bluuebunny/crossref_metadata_2025 huggingface dataset:
Dripping into subterranean cavities from unsaturated fractures under evaporative conditions
Authors: Or Dani , Ghezzehei Teamrat A.
Published: September 2002

Water dripping into subterranean cavities within fractured porous media is studied in order to improve estimates of dripping rates, drop sizes, and chemical composition of droplets that could affect long‐term integrity of waste disposal canisters placed in caverns. Steady state liquid flux in fracture surfaces supported by flow in partially liquid‐filled grooves and liquid films in adjacent planes was calculated as a function of the matric potential (vapor pressure) of the fracture. At an intersection of a vertical fracture with a wider cavity the liquid flux feeds a growing pendant drop that eventually detaches. Equilibrium state size and approximate shape of liquid drops suspended from the cavity ceiling were determined from lateral and vertical force balance considering capillarity, gravity, and hydrostatic pressure. A one‐dimensional, viscous extension model with appropriate gravitational and surface tension components was employed to determine dripping rate from specified fracture roughness geometry as a function of matric potential (flux). The effect of evaporation from drop surface during drop formation was incorporated; the resulting alterations in drop volume, dripping rate, and drop solute concentration were determined. To facilitate experimental testing of the proposed model, a decoupled solution that considers independently controlled flux and evaporation is presented. Under evaporative conditions, dripping in finite period is possible only when volumetric flux exceeds evaporative demand. Calculations indicate that dripping rate and solute concentration are extremely sensitive to ambient matric potential. The results of this work may be extended to study other phenomena including formation and growth of stalactites and rivulet flow in cave ceilings.
New evidence on the economic benefits of controlling salinity in domestic water supplies
Authors: Ragan Guy E. , Young Robert A. , Makela Carole J.
Published: September 2002

To study the economic benefits of controlling salinity in residential water supplies, we surveyed households and appliance repair shops along the Arkansas River Basin in Colorado, where salinity ranges from 100 to 3600 mg/L. To avoid a downward bias on estimated appliance lives, we obtained and used data on both ages of in‐service appliances and ages at failure of failed appliances. We adapted the accelerated testing method to model the effect of salinity on appliance lives. Dishwashers, water heaters, garbage disposers, water softeners, and evaporative coolers showed statistically significant reductions in service life with increasing salinity. In comparison with the most cited previous study, we found no statistically significant effects for some appliances; for appliances common to both studies our estimates of salinity damages are one third or less as high. These differences may originate from inclusion of in‐service appliances or reduced damage due to technological improvements.
Transient temperature solution for a river with distributed inflows
Authors: Polehn R. A. , Kinsel W. C.
Published: September 2002

A one‐dimensional exact solution for the advective, transient thermal response of river flow is presented for the case of linear, position‐dependent volume flow rate. For reasonable restrictions appropriate to river flow it is shown that for the special quasi‐linear case of nonlinear heat source functions, the same equations are produced as those obtained from the method of characteristics for linear source functions. This approach avoids heat source linearization with the associated degradation in accuracy and enables the use of an accurate numerical solution procedure for a wider range of advective flows. The proposed solution method was used to investigate the thermal response due to longitudinal variation of volume flow rate, river speed, width, and depth.
Incoherent scatter radar measurement of vertical winds in the mesosphere
Authors: Zhou Qihou H.
Published: September 2002

We report a significant improvement in the measurement of mesospheric winds using the incoherent scatter radar technique. With a height resolution of 600 m and a time resolution of 1 min, we show that the accuracy of the vertical wind measured by the Arecibo incoherent scatter radar is about 1 m/s in the altitude range of 68–88 km. The observed vertical wind amplitude was of the order of a few meters per second. The wind variation was dominated by gravity waves having an apparent period of 34 min below 80 km and 13.8 min above 80 km. The vertical wavelength of the latter gravity wave was 36 km, which was more than twice that of the former. The much improved accuracy was achieved by changing the radar inter‐pulse‐period from 1 ms to 4 ms. This simple change shortens the integration time by about two orders of magnitude comparing with the scheme used in the past. The improved efficiency ought to provide new research opportunities in the D‐region using the incoherent scatter radar technique.
Geochemical evidence of melt intrusions along lithospheric faults of the Southern Apennines, Italy: Geodynamic and seismogenic implications
Authors: Italiano Francesco , Martelli Mauro , Martinelli Giovanni , Nuccio P. Mario
Published: September 2002

