163 Matching Results

Search Results

Advanced search parameters have been applied.

Turbulence and Heat Stratification

Description: With applications to meteorology in view, the method of small oscillations is used to investigate the stability of a plane laminar boundary layer in which the density depends in a special way on the distance from the plate. It is found that for a constant Froude number the flow becomes more stable as the Richardson number increases until, at a critical value of the Richardson number that depends on the Froude number, the flow is stable for all disturbance wave lengths and Reynolds numbers. The calculated results are verified by experiment.
Date: October 1950
Creator: Schlichting, Hermann
Partner: UNT Libraries Government Documents Department

Classless: on Being Middle Class in America

Description: Classless: On Being Middle Class in America is a documentary film that explores what it means to be middle class in America. The film combines personal narrative, folksy reporting, and comedy as the film's director— Joe Brown, tries to reconcile his own status anxiety with everyday understandings of social class. Classless takes the form of a journey; the film travels through the American South, Northeast, and the Mountain West while trying to get at the heart of our middle class American Dream. Classless forwards three main arguments: (1) the American middle class is not as all-encompassing as seems; (2) Americans are more concerned about inequality than both politicians and the media suggest; and (3) many Americans are not actually middle class, economically speaking.
Date: May 2013
Creator: Brown, Joseph V.
Partner: UNT Libraries


Description: To investigate the extent of genetic stratification in structured microbial communities, we compared the metagenomes of 10 successive layers of a phylogenetically complex hypersaline mat from Guerrero Negro, Mexico. We found pronounced millimeter-scale genetic gradients that are consistent with the physicochemical profile of the mat. Despite these gradients, all layers displayed near identical and acid-shifted isoelectric point profiles due to a molecular convergence of amino acid usage indicating that hypersalinity enforces an overriding selective pressure on the mat community.
Date: April 30, 2008
Creator: Fenner, Marsha W; Kunin, Victor; Raes, Jeroen; Harris, J. Kirk; Spear, John R.; Walker, Jeffrey J. et al.
Partner: UNT Libraries Government Documents Department

An efficient modeling method for thermal stratification simulation in a BWR suppression pool

Description: The suppression pool in a BWR plant not only is the major heat sink within the containment system, but also provides major emergency cooling water for the reactor core. In several accident scenarios, such as LOCA and extended station blackout, thermal stratification tends to form in the pool after the initial rapid venting stage. Accurately predicting the pool stratification phenomenon is important because it affects the peak containment pressure; and the pool temperature distribution also affects the NPSHa (Available Net Positive Suction Head) and therefore the performance of the pump which draws cooling water back to the core. Current safety analysis codes use 0-D lumped parameter methods to calculate the energy and mass balance in the pool and therefore have large uncertainty in prediction of scenarios in which stratification and mixing are important. While 3-D CFD methods can be used to analyze realistic 3D configurations, these methods normally require very fine grid resolution to resolve thin substructures such as jets and wall boundaries, therefore long simulation time. For mixing in stably stratified large enclosures, the BMIX++ code has been developed to implement a highly efficient analysis method for stratification where the ambient fluid volume is represented by 1-D transient partial differential equations and substructures such as free or wall jets are modeled with 1-D integral models. This allows very large reductions in computational effort compared to 3-D CFD modeling. The POOLEX experiments at Finland, which was designed to study phenomena relevant to Nordic design BWR suppression pool including thermal stratification and mixing, are used for validation. GOTHIC lumped parameter models are used to obtain boundary conditions for BMIX++ code and CFD simulations. Comparison between the BMIX++, GOTHIC, and CFD calculations against the POOLEX experimental data is discussed in detail.
Date: September 1, 2012
Creator: Zhao, Haihua; Zou, Ling; Zhang, Hongbin; Li, Hua; Villanueva, Walter & Kudinov, Pavel
Partner: UNT Libraries Government Documents Department

Suspended sediment transport in the benthic nepheloid layer in southeastern Lake Michigan

