An in vitro study of the interactions of bacteria from the human colon.

An in vitro model system inoculated with human faeces was used to study the fermentation of mixtures of bran, cabbage, turnip, carrot and apple dietary fibres. The results suggested that the mixture in which a dietary fibre is supplied influenced its digestibility even though the chemical composition of the different mixtures was very similar. The pentose fractions of the fibre were the least digestible. Starch-, xylan- and pectin-degrading bacteria were enumerated and the majority of isolates were capable of more than one activity. These results highlight the potential for metabolic diversity amongst the predominant bacteria in vivo. Total numbers of bacteria were relatively constant throughout the experiments and close to estimates of bacterial numbers in the human colon. The volatile fatty acids, acetate, propionate and butyrate were the major bacterial end-products and were produced in molar ratios close to those observed in vivo. Small amounts of methane and hydrogen were produced during all experiments but there was no evidence of a product-precursor relationship. It is postulated that the production of acetate from H2 and CO2 during homoacetic acid fermentation was the major hydrogenotrophic reaction taking place. Nitrate was reduced to N2 during dissimilatory nitrate reduction and nitrite only appeared as a transient intermediate when nitrate concentrations increased. Ammonia was always produced in the fermentor as a by-product of the fermentation of amino acids. Sulphate was reduced to H2S and this process was inhibited by increased concentrations of nitrate

The Mackintosh Library: An Active Learning Space

The content of this paper was presented at the Building on Mackintosh symposium held at the Glasgow School of Art in April 201

Modelling the effect of nuclear motion on the attosecond time-resolved photoelectron spectra of ethylene

Using time dependent density functional theory (TDDFT) we examine the energy, angular and time-resolved photoelectron spectra (TRPES) of ethylene in a pump-probe setup. To simulate TRPES we expose ethylene to an ultraviolet (UV) femtosecond pump pulse, followed by a time delayed extreme ultraviolet (XUV) probe pulse. Studying the photoemission spectra as a function of this delay provides us direct access to the dynamic evolution of the molecule's electronic levels. Further, by including the nuclei's motion, we provide direct chemical insight into the chemical reactivity of ethylene. These results show how angular and energy resolved TRPES could be used to directly probe electron and nucleus dynamics in molecules.Comment: 9 pages, 6 figure

The end of vagueness : technological epistemicism, surveillance capitalism, and explainable Artificial Intelligence

Artificial Intelligence (AI) pervades humanity in 2022, and it is notoriously difficult to understand how certain aspects of it work. There is a movement—Explainable Artificial Intelligence (XAI)—to develop new methods for explaining the behaviours of AI systems. We aim to highlight one important philosophical significance of XAI—it has a role to play in the elimination of vagueness. To show this, consider that the use of AI in what has been labeled surveillance capitalism has resulted in humans quickly gaining the capability to identify and classify most of the occasions in which languages are used. We show that the knowability of this information is incompatible with what a certain theory of vagueness—epistemicism—says about vagueness. We argue that one way the epistemicist could respond to this threat is to claim that this process brought about the end of vagueness. However, we suggest an alternative interpretation, namely that epistemicism is false, but there is a weaker doctrine we dub technological epistemicism, which is the view that vagueness is due to ignorance of linguistic usage, but the ignorance can be overcome. The idea is that knowing more of the relevant data and how to process it enables us to know the semantic values of our words and sentences with higher confidence and precision. Finally, we argue that humans are probably not going to believe what future AI algorithms tell us about the sharp boundaries of our vague words unless the AI involved can be explained in terms understandable by humans. That is, if people are going to accept that AI can tell them about the sharp boundaries of the meanings of their words, then it is going to have to be XAI.Publisher PDFPeer reviewe

