Letteratura scientifica selezionata sul tema "Aggregation of convection"
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Articoli di riviste sul tema "Aggregation of convection":
1
Shamekh, Sara, Caroline Muller, Jean-Philippe Duvel e Fabio D’Andrea. "How Do Ocean Warm Anomalies Favor the Aggregation of Deep Convective Clouds?" Journal of the Atmospheric Sciences 77, n. 11 (1 novembre 2020): 3733–45. http://dx.doi.org/10.1175/jas-d-18-0369.1.
Abstract (sommario):
AbstractWe investigate the role of a warm sea surface temperature (SST) anomaly (hot spot of typically 3 to 5 K) on the aggregation of convection using cloud-resolving simulations in a nonrotating framework. It is well known that SST gradients can spatially organize convection. Even with uniform SST, the spontaneous self-aggregation of convection is possible above a critical SST (here 295 K), arising mainly from radiative feedbacks. We investigate how a circular hot spot helps organize convection, and how self-aggregation feedbacks modulate this organization. The hot spot significantly accelerates aggregation, particularly for warmer/larger hot spots, and extends the range of SSTs for which aggregation occurs; however, at cold SST (290 K) the aggregated cluster disaggregates if we remove the hot spot. A large convective instability over the hot spot leads to stronger convection and generates a large-scale circulation which forces the subsidence drying outside the hot spot. Indeed, convection over the hot spot brings the atmosphere toward a warmer temperature. The warmer temperatures are imprinted over the whole domain by gravity waves and subsidence warming. The initial transient warming and concomitant subsidence drying suppress convection outside the hot spot, thus driving the aggregation. The hot-spot-induced large-scale circulation can enforce the aggregation even without radiative feedbacks for hot spots sufficiently large/warm. The strength of the large-scale circulation, which defines the speed of aggregation, is a function of the hot spot fractional area. At equilibrium, once the aggregation is well established, the moist convective region with upward midtropospheric motion, centered over the hot spot, has an area surprisingly independent of the hot spot size.
2
Jung, Hyunju, Ann Kristin Naumann e Bjorn Stevens. "Convective self–aggregation in a mean flow". Atmospheric Chemistry and Physics 21, n. 13 (8 luglio 2021): 10337–45. http://dx.doi.org/10.5194/acp-21-10337-2021.
Abstract (sommario):
Abstract. Convective self-aggregation is an atmospheric phenomenon seen in numerical simulations in a radiative convective equilibrium framework thought to be informative of some aspects of the behavior of real-world convection in the deep tropics. We impose a background mean wind flow on convection-permitting simulations through the surface flux calculation in an effort to understand how the asymmetry imposed by a mean wind influences the propagation of aggregated structures in convection. The simulations show that, with imposing mean flow, the organized convective system propagates in the direction of the flow but slows down compared to what pure advection would suggest, and it eventually becomes stationary relative to the surface after 15 simulation days. The termination of the propagation arises from momentum flux, which acts as a drag on the near-surface horizontal wind. In contrast, the thermodynamic response through the wind-induced surface heat exchange feedback is a relatively small effect, which slightly retards the propagation of the convection relative to the mean wind.
3
Bretherton, Christopher S., Peter N. Blossey e Marat Khairoutdinov. "An Energy-Balance Analysis of Deep Convective Self-Aggregation above Uniform SST". Journal of the Atmospheric Sciences 62, n. 12 (1 dicembre 2005): 4273–92. http://dx.doi.org/10.1175/jas3614.1.
Abstract (sommario):
Abstract The spatial organization of deep moist convection in radiative–convective equilibrium over a constant sea surface temperature is studied. A 100-day simulation is performed with a three-dimensional cloud-resolving model over a (576 km)2 domain with no ambient rotation and no mean wind. The convection self-aggregates within 10 days into quasi-stationary mesoscale patches of dry, subsiding and moist, rainy air columns. The patches ultimately merge into a single intensely convecting moist patch surrounded by a broad region of very dry subsiding air. The self-aggregation is analyzed as an instability of a horizontally homogeneous convecting atmosphere driven by convection–water vapor–radiation feedbacks that systematically dry the drier air columns and moisten the moister air columns. Column-integrated heat, water, and moist static energy budgets over (72 km)2 horizontal blocks show that this instability is primarily initiated by the reduced radiative cooling of air columns in which there is extensive anvil cirrus, augmented by enhanced surface latent and sensible heat fluxes under convectively active regions due to storm-induced gustiness. Mesoscale circulations intensify the later stages of self-aggregation by fluxing moist static energy from the dry to the moist regions. A simple mathematical model of the initial phase of self-aggregation is proposed based on the simulations. In accordance with this model, the self-aggregation can be suppressed by horizontally homogenizing the radiative cooling or surface fluxes. Lower-tropospheric wind shear leads to slightly slower and less pronounced self-aggregation into bands aligned along the shear vector. Self-aggregation is sensitive to the ice microphysical parameterization, which affects the location and extent of cirrus clouds and their radiative forcing. Self-aggregation is also sensitive to ambient Coriolis parameter f, and can induce spontaneous tropical cyclogenesis for large f. Inclusion of an interactive mixed-layer ocean slows but does not prevent self-aggregation.
4
Schulz, Hauke, e Bjorn Stevens. "Observing the Tropical Atmosphere in Moisture Space". Journal of the Atmospheric Sciences 75, n. 10 (ottobre 2018): 3313–30. http://dx.doi.org/10.1175/jas-d-17-0375.1.
Abstract (sommario):
Measurements from the Barbados Cloud Observatory are analyzed to identify the processes influencing the distribution of moist static energy and the large-scale organization of tropical convection. Five years of water vapor and cloud profiles from a Raman lidar and cloud radar are composed to construct the structure of the observed atmosphere in moisture space. The large-scale structure of the atmosphere is similar to that now familiar from idealized studies of convective self-aggregation, with shallow clouds prevailing over a moist marine layer in regions of low-rank humidity, and deep convection in a nearly saturated atmosphere in regions of high-rank humidity. With supplementary reanalysis datasets the overall circulation pattern is reconstructed in moisture space, and shows evidence of a substantial lower-tropospheric component to the circulation. This shallow component of the circulation helps support the differentiation between the moist and dry columns, similar to what is found in simulations of convective self-aggregation. Radiative calculations show that clear-sky radiative differences can explain a substantial part of this circulation, with further contributions expected from cloud radiative effects. The shallow component appears to be important for maintaining the low gross moist stability of the convecting column. A positive feedback between a shallow circulation driven by differential radiative cooling and the low-level moisture gradients that help support it is hypothesized to play an important role in conditioning the atmosphere for deep convection. The analysis suggests that the radiatively driven shallow circulations identified by modeling studies as contributing to the self-aggregation of convection in radiative–convective equilibrium similarly play a role in shaping the intertropical convergence zone and, hence, the large-scale structure of the tropical atmosphere.
