1
|
Oprisan A, Baettig-Arriagada E, Baeza-Delgado C, Martí-Bonmatí L. Prevalence of burnout syndrome in Spanish radiologists. Radiologia (Engl Ed) 2023; 65:307-314. [PMID: 37516484 DOI: 10.1016/j.rxeng.2021.09.013] [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] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2021] [Accepted: 09/07/2021] [Indexed: 07/31/2023]
Abstract
BACKGROUND AND AIMS The primary objective was to analyze the prevalence and degree of professional burnout in radiologists in Spain. Secondary objectives were to identify possible factors that increase or decrease the risk of burnout to enable preventive and corrective measures, decrease the stress associated with this condition, and thereby increase radiologists' performance and satisfaction at work. MATERIAL AND METHODS This cross-sectional observational study used a voluntary, anonymous online survey of attending radiologists and residents through Google Forms®. The survey was structured into three sections: a qualitative assessment of the degree of professional burnout with the Maslach Burnout Inventory Human Services Survey (MBI-HSS), a series of sociodemographic and work-related questions, and a final section centered on possible causes of stress and improvements to the working environment. The results of the survey were analyzed statistically to determine which variables were associated with burnout syndrome as well as to identify possible risk factors and protective factors. RESULTS After disseminating the survey through social networks and email contacts, we received a total of 226 responses (175 from attending radiologists and 51 from residents; 52% men; mean age, 41 ± 11 years; age range, 25-68). The prevalence of the syndrome was 33%, without significant differences between attending radiologists and residents. No risk factors associated with burnout were identified. Teaching in the workplace was the only protective factor. CONCLUSIONS One-third of the respondents had burnout syndrome. Because the consequences of this syndrome can affect professionals' personal life and their ability to do their jobs, early detection and intervention should be prioritized.
Collapse
Affiliation(s)
- A Oprisan
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain.
| | - E Baettig-Arriagada
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain
| | - C Baeza-Delgado
- Grupo de Investigación Biomédica en Imagen (GIBI230), Instituto de Investigación Sanitaria La Fe, Valencia, Spain
| | - L Martí-Bonmatí
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain; Grupo de Investigación Biomédica en Imagen (GIBI230), Instituto de Investigación Sanitaria La Fe, Valencia, Spain; Académico de Número de la Real Academia Nacional de Medicina de España, Spain
| |
Collapse
|
2
|
Oprisan A, Baettig-Arriagada E, Baeza-Delgado C, Martí-Bonmatí L. Prevalence of burnout syndrome during the COVID-19 pandemic and associated factors. Radiología (English Edition) 2022; 64:119-127. [PMID: 35504677 PMCID: PMC9055794 DOI: 10.1016/j.rxeng.2021.09.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2021] [Accepted: 09/07/2021] [Indexed: 12/11/2022]
Affiliation(s)
- A Oprisan
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain.
| | - E Baettig-Arriagada
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain
| | - C Baeza-Delgado
- Grupo de Investigación Biomédica en Imagen (GIBI230), Instituto de Investigación Sanitaria La Fe, Valencia, Spain
| | - L Martí-Bonmatí
- Área Clínica de Imagen Médica, Hospital Universitario y Politécnico La Fe, Valencia, Spain; Grupo de Investigación Biomédica en Imagen (GIBI230), Instituto de Investigación Sanitaria La Fe, Valencia, Spain; Académico de Número de la Real Academia Nacional de Medicina de España
| |
Collapse
|
3
|
|
4
|
Liu E, Zhu H, Yi J, Kobbekaduwa K, Adhikari P, Liu J, Shi Y, Zhang J, Li H, Oprisan A, Rao AM, Sanabria H, Chen O, Gao J. Manipulating Charge Transfer from Core to Shell in CdSe/CdS/Au Heterojunction Quantum Dots. ACS Appl Mater Interfaces 2019; 11:48551-48555. [PMID: 31782302 PMCID: PMC7325308 DOI: 10.1021/acsami.9b17339] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The photophysics of charge-transfer and recombination mechanisms in a heterojunction structure of CdSe/CdS/Au quantum dots (QDs) are studied by temperature-dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL). We manipulate the charge transfer from core to shell surface by varying the tunneling barrier height resulting from temperature variation and the barrier width resulting from shell thickness variation. The charge-transfer process, which can be described by a tunneling transmission model, is manifested by two competitive recombination processes, an intrinsic exciton emission and a trap emission in the near-infrared (NIR) range. Our study establishes the photophysics foundation for the core/shell/metal application in photocatalyst and optoelectronics.