Several gas emissions, distributed along 200 km of the Southern Apennine axial zone, have been investigated. This portion of the sedimentary chain, which constitutes the accretionary prism of the westward subduction of the Adriatic plate, is subjected to a tensile stress field responsible of high‐magnitude earthquakes. The studied emissions are generally CO2‐dominated, have 3He/4He ratios in the range of 0.09–2.84 Ra, and display both 3He and 4He outputs in the range of those reported for the Italian active volcanoes Phlegrean Fields and Vulcano. The helium isotope ratios, together with the amount of released gas, indicate that a huge amount of mantle‐derived helium is released over all the investigated area. Our geochemical data and the geophysical peculiarities of the region, such as the high heat flow and the low resistivity of rocks below a depth of 15 km, coherently indicate the presence of melt intruded into the crust along lithospheric faults. Magma intrusions along the axial part of the Southern Apennine sedimentary chain are certainly unusual, since volcanism in central and southern Italy is concentrated along the peri‐Tyrrhenian margin of the peninsula. We suggest that melt is promoted by adiabatic uprise of the asthenosphere in the mantle wedge beneath the Apennines and it is subsequently intruded along tensile lithospheric faults, strongly affecting the thermal state of the lower crust. An interrelationship between the geodynamics, the melt intrusions, and the genesis of the large earthquakes (up to M = 7.1) in the region is suggested.
Stratospheric ozone in 3‐D models: A simple chemistry and the cross‐tropopause flux
Authors: McLinden C. A. , Olsen S. C. , Hannegan B. , Wild O. , Prather M. J. , Sundet J.
Published: September 2002

Two simple and computationally efficient models for simulating stratospheric ozone in three‐dimensional global transport models are presented. The first, linearized ozone (or Linoz), is a first‐order Taylor expansion of stratospheric chemical rates in which the ozone tendency has been linearized about the local ozone mixing ratio, temperature, and the overhead column ozone density. The second, synthetic ozone (or Synoz), is a passive, ozone‐like tracer released into the stratosphere at a rate equivalent to that of the cross‐tropopause ozone flux which, based on measurements and tracer‐tracer correlations, we have calculated to be 475±120 Tg/yr. Linoz and Synoz have been evaluated in the UC Irvine chemical transport model (CTM) with three different archived meteorological fields: the Goddard Institute for Space Studies (GISS) general circulation model (GCM) version II′, the GISS GCM version II, and merged forecast data from the European Centre forecast model (EC/Oslo). Linoz produced realistic annual, cross‐tropopause fluxes of 421 Tg/yr for the GISS II′ winds and 458 Tg/yr for the EC/Oslo winds; the GISS II winds produced an unrealistic flux of 790 Tg/yr. Linoz and Synoz profiles in the vicinity of the tropopause using the GISS II′ and EC/Oslo winds were found to be in good agreement with observations. We conclude that either approach may be adequate for a CTM focusing on tropospheric chemistry but that Linoz can also be used for calculating ozone fields interactively with the stratospheric circulation in a GCM. A future version of Linoz will allow for evolving background concentrations of key source gases, such as CH4 and N2O, and thus be applicable for long‐term climate simulations.
Ozone and sulfur dioxide dry deposition to forests: Observations and model evaluation
Authors: Finkelstein Peter L. , Ellestad Thomas G. , Clarke John F. , Meyers Tilden P. , Schwede Donna B. , Hebert Eric O. , Neal Julie A.
Published: September 2002

Fluxes and deposition velocities of O3 and SO2 were measured over both a deciduous and a mixed coniferous‐deciduous forest for full growing seasons. Fluxes and deposition velocities of O3 were measured over a coniferous forest for a month. Mean deposition velocities of 0.35 to 0.48 cm/s for O3 and 0.6 to 0.72 cm/s for SO2 were observed during the growing seasons of 1997 and 1998. Weekly averages of O3 deposition velocity ranged from 0.25 cm/s at the beginning and end of the season to 1.25 cm/s in late June. SO2 had a smaller seasonal variation, from 0.75 to 1.5 cm/s between the beginning and peak of the season. Because O3 concentrations are higher, the flux of O3 to forests is considerably greater than the flux of SO2. Daytime deposition velocities are very similar at each site, from 0.75 to 0.79 cm/s for O3, and from 1.01 to 1.04 cm/s for SO2. Diurnal cycles for both gases are discussed, as are the impact of some weather events. The peak time for O3 deposition velocity is in midmorning, while it is near midday for SO2. Surface wetness is usually associated with a small increase in deposition velocity, but for some rain events a major increase was noted. Minimum deposition velocities usually occur at night and increase slowly in the predawn hours before light. Comparisons are made between observations of deposition velocity and predictions made with the Meyers multilayer deposition velocity model. While the model is, on average, unbiased for O3, it tends to underpredict the higher deposition velocity values. The model is slightly biased low (underpredicts) for SO2 deposition velocity. The strengths of the model are noted, as are opportunities for improvement.
Ocean‐atmosphere exchange and atmospheric speciation of ammonia and methylamines in the region of the NW Arabian Sea
Authors: Gibb Stuart W. , Mantoura R. Fauzi C. , Liss Peter S.
Published: September 2002

