Recent research suggests that increased adiposity is associated with poor cognitive performance, independently of associated medical conditions. The evidence regarding this relationship is examined ...in this review article. A relatively consistent finding across the lifespan is that obesity is associated with cognitive deficits, especially in executive function, in children, adolescents and adults. However, as illustrated by contradictory studies, the relationship between obesity and cognition is uncertain in the elderly, partly because of inaccuracy of body mass index as a measure of adiposity as body composition changes with aging. This review further discusses whether obesity is a cause or a consequence of these cognitive deficits, acknowledging the possible bidirectional relationship. The possible effects of increased adiposity on the brain are summarized. Our investigations suggest that weight gain results, at least in part, from a neurological predisposition characterized by reduced executive function, and in turn obesity itself has a compounding negative impact on the brain via mechanisms currently attributed to low‐grade systemic inflammation, elevated lipids and/or insulin resistance. The possible role of cognitive remediation treatment strategies to prevent and/or treat obesity is discussed.
Repeated outbreaks of emerging pathogens underscore the need for preparedness plans to prevent, detect, and respond. As countries develop and improve National Action Plans for Health Security, ...addressing subnational variation in preparedness is increasingly important. One facet of preparedness and mitigating disease transmission is health facility accessibility, linking infected persons with health systems and vice versa. Where potential patients can access care, local facilities must ensure they can appropriately diagnose, treat, and contain disease spread to prevent secondary transmission; where patients cannot readily access facilities, alternate plans must be developed. Here, we use travel time to link facilities and populations at risk of viral hemorrhagic fevers (VHFs) and identify spatial variation in these respective preparedness demands.
We used geospatial resources of travel friction, pathogen environmental suitability, and health facilities to determine facility accessibility of any at-risk location within a country. We considered in-country and cross-border movements of exposed populations and highlighted vulnerable populations where current facilities are inaccessible and new infrastructure would reduce travel times. We developed profiles for 43 African countries. Resulting maps demonstrate gaps in health facility accessibility and highlight facilities closest to areas at risk for VHF spillover. For instance, in the Central African Republic, we identified travel times of over 24 h to access a health facility. Some countries had more uniformly short travel times, such as Nigeria, although regional disparities exist. For some populations, including many in Botswana, access to areas at risk for VHF nationally was low but proximity to suitable spillover areas in bordering countries was high. Additional analyses provide insights for considering future resource allocation. We provide a contemporary use case for these analyses for the ongoing Ebola outbreak.
These maps demonstrate the use of geospatial analytics for subnational preparedness, identifying facilities close to at-risk populations for prioritizing readiness to detect, treat, and respond to cases and highlighting where gaps in health facility accessibility exist. We identified cross-border threats for VHF exposure and demonstrate an opportunity to improve preparedness activities through the use of precision public health methods and data-driven insights for resource allocation as part of a country's preparedness plans.
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► Vibrational spectrum of PET complicated by the presence of rotational isomers and changes on crystallization. ► Synchronous and asynchronous correlation spectra enables the ...absorption bands to be unambiguously assigned. ► Fractional crystallinity can be directly determined from the amorphous and crystalline band ratio.
The vibrational spectrum of partially crystalline poly(ethylene terephthalate), PET, appears to be unduly complex in that the absorption bands are split into amorphous and crystalline modes and are sensitive to chain configuration and orientation. Assignment of the bands has accordingly proved to be difficult and lead to differences in interpretation. Two-dimensional infrared spectroscopy is a recent novel analytical technique in vibrational spectroscopy which can be used to interpret differences in the spectra with time or temperature accompanying changes in structure and morphology and has been used to analyze the development of crystallinity within a polymer in which amorphous regions are transformed into crystalline regions and involving changes in molecular configuration.
Two-dimensional IR correlation spectroscopy has been successfully applied to these problems in the attempt to measure the fractional extent of crystallinity in PET as a function of time and crystallization temperature as well as changes to molecular configuration.
The procedures adopted and the inherent assumptions made in the measurement of crystallinity of polymers by differential scanning calorimetry (DSC) are reviewed. The inherent problem in all DSC ...measurements is concurrent recrystallisation and melting of the polymer sample on heating to the melting point and the variation of the enthalpies of crystallisation and melting, heat capacities and degree of crystallinity with temperature. A First Law procedure is suggested which involves heating the sample between two set temperatures,
T
1 and
T
2.
T
1 is selected by the requirement that the degree of crystallinity of the sample should not change either with temperature or time, and be representative of the sample during its use.
T
1 is taken to be ambient or just above the glass transition temperature.
T
2 is taken to be just above the observed last trace of crystallinity. Integrating the observed specific heat difference between the sample and the completely amorphous material during these two temperature ranges determined the residual enthalpy of fusion at
T
1. Problems are noted in the use of this procedure in that the specific heat of the liquid should not be arbitrarily chosen since this leads to systematic errors in the heat of crystallisation.
The degrees of crystallinity of metallocene polyethylene (m-PE) and polyethylene terephthalate (PET) measured by this procedure have been compared with values measured by density, determined at room temperature.
