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Rosengarten, G., G. Morrison i M. Behnia. "A Second Law Approach to Characterising Thermally Stratified Hot Water Storage With Application to Solar Water Heaters". Journal of Solar Energy Engineering 121, nr 4 (1.11.1999): 194–200. http://dx.doi.org/10.1115/1.2888166.
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This paper presents a method of characterising and evaluating the performance of hot water storage systems in terms of their temperature distribution. The change in exergy from the stratified state to the delivery state depends on the stored energy and the stratification. It can thus he used to define the storage efficiency for sensible heat storage devices. A new parameter that isolates the stratification component of the exergy is defined and called the stratification efficiency. The effect of temperature distribution, delivery temperature and tank cross-section on exergy and stratification efficiency is investigated. The advantage that stratification offers over a mixed tank is examined in terms of the storage efficiency and overall solar water heating system performance. Exergy is used to assess the operation of mantle heat exchangers in solar water heating systems and it is shown that exergy and stratification efficiency, as well as energy, should be used to ascertain the performance of such heat exchangers.
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Sadooghi-Alvandi, S. M. "A NOTE ON THE EFFICIENCY OF PROPORTIONAL STRATIFICATION". Australian Journal of Statistics 30, nr 2 (czerwiec 1988): 196–99. http://dx.doi.org/10.1111/j.1467-842x.1988.tb00850.x.
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Roberts, Scott D., James N. Long i Frederick W. Smith. "Canopy stratification and leaf area efficiency: a conceptualization". Forest Ecology and Management 60, nr 1-2 (sierpień 1993): 143–56. http://dx.doi.org/10.1016/0378-1127(93)90028-l.
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Myllymäki, Mari, Terje Gobakken, Erik Næsset i Annika Kangas. "The efficiency of poststratification compared with model-assisted estimation". Canadian Journal of Forest Research 47, nr 4 (kwiecień 2017): 515–26. http://dx.doi.org/10.1139/cjfr-2016-0383.
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Survey sampling with model-assisted estimation has recently gained popularity in forest inventory. Another option for utilizing the auxiliary information is to use poststratification, which is a special case of model-assisted estimation with class variables as explanatory variables. In this study, we compared the efficiency of poststratification with an increasing number of strata with model-assisted estimation. We carried out a study based on a simulated population. We considered four different types of poststratifications, namely (i) stratification based on predictions of a linear model, (ii) stratification based on a regression tree model, (iii) stratification based on the first principal component of the explanatory variables, and (iv) stratification based on the regression tree model with the first principal component as the only explanatory variable. Furthermore, we examined both the traditional poststratification mean and variance estimators and the difference estimator and its variance estimator for poststratification. Within the recommended range of number of strata, the model-assisted approach was more efficient than poststratification. With a large number of strata, poststratification produced smaller standard error of estimates, but problems such as empty strata were encountered with small sample sizes. Using the first principal component directly for stratification or as an explanatory variable was the most efficient approach.
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Xie, Bing, John D. Clark i David D. L. Minh. "Efficiency of Stratification for Ensemble Docking Using Reduced Ensembles". Journal of Chemical Information and Modeling 58, nr 9 (16.08.2018): 1915–25. http://dx.doi.org/10.1021/acs.jcim.8b00314.
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Ferrarini, Luca, Giancarlo Mantovani i Marta Pagliarini. "Improving Energy Efficiency in Large Buildings with Thermal Stratification". IFAC Proceedings Volumes 47, nr 3 (2014): 4885–90. http://dx.doi.org/10.3182/20140824-6-za-1003.02532.
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Trinuruk, Piyatida, Papangkorn Jenyongsak i Somchai Wongwises. "Comparative Study of Inlet Structure and Obstacle Plate Designs Affecting the Temperature Stratification Characteristics". Energies 15, nr 6 (10.03.2022): 2032. http://dx.doi.org/10.3390/en15062032.
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Temperature stratification between outgoing hot water and incoming cold water is a key factor in diminishing energy loss during the discharging process and maximizing the useful hot water delivered from the tank or enhancing the thermal efficiency of the heating device during the heating process. In this study, the inlet structure and the obstacle plate were designed and modified based on two main factors, the reduction of inlet water velocity and the stipulation of the water recirculation area, to develop temperature stratification through the computational fluid dynamics method. The simulation model’s accuracy was validated against the experimental results. The results showed that using the equalizer as an inlet pipe’s auxiliary device was the best approach for decreasing the inlet water velocity, which resulted in enhancing temperature stratification. The discharging efficiency improved from 77.3% for the original tank model to 86.1% for the tank with equalizer IV model, which meant an additional 45 L of useful hot water was gained from the good temperature stratification storage tank. The installation of the obstacle plate for controlling the turbulence zone could not improve temperature stratification significantly, which resulted in an increase in discharging efficiency by only 4% more than the original tank model.
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Han, Wang Kook, Jin Man Kim, Tae Hun Lim, Hae Eun Song i Young Chull Ahn. "Temperature stratification using an air-cooled heat pump system with a mixing valve". Advances in Mechanical Engineering 12, nr 12 (grudzień 2020): 168781402098465. http://dx.doi.org/10.1177/1687814020984653.
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The main factor determining the performance of a thermal storage method is the temperature stratification in the storage tank. At the ideal stratification, the energy efficiency of the storage tank is extremely high. However, when the heat pump is applied, the stratification is disrupted by heat exchange between the layers of the heat medium, and consequent convection in the tank. Therefore, this study analyzed the influence of stratification-related design factors in the water-piping facility area outside a tank heated by a heat pump. In particular, it assessed the thermal stratification and energy efficiency in the storage tank installed with a mixing valve. In the system using the mixing valve, hot water of constant temperature was supplied to the top of the storage tank, reducing the mixing effect of the hot and cold waters; consequently, the stratification index was maximized at 0.42. Comparing the times at which the temperature of the uppermost part reached 70°C in the systems with and without the mixing valve (30 and 75 min, respectively), we find that the mixing valve reduced the time of obtaining effectively hot water by approximately 60%.
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Wissink, Martin, i Rolf Reitz. "The role of the diffusion-limited injection in direct dual fuel stratification". International Journal of Engine Research 18, nr 4 (20.08.2016): 351–65. http://dx.doi.org/10.1177/1468087416661867.
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Low-temperature combustion offers an attractive combination of high thermal efficiency and low NO x and soot formation at moderate engine load. However, the kinetically-controlled nature of low-temperature combustion yields little authority over the rate of heat release, resulting in a tradeoff between load, noise, and thermal efficiency. While several single-fuel strategies have achieved full-load operation through the use of equivalence ratio stratification, they uniformly require retarded combustion phasing to maintain reasonable noise levels, which comes at the expense of thermal efficiency and combustion stability. Previous work has shown that control over heat release can be greatly improved by combining reactivity stratification in the premixed charge with a diffusion-limited injection that occurs after low-temperature heat release, in a strategy called direct dual fuel stratification. While the previous work has shown how the heat release control offered by direct dual fuel stratification differs from other strategies and how it is enabled by the reactivity stratification created by using two fuels, this paper investigates the effects of the diffusion-limited injection. In particular, the influence of fuel selection and the pressure, timing, and duration of the diffusion-limited injection are examined. Diffusion-limited injection fuel type had a large impact on soot formation, but no appreciable effect on performance or other emissions. Increasing injection pressure was observed to decrease filter smoke number exponentially while improving combustion efficiency. The timing and duration of the diffusion-limited injection offered precise control over the heat release event, but the operating space was limited by a tradeoff between NO x and soot.
