scholarly journals A Three-Dimensional Mechanistic Model of Prorocentrum minimum Blooms in Eutrophic Chesapeake Bays

2021 ◽  
pp. 144528
Author(s):  
Fan Zhang ◽  
Ming Li ◽  
Patricia M. Glibert ◽  
So Hyun (Sophia) Ahn
Keyword(s):  
Mechanistic Model ◽  
Three Dimensional ◽  
Prorocentrum Minimum

Prediction of Electrical Properties of Plain-Weave Fabric Composites for Printed Wiring Board Design

1993 ◽  
Vol 115 (2) ◽  
pp. 219-224 ◽  
Author(s):  
R. K. Agarwal ◽  
A. Dasgupta
Keyword(s):  
Dielectric Constant ◽  
Loss Tangent ◽  
Effective Properties ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Unit Cell ◽  
Woven Fabric ◽  
Effective Dielectric Constant ◽  
Low Loss ◽  
Dielectric Constant And Loss

A mechanistic model is presented for predicting the effective dielectric constant and loss tangent of woven-fabric reinforced composites with low-loss constituents. A two-scale asymptotic homogenization scheme is used to predict the orthotropic effective properties. A three-dimensional unit-cell enclosing the characteristic periodic repeat pattern in the fabric weave is isolated and modeled mathematically. Electrostatic boundary value problems (BVP’s) are formulated in the unit-cell and are solved analytically to predict effective dielectric constant of the composite, using three-dimensional series-parallel reactance nets. Results are also verified numerically, using finite element methods. The effective dielectric constant and the effective loss tangent are then obtained, analogous to mechanical viscoelastic problems for low-loss materials. The predicted dielectric constant and loss tangent are compared with experimental results for E-glass/epoxy laminates. Frequency dependence of the effective dielectric constant and loss tangent is obtained from the corresponding behavior of the constituent materials. Trade-off studies are conducted to investigate the effect of the constituent material properties on orthotropic effective dielectric permittivity.

Air mass exchange across the polar vortex edge during a simulated major stratospheric warming

1995 ◽  
Vol 13 (7) ◽  
pp. 745-756 ◽  
Author(s):  
G. Günther ◽  
M. Dameris
Keyword(s):  
Cross Sections ◽  
Middle Atmosphere ◽  
Model Simulation ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Polar Vortex ◽  
Small Scale ◽  
Stratospheric Warming ◽  
Air Masses ◽  
Physical And Chemical

Abstract. The dynamics of the polar vortex in winter and spring play an important role in explaining observed low ozone values. A quantification of physical and chemical processes is necessary to obtain information about natural and anthropogenic causes of fluctuations of ozone. This paper aims to contribute to answering the question of how permeable the polar vortex is. The transport into and out of the vortex ("degree of isolation") remains the subject of considerable debate. Based on the results of a three-dimensional mechanistic model of the middle atmosphere, the possibility of exchange of air masses across the polar vortex edge is investigated. Additionally the horizontal and vertical structure of the polar vortex is examined. The model simulation used for this study is related to the major stratospheric warming observed in February 1989. The model results show fair agreement with observed features of the major warming of 1989. Complex structures of the simulated polar vortex are illustrated by horizontal and vertical cross sections of potential vorticity and inert tracer. A three-dimensional view of the polar vortex enables a description of the vortex as a whole. During the simulation two vortices and an anticyclone, grouped together in a very stable tripolar structure, and a weaker, more amorphous anticyclone are formed. This leads to the generation of small-scale features. The results also indicate that the permeability of the vortex edges is low because the interior of the vortices remain isolated during the simulation.

