Towards optimisation of load-time conditions for producing viscoelastically prestressed polymeric matrix composites

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying a tensile creep load to polymeric fibres, the load being released before the fibres are moulded into a polymeric matrix. The viscoelastically recovering fibres induce compressive stresses within the matrix, which can improve mechanical properties by up to 50%. This study investigates the feasibility of reducing the creep loading period for VPPMC production. By using nylon 6,6 fibres, we have demonstrated that the previously adopted viscoelastic creep strain, requiring 330 MPa for 24 h, can be achieved over a shorter duration, tn, using increased creep stress. Thus tn was 92 min at 460 MPa and 37 min at 590 MPa. Subject to avoiding fibre damage however, it may be possible to reduce tn further. From the three creep settings, elapsed recovery strain values were similar, as were the Charpy impact test data from corresponding VPPMC samples; i.e. there were no significant differences in impact energy absorption, these being ∼56% greater than their control (unstressed) counterparts

A bistable morphing composite using viscoelastically generated prestress

Elastically generated prestress within polymeric composites can be used to create bistable morphing structures; i.e. they can ‘snap through’ between one of two states. In this paper, a morphing bistable structure has been produced, utilising viscoelastically generated prestress. Here, polymeric fibres are subjected to a tensile (viscoelastic) creep load which is released before the fibres are moulded into a matrix. Following curing, the previously strained fibres continue to attempt viscoelastic recovery, creating compressive stresses within the matrix that are counterbalanced by residual tension in the fibres. The bistable structure consists of prestressing strips bonded to the sides of a thin, flexible resin-impregnated fibre-glass sheet. Bistability is achieved through pairs of strips orientated to give opposing cylindrical configurations within the sheet. It is envisaged that viscoelastically prestressed morphing structures may overcome the potential limitations of elastic prestressing; i.e. production flexibility and product longevity

The deepest splits in Chloranthaceae as resolved by chloroplast sequences

Evidence from the fossil record, comparative morphology, and molecular phylogenetic analyses indicates that Chloranthaceae are among the oldest lineages of flowering plants alive today. Their four genera (ca. 65 species) today are disjunctly distributed in the Neotropics, China, tropical Asia, and Australasia, with a single species in Madagascar but none in mainland Africa. In the Cretaceous, Chloranthaceae occurred in much of Laurasia as well as Africa, Australia, and southern South America. We used DNA sequence data from the plastid rbcL gene, the rpl20-rps12 spacer, the trnL intron, and the trnL-F spacer to evaluate intra-Chloranthaceae relationships and geographic disjunctions. In agreement with earlier analyses, Hedyosmum was found to be sister to the remaining genera, followed by Ascarina and Chloranthus + Sarcandra. Bayesian and parsimony analyses of the combined data yielded resolved and well-supported trees except for polytomies among Andean Hedyosmum and Madagascan-Australasian-Polynesian Ascarina. The sole Asiatic species of Hedyosmum, Hedyosmum orientale from Hainan, China, was sister to Caribbean and Neotropical species. Likelihood ratio tests on the rbcL data set did not reject the assumption of a clock as long as the long-branched outgroup Canella was excluded. Two alternative fossil calibrations were used to convert genetic distances into absolute ages. Calibrations with Hedyosmum-like flowers from the Barremian-Aptian or Chloranthus-like androecia from the Turonian yielded substitution rates that differed by a factor of two, illustrating a perhaps unsolvable problem in molecular clock–based studies that use several calibration fossils. The alternative rates place the onset of divergence among crown group (extant) species of Hedyosmum at 60 or 29 Ma, between the Paleocene and the Oligocene; that among extant Chloranthus at 22 or 11 Ma; and that among extant Ascarina at 18 or 9 Ma, implying long-distance dispersal between Madagascar and Australasia-Polynesia

A chloroplast phylogeny of Arisaema (Araceae) illustrates Tertiary floristic links between Asia, North America, and East Africa

The evolution of Arisaema is reconstructed, based on combined sequences (2048 aligned bases) from the chloroplast trnL intron, trnL-trnF spacer, and rpl20-rps12 spacer obtained for species from all 11 sections, including sectional type species and geographically disjunct East African and North American/Mexican species. Analyses were rooted with a representative sample of the closest outgroups, Pinellia and Typhonium, to rigorously test the monophyly of Arisaema. Sections in Arisaema are mostly based on leaf, stem, and inflorescence characters and, with one exception, are not rejected by the molecular data; however, statistical support for sectional relationships in the genus remains poor. Section Tortuosa, which includes eastern North American A. dracontium and Mexican A. macrospathum, is demonstrably polyphyletic. The third New World species, A. triphyllum, also occurs in eastern North America and groups with a different Asian clade than do A. dracontium/A. macrospathum. The genus thus appears to have entered North America twice. Fossil infructescences similar to those of A. triphyllum are known from approximately 18 million-year-old deposits inWashington State and can serve to calibrate a molecular clock. Constraining the age of A. triphyllum to 18 million years (my) and applying either a semiparametric or an ultrametric clock model to the combined data yields an age of approximately 31–49 my for the divergence of A. dracontium/A. macrospathum from their Asian relatives and of 19–32 my for the divergence between African A. schimperianum and a Tibetan/Nepalese relative. The genus thus provides an example of the Oligocene/Miocene floristic links between East Africa, Arabia, the Himalayan region, China, and North America. The phylogeny also suggests secondary loss of the environmental sex determination strategy that characterizes all arisaemas except for two subspecies of A. flavum, which have consistently bisexual spathes. These subspecies are tetraploid and capable of selfing, while a third subspecies of A. flavum is diploid and retains the sex-changing strategy. In the molecular trees, the sex-changing subspecies is sister to the two non-sex-changing ones, and the entire species is not basal in the genus