Collapse
Affiliation(s)
- Exian Liu
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics , Hunan University , Changsha 410082 , China
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Hua Zhu
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Jun Yi
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics , Hunan University , Changsha 410082 , China
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Kanishka Kobbekaduwa
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Pan Adhikari
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Jianjun Liu
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education, Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics , Hunan University , Changsha 410082 , China
| | - Ying Shi
- Institute of Atomic and Molecular Physics, Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy , Jilin University , Changchun 130012 , China
| | - Jianbing Zhang
- School of Optical and Electronic Information , Huazhong University of Science and Technology , Wuhan 430074 , China
| | - Hongbo Li
- School of Materials Science and Engineering , Beijing Institute of Technology , Beijing 100081 , China
| | - Ana Oprisan
- Department of Physics and Astronomy , College of Charleston , Charleston , South Carolina 29401 , United States
| | - Apparao M Rao
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Hugo Sanabria
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| | - Ou Chen
- Department of Chemistry , Brown University , Providence , Rhode Island 02912 , United States
| | - Jianbo Gao
- Department of Physics and Astronomy, Ultrafast Photophysics of Quantum Devices Laboratory , Clemson University , Clemson , South Carolina 29634 , United States
| |
Collapse
|
5
|
Oprisan A, Gandikota G, Chatain D, Garrabos Y, Beysens D. Turbidity data obtained from image analysis in near critical hydrogen. Phys Rev E 2019; 100:052112. [PMID: 31869978 DOI: 10.1103/physreve.100.052112] [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: 06/13/2019] [Indexed: 11/07/2022]
Abstract
Video images are being used with increased frequency in science, supplanting current methods such as light scattering by statistical evaluation of the images. In this study we use light turbidity data due to density-induced refractive index fluctuations to obtain critical amplitudes from image analysis. In order to bring hydrogen (H_{2}) very close to its critical point, we place the sample cell under weightlessness using a magnetic levitation device. Images of an H_{2}-filled cell are taken near its critical temperature of 33 K by illuminating the cell with three different filters. We fit the turbidity data to a theoretical expression that allows us to estimate the critical amplitudes of isothermal compressibility and fluctuation correlation length. The values of isothermal compressibility and correlation length obtained from turbidity fitting are compared against literature values. Our data analysis shows a large sensitivity of the fitting parameters to the refractive index value and to even minute density deviations from criticality.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, 66 George Street, Charleston, South Carolina 29424, USA
| | | | - Denis Chatain
- Université Grenoble Alpes and DSBT, IRIG, CEA, 38000 Grenoble, France
| | - Yves Garrabos
- ICMCB, UMR No. 5026, CNRS, Université de Bordeaux, and Bordeaux INP, 33600 Pessac, France
| | - Daniel Beysens
- Physique et Mécanique des Milieux Hétérogènes, CNRS, ESPCI, PSL Research University, and Sorbonne Université, Sorbonne Paris Cité, Universités Paris 6 & Paris 7, 10 rue Vauquelin, 75005 Paris, France and Université Grenoble Alpes and DSBT, IRIG, CEA, 38000 Grenoble, France
| |
Collapse
|
6
|
Oprisan A, Garrabos Y, Lecoutre C, Beysens D. Pattern Evolution during Double Liquid-Vapor Phase Transitions under Weightlessness. Molecules 2017; 22:molecules22060947. [PMID: 28598367 PMCID: PMC6152690 DOI: 10.3390/molecules22060947] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2017] [Revised: 05/31/2017] [Accepted: 06/02/2017] [Indexed: 11/16/2022] Open
Abstract
Phase transition in fluids is ubiquitous in nature and has important applications in areas such as the food industry for volatile oils' extraction or in nuclear plants for heat transfer. Fundamentals are hampered by gravity effects on Earth. We used direct imaging to record snapshots of phase separation that takes place in sulfur hexafluoride, SF₆, under weightlessness conditions on the International Space Station (ISS). The system was already at liquid-vapor equilibrium slightly below the critical temperature and further cooled down by a 0.2-mK temperature quench that produced a new phase separation. Both full view and microscopic views of the direct observation cell were analyzed to determine the evolution of the radii distributions. We found that radii distributions could be well approximated by a lognormal function. The fraction of small radii droplets declined while the fraction of large radii droplets increased over time. Phase separation at the center of the sample cell was visualized using a 12× microscope objective, which corresponds to a depth of focus of about 5 μ m. We found that the mean radii of liquid droplets exhibit a t 1 / 3 evolution, in agreement with growth driven by Brownian coalescence. It was also found that the mean radii of the vapor bubbles inside the liquid majority phase exhibit a t 1 / 2 evolution, which suggest a possible directional motion of vapor bubbles due to the influence of weak remaining gravitational field and/or a composition Marangoni force.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424, USA.
| | - Yves Garrabos
- ESEME,Institut de Chimie de la Matiere Condensee de Bordeaux, CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France.
