13 results
11 - Parental Care
- Edited by Jeremy Koster, Max Planck Institute for Evolutionary Anthropology, Leipzig, Brooke Scelza, University of California, Los Angeles, Mary K. Shenk, Pennsylvania State University
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- Book:
- Human Behavioral Ecology
- Published online:
- 07 March 2024
- Print publication:
- 14 March 2024, pp 256-282
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Summary
Parental care in humans is remarkably extensive, with many individuals living only a fraction of their lives outside of the sphere of parental influence, and parental care is exceptionally plastic, with the extent and form of care varying across contexts and individuals. Behavioral ecological studies of parenting fall into three main foci. First, parental care is studied in terms of life history tradeoffs, including between mating and parenting effort, and between fertility and investment per offspring. Second, parental care is studied as a conflict trait, including sibling conflict, parent-offspring conflict, and sexual conflict between mothers and fathers. Finally, parental investment theory addresses how individual characteristics, such as birth order, sex and putative relatedness, influence parental strategies. For each focus, predictions are context-specific with socioecology dictating the local costs and payoffs to parental care. Over 50 years of behavioral ecological studies of parenting have transformed understandings of the human family, exposing the fragile mix of cooperation and competition underlying family relationships. Questions remain, however, particularly with regard to parental strategies in nonnuclear family structures, the role of physiological, psychological and cultural mechanisms in regulating adaptive strategies, and the coevolution of parental care with culturally variable beliefs about kinship, gender and reproduction.
Misperception of peer beliefs reinforces inequitable gender norms among Tanzanian men
- David W. Lawson, Zhian Chen, Joseph A. Kilgallen, Charlotte O. Brand, Alexander M. Ishungisa, Susan B. Schaffnit, Yusufu Kumogola, Mark Urassa
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- Journal:
- Evolutionary Human Sciences / Volume 6 / 2024
- Published online by Cambridge University Press:
- 21 February 2024, e17
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Gender role ideology, i.e. beliefs about how genders should behave, is shaped by social learning. Accordingly, if perceptions about the beliefs of others are inaccurate this may impact trajectories of cultural change. Consistent with this premise, recent studies report evidence of a tendency to overestimate peer support for inequitable gender norms, especially among men, and that correcting apparent ‘norm misperception’ promotes transitions to relatively egalitarian beliefs. However, supporting evidence largely relies on self-report measures vulnerable to social desirability bias. Consequently, observed patterns may reflect researcher measurement error rather than participant misperception. Addressing this shortcoming, we examine men's gender role ideology using both conventional self-reported and a novel wife-reported measure of men's beliefs in an urbanising community in Tanzania. We confirm that participants overestimate peer support for gender inequity. However, the latter measure, which we argue more accurately captures men's true beliefs, implies that this tendency is relatively modest in magnitude and scope. Overestimation was most pronounced among men holding relatively inequitable beliefs, consistent with misperception of peer beliefs reinforcing inequitable norms. Furthermore, older and poorly educated men overestimated peer support for gender inequity the most, suggesting that outdated and limited social information contribute to norm misperception in this context.
Gendered conflict in the human family
- David W. Lawson, Sarah Alami, Oluwaseyi Dolapo Somefun
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- Journal:
- Evolutionary Human Sciences / Volume 5 / 2023
- Published online by Cambridge University Press:
- 24 April 2023, e12
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Sexual conflict is a thriving area of animal behaviour research. Yet parallel research in the evolutionary human sciences remains underdeveloped and has become mired by controversy. In this special collection, we aim to invigorate the study of fitness-relevant conflicts between women and men, advocating for three synergistic research priorities. First, we argue that a commitment to diversity is required to innovate the field, achieve ethical research practice, and foster fruitful dialogue with neighbouring social sciences. Accordingly, we have prioritised issues of diversity as editors, aiming to stimulate new connections and perspectives. Second, we call for greater recognition that human sex/gender roles and accompanying conflict behaviours are both subject to natural selection and culturally determined. This motivates our shift in terminology from sexual to gendered conflict when addressing human behaviour, countering stubborn tendencies to essentialise differences between women and men and directing attention to the role of cultural practices, normative sanctions and social learning in structuring conflict battlegrounds. Finally, we draw attention to contemporary policy concerns, including the wellbeing consequences of marriage practices and the gendered implications of market integration. Focus on these themes, combined with attendance to the dangers of ethnocentrism, promises to inform culturally sensitive interventions promoting gender equality worldwide.
