scholarly journals Chirality-induced bacterial rheotaxis in bulk shear flows

2020 ◽  
Vol 6 (28) ◽  
pp. eabb2012 ◽  
Author(s):  
Guangyin Jing ◽  
Andreas Zöttl ◽  
Éric Clément ◽  
Anke Lindner
Keyword(s):  
Theoretical Analysis ◽  
Scaling Laws ◽  
Shear Flows ◽  
Kinematic Model ◽  
Marginal Stability ◽  
Complex Environments ◽  
Shear Rates ◽  
Spatially Resolved ◽  
Swimming Bacteria ◽  
Reorientation Dynamics

Interaction of swimming bacteria with flows controls their ability to explore complex environments, crucial to many societal and environmental challenges and relevant for microfluidic applications such as cell sorting. Combining experimental, numerical, and theoretical analysis, we present a comprehensive study of the transport of motile bacteria in shear flows. Experimentally, we obtain with high accuracy and, for a large range of flow rates, the spatially resolved velocity and orientation distributions. They are in excellent agreement with the simulations of a kinematic model accounting for stochastic and microhydrodynamic properties and, in particular, the flagella chirality. Theoretical analysis reveals the scaling laws behind the average rheotactic velocity at moderate shear rates using a chirality parameter and explains the reorientation dynamics leading to saturation at large shear rates from the marginal stability of a fixed point. Our findings constitute a full understanding of the physical mechanisms and relevant parameters of bacteria bulk rheotaxis.

scholarly journals Performance Analysis of Switched Control Systems Under Common-source Digital Upsets Modeled by MDHMM

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Rui Wang ◽  
Yanxiao Li ◽  
Hui Sun ◽  
Youmin Zhang ◽  
Yigang Sun
Keyword(s):  
Theoretical Analysis ◽  
Control Systems ◽  
Systems Design ◽  
Performance Degradation ◽  
Common Source ◽  
Complex Environments ◽  
Analysis Model ◽  
Redundant Design ◽  
Control Systems Design ◽  
The Relationship

This paper proposes the theoretical model to analyze the performance degradation of control systems subject to common-source digital upsets. In this paper, a multidimensional hidden Markov model (MDHMM) is used to characterize the correlated upsets and reveals the relationship between complex environments and stochastic random digital upsets injected into the control systems. These digital upsets coming from artificial complex environments are operated on distributed redundant processing controllers. Furthermore, this paper develops the theoretical analysis model for performance degradation of control systems under common-source digital interferences modeled by MDHMM. Theoretical estimations for different redundant configurations are analyzed. Then corresponding simulation verifications for a specific control system are also conducted in details and compared with the theoretical analysis results. These analyses can help to select an optimal redundant design and provide an example for control systems design. This analysis also helps to balance the performance of system, reliability of system, and costs of system design in applications.

A PEEM STUDY OF SMALL AGGLOMERATES OF COLLOIDAL IRON OXIDE NANOCRYSTALS

2002 ◽  
Vol 09 (01) ◽  
pp. 437-440 ◽  
Author(s):  
F. NOLTING ◽  
J. LÜNING ◽  
J. ROCKENBERGER ◽  
J. HU ◽  
A. P. ALIVISATOS
Keyword(s):  
Iron Oxide ◽  
Absorption Spectra ◽  
Scaling Laws ◽  
Average Diameter ◽  
Colloidal Iron ◽  
X Ray ◽  
Spatially Resolved ◽  
Particle Size And Shape ◽  
Colloidal Iron Oxide ◽  
X Ray Absorption