Concentrations of ammonia / ammonium (NH3 /NH4+) and its methyl‐derivatives the methylamines (MAs) were determined in seawater, atmospheric, and rainwater samples during the U.K. Joint Global Ocean Flux Study ARABESQUE program in the Arabian Sea (August ‐ December 1994). In seawater, concentrations Of NH3/NH4+ were shown to be 10–100 times greater than those of MAs, of which monomethylamine was the most abundant. Concentrations of all analytes were highest in the productive coastal waters off Oman, and lowest in offshore oligotrophic regimes. Calculations demonstrated that both coastal and offshore waters vented NH3 to atmosphere, and that while coastal waters could act as sources or sinks of atmospheric MAs, offshore waters were a consistent sink. NH3 /NH4+ was the dominant atmospheric base, with MAs contributing 16–20% of total measured gaseous base and 5.9–12% of total measured aerosol base (sub‐micron). Although photochemical destruction was calculated to be more significant for MAs than for NH3, removal of all species from the atmosphere was dominated by wet deposition. Atmospheric deposition was estimated to fuel less than 1% of the nitrogen requirements of “new” production in oligotrophic regions of the Arabian Sea. With aerosol scavenging calculated to contribute under 0.5% of rainwater NH4+ and MAs, the gas phase was inferred as the dominant source of rainwater MAs and NH+4. However, equilibria calculations demonstrated rainwater to be undersaturated with respect to gaseous MA and NH3 concentrations, and that paradoxically it was not possible for Henry's law to hold for all analytes simultaneously.
Ten‐second Love‐wave propagation and strong ground motions in Taiwan
Authors: Chen Chau‐Huei , Teng Ta‐Liang , Gung Yuan‐Cheng
Published: September 2002

Applying the surface‐wave Gaussian beam method to a three‐dimensional (3‐D) structure of Taiwan, we have studied the generation and propagation of short‐period (10‐s) surface waves in a region of pronounced crustal heterogeneity, especially in a region defined to be at an epicentral distance larger than a few focal depths away, where high‐frequency near‐field motions are largely attenuated and surface waves are adequately developed. By perturbing the source model as well as the crustal model in an iterative inversion process, we have achieved an excellent fit to the recent strong‐motion observations recorded during the Tung‐Ao earthquake (June 5, 1994, ML = 6.0) in Taiwan. This allows us to (1) obtain a refined 3‐D crustal model of Taiwan from an initial model that was derived from recent tomographic results and, more important, (2) explain the distribution patterns of the strong shaking reported in terms of intensity maps for historical large earthquakes, and predict the long‐period strong‐motion distribution patterns for future large earthquakes in Taiwan. With an improved 3‐D structure, we have gained better insight into short‐period surface‐wave propagations as they are modified by crustal lateral heterogeneity. Focusing and defocusing are clearly demonstrated. Of particular interest is the Central Mountain Range, a massive Tertiary metamorphic body forming the backbone of Taiwan, that seems to serve as a “divergent lens” for the propagating surface waves, whereas the large sedimentary basin in southwestern Taiwan seems to focus the wavefronts instead. The computed distortions of the propagating surface‐wave field due to lateral heterogeneity are correctly reflected by the observations.
Geometry and mechanics of secondary fracturing around small three‐dimensional faults in granitic rock
Authors: Martel Stephen J. , Boger William A.
Published: September 2002

The orientations, locations, sizes, and relative abundances of secondary fractures observed along small natural faults can be accounted for by a three‐dimensional elastic model. Secondary fractures along small subvertical left‐lateral strike‐slip faults in massive granitic rock of the Sierra Nevada of California (1) consistently strike 25°±10° counterclockwise from their host faults and dip at angles greater than 80°; (2) generally are absent along the central portions of the fault traces; (3) are numerous near the ends of some fault traces but absent along others; and (4) in rare cases form echelon arrays either centered along a fault trace or just past the fault trace ends. These observations are consistent with secondary fractures that nucleated near the perimeter of an elliptical fault along a “cohesive rim” of high slip resistance and propagated in three dimensions normal to the local most tensile stress. The fracture orientations relative to the faults reflect small stress drops during slip on the faults. The observations and model together have direct implications for how faults grow and conduct fluids. Secondary fractures are likely to be larger at the ends of small strike‐slip faults rather than at their tops and bottoms. As a result, if strike‐slip faults grow in an unrestricted manner, they are more likely to be linked end‐to‐end rather than top‐to‐bottom, especially where slip is small. Hydraulic conductivity is likely to be enhanced at the linkages between faults, so highly conductive regions along linked strike‐slip faults are more likely to be vertical rather than horizontal.
Emissions lifetimes and ozone formation in power plant plumes
Authors: Ryerson T. B. , Buhr M. P. , Frost G. J. , Goldan P. D. , Holloway J. S. , Hübler G. , Jobson B. T. , Kuster W. C. , McKeen S. A. , Parrish D. D. , Roberts J. M. , Sueper D. T. , Trainer M. , Williams J. , Fehsenfeld F. C.
Published: September 2002

The concept of ozone production efficiency (OPE) per unit NOx is based on photochemical models and provides a tool with which to assess potential regional tropospheric ozone control strategies involving NOx emissions reductions. An aircraft study provided data from which power plant emissions removal rates and measurement‐based estimates of OPE are estimated. This study was performed as part of the Southern Oxidants Study‐1995 Nashville intensive and focuses on the evolution of NOx, SO2, and ozone concentrations in power plant plumes during transport. Two approaches are examined. A mass balance approach accounts for mixing effects within the boundary layer and is used to calculate effective boundary layer removal rates for NOx and SO2 and to estimate net OPE. Net OPE is more directly comparable to photochemical model results than previous measurement‐based estimates. Derived net production efficiencies from mass balance range from 1 to 3 molecules of ozone produced per molecule of NOx emitted. A concentration ratio approach provides an estimate of removal rates of primary emissions relative to a tracer species. This approach can be combined with emissions ratio information to provide upper limit estimates of OPE that range from 2 to 7. Both approaches illustrate the dependence of ozone production on NOx source strength in these large point source plumes. The dependence of total ozone production, ozone production efficiency, and the rate of ozone production on NOx source strength is examined. These results are interpreted in light of potential ozone control strategies for the region.
Aeolian features and processes at the Mars Pathfinder landing site
Authors: Greeley Ronald , Kraft Michael , Sullivan Robert , Wilson Gregory , Bridges Nathan , Herkenhoff Ken , Kuzmin Ruslan O. , Malin Michael , Ward Wes
Published: September 2002

