Nest site selection by a neotropical swarm-founding wasp: seasonal alternation of nest orientation

Nest orientation in social insects has been intensively studied in warmer and cooler climates, particularly in the northern hemisphere. Previous studies have consistently shown that species subjected to these climatic conditions prefer to select mostly southern locations where the nests can gain direct sunlight. However, very little is known on nest orientation in tropical and subtropical social insects. We studied nest orientations initiated by swarms throughout a year in a Brazilian swarm-founding wasp, Polybia paulista von Ihering (Hymenoptera: Polistinae). Swarms selected various orientations as nest sites, but there was a particular trend in that swarms in the winter period (May-August) preferred to build northward-facing nests. This preference is opposite from that of social wasps observed in the northern hemisphere. Colonies of this species can potentially last for many years with continuous nesting, but nesting activities of colonies during the winter are severely limited due to cool temperature and a shortened day length. Northward-facing nests are warmer through the gain of direct solar heat during the winter period; consequently, choosing northward-facing sites may be advantageous for swarms in terms of a shortened brood development and shortened time needed to increase metabolic rates during warm-up for flight.

Gender-role alternation in the simultaneously hermaphroditic freshwater snail Physa acuta: not with the same partner

In simultaneous hermaphrodites, gender conflicts that arise from two potential mates sharing the same gender preference may be solved through conditional reciprocity (or gamete trading). Conditional reciprocity had initially been considered widespread, but recent studies suggest that its real occurrence may have been overestimated, possibly because most mating observations have been performed on isolated pairs of individuals. Some resulting patterns (e. g., non-random alternation of sexual roles) were indeed compatible with conditional reciprocity but could also have stemmed from the two partners independently executing their own mating strategy and being experimentally enforced to do so with the same partner. Non-random alternation of gender roles was recently documented in the simultaneously hermaphroditic freshwater snail Physa acuta. To distinguish between conditional and unconditional gender alternations, we observed copulations of individually marked snails reared at three contrasted densities. We showed that density affected the overall frequency of copulations during the first 2 days of the experiment with high-density boxes showing more copulations than low density boxes, but it did not affect gender alternation patterns. A change in gender role was observed more often than expected by chance over two successive copulations by the same individual, confirming previous studies. However, gender switches did not preferentially occur with the same partner. We conclude that gender alternation is not due to conditional reciprocity in P. acuta. It may rather stem from each individual having a preference for gender alternation. We finally discuss the mechanisms and the potential extent of this unconditional reciprocity.

Alternation and Cooperation in a Two-party System: Implications for Resource-Based Developing Economies

This paper studies cooperation in a political system dominated by two opportunistic parties competing in a resource-based economy. Since a binding agreement as an external solution might be difficult to enforce due to the close association between the incumbent party and the government, the paper explores the extent to which co-operation between political parties that alternate in office can rely on self-enforcing strategies to provide an internal solution. We show that, for appropriate values of the probability of re-election and the discount factor cooperation in maintaining the value of a state variable is possible, but fragile. Another result is that, in such political framework, debt decisions contain an externality element linked to electoral incentives that creates a bias towards excessive borrowing.

Playful language alternation in an online discussion forum: the example of digital code plays

This paper explores the linguistic practice of digital code plays in an online discussion forum, used by the community of English-speaking Germans living in Britain. By adopting a qualitative approach of Computer-Mediated Discourse Analysis, the article examines the ways in which these bilinguals deploy linguistic and other semiotic resources on the forum to co-construct humorous code plays. These performances occur in the context of negotiating language norms and are based on conscious manipulations of both codes, English and German. They involve play with codes at three levels: play with forms, meanings, and frames. Although, at first sight, such alternations appear to be used mainly for a comic effect, there is more to this than just humour. By mixing both codes at all levels, the participants deliberately produce aberrant German ‘polluted’ with English and, in so doing, dismantle the ideology of language purity upheld by the purist movement. The deliberate character of this type of code alternation demonstrates heightened metalinguistic awareness as well as creativity and criticality. By exploring the practice of digital code plays, the current study contributes to the growing body of research on networked multilingualism as well as to practices associated with translanguaging, poly- and metrolingualism.

Effect of sodium hypochlorite and edta irrigation, individually and in alternation, on dentin microhardness at the furcation area of mandibular molars

The aim of this study was to evaluate the effect of irrigation regimens on dentin microhardness at the furcation area of mandibular molars, using sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA), individually and in alternation. The occlusal surface and the roots of 20 non-carious extracted human permanent mandibular molars were cut transversally and discarded. The tooth blocks were embedded in acrylic resin and randomly assigned to 4 groups (n=5) according to the irrigating regimens: 1% NaOCl solution, 17% EDTA solution, 1% NaOCl and 17% EDTA and distilled water (control). Knoop microhardness of dentin at the furcation area was evaluated. Data were analyzed using one-way ANOVA and Tukey's multiple comparison tests (α=0.05). The results of this study indicated that all irrigation solutions, except for distilled water (control), decreased dentin microhardness. EDTA did not show a significant difference with NaOCl/EDTA (p>0.05), but showed a significant difference with NaOCl (p<0.01). EDTA and NaOCl/EDTA showed a maximum decrease in microhardness. The 17% EDTA solution, either alone or in combination with 1% NaOCl reduced significantly dentin microhardness at the furcation area of mandibular molars.

