On the Impact of Bootstrap in Stratified Random Sampling
LIU Cheng; ZHAO Lian-wen
2009-01-01
In general the accuracy of mean estimator can be improved by stratified random sampling. In this paper, we provide an idea different from empirical methods that the accuracy can be more improved through bootstrap resampling method under some conditions. The determination of sample size by bootstrap method is also discussed, and a simulation is made to verify the accuracy of the proposed method. The simulation results show that the sample size based on bootstrapping is smaller than that based on central limit theorem.
Investigation of spectral analysis techniques for randomly sampled velocimetry data
Sree, Dave
1993-01-01
It is well known that velocimetry (LV) generates individual realization velocity data that are randomly or unevenly sampled in time. Spectral analysis of such data to obtain the turbulence spectra, and hence turbulence scales information, requires special techniques. The 'slotting' technique of Mayo et al, also described by Roberts and Ajmani, and the 'Direct Transform' method of Gaster and Roberts are well known in the LV community. The slotting technique is faster than the direct transform method in computation. There are practical limitations, however, as to how a high frequency and accurate estimate can be made for a given mean sampling rate. These high frequency estimates are important in obtaining the microscale information of turbulence structure. It was found from previous studies that reliable spectral estimates can be made up to about the mean sampling frequency (mean data rate) or less. If the data were evenly samples, the frequency range would be half the sampling frequency (i.e. up to Nyquist frequency); otherwise, aliasing problem would occur. The mean data rate and the sample size (total number of points) basically limit the frequency range. Also, there are large variabilities or errors associated with the high frequency estimates from randomly sampled signals. Roberts and Ajmani proposed certain pre-filtering techniques to reduce these variabilities, but at the cost of low frequency estimates. The prefiltering acts as a high-pass filter. Further, Shapiro and Silverman showed theoretically that, for Poisson sampled signals, it is possible to obtain alias-free spectral estimates far beyond the mean sampling frequency. But the question is, how far? During his tenure under 1993 NASA-ASEE Summer Faculty Fellowship Program, the author investigated from his studies on the spectral analysis techniques for randomly sampled signals that the spectral estimates can be enhanced or improved up to about 4-5 times the mean sampling frequency by using a suitable
Lapeyrouse, L M; Morera, O; Heyman, J M C; Amaya, M A; Pingitore, N E; Balcazar, H
2012-04-01
Examination of border-specific characteristics such as trans-border mobility and transborder health service illuminates the heterogeneity of border Hispanics and may provide greater insight toward understanding differential health behaviors and status among these populations. In this study, we create a descriptive profile of the concept of trans-border mobility by exploring the relationship between mobility status and a series of demographic, economic and socio-cultural characteristics among mobile and non-mobile Hispanics living in the El Paso-Juarez border region. Using a two-stage stratified random sampling design, bilingual interviewers collected survey data from border residents (n = 1,002). Findings show that significant economic, cultural, and behavioral differences exist between mobile and non-mobile respondents. While non-mobile respondents were found to have higher social economic status than their mobile counterparts, mobility across the border was found to offer less acculturated and poorer Hispanics access to alternative sources of health care and other services.
Stratified source-sampling techniques for Monte Carlo eigenvalue analysis.
Mohamed, A.
1998-07-10
In 1995, at a conference on criticality safety, a special session was devoted to the Monte Carlo ''Eigenvalue of the World'' problem. Argonne presented a paper, at that session, in which the anomalies originally observed in that problem were reproduced in a much simplified model-problem configuration, and removed by a version of stratified source-sampling. In this paper, stratified source-sampling techniques are generalized and applied to three different Eigenvalue of the World configurations which take into account real-world statistical noise sources not included in the model problem, but which differ in the amount of neutronic coupling among the constituents of each configuration. It is concluded that, in Monte Carlo eigenvalue analysis of loosely-coupled arrays, the use of stratified source-sampling reduces the probability of encountering an anomalous result over that if conventional source-sampling methods are used. However, this gain in reliability is substantially less than that observed in the model-problem results.
Generation and Analysis of Constrained Random Sampling Patterns
Pierzchlewski, Jacek; Arildsen, Thomas
2016-01-01
indicates signal sampling points in time. Practical random sampling patterns are constrained by ADC characteristics and application requirements. In this paper, we introduce statistical methods which evaluate random sampling pattern generators with emphasis on practical applications. Furthermore, we propose...... a new random pattern generator which copes with strict practical limitations imposed on patterns, with possibly minimal loss in randomness of sampling. The proposed generator is compared with existing sampling pattern generators using the introduced statistical methods. It is shown that the proposed......Random sampling is a technique for signal acquisition which is gaining popularity in practical signal processing systems. Nowadays, event-driven analog-to-digital converters make random sampling feasible in practical applications. A process of random sampling is defined by a sampling pattern, which...
Wilhelm, S W; Brigden, S M; Suttle, C A
2002-01-01
The abundance of heterotrophic bacteria and viruses, as well as rates of viral production and virus-mediated mortality, were measured in Discovery Passage and the Strait of Georgia (British Columbia, Canada) along a gradient of tidal mixing ranging from well mixed to stratified. The abundances of bacteria and viruses were approximately 10(6) and 10(7) mL(-1), respectively, independent of mixing regime. Viral production estimates, monitored by a dilution technique, demonstrated that new viruses were produced at rates of 10(6) and 10(7) mL(-1)h(-1) across the different mixing regimes. Using an estimated burst size of 50 viruses per lytic event, ca. 19 to 27% of the standing stock of bacteria at the stratified stations and 46 to 137% at the deep-mixed stations were removed by viruses. The results suggest that mixing of stratified waters during tidal exchange enhances virus-mediated bacterial lysis. Consequently, viral lysis recycled a greater proportion of the organic carbon required for bacterial growth under non-steady-state compared to steady-state conditions.
Adapted random sampling patterns for accelerated MRI.
Knoll, Florian; Clason, Christian; Diwoky, Clemens; Stollberger, Rudolf
2011-02-01
Variable density random sampling patterns have recently become increasingly popular for accelerated imaging strategies, as they lead to incoherent aliasing artifacts. However, the design of these sampling patterns is still an open problem. Current strategies use model assumptions like polynomials of different order to generate a probability density function that is then used to generate the sampling pattern. This approach relies on the optimization of design parameters which is very time consuming and therefore impractical for daily clinical use. This work presents a new approach that generates sampling patterns by making use of power spectra of existing reference data sets and hence requires neither parameter tuning nor an a priori mathematical model of the density of sampling points. The approach is validated with downsampling experiments, as well as with accelerated in vivo measurements. The proposed approach is compared with established sampling patterns, and the generalization potential is tested by using a range of reference images. Quantitative evaluation is performed for the downsampling experiments using RMS differences to the original, fully sampled data set. Our results demonstrate that the image quality of the method presented in this paper is comparable to that of an established model-based strategy when optimization of the model parameter is carried out and yields superior results to non-optimized model parameters. However, no random sampling pattern showed superior performance when compared to conventional Cartesian subsampling for the considered reconstruction strategy.
Blank, Jeff T
2003-02-01
Although many tooth-colored indirect restorative materials are available, dentists frequently employ direct composite resins as a primary tooth-colored restorative material. Direct resin systems that are suited for stratification, or layering of various opacities and colors of dental composite, offer dentists the opportunity to accurately reproduce natural teeth in ways that rival the esthetics of most indirect systems. This article presents a simplified version of the classical three-layered technique originally described by Dietschi, and demonstrates the application of a recently introduced composite resin system.
Occupational position and its relation to mental distress in a random sample of Danish residents
Rugulies, Reiner Ernst; Madsen, Ida E H; Nielsen, Maj Britt D
2010-01-01
PURPOSE: To analyze the distribution of depressive, anxiety, and somatization symptoms across different occupational positions in a random sample of Danish residents. METHODS: The study sample consisted of 591 Danish residents (50% women), aged 20-65, drawn from an age- and gender-stratified random...... sample of the Danish population. Participants filled out a survey that included the 92 item version of the Hopkins Symptom Checklist (SCL-92). We categorized occupational position into seven groups: high- and low-grade non-manual workers, skilled and unskilled manual workers, high- and low-grade self...
Kuntoro, Hadiyan Yusuf, E-mail: hadiyan.y.kuntoro@mail.ugm.ac.id; Majid, Akmal Irfan; Deendarlianto, E-mail: deendarlianto@ugm.ac.id [Center for Energy Studies, Gadjah Mada University, Sekip K-1A Kampus UGM, Yogyakarta 55281 (Indonesia); Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika 2, Yogyakarta 55281 (Indonesia); Hudaya, Akhmad Zidni; Dinaryanto, Okto [Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika 2, Yogyakarta 55281 (Indonesia)
2016-06-03
Due to the importance of the two-phase flow researches for the industrial safety analysis, many researchers developed various methods and techniques to study the two-phase flow phenomena on the industrial cases, such as in the chemical, petroleum and nuclear industries cases. One of the developing methods and techniques is image processing technique. This technique is widely used in the two-phase flow researches due to the non-intrusive capability to process a lot of visualization data which are contain many complexities. Moreover, this technique allows to capture direct-visual information data of the flow which are difficult to be captured by other methods and techniques. The main objective of this paper is to present an improved algorithm of image processing technique from the preceding algorithm for the stratified flow cases. The present algorithm can measure the film thickness (h{sub L}) of stratified flow as well as the geometrical properties of the interfacial waves with lower processing time and random-access memory (RAM) usage than the preceding algorithm. Also, the measurement results are aimed to develop a high quality database of stratified flow which is scanty. In the present work, the measurement results had a satisfactory agreement with the previous works.
Kuntoro, Hadiyan Yusuf; Hudaya, Akhmad Zidni; Dinaryanto, Okto; Majid, Akmal Irfan; Deendarlianto
2016-06-01
Due to the importance of the two-phase flow researches for the industrial safety analysis, many researchers developed various methods and techniques to study the two-phase flow phenomena on the industrial cases, such as in the chemical, petroleum and nuclear industries cases. One of the developing methods and techniques is image processing technique. This technique is widely used in the two-phase flow researches due to the non-intrusive capability to process a lot of visualization data which are contain many complexities. Moreover, this technique allows to capture direct-visual information data of the flow which are difficult to be captured by other methods and techniques. The main objective of this paper is to present an improved algorithm of image processing technique from the preceding algorithm for the stratified flow cases. The present algorithm can measure the film thickness (hL) of stratified flow as well as the geometrical properties of the interfacial waves with lower processing time and random-access memory (RAM) usage than the preceding algorithm. Also, the measurement results are aimed to develop a high quality database of stratified flow which is scanty. In the present work, the measurement results had a satisfactory agreement with the previous works.
Ronald E. McRoberts; Mark D. Nelson; Daniel G. Wendt
2002-01-01
For two large study areas in Minnesota, USA, stratified estimation using classified Landsat Thematic Mapper satellite imagery as the basis for stratification was used to estimate forest area. Measurements of forest inventory plots obtained for a 12-month period in 1998 and 1999 were used as the source of data for within-stratum estimates. These measurements further...
A Bayesian Justification for Random Sampling in Sample Survey
Glen Meeden
2012-07-01
Full Text Available In the usual Bayesian approach to survey sampling the sampling design, plays a minimal role, at best. Although a close relationship between exchangeable prior distributions and simple random sampling has been noted; how to formally integrate simple random sampling into the Bayesian paradigm is not clear. Recently it has been argued that the sampling design can be thought of as part of a Bayesian's prior distribution. We will show here that under this scenario simple random sample can be given a Bayesian justification in survey sampling.
Kuntoro, Hadiyan Yusuf; Dinaryanto, Okto; Deendarlianto,; Indarto,
2015-01-01
Experimental series of stratified gas-liquid two-phase flows had been carried out in a 26 mm i.d. transparent acrylic horizontal pipe. The study was aimed to determine the interfacial wave characteristics of the flow and to develop a high quality database of it. The longitudinal section of the pipe was used as the reference section of image recording. Air and water were used as the test fluids, flowing co-currently inside the pipe. The flow behavior was recorded by using a high-speed video camera around 5 m in axial distance from the inlet pipe to ensure the fully-developed stratified gas-liquid two-phase flow. To correct the refraction due to the acrylic pipe, a correction box was employed in the visualization test section. The group of stratified smooth and wavy two-phase flows were successfully recorded and classified on the basis of the visualization study from 24 couples of test condition of superficial water and air velocities. Digital image processing technique was then used to perform quantitative ana...
S. Mau
2013-04-01
Full Text Available The bacterially mediated aerobic methane oxidation (MOx is a key mechanism in controlling methane (CH4 emissions from the world's oceans to the atmosphere. In this study, we investigated MOx in the Arctic fjord Storfjorden (Spitsbergen by applying a combination of radio-tracer based incubation assays (3H-CH4 and 14H-CH4, stable C-CH4 isotope measurements, and molecular tools (16S rRNA DGGE-fingerprinting, pmoA- and mxaF gene analyses. Strofjorden is stratified in the summertime with melt water (MW in the upper 60 m of the water column, Arctic water (ArW between 60–100 m and brine-enriched shelf water (BSW down to 140 m. CH4 concentrations were supersaturated with respect to the atmospheric equilibrium (∼3 nM throughout the water column, increasing from ∼20 nM at the surface to a maximum of 72 nM at 60 m and decreasing below. MOx rate measurements at near in situ CH4 concentrations (here measured with 3H-CH4 raising the ambient CH4 pool by −1 at 60 m followed by a decrease in the deeper ArW/BSW. In contrast, rate measurements with 14H-CH4 at elevated CH4 concentrations (incubations were spiked with ∼450 nM of 14H-CH4, providing an estimate of the CH4 oxidation potential showed comparably low turnover rates (−1 at 60 m, but peaked in ArW/BSW at ∼100 m water depth, concomitant with increasing 14C-values in the residual CH4 pool. Our results indicate that the MOx community in the surface MW is adapted to relatively low CH4 concentrations. In contrast, the activity of the deep water MOx community is relatively low at the ambient, summertime CH4 concentrations but has the potential to increase rapidly in response to CH4 availability. A similar distinction between surface and deep water MOx is also suggested by our molecular analyses. Although, we found pmoA and maxF gene sequences throughout the water column attesting the ubiquitous presence of MOx communities in Storfjorden, deep water amplicons of pmoA and maxF were unusually long
Improved Compressive Sensing of Natural Scenes Using Localized Random Sampling
Barranca, Victor J.; Kovačič, Gregor; Zhou, Douglas; Cai, David
2016-08-01
Compressive sensing (CS) theory demonstrates that by using uniformly-random sampling, rather than uniformly-spaced sampling, higher quality image reconstructions are often achievable. Considering that the structure of sampling protocols has such a profound impact on the quality of image reconstructions, we formulate a new sampling scheme motivated by physiological receptive field structure, localized random sampling, which yields significantly improved CS image reconstructions. For each set of localized image measurements, our sampling method first randomly selects an image pixel and then measures its nearby pixels with probability depending on their distance from the initially selected pixel. We compare the uniformly-random and localized random sampling methods over a large space of sampling parameters, and show that, for the optimal parameter choices, higher quality image reconstructions can be consistently obtained by using localized random sampling. In addition, we argue that the localized random CS optimal parameter choice is stable with respect to diverse natural images, and scales with the number of samples used for reconstruction. We expect that the localized random sampling protocol helps to explain the evolutionarily advantageous nature of receptive field structure in visual systems and suggests several future research areas in CS theory and its application to brain imaging.
Improved Compressive Sensing of Natural Scenes Using Localized Random Sampling.
Barranca, Victor J; Kovačič, Gregor; Zhou, Douglas; Cai, David
2016-08-24
Compressive sensing (CS) theory demonstrates that by using uniformly-random sampling, rather than uniformly-spaced sampling, higher quality image reconstructions are often achievable. Considering that the structure of sampling protocols has such a profound impact on the quality of image reconstructions, we formulate a new sampling scheme motivated by physiological receptive field structure, localized random sampling, which yields significantly improved CS image reconstructions. For each set of localized image measurements, our sampling method first randomly selects an image pixel and then measures its nearby pixels with probability depending on their distance from the initially selected pixel. We compare the uniformly-random and localized random sampling methods over a large space of sampling parameters, and show that, for the optimal parameter choices, higher quality image reconstructions can be consistently obtained by using localized random sampling. In addition, we argue that the localized random CS optimal parameter choice is stable with respect to diverse natural images, and scales with the number of samples used for reconstruction. We expect that the localized random sampling protocol helps to explain the evolutionarily advantageous nature of receptive field structure in visual systems and suggests several future research areas in CS theory and its application to brain imaging.
Srivastava, Abhishek; Chopra, Sameer; Pham, Anthony; Sooriakumaran, Prasanna; Durand, Matthieu; Chughtai, Bilal; Gruschow, Siobhan; Peyser, Alexandra; Harneja, Niyati; Leung, Robert; Lee, Richard; Herman, Michael; Robinson, Brian; Shevchuk, Maria; Tewari, Ashutosh
2013-03-01
The impact of nerve sparing (NS) on urinary continence recovery after robot-assisted laparoscopic radical prostatectomy (RALP) has yet to be defined. To evaluate the effect of a risk-stratified grade of NS technique on early return of urinary continence. Data were collected from 1546 patients who underwent RALP by a single surgeon at a tertiary care center from December 2008 to October 2011. Patients were categorized preoperatively by a risk-stratified approach into risk grades 1-4, with risk grade 1 patients more likely to receive NS grade 1 or complete hammock preservation. This categorization was also conducted for risk grades 2-4, with grade 4 patients receiving a non-NS procedure. Risk-stratified grading of NS RALP. Univariate and multivariate analysis identified predictors of early return of urinary continence, defined as no pad use at ≤ 12 wk postoperatively. Early return of continence was achieved by 791 of 1417 men (55.8%); of those, 199 of 277 (71.8%) were in NS grade 1, 440 of 805 (54.7%) were in NS grade 2, 132 of 289 (45.7%) were in NS grade 3, and 20 of 46 (43.5%) were in NS grade 4 (preturn of urinary continence when NS grade 1 was the reference variable compared with NS grade 2 (preturn of urinary continence. Positive surgical margin rates were 7.2% (20 of 277) of grade 1 cases, 7.6% (61 of 805) of grade 2 cases, 7.6% (22 of 289) of grade 3 cases, and 17.4% (8 of 46) of grade 4 cases (p=0.111). Extraprostatic extension occurred in 6.1% (17 of 277) of NS grade 1 cases, 17.5% (141 of 805) of NS grade 2 cases, 42.5% (123 of 289) of NS grade 3 cases, and 63% (29 of 46) of NS grade 4 cases (prisk-stratified grade of NS technique and early return of urinary continence as patients with a lower grade (higher degree) of NS achieved an early return of urinary continence without compromising oncologic safety. Copyright © 2012 European Association of Urology. Published by Elsevier B.V. All rights reserved.
Reduction of noise and bias in randomly sampled power spectra
Buchhave, Preben; Velte, Clara Marika
2015-01-01
We consider the origin of noise and distortion in power spectral estimates of randomly sampled data, specifically velocity data measured with a burst-mode laser Doppler anemometer. The analysis guides us to new ways of reducing noise and removing spectral bias, e.g., distortions caused by modific......We consider the origin of noise and distortion in power spectral estimates of randomly sampled data, specifically velocity data measured with a burst-mode laser Doppler anemometer. The analysis guides us to new ways of reducing noise and removing spectral bias, e.g., distortions caused...
Recording 2-D Nutation NQR Spectra by Random Sampling Method.
Glotova, Olga; Sinyavsky, Nikolaj; Jadzyn, Maciej; Ostafin, Michal; Nogaj, Boleslaw
2010-10-01
The method of random sampling was introduced for the first time in the nutation nuclear quadrupole resonance (NQR) spectroscopy where the nutation spectra show characteristic singularities in the form of shoulders. The analytic formulae for complex two-dimensional (2-D) nutation NQR spectra (I = 3/2) were obtained and the condition for resolving the spectral singularities for small values of an asymmetry parameter η was determined. Our results show that the method of random sampling of a nutation interferogram allows significant reduction of time required to perform a 2-D nutation experiment and does not worsen the spectral resolution.
Describing Typical Capstone Course Experiences from a National Random Sample
Grahe, Jon E.; Hauhart, Robert C.
2013-01-01
The pedagogical value of capstones has been regularly discussed within psychology. This study presents results from an examination of a national random sample of department webpages and an online survey that characterized the typical capstone course in terms of classroom activities and course administration. The department webpages provide an…
Klaff, D
2001-01-01
Composite resin restorations play an ever-increasing role as routine restorations in everyday clinical practice. However, the long-term prognosis of these restorations is still widely debated and open to question. The restorative protocols are still evolving, whether for direct or indirect placement, and little evidence is available in the scientific literature as to the ideal choice of site, technique, and category for placement. This article discusses the problems encountered and suggests a clinical restorative protocol to optimize composite resin placement.
CODRUŢA DURA
2010-01-01
Full Text Available The sample represents a particular segment of the statistical populationchosen to represent it as a whole. The representativeness of the sample determines the accuracyfor estimations made on the basis of calculating the research indicators and the inferentialstatistics. The method of random sampling is part of probabilistic methods which can be usedwithin marketing research and it is characterized by the fact that it imposes the requirementthat each unit belonging to the statistical population should have an equal chance of beingselected for the sampling process. When the simple random sampling is meant to be rigorouslyput into practice, it is recommended to use the technique of random number tables in order toconfigure the sample which will provide information that the marketer needs. The paper alsodetails the practical procedure implemented in order to create a sample for a marketingresearch by generating random numbers using the facilities offered by Microsoft Excel.
Random sampling of lattice paths with constraints, via transportation
Gerin, Lucas
2010-01-01
We discuss a Monte Carlo Markov Chain (MCMC) procedure for the random sampling of some one-dimensional lattice paths with constraints, for various constraints. We show that an approach inspired by optimal transport allows us to bound efficiently the mixing time of the associated Markov chain. The algorithm is robust and easy to implement, and samples an "almost" uniform path of length $n$ in $n^{3+\\eps}$ steps. This bound makes use of a certain contraction property of the Markov chain, and is also used to derive a bound for the running time of Propp-Wilson's CFTP algorithm.
Koch, David E; Mohler, Rhett L; Goodin, Douglas G
2007-11-01
Landscape epidemiology has made significant strides recently, driven in part by increasing availability of land cover data derived from remotely-sensed imagery. Using an example from a study of land cover effects on hantavirus dynamics at an Atlantic Forest site in eastern Paraguay, we demonstrate how automated classification methods can be used to stratify remotely-sensed land cover for studies of infectious disease dynamics. For this application, it was necessary to develop a scheme that could yield both land cover and land use data from the same classification. Hypothesizing that automated discrimination between classes would be more accurate using an object-based method compared to a per-pixel method, we used a single Landsat Enhanced Thematic Mapper+ (ETM+) image to classify land cover into eight classes using both per-pixel and object-based classification algorithms. Our results show that the object-based method achieves 84% overall accuracy, compared to only 43% using the per-pixel method. Producer's and user's accuracies for the object-based map were higher for every class compared to the per-pixel classification. The Kappa statistic was also significantly higher for the object-based classification. These results show the importance of using image information from domains beyond the spectral domain, and also illustrate the importance of object-based techniques for remote sensing applications in epidemiological studies.
David E. Koch
2007-11-01
Full Text Available Landscape epidemiology has made significant strides recently, driven in part by increasing availability of land cover data derived from remotely-sensed imagery. Using an example from a study of land cover effects on hantavirus dynamics at an Atlantic Forest site in eastern Paraguay, we demonstrate how automated classification methods can be used to stratify remotely-sensed land cover for studies of infectious disease dynamics. For this application, it was necessary to develop a scheme that could yield both land cover and land use data from the same classification. Hypothesizing that automated discrimination between classes would be more accurate using an object-based method compared to a per-pixel method, we used a single Landsat Enhanced Thematic Mapper+ (ETM+ image to classify land cover into eight classes using both per-pixel and object-based classification algorithms. Our results show that the objectbased method achieves 84% overall accuracy, compared to only 43% using the per-pixel method. Producer’s and user’s accuracies for the object-based map were higher for every class compared to the per-pixel classification. The Kappa statistic was also significantly higher for the object-based classification. These results show the importance of using image information from domains beyond the spectral domain, and also illustrate the importance of object-based techniques for remote sensing applications in epidemiological studies.
Sublinear Time Approximate Sum via Uniform Random Sampling
Fu, Bin; Peng, Zhiyong
2012-01-01
We investigate the approximation for computing the sum $a_1+...+a_n$ with an input of a list of nonnegative elements $a_1,..., a_n$. If all elements are in the range $[0,1]$, there is a randomized algorithm that can compute an $(1+\\epsilon)$-approximation for the sum problem in time ${O({n(\\log\\log n)\\over\\sum_{i=1}^n a_i})}$, where $\\epsilon$ is a constant in $(0,1)$. Our randomized algorithm is based on the uniform random sampling, which selects one element with equal probability from the input list each time. We also prove a lower bound $\\Omega({n\\over \\sum_{i=1}^n a_i})$, which almost matches the upper bound, for this problem.
Javid Shabbir
2012-01-01
Full Text Available In this paper we propose a combined exponential ratio type estimator of finite population mean utilizing information on the auxiliary attribute(s under non-response. Expressions for bias and MSE of the proposed estimator are derived up to first order of approximation. An empirical study is carried out to observe the performances of the estimators.
The Effect of Dead Time in Random Sampling of the LDA
Velte, Clara; Buchhave, Preben; George, William
2012-11-01
The random sampling emanating from the acquisition of velocities of randomly arriving particles in LDA measurements has since Gaster and Roberts commonly been believed to eliminate aliasing. For a perfect signal, in the sense that acquisition is truly instant and random, this is in principle correct. For real signals however, the acquisition is always afflicted with some finite time/space averaging. This hinders the capture of all realizations, and re-introduces aliasing. Contrary to common practice, using the time slot approximation autocorrelation to obtain the power spectrum also re-introduces aliasing (as noted even by Blackman and Tukey). We will demonstrate techniques for minimizing adverse effects.
A Table-Based Random Sampling Simulation for Bioluminescence Tomography
Xiaomeng Zhang
2006-01-01
Full Text Available As a popular simulation of photon propagation in turbid media, the main problem of Monte Carlo (MC method is its cumbersome computation. In this work a table-based random sampling simulation (TBRS is proposed. The key idea of TBRS is to simplify multisteps of scattering to a single-step process, through randomly table querying, thus greatly reducing the computing complexity of the conventional MC algorithm and expediting the computation. The TBRS simulation is a fast algorithm of the conventional MC simulation of photon propagation. It retained the merits of flexibility and accuracy of conventional MC method and adapted well to complex geometric media and various source shapes. Both MC simulations were conducted in a homogeneous medium in our work. Also, we present a reconstructing approach to estimate the position of the fluorescent source based on the trial-and-error theory as a validation of the TBRS algorithm. Good agreement is found between the conventional MC simulation and the TBRS simulation.
Long, Jiang; Liu, Tie-Qiao; Liao, Yan-Hui; Qi, Chang; He, Hao-Yu; Chen, Shu-Bao; Billieux, Joël
2016-11-17
Smartphones are becoming a daily necessity for most undergraduates in Mainland China. Because the present scenario of problematic smartphone use (PSU) is largely unexplored, in the current study we aimed to estimate the prevalence of PSU and to screen suitable predictors for PSU among Chinese undergraduates in the framework of the stress-coping theory. A sample of 1062 undergraduate smartphone users was recruited by means of the stratified cluster random sampling strategy between April and May 2015. The Problematic Cellular Phone Use Questionnaire was used to identify PSU. We evaluated five candidate risk factors for PSU by using logistic regression analysis while controlling for demographic characteristics and specific features of smartphone use. The prevalence of PSU among Chinese undergraduates was estimated to be 21.3%. The risk factors for PSU were majoring in the humanities, high monthly income from the family (≥1500 RMB), serious emotional symptoms, high perceived stress, and perfectionism-related factors (high doubts about actions, high parental expectations). PSU among undergraduates appears to be ubiquitous and thus constitutes a public health issue in Mainland China. Although further longitudinal studies are required to test whether PSU is a transient phenomenon or a chronic and progressive condition, our study successfully identified socio-demographic and psychological risk factors for PSU. These results, obtained from a random and thus representative sample of undergraduates, opens up new avenues in terms of prevention and regulation policies.
Jeong, Hae-Yong; Park, Moon-Ghu [Sejong University, Seoul (Korea, Republic of)
2015-05-15
In most existing evaluation methodologies, which follow a conservative approach, the most conservative initial conditions are searched for each transient scenario through tremendous assessment for wide operating windows or limiting conditions for operation (LCO) allowed by the operating guidelines. In this procedure, a user effect could be involved and a remarkable time and human resources are consumed. In the present study, we investigated a more effective statistical method for the selection of the most conservative initial condition by the use of random sampling of operating parameters affecting the initial conditions. A method for the determination of initial conditions based on random sampling of plant design parameters is proposed. This method is expected to be applied for the selection of the most conservative initial plant conditions in the safety analysis using a conservative evaluation methodology. In the method, it is suggested that the initial conditions of reactor coolant flow rate, pressurizer level, pressurizer pressure, and SG level are adjusted by controlling the pump rated flow, setpoints of PLCS, PPCS, and FWCS, respectively. The proposed technique is expected to contribute to eliminate the human factors introduced in the conventional safety analysis procedure and also to reduce the human resources invested in the safety evaluation of nuclear power plants.
A FAMILY OF ESTIMATORS FOR ESTIMATING POPULATION MEAN IN STRATIFIED SAMPLING UNDER NON-RESPONSE
Chaudhary, Manoj K.; RAJESH SINGH; Rakesh K. Shukla; MUKESH KUMAR; FLORENTIN SMARANDACHE
2015-01-01
Khoshnevisan et al. (2007) proposed a general family of estimators for population mean using known value of some population parameters in simple random sampling. The objective of this paper is to propose a family of combined-type estimators in stratified random sampling adapting the family of estimators proposed by Khoshnevisan et al. (2007) under non-response. The properties of proposed family have been discussed. We have also obtained the expressions for optimum sampl...
A FAMILY OF ESTIMATORS FOR ESTIMATING POPULATION MEAN IN STRATIFIED SAMPLING UNDER NON-RESPONSE
Chaudhary, Manoj K.; Rajesh Singh; Rakesh K. Shukla; Mukesh Kumar; Florentin Smarandache
2009-01-01
Khoshnevisan et al. (2007) proposed a general family of estimators for population mean using known value of some population parameters in simple random sampling. The objective of this paper is to propose a family of combined-type estimators in stratified random sampling adapting the family of estimators proposed by Khoshnevisan et al. (2007) under non-response. The properties of proposed family have been discussed. We have also obtained the expressions for optimum sample sizes of the strata i...
Zimmermann, D.; Kerek, Z.; Wirth, M. [Ford Motor Co. (Germany); Gansert, K.P.; Grzeszik, R.; Storch, A. [Robert Bossch GmbH (Germany); Josefsson, G.; Sandquist, H. [Volvo Car Corp. (Sweden)
2004-07-01
Stratified combustion in spray guided DI gasoline engines is characterized by a maximum of fuel economy potential but also by critical design parameters related to the geometric layout of the combustion system. The relative position between fuel spray and ignition location is essential as well as the dedicated design of the spark plug itself. This could be assessed in multicylinder engine experiments creating the base information for subsequent system component optimizations. The combustion system and component design can be supported to a large extend by in-cylinder investigations of the ignition process. High speed video imaging techniques have been applied in a transparent engine in order to gain a deep understanding of different spark discharge events including successful ignitions as well as misfires. The simultaneous application of imaging and high resolution electrical spark discharge analysis coupled with statistical analysis methods provide valuable insights into the specific conditions of the stratified DI ignition requirements. (orig.)
Rao, R. G. S.; Ulaby, F. T.
1977-01-01
The paper examines optimal sampling techniques for obtaining accurate spatial averages of soil moisture, at various depths and for cell sizes in the range 2.5-40 acres, with a minimum number of samples. Both simple random sampling and stratified sampling procedures are used to reach a set of recommended sample sizes for each depth and for each cell size. Major conclusions from statistical sampling test results are that (1) the number of samples required decreases with increasing depth; (2) when the total number of samples cannot be prespecified or the moisture in only one single layer is of interest, then a simple random sample procedure should be used which is based on the observed mean and SD for data from a single field; (3) when the total number of samples can be prespecified and the objective is to measure the soil moisture profile with depth, then stratified random sampling based on optimal allocation should be used; and (4) decreasing the sensor resolution cell size leads to fairly large decreases in samples sizes with stratified sampling procedures, whereas only a moderate decrease is obtained in simple random sampling procedures.
An alternative procedure for estimating the population mean in simple random sampling
Housila P. Singh
2012-03-01
Full Text Available This paper deals with the problem of estimating the finite population mean using auxiliary information in simple random sampling. Firstly we have suggested a correction to the mean squared error of the estimator proposed by Gupta and Shabbir [On improvement in estimating the population mean in simple random sampling. Jour. Appl. Statist. 35(5 (2008, pp. 559-566]. Later we have proposed a ratio type estimator and its properties are studied in simple random sampling. Numerically we have shown that the proposed class of estimators is more efficient than different known estimators including Gupta and Shabbir (2008 estimator.
A coupled well-balanced and random sampling scheme for computing bubble oscillations*
Jung Jonathan
2012-04-01
Full Text Available We propose a finite volume scheme to study the oscillations of a spherical bubble of gas in a liquid phase. Spherical symmetry implies a geometric source term in the Euler equations. Our scheme satisfies the well-balanced property. It is based on the VFRoe approach. In order to avoid spurious pressure oscillations, the well-balanced approach is coupled with an ALE (Arbitrary Lagrangian Eulerian technique at the interface and a random sampling remap. Nous proposons un schéma de volumes finis pour étudier les oscillations d’une bulle sphérique de gaz dans l’eau. La symétrie sphérique fait apparaitre un terme source géométrique dans les équations d’Euler. Notre schéma est basé sur une approche VFRoe et préserve les états stationnaires. Pour éviter les oscillations de pression, l’approche well-balanced est couplée avec une approche ALE (Arbitrary Lagrangian Eulerian, et une étape de projection basée sur un échantillonage aléatoire.
Maziero, Jonas
2015-12-01
The numerical generation of random quantum states (RQS) is an important procedure for investigations in quantum information science. Here, we review some methods that may be used for performing that task. We start by presenting a simple procedure for generating random state vectors, for which the main tool is the random sampling of unbiased discrete probability distributions (DPD). Afterwards, the creation of random density matrices is addressed. In this context, we first present the standard method, which consists in using the spectral decomposition of a quantum state for getting RQS from random DPDs and random unitary matrices. In the sequence, the Bloch vector parametrization method is described. This approach, despite being useful in several instances, is not in general convenient for RQS generation. In the last part of the article, we regard the overparametrized method (OPM) and the related Ginibre and Bures techniques. The OPM can be used to create random positive semidefinite matrices with unit trace from randomly produced general complex matrices in a simple way that is friendly for numerical implementations. We consider a physically relevant issue related to the possible domains that may be used for the real and imaginary parts of the elements of such general complex matrices. Subsequently, a too fast concentration of measure in the quantum state space that appears in this parametrization is noticed.
Maziero, Jonas, E-mail: jonas.maziero@ufsm.br [Universidade Federal de Santa Maria (UFSM), Santa Maria, RS (Brazil). Dept. de Fisica
2015-12-15
The numerical generation of random quantum states (RQS) is an important procedure for investigations in quantum information science. Here, we review some methods that may be used for performing that task. We start by presenting a simple procedure for generating random state vectors, for which the main tool is the random sampling of unbiased discrete probability distributions (DPD). Afterwards, the creation of random density matrices is addressed. In this context, we first present the standard method, which consists in using the spectral decomposition of a quantum state for getting RQS from random DPDs and random unitary matrices. In the sequence, the Bloch vector parametrization method is described. This approach, despite being useful in several instances, is not in general convenient for RQS generation. In the last part of the article, we regard the overparametrized method (OPM) and the related Ginibre and Bures techniques. The OPM can be used to create random positive semidefinite matrices with unit trace from randomly produced general complex matrices in a simple way that is friendly for numerical implementations. We consider a physically relevant issue related to the possible domains that may be used for the real and imaginary parts of the elements of such general complex matrices. Subsequently, a too fast concentration of measure in the quantum state space that appears in this parametrization is noticed. (author)
STRATIFIED MODEL FOR ESTIMATING FATIGUE CRACK GROWTH RATE OF METALLIC MATERIALS
YANG Yong-yu; LIU Xin-wei; YANG Fan
2005-01-01
The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic component parts. In order to have a morereasonable use of testing data, samples from population were stratified suggested by the stratified random sample model (SRAM). The data in each stratum corresponded to the same experiment conditions. A suitable weight was assigned to each stratified sample according to the actual working states of the pressure vessel, so that the estimation of fatigue crack growth rate equation was more accurate for practice. An empirical study shows that the SRAM estimation by using fatigue crack growth rate data from different stoves is obviously better than the estimation from simple random sample model.
Nitrogen transformations in stratified aquatic microbial ecosystems
Revsbech, Niels Peter; Risgaard-Petersen, N.; Schramm, Andreas
2006-01-01
Abstract New analytical methods such as advanced molecular techniques and microsensors have resulted in new insights about how nitrogen transformations in stratified microbial systems such as sediments and biofilms are regulated at a µm-mm scale. A large and ever-expanding knowledge base about n...
Fluttering in Stratified Flows
Lam, Try; Vincent, Lionel; Kanso, Eva
2016-11-01
The descent motion of heavy objects under the influence of gravitational and aerodynamic forces is relevant to many branches of engineering and science. Examples range from estimating the behavior of re-entry space vehicles to studying the settlement of marine larvae and its influence on underwater ecology. The behavior of regularly shaped objects freely falling in homogeneous fluids is relatively well understood. For example, the complex interaction of a rigid coin with the surrounding fluid will cause it to either fall steadily, flutter, tumble, or be chaotic. Less is known about the effect of density stratification on the descent behavior. Here, we experimentally investigate the descent of discs in both pure water and in a linearly salt-stratified fluids where the density is varied from 1.0 to 1.14 of that of water where the Brunt-Vaisala frequency is 1.7 rad/sec and the Froude number Fr robots for space exploration and underwater missions.
A FAMILY OF ESTIMATORS FOR ESTIMATING POPULATION MEAN IN STRATIFIED SAMPLING UNDER NON-RESPONSE
Manoj K. Chaudhary
2009-01-01
Full Text Available Khoshnevisan et al. (2007 proposed a general family of estimators for population mean using known value of some population parameters in simple random sampling. The objective of this paper is to propose a family of combined-type estimators in stratified random sampling adapting the family of estimators proposed by Khoshnevisan et al. (2007 under non-response. The properties of proposed family have been discussed. We have also obtained the expressions for optimum sample sizes of the strata in respect to cost of the survey. Results are also supported by numerical analysis.
Do "Instant Polls" Hit the Spot? Phone-In vs. Random Sampling of Public Opinion.
Bates, Benjamin; Harmon, Mark
1993-01-01
Compares television phone-in polls to random sample polling. Finds significant differences between the two types of opinion indicators. Shows that persons with strongly held opinions and a pro-change, activist stance are more likely to respond in phone-in polls. (SR)
Random sampling for the monomer-dimer model on a lattice
J. van den Berg (Rob); R.M. Brouwer (Rachel)
1999-01-01
textabstractIn the monomer-dimer model on a graph, each matching (collection of non-overlapping edges) ${M$ has a probability proportional to $lambda^{|M|$, where $lambda > 0$ is the model parameter, and $|M|$ denotes the number of edges in $M$. An approximate random sample from the monomer-dimer
Random number datasets generated from statistical analysis of randomly sampled GSM recharge cards.
Okagbue, Hilary I; Opanuga, Abiodun A; Oguntunde, Pelumi E; Ugwoke, Paulinus O
2017-02-01
In this article, a random number of datasets was generated from random samples of used GSM (Global Systems for Mobile Communications) recharge cards. Statistical analyses were performed to refine the raw data to random number datasets arranged in table. A detailed description of the method and relevant tests of randomness were also discussed.
Quality Assessment of Attribute Data in GIS Based on Simple Random Sampling
LIU Chun; SHI Wenzhong; LIU Dajie
2003-01-01
On the basis of the principles of simple random sampling, the statistical model of rate of disfigurement (RD) is put forward and described in detail. According to the definition of simple random sampling for the attribute data in GIS, the mean and variance of the RD are deduced as the characteristic value of the statistical model in order to explain the feasibility of the accuracy measurement of the attribute data in GIS by using the RD. Moreover, on the basis of the mean and variance of the RD, the quality assessment method for attribute data of vector maps during the data collecting is discussed. The RD spread graph is also drawn to see whether the quality of the attribute data is under control. The RD model can synthetically judge the quality of attribute data, which is different from other measurement coefficients that only discuss accuracy of classification.
Knowledge of health information and services in a random sample of the population of Glasgow.
Moynihan, M; Jones, A K; Stewart, G T; Lucas, R W
1980-01-01
A RANDOM sample of adults in Glasgow was surveyed by trained interviewers to determine public knowledge on four topics chosen specifically for each of four age groups. The topics were: Welfare rights and services; Coronary Heart Disease (CHD) and individual action that can reduce risk; The dangers of smoking in pregnancy; and fluoride and its functions and the connections between good health and habitual behaviour.
Ratio Estimators in Simple Random Sampling Using Information on Auxiliary Attribute
Rajesh Singh
2008-01-01
Full Text Available Some ratio estimators for estimating the population mean of the variable under study, which make use of information regarding the population proportion possessing certain attribute, are proposed. Under simple random sampling without replacement (SRSWOR scheme, the expressions of bias and mean-squared error (MSE up to the first order of approximation are derived. The results obtained have been illustrated numerically by taking some empirical population considered in the literature.
Atta Ullah
2014-01-01
Full Text Available In practical utilization of stratified random sampling scheme, the investigator meets a problem to select a sample that maximizes the precision of a finite population mean under cost constraint. An allocation of sample size becomes complicated when more than one characteristic is observed from each selected unit in a sample. In many real life situations, a linear cost function of a sample size nh is not a good approximation to actual cost of sample survey when traveling cost between selected units in a stratum is significant. In this paper, sample allocation problem in multivariate stratified random sampling with proposed cost function is formulated in integer nonlinear multiobjective mathematical programming. A solution procedure is proposed using extended lexicographic goal programming approach. A numerical example is presented to illustrate the computational details and to compare the efficiency of proposed compromise allocation.
Evidence for non-random sampling in randomised, controlled trials by Yuhji Saitoh.
Carlisle, J B; Loadsman, J A
2017-01-01
A large number of randomised trials authored by Yoshitaka Fujii have been retracted, in part as a consequence of a previous analysis finding a very low probability of random sampling. Dr Yuhji Saitoh co-authored 34 of those trials and he was corresponding author for eight of them. We found a number of additional randomised, controlled trials that included baseline data, with Saitoh as corresponding author, that Fujii did not co-author. We used Monte Carlo simulations to analyse the baseline data from 32 relevant trials in total as well as an outcome (muscle twitch recovery ratios) reported in several. We also compared a series of muscle twitch recovery graphs appearing in a number of Saitoh's publications. The baseline data in 14/32 randomised, controlled trials had p sampling. Combining the continuous and categorical probabilities of the 32 included trials, we found a very low likelihood of random sampling: p = 1.27 × 10(-8) (1 in 100,000,000). The high probability of non-random sampling and the repetition of lines in multiple graphs suggest that further scrutiny of Saitoh's work is warranted. © 2016 The Association of Anaesthetists of Great Britain and Ireland.
Conflict-cost based random sampling design for parallel MRI with low rank constraints
Kim, Wan; Zhou, Yihang; Lyu, Jingyuan; Ying, Leslie
2015-05-01
In compressed sensing MRI, it is very important to design sampling pattern for random sampling. For example, SAKE (simultaneous auto-calibrating and k-space estimation) is a parallel MRI reconstruction method using random undersampling. It formulates image reconstruction as a structured low-rank matrix completion problem. Variable density (VD) Poisson discs are typically adopted for 2D random sampling. The basic concept of Poisson disc generation is to guarantee samples are neither too close to nor too far away from each other. However, it is difficult to meet such a condition especially in the high density region. Therefore the sampling becomes inefficient. In this paper, we present an improved random sampling pattern for SAKE reconstruction. The pattern is generated based on a conflict cost with a probability model. The conflict cost measures how many dense samples already assigned are around a target location, while the probability model adopts the generalized Gaussian distribution which includes uniform and Gaussian-like distributions as special cases. Our method preferentially assigns a sample to a k-space location with the least conflict cost on the circle of the highest probability. To evaluate the effectiveness of the proposed random pattern, we compare the performance of SAKEs using both VD Poisson discs and the proposed pattern. Experimental results for brain data show that the proposed pattern yields lower normalized mean square error (NMSE) than VD Poisson discs.
Electromagnetic waves in stratified media
Wait, James R; Fock, V A; Wait, J R
2013-01-01
International Series of Monographs in Electromagnetic Waves, Volume 3: Electromagnetic Waves in Stratified Media provides information pertinent to the electromagnetic waves in media whose properties differ in one particular direction. This book discusses the important feature of the waves that enables communications at global distances. Organized into 13 chapters, this volume begins with an overview of the general analysis for the electromagnetic response of a plane stratified medium comprising of any number of parallel homogeneous layers. This text then explains the reflection of electromagne
Improved river flow and random sample consensus for curve lane detection
Huachun Tan
2015-07-01
Full Text Available Accurate and robust lane detection, especially the curve lane detection, is the premise of lane departure warning system and forward collision warning system. In this article, an algorithm based on improved river flow and random sample consensus is proposed to detect curve lane under challenging conditions including the dashed lane markings and vehicle occlusion. The curve lanes are modeled as hyperbola pair. To determine the coefficient of curvature, an improved river flow method is presented to search feature points in the far vision field guided by the results of detected straight lines in near vision field or the curved lines from the last frame, which can connect dashed lane markings or obscured lane markings. As a result, it is robust on dashed lane markings and vehicle occlusion conditions. Then, random sample consensus is utilized to calculate the curvature, which can eliminate noisy feature points obtained from improved river flow. The experimental results show that the proposed method can accurately detect lane under challenging conditions.
Stratified medicine and reimbursement issues
Fugel, Hans-Joerg; Nuijten, Mark; Postma, Maarten
2012-01-01
Stratified Medicine (SM) has the potential to target patient populations who will most benefit from a therapy while reducing unnecessary health interventions associated with side effects. The link between clinical biomarkers/diagnostics and therapies provides new opportunities for value creation to
van Essen, J; Hübner, M; von Mittelstaedt, G
2007-03-01
Hospital billing converted to "German diagnosis-related groups" (G-DRG) for in-patient treatment in Germany is reviewed, except in psychiatry where per-diems are still in use. Currently thousands of bills are sent to the Medical Service for scrutiny. In addition, the law relating to Hospital Financing (Krankenhausfinanzierungsgesetz, para. 17 c) provides for systematic checks on a random sample of bills from a given hospital. The Medical Service of the Social Security Health Insurance reports on the experience in the State of Hessen. Present regulations exclude from the random sample those bills that have already been presented for a check on a case by case basis. Excluding these cases from the random sample introduces a bias in an avoidable way. The present rule is contrary to valid conclusions from the random sampling and should be abolished.
Melvin, Neal R; Poda, Daniel; Sutherland, Robert J
2007-10-01
When properly applied, stereology is a very robust and efficient method to quantify a variety of parameters from biological material. A common sampling strategy in stereology is systematic random sampling, which involves choosing a random sampling [corrected] start point outside the structure of interest, and sampling relevant objects at [corrected] sites that are placed at pre-determined, equidistant intervals. This has proven to be a very efficient sampling strategy, and is used widely in stereological designs. At the microscopic level, this is most often achieved through the use of a motorized stage that facilitates the systematic random stepping across the structure of interest. Here, we report a simple, precise and cost-effective software-based alternative to accomplishing systematic random sampling under the microscope. We believe that this approach will facilitate the use of stereological designs that employ systematic random sampling in laboratories that lack the resources to acquire costly, fully automated systems.
Alireza Goli
2015-09-01
Full Text Available Distribution and optimum allocation of emergency resources are the most important tasks, which need to be accomplished during crisis. When a natural disaster such as earthquake, flood, etc. takes place, it is necessary to deliver rescue efforts as quickly as possible. Therefore, it is important to find optimum location and distribution of emergency relief resources. When a natural disaster occurs, it is not possible to reach some damaged areas. In this paper, location and multi-depot vehicle routing for emergency vehicles using tour coverage and random sampling is investigated. In this study, there is no need to visit all the places and some demand points receive their needs from the nearest possible location. The proposed study is implemented for some randomly generated numbers in different sizes. The preliminary results indicate that the proposed method was capable of reaching desirable solutions in reasonable amount of time.
Effectiveness of hand hygiene education among a random sample of women from the community.
Ubheeram, J; Biranjia-Hurdoyal, S D
2017-03-01
The effectiveness of hand hygiene education was investigated by studying the hand hygiene awareness and bacterial hand contamination among a random sample of 170 women in the community. Questionnaire was used to assess the hand hygiene awareness score, followed by swabbing of the dominant hand. Bacterial identification was done by conventional biochemical tests. Better hand hygiene awareness score was significantly associated with age, scarce bacterial growth and absence of potential pathogen (p soap as compared to antiseptic soaps (69.7% vs 30.3%, p = 0.000; OR = 4.11; 95% CI: 1.67-10.12). Level of hand hygiene awareness among the participants was satisfactory but not the compliance of hand washing practice, especially among the elders.
An inversion method based on random sampling for real-time MEG neuroimaging
Pascarella, Annalisa
2016-01-01
The MagnetoEncephaloGraphy (MEG) has gained great interest in neurorehabilitation training due to its high temporal resolution. The challenge is to localize the active regions of the brain in a fast and accurate way. In this paper we use an inversion method based on random spatial sampling to solve the real-time MEG inverse problem. Several numerical tests on synthetic but realistic data show that the method takes just a few hundredths of a second on a laptop to produce an accurate map of the electric activity inside the brain. Moreover, it requires very little memory storage. For this reasons the random sampling method is particularly attractive in real-time MEG applications.
Bjork, J; Brown, C; Friedlander, H; Schiffman, E; Neitzel, D
2016-08-03
Many disease surveillance programs, including the Massachusetts Department of Public Health and the Minnesota Department of Health, are challenged by marked increases in Lyme disease (LD) reports. The purpose of this study was to retrospectively analyse LD reports from 2005 through 2012 to determine whether key epidemiologic characteristics were statistically indistinguishable when an estimation procedure based on sampling was utilized. Estimates of the number of LD cases were produced by taking random 20% and 50% samples of laboratory-only reports, multiplying by 5 or 2, respectively, and adding the number of provider-reported confirmed cases. Estimated LD case counts were compared to observed, confirmed cases each year. In addition, the proportions of cases that were male, were ≤12 years of age, had erythema migrans (EM), had any late manifestation of LD, had a specific late manifestation of LD (arthritis, cranial neuritis or carditis) or lived in a specific region were compared to the proportions of cases identified using standard surveillance to determine whether estimated proportions were representative of observed proportions. Results indicate that the estimated counts of confirmed LD cases were consistently similar to observed, confirmed LD cases and accurately conveyed temporal trends. Most of the key demographic and disease manifestation characteristics were not significantly different (P < 0.05), although estimates for the 20% random sample demonstrated greater deviation than the 50% random sample. Applying this estimation procedure in endemic states could conserve limited resources by reducing follow-up effort while maintaining the ability to track disease trends.
Sample size estimation and sampling techniques for selecting a representative sample
Aamir Omair
2014-01-01
Full Text Available Introduction: The purpose of this article is to provide a general understanding of the concepts of sampling as applied to health-related research. Sample Size Estimation: It is important to select a representative sample in quantitative research in order to be able to generalize the results to the target population. The sample should be of the required sample size and must be selected using an appropriate probability sampling technique. There are many hidden biases which can adversely affect the outcome of the study. Important factors to consider for estimating the sample size include the size of the study population, confidence level, expected proportion of the outcome variable (for categorical variables/standard deviation of the outcome variable (for numerical variables, and the required precision (margin of accuracy from the study. The more the precision required, the greater is the required sample size. Sampling Techniques: The probability sampling techniques applied for health related research include simple random sampling, systematic random sampling, stratified random sampling, cluster sampling, and multistage sampling. These are more recommended than the nonprobability sampling techniques, because the results of the study can be generalized to the target population.
Cognitive deficits and morphological cerebral changes in a random sample of social drinkers.
Bergman, H
1985-01-01
A random sample of 200 men and 200 women taken from the general population as well as subsamples of 31 male and 17 female excessive social drinkers were investigated with neuropsychological tests and computed tomography of the brain. Relatively high alcohol intake per drinking occasion did not give evidence of cognitive deficits or morphological cerebral changes. However, in males, mild cognitive deficits and morphological cerebral changes as a result of high recent alcohol intake, particularly during the 24-hr period prior to the investigation, were observed. When excluding acute effects of recent alcohol intake, mild cognitive deficits but not morphological cerebral changes that are apparently due to long-term excessive social drinking were observed in males. In females there was no association between the drinking variables and cognitive deficits or morphological cerebral changes, probably due to their less advanced drinking habits. It is suggested that future risk evaluations and estimations of safe alcohol intake should take into consideration the potential risk for brain damage due to excessive social drinking. However, it is premature to make any definite statements about safe alcohol intake and the risk for brain damage in social drinkers from the general population.
Huang, Rimao; Qiu, Xuesong; Rui, Lanlan
2011-01-01
Fault detection for wireless sensor networks (WSNs) has been studied intensively in recent years. Most existing works statically choose the manager nodes as probe stations and probe the network at a fixed frequency. This straightforward solution leads however to several deficiencies. Firstly, by only assigning the fault detection task to the manager node the whole network is out of balance, and this quickly overloads the already heavily burdened manager node, which in turn ultimately shortens the lifetime of the whole network. Secondly, probing with a fixed frequency often generates too much useless network traffic, which results in a waste of the limited network energy. Thirdly, the traditional algorithm for choosing a probing node is too complicated to be used in energy-critical wireless sensor networks. In this paper, we study the distribution characters of the fault nodes in wireless sensor networks, validate the Pareto principle that a small number of clusters contain most of the faults. We then present a Simple Random Sampling-based algorithm to dynamic choose sensor nodes as probe stations. A dynamic adjusting rule for probing frequency is also proposed to reduce the number of useless probing packets. The simulation experiments demonstrate that the algorithm and adjusting rule we present can effectively prolong the lifetime of a wireless sensor network without decreasing the fault detected rate.
Carlisle, J B; Dexter, F; Pandit, J J; Shafer, S L; Yentis, S M
2015-07-01
In a previous paper, one of the authors (JBC) used a chi-squared method to analyse the means (SD) of baseline variables, such as height or weight, from randomised controlled trials by Fujii et al., concluding that the probabilities that the reported distributions arose by chance were infinitesimally small. Subsequent testing of that chi-squared method, using simulation, suggested that the method was incorrect. This paper corrects the chi-squared method and tests its performance and the performance of Monte Carlo simulations and ANOVA to analyse the probability of random sampling. The corrected chi-squared method and ANOVA method became inaccurate when applied to means that were reported imprecisely. Monte Carlo simulations confirmed that baseline data from 158 randomised controlled trials by Fujii et al. were different to those from 329 trials published by other authors and that the distribution of Fujii et al.'s data were different to the expected distribution, both p non-random (i.e. unreliable) data in randomised controlled trials submitted to journals. © 2015 The Association of Anaesthetists of Great Britain and Ireland.
Image reconstruction in EIT with unreliable electrode data using random sample consensus method
Jeon, Min Ho; Khambampati, Anil Kumar; Kim, Bong Seok; In Kang, Suk; Kim, Kyung Youn
2017-04-01
In electrical impedance tomography (EIT), it is important to acquire reliable measurement data through EIT system for achieving good reconstructed image. In order to have reliable data, various methods for checking and optimizing the EIT measurement system have been studied. However, most of the methods involve additional cost for testing and the measurement setup is often evaluated before the experiment. It is useful to have a method which can detect the faulty electrode data during the experiment without any additional cost. This paper presents a method based on random sample consensus (RANSAC) to find the incorrect data on fault electrode in EIT data. RANSAC is a curve fitting method that removes the outlier data from measurement data. RANSAC method is applied with Gauss Newton (GN) method for image reconstruction of human thorax with faulty data. Numerical and phantom experiments are performed and the reconstruction performance of the proposed RANSAC method with GN is compared with conventional GN method. From the results, it can be noticed that RANSAC with GN has better reconstruction performance than conventional GN method with faulty electrode data.
Stratified Medicine and Reimbursement Issues
Hans-Joerg eFugel
2012-10-01
Full Text Available Stratified Medicine (SM has the potential to target patient populations who will most benefit from a therapy while reducing unnecessary health interventions associated with side effects. The link between clinical biomarkers/diagnostics and therapies provides new opportunities for value creation to strengthen the value proposition to pricing and reimbursement (P&R authorities. However, the introduction of SM challenges current reimbursement schemes in many EU countries and the US as different P&R policies have been adopted for drugs and diagnostics. Also, there is a lack of a consistent process for value assessment of more complex diagnostics in these markets. New, innovative approaches and more flexible P&R systems are needed to reflect the added value of diagnostic tests and to stimulate investments in new technologies. Yet, the framework for access of diagnostic–based therapies still requires further development while setting the right incentives and appropriate align stakeholders interests when realizing long- term patient benefits. This article addresses the reimbursement challenges of SM approaches in several EU countries and the US outlining some options to overcome existing reimbursement barriers for stratified medicine.
Yang, J; Cai, D; Wang, F; He, D; Ma, L; Jin, Y; Que, K
2016-12-01
This study investigated the prevalence, risk factors and association of occlusive wear with non-carious cervical lesions (NCCLs) in the general Chinese population. A total of 1320 subjects were recruited, and multistage and random sampling methods of survey spots were performed. All age groups comprised similar numbers of participants and equal numbers of males and females. Each subject completed a structured interview, and all teeth of each subject were examined by a practitioner to determine NCCLs and occlusive wear. Binary logistic regression was conducted by analysing the association of risk factors with the occurrence of NCCLs. Bivariate correlation analysis was performed by determining the association of NCCLs dimension or depth with the range of occlusive wear facets. Clinical assessment showed that the overall prevalence of subjects diagnosed with NCCLs was 63%. The proportion of subjects or teeth with NCCLs significantly increased with age. Pre-molars were the most commonly affected teeth. Single variables and interactive effects of variables associated with the occurrence of NCCLs include the following: age group, intensity of toothbrushing, frequency of fresh fruit consumption and interactive effect between intensity of toothbrushing and frequency of fresh fruit consumption. A weak positive correlation of the grading index was found between NCCLs dimension, size or depth and range of occlusive wear facets. This study reported the higher prevalence of NCCLs in the general Chinese population. Implementation of a combined strategy to reduce risk factors of NCCLs could be more effective than individual techniques; meanwhile, the occurrence of NCCL could be related to the wear degree of occlusive defects in the population studied. © 2016 John Wiley & Sons Ltd.
Biro, Peter A
2013-02-01
Sampling animals from the wild for study is something nearly every biologist has done, but despite our best efforts to obtain random samples of animals, 'hidden' trait biases may still exist. For example, consistent behavioral traits can affect trappability/catchability, independent of obvious factors such as size and gender, and these traits are often correlated with other repeatable physiological and/or life history traits. If so, systematic sampling bias may exist for any of these traits. The extent to which this is a problem, of course, depends on the magnitude of bias, which is presently unknown because the underlying trait distributions in populations are usually unknown, or unknowable. Indeed, our present knowledge about sampling bias comes from samples (not complete population censuses), which can possess bias to begin with. I had the unique opportunity to create naturalized populations of fish by seeding each of four small fishless lakes with equal densities of slow-, intermediate-, and fast-growing fish. Using sampling methods that are not size-selective, I observed that fast-growing fish were up to two-times more likely to be sampled than slower-growing fish. This indicates substantial and systematic bias with respect to an important life history trait (growth rate). If correlations between behavioral, physiological and life-history traits are as widespread as the literature suggests, then many animal samples may be systematically biased with respect to these traits (e.g., when collecting animals for laboratory use), and affect our inferences about population structure and abundance. I conclude with a discussion on ways to minimize sampling bias for particular physiological/behavioral/life-history types within animal populations.