The Mars Pathfinder landing site contains abundant features attributed to aeolian, or wind, processes. These include wind tails, drift deposits, duneforms of various types, ripplelike features, and ventifacts (the first clearly seen on Mars). Many of these features are consistant with formation involving sand‐size particles. Although some features, such as dunes, could develop from saltating sand‐size aggregates of finer grains, the discovery of ventifact flutes cut in rocks strongly suggests that at least some of the grains are crystalline, rather than aggregates. Excluding the ventifacts, the orientations of the wind‐related features correlate well with the orientations of bright wind steaks seen on Viking Orbiter images in the general area. They also correlate with wind direction predictions from the NASA‐Ames General Circulation Model (GCM) which show that the strongest winds in the area occur in the northern hemisphere winter and are directed toward 209°.
Development of regional regression relationships with censored data
Authors: Kroll Charles N. , Stedinger Jery R.
Published: September 2002

When no discharge record is available for a site, a regional regression relationship can be used to estimate low‐flow quantiles. Problems arise in the derivation of such models when some at‐site quantile estimates are reported as zero. One concern is that quantile estimates reported as zero may be in the range from zero to the measurement threshold. A second concern is that a logarithmic transformation cannot be used with zero quantile estimates, so traditional log linear least squares estimators cannot be computed. This paper uses visual examples and Monte Carlo simulation to compare the performance of techniques for estimating the parameters of a regional regression model when some at‐site quantile estimates are zero. Ordinary least squares (OLS) techniques employed in practice include adding a small constant to all at‐site quantile estimates (denoted OLSC), or neglecting all observation reported as zero (denoted OLSD). OLSC and OLSD performed poorly compared to the use of a Tobit model, which is a maximum likelihood estimator (MLE) procedure that represents the below threshold estimates as a range from zero to the threshold level. For a small amount of censoring, the OLSD method can be acceptable. A weighted Tobit model that accounts for the heteroscedasticity of the residuals in the regression model provided relatively little gain over the ordinary Tobit model.
Integration of cytogenetic landmarks into the draft sequence of the human genome
Authors: BAC Resource Consortium The , Cheung V. G. , Nowak N. , Jang W. , Kirsch I. R. , Zhao S. , Chen X.-N. , Furey T. S. , Kim U.-J. , Kuo W.-L. , Olivier M. , Conroy J. , Kasprzyk A. , Massa H. , Yonescu R. , Sait S. , Thoreen C. , Snijders A. , Lemyre E. , Bailey J. A. , Bruzel A. , Burrill W. D. , Clegg S. M. , Collins S. , Dhami P. , Friedman C. , Han C. S. , Herrick S. , Lee J. , Ligon A. H. , Lowry S. , Morley M. , Narasimhan S. , Osoegawa K. , Peng Z. , Plajzer-Frick I. , Quade B. J. , Scott D. , Sirotkin K. , Thorpe A. A. , Gray J. W. , Hudson J. , Pinkel D. , Ried T. , Rowen L. , Shen-Ong G. L. , Strausberg R. L. , Birney E. , Callen D. F. , Cheng J.-F. , Cox D. R. , Doggett N. A. , Carter N. P. , Eichler E. E. , Haussler D. , Korenberg J. R. , Morton C. C. , Albertson D. , Schuler G. , de Jong P. J. , Trask B. J.
Published: September 2002

We have placed 7,600 cytogenetically defined landmarks on the draft sequence of the human genome to help with the characterization of genes altered by gross chromosomal aberrations that cause human disease. The landmarks are large-insert clones mapped to chromosome bands by fluorescence in situ hybridization. Each clone contains a sequence tag that is positioned on the genomic sequence. This genome-wide set of sequence-anchored clones allows structural and functional analyses of the genome. This resource represents the first comprehensive integration of cytogenetic, radiation hybrid, linkage and sequence maps of the human genome; provides an independent validation of the sequence map1,2 and framework for contig order and orientation; surveys the genome for large-scale duplications, which are likely to require special attention during sequence assembly; and allows a stringent assessment of sequence differences between the dark and light bands of chromosomes. It also provides insight into large-scale chromatin structure and the evolution of chromosomes and gene families and will accelerate our understanding of the molecular bases of human disease and cancer.
Fabrication and characterization of nanoscale, Er3+-doped, ultratransparent oxy-fluoride glass ceramics
Authors: Tikhomirov V. K. , Furniss D. , Seddon A. B. , Reaney I. M. , Beggiora M. , Ferrari M. , Montagna M. , Rolli R.
Published: September 2002

