A System on Chip design for fast time domain impedance spectroscopy

© 2017 IEEE. Impedance spectroscopy is a powerful technique that can be employed to determine the physical properties of different materials. In principle the technique can be implemented in the time domain using pulsed signal excitation rather than sweeping across frequencies. The advantage is particularly apparent when the measuring instrument is either traveling through the material medium rapidly, as in the case of a satellite moving through space plasma, or if the medium is for example a fluid that flows past an instrument quickly. Here we describe a Time Domain Impedance Probe (TDIP) circuit design that is used to measure the absolute density of ionospheric plasmas. A preliminary version of this instrument was flown on a sounding rocket, but here we outline the system and circuit design that is being implemented for a Low Earth Orbit (LEO) micro-satellite. The design employs a bridge architecture together with a software adaptive filter and LMS algorithm for fast calibration and data compression. We propose that the design can be generalized, and we present a System On Chip (SOC) concept based on the time domain architecture. The proposed concept appears to be well suited to ultra-fast time domain spectroscopic measurements, but does have some inherent limitations such as increased noise. We suggest that this unavoidable shortcoming can be somewhat mitigated through repetitive pulsing and averaging during the measurement process

First results from a time domain impedance probe for measuring plasma properties in the ionosphere

© 2017 IEEE. A new Time Domain Impedance Probe (TDIP) is presented in this paper. The new instrument is able to make measurements of absolute electron density and electron neutral collision frequency in the ionosphere at temporal and spatial resolutions not previously attained. A single measurement is made in 100 microseconds, which yields an instantaneous spatial resolution of 0.1 meters for sounding rocket experiments. A prototype of this instrument was integrated into the payload of a NASA USIP sounding rocket launched out of Wallops Island on March 1 2016. The sounding rocket launched at 8:50 am and reached an reached an altitude of 170 km, passing through the D and E and F layers of the ionosphere. The TDIP was active for 206 seconds during the flight. Here we describe the instrument, and present some time domain data obtained from the sounding rocket experiment. A 6 Volt amplitude Gaussian derivative excitation was applied to a dipole probe structure, and the current through the probe terminals measured with a balanced active bridge circuit. The time domain current response was sampled at 5 MS/s, at 12 bit resolution. In the course of the flight, the instrument measured what appeared to be a highly nonlinear response of the plasma because of the large input voltage signal applied. These are the first measurements of this type of response, to our knowledge. Post-flight laboratory calibration indicated that the instrument worked correctly through the flight. Further modeling, simulation and theoretical work needs to be performed to understand and interpret the measurements

Influence of the Partitioning of Osmolytes by the Cytoplasm on the Passive Response of Cells to Osmotic Loading

Due to the dense organization of organelles, cytoskeletal elements, and protein complexes that make up the intracellular environment, it is likely that membrane-permeant solutes may be excluded from a fraction of the interstitial space of the cytoplasm via steric restrictions, electrostatic interactions, and other long-range intermolecular forces. This study investigates the hypothesis that the intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery in response to hyperosmotic loading, based on prior theoretical and biomimetic experimental studies. Osmotic loading experiments are performed on immature bovine chondrocytes using culture conditions where regulatory volume responses are shown to be insignificant. Osmotic loading with membrane-permeant glycerol (92 Da) and urea (60 Da) are observed to produce partial volume recoveries consistent with the proposed hypothesis, whereas loading with 1,2-propanediol (76 Da) produces complete volume recovery. Combining these experimental results with the previous theoretical framework produces a measure for the intracellular partition coefficient of each of these solutes. At 1000 mOsm, 1,2-propanediol is the only osmolyte to yield a partition coefficient not statistically different from unity, κpi = 1.00 ± 0.02. For glycerol, the partition coefficient increases with osmolarity from κpi = 0.48 ± 0.19 at 200 mOsm to κpi = 0.80 ± 0.07 at 1000 mOsm; urea exhibits no such dependence, with an average value of κpi = 0.87 ± 0.07 for all osmolarities from 200 to 1000 mOsm. The finding that intracellular partitioning of membrane-permeant solutes manifests itself as a partial volume recovery under osmotic loading offers a simple method for characterizing the partition coefficient. These measurements suggest that significant partitioning may occur even for small membrane-permeant osmolytes. Furthermore, a positive correlation is observed, suggesting that a solute's cytoplasmic partition coefficient increases with increasing hydrophobicity