5,341 research outputs found
Relationship of hypoxia to metastatic ability in rodent tumours
The relationship between tumour oxygenation in vivo and metastatic potential was investigated in 2 rodent tumour models, KHT-C fibrosarcoma and SCC-VII squamous cell carcinoma. The oxygen status in these rodent tumours transplanted intramuscularly in syngeneic mice was measured using the Eppendorf pO 2 Histograph. The results indicate a considerable heterogeneity in oxygenation between individual tumours within each tumour cell line. At different tumour sizes, animals were killed and lung lobes were examined for macroscopic and microscopic lung metastases. In the KHT-C tumours, a significant increase in early pulmonary metastasis formation was observed in mice with hypoxic primary tumours. Hypoxic SCC-VII tumours did not give rise to enhanced lung metastasis formation despite oxygenation in a range similar to the KHT-C tumours. However, the overall metastasis incidence in the SCC-VII model was very low. The results obtained in the KHT-C model, which show that hypoxic tumours are more likely to metastasize, are in agreement with recent clinical data suggesting that a hypoxic environment might be implicated in metastatic ability of human tumours. © 2001 Cancer Research Campaign http://www.bjcancer.co
On the complexity of some birational transformations
Using three different approaches, we analyze the complexity of various
birational maps constructed from simple operations (inversions) on square
matrices of arbitrary size. The first approach consists in the study of the
images of lines, and relies mainly on univariate polynomial algebra, the second
approach is a singularity analysis, and the third method is more numerical,
using integer arithmetics. Each method has its own domain of application, but
they give corroborating results, and lead us to a conjecture on the complexity
of a class of maps constructed from matrix inversions
Breakdown of self-organized criticality
We introduce two sandpile models which show the same behavior of real
sandpiles, that is, an almost self-organized critical behavior for small
systems and the dominance of large avalanches as the system size increases. The
systems become fully self-organized critical, with the critical exponents of
the Bak, Tang and Wiesenfeld model, as the system parameters are changed,
showing that these systems can make a bridge between the well known theoretical
and numerical results and what is observed in real experiments. We find that a
simple mechanism determines the boundary where self-organized can or cannot
exist, which is the presence of local chaos.Comment: 3 pages, 4 figure
Molecular convergence by differential domain acquisition is a hallmark of chromosomal passenger complex evolution
The chromosomal passenger complex (CPC) is a heterotetrameric regulator of eukaryotic cell division, consisting of an Aurora-type kinase and a scaffold built of INCENP, Borealin, and Survivin. While most CPC components are conserved across eukaryotes, orthologs of the chromatin reader Survivin have previously only been found in animals and fungi, raising the question of how its essential role is carried out in other eukaryotes. By characterizing proteins that bind to the
Arabidopsis
Borealin ortholog, we identified BOREALIN RELATED INTERACTOR 1 and 2 (BORI1 and BORI2) as redundant Survivin-like proteins in the context of the CPC in plants. Loss of BORI function is lethal and a reduced expression of
BORI
s causes severe developmental defects. Similar to Survivin, we find that the BORIs bind to phosphorylated histone H3, relevant for correct CPC association with chromatin. However, this interaction is not mediated by a BIR domain as in previously recognized Survivin orthologs but by an FHA domain, a widely conserved phosphate-binding module. We find that the unifying criterion of Survivin-type proteins is a helix that facilitates complex formation with the other two scaffold components and that the addition of a phosphate-binding domain, necessary for concentration at the inner centromere, evolved in parallel in different eukaryotic groups. Using sensitive similarity searches, we find conservation of this helical domain between animals and plants and identify the missing CPC component in most eukaryotic supergroups. Interestingly, we also detect Survivin orthologs without a defined phosphate-binding domain, likely reflecting the situation in the last eukaryotic common ancestor.
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Nearest pattern interaction and global pattern formation
We studied the effect of nearest pattern interaction on a globally pattern
formation in a 2-dimensional space, where patterns are to grow initially from a
noise in the presence of periodic supply of energy. Although our approach is
general, we found that this study is relevant in particular to the pattern
formation on a periodically vibrated granular layer, as it gives a unified
perspective of the experimentally observed pattern dynamics such as oscillon
and stripe formations, skew-varicose and crossroll instabilities, and also a
kink formation and decoration
Silicates in D-type symbiotic stars: an ISO overview
We investigate the IR spectral features of a sample of D-type symbiotic
stars. Analyzing unexploited ISO-SWS data, deriving the basic observational
parameters of dust bands and comparing them with respect to those observed in
other astronomical sources, we try to highlight the effect of environment on
grain chemistry and physic. We find strong amorphous silicate emission bands at
10 micron and 18 micron in a large fraction of the sample. The analysis of the
10 micron band, along with a direct comparison with several astronomical
sources, reveals that silicate dust in symbiotic stars shows features between
the characteristic circumstellar environments and the interstellar medium. This
indicates an increasing reprocessing of grains in relation to specific
symbiotic behavior of the objects. A correlation between the central wavelength
of the 10 and 18 micron dust bands is found. By the modeling of IR spectral
lines we investigate also dust grains conditions within the shocked nebulae.
Both the unusual depletion values and the high sputtering efficiency might be
explained by the formation of SiO moleculae, which are known to be a very
reliable shock tracer. We conclude that the signature of dust chemical
disturbance due to symbiotic activity should be looked for in the outer,
circumbinary, expanding shells where the environmental conditions for grain
processing might be achieved. Symbiotic stars are thus attractive targets for
new mid-infrared and mm observations.Comment: 24 pages, 6 figures, 5 tables - to be published in A
Possible Stratification Mechanism in Granular Mixtures
We propose a mechanism to explain what occurs when a mixture of grains of
different sizes and different shapes (i.e. different repose angles) is poured
into a quasi-two-dimensional cell. Specifically, we develop a model that
displays spontaneous stratification of the large and small grains in
alternating layers. We find that the key requirement for stratification is a
difference in the repose angles of the two pure species, a prediction confirmed
by experimental findings. We also identify a kink mechanism that appears to
describe essential aspects of the dynamics of stratification.Comment: 4 pages, 4 figures, http://polymer.bu.edu/~hmakse/Home.htm
Life cycle assessment and valuation of the packaging waste recycling system in Belgium
This study analyses the packaging waste management system in Belgium. Waste management operations involve a significant number of processes associated with energy consumption and emission of pollutants in air and water. To assess the impact on the environment of the several waste management operations, a life cycle assessment was developed. The operations of selective and refuse collection, sorting, recycling and incineration of packaging waste were considered. A comparison between two scenarios was developed. The first scenario comprised the packaging waste management system in operation in 2010. This system comprises the waste management operations envisaging the recycling of the packaging materials. The second scenario was developed based on the hypothesis that there was no recycling system and all packaging waste would be collected in the refuse collection system. An environmental valuation was performed to convert the environmental results into a common unit (EUR). To accomplish this valuation, three methods were used: Ecocost, Ecovalue and Stepwise. These methods were developed in Europe and follow different methodologies. The environmental results were compared using the three methods and they were consistent with the conclusion that the recycling scenario (i.e. the actual situation in 2010) is more environmentally sound
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