Random sampling causes the low reproducibility of rare eukaryotic OTUs in Illumina COI metabarcoding
Knowlton, Nancy
2017-01-01
DNA metabarcoding, the PCR-based profiling of natural communities, is becoming the method of choice for biodiversity monitoring because it circumvents some of the limitations inherent to traditional ecological surveys. However, potential sources of bias that can affect the reproducibility of this method remain to be quantified. The interpretation of differences in patterns of sequence abundance and the ecological relevance of rare sequences remain particularly uncertain. Here we used one artificial mock community to explore the significance of abundance patterns and disentangle the effects of two potential biases on data reproducibility: indexed PCR primers and random sampling during Illumina MiSeq sequencing. We amplified a short fragment of the mitochondrial Cytochrome c Oxidase Subunit I (COI) for a single mock sample containing equimolar amounts of total genomic DNA from 34 marine invertebrates belonging to six phyla. We used seven indexed broad-range primers and sequenced the resulting library on two consecutive Illumina MiSeq runs. The total number of Operational Taxonomic Units (OTUs) was ∼4 times higher than expected based on the composition of the mock sample. Moreover, the total number of reads for the 34 components of the mock sample differed by up to three orders of magnitude. However, 79 out of 86 of the unexpected OTUs were represented by important. Our results further reinforce the need for technical replicates (parallel PCR and sequencing from the same sample) in metabarcoding experimental designs. Data reproducibility should be determined empirically as it will depend upon the sequencing depth, the type of sample, the sequence analysis pipeline, and the number of replicates. Moreover, estimating relative biomasses or abundances based on read counts remains elusive at the OTU level.
Reality check for the Chinese microblog space: a random sampling approach.
King-wa Fu
Full Text Available Chinese microblogs have drawn global attention to this online application's potential impact on the country's social and political environment. However, representative and reliable statistics on Chinese microbloggers are limited. Using a random sampling approach, this study collected Chinese microblog data from the service provider, analyzing the profile and the pattern of usage for 29,998 microblog accounts. From our analysis, 57.4% (95% CI 56.9%,58.0% of the accounts' timelines were empty. Among the 12,774 non-zero statuses samples, 86.9% (95% CI 86.2%,87.4% did not make original post in a 7-day study period. By contrast, 0.51% (95% CI 0.4%,0.65% wrote twenty or more original posts and 0.45% (95% CI 0.35%,0.60% reposted more than 40 unique messages within the 7-day period. A small group of microbloggers created a majority of contents and drew other users' attention. About 4.8% (95% CI 4.4%,5.2% of the 12,774 users contributed more than 80% (95% CI,78.6%,80.3% of the original posts and about 4.8% (95% CI 4.5%,5.2% managed to create posts that were reposted or received comments at least once. Moreover, a regression analysis revealed that volume of followers is a key determinant of creating original microblog posts, reposting messages, being reposted, and receiving comments. Volume of friends is found to be linked only with the number of reposts. Gender differences and regional disparities in using microblogs in China are also observed.
Suppression of stratified explosive interactions
Meeks, M.K.; Shamoun, B.I.; Bonazza, R.; Corradini, M.L. [Wisconsin Univ., Madison, WI (United States). Dept. of Nuclear Engineering and Engineering Physics
1998-01-01
Stratified Fuel-Coolant Interaction (FCI) experiments with Refrigerant-134a and water were performed in a large-scale system. Air was uniformly injected into the coolant pool to establish a pre-existing void which could suppress the explosion. Two competing effects due to the variation of the air flow rate seem to influence the intensity of the explosion in this geometrical configuration. At low flow rates, although the injected air increases the void fraction, the concurrent agitation and mixing increases the intensity of the interaction. At higher flow rates, the increase in void fraction tends to attenuate the propagated pressure wave generated by the explosion. Experimental results show a complete suppression of the vapor explosion at high rates of air injection, corresponding to an average void fraction of larger than 30%. (author)
Rudd, Timothy R; Macchi, Eleonora; Gardini, Cristina; Muzi, Laura; Guerrini, Marco; Yates, Edwin A; Torri, Giangiacomo
2012-08-07
Risks of contamination of the major clinical anticoagulant heparin can arise from deliberate adulteration with unnatural or natural polysaccharides, including heparin from other animal sources, other natural products, or artifacts of manufacture, and these can escape detection by conventional means. Currently, there is no generally applicable, objective test recommended by regulators that can detect these in pharmaceutical heparin, and this continues to leave heparin exposed to contamination risks. Two-dimensional correlation spectroscopic-filtering with iterative random sampling (2D-COS-firs) is reported. It employs a difference covariance matrix with iterative random sampling, and is capable of revealing contamination in pharmaceutical heparin to a high level of sensitivity irrespective of the nature of those features. The technique is suitable to any situation in which a comparison of a single entity to a family of heterogeneous entities, particularly natural products and biosimilars, needs to be made, and will find application in pharmaceutical monitoring, manufacturing quality control, materials science, biotechnology, and metabolomic investigations.
Fuel Burning Rate Model for Stratified Charge Engine
SONG Jin'ou; JIANG Zejun; YAO Chunde; WANG Hongfu
2006-01-01
A zero-dimensional single-zone double-curve model is presented to predict fuel burning rate in stratified charge engines, and it is integrated with GT-Power to predict the overall performance of the stratified charge engines.The model consists of two exponential functions for calculating the fuel burning rate in different charge zones.The model factors are determined by a non-linear curve fitting technique, based on the experimental data obtained from 30 cases in middle and low loads.The results show good agreement between the measured and calculated cylinder pressures,and the deviation between calculated and measured cylinder pressures is less than 5%.The zerodimensional single-zone double-curve model is successful in the combustion modeling for stratified charge engines.
Hillson, Roger; Alejandre, Joel D; Jacobsen, Kathryn H; Ansumana, Rashid; Bockarie, Alfred S; Bangura, Umaru; Lamin, Joseph M; Stenger, David A
2015-01-01
There is a need for better estimators of population size in places that have undergone rapid growth and where collection of census data is difficult. We explored simulated estimates of urban population based on survey data from Bo, Sierra Leone, using two approaches: (1) stratified sampling from across 20 neighborhoods and (2) stratified single-stage cluster sampling of only four randomly-sampled neighborhoods. The stratification variables evaluated were (a) occupants per individual residence, (b) occupants per neighborhood, and (c) residential structures per neighborhood. For method (1), stratification variable (a) yielded the most accurate re-estimate of the current total population. Stratification variable (c), which can be estimated from aerial photography and zoning type verification, and variable (b), which could be ascertained by surveying a limited number of households, increased the accuracy of method (2). Small household-level surveys with appropriate sampling methods can yield reasonably accurate estimations of urban populations.
Stratified wake of an accelerating hydrofoil
Ben-Gida, Hadar; Gurka, Roi
2015-01-01
Wakes of towed and self-propelled bodies in stratified fluids are significantly different from non-stratified wakes. Long time effects of stratification on the development of the wakes of bluff bodies moving at constant speed are well known. In this experimental study we demonstrate how buoyancy affects the initial growth of vortices developing in the wake of a hydrofoil accelerating from rest. Particle image velocimetry measurements were applied to characterize the wake evolution behind a NACA 0015 hydrofoil accelerating in water and for low Reynolds number and relatively strong and stably stratified fluid (Re=5,000, Fr~O(1)). The analysis of velocity and vorticity fields, following vortex identification and an estimate of the circulation, reveal that the vortices in the stratified fluid case are stretched along the streamwise direction in the near wake. The momentum thickness profiles show lower momentum thickness values for the stratified late wake compared to the non-stratified wake, implying that the dra...
How stratified is mantle convection?
Puster, Peter; Jordan, Thomas H.
1997-04-01
We quantify the flow stratification in the Earth's mid-mantle (600-1500 km) in terms of a stratification index for the vertical mass flux, Sƒ (z) = 1 - ƒ(z) / ƒref (z), in which the reference value ƒref(z) approximates the local flux at depth z expected for unstratified convection (Sƒ=0). Although this flux stratification index cannot be directly constrained by observations, we show from a series of two-dimensional convection simulations that its value can be related to a thermal stratification index ST(Z) defined in terms of the radial correlation length of the temperature-perturbation field δT(z, Ω). ST is a good proxy for Sƒ at low stratifications (SƒUniformitarian Principle. The bound obtained here from global tomography is consistent with local seismological evidence for slab flux into the lower mantle; however, the total material flux has to be significantly greater (by a factor of 2-3) than that due to slabs alone. A stratification index, Sƒ≲0.2, is sufficient to exclude many stratified convection models still under active consideration, including most forms of chemical layering between the upper and lower mantle, as well as the more extreme versions of avalanching convection governed by a strong endothermic phase change.
Core science: Stratified by a sunken impactor
Nakajima, Miki
2016-10-01
There is potential evidence for a stratified layer at the top of the Earth's core, but its origin is not well understood. Laboratory experiments suggest that the stratified layer could be a sunken remnant of the giant impact that formed the Moon.
A Fixpoint Semantics for Stratified Databases
沈一栋
1993-01-01
Przmusinski extended the notion of stratified logic programs,developed by Apt,Blair and Walker,and by van Gelder,to stratified databases that allow both negative premises and disjunctive consequents.However,he did not provide a fixpoint theory for such class of databases.On the other hand,although a fixpoint semantics has been developed by Minker and Rajasekar for non-Horn logic programs,it is tantamount to traditional minimal model semantics which is not sufficient to capture the intended meaning of negation in the premises of clauses in stratified databases.In this paper,a fixpoint approach to stratified databases is developed,which corresponds with the perfect model semantics.Moreover,algorithms are proposed for computing the set of perfect models of a stratified database.
Local time estimation for the slotted correlation function of randomly sampled LDA data
Nobach, H. [Fachgebiet Stroemungslehre und Aerodynamik, Technische Universitaet Darmstadt (Germany)
2002-03-01
The task of autocorrelation and power spectral density estimation from velocity data sampled irregularly in time by a laser-Doppler anemometer (LDA) is addressed in this article. A new method based on the slotting technique was found to be a very reliable estimator. This article describes specific improvements of the slotting technique, the model-based variance estimation and the spectral transform leading to more accurate estimates of the autocorrelation function and the power spectral density. Furthermore, the new method yields more information especially at short time lags of the autocorrelation function, which can be used to derive improved estimates of the Taylor time scale. (orig.)
The contribution of simple random sampling to observed variations in faecal egg counts.
Torgerson, Paul R; Paul, Michaela; Lewis, Fraser I
2012-09-10
It has been over 100 years since the classical paper published by Gosset in 1907, under the pseudonym "Student", demonstrated that yeast cells suspended in a fluid and measured by a haemocytometer conformed to a Poisson process. Similarly parasite eggs in a faecal suspension also conform to a Poisson process. Despite this there are common misconceptions how to analyse or interpret observations from the McMaster or similar quantitative parasitic diagnostic techniques, widely used for evaluating parasite eggs in faeces. The McMaster technique can easily be shown from a theoretical perspective to give variable results that inevitably arise from the random distribution of parasite eggs in a well mixed faecal sample. The Poisson processes that lead to this variability are described and illustrative examples of the potentially large confidence intervals that can arise from observed faecal eggs counts that are calculated from the observations on a McMaster slide. Attempts to modify the McMaster technique, or indeed other quantitative techniques, to ensure uniform egg counts are doomed to failure and belie ignorance of Poisson processes. A simple method to immediately identify excess variation/poor sampling from replicate counts is provided.
Strategies for Stratified Cartilage Bioprinting
Schuurman, W.
2012-01-01
Multiple materials, cells and growth factors can be combined into one construct by the use of a state–of-the-art bioprinter. This technique may in the future make the fabrication of complete tissues or organs possible. In this thesis the feasibility of the bioprinting of cartilage and the difference
Stratified medicine for mental disorders
Schumann, G.; Binder, E.B.; Holte, A.; Kloet, E.R. de; Oedegaard, K.J.; Robbins, T.W.; Walker-Tilley, T.R.; Bitter, I.; Brown, V.J.; Buitelaar, J.; Ciccocioppo, R.; Cools, R.; Escera, C.; Fleischhacker, W.; Flor, H.; Frith, C.D.; Heinz, A.; Johnsen, E.; Kirschbaum, C.; Klingberg, T.; Lesch, K.P.; Lewis, S.; Maier, W.; Mann, K.; Martinot, J.L.; Meyer-Lindenberg, A.; Muller, C.P.; Muller, W.E.; Nutt, D.J.; Persico, A.; Perugi, G.; Pessiglione, M.; Preuss, U.W.; Roiser, J.P.; Rossini, P.M.; Rybakowski, J.K.; Sandi, C.; Stephan, K.E.; Undurraga, J.; Vieta, E.; Wee, N. van der; Wykes, T.; Haro, J.M.; Wittchen, H.U.
2014-01-01
There is recognition that biomedical research into the causes of mental disorders and their treatment needs to adopt new approaches to research. Novel biomedical techniques have advanced our understanding of how the brain develops and is shaped by behaviour and environment. This has led to the
Andreas Steimer
Full Text Available Oscillations between high and low values of the membrane potential (UP and DOWN states respectively are an ubiquitous feature of cortical neurons during slow wave sleep and anesthesia. Nevertheless, a surprisingly small number of quantitative studies have been conducted only that deal with this phenomenon's implications for computation. Here we present a novel theory that explains on a detailed mathematical level the computational benefits of UP states. The theory is based on random sampling by means of interspike intervals (ISIs of the exponential integrate and fire (EIF model neuron, such that each spike is considered a sample, whose analog value corresponds to the spike's preceding ISI. As we show, the EIF's exponential sodium current, that kicks in when balancing a noisy membrane potential around values close to the firing threshold, leads to a particularly simple, approximative relationship between the neuron's ISI distribution and input current. Approximation quality depends on the frequency spectrum of the current and is improved upon increasing the voltage baseline towards threshold. Thus, the conceptually simpler leaky integrate and fire neuron that is missing such an additional current boost performs consistently worse than the EIF and does not improve when voltage baseline is increased. For the EIF in contrast, the presented mechanism is particularly effective in the high-conductance regime, which is a hallmark feature of UP-states. Our theoretical results are confirmed by accompanying simulations, which were conducted for input currents of varying spectral composition. Moreover, we provide analytical estimations of the range of ISI distributions the EIF neuron can sample from at a given approximation level. Such samples may be considered by any algorithmic procedure that is based on random sampling, such as Markov Chain Monte Carlo or message-passing methods. Finally, we explain how spike-based random sampling relates to existing
da Costa, Nuno Maçarico; Hepp, Klaus; Martin, Kevan A C
2009-05-30
Synapses can only be morphologically identified by electron microscopy and this is often a very labor-intensive and time-consuming task. When quantitative estimates are required for pathways that contribute a small proportion of synapses to the neuropil, the problems of accurate sampling are particularly severe and the total time required may become prohibitive. Here we present a sampling method devised to count the percentage of rarely occurring synapses in the neuropil using a large sample (approximately 1000 sampling sites), with the strong constraint of doing it in reasonable time. The strategy, which uses the unbiased physical disector technique, resembles that used in particle physics to detect rare events. We validated our method in the primary visual cortex of the cat, where we used biotinylated dextran amine to label thalamic afferents and measured the density of their synapses using the physical disector method. Our results show that we could obtain accurate counts of the labeled synapses, even when they represented only 0.2% of all the synapses in the neuropil.
Jannink, I; Bennen, J N; Blaauw, J; van Diest, P J; Baak, J P
1995-01-01
This study compares the influence of two different nuclear sampling methods on the prognostic value of assessments of mean and standard deviation of nuclear area (MNA, SDNA) in 191 consecutive invasive breast cancer patients with long term follow up. The first sampling method used was 'at convenience' sampling (ACS); the second, systematic random sampling (SRS). Both sampling methods were tested with a sample size of 50 nuclei (ACS-50 and SRS-50). To determine whether, besides the sampling methods, sample size had impact on prognostic value as well, the SRS method was also tested using a sample size of 100 nuclei (SRS-100). SDNA values were systematically lower for ACS, obviously due to (unconsciously) not including small and large nuclei. Testing prognostic value of a series of cut off points, MNA and SDNA values assessed by the SRS method were prognostically significantly stronger than the values obtained by the ACS method. This was confirmed in Cox regression analysis. For the MNA, the Mantel-Cox p-values from SRS-50 and SRS-100 measurements were not significantly different. However, for the SDNA, SRS-100 yielded significantly lower p-values than SRS-50. In conclusion, compared with the 'at convenience' nuclear sampling method, systematic random sampling of nuclei is not only superior with respect to reproducibility of results, but also provides a better prognostic value in patients with invasive breast cancer.
Computation of mixing in large stably stratified enclosures
Zhao, Haihua
This dissertation presents a set of new numerical models for the mixing and heat transfer problems in large stably stratified enclosures. Basing on these models, a new computer code, BMIX++ (Berkeley mechanistic MIXing code in C++), was developed by Christensen (2001) and the author. Traditional lumped control volume methods and zone models cannot model the detailed information about the distributions of temperature, density, and pressure in enclosures and therefore can have significant errors. 2-D and 3-D CFD methods require very fine grid resolution to resolve thin substructures such as jets, wall boundaries, yet such fine grid resolution is difficult or impossible to provide due to computational expense. Peterson's scaling (1994) showed that stratified mixing processes in large stably stratified enclosures can be described using one-dimensional differential equations, with the vertical transport by free and wall jets modeled using standard integral techniques. This allows very large reductions in computational effort compared to three-dimensional numerical modeling of turbulent mixing in large enclosures. The BMIX++ code was developed to implement the above ideas. The code uses a Lagrangian approach to solve 1-D transient governing equations for the ambient fluid and uses analytical models or 1-D integral models to compute substructures. 1-D transient conduction model for the solid boundaries, pressure computation and opening models are also included to make the code more versatile. The BMIX++ code was implemented in C++ and the Object-Oriented-Programming (OOP) technique was intensively used. The BMIX++ code was successfully applied to different types of mixing problems such as stratification in a water tank due to a heater inside, water tank exchange flow experiment simulation, early stage building fire analysis, stratification produced by multiple plumes, and simulations for the UCB large enclosure experiments. Most of these simulations gave satisfying
Vongsack Latsamy
2009-07-01
Full Text Available Abstract Background Counterfeit oral artesunate has been a major public health problem in mainland SE Asia, impeding malaria control. A countrywide stratified random survey was performed to determine the availability and quality of oral artesunate in pharmacies and outlets (shops selling medicines in the Lao PDR (Laos. Methods In 2003, 'mystery' shoppers were asked to buy artesunate tablets from 180 outlets in 12 of the 18 Lao provinces. Outlets were selected using stratified random sampling by investigators not involved in sampling. Samples were analysed for packaging characteristics, by the Fast Red Dye test, high-performance liquid chromatography (HPLC, mass spectrometry (MS, X-ray diffractometry and pollen analysis. Results Of 180 outlets sampled, 25 (13.9% sold oral artesunate. Outlets selling artesunate were more commonly found in the more malarious southern Laos. Of the 25 outlets, 22 (88%; 95%CI 68–97% sold counterfeit artesunate, as defined by packaging and chemistry. No artesunate was detected in the counterfeits by any of the chemical analysis techniques and analysis of the packaging demonstrated seven different counterfeit types. There was complete agreement between the Fast Red dye test, HPLC and MS analysis. A wide variety of wrong active ingredients were found by MS. Of great concern, 4/27 (14.8% fakes contained detectable amounts of artemisinin (0.26–115.7 mg/tablet. Conclusion This random survey confirms results from previous convenience surveys that counterfeit artesunate is a severe public health problem. The presence of artemisinin in counterfeits may encourage malaria resistance to artemisinin derivatives. With increasing accessibility of artemisinin-derivative combination therapy (ACT in Laos, the removal of artesunate monotherapy from pharmacies may be an effective intervention.
Stably stratified magnetized stars in general relativity
Yoshida, Shijun; Shibata, Masaru
2012-01-01
We construct magnetized stars composed of a fluid stably stratified by entropy gradients in the framework of general relativity, assuming ideal magnetohydrodynamics and employing a barotropic equation of state. We first revisit basic equations for describing stably-stratified stationary axisymmetric stars containing both poloidal and toroidal magnetic fields. As sample models, the magnetized stars considered by Ioka and Sasaki (2004), inside which the magnetic fields are confined, are modified to the ones stably stratified. The magnetized stars newly constructed in this study are believed to be more stable than the existing relativistic models because they have both poloidal and toroidal magnetic fields with comparable strength, and magnetic buoyancy instabilities near the surface of the star, which can be stabilized by the stratification, are suppressed.
Thermals in stratified regions of the ISM
Rodriguez-Gonzalez, Ary
2013-01-01
We present a model of a "thermal" (i.e., a hot bubble) rising within an exponentially stratified region of the ISM. This model includes terms representing the ram pressure braking and the entrainment of environmental gas into the thermal. We then calibrate the free parameters associated with these two terms through a comparison with 3D numerical simulations of a rising bubble. Finally, we apply our "thermal" model to the case of a hot bubble produced by a SN within the stratified ISM of the Galactic disk.
On Stratified Vortex Motions under Gravity.
2014-09-26
AD-A156 930 ON STRATIFIED VORTEX MOTIONS UNDER GRAVITY (U) NAVAL i/i RESEARCH LAB WASHINGTON DC Y T FUNG 20 JUN 85 NRL-MIR-5564 UNCLASSIFIED F/G 20/4...Under Gravity LCn * Y. T. Fung Fluid Dynamics Branch - Marine Technologyv Division June 20, 1985 SO Cyk. NAVAL RESEARCH LABORATORY Washington, D.C...DN880-019 TITLE (Include Security Classification) On Stratified Vortex Motions Under Gravity 12 PERSONAL AUTHOR(S) Funa, Y.T. 13a. TYPE OF REPORT 13b
Mixing by microorganisms in stratified fluids
Wagner, Gregory L; Lauga, Eric
2014-01-01
We examine the vertical mixing induced by the swimming of microorganisms at low Reynolds and P\\'eclet numbers in a stably stratified ocean, and show that the global contribution of oceanic microswimmers to vertical mixing is negligible. We propose two approaches to estimating the mixing efficiency, $\\eta$, or the ratio of the rate of potential energy creation to the total rate-of-working on the ocean by microswimmers. The first is based on scaling arguments and estimates $\\eta$ in terms of the ratio between the typical organism size, $a$, and an intrinsic length scale for the stratified flow, $\\ell = \\left ( \
THERMALS IN STRATIFIED REGIONS OF THE ISM
A. Rodríguez-González
2013-01-01
Full Text Available We present a model of a “thermal” (i.e., a hot bubble rising within an exponentially stratified region of the ISM. This model includes terms representing the ram pressure braking and the entrainment of environmental gas into the thermal. We then calibrate the free parameters associated with these two terms through a comparison with 3D numerical simulations of a rising bubble. Finally, we apply our “thermal” model to the case of a hot bubble produced by a SN within the stratified ISM of the Galactic disk.
Media Use and Source Trust among Muslims in Seven Countries: Results of a Large Random Sample Survey
Steven R. Corman
2013-12-01
Full Text Available Despite the perceived importance of media in the spread of and resistance against Islamist extremism, little is known about how Muslims use different kinds of media to get information about religious issues, and what sources they trust when doing so. This paper reports the results of a large, random sample survey among Muslims in seven countries Southeast Asia, West Africa and Western Europe, which helps fill this gap. Results show a diverse set of profiles of media use and source trust that differ by country, with overall low trust in mediated sources of information. Based on these findings, we conclude that mass media is still the most common source of religious information for Muslims, but that trust in mediated information is low overall. This suggests that media are probably best used to persuade opinion leaders, who will then carry anti-extremist messages through more personal means.
Kretzschmar, A; Durand, E; Maisonnasse, A; Vallon, J; Le Conte, Y
2015-06-01
A new procedure of stratified sampling is proposed in order to establish an accurate estimation of Varroa destructor populations on sticky bottom boards of the hive. It is based on the spatial sampling theory that recommends using regular grid stratification in the case of spatially structured process. The distribution of varroa mites on sticky board being observed as spatially structured, we designed a sampling scheme based on a regular grid with circles centered on each grid element. This new procedure is then compared with a former method using partially random sampling. Relative error improvements are exposed on the basis of a large sample of simulated sticky boards (n=20,000) which provides a complete range of spatial structures, from a random structure to a highly frame driven structure. The improvement of varroa mite number estimation is then measured by the percentage of counts with an error greater than a given level.
Turbulent Mixing in Stably Stratified Flows
2008-03-01
Liege Colloquium on Ocean Hydrodynamics, volume 46, page 19889898. Elsevier, 1987. R. M. Kerr. Higher-order derivative correlations and the alignment of...19th International Liege Colloquium on Ocean Hydrodynamics, volume 46, pages 3-9. Elsevier, 1988. P. Meunier and G. Spedding. Stratified propelled
Mir Mustafizur Rahman
2014-11-01
Full Text Available Thermal Infrared (TIR remote sensing images of urban environments are increasingly available from airborne and satellite platforms. However, limited access to high-spatial resolution (H-res: ~1 m TIR satellite images requires the use of TIR airborne sensors for mapping large complex urban surfaces, especially at micro-scales. A critical limitation of such H-res mapping is the need to acquire a large scene composed of multiple flight lines and mosaic them together. This results in the same scene components (e.g., roads, buildings, green space and water exhibiting different temperatures in different flight lines. To mitigate these effects, linear relative radiometric normalization (RRN techniques are often applied. However, the Earth’s surface is composed of features whose thermal behaviour is characterized by complexity and non-linearity. Therefore, we hypothesize that non-linear RRN techniques should demonstrate increased radiometric agreement over similar linear techniques. To test this hypothesis, this paper evaluates four (linear and non-linear RRN techniques, including: (i histogram matching (HM; (ii pseudo-invariant feature-based polynomial regression (PIF_Poly; (iii no-change stratified random sample-based linear regression (NCSRS_Lin; and (iv no-change stratified random sample-based polynomial regression (NCSRS_Poly; two of which (ii and iv are newly proposed non-linear techniques. When applied over two adjacent flight lines (~70 km2 of TABI-1800 airborne data, visual and statistical results show that both new non-linear techniques improved radiometric agreement over the previously evaluated linear techniques, with the new fully-automated method, NCSRS-based polynomial regression, providing the highest improvement in radiometric agreement between the master and the slave images, at ~56%. This is ~5% higher than the best previously evaluated linear technique (NCSRS-based linear regression.
Shudo, Toshio [Applied Energy System Group, Division of Energy and Environmental Systems, Hokkaido University, N13 W8 Kita-Ward, Sapporo, Hokkaido 060-8628 (Japan); Oba, Shuji [Mazda Motor Corporation, Hiroshima 730-8670 (Japan)
2009-03-15
Reduction in cooling loss due to the heat transfer from burning gas to the combustion chamber wall is very important for improving the thermal efficiency in hydrogen engines. The previous research has shown that the direct injection stratified charge can be a technique to reduce the cooling loss and improve thermal efficiency in hydrogen combustion. For effective reductions in cooling loss by the stratified charge, it is very important to know the relation between the fuel injection conditions and mixture distribution. The current research employs the laser induced breakdown spectroscopy as a method to measure the hydrogen concentration distribution in the direct injection stratified charge. Measurement of instantaneous local equivalence ratio by the method clears the characteristics of mixture formation in hydrogen direct injection stratified charge. This research also tries to actively control the mixture distribution using a split fuel injection. (author)
Drainage in a model stratified porous medium
Datta, Sujit S; 10.1209/0295-5075/101/14002
2013-01-01
We show that when a non-wetting fluid drains a stratified porous medium at sufficiently small capillary numbers Ca, it flows only through the coarsest stratum of the medium; by contrast, above a threshold Ca, the non-wetting fluid is also forced laterally, into part of the adjacent, finer strata. The spatial extent of this partial invasion increases with Ca. We quantitatively understand this behavior by balancing the stratum-scale viscous pressure driving the flow with the capillary pressure required to invade individual pores. Because geological formations are frequently stratified, we anticipate that our results will be relevant to a number of important applications, including understanding oil migration, preventing groundwater contamination, and sub-surface CO$_{2}$ storage.
Stably Stratified Flow in a Shallow Valley
Mahrt, L.
2017-01-01
Stratified nocturnal flow above and within a small valley of approximately 12-m depth and a few hundred metres width is examined as a case study, based on a network of 20 sonic anemometers and a central 20-m tower with eight levels of sonic anemometers. Several regimes of stratified flow over gentle topography are conceptually defined for organizing the data analysis and comparing with the existing literature. In our case study, a marginal cold pool forms within the shallow valley in the early evening but yields to larger ambient wind speeds after a few hours, corresponding to stratified terrain-following flow where the flow outside the valley descends to the valley floor. The terrain-following flow lasts about 10 h and then undergoes transition to an intermittent marginal cold pool towards the end of the night when the larger-scale flow collapses. During this 10-h period, the stratified terrain-following flow is characterized by a three-layer structure, consisting of a thin surface boundary layer of a few metres depth on the valley floor, a deeper boundary layer corresponding to the larger-scale flow, and an intermediate transition layer with significant wind-directional shear and possible advection of lee turbulence that is generated even for the gentle topography of our study. The flow in the valley is often modulated by oscillations with a typical period of 10 min. Cold events with smaller turbulent intensity and duration of tens of minutes move through the observational domain throughout the terrain-following period. One of these events is examined in detail.
Multi Dimensional CTL and Stratified Datalog
Theodore Andronikos
2010-02-01
Full Text Available In this work we define Multi Dimensional CTL (MD-CTL in short by extending CTL which is thedominant temporal specification language in practice. The need for Multi Dimensional CTL is mainlydue to the advent of semi-structured data. The common path nature of CTL and XPath which provides asuitable model for semi-structured data, has caused the emergence of work on specifying a relation amongthem aiming at exploiting the nice properties of CTL. Although the advantages of such an approach havealready been noticed [36, 26, 5], no formal definition of MD-CTL has been given. The goal of this workis twofold; a we define MD-CTL and prove that the “nice” properties of CTL (linear model checking andbounded model property transfer also to MD-CTL, b we establish new results on stratified Datalog. Inparticular, we define a fragment of stratified Datalog called Multi Branching Temporal (MBT in shortprograms that has the same expressive power as MD-CTL. We prove that by devising a linear translationbetween MBT and MD-CTL. We actually give the exact translation rules for both directions. We furtherbuild on this relation to prove that query evaluation is linear and checking satisfiability, containment andequivalence are EXPTIME–complete for MBT programs. The class MBT is the largest fragment of stratifiedDatalog for which such results exist in the literature.
Thermal mixing in a stratified environment
Kraemer, Damian; Cotel, Aline
1999-11-01
Laboratory experiments of a thermal impinging on a stratified interface have been performed. The thermal was released from a cylindrical reservoir located at the bottom of a Lucite tank. The stratified interface was created by filling the tank with two different saline solutions. The density of the lower layer is greater than that of the upper layer and the thermal fluid, thereby creating a stable stratification. A pH indicator, phenolphthalein, is used to visualize and quantify the amount of mixing produced by the impingement of the thermal at the interface. The upper layer contains a mixture of water, salt and sodium hydroxide. The thermal fluid is composed of water, sulfuric acid and phenolphthalein. When the thermal entrains and mixes fluid from the upper layer, a chemical reaction takes place, and the resulting mixed fluid is now visible. The ratio of base to acid, called the equivalence ratio, was varied throughout the experiments, as well as the Richardson number. The Richardson number is the ratio of potential to kinetic energy, and is based on the thermal quantities at the interface. Results indicate that the amount of mixing produced is proportional to the Richardson number raised to the -3/2 power. Previous experiments (Zhang and Cotel 1999) revealed that the entrainment rate of a thermal in a stratified environment follows the same power law.
Rhodes, Scott D.; McCoy, Thomas P.; Wilkin, Aimee M.; Wolfson, Mark
2013-01-01
This internet-based study was designed to compare health risk behaviors of gay and non-gay university students from stratified random cross-sectional samples of undergraduate students. Mean age of the 4,167 male participants was 20.5 (±2.7) years. Of these, 206 (4.9%) self-identified as gay and 3,961 (95.1%) self-identified as heterosexual. After adjusting for selected characteristics and clustering within university, gay men had higher odds of reporting: multiple sexual partners; cigarette smoking; methamphetamine use; gamma-hydroxybutyrate (GHB) use; other illicit drug use within the past 30 days and during lifetime; and intimate partner violence (IPV). Understanding the health risk behaviors of gay and heterosexual men is crucial to identifying associated factors and intervening upon them using appropriate and tailored strategies to reduce behavioral risk disparities and improve health outcomes. PMID:19882428
Jiang Houlong
2016-01-01
Full Text Available Sampling methods are important factors that can potentially limit the accuracy of predictions of spatial distribution patterns. A 10 ha tobacco-planted field was selected to compared the accuracy in predicting the spatial distribution of soil properties by using ordinary kriging and cross validation methods between grid sampling and simple random sampling scheme (SRS. To achieve this objective, we collected soil samples from the topsoil (0-20 cm in March 2012. Sample numbers of grid sampling and SRS were both 115 points each. Accuracies of spatial interpolation using the two sampling schemes were then evaluated based on validation samples (36 points and deviations of the estimates. The results suggested that soil pH and nitrate-N (NO3-N had low variation, whereas all other soil properties exhibited medium variation. Soil pH, organic matter (OM, total nitrogen (TN, cation exchange capacity (CEC, total phosphorus (TP and available phosphorus (AP matched the spherical model, whereas the remaining variables fit an exponential model with both sampling methods. The interpolation error of soil pH, TP, and AP was the lowest in SRS. The errors of interpolation for OM, CEC, TN, available potassium (AK and total potassium (TK were the lowest for grid sampling. The interpolation precisions of the soil NO3-N showed no significant differences between the two sampling schemes. Considering our data on interpolation precision and the importance of minerals for cultivation of flue-cured tobacco, the grid-sampling scheme should be used in tobacco-planted fields to determine the spatial distribution of soil properties. The grid-sampling method can be applied in a practical and cost-effective manner to facilitate soil sampling in tobacco-planted field.
The fully nonlinear stratified geostrophic adjustment problem
Coutino, Aaron; Stastna, Marek
2017-01-01
The study of the adjustment to equilibrium by a stratified fluid in a rotating reference frame is a classical problem in geophysical fluid dynamics. We consider the fully nonlinear, stratified adjustment problem from a numerical point of view. We present results of smoothed dam break simulations based on experiments in the published literature, with a focus on both the wave trains that propagate away from the nascent geostrophic state and the geostrophic state itself. We demonstrate that for Rossby numbers in excess of roughly 2 the wave train cannot be interpreted in terms of linear theory. This wave train consists of a leading solitary-like packet and a trailing tail of dispersive waves. However, it is found that the leading wave packet never completely separates from the trailing tail. Somewhat surprisingly, the inertial oscillations associated with the geostrophic state exhibit evidence of nonlinearity even when the Rossby number falls below 1. We vary the width of the initial disturbance and the rotation rate so as to keep the Rossby number fixed, and find that while the qualitative response remains consistent, the Froude number varies, and these variations are manifested in the form of the emanating wave train. For wider initial disturbances we find clear evidence of a wave train that initially propagates toward the near wall, reflects, and propagates away from the geostrophic state behind the leading wave train. We compare kinetic energy inside and outside of the geostrophic state, finding that for long times a Rossby number of around one-quarter yields an equal split between the two, with lower (higher) Rossby numbers yielding more energy in the geostrophic state (wave train). Finally we compare the energetics of the geostrophic state as the Rossby number varies, finding long-lived inertial oscillations in the majority of the cases and a general agreement with the past literature that employed either hydrostatic, shallow-water equation-based theory or
Inverse scattering of dispersive stratified structures
Skaar, Johannes
2012-01-01
We consider the inverse scattering problem of retrieving the structural parameters of a stratified medium consisting of dispersive materials, given knowledge of the complex reflection coefficient in a finite frequency range. It is shown that the inverse scattering problem does not have a unique solution in general. When the dispersion is sufficiently small, such that the time-domain Fresnel reflections have durations less than the round-trip time in the layers, the solution is unique and can be found by layer peeling. Numerical examples with dispersive and lossy media are given, demonstrating the usefulness of the method for e.g. THz technology.
Topological Structures in Rotating Stratified Flows
Redondo, J. M.; Carrillo, A.; Perez, E.
2003-04-01
Detailled 2D Particle traking and PIV visualizations performed on a series of large scale laboratory experiments at the Coriolis Platform of the SINTEF in Trondheim have revealed several resonances which scale on the Strouhal, the Rossby and the Richardson numbers. More than 100 experiments spanned a wide range of Rossby Deformation Radii and the topological structures (Parabolic /Eliptic /Hyperbolic) of the quasi-balanced stratified-rotating flows were studied when stirring (akin to coastal mixing) occured at a side of the tank. The strong asymetry favored by the total vorticity produces a wealth of mixing patterns.
Penetrative convection in stratified fluids: velocity and temperature measurements
M. Moroni
2006-01-01
Full Text Available The flux through the interface between a mixing layer and a stable layer plays a fundamental role in characterizing and forecasting the quality of water in stratified lakes and in the oceans, and the quality of air in the atmosphere. The evolution of the mixing layer in a stably stratified fluid body is simulated in the laboratory when "Penetrative Convection" occurs. The laboratory model consists of a tank filled with water and subjected to heating from below. The methods employed to detect the mixing layer growth were thermocouples for temperature data and two image analysis techniques, namely Laser Induced Fluorescence (LIF and Feature Tracking (FT. LIF allows the mixing layer evolution to be visualized. Feature Tracking is used to detect tracer particle trajectories moving within the measurement volume. Pollutant dispersion phenomena are naturally described in the Lagrangian approach as the pollutant acts as a tag of the fluid particles. The transilient matrix represents one of the possible tools available for quantifying particle dispersion during the evolution of the phenomenon.
Feeding patterns and dietary intake in a random sample of a Swedish population of insured-dogs.
Sallander, Marie; Hedhammar, Ake; Rundgren, Margareta; Lindberg, Jan E
2010-07-01
We used a validated mail and telephone questionnaire to investigate baseline data on feeding patterns and dietary intake in a random sample of 460 Swedish dogs. In 1999, purebred individuals 1-3 years old in the largest insurance database of Sweden completed the study. Most dogs were fed restricted amounts twice a day, and the feeding patterns seldom were changed after the age of 6 months. Typically, the main constituent of the meals was dry food [representing 69% of dry matter (DM)]. Four out of five dogs also got foods that (in descending order of the amount of energy provided) consisted of vegetable oil, meat, sour milk, bread, potatoes, pasta, lard/tallow, sausage, cheese, rice and fish. The heavier the dog (kg), the more dry dog food was consumed (g DM/d). The dry-food intakes (g DM/d) increased linearly with body weight (BW, in kg): intake=-15.3+8.33 BW (P=0.0001; r=0.998), a clear relationship that was not observed for other commercial foods. The non-commercial part of the diet had higher fat (13 and 8 g/megajoule, MJ, respectively; P=0.00001) and lower protein (12 and 16 g/MJ, respectively; P=0.00001) compared to the commercial part of the diet. Six out of ten dogs were given treats, and one-fourth was given vitamin/mineral supplements (most commonly daily). Most dogs consumed diets that were nutritionally balanced. No dogs in the study consumed diets that supplied lower amounts of protein than recommended by the NRC (2006). Only two individuals (<1%) were given total diets that were lower than the nutrient profiles in fat. Few dogs consumed total diets that were lower than recommended by the NRC (2006) in calcium, phosphorus, and vitamins A, D and E (2, 1, 3, 5, and 3% of the individuals, respectively). A few individuals consumed higher levels of vitamins A and D (<1 and 4%, respectively) than recommended. Diets that deviated from recommended levels were those consisting of only table foods with no supplements (too-low in vitamins and minerals) or
Chien, Ming-Hung; Guo, How-Ran
2014-01-01
Background Falls are common in older people and may lead to functional decline, disability, and death. Many risk factors have been identified, but studies evaluating effects of nutritional status are limited. To determine whether nutritional status is a predictor of falls in older people living in the community, we analyzed data collected through the Survey of Health and Living Status of the Elderly in Taiwan (SHLSET). Methods SHLSET include a series of interview surveys conducted by the government on a random sample of people living in community dwellings in the nation. We included participants who received nutritional status assessment using the Mini Nutritional Assessment Taiwan Version 2 (MNA-T2) in the 1999 survey when they were 53 years or older and followed up on the cumulative incidence of falls in the one-year period before the interview in the 2003 survey. Results At the beginning of follow-up, the 4440 participants had a mean age of 69.5 (standard deviation = 9.1) years, and 467 participants were “not well-nourished,” which was defined as having an MNA-T2 score of 23 or less. In the one-year study period, 659 participants reported having at least one fall. After adjusting for other risk factors, we found the associated odds ratio for falls was 1.73 (95% confidence interval, 1.23, 2.42) for “not well-nourished,” 1.57 (1.30, 1.90) for female gender, 1.03 (1.02, 1.04) for one-year older, 1.55 (1.22, 1.98) for history of falls, 1.34 (1.05, 1.72) for hospital stay during the past 12 months, 1.66 (1.07, 2.58) for difficulties in activities of daily living, and 1.53 (1.23, 1.91) for difficulties in instrumental activities of daily living. Conclusion Nutritional status is an independent predictor of falls in older people living in the community. Further studies are warranted to identify nutritional interventions that can help prevent falls in the elderly. PMID:24614184
Deal, J. H.
1975-01-01
One approach to the problem of simplifying complex nonlinear filtering algorithms is through using stratified probability approximations where the continuous probability density functions of certain random variables are represented by discrete mass approximations. This technique is developed in this paper and used to simplify the filtering algorithms developed for the optimum receiver for signals corrupted by both additive and multiplicative noise.
龚金海; 梁法春; 刘德绪; 燕慧
2012-01-01
Traditional invasive liquid film measurement method such as conductance probe technique is not suitable for the gas-liquid two-phase flow system with high pressure, flammable,combustible and corrosity medium. A novel method was proposed based on infrared imaging for gas-liquid two phase stratified flow liquid film height measurement. In order to improve the measurement accuracy, a heating belt was applied to improve the temperature difference between the gas and liquid,the film height was obtained using infrared imaging to distinguish gas-liquid interface. A VOF multiphase flow model was used to simulate the temperature distribution of the pipe section under constant heat flux,based on this,the experiments were carried out at an air-water two-phase flow loop and the infrared image were obtained using an infrared camera. The gas-liquid interface position was determined according to the temperature gradient characteristics. The measurement results were compared with capacitance probe method. It showed during the experimental range,the maximum measurement error was 8. 2% .%对于输送高压、易燃易爆、强腐蚀性介质的气液两相流管道,电导探针等传统的介入式液膜厚度测量方法不适用.针对这种情况,提出了通过红外热像测量气液两相分层流液膜厚度的新方法:在管道外壁敷设加热带,通过施加恒定热流密度来增加气液相温差,通过采集红外图像识别气液界面获得液膜高度.在建立VOF多相流模型模拟恒定热流密度条件下管截面上温度分布特征基础上,实验在气液两相流环道上进行,采用热像仪采集管壁红外图像,真实液膜厚度由介入式电容探针测量,在试验范围内红外方法液膜厚度测量最大误差8.2％.
Stratified growth in Pseudomonas aeruginosa biofilms
Werner, E.; Roe, F.; Bugnicourt, A.;
2004-01-01
In this study, stratified patterns of protein synthesis and growth were demonstrated in Pseudomonas aeruginosa biofilms. Spatial patterns of protein synthetic activity inside biofilms were characterized by the use of two green fluorescent protein (GFP) reporter gene constructs. One construct...... carried an isopropyl-beta-D-thiogalactopyranoside (IPTG)-inducible gfpmut2 gene encoding a stable GFP. The second construct carried a GFP derivative, gfp-AGA, encoding an unstable GFP under the control of the growth-rate-dependent rrnBp(1) promoter. Both GFP reporters indicated that active protein...... of oxygen limitation in the biofilm. Oxygen microelectrode measurements showed that oxygen only penetrated approximately 50 mum into the biofilm. P. aeruginosa was incapable of anaerobic growth in the medium used for this investigation. These results show that while mature P. aeruginosa biofilms contain...
Bayesian Stratified Sampling to Assess Corpus Utility
Hochberg, J; Thomas, T; Hall, S; Hochberg, Judith; Scovel, Clint; Thomas, Timothy; Hall, Sam
1998-01-01
This paper describes a method for asking statistical questions about a large text corpus. We exemplify the method by addressing the question, "What percentage of Federal Register documents are real documents, of possible interest to a text researcher or analyst?" We estimate an answer to this question by evaluating 200 documents selected from a corpus of 45,820 Federal Register documents. Stratified sampling is used to reduce the sampling uncertainty of the estimate from over 3100 documents to fewer than 1000. The stratification is based on observed characteristics of real documents, while the sampling procedure incorporates a Bayesian version of Neyman allocation. A possible application of the method is to establish baseline statistics used to estimate recall rates for information retrieval systems.
Clustering of floating particles in stratified turbulence
Boffetta, Guido; de Lillo, Filippo; Musacchio, Stefano; Sozza, Alessandro
2016-11-01
We study the dynamics of small floating particles transported by stratified turbulence in presence of a mean linear density profile as a simple model for the confinement and the accumulation of plankton in the ocean. By means of extensive direct numerical simulations we investigate the statistical distribution of floaters as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of non-neutral particles in turbulence, depends on the particle relaxation time and is only weakly dependent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed.
On turbulence in a stratified environment
Sarkar, Sutanu
2015-11-01
John Lumley, motivated by atmospheric observations, made seminal contributions to the statistical theory (Lumley and Panofsky 1964, Lumley 1964) and second-order modeling (Zeman and Lumley 1976) of turbulence in the environment. Turbulent processes in the ocean share many features with the atmosphere, e.g., shear, stratification, rotation and rough topography. Results from direct and large eddy simulations of two model problems will be used to illustrate some of the features of turbulence in a stratified environment. The first problem concerns a shear layer in nonuniform stratification, a situation typical of both the atmosphere and the ocean. The second problem, considered to be responsible for much of the turbulent mixing that occurs in the ocean interior, concerns topographically generated internal gravity waves. Connections will be made to data taken during observational campaigns in the ocean.
Stratified scaffold design for engineering composite tissues.
Mosher, Christopher Z; Spalazzi, Jeffrey P; Lu, Helen H
2015-08-01
A significant challenge to orthopaedic soft tissue repair is the biological fixation of autologous or allogeneic grafts with bone, whereby the lack of functional integration between such grafts and host bone has limited the clinical success of anterior cruciate ligament (ACL) and other common soft tissue-based reconstructive grafts. The inability of current surgical reconstruction to restore the native fibrocartilaginous insertion between the ACL and the femur or tibia, which minimizes stress concentration and facilitates load transfer between the soft and hard tissues, compromises the long-term clinical functionality of these grafts. To enable integration, a stratified scaffold design that mimics the multiple tissue regions of the ACL interface (ligament-fibrocartilage-bone) represents a promising strategy for composite tissue formation. Moreover, distinct cellular organization and phase-specific matrix heterogeneity achieved through co- or tri-culture within the scaffold system can promote biomimetic multi-tissue regeneration. Here, we describe the methods for fabricating a tri-phasic scaffold intended for ligament-bone integration, as well as the tri-culture of fibroblasts, chondrocytes, and osteoblasts on the stratified scaffold for the formation of structurally contiguous and compositionally distinct regions of ligament, fibrocartilage and bone. The primary advantage of the tri-phasic scaffold is the recapitulation of the multi-tissue organization across the native interface through the layered design. Moreover, in addition to ease of fabrication, each scaffold phase is similar in polymer composition and therefore can be joined together by sintering, enabling the seamless integration of each region and avoiding delamination between scaffold layers.
Stratified sampling design based on data mining.
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.
Information content of household-stratified epidemics
T.M. Kinyanjui
2016-09-01
Full Text Available Household structure is a key driver of many infectious diseases, as well as a natural target for interventions such as vaccination programs. Many theoretical and conceptual advances on household-stratified epidemic models are relatively recent, but have successfully managed to increase the applicability of such models to practical problems. To be of maximum realism and hence benefit, they require parameterisation from epidemiological data, and while household-stratified final size data has been the traditional source, increasingly time-series infection data from households are becoming available. This paper is concerned with the design of studies aimed at collecting time-series epidemic data in order to maximize the amount of information available to calibrate household models. A design decision involves a trade-off between the number of households to enrol and the sampling frequency. Two commonly used epidemiological study designs are considered: cross-sectional, where different households are sampled at every time point, and cohort, where the same households are followed over the course of the study period. The search for an optimal design uses Bayesian computationally intensive methods to explore the joint parameter-design space combined with the Shannon entropy of the posteriors to estimate the amount of information in each design. For the cross-sectional design, the amount of information increases with the sampling intensity, i.e., the designs with the highest number of time points have the most information. On the other hand, the cohort design often exhibits a trade-off between the number of households sampled and the intensity of follow-up. Our results broadly support the choices made in existing epidemiological data collection studies. Prospective problem-specific use of our computational methods can bring significant benefits in guiding future study designs.
Behtani, A.; Bouazzouni, A.; Khatir, S.; Tiachacht, S.; Zhou, Y.-L.; Abdel Wahab, M.
2017-05-01
In this paper, the problem of using measured modal parameters to detect and locate damage in beam composite stratified structures with four layers of graphite/epoxy [0°/902°/0°] is investigated. A technique based on the residual force method is applied to composite stratified structure with different boundary conditions, the results of damage detection for several damage cases demonstrate that using residual force method as damage index, the damage location can be identified correctly and the damage extents can be estimated as well.
Strongly Stratified Turbulence Wakes and Mixing Produced by Fractal Wakes
Dimitrieva, Natalia; Redondo, Jose Manuel; Chashechkin, Yuli; Fraunie, Philippe; Velascos, David
2017-04-01
This paper describes Shliering and Shadowgraph experiments of the wake induced mixing produced by tranversing a vertical or horizontal fractal grid through the interfase between two miscible fluids at low Atwood and Reynolds numbers. This is a configuration design to models the mixing across isopycnals in stably-stratified flows in many environmental relevant situations (either in the atmosphere or in the ocean. The initial unstable stratification is characterized by a reduced gravity: g' = gΔρ ρ where g is gravity, Δρ being the initial density step and ρ the reference density. Here the Atwood number is A = g' _ 2 g . The topology of the fractal wake within the strong stratification, and the internal wave field produces both a turbulent cascade and a wave cascade, with frecuen parametric resonances, the envelope of the mixing front is found to follow a complex non steady 3rd order polinomial function with a maximum at about 4-5 Brunt-Vaisalla non-dimensional time scales: t/N δ = c1(t/N) + c2g Δρ ρ (t/N)2 -c3(t/N)3. Conductivity probes and Shliering and Shadowgraph visual techniques, including CIV with (Laser induced fluorescence and digitization of the light attenuation across the tank) are used in order to investigate the density gradients and the three-dimensionality of the expanding and contracting wake. Fractal analysis is also used in order to estimate the fastest and slowest growing wavelengths. The large scale structures are observed to increase in wave-length as the mixing progresses, and the processes involved in this increase in scale are also examined.Measurements of the pointwise and horizontally averaged concentrations confirm the picture obtained from past flow visualization studies. They show that the fluid passes through the mixing region with relatively small amounts of molecular mixing,and the molecular effects only dominate on longer time scales when the small scales have penetrated through the large scale structures. The Non
Effect of turbulent fluctuations on the behaviour of fountains in stratified environments
Freire, D.; Cabeza, C.; Pauletti, S.; Sarasúa, G.; Bove, I.; Usera, G.; Martí, A. C.
2010-09-01
The interaction between a turbulent fountain and its stratified environment was studied. A heavy fluid, cold water, was injected vertically upwards into a linearly stratified medium. The round heavy-fluid jet reaches a maximum height before it begins to fall due to the effect of gravity. Because of the effects of friction and mixing, the vertical momentum and density of the jet fluid decrease as it submerges to an intermediate height of zero buoyancy. At this point, the jet fluid spreads as a horizontal front, intruding into the stratified environment. The degree of fluctuation in the proximity of the injection point was studied under both unrestricted- and restricted-flow configurations at the injection, using two differently sized stainless-steel woven-wire screens at the injection port as flow-restricting means. Using visualization and velocimetry techniques, both maximum and spreading heights were found to decrease with increasing turbulence at the point of injection.
A NONHYDROSTATIC NUMERICAL MODEL FOR DENSITY STRATIFIED FLOW AND ITS APPLICATIONS
无
2008-01-01
A modular numerical model was developed for simulating density-stratified flow in domains with irregular bottom topography. The model was designed for examining interactions between stratified flow and topography, e.g., tidally driven flow over two-dimensional sills or internal solitary waves propagating over a shoaling bed. The model was based on the non-hydrostatic vorticity-stream function equations for a continuously stratified fluid in a rotating frame. A self-adaptive grid was adopted in the vertical coordinate, the Alternative Direction Implicit (ADI) scheme was used for the time marching equations while the Poisson equation for stream-function was solved based on the Successive Over Relaxation (SOR) iteration with the Chebyshev acceleration. The numerical techniques were described and three applications of the model were presented.
Pita-Fernández, Salvador; González-Martín, Cristina; Seoane-Pillado, Teresa; López-Calviño, Beatriz; Pértega-Díaz, Sonia; Gil-Guillén, Vicente
2015-01-01
Background Research is needed to determine the prevalence and variables associated with the diagnosis of flatfoot, and to evaluate the validity of three footprint analysis methods for diagnosing flatfoot, using clinical diagnosis as a benchmark. Methods We conducted a cross-sectional study of a population-based random sample ≥40 years old (n = 1002) in A Coruña, Spain. Anthropometric variables, Charlson’s comorbidity score, and podiatric examination (including measurement of Clarke’s angle, t...
Magnetic flux concentrations from turbulent stratified convection
Käpylä, P J; Kleeorin, N; Käpylä, M J; Rogachevskii, I
2015-01-01
(abridged) Context: The mechanisms that cause the formation of sunspots are still unclear. Aims: We study the self-organisation of initially uniform sub-equipartition magnetic fields by highly stratified turbulent convection. Methods: We perform simulations of magnetoconvection in Cartesian domains that are $8.5$-$24$ Mm deep and $34$-$96$ Mm wide. We impose either a vertical or a horizontal uniform magnetic field in a convection-driven turbulent flow. Results: We find that super-equipartition magnetic flux concentrations are formed near the surface with domain depths of $12.5$ and $24$ Mm. The size of the concentrations increases as the box size increases and the largest structures ($20$ Mm horizontally) are obtained in the 24 Mm deep models. The field strength in the concentrations is in the range of $3$-$5$ kG. The concentrations grow approximately linearly in time. The effective magnetic pressure measured in the simulations is positive near the surface and negative in the bulk of the convection zone. Its ...
[Phylogenetic diversity of bacteria in soda lake stratified sediments].
Tourova, T P; Grechnikova, M A; Kuznetsov, V V; Sorokin, D Yu
2014-01-01
Various previously developed techniques for DNA extraction from the samples with complex physicochemical structure (soils, silts, and sediments) and modifications of these techniques developed in the present work were tested. Their usability for DNA extraction from the sediments of the Kulunda Steppe hypersaline soda lakes was assessed, and the most efficient procedure for indirect (two-stage) DNA extraction was proposed. Almost complete separation of the cell fraction was shown, as well as the inefficiency of nested PCR for analysis of the clone libraries obtained from washed sediments by amplification of the 16S rRNA gene fragments. Analysis of the clone library obtained from the cell fractions of stratified sediments (upper, medium, and lower layers) revealed that in the sediments of Lake Gorchina-3 most eubacterial phylotypes belonged to the class Clostridia, phylum Firmicutes. They were probably specific for this habitatand formed a new, presently unknown high-rank taxon. The data obtained revealed no pronounced stratification of the spe- cies diversity of the eubacterial component of the microbial community inhabiting the sediments (0-20 cm) in the inshore zone of Lake Gorchina-3.
Stratified spaces constitute a Fra\\"iss\\'e category
Mijares, José Gregorio
2010-01-01
We prove that stratified spaces and stratified pseudomanifolds satisfy categorical Fra\\"{\\i}ss\\'e properties. This result was presented for the First Meeting of Logic and Algebra in Bogot\\'a, on Sept. 2010. This article has been submitted to the Revista Colombiana de Matem\\'aticas.
Gas slug ascent through rheologically stratified conduits
Capponi, Antonio; James, Mike R.; Lane, Steve J.
2016-04-01
Textural and petrological evidence has indicated the presence of viscous, degassed magma layers at the top of the conduit at Stromboli. This layer acts as a plug through which gas slugs burst and it is thought to have a role in controlling the eruptive dynamics. Here, we present the results of laboratory experiments which detail the range of slug flow configurations that can develop in a rheologically stratified conduit. A gas slug can burst (1) after being fully accommodated within the plug volume, (2) whilst its base is still in the underlying low-viscosity liquid or (3) within a low-viscosity layer dynamically emplaced above the plug during the slug ascent. We illustrate the relevance of the same flow configurations at volcanic-scale through a new experimentally-validated 1D model and 3D computational fluid dynamic simulations. Applied to Stromboli, our results show that gas volume, plug thickness, plug viscosity and conduit radius control the transition between each configuration; in contrast, the configuration distribution seems insensitive to the viscosity of magma beneath the plug, which acts mainly to deliver the slug into the plug. Each identified flow configuration encompasses a variety of processes including dynamic narrowing and widening of the conduit, generation of instabilities along the falling liquid film, transient blockages of the slug path and slug break-up. All these complexities, in turn, lead to variations in the slug overpressure, mirrored by changes in infrasonic signatures which are also associated to different eruptive styles. Acoustic amplitudes are strongly dependent on the flow configuration in which the slugs burst, with both acoustic peak amplitudes and waveform shapes reflecting different burst dynamics. When compared to infrasonic signals from Stromboli, the similarity between real signals and laboratory waveforms suggests that the burst of a slug through a plug may represent a viable first-order mechanism for the generation of
Methane metabolism in a stratified boreal lake
Nykänen, Hannu; Peura, Sari; Kankaala, Paula; Jones, Roger
2013-04-01
Stratified lakes, typical of the boreal zone, are naturally anoxic from their bottoms. In these lakes methanogenesis can account for up to half of organic matter degradation. However, a major part of the methane (CH4) is oxidized in the water column before reaching the atmosphere. Since methanotrophs use CH4 as their sole carbon and energy source, much CH4-derived carbon is incorporated into their biomass. Microbially produced CH4 has strongly negative δ13C compared to other carbon forms in ecosystems, making it possible to follow its route in food webs. However, only a few studies have estimated the amount of this microbial biomass or its carbon stable isotopic composition due to difficulties in separating it from other biomass or from other carbon forms in the water column. We estimated methanotrophic biomass from measured CH4 oxidation, and δ13C of the biomass from measured δ13C values of CH4, DIC, POM and DOC. An estimate of the fraction of methanotrophs in total microbial biomass is derived from bacterial community composition measurements. The study was made in, Alinen Mustajärvi, a small (area 0.75 ha, maximum depth 6.5 m, mean depth 4.2 m,), oligotrophic, mesohumic headwater lake located in boreal coniferous forest in southern Finland. CH4 and DIC concentrations and their δ13C were measured over the deepest point of the lake at 1 m intervals. 13C of DOM and POM were analyzed from composite samples from epi-, meta-, and hypolimnion. Evasion of CH4 and carbon dioxide from the lake surface to the atmosphere was estimated with boundary layer diffusion equations. CH4oxidation was estimated by comparing differences between observed concentrations and CH4potentially transported by turbulent diffusion between different vertical layers in the lake and also by actual methanotrophy measurements and from vertical differences in δ13C-CH4. The estimate of CH4 production was based on the sum of oxidized and released CH4. Molecular microbiology methods were used to
The Universal Aspect Ratio of Vortices in Rotating Stratifi?ed Flows: Experiments and Observations
Aubert, Oriane; Gal, Patrice Le; Marcus, Philip S
2012-01-01
We validate a new law for the aspect ratio $\\alpha = H/L$ of vortices in a rotating, stratified flow, where $H$ and $L$ are the vertical half-height and horizontal length scale of the vortices. The aspect ratio depends not only on the Coriolis parameter f and buoyancy (or Brunt-Vaisala) frequency $\\bar{N}$ of the background flow, but also on the buoyancy frequency $N_c$ within the vortex and on the Rossby number $Ro$ of the vortex such that $\\alpha = f \\sqrt{[Ro (1 + Ro)/(N_c^2- \\bar{N}^2)]}$. This law for $\\alpha$ is obeyed precisely by the exact equilibrium solution of the inviscid Boussinesq equations that we show to be a useful model of our laboratory vortices. The law is valid for both cyclones and anticyclones. Our anticyclones are generated by injecting fluid into a rotating tank filled with linearly-stratified salt water. The vortices are far from the top and bottom boundaries of the tank, so there is no Ekman circulation. In one set of experiments, the vortices viscously decay, but as they do, they c...
