bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simple Method to Synthesize Cadmium Hydroxide Nanobelts
Authors: Zhang DE , Pan XD , Zhu H , Li SZ , Xu GY , Zhang XB , Ying AL , Tong ZW
Published: August 2008

Cd(OH)2nanobelts have been synthesized in high yield by a convenient polyol method for the first time. XRD, XPS, FESEM, and TEM were used to characterize the product, which revealed that the product consisted of belt-like crystals about 40 nm in thickness and length up to several hundreds of micrometers. Studies found that the viscosity of the solvent has important influence on the morphology of the final products. The optical absorption spectrum indicates that the Cd(OH)2nanobelts have a direct band gap of 4.45 eV.
Crystallization Behavior of Fatty Acid Methyl Esters
Authors: Dunn Robert O.
Published: August 2008

Biodiesel from most agricultural feedstocks has flow properties that are prone to startup and operability problems during cold weather. Biodiesel from soybean oil is generally a mixture of long‐chain fatty acid alkyl esters composed of 0.15–0.20 mass fraction saturated esters (melting point [MP] ≫ 0 °C) mixed with unsaturated esters (MP < 0 °C). This work investigates the crystallization properties of two saturated fatty acid methyl esters (FAME) commonly found in biodiesel from soybean oil. Differential scanning calorimetry (DSC) heating and cooling scans of methyl palmitate (MeC16), methyl stearate (MeC18) and methyl oleate (MeC18:1) in pure form were analyzed. Crystallization behavior in ternary FAME mixtures was inferred by the application of thermodynamic models based on ideal solution and freezing‐point depression theories. Activity coefficients for MeC16 and MeC18 in MeC18:1 solvent were determined by analyzing DSC cooling curves for binary FAME mixtures. Eutectic points were predicted by both models. Crystallization onset temperatures inferred from freezing point depression theory were more accurate than those for ideal solutions with respect to a direct DSC cooling curve analysis of corresponding ternary mixtures. This work shows that the crystallization onset temperature (cloud point) of biodiesel may be predicted by freezing‐point depression theory if the activity coefficients of the component FAME are known.
WHAT IS AN INTEGRATED PEST MANAGEMENT ‘STRATEGY’? EXPLORATIONS IN SOUTHERN MALAWI
Authors: Orr A. , Mwale B. , Saitis D.
Published: August 2008

The concept of an integrated pest management (IPM) strategy is explored using case-study evidence from smallholder agriculture in southern Malawi. The conventional concept of strategy as a ‘plan’ is contrasted with the use of strategy as a game, as a performance, and as an accident. This pluralistic view is echoed in recent literature on business strategy. A typology is developed that relates farmers' choice of IPM strategy to the predictability of crop losses, the stability of the crop environment, and farmers' knowledge of pests. Some implications for IPM are explored. Where conditions favour ‘adaptive’ rather than planned IPM strategies, formal experimentation to verify farmers' strategies may be an inefficient use of resources. Where the crop environment is volatile and several pests attack the crop simultaneously, there may be limited scope to increase the adoption of IPM strategies by improving farmer knowledge of pest biology. Addressing the interactions between pest and crop management is critical in making IPM relevant for resource-poor farmers. A deeper understanding of farmers' management strategies is required to frame meaningful recommendations.
ACCEPTABILITY OF FORAGE LEGUMES FOR IMPROVED FALLOWS – FIRST EXPERIENCES OF AGRO-PASTORALISTS IN SUBHUMID SOUTHWEST NIGERIA
Authors: Muhr L. , Tarawali S. A. , Peters M. , Schultze-Kraft R.
Published: August 2008

In the process of developing an improved fallow system based on forage legumes, the potential interest of crop-livestock farmers in enhancing soil fertility restoration and dry-season feed supply was assessed during a socio-economic study on 11 farms of settled agro-pastoralists in the subhumid zone of West Africa. Simultaneously, eight farmers in the group participated in simple and largely farmer-managed on-farm experiments testing the establishment of selected forage legumes on fallow land. In addition to agronomic parameters, the participatory approach included an evaluation of the technology by farmers both during farm visits and field days.

With cropping and dry-season feeding strategies increasingly being limited by land availability, the agronomic performance of some of the tested legume species, in particular Stylosanthes guianensis, promised substantial productivity gains once they could be integrated into the traditional fallow system. The major concerns of the farmers were animal health and labour supply for cropping activities, rather than soil fertility and feed constraints. The need for initial weed control within most of the legume species, therefore, limited their acceptability by farmers at this early stage of innovation testing. Nevertheless, farmers' interest grew remarkably in the course of the study. Options for the selection of appropriate species and management practices, which aimed at facilitating the establishment of legumes on fallow land, are discussed as a means of enhancing further adoption of the innovation.
SHORT DURATION CHICKPEA TO REPLACE FALLOW AFTER AMAN RICE: THE ROLE OF ON-FARM SEED PRIMING IN THE HIGH BARIND TRACT OF BANGLADESH
Authors: Musa A. M. , Harris D. , Johansen C. , Kumar J.
Published: August 2008

Chickpea (Cicer arietinum) is a promising post-wet-season crop to follow rainfed rice (Oryza sativa) in the High Barind Tract of northwestern Bangladesh. Yields in farmers' fields, however, remain low (<1 t ha−1) primarily due to such factors as poor crop establishment, late sowing, and terminal drought and heat stress. Having been shown to improve plant stand and yield of chickpea in other environments, seed priming – soaking the seed overnight before surface drying and sowing the next day – was tested for its efficacy under Barind conditions.