5
Tobin, Isabelle, Sandrine Bony e Remy Roca. "Observational Evidence for Relationships between the Degree of Aggregation of Deep Convection, Water Vapor, Surface Fluxes, and Radiation". Journal of Climate 25, n. 20 (4 giugno 2012): 6885–904. http://dx.doi.org/10.1175/jcli-d-11-00258.1.
Abstract (sommario):
Abstract Tropical deep convection exhibits complex organization over a wide range of scales. This study investigates the relationships between the spatial organization of deep convection and the large-scale atmospheric state. By using several satellite datasets and reanalyses, and by defining a simple diagnostic of convective aggregation, relationships between the degree of convective aggregation and the amount of water vapor, turbulent surface fluxes, and radiation are highlighted above tropical oceans. When deep convection is more aggregated, the middle and upper troposphere are drier in the convection-free environment, turbulent surface fluxes are enhanced, and the low-level and midlevel cloudiness is reduced in the environment. Humidity and cloudiness changes lead to a large increase in outgoing longwave radiation. Cloud changes also result in reduced reflected shortwave radiation. Owing to these opposing effects, the sensitivity of the radiative budget at the top of the atmosphere to convective aggregation turns out to be weak, but the distribution of radiative heating throughout the troposphere is affected. These results suggest that feedbacks between convective aggregation and the large-scale atmospheric state might influence large-scale dynamics and the transports of water and energy and, thus, play a role in the climate variability and change. These observational findings are qualitatively consistent with previous cloud-resolving model results, except for the effects on cloudiness and reflected shortwave radiation. The proposed methodology may be useful for assessing the representation of convective aggregation and its interaction with the large-scale atmospheric state in various numerical models.
6
Warren, P. B., R. C. Ball e A. Boelle. "Convection-Limited Aggregation". Europhysics Letters (EPL) 29, n. 4 (1 febbraio 1995): 339–44. http://dx.doi.org/10.1209/0295-5075/29/4/012.
7
Li, Bo-Wei, Min-Cheng Zhong e Feng Ji. "Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection". Applied Sciences 10, n. 21 (3 novembre 2020): 7795. http://dx.doi.org/10.3390/app10217795.
Abstract (sommario):
Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation.
8
Muller, Caroline J., e Isaac M. Held. "Detailed Investigation of the Self-Aggregation of Convection in Cloud-Resolving Simulations". Journal of the Atmospheric Sciences 69, n. 8 (1 agosto 2012): 2551–65. http://dx.doi.org/10.1175/jas-d-11-0257.1.
Abstract (sommario):
Abstract In models of radiative–convective equilibrium it is known that convection can spontaneously aggregate into one single localized moist region if the domain is large enough. The large changes in the mean climate state and radiative fluxes accompanying this self-aggregation raise questions as to what simulations at lower resolutions with parameterized convection, in similar homogeneous geometries, should be expected to produce to be considered successful in mimicking a cloud-resolving model. The authors investigate this self-aggregation in a nonrotating, three-dimensional cloud-resolving model on a square domain without large-scale forcing. It is found that self-aggregation is sensitive not only to the domain size, but also to the horizontal resolution. With horizontally homogeneous initial conditions, convective aggregation only occurs on domains larger than about 200km and with resolutions coarser than about 2km in the model examined. The system exhibits hysteresis, so that with aggregated initial conditions, convection remains aggregated even at our finest resolution, 500m, as long as the domain is greater than 200–300km. The sensitivity of self-aggregation to resolution and domain size in this model is due to the sensitivity of the distribution of low clouds to these two parameters. Indeed, the mechanism responsible for the aggregation of convection is the dynamical response to the longwave radiative cooling from low clouds. Strong longwave cooling near cloud top in dry regions forces downward motion, which by continuity generates inflow near cloud top and near-surface outflow from dry regions. This circulation results in the net export of moist static energy from regions with low moist static energy, yielding a positive feedback.
9
Windmiller, Julia M., e George C. Craig. "Universality in the Spatial Evolution of Self-Aggregation of Tropical Convection". Journal of the Atmospheric Sciences 76, n. 6 (1 giugno 2019): 1677–96. http://dx.doi.org/10.1175/jas-d-18-0129.1.
Abstract (sommario):
Abstract Self-aggregation in numerical simulations of tropical convection is described by an upscale growth and intensification of dry and moist regions. Previous work has focused on determining the relevant mechanism that induces moist regions to get moister and dry regions to get drier. Though different mechanisms have been identified, the spatial evolution of self-aggregation is remarkably universal. The first part of this study shows that different mechanisms can lead to a similar evolution of self-aggregation, if self-aggregation is described by a phase separation of moist and dry regions, through a process called coarsening. Though it was previously introduced based on a convection–humidity feedback, coarsening, importantly, is not tied to a specific feedback process but only requires an intensification of local humidity perturbations. Based on different feedback loops, three simple models of the evolution of the humidity field are introduced, all of which lead to coarsening. In each model, diffusive transport of humidity is assumed, which approximates a humidity increase due to convection, within a finite region around convective cores. In the second part, predictions made by coarsening are compared with atmospheric model simulations. Analyzing a set of radiative–convective equilibrium simulations shows that coarsening correctly predicts the upscale growth of the moist and dry regions in the early stages of self-aggregation. In addition, coarsening can explain why self-aggregation is not observed for small domains and why the shape of the final moist region changes with the shape of the domain.
10
Boos, William R., Alexey Fedorov e Les Muir. "Convective Self-Aggregation and Tropical Cyclogenesis under the Hypohydrostatic Rescaling". Journal of the Atmospheric Sciences 73, n. 2 (27 gennaio 2016): 525–44. http://dx.doi.org/10.1175/jas-d-15-0049.1.