Large eddy simulation of unsteady lean stratified premixed combustion
Duwig, C. [Division of Fluid Mechanics, Department of Energy Sciences, Lund University, SE 221 00 Lund (Sweden); Fureby, C. [Division of Weapons and Protection, Warheads and Propulsion, The Swedish Defense Research Agency, FOI, SE 147 25 Tumba (Sweden)
2007-10-15
Premixed turbulent flame-based technologies are rapidly growing in importance, with applications to modern clean combustion devices for both power generation and aeropropulsion. However, the gain in decreasing harmful emissions might be canceled by rising combustion instabilities. Unwanted unsteady flame phenomena that might even destroy the whole device have been widely reported and are subject to intensive studies. In the present paper, we use unsteady numerical tools for simulating an unsteady and well-documented flame. Computations were performed for nonreacting, perfectly premixed and stratified premixed cases using two different numerical codes and different large-eddy-simulation-based flamelet models. Nonreacting simulations are shown to agree well with experimental data, with the LES results capturing the mean features (symmetry breaking) as well as the fluctuation level of the turbulent flow. For reacting cases, the uncertainty induced by the time-averaging technique limited the comparisons. Given an estimate of the uncertainty, the numerical results were found to reproduce well the experimental data in terms both of mean flow field and of fluctuation levels. In addition, it was found that despite relying on different assumptions/simplifications, both numerical tools lead to similar predictions, giving confidence in the results. Moreover, we studied the flame dynamics and particularly the response to a periodic pulsation. We found that above a certain excitation level, the flame dynamic changes and becomes rather insensitive to the excitation/instability amplitude. Conclusions regarding the self-growth of thermoacoustic waves were drawn. (author)
Numerical Study of Stratified Charge Combustion in Wave Rotors
Nalim, M. Razi
1997-01-01
A wave rotor may be used as a pressure-gain combustor effecting non-steady flow, and intermittent, confined combustion to enhance gas turbine engine performance. It will be more compact and probably lighter than an equivalent pressure-exchange wave rotor, yet will have similar thermodynamic and mechanical characteristics. Because the allowable turbine blade temperature limits overall fuel/air ratio to sub-flammable values, premixed stratification techniques are necessary to burn hydrocarbon fuels in small engines with compressor discharge temperature well below autoignition conditions. One-dimensional, unsteady numerical simulations of stratified-charge combustion are performed using an eddy-diffusivity turbulence model and a simple reaction model incorporating a flammability limit temperature. For good combustion efficiency, a stratification strategy is developed which concentrates fuel at the leading and trailing edges of the inlet port. Rotor and exhaust temperature profiles and performance predictions are presented at three representative operating conditions of the engine: full design load, 40% load, and idle. The results indicate that peak local gas temperatures will result in excessive temperatures within the rotor housing unless additional cooling methods are used. The rotor itself will have acceptable temperatures, but the pattern factor presented to the turbine may be of concern, depending on exhaust duct design and duct-rotor interaction.
Dielectric Properties Determination of a Stratified Medium
P. Yoiyod
2015-04-01
Full Text Available The method of detection of variation in dielectric properties of a material covered with another material, which requires nondestructive measurement, has numerous applications and the accurate measurement system is desirable. This paper presents a dielectric properties determination technique whereby the dielectric constant and loss factor are extracted from the measured reflection coefficient. The high frequency reflection coefficient shows the effect of the upper layer, while the dielectric properties of the lower layer can be determined at the lower frequency. The proposed technique is illustrated in 1-11 GHz band using 5 mm-thick water and 5% saline solution. The fluctuation of the dielectric properties between the high frequency and the low frequency, results from the edge diffraction in the material and the multiple reflections at the boundary of the two media, are invalid results. With the proposed technique, the dielectric properties of the lower layer can be accurately determined. The system is validated by measurement and good agreement is obtained at the frequency below 3.5 GHz. It can be applied for justifying variation of the material in the lower layer which is important in industrial process.
Hunge, Y. M.; Mahadik, M. A.; Moholkar, A. V.; Bhosale, C. H.
2017-10-01
In the present work, stratified WO3/ZnO thin films have been prepared by simple chemical spray pyrolysis technique. The structural, morphological, compositional and photoelectrocatalytic properties of the stratified WO3/ZnO thin films are studied. The photoelectrochemical (PEC) study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc = 1.023 mA and Voc = 0.980 V) relatively high at 40 ml spraying quantity of ZnO solution on pre-deposited WO3 thin films. XRD analysis reveals that stratified WO3/ZnO thin films are polycrystalline with monoclinic and hexagonal crystal structures for WO3 and ZnO respectively. The specific surface area of the stratified WO3/ZnO thin film is found to be 48.12 m2 g-1. The enhanced photoelectrocatalytic activity of stratified WO3/ZnO is mainly due to the suppressing the recombination of photo generated electron-hole pairs. The end result shows that the degradation percentage of phthalic acid (PA) using stratified WO3/ZnO photo electrode has reached 63.63% after 320 min. under sunlight illumination. The amount of mineralization of phthalic acid is studied with the help of chemical oxygen demand (COD) measurement.
Tangling clustering instability for small particles in temperature stratified turbulence
Elperin, Tov; Liberman, Michael; Rogachevskii, Igor
2013-01-01
We study particle clustering in a temperature stratified turbulence with small finite correlation time. It is shown that the temperature stratified turbulence strongly increases the degree of compressibility of particle velocity field. This results in the strong decrease of the threshold for the excitation of the tangling clustering instability even for small particles. The tangling clustering instability in the temperature stratified turbulence is essentially different from the inertial clustering instability that occurs in non-stratified isotropic and homogeneous turbulence. While the inertial clustering instability is caused by the centrifugal effect of the turbulent eddies, the mechanism of the tangling clustering instability is related to the temperature fluctuations generated by the tangling of the mean temperature gradient by the velocity fluctuations. Temperature fluctuations produce pressure fluctuations and cause particle clustering in regions with increased pressure fluctuations. It is shown that t...
Effects of rotation on turbulent buoyant plumes in stratified environments
Fabregat Tomàs, Alexandre; Poje, Andrew C; Özgökmen, Tamay M; Dewar, William K
2016-01-01
We numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large Rossby numbers characteristic of deep oceanic releases...
The Influence of Instructional Materials on Academic Performance of ...
... State through simple random sampling and stratified random sampling techniques. ... significant level while the Pearson product moment correlation coefficient at ... use of instructional materials generally improved students' understanding of ...
Numerical Study on Saltwater Instrusion in a Heterogeneous Stratified Aquifer
2000-01-01
In a costal aquifer, saltwater intrusion is frequently observed due to an excess exploitation. There are many researches focused on the saltwater intrusion. However, there are few researches, which take into consideration the mixing processes in a stratified heterogeneous aquifer. In the present study, a laboratory experiment and numerical simulation are made in order to understand the phenomena in a stratified heterogeneous aquifer. The result of the numerical analysis agrees well with the m...
Assessing iron dynamics in the release from a stratified reservoir
Ashby, S.L.; Faulkner, S.P.; Gambrell, R.P.; Smith, B.A.
2004-01-01
Field and laboratory studies were conducted to describe the fate of total, dissolved, and ferrous (Fe2.) iron in the release from a stratified reservoir with an anoxic hypolimnion. Concentrations of total iron in the tail water indicated a first order removal process during a low flow release (0.6 m3sec1), yet negligible loss was observed during a period of increased discharge (2.8 m 3 sec-1). Dissolved and ferrous iron concentrations in the tailwater were highly variable during both release regimes and did not follow responses based on theoretical predictions. Ferrous iron concentrations in unfiltered samples were consistently greater than concentrations observed in samples filtered separately through 0.4, 0.2, and 0.1 ??m filters. Total iron removal in laboratory studies followed first order kinetics, but was twice that rate (0.077 mg.L-1 .hr 1) observed during low flow discharge in the tailwater (0.036 mg. L1 .hr1). Dissolved and ferrous iron losses in laboratory studies were rapid (???75% in the first 15 minutes and 95% within 1 hour), followed theoretical predictions, and were much faster than observations in the tailwater (???30% within the first hour). The presence of particulate forms of ferrous iron in the field and differences in removal rates observed in field and laboratory studies indicate a need for improved field assessment techniques and consideration of complexation reactions when assessing the dynamics of iron in reservoir releases and downstream impacts as a result of operation regimes. ?? Copyright by the North American Lake Management Society 2004.
Lisovskiy, V. A.; Koval, V. A.; Artushenko, E. P.; Yegorenkov, V. D.
2012-01-01
In this paper we suggest a simple technique for validating the Goldstein-Wehner law for a stratified positive column of dc glow discharge while studying the properties of gas discharges in an undergraduate laboratory. To accomplish this a simple device with a pre-vacuum mechanical pump, dc source and gas pressure gauge is required. Experiments may…
Huang, S.R. [Feng Chia Univ., Taichung (Taiwan, Province of China). Electrical Engineering Dept.
1997-03-01
A combined Monte Carlo and optimum stratified sampling method is presented to better estimate copper loss of a transmission system during a prespecified future period. This design seeks to enhance the precision of copper loss of transmission system estimation, while reducing computation time. The techniques included are optimum stratified sampling and separate ratio estimation. The optimum stratification rule aims to remove any judgemental input and to render the stratification process entirely mechanistic. The estimator, provided by ratio statistics of the sample, can avoid identification of the regression model and thus save computation time. The effectiveness of precision improvement is demonstrated. (UK)
Stability of stratified two-phase flows in horizontal channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima; Vitoshkin, Helen
2016-01-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems the stratified flow with smooth interface is stable only in confined zone of relatively lo...
Background Oriented Schlieren in a Density Stratified Fluid
Verso, Lilly
2015-01-01
Non-intrusive quantitative fluid density measurements methods are essential in stratified flow experiments. Digital imaging leads to synthetic Schlieren methods in which the variations of the index of refraction are reconstructed computationally. In this study, an important extension to one of these methods, called Background Oriented Schlieren (BOS), is proposed. The extension enables an accurate reconstruction of the density field in stratified liquid experiments. Typically, the experiments are performed by the light source, background pattern, and the camera positioned on the opposite sides of a transparent vessel. The multi-media imaging through air-glass-water-glass-air leads to an additional aberration that destroys the reconstruction. A two-step calibration and image remapping transform are the key components that correct the images through the stratified media and provide non-intrusive full-field density measurements of transparent liquids.
Background oriented schlieren in a density stratified fluid
Verso, Lilly; Liberzon, Alex
2015-10-01
Non-intrusive quantitative fluid density measurement methods are essential in the stratified flow experiments. Digital imaging leads to synthetic schlieren methods in which the variations of the index of refraction are reconstructed computationally. In this study, an extension to one of these methods, called background oriented schlieren, is proposed. The extension enables an accurate reconstruction of the density field in stratified liquid experiments. Typically, the experiments are performed by the light source, background pattern, and the camera positioned on the opposite sides of a transparent vessel. The multimedia imaging through air-glass-water-glass-air leads to an additional aberration that destroys the reconstruction. A two-step calibration and image remapping transform are the key components that correct the images through the stratified media and provide a non-intrusive full-field density measurements of transparent liquids.
SINDA/FLUINT Stratified Tank Modeling for Cryrogenic Propellant Tanks
Sakowski, Barbara
2014-01-01
A general purpose SINDA/FLUINT (S/F) stratified tank model was created to simulate self-pressurization and axial jet TVS; Stratified layers in the vapor and liquid are modeled using S/F lumps.; The stratified tank model was constructed to permit incorporating the following additional features:, Multiple or singular lumps in the liquid and vapor regions of the tank, Real gases (also mixtures) and compressible liquids, Venting, pressurizing, and draining, Condensation and evaporation/boiling, Wall heat transfer, Elliptical, cylindrical, and spherical tank geometries; Extensive user logic is used to allow detailed tailoring - Don't have to rebuilt everything from scratch!!; Most code input for a specific case is done through the Registers Data Block:, Lump volumes are determined through user input:; Geometric tank dimensions (height, width, etc); Liquid level could be input as either a volume percentage of fill level or actual liquid level height
Numerical Simulation on Stratified Flow over an Isolated Mountain Ridge
LI Ling; Shigeo Kimura
2007-01-01
The characteristics of stratified flow over an isolated mountain ridge have been investigated numerically. The two-dimensional model equations, based on the time-dependent Reynolds averaged NavierStokes equations, are solved numerically using an implicit time integration in a fitted body grid arrangement to simulate stratified flow over an isolated ideally bell-shaped mountain. The simulation results are in good agreement with the existing corresponding analytical and approximate solutions. It is shown that for atmospheric conditions where non-hydrostatic effects become dominant, the model is able to reproduce typical flow features. The dispersion characteristics of gaseous pollutants in the stratified flow have also been studied. The dispersion patterns for two typical atmospheric conditions are compared. The results show that the presence of a gravity wave causes vertical stratification of the pollutant concentration and affects the diffusive characteristics of the pollutants.
Stability of stratified two-phase flows in inclined channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima
2016-01-01
Linear stability of stratified gas-liquid and liquid-liquid plane-parallel flows in inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict parameter regions in which stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of steady state solutions are presented on the flow pattern map and are accompanied by critical wavenumbers and spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of ...
Linear Inviscid Damping for Couette Flow in Stratified Fluid
Yang, Jincheng
2016-01-01
We study the inviscid damping of Coutte flow with an exponentially stratified density. The optimal decay rates of the velocity field and density are obtained for general perturbations with minimal regularity. For Boussinesq approximation model, the decay rates we get are consistent with the previous results in the literature. We also study the decay rates for the full equations of stratified fluids, which were not studied before. For both models, the decay rates depend on the Richardson number in a very similar way. Besides, we also study the inviscid damping of perturbations due to the exponential stratification when there is no shear.
Bases of Schur algebras associated to cellularly stratified diagram algebras
Bowman, C
2011-01-01
We examine homomorphisms between induced modules for a certain class of cellularly stratified diagram algebras, including the BMW algebra, Temperley-Lieb algebra, Brauer algebra, and (quantum) walled Brauer algebra. We define the `permutation' modules for these algebras, these are one-sided ideals which allow us to study the diagrammatic Schur algebras of Hartmann, Henke, Koenig and Paget. We construct bases of these Schur algebras in terms of modified tableaux. On the way we prove that the (quantum) walled Brauer algebra and the Temperley-Lieb algebra are both cellularly stratified and therefore have well-defined Specht filtrations.
Kemp, Alan E. S.; Villareal, Tracy A.
2013-12-01
It is widely held that increased stratification and reduced vertical mixing in the ocean driven by global warming will promote the replacement of diatoms by smaller phytoplankton and lead to an overall decrease in productivity and carbon export. Here we present contrary evidence from a synergy of modern observations and palaeo-records that reveal high diatom production and export from stratified waters. Diatom adaptations to stratified waters include the ability to grow in low light conditions in deep chlorophyll maxima; vertical migrations between nutricline depths and the surface, and symbioses with N2-fixing cyanobacteria in diatom-diazotroph associations (DDA). These strategies foster the maintenance of seed populations that may then exploit mixing events induced by storms or eddies, but may also inherently promote blooms. Recent oceanographic observations in the subtropical gyres, at increasingly high temporal and spatial resolutions, have monitored short-lived but often substantial blooms and export of stratified-adapted diatoms including rhizosolenids and the diazotroph-associated Hemiaulus hauckii. Aggregate formation by such diatoms is common and promotes rapid settling thereby minimizing water column remineralization and optimizing carbon flux. Convergence zones associated with oceanic fronts or mesoscale features may also generate substantial flux of stratified-adapted diatom species. Conventional oceanographic observing strategies and sampling techniques under-represent such activity due to the lack of adequate capability to sample the large sized diatoms and colonies involved, the subsurface location of many of these blooms, their common development in thin global warming. However, the key genera involved in such potential feedbacks are underrepresented in both laboratory and field studies and are poorly represented in models. Our findings suggest that a reappraisal is necessary of the way diatoms are represented as plankton functional types (PFTs) in
Miller, Ezer; Huppert, Amit; Novikov, Ilya; Warburg, Alon; Hailu, Asrat; Abbasi, Ibrahim; Freedman, Laurence S
2015-11-10
In this work, we describe a two-stage sampling design to estimate the infection prevalence in a population. In the first stage, an imperfect diagnostic test was performed on a random sample of the population. In the second stage, a different imperfect test was performed in a stratified random sample of the first sample. To estimate infection prevalence, we assumed conditional independence between the diagnostic tests and develop method of moments estimators based on expectations of the proportions of people with positive and negative results on both tests that are functions of the tests' sensitivity, specificity, and the infection prevalence. A closed-form solution of the estimating equations was obtained assuming a specificity of 100% for both tests. We applied our method to estimate the infection prevalence of visceral leishmaniasis according to two quantitative polymerase chain reaction tests performed on blood samples taken from 4756 patients in northern Ethiopia. The sensitivities of the tests were also estimated, as well as the standard errors of all estimates, using a parametric bootstrap. We also examined the impact of departures from our assumptions of 100% specificity and conditional independence on the estimated prevalence. Copyright © 2015 John Wiley & Sons, Ltd.
Analysis of photonic band-gap structures in stratified medium
Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong;
2005-01-01
Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...
Plane Stratified Flow in a Room Ventilated by Displacement Ventilation
Nielsen, Peter Vilhelm; Nickel, J.; Baron, D. J. G.
2004-01-01
The air movement in the occupied zone of a room ventilated by displacement ventilation exists as a stratified flow along the floor. This flow can be radial or plane according to the number of wall-mounted diffusers and the room geometry. The paper addresses the situations where plane flow...
Bacterial production, protozoan grazing and mineralization in stratified lake Vechten.
Bloem, J.
1989-01-01
The role of heterotrophic nanoflagellates (HNAN, size 2-20 μm) in grazing on bacteria and mineralization of organic matter in stratified Lake Vechten was studied.Quantitative effects of manipulation and fixation on HNAN were checked. Considerable losses were caused by centrifugation, even at low spe
Population dynamics of sinking phytoplankton in stratified waters
Huisman, J.; Sommeijer, B.P.
2002-01-01
We analyze the predictions of a reaction-advection-diffusion model to pinpoint the necessary conditions for bloom development of sinking phytoplanktonspecies in stratified waters. This reveals that there are two parameter windows that can sustain sinking phytoplankton, a turbulence window and atherm
Gravity-induced stresses in stratified rock masses
Amadei, B.; Swolfs, H.S.; Savage, W.Z.
1988-01-01
This paper presents closed-form solutions for the stress field induced by gravity in anisotropic and stratified rock masses. These rocks are assumed to be laterally restrained. The rock mass consists of finite mechanical units, each unit being modeled as a homogeneous, transversely isotropic or isotropic linearly elastic material. The following results are found. The nature of the gravity induced stress field in a stratified rock mass depends on the elastic properties of each rock unit and how these properties vary with depth. It is thermodynamically admissible for the induced horizontal stress component in a given stratified rock mass to exceed the vertical stress component in certain units and to be smaller in other units; this is not possible for the classical unstratified isotropic solution. Examples are presented to explore the nature of the gravity induced stress field in stratified rock masses. It is found that a decrease in rock mass anisotropy and a stiffening of rock masses with depth can generate stress distributions comparable to empirical hyperbolic distributions previously proposed in the literature. ?? 1988 Springer-Verlag.
Dispersion of (light) inertial particles in stratified turbulence
van Aartrijk, M.; Clercx, H.J.H.; Armenio, Vincenzo; Geurts, Bernardus J.; Fröhlich, Jochen
2010-01-01
We present a brief overview of a numerical study of the dispersion of particles in stably stratified turbulence. Three types of particles arc examined: fluid particles, light inertial particles ($\\rho_p/\\rho_f = \\mathcal{O}(1)$) and heavy inertial particles ($\\rho_p/\\rho_f \\gg 1$). Stratification
The dynamics of small inertial particles in weakly stratified turbulence
van Aartrijk, M.; Clercx, H.J.H.
We present an overview of a numerical study on the small-scale dynamics and the large-scale dispersion of small inertial particles in stably stratified turbulence. Three types of particles are examined: fluid particles, light inertial particles (with particle-to-fluid density ratio 1Ͽp/Ͽf25) and
Characterization of Inlet Diffuser Performance for Stratified Thermal Storage
Cimbala, John M.; Bahnfleth, William; Song, Jing
1999-11-01
Storage of sensible heating or cooling capacity in stratified vessels has important applications in central heating and cooling plants, power production, and solar energy utilization, among others. In stratified thermal storage systems, diffusers at the top and bottom of a stratified tank introduce and withdraw fluid while maintaining a stable density gradient and causing as little mixing as possible. In chilled water storage applications, mixing during the formation of the thermocline near an inlet diffuser is the single greatest source of thermal losses. Most stratified chilled water storage tanks are cylindrical vessels with diffusers that are either circular disks that distribute flow radially outward or octagonal rings of perforated pipe that distribute flow both inward and outward radially. Both types produce gravity currents that are strongly influenced by the inlet Richardson number, but the significance of other parameters is not clear. The present investigation considers the dependence of the thermal performance of a perforated pipe diffuser on design parameters including inlet velocity, ambient and inlet fluid temperatures, and tank dimensions for a range of conditions representative of typical chilled water applications. Dimensional analysis is combined with a parametric study using results from computational fluid dynamics to obtain quantitative relationships between design parameters and expected thermal performance.
Global and Partial Errors in Stratified and Clustering Sampling
Giovanna Nicolini; Anna Lo Presti
2005-01-01
In this paper we split up the sampling error occurred in stratified and clustering sampling, called global error and measured by the variance of estimator, in many partial errors each one referred to a single stratum or cluster. In particular, we study, for clustering sampling, the empirical distribution of the homogeneity coefficient that is very important for settlement of partial errors.
Sainath, Kamalesh; Teixeira, Fernando L; Donderici, Burkay
2014-01-01
We develop a general-purpose formulation, based on two-dimensional spectral integrals, for computing electromagnetic fields produced by arbitrarily oriented dipoles in planar-stratified environments, where each layer may exhibit arbitrary and independent anisotropy in both its (complex) permittivity and permeability tensors. Among the salient features of our formulation are (i) computation of eigenmodes (characteristic plane waves) supported in arbitrarily anisotropic media in a numerically robust fashion, (ii) implementation of an hp-adaptive refinement for the numerical integration to evaluate the radiation and weakly evanescent spectra contributions, and (iii) development of an adaptive extension of an integral convergence acceleration technique to compute the strongly evanescent spectrum contribution. While other semianalytic techniques exist to solve this problem, none have full applicability to media exhibiting arbitrary double anisotropies in each layer, where one must account for the whole range of possible phenomena (e.g., mode coupling at interfaces and nonreciprocal mode propagation). Brute-force numerical methods can tackle this problem but only at a much higher computational cost. The present formulation provides an efficient and robust technique for field computation in arbitrary planar-stratified environments. We demonstrate the formulation for a number of problems related to geophysical exploration.
Hassanzadeh, Pedram
infer the height and internal stratification of some astrophysical and geophysical vortices because direct measurements of their vertical structures are difficult. In Chapter 3, we show numerically and experimentally that localized suction in rotating continuously stratified flows produces three-dimensional baroclinic cyclones. As expected from Chapter 2, the interiors of these cyclones are super-stratified. Suction, modeled as a small spherical sink in the simulations, creates an anisotropic flow toward the sink with directional dependence changing with the ratio of the Coriolis parameter to the Brunt-Vaisala frequency. Around the sink, this flow generates cyclonic vorticity and deflects isopycnals so that the interior of the cyclone becomes super-stratified. The super-stratified region is visualized in the companion experiments that we helped to design and analyze using the synthetic schlieren technique. Once the suction stops, the cyclones decay due to viscous dissipation in the simulations and experiments. The numerical results show that the vertical velocity of viscously decaying cyclones flows away from the cyclone's midplane, while the radial velocity flows toward the cyclone's center. This observation is explained based on the cyclo-geostrophic balance. This vertical velocity mixes the flow inside and outside of cyclone and reduces the super-stratification. We speculate that the predominance of anticyclones in geophysical and astrophysical flows is due to the fact that anticyclones require sub-stratification, which occurs naturally by mixing, while cyclones require super-stratification. In Chapter 4, we show that a previously unknown instability creates space-filling lattices of 3D turbulent baroclinic vortices in linearly-stable, rotating, stratified shear flows. The instability starts from a newly discovered family of easily-excited critical layers. This new family, named the baroclinic critical layer, has singular vertical velocities; the traditional family
Study of MRI in Stratified Viscous Plasma Configuration
Carlevaro, Nakia; Renzi, Fabrizio
2016-01-01
We analyze the morphology of the Magneto-rotational Instability (MRI) for a stratified viscous plasma disk configuration in differential rotation, taking into account the so-called corotation theorem for the background profile. In order to select the intrinsic Alfv\\'enic nature of MRI, we deal with an incompressible plasma and we adopt a formulation of the perturbation analysis based on the use of the magnetic flux function as a dynamical variable. Our study outlines, as consequence of the corotation condition, a marked asymmetry of the MRI with respect to the equatorial plane, particularly evident in a complete damping of the instability over a positive critical height on the equatorial plane. We also emphasize how such a feature is already present (although less pronounced) even in the ideal case, restoring a dependence of the MRI on the stratified morphology of the gravitational field.
FC-normal and extended stratified logic program
许道云; 丁德成
2002-01-01
This paper investigates the consistency property of FC-normal logic program and presentsan equivalent deciding condition whether a logic program P is an FC-normal program. The decidingcondition describes the characterizations of FC-normal program. By the Petri-net presentation ofa logic program, the characterizations of stratification of FC-normal program are investigated. Thestratification of FC-normal program motivates us to introduce a new kind of stratification, extendedstratification, over logic program. It is shown that an extended (locally) stratified logic program isan FC-normal program. Thus, an extended (locally) stratified logic program has at least one stablemodel. Finally, we have presented algorithms about computation of consistency property and a fewequivalent deciding methods of the finite FC-normal program.
Turbulent thermal diffusion in strongly stratified turbulence: theory and experiments
Amir, G; Eidelman, A; Elperin, T; Kleeorin, N; Rogachevskii, I
2016-01-01
Turbulent thermal diffusion is a combined effect of the temperature stratified turbulence and inertia of small particles. It causes the appearance of a non-diffusive turbulent flux of particles in the direction of the turbulent heat flux. This non-diffusive turbulent flux of particles is proportional to the product of the mean particle number density and the effective velocity of inertial particles. The theory of this effect has been previously developed only for small temperature gradients and small Stokes numbers (Phys. Rev. Lett. {\\bf 76}, 224, 1996). In this study a generalized theory of turbulent thermal diffusion for arbitrary temperature gradients and Stokes numbers has been developed. The laboratory experiments in the oscillating grid turbulence and in the multi-fan produced turbulence have been performed to validate the theory of turbulent thermal diffusion in strongly stratified turbulent flows. It has been shown that the ratio of the effective velocity of inertial particles to the characteristic ve...
Numerical Simulation of Wakes in a Weakly Stratified Fluid
Rottman, James W; Innis, George E; O'Shea, Thomas T; Novikov, Evgeny
2014-01-01
This paper describes some preliminary numerical studies using large eddy simulation of full-scale submarine wakes. Submarine wakes are a combination of the wake generated by a smooth slender body and a number of superimposed vortex pairs generated by various control surfaces and other body appendages. For this preliminary study, we attempt to gain some insight into the behavior of full-scale submarine wakes by computing separately the evolution the self-propelled wake of a slender body and the motion of a single vortex pair in both a non-stratified and a stratified environment. An important aspect of the simulations is the use of an iterative procedure to relax the initial turbulence field so that turbulent production and dissipation are in balance.
Helicity dynamics in stratified turbulence in the absence of forcing
Rorai, C; Pouquet, A; Mininni, P D
2012-01-01
A numerical study of decaying stably-stratified flows is performed. Relatively high stratification and moderate Reynolds numbers are considered, and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations). The problem is tackled by integrating the Boussinesq equations in a periodic cubical domain using different initial conditions: a non-helical Taylor-Green (TG) flow, a fully helical Beltrami (ABC) flow, and random flows with a tunable helicity. We show that for stratified ABC flows helicity undergoes a substantially slower decay than for unstratified ABC flows. This fact is likely associated to the combined effect of stratification and large scale coherent structures. Indeed, when the latter are missing, as in random flows, helicity is rapidly destroyed by the onset of gravitational waves. A type of large-scale dissipative "cyclostrophic" balance can be invoked to explain this behavior. When helicity survives in the system it strongly affects the temporal energy decay and t...
Axisymmetric modes in vertically stratified self-gravitating discs
Mamatsashvili, George
2010-01-01
We perform linear analysis of axisymmetric vertical normal modes in stratified compressible self-gravitating polytropic discs in the shearing box approximation. We study specific dynamics for subadiabatic, adiabatic and superadiabatic vertical stratifications. In the absence of self-gravity, four well-known principal modes can be identified in a stratified disc: acoustic p-, surface gravity f-, buoyancy g- and inertial r-modes. After characterizing modes in the non-self-gravitating case, we include self-gravity and investigate how it modifies the properties of these modes. We find that self-gravity, to a certain degree, reduces their frequencies and changes the structure of the dispersion curves and eigenfunctions at radial wavelengths comparable to the disc height. Its influence on the basic branch of the r-mode, in the case of subadiabatic and adiabatic stratifications, and on the basic branch of the g-mode, in the case of superadiabatic stratification (which in addition exhibits convective instability), do...
Elementary stratified flows with stability at low Richardson number
Barros, Ricardo [Mathematics Applications Consortium for Science and Industry (MACSI), Department of Mathematics and Statistics, University of Limerick, Limerick (Ireland); Choi, Wooyoung [Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey 07102-1982 (United States)
2014-12-15
We revisit the stability analysis for three classical configurations of multiple fluid layers proposed by Goldstein [“On the stability of superposed streams of fluids of different densities,” Proc. R. Soc. A. 132, 524 (1931)], Taylor [“Effect of variation in density on the stability of superposed streams of fluid,” Proc. R. Soc. A 132, 499 (1931)], and Holmboe [“On the behaviour of symmetric waves in stratified shear layers,” Geophys. Publ. 24, 67 (1962)] as simple prototypes to understand stability characteristics of stratified shear flows with sharp density transitions. When such flows are confined in a finite domain, it is shown that a large shear across the layers that is often considered a source of instability plays a stabilizing role. Presented are simple analytical criteria for stability of these low Richardson number flows.
Experiments on the dryout behavior of stratified debris beds
Leininger, Simon; Kulenovic, Rudi; Laurien, Eckart [Stuttgart Univ. (Germany). Inst. of Nuclear Technology and Energy Systems (IKE)
2015-10-15
In case of a severe accident with loss of coolant and core meltdown a particle bed (debris) can be formed. The removal of decay heat from the debris bed is of prime importance for the bed's long-term coolability to guarantee the integrity of the RPV. In contrast to previous experiments, the focus is on stratified beds. The experiments have pointed out that the bed's coolability is significantly affected.
A statistical mechanics approach to mixing in stratified fluids
Venaille, A.; Gostiaux, L.; Sommeria, J.
2017-01-01
Predicting how much mixing occurs when a given amount of energy is injected into a Boussinesq fluid is a longstanding problem in stratified turbulence. The huge number of degrees of freedom involved in those processes renders extremely difficult a deterministic approach to the problem. Here we present a statistical mechanics approach yielding prediction for a cumulative, global mixing efficiency as a function of a global Richardson number and the background buoyancy profile.
Corticosteroids and pediatric septic shock outcomes: a risk stratified analysis.
Sarah J Atkinson
Full Text Available The potential benefits of corticosteroids for septic shock may depend on initial mortality risk.We determined associations between corticosteroids and outcomes in children with septic shock who were stratified by initial mortality risk.We conducted a retrospective analysis of an ongoing, multi-center pediatric septic shock clinical and biological database. Using a validated biomarker-based stratification tool (PERSEVERE, 496 subjects were stratified into three initial mortality risk strata (low, intermediate, and high. Subjects receiving corticosteroids during the initial 7 days of admission (n = 252 were compared to subjects who did not receive corticosteroids (n = 244. Logistic regression was used to model the effects of corticosteroids on 28-day mortality and complicated course, defined as death within 28 days or persistence of two or more organ failures at 7 days.Subjects who received corticosteroids had greater organ failure burden, higher illness severity, higher mortality, and a greater requirement for vasoactive medications, compared to subjects who did not receive corticosteroids. PERSEVERE-based mortality risk did not differ between the two groups. For the entire cohort, corticosteroids were associated with increased risk of mortality (OR 2.3, 95% CI 1.3-4.0, p = 0.004 and a complicated course (OR 1.7, 95% CI 1.1-2.5, p = 0.012. Within each PERSEVERE-based stratum, corticosteroid administration was not associated with improved outcomes. Similarly, corticosteroid administration was not associated with improved outcomes among patients with no comorbidities, nor in groups of patients stratified by PRISM.Risk stratified analysis failed to demonstrate any benefit from corticosteroids in this pediatric septic shock cohort.
Dust particle charge distribution in a stratified glow discharge
Sukhinin, Gennady I [Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Lavrentyev Ave., 1, Novosibirsk 630090 (Russian Federation); Fedoseev, Alexander V [Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Lavrentyev Ave., 1, Novosibirsk 630090 (Russian Federation); Ramazanov, Tlekkabul S [Institute of Experimental and Theoretical Physics, Al Farabi Kazakh National University, Tole Bi, 96a, Almaty 050012 (Kazakhstan); Dzhumagulova, Karlygash N [Institute of Experimental and Theoretical Physics, Al Farabi Kazakh National University, Tole Bi, 96a, Almaty 050012 (Kazakhstan); Amangaliyeva, Rauan Zh [Institute of Experimental and Theoretical Physics, Al Farabi Kazakh National University, Tole Bi, 96a, Almaty 050012 (Kazakhstan)
2007-12-21
The influence of a highly pronounced non-equilibrium characteristic of the electron energy distribution function in a stratified dc glow discharge on the process of dust particle charging in a complex plasma is taken into account for the first time. The calculated particle charge spatial distribution is essentially non-homogeneous and it can explain the vortex motion of particles at the periphery of a dusty cloud obtained in experiments.
Stability of stratified two-phase flows in inclined channels
Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.
2016-08-01
Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.
Thermal stratification built up in hot water tank with different inlet stratifiers
Dragsted, Janne; Furbo, Simon; Dannemand, Mark
2017-01-01
H is a rigid plastic pipe with holes for each 30 cm. The holes are designed with flaps preventing counter flow into the pipe. The inlet stratifier from EyeCular Technologies ApS is made of a flexible polymer with openings all along the side and in the full length of the stratifier. The flexibility...... in order to elucidate how well thermal stratification is established in the tank with differently designed inlet stratifiers under different controlled laboratory conditions. The investigated inlet stratifiers are from Solvis GmbH & Co KG and EyeCular Technologies ApS. The inlet stratifier from Solvis Gmb...... of the stratifier prevents counterflow. The tests have shown that both types of inlet stratifiers had an ability to create stratification in the test tank under the different test conditions. The stratifier from EyeCular Technologies ApS had a better performance at low flows of 1-2 l/min and the stratifier...
Stability of stratified two-phase flows in horizontal channels
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
Continuous Dependence on the Density for Stratified Steady Water Waves
Chen, Robin Ming; Walsh, Samuel
2016-02-01
There are two distinct regimes commonly used to model traveling waves in stratified water: continuous stratification, where the density is smooth throughout the fluid, and layer-wise continuous stratification, where the fluid consists of multiple immiscible strata. The former is the more physically accurate description, but the latter is frequently more amenable to analysis and computation. By the conservation of mass, the density is constant along the streamlines of the flow; the stratification can therefore be specified by prescribing the value of the density on each streamline. We call this the streamline density function. Our main result states that, for every smoothly stratified periodic traveling wave in a certain small-amplitude regime, there is an L ∞ neighborhood of its streamline density function such that, for any piecewise smooth streamline density function in that neighborhood, there is a corresponding traveling wave solution. Moreover, the mapping from streamline density function to wave is Lipschitz continuous in a certain function space framework. As this neighborhood includes piecewise smooth densities with arbitrarily many jump discontinues, this theorem provides a rigorous justification for the ubiquitous practice of approximating a smoothly stratified wave by a layered one. We also discuss some applications of this result to the study of the qualitative features of such waves.
Survival analysis of cervical cancer using stratified Cox regression
Purnami, S. W.; Inayati, K. D.; Sari, N. W. Wulan; Chosuvivatwong, V.; Sriplung, H.
2016-04-01
Cervical cancer is one of the mostly widely cancer cause of the women death in the world including Indonesia. Most cervical cancer patients come to the hospital already in an advanced stadium. As a result, the treatment of cervical cancer becomes more difficult and even can increase the death's risk. One of parameter that can be used to assess successfully of treatment is the probability of survival. This study raises the issue of cervical cancer survival patients at Dr. Soetomo Hospital using stratified Cox regression based on six factors such as age, stadium, treatment initiation, companion disease, complication, and anemia. Stratified Cox model is used because there is one independent variable that does not satisfy the proportional hazards assumption that is stadium. The results of the stratified Cox model show that the complication variable is significant factor which influent survival probability of cervical cancer patient. The obtained hazard ratio is 7.35. It means that cervical cancer patient who has complication is at risk of dying 7.35 times greater than patient who did not has complication. While the adjusted survival curves showed that stadium IV had the lowest probability of survival.
Wu, Huai-Hui; Wang, Chih-Yuan; Teng, Hwa-Jen; Lin, Cheo; Lu, Liang-Chen; Jian, Shu-Wan; Chang, Niann-Tai; Wen, Tzai-Hung; Wu, Jhy-Wen; Liu, Ding-Ping; Lin, Li-Jen; Norris, Douglas E; Wu, Ho-Sheng
2013-03-01
Aedes aegypti L. is the primary dengue vector in southern Taiwan. This article is the first report on a large-scale surveillance program to study the spatial-temporal distribution of the local Ae. aegytpi population using ovitraps stratified according to the human population in high dengue-risk areas. The sampling program was conducted for 1 yr and was based on weekly collections of eggs and adults in Kaohsiung City. In total, 10,380 ovitraps were placed in 5,190 households. Paired ovitraps, one indoors and one outdoors were used per 400 people. Three treatments in these ovitraps (paddle-shaped wooden sticks, sticky plastic, or both) were assigned by stratified random sampling to two areas (i.e., metropolitan or rural, respectively). We found that the sticky plastic alone had a higher sensitivity for detecting the occurrence of indigenous dengue cases than other treatments with time lags of up to 14 wk. The wooden paddle alone detected the oviposition of Ae. aegypti throughout the year in this study area. Furthermore, significantly more Ae. aegypti females were collected indoors than outdoors. Therefore, our survey identified the whole year oviposition activity, spatial-temporal distribution of the local Ae. aegypti population and a 14 wk lag correlation with dengue incidence to plan an effectively proactive control.
Sainath, K; Donderici, B
2013-01-01
We develop a general-purpose formulation, based on two-dimensional spectral integrals, for computing electromagnetic fields produced by arbitrarily-oriented dipoles in planar-stratified environments, where each layer may exhibit arbitrary and independent anisotropy in both the (complex) permittivity and permeability. Among the salient features of our formulation are (1) computation of eigenmodes (characteristic plane waves) supported in arbitrarily anisotropic media in a numerically robust fashion, (2) implementation of an hp-adaptive refinement for the numerical integration to evaluate the radiation and weakly-evanescent spectra contributions, and (3) development of an adaptive extension of an integral convergence acceleration technique to compute the strongly-evanescent spectrum contribution. While other semianalytic techniques exist to solve this problem, none have full applicability to media exhibiting arbitrary double anisotropies in each layer, where one must account for the whole range of possible phen...
A Fast MHD Code for Gravitationally Stratified Media using Graphical Processing Units: SMAUG
M. K. Griffiths; V. Fedun; R.Erdélyi
2015-03-01
Parallelization techniques have been exploited most successfully by the gaming/graphics industry with the adoption of graphical processing units (GPUs), possessing hundreds of processor cores. The opportunity has been recognized by the computational sciences and engineering communities, who have recently harnessed successfully the numerical performance of GPUs. For example, parallel magnetohydrodynamic (MHD) algorithms are important for numerical modelling of highly inhomogeneous solar, astrophysical and geophysical plasmas. Here, we describe the implementation of SMAUG, the Sheffield Magnetohydrodynamics Algorithm Using GPUs. SMAUG is a 1–3D MHD code capable of modelling magnetized and gravitationally stratified plasma. The objective of this paper is to present the numerical methods and techniques used for porting the code to this novel and highly parallel compute architecture. The methods employed are justified by the performance benchmarks and validation results demonstrating that the code successfully simulates the physics for a range of test scenarios including a full 3D realistic model of wave propagation in the solar atmosphere.
Kerkhof, M; Droste, JHJ; deMonchy, JGR; Schouten, JP; Rijcken, B
1996-01-01
To describe the distribution of serum total IgE and specific IgE to common aeroallergens by sex and age and to study their relationship to each other, we measured serum total IgE and specific IgE (CAP) to house-dust mile, timothy grass, cat, birch, and Cladosporium in a random sample of 2496 subject
Coll-de-Tuero Gabriel
2012-08-01
Full Text Available Abstract Background Kidney disease is associated with an increased total mortality and cardiovascular morbimortality in the general population and in patients with Type 2 diabetes. The aim of this study is to determine the prevalence of kidney disease and different types of renal disease in patients with type 2 diabetes (T2DM. Methods Cross-sectional study in a random sample of 2,642 T2DM patients cared for in primary care during 2007. Studied variables: demographic and clinical characteristics, pharmacological treatments and T2DM complications (diabetic foot, retinopathy, coronary heart disease and stroke. Variables of renal function were defined as follows: 1 Microalbuminuria: albumin excretion rate & 30 mg/g or 3.5 mg/mmol, 2 Macroalbuminuria: albumin excretion rate & 300 mg/g or 35 mg/mmol, 3 Kidney disease (KD: glomerular filtration rate according to Modification of Diet in Renal Disease 2 and/or the presence of albuminuria, 4 Renal impairment (RI: glomerular filtration rate 2, 5 Nonalbuminuric RI: glomerular filtration rate 2 without albuminuria and, 5 Diabetic nephropathy (DN: macroalbuminuria or microalbuminuria plus diabetic retinopathy. Results The prevalence of different types of renal disease in patients was: 34.1% KD, 22.9% RI, 19.5% albuminuria and 16.4% diabetic nephropathy (DN. The prevalence of albuminuria without RI (13.5% and nonalbuminuric RI (14.7% was similar. After adjusting per age, BMI, cholesterol, blood pressure and macrovascular disease, RI was significantly associated with the female gender (OR 2.20; CI 95% 1.86–2.59, microvascular disease (OR 2.14; CI 95% 1.8–2.54 and insulin treatment (OR 1.82; CI 95% 1.39–2.38, and inversely associated with HbA1c (OR 0.85 for every 1% increase; CI 95% 0.80–0.91. Albuminuria without RI was inversely associated with the female gender (OR 0.27; CI 95% 0.21–0.35, duration of diabetes (OR 0.94 per year; CI 95% 0.91–0.97 and directly associated with HbA1c (OR 1.19 for every
Magnetic Field in the Gravitationally Stratified Coronal Loops
B. N. Dwivedi; A. K. Srivastava
2015-03-01
We study the effect of gravitational stratification on the estimation of magnetic fields in the coronal loops. By using the method of MHD seismology of kink waves for the estimation of magnetic field of coronal loops, we derive a new formula for the magnetic field considering the effect of gravitational stratification. The fast-kink wave is a potential diagnostic tool for the estimation of magnetic field in fluxtubes. We consider the eleven kink oscillation cases observed by TRACE between July 1998 and June 2001. We calculate magnetic field in the stratified loops (str) and compare them with the previously calculated absolute magnetic field (abs). The gravitational stratification efficiently affects the magnetic field estimation in the coronal loops as it affects also the properties of kink waves. We find ≈22% increment in the magnetic field for the smallest ( = 72 Mm) while ≈42% increment in the absolute magnetic field for the longest ( = 406 Mm) coronal loops. The magnetic fields str and abs also increase with the number density, if the loop length does not vary much. The increment in the magnetic field due to gravitational stratification is small at the lower number densities, however, it is large at the higher number densities. We find that damping time of kink waves due to phase-mixing is less in the case of gravitationally stratified loops compared to nonstratified ones. This indicates the more rapid damping of kink waves in the stratified loops. In conclusion, we find that the gravitational stratification efficiently affects the estimation of magnetic field and damping time estimation especially in the longer coronal loops.
Experimental Study of Fluorine Transport Rules in Unsaturated Stratified Soil
ZHANG Hong-mei; SU Bao-yu; LIU Peng-hua; ZHANG Wei
2007-01-01
With the aid of soil column test models, the transport rules of fluorine contaminants in unsaturated stratified soils are discussed. Curves of F- concentrations at different times and sites in the unsaturated stratified soil were obtained under conditions of continuous injection of fluoride contaminants and water. Based on the analysis of the actual observation data, the values between computed results and observed data were compared. It is shown that the chemical properties of fluorine ions are active. The migration process of fluorine ions in soils is complex. Because of the effect of adsorption and desorption, the curve of the fluorine ion breakthrough curve is not symmetric. Its concentration peak value at each measuring point gradually decays. The tail of the breakthrough curve is long and the process of leaching and purifying using water requires considerable time. Along with the release of OHˉ in the process of fluorine absorption, the pH value of the soil solution changed from neutral to alkalinity during the test process. The first part of the breakthrough curve fitted better than the second part. The main reason is that fluorine does not always exist in the form of fluorinions in groundwater. Given the long test time, fluorinions possibly react with other ions in the soil solution to form complex water-soluble fluorine compounds. Only the retardation factor and source-sink term have been considered in our numerical model, which may leads to errors of computed values. But as a whole the migration rules of fluorine ions are basically correct, which indicates that the established numerical model can be used to simulate the transport rules of fluorine contaminants in unsaturated stratified soils.
Stratified spin-up in a sliced, square cylinder
Munro, R. J. [Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Foster, M. R. [Department of Mathematical Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)
2014-02-15
We previously reported experimental and theoretical results on the linear spin-up of a linearly stratified, rotating fluid in a uniform-depth square cylinder [M. R. Foster and R. J. Munro, “The linear spin-up of a stratified, rotating fluid in a square cylinder,” J. Fluid Mech. 712, 7–40 (2012)]. Here we extend that analysis to a “sliced” square cylinder, which has a base-plane inclined at a shallow angle α. Asymptotic results are derived that show the spin-up phase is achieved by a combination of the Ekman-layer eruptions (from the perimeter region of the cylinder's lid and base) and cross-slope-propagating stratified Rossby waves. The final, steady state limit for this spin-up phase is identical to that found previously for the uniform depth cylinder, but is reached somewhat more rapidly on a time scale of order E{sup −1/2}Ω{sup −1}/log (α/E{sup 1/2}) (compared to E{sup −1/2}Ω{sup −1} for the uniform-depth cylinder), where Ω is the rotation rate and E the Ekman number. Experiments were performed for Burger numbers, S, between 0.4 and 16, and showed that for S≳O(1), the Rossby modes are severely damped, and it is only at small S, and during the early stages, that the presence of these wave modes was evident. These observations are supported by the theory, which shows the damping factors increase with S and are numerically large for S≳O(1)
2013-01-01
Background Antibiograms created by aggregating hospital-wide susceptibility data from diverse patients can be misleading. To demonstrate the utility of age- and location-stratified antibiograms, we compared stratified antibiograms for three common bacterial pathogens, E. coli, S. aureus, and S. pneumoniae. We created stratified antibiograms based on patient age (/=65 years), and inpatient or outpatient location using all 2009 E. coli and S. aureus, and all 2008–2009 S. pneumoniae isolates sub...
Electromagnetic fields due to dipole antennas over stratified anisotropic media.
Kong, J. A.
1972-01-01
Solutions to the problem of radiation of dipole antennas in the presence of a stratified anisotropic media are facilitated by decomposing a general wave field into transverse magnetic (TM) and transverse electric (TE) modes. Employing the propagation matrices, wave amplitudes in any region are related to those in any other regions. The reflection coefficients, which embed all the information about the geometrical configuration and the physical constituents of the medium, are obtained in closed form. In view of the general formulation, various special cases are discussed.
Instabilities developed in stratified flows over pronounced obstacles
Varela, J.; Araújo, M.; Bove, I.; Cabeza, C.; Usera, G.; Martí, Arturo C.; Montagne, R.; Sarasúa, L. G.
2007-12-01
In the present work we study numerical and experimentally the flow of a two-layer stratified fluid over a topographic obstacle. The problem reflects a wide number of oceanographic and meteorological situations, where the stratification plays an important role. We identify the different instabilities developed by studying the pycnocline deformation due to a pronounced obstacle. The numerical simulations were made using the model caffa3D.MB which works with a numerical model of Navier-Stokes equations with finite volume elements in curvilinear meshes. The experimental results are contrasted with numerical simulations. Linear stability analysis predictions are checked with particle image velocimetry (PIV) measurements.
Stratified waveguide grating coupler for normal fiber incidence.
Wang, Bin; Jiang, Jianhua; Chambers, Diana M; Cai, Jingbo; Nordin, Gregory P
2005-04-15
We propose a new stratified waveguide grating coupler (SWGC) to couple light from a fiber at normal incidence into a planar waveguide. SWGCs are designed to operate in the strong coupling regime without intermediate optics between the fiber and the waveguide. Two-dimensional finite-difference time-domain simulation in conjunction with microgenetic algorithm optimization shows that approximately 72% coupling efficiency is possible for fiber (core size of 8.3 microm and delta=0.36%) to slab waveguide (1.2-microm core and delta=3.1%) coupling. We show that the phase-matching and Bragg conditions are simultaneously satisfied through the fundamental leaky mode.
Magnetorotational instability in weakly ionised, stratified accretion discs
Salmeron, Roberto Aureliano; Salmeron, Raquel; Wardle, Mark
2003-01-01
The magnetorotational instability (MRI) (Balbus and Hawley 1991, Hawley and Balbus 1991) transports angular momentum radially outwards in accretion discs through the distortion of the magnetic field lines that connect fluid elements. In protostellar discs, low conductivity is important, especially in the inner regions (Gammie 1996, Wardle 1997). As a result, low k modes are relevant and vertical stratification is a key factor of the analysis. However, most models of the MRI in these environments have adopted either the ambipolar diffusion or resistive approximations and have not simultaneously treated stratification and Hall conductivity. We present here a linear analysis of the MRI, including the Hall effect, in a stratified disc.
Enhanced charge transport kinetics in anisotropic, stratified photoanodes.
Yazdani, Nuri; Bozyigit, Deniz; Utke, Ivo; Buchheim, Jakob; Youn, Seul Ki; Patscheider, Jörg; Wood, Vanessa; Park, Hyung Gyu
2014-02-12
The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs.
Masanobu Iwanaga
2015-05-01
Full Text Available Metamaterials (MMs are subwavelength-structured materials that have been rapidly developed in this century and have various potentials to realize novel phenomena, such as negative refraction, cloaking and super-resolution. Theoretical proposals for super-resolution image transfer using metallic thin films were experimentally demonstrated at ultraviolet and violet wavelengths from 365 to 405 nm. However, the most preferred wavelengths of optical imaging are green wavelengths around 500 nm, because optical microscopy is most extensively exploited in the area of biotechnology. In order to make the super-resolution techniques using MMs more practical, we propose the design of a stratified metal-insulator MM that has super-resolution image transfer modes at green wavelengths, which we here call hyper modes. The design assumed only Ag and SiO2 as constituent materials and was found employing Bloch-state analysis, which is based on a rigorous transfer-matrix method for the metal-insulator MMs. It is numerically substantiated that the designed stratified metal-insulator metamaterial (SMIM is capable of forming super-resolution images at the green wavelengths, and optical loss reduction is also studied. We discuss the results derived by the Bloch-state analysis and by effective medium models usually used for the metal-insulator MMs and show that the Bloch-state analysis is more suitable to reproduce the experimental data.
Jet-mixing of initially-stratified liquid-liquid pipe flows: experiments and numerical simulations
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.
A-Stratified Computerized Adaptive Testing with Unequal Item Exposure across Strata.
Deng, Hui; Chang, Hua-Hua
The purpose of this study was to compare a proposed revised a-stratified, or alpha-stratified, USTR method of test item selection with the original alpha-stratified multistage computerized adaptive testing approach (STR) and the use of maximum Fisher information (FSH) with respect to test efficiency and item pool usage using simulated computerized…
Sequential stratified sampling belief propagation for multiple targets tracking
无
2006-01-01
Rather than the difficulties of highly non-linear and non-Gaussian observation process and the state distribution in single target tracking, the presence of a large, varying number of targets and their interactions place more challenge on visual tracking. To overcome these difficulties, we formulate multiple targets tracking problem in a dynamic Markov network which consists of three coupled Markov random fields that model the following: a field for joint state of multi-target, one binary process for existence of individual target, and another binary process for occlusion of dual adjacent targets. By introducing two robust functions, we eliminate the two binary processes, and then apply a novel version of belief propagation called sequential stratified sampling belief propagation algorithm to obtain the maximum a posteriori (MAP) estimation in the dynamic Markov network. By using stratified sampler, we incorporate bottom-up information provided by a learned detector (e.g. SVM classifier) and belief information for the messages updating. Other low-level visual cues (e.g. color and shape) can be easily incorporated in our multi-target tracking model to obtain better tracking results. Experimental results suggest that our method is comparable to the state-of-the-art multiple targets tracking methods in several test cases.
STRESS DISTRIBUTION IN THE STRATIFIED MASS CONTAINING VERTICAL ALVEOLE
Bobileva Tatiana Nikolaevna
2017-08-01
Full Text Available Almost all subsurface rocks used as foundations for various types of structures are stratified. Such heterogeneity may cause specific behaviour of the materials under strain. Differential equations describing the behaviour of such materials contain rapidly fluctuating coefficients, in view of this, solution of such equations is more time-consuming when using today’s computers. The method of asymptotic averaging leads to getting homogeneous medium under study to averaged equations with fixed factors. The present article is concerned with stratified soil mass consisting of pair-wise alternative isotropic elastic layers. In the results of elastic modules averaging, the present soil mass with horizontal rock stratification is simulated by homogeneous transversal-isotropic half-space with isotropy plane perpendicular to the standing axis. Half-space is loosened by a vertical alveole of circular cross-section, and virgin ground is under its own weight. For horizontal parting planes of layers, the following two types of surface conditions are set: ideal contact and backlash without cleavage. For homogeneous transversal-isotropic half-space received with a vertical alveole, the analytical solution of S.G. Lekhnitsky, well known in scientific papers, is used. The author gives expressions for stress components and displacements in soil mass for different marginal conditions on the alveole surface. Such research problems arise when constructing and maintaining buildings and when composite materials are used.
Stability of steam-water countercurrent stratified flow
Lee, S C
1985-10-01
Two flow instabilities which limit the normal condensation processes in countercurrent stratified steam-water flow have been identified experimentally: flooding and condensation-induced waterhammer. In order to initiate condensation-induced waterhammer in nearly horizontal or moderately-inclined steam/subcooled-water flow, two conditions, the appearance of a wavy interface and complete condensation of the incoming steam, are necessary. Analyses of these conditions are performed on a basis of flow stability and heat transfer considerations. Flooding data for several inclinations and channel heights are collected. Effects of condensation, inclination angle and channel height on the flooding characteristics are discussed. An envelope theory for the onset of flooding in inclined stratified flow is developed, which agrees well with the experimental data. Some empirical information on basic flow parameters, such as mean film thickness and interfacial friction factor required for this theory are measured. The previous viewpoints on flooding appear not to conflict with the present experimental data in nearly horizontal flow but the flooding phenomena in nearly vertical flow appear to be more complicated than those described by these viewpoints because of liquid droplet entrainment.
Böhmer, L; Hildebrandt, G
1998-01-01
In contrast to the prevailing automatized chemical analytical methods, classical microbiological techniques are linked with considerable material- and human-dependent sources of errors. These effects must be objectively considered for assessing the reliability and representativeness of a test result. As an example for error analysis, the deviation of bacterial counts and the influence of the time of testing, bacterial species involved (total bacterial count, coliform count) and the detection method used (pour-/spread-plate) were determined in a repeated testing of parallel samples of pasteurized (stored for 8 days at 10 degrees C) and raw (stored for 3 days at 6 degrees C) milk. Separate characterization of deviation components, namely, unavoidable random sampling error as well as methodical error and variation between parallel samples, was made possible by means of a test design where variance analysis was applied. Based on the results of the study, the following conclusions can be drawn: 1. Immediately after filling, the total count deviation in milk mainly followed the POISSON-distribution model and allowed a reliable hygiene evaluation of lots even with few samples. Subsequently, regardless of the examination procedure used, the setting up of parallel dilution series can be disregarded. 2. With increasing storage period, bacterial multiplication especially of psychrotrophs leads to unpredictable changes in the bacterial profile and density. With the increase in errors between samples, it is common to find packages which have acceptable microbiological quality but are already spoiled by the time of the expiry date labeled. As a consequence, a uniform acceptance or rejection of the batch is seldom possible. 3. Because the contamination level of coliforms in certified raw milk mostly lies near the detection limit, coliform counts with high relative deviation are expected to be found in milk directly after filling. Since no bacterial multiplication takes place
Teaching Techniques, Types of Personality, and English Listening Skill
Ni Made Ratminingsih
2013-01-01
Abstract: Teaching Techniques, Types of Personality, and English Listening Skill. This study investigated the effect of teaching techniques and types of personality on English listening skill. This experimental study involved 88 students under investigation, which were determined randomly through multi-stage random sampling technique. The results of the research indicate that there is an interaction effect between the teaching techniques and types of personality on the English listening ski...
Prediction of Potato Crop Yield Using Precision Agriculture Techniques.
Al-Gaadi, Khalid A; Hassaballa, Abdalhaleem A; Tola, ElKamil; Kayad, Ahmed G; Madugundu, Rangaswamy; Alblewi, Bander; Assiri, Fahad
2016-01-01
Crop growth and yield monitoring over agricultural fields is an essential procedure for food security and agricultural economic return prediction. The advances in remote sensing have enhanced the process of monitoring the development of agricultural crops and estimating their yields. Therefore, remote sensing and GIS techniques were employed, in this study, to predict potato tuber crop yield on three 30 ha center pivot irrigated fields in an agricultural scheme located in the Eastern Region of Saudi Arabia. Landsat-8 and Sentinel-2 satellite images were acquired during the potato growth stages and two vegetation indices (the normalized difference vegetation index (NDVI) and the soil adjusted vegetation index (SAVI)) were generated from the images. Vegetation index maps were developed and classified into zones based on vegetation health statements, where the stratified random sampling points were accordingly initiated. Potato yield samples were collected 2-3 days prior to the harvest time and were correlated to the adjacent NDVI and SAVI, where yield prediction algorithms were developed and used to generate prediction yield maps. Results of the study revealed that the difference between predicted yield values and actual ones (prediction error) ranged between 7.9 and 13.5% for Landsat-8 images and between 3.8 and 10.2% for Sentinel-2 images. The relationship between actual and predicted yield values produced R2 values ranging between 0.39 and 0.65 for Landsat-8 images and between 0.47 and 0.65 for Sentinel-2 images. Results of this study revealed a considerable variation in field productivity across the three fields, where high-yield areas produced an average yield of above 40 t ha-1; while, the low-yield areas produced, on the average, less than 21 t ha-1. Identifying such great variation in field productivity will assist farmers and decision makers in managing their practices.
Prediction of Potato Crop Yield Using Precision Agriculture Techniques
Al-Gaadi, Khalid A.; Hassaballa, Abdalhaleem A.; Tola, ElKamil; Kayad, Ahmed G.; Madugundu, Rangaswamy; Alblewi, Bander; Assiri, Fahad
2016-01-01
Crop growth and yield monitoring over agricultural fields is an essential procedure for food security and agricultural economic return prediction. The advances in remote sensing have enhanced the process of monitoring the development of agricultural crops and estimating their yields. Therefore, remote sensing and GIS techniques were employed, in this study, to predict potato tuber crop yield on three 30 ha center pivot irrigated fields in an agricultural scheme located in the Eastern Region of Saudi Arabia. Landsat-8 and Sentinel-2 satellite images were acquired during the potato growth stages and two vegetation indices (the normalized difference vegetation index (NDVI) and the soil adjusted vegetation index (SAVI)) were generated from the images. Vegetation index maps were developed and classified into zones based on vegetation health statements, where the stratified random sampling points were accordingly initiated. Potato yield samples were collected 2–3 days prior to the harvest time and were correlated to the adjacent NDVI and SAVI, where yield prediction algorithms were developed and used to generate prediction yield maps. Results of the study revealed that the difference between predicted yield values and actual ones (prediction error) ranged between 7.9 and 13.5% for Landsat-8 images and between 3.8 and 10.2% for Sentinel-2 images. The relationship between actual and predicted yield values produced R2 values ranging between 0.39 and 0.65 for Landsat-8 images and between 0.47 and 0.65 for Sentinel-2 images. Results of this study revealed a considerable variation in field productivity across the three fields, where high-yield areas produced an average yield of above 40 t ha-1; while, the low-yield areas produced, on the average, less than 21 t ha-1. Identifying such great variation in field productivity will assist farmers and decision makers in managing their practices. PMID:27611577
Hydrodynamics of stratified epithelium: steady state and linearized dynamics
Yeh, Wei-Ting
2015-01-01
A theoretical model for stratified epithelium is presented. The viscoelastic properties of the tissue is assumed to be dependent on the spatial distribution of proliferative and differentiated cells. Based on this assumption, a hydrodynamic description for tissue dynamics at long-wavelength, long-time limit is developed, and the analysis reveals important insight for the dynamics of an epithelium close to its steady state. When the proliferative cells occupy a thin region close to the basal membrane, the relaxation rate towards the steady state is enhanced by cell division and cell apoptosis. On the other hand, when the region where proliferative cells reside becomes sufficiently thick, a flow induced by cell apoptosis close to the apical surface could enhance small perturbations. This destabilizing mechanism is general for continuous self-renewal multi-layered tissues, it could be related to the origin of certain tissue morphology and developing pattern.
