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At least 163 records · Page 9Linked to original sources
PubMed2005

Subdiffusive axial transport of granular materials in a long drum mixer.

Granular mixtures segregate radially by size when tumbled in a partially filled horizontal drum. The smaller component moves toward the axis of rotation and forms a buried core, which then splits into axial bands. Models have generally assumed that the axial segregation is opposed by diffusion. Using narrow pulses of the smaller component as initial conditions, we have characterized axial transport in the core. We find that the axial advance of the segregated core is well described by a self-similar concentration profile whose width scales as talpha, with alpha approximately 0.3<1/2. Thus, the process is subdiffusive rather than diffusive as previously assumed. We compare our results to two one-dimensional model equations which contain self-similarity and subdiffusion: a linear fractional diffusion model and the nonlinear porous medium equation.

Journal Article↗
PubMed1982

Prevention of accidents associated with air-oxygen mixers.

Some time ago three patients were threatened by severe hypoxia. They did not demonstrate any adverse late effects, though the situation could as well have brought a fatal outcome. The incidents were related to the use of an oxygen-air mixing device. As this apparatus is widely used it is worthy of comment regarding its potential danger.

Accident Prevention↗
PubMed2002

Chaotic mixer for microchannels.

It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar-the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Péclet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.

Chemical Phenomena↗
PubMed1979

Measurement of the inactivation kinetics of poliovirus by ozone in a fast-flow mixer.

Inactivation kinetics of poliovirus type 1 in ozone demand-free water was investigated by utilizing a fast-flow mixing apparatus. Ozonated water and a solution of ozone demand-free water containing a known quantity of poliovirus type 1 were introduced simultaneously into a mixing chamber, both at a constant rate. This mixture was then passed through a narrow tube of known length and diameter into a neutralizing solution. By altering the rate of introduction and/or tube length, different contact periods between ozone and virus could be determined with an accuracy of 0.01 s. Inactivation of the poliovirus occurred in two steps. During the first step, which lasted for 0.2 to 1.0 s, 95 to 99% of the virus was inactivated, depending on the ozone concentration (which ranged from 0.1 to 2.0 mg/liter). The second step apparently continued for several minutes; in this period the remainder of the virus was inactivated. An obvious dose-response relationship was demonstrated during the first step of the inactivation curve. The pH of the water slightly affected the viral inactivation rate, but these small differences seem to have no practical value.

Buffers↗
PubMed1980

Programmable gas mixer for controlling concentration as a function of time.

A device for controlling gas concentration as a function of time according to a predetermined program is described. The apparatus is capable of producing any arbitrary time-varying gas concentration at frequencies up to about 4 Hz and can be set to ultra-low frequencies with excellent accuracy and repeatability. The apparatus consists of a single on/off solenoid valve for each gas in the mixture, all controlled by a microcomputer. The valve is rapidly pulsed open and closed, and the concentration of the corresponding gas in the mixture is proportional to the fraction of the cycle for which the valve remains open. Prior to an experiment, numerical values representing the amplitude of the desired concentration wave form at successive time intervals are entered into the computer memory. When the program is run, the microcomputer successively translates each of these values into a pulse-width modulated signal that opens and closes the valves via optically isolated relays. The processor can also translate an external control signal into the corresponding pulse train, permitting manual or automatic control of the mixture. The apparatus can be assembled in several hours from readily available components costing under $600, including the microcomputer.

Carbon Dioxide↗