In the 1998–99 season, 30 trials grown entirely on residual soil moisture were conducted in farmers' fields. A statistically significant mean yield response to priming of 47% was obtained. In 1999–2000, 105 on-farm trials and 15 demonstrations comparing presence and absence of priming were conducted. The crop received rain during this growing season. In a randomly chosen subset of 35 trials, scientists recorded a mean yield increase due to priming of 20%; it was 22% (from 1.02 to 1.25 t ha−1) in the remaining 64 trials (6 of the 105 trials were abandoned) where farmers recorded yields. Using a different variety, the mean yield response to priming in 15 demonstrations was 17% (from 1.25 to 1.46 t ha−1).

The priming response was attributed mainly to rapid seedling establishment, with higher plant stand and earlier crop maturity allowing escape from end-of-season stresses. Priming also reduced the incidence of stem and root diseases, and increased nodulation by native rhizobia. This simple technology can substantially increase chickpea yields to remunerative levels for the resource-poor farmers in this difficult environment. Further, it is suggested that this technology can act as a catalyst for the introduction of further technologies that will permit reliable and profitable cultivation of post-rainy-season crops and thus improve the livelihoods of the rural population.
Labour Politics in a Naval Dockyard: The Case of Karlskrona, Sweden c. 1880–1925
Authors: Hilson Mary
Published: August 2008

Naval dockyards have been largely neglected by labour historians, a surprising omission given their importance as industrial workplaces with a distinct culture of labour and labour relations. This article considers labour politics in Karlskrona dockyard, Sweden, in the light of a growing body of research on work and labour relations in the British and other European dockyards. Evidence from Karlskrona suggests that, rather than being repressed by military discipline or bought off by generous state benefits, the dockyard workforce drew on aspects of its unique relationship with the national state to improve working conditions. Particular attention is given to the role of the dockyard trade union in creating a sense of workforce identity as state employees. This is in contrast to the British dockyards where unionism was founded on the rigid division of labour in the shipbuilding industry.
Working Through Partition: Making a Living in the Bengal Borderlands
Authors: van Schendel Willem
Published: August 2008

Partition, the break-up of colonial India in 1947, has been the subject of considerable serious historical research, but almost exclusively from two distinctive perspectives: as a macropolitical event; or as a cultural and personal disaster. Remarkably, very little is known about the socioeconomic impact of Partition on different localities and individuals. This exploratory essay considers how Partition affected working people's livelihood and labour relations. The essay focuses on the northeastern part of the subcontinent, where Partition created an international border separating East Bengal – which became East Pakistan, then Bangladesh – from West Bengal, Bihar, Assam, and other regions which joined the new state of India. Based largely on evidence contained in “low-level” state records, the author explores how labour relations for several categories of workers in the new borderland changed during the period of the late 1940s and 1950s.
Global Labor History and “the Modern World-System”: Thoughts at the Twenty-Fifth Anniversary of the Fernand Braudel Center
Authors: van der Linden Marcel
Published: August 2008

I regard the work of the past 20 years and of some years to come as the work of
clearing the underbrush, so that we may build a more useful framework for social
science.

Immanuel Wallerstein (1996)

In September 1976, the Fernand Braudel Center for the Study of Economies,
Historical Systems, and Civilizations opened its doors at the State University
of New York - Binghamton. The new institution made a flying start. After
three months it presented its “Proposed Research Programs” in a substantial
booklet. In the summer of 1977, the first issue of its journal, Review, came
out. That same year, a section on the “Political Economy of World-Systems”
(PEWS), inspired by the Braudel Center, was established within the
American Sociological Association. The PEWS section has held annual
conferences and published their proceedings ever since. Since 1979, the
Center, together with the Maison des sciences de l'homme of Paris, has
sponsored a book series called “Studies in Modern Capitalism”, published by
Cambridge University Press.
Petitions and the Social Context of Political Mobilization in the Revolution of 1848/49: A Microhistorical Actor-Centred Network Analysis
Authors: Lipp Carola , Krempel Lothar
Published: August 2008

A great part of the political movement in the Revolution of 1848 took place in the form of group and mass petitions. The National Assembly in Frankfurt, the first national German parliament, received 17,000 petitions from more than three million people. A great number of petitions, analysed by German scholars such as Best, dealt with the question of a liberal market economy, with problems resulting out of the developing process of industrialization, and with protective duties. The petitions expressed different group interests, articulated by craftsmen, merchants, entrepreneurs, and workers, who responded to current economic and social restraints. Another complex of petitions formulated requests regarding the constitution, the liberalization of the political system, or the organization of education, especially the separation of church and state. Another large mass of revolutionary petitions was addressed to the rulers or the ruling bodies of the different German states and was concerned with regional conflicts, and the adoption of ideas that were developed at national level.
Supplications between Politics and Justice: The Northern and Central Italian States in the Early Modern Age
Authors: Nubola Cecilia
Published: August 2008

