Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors

With microsensors, we measured the steady‐state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m‐2 s‐1), Ca2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calcification cannot supply sufficient protons and CO2 to sustain photosynthesis

Technical report on chemical sensors performance

The report will present an overview of sensors that are useful for the study of seeps, and present a detailed comparison of commercial and prototype CO2 and pH sensors. CO2 sensors: 1) Severinghaus CO2 sensors (Microelectrodes ltd), 2) the HydroC-­‐CO2 logger sensor (CONTROS GmbH), 3) the “GasPro-­‐pCO2” (developed by the team coordinated by Prof. S. Lombardi; Sapienza -­‐ University of Rome-­‐CERI), 4) the MuFo (Multifiber Optode logger, developed in this project in a collaboration between Prof. I. Klimant University Graz and the MPI-­‐MM). pH sensors: 1) glass electrodes Microelectrodes ltd), 2) optodes (developed in this project in a collaboration between Prof. I. Klimant University Graz and the MPI-­‐MM), 3) SeaFET (ion-­‐selective field-­‐effect transistor, Satlantic)

Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

We studied the interaction between phototrophic and chemolithoautotrophic sulphide-oxidizing microorganisms in natural microbial mats forming in sulphidic streams. The structure of these mats varied between two end-members: one characterized by a layer dominated by large sulphur-oxidizing bacteria (SOB; mostly Beggiatoa-like) on top of a cyanobacterial layer (B/C mats) and the other with an inverted structure (C/B mats). C/B mats formed where the availability of oxygen from the water column was limited (<5 mu M). Aerobic chemolithotrophic activity of the SOB depended entirely on oxygen produced locally by cyanobacteria during high light conditions. In contrast, B/C mats formed at locations where oxygen in the water column was comparatively abundant (445 mu M) and continuously present. Here SOB were independent of the photosynthetic activity of cyanobacteria and outcompeted the cyanobacteria in the uppermost layer of the mat where energy sources for both functional groups were concentrated. Outcompetition of photosynthetic microbes in the presence of light was facilitated by the decoupling of aerobic chemolithotrophy and oxygenic phototrophy. Remarkably, the B/C mats conserved much less energy than the C/B mats, although similar amounts of light and chemical energy were available. Thus ecosystems do not necessarily develop towards optimal energy usage. Our data suggest that, when two independent sources of energy are available, the structure and activity of microbial communities is primarily determined by the continuous rather than the intermittent energy source, even if the time-integrated energy flux of the intermittent energy source is greater

Fine‐scale measurement of diffusivity in a microbial mat with nuclear magnetic resonance imaging

Noninvasive 1H‐nuclear magnetic resonance (NMR) imaging was used to investigate the diffusive properties of microbial mats in two dimensions. Pulsed field gradient NMR was used to acquire images of the H2O diffusion coefficient, Ds, and multiecho imaging NMR was used to obtain images of the water density in two structurally different microbial mats sampled from Solar Lake (Egypt). We found a pronounced lateral and vertical variability of both water density and water diffusion coefficient, correlated with the laminated and heterogeneous distribution of microbial cells and exopolymers within the mats. The average water density varied from 0.5 to 0.9, whereas the average water diffusion coefficient ranged from 0.4 to 0.9 relative to the values obtained in the stagnant water above the mat samples. The apparent water diffusivities estimated from NMR imaging compared well to apparent O2 diffusivities measured with a diffusivity microsensor. Analysis of measured O2 concentration profiles with a diffusion‐reaction model showed that both the magnitude of calculated rates and the depth distribution of calculated O2 consumption/production zones changed when the observed variations of diffusivity were taken into account. With NMR imaging, diffusivity can be determined at high spatial resolution, which can resolve inherent lateral and vertical heterogeneities found in most natural benthic systems

Beyond persons: extending the personal / subpersonal distinction to non-rational animals and artificial agents

The distinction between personal level explanations and subpersonal ones has been subject to much debate in philosophy. We understand it as one between explanations that focus on an agent’s interaction with its environment, and explanations that focus on the physical or computational enabling conditions of such an interaction. The distinction, understood this way, is necessary for a complete account of any agent, rational or not, biological or artificial. In particular, we review some recent research in Artificial Life that pretends to do completely without the distinction, while using agent-centered concepts all the way. It is argued that the rejection of agent level explanations in favour of mechanistic ones is due to an unmotivated need to choose among representationalism and eliminativism. The dilemma is a false one if the possibility of a radical form of externalism is considered

