Top PDF Dynamics of Chemically Active Suspensions

Dynamics of Chemically Active Suspensions

Dynamics of Chemically Active Suspensions

Hydrodynamics is a more important component, and can be added to this simulation with the method of Accelerated Stokesian Dynamics (ASD) (Sierou & Brady, 2001). With the assumption that solutes diffuse very fast, D R D , the Stokes flow has no effect on the c field. So the calculation of c equation is mostly decoupled from the Stokes flow. In a rough approximation, the boundary condition for the Stokes flow is still no-slip, and in this case the Stokes flow and solutes transport are completely decoupled. All we need to do in this case is to replace the Stokes drag 6 πη a in (6.1) by the full resistance matrix R FU . A more satisfactory approximation is that the boundary condition for the Stokes flow should be determined by the local concentration field c , in the presence of a surface slip velocity (Anderson, 1989; Brady, 2011). In this case, the Stokes flow can be solved after the solution of the solute field c . This is one-way coupling and still solvable by the method of ASD, with some minor modifications due to slip velocity on the lubrication correction and the Faxen laws relating Stokes flow multipoles (force F , torque L , and stresslet S ) to the surrounding flow. At this stage, the role of hydrodynamics in the clustering process and the steady state structure is unclear. In principle it increases the drag when clustering happens and slows down both translational and rotational motion. A particle-tracking simulation is necessary to probe the systems and it is one of our future topics.
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Uncertainty and Disturbance Estimator based Control of Active Suspensions with a Hydraulic Actuator

Uncertainty and Disturbance Estimator based Control of Active Suspensions with a Hydraulic Actuator

For a quarter-car active suspension system with uncertainties, a novel robust control method is presented. For the nonlinear dynamics of hydraulic actuator, the whole system is repartitioned into a linear subsystem and a nonlinear subsystem, instead of dividing into actuator subsystem and suspension subsystem. The repartition facilitates the controller design greatly. For the linear subsystem, a reference model is offered based on sky-hook damper at first, and then the Uncertainty and Disturbance Estimator (UDE) control approach is used to get desired fictitious input of linear subsystem. For the nonlinear subsystem, sliding mode control (SMC) strategy is employed to construct controller in order to force the output of nonlinear subsystem to track the desired fictitious input of linear subsystem. Simulation on two kinds of road surfaces are given, the results verify that the proposed method has good performance.
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Vortex formation and dynamics of defects in active nematic shells

Vortex formation and dynamics of defects in active nematic shells

Active liquid crystals [1–3] (ALCs) have proved successful as a paradigm for living systems on the microscale, providing insight into processes like cell motility [4–6] and division[7–9], development of cell shapes [10, 11], and growth of cell colonies [ 12 ] . Certain fundamental motifs have been developed such as the instability of uniformly aligned states, the emergence of spontaneous flows, the creation and self-propulsion of topological defects and the shear-thinning character of extensile gels. More recently another motif has emerged around con fi nement of ALCs, where the prominent feature is the emergence of stable fl ow vortices. For instance, confinement gives rise to a stable single vortex state in dense bacterial suspensions [13, 14], active nematic suspensions [15, 16] and cell monolayers [17, 18]. Circulatory flows are also characteristic of cytoplasmic streaming [ 6, 16, 19,20 ] . As the system size is increased such vortices become unstable [ 21 ] and turbulent fl ows develop, a prevalent feature in bulk active fluids [22–24]. In active systems with high frictional dissipation stable vortices can also arise in the absence of spatial confinement [25–27]. Recent experiments by Keber et al on microtubule-based extensile active nematics [ 28 ] are realisations of a different type of con fi ned geometry, in which the ALC adheres to the surface of a vesicle. The primary behaviour reported is of four motile +1/2 defects in the orientation that undergo regular oscillations between tetrahedral and planar configurations. Here, we develop a hydrodynamic model for a spherical shell of ALC, with arbitrary defect con fi guration, and fi nd topologically stabilised vortices as a prominent feature of the flow, which reproduces the defect motion from experiments.
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The Effects of Trading Suspensions in China

