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Articles 1 - 30 of 252
Full-Text Articles in Physics
Serpentine Micromixers Using Extensional Mixing Elements, George Tomaras, Chandrasekhar R. Kothapalli, Petru S. Fodor
Serpentine Micromixers Using Extensional Mixing Elements, George Tomaras, Chandrasekhar R. Kothapalli, Petru S. Fodor
Physics Faculty Publications
Computational fluid dynamics modeling was used to characterize the effect of the integration of constrictions defined by the vertices of hyperbolas on the flow structure in microfluidic serpentine channels. In the new topology, the Dean flows characteristic of the pressure-driven fluid motion along curved channels are combined with elongational flows and asymmetric longitudinal eddies that develop in the constriction region. The resulting complex flow structure is characterized by folding and stretching of the fluid volumes, which can promote enhanced mixing. Optimization of the geometrical parameters defining the constriction region allows for the development of an efficient micromixer topology that shows …
Physics Of Martial Arts: Incorporation Of Angular Momentum To Model Body Motion And Strikes, Alexis Merk, Andrew Resnick
Physics Of Martial Arts: Incorporation Of Angular Momentum To Model Body Motion And Strikes, Alexis Merk, Andrew Resnick
Physics Faculty Publications
We develop a physics-based kinematic model of martial arts movements incorporating rotation and angular momentum, extending prior analyses. Here, our approach is designed for a classroom environment; we begin with a warm-up exercise introducing counter-intuitive aspects of rotational motion before proceeding to a set of model collision problems that are applied to martial arts movements. Finally, we develop a deformable solid-body mechanics model of a martial arts practitioner suitable for an intermediate mechanics course. We provide evidence for our improved model based on calculations from biomechanical data obtained from prior reports as well as time-lapse images of several different kicks. …
Examining The Temperature Dependence Of Louche Formation In Absinthe, Jessica E. Bickel, Anna Ellis, Andrew Resnick
Examining The Temperature Dependence Of Louche Formation In Absinthe, Jessica E. Bickel, Anna Ellis, Andrew Resnick
Physics Faculty Publications
Absinthe is an anise-flavored alcohol that is typically served by adding cold water to form a cloudy green louche, similar to the cloudy white louche of ouzo. This microemulsion formation, due to the competing interactions within the oil-alcohol-water system, has been termed the ouzo effect. Previous work has examined the ternary oil-alcohol-water phase diagram in ouzo and limoncello. Additional work has also characterized the droplet size and stability of microemulsions in ouzo, limoncello, and pastis. However, less work has been done to examine the effect of temperature on louche formation despite the fact that the louche is traditionally formed by …
Effects Of Surface And Top Wind Shear On The Spatial Organization Of Marine Stratocumulus-Topped Boundary Layers, Monica Zamora Zapata, Thijs Heus, Jan Kleissl
Effects Of Surface And Top Wind Shear On The Spatial Organization Of Marine Stratocumulus-Topped Boundary Layers, Monica Zamora Zapata, Thijs Heus, Jan Kleissl
Physics Faculty Publications
The convective nature of Stratocumulus topped boundary layers (STBL) involves the motion of updrafts and downdrafts, driven by surface fluxes and radiative cooling, respectively. The balance between shear and buoyant forcings at the surface can determine the organization of updrafts between cellular and roll structures. We investigate the effect of varying shear at the surface and top of the STBL using Large Eddy Simulations, taking DYCOMS II RF01 as a base case. We focus on spatial identification of the following features: coherent updrafts and downdrafts, and observe how they are affected by varying shear. Stronger surface shear organizes the updrafts …
Analogy Between Thermodynamic Phase Transitions And Creeping Flows In Rectangular Cavities, Miron Kaufman, Petru S. Fodor
Analogy Between Thermodynamic Phase Transitions And Creeping Flows In Rectangular Cavities, Miron Kaufman, Petru S. Fodor
Physics Faculty Publications
