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Varghese N, Sykes TC, Quetzeri-Santiago MA, Castrejón-Pita AA, Castrejón-Pita JR. Effect of Surfactants on the Splashing Dynamics of Drops Impacting Smooth Substrates. Langmuir 2024. [PMID: 38444249 DOI: 10.1021/acs.langmuir.3c03248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2024]
Abstract
We present the results of a systematic study elucidating the role that dynamic surface tension has on the spreading and splashing dynamics of surfactant-laden droplets during the impact on hydrophobic substrates. Using four different surfactants at various concentrations, we generated a range of solutions whose dynamic surface tension were characterized to submillisecond timescales using maximum bubble-pressure tensiometry. Impact dynamics of these solutions were observed by high-speed imaging with subsequent quantitative image processing to determine the impact parameters (droplet size and speed) and dynamic wetting properties (dynamic contact angle). Droplets were slowly formed by dripping to allow the surfactants to achieve equilibrium at the free surface prior to impact. Our results indicate that while only the fastest surfactants appreciably affect the maximum spreading diameter, the droplet morphology during the initial stages of spreading is different to water for all surfactant solutions studied. Moreover, we show that surfactant-laden droplets splash more easily than pure liquid (water). Based on the association of the splashing ratio to our tensiometry measurements, we are able to predict the effective surface tension acting during splashing. These results suggest that droplet splashing characteristics are primarily defined by the stretching of the equilibrated droplet free surface.
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Affiliation(s)
- Nonu Varghese
- School of Engineering and Material Sciences, Queen Mary University of London, London, E1 4NS, U.K
- Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE, U.K
| | - Thomas C Sykes
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, U.K
| | - Miguel A Quetzeri-Santiago
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, U.K
- Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Cd. Universitaria, Mexico City 04530, Mexico
| | | | - J Rafael Castrejón-Pita
- Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE, U.K
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Holland J, Castrejón-Pita AA, Tuinier R, Aarts DGAL, Nott TJ. Surface tension measurement and calculation of model biomolecular condensates. Soft Matter 2023; 19:8706-8716. [PMID: 37791635 PMCID: PMC10663989 DOI: 10.1039/d3sm00820g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 09/20/2023] [Indexed: 10/05/2023]
Abstract
The surface tension of liquid-like protein-rich biomolecular condensates is an emerging physical principle governing the mesoscopic interior organisation of biological cells. In this study, we present a method to evaluate the surface tension of model biomolecular condensates, through straighforward sessile drop measurements of capillary lengths and condensate densities. Our approach bypasses the need for characterizing condensate viscosities, which was required in previously reported techniques. We demonstrate this method using model condensates comprising two mutants of the intrinsically disordered protein Ddx4N. Notably, we uncover a detrimental impact of increased protein net charge on the surface tension of Ddx4N condensates. Furthermore, we explore the application of Scheutjens-Fleer theory, calculating condensate surface tensions through a self-consistent mean-field framework using Flory-Huggins interaction parameters. This relatively simple theory provides semi-quantitative accuracy in predicting Ddx4N condensate surface tensions and enables the evaluation of molecular organisation at condensate surfaces. Our findings shed light on the molecular details of fluid-fluid interfaces in biomolecular condensates.
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Affiliation(s)
- Jack Holland
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, UK.
- Dept. of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
| | | | - Remco Tuinier
- Laboratory of Physical Chemistry, Department of Chemical Engineering and Chemistry & Institute for Complex Molecular Systems (ICMS), Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| | - Dirk G A L Aarts
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, UK.
| | - Timothy J Nott
- Dept. of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
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Cimpeanu R, Castrejón-Pita AA, Lim LN, Vatish M, Georgiou EX. A new flow-based design for double-lumen needles. J Biomech 2023; 160:111832. [PMID: 37837837 DOI: 10.1016/j.jbiomech.2023.111832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 08/28/2023] [Accepted: 10/05/2023] [Indexed: 10/16/2023]
Abstract
Oocyte retrieval forms a crucial part of in vitro fertilisation treatment and its ultimate outcome. Standard double-lumen needles, which include a sequence of aspiration and flushing steps, are characterised by a similar success rate to single-lumen needles, despite their increased cost. A novel hydrodynamics-based needle called the OxIVF needle is proposed here, which is geared towards the generation of an internal flow field within the full follicular volume via laterally, rather than frontally, oriented flushing, leading to successful retrievals with no additional stress on the oocyte. A two-dimensional digital twin of the follicular environment is created and tested via multi-phase flow direct numerical simulation. Oocyte initial location within the follicle is varied, while quantities of interest such as velocity magnitude and vorticity are measured with a high level of precision. This provides insight into the overall fluid motion, as well as the trajectory and stresses experienced by the oocyte. A comparative benchmark set of tests indicated a higher success rate of the OxIVF needle of up to 100%, marking a significant improvement over the traditional double-lumen design whose success rate of no more than 75% was also highly dependent on the location of the needle tip inside the follicle. All forces measured during these tests showcase how the oocyte experiences stresses which are no larger than at the aspiration point, with the flow field providing a gentle steering effect towards the extraction region. Finally, the flow generation strategy maximises oocyte yield, unlocking new capabilities in both human and veterinary contexts.
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Affiliation(s)
- Radu Cimpeanu
- Mathematics Institute, University of Warwick, Coventry, CV4 7AL, United Kingdom; Mathematical Institute, University of Oxford, Oxford, OX2 6GG, United Kingdom.
| | | | - Lee Nai Lim
- Gynaecology Department, Oxford University Hospital NHS Foundation Trust, Oxford, OX3 9DU, United Kingdom
| | - Manu Vatish
- Nuffield Department of Women's Health and Reproductive Research, University of Oxford, Oxford, OX3 9DU, United Kingdom
| | - Ektoras X Georgiou
- Gynaecology Department, Oxford University Hospital NHS Foundation Trust, Oxford, OX3 9DU, United Kingdom
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Fudge BD, Cimpeanu R, Antkowiak A, Castrejón-Pita JR, Castrejón-Pita AA. Drop splashing after impact onto immiscible pools of different viscosities. J Colloid Interface Sci 2023; 641:585-594. [PMID: 36963252 DOI: 10.1016/j.jcis.2023.03.040] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 02/14/2023] [Accepted: 03/05/2023] [Indexed: 03/19/2023]
Abstract
Droplet impact onto liquid pools is a canonical scenario relevant to numerous natural phenomena and industrial processes. However, despite their ubiquity, multi-fluid systems with the drop and pool consisting of different liquids are far less well understood. Our hypothesis is that the post-impact dynamics greatly depends on the pool-to-droplet viscosity ratioμp/μd, which we explore over a range of six orders of magnitude using a combination of experiments and theoretical approaches (mathematical modelling and direct numerical simulation). Our findings indicate that in this scenario the splashing threshold and the composition of the ejecta sheet are controlled by the viscosity ratio. We uncover that increasing the pool viscosity decreases the splashing threshold for high viscosity pools (μp/μd≳35) when the splash comes from the droplet. By contrast, for low viscosity pools, the splash sheet comes from the pool and increasing the pool viscosity increases the splashing threshold. Surprisingly, there are conditions for which no splashing is observed under the conditions attainable in our laboratory. Furthermore, considering the interface velocity together with asymptotic arguments underlying the generation of the ejecta has allowed us to understand meaningful variations in the pressure during impact and rationalise the observed changes in the splashing threshold.