The Effects of Trading Suspensions in China

volume and volatility. Tan and Yeo (2003) investigate the effects of trading halts on the Singapore Stock Exchange. They find that the ‘good news’ group experience significantly positive abnormal returns around the event date, while the ‘bad news’ group suffers a prolonged decline. Xu et al., (2014) assessed the effects of trading halts on absolute return, trading volume and bid-ask spread using high-frequency data from the Shanghai Stock Exchange. Our analysis extends this literature in several dimensions. First, to the best of our knowledge, this study represents the first attempt to comprehensively investigate the efficiency of mandatory and voluntary trading suspensions in China. Second, we carefully investigate the patterns of stock price, volatility and trading volume before and after trading suspensions and relate them to corporate governance, accounting variables and suspension duration. Finally, we investigate the importance of ownership structure on the effects of trading suspensions.
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Forces, Stresses, and the (Thermo?) Dynamics of Active Matter: The Swim Pressure

Forces, Stresses, and the (Thermo?) Dynamics of Active Matter: The Swim Pressure

We analyze the stress, dispersion, and average swimming speed of self-propelled particles subjected to an external field that a ff ects their orientation and speed. The swimming trajectory is governed by a competition between the orienting influence (i.e., taxis) associated with the external (e.g., magnetic, gravitational, thermal, nu- trient concentration) field versus the e ff ects that randomize the particle orientations (e.g., rotary Brownian motion and / or an intrinsic tumbling mechanism like the flag- ella of bacteria). The swimmers’ motion is characterized by a mean drift velocity and an e ff ective translational di ff usivity that becomes anisotropic in the presence of the orienting field. Since the di ff usivity yields information about the microme- chanical stress, the anisotropy generated by the external field creates a normal stress di ff erence in the recently developed “swim stress” tensor [1]. This property can be exploited in the design of soft, compressible materials in which their size, shape, and motion can be manipulated and tuned by loading the material with active swim- mers. Since the swimmers exert di ff erent normal stresses in di ff erent directions, the material can compress / expand, elongate, and translate depending on the external field strength. Such an active system can be used as nano / micromechanical devices and motors. Analytical solutions are corroborated by Brownian dynamics simula- tions.
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Particle dynamics in a non flaring solar active region model

Particle dynamics in a non flaring solar active region model

Results. Two distinct particle acceleration behaviours are recovered, which a ff ect both electrons and protons: (i) direct acceleration along field lines and (ii) tangential drifting of guiding centres with respect to local magnetic field. However, up to 40% of all particles actually experience a form of (high energy) particle trap, because of changes in the direction of the electric field and unrelated to the strength of the magnetic field; such particles are included in the first category. Additionally, category (i) electron and proton orbits undergo surprisingly strong acceleration to non-thermal energies (42 MeV), because of the strength and extent of super-Dreicer electric fields created by the MHD simulation. Reducing the electric field strength of the MHD model does not significantly affect the efficiency of the (electric field-based) trapping mechanism, but does reduce the peak energies gained by orbits. We discuss the implications for future experiments, which aim to simulate non-flaring active region heating and reconnection.
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Active suspension force control with electro hydraulic actuator dynamics

Active suspension force control with electro hydraulic actuator dynamics

This work discussed in detail the mathematical model of a nonlinear, half vehicle active suspension system with hydraulic actuator dynamics. Simulation studies was done and the overall system performances for active suspension system parameters with road input uncertainties was found better when compared to the passive suspension systems for a random road input disturbances, providing a better passengers ride comfort and also minimizing the suspension travel rattle space.

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Magnetic and thermal structuring and dynamics of solar coronal active regions

Magnetic and thermal structuring and dynamics of solar coronal active regions

dence is very similar, with the loss of stable solutions close to β = 1 (see section 6.3.3). The magnetic field along loop D, however, has a significantly higher level of the constant com- ponent, which increases the range of β for which stable solutions exist. In the extreme case, if the magnetic field strength is nearly constant along the loop, the heating rate B(s) β would vary very little along the loop even for large values of β, resembling the case of nearly con- stant heating rate. Such loops are found to have stable solutions up to large values of β > 10 but offer very little diagnostics capability in the range 0 < β < 2. A survey of a number of loops in the active region under study reveals that such loops with a flat distribution of B(s) indeed appear to exist, particularly for shorter lengths below 60 Mm. Whether this comes from the complexity of the magnetic field in the active region core or from an inadequate spatial resolution of our 3D data cube is not clear. Therefore, the diagnostics presented in Figs. 6.12-6.15 is applicable only to some of the loops with steeply decreasing B(s) and a low constant component of B(s).
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Driver behavior models for evaluating automotive active safety: From neural dynamics to vehicle dynamics

