Drift and Trapping in Biased Diffusion on Disordered Lattices

We re-examine the theory of transition from drift to no-drift in biased diffusion on percolation networks. We argue that for the bias field B equal to the critical value Bc, the average velocity at large times t decreases to zero as 1/ log (t). For B<Bc, the time required to reach the steady-state velocity diverges as exp ( const /|Bc-B|). We propose an extrapolation form that describes the behavior of average velocity as a function of time at intermediate time scales. This form is found to have a very good agreement with the results of extensive Monte Carlo simulations on a three-dimensional site-percolation network and moderate bias.

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On the stability for three-dimensional disturbances of viscous fluid flow between parallel walls

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1933.0193 ◽

1933 ◽

Vol 142 (847) ◽

pp. 621-628 ◽

Cited By ~ 458

Keyword(s):

Reynolds Number ◽

Three Dimensional ◽

Finite Size ◽

Critical Value ◽

The Stability ◽

The One ◽

Von Mises ◽

Shearing Motion ◽

Determining Factor ◽

Good Agreement

The turbulence problem is still unsolved, through a number of valuable papers have been published on it comparatively recently. But, since Hopf and von Mises proved that uniform shearing motion between two parallel planes was stable for infinitesimal disturbances but unstable for disturbances of a finite size has become more and more widely held. Von mises suggested that the reoughness of the walls might be the determining factor, but the experiments of Schiller have shown that the degree of roughness of the walls is of negligible influence on the critical value of Reynold's number. He concluded that the breakdown of laminar flow depended primarily on the size of the initial disturbance, in agreement eith Osborne Reynold's view. Important papers have been published by Noether and Tollmien, whose conclusions are in contradiction to one another. On the one hand, Noether, by a formal investigation of the asymptotic solutions of the equation governing the two-dimensional disturbances of flow between parallel walls, claims to have proved that all velocity profiles are stable for all values of Reynolds' number. On the other hand, Tollmien has determined a critical value of Reynolds' number for the flow past a flat plate placed edgeways to the stream. This value is in good agreement with the experimental results. There are, however, certain points in his analysis which are not clear and it would be useful to know if the method gave results in agreement with those derived more strictly.

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Ionospheric conductance distribution and MHD wave structure: observation and model

Annales Geophysicae ◽

10.1007/s00585-998-0140-8 ◽

1998 ◽

Vol 16 (2) ◽

pp. 140-147 ◽

Cited By ~ 14

Author(s):

F. Budnik ◽

M. Stellmacher ◽

K.-H. Glassmeier ◽

S. C. Buchert

Keyword(s):

Three Dimensional ◽

Wave Structure ◽

Critical Value ◽

Auroral Oval ◽

Mhd Waves ◽

Magnetohydrodynamic Waves ◽

Structure Observation ◽

Mhd Waves And Instabilities ◽

Conductance Distribution ◽

Good Agreement

Abstract. The ionosphere influences magnetohydrodynamic waves in the magnetosphere by damping because of Joule heating and by varying the wave structure itself. There are different eigenvalues and eigensolutions of the three dimensional toroidal wave equation if the height integrated Pedersen conductivity exceeds a critical value, namely the wave conductance of the magnetosphere. As a result a jump in frequency can be observed in ULF pulsation records. This effect mainly occurs in regions with gradients in the Pedersen conductances, as in the auroral oval or the dawn and dusk areas. A pulsation event recorded by the geostationary GOES-6 satellite is presented. We explain the observed change in frequency as a change in the wave structure while crossing the terminator. Furthermore, selected results of numerical simulations in a dipole magnetosphere with realistic ionospheric conditions are discussed. These are in good agreement with the observational data.Key words. Ionosphere · (Ionosphere · magnetosphere interactions) · Magnetospheric physics · Magnetosphere · ionosphere interactions · MHD waves and instabilities.

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A Free Energy Perturbation Approach to Estimate the Intrinsic Solubilities of Drug-like Small Molecules

10.26434/chemrxiv.10263077.v1 ◽

2019 ◽

Author(s):

Sayan Mondal ◽

Gary Tresadern ◽

Jeremy Greenwood ◽

Byungchan Kim ◽

Joe Kaus ◽

...

Keyword(s):

Solid State ◽

Small Molecules ◽

Three Dimensional ◽

Aqueous Solubility ◽

Computational Approach ◽

Free Energy Perturbation ◽

Perturbation Approach ◽

Energy Perturbation ◽

State Form ◽

Good Agreement

<p>Optimizing the solubility of small molecules is important in a wide variety of contexts, including in drug discovery where the optimization of aqueous solubility is often crucial to achieve oral bioavailability. In such a context, solubility optimization cannot be successfully pursued by indiscriminate increases in polarity, which would likely reduce permeability and potency. Moreover, increasing polarity may not even improve solubility itself in many cases, if it stabilizes the solid-state form. Here we present a novel physics-based approach to predict the solubility of small molecules, that takes into account three-dimensional solid-state characteristics in addition to polarity. The calculated solubilities are in good agreement with experimental solubilities taken both from the literature as well as from several active pharmaceutical discovery projects. This computational approach enables strategies to optimize solubility by disrupting the three-dimensional solid-state packing of novel chemical matter, illustrated here for an active medicinal chemistry campaign.</p>