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Affiliation(s)
- Ben D Fudge
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom.
| | - Radu Cimpeanu
- Mathematics Institute, University of Warwick, Coventry CV4 7AL, United Kingdom; Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom; Department of Mathematics, Imperial College London, London SW7 2AZ, United Kingdom.
| | - Arnaud Antkowiak
- Institut Jean le Rond ∂'Alembert, Sorbonne Université, CNRS, F-75005 Paris, France.
| | - J Rafael Castrejón-Pita
- Department of Mechanical Engineering, University College London, London WC1E 7JE, United Kingdom.
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5
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Sykes TC, Fudge BD, Quetzeri-Santiago MA, Castrejón-Pita JR, Castrejón-Pita AA. Droplet splashing on curved substrates. J Colloid Interface Sci 2022; 615:227-235. [DOI: 10.1016/j.jcis.2022.01.136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 01/20/2022] [Accepted: 01/21/2022] [Indexed: 10/19/2022]
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Beale R, Rosendo JB, Bergeles C, Beverly A, Camporota L, Castrejón-Pita AA, Crockett DC, Cronin JN, Denison T, East S, Edwardes C, Farmery AD, Fele F, Fisk J, Fuenteslópez CV, Garstka M, Goulart P, Heaysman C, Hussain A, Jha P, Kempf I, Kumar AS, Möslein A, Orr ACJ, Ourselin S, Salisbury D, Seneci C, Staruch R, Steel H, Thompson M, Tran MC, Vitiello V, Xochicale M, Zhou F, Formenti F, Kirk T. OxVent: Design and evaluation of a rapidly-manufactured Covid-19 ventilator. EBioMedicine 2022; 76:103868. [PMID: 35172957 PMCID: PMC8842095 DOI: 10.1016/j.ebiom.2022.103868] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 12/08/2021] [Accepted: 01/21/2022] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND The manufacturing of any standard mechanical ventilator cannot rapidly be upscaled to several thousand units per week, largely due to supply chain limitations. The aim of this study was to design, verify and perform a pre-clinical evaluation of a mechanical ventilator based on components not required for standard ventilators, and that met the specifications provided by the Medicines and Healthcare Products Regulatory Agency (MHRA) for rapidly-manufactured ventilator systems (RMVS). METHODS The design utilises closed-loop negative feedback control, with real-time monitoring and alarms. Using a standard test lung, we determined the difference between delivered and target tidal volume (VT) at respiratory rates between 20 and 29 breaths per minute, and the ventilator's ability to deliver consistent VT during continuous operation for >14 days (RMVS specification). Additionally, four anaesthetised domestic pigs (3 male-1 female) were studied before and after lung injury to provide evidence of the ventilator's functionality, and ability to support spontaneous breathing. FINDINGS Continuous operation lasted 23 days, when the greatest difference between delivered and target VT was 10% at inspiratory flow rates >825 mL/s. In the pre-clinical evaluation, the VT difference was -1 (-90 to 88) mL [mean (LoA)], and positive end-expiratory pressure (PEEP) difference was -2 (-8 to 4) cmH2O. VT delivery being triggered by pressures below PEEP demonstrated spontaneous ventilation support. INTERPRETATION The mechanical ventilator presented meets the MHRA therapy standards for RMVS and, being based on largely available components, can be manufactured at scale. FUNDING Work supported by Wellcome/EPSRC Centre for Medical Engineering,King's Together Fund and Oxford University.
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Affiliation(s)
- Richard Beale
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | - Christos Bergeles
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Anair Beverly
- Department of Engineering Science, University of Oxford, UK
| | - Luigi Camporota
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Intensive Care Unit, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | | | - Douglas C Crockett
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Milton Keynes University Hospital NHS Foundation Trust, Milton Keynes, UK
| | - John N Cronin
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Department of Anaesthesia, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Timothy Denison
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Sebastian East
- Department of Engineering Science, University of Oxford, UK
| | | | - Andrew D Farmery
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK
| | - Filiberto Fele
- Department of Engineering Science, University of Oxford, UK
| | - James Fisk
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Carla V Fuenteslópez
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | | | - Paul Goulart
- Department of Engineering Science, University of Oxford, UK
| | - Clare Heaysman
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | | | - Prashant Jha
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Idris Kempf
- Department of Engineering Science, University of Oxford, UK
| | | | - Annika Möslein
- Department of Engineering Science, University of Oxford, UK
| | - Andrew C J Orr
- Department of Engineering Science, University of Oxford, UK
| | - Sebastien Ourselin
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - David Salisbury
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Carlo Seneci
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Robert Staruch
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK; Nuffield Department of Orthopaedic, Rheumatology and Musculoskeletal Sciences, University of Oxford, UK; The Academic Department of Military Surgery and Trauma, Birmingham, UK
| | - Harrison Steel
- Department of Engineering Science, University of Oxford, UK
| | - Mark Thompson
- Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK
| | - Minh C Tran
- Department of Engineering Science, University of Oxford, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, UK
| | - Valentina Vitiello
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Miguel Xochicale
- School of Biomedical Engineering and Imaging Sciences, King's College London, UK
| | - Feibiao Zhou
- Department of Engineering Science, University of Oxford, UK
| | - Federico Formenti
- Centre for Human and Applied Physiological Sciences, King's College London, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Department of Biomechanics, University of Nebraska Omaha, Omaha, NE, USA.
| | - Thomas Kirk
- Nuffield Department of Clinical Neurosciences, University of Oxford, UK; Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, UK.
