175 research outputs found
General Blending Models for Data From Mixture Experiments
<div><p>We propose a new class of models providing a powerful unification and extension of existing statistical methodology for analysis of data obtained in mixture experiments. These models, which integrate models proposed by Scheffé and Becker, extend considerably the range of mixture component effects that may be described. They become complex when the studied phenomenon requires it, but remain simple whenever possible. This article has supplementary material online.</p></div
Nonequilibrium steady states in a vibrated-rod monolayer: tetratic, nematic and smectic correlations
We study experimentally the nonequilibrium phase behaviour of a horizontal
monolayer of macroscopic rods. The motion of the rods in two dimensions is
driven by vibrations in the vertical direction. Aside from the control
variables of packing fraction and aspect ratio that are typically explored in
molecular liquid crystalline systems, due to the macroscopic size of the
particles we are also able to investigate the effect of the precise shape of
the particle on the steady states of this driven system. We find that the shape
plays an important role in determining the nature of the orientational ordering
at high packing fraction. Cylindrical particles show substantial tetratic
correlations over a range of aspect ratios where spherocylinders have
previously been shown by Bates et al (JCP 112, 10034 (2000)) to undergo
transitions between isotropic and nematic phases. Particles that are thinner at
the ends (rolling pins or bails) show nematic ordering over the same range of
aspect ratios, with a well-established nematic phase at large aspect ratio and
a defect-ridden nematic state with large-scale swirling motion at small aspect
ratios. Finally, long-grain, basmati rice, whose geometry is intermediate
between the two shapes above, shows phases with strong indications of smectic
order.Comment: 18 pages and 13 eps figures, references adde
Numerical Study of the Stress Response of Two-Dimensional Dense Granular Packings
We investigate the Green function of two-dimensional dense random packings of
grains in order to discriminate between the different theories of stress
transmission in granular materials. Our computer simulations allow for a
detailed quantitative investigation of the dynamics which is difficult to
obtain experimentally. We show that both hyperbolic and parabolic models of
stress transmission fail to predict the correct stress distribution in the
studied region of the parameters space. We demonstrate that the compressional
and shear components of the stress compare very well with the predictions of
isotropic elasticity for a wide range of pressures and porosities and for both
frictional and frictionless packings. However, the states used in this study do
not include the critical isostatic point for frictional particles, so that our
results do not preclude the fact that corrections to elasticity may appear at
the critical point of jamming, or for other sample preparation protocols, as
discussed in the main text. We show that the agreement holds in the bulk of the
packings as well as at the boundaries and we validate the linear dependence of
the stress profile width with depth.Comment: 7 pages, 5 figure
Observational study on variability between biobanks in the estimation of DNA concentration.
BACKGROUND: There is little confidence in the consistency of estimation of DNA concentrations when samples move between laboratories. Evidence on this consistency is largely anecdotal. Therefore there is a need first to measure this consistency among different laboratories and then identify and implement remedies. A pilot experiment to test logistics and provide initial data on consistency was therefore conceived. METHODS: DNA aliquots at nominal concentrations between 10 and 300 ng/mul were dispensed into the wells of 96-well plates by one participant - the coordinating centre. Participants estimated the concentration in each well and returned estimates to the coordinating centre. RESULTS: Considerable overall variability was observed among estimates. There were statistically significant differences between participants' measurements and between fluorescence emission and absorption spectroscopy. CONCLUSION: Anecdotal evidence of variability in DNA concentration estimation has been substantiated. Reduction in variability between participants will require the identification of major sources of variation, specification of effective remedies and their implementation
European Space Agency experiments on thermodiffusion of fluid mixtures in space
Abstract.: This paper describes the European Space Agency (ESA) experiments devoted to study thermodiffusion of fluid mixtures in microgravity environment, where sedimentation and convection do not affect the mass flow induced by the Soret effect. First, the experiments performed on binary mixtures in the IVIDIL and GRADFLEX experiments are described. Then, further experiments on ternary mixtures and complex fluids performed in DCMIX and planned to be performed in the context of the NEUF-DIX project are presented. Finally, multi-component mixtures studied in the SCCO project are detailed
