15,924 research outputs found
The free energy of biomembrane and nerve excitation and the role of anesthetics
In the electromechanical theory of nerve stimulation, the nerve impulse
consists of a traveling region of solid membrane in a liquid environment.
Therefore, the free energy necessary to stimulate a pulse is directly related
to the free energy difference necessary to induce a phase transition in the
nerve membrane. It is a function of temperature and pressure, and it is
sensitively dependent on the presence of anesthetics which lower melting
transitions. We investigate the free energy difference of solid and liquid
membrane phases under the influence of anesthetics. We calculate
stimulus-response curves of electromechanical pulses and compare them to
measured stimulus-response profiles in lobster and earthworm axons. We also
compare them to stimulus-response experiments on human median nerve and frog
sciatic nerve published in the literature.Comment: 10 pages, 6 figure
Extended modal realism â a new solution to the problem of intentional inexistence
Kriegel described the problem of intentional inexistence as one of the âperennial problems of philosophyâ (Kriegel Philosophical Perspectives 21(1), 307â340, 2007: 307). In the same paper, Kriegel alluded to a modal realist solution to the problem of intentional inexistence. However, Kriegel does not state by name who defends the kind of modal realist solution he has in mind. Kriegel also points out that even what he believes to be the strongest version of modal realism does not pass the âprinciple of representationâ and thus modal realism is not an adequate solution to the problem of intentional inexistence. In this paper, I respond to Kriegel by defending a modal realist solution that he did not consider in 2007, called âextended modal realismâ (EMR). EMR is a version of modal realism where possible worlds are not completely isolated as they are under the Lewisian model. Rather, under EMR worlds are, in a way, spatiotemporally related. The fact EMR worlds are related allows EMR to sufficiently pass the principle of representation and thus can be deemed a legitimate solution to the problem of intentional inexistence. I conclude that either EMR can pass the principle of representation in some cases or, and I think the more sensible option, we give up on the principle of representation altogether
Derivation of supply curves for catchment water effluents meeting specific salinity concentration targets in 2050: linking farm and catchment level models or âFootprints on future salt / water planesâ
The salt burden in a stream reflects the blend of salty and fresh flows from different soil areas in its catchment. Depending not only on long-run rainfall, water yields from a soil are also determined by land cover: lowest if the area is forested and greatest if cleared. Water yields under agro-forestry, lucerne pasture, perennial grass pasture, and annual pasture or cropping options span the range of water yields between the extremes of forested and cleared lands. This study explores quantitative approaches for connecting the hydrologic and economic consequences of farm-level decisions on land cover (productive land uses) to the costs of attaining different catchment level targets of water volumes and salt reaching downstream users; environmental, agricultural, domestic, commercial and industrial. This connection is critical for the resolution of the externality dilemma of meeting downstream demands for water volume and quality. New technology, new products and new markets will expand options for salinity abatement measures in the dryland farming areas of watershed catchments. The development of appropriate policy solutions to address demands for water volumes and quality depends on the possibility of inducing targeted land use change in those catchments or parts of catchments where decreased saline flows or increased fresh water flows can return the best value for money. This study provides such a link.salinity, targets, opportunity cost, concentration, dilution, effluent, externality, supply, demand, policy, water quality, new technology, new markets, Resource /Energy Economics and Policy,
Intercomparison of phenological transition dates derived from the PhenoCam Dataset V1.0 and MODIS satellite remote sensing
Phenology is a valuable diagnostic of ecosystem health, and has applications to environmental monitoring and management. Here, we conduct an intercomparison analysis using phenological transition dates derived from near-surface PhenoCam imagery and MODIS satellite remote sensing. We used approximately 600 site-years of data, from 128 camera sites covering a wide range of vegetation types and climate zones. During both âgreenness risingâ and âgreenness fallingâ transition phases, we found generally good agreement between PhenoCam and MODIS transition dates for agricultural, deciduous forest, and grassland sites, provided that the vegetation in the camera field of view was representative of the broader landscape. The correlation between PhenoCam and MODIS transition dates was poor for evergreen forest sites. We discuss potential reasons (including sub-pixel spatial heterogeneity, flexibility of the transition date extraction method, vegetation index sensitivity in evergreen systems, and PhenoCam geolocation uncertainty) for varying agreement between time series of vegetation indices derived from PhenoCam and MODIS imagery. This analysis increases our confidence in the ability of satellite remote sensing to accurately characterize seasonal dynamics in a range of ecosystems, and provides a basis for interpreting those dynamics in the context of tangible phenological changes occurring on the ground
Solitary electromechanical pulses in Lobster neurons
Investigations of nerve activity have focused predominantly on electrical
phenomena. Nerves, however, are thermodynamic systems, and changes in
temperature and in the dimensions of the nerve can also be observed during the
action potential. Measurements of heat changes during the action potential
suggest that the nerve pulse shares many characteristics with an adiabatic
pulse. First experiments in the 1980s suggested small changes in nerve
thickness and length during the action potential. Such findings have led to the
suggestion that the action potential may be related to electromechanical
solitons traveling without dissipation. However, they have been no modern
attempts to study mechanical phenomena in nerves. Here, we present
ultrasensitive AFM recordings of mechanical changes on the order of 2 - 12
{\AA} in the giant axons of the lobster. We show that the nerve thickness
changes in phase with voltage change. When stimulated at opposite ends of the
same axon, colliding action potentials pass through one another and do not
annihilate. These observations are consistent with a mechanical interpretation
of the nervous impulse.Comment: 9 pages, 4 figure
Mathematical optimisation of drainage and economic land use for target water and salt yields
Land managers in upper catchments are being asked to make expensive changes in land use, such as by planting trees, to attain environmental service targets, including reduced salt loads in rivers, to meet needs of downstream towns, farms and natural habitats. End-of-valley targets for salt loads have sometimes been set without a quantitative model of cause and effect regarding impacts on water yields, economic efficiency or distribution of costs and benefits among stakeholders. This paper presents a method for calculating a âmenuâ of technically feasible options for changes from current to future mean water yields and salt loads from upstream catchments having local groundwater flow systems, and the land-use changes to attain each of these options at minimum cost. It sets the economic stage for upstream landholders to negotiate with downstream parties future water-yield and salt-load targets, on the basis of what it will cost to supply these ecosystem services.discounting, landuse, NPV, opportunity-cost, salinity, Resource /Energy Economics and Policy,
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