bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spanwise oscillatory wall motion in channel flow: drag-reduction mechanisms inferred from DNS-predicted phase-wise property variations at
Authors: Agostini L. , Touber E. , Leschziner M. A. 
Published: March 2014

AbstractA direct-numerical-simulation-based study is presented, which focuses on the response of near-wall turbulence and skin friction to the imposition of an oscillatory spanwise wall motion in channel flow. One point of contrast to earlier studies is the relatively high Reynolds number of the flow, namely $Re_\tau =1000$ in the unforced baseline flow. Another is the focus on transients in the drag that are in the form of moderate oscillatory variations in the skin friction and near-wall turbulence around the low-drag state at a sub-optimal actuation period. These conditions allow phase-averaged statistics to be extracted, during the periodic drag decrease and rise, that shed light on the interaction between turbulence and the unsteady Stokes strain. Results are presented for, among others, the phase-averaged second moments of stochastic fluctuations and their budgets, enstrophy components and joint probability density functions. The study identifies velocity skewness – the wall-normal derivative of the angle of the velocity vector – as playing a significant role in the streak-damping process during the drag-reduction phase. Furthermore, the phase-wise asymmetry in the skewness is identified as the source of a distinctive hysteresis in all properties, wherein the drag decrease progresses over a longer proportion of the actuation cycle than the drag increase. This feature, coupled with the fact that the streak-generation time scale limits the ability of the streaks to re-establish themselves during the low-skewness phase when the actuation period is sufficiently short, is proposed to drive the drag-reduction process. The observations in the study thus augment a previously identified mechanism proposed by two of the present authors, in which the drag-reduction process was linked to the rate of change in the Stokes strain in the upper region of the viscous sublayer where the streaks are strongest. Furthermore, an examination of the stochastic-stress budgets and the enstrophy lead to conclusions contrasting with those recently proposed by other authors, according to which the drag-reduction process is linked to increases in enstrophy and turbulence-energy dissipation. It is shown, both for the transient drag-reduction phase and the periodic drag fluctuations around the low-drag state, that the drag decrease/increase phases are correlated with decreases/increases in both enstrophy and dissipation.
On the anisotropy of the turbulent passive scalar in the presence of a mean scalar gradient
Authors: Bos Wouter J. T. 
Published: March 2014

AbstractWe investigate the origin of the scalar gradient skewness in isotropic turbulence on which a mean scalar gradient is imposed. The problem of the advection of an anisotropic scalar field is reformulated in terms of the advection of an isotropic vector field. For this field, triadic closure equations are derived. It is shown how the scaling of the scalar gradient skewness depends on the choice of the time scale used for the Lagrangian decorrelation of the vector field. The persistent anisotropy in the small scales for the third-order statistics is shown to be perfectly compatible with Corrsin–Obukhov scaling for second-order quantities, since second- and third-order scalar quantities are governed by a different triad correlation time scale. Whereas the inertial range dynamics of second-order scalar quantities is governed by the Lagrangian velocity correlation time, the third-order quantities remain correlated over a time related to the large-scale dynamics of the scalar field. It is argued that this time is determined by the average time it takes for a fluid particle to travel between ramp-cliff scalar structures.
Subgrid-scale backscatter in reacting and inert supersonic hydrogen–air turbulent mixing layers
Authors: O’Brien J. , Urzay J. , Ihme M. , Moin P. , Saghafian A. 
Published: March 2014