- Service des Basses Temperatures, CEA-Grenoble et Universite Joseph Fourier, 38054 Grenoble, France.
| | - Carole Lecoutre
- ESEME,Institut de Chimie de la Matiere Condensee de Bordeaux, CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France.
- Service des Basses Temperatures, CEA-Grenoble et Universite Joseph Fourier, 38054 Grenoble, France.
| | - Daniel Beysens
- Physique et Mecanique des Milieux Heterogenes, UMR 7636 CNRS-ESPCI-Universite Pierre et Marie Curie-Universite Paris Diderot, 10 rue Vauquelin, 75005 Paris, France.
| |
Collapse
|
7
|
Oprisan A, Rice A, Oprisan SA, Giraudet C, Croccolo F. Non-equilibrium concentration fluctuations in superparamagnetic nanocolloids. Eur Phys J E Soft Matter 2017; 40:14. [PMID: 28181056 DOI: 10.1140/epje/i2017-11503-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Accepted: 01/11/2017] [Indexed: 06/06/2023]
Abstract
We investigate non-equilibrium concentration fluctuations during the free diffusion of a colloidal suspension against pure water. We investigate Fe2O3 superparamagnetic nanocolloids with sizes between 1 and 10 nm by means of a shadowgraph apparatus to determine the mixture mass diffusion coefficient and kinematic viscosity. The experiments were performed in three distinct conditions: Experiment 1 is without any magnetic field; Experiment 2 with a vertical magnetic field; Experiment 3 after turning off the magnetic field. We found no correlation between the kinematic viscosity coefficient and the external magnetic field. Conversely, we found that the mass diffusion coefficient decreases in the presence of the external magnetic field and slowly rebounds after the magnetic field was turned off.
Collapse
Affiliation(s)
- Ana Oprisan
- College of Charleston, Department of Physics and Astronomy, Charleston, SC, USA.
| | - Ashley Rice
- College of Charleston, Department of Physics and Astronomy, Charleston, SC, USA
| | - Sorinel A Oprisan
- College of Charleston, Department of Physics and Astronomy, Charleston, SC, USA
| | - Cédric Giraudet
- Erlangen Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen-Nuremberg, Erlangen, Germany
| | - Fabrizio Croccolo
- Laboratoire des Fluides Complexes et leurs Réservoirs - UMR5150, Université de Pau et des Pays de l'Adour, Anglet, France
- Centre Nationale d'Etudes Spatiales (CNES), Paris, France
| |
Collapse
|
8
|
Oprisan A, Oprisan SA, Hegseth JJ, Garrabos Y, Lecoutre C, Beysens D. Direct imaging of long-range concentration fluctuations in a ternary mixture. Eur Phys J E Soft Matter 2015; 38:17. [PMID: 25788436 DOI: 10.1140/epje/i2015-15017-4] [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: 07/03/2014] [Revised: 11/10/2014] [Accepted: 02/04/2015] [Indexed: 06/04/2023]
Abstract
We used a direct imaging technique to investigate concentration fluctuations enhanced by thermal fluctuations in a ternary mixture of methanol (Me), cyclohexane (C), and partially deuterated cyclohexane (C*) within 1mK above its consolute critical point. The experimental setup used a low-coherence white-light source and a red filter to visualize fluctuation images. The red-filtered images were analyzed off-line using a differential dynamic microscopy algorithm that allowed us to determine the correlation time, τ, of concentration fluctuations. From τ, we determined the mutual mass diffusion coefficient, D, very near and above the critical point of Me-CC* mixtures. We also numerically estimated both the background and critical contributions to D and compared the results against our experimental values determined from τ. We found that the experimental value of D is close to the prediction based on Stokes-Einstein diffusion law with Kawasaki's correction.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, 29424, Charleston, SC, USA,
| | | | | | | | | | | |
Collapse
|
9
|
Oprisan A, Oprisan SA, Hegseth JJ, Garrabos Y, Lecoutre-Chabot C, Beysens D. Dimple coalescence and liquid droplets distributions during phase separation in a pure fluid under microgravity. Eur Phys J E Soft Matter 2014; 37:41. [PMID: 25260326 DOI: 10.1140/epje/i2014-14085-2] [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: 03/23/2014] [Revised: 08/14/2014] [Accepted: 08/26/2014] [Indexed: 06/03/2023]
Abstract
