Focusing, hydrodynamic

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instmment are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instmment is caUbrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation estabUshes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

Figure 2.45 Design of a multilamination mixer with hydrodynamic focusing (upper left) and flow pattern in such a mixer for a total volume flow of 10 ml h of water (lower left), taken from [141. The right side of the figure shows the orientation of liquid lamellae over a cross-section of the constriction for different Reynolds numbers [142].

Fig. 6 (a) Schematic illustration of a flow cytometer used in a suspension array. The sample microspheres are hydrodynamically focused in a fluidic system and read-out by two laser beams. Laser 1 excites the encoding dyes and the fluorescence is detected at two wavelengths. Laser 2 is used to quantify the analyte, (b) Scheme of randomly ordered bead array concept. Beads are pooled and adsorbed into the etched wells of an optical fiber, (c) Scheme of randomly-ordered sedimentation array. A set of encoded microspheres is added to the analyte solution. Subsequent to binding of the analyte, microparticles sediment and assemble at the transparent bottom of a sample tube generating a randomly ordered array. This array is evaluated by microscope optics and a CCD-camera. Reproduced with permission from Refs. [85] and [101]. Copyright 1999, 2008 American Chemical Society... 

The point is now to estimate the maximum number of photons that can be detected from a burst. The maximum rate at which a molecule can emit is roughly the reciprocal of the excited-state lifetime. Therefore, the maximum number of photons emitted in a burst is approximately equal to the transit time divided by the excited-state lifetime. For a transit time of 1 ms and a lifetime of 1 ns, the maximum number is 106. However, photobleaching limits this number to about 105 photons for the most stable fluorescent molecules. The detection efficiency of specially designed optical systems with high numerical aperture being about 1%, we cannot expect to detect more than 1000 photons per burst. The background can be minimized by careful dean-up of the solvent and by using small excitation volumes ( 1 pL in hydrodynamically focused sample streams, 1 fL in confocal exdtation and detection with one- and two-photon excitation, and even smaller volumes with near-field excitation). 

Hydrodynamic focusing and electronic cell-sizing techniques (with M.L. Shuler and H.M. Tsuchiya). Appl. Microbiol. 24,384-388 (1972). 

The technical term for this is hydrodynamic focusing, flow of a sample stream within the center core of a sheath stream is called coaxial flow. The exact diameter of that central sample core within the sheath stream is related to, among other things, the rate at which the sample is injected into the sheath stream a 100 pm sheath stream may, depending on sample injection velocity, have a core width of perhaps 5-20 pm (Fig. 3.4). Because hydrodynamic focusing tends to confine the cell sample to this central core, there is little mixing of sample with sheath fluid (but diffusion of small molecules will occur). The reason that this type of coaxial sample flow suits flow cytometry... 

Hydrodynamic focusing Hydrodynamic focusing is the property of laminar flow in a stream of increasing velocity that maintains particles in the narrowing central core of a column of fluid. 

Hydrodynamic Focusing Cross-Injection Mixing Most Relevant Citations... 

Mixer 32 [M 32] Hydrodynamic Focusing Cross-injection Micro Mixer... 

Figure 1.67 Hydrodynamic focusing mixing element with cross-like structure [112]...

Mixer type Hydrodynamic focusing crossinjection micro Channel width 10 pm... 

M 32] ]P 30] It was found that hydrodynamic focusing was achievable in the mixer over a wide range of volume flow ratios, expressed as the ratio a of the corresponding pressures, defined as follows ... 

M 36] [P 39] Hydrodynamic focusing was achieved in a rectangular interdigital mixer by setting the two flow rates of the liquids at different levels [20], In this way, one set of lamellae can be thinned considerably. The corresponding flow pattern are described as a function fo the ratio of the individual flow rates of the two liquids. 

J. P., Austin, R. H., Hydrodynamic focusing on a silicon chip mixing nanoliters in microseconds, Phys. Rev. 

The time resolution of the measurement also depends on several important mixer parameters the diffusive mixing time (determined by the jet width and the diffusion coefficient of the ions (Knight et al., 1998)), the beam size, uncertainty in the mixing time resulting from the hydrodynamic focusing process, and depth-dependent variations in the flow speed of the jet. Each of these issues has been addressed independently, but will be briefly reviewed here for completeness. 

Figure 12.3 A more realistic depiction of the hydrodynamic focusing mixer used for time-resolved SAXS studies. This figure, adapted from Lisa Kwok s thesis (Ph.D. Cornell), illustrates the multilayer construction of the mixing device.

FIGURE 3.36 Schematic representation of a micromachined pre-focused 2x6 flow switch with six inlet ports and six outlet ports. The flow switch integrates two important microfluidic phenomena, including hydrodynamic focusing and valveless flow switching. The pre-focused samples can be injected into desired outlet ports precisely [263]. Reprinted with permission from the Institute of Physics Publishing. 

Another configuration for hydrodynamic focusing is to create a non-axial sheath flow, as shown in Figure 8.39. The sheath inlet resembles the one used in usual microchip focusing experiments. The non-axial sheath flows are supplied... 

Transverse IEF was also conducted in a pressure-driven flow for BSA and soybean lectin separation on-chip [1040], Here, Pd electrodes were used (in preference to Au) because of the non-gassing character of Pd. In addition, the protein sample was sandwiched between two buffer streams and was prevented from direct contact with the channel wall (and hence the electrode), a process akin to hydrodynamic focusing [1040],... 

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