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 $0.18$ and $0.30$~\mypermil and compatible with the ice core CO2 record