bluuebunny/crossref_metadata_2025 huggingface dataset:
A Chemical Fractionation for Structure–Function Relations of Soil Organic Matter in Nutrient Cycling
Authors: Olk Daniel C.
Published: April 2006

Chemical extractions of soil organic matter (SOM) have not been widely used to elucidate the dynamics of SOM in field settings, especially to address issues of nutrient cycling. To illustrate potential applications of chemical extractions to nutrient issues, this report reviews studies in which the extraction of SOM fractions was based on their binding to polyvalent soil cations. Radiocarbon ages and cycling rates of13C and15N indicated that the unbound mobile humic acid (MHA) fraction cycled faster than did the cationic‐bound calcium humate (CaHA) fraction. Analyses for C, N, H, and O concentrations and for biochemical groups including carboxyl, phenol, amino, diester P, and free radicals demonstrated that the MHA consisted of more labile and less humified materials than did the CaHA. Quantities and chemical natures of both fractions responded to recent crop management, especially those of the MHA. Three case studies are described in which characterization of the MHA and CaHA contributed toward a process‐level understanding of nutrient cycling: (i) a phenol accumulation in the MHA fraction was linked to an inhibition of N mineralization in tropical lowland soils under continuous rice (Oryza sativaL.) cropping, (ii) addition of the MHA to California cotton (Gossypium hirstumL.) soils in laboratory studies resulted in increased K availability and plant K uptake, reproducing the benefit of animal manure application in field conditions, and (iii) effects of straw management and winter flooding on N cycling in California rice soils were elucidated by studying a fraction comparable to the MHA fraction. This fractionation is well suited for studying N dynamics, especially in soils enriched in phenolic compounds, and it enabled the linkage of SOM function with chemical nature. It worked well in C‐rich flooded soils but needs further evaluation in upland aerobic soils. Further insight into chemical structure and function relations might be achieved by its integration with physical and biological extractions.
Importance of Soil Organic Matter Fractions in Soil‐Landscape and Regional Assessments of Pesticide Sorption and Leaching in Soil
Authors: Farenhorst Annemieke
Published: April 2006

Agricultural policy frameworks aim to develop scientifically sound measures that can be used to assess the environmental performance and risks associated with agricultural systems. As part of this assessment, pesticide leaching models are applied at large scales to assess the risk of pesticide groundwater contamination across soil series, agricultural fields, watersheds, or regions. Measurements of pesticide sorption by soil are among the most sensitive input parameters in pesticide leaching models. Soil organic matter (SOM) is the single most important soil constituent influencing pesticide sorption in soils. The interaction of pesticides with SOM is often studied in the laboratory using batch‐equilibrium experiments in combination with techniques that quantify chemical and structural characteristics of SOM. This paper reviews these laboratory studies and discusses their importance to the development of agricultural policy frameworks. This review paper was written as part of a symposium on “Meaningful pools in determining soil C and N dynamics” which was held by the SSSA and the Canadian Soil Science Society during the 2004 ASA‐CSSA‐SSSA International Annual Meetings in Seattle, WA.
Effects of Irrigation and Plastic Mulch on Soil Properties on Semiarid Abandoned Fields
Authors: van der Meulen E. S. , Nol L. , Cammeraat L. H.
Published: April 2006

The Guadalentín Basin in Spain is one of the driest areas of Europe and has problems with high evaporation rates, and high risks of desertification exist including soil quality loss and soil erosion. Farmers in this semiarid region use polyethylene covers on their irrigated croplands to reduce evaporation to enhance crop yield. When farmers abandon the acres, they leave the plastic covers on the fields. Up to now research has been concentrating on the effects of plastic covers on crop yield and microclimate under these covers but there is little known about the effects of plastic covers and irrigation on soil quality, erosion susceptibility, and hydrology after abandonment of these fields. The research question in this paper is: How do the former irrigation practices and plastic soil covers affect organic C content, aggregate stability, hydrological properties, and erosion susceptibility? Organic C content and aggregate stability are important soil quality parameters that are easy to measure. Beside these two parameters, soil crusting, infiltration rates, and sediment yields have been determined for a set of irrigated fields that have been abandoned at different times (up to 20 yr) and where plastic covers have been used. The properties of these fields were compared with control sites with comparable periods of abandonment and substrate, but where only classical rain fed cropping systems have been applied. It was expected that leaving plastic remains in the soil after abandonment would be harmful to soil quality and would lower infiltration. The first associations with seeing the plastic are those of garbage and pollution. In fact, most of the indicators of soil quality considered in this survey turned out to be better or the same on the fields where irrigation and plastic covers had been used, when compared with control fields. Organic C contents were up to 40% higher on fields where plastic sheets remain and soil aggregates were more stabile. Fields where plastic had been mixed with the soil by tillage showed lower erosion susceptibilities.
A Lost Letter of Fra Girolamo Savonarola*
Authors: Weinstein Donald
Published: April 2006

