3,250 research outputs found
Damage states in laminated composite three-point bend specimens: An experimental-analytical correlation study
Damage states in laminated composites were studied by considering the model problem of a laminated beam subjected to three-point bending. A combination of experimental and theoretical research techniques was used to correlate the experimental results with the analytical stress distributions. The analytical solution procedure was based on the stress formulation approach of the mathematical theory of elasticity. The solution procedure is capable of calculating the ply-level stresses and beam displacements for any laminated beam of finite length using the generalized plane deformation or plane stress state assumption. Prior to conducting the experimental phase, the results from preliminary analyses were examined. Significant effects in the ply-level stress distributions were seen depending on the fiber orientation, aspect ratio, and whether or not a grouped or interspersed stacking sequence was used. The experimental investigation was conducted to determine the different damage modes in laminated three-point bend specimens. The test matrix consisted of three-point bend specimens of 0 deg unidirectional, cross-ply, and quasi-isotropic stacking sequences. The dependence of the damage initiation loads and ultimate failure loads were studied, and their relation to damage susceptibility and damage tolerance of the mean configuration was discussed. Damage modes were identified by visual inspection of the damaged specimens using an optical microscope. The four fundamental damage mechanisms identified were delaminations, matrix cracking, fiber breakage, and crushing. The correlation study between the experimental results and the analytical results were performed for the midspan deflection, indentation, damage modes, and damage susceptibility
Asymmetric growth of root epidermal cells is related to the differentiation of root hair cells in Hordeum vulgare (L.)
The root epidermis of most vascular plants harbours two cell types, namely trichoblasts (capable of producing a root
hair) and atrichoblasts. Here, in vivo analysis, confocal laser-scanning microscopy, transmission electron microscopy,
histological analysis, and three-dimensional reconstruction were used to characterize the cell types present in the
barley root epidermis and their distribution in the tissue. Both trichoblasts and atrichoblasts were present in the wildtype
cultivars and could be distinguished from one another at an early stage. Trichoblast/atrichoblast differentiation
depended on asymmetric cell expansion after a period of symmetrical cell division. After asymmetric growth, only the
shorter epidermal cells could produce root hairs, whereas the longer cells became atrichoblasts. Moreover, the root
epidermis did not develop root hairs at all if the epidermal cells did not differentiate into two asymmetric cell types.
The root hairless phenotype of bald root barley (brb) and root hairless 1.b (rhl1.b) mutants was caused by a mutation
in a gene related to the asymmetric expansion of the root epidermal cells. Additionally, the results showed that
the mechanism of trichoblast/atrichoblast differentiation is not evolutionally conserved across the subfamilies of the
Poaceae; in the Pooideae subfamily, both asymmetric division and asymmetric cell expansion have been observed
‘Should We Be Doing It, Should We Not Be Doing It, Who Could Be Harmed?’
Many science educators have argued in favour of including socioscientific issues (SSI) in general, and ethical issues in particular, in school science. However, there have been a number of objections to this proposal, and it is widely acknowledged that such teaching places additional demands on science teachers. This study examined the curricula, textbooks and views of both student teachers and established teachers in England and in Germany regarding the teaching of ethical issues in secondary school science, particularly the ethical issues surrounding animal tests. Analysis of the curriculum documents for secondary or upper secondary school science showed that in both countries, ethical considerations feature strongly. However, in both countries, the overall treatments in the school textbooks of the ethical issues of animal testing were generally ‘thin’, and little opportunity was given for students to consider different ethical frameworks. The teacher and student teacher interviews revealed that interviewees generally gave ethical issues less emphasis than fundamental science. A number of interviewees referred to a lack of appropriate teaching material, and many of them also had concerns that such teaching could give rise to classroom management issues or that they might be accused of indoctrinating their students. Given the increasing acknowledgement of the need for school science to address so-called wicked socioscientific problems, these findings are a concern. We end with recommendations for curricula, for textbooks and for teacher education
Uncertainty Averse Pushing with Model Predictive Path Integral Control
Planning robust robot manipulation requires good forward models that enable
robust plans to be found. This work shows how to achieve this using a forward
model learned from robot data to plan push manipulations. We explore learning
methods (Gaussian Process Regression, and an Ensemble of Mixture Density
Networks) that give estimates of the uncertainty in their predictions. These
learned models are utilised by a model predictive path integral (MPPI)
controller to plan how to push the box to a goal location. The planner avoids
regions of high predictive uncertainty in the forward model. This includes both
inherent uncertainty in dynamics, and meta uncertainty due to limited data.