Abstract (sommario):
Abstract The behavior of rotating and nonrotating aggregated convection is examined at various horizontal resolutions using the hypohydrostatic, or reduced acceleration in the vertical (RAVE), rescaling. This modification of the equations of motion reduces the scale separation between convective- and larger-scale motions, enabling the simultaneous and explicit representation of both types of flow in a single model without convective parameterization. Without the RAVE rescaling, a dry bias develops when simulations of nonrotating radiative–convective equilibrium are integrated at coarse resolution in domains large enough to permit convective self-aggregation. The rescaling reduces this dry bias, and here it is suggested that the rescaling moistens the troposphere by weakening the amplitude and slowing the group velocity of gravity waves, thus reducing the subsidence drying around aggregated convection. Separate simulations of rotating radiative–convective equilibrium exhibit tropical cyclogenesis; as horizontal resolution is coarsened without the rescaling, the resulting storms intensify more slowly and achieve lower peak intensities. At a given horizontal resolution, using RAVE increases peak storm intensity and reduces the time needed for tropical cyclogenesis—effects here suggested to be caused at least in part by the environmental moistening produced by RAVE. Consequently, the RAVE rescaling has the potential to improve simulations of tropical cyclones and other aggregated convection in models with horizontal resolutions of order 10–100 km.
Tesi sul tema "Aggregation of convection":
1
Shamekh, Sara. "The impact of sea surface temperature on the aggregation of deep convective clouds". Electronic Thesis or Diss., Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLE041.
Abstract (sommario):
Cette thèse examine l’impact des hétérogénéités de température de surface de la mer (SST) sur l’agrégation des nuages convectifs, à l’aide de simulations 3D de l’équilibre radiatifconvectif. Les hétérogénéités de température étudiées sont soit imposées, soit interactives. Dans le premier cas, un point chaud de rayon R et d’anomalie de température ΔT est introduit à la surface. Le point chaud accélère l’agrégation et étend les valeurs de SST pour lesquelles la convection agrège. L’augmentation de l’instabilité sur le point chaud renforce la convection et la circulation grande échelle, forçant la subsidence et l’assèchement à l’extérieur du point chaud. Une anomalie suffisamment large ou chaude provoque l’agrégation même sans rétroactions radiatives. Dans le cas d’hétérogénéités interactives, l’océan est modélisé par une couche de température moyenne constante mais variant dans l’espace. La SST interactive ralentit l’agrégation, d’autant plus que la couche océanique est peu profonde. L’anomalie de SST dans les régions sèches est d’abord positive, s’opposant à la circulation divergente dans la couche limite, connue pour favoriser l’auto-agrégation. à un seuil de sécheresse plus élevé, l’anomalie devient négative et favorise cette circulation. La circulation peu profonde est corrélée à la vitesse d’agrégation. Elle est due à une haute pression, elle-même liée aux anomalies de SST et au refroidissement radiatif de la couche limite. L’inclusion d’un cycle diurne dans les simulations avec SST interactive accélère l’apparition de zones sèches et l’agrégation pour les couches océaniques peu profondes, réduisant ainsi la dépendance de l’agrégation à la profondeur de la couche océaniqueThis study investigates the impact of Sea Surface Temperature (SST) heterogeneities on the aggregation of convective clouds, using 3D cloudresolving simulations of radiativeconvective equilibrium. The SST heterogeneities are either imposed or interactive. In imposed cases, a spatiotemporally fixed warm SST anomaly (Hot-spot) with radius R and temperature anomaly ΔT is introduced at the center of the domain. The hot-spot significantly accelerates aggregation and extends the range of SSTs for which aggregation occurs. A convective instability over the hot-spot leads to stronger convection and generates a large-scale circulation, forcing subsidence drying outside the hot-spot. A large/warm hot-spot drives the aggregation even without radiative feedbacks. In cases where SST heterogeneities are interactive, the ocean is modeled as one layer slab ocean, with a constant mean but spatially varying temperature. The interactive SST decelerates the aggregation, especially with shallower slab. SST anomaly in dry regions is positive at first, thus opposing the diverging shallow circulation known to favor self-aggregation. With further drying, it becomes negative and favors the shallow circulation. The shallow circulation is found to be well correlated with the aggregation speed. It can be linked to a positive surface pressure anomaly, itself the consequence of SST anomalies and boundary layer radiative cooling. Including a diurnal cycle in simulations with interactive SST results in faster triggering of dry patches and accelerates the aggregation for shallow slabs, thus reducing the dependency of aggregation on slab depth
2
Wing, Allison A. "Physical mechanisms controlling self-aggregation of convection in idealized numerical modeling simulations". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90606.
Abstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 141-146).
The ubiquity of cloud clusters and their role in modulating radiative cooling and the moisture distribution underlines the importance of understanding how and why tropical convection organizes. In this work, the fundamental mechanism underlying the self-aggregation of convection is explored using a cloud resolving model. The objective is to identify and quantify the interactions between the environment and the convection that allow the convection to spontaneously organize into a single cluster. Specifically, the System for Atmospheric Modeling is used to perform 3-d cloud system resolving simulations of radiative-convective equilibrium in a non-rotating framework, with interactive radiation and surface fluxes and fixed sea surface temperature. Self-aggregation only occurs at sea surface temperatures above a certain threshold. As the system evolves to an aggregated state, there are large changes to domain averaged quantities important to climate, such as radiative fluxes and moisture. Notably, self-aggregation begins as a dry patch that expands, eventually forcing all the convection into a single clump. Thus, when examining the initiation of self-aggregation, we focus on processes that can amplify this initial dry patch. Sensitivity tests suggest that wind-dependent surface fluxes and interactive longwave radiative fluxes are important for permitting self-aggregation. A novel method is introduced to quantify the magnitudes of the various feedbacks that control self-aggregation within the framework of the budget for the spatial variance of column - integrated frozen moist static energy. The absorption of shortwave radiation by atmospheric water vapor is found to be a key positive feedback in the evolution of aggregation. In addition, there is a positive wind speed - surface flux feedback whose role is to counteract a negative air-sea enthalpy disequilibrium - surface flux feedback. The longwave radiation - water vapor feedback transitions from positive to negative in the early and intermediate stages of aggregation. The long-wave radiation - cloud feedback is the dominant positive feedback that maintains the aggregated state once it develops. Importantly, the mechanisms that maintain the aggregated state are distinct from those that instigate the evolution of self-aggregation. These results and those of a companion study suggest that the temperature dependence of self-aggregation enters through the longwave feedback term.
by Allison A. Wing.
Ph. D.
3
Su, Hui. "A modeling study of self-aggregation and large-scale control of tropical deep convection /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10018.