© 2020, MDPI AG. All rights reserved. An analogy is found between the streamline function corresponding to Stokes flows in rectangular cavities and the thermodynamics of phase transitions and critical points. In a rectangular cavity flow, with no-slip boundary conditions at the walls, the corners are fixed points. The corners defined by a stationary and a moving wall, are found to be analogous to a thermodynamic first-order transition point. In contrast, the corners defined by two stationary walls correspond to thermodynamic critical points. Here, flow structures, also known as Moffatt eddies, form and act as stagnation regions where mixing is …
Size Dependence In Chord Characteristics From Simulated And Observed Continental Shallow Cumulus, Philipp J. Griewank, Thijs Heus, Neil P. Lareau, Roel A. J. Neggers
Size Dependence In Chord Characteristics From Simulated And Observed Continental Shallow Cumulus, Philipp J. Griewank, Thijs Heus, Neil P. Lareau, Roel A. J. Neggers
Physics Faculty Publications
© 2020 American Institute of Physics Inc.. All rights reserved. In this study we compare long-Term Doppler and Raman lidar observations against a full month of large eddy simulations of continental shallow cumulus clouds. The goal is to evaluate if the simulations can reproduce the mean observed vertical velocity and moisture structure of cumulus clouds and their associated subcloud circulations, as well as to establish if these properties depend on the size of the cloud.We propose methods to compare continuous chords of cloud detected from Doppler and Raman lidars with equivalent chords derived from 1D and 3D model output. While …
Dynamics Of Subsiding Shells In Actively Growing Clouds With Vertical Updrafts, Vishnu Nair, Thijs Heus, Maarten Van Reeuwijk
Dynamics Of Subsiding Shells In Actively Growing Clouds With Vertical Updrafts, Vishnu Nair, Thijs Heus, Maarten Van Reeuwijk
Physics Faculty Publications
© 2020 American Meteorological Society. The dynamics of a subsiding shell at the edges of actively growing shallow cumulus clouds with updrafts is analyzed using direct numerical simulation. The actively growing clouds have a fixed in-cloud buoyancy and velocity. Turbulent mixing and evaporative cooling at the cloud edges generate a subsiding shell that grows with time. A self-similar regime is observed for first-and second-order moments when normalized with respective maximum values. Internal scales derived from integral properties of the flow problem are identified. A self-similarity analysis using these scales reveals that contrary to classical self-similar flows, the turbulent kinetic energy …
Primary Cilia Have A Length-Dependent Persistence Length, Justin Flaherty, Zhe Feng, Zhangli Peng, Y. N. Young, Andrew Resnick
Primary Cilia Have A Length-Dependent Persistence Length, Justin Flaherty, Zhe Feng, Zhangli Peng, Y. N. Young, Andrew Resnick
Physics Faculty Publications
© 2019, The Author(s). The fluctuating position of an optically trapped cilium tip under untreated and Taxol-treated conditions was used to characterize mechanical properties of the cilium axoneme and its basal body by combining experimental, analytical,and computational tools. We provide, for the first time, evidence that the persistence length of a ciliary axoneme is length-dependent; longer cilia are stiffer than shorter cilia. We demonstrate that this apparent length dependence can be understood by a combination of modeling axonemal microtubules as anisotropic elastic shells and including actomyosin-driven stochastic basal body motion.Our results also demonstrate the possibility of using observable ciliary dynamics …
Sociophysics Analysis Of Multi-Group Conflicts, Miron Kaufman, Hung T. Diep, Sanda Kaufman
Sociophysics Analysis Of Multi-Group Conflicts, Miron Kaufman, Hung T. Diep, Sanda Kaufman
Physics Faculty Publications
© 2020 by the authors. We present our research on the application of statistical physics techniques to multi-group social conflicts. We identify real conflict situations of which the characteristics correspond to the model. We offer realistic assumptions about conflict behaviors that get factored into model-generated scenarios. The scenarios can inform conflict research and strategies for conflict management. We discuss model applications to two-and three-group conflicts. We identify chaotic time evolution of mean attitudes and the occurrence of strange attractors. We examine the role that the range of interactions plays with respect to the occurrence of chaotic behavior.