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SON, HYO SEOK, JAE-WOOK KWON, SEONG HOON LEE, CHUL KIM i HIKI HONG. "THE EFFECT OF UPPER-HEATING SYSTEM IN SOLAR WATER STORAGE TANK". International Journal of Air-Conditioning and Refrigeration 22, nr 04 (grudzień 2014): 1450027. http://dx.doi.org/10.1142/s2010132514500278.
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Thermal stratification in the water storage tank of solar heating system is essential to increase the collection efficiency. We previously investigated the stratification performance of side-heating system, where the hot water returning from the collector heats up the side wall of storage tank. Subsequently, we studied an evolved heating system for further improvement, where we added an upper-heating to the side-heating. Here we thoroughly examine the stratification performance of the evolved heating system using TRNSYS-based simulation. As the essential result, contrary to expectation, evolved system does not show substantial improvement of collection efficiency compared to side-heating. However, we confirm that evolved system excels in the useful energy.
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SAAD, ALIA. "Post Two Way Stratification Analysis for Vaccinations in Sudan". International Journal for Innovation Education and Research 7, nr 12 (31.12.2019): 08–14. http://dx.doi.org/10.31686/ijier.vol7.iss12.1689.
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The present research deal with post two stratification analysis for vaccinations data of MICS5 in Sudan. In order to guarantee more precision for estimated indicators: percentage of Child ever given BCG, Polio, PENTA and Measles or MMR vaccination. State and mother education level are determined as two stratification variables since the correlation between them is small and the correlation with target indicators are some of size. So the two way stratification analysis for the four indicators gives more precise estimates the post stratification with high relative efficiency.
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Monismith, Stephen G., Jeffrey R. Koseff i Brian L. White. "Mixing Efficiency in the Presence of Stratification: When Is It Constant?" Geophysical Research Letters 45, nr 11 (14.06.2018): 5627–34. http://dx.doi.org/10.1029/2018gl077229.
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Xie, Bing, John D. Clark i David D. L. Minh. "Correction to “Efficiency of Stratification for Ensemble Docking Using Reduced Ensembles”". Journal of Chemical Information and Modeling 59, nr 2 (7.02.2019): 944. http://dx.doi.org/10.1021/acs.jcim.9b00077.
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Yin, Lianhao, Gabriel Turesson, Tianhao Yang, Rolf Johansson i Per Tunestål. "Partially Premixed Combustion (PPC) Stratification Control to Achieve High Engine Efficiency". IFAC-PapersOnLine 51, nr 31 (2018): 694–99. http://dx.doi.org/10.1016/j.ifacol.2018.10.160.
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Sahoo, Goloka Behari, i David Luketina. "Bubbler design for reservoir destratification". Marine and Freshwater Research 54, nr 3 (2003): 271. http://dx.doi.org/10.1071/mf02045.
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Two important bubbler-performance criteria, the mechanical efficiency, ηmech, and the destratification time, Γ, were analysed as functions of two dimensionless parameters, G, the strength of stratification, and M, the source strength. Equations to estimate the optimum airflow rate (via M) and corresponding ηmech and Γ for a known linear stratification G in a reservoir were derived. Owing to difficulties in accurately determining the actual G, it was demonstrated that it is appropriate practice to reduce the design G value by around 10%. It was shown that the equivalent linear stratification method might lead to sub-optimal design for stratification profiles that deviate substantially from a linear profile. Rather, a bubble-plume model should be applied. Finally, the effects of incorporating changes in bubble radius in a bubble-plume model were examined. ηmech and Γ were found to be relatively insensitive to bubble radius; however, the ideal bubble size for maintaining a suitable oxygen dissolution efficiency is 1 mm.
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Lawrie, Andrew G. W., i Stuart B. Dalziel. "Rayleigh–Taylor mixing in an otherwise stable stratification". Journal of Fluid Mechanics 688 (3.11.2011): 507–27. http://dx.doi.org/10.1017/jfm.2011.398.
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AbstractWe seek to understand the distribution of irreversible energy conversions (mixing efficiency) between quiescent initial and final states in a miscible Rayleigh–Taylor driven system. The configuration we examine is a Rayleigh–Taylor unstable interface sitting between stably stratified layers with linear density profiles above and below. Our experiments in brine solution measure vertical profiles of density before and after the unstable interface is allowed to relax to a stable state. Our analysis suggests that less than half the initially available energy is irreversibly released as heat due to viscous dissipation, while more than half irreversibly changes the probability density function of the density field by scalar diffusion and therefore remains as potential energy, but in a less useful form. While similar distributions are observed in Rayleigh–Taylor driven mixing flows between homogeneous layers, our new configuration admits energetically consistent end-state density profiles that span all possible mixing efficiencies, ranging from all available energy being expended as dissipation, to none. We present experiments that show that the fluid relaxes to a state with a significantly lower mixing efficiency than the value for ideal mixing in this configuration, and deduce that this mixing efficiency more accurately characterizes Rayleigh–Taylor driven mixing than previous measurements. We argue that the physical mechanisms intrinsic to Rayleigh–Taylor instability are optimal conditions for mixing, and speculate that we have observed an upper bound to fluid mixing in general.
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Grujic, I., A. Davinic, N. Stojanovic, J. Doric i S. Narayan. "The influence of the fuel stratification on the IC engine working cycle with the compressed natural gas". IOP Conference Series: Materials Science and Engineering 1271, nr 1 (1.12.2022): 012004. http://dx.doi.org/10.1088/1757-899x/1271/1/012004.
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Abstract The gaseous fuels are very convenient from the economic aspect as well as from the ecology aspect. Fuel stratification allows the engine work with the globally lean mixture and in this way increase the engine efficiency and reduces the pump losses. The separation of the engine working space, on the area where the mixture will be always rich, and on the area where the mixture will be always lean, allows the spark ignition engine work with the globally lean mixture. In the paper it was investigated, how the fuel stratification ratio influences on the combustion process of the compressed natural gas in the spark ignition engine. It was found that the stratification ratio has a great influence on the combustion process, as well as on the engine performances and the efficiency. Based on the research it was identified the optimal combustion process from the aspect of the performances and the efficiency.
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Moreno, Y. M., A. A. Gardea i A. N. Azarenko. "CALORIMETRIC MEASUREMENTS OF STRATIFYING PEACH SEEDS AND SEEDLING GROWTH". HortScience 27, nr 6 (czerwiec 1992): 685a—685. http://dx.doi.org/10.21273/hortsci.27.6.685a.
