1,006 research outputs found
The effect of a concentration-dependent viscosity on\ud particle transport in a channel flow with porous walls
We analyse the transport of a dilute suspension of particles through a channel with porous walls accounting for the concentration dependence of the viscosity. Two cases of leakage flow of fluid through the porous channel walls are studied: (i) constant flux, and (ii) dependent on the pressure drop across the wall. The effect of mixing the suspension first compared with point injection is examined by considering inlet concentration distributions of different widths. We find that a pessimal distribution width exists that maximizes the required hydrodynamic pressure for a constant fluid influx. We also show that the presence of an osmotic pressure may lead to fluid being sucked into the channel. We consider how the application of an external hydrodynamic pressure affects this observation and discuss the significance of our results for water filtration
Feeding, defaecation and absorption efficiency in the seaurchin, Parechinus angulosus Leske
No Abstract
From rhizoids to roots? Experimental evidence of mutualism between liverworts and ascomycete fungi
Background and Aims
The rhizoids of leafy liverworts (Jungermanniales, Marchantiophyta) are commonly colonized by the ascomycete fungus Pezoloma ericae. These associations are hypothesized to be functionally analogous to the ericoid mycorrhizas (ErMs) formed by P. ericae with the roots of Ericaceae plants in terms of bi-directional phosphorus for carbon exchange; however, this remains unproven. Here, we test whether associations between the leafy liverwort Cephalozia bicuspidata and P. ericae are mutualistic.
Methods
We measured movement of phosphorus and carbon between C. bicuspidata and P. ericae using [33P]orthophosphate and 14CO2 isotope tracers in monoxenic cultures. We also measured leafy liverwort growth, with and without P. ericae.
Key Results
We present the first demonstration of nutritionally mutualistic symbiosis between a non-vascular plant and an ErM-forming fungus, showing transfer of fungal-acquired P to the liverwort and of liverwort-fixed C to the fungus alongside increased growth in fungus-colonized liverworts.
Conclusions
Thus, this ascomyceteâliverwort symbiosis can now be described as mycorrhiza-like, providing further insights into ericoid mycorrhizal evolution and adding Ascomycota fungi to mycorrhizal fungal groups engaging in mutualisms with plants across the land plant phylogeny. As P. ericae also colonizes the rhizoids of Schistochilaceae liverworts, which originated in the Triassic and are sister to all other jungermannialean liverworts associated with fungi, our findings point toward an early origin of ascomyceteâliverwort symbioses, possibly pre-dating their evolution in the Ericales by some 150 million years
Recovery from addiction: Behavioral economics and value-based decision making.
Behavioral economics provides a general framework to explain the shift in behavioral allocation from substance use to substance-free activities that characterizes recovery from addiction, but it does not attempt to explain the internal processes that prompt those behavioral changes. In this article we outline a novel analysis of addiction recovery based on computational work on value-based decision making (VBDM), which can explain how people with addiction are able to overcome the reinforcement pathologies and decision-making vulnerabilities that characterize the disorder. The central tenet of this account is that shifts in molar reinforcer preferences over time from substance use to substance-free activities can be attributed to changes in evidence accumulation rates and response thresholds in the context of choices involving substance use and substance-free alternatives. We discuss how this account can be reconciled with the established mechanisms of action of psychosocial interventions for addiction and demonstrate how it has the potential to empirically address longstanding debates regarding the nature of impairments to self-control in addiction. We also highlight conceptual and methodological issues that require careful consideration in translating VBDM to addiction and recovery
Meaning in life: investigating protective and risk factors for harmful alcohol consumption
Background
Individuals with greater meaning in life tend to consume less alcohol. However, research elucidating pathways through which meaning in life influences consumption is lacking. Behavioral economic theories posit that distortions in valuation processes, whilst negative reinforcement models posit that avoidance or regulation of negative internal states, are central in decisions to consume alcohol.
Method
Pre-registered, cross-sectional design. Five hundred forty-six regular alcohol consumers (â„18âyears old) completed an online questionnaire which asked about alcohol use, meaning in life, alcohol-free reinforcement, alcohol value, depressive symptoms, and drinking to cope motives.
Results
Presence of meaning had a significant negative association with AUDIT scores (ÎČ = â.26, p .53). Subsequent path analyses revealed a significant indirect effect of presence of meaning on AUDIT scores through lower alcohol value (95% CIâ=ââ.17 to â.08) and drinking to cope (95% CIâ=ââ.07 to â.00), and a serial mediation effect through both lower depressive symptoms and drinking to cope (95% CIâ=ââ.09 to â.04). Although search for meaning was not a direct predictor of AUDIT scores, there was a significant indirect effect through greater drinking to cope (95% CI = .01 to .06) and a serial mediation effect through both greater depressive symptoms and drinking to cope (95% CI = .01 to .04).