Why marry early? Parental influence, agency and gendered conflict in Tanzanian marriages
- Jitihada Baraka, David W Lawson, Susan B Schaffnit, Joyce Wamoyi, Mark Urassa
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- Journal:
- Evolutionary Human Sciences / Volume 4 / 2022
- Published online by Cambridge University Press:
- 21 October 2022, e49
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Global health interventions increasingly target the abolishment of ‘child marriage’ (marriage under 18 years, hereafter referred to as ‘early marriage’). Guided by human behavioural ecology theory, and drawing on focus groups and in-depth interviews in an urbanising Tanzanian community where female early marriage is normative, we examine the common assumption that it is driven by the interests and coercive actions of parents and/or men. We find limited support for parent–offspring conflict. Parents often encouraged early marriages, but were motivated by the promise of social and economic security for daughters, rather than bridewealth transfers alone. Moreover, forced marriage appears rare, and adolescent girls and young women (AGYW) were active agents in the transition to marriage, sometimes marrying against parental wishes. Support for gendered conflict was stronger. AGYW were described as being lured into unstable relationships by men misrepresenting their long-term intentions. Community members voiced concerns over these marriages. Overall, early marriage appears rooted in limited options, encouraging strategic, but risky choices on the marriage market. Our results highlight plurality and context dependency in drivers of early marriage, even within a single community. We conclude that engaging with the importance of context is fundamental in forging culturally sensitive policies and programs on early marriage.
Characterisation of age and polarity at onset in bipolar disorder
- Janos L. Kalman, Loes M. Olde Loohuis, Annabel Vreeker, Andrew McQuillin, Eli A. Stahl, Douglas Ruderfer, Maria Grigoroiu-Serbanescu, Georgia Panagiotaropoulou, Stephan Ripke, Tim B. Bigdeli, Frederike Stein, Tina Meller, Susanne Meinert, Helena Pelin, Fabian Streit, Sergi Papiol, Mark J. Adams, Rolf Adolfsson, Kristina Adorjan, Ingrid Agartz, Sofie R. Aminoff, Heike Anderson-Schmidt, Ole A. Andreassen, Raffaella Ardau, Jean-Michel Aubry, Ceylan Balaban, Nicholas Bass, Bernhard T. Baune, Frank Bellivier, Antoni Benabarre, Susanne Bengesser, Wade H Berrettini, Marco P. Boks, Evelyn J. Bromet, Katharina Brosch, Monika Budde, William Byerley, Pablo Cervantes, Catina Chillotti, Sven Cichon, Scott R. Clark, Ashley L. Comes, Aiden Corvin, William Coryell, Nick Craddock, David W. Craig, Paul E. Croarkin, Cristiana Cruceanu, Piotr M. Czerski, Nina Dalkner, Udo Dannlowski, Franziska Degenhardt, Maria Del Zompo, J. Raymond DePaulo, Srdjan Djurovic, Howard J. Edenberg, Mariam Al Eissa, Torbjørn Elvsåshagen, Bruno Etain, Ayman H. Fanous, Frederike Fellendorf, Alessia Fiorentino, Andreas J. Forstner, Mark A. Frye, Janice M. Fullerton, Katrin Gade, Julie Garnham, Elliot Gershon, Michael Gill, Fernando S. Goes, Katherine Gordon-Smith, Paul Grof, Jose Guzman-Parra, Tim Hahn, Roland Hasler, Maria Heilbronner, Urs Heilbronner, Stephane Jamain, Esther Jimenez, Ian Jones, Lisa Jones, Lina Jonsson, Rene S. Kahn, John R. Kelsoe, James L. Kennedy, Tilo Kircher, George Kirov, Sarah Kittel-Schneider, Farah Klöhn-Saghatolislam, James A. Knowles, Thorsten M. Kranz, Trine Vik Lagerberg, Mikael