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`Lovell' peach seeds were stratified for 0 to 13 weeks at 4C under moist conditions. Heat of metabolism and CO2 evolution, measured by Differential Scanning Calorimetry, increased with stratification time. The calorespirometric ratio increased between 0 and 6 weeks and then remained constant until 13 weeks. Germination percentages paralleled this ratio and reached 80% only after 6 weeks of stratification. After radicle emergence, seedlings from different stratification treatments were grown for 3 weeks. Increasing stratification time resulted in taller seedling growth. Calorimetrically measured CO2, evolution and the calorespirometric ratio of the apex (one cm) of the seedling increased with longer stratification time. Contrary to the observations of the seeds, metabolic heat rates decreased as stratification time increased. Yet, seedling sustained higher growth rates. These data suggest that the stratification treatment resulted in an improvement in metabolic efficiency.
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Xu, Shu Hui, Feng Jiao Zhang, Jian Kai Wang i Chang Liu. "Numerical Simulation Study of a New Type Solar Collector Wall System". Advanced Materials Research 860-863 (grudzień 2013): 98–102. http://dx.doi.org/10.4028/www.scientific.net/amr.860-863.98.
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In this paper, a new kind of solar collector wall system was designed. Numerical simulation for the orifice plate solar collector wall was carried out to analyze the change of the distributions of the temperature and velocity and the heat collecting efficiency under the conditions of different air inlet velocity. The results shows that the temperature stratification decreases with the increase of the inlet velocity, and the velocity field stratification enhances with the increase of the inlet velocity, and the collection efficiency first increases then decreases with the constantly increasing inlet velocity, and the collection efficiency is the highest when the inlet velocity is 2.5 m/s, up to 81.34%.
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Dong, Shiwei, Hui Guo, Ziyue Chen, Yuchun Pan i Bingbo Gao. "Spatial Stratification Method for the Sampling Design of LULC Classification Accuracy Assessment: A Case Study in Beijing, China". Remote Sensing 14, nr 4 (11.02.2022): 865. http://dx.doi.org/10.3390/rs14040865.
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Spatial sampling design is important for accurately assessing land use and land cover (LULC) classification results from remote sensing data. Spatial stratification can dramatically improve spatial sampling efficiency by dividing the study area into several strata when classification correctness is spatially stratified heterogeneous. By integrating the LULC classification results from different sources and spatial resolutions, a spatial stratification method for spatial sampling of accuracy assessment is presented in this paper. Its efficiency is demonstrated in the case study using LULC data of Beijing, China, in the following steps. First, we standardized and reclassified multiresolution remote sensing data, including China’s land use/cover datasets (CLUDs) from 2017 (resolution: 30 m), 500 m MCD12Q1, and 10 m FROM-GLC10 data, into six classes. Second, we customized stratification rules, formulated a technical specification to realize 11 strata using CLUDs and MCD12Q1, and employed FROM-GLC10 as the reference data for accuracy assessment. Furthermore, six sample sets with sizes of 16,417; 1821; 652; 337; 198; and 142 were drawn using different methods, and their overall accuracy (OA), deviation accuracy (DA), root-mean-square error (RMSE), and standard deviation (STDEV) values were also evaluated to demonstrate the efficiency brought by spatial stratification. Compared with the spatial even sampling method, the OAs of the stratified even sampling method adopting the proposed stratification method was much closer to the true OA, and the corresponding RMSE and STDEV results decreased from 2.097% and 2.127% to 0.914% and 0.713%, respectively, due to the contribution of spatial stratification in the sampling scheme. The method can be used to distinguish the differences and improve the representativeness of samples, and it can be employed to select validation samples for LULC classification.
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O’Mahony, James F. "Risk Stratification in Cost-Effectiveness Analyses of Cancer Screening: Intervention Eligibility, Strategy Choice, and Optimality". Medical Decision Making 42, nr 4 (11.10.2021): 513–23. http://dx.doi.org/10.1177/0272989x211050918.
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Introduction There is increasing interest in risk-stratified approaches to cancer screening in cost-effectiveness analysis (CEA). Current CEA practice regarding risk stratification is heterogeneous and guidance on the best approach is lacking. This article suggests how stratification in CEA can be improved. Methods I use a simple example of a hypothetical screening intervention with 3 potential recipient risk strata. The screening intervention has 6 alternative intensities, each with different costs and effects, all of which vary between strata. I consider a series of alternative stratification approaches, demonstrating the consequences for estimated costs, effects, and the choice of optimal strategy. I supplement this analysis with applied examples from the literature. Results Adopting the same screening policy for all strata yields the least efficient strategies, where efficiency is understood as the volume of net health benefit generated across a range of cost-effectiveness threshold values. Basic stratification that withholds screening from lower-risk strata while adopting a common strategy for those screened increases efficiency. Greatest efficiency is achieved when different strata receive separate strategies. While complete optimization can be achieved within a single analysis by considering all possible policy combinations, the resulting number of strategy combinations may be inconveniently large. Optimization with separate strata-specific analyses is simpler and more transparent. Despite this, there can be good reasons to simulate all strata together in a single analysis. Conclusions If the benefits of risk stratification are to be fully realized, policy makers need to consider the extent to which stratification is feasible, and modelers need to simulate those choices adequately. It is hoped this analysis will clarify those policy and modeling choices and therefore lead to improved population health outcomes.
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Brown, John P., i Richard G. Oderwald. "Sampling estimators of total mill receipts for use in timber product output studies". Canadian Journal of Forest Research 42, nr 3 (marzec 2012): 476–89. http://dx.doi.org/10.1139/x11-183.
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Data from the 2001 timber product output study for Georgia was explored to determine new methods for stratifying mills and finding suitable sampling estimators. Estimators for roundwood receipts totals comprised several types: simple random sample, ratio, stratified sample, and combined ratio. Two stratification methods were examined: the Dalenius–Hodges (DH) square root of the frequency method and a cluster analysis method. Three candidate sizes for the number of groups were selected from the cluster analysis and subsequently used in the DH stratification as well. Relative efficiency improved when the number of groups increased and when using a ratio estimator, particularly a combined ratio. The two stratification methods performed similarly. Neither the DH method nor the cluster analysis method performed better than the other. Six bound sizes (1%, 5%, 10%, 15%, 20%, and 25%) were considered for deriving samples sizes for the total volume of roundwood receipts. The minimum achievable bound size was found to be 10% of the total receipts volume for the DH method using a two-group stratification. This was true for both the stratified and combined ratio estimators. In addition, for the stratified and combined ratio estimators, only the DH method stratifications were able to reach a 15% bound on the total (six of the 12 stratified estimators). These results demonstrate that the utilized classification methods are compatible with stratified totals estimators and can provide users with the opportunity to develop viable sampling procedures as opposed to complete mill censuses.
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Górnik, Krzysztof, Mieczysław Grzesik, Regina Janas, Edward Żurawicz, Ewa Chojnowska i Renata Góralska. "The Effect of Apple Seed Stratification with Growth Regulators on Breaking the Dormancy of Seeds, the Growth of Seedlings and Chlorophyll Fluorescence". Journal of Horticultural Research 26, nr 1 (1.06.2018): 37–44. http://dx.doi.org/10.2478/johr-2018-0004.
