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pREDICTION OF THE GRAIN SIZE OF SUSpENDED SEDIMENT:IMpLICATIONS FOR CALCULATING SUSpENDED SEDIMENT CONCENTRATIONS USING SINGLE FREQUENCY ACOUSTIC BACKSCATTER

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International Journal of Sediment Research 2007年第1期22卷 1-15页

作者： R. A. KUHNLE D. G. wren J. p. CHAMBERS Dr.Research Hydraulic Engineer National Sedimentation Laboratory U. S. Department of Agriculture Agricultural Research Service Oxford Mississippi 38655 USA Senior Research Scientist National Center for Physical Acoustics University of Mississippi University Mississippi 38677 USA

Collection of samples of suspended sediment transported by streams and rivers is difficult and expensive. Emerging technologies, such as acoustic backscatter, have promise to decrease costs and allow more thorough sampling of transported sediment in streams and rivers. Acoustic backscatter information may be used to calculate the concentration of suspended sand-sized sediment given the vertical distribution of sediment size. Therefore, procedures to accurately compute suspended sediment size distributions from easily obtained river data are badly needed. In this study, techniques to predict the size of suspended sand are examined and their application to measuring concentrations using acoustic backscatter data are explored. Three methods to predict the size of sediment in suspension using bed sediment, flow criteria, and a modified form of the Rouse equation yielded mean suspended sediment sizes that differed from means of measured data by 7 to 50 percent. When one sample near the bed was used as a reference, mean error was reduced to about 5 percent. These errors in size determination translate into errors of 7 to 156 percent in the prediction of sediment concentration using backscatter data from 1 MHz single frequency acoustics.

关键词： Suspended sediment Grain size Acoustic backscatter Concentration errors

Measurements of coupled fluid and sediment motion over mobile sand dunes in a laboratory flume

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International Journal of Sediment Research 2008年第4期23卷 329-337页

作者： Daniel G.wren Roger A.KUHNLE Research Hydraulic Engineer USD A-ARS-National Sedimentation LaboratoryPh.D Research Hydraulic Engineer USD A-ARS-National Sedimentation Laboratory

The relationship between turbulent fluid motions and sediment particle motions over mobile sand dunes was investigated by using a laser Doppler velocimeter and an acoustic backscatter system in laboratory experiments performed at the USDA-ARS-National Sedimentation Laboratory. profiles of acoustic backscatter from particles and at-a-point turbulence data were collected while translating both measurement devices downstream at the speed of mobile dune bedforms. The resulting data set was used to examine the frequency (recurrence frequency) at which the fluctuating backscatter and fluid velocity signals exceeded magnitude thresholds based on the standard deviation (σ) of the local velocity and the magnitude the acoustic signal resulting from backscatter from suspended particles. The slope of the downstream and vertical velocity recurrence frequencies generally indicated a gradually increasing recurrence time with increasing elevation. The recurrence frequency for acoustic backscatter data was not strongly variable with elevation. The closest correspondence between the recurrence frequencies of sediment backscatter and vertical velocities at the 1σ magnitude threshold was in a region defined by X/L<0.4 and y<6 cm. The downstream velocity was most closely related to backscatter in a small region at 0.4

关键词： Turbulence Suspended sediment Acoustic backscatter Dunes

Effects of silt loading on turbulence and sand transport

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International Journal of Sediment Research 2012年第4期27卷 451-459页

作者： Daniel G.wren Roger A.KUHNLE USDA-Agricultural Research Service-National Sedimentation Laboratory

The transport of bed material and fluid turbulence are affected by many factors,including the fine sediment load being carried in a *** research has focused on sand-sized particles introduced to gravel beds,while the effect of silt load on sand transport has received less attention. Experiments on the effects of silt load,in concentrations 0-26,900 mg l-1,on sand transport were performed with a recirculating laboratory flume using three different sand bed configurations:ripples （Fr=0.24）,dunes（Fr=0.34）,and dunes（Fr=0.48）.Three Acoustic Doppler Velocimeters were arranged to measure flow and turbulence quantities simultaneously in one *** transport did not change in a consistent manner with increasing silt load,increasing up to 4,000 mg l-1for dunes （Fr=0.48） and up to 2,000 mg l-1for dunes（Fr=0.34） and then declining to near the clear water case with increasing silt *** addition for the ripple case caused a relatively small change in sand transport,decreasing with added silt up to approximately 2,000 mg l-1and then increasing as silt went up to approximately 10,000 mg ***（Fr=0.48） decreased in length and height as silt increased,while dunes（Fr=0.34） did not show a consistent trend.A clear trend of decreasing Reynolds stress with increasing silt concentration was observed in the ripple case,with a 33% reduction in near-bed Reynolds stress caused by an 8,900 mg l-1concentration of silt.