Landen, William B. Lawson, Marion Leboyer, Qingqin S. Li, Mario Maj, Dolores Malaspina, Mirko Manchia, Fermin Mayoral, Susan L. McElroy, Melvin G. McInnis, Andrew M. McIntosh, Helena Medeiros, Ingrid Melle, Vihra Milanova, Philip B. Mitchell, Palmiero Monteleone, Alessio Maria Monteleone, Markus M. Nöthen, Tomas Novak, John I. Nurnberger, Niamh O'Brien, Kevin S. O'Connell, Claire O'Donovan, Michael C. O'Donovan, Nils Opel, Abigail Ortiz, Michael J. Owen, Erik Pålsson, Carlos Pato, Michele T. Pato, Joanna Pawlak, Julia-Katharina Pfarr, Claudia Pisanu, James B. Potash, Mark H Rapaport, Daniela Reich-Erkelenz, Andreas Reif, Eva Reininghaus, Jonathan Repple, Hélène Richard-Lepouriel, Marcella Rietschel, Kai Ringwald, Gloria Roberts, Guy Rouleau, Sabrina Schaupp, William A Scheftner, Simon Schmitt, Peter R. Schofield, K. Oliver Schubert, Eva C. Schulte, Barbara Schweizer, Fanny Senner, Giovanni Severino, Sally Sharp, Claire Slaney, Olav B. Smeland, Janet L. Sobell, Alessio Squassina, Pavla Stopkova, John Strauss, Alfonso Tortorella, Gustavo Turecki, Joanna Twarowska-Hauser, Marin Veldic, Eduard Vieta, John B. Vincent, Wei Xu, Clement C. Zai, Peter P. Zandi, Psychiatric Genomics Consortium (PGC) Bipolar Disorder Working Group, International Consortium on Lithium Genetics (ConLiGen), Colombia-US Cross Disorder Collaboration in Psychiatric Genetics, Arianna Di Florio, Jordan W. Smoller, Joanna M. Biernacka, Francis J. McMahon, Martin Alda, Bertram Müller-Myhsok, Nikolaos Koutsouleris, Peter Falkai, Nelson B. Freimer, Till F.M. Andlauer, Thomas G. Schulze, Roel A. Ophoff
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- Journal:
- The British Journal of Psychiatry / Volume 219 / Issue 6 / December 2021
- Published online by Cambridge University Press:
- 25 August 2021, pp. 659-669
- Print publication:
- December 2021
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Background
Studying phenotypic and genetic characteristics of age at onset (AAO) and polarity at onset (PAO) in bipolar disorder can provide new insights into disease pathology and facilitate the development of screening tools.
AimsTo examine the genetic architecture of AAO and PAO and their association with bipolar disorder disease characteristics.
MethodGenome-wide association studies (GWASs) and polygenic score (PGS) analyses of AAO (n = 12 977) and PAO (n = 6773) were conducted in patients with bipolar disorder from 34 cohorts and a replication sample (n = 2237). The association of onset with disease characteristics was investigated in two of these cohorts.
ResultsEarlier AAO was associated with a higher probability of psychotic symptoms, suicidality, lower educational attainment, not living together and fewer episodes. Depressive onset correlated with suicidality and manic onset correlated with delusions and manic episodes. Systematic differences in AAO between cohorts and continents of origin were observed. This was also reflected in single-nucleotide variant-based heritability estimates, with higher heritabilities for stricter onset definitions. Increased PGS for autism spectrum disorder (β = −0.34 years, s.e. = 0.08), major depression (β = −0.34 years, s.e. = 0.08), schizophrenia (β = −0.39 years, s.e. = 0.08), and educational attainment (β = −0.31 years, s.e. = 0.08) were associated with an earlier AAO. The AAO GWAS identified one significant locus, but this finding did not replicate. Neither GWAS nor PGS analyses yielded significant associations with PAO.