An effective genetic algorithm for network coding

The network coding problem (NCP), which aims to minimize network coding resources such as nodes and links, is a relatively new application of genetic algorithms (GAs) and hence little work has so far been reported in this area. Most of the existing literature on NCP has concentrated primarily on the static network coding problem (SNCP). There is a common assumption in work to date that a target rate is always achievable at every sink as long as coding is allowed at all nodes. In most real-world networks, such as wireless networks, any link could be disconnected at any time. This implies that every time a change occurs in the network topology, a new target rate must be determined. The SNCP software implementation then has to be re-run to try to optimize the coding based on the new target rate. In contrast, the GA proposed in this paper is designed with the dynamic network coding problem (DNCP) as the major concern. To this end, a more general formulation of the NCP is described. The new NCP model considers not only the minimization of network coding resources but also the maximization of the rate actually achieved at sinks. This is particularly important to the DNCP, where the target rate may become unachievable due to network topology changes. Based on the new NCP model, an effective GA is designed by integrating selected new problem-specific heuristic rules into the evolutionary process in order to better diversify chromosomes. In dynamic environments, the new GA does not need to recalculate target rate and also exhibits some degree of robustness against network topology changes. Comparative experiments on both SNCP and DNCP illustrate the effectiveness of our new model and algorithm

Quantum discord amplification induced by quantum phase transition via a cavity-Bose-Einstein-condensate system

We propose a theoretical scheme to realize a sensitive amplification of quantum discord (QD) between two atomic qubits via a cavity-Bose-Einstein condensate (BEC) system which was used to firstly realize the Dicke quantum phase transition (QPT) [Nature 464, 1301 (2010)]. It is shown that the influence of the cavity-BEC system upon the two qubits is equivalent to a phase decoherence environment. It is found that QPT in the cavity-BEC system is the physical mechanism of the sensitive QD amplification.Comment: 5 pages, 3 figure

Tensor-polarized structure function b1b_1 in the standard convolution description of the deuteron

Tensor-polarized structure functions of a spin-1 hadron are additional observables which do not exist for the spin-1/2 nucleon. They could probe novel aspects of the internal hadron structure. Twist-2 tensor-polarized structure functions are $b_1$ and $b_2$, and they are related by the Callan-Gross-like relation in the Bjorken scaling limit. In this work, we theoretically calculate $b_1$ in the standard convolution description for the deuteron. Two different theoretical models, a basic convolution description and a virtual nucleon approximation, are used for calculating $b_1$ and their results are compared with the HERMES measurement. We found large differences between our theoretical results and the data. Although there is still room to improve by considering higher-twist effects and in the experimental extraction of $b_1$ from the spin asymmetry $A_{zz}$, there is a possibility that the large differences require physics beyond the standard deuteron model for their interpretation. Future $b_1$ studies could shed light on a new field of hadron physics. In particular, detailed experimental studies of $b_1$ will start soon at the Thomas Jefferson National Accelerator Facility. In addition, there are possibilities to investigate tensor-polarized parton distribution functions and $b_1$ at Fermi National Accelerator Laboratory and a future electron-ion collider. Therefore, further theoretical studies are needed for understanding the tensor structure of the spin-1 deuteron, including a new mechanism to explain the large differences between the current data and our theoretical results.Comment: 12 pages, 7 eps figures, 3 style files, typos are corrected as published in Phys. Rev. D 95, 074036 (2017

Gluon saturation and pseudo-rapidity distributions of charged hadrons at RHIC energy regions

We modified the gluon saturation model by rescaling the momentum fraction according to saturation momentum and introduced the Cooper-Frye hydrodynamic evolution to systematically study the pseudo-rapidity distributions of final charged hadrons at different energies and different centralities for Au-Au collisions in relativistic heavy-ion collisions at BNL Relativistic Heavy Ion Collider (RHIC). The features of both gluon saturation and hydrodynamic evolution at different energies and different centralities for Au-Au collisions are investigated in this paper.Comment: 14 pages, 4 figure