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A Numerical Study of Sub-Millisecond Integrated Mix-and-Inject Microfluidic Devices for Sample Delivery at Synchrotron and XFELs

Applied Sciences ◽

10.3390/app11083404 ◽

2021 ◽

Vol 11 (8) ◽

pp. 3404

Author(s):

Majid Hejazian ◽

Eugeniu Balaur ◽

Brian Abbey

Keyword(s):

Molecular Dynamics ◽

Flow Rate ◽

Numerical Study ◽

Three Dimensional ◽

Microfluidic Devices ◽

Liquid Jets ◽

Mixing Efficiency ◽

X Ray Diffraction ◽

Cross Sectional ◽

Time Required

Microfluidic devices which integrate both rapid mixing and liquid jetting for sample delivery are an emerging solution for studying molecular dynamics via X-ray diffraction. Here we use finite element modelling to investigate the efficiency and time-resolution achievable using microfluidic mixers within the parameter range required for producing stable liquid jets. Three-dimensional simulations, validated by experimental data, are used to determine the velocity and concentration distribution within these devices. The results show that by adopting a serpentine geometry, it is possible to induce chaotic mixing, which effectively reduces the time required to achieve a homogeneous mixture for sample delivery. Further, we investigate the effect of flow rate and the mixer microchannel size on the mixing efficiency and minimum time required for complete mixing of the two solutions whilst maintaining a stable jet. In general, we find that the smaller the cross-sectional area of the mixer microchannel, the shorter the time needed to achieve homogeneous mixing for a given flow rate. The results of these simulations will form the basis for optimised designs enabling the study of molecular dynamics occurring on millisecond timescales using integrated mix-and-inject microfluidic devices.

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Simulation of Thermal and Electric Field Distribution in Packaged Sausages Heated in a Stationary Versus a Rotating Microwave Oven

Foods ◽

10.3390/foods10071622 ◽

2021 ◽

Vol 10 (7) ◽

pp. 1622

Author(s):

Wipawee Tepnatim ◽

Witchuda Daud ◽

Pitiya Kamonpatana

Keyword(s):

Temperature Distribution ◽

Electric Field ◽

Three Dimensional ◽

Development Stage ◽

Microwave Oven ◽

Computational Time ◽

Plastic Package ◽

Heating Uniformity ◽

The Cost ◽

Good Agreement

The microwave oven has become a standard appliance to reheat or cook meals in households and convenience stores. However, the main problem of microwave heating is the non-uniform temperature distribution, which may affect food quality and health safety. A three-dimensional mathematical model was developed to simulate the temperature distribution of four ready-to-eat sausages in a plastic package in a stationary versus a rotating microwave oven, and the model was validated experimentally. COMSOL software was applied to predict sausage temperatures at different orientations for the stationary microwave model, whereas COMSOL and COMSOL in combination with MATLAB software were used for a rotating microwave model. A sausage orientation at 135° with the waveguide was similar to that using the rotating microwave model regarding uniform thermal and electric field distributions. Both rotating models provided good agreement between the predicted and actual values and had greater precision than the stationary model. In addition, the computational time using COMSOL in combination with MATLAB was reduced by 60% compared to COMSOL alone. Consequently, the models could assist food producers and associations in designing packaging materials to prevent leakage of the packaging compound, developing new products and applications to improve product heating uniformity, and reducing the cost and time of the research and development stage.

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3D-Volume Rendering of the Pelvis with Emphasis on Paraurethral Structures Based on MRI Scans and Comparisons between 3D Slicer and OsiriX®

Journal of Medical Systems ◽

10.1007/s10916-020-01695-3 ◽

2021 ◽

Vol 45 (3) ◽

Author(s):

C. M. Durnea ◽

S. Siddiqi ◽

D. Nazarian ◽

G. Munneke ◽

P. M. Sedgwick ◽

...

Keyword(s):

Image Processing ◽

Secondary Analysis ◽

Three Dimensional ◽

3D Models ◽

Clinical Role ◽

Cross Sectional ◽

3D Slicer ◽

Mri Scans ◽

3D Volume ◽

Good Agreement

AbstractThe feasibility of rendering three dimensional (3D) pelvic models of vaginal, urethral and paraurethral lesions from 2D MRI has been demonstrated previously. To quantitatively compare 3D models using two different image processing applications: 3D Slicer and OsiriX. Secondary analysis and processing of five MRI scan based image sets from female patients aged 29–43 years old with vaginal or paraurethral lesions. Cross sectional image sets were used to create 3D models of the pelvic structures with 3D Slicer and OsiriX image processing applications. The linear dimensions of the models created using the two different methods were compared using Bland-Altman plots. The comparisons demonstrated good agreement between measurements from the two applications. The two data sets obtained from different image processing methods demonstrated good agreement. Both 3D Slicer and OsiriX can be used interchangeably and produce almost similar results. The clinical role of this investigation modality remains to be further evaluated.