Conclusions
Meaning in life subscales predict alcohol consumption indirectly via individual differences in alcohol value, depressive symptoms, and drinking to cope
Mucoromycotina fine root endophyte fungi form nutritional mutualisms with vascular plants
Fungi and plants have engaged in intimate symbioses that are globally widespread and have driven terrestrial biogeochemical processes since plant terrestrialization >500 million years ago. Recently, hitherto unknown nutritional mutualisms involving ancient lineages of fungi and nonvascular plants have been discovered, although their extent and functional significance in vascular plants remain uncertain. Here, we provide evidence of carbon-for-nitrogen exchange between an early-diverging vascular plant (Lycopodiella inundata) and Mucoromycotina (Endogonales) fine root endophyte fungi. Furthermore, we demonstrate that the same fungal symbionts colonize neighboring nonvascular and flowering plants. These findings fundamentally change our understanding of the physiology, interrelationships, and ecology of underground plantâfungal symbioses in modern terrestrial ecosystems by revealing the nutritional role of Mucoromycotina fungal symbionts in vascular plants
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Integrating risks of climate change into water management
The Working Group II contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change critically reviewed and assessed tens of thousands of recent publications to inform about the assess current scientific knowledge on climate change impacts, vulnerability and adaptation. Chapter 3 of the report focuses on freshwater resources, but water issues are also prominent in other sectoral chapters and in the regional chapters of the Working Group II report as well as in various chapters of Working Group I. With this paper, the lead authors, a review editor and the chapter scientist of the freshwater chapter of the WGII AR5 wish to summarize their assessment of the most relevant risks of climate change related to freshwater systems and to show how assessment and reduction of those risks can be integrated into water management
âDrinkers like meâ : a thematic analysis of comments responding to an online article about moderating alcohol consumption
Background: There has been media coverage surrounding the dangers of heavy drinking and benefits of moderation, with TV and radio presenter, Adrian Chiles, documenting his experience of moderating alcohol consumption in an online article for the Guardian. By analysing the comments in response to Chilesâ article, this study aimed to explore (i) postersâ (someone who has posted a comment in response to the article) attitudes or beliefs toward moderating alcohol and (ii) postersâ experiences of moderating or abstaining from alcohol.
Method: A secondary qualitative analysis of online comments in response to an article about moderating alcohol consumption. Main outcome measures: Comments (n = 784) in response to a United Kingdom online news article about moderating alcohol consumption were extracted and inductive thematic analysis was used.
Results: For aim one, two themes were developed; âgeneral attitudes toward drinkingâ and âgeneral attitudes toward reducing consumptionâ. These themes reflect negative perceptions of alcohol and issues around changing attitudes. For aim two, three themes were developed: âmoderation vs. abstentionâ, âreflection on past drinking behavioursâ, and âcurrent drinking behavioursâ. These themes represent postersâ experiences and implications changing their drinking habits.
Conclusion: Our analysis provides a novel insight into perceptions and experiences of moderating or abstaining from alcohol. Alcohol is embedded within United Kingdom culture, creating difficulties for those who choose to moderate or abstain from alcohol. Our analysis highlights the need for public health to focus on shifting the current drinking culture, through clearer drinking guidelines and a wider availability of alcohol-free alternatives
Avalanche dynamics, surface roughening and self-organized criticality - experiments on a 3 dimensional pile of rice
We present a two-dimensional system which exhibits features of self-organized
criticality. The avalanches which occur on the surface of a pile of rice are
found to exhibit finite size scaling in their probability distribution. The
critical exponents are = 1.21(2) for the avalanche size distribution and
= 1.99(2) for the cut-off size. Furthermore the geometry of the avalanches
is studied leading to a fractal dimension of the active sites of =
1.58(2). Using a set of scaling relations, we can calculate the roughness
exponent = 0.41(3) and the dynamic exponent = 1.56(8). This result is compared with that obtained from a power
spectrum analysis of the surface roughness, which yields = 0.42(3) and
= 1.5(1) in excellent agreement with those obtained from the scaling
relations.Comment: 7 pages, 8 figures, accepted for publication in PR
Dynamics of coupled cell networks: synchrony, heteroclinic cycles and inflation
Copyright © 2011 Springer. The final publication is available at www.springerlink.comWe consider the dynamics of small networks of coupled cells. We usually assume asymmetric inputs and no global or local symmetries in the network and consider equivalence of networks in this setting; that is, when two networks with different architectures give rise to the same set of possible dynamics. Focussing on transitive (strongly connected) networks that have only one type of cell (identical cell networks) we address three questions relating the network structure to dynamics. The first question is how the structure of the network may force the existence of invariant subspaces (synchrony subspaces). The second question is how these invariant subspaces can support robust heteroclinic attractors. Finally, we investigate how the dynamics of coupled cell networks with different structures and numbers of cells can be related; in particular we consider the sets of possible âinflationsâ of a coupled cell network that are obtained by replacing one cell by many of the same type, in such a way that the original network dynamics is still present within a synchrony subspace. We illustrate the results with a number of examples of networks of up to six cells
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