ConclusionsAAO and PAO are associated with indicators of bipolar disorder severity. Individuals with an earlier onset show an increased polygenic liability for a broad spectrum of psychiatric traits. Systematic differences in AAO across cohorts, continents and phenotype definitions introduce significant heterogeneity, affecting analyses.
He for she? Variation and exaggeration in men's support for women's empowerment in northern Tanzania
- David W. Lawson, Susan B. Schaffnit, Joseph A. Kilgallen, Yusufu Kumogola, Anthony Galura, Mark Urassa
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- Journal:
- Evolutionary Human Sciences / Volume 3 / 2021
- Published online by Cambridge University Press:
- 18 March 2021, e27
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Achieving gender equality fundamentally requires a transfer of power from men to women. Yet data on men's support for women's empowerment (WE) remains scant and limited by reliance on self-report methodologies. Here, we examine men's support for WE as a sexual conflict trait, both via direct surveys (n = 590) and indirectly by asking men's wives (n = 317) to speculate on their husband's views. Data come from a semi-urban community in Mwanza, Tanzania. Consistent with reduced resource competition and increased exposure to relatively egalitarian gender norms, higher socioeconomic status predicted greater support for WE. However, potential demographic indicators of sexual conflict (high fertility, polygyny, large spousal age gap) were largely unrelated to men's support for WE. Contrasting self- and wife-reported measures suggests that men frequently exaggerate their support for women in self-reported attitudes. Discrepancies were especially pronounced among men claiming the highest support for WE, but smallest among men who held a professional occupation and whose wife participated in wage labour, indicating that these factors predict genuine support for WE. We discuss the implications of these results for our understanding of both individual variation and patriarchal gender norms, emphasising the benefits of greater exchange between the evolutionary human sciences and global health research on these themes.
Telehealth Delivery of Memory Rehabilitation Following Stroke
- David W. Lawson, Renerus J. Stolwyk, Jennie L. Ponsford, Dean P. McKenzie, Marina G. Downing, Dana Wong
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- Journal:
- Journal of the International Neuropsychological Society / Volume 26 / Issue 1 / January 2020
- Published online by Cambridge University Press:
- 27 January 2020, pp. 58-71
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Objective:
Rehabilitation of memory after stroke remains an unmet need. Telehealth delivery may overcome barriers to accessing rehabilitation services.
Method:We conducted a non-randomized intervention trial to investigate feasibility and effectiveness of individual telehealth (internet videoconferencing) and face-to-face delivery methods for a six-week compensatory memory rehabilitation program. Supplementary analyses investigated non-inferiority to an existing group-based intervention, and the role of booster sessions in maintaining functional gains. The primary outcome measure was functional attainment of participants’ goals. Secondary measures included subjective reports of lapses in everyday memory and prospective memory, reported use of internal and external memory strategies, and objective measures of memory functioning.
Results:Forty-six stroke survivors were allocated to telehealth and face-to-face intervention delivery conditions. Feasibility of delivery methods was supported, and participants in both conditions demonstrated treatment-related improvements in goal attainment, and key subjective outcomes of everyday memory, and prospective memory. Gains on these measures were maintained at six-week follow-up. Short-term gains in use of internal strategies were also seen. Non-inferiority to group-based delivery was established only on the primary measure for the telehealth delivery condition. Booster sessions were associated with greater maintenance of gains on subjective measures of everyday memory and prospective memory.
Conclusions:This exploratory study supports the feasibility and potential effectiveness of telehealth options for remote delivery of compensatory memory skills training after a stroke. These results are also encouraging of a role for booster sessions in prolonging functional gains over time.
