whether serum liver enzyme levels in the general population are associated with bone mineral density. This was an observational, cross-sectional study. Participants and Main Outcome: Data on 13 849 adult participants of the Third National Health and Nutrition Examination Survey were used to quantify the independent associations of γ-glutamyltransferase, alanine transaminase, and aspartate transaminase with femoral neck bone mineral density assessed by dual-energy x-ray absorptiometry. In multiple regression models adjusting for numerous confounding variables, γ-glutamyltransferase showed a weak inverse association with bone mineral density (P = .0063). There also was limited evidence of a nonmonotonous relationship with alanine transaminase, with peak bone mineral density in the second quartile of enzyme activity (P = .0039). No association was found for aspartate transaminase. Although mechanistically plausible associations were found in the present study, the rather weak nature of these patterns renders it unlikely that liver enzyme levels could be of substantial use for osteoporosis risk stratification in the general population.

Intermediate outcomes in randomized clinical trials: an introduction

PubMed Central

2013-01-01

Background Intermediate outcomes are common and typically on the causal pathway to the final outcome. Some examples include noncompliance, missing data, and truncation by death like pregnancy (e.g. when the trial intervention is given to non-pregnant women and the final outcome is preeclampsia, defined only on pregnant women). The intention-to-treat approach does not account properly for them, and more appropriate alternative approaches like principal stratification are not yet widely known. The purposes of this study are to inform researchers that the intention-to-treat approach unfortunately does not fit all problems we face in experimental research, to introduce the principal stratification approach for dealing with intermediate outcomes, and to illustrate its application to a trial of long term calcium supplementation in women at high risk of preeclampsia. Methods Principal stratification and related concepts are introduced. Two ways for estimating causal effects are discussed and their application is illustrated using the calcium trial, where noncompliance and pregnancy are considered as intermediate outcomes, and preeclampsia is the main final outcome. Results The limitations of traditional approaches and methods for dealing with intermediate outcomes are demonstrated. The steps, assumptions and required calculations involved in the application of the principal stratification approach are discussed in detail in the case of our calcium trial. Conclusions The intention-to-treat approach is a very sound one but unfortunately it does not fit all problems we find in randomized clinical trials; this is particularly the case for intermediate outcomes, where alternative approaches like principal stratification should be considered. PMID:23510143

Risk assessment and clinical decision making for colorectal cancer screening.

PubMed

Schroy, Paul C; Caron, Sarah E; Sherman, Bonnie J; Heeren, Timothy C; Battaglia, Tracy A

2015-10-01

Shared decision making (SDM) related to test preference has been advocated as a potentially effective strategy for increasing adherence to colorectal cancer (CRC) screening, yet primary care providers (PCPs) are often reluctant to comply with patient preferences if they differ from their own. Risk stratification advanced colorectal neoplasia (ACN) provides a rational strategy for reconciling these differences. To assess the importance of risk stratification in PCP decision making related to test preference for average-risk patients and receptivity to use of an electronic risk assessment tool for ACN to facilitate SDM. Mixed methods, including qualitative key informant interviews and a cross-sectional survey. PCPs at an urban, academic safety-net institution. Screening preferences, factors influencing patient recommendations and receptivity to use of a risk stratification tool. Nine PCPs participated in interviews and 57 completed the survey. Despite an overwhelming preference for colonoscopy by 95% of respondents, patient risk (67%) and patient preferences (63%) were more influential in their decision making than patient comorbidities (31%; P < 0.001). Age was the single most influential risk factor (excluding family history), with <20% of respondents choosing factors other than age. Most respondents reported that they would be likely to use a risk stratification tool in their practice either 'often' (43%) or sometimes (53%). Risk stratification was perceived to be important in clinical decision making, yet few providers considered risk factors other than age for average-risk patients. Providers were receptive to the use of a risk assessment tool for ACN when recommending an appropriate screening test for select patients. © 2013 John Wiley & Sons Ltd.

Effects of a semi-infinite stratification on the Rayleigh-Taylor instability in an interface with surface tension

NASA Astrophysics Data System (ADS)

de Andrea González, Ángel; González-Gutiérrez, Leo M.

2017-09-01

The Rayleigh-Taylor instability (RTI) in an infinite slab where a constant density lower fluid is initially separated from an upper stratified fluid is discussed in linear regime. The upper fluid is of increasing exponential density and surface tension is considered between both of them. It was found useful to study stability by using the initial value problem approach (IVP), so that we ensure the inclusion of certain continuum modes, otherwise neglected. This methodology includes the branch cut in the complex plane, consequently, in addition to discrete modes (surface RTI modes), a set of continuum modes (internal RTI modes) also appears. As a result, the usual information given by the normal mode method is now complete. Furthermore, a new role is found for surface tension: to transform surface RTI modes (discrete spectrum) into internal RTI modes belonging to a continuous spectrum at a critical wavenumber. As a consequence, the cut-off wavenumber disappears: i.e. the growth rate of the RTI surface mode does not decay to zero at the cut-off wavenumber, as previous researchers used to believe. Finally, we found that, due to the continuum, the asymptotic behavior of the perturbation with respect to time is slower than the exponential when only the continuous spectrum exists.

Nonlinear anelastic modal theory for solar convection

NASA Technical Reports Server (NTRS)

Latour, J.; Toomre, J.; Zahn, J.-P.

1983-01-01

Solar envelope models are developed using single-mode anelastic equations as a description of turbulent convection which provide estimates for the variation with depth of the largest convective cellular flows, with horizontal sizes comparable to the total depth of the convection zone. These models can be used to describe compressible motions occurring over many density scale heights. Single-mode anelastic solutions are obtained for a solar envelope whose mean stratification is nearly adiabatic over most of its vertical extent because of the enthalpy flux explicitly carried by the big cell, while a subgrid scale representation of turbulent heat transport is incorporated into the treatment near the surface. It is shown that the single-mode equations allow two solutions for the same horizontal wavelength which are distinguished by the sense of the vertical velocity at the center of the three-dimensional cell. It is found that the upward directed flow experiences large pressure effects which can modify the density fluctuations so that the sense of the buoyancy force is changed, with buoyancy braking actually achieved near the top of the convection zone. It is suggested that such dynamical processes may explain why the amplitudes of flows related to the largest scales of convection are so weak in the solar atmosphere.

Palaeoceanography. Antarctic stratification and glacial CO2.

PubMed

Keeling, R F; Visbeck, M

2001-08-09

One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis, which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica. As discussed by Sigman and Boyle, this hypothesis assumes that increased stratification in the Antarctic zone (Fig. 1) was associated with reduced upwelling of deep waters around Antarctica, thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline, which is consistent with Antarctic sediment records. We point out here, however, that the response of ocean eddies to increased Antarctic stratification can be expected to increase, rather than reduce, the upwelling rate of deep waters around Antarctica. The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods.

Proposal for a new risk stratification classification for meningioma based on patient age, WHO tumor grade, size, localization, and karyotype

PubMed Central

Domingues, Patrícia Henriques; Sousa, Pablo; Otero, Álvaro; Gonçalves, Jesus Maria; Ruiz, Laura; de Oliveira, Catarina; Lopes, Maria Celeste; Orfao, Alberto; Tabernero, Maria Dolores

2014-01-01

Background Tumor recurrence remains the major clinical complication of meningiomas, the majority of recurrences occurring among WHO grade I/benign tumors. In the present study, we propose a new scoring system for the prognostic stratification of meningioma patients based on analysis of a large series of meningiomas followed for a median of >5 years. Methods Tumor cytogenetics were systematically investigated by interphase fluorescence in situ hybridization in 302 meningioma samples, and the proposed classification was further validated in an independent series of cases (n = 132) analyzed by high-density (500K) single-nucleotide polymorphism (SNP) arrays. Results Overall, we found an adverse impact on patient relapse-free survival (RFS) for males, presence of brain edema, younger patients (<55 years), tumor size >50 mm, tumor localization at intraventricular and anterior cranial base areas, WHO grade II/III meningiomas, and complex karyotypes; the latter 5 variables showed an independent predictive value in multivariate analysis. Based on these parameters, a prognostic score was established for each individual case, and patients were stratified into 4 risk categories with significantly different (P < .001) outcomes. These included a good prognosis group, consisting of approximately 20% of cases, that showed a RFS of 100% ± 0% at 10 years and a very poor-prognosis group with a RFS rate of 0% ± 0% at 10 years. The prognostic impact of the scoring system proposed here was also retained when WHO grade I cases were considered separately (P < .001). Conclusions Based on this risk-stratification classification, different strategies may be adopted for follow-up, and eventually also for treatment, of meningioma patients at different risks for relapse. PMID:24536048

Value of the Definition of Severe Familial Hypercholesterolemia for Stratification of Heterozygous Patients.

PubMed

Pérez-Calahorra, Sofia; Sánchez-Hernández, Rosa María; Plana, Núria; Marco-Benedi, Victoria; Pedro-Botet, Juan; Almagro, Fátima; Brea, Angel; Ascaso, Juan Francisco; Lahoz, Carlos; Civeira, Fernando

2017-03-01

Familial hypercholesterolemia (FH) is characterized by high low-density lipoprotein (LDL) cholesterol with co-dominant transmission and high risk of cardiovascular disease (CVD), although with high variability among subjects. Currently, CVD stratification tools for heterozygous FH (HeFH) are not available. A definition of severe HeFH has been recently proposed by the International Atherosclerosis Society (IAS), but it has not been validated. Our study aims to see clinical characteristics and prevalence of CVD in subjects defined as severe HeFH by IAS criteria. Probable or definite HeFH introduced in the Dyslipidemia Registry of Spanish Arteriosclerosis Society were analyzed by the IAS criteria. Univariate and multivariate analysis was used to assess the association of CVD with the IAS criteria. About 1,732 HeFH cases were analyzed. Severe HeFH had higher prevalence of familial history of CVD, personal history of tendon xanthomas, LDL cholesterol, and CVD than nonsevere HeFH. A total of 656 (77.1%) and 441 (50.1%) of men and women, respectively, fulfilled the IAS criteria of severe HeFH. In the univariate analysis, subjects defined as severe HeFH showed odds ratio 3.016 (95% CI 3.136 to 4.257, p <0.001) for CVD. However, when traditional risk factors were included in the multivariate analysis, only the presence of cholesterol >400 mg/dl had a statistically significant association with CVD odds ratio 8.76 (95% CI 3.90 to 19.69, p <0.001). In conclusion, the IAS definition of severe HeFH is not significantly associated with CVD when adjusted for classic risk factors. Risk stratification in HeFH is an important issue, but the proposed criteria do not seem to solve this problem. Copyright © 2016 Elsevier Inc. All rights reserved.

Phytoplankton Functional Diversity and New Production during Spring and Summer Blooms in the Subarctic Atlantic Ocean

NASA Astrophysics Data System (ADS)

Van Oostende, N.; Fawcett, S. E.; Ji, Q.; Marconi, D.; Lueders-Dumont, J.; Sigman, D. M.; Ward, B. B.

2016-02-01

In the subarctic Atlantic Ocean, strong seasonal cycles in heat flux drive water column stratification, which governs the supply of nutrients to the euphotic zone that fuels the biological pump. The export efficiency of this pump is largely determined by the degree of phytoplankton nitrate (NO3-) assimilation and phytoplankton community size structure. We investigated nitrogen assimilation and phytoplankton community diversity and size structure on spring and summer cruises to 50-60°N, by using a combination of stable isotope tracer incubations, flow cytometry, microscopy, size-fractionated algal pigments, and nitrogen stable isotope measurements. As expected in springtime, the phytoplankton community was dominated by large (>20 µm) cells while in late summer these constituted only a minor fraction of the assemblage. The weaker density stratification of the water column in the spring compared to the summer allowed for surface nutrient concentrations that were not limiting phytoplankton growth (e.g., [NO3-] >5 µM). Despite stronger water column stratification in the summer, partial consumption of subsurface NO3-, which had recently been supplied to surface waters, allowed for total chlorophyll and particulate nitrogen (PN) to attain similar levels during both seasons. High 15N/14N of NO3- and PN in surface waters is consistent with NO3- utilization. In springtime, however, the phytoplankton community consumed NO3- at PN-normalized rates up to fivefold higher than in summer, despite having comparable uptake rates for ammonium and inorganic carbon. This observation implies that the large phytoplankton species that are abundant in spring, mostly diatoms, contribute disproportionally more to new production than summer phytoplankton communities that are devoid of these large species.

Stratification during evaporative assembly of multicomponent nanoparticle films

DOE PAGES

Liu, Xiao; Liu, Weiping; Carr, Amanda J.; ...

2018-01-03

Multicomponent coatings with layers comprising different functionalities are of interest for a variety of applications, including electronic devices, energy storage, and biomaterials. Rather than creating such a film using multiple deposition steps, we explore a single-step method to create such films by varying the particle Peclet numbers, Pe. Our hypothesis, based on recent theoretical descriptions of the stratification process, is that by varying particle size and evaporation rate such that Pe of large and small particles are above and below unity, we can create stratified films of polymeric and inorganic particles. In this paper, we present AFM on the surfacemore » composition of films comprising poly(styrene) nanoparticles (diameter 25–90 nm) and silica nanoparticles (diameter 8–14 nm). Previous studies on films containing both inorganic and polymeric particles correspond to large Pe values (e.g., 120–460), while we utilize Pe ~ 0.3–4, enabling us to test theories that have been developed for different regimes of Pe. We demonstrate evidence of stratification and effect of the Pe ratio, although our results agree only qualitatively with theory. Finally, our results also provide validation of recent theoretical descriptions of the film drying process that predict different regimes for large-on-top and small-on-top stratification.« less

Ion species stratification within strong shocks in two-ion plasmas

DOE PAGES

Keenan, Brett D.; Simakov, Andrei N.; Taitano, William T.; ...

2018-03-01

We report strong collisional shocks in multi-ion plasmas are featured in many environments, with Inertial Confinement Fusion (ICF) experiments being one prominent example. Recent work [Keenan et al., Phys. Rev. E 96, 053203 (2017)] answered in detail a number of outstanding questions concerning the kinetic structure of steady-state, planar plasma shocks, e.g., the shock width scaling by the Mach number, M. However, it did not discuss shock-driven ion-species stratification (e.g., relative concentration modification and temperature separation). These are important effects since many recent ICF experiments have evaded explanation by standard, single-fluid, radiation-hydrodynamic (rad-hydro) numerical simulations, and shock-driven fuel stratification likelymore » contributes to this discrepancy. Employing the state-of-the-art Vlasov-Fokker-Planck code, iFP, along with multi-ion hydro simulations and semi-analytics, we quantify the ion stratification by planar shocks with the arbitrary Mach number and the relative species concentration for two-ion plasmas in terms of ion mass and charge ratios. In particular, for strong shocks, we find that the structure of the ion temperature separation has a nearly universal character across ion mass and charge ratios. Lastly, we find that the shock fronts are enriched with the lighter ion species and the enrichment scales as M 4 for M»1.« less

Ion species stratification within strong shocks in two-ion plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keenan, Brett D.; Simakov, Andrei N.; Taitano, William T.