Phase separation has important implications for the mechanical, thermal, and electrical properties of materials. Weightless conditions prevent buoyancy and sedimentation from affecting the dynamics of phase separation and the morphology of the domains. In our experiments, sulfur hexafluoride (SF6) was initially heated about 1K above its critical temperature under microgravity conditions and then repeatedly quenched using temperature steps, the last one being of 3.6 mK, until it crossed its critical temperature and phase-separated into gas and liquid domains. Both full view (macroscopic) and microscopic view images of the sample cell unit were analyzed to determine the changes in the distribution of liquid droplet diameters during phase separation. Previously, dimple coalescences were only observed in density-matched binary liquid mixture near its critical point of miscibility. Here we present experimental evidences in support of dimple coalescence between phase-separated liquid droplets in pure, supercritical, fluids under microgravity conditions. Although both liquid mixtures and pure fluids belong to the same universality class, both the mass transport mechanisms and their thermophysical properties are significantly different. In supercritical pure fluids the transport of heat and mass are strongly coupled by the enthalpy of condensation, whereas in liquid mixtures mass transport processes are purely diffusive. The viscosity is also much smaller in pure fluids than in liquid mixtures. For these reasons, there are large differences in the fluctuation relaxation time and hydrodynamics flows that prompted this experimental investigation. We found that the number of droplets increases rapidly during the intermediate stage of phase separation. We also found that above a cutoff diameter of about 100 microns the size distribution of droplets follows a power law with an exponent close to -2, as predicted from phenomenological considerations.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, 29424, Charleston, SC, USA,
| | | | | | | | | | | |
Collapse
|
10
|
Hegseth JJ, Oprisan A, Garrabos Y, Beysens D. Imaging critical fluctuations of pure fluids and binary mixtures. Phys Rev E Stat Nonlin Soft Matter Phys 2014; 90:022127. [PMID: 25215709 DOI: 10.1103/physreve.90.022127] [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] [Received: 03/24/2014] [Indexed: 06/03/2023]
Abstract
We use optical microscopy techniques to directly visualize the structures that emerge in binary mixtures and pure fluids near their respective critical points. We attempt to understand these structures by studying the image formation using both a phase contrast and a dark field filter to our microscope. We found that images of critical fluctuations for both liquid-liquid and liquid-gas critical systems have gray level intensity histograms with Gaussian shape. For all fluids investigated, the temperature-dependent standard deviation of the Gaussian histogram follows a power law with the same exponent. Since the image intensity fluctuations are determined by order parameter fluctuations, this direct imaging method allowed us to estimate the critical exponent of compressibility with very good accuracy.
Collapse
Affiliation(s)
- John J Hegseth
- Department of Physics, University of New Orleans, New Orleans, Louisiana 70148, USA
| | - Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, Charleston, South Carolina 29424, USA
| | - Yves Garrabos
- ESEME, Institut de Chimie de la Matière Condensée de Bordeaux, UPR 9048, CNRS, Université de Bordeaux I, Avenue du Dr. Schweitzer, F-33608 Pessac Cedex, France
| | - Daniel Beysens
- Physique et Mécanique des Milieux Hétérogènes, UMR 7636 CNRS - ESPCI - Université Pierre et Marie Curie - Université Paris Diderot, 10 rue Vauquelin, 75005 Paris, France and Service des Basses Températures, CEA-Grenoble & Université Joseph Fourier, Grenoble, France
| |
Collapse
|
11
|
Oprisan A, Oprisan SA, Bayley B, Hegseth JJ, Garrabos Y, Lecoutre-Chabot C, Beysens D. Dynamic structure factor of density fluctuations from direct imaging very near (both above and below) the critical point of SF(6). Phys Rev E Stat Nonlin Soft Matter Phys 2012; 86:061501. [PMID: 23367952 DOI: 10.1103/physreve.86.061501] [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: 08/12/2012] [Revised: 10/02/2012] [Indexed: 06/01/2023]
Abstract