“Those who think to do away with petitions would overthrow the entire system of the State”. This remark – taken from an anonymous eighteenth-century account of the political organization of the Duchy of Parma and Piacenza – describes well the importance attributed to complaints in the organization of the state. Through complaints, or petitions, it is generally possible to verify a number of fundamental forms and modes of communication between society and the institutions of the ancien regime, and to reconstruct the procedures of mediation, repression, acceptance, and agreement adopted by princes, sovereigns, or magistracies in response to social demands.
The Power of Petitions: Women and the New Hampshire Provincial Government, 1695–1770
Authors: Schmidt Blaine Marcia
Published: August 2008

There are very few sources available to historians which allow us to hear the voices of Anglo-American women. How can we understand what ordinary women believed were their responsibilities to their families and communities and the responsibilities of their government to them? Petitions provide historians with one of the few opportunities to “hear” non-elite women voice their concerns. In provincial New Hampshire, women regularly approached the royal government with individual requests. By viewing the rights associated with petitioning, the procedure involved, and the variety of applications for petition use, female agency in colonial society becomes more apparent. Through petitions, it is possible to understand under what circumstances women turned to the government for assistance, and under what circumstances the government granted their petitions.
Deference and Defiance: The Changing Nature of Petitioning in British Naval Dockyards
Authors: Lunn Ken , Day Ann
Published: August 2008

Petitioning as a method of expressing grievances in British history was not peculiar to any particular set of individuals, but was widely used by all sections of society for a range of issues. Given its origins, however, it became ritualized as the means of labour negotiation for workers who were employed by the state, and, by the nineteenth century, by municipal authorities. This was before the institutionalization of trade unions and their recognition as representative agencies for industrial bargaining. One of these groups of workers in the state sector were naval dockyard employees, engaged in the construction, repair, and maintenance of British naval ships. For these workers, the nature of labour relations, and the importance of petitioning as an instrument of negotiation between employees and employer, was both complex and dynamic.
The Image of Jews in Byelorussia: Petitions as a Source for Popular Consciousness in the Early Twentieth Century
Authors: Bukhovets Oleg G.
Published: August 2008

The disintegration of the USSR, and of the communist system, in the last decade of the twentieth century, the rekindling of ethnic strife, and scholarly research into nationalism – all have renewed interest in the images that different ethnic and religious groups in eastern Europe have had of each other. In this context, the image of Jewishness has been of particular importance, both in political science and in history. An adequate analysis of ideas about Jewishness requires access to numerous mass sources. However, the number of sources available for this kind of enquiry is limited, compared, for instance, to the sources open for traditional Hebrew studies. This is especially true when we speak about the periods of autocracy and dictatorship. Both the Russian Empire and the USSR had – besides periods of overt anti-Semitism – a tradition of hidden anti-Semitism. The hidden and unofficial nature of this prejudice would not allow for mass opinion polls on anti-Semitism before the fall of the USSR.
University Cultural Wars: Rival
Protestant Pieties in Early
Twentieth-Century Princeton
Authors: KEMENY P. C.
Published: August 2008

Contrary to conventional wisdom, liberal Protestants, not fundamentalists, attempted to preserve
Princeton University's traditional religious mission during the rapid intellectual and social change
reshaping American higher education in the early twentieth century. In fact, when fundamentalists
in the university community demanded the secularisation of the undergraduate programme, liberal
Protestants spurned their efforts. Although American liberal Protestantism gradually dissolved into
the surrounding secular culture over the course of the twentieth century, the conflict between the rival
pieties of liberal and conservative Protestants reveals how and why liberal Protestantism was able
to maintain hegemony over one key institution of American culture – the university – well into the
mid-twentieth century.
Three-dimensional natural convective states in a narrow-gap horizontal annulus
Authors: DYKO MARK P. , VAFAI KAMBIZ
Published: August 2008