We report strong collisional shocks in multi-ion plasmas are featured in many environments, with Inertial Confinement Fusion (ICF) experiments being one prominent example. Recent work [Keenan et al., Phys. Rev. E 96, 053203 (2017)] answered in detail a number of outstanding questions concerning the kinetic structure of steady-state, planar plasma shocks, e.g., the shock width scaling by the Mach number, M. However, it did not discuss shock-driven ion-species stratification (e.g., relative concentration modification and temperature separation). These are important effects since many recent ICF experiments have evaded explanation by standard, single-fluid, radiation-hydrodynamic (rad-hydro) numerical simulations, and shock-driven fuel stratification likelymore » contributes to this discrepancy. Employing the state-of-the-art Vlasov-Fokker-Planck code, iFP, along with multi-ion hydro simulations and semi-analytics, we quantify the ion stratification by planar shocks with the arbitrary Mach number and the relative species concentration for two-ion plasmas in terms of ion mass and charge ratios. In particular, for strong shocks, we find that the structure of the ion temperature separation has a nearly universal character across ion mass and charge ratios. Lastly, we find that the shock fronts are enriched with the lighter ion species and the enrichment scales as M 4 for M»1.« less

Ion species stratification within strong shocks in two-ion plasmas

NASA Astrophysics Data System (ADS)

Keenan, Brett D.; Simakov, Andrei N.; Taitano, William T.; Chacón, Luis

2018-03-01

Strong collisional shocks in multi-ion plasmas are featured in many environments, with Inertial Confinement Fusion (ICF) experiments being one prominent example. Recent work [Keenan et al., Phys. Rev. E 96, 053203 (2017)] answered in detail a number of outstanding questions concerning the kinetic structure of steady-state, planar plasma shocks, e.g., the shock width scaling by the Mach number, M. However, it did not discuss shock-driven ion-species stratification (e.g., relative concentration modification and temperature separation). These are important effects since many recent ICF experiments have evaded explanation by standard, single-fluid, radiation-hydrodynamic (rad-hydro) numerical simulations, and shock-driven fuel stratification likely contributes to this discrepancy. Employing the state-of-the-art Vlasov-Fokker-Planck code, iFP, along with multi-ion hydro simulations and semi-analytics, we quantify the ion stratification by planar shocks with the arbitrary Mach number and the relative species concentration for two-ion plasmas in terms of ion mass and charge ratios. In particular, for strong shocks, we find that the structure of the ion temperature separation has a nearly universal character across ion mass and charge ratios. Additionally, we find that the shock fronts are enriched with the lighter ion species and the enrichment scales as M4 for M ≫ 1.

Stratification during evaporative assembly of multicomponent nanoparticle films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiao; Liu, Weiping; Carr, Amanda J.

Multicomponent coatings with layers comprising different functionalities are of interest for a variety of applications, including electronic devices, energy storage, and biomaterials. Rather than creating such a film using multiple deposition steps, we explore a single-step method to create such films by varying the particle Peclet numbers, Pe. Our hypothesis, based on recent theoretical descriptions of the stratification process, is that by varying particle size and evaporation rate such that Pe of large and small particles are above and below unity, we can create stratified films of polymeric and inorganic particles. In this paper, we present AFM on the surfacemore » composition of films comprising poly(styrene) nanoparticles (diameter 25–90 nm) and silica nanoparticles (diameter 8–14 nm). Previous studies on films containing both inorganic and polymeric particles correspond to large Pe values (e.g., 120–460), while we utilize Pe ~ 0.3–4, enabling us to test theories that have been developed for different regimes of Pe. We demonstrate evidence of stratification and effect of the Pe ratio, although our results agree only qualitatively with theory. Finally, our results also provide validation of recent theoretical descriptions of the film drying process that predict different regimes for large-on-top and small-on-top stratification.« less

A role for jasmonates in the release of dormancy by cold stratification in wheat

PubMed Central

Xu, Qian; Truong, Thy T.; Barrero, Jose M.; Jacobsen, John V.; Hocart, Charles H.; Gubler, Frank

2016-01-01

Hydration at low temperatures, commonly referred to as cold stratification, is widely used for releasing dormancy and triggering germination in a wide range of species including wheat. However, the molecular mechanism that underlies its effect on germination has largely remained unknown. Our previous studies showed that methyl-jasmonate, a derivative of jasmonic acid (JA), promotes dormancy release in wheat. In this study, we found that cold-stimulated germination of dormant grains correlated with a transient increase in JA content and expression of JA biosynthesis genes in the dormant embryos after transfer to 20 oC. The induction of JA production was dependent on the extent of cold imbibition and precedes germination. Blocking JA biosynthesis with acetylsalicylic acid (ASA) inhibited the cold-stimulated germination in a dose-dependent manner. In addition, we have explored the relationship between JA and abscisic acid (ABA), a well-known dormancy promoter, in cold regulation of dormancy. We found an inverse relationship between JA and ABA content in dormant wheat embryos following stratification. ABA content decreased rapidly in response to stratification, and the decrease was reversed by addition of ASA. Our results indicate that the action of JA on cold-stratified grains is mediated by suppression of two key ABA biosynthesis genes, TaNCED1 and TaNCED2. PMID:27140440

Modeling the periodic stratification and gravitational circulation in San Francisco Bay, California

USGS Publications Warehouse

Cheng, Ralph T.; Casulli, Vincenzo

1996-01-01

A high resolution, three-dimensional (3-D) hydrodynamic numerical model is applied to San Francisco Bay, California to simulate the periodic tidal stratification caused by tidal straining and stirring and their long-term effects on gravitational circulation. The numerical model is formulated using fixed levels in the vertical and uniform computational mesh on horizontal planes. The governing conservation equations, the 3-D shallow water equations, are solved by a semi-implicit finite-difference scheme. Numerical simulations for estuarine flows in San Francisco Bay have been performed to reproduce the hydrodynamic properties of tides, tidal and residual currents, and salt transport. All simulations were carried out to cover at least 30 days, so that the spring-neap variance in the model results could be analyzed. High grid resolution used in the model permits the use of a simple turbulence closure scheme which has been shown to be sufficient to reproduce the tidal cyclic stratification and well-mixed conditions in the water column. Low-pass filtered 3-D time-series reveals the classic estuarine gravitational circulation with a surface layer flowing down-estuary and an up-estuary flow near the bottom. The intensity of the gravitational circulation depends upon the amount of freshwater inflow, the degree of stratification, and spring-neap tidal variations.

The wind geometry of the Wolf-Rayet star HD 191765

NASA Technical Reports Server (NTRS)

Schulte-Ladbeck, R. F.; Nordsieck, K. H.; Taylor, M.; Bjorkman, K. S.; Magalhaes, A. M.; Wolff, M. J.

1992-01-01

A time-dependent spectropolarimetric data set of HD 191765 in the wavelength range 3159-7593 A is presented. At all epochs the present observations display a large and strongly wavelength-dependent continuum polarization and reduced levels of polarization across the emission lines. The data imply a significant intrinsic continuum polarization which requires a general deviation of the electron distribution from spherical symmetry. The global shape is quite stable as a function of time; small fluctuations may arise from localized density/temperature changes. The line polarizations are consistent with an axisymmetric wind geometry and ionization stratification. A qualitative model for polarization in a Wolf-Rayet atmosphere is developed. It is argued that the blueward rise of the continuum polarization in HD 191765 can be explained if the density in the wind is high, resulting in a competition of thermal and electron-scattering continuum opacity in the vertical.

Gelled-electrolyte batteries for electric vehicles

NASA Astrophysics Data System (ADS)

Tuphorn, Hans

Increasing problems of air pollution have pushed activities of electric vehicle projects worldwide and in spite of projects for developing new battery systems for high energy densities, today lead/acid batteries are almost the single system, ready for technical usage in this application. Valve-regulated lead/acid batteries with gelled electrolyte have the advantage that no maintenance is required and because the gel system does not cause problems with electrolyte stratification, no additional appliances for central filling or acid addition are required, which makes the system simple. Those batteries with high density active masses indicate high endurance results and field tests with 40 VW-CityStromers, equipped with 96 V/160 A h gel batteries with thermal management show good results during four years. In addition, gelled lead/acid batteries possess superior high rate performance compared with conventional lead/acid batteries, which guarantees good acceleration results of the car and which makes the system recommendable for application in electric vehicles.

Sun-stirred Kraken Mare: Circulation in Titan's seas induced by solar heating and methane precipitation

NASA Astrophysics Data System (ADS)

Tokano, T.; Lorenz, R. D.

2015-10-01

Density-driven circulation in Titan's seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Strong summer precipitation at high latitudes causes compositional stratification and increase of the nearsurface methane mole fraction towards the north pole. The resultant latitudinal density contrast drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. Weak precipitation induces gyres rather than meridional overturning.

Variability of stratification according to operation of the tidal power plant in Lake Sihwa, South Korea.

NASA Astrophysics Data System (ADS)

Woo, S. B.; Song, J. I.; Jang, T. H.; Park, C. J.; Kwon, H. K.

2017-12-01

Artificial forcing according to operation of the tidal power plant (TPP) affects the physical environmental changes near the power plant. Strong turbulence by generation is expected to change the stratification structure of the Lake Sihwa inside. In order to examine the stratification changes by the power plant operation, ship bottom mounted observation were performed for 13 hours using an acoustic Doppler current profiler (ADCP) and Conductivity-Temperature-Depth (CTD) in Lake Sihwa at near TPP. The strong stratification in Sihwa Lake is maintained before TPP operation. The absence of external forces and freshwater inflow from the land forms the stratification in the Lake. Strong winds in a stratification statement lead to two-layer circulation. After wind event, multi-layer velocity structure is formed which lasted for approximately 4 h. After TPP operation, the jet flow was observed in entire water column at the beginning of the power generation. Vortex is formed by strong jet flow and maintained throughout during power generation period. Strong turbulence flow is generated by the turbine blades, enhancing vertical mixing. External forces, which dominantly affect Lake Sihwa, have changed from the wind to the turbulent flow. The stratification was extinguished by strong turbulent flow and becomes fully-mixed state. Changes in stratification structure are expected to affect material transport and ecological environment change continuously.

Buoyancy effects on the radiative magneto Micropolar nanofluid flow with double stratification, activation energy and binary chemical reaction.

PubMed

Ramzan, M; Ullah, Naeem; Chung, Jae Dong; Lu, Dianchen; Farooq, Umer

2017-10-10

A mathematical model has been developed to examine the magneto hydrodynamic micropolar nanofluid flow with buoyancy effects. Flow analysis is carried out in the presence of nonlinear thermal radiation and dual stratification. The impact of binary chemical reaction with Arrhenius activation energy is also considered. Apposite transformations are engaged to transform nonlinear partial differential equations to differential equations with high nonlinearity. Resulting nonlinear system of differential equations is solved by differential solver method in Maple software which uses Runge-Kutta fourth and fifth order technique (RK45). To authenticate the obtained results, a comparison with the preceding article is also made. The evaluations are executed graphically for numerous prominent parameters versus velocity, micro rotation component, temperature, and concentration distributions. Tabulated numerical calculations of Nusselt and Sherwood numbers with respective well-argued discussions are also presented. Our findings illustrate that the angular velocity component declines for opposing buoyancy forces and enhances for aiding buoyancy forces by changing the micropolar parameter. It is also found that concentration profile increases for higher values of chemical reaction parameter, whereas it diminishes for growing values of solutal stratification parameter.

Study of thermal and hydraulic efficiency of supersonic tube of temperature stratification

NASA Astrophysics Data System (ADS)

Tsynaeva, Anna A.; Nikitin, Maxim N.; Tsynaeva, Ekaterina A.

2017-10-01

Efficiency of supersonic pipe for temperature stratification with finned subsonic surface of heat transfer is the major of this paper. Thermal and hydraulic analyses of this pipe were conducted to asses effects from installation of longitudinal rectangular and parabolic fins as well as studs of cylindrical, rectangular and parabolic profiles. The analysis was performed based on refined empirical equations of similarity, dedicated to heat transfer of high-speed gas flow with plain wall, and Kármán equation with Nikuradze constants. Results revealed cylindrical studs (with height-to-diameter ratio of 5:1) to be 1.5 times more efficient than rectangular fins of the same height. At the same time rectangular fins (with height-to-thickness ratio of 5:1) were tend to enhance heat transfer rate up to 2.67 times compared to bare walls from subsonic side of the pipe. Longitudinal parabolic fins have minuscule effect on combined efficiency of considered pipe since extra head losses void any gain of heat transfer. Obtained results provide perspective of increasing efficiency of supersonic tube for temperature stratification. This significantly broadens device applicability in thermostatting systems for equipment, cooling systems for energy converting machinery, turbine blades and aerotechnics.

Zombie Vortex Instability: Effects of Non-uniform Stratification & Thermal Cooling

NASA Astrophysics Data System (ADS)

Barranco, Joseph; Pei, Suyang; Marcus, Phil; Jiang, Chung-Hsiang

2015-11-01

The Zombie Vortex Instability (ZVI) is a nonlinear instability in rotating, stratified, shear flows, such as in protoplanetary disks (PPD) of gas and dust orbiting new stars. The instability mechanism is the excitation of baroclinic critical layers, leading to vorticity amplification and nonlinear evolution into anticyclonic vortices and cyclonic sheets. ZVI is most robust when the Coriolis frequency, shear rate, and Brunt-Väisälä (BV) frequency are of the same order. Previously, we investigated ZVI with uniform stratification and without thermal cooling. Here, we explore the role of non-uniform stratification as would be found in PPDs in which the BV frequency is zero in the disk midplane, and increases away from the midplane. We find that ZVI is vigorous 1-3 pressure scale heights away from the midplane, but the non-isotropic turbulence generated by ZVI can penetrate into the midplane. We also explore the effect of thermal cooling and find that ZVI is still robust for cooling times as short as 5 orbital periods. ZVI may play important roles in transporting angular momentum in PPDs, and in trapping dust grains, which may trigger gravitational clumping into planetesimals.

Areal Control Using Generalized Least Squares As An Alternative to Stratification

Treesearch

Raymond L. Czaplewski

2001-01-01

Stratification for both variance reduction and areal control proliferates the number of strata, which causes small sample sizes in many strata. This might compromise statistical efficiency. Generalized least squares can, in principle, replace stratification for areal control.

An Ecology of Prestige in New York City: Examining the Relationships Among Population Density, Socio-economic Status, Group Identity, and Residential Canopy Cover

NASA Astrophysics Data System (ADS)

Grove, J. Morgan; Locke, Dexter H.; O'Neil-Dunne, Jarlath P. M.

2014-09-01

Several social theories have been proposed to explain the uneven distribution of vegetation in urban residential areas: population density, social stratification, luxury effect, and ecology of prestige. We evaluate these theories using a combination of demographic and socio-economic predictors of vegetative cover on all residential lands in New York City. We use diverse data sources including the City's property database, time-series demographic and socio-economic data from the US Census, and land cover data from the University of Vermont's Spatial Analysis Lab (SAL). These data are analyzed using a multi-model inferential, spatial econometrics approach. We also examine the distribution of vegetation within distinct market categories using Claritas' Potential Rating Index for Zipcode Markets (PRIZM™) database. These categories can be disaggregated, corresponding to the four social theories. We compare the econometric and categorical results for validation. Models associated with ecology of prestige theory are more effective for predicting the distribution of vegetation. This suggests that private, residential patterns of vegetation, reflecting the consumption of environmentally relevant goods and services, are associated with different lifestyles and lifestages. Further, our spatial and temporal analyses suggest that there are significant spatial and temporal dependencies that have theoretical and methodological implications for understanding urban ecological systems. These findings may have policy implications. Decision makers may need to consider how to most effectively reach different social groups in terms of messages and messengers in order to advance land management practices and achieve urban sustainability.

An ecology of prestige in New York City: examining the relationships among population density, socio-economic status, group identity, and residential canopy cover.