Description: Time series observations of water temperature, water transparency, and current velocity were made at four stations located on the lake slope of southeastern Lake Michigan. The observations show that during stratified conditions the benthic nepheloid layer is probably not maintained by the local resuspension of bottom sediment. A more likely source is sediment resuspended further inshore and then transported across the shelf and slope during downwelling events. Internal wave action may be an important source of energy for this transport. Although sediment trap studies suggest that resuspension does occur, it is more likely that increased fluxes observed near the bottom are due to the vertical redistribution of material already in suspension. A benthic nepheloid layer also exists at times during the unstratified period, when occassionally enough energy reaches the bottom to directly resuspend bottom material at the sites.
Date: February 1, 1995
Creator: Hawley, N. & Lesht, B.M.
Partner: UNT Libraries Government Documents Department

Determination of the Optimal Number of Strata for Bias Reduction in Propensity Score Matching.

Description: Previous research implementing stratification on the propensity score has generally relied on using five strata, based on prior theoretical groundwork and minimal empirical evidence as to the suitability of quintiles to adequately reduce bias in all cases and across all sample sizes. This study investigates bias reduction across varying number of strata and sample sizes via a large-scale simulation to determine the adequacy of quintiles for bias reduction under all conditions. Sample sizes ranged from 100 to 50,000 and strata from 3 to 20. Both the percentage of bias reduction and the standardized selection bias were examined. The results show that while the particular covariates in the simulation met certain criteria with five strata that greater bias reduction could be achieved by increasing the number of strata, especially with larger sample sizes. Simulation code written in R is included.
Date: May 2010
Creator: Akers, Allen
Partner: UNT Libraries

Atlantic Coastal Experiment III: R/V KNORR cruise 68, 4-30 August 1977; FRV ALBATROSS IV cruise 77-07, 1-4, 16-31 August 1977. Data report, volume 1

Description: Data are reported from KNORR cruise 68, the major investigation of the third Atlantic Coastal Experiment (ACE), conducted during a period of pro-nounced water-column stratification. One hundred fifty-five stations, including 6 time-series sitings, were occupied within the shelf and shelf- break regimes of New York Bight. Measurements were made to assess water-mass characterization, nutrient cycling, carbon/nitrogen assimilation, bio-mass distribution and diel dynamics and benthic/water-column interfacial exchange. Data are also included from the cruise of ALBATROSS IV carried out contemporaneously with the KNORR investigations, in an area ranging from Nantucket Shoals to the upper reaches of the Gulf of Maine. 20 hydrographic stations were used to augment underway mapping in order to elucidate surface-layer chlorophyll and nutrient distributions occurring at an impor-tant boundary of the New York Bight.
Date: March 1, 1983
Creator: Judkins, D.C. & von Bock, K.
Partner: UNT Libraries Government Documents Department

Performance of underfloor air distribution in a fieldsetting

Description: Underfloor air distribution (UFAD) is a new method of supplying heated or cooled air throughout a building. Reported advantages of UFAD include energy savings and improved indoor air quality (IAQ). We measured several aspects of the performance of an UFAD system installed in a medium-size office building. The measured air change effectiveness was very close to unity, which is comparable to that measured in buildings with typical overhead air distribution. The pollutant removal efficiency for carbon dioxide was 13% higher than expected in a space with well-mixed air, suggesting a 13% reduction in exposures to occupant generated pollutants. The increase in indoor air temperatures with height above the floor was only 1 to 2 C. This amount of thermal stratification could reduce the sensible energy requirements for cooling of outdoor air by approximately 10%. The occupant's level of satisfaction with thermal conditions was well above average and this high satisfaction rating could possibly be due, in all or part, to the use of a UFAD system. The results of this study provide some evidence of moderate energy and IAQ-related benefits of UFAD. Before general conclusions are drawn, the benefits need to be confirmed in other studies.
Date: October 1, 2005
Creator: Fisk, W.J.; Faulkner, D.; Sullivan, D.P.; Chao, C.; Wan, M.P.; Zagreus, L. et al.
Partner: UNT Libraries Government Documents Department

Numerically Simulating the Hydrodynamic and Water Quality Environment for Migrating Salmon in the Lower Snake River, 2002-2003 Technical Report.