Among the letters of Savonarola listed as now lost is one to Fra Benedetto di Paolo. The existence of such a letter is known from an entry in the sixteenth-century catalog of Savonarola's letters compiled by Fra Bernardo Castiglione. This catalog has also disappeared but Vincenzo Marchese saw it in the San Marco archives in the mid-nineteenth century and noted Castiglione's seventh entry as follows: 'Scripsit cuidam F. Benedicto Pauli reprehensivam epistolam de quadam eius inobedientia, quae incipit: F. Benedetto. A Dio non è piaciuto questa vostra inobedientia, ec.’ Marchese identified the recipient as Fra Benedetto di Paolo of Florence, the miniaturist and author of Cedrus Libani, a life of Savonarola in verse, which Marchese had just published.The letter itself was lost.
Amorum Emblemata: Tristan I'Hermite and the Emblematic Tradition
Authors: Johnson L. W.
Published: April 2006

In 1626 Tristan I'Hermite was commissioned to write a poetic description of Berny, the country house near Bourg-la-Reine to which the Marquise de Puisieux had been obliged to withdraw following her husband's disgrace at court. The chateau, a handsome maison de plaisance surrounded by extensive formal gardens, was one of the earliest designed by François Mansard and had been built for the father-in-law of the marquise, the Chancellor Sillery.
A Newly Discovered Chronicle by Marco Parenti
Authors: Phillips Mark
Published: April 2006

Among the manuscripts of the Biblioteca Nazionale in Florence there is a copy of an extensive eyewitness account of Florentine politics in the 1460's which appears to have been overlooked by historians of Florentine politics and historiography. Catalogued as Magliabecchi xxv, 272, it is described as an anonymous sixteenth-century manuscript containing ‘Diverse notizie istoriche d'Italia, delle potenze che la dominavano nel 1464 e delle cose seguite in Firenze contro la fazione de’ Medici fino al 1467.’ Although the manuscript is not a fifteenth-century autograph, there can be little doubt as to the authenticity of its contents. Not only does it contain a considerable amount of specific information that could only come from a firsthand source, but several self-references make it apparent that it is the work of the silk merchant and humanist Marco Parenti.
François de Bellefwest's La Pyrénée: The First French Pastoral Novel
Authors: Weitz Margaret Collins
Published: April 2006

La Pyrénée (1571) stands out in the very considerable corpus of writings of François de Belleforest. The work was long thought to be a translation, or at best an adaptation, of Sannazaro's Arcadia (1502-1504). While Jules Marsan in his study of the pastorale dramatique published at the beginning of this century suggested that Belleforest might have been familiar with Montemayor's Diana (1550), no one has yet undertaken a study of La Pyrénée. Unlike Vauquelin de la Fresnaye's Foresteries (1555) or Remy Belleau's Bergeries (1565), both of which employ prose passages as a mere framework for the inclusion of poems, Belleforest's La Pyrénée is the first work in prose in French literature to which the term ‘pastoral novel’ might accurately be applied.
An Early Interpretation of Tasso's Gerusalemme liberata
Authors: Carman Charles H.
Published: April 2006

The National Gallery of Ireland in Dublin has a painting of The Liberation of Jerusalem in its collection (fig. l). One enters the carefully arranged and brilliantly colored composition through the most prominent figure on a rearing horse who signals the onslaught enacted to the right. In sharp contrast is the relaxed and somewhat melancholy allegory of victory reclining in the foreground. By combining a keen historical accuracy with an allegorical figure to suggest the context and purpose of action, the painter reveals himself to be acutely sensitive to Torquato Tasso's epic poem Gerusalemme liberata. Before pursuing this relationship, however, there is a question of authorship to resolve.
The Artis Grammaticae Opusculum of Bartolomeo Sulmonese: A Newly Discovered Latin Grammar of the Quattrocento
Authors: Keith Percival W.
Published: April 2006

In the course of collecting manuscript copies of the Latin grammar of Guarino Veronese (1376-1460) I recently chanced to examine Codex Palatinus Latinus 1760, which according to the inventory in the Vatican Library contains a copy of Guarino's grammar. The inventory is correct: this manuscript does indeed contain the work in question, but as I quickly discovered, it also contains another grammatical work, unnoticed by the compiler of the inventory.

This is a manuscript of eighty-two leaves, of which the text of Guarino's grammar occupies the first thirty-two (fols. 1-32), and the second work the remainder (fols. 33-82), with a blank page (fol. 32v) between the two.
More's Letter to Dorp: Remapping the Trivium
Authors: Kinney Daniel
Published: April 2006

Thomas More's long letter to Martin van Dorp, Louvain humanist turned theologian, has begun to distinguish itself in the minds of many Renaissance scholars as something more than indifferent episode in the long and inconclusive history of Erasmus' personal differences with Dorp. In fact, More's letter is one of the first systematic defenses of humanist method, encompassing a critique of Scholastic grammar, dialectic, and theology, as well as a tightly argued defense of the new philological theology. More's debt to Valla, long obscured by More's strategic unwillingness in this letter to make much of a figure whom Dorp so detests, has finally begun to receive due attention.
Stuart Civic Pageants and Textual Performance
Authors: Bergeron David M.
Published: April 2006