Fathers favour sons, mothers don't discriminate: Sex-biased parental care in northwestern Tanzania
- Anushé Hassan, Susan B. Schaffnit, Rebecca Sear, Mark Urassa, David W. Lawson
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- Journal:
- Evolutionary Human Sciences / Volume 1 / 2019
- Published online by Cambridge University Press:
- 04 December 2019, e13
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Variation in parental care by child's sex is evident across cultures. Evolutionary theory provides a functional explanation for this phenomenon, predicting that parents will favour specific children if this results in greater fitness payoffs. Here, we explore evidence for sex-biased parental care in a high-fertility, patriarchal and polygynous population in Tanzania, predicting that both mothers and fathers will favour sons in this cultural setting. Our data come from a cross-sectional study in rural northwestern Tanzania, which included surveys with mothers/guardians of 808 children under age 5. We focus on early childhood, a period with high mortality risk which is fundamental in establishing later-life physical and cognitive development. Examining multiple measures of direct/physical care provision (washing, feeding, playing with, supervising, co-sleeping and caring when sick), we demonstrate that fathers favour sons for washing, feeding and supervising, while maternal care is both more intensive and unrelated to child sex. We find no difference in parental care between girls and boys regarding the allocation of material resources and the duration of breastfeeding; or in terms of parental marital and co-residence status. This bias towards sons may result from higher returns to investment for fathers than mothers, and local gender norms about physical care provision.
Contributors
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- By Rony A. Adam, Gloria Bachmann, Nichole M. Barker, Randall B. Barnes, John Bennett, Inbar Ben-Shachar, Jonathan S. Berek, Sarah L. Berga, Monica W. Best, Eric J. Bieber, Frank M. Biro, Shan Biscette, Anita K. Blanchard, Candace Brown, Ronald T. Burkman, Joseph Buscema, John E. Buster, Michael Byas-Smith, Sandra Ann Carson, Judy C. Chang, Annie N. Y. Cheung, Mindy S. Christianson, Karishma Circelli, Daniel L. Clarke-Pearson, Larry J. Copeland, Bryan D. Cowan, Navneet Dhillon, Michael P. Diamond, Conception Diaz-Arrastia, Nicole M. Donnellan, Michael L. Eisenberg, Eric Eisenhauer, Sebastian Faro, J. Stuart Ferriss, Lisa C. Flowers, Susan J. Freeman, Leda Gattoc, Claudine Marie Gayle, Timothy M. Geiger, Jennifer S. Gell, Alan N. Gordon, Victoria L. Green, Jon K. Hathaway, Enrique Hernandez, S. Paige Hertweck, Randall S. Hines, Ira R. Horowitz, Fred M. Howard, William W. Hurd, Fidan Israfilbayli, Denise J. Jamieson, Carolyn R. Jaslow, Erika B. Johnston-MacAnanny, Rohna M. Kearney, Namita Khanna, Caroline C. King, Jeremy A. King, Ira J. Kodner, Tamara Kolev, Athena P. Kourtis, S. Robert Kovac, Ertug Kovanci, William H. Kutteh, Eduardo Lara-Torre, Pallavi Latthe, Herschel W. Lawson, Ronald L. Levine, Frank W. Ling, Larry I. Lipshultz, Steven D. McCarus, Robert McLellan, Shruti Malik, Suketu M. Mansuria, Mohamed K. Mehasseb, Pamela J. Murray, Saloney Nazeer, Farr R. Nezhat, Hextan Y. S. Ngan, Gina M. Northington, Peggy A. Norton, Ruth M. O'Regan, Kristiina Parviainen, Resad P. Pasic, Tanja Pejovic, K. Ulrich Petry, Nancy A. Phillips, Ashish Pradhan, Elizabeth E. Puscheck, Suneetha Rachaneni, Devon M. Ramaeker, David B. Redwine, Robert L. Reid, Carla P. Roberts, Walter Romano, Peter G. Rose, Robert L. Rosenfield, Shon P. Rowan, Mack T. Ruffin, Janice M. Rymer, Evis Sala, Ritu Salani, Joseph S. Sanfilippo, Mahmood I. Shafi, Roger P. Smith, Meredith L. Snook, Thomas E. Snyder, Mary D. Stephenson, Thomas G. Stovall, Richard L. Sweet, Philip M. Toozs-Hobson, Togas Tulandi, Elizabeth R. Unger, Denise S. Uyar, Marion S. Verp, Rahi Victory, Tamara J. Vokes, Michelle J. Washington, Katharine O'Connell White, Paul E. Wise, Frank M. Wittmaack, Miya P. Yamamoto, Christine Yu, Howard A. Zacur
- Edited by Eric J. Bieber, Joseph S. Sanfilippo, University of Pittsburgh, Ira R. Horowitz, Emory University, Atlanta, Mahmood I. Shafi
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- Book:
- Clinical Gynecology
- Published online:
- 05 April 2015
- Print publication:
- 23 April 2015, pp viii-xiv
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Contributors