Simulations of Dynamics and Transport during the September 2002 Antarctic Major Warming

2005 ◽  
Vol 62 (3) ◽  
pp. 690-707 ◽  
Author(s):  
Gloria L. Manney ◽  
Joseph L. Sabutis ◽  
Douglas R. Allen ◽  
William A. Lahoz ◽  
Adam A. Scaife ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Model Simulation ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Lower Boundary ◽  
High Sensitivity ◽  
Latitudinal Gradients ◽  
Trace Gas ◽  
High Latitudes ◽  
Vortex Split

Abstract A mechanistic model simulation initialized on 14 September 2002, forced by 100-hPa geopotential heights from Met Office analyses, reproduced the dynamical features of the 2002 Antarctic major warming. The vortex split on ∼25 September; recovery after the warming, westward and equatorward tilting vortices, and strong baroclinic zones in temperature associated with a dipole pattern of upward and downward vertical velocities were all captured in the simulation. Model results and analyses show a pattern of strong upward wave propagation throughout the warming, with zonal wind deceleration throughout the stratosphere at high latitudes before the vortex split, continuing in the middle and upper stratosphere and spreading to lower latitudes after the split. Three-dimensional Eliassen–Palm fluxes show the largest upward and poleward wave propagation in the 0°–90°E sector prior to the vortex split (coincident with the location of strongest cyclogenesis at the model’s lower boundary), with an additional region of strong upward propagation developing near 180°–270°E. These characteristics are similar to those of Arctic wave-2 major warmings, except that during this warming, the vortex did not split below ∼600 K. The effects of poleward transport and mixing dominate modeled trace gas evolution through most of the mid- to high-latitude stratosphere, with a core region in the lower-stratospheric vortex where enhanced descent dominates and the vortex remains isolated. Strongly tilted vortices led to low-latitude air overlying vortex air, resulting in highly unusual trace gas profiles. Simulations driven with several meteorological datasets reproduced the major warming, but in others, stronger latitudinal gradients at high latitudes at the model boundary resulted in simulations without a complete vortex split in the midstratosphere. Numerous tests indicate very high sensitivity to the boundary fields, especially the wave-2 amplitude. Major warmings occurred for initial fields with stronger winds and larger vortices, but not smaller vortices, consistent with the initiation of wind deceleration by upward-propagating waves near the poleward edge of the region where wave 2 can propagate above the jet core. Thus, given the observed 100-hPa boundary forcing, stratospheric preconditioning is not needed to reproduce a major warming similar to that observed. The anomalously strong forcing in the lower stratosphere can be viewed as the primary direct cause of the major warming.

A Mechanistic Model for Predicting Subcooled Boiling Flow

2003 ◽  
Author(s):  
G. H. Yeoh ◽  
J. Y. Tu
Keyword(s):  
Void Fraction ◽  
Liquid Velocity ◽  
Fluid Model ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Annular Channel ◽  
Heat Fluxes ◽  
Group Model ◽  
Subcooled Boiling ◽  
Boiling Flow

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapor velocity. Work is in progress to circumvent the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation.

Ensemble modeling of E. coli in the Charles River, Boston, Massachusetts, USA

2007 ◽  
Vol 56 (6) ◽  
pp. 39-46 ◽  
Author(s):  
F.L. Hellweger
Keyword(s):  
Time Series ◽  
Error Rate ◽  
Mechanistic Model ◽  
Total Error ◽  
Geometric Mean ◽  
Three Dimensional ◽  
Ensemble Modeling ◽  
Quality Model ◽  
E Coli ◽  
Total Error Rate