Buoyancy-driven flow in a narrow-gap annulus formed by two concentric horizontal
cylinders is investigated numerically. The three-dimensional transient equations of
fluid motion and heat transfer are solved to study multiple supercritical states occurring
within annuli having impermeable endwalls, which are encountered in various
applications. For the first time, three-dimensional supercritical states are shown to
occur in a narrow-gap annulus and the existence of four such states is established.
These four states are characterized by the orientations and directions of rotation of
counter-rotating rolls that form in the upper part of the annulus owing to thermal
instability, and exhibit (i) transverse rolls, (ii) transverse rolls with reversed directions
of rotation, (iii) longitudinal rolls in combination with transverse rolls, and (iv)
longitudinal rolls with reversed directions of rotation in combination with transverse
rolls, respectively. Simulations are performed at Rayleigh numbers approaching and
exceeding the critical value to gain insight into the physical processes influencing
development of the secondary flow structures. The evolution of the supercritical flow
fields and temperature distributions with increasing Rayleigh number and the interaction
between the secondary and primary flows are thoroughly investigated. Factors
influencing the number of rolls are studied for each supercritical state. Heat transfer
results are presented in the form of local Nusselt number distributions and overall
annulus Nusselt numbers. Two-dimensional natural convection occurring early in the
transient evolution of the flow field is also examined. Results obtained for a wide
range of annulus radius ratios and Rayleigh numbers are shown to be in excellent
agreement with results from previous experimental and numerical studies, thereby
validating the present numerical scheme.
Non-axisymmetric instability of centrifugally stable stratified Taylor–Couette flow
Authors: YAVNEH IRAD , MCWILLIAMS JAMES C. , MOLEMAKER M. JEROEN
Published: August 2008

The stability is investigated of the swirling flow between two concentric cylinders in
the presence of stable axial linear density stratification, for flows not satisfying the
well-known Rayleigh criterion for inviscid centrifugal instability, d(Vr)2/dr < 0. We
show by a linear stability analysis that a sufficient condition for non-axisymmetric
instability is, in fact, d(V/r)2/dr < 0, which implies a far wider range of instability
than previously identified. The most unstable modes are radially smooth and occur
for a narrow range of vertical wavenumbers. The growth rate is nearly independent of
the stratification when the latter is strong, but it is proportional to it when it is weak,
implying stability for an unstratified flow. The instability depends strongly on a
non-dimensional parameter, S, which represents the ratio between the strain rate and twice
the angular velocity of the flow. The instabilities occur for anti-cyclonic flow (S < 0).
The optimal growth rate of the fastest-growing mode, which is non-oscillatory in time,
decays exponentially fast as S (which can also be considered a Rossby number) tends
to 0. The mechanism of the instability is an arrest and phase-locking of Kelvin waves
along the boundaries by the mean shear flow. Additionally, we identify a family of
(probably infinitely many) unstable modes with more oscillatory radial structure and
slower growth rates than the primary instability. We determine numerically that the
instabilities persist for finite viscosity, and the unstable modes remain similar to the
inviscid modes outside boundary layers along the cylinder walls. Furthermore, the
nonlinear dynamics of the anti-cyclonic flow are dominated by the linear instability
for a substantial range of Reynolds numbers.
A correlation for the lift-off of many particles in plane Poiseuille flows of Newtonian fluids
Authors: PATANKAR N. A. , KO T. , CHOI H. G. , JOSEPH D. D.
Published: August 2008

Choi & Joseph (2001) reported a two-dimensional numerical investigation of the
lift-off of 300 circular particles in plane Poiseuille flows of Newtonian fluids. We
perform similar simulations. Particles heavier than the fluid are initially placed in
a closely packed ordered configuration at the bottom of a periodic channel. The
fluid–particle mixture is driven by an external pressure gradient. The particles are
suspended or fluidized by lift forces that balance the buoyant weight perpendicular
to the flow. Pressure waves corresponding to the waves at the fluid–mixture interface
are observed. During the initial transient, these waves grow, resulting in bed erosion.
At sufficiently large shear Reynolds numbers the particles occupy the entire channel
width during the transient. The particle bed eventually settles to an equilibrium height
which increases as the shear Reynolds number is increased. Heavier particles are lifted
to a smaller equilibrium height at the same Reynolds number. A correlation for the
lift-off of many particles is obtained from the numerical data. The correlation is used
to estimate the critical shear Reynolds number for lift-off of many particles. The
critical shear Reynolds number for lift-off of a single particle is found to be greater
than that for many particles. The procedures used here to obtain correlations from
direct simulations in two dimensions and the type of correlations that emerge should
generalize to three-dimensional simulations at present underway.
Propagation of unsteady disturbances in a slowly varying duct with mean swirling flow
Authors: COOPER A. J. , PEAKE N.
Published: August 2008

The propagation of unsteady disturbances in a slowly varying cylindrical duct carrying
mean swirling flow is described. A consistent multiple-scales solution for the mean
flow and disturbance is derived, and the effect of finite-impedance boundaries on the
propagation of disturbances in mean swirling flow is also addressed.

Two degrees of mean swirl are considered: first the case when the swirl velocity is
of the same order as the axial velocity, which is applicable to turbomachinery flow
behind a rotor stage; secondly a small swirl approximation, where the swirl velocity
is of the same order as the axial slope of the duct walls, which is relevant to the flow
downstream of the stator in a turbofan engine duct.

The presence of mean vorticity couples the acoustic and vorticity equations and the
associated eigenvalue problem is not self-adjoint as it is for irrotational mean flow.
In order to obtain a secularity condition, which determines the amplitude variation
along the duct, an adjoint solution for the coupled system of equations is derived.
The solution breaks down at a turning point where a mode changes from cut on to
cut off. Analysis in this region shows that the amplitude here is governed by a form
of Airy's equation, and that the effect of swirl is to introduce a small shift in the
location of the turning point. The reflection coefficient at this corrected turning point
is shown to be exp (iπ/2).

