Particle, response time

To generalize the above results, it is convenient to invoke the nondimensional Stokes number (St) which is a ratio of the particle response time to a characteris-... 

Surface tension, Pa m Stress tensor. Pa Particle response time, s Kolmogorov time scale, s Chemical conversion... 

For PIV measurements in liquid flow, it is not difficult to identify particles with matching densities. Therefore, the velocity lag (Viag) and gravity-induced velocity (F ) issues are not so severe. For a typical p-PIV measurement in water using 300 nm diameter polystyrene latex spheres, the particle response time, -r, can be calculated to be equal to 10 s. This response time is much smaller than the time scale requirement of any realistic flow field. For the case of slip flow in gases, it is possible to use the corrections of Stokes drag relation to quantity particle dynamics (see Beskok et al, 1996). 

The linearization of the previously mentioned ODEs can be applied since in the present studies the time step At which is the same for fluid flow and particle motion is several times smaller than the particle response time xp. Accordingly, the ratio Atkp lies in between [6.17 x 10 , 2.5 x 10 ]. Furthermore, the equation... 

For insuring different hydrodynamic interaction prior to particle-particle collisions in the individual runs, various dynamic fluid viscosities r] and particle material densities pp were used. The corresponding fluid and particle properties are summarized in Table 1. In the present study, the particle Reynolds number Rep and the particle Stokes number St are defined by Rep = ydpp/ilr]) and St = xpupx/dp, respectively, in which xp is the particle response time with xp = ppdp/ r] and upx the mean stream-wise initial velocity of all primary particles. This velocity corresponds to the undisturbed fluid velocity at the particle initial location as described below. As shown in Table 1, Rep and St vary between [0.1, 10.1] and [0.1, 13.8], respectively. 

It will be noted that the relevant characteristic dimension in the Biot number is defined as the ratio of the volume to the external surface area of the particle (V/Ae), and the higher the value of V/Ae, then the slower will be the response time. With the characteristic dimension defined in this way, this analysis is valid for particles of any shape at values of the Biot number less than 0.1... 

This response time should be compared to the turbulent eddy lifetime to estimate whether the drops will follow the turbulent flow. The timescale for the large turbulent eddies can be estimated from the turbulent kinetic energy k and the rate of dissipation e, Xc = 30-50 ms, for most chemical reactors. The Stokes number is an estimation of the effect of external flow on the particle movement, St = r /tc. If the Stokes number is above 1, the particles will have some random movement that increases the probability for coalescence. If St 1, the drops move with the turbulent eddies, and the rates of collisions and coalescence are very small. Coalescence will mainly be seen in shear layers at a high volume fraction of the dispersed phase. 

During the studies of adsorption-caused response in a and p by donor particles we monitored both kinetics of the change in above characteristics and dependence of their stationary values on concentration of adsorption particles. The partial pressure in gaseous phase (and in case of atom particles the time of treatment of the surface of adsorbent by the flux of above particles) used to be the measure of the quantity of absorbed particles during adsorption of molecular particles. 

With regard to the response time of the gel, polyelectrolyte gels require seconds to minutes to deform in electric fields. Needless to say, the deformation speed depends on the thickness of the gel and the intensity of the applied field. In 1993, a fast-responsive gel was found by Nanavati and Fernandez. A secretory granule gel particle obtained from beige mice and having a diameter of 3 pm at negative potentials was transparent and swollen within milliseconds of the application of an electric field of 5000 V/cm [19]. 

The first sensor proposed for detecting gastric and oesophageal pH24, made use of two fluorophores, fluorescein and eosin, immobilised onto fibrous particles of amino-ethyl cellulose, fixed on polyester foils. Only tested in vitro, the sensor reveals a satisfactory response time of around 20 seconds. 

The definition of a fine particle can be made more quantitative by introducing the article Stokes number St, which measures the particle-to-fluid response-time ratio to changes in the velocity (Fuchs, 1964) ... 

Dynode strings can be constructed in many ways and the response time and range of linearity of the detector depend on the configuration. In the Venetian blind configuration (Fig. 2.21c) the dynodes are wide strips of material placed at an angle of 45° with respect to the electron cascade axis. This system offers a large input area to the incident primary particles. The advantage is that the dynodes are easily placed in line and the dimensions... 

