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- Author or Editor: M. Matthews x
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Abstract
Dielectric Thermal Analysis (DETA) of drugs, proteins and amino acids reveals a strongly linear conductivity increase prior to and peaking at the melt, associated with dielectric viscoelastic properties of the material. Premelt onset and peak are shown to depend on thermal history. Comparisons of neat amino acid samples to samples heated to 150 °C; dried in a desiccator; or heated above their melting point and cooled show significant premelt and melt shifts. Melts are also correlated with phase transitions observed by Differential Scanning Calorimetry (DSC). Activation energies attributed to charging in the premelt for amino acids were typically 250 J/mole.
Abstract
Advances in science and technology are now at the heart of the global economy, but the number of students earning degrees in the sciences, technology, engineering, and math (STEM) fields has stalled. According to the National Association for Colleges and Employers (NACE), programs have been initiated nationwide to nurture interest in the sciences, including research competitions, co-ops and internships, and K-12 STEM education. Senior thermal analysis scientists are not only researchers, they are role models, mentors and teachers intimately involved in the recruitment and training of young scientists. The authors present guidelines for thermal analysis research project planning for high school students, undergraduate students and master’s and doctoral candidates. Project planning includes developmentally appropriate techniques, methods, instruments, scope and significance. Case studies illustrate examples of short-term, concrete materials analysis projects tailored to younger student researchers, as well as master’s level projects making significant contributions to the state of the science and innovative doctoral research. In addition to designing projects for students at all levels, senior thermal analysis scientists can use specific teaching and training techniques to help young scientists develop their abilities in the lab and at the podium.
Summary
Finland has the operational capability to take airborne gamma-ray measurements in emergency situations. The original purpose of airborne radiation mapping in Finland was to identify hazardous areas containing radioactive fall-out after a nuclear accident or use of nuclear weapons. Regular exercises are held annually to keep the operational functionality at a high level. The achieved capability has been well demonstrated in international INEX-2-FIN 1997 and Barents Rescue 2001 exercises. The knowledge and competence achieved can easily be applied in international radiation monitoring campaigns designed to expose undeclared nuclear materials or other clandestine nuclear activities. The essential improvements in the detection system are linked to the ability to locate point-like radiation sources rather than large areas of fall-out. This paper describes the aerial gamma-ray measurement method and its usability for the detection of nuclear material production chains and trails of fission or activation products. The ability of airborne detection systems in revealing the use of undeclared nuclear materials has been tested. Various scenarios for exposing clandestine nuclear material production, enrichment and nuclear waste trails have been considered. Based on detection capability calculations and testing in practice, it was found that the detection of one un-shielded significant quantity of natural uranium (10 tons of yellow cake in storage barrels) is possible through the daughter products, using one single 6"'4" NaI detector on the airplane. The developed fixed wing gamma measurement technique is now able to detect significant amounts of nuclear material conveniently and cost-effectively. Large areas can be screened to identify suspicious sub-areas for more detailed ground-based inspection.
Abstract
The conditions under which the Poisson statistical density function adequately describes the counting of a radioactive isotope are examined and found that for counting processes where λt≳1, where λ is the decay constant and t the counting period, one of the fundamental properties, namely the condition of stationarity, is violated rendering application of Poisson statistics invalid. The Ruark-Devol statistical density function, a binomial, is instead shown to be satisfactory since it is capable of describing radioactive disintegration where the only fundamental property is independence and its use is recommended in both activation analysis and medical imaging when the half-life of the isotope of interest is short compared to the period of observation. It is pointed out that no satisfactory expression incorporating the distortion produced by dead-time on the statistical density function has yet been derived but the practical implications of the adoption of the Ruark-Devol function are discussed with respect to standard deviation and precision of the measurement. It is shown how the application of the Poisson statistical density function, under conditions of tλ≳1, is not only invalid but also overestimates the standard deviation significantly.