Playwrights increasingly intend the pageant texts for readers; these texts become commemorative books that both capture the event and add to it. They assume an expository and narrative function that sets them apart from the typical dramatic text. By examining the extant printed texts of Jacobean and Caroline Lord Mayor's Shows, I argue that these publications do not obliterate theatrical performance or displace it so much as they complete it. Dramatists and printers come to recognize the lasting value of textual performance in civic pageants.
Portraits and Masks in the Art of Lorenzo de’ Medici, Botticelli, and Politian's Stanze per la Giostra
Authors: Dempsey Charles
Published: April 2006

The subject of my lecture is the phenomenon of masking in the Florence of Lorenzo de' Medici. I begin with an overview of the evidence in favor of the early claims that Lorenzo himself invented the modern masquerade, and continue with an examination of images of Triumphs in art, showing how these evolved into quasi-theatrical displays with masqued participants. I then turn to the phenomenon of masking in the high art of Lorenzo himself Botticelli and Politian. My lecture ends with a consideration of Politian's Stanze per la giostra di Giuliano de’ Medici, claiming that the poem commemorates and interprets the death of Giuliano by showing him to have been deluded by Cupid and by his mother Venus hidden behind the false masks of Pallas and Glory.
Prognostic significance of Fas (CD95/APO‐1) positivity in patients with primary nodal diffuse large B‐cell lymphoma
Authors: Eser Bulent , Sari Ismail , Canoz Ozlem , Altuntas Fevzi , Cakmak Erol , Ozturk Ahmet , Ozkan Metin , Er Ozlem , Cetin Mustafa , Unal Ali
Published: April 2006

Fas (CD95/APO‐1) is a protein that is mainly related to apoptosis of lymphoid cells. The increment of Fas expression is associated with long‐term survival in various malignancies. However, there are limited studies regarding the effect of Fas expression on the course and prognosis of non‐Hodgkin's lymphoma. The aim of this study was to investigate the significance of immunohistochemical Fas expression on the prognosis of nodal diffuse large B‐cell lymphoma.

A total of 63 patients with primary nodal diffuse large B‐cell lymphoma diagnosed in the Erciyes University Department of Hematology between 1990 and 2003 were included in the study. The median age of the patients was 55 years old (range 19–102 years old). The median follow‐up period was 19 months (2–132 months). Histopathological sections were stained immunohistochemically and evaluated by light microscopy for Fas, bcl‐2, and p53. Clinical and laboratory parameters including Fas, bcl‐2, and p53 positivity, age, sex, performance status, clinical stage, presence of B symptoms, bone marrow involvement, extranodal involvement, and lactic dehydrogenase levels were evaluated to compare overall survival.

Complete remission was obtained in 28 patients (44.4%) after first‐line chemotherapy. Fas positivity, male gender, good performance status, clinical stage I‐II, absence of B symptoms, normal lactic dehydrogenase value, and absence of bone marrow involvement were favorable prognostic factors for complete remission in statistical analysis. Multivariate analysis revealed that positive Fas expression and ECOG performance status were independent prognostic factors for overall survival. Also, Fas‐positive patiens had significantly prolonged progression‐free survival.

Immunohistochemical Fas positivity was a favorable prognostic factor for complete remission and overall and progression‐free survival in primary nodal diffuse large B‐cell lymphoma. Am. J. Hematol. 81:307–314, 2006. © 2006 Wiley‐Liss, Inc.
Quantum‐Dot‐Labeled DNA Probes for Fluorescence In Situ Hybridization (FISH) in the Microorganism Escherichia coli
Authors: Wu Sheng‐Mei , Zhao Xiang , Zhang Zhi‐Ling , Xie Hai‐Yan , Tian Zhi‐Quan , Peng Jun , Lu Zhe‐Xue , Pang Dai‐Wen , Xie Zhi‐Xiong
Published: April 2006

Semiconductor quantum dots (QDs) as a kind of nonisotopic biological labeling material have many unique fluorescent properties relative to conventional organic dyes and fluorescent proteins, such as composition‐ and size‐dependent absorption and emission, a broad absorption spectrum, photostability, and single‐dot sensitivity. These properties make them a promising stable and sensitive label, which can be used for long‐term fluorescent tracking and subcellular location of genes and proteins. Here, a simple approach for the construction of QD‐labeled DNA probes was developed by attaching thiol‐ssDNA to QDs via a metal–thiol bond. The as‐prepared QD‐labeled DNA probes had high dispersivity, bioactivity, and specificity for hybridization. Based on such a kind of probe with a sequence complementary to multiple clone sites in plasmid pUC18, fluorescence in situ hybridization of the tiny bacterium Escherichia coli has been realized for the first time.
Application of lentivirus‐mediated RNAi in studying gene function in mammalian tooth development
Authors: Song Yiqiang , Zhang Zunyi , Yu Xueyan , Yan Minquan , Zhang Xiaoyun , Gu Shuping , Stuart Thomas , Liu Chao , Reiser Jakob , Zhang Yanding , Chen Yiping
Published: April 2006