Thus, pushing tasks are completed in a robust fashion with respect to estimated
uncertainty in the forward model and without the need of differentiable cost
functions. We demonstrate the method on a real robot, and show that learning
can outperform physics simulation. Using simulation, we also show the ability
to plan uncertainty averse paths.Comment: Humanoids 2017. Supplementary video: https://youtu.be/LjYruxwxkP
Increased symplasmic permeability in barley root epidermal cells correlates with defects in root hair development
It is well known that the process of plant cell differentiation depends on the symplasmic
isolation of cells. Before starting the differentiation programme, the individual
cell or group of cells should restrict symplasmic communication with neighbouring
cells. We tested the symplasmic communication between epidermal cells in the different
root zones of parental barley plants Hordeum vulgare L., cv. ‘Karat’ with normal
root hair development, and two root hairless mutants (rhl1.a and rhl1.b). The results
clearly show that symplasmic communication was limited during root hair differentiation
in the parental variety, whereas in both root hairless mutants epidermal cells
were still symplasmically connected in the corresponding root zone. This paper is the
first report on the role of symplasmic isolation in barley root cell differentiation, and
additionally shows that a disturbance in the restriction of symplasmic communication
is present in root hairless mutants
Phonon-assisted transitions from quantum dot excitons to cavity photons
For a single semiconductor quantum dot embedded in a microcavity, we
theoretically and experimentally investigate phonon-assisted transitions
between excitons and the cavity mode. Within the framework of the independent
boson model we find that such transitions can be very efficient, even for
relatively large exciton-cavity detunings of several millielectron volts.
Furthermore, we predict a strong detuning asymmetry for the exciton lifetime
that vanishes for elevated lattice temperature. Our findings are corroborated
by experiment, which turns out to be in good quantitative and qualitative
agreement with theory
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Silencing HoxA1 by Intraductal Injection of siRNA Lipidoid Nanoparticles Prevents Mammary Tumor Progression in Mice
With advances in screening, the incidence of detection of premalignant breast lesions has increased in recent decades; however, treatment options remain limited to surveillance or surgical removal by lumpectomy or mastectomy. We hypothesized that disease progression could be blocked by RNA interference (RNAi) therapy and set out to develop a targeted therapeutic delivery strategy. Using computational gene network modeling, we identified HoxA1 as a putative driver of early mammary cancer progression in transgenic C3(1)-SV40TAg mice. Silencing this gene in cultured mouse or human mammary tumor spheroids resulted in increased acinar lumen formation, reduced tumor cell proliferation, and restoration of normal epithelial polarization. When the HoxA1 gene was silenced in vivo via intraductal delivery of nanoparticle-formulated small interfering RNA (siRNA) through the nipple of transgenic mice with early-stage disease, mammary epithelial cell proliferation rates were suppressed, loss of estrogen and progesterone receptor expression was prevented, and tumor incidence was reduced by 75%. This approach that leverages new advances in systems biology and nanotechnology offers a novel noninvasive strategy to block breast cancer progression through targeted silencing of critical genes directly within the mammary epithelium.Engineering and Applied Science
Rate of Convergence to Barenblatt Profiles for the Fast Diffusion Equation
We study the asymptotic behaviour of positive solutions of the Cauchy problem
for the fast diffusion equation near the extinction time. We find a continuum
of rates of convergence to a self-similar profile. These rates depend
explicitly on the spatial decay rates of initial data
CFD Growth of 3C-SiC on 4H/6H Mesas
This article describes growth and characterization of the highest quality reproducible 3C-SiC heteroepitaxial films ever reported. By properly nucleating 3C-SiC growth on top of perfectly on-axis (0001) 4H-SiC mesa surfaces completely free of atomic scale steps and extended defects, growth of 3C-SiC mesa heterofilms completely free of extended crystal defects can be achieved. In contrast, nucleation and growth of 3C-SiC mesa heterofilms on top of 4H-SiC mesas with atomic-scale steps always results in numerous observable dislocations threading through the 3C-SiC epilayer. High-resolution X-ray diffraction and transmission electron microscopy measurements indicate non-trivial in-plane lattice mismatch between the 3C and 4H layers. This mismatch is somewhat relieved in the step-free mesa case via misfit dislocations confined to the 3C/4H interfacial region without dislocations threading into the overlying 3C-SiC layer. These results indicate that the presence or absence of steps at the 3C/4H heteroepitaxial interface critically impacts the quality, defect structure, and relaxation mechanisms of single-crystal heteroepitaxial 3C-SiC films
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