4
Coppin, David. "Agrégation de la convection dans un modèle de circulation générale : mécanismes physiques et rôle climatique". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066057/document.
Abstract (sommario):
Cette thèse porte sur l'agrégation de la convection dans le modèle de circulation générale LMDZ5A à l'équilibre radiatif-convectif (RCE). L'instabilité du RCE mise en évidence nous permet d'étudier les mécanismes d'initiation de l'agrégation et leur dépendance à la température de surface océanique (SST). A basse SST, l'agrégation résulte d'un couplage entre la circulation grande-échelle et les effets radiatifs des nuages bas. A haute SST, elle provient d'un couplage entre la circulation de grande-échelle et les flux turbulents à la surface. Le couplage de l'atmosphère avec une couche de mélange océanique rend l'initiation de l'agrégation moins dépendante de la SST et des mécanismes d'initiation, à l'exception des effets radiatifs des nuages hauts. L'impact de l'agrégation sur la sensibilité climatique et la température de surface est aussi analysé. En favorisant la formation de zones ciel clair sèches, l'agrégation refroidit fortement le système climatique. Toutefois, cet effet est limité par l'effet des changements de gradients de SST et de fraction de nuages bas qui tendent au contraire à faire augmenter la sensibilité climatique. Aux plus courtes échelles temporelles, en revanche, le couplage entre océan et agrégation de la convection est à l'origine d'une boucle de rétroaction stabilisatrice qui contrôle l'agrégation et renverse complètement son effet. Ainsi, l'effet de l'agrégation sur la sensibilité climatique est assez faible par rapport à ce que laissent penser les simulations où le couplage océan-atmosphère est absent. Ces résultats montrent l'importance de considérer le couplage océan-atmosphère dans l'étude du rôle de l'agrégation dans le climatThis thesis focuses on the study of convective aggregation in LMDZ5A general circulation model, used in Radiative-Convective Equilibrium (RCE) configuration. The instability of the RCE allows us to look at the mechanisms controlling the initiation of convective aggregation and its dependence on sea surface temperatures (SST). At low SSTs, a coupling between the large-scale circulation and the radiative effects of low clouds is needed to trigger self-aggregation. At high SSTs, the coupling between the large-scale circulation and the surface fluxes controls this initiation. When the atmosphere is coupled to a slab ocean mixed layer, SST gradients facilitate the initiation of convective aggregation. Except for the high-cloud radiative effects, triggering mechanisms are less crucial. Convection also becomes less dependent on the SST.The impact of convective aggregation on the climate sensitivity and surface temperature is also analyzed. Convective aggregation is found to increase the area of dry clear-sky zones. Thus, it tends to cool the system very efficiently. However, the negative feedback associated with an increase in aggregation is generally balanced by offsetting changes in SST gradients and low clouds that tend to increase the climate sensitivity. In contrast, at shorter timescales, the coupling between ocean and convective aggregation also controls the strength of convective aggregation and overturn its effect. Thus the impact of convective aggregation may not be as strong as what can be inferred from experiments with uniform SSTs.These results emphasize the importance of considering ocean-atmosphere coupling when studying the role of aggregation in climate
5
Coppin, David. "Agrégation de la convection dans un modèle de circulation générale : mécanismes physiques et rôle climatique". Electronic Thesis or Diss., Paris 6, 2017. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2017PA066057.pdf.
Abstract (sommario):
Cette thèse porte sur l'agrégation de la convection dans le modèle de circulation générale LMDZ5A à l'équilibre radiatif-convectif (RCE). L'instabilité du RCE mise en évidence nous permet d'étudier les mécanismes d'initiation de l'agrégation et leur dépendance à la température de surface océanique (SST). A basse SST, l'agrégation résulte d'un couplage entre la circulation grande-échelle et les effets radiatifs des nuages bas. A haute SST, elle provient d'un couplage entre la circulation de grande-échelle et les flux turbulents à la surface. Le couplage de l'atmosphère avec une couche de mélange océanique rend l'initiation de l'agrégation moins dépendante de la SST et des mécanismes d'initiation, à l'exception des effets radiatifs des nuages hauts. L'impact de l'agrégation sur la sensibilité climatique et la température de surface est aussi analysé. En favorisant la formation de zones ciel clair sèches, l'agrégation refroidit fortement le système climatique. Toutefois, cet effet est limité par l'effet des changements de gradients de SST et de fraction de nuages bas qui tendent au contraire à faire augmenter la sensibilité climatique. Aux plus courtes échelles temporelles, en revanche, le couplage entre océan et agrégation de la convection est à l'origine d'une boucle de rétroaction stabilisatrice qui contrôle l'agrégation et renverse complètement son effet. Ainsi, l'effet de l'agrégation sur la sensibilité climatique est assez faible par rapport à ce que laissent penser les simulations où le couplage océan-atmosphère est absent. Ces résultats montrent l'importance de considérer le couplage océan-atmosphère dans l'étude du rôle de l'agrégation dans le climatThis thesis focuses on the study of convective aggregation in LMDZ5A general circulation model, used in Radiative-Convective Equilibrium (RCE) configuration. The instability of the RCE allows us to look at the mechanisms controlling the initiation of convective aggregation and its dependence on sea surface temperatures (SST). At low SSTs, a coupling between the large-scale circulation and the radiative effects of low clouds is needed to trigger self-aggregation. At high SSTs, the coupling between the large-scale circulation and the surface fluxes controls this initiation. When the atmosphere is coupled to a slab ocean mixed layer, SST gradients facilitate the initiation of convective aggregation. Except for the high-cloud radiative effects, triggering mechanisms are less crucial. Convection also becomes less dependent on the SST.The impact of convective aggregation on the climate sensitivity and surface temperature is also analyzed. Convective aggregation is found to increase the area of dry clear-sky zones. Thus, it tends to cool the system very efficiently. However, the negative feedback associated with an increase in aggregation is generally balanced by offsetting changes in SST gradients and low clouds that tend to increase the climate sensitivity. In contrast, at shorter timescales, the coupling between ocean and convective aggregation also controls the strength of convective aggregation and overturn its effect. Thus the impact of convective aggregation may not be as strong as what can be inferred from experiments with uniform SSTs.These results emphasize the importance of considering ocean-atmosphere coupling when studying the role of aggregation in climate
6
Wu, Wei-Lin, e 吳蔚琳. "The Characteristics of Convective Aggregation in Rotating Radiative-Convective Equilibrium Simulated by a Cloud-Resolving Model". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/ghfzzw.