Description: Summer temperatures in the Lower Snake River can be altered by releasing cold waters that originate from deep depths within Dworshak Reservoir. These cold releases are used to lower temperatures in the Clearwater and Lower Snake Rivers and to improve hydrodynamic and water quality conditions for migrating aquatic species. This project monitored the complex three-dimensional hydrodynamic and thermal conditions at the Clearwater and Snake River confluence and the processes that led to stratification of Lower Granite Reservoir (LGR) during the late spring, summer, and fall of 2002. Hydrodynamic, water quality, and meteorological conditions around the reservoir were monitored at frequent intervals, and this effort is continuing in 2003. Monitoring of the reservoir is a multi-year endeavor, and this report spans only the first year of data collection. In addition to monitoring the LGR environment, a three-dimensional hydrodynamic and water quality model has been applied. This model uses field data as boundary conditions and has been applied to the entire 2002 field season. Numerous data collection sites were within the model domain and serve as both calibration and validation locations for the numerical model. Errors between observed and simulated data varied in magnitude from location to location and from one time to another. Generally, errors were small and within expected ranges, although, as additional 2003 field data becomes available, model parameters may be improved to minimize differences between observed and simulated values. A two-dimensional, laterally-averaged hydrodynamic and water quality model was applied to the three reservoirs downstream of LGR (the pools behind Little Goose, Lower Monumental, and Ice Harbor Dams). A two-dimensional model is appropriate for these reservoirs because observed lateral thermal variations during summer and fall 2002 were almost negligible; however, vertical thermal variations were quite large (see USACE 2003). The numerical model was applied to each reservoir independently to ...
Date: June 1, 2003
Creator: Cook, C.; Richmond, M. & Coleman, A. (Pacific Northwest National Laboratory)
Partner: UNT Libraries Government Documents Department

Material-based Stratification

Description: A simple probability model was applied to detection sampling in a room or space in which different surface materials are present. The model assesses the overall detection capability when the sampling and analytical methods have different performance properties for the different materials. The results suggest that some common sampling strategies may not be ideal. In particular: (1) In a single room or area that includes different surface types with different detection properties, do not use a single sampling grid with a common spacing throughout. (2) If it is known or strongly suspected that one material has better detection properties than the other, place all samples on that material. (3) When it is completely unknown which material has the better detection properties, allocate the samples equally between them.
Date: May 31, 2007
Creator: MacQueen, D H
Partner: UNT Libraries Government Documents Department

Final Technical Report DE-FG02-99ER14933 Inversion of multicomponent seismic data and rock physics interpretation

Description: An important accomplishment was to understand the seismic velocity anisotropy resulting from the combined roles of depositional stratification and stress in unconsolidated sands. The report presents an experimental study of velocity anisotropy in unconsolidated sands at measured compressive stresses up to 40 bars, which correspond to the first hundred meters of the subsurface. Two types of velocity anisotropy are considered, that due to intrinsic textural anisotropy, and that due to stress anisotropy. We found that sand samples display a bi-linear dependence of velocity anisotropy with stress anisotropy. There exists a transition stress beyond which the stress-induced anisotropy outweighs the intrinsic anisotropy for three different sands.
Date: March 15, 2006
Creator: Mavko, G.
Partner: UNT Libraries Government Documents Department

The Role of Eddy-Tansport in the Thermohaline Circulation

Description: Several research themes were developed during the course of this project. (1) Low-frequency oceanic varibility; (2) The role of eddies in the Antarctic Circumpolar Current (ACC) region; (3) Deep stratification and the overturning circulation. The key findings were as follows: (1) The stratification below the main thermocline (at about 500m) is determined in the circumpolar region and then communicated to the enclosed portions of the oceans through the overturning circulation. (2) An Atlantic pole-to-pole overturning circulation can be maintained with very small interior mixing as long as surface buoyancy values are shared between the northern North Atlantic and the ACC region.
Date: November 17, 2011
Creator: Cessi, Dr. Paola
Partner: UNT Libraries Government Documents Department

Integrated Genomic Analysis Identifies Clinically Relevant Subtypes of Glioblastoma Characterized by Abnormalities in PDGFRA, IDH1, EGFR, and NF1