We show that oxy-fluoride glass ceramics, with typical composition, 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2): 3.5(ErF3) mol % have potential applications in telecommunications. Upon heat treatment, Er3+ nucleates the growth of the nanocrystalline β-PbF2, which acts as its host. Heat treatment at 440 °C for 5 h and at 390 °C for 3 h gave rise to ∼12 and ∼2.5 nm diameter crystals, respectively. The emission band of Er3+ in the 1.54 μm telecommunications window (4I13/2→4I15/2 transition, at the half-height width) was 75 nm in the former and 90 nm in the latter case, while I13/24↔I15/24 absorption and emission bands became wavelength divergent in both cases. Also in the latter case, the spectrum was flat from 1.53 to 1.56 μm. The evolution of spectral behavior is explained by changes in average site geometry of the Er3+ dopant, related to the α→β phase transition of PbF2, which is stimulated by heat treatment.
Mechanical properties related to the relaxor-ferroelectric phase transition of titanium-doped lead magnesium niobate
Authors: Bao P. , Yan F. , Li W. , Dai Y. R. , Shen H. M. , Zhu J. S. , Wang Y. N. , Chan Helen L. W. , Choy Chung-Loong
Published: September 2002

The dielectric properties, internal friction, and Young’s modulus of (1−x%) Pb(Mg1/3Nb2/3)O3−x%PbTiO3 (for x=13, 23, and 33) ceramics have been measured. A phase-transition-like internal friction peak associated with Young’s modulus softening has been observed at temperature TR–F, which can be attributed to the relaxor-to-ferroelectrics (R–F) phase transition. Therefore, the R–F phase transition can be explained in terms of the paraelectric-to-ferroelectric phase transition of paraelectric matrix in the materials.
Increased nucleation temperature of NiSi2 in the reaction of Ni thin films with Si1−xGex
Authors: Seger J. , Zhang S.-L. , Mangelinck D. , Radamson H. H.
Published: September 2002

The formation of a ternary solid solution NiSi1−xGex, instead of a mixture of NiSi and NiGe, is found during solid-state interactions between Ni and various Si1−xGex films ranging from pure Si to pure Ge. The lattice parameters of the solid solution of orthorhombic structure increase linearly with Ge content (x) as: a=5.24+0.19x Å, b=3.25+0.16x Å, and c=5.68+0.15x Å. The specific resistivity increases from 17 μΩ cm for NiSi to 21 μΩ cm for NiSi0.71Ge0.29 and NiSi0.42Ge0.58. Although the Ge content rapidly drops from 30–60 to about 10 at. % in the solid solutions formed above 600 °C, the crystallographic structure remains unchanged and no NiSi2 [or Ni(Si,Ge)2] is found in the Si1−xGex samples even after annealing at 850 °C. Without Ge, the NiSi completely disappears at 750 °C. These results indicate a strong effect of the entropy of mixing in NiSi–NiGe on the nucleation of NiSi2.
Experimental study of wave characteristics on a thin layer of de/anti-icing fluid
Authors: Özgen S. , Carbonaro M. , Sarma G. S. R.
Published: September 2002

Several series of experiments were conducted in order to investigate wave formation and wave characteristics on a thin layer of de/anti-icing fluid using a nonintrusive technique. The configuration consists of a thin layer of de/anti-icing fluid deposited on the lower wall of the wind tunnel section, sheared by a turbulent airflow. Beyond a critical value of the wind speed, two-dimensional surface waves could be observed. The characteristics of these waves like the wavelength and the wave speed could be measured using the light absorption technique. The main purpose of the study is to augment the already existing experimental data for wave characteristics of Newtonian liquid layers in the literature. The non-Newtonian character and the high viscosities of the fluids used render these experiments and their results original. The results obtained from the experiments have been compared with the results of an already existing code utilizing linear stability theory and the agreement was seen to be very good provided that the liquid film is not too thin.
Continuous chain of bubbles in concentrated polymeric solutions
Authors: Kliakhandler Igor L.
Published: September 2002

Motion of bubbles in a liquid is a ubiquitous yet very nontrivial phenomenon. The available body of knowledge and even its language connotation consider bubbles only as a discrete, detached from each other, units. It turns out that in concentrated polymer solutions bubbles may form a qualitatively new structure. The experimental study reported below shows that bubbles may form a very stable, continuous, slowly rising, connected long chain similar to beads, or bubble “sausage.”
The influence of developed cavitation on the flow of a turbulent shear layer
Authors: Iyer Claudia O. , Ceccio Steven L.
Published: September 2002

Developed cavitation in a shear layer was studied experimentally in order to determine the effect that the growth and collapse of cavitation have on the dynamics of shear flows. Planar particle imaging velocimetry (PIV) was used to measure the velocity field, the vorticity, strain rates, and Reynolds stresses of the flow downstream of the cavitating and noncavitating shear layer; the flow pressures and void fraction were also measured. The flow downstream of a cavitating shear flow was compared to the noncavitating shear flow. For cavitating shear layers with void fractions of up to 1.5%, the growth rate of the shear layer and the mean flow downstream of the shear layer were modified by the growth and collapse of cavitation bubbles. The cross-stream velocity fluctuations and the Reynolds stresses measured downstream of the cavitating shear layer were reduced compared to the entirely noncavitating flow. This result is inconsistent with a scaling of the shear stress within the shear flow based on the mean flow. The decrease in the cross-stream fluctuations and Reynolds stresses suggests that the cavitation within the cores of strong streamwise vortices has decreased the coupling between the streamwise and cross-stream velocity fluctuations.
An evaluation of linear instability waves as sources of sound in a supersonic turbulent jet
Authors: Mohseni Kamran , Colonius Tim , Freund Jonathan B.
Published: September 2002