Capitoli di libri sul tema "Aggregation of convection":
1
Jensen, Mogens H. "Muitifractals in Convection and Aggregation". In Random Fluctuations and Pattern Growth: Experiments and Models, 292–309. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2653-0_41.
2
Saito, Yukio, Makio Uwaha e Susumu Seki. "Dynamics and Structure of an Aggregation Growing from a Diffusion Field". In Interactive Dynamics of Convection and Solidification, 27–29. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2809-4_5.
3
Khelifi, Sana, Namane Méchitoua, Frank Hülsemann e Frédéric Magoulès. "An Aggregation Based Algebraic Multigrid Method Applied to Convection-Diffusion Operators". In Finite Volumes for Complex Applications VI Problems & Perspectives, 597–604. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-20671-9_63.
4
Xu, Liu-Jun, e Ji-Ping Huang. "Theory for Thermal Wave Nonreciprocity: Angular Momentum Bias". In Transformation Thermotics and Extended Theories, 277–90. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-5908-0_20.
Abstract (sommario):
AbstractIn this chapter, we demonstrate that an angular momentum bias generated by a volume force can also lead to modal splitting in convection-diffusion systems but with different features. We further reveal the thermal Zeeman effect by studying the temperature field propagation in an angular-momentum-biased ring with three ports (one for input and two for output). With an optimal volume force, temperature field propagation is allowed at one output port but isolated at the other, and the rectification coefficient can reach a maximum value of 1. The volume forces corresponding to the rectification coefficient peaks can also be quantitatively predicted by scalar (i.e., temperature) interference. Compared with existing mechanisms for thermal nonreciprocity, an angular momentum bias does not require temperature-dependent and phase-change materials, which has an advantage in wide-temperature-range applicability. These results may provide insights into thermal stabilization and thermal topology. The related mechanism is also universal for other convection-diffusion systems such as mass transport, chemical mixing, and colloid aggregation.
5
Yuan, Leqi, Kun Cheng, Haozhi Bian, Yaping Liao e Chenxi Jiang. "Numerical Simulation of Flow Boiling Heat Transfer in Helical Tubes Under Marine Conditions". In Springer Proceedings in Physics, 1015–30. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-1023-6_86.
Abstract (sommario):
AbstractLead-based cooled reactors in most countries and some small reactors at sea use helical tube steam generators. Compared with U-tubes, the convection heat transfer coefficient in the spiral tube is higher, the structure is more compact, and the secondary flow is generated under the action of centrifugal force and gravity, which can achieve the effect of wetting the inner wall of the tube. However, due to the importance of the steam generator in the reactor and the complexity of the flow and boiling in the helical tube, the aggregation behavior of bubbles, the distribution of the two-phase interface and the secondary flow in the tube will significantly affect the heat transfer characteristics, so the gas-liquid phase in the tube is studied. Distribution, changes in heat transfer coefficients, and fluid flow characteristics are very important.In order to study the boiling heat transfer characteristics of helical once-through steam generators under static and marine conditions to provide safe and reliable energy supply for offshore facilities such as marine floating, this study uses STAR-CCM+ software, VOF method and Rohsenow boiling model to study the heat transfer capacity and flow characteristics of flow boiling in a helical tube under swaying and tilting conditions. The gas-liquid phase distribution characteristics, secondary flow variation characteristics and convective heat transfer coefficient of the fluid under different swing functions and inclined positions are obtained by numerical calculation, and the law of physical parameters changing with the cycle is found. The research results show that the secondary flow and heat transfer capacity in the tube change with the cycle, and the change is most obvious at the tube length of 0.8m. 5% of the normal condition; when the inclination angle is 45°, the maximum increase of the convection heat transfer coefficient is 16.8%, and the maximum decrease is 6.6%.
6
Holloway, Christopher E., Allison A. Wing, Sandrine Bony, Caroline Muller, Hirohiko Masunaga, Tristan S. L’Ecuyer, David D. Turner e Paquita Zuidema. "Observing Convective Aggregation". In Space Sciences Series of ISSI, 27–64. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-77273-8_2.
7
Leibovich, Sidney. "Spatial Aggregation Arising from Convective Processes". In Lecture Notes in Biomathematics, 110–24. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-50155-5_9.
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Wing, Allison A., Kerry Emanuel, Christopher E. Holloway e Caroline Muller. "Convective Self-Aggregation in Numerical Simulations: A Review". In Space Sciences Series of ISSI, 1–25. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-77273-8_1.
9
Smith, Alan D. "B″ not D″ as the source of intraplate volcanism". In In the Footsteps of Warren B. Hamilton: New Ideas in Earth Science. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2553(29).
Abstract (sommario):
ABSTRACT Under fast-moving oceanic plates, the asthenosphere seismic B″ region becomes isolated from the convecting mantle by plate drag and acts as an advecting layer, which can serve as a long-lived source for intraplate volcanism. Geochemical enrichment of B″ can occur via infiltration by melts generated from the breakdown of serpentinite at ~200 km depth in subducting slabs. Ocean-island chains arise when melts generated within metasomatized B″ by shear melting and localized convection are released along lithospheric fractures controlled by the stress field of the plate. Intersection of metasomatized B″ with ocean-ridge systems produces oceanic plateaus. A strong anisotropy anomaly (VSH/VSV >1) at depths of ~150 km in the Pacific asthenosphere marks a metasomatized B″ domain that originated in the western paleo-Pacific basin in the Carboniferous, and that is now associated with Hawaiian volcanism. Metasomatized B″ can be trapped beneath orogenic belts during continental aggregation and tapped by edge-driven convection upon rifting to produce the correlation between intraplate volcanism and the fabric of sutures in opening ocean basins such as the Atlantic Ocean basin.
10
Pérez-Ramirez, Yolanda, Anthony Graziani, Paul-Antoine Santoni, Virginie Tihay-Felicelli e William Mell. "Numerical characterization of structures heat exposure at WUI". In Advances in Forest Fire Research 2022, 719–24. Imprensa da Universidade de Coimbra, 2022. http://dx.doi.org/10.14195/978-989-26-2298-9_110.