Parasitism and environmental sex determination in Daphnia

International audienceHypothesis: Daphnia exposed to cues associated with the onset of a parasite epidemic will have more males and resting eggs.Organisms: Seven clones of Daphnia magna (chosen for high levels of sexual reproduction) and the bacterial parasite Pasteuria ramosa.Methods: We explored how parasite infection (simulated by creating crowding conditions using infected hosts) might influence male and resting egg production compared with crowding conditions created using healthy hosts. We also explored the effects of putting bacterial spores in water. Conclusions: Both crowding and crowding with infected hosts led to higher numbers of males and resting eggs. Direct exposure to parasite transmission spores had no effect. Male production in response to treatment was host-clone specific, with some clones responding strongly to the presence of infected hosts, but others not responding or only responding to water crowded with healthy Daphnia. Resting-egg production in response to treatment was also host-clone specific, but differences were not affected by crowding conditions

Density-and trait-mediated effects of a parasite and a predator in a tri-trophic food web

1. Despite growing interest in ecological consequences of parasitism in food webs, relatively little is known about effects of parasites on long-term population dynamics of non-host species or about whether such effects are density- or trait- mediated. 2. We studied a tri-trophic food chain comprised of: (i) a bacterial basal resource (Serratia fonticola), (ii) an intermediate consumer (Paramecium caudatum), (iii) a top predator (Didinium nasutum), and (iv) a parasite of the intermediate consumer (Holospora undulata). A fully-factorial experimental manipulation of predator and parasite presence/absence was combined with analyses of population dynamics, modelling, and analyses of host (Paramecium) morphology and behavior. 3. Predation and parasitism each reduced the abundance of the intermediate consumer (Paramecium), and parasitism indirectly reduced the abundance of the basal resource (Serratia). However, in combination, predation and parasitism had non-additive effects on the abundance of the intermediate consumer, as well as on that of the basal resource. In both cases, the negative effect of parasitism seemed to be effaced by predation. 4. Infection of the intermediate consumer reduced predator abundance. Modelling and additional experimentation revealed that this was most likely due to parasite reduction of intermediate host abundance (a density-mediated effect), as opposed to changes in predator functional or numerical response. 5. Parasitism altered morphological and behavioural traits, by reducing host cell length and increasing the swimming speed of cells with moderate parasite loads. Additional tests showed no significant difference in Didinium feeding rate on infected and uninfected hosts, suggesting that the combination of these modifications does not affect host vulnerability to predation. However, estimated rates of encounter with Serratia based on these modifications were higher for infected Paramecium than for uninfected Paramecium. 6. A mixture of density-mediated and trait-mediated indirect effects of parasitism on non- host species creates rich and complex possibilities for effects of parasites in food webs that should be included in assessments of possible impacts of parasite eradication or introduction

Scattering of light with angular momentum from an array of particles

Understanding the scattering properties of various media is of critical importance in many applications, from secure high-bandwidth communications to extracting information about biological and mineral particles dissolved in sea water. In this paper we demonstrate how beams carrying orbital angular momentum can be used to detect the presence of symmetric or chiral subsets of particles in disordered media. Using a generalized Mie theory, we calculate analytical expressions for quasimonochromatic structured light scattered by dilute distributions of micro- and nanoparticles. These allow us to determine the angular momentum of the scattered field as a function of the angular momentum of the incident beam and of the spatial distributions of scattering particles. Our numerical results show that we can distinguish structured from random distributions of particles, even when the number density of ordered particles is a few percent of the total istribution. We also find that the signal-to-noise ratio, in the forward direction, is equivalent for all orders of the Laguerre-Gaussian modes in relatively dense (but still dilute) distributions of particles smaller than the beam waist and the Rayleigh range of the beam

The health and safety implications of socio-cultural context for community construction projects in developing countries

Community participation in construction during rural infrastructure projects in developing countries is encouraged by many non-governmental organizations. The health and safety aspects of this type of development model have not previously been adequately researched, however. The aim is to identify the socio-cultural factors that motivate community members to participate in construction activities which they perceive as hazardous during a case study of a water and sanitation project in rural Ghana. This is a step towards understanding how health and safety can be more effectively managed during community development projects. A qualitative approach has been taken, using interview, observation and reflection. It was found that the communal culture of the local context resulted in community members feeling pressurized to participate in hazardous construction activities. Local customary laws further compelled individuals as they were concerned they could be fined or arrested should they not fulfil their communal obligations. Further work is required to determine the boundaries within which findings apply but it is likely that there are implications for others managing community construction projects both in Ghana and further afield