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A Transient Simulation of Heated Soil Vapor Extraction System

Volume 1 ◽

10.1115/ht-fed2004-56425 ◽

2004 ◽

Cited By ~ 1

Author(s):

T. Roy ◽

R. S. Amano ◽

J. Jatkar

Keyword(s):

Heat Source ◽

Three Dimensional ◽

Soil Vapor Extraction ◽

Extraction System ◽

Vapor Extraction ◽

Predictive Tool ◽

Heating Source ◽

Time Required ◽

Heated Soil ◽

Remediation Process

Soil remediation process by heated soil vapor extraction system has drawn considerably attention for the last few years. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. Our present study is concentrated on modeling one transient Heated Soil Vapor Extraction System and predicting the time required for effective remediation. The process developed by Advanced Remedial Technology, consists of a heating source pipe and the extraction well embedded in the soil. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. A three-dimensional meshed geometry was developed using gambit. Different boundary conditions were used for heating and suction well and for other boundaries. Concentrations of different chemicals were collected from the actual site and this data was used as an initial condition. The analysis uses the species transport and discrete phase modeling to predict the time required to clean the soil under specific conditions. This analysis could be used for predicting the changes of chemical concentrations in the soil during the remediation process. This will give us more insight to the physical phenomena and serve as a numerical predictive tool for more efficient process.

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Experimental and Numerical Investigation about Small Clearance Journal Bearings under Static Load Conditions

Advances in Tribology ◽

10.1155/2020/8844879 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Carlo Alberto Niccolini Marmont Du Haut Champ ◽

Fabrizio Stefani ◽

Paolo Silvestri

Keyword(s):

Three Dimensional ◽

Journal Bearings ◽

Radial Clearance ◽

Small Scale ◽

Test Rig ◽

Small Clearance ◽

Dimensional Simulation ◽

Dynamic Loading Conditions ◽

Static And Dynamic Loading ◽

Good Agreement

The aim of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., microgas turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed and the performance of its bearings was investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial rotor kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for thermoelasto-hydrodynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this paper, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RKs, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results.

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The Reduction of Bias Error in Transfer Function Estimates Using FFT-Based Analyzers

Journal of Vibration and Acoustics ◽

10.1115/1.3269148 ◽

1984 ◽

Vol 106 (1) ◽

pp. 29-35 ◽

Cited By ~ 7

Author(s):

P. Cawley

Keyword(s):

Transfer Function ◽

Random Excitation ◽

Analogue Computer ◽

Bias Error ◽

Testing Time ◽

Theoretical Predictions ◽

Set Up ◽

Modal Mass ◽

Time Required ◽

Good Agreement

The susceptibility to bias error of two methods for computing transfer (frequency response) functions from spectra produced by FFT-based analyzers using random excitation has been investigated. Results from tests with an FFT analyzer on a single degree-of-freedom system set up on an analogue computer show good agreement with the theoretical predictions. It has been shown that, around resonance, the bias error in the transfer function estimate H2 (Syy/Sxy*) is considerably less than that in the more commonly used estimate, H1 (Sxy/Sxx). The record length, and hence the testing time, required for a given accuracy is reduced by over 50 percent if the H2 calculation procedure is used. The analysis has also shown that if shaker excitation is used on lightly damped structures with low modal mass, it is important to minimize the mass of the force gage and the moving element of the shaker.

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A NEW APPROACH TO DYNAMIC FINITE-SIZE SCALING

International Journal of Modern Physics C ◽

10.1142/s012918310300508x ◽

2003 ◽

Vol 14 (07) ◽

pp. 945-954 ◽

Cited By ~ 1

Author(s):

MEHMET DİLAVER ◽

SEMRA GÜNDÜÇ ◽

MERAL AYDIN ◽

YİĞİT GÜNDÜÇ

Keyword(s):

Three Dimensional ◽

Finite Size ◽

Taylor Series Expansion ◽

Scaling Behavior ◽

Dynamic Scaling ◽

Finite Size Scaling ◽

New Approach ◽

Size Scaling ◽

Dynamic Exponent ◽

Good Agreement

In this work we have considered the Taylor series expansion of the dynamic scaling relation of the magnetization with respect to small initial magnetization values in order to study the dynamic scaling behavior of two- and three-dimensional Ising models. We have used the literature values of the critical exponents and of the new dynamic exponent x0 to observe the dynamic finite-size scaling behavior of the time evolution of the magnetization during early stages of the Monte Carlo simulation. For the three-dimensional Ising model we have also presented that this method opens the possibility of calculating z and x0 separately. Our results show good agreement with the literature values. Measurements done on lattices with different sizes seem to give very good scaling.

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