PubMed

Grove, J Morgan; Locke, Dexter H; O'Neil-Dunne, Jarlath P M

2014-09-01

Several social theories have been proposed to explain the uneven distribution of vegetation in urban residential areas: population density, social stratification, luxury effect, and ecology of prestige. We evaluate these theories using a combination of demographic and socio-economic predictors of vegetative cover on all residential lands in New York City. We use diverse data sources including the City's property database, time-series demographic and socio-economic data from the US Census, and land cover data from the University of Vermont's Spatial Analysis Lab (SAL). These data are analyzed using a multi-model inferential, spatial econometrics approach. We also examine the distribution of vegetation within distinct market categories using Claritas' Potential Rating Index for Zipcode Markets (PRIZM™) database. These categories can be disaggregated, corresponding to the four social theories. We compare the econometric and categorical results for validation. Models associated with ecology of prestige theory are more effective for predicting the distribution of vegetation. This suggests that private, residential patterns of vegetation, reflecting the consumption of environmentally relevant goods and services, are associated with different lifestyles and lifestages. Further, our spatial and temporal analyses suggest that there are significant spatial and temporal dependencies that have theoretical and methodological implications for understanding urban ecological systems. These findings may have policy implications. Decision makers may need to consider how to most effectively reach different social groups in terms of messages and messengers in order to advance land management practices and achieve urban sustainability.

Rainfall as a trigger for stratification and winter phytoplankton growth in temperate shelf seas

NASA Astrophysics Data System (ADS)

Jardine, Jenny; Palmer, Matthew; Mahaffey, Claire; Holt, Jason; Mellor, Adam; Wakelin, Sarah

2017-04-01

We present new data from ocean gliders to investigate physical controls on stratification and phytoplankton dynamics, collected in the Celtic Sea between November 2014 and August 2015 as part of the UK Shelf Sea Biogeochemistry programme. This presentation focuses on the winter period (Jan-March) when the diurnal heating cycle results in regular but weak near surface stratification followed by night-time convection. Despite low light conditions, this daily cycle often promotes a daytime increase in observed chlorophyll fluorescence, indicative of phytoplankton growth. This daily cycle is occasionally interrupted when buoyancy inputs are sufficient to outcompete night-time convection and result in short-term periods of sustained winter stratification, typically lasting 2-3 days. Sustained stratification often coincides with periods of heavy rainfall, suggesting freshwater input from precipitation may play a role on these events by producing a subtle yet significant freshening of the surface layer of the order of 0.005 PSU. Comparing rainfall estimates with observed salinity changes confirms rainfall to often be the initiator of these winter stratification periods. As winter winds subside and solar heating increases towards spring, the water column becomes more susceptible to periods of halo-stratification, such that heavy rainfall during the winter-spring transition is likely to promote sustained stratification. The timing and extent of a heavy rainfall event in March 2015 does suggest it may be the critical trigger for shelf-wide stratification that eventually instigates the spring bloom. We propose that the timing of these downpours relative to the daily heating cycle can be a triggering mechanism for both short term and seasonal stratification in shelf seas, and so play a critical role in winter and early spring phytoplankton growth and the shelf sea carbon cycle. We further test the importance of this process using historical data, and results from the NEMO-AMM7 model to test how rainfall events have affected previous winter and spring conditions.

Observations of a tidal intrusion front in a tidal channel

NASA Astrophysics Data System (ADS)

Lu, Shasha; Xia, Xiaoming; Thompson, Charlie E. L.; Cao, Zhenyi; Liu, Yifei

2017-11-01

A visible front indicated by a surface colour change, and sometimes associated with foam or debris lines, was observed in a tidal channel during neap tide. This is an example of a tidal intrusion front occurring in the absence of sudden topographical changes or reversing flows, typically reported to be associated with such fronts. Detailed Acoustic Doppler Current Profiler and conductivity/temperature/depth measurements were taken on repeated transects both with fronts apparent and with fronts absent. The results indicated that the front occurred as a result of stratification, which was sustained by the buoyancy flux and the weak tide-induced mixing during neap ebb tide. The stronger tide-induced mixing during spring tide restrained stratification, leading to the absence of a front. The mechanism of the frontogenesis was the density gradient between the stratified water formed during neap ebb tide, and the more mixed seawater during neap flood tide; thus, the water on the landward (southwestern) side of the front was stratified, and that on the seaward side (northeastern) of the front was vertically well mixed. Gradient Richardson number estimates suggest that the flow between the stratified and mixed water was near the threshold 0.25 for shear instability. Meanwhile, the density gradient would provide an initial baroclinic contribution to velocity convergence, which is indicated by the accumulation of buoyant matter such as foam, grass, and debris into a sharply defined line along the surface. The front migrates with the flood current, with a local maximum towards the eastern side of the channel, leading to an asymmetrical shape with the eastern side of the front driven further into the Tiaozhoumen tidal channel.

Estimating Volume, Biomass, and Carbon in Hedmark County, Norway Using a Profiling LiDAR

NASA Technical Reports Server (NTRS)

Nelson, Ross; Naesset, Erik; Gobakken, T.; Gregoire, T.; Stahl, G.

2009-01-01

A profiling airborne LiDAR is used to estimate the forest resources of Hedmark County, Norway, a 27390 square kilometer area in southeastern Norway on the Swedish border. One hundred five profiling flight lines totaling 9166 km were flown over the entire county; east-west. The lines, spaced 3 km apart north-south, duplicate the systematic pattern of the Norwegian Forest Inventory (NFI) ground plot arrangement, enabling the profiler to transit 1290 circular, 250 square meter fixed-area NFI ground plots while collecting the systematic LiDAR sample. Seven hundred sixty-three plots of the 1290 plots were overflown within 17.8 m of plot center. Laser measurements of canopy height and crown density are extracted along fixed-length, 17.8 m segments closest to the center of the ground plot and related to basal area, timber volume and above- and belowground dry biomass. Linear, nonstratified equations that estimate ground-measured total aboveground dry biomass report an R(sup 2) = 0.63, with an regression RMSE = 35.2 t/ha. Nonstratified model results for the other biomass components, volume, and basal area are similar, with R(sup 2) values for all models ranging from 0.58 (belowground biomass, RMSE = 8.6 t/ha) to 0.63. Consistently, the most useful single profiling LiDAR variable is quadratic mean canopy height, h (sup bar)(sub qa). Two-variable models typically include h (sup bar)(sub qa) or mean canopy height, h(sup bar)(sub a), with a canopy density or a canopy height standard deviation measure. Stratification by productivity class did not improve the nonstratified models, nor did stratification by pine/spruce/hardwood. County-wide profiling LiDAR estimates are reported, by land cover type, and compared to NFI estimates.

Landscape selection by piping plovers has implications for measuring habitat and population size

USGS Publications Warehouse

Anteau, Michael J.; Shaffer, Terry L.; Wiltermuth, Mark T.; Sherfy, Mark H.

2014-01-01

How breeding birds distribute in relation to landscape-scale habitat features has important implications for conservation because those features may constrain habitat suitability. Furthermore, knowledge of these associations can help build models to improve area-wide demographic estimates or to develop a sampling stratification for research and monitoring. This is particularly important for rare species that have uneven distributions across vast areas, such as the federally listed piping plover (Charadrius melodus; hereafter plover). We examined how remotely-sensed landscape features influenced the distribution of breeding plover pairs among 2-km shoreline segments during 2006–2009 at Lake Sakakawea in North Dakota, USA. We found strong associations between remotely-sensed landscape features and plover abundance and distribution (R2 = 0.65). Plovers were nearly absent from segments with bluffs (>25 m elevation increase within 250 m of shoreline). Relative plover density (pairs/ha) was markedly greater on islands (4.84 ± 1.22 SE) than on mainlands (0.85 ± 0.17 SE). Pair numbers increased with abundance of nesting habitat (unvegetated-flat areas β^=0.28±0.08SE ). On islands, pair numbers also increased with the relative proportion of the total area that was habitat ( β^=3.27±0.46SE ). Our model could be adapted to estimate the breeding population of plovers or to make predictions that provide a basis for stratification and design of future surveys. Knowledge of landscape features, such as bluffs, that exclude use by birds refines habitat suitability and facilitates more accurate estimates of habitat and population abundance, by decreasing the size of the sampling universe. Furthermore, techniques demonstrated here are applicable to other vast areas where birds breed in sparse or uneven densities.

The seasonal cycle of the epipelagic mesozooplankton in the northern Gulf of Aqaba (Red Sea)

NASA Astrophysics Data System (ADS)

Cornils, A.; Schnack-Schiel, S. B.; Al-Najjar, T.; Badran, M. I.; Rasheed, M.; Manasreh, R.; Richter, C.

2007-11-01

The abundance and composition of the mesozooplankton were studied in the upper 100 m of the northern Gulf of Aqaba over a period of 22 months between February 2002 and December 2003. The samples were collected monthly with a Nansen net of 200 μm mesh size. The abundance of total mesozooplankton ranged between 245 and 3065 ind. m - 3 . Highest densities in 2002 were recorded in spring (March/April) and in autumn (October/November), while several peaks occurred in 2003 with maximum abundance in early summer (June/July). Copepods dominated the mesozooplankton community during the whole sampling period (mean 79%). Molluscs ranked secondly (8%), followed by appendicularians (2.5%) and chaetognaths (2.4%). All other taxa contributed only a small fraction of the total mesozooplankton population (0.3%). Within the copepods, calanoids were predominant throughout the sampling period (41-83%. mean 61%). Cyclopoid copepods accounted for 17 and 59% (mean 37%) while harpacticoids occurred only in very low numbers (less than 1%). Within the calanoid copepods, smaller sized taxa were abundant, belonging to the families of Clausocalanidae, Paracalanidae, Calocalanidae, Acartiidae and Mecynoceridae. Together they accounted for 84 to 98% of the calanoids. A performed cluster analysis revealed significant difference between the samples from January to May and those from June to December. Accordingly, the abundant calanoid copepod taxa could be divided into two groups: firstly, taxa with high abundance during the transition from winter-spring transition (onset of thermal stratification) and secondly, taxa with high densities during the disintegration of the stratification in autumn. The taxa of the second group showed a positive significant correlation to the annual cycle of temperature, indicating a strong relationship with seasonal changes in the hydrographic features of the Gulf of Aqaba.

Spectral models for early time SN 2011fe observations

NASA Astrophysics Data System (ADS)

Baron, E.; Hoeflich, P.; Friesen, Brian; Sullivan, M.; Hsiao, E.; Ellis, R. S.; Gal-Yam, A.; Howell, D. A.; Nugent, P. E.; Dominguez, I.; Krisciunas, K.; Phillips, M. M.; Suntzeff, N.; Wang, L.; Thomas, R. C.

2015-12-01

We use observed UV through near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae (SNe Ia) and to examine its individual peculiarities. As a benchmark, we use a delayed-detonation model with a progenitor metallicity of Z⊙/20. We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model with a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer ≈0.1 M⊙ than does the model. We discuss several explanations for the discrepancies. Finally, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. We do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum.

Fast Genome-Wide QTL Association Mapping on Pedigree and Population Data.

PubMed

Zhou, Hua; Blangero, John; Dyer, Thomas D; Chan, Kei-Hang K; Lange, Kenneth; Sobel, Eric M

2017-04-01

Since most analysis software for genome-wide association studies (GWAS) currently exploit only unrelated individuals, there is a need for efficient applications that can handle general pedigree data or mixtures of both population and pedigree data. Even datasets thought to consist of only unrelated individuals may include cryptic relationships that can lead to false positives if not discovered and controlled for. In addition, family designs possess compelling advantages. They are better equipped to detect rare variants, control for population stratification, and facilitate the study of parent-of-origin effects. Pedigrees selected for extreme trait values often segregate a single gene with strong effect. Finally, many pedigrees are available as an important legacy from the era of linkage analysis. Unfortunately, pedigree likelihoods are notoriously hard to compute. In this paper, we reexamine the computational bottlenecks and implement ultra-fast pedigree-based GWAS analysis. Kinship coefficients can either be based on explicitly provided pedigrees or automatically estimated from dense markers. Our strategy (a) works for random sample data, pedigree data, or a mix of both; (b) entails no loss of power; (c) allows for any number of covariate adjustments, including correction for population stratification; (d) allows for testing SNPs under additive, dominant, and recessive models; and (e) accommodates both univariate and multivariate quantitative traits. On a typical personal computer (six CPU cores at 2.67 GHz), analyzing a univariate HDL (high-density lipoprotein) trait from the San Antonio Family Heart Study (935,392 SNPs on 1,388 individuals in 124 pedigrees) takes less than 2 min and 1.5 GB of memory. Complete multivariate QTL analysis of the three time-points of the longitudinal HDL multivariate trait takes less than 5 min and 1.5 GB of memory. The algorithm is implemented as the Ped-GWAS Analysis (Option 29) in the Mendel statistical genetics package, which is freely available for Macintosh, Linux, and Windows platforms from http://genetics.ucla.edu/software/mendel. © 2016 WILEY PERIODICALS, INC.

Effect of gravitational stratification on the propagation of a CME

NASA Astrophysics Data System (ADS)

Pagano, P.; Mackay, D. H.; Poedts, S.

2013-12-01

Context. Coronal mass ejections (CMEs) are the most violent phenomenon found on the Sun. One model that explains their occurrence is the flux rope ejection model. A magnetic flux rope is ejected from the solar corona and reaches the interplanetary space where it interacts with the pre-existing magnetic fields and plasma. Both gravity and the stratification of the corona affect the early evolution of the flux rope. Aims: Our aim is to study the role of gravitational stratification on the propagation of CMEs. In particular, we assess how it influences the speed and shape of CMEs and under what conditions the flux rope ejection becomes a CME or when it is quenched. Methods: We ran a set of MHD simulations that adopt an eruptive initial magnetic configuration that has already been shown to be suitable for a flux rope ejection. We varied the temperature of the backgroud corona and the intensity of the initial magnetic field to tune the gravitational stratification and the amount of ejected magnetic flux. We used an automatic technique to track the expansion and the propagation of the magnetic flux rope in the MHD simulations. From the analysis of the parameter space, we evaluate the role of gravitational stratification on the CME speed and expansion. Results: Our study shows that gravitational stratification plays a significant role in determining whether the flux rope ejection will turn into a full CME or whether the magnetic flux rope will stop in the corona. The CME speed is affected by the background corona where it travels faster when the corona is colder and when the initial magnetic field is more intense. The fastest CME we reproduce in our parameter space travels at ~850 km s-1. Moreover, the background gravitational stratification plays a role in the side expansion of the CME, and we find that when the background temperature is higher, the resulting shape of the CME is flattened more. Conclusions: Our study shows that although the initiation mechanisms of the CME are purely magnetic, the background coronal plasma plays a key role in the CME propagation, and full MHD models should be applied when one focuses especially on the production of a CME from a flux rope ejection. Movies are available in electronic form at http://www.aanda.org

The use of an aeration system to prevent thermal stratification of a freshwater impoundment and its effect on downstream fish assemblages.

PubMed

Miles, N G; West, R J

2011-03-01

Warm-water riverine fish assemblages were investigated downstream of an impoundment before and after thermal stratification and the associated cold-water pollution was prevented using an aeration system. Temperatures below the dam significantly increased after installation of the aeration system and this correlated with an increased abundance and greater number of species downstream. Overall, aeration appeared to be beneficial for both the lake (upstream) and the downstream riverine environments. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

Influence of thermal stratification and slip conditions on stagnation point flow towards variable thicked Riga plate

NASA Astrophysics Data System (ADS)

Anjum, A.; Mir, N. A.; Farooq, M.; Khan, M. Ijaz; Hayat, T.