Bl), based on a time-averaged form of Eq. (11-44) and applicable to any form of oscillation if the period is long compared with the response time of the fluid (see below). At the other extreme of simplification, Rschevkin (R5) showed that if all effects except added mass and pressure gradient are omitted from Eq. (11-44), a particle moves in phase with the fluid oscillations (i.e., P = 0) with amplitude ratio ... 

Punte ec al.3 exposed volunteers to aerosol particles of 0.5-1.0 um. The windspeed was 5 mph. Figure 4-3 shows the variability in response times, especially at low concentrations. These experiments were continued with exposures at various temperatures, with exercise, and with repeated exposures and long low-concentration exposures to develop tolerance. High temperatures and humidity reduce the response time, as does exercise. After tolerance was developed, men given simple problems required more time to complete them, but accuracy was not impaired. Airway resistance did not increase during exposure to CS. One group exposed 10 times over 2 wk at up to 13 mg/m3 had normal blood electrolytes. Only minor adverse effects were observed in 75 men exposed in these experiments. 

In the last step (Part 3), the sedimentary compartment (the surface mixed sediment layer , SMSL) was treated as an independent box (Table 23.7). The steady-state solution of the combined sediment/water system explained another characteristic of the observed concentrations, which, as mentioned above, could not be resolved by the one-box model. As shown in Table 23.8, for both congeners the concentration measured on particles suspended in the lake is larger than on sediment particles. The two-box model explained this difference in terms of the different relative organic carbon content of epilimnetic and sedimentary particles. This model also gave a more realistic value for the response time of the combined lake/sediment system with respect to changes in external loading of PCBs. However, major differences between modeled and observed concentrations remained unexplained. 

The operating principle of the CSIRO (Australian Commonwealth Scientific and Industrial Research Organization) King probe (Particle Measuring Systems Inc., Boulder, Colorado) is similar in concept to that of the Johnson-Williams probe. The King probe measures the amount of power necessary to maintain a heated wire at a constant temperature, whereas the Johnson-Williams probe measures the change in resistance due to cooling of the wire by water evaporation. The probe consists of a heated coil of wire that is maintained at a constant temperature. The amount of excess power required to maintain the wire at this temperature when it is impacted by water droplets is measured and is proportional to the cloud liquid water content. The nominal response time of the instrument is 0.05 s, and it has an accuracy of 20%. This instrument uses less power than a Johnson-Williams probe, an important consideration in aircraft applications. 

With electrochemical methods, we determine thermodynamic potentials of components in systems which contain a sufficiently large number of atomic particles. Since the systematic investigation of solid electrolytes in the early 1920 s, it is possible to change the mole number of a component in a crystal via the corresponding flux across an appropriate electrolyte (1 mA times 1 s corresponds to ca. 10 s mol). Simultaneously, the chemical potential of the component can be determined with the same set-tip under open circuit conditions. Provided both the response time and the buffer capacity of the galvanic cells are sufficiently small, we can then also register the time dependence of the component chemical potentials in the reacting solids. ... 

The promethazine imprinted MIP particles were used as the recognition element to fabricate a relevant potentiometric chemosensor [200], These particles, prepared with the vinylbenzene functional monomer and the divinylbenzene cross-linker, effectively bound promethazine as compared to the MIP particles prepared with the MAA or vinylbenzene monomer and the EGDMA cross-linker. The MIP particles were embedded in a PVC membrane attached to one end of a glass tube, which was filled with 1 mM promethazine. The chemosensor was able to detect promethazine potentiometrically with LOD as low as 1.0 x 10-7 M and the dynamic linear concentration range from 5.0 x 10-7 to 1.0 x 10-1 M. With this chemosensor, promethazine concentration can be determined in syrup samples and biological fluids with a response time of 50 s. 

Finally, our group reported on gold nanoparticles decorated with bent-core liquid crystals showing pattern formation on TEM grids after slow solvent evaporation (18 in Fig. 22). These particles showed interesting self-assembly effects in different bent-core liquid crystal hosts (SmCPA and Colr) and slightly improved electro-optic effects such as shorter response time, x, and unaltered spontaneous polarization in the SmCPA host, but no mesophase formation [547]. 

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