The evolution of axial wavenumbers and cross-sectionally averaged amplitudes
along the duct are calculated and comparisons made between the cases of zero mean
swirl, small mean swirl and O(1) mean swirl. In a hard-walled duct it is found that
small mean swirl only affects the phase of the amplitude, but O(1) mean swirl produces
a much larger amplitude variation along the duct compared with a non-swirling mean
flow. In a duct with finite-impedance walls, mean swirl has a large damping effect
when the modes are co-rotating with the swirl. If the modes are counter-rotating then
an upstream-propagating mode can be amplified compared to the no-swirl case, but
a downstream-propagating mode remains more damped.
Along-slope current generation by obliquely incident internal waves
Authors: ZIKANOV OLEG , SLINN DONALD N.
Published: August 2008

A series of numerical experiments is performed to investigate the breaking of obliquely
incident internal waves propagating towards a bottom slope. The case of critical
reflection is considered, where the angle between the wave group velocity vector
and the horizontal matches the bottom slope angle. The flow evolution is found
to be significantly different from the evolution observed previously in simulations
of normally incident waves. The divergence of the Reynolds stress in the breaking
zone causes a strong along-slope mean current, which changes the flow structure
dramatically. The wave does not penetrate the current but breaks down at its upper
surface as the result of a critical layer interaction. A continuously broadening mean
along-slope current with an approximately constant velocity is produced. We propose
a simple model of the process based on the momentum conservation law and the
radiation stress concept. The model predictions are verified against the numerical
results and are used to evaluate the possible strength of along-slope currents generated
by this process in the ocean.
Viscous potential flow analysis of Kelvin–Helmholtz instability in a channel
Authors: FUNADA T. , JOSEPH D. D.
Published: August 2008

We study the stability of stratified gas–liquid flow in a horizontal rectangular channel
using viscous potential flow. The analysis leads to an explicit dispersion relation
in which the effects of surface tension and viscosity on the normal stress are not
neglected but the effect of shear stresses is. Formulas for the growth rates, wave
speeds and neutral stability curve are given in general and applied to experiments in
air–water flows. The effects of surface tension are always important and determine
the stability limits for the cases in which the volume fraction of gas is not too small.
The stability criterion for viscous potential flow is expressed by a critical value of the
relative velocity. The maximum critical value is when the viscosity ratio is equal to
the density ratio; surprisingly the neutral curve for this viscous fluid is the same as
the neutral curve for inviscid fluids. The maximum critical value of the velocity of
all viscous fluids is given by that for inviscid fluid. For air at 20°C and liquids with
density ρ = 1 g cm−3 the liquid viscosity for the critical conditions is 15 cP: the critical
velocity for liquids with viscosities larger than 15 cP is only slightly smaller but the
critical velocity for liquids with viscosities smaller than 15 cP, like water, can be much
lower. The viscosity of the liquid has a strong effect on the growth rate. The viscous
potential flow theory fits the experimental data for air and water well when the gas
fraction is greater than about 70%.
The Fanno model for turbulent compressible flow
Authors: OCKENDON H. , OCKENDON J. R. , FALLE S. A. E. G.
Published: August 2008

The paper considers the derivation and properties of the Fanno model for nearly
unidirectional turbulent flow of gas in a tube. The model is relevant to many industrial
processes. Approximate solutions are derived and numerically validated for evolving
flows of initially small amplitude, and these solutions reveal the prevalence of localized
large-time behaviour, which is in contrast to inviscid acoustic theory. The properties
of large-amplitude travelling waves are summarized, which are also surprising when
compared to those of inviscid theory.
Vibrational effects on convection in a square cavity at zero gravity
Authors: HIRATA KATSUYA , SASAKI TOMOAKI , TANIGAWA HIROCHIKA
Published: August 2008

In this numerical study, we investigate natural convection in a two-dimensional
square-section enclosure vibrating sinusoidally parallel to the applied temperature
gradient in a zero-gravity field. The full Navier–Stokes equations are simplified with
the Boussinesq approximation and solved by a finite difference method. Whereas
the Prandtl number Pr is fixed to 7.1 (except for some test cases with Pr = 7.0,
6.8), the vibrational Rayleigh number Ra based on acceleration amplitude is varied
from 1.0 × 104 to 1.0 × 105, and dimensionless angular frequency ω is varied
from 1.0 × 100 to 1.0 × 103. In the tested range,
time evolutions exhibit synchronous, 1/2-subharmonic
and non-periodic responses, and flow patterns are characterized mainly
by one- or two-cell structures. Flow-regime diagrams show considerable differences
from results in a non-zero-mean-gravity field even at large acceleration amplitudes,
and suggest that some parts of non-periodic-response regimes may be related to
transitions between flow patterns. The amplitude of fluctuations in spatially averaged
kinetic energy density K (equal to the difference between maximum and minimum
kinetic energies over a cycle) tends to be large when fluid is stationary everywhere over
some interval of time during each period, and has a peak when fluid begins to move
continuously throughout one period. Such peaks are caused by impulsively started
convection, and are not connected to resonant oscillations in a constant-gravity field.
Compressible particle-driven gravity currents
Authors: TIMMERMANS MARY-LOUISE E. , LISTER JOHN R. , HUPPERT HERBERT E.
Published: August 2008