Description: The Cancer Genome Atlas Network recently cataloged recurrent genomic abnormalities in glioblastoma multiforme (GBM). We describe a robust gene expression-based molecular classification of GBM into Proneural, Neural, Classical, and Mesenchymal subtypes and integrate multidimensional genomic data to establish patterns of somatic mutations and DNA copy number. Aberrations and gene expression of EGFR, NF1, and PDGFRA/IDH1 each define the Classical, Mesenchymal, and Proneural subtypes, respectively. Gene signatures of normal brain cell types show a strong relationship between subtypes and different neural lineages. Additionally, response to aggressive therapy differs by subtype, with the greatest benefit in the Classical subtype and no benefit in the Proneural subtype. We provide a framework that unifies transcriptomic and genomic dimensions for GBM molecular stratification with important implications for future studies.
Date: September 3, 2009
Creator: Verhaak, Roel GW; Hoadley, Katherine A; Purdom, Elizabeth; Wang, Victoria; Qi, Yuan; Wilkerson, Matthew D et al.
Partner: UNT Libraries Government Documents Department

Normalized sensitivities and parameter identifiability of in situ diffusion experiments on Callovo-Oxfordian clay at Bure site

Description: DIR (Diffusion of Inert and Reactive tracers) is an experimental program performed by ANDRA at Bure underground research laboratory in Meuse/Haute Marne (France) to characterize diffusion and retention of radionuclides in Callovo-Oxfordian (C-Ox) argillite. In situ diffusion experiments were performed in vertical boreholes to determine diffusion and retention parameters of selected radionuclides. C-Ox clay exhibits a mild diffusion anisotropy due to stratification. Interpretation of in situ diffusion experiments is complicated by several non-ideal effects caused by the presence of a sintered filter, a gap between the filter and borehole wall and an excavation disturbed zone (EdZ). The relevance of such non-ideal effects and their impact on estimated clay parameters have been evaluated with numerical sensitivity analyses and synthetic experiments having similar parameters and geometric characteristics as real DIR experiments. Normalized dimensionless sensitivities of tracer concentrations at the test interval have been computed numerically. Tracer concentrations are found to be sensitive to all key parameters. Sensitivities are tracer dependent and vary with time. These sensitivities are useful to identify which are the parameters that can be estimated with less uncertainty and find the times at which tracer concentrations begin to be sensitive to each parameter. Synthetic experiments generated with prescribed known parameters have been interpreted automatically with INVERSE-CORE{sup 2D} and used to evaluate the relevance of non-ideal effects and ascertain parameter identifiability in the presence of random measurement errors. Identifiability analysis of synthetic experiments reveals that data noise makes difficult the estimation of clay parameters. Parameters of clay and EdZ cannot be estimated simultaneously from noisy data. Models without an EdZ fail to reproduce synthetic data. Proper interpretation of in situ diffusion experiments requires accounting for filter, gap and EdZ. Estimates of the effective diffusion coefficient and the porosity of clay are highly correlated, indicating that these parameters cannot be estimated ...
Date: October 1, 2009
Creator: Samper, J.; Dewonck, S.; Zheng, L.; Yang, Q. & Naves, A.
Partner: UNT Libraries Government Documents Department

Year-round observations of carbon biomass and flux variability in the Southern Ocean

Description: Three Carbon Explorer (CE) floats profiling to kilometer depths in the Southern Ocean tracked dawn-dusk variations of mixing/stratification, particulate organic carbon (POC), and light scattering and sedimentation at 100, 250, and 800 m continuously from January 2002 to April 2003. Data were analyzed in conjunction with contemporaneous satellite winds and chlorophyll and derived subsurface light fields. The CE deployed at 66{sup o}S 172{sup o}W operated in the ice edge zone in absence of light. Two CEs deployed at 55{sup o}S 172{sup o}W recorded wintertime mixing to {approx}400 m, yet observed very different bloom dynamics and sedimentation the following spring. Four hypotheses are explored. The strongest is that shallow transient stratification of the deep winter mixed layer to shallower than photosynthetic critical depth occurred more frequently in the non-bloom/higher sedimentation case. The lower particle export to 800 m under the bloom was hypothesized to be due to higher interception of sinking carbon by a relatively starved over wintering zooplankton population. In the Southern Ocean surface phytoplankton biomass may counter indicate particle flux at kilometer depths.
Date: February 1, 2009
Creator: Bishop, James K.B. & Wood, Todd
Partner: UNT Libraries Government Documents Department