Large density fluctuations were observed by illuminating a cylindrical cell filled with sulfur hexafluoride (SF(6)), very near its liquid-gas critical point (|T-T(c)|< 300 μK) and recorded using a microscope with 3 μm spatial resolution. Using a dynamic structure factor algorithm, we determined from the recorded images the structure factor (SF), which measures the spatial distribution of fluctuations at different moments, and the correlation time of fluctuations. This method authorizes local measurements in contrast to the classical scattering techniques that average fluctuations over the illuminating beam. We found that during the very early stages of phase separation the SF scales with the wave vector q according to the Lorentzian q(-2), which shows that the liquid and vapor domains are just emerging. The critical wave number, which is related to the characteristic length of fluctuations, steadily decreases over time, supporting a sustained increase in the spatial scale of the fluctuating domains. The scaled evolution of the critical wave number obeys the universal evolution for the interconnected domains at high volume fraction with an apparent power law exponent of -0.35 ± 0.02. We also determined the correlation time of the fluctuations and inferred values for thermal diffusivity coefficient very near the critical point, above and below. The values were used to pinpoint the crossing of T(c) within 13 μK.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, 66 George Street, Charleston, South Carolina 29424, USA
| | | | | | | | | | | | | |
Collapse
|
12
|
Oprisan A, Hegseth JJ, Smith GM, Lecoutre C, Garrabos Y, Beysens DA. Dynamics of a wetting layer and Marangoni convection in microgravity. Phys Rev E Stat Nonlin Soft Matter Phys 2011; 84:021202. [PMID: 21928983 DOI: 10.1103/physreve.84.021202] [Citation(s) in RCA: 3] [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: 03/22/2011] [Revised: 07/04/2011] [Indexed: 05/31/2023]
Abstract
Near the liquid-vapor critical point in pure fluids, material and thermal properties vary considerably with temperature. In a series of microgravity experiments, sulfur hexafluoride (SF6) was heated ∼1 K above its critical temperature, then quenched below the critical temperature in order to form gas and liquid domains. We found a power law exponent of 0.389 ± 0.010 for the growth of the wetting layer thickness during the intermediate stage of phase separation. Full and microscopic view images of the sample cell unit were analyzed to determine the changes in the size distribution of liquid droplets inside the gas phase over time. We found that the distribution of diameters for liquid droplets always contains a fraction of very small droplets, presumably due to a continuous nucleation process. At the same time, the size distribution flattens over time and rapidly includes large-size droplets, presumably generated through a coalescence mechanism. By following both a large gas bubble over two hours of video recordings, we found periodic and synchronous motion of the gas bubble along both the x and y directions. By following a large liquid droplet embedded into the large gas bubble, we found periodic, out of phase motions, which we related to Marangoni convection. The experimentally measured velocity of the liquid droplet is in good agreement with the theoretical predicted velocity of ∼0.386 μm/s obtained from Young's thermocapillary effect.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424, USA.
| | | | | | | | | | | |
Collapse
|
13
|
Oprisan A, Oprisan S, Teklu A. Experimental study of nonequilibrium fluctuations during free diffusion in nanocolloids using microscopic techniques. Appl Opt 2010; 49:86-98. [PMID: 20062494 DOI: 10.1364/ao.49.000086] [Citation(s) in RCA: 3] [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] [Indexed: 05/28/2023]
Abstract
We report quantitative experimental results regarding concentration fluctuations based on a small-angle light-scattering setup. A shadowgraph technique was used to record concentration fluctuations in a free-diffusion cell filled with colloids. Our experimental setup includes an objective attached to the CCD camera to increase the field of view. We performed two separate experiments, one with 20 nm gold and the other with 200 nm silica colloids, and extracted both the structure factors and the correlation time during the early stages of concentration fluctuations. The temporal evolution of fluctuations was also qualitatively investigated using recursive plots and spatial-temporal sections of fluctuating images. We found that the correlation time versus wavenumber for gold nanocolloids is concave shaped, whereas, for silica colloids, it is convex shaped. The difference in correlation time behavior is not only due to the size of the particle, but also to possible plasmonic interactions in gold colloids.