Large-scale particle-driven gravity currents occur in the atmosphere, often in the
form of pyroclastic flows that result from explosive volcanic eruptions. The behaviour
of these gravity currents is analysed here and it is shown that compressibility can
be important in flow of such particle-laden gases because the presence of particles
greatly reduces the density scale height, so that variations in density due to compressibility
are significant over the thickness of the flow. A shallow-water model of the
flow is developed, which incorporates the contribution of particles to the density and
thermodynamics of the flow. Analytical similarity solutions and numerical solutions
of the model equations are derived. The gas–particle mixture decompresses upon
gravitational collapse and such flows have faster propagation speeds than incompressible
currents of the same dimensions. Once a compressible current has spread
sufficiently that its thickness is less than the density scale height it can be treated as
incompressible. A simple ‘box-model’ approximation is developed to determine the
effects of particle settling. The major effect is that a small amount of particle settling
increases the density scale height of the particle-laden mixture and leads to a more
rapid decompression of the current.
Linear stability of co-flowing liquid–gas jets
Authors: GORDILLO J. M. , PÉREZ-SABORID M. , GAÑÁN-CALVO A. M.
Published: August 2008

A temporal, inviscid, linear stability analysis of a liquid jet and the co-flowing gas
stream surrounding the jet has been performed. The basic liquid and gas velocity
profiles have been computed self-consistently by solving numerically the appropriate
set of coupled Navier–Stokes equations reduced using the slenderness approximation.
The analysis in the case of a uniform liquid velocity profile recovers the classical
Rayleigh and Weber non-viscous results as limiting cases for well-developed and
very thin gas boundary layers respectively, but the consideration of realistic liquid
velocity profiles brings to light new families of modes which are essential to explain
atomization experiments at large enough Weber numbers, and which do not appear in
the classical stability analyses of non-viscous parallel streams. In fact, in atomization
experiments with Weber numbers around 20, we observe a change in the breakup
pattern from axisymmetric to helicoidal modes which are predicted and explained
by our theory as having an hydrodynamic origin related to the structure of the
liquid-jet basic velocity profile. This work has been motivated by the recent discovery
by Gañán-Calvo (1998) of a new atomization technique based on the acceleration
to large velocities of coaxial liquid and gas jets by means of a favourable pressure
gradient and which are of emerging interest in microfluidic applications (high-quality
atomization, micro-fibre production, biomedical applications, etc.).
Large-scale modes of turbulent channel flow: transport and structure
Authors: LIU Z. , ADRIAN R. J. , HANRATTY T. J.
Published: August 2008

Turbulent flow in a rectangular channel is investigated to determine the scale and
pattern of the eddies that contribute most to the total turbulent kinetic energy and
the Reynolds shear stress. Instantaneous, two-dimensional particle image velocimeter
measurements in the streamwise-wall-normal plane at Reynolds numbers Reh = 5378
and 29 935 are used to form two-point spatial correlation functions, from which
the proper orthogonal modes are determined. Large-scale motions – having length
scales of the order of the channel width and represented by a small set of low-order
eigenmodes – contain a large fraction of the kinetic energy of the streamwise velocity
component and a small fraction of the kinetic energy of the wall-normal velocities.
Surprisingly, the set of large-scale modes that contains half of the total turbulent
kinetic energy in the channel, also contains two-thirds to three-quarters of the total
Reynolds shear stress in the outer region. Thus, it is the large-scale motions, rather
than the main turbulent motions, that dominate turbulent transport in all parts of the
channel except the buffer layer. Samples of the large-scale structures associated with
the dominant eigenfunctions are found by projecting individual realizations onto the
dominant modes. In the streamwise wall-normal plane their patterns often consist
of an inclined region of second quadrant vectors separated from an upstream region
of fourth quadrant vectors by a stagnation point/shear layer. The inclined Q4/shear
layer/Q2 region of the largest motions extends beyond the centreline of the channel
and lies under a region of fluid that rotates about the spanwise direction. This pattern
is very similar to the signature of a hairpin vortex. Reynolds number similarity of the
large structures is demonstrated, approximately, by comparing the two-dimensional
correlation coefficients and the eigenvalues of the different modes at the two Reynolds
numbers.
Coupled pulsation and translation of two gas bubbles in a liquid
Authors: HARKIN ANTHONY , KAPER TASSO J. , NADIM ALI
Published: August 2008

