7,879 research outputs found
Specific and non specific hybridization of oligonucleotide probes on microarrays
Gene expression analysis by means of microarrays is based on the sequence
specific binding of mRNA to DNA oligonucleotide probes and its measurement
using fluorescent labels. The binding of RNA fragments involving other
sequences than the intended target is problematic because it adds a "chemical
background" to the signal, which is not related to the expression degree of the
target gene. The paper presents a molecular signature of specific and non
specific hybridization with potential consequences for gene expression
analysis. We analyzed the signal intensities of perfect match (PM) and mismatch
(MM) probes of GeneChip microarrays to specify the effect of specific and non
specific hybridization. We found that these events give rise to different
relations between the PM and MM intensities as function of the middle base of
the PMs, namely a triplet- (C>G=T>A>0) and a duplet-like (C=T>0>G=A) pattern of
the PM-MM log-intensity difference upon binding of specific and non specific
RNA fragments, respectively. The systematic behaviour of the intensity
difference can be rationalized on the level of base pairings of DNA/RNA
oligonucleotide duplexes in the middle of the probe sequence. Non-specific
binding is characterized by the reversal of the central Watson Crick (WC)
pairing for each PM/MM probe pair, whereas specific binding refers to the
combination of a WC and a self complementary (SC) pairing in PM and MM probes,
respectively. The intensity of complementary MM introduces a systematic source
of variation which decreases the precision of expression measures based on the
MM intensities
On the occurrence of bryophytes and macrolichens in different lowland rain forest types at Mabura Hill, Guyana
A floristic and ecological study of bryophytes and macrolichens in different lowland rain forest types around Mabura Hill, Guyana, South America, yielded 170 species: 52 mosses, 82 liverworts and 36 macrolichens. Lejeuneaceae account for about 30% of the species and are the dominant cryptogamic family of the lowland rain forest. Special attention was paid to the flora of the forest canopy, by using mountaineering techniques. It appeared that 50% of the bryophyte species and 86% of the macrolichens occurred exclusively in the canopy. Dry evergreen 'walaba' forest on white sand is particularly rich in lichens whereas the more humid 'mixed' forest on loamy soil is characterized by a rather rich liverwort flora. More species are exclusive to the mixed forest than to dry evergreen forest due to the 'canopy effect', i.e. the occurrence of xerophytic species in the outer canopy of both dry and humid forests. Furthermore, canopy species have wider vertical distributions on trees in the dry evergreen forest than in the mixed forest, due to the more open canopy foliage of the dry evergreen forest
Constitutional Design: Separation of Financing and Project Decision
We examine the provision of public projects under separate tax and subsidy rules. We find that tax rules separated from project cum subsidy decisions exhibit several advantages when incentive problems of the agenda-setter are taken into account. In particular, tax rules may prevent the proposal of inefficient projects which benefit only a small lobby group. We propose “redistribution efficiency” as a socially desirable property of proposals and find that tax rules always guarantee redistribution efficiency. We show that rules on subsidies combined with discretion regarding taxes always yield socially inferior proposals. Finally, tax rules induce the agenda-setter to look for potential improvements of public projects.constitutional design, provision of public projects, voting, taxes and subsidies
Simultaneous description of bulk and interfacial properties of fluids by the Mie potential
The vapor-liquid equilibrium (VLE) of the Mie potential, where the dispersive
exponent is constant (m = 6) while the repulsive exponent n is varied between 9
and 48, is systematically investigated by molecular simulation. For systems
with planar vapor-liquid interfaces, long-range correction expressions are
derived, so that interfacial and bulk properties can be computed accurately.
The present simulation results are found to be consistent with the available
body of literature on the Mie fluid which is substantially extended. On the
basis of correlations for the considered thermodynamic properties, a
multicriteria optimization becomes viable. Thereby, users can adjust the three
parameters of the Mie potential to the properties of real fluids, weighting
different thermodynamic properties according to their importance for a
particular application scenario. In the present work, this is demonstrated for
carbon dioxide for which different competing objective functions are studied
which describe the accuracy of the model for representing the saturated liquid
density, the vapor pressure and the surface tension. It is shown that models
can be found which describe simultaneously the saturated liquid density and
vapor pressure with good accuracy, and it is discussed to what extent this
accuracy can be upheld as the model accuracy for the surface tension is further
improved
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