Sandstone response to salt weathering following simulated fire damage: a comparison of furnace heating and fire.

Fire has long been recognized as an agent of rock weathering. Our understanding of the impact of fire on stone comes either from early anecdotal evidence, or from more recent laboratory simulation studies, using furnaces to simulate the effects of fire. This paper suggests that knowledge derived from simulated heating experiments is based on the preconceptions of the experiment designer – when using a furnace to simulate fire, the operator decides on the maximum temperature and the duration of the experiment. These are key factors in determining the response of the stone to fire, and if these are removed from realworld observations then knowledge based on these simulations must be questioned. To explore the differences between heating sandstone in a furnace and a real fire, sample blocks of Peakmoor Sandstone were subjected to different stress histories in combination (lime rendering and removal, furnace heating or fire, frost and salt weathering). Block response to furnace heating and fire is discussed, with emphasis placed on the non-uniformity of the fire and of block response to fire in contrast to the uniform response to surface heating in a furnace. Subsequent response to salt weathering (by a 10% solution of sodium chloride and magnesium sulphate) was then monitored by weight loss. Blocks that had experienced fire showed a more unpredictable response to salt weathering than those that had undergone furnace heating – spalling of corners and rapid catastrophic weight loss were evidenced in blocks that had been subjected to fire, after periods of relative quiescence. An important physical side-effect of the fire was soot accumulation, which created a waxy, relatively impermeable layer on some blocks. This layer repelled water and hindered salt ingress, but eventually detached when salt, able to enter the substrate through more permeable areas, concentrated and crystallized behind it, resulting in rapid weight loss and accelerated decay. Copyright ©2007 John Wiley & Sons, Ltd.

Simulated predator extinctions: Predator identity affects survival and recruitment of oysters

The rate of species loss is increasing at a global scale, and human-induced extinctions are biased toward predator species. We examined the effects of predator extinctions on a foundation species, the eastern oyster (Crassostrea virginica). We performed a factorial experiment manipulating the presence and abundance of three of the most common predatory crabs, the blue crab (Callinectes sapidus), stone crab (Menippe mercenaria), and mud crab (Panopeus herbstii) in estuaries in the eastern United States. We tested the effects of species richness and identity of predators on juvenile oyster survival, oyster recruitment, and organic matter content of sediment. We also manipulated the density of each of the predators and controlled for the loss of biomass of species by maintaining a constant mass of predators in one set of treatments and simultaneously using an additive design. This design allowed us to test the density dependence of our results and test for functional compensation by other species. The identity of predator species, but not richness, affected oyster populations. The loss of blue crabs, alone or in combination with either of the other species, affected the survival rate of juvenile oysters. Blue crabs and stone crabs both affected oyster recruitment and sediment organic matter negatively. Mud crabs at higher than ambient densities, however, could fulfill some of the functions of blue and stone crabs, suggesting a level of ecological redundancy. Importantly, the strong effects of blue crabs in all processes measured no longer occurred when individuals were present at higher-than-ambient densities. Their role as dominant predator is, therefore, dependent on their density within the system and the density of other species within their guild (e.g., mud crabs). Our findings support the hypothesis that the effects of species loss at higher trophic levels are determined by predator identity and are subject to complex intraguild interactions that are largely density dependent. Understanding the role of biodiversity in ecosystem functioning or addressing practical concerns, such as loss of predators owing to overharvesting, remains complicated because accurate predictions require detailed knowledge of the system and should be drawn from sound experimental evidence, not based on observations or generalized models.

Investigation of the impact of simulated commercial centrifugation and microfiltration conditions on levels of Mycobacterium avium subsp. paratuberculosis in milk

The potential for physical removal of Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) from milk by centrifugation and microfiltration was investigated by simulating commercial processing conditions in the laboratory by means of a microcentrifuge and syringe filters, respectively. Results indicated that both centrifugation of preheated milk (60 degrees C) at 7000 x g for 10 s, and microfiltration through a filter of pore size 1.2 mu m, were capable of removing up to 95-99.9% of M. paratuberculosis cells from spiked whole milk and Middlebrook 7H9 broth suspensions, respectively. Centrifugation and microfiltration may therefore have potential application within the dairy industry as pretreatments to reduce M. paratuberculosis contamination of raw milk.

An experiment in group learning technology: evaluating critical thinking in face-to-face and computer-supported seminars

Can learning quality be maintained in the face of increasing class size by the use of Computer Supported Co-operative Learning (CSCL) technologies? In particular, can Computer-Mediated Communication promote critical thinking in addition to surface information transfer? We compared face-to-face seminars with asynchronous computer conferencing in the same Information Management class. From Garrison's theory of critical thinking and Henri's critical reasoning skills, we developed two ways of evaluating critical thinking: a student questionnaire and a content analysis technique. We found evidence for critical thinking in both situations, with some subtle differences in learning style. This paper provides an overview of this work.

An Experiment in Helping Foster-Carers Manage Challenging Behaviour

This article takes issue with those who assume that the responsibility for bad outcomes in social work, such as child deaths, is appropriately laid at the feet of individual workers. It examines the philosophical origins of such arguments, some recent applications within social work literature and their appropriateness to the realities of social work practice. The author argues that a morality of social work must recognize the social and organizational context in which it occurs.

State defining experiment in chemical kinetics. Primary characterization of catalyst activity in a TAP experiment

This paper presents a new strategy, “state-by-state transient screening”, for kinetic characterization of states of a multicomponent catalyst as applied to TAP pulse-response experiments. The key idea is to perform an insignificant chemical perturbation of the catalytic system so that the known essential characteristics of the catalyst (e.g. oxidation degree) do not change during the experiment. Two types of catalytic substances can be distinguished: catalyst state substances, which determine the catalyst state, and catalyst dynamic substances, which are created by the perturbation. The general methodological and theoretical framework for multi-pulse TAP experiments is developed, and the general model for a one-pulse TAP experiment is solved. The primary kinetic characteristics, basic kinetic coefficients, are extracted from diffusion–reaction data and calculated as functions of experimentally measured exit-flow moments without assumptions regarding the detailed kinetic mechanism. The new strategy presented in this paper provides essential information, which can be a basis for developing a detailed reaction mechanism. The theoretical results are illustrated using furan oxidation over a VPO catalyst.

Three primary kinetic characteristics observed in a pulse-response TAP experiment

The state-by-state transient screening approach based on a pulse-response thin-zone TAP experiment is further developed whereby single-pulse kinetic tests are treated as small perturbations to catalyst compositions and analyzed using integral method of moments. Results on three primary kinetic characteristics, termed basic kinetic coefficients, are presented. These three coefficients were introduced as main observables from experimentally measured TAP-responses in a kinetic-model-free manner. Each was analytically determined from moments of responses with no assumption about the detailed kinetic model. In this paper, the inverse question of how well these coefficients represent the time evolution of the observed responses is addressed. Sets of three basic kinetic coefficients are calculated from model and experimental responses and these calculated values are used to generate 3-coefficient curves in a kinetic-model-free manner. The comparison of these 3-coefficient curves with original responses shows that three basic kinetic coefficients can be sufficient to describe the observed kinetics of exit flow time dependencies with no assumption regarding the detailed kinetic model.