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- By Michael H. Allen, Leora Amira, Victoria Arango, David W. Ayer, Helene Bach, Christopher R. Bailey, Ross J. Baldessarini, Kelsey Ball, Alan L. Berman, Marian E. Betz, Emily A. Biggs, R. Warwick Blood, Kathleen T. Brady, David A. Brent, Jeffrey A. Bridge, Gregory K. Brown, Anat Brunstein Klomek, A. Jacqueline Buchanan, Michelle J. Chandley, Tim Coffey, Jessica Coker, Yeates Conwell, Scott J. Crow, Collin L. Davidson, Yogesh Dwivedi, Stacey Espaillat, Jan Fawcett, Steven J. Garlow, Robert D. Gibbons, Catherine R. Glenn, Deborah Goebert, Erica Goldstein, Tina R. Goldstein, Madelyn S. Gould, Kelly L. Green, Alison M. Greene, Philip D. Harvey, Robert M. A. Hirschfeld, Donna Holland Barnes, Andres M. Kanner, Gary J. Kennedy, Stephen H. Koslow, Benoit Labonté, Alison M. Lake, William B. Lawson, Steve Leifman, Adam Lesser, Timothy W. Lineberry, Amanda L. McMillan, Herbert Y. Meltzer, Michael Craig Miller, Michael J. Miller, James A. Naifeh, Katharine J. Nelson, Charles B. Nemeroff, Alexander Neumeister, Matthew K. Nock, Jennifer H. Olson-Madden, Gregory A. Ordway, Michael W. Otto, Ghanshyam N. Pandey, Giampaolo Perna, Jane Pirkis, Kelly Posner, Anne Rohs, Pedro Ruiz, Molly Ryan, Alan F. Schatzberg, S. Charles Schulz, M. Katherine Shear, Morton M. Silverman, April R. Smith, Marcus Sokolowski, Barbara Stanley, Zachary N. Stowe, Sarah A. Struthers, Leonardo Tondo, Gustavo Turecki, Robert J. Ursano, Kimberly Van Orden, Anne C. Ward, Danuta Wasserman, Jerzy Wasserman, Melinda K. Westlund, Tracy K. Witte, Kseniya Yershova, Alexandra Zagoloff, Sidney Zisook
- Edited by Stephen H. Koslow, University of Miami, Pedro Ruiz, University of Miami, Charles B. Nemeroff, University of Miami
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- Book:
- A Concise Guide to Understanding Suicide
- Published online:
- 05 October 2014
- Print publication:
- 18 September 2014, pp vii-x
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Swirling flow of viscoelastic fluids. Part 2. Elastic effects
- JASON R. STOKES, LACHLAN J. W. GRAHAM, NICK J. LAWSON, DAVID V. BOGER
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- Journal:
- Journal of Fluid Mechanics / Volume 429 / 25 February 2001
- Published online by Cambridge University Press:
- 01 March 2001, pp. 117-153
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A torsionally driven cavity has been used to examine the influence of elasticity on the swirling flow of constant-viscosity elastic liquids (Boger fluids). A wealth of phenomena is observed as the degree of inertia, elasticity and viscous forces are varied by using a range of low- to high-viscosity flexible polyacrylamide Boger fluids and a semi-rigid xanthan gum Boger fluid. As the inertia is decreased and elasticity increased by using polyacrylamide Boger fluids, the circulation rates for a ‘Newtonian-like’ secondary flow decreases until flow reversal occurs owing to the increasing magnitude of the primary normal stress difference. For each polyacrylamide fluid, the flow becomes highly unstable at a critical combination of Reynolds number and Weissenberg number resulting in a new time-dependent elastic instability. Each fluid is characterized by a dimensionless elasticity number and a correlation with Reynolds number is found for the occurrence of the instability. In the elasticity dominated flow of the polyacrylamide Boger fluids, the instability disrupts the flow dramatically and causes an increase in the peak axial velocity along the central axis by as much as 400%. In this case, the core vortex spirals with the primary motion of fluid and is observed in some cases at Reynolds numbers much less than unity. Elastic ‘reverse’ flow is observed for the xanthan gum Boger fluid at high Weissenberg number. As the Weissenberg number decreases, and Reynolds number increases, counter-rotating vortices flowing in the inertial direction form on the rotating lid. The peak axial velocity decreases for the xanthan gum Boger fluid with decreasing Weissenberg number. In addition, several constitutive models are used to describe accurately the rheological properties of the fluids used in this work in shear and extensional flow. This experimental investigation of a complex three-dimensional flow using well-characterized fluids provides the information necessary for the validation of non-Newtonian constitutive models through numerical analysis of the torsionally driven cavity flow.