A case study of ensemble modeling of Escherichia coli (E. coli) densities in surface waters in the context of public health risk prediction is presented. The output of two different models, mechanistic and empirical, are combined and compared to data. The mechanistic model is a high-resolution, time-variable, three-dimensional coupled hydrodynamic and water quality model. It generally reproduces the mechanisms of E. coli fate and transport in the river, including the presence and absence of a plume in the study area under similar input, but different hydrodynamic conditions caused by the operation of a downstream dam and wind. At the time series station, the model has a root mean square error (RMSE) of 370 CFU/100mL, a total error rate (with respect to the EPA-recommended single sample criteria value of 235 CFU/100mL) (TER) of 15% and negative error rate (NER) of 30%. The empirical model is based on multiple linear regression using the forcing functions of the mechanistic model as independent variables. It has better overall performance (at the time series station), due to a strong correlation of E. coli density with upstream inflow for this time period (RMSE =200 CFU/100mL, TER =13%, NER =1.6%). However, the model is mechanistically incorrect in that it predicts decreasing densities with increasing Combined Sewer Overflow (CSO) input. The two models are fundamentally different and their errors are uncorrelated (R2 =0.02), which motivates their combination in an ensemble. Two combination approaches, a geometric mean ensemble (GME) and an “either exceeds” ensemble (EEE), are explored. The GME model outperforms the mechanistic and empirical models in terms of RMSE (190 CFU/100mL) and TER (11%), but has a higher NER (23%). The EEE has relatively high TER (16%), but low NER (0.8%) and may be the best method for a conservative prediction. The study demonstrates the potential utility of ensemble modeling for pathogen indicators, but significant further research is needed to establish the approach for the Charles River, as outlined in the paper.

Validation of Equilibrium-Based, One-Dimensional, Two-Phase Pipe Flow Models With Transient, Three-Dimensional, CFD Simulations for Horizontal Flows

2015 ◽  
Author(s):  
Florentina Popa ◽  
Andrey Filippov ◽  
Brent C. Houchens
Keyword(s):  
Pipe Flow ◽  
Mechanistic Model ◽  
Three Dimensional ◽  
Cfd Simulations ◽  
Two Phase ◽  
Horizontal Pipe ◽  
One Dimensional ◽  
Flow Models ◽  
Horizontal Flows ◽  
Closure Relations

One-dimensional (1D), equilibrium-based mechanistic model predictions are compared to three-dimensional (3D) transient computational fluid dynamics results for horizontal two-phase, gas-liquid pipe flow. The 3D regions of interest include both those expected to be in equilibrium conditions and those where transitions between flow regimes occur. Equilibrium simulations, such as those for stratified flow in a horizontal pipe, allow crucial validation of the equilibrium-based closure relations by means of numerical experiments. In the transitional regions, fully 3D, time-dependent numerical simulations provide a means to estimate the error in the equilibrium-based models and suggest how reasonable approximations can be made in these regions.

scholarly journals Nonmechanical parfocal and autofocus features based on wave propagation distribution in lensfree holographic microscopy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Agus Budi Dharmawan ◽  
Shinta Mariana ◽  
Gregor Scholz ◽  
Philipp Hörmann ◽  
Torben Schulze ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Moving Objects ◽  
Light Emitting Diode ◽  
Three Dimensional ◽  
Prorocentrum Minimum ◽  
Distribution Analysis ◽  
Holographic Microscopy ◽  
3D Information ◽  
Point Light

AbstractPerforming long-term cell observations is a non-trivial task for conventional optical microscopy, since it is usually not compatible with environments of an incubator and its temperature and humidity requirements. Lensless holographic microscopy, being entirely based on semiconductor chips without lenses and without any moving parts, has proven to be a very interesting alternative to conventional microscopy. Here, we report on the integration of a computational parfocal feature, which operates based on wave propagation distribution analysis, to perform a fast autofocusing process. This unique non-mechanical focusing approach was implemented to keep the imaged object staying in-focus during continuous long-term and real-time recordings. A light-emitting diode (LED) combined with pinhole setup was used to realize a point light source, leading to a resolution down to 2.76 μm. Our approach delivers not only in-focus sharp images of dynamic cells, but also three-dimensional (3D) information on their (x, y, z)-positions. System reliability tests were conducted inside a sealed incubator to monitor cultures of three different biological living cells (i.e., MIN6, neuroblastoma (SH-SY5Y), and Prorocentrum minimum). Altogether, this autofocusing framework enables new opportunities for highly integrated microscopic imaging and dynamic tracking of moving objects in harsh environments with large sample areas.

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