The role of complex formation in the anionic polymerization of l-lactide

The rate lowering effect of crown ethers in the anionic polymerization of l-lactide is interpreted by the formation of activated monomer-cation complex. This interpretation is supported by molecular mechanics calculations. The formation of a 1 : 1 complex between lithium ion and l-lactide in THF was proved by ¹H NMR and the formation constant was measured to be 3.8 M⁻¹. Received: 15 January 1997/Accepted: 10 March 1997     

Conspecific and Heterogeneric Lacewings Respond to (<Emphasis Type="Italic">Z</Emphasis>)-4-Tridecene Identified from <Emphasis Type="Italic">Chrysopa formosa</Emphasis> (Neuroptera: Chrysopidae)

Green lacewings (Chrysopidae) are predators of soft-bodied pest insects and are among the most important biological control agents in crop protection. Chrysopa spp. are of special importance since, unlike most green lacewing species, adults are also predatory. The current study was undertaken in search of Chrysopa formosa compounds with semiochemical activity. Using coupled gas chromatography-electroantennography (GC-EAG), head and thorax extracts of C. formosa elicited EAG responses to a compound subsequently identified by coupled GC/mass spectrometry, microchemistry, chemical synthesis and GC peak enhancement as (Z)-4-tridecene. In field experiments, this compound decreased attraction of adult C. formosa to (1R,4aS,7S,7aR)-nepetalactol and that of Chrysoperla carnea species-complex to a ternary floral lure, with the inhibitory effect found to be dose-dependent. Our results suggest that (Z)-4-tridecene may serve as a general warning signal among multiple green lacewing species. Perspectives for potential practical applications are discussed.     

Toughening of silicon nitride ceramics by addition of multilayer graphene

Silicon nitride (Si₃N₄) ceramics have superior mechanical properties allowing their broad application in many technical fields. In this work, Si₃N₄-based composites with 1–5?wt% multilayer graphene (MLG) content were fabricated by spark plasma sintering at different temperatures and holding time in order to improve the fracture resistance of the Si₃N₄ ceramic. Our investigation focused on understanding the relationships between the microstructure and mechanical properties with special attention to the intergranular phases between Si₃N₄ matrix and MLG reinforcement.We have found that nanopores developed at the Si₃N₄-MLG interface due to a reaction between carbon and the oxygen available in the topmost layer of the Si₃N₄ particles. Interface porosity has an optimum for the toughening effect. In 1?wt% MLG/Si₃N₄ composites nanopores are local, but separated at the Si₃N₄-MLG interface, which promote the MLG pull-out mechanism imparting a significant toughening effect on the composite. Beyond the optimal 1?wt% MLG content, MLG platelets agglomerate and excessive porosity are developed at the Si₃N₄-MLG interfaces, leading to weaker matrix- graphene adhesion and thus lower fracture toughness.     

Hypo-Steiner heuristic for multicast routing in all-optical WDM mesh networks

In sparse light splitting all-optical WDM networks, the more destinations a light-tree can accommodate, the fewer light-trees and wavelengths a multicast session will require. In this article, a Hypo-Steiner light-tree algorithm (HSLT) is proposed to construct a HSLT light-tree to include as many destinations as possible. The upper bound cost of the light-trees built by HSLT is given as N(N − 1)/2, where N is the number of nodes in the network. The analytical model proves that, under the same condition, more destinations could be held in a HSLT than a Member-Only (Zhang et al., J. Lightware Technol, 18(12), 1917–1927 2000.) light-tree. Extensive simulations not only validate the proof but also show that the proposed heuristic outperforms the existing multicast routing algorithms by a large margin in terms of link stress, throughput, and efficiency of wavelength usage.     

All-optical multipoint-to-point routing in WDM mesh networks

In this article, the routing and wavelength assignment (RWA) problem for supporting multipoint-to-point communications in all-optical WDM mesh networks is investigated. Two efficient algorithms, namely reverse shortest path tree routing (RSPT) and k-bounded edge disjoint path routing (EDPR), are proposed. We proved that the problem of minimizing the total cost while establishing a multipoint-to-point session can be solved in polynomial time of O(|V|log|V|?+?|V|?+?|E|) by the RSPT algorithm, where |V| and |E| denote the number of nodes and the number of edges in the network, respectively. Nevertheless, the solution provided by the EDPR algorithm produces a significant reduction in the maximum number of wavelengths required per link (i.e., the link stress) for a multipoint-to-point session compared to RSPT algorithm. EDPR algorithm can also approximate to the optimal total cost with a ratio of k. Simulations are done to assess these two algorithms. Numerical results demonstrate their efficiencies in supporting multipoint-to-point communications in all-optical WDM networks.     

Verbal Attention Getting as a Key Factor in Social Learning Between Dog (Canis familiaris) and Human.

Pet dogs (Canis familiaris) learn to detour a V-shaped fence effectively from an unfamiliar human demonstrator. In this article, 4 main features of the demonstrator's behavior are highlighted: (a) the manipulation of the target, (b) the familiarity of the demonstrator, (c) the role of verbal attention-getting behavior, and (d) whether a strange trained dog could also be an effective demonstrator. The results show that the main factor of a successful human demonstration is the continuous verbal communication with the dog during detouring. It was also found that an unfamiliar dog demonstrator was as efficient as the unfamiliar experimenter. The experiments provide evidence that in adult dogs, communicative context with humans is needed for effective interspecific social learning to take place. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of antipredator behavior in paradise fish larvae (Macropodus opercularis) IV. The effect of exposure to siblings

Twenty-five-day-old larval paradise fish show less avoidance behavior toward a model predator than 20-day-old fish larvae. Laboratory experiments tested two possible hypotheses: The decrease of avoidance behavior is the result of (a) change in the size ratio of larvae/model, or (b) experience with larval siblings. Larval paradise fish did not show greater avoidance of larger models or models with larger eyespots. However, if isolated for 3 days, the antipredator behavior of 25-day-old larvae became similar to younger ones. In further experiments, we raised the larvae in a larger holding tank in order to decrease the rate of encounters among conspecifics. In line with our assumptions, these larvae also showed enhanced avoidance toward a model predator. In sum, our experiments revealed that the continuous exposure to conspecific larvae was the main cause for the reduced antipredator behavior toward models. To account for our results, we suggest that larvae of nonschooling paradise fish habituate to the continuous presence of larval conspecifics and, as a result, they show decreased avoidance to the model predator. We hypothesize that this habituation process might not work in other fish species that show early schooling behavior in their development. In other words, they would not generalize the experience of conspecifics to potential predators.     

Attachment behavior in dogs (Canis familiaris): A new application of Ainsworth's (1969) Strange Situation Test.

Fifty-one owner–dog pairs were observed in a modified version of M. D. S. Ainsworth's (1969) Strange Situation Test. The results demonstrate that adult dogs (Canis familiaris) show patterns of attachment behavior toward the owner. Although there was considerable variability in dogs' attachment behavior to humans, the authors did not find any effect of gender, age, living conditions, or breed on most of the behavioral variables. The human–dog relationship was described by means of a factor analysis in a 3-dimensional factor space: Anxiety, Acceptance, and Attachment. A cluster analysis revealed 5 substantially different classes of dogs, and dogs could be categorized along the secure–insecure attached dimensions of Ainsworth's original test. A dog's relationship to humans is analogous to child–parent and chimpanzee–human attachment behavior because the observed behavioral phenomena and the classification are similar to those described in mother–infant interactions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)