Abstract (sommario):
In the forthcoming years, self-protection of communities will be a first priority over fire suppression in order to tend to more fire-resistant and resilient WUI communities. All around the world, countries facing WUI fires apply different recommendations or regulations often issued from post-fire surveys. Still, more efforts are necessary to understand how and why dwellings are damaged or completely destroyed under WUI fires attack. In particular, there is a need to quantitatively assess the effectiveness of the current legal prescriptions for homeowners concerning the defensible space around dwellings. Three-dimensional, time dependent, computational fluid dynamics fire behavior models can take into account the factors interacting and contributing to WUI fires (i.e., weather conditions, terrain configuration, fire, vegetation and structures). Moreover, they allow the spatially-explicit modelling of vegetation elements (i.e., trees, shrubs, etc.). Thus, they can be supporting tools to quantitatively assess the heat (radiative and convective) exposure of structures during the approach of a WUI fire, in order to investigate how the characteristics of the defensible space can protect a dwelling or not against such a fire. This study addresses the characterization of heat exposure conditions of a dwelling in common Mediterranean WUI scenarios by using the three-dimensional, time dependent, computational fluid dynamics forest fire behavior model WFDS. To this purpose, WUI fire simulations have been carried out at the landscape scale, taking into account the different zones that a fire burns before it might approach and reach a home structure. This is, a forested area and the defensible space or cleared area around a dwelling. Two different scenarios have been studied, where different spatial patterns for the raised vegetation at the defensible space have been considered. One vegetation pattern has a low level of aggregation corresponding to a sparse spatial distribution of plants, whereas the other vegetation pattern has a higher level of aggregation representative of a clumpy distribution of plants. Both scenarios, in agreement with the current regulations in Corsica, have the same amount of available fuel load, as well as, the same number and characteristics of raised vegetation elements. Fire simulations for these two scenarios have been carried out at different wind and ambient conditions representatives on one side of normal dry summer conditions and on the other side of particularly dry summer conditions. Heat exposure conditions have been characterized in terms of radiative and convective heat fluxes received by the structure. Special attention has been given on the role of fire – vegetation – wind interactions for the results and discussion.
Atti di convegni sul tema "Aggregation of convection":
1
Mateen, Khalid, e Eric William Smith. "Asphaltene Deposition Simulator with Aggregation". In Offshore Technology Conference. OTC, 2023. http://dx.doi.org/10.4043/32421-ms.
Abstract (sommario):
Abstract Asphaltene stability, aggregation, and transport are coupled with hydraulic and heat transfer equations to predict the effects of asphaltene deposition in wellbores and pipelines. The model uses lab measurements to characterize the asphaltene in solution and develop a precipitation curve in a pre-processing step. Smoluchowski coagulation theory predicts the rate of aggregation of smaller particles into larger particles in a geometric distribution. Finally, the resulting concentration of asphaltene particles diffuses to the wall as determined by mass convection theory. An innovative approach (Saidoun 2000), where only the primary particles, and not the aggregates, contribute to the deposit is also formulated. This second model has been successfully used to match 9 years of production data and screen a greenfield system for asphaltene risks. The simulator is deployed as a standalone desktop application built on React.JS and electron communicating to a Wolfram Engine kernel over gRPC.
2
Carlton, Hayden, Preethi Korangath, Nageshwar Arepally, Anilchandra Attaluri e Robert Ivkov. "Monitoring Perfusion-Based Convection in Cancer Tumor Tissue Undergoing Nanoparticle Heating by Analyzing Temperature Responses to Transient Pulsed Heating". In ASME 2023 Heat Transfer Summer Conference collocated with the ASME 2023 17th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/ht2023-105470.
Abstract (sommario):
Abstract The dynamic nature of perfusion in living tissues, such as solid tumors during thermal therapy, produces challenging spatiotemporal thermal boundary conditions. Changes in perfusion can manifest as changes in convective heat transfer that influence temperature changes during cyclic heating. Herein, we propose a method to actively monitor changes in local convection (perfusion) in vivo by using a transient thermal pulsing analysis. Syngeneic 4T1 tumor cells were injected subcutaneously into BALB/c mice and followed by caliper measurements. When tumor volumes measured 150–400 mm3, mice were randomly divided into one of two groups to receive intratumor injections of one of two iron oxide nanoparticle formulations for pulsed heating with an alternating magnetic field (AMF). The nanoparticles differed in both heating characteristics and coating. Intratumor temperature near the injection site as well as rectal temperature were measured with an optic fiber temperature probe. Following heating, mice were euthanized and tumors harvested and prepared for histological evaluation of nanoparticle distribution. To ascertain the heat transfer coefficient from heating and cooling pulses, we fit a lumped capacitance, Box-Lucas model to the time-temperature data assuming fixed tumor geometry and constant experimental conditions. For the first particle set, the injected nanoparticles dispersed evenly throughout the tumor with minimal aggregation, and with minimal change in convection. On the other hand, heating with the second particle generated a measurable decline in convective performance and histology analysis showed substantial aggregation near the injection site. We consider it likely that though the second nanoparticle type produced less heating per unit mass, its tendency to aggregate led to more intense local heating and tissue damage. Further analysis and experimentation is warranted to establish quantitative correlations between measured temperature changes, perfusion, and tissue damage responses. Implementing this type of analysis may stimulate development of robust and adaptive temperature controllers for medical device applications.
3
Fiechter, Jerome, e David N. Ku. "Numerical Study of Platelet Transport in Flowing Blood". In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0006.
Abstract (sommario):
Abstract Platelet transport in flowing blood is a critical issue in the prediction of thrombus formation. Since available data on platelet aggregation are essentially from experiments, the goal of this work is to investigate numerical solutions for platelet transport and predict the relative influence of convection and diffusion on platelet deposition at the arterial wall. The results obtained for laminar flow in an aneurysm show that both species transport and discrete phase models predict accurately the effects of convective and diffusive mechanisms and match experimental data closely. The species transport model also appears to estimate correctly platelet deposition in turbulent flow through a stenosis.
4
Kim, Kyung Chun, e Dong Kim. "Numerical Simulation on the Formation of a Toroidal Microvortex by the Optoelectrokinetic Effect". In ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icnmm2014-21439.