Hydrodynamics of stratified epithelium: Steady state and linearized dynamics
Yeh, Wei-Ting; Chen, Hsuan-Yi
2016-05-01
A theoretical model for stratified epithelium is presented. The viscoelastic properties of the tissue are assumed to be dependent on the spatial distribution of proliferative and differentiated cells. Based on this assumption, a hydrodynamic description of tissue dynamics at the long-wavelength, long-time limit is developed, and the analysis reveals important insights into the dynamics of an epithelium close to its steady state. When the proliferative cells occupy a thin region close to the basal membrane, the relaxation rate towards the steady state is enhanced by cell division and cell apoptosis. On the other hand, when the region where proliferative cells reside becomes sufficiently thick, a flow induced by cell apoptosis close to the apical surface enhances small perturbations. This destabilizing mechanism is general for continuous self-renewal multilayered tissues; it could be related to the origin of certain tissue morphology, tumor growth, and the development pattern.
Local Radiation MHD Instabilities in Magnetically Stratified Media
Tao, Ted
2011-01-01
We study local radiation magnetohydrodynamic instabilities in static, optically thick, vertically stratified media with constant flux mean opacity. We include the effects of vertical gradients in a horizontal background magnetic field. Assuming rapid radiative diffusion, we use the zero gas pressure limit as an entry point for investigating the coupling between the photon bubble instability and the Parker instability. Apart from factors that depend on wavenumber orientation, the Parker instability exists for wavelengths longer than a characteristic wavelength lambda_{tran}, while photon bubbles exist for wavelengths shorter than lambda_{tran}. The growth rate in the Parker regime is independent of the orientation of the horizontal component of the wavenumber when radiative diffusion is rapid, but the range of Parker-like wavenumbers is extended if there exists strong horizontal shear between field lines (i.e. horizontal wavenumber perpendicular to the magnetic field). Finite gas pressure introduces an additio...
The Risk-Stratified Osteoporosis Strategy Evaluation study (ROSE)
Rubin, Katrine Hass; Holmberg, Teresa; Rothmann, Mette Juel
2015-01-01
The risk-stratified osteoporosis strategy evaluation study (ROSE) is a randomized prospective population-based study investigating the effectiveness of a two-step screening program for osteoporosis in women. This paper reports the study design and baseline characteristics of the study population....... 35,000 women aged 65-80 years were selected at random from the population in the Region of Southern Denmark and-before inclusion-randomized to either a screening group or a control group. As first step, a self-administered questionnaire regarding risk factors for osteoporosis based on FRAX......(®) was issued to both groups. As second step, subjects in the screening group with a 10-year probability of major osteoporotic fractures ≥15 % were offered a DXA scan. Patients diagnosed with osteoporosis from the DXA scan were advised to see their GP and discuss pharmaceutical treatment according to Danish...
Short-wave vortex instability in stratified flow
Bovard, Luke
2014-01-01
In this paper we investigate a new instability of the Lamb-Chaplygin dipole in a stratified fluid. Through numerical linear stability analysis, a secondary peak in the growth rate emerges at vertical scales about an order of magnitude smaller than the buoyancy scale $L_{b}=U/N$ where $U$ is the characteristic velocity and $N$ is the Brunt-V\\"{a}is\\"{a}l\\"{a} frequency. This new instability exhibits a growth rate that is similar to, and even exceeds, that of the zigzag instability, which has the characteristic length of the buoyancy scale. This instability is investigated for a wide range of Reynolds $Re=2000-20000$ and horizontal Froude numbers $F_{h}=0.05-0.2$, where $F_{h}=U/NR$, $Re=UR/\
Internal combustion engine using premixed combustion of stratified charges
Marriott, Craig D.; Reitz, Rolf D. (Madison, WI
2003-12-30
During a combustion cycle, a first stoichiometrically lean fuel charge is injected well prior to top dead center, preferably during the intake stroke. This first fuel charge is substantially mixed with the combustion chamber air during subsequent motion of the piston towards top dead center. A subsequent fuel charge is then injected prior to top dead center to create a stratified, locally richer mixture (but still leaner than stoichiometric) within the combustion chamber. The locally rich region within the combustion chamber has sufficient fuel density to autoignite, and its self-ignition serves to activate ignition for the lean mixture existing within the remainder of the combustion chamber. Because the mixture within the combustion chamber is overall premixed and relatively lean, NO.sub.x and soot production are significantly diminished.
A study of stratified gas-liquid pipe flow
Johnson, George W.
2005-07-01
This work includes both theoretical modelling and experimental observations which are relevant to the design of gas condensate transport lines. Multicomponent hydrocarbon gas mixtures are transported in pipes over long distances and at various inclinations. Under certain circumstances, the heavier hydrocarbon components and/or water vapour condense to form one or more liquid phases. Near the desired capacity, the liquid condensate and water is efficiently transported in the form of a stratified flow with a droplet field. During operating conditions however, the flow rate may be reduced allowing liquid accumulation which can create serious operational problems due to large amounts of excess liquid being expelled into the receiving facilities during production ramp-up or even in steady production in severe cases. In particular, liquid tends to accumulate in upward inclined sections due to insufficient drag on the liquid from the gas. To optimize the transport of gas condensates, a pipe diameters should be carefully chosen to account for varying flow rates and pressure levels which are determined through the knowledge of the multiphase flow present. It is desirable to have a reliable numerical simulation tool to predict liquid accumulation for various flow rates, pipe diameters and pressure levels which is not presently accounted for by industrial flow codes. A critical feature of the simulation code would include the ability to predict the transition from small liquid accumulation at high flow rates to large liquid accumulation at low flow rates. A semi-intermittent flow regime of roll waves alternating with a partly backward flowing liquid film has been observed experimentally to occur for a range of gas flow rates. Most of the liquid is transported in the roll waves. The roll wave regime is not well understood and requires fundamental modelling and experimental research. The lack of reliable models for this regime leads to inaccurate prediction of the onset of
Turbulent reconnection of magnetic bipoles in stratified turbulence
Jabbari, Sarah; Mitra, Dhrubaditya; Kleeorin, Nathan; Rogachevskii, Igor
2016-01-01
We consider strongly stratified forced turbulence in a plane-parallel layer with helicity and corresponding large-scale dynamo action in the lower part and nonhelical turbulence in the upper. The magnetic field is found to develop strongly concentrated bipolar structures near the surface. They form elongated bands with a sharp interface between opposite polarities. Unlike earlier experiments with imposed magnetic field, the inclusion of rotation does not strongly suppress the formation of these structures. We perform a systematic numerical study of this phenomenon by varying magnetic Reynolds number, scale separation ratio, and Coriolis number. We also focus on the formation of the current sheet between bipolar regions where reconnection of oppositely oriented field lines occurs. We determine the reconnection rate by measuring either the inflow velocity in the vicinity of the current sheet or by measuring the electric field in the reconnection region. We demonstrate that for small Lundquist number, S1000, the...
Direct simulation of the stably stratified turbulent Ekman layer
Coleman, G. N.; Ferziger, J. H.; Spalart, P. R.
1992-01-01
The Navier-Stokes equations and the Boussinesq approximation were used to compute a 3D time-dependent turbulent flow in the stably stratified Ekman layer over a smooth surface. The simulation data are found to be in very good agreement with atmospheric measurements when nondimensionalized according to Nieuwstadt's local scaling scheme. Results suggest that, when Reynolds number effects are taken into account, the 'constant Froud number' stable layer model (Brost and Wyngaard, 1978) and the 'shearing length' stable layer model (Hunt, 1985) for the dissipitation rate of turbulent kinetic energy are both valid. It is concluded that there is good agreement between the direct numerical simulation results and large-eddy simulation results obtained by Mason and Derbyshire (1990).
Inertial modes of non-stratified superfluid neutron stars
Prix, R; Andersson, N
2004-01-01
We present results concerning adiabatic inertial-mode oscillations of non-stratified superfluid neutron stars in Newtonian gravity, using the anelastic and slow-rotation approximations. We consider a simple two-fluid model of a superfluid neutron star, where one fluid consists of the superfluid neutrons and the second fluid contains all the comoving constituents (protons, electrons). The two fluids are assumed to be ``free'' in the sense that vortex-mediated forces like mutual friction or pinning are absent, but they can be coupled by the equation of state, in particular by entrainment. The stationary background consists of the two fluids rotating uniformly around the same axis with potentially different rotation rates. We study the special cases of co-rotating backgrounds, vanishing entrainment, and the purely toroidal r-modes, analytically. We calculate numerically the eigenfunctions and frequencies of inertial modes in the general case of non co-rotating backgrounds, and study their dependence on the relat...
Magnetorotational instability in stratified, weakly ionised accretion discs
Salmeron, Roberto Aureliano; Salmeron, Raquel; Wardle, Mark
2003-01-01
We present a linear analysis of the vertical structure and growth of the magnetorotational instability in stratified, weakly ionised accretion discs, such as protostellar and quiescent dwarf novae systems. The method includes the effects of the magnetic coupling, the conductivity regime of the fluid and the strength of the magnetic field, which is initially vertical. The conductivity is treated as a tensor and assumed constant with height. We obtained solutions for the structure and growth rate of global unstable modes for different conductivity regimes, strengths of the initial magnetic field and coupling between ionised and neutral components of the fluid. The envelopes of short-wavelenght perturbations are determined by the action of competing local growth rates at different heights, driven by the vertical stratification of the disc. Ambipolar diffusion perturbations peak consistently higher above the midplane than modes including Hall conductivity. For weak coupling, perturbations including the Hall effec...
Second order closure for stratified convection: bulk region and overshooting
Biferale, L; Sbragaglia, M; Scagliarini, A; Toschi, F; Tripiccione, R
2011-01-01
The parameterization of small-scale turbulent fluctuations in convective systems and in the presence of strong stratification is a key issue for many applied problems in oceanography, atmospheric science and planetology. In the presence of stratification, one needs to cope with bulk turbulent fluctuations and with inversion regions, where temperature, density -or both- develop highly non-linear mean profiles due to the interactions between the turbulent boundary layer and the unmixed -stable- flow above/below it. We present a second order closure able to cope simultaneously with both bulk and boundary layer regions, and we test it against high-resolution state-of-the-art 2D numerical simulations in a convective and stratified belt for values of the Rayleigh number, up to Ra = 10^9. Data are taken from a Rayleigh-Taylor system confined by the existence of an adiabatic gradient.
Oxygenation of Stratified Reservoir Using Air Bubble Plume
Schladow, S. G.
2006-12-01
Excess nutrients loading from urban area and watershed into lakes and reservoirs increases the content of organic matter, which, through decomposition, needs increased dissolve oxygen (DO). Many eutrophic reservoirs and lakes cannot meet the DO requirement during stratified season and suffers from the hypolimnetic anoxia. As a result, benthic sediment produces anoxic products such as methane, hydrogen sulphide, ammonia, iron, manganese, and phosphorus. In order to address the hypolimnetic anoxia, oxygen is artificially supplied into reservoir using an aeration system (i.e., bubbler). The most common result of lake/reservoir aeration is to destratify the reservoir so that the water body may completely mix under natural phenomena and remain well oxygenated throughout. Other advantages of destratification are: (1) allows warm- water fish to inhabit the entire reservoir, (2) suppress the nutrient release from sediment, and (3) decreases the algal growth by sending them to the darker zone. A one-dimensional reservoir-bubbler model is developed and applied to examine the effects of an aeration system on mixing and dissolved oxygen dynamics in the Upper Peirce Reservoir, Singapore. After introduction of the aeration system in the reservoir, it was found that the hypolimnetic DO increased significantly, and the concentration of algae, soluble manganese and iron substantially reduced. It is found that the reservoir-bubbler model predicts the mixing (temperature as mixing parameter) and dissolved oxygen concentration in the reservoir with acceptable accuracy. It is shown in terms of bubbler mechanical efficiency (i.e., operating cost) and total DO contribution from the aeration system into the reservoir that the selections of airflow rate per diffuser, air bubble radius, and total number of diffusers are important design criteria of a bubbler system. However, the overall bubbler design also depends on the reservoir size and stratified area of interest, ambient climate, and
Nonlinear gravity-wave interactions in stratified turbulence
Remmel, Mark; Sukhatme, Jai; Smith, Leslie M.
2014-04-01
To investigate the dynamics of gravity waves in stratified Boussinesq flows, a model is derived that consists of all three-gravity-wave-mode interactions (the GGG model), excluding interactions involving the vortical mode. The GGG model is a natural extension of weak turbulence theory that accounts for exact three-gravity-wave resonances. The model is examined numerically by means of random, large-scale, high-frequency forcing. An immediate observation is a robust growth of the so-called vertically sheared horizontal flow (VSHF). In addition, there is a forward transfer of energy and equilibration of the nonzero-frequency (sometimes called "fast") gravity-wave modes. These results show that gravity-wave-mode interactions by themselves are capable of systematic interscale energy transfer in a stratified fluid. Comparing numerical simulations of the GGG model and the full Boussinesq system, for the range of Froude numbers ( Fr) considered (0.05 ≤ Fr ≤ 1), in both systems the VSHF is hardest to resolve. When adequately resolved, VSHF growth is more vigorous in the GGG model. Furthermore, a VSHF is observed to form in milder stratification scenarios in the GGG model than the full Boussinesq system. Finally, fully three-dimensional nonzero-frequency gravity-wave modes equilibrate in both systems and their scaling with vertical wavenumber follows similar power-laws. The slopes of the power-laws obtained depend on Fr and approach -2 (from above) at Fr = 0.05, which is the strongest stratification that can be properly resolved with our computational resources.
Visualization periodic flows in a continuously stratified fluid.
Bardakov, R.; Vasiliev, A.
2012-04-01
To visualize the flow pattern of viscous continuously stratified fluid both experimental and computational methods were developed. Computational procedures were based on exact solutions of set of the fundamental equations. Solutions of the problems of flows producing by periodically oscillating disk (linear and torsion oscillations) were visualized with a high resolutions to distinguish small-scale the singular components on the background of strong internal waves. Numerical algorithm of visualization allows to represent both the scalar and vector fields, such as velocity, density, pressure, vorticity, stream function. The size of the source, buoyancy and oscillation frequency, kinematic viscosity of the medium effects were traced in 2D an 3D posing problems. Precision schlieren instrument was used to visualize the flow pattern produced by linear and torsion oscillations of strip and disk in a continuously stratified fluid. Uniform stratification was created by the continuous displacement method. The buoyancy period ranged from 7.5 to 14 s. In the experiments disks with diameters from 9 to 30 cm and a thickness of 1 mm to 10 mm were used. Different schlieren methods that are conventional vertical slit - Foucault knife, vertical slit - filament (Maksoutov's method) and horizontal slit - horizontal grating (natural "rainbow" schlieren method) help to produce supplementing flow patterns. Both internal wave beams and fine flow components were visualized in vicinity and far from the source. Intensity of high gradient envelopes increased proportionally the amplitude of the source. In domains of envelopes convergence isolated small scale vortices and extended mushroom like jets were formed. Experiments have shown that in the case of torsion oscillations pattern of currents is more complicated than in case of forced linear oscillations. Comparison with known theoretical model shows that nonlinear interactions between the regular and singular flow components must be taken
Carlisle, J B
2017-08-01
10(-10) . The difference between the distributions of these two subgroups was confirmed by comparison of their overall distributions, p = 5.3 × 10(-15) . Each journal exhibited the same abnormal distribution of baseline means. There was no difference in distributions of baseline means for 1453 trials in non-anaesthetic journals and 3634 trials in anaesthetic journals, p = 0.30. The rate of retractions from JAMA and NEJM, 6/1453 or 1 in 242, was one-quarter the rate from the six anaesthetic journals, 66/3634 or 1 in 55, relative risk (99%CI) 0.23 (0.08-0.68), p = 0.00022. A probability threshold of 1 in 10,000 identified 8/72 (11%) retracted trials (7 by Fujii et al.) and 82/5015 (1.6%) unretracted trials. Some p values were so extreme that the baseline data could not be correct: for instance, for 43/5015 unretracted trials the probability was less than 1 in 10(15) (equivalent to one drop of water in 20,000 Olympic-sized swimming pools). A probability threshold of 1 in 100 for two or more trials by the same author identified three authors of retracted trials (Boldt, Fujii and Reuben) and 21 first or corresponding authors of 65 unretracted trials. Fraud, unintentional error, correlation, stratified allocation and poor methodology might have contributed to the excess of randomised, controlled trials with similar or dissimilar means, a pattern that was common to all the surveyed journals. It is likely that this work will lead to the identification, correction and retraction of hitherto unretracted randomised, controlled trials. © 2017 The Association of Anaesthetists of Great Britain and Ireland.
Stratified flows with variable density: mathematical modelling and numerical challenges.
Murillo, Javier; Navas-Montilla, Adrian
2017-04-01
Stratified flows appear in a wide variety of fundamental problems in hydrological and geophysical sciences. They may involve from hyperconcentrated floods carrying sediment causing collapse, landslides and debris flows, to suspended material in turbidity currents where turbulence is a key process. Also, in stratified flows variable horizontal density is present. Depending on the case, density varies according to the volumetric concentration of different components or species that can represent transported or suspended materials or soluble substances. Multilayer approaches based on the shallow water equations provide suitable models but are not free from difficulties when moving to the numerical resolution of the governing equations. Considering the variety of temporal and spatial scales, transfer of mass and energy among layers may strongly differ from one case to another. As a consequence, in order to provide accurate solutions, very high order methods of proved quality are demanded. Under these complex scenarios it is necessary to observe that the numerical solution provides the expected order of accuracy but also converges to the physically based solution, which is not an easy task. To this purpose, this work will focus in the use of Energy balanced augmented solvers, in particular, the Augmented Roe Flux ADER scheme. References: J. Murillo , P. García-Navarro, Wave Riemann description of friction terms in unsteady shallow flows: Application to water and mud/debris floods. J. Comput. Phys. 231 (2012) 1963-2001. J. Murillo B. Latorre, P. García-Navarro. A Riemann solver for unsteady computation of 2D shallow flows with variable density. J. Comput. Phys.231 (2012) 4775-4807. A. Navas-Montilla, J. Murillo, Energy balanced numerical schemes with very high order. The Augmented Roe Flux ADER scheme. Application to the shallow water equations, J. Comput. Phys. 290 (2015) 188-218. A. Navas-Montilla, J. Murillo, Asymptotically and exactly energy balanced augmented flux
Deep silicon maxima in the stratified oligotrophic Mediterranean Sea
Y. Crombet
2011-02-01
Full Text Available The silicon biogeochemical cycle has been studied in the Mediterranean Sea during late summer/early autumn 1999 and summer 2008. The distribution of nutrients, particulate carbon and silicon, fucoxanthin (Fuco, and total chlorophyll-a (TChl-a were investigated along an eastward gradient of oligotrophy during two cruises (PROSOPE and BOUM encompassing the entire Mediterranean Sea during the stratified period. At both seasons, surface waters were depleted in nutrients and the nutriclines gradually deepened towards the East, the phosphacline being the deepest in the easternmost Levantine basin. Following the nutriclines, parallel deep maxima of biogenic silica (DSM, fucoxanthin (DFM and TChl-a (DCM were evidenced during both seasons with maximal concentrations of 0.45 μmol L^{−1} for BSi, 0.26 μg L^{−1} for Fuco, and 1.70 μg L^{−1} for TChl-a, all measured during summer. Contrary to the DCM which was a persistent feature in the Mediterranean Sea, the DSM and DFMs were observed in discrete areas of the Alboran Sea, the Algero-Provencal basin, the Ionian sea and the Levantine basin, indicating that diatoms were able to grow at depth and dominate the DCM under specific conditions. Diatom assemblages were dominated by Chaetoceros spp., Leptocylindrus spp., Pseudonitzschia spp. and the association between large centric diatoms (Hemiaulus hauckii and Rhizosolenia styliformis and the cyanobacterium Richelia intracellularis was observed at nearly all sites. The diatom's ability to grow at depth is commonly observed in other oligotrophic regions and could play a major role in ecosystem productivity and carbon export to depth. Contrary to the common view that Si and siliceous phytoplankton are not major components of the Mediterranean biogeochemistry, we suggest here that diatoms, by persisting at depth during the stratified period, could contribute to a
Fishing and the oceanography of a stratified shelf sea
Sharples, Jonathan; Ellis, Jim R.; Nolan, Glenn; Scott, Beth E.
2013-10-01
Fishing vessel position data from the Vessel Monitoring System (VMS) were used to investigate fishing activity in the Celtic Sea, a seasonally-stratifying, temperate region on the shelf of northwest Europe. The spatial pattern of fishing showed that three main areas are targeted: (1) the Celtic Deep (an area of deeper water with fine sediments), (2) the shelf edge, and (3) an area covering several large seabed banks in the central Celtic Sea. Data from each of these regions were analysed to examine the contrasting seasonality of fishing activity, and to highlight where the spring-neap tidal cycle appears to be important to fishing. The oceanographic characteristics of the Celtic Sea were considered alongside the distribution and timing of fishing, illustrating likely contrasts in the underlying environmental drivers of the different fished regions. In the central Celtic Sea, fishing mainly occurred during the stratified period between April and August. Based on evidence provided in other papers of this Special Issue, we suggest that the fishing in this area is supported by (1) a broad increase in primary production caused by lee-waves generated by seabed banks around spring tides driving large supplies of nutrients into the photic zone, and (2) greater concentrations of zooplankton within the region influenced by the seabed banks and elevated primary production. In contrast, while the shelf edge is a site of elevated surface chlorophyll, previous work has suggested that the periodic mixing generated by an internal tide at the shelf edge alters the size-structure of the phytoplankton community which fish larvae from the spawning stocks along the shelf edge are able to exploit. The fishery for Nephrops norvegicus in the Celtic Deep was the only one to show a significant spring-neap cycle, possibly linked to Nephrops foraging outside their burrows less during spring tides. More tentatively, the fishery for Nephrops correlated most strongly with a localised shift in
Walton, Karl; Blunt, Liam; Fleming, Leigh
2015-09-01
Mass finishing is amongst the most widely used finishing processes in modern manufacturing, in applications from deburring to edge radiusing and polishing. Processing objectives are varied, ranging from the cosmetic to the functionally critical. One such critical application is the hydraulically smooth polishing of aero engine component gas-washed surfaces. In this, and many other applications the drive to improve process control and finish tolerance is ever present. Considering its widespread use mass finishing has seen limited research activity, particularly with respect to surface characterization. The objectives of the current paper are to; characterise the mass finished stratified surface and its development process using areal surface parameters, provide guidance on the optimal parameters and sampling method to characterise this surface type for a given application, and detail the spatial variation in surface topography due to coupon edge shadowing. Blasted and peened square plate coupons in titanium alloy are wet (vibro) mass finished iteratively with increasing duration. Measurement fields are precisely relocated between iterations by fixturing and an image superimposition alignment technique. Surface topography development is detailed with ‘log of process duration’ plots of the ‘areal parameters for scale-limited stratified functional surfaces’, (the Sk family). Characteristic features of the Smr2 plot are seen to map out the processing of peak, core and dale regions in turn. These surface process regions also become apparent in the ‘log of process duration’ plot for Sq, where lower core and dale regions are well modelled by logarithmic functions. Surface finish (Ra or Sa) with mass finishing duration is currently predicted with an exponential model. This model is shown to be limited for the current surface type at a critical range of surface finishes. Statistical analysis provides a group of areal parameters including; Vvc, Sq, and Sdq
Tareki, Abubaker M.; Kim, Wonkyu; Guo, Junpeng; Lindquist, Robert G.
2016-09-01
Electro-optic (EO) modulation of the amplitude and phase of electromagnetic waves using liquid crystals (LCs) is commonplace in the optical and infrared regions. This effort has led to commercially available components used in spectral filtering, polarization management, beam steering, transmitters, displays, etc. However, electro-optic techniques have had limited success in the terahertz (THz) region due to several practical design challenges. The growth in applications has led to an interest in the development of a spatial light modulator (SLM) for the terahertz region. In the visible region, the most common SLMs use electro-optic materials such as liquid crystals to spatially modulate a beam. However, this approach to achieve a practical SLM in the terahertz regime has been difficult. The primary barrier for components is the long interaction lengths required to modulate a THz wave. Since the EO modulation depth is directly proportional to the multiplication of the change of permittivity and the ratio of interaction length over wavelength, THz systems with wavelengths ranging from 150 μm to 1mm pose a challenge. To overcome this barrier, longitudinal stratified sub-wavelength liquid crystal structures have been engineered and fabricated. The stratified structures introduce the challenge in the selection and design of the electrodes. By using multiple layers the tunable films can be maintained at manageable thicknesses (25 to 200 μm). The reduced individual film thickness will significantly improve the requisite drive voltage and response time. However, the layered structure with multiple conducting layers adds considerable challenges to the design of the transparent electrode. Both simulation and experimental data will be presented.
Turbulence comes in bursts in stably stratified flows
Rorai, C; Pouquet, A
2013-01-01
There is a clear distinction between simple laminar and complex turbulent fluids. But in some cases, as for the nocturnal planetary boundary layer, a stable and well-ordered flow can develop intense and sporadic bursts of turbulent activity which disappear slowly in time. This phenomenon is ill-understood and poorly modeled; and yet, it is central to our understanding of weather and climate dynamics. We present here a simple model which shows that in stably stratified turbulence, the stronger bursts can occur when the flow is expected to be more stable. The bursts are generated by a rapid non-linear amplification of energy stored in waves, and are associated with energetic interchanges between vertical velocity and temperature (or density) fluctuations. Direct numerical simulations on grids of 2048^3 points confirm this somewhat paradoxical result of measurably stronger events for more stable flows, displayed not only in the temperature and vertical velocity derivatives, but also in the amplitude of the field...
DNS of stratified spatially-developing turbulent thermal boundary layers
Araya, Guillermo; Castillo, Luciano; Jansen, Kenneth
2012-11-01
Direct numerical simulations (DNS) of spatially-developing turbulent thermal boundary layers under stratification are performed. It is well known that the transport phenomena of the flow is significantly affected by buoyancy, particularly in urban environments where stable and unstable atmospheric boundary layers are encountered. In the present investigation, the Dynamic Multi-scale approach by Araya et al. (JFM, 670, 2011) for turbulent inflow generation is extended to thermally stratified boundary layers. Furthermore, the proposed Dynamic Multi-scale approach is based on the original rescaling-recycling method by Lund et al. (1998). The two major improvements are: (i) the utilization of two different scaling laws in the inner and outer parts of the boundary layer to better absorb external conditions such as inlet Reynolds numbers, streamwise pressure gradients, buoyancy effects, etc., (ii) the implementation of a Dynamic approach to compute scaling parameters from the flow solution without the need of empirical correlations as in Lund et al. (1998). Numerical results are shown for ZPG flows at high momentum thickness Reynolds numbers (~ 3,000) and a comparison with experimental data is also carried out.
Stratified patterns of divorce: Earnings, education, and gender
Amit Kaplan
2015-05-01
Full Text Available Background: Despite evidence that divorce has become more prevalent among weaker socioeconomic groups, knowledge about the stratification aspects of divorce in Israel is lacking. Moreover, although scholarly debate recognizes the importance of stratificational positions with respect to divorce, less attention has been given to the interactions between them. Objective: Our aim is to examine the relationship between social inequality and divorce, focusing on how household income, education, employment stability, relative earnings, and the intersection between them affect the risk of divorce in Israel. Methods: The data is derived from combined census files for 1995-2008, annual administrative employment records from the National Insurance Institute and the Tax Authority, and data from the Civil Registry of Divorce. We used a series of discrete-time event-history analysis models for marital dissolution. Results: Couples in lower socioeconomic positions had a higher risk of divorce in Israel. Higher education in general, and homogamy in terms of higher education (both spouses have degrees in particular, decreased the risk of divorce. The wife's relative earnings had a differential effect on the likelihood of divorce, depending on household income: a wife who outearned her husband increased the log odds of divorce more in the upper tertiles than in the lower tertile. Conclusions: Our study shows that divorce indeed has a stratified pattern and that weaker socioeconomic groups experience the highest levels of divorce. Gender inequality within couples intersects with the household's economic and educational resources.
Self-Knowledge and Risk in Stratified Medicine.
Hordern, Joshua
2017-04-01
This article considers why and how self-knowledge is important to communication about risk and behaviour change by arguing for four claims. First, it is doubtful that genetic knowledge should properly be called 'self-knowledge' when its ordinary effects on self-motivation and behaviour change seem so slight. Second, temptations towards a reductionist, fatalist, construal of persons' futures through a 'molecular optic' should be resisted. Third, any plausible effort to change people's behaviour must engage with cultural self-knowledge, values and beliefs, catalysed by the communication of genetic risk. For example, while a Judaeo-Christian notion of self-knowledge is distinctively theological, people's self-knowledge is plural in its insight and sources. Fourth, self-knowledge is found in compassionate, if tense, communion which yields freedom from determinism even amidst suffering. Stratified medicine thus offers a newly precise kind of humanising health care through societal solidarity with the riskiest. However, stratification may also mean that molecularly unstratified, 'B' patients' experience involves accentuated suffering and disappointment, a concern requiring further research.
Stratified Flow Past a Hill: Dividing Streamline Concept Revisited
Leo, Laura S.; Thompson, Michael Y.; Di Sabatino, Silvana; Fernando, Harindra J. S.
2016-06-01
The Sheppard formula (Q J R Meteorol Soc 82:528-529, 1956) for the dividing streamline height H_s assumes a uniform velocity U_∞ and a constant buoyancy frequency N for the approach flow towards a mountain of height h, and takes the form H_s/h=( {1-F} ) , where F=U_{∞}/Nh. We extend this solution to a logarithmic approach-velocity profile with constant N. An analytical solution is obtained for H_s/h in terms of Lambert-W functions, which also suggests alternative scaling for H_s/h. A `modified' logarithmic velocity profile is proposed for stably stratified atmospheric boundary-layer flows. A field experiment designed to observe H_s is described, which utilized instrumentation from the spring field campaign of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program. Multiple releases of smoke at F≈ 0.3-0.4 support the new formulation, notwithstanding the limited success of experiments due to logistical constraints. No dividing streamline is discerned for F≈ 10, since, if present, it is too close to the foothill. Flow separation and vortex shedding is observed in this case. The proposed modified logarithmic profile is in reasonable agreement with experimental observations.
Economic evaluation in stratified medicine: methodological issues and challenges
Hans-Joerg eFugel
2016-05-01
Full Text Available Background: Stratified Medicine (SM is becoming a practical reality with the targeting of medicines by using a biomarker or genetic-based diagnostic to identify the eligible patient sub-population. Like any healthcare intervention, SM interventions have costs and consequences that must be considered by reimbursement authorities with limited resources. Methodological standards and guidelines exist for economic evaluations in clinical pharmacology and are an important component for health technology assessments (HTAs in many countries. However, these guidelines have initially been developed for traditional pharmaceuticals and not for complex interventions with multiple components. This raises the issue as to whether these guidelines are adequate to SM interventions or whether new specific guidance and methodology is needed to avoid inconsistencies and contradictory findings when assessing economic value in SM.Objective: This article describes specific methodological challenges when conducting health economic (HE evaluations for SM interventions and outlines potential modifications necessary to existing evaluation guidelines /principles that would promote consistent economic evaluations for SM.Results/Conclusions: Specific methodological aspects for SM comprise considerations on the choice of comparator, measuring effectiveness and outcomes, appropriate modelling structure and the scope of sensitivity analyses. Although current HE methodology can be applied for SM, greater complexity requires further methodology development and modifications in the guidelines.
BIPOLAR MAGNETIC SPOTS FROM DYNAMOS IN STRATIFIED SPHERICAL SHELL TURBULENCE
Jabbari, Sarah; Brandenburg, Axel; Kleeorin, Nathan; Mitra, Dhrubaditya; Rogachevskii, Igor, E-mail: sarahjab@kth.se [Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)
2015-06-01
Recent work by Mitra et al. (2014) has shown that in strongly stratified forced two-layer turbulence with helicity and corresponding large-scale dynamo action in the lower layer, and nonhelical turbulence in the upper, a magnetic field occurs in the upper layer in the form of sharply bounded bipolar magnetic spots. Here we extend this model to spherical wedge geometry covering the northern hemisphere up to 75° latitude and an azimuthal extent of 180°. The kinetic helicity and therefore also the large-scale magnetic field are strongest at low latitudes. For moderately strong stratification, several bipolar spots form that eventually fill the full longitudinal extent. At early times, the polarity of spots reflects the orientation of the underlying azimuthal field, as expected from Parker’s Ω-shaped flux loops. At late times their tilt changes such that there is a radial field of opposite orientation at different latitudes separated by about 10°. Our model demonstrates the spontaneous formation of spots of sizes much larger than the pressure scale height. Their tendency to produce filling factors close to unity is argued to be reminiscent of highly active stars. We confirm that strong stratification and strong scale separation are essential ingredients behind magnetic spot formation, which appears to be associated with downflows at larger depths.
Local properties of countercurrent stratified steam-water flow
Kim, H J
1985-10-01
A study of steam condensation in countercurrent stratified flow of steam and subcooled water has been carried out in a rectangular channel/flat plate geometry over a wide range of inclination angles (4/sup 0/-87/sup 0/) at several aspect ratios. Variables were inlet water and steam flow rates, and inlet water temperature. Local condensation rates and pressure gradients were measured, and local condensation heat transfer coefficients and interfacial shear stress were calculated. Contact probe traverses of the surface waves were made, which allowed a statistical analysis of the wave properties. The local condensation Nusselt number was correlated in terms of local water and steam Reynolds or Froude numbers, as well as the liquid Prandtl number. A turbulence-centered model developed by Theofanous, et al. principally for gas absorption in several geometries, was modified. A correlation for the interfacial shear stress and the pressure gradient agreed with measured values. Mean water layer thicknesses were calculated. Interfacial wave parameters, such as the mean water layer thickness, liquid fraction probability distribution, wave amplitude and wave frequency, are analyzed.
Stratifying the Risk of Venous Thromboembolism in Otolaryngology
Shuman, Andrew G.; Hu, Hsou Mei; Pannucci, Christopher J.; Jackson, Christopher R.; Bradford, Carol R.; Bahl, Vinita
2015-01-01
Objective The consequences of perioperative venous thromboembolism (VTE) are devastating; identifying patients at risk is an essential step in reducing morbidity and mortality. The utility of perioperative VTE risk assessment in otolaryngology is unknown. This study was designed to risk-stratify a diverse population of otolaryngology patients for VTE events. Study Design Retrospective cohort study. Setting Single-institution academic tertiary care medical center. Subjects and Methods Adult patients presenting for otolaryngologic surgery requiring hospital admission from 2003 to 2010 who did not receive VTE chemoprophylaxis were included. The Caprini risk assessment was retrospectively scored via a validated method of electronic chart abstraction. Primary study variables were Caprini risk scores and the incidence of perioperative venous thromboembolic outcomes. Results A total of 2016 patients were identified. The overall 30-day rate of VTE was 1.3%. The incidence of VTE in patients with a Caprini risk score of 6 or less was 0.5%. For patients with scores of 7 or 8, the incidence was 2.4%. Patients with a Caprini risk score greater than 8 had an 18.3% incidence of VTE and were significantly more likely to develop a VTE when compared to patients with a Caprini risk score less than 8 (P otolaryngology patients for 30-day VTE events and allows otolaryngologists to identify patient subgroups who have a higher risk of VTE in the absence of chemoprophylaxis. PMID:22261490
Mixing efficiency of turbulent patches in stably stratified flows
Garanaik, Amrapalli; Venayagamoorthy, Subhas Karan
2016-11-01
A key quantity that is essential for estimating the turbulent diapycnal (irreversible) mixing in stably stratified flow is the mixing efficiency Rf*, which is a measure of the amount of turbulent kinetic energy that is irreversibly converted into background potential energy. In particular, there is an ongoing debate in the oceanographic mixing community regarding the utility of the buoyancy Reynolds number (Reb) , particularly with regard to how mixing efficiency and diapycnal diffusivity vary with Reb . Specifically, is there a universal relationship between the intensity of turbulence and the strength of the stratification that supports an unambiguous description of mixing efficiency based on Reb ? The focus of the present study is to investigate the variability of Rf* by considering oceanic turbulence data obtained from microstructure profiles in conjunction with data from laboratory experiments and DNS. Field data analysis has done by identifying turbulent patches using Thorpe sorting method for potential density. The analysis clearly shows that high mixing efficiencies can persist at high buoyancy Reynolds numbers. This is contradiction to previous studies which predict that mixing efficiency should decrease universally for Reb greater than O (100) . Funded by NSF and ONR.
Simulation and study of stratified flows around finite bodies
Gushchin, V. A.; Matyushin, P. V.
2016-06-01
The flows past a sphere and a square cylinder of diameter d moving horizontally at the velocity U in a linearly density-stratified viscous incompressible fluid are studied. The flows are described by the Navier-Stokes equations in the Boussinesq approximation. Variations in the spatial vortex structure of the flows are analyzed in detail in a wide range of dimensionless parameters (such as the Reynolds number Re = Ud/ ν and the internal Froude number Fr = U/( Nd), where ν is the kinematic viscosity and N is the buoyancy frequency) by applying mathematical simulation (on supercomputers of Joint Supercomputer Center of the Russian Academy of Sciences) and three-dimensional flow visualization. At 0.005 < Fr < 100, the classification of flow regimes for the sphere (for 1 < Re < 500) and for the cylinder (for 1 < Re < 200) is improved. At Fr = 0 (i.e., at U = 0), the problem of diffusion-induced flow past a sphere leading to the formation of horizontal density layers near the sphere's upper and lower poles is considered. At Fr = 0.1 and Re = 50, the formation of a steady flow past a square cylinder with wavy hanging density layers in the wake is studied in detail.
Hanasoge, S M; Gizon, L
2010-01-01
Perfectly matched layers are a very efficient and accurate way to absorb waves in media. We present a stable convolutional unsplit perfectly matched formulation designed for the linearized stratified Euler equations. However, the technique as applied to the Magneto-hydrodynamic (MHD) equations requires the use of a sponge, which, despite placing the perfectly matched status in question, is still highly efficient at absorbing outgoing waves. We study solutions of the equations in the backdrop of models of linearized wave propagation in the Sun. We test the numerical stability of the schemes by integrating the equations over a large number of wave periods.
Jerzy Czerski
2014-02-01
Full Text Available The germination of whole seeds, the seeds without coat and isolated embryos of apple cv. "Antonówka Zwykła" after 90 days of cold-stratification was compared with the germination of embryos isolated from non-stratified seeds. They were germinated under 16hrs during a day at temperature 25°C and 20°C during the night. It has been found that after 2 weeks whole stratified seeds germinated in 5 per cent, seeds without coat in 25 per cent and isolated embryos in 98 per cent. Isolated embryos from nun-stratified seeds, after 2 weeks, germinated in the range from 75 to 88 per cent. The results indicate the similar germination ability of embryos isolated from nun-stratified seeds. The seedling populations obtained from embryo's stratified and non-stratified seeds were fully comparable and they evaluated: 1 a wide range of individual differences within population, 2 a similar number of seedlings in each class of shoot length, 3 a similar morphological habitus in each class of shoot length, 4 a similar fresh leaf weight and whole plant increment.
STUDIES OF TWO-PHASE PLUMES IN STRATIFIED ENVIRONMENTS
Scott A. Socolofsky; Brian C. Crounse; E. Eric Adams
1998-11-18
Two-phase plumes play an important role in the more practical scenarios for ocean sequestration of CO{sub 2}--i.e. dispersing CO{sub 2} as a buoyant liquid from either a bottom-mounted or ship-towed pipeline. Despite much research on related applications, such as for reservoir destratification using bubble plumes, our understanding of these flows is incomplete, especially concerning the phenomenon of plume peeling in a stratified ambient. To address this deficiency, we have built a laboratory facility in which we can make fundamental measurements of plume behavior. Although we are using air, oil and sediments as our sources of buoyancy (rather than CO{sub 2}), by using models, our results can be directly applied to field scale CO{sub 2} releases to help us design better CO{sub 2} injection systems, as well as plan and interpret the results of our up-coming international field experiment. The experimental facility designed to study two-phase plume behavior similar to that of an ocean CO{sub 2} release includes the following components: 1.22 x 1.22 x 2.44 m tall glass walled tank; Tanks and piping for the two-tank stratification method for producing step- and linearly-stratified ambient conditions; Density profiling system using a conductivity and temperature probe mounted to an automated depth profiler; Lighting systems, including a virtual point source light for shadowgraphs and a 6 W argon-ion laser for laser induced fluorescence (LIF) imaging; Imaging system, including a digital, progressive scanning CCD camera, computerized framegrabber, and image acquisition and analysis software; Buoyancy source diffusers having four different air diffusers, two oil diffusers, and a planned sediment diffuser; Dye injection method using a Mariotte bottle and a collar diffuser; and Systems integration software using the Labview graphical programming language and Windows NT. In comparison with previously reported experiments, this system allows us to extend the parameter range of
A model for evaluating the ballistic resistance of stratified packs
Pirvu, C.; Georgescu, C.; Badea, S.; Deleanu, L.
2016-08-01
Models for evaluating the ballistic performance of stratified packs are useful in reducing the time for laboratory tests, understanding the failure process and identifying key factors to improve the architecture of the packs. The authors present the results of simulating the bullet impact on a packs made of 24 layers, taking into consideration the friction between layers (μ = 0.4) and the friction between bullet and layers (μ = 0.3). The aim of this study is to obtain a number of layers that allows for the bullet arrest in the packs and to have several layers undamaged in order to offer a high level of safety for this kind of packs that could be included in individual armors. The model takes into account the yield and fracture limits of the two materials the bullet is made of and those for one layer, here considered as an orthotropic material, having maximum equivalent plastic strain of 0.06. All materials are considered to have bilinear isotropic hardening behavior. After documentation, the model was designed as isothermal because thermal influence of the impact is considered low for these impact velocities. The model was developed with the help of Ansys 14.5. Each layer has 200 mm × 200 × 0.35 mm. The bullet velocity just before impact was 400 m/s, a velocity characterizing the average values obtained in close range with a ballistic barrel and the bullet model is following the shape and dimensions of the 9 mm FMJ (full metal jacket). The model and the results concerning the number of broken layers were validated by experiments, as the number of broken layers for the actual pack (made of 24 layers of LFT SB1) were also seven...eight. The models for ballistic impact are useful when they are particularly formulated for resembling to the actual system projectile - target.
Internal and vorticity waves in decaying stratified flows
Matulka, A.; Cano, D.
2009-04-01
Most predictive models fail when forcing at the Rossby deformation Radius is important and a large range of scales have to be taken into account. When mixing of reactants or pollutants has to be accounted, the range of scales spans from hundreds of Kilometers to the Bachelor or Kolmogorov sub milimiter scales. We present some theoretical arguments to describe the flow in terms of the three dimensional vorticity equations, using a lengthscale related to the vorticity (or enstrophy ) transport. Effect of intermittent eddies and non-homogeneity of diffusion are also key issues in the environment because both stratification and rotation body forces are important and cause anisotropy/non-homogeneity. These problems need further theoretical, numerical and observational work and one approach is to try to maximize the relevant geometrical information in order to understand and therefore predict these complex environmental dispersive flows. The importance of the study of turbulence structure and its relevance in diffusion of contaminants in environmental flows is clear when we see the effect of environmental disasters such as the Prestige oil spill or the Chernobil radioactive cloud spread in the atmosphere. A series of Experiments have been performed on a strongly stratified two layer fluid consisting of Brine in the bottom and freshwater above in a 1 square meter tank. The evolution of the vortices after the passage of a grid is video recorded and Particle tracking is applied on small pliolite particles floating at the interface. The combination of internal waves and vertical vorticity produces two separate time scales that may produce resonances. The vorticity is seen to oscilate in a complex way, where the frecuency decreases with time.
The nonlinear evolution of modes on unstable stratified shear layers
Blackaby, Nicholas; Dando, Andrew; Hall, Philip
1993-06-01
The nonlinear development of disturbances in stratified shear flows (having a local Richardson number of value less than one quarter) is considered. Such modes are initially fast growing but, like related studies, we assume that the viscous, non-parallel spreading of the shear layer results in them evolving in a linear fashion until they reach a position where their amplitudes are large enough and their growth rates have diminished sufficiently so that amplitude equations can be derived using weakly nonlinear and non-equilibrium critical-layer theories. Four different basic integro-differential amplitude equations are possible, including one due to a novel mechanism; the relevant choice of amplitude equation, at a particular instance, being dependent on the relative sizes of the disturbance amplitude, the growth rate of the disturbance, its wavenumber, and the viscosity of the fluid. This richness of choice of possible nonlinearities arises mathematically from the indicial Frobenius roots of the governing linear inviscid equation (the Taylor-Goldstein equation) not, in general, differing by an integer. The initial nonlinear evolution of a mode will be governed by an integro-differential amplitude equations with a cubic nonlinearity but the resulting significant increase in the size of the disturbance's amplitude leads on to the next stage of the evolution process where the evolution of the mode is governed by an integro-differential amplitude equations with a quintic nonlinearity. Continued growth of the disturbance amplitude is expected during this stage, resulting in the effects of nonlinearity spreading to outside the critical level, by which time the flow has become fully nonlinear.
A new scoring system to stratify risk in unstable angina
Salzberg Simón
2003-08-01
Full Text Available Abstract Background We performed this study to develop a new scoring system to stratify different levels of risk in patients admitted to hospital with a diagnosis of unstable angina (UA, which is a complex syndrome that encompasses different outcomes. Many prognostic variables have been described but few efforts have been made to group them in order to enhance their individual predictive power. Methods In a first phase, 473 patients were prospectively analyzed to determine which factors were significantly associated with the in-hospital occurrence of refractory ischemia, acute myocardial infarction (AMI or death. A risk score ranging from 0 to 10 points was developed using a multivariate analysis. In a second phase, such score was validated in a new sample of 242 patients and it was finally applied to the entire population (n = 715. Results ST-segment deviation on the electrocardiogram, age ≥ 70 years, previous bypass surgery and troponin T ≥ 0.1 ng/mL were found as independent prognostic variables. A clear distinction was shown among categories of low, intermediate and high risk, defined according to the risk score. The incidence of the triple end-point was 6 %, 19.2 % and 44.7 % respectively, and the figures for AMI or death were 2 %, 11.4 % and 27.6 % respectively (p Conclusions This new scoring system is simple and easy to achieve. It allows a very good stratification of risk in patients having a clinical diagnosis of UA. They may be divided in three categories, which could be of help in the decision-making process.
Interfacial instabilities in a stratified flow of two superposed fluids
Schaflinger, Uwe
1994-06-01
Here we shall present a linear stability analysis of a laminar, stratified flow of two superposed fluids which are a clear liquid and a suspension of solid particles. The investigation is based upon the assumption that the concentration remains constant within the suspension layer. Even for moderate flow-rates the base-state results for a shear induced resuspension flow justify the latter assumption. The numerical solutions display the existence of two different branches that contribute to convective instability: long and short waves which coexist in a certain range of parameters. Also, a range exists where the flow is absolutely unstable. That means a convectively unstable resuspension flow can be only observed for Reynolds numbers larger than a lower, critical Reynolds number but still smaller than a second critical Reynolds number. For flow rates which give rise to a Reynolds number larger than the second critical Reynolds number, the flow is absolutely unstable. In some cases, however, there exists a third bound beyond that the flow is convectively unstable again. Experiments show the same phenomena: for small flow-rates short waves were usually observed but occasionally also the coexistence of short and long waves. These findings are qualitatively in good agreement with the linear stability analysis. Larger flow-rates in the range of the second critical Reynolds number yield strong interfacial waves with wave breaking and detached particles. In this range, the measured flow-parameters, like the resuspension height and the pressure drop are far beyond the theoretical results. Evidently, a further increase of the Reynolds number indicates the transition to a less wavy interface. Finally, the linear stability analysis also predicts interfacial waves in the case of relatively small suspension heights. These results are in accordance with measurements for ripple-type instabilities as they occur under laminar and viscous conditions for a mono-layer of particles.
Magnetoacoustic Waves in Stratified Atmospheres with a Magnetic Null Point
Tarr, Lucas A.; Linton, Mark; Leake, James E.
2016-05-01
Magnetic fields strongly modify the propagation of MHD waves from the photosphere to the low corona, as can be shown exactly for the most simple case of a uniform magnetic field and isothermally stratrified atmosphere. For slightly more realistic scenarios, where both the atmospheric parameters and the magnetic field vary spatially, the linear MHD equations typically cannot be solved analytically. We use the Lagrangian Remap code--a nonlinear, shock-capturing MHD code--to study the propagation of initially acoustic wavepackets through a model 2D atmosphere that includes a gravitationally stratified chromosphere, transition region, and low corona. The magnetic field is formed by three photospheric concentrations and includes a single magnetic null point, resulting in an inhomogeneous system with a magnetic dome topology. A portion of an introduced wavepacket will refract toward the null due to the varying Alfven speed. Waves incident on the equipartition contour surrounding the null, where the sound and Alfven speeds coincide, partially transmit, reflect, and mode convert between branches of the local dispersion relation. Outward propagating slow modes generated during conversion become strongly concentrated along the set of field lines passing near the null. Acoustic energy is beamed back downwards towards each photospheric foot point, and upwards along one separatrix that exits the top of the numerical domain. Changes in the dominant restoring force for the wavepacket, between the Lorentz and pressure gradient forces, lead to a buildup of current density along topologically important features of the system (the null point and its four separatrices) and can drive reconnection at the null point itself. Ohmic dissipation of the currents locally heats the plasma. We find that the amount of current accumulation depends on where the centroid of a wavepacket initial crosses the photosphere, but does not simply coincide with regions of open versus closed magnetic field or
Stability characteristics of jets in linearly-stratified, rotating fluids
Chen, Rui-Rong; Boyer, Don L.; Tao, Lijun
A series of laboratory experiments are conducted concerning an azimuthal jet of a linearly stratified rotating fluid in a cylindrical geometry. The jet is characterized by vertical and horizontal shear and the question of the stability of the flow is considered experimentally. The jet is driven by a source-sink method characterized by a volume flow rate of strength Q. BecauseQ has no direct geophysical significance a combined external set of dimensionless parameters is introduced. These include the Rossby, Richardson and Ekman numbers, the jet aspect ratio and two geometrical parameters. A RossbyRo against RichardsonRi number flow regime diagram is presented which shows that the wave mode of the instability generally decreases with increasingRo andRi, for fixedRi andRo, respectively. In accordance with Killworth's (1980) linear stability analysis, the wave mode for smallRi (Ri ⪉ 15) depends principally onRi with the instability being largely a baroclinic one. For largerRi(Ri ⪉ 100), again as predicted by Killworth's theory, the wave mode depends primarily onRo, the instability being a barotropic one. The regime diagram can be used to estimate the wave-length of jet instabilities in the atmosphere and oceans. These estimates suggest that the wave-lengths decrease with increasing jet velocity, decreasing jet width (equivalent to increasing horizontal shear) and increasing vertical shear, other parameters being fixed. An azimuthal topography aligned along the jet has the tendency to stabilize the jet in the sense that the amplitude of the instability is shown to be dramatically smaller in the presence of the topography, other parameters being fixed. The topography also tends to increase the wave-length of the instability. A scaling analysis is advanced, and supporting experimental data presented, relating the external and internal parameters utilized.
Tempia, S; Salman, M D; Keefe, T; Morley, P; Freier, J E; DeMartini, J C; Wamwayi, H M; Njeumi, F; Soumaré, B; Abdi, A M
2010-12-01
A cross-sectional sero-survey, using a two-stage cluster sampling design, was conducted between 2002 and 2003 in ten administrative regions of central and southern Somalia, to estimate the seroprevalence and geographic distribution of rinderpest (RP) in the study area, as well as to identify potential risk factors for the observed seroprevalence distribution. The study was also used to test the feasibility of the spatially integrated investigation technique in nomadic and semi-nomadic pastoral systems. In the absence of a systematic list of livestock holdings, the primary sampling units were selected by generating random map coordinates. A total of 9,216 serum samples were collected from cattle aged 12 to 36 months at 562 sampling sites. Two apparent clusters of RP seroprevalence were detected. Four potential risk factors associated with the observed seroprevalence were identified: the mobility of cattle herds, the cattle population density, the proximity of cattle herds to cattle trade routes and cattle herd size. Risk maps were then generated to assist in designing more targeted surveillance strategies. The observed seroprevalence in these areas declined over time. In subsequent years, similar seroprevalence studies in neighbouring areas of Kenya and Ethiopia also showed a very low seroprevalence of RP or the absence of antibodies against RP. The progressive decline in RP antibody prevalence is consistent with virus extinction. Verification of freedom from RP infection in the Somali ecosystem is currently in progress.
Yadav, Bechu K V; Nandy, S
2015-05-01
Mapping forest biomass is fundamental for estimating CO₂ emissions, and planning and monitoring of forests and ecosystem productivity. The present study attempted to map aboveground woody biomass (AGWB) integrating forest inventory, remote sensing and geostatistical techniques, viz., direct radiometric relationships (DRR), k-nearest neighbours (k-NN) and cokriging (CoK) and to evaluate their accuracy. A part of the Timli Forest Range of Kalsi Soil and Water Conservation Division, Uttarakhand, India was selected for the present study. Stratified random sampling was used to collect biophysical data from 36 sample plots of 0.1 ha (31.62 m × 31.62 m) size. Species-specific volumetric equations were used for calculating volume and multiplied by specific gravity to get biomass. Three forest-type density classes, viz. 10-40, 40-70 and >70% of Shorea robusta forest and four non-forest classes were delineated using on-screen visual interpretation of IRS P6 LISS-III data of December 2012. The volume in different strata of forest-type density ranged from 189.84 to 484.36 m(3) ha(-1). The total growing stock of the forest was found to be 2,024,652.88 m(3). The AGWB ranged from 143 to 421 Mgha(-1). Spectral bands and vegetation indices were used as independent variables and biomass as dependent variable for DRR, k-NN and CoK. After validation and comparison, k-NN method of Mahalanobis distance (root mean square error (RMSE) = 42.25 Mgha(-1)) was found to be the best method followed by fuzzy distance and Euclidean distance with RMSE of 44.23 and 45.13 Mgha(-1) respectively. DRR was found to be the least accurate method with RMSE of 67.17 Mgha(-1). The study highlighted the potential of integrating of forest inventory, remote sensing and geostatistical techniques for forest biomass mapping.
Distribution of vaccine/antivirals and the 'least spread line' in a stratified population
Goldstein, E.; Apolloni, A.; Lewis, B.; Miller, J. C.; Macauley, M.; Eubank, S.; Lipsitch, M.; Wallinga, J.
2010-01-01
We describe a prioritization scheme for an allocation of a sizeable quantity of vaccine or antivirals in a stratified population. The scheme builds on an optimal strategy for reducing the epidemic's initial growth rate in a stratified mass-action model. The strategy is tested on the EpiSims network
Implementing content constraints in alpha-stratified adaptive using a shadow test approach
Linden, van der Wim J.; Chang, Hua-Hua
2003-01-01
The methods of alpha-stratified adaptive testing and constrained adaptive testing with shadow tests are combined. The advantages are twofold: First, application of the shadow test approach allows the implementation of any type of constraint on item selection in alpha-stratified adaptive testing. Sec
van der Linden, Wim J.; Chang, Hua-Hua
The methods of alpha-stratified adaptive testing and constrained adaptive testing with shadow tests are combined in this study. The advantages are twofold. First, application of the shadow test allows the researcher to implement any type of constraint on item selection in alpha-stratified adaptive testing. Second, the result yields a simple set of…
Carmo, Carolina; Dumont, Olivier; Nielsen, Mads Pagh
2015-01-01
The use of stratified hot water tanks in solar energy systems - including ORC systems - as well as heat pump systems is paramount for a better performance of these systems. However, the availability of effective and reliable models to predict the annual performance of stratified hot water tanks c...
Lindsay, Colin R; Shaw, Emily; Walker, Ian; Johnson, Peter W M
2015-03-01
The implementation of stratified medicine in modern cancer care presents substantial opportunity to refine diagnosis and treatment but also numerous challenges. Through experience in a UK tumor profiling initiative, we have gained valuable insights into the complexities and possible solutions for routine delivery of stratified cancer medicine.
Optimal stratification of item pools in α-stratified computerized adaptive testing
Chang, Hua-Hua; Linden, van der Wim J.
2003-01-01
A method based on 0-1 linear programming (LP) is presented to stratify an item pool optimally for use in α-stratified adaptive testing. Because the 0-1 LP model belongs to the subclass of models with a network flow structure, efficient solutions are possible. The method is applied to a previous item
Mixed convection flow with non-uniform heat source/sink in a doubly stratified magnetonanofluid
Mehmood, K.; Hussain, S.; Sagheer, M.
2016-06-01
In this study, we explore the unsteady flow of viscous nanofluid driven by an inclined stretching sheet. The novelty of the present study is to account for the effect of a non-uniform heat source/sink in a thermally and solutally stratified magnetonanofluid. Governing system of nonlinear partial differential equations is converted into a system of nonlinear ordinary differential equations. Solution of the transformed system is obtained using RK4 method with shooting technique. It is observed that increase in the values of thermal and mass stratification parameter reduce the velocity profile and increase in the values of variable thermal conductivity parameter and non-uniform heat source/sink parameters enhance the temperature distribution. Moreover, skin friction coefficient, Nusselt number and Sherwood number are discussed. Obtained results are displayed both graphically and in tabular form to illustrate the effect of different parameters on the velocity, temperature and concentration profiles. Numerical results are compared with previous published results and found to be in good agreement for special cases of the emerging parameters.
Fast and Accurate Prediction of Stratified Steel Temperature During Holding Period of Ladle
Deodhar, Anirudh; Singh, Umesh; Shukla, Rishabh; Gautham, B. P.; Singh, Amarendra K.
2017-04-01
Thermal stratification of liquid steel in a ladle during the holding period and the teeming operation has a direct bearing on the superheat available at the caster and hence on the caster set points such as casting speed and cooling rates. The changes in the caster set points are typically carried out based on temperature measurements at the end of tundish outlet. Thermal prediction models provide advance knowledge of the influence of process and design parameters on the steel temperature at various stages. Therefore, they can be used in making accurate decisions about the caster set points in real time. However, this requires both fast and accurate thermal prediction models. In this work, we develop a surrogate model for the prediction of thermal stratification using data extracted from a set of computational fluid dynamics (CFD) simulations, pre-determined using design of experiments technique. Regression method is used for training the predictor. The model predicts the stratified temperature profile instantaneously, for a given set of process parameters such as initial steel temperature, refractory heat content, slag thickness, and holding time. More than 96 pct of the predicted values are within an error range of ±5 K (±5 °C), when compared against corresponding CFD results. Considering its accuracy and computational efficiency, the model can be extended for thermal control of casting operations. This work also sets a benchmark for developing similar thermal models for downstream processes such as tundish and caster.
Li, Jiao Jiao; Kim, Kyungsook; Roohani-Esfahani, Seyed-Iman; Guo, Jin; Kaplan, David L; Zreiqat, Hala
2015-07-14
Significant clinical challenges encountered in the effective long-term treatment of osteochondral defects have inspired advancements in scaffold-based tissue engineering techniques to aid repair and regeneration. This study reports the development of a biphasic scaffold produced via a rational combination of silk fibroin and bioactive ceramic with stratified properties to satisfy the complex and diverse regenerative requirements of osteochondral tissue. Structural examination showed that the biphasic scaffold contained two phases with different pore morphologies to match the cartilage and bone segments of osteochondral tissue, which were joined at a continuous interface. Mechanical assessment showed that the two phases of the biphasic scaffold imitated the load-bearing behaviour of native osteochondral tissue and matched its compressive properties. In vitro testing showed that different compositions in the two phases of the biphasic scaffold could direct the preferential differentiation of human mesenchymal stem cells towards the chondrogenic or osteogenic lineage. By featuring simple and reproducible fabrication and a well-integrated interface, the biphasic scaffold strategy established in this study circumvented the common problems experienced with integrated scaffold designs and could provide an effective approach for the regeneration of osteochondral tissue.
Fast and Accurate Prediction of Stratified Steel Temperature During Holding Period of Ladle
Deodhar, Anirudh; Singh, Umesh; Shukla, Rishabh; Gautham, B. P.; Singh, Amarendra K.
2016-12-01
Thermal stratification of liquid steel in a ladle during the holding period and the teeming operation has a direct bearing on the superheat available at the caster and hence on the caster set points such as casting speed and cooling rates. The changes in the caster set points are typically carried out based on temperature measurements at the end of tundish outlet. Thermal prediction models provide advance knowledge of the influence of process and design parameters on the steel temperature at various stages. Therefore, they can be used in making accurate decisions about the caster set points in real time. However, this requires both fast and accurate thermal prediction models. In this work, we develop a surrogate model for the prediction of thermal stratification using data extracted from a set of computational fluid dynamics (CFD) simulations, pre-determined using design of experiments technique. Regression method is used for training the predictor. The model predicts the stratified temperature profile instantaneously, for a given set of process parameters such as initial steel temperature, refractory heat content, slag thickness, and holding time. More than 96 pct of the predicted values are within an error range of ±5 K (±5 °C), when compared against corresponding CFD results. Considering its accuracy and computational efficiency, the model can be extended for thermal control of casting operations. This work also sets a benchmark for developing similar thermal models for downstream processes such as tundish and caster.