2018-06-01

This article addresses thermally stratified stagnation point flow of viscous fluid induced by a non-linear variable thicked Riga plate. Velocity and thermal slip effects are incorporated to disclose the flow analysis. Solar thermal radiation phenomenon is implemented to address the characteristics of heat transfer. Variations of different physical parameters on the horizontal velocity and temperature distributions are described through graphs. Graphical interpretations of skin friction coefficient (drag force at the surface) and Nusselt number (rate of heat transfer) are also addressed. Modified Hartman number and thermal stratification parameter result in reduction of temperature distribution.

FOCIS: A forest classification and inventory system using LANDSAT and digital terrain data

NASA Technical Reports Server (NTRS)

Strahler, A. H.; Franklin, J.; Woodcook, C. E.; Logan, T. L.

1981-01-01

Accurate, cost-effective stratification of forest vegetation and timber inventory is the primary goal of a Forest Classification and Inventory System (FOCIS). Conventional timber stratification using photointerpretation can be time-consuming, costly, and inconsistent from analyst to analyst. FOCIS was designed to overcome these problems by using machine processing techniques to extract and process tonal, textural, and terrain information from registered LANDSAT multispectral and digital terrain data. Comparison of samples from timber strata identified by conventional procedures showed that both have about the same potential to reduce the variance of timber volume estimates over simple random sampling.

A new stratification of mourning dove call-count routes

USGS Publications Warehouse

Blankenship, L.H.; Humphrey, A.B.; MacDonald, D.

1971-01-01

The mourning dove (Zenaidura macroura) call-count survey is a nationwide audio-census of breeding mourning doves. Recent analyses of the call-count routes have utilized a stratification based upon physiographic regions of the United States. An analysis of 5 years of call-count data, based upon stratification using potential natural vegetation, has demonstrated that this uew stratification results in strata with greater homogeneity than the physiographic strata, provides lower error variance, and hence generates greatet precision in the analysis without an increase in call-count routes. Error variance was reduced approximately 30 percent for the contiguous United States. This indicates that future analysis based upon the new stratification will result in an increased ability to detect significant year-to-year changes.

System Validation Experiments for Obtaining Tracer Laser-Induced Fluorescence Data at Elevated Pressure and Temperature.

PubMed

Hartwig, Jason; Mittal, Gaurav; Kumar, Kamal; Sung, Chih-Jen

2018-04-01

This paper presents a set of system validation experiments that can be used to qualify either static or flow experimental systems for gathering tracer photophysical data or conducting laser diagnostics at high pressure and temperature in order to establish design and operation limits and reduce uncertainty in data interpretation. Tests demonstrated here quantify the effect of tracer absorption at the test cell walls, stratification, photolysis, pyrolysis, adequacy of mixing and seeding, and reabsorption of laser light using acetone as the tracer and 282 nm excitation. Results show that acetone exhibits a 10% decrease in fluorescence signal over 36 000 shots at 127.4 mJ/cm 2 , and photolysis is negligible below 1000 shots collected. Meanwhile, appropriately chosen gas residence times can mitigate risks due to pyrolysis and inadequate mixing and seeding; for the current work 100 ms residence time ensured <0.5% alteration of tracer number density due to thermal destruction. Experimental results here are compared to theoretical values from the literature.

Liquid-Gas-Like Phase Transition in Sand Flow Under Microgravity

NASA Astrophysics Data System (ADS)

Huang, Yu; Zhu, Chongqiang; Xiang, Xiang; Mao, Wuwei

2015-06-01

In previous studies of granular flow, it has been found that gravity plays a compacting role, causing convection and stratification by density. However, there is a lack of research and analysis of the characteristics of different particles' motion under normal gravity contrary to microgravity. In this paper, we conduct model experiments on sand flow using a model test system based on a drop tower under microgravity, within which the characteristics and development processes of granular flow under microgravity are captured by high-speed cameras. The configurations of granular flow are simulated using a modified MPS (moving particle simulation), which is a mesh-free, pure Lagrangian method. Moreover, liquid-gas-like phase transitions in the sand flow under microgravity, including the transitions to "escaped", "jumping", and "scattered" particles are highlighted, and their effects on the weakening of shear resistance, enhancement of fluidization, and changes in particle-wall and particle-particle contact mode are analyzed. This study could help explain the surface geology evolution of small solar bodies and elucidate the nature of granular interaction.

How-to-Do-It: A Practical Method for Teaching Seed Stratification.

ERIC Educational Resources Information Center

Englert, Karen M.; Shontz, Nancy N.

1989-01-01

Described is a laboratory procedure for teaching seed stratification. Materials, methods, results, and applicability of the experiment are explained. Diagrams showing the percent of total germination as a function of stratification time and the germination rate of stratified seeds are included. (RT)

Educational Stratification in Russia during the Soviet Period.

ERIC Educational Resources Information Center

Gerber, Theodore P.; Hout, Michael

1995-01-01

Maintains that, in spite of state efforts to reduce educational inequities, stratification actually increased during the Soviet period. Removing gender preferences for men corrected some inequity. However, parents' education, occupation, and geographical origin contributed to the stratification. Contains a concise history of Soviet educational…

BAYESIAN BICLUSTERING FOR PATIENT STRATIFICATION.

PubMed

Khakabimamaghani, Sahand; Ester, Martin

2016-01-01

The move from Empirical Medicine towards Personalized Medicine has attracted attention to Stratified Medicine (SM). Some methods are provided in the literature for patient stratification, which is the central task of SM, however, there are still significant open issues. First, it is still unclear if integrating different datatypes will help in detecting disease subtypes more accurately, and, if not, which datatype(s) are most useful for this task. Second, it is not clear how we can compare different methods of patient stratification. Third, as most of the proposed stratification methods are deterministic, there is a need for investigating the potential benefits of applying probabilistic methods. To address these issues, we introduce a novel integrative Bayesian biclustering method, called B2PS, for patient stratification and propose methods for evaluating the results. Our experimental results demonstrate the superiority of B2PS over a popular state-of-the-art method and the benefits of Bayesian approaches. Our results agree with the intuition that transcriptomic data forms a better basis for patient stratification than genomic data.

Implementing system-wide risk stratification approaches: A review of critical success and failure factors.

PubMed

Huckel Schneider, Carmen; Gillespie, James A; Wilson, Andrew

2017-05-01

Risk stratification has become a widely used tool for linking people identified at risk of health deterioration to the most appropriate evidence-based care. This article systematically reviews recent literature to determine key factors that have been identified as critical enablers and/or barriers to successful implementation of risk stratification tools at a system level. A systematic search found 23 articles and four promising protocols for inclusion in the review, covering the use to 20 different risk stratification tools. These articles reported on only a small fraction of the risk stratification tools used in health systems; suggesting that while the development and statistical validation of risk stratification algorithms is widely reported, there has been little published evaluation of how they are implemented in real-world settings. Controlled studies provided some evidence that the use of risk stratification tools in combination with a care management plan offer patient benefits and that the use of a risk stratification tool to determine components of a care management plan may contribute to reductions in hospital readmissions, patient satisfaction and improved patient outcomes. Studies with the strongest focus on implementation used qualitative and case study methods. Among these, the literature converged on four key areas of implementation that were found to be critical for overcoming barriers to success: the engagement of clinicians and safeguarding equity, both of which address barriers of acceptance; the health system context to address administrative, political and system design barriers; and data management and integration to address logistical barriers.

Mechanisms of double stratification and magnetic field in flow of third grade fluid over a slendering stretching surface with variable thermal conductivity

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Qayyum, Sajid; Alsaedi, Ahmed; Ahmad, Bashir

2018-03-01

This article addresses the magnetohydrodynamic (MHD) stagnation point flow of third grade fluid towards a nonlinear stretching sheet. Energy expression is based through involvement of variable thermal conductivity. Heat and mass transfer aspects are described within the frame of double stratification effects. Boundary layer partial differential systems are deduced. Governing systems are then converted into ordinary differential systems by invoking appropriate variables. The transformed expressions are solved through homotopic technique. Impact of embedded variables on velocity, thermal and concentration fields are displayed and argued. Numerical computations are presented to obtain the results of skin friction coefficient and local Nusselt and Sherwood numbers. It is revealed that larger values of magnetic parameter reduces the velocity field while reverse situation is noticed due to wall thickness variable. Temperature field and local Nusselt number are quite reverse for heat generation/absorption parameter. Moreover qualitative behaviors of concentration field and local Sherwood number are similar for solutal stratification parameter.

A Practical Risk Stratification Approach for Implementing a Primary Care Chronic Disease Management Program in an Underserved Community.

PubMed

Xu, Junjun; Williams-Livingston, Arletha; Gaglioti, Anne; McAllister, Calvin; Rust, George

2018-01-01

The use of value metrics is often dependent on payer-initiated health care management incentives. There is a need for practices to define and manage their own patient panels regardless of payer to participate effectively in population health management. A key step is to define a panel of primary care patients with high comorbidity profiles. Our sample included all patients seen in an urban academic family medicine clinic over a two-year period. The simplified risk stratification was built using internal electronic health record and billing system data based on ICD-9 codes. There were 347 patients classified as high-risk out of the 5,364 patient panel. Average age was 59 years (SD 15). Hypertension (90%), hyperlipidemia (62%), and depression (55%) were the most common conditions among high-risk patients. Simplified risk stratification provides a feasible option for our team to understand and respond to the nuances of population health in our underserved community.

Utility of the exercise electrocardiogram testing in sudden cardiac death risk stratification.

PubMed

Refaat, Marwan M; Hotait, Mostafa; Tseng, Zian H

2014-07-01

Sudden cardiac death (SCD) remains a major public health problem. Current established criteria identifying those at risk of sudden arrhythmic death, and likely to benefit from implantable cardioverter defibrillators (ICDs), are neither sensitive nor specific. Exercise electrocardiogram (ECG) testing was traditionally used for information concerning patients' symptoms, exercise capacity, cardiovascular function, myocardial ischemia detection, and hemodynamic responses during activity in patients with hypertrophic cardiomyopathy. We conducted a systematic review of MEDLINE on the utility of exercise ECG testing in SCD risk stratification. Exercise testing can unmask suspected primary electrical diseases in certain patients (catecholaminergic polymorphic ventricular tachycardia or concealed long QT syndrome) and can be effectively utilized to risk stratify patients at an increased (such as early repolarization syndrome and Brugada syndrome) or decreased risk of SCD, such as the loss of preexcitation on exercise testing in asymptomatic Wolff-Parkinson-White syndrome. Exercise ECG testing helps in SCD risk stratification in patients with and without arrhythmogenic hereditary syndromes. © 2014 Wiley Periodicals, Inc.

Tracking composition of microbial communities for simultaneous nitrification and denitrification in polyurethane foam.

PubMed

Chen, Yuan; Wang, Li; Ma, Fang; Yang, Ji-xian; Qiu, Shan

2014-01-01

The process of simultaneous nitrification and denitrification (SND) of immobilized microorganisms in polyurethane form is discussed. The effect of different positions within the polyurethane carrier on microbial community response for the SND process is investigated by a combination of denaturing gradient gel electrophoresis profiles of the 16S rRNA gene V3 region and scanning electron microscopy. Results show that polyurethane, which consists of a unique porous structure, is an ideal platform for biofilm stratification of aerobe, anaerobe and facultative microorganisms in regard to the SND process. The community structure diversity response to different positions was distinct. The distributions of various functional microbes, detected from the surface aerobic stratification to the interior anaerobic stratification of polyurethane, were mainly nitrifying and denitrifying bacteria. Meanwhile aerobic denitrifying bacteria such as Paracoccus sp., Agrobacterium rubi and Ochrobactrum sp. were also adhered to the interior and surface of polyurethane. The SND process occurring on polyurethane foam was carried out by two independent processes: nitrogen removal and aerobic denitrification.

Connections between centrifugal, stratorotational, and radiative instabilities in viscous Taylor-Couette flow

NASA Astrophysics Data System (ADS)

Leclercq, Colin; Nguyen, Florian; Kerswell, Rich R.

2016-10-01

The "Rayleigh line" μ =η2 , where μ =Ωo/Ωi and η =ri/ro are respectively the rotation and radius ratios between inner (subscript i ) and outer (subscript o ) cylinders, is regarded as marking the limit of centrifugal instability (CI) in unstratified inviscid Taylor-Couette flow, for both axisymmetric and nonaxisymmetric modes. Nonaxisymmetric stratorotational instability (SRI) is known to set in for anticyclonic rotation ratios beyond that line, i.e., η2<μ <1 for axially stably stratified Taylor-Couette flow, but the competition between CI and SRI in the range μ <η2 has not yet been addressed. In this paper, we establish continuous connections between the two instabilities at finite Reynolds number Re, as previously suggested by Le Bars and Le Gal [Phys. Rev. Lett. 99, 064502 (2007), 10.1103/PhysRevLett.99.064502], making them indistinguishable at onset. Both instabilities are also continuously connected to the radiative instability at finite Re. These results demonstrate the complex impact viscosity has on the linear stability properties of this flow. Several other qualitative differences with inviscid theory were found, among which are the instability of a nonaxisymmetric mode localized at the outer cylinder without stratification and the instability of a mode propagating against the inner cylinder rotation with stratification. The combination of viscosity and stratification can also lead to a "collision" between (axisymmetric) Taylor vortex branches, causing the axisymmetric oscillatory state already observed in past experiments. Perhaps more surprising is the instability of a centrifugal-like helical mode beyond the Rayleigh line, caused by the joint effects of stratification and viscosity. The threshold μ =η2 seems to remain, however, an impassable instability limit for axisymmetric modes, regardless of stratification, viscosity, and even disturbance amplitude.

Final Report for The Creation of a Physics-based Ground-effect Model, Phase 2 - Inclusion of the Effects of Wind, Stratification, and Shear into the New Ground Effect Model

NASA Technical Reports Server (NTRS)

Sarpkaya, Turgut

2006-01-01

The reduction of the separation of the leading and following aircrafts is desirable to enhance the airport capacity provided that there is a physics-based operational model applicable to all regions of the flight domain (out of ground effect, OGE; near ground effect, NGE; and in ground effect, IGE) and that the quality of the quantitative input from the measurements of the prevailing atmospheric conditions and the quality of the total airport operations regarding the safety and the sound interpretation of the prevailing conditions match the quality of the analysis and numerical simulations. In the absence of an analytical solution, the physics of the flow is best expressed by a mathematical model based on numerical simulations, field and laboratory experiments, and heuristic reasoning. This report deals with the creation of a sound physics-based real-time IGE model of the aircraft wake vortices subjected to crosswind, stratification and shear.

Evaluation of a Stratified National Breast Screening Program in the United Kingdom: An Early Model-Based Cost-Effectiveness Analysis.

