Development of autoclavable polyimides

A poly(Diels-Alder) (PDA) resin approach was investigated as a means to achieve autoclavability of high temperature resistant resin/fiber composites under mild fabrication procedures. Low void content Type A-S graphite reinforced composites were autoclave fabricated from a PDA resin/fiber prepared from an acetone:methanol:dioxane varnish. Autoclave conditions were 477K (400F) and 0.7 MN/sq m (100 psi) for up to two hours duration. After postcure at temperatures up to 589K (600F), the composites demonstrated high initial mechanical properties at temperatures up to 561K (550F). The results from isothermal aging studies in air for 1000 hours indicated potential for long-term ( 1000 hours) use at 533K (500F) and shorter-term (up to 1000 hours) at 561K (550F)

The Genus viola in the Balearic Islands

S'ha dut a terme l'estudi del gènere Viola a les illes Balears. Es proposen dues noves combinacions nomenclaturals: Viola suavis Bieb. subsp. barceloi (Nyman) Orell & Romo, comb. nova i Viola odorata L. subsp. stolonifera (Rodríguez Femenías) Orell & Romo, comb. nova. Es descriuen tres noves notosubspècies de l'illa de Mallorca: Viola alba L. nothosubsp. neusii Orell & Romo, nothosubsp. nova (=Viola alba subsp. dehnhardtii x V. jaubertiana); Viola alba L. nothosubsp. bonaefidei Orell & Romo, nothosubsp. nova (=V. alba subsp. dehnhardtii x V. suavis subsp. barceloi); i Viola suavis Bieb. nothosubsp. cardonae nothopsubsp. nova (=Viola suavis subsp. barceloi x V. jaubertiana). S'exposen la corologia i l'ecologia dels tàxons de Viola presents a les Illes i es valoren algunes citacions antigues, probablement errònies.Following the study of Balearic taxa of the genus Viola, two new nomenclatural combinations are proposed: Viola suavis Bieb. subsp. barceloi (Nyman) Orell & Romo, comb. nova; and Viola odorata L. subsp. stolonifera (Rodríguez Femenías) Orell & Romo, comb. nova. Three new nothosubspecies from the island of Majorca are described: Viola alba L. nothosubsp. neusii Orell & Romo, nothosusp. nova (= Viola alba subsp. dehnhardtii x V. jaubertiana); Viola alba L. nothosubsp. bonaefidei Orell & Romo, nothosubsp. nova (= V. Alba subsp. dehnhardtii x V. suavis subsp. barceloi); and Viola suavis Bieb. nothosubsp. cardonae nothosubsp. nova (= Viola suavis subsp. barceloi x V. Jaubertiana). The chorology and ecology of the Balearic taxa of the genus Viola are presented and some of the oldest reports, which are probably erroneous, are discussed

Sampled Policy Gradient for Learning to Play the Game Agar.io

In this paper, a new offline actor-critic learning algorithm is introduced: Sampled Policy Gradient (SPG). SPG samples in the action space to calculate an approximated policy gradient by using the critic to evaluate the samples. This sampling allows SPG to search the action-Q-value space more globally than deterministic policy gradient (DPG), enabling it to theoretically avoid more local optima. SPG is compared to Q-learning and the actor-critic algorithms CACLA and DPG in a pellet collection task and a self play environment in the game Agar.io. The online game Agar.io has become massively popular on the internet due to intuitive game design and the ability to instantly compete against players around the world. From the point of view of artificial intelligence this game is also very intriguing: The game has a continuous input and action space and allows to have diverse agents with complex strategies compete against each other. The experimental results show that Q-Learning and CACLA outperform a pre-programmed greedy bot in the pellet collection task, but all algorithms fail to outperform this bot in a fighting scenario. The SPG algorithm is analyzed to have great extendability through offline exploration and it matches DPG in performance even in its basic form without extensive sampling