AbstractThis study addresses the dynamics of backscatter of kinetic energy in the context of large-eddy simulations (LES) of high-speed turbulent reacting flows. A priori analyses of direct numerical simulations (DNS) of reacting and inert supersonic, time-developing, hydrogen–air turbulent mixing layers with complex chemistry and multicomponent diffusion are conducted here in order to examine the effects of compressibility and combustion on subgrid-scale (SGS) backscatter of kinetic energy. The main characteristics of the aerothermochemical field in the mixing layer are outlined. A selfsimilar period is identified in which some of the turbulent quantities grow in a quasi-linear manner. A differential filter is applied to the DNS flow field to extract filtered quantities of relevance for the large-scale kinetic-energy budget. Spatiotemporal analyses of the flow-field statistics in the selfsimilar regime are performed, which reveal the presence of considerable amounts of SGS backscatter. The dilatation field becomes spatially intermittent as a result of the high-speed compressibility effect. In addition, the large-scale pressure-dilatation work is observed to be an essential mechanism for the local conversion of thermal and kinetic energies. A joint probability density function (PDF) of SGS dissipation and large-scale pressure-dilatation work is provided, which shows that backscatter occurs primarily in regions undergoing volumetric expansion; this implies the existence of an underlying physical mechanism that enhances the reverse energy cascade. Furthermore, effects of SGS backscatter on the Boussinesq eddy viscosity are studied, and a regime diagram demonstrating the relationship between the different energy-conversion modes and the sign of the eddy viscosity is provided along with a detailed budget of the volume fraction in each mode. A joint PDF of SGS dissipation and SGS dynamic-pressure dilatation work is calculated, which shows that high-speed compressibility effects lead to a decorrelation between SGS backscatter and negative eddy viscosities, which increases for increasingly large values of the SGS Mach number and filter width. Finally, it is found that the combustion dynamics have a marginal impact on the backscatter and flow-dilatation distributions, which are mainly dominated by the high-Mach-number effects.
Numerical study on unstable surfaces of oblique detonations
Authors: Teng Hong Hui , Jiang Zong Lin , Ng Hoi Dick 
Published: March 2014

AbstractIn this study, the onset of cellular structure on oblique detonation surfaces is investigated numerically using a one-step irreversible Arrhenius reaction kinetic model. Two types of oblique detonations are observed from the simulations. One is weakly unstable characterized by the existence of a planar surface, and the other is strongly unstable characterized by the immediate formation of the cellular structure. It is found that a high degree of overdrive suppresses the formation of cellular structures as confirmed by the results of many previous studies. However, the present investigation demonstrates that cellular structures also appear with degree of overdrive of 2.06 and 2.37, values much higher than ${\sim }$1.8 suggested previously in the literature for the critical value defining the instability boundary of oblique detonations. This contradiction could be explained by the use of differently shaped walls, a straight wall used in this study and a custom-designed curved wedge system so as to induce straight oblique detonations in previous studies. Another possible reason could be due to the low and possibly insufficient resolution used in previously published studies. Hence, simulations with different grid sizes are also performed to examine the effect of resolution on the numerical solutions. Using the present results, analysis also shows that although the characteristic lengths of unstable surfaces are different when the incident Mach number changes, these length scales are proportional to tangential velocities. Hence, the interior time determined by the overdrive degree is identified, and its limitation as the instability parameter is discussed.
Interest Rate Risk and the Cross Section of Stock Returns
Authors: Lioui Abraham , Maio Paulo 
Published: March 2014

AbstractWe derive a macroeconomic asset pricing model in which the key factor is the opportunity cost of money. The model explains well the cross section of stock returns in addition to the excess market return. The interest rate factor is priced and seems to drive most of the explanatory power of the model. In this model, both value stocks and past long-term losers enjoy higher average (excess) returns because they have higher interest rate risk than growth/past winner stocks. The model significantly outperforms the nested models (capital asset pricing model (CAPM) and consumption CAPM (CCAPM)) and compares favorably with alternative macroeconomic models.
Socio-spatial aspects of ageing in an urban context: an example from three Czech Republic cities
Authors: GALČANOVÁ LUCIE , SÝKOROVÁ DANA 
Published: March 2014