A common limitation in nanostructure research is often the requirement to perform experiments on ensembles of nanoparticles, therefore averaging over inherent distributions with respect to particle size and shape, chemical composition, crystallinity and defect structure. This limitation can be overcome by studying the properties of a single nanostructure individually, which will allow one to truly correlate scaling laws of material properties with changes in size. Here we report the first experiments to explore the feasibility of spectromicroscopy using a photoemission electron microscope (PEEM) to record the X-ray absorption spectra of single nanocrystals. Colloidal iron oxide nanocrystals with an average diameter and standard deviation of 13 nm and 2 nm, respectively, were deposited on graphite (HOPG) forming small islands of agglomerated γ- Fe 2 O 3 nanocrystals (4–30 particles) as determined by scanning electron microscopy. Spatially resolved soft X-ray absorption spectra at the Fe L 3,2 edges of these individual islands were recorded with the PEEM2 instrument of the Advanced Light Source (ALS).

Quantitative characterization of postnatal growth trends in proximal pulmonary arteries in rats by phase-contrast magnetic resonance imaging

2011 ◽  
Vol 301 (3) ◽  
pp. L368-L379 ◽  
Author(s):  
Hedi Razavi ◽  
Shahrzad Y. Zarafshar ◽  
Hirofumi Sawada ◽  
Charles A. Taylor ◽  
Jeffrey A. Feinstein
Keyword(s):  
Phase Contrast ◽  
Scaling Laws ◽  
Main Pulmonary Artery ◽  
Pulmonary Arteries ◽  
Left Lung ◽  
Mean Flow ◽  
Phase Contrast Mri ◽  
Arterial Distensibility ◽  
Growth Trends ◽  
Shear Rates

Malformations of the pulmonary arteries can increase right heart workload and result in morbidity, heart failure, and death. With the increased use of murine models to study these malformations, there is a pressing need for an accurate and noninvasive experimental technique that is capable of characterizing pulmonary arterial hemodynamics in these animals. We describe the growth trends of pulmonary arteries in 13 male Sprague-Dawley rats at 20, 36, 52, 100, and 160 days of age with the introduction of phase-contrast MRI as such a technique. PCMRI results correlated closely with cardiac output measurements by ultrasound echocardiography and with fluorescent microspheres in right-left lung flow split (flow partition). Mean flow, average cross-sectional area, distensibility, and shear rates for the right and left pulmonary arteries (RPA and LPA) were calculated. The RPA was larger and received more flow at all times than the LPA ( P < 0.0001). Right-left flow split did not change significantly with age, and arterial distensibility was not significantly different between RPA and LPA, except at 160 days ( P < 0.01). Shear rates were much higher for the LPA than the RPA ( P < 0.0001) throughout development. The RPA and LPA showed different structure-function relationships but obeyed similar allometric scaling laws, with scaling exponents comparable to those of the main pulmonary artery. This study is the first to quantitatively describe changes in RPA and LPA flows and sizes with development and to apply phase-contrast MRI techniques to pulmonary arteries in rats.

scholarly journals Deviations from Taylor’s frozen hypothesis and scaling laws in inhomogeneous jet flows

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Sukesh Roy ◽  
Joseph D. Miller ◽  
Gemunu H. Gunaratne
Keyword(s):  
High Resolution ◽  
Turbulent Flows ◽  
Scaling Laws ◽  
Flow Direction ◽  
Laser System ◽  
Rapid Evolution ◽  
Spectral Energy ◽  
Jet Flows ◽  
Small Scale ◽  
Spatially Resolved

AbstractDifficulties in studying turbulent flows stem, in part, from the lack of high-frequency, high-resolution measurements to interrogate small-scale structures and their rapid evolution. We present analysis of data from experiments employing a burst-mode laser system to capture both spatially resolved velocity fields and their dynamics using high-resolution particle image velocimetry measurements at 100 kHz. We show directly that velocity fluctuations in axisymmetric jet flows are inhomogeneous and anisotropic. The peak of the time-delayed cross correlation function decays exponentially in time and its velocity is smaller than the convection velocity; thus, Taylor’s frozen hypothesis fails to generalize for these inhomogeneous flows. Structure functions are isotropic only at small distances. They exhibit extended self-similarity, but no inertial range is found where the Kolmogorov $$\frac{2}{3}$$ 2 3 -law is satisfied. Spectral-energy density of the flow, although anisotropic, is consistent with the Kolmogorov–Obukhov $$\frac{5}{3}$$ 5 3 -law in the flow direction.