Abstract (sommario):
Optoelectrokinetic effects were effectively used for rapid concentration of particles in microfluidics. In this study, we clarified detail mechanism of particle aggregation by numerical simulation using COMSOL v4.2a multiphysics software. A 3D simulation was conducted with axisymmetric boundary conditions. AC voltage was applied to the two parallel electrodes in a microchannel to generate temperature gradient in the fluids. In addition to the AC electrothermal (ACET) effect, local heating by a laser illumination was also considered. Numerical simulations were carried out for dielectric fluids. A toroidal microvortex induced by the optoelectrokinetic effect shows that fluid motions in the middle of bottom boundary are cancelled out by flows in opposite directions and consequently producing stagnation. It is expected that micro/nano particles can be deposited in the bottom electrode. Local heating by the laser illumination enhanced the intensity of microvortex substantially. It is confirmed that the dominant driving force for the microvortex is natural convection by the laser illumination, however AC voltage is necessary for particle aggregation in the spot area.
5
Zhang, Peng, Jawaad Sheriff, João S. Soares, Chao Gao, Seetha Pothapragada, Na Zhang, Yuefan Deng e Danny Bluestein. "Multiscale Modeling of Flow Induced Thrombogenicity Using Dissipative Particle Dynamics and Coarse Grained Molecular Dynamics". In ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14187.
Abstract (sommario):
The coagulation cascade of blood may be initiated by flow induced platelet activation, which prompts clot formation in prosthetic cardiovascular devices and arterial disease processes. While platelet activation may be induced by biochemical agonists, shear stresses arising from pathological flow patterns enhance the propensity of platelets to activate and initiate the intrinsic pathway of coagulation, leading to thrombosis. Upon activation platelets undergo complex biochemical and morphological changes: organelles are centralized, membrane glycoproteins undergo conformational changes, and adhesive pseudopods are extended. Activated platelets polymerize fibrinogen into a fibrin network that enmeshes red blood cells. Activated platelets also cross-talk and aggregate to form thrombi. Current numerical simulations to model this complex process mostly treat blood as a continuum and solve the Navier-Stokes equations governing blood flow, coupled with diffusion-convection-reaction equations. It requires various complex constitutive relations or simplifying assumptions, and is limited to μm level scales. However, molecular mechanisms governing platelet shape change upon activation and their effect on rheological properties can be in the nm level scales. To address this challenge, a multiscale approach which departs from continuum approaches, may offer an effective means to bridge the gap between macroscopic flow and cellular scales. Coarse Grained Molecular dynamics (CGMD) and discrete/dissipative particle dynamics (DPD) methods have been employed in recent years to simulate complex processes at the molecular scales, and various viscous fluids at low-to-high Reynolds numbers at mesoscopic scales. Such particle methods possess important properties at the mesoscopic scale: complex fluids with heterogeneous particles can be modeled, allowing the simulation of processes which are otherwise very difficult to solve by continuum approaches. It is becoming a powerful tool for simulating complex blood flow, red blood cells interactions, and platelet-mediated thrombosis involving platelet activation, aggregation, and adhesion.
6
Bluestein, Danny, João S. Soares, Peng Zhang, Chao Gao, Seetha Pothapragada, Na Zhang, Marvin J. Slepian e Yuefan Deng. "Multiscale Modeling of Flow Induced Thrombogenicity Using Dissipative Particle Dynamics and Molecular Dynamics". In ASME 2013 2nd Global Congress on NanoEngineering for Medicine and Biology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/nemb2013-93094.
Abstract (sommario):
The coagulation cascade of blood may be initiated by flow induced platelet activation, which prompts clot formation in prosthetic cardiovascular devices and arterial disease processes. While platelet activation may be induced by biochemical agonists, shear stresses arising from pathological flow patterns enhance the propensity of platelets to activate and initiate the intrinsic pathway of coagulation, leading to thrombosis. Upon activation platelets undergo complex biochemical and morphological changes: organelles are centralized, membrane glycoproteins undergo conformational changes, and adhesive pseudopods are extended. Activated platelets polymerize fibrinogen into a fibrin network that enmeshes red blood cells. Activated platelets also cross-talk and aggregate to form thrombi. Current numerical simulations to model this complex process mostly treat blood as a continuum and solve the Navier-Stokes equations governing blood flow, coupled with diffusion-convection-reaction equations. It requires various complex constitutive relations or simplifying assumptions, and is limited to μm level scales. However, molecular mechanisms governing platelet shape change upon activation and their effect on rheological properties can be in the nm level scales. To address this challenge, a multiscale approach which departs from continuum approaches, may offer an effective means to bridge the gap between macroscopic flow and cellular scales. Molecular dynamics (MD) and dissipative particle dynamics (DPD) methods have been employed in recent years to simulate complex processes at the molecular scales, and various viscous fluids at low-to-high Reynolds numbers at mesoscopic scales. Such particle methods possess important properties at the mesoscopic scale: complex fluids with heterogeneous particles can be modeled, allowing the simulation of processes which are otherwise very difficult to solve by continuum approaches. It is becoming a powerful tool for simulating complex blood flow, red blood cells interactions, and platelet-mediated thrombosis involving platelet activation, aggregation, and adhesion.
7
Bluestein, Danny, João S. Soares, Peng Zhang, Chao Gao, Seetha Pothapragada, Na Zhang, Marvin J. Slepian e Yuefan Deng. "Multiscale Modeling of Flow Induced Thrombogenicity With Dissipative Particle Dynamics (DPD) and Molecular Dynamics (MD)". In ASME 2013 Conference on Frontiers in Medical Devices: Applications of Computer Modeling and Simulation. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/fmd2013-16176.
Abstract (sommario):
The coagulation cascade of blood may be initiated by flow induced platelet activation, which prompts clot formation in prosthetic cardiovascular devices and arterial disease processes. While platelet activation may be induced by biochemical agonists, shear stresses arising from pathological flow patterns enhance the propensity of platelets to activate and initiate the intrinsic pathway of coagulation, leading to thrombosis. Upon activation platelets undergo complex biochemical and morphological changes: organelles are centralized, membrane glycoproteins undergo conformational changes, and adhesive pseudopods are extended. Activated platelets polymerize fibrinogen into a fibrin network that enmeshes red blood cells. Activated platelets also cross-talk and aggregate to form thrombi. Current numerical simulations to model this complex process mostly treat blood as a continuum and solve the Navier-Stokes equations governing blood flow, coupled with diffusion-convection-reaction equations. It requires various complex constitutive relations or simplifying assumptions, and is limited to μm level scales. However, molecular mechanisms governing platelet shape change upon activation and their effect on rheological properties can be in the nm level scales. To address this challenge, a multiscale approach which departs from continuum approaches, may offer an effective means to bridge the gap between macroscopic flow and cellular scales. Molecular dynamics (MD) and dissipative particle dynamics (DPD) methods have been employed in recent years to simulate complex processes at the molecular scales, and various viscous fluids at low-to-high Reynolds numbers at mesoscopic scales. Such particle methods possess important properties at the mesoscopic scale: complex fluids with heterogeneous particles can be modeled, allowing the simulation of processes which are otherwise very difficult to solve by continuum approaches. It is becoming a powerful tool for simulating complex blood flow, red blood cells interactions, and platelet-mediated thrombosis involving platelet activation, aggregation, and adhesion.