Validating The Water Vapor Variance Similarity Relationship In The Interfacial Layer Using Observations And Large-Eddy Simulations, M. K. Osman, D. D. Turner, Thijs Heus, V. Wulfmeyer
Validating The Water Vapor Variance Similarity Relationship In The Interfacial Layer Using Observations And Large-Eddy Simulations, M. K. Osman, D. D. Turner, Thijs Heus, V. Wulfmeyer
Physics Faculty Publications
In previous work, the similarity relationship for the water vapor variance in the interfacial layer (IL) at the top of the convective boundary layer (CBL) was proposed to be proportional to the convective velocity scale and the gradients of the water vapor mixing ratio and the Brunt‐Vaisala frequency in the entrainment zone. In the presence of wind shear in the IL, the similarity relationship was hypothesized to also include a dependence on the gradient Richardson number. Simultaneous measurements of the surface buoyancy flux, wind‐shear profiles from a radar wind profiler, water vapor mixing ratio and temperature measurements and their gradients …
Power-Law Scaling In The Internal Variability Of Cumulus Cloud Size Distributions Due To Subsampling And Spatial Organization, R. A. J. Neggers, P. J. Griewank, Thijs Heus
Power-Law Scaling In The Internal Variability Of Cumulus Cloud Size Distributions Due To Subsampling And Spatial Organization, R. A. J. Neggers, P. J. Griewank, Thijs Heus
Physics Faculty Publications
In this study, the spatial structure of cumulus cloud populations is investigated using three-dimensional snapshots from large-domain LES experiments. The aim is to understand and quantify the internal variability in cloud size distributions due to subsampling effects and spatial organization. A set of idealized shallow cumulus cases is selected with varying degrees of spatial organization, including a slowly organizing marine precipitating case and five more quickly organizing diurnal cases over land. A subdomain analysis is applied, yielding cloud number distributions at sample sizes ranging from severely undersampled to nearly complete. A strong power-law scaling is found in the relation between …
The Second Arm Training And Science Application Event: Training The Next Generation Of Atmospheric Scientists, Virendra P. Ghate, Pavlos Kollias, Susanne Crewell, Ann M. Fridlind, Thijs Heus, Ulrich Löehnert, Maximilian Maahn, Greg M. Mcfarquhar, Dmitri Moisseev, Mariko Oue, Manfred Wendisch, Christopher Williams
The Second Arm Training And Science Application Event: Training The Next Generation Of Atmospheric Scientists, Virendra P. Ghate, Pavlos Kollias, Susanne Crewell, Ann M. Fridlind, Thijs Heus, Ulrich Löehnert, Maximilian Maahn, Greg M. Mcfarquhar, Dmitri Moisseev, Mariko Oue, Manfred Wendisch, Christopher Williams
Physics Faculty Publications
No abstract provided.
A New Research Approach For Observing And Characterizing Land-Atmosphere Feedback, Volker Wulfmeyer, David D. Turner, B. Baker, R. Banta, A. Behrendt, T. Bonin, W. A. Brewer, M. Buban, A. Choukulkar, R. Dumas, R. M. Hardesty, T. Heus, J. Ingwersen, D. Lange, T. R. Lee, S. Metzendorf, S. K. Muppa, T. Meyers, R. Newsom, M. Osman, S. Raasch, J. Santanello, C. Senff, F. Späth, T. Wagner, T. Weckwerth
A New Research Approach For Observing And Characterizing Land-Atmosphere Feedback, Volker Wulfmeyer, David D. Turner, B. Baker, R. Banta, A. Behrendt, T. Bonin, W. A. Brewer, M. Buban, A. Choukulkar, R. Dumas, R. M. Hardesty, T. Heus, J. Ingwersen, D. Lange, T. R. Lee, S. Metzendorf, S. K. Muppa, T. Meyers, R. Newsom, M. Osman, S. Raasch, J. Santanello, C. Senff, F. Späth, T. Wagner, T. Weckwerth
Physics Faculty Publications
No abstract provided.