关键词： Turbulence modulation Bedforms Dunes Sand transport Silt loading

Detailed bed topography and sediment load measurements for two stepdown flows in a laboratory flume

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International Journal of Sediment Research 2022年第3期37卷 287-298页

作者： Daniel wren Roger Kuhnle Tate Mc Alpin David Abraham Keaton Jones United States Department of Agriculture Agricultural Research Service National Sedimentation Laboratory U.S.Army Research and Development Center Coastal and Hydraulics Laboratory

Streams and rivers, particularly smaller ones, often do not maintain steady flow rates for long enough to reach equilibrium conditions for sediment transport and bed topography. In particular, streams in small watersheds may be subject to rapidly changing hydrographs, and relict bedforms from previous high flows can cause further disequilibrium that complicates the prediction of sediment transport rates. In order to advance the understanding of how bedforms respond to rapid changes in flow rate, a series of flume experiments were performed where the flow was reduced rapidly from equilibrium *** transport rates and bed elevation data across the flume and over a 15-meter-long test section were collected during the experiments to allow detailed examination of evolving bedform dynamics. It was found that relict bedforms stopped moving completely after flow reductions, and the mode of sediment transport was shifted to small bedforms that arose rapidly over dune stoss sections throughout the test section. The changes in sediment transport with time as the sand bed adjusted to the new flow rate was found to agree with predictions based on the relations proposed in wren et al.(2020). Wavelet analysis is used to visualize changes in length and amplitude scales during the bed transition process.

关键词： Sediment transport Bedforms Dunes Wavelets

Fabrication and multiscale characterization of 3D silver containing bioactive glass-ceramic scaffolds

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Bioactive Materials 2019年第1期4卷 215-223页

作者： Adam C.Marsh Nathan p.Mellott Natalia pajares-Chamorro Martin Crimp.a.thony wren Neal D.Hammer Xanthippi Chatzistavrou Department of Chemical Engineering&Materials Science Michigan State UniversityEast LansingMIUSA Alfred University Kazuo Inamori School of EngineeringAlfredNYUSA Department of Microbiology&Molecular Genetics Michigan State UniversityEast LansingMIUSA

In this work,we fabricated and characterized bioactive 3D glass-ceramic scaffolds with inherent antibacterial *** sol-gel(solution-gelation)technique and the sacrificial temp.a.e method were applied for the fabrication of 3D highly porous scaffolds in the 58.6SiO2-24.9CaO-7.2p2O5-4.2Al2O3–1.5Na2O−1.5K2O–2.1Ag2O system(Ag-BG).This system is known for its advanced bioactive and antibacterial *** fabrication of 3D scaffolds has potential applications that impact tissue *** study of the developed scaffolds from macro-characteristics to nano-,revealed a strong correlation between the macroscale properties such as antibacterial action,bioactivity with the microstructural characteristics such as elemental analysis,*** homogeneity,morphological,and microstructural characteristics of the scaffolds were studied by scanning electron microscopy associated with energy dispersive spectroscopy(SEM-EDS),transmittance electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XpS),Fourier transform infrared spectroscopy(FTIR),and UV-visible spectroscopy *** compressive strength of the 3D scaffolds was measured within the range of values for glass-ceramic scaffolds with similar compositions,porosity,and pore *** capability of the scaffolds to form an apatite-like p.a.e was tested by immersing the scaffolds in simulated body fluid(SBF)and the antibacterial response against methicillin-resistant Staphylococcus aureus(MRSA)was *** formation of an apatite p.a.e was observed after two weeks of immersion in SBF and the anti-MRSA effect occurs after both direct and indirect exposure.

关键词： 3D glass-ceramic scaffolds Nano and macro structural properties Bioactivity Antibacterial properties Silver

Sperm retrieval success and testicular histopathology in idiopathic nonobstructive azoospermia

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Asian Journal of Andrology 2020年第6期22卷 555-559页

作者： Arighno Das Joshua A Halpern Annie L Darves-Bornoz Mehul patel James wren Mary Kate Keeter Robert E Brannigan Department of Urology Northwestern University Feinberg School of MedicineChicagoIL 60611USA

prior studies have investigated sperm retrieval rates in men with non obstructive azoospermia(NOA)secondary to specific etiologies,yet most cases of NOA are *** compared sperm retrieval rates and testicular histopathology in idiopathic NOA(iNOA)and nonidiopathic NOA(niNOA).We performed a retrospective review of men with NOA who underwent microdissection testicular sperm extraction(microTESE)between 2000 and *** with no history of malignancy or cryptorchidism and negative genetic evaluation were considered *** regression determined the association between idiopathic etiology and primary outcomes of sperm retrieval and active spermatogenesis on *** 224 men,86(38.4%)were idiopathic,75(33.5%)were nonidiopathic,and 63(28.1%)did not undergo genetic *** age and serum testosterone were higher among iNOA or no testing versus *** follicle-stimulating hormone(FSH)was lower among iNOA or no testing versus niNOA.A higher proportion of iNOA or no testing versus niNOA had a clinical *** retrieval rates were similar between iNOA,niNOA,and no testing(41.8%vs 48.0%vs 55.6%,respectively;p=0.255).Active spermatogenesis was seen in a higher proportion of iNOA or no testing versus niNOA(31.4%and 27.0%vs 16.0%,p=0.073).On multivariable analysis,iNOA was not associated with sperm retrieval or spermatogenesis(p=0.430 and p=0.078,respectively).Rates of sperm retrieval and spermatogenesis on testis pathology were similar in men with iNOA and *** data will be useful to clinicians in preoperative counseling for men with NOA and negative genetic evaluation.

关键词： microdissection testicular sperm extraction nonobstructive azoospermia sperm retrieval rate