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Abstract The aim of the study was to shorten the period of breaking dormancy in apple seeds and to improve the growth of the seedlings of ‘Gold Milenium’, ‘Ligol’ and ‘Szampion’. The whole seeds were removed from fruits directly after the harvest and were subjected to stratification (3 °C for 90 days in darkness) in distilled water or an aqueous solutions of 500 mM salicylic acid (SA), 10−3 M jasmonic acid (JA), gibberellin A3 (GA3) and 6-benzylaminopurine (BAP) at 250 mg·dm−3 and 100 mg·dm−3, respectively. Growth regulators were applied separately or in a mixture containing SA, JA, GA3 and BAP. The germinability and seed germination rate, seedlings growth, chlorophyll content index and the maximum quantum efficiency of Photosystem II (Fv/Fm) were investigated. The obtained results revealed that stratification in water positively affected the dormancy removal in ‘Gold Milenium’, ‘Ligol’ and ‘Szampion’ seeds. Application of SA, GA3, BAP, JA during seed stratification additionally stimulated the seeds’ germination rate as well as the growth of seedlings, index of chlorophyll content and maximum PSII efficiency (Fv/Fm). The most pronounced results were obtained after the seed stratification in GA3 alone or in a mixture containing SA, GA3, BAP and JA. Due to such a treatment, the germination of ‘Ligol’ seeds increased by 40% and they germinated faster in comparison to the control seeds. Such treatments also promoted the growth of seedlings, chlorophyll content and maximum quantum efficiency of Photosystem II (Fv/Fm). The present study indicates that the application of GA3 or the mixture of SA, GA3, BAP and JA during the stratification of seeds is an effective method to increase and accelerate the germination of seeds and juvenile seedlings’ growth in order to shorten the apple breeding cycle. Further studies are needed to optimize the appropriate concentration of growth regulators applied simultaneously during seeds stratification.
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Kovalnogov, V. N., R. V. Fedorov i D. A. Generalov. "Study of the thermal state of urbomachine blades by means of software complex". Izvestiya MGTU MAMI 8, nr 4-1 (20.02.2014): 27–32. http://dx.doi.org/10.17816/2074-0530-67641.
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The article considers the method for calculating of thermal state of turbomachine blades using software complex. The authors consider the possibility of using of gas dynamic temperature stratification phenomenon to improve efficiency of turbomachine blade cooling systems. The mathematical formulation is given for non-stationary problem of calculating of blades thermal state under the gas-dynamic temperature stratification.
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Tsynaeva, A. A., E. A. Tsynaeva i E. V. Shkolin. "Using heat pipes to improve the efficiency of gas-dynamic thermal stratification". VESTNIK of the Samara State Aerospace University, nr 3-2(41) (25.12.2013): 192. http://dx.doi.org/10.18287/1998-6629-2013-0-3-2(41)-192-197.
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Yelskyi, I. K., A. A. Vasylyev i N. L. Smirnov. "THE EFFICIENCY OF PROGNOSTIC SCALES IN STRATIFICATION OF ACUTE PANCREATITIS. LITERATURE REVIEW". Surgical practice, nr 3 (4.12.2020): 17–28. http://dx.doi.org/10.38181/2223-2427-2020-3-17-28.
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The work carried out by analyzes of the literature data on assessing the severity of acute pancreatitis and predicting its course and mortality. A comparison of traditional point scales for assessing the severity of AP was made.As a result of a comparative analysis, it was found that the most objective instrumental method for diagnosing acute pancreatitis and its complications was MSCT with the determination of the CT index of severity. Balthazar scale allows assessing the severity of the disease and forming a prognosis for the development of complications. However, computed or magnetic resonance imaging with intravenous contrast enhancement allows an accurate assessment of the severity of the disease not earlier than 72 hours and has some contraindications.Estimating and predictive systems Ranson, APACHE, Krasnorogov, Bozhenkov systems, Pugaeva and Achkasova, BISAP and HAPS allow identyfying the severity of the clinical course of acute pancreatitis, have a high sensitivity, but at the same time require significant time and resources for execution. Glasgow-Imrie, SAPS, MODS, and SOFA scales mainly calculate mortality and degree of multiple organ failure in critically ill patients; these severity assessment systems are not specific for patients with acute pancreatitis.The optimal scale for assessing the severity of AP should allow assessing the patient's condition and prognosis from the moment of admission to the outcome of the disease. The practicing surgeon will be interested in an affordable, inexpensive, easy-to-use system for determining the severity of acute pancreatitis. For surgeons, the time factor plays a key role in determining tactics, and, therefore, improves the prognosis of the disease.
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Tsynaeva, Anna A., Maxim N. Nikitin i Ekaterina A. Tsynaeva. "Study of thermal and hydraulic efficiency of supersonic tube of temperature stratification". Journal of Physics: Conference Series 891 (10.11.2017): 012047. http://dx.doi.org/10.1088/1742-6596/891/1/012047.
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Dandekar, Rajat, Vaseem A. Shaik i Arezoo M. Ardekani. "Swimming sheet in a density-stratified fluid". Journal of Fluid Mechanics 874 (4.07.2019): 210–34. http://dx.doi.org/10.1017/jfm.2019.445.
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In this work, we theoretically investigate the swimming velocity of a Taylor swimming sheet immersed in a linearly density-stratified fluid. We use a regular perturbation expansion approach to estimate the swimming velocity up to second order in wave amplitude. We divide our analysis into two regimes of low ($\ll O(1)$) and finite Reynolds numbers. We use our solution to understand the effect of stratification on the swimming behaviour of organisms. We find that stratification significantly influences motility characteristics of the swimmer such as the swimming speed, hydrodynamic power expenditure, swimming efficiency and the induced mixing, quantified by mixing efficiency and diapycnal eddy diffusivity. We explore this dependence in detail for both low and finite Reynolds number and elucidate the fundamental insights obtained. We expect our work to shed some light on the importance of stratification in the locomotion of organisms living in density-stratified aquatic environments.
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JOURDAIN, BENJAMIN, BERNARD LAPEYRE i PIERGIACOMO SABINO. "CONVENIENT MULTIPLE DIRECTIONS OF STRATIFICATION". International Journal of Theoretical and Applied Finance 14, nr 06 (wrzesień 2011): 867–97. http://dx.doi.org/10.1142/s0219024911006772.
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This paper investigates the use of multiple directions of stratification as a variance reduction technique for Monte Carlo simulations of path-dependent options driven by Gaussian vectors. The precision of the method depends on the choice of the directions of stratification and the allocation rule within each strata. Several choices have been proposed but, even if they provide variance reduction, their implementation is computationally intensive and not applicable to realistic payoffs, in particular not to Asian options with barrier. Moreover, all these previously published methods employ orthogonal directions for multiple stratification. In this work we investigate the use of algorithms producing convenient directions, generally non-orthogonal, combining a lower computational cost with a comparable variance reduction. In addition, we study the accuracy of optimal allocation in terms of variance reduction compared to the Latin Hypercube Sampling. We consider the directions obtained by the Linear Transformation and the Principal Component Analysis. We introduce a new procedure based on the Linear Approximation of the explained variance of the payoff using the law of total variance. In addition, we exhibit a novel algorithm that permits to correctly generate normal vectors stratified along non-orthogonal directions. Finally, we illustrate the efficiency of these algorithms in the computation of the price of different path-dependent options with and without barriers in the Black-Scholes and in the Cox-Ingersoll-Ross markets.