Entropy Driven Phase Transition In Polymer Gels: Mean Field Theory, Miron Kaufman
Entropy Driven Phase Transition In Polymer Gels: Mean Field Theory, Miron Kaufman
Physics Faculty Publications
We present a mean field model of a gel consisting of P polymers, each of length L and Nz polyfunctional monomers. Each polyfunctional monomer forms z covalent bonds with the 2P bifunctional monomers at the ends of the linear polymers. We find that the entropy dependence on the number of polyfunctional monomers exhibits an abrupt change at Nz = 2P/z due to the saturation of possible crosslinks. This non-analytical dependence of entropy on the number of polyfunctionals generates a first-order phase transition between two gel phases: one poor and the other rich in poly-functional molecules.
Mixing Enhancement In Serpentine Micromixers With A Non-Rectangular Cross-Section, Joshua Clark, Miron Kaufman, Petru S. Fodor
Mixing Enhancement In Serpentine Micromixers With A Non-Rectangular Cross-Section, Joshua Clark, Miron Kaufman, Petru S. Fodor
Physics Faculty Publications
In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement the …
Erosion In Extruder Flows: Analytical And Numerical Study, Miron Kaufman, Petru S. Fodor
Erosion In Extruder Flows: Analytical And Numerical Study, Miron Kaufman, Petru S. Fodor
Physics Faculty Publications
© 2017 Author(s). We consider the erosion of particles (e.g. carbonblack agglomerates) advected by the polymeric flow in a single screw extruder. We assume a particle to be made of primary fragments bound together. In the erosion process a primary fragment breaks out of a given particle. Particles disperse because of the shear stresses imparted by the fluid. The time evolution of the numbers of particles of different sizes is described by the Bateman coupled differential equations developed a century ago to model radioactivity. Using the particle size distribution we compute an entropic fragmentation index which varies from 0 for …
Endothelial Nitric Oxide Synthase Oxygenase On Lipid Nanodiscs: A Nano-Assembly Reflecting Native-Like Function Of Enos, Ghaith Altawallbeh, Mohammad M. Haque, Kiril A. Streletzky, Dennis J. Stuehr, Mekki Bayachou
Endothelial Nitric Oxide Synthase Oxygenase On Lipid Nanodiscs: A Nano-Assembly Reflecting Native-Like Function Of Enos, Ghaith Altawallbeh, Mohammad M. Haque, Kiril A. Streletzky, Dennis J. Stuehr, Mekki Bayachou
Physics Faculty Publications
© 2017 Elsevier Inc. Endothelial nitric oxide synthase (eNOS) is a membrane-anchored enzyme. To highlight the potential role and effect of membrane phospholipids on the structure and activity of eNOS, we have incorporated the recombinant oxygenase subunit of eNOS into lipid nanodiscs. Two different size distribution modes were detected by multi-angle dynamic light scattering both for empty nanodiscs, and nanodiscs-bound eNOSoxy. The calculated hydrodynamic diameter for mode 1 species was 9.0 nm for empty nanodiscs and 9.8 nm for nanodisc bound eNOSoxy. Spectroscopic Griess assay was used to measure the enzymatic activity. Remarkably, the specific activity of nanodisc-bound eNOSoxy is …
Stabilization Of Hypoxia Inducible Factor By Cobalt Chloride Can Alter Renal Epithelial Transport, Subhra Nag, Andrew Resnick
Stabilization Of Hypoxia Inducible Factor By Cobalt Chloride Can Alter Renal Epithelial Transport, Subhra Nag, Andrew Resnick
Physics Faculty Publications