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7
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Fudge BD, Cimpeanu R, Castrejón-Pita AA. Dipping into a new pool: The interface dynamics of drops impacting onto a different liquid. Phys Rev E 2021; 104:065102. [PMID: 35030956 DOI: 10.1103/physreve.104.065102] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Accepted: 11/16/2021] [Indexed: 06/14/2023]
Abstract
When a drop impacts onto a pool of another liquid, the common interface will move down at a well-defined speed for the first few milliseconds. While simple mechanistic models and experiments with the same fluid used for the drop and pool have predicted this speed to be half the impacting drop speed, this is only one small part in a rich and intricate behavior landscape. Factors such as viscosity and density ratios greatly affect the penetration speed. By using a combination of high-speed photography, high-resolution numerical simulations, and physical modeling, we disentangle the different roles that physical fluid properties play in determining the true value of the postimpact interfacial velocity.
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Affiliation(s)
- Ben D Fudge
- Department of Engineering Science, University of Oxford, OX1 3PJ Oxford, United Kingdom
| | - Radu Cimpeanu
- Mathematics Institute, University of Warwick, Coventry CV4 7AL, United Kingdom
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
- Department of Mathematics, Imperial College London, London SW7 2AZ, United Kingdom
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8
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Quetzeri-Santiago MA, Castrejón-Pita JR, Castrejón-Pita AA. Scientific reports controlling droplet splashing and bouncing by dielectrowetting. Sci Rep 2021; 11:21410. [PMID: 34725382 PMCID: PMC8560918 DOI: 10.1038/s41598-021-00771-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Accepted: 09/21/2021] [Indexed: 11/18/2022] Open
Abstract
Stopping droplets from bouncing or splashing after impacting a surface is fundamental in preventing cross-contamination, and the spreading of germs and harmful substances. Here we demonstrate that dielectrowetting can be applied to actively control the dynamics of droplet impact. Moreover, we demonstrate that dielectrowetting can be used to prevent droplet bouncing and suppress splashing. In our experiments, the dielectrowetting effect is produced on a flat substrate by two thin interdigitated electrodes connected to an alternating current potential. Our findings show that the strength of the electric potential can affect the dynamic contact angle and regulate the spreading, splashing and receding dynamics at the right time-scales.
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Affiliation(s)
- M A Quetzeri-Santiago
- Department of Engineering Science, University of Oxford, Oxford, OX1 3PJ, UK.,Mesoscale Chemical Systems Group, MESA+ Institute and Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500AE, Enschede, The Netherlands
| | - J R Castrejón-Pita
- School of Engineering and Materials Science, Queen Mary University of London, London, E1 4NS, UK
| | - A A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Oxford, OX1 3PJ, UK.
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9
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Soitu C, Panea M, Castrejón-Pita AA, Cook PR, Walsh EJ. Creating wounds in cell monolayers using micro-jets. Biomicrofluidics 2021; 15:014108. [PMID: 33598064 PMCID: PMC7872715 DOI: 10.1063/5.0043312] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Accepted: 01/26/2021] [Indexed: 06/12/2023]
Abstract
Many wound-healing assays are used in cell biology and biomedicine; they are often labor intensive and/or require specialized and costly equipment. We describe a contactless method to create wounds with any imaginable 2D pattern in cell monolayers using the micro-jets of either media or an immiscible and biocompatible fluorocarbon (i.e., FC40). We also combine this with another method that allows automation and multiplexing using standard Petri dishes. A dish is filled with a thin film of media overlaid with FC40, and the two liquids are reshaped into an array of microchambers within minutes. Each chamber in such a grid is isolated from others by the fluid walls of FC40. Cells are now added, allowed to grow into a monolayer, and wounds are created using the microjets; then, healing is monitored by microscopy. As arrays of chambers can be made using media and Petri dishes familiar to biologists, and as dishes fit seamlessly into their incubators, microscopes, and workflows, we anticipate that this assay will find wide application in wound healing.
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Affiliation(s)
- Cristian Soitu
- Osney Thermofluids Institute, Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, United Kingdom
| | - Mirela Panea
- Neurosciences Group, Nuffield Department of Clinical Neurosciences, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom
| | | | - Peter R. Cook
- The Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom
| | - Edmond J. Walsh
- Osney Thermofluids Institute, Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, United Kingdom
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10
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Langley KR, Castrejón-Pita AA, Thoroddsen ST. Droplet impacts onto soft solids entrap more air. Soft Matter 2020; 16:5702-5710. [PMID: 32525194 DOI: 10.1039/d0sm00713g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We investigate the effects of surface stiffness on the air cushioning at the bottom of a liquid drop impacting onto a soft solid and the resulting entrapment of a central bubble. This was achieved using ultra-high-speed interferometry at 5 million frames per second and spatial resolution of 1.05 μm per pixel. The soft solid delays the effects of gas compressibility resulting in much larger air discs than corresponding impacts onto rigid surfaces. Using an effective impact velocity equal to half of the actual impact velocity brings the soft solid scaling behavior better in line with rigid substrate scaling. We also observe extended gliding of the drop as it initially avoids contact with the surface spreading over a thin layer of air and investigate the threshold velocity for the transition from gliding to ring contact. Such extended gliding layers have previously been seen for high-viscosity drop impacts, but not for low-viscosity liquids at the impact velocities used herein.
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Affiliation(s)
- Kenneth R Langley
- Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
| | | | - Sigurdur T Thoroddsen
- Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia.
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11
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McCarthy J, Vella D, Castrejón-Pita AA. Dynamics of droplets on cones: self-propulsion due to curvature gradients. Soft Matter 2019; 15:9997-10004. [PMID: 31761923 DOI: 10.1039/c9sm01635j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We study the dynamics of droplets driven by a gradient of curvature, as may be achieved by placing a drop on the surface of a cone. The curvature gradient induces a pressure gradient within the drop, which in turn leads to spontaneous propulsion of the droplet. To investigate the resulting driving force we perform a series of experiments in which we track a droplet's displacement, s, from the apex of a cone whose surface is treated to exhibit near-zero pinning effects. We find an s ∼ t1/4 scaling at sufficiently late times t. To shed light upon these dynamics, we perform an asymptotic calculation of the equilibrium shape of a droplet on a weakly curved cylinder, deriving the curvature-induced force responsible for its propulsion. By balancing this driving force with viscous dissipation, we recover a differential equation for the droplet displacement, whose predictions are found to be in good agreement with our experimental results.
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Affiliation(s)
- John McCarthy
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK.