Mach wave radiation from supersonic jets is revisited to better quantify the extent to which linearized equations represent the details of the actual mechanism. To this end, we solve the linearized Navier–Stokes equations (LNS) with precisely the same mean flow and inflow disturbances as a previous direct numerical simulation (DNS) of a perfectly expanded turbulent M=1.92 jet [Freund et al., AIAA J. 38, 2023 (2000)]. We restrict our attention to the first two azimuthal modes, n=0 and n=1, which constitute most of the acoustic field. The direction of peak radiation and the peak Strouhal number matches the DNS reasonably well, which is in accord with previous experimental justification of the linear theory. However, it is found that the sound pressure level predicted by LNS is significantly lower than that from DNS. In order to investigate the discrepancy, individual frequency components of the solution are examined. These confirm that near the peak Strouhal number, particularly for the first helical mode n=1, the amplification of disturbances in the LNS closely matches the DNS. However, away from the peak frequency (and generally for the azimuthal mode n=0), modes in the LNS are damped while those in the DNS grow at rates comparable to those at the peak Strouhal number.
Dielectric mapping of a Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 ternary phase spread
Authors: Chang Hauyee , Yu K.-M. , Dong Y. , Xiang Xiao-Dong
Published: September 2002

Lead perovskite compounds possess very rich and complex phase diagrams. They also have great potential in a variety of commercial applications. However, due in part to the very complicated nature of these materials, very few systematic studies of their ternary phase diagrams with respect to electrical properties have been performed. In this letter, we report the microwave dielectric property mapping of a ternary Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 composition spread using a scanning evanescent microwave probe. We identified composition regions with dielectric constants higher than 600 at 1 GHz.
Instabilities and drop formation in cylindrical liquid jets in reduced gravity
Authors: Edwards A. P. R. , Osborne B. P. , Stoltzfus J. M. , Howes T. , Steinberg T. A.
Published: September 2002

The effects of convective and absolute instabilities on the formation of drops formed from cylindrical liquid jets of glycerol/water issuing into still air were investigated. Medium-duration reduced gravity tests were conducted aboard NASA’s KC-135 and compared to similar tests performed under normal gravity conditions to aid in understanding the drop formation process. In reduced gravity, the Rayleigh–Chandrasekhar Equation was found to accurately predict the transition between a region of absolute and convective instability as defined by a critical Weber number. Observations of the physics of the jet, its breakup, and subsequent drop dynamics under both gravity conditions and the effects of the two instabilities on these processes are presented. All the normal gravity liquid jets investigated, in regions of convective or absolute instability, were subject to significant stretching effects, which affected the subsequent drop and associated geometry and dynamics. These effects were not displayed in reduced gravity and, therefore, the liquid jets would form drops which took longer to form (reduction in drop frequency), larger in size, and more spherical (surface tension effects). Most observed changes, in regions of either absolute or convective instabilities, were due to a reduction in the buoyancy force and an increased importance of the surface tension force acting on the liquid contained in the jet or formed drop. Reduced gravity environments allow better investigations to be performed into the physics of liquid jets, subsequently formed drops, and the effects of instabilities on these systems. In reduced gravity, drops form up to three times more slowly and as a consequence are up to three times larger in volume in the theoretical absolute instability region than in the theoretical convective instability region. This difference was not seen in the corresponding normal gravity tests due to the masking effects of gravity. A drop is shown to be able to form and detach in a region of absolute instability, and spanning the critical Weber number (from a region of convective to absolute instability) resulted in a marked change in dynamics and geometry of the liquid jet and detaching drops.
An experimental and numerical study of the spatial evolution of unidirectional nonlinear water-wave groups
Authors: Shemer Lev , Kit Eliezer , Jiao Haiying
Published: September 2002

Spatial evolution of nonlinear narrow-spectrum deep-water wave groups is studied experimentally in a wave tank. The experimental results are compared with the computations based on the unidirectional Zakharov equation and the Dysthe model. The very good agreement between the computational results based on both models with the experiments prompted an attempt to perform simulations for a wider initial spectral width, that formally violate the assumptions adopted in the derivation of the Dysthe model. The accuracy of the results based on the Dysthe model is checked against the solutions of the Zakharov equation, which is free of restrictions on the spectral width. Conclusions regarding the domain of validity of the Dysthe model are drawn.
Optical properties of a light-emitting polymer directly patterned by soft lithography
Authors: Lawrence J. R. , Andrew P. , Barnes W. L. , Buck M. , Turnbull G. A. , Samuel I. D. W.
Published: September 2002