RNA interference (RNAi) has recently become a powerful tool to silence gene expression in mammalian cells, but its application in assessing gene function in mammalian developing organs remains highly limited. Here we describe several unique developmental properties of the mouse molar germ. Embryonic molar mesenchyme, but not the incisor mesenchyme, once dissociated into single cell suspension and re‐aggregated, retains its odontogenic potential, the capability of a tissue to instruct an adjacent tissue to initiate tooth formation. Dissociated molar mesenchymal cells, even after being plated in cell culture, retain odontogenic competence, the capability of a tissue to respond to odontogenic signals and to support tooth formation. Most interestingly, while dissociated epithelial and mesenchymal cells of molar tooth germ are mixed and re‐aggregated, the epithelial cells are able to sort out from the mesenchymal cells and organize into a well‐defined dental epithelial structure, leading to the formation of a well‐differentiated tooth organ after sub‐renal culture. These unique molar developmental properties allow us to develop a strategy using a lentivirus‐mediated RNAi approach to silence gene expression in dental mesenchymal cells and assess gene function in tooth development. We show that knockdown of Msx1 or Dlx2 expression in the dental mesenchyme faithfully recapitulates the tooth phenotype of their targeted mutant mice. Silencing of Barx1 expression in the dental mesenchyme causes an arrest of tooth development at the bud stage, demonstrating a crucial role for Barx1 in tooth formation. Our studies have established a reliable and rapid assay that would permit large‐scale analysis of gene function in mammalian tooth development. Developmental Dynamics 235:1334–1344, 2006. © 2006 Wiley‐Liss, Inc.
Combining desorption electrospray ionization mass spectrometry and nuclear magnetic resonance for differential metabolomics without sample preparation
Authors: Chen Huanwen , Pan Zhengzheng , Talaty Nari , Raftery Daniel , Cooks R. Graham
Published: April 2006

Desorption electrospray ionization mass spectrometry (DESI‐MS) and nuclear magnetic resonance (NMR) spectroscopy are used to provide data on urine examined without sample preparation to allow differentiation between diseased (lung cancer) and healthy mice. Principal component analysis (PCA) is used to shortlist compounds with potential for biomarker screening which are responsible for significant differences between control urine samples and samples from diseased animals. Similar PCA score plots have been achieved by DESI‐MS and NMR, using a subset of common detected metabolites. The common compounds detected by DESI and NMR have the same changes in sign of their concentrations thereby indicating the usefulness of corroborative analytical methods. The effects of different solvents and surfaces on the DESI mass spectra are also evaluated and optimized. Over 80 different metabolites were successfully identified by DESI‐MS and tandem mass spectrometry experiments, with no prior sample preparation. Copyright © 2006 John Wiley & Sons, Ltd.
The ‘preferred mode’ of the axisymmetric jet
Authors: Hussain A. K. M. F. , Zaman K. B. M. Q.
Published: April 2006

The ‘preferred mode’ of an incompressible axisymmetric free jet has been organized through controlled perturbation, and spatial distributions of time-average as well as phase-average flow properties in the near field are documented. The excitation produces noticeable changes in the time-average measures of the jet, although these changes are less dramatic than those for the excitation producing stable vortex pairing. For different stages in the evolution of the preferred-mode coherent structure, the phase-average vorticity, coherent Reynolds stress, and incoherent turbulence intensities and Reynolds stress have been educed through phase-locked hot-wire measurements, over the spatial extent of the structure and without invoking the Taylor hypothesis. For a particular stage of the evolution (i.e. when the structure is centred at x/D ≃ 3) the distributions of these quantities have been compared for both initially laminar and fully turbulent exit boundary layers, and for four jet Reynolds numbers. The relative merits of the coherent structure streamline and pseudo-stream-function patterns, as compared with phase-average velocity contours, for structure boundary identification have been discussed. The structure shape and size agree closely with those inferred from the average streamline pattern of the natural structure educed by Yule (1978).

These data as well as τ-spectra show that even excitation at the preferred mode cannot sustain the initially organized large-scale coherent structure beyond eight diameters from the jet exit. The background turbulence is organized by the coherent motions in such a way that the maximum rate of decrease of the coherent vorticity occurs at the structure centres which are the saddle points of the background-turbulence Reynolds-stress distributions. The structure centres are also the locations of peak phase-average turbulence intensities. The evolving shape of the structure as it travels downstream helps explain the transverse variations of the wavelength and convection velocity across the mixing layer. The coherent structure characteristics are found to be independent of whether the initial boundary layer is laminar or turbulent, but depend somewhat on the jet Reynolds number. With increasing Reynolds number, the structure decreases in the streamwise length and increases in the radial width and becomes relatively more energetic, and more efficient in the production of coherent Reynolds stress.
Wave propagation over a rectangular trench
Authors: Lee Jiin-Jen , Ayer Robert M.
Published: April 2006

An analysis is presented for the propagation of water waves past a rectangular submarine trench. Two-dimensional, linearized potential flow is assumed. The fluid domain is divided into two regions along the mouth of the trench. Solutions in each region are expressed in terms of the unknown normal derivative of the potential function along this common boundary with the final solution obtained by matching. Reflection and transmission coefficients are found for various submarine geometries. The result shows that, for a particular flow configuration, thereexists an infinite number of discrete wave frequencies at which waves are completely transmitted. The validity of the solution in the infinite constant-water-depth region is shown by comparing with the results using the boundary integral method for given velocity distributions along the mouth of the trench. The accuracy of the matching procedure is also demonstrated through the results of the boundary integral technique. In addition, laboratory experiments were performed and are compared with the theory for two of the cases considered.
The translational and rotational drag on a cylinder moving in a membrane
Authors: Hughes B. D. , Pailthorpe B. A. , White L. R.
Published: April 2006