PubMed

Gray, Ewan; Donten, Anna; Karssemeijer, Nico; van Gils, Carla; Evans, D Gareth; Astley, Sue; Payne, Katherine

2017-09-01

To identify the incremental costs and consequences of stratified national breast screening programs (stratified NBSPs) and drivers of relative cost-effectiveness. A decision-analytic model (discrete event simulation) was conceptualized to represent four stratified NBSPs (risk 1, risk 2, masking [supplemental screening for women with higher breast density], and masking and risk 1) compared with the current UK NBSP and no screening. The model assumed a lifetime horizon, the health service perspective to identify costs (£, 2015), and measured consequences in quality-adjusted life-years (QALYs). Multiple data sources were used: systematic reviews of effectiveness and utility, published studies reporting costs, and cohort studies embedded in existing NBSPs. Model parameter uncertainty was assessed using probabilistic sensitivity analysis and one-way sensitivity analysis. The base-case analysis, supported by probabilistic sensitivity analysis, suggested that the risk stratified NBSPs (risk 1 and risk-2) were relatively cost-effective when compared with the current UK NBSP, with incremental cost-effectiveness ratios of £16,689 per QALY and £23,924 per QALY, respectively. Stratified NBSP including masking approaches (supplemental screening for women with higher breast density) was not a cost-effective alternative, with incremental cost-effectiveness ratios of £212,947 per QALY (masking) and £75,254 per QALY (risk 1 and masking). When compared with no screening, all stratified NBSPs could be considered cost-effective. Key drivers of cost-effectiveness were discount rate, natural history model parameters, mammographic sensitivity, and biopsy rates for recalled cases. A key assumption was that the risk model used in the stratification process was perfectly calibrated to the population. This early model-based cost-effectiveness analysis provides indicative evidence for decision makers to understand the key drivers of costs and QALYs for exemplar stratified NBSP. Copyright © 2017 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.

Education and Social Stratification Processes in Comparative Perspective.

ERIC Educational Resources Information Center

Kerckhoff, Alan C.

2001-01-01

Discusses three characteristics of educational systems that have been used to explain social stratification processes: stratification, standardization, and vocational specificity. Describes how these characteristics affect the movement of students through school and into the labor force in France, Germany, Great Britain, and the United States.…

A numerical study of thermal stratification due to transient natural convection in densified liquid propellant tanks

NASA Astrophysics Data System (ADS)

Manalo, Lawrence B.

A comprehensive, non-equilibrium, two-domain (liquid and vapor), physics based, mathematical model is developed to investigate the onset and growth of the natural circulation and thermal stratification inside cryogenic propellant storage tanks due to heat transfer from the surroundings. A two-dimensional (planar) model is incorporated for the liquid domain while a lumped, thermodynamic model is utilized for the vapor domain. The mathematical model in the liquid domain consists of the conservation of mass, momentum, and energy equations and incorporates the Boussinesq approximation (constant fluid density except in the buoyancy term of the momentum equation). In addition, the vapor is assumed to behave like an ideal gas with uniform thermodynamic properties. Furthermore, the time-dependent nature of the heat leaks from the surroundings to the propellant (due to imperfect tank insulation) is considered. Also, heterogeneous nucleation, although not significant in the temperature range of study, has been included. The transport of mass and energy between the liquid and vapor domains leads to transient ullage vapor temperatures and pressures. (The latter of which affects the saturation temperature of the liquid at the liquid-vapor interface.) This coupling between the two domains is accomplished through an energy balance (based on a micro-layer concept) at the interface. The resulting governing, non-linear, partial differential equations (which include a Poisson's equation for determining the pressure distribution) in the liquid domain are solved by an implicit, finite-differencing technique utilizing a non-uniform (stretched) mesh (in both directions) for predicting the velocity and temperature fields. (The accuracy of the numerical scheme is validated by comparing the model's results to a benchmark numerical case as well as to available experimental data.) The mass, temperature, and pressure of the vapor is determined by using a simple explicit finite-differencing technique. With the model at hand, the effects of variable fluid transport/thermo-physical properties, levels of initial sub-cooling, operating pressure, and initial liquid aspect ratio on the natural circulation patterns and thermal stratification are numerically investigated. Liquid oxygen (LOx) is the primary working fluid in the study. However, a simulation with liquid nitrogen (LN2) as the propellant is also carried out for comparison purposes.

Resonant tidal excitation of oscillation modes in merging binary neutron stars: Inertial-gravity modes

NASA Astrophysics Data System (ADS)

Xu, Wenrui; Lai, Dong

2017-10-01

In coalescing neutron star (NS) binaries, tidal force can resonantly excite low-frequency (≲500 Hz ) oscillation modes in the NS, transferring energy between the orbit and the NS. This resonant tide can induce phase shift in the gravitational waveforms, and potentially provide a new window of studying NS interior using gravitational waves. Previous works have considered tidal excitations of pure g-modes (due to stable stratification of the star) and pure inertial modes (due to Coriolis force), with the rotational effect treated in an approximate manner. However, for realistic NSs, the buoyancy and rotational effects can be comparable, giving rise to mixed inertial-gravity modes. We develop a nonperturbative numerical spectral code to compute the frequencies and tidal coupling coefficients of these modes. We then calculate the phase shift in the gravitational waveform due to each resonance during binary inspiral. Given the uncertainties in the NS equation of state and stratification property, we adopt polytropic NS models with a parametrized stratification. We derive relevant scaling relations and survey how the phase shift depends on various properties of the NS. We find that for canonical NSs (with mass M =1.4 M⊙ and radius R =10 km ) and modest rotation rates (≲300 Hz ), the gravitational wave phase shift due to a resonance is generally less than 0.01 radian. But the phase shift is a strong function of R and M , and can reach a radian or more for low-mass NSs with larger radii (R ≳15 km ). Significant phase shift can also be produced when the combination of stratification and rotation gives rise to a very low frequency (≲20 Hz in the inertial frame) modified g-mode. As a by-product of our precise calculation of oscillation modes in rotating NSs, we find that some inertial modes can be strongly affected by stratification; we also find that the m =1 r -mode, previously identified to have a small but finite inertial-frame frequency based on the Cowling approximation, in fact has essentially zero frequency, and therefore cannot be excited during the inspiral phase of NS binaries.

Observations of turbulence in a partially stratified estuary

USGS Publications Warehouse

Stagey, M.T.; Monismith, Stephen G.; Burau, J.R.

1999-01-01

The authors present a field study of estuarine turbulence in which profiles of Reynolds stresses were directly measured using an ADCP throughout a 25-h tidal day. The dataset that is discussed quantifies turbulent mixing for a water column in northern San Francisco Bay that experiences a sequence of states that includes a weak ebb and flood that are stratified, followed by a strong, and eventually unstratified, ebb and flood. These measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification. Examination of individual Reynolds stress profiles along with profiles of Richardson number and turbulent Froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects. Using the measured turbulence production rate P, the dissipation rate e. is estimated. The observed turbulence had values of e/vN2 > 20 all of the time and e/vN2 > 200 most of the time, suggesting that the observed motions were buoyancy affected turbulence rather than internal waves. However, at times, turbulent Froude numbers in much of the upper-water column were less than one, indicating important stratification effects. Taken as a whole, the data show that stratification affects the turbulent velocity variance q2 most severely; that is, observed reductions in u'w' are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes. Finally, the dataset is compared to predictions made using the popular Mellor-Yamada level 2.5 closure. These comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions. The length scale does not appear to compensate for these errors, and, as a result, similar errors are seen in the eddy viscosity predictions. It is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self-transport from the near-bed region to the overlying stratification. ?? 1999 American Meteorological Society.

Forest inventory and stratified estimation: a cautionary note

Treesearch

John Coulston

2008-01-01

The Forest Inventory and Analysis (FIA) Program uses stratified estimation techniques to produce estimates of forest attributes. Stratification must be unbiased and stratification procedures should be examined to identify any potential bias. This note explains simple techniques for identifying potential bias, discriminating between sample bias and stratification bias,...

Cardiac risk stratification in cardiac rehabilitation programs: a review of protocols

PubMed Central

da Silva, Anne Kastelianne França; Barbosa, Marianne Penachini da Costa de Rezende; Bernardo, Aline Fernanda Barbosa; Vanderlei, Franciele Marques; Pacagnelli, Francis Lopes; Vanderlei, Luiz Carlos Marques

2014-01-01

Objective Gather and describe general characteristics of different protocols of risk stratification for cardiac patients undergoing exercise. Methods We conducted searches in LILACS, IBECS, MEDLINE, Cochrane Library, and SciELO electronic databases, using the following descriptors: Cardiovascular Disease, Rehabilitation Centers, Practice Guideline, Exercise and Risk Stratification in the past 20 years. Results Were selected eight studies addressing methods of risk stratification in patients undergoing exercise. Conclusion None of the methods described could cover every situation the patient can be subjected to; however, they are essential to exercise prescription. PMID:25140477

Breakup of last glacial deep stratification in the South Pacific

NASA Astrophysics Data System (ADS)

Basak, Chandranath; Fröllje, Henning; Lamy, Frank; Gersonde, Rainer; Benz, Verena; Anderson, Robert F.; Molina-Kescher, Mario; Pahnke, Katharina

2018-02-01

Stratification of the deep Southern Ocean during the Last Glacial Maximum is thought to have facilitated carbon storage and subsequent release during the deglaciation as stratification broke down, contributing to atmospheric CO2 rise. Here, we present neodymium isotope evidence from deep to abyssal waters in the South Pacific that confirms stratification of the deepwater column during the Last Glacial Maximum. The results indicate a glacial northward expansion of Ross Sea Bottom Water and a Southern Hemisphere climate trigger for the deglacial breakup of deep stratification. It highlights the important role of abyssal waters in sustaining a deep glacial carbon reservoir and Southern Hemisphere climate change as a prerequisite for the destabilization of the water column and hence the deglacial release of sequestered CO2 through upwelling.

Design of an efficient electrolyte circulation system for the lead-acid battery

NASA Astrophysics Data System (ADS)

Thuerk, D.

The design and operation of an electrolyte circulation system are described. Application of lead acid batteries to electric vehicle and other repetitive deep cycle services produces a nondesirable state in the battery cells, electrolyte stratification. This stratification is the result of acid and water generation at the electrodes during cycling. With continued cycling, the extent of the stratification increases and prevents complete charging with low percentages of overcharge. Ultimately this results in extremely short life for the battery system. The stratification problem was overcome by substantially overcharging the battery. This abusive overcharge produces gassing rates sufficient to mix the electrolyte during the end portion of the charge. Overcharge, even though it is required to eliminate stratification, produces the undesirable results related to high voltage and gassing rates.

Patient characteristics and stratification in medical treatment studies for metastatic colorectal cancer: a proposal for standardization of patient characteristic reporting and stratification.

PubMed

Sorbye, H; Köhne, C-H; Sargent, D J; Glimelius, B

2007-10-01

Prognostic factors have the potential to determine the survival of patients to a greater extent than current antineoplastic agents. Despite this knowledge, there is no consensus on, first, what patient characteristics to report and, second, what stratification factors to use in metastatic colorectal cancer trials. Seven leading oncology and medical journals were reviewed for phase II and III publications reporting on medical treatment of metastatic colorectal cancer patients during 2001-2005. One hundred and forty-three studies with 21 214 patients were identified. The reporting of patient characteristics and use of stratification was noted. Age, gender, performance status, metastases location, sites and adjuvant chemotherapy were often reported (99-63%). Laboratory values as alkaline phosphatase, lactate dehydrogenase and white blood cell count, repeatedly found to be of prognostic relevance, were rarely reported (5-9%). Stratification was used in all phase III trials; however, only study centre was used with any consistency. There is considerable inconsistency in the reporting of patient characteristics and use of stratification factors in metastatic colorectal cancer trials. We propose a standardization of patient characteristics reporting and stratification factors. A common set of characteristics and strata will aid in trial reporting, interpretation and future meta-analyses.

Factors Influencing the Clinical Stratification of Suitability to Drive after Stroke: A Qualitative Study.

PubMed

Stapleton, Tadhg; Connolly, Deirdre; O'Neill, Desmond

2015-01-01

While a clinical pre-selection screening process for a stroke patient's suitability for driving has been acknowledged, little is known about the factors or processes influencing this screening typically conducted by clinicians practicing at a generalist level. This study explored this clinical stratification process through the use of semi-structured interviews with senior occupational therapists (n = 17) and stroke physicians (n = 7) using qualitative description methodology. The findings revealed a trichotomy stratification of stroke patients for driving in the clinical setting; those who are fit to drive, unfit to drive, and a "maybe" group who need more detailed assessment and observation. Factors that had a major influence on this clinical-based stratification of driving suitability were client's levels of awareness, insight, and impulsivity. A period of prolonged contact with the client was preferential to guide the stratification decision in order for clinicians to build a comprehensive picture of the person. A mix of assessment approaches including standardized assessment but with increased emphasis on naturalistic observation of functional performance underpinned the clinical stratification process. This study uncovers some of the factors and processes influencing the early clinical-based stratification of driving suitability after stroke, and highlights the contribution of the generalist practitioner in the assessment of fitness to drive continuum.

TASS Model Application for Testing the TDWAP Model

NASA Technical Reports Server (NTRS)

Switzer, George F.

2009-01-01

One of the operational modes of the Terminal Area Simulation System (TASS) model simulates the three-dimensional interaction of wake vortices within turbulent domains in the presence of thermal stratification. The model allows the investigation of turbulence and stratification on vortex transport and decay. The model simulations for this work all assumed fully-periodic boundary conditions to remove the effects from any surface interaction. During the Base Period of this contract, NWRA completed generation of these datasets but only presented analysis for the neutral stratification runs of that set (Task 3.4.1). Phase 1 work began with the analysis of the remaining stratification datasets, and in the analysis we discovered discrepancies with the vortex time to link predictions. This finding necessitated investigating the source of the anomaly, and we found a problem with the background turbulence. Using the most up to date version TASS with some important defect fixes, we regenerated a larger turbulence domain, and verified the vortex time to link with a few cases before proceeding to regenerate the entire 25 case set (Task 3.4.2). The effort of Phase 2 (Task 3.4.3) concentrated on analysis of several scenarios investigating the effects of closely spaced aircraft. The objective was to quantify the minimum aircraft separations necessary to avoid vortex interactions between neighboring aircraft. The results consist of spreadsheets of wake data and presentation figures prepared for NASA technical exchanges. For these formation cases, NASA carried out the actual TASS simulations and NWRA performed the analysis of the results by making animations, line plots, and other presentation figures. This report contains the description of the work performed during this final phase of the contract, the analysis procedures adopted, and sample plots of the results from the analysis performed.

Combining abdominal and cosmetic breast surgery does not increase short-term complication rates: a comparison of each individual procedure and pretreatment risk stratification tool.

PubMed

Khavanin, Nima; Jordan, Sumanas W; Vieira, Brittany L; Hume, Keith M; Mlodinow, Alexei S; Simmons, Christopher J; Murphy, Robert X; Gutowski, Karol A; Kim, John Y S

2015-11-01

Combined abdominal and breast surgery presents a convenient and relatively cost-effective approach for accomplishing both procedures. This study is the largest to date assessing the safety of combined procedures, and it aims to develop a simple pretreatment risk stratification method for patients who desire a combined procedure. All women undergoing abdominoplasty, panniculectomy, augmentation mammaplasty, and/or mastopexy in the TOPS database were identified. Demographics and outcomes for combined procedures were compared to individual procedures using χ(2) and Student's t-tests. Multiple logistic regression provided adjusted odds ratios for the effect of a combined procedure on 30-day complications. Among combined procedures, a logistic regression model determined point values for pretreatment risk factors including diabetes (1 point), age over 53 (1), obesity (2), and 3+ ASA status (3), creating a 7-point pretreatment risk stratification tool. A total of 58,756 cases met inclusion criteria. Complication rates among combined procedures (9.40%) were greater than those of aesthetic breast surgery (2.66%; P < .001) but did not significantly differ from abdominal procedures (9.75%; P = .530). Nearly 77% of combined cases were classified as low-risk (0 points total) with a 9.78% complication rates. Medium-risk patients (1 to 3 points) had a 16.63% complication rate, and high-risk (4 to 7 points) 38.46%. Combining abdominal and breast procedures is safe in the majority of patients and does not increase 30-day complications rates. The risk stratification tool can continue to ensure favorable outcomes for patients who may desire a combined surgery. 4 Risk. © 2015 The American Society for Aesthetic Plastic Surgery, Inc. Reprints and permission: journals.permissions@oup.com.