ABSTRACTThe purpose of this study is to examine how older people make sense of the changing urban environment – that is, how they experience, perceive and interpret their everyday interaction with its materiality, as well as their social ties, networks and relations. The results, based on seven focus groups and 37 individual in-depth interviews with older residents of the three most populous Czech cities, show how older people maintain the continuity of their activities, autonomy and independence within the limits of their personal resources in an active relationship with a changing urban environment and within the post-socialist context. The research supports the results of former studies that emphasise the ability of older adults to negotiate their position and actively cope with change while they age in place.
Est modus in rebus: a longitudinal study of intergenerational solidarity and Locus of Control
Authors: BORDONE VALERIA 
Published: March 2014

ABSTRACTThis study challenges the persistent assumption behind research on intergenerational relationships, wondering: ‘can there be too much of a good thing’? The guiding hypothesis states that intergenerational solidarity, although beneficial for older parents' wellbeing at moderate levels, may be negatively associated with their individual sense of control at high levels. In contrast to previous studies, fixed-effects regression models on panel data from the English Longitudinal Study of Ageing control for selection in solidarity and changes in health. The analysis of 4,811 women and 3,847 men above the age of 50 also accounts for intergenerational conflict. Using multiple dimensions of intergenerational solidarity, our findings offer insight into the different roles of the various types of solidarity and can aid the design of formal and informal social support interventions.
A swarm optimization approach for solving workspace determination of parallel manipulators
Authors: Saputra V. B. , Ong S. K. , Nee A. Y. C. 
Published: March 2014

SUMMARYThis paper presents a novel method to determine the workspace of parallel manipulators using a variant of the Firefly Algorithm, which is one of the emerging techniques in swarm artificial intelligence. The workspace is defined as a set of all the coordinates in the search space that are accessible by the parallel manipulator end effector. The workspace formulation of the parallel manipulator considered in this paper has actuated and passive joint displacements which values are limited by their physical constraints. A special fitness function that discriminates between accessible and inaccessible coordinates is formulated based on the joint limitations. By finding these coordinates using the proposed Firefly Algorithm, the workspace of the manipulator can be constructed. The proposed method is an easy-to-implement alternative solution to the current numerical methods for workspace determination. The method consists of two stages of operation. The first stage maps the workspace to find the initial results with a space filling approach, in which a number of coordinates in the workspace are identified. The second stage refines the results with a boundary detection approach which focuses on the mapping of the boundaries of the workspace. The method is illustrated by its application to determine the 2D, 3D, and 6D workspaces of a Gough--Stewart Platform manipulator. Furthermore, the method is compared with a more rigorous interval analysis method in terms of computational cost and accuracy.
Leakage-proof nozzle design for RepRap community 3D printer
Authors: Kłodowski Adam , Eskelinen Harri , Semken Scott 
Published: March 2014

SUMMARYThe RepRap 3D printer development project is a fast growing, open-hardware initiative relying on the input of hobbyist designers. One of its key components is the printer nozzle. The performance and reliability deficiencies of currently available nozzle designs are common topics in the RepRap community, and our own experience with a RepRap 3D printer has identified a need for improvement in a few particular areas. We set out to eliminate melt leakage, improve thermal isolation, and develop a more effective method of nozzle assembly attachment. Here, we review the issues, describe design efforts, and report results.
Succession and environmental variation influence soil exploration potential by fine roots and mycorrhizal fungi in an Atlantic ecosystem in southern Brazil
Authors: Zangaro Waldemar , de Almeida Alves Ricardo , de Souza Priscila Bochi , Rostirola Leila Vergal , Lescano Luiz Eduardo Azevedo Marques , Rondina Artur Berbel Lírio , Nogueira Marco Antonio 
Published: March 2014