Swirling flow of viscoelastic fluids. Part 1. Interaction between inertia and elasticity
- JASON R. STOKES, LACHLAN J. W. GRAHAM, NICK J. LAWSON, DAVID V. BOGER
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- Journal:
- Journal of Fluid Mechanics / Volume 429 / 25 February 2001
- Published online by Cambridge University Press:
- 01 March 2001, pp. 67-115
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A torsionally driven cavity, consisting of a fully enclosed cylinder with rotating bottom lid, is used to examine the confined swirling flow of low-viscosity Boger fluids for situations where inertia dominates the flow field. Flow visualization and the optical technique of particle image velocimetry (PIV) are used to examine the effect of small amounts of fluid elasticity on the phenomenon of vortex breakdown. Low-viscosity Boger fluids are used which consist of dilute concentrations of high molecular weight polyacrylamide or semi-dilute concentrations of xanthan gum in a Newtonian solvent. The introduction of elasticity results in a 20% and 40% increase in the minimum critical aspect ratio required for vortex breakdown to occur using polyacrylamide and xanthan gum, respectively, at concentrations of 45 p.p.m. When the concentrations of either polyacrylamide or xanthan gum are raised to 75 p.p.m., vortex breakdown is entirely suppressed for the cylinder aspect ratios examined. Radial and axial velocity measurements along the axial centreline show that the alteration in existence domain is linked to a decrease in the magnitude of the peak in axial velocity along the central axis. The minimum peak axial velocities along the central axis for the 75 p.p.m. polyacrylamide and 75 p.p.m. xanthan gum Boger fluids are 67% and 86% lower in magnitude, respectively, than for the Newtonian fluid at Reynolds number of Re ≈ 1500–1600. This decrease in axial velocity is associated with the interaction of elasticity in the governing boundary on the rotating base lid and/or the interaction of extensional viscosity in areas with high velocity gradients. The low-viscosity Boger fluids used in this study are rheologically characterized and the steady complex flow field has well-defined boundary conditions. Therefore, the results will allow validation of non-Newtonian constitutive models in a numerical model of a torsionally driven cavity flow.
Strain and Particle Size of Palladium Metal Powders by Time-of-Flight Neutron Diffraction
- A. C. Lawson, J. W. Conant, C. L. Talcott, M. A. David, J. Vaninetti, J. A. Goldstone, A. Williams, R. B. Roof, R. B. Von Dreele, R. L. Hitterman, J. W. Richardson, Jr., J. Faber, Jr.
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- Journal:
- Advances in X-ray Analysis / Volume 33 / 1989
- Published online by Cambridge University Press:
- 06 March 2019, pp. 403-407
- Print publication:
- 1989
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We have determined the strain and particle size for several samples of palladium powder by time-of-flight nrutron powder diffraction on two different diffractometers and by x-ray powder diffraction. The results are compared and found to be in fair agreement. The time-of-flight method gives good enough precision to reveal deficiencies in the simple models used for strain and particle size line broadening.