© 2017 The Authors. Given the importance of the transcriptional regulator hypoxia-inducible factor-1 (HIF-1) for adaptive hypoxia responses, we examined the effect of stabilized HIF-1α on renal epithelial permeability and directed sodium transport. This study was motivated by histological analysis of cystic kidneys showing increased expression levels of HIF-1α and HIF-2α. We hypothesize that compression induced localized ischemia-hypoxia of normal epithelia near a cyst leads to local stabilization of HIF-1α, leading to altered transepithelial transport that encourages cyst expansion. We found that stabilized HIF-1α alters both transcellular and paracellular transport through renal epithelial monolayers in a manner consistent with secretory …
Evaluation Of Wrf Scm Simulations Of Stratocumulus-Topped Marine And Coastal Boundary Layers And Improvements To Turbulence And Entrainment Parameterizations, Mohamed S. Ghonima, Handa Yang, Chang Ki Kim, Thijs Heus, Jan Kleissl
Evaluation Of Wrf Scm Simulations Of Stratocumulus-Topped Marine And Coastal Boundary Layers And Improvements To Turbulence And Entrainment Parameterizations, Mohamed S. Ghonima, Handa Yang, Chang Ki Kim, Thijs Heus, Jan Kleissl
Physics Faculty Publications
© 2017. The Authors. Stratocumulus-topped boundary layers (STBLs) are notoriously difficult to parameterize in single-column models due to the strong inversion layer across which entrainment mixing plays an important role in modulating the boundary layer mass, energy, and moisture balances. We compare three different WRF planetary boundary layer (PBL) schemes (Yonsei University, YSU; Asymmetric Convective Model version 2, ACM2; Mellor-Yamada-Nakanishi-Niino, MYNN) against large eddy simulations (LES) to find out that they underestimate entrainment flux in stratocumulus over both ocean and coastal land. Hence, the PBL schemes produce a cooler, moister STBL with higher liquid water content. In order to improve …
Microhh 1.0: A Computational Fluid Dynamics Code For Direct Numerical Simulation And Large-Eddy Simulation Of Atmospheric Boundary Layer Flows, Chiel C. Van Heerwaarden, Bart J.H. Van Stratum, Thijs Heus, Jeremy A. Gibbs, Evgeni Fedorovich, Juan Pedro Mellado
Microhh 1.0: A Computational Fluid Dynamics Code For Direct Numerical Simulation And Large-Eddy Simulation Of Atmospheric Boundary Layer Flows, Chiel C. Van Heerwaarden, Bart J.H. Van Stratum, Thijs Heus, Jeremy A. Gibbs, Evgeni Fedorovich, Juan Pedro Mellado
Physics Faculty Publications
© 2017 Author(s). This paper describes MicroHH 1.0, a new and open-source (www.microhh.org) computational fluid dynamics code for the simulation of turbulent flows in the atmosphere. It is primarily made for direct numerical simulation but also supports large-eddy simulation (LES). The paper covers the description of the governing equations, their numerical implementation, and the parameterizations included in the code. Furthermore, the paper presents the validation of the dynamical core in the form of convergence and conservation tests, and comparison of simulations of channel flows and slope flows against well-established test cases. The full numerical model, including the associated parameterizations for …
Electrostatics At The Molecular Level, Ulrich Zurcher
Electrostatics At The Molecular Level, Ulrich Zurcher
Physics Faculty Publications
In molecular systems, positive and negative charges are separated, making them ideal systems to examine electrostatic interactions. The attractive force between positive and negative charges is balanced by repulsive ‘forces’ that are quantum-mechanical in origin. We introduce an ‘effective’ potential energy that captures the repulsion; it allows us to obtain fairly accurate estimates of the bonding properties of molecular systems. We use units (e.g., kcal mol–1 for energy) that emphasize the relevance of electrostatics to macroscopic behavior.