We present the optical properties of a directly patterned light-emitting polymer. The patterned poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-paraphenylenevinylene film is fabricated using hot embossing lithography. The effect of the embossed microstructure on the light emitted from the polymer is examined by measuring the angle-dependent photoluminescence and its photonic band structure. The imposed grating modifies the emitted light by Bragg scattering into free space light that would otherwise be trapped as waveguide modes. This simple patterning technique may find application in improving the performance of light-emitting polymer devices.
Near wake of an impulsively started disk
Authors: Johari H. , Stein K.
Published: September 2002

The near wake of an impulsively started disk was studied computationally by a finite element code with a Smagorinsky turbulence model. The shear layer separating from the disk lip rolled up into a symmetric starting vortex ring at first. As time evolved, the vortex stretched in the downstream direction and flow instabilities caused the vortex ring to become wavy eventually leading to the breakup of the ring. The complete breakup and shedding of the starting vortex ring took a time of approximately 14D/U, where D is the disk diameter and U is the freestream velocity. The starting vortex ring circulation attained a plateau of ≈2.6UD at a time of about 4D/U, in good agreement with the experimental findings by Balligand (2000). The radial circulation profiles are Gaussian during the symmetric phase and collapse together at a time of 4D/U. Beyond this time, the vortex ring celerity is constant and vorticity extends to the symmetry axis. The base pressure coefficient becomes positive as the vortex ring moves away from the disk and remains positive until the ring is completely shed. The breakup of the starting vortex ring is concurrent with the appearance of an azimuthal pressure gradient and core flow. Following the breakup of the starting vortex ring, the flow became three-dimensional and settled into an open wake. The mean drag and base pressure coefficients were nearly constant after a time of approximately 30D/U and matched very well against experimental data.
Transient growth in Taylor–Couette flow
Authors: Hristova Hristina , Roch Sébastien , Schmid Peter J. , Tuckerman Laurette S.
Published: September 2002

Transient growth due to non-normality is investigated for the Taylor–Couette problem with counter-rotating cylinders as a function of aspect ratio η and Reynolds number Re. For all Re⩽500, transient growth is enhanced by curvature, i.e., is greater for η<1 than for η=1, the plane Couette limit. For fixed Re<130 it is found that the greatest transient growth is achieved for η between the Taylor–Couette linear stability boundary, if it exists, and one, while for Re>130 the greatest transient growth is achieved for η on the linear stability boundary. Transient growth is shown to be approximately 20% higher near the linear stability boundary at Re=310, η=0.986 than at Re=310, η=1, near the threshold observed for transition in plane Couette flow. The energy in the optimal inputs is primarily meridional; that in the optimal outputs is primarily azimuthal. Pseudospectra are calculated for two contrasting cases. For large curvature, η=0.5, the pseudospectra adhere more closely to the spectrum than in a narrow gap case, η=0.99.
A glimpse of hydrodynamics beyond the Navier–Stokes equations
Authors: Baganoff D.
Published: September 2002

A solution of Maxwell’s moment equations is obtained for the steady, one-dimensional flow through a normal shock wave in a Maxwellian gas. The solution method makes use of a new representation for the conservation equations, a closure relation for a single third-order moment, and a spatially integrated form of Maxwell’s equations of transfer. The integrated equations of transfer act as constraints in evaluating two sets of coefficients introduced in the conservation equations and the single closure relation. A total of only four coefficients are found to be fully sufficient when comparisons are made with results from the direct simulation Monte Carlo method, which show excellent agreement across all hydrodynamic variables including two fourth-order moments which the theory predicts.
Impact of water drops on small targets
Authors: Rozhkov A. , Prunet-Foch B. , Vignes-Adler M.
Published: September 2002

The collision of water drops against small targets was studied experimentally by means of a high-speed photography technique. The drop impact velocity was about 3.5 m/s. Drop diameters were in the range of 2.8–4.0 mm. The target was a stainless steel disk of 3.9 mm diameter. The drop spread beyond the target like a central cap surrounded by a thin, slightly conical lamella bounded by a thicker rim. By mounting a small obstacle near the target, surface-tension driven Mach waves in the flowing lamella were generated, which are formally equivalent to the familiar compressibility driven Mach waves in gas dynamics. From the measurement of the Mach angle, the values of some flow parameters could be obtained as functions of time, which provided insight into the flow structure. The liquid flowed from the central cap to the liquid rim through the thin lamella at constant momentum flux. At a certain stage of the process, most of the liquid accumulated in the rim and the internal part of the lamella became metastable. In this situation, a rupture wave propagating through the metastable internal part of the lamella caused the rim to retract while forming outwardly directed secondary jets. The jets disintegrated into secondary droplets due to the Savart–Plateau–Rayleigh instability. Prior to the end of the retraction, an internal circular wave of rupture was formed. It originated at the target and then it propagated to meet the retracting rim. Their meeting resulted in a crown of tiny droplets. A theoretical analysis of the ejection process is proposed.
Morphology and electronic structure in nitrogen-doped ultrananocrystalline diamond
Authors: Birrell James , Carlisle J. A. , Auciello O. , Gruen D. M. , Gibson J. M.
Published: September 2002