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12
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Abstract
Single-cell isolation and cloning are essential steps in many applications, ranging from the production of biotherapeutics to stem cell therapy. Having confidence in monoclonality in such applications is essential from both research and commercial perspectives, for example, to ensure that data are of high quality and regulatory requirements are met. Consequently, several approaches have been developed to improve confidence in monoclonality. However, ensuring monoclonality using standard well plate formats remains challenging, primarily due to edge effects; the solid wall around a well can prevent a clear view of how many cells might be in a well. We describe a method that eliminates such edge effects: solid confining walls are replaced by transparent fluid ones, and standard low-cost optics can confirm monoclonality.
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Affiliation(s)
- Cristian Soitu
- Department of Engineering Science, University of Oxford, Oxford, UK
| | - Cyril Deroy
- Department of Engineering Science, University of Oxford, Oxford, UK
| | | | - Peter R Cook
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
| | - Edmond J Walsh
- Department of Engineering Science, University of Oxford, Oxford, UK
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13
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García FJ, González H, Gómez-Aguilar FJ, Castrejón-Pita AA, Castrejón-Pita JR. Evolution of Gaussian wave packets in capillary jets. Phys Rev E 2019; 100:053111. [PMID: 31869957 DOI: 10.1103/physreve.100.053111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Indexed: 06/10/2023]
Abstract
A temporal analysis of the evolution of Gaussian wave packets in cylindrical capillary jets is presented through both a linear two-mode formulation and a one-dimensional nonlinear numerical scheme. These analyses are normally applicable to arbitrary initial conditions but our study focuses on pure-impulsive ones. Linear and nonlinear findings give consistent results in the stages for which the linear theory is valid. The inverse Fourier transforms representing the formal linear solution for the jet shape is both numerically evaluated and approximated by closed formulas. After a transient, these formulas predict an almost Gaussian-shape deformation with (i) a progressive drift of the carrier wave number to that given by the maximum of the Rayleigh dispersion relation, (ii) a progressive increase of its bell width, and (iii) a quasiexponential growth of its amplitude. These parameters agree with those extracted from the fittings of Gaussian wave packets to the numerical simulations. Experimental results are also reported on near-Gaussian pulses perturbing the exit velocity of a 2-mm diameter water jet. The possibility of controlling the breakup location along the jet and other features, such as pinch-off simultaneity, are demonstrated.
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Affiliation(s)
- F J García
- Departamento de Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla, c/ Virgen de África, 7, 41011-Sevilla, Spain
| | - H González
- Departamento de Física Aplicada III. Escuela Técnica Superior de Ingeniería, Universidad de Sevilla, Camino de los Descubrimientos, s/n, 41092-Sevilla, Spain
| | - F J Gómez-Aguilar
- Departamento de Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla, c/ Virgen de África, 7, 41011-Sevilla, Spain
| | - A A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom
| | - J R Castrejón-Pita
- School of Engineering and Material Science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
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14
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Quetzeri-Santiago MA, Castrejón-Pita AA, Castrejón-Pita JR. The Effect of Surface Roughness on the Contact Line and Splashing Dynamics of Impacting Droplets. Sci Rep 2019; 9:15030. [PMID: 31636321 PMCID: PMC6803702 DOI: 10.1038/s41598-019-51490-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Accepted: 10/02/2019] [Indexed: 12/02/2022] Open
Abstract
Whether a droplet splashes upon impact onto a solid is known to depend not only on the fluid properties and its speed, but also on the substrate characteristics. Past research has shown that splashing is heavily influenced by the substrate roughness. Indeed, in this manuscript, we demonstrate that splashing is ruled by the surface roughness, the splashing ratio, and the dynamic contact angle. Experiments consist of water and ethanol droplets impacting onto solid substrates with varying degrees of roughness. High speed imaging is used to extract the dynamic contact angle as a function of the spreading speed for these impacting droplets. During the spreading phase, the dynamic contact angle achieves an asymptotic maximum value, which depends on the substrate roughness and the liquid properties. We found that this maximum dynamic contact angle, together with the liquid properties, the ratio of the peak to peak roughness and the surface feature mean width, determines the splashing to no-splashing threshold. In addition, these parameters consistently differentiate the splashing behaviour of impacts onto smooth hydrophilic, hydrophobic and superhydrophobic surfaces.
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Affiliation(s)
| | | | - J Rafael Castrejón-Pita
- Queen Mary University of London, School of Engineering and Materials Science, London, E1 4NS, UK.
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15
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Abstract
The wrinkling of thin elastic objects provides a means of generating regular patterning at small scales in applications ranging from photovoltaics to microfluidic devices. Static wrinkle patterns are known to be governed by an energetic balance between the object's bending stiffness and an effective substrate stiffness, which may originate from a true substrate stiffness or from tension and curvature along the wrinkles. Here, we investigate dynamic wrinkling induced by the impact of a solid sphere onto an ultrathin polymer sheet floating on water. The vertical deflection of the sheet's center induced by impact draws material radially inward, resulting in an azimuthal compression that is relieved by the wrinkling of the entire sheet. We show that this wrinkling is truly dynamic, exhibiting features that are qualitatively different to those seen in quasistatic wrinkling experiments. Moreover, we show that the wrinkles coarsen dynamically because of the inhibiting effect of the fluid inertia. This dynamic coarsening can be understood heuristically as the result of a dynamic stiffness, which dominates the static stiffnesses reported thus far, and allows control of wrinkle wavelength.
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Affiliation(s)
- Finn Box
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Doireann O'Kiely
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Ousmane Kodio
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Maxime Inizan
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | | | - Dominic Vella
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom;
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16
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Arcenegui-Troya J, Belman-Martínez A, Castrejón-Pita AA, Castrejón-Pita JR. A simple levitated-drop tensiometer. Rev Sci Instrum 2019; 90:095109. [PMID: 31575257 DOI: 10.1063/1.5096959] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Accepted: 09/03/2019] [Indexed: 05/19/2023]
Abstract
A reliable, simple, and affordable liquid tensiometer is presented in this paper. The instrument consists of 72 ultrasonic transmitters in a tractor beam configuration that levitates small liquid samples (droplets) in air. Under operation, the instrument imparts a pressure instability that causes the droplet to vibrate while still levitating. Droplet oscillations are then detected by a photodiode, and the signal is recorded by an oscilloscope. The frequency of these oscillations is obtained and then used to obtain the effective surface tension of the sample. The instrument operates at the millisecond scale time (t < 12.5 ms), with very small liquid volumes (∼0.5 μl), and the sample is recoverable after testing. The instrument has been experimentally validated with acetone, ethanol, Fluorinert FC-40, water, and whole milk.
