Catastrophic or nearly-catastrophic collisions are the most important physical process affecting the evolution of asteroids following the primordial phases. After a generál review of the current ideas about collisional evolution, also in the light of laboratory impact experiments, the problems concerning
the interpretation of asteroid families as outcomes of catastrophic processes are discussed. Finally, it is shown how the present, non completely satisfactory, knowledge of collisional processes
can give important indications on the early phases of evolution of the asteroid belt.
In an open channel with a mobile bed, intense transport of bed load is associated with high-concentrated sediment-laden flow over a plane surface of the eroded bed due to high bed shear. Typically, the flow exhibits a layered internal structure in which virtually all sediment grains are transported through a collisional layer above the bed. Our investigation focuses on steady uniform turbulent open-channel flow with a developed collisional transport layer and combines modelling and experiment to relate integral quantities, as the discharge of solids, discharge of mixture, and flow depth with the longitudinal slope of the bed and the internal structure of the flow above the bed. A transport model is presented which considers flow with the internal structure described by linear vertical distributions of granular velocity and concentration across the collisional layer. The model employs constitutive relations based on the classical kinetic theory of granular flows selected by our previous experimental testing as appropriate for the flow and transport conditions under consideration. For given slope and depth of the flow, the model predicts the total discharge and the discharge of sediment. The model also predicts the layered structure of the flow, giving the thickness of the dense layer, collisional layer, and water layer. Model predictions are compared with results of intense bed-load experiment carried out for lightweight sediment in our laboratory tilting flume.
During shock, prognosis of a patient depends largely on intestinal barrier function. The potency of gut epithelium to represent an obstacle to toxins is determined by the blood supply. All established methods of mucosal function determination necessitate the functional involvement of bloodstream. Microdialysis allows monitoring of extracellular substances in the gut submucosa, but its potential use for gut barrier integrity assessment is unknown. Twelve rats underwent perfusion of the descending colon either with 20 % ethanol or control medium (vehicle). Both media contained equal amounts of a radioactive tracer substance (51Cr-EDTA). Mucosal permeability for 51Cr-EDTA was assessed by microdialysate to luminal perfusate activity ratios. Sampling was performed using the colon submucosal microdialysis technique. The group subjected to ethanol treatment had profound macro- and microscopical alterations in perfused colonic segment associated with a significant increase in tracer permeability during ethanol exposure (2.354±0.298 % for ethanol as opposed to 0.209±0.102 % for control group, p<0.01), which remained elevated for 60 min after cessation of ethanol administration (3.352±0.188 % for ethanol compared to 0.140± 0.0838 % for the control group, p<0.001). Submucosal microdialysis with radioactive tracer substance can be considered a feasible and advantageous alternative of gut barrier function estimation. Parallel monitoring of local tissue chemistry with this method remains a challenge in the future., N. Cibiček, H. Živná, Z. Zadák, J. Kulíř, E. Čermáková, V. Palička., and Obsahuje bibliografii a bibliografické odkazy
This paper challenges two paradigms long held in relation to the ecology of parasites in freshwater systems: (1) autogenic species are poorer colonisers than allogenic ones; and (2) parasites with direct life cycles are more successful colonisers than those with complex life cycles. Using new and existing data for Acanthocephala in freshwater fish from the British Isles, it is suggested that all six species present have been able to colonise and persist successfully, in spite of the supposed limitations of their autogenic life-style. It is proposed that these parasites have overcome these limitations by a variety of means, which apply equally to all species considered. Foremost among these is the utilisation of a migratory fish host as either a preferred or a suitable host in their life cycle, allowing colonisation of new areas and rescue effects in established areas, whilst equally important is the use of a common and widespread crustacean as the intermediate host. In addition, all six species appear to exhibit resource partitioning by host at either or both the larval and adult stages, thus reducing the potential for competition and further facilitating colonisation and survival. This hypothesis is supported by data from previous studies both on acanthocephalans from Europe and North America and on other autogenic parasites. It also provides an explanation for the apparently atypical host utilisation patterns of some acanthocephalan species in areas on the edge of their distributions, notably in Ireland.
Pistacia palaestina (Anacardiaceae) is a common tree in the natural forest of Mt. Carmel, Israel, and the primary host of five common species of gall-forming aphids (Sternorrhyncha: Aphidoidea: Pemphigidae: Fordinae).
After a forest fire, resprouting P. palaestina trees, which are colonized by migrants from outside the burned area, become \"ecological islands\" for host-specific herbivores.
A portion of the Carmel National Park was destroyed by fire in September of 1989. The same winter, thirty-nine resprouting trees that formed green islands in the otherwise barren environment were identified and marked. Tree growth was extraordinarily Vigorous during the first year after the fire, but shoot elongation declined markedly in subsequent years. Recolonization of the 39 \"islands\" by the Fordinae was studied for six consecutive years. Although the life cycle of the aphids and the deciduous phenology of the tree dictate that the \"islands\" must be newly recolonized every year, the results of this study show that trees are persistently occupied once colonized. This is probably due to establishment of aphid colonies on the roots of secondary hosts near each tree following the first successful production of a gall.
Differences in colonization success of different species could be related to both the abundance of different aphid species in the unburned forest and the biological characteristics of each aphid species.
In this paper, a real-time watermarking scheme based on Regularized Extreme Learning Machine (RELM) is proposed. Using the information provided by the reference positions, RELM can be trained at the embedding procedure and watermark is adaptively embedded into the blue channel of the original image by considering the human visual system. Due to the extreme training speed (always hundreds of times faster than BP neural network and Support Vector Machine (SVM)) and good generalized performance, the trained RELM can exactly extract the watermark from the watermarked image against image processing attacks within very short time, and this makes this method applicable in real-time environment. Extensive experimental results illustrate that our technique outperforms Kutter's and Yu's method against simple and multiple attacks.
An image recognition system can be based on a single-layer neural network composed of Min/Max nodes. This principle is easy to use for greyscale images. However, this article deals with the possibilities of utilising neural nets for colour image recognition. Several principles are demonstrated and tested by recently developed software. A new modified Min/Max node Single Layer Net, suitable for recognition in HSV (Hue Saturation Value) colour space, is presented in this paper.