Indications for tonsillectomy stratified by the level of evidence
Windfuhr, Jochen P.
2016-01-01
Background: One of the most significant clinical trials, demonstrating the efficacy of tonsillectomy (TE) for recurrent throat infection in severely affected children, was published in 1984. This systematic review was undertaken to compile various indications for TE as suggested in the literature after 1984 and to stratify the papers according to the current concept of evidence-based medicine. Material and methods: A systematic Medline research was performed using the key word of “tonsillectomy“ in combination with different filters such as “systematic reviews“, “meta-analysis“, “English“, “German“, and “from 1984/01/01 to 2015/05/31“. Further research was performed in the Cochrane Database of Systematic Reviews, National Guideline Clearinghouse, Guidelines International Network and BMJ Clinical Evidence using the same key word. Finally, data from the “Trip Database” were researched for “tonsillectomy” and “indication“ and “from: 1984 to: 2015“ in combination with either “systematic review“ or “meta-analysis“ or “metaanalysis”. Results: A total of 237 papers were retrieved but only 57 matched our inclusion criteria covering the following topics: peritonsillar abscess (3), guidelines (5), otitis media with effusion (5), psoriasis (3), PFAPA syndrome (6), evidence-based indications (5), renal diseases (7), sleep-related breathing disorders (11), and tonsillitis/pharyngitis (12), respectively. Conclusions: 1) The literature suggests, that TE is not indicated to treat otitis media with effusion. 2) It has been shown, that the PFAPA syndrome is self-limiting and responds well to steroid administration, at least in a considerable amount of children. The indication for TE therefore appears to be imbalanced but further research is required to clarify the value of surgery. 3) Abscesstonsillectomy as a routine is not justified and indicated only for cases not responding to other measures of treatment, evident complications
Transport Phenomena in Stratified Multi-Fluid Flow in the Presence and Absence of Gravity
Chigier, Norman; Humphrey, William
1996-01-01
Experiments are being conducted to study the effects of buoyancy on planar density-stratified shear flows. A wind tunnel generates planar flows separated by an insulating splitter plate, with either flow heated, which emerge from a two-dimensional nozzle. The objective is to isolate and define the effect of gravity and buoyancy on a stratified shear layer. To this end, both stably and unstably stratified layers will be investigated. This paper reports on the results of temperature and velocity measurements across the nozzle exit plane and downstream along the nozzle center plane.
洁净室检测采样方法中的随机抽样理论%The Random Sampling Theory Embodied in Sampling Method for Cleanroom Testing
王大千
2012-01-01
结合对ISO14644—1洁净室及相关受控环境第一部分：空气洁净度等级中洁净度检测的讨论，说明现有采样方法和新方法在采样点数量和位置上所体现的随机抽样理论。%The random sampling theory embodied in selection of number and position of sampling points in both existing test method and the new method in discussion was compared and discussed, combined with discussions on cleanroom cleanliness test specified in ISO 14644-1： Air borne Cleanliness Classification, Cleanroom and Associated ConttroUed Environments.
Power Spectrum Estimation of Randomly Sampled Signals
Velte, Clara M.; Buchhave, Preben; K. George, William
2014-01-01
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challengesdue to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors.To obtain the desired non-biased statistics, it has previously been shown...... analytically as well as empirically thatresidence time weighting is the suitable choice. Unfortunately, due to technical problems related to the processors providing erroneous measurements of the residence times, this previously widely accepted theory has been questioned and instead a wide spectrum...... of alternative methods attempting to produce correct power spectra have been invented andtested. The objective of the current study is to create a simple computer generated signal for baseline testing of residence time weighting and some of the most commonly proposed algorithms (or algorithms which most...
Control of Randomly Sampled Robotic Systems
1989-05-01
Artificial Inteligence Laboratory, 1972. PumA26O.c Ned Mar 8 17:51:04 1989 1 #include <rnath.h> #define real float #define mm 6 #define G 9.83. #define M6...systems through communications. Communication between processes sharing a single processor are also subject to random delays due to memory management ...processes sharing a single processor are also subject to random delays due to memory management and interrupt latency. Communications between processors
Power Spectrum Estimation of Randomly Sampled Signals
Velte, C. M.; Buchhave, P.; K. George, W.
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challenges due to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors. To obtain the desired non-biased statistics, it has previously been shown...... is that if the algorithms are not able to produce correct statistics from this simple signal, then they will certainly not be able to function well for a more complex measured LDA signal. This is, of course, true also for other methods that are based on the tested algorithms. The extremes are tested by increasing, e....... Residence time weighting provides non-biased estimates regardless of setting. The free-running processor was also tested and compared to residence time weighting using actual LDA measurements in a turbulent round jet. Power spectra from measurements on the jet centerline and the outer part of the jet...
QIU Xiang
2006-01-01
Turbulence structures and turbulent Counter-Gradient Transport(CGT) properties in the stratified flows with a sharp temperature interface are investigated by experimental measurements using LIF and PIV, by LES and by correlation analysis.
Development of a Curved, Stratified, In Vitro Model to Assess Ocular Biocompatibility: e96448
Cameron K Postnikoff; Robert Pintwala; Sara Williams; Ann M Wright; Denise Hileeto; Maud B Gorbet
2014-01-01
.... Methods Immortalized human corneal epithelial cells were grown to confluency on curved cellulose filters for seven days, and were then differentiated and stratified using an air-liquid interface...
Banakh, Taras
2008-01-01
We introduce and study (metrically) quarter-stratifiable spaces and then apply them to generalize Rudin and Kuratowski-Montgomery theorems about the Baire and Borel complexity of separately continuous functions.
Stratified shear flow in an inclined duct: coherent structures and mixing
Lefauve, Adrien; Partridge, Jamie; Dalziel, Stuart; Linden, Paul
2016-11-01
We present laboratory experiments on the exchange flow in an inclined square duct connecting two reservoirs at different densities. This system generates and maintains a stratified shear flow, which can be laminar, wavy or turbulent depending on the density difference and inclination angle. It is believed that the mean dissipation is set by the angle, and that high buoyancy Reynolds numbers (i.e. turbulent intensity) can be maintained, making this system suited for the study of continuously forced stratified turbulence. The talk will focus on the analysis of time-resolved, near-instantaneous 3D velocity and density data obtained by stereo particle image velocimetry (PIV) and laser induced fluorescence (LIF). This data allow for the visualisation of 3D coherent structures as well as turbulent mixing properties, which are key in understanding the dynamics of stratified turbulence. Supported by EPSRC Programme Grant EP/K034529/1 entitled "Mathematical Underpinnings of Stratified Turbulence".
Fugel, Hans-Joerg; Nuijten, Mark; Postma, Maarten
2016-01-01
RATIONALE: Stratified Medicine (SM) is becoming a natural result of advances in biomedical science and a promising path for the innovation-based biopharmaceutical industry to create new investment opportunities. While the use of biomarkers to improve R&D efficiency and productivity is very much
Barros, L. de
2007-12-15
Characterization of porous media parameters, and particularly the porosity, permeability and fluid properties are very useful in many applications (hydrologic, natural hazards or oil industry). The aim of my research is to evaluate the possibility to determine these properties from the full seismic wave fields. First, I am interested in the useful parameters and the specific properties of the seismic waves in the poro-elastic theory, often called Biot (1956) theory. I then compute seismic waves propagation in fluid saturated stratified porous media with a reflectivity method coupled with the discrete wavenumber integration method. I first used this modeling to study the possibilities to determine the carbon dioxide concentration and localization thanks to the reflected P-waves in the case of the deep geological storage of Sleipner (North Sea). The sensitivity of the seismic response to the poro-elastic parameters are then generalized by the analytical computation of the Frechet derivatives which are expressed in terms of the Green's functions of the unperturbed medium. The numerical tests show that the porosity and the consolidation are the main parameters to invert. The sensitivity operators are then introduced in a inversion algorithm based on iterative modeling of the full waveform. The classical algorithm of generalized least-square inverse problem is solved by the quasi-Newton technique (Tarantola, 1984). The inversion of synthetic data show that we can invert for the porosity and the fluid and solid parameters (densities and mechanical modulus, or volume rate of fluid and mineral) can be correctly rebuilt if the other parameters are well known. However, the strong seismic coupling of the porous parameters leads to difficulties to invert simultaneously for several parameters. One way to get round these difficulties is to use additional information and invert for one single parameter for the fluid properties (saturating rate) or for the lithology. An other
时序干涉测量中大气垂直分层延迟校正研究%CORRECTION OF STRATIFIED ATMOSPHERE DELAY INSAR INTERFEROMETRY
顾兆芹; 宫辉力; 张有全; 杜钊锋; 刘欢欢; 王洒; 卢学辉
2014-01-01
合成孔径雷达干涉测量(InSAR)技术在提取大区域、缓慢地表形变时一个主要限制因素是大气延迟误差.传统的干涉测量方法有时很难将大气垂直分层延迟与轨道误差、形变信号分离,在有些地区残余分层延迟甚至可以达到形变幅度,容易模糊形变相位.针对这一问题,选取美国Las Vegas地区为研究区,在大气模型识别大气延迟组分特征的基础上,采用多尺度分解方法评估大气垂直分层延迟,可以有效缓解时序干涉测量中的大气垂直分层延迟.%Atmospheric delay is one of the main limiting factors for extracting groundsurface deformation with small rate over a large area with Interferometric Synthetic Aperture Radar(InSAR) technology.The delay consists of two components:the stratified component and the turbulent component.Stratified atmosphere delay can be plagued by both orbital error and deformation signal.It is difficult to separate this component by traditional interference methods.The residual error of stratified atmosphere delay sometimes could reach the range of deformation in some regions,which seriously impacts the accuracy of SAR interferometry measurement.A multi-scale decomposition technique is proposed to evaluate stratified atmosphere delay,based on recognition of atmospheric components using North America NARR model.The results demonstrate that the method can effectively reduce the stratified components in InSAR interferometric phase.
Simulation model of stratified thermal energy storage tank using finite difference method
Waluyo, Joko
2016-06-01
Stratified TES tank is normally used in the cogeneration plant. The stratified TES tanks are simple, low cost, and equal or superior in thermal performance. The advantage of TES tank is that it enables shifting of energy usage from off-peak demand for on-peak demand requirement. To increase energy utilization in a stratified TES tank, it is required to build a simulation model which capable to simulate the charging phenomenon in the stratified TES tank precisely. This paper is aimed to develop a novel model in addressing the aforementioned problem. The model incorporated chiller into the charging of stratified TES tank system in a closed system. The model was developed in one-dimensional type involve with heat transfer aspect. The model covers the main factors affect to degradation of temperature distribution namely conduction through the tank wall, conduction between cool and warm water, mixing effect on the initial flow of the charging as well as heat loss to surrounding. The simulation model is developed based on finite difference method utilizing buffer concept theory and solved in explicit method. Validation of the simulation model is carried out using observed data obtained from operating stratified TES tank in cogeneration plant. The temperature distribution of the model capable of representing S-curve pattern as well as simulating decreased charging temperature after reaching full condition. The coefficient of determination values between the observed data and model obtained higher than 0.88. Meaning that the model has capability in simulating the charging phenomenon in the stratified TES tank. The model is not only capable of generating temperature distribution but also can be enhanced for representing transient condition during the charging of stratified TES tank. This successful model can be addressed for solving the limitation temperature occurs in charging of the stratified TES tank with the absorption chiller. Further, the stratified TES tank can be
Cenedese, A.; Dore, V.; Moroni, M.
2009-05-01
Free thermal convection refers to the motion of vertical turbulent plumes or domes, which can occur when, an initially in-rest stratified fluid, is submitted to buoyancy forces, caused by a permanent perturbation associated to a heat transfer mechanism. When a fluid, in equilibrium, is stably stratified the external forcing can produce an unstable configuration ensuing the increasing in amplitude of internal waves, and, if it has strength enough, it can definitely erode the stratification, involving an increasing thickness of fluid volume. The entrainment phenomenon justifies the penetrative feature of convection and causes the growth of a convective boundary layer of well mixed fluid (Convective Mixing Layer) against the adjacent stable stratified layer. The non-steady phenomenon of penetrative convection in a stably stratified fluid has been reproduced in laboratory employing a tank filled with water and subjected to heating from below. The goal in the experiment is predicting the convective boundary layer growth as a function of initial and boundary conditions and describing the fate of a tracer dissolved in the fluid phase. The motivations of the research are mostly related to its connections to environmental topics. In nature the dynamics of penetrative convection influences the transport and mixing features of stratified fluids, playing a fundamental role in characterizing and forecasting the distribution of chemical species, with implication for water or air quality in the upper oceans and lakes or in the lower troposphere. When studying turbulent convective phenomenon, dispersion is mostly due to transport by large organized structures while molecular diffusion can be neglected. The knowledge of the horizontal and vertical extension of the structures dominating the flow field appears to be mandatory. In order to better understanding and likely describing the evolution of turbulent structures inside the convective layer, a fully three dimensional
Senocak, I.; Ackerman, A. S.; Kirkpatrick, M. P.; Stevens, D. E.; Mansour, N. N.
2004-01-01
Large-eddy simulation (LES) is a widely used technique in armospheric modeling research. In LES, large, unsteady, three dimensional structures are resolved and small structures that are not resolved on the computational grid are modeled. A filtering operation is applied to distinguish between resolved and unresolved scales. We present two near-surface models that have found use in atmospheric modeling. We also suggest a simpler eddy viscosity model that adopts Prandtl's mixing length model (Prandtl 1925) in the vicinity of the surface and blends with the dynamic Smagotinsky model (Germano et al, 1991) away from the surface. We evaluate the performance of these surface models by simulating a neutraly stratified atmospheric boundary layer.
Chen Xiao-Gang; Guo Zhi-Ping; Song Jin-Bao
2008-01-01
In the present paper,the random interfacial waves in N-layer density-stratified fluids moving at different steady uniform speeds are researched by using an expansion technique,and the second-order asymptotic solutions of the random displacements of the density interfaces and the associated velocity potentials in N-layer fluid are presented based on the small amplitude wave theory.The obtained results indicate that the wave-wave second-order nonlinear interactions of the wave components and the second-order nonlinear interactions between the waves and currents are described.As expected,the solutions include those derived by Chen(2006)as a special case where the steady uniform currents of the N-layer fluids are taken as zero,and the solutions also reduce to those obtained by Song(2005)for second-order solutions for random interracial waves with steady uniform currents if N=2.
Scattering of flexural--gravity waves by a group of elastic plates floating on a stratified fluid
Meng, Q R
2016-01-01
A hydroelastic problem of flexural--gravity wave scattering by the demarcation between two floating elastic plates is investigated within the frame of linear potential theory, where the method of matched eigenfunction expansions is employed for analysis. A generalised extension is subsequently derived to promote the formulations to the case of multiple elastic plates on a stratified fluid with multiple layers, which is helpful to study the hydrodynamic behaviours of inhomogeneous floating covers as well as the effects of density stratification in seawater. The eigenfunction expansions are numerically calculated by an inner product technique, in which an orthogonal definition proposed with an explicit differential term exhibits the effectiveness for a multiple layer fluid in dealing with the matching relations between adjacent regions covered by different elastic plates. By use of Green's theorem, an energy conversation relation is deduced to assure the convergence of the calculation to the physical reality, a...
Roland
adopted a descriptive survey research design and used the stratified and simple random sampling techniques to ... A total of two hundred questionnaires was ... retrieve and evaluate information has ... on content, communication, analysis,.
Computer program uses Monte Carlo techniques for statistical system performance analysis
Wohl, D. P.
1967-01-01
Computer program with Monte Carlo sampling techniques determines the effect of a component part of a unit upon the overall system performance. It utilizes the full statistics of the disturbances and misalignments of each component to provide unbiased results through simulated random sampling.
Haralambous, Yannis
2012-01-01
We present an extension of the Explicit Semantic Analysis method by Gabrilovich and Markovitch. Using their semantic relatedness measure, we weight the Wikipedia categories graph. Then, we extract a minimal spanning tree, using Chu-Liu-Edmonds' algorithm. We define a notion of stratified tfidf where the stratas, for a given Wikipedia page and a given term, are the classical tfidf and categorical tfidfs of the term in the ancestor categories of the page (ancestors in the sense of the minimal spanning tree). Our method is based on this stratified tfidf, which adds extra weight to terms that "survive" when climbing up the category tree. We evaluate our method by a text classification on the WikiNews corpus: it increases precision by 18%. Finally, we provide hints for future research.
基于多线程的不等概率的随机抽取算法%The Random sample Algorithm of unequal probability Based on Multi Thread
容飞龙
2015-01-01
Random sample of unequal probability based on variable parameters has been widely used in the society,for example the lottery according to the amount of consumption and random play of music player. This paper presents a algorithm of unequal probability based on multi thread. The core of the algorithm is:sleep() of thread in proportion to the variable parameter. This algorithm can meet the needs of a variety of complex.%基于可变参数的不等概率的随机抽取已经在社会上广泛应用，比如根据消费金额的抽奖和音乐播放器的随机播放。本文提出了基于多线程的不等概率随机抽取的算法。该方法的核心在于：线程的sleep()的时间和可变参数成比例。可以满足多种复杂多变的需要。
[Individualized, personalized and stratified medicine: a challenge for allergology in ENT?].
Chaker, Adam M; Klimek, L
2015-05-01
Individualized, personalized or stratified medicine approaches offer emerging opportunities in the field of allergy and ENT. Avoidance of side effects, targeted therapy approaches and stratified prevention promise better outcomes and optimal results for patients. Conceptual incongruencies remain with regard to definitions and perceptions of "personalized medicine". Serious ethical considerations have to be taken into account. The development of pharmacogenomics, molecular phenotyping, genomic sequencing and other -omics opens the door to unique mechanistic therapeutic advances. The molecular allergology and recombinant diagnostics available are tools that offer substantial improved diagnostics for the benefit of allergic patients, e. g. in anaphylaxis and food allergy. For stratified therapeutic approaches, however, regulatory affairs will have to keep pace with medical and scientific discovery.
A dynamic subgrid-scale model for the large eddy simulation of stratified flow
刘宁宇; 陆夕云; 庄礼贤
2000-01-01
A new dynamic subgrid-scale (SGS) model, including subgrid turbulent stress and heat flux models for stratified shear flow is proposed by using Yoshizawa’ s eddy viscosity model as a base model. Based on our calculated results, the dynamic subgrid-scale model developed here is effective for the large eddy simulation (LES) of stratified turbulent channel flows. The new SGS model is then applied to the large eddy simulation of stratified turbulent channel flow under gravity to investigate the coupled shear and buoyancy effects on the near-wall turbulent statistics and the turbulent heat transfer at different Richardson numbers. The critical Richardson number predicted by the present calculation is in good agreement with the value of theoretical analysis.
A dynamic subgrid-scale model for the large eddy simulation of stratified flow
无
2000-01-01
A new dynamic subgrid-scale (SGS) model, including subgrid turbulent stress and heat flux models for stratified shear flow is proposed by using Yoshizawa's eddy viscosity model as a base model. Based on our calculated results, the dynamic subgrid-scale model developed here is effective for the large eddy simulation (LES) of stratified turbulent channel flows. The new SGS model is then applied to the large eddy simulation of stratified turbulent channel flow under gravity to investigate the coupled shear and buoyancy effects on the near-wall turbulent statistics and the turbulent heat transfer at different Richardson numbers. The critical Richardson number predicted by the present calculation is in good agreement with the value of theoretical analysis.
A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow
Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)] [and others
1995-09-01
This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.
Third Annual Open Meeting of the UK Pharmacogenomics and Stratified Medicine Network Conference.
Bradshaw, Elizabeth H
2015-07-01
Third Annual Open Meeting of the UK Pharmacogenetics and Stratified Medicine Network 14 January 2015, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK The third Annual Open Meeting of the UK Pharmacogenetics and Stratified Medicine Network was held on 14 January 2015 in association with the Wellcome Trust on the Wellcome Trust Genome Campus at Hinxton, Cambridge, UK. In the morning, speakers from Cancer Research UK, the Medical Research Council, Genomics England, Innovate UK (formerly TSB) and the Department of Health described the current major projects they are funding. In the afternoon, speakers from various universities around the United Kingdom presented data on pharmacogenetics and stratified medicine research covering diverse disease areas including cancers, warfarin dosing, Gaucher disease and rheumatoid arthritis.
Convective heat transport in stratified atmospheres at low and high Mach number
Anders, Evan H
2016-01-01
Convection in astrophysical systems is stratified and often occurs at high Rayleigh number (Ra) and low Mach number (Ma). Here we study stratified convection in the context of plane-parallel, polytropically stratified atmospheres. We hold the density stratification ($n_{\\rho}$) and Prandtl number (Pr) constant while varying Ma and Ra to determine the behavior of the Nusselt number (Nu), which quantifies the efficiency of convective heat transport. As Ra increases and $\\text{Ma} \\rightarrow 1$, a scaling of Nu $\\propto$ Ra$^{0.45}$ is observed. As Ra increases to a regime where Ma $\\geq 1$, this scaling gives way to a weaker Nu $\\propto$ Ra$^{0.19}$. In the regime of Ma $\\ll 1$, a consistent Nu $\\propto$ Ra$^{0.31}$ is retrieved, reminiscent of the Nu $\\propto$ Ra$^{2/7}$ seen in Rayleigh-B\\'{e}nard convection.
Prediction of Stratified Flow Temperature Profiles in a Fully Insulated Environment
Ahmad S. Awad
2014-07-01
Full Text Available The aim of the study is to present an analytical model to predict the temperature profiles in thermal stratified environment. Thermal stratification is encountered in many situations. The flow of contaminants and hydrocarbons in environment often get stratified. The prediction of temperature profiles and flow characteristics are essential for HVAC applications, environment and energy management. The temperature profiles in the stratified region are successfully obtained, in terms of flow-operating functions. The analytical model agrees well with the published experimental data as well as the related closed-form solutions, which is helpful for HVAC applications. The model will be further developed and incorporated within a numerical model in order to investigate the flow field characteristics and establish correlations for a wide range of parameters.
Hameed, Omar; Humphrey, Peter A
2006-07-01
Typically glands of prostatic adenocarcinoma have a single cell lining, although stratification can be seen in invasive carcinomas with a cribriform architecture, including ductal carcinoma. The presence and diagnostic significance of stratified cells within non-cribriform carcinomatous prostatic glands has not been well addressed. The histomorphological features and immunohistochemical profile of cases of non-cribriform prostatic adenocarcinoma with stratified malignant glandular epithelium were analyzed. These cases were identified from needle biopsy cases from the consultation files of one of the authors and from a review of 150 consecutive in-house needle biopsy cases of prostatic adenocarcinoma. Immunohistochemistry was performed utilizing antibodies reactive against high molecular weight cytokeratin (34betaE12), p63 and alpha-methylacyl-coenzyme-A racemase (AMACR). A total of 8 cases were identified, including 2 from the 150 consecutive in-house cases (1.3%). In 4 cases, the focus with glands having stratified epithelium was the sole carcinomatous component in the biopsy, while such a component represented 5-30% of the invasive carcinoma seen elsewhere in the remaining cases. The main attribute in all these foci was the presence of glandular profiles lined by several layers of epithelial cells with cytological and architectural features resembling flat or tufted high-grade prostatic intraepithelial neoplasia, but lacking basal cells as confirmed by negative 34betaE12 and/or p63 immunostains in all cases. The AMACR staining profile of the stratified foci was variable, with 4 foci showing positivity, and 3 foci being negative, including two cases that displayed AMACR positivity in adjacent non-stratified prostatic adenocarcinoma. Prostatic adenocarcinoma with stratified malignant glandular epithelium can be identified in prostate needle biopsy samples harboring non-cribriform prostatic adenocarcinoma and resembles glands with high-grade prostatic
T.J. Akingbade
2014-09-01
Full Text Available This research work compares the one-stage sampling technique (Simple Random Sampling and two-stage sampling technique for estimating the population total of Nigerians using the 2006 census result of Nigerians. A sample size of twenty (20 states was selected out of a population of thirty six (36 states at the Primary Sampling Unit (PSU and one-third of each state selected at the PSU was sample at the Secondary Sampling Unit (SSU and analyzed. The result shows that, with the same sample size at the PSU, one-stage sampling technique (Simple Random Sampling is more efficient than two-stage sampling technique and hence, recommended.
Sjoberg, Daniel
2008-01-01
This paper presents an overview of how circuit models can be used for analysing wave propagation in stratified structures. Relatively complex structures can be analysed using models which are accessible to undergraduate students. Homogeneous slabs are modelled as transmission lines, and thin sheets between the slabs are modelled as lumped…
Leung, Chi-Keung; Chang, Hua-Hua; Hau, Kit-Tai
The multistage alpha-stratified computerized adaptive testing (CAT) design advocated a new philosophy of pool management and item selection using low discriminating items first. It has been demonstrated through simulation studies to be effective both in reducing item overlap rate and enhancing pool utilization with certain pool types. Based on…
Experimental investigation on isothermal stratified flow mixing in a horizontal T-junction
Isaev, Alexander; Kulenovic, Rudi; Laurien, Eckart [Stuttgart Univ. (Germany). Inst. fuer Kernenergetik und Energiesysteme (IKE)
2016-10-15
Turbulent and stratified flows can lead to thermal fatigue in piping systems of nuclear power plants (NPP). Such flows can be investigated in the University of Stuttgart Fluid-Structure-Interaction (FSI) facility with a T-Junction at thermal conditions with temperature differences of up to 255 K and at pressures of maximum 75 bars.
Analysing stratified medicine business models and value systems: innovation-regulation interactions.
Mittra, James; Tait, Joyce
2012-09-15
Stratified medicine offers both opportunities and challenges to the conventional business models that drive pharmaceutical R&D. Given the increasingly unsustainable blockbuster model of drug development, due in part to maturing product pipelines, alongside increasing demands from regulators, healthcare providers and patients for higher standards of safety, efficacy and cost-effectiveness of new therapies, stratified medicine promises a range of benefits to pharmaceutical and diagnostic firms as well as healthcare providers and patients. However, the transition from 'blockbusters' to what might now be termed 'niche-busters' will require the adoption of new, innovative business models, the identification of different and perhaps novel types of value along the R&D pathway, and a smarter approach to regulation to facilitate innovation in this area. In this paper we apply the Innogen Centre's interdisciplinary ALSIS methodology, which we have developed for the analysis of life science innovation systems in contexts where the value creation process is lengthy, expensive and highly uncertain, to this emerging field of stratified medicine. In doing so, we consider the complex collaboration, timing, coordination and regulatory interactions that shape business models, value chains and value systems relevant to stratified medicine. More specifically, we explore in some depth two convergence models for co-development of a therapy and diagnostic before market authorisation, highlighting the regulatory requirements and policy initiatives within the broader value system environment that have a key role in determining the probable success and sustainability of these models.
Sjoberg, Daniel
2008-01-01
This paper presents an overview of how circuit models can be used for analysing wave propagation in stratified structures. Relatively complex structures can be analysed using models which are accessible to undergraduate students. Homogeneous slabs are modelled as transmission lines, and thin sheets between the slabs are modelled as lumped…
"Being" Black and Strategizing for Excellence in a Racially Stratified Academic Hierarchy
O'Connor, Carla; Mueller, Jennifer; Lewis, R. L'Heureux; Rivas-Drake, Deborah; Rosenberg, Seneca
2011-01-01
This article reports the findings of an ethnographic study of Black identity and achievement in one predominantly White high school featuring a racially stratified academic hierarchy (RSAH). Foregrounding the experiences of three exceptionally achieving Black girls against those of other high-achieving but less stellar students, the study…
van Aartrijk, M.; Clercx, H.J.H.
2010-01-01
The dispersion of light inertial particles $\\rho_p/\\rho_f = \\mathcal{O}(1)$ in statistically stationary stably stratified turbulence is studied by means of direct numerical simulations. The light particle dispersion behavior is found to be comparable to that of heavy particles when displayed as a
Stratified Flow in a Room with Displacement Ventilation and Wall-Mounted Air Terminal devices
Nielsen, Peter V.
This paper describes experiments with wall-mounted air terminal devices. The stratified flow in the room is analyzed, and the influence of stratification and the influence of room dimensions on the velocity level and on the length scale are proved. The velocity level in the occupied zone can be d...
Carmo, Carolina; Dumont, Olivier; Nielsen, Mads Pagh
2015-01-01
coupled with energy system solutions is limited. In this poster, a discretized model of a stratified tank developed in Modelica is presented. The physical phenoma to be considered are the thermal transfers by conduction and convection – stratification, heat loss to ambient, charging and discharging...
Modified Limiting Equilibrium Method for Stability Analysis of Stratified Rock Slopes
Rui Yong
2016-01-01
Full Text Available The stratified rock of Jurassic strata is widely distributed in Three Gorges Reservoir Region. The limit equilibrium method is generally utilized in the stability analysis of rock slope with single failure plane. However, the stratified rock slope cannot be accurately estimated by this method because of different bedding planes and their variable shear strength parameters. Based on the idealized model of rock slope with bedding planes, a modified limiting equilibrium method is presented to determine the potential sliding surface and the factor of safety for the stratified rock slope. In this method, the S-curve model is established to define the spatial variations of the shear strength parameters c and φ of bedding plane and the tensile strength of rock mass. This method was applied in the stability evaluation of typical stratified rock slope in Three Gorges Reservoir Region, China. The result shows that the factor of safety of the case study is 0.973, the critical sliding surface for the potential slip surface appears at bedding plane C, and the tension-controlled failure occurs at 10.5 m to the slope face.
Study on Reform of College English Stratified Teaching Based on School-Based Characteristics
Yang, Liu
2012-01-01
Considering the status quo of college English teaching, we implement stratified teaching, which reflects the idea of stratification in terms of teaching objects, teaching management, teaching process and assessment and evaluation, makes each students get development to the greatest extent in interactive teaching practice of teaching and learning…
Fabiano, B.; Kersten, R.J.A.; Opschoor, G.; Pastorino, R.
2002-01-01
The occurrence of a rapid phase transition, or so-called explosive boiling, when a cold volatile liquid comes into contact with a hot liquid or hot surface is a potential hazard in industry. This study was focused on the explosive boiling potential of thermally stratified liquid-liquid systems that
Measures to assess the prognostic ability of the stratified Cox proportional hazards model
(Tybjaerg-Hansen, A.) The Fibrinogen Studies Collaboration.The Copenhagen City Heart Study; Tybjærg-Hansen, Anne
2009-01-01
Many measures have been proposed to summarize the prognostic ability of the Cox proportional hazards (CPH) survival model, although none is universally accepted for general use. By contrast, little work has been done to summarize the prognostic ability of the stratified CPH model; such measures w...
Developing spatially stratified N{sub 2}O emission factors for Europe
Leip, Adrian, E-mail: adrian.leip@jrc.ec.europa.eu [European Commission-Joint Research Centre, Institute for Environment and Sustainability, Ispra (Italy); Busto, Mirko [International Institute for Applied Systems Analysis, Laxenburg (Austria); Winiwarter, Wilfried [International Institute for Applied Systems Analysis, Laxenburg (Austria); AIT Austrian Institute of Technology, Vienna (Austria)
2011-11-15
We investigate the possibility to replace the - so-called - Tier 1 IPCC approach to estimate soil N{sub 2}O emissions with stratified emissions factors that take into account both N-input and the spatial variability of the environmental conditions within the countries of the European Union, using the DNDC-Europe model. Spatial variability in model simulations is high and corresponds to the variability reported in literature for field data. Our results indicate that (a) much of the observed variability in N{sub 2}O fluxes reflects the response of soils to external conditions, (b) it is likely that national inventories tend to overestimate the uncertainties in their estimated direct N{sub 2}O emissions from arable soils; (c) on average over Europe, the fertilizer-induced emissions (FIE) coincide with the IPCC factors, but they display large spatial variations. Therefore, at scales of individual countries or smaller, a stratified approach considering fertilizer type, soil characteristics and climatic parameters is preferable. - Highlights: > Stratified modelling improves estimates of direct N2O emissions from arable soils. > Large variability between strata (expressed as countries) becomes evident. > Fertilizer-induced emissions of N{sub 2}O differ by N input (manure or mineral fertilizer). > National inventories likely overestimate the uncertainties for direct N2O emissions - Model simulations suggest that stratified country-specific N{sub 2}O emission factors are useful to better describe the soil emission behaviour of the European Union countries.
Masada, Youhei
2016-01-01
We report the first successful simulation of spontaneous formation of surface magnetic structures from a large-scale dynamo by strongly-stratified thermal convection in Cartesian geometry. The large-scale dynamo observed in our strongly-stratified model has physical properties similar to those in earlier weakly-stratified convective dynamo simulations, indicating that the $\\alpha^2$-type mechanism is responsible for it. Additionally to the large-scale dynamo, we find that large-scale structures of the vertical magnetic field are spontaneously formed in the convection zone surface only for the case of strongly-stratified atmosphere. The organization of the vertical magnetic field proceeds in the upper convection zone within tens of convective turn-over time and band-like bipolar structures are recurrently-appeared in the dynamo-saturated stage. We examine possibilities of several candidates as the origin of the surface magnetic structure formation, and then suggest the existence of an as-yet-unknown mechanism ...
ON THE EMBEDDING OF TOP IN THE CATEGORY OF STRATIFIED L-TOPOLOGICAL SPACES
LAI HONGLIANG; ZHANG DEXUE
2005-01-01
Let L be a meet continuous lattice. It is proved that the category Top of topological spaces can be embedded in the category of stratified L-topological spaces as a concretely both reflective and coreflective full subcategory if and only if L is a continuous lattice.
Computational Fluid Dynamics model of stratified atmospheric boundary-layer flow
Koblitz, Tilman; Bechmann, Andreas; Sogachev, Andrey;
2015-01-01
For wind resource assessment, the wind industry is increasingly relying on computational fluid dynamics models of the neutrally stratified surface-layer. So far, physical processes that are important to the whole atmospheric boundary-layer, such as the Coriolis effect, buoyancy forces and heat...
Coherence theory of electromagnetic wave propagation through stratified N-layer media
Hoenders, B.J.; Bertolotti, M.
The theory of second-order coherence in connection with wave propagation through a stratified N-layer (SNL) medium is developed. Especially, the influence of the SNL medium on the propagation of the coherence generated by a given state of coherence at the entrance plane of the medium is considered.
Seasonal cyclogenesis and the role of near-surface stratified layer in the Bay of Bengal
Murty, V.S.N.; Sarma, M.S.S.; Tilvi, V.
The role of the near-surface stratified layer developed due to the spread of low salinity waters under the influence of freshwater influx on the cyclogenesis over the Bay of Bengal is addressed. The seasonal variation of the Effective Oceanic Layer...
Tong, M.S.; Lu, Y.; Chen, Y.
2005-01-01
A planar stratified dielectric slab medium, which is an interesting problem in optics and geophysics, is studied using a pseudo-spectral time-domain (PSTD) algorithm. Time domain electric fields and frequency domain propagation characteristics of both single and periodic dielectric slab...
ZHONG; Fengquan(仲峰泉); LIU; Nansheng(刘难生); LU; Xiyun(陆夕云); ZHUANG; Lixian(庄礼贤)
2002-01-01
In the present paper, a new dynamic subgrid-scale (SGS) model of turbulent stress and heat flux for stratified shear flow is proposed. Based on our calculated results of stratified channel flow, the dynamic subgrid-scale model developed in this paper is shown to be effective for large eddy simulation (LES) of stratified turbulent shear flows. The new SGS model is then applied to the LES of the stratified turbulent channel flow to investigate the coupled shear and buoyancy effects on the behavior of turbulent statistics, turbulent heat transfer and flow structures at different Richardson numbers.
Hossain, Delowar; Samad, Abdus; Alam, Mahmud
2017-06-01
The ion-slip effects on unsteady MHD free convection flow past an infinite vertical porous plate with the effect of temperature stratified porous medium in a rotating system with viscous dissipation and Joule heating has been studied numerically. Introducing a time dependent suction to the plate, a similarity procedure has been adopted by taking a time dependent similarity parameter. The governing differential equations are transformed by introducing usual similarity variables. The resultant equations are solved numerically using Runge-Kutta method along with shooting technique. Resulting non-dimensional velocity and temperature profiles are then presented graphically for different values of the parameters entering into the problem.
Marcos Adami
2010-06-01
Full Text Available O objetivo deste trabalho foi avaliar o desempenho de um modelo probabilístico de amostragem estratificada por pontos, e definir um tamanho de amostra adequado para estimar a área cultivada com soja no Rio Grande do Sul. A área foi estratificada de acordo com a percentagem de soja cultivada em cada município do estado: menor que 20, de 20 a 40 e maior que 40%. Foram avaliadas estimativas obtidas por meio de seis tamanhos de amostras, resultantes da combinação de três níveis de significância (10, 5 e 1% e dois valores de erro amostral (5 e 2,5%. Para cada tamanho de amostra, foram realizados 400 sorteios aleatórios. As estimativas foram avaliadas com base na área de soja obtida de um mapa temático de referência proveniente de uma cuidadosa classificação automática e visual de imagens multitemporais dos satélites TM/Landsat-5 e ETM+/Landsat-7 disponível para a safra 2000/2001. A área de soja no Rio Grande do Sul pode ser estimada por meio de um modelo de amostragem probabilística estratificada por pontos, sendo que a melhor estimativa é obtida para o maior tamanho amostral (1.990 pontos, com diferença de apenas -0,14% em relação à estimativa do mapa de referência e um coeficiente de variação de 6,98%.The objective of this work was to evaluate the performance of a probabilistic sampling model stratified by points and to define an appropriate sample size to estimate the cultivated soybean area in the state of Rio Grande do Sul, Brazil. The area was stratified according to the percentage of soybean cultivated in each state municipality: less than 20, from 20 to 40 and more than 40%. Estimates were evaluated based on six sample sizes, resulting from the combination of three significance levels (10, 5 and 1% and two sampling errors (5 and 2,5%, choosing 400 random samples for each sample size. The estimates were compared to a reference soybean thematic map available for the crop year 2000/2001 that was derived from a careful
Garaud, Pascale; Gagnier, Damien; Verhoeven, Jan
2017-03-01
Shear-induced turbulence could play a significant role in mixing momentum and chemical species in stellar radiation zones, as discussed by Zahn. In this paper we analyze the results of direct numerical simulations of stratified plane Couette flows, in the limit of rapid thermal diffusion, to measure the turbulent viscosity and the turbulent diffusivity of a passive tracer as a function of the local shear and the local stratification. We find that the stability criterion proposed by Zahn, namely that the product of the gradient Richardson number and the Prandtl number must be smaller than a critical values {(J\\Pr )}c for instability, adequately accounts for the transition to turbulence in the flow, with {(J\\Pr )}c≃ 0.007. This result recovers and confirms the prior findings of Prat et al. Zahn’s model for the turbulent diffusivity and viscosity, namely that the mixing coefficient should be proportional to the ratio of the thermal diffusivity to the gradient Richardson number, does not satisfactorily match our numerical data. It fails (as expected) in the limit of large stratification where the Richardson number exceeds the aforementioned threshold for instability, but it also fails in the limit of low stratification where the turbulent eddy scale becomes limited by the computational domain size. We propose a revised model for turbulent mixing by diffusive stratified shear instabilities that properly accounts for both limits, fits our data satisfactorily, and recovers Zahn’s model in the limit of large Reynolds numbers.
Qvist I
2014-02-01
Full Text Available Ina Qvist,1 Marie D Thomsen,2 Jes S Lindholt,2,3 Hans Ibsen,4 Jeroen ML Hendriks,5 Lars Frost1 1Department of Medicine, Diagnostic Centre, University Research Clinic for Innovative Patient Pathways, Silkeborg Regional Hospital, Silkeborg, Denmark; 2Department of Vascular Surgery, Viborg Regional Hospital and Institute of Clinical Medicine, Aarhus University Hospital, Aarhus, Denmark; 3Centre of Individualized Medicine in Arterial Diseases, Department of Cardiothoracic and Vascular Department T, Odense University Hospital, Odense, Denmark; 4Department of Medicine, Holbæk Hospital, Holbæk, Denmark; 5Department of Cardiology, Maastricht University Medical Centre, Maastricht, the Netherlands Background: In general, it is assumed that patient education, by increasing knowledge, may change behavior and lifestyle and promote health. In this context, it is a surprise that knowledge and awareness about blood pressure and hypertension among elderly people is poor. We hypothesized that knowledge about blood pressure and hypertension would be better among individuals with self-reported hypertension compared with subjects without self-reported hypertension. Methods: We mailed a questionnaire to a random sample of 1,000 subjects living in the municipality of Silkeborg, Denmark. The study sample was drawn from the Central Person Registry. Results: The response rate was 72%. Of these, 43% of responders had self-reported hypertension. The people with self-reported hypertension were older, less educated, had higher self-reported blood cholesterol levels, had higher body weight, and more often had a family history of hypertension. More than 80% reported that overweight and obesity increases blood pressure. More than 60% reported that untreated hypertension may cause heart disease or stroke. More than half of the responders did not know their blood pressure, and only 21% knew that hypertension can occur without symptoms. Knowledge about hypertension was
Grol, MEC; Eimers, JM; Alberts, JF; Bouter, LM; Gerstenbluth, [No Value; Halabi, Y; van Sonderen, E; van den Heuvel, WJA
1997-01-01
OBJECTIVE: The aim of the article is to report the prevalence of obesity, abdominal fatness and waist circumference in different socioeconomic classes in Curacao. DESIGN: In 1993/1994 a health interview survey (the Curacao Health Study) was carried out among a random sample (n = 2248, response rate
Numerical modeling of mixing in large stably stratified enclosures using TRACMIX++
Christensen, Jakob
This PhD dissertation focuses on the numerical modeling of stably stratified large enclosures. In stably stratified volumes, the distribution of temperature, species concentration etc become essentially 1-D throughout most of the enclosure. When the fluid in an enclosure is stratified, wall boundary buoyant jets, forced buoyant jets (injection of fluid) and natural convection plumes become the primary sources of mixing. The time constants for the buoyant jets may be considered as much smaller than the time constant for the mixing of the stratified ambient fluid, provided the combined volume occupied by the buoyant jets is small compared to the volume of the enclosure. Therefore, fluid transport by the buoyant jets may be considered as occurring instantaneously. For this reason this work focuses on deriving a numerical method which is able to solve the 1-D vertical fluid conservation equations, as given in Peterson (1994). Starting with the Eulerian fluid conservation equations given in Peterson (1994), a set of Lagrangian fluid conservation equations were derived. Combining the Lagrangian approach with operator splitting such that the convective step and the diffusive step is separated renders a very efficient, accurate, and stable numerical method as it is shown in this text. Since the stratified flow field frequently exhibits very strong gradients or so-called fronts, the generation of these fronts has to be accurately detected and tracked by the numerical method. Flow in stably stratified large enclosure has typically been modeled in the past using 1- or 2-zone models. The present model is new in that it belongs to the K-zone models where the number of zones is arbitrarily large and depends on the complexity of the solution and the accuracy requirement set by the user. Because fronts are present in the flow field, a Lagrangian type numerical method is used. A Lagrangian method facilitates front tracking and prevents numerical diffusion from altering the shape of
Flow and transport within a coastal aquifer adjacent to a stratified water body
Oz, Imri; Yechieli, Yoseph; Eyal, Shalev; Gavrieli, Ittai; Gvirtzman, Haim
2016-04-01
The existence of a freshwater-saltwater interface and the circulation flow of saltwater beneath the interface is a well-known phenomenon found at coastal aquifers. This flow is a natural phenomenon that occurs due to density differences between fresh groundwater and the saltwater body. The goals of this research are to use analytical, numerical, and physical models in order to examine the configuration of the freshwater-saltwater interface and the density-driven flow patterns within a coastal aquifer adjacent to long-term stratified saltwater bodies (e.g. meromictic lake). Such hydrological systems are unique, as they consist of three different water types: the regional fresh groundwater, and low and high salinity brines forming the upper and lower water layers of the stratified water body, respectively. This research also aims to examine the influence of such stratification on hydrogeological processes within the coastal aquifer. The coastal aquifer adjacent to the Dead Sea, under its possible future meromictic conditions, serves as an ideal example to examine these processes. The results show that adjacent to a stratified saltwater body three interfaces between three different water bodies are formed, and that a complex flow system, controlled by the density differences, is created, where three circulation cells are developed. These results are significantly different from the classic circulation cell that is found adjacent to non-stratified water bodies (lakes or oceans). In order to obtain a more generalized insight into the groundwater behavior adjacent to a stratified water body, we used the numerical model to perform sensitivity analysis. The hydrological system was found be sensitive to three dimensionless parameters: dimensionless density (i.e. the relative density of the three water bodies'); dimensionless thickness (i.e. the ratio between the relative thickness of the upper layer and the whole thickness of the lake); and dimensionless flux. The results
Mirajkar, Harish N
2016-01-01
The presence of stratified layer in atmosphere and ocean leads to buoyant vertical motions, commonly referred to as plumes. It is important to study the mixing dynamics of a plume at a local scale in order to model their evolution and growth. Such a characterization requires measuring the velocity and density of the mixing fluids simultaneously. Here, we present the results of a buoyant plume propagating in a linearly stratified medium with a density difference of 0.5%, thus yielding a buoyancy frequency of N=0.15 s^{-1}. To understand the plume behaviour, statistics such as centerline and axial velocities along varying downstream locations, turbulent kinetic energy, Reynolds stress, and buoyancy flux were measured. The centerline velocity was found to decrease with increase in height. The Reynolds stress and buoyancy flux profiles showed the presence of a unstable layer and the mixing associated within that layer.
Reconstruction of stratified steady water waves from pressure readings on the ocean bed
Chen, Robin Ming
2015-01-01
Consider a two-dimensional stratified solitary wave propagating through a body of water that is bounded below by an impermeable ocean bed. In this work, we study how such a wave can be reconstructed from data consisting of the wave speed, upstream and downstream density profile, and the trace of the pressure on the bed. First, we prove that this data uniquely determines the wave, both in the (real) analytic and Sobolev regimes. Second, for waves that consist of multiple layers of constant density immiscible fluids, we provide an exact formula describing each of the interfaces in terms of the data. Finally, for continuously stratified fluids, we detail a reconstruction scheme based on approximation by layer-wise constant density flows.
Numerical simulation of stratified shear flow using a higher order Taylor series expansion method
Iwashige, Kengo; Ikeda, Takashi [Hitachi, Ltd. (Japan)
1995-09-01
A higher order Taylor series expansion method is applied to two-dimensional numerical simulation of stratified shear flow. In the present study, central difference scheme-like method is adopted for an even expansion order, and upwind difference scheme-like method is adopted for an odd order, and the expansion order is variable. To evaluate the effects of expansion order upon the numerical results, a stratified shear flow test in a rectangular channel (Reynolds number = 1.7x10{sup 4}) is carried out, and the numerical velocity and temperature fields are compared with experimental results measured by laser Doppler velocimetry thermocouples. The results confirm that the higher and odd order methods can simulate mean velocity distributions, root-mean-square velocity fluctuations, Reynolds stress, temperature distributions, and root-mean-square temperature fluctuations.
Double criticality and the two-way Boussinesq equation in stratified shallow water hydrodynamics
Bridges, Thomas J.; Ratliff, Daniel J.
2016-06-01
Double criticality and its nonlinear implications are considered for stratified N-layer shallow water flows with N = 1, 2, 3. Double criticality arises when the linearization of the steady problem about a uniform flow has a double zero eigenvalue. We find that there are two types of double criticality: non-semisimple (one eigenvector and one generalized eigenvector) and semi-simple (two independent eigenvectors). Using a multiple scales argument, dictated by the type of singularity, it is shown that the weakly nonlinear problem near double criticality is governed by a two-way Boussinesq equation (non-semisimple case) and a coupled Korteweg-de Vries equation (semisimple case). Parameter values and reduced equations are constructed for the examples of two-layer and three-layer stratified shallow water hydrodynamics.
Large eddy simulation of turbulent statistical and transport properties in stably stratified flows
Xiang QIU; Yong-xiang HUANG; Zhi-ming LU; Yu-lu LIU
2009-01-01
Three dimensional large eddy simulation (LES) is performed in the inves-tigation of stably stratified turbulence with a sharp thermal interface. Main results are focused on the turbulent characteristic scale, statistical properties, transport properties,and temporal and spatial evolution of the scalar field. Results show that the buoyancy scale increases first, and then goes to a certain constant value. The stronger the mean shear, the larger the buoyancy scale. The overturning scale increases with the flow, and the mean shear improves the overturning scale. The flatness factor of temperature de-parts from the Ganssian distribution in a fairly large region, and its statistical properties are clearly different from those of the velocity fluctuations in strong stratified cases. Tur-bulent mixing starts from small scale motions, and then extends to large scale motions.
A 3D Spectral Anelastic Hydrodynamic Code for Shearing, Stratified Flows
Barranco, J A; Barranco, Joseph A.; Marcus, Philip S.
2005-01-01
We have developed a three-dimensional (3D) spectral hydrodynamic code to study vortex dynamics in rotating, shearing, stratified systems (e.g. the atmosphere of gas giant planets, protoplanetary disks around newly forming protostars). The time-independent background state is stably stratified in the vertical direction and has a unidirectional linear shear flow aligned with one horizontal axis. Superposed on this background state is an unsteady, subsonic flow that is evolved with the Euler equations subject to the anelastic approximation to filter acoustic phenomena. A Fourier-Fourier basis in a set of quasi-Lagrangian coordinates that advect with the background shear is used for spectral expansions in the two horizontal directions. For the vertical direction, two different sets of basis functions have been implemented: (1) Chebyshev polynomials on a truncated, finite domain, and (2) rational Chebyshev functions on an infinite domain. Use of this latter set is equivalent to transforming the infinite domain to ...
The Hand Burn Severity (HABS) score: A simple tool for stratifying severity of hand burns.
Bache, Sarah E; Fitzgerald O'Connor, Edmund; Theodorakopoulou, Evgenia; Frew, Quentin; Philp, Bruce; Dziewulski, Peter
2017-02-01
Hand burns represent a unique challenge to the burns team due to the intricate structure and unrivalled functional importance of the hand. The initial assessment and prognosis relies on consideration of the specific site involved as well as depth of the burn. We created a simple severity score that could be used by referring non-specialists and researchers alike. The Hand Burn Severity (HABS) score stratifies hand burns according to severity with a numerical value of between 0 (no burn) and 18 (most severe) per hand. Three independent assessors scored the photographs of 121 burned hands of 106 adult and paediatric patients, demonstrating excellent inter-rater reliability (r=0.91, pburn depth alone. The HABS score is a simple to use tool to stratify severity at initial presentation of hand burns which will be useful when referring, and when reporting outcomes. Copyright © 2016 Elsevier Ltd and ISBI. All rights reserved.
Nonlinear dynamics at the interface of two-layer stratified flows over pronounced obstacles
Cabeza, C; Bove, I; Freire, D; Marti, Arturo C; Sarasua, L G; Usera, G; Montagne, R; Araújo, M
2008-01-01
The flow of a two--layer stratified fluid over an abrupt topographic obstacle, simulating relevant situations in oceanographic problems, is investigated numerically and experimentally in a simplified two--dimensional situation. Experimental results and numerical simulations are presented at low Froude numbers in a two-layer stratified flow and for two abrupt obstacles, semi--cylindrical and prismatic. We find four different regimes of the flow immediately past the obstacles: sub-critical (I), internal hydraulic jump (II), Kelvin-Helmholtz at the interface (III) and shedding of billows (IV). The critical condition for delimiting the experiments is obtained using the hydraulic theory. Moreover, the dependence of the critical Froude number on the geometry of the obstacle are investigated. The transition from regime III to regime IV is explained with a theoretical stability analysis. The results from the stability analysis are confirmed with the DPIV measurements. In regime (IV), when the velocity upstream is lar...
Mixed Convection Flow along a Stretching Cylinder in a Thermally Stratified Medium
Swati Mukhopadhyay
2012-01-01
Full Text Available An analysis for the axisymmetric laminar boundary layer mixed convection flow of a viscous and incompressible fluid towards a stretching cylinder immersed in a thermally stratified medium is presented in this paper. Similarity transformation is employed to convert the governing partial differential equations into highly nonlinear ordinary differential equations. Numerical solutions of these equations are obtained by a shooting method. It is found that the heat transfer rate at the surface is lower for flow in a thermally stratified medium compared to that of an unstratified medium. Moreover, both the skin friction coefficient and the heat transfer rate at the surface are larger for a cylinder compared to that for a flat plate.
Laboratory Studies of the Stratified Rotating Flow Passing over an Isolated Obstacle
高守亭; 平凡
2003-01-01
We study the flow of a density-stratified fluid passing over an isolated obstacle, using towing-tank experiments.Our special concern is the response of the flow with different Froude numbers passing over a three-dimensional obstacle. A series of experiments of the stratified rotating flow passing over an isolated obstacle was carried out with the towering-tank controlled by the similarity laws and dynamic non-dimension parameters. These experiments show that the Froude number is a very important parameter, and the lee wave and the eddy structure appear simultaneously under an appropriate conditions. The effect of rotation on the lee wave is mainly to change wave amplitude, particularly to restrain the development of the lee wave and to promote the formation of an eddy.
Elperin, T; Krasovitov, B; Kulmala, M; Liberman, M; Rogachevskii, I; Zilitinkevich, S
2013-01-01
Condensation of water vapor on active cloud condensation nuclei produces micron-size water droplets. To form rain, they must grow rapidly into at least 50-100 micron-size droplets. Observations show that this process takes only 15-20 minutes. The unexplained physical mechanism of such fast growth, is crucial for understanding and modeling of rain, and known as "condensation-coalescence bottleneck in rain formation". We show that the recently discovered phenomenon of the tangling clustering instability of small droplets in temperature-stratified turbulence (Phys. Fluids 25, 085104, 2013) results in the formation of droplet clusters with drastically increased droplet number densities and strong five-orders-of-magnitude enhancement of the collision-coalescence rate inside the clusters. The mechanism of tangling clustering instability in the temperature-stratified turbulence is much more effective than the previously considered pure inertial clustering caused by the centrifugal effect of turbulent vortices. Our a...
Numerical study of thermally stratified flows of a fluid overlying a highly porous material
Antoniadis, Panagiotis D.; Papalexandris, Miltiadis V.
2014-11-01
In this talk we are concerned with thermally stratified flows in domains that contain a macroscopic interface between a highly porous material and a pure-fluid domain. Our study is based on the single-domain approach according to which the same set of governing equations is employed both inside the porous medium and in the pure-fluid domain. Also, the mathematical model that we employ treats the porous skeleton as a rigid solid that is in thermal non-equilibrium with the fluid. First, we present briefly the basic steps of the derivation of the mathematical model. Then, we present and discuss numerical results for both thermally stratified shear flows and natural convection. Our discussion focuses on the role of thermal stratification on the flows of interest and on the effect of thermal non-equilibrium between the solid matrix and the fluid inside the porous medium. This work is supported by the National Fund for Scientific Research (FNRS), Belgium.
Simulations of surfactant-laden drops rising in a density-stratified medium
Martin, David W.; Blanchette, François
2017-02-01
We present simulations of the effects of insoluble surfactant on drops rising in unstratified media and density-stratified media. We consider an oil drop rising in water, and we track surfactant concentration on the drop surface. We first consider a drop coated with insoluble surfactant rising through an unstratified ambient. The drop speed is computed for various Marangoni numbers, and inertial and surface diffusion effects are also examined. In the second setup, we compare clean and contaminated drops rising through a linear density-stratified fluid. The entrained buoyancy is computed for various density gradients, and the effects of inertia and Marangoni number are characterized. We find that the entrained fluid slows the drop in a manner comparable to a vertical shift in the ambient density gradient.
Wei, Qiangbing; Yu, Bo; Wang, Xiaolong; Zhou, Feng
2014-06-01
Stratified polymer brushes are fabricated using microcontact printing (μCP) of initiator integrated polydopamine (PDOPBr) on polymer brush surfaces and the following surface initiated atom transfer radical polymerization (SI-ATRP). It is found that the surface energy, chemically active groups, and the antifouling ability of the polymer brushes affect transfer efficiency and adhesive stability of the polydopamine film. The stickiness of the PDOPBr pattern on polymer brush surfaces is stable enough to perform continuous μCP and SI-ATRP to prepare stratified polymer brushes with a 3D topography, which have broad applications in cell and protein patterning, biosensors, and hybrid surfaces. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hirota, Makoto, E-mail: hirota@dragon.ifs.tohoku.ac.jp [Institute of Fluid Science, Tohoku University, Sendai, Miyagi 980-8577 (Japan); Morrison, Philip J. [Department of Physics and Institute for Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States)
2016-05-06
Highlights: • New stability criteria of stably stratified shear flow are discovered. • Our criteria substantially improve the Howard–Miles criterion (1961). • Our criteria also generalize Rayleigh's inflection point theorem. • The novel approach we found is also efficient as a numerical approach. - Abstract: Linear stability of inviscid, parallel, and stably stratified shear flow is studied under the assumption of smooth strictly monotonic profiles of shear flow and density, so that the local Richardson number is positive everywhere. The marginally unstable modes are systematically found by solving a one-parameter family of regular Sturm–Liouville problems, which can determine the stability boundaries more efficiently than solving the Taylor–Goldstein equation directly. By arguing for the non-existence of a marginally unstable mode, we derive new sufficient conditions for stability, which generalize the Rayleigh–Fjørtoft criterion for unstratified shear flows.
Doubly stratified mixed convection flow of Maxwell nanofluid with heat generation/absorption
Abbasi, F.M., E-mail: abbasisarkar@gmail.com [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Hayat, T. [Department of Mathematics, Quaid-i-Azam University, 45320, Islamabad 44000 (Pakistan); NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Ahmad, B. [NAAM Research Group, Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)
2016-04-15
Magnetohydrodynamic (MHD) doubly stratified flow of Maxwell nanofluid in presence of mixed convection is analyzed in this article. Effects of thermophoresis, Brownian motion and heat generation/absorption are present. The flow is induced due to linear stretching of sheet. Mathematical formulation is made under boundary layer approach. Expressions of velocity, temperature and nanoparticles concentration are developed. The obtained results are plotted and discussed to examine the variations in temperature and nanoparticles concentration due to different physical parameters. Numerical computations are made to obtain the values of local Nusselt and Sherwood numbers. Impact of sundry parameters on the flow quantities is analyzed graphically. - Highlights: • Double stratified flow of Maxwell nanofluid with mixed convection is modeled. • Thermophoresis and Brownian motion effects are encountered. • Computations are made to obtain the solution expressions. • Numerical values of local Nusselt and Sherwood numbers are computed and examined.
Experimental study of temperature fluctuations in forced stably stratified turbulent flows
Eidelman, A; Gluzman, Y; Kleeorin, N; Rogachevskii, I
2013-01-01
We study experimentally temperature fluctuations in stably stratified forced turbulence in air flow. In the experiments with an imposed vertical temperature gradient, the turbulence is produced by two oscillating grids located nearby the side walls of the chamber. Particle Image Velocimetry is used to determine the turbulent and mean velocity fields, and a specially designed temperature probe with sensitive thermocouples is employed to measure the temperature field. We found that the ratio [(\\ell_x \
Nielsen, Peter V.; Jensen, Rasmus Lund; Litewnicki, Michal;
2009-01-01
This study investigates the characteristics of human exhalation. Experiments are performed on a breathing thermal manikin in a test room. The manikin is heated, and an artificial lung is used to generate varying air flows with specific flow rates and temperatures for breathing. Smoke visualisation...... is used to show the formation, movement and disappearance of the exhalation jets from both nose and mouth. The exhalation of breathing without ventilation in the room, and with stratified surroundings (displacement ventilation) is analysed....
Indicators of problems evaluated by parents and children stratified by birth weight
RODRIGUES-PALUCCI,Claudia Mazzer; Loureiro,Sonia Regina
2017-01-01
Abstract Studies on the impact of birth weight on child development require the participation of children as informants. The objective of this study was to compare the indicators of behavioral problems and depression in a cohort of school-age children stratified by birth weight and to investigate possible associations between the indicators of behavioral problems, evaluated by the parents, and depression, evaluated by the children. A total of 665 children, aged 10-11 years, distributed into f...
A Model for Predicting Holdup and Pressure Drop in Gas-Liquid Stratified Flow
无
2001-01-01
The time-dependent liquid film thickness and pressure drop were measured by using parallel-wire conductance probes and capacitance differential-preesure transducers. Applying the eddy viscosity theory and an appropriate correlation of interfacial sear stress,a new two-dimensional separated model of holdup and pressure drop of turbulent/turbulent gas-liquid stratified flow was presented. Prediction results agreed well with experimental data.
Brandenburg, Axel; Kleeorin, Nathan
2016-01-01
In the presence of strong density stratification, hydromagnetic turbulence attains qualitatively new properties: the formation of magnetic flux concentrations. We review here the theoretical foundations of this mechanism in terms of what is now called the negative effective magnetic pressure instability. We also present direct numerical simulations of forced turbulence in strongly stratified layers and discuss the qualitative and quantitative similarities with corresponding mean-field simulations. Finally, the relevance to sunspot formation is discussed.