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Affiliation(s)
- J Arcenegui-Troya
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom
| | - A Belman-Martínez
- School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom
| | - A A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom
| | - J R Castrejón-Pita
- School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom
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17
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Quetzeri-Santiago MA, Yokoi K, Castrejón-Pita AA, Castrejón-Pita JR. Role of the Dynamic Contact Angle on Splashing. Phys Rev Lett 2019; 122:228001. [PMID: 31283297 DOI: 10.1103/physrevlett.122.228001] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Indexed: 06/09/2023]
Abstract
In this Letter, we study the splashing behavior of droplets upon impact onto a variety of substrates with different wetting properties, ranging from hydrophilic to superhydrophobic surfaces. In particular, we study the effects of the dynamic contact angle on splashing. The experimental approach uses high-speed imaging and image analysis to recover the apparent contact angle as a function of the spreading speed. Our results show that neither the Capillary number nor the so-called splashing parameter are appropriate to characterize the splashing behavior under these circumstances. However, we show that the maximum dynamic advancing contact angle and the splashing ratio β adequately characterize the splashing behavior.
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Affiliation(s)
- Miguel A Quetzeri-Santiago
- School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom
| | - Kensuke Yokoi
- School of Engineering, Cardiff University, Queen's Buildings, The Parade, Cardiff CF24 3AA, United Kingdom
| | - Alfonso A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom
| | - J Rafael Castrejón-Pita
- School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom
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18
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Soitu C, Feuerborn A, Deroy C, Castrejón-Pita AA, Cook PR, Walsh EJ. Raising fluid walls around living cells. Sci Adv 2019; 5:eaav8002. [PMID: 31183401 PMCID: PMC6551168 DOI: 10.1126/sciadv.aav8002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2018] [Accepted: 04/29/2019] [Indexed: 05/04/2023]
Abstract
An effective transformation of the cell culture dishes that biologists use every day into microfluidic devices would open many avenues for miniaturizing cell-based workflows. In this article, we report a simple method for creating microfluidic arrangements around cells already growing on the surface of standard petri dishes, using the interface between immiscible fluids as a "building material." Conventional dishes are repurposed into sophisticated microfluidic devices by reshaping, on demand, the fluid structures around living cells. Moreover, these microfluidic arrangements can be further reconfigured during experiments, which is impossible with most existing microfluidic platforms. The method is demonstrated using workflows involving cell cloning, the selection of a particular clone from among others in a dish, drug treatments, and wound healing. The versatility of the approach and its biologically friendly aspects may hasten uptake by biologists of microfluidics, so the technology finally fulfills its potential.
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Affiliation(s)
- Cristian Soitu
- Oxford Thermofluids Institute, Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, UK
| | - Alexander Feuerborn
- The Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
- Iota Sciences Ltd., Begbroke Science Park, Begbroke, Oxfordshire OX5 1PF, UK
| | - Cyril Deroy
- Oxford Thermofluids Institute, Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, UK
| | | | - Peter R. Cook
- The Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK
| | - Edmond J. Walsh
- Oxford Thermofluids Institute, Department of Engineering Science, University of Oxford, Osney Mead, Oxford OX2 0ES, UK
- Iota Sciences Ltd., Begbroke Science Park, Begbroke, Oxfordshire OX5 1PF, UK
- Corresponding author.
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19
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Ismail AS, Gañán-Calvo AM, Castrejón-Pita JR, Herrada MA, Castrejón-Pita AA. Controlled cavity collapse: scaling laws of drop formation. Soft Matter 2018; 14:7671-7679. [PMID: 30176036 DOI: 10.1039/c8sm00114f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The formation of transient cavities at liquid interfaces occurs in an immense variety of natural processes, among which the bursting of surface bubbles and the impact of a drop on a liquid pool are salient. The collapse of a surface liquid cavity is a well documented natural process that leads to the ejection of a thin and fast jet. Droplets generated through this process can be one order of magnitude smaller than the cavity's aperture, and they are consequently of interest in drop on demand inkjet applications. In this work, the controlled formation and collapse of a liquid cavity is analyzed, and the conditions for minimizing the resulting size and number of ejected drops are determined. The experimental and numerical models are simple and consist of a liquid reservoir, a nozzle plate with the discharge orifice, and a moving piston actuated by single half-sine-shaped pull-mode pulses. The size of the jetted droplet is described by a physical model resulting in a scaling law that is numerically and experimentally validated.
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Affiliation(s)
- A Said Ismail
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, UK.
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20
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Read PL, Morice-Atkinson X, Allen EJ, Castrejón-Pita AA. Phase synchronization of baroclinic waves in a differentially heated rotating annulus experiment subject to periodic forcing with a variable duty cycle. Chaos 2017; 27:127001. [PMID: 29289032 DOI: 10.1063/1.5001817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A series of laboratory experiments in a thermally driven, rotating fluid annulus are presented that investigate the onset and characteristics of phase synchronization and frequency entrainment between the intrinsic, chaotic, oscillatory amplitude modulation of travelling baroclinic waves and a periodic modulation of the (axisymmetric) thermal boundary conditions, subject to time-dependent coupling. The time-dependence is in the form of a prescribed duty cycle in which the periodic forcing of the boundary conditions is applied for only a fraction δ of each oscillation. For the rest of the oscillation, the boundary conditions are held fixed. Two profiles of forcing were investigated that capture different parts of the sinusoidal variation and δ was varied over the range 0.1≤δ≤1. Reducing δ was found to act in a similar way to a reduction in a constant coupling coefficient in reducing the width of the interval in forcing frequency or period over which complete synchronization was observed (the "Arnol'd tongue") with respect to the detuning, although for the strongest pulse-like forcing profile some degree of synchronization was discernible even at δ=0.1. Complete phase synchronization was obtained within the Arnol'd tongue itself, although the strength of the amplitude modulation of the baroclinic wave was not significantly affected. These experiments demonstrate a possible mechanism for intraseasonal and/or interannual "teleconnections" within the climate system of the Earth and other planets that does not rely on Rossby wave propagation across the planet along great circles.
