A Universal Biological Interval Timer

A circuit for the measurement of biological time intervals from 0.1 ms to 10 s is described. This device accepts biopotentials, stimuli, or transducer signals to produce an instantaneous dc voltage readout proportional to the time between two successive input signals. Digital preconditioning and analog integration are used to simplify the design.     

Design Techniques for Hardened Fiber Optic Receivers

Hardened design techniques have been developed for fiber optic receivers that consider transient ionization and permanent damage effects. The results show that there is a fundamental trade-off between optical sensitivity and transient ionization hardness that depends primarily on the bit rate and the physical characteristics of the detector. In addition, various input stage designs and modulation methods can be considered in order to optimize both the optical sensitivity and radiation hardness. Radiation test results are included for three different receiver designs that were tested in five different radiation environments. The results show good agreement with design equations that were developed for different types of input stages, and demonstrate the hardness levels that can be achieved with currently available optical and semiconductor components.     

GEANT4 simulations of Cherenkov reaction history diagnostics

This paper compares the results from a GEANT4 simulation of the gas Cherenkov detector 1 (GCD1) with previous simulations and experimental data from the Omega laser facility. The GCD1 collects gammas emitted during a deuterium-tritium capsule implosion and converts them, through several processes, to Cherenkov light. Photon signals are recorded using subnanosecond photomultiplier tubes, producing burn reaction histories. The GEANT4 GCD1 simulation is first benchmarked against ACCEPT, an integrated tiger series code, with good agreement. The simulation is subsequently compared with data from the Omega laser facility, where experiments have been performed to measure the effects of Hohlraum materials on reaction history signals, in preparation for experiments at the National Ignition Facility.     

Investigations of deep resistivity structures at the Wairakei geothermal field

The Wairakei geothermal field was the proving ground for the use of electrical resistivity methods for geothermal exploration. At this site it was first demonstrated that a large contrast in resistivity existed between geothermal ground and the cold surroundings. Within the top 500 m of the geothermal field, low-resistivity (5–10 Ωm) reflects the effects of both the hot saline water in the pore spaces and the conductive rock-matrix. The first surveys at Wairakei used a Wenner array (a ∼550 m) to measure the resistivity values along tracks throughout the field; contour maps of the resistivities were used to estimate the lateral extent of the geothermal waters at a few hundred metres depth. In the late 1960s the Wenner array was superseded by the Schlumberger array (AB/2 = 500 m and 1000 m), which enabled deeper penetration and better definition of the extent of the geothermal waters. These early surveys showed that the bounds of the geothermal waters were often sharp, leading to the concept that a ‘resistivity boundary’ could be defined for New Zealand's liquid-dominated geothermal fields. As new methods of measuring electrical structure with greater precision became available, Wairakei was often chosen as the testing ground.     

Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant‐Derived,Low‐Acid Foods,and Biomaterials

Cycle threshold (Ct) increase, quantifying plant‐derived DNA fragmentation, was evaluated for its utility as a time‐temperature integrator. This novel approach to monitoring thermal processing of fresh, plant‐based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time‐temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low‐acid product and simple linear regression, Ct value was highly correlated to time‐temperature treatment (R² = 0.87); the logarithmic reduction (log CFU/mL) of the spore‐forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R² = 0.87); and cumulative F‐value (min) in a canned retort process (R² = 0.88), all comparisons conducted at 121 °C. D₁₂₁ and z‐values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D₁₂₁ and z‐values for a 174‐bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof‐of‐concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low‐acid plant products.     

42—THE ESTIMATION OF CROSS-LINKS IN WOOL FROM THE EXTENT OF SWELLING IN FORMIC ACID

An account is given of the application of a gravimetric method for measuring the extent of swelling of wool in formic acid to a series of wool samples containing decreasing amounts of randomly distributed disulphide bonds. In accordance with the Flory-Rehner equation, a linear relation was observed between disulphide content and V 5/3, where V is the volume of dry wool expressed as a fraction of the volume of swollen wool. This calibration curve was then used in conjunction with swelling data to assess the number of cross-links introduced on the treatment of wool with formaldehyde and other bifunctional reagents. The method is particularly useful for ranking in order relatively high levels of cross-linking.     

Designing Microgels for Cell Culture and Controlled Assembly of Tissue Microenvironments

Micrometer‐sized hydrogels, termed microgels, are emerging as multifunctional platforms that can recapitulate tissue heterogeneity in engineered cell microenvironments. The microgels can function as either individual cell culture units or can be assembled into larger scaffolds. In this manner, individual microgels can be customized for single or multicell coculture applications, or heterogeneous populations can be used as building blocks to create microporous assembled scaffolds that more closely mimic tissue heterogeneities. The inherent versatility of these materials allows user‐defined control of the microenvironments, from the order of singly encapsulated cells to entire 3D cell scaffolds. These hydrogel scaffolds are promising for moving towards personalized medicine approaches and recapitulating the multifaceted microenvironments that exist in vivo.     

INCREASE IN REFRACTORINESS IN CERAMIC BODIES IN INTERRUPTED HEAT TREATMENT1

The increase in refractoriness referred to here is usually termed freezing. The study was undertaken to overcome the tendency of pyrometric cones to set or freeze when subjected to prolonged heat treatment when the temperature is more or less fluctuating. The work includes a study of the freezing tendency of some natural clays, of several pottery bodies, and of pyrometric cones. A body was developed that does not freeze under the treatment that produces the phenomenon in the other materials tested but the cause is not established.     

Chlorination of polyesters

By photochemical chlorination chlorine was substituted on the gem-dimethyl groups of the polyterephthalate and polycarbonate of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, the polyterephthalate of 2,2-dimethyl-1,3-propanediol, and the polycarbonate of 4,4′-isopropylidenediphenol (bisphenol A). The factors affecting polyester degradation, the efficiency of chlorination, and the degree of chlorination were investigated, and the effects of chlorine content on the solubility, flammability, density, hydrolytic stability, thermal stability, tensile properties, electrical properties, and heat-distortion temperatures of cast films were determined. The chlorinated polyesters of particular interest, because of their properties, are the polycarbonates of 2,2,4,4-tetramethyl-1,3-cyclobutanediol and bisphenol A.