8
Han, Zenghu, e Bao Yang. "Natural Convective Heat Transfer of Water-in-FC72 Nanoemulsion Fluids". In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52351.
Abstract (sommario):
The use of SOLID-particles has long been a common way of increasing fluid thermal conductivity. In this paper, nanoemulsion fluids—dispersions of LIQUID-nanodroplets—are proposed. As an example, water-in-FC72 nanoemulsion fluids are developed, and their thermophysical properties and impact on natural convective heat transfer are investigated experimentally. A significant increase in thermal conductivity—up to 52% for 12vol% of water nanodroplets (or 7.1 wt%)—is observed in the fluids. The enhancement in conductivity and viscosity of the fluids is found to be nonlinear with water loading, indicating an important role of the hydrodynamic interaction and aggregation of nanodroplets. However, the relative viscosity is found to be about two times the relative conductivity if compared at the same water loading. The presence of water nanodroplets is found to systematically increase the natural convective heat transfer coefficient in these fluids, in contrast to the observation in several conventional nanofluids containing solid nanoparticles.
9
Schinnerl, Mario, Wolfgang Beer e Reinhard Willinger. "Interpretation of Unexpected Aggregation of Condensate in Shrouded HP-Stages of an Industrial Steam Turbine". In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-26083.
Abstract (sommario):
Unexplainable rotor oscillations occured at an industrial steam turbine with air condenser shortly after startup of the plant, but already at specified load points. These oscillations led to immediate shutdowns and were not explainable with conventional reasons at that time. After several oscillation measurements and analysis a hypothesis was developed to explain the oscillation phenomena: The reason of the oscillations is an aggregation of condensate in a labyrinth seal of one or more turbine stages which acts like additional bearings and shifts the eigenfrequencies of the whole system. This work presents an analytical steady-state heat transfer model to explain, how condensation can occur in high-pressure sections of a steam turbine. With this model it is possible to take into account heat exchange in single turbine stages. The occurring heat fluxes are calculated row by row in each stator and rotor blade row. A new approach for considering the heat fluxes due to heat conduction between guide blades and guide blade carrier is presented. Due to the absence of measured surface temperatures the determination of convective heat transfer coefficients plays a major role in this work.
10
Liu, Wing Kam, e Ashfaq Adnan. "Multiscale Modeling and Simulation for Nanodiamond-Based Therapeutic Delivery". In ASME 2010 First Global Congress on NanoEngineering for Medicine and Biology. ASMEDC, 2010. http://dx.doi.org/10.1115/nemb2010-13273.
Abstract (sommario):
It has been demonstrated from recent research that nanodiamond(ND)-enabled drug delivery as cancer therapeutics represents an important component of optimized device functionality. The goal of the current research is to develop a multiscale modeling technique to understand the fundamental mechanism of a ND-based cancer therapeutic drug delivery system. The major components of the proposed device include nanodiamonds (ND), parylene buffer layer and doxorubicin (DOX) drugs, where DOX loaded self-assembled nanodiamonds are packed inside parylene capsule. The efficient functioning of the device is characterized by its ability to precisely detect targets (cancer cells) and then to release drugs at a controlled manner. The fundamental science issues concerning the development of the ND-based device includes (a) a precise identification of the equilibrium structure, surface electrostatics and self assembled morphology of nanodiamonds, (b) understanding of the drug/biomarker adsorption and desorption process to and from NDs, (c) rate of drug release through the parylene buffers, and finally, (d) device performance under physiological condition. In this study, we aim to systematically address these issues using a multscale computational framework. Specifically, the structure and electrostatics of the functionalized NDs are predicted by quantum scale calculation (Density Functional Tight Binding). The DFTB) study on smaller NDs suggests a facet dependent charge distributions on ND surfaces. Using the charges for smaller NDs (∼ valid for 1–3.3 nm dia ND), we then determined surface charges for larger (4–10 nm) truncated octahedral nanodiamonds (TOND). We found that the [100] face and the [111] face contain positively and negatively charged atoms, respectively. Employing this surface electrostatics of nanodiamonds, atomistic-scale simulations are performed to simulate the self-assembly process of the NDs and drug molecules in a solution as well as to evaluate nanoscale diffusion coefficient of DOX molecules. In order to quantify the nature of the aggregate morphology, a fractal analysis has been performed. The mass fractal dimensions for a variety of aggregate size have been obtained from molecular simulations assuming ‘diffusion-limited aggregation (DLA)’ process. Then, by considering the experimentally observed aggregate dimensions, by using DLA based fractal analysis and by utilizing Lagvankar-Gemmell Model for aggregate density, a continuum model for larger aggregates will be developed to characterize aggregate strengths and break-up mechanism, which in turn will help us to understand how aggregate size can be reduced. In this talk, an outline for this continuum model will be discussed. In addition, we have been performing molecular simulations on DOX-ND where multiple drug molecules are allowed to interact with a cluster of self-assembled nanodiamonds in pH controlled solution. The purpose of this study is to find the effect of solution pH on the loading and release of drug to and from nanodiamonds. Our initial results show that a higher pH is necessary to ensure drug release from nanodiamonds. Once we completely understand the essential physics of pH controlled drug loading and release, we plan to develop multiscale models of tumor nodules to represent them as a collection of individual tumor cells. Each cell will be then modeled as a deformable body comprised of three homogenous materials: cortex membrane, cytosol and nucleus. The cortex membrane and the cytosol will serve as a weak permeable medium where the absorption coefficients of the doxorubicin remain constant and obey Fick’s law. In this study, it will be assumed that drug release from the microdevice to its outer periphery will be governed by Fickian Diffusion. It will also be assumed that the complex flow of drug through the interstitial fluid of the body will be dictated by Darcy’s law. It will be assumed that the solute drug transport in these regions will be due to a combination of convection, diffusion, elimination in the intra- and extra-cellular space, receptive cell internalization and degradation. Results from this study will provide fundamental insight on the definitive targeting of infected cells and high resolution controlling of drug molecules.