2014-05-26
parametric subharmonic instability. 15. SUBJECT TERMS Stratified turbulent wakes, high Reynolds numbers, internal waves, nonlinear effects, harmonics, mean...beam and the potential for parametric subharmonic instability. In all these efforts, a uniform linear stratification was considered. A subset of our...found for all simulated waves. c) For sufficiently high-amplitude beams, a parametric subharmonic instability is observed after a long enough time
An immersed interface method for two-dimensional modelling of stratified flow in pipes
Berthelsen, Petter Andreas
2004-01-01
This thesis deals with the construction of a numerical method for solving two-dimensional elliptic interface problems, such as fully developed stratified flow in pipes. Interface problems are characterized by its non-smooth and often discontinuous behaviour along a sharp boundary separating the fluids or other materials. Classical numerical schemes are not suitable for these problems due to the irregular geometry of the interface. Standard finite difference discretization across the interface...
Propagation of Long-Wavelength Nonlinear Slow Sausage Waves in Stratified Magnetic Flux Tubes
Barbulescu, M.; Erdélyi, R.
2016-05-01
The propagation of nonlinear, long-wavelength, slow sausage waves in an expanding magnetic flux tube, embedded in a non-magnetic stratified environment, is discussed. The governing equation for surface waves, which is akin to the Leibovich-Roberts equation, is derived using the method of multiple scales. The solitary wave solution of the equation is obtained numerically. The results obtained are illustrative of a solitary wave whose properties are highly dependent on the degree of stratification.
A Model of Turbulent-Laminar Gas-Liquid Stratified Flow
无
2001-01-01
The time-dependent liquid film thickness and pressure drop are measured by using parallel-wire conduc tance probes and capacitance differential-pressure transducer. A mathematical model with iterative procedure to calculate holdup and pressure drop in horizontal and inclined gas-liquid stratified flow is developed. The predictions agree well with over a hundred experimental data in 0.024 and 0.04 m diameter pipelines.
The Near Wake of Bluff Bodies in Stratified Fluids and the Emergence of Late Wake Characteristics
2010-10-29
Kundu and Ira Cohen. Fluid Mechanics , Third Edition. Elsevier Inc., 2004. [27] S. Lee. A numerical study of the unsteady wake behind a sphere in a...found in the stratified fluid flows is the existence of the standing lee wave, which is a laminar mechanism . Above a Reynolds number of 2000, it is...computational cost to both model the proper fluid mechanics on the sphere and reproduce the far-wake is prohibitively expensive with current
Petit, J.L.
1997-07-21
This thesis is devoted to the inversion of VSP (vertical seismic profile) seismic data in order to determine the elastic properties of horizontally stratified media. The VSP records are computed using the full wave elastic modelling in isotropic and transversely isotropic media using Hankel transform, a finite difference scheme and an inverse Hankel transform algorithm, and the propagation equations are determined and numerically solved; the importance of considering a 3D wave propagation model instead of a 1 D one is emphasized. The theoretical VSP inverse problem is then considered, with the seismic waveform inversion set as a least-squares problem, consisting in recovering the distribution of physical parameters which minimize the misfit between calculated and observed VSP. The corresponding problem requires the knowledge of the source function
Quasi-geostrophic modes in the Earth's fluid core with an outer stably stratified layer
Vidal, Jérémie
2015-01-01
Seismic waves sensitive to the outermost part of the Earth's liquid core seem to be affected by a stably stratified layer at the core-mantle boundary. Such a layer could have an observable signature in both long-term and short-term variations of the magnetic field of the Earth, which are used to probe the flow at the top of the core. Indeed, with the recent SWARM mission, it seems reasonable to be able to identify waves propagating in the core with period of several months, which may play an important role in the large-scale dynamics. In this paper, we characterize the influence of a stratified layer at the top of the core on deep quasi-geostrophic (Rossby) waves. We compute numerically the quasi-geostrophic eigenmodes of a rapidly rotating spherical shell, with a stably stratified layer near the outer boundary. Two simple models of stratification are taken into account, which are scaled with commonly accepted values of the Brunt-V{\\"a}is{\\"a}l{\\"a} frequency in the Earth's core. In the absence of magnetic fi...
Diamessis, P.; Gurka, R.; Liberzon, A.
2008-11-01
Proper orthogonal decomposition (POD) is applied to 2-D slices of vorticity and horizontal divergence obtained from the 3-D DNS of the stratified turbulent wake of a towed sphere at Re=5x10^3 and Fr=4. Slices are sampled along the stream-depth (Oxz) and stream-span planes (Oxy) at 231 times during the interval Nt[12,35]. POD was chosen amongst the available statistical tools due to its advantage in characterization of simulated and experimentally measured velocity gradient fields, as previously demonstrated for turbulent boundary layers. In the Oxz planes, at the wake centerline, the higher most energetic modes reveal a structure similar of the structure of late-time stratified wakes. Off-set from centerline, the signature of internal waves in the form of forward-inclined coherent beams extending into the ambient becomes evident. The angle of inclination becomes progressively vertical with increasing POD mode. Lower POD modes on the Oyz planes show a layered structure in the wake core with coherent beams radiating out into the ambient over a broad range of angles. Further insight is provided through the relative energy spectra distribution of the vorticity eigenmodes. POD analysis has provided a statistical description of the geometrical features previously observed in instantaneous flow fields of stratified turbulent wakes.
Node Redeployment Algorithm Based on Stratified Connected Tree for Underwater Sensor Networks
Jun Liu
2016-12-01
Full Text Available During the underwater sensor networks (UWSNs operation, node drift with water environment causes network topology changes. Periodic node location examination and adjustment are needed to maintain good network monitoring quality as long as possible. In this paper, a node redeployment algorithm based on stratified connected tree for UWSNs is proposed. At every network adjustment moment, self-examination and adjustment on node locations are performed firstly. If a node is outside the monitored space, it returns to the last location recorded in its memory along straight line. Later, the network topology is stratified into a connected tree that takes the sink node as the root node by broadcasting ready information level by level, which can improve the network connectivity rate. Finally, with synthetically considering network coverage and connectivity rates, and node movement distance, the sink node performs centralized optimization on locations of leaf nodes in the stratified connected tree. Simulation results show that the proposed redeployment algorithm can not only keep the number of nodes in the monitored space as much as possible and maintain good network coverage and connectivity rates during network operation, but also reduce node movement distance during node redeployment and prolong the network lifetime.
On a new non-Boussinesq instability in stratified lakes and oceans
Shete, Mihir H
2016-01-01
Lakes and many other geophysical flows are shallow, density stratified, and contain a free-surface. Conventional studies on stratified shear instabilities make Boussinesq approximation. Free-surface arising due to large density variations between air and water cannot be taken into consideration under this approximation. Hence the free-surface is usually replaced by a rigid-lid, and therefore has little effect on the stability of the fluid below it. In this paper we have performed non-Boussinesq linear stability analyses of a double circulation velocity profile prevalent in two-layered density stratified lakes. One of our analyses is performed by considering the presence of wind, while the other one considers quiescent air. Both analyses have shown similar growth rates and stability boundaries. We have compared our non-Boussinesq study with a corresponding Boussinesq one. The maximum non-Boussinesq growth rate is found to be an order of magnitude greater than the maximum Boussinesq growth rate. Furthermore, th...
Turbulent fluxes of entropy and internal energy in temperature stratified flows
Rogachevskii, Igor
2015-01-01
We derive equations for the mean entropy and the mean internal energy in the low-Mach-number temperature stratified turbulence (i.e., for turbulent convection or stably stratified turbulence), and show that turbulent flux of entropy is given by ${\\bf F}_s=\\overline{\\rho} \\, \\overline{{\\bf u} s}$, where $\\overline{\\rho}$ is the mean fluid density, $s$ are fluctuations of entropy and overbars denote averaging over an ensemble of turbulent velocity field, ${\\bf u}$. We demonstrate that the turbulent flux of entropy is different from the turbulent convective flux, ${\\bf F}_c=\\overline{T} \\, \\overline{\\rho} \\, \\overline{{\\bf u} s}$, of the fluid internal energy, where $\\overline{T}$ is the mean fluid temperature. This turbulent convective flux is well-known in the astrophysical and geophysical literature, and it cannot be used as a turbulent flux in the equation for the mean entropy. This result is exact for low-Mach-number temperature stratified turbulence and is independent of the model used. We also derive equa...
Waves and vortices in the inverse cascade regime of stratified turbulence with or without rotation
Herbert, Corentin; Rosenberg, Duane; Pouquet, Annick
2015-01-01
We study the partition of energy between waves and vortices in stratified turbulence, with or without rotation, for a variety of parameters, focusing on the behavior of the waves and vortices in the inverse cascade of energy towards the large scales. To this end, we use direct numerical simulations in a cubic box at a Reynolds number Re=1000, with the ratio between the Brunt-V\\"ais\\"al\\"a frequency N and the inertial frequency f varying from 1/4 to 20, together with a purely stratified run. The Froude number, measuring the strength of the stratification, varies within the range 0.02 < Fr < 0.32. We find that the inverse cascade is dominated by the slow quasi-geostrophic modes. Their energy spectra and fluxes exhibit characteristics of an inverse cascade, even though their energy is not conserved. Surprisingly, the slow vortices still dominate when the ratio N/f increases, also in the stratified case, although less and less so. However, when N/f increases, the inverse cascade of the slow modes becomes we...
Gonzalez-Andrades, Miguel; Alonso-Pastor, Luis; Mauris, Jérôme; Cruzat, Andrea; Dohlman, Claes H; Argüeso, Pablo
2016-01-13
The repair of wounds through collective movement of epithelial cells is a fundamental process in multicellular organisms. In stratified epithelia such as the cornea and skin, healing occurs in three steps that include a latent, migratory, and reconstruction phases. Several simple and inexpensive assays have been developed to study the biology of cell migration in vitro. However, these assays are mostly based on monolayer systems that fail to reproduce the differentiation processes associated to multilayered systems. Here, we describe a straightforward in vitro wound assay to evaluate the healing and restoration of barrier function in stratified human corneal epithelial cells. In this assay, circular punch injuries lead to the collective migration of the epithelium as coherent sheets. The closure of the wound was associated with the restoration of the transcellular barrier and the re-establishment of apical intercellular junctions. Altogether, this new model of wound healing provides an important research tool to study the mechanisms leading to barrier function in stratified epithelia and may facilitate the development of future therapeutic applications.
Turbulent circulation above the surface heat source in stably stratified atmosphere
Kurbatskii, A. F.; Kurbatskaya, L. I.
2016-10-01
The 3-level RANS approach for simulating a turbulent circulation over the heat island in a stably stratified environment under nearly calm conditions is formulated. The turbulent kinetic energy its spectral consumption (dissipation) and the dispersion of turbulent fluctuations of temperature are found from differential equations, thus the correct modeling of transport processes in the interface layer with the counter-gradient heat flux is assured. The three-parameter turbulence RANS approach minimizes difficulties in simulating the turbulent transport in a stably stratified environment and reduces efforts needed for the numerical implementation of the 3-level RANS approach. Numerical simulation of the turbulent structure of the penetrative convection over the heat island under conditions of stably stratified atmosphere demonstrates that the three-equation model is able to predict the thermal circulation induced by the heat island. The temperature distribution, root-mean-square fluctuations of the turbulent velocity and temperature fields and spectral turbulent kinetic energy flux are in good agreement with the experimental data. The model describes such thin physical effects, as a crossing of vertical profiles of temperature of a thermal plume with the formation of the negative buoyancy area testifying to development of the dome-shaped form at the top part of a plume in the form of "hat".
An affordable and accurate conductivity probe for density measurements in stratified flows
Carminati, Marco; Luzzatto-Fegiz, Paolo
2015-11-01
In stratified flow experiments, conductivity (combined with temperature) is often used to measure density. The probes typically used can provide very fine spatial scales, but can be fragile, expensive to replace, and sensitive to environmental noise. A complementary instrument, comprising a low-cost conductivity probe, would prove valuable in a wide range of applications where resolving extremely small spatial scales is not needed. We propose using micro-USB cables as the actual conductivity sensors. By removing the metallic shield from a micro-B connector, 5 gold-plated microelectrodes are exposed and available for 4-wire measurements. These have a cell constant ~550m-1, an intrinsic thermal noise of at most 30pA/Hz1/2, as well as sub-millisecond time response, making them highly suitable for many stratified flow measurements. In addition, we present the design of a custom electronic board (Arduino-based and Matlab-controlled) for simultaneous acquisition from 4 sensors, with resolution (in conductivity, and resulting density) exceeding the performance of typical existing probes. We illustrate the use of our conductivity-measuring system through stratified flow experiments, and describe plans to release simple instructions to construct our complete system for around 200.
ENDERS NAILING A NOVEL TECHNIQUE
Mani Kumar
2015-10-01
Full Text Available 30 paediatric cases of tibial and femoral fractures between ages of 2 to 12 years have been treated by enders nailing during the period between M ay 2012 and A pril 2014 at our institute of Resident Dept . of Orthopaedics Rangaraya Medical College, Kakinada. The cases were stratified and meticulously studied and the results were analyzed both anato mically and functionally. The results were methodically compared with previous studies. The technique of enders nailing is having an easy learning curve and promising results are being attained with respect to conservative mode of treatment avoiding fractu re disease.
Experimental techniques; Techniques experimentales
Roussel-Chomaz, P. [GANIL CNRS/IN2P3, CEA/DSM, 14 - Caen (France)
2007-07-01
This lecture presents the experimental techniques, developed in the last 10 or 15 years, in order to perform a new class of experiments with exotic nuclei, where the reactions induced by these nuclei allow to get information on their structure. A brief review of the secondary beams production methods will be given, with some examples of facilities in operation or under project. The important developments performed recently on cryogenic targets will be presented. The different detection systems will be reviewed, both the beam detectors before the targets, and the many kind of detectors necessary to detect all outgoing particles after the reaction: magnetic spectrometer for the heavy fragment, detection systems for the target recoil nucleus, {gamma} detectors. Finally, several typical examples of experiments will be detailed, in order to illustrate the use of each detector either alone, or in coincidence with others. (author)
Fernando Sergio Leitão Filho
2009-12-01
Full Text Available OBJETIVO: Divulgar os dados de um estudo transversal randomizado, realizado em 2001, pelo Centro Brasileiro de Informações sobre Drogas Psicotrópicas. MÉTODOS: A população pesquisada neste levantamento incluiu indivíduos com 12-65 anos de idade, residentes nos 107 maiores municípios do Brasil (com mais de 200 mil habitantes, o que representou 27,7% da população brasileira na época, estimada em 169.799.170 habitantes. Foram realizadas no total 8.589 entrevistas. Utilizou-se o questionário Substance Abuse and Mental Health Services Administration, que foi traduzido e adaptado para o uso no Brasil. RESULTADOS: Do total, 41,1% dos entrevistados disseram já ter utilizado produtos derivados de tabaco alguma vez na vida. A prevalência de uso diário de tabaco foi de 17,4% da amostra (20,3% entre os homens e 14,8% entre as mulheres. Observou-se que 9% da população (10,1% entre os homens e 7,9% entre as mulheres são dependentes da nicotina, segundo os critérios do National Household Surveys on Drug Abuse. CONCLUSÕES: A prevalência do uso diário de tabaco, nos maiores municípios brasileiros, é significativamente menor na presente década do que a prevalência nacional ao final do século passado.OBJECTIVE: To provide access to the results of a randomized cross-sectional study conducted by the Brazilian Center for Information on Psychotropic Drugs in 2001. METHODS: This survey involved a random sample of individuals ranging from 12 to 65 years of age and residing in the 107 largest cities (over 200,000 inhabitants in Brazil, which represented 27.7% of the Brazilian population, estimated to be 169,799,170 inhabitants at the time. A total of 8,589 interviews were conducted. The Substance Abuse and Mental Health Services Administration questionnaire, translated and adapted for use in Brazil, was used in the interviews. RESULTS: Of the sample as a whole, 41.1% of the interviewees reported having experimented with tobacco products. The
Implications of Air Ingress Induced by Density-Difference Driven Stratified Flow
Chang Oh; Eung Soo Kim; Richard Schultz; David Petti; C. P. Liou
2008-06-01
One of the design basis accidents for the Next Generation Nuclear Plant (NGNP), a high temperature gas-cooled reactor, is air ingress subsequent to a pipe break. Following a postulated double-ended guillotine break in the hot duct, and the subsequent depressurization to nearly reactor cavity pressure levels, air present in the reactor cavity will enter the reactor vessel via density-gradient-driven-stratified flow. Because of the significantly higher molecular weight and lower initial temperature of the reactor cavity air-helium mixture, in contrast to the helium in the reactor vessel, the air-helium mixture in the cavity always has a larger density than the helium discharging from the reactor vessel through the break into the reactor cavity. In the later stages of the helium blowdown, the momentum of the helium flow decreases sufficiently for the heavier cavity air-helium mixture to intrude into the reactor vessel lower plenum through the lower portion of the break. Once it has entered, the heavier gas will pool at the bottom of the lower plenum. From there it will move upwards into the core via diffusion and density-gradient effects that stem from heating the air-helium mixture and from the pressure differences between the reactor cavity and the reactor vessel. This scenario (considering density-gradient-driven stratified flow) is considerably different from the heretofore commonly used scenario that attributes movement of air into the reactor vessel and from thence to the core region via diffusion. When density-gradient-driven stratified flow is considered as a contributing phenomena for air ingress into the reactor vessel, the following factors contribute to a much earlier natural circulation-phase in the reactor vessel: (a) density-gradient-driven stratified flow is a much more rapid mechanism (at least one order of magnitude) for moving air into the reactor vessel lower plenum than diffusion, and consequently, (b) the diffusion dominated phase begins with a
K. Lee
2002-01-01
Full Text Available This paper reports the application to vegetation canopies of a coherent model for the propagation of electromagnetic radiation through a stratified medium. The resulting multi-layer vegetation model is plausibly realistic in that it recognises the dielectric permittivity of the vegetation matter, the mixing of the dielectric permittivities for vegetation and air within the canopy and, in simplified terms, the overall vertical distribution of dielectric permittivity and temperature through the canopy. Any sharp changes in the dielectric profile of the canopy resulted in interference effects manifested as oscillations in the microwave brightness temperature as a function of canopy height or look angle. However, when Gaussian broadening of the top and bottom of the canopy (reflecting the natural variability between plants was included within the model, these oscillations were eliminated. The model parameters required to specify the dielectric profile within the canopy, particularly the parameters that quantify the dielectric mixing between vegetation and air in the canopy, are not usually available in typical field experiments. Thus, the feasibility of specifying these parameters using an advanced single-criterion, multiple-parameter optimisation technique was investigated by automatically minimizing the difference between the modelled and measured brightness temperatures. The results imply that the mixing parameters can be so determined but only if other parameters that specify vegetation dry matter and water content are measured independently. The new model was then applied to investigate the sensitivity of microwave emission to specific vegetation parameters. Keywords: passive microwave, soil moisture, vegetation, SMOS, retrieval
Moriyoshi, Y.; Morikawa, H. [Chiba University, Chiba (Japan); Kamimoto, T. [Tokyo Institute of Technology, Tokyo (Japan)
1997-10-01
Since the local inhomogeneity of mixture concentration inside the cylinder affects the combustion characteristics, a basic research on combustion phenomenon in stratified charge conditions is required. The authors have made experiments with a constant-volume chamber, which can simulate an idealized stratified charge field by using a removable partition, to obtain the combustion characteristics. Also, numerical calculations are made using some combustion models. As a result, the important feature that the combustion speed is faster in stratified condition than in homogeneous condition can be predicted by the two-step reaction model. 4 refs., 8 figs.
Lakghomi, B; Lawryshyn, Y; Hofmann, R
2015-01-01
An analytical model and a computational fluid dynamic model of particle removal in dissolved air flotation were developed that included the effects of stratified flow and bubble-particle clustering. The models were applied to study the effect of operating conditions and formation of stratified flow on particle removal. Both modeling approaches demonstrated that the presence of stratified flow enhanced particle removal in the tank. A higher air fraction was shown to be needed at higher loading rates to achieve the same removal efficiency. The model predictions showed that an optimum bubble size was present that increased with an increase in particle size.
Biomimetic stratified scaffold design for ligament-to-bone interface tissue engineering.
Lu, Helen H; Spalazzi, Jeffrey P
2009-07-01
The emphasis in the field of orthopaedic tissue engineering is on imparting biomimetic functionality to tissue engineered bone or soft tissue grafts and enabling their translation to the clinic. A significant challenge in achieving extended graft functionality is engineering the biological fixation of these grafts with each other as well as with the host environment. Biological fixation will require re-establishment of the structure-function relationship inherent at the native soft tissue-to-bone interface on these tissue engineered grafts. To this end, strategic biomimicry must be incorporated into advanced scaffold design. To facilitate integration between distinct tissue types (e.g., bone with soft tissues such as cartilage, ligament, or tendon), a stratified or multi-phasic scaffold with distinct yet continuous tissue regions is required to pre-engineer the interface between bone and soft tissues. Using the ACL-to-bone interface as a model system, this review outlines the strategies for stratified scaffold design for interface tissue engineering, focusing on identifying the relevant design parameters derived from an understanding of the structure-function relationship inherent at the soft-to-hard tissue interface. The design approach centers on first addressing the challenge of soft tissue-to-bone integration ex vivo, and then subsequently focusing on the relatively less difficult task of bone-to-bone integration in vivo. In addition, we will review stratified scaffold design aimed at exercising spatial control over heterotypic cellular interactions, which are critical for facilitating the formation and maintenance of distinct yet continuous multi-tissue regions. Finally, potential challenges and future directions in this emerging area of advanced scaffold design will be discussed.
Rapid shelf-wide cooling response of a stratified coastal ocean to hurricanes
Seroka, Greg; Miles, Travis; Xu, Yi; Kohut, Josh; Schofield, Oscar; Glenn, Scott
2017-06-01
Large uncertainty in the predicted intensity of tropical cyclones (TCs) persists compared to the steadily improving skill in the predicted TC tracks. This intensity uncertainty has its most significant implications in the coastal zone, where TC impacts to populated shorelines are greatest. Recent studies have demonstrated that rapid ahead-of-eye-center cooling of a stratified coastal ocean can have a significant impact on hurricane intensity forecasts. Using observation-validated, high-resolution ocean modeling, the stratified coastal ocean cooling processes observed in two U.S. Mid-Atlantic hurricanes were investigated: Hurricane Irene (2011)—with an inshore Mid-Atlantic Bight (MAB) track during the late summer stratified coastal ocean season—and Tropical Storm Barry (2007)—with an offshore track during early summer. For both storms, the critical ahead-of-eye-center depth-averaged force balance across the entire MAB shelf included an onshore wind stress balanced by an offshore pressure gradient. This resulted in onshore surface currents opposing offshore bottom currents that enhanced surface to bottom current shear and turbulent mixing across the thermocline, resulting in the rapid cooling of the surface layer ahead-of-eye-center. Because the same baroclinic and mixing processes occurred for two storms on opposite ends of the track and seasonal stratification envelope, the response appears robust. It will be critical to forecast these processes and their implications for a wide range of future storms using realistic 3-D coupled atmosphere-ocean models to lower the uncertainty in predictions of TC intensities and impacts and enable coastal populations to better respond to increasing rapid intensification threats in an era of rising sea levels.
Evolution and breaking of a propagating internal wave in stratified ocean
LI Bingrui; FAN Haimei; TIAN Jiwei; SUN Bo; ZHANG Zhanhai
2008-01-01
The evolution and breaking of a propagating internal wave are directly numerically simulated using a pseudo-spectral method.The mechanism of PSI (parametric subharmonic instability) involved in the evolution is testified clearly.It dominates gradually in nonlinear resonant interactions.As a consequence,the energy cascades to a second plant wave packet which has lower frequencies and higher wavenumbers than that of the primary wave.With the growth of this wave packet,wave breaking occurs and causes strongly nonlinear regime,I.e.stratified turbulence.The strong mixing and intermittent of the turbulence can be learned from the evolution of the total energy and kurtosis of vortieity vs.time.Some statistic properties of the stratified turbulence are also ana- lyzed,including the spectra of KE (kinetic energy) and PE (potential energy).The results show that the PE spectra display a wavenumber range scaling as 0.2 N4k-3r(N is the Brunt-Vaisala frequency,ky is the vertical wavenumber),which is called buoyancy sub-range.However,the KE spectra cannot satisfy the negative cubic law of vertical wavenumber,which have a much larger downtrend than that of the PE spectra,for the potential energy is transferred more efficiently toward small scales than the ki-netic energy.The Cox number of diapycnal diffusivity is also calculated,and it shows a good consistency with the observations and deductions in the ocean interior,during the stage of the stratified turbulence maintaining a fairly active level.
Rapid shelf‐wide cooling response of a stratified coastal ocean to hurricanes
Miles, Travis; Xu, Yi; Kohut, Josh; Schofield, Oscar; Glenn, Scott
2017-01-01
Abstract Large uncertainty in the predicted intensity of tropical cyclones (TCs) persists compared to the steadily improving skill in the predicted TC tracks. This intensity uncertainty has its most significant implications in the coastal zone, where TC impacts to populated shorelines are greatest. Recent studies have demonstrated that rapid ahead‐of‐eye‐center cooling of a stratified coastal ocean can have a significant impact on hurricane intensity forecasts. Using observation‐validated, high‐resolution ocean modeling, the stratified coastal ocean cooling processes observed in two U.S. Mid‐Atlantic hurricanes were investigated: Hurricane Irene (2011)—with an inshore Mid‐Atlantic Bight (MAB) track during the late summer stratified coastal ocean season—and Tropical Storm Barry (2007)—with an offshore track during early summer. For both storms, the critical ahead‐of‐eye‐center depth‐averaged force balance across the entire MAB shelf included an onshore wind stress balanced by an offshore pressure gradient. This resulted in onshore surface currents opposing offshore bottom currents that enhanced surface to bottom current shear and turbulent mixing across the thermocline, resulting in the rapid cooling of the surface layer ahead‐of‐eye‐center. Because the same baroclinic and mixing processes occurred for two storms on opposite ends of the track and seasonal stratification envelope, the response appears robust. It will be critical to forecast these processes and their implications for a wide range of future storms using realistic 3‐D coupled atmosphere‐ocean models to lower the uncertainty in predictions of TC intensities and impacts and enable coastal populations to better respond to increasing rapid intensification threats in an era of rising sea levels. PMID:28944132
Rapid shelf-wide cooling response of a stratified coastal ocean to hurricanes.
Seroka, Greg; Miles, Travis; Xu, Yi; Kohut, Josh; Schofield, Oscar; Glenn, Scott
2017-06-01
Large uncertainty in the predicted intensity of tropical cyclones (TCs) persists compared to the steadily improving skill in the predicted TC tracks. This intensity uncertainty has its most significant implications in the coastal zone, where TC impacts to populated shorelines are greatest. Recent studies have demonstrated that rapid ahead-of-eye-center cooling of a stratified coastal ocean can have a significant impact on hurricane intensity forecasts. Using observation-validated, high-resolution ocean modeling, the stratified coastal ocean cooling processes observed in two U.S. Mid-Atlantic hurricanes were investigated: Hurricane Irene (2011)-with an inshore Mid-Atlantic Bight (MAB) track during the late summer stratified coastal ocean season-and Tropical Storm Barry (2007)-with an offshore track during early summer. For both storms, the critical ahead-of-eye-center depth-averaged force balance across the entire MAB shelf included an onshore wind stress balanced by an offshore pressure gradient. This resulted in onshore surface currents opposing offshore bottom currents that enhanced surface to bottom current shear and turbulent mixing across the thermocline, resulting in the rapid cooling of the surface layer ahead-of-eye-center. Because the same baroclinic and mixing processes occurred for two storms on opposite ends of the track and seasonal stratification envelope, the response appears robust. It will be critical to forecast these processes and their implications for a wide range of future storms using realistic 3-D coupled atmosphere-ocean models to lower the uncertainty in predictions of TC intensities and impacts and enable coastal populations to better respond to increasing rapid intensification threats in an era of rising sea levels.
Claudia Chavez-Munoz
Full Text Available Skin regeneration is an important area of research in the field of tissue-engineering, especially for cases involving loss of massive areas of skin, where current treatments are not capable of inducing permanent satisfying replacements. Human adipose-derived stem cells (ASC have been shown to differentiate in-vitro into both mesenchymal lineages and non-mesenchymal lineages, confirming their transdifferentiation ability. This versatile differentiation potential, coupled with their ease of harvest, places ASC at the advancing front of stem cell-based therapies. In this study, we hypothesized that ASC also have the capacity to transdifferentiate into keratinocyte-like cells and furthermore are able to engineer a stratified epidermis. ASC were successfully isolated from lipoaspirates and cell sorted (FACS. After sorting, ASC were either co-cultured with human keratinocytes or with keratinocyte conditioned media. After a 14-day incubation period, ASC developed a polygonal cobblestone shape characteristic of human keratinocytes. Western blot and q-PCR analysis showed the presence of specific keratinocyte markers including cytokeratin-5, involucrin, filaggrin and stratifin in these keratinocyte-like cells (KLC; these markers were absent in ASC. To further evaluate if KLC were capable of stratification akin to human keratinocytes, ASC were seeded on top of human decellularized dermis and cultured in the presence or absence of EGF and high Ca(2+ concentrations. Histological analysis demonstrated a stratified structure similar to that observed in normal skin when cultured in the presence of EGF and high Ca(2+. Furthermore, immunohistochemical analysis revealed the presence of keratinocyte markers such as involucrin, cytokeratin-5 and cytokeratin-10. In conclusion this study demonstrates for the first time that ASC have the capacity to transdifferentiate into KLC and engineer a stratified epidermis. This study suggests that adipose tissue is potentially a
Burch, Tanya C; Morris, Margaret A; Campbell-Thompson, Martha; Pugliese, Alberto; Nadler, Jerry L; Nyalwidhe, Julius O
2015-01-01
Type 1 diabetes (T1D) and type 2 diabetes (T2D) are associated with functional beta cell loss due to ongoing inflammation. Despite shared similarities, T1D is an autoimmune disease with evidence of autoantibody production, as well as a role for exocrine pancreas involvement. Our hypothesis is that differential protein expression occurs in disease stratified pancreas tissues and regulated proteins from endocrine and exocrine tissues are potential markers of disease and potential therapeutic targets. The study objective was to identify novel proteins that distinguish the pancreas from donors with T1D from the pancreas from patients with T2D, or autoantibody positive non-diabetic donors. Detailed quantitative comprehensive proteomic analysis was applied to snap frozen human pancreatic tissue lysates from organ donors without diabetes, with T1D-associated autoantibodies in the absence of diabetes, with T1D, or with T2D. These disease-stratified human pancreas tissues contain exocrine and endocrine tissues (with dysfunctional islets) in the same microenvironment. The expression profiles of several of the proteins were further verified by western blot. We identified protein panels that are significantly and uniquely upregulated in the three disease-stratified pancreas tissues compared to non-disease control tissues. These proteins are involved in inflammation, metabolic regulation, and autoimmunity, all of which are pathways linked to, and likely involved in, T1 and T2 diabetes pathogenesis. Several new proteins were differentially upregulated in prediabetic, T1D, and T2D pancreas. The results identify proteins that could serve as novel prognostic, diagnostic, and therapeutic tools to preserve functional islet mass in Type 1 Diabetes.
Teaching Techniques, Types of Personality, and English Listening Skill
Ni Made Ratminingsih
2013-01-01
Full Text Available Abstract: Teaching Techniques, Types of Personality, and English Listening Skill. This study investigated the effect of teaching techniques and types of personality on English listening skill. This experimental study involved 88 students under investigation, which were determined randomly through multi-stage random sampling technique. The results of the research indicate that there is an interaction effect between the teaching techniques and types of personality on the English listening skill; there is no significant difference in the listening skill between the group of students who learn using the game technique and those who learn using the song technique; the listening skill of students having extrovert personality is better than those having introvert personality; the listening skill of students having extrovert personality who learn using the game technique is lower than those who learn using the song technique; and the listening skill of students having introvert personality who learn using the game technique is higher than those who learn using the song technique. Abstrak: Teknik Pembelajaran, Tipe Kepribadian, dan Keterampilan Mendengarkan Bahasa Inggris. Penelitian ini bertujuan untuk mengetahui pengaruh teknik pembelajaran dan tipe kepribadian terhadap keterampilan mendengarkan bahasa Inggris. Penelitian ini melibatkan 88 orang siswa, yang ditentukan secara acak melalui multi stage random sampling technique. Hasil penelitian menunjukkan bahwa terdapat pengaruh interaksi antara teknik pembelajaran dan tipe kepribadian terhadap keterampilan mendengarkan bahasa Inggris; tidak terdapat perbedaan yang signifikan pada keterampilan mendengarkan antara siswa yang belajar dengan teknik pembelajaran permainan dan lagu; keterampilan mendengarkan siswa yang berkepribadian ekstroversi lebih baik daripada yang berkepribadian introversi; keterampilan mendengarkan siswa yang berkepribadian ekstroversi, yang belajar dengan teknik pembelajaran
林桂潮; 邹湘军; 罗陆锋; 莫宇达
2015-01-01
果园道路检测的目的是为农业采摘机器人鲁棒实时地规划出合适的行走路径，因果园环境的复杂性，例如光照变化、杂草和落叶遮挡等因素的影响造成视觉检测算法鲁棒性差，为此提出融合边缘提取和改进随机样本一致性的弯曲果园道路检测方法。首先，根据果园道路的颜色分布特征和几何形状特征，使用有限差分算子提取图像边缘，再使用灰度值对比度约束和霍夫直线检测去除噪声，实现道路边缘点提取。然后，提出多项式函数描述直线和弯曲道路，使用改进的随机样本一致性算法和线性最小二乘法拟合道路边缘点，以估计多项式函数的参数，实现果园道路检测。在华南农业大学果园采集240张道路图像作为试验对象。试验表明：在光照变化、阴影和遮挡背景的影响下，该方法能有效地提取果园道路边缘点，并能正确地拟合道路以实现道路检测，平均正确检测率为89.1%，平均检测时间为0.2639 s，能够满足视觉导航系统的要求。该研究为农业采摘机器人的视觉导航的鲁棒性和实时性提供指导。%Agricultural mobile robot and sightseeing agriculture is a direction of agricultural development in recent years. Agricultural mobile robot, a kind of efficient transportation equipment and means of transport, was of great significance in the orchard sightseeing agriculture. Road detection is the key technology and an important prerequisite for mobile agricultural robot to achieve autonomous navigation. In practical applications, the complexity of the orchard environment,e.g., the impact of illumination changes, shadows and occlusion, has resulted in poor robustness of vision detection algorithm. Therefore, the orchard road detection algorithm is required to be improved. So a method fusing edge detection and improved random sample consensus for winding orchard path detection was proposed. The
Tsang, L.; Brown, R.; Kong, J. A.; Simmons, G.
1974-01-01
Two numerical methods are used to evaluate the integrals that express the em fields due to dipole antennas radiating in the presence of a stratified medium. The first method is a direct integration by means of Simpson's rule. The second method is indirect and approximates the kernel of the integral by means of the fast Fourier transform. In contrast to previous analytical methods that applied only to two-layer cases the numerical methods can be used for any arbitrary number of layers with general properties.
Stratlets: Low Reynolds Number Point-Force Solutions in a Stratified Fluid
Ardekani, A. M.; Stocker, R.
2010-08-01
We present fundamental solutions of low Reynolds number flows in a stratified fluid, including the case of a point force (Stokeslet) and a doublet. Stratification dramatically alters the flow by creating toroidal eddies, and velocity decays much faster than in a homogeneous fluid. The fundamental length scale is set by the competition of buoyancy, diffusion and viscosity, and is O(100μm-1mm) in aquatic environments. Stratification can therefore affect the swimming of small organisms and the sinking of marine snow particles, and diminish the effectiveness of mechanosensing in the ocean.
Interfacial shear stress in stratified flow in a horizontal rectangular duct
Lorencez, C.; Kawaji, M. [Univ. of Toronto (Canada); Murao, Y. [Tokushima Univ. (Japan)] [and others
1995-09-01
Interfacial shear stress has been experimentally examined for both cocurrent and countercurrent stratified wavy flows in a horizontal interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress from the measurements were examined and the results have been compared with existing correlations. Some differences were found in the estimated interfacial shear stress values at high gas flow rates which could be attributed to the assumptions and procedures involved in each method. The interfacial waves and secondary motions were also found to have significant effects on the accuracy of Reynolds stress and turbulence kinetic energy extrapolation methods.
Müller-Berghaus, J; Volkers, P; Scherer, J; Cichutek, K
2013-11-01
The term individualised medicine, also called personalised medicine, is commonly used as an equivalent to stratified medicine. However, this is erroneous since quite often it is forgotten that especially biological medicinal products have other aspects of individualization that go beyond mere stratification. The principles of stratified medicine have been applied for biological medicinal products for many years. A historical example is diphtheria antitoxin made from horse serum, while current examples are transfusion of red blood cells and the administration of factor VIII in haemophilia A. The stratifying aspects of these medicinal products are given by the following considerations: diphtheria antitoxin is only administered after a diagnosis of diphtheria and not in other forms of tonsillitis, red blood cells should only be transfused once blood group compatibility as been established and factor VIII replacement is only administered in haemophilia A as opposed to other acquired or hereditary disease of the coagulation system. The peculiarities of biological medicinal products, in particular the inherent variability of the drug, are especially important for autologous cellular medicinal products. In addition to the expected variability of the biological source material there is interindividual variability of patients as cell donors, which make definition of specifications and determination of criteria for pharmaceutical quality and potency tests difficult. Therapy with modified autologous cells, a common and important application of advanced therapy medicinal products, is exemplary for the special considerations that must be made when evaluating pharmaceutical quality, mode of action and toxicological properties of the biological medicine. The clinical investigation of advanced therapy medicinal products with the intent of demonstrating safety and efficacy is particularly challenging because of the complexity of therapy, which often involves invasive interventions
van Oers, Alexander M.; Maas, Leo R. M.; Bokhove, Onno
2017-02-01
The linear equations governing internal gravity waves in a stratified ideal fluid possess a Hamiltonian structure. A discontinuous Galerkin finite element method has been developed in which this Hamiltonian structure is discretized, resulting in conservation of discrete analogs of phase space and energy. This required (i) the discretization of the Hamiltonian structure using alternating flux functions and symplectic time integration, (ii) the discretization of a divergence-free velocity field using Dirac's theory of constraints and (iii) the handling of large-scale computational demands due to the 3-dimensional nature of internal gravity waves and, in confined, symmetry-breaking fluid domains, possibly its narrow zones of attraction.
A stratified layer of light elements at the top of the outer core
McDonough, W. F.; Buffett, B. A.; Cormier, V. F.; Cottaar, S.; Day, E. A.; Dou, S.; French, S. W.; Irving, J. C.; Kavner, A.; Panning, M. P.; Parai, R.; Rose, I.
2010-12-01
Earth’s core is thought to have formed from sinking metal diapirs that segregated at mid-mantle conditions. Consequently, the core and mantle may not be in chemical equilibrium. Recent experiments suggest that at the pressures and temperatures of the core, lower mantle oxides and silicates may have an increased solubility in iron. Geodynamic calculations predict that if a core/mantle chemical reaction delivers a flux of oxygen to the core, a low-density, stratified layer, estimated to be 60-70 km thick, may form at the top of the core. Seismological, geochemical, and mineral physics data pertinent to the conditions at the top of the core combined with geodynamic models provide critical tests of the stratified outer core hypothesis. A linear combination of normal mode observations with a composite sensitivity restricted to VP in the outermost outer core is inverted. Travel time measurements of SmKS and PmKP are obtained from seismograms stacked over dense arrays. Forward modeling tests the sensitivity of these different data to predicted seismic models, and aids in identifying features that might mask the signal, e.g., topography on the core-mantle boundary, ultra-low velocity zones, and heterogeneities in the lowermost mantle. Chemical and isotopic ratios are used to consider the residual products of putative core-mantle exchange events, together with mass and charge balance, and allow to assess compositional constraints on both the core and mantle. Development of a stable, stratified O-enriched layer at the top of the outer core over Earth history may ultimately limit chemical communication between the mantle and the rest of the outer core. Implications for movement of siderophile trace elements (e.g. W, P and Pb) across the CMB over time are evaluated. Mineral physics estimates of high pressure and temperature equations of state of relevant mantle and core materials provide data to calculate density and sound velocities at outer core conditions to predict
Experiments on the transition from stratified to slug flow in multiphase pipe flow
Kristiansen, Olav
2004-12-01
Severe slugging is reported from some field operations, where an increase in the production rate leads to a transition from steady stratified flow to slug flow in the pipeline. The slugs can be longer than anticipated for hydrodynamic slugging and the flow transients can then be a limitation for the production capacity. The objective was to perform a study on the flow pattern transition from stratified to slug flow. A particular point of interest was the possible occurrence of metastable flow and large initial slugs at elevated pressures. New data have been acquired in an experimental investigation of the transition from stratified to slug flow in horizontal and near-horizontal pipes at atmospheric and pressurised conditions. The experiments were performed with two-phase gas liquid and three-phase gas-liquid-liquid flows. Two flow facilities were used the NTNU Multiphase Flow Laboratory (short flow loop) and the SINTEF Multi-phase Flow Laboratory (long flow loop). Hold-up and pressure drop were measured, and flow patterns were determined visually and by evaluation of hold-up time traces. The following parameters were varied: 1) Inlet flow condition by variation of inlet pipe inclination. 2) System pressure (gas density). 3) Test section inclination (horizontal and near-horizontal). 4) Water cut. 5) Gas and liquid flow rates. 6) Pipe length. Slug flow or stratified flow was introduced upstream to promote either early or delayed transition to slug flow in the test section. A time series analysis was performed on the hold-up time traces, and average and distribution slug characteristics are reported, e.g. slug frequency, bubble propagation velocity, slug fraction, slug length, and growth rate. The results have been compared with steady state model predictions. The work consists of the following parts. 1) An initial study was performed at atmospheric air-water conditions in a short pipe. 2) Experiments at atmospheric and elevated pressures were performed in the medium
Optics of an opal modeled with a stratified effective index and the effect of the interface
Maurin, Isabelle; Laliotis, Athanasios; Bloch, Daniel
2015-01-01
Reflection and transmission for an artificial opal are described through a model of stratified medium based upon a one-dimensional variation of an effective index. The model is notably applicable to a Langmuir-Blodgett type disordered opal. Light scattering is accounted for by a phenomenological absorption. The interface region between the opal and the substrate -or the vacuum- induces a periodicity break in the photonic crystal arrangement, which exhibits a prominent influence on the reflection, notably away from the Bragg reflection peak. Experimental results are compared to our model. The model is extendable to inverse opals, stacked cylinders, or irradiation by evanescent waves
Hirota, Makoto; Morrison, Philip J.
2016-05-01
Linear stability of inviscid, parallel, and stably stratified shear flow is studied under the assumption of smooth strictly monotonic profiles of shear flow and density, so that the local Richardson number is positive everywhere. The marginally unstable modes are systematically found by solving a one-parameter family of regular Sturm-Liouville problems, which can determine the stability boundaries more efficiently than solving the Taylor-Goldstein equation directly. By arguing for the non-existence of a marginally unstable mode, we derive new sufficient conditions for stability, which generalize the Rayleigh-Fjørtoft criterion for unstratified shear flows.
Asymptotic behavior of a stratified perturbation in a three dimensional expanding Universe
Fanelli, D
2002-01-01
The non-linear evolution of a stratified perturbation in a three dimensional expanding Universe is considered. A general Lagrangian scheme (Q model) is introduced and numerical investigations are performed. The asymptotic contraction of the core of the agglomeration is studied. A power-law scaling is detected and an heuristic interpretation of the numerical findings is provided. An asymptotic equation for the multi-stream velocity flow is derived and it is shown to agree quantitatively with the dynamics of the Q model. The relation to the adhesion model is discussed.
Garaud, P; Verhoeven, J
2016-01-01
Shear-induced turbulence could play a significant role in mixing momentum and chemical species in stellar radiation zones, as discussed by Zahn (1974). In this paper we analyze the results of direct numerical simulations of stratified plane Couette flows, in the limit of rapid thermal diffusion, to measure the turbulent diffusivity and turbulent viscosity as a function of the local shear and the local stratification. We find that the stability criterion proposed by Zahn (1974), namely that the product of the gradient Richardson number and the Prandtl number must be smaller than a critical values $(J\\Pr)_c$ for instability, adequately accounts for the transition to turbulence in the flow, with $(J\\Pr)_c \\simeq 0.007$. This result recovers and confirms the prior findings of Prat et al. (2016). Zahn's model for the turbulent diffusivity and viscosity (Zahn 1992), namely that the mixing coefficient should be proportional to the ratio of the thermal diffusivity to the gradient Richardson number, does not satisfact...
Billington, Jennifer
2012-08-07
AbstractBackgroundThe STRATIFY score is a clinical prediction rule (CPR) derived to assist clinicians to identify patients at risk of falling. The purpose of this systematic review and meta-analysis is to determine the overall diagnostic accuracy of the STRATIFY rule across a variety of clinical settings.MethodsA literature search was performed to identify all studies that validated the STRATIFY rule. The methodological quality of the studies was assessed using the Quality Assessment of Diagnostic Accuracy Studies tool. A STRATIFY score of ≥2 points was used to identify individuals at higher risk of falling. All included studies were combined using a bivariate random effects model to generate pooled sensitivity and specificity of STRATIFY at ≥2 points. Heterogeneity was assessed using the variance of logit transformed sensitivity and specificity.ResultsSeventeen studies were included in our meta-analysis, incorporating 11,378 patients. At a score ≥2 points, the STRATIFY rule is more useful at ruling out falls in those classified as low risk, with a greater pooled sensitivity estimate (0.67, 95% CI 0.52–0.80) than specificity (0.57, 95% CI 0.45 – 0.69). The sensitivity analysis which examined the performance of the rule in different settings and subgroups also showed broadly comparable results, indicating that the STRATIFY rule performs in a similar manner across a variety of different ‘at risk’ patient groups in different clinical settings.ConclusionThis systematic review shows that the diagnostic accuracy of the STRATIFY rule is limited and should not be used in isolation for identifying individuals at high risk of falls in clinical practice.
Deepak Swami; P K Sharma; C S P Ojha
2014-12-01
In this paper, we have studied the behaviour of reactive solute transport through stratified porous medium under the influence of multi-process nonequilibrium transport model. Various experiments were carried out in the laboratory and the experimental breakthrough curves were observed at spatially placed sampling points for stratified porous medium. Batch sorption studies were also performed to estimate the sorption parameters of the material used in stratified aquifer system. The effects of distance dependent dispersion and tailing are visible in the experimental breakthrough curves. The presence of physical and chemical non-equilibrium are observed from the pattern of breakthrough curves. Multi-process non-equilibrium model represents the combined effect of physical and chemical non-ideality in the stratified aquifer system. The results show that the incorporation of distance dependent dispersivity in multi-process non-equilibrium model provides best fit of observed data through stratified porous media. Also, the exponential distance dependent dispersivity is more suitable for large distances and at small distances, linear or constant dispersivity function can be considered for simulating reactive solute in stratified porous medium.
Cross-cultural adaptation of the STRATIFY tool in detecting and predicting risk of falling.
Enríquez de Luna-Rodríguez, Margarita; Aranda-Gallardo, Marta; Canca-Sánchez, José Carlos; Vazquez-Blanco, M José; Moya-Suárez, Ana Belén; Morales-Asencio, José Miguel
To adapt to Spanish language the STRATIFY tool for clinical use in the Spanish-speaking World. A multicenter, 2 care settings cross-sectional study cultural adaptation study in acute care hospitals and nursing homes was performed in Andalusia during 2014. The adaptation process was divided into 4 stages: translation, back-translation, equivalence between the 2 back-translations and piloting of the Spanish version, thus obtaining the final version. The validity of appearance, content validity and the time required to complete the scale were taken into account. For analysis, the median, central tendency and dispersion of scores, the interquartile range, and the interquartile deviation for the possible variability in responses it was calculated. Content validity measured by content validity index reached a profit of 1. For the validity aspect the clarity and comprehensibility of the questions were taken into account. Of the 5 questions of the instrument, 2 had a small disagreement solved with the introduction of an explanatory phrase to achieve conceptual equivalence. Median both questions were equal or superior to 5. The average time for completion of the scale was less than 3 minutes. The process of adaptation to Spanish of STRATIFY has led to a semantic version and culturally equivalent to the original for easy filling and understanding for use in the Spanish-speaking world. Copyright © 2016 Elsevier España, S.L.U. All rights reserved.
Stratified familialism: the care regime in India through the lens of childcare.
Palriwala, Rajni; Neetha, N
2011-01-01
This article explores the political and social economy of care in India through a focus on childcare practices, from the viewpoint of the care giver — a perspective frequently ignored or touched on only generally in earlier discussions on development or social policy. It is argued that the care regime is an ad hoc summation of informal, stratified practices. It is shaped by the institutional context, in particular the economic and social inequalities of work and livelihoods, as well as trends and absences in state economic and social policy. Central to the dynamics of care practices in India is the ideology of gendered familialism in public discourse and policy, which reiterates care as a familial and female responsibility and works to devalue and diminish the dimensions of care. By delineating the range of institutions through which everyday childcare practices are organized, this contribution draws out the differentiations and actualities of stratified familialism and care. At one end of the spectrum are those who have the possibility to retain familial carers at home and supplement them with paid and other institutional carers; at the other are those who are neither able to retain family members at home nor fill the care gap through formal institutions.
Chowdhury, Susmita; Henneman, Lidewij; Dent, Tom; Hall, Alison; Burton, Alice; Pharoah, Paul; Pashayan, Nora; Burton, Hilary
2015-06-09
There is growing evidence that inclusion of genetic information about known common susceptibility variants may enable population risk-stratification and personalized prevention for common diseases including cancer. This would require the inclusion of genetic testing as an integral part of individual risk assessment of an asymptomatic individual. Front line health professionals would be expected to interact with and assist asymptomatic individuals through the risk stratification process. In that case, additional knowledge and skills may be needed. Current guidelines and frameworks for genetic competencies of non-specialist health professionals place an emphasis on rare inherited genetic diseases. For common diseases, health professionals do use risk assessment tools but such tools currently do not assess genetic susceptibility of individuals. In this article, we compare the skills and knowledge needed by non-genetic health professionals, if risk-stratified prevention is implemented, with existing competence recommendations from the UK, USA and Europe, in order to assess the gaps in current competences. We found that health professionals would benefit from understanding the contribution of common genetic variations in disease risk, the rationale for a risk-stratified prevention pathway, and the implications of using genomic information in risk-assessment and risk management of asymptomatic individuals for common disease prevention.
Susmita Chowdhury
2015-06-01
Full Text Available There is growing evidence that inclusion of genetic information about known common susceptibility variants may enable population risk-stratification and personalized prevention for common diseases including cancer. This would require the inclusion of genetic testing as an integral part of individual risk assessment of an asymptomatic individual. Front line health professionals would be expected to interact with and assist asymptomatic individuals through the risk stratification process. In that case, additional knowledge and skills may be needed. Current guidelines and frameworks for genetic competencies of non-specialist health professionals place an emphasis on rare inherited genetic diseases. For common diseases, health professionals do use risk assessment tools but such tools currently do not assess genetic susceptibility of individuals. In this article, we compare the skills and knowledge needed by non-genetic health professionals, if risk-stratified prevention is implemented, with existing competence recommendations from the UK, USA and Europe, in order to assess the gaps in current competences. We found that health professionals would benefit from understanding the contribution of common genetic variations in disease risk, the rationale for a risk-stratified prevention pathway, and the implications of using genomic information in risk-assessment and risk management of asymptomatic individuals for common disease prevention.
Risk Factors for Emergency Department Short Time Readmission in Stratified Population
Ariadna Besga
2015-01-01
Full Text Available Background. Emergency department (ED readmissions are considered an indicator of healthcare quality that is particularly relevant in older adults. The primary objective of this study was to identify key factors for predicting patients returning to the ED within 30 days of being discharged. Methods. We analysed patients who attended our ED in June 2014, stratified into four groups based on the Kaiser pyramid. We collected data on more than 100 variables per case including demographic and clinical characteristics and drug treatments. We identified the variables with the highest discriminating power to predict ED readmission and constructed classifiers using machine learning methods to provide predictions. Results. Classifier performance distinguishing between patients who were and were not readmitted (within 30 days, in terms of average accuracy (AC. The variables with the greatest discriminating power were age, comorbidity, reasons for consultation, social factors, and drug treatments. Conclusions. It is possible to predict readmissions in stratified groups with high accuracy and to identify the most important factors influencing the event. Therefore, it will be possible to develop interventions to improve the quality of care provided to ED patients.
Hunt, Julian C. R.; Moustaoui, Mohamed; Mahalov, Alex
2015-09-01
High resolution three-dimensional simulations are presented of the interactions between turbulent shear flows moving with mean relative velocity ΔU below a stably stratified region with buoyancy frequency (N+). An artificial forcing in the simulation, with a similar effect as a small negative eddy viscosity, leads to a steady state flow which models thin interfaces. Characteristic eddies of the turbulence have length scale L. If the bulk Richardson number Rib=(LN+/ΔU)2 lies between lower and upper critical values denoted as Ri∗(temperature. Comparisons are made with shear turbulent interfaces with no stratification. When Rib>R~i, vertical propagating waves are generated, with shear stresses carrying significant momentum flux and progressively less as Rib increases. Simulations for a jet and a turbulent mixing layer show similar results. A perturbation analysis, using inhomogeneous Rapid Distortion Theory, models the transition zone between shear eddies below the interface and the fluctuations in the stratified region, consistent with the simulations. It demonstrates how the wave-momentum-flux has a maximum when Rib˜2 and then decreases as Rib increases. This coupling mechanism between eddies and waves, which is neglected in eddy viscosity models for shear layers, can drive flows in the stratosphere and the deeper ocean, with significant consequences for short- and long-term flow phenomena. The "detached layer" is a mechanism that contributes to the formation of stratus clouds and polluted layers above the atmospheric boundary layer.
A Sweeping based Kinematic Simulation for the Stably Stratified Surface Layer
Ghate, Aditya; Lele, Sanjiva
2014-11-01
A Kinematic Simulation (KS) for a statistically stationary and stably stratified surface layer is proposed. The Fourier coefficients are obtained by numerically solving the linearized NS equations with Boussinesq approximation in spectral space, under the assumption of ``rapid'' deformation (RDT) due to combined shear and stratification. The linearization of RDT, which is unrealistic for the surface layer, is rectified using Mann's (JFM, 1994) idea of wavenumber dependent eddy lifetime. The input parameters required by the KS are estimated using either Monin-Obukhov theory, or an appropriate Second Moment Closure. In order to overcome the frozen turbulence hypothesis made in the Mann model, we incorporate inter-scale ``sweeping'' of eddies following the ideas of Fung et al. (JFM, 1992), along with temporal decorrelation associated with the natural eddy time scale. The solenoidal velocity field generated by the KS allows inclusion of a wide range of scales with correct space-time correlations, making it ideal to investigate particle dispersion in a stably stratified environment, and can also serve as inflow for the study of Wind Farm-PBL interactions. The effect of varying Obukhov length will be discussed by analyzing the frozen Eulerian spectra and Lagrangian particle dispersion.
p21 suppresses inflammation and tumorigenesis on pRB-deficient stratified epithelia.
Saiz-Ladera, C; Lara, M F; Garín, M; Ruiz, S; Santos, M; Lorz, C; García-Escudero, R; Martínez-Fernández, M; Bravo, A; Fernández-Capetillo, O; Segrelles, C; Paramio, J M
2014-09-11
The retinoblastoma gene product (pRb) controls proliferation and differentiation processes in stratified epithelia. Importantly, and in contrast to other tissues, Rb deficiency does not lead to spontaneous skin tumor formation. As the cyclin-dependent kinase inhibitor p21 regulates proliferation and differentiation in the absence of pRb, we analyzed the consequences of deleting p21 in pRb-ablated stratified epithelia (hereafter pRb(ΔEpi);p21-/-). These mice display an enhancement of the phenotypic abnormalities observed in pRb(ΔEpi) animals, indicating that p21 partially compensates pRb absence. Remarkably, pRb(ΔEpi);p21-/- mice show an acute skin inflammatory phenotype and develop spontaneous epithelial tumors, particularly affecting tongue and oral tissues. Biochemical analyses and transcriptome studies reveal changes affecting multiple pathways, including DNA damage and p53-dependent signaling responses. Comparative metagenomic analyses, together with the histopathological profiles, indicate that these mice constitute a faithful model for human head and neck squamous cell carcinomas. Collectively, our findings demonstrate that p21, in conjunction with pRb, has a central role in regulating multiple epithelial processes and orchestrating specific tumor suppressor functions.
Phenomenology of two-dimensional stably stratified turbulence under large-scale forcing
Kumar, Abhishek; Sukhatmae, Jai
2016-01-01
In this paper we characterize the scaling of energy spectra, and the interscale transfer of energy and enstrophy, for strongly, moderately and weakly stably stratified two-dimensional (2D) turbulence under large-scale random forcing. In the strongly stratified case, a large-scale vertically sheared horizontal flow (VSHF) co-exists with small scale turbulence. The VSHF consists of internal gravity waves and the turbulent flow has a kinetic energy (KE) spectrum that follows an approximate $k^{-3}$ scaling with zero KE flux and a robust positive enstrophy flux. The spectrum of the turbulent potential energy (PE) also approximately follows a $k^{-3}$ power-law and its flux is directed to small scales. For moderate stratification, there is no VSHF and the KE of the turbulent flow exhibits Bolgiano-Obukhov scaling that transitions from a shallow $k^{-11/5}$ form at large scales, to a steeper approximate $k^{-3}$ scaling at small scales. The entire range of scales shows a strong forward enstrophy flux, and interesti...
Uchino, Yuichi; Woodward, Ashley M; Argüeso, Pablo
2016-12-01
Mucins are a group of highly glycosylated glycoproteins responsible for the protection of wet-surfaced epithelia. Recent data indicate that transmembrane mucins differ in their contribution to the protective function of the ocular surface, with MUC16 being the most effective barrier on the apical surface glycocalyx. Here, we investigated the role of the mucoprotective drug rebamipide in the regulation of transmembrane mucin biosynthesis using stratified cultures of human corneal and conjunctival epithelial cells. We find that the addition of rebamipide to corneal, but not conjunctival, epithelial cells increased MUC16 protein biosynthesis. Rebamipide did not affect the levels of MUC1, 4 and 20 compared to control. In these experiments, rebamipide had no effect on the expression levels of Notch intracellular domains, suggesting that the rebamipide-induced increase in MUC16 biosynthesis in differentiated corneal cultures is not regulated by Notch signaling. Overall these findings indicate that rebamipide induces the differential upregulation of MUC16 in stratified cultures of human corneal epithelial cells, which may have implications to the proper restoration of barrier function in ocular surface disease. Copyright © 2016 Elsevier Ltd. All rights reserved.
Newly recorded Karlodinium veneficum dinoflagellate blooms in stratified water of the East China Sea
Dai, Xinfeng; Lu, Douding; Guan, Weibing; Wang, Hongxia; He, Piaoxia; Xia, Ping; Yang, Huajie
2014-03-01
Karlodinium veneficum is a cosmopolitan species, but has been poorly recorded in the East China Sea (ECS) due to its small size and difficulty in identification. The bloom dynamics of this species is not well understood globally. In this study, we examined its morphological characteristics that suggest the K. veneficum is the co-occurring bloom causative species of large scale Prorocentrum donghaiense blooms in spring 2011. The epicone of K. veneficum recorded in the investigated area is conical or rounded, and the hypocone is hemispherically rounded. The ventral pore is located at the left side of the apical groove. Nucleus is positioned centrally within the hypocone. Four large irregular chloroplasts are equally distributed in the epicone and hypocone. The mean length of cultured cells was 13.6±1.2 μm (range 11.0-15.8 μm) and the mean width was 10.0±1.1 μm (range 8.0-12 μm) (n=50). Cell abundance of K. veneficum population was low, in the region 1000-1600 cells L-1, along a transect in the East China Sea on April 19, 2011, when the water column was not distinctly stratified. Cell densities reached 3×107 cells L-1 along the same transect on May 13 2011 when the bloom occurred in the 10 m layer surface and the water column was distinctly stratified. Cell abundances therefore appear closely related to water column stratification.
On the lifetime of a pancake anticyclone in a rotating stratified flow
Facchini, Giulio; Le Bars, Michael
2016-11-01
We present an experimental study of the time evolution of an isolated anticyclonic pancake vortex in a laboratory rotating stratified flow. Motivations come from the variety of compact anticyclones observed to form and persist for a strikingly long lifetime in geophysical and astrophysical settings combining rotation and stratification. We generate anticyclones by injecting a small amount of isodense fluid at the center of a rotating tank filled with salty water linearly stratified in density. Our two control parameters are the Coriolis parameter f and the Brunt-Väisälä frequency N. We observe that anticyclones always slowly decay by viscous diffusion, spreading mainly in the horizontal direction irrespective of the initial aspect ratio. This behavior is correctly explained by a linear analytical model in the limit of small Rossby and Ekman numbers, where density and velocity equations reduce to a single equation for the pressure. Direct numerical simulations further confirm the theoretical predictions. Notably, they show that the azimuthal shear stress generates secondary circulations, which advect the density anomaly: this mechanism is responsible for the slow time evolution, rather than the classical viscous dissipation of the azimuthal kinetic energy.