What Determines The Fate Of Rising Parcels In A Heterogeneous Environment?, Maren Brast, Roel A.J. Neggers, Thijs Heus
What Determines The Fate Of Rising Parcels In A Heterogeneous Environment?, Maren Brast, Roel A.J. Neggers, Thijs Heus
Physics Faculty Publications
© 2016. The Authors. We investigate the potential impact of the local environment on rising parcels in a convective boundary layer. To this end, we use data from an LES simulation of a shallow convective cloud field to feed a parcel model with a range of different local environments, representative of the heterogeneous environment inside a shallow cumulus cloud layer. With this method we can study the statistics of an ensemble of rising parcels, but also the behavior of individual parcels. Through the use of a heterogeneous environment, the interactions between different parcels are indirectly represented. The method, despite its …
Cgils Phase 2 Les Intercomparison Of Response Of Subtropical Marine Low Cloud Regimes To Co2 Quadrupling And A Cmip3 Composite Forcing Change, Peter N. Blossey, Christopher S. Bretherton, Anning Cheng, Satoshi Endo, Thijs Heus, Adrian P. Lock, Johan J. Van Der Dussen
Cgils Phase 2 Les Intercomparison Of Response Of Subtropical Marine Low Cloud Regimes To Co2 Quadrupling And A Cmip3 Composite Forcing Change, Peter N. Blossey, Christopher S. Bretherton, Anning Cheng, Satoshi Endo, Thijs Heus, Adrian P. Lock, Johan J. Van Der Dussen
Physics Faculty Publications
© 2016. The Authors. Phase 1 of the CGILS large-eddy simulation (LES) intercomparison is extended to understand if subtropical marine boundary-layer clouds respond to idealized climate perturbations consistently in six LES models. Here the responses to quadrupled carbon dioxide (“fast adjustment”) and to a composite climate perturbation representative of CMIP3 multimodel mean 2×CO2 near-equilibrium conditions are analyzed. As in Phase 1, the LES is run to equilibrium using specified steady summertime forcings representative of three locations in the Northeast Pacific Ocean in shallow well-mixed stratocumulus, decoupled stratocumulus, and shallow cumulus cloud regimes. The results are generally consistent with a single-LES …
Hif Stabilization Weakens Primary Cilia, Andrew Resnick
Hif Stabilization Weakens Primary Cilia, Andrew Resnick
Physics Faculty Publications
© 2016 Andrew Resnick. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Although solitary or sensory cilia are present in most cells of the body and their existence has been known since the sixties, very little is known about their functions. One suspected function is fluid flow sensing-physical bending of cilia produces an influx of Ca++, which can then result in a variety of activated signaling pathways. Defective cilia and ciliary-associated proteins have been …
Factors Controlling Stratocumulus Cloud Lifetime Over Coastal Land, Mohamed S. Ghonima, Thijs Heus, Joel R. Norris, Jan Kleissl
Factors Controlling Stratocumulus Cloud Lifetime Over Coastal Land, Mohamed S. Ghonima, Thijs Heus, Joel R. Norris, Jan Kleissl
Physics Faculty Publications
The breakup of stratocumulus clouds over coastal land areas is studied using a combination of large-eddy simulations (LESs) and mixed-layer models (MLMs) with a focus on mechanisms regulating the timing of the breakup. In contrast with stratocumulus over ocean, strong sensible heat flux over land prevents the cloud layer from decoupling during day. As the cloud thins during day, turbulence generated by surface flux becomes larger than turbulence generated by longwave cooling across the cloud layer. To capture this shift in turbulence generation in the MLM, an existing entrainment parameterization is extended. The MLM is able to mimic cloud evolution …
Consequences Of The Angular Spectrum Decomposition Of A Focused Beam, Including Slower Than C Beam Propagation, Gérard Gouesbet, James A. Lock
Consequences Of The Angular Spectrum Decomposition Of A Focused Beam, Including Slower Than C Beam Propagation, Gérard Gouesbet, James A. Lock
Physics Faculty Publications
When dealing with light scattering and propagation of an electromagnetic beam, there are essentially two kinds of expansions which have been used to describe the incident beam (i) a discrete expansion involving beam shape coefficients and (ii) a continuous expansion in terms of an angular spectrum of plane waves. In this paper, we demonstrate that the angular spectrum decomposition readily leads to two important consequences, (i) laser light beams travel in free space with an effective velocity that is smaller than the speed of light c, and (ii) the optical theorem does not hold for arbitrary shaped beams, both …