Creation of residual flows in a partially stratified estuary

USGS Publications Warehouse

Stacey, M.T.; Burau, J.R.; Monismith, Stephen G.

2001-01-01

The creation of residual flows in estuaries is examined using acoustic Doppler current profiler data sets from northern San Francisco Bay. The data sets are analyzed using principal component analysis to examine the temporal variability of the flows which create the residual circulation. It is seen that in this periodically and partially stratified estuary the residual flows are created through a series of pulses with strong variability at the 24-hour timescale, through the interaction of shear, stratification and mixing. This interaction is captured through the use of a dimensionless number, the horizontal Richardson number (Rix), which is developed to examine the local balance between the stratifying and destratifying forces at the tidal timescale. It is seen that Rix is a valuable parameter in predicting the onset of the residual-creating events, with a threshold value of ??? 3 on ebb tides. This critical value is argued to be a threshold, above which the stratification and shear flow create a feedback effect, each further intensifying the other. This feedback results in a highly variable exchange flow which creates the estuarine residual in intermittent pulses rather than as a steady flow. Although typically attributed to baroclinic forcing, an argument is made that these pulses of residual-creating exchange flow could be created by barotropic forcing in the presence of variable stratification which is asymmetric between flood and ebb tides. This result poses a great challenge for turbulence modeling, as the timing and magnitude of stratification and shear must be correctly simulated on the tidal timescale in order to reproduce the effects seen in the data sets presented. Copyright 2001 by the American Geophysical Union.

Electrophysiologic profile and results of invasive risk stratification in asymptomatic children and adolescents with the Wolff-Parkinson-White electrocardiographic pattern.

PubMed

Kubuš, Peter; Vít, Pavel; Gebauer, Roman A; Materna, Ondřej; Janoušek, Jan

2014-04-01

Data on the results and clinical effect of an invasive risk stratification strategy in asymptomatic young patients with the Wolff-Parkinson-White electrocardiographic pattern are scarce. Eighty-five consecutive patients aged<18 years with a Wolff-Parkinson-White pattern and persistent preexcitation at maximum exercise undergoing invasive risk stratification were retrospectively studied. Adverse accessory pathway (AP) properties were defined according to currently consented criteria as any of the following: shortest preexcited RR interval during atrial fibrillation/rapid atrial pacing≤250 ms (or antegrade effective refractory period≤250 ms if shortest preexcited RR interval was not available) or inducible atrioventricular re-entrant tachycardia. Age at evaluation was median 14.9 years. Eighty-two patients had a structurally normal heart and 3 had hypertrophic cardiomyopathy. A single manifest AP was present in 80, 1 manifest and 1 concealed AP in 4, and 2 manifest APs in 1 patient. Adverse AP properties were present in 32 of 85 patients (37.6%) at baseline and in additional 16 of 44 (36.4%) after isoproterenol. Ablation was performed in 41 of these 48 patients. Ablation was deferred in the remaining 7 for pathway proximity to the atrioventricular node. In addition, 18 of the low-risk patients were ablated based on patient/parental decision. Adverse AP properties at baseline were exhibited by 37.6% of the evaluated patients with an asymptomatic Wolff-Parkinson-White preexcitation persisting at peak exercise. Isoproterenol challenge yielded additional 36.4% of those tested at higher risk. Ablation was performed in a total of 69.4% of patients subjected to invasive risk stratification.

Ocean science. Enhanced: internal tides and ocean mixing.

PubMed

Garrett, Chris

2003-09-26

Recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features, a substantial amount of energy is transferred from the main ocean tides into "internal tides." In his Perspective, Garrett explains how these internal waves with tidal periods propagate through the density-stratified deep ocean and eventually break down into turbulence. The resulting mixing affects ocean stratification and ocean circulation. It thus influences climate as well as biological production. The energy for the internal tides is derived from the rotational energy of the Earth-Moon system changes of the length of the day and the distance to the Moon.

Seed dormancy and germination changes of snowbed species under climate warming: the role of pre- and post-dispersal temperatures

PubMed Central

Bernareggi, Giulietta; Carbognani, Michele; Mondoni, Andrea; Petraglia, Alessandro

2016-01-01

Background and Aims Climate warming has major impacts on seed germination of several alpine species, hence on their regeneration capacity. Most studies have investigated the effects of warming after seed dispersal, and little is known about the effects a warmer parental environment may have on germination and dormancy of the seed progeny. Nevertheless, temperatures during seed development and maturation could alter the state of dormancy, affecting the timing of emergence and seedling survival. Here, the interplay between pre- and post-dispersal temperatures driving seed dormancy release and germination requirements of alpine plants were investigated. Methods Three plant species inhabiting alpine snowbeds were exposed to an artificial warming treatment (i.e. +1·5 K) and to natural conditions in the field. Seeds produced were exposed to six different periods of cold stratification (0, 2, 4, 8, 12 and 20 weeks at 0 °C), followed by four incubation temperatures (5, 10, 15 and 20 °C) for germination testing. Key Results A warmer parental environment produced either no or a significant increase in germination, depending on the duration of cold stratification, incubation temperatures and their interaction. In contrast, the speed of germination was less sensitive to changes in the parental environment. Moreover, the effects of warming appeared to be linked to the level of (physiological) seed dormancy, with deeper dormant species showing major changes in response to incubation temperatures and less dormant species in response to cold stratification periods. Conclusions Plants developed under warmer climates will produce seeds with changed germination responses to temperature and/or cold stratification, but the extent of these changes across species could be driven by seed dormancy traits. Transgenerational plastic adjustments of seed germination and dormancy shown here may result from increased seed viability, reduced primary and secondary dormancy state, or both, and may play a crucial role in future plant adaptation to climate change. PMID:27390354

Stratified flows in complex terrain

NASA Astrophysics Data System (ADS)

Retallack, Charles

The focus of this dissertation is the study of stratified atmospheric flows in the presence of complex terrain. Two large-scale field study campaigns were carried out, each with a focus on a specific archetypal terrain. Each field study involved the utilization of remote and in-situ atmospheric monitoring devices to collect experimental data. The first of the two field studies focused on pollution transport mechanisms near an escarpment. The analysis aimed to determine the combined effect of the escarpment and ambient density stratification on the flow and aerosol pollution transport. It was found that under specific atmospheric conditions, the escarpment prompted the channeling, down-mixing, and trapping of aerosol pollutant plumes. The objective of the second field campaign was the study of stratified flows in a mountain valley. Analysis revealed that buoyancy driven katabatic currents originating on the surrounding valley slopes created a scenario in which a down-slope gravity current transitioned into an intrusive gravity current. The intrusive gravity current propagated near the interface of a density stratified lower ambient layer and a non-stratified upper ambient layer. A combination of shallow water theory and energy arguments is used to produce a model for the propagation of a gravity current moving along the interface of a homogeneous ambient layer and a linearly stratified layer. It is found that the gravity current propagating entirely within the homogeneous layer travels at the greatest speed. As the relative density of the gravity current is increased, the gravity current begins to slump below the interface of the two layers and the propagation speed decreases.

Ultrasound follow-up of infantile hypertrophic pyloric stenosis (IHPS) during conservative therapy: ultrasound findings as criteria for diagnosis and cure.

PubMed

Miura, Sachiko; Haku, Eijitsu; Hirai, Toshiko; Marugami, Nagaaki; Itoh, Takahiro; Tanaka, Takehiro; Kichikawa, Kimihiko; Ohishi, Hajime

2008-06-01

During conservative therapy of infantile hypertrophic pyloric stenosis (IHPS) with atropine sulfate, there are many patients who do not achieve normal values of pyloric wall thickness and canal length even though they are clinically cured (vomiting has ceased); an objective criterion for cure has not yet been established. The aim of this study was to examine whether the appearance of pyloric wall stratification can be used as a criterion for cure. Twenty infants with IHPS who were treated conservatively were enrolled. Two of them ultimately required surgery. Ultrasound examinations were done serially and the pyloric wall thickness and canal length were measured. The echogenicity of the pyloric wall and the presence of wall stratification were noted. On admission, all infants satisfied the ultrasound criteria for IHPS and had a heterogeneous pyloric wall without stratification. With conservative therapy, symptoms disappeared, the pyloric wall thickness and the canal length gradually decreased, the echogenicity gradually became homogeneous and hypoechoic, and wall stratification appeared (in most cases before the pyloric wall thickness and the canal length had normalized). The absence of wall stratification suggests that cellular interstitial changes, such as edema or inflammation, are present in the pyloric wall in the acute stage. Pyloric wall stratification was absent during the acute stage, but it appeared after initiation of treatment but before the pyloric wall thickness and the canal length had normalized. The presence of pyloric wall stratification can be used as a criterion for cure; the absence of wall stratification can be added to ultrasound diagnostic criteria for IHPS.

On Stratification in Changing Higher Education: The "Analysis of Status" Revisited

ERIC Educational Resources Information Center

Bloch, Roland; Mitterle, Alexander

2017-01-01

This article seeks to shed light on current dynamics of stratification in changing higher education and proposes an analytical perspective to account for these dynamics based on Martin Trow's work on "the analysis of status." In research on higher education, the term "stratification" is generally understood as a metaphor that…

IGF-I and mammographic density in four geographic locations: a pooled analysis.

PubMed

Maskarinec, Gertraud; Takata, Yumie; Chen, Zhao; Gram, Inger Torhild; Nagata, Chisato; Pagano, Ian; Hayashi, Kentaro; Arendell, Leslie; Skeie, Guri; Rinaldi, Sabina; Kaaks, Rudolph

2007-10-15

Insulin-like growth factor (IGF-I) and prolactin have been found to be associated with breast cancer risk and with mammographic density. In a pooled analysis from 4 geographic locations, we investigated the association of percent mammographic density with serum levels of IGF-I, IGFBP-3 and prolactin. The pooled data set included 1,327 pre- and postmenopausal women: Caucasians from Norway, Arizona and Hawaii, Japanese from Hawaii and Japan, Latina from Arizona, and Native Hawaiians from Hawaii. Serum samples were assayed for IGF-I, IGFBP-3 and prolactin levels using ELISA assays. Mammographic density was quantified using a computer-assisted density method. After stratification by menopausal status, multiple regression models estimated the relation between serum analytes and breast density. All serum analytes except prolactin among postmenopausal women differed significantly by location/ethnicity group. Among premenopausal subjects, IGF-I levels and the molar ratio were highest in Hawaii, intermediate in Japan and lowest in Arizona. For IGFBP-3, the order was reversed. Among postmenopausal subjects, Norwegian women had the highest IGF-I levels and women in Arizona had the lowest while women in Japan and Hawaii had intermediate levels. We observed no significant relation between percent density and IGF-I or prolactin levels among pre-and postmenopausal women. The significant differences in IGF-I levels by location but not ethnicity suggest that environmental factors influence IGF-I levels, whereas percent breast density varies more according to ethnic background than by location. Based on this analysis, the influence of circulating levels of IGF-I, IGFBP-3, and prolactin on percent density appears to be very small. (c) 2007 Wiley-Liss, Inc.

Preablation 131-I scans with SPECT/CT contribute to thyroid cancer risk stratification and 131-I therapy planning.

PubMed

Avram, Anca M; Esfandiari, Nazanene H; Wong, Ka Kit

2015-05-01

The use of preablation diagnostic radioiodine scans for risk stratification and radioiodine therapy planning for differentiated thyroid cancer (DTC) remains controversial. The objective was to assess the contribution of preablation diagnostic 131-I scans with SPECT/CT (Dx 131-I scan) to (1) the risk stratification and (2) the postoperative management of DTC. The study was designed as a prospective sequential patient series. The study was conducted at a University hospital. Three hundred twenty patients (pts) with DTC (219F; 101M, mean age 47.3 ± 16.4 y, range 10-90) were studied. Using clinical and histopathology information an endocrinologist performed risk stratification and determined postoperative management with respect to radioiodine therapy (RAI) planning. The decision to withhold or to administer RAI, and the recommended low, medium or high therapeutic 131-I activity were recorded. Dx 131-I scans were performed and interpreted by two nuclear medicine physicians as showing thyroid remnant, cervical nodal, or distant metastases. The endocrinologist then reperformed risk stratification and reformulated management after consideration of Dx 131-I scans and stimulated thyroglobulin (Tg) information. Main outcome measures were changes in risk stratification and management after Dx 131-I scans. Detection of unsuspected nodal and distant metastases and elevated stimulated Tg levels resulted in a change in the estimated risk of recurrence in 15% of patients, and management in 31% of patients, as compared to initial risk stratification and management based on histopathology alone. Both imaging data and stimulated thyroglobulin levels acquired at the time of Dx 131-I scans are consequential for 131-I therapy planning, providing information that changes risk stratification in 15% of patients as compared to recurrence risk estimation based on histopathology alone. Dx 131-I scans contribute to risk stratification by defining residual nodal and distant metastatic disease, changing clinical management in 29.4% of patients.

Social stratification, classroom climate, and the behavioral adaptation of kindergarten children.

PubMed

Boyce, W Thomas; Obradovic, Jelena; Bush, Nicole R; Stamperdahl, Juliet; Kim, Young Shin; Adler, Nancy

2012-10-16

Socioeconomic status (SES) is the single most potent determinant of health within human populations, from infancy through old age. Although the social stratification of health is nearly universal, there is persistent uncertainty regarding the dimensions of SES that effect such inequalities and thus little clarity about the principles of intervention by which inequalities might be abated. Guided by animal models of hierarchical organization and the health correlates of subordination, this prospective study examined the partitioning of children's adaptive behavioral development by their positions within kindergarten classroom hierarchies. A sample of 338 5-y-old children was recruited from 29 Berkeley, California public school classrooms. A naturalistic observational measure of social position, parent-reported family SES, and child-reported classroom climate were used in estimating multilevel, random-effects models of children's adaptive behavior at the end of the kindergarten year. Children occupying subordinate positions had significantly more maladaptive behavioral outcomes than their dominant peers. Further, interaction terms revealed that low family SES and female sex magnified, and teachers' child-centered pedagogical practices diminished, the adverse influences of social subordination. Taken together, results suggest that, even within early childhood groups, social stratification is associated with a partitioning of adaptive behavioral outcomes and that the character of larger societal and school structures in which such groups are nested can moderate rank-behavior associations.

The bio-optical properties of CDOM as descriptor of lake stratification.

PubMed

Bracchini, Luca; Dattilo, Arduino Massimo; Hull, Vincent; Loiselle, Steven Arthur; Martini, Silvia; Rossi, Claudio; Santinelli, Chiara; Seritti, Alfredo

2006-11-01

Multivariate statistical techniques are used to demonstrate the fundamental role of CDOM optical properties in the description of water masses during the summer stratification of a deep lake. PC1 was linked with dissolved species and PC2 with suspended particles. In the first principal component that the role of CDOM bio-optical properties give a better description of the stratification of the Salto Lake with respect to temperature. The proposed multivariate approach can be used for the analysis of different stratified aquatic ecosystems in relation to interaction between bio-optical properties and stratification of the water body.

