Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics.

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.

Biomorphic Ceramics: Synthesis and Characterization of Preceramic Polymer-Modified Melanin.

Recent efforts have demonstrated that the morphology of ceramics can be manipulated to control both their deformation mechanism and mechanical performance. However, precise control of the ceramic nanostructure is still difficult to achieve. Biotemplating, leading to biomorphic materials, provides a facile route to manipulate the nanostructure of the resulting materials, and the use of melanin as a coating provides a new route to biotemplated materials. Melanin is underutilized for structural materials partly due to the cost of procuring it from natural sources and the inability to control the shape and sizes of melanin particles. Taking a combined synthetic biology and chemical synthesis approach, we report the melanization of Escherichia coli and its subsequent silanization and functionalization with preceramic polymers to make novel biomorphic silicon-based ceramic materials. Graft-to and graft-from reactions were used to append preceramic polymers to the melanin, followed by pyrolysis under argon. Samples were analyzed by FTIR, XRD, XPS, and TEM and found to retain the shape and size of the original cells with high fidelity. The homogeneity of coverage and yield of the resulting ceramic materials depended on the type of grafting reaction. This work provides a promising proof-of-concept that bacterial-templated ceramics can be readily made and opens a host of possibilities for further studies and applications.

Cancers in Australia in 2010 attributable to tobacco smoke.

OBJECTIVES: To estimate the population attributable fraction (PAF) and numbers of cancers occurring in Australia in 2010 attributable to tobacco smoking, both personal and by a partner. METHODS: We used a modified Peto-Lopez approach to calculate the difference between the number of lung cancer cases observed and the number expected assuming the entire population developed lung cancer at the same rate as never smokers. For cancers other than lung, we applied the standard PAF formula using relative risks from a large cohort and derived notional smoking prevalence. To estimate the PAF for partners' smoking, we used the standard formula incorporating the proportion of non-smoking Australians living with an ever-smoking partner and relative risks associated with partner smoking. RESULTS: An estimated 15,525 (13%) cancers in Australia in 2010 were attributable to tobacco smoke, including 8,324 (81%) lung, 1,973 (59%) oral cavity and pharynx, 855 (60%) oesophagus and 951 (6%) colorectal cancers. Of these, 136 lung cancers in non-smokers were attributable to partner tobacco smoke. CONCLUSIONS: More than one in eight cancers in Australia is attributable to tobacco smoking and would be avoided if nobody smoked. IMPLICATIONS: Strategies to reduce the prevalence of smoking remain a high priority for cancer control.

Air pollution events from forest fires and emergency department attendances in Sydney, Australia 1996-2007: a case-crossover analysis.

BACKGROUND: Severe air pollution generated by forest fires is becoming an increasingly frequent public health management problem. We measured the association between forest fire smoke events and hospital emergency department (ED) attendances in Sydney from 1996-2007. METHODS: A smoke event occurred when forest fires caused the daily citywide average concentration of particulate matter (PM10 or PM2.5) to exceed the 99th percentile of the entire study period. We used a time-stratified case-crossover design and conditional logistic regression models adjusted for meteorology, influenza epidemics, and holidays to estimate odds ratios (OR) and 95% confidence intervals (CI) for ED attendances on event days compared with non-event days for all non-trauma ED attendances and selected cardiorespiratory conditions. RESULTS: The 46 validated fire smoke event days during the study period were associated with same day increases in ED attendances for all non-trauma conditions (1.03, 95% CI 1.02, 1.04), respiratory conditions (OR 1.07, 95% CI 1.04, 1.10), asthma (OR 1.23, 95% CI 1.15, 1.30), and chronic obstructive pulmonary disease (OR 1.12, 95% CI 1.02, 1.24). Positive associations persisted for one to three days after the event. Ischaemic heart disease ED attendances were increased at a lag of two days (OR 1.07, 95% CI 1.01, 1.15) while arrhythmias had an inverse association at a lag of two days (OR 0.91, 95% CI 0.83, 0.99). In age-specific analyses, no associations present in children less than 15 years of age for any outcome, although a non-significant trend towards a positive association was seen with childhood asthma. A further association between smoke event and heart failure attendances was present for the 15-65 year age group, but not older adults at a lag of two days (OR 1.37 95% CI 1.05, 1.78). CONCLUSION: Smoke events were associated with an immediate increase in presentations for respiratory conditions and a lagged increase in attendances for ischaemic heart disease and heart failure. Respiratory impacts were either absent or considerably attenuated in those <15 years. Similar to previous studies we found inconsistent associations between fire smoke and cardiovascular diseases. Better characterisation of the spectrum of population health risks is needed to guide public heath responses to severe smoke events as this exposure becomes increasingly common with global climate change.

Air pollution from bushfires and their association with hospital admissions in Sydney, Newcastle and Wollongong, Australia 1994-2007.