We present and analyse a model for the spherical pulsations and translational motions
of a pair of interacting gas bubbles in an incompressible liquid. The model is derived
rigorously in the context of potential flow theory and contains all terms up to and
including fourth order in the inverse separation distance between the bubbles. We use
this model to study the cases of both weak and moderate applied acoustic forcing. For
weak acoustic forcing, the radial pulsations of the bubbles are weakly coupled, which
allows us to obtain a nonlinear time-averaged model for the relative distance between
the bubbles. The two parameters of the time-averaged model classify four different
dynamical regimes of relative translational motion, two of which correspond to the
attraction and repulsion of classical secondary Bjerknes theory. Also predicted is a
pattern in which the bubbles exhibit stable, time-periodic translational oscillations
along the line connecting their centres, and another pattern in which there is an
unstable separation distance such that bubble pairs can either attract or repel each
other depending on whether their initial separation distance is smaller or larger
than this value. Moreover, it is shown that the full governing equations possess the
dynamics predicted by the time-averaged model. We also study the case of moderate-amplitude
acoustic forcing, in which the bubble pulsations are more strongly coupled
to each other and bubble translation also affects the radial pulsations. Here, radial
harmonics and nonlinear phase shifting play a significant role, as bubble pairs near
resonances are observed to translate in patterns opposite to those predicted by
classical secondary Bjerknes theory. In this work, dynamical systems techniques and
the method of averaging are the primary mathematical methods that are employed.
Moderate-Reynolds-number flows in ordered and random arrays of spheres
Authors: HILL REGHAN J. , KOCH DONALD L. , LADD ANTHONY J. C.
Published: August 2008

Lattice-Boltzmann simulations are used to examine the effects of fluid inertia, at
moderate Reynolds numbers, on flows in simple cubic, face-centred cubic and random
arrays of spheres. The drag force on the spheres, and hence the permeability of the
arrays, is calculated as a function of the Reynolds number at solid volume fractions
up to the close-packed limits of the arrays. At Reynolds numbers up to O(102), the
non-dimensional drag force has a more complex dependence on the Reynolds number
and the solid volume fraction than suggested by the well-known Ergun correlation,
particularly at solid volume fractions smaller than those that can be achieved in
physical experiments. However, good agreement is found between the simulations
and Ergun's correlation at solid volume fractions approaching the close-packed limit.
For ordered arrays, the drag force is further complicated by its dependence on the
direction of the flow relative to the axes of the arrays, even though in the absence
of fluid inertia the permeability is isotropic. Visualizations of the flows are used to
help interpret the numerical results. For random arrays, the transition to unsteady
flow and the effect of moderate Reynolds numbers on hydrodynamic dispersion are
discussed.
The first effects of fluid inertia on flows in ordered and random arrays of spheres
Authors: HILL REGHAN J. , KOCH DONALD L. , LADD ANTHONY J. C.
Published: August 2008

Theory and lattice-Boltzmann simulations are used to examine the effects of fluid
inertia, at small Reynolds numbers, on flows in simple cubic, face-centred cubic and
random arrays of spheres. The drag force on the spheres, and hence the permeability
of the arrays, is determined at small but finite Reynolds numbers, at solid volume
fractions up to the close-packed limits of the arrays. For small solid volume fraction,
the simulations are compared to theory, showing that the first inertial contribution
to the drag force, when scaled with the Stokes drag force on a single sphere in
an unbounded fluid, is proportional to the square of the Reynolds number. The
simulations show that this scaling persists at solid volume fractions up to the
close-packed limits of the arrays, and that the first inertial contribution to the drag
force relative to the Stokes-flow drag force decreases with increasing solid volume
fraction. The temporal evolution of the spatially averaged velocity and the drag
force is examined when the fluid is accelerated from rest by a constant average
pressure gradient toward a steady Stokes flow. Theory for the short- and long-time
behaviour is in good agreement with simulations, showing that the unsteady force
is dominated by quasi-steady drag and added-mass forces. The short- and long-time
added-mass coefficients are obtained from potential-flow and quasi-steady
viscous-flow approximations, respectively.
Theory of the Eulerian tail in the spectra of atmospheric and oceanic internal gravity waves
Authors: HINES COLIN O.
Published: August 2008

Observed atmospheric and oceanic internal wave spectra, when analysed in an
Eulerian frame of reference, exhibit a large-wavenumber ‘tail’. In one-dimensional
vertical-wavenumber (k3) spectra, it is typically proportional to |k3|−3.

In 1989, K. R. Allen and R. I. Joseph showed that a large-wavenumber tail was to
be anticipated as a consequence of Eulerian nonlinearity, and they derived relations
for the coefficients of both horizontal and vertical spectra of the form |k|−3. The coefficients were obtained only for the wave-induced vertical-displacement spectra,
and only for an input spectrum having a certain ‘canonical’ frequency variation
derived on other grounds.

The present work builds on that of Allen & Joseph. It is more general in some
respects, more limited in others. It provides a more transparent form of analysis,
it treats a broad class of wave variables, and it does so for input (Lagrangian)
spectra that can be chosen by the user, free from any constraint to canonical or
other restricted forms. It provides relations whereby the full Eulerian spectrum may
be determined numerically, once the input spectrum has been chosen, and it provides
analytic forms applicable at large wavenumbers for horizontally isotropic spectra.
The derived one-dimensional vertical-wavenumber spectra are discussed in relation
to observations.