Abstract:Fast-growing plant species are plentiful at the early stages of succession and possess roots with greater capacity for soil exploration than slow-growing plant species of late stages. Thus, the dynamics of fine-root production, morphological traits and arbuscular mycorrhizal fungal (AMF) infection intensity were assessed monthly over 1 y in the grassland, scrub, secondary and mature forests of the Atlantic Forest ecosystem, amounting to 13 consecutive samplings. Fine roots were sampled in three 100 × 100-m plots at each study site. Each plot was subdivided in five 20 × 100-m subplots and 15 soil samples were randomly taken from a depth of 0–5 cm in soil within each plot. The average of the fine-root dry mass increased from 1.39 mg cm−3 soil in the grassland to 3.37 mg cm−3 in the secondary forest; fine-root tip diameter varied from 146 μm in the grassland to 303 μm in the mature forest; tissue density from 0.24 g cm−3 root in the grassland to 0.30 g cm−3 in the mature forest and fine-root length was 4.52 cm cm−3 soil in the grassland and 6.48 cm cm−3 soil in the secondary forest. On the other hand, fine-root specific length decreased from 43.9 m g−1 root to 18.3 m g−1 root in the mature forest; incidence of root hairs was 67% in the grassland and 30% in the mature forest; the length of root hairs was 215 μm in the grassland and 112 μm in the mature forest; and the intensity of AMF infection decreased from 66% in the grassland to 17% in the mature forest. In addition to AMF infection, the environmental variation also affected dry mass production and morphological traits of fine roots. During the cool season, fine-root dry mass, fine-root length, incidence and length of root hairs and intensity of AMF infection decreased compared with the warm season. We verified that the potential for soil exploration, that expresses the capacity for nutrient acquisition via fine roots and AMF infection intensity, decreased during the cool season and with the advance of the successional groups. These results indicate that fine-root traits and intensity of AMF infection are influenced by the intrinsic nutrient requirements of the plant species in each ecological group.
Biogeochemical responses to nutrient, moisture and temperature manipulations of soil from Signy Island, South Orkney Islands in the Maritime Antarctic
Authors: Benhua Sun , Dennis P.G. , Laudicina V.A. , Ord V.J. , Rushton S.P. , O’Donnell A.G. , Newsham K.K. , Hopkins D.W. 
Published: March 2014

AbstractWe have investigated how the microbially-driven processes of carbon (C) mineralization (respiration) and nitrogen (N) mineralization/immobilization in a soil from the northern Maritime Antarctic respond to differences in water availability (20% and 80% water-holding capacity) and temperature (5°C and 15°C) in the presence and absence of different organic substrates (2 mg C as either glucose, glycine or tryptone soy broth (TSB) powder (a complex microbial growth medium)) in a controlled laboratory experiment over 175 days. Soil respiration and N mineralization/immobilization in the presence of a C-rich substrate (glucose) increased with increases in water and temperature. These factors were influential individually and had an additive effect when applied together. For the N-rich substrates (glycine and TSB), microbial responses to increased water or temperature alone were weak or not significant, but these factors interacted to give significantly positive increases when applied together. These data indicate that under the expected changes in environmental conditions in the Maritime Antarctic, where temperature and the availability of water and organic substrates will probably increase, soil microbial activity will lead to more rapid C and N cycling and have a positive feedback on these biogeochemical processes, particularly where or when these factors increase concurrently.
Tithe Series and Grain Production in Central Spain, 1700–1800
Authors: SANTIAGO-CABALLERO CARLOS 
Published: March 2014

AbstractThe following paper presents the original tithe series for the province of Guadalajara in central Spain. The new series contribute to recent debates on pre-modern economic growth, thus improving knowledge of a key region of Spain. The study includes analysis of the four main grains, wheat, barley, rye and oats, and the evolution of their production during the eighteenth century. The series complete previous estimates of grain production for New Castile and suggest that this was a period of growth. However, the increase was not a sustained process but one with intense imbalances, with production reaching its peak in the mid 1750s followed by a deep crisis and very weak recovery. Wheat was clearly the most important of the four grains in volume and especially in value. Its predominance was maintained thanks to a demand encouraged by the demographic growth that took place during the eighteenth century. The production of wheat was also the most stable, followed by barley, oats and rye, as might be expected given that the grain was usually cultivated in the most fertile lands. A comparison with other tithe series from the interior of Spain reveals similarities, such as the crisis of the 1760s, but also different recuperation trends. The findings indicate that Guadalajara followed a growth pattern characteristic of a traditional economy in the interior of Spain.
LONG VACATION PASTORALS: CLOUGH, TENNYSON, AND THE POETRY OF THE LIBERAL UNIVERSITY
Authors: Barton Anna 
Published: March 2014