Charging of dust grains in a nonequilibrium plasma of a stratified glow discharge
Sukhinin, G. I.; Fedoseev, A. V.
2007-12-01
A theoretical model is presented that describes the charging of dust grains in the positive plasma column of a stratified glow dc discharge in argon. A one-dimensional self-consistent model is used to obtain axial profiles of the electric field, as well as the electron energy distribution function along the axis of the discharge tube. Radial profiles of the electric field are determined in the ambipolar diffusion approximation. It is assumed that, in the radial direction, the electron distribution function depends only on the total electron energy. Two-dimensional distributions of the discharge plasma parameters are calculated and used to determine the potential and charge of a test dust grain at a certain point within the discharge and the electrostatic forces acting on it. It is shown that the grain charge distribution depends strongly on the nonequilibrium electron distribution function and on the nonuniform distribution of the electric field in a stratified glow discharge. A discussion is presented on the suspension of dust grains, the separation of grains by size in the discharge striations, and a possible mechanism for the onset of vortex dust motion at the edge of a dust cloud.
Steady internal waves in an exponentially stratified two-layer fluid
Makarenko, Nikolay; Maltseva, Janna; Ivanova, Kseniya
2016-04-01
The problem on internal waves in a weakly stratified two-layered fluid is studied analytically. We suppose that the fluid possess exponential stratification in both the layers, and the fluid density has discontinuity jump at the interface. By that, we take into account the influence of weak continuous stratification outside of sharp pycnocline. The model equation of strongly nonlinear interfacial waves propagating along the pycnocline is considered. This equation extends approximate models [1-3] suggested for a two-layer fluid with one homogeneous layer. The derivation method uses asymptotic analysis of fully nonlinear Euler equations. The perturbation scheme involves the long wave procedure with a pair of the Boussinesq parameters. First of these parameters characterizes small density slope outside of pycnocline and the second one defines small density jump at the interface. Parametric range of solitary wave solutions is characterized, including extreme regimes such as plateau-shape solitary waves. This work was supported by RFBR (grant No 15-01-03942). References [1] N. Makarenko, J. Maltseva. Asymptotic models of internal stationary waves, J. Appl. Mech. Techn. Phys, 2008, 49(4), 646-654. [2] N. Makarenko, J. Maltseva. Phase velocity spectrum of internal waves in a weakly-stratified two-layer fluid, Fluid Dynamics, 2009, 44(2), 278-294. [3] N. Makarenko, J. Maltseva. An analytical model of large amplitude internal solitary waves, Extreme Ocean Waves, 2nd ed. Springer 2015, E.Pelinovsky and C.Kharif (Eds), 191-201.
Effects of unstratified and centre-stratified randomization in multi-centre clinical trials.
Anisimov, Vladimir V
2011-01-01
This paper deals with the analysis of randomization effects in multi-centre clinical trials. The two randomization schemes most often used in clinical trials are considered: unstratified and centre-stratified block-permuted randomization. The prediction of the number of patients randomized to different treatment arms in different regions during the recruitment period accounting for the stochastic nature of the recruitment and effects of multiple centres is investigated. A new analytic approach using a Poisson-gamma patient recruitment model (patients arrive at different centres according to Poisson processes with rates sampled from a gamma distributed population) and its further extensions is proposed. Closed-form expressions for corresponding distributions of the predicted number of the patients randomized in different regions are derived. In the case of two treatments, the properties of the total imbalance in the number of patients on treatment arms caused by using centre-stratified randomization are investigated and for a large number of centres a normal approximation of imbalance is proved. The impact of imbalance on the power of the study is considered. It is shown that the loss of statistical power is practically negligible and can be compensated by a minor increase in sample size. The influence of patient dropout is also investigated. The impact of randomization on predicted drug supply overage is discussed.
Golmakaniyoon, Sepideh; Hernandez-Martinez, Pedro Ludwig; Demir, Hilmi Volkan; Sun, Xiao Wei
2016-01-01
Surface plasmon (SP) coupling has been successfully applied to nonradiative energy transfer via exciton-plasmon-exciton coupling in conventionally sandwiched donor-metal film-acceptor configurations. However, these structures lack the desired efficiency and suffer poor photoemission due to the high energy loss. Here, we show that the cascaded exciton-plasmon-plasmon-exciton coupling in stratified architecture enables an efficient energy transfer mechanism. The overlaps of the surface plasmon modes at the metal-dielectric and dielectric-metal interfaces allow for strong cross-coupling in comparison with the single metal film configuration. The proposed architecture has been demonstrated through the analytical modeling and numerical simulation of an oscillating dipole near the stratified nanostructure of metal-dielectric-metal-acceptor. Consistent with theoretical and numerical results, experimental measurements confirm at least 50% plasmon resonance energy transfer enhancement in the donor-metal-dielectric-metal-acceptor compared to the donor-metal-acceptor structure. Cascaded plasmon-plasmon coupling enables record high efficiency for exciton transfer through metallic structures. PMID:27698422
Modeling and Assessment of Buoyancy-Driven Stratified Airflow in High-Space Industrial Hall
WANG Han-qing; CHEN Ke; HU Jian-jun; KOU Guang-xiao; WANG Zhi-yong
2009-01-01
In industrial environment,heat sources often are contaminant sources and health threatening con-taminants are mainly passive,so a detailed understanding of airflow mode can assist in work environment hy-giene measurement and prevention.This paper presented a numerical investigation of stratified airflow scenario in a high-space industrial hall with validated commercial code and experimentally acquired boundary conditions.Based upon an actually undergoing engineering project,this study investigated the performance of the buoyancy-driven displacement ventilation in a large welding hall with big components manufactured.The results have demonstrated that stratified airflow sustained by thermal buoyancy provides zoning effect in terms of clean and polluted regions except minor stagnant eddy areas.The competition between negative buoyant jets from displace-ment radial diffusers and positive buoyant plume from bulk object constitutes the complex transport characteris-tics under and above stratification interface.Entrainment,downdraft and turbulent eddy motion complicate the upper mixing zone,but the exhaust outlet plays a less important role in the whole field flow.And the corre-sponding suggestions concerning computational stability and convergence,further improvements in modeling and measurements were given.
Non-local effects in a stratified glow discharge with dust particles
Sukhinin, G I; Fedoseev, A V [Institute of Thermophysics SB RAS, Lavrentyev Ave., 1, Novosibirsk, 630090 (Russian Federation); Ramazanov, T S; Amangaliyeva, R Zh; Dosbalayev, M K; Jumabekov, A N [Institute of Experimental and Theoretical Physics, Al Farabi Kazakh National University, Tole Bi, 96a, Almaty, 050012 (Kazakhstan)], E-mail: fedoseev@itp.nsc.ru
2008-12-21
The work is aimed at describing non-local effects in the positive column of a low-pressure stratified dc glow discharge in argon with dust particles in a vertical cylindrical discharge tube. Numerical calculations of plasma parameters in the axis of the discharge tube were performed with the help of a hybrid model based on the solution of a non-local Boltzmann equation for electron energy distribution function (EEDF). Axial distributions of optical emission from striations with dust particles were measured experimentally. Negatively charged dust particles in a low-pressure stratified gas discharge should levitate at the anode-side branch of an electric field distribution above its maximum. At the same time the experiments showed that the dust particles levitate at the cathode side of a stratum. This paradox is explained by the fact that in a low-pressure striated discharge the optical emission distribution is displaced relative to the electric field distribution that was shown both by numerical simulations and experimental measurements.
Understanding harmful algae in stratified systems: Review of progress and future directions
Berdalet, E.; McManus, M. A.; Ross, O. N.; Burchard, H.; Chavez, F. P.; Jaffe, J. S.; Jenkinson, I. R.; Kudela, R.; Lips, I.; Lips, U.; Lucas, A.; Rivas, D.; Ruiz-de la Torre, M. C.; Ryan, J.; Sullivan, J. M.; Yamazaki, H.
2014-03-01
The Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) program of the Scientific Committee on Oceanic Research (SCOR) and the Intergovernmental Oceanographic Commission (IOC) of UNESCO, was created in 1999 to foster research on the ecological and oceanographic mechanisms underlying the population dynamics of harmful algal blooms (HABs). The ultimate goal of this research is to develop observational systems and models that will eventually enable the prediction of HABs and thereby minimize their impact on marine ecosystems, human health and economic activities. In August of 2012, a workshop was held under the umbrella of the GEOHAB program at the Monterey Bay Aquarium Research Institute (MBARI). The over arching goal of this workshop was to review the current understanding of the processes governing the structure and dynamics of HABs in stratified systems, and to identify how best to couple physical/chemical and biological measurements at appropriate spatial and temporal scales to quantify the dynamics of HABs in these systems, paying particular attention to thin layers. This contribution provides a review of recent progress in the field of HAB research in stratified systems including thin layers, and identifies the gaps in knowledge that our scientific community should strive to understand in the next decade.
On the Orientation of Turbulent Structures in Stably Stratified Shear Flows
Jacobitz, Frank; Moreau, Adam; Aguirre, Joylene
2016-11-01
The orientation of turbulent structures in stably stratified shear flows are investigated using the results of a series of direct numerical simulations. The Richardson number is varied from Ri = 0 , corresponding to unstratified shear flow, to Ri = 1 , corresponding to strongly stratified shear flow. The evolution of the turbulent kinetic energy changes from growth for small Richardson numbers to decay for strong stratification. The orientation of turbulent structures in the flows is determined by the three-dimensional two-point autocorrelation coefficient of velocity magnitude, vorticity magnitude, and fluctuating density. An ellipsoid is fitted to the surface given by a constant autocorrelation coefficient value and the major and minor axes are used to determine the inclination angle of turbulent structures in the plane of shear. The inclination angle is observed to be fairly unaffected by the choice of the autocorrelation coefficient value. In was found that the inclination angle decreases with increasing Richardson number. The structure of the turbulent motion, as characterized by the inclination angle, is therefore directly related to the eventual evolution of the turbulence, as described by the growth or decay rate of the turbulent kinetic energy.
Testing of RANS Turbulence Models for Stratified Flows Based on DNS Data
Venayagamoorthy, S. K.; Koseff, J. R.; Ferziger, J. H.; Shih, L. H.
2003-01-01
In most geophysical flows, turbulence occurs at the smallest scales and one of the two most important additional physical phenomena to account for is strati cation (the other being rotation). In this paper, the main objective is to investigate proposed changes to RANS turbulence models which include the effects of stratifi- cation more explicitly. These proposed changes were developed using a DNS database on strati ed and sheared homogenous turbulence developed by Shih et al. (2000) and are described more fully in Ferziger et al. (2003). The data generated by Shih, et al. (2000) (hereinafter referred to as SKFR) are used to study the parameters in the k- model as a function of the turbulent Froude number, Frk. A modified version of the standard k- model based on the local turbulent Froude number is proposed. The proposed model is applied to a stratified open channel flow, a test case that differs significantly from the flows from which the modified parameters were derived. The turbulence modeling and results are discussed in the next two sections followed by suggestions for future work.
Royle, J. Andrew; Converse, Sarah J.
2014-01-01
Capture–recapture studies are often conducted on populations that are stratified by space, time or other factors. In this paper, we develop a Bayesian spatial capture–recapture (SCR) modelling framework for stratified populations – when sampling occurs within multiple distinct spatial and temporal strata.We describe a hierarchical model that integrates distinct models for both the spatial encounter history data from capture–recapture sampling, and also for modelling variation in density among strata. We use an implementation of data augmentation to parameterize the model in terms of a latent categorical stratum or group membership variable, which provides a convenient implementation in popular BUGS software packages.We provide an example application to an experimental study involving small-mammal sampling on multiple trapping grids over multiple years, where the main interest is in modelling a treatment effect on population density among the trapping grids.Many capture–recapture studies involve some aspect of spatial or temporal replication that requires some attention to modelling variation among groups or strata. We propose a hierarchical model that allows explicit modelling of group or strata effects. Because the model is formulated for individual encounter histories and is easily implemented in the BUGS language and other free software, it also provides a general framework for modelling individual effects, such as are present in SCR models.
The Universal Aspect Ratio of Vortices in Rotating Stratified Flows: Theory and Simulation
Hassanzadeh, Pedram; Gal, Patrice Le
2012-01-01
We derive a relationship for the vortex aspect ratio $\\alpha$ (vertical half-thickness over horizontal length scale) for steady and slowly evolving vortices in rotating stratified fluids, as a function of the Brunt-Vaisala frequencies within the vortex $N_c$ and in the background fluid outside the vortex $\\bar{N}$, the Coriolis parameter $f$, and the Rossby number $Ro$ of the vortex: $\\alpha^2 = Ro(1+Ro) f^2/(N_c^2-\\bar{N}^2)$. This relation is valid for cyclones and anticyclones in either the cyclostrophic or geostrophic regimes; it works with vortices in Boussinesq fluids or ideal gases, and the background density gradient need not be uniform. Our relation for $\\alpha$ has many consequences for equilibrium vortices in rotating stratified flows. For example, cyclones must have $N_c^2 > \\bar{N}^2$; weak anticyclones (with $|Ro| \\bar{N}^2$. We verify our relation for $\\alpha$ with numerical simulations of the three-dimensional Boussinesq equations for a wide variety of vortices, including: vortices that are i...
Mixing process of a binary gas in a density stratified layer
Takeda, Tetsuaki [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment
1997-09-01
This study is to investigate the effect of natural convection on the mixing process by molecular diffusion in a vertical stratified layer of a binary fluid. There are many experimental and analytical studies on natural convection in the vertical fluid layer. However, there are few studies on natural convection with molecular diffusion in the vertical stratified layer of a binary gas. Experimental study has been performed on the combined phenomena of molecular diffusion and natural convection in a binary gas system to investigate the mixing process of the binary gas in a vertical slot consisting of one side heated and the other side cooled. The range of Rayleigh number based on the slot width was about 0 < Ra{sub d} < 7.5 x 10{sup 4}. The density change of the gas mixture and the temperature distribution in the slot was obtained and the mixing process when the heavier gas ingress into the vertical slot filled with the lighter gas from the bottom side of the slot was discussed. The experimental results showed that the mixing process due to molecular diffusion was affected significantly by the natural convection induced by the slightly temperature difference between both vertical walls even if a density difference by the binary gas is larger than that by the temperature difference. (author). 81 refs.
Self-regulation of mean flows in strongly stratified sheared turbulence
Salehipour, Hesam; Caulfield, Colm-Cille; Peltier, W. Richard
2016-11-01
We investigate the near-equilibrium state of shear-driven stratified turbulence generated by the breaking of Holmboe wave instability (HWI) and Kelvin-Helmholtz instability (KHI). We discuss DNS analyses associated with HWI under various initial conditions. We analyze the time-dependent distribution of the gradient Richardson number, Rig (z , t) associated with the horizontally-averaged velocity and density fields. We demonstrate that unlike the KHI-induced turbulence, the fully turbulent flow that is generated by HWI is robustly characterized by its high probability of Rig 0 . 2 - 0 . 25 , independent of the strength of the initial stratification and furthermore that the turbulence evolves in a 'near-equilibrium' state. The KHI-induced turbulence may become grossly 'out of equilibrium', however, and therefore decays rapidly when the initial value at the interface, Rig (0 , 0) , is closer to the critical value of 1/4; otherwise as Rig (0 , 0) -> 0 the KHI-induced turbulence is close to a state of equilibrium and hence is much more long-lived. We conjecture that stratified shear turbulence tends to adjust to a state of 'near-equilibrium' with horizontally-averaged flows characterized by a high probability of Rig <= 1 / 4 , and hence sustained turbulence over relatively long times.
Dynamics of motile micro-organisms in stably-stratified turbulence
Lovecchio, Salvatore; Zonta, Francesco; Marchioli, Cristian; Soldati, Alfredo
2016-11-01
Motile micro-organisms populating terrestrial water bodies swim upward towards the air-water interface to capture light and activate photosynthesis. These micro-organisms have the center of mass displaced below the center of buoyancy and are usually called gyrotactic swimmers. Gyrotactic swimmers (which are almost neutrally-buoyant) are extremely sensitive to the local flow field, which is often stably stratified (due to solar heating at the water surface). Stable stratification has a deep influence on the transport processes of mass, momentum, heat and chemical species at the water surface. In this work we use Direct Numerical Simulation (DNS) and Lagrangian Particle Tracking (LPT) to analyze the dynamics of gyrotactic swimmers in stratified turbulence. Our results show that swimmers surfacing and clustering at the surface depend strongly on the re-orientation time of swimmers and on the level of stratification. Obtaining accurate predictions of the surfacing time for gyrotactic swimmers is extremely important to estimate the global CO2 exchange across the air-water interface.
Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume
Jurisa, Joseph T.; Nash, Jonathan D.; Moum, James N.; Kilcher, Levi F.
2016-08-01
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. Observed ..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.
Ventura, Sandra Rua; Ramos, Isabel; Rodrigues, Pedro Pereira
2015-01-01
Background Mammography is considered the best imaging technique for breast cancer screening, and the radiographer plays an important role in its performance. Therefore, continuing education is critical to improving the performance of these professionals and thus providing better health care services. Objective Our goal was to develop an e-learning course on breast imaging for radiographers, assessing its efficacy, effectiveness, and user satisfaction. Methods A stratified randomized controlled trial was performed with radiographers and radiology students who already had mammography training, using pre- and post-knowledge tests, and satisfaction questionnaires. The primary outcome was the improvement in test results (percentage of correct answers), using intention-to-treat and per-protocol analysis. Results A total of 54 participants were assigned to the intervention (20 students plus 34 radiographers) with 53 controls (19+34). The intervention was completed by 40 participants (11+29), with 4 (2+2) discontinued interventions, and 10 (7+3) lost to follow-up. Differences in the primary outcome were found between intervention and control: 21 versus 4 percentage points (pp), Pstudents (18 pp vs 5 pp; P=.098). Nonetheless, differences in students’ posttest results were found (88% vs 63%; P=.003), which were absent in pretest (63% vs 63%; P=.106). The per-protocol analysis showed a higher effect (26 pp vs 2 pp; Pstudents (25 pp vs 3 pp; P=.004) and radiographers (27 pp vs 2 pp; P<.001). Overall, 85% were satisfied with the course, and 88% considered it successful. Conclusions This e-learning course is effective, especially for radiographers, which highlights the need for continuing education. PMID:25560547
Alan Karthikesalingam
Full Text Available Lifelong surveillance after endovascular repair (EVAR of abdominal aortic aneurysms (AAA is considered mandatory to detect potentially life-threatening endograft complications. A minority of patients require reintervention but cannot be predictively identified by existing methods. This study aimed to improve the prediction of endograft complications and mortality, through the application of machine-learning techniques.Patients undergoing EVAR at 2 centres were studied from 2004-2010. Pre-operative aneurysm morphology was quantified and endograft complications were recorded up to 5 years following surgery. An artificial neural networks (ANN approach was used to predict whether patients would be at low- or high-risk of endograft complications (aortic/limb or mortality. Centre 1 data were used for training and centre 2 data for validation. ANN performance was assessed by Kaplan-Meier analysis to compare the incidence of aortic complications, limb complications, and mortality; in patients predicted to be low-risk, versus those predicted to be high-risk.761 patients aged 75 +/- 7 years underwent EVAR. Mean follow-up was 36+/- 20 months. An ANN was created from morphological features including angulation/length/areas/diameters/volume/tortuosity of the aneurysm neck/sac/iliac segments. ANN models predicted endograft complications and mortality with excellent discrimination between a low-risk and high-risk group. In external validation, the 5-year rates of freedom from aortic complications, limb complications and mortality were 95.9% vs 67.9%; 99.3% vs 92.0%; and 87.9% vs 79.3% respectively (p<0.001.This study presents ANN models that stratify the 5-year risk of endograft complications or mortality using routinely available pre-operative data.
Abdullah Ahmed Foisal
2016-01-01
Full Text Available MHD free convection over an inclined plate in a thermally stratified high porous medium in the presence of a magnetic field has been studied. The dimensionless momentum and temperature equations have been solved numerically by explicit finite difference technique with the help of a computer programming language Compaq Visual Fortran 6.6a. The obtained results of these studies have been discussed for the different values of well known parameters with different time steps. Also, the stability conditions and convergence criteria of the explicit finite difference scheme has been analyzed for finding the restriction of the values of various parameters to get more accuracy. The effects of various governing parameters on the fluid velocity, temperature, local and average shear stress and Nusselt number has been investigated and presented graphically.
Om Prakash; Devendra Kumar; Y K Dwivedi
2012-12-01
The paper investigates the effects of heat transfer in MHD flow of viscoelastic stratified fluid in porous medium on a parallel plate channel inclined at an angle . A laminar convection flow for incompressible conducting fluid is considered. It is assumed that the plates are kept at different temperatures which decay with time. The partial differential equations governing the flow are solved by perturbation technique. Expressions for the velocity of fluid and particle phases, temperature field, Nusselt number, skin friction and flow flux are obtained within the channel. The effects of various parameters like stratification factor, magnetic field parameter, Prandtl number on temperature field, heat transfer, skin friction, flow flux, velocity for both the fluid and particle phases are displayed through graphs and discussed numerically.
Mo Isotopes Record Destabilization of a Stratified Ocean at the Precambrian-Cambrian Boundary
Wille, M.; Nägler, T. F.; Schröder, S.; Lehmann, B.; Kramers, J. D.
2007-12-01
Here we present Mo isotope signatures in black shales from two sample sets (Ara group, Oman and Yangtze Platform, China) which were deposited at and shortly after the Precambrian-Cambrian boundary (PC-C). At the first view, the overall Mo isotopic signatures (delta98/95Mo) of the Early Cambrian black shales is 1.2 permil below recent ocean water, similar to the signature found in Mesoproterozoic shales (Arnold et al. 2004), indicating a larger proportion of Mo sedimentation under strongly euxinic conditions compared to recent oceans. A chemically stratified ocean with sulfidic deep waters and modestly oxygenated surface waters as proposed by Canfield (1998) for the Paleoproterozoic and Mesoproterozoic ocean, and Jiang et al. (2007) reported Carbon isotope data from the Ediacaran Yangtze platform (635-542 Ma) to be consistent with long-term deep ocean anoxia/euxinia. A stratified ocean therefore provides a plausible scenario to explain our new PC-C Mo isotope data. On closer inspection, a transient Mo isotopic signal following immediately after the PC-C boundary in both sample sets indicates a short but intense global non-steady state situation. In particular, a short term, drastic decrease of the Mo ocean inventory to almost zero is required to reconcile the observed Mo isotope data. Combined with the extreme Mo enrichment, found in the Chinese sulfide marker bed at the PC-C boundary, this signal has to be explained with a non-uniformitarian Mo scavenging mechanism. We put forward the hypothesis of mixing of oxidized, i.e. Mo rich surface waters with upwelling euxinic bottom water masses of the stratified ocean, as H2S is the most efficient Mo scavenging reagent. This scenario not only explains the transient isotopic signal, it can also be responsible for the sudden extinction of the Ediacaran fauna by H2S poisoning. In contrast, mass extinction scenarios like bolide impact, flood basalt eruptions or methane release, do not provide a direct explanation for the
An experimental study on the formation and survival of stratified subsurface eddies
Bormans, Myriam
1992-12-01
We report the results of laboratory experiments on the formation and survival of internally stratified subsurface eddies in a rotating fluid. The eddies were created by injecting a dense turbulent plume at the surface of a linearly stratified environment. The relative vorticity of the lenses was always negative but larger than that of homogeneous lenses created by laminar injection. During the first 100 revolutions, the eddies shed fluid in two symmetric arms. The shedding which is believed to result from shear instabilities always resulted in a stationary axisymmetric eddy. After the eddy had spun down, the remnant fluid persisted for thousands of rotations as a circular feature with internal stratification identical to that of the environment. We created eddies with and without double diffusive convective instabilities and compared the volume of dyed fluid and the evolution of their aspect ratios. Sugar and salt were used as laboratory analogues of salt and heat, respectively. The Burger number of the lenses decreased rapidly within the first 200 revolutions and then much more slowly to reach a value between 0.2 and 0.4, These latter values are larger than those predicted by Gill (1981) for a homogeneous lens due to the internal stratification of the lenses. Radial spreading of the lens due to double diffusive intrusions was found to be larger, but of the same order of magnitude, as that induced by the vertical exchange of momentum in the absence of double diffusive convection. We formed eddies internally stratified in the diffusive sense (stable sugar gradient and unstable salt gradient) or doubly stable (stable sugar and salt gradients) by changing the ratio of the volume flux at the source to the volume flux at the spreading level as described by Bormans and Turner (1990). When the stratification in the eddies was doubly stable, three distinctive regions were observed: a region of convective layers and diffusive density interfaces at the top, a central region
Regional variations of cell surface carbohydrates in human oral stratified epithelium
Vedtofte, P; Dabelsteen, Erik; Hakomori, S
1984-01-01
such as non-keratinized, parakeratinized, and orthokeratinized stratified squamous epithelium. The material included buccal and palatal epithelium from 20 persons with blood group A or O, gingival, and alveolar epithelium from 10 persons with blood group A or B, and buccal metaplastically keratinized......-acetyllactosamine by murine monoclonal antibodies. Each antigen showed a similar staining pattern in buccal and alveolar epithelium (non-keratinized) which differed considerably from that seen in palatal and gingival epithelium (ortho- and parakeratinized). The expression of blood group antigens A or B and the precursor...... antigen H type 2 chains in metaplastically keratinized buccal epithelium was found to differ significantly from that seen in normal non-keratinized buccal epithelium. The regional variations demonstrated in cell surface carbohydrates are suggested to reflect differences in tissue differentiation....
Numerical study on interaction of local air cooler with stratified hydrogen cloud in a large vessel
Liang, Z. [Atomic Energy of Canada Limited, Chalk River Laboratories, ON K0J 1J0 (Canada); Andreani, M. [Laboratory for Thermal-Hydraulics, Paul Scherrer Institut, 5232 Villigen (Switzerland)
2012-07-01
Within the framework of the ERCOSAM project, planning calculations are performed to examine sensitivity parameters that can affect the break-up (erosion) of a helium layer by mitigation devices (i.e., cooler, spray, or Passive Autocatalytic Recombiner - PAR). This paper reports the GOTHIC analysis results for the cooler tests to be performed in the PANDA facility. The cooler elevation and geometry, helium layer thickness, steam distribution in the vessel, and the vessel geometry (inter-connected multi-compartments versus a single volume) on the erosion process as well as the cooling capacity are studied. This analysis is valuable because only a limited number of conditions will be examined in the planned experiments. The study provides a useful understanding of the interaction of a cooler with a stratified atmosphere. (authors)
Kim, Seulong
2016-01-01
Bi-isotropic media, which include isotropic chiral media and Tellegen media as special cases, are the most general form of linear isotropic media where the electric displacement and the magnetic induction are related to both the electric field and the magnetic intensity. In inhomogeneous bi-isotropic media, electromagnetic waves of two different polarizations are coupled to each other. In this paper, we develop a generalized version of the invariant imbedding method for the study of wave propagation in arbitrarily-inhomogeneous stratified bi-isotropic media, which can be used to solve the coupled wave propagation problem accurately and efficiently. We verify the validity and usefulness of the method by applying it to several examples, including the wave propagation in a uniform chiral slab, the surface wave excitation in a bilayer system made of a layer of Tellegen medium and a metal layer, and the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations in inhomogeneous Telle...
Finite difference methods for transient signal propagation in stratified dispersive media
Lam, D. H.
1975-01-01
Explicit difference equations are presented for the solution of a signal of arbitrary waveform propagating in an ohmic dielectric, a cold plasma, a Debye model dielectric, and a Lorentz model dielectric. These difference equations are derived from the governing time-dependent integro-differential equations for the electric fields by a finite difference method. A special difference equation is derived for the grid point at the boundary of two different media. Employing this difference equation, transient signal propagation in an inhomogeneous media can be solved provided that the medium is approximated in a step-wise fashion. The solutions are generated simply by marching on in time. It is concluded that while the classical transform methods will remain useful in certain cases, with the development of the finite difference methods described, an extensive class of problems of transient signal propagating in stratified dispersive media can be effectively solved by numerical methods.
Amiruddin Hilmi
2017-01-01
Full Text Available This paper presents the results from 1.6 litre, 4 cylinders stratified charge compressed natural gas (CNG direct injection engine with boosting device. A turbocharger with compressor trim of 40 was used to increase engine output. The engine was tested at wide open throttle (WOT and speed ranging from 1000 to 5000 rpm. Engine performance and emissions data were recorded under steady state condition. Results show turbocharged CNG engine produced an average of 26% increment in brake power and 24% additional maximum brake torque as compared with natural aspirated (NA CNG engine. Turbocharged CNG engine improved brake specific fuel consumption (BSFC and yielded higher fuel conversion efficiency (FCE. Relatively turbocharged CNG engine showed lower emission of hydrocarbon (HC and carbon monoxide (CO throughout tested engine speed. Conversely, the carbon dioxide (CO2 and nitrogen oxide (NOx emission produced were slightly higher compared with NA CNG engine.
Law of the wall in an unstably stratified turbulent channel flow
Scagliarini, Andrea; Gylfason, Ármann; Toschi, Federico
2015-01-01
We perform direct numerical simulations of an unstably stratified turbulent channel flow to address the effects of buoyancy on the boundary layer dynamics and mean field quantities. We systematically span a range of parameters in the space of friction Reynolds number ($Re_{\\tau}$) and Rayleigh number ($Ra$). Our focus is on deviations from the logarithmic law of the wall due to buoyant motion. The effects of convection in the relevant ranges are discussed providing measurements of mean profiles of velocity, temperature and Reynolds stresses as well as of the friction coefficient. A phenomenological model is proposed and shown to capture the observed deviations of the velocity profile in the log-law region from the non-convective case.
A universal expression of near-filed/far-field boundary in stratified structures
Li, Chao; Wang, Huai Yu; Wang, Xue Hua
2015-01-01
The division of the near-field and far-field zones for electromagnetic waves is important for simplifying theoretical calculations and applying far-field results. In this paper, we have studied the far-field asymptotic behaviors of dipole radiations in stratified backgrounds and obtained a universal empirical expression of near-field/far-field (NFFF) boundary. The boundary is mainly affected by lateral waves, which corresponds to branch point contributions in Sommerfeld integrals. In a semispace with a higher refractive index, the NFFF boundary is determined by a dimensional parameter and usually larger than the operating wavelength by at least two orders of magnitude. In a semispace with the lowest refractive index in the structure (usually air), the NFFF boundary is about ten wavelengths. Moreover, different treatments in the asymptotic method are discussed and numerically compared. An equivalence between the field expressions obtained from the asymptotic method and those from reciprocal theorem is demonstr...
Morphological instabilities of stratified epithelia: a mechanical instability in tumour formation
Risler, Thomas
2013-01-01
Interfaces between stratified epithelia and their supporting stromas commonly exhibit irregular shapes. Undulations are particularly pronounced in dysplastic tissues and typically evolve into long, finger-like protrusions in carcinomas. In a previous work (Basan et al., Phys. Rev. Lett. 106, 158101 (2011)), we demonstrated that an instability arising from viscous shear stresses caused by the constant flow due to cell turnover in the epithelium could drive this phenomenon. While interfacial tension between the two tissues as well as mechanical resistance of the stroma tend to maintain a flat interface, an instability occurs for sufficiently large viscosity, cell-division rate and thickness of the dividing region in the epithelium. Here, extensions of this work are presented, where cell division in the epithelium is coupled to the local concentration of nutrients or growth factors diffusing from the stroma. This enhances the instability by a mechanism similar to that of the Mullins-Sekerka instability in single...
Kozitsyna, M. V.; Trufanova, N. M.
2017-01-01
Today the process of coextrusion is the most technological in the cable production with cross-linked polyethylene, composed of two or more layers of polymeric insulation. Since the covering technology is a simultaneous imposition of all necessary layers (two semiconducting shields on the insulation and conductor and one - on insulation), the main focus of this study is the analysis of significance of various factors influence on stratified flows characteristics. This paper has considered the flow of two abnormally viscous liquids in the cable head. The problem has been solved through a three-dimensional statement by applying the finite element method in the Ansys software package. The influence has been estimated by varying the rheological properties of materials to create all necessary layers thickness.
Jianxiu Wang
2013-01-01
Full Text Available Based on the Yishan Metro Station Project of Shanghai Metro Line number 9, a centrifugal model test was conducted to investigate the behavior of stratified settlement and rebound (SSR of Shanghai soft clay caused by dewatering in deep subway station pit. The soil model was composed of three layers, and the dewatering process was simulated by self-invention of decompressing devise. The results indicate that SSR occurs when the decompression was carried out, and only negative rebound was found in sandy clay, but both positive and negative rebound occurred in the silty clay, and the absolute value of rebound in sandy clay was larger than in silty clay, and the mechanism of SSR was discussed with mechanical sandwich model, and it was found that the load and cohesive force of different soils was the main source of different responses when decompressed.
Numerical study of the evolution of vortices in a linearly stratified fluid
Beckers, M.; Clercx, H.J.H.; Van Heijst, G.J.F. [Eindhoven University of Technology, Eindhoven (Netherlands). J.M. Burgers Centre fro Fluid Dynamics; Verzicco, R. [Rome Univ. La Sapienza, Rome (Italy). Dipt. di Meccanica e Aeronautica
1999-12-01
This paper presents a numerical study in which the evolution of vortices in a Stafford fluid is compared to the evolution of two-dimensional vortices. The influence of the Reynolds number and the Froude number are investigated, for the evolution of axisymmetric vortices, for their azimuthal instability and for the subsequent formation of tripoles. It is found that due to radial diffusion axisymmetric vortices with various initial vorticity profiles all evolve towards the same profile. This evolution reduces the growth of azimuthal instabilities which may lead to the formation of a tripole. For vortices in a stratified fluid the effect of the ambient stratification on the evolution of the vortices is investigated. It is found that a process of vortex stretching, which becomes more pronounced for increasing Froude numbers, leads to a weaker tripole formation.
Gaussian Beam Tunneling through a Gyrotropic-Nihility Finely-Stratified Structure
Tuz, Vladimir R
2014-01-01
The three-dimensional Gaussian beam transmission through a ferrite-semiconductor finely-stratified structure being under an action of an external static magnetic field in the Faraday geometry is considered. The beam field is represented by an angular continuous spectrum of plane waves. In the long-wavelength limit, the studied structure is described as a gyroelectromagnetic medium defined by the effective permittivity and effective permeability tensors. The investigations are carried out in the frequency band where the real parts of the on-diagonal elements of both effective permittivity and effective permeability tensors are close to zero while the off-diagonal ones are non-zero. In this frequency band the studied structure is referred to a gyrotropic-nihility medium. It is found out that a Gaussian beam keeps its parameters unchanged (beam width and shape) when passing through the layer of such a medium except of a portion of the absorbed energy.
Kim, Kihong; Phung, D K; Rotermund, F; Lim, H
2008-01-21
We develop a generalized version of the invariant imbedding method, which allows us to solve the electromagnetic wave equations in arbitrarily inhomogeneous stratified media where both the dielectric permittivity and magnetic permeability depend on the strengths of the electric and magnetic fields, in a numerically accurate and efficient manner. We apply our method to a uniform nonlinear slab and find that in the presence of strong external radiation, an initially uniform medium of positive refractive index can spontaneously change into a highly inhomogeneous medium where regions of positive or negative refractive index as well as metallic regions appear. We also study the wave transmission properties of periodic nonlinear media and the influence of nonlinearity on the mode conversion phenomena in inhomogeneous plasmas. We argue that our theory is very useful in the study of the optical properties of a variety of nonlinear media including nonlinear negative index media fabricated using wires and split-ring resonators.
Geostrophic balance and the emergence of helicity in rotating stratified turbulence
Marino, Raffaele; Rosenberg, Duane; Pouquet, Annick
2012-01-01
We perform numerical simulations of decaying rotating stratified turbulence and show, in the Boussinesq framework, that helicity (velocity-vorticity correlation), as observed in super-cell storms and hurricanes, is spontaneously created due to geostrophic balance common to large-scale atmospheric and oceanic flows. Helicity emerges from the joint action of eddies and of inertial and gravity waves of respective frequencies $f$ and $N$, and it occurs when the waves are sufficiently strong. For $N/f < 3$ the amount of helicity produced is correctly predicted by a linear balance equation. Outside this regime, and up to the highest Reynolds number obtained in this study, namely $Re\\approx 10000$, helicity production is found to be persistent for $N/f$ as large as $\\approx 17$ and for $ReFr^2$ and $ReRo^2 $ as large as $\\approx 100, \\approx 24000 $.
An experimental investigation of stratified two-phase pipe flow at small inclinations
Espedal, Mikal
1998-12-31
The prediction of stratified flow is important for several industrial applications. Stratified flow experiments were carefully performed in order to investigate the performance of a typical model which uses wall friction factors based on single phase pipe flow as described above. The test facility has a 18.5 m long and 60 mm i.d. (L/D=300) acrylic test section which can be inclined between -10 {sup o} and +10 {sup o}. The liquid holdup was measured by using fast closing valves and the pressure gradients by using three differential pressure transducers. Interfacial waves were measured by thin wire conductance probes mounted in a plane perpendicular to the main flow. The experiments were performed using water and air at atmospheric pressure. The selected test section inclinations were between -3 {sup o} and +0.5 {sup o} to the horizontal plane. A large number of experiments were performed for different combinations of air and water flow rates and the rates were limited to avoid slug flow and stratified flow with liquid droplets. The pressure gradient and the liquid holdup were measured. In addition the wave probes were used to find the wave heights and the wave power spectra. The results show that the predicted pressure gradient using the standard models is approximately 30% lower than the measured value when large amplitude waves are present. When the flow is driven by the interfacial force the test section inclination has minor influence on the deviation between predicted and measured pressure gradients. Similar trends are apparent in data from the literature, although they seem to have gone unnoticed. For several data sets large spread in the predictions are observed when the model described above was used. Gas wall shear stress experiments indicate that the main cause of the deviation between measured and predicted pressure gradient and holdup resides in the modelling of the liquid wall friction term. Measurements of the liquid wall shear stress distribution
Thiele, Uwe; Frastia, Lubor
2007-01-01
A dynamical model is proposed to describe the coupled decomposition and profile evolution of a free surface film of a binary mixture. An example is a thin film of a polymer blend on a solid substrate undergoing simultaneous phase separation and dewetting. The model is based on model-H describing the coupled transport of the mass of one component (convective Cahn-Hilliard equation) and momentum (Navier-Stokes-Korteweg equations) supplemented by appropriate boundary conditions at the solid substrate and the free surface. General transport equations are derived using phenomenological non-equilibrium thermodynamics for a general non-isothermal setting taking into account Soret and Dufour effects and interfacial viscosity for the internal diffuse interface between the two components. Focusing on an isothermal setting the resulting model is compared to literature results and its base states corresponding to homogeneous or vertically stratified flat layers are analysed.
Nonlinear waves in stratified Taylor--Couette flow. Part 1. Layer formation
Leclercq, Colin; Augier, Pierre; Caulfield, Colm-Cille P; Dalziel, Stuart B; Linden, Paul F
2016-01-01
This paper is the first part of a two-fold study of mixing, i.e. the formation of layers and upwelling of buoyancy, in axially stratified Taylor--Couette flow, with fixed outer cylinder. Using linear analysis and direct numerical simulation, we show the critical role played by non-axisymmetric instability modes, despite the fact that the flow is centrifugally unstable in the sense of Rayleigh's criterion. Interactions between helical modes of opposite handedness leads to the formation of nonlinear coherent structures: (mixed)-ribbons and (mixed)-cross-spirals. These give birth to complex density interface patterns, seemingly appearing and disappearing periodically as the coherent structure slowly rotates around the annulus. These coherent structures seem to be responsible for the formation of layers reported in a recent experiment by Oglethorpe et al. (2013). We distinguish `dynamic layering', instantaneous, localized and caused by the vortical motions, from `static layering' corresponding to the formation of...
Experimental study of the initial growth of a localized turbulent patch in a stably stratified fluid
Verso, Lilly; Gurka, Roi; Diamessis, Peter J; Taylor, Zachary J; Liberzon, Alex
2016-01-01
We present a laboratory experiment of the growth of a turbulent patch in a stably stratified fluid, due to a localized source of turbulence, generated by an oscillating grid. Synchronized and overlapping particle image velocimetry and planar laser induced fluorescence measurements have been conducted capturing the evolution of the patch through its initial growth until it reached a maximum size, followed by its collapse. The simultaneous measurements of density and velocity fields allow for a direct quantification of the degree of mixing within the patch, the propagation speed of the turbulent/non-turbulent interface and its thickness. The velocity measurements indicate significant non-equilibrium effects inside the patch which are not consistent with the classical used grid-action model. A local analysis of the turbulent/non-turbulent interface provides direct measurements of the entrainment velocity $w_{e}$ as compared to the local vertical velocity and turbulent intensity at the proximity of the interface....
Mohd Hafizi Mat Yasin
2013-01-01
Full Text Available We present the numerical investigation of the steady mixed convection boundary layer flow over a vertical surface embedded in a thermally stratified porous medium saturated by a nanofluid. The governing partial differential equations are reduced to the ordinary differential equations, using the similarity transformations. The similarity equations are solved numerically for three types of metallic or nonmetallic nanoparticles, namely, copper (Cu, alumina (Al2O3, and titania (TiO2, in a water-based fluid to investigate the effect of the solid volume fraction or nanoparticle volume fraction parameter φ of the nanofluid on the flow and heat transfer characteristics. The skin friction coefficient and the velocity and temperature profiles are presented and discussed.
Large-scale confinement and small-scale clustering of floating particles in stratified turbulence
Sozza, A; Musacchio, S; Boffetta, G
2015-01-01
We study the motion of small inertial particles in stratified turbulence. We derive a simplified model, valid within the Boussinesq approximation, for the dynamics of small particles in presence of a mean linear density profile. By means of extensive direct numerical simulations, we investigate the statistical distribution of particles as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of inertial particles in turbulence, depends on the particle relaxation time and is almost independent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed.
Moon, H., E-mail: haksu.moon@gmail.com [ElectroScience Laboratory, The Ohio State University, Columbus, OH 43212 (United States); Donderici, B., E-mail: burkay.donderici@halliburton.com [Sensor Physics & Technology, Halliburton Energy Services, Houston, TX 77032 (United States); Teixeira, F.L., E-mail: teixeira@ece.osu.edu [ElectroScience Laboratory, The Ohio State University, Columbus, OH 43212 (United States)
2016-11-15
We present a robust algorithm for the computation of electromagnetic fields radiated by point sources (Hertzian dipoles) in cylindrically stratified media where each layer may exhibit material properties (permittivity, permeability, and conductivity) with uniaxial anisotropy. Analytical expressions are obtained based on the spectral representation of the tensor Green's function based on cylindrical Bessel and Hankel eigenfunctions, and extended for layered uniaxial media. Due to the poor scaling of these eigenfunctions for extreme arguments and/or orders, direct numerical evaluation of such expressions can produce numerical instability, i.e., underflow, overflow, and/or round-off errors under finite precision arithmetic. To circumvent these problems, we develop a numerically stable formulation through suitable rescaling of various expressions involved in the computational chain, to yield a robust algorithm for all parameter ranges. Numerical results are presented to illustrate the robustness of the formulation including cases of practical interest.
Moon, H.; Donderici, B.; Teixeira, F. L.
2016-11-01
We present a robust algorithm for the computation of electromagnetic fields radiated by point sources (Hertzian dipoles) in cylindrically stratified media where each layer may exhibit material properties (permittivity, permeability, and conductivity) with uniaxial anisotropy. Analytical expressions are obtained based on the spectral representation of the tensor Green's function based on cylindrical Bessel and Hankel eigenfunctions, and extended for layered uniaxial media. Due to the poor scaling of these eigenfunctions for extreme arguments and/or orders, direct numerical evaluation of such expressions can produce numerical instability, i.e., underflow, overflow, and/or round-off errors under finite precision arithmetic. To circumvent these problems, we develop a numerically stable formulation through suitable rescaling of various expressions involved in the computational chain, to yield a robust algorithm for all parameter ranges. Numerical results are presented to illustrate the robustness of the formulation including cases of practical interest.
Free convective flow of a stratified fluid through a porous medium bounded by a vertical plane
H. K. Mondal
1994-01-01
Full Text Available Steady two-dimensional free convection flow of a thermally stratified viscous fluid through a highly porous medium bounded by a vertical plane surface of varying temperature, is considered. Analytical expressions for the velocity, temperature and the rate of heat transfer are obtained by perturbation method. Velocity distribution and rate of heat transfer for different values of parameters are shown in graphs. Velocity distribution is also obtained for certain values of the parameters by integrating the coupled differential equations by Runge-Kutta method and compared with the analytical solution. The chief concern of the paper is to study the effect of equilibrium temperature gradient on the velocity and the rate of heat transfer.
Prediction of the bed-load transport by gas-liquid stratified flows in horizontal ducts
Franklin, Erick de Moraes
2016-01-01
Solid particles can be transported as a mobile granular bed, known as bed-load, by pressure-driven flows. A common case in industry is the presence of bed-load in stratified gas-liquid flows in horizontal ducts. In this case, an initially flat granular bed may be unstable, generating ripples and dunes. This three-phase flow, although complex, can be modeled under some simplifying assumptions. This paper presents a model for the estimation of some bed-load characteristics. Based on parameters easily measurable in industry, the model can predict the local bed-load flow rates and the celerity and the wavelength of instabilities appearing on the granular bed.
Computer animation of the stratified mixture shape in gasoline direct injection engine
Sendyka, B.; Pisarczyk, W.; Pajak, M. [Cracow University of Technology (Poland); Lindberg, W. [University of Wyoming (United States)
1999-07-01
The present method of direct fuel injection in Gasoline Direct Injection Engines (GDIE) creates a conical fuel stream, which is inefficient for GDIE. In this paper we analyzed how to achieve stratified conical shape of the rich fuel mixture. The kernel of the rich mixture should be located between the electrodes of the spark plug. This is achieved when the conical stream is bounced back from the surface of the bowl of the piston. The computer animation of the trajectory of the convergent fuel stream was based on equations of the parameters for fuel stream, injection pressure and angle of fuel injector. The presented animation allows us to determine the movement of the stream, from the beginning of injection to the electrodes of the spark plug, where the combustion process of the rich mixture kernel starts. (author)
Deformation and failure of stratified weak roof strata of longwall roadway
无
2007-01-01
A comprehensive underground monitoring was conducted in a coal mine. The purpose of this research was to clarify the deformation and failure behavior of stratified weak roof strata of longwall roadway in adverse ground conditions. The field investigation incorporating a range of geotechnical instrumentation was conducted over a period of time ever since the formation of opening the site was buried into the goaf of a retreating longwall panel. The roof layer deformation and failure characteristics associated with the three stages of heading development, after development and before extraction, as well as after longwall extraction were identified on the basis of field investigation and analyticai study, the results clearly demonstrated that how the roof deformation and failure progress were strongly related to these three stages of the mining activities mentioned.
Tsap, Y. T.; Stepanov, A. V.; Kopylova, Y. G.
2016-09-01
Based on the linearized magnetohydrodynamic (MHD) equations within the framework of the thin flux tube approximation, the phase relationships between the disturbed quantities of evanescent acoustic and slow sausage MHD modes excited in the adiabatically stratified solar atmosphere are considered. It has been shown that the sign of the phase differences (equal to ±π/2) between the velocity and other disturbed quantities such as pressure, density, magnetic field, and temperature, depends on the wave frequency ω. The obtained phase relationships agree well with SOT/Hinode observations obtained by Fujimura and Tsuneta (Astrophys. J. 702, 1443, 2009) when ω≈ωc, where ωc is the cutoff frequency. The role of various modes excited in the solar atmosphere in the light of the chromospheric and coronal heating problems are discussed.
Wang, Junfeng; Miesch, Mark S
2015-01-01
We present a novel and powerful Compressible High-ORder Unstructured Spectral-difference (CHORUS) code for simulating thermal convection and related fluid dynamics in the interiors of stars and planets. The computational geometries are treated as rotating spherical shells filled with stratified gas. The hydrodynamic equations are discretized by a robust and efficient high-order Spectral Difference Method (SDM) on unstructured meshes. The computational stencil of the spectral difference method is compact and advantageous for parallel processing. CHORUS demonstrates excellent parallel performance for all test cases reported in this paper, scaling up to 12,000 cores on the Yellowstone High-Performance Computing cluster at NCAR. The code is verified by defining two benchmark cases for global convection in Jupiter and the Sun. CHORUS results are compared with results from the ASH code and good agreement is found. The CHORUS code creates new opportunities for simulating such varied phenomena as multi-scale solar co...
Insights from a 3-D temperature sensors mooring on stratified ocean turbulence
Haren, Hans; Cimatoribus, Andrea A.; Cyr, Frédéric; Gostiaux, Louis
2016-05-01
A unique small-scale 3-D mooring array has been designed consisting of five parallel lines, 100 m long and 4 m apart, and holding up to 550 high-resolution temperature sensors. It is built for quantitative studies on the evolution of stratified turbulence by internal wave breaking in geophysical flows at scales which go beyond that of a laboratory. Here we present measurements from above a steep slope of Mount Josephine, NE Atlantic where internal wave breaking occurs regularly. Vertical and horizontal coherence spectra show an aspect ratio of 0.25-0.5 near the buoyancy frequency, evidencing anisotropy. At higher frequencies, the transition to isotropy (aspect ratio of 1) is found within the inertial subrange. Above the continuous turbulence spectrum in this subrange, isolated peaks are visible that locally increase the spectral width, in contrast with open ocean spectra. Their energy levels are found to be proportional to the tidal energy level.
Gent, Frederick A; Erd'elyi, Rebertus
2014-01-01
A system of multiple open magnetic flux tubes spanning the solar photosphere and lower corona is modelled analytically, within a realistic stratified atmosphere subject to solar gravity. This extends results for a single magnetic flux tube in magnetohydrostatic equilibrium, described in Gent et al. (MNRAS, 435, 689, 2013). Self-similar magnetic flux tubes are combined to form magnetic structures, which are consistent with high-resolution observations. The observational evidence supports the existence of strands of open flux tubes and loops persisting in a relatively steady state. Self-similar magnetic flux tubes, for which an analytic solution to the plasma density and pressure distribution is possible, are combined. We calculate the appropriate balancing forces, applying to the equations of momentum and energy conservation to preserve equilibrium. Multiplex flux tube configurations are observed to remain relatively stable for up to a day or more, and it is our aim to apply our model as the background conditi...
TenHoeve, J. E.; Remer, L. A.; Jacobson, M. Z.
2010-01-01
This study analyzes changes in the number of fires detected on forest, grass, and transition lands during the 2002-2009 biomass burning seasons using fire detection data and co-located land cover classifications from the Moderate Resolution Imaging Spectroradiometer (MODIS). We find that the total number of detected fires correlates well with MODIS mean aerosol optical depth (AOD) from year to year, in accord with other studies. However, we also show that the ratio of forest to savanna fires varies substantially from year to year. Forest fires have trended downward, on average, since the beginning of 2006 despite a modest increase in 2007. Our study suggests that high particulate matter loading detected in 2007 was likely due to a large number of savanna/agricultural fires that year. Finally, we illustrate that the correlation between annual Brazilian deforestation estimates and MODIS fires is considerably higher when fires are stratified by MODIS-derived land cover classifications.
Brown, Adam J; Costopoulos, Charis; West, Nick Ej; Bennett, Martin R
2015-01-01
Atherosclerotic plaque rupture is responsible for the majority of myocardial infarctions, with ruptured plaques exhibiting specific morphological features, including large lipid cores, thinner overlying fibrous caps and micro-calcifications. Contemporary imaging modalities are increasingly able to characterize plaques, potentially leading to the identification of precursor lesions that are at high risk of rupture. Observational studies using invasive imaging consistently find that plaques responsible for an acute coronary event display these high-risk morphological features, and recent prospective imaging studies have now established links between baseline plaque characteristics and future cardiovascular events. Despite these promising advances, subsequent overall event rates remain too low for clinical utility. Novel technologies are now required to refine and improve our ability to identify and risk-stratify lesions at risk of rupture, if plaque-based risk evaluation is ever to become reality.
A study of refraction of a cylindrical laser beam in stratified liquid
Rinkevichyus, B. S.; Sapronov, M. V.; Pavlov, I. N.
2016-09-01
Refraction of a cylindrical laser beam in a transition layer at the interface of two liquids with different optical characteristics is studied theoretically and experimentally. A theoretical basis for calculations of the beam trajectory in the transition layer of stratified liquid is given. Two- and three-dimensional images (2D and 3D refractograms) of a cylindrical laser beam inside and outside the media are obtained on the basis of a tangential model of the refractive index profile. The influence of the parameters of the laser beam and media on the appearance of refractograms is studied and the optimal experimental conditions are selected with the use of computer simulation. A scheme of the setup for recording digital 2D refractogram and experimental results are presented. Algorithms for digitizing experimental images and for their comparison with calculated refractograms to determine the refractive index profile in the transition layer based on the tangential model are developed.
First detection of mycobacteria in African rodents and insectivores, using stratified pool screening
Durnez, L.; Eddyani, M.; Mgode, G. F.;
2007-01-01
With the rising number of patients with human immunodeficiency virus (HIV)/AIDS in developing countries, the control of mycobacteria is of growing importance. Previous studies have shown that rodents and insectivores are carriers of mycobacteria. However, it is not clear how widespread mycobacteria...... are in these animals and what their role is in spreading them. Therefore, the prevalence of mycobacteria in rodents and insectivores was studied in and around Morogoro, Tanzania. Live rodents were trapped, with three types of live traps, in three habitats. Pieces of organs were pooled per habitat, species, and organ...... spp.) were isolated from C. gambianus, Mastomys natalensis, and C. hirta. This study is the first to report findings of mycobacteria in African rodents and insectivores and the first in mycobacterial ecology to estimate the prevalence of mycobacteria after stratified pool screening. The fact...
Implications of the modelling of stratified hot water storage tanks in the simulation of CHP plants
Campos Celador, A., E-mail: alvaro.campos@ehu.es [ENEDI Research Group-University of the Basque Country, Departamento de Maquinas y Motores Termicos, E.T.S.I. de Bilbao Alameda de Urquijo, s/n 48013 Bilbao, Bizkaia (Spain); Odriozola, M.; Sala, J.M. [ENEDI Research Group-University of the Basque Country, Departamento de Maquinas y Motores Termicos, E.T.S.I. de Bilbao Alameda de Urquijo, s/n 48013 Bilbao, Bizkaia (Spain)
2011-08-15
Highlights: {yields} Three different modelling approaches for simulation of hot water tanks are presented. {yields} The three models are simulated within a residential cogeneration plant. {yields} Small differences in the results are found by an energy and exergy analysis. {yields} Big differences between the results are found by an advanced exergy analysis. {yields} Results on the feasibility study are explained by the advanced exergy analysis. - Abstract: This paper considers the effect that different hot water storage tank modelling approaches have on the global simulation of residential CHP plants as well as their impact on their economic feasibility. While a simplified assessment of the heat storage is usually considered in the feasibility studies of CHP plants in buildings, this paper deals with three different levels of modelling of the hot water tank: actual stratified model, ideal stratified model and fully mixed model. These three approaches are presented and comparatively evaluated under the same case of study, a cogeneration plant with thermal storage meeting the loads of an urbanisation located in the Bilbao metropolitan area (Spain). The case of study is simulated by TRNSYS for each one of the three modelling cases and the so obtained annual results are analysed from both a First and Second-Law-based viewpoint. While the global energy and exergy efficiencies of the plant for the three modelling cases agree quite well, important differences are found between the economic results of the feasibility study. These results can be predicted by means of an advanced exergy analysis of the storage tank considering the endogenous and exogenous exergy destruction terms caused by the hot water storage tank.
Risk stratification in acute heart failure: rationale and design of the STRATIFY and DECIDE studies.
Collins, Sean P; Lindsell, Christopher J; Jenkins, Cathy A; Harrell, Frank E; Fermann, Gregory J; Miller, Karen F; Roll, Sue N; Sperling, Matthew I; Maron, David J; Naftilan, Allen J; McPherson, John A; Weintraub, Neal L; Sawyer, Douglas B; Storrow, Alan B
2012-12-01
A critical challenge for physicians facing patients presenting with signs and symptoms of acute heart failure (AHF) is how and where to best manage them. Currently, most patients evaluated for AHF are admitted to the hospital, yet not all warrant inpatient care. Up to 50% of admissions could be potentially avoided and many admitted patients could be discharged after a short period of observation and treatment. Methods for identifying patients that can be sent home early are lacking. Improving the physician's ability to identify and safely manage low-risk patients is essential to avoiding unnecessary use of hospital beds. Two studies (STRATIFY and DECIDE) have been funded by the National Heart Lung and Blood Institute with the goal of developing prediction rules to facilitate early decision making in AHF. Using prospectively gathered evaluation and treatment data from the acute setting (STRATIFY) and early inpatient stay (DECIDE), rules will be generated to predict risk for death and serious complications. Subsequent studies will be designed to test the external validity, utility, generalizability and cost-effectiveness of these prediction rules in different acute care environments representing racially and socioeconomically diverse patient populations. A major innovation is prediction of 5-day as well as 30-day outcomes, overcoming the limitation that 30-day outcomes are highly dependent on unpredictable, post-visit patient and provider behavior. A novel aspect of the proposed project is the use of a comprehensive cardiology review to correctly assign post-treatment outcomes to the acute presentation. Finally, a rigorous analysis plan has been developed to construct the prediction rules that will maximally extract both the statistical and clinical properties of every data element. Upon completion of this study we will subsequently externally test the prediction rules in a heterogeneous patient cohort. Copyright © 2012 Mosby, Inc. All rights reserved.
TURBULENT TRANSPORT IN A STRONGLY STRATIFIED FORCED SHEAR LAYER WITH THERMAL DIFFUSION
Garaud, Pascale [Department of Applied Mathematics and Statistics, Baskin School of Engineering, University of California at Santa Cruz, 1156 High Street, Santa Cruz CA 95064 (United States)
2016-04-10
This work presents numerical results on the transport of heat and chemical species by shear-induced turbulence in strongly stratified, thermally diffusive environments. The shear instabilities driven in this regime are sometimes called “secular” shear instabilities, and can take place when the Richardson number of the flow is large, provided the Péclet number is small. We have identified a set of simple criteria to determine whether these instabilities can take place or not. Generally speaking, we find that they may be relevant whenever the thermal diffusivity of the fluid is very large (typically larger than 10{sup 14} cm{sup 2} s{sup −1}), which is the case in the outer layers of high-mass stars (M ≥ 10 M{sub ⊙}), for instance. Using a simple model setup in which the shear is forced by a spatially sinusoidal, constant-amplitude body-force, we have identified several regimes ranging from effectively unstratified to very strongly stratified, each with its own set of dynamical properties. Unless the system is in one of the two extreme regimes (effectively unstratified or completely stable), however, we find that (1) only about 10% of the input power is used toward heat transport, while the remaining 90% is viscously dissipated; (2) that the effective compositional mixing coefficient is well-approximated by the model of Zahn, with D ≃ 0.02κ{sub T}/J where κ{sub T} is the thermal diffusivity and J is the Richardson number. These results need to be confirmed, however, with simulations in different model setups and at higher effective Reynolds number.
