Influence of Compressible Aerogel Electrodes on the Properties of an Electrochemical Cell

In the biomedical field the need for intra organ pressure measurement can only be facilitated by adapting existing pressure sensing technology to the specific tissues under test. The customization of these sensors has only driven up cost and the need to explore new technologies has become increasingly more important. For this dissertation, we explore the use of a new technology, particularly electrochemical pressure sensing to provide a low-cost pressure sensor to fill this need. Preliminary testing showed that electrically conductive polymers exhibited a change in voltage when pressurized if bubbles were first electrolyzed in the gel creating an aerogel, and that this effect was virtually undetectable without the bubbles present. Using electrochemical impedance spectroscopy (EIS) and model fitting, it was shown that this effect occurs at the electrode interface. Theoretical derivation supported by potentiostatic voltage measurements indicated that a change in the electrode surface area in contact with the fluid was responsible for the effect. Optical micrographs were taken as a bubble along the electrode was pressurized. Using image analysis, the relationship of the change in surface area of the bubble correlated to the relationship of the change in impedance of the electrochemical cell (ECC). The results further demonstrated that the electrochemical response to pressure of a gelatin aerogel electrode was linear for the pressure range of 0 to1034 mmHg. This finding lends itself well for use in medical devices. A new device was invented along with a manufacturing process for an electrochemical pressure transducer (EPT). The EPT was subject to in vitro testing using simulated gastric fluid to create a baseline efficacy of the device for use in the gastrointestinal tract. Multiple design specific techniques were developed to improve sensor performance during physiological conditions

A Recurrence-type Strong Borel--Cantelli Lemma for Axiom A Diffeomorphisms

Let $(X,\mu,T,d)$ be a metric measure-preserving dynamical system such that $3$-fold correlations decay exponentially for H\"older continuous observables. Given a sequence $(M_k)$ that converges to $0$ slowly enough we obtain a strong dynamical Borel--Cantelli result for recurrence, i.e., for $\mu$-a.e. $x\in X$ $$\lim_{n \to \infty}\frac{\sum_{k=1}^{n} \mathbf{1}_{B_k(x)}(T^{k}x)} {\sum_{k=1}^{n} \mu(B_k(x))} = 1,$$ where $\mu(B_k(x)) = M_k$. In particular, we show that this result holds for Axiom A diffeomorphisms and certain equilibrium states.Comment: 18 pages, 0 figure

Experimental study of carbon-isotope fractionation between diet, hair, and feces of mammalian herbivores

Journal ArticleThe carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal ?13C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary ?13C values and those of hair and feces

Stable isotope evidence of meat eating and hunting specialization in adult male chimpanzees

Observations of hunting and meat eating in our closest living relatives, chimpanzees (Pan troglodytes), suggest that among primates, regular inclusion of meat in the diet is not a characteristic unique to Homo. Wild chimpanzees are known to consume vertebrate meat, but its actual dietary contribution is, depending on the study population, often either unknown or minimal. Constraints on continual direct observation throughout the entire hunting season mean that behavioral observations are limited in their ability to accurately quantify meat consumption. Here we present direct stable isotope evidence supporting behavioral observations of frequent meat eating among wild adult male chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d’Ivoire. Meat eating among some of the male chimpanzees is significant enough to result in a marked isotope signal detectable on a short-term basis in their hair keratin and long-term in their bone collagen. Although both adult males and females and juveniles derive their dietary protein largely from daily fruit and seasonal nut consumption, our data indicate that some adult males also derive a large amount of dietary protein from hunted meat. Our results reinforce behavioral observations of male-dominated hunting and meat eating in adult Taï chimpanzees, suggesting that sex differences in food acquisition and consumption may have persisted throughout hominin evolution, rather than being a recent development in the human lineage

The confounding effects of source isotopic heterogeneity on consumer-diet and tissue-tissue stable isotope relationships

Stable isotope analysis of consumer tissues document patterns of resource use because data are linearly related to isotope compositions of their source(s) (i.e., food, water, etc.). Deviations in parameters estimated for these relationships can arise from variations in consumer tissue-diet spacing (Δ TS ) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of Δ TS and source isotope heterogeneity. The latter may arise via mixed diets, during tissue turnover, or by isotopic routing of dietary components. We apply these concepts to stable carbon and nitrogen isotope relationships between gut contents and body tissues of large mammal herbivores from mixed C3/C4 South African savannas and test predictions based on the compound- and/or time-specific data archived within each material. Predicted effects of source isotope heterogeneity are readily detected in carbon isotope relationships between materials representing different time periods or comprising bulk versus protein-only diet components. Differences in Δ TS of carbon isotopes across mammal herbivore species with very different feeding niches (and diet isotope compositions) are likely to be small or non-existent in these habitats. Variations in Δ TS estimated for nitrogen isotopes are much greater, leading to inconsistencies that cannot be explained by diet or trophic level effects alone. The effects of source heterogeneity on isotopic relationships generate numerical artefacts that have been misinterpreted as variations in Δ TS . We caution against generalized application of hypotheses based on assumptions of source isotopic homogeneity, even for single diets commonly used in laboratory studies. More careful consideration of how heterogeneity affects consumer-diet relationships is needed for many field and laboratory system

