Thermoelectric Transport Phenomena in Semiconducting Nanostructures

The efficiencies of state-of-the-art thermoelectric devices made from bulk materials remain too low for widespread application. Early predictions by Hicks and Dresselhaus indicated that one potential route for improving the thermoelectric properties of materials was through nanostructuring. This predicted improvement was due to two effects: an increase in the thermoelectric power factor and a decrease in the lattice thermal conductivity. In this thesis, new models are developed for calculation of the thermoelectric transport properties of nanostructures. The results of these models are in line with what has been seen experimentally in the field of nanostructured thermoelectrics: the power factor of nanostructures falls below the bulk value for sizes accessible by current experimental techniques. While this is demonstrated first for a particular system (cylindrical InSb nanowires), this result is shown to hold true regardless of the dimensionality of the system, the material of interest or the temperature. Using the analytical forms of the transport properties of nanostructured systems, we derive universal scaling relations for the power factor which further point to the fundamental and general nature of this result. Calculations done for nanostructured systems in which the scattering time is a function of carrier energy indicate that the introduction of nanoscale grain boundaries can lead to improvements in the power factor. We present experimental methods for the fabrication and characterization of porous bismuth-antimony-telluride (Bi2-xSbxTe3) thin films using a templated deposition technique. Preliminary results from this experimental work indicate that the nanostructured morphology of the templates used for the deposition of porous films limits diffusion during grain growth, and thus the crystal structure of these porous films differs from that of films deposited on dense substrates. For fundamental investigation of the effects of porosity on thermoelectric transport, future studies should therefore focus on Bi2-xSbxTe3 thin films made by top-down patterning techniques

Mercury from chlor-alkali plants: measured concentrations in food product sugar

Mercury cell chlor-alkali products are used to produce thousands of other products including food ingredients such as citric acid, sodium benzoate, and high fructose corn syrup. High fructose corn syrup is used in food products to enhance shelf life. A pilot study was conducted to determine if high fructose corn syrup contains mercury, a toxic metal historically used as an anti-microbial. High fructose corn syrup samples were collected from three different manufacturers and analyzed for total mercury. The samples were found to contain levels of mercury ranging from below a detection limit of 0.005 to 0.570 micrograms mercury per gram of high fructose corn syrup. Average daily consumption of high fructose corn syrup is about 50 grams per person in the United States. With respect to total mercury exposure, it may be necessary to account for this source of mercury in the diet of children and sensitive populations

Decline in subarachnoid haemorrhage volumes associated with the first wave of the COVID-19 pandemic

BACKGROUND: During the COVID-19 pandemic, decreased volumes of stroke admissions and mechanical thrombectomy were reported. The study\u27s objective was to examine whether subarachnoid haemorrhage (SAH) hospitalisations and ruptured aneurysm coiling interventions demonstrated similar declines. METHODS: We conducted a cross-sectional, retrospective, observational study across 6 continents, 37 countries and 140 comprehensive stroke centres. Patients with the diagnosis of SAH, aneurysmal SAH, ruptured aneurysm coiling interventions and COVID-19 were identified by prospective aneurysm databases or by International Classification of Diseases, 10th Revision, codes. The 3-month cumulative volume, monthly volumes for SAH hospitalisations and ruptured aneurysm coiling procedures were compared for the period before (1 year and immediately before) and during the pandemic, defined as 1 March-31 May 2020. The prior 1-year control period (1 March-31 May 2019) was obtained to account for seasonal variation. FINDINGS: There was a significant decline in SAH hospitalisations, with 2044 admissions in the 3 months immediately before and 1585 admissions during the pandemic, representing a relative decline of 22.5% (95% CI -24.3% to -20.7%, p\u3c0.0001). Embolisation of ruptured aneurysms declined with 1170-1035 procedures, respectively, representing an 11.5% (95%CI -13.5% to -9.8%, p=0.002) relative drop. Subgroup analysis was noted for aneurysmal SAH hospitalisation decline from 834 to 626 hospitalisations, a 24.9% relative decline (95% CI -28.0% to -22.1%, p\u3c0.0001). A relative increase in ruptured aneurysm coiling was noted in low coiling volume hospitals of 41.1% (95% CI 32.3% to 50.6%, p=0.008) despite a decrease in SAH admissions in this tertile. INTERPRETATION: There was a relative decrease in the volume of SAH hospitalisations, aneurysmal SAH hospitalisations and ruptured aneurysm embolisations during the COVID-19 pandemic. These findings in SAH are consistent with a decrease in other emergencies, such as stroke and myocardial infarction