First-Principles Definition And Measurement Of Planetary Electromagnetic-Energy Budget, Michael I. Mishchenko, James A. Lock, Andrew A. Lacis, Larry D. Travis, Brian Cairns
First-Principles Definition And Measurement Of Planetary Electromagnetic-Energy Budget, Michael I. Mishchenko, James A. Lock, Andrew A. Lacis, Larry D. Travis, Brian Cairns
Physics Faculty Publications
The imperative to quantify the Earths electromagnetic-energy budget with an extremely high accuracy has been widely recognized but has never been formulated in the framework of fundamental physics. In this paper we give a first-principles definition of the planetary electromagnetic-energy budget using the Poynting- vector formalism and discuss how it can, in principle, be measured. Our derivation is based on an absolute minimum of theoretical assumptions, is free of outdated notions of phenomenological radiometry, and naturally leads to the conceptual formulation of an instrument called the double hemispherical cavity radiometer (DHCR). The practical measurement of the planetary energy budget would …
Large-Eddy Simulation Of The Transient And Near-Equilibrium Behavior Of Precipitating Shallow Convection, Axel Seifert, Thijs Heus, Robert Pincus, Bjorn Stevens
Large-Eddy Simulation Of The Transient And Near-Equilibrium Behavior Of Precipitating Shallow Convection, Axel Seifert, Thijs Heus, Robert Pincus, Bjorn Stevens
Physics Faculty Publications
Large-eddy simulation is used to study the sensitivity of trade wind cumulus clouds to perturbations in cloud droplet number concentrations. We find that the trade wind cumulus system approaches a radiative-convective equilibrium state, modified by net warming and drying from imposed large-scale advective forcing. The system requires several days to reach equilibrium when cooling rates are specified but much less time, and with less sensitivity to cloud droplet number density, when radiation depends realistically on the vertical distribution of water vapor. The transient behavior and the properties of the near-equilibrium cloud field depend on the microphysical state and therefore on …
Overlap Statistics Of Shallow Boundary Layer Clouds: Comparing Ground-Based Observations With Large-Eddy Simulations, G. Corbetta, E. Orlandi, Thijs Heus, Roel Neggers, S. Crewell
Overlap Statistics Of Shallow Boundary Layer Clouds: Comparing Ground-Based Observations With Large-Eddy Simulations, G. Corbetta, E. Orlandi, Thijs Heus, Roel Neggers, S. Crewell
Physics Faculty Publications
High-resolution ground-based measurements are used to assess the realism of fine-scale numerical simulations of shallow cumulus cloud fields. The overlap statistics of cumuli as produced by large-eddy simulations (LES) are confronted with Cloudnet data sets at the Jülich Observatory for Cloud Evolution. The Cloudnet pixel is small enough to detect cumuliform cloud overlap. Cloud fraction masks are derived for five different cases, using gridded time-height data sets at various temporal and vertical resolutions. The overlap ratio (R), i.e., the ratio between cloud fraction by volume and by area, is studied as a function of the vertical resolution. Good agreement is …
Mechanical Properties Of A Primary Cilium As Measured By Resonant Oscillation, Andrew Resnick
Mechanical Properties Of A Primary Cilium As Measured By Resonant Oscillation, Andrew Resnick
Physics Faculty Publications
Primary cilia are ubiquitous mammalian cellular substructures implicated in an ever-increasing number of regulatory pathways. The well-established ciliary hypothesis states that physical bending of the cilium (for example, due to fluid flow) initiates signaling cascades, yet the mechanical properties of the cilium remain incompletely measured, resulting in confusion regarding the biological significance of flow-induced ciliary mechanotransduction. In this work we measure the mechanical properties of a primary cilium by using an optical trap to induce resonant oscillation of the structure. Our data indicate 1) the primary cilium is not a simple cantilevered beam; 2) the base of the cilium may …