Collapse
Affiliation(s)
- Ana Oprisan
- Physics and Astronomy, College of Charleston, Charleston, South Carolina 29424, USA.
| | | | | |
Collapse
|
14
|
Hegseth J, Oprisan A, Garrabos Y, Lecoutre-Chabot C, Nikolayev VS, Beysens D. Near-critical fluid boiling: overheating and wetting films. Eur Phys J E Soft Matter 2008; 26:345-353. [PMID: 19230113 DOI: 10.1140/epje/i2007-10333-x] [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: 05/27/2023]
Abstract
The heating of coexisting gas and liquid phases of pure fluid through its critical point makes the fluid extremely compressible, expandable, slows the diffusive transport, and decreases the contact angle to zero (perfect wetting by the liquid phase). We have performed experiments on near-critical fluids in a variable volume cell in the weightlessness of an orbiting space vehicle, to suppress buoyancy-driven flows and gravitational constraints on the liquid-gas interface. The high compressibility, high thermal expansion, and low thermal diffusivity lead to a pronounced adiabatic heating called the piston effect. We have directly visualized the near-critical fluid's boundary layer response to a volume quench when the external temperature is held constant. We have found that when the system's temperature T is increased at a constant rate past the critical temperature T(c), the interior of the fluid gains a higher temperature than the hot wall (overheating). This extends previous results in temperature quenching experiments in a similarly prepared system when the gas is clearly isolated from the wall. Large elliptical wetting film distortions are also seen during these ramps. By ray tracing through the elliptically shaped wetting film, we find very thick wetting film on the walls. This wetting film is at least one order of magnitude thicker than films that form in the Earth's gravity. The thick wetting film isolates the gas bubble from the wall allowing gas overheating to occur due to the difference in the piston effect response between gas and liquid. Remarkably, this overheating continues and actually increases when the fluid is ramped into the single-phase supercritical phase.
Collapse
Affiliation(s)
- J Hegseth
- Department of Physics, University of New Orleans, New Orleans, LA 70148, USA.
| | | | | | | | | | | |
Collapse
|
15
|
Oprisan A, Oprisan SA, Hegseth JJ, Garrabos Y, Lecoutre-Chabot C, Beysens D. Universality in early-stage growth of phase-separating domains near the critical point. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:051118. [PMID: 18643037 DOI: 10.1103/physreve.77.051118] [Citation(s) in RCA: 3] [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: 02/09/2008] [Indexed: 05/26/2023]
Abstract
We present both the experimental and computational methods and results of phase-separating experiments performed with sulfur hexafluoride (SF6) close to its critical density. These experiments were performed in microgravity to suppress buoyancy and convection-driven effects. Phase separation under reduced gravity is analyzed for both 0.3 mK and 3.6 mK temperature quenches in order to derive the early-stage growth law. We found a 1/3 growth law for early stages of phase separation for a volume fraction of minority domains of 50%. Our findings support the hypothesis of a crossover between Brownian motion and hydrodynamic effects in the early stages of phase separation. The temperature inside the bulk of the pure fluid was estimated using a proposed histogram method. Our histogram method allowed temperature estimation below thermistors' sensitivity and detected small temperature variations inside the bulk of the pure fluid.
Collapse
Affiliation(s)
- Ana Oprisan
- Department of Physics and Astronomy, College of Charleston, 60 George Street, Charleston, South Carolina 29424, USA
| | | | | | | | | | | |
Collapse
|
16
|
Hegseth J, Oprisan A, Garrabos Y, Nikolayev VS, Lecoutre-Chabot C, Beysens D. Wetting film dynamics during evaporation under weightlessness in a near-critical fluid. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:031602. [PMID: 16241449 DOI: 10.1103/physreve.72.031602] [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: 05/03/2004] [Revised: 05/18/2005] [Indexed: 05/05/2023]
Abstract
By performing near-critical fluid experiments in the weightlessness of an orbiting space vehicle, we have suppressed buoyancy-driven flows and gravitational constraints on the liquid-gas interface of a large gas bubble. At equilibrium, the liquid completely wets the walls of a cylindrical cell, and the bubble is pushed to the sidewall. In these experiments the system's temperature T is increased at a constant rate past the critical temperature T(C), pushing it slightly out of equilibrium. The wetting film shows a large mechanical response to this heating, including contact lines that recede on a solid surface and a spreading bubble. Near T(C), the receding contact lines make the entire bubble appear to spread along the copper sidewall. The spreading bubble is a manifestation of the boiling crisis near the critical point. We present quantitative data of the receding contact lines that are observed prior to the near-critical boiling crisis. We analyze the receding contact lines in detail, and find that they are driven by vapor recoil from evaporation, as is the spreading bubble of the boiling crisis.
Collapse
Affiliation(s)
- John Hegseth
- Department of Physics, University of New Orleans, New Orleans, Louisiana 70148, USA
| | | | | | | | | | | |
Collapse
|