76 research outputs found
Boolean Dynamics with Random Couplings
This paper reviews a class of generic dissipative dynamical systems called
N-K models. In these models, the dynamics of N elements, defined as Boolean
variables, develop step by step, clocked by a discrete time variable. Each of
the N Boolean elements at a given time is given a value which depends upon K
elements in the previous time step.
We review the work of many authors on the behavior of the models, looking
particularly at the structure and lengths of their cycles, the sizes of their
basins of attraction, and the flow of information through the systems. In the
limit of infinite N, there is a phase transition between a chaotic and an
ordered phase, with a critical phase in between.
We argue that the behavior of this system depends significantly on the
topology of the network connections. If the elements are placed upon a lattice
with dimension d, the system shows correlations related to the standard
percolation or directed percolation phase transition on such a lattice. On the
other hand, a very different behavior is seen in the Kauffman net in which all
spins are equally likely to be coupled to a given spin. In this situation,
coupling loops are mostly suppressed, and the behavior of the system is much
more like that of a mean field theory.
We also describe possible applications of the models to, for example, genetic
networks, cell differentiation, evolution, democracy in social systems and
neural networks.Comment: 69 pages, 16 figures, Submitted to Springer Applied Mathematical
Sciences Serie
Successful treatment of tracheal stenosis by rigid bronchoscopy and topical mitomycin C: a case report
Tracheal stenosis is a known complication of prolonged intubation. It is difficult to treat and traditional surgical approach is associated with significant risk and complications. Recurrent stenosis due to granulation tissue necessitates repeated procedures. We describe a case of short web-like tracheal stenosis (concentric membranous stenosis less than 1 cm in length without associated cartilage damage) managed by a minimally invasive thoracic endoscopic approach. Topical application of Mitomycin C, a potent fibroblast inhibitor reduces granulation tissue formation and prevents recurrence
Low-mass and sub-stellar eclipsing binaries in stellar clusters
We highlight the importance of eclipsing double-line binaries in our
understanding on star formation and evolution. We review the recent discoveries
of low-mass and sub-stellar eclipsing binaries belonging to star-forming
regions, open clusters, and globular clusters identified by ground-based
surveys and space missions with high-resolution spectroscopic follow-up. These
discoveries provide benchmark systems with known distances, metallicities, and
ages to calibrate masses and radii predicted by state-of-the-art evolutionary
models to a few percent. We report their density and discuss current
limitations on the accuracy of the physical parameters. We discuss future
opportunities and highlight future guidelines to fill gaps in age and
metallicity to improve further our knowledge of low-mass stars and brown
dwarfs.Comment: 30 pages, 5 figures, no table. Review pape
Chlorophyll-nutrient relationships of different lake types using a large European dataset
In Europe there is a renewed focus on relationships between chemical determinands and ecological impact as a result of the Water Framework Directive (WFD). In this paper we use regression analysis to examine the relationship of growing season mean chlorophyll a concentration with total phosphorus and total nitrogen using summary data from over 1,000 European lakes. For analysis, lakes were grouped into types with three categories of mean depth, alkalinity and humic content. The lakes were also divided into broad geographic regions covering Atlantic, Northern, Central/Baltic and for some types the Mediterranean areas of Europe. Chlorophyll a was found to be significantly related to both total phosphorus and total nitrogen, although total phosphorus was almost always found to be the best predictor of chlorophyll. Different nutrient chlorophyll relationships were found for lakes according to mean depth and alkalinity, although no significant effect of geographic region or humic content was found for the majority of lake types. We identified three groups of lakes with significantly different responses. Deep lakes had the lowest yield of chlorophyll per unit of nutrient, low and moderate alkalinity shallow lakes the highest and high alkalinity lakes were intermediate. We recommend that the regression models provided for these three lake groups should be used for lake management in Europe and discuss the limitations of such model
Simulated changes in vegetation distribution, land carbon storage, and atmospheric CO2 in response to a collapse of the North Atlantic thermohaline circulation
Measurements on glacial ice show that atmospheric CO2 varied by 20ppmv with large iceberg discharges into the North Atlantic (NA) and themost prominent Dansgaard/ Oeschger (D/O) climate fluctuations. CO2variations during less pronounced D/O events were smaller than a fewppm. The D/O fluctuations have been linked to changes in the NAThermohaline Circulation (THC). Here, we analyse how abrupt changes inthe NA THC affect the terrestrial carbon cycle by forcing theLund-Potsdam-Jena Dynamic Global Vegetation Model with climateperturbations from freshwater experiments with the ECBILT-CLIOgeneral circulation model. Changes in the marine carbon cycle are notaddressed. Modelled NA THC collapsed and recovered after about amillennium in response to prescribed freshwater forcing. The initialcooling of several Kelvin over Eurasia causes a reduction ofextant boreal and temperate forests and a decrease in carbon storage inhigh northern latitudes, whereas improved growing conditions andslower soil decomposition rates lead to enhanced storage inmid-latitudes. The magnitude and evolution of global terrestrialcarbon storage in response to abrupt THC changes depends sensitivelyon the initial climate conditions. Terrestrial storage varies between-67 and +50 PgC for arange of experiments that start at different times during the last21,000 years. Simulated peak-to-peak differences in atmospheric CO2and d13C are between {6 and 18 ppmv} and and ~\mypermil and compatible with the ice core CO2 record
A Comparison of Intraosseous and Intravenous Routes of Administration for Antiseizure Agents
Three-Dimensional Ocean Models for Predicting the Distribution of CO2 Between the Ocean and Atmosphere
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