A Prediction Rule to Stratify Mortality Risk of Patients with Pulmonary Tuberculosis
Osório, Nuno S.; Castro, António Gil; Ramos, Angélica; Carvalho, Teresa; Meira, Leonor; Araújo, David; Almeida, Leonor; Boaventura, Rita; Fragata, Patrícia; Chaves, Catarina; Costa, Patrício; Portela, Miguel; Ferreira, Ivo; Magalhães, Sara Pinto; Rodrigues, Fernando; Sarmento-Castro, Rui; Duarte, Raquel; Guimarães, João Tiago; Saraiva, Margarida
2016-01-01
Tuberculosis imposes high human and economic tolls, including in Europe. This study was conducted to develop a severity assessment tool for stratifying mortality risk in pulmonary tuberculosis (PTB) patients. A derivation cohort of 681 PTB cases was retrospectively reviewed to generate a model based on multiple logistic regression analysis of prognostic variables with 6-month mortality as the outcome measure. A clinical scoring system was developed and tested against a validation cohort of 103 patients. Five risk features were selected for the prediction model: hypoxemic respiratory failure (OR 4.7, 95% CI 2.8–7.9), age ≥50 years (OR 2.9, 95% CI 1.7–4.8), bilateral lung involvement (OR 2.5, 95% CI 1.4–4.4), ≥1 significant comorbidity—HIV infection, diabetes mellitus, liver failure or cirrhosis, congestive heart failure and chronic respiratory disease–(OR 2.3, 95% CI 1.3–3.8), and hemoglobin <12 g/dL (OR 1.8, 95% CI 1.1–3.1). A tuberculosis risk assessment tool (TReAT) was developed, stratifying patients with low (score ≤2), moderate (score 3–5) and high (score ≥6) mortality risk. The mortality associated with each group was 2.9%, 22.9% and 53.9%, respectively. The model performed equally well in the validation cohort. We provide a new, easy-to-use clinical scoring system to identify PTB patients with high-mortality risk in settings with good healthcare access, helping clinicians to decide which patients are in need of closer medical care during treatment. PMID:27636095
Invited Review. Combustion instability in spray-guided stratified-charge engines. A review
Fansler, Todd D. [Univ. of Wisconsin, Madison, WI (United States); Reuss, D. L. [Univ. of Michigan, Ann Arbor, MI (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States); Sick, V. [Univ. of Michigan, Ann Arbor, MI (United States); Dahms, R. N. [Sandia National Lab. (SNL-CA), Livermore, CA (United States)
2015-02-02
Our article reviews systematic research on combustion instabilities (principally rare, random misfires and partial burns) in spray-guided stratified-charge (SGSC) engines operated at part load with highly stratified fuel -air -residual mixtures. Results from high-speed optical imaging diagnostics and numerical simulation provide a conceptual framework and quantify the sensitivity of ignition and flame propagation to strong, cyclically varying temporal and spatial gradients in the flow field and in the fuel -air -residual distribution. For SGSC engines using multi-hole injectors, spark stretching and locally rich ignition are beneficial. Moreover, combustion instability is dominated by convective flow fluctuations that impede motion of the spark or flame kernel toward the bulk of the fuel, coupled with low flame speeds due to locally lean mixtures surrounding the kernel. In SGSC engines using outwardly opening piezo-electric injectors, ignition and early flame growth are strongly influenced by the spray's characteristic recirculation vortex. For both injection systems, the spray and the intake/compression-generated flow field influence each other. Factors underlying the benefits of multi-pulse injection are identified. Finally, some unresolved questions include (1) the extent to which piezo-SGSC misfires are caused by failure to form a flame kernel rather than by flame-kernel extinction (as in multi-hole SGSC engines); (2) the relative contributions of partially premixed flame propagation and mixing-controlled combustion under the exceptionally late-injection conditions that permit SGSC operation on E85-like fuels with very low NO_{x} and soot emissions; and (3) the effects of flow-field variability on later combustion, where fuel-air-residual mixing within the piston bowl becomes important.
A Prediction Rule to Stratify Mortality Risk of Patients with Pulmonary Tuberculosis.
Bastos, Helder Novais; Osório, Nuno S; Castro, António Gil; Ramos, Angélica; Carvalho, Teresa; Meira, Leonor; Araújo, David; Almeida, Leonor; Boaventura, Rita; Fragata, Patrícia; Chaves, Catarina; Costa, Patrício; Portela, Miguel; Ferreira, Ivo; Magalhães, Sara Pinto; Rodrigues, Fernando; Sarmento-Castro, Rui; Duarte, Raquel; Guimarães, João Tiago; Saraiva, Margarida
2016-01-01
Tuberculosis imposes high human and economic tolls, including in Europe. This study was conducted to develop a severity assessment tool for stratifying mortality risk in pulmonary tuberculosis (PTB) patients. A derivation cohort of 681 PTB cases was retrospectively reviewed to generate a model based on multiple logistic regression analysis of prognostic variables with 6-month mortality as the outcome measure. A clinical scoring system was developed and tested against a validation cohort of 103 patients. Five risk features were selected for the prediction model: hypoxemic respiratory failure (OR 4.7, 95% CI 2.8-7.9), age ≥50 years (OR 2.9, 95% CI 1.7-4.8), bilateral lung involvement (OR 2.5, 95% CI 1.4-4.4), ≥1 significant comorbidity-HIV infection, diabetes mellitus, liver failure or cirrhosis, congestive heart failure and chronic respiratory disease-(OR 2.3, 95% CI 1.3-3.8), and hemoglobin <12 g/dL (OR 1.8, 95% CI 1.1-3.1). A tuberculosis risk assessment tool (TReAT) was developed, stratifying patients with low (score ≤2), moderate (score 3-5) and high (score ≥6) mortality risk. The mortality associated with each group was 2.9%, 22.9% and 53.9%, respectively. The model performed equally well in the validation cohort. We provide a new, easy-to-use clinical scoring system to identify PTB patients with high-mortality risk in settings with good healthcare access, helping clinicians to decide which patients are in need of closer medical care during treatment.
Oh, Junho; Kim, Kue-Young; Han, Weon Shik; Park, Eungyu; Kim, Jeong-Chan
2015-10-01
Multiple scenarios of upward CO2 migration driven by both injection-induced pressure and buoyancy force were investigated in a horizontally and vertically stratified core utilizing a core-flooding system with a 2-D X-ray scanner. Two reservoir-type scenarios were considered: (1) the terrestrial reservoir scenario (10 MPa and 50°C), where CO2 exists in a supercritical state and (2) the deep-sea sediment reservoir scenario (28 MPa and 25°C), where CO2 is stored in the liquid phase. The core-flooding experiments showed a 36% increase in migration rate in the vertical core setting compared with the horizontal setting, indicating the significance of the buoyancy force under the terrestrial reservoir scenario. Under both reservoir conditions, the injected CO2 tended to find a preferential flow path (low capillary entry pressure and high-permeability (high-k) path) and bypass the unfavorable pathways, leaving low CO2 saturation in the low-permeability (low-k) layers. No distinctive fingering was observed as the CO2 moved upward, and the CO2 movement was primarily controlled by media heterogeneity. The CO2 saturation in the low-k layers exhibited a more sensitive response to injection rates, implying that the increase in CO2 injection rates could be more effective in terms of storage capacity in the low-k layers in a stratified reservoir. Under the deep-sea sediment condition, the storage potential of liquid CO2 was more than twice as high as that of supercritical CO2 under the terrestrial reservoir scenario. In the end, multiphase transport simulations were conducted to assess the effects of heterogeneity on the spatial variation of pressure buildup, CO2 saturation, and CO2 flux. Finally, we showed that a high gravity number (Ngr) tended to be more influenced by the heterogeneity of the porous media.
Phenomenology of two-dimensional stably stratified turbulence under large-scale forcing
Kumar, Abhishek
2017-01-11
In this paper, we characterise the scaling of energy spectra, and the interscale transfer of energy and enstrophy, for strongly, moderately and weakly stably stratified two-dimensional (2D) turbulence, restricted in a vertical plane, under large-scale random forcing. In the strongly stratified case, a large-scale vertically sheared horizontal flow (VSHF) coexists with small scale turbulence. The VSHF consists of internal gravity waves and the turbulent flow has a kinetic energy (KE) spectrum that follows an approximate k−3 scaling with zero KE flux and a robust positive enstrophy flux. The spectrum of the turbulent potential energy (PE) also approximately follows a k−3 power-law and its flux is directed to small scales. For moderate stratification, there is no VSHF and the KE of the turbulent flow exhibits Bolgiano–Obukhov scaling that transitions from a shallow k−11/5 form at large scales, to a steeper approximate k−3 scaling at small scales. The entire range of scales shows a strong forward enstrophy flux, and interestingly, large (small) scales show an inverse (forward) KE flux. The PE flux in this regime is directed to small scales, and the PE spectrum is characterised by an approximate k−1.64 scaling. Finally, for weak stratification, KE is transferred upscale and its spectrum closely follows a k−2.5 scaling, while PE exhibits a forward transfer and its spectrum shows an approximate k−1.6 power-law. For all stratification strengths, the total energy always flows from large to small scales and almost all the spectral indicies are well explained by accounting for the scale-dependent nature of the corresponding flux.
Modified STOP-Bang Tool for Stratifying Obstructive Sleep Apnea Risk in Adolescent Children.
Daniel Combs
Full Text Available Obstructive sleep apnea (OSA is prevalent in children and diagnostic polysomnography is costly and not readily available in all areas. We developed a pediatric modification of a commonly used adult clinical prediction tool for stratifying the risk of OSA and the need for polysomnography.A total of 312 children (age 9-17 years from phase 2 of the Tucson Children's Assessment of Sleep Apnea cohort study, with complete anthropomorphic data, parent questionnaires, and home polysomnograms were included. An adolescent modification of STOP-Bang (teen STOP-Bang was developed and included snoring, tired, observed apnea, blood pressure ≥ 95th percentile, BMI > 95th percentile, academic problems, neck circumference >95th percentile for age, and male gender. An apnea-hypopnea index ≥ 1.5 events/hour was considered diagnostic of OSA.Receiver Operator Characteristic (ROC curves for parent-reported STOP-Bang scores were generated for teenage and pre-teen children. A STOP-Bang score of < 3 in teenagers was associated with a negative predictive value of 0.96. ROC curves were also generated based upon child-reported sexual maturity rating (SMR; n = 291. The ability of teen STOP-Bang to discriminate the presence or absence of OSA as measured by the AUC for children with SMR ≥ 4 (0.83; 95%CI 0.71-0.95 was better than children with SMR < 4 (0.63; 95%CI 0.46-0.81; p = 0.048.In community dwelling adolescents, teen STOP-Bang may be useful in stratifying the risk of OSA.
Experimental study of stratified jet by simultaneous measurements of velocity and density fields
Xu, Duo; Chen, Jun
2012-07-01
Stratified flows with small density difference commonly exist in geophysical and engineering applications, which often involve interaction of turbulence and buoyancy effect. A combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) system is developed to measure the velocity and density fields in a dense jet discharged horizontally into a tank filled with light fluid. The illumination of PIV particles and excitation of PLIF dye are achieved by a dual-head pulsed Nd:YAG laser and two CCD cameras with a set of optical filters. The procedure for matching refractive indexes of two fluids and calibration of the combined system are presented, as well as a quantitative analysis of the measurement uncertainties. The flow structures and mixing dynamics within the central vertical plane are studied by examining the averaged parameters, turbulent kinetic energy budget, and modeling of momentum flux and buoyancy flux. At downstream, profiles of velocity and density display strong asymmetry with respect to its center. This is attributed to the fact that stable stratification reduces mixing and unstable stratification enhances mixing. In stable stratification region, most of turbulence production is consumed by mean-flow convection, whereas in unstable stratification region, turbulence production is nearly balanced by viscous dissipation. Experimental data also indicate that at downstream locations, mixing length model performs better in mixing zone of stable stratification regions, whereas in other regions, eddy viscosity/diffusivity models with static model coefficients represent effectively momentum and buoyancy flux terms. The measured turbulent Prandtl number displays strong spatial variation in the stratified jet.
Extent of atypical hyperplasia stratifies breast cancer risk in 2 independent cohorts of women.
Degnim, Amy C; Dupont, William D; Radisky, Derek C; Vierkant, Robert A; Frank, Ryan D; Frost, Marlene H; Winham, Stacey J; Sanders, Melinda E; Smith, Jeffrey R; Page, David L; Hoskin, Tanya L; Vachon, Celine M; Ghosh, Karthik; Hieken, Tina J; Denison, Lori A; Carter, Jodi M; Hartmann, Lynn C; Visscher, Daniel W
2016-10-01
Women with atypical hyperplasia (AH) on breast biopsy have a substantially increased risk of breast cancer (BC). Here the BC risk for the extent and subtype of AH is reported for 2 separate cohorts. All samples containing AH were included from 2 cohorts of women with benign breast disease (Mayo Clinic and Nashville). Histology review quantified the number of foci of atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH). The BC risk was stratified for the number of AH foci within AH subtypes. The study included 708 Mayo AH subjects and 466 Nashville AH subjects. In the Mayo cohort, an increasing number of foci of AH was associated with a significant increase in the risk of BC both for ADH (relative risks of 2.61, 5.21, and 6.36 for 1, 2, and ≥3 foci, respectively; P for linear trend = .006) and for ALH (relative risks of 2.56, 3.50, and 6.79 for 1, 2, and ≥3 foci, respectively; P for linear trend = .001). In the Nashville cohort, the relative risks of BC for ADH were 2.70, 5.17, and 15.06 for 1, 2, and ≥3 foci, respectively (P for linear trend < .001); for ALH, the relative risks also increased but not significantly (2.61, 3.48, and 4.02, respectively; P = .148). When the Mayo and Nashville samples were combined, the risk increased significantly for 1, 2, and ≥3 foci: the relative risks were 2.65, 5.19, and 8.94, respectively, for ADH (P < .001) and 2.58, 3.49, and 4.97, respectively, for ALH (P = .001). In 2 independent cohort studies of benign breast disease, the extent of atypia stratified the long-term BC risk for ADH and ALH. Cancer 2016;122:2971-2978. © 2016 American Cancer Society. © 2016 American Cancer Society.
Clinical prediction rule for stratifying risk of pulmonary multidrug-resistant tuberculosis.
Martínez, Dalila; Heudebert, Gustavo; Seas, Carlos; Henostroza, German; Rodriguez, Martin; Zamudio, Carlos; Centor, Robert M; Herrera, Cesar; Gotuzzo, Eduardo; Estrada, Carlos
2010-08-11
Multidrug-resistant tuberculosis (MDR-TB), resistance to at least isoniazid and rifampin, is a worldwide problem. To develop a clinical prediction rule to stratify risk for MDR-TB among patients with pulmonary tuberculosis. Derivation and internal validation of the rule among adult patients prospectively recruited from 37 health centers (Perú), either a) presenting with a positive acid-fast bacillus smear, or b) had failed therapy or had a relapse within the first 12 months. Among 964 patients, 82 had MDR-TB (prevalence, 8.5%). Variables included were MDR-TB contact within the family, previous tuberculosis, cavitary radiologic pattern, and abnormal lung exam. The area under the receiver-operating curve (AUROC) was 0.76. Selecting a cut-off score of one or greater resulted in a sensitivity of 72.6%, specificity of 62.8%, likelihood ratio (LR) positive of 1.95, and LR negative of 0.44. Similarly, selecting a cut-off score of two or greater resulted in a sensitivity of 60.8%, specificity of 87.5%, LR positive of 4.85, and LR negative of 0.45. Finally, selecting a cut-off score of three or greater resulted in a sensitivity of 45.1%, specificity of 95.3%, LR positive of 9.56, and LR negative of 0.58. A simple clinical prediction rule at presentation can stratify risk for MDR-TB. If further validated, the rule could be used for management decisions in resource-limited areas.
Clinical prediction rule for stratifying risk of pulmonary multidrug-resistant tuberculosis.
Dalila Martínez
Full Text Available BACKGROUND: Multidrug-resistant tuberculosis (MDR-TB, resistance to at least isoniazid and rifampin, is a worldwide problem. OBJECTIVE: To develop a clinical prediction rule to stratify risk for MDR-TB among patients with pulmonary tuberculosis. METHODS: Derivation and internal validation of the rule among adult patients prospectively recruited from 37 health centers (Perú, either a presenting with a positive acid-fast bacillus smear, or b had failed therapy or had a relapse within the first 12 months. RESULTS: Among 964 patients, 82 had MDR-TB (prevalence, 8.5%. Variables included were MDR-TB contact within the family, previous tuberculosis, cavitary radiologic pattern, and abnormal lung exam. The area under the receiver-operating curve (AUROC was 0.76. Selecting a cut-off score of one or greater resulted in a sensitivity of 72.6%, specificity of 62.8%, likelihood ratio (LR positive of 1.95, and LR negative of 0.44. Similarly, selecting a cut-off score of two or greater resulted in a sensitivity of 60.8%, specificity of 87.5%, LR positive of 4.85, and LR negative of 0.45. Finally, selecting a cut-off score of three or greater resulted in a sensitivity of 45.1%, specificity of 95.3%, LR positive of 9.56, and LR negative of 0.58. CONCLUSION: A simple clinical prediction rule at presentation can stratify risk for MDR-TB. If further validated, the rule could be used for management decisions in resource-limited areas.
Toneatti, Diego M.; Albarracín, Virginia H.; Flores, Maria R.; Polerecky, Lubos; Farías, María E.
2017-01-01
At an altitude of 3,570 m, the volcanic lake Socompa in the Argentinean Andes is presently the highest site where actively forming stromatolite-like structures have been reported. Interestingly, pigment and microsensor analyses performed through the different layers of the stromatolites (50 mm-deep) showed steep vertical gradients of light and oxygen, hydrogen sulfide and pH in the porewater. Given the relatively good characterization of these physico-chemical gradients, the aim of this follow-up work was to specifically address how the bacterial diversity stratified along the top six layers of the stromatolites which seems the most metabolically important and diversified zone of the whole microbial community. We herein discussed how, in only 7 mm, a drastic succession of metabolic adaptations occurred: i.e., microbial communities shift from a UV-high/oxic world to an IR-low/anoxic/high H2S environment which force stratification and metabolic specialization of the bacterial community, thus, modulating the chemical faces of the Socompa stromatolites. The oxic zone was dominated by Deinococcus sp. at top surface (0.3 mm), followed by a second layer of Coleofasciculus sp. (0.3 to ∼2 mm). Sequences from anoxygenic phototrophic Alphaproteobacteria, along with an increasing diversity of phyla including Bacteroidetes, Spirochaetes were found at middle layers 3 and 4. Deeper layers (5–7 mm) were mostly occupied by sulfate reducers of Deltaproteobacteria, Bacteroidetes and Firmicutes, next to a high diversity and equitable community of rare, unclassified and candidate phyla. This analysis showed how microbial communities stratified in a physicochemical vertical profile and according to the light source. It also gives an insight of which bacterial metabolic capabilities might operate and produce a microbial cooperative strategy to thrive in one of the most extreme environments on Earth. PMID:28446906
Surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea
Lincoln, B. J.; Rippeth, T. P.; Simpson, J. H.
2016-08-01
Inertial oscillations are a ubiquitous feature of the surface ocean. Here we combine new observations with a numerical model to investigate the role of inertial oscillations in driving deepening of the surface mixed layer in a seasonally stratified sea. Observations of temperature and current structure, from a mooring in the Western Irish Sea, reveal episodes of strong currents (>0.3 m s-1) lasting several days, resulting in enhanced shear across the thermocline. While the episodes of strong currents are coincident with windy periods, the variance in the shear is not directly related to the wind stress. The shear varies on a subinertial time scale with the formation of shear maxima lasting several hours occurring at the local inertial period of 14.85 h. These shear maxima coincide with the orientation of the surface current being at an angle of approximately 90° to the right of the wind direction. Observations of the water column structure during windy periods reveal deepening of the surface mixed layer in a series of steps which coincide with a period of enhanced shear. During the periods of enhanced shear gradient, Richardson number estimates indicate Ri-1 ≥ 4 at the base of the surface mixed layer, implying the deepening as a result of shear instability. A one-dimensional vertical exchange model successfully reproduces the magnitude and phase of the shear spikes as well as the step-like deepening. The observations and model results therefore identify the role of wind shear alignment as a key entrainment mechanism driving surface mixed layer deepening in a shallow, seasonally stratified sea.
Stratifying the risk of lymph node metastasis in undifferentiated-type early gastric cancer
Asakawa, Yukiko; Ohtaka, Masahiko; Maekawa, Shinya; Fukasawa, Mitsuharu; Nakayama, Yasuhiro; Yamaguchi, Tatsuya; Inoue, Taisuke; Uetake, Tomoyoshi; Sakamoto, Minoru; Sato, Tadashi; Kawaguchi, Yoshihiko; Fujii, Hideki; Mochizuki, Kunio; Hada, Masao; Oyama, Toshio; Yasumura, Tomotaka; Omata, Kosaku; Nishiyama, Atsushi; Naito, Keiichi; Hata, Hideo; Haba, Yoshiaki; Miyata, Kazuyuki; Saitoh, Haruhisa; Yamadera, Yoichi; Miura, Kazuo; Kawaoi, Akira; Abe, Tohru; Tsunoda, Hajime; Honda, Yuji; Kurosaki, Masayuki; Enomoto, Nobuyuki
2015-01-01
AIM: To study how lymph node metastasis (LNM) risk is stratified in undifferentiated-type early gastric cancer (undiff-EGC) dependent on combinations of risk factors. METHODS: Five hundred and sixty-seven cases with undiff-EGC undergoing gastrectomy with lymphadenectomy were examined retrospectively. Using clinicopathological factors of patient age, location, size, an endoscopic macroscopic tumor form, ulceration, depth, histology, lymphatic involvement (LI) and venous involvement (VI), LNM risk was examined and stratified by conventional statistical analysis and data-mining analysis. RESULTS: LNM was positive in 44 of 567 cases (7.8%). Univariate analysis revealed > 2 cm, protrusion, submucosal (sm), mixed type, LI and VI as significant prognostic factors and > 2 cm and LI-positive were independent factors by multivariate analysis. In preoperatively evaluable factors excluding LVI, sm and > 2 cm were independent factors. According to the depth and size, cases were categorized into the low-risk group [m and ≤ 2 cm, 0% (LNM incidence)], the moderate-risk group (m and > 2 cm, 5.6%; and sm and ≤ 2 cm, 6.0%), and the high-risk group (sm and > 2 cm, 19.3%). On the other hand, LNM occurred in 1.4% in all LI-negative cases, greatly lower than 28.2% in all LI-positive cases, and LNM incidence was low in LI-negative cases even in the moderate- and high-risk groups. CONCLUSION: LNM-related factors in undiff-EGC were depth and size preoperatively while those were LI and size postoperatively. Among these factors, LI was the most significantly correlated factor. PMID:25759537
Vallee, Christophe
2012-08-22
Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with highresolution in space and time as needed for CFD code validation. Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results. The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at
Weijia Xing
2010-05-01
Full Text Available BACKGROUND: Outbreaks of emerging infectious diseases, especially those of a global nature, require rapid epidemiological analysis and information dissemination. The final products of those activities usually comprise internal memoranda and briefs within public health authorities and original research published in peer-reviewed journals. Using the 2003 severe acute respiratory syndrome (SARS epidemic as an example, we conducted a comprehensive time-stratified review of the published literature to describe the different types of epidemiological outputs. METHODS AND FINDINGS: We identified and analyzed all published articles on the epidemiology of the SARS outbreak in Hong Kong or Toronto. The analysis was stratified by study design, research domain, data collection, and analytical technique. We compared the SARS-case and matched-control non-SARS articles published according to the timeline of submission, acceptance, and publication. The impact factors of the publishing journals were examined according to the time of publication of SARS articles, and the numbers of citations received by SARS-case and matched-control articles submitted during and after the epidemic were compared. Descriptive, analytical, theoretical, and experimental epidemiology concerned, respectively, 54%, 30%, 11%, and 6% of the studies. Only 22% of the studies were submitted, 8% accepted, and 7% published during the epidemic. The submission-to-acceptance and acceptance-to-publication intervals of the SARS articles submitted during the epidemic period were significantly shorter than the corresponding intervals of matched-control non-SARS articles published in the same journal issues (p<0.001 and p<0.01, respectively. The differences of median submission-to-acceptance intervals and median acceptance-to-publication intervals between SARS articles and their corresponding control articles were 106.5 d (95% confidence interval [CI] 55.0-140.1 and 63.5 d (95% CI 18
Vincze, Miklos; Harlander, Uwe; Gal, Patrice Le
2016-01-01
A water-filled differentially heated rotating annulus with initially prepared stable vertical salinity profiles is studied in the laboratory. Based on two-dimensional horizontal particle image velocimetry (PIV) data, and infrared camera visualizations, we describe the appearance and the characteristics of the baroclinic instability in this original configuration. First, we show that when the salinity profile is linear and confined between two non stratified layers at top and bottom, only two separate shallow fluid layers can be destabilized. These unstable layers appear nearby the top and the bottom of the tank with a stratified motionless zone between them. This laboratory arrangement is thus particularly interesting to model geophysical or astrophysical situations where stratified regions are often juxtaposed to convective ones. Then, for more general but stable initial density profiles, statistical measures are introduced to quantify the extent of the baroclinic instability at given depths and to analyze t...
Sung, Chang Kyung [Korea Electric Power Research Institute, Taejon (Korea, Republic of)
1997-12-31
This paper presents a theoretical approach of the instability criterion from stratified to nonstratified flow in horizontal pipe at cocurrent flow conditions. The new theoretical instability criterion for the stratified and nonstratified flow transition in horizontal pipe has been developed by hyperbolic equations in two-phase flow. Critical flow condition criterion and onset of slugging at cocurrent flow condition correspond to zero and imaginary characteristics which occur when the hyperbolicity of a stratified two-phase flow is broken, respectively. Through comparison between results predicted by the present flow is broken, respectively. Through comparison between results predicted by the present theory and the Kukita et al. [1] experimental data of pipes, it is shown that they are in good agreement with data. 4 refs., 2 figs. (Author)
E. J. Suarez-Dominguez
2016-12-01
Full Text Available Production of heavy crude oil in Mexico, and worldwide, is increasing which has led to the application of different methods to reduce viscosity or to enhance transport through stratified flow to continue using the existing infrastructures. In this context, injecting a viscosity improver that does not mix completely with the crude, establishes a liquid-liquid stratified flow. On the basis of a parallel plates model, comparing the increase of flow that occurs in the one-phase case which assumes a complete mixture between the crude and the viscosity improver against another stratified liquid-liquid (no mixing between the oil and compared improver; it was found that in both cases there is a flow increase for the same pressure drop with a maximum for the case in which the flow improver is between the plates and the crude.
Latour, G; Elias, M; Frigerio, J M
2007-10-01
The diffuse reflectance spectra and the trichromatic coordinates of diffusing stratified paints are modeled. Each layer contains its own pigments, and their optical properties are first determined from experiments. The radiative transfer equation is then solved by the auxiliary function method for modeling the total light scattered by the stratified systems. The results are in good agreement with experimental spectra and validate the modeling. The calculations are then applied on the same stratified systems to study the influence of the observation angle in a bidirectional configuration and to study the influence of the thickness of the layers in a given configuration. In both cases, the reflectance spectra and the trichromatic coordinates are calculated and compared.
L-fuzzy Stratified Order-preserving Operator Space%L-fuzzy层保序算子空间
吴修云
2011-01-01
在L拓扑空间中引入层保序算子、层连续等概念,讨论他们的基本性质,给出了它们的特征性质刻画.说明了可拓扑生成的层保序算子拓扑空间与一般拓扑中的保序算子空间之间的关系.%In this paper, the concepts of stratified order-preserving operators, stratified continuity are introduced in L-topological spaces. Their basic properties are discussed, and their characteristic properties are observed. The relationship between inducible stratified order-preserving topological spaces and general order-preserving operator topological spaces is studied.
De Colle, Fabio; Granot, Jonathan; Lopez-Camara, Diego
2011-01-01
The dynamics of GRB jets during the afterglow phase is most reliably and accurately modelled using hydrodynamic simulations. All published simulations, however, have considered only a uniform external medium, while a stratified external medium is expected around long duration GRB progenitors. Here we present simulations of the dynamics of GRB jets and the resulting afterglow emission for both uniform and stratified external media with $\\rho \\propto r^{-k}$ for k = 0, 1, 2. The simulations are performed in 2D using the special relativistic version of the Mezcal code. The dynamics for stratified external media are broadly similar to those derived for expansion into a uniform external medium. The jet half-opening angle start increasing logarithmically with time once the Lorentz factor drops below 1/theta_0. For larger k values the lateral expansion is faster at early times and slower at late times with the jet expansion becoming Newtonian and slowly approaching spherical symmetry over progressively longer timesc...
Muroki, T. [Kanagawa Inst. of Technology, Dept. of Mechanical Engineering, Kanagawa (Japan); Moriyoshi, Y. [Chiba Univ., Dept. of Electronics and Mechanical Engineering, Chiba (Japan)
2000-11-01
In a stratified charge engine, a glow plug pilot flame ignition system has been compared with a spark-ignition system for a model stratified charge Wankel combustion chamber. A motored two-stroke diesel engine was operated as a rapid compression and expansion machine with the cylinder head replaced by a model Wankel combustion chamber designed to simulate the temporal changes of air flow and pressure fields inside the chamber of an actual engine. It was found that the pilot flame ignition system had better ignitability and improved combustion characteristics, especially in the lean mixture range, relative to the spark-ignition system. (Author)
Macia, R.; Correig, A.M.
1987-01-01
Seismic wave propagation is described by a second order differential equation for medium desplacement. By Fourier transforming with respect to time and space, wave equation transforms into a system of first order linear differential equations for the Fourier transform of displacement and stress. This systen of differential equations is solved by means of Matrx Propagator and applied to the propagation of body waves in stratified media. The matrix propagators corresponding to P-SV and SH waves in homogeneous medium are found as an intermediate step to obtain the spectral response of body waves propagating through a stratified medium with homogeneous layers. (Author)
Vertical stratification of bacteria and archaea in sediments of a boreal stratified humic lake
Rissanen, Antti J.; Mpamah, Promise; Peura, Sari; Taipale, Sami; Biasi, Christina; Nykänen, Hannu
2015-04-01
Boreal stratified humic lakes, with steep redox gradients in the water column and in the sediment, are important sources of methane (CH4) to the atmosphere. CH4 flux from these lakes is largely controlled by the balance between CH4-production (methanogenesis), which takes place in the organic rich sediment and in the deepest water layers, and CH4-consumption (methanotrophy), which takes place mainly in the water column. While there is already some published information on the activity, diversity and community structure of bacteria in the water columns of these lakes, such information on sediment microbial communities is very scarce. This study aims to characterize the vertical variation patterns in the diversity and the structure of microbial communities in sediment of a boreal stratified lake. Particular focus is on microbes with the potential to contribute to methanogenesis (fermentative bacteria and methanogenic archaea) and to methanotrophy (methanotrophic bacteria and archaea). Two sediment cores (26 cm deep), collected from the deepest point (~6 m) of a small boreal stratified lake during winter-stratification, were divided into depth sections of 1 to 2 cm for analyses. Communities were studied from DNA extracted from sediment samples by next-generation sequencing (Ion Torrent) of polymerase chain reaction (PCR) - amplified bacterial and archaeal 16S rRNA gene amplicons. The abundance of methanogenic archaea was also specifically studied by quantitative-PCR of methyl coenzyme-M reductase gene (mcrA) amplicons. Furthermore, the community structure and the abundance of bacteria were studied by phospholipid fatty acid (PLFA) analysis. Dominant potential fermentative bacteria belonged to families Syntrophaceae, Clostridiaceae and Peptostreptococcaceae. There were considerable differences in the vertical distribution among these groups. The relative abundance of Syntrophaceae started to increase from the sediment surface, peaked at depth layer from 5 to 10 cm (up
Helicity, geostrophic balance and mixing in rotating stratified turbulence: a multi-scale problem
Pouquet, A.; Marino, R.; Mininni, P.; Rorai, C.; Rosenberg, D. L.
2012-12-01
Helicity, geostrophic balance and mixing in rotating stratified turbulence: a multi-scale problem A. Pouquet, R. Marino, P. D. Mininni, C. Rorai & D. Rosenberg, NCAR Interactions between winds and waves have important roles in planetary and oceanic boundary layers, affecting momentum, heat and CO2 transport. Within the Abyssal Southern Ocean at Mid latitude, this may result in a mixed layer which is too shallow in climate models thereby affecting the overall evolution because of poor handling of wave breaking as in Kelvin-Helmoltz instabilities: gravity waves couple nonlinearly on slow time scales and undergo steepening through resonant interactions, or due to the presence of shear. In the oceans, sub-mesoscale frontogenesis and significant departure from quasi-geostrophy can be seen as turbulence intensifies. The ensuing anomalous vertical dispersion may not be simply modeled by a random walk, due to intermittent structures, wave propagation and to their interactions. Conversely, the energy and seeds required for such intermittent events to occur, say in the stable planetary boundary layer, may come from the wave field that is perturbed, or from winds and the effect of topography. Under the assumption of stationarity, weak nonlinearities, dissipation and forcing, one obtains large-scale geostrophic balance linking pressure gradient, gravity and Coriolis force. The role of helicity (velocity-vorticity correlations) has not received as much attention, outside the realm of astrophysics when considering the growth of large-scale magnetic fields. However, it is measured routinely in the atmosphere in order to gauge the likelihood of supercell convective storms to strengthen, and it may be a factor to consider in the formation of hurricanes. In this context, we examine the transition from a wave-dominated regime to an isotropic small-scale turbulent one in rotating flows with helical forcing. Using a direct numerical simulation (DNS) on a 3072^3 grid with Rossby and
Kreitinger, Elizabeth A.; Kappel, William M.
2014-01-01
The Village of Endicott, New York, is seeking an alternate source of public drinking water with the potential to supplement their current supply, which requires treatment due to legacy contamination. The southerly-draining Nanticoke Creek valley, located north of the village, was identified as a potential water source and the local stratified-drift (valley fill) aquifer was investigated to determine its hydrogeologic and water-quality characteristics. Nanticoke Creek and its aquifer extend from the hamlet of Glen Aubrey, N.Y., to the village of Endicott, a distance of about 15 miles, where it joins the Susquehanna River and its aquifer. The glacial sediments that comprise the stratified-drift aquifer vary in thickness and are generally underlain by glacial till over Devonian-aged shale and siltstone. Groundwater is more plentiful in the northern part of the aquifer where sand and gravel deposits are generally more permeable than in the southern part of the aquifer where less-permeable unconsolidated deposits are found. Generally there is enough groundwater to supply most homeowner wells and in some cases, supply small public-water systems such as schools, mobile-home parks, and small commercial/industrial facilities. The aquifer is recharged by precipitation, runoff, and tributary streams. Most tributary streams flowing across alluvial deposits lose water to the aquifer as they flow off of their bedrock-lined channels and into the more permeable alluvial deposits at the edges of the valley. The quality of both surface water and groundwater is generally good. Some water wells do have water-quality issues related to natural constituents (manganese and iron) and several homeowners noted either the smell and (or) taste of hydrogen sulfide in their drinking water. Dissolved methane concentrations from five drinking-water wells were well below the potentially explosive value of 28 milligrams per liter. Samples from surface and groundwater met nearly all State and Federal
Self-protection and self-similarity of the stably-stratified geophysical turbulence
Zilitinkevich, Sergej; Kleeorin, Nathan; Rogachevskii, Igor
2014-05-01
Following Richardson (1920), the effect of stratification on the shear-generated geophysical turbulence is determined by the gradient Richardson number Ri = (N/S)2, where Nis the Brunt-Vaisala frequency, S = dU/dz is vertical shear of the mean wind/current velocity U, and z is vertical coordinate. The concept of Richardson-number similarity postulates that dimensionless characteristics of turbulence are universal functions of Ri. Monin and Obukhov (1954) have proposed for the atmospheric surface layer a widely recognised Monin-Obukhov similarity theory (MOST). This theory postulates that dimensionless characteristics of turbulence are fully determined by the ratio z/L, where L = -u*3/Fb is the Obukhov length scale, u* is friction velocity and Fb is vertical turbulent flux of buoyancy. Nieuwstadt (1984) has employed local,z-dependent values of Fb and u* instead of the surface values, and demonstrated applicability of such version of MOST to the almost entire stably stratified planetary boundary layer. MOST is consistent with the Ri-similarity: in the surface layer Ri is a monotonously increasing function of z/L and vice versa (e.g., Sorbjan, 2010). In the strongly unstable stratification, MOST and Ri-similarity fail because of the self-organisation of convective turbulence (Elperin et al., 2006; Zilitinkevich et al., 2006). In this paper we employ the EFB turbulence closure theory (Zilitinkevich et al, 2013) together with available experimental, LES and DNS data to explain the most puzzling feature of the stably stratified geophysical turbulence, namely, its self-protection in very stable stratification, due to the counter-gradient heat-transfer mechanism missed in the traditional theory. We also explain the self-similarity of turbulence, due to the Kolmogorov's nature of dissipation for the turbulent kinetic energy (TKE), turbulent potential energy (TPE) and turbulent fluxes of heat and momentum. In non-steady regimes, traditional similarity criteria, such as z
Advantages of vertically adaptive coordinates in numerical models of stratified shelf seas
Gräwe, Ulf; Holtermann, Peter; Klingbeil, Knut; Burchard, Hans
2015-08-01
Shelf seas such as the North Sea and the Baltic Sea are characterised by spatially and temporally varying stratification that is highly relevant for their physical dynamics and the evolution of their ecosystems. Stratification may vary from unstably stratified (e.g., due to convective surface cooling) to strongly stratified with density jumps of up to 10 kg/m3 per m (e.g., in overflows into the Baltic Sea). Stratification has a direct impact on vertical turbulent transports (e.g., of nutrients) and influences the entrainment rate of ambient water into dense bottom currents which in turn determine the stratification of and oxygen supply to, e.g., the central Baltic Sea. Moreover, the suppression of the vertical diffusivity at the summer thermocline is one of the limiting factors for the vertical exchange of nutrients in the North Sea. Due to limitations of computational resources and since the locations of such density jumps (either by salinity or temperature) are predicted by the model simulation itself, predefined vertical coordinates cannot always reliably resolve these features. Thus, all shelf sea models with a predefined vertical coordinate distribution are inherently subject to under-resolution of the density structure. To solve this problem, Burchard and Beckers (2004) and Hofmeister et al. (2010) developed the concept of vertically adaptive coordinates for ocean models, where zooming of vertical coordinates at locations of strong stratification (and shear) is imposed. This is achieved by solving a diffusion equation for the position of the coordinates (with the diffusivity being proportional to the stratification or shear frequencies). We will show for a coupled model system of the North Sea and the Baltic Sea (resolution ˜ 1.8 km) how numerical mixing is substantially reduced and model results become significantly more realistic when vertically adaptive coordinates are applied. We additionally demonstrate that vertically adaptive coordinates perform well
Cross-stratified Facies Observed by the Mars Science Laboratory Rover at Gale Crater, Mars
Edgar, Lauren; Rubin, Dave; Grotzinger, John; Bell, Jim; Calef, Fred; Dromart, Gilles; Gupta, Sanjeev; Kah, Linda; Lewis, Kevin; Mangold, Nicolas; Schieber, Jurgen; Stack, Katie; Sumner, Dawn; MSL Science Team
2013-04-01
The Mars Science Laboratory Curiosity rover has investigated a number of sedimentary rock outcrops since landing in Gale crater. From the Rocknest location, during sols 59 to 100, Curiosity observed a range of cross-bedded deposits spanning more than 60 m in lateral extent. Cross-bedding is best exposed in an ~80-cm-thick outcrop known as Shaler. Observations using the Mast Cameras of cross-bedding both at Shaler and Rocknest enabled the recognition of several distinct cross-bedded facies. Analysis of cross-bedding geometries provides insight into the depositional environment. On the basis of inferred grain size, erosional resistance, color, and sedimentary structures, we have identified four facies: 1) resistant cross-stratified facies, 2) smooth, fine-grained cross-stratified facies, 3) dark gray, pitted facies, and 4) recessive, vertically fractured facies. Sedimentary structures include simple and compound cross-bedding, angular discontinuities between lamina sets, and potential soft-sediment deformation. Trough cross-bedding suggests that bedforms had sinuous crestlines. Cross-bed sets range from centimeter to decimeter in scale. Small cm-scale climbing ripples were identified in the vicinity of Rocknest. Where climbing bedforms are visible, they climb at subcritical angles, resulting in preservation of only the lee slopes. Analysis of cross-bedding dip directions indicate a range of sediment transport directions. Grain transport under turbulent flows was required to produce the observed cross-bedded facies. We consider three possible depositional environments: eolian, fluvial, and pyroclastic surge. Pyroclastic surge deposits often contain bedforms with supercritical angles of climb, evidence for unidirectional transport radially away from a point source, contain volcanic indicators such as bombs and accretionary lapilli, and display distinct trends in grain size and facies from proximal to distal deposits or in vertical section. These characteristics do not
Differences in Gene-Gene Interactions in Graves' Disease Patients Stratified by Age of Onset.
Beata Jurecka-Lubieniecka
Full Text Available Graves' disease (GD is a complex disease in which genetic predisposition is modified by environmental factors. Each gene exerts limited effects on the development of autoimmune disease (OR = 1.2-1.5. An epidemiological study revealed that nearly 70% of the risk of developing inherited autoimmunological thyroid diseases (AITD is the result of gene interactions. In the present study, we analyzed the effects of the interactions of multiple loci on the genetic predisposition to GD. The aim of our analyses was to identify pairs of genes that exhibit a multiplicative interaction effect.A total of 709 patients with GD were included in the study. The patients were stratified into more homogeneous groups depending on the age at time of GD onset: younger patients less than 30 years of age and older patients greater than 30 years of age. Association analyses were performed for genes that influence the development of GD: HLADRB1, PTPN22, CTLA4 and TSHR. The interactions among polymorphisms were analyzed using the multiple logistic regression and multifactor dimensionality reduction (MDR methods.GD patients stratified by the age of onset differed in the allele frequencies of the HLADRB1*03 and 1858T polymorphisms of the PTPN22 gene (OR = 1.7, p = 0.003; OR = 1.49, p = 0.01, respectively. We evaluated the genetic interactions of four SNPs in a pairwise fashion with regard to disease risk. The coexistence of HLADRB1 with CTLA4 or HLADRB1 with PTPN22 exhibited interactions on more than additive levels (OR = 3.64, p = 0.002; OR = 4.20, p < 0.001, respectively. These results suggest that interactions between these pairs of genes contribute to the development of GD. MDR analysis confirmed these interactions.In contrast to a single gene effect, we observed that interactions between the HLADRB1/PTPN22 and HLADRB1/CTLA4 genes more closely predicted the risk of GD onset in young patients.
Rapaka, Narsimha R.; Sarkar, Sutanu
2016-10-01
A sharp-interface Immersed Boundary Method (IBM) is developed to simulate density-stratified turbulent flows in complex geometry using a Cartesian grid. The basic numerical scheme corresponds to a central second-order finite difference method, third-order Runge-Kutta integration in time for the advective terms and an alternating direction implicit (ADI) scheme for the viscous and diffusive terms. The solver developed here allows for both direct numerical simulation (DNS) and large eddy simulation (LES) approaches. Methods to enhance the mass conservation and numerical stability of the solver to simulate high Reynolds number flows are discussed. Convergence with second-order accuracy is demonstrated in flow past a cylinder. The solver is validated against past laboratory and numerical results in flow past a sphere, and in channel flow with and without stratification. Since topographically generated internal waves are believed to result in a substantial fraction of turbulent mixing in the ocean, we are motivated to examine oscillating tidal flow over a triangular obstacle to assess the ability of this computational model to represent nonlinear internal waves and turbulence. Results in laboratory-scale (order of few meters) simulations show that the wave energy flux, mean flow properties and turbulent kinetic energy agree well with our previous results obtained using a body-fitted grid (BFG). The deviation of IBM results from BFG results is found to increase with increasing nonlinearity in the wave field that is associated with either increasing steepness of the topography relative to the internal wave propagation angle or with the amplitude of the oscillatory forcing. LES is performed on a large scale ridge, of the order of few kilometers in length, that has the same geometrical shape and same non-dimensional values for the governing flow and environmental parameters as the laboratory-scale topography, but significantly larger Reynolds number. A non-linear drag law
Rodgers-Lee, Donna; Downes, Turlough P
2016-01-01
The redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disk (PPD) evolution. The magnetorotational instability (MRI) is considered a likely mechanism. We present the results of a study involving multifluid global simulations including Ohmic dissipation, ambipolar diffusion and the Hall effect in a dynamic, self-consistent way. We focus on the turbulence resulting from the non-linear development of the MRI in radially stratified PPDs and compare with ideal MHD simulations. In the multifluid simulations the disk is initially set up to transition from a weak Hall dominated regime, where the Hall effect is the dominant non-ideal effect but approximately the same as or weaker than the inductive term, to a strong Hall dominated regime, where the Hall effect dominates the inductive term. As the simulations progress a substantial portion of the disk develops into a weak Hall dominated disk. We find a transition from turbulent to laminar flow in the inner regions of th...
Dolgin, Madlena; Einziger, Pinchas D
2010-05-01
Image reconstruction in electrical impedance tomography is, generally, an ill-posed nonlinear inverse problem. Regularization methods are widely used to ensure a stable solution. Herein, we present a case study, which uses a novel electrical impedance tomography method for reconstruction of layered biological tissues with piecewise continuous plane-stratified profiles. The algorithm implements the recently proposed reconstruction scheme for piecewise constant conductivity profiles, utilizing Legendre expansion in conjunction with improved Prony method. It is shown that the proposed algorithm is capable of successfully reconstructing piecewise continuous conductivity profiles with moderate slop. This reconstruction procedure, which calculates both the locations and the conductivities, repetitively provides inhomogeneous depth discretization, i.e., the depths grid is not equispaced. Incorporation of this specific inhomogeneous grid in the widely used mean least square reconstruction procedure results in a stable and accurate reconstruction, whereas, the commonly selected equispaced depth grid leads to unstable reconstruction. This observation establishes the main result of our investigation, highlighting the impact of physical phenomenon (the image series expansion) on electrical impedance tomography, leading to a physically motivated stabilization of the inverse problem, i.e., an inhomogeneous depth discretization renders an inherent regularization of the mean least square algorithm. The effectiveness and the significance of inhomogeneous discretization in electrical impedance tomography reconstruction procedure is further demonstrated and verified via numerical simulations.
Long ring waves in a stratified fluid over a shear flow
Khusnutdinova, K R
2014-01-01
Oceanic waves registered by satellite observations often have curvilinear fronts and propagate over various currents. In this paper, we study long linear and weakly-nonlinear ring waves in a stratified fluid in the presence of a depth-dependent horizontal shear flow. It is shown that despite the clashing geometries of the waves and the shear flow, there exists a linear modal decomposition (different from the known decomposition in Cartesian geometry), which can be used to describe distortion of the wavefronts of surface and internal waves, and systematically derive a 2+1 - dimensional cylindrical Korteweg - de Vries - type equation for the amplitudes of the waves. The general theory is applied to the case of the waves in a two-layer fluid with a piecewise - constant shear flow, with an emphasis on the effect of the shear flow on the geometry of the wavefronts. The distortion of the wavefronts is described by the singular solution (envelope of the general solution) of the nonlinear first-order differential equ...
CFD Code Validation against Stratified Air-Water Flow Experimental Data
F. Terzuoli
2008-01-01
Full Text Available Pressurized thermal shock (PTS modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV lifetime is the cold water emergency core cooling (ECC injection into the cold leg during a loss of coolant accident (LOCA. Since it represents a big challenge for numerical simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM Integrated Project as a reference two-phase problem for computational fluid dynamics (CFDs code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mécanique des Fluides de Toulouse in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX, and a research code (NEPTUNE CFD. The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag modelling.
Stability of 3D Gaussian vortices in rotating stratified Boussinesq flows: Linear analysis
Mahdinia, Mani; Jiang, Chung-Hsiang
2016-01-01
The linear stability of three-dimensional (3D) vortices in rotating, stratified flows has been studied by analyzing the non-hydrostatic inviscid Boussinesq equations. We have focused on a widely-used model of geophysical and astrophysical vortices, which assumes an axisymmetric Gaussian structure for pressure anomalies in the horizontal and vertical directions. For a range of Rossby number ($-0.5 < Ro < 0.5$) and Burger number ($0.02 < Bu < 2.3$) relevant to observed long-lived vortices, the growth rate and spatial structure of the most unstable eigenmodes have been numerically calculated and presented as a function of $Ro-Bu$. We have found neutrally-stable vortices only over a small region of the $Ro-Bu$ parameter space: cyclones with $Ro \\sim 0.02-0.05$ and $Bu \\sim 0.85-0.95$. However, we have also found that anticyclones in general have slower growth rates compared to cyclones. In particular, growth rate of the most unstable eigenmode for anticyclones in a large region of the parameter space ...
Adsorptive Removal of Para-chlorophenol Using Stratified Tapered Activated Carbon Column
M.EE Sze; G. McKay
2012-01-01
The feasibility of adsorptive removal of single component organic compound （para-chlorophenol） by Calgon Filtrasorb 400 （F400） carbon was investigated. The Redlich-Peterson equation was found to be the best fit model for describing the equilibrium relationship between the para-chlorophenol adsorption onto F400 carbon. Four adsorption columns with different column geometry and adsorbent particle stratification were used to examine the adsorption kinetics onto F400 carbons. The Bed Depth Service Time （BDST） model was applied and modified to analyse the performance of the columns and the effect of different operating variables. When combining the effects of adsorption efficiency and the associated pressure drop of each type of adsorption columns tested, the carbon stratified tapered column has been determined to be the most efficient engineering option for removing organics, in which the enhancement of the adsorbent bed in terms of longer breakthrough time and higher saturation percentage is the greatest amongst the four types of columns with reasonably small pressure drop across the fixed-bed column.
Stratified spectral mixture analysis of medium resolution imagery for impervious surface mapping
Sun, Genyun; Chen, Xiaolin; Ren, Jinchang; Zhang, Aizhu; Jia, Xiuping
2017-08-01
Linear spectral mixture analysis (LSMA) is widely employed in impervious surface estimation, especially for estimating impervious surface abundance in medium spatial resolution images. However, it suffers from a difficulty in endmember selection due to within-class spectral variability and the variation in the number and the type of endmember classes contained from pixel to pixel, which may lead to over or under estimation of impervious surface. Stratification is considered as a promising process to address the problem. This paper presents a stratified spectral mixture analysis in spectral domain (Sp_SSMA) for impervious surface mapping. It categorizes the entire data into three groups based on the Combinational Build-up Index (CBI), the intensity component in the color space and the Normalized Difference Vegetation Index (NDVI) values. A suitable endmember model is developed for each group to accommodate the spectral variation from group to group. The unmixing into the associated subset (or full set) of endmembers in each group can make the unmixing adaptive to the types of endmember classes that each pixel actually contains. Results indicate that the Sp_SSMA method achieves a better performance than full-set-endmember SMA and prior-knowledge-based spectral mixture analysis (PKSMA) in terms of R, RMSE and SE.
Patel, Sejal; Park, Min Tae M; Chakravarty, M Mallar; Knight, Jo
2016-01-01
Imaging genetics is an emerging field in which the association between genes and neuroimaging-based quantitative phenotypes are used to explore the functional role of genes in neuroanatomy and neurophysiology in the context of healthy function and neuropsychiatric disorders. The main obstacle for researchers in the field is the high dimensionality of the data in both the imaging phenotypes and the genetic variants commonly typed. In this article, we develop a novel method that utilizes Gene Ontology, an online database, to select and prioritize certain genes, employing a stratified false discovery rate (sFDR) approach to investigate their associations with imaging phenotypes. sFDR has the potential to increase power in genome wide association studies (GWAS), and is quickly gaining traction as a method for multiple testing correction. Our novel approach addresses both the pressing need in genetic research to move beyond candidate gene studies, while not being overburdened with a loss of power due to multiple testing. As an example of our methodology, we perform a GWAS of hippocampal volume using both the Enhancing NeuroImaging Genetics through Meta-Analysis (ENIGMA2) and the Alzheimer's Disease Neuroimaging Initiative datasets. The analysis of ENIGMA2 data yielded a set of SNPs with sFDR values between 10 and 20%. Our approach demonstrates a potential method to prioritize genes based on biological systems impaired in a disease.
Interfacial friction factors for air-water co-current stratified flow in inclined channels
Choi, Ki Yong; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)
1997-12-31
The interfacial shear stress is experimentally investigated for co-current air-water stratified flow in inclined rectangular channels having a length of 1854mm, width of 120 mm and height of 40mm at almost atmospheric pressure. Experiments are carried out in several inclinations from 0 deg up to 10 deg. The local film thickness and the wave height are measured at three locations, i.e., L/H = 8,23, and 40. According to the inclination angle, the experimental data are categorized into two groups; nearly horizontal data group (0 deg {<=} {theta} {<=} 0.7 deg), and inclined channel data group (0.7 deg {<=} {theta} {<=} 10 deg ). Experimental observations for nearly horizontal data group show that the flow is not fully developed due to the water level gradient and the hydraulic jump within the channel. For the inclined channel data group, a dimensionless wave height, {Delta}h/h, is empirically correlated in terms of Re{sub G} and h/H. A modified root-mean-square wave height is proposed to consider the effects of the interfacial and wave propagation velocities. It is found that an equivalent roughness has a linear relationship with the modified root-mean-square wave height and its relationship is independent of the inclination. 10 refs., 6 figs., 1 tab. (Author)
Investigations of non-hydrostatic, stably stratified and rapidly rotating flows
Nieves, David; Juilen, Keith; Weiss, Jeffrey B
2016-01-01
We present an investigation of rapidly rotating (small Rossby number $Ro\\ll 1$) and stratified turbulence where the stratification strength is varied from weak (large Froude number $Fr\\gg1$) to strong ($Fr\\ll1$). The investigation is set in the context of a reduced model derived from the Boussinesq equations that efficiently retains anisotropic inertia-gravity waves with order-one frequencies and highlights a regime of wave-eddy interactions. Numerical simulations of the reduced model are performed where energy is injected by a stochastic forcing of vertical velocity, which forces wave modes only. The simulations reveal two regimes characterized by the presence of well-formed, persistent and thin turbulent layers of locally-weakened stratification at small Froude numbers, and by the absence of layers at large Froude numbers. Both regimes are characterized by a large-scale barotropic dipole enclosed by small-scale turbulence. When the Reynolds number is not too large a direct cascade of barotropic kinetic ener...
Sheared stably stratified turbulence and large-scale waves in a lid driven cavity
Cohen, N; Elperin, T; Kleeorin, N; Rogachevskii, I
2014-01-01
We investigated experimentally stably stratified turbulent flows in a lid driven cavity with a non-zero vertical mean temperature gradient in order to identify the parameters governing the mean and turbulent flows and to understand their effects on the momentum and heat transfer. We found that the mean velocity patterns (e.g., the form and the sizes of the large-scale circulations) depend strongly on the degree of the temperature stratification. In the case of strong stable stratification, the strong turbulence region is located in the vicinity of the main large-scale circulation. We detected the large-scale nonlinear oscillations in the case of strong stable stratification which can be interpreted as nonlinear internal gravity waves. The ratio of the main energy-containing frequencies of these waves in velocity and temperature fields in the nonlinear stage is about 2. The amplitude of the waves increases in the region of weak turbulence (near the bottom wall of the cavity), whereby the vertical mean temperat...
Turbulent transport in a strongly stratified forced shear layer with thermal diffusion
Garaud, Pascale
2015-01-01
This work presents numerical results on the transport of heat and chemical species by shear-induced turbulence in strongly stratified but thermally diffusive environments. The shear instabilities driven in this regime are sometimes called "secular" shear instabilities, and can take place even when the gradient Richardson number of the flow (the square of the ratio of the buoyancy frequency to the shearing rate) is large, provided the P\\'eclet number (the ratio of the thermal diffusion timescale to the turnover timescale of the turbulent eddies) is small. We have identified a set of simple criteria to determine whether these instabilities can take place or not. Generally speaking, we find that they may be relevant whenever the thermal diffusivity of the fluid is very large (typically larger than $10^{14}$cm$^2$/s), which is the case in the outer layers of high-mass stars ($M\\ge 10 M_\\odot$) for instance. Using a simple model setup in which the shear is forced by a spatially sinusoidal, constant-amplitude body-...
Time-resolved PIV investigation of flashback in stratified swirl flames of hydrogen-rich fuel
Ranjan, Rakesh; Clemens, Noel
2016-11-01
Hydrogen is one of the promising alternative fuels to achieve greener power generation. However, susceptibility of flashback in swirl flames of hydrogen-rich fuels acts as a major barrier to its adoption in gas turbine combustors. The current study seeks to understand the flow-flame interaction during the flashback of the hydrogen-rich flame in stratified conditions. Flashback experiments are conducted with a model combustor equipped with an axial swirler and a center-body. Fuel is injected in the main swirl flow via the fuel ports on the swirler vanes. To achieve mean radial stratification, these fuel ports are located at a radial location closer to the outer wall of the mixing tube. Stratification in the flow is assessed by employing Anisole PLIF imaging. Flashback is triggered by a rapid increase in the global equivalence ratio. The upstream propagation of the flame is investigated by employing time-resolved stereoscopic PIV and chemiluminescence imaging. Stratification leads to substantially different flame propagation behavior as well as increased flame surface wrinkling. We gratefully acknowledge the sponsorship by the DOE NETL under Grant DEFC2611-FE0007107.
Martizzi, Davide; Faucher-Giguere, Claude-Andre; Quataert, Eliot
2016-01-01
We use local Cartesian simulations with a vertical gravitational potential to study how supernova (SN) feedback in stratified galactic discs drives turbulence and launches galactic winds. Our analysis includes three disc models with gas surface densities ranging from Milky Way-like galaxies to gas-rich ultra-luminous infrared galaxies (ULIRGs), and two different SN driving schemes (random and correlated with local gas density). In order to isolate the physics of SN feedback, we do not include additional feedback processes. We find that, in these local box calculations, SN feedback excites relatively low mass-weighted gas turbulent velocity dispersions ~3-7 km/s and low wind mass loading factors <1 in all the cases we study. The low turbulent velocities and wind mass loading factors predicted by our local box calculations are significantly below those suggested by observations of gas-rich and rapidly star-forming galaxies; they are also in tension with global simulations of disc galaxies regulated by stella...
Disparate patterns of prenatal care utilization stratified by medical and psychosocial risk.
Krans, Elizabeth E; Davis, Matthew M; Palladino, Christie L
2013-05-01
To evaluate patterns of prenatal care utilization stratified by medical and psychosocial risk. A retrospective cohort of 786 pregnant women who subsequently delivered live births from 1999 to 2003 at the University of Michigan were classified into high medical, high psychosocial, high medical and high psychosocial (dual high risk) and low-risk pregnancies. Chi-square and logistic regression analyses assessed the association between risk and prenatal care utilization using the Kotelchuck Index. Of 786 pregnancies, 202 (25.7%) were high medical risk, 178 (22.7%) were high psychosocial risk, 227 (28.9%) were dual high risk and 179 (22.8%) were low-risk. Over 31% of dual high risk and 25% of high medical risk pregnancies received "adequate plus" prenatal care versus 10% of high psychosocial risk pregnancies. In multivariate analyses, adjusted for risk, race and insurance, high psychosocial risk pregnancies (OR = 1.69; 95% CI 1.06-2.72) were significantly more likely to receive inadequate prenatal care than care of greater intensity. Many high psychosocial risk pregnancies do not receive adequate prenatal care.
Bommaraju, Aalap; Kavanaugh, Megan L; Hou, Melody Y; Bessett, Danielle
2016-12-01
To examine whether race and reported history of abortion are associated with abortion stigma and miscarriage stigma, both independently and comparatively. Self-administered surveys with 306 new mothers in Boston and Cincinnati, United States. Abortion stigma perception (ASP); miscarriage stigma perception (MSP); and comparative stigma perception (CSP: abortion stigma perception net of miscarriage stigma perception). Regardless of whether or not they reported having an abortion, white women perceived abortion (ASP) to be more stigmatizing than Black and Latina women. Perceptions of miscarriage stigma (MSP), on the other hand, were dependent on reporting an abortion. Among those who reported an abortion, Black women perceived more stigma from miscarriage than white women, but these responses were flipped for women who did not report abortion. Reporting abortion also influenced our comparative measure (CSP). Among those who did report an abortion, white women perceived more stigma from abortion than miscarriage, while Black and Latina women perceived more stigma from miscarriage than abortion. By measuring abortion stigma in comparison to miscarriage stigma, we can reach a more nuanced understanding of how perceptions of reproductive stigmas are stratified by race and reported reproductive history. Clinicians should be aware that reproductive stigmas do not similarly affect all groups. Stigma from specific reproductive outcomes is more or less salient dependent upon a woman's social position and lived experience. Copyright © 2016 Elsevier B.V. All rights reserved.
Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica
Obryk, M. K.; Doran, P. T.; Hicks, J. A.; McKay, C. P.; Priscu, J. C.
2016-01-01
A one-dimensional ice cover model was developed to predict and constrain drivers of long term ice thickness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface radiative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 years (between 1996 and 2012) of ice thickness changes for west lobe of Lake Bonney (average ice thickness = 3.53 m; RMSE = 0.09 m, n = 118) and Lake Fryxell (average ice thickness = 4.22 m; RMSE = 0.21 m, n = 128). Long-term ice thickness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or facilitate ice thickness change depending on the predominant climatic trend (temperature cooling or warming). As such, shallow (< 20 m deep water columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation.
Nonlinear waves in stratified Taylor--Couette flow. Part 2. Buoyancy flux
Leclercq, Colin; Caulfield, Colm-Cille P; Dalziel, Stuart B; Linden, Paul F
2016-01-01
This paper is the second part of a two-fold study of mixing, i.e. the formation of layers and upwelling of buoyancy, in axially stratified Taylor--Couette flow, with fixed outer cylinder. In a first paper, we showed that the dynamics of the flow was dominated by coherent structures made of a superposition of nonlinear waves. (Mixed)-ribbons and (mixed)-cross-spirals are generated by interactions between a pair of linearly unstable helical modes of opposite `handedness', and appear to be responsible for the formation of well-mixed layers and sharp density interfaces. In this paper, we show that these structures are also fully accountable for the upwards buoyancy flux in the simulations. The mechanism by which this occurs is a positive coupling between the density and vertical velocity components of the most energetic waves. This coupling is primarily caused by diffusion of density at low Schmidt number Sc, but can also be a nonlinear effect at larger Sc. Turbulence was found to contribute negatively to the buo...