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Ijichi, Takashi, i Toshiyuki Hibiya. "Observed Variations in Turbulent Mixing Efficiency in the Deep Ocean". Journal of Physical Oceanography 48, nr 8 (sierpień 2018): 1815–30. http://dx.doi.org/10.1175/jpo-d-17-0275.1.
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AbstractRecent progress in direct numerical simulations (DNSs) of stratified turbulent flows has led to increasing attention to the validity of the constancy of the dissipation flux coefficient Γ in the Osborn’s eddy diffusivity model. Motivated by lack of observational estimates of Γ, particularly under weakly stratified deep-ocean conditions, this study estimates Γ using deep microstructure profiles collected in various regions of the North Pacific and Southern Oceans. It is shown that Γ is not constant but varies significantly with the Ozmidov/Thorpe scale ratio ROT in a fashion similar to that obtained by previous DNS studies. Efficient mixing events with Γ ~ O(1) and ROT ~ O(0.1) tend to be frequently observed in the deep ocean (i.e., weak stratification), while moderate mixing events with Γ ~ O(0.1) and ROT ~ O(1) tend to be observed in the upper ocean (i.e., strong stratification). The observed negative relationship between Γ and ROT is consistent with a simple scaling that can be derived from classical turbulence theories. In contrast, the observed results exhibit no definite relationships between Γ and the buoyancy Reynolds number Reb, although Reb has long been thought to be another key parameter that controls Γ.
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de Lavergne, Casimir, Gurvan Madec, Julien Le Sommer, A. J. George Nurser i Alberto C. Naveira Garabato. "The Impact of a Variable Mixing Efficiency on the Abyssal Overturning". Journal of Physical Oceanography 46, nr 2 (luty 2016): 663–81. http://dx.doi.org/10.1175/jpo-d-14-0259.1.
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AbstractIn studies of ocean mixing, it is generally assumed that small-scale turbulent overturns lose 15%–20% of their energy in eroding the background stratification. Accumulating evidence that this energy fraction, or mixing efficiency Rf, significantly varies depending on flow properties challenges this assumption, however. Here, the authors examine the implications of a varying mixing efficiency for ocean energetics and deep-water mass transformation. Combining current parameterizations of internal wave-driven mixing with a recent model expressing Rf as a function of a turbulence intensity parameter Reb = εν/νN2, the ratio of dissipation εν to stratification N2 and molecular viscosity ν, it is shown that accounting for reduced mixing efficiencies in regions of weak stratification or energetic turbulence (high Reb) strongly limits the ability of breaking internal waves to supply oceanic potential energy and drive abyssal upwelling. Moving from a fixed Rf = 1/6 to a variable efficiency Rf(Reb) causes Antarctic Bottom Water upwelling induced by locally dissipating internal tides and lee waves to fall from 9 to 4 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) and the corresponding potential energy source to plunge from 97 to 44 GW. When adding the contribution of remotely dissipating internal tides under idealized distributions of energy dissipation, the total rate of Antarctic Bottom Water upwelling is reduced by about a factor of 2, reaching 5–15 Sv, compared to 10–33 Sv for a fixed efficiency. The results suggest that distributed mixing, overflow-related boundary processes, and geothermal heating are more effective in consuming abyssal waters than topographically enhanced mixing by breaking internal waves. These calculations also point to the importance of accurately constraining Rf(Reb) and including the effect in ocean models.
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Hassan, Jafar Mehdi, Qussai Jihad Abdul-Ghafour i Mohammed Fowzi Mohammed. "Experimental Study of the Thermal Performance of Flat Plate Solar Collectors Array by Different Connection Configurations". Journal of Engineering 21, nr 5 (1.05.2015): 55–71. http://dx.doi.org/10.31026/j.eng.2015.05.05.
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The current research illustrates experimentally the effect of series and parallel connection (Z-I Configurations) of flat plate water solar collectors array on the thermal performance of closed loop solar heating system. The study includes the effect of changing the water flow rate on the thermal efficiency. The results show that, the collector's efficiency in series connection is higher than the parallel connection within flow rate level less than (100) ℓ/hr. Moreover, the collector efficiency in parallel connection of (I-Configurations) is more than the (Z- Configurations) with increasing the water flow rate .The maximum daily efficiency for parallel (I-Configurations) and (Z- Configurations) are (55%) and (51%) at water flow rate (150) ℓ/ hr. It was also noted that the thermal stratification of storage tank in case of series connection is higher than that of parallel connection. Also, when the flow rate increases, the thermal stratification of storage tank reduces.
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Jackson, P. Ryan, i Chris R. Rehmann. "Laboratory Measurements of Differential Diffusion in a Diffusively Stable, Turbulent Flow". Journal of Physical Oceanography 33, nr 8 (1.08.2003): 1592–603. http://dx.doi.org/10.1175/2405.1.
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Abstract Laboratory experiments were performed to determine the conditions under which differential diffusion occurs and to evaluate its effect on the mixing efficiency. Diffusively stable profiles of temperature and salinity were stirred steadily by horizontally oscillating vertical rods. The two-component stratification ensures that both scalars experience the same stratification and forcing, or Richardson and Reynolds numbers. The eddy diffusivities KT and KS, for temperature and salinity, were estimated by fitting theoretical solutions of diffusion equations to measured profiles, and the mixing efficiency was computed as the ratio of the potential energy change during a stirring interval to the work done in that interval. Differential diffusion occurred for ɛa/νN2 < 300–500, where ɛa is an average dissipation rate computed from an integrated energy budget. The diffusivity ratio d = KS/KT varied between 0.5 and 1 in the range 50 < ɛa/νN2 < 500. The experiments also show that differential diffusion can significantly affect the mixing efficiency. An important dimensionless parameter is the density ratio Rρ, which is the ratio of the density change due to temperature to that due to salinity. Measurements in cases with low density ratio (Rρ ≈ 0.25) and high density ratio (Rρ ≈ 5) showed that the mixing efficiencies agreed well for weak stratification, or small Richardson number. For larger Richardson number, the efficiency for the high-density-ratio case exceeded that for the low-density-ratio case by as much as a factor of 1.5.
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Rabiu, Adam, Abubakar Yahaya i Muhammad Abdulkarim. "MODIFICATION OF SEPARATE RATIO TYPE EXPONENTIAL ESTIMATOR: A POST-STRATIFICATION APPROACH". FUDMA JOURNAL OF SCIENCES 5, nr 2 (10.07.2021): 404–12. http://dx.doi.org/10.33003/fjs-2021-0502-629.
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In this research, modification of separate ratio type exponential estimator introduced in an earlier study is proposed. Expressions for the bias and mean square error (MSE) of the proposed estimator up to first degree of approximation are derived. The optimum value of the constant which minimize the MSE of the suggested estimator is also obtained. In the same vein, efficiency comparisons between the proposed estimator and some related existing ones under the case of post-stratification is conducted. Empirical studies have been conducted to demonstrate the efficiencies of the suggested estimators over other considered estimators. The proposed MSE and Percentage Relative Efficiency (PRE) were used to evaluate the achievement of the modified estimator.