Effect of Interfacial Turbulence and Accommodation Coefficient on CFD Predictions of Pressurization and Pressure Control in Cryogenic Storage Tank

NASA Technical Reports Server (NTRS)

Kassemi, Mohammad; Kartuzova, Olga; Hylton, Sonya

2015-01-01

Laminar models agree closely with the pressure evolution and vapor phase temperature stratification but under-predict liquid temperatures. Turbulent SST k-w and k-e models under-predict the pressurization rate and extent of stratification in the vapor but represent liquid temperature distributions fairly well. These conclusions seem to equally apply to large cryogenic tank simulations as well as small scale simulant fluid pressurization cases. Appropriate turbulent models that represent both interfacial and bulk vapor phase turbulence with greater fidelity are needed. Application of LES models to the tank pressurization problem can serve as a starting point.

A High-Resolution, Three-Dimensional Model of Jupiter's Great Red Spot

NASA Technical Reports Server (NTRS)

Cho, James Y.-K.; delaTorreJuarez, Manuel; Ingersoll, Andrew P.; Dritschel, David G.

2001-01-01

The turbulent flow at the periphery of the Great Red Spot (GRS) contains many fine-scale filamentary structures, while the more quiescent core, bounded by a narrow high- velocity ring, exhibits organized, possibly counterrotating, motion. Past studies have neither been able to capture this complexity nor adequately study the effect of vertical stratification L(sub R)(zeta) on the GRS. We present results from a series of high-resolution, three-dimensional simulations that advect the dynamical tracer, potential vorticity. The detailed flow is successfully captured with a characteristic value of L(sub R) approx. equals 2000 km, independent of the precise vertical stratification profile.

Do predators influence the distribution of age-0 kokanee in a Colorado Reservoir?

USGS Publications Warehouse

Hardiman, J.M.; Johnson, B.M.; Martinez, P.J.

2004-01-01

Seasonal changes in reservoir conditions such as productivity, light, and temperature create spatiotemporal variation in habitat that may segregate or aggregate predators and prey, producing implications for the distribution, growth, and survival of fishes. We used hydroacoustics to document the diel vertical distribution of age-0 kokanee Oncorhynchus nerka relative to environmental gradients at Blue Mesa Reservoir, Colorado, during May-August of 2002. Temperature, light, and zooplankton density profiles were examined relative to foraging conditions for kokanee and their primary predator, lake trout Salvelinus namaycush. Age-0 kokanee displayed large diel vertical migrations in May despite the lack of an energetic advantage before reservoir stratification. Age-0 kokanee minimized near-surface foraging at this time, perhaps to avoid predation by visual predators, such as lake trout, in the well-lit surface waters. Strong reservoir stratification in midsummer appeared to provide a thermal refuge from lake trout that the kokanee exploited. By August vertical migrations were shallow and most kokanee remained in the epilimnion throughout the day. Although the energetic implications of the late-summer strategy are unclear, it appears that kokanee were responding to changes in their predator environment. A robust model for kokanee diel vertical migration across a range of systems should include a predator avoidance component.

Vertical and temporal dynamics of cyanobacteria in the Carpina potable water reservoir in northeastern Brazil.

PubMed

Moura, A N; Dantas, E W; Oliveira, H S B; Bittencourt-Oliveira, M C

2011-05-01

This study analysed vertical and temporal variations of cyanobacteria in a potable water supply in northeastern Brazil. Samples were collected from four reservoir depths in the four months; September and December 2007; and March and June 2008. The water samples for the determination of nutrients and cyanobacteria were collected using a horizontal van Dorn bottle. The samples were preserved in 4% formaldehyde for taxonomic analysis using an optical microscope, and water aliquots were preserved in acetic Lugol solution for determination of density using an inverted microscope. High water temperatures, alkaline pH, low transparency, high phosphorous content and limited nitrogen content were found throughout the study. Dissolved oxygen stratification occurred throughout the study period whereas temperature stratification occurred in all sampling months, with the exception of June. No significant vertical differences were recorded for turbidity or total and dissolved forms of nutrients. There were high levels of biomass arising from Planktothrix agardhii, Cylindrospermopsis raciborskii, Geitlerinema amphibium and Pseudanabaena catenata. The study demonstrates that, in a tropical eutrophic environment with high temperatures throughout the water column, perennial multi-species cyanobacterial blooms, formed by species capable of regulating their position in the water column (those that have gas vesicles for buoyancy), are dominant in the photic and aphotic strata.

How Global Academic Stratification Affects Local Academies: The Inflated Role of Knowledge Reception in the Philosophy Discipline in Modern Japan

ERIC Educational Resources Information Center

Chew, Matthew M.

2008-01-01

Sociologists of knowledge find that academic stratification is present among individual scholars, genders, networks, fields, and all kinds of scientific organizations, while communications scholars have been studying global cultural asymmetry for a long time. Yet few researchers have explored the global dimension of academic stratification. In…

Optimized endogenous post-stratification in forest inventories

Treesearch

Paul L. Patterson

2012-01-01

An example of endogenous post-stratification is the use of remote sensing data with a sample of ground data to build a logistic regression model to predict the probability that a plot is forested and using the predicted probabilities to form categories for post-stratification. An optimized endogenous post-stratified estimator of the proportion of forest has been...

Strategies for Primary Prevention of Coronary Heart Disease Based on Risk Stratification by the ACC/AHA Lipid Guidelines, ATP III Guidelines, Coronary Calcium Scoring, and C-Reactive Protein, and a Global Treat-All Strategy: A Comparative--Effectiveness Modeling Study

PubMed Central

Galper, Benjamin Z.; Wang, Y. Claire; Einstein, Andrew J.

2015-01-01

Background Several approaches have been proposed for risk-stratification and primary prevention of coronary heart disease (CHD), but their comparative and cost-effectiveness is unknown. Methods We constructed a state-transition microsimulation model to compare multiple approaches to the primary prevention of CHD in a simulated cohort of men aged 45–75 and women 55–75. Risk-stratification strategies included the 2013 American College of Cardiology/American Heart Association (ACC/AHA) guidelines on the treatment of blood cholesterol, the Adult Treatment Panel (ATP) III guidelines, and approaches based on coronary artery calcium (CAC) scoring and C-reactive protein (CRP). Additionally we assessed a treat-all strategy in which all individuals were prescribed either moderate-dose or high-dose statins and all males received low-dose aspirin. Outcome measures included CHD events, costs, medication-related side effects, radiation-attributable cancers, and quality-adjusted-life-years (QALYs) over a 30-year timeframe. Results Treat-all with high-dose statins dominated all other strategies for both men and women, gaining 15.7 million QALYs, preventing 7.3 million myocardial infarctions, and saving over $238 billion, compared to the status quo, far outweighing its associated adverse events including bleeding, hepatitis, myopathy, and new-onset diabetes. ACC/AHA guidelines were more cost-effective than ATP III guidelines for both men and women despite placing 8.7 million more people on statins. For women at low CHD risk, treat-all with high-dose statins was more likely to cause a statin-related adverse event than to prevent a CHD event. Conclusions Despite leading to a greater proportion of the population placed on statin therapy, the ACC/AHA guidelines are more cost-effective than ATP III. Even so, at generic prices, treating all men and women with statins and all men with low-dose aspirin appears to be more cost-effective than all risk-stratification approaches for the primary prevention of CHD. Especially for low-CHD risk women, decisions on the appropriate primary prevention strategy should be based on shared decision making between patients and healthcare providers. PMID:26422204

The role of thermal stratification in tidal exchange at the mouth of San Diego Bay

USGS Publications Warehouse

Chadwick, D. B.; Largier, J. L.; Cheng, R.T.; Aubrey, D.G.; Friedrichs, C.T.; Aubrey, D.G.; Friedrichs, C.T.

1996-01-01

We have examined, from an observational viewpoint, the role of thermal stratification in the tidal exchange process at the mouth of San Diego Bay. In this region, we found that both horizontal and vertical exchange processes appear to be active. The vertical exchange in this case was apparently due to the temperature difference between the'bay water and ocean water. We found that the structure of the outflow and the nature of the tidal exchange process both appear to be influenced by thermal stratification. The tidal outflow was found to lift-off tan the bottom during the initial and later stages of the ebb flow when barotropic forcing was weak. During the peak ebb flow, the mouth section was flooded, and the outflow extended to the bottom. As the ebb flow weakened, a period of two-way exchange occurred, with the surface layer flowing seaward, and the deep layer flowing into the bay. The structure of the tidal-residual flow and the residual transport of a measured tracer were strongly influenced by this vertical exchange. Exchange appeared to occur laterally as well, in a manner consistent with the tidal-pumping mechanism described by Stommel and Farmer [1952]. Tidal cycle variations in shear and stratification were characterized by strong vertical shear and breakdown of stratification during the ebb, and weak vertical shear and build-up of stratification on the flood. Evaluation of multiple tidal-cycles from time-series records of flow and temperature indicated that the vertical variations of the flow and stratification observed during the cross-sectional measurements are a general phenomenon during the summer. Together, these observations suggest that thermal stratification can play an important role in regulating the tidal exchange of low-inflow estuaries.

Simultaneous observations of F2 layer stratification and spread F at postmidnight over a northern equatorial anomaly region

NASA Astrophysics Data System (ADS)

Jiang, Chunhua; Yang, Guobin; Deng, Chi; Zhou, Chen; Zhu, Peng; Yokoyama, Tatsuhiro; Song, Huan; Lan, Ting; Ni, Binbin; Zhao, Zhengyu; Zhang, Yuannong

2015-12-01

Simultaneous observations of F2 layer stratification and spread F at postmidnight (00:00 LT to 05:00 LT) were carried out on 22, 23, and 28 November 2013, using ionosondes distributed over a northern equatorial anomaly region at three specific locations, i.e., Puer (PUR, 22.7°N, 101.05°E, dip latitude 12.9°N), Chiang Mai (CMU, 18.8°N, 98.9°E, dip latitude 9.04°N), and Chumphon (CPN, 10.7°N, 99.4°E, dip latitude 0.93°N). The results show that both the PUR and CMU stations observed the F2 layer stratification at postmidnight in the Northern Hemisphere, frequently accompanied with gravity waves (the periods~30-100 min). It is reported that F2 layer stratification at postmidnight can be observed in the Northern Hemisphere for the first time. It is suggested that the thermospheric neutral wind triggered by gravity waves strongly contribute to the altitude dependence of the combined vertical plasma velocity, which consequently poses significant impacts on the occurrence of the low-latitude F2 layer stratification at postmidnight. In addition, the spread F other than F2 layer stratification was observed at the CPN station located at the geomagnetic equator, suggesting that smaller geomagnetic inclination tend to inhibit the postmidnight F2 layer stratification in the equatorial region. Furthermore, on 23 November 2013 a good correlation was identified between the F2 layer stratification at PUR and the spread F at both CMU and CPN, possibly due to that the large-scale gravity waves originating at middle latitudes contribute to the nighttime spread F observed in the low-latitude and equatorial regions.

Breakup of last glacial deep stratification in the South Pacific.

PubMed

Basak, Chandranath; Fröllje, Henning; Lamy, Frank; Gersonde, Rainer; Benz, Verena; Anderson, Robert F; Molina-Kescher, Mario; Pahnke, Katharina

2018-02-23

Stratification of the deep Southern Ocean during the Last Glacial Maximum is thought to have facilitated carbon storage and subsequent release during the deglaciation as stratification broke down, contributing to atmospheric CO 2 rise. Here, we present neodymium isotope evidence from deep to abyssal waters in the South Pacific that confirms stratification of the deepwater column during the Last Glacial Maximum. The results indicate a glacial northward expansion of Ross Sea Bottom Water and a Southern Hemisphere climate trigger for the deglacial breakup of deep stratification. It highlights the important role of abyssal waters in sustaining a deep glacial carbon reservoir and Southern Hemisphere climate change as a prerequisite for the destabilization of the water column and hence the deglacial release of sequestered CO 2 through upwelling. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Contrasting Drainage and Stratification in Horizontal Vs Vertical Micellar Foam Films

NASA Astrophysics Data System (ADS)

Wojcik, Ewelina; Yilixiati, Subinuer; Zhang, Yiran; Sharma, Vivek

Understanding and controlling the drainage kinetics of thin films is an important problem that underlies the stability, lifetime and rheology of foams and emulsions. In foam films formed with micellar solutions, the surfactant is present as interfacially-adsorbed layer at both liquid-air interfaces, as well as in bulk as self-assembled supramolecular structures called micelles. Ultrathin micellar films exhibit stratification due to confinement-induced structuring and layering of micelles. Stratification in micellar foam films is manifested as stepwise thinning over time, and it leads to the coexistence of flat domains with discretely different thicknesses. In this contribution we use Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols to visualize and analyze thickness transitions and variations associated with stratification in micellar foam films made with sodium dodecyl sulfate (SDS). We contrast the drainage and stratification dynamics in horizontal and vertical foam films, and investigate the role played by gravitational, viscous, interfacial and surface forces.

Steady state RANS simulations of temperature fluctuations in single phase turbulent mixing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kickhofel, J.; Fokken, J.; Kapulla, R.

2012-07-01

Single phase turbulent mixing in nuclear power plant circuits where a strong temperature gradient is present is known to precipitate pipe failure due to thermal fatigue. Experiments in a square mixing channel offer the opportunity to study the phenomenon under simple and easily reproducible boundary conditions. Measurements of this kind have been performed extensively at the Paul Scherrer Inst. in Switzerland with a high density of instrumentation in the Generic Mixing Experiment (GEMIX). As a fundamental mixing phenomena study closely related to the thermal fatigue problem, the experimental results from GEMIX are valuable for the validation of CFD codes strivingmore » to accurately simulate both the temperature and velocity fields in single phase turbulent mixing. In the experiments two iso-kinetic streams meet at a shallow angle of 3 degrees and mix in a straight channel of square cross-section under various degrees of density, temperature, and viscosity stratification over a range of Reynolds numbers ranging from 5*10{sup 3} to 1*10{sup 5}. Conductivity measurements, using wire-mesh and wall sensors, as well as optical measurements, using particle image velocimetry, were conducted with high temporal and spatial resolutions (up to 2.5 kHz and 1 mm in the case of the wire mesh sensor) in the mixing zone, downstream of a splitter plate. The present paper communicates the results of RANS modeling of selected GEMIX tests. Steady-state CFD calculations using a RANS turbulence model represent an inexpensive method for analyzing large and complex components in commercial nuclear reactors, such as the downcomer and reactor pressure vessel heads. Crucial to real world applicability, however, is the ability to model turbulent heat fluctuations in the flow; the Turbulent Heat Flux Transport model developed by ANSYS CFX is capable, by implementation of a transport equation for turbulent heat fluxes, of readily modeling these values. Furthermore, the closure of the turbulent heat flux transport equation evokes a transport equation for the variance of the enthalpy. It is therefore possible to compare the modeled fluctuations of the liquid temperature directly with the scalar fluctuations recorded experimentally with the wire-mesh. Combined with a working Turbulent Heat Flux Transport model, complex mixing problems in large geometries could be better understood. We aim for the validation of Reynolds Stress based RANS simulations extended by the Turbulent Heat Flux Transport model by modeling the GEMIX experiments in detail. Numerical modeling has been performed using both BSL and SSG Reynolds Stress Models in a test matrix comprising experimental trials at the GEMIX facility. We expand on the turbulent mixing RANS CFD results of (Manera 2009) in a few ways. In the GEMIX facility we introduce density stratification in the flow while removing the characteristic large scale vorticity encountered in T-junctions and therefore find better conditions to check the diffusive conditions in the model. Furthermore, we study the performance of the model in a very different, simpler scalar fluctuation spectrum. The paper discusses the performance of the model regarding the dissipation of the turbulent kinetic energy and dissipation of the enthalpy variance. A novel element is the analyses of cases with density stratification. (authors)« less

Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuador.