OBJECTIVE: We examined the association between validated bushfire smoke pollution events and hospital admissions in three eastern Australian cities from 1994 to 2007. METHODS: Smoke events were defined as days on which bushfire smoke caused the 24-hour citywide average concentration of airborne particles to exceed the 99(th) percentile of the daily distribution for the study period. We used a time-stratified case-crossover design to assess the association between smoke events and hospital admissions. Odds ratios (OR) and 95% confidence intervals (CI) were estimated for cardiovascular and respiratory conditions on event days compared with non-event days. Models were adjusted for daily meteorology, influenza epidemics and holidays. RESULTS: Smoke events occurred on 58 days in Sydney (population: 3,862,000), 33 days in Wollongong (population: 406,000) and 50 days in Newcastle (population: 278,000). In Sydney, events were associated with a 6% (OR=1.06, 95%CI=1.02-1.09) same day increase in respiratory hospital admissions. Same day chronic obstructive pulmonary disease admissions increased 13% (OR=1.13, 95%CI=1.05-1.22) and asthma admissions by 12% (OR=1.12, 95%CI=1.05-1.19). Events were also associated with increased admissions for respiratory conditions in Newcastle and Wollongong. CONCLUSIONS: Smoke events were associated with increased hospital admissions for respiratory but not cardiovascular conditions. Large populations are needed to assess the impacts of brief exposures. Implications : Public health impacts from bushfire pollution events are likely to increase in association with a warming climate and more frequent severe fire weather.

Cognitive function modifies the effect of physiological function on the risk of multiple falls--a population-based study.

BACKGROUND: There is a poor understanding of the interplay between cognitive and physiological functions in leading to falls. We hypothesized that poorer physiological function would modify the effect of poorer cognitive function on increased risk of falling in older people. METHODS: A range of cognitive (executive function/attention, memory, processing speed, and visuospatial ability) and physiological functions (vision, proprioception, sway, leg strength, reaction time) were measured using standardized tests in 386 randomly selected adults aged 60-86. Incident falls were recorded over 12 months. Log-multinomial regression was used to model the relationships and test for interactions between cognition and physiological function in explaining the risk of single or multiple falls. RESULTS: Overall, 94 people (24.4%) had a single fall, and 78 (20.2%) had multiple falls. No significant associations were observed between cognitive function and the risk of single falls. The risk of multiple falls was increased with poorer function in Stroop dot time (RR = 1.03, 95% CI [1.01, 1.05], p = .002) and Stroop word time (RR = 1.02 [1.01, 1.03], p = .001) and reduced with better function in Category Fluency (RR = 0.94 [0.91, 0.98], p = .001) and visuospatial function (RR = 0.95 [0.92, 0.98], p < .001). These associations were amplified by the presence of greater body sway, less ambulatory physical activity, slower reaction time and gait speed, weaker muscle strength, and poorer visual contrast (p for interactions <.05). CONCLUSIONS: Preventing falls due to physiological impairments in community-dwelling older people may need to be tailored based on cognitive impairment, a key factor in their inability to compensate for physical decline.

Cognitive function, gait, and gait variability in older people: a population-based study.

BACKGROUND: Gait impairments are associated with falls and loss of independence. The study of factors associated with poorer gait may assist in developing methods to preserve mobility in older people. The aim of this study was to examine the associations between a range of cognitive functions and gait and gait variability in a population-based sample of older people. METHODS: Gait and intra-individual gait variability measures were obtained using the GAITRite walkway in a sample of older people, aged 60-85 years (N = 422), randomly selected from the Tasmanian electoral roll. Raw scores from a cognitive battery were subjected to principal component analyses deriving four summary domains: executive function/attention, processing speed, memory, and visuospatial ability. Multivariable linear regression was used to examine associations between cognitive domains and gait measures adjusting for age, sex, ambulatory activity, medication use, and mood. RESULTS: The mean age of the sample was 72.0 years (SD = 7.0), with 238 men (56%). Poorer executive function was independently associated with poorer performance in most absolute gait measures and with greater variability in double support phase and step time. Processing speed was associated with absolute gait measures and double support phase variability. Visuospatial ability was only associated with greater double support phase variability, independently of executive function and processing speed. Memory was not independently associated with any gait measure. CONCLUSIONS: In community-dwelling older people, executive function/attention and processing speed were associated with many aspects of gait, whereas visuospatial ability may only play a role in double support phase variability.

Gait, gait variability and the risk of multiple incident falls in older people: a population-based study.

BACKGROUND: it is uncertain as to which measures of gait best predict those who are likely to fall. Our aim was to investigate the associations of gait and gait variability measures with incident falls risk. METHODS: individuals aged 60-86 years (n = 412) were randomly selected from the Tasmanian electoral roll. Average gait and gait variability measures were collected on a computerised walkway. Falls were recorded prospectively over 12 months. Log multinomial regression was used to estimate the relative risk of single and multiple falls associated with gait measures. Covariates included age, sex, sensorimotor and cognitive measures, mood and medications. RESULTS: in this population-based study greater intra-individual variability in step length and double-support phase were linearly associated with increased risk of multiple falls (P = 0.04). Non-linear associations with multiple falls were found for gait speed P = 0.002, cadence P = 0.004 and step time variability P = 0.03. None of the gait measures predicted risk of single falls. CONCLUSION: there is an increased risk of multiple falls, but not single falls, in older people with poorer gait. Specific measures of gait and gait variability seem to confer this risk and may be amenable to interventions designed to reduce the risk of multiple falls in older people.