The translational and rotational drag coefficients for a cylinder undergoing uniform translational and rotational motion in a model lipid bilayer membrane is calculated from the appropriate linearized Navier–Stokes equations. The calculation serves as a model for the lateral and rotational diffusion of membrane-bound particles and can be used to infer the ‘microviscosity’ of the membrane from the measured diffusion coefficients. The drag coefficients are obtained exactly using dual integral equation techniques. The region of validity of an earlier asymptotic solution obtained by Saffman (1976) is elucidated.
Diffraction of gravity waves by a barrier reef
Authors: Miles John W.
Published: April 2006

The gravity-wave scattering matrix for a barrier reef that separates two different depths of water is calculated by an extension of a variational analysis of diffraction by a discontinuity in depth (Miles 1967). The resulting transmission coefficient for equal depths differs from that obtained by Johnson, Fuchs & Morison (1951), which appears to be incorrect. The results are applied to the calculation of resonant amplification of incoming swell or tsunamis by a shallow lagoon that is bounded by the reef and a vertical inner boundary. The results for this last problem agree closely (exactly for equal depths) with those obtained by Tuck (1980) through a rather different approach.
The ‘colour polarigraph’ -a simple method for determining the two-dimensional distribution of sugar concentration
Authors: Ruddick Barry R.
Published: April 2006

A method is described for photographically recording the two-dimensional distribution of sugar concentration in a tank, which typically yields a resolution of 0·01 in weight fraction sugar. The tank image is coloured according to the sugar concentration, giving a quantitative visual record of sugar contours. The technique is demonstrated in photographs of a laboratory model of an oceanic front, in which interleaving quasi-horizontal layers are formed by double-diffusive effects.
On the transition between regular and Mach reflection in truly non-stationary flows
Authors: Itoh S. , Okazaki N. , Itaya M.
Published: April 2006

Shock reflections over a convex and a concave wedge were investigated by using a 5 × 7 cm ordinary pressure-driven shock tube. Dry air was used for both the driving and driven gases. The large difference between the transition from regular (RR) to Mach reflection (MR) and that from MR to RR was observed, confirming the results obtained by Ben-Dor, Takayama & Kawauchi (1980). These results contradict all of the previous theoretical transition criteria. A new theory on the transition between RR and MR was developed by applying Whitham's ‘ray shock’ theory. This new theory agrees quite well with the experimental results.
A numerical and experimental investigation of the stability of spiral Poiseuille flow
Authors: Takeuchi Donald I. , Jankowski Daniel F.
Published: April 2006

The linear stability of the spiral motion induced between concentric cylinders by an axial pressure gradient and independent cylinder rotation is studied numerically and experimentally for a wide-gap geometry. A three-dimensional disturbance is considered. Linear stability limits in the form of Taylor numbers TaL are computed for the rotation ratios μ, = 0, 0·2, and -0·5 and for values of the axial Reynolds number Re up to 100. Depending on the values of μ and Re, the disturbance which corresponds to TaL can have a toroidal vortex structure or a spiral form. Aluminium-flake flow visualization is used to determine conditions for the onset of a secondary motion and its structure at finite amplitude. The experimental results agree with the predicted values of TaL for μ [ges ] 0, and low Reynolds number. For other cases in which agreement is only fair, apparatus length is shown to be a contributing influence. The comparison between experimental and predicted wave forms shows good agreement in overall trends.
Experiments on heat-stabilized laminar boundary layers in water
Authors: Barker Steven J. , Gile Douglas
Published: April 2006

There has been much recent interest in the stabilization of water boundary layers by wall heating. Calculations based upon linear stability theory have predicted transition Reynolds numbers as high as 200 million for a zero pressure gradient boundary layer over a heated wall. The experiment described in this paper was intended to investigate these predictions. The test boundary layer develops on the inside surface of a cylindrical tube which is 0·1 m in diameter and 6·1 m in length. The displacement thickness is small relative to the tube radius under all conditions of interest. The tube is heated by electrical heaters on the outside wall. The location of transition is determined by flush-mounted hot-film probes, or by flow visualization at the tube exit.

A transition Reynolds number of 15 million has been obtained without heat, which shows that free-stream turbulence and other perturbations are well controlled. A transition Reynolds number of 47 million has been obtained with an 8 °C wall overheat. However, as temperature is further increased there are no additional increases in transition Reynolds number, which is in contradiction to the theory. Several possible reasons for the discrepancy between theory and experiment have been investigated.
A visual study of turbulent spots
Authors: Perry A. E. , Lim T. T. , Teh E. W.
Published: April 2006

From the results of a flow visualization experiment, certain physical characteristics of a turbulent spot are suggested by the authors. The spot was artificially initiated at a point by a small intermittent wall jet. The authors also carried out experiments behind vibrating trip wires and observed the ‘signatures’ or ‘footprints’ of the A-shaped vortices seen by other workers. The fact that these ‘signatures’ are also observed in a turbulent spot leads one to suspect that these spots consist essentially of an array of A-shaped vortices. The formation of the spot is subsequently described in terms of three-dimensional disturbances of the cross-stream vortex filaments.