Differential Scanning Calorimetry has been used to study the isothermal crystallization kinetics and melting behaviour of PET. Kinetic analysis indicated that the overall crystallization of PET ...involved two processes, attributed to primary and secondary crystallization. Secondary crystallization occurred consecutively with primary and both processes obey different Avrami time dependences. The primary process was that of heterogeneous nucleation and three-dimensional spherical growth that was confirmed by direct observation of spherulites by SEM. Secondary crystallization was that of one dimensional growth involving fibrillar growth between the primary lamellae of the spherulites. Accordingly primary crystallization has a stronger temperature dependence on temperature than secondary. Further analysis based on Hoffman–Lauritzen theory revealed that PET crystallization followed regime I kinetics at temperatures between 490 and 564
K. Below 490
K, regime II kinetics were operational. Multiple endotherms were observed in melting PET and attributed to the effect of crystal perfection and re-crystallization on heating from the crystallization temperature to the m.pt. Increasing the crystallization temperature and the rates of heating during melting scans minimized these effects.
Increases in yield stress, yield strain and decrease in elongation at break with crystallinity were ascribed to the strengthening effect of the crystals on the amorphous matrix, accompanied by the change in mechanism of tensile deformation from ductile yielding to craze-crack growth.
Describes the thermal degradation of polyvinyl alcohol, both in the solid and molten state. Initially, thermal degradation in the solid state was considered to be due to the elimination of hydroxyl ...side groups, but this process should have produced appreciable amounts of isolated and conjugated polyenes in the degradation residue and small amounts of carbonyl group were detected. Side group elimination was followed by a reduction in the melting point and the degree of crystallinity. In the molten state, thermal degradation led to the production of volatile saturated and unsaturated aldehydes and ketones, as well as water. It was considered that the greater flexibility of the polymer chains in the melt facilitated fragmentation of the chain and elimination of chain segments. (Original abstract)
Changes to infra-red spectra of poly(ethylene terephthalate) on heating and cooling. Display omitted
► Microgram samples have been analysed to determine glass transition, crystallization and melting ...behaviour of PET. ► The absorbance of cis/trans bands have been followed with temperature on heating and cooling. ► Fractional crystallinity was determined directly without calibration. ► The IR absorption bands are characterized as type I or type II according to their behaviour with temperature.
Thermal analysis-FTIR spectroscopy, TA-FTIR, has been used to characterize the phase transitions in thin films of poly(ethylene terephthalate) and it has been shown to have distinct advantages over other TA techniques in particular it was not so limited in sensitivity. Since the technique measured property, such as amorphous content or fractional crystallinity directly rather than the rate of change of the properties with time or temperature, it was not so restricted in the time scale over which measurements were made. It also had the advantage of measuring the change in concentration of different functional groups with temperature and determining the temperature range over which chain mobility set in and defining the type of molecular groups involved in the configurational changes.
The change in absorbance and shift in peak position with temperature are discussed in terms of the separation of crystalline and amorphous bands as well as defining the cis/trans ratio as a function of temperature.
Depending on the change in absorbance or peak position with temperature of the IR bands, they have been characterized as type I or type II behaviour. Measurements on both have been used to characterize the glass transition, crystallization and melting behaviour of PET.
The thermal degradation of two commercial poly(ethylene terephthalate) (PET) samples and two laboratory prepared polyesters, poly(ethylene isophthalate) and poly(diethylene glycol terephthalate), was ...studied using thermogravimetry and thermal analysis–Fourier transform infrared spectroscopy. The commercial PET samples were copolymerised with diethylene glycol and isophthalic acid groups in different proportions, and their thermal stabilities were found to differ. Through a study of the thermal degradation of poly(diethylene glycol terephthalate) and poly(ethylene isophthalate), it was found that diethylene glycol and isophthalate units promoted thermal degradation through increased chain flexibility and more favourable bond angles, respectively. The thermal degradation of all the polyesters tested lead to the formation of non-volatile residue. Infrared spectroscopic analysis indicated that the residue consisted almost exclusively of interconnected aromatic rings.
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•Vibrational spectrum of PCL is complicated by changes on crystallization.•TA–FTIR spectroscopy enables the absorption bands to be unambiguously assigned.•Crystallinity can be ...determined from the ratio of crystalline and amorphous bands.
Vibrational spectra of poly(ε-caprolactone) have been measured as a function of temperature and time to assign the molecular origins of the absorption bands, to distinguish crystalline and amorphous bands and measure fractional crystallinity. While many changes occur within the spectrum on crystallization and melting those which occur to the carbonyl absorption band proved to be the most useful in determining the fractional crystallinity and following the development of crystallinity with time.
Two-dimensional IR correlation mapping applied to the carbonyl band clearly showed that the broad band at 1735cm−1 was due to the stretching of the ester carbonyl group in the amorphous regions which decreased in intensity on isothermal crystallization. At the same time a narrower more intense band developed at 1725cm−1 attributed to the absorption of the ester carbonyl group in the crystalline regions. Deconvoluting the band into these components enabled the intensities of the two to be determined and the fractional crystallinity measured.
Crystalline polymers are not in thermal equilibrium and thermodynamic parameters such as enthalpy of fusion as determined by differential scanning calorimetry from the area under the melting ...endotherm over a wide temperature range have not been measured under equilibrium conditions. Accordingly measurements of the degree of crystallinity based on the enthalpy of fusion reflect experimental conditions, are incorrect in that they do not usually agree with those determined by other analytical procedures, such as density and WAX scattering, particularly when measured at ambient temperatures. While this has been repeatedly pointed out procedures used to determine the fractional crystallinity of polymers based on the enthalpy of fusion continue to be widely used.
Using the First Law method, the enthalpy of fusion and fractional crystallinity have been measured as a function of temperature for metallocene polyethylene and polyethylene terephthalate during heating. The crystallinity measured on the sample prior to heating is in good agreement with that determined by density and wide angle X-ray diffraction.
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