A University Consortium on Low Temperature Combustion for High Efficiency, Ultra-Low Emission Engines

Description: The objective of the University consortium was to investigate the fundamental processes that determine the practical boundaries of Low Temperature Combustion (LTC) engines and develop methods to extend those boundaries to improve the fuel economy of these engines, while operating with ultra low emissions. This work involved studies of thermal effects, thermal transients and engine management, internal mixing and stratification, and direct injection strategies for affecting combustion stability. This work also examined spark-assisted Homogenous Charge Compression Ignition (HCCI) and exhaust after-treatment so as to extend the range and maximize the benefit of Homogenous Charge Compression Ignition (HCCI)/ Partially Premixed Compression Ignition (PPCI) operation. In summary the overall goals were:  Investigate the fundamental processes that determine the practical boundaries of Low Temperature Combustion (LTC) engines.  Develop methods to extend LTC boundaries to improve the fuel economy of HCCI engines fueled on gasoline and alternative blends, while operating with ultra low emissions.  Investigate alternate fuels, ignition and after-treatment for LTC and Partially Premixed compression Ignition (PPCI) engines.
Date: December 31, 2009
Creator: Assanis, Dennis N.; Atreya, Arvind; Chen, Jyh-Yuan; Cheng, Wai K.; Dibble, Robert W.; Edwards, Chris et al.
Partner: UNT Libraries Government Documents Department

Deep convection in the Arctic: The evaluation of results from an OGCM with a new convection parameterization

Description: The current generation of ocean general circulation models (OGCMS) uses a convective adjustment scheme to remove static instabilities and to parameterize shallow and deep convection. In simulations used to examine climate-related scenarios, investigators found that in the Arctic regions, the OGCM simulations did not produce a realistic vertical density structure, did not create the correct quantity of deep water, and did not use a time-scale of adjustment that is in agreement with tracer ages or observations. A possible weakness of the models is that the convective adjustment scheme does not represent the process of deep convection adequately. Consequently, a penetrative plume mixing scheme has been developed to parameterize the process of deep open-ocean convection in OGCMS. This new deep convection parameterization was incorporated into the Semtner and Chervin (1988) OGCM. The modified model (with the new parameterization) was run in a simplified Nordic Seas test basin: under a cyclonic wind stress and cooling, stratification of the basin-scale gyre is eroded and deep mixing occurs in the center of the gyre. In contrast, in the OGCM experiment that uses the standard convective adjustment algorithm, mixing is delayed and is wide-spread over the gyre.
Date: January 1, 1995
Creator: Paluszkiewicz, T.; Hibler, L.F. & Romea, R.D.
Partner: UNT Libraries Government Documents Department

The interaction of katabatic winds and mountain waves

Description: The variation in the oft-observed, thermally-forced, nocturnal katabatic winds along the east side of the Rocky Mountains can be explained by either internal variability or interactions with various other forcings. Though generally katabatic flows have been studied as an entity protected from external forcing by strong thermal stratification, this work investigates how drainage winds along the Colorado Front Range interact with, in particular, topographically forced mountain waves. Previous work has shown, based on measurements taken during the Atmospheric Studies in Complex Terrain 1993 field program, that the actual dispersion in katabatic flows is often greater than reflected in models of dispersion. The interaction of these phenomena is complicated and non-linear since the amplitude, wavelength and vertical structure of mountain waves developed by flow over the Rocky Mountain barrier are themselves partly determined by the evolving atmospheric stability in which the drainage flows develop. Perturbations to katabatic flow by mountain waves, relative to their more steady form in quiescent conditions, are found to be caused by both turbulence and dynamic pressure effects. The effect of turbulent interaction is to create changes to katabatic now depth, katabatic flow speed, katabatic jet height and, vertical thermal stratification. The pressure effect is found to primarily influence the variability of a given katabatic now through the evolution of integrated column wave forcing on surface pressure. Variability is found to occur on two scales, on the mesoscale due to meso-gamma scale mountain wave evolution, and on the microscale, due to wave breaking. Since existing parameterizations for the statically stable case are predominantly based on nearly flat terrain atmospheric measurements under idealized or nearly quiescent conditions, it is no surprise that these parameterizations often contribute to errors in prediction, particularly in complex terrain.
Date: January 1, 1997
Creator: Poulos, G.S.
Partner: UNT Libraries Government Documents Department