The basic structure of the turbulent spot proposed here is similar to the suggested structure of fully developed turbulent boundary layers first put forward by Theodorsen (1955) and more recently by Bandyopadhyay & Head (1979).
Droplet drag in an accelerating and decelerating flow
Authors: Temkin S. , Mehta H. K.
Published: April 2006

An experimental study of the motion of small water droplets in both accelerating and decelerating conditions is presented. Droplets with diameters in the range 115-187μm were exposed to propagating N-waves having strengths smaller than 0.03. Droplet-displacement data were obtained by single-frame stroboscopic photography, at an equivalent framing rate of 4000 pictures per second. The data were fitted by means of best-fit polynomials in time, which were used to obtain drag coefficients in accelerating and decelerating flow conditions. In addition to providing drag data for impulsive-type motions, these data show that the unsteady drag follows two entirely distinct trends. In one, applicable to decelerating relative flows, the unsteady drag is always larger than the steady drag at the same Reynolds number. In the other, applicable to accelerating relative flows, the unsteady drag is always smaller than the corresponding steady value. These trends have not been previously known. They give some support to a mechanism recently proposed (see Temkin & Kim 1980) to explain departures of the drag coefficient for a sphere from its steady value; namely, the changes in size of the recirculating region behind the sphere, relative to its steady counterpart at the same Reynolds number.
Couette flow of dilute solutions of macromolecules: embryo cells and overstability
Authors: Green J. , Jones W. M.
Published: April 2006

The outer cylinder was kept stationary whilst the inner rotated. Weak circulatory motion (‘embryo cells’) was observed in all the fluids investigated at Taylor numbers Ta less than the critical Taylor number Tac. These cells grew with increasing Ta, then burst into vigorous Taylor vortices at Ta = Tac. In solutions of rigid elongated molecules having concentrations above a minimum concentration, an axial oscillation (overstability?) of the embryo cells was observed. The oscillation did not occur in solutions of flexible folded molecules nor in the solvent. The oscillation was observed over a range Ta0 ≤ Ta ≤ Tac. For concentrations above the minimum Ta0/Tac decreased with increasing concentration.

Other phenomena of the flow were also studied. It was found for solvent and solutions that the torque on the outer cylinder increased relatively less rapidly with the speed of rotation of the inner cylinder when
\[
Ta/Ta_c > 1.08
\]
than it did when
\[
1 < Ta/Ta_c\leqslant 1.08.
\]
In this latter range there was a torque reduction in the flow of the solutions relative to that in the flow of solvent. At sufficiently high speeds of rotation circumferential waves occurred in the fully developed Taylor cells (at Ta = Taw) and it was found that when R1/R2 = 0·95 then Taw/Tac = 1·5 for the solvent, whereas for the solutions Taw/Tac ≥ 1·5. When R1/R2 = 0·90 then Taw/Tac = 1·25, and for the solutions Taw/Tac > 1·25. No experiment was done at Ta > Taw. The normal-stress coefficients of the solution have been evaluated from the results.
Development of mixing and isotropy in inviscid homogeneous turbulence
Authors: Lee Jon
Published: April 2006

We have investigated a sequence of dynamical systems corresponding to spherical truncations of the incompressible three-dimensional Navier-Stokes equations in Fourier space. For lower-order truncated systems up to the spherical truncation of wavenumber radius 4, it is concluded that the inviscid Navier-Stokes system will develop mixing (and a fortiori ergodicity) on the constant energy-helicity surface, and also isotropy of the covariance spectral tensor. This conclusion is, however, drawn not directly from the mixing definition but from the observation that one cannot evolve the trajectory numerically much beyond several characteristic corre- lation times of the smallest eddy owing to the accumulation of round-off errors. The limited evolution time is a manifestation of trajectory instability (exponential orbit separation) which underlies not only mixing, but also the stronger dynamical charac- terization of positive Kolmogorov entropy (K-system).
Path-integral methods for turbulent diffusion
Authors: Drummond I. T.
Published: April 2006

We derive a path-integral representation for the effective diffusion function of a passive scalar field. We use it to calculate the long-time effective diffusivity in Gaussian turbulence in the near-Markovian limit. Our results confirm the negative effect of vorticity predicted by previous discussions. They also demonstrate that the helicity of the turbulence when present may be as important an influence as the vorticity.
Transition from regular to Mach reflection of shock waves Part 1. The effect of viscosity in the pseudosteady case
Authors: Hornung H. G. , Taylor J. R.
Published: April 2006

It is demonstrated experimentally that the influence of viscosity on the transition condition in pseudosteady flow is very significant. A mechanism is proposed for this effect, which explains the features of the observed behaviour. In particular, an experimental method of finding the inviscid transition condition, by extrapolation to infinite Reynolds number, gives excellent agreement with the calcwlatcd inviscid sonic criterion. It is thought that this provides the explanation for the usual persistence of regular reflection beyond the sonic: condition.
Flow in a differentially rotated cylindrical drop at low Reynolds number
Authors: Harriott George M. , Brown Robert A.
Published: April 2006