Driver behavior models for evaluating automotive active safety: From neural dynamics to vehicle dynamics

Another important assumption, which may not be surpris- ing given what has been said so far, is that the magnitude of each control adjustment is affected by the situation at hand. Specifically, it is suggested here that in routine, steady state driving, each control adjustment aims to resolve the situation that triggered it. A steering adjustment caused by a moving far point aims to immobilize the far point, a brake application caused by a looming lead vehicle aims to stop the looming. For often-encountered driving situations, drivers will have had ample time to learn suitable mappings from sensory in- put to control adjustment, acquiring a near-optimal trade-off between effort and performance, and what can be interpreted as a thorough understanding of their vehicle’s dynamics. See (Markkula, 2013) for a sketch of how the far point control law suggested by Salvucci and Gray (2004) could be un- derstood in this way. However, in more critical situations, typically previously unexperienced by the driver, the same mappings may no longer be as well-tuned to the situation or to the vehicle (Markkula et al., submitted), and this could explain reports of driver overreactions or underreactions in near-accident maneuvering. Furthermore, a possibly relevant neurobiological phenomenon in this context is motor noise, inherent variability in motor output which typically scales with movement amplitude (Franklin & Wolpert, 2011), such that large pedal or steering movements will be more likely to turn out far from what was intended by the driver.
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Derivation of turbulent energy of fiber suspensions

Derivation of turbulent energy of fiber suspensions

The resulting Eq. (14) has been developed in terms of second order correlation tensors when fiber was suspended into the turbulent flow. The equation was derived by averaging procedure, which includes the effect of fibers and the correlations between the pressure fluctuations and velocity fluctuations at two points of the flow field. Fiber suspensions in a turbulent fluid undergo mean motion due to the mean fluid velocity and random motion due to the fluctuating component of fluid velocity. Velocity of fiber fluctuates around the mean velocity of flow. Fluctuation velocity of turbulence at two points A and B of the flow field leads to the weakening of the concentration of the fiber orientation distribution on small angle. This concentration leads to be weaker and orientation distribution of the fiber becomes more uniform as Reynolds numbers increase and flow fluctuation velocity becomes stringer. The fiber velocity has the same fluctuation property as fluid velocity due to its strong following ability. The fluctuation velocity of fiber on flow direction is more energetic than that on lateral direction. As Reynolds number increases, the intensity of fluctuation velocity is enhanced, flow velocity gradient becomes more irregular, and orientation distribution of fiber becomes wider. For non-suspending fluid in the flow, the apparent viscosity of the fluid vanishes; that is
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Suspensions AUTOMOTIVE COMFORT AND CONTROL

Suspensions AUTOMOTIVE COMFORT AND CONTROL

FIGURE 13—A modified MacPherson strut suspension uses a portion of the frame or cross member instead of an upper control arm as the upper coil spring mount.... Once again, the strut asse[r]

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Floc properties in stirred suspensions

Floc properties in stirred suspensions

aggregated sample was released from a vessel to the monitoring cell a t 30 seconds. This procedure encouraged aggregation 10 seconds before the actual m onitoring of the sample. This resulted in higher ratio values m easured a t 30—40 seconds for 30, 50 and 70 mMol th an for the other concentrations in Fig. 4.9 though this behaviour is not clearly observed in Figs. 4.8, 4.10 and 4.11 in this section. Figs. 4.5(a), (b), and (c) are presented to display the examples of changes in T during aggregation. It is generally observed th a t the turb id ity of suspension usually decreases as aggregates begin to form, reflecting th e reduced sum of in­ dividual scattering cross-sections. Figs. 4.5(a) and (b) also dem onstrate th a t the turbidity (T) of aggregated latex and silica suspensions decrease as aggregation occurs. The salt concentration which leads to the high ratio increase also leads to high turbidity reduction and this trend applies vice versa for the salt con­ centration with the low ratio increase. The latex aggregation by 50 mMol Ca^+ concentration results in the highest decrease in turbidity, and the highest peak ra­ tio is shown with this concentration, while the calcium concentration of 80 mMol leads to the largest ratio increase and T reduction for silica aggregation as shown in Figs. 4.5(b) and 4.10(c).
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The Chemically Abused Child

The Chemically Abused Child

Pediatrics 68:119-121, 1981; child abuse, battered child, poisoning, chlorpromazine.. Since the original description of the battered.[r]

