ACT3: a high-speed, high-precision electrical impedance tomograph

Presents the design, implementation, and performance of Rensselaer's third-generation adaptive current tomograph, ACT3. This system uses 32 current sources and 32 phase-sensitive voltmeters to make a 32-electrode system that is capable of applying arbitrary spatial patterns of current. The instrumentation provides 16 b precision on both the current values and the real and reactive voltage readings and can collect the data for a single image in 133 ms. Additionally, the instrument is able to automatically calibrate its voltmeters and current sources and adjust the current source output impedance under computer control. The major system components are discussed in detail and performance results are given. Images obtained using stationary agar targets and a moving pendulum in a phantom as well as in vivo resistivity profiles showing human respiration are shown     

Preferential glycerol transport by electroosmosis through ionic membranes

This paper describes a process in which glycerol is preferentially sorbed relative to water by an ionic membrane and transported into the product solution by electroosmosis at a significantly higher concentration than that in the feed solution. Direct measurement of the membrane distribution coefficient demonstrated preferential glycerol sorbtion for Neosepta CL-25T and AV-4T membranes. Both DC and AC electric currents significantly increase glycerol transport over that of a concentration difference alone.     

Energy spectra for decaying 2D turbulence in a bounded domain

We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T(K) and the specific heat in the low temperature phase.     

The synthesis and some reactions of pentafluoroethyl vinyl ketone

The title compound has been prepared in a four step synthesis starting from acrolein. Both its dimerization, which yields a 3.4-dihydropyranyl derivative, and the uncatalyzed addition of ethanol across the CCbond take place at 20°, reflecting the high reactivity of this α,β-unsaturated ketone.     

An ultrafiltration monitor for hemodialysis research

The ultrafitration rate of hemodialysis membranes should be carefully controlled for maximum patient benefit. A special purpose instrument is described that takes in analog pressure information and the analog output of an appropriate weighing system and produces both digital displays and analog outputs (for a strip-chart recorder) of ultrafiltration rate and ultrafiltration index as well as the averaged mean transmembrane hydrostatic pressure drop and volume of ultrafiltrate. The instrument normally uses an averaging time of about 2 min.     

Carbon-13 NMR measurments of polybutadiene local dynamics in dilute solution: Further evidence for non-Kramers' behavior

The local segmental dynamics of cis-polybutadiene in dilute solutions have been investigated using natural abundance ¹³C NMR spectroscopy. The time integral of the C? H orientation autocorrelation function 〈σ〉 is extracted from T₁ measurements in five solvents covering a viscosity range of two decades. The hydrodynamic Kramers' equation, which is generally assumed to be appropriate for local polymer dynamics in dilute solution, cannot describe these results. 〈σ〉 is found to depend upon the solvent viscosity η raised to the 0.33 power whether η is varied by changing the temperature or the solvent. This apparent power law behavior has been observed for other polymers in dilute solution and can be rationalized if the solvent is viewed as viscoelastic. This view is supported by experimental results which show that local polymer dynamics can occur as much as an order of magnitude faster than solvent reorientation. Trends for a mixed microstructure polybutadiene are similar to those of cis-polybutadiene. © 1994 John Wiley & Sons, Inc.