The physical and thermal properties of modified rotational molding grade silane cross-linked polyethylene compound

This study is aimed at investigating the physical and thermal properties of the modified rotational molding grade cross-linked polyethylene compound with respect to process ability. Rotational molding grade High Density Polyethylene (HDPE) was blended at various compositions with HDPE and Low Density Polyethylene (LDPE) using twin screw extruder. The melt index of the blends was studied according to ASTM D 1238. The blended compositions were chemically cross-linked with various amount of silane cross-linking agent using two roll-mill. Water curing was then undertaken at 100°C in water bath for 4 and 8 hours. Gel content was measured according to ASTM D 2765 to determine the degree of cross-linking. For thermal analysis, only samples crosslinked with 2.0 phr silane cross-linking agent were investigated on the Differential Scanning Calorimetry (DSC) according to ASTM D 3417. The thermal stability test of the silane Crosslinkable Polyethylene (XLPE) was performed by Thermogravimetric Analyzer (TGA) according to ASTM D 3850. Results on melt index (MI) indicated that the rotational molding grade HDPE blended with HDPE showed higher MI compared to that with LDPE thus improved process ability. The density of rotational molding grade HDPE with HDPE was slightly increased whereas that blended with LDPE was slightly decreased. Samples blended with HDPE, melting temperature, Tm, barely changed and degree of crystallinity, Xc, decreased with compositions. Samples with LDPE Tm and Xc decreased with compositions thus improved process ability. As the silane concentrations increased, the gel content after curing was also increased but independent of compositions. Longer curing time resulted in higher gel content. Thermal stability of the crosslinked HDPE was higher than the uncross-linked HDPE, thus silane cross-linking help to stabilize the blends

The ultrasonic nondestructive evaluation of welds in plastic pipes.

Imperial Users onl

k-connectivity of Random Graphs and Random Geometric Graphs in Node Fault Model

k-connectivity of random graphs is a fundamental property indicating reliability of multi-hop wireless sensor networks (WSN). WSNs comprising of sensor nodes with limited power resources are modeled by random graphs with unreliable nodes, which is known as the node fault model. In this paper, we investigate k-connectivity of random graphs in the node fault model by evaluating the network breakdown probability, i.e., the disconnectivity probability of random graphs after stochastic node removals. Using the notion of a strongly typical set, we obtain universal asymptotic upper and lower bounds of the network breakdown probability. The bounds are applicable both to random graphs and to random geometric graphs. We then consider three representative random graph ensembles: the Erdos-Renyi random graph as the simplest case, the random intersection graph for WSNs with random key predistribution schemes, and the random geometric graph as a model of WSNs generated by random sensor node deployment. The bounds unveil the existence of the phase transition of the network breakdown probability for those ensembles.Comment: 6 page

Cluster X-ray line at 3.5 keV3.5\,{\rm keV} from axion-like dark matter

The recently reported X-ray line signal at $E_\gamma \simeq 3.5\, {\rm keV}$ from a stacked spectrum of various galaxy clusters and the Andromeda galaxy may be originating from a decaying dark matter particle of the mass $2 E_\gamma$. A light axion-like scalar is suggested as a natural candidate for dark matter and its production mechanisms are closely examined. We show that the right amount of axion relic density with the preferred parameters, $m_a \simeq 7 \,{\rm keV}$ and $f_a \simeq 4\times 10^{14}\, {\rm GeV}$, can be naturally obtainable from the decay of inflaton. If the axions were produced from the saxion decay, it could not have constituted the total relic density due to the bound from structure formation. Nonetheless, the saxion decay is an interesting possibility, because the $3.5\, {\rm keV}$ line and dark radiation can be addressed simultaneously, being consistent with the Planck data. Small misalignment angles of the axion, ranging between $\theta_a\sim 10^{-4} -10^{-1}$ depending on the reheating temperature, can also be the source of axion production. The model with axion misalignment can satisfy the constraints for structure formation and iso-curvature perturbation.Comment: 14 pages, significant changes in the form, matched to the journal versio

Retrieving landscape: Drawing(s) as key to the development of alternative biographical readings of Nanhai in the Pearl River Delta

This article focuses on two methods employed in the selection, interpretation, and representation of diverse source materials for developing alternative biographies for my ancestral landscape - Nanhai district in the Pearl River Delta in southern China. These biographies aim to approach Nanhai from a long view of continual transformation, as opposed to prevalent readings of the region that focus on the striking spatial contrasts and large-scale developments that have only come about in recent decades.  The chronological reading explores a critical shift in the cosmological understanding of the landscape situated in the 19th century through a selection of historical gazetteer maps, while in the excavational reading the diffuse continuity of the lineage in the present-day landscape of Nanhai is traced. In both methods, the drawing functions as a crucial (research) tool to engage the range of source materials