11,629 research outputs found
Prediction of crushing stress in composite materials
A simple mathematical model for predicting the crushing stress of composite materials was derived and presented in this paper. The present knowledge of fracture mechanics and strength of materials are used as the basis for the model. The fracture mechanics part of the analysis was based on energy release rate approach; the energy release rate, G, of the proposed model was determined by this approach. This energy release rate was based on the Mode I (opening or tensile mode) failure. As for the strength of materials part analysis, buckling theory was used to determine the critical load of the fibre beams. These two engineering concepts were combined to form the equation for the proposed model. The derived equation is a function of the materials properties, geometric and physical parameters of the composite materials. The calculated stresses from the derived equation were compared with experimental data from technical and research papers. Good agreements shown in the results are encouraging and recommendations for future analysis with different modes of failure were also presented. This paper enables engineering designers to predict crushing stress in composite materials with confidence and makes their work more efficient and reliable
Dark Matter in Gauge Mediation from Emergent Supersymmetry
We investigated the viability of neutralino dark matter in the gauge
mediation from emergent supersymmetry proposal. In this proposal, supersymmetry
is broken at Planck scale and consequently, the gravitino is superheavy and
completely decouples from the low energy theory. Squarks and sleptons obtain
their soft masses dominantly through gauge mediation with other mechanisms
highly suppressed. The lightest supersymmetric partner, in contrast to
traditional gauge mediation, is a neutralino which is also a dark matter
candidate. By explicit calculation of the low energy spectra, the parameter
space was constrained using the WMAP observed relic density of dark matter,
LEP2 Higgs mass bounds, collider bounds on supersymmetric partners and exotic
B-meson decays. We found that the model has intriguing hybrid features such as
a nearly gauge-mediated spectrum (the exception being the superheavy gravitino)
but with a dominant mSUGRA-like bino-stau coannihilation channel and at large
, A-resonance-like annihilation.Comment: 14 pages, 4 figure
A system to enrich for primitive streak-derivatives, definitive endoderm and mesoderm, from pluripotent cells in culture
Two lineages of endoderm develop during mammalian embryogenesis, the primitive endoderm in the pre-implantation blastocyst and the definitive endoderm at gastrulation. This complexity of endoderm cell populations is mirrored during pluripotent cell differentiation in vitro and has hindered the identification and purification of the definitive endoderm for use as a substrate for further differentiation. The aggregation and differentiation of early primitive ectoderm-like (EPL) cells, resulting in the formation of EPL-cell derived embryoid bodies (EPLEBs), is a model of gastrulation that progresses through the sequential formation of primitive streak-like intermediates to nascent mesoderm and more differentiated mesoderm populations. EPL cell-derived EBs have been further analysed for the formation of definitive endoderm by detailed morphological studies, gene expression and a protein uptake assay. In comparison to embryoid bodies derived from ES cells, which form primitive and definitive endoderm, the endoderm compartment of embryoid bodies formed from EPL cells was comprised almost exclusively of definitive endoderm. Definitive endoderm was defined as a population of squamous cells that expressed Sox17, CXCR4 and Trh, which formed without the prior formation of primitive endoderm and was unable to endocytose horseradish peroxidase from the medium. Definitive endoderm formed in EPLEBs provides a substrate for further differentiation into specific endoderm lineages; these lineages can be used as research tools for understanding the mechanisms controlling lineage establishment and the nature of the transient intermediates formed. The similarity between mouse EPL cells and human ES cells suggests EPLEBs can be used as a model system for the development of technologies to enrich for the formation of human ES cell-derived definitive endoderm in the future.Sveltana Vassilieva, Hweee Ngee Goh, Kevin X. Lau, James N. Hughes, Mary Familari, Peter D. Rathjen and Joy Rathje
A box-covering algorithm for fractal scaling in scale-free networks
A random sequential box-covering algorithm recently introduced to measure the
fractal dimension in scale-free networks is investigated. The algorithm
contains Monte Carlo sequential steps of choosing the position of the center of
each box, and thereby, vertices in preassigned boxes can divide subsequent
boxes into more than one pieces, but divided boxes are counted once. We find
that such box-split allowance in the algorithm is a crucial ingredient
necessary to obtain the fractal scaling for fractal networks; however, it is
inessential for regular lattice and conventional fractal objects embedded in
the Euclidean space. Next the algorithm is viewed from the cluster-growing
perspective that boxes are allowed to overlap and thereby, vertices can belong
to more than one box. Then, the number of distinct boxes a vertex belongs to is
distributed in a heterogeneous manner for SF fractal networks, while it is of
Poisson-type for the conventional fractal objects.Comment: 12 pages, 11 figures, a proceedings of the conference, "Optimization
in complex networks." held in Los Alamo
Safely dissolvable and healable active packaging films based on alginate and pectin
Extensive usage of long-lasting petroleum based plastics for short-lived application such as packaging has raised concerns regarding their role in environmental pollution. In this research, we have developed active, healable, and safely dissolvable alginate-pectin based biocomposites that have potential applications in food packaging. The morphological study revealed the rough surface of these biocomposite films. Tensile properties indicated that the fabricated samples have mechanical properties in the range of commercially available packaging films while possessing excellent healing effciency. Biocomposite films exhibited higher hydrophobicity properties compared to neat alginate films. Thermal analysis indicated that crosslinked biocomposite samples possess higher thermal stability in temperatures below 120 °C, while antibacterial analysis against E. coli and S. aureus revealed the antibacterial properties of the prepared samples against different bacteria. The fabricated biodegradable multi-functional biocomposite films possess various imperative properties, making them ideal for utilization as packaging material
Strong suppression of superconductivity by divalent Ytterbium Kondo-holes in CeCoIn_5
To study the nature of partially substituted Yb-ions in a Ce-based Kondo
lattice, we fabricated high quality Ce_{1-x}Yb_xCoIn_5 epitaxial thin films
using molecular beam epitaxy. We find that the Yb-substitution leads to a
linear decrease of the unit cell volume, indicating that Yb-ions are divalent
forming Kondo-holes in Ce_{1-x}Yb_xCoIn_5, and leads to a strong suppression of
the superconductivity and Kondo coherence. These results, combined with the
measurements of Hall effect, indicate that Yb-ions act as nonmagnetic impurity
scatters in the coherent Kondo lattice without serious suppression of the
antiferromagnetic fluctuations. These are in stark contrast to previous studies
performed using bulk single crystals, which claim the importance of valence
fluctuations of Yb-ions. The present work also highlights the suitability of
epitaxial films in the study of the impurity effect on the Kondo lattice.Comment: 5 pages, 4 figure
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