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Affiliation(s)
- P L Read
- Department of Physics, University of Oxford, Oxford, United Kingdom
| | | | - E J Allen
- Department of Physics, University of Oxford, Oxford, United Kingdom
| | - A A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Oxford, United Kingdom
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Howland CJ, Antkowiak A, Castrejón-Pita JR, Howison SD, Oliver JM, Style RW, Castrejón-Pita AA. It's Harder to Splash on Soft Solids. Phys Rev Lett 2016; 117:184502. [PMID: 27835002 DOI: 10.1103/physrevlett.117.184502] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Indexed: 06/06/2023]
Abstract
Droplets splash when they impact dry, flat substrates above a critical velocity that depends on parameters such as droplet size, viscosity, and air pressure. By imaging ethanol drops impacting silicone gels of different stiffnesses, we show that substrate stiffness also affects the splashing threshold. Splashing is reduced or even eliminated: droplets on the softest substrates need over 70% more kinetic energy to splash than they do on rigid substrates. We show that this is due to energy losses caused by deformations of soft substrates during the first few microseconds of impact. We find that solids with Young's moduli ≲100 kPa reduce splashing, in agreement with simple scaling arguments. Thus, materials like soft gels and elastomers can be used as simple coatings for effective splash prevention. Soft substrates also serve as a useful system for testing splash-formation theories and sheet-ejection mechanisms, as they allow the characteristics of ejection sheets to be controlled independently of the bulk impact dynamics of droplets.
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Affiliation(s)
| | - Arnaud Antkowiak
- Institut Jean Le Rond d'Alembert, UMR 7190 CNRS/UPMC, Sorbonne Universités, F-75005 Paris, France
- Surface du Verre et Interfaces, UMR 125 CNRS/Saint-Gobain, F-93303 Aubervilliers, France
| | - J Rafael Castrejón-Pita
- School of Engineering and Materials Science, Queen Mary, University of London, London E1 4NS, United Kingdom
| | - Sam D Howison
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - James M Oliver
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Robert W Style
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
- Department of Materials, ETH Zürich, Zürich 8093, Switzerland
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22
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Abstract
In this paper, a novel mechanism allowing greater control over the formation of droplets is presented. This is achieved via the use of a dynamic nozzle of adjustable diameter. It is demonstrated that, by using such a nozzle, it is possible to greatly modify the formation and breakup of the ligament behind the main drop, leading to an overall reduction in the number of satellite droplets. Furthermore, by adjusting the delay between the beginning of the forming of the drop and the start of the nozzle constriction, a greater control over both the number of satellites and the size of the main drop can be achieved. It is also shown that only a minimal reduction of the nozzle's effective diameter is required in order to exploit the positive effects of the technique presented here. This opens the possibility of incorporating the technique into current droplet generator systems, e.g., via the use of piezoelectric driven nozzles or other micro-mechanical actuation technology.
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Affiliation(s)
- J R Castrejón-Pita
- School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, United Kingdom
| | - S J Willis
- Wolfson College, University of Cambridge, Cambridge CB3 9BB, United Kingdom
| | - A A Castrejón-Pita
- Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, United Kingdom
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23
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Castrejón-Pita JR, Kubiak KJ, Castrejón-Pita AA, Wilson MCT, Hutchings IM. Mixing and internal dynamics of droplets impacting and coalescing on a solid surface. Phys Rev E Stat Nonlin Soft Matter Phys 2013; 88:023023. [PMID: 24032939 DOI: 10.1103/physreve.88.023023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Indexed: 05/28/2023]
Abstract
The coalescence and mixing of a sessile and an impacting liquid droplet on a solid surface are studied experimentally and numerically in terms of lateral separation and droplet speed. Two droplet generators are used to produce differently colored droplets. Two high-speed imaging systems are used to investigate the impact and coalescence of the droplets in color from a side view with a simultaneous gray-scale view from below. Millimeter-sized droplets were used with dynamical conditions, based on the Reynolds and Weber numbers, relevant to microfluidics and commercial inkjet printing. Experimental measurements of advancing and receding static contact angles are used to calibrate a contact angle hysteresis model within a lattice Boltzmann framework, which is shown to capture the observed dynamics qualitatively and the final droplet configuration quantitatively. Our results show that no detectable mixing occurs during impact and coalescence of similar-sized droplets, but when the sessile droplet is sufficiently larger than the impacting droplet vortex ring generation can be observed. Finally we show how a gradient of wettability on the substrate can potentially enhance mixing.
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Affiliation(s)
- J R Castrejón-Pita
- Department of Engineering, University of Cambridge, 17 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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24
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Castrejón-Pita AA, Castrejón-Pita JR, Hutchings IM. Experimental observation of von Kármán vortices during drop impact. Phys Rev E Stat Nonlin Soft Matter Phys 2012; 86:045301. [PMID: 23214641 DOI: 10.1103/physreve.86.045301] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Indexed: 06/01/2023]
Abstract
The observation of von Kármán type vortices during the impact of water droplets onto a pool of water is reported. Shadowgraph imaging and laser-sheet visualization are used to document these events. The appearance of these vortices occurs within theoretically predicted regions in a Reynolds-splash number parameter space. In addition, and also in agreement with theoretical predictions, smooth splashing, with vortices absent, is found for smaller Reynolds number.
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Affiliation(s)
- A A Castrejón-Pita
- Department of Engineering, University of Cambridge, 17 Charles Babbage Road, Cambridge CB3 0FS, UK
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25
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Castrejón-Pita JR, Castrejón-Pita AA, Hinch EJ, Lister JR, Hutchings IM. Self-similar breakup of near-inviscid liquids. Phys Rev E Stat Nonlin Soft Matter Phys 2012; 86:015301. [PMID: 23005482 DOI: 10.1103/physreve.86.015301] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Indexed: 05/14/2023]
Abstract
The final stages of pinchoff and breakup of dripping droplets of near-inviscid Newtonian fluids are studied experimentally for pure water and ethanol. High-speed imaging and image analysis are used to determine the angle and the minimum neck size of the cone-shaped extrema of the ligaments attached to dripping droplets in the final microseconds before pinchoff. The angle is shown to steadily approach the value of 18.0 ± 0.4°, independently of the initial flow conditions or the type of breakup. The filament thins and necks following a τ(2/3) law in terms of the time remaining until pinchoff, regardless of the initial conditions. The observed behavior confirms theoretical predictions.