Product and process innovations by means of rapid technologies

Published ArticleOver the past few years, methods of layered manufacturing (LM) have advanced substantially to the point where they now provide vital strategic benefits to various organisations. One area of application where LM technologies have begun to reach a critical mass is in the development and production of high-performance tooling in different forming processes. With these tooling capabilities now available, the next challenge becomes the development of optimal process chains to minimise lead times and production costs, while still ensuring high quality of castings. The relevant issues that influence where a break-even point will be between different process chains and thereby also the point of selection between such optimal process chains according to different situations include among others: the size of production runs, part size and complexity, and the cast materials involved. This paper reflects some of the experiences gained from an investigation towards developing a set of generic rules (guidelines) for the design of optimal process chains for sand casting prototypes of automotive components using LM methods, and more specifically the 3D Printing process

Rapid tooling application for the evaluation of a greensand casting defect

Abstract: The ability to produce production quality tooling, directly from CAD data, through additive manufacturing (AM) processes has obvious advantages with regards to the reduced lead time and labour costs. This, together with the ability to simulate the metal casting process, opens new doors for researchers in the field of metal casting. This paper reviews the suitability of tooling produced in PA 2200 polyamide material, for use in a research environment, where the failure of greensand, a mixture of silica sand, bentonite (clay) and water, is to be replicated as it would occur in an industrial setting

Advances in Three Dimensional Printing - state of the art and future perspectives

Published ArticleThis paper surveys the current state and capabilities of Three Dimensional Printing (3DP). Based on its technical background - the ink jet printing as known from the printer and plotter industry - a classification structure has been developed and proposed. Different printing techniques and process concepts, together with their advantages and limitations are described and analysed. A large variety of manufacturing applications such as rapid pattern making and rapid tooling using the 3DP process directly or as core technology, as well as further implications in design and engineering analysis, medicine, and architecture are presented and evaluated. Some research issues are also discussed. An attempt, based on the state of the art, to show weaknesses and opportunities, and to draw conclusions about the future of this important process wraps up this paper

Predicting work performance through selection interview ratings and psychological assessment.

The aim of the study was to establish whether selection interviews used in conjunction with psychological assessments of personality traits and cognitive functioning contribute to predicting work performance. The sample consisted of 102 managers who were appointed recently in a retail organisation. The independent variables were selection interview ratings obtained on the basis of structured competency-based interview schedules by interviewing panels, five broad dimensions of personality defined by the Five Factor Model as measured by the 15 Factor Questionnaire (15FQ+), and cognitive processing variables (current level of work, potential level of work, and 12 processing competencies) measured by the Cognitive Process Profile (CPP). Work performance was measured through annual performance ratings that focused on measurable outputs of performance objectives. Only two predictor variables correlated statistically significantly with the criterion variable, namely interview ratings (r = 0.31) and CPP Verbal Abstraction (r = 0.34). Following multiple regression, only these variables contributed significantly to predicting work performance, but only 17.8% of the variance of the criterion was accounted for

Missed opportunities for immunisation at hospitals in the western Cape - a reappraisal

Immunisation practices were examined at 6 hospitals in the western Cape during the latter half of 1992 to determine whether these practices had improved subsequent to the February 1991 resolution of the Health Matters Committee (HMC) on immunisation in hospitals, and since a similar study was undertaken in 1990. Exit interviews were conducted with the escorts of all children aged 3 - 59 months who attended the study hospitals on the days designated for the study.In the second study, 88 of the 311 children studied (28,3%) were in need of immunisation on arrival, but only 12 of the 88 (13,6%) were immunised during the hospital visit. There was no evidence of an increase in requests to see children's Road-to-Health cards (37,1% compared with 35,2% previously). The  incidence of missed opportunities for measles immunisation in children aged 6 - 59 months remained unacceptably high (51,4% compared with 63,7% previously, when a strict definition was used; and 15,7% compared with 18,1% previously, when a lenient definition was used).Health authorities at all levels need to take urgent action to address the problem of missed opportunities for immunisation at hospitals