Abstract
This biomaterials overview for selecting polymers for medical devices focuses on polymer materials, properties and performance. An improved understanding of thermoplastics and thermoset properties is accomplished by thermal analysis for device applications. The medical applications and requirements as well as the oxidative and mechanical stability of currently used polymers in devices are discussed. The tools used to aid the ranking of the thermoplastics and thermosets are differential scanning calorimetry (DSC), thermogravimetry (TG), thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) as well as a number of key ASTM polymer tests. This paper will spotlight the thermal and mechanical characterization of the bio-compatible polymers e.g., olefins, nylon, polyacetals, polyvinyl chloride and polyesters.
Abstract
Dielectric analysis (DEA), supported by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), powder X-ray diffraction analysis (PXRD) and photomicrography, reveal the chiral difference in the amino acids. The acids are classified as dielectric materials based on their structure, relating chirality to the vector sum of the average dipole moment, composed of the constant optical (electronic) and infra-red (atomic) polarizabilities, as well as dipole orientation. This study encompasses 14 L-and D-amino acid isomers. Physical properties recorded include AC electrical conductivity, charge transfer complexes, melting, recrystallization, amorphous and crystalline phases, and relaxation spectra, activation energies and polarization times for the electrical charging process.
Abstract
The thermal analytical study of most hydrophobic and hydrophilic D/L amino acids reveals significant hydropathy index correlation between the presence of water and crystalline amino acids. The TG derivative mass profiles for arginine and lysine (hydrophilic acids) at various time intervals of atmospheric exposure, show two distinct peaks, one between 50 and 60°C (unbound water), and one close to 100°C (bound-like water). The DSC heat-cool profiles for lysine and arginine confirmed the presence of these multiple waters with two heats of vaporization. The absence of these patterns from the TG and DSC for cysteine and phenylalanine (hydrophobic acids) further supports the conclusions.
Abstract
Novel dielectric behavior of a linear increase in ionic conductivity prior to melt temperature was observed for active pharmaceutical ingredients (APIs), organic chemicals, amino acids, and carbohydrates. Though, there are solids like polyolefins and long chain organic compounds (tetracosane, pentacosane) which do not exhibit this premelt behavior (i.e., the temperature where the onset of increase in ionic conductivity to melt temperature). We have discovered novel electrical conductivity properties and other physical analytical variations which can lead to unique synthetic routes of certain chemical entities. The above-mentioned unique variations are not related to solid–solid transitions which are quite often observed in pharmaceutical crystalline solids. These new properties are related to amorphous crystalline behavior of a solid. We have also studied the effect of various experimental variables: such as amount of mass tested, applied frequency at a given electric field and heating rate, which results in varying the onset temperature of the increase in ionic conductivity. Melting of the solids was correlated using differential scanning calorimetry (DSC). Activation energies for all the solids were measured in the premelt region using an Arrhenius plot at a specific frequency since we observed changes in the conductivity with frequency. This study focused on frequencies 0.1 to 10 Hz, since the conductivity at these frequencies related to surface analysis. This new physical properties are leading to new electro synthetic procedures to modify or prepare chemicals.
Abstract
Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts. Phase transitions, including glass transition (T g) and melting temperature (T m), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and solid–liquid transitions.
Abstract
The Lawrence Livermore National Laboratory (LLNL) and the Idaho National Engineering Laboratory (INEL) are jointly investigating the decomposition of chlorinated hydrocarbons using bremsstrahlung radiation produced by electron accelerators and gamma photons from spent reactor fuel. Experimental results demonstrate an exponential type decay of concentration with dose for volatile organic compounds (VOCs) in ground water and for both polychlorinated biphenyls (PCBs) and insecticides in organic solutions. Experiments were performed at several photon energies and dose rates with various initial concentrations. Mass balance analysis suggests complete mineralization of VOCs in ground water and indicates significant degradation of PCBs and insecticides to VOC type compounds in organic solutions.