PubMed

Douillet, Guilhem Amin; Pacheco, Daniel Alejandro; Kueppers, Ulrich; Letort, Jean; Tsang-Hin-Sun, Ève; Bustillos, Jorge; Hall, Minard; Ramón, Patricio; Dingwell, Donald B

A series of pyroclastic density currents were generated at Tungurahua volcano (Ecuador) during a period of heightened activity in August 2006. Dense pyroclastic flows were confined to valleys of the drainage network, while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross-stratified ash exposed on the surface. Here, the description, measurement, and classification of more than 300 dune bedforms are presented. Four types of dune bedforms are identified with respect to their shape, internal structure, and geometry (length, width, thickness, stoss and lee face angles, and stoss face length). (1) "Elongate dune bedforms" have smooth shapes and are longer (in the flow direction) than wide or thick. Internal stratification consists of stoss-constructional, thick lensoidal layers of massive and coarse-grained material, alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests. (2) "Transverse dune bedforms" show linear crests perpendicular to the flow direction, with equivalent lengths and widths. Internally, these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration. Steep truncations of the bedsets are visible on the stoss side only. (3) "Lunate dune bedforms" display a barchanoidal shape and have stratification patterns similar to those of the transverse ones. Finally, (4) "two-dimensional dune bedforms" are much wider than long, exhibit linear crests and are organized into trains. Elongate dune bedforms are found exclusively in proximal deposition zones. Transverse, lunate, and two-dimensional dune bedforms are found in distal ash bodies. The type of dune bedform developed varies spatially within an ash body, transverse dune bedforms occurring primarily at the onset of deposition zones, transitioning to lunate dune bedforms in intermediate zones, and two-dimensional dune bedforms exclusively on the lateral and distal edges of the deposits. The latter are also found where flows moved upslope. Elongate dune bedforms were deposited from flows with both granular-based and tractional flow boundaries that possessed high capacity and competence. They may have formed in a subcritical context by the blocking of material on the stoss side. We do not interpret them as antidune or "chute-and-pool" structures. The dimensions and cross-stratification patterns of transverse dune bedforms are interpreted as resulting from low competence currents with a significant deposition rate, but we rule out their interpretation as "antidunes". A similar conclusion holds for lunate dune bedforms, whose curved shape results from a sedimentation rate dependent on the thickness of the bedform. Finally, two-dimensional dune bedforms were formed where lateral transport exceeds longitudinal transport; i.e., in areas where currents were able to spread laterally in low velocity zones. We suggest that the aggrading ash bedsets with upstream crest migration were formed under subcritical flow conditions where the tractional bedload transport was less important than the simultaneous fallout from suspension. This produced differential draping with no further reworking. We propose the name "regressive climbing dunes" for structures produced by this process. A rapid decrease in current velocity, possibly triggered by hydraulic jumps affecting the entire parent flows, is inferred to explain their deposition. This process can in principle hold for any kind of particulate density current.

Bioconvective Plumes and Bacterial Self-Concentration at a Slanting Meniscus

NASA Astrophysics Data System (ADS)

Dombrowski, Christopher; Chatkaew, Sunita; Goldstein, Raymond; Kessler, John

2004-03-01

Aerobic bacteria, e.g. Bacillus subtilis, consume oxygen. For populations of ˜ 10^9 cells/cm^3, volume fraction ˜ 0.001, the resultant oxygen deficit results in the creation of an oxygen concentration gradient due to influx from air/fluid interfaces. The bacteria swim up that gradient. Since the cells are denser than water by ˜ 10%, the mean density of the supension increases proportionally to cell concentration, producing unstable stratification, sinking blobs, plumes and the like. This well known effect is constructively modified when the oxygen-supplying interface is not perpendicular to gravity. In that case, where there is no threshold to collective instability, the organisms near the interface descend along it, usually in the form of plumes. This phenomenon is somewhat analogous to the Boycott Effect in sedimentation, in which tilting the chamber walls results in large-scale flows. Data on such curved interfaces, achieved at corners, and with droplets of suspension, sessile and pendant, will be presented. The practical significance of the phenomenon is self-concentration of bacteria, in nature and in the laboratory. We shall also present insights derived from a mathematical model and computer simulations.

Average glandular dose in paired digital mammography and digital breast tomosynthesis acquisitions in a population based screening program: effects of measuring breast density, air kerma and beam quality

NASA Astrophysics Data System (ADS)

Helge Østerås, Bjørn; Skaane, Per; Gullien, Randi; Catrine Trægde Martinsen, Anne

2018-02-01

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra™). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra™. AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Air pollution and survival within the Washington University-EPRI veterans cohort: risks based on modeled estimates of ambient levels of hazardous and criteria air pollutants.

PubMed

Lipfert, Frederick W; Wyzga, Ronald E; Baty, Jack D; Miller, J Philip

2009-04-01

For this paper, we considered relationships between mortality, vehicular traffic density, and ambient levels of 12 hazardous air pollutants, elemental carbon (EC), oxides of nitrogen (NOx), sulfur dioxide (SO2), and sulfate (SO4(2-)). These pollutant species were selected as markers for specific types of emission sources, including vehicular traffic, coal combustion, smelters, and metal-working industries. Pollutant exposures were estimated using emissions inventories and atmospheric dispersion models. We analyzed associations between county ambient levels of these pollutants and survival patterns among approximately 70,000 U.S. male veterans by mortality period (1976-2001 and subsets), type of exposure model, and traffic density level. We found significant associations between all-cause mortality and traffic-related air quality indicators and with traffic density per se, with stronger associations for benzene, formaldehyde, diesel particulate, NOx, and EC. The maximum effect on mortality for all cohort subjects during the 26-yr follow-up period is approximately 10%, but most of the pollution-related deaths in this cohort occurred in the higher-traffic counties, where excess risks approach 20%. However, mortality associations with diesel particulates are similar in high- and low-traffic counties. Sensitivity analyses show risks decreasing slightly over time and minor differences between linear and logarithmic exposure models. Two-pollutant models show stronger risks associated with specific traffic-related pollutants than with traffic density per se, although traffic density retains statistical significance in most cases. We conclude that tailpipe emissions of both gases and particles are among the most significant and robust predictors of mortality in this cohort and that most of those associations have weakened over time. However, we have not evaluated possible contributions from road dust or traffic noise. Stratification by traffic density level suggests the presence of response thresholds, especially for gaseous pollutants. Because of their wider distributions of estimated exposures, risk estimates based on emissions and atmospheric dispersion models tend to be more precise than those based on local ambient measurements.

Average glandular dose in paired digital mammography and digital breast tomosynthesis acquisitions in a population based screening program: effects of measuring breast density, air kerma and beam quality.

PubMed

Østerås, Bjørn Helge; Skaane, Per; Gullien, Randi; Martinsen, Anne Catrine Trægde

2018-01-25

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra ™ ). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra ™ . AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Buried layers: On the origins, rise, and fall of stratification theories.

PubMed

Wieser, Martin

2018-02-01

This article presents a historical analysis of the origins, rise, and demise of theories of stratification ( Schichtentheorien ). Following their roots in the ancient metaphysical idea of the "great chain of being," Aristotle's scala naturae , the medieval "Jacob's ladder," and Leibniz's concept of the lex continua, I argue that theories of stratification represent the modern heir to the ancient cosmological idea of a harmonious, hierarchical, and unified universe. Theories of stratification reached their heyday during the interwar period within German academia, proliferating over a vast number of disciplines and rising to special prominence within personality psychology, feeding the hope for a unitary image of the world and of human beings, their biological and mental development, their social organization and cultural creations. This article focuses on the role of visuality as a distinct mode of scientific knowledge within theories of stratification as well as the cultural context that provided the fertile ground for their flowering in the Weimar Republic. Finally, the rapid demise of theories of stratification during the 1950s is discussed, and some reasons for their downfall during the second half of the 20th century are explored. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

A fast and cost-effective method for apolipoprotein E isotyping as an alternative to APOE genotyping for patient screening and stratification.

PubMed

Calero, Olga; García-Albert, Luis; Rodríguez-Martín, Andrés; Veiga, Sergio; Calero, Miguel

2018-04-13

Apolipoprotein E (apoE) is a 34 kDa glycoprotein involved in lipid metabolism. The human APOE gene encodes for three different apoE protein isoforms: E2, E3 and E4. The interest in apoE isoforms is high for epidemiological research, patient stratification and identification of those at increased risk for clinical trials and prevention. The isoform apoE4 is associated with increased risk for coronary heart and Alzheimer's diseases. This paper describes a method for specifically detecting the apoE4 isoform from biological fluids by taking advantage of the capacity of apoE to bind "specifically" to polystyrene surfaces as capture and a specific anti-apoE4 monoclonal antibody as reporter. Our results indicate that the apoE-polystyrene binding interaction is highly stable, resistant to detergents and acid and basic washes. The methodology here described is accurate, easily implementable, fast and cost-effective. Although at present, our technique is unable to discriminate homozygous APOE ε4/ε4 from APOE ε3/ε4 and ε2/ε4 heterozygous, it opens new avenues for the development of inexpensive, yet effective, tests for the detection of apoE4 for patients' stratification. Preliminary results indicated that this methodology is also adaptable into turbidimetric platforms, which make it a good candidate for clinical implementation through its translation to the clinical analysis routine.

Variants for HDL-C, LDL-C, and triglycerides identified from admixture mapping and fine-mapping analysis in African American families.

PubMed

Shetty, Priya B; Tang, Hua; Feng, Tao; Tayo, Bamidele; Morrison, Alanna C; Kardia, Sharon L R; Hanis, Craig L; Arnett, Donna K; Hunt, Steven C; Boerwinkle, Eric; Rao, Dabeeru C; Cooper, Richard S; Risch, Neil; Zhu, Xiaofeng

2015-02-01

Admixture mapping of lipids was followed-up by family-based association analysis to identify variants for cardiovascular disease in African Americans. The present study conducted admixture mapping analysis for total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides. The analysis was performed in 1905 unrelated African American subjects from the National Heart, Lung and Blood Institute's Family Blood Pressure Program (FBPP). Regions showing admixture evidence were followed-up with family-based association analysis in 3556 African American subjects from the FBPP. The admixture mapping and family-based association analyses were adjusted for age, age(2), sex, body mass index, and genome-wide mean ancestry to minimize the confounding caused by population stratification. Regions that were suggestive of local ancestry association evidence were found on chromosomes 7 (low-density lipoprotein cholesterol), 8 (high-density lipoprotein cholesterol), 14 (triglycerides), and 19 (total cholesterol and triglycerides). In the fine-mapping analysis, 52 939 single-nucleotide polymorphisms (SNPs) were tested and 11 SNPs (8 independent SNPs) showed nominal significant association with high-density lipoprotein cholesterol (2 SNPs), low-density lipoprotein cholesterol (4 SNPs), and triglycerides (5 SNPs). The family data were used in the fine-mapping to identify SNPs that showed novel associations with lipids and regions, including genes with known associations for cardiovascular disease. This study identified regions on chromosomes 7, 8, 14, and 19 and 11 SNPs from the fine-mapping analysis that were associated with high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and triglycerides for further studies of cardiovascular disease in African Americans. © 2014 American Heart Association, Inc.

Spectral models for early time SN 2011fe observations

DOE PAGES

Baron, E.; Hoeflich, P.; Friesen, Brian; ...

2015-10-13

We use observed UV through near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae (SNe Ia) and to examine its individual peculiarities. As a benchmark, we use a delayed-detonationmodel with a progenitormetallicity of Z ⊙/20. We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model withmore » a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer ≈0.1 M ⊙ than does the model. We discuss several explanations for the discrepancies. Lastly, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. Here we do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum.« less

Concordance of Commercial Data Sources for Neighborhood-Effects Studies

PubMed Central

Schootman, Mario

2010-01-01

Growing evidence supports a relationship between neighborhood-level characteristics and important health outcomes. One source of neighborhood data includes commercial databases integrated with geographic information systems to measure availability of certain types of businesses or destinations that may have either favorable or adverse effects on health outcomes; however, the quality of these data sources is generally unknown. This study assessed the concordance of two commercial databases for ascertaining the presence, locations, and characteristics of businesses. Businesses in the St. Louis, Missouri area were selected based on their four-digit Standard Industrial Classification (SIC) codes and classified into 14 business categories. Business listings in the two commercial databases were matched by standardized business name within specified distances. Concordance and coverage measures were calculated using capture–recapture methods for all businesses and by business type, with further stratification by census-tract-level population density, percent below poverty, and racial composition. For matched listings, distance between listings and agreement in four-digit SIC code, sales volume, and employee size were calculated. Overall, the percent agreement was 32% between the databases. Concordance and coverage estimates were lowest for health-care facilities and leisure/entertainment businesses; highest for popular walking destinations, eating places, and alcohol/tobacco establishments; and varied somewhat by population density. The mean distance (SD) between matched listings was 108.2 (179.0) m with varying levels of agreement in four-digit SIC (percent agreement = 84.6%), employee size (weighted kappa = 0.63), and sales volume (weighted kappa = 0.04). Researchers should cautiously interpret findings when using these commercial databases to yield measures of the neighborhood environment. PMID:20480397

The Relation Between Inflation in Type-I and Type-II Error Rate and Population Divergence in Genome-Wide Association Analysis of Multi-Ethnic Populations.

PubMed

Derks, E M; Zwinderman, A H; Gamazon, E R

2017-05-01

Population divergence impacts the degree of population stratification in Genome Wide Association Studies. We aim to: (i) investigate type-I error rate as a function of population divergence (F ST ) in multi-ethnic (admixed) populations; (ii) evaluate the statistical power and effect size estimates; and (iii) investigate the impact of population stratification on the results of gene-based analyses. Quantitative phenotypes were simulated. Type-I error rate was investigated for Single Nucleotide Polymorphisms (SNPs) with varying levels of F ST between the ancestral European and African populations. Type-II error rate was investigated for a SNP characterized by a high value of F ST . In all tests, genomic MDS components were included to correct for population stratification. Type-I and type-II error rate was adequately controlled in a population that included two distinct ethnic populations but not in admixed samples. Statistical power was reduced in the admixed samples. Gene-based tests showed no residual inflation in type-I error rate.

Example study for granular bioreactor stratification: Three-dimensional evaluation of a sulfate-reducing granular bioreactor

PubMed Central

Hao, Tian-wei; Luo, Jing-hai; Su, Kui-zu; Wei, Li; Mackey, Hamish R.; Chi, Kun; Chen, Guang-Hao

2016-01-01

Recently, sulfate-reducing granular sludge has been developed for application in sulfate-laden water and wastewater treatment. However, little is known about biomass stratification and its effects on the bioprocesses inside the granular bioreactor. A comprehensive investigation followed by a verification trial was therefore conducted in the present work. The investigation focused on the performance of each sludge layer, the internal hydrodynamics and microbial community structures along the height of the reactor. The reactor substratum (the section below baffle 1) was identified as the main acidification zone based on microbial analysis and reactor performance. Two baffle installations increased mixing intensity but at the same time introduced dead zones. Computational fluid dynamics simulation was employed to visualize the internal hydrodynamics. The 16S rRNA gene of the organisms further revealed that more diverse communities of sulfate-reducing bacteria (SRB) and acidogens were detected in the reactor substratum than in the superstratum (the section above baffle 1). The findings of this study shed light on biomass stratification in an SRB granular bioreactor to aid in the design and optimization of such reactors. PMID:27539264