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Tsynaeva, A. A., i M. N. Nikitin. "Effect of Heat Transfer Surface Shape on Efficiency of Gas Dynamic Temperature Stratification". Russian Aeronautics 60, nr 4 (październik 2017): 627–31. http://dx.doi.org/10.3103/s1068799817040213.
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Arnold, Christian Cornelius, Jens von der Grün, Mark Christoph Brekner, Jörg Licher, Emmanouil Fokas, Claus Rödel i Maximilian Fleischmann. "Risk stratification by anamnesis increases SARS-CoV-2 test efficiency in cancer patients". Strahlentherapie und Onkologie 198, nr 4 (7.10.2021): 354–60. http://dx.doi.org/10.1007/s00066-021-01853-7.
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Abstract Purpose To evaluate the impact of testing asymptomatic cancer patients, we analyzed all tests for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) before and during radiotherapy at a tertiary cancer center throughout the second wave of the pandemic in Germany. Methods Results of all real-time polymerase chain reaction (RT-PCR) tests for SARS-CoV‑2 performed at our radio-oncology department between 13 October 2020 and 11 March 2021 were included. Clinical data and anamnestic information at the time of testing were documented and examined for (i) the presence of COVID-19-related symptoms and (ii) virus-related anamnesis (high-risk [prior positive test or contact to a positive tested person within the last 14 days] or low-risk [inconspicuous anamnesis within the last 14 days]). Results A total of 1056 SARS-CoV‑2 tests in 543 patients were analyzed. Of those, 1015 tests were performed in asymptomatic patients and 41 tests in patients with COVID-19-associated symptoms. Two of 940 (0.2%) tests in asymptomatic patients with low-risk anamnesis and three of 75 (4.0%) tests in asymptomatic patients with high-risk anamnesis showed a positive result. For symptomatic patients, SARS-CoV‑2 was detected in three of 36 (8.3%) low-risk and three of five (60.0%) high-risk tests. Conclusion To the best of our knowledge, this is the first study evaluating the correlation between individual risk factors and positivity rates of SARS-CoV‑2 tests in cancer patients. The data demonstrate that clinical and anamnestic assessment is a simple and effective measure to distinctly increase SARS-CoV‑2 test efficiency. This might enable cancer centers to adjust test strategies in asymptomatic patients, especially when test resources are scarce.
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Otto, Henning, Christian Resagk i Christian Cierpka. "Optical Measurements on Thermal Convection Processes inside Thermal Energy Storages during Stand-By Periods". Optics 1, nr 1 (29.04.2020): 155–72. http://dx.doi.org/10.3390/opt1010011.
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Thermal energy storages (TES) are increasingly important for storing energy from renewable energy sources. TES that work with liquid storage materials are used in their most efficient way by stratifying the storage fluid by its thermal density gradient. Mixing of the stratification layers during stand-by periods decreases the thermal efficiency of the TES. Tank sidewalls, unlike the often poorly heat-conducting storage fluids, promote a heat flux from the hot to the cold layer and lead to thermal convection. In this experimental study planar particle image velocimetry (PIV) measurements and background-oriented schlieren (BOS) temperature measurements are performed in a model experiment of a TES to characterise the influence of the thermal convection on the stratification and thus the storage efficiency. The PIV results show two vertical, counter-directed wall jets that approach in the thermocline between the stratification layers. The wall jet in the hot part of the thermal stratification shows compared to the wall jet in the cold region strong fluctuations in the vertical velocity, that promote mixing of the two layers. The BOS measurements have proven that the technique is capable of measuring temperature fields in thermally stratified storage tanks. The density gradient field as an intermediate result during the evaluation of the temperature field can be used to indicate convective structures that are in good agreement to the measured velocity fields.
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Hu, Zongjie, Junjie Zhang, Magnus Sjöberg i Wei Zeng. "The use of partial fuel stratification to enable stable ultra-lean deflagration-based Spark-Ignition engine operation with controlled end-gas autoignition of gasoline and E85". International Journal of Engine Research 21, nr 9 (19.12.2019): 1678–95. http://dx.doi.org/10.1177/1468087419889702.
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Lean operation of Spark-Ignition engines can provide higher thermal efficiency compared to standard stoichiometric operation. However, for a homogeneous lean mixture, the associated reduction of flame speeds becomes an important issue from the perspective of robust ignition and fast flame spread throughout the charge. This study is focused on the use of a lean partial fuel stratification strategy that can stabilize the deflagration, while sufficiently fast combustion is ensured via the use of end-gas autoignition. The engine has a spray-guided Direct-Injection Spark-Ignition combustion system and was fueled with either a high-octane certification gasoline or E85. Partial fuel stratification was achieved using several fuel injections during the intake stroke in combination with a small pilot-injection concurrent with the Spark-Ignition. The results reveal that partial fuel stratification enables very stable combustion, offering higher thermal efficiency for parts of the load range in comparison to well-mixed lean and stoichiometric combustion. The heat release and flame imaging demonstrate that the combustion often has three distinct stages. The combustion of the pilot-injected fuel, ignited by the normal spark, acts as a “super igniter,” ensuring a very repeatable initiation of combustion, and flame incandescence reveals locally rich conditions. The second stage is mainly composed of blue flame propagation in a well-mixed lean mixture. The third stage is the compression autoignition of a well-mixed and typically very lean end-gas. The end-gas autoignition is critical for achieving high combustion efficiency, high thermal efficiency, and stable combustion. Partial fuel stratification enables very effective combustion-phasing control, which is critical for controlling the occurrence and intensity of end-gas autoignition. Comparing the gasoline and E85 fuels, it is noted that achieving end-gas autoignition for the higher octane E85 requires a more aggressive compression of the end-gas via the use of a more advanced combustion phasing or higher intake-air temperature.
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Chung, Bryan Ping Ho. "Stratification of stroke rehabilitation: Five-year profiles of functional outcomes". Hong Kong Physiotherapy Journal 38, nr 02 (grudzień 2018): 141–47. http://dx.doi.org/10.1142/s1013702518500129.