A liquid drop held captive between parallel disks that are differentially rotated is a model for the swirling flows induced by crystal rotation in the floating-zone process for growing semiconductor materials. An asymptotic analysis for a cylindrical drop is presented that elucidates the structure of the axisymmetric cellular motions caused by disk rotation at low Reynolds number. Variations of meniscus shape induced by these flows are described in the limit of small capillary number. Most cellular flow fields break the bifurcation point that corresponds to the Plateau–Rayleigh limit for the length of a static drop into two disjoint shape families and lower the maximum stable drop length. This effect is studied by a singular bifurcation analysis.
Large-scale modulations of edge waves
Authors: Akylas T. R.
Published: April 2006

The temporal and spatial evolution of large-scale modulations of weakly nonlinear edge waves on a uniformly sloping beach is studied using the full water-wave formulation for beach angles α = π/2N. Equations governing the evolution of envelopes of edge waves, excited by resonant interactions with incident wavetrains, are derived. It is deduced that a uniform train of free periodic edge waves is always unstable to large-scale variations, so that envelope solitons will develop; the resulting three-dimensional solitons are described in detail. In addition, it is shown that steady-state standing subharmonic edge waves, excited by incident wavetrains on a long, mildly sloping beach, can be unstable to large-scale modulations. The possible physical significance of these findings is discussed.
Longshore motion due to an obliquely incident wave group
Authors: Ryrie S. C.
Published: April 2006

We consider longshore motion generated within the surf zone by obliquely incident breaking waves, and seek to describe the effect on such motion of variations, caused by wave grouping, in the incident longshore momentum flux. The effects of associated variations in set-up are not considered.

We use the linear long-wave equations to describe the motion resulting from the longshore momentum contained in a wave group. This consists of a succession of edge waves which disperse along the beach, and, for the example considered, an eventual steady circulation cell at the position of the wave group. We suggest that such a cell is always likely to be formed if the wave group is sufficiently localized, and that higher-modenumber edge waves are more likely to be excited.

We find timescales for the dispersal of the edge waves, and for the decay, due to bottom friction, of the circulation cell: we suggest that the latter may more generally be used, as a timescale for the effect of friction on longshore motion.
A nonlinear convective system with oscillatory behaviour for certain parameter regimes
Authors: Lundberg Peter , Rahm Lars
Published: April 2006

The behaviour of a fluid system governed by a quadratic equation of state for the temperature is studied. The model consists of two well-mixed and interconnected vessels subjected to external thermal forcing. If inertial effects are neglected the temperature response of the fluid is governed by two autonomous ordinary differential equations in time. An investigation of these equations revealed that, depending upon the choice of parameters, the system has two possible final states: one stationary, the other a relaxation oscillation. The transitions between these states occur as sub- and supercritically unstable Hopf bifurcations. For certain parameter ranges, a stationary solution can thus coexist with a relaxation oscillation, the initial conditions determining which of these is realized.
The effect of surface contamination on thermocapillary flow in a two-dimensional slot
Authors: Homsy G. M. , Meiburg E.
Published: April 2006

We consider the effect of insoluble surfactants on the steady thermocapillary flow in a differentially heated slot treated previously by Sen & Davis (1982). The equation of state for interfacial tension is taken to be linear in both temperature and surfactant concentration. We treat the problem in the limit of shallow slots and low thermal Marangoni numbers so that the effect of surfactants is described by only two parameters: a surface Péclet number Pe and an elasticity parameter denoted by E, the ratio of the compositional elasticity to the tension difference due to the imposed temperature difference. Using lubrication theory and matched asymptotic expansions, we reduce the problem to a single nonlinear integral–algebraic equation (for the outer core variables), which we solve both numerically and in various asymptotic limits by perturbation theory. It is shown that the general effect of surfactants is to retard the strength of the motion, but that this retardation is not necessarily uniform in space. Surprisingly, there are only extreme cases in which condensed surfactant layers will form, these being E [Lt ] 1, Pe [Gt ] 1. Sharp gradients in surfactant concentrations will not form in the general case of E = O(1). This behaviour is due to the strong coupling between the flow and the interfacial stress, and is contrasted with certain well-known forced-convection problems.
The transition from roll to square-cell solutions in Rayleigh–Bénard convection
Authors: Jenkins D. R. , Proctor M. R. E.
Published: April 2006

We consider three-dimensional finite-amplitude thermal convection in a fluid layer with boundaries of finite conductivity. Busse & Riahi (1980) and Proctor (1981) showed that the preferred planform of convection in such a system is a square-cell tesselation provided that the boundaries are much poorer conductors than the fluid, in contrast to the roll solutions which are obtained for perfectly conducting boundaries. We determine here the conductivity of the boundaries at which the preferred planform changes from roll to square-cell type. We show that, for low-Prandtl-number fluids (e.g. mercury), square-cell solutions are realized only when the boundaries are almost insulating; while, for high-Prandtl-number fluids (e.g. silicone oils), square-cell solutions are stable when the boundaries have conductivity comparable to that of the fluid.
The dynamics of thin liquid jets in air
Authors: Entov V. M. , Yarin A. L.
Published: April 2006

The dynamics of propagation and disintegration of laminar liquid jets moving in air has been investigated theoretically. It is assumed that the jet is thin, i.e. the ratio of the characteristic transverse size to the longitudinal one is small. It is assumed also that the lateral surface of the jet is free of shearing forces and is ‘almost free’ of normal ones in the sense that the normal tractions other than isotropic pressure are small in comparison with the internal stresses acting in the jet cross-section.