In the opening passage ofA Room of One's Own, Virginia Woolf catches herself, and is subsequently caught out, in a moment of reflection on the banks of a river, within the grounds of a barely fictionalised “Oxbridge University”:Here then was I (call me Mary Beton, Mary Seton, Mary Carmichael or by any name you please – it is not a matter of any importance) sitting on the banks of a river a week or two ago in fine October weather, lost in thought. That collar I have spoken of, women and fiction, the need of coming to some conclusion on a subject that raises all sorts of prejudices and passions, bowed my head to the ground. To the right and left bushes of some sort, golden and crimson, glowed with the colour, even it seemed burnt with the heat, of fire. On the further bank the willows wept in perpetual lamentation, their hair about their shoulders. The river reflected whatever it chose of sky and bridge and burning tree, and when the undergraduate had oared his boat through the reflections they closed again, completely, as if he had never been. There one might have sat the clock round lost in thought. (6–7)In this fictional account of her trespass on university property, Woolf forges a close association between the environment in which she does her thinking and what she thinks, so that body, mind, and text are shown to be engaged in the same work. Her thoughts, she suggests, have a physical weight: they bow her head to the ground. The landscape bows with her so that a momentarily surreal vista of flaming leaves and long-haired trees is at once the place she is sitting and the space of her imagination, and the “reflections” through which the undergraduate oars take on a double meaning as the boat floats through her consciousness and back out again. The interruption of the beadle causes her to lose her train of thought: it is a fish that jumps and then disappears back into the river. This reverie, which rehearses the lecture's central argument concerning the material conditions required for gender equality, identifies the university as a case in point. Oxbridge is experienced by Woolf's fictional avatar as a place where intellectual freedom is achieved within a series of carefully regulated spaces, and her essay balances the attraction and acknowledged value of these exclusive spaces against the experience of her own exclusion. As so often in her work, the geography of Woolf's prose is haunted by the Victorians, whose lyric voices she can only half hear as she sits at a college window. Her essay therefore invites a return to nineteenth-century accounts of university life that pay attention to the material, or formal, delineations of the university.
THE GOVERNESS, HER BODY, AND THRESHOLDS INTHE ROMANCE OF LUST
Authors: Dau Duc 
Published: March 2014

In his groundbreaking study ofVictorian pornography,The Other Victorians, Steven Marcus draws on passages fromThe Romance of Lust(1873–76) to elucidate his now-famous term, “pornotopia.” To Marcus's mind, this text, like other pornographic novels, has few, if any, redeeming features. While the literary novel fleshes out the lives of its characters, pornography dwells endlessly on fleshly relations, he argues. Pornography, in fact, tends towards utopian fantasy, towards pornotopia. “More than most utopias,” says Marcus, “pornography takes the injunction of its etymology literally – it may be said largely to exist at no place, and to take place in nowhere” (268). In a pornotopia, time is always bedtime (269), life begins not at birth but at the moment of sexual awakening (270), and relations between characters are merely juxtapositions of bodies, body parts, and organs (274). Introducing an orgy scene fromThe Romance of Lust, Marcus asserts, “[t]his novel comes as close as anything I know to being a pure pornotopia in the sense that almost every human consideration apart from sexuality is excluded from it” (274). Pornography's lack, that is, its apparent disconnection from realistic settings and human relations, is a consequence and sign of human deprivation. “Pornotopia could in fact only have been imagined by persons who have suffered extreme deprivation,” he holds, “and I do not by this mean sexual deprivation in the genital sense alone. . . . The insatiability depicted in it seems to me to be literal insatiability, and the orgies endlessly represented are the visions of permanently hungry men” (273). Thus, “[i]nside of every pornographer there is an infant screaming for the breast from which he has been torn” (274).