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Background: Stroke rehabilitation in inpatient setting requires high intensity of manpower and resources. Early stratification of patients with stroke could facilitate early discharge plan and reduce avoidable length of stay (LOS) in hospital. Stratification of patients with stroke in clinical setting is usually based on functional scores which are quite time-consuming and require a special training to complete the full score.Objective: The objective of the study was to explore whether Modified Functional Ambulation Category (MFAC) can serve as a stratification tool of patients with stroke in inpatient rehabilitation.Methods: This was a retrospective, descriptive study of the demographic, functional outcomes of patients with stroke in an inpatient rehabilitation center. A total of 2,722 patients completed a stroke rehabilitation program from 2011 to 2015 were recruited. The patients were divided into seven groups according to their admission MFAC. The between-group difference in LOS, functional outcomes at admission and discharge including Modified Rivermead Mobility Index (MRMI) and Modified Barthel Index (MBI) as well as MRMI gain, MRMI efficiency, MBI gain, and MBI efficiency were analyzed.Results: Subjects with admission categories of MFAC 2 and 3 had a highly significant ([Formula: see text]) MRMI gain (6.2 and 6.6, respectively) and subjects with admission categories of MFAC 3 to 5 had highly significant ([Formula: see text]) MRMI efficiency (0.34, 0.40, and 0.39, respectively). The subjects with admission categories of MFAC 2 to 5 had a highly significant ([Formula: see text]) MBI gain (9.7, 10.2, 9.3, and 7.0, respectively) and the subjects with admission categories of MFAC 4 to 5 had a highly significant ([Formula: see text]) MBI efficiency (0.70 and 0.72, respectively). The subjects with admission categories of MFAC 1 and 2 had a highly significant ([Formula: see text]) LOS (27.7 and 26.6, respectively). MFAC profile was also established to represent the distribution of discharge MFAC of subjects according to their admission MFAC. The chance of subjects with admission categories of MFAC 1 and MFAC 2 progress to any kind of walker (MFAC [Formula: see text] 2) is 12.7% and 58.2%, respectively. The chance of subjects with admission MFAC 3, MFAC 4 and MFAC 5 progress to independent walker (MFAC [Formula: see text] 5) is 6.7%, 14.8%, and 50.3%, respectively. Both admission MFAC and admission MBI had strong correlations with discharge MFAC ([Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], respectively), discharge MRMI ([Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], respectively) and discharge MBI ([Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], respectively).Conclusion: This study showed that patients on admission with moderate disability in term of MFAC had the greatest mobility gain and basic activities of daily living (ADL) gain from inpatient stroke rehabilitation. Admission MFAC could be a stratification tool of patients with stroke in inpatient rehabilitation.
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Poletto, Tales, Marlove Fátima Brião Muniz, Igor Poletto, Valdir Marcos Stefenon, Caciara Gonzatto Maciel i Jéssica Emilia Rabusque. "Dormancy overcome and seedling quality of pecan in nursery". Ciência Rural 46, nr 11 (29.08.2016): 1980–85. http://dx.doi.org/10.1590/0103-8478cr20150835.
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ABSTRACT: This study evaluated the efficiency of methods to overcome seed dormancy in different storage periods in the production of pecan seedlings. Seeds were submitted to the following treatments: T1, T4 and T7 - control treatments (seeds with no treatment, stored at room temperature for 30, 60 and 90 days, respectively), T2, T5 and T8 - stratification (seeds were distributed in boxes with wet sand maintained at a temperature of 4°C for 30, 60 and 90 days, respectively), T3, T6 and T9 - scarification + stratification (seeds scarified with sandpaper n.80 and stratified by 30, 60 and 90 days, respectively), in completely random experimental design. Plant height, stem diameter, number of leaves, full emergence and emergence speed index (ESI) were evaluated after 14 weeks of sowing. The best development of pecan 'plants, their emergence, and ESI were observed in the stratification treatment for 90 day as well as in the scarification + stratification treatment for 90 day. Storing seeds in uncontrolled environment reduced their viability.
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Alvandi, Amirhossein, i Armin Hatefi. "Analysis of Ordinal Populations from Judgment Post-Stratification". Stats 6, nr 3 (9.08.2023): 812–38. http://dx.doi.org/10.3390/stats6030052.
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In surveys requiring cost efficiency, such as medical research, measuring the variable of interest (e.g., disease status) is expensive and/or time-consuming; however, we often have access to easily obtainable characteristics about sampling units. These characteristics are not typically employed in the data collection process. Judgment post-stratification (JPS) sampling enables us to supplement the random samples from the population of interest with these characteristics as ranking information. This paper develops methods based on the JPS samples for estimating categorical ordinal populations. We develop various estimators from the JPS data even for situations where the JPS suffers from empty strata. We also propose the JPS estimators using multiple ranking resources. Through extensive numerical studies, we evaluate the performance of the methods in estimating the population. Finally, the developed estimation methods are applied to bone mineral data to estimate the bone disorder status of women aged 50 and older.
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Smusz, Robert, Paweł Kielan i Damian Mazur. "Analysis of thermal stratified storage tank". Archives of Electrical Engineering 66, nr 3 (1.09.2017): 631–42. http://dx.doi.org/10.1515/aee-2017-0048.
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Abstract The basic aim of the task is to compile a temperature stratification system in an accumulation tank. The range of the thesis concerns the shape and dimensions of a stratification system for an accumulation tank. Thermal stratification is a process that comprises the maintaining of temperature stratification at different levels of an accumulation tank which reduce to a minimum the process of temperature equalization. It results from the fact that the thermal stratification in a tank significantly increases the installation efficiency and improves the process of energy storing. It is connected with a thermodynamic element quality, that is the higher the temperature, the higher the energy, and, thus, the thermos-dynamic element quality. In this phenomenon, thanks to the same amount of accumulated thermal energy and average temperature, as in a fully mixed tank, the user has a higher temperature in the upper part of the tank at his disposal. It has significant importance in the case when there is a low-temperature heating medium that transfers heat to the accumulation tank. Such a situation occurs when heat is absorbed from synthetic freons used in cooling and air-conditioning systems.
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Houšková, Kateřina, Jan Klepárník i Oldřich Mauer. "How to accelerate the germination of Scots pine and Norway spruce seeds?" Journal of Forest Science 67, No. 3 (5.03.2021): 134–42. http://dx.doi.org/10.17221/133/2020-jfs.
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The aim of the study was to confirm and compare efficiency of methods enhancing the vitality of Scots pine and Norway spruce seeds: soaking in water, cold stratification, additional moistening and incubation according to IDS method. The examined parameters included water content in the seeds, germination energy, mean germination time and germination capacity before the seed treatment, after its treatment by the tested methods and after drying. Results show that all the tested methods accelerate germination of seeds; cold stratification is the most efficient and recommended method for Scots pine and soaking of seeds in water is the most efficient and recommended for Norway spruce. The best results in spruce were also obtained with cold stratification (comparable with soaking in water) but the method is complicated, longer-lasting and more costly than soaking in water.
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Suverneva, A. A., i I. V. Ignatko. "Current approach to perinatal risk stratification". Voprosy ginekologii, akušerstva i perinatologii 20, nr 4 (2021): 69–77. http://dx.doi.org/10.20953/1726-1678-2021-4-69-77.