Piezo-Impact-Driven X-Y Stage and Precise Sample Holder for Accurate Microlens Alignment

2009 ◽  
Vol 21 (5) ◽  
pp. 635-641 ◽  
Author(s):  
Yuuka Irie ◽  
◽  
Hisayuki Aoyama ◽  
Junichi Kubo ◽  
Takahiro Fujioka ◽  
...  
Keyword(s):  
Theoretical Analysis ◽  
Interference Fringe ◽  
Kinematic Model ◽  
Sample Holder ◽  
Laser Interference ◽  
Optical Lens ◽  
Practical Applications ◽  
Piezo Element ◽  
Component Assembly

This paper details the development of an inertia-driven X-Y microstage and simple gripper for a pick-up lens in Blu-ray disc alignment incorporating inertia-driven microsliders on V-shaped grooves and a micropart handler. The microslider is driven by impact generated by a mass connected with a piezo element. We made a kinematic model for theoretical analysis on the X-Y microstage and gave the microinertia X-Y stage a sophisticated design.The X stage is stacked on the Y stage to provide fine in-plane positioning. Practical applications include multiple lens component assembly in which the optical lens must be centered within a tolerance of less than 100 nm. Experiments confirmed successful achievement of this microlens positioning in the center of the reference lens axis as observed by the laser interference fringe.

Heat Transfer Coefficient Distribution on Oil Injection Cooled Gears: Experimental Method, Uncertainty and Results

2020 ◽  
pp. 1-25
Author(s):  
Felix C. von Plehwe ◽  
Corina Schwitzke ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Kinematic Model ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Spatially Resolved ◽  
Oil Injection

Abstract To design gearboxes with very high power densities, an effective means of cooling the gears and knowledge of the achievable heat transfer coefficients are necessary. In this paper, a method to measure heat transfer coefficients for oil injection cooled gears is presented. Contrary to other experimental investigations, a single hollow spur gear is used. To measure heat transfer coefficients, a temperature gradient between the gear and the hot oil needs to be induced. This is achieved by injecting hot oil at realistic temperatures and cooling the inside diameter of the gear. This enables the measurement of heat transfer coefficients in absence of any dissipative or frictional losses, decreasing the measurement uncertainty. In addition, the novel method yields spatially resolved HTC data. The uncertainty of the method is assessed using Monte Carlo simulations. Experimental results for various operating conditions are presented. For all investigated oil flow rates, the same characteristic behavior of average heat transfer coefficient versus rotational speed was observed. This observation can be explained by using a kinematic model of the oil jet. The geometry of the gear and the cooling arrangement as well as the spatially resolved HTC data presented in this paper provide a complete basis for the validation of numerical simulations.

scholarly journals On the Buoyancy Subrange in Stratified Turbulence

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 659
Author(s):  
Victor Avsarkisov
Keyword(s):  
Energy Spectrum ◽  
Theoretical Analysis ◽  
Potential Energy ◽  
Froude Number ◽  
Scaling Laws ◽  
Turbulent Flux ◽  
Geophysical Flows ◽  
Energy Spectra ◽  
Stratified Turbulence ◽  
Buoyancy Subrange

This study is motivated by the importance of the stratified turbulence in geophysical flows. We present a theoretical analysis of the buoyancy subrange based on the theory of strongly stratified turbulence. Some important turbulent scales and their relations are explored. Scaling constants of the buoyancy subrange scaling laws for both kinetic and potential energy spectra are derived and analyzed. It is found that these constants are functions of the horizontal Froude number F r h . For the potential energy spectrum, the scaling constant also depends on the turbulent flux coefficient of Γ .

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