Ultrananocrystalline diamond (UNCD) thin films consist of 2–5 nm grains of pure sp3-bonded carbon and ∼0.5-nm-wide grain boundaries with a disordered mixture of sp2- and sp3-bonded carbon. UNCD exhibits many interesting materials properties that are a direct consequence of its nanoscale morphology. In this work, we report the changes in morphology induced in UNCD by the addition of nitrogen gas to the Ar/CH4 microwave plasma, as studied using high-resolution transmission electron microscopy and nanoprobe-based electron energy-loss spectroscopy. Both the grain size and grain-boundary widths increase with the addition of N2, but the overall bonding structure in both regions remains mostly unchanged. These results are used to explain the variation of materials properties of nitrogen-incorporated UNCD films.
Cavitation inception following shock wave passage
Authors: Ohl C. D.
Published: September 2002

Cavitation bubble nucleation following the passage of an extracorporeal shock wave lithotripter pulse is investigated experimentally and numerically. In the experiments two configurations are considered: Free passage of the shock wave, and reflection of the shock wave from a rigid reflector. The nucleation and the early growth phase of the bubbles including radial and translatory motion is compared with a commonly used model for bubble dynamics, the Gilmore model, which is coupled to a one-dimensional model for translatory motion. Reasonable agreement is found for the predicted translatory motion of the bubble center; however, considerable disagreement between a simple cavitation inception theory and the experiment exists: Cavitation bubbles expand later than predicted pointing to a more complex inception scenario than a single stabilized gas pocket. A hypothesis is proposed to explain the delayed growth of the bubbles. Additional findings are the formation of bands with diminished bubble activity, which very much resemble the structure found by Sokolov et al. (2001). High-speed photographs suggest that bubble–bubble interaction plays an important role in the formation of structured bands.
Effective-medium theories for predicting hydrodynamic transport properties of bidisperse suspensions
Authors: Koo Sangkyun , Sangani Ashok S.
Published: September 2002

Effective-medium theories for predicting conditionally averaged velocity field and hydrodynamic transport coefficients of monodisperse suspensions are extended to bidisperse suspensions. The predictions of the theory are shown to agree very well with the results of direct numerical simulations of bidisperse suspensions with hard-sphere configurations up to volume fractions at which phase separation in bidisperse hard-sphere systems are observed.
Radial oscillations of encapsulated microbubbles in viscoelastic liquids
Authors: Khismatullin Damir B. , Nadim Ali
Published: September 2002

The small-amplitude radial oscillations of a gas microbubble encapsulated by a viscoelastic solid shell and surrounded by a slightly compressible viscoelastic liquid are studied theoretically. The Kelvin–Voigt and 4-constant Oldroyd models are used to describe the viscoelastic properties of the shell and liquid, respectively. The equation for radial oscillation is derived using the method of matched asymptotic expansions. Based on this equation, we present the expressions for damping coefficients and scattering cross sections at the fundamental frequency and at twice that frequency. The numerical maximization of the amplitude-frequency response function shows that the resonance frequency for the encapsulated microbubble highly depends on viscous damping, and therefore, significantly differs from the undamped natural frequency. The effects of the shell and liquid parameters on the resonance frequency and scattering cross sections are analyzed.
Effects of vertical vibration on hopper flows of granular material
Authors: Wassgren C. R. , Hunt M. L. , Freese P. J. , Palamara J. , Brennen C. E.
Published: September 2002

The discharge of granular material from a hopper subject to vertical sinusoidal oscillations was investigated using experiments and discrete element computer simulations. With the hopper exit closed, side-wall convection cells are observed, oriented such that particles move up along the inclined walls of the hopper and down at the center line. The convection cells are a result of the granular bed dilation during free fall and the subsequent interaction with the hopper walls. The mass discharge rate for a vibrating hopper scaled by the discharge rate without vibration reaches a maximum value at a dimensionless velocity amplitude just greater than 1. Further increases in the velocity decrease the discharge rate. This decrease occurs due to a decrease in the bulk density of the discharging material when vibration is applied.
Interfacial gravity currents. II. Wave excitation
Authors: Mehta A. P. , Sutherland B. R. , Kyba P. J.
Published: September 2002

We examine the response of a two- and three-layer salt-stratified fluid to the collapse of a mixed region intruding along the middle layer. For sufficiently deep middle layers, the intrusion (an interfacial gravity current) excites a double-humped solitary wave appearing in the interfacial layer in front of the intrusion head. When the solitary wave is generated the current stops propagating. Trailing the intrusion are large-amplitude trapped internal waves. We study the effect of middle-layer depth and density difference to determine the conditions under which a solitary wave is generated. We propose that this transition occurs because the intrusion resonantly couples with trapped internal waves for a sufficiently thick interface.
A technique for real-time visualization of flow structure in high-speed flows
Authors: Thurow Brian , Hileman James , Lempert Walter , Samimy Mo
Published: September 2002

A newly developed MHz rate imaging system that provides real-time flow visualization is described. The technique utilizes a custom-built Nd:YAG pulse burst laser and an ultra high-speed digital camera and is capable of capturing 17 images over 150 microseconds. The system was used to visualize a Mach 1.3 (Mc=0.6) axisymmetric jet. Sample results indicate the potential of the technique to provide detailed information on the dynamic characteristics of large-scale structures. A two-dimensional cross-correlation technique was used to calculate the convective velocity of large-scale structures. Present results generally agree with the findings of earlier investigations that indicate a significant deviation of the convective velocity from theoretical predictions.