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Affiliation(s)
- J R Castrejón-Pita
- Department of Engineering, University of Cambridge, Cambridge CB3 0FS, United Kingdom
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Abstract
Whether a thin filament of liquid separates into two or more droplets or eventually condenses lengthwise to form a single larger drop depends on the liquid's density, viscosity, and surface tension and on the initial dimensions of the filament. Surface tension drives two competing processes, pinching-off and shortening, and the relative time scales of these, controlled by the balance between capillary and viscous forces, determine the final outcome. Here we provide experimental evidence for the conditions under which a liquid filament will break up into drops, in terms of a wide range of two dimensionless quantities: the aspect ratio of the filament and the Ohnesorge number. Filaments which do not break up into multiple droplets demand a high liquid viscosity or a small aspect ratio.
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Castrejón-Pita AA, Read PL. Synchronization in a pair of thermally coupled rotating baroclinic annuli: understanding atmospheric teleconnections in the laboratory. Phys Rev Lett 2010; 104:204501. [PMID: 20867030 DOI: 10.1103/physrevlett.104.204501] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Revised: 03/29/2010] [Indexed: 05/29/2023]
Abstract
Synchronization phenomena in a fluid dynamical analogue of atmospheric circulation is studied experimentally by investigating the dynamics of a pair of thermally coupled, rotating baroclinic annulus systems. The coupling between the systems is in the well-known master-slave configuration in both periodic and chaotic regimes. Synchronization tools such as phase dynamics analysis are used to study the dynamics of the coupled system and demonstrate phase synchronization and imperfect phase synchronization, depending upon the coupling strength and parameter mismatch.
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Affiliation(s)
- A A Castrejón-Pita
- Atmospheric, Oceanic & Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom
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Castrejón-García R, Castrejón-Pita JR, Castrejón-Pita AA. Design, development, and evaluation of a simple blackbody radiative source. Rev Sci Instrum 2010; 81:055106. [PMID: 20515171 DOI: 10.1063/1.3422258] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
This paper presents a simple design and the testing of a blackbody prototype. The physical properties and geometry of the cavity produce a radiator or blackbody with an emissivity greater than 0.99. The prototype has the advantages of having a traditional spherical cavity made of alumina refractory cement and a radiative emission very close to that of an ideal blackbody. The prototype can be used as a calibration standard for other radiation measuring instruments or sensors. Experimental measurements of radiant flux of the prototype measured with a calibrated infrared radiometer and a wide spectrum radiometer are also presented. The prototype is easy to construct and the material required are available to most research centers, laboratories, industries, and universities.
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Affiliation(s)
- R Castrejón-García
- Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Priv. Xochicalco s/n, Temixco, Mor. 62580, Mexico
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29
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Eccles FJR, Read PL, Castrejón-Pita AA, Haine TWN. Synchronization of modulated traveling baroclinic waves in a periodically forced, rotating fluid annulus. Phys Rev E Stat Nonlin Soft Matter Phys 2009; 79:015202. [PMID: 19257097 DOI: 10.1103/physreve.79.015202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Indexed: 05/27/2023]
Abstract
Frequency entrainment and nonlinear synchronization are commonly observed between simple oscillatory systems, but their occurrence and behavior in continuum fluid systems are much less well understood. Motivated by possible applications to geophysical fluid systems, such as in atmospheric circulation and climate dynamics, we have carried out an experimental study of the interaction of fully developed baroclinic instability in a differentially heated, rotating fluid annulus with an externally imposed periodic modulation of the thermal boundary conditions. In quasiperiodic and chaotic amplitude-modulated traveling wave regimes, the results demonstrate a strong interaction between the natural periodic modulation of the wave amplitude and the externally imposed forcing. This leads to partial or complete phase synchronization. Synchronization effects were observed even with very weak amplitudes of forcing, and were found with both 1:1 and 1:2 frequency ratios between forcing and natural oscillations.
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Affiliation(s)
- F J R Eccles
- Atmospheric, Oceanic & Planetary Physics, Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom
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Castrejón-Pita AA, Castrejón-Pita JR, Huelsz G, Sarmiento-Galán A. Comment on "Acoustic chaos in a duct with two separate sound sources" [J. Acoust. Soc. Am. 110, 120-126 (2001)]. J Acoust Soc Am 2008; 124:2702-2705. [PMID: 19045755 DOI: 10.1121/1.2978081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
In a paper published in this journal in 2001 by Dong et al. [W. G. Dong, X. Y. Huang, and Q. L. Wo, J. Acoust. Soc. Am. 110, 120-126 (2001)] it was claimed that acoustic chaos was obtained experimentally by the nonlinear interaction of two acoustic waves in a duct. In this comment a simple experimental setup and an analytical model is used to show that the dynamics of such systems corresponds to a quasiperiodic motion, and not to a chaotic one.
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Affiliation(s)
- A A Castrejón-Pita
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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Torralba M, Castrejón-Pita AA, Hernández G, Huelsz G, del Río JA, Ortín J. Instabilities in the oscillatory flow of a complex fluid. Phys Rev E 2007; 75:056307. [PMID: 17677164 DOI: 10.1103/physreve.75.056307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Indexed: 05/16/2023]
Abstract
The dynamics of a fluid in a vertical tube, subjected to an oscillatory pressure gradient, is studied experimentally for both a Newtonian and a viscoelastic shear-thinning fluid. Particle image velocimetry is used to determine the two-dimensional velocity fields in the vertical plane of the tube axis, in a range of driving amplitudes from 0.8 to 2.5 mm and of driving frequencies from 2.0 to 11.5 Hz. The Newtonian fluid exhibits a laminar flow regime, independent of the axial position, in the whole range of drivings. For the complex fluid, instead, the parallel shear flow regime exhibited at low amplitudes [Torralba, Phys. Rev. E 72, 016308 (2005)] becomes unstable at higher drivings against the formation of symmetric vortices, equally spaced along the tube. At even higher drivings the vortex structure itself becomes unstable, and complex nonsymmetric structures develop. Given that inertial effects remain negligible even at the hardest drivings (Re < 10(-1)), it is the complex rheology of the fluid that is responsible for the instabilities observed. The system studied represents an interesting example of the development of shear-induced instabilities in nonlinear complex fluids in purely parallel shear flow.