Description: The U. S. Department of Energy (DOE), Electric Power Research Institute (EPRI), Pennsylvania Electric Energy Research Council, (PEERC), New York State Electric and Gas and GPU Generation, Inc. jointly funded a demonstration to determine the capabilities for Hybrid SNCR/SCR (Selective Non-Catalytic Reduction/Selective Catalytic Reduction) technology. The demonstration site was GPU Generation's Seward Unit No.5 (147MW) located in Seward Pennsylvania. The demonstration began in October of 1997 and ended in December 1998. DOE funding was provided through Grant No. DE-FG22-96PC96256 with T. J. Feeley as the Project Manager. EPRI funding was provided through agreements TC4599-001-26999 and TC4599-002-26999 with E. Hughes as the Project Manager. This project demonstrated the operation of the Hybrid SNCR/SCR NO{sub x} control process on a full-scale coal fired utility boiler. The hybrid technology was expected to provide a cost-effective method of reducing NO{sub x} while balancing capital and operation costs. An existing urea based SNCR system was modified with an expanded-duct catalyst to provide increased NO{sub x} reduction efficiency from the SNCR while producing increased ammonia slip levels to the catalyst. The catalyst was sized to reduce the ammonia slip to the air heaters to less than 2 ppm while providing equivalent NO{sub x} reductions. The project goals were to demonstrate hybrid technology is capable of achieving at least a 55% reduction in NO{sub x} emissions while maintaining less than 2ppm ammonia slip to the air heaters, maintain flyash marketability, verify the cost benefit and applicability of Hybrid post combustion technology, and reduce forced outages due to ammonium bisulfate (ABS) fouling of the air heaters. Early system limitations, due to gas temperature stratification, restricted the Hybrid NO{sub x} reduction capabilities to 48% with an ammonia slip of 6.1 mg/Nm{sup 3} (8 ppm) at the catalyst inlet. After resolving the stratification problem, the catalyst did not have sufficient ...
Date: May 1, 1999
Creator: Urbas, Jerry B.
Partner: UNT Libraries Government Documents Department

CO{sub 2} injection for enhanced gas production and carbon sequestration

Description: Analyses suggest that carbon dioxide (CO{sub 2}) can be injected into depleted gas reservoirs to enhance methane (CH{sub 4}) recovery for periods on the order of 10 years, while simultaneously sequestering large amounts of CO{sub 2}. Simulations applicable to the Rio Vista Gas Field in California show that mixing between CO{sub 2} and CH{sub 4} is slow relative to repressurization, and that vertical density stratification favors enhanced gas recovery.
Date: November 15, 2001
Creator: Oldenburg, Curtis M. & Benson, Sally M.
Partner: UNT Libraries Government Documents Department

Dispersive internal long wave models

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work is a joint analytical and numerical study of internal dispersive water wave propagation in a stratified two-layer fluid, a problem that has important geophysical fluid dynamics applications. Two-layer models can capture the main density-dependent effects because they can support, unlike homogeneous fluid models, the observed large amplitude internal wave motion at the interface between layers. The authors have derived new model equations using multiscale asymptotics in combination with the method they have developed for vertically averaging velocity and vorticity fields across fluid layers within the original Euler equations. The authors have found new exact conservation laws for layer-mean vorticity that have exact counterparts in the models. With this approach, they have derived a class of equations that retain the full nonlinearity of the original Euler equations while preserving the simplicity of known weakly nonlinear models, thus providing the theoretical foundation for experimental results so far unexplained.
Date: November 1, 1998
Creator: Camassa, R.; Choi, W.; Holm, D.D.; Levermore, C.D. & Lvov, Y.
Partner: UNT Libraries Government Documents Department