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Food suspensions study with SR microtomography

Food suspensions study with SR microtomography

The suspensions were transferred using a pipette into cellulose straws (each sample was added to a new cellulose straw, 7 samples in total, 5.75 mm diameter, Fishers Ideas, UK) which were glued (to prevent leakage of sunflower oil) to a plastic chuck precisely designed for the X-ray µCT experiments. A lid was then placed on top which had a hole in the centre ensuring the depositing of the secondary liquid using an electronic pipette (Eppendorf Xplorer, UK) on the central axis of the sample. After the addition of secondary liquid, the lid was replaced with another containing no hole to prevent any evaporation of the secondary liquid during the experiment.
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Kinetics of DCOD Consumption by Bacterial Suspensions

Kinetics of DCOD Consumption by Bacterial Suspensions

The primary purpose of wastewater treatment is to remove the suspended and soluble organic constituents measured as chemical oxygen demand (COD) or biochemical oxygen demand (BOD). Biological treatment processes are used to degrade the organics in the wastewater before it is discharged (Murthy, 1998). Of the numerous methods available , the activated sludge system is one of the most popular and versatile and perhaps the most common biological process for wastewater treatment. According to Pavoni et al. (1972) this process inherently relies on two independent characteristics for the production of an acceptable effluent. The first is the assimilation of the suspended, colloidal and dissolved organic material by the active mass of microorganism to a final end product of carbon dioxide, water and inert material. The second phase, and ultimately the most significant, is the flocculation of the biomass and other suspended and colloidal material into units large and dense enough to settle out of solution so that a high-quality effluent can be obtained.
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The Behavior of Zeta Potential of Silica  Suspensions

The Behavior of Zeta Potential of Silica Suspensions

SiO − coordination tetrahedron is imperfect leaving silicon and oxygen unsatis- fied bonds at each particle surface. In aqueous suspensions of silica particles, these free bonds are neutralized by OH − and H + species. In this sense partial or total particle surface hydroxylation can result in the formation of si- lanol groups [Si(OH) n ]. The silanol groups in pure water dissociate through the following reactions:

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A Comparative Study of YSZ Suspensions and Coatings

A Comparative Study of YSZ Suspensions and Coatings

In Figure 3 showing the SEM images of the dried suspensions and the original powders, one can note that the sizes and rounded shapes of the particles in the home-made suspensions and in suspension C1 are very similar. On the other hand, the particles in suspension C2 are roughly 2-3 times larger presenting mainly angular/faceted shapes. As all spray parameters are almost identical for all suspensions and as their rheological properties do not correlate well with the observed microstructures, one can speculate that the different observed structures are linked with the actual particle size and shape that may influence the fragmentation behavior of the suspensions as well as the way particles merge together in flight after the solvent (ethanol) is fully evaporated. These phenomena are not well understood today and can have a significant influence on the final particle size and speed before impact on the substrate.
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Magneto Rheological Dampersin Automotive Suspensions

Magneto Rheological Dampersin Automotive Suspensions

suspension are the suspension in which with the help of onboard system damping can be control which in passive suspension purely depends on road irregularities. Active suspension are further divide into fully active and semi active suspensions. In fully active suspension actuators are used that case lift chassis as per the road irregularities while in semi-active suspension viscosity of fluid can be vary which can give required damping.MR Dampers stands in semi- active suspension family.
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Treatment of mine water with colloidal suspensions

Treatment of mine water with colloidal suspensions

Treatment of Mine Water with Colloidal Suspensions Chapter 2 Literature Review When gypsum is used, the water needs to stand for a few days so that the particles can settle out before th[r]

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Pipe Flow of Suspensions Containing Bubbles

Pipe Flow of Suspensions Containing Bubbles

Foams become more important in industrial applications, but also in food pro- duction because of many advantages, including low weight, thermal insulation and special texture characteristics. Relevant constitutive equations were devel- oped by Oldroyd [1] [2] [3] [4] and by Frankel and Acrivos [5] [6]. They studied the rheological behavior of dilute emulsions in steady or weakly time-dependent flows. The models have also been used to describe the rheological behavior of dilute bubble suspensions. Contributions were provided by Llewellin, Mader and Wilson [7] [8], by Llewellin and Manga [9] and by Pal [10] [11] among others. How to cite this paper: Gladbach, K.,
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