Development of autoclavable addition type polyimides

Two highly promising approaches to yield autoclavable addition-type polyimides were identified and evaluated in the program. Conditions were established for autoclave preparation of Hercules HMS graphite fiber reinforced composites in the temperature range of 473 K to 505 K under an applied pressure of 0.7 MN/m2 (100 psi) for time durations up to four hours. Upon oven postcure in air at 589 K, composite samples demonstrated high mechanical property retention at 561 K after isothermal aging in air for 1000 hours. Promise was shown for shorter term mechanical property retention at 589 K upon exposure in air at this temperature

Development of autoclave moldable addition-type polyimides

Chemistry and processing modifications of the poly(Diels Alder) polyimide (PDA) resin were performed to obtain structural composites suitable for 589 K (600 F) service. This work demonstrated that the PDA resin formulation is suitable for service at 589 K (600 F) for up to 125 hours when used in combination with Hercules HTS graphite fiber. Sandwich panels were autoclave molded using PDA/HTS skins and polyimide/glass honeycomb core. Excellent adhesion between honeycomb core and the facing skins was demonstrated. Fabrication ease was demonstrated by autoclave molding three-quarter scale YF-12 wing panels

Improved high-temperature resistant matrix resins

A study was performed with the objective of developing matrix resins that exhibit improved thermo-oxidative stability over state-of-the-art high temperature resins for use at temperatures up to 644 K (700 F) and air pressures up to 0.7 MPa (100 psia). The work was based upon a TRW discovered family of polyimides currently licensed to and marketed by Ethyl Corporation as EYMYD(R) resins. The approach investigated to provide improved thermo-oxidative properties was to use halogenated derivatives of the diamine, 2, 2-bis (4-(4-aminophenoxy)phenyl) hexafluoropropane (4-BDAF). Polyimide neat resins and Celion(R) 12,000 composites prepared from fluorine substituted 4-BDAF demonstrated unexpectedly lower glass transition temperatures (Tg) and thermo-oxidative stabilities than the baseline 4-BDAF/PMDA polymer

Single nucleotide polymorphisms to discriminate different classes of hybrid between wild Atlantic salmon and aquaculture escapees

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Synthesis of improved moisture resistant polymers

The use of difluoromaleimide-capped prepolymers to provide improved moisture resistant polymers was investigated. Six different prepolymer formulations were prepared by two different methods. One method utilized the PMR approach to polyimides and the second method employed the normal condensation route to provide fully imidized prepolymers. Polymer specimens cured at 450 F exhibited adequate long-term stability in air at 400 F. Moisture absorption studies were conducted on one polymer formulation. Neat Polymer specimens exhibited weight gains of up to 2% (w/w) after exposure to 100% relative humidity at 344K (160 F) for 400 hours

Nest-site competition between bumblebees (Bombidae), social wasps (Vespidae) and cavity-nesting birds in Britain and the Western Palearctic

Capsule: There is no evidence of widespread significant nest-site competition in Britain or the Western Palearctic between cavity-nesting birds and bumblebees or social wasps. Aims: To investigate competition between cavity-nesting birds and bumblebees and wasps, particularly the range-expanding Tree Bumblebee, Saxon Wasp and European Hornet in Britain, and review evidence throughout the Western Palearctic. Methods: We compared field data from English and Polish studies of tits and woodpeckers breeding in nest-boxes and/or tree holes to assess nest-site competition with bumblebees and wasps. We reviewed the literature quantifying nest-site competition between birds and these insects in the Western Palearctic. Results: Bumblebees and wasps are capable of usurping small passerines from nests. In England, these insects commandeered a mean annual 4.1% of tit nests initiated in nest-boxes; occurrence of hornets showed a long-term increase, but not other wasps or bumblebees. Across the Western Palearctic, insect occupation of nest-boxes was generally low, and was lower in England than in Poland. No insects were discovered in tree cavities, including those created by woodpeckers (Picidae). Conclusion: Nest-site competition between cavity-nesting birds and bumblebees and wasps appears to be a ‘nest-box phenomenon’, which may occasionally interfere with nest-box studies, but appears negligible in natural nest-sites