Asymptotic quasi-one-dimensional equations of the continuity, momentum and moment of momentum of liquid motion in the jet have been derived. These equations were used as a basis for studying the process of growth of long-wave bending (transverse) disturbances of high-velocity jets of circular cross-section during their motion through air. The instability condition has been obtained and the growth rate of small bending disturbances of the jet has been found; the evolution of the jet shape at the stage of finite disturbances is investigated.
Stirring and transport of tracer fields by geostrophic turbulence
Authors: Holloway Greg , Kristmannsson Stefan S.
Published: April 2006

We investigate the interaction of concentration fields of passive tracer with velocity fields characterizing geostrophic turbulence. We develop and compare results from equilibrium statistical mechanics, from turbulence-closure theory and from numerical simulation. A consistent account emerges. Among the results we show (1) that velocity fields efficiently scatter tracer variance to all scales, (2) that tracer variance evolves toward an equilibrium spectrum which is different from the equilibrium spectrum for vorticity variance, and (3) that intermittency of the tracer field is characteristic of a cascade of tracer variance across wavenumber space. The greater efficiency of the cascade of tracer variance relative to a vorticity cascade is due to wavenumber-local advective terms which affect tracer but not vorticity. We suggest that the more efficient tracer cascade results in shorter Lagrangian autocorrelation times for tracer than for vorticity.

We investigate the spatial flux of tracer when a uniform gradient of average tracer concentration is imposed. We show (1) that the spatial flux has dominant contributions from fluctuations on scales slightly larger than the dominant energetic scales, (2) that an effective eddy-diffusivity formulation is valid and that the diffusivity agrees with simple mixing-length estimates, and (3) that eddy diffusivity is significantly anisotropic if Rossby-wave propagation occurs. Meridional diffusivity is suppressed relative to zonal diffusivity.

We complement the study of stirring down from a uniform gradient with a numerical investigation of the stirring out of an initially concentrated spot. We see that eddy diffusivity can be a dangerous concept for such problems.
Non-uniqueness and stability of the configuration of flow of immiscible fluids with different viscosities
Authors: Joseph D. D. , Nguyen K. , Beavers G. S.
Published: April 2006

High-viscosity liquids hate to work. Low-viscosity liquids are the victims of the laziness of high-viscosity liquids because they are easy to push around.

The arrangement of components in steady flow of immiscible liquids is typically non-unique. The problem of selection of arrangements is defined here and is studied by variational methods under the hypothesis that the realized arrangements are the ones that maximize the speed on exterior boundaries for prescribed boundary tractions, or the ones that minimize the tractions for prescribed speeds. The arrangements which minimize tractions also minimize the dissipation by putting low-viscosity liquid in regions of high shear. The variational problem is used as a guide to intuition in the design and interpretation of experiments when results of analysis of stability are unavailable. In fact we always observe some kind of shielding of high-viscosity liquid. This can occur by sheet coating in which low-viscosity liquid encapsulates high-viscosity liquid, or through the formation of rigidly rotating masses of high-viscosity liquid which we call rollers. In other cases we get emulsions of low-viscosity liquid in a high-viscosity foam. The emulsions arise from a fingering instability. The low-viscosity liquid fingers into the high-viscosity liquid and then low-viscosity bubbles are pinched off the fingers. The emulsions seem to have a very low effective viscosity and they shield the high-viscosity liquid from shearing. In the problem of Taylor instability with two fluids, low-viscosity Taylor cells are separated by stable high-viscosity rollers.
The emergence of isolated coherent vortices in turbulent flow
Authors: Mcwilliams James C.
Published: April 2006

A study is made of some numerical calculations of two-dimensional and geostrophic turbulent flows. The primary result is that, under a broad range of circumstances, the flow structure has its vorticity concentrated in a small fraction of the spatial domain, and these concentrations typically have lifetimes long compared with the characteristic time for nonlinear interactions in turbulent flow (i.e. an eddy turnaround time). When such vorticity concentrations occur, they tend to assume an axisymmetric shape and persist under passive advection by the large-scale flow, except for relatively rare encounters with other centres of concentration. These structures can arise from random initial conditions without vorticity concentration, evolving in the midst of what has been traditionally characterized as the ‘cascade’ of isotropic, homogeneous, large-Reynolds-number turbulence: the systematic elongation of isolines of vorticity associated with the transfer of vorticity to smaller scales, eventually to dissipation scales, and the transfer of energy to larger scales. When the vorticity concentrations are a sufficiently dominant component of the total vorticity field, the cascade processes are suppressed. The demonstration of persistent vorticity concentrations on intermediate scales - smaller than the scale of the peak of the energy spectrum and larger than the dissipation scales - does not invalidate many of the traditional characterizations of two-dimensional and geostrophic turbulence, but I believe it shows them to be substantially incomplete with respect to a fundamental phenomenon in such flows.