Certain shortcomings in the development, both as given by Allen & Joseph and as
found here, are identified and discussed.
Vortex-induced vibrations of a cylinder with tripping wires
Authors: HOVER F. S. , TVEDT H. , TRIANTAFYLLOU M. S.
Published: August 2008

Thin wires are attached on the outer surface and parallel to the axis of a smooth
circular cylinder in a steady cross-stream, modelling the effect of protrusions and
attachments. The impact of the wires on wake properties, and vortex-induced loads
and vibration are studied at Reynolds numbers up to 4.6
× 104, with 3.0 × 104 as
a focus point. For a stationary cylinder, wires cause significant reductions in drag
and lift coefficients, as well as an increase in the Strouhal number to a value around
0.25–0.27. For a cylinder forced to oscillate harmonically, the main observed wire
effects are: (a) an earlier onset of frequency lock-in, when compared with the smooth
cylinder case; (b) at moderate amplitude/cylinder diameter (A/D) ratios (0.2 and 0.5),
changes in the phase of wake velocity and of lift with respect to motion are translated
to higher forcing frequencies, and (c) at A/D = 1.0, no excitation region exists; the
lift force is always dissipative.

The flow-induced response of a flexibly mounted cylinder with attached wires is
significantly altered as well, even far away from lock-in. Parameterizing the response
using nominal reduced velocity Vrn = U/fnD, we found that frequency lock-in occurs
and lift phase angles change through 180° at Vrn
[thkap ] 4.9; anemometry in the wake
confirms that a mode transition accompanies this premature lock-in. A plateau
of constant response is established in the range Vrn = 5.1–6.0, reducing the peak
amplitude moderately, and then vibrations are drastically reduced or eliminated
above Vrn = 6.0. The vortex-induced vibration response of the cylinder with wires is
extremely sensitive to angular bias near the critical value of Vrn = 6.0, and moderately
so in the regime of suppressed vibration.
Motion of a drop in a vertical temperature gradient at small Marangoni number – the critical role of inertia
Authors: ZHANG LU , SUBRAMANIAN R. SHANKAR , BALASUBRAMANIAM R.
Published: August 2008

When a drop moves in a uniform vertical temperature gradient under the combined
action of gravity and thermocapillarity at small values of the thermal Péclet number,
it is shown that inclusion of inertia is crucial in the development of an asymptotic
solution for the temperature field. If inertia is completely ignored, use of the method
of matched asymptotic expansions, employing the Péclet number (known as the
Marangoni number) as the small parameter, leads to singular behaviour of the outer
temperature field. The origin of this behaviour can be traced to the interaction of the
slowly decaying Stokeslet, arising from the gravitational contribution to the motion
of the drop, with the temperature gradient field far from the drop. When inertia is
included, and the method of matched asymptotic expansions is used, employing the
Reynolds number as a small parameter, the singular behaviour of the temperature
field is eliminated. A result is obtained for the migration velocity of the drop that is
correct to O(Re2 log Re).
Hysteresis phenomena in the interaction process of conical shock waves: experimental and numerical investigations
Authors: BEN-DOR G. , VASILIEV E. I. , ELPERIN T. , CHPOUN A.
Published: August 2008

The interaction of two conical shock waves, one converging and straight and the
other diverging and curvilinear, in an axisymmetric flow was investigated both
experimentally and numerically. A double-loop hysteresis was discovered in the course of
the experimental investigation. The double-loop hysteresis consisted of a major one,
associated with the interaction between the boundary layer and the wave
configuration, and a minor one, associated with the dual-solution phenomenon, which is known
to be non-viscous-dependent. The minor hysteresis loop was found to be an internal
hysteresis loop of the major one. As expected the numerical Euler calculations failed
to detect the viscous-dependent major hysteresis loop but did succeed in obtaining
the non-viscous-dependent minor (internal) hysteresis loop. In addition, multiple
hysteresis loops, associated with the interaction between the shock wave configuration
and the edge of the curvilinear mobile cone were also observed. The non-viscous
minor hysteresis loop involved different overall shock wave reflection configurations,
and the other hysteresis loops involved the same shock wave reflection configuration
but different flow patterns.
Anisotropy of small-scale scalar turbulence
Authors: KURIEN SUSAN , AIVALIS KONSTANTINOS G. , SREENIVASAN KATEPALLI R.
Published: August 2008

The anisotropy of small-scale temperature fluctuations in shear flows is analysed
by making measurements in high-Reynolds-number atmospheric surface layers. A
spherical harmonics representation of the moments of scalar increments is proposed,
such that the isotropic part corresponds to the index j = 0 and increasing degrees
of anisotropy correspond to increasing j. The parity and angular dependence of
the odd moments of the scalar increments show that the moments cannot contain
any isotropic part (j = 0), but can be satisfactorily represented by the lowest-order
anisotropic term corresponding to j = 1. Thus, the skewnesses of scalar increments
(and derivatives) are inherently anisotropic quantities, and are not suitable indicators
of the tendency towards isotropy.