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Objective. To develop a new approach to perinatal risk stratification based on the determination of prognostic criteria for antepartum and intrapartum fetal death, and early neonatal death to improve the efficiency of predicting adverse perinatal outcomes. Patients and methods. A retrospective case-control study with the participation of patients with antepartum (n = 134) and intrapartum (n = 41) fetal death, early neonatal death (n = 61), and favorable perinatal outcome (n = 50) was carried out. The Bayes–Wald–Gubler method was used to determine prognostic criteria. Comparative evaluation of the efficacy of the proposed prognostic method and the generally accepted determination of perinatal risk was performed retrospectively in patients with perinatal loss (n = 102) and favorable perinatal outcome (n = 100); ROC analysis was performed. Results. Forty-two risk factors were identified and divided into three groups: universal for all types of perinatal loss, common for two of them, and specific for each of them (antepartum and intrapartum fetal death, early neonatal death). The prognostic value of factors in their presence and absence was determined. It was found that universal and common risk factors for each type of perinatal loss had different prognostic value. The method of differential prediction of perinatal loss was presented. The sensitivity of the new and generally accepted prognostic methods was 95.1 and 69.6%, the specificity was 80 and 53%, and the accuracy of predicting adverse outcomes was 87.6 and 61.4%, respectively. Conclusion. The conducted study allowed to suggest a new approach to perinatal risk stratification based on differential prediction of perinatal loss, which is superior to the traditional risk assessment methods in terms of the effectiveness of predicting adverse perinatal outcomes. Key words: antepartum fetal death, intrapartum fetal death, perinatal outcomes, prediction, early neonatal death
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Haller, Michel Y., Cynthia A. Cruickshank, Wolfgang Streicher, Stephen J. Harrison, Elsa Andersen i Simon Furbo. "Methods to determine stratification efficiency of thermal energy storage processes – Review and theoretical comparison". Solar Energy 83, nr 10 (październik 2009): 1847–60. http://dx.doi.org/10.1016/j.solener.2009.06.019.
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Azanov, Georgii M., i Alexander N. Osiptsov. "The efficiency of one method of machineless gasdynamic temperature stratification in a gas flow". International Journal of Heat and Mass Transfer 106 (marzec 2017): 1125–33. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2016.10.090.
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Rosen, M. A., i I. Dincer. "THERMAL STORAGE AND EXERGY ANALYSIS: THE IMPACT OF STRATIFICATION". Transactions of the Canadian Society for Mechanical Engineering 23, nr 1B (maj 1999): 173–86. http://dx.doi.org/10.1139/tcsme-1999-0012.
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The importance and usefulness of second-law analysis for evaluating and comparing thermal energy storage (TES) systems in meaningful ways is discussed. Some of the main thermodynamic factors to be considered in evaluating TES performance are identified and described, including determining important analysis quantities, obtaining appropriate measures of efficiency, pinpointing losses, assessing the effects of stratification, and accounting for time duration of storage. As an illustrative example, exergy analysis, a particular type of second-law analysis, is applied to stratified TES systems in order to evaluate the effects and benefits of thermal stratification. It is concluded based on the results of the example that (i) the use of stratification in thermal storage designs should be considered as it increases the exergy storage capacity of a thermal storage, and (ii) exergy analysis should be applied in the analysis and comparison of stratified thermal storage systems.
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Macdonald, R. J., i A. Ernst. "Disinfection Efficiency and Problems Associated with Maturation Ponds". Water Science and Technology 18, nr 10 (1.10.1986): 19–29. http://dx.doi.org/10.2166/wst.1986.0107.
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Reductions in densities of indicator organisms and pathogens were measured in maturation ponds receiving secondary effluents from trickling filter and activated sludge treatment works. Effluent detention times in the ponds were determined using dye tracing techniques and compared with nominal detention times calculated from pond volumes and effluent flow rates. Median detention times were substantially less than nominal times because of short circuiting due to pond design aspects and thermal stratification. Maturation ponds of 10 days median detention time were found to successfully disinfect a poor quality trickling filter effluent and were effective at removing parasite ova and reducing virus densities. Continued use of maturation ponds should be encouraged in developed and developing countries as they have low cost, operational, maintenance and skilled operator requirements and are an effective disinfection process. Pond designs should minimize short circuiting and thus the areal requirements of the ponds.
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Macdonald, R. J., i A. Ernst. "Disinfection Efficiency and Problems Associated with Maturation Ponds". Water Science and Technology 19, nr 3-4 (1.03.1987): 557–67. http://dx.doi.org/10.2166/wst.1987.0235.
Pełny tekst źródłaStreszczenie:
Reductions in densities of indicator organisms and pathogens were measured in maturation ponds receiving secondary effluents from trickling filter and activated sludge treatment works. Effluent detention times in the ponds were determined using dye tracing techniques and compared with nominal detention times calculated from pond volumes and effluent flow rates. Median detention times were substantially less than nominal times because of short circuiting due to pond design aspects and thermal stratification. Maturation ponds of 10 days median detention time were found to successfully disinfect a poor quality trickling filter effluent and were effective at removing parasite ova and reducing virus densities. Continued use of maturation ponds should be encouraged in developed and developing countries as they have low cost, operational, maintenance and skilled operator requirements and are an effective disinfection process. Pond designs should minimize short circuiting and thus the areal requirements of the ponds.
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Varodompun, Jatuwat, i Mojtaba Navvab. "HVAC Ventilation Strategies: The Contribution for Thermal Comfort, Energy Efficiency, and Indoor Air Quality". Journal of Green Building 2, nr 2 (1.05.2007): 131–50. http://dx.doi.org/10.3992/jgb.2.2.131.
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In Heating Ventilating and Air Conditioning (HVAC) systems, ventilation strategies impact building energy consumption, occupants' thermal comfort and Indoor Air Quality (IAQ). Ventilation strategies such as Mixing Jet Ventilation (MJV), Displacement Ventilation (DV), and Impinging Jet Ventilation (IJV) are operated on the different principals. MJV relies on dilution, while DV and IJV rely on both dilution and stratification. Due to climatic variation, ventilation strategies must be operated under different cooling and heating load scenarios. Typically, each ventilation strategy controls the indoor environment through a single adequate flow rate with suitable supply parameters such as temperature, pollutant concentration, vapor, velocity, etc. Hence, the indoor thermal and IAQ condition are independently impacted. A room with excellent thermal condition is possible to have poor IAQ. Given this limitation, vast air flow variables, and occupants' activities, the performances evaluation of these strategies are complicated. In this study, three ventilation strategies, MJV, DV, and IJV are thoroughly investigated. The Computational Fluid Dynamics (CFD) simulation was mainly utilized to handle the complexity of this study. The parametric studies of 48 CFD simulations are presented. Referring to ASHRAE RP-1133, the experimental data from a specially built HVAC-IEQ laboratory was used to validate the CFD data. The research results indicate both advantages and disadvantages in all three strategies. In addition, there is no single strategy that can perform excellently in all indexes. Using the well-known index called ventilation effectiveness (VEF), DV performs outstandingly. However, under a newly proposed index called ventilation performances, DV fails because the stratification discomfort exceeds 36% of room area. MJV suffers from low VEF and excessive draft. However, the IAQ of MJV is not as poor as expected. IJV can be an alternative especially for space where sleeping and sitting activities dominate. IJV can conserve HVAC energy, while maintaining good IAQ. Compared to DV, although VEF is lower, stratification discomfort is minimized to 24%–12% (depending on supply velocity). Overall, this study demonstrates that ventilation strategies are the key to enhance IAQ. Therefore, the utilization of an appropriate ventilation strategy might increase, Leadership in Energy and Environmental Design (LEED) score, particularly for Indoor Environmental Quality, Innovation and Design Process, and Energy and Atmospheric categories.