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Affiliation(s)
- M Torralba
- Departament ECM, Facultat de Física, Universitat de Barcelona, Avenida Diagonal 647, E-08028 Barcelona, Catalonia, Spain
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Castrejón-Pita AA, Read PL. Baroclinic waves in an air-filled thermally driven rotating annulus. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 75:026301. [PMID: 17358416 DOI: 10.1103/physreve.75.026301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Indexed: 05/14/2023]
Abstract
In this study an experimental investigation of baroclinic waves in air in a differentially heated rotating annulus is presented. Air has a Prandtl number of 0.707, which falls within a previously unexplored region of parameter space for baroclinic instability. The flow regimes encountered include steady waves, periodic amplitude vacillations, modulated amplitude vacillations, and either monochromatic or mixed wave number weak waves, the latter being characterized by having amplitudes less than 5% of the applied temperature contrast. The distribution of these flow regimes in parameter space are presented in a regime diagram. It was found that the progression of transitions between different regimes is, as predicted by recent numerical modeling results, in the opposite sense to that usually found in experiments with high Prandtl number liquids. No hysteresis in the flow type, with respect to variations in the rotation rate, was found in this investigation.
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Affiliation(s)
- A A Castrejón-Pita
- Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, OX1 3PU, United Kingdom
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Castrejón-Pita JR, Castrejón-Pita AA, Huelsz G, Tovar R. Experimental demonstration of the Rayleigh acoustic viscous boundary layer theory. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 73:036601. [PMID: 16605671 DOI: 10.1103/physreve.73.036601] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2005] [Indexed: 05/08/2023]
Abstract
Amplitude and phase velocity measurements on the laminar oscillatory viscous boundary layer produced by acoustic waves are presented. The measurements were carried out in acoustic standing waves in air with frequencies of 68.5 and 114.5 Hz using laser Doppler anemometry and particle image velocimetry. The results obtained by these two techniques are in good agreement with the predictions made by the Rayleigh viscous boundary layer theory and confirm the existence of a local maximum of the velocity amplitude and its expected location.
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Affiliation(s)
- J R Castrejón-Pita
- Centro de Investigación en Energía, UNAM A. P. 34, 62580 Temixco, Morelos, Mexico
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Torralba M, Castrejón-Pita JR, Castrejón-Pita AA, Huelsz G, del Río JA, Ortín J. Measurements of the bulk and interfacial velocity profiles in oscillating Newtonian and Maxwellian fluids. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:016308. [PMID: 16090087 DOI: 10.1103/physreve.72.016308] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2004] [Indexed: 05/03/2023]
Abstract
We present the dynamic velocity profiles of a Newtonian fluid (glycerol) and a viscoelastic Maxwell fluid (CPyCl-NaSal in water) driven by an oscillating pressure gradient in a vertical cylindrical pipe. The frequency range explored has been chosen to include the first three resonance peaks of the dynamic permeability of the viscoelastic-fluid--pipe system. Three different optical measurement techniques have been employed. Laser Doppler anemometry has been used to measure the magnitude of the velocity at the center of the liquid column. Particle image velocimetry and optical deflectometry are used to determine the velocity profiles at the bulk of the liquid column and at the liquid-air interface respectively. The velocity measurements in the bulk are in good agreement with the theoretical predictions of a linear theory. The results, however, show dramatic differences in the dynamic behavior of Newtonian and viscoelastic fluids, and demonstrate the importance of resonance phenomena in viscoelastic fluid flows, biofluids in particular, in confined geometries.
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Affiliation(s)
- M Torralba
- Departament d'Estructura i Constituents de la Matèria, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona, Spain
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Castrejón-Pita AA, Sarmiento-Galán A, Castrejón-Pita JR, Castrejón-García R. Fractal dimension in butterflies' wings: a novel approach to understanding wing patterns? J Math Biol 2004; 50:584-94. [PMID: 15614549 DOI: 10.1007/s00285-004-0302-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2004] [Indexed: 10/26/2022]
Abstract
The geometrical complexity in the wings of several, taxonomically different butterflies, is analyzed in terms of their fractal dimension. Preliminary results provide some evidence on important questions about the (dis)similarity of the wing patterns in terms of their fractal dimension. The analysis is restricted to two groups which are widely used in the literature as typical examples of mimicry, and a small number of unrelated species, thus implying the consideration of only a fraction of the wing pattern diversity. The members of the first mimicry ring, composed by the species Danaus plexippus (better known as the monarch butterfly), and the two subspecies Basilarchia archippus obsoleta (or northern viceroy) and Basilarchia archippus hoffmanni (or tropical viceroy), are found to have a very similar value for the fractal dimension of their wing patterns, even though they do not look very similar at first sight. It is also found that the female of another species (Neophasia terlootii), which looks similar to the members of the previous group, does not share the same feature, while the Lycorea ilione albescens does share it. For the members of the second group of mimicry related butterflies, the Greta nero nero and the Hypoleria cassotis, it is shown that they also have very close values for the fractal dimension of their wing patterns. Finally, it is shown that other species, which apparently have very similar wing patterns, do not have the same fractal dimension. A possible, not completely tested hypothesis is then conjectured: the formation of groups by individuals whose wing patterns have an almost equal fractal dimension may be due to the fact that they do share the same developmental raw material, and that this common feature is posteriorly modified by natural selection, possibly through predation.
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Affiliation(s)
- A A Castrejón-Pita
- Instituto de Matemáticas, UNAM. Ave. Universidad s/n, 62200, Chamilpa, Morelos, México.
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Castrejón-Pita JR, del Río JA, Castrejón-Pita AA, Huelsz G. Experimental observation of dramatic differences in the dynamic response of Newtonian and Maxwellian fluids. ACTA ACUST UNITED AC 2003; 68:046301. [PMID: 14683038 DOI: 10.1103/physreve.68.046301] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2003] [Indexed: 11/07/2022]
Abstract
An experimental study of the dynamic response of a Newtonian fluid and a Maxwellian fluid under an oscillating pressure gradient is presented. Laser Doppler anemometry is used in order to determine the velocity of the fluid inside a cylindrical tube. In the case of the Newtonian fluid, the dissipative nature is observed. In the dynamic response of the Maxwellian fluid an enhancement at the frequencies predicted by theory is observed.
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Affiliation(s)
- J R Castrejón-Pita
- Centro de Investigación en Energía, UNAM, Apartado Postal 34, 62580 Temixco, Morelos, Mexico
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Abstract
We analyze the geometrical structure of the astonishing Nasca geoglyphs in terms of their fractal dimension with the idea of dating these manifestations of human cultural engagements in relation to one another. Our findings suggest that the first delineated images consist of straight, parallel lines and that having sophisticated their abilities, the Nasca artists moved on to the design of more complex structures.
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Affiliation(s)
- J R Castrejón-Pita
- Instituto de Matematicas, UNAM, Ave. Universidad s/n, 62200 Chamilpa, Morelos, Mexico
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