Neuronal markers are expressed in human gliomas and NSE knockdown sensitizes glioblastoma cells to radiotherapy and temozolomide
<p>Abstract</p> <p>Background</p> <p>Expression of neuronal elements has been identified in various glial tumors, and glioblastomas (GBMs) with neuronal differentiation patterns have reportedly been associated with longer survival. However, the neuronal class III β-tubulin has been linked to increasing malignancy in astrocytomas. Thus, the significance of neuronal markers in gliomas is not established.</p> <p>Methods</p> <p>The expressions of class III β-tubulin, neurofilament protein (NFP), microtubule-associated protein 2 (MAP2) and neuron-specific enolase (NSE) were investigated in five GBM cell lines and two GBM biopsies with immunocytochemistry and Western blot. Moreover, the expression levels were quantified by real-time qPCR under different culture conditions. Following NSE siRNA treatment we used Electric cell-substrate impedance sensing (ECIS) to monitor cell growth and migration and MTS assays to study viability after irradiation and temozolomide treatment. Finally, we quantitated NSE expression in a series of human glioma biopsies with immunohistochemistry using a morphometry software, and collected survival data for the corresponding patients. The biopsies were then grouped according to expression in two halves which were compared by survival analysis.</p> <p>Results</p> <p>Immunocytochemistry and Western blotting showed that all markers except NFP were expressed both in GBM cell lines and biopsies. Notably, qPCR demonstrated that NSE was upregulated in cellular stress conditions, such as serum-starvation and hypoxia, while we found no uniform pattern for the other markers. NSE knockdown reduced the migration of glioma cells, sensitized them to hypoxia, radio- and chemotherapy. Furthermore, we found that GBM patients in the group with the highest NSE expression lived significantly shorter than patients in the low-expression group.</p> <p>Conclusions</p> <p>Neuronal markers are aberrantly expressed in human GBMs, and NSE is consistently upregulated in different cellular stress conditions. Knockdown of NSE reduces the migration of GBM cells and sensitizes them to hypoxia, radiotherapy and chemotherapy. In addition, GBM patients with high NSE expression had significantly shorter survival than patients with low NSE expression. Collectively, these data suggest a role for NSE in the adaption to cellular stress, such as during treatment.</p
Dealing with Food and Eggs in Mouthbrooding Cichlids: Structural and Functional Trade-Offs in Fitness Related Traits
As in any vertebrate, heads of fishes are densely packed with functions. These functions often impose conflicting mechanical demands resulting in trade-offs in the species-specific phenotype. When phenotypical traits are linked to gender-specific parental behavior, we expect sexual differences in these trade-offs. This study aims to use mouthbrooding cichlids as an example to test hypotheses on evolutionary trade-offs between intricately linked traits that affect different aspects of fitness. We focused on the oral apparatus, which is not only equipped with features used to feed and breathe, but is also used for the incubation of eggs. We used this approach to study mouthbrooding as part of an integrated functional system with diverging performance requirements and to explore gender-specific selective environments within a species.Because cichlids are morphologically very diverse, we hypothesize that the implications of the added constraint of mouthbrooding will primarily depend on the dominant mode of feeding of the studied species. To test this, we compared the trade-off for two maternal mouthbrooding cichlid species: a "suction feeder" (Haplochromis piceatus) and a "biter" (H. fischeri). The comparison of morphology and performance of both species revealed clear interspecific and intersex differences. Our observation that females have larger heads was interpreted as a possible consequence of the fact that in both the studied species mouthbrooding is done by females only. As hypothesized, the observed sexual dimorphism in head shape is inferred as being suboptimal for some aspects of the feeding performance in each of the studied species. Our comparison also demonstrated that the suction feeding species had smaller egg clutches and more elongated eggs.Our findings support the hypothesis that there is a trade-off between mouthbrooding and feeding performance in the two studied haplochromine cichlids, stressing the importance of including species-specific information at the gender level when addressing interspecific functional/morphological differences
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