Saving old bones: A non-destructive method for bone collagen prescreening

Bone collagen is an important material for radiocarbon, paleodietary, and paleoproteomic analyses, but it degrades over time, making such analyses more difficult with older material. Collagen preservation between and within archaeological sites is also variable, so that much time, effort, and money can go into the preparation and initial analysis of samples that will not yield meaningful results. To avoid this, various methods are employed to prescreen bone for collagen preservation (e.g., %N, microporosity, and FTIR spectroscopic analyses), but these are often destructive and/or require exportation for analysis. Here, we explore near-infrared spectroscopy as a tool for gauging the collagen content of ground and whole bone from about 500 to 45,000 years ago. We show that a portable spectrometer’s ability to quantify collagen content and classify specimens by preservation status is comparable to that of other popular prescreening methods. Moreover, near-infrared spectroscopy is non-destructive and spectra can be acquired in a few seconds

Animal diets in the Waterberg based on stable isotopic composition of faeces

Faecal analysis of diet in free-ranging mammals can provide insight into local habitat conditions by reflecting the resources actually utilized. Here we used stable light isotope analysis of faeces to qualify, as well as quantify, certain aspects of mammal food selection in a recovering, nutrient-poor, savanna habitat in the Waterberg. Stable carbon isotope ratios in faeces reflect proportions of C3-foods (browse) to C4-foods (grass) consumed, whereas stable nitrogen isotope ratios reflect a combination of trophic behaviour, protein intake, and water and nutritional stress. Percentage nitrogen indicates the nutritional quality of the diet, at least in terms of crude protein intake. We used these data to reconstruct and compare the diets of various mammal species from two reserves in the Waterberg: the Welgevonden Private Game Reserve and Zoetfontein Private Game Farm

Problems with paranthropus

Carbon isotopic analysis has been challenging our ideas about hominin diet for nearly 30 years. The first study in 1994 revealed that Paranthropus robustus from South Africa consumed principally C3 foods (e.g., tree fruits and leaves) but also about 25% C4/CAM resources (e.g., tropical grasses and sedges). This result was largely consistent with morphological and dental microwear evidence suggesting P. robustus had a diet which included hard objects like nuts and seeds. Decades later, however, P. boisei from eastern Africa was shown to have eaten nearly 80% C4/CAM plants like the contemporaneous grass-eating primate Theropithecus. Moreover, dental microwear revealed no evidence of hard object consumption in P. boisei, suggesting a diet of tough foods such as grass or sedge leaf and stem. So Paranthropus presents us with two central problems: 1) Why do dietary proxies suggest different diets for the two robust australopiths despite their morphological congruity; and 2) How could P. boisei have consumed tough foods with teeth that seem unsuited to the task. Here we review these questions and more with a particular focus on new isotopic data from the Omo and insights that can be gleaned from mammals outside the haplorrhine primates. We argue that extant Primates do not capture the ecomorphological diversity of P. boisei and other extinct primates and should not narrowly circumscribe the behaviors we ascribe to extinct taxa. We also discuss possible digestive strategies for P. boisei in light of its morphology, dietary proxy data, food mechanical properties, and comparative data on mammalian digestive kinetics.info:eu-repo/semantics/publishedVersio

Utilization of savanna-based resources by Plio-Pleistocene baboons

We have determined the tooth enamel carbonate 13C values of five cercopithecoid taxa from the Plio-Pleistocene deposits of Swartkrans Members 1 and 2 and Sterkfontein Member 4. These data were used to determine the relative proportions of C3 and C4 biomass consumed by extinct baboons and contemporary non-human primates. We compared these results with data on modern Papio hamadryas ursinus from different savanna areas in South Africa, as well as with published isotopic data and dietary interpretations based on molar morphology of these taxa. The data reveal little evidence for use of grasses or grass-based foods by modern South African baboons. The fossil papionins Papio hamadryas robinsoni, Papio (Dinopithecus) ingens, and Parapapio spp., however, utilized more savanna-based C4 resources than previously predicted (particularly in the case of P. (D.) ingens). Theropithecus oswaldi had 13C values depicting, as expected, a largely grass-based diet, and we confirm earlier conclusions that this species incorporated a wider range of food items into its diet than do modern T. gelada, as reported in the literature. The colobine monkey, Cercopithecoides williamsi, made extensive use of savanna-.based C4 foods, confirming some degree of terrestrial foraging by the species

Using carbon isotope data of fossil bovid communities for palaeoenvironmental reconstruction

Reconstructing palaeoenvironments is a major focus of palaeoanthropological research. While many techniques are now available for exploring past environments, fossil bovids remain amongst the most widely utilized sources of environmental information. Most studies of fossil bovids, however, assume implicitly that bovid ecology is the same now as it was in the distant past. Because such uniformitarianist assumptions are not always valid, we have developed a method to provide palaeoenvironmental information from fossil bovids that requires no ecological assumptions. Here, we show that the percentages of C3 and C4 vegetation-consuming bovids in modern environments generally vary according to the amount of woody vegetation present. Application of this C3 / C4 index to the fossil bovid assemblage at Makapansgat shows that, based on carbon isotope data, the percentage of C3-consuming bovids is high, suggesting a great deal of woody vegetation in this vicinity about 3 million years ago