Even-odd alternation in mass spectrum of thymine and uracil clusters: Evidence of intracluster photodimerization

Multiphoton ionization of thymine and uracil clusters generated by a supersonic molecular beam gave rise to a remarkable alternation of mass spectral intensities between even- and odd-numbered clusters. Such alternation was observed in clusters of up to 30 molecules. Excitation to the two lowest electronically excited states seemed to be a strong prerequisite. In view of the well known photodimerization reaction of thymine and uracil in the bulk phase, it is proposed that such alternation in the mass spectral intensity resulted from formation of photodimer units within the cluster on intense UV irradiation. Several analogues of thymine with no known propensity for photodimerization in the bulk phase did not exhibit any sign of such alternation in the cluster mass spectrum. The intrinsic UV window for photodimerization, and hence photoinduced mammalian mutagenesis, was estimated to be approximately 210–280 nm, significantly narrower than the previously reported bulk values of 150–300 nm.

The poor law : is any alternation of it necessary or tolerably practicable?

Mode of access: Internet.

The origin of a land flora, a theory based upon the facts of alternation,

Mode of access: Internet.

Token codeswitching and language alternation in narrative discourse: a functional-pragmatic approach

This study is concerned with two phenomena of language alternation in biographic narrations in Yiddish and Low German, based on spoken language data recorded between 1988 and 1995. In both phenomena language alternation serves as an additional communicative tool which can be applied by bilingual speakers to enlarge their set of interactional devices in order to ensure a smoother or more pointed processing of communicative aims. The first phenomenon is a narrative strategy I call Token Cod-eswitching: In a bilingual narrative culminating in a line of reported speech, a single element of L2 indicates the original language of the reconstructed dialogue – a token for a quote. The second phenomenon has to do with directing procedures, carried out by the speaker and aimed at guiding the hearer's attention, which are frequently carried out in L2, supporting the hearer's attention at crucial points in the interaction. Both phenomena are analyzed following a model of narrative discourse as proposed in the framework of Functional Pragmatics. The model allows the adoption of an integral approach to previous findings in code-switching research.

Double Hybrid Functionals and the Π-System Bond Length Alternation Challenge: Rivaling Accuracy of Post-HF Methods

Predicting accurate bond length alternations (BLAs) in long conjugated oligomers has been a significant challenge for electronic-structure methods for many decades, made particularly important by the close relationships between BLA and the rich optoelectronic properties of π-delocalized systems. Here, we test the accuracy of recently developed, and increasingly popular, double hybrid (DH) functionals, positioned at the top of Jacobs Ladder of DFT methods of increasing sophistication, computational cost, and accuracy, due to incorporation of MP2 correlation energy. Our test systems comprise oligomeric series of polyacetylene, polymethineimine, and polysilaacetylene up to six units long. MP2 calculations reveal a pronounced shift in BLAs between the 6-31G(d) basis set used in many studies of BLA to date and the larger cc-pVTZ basis set, but only modest shifts between cc-pVTZ and aug-cc-pVQZ results. We hence perform new reference CCSD(T)/cc-pVTZ calculations for all three series of oligomers against which we assess the performance of several families of DH functionals based on BLYP, PBE, and TPSS, along with lower-rung relatives including global- and range-separated hybrids. Our results show that DH functionals systematically improve the accuracy of BLAs relative to single hybrid functionals. xDH-PBE0 (N4 scaling using SOS-MP2) emerges as a DH functional rivaling the BLA accuracy of SCS-MP2 (N5 scaling), which was found to offer the best compromise between computational cost and accuracy the last time the BLA accuracy of DFT- and wave function-based methods was systematically investigated. Interestingly, xDH-PBE0 (XYG3), which differs to other DHs in that its MP2 term uses PBE0 (B3LYP) orbitals that are not self-consistent with the DH functional, is an outlier of trends of decreasing average BLA errors with increasing fractions of MP2 correlation and HF exchange.

Some considerations on the alternation of generations in plants,

Mode of access: Internet.

Abundância de ramos reprodutivos e produção de sementes em populações de Ipomoea pes-caprae (L.) R. Br. na Ilha de Santa Catarina, Brasil

The variation in the proportion of reproductive branches, fruit, and seed production of Ipomoea pes-caprae (L.) R. Br. (Convolvulaceae) were evaluated at ten beaches on Santa Catarina Island, state of Santa Catarina, Brazil. Three patches per beach of Ipomoea pes-caprae were monitored, involving two reproductive cycles. Ipomoea pes-caprae presented initially an average length of patches of 14 m, with 9.6 branches/m² and 39% of reproductive branches. The proportion of reproductive branches varied between the cycles, but there was not noticed an alternation of reproductive effort between the subsequent cycles. There was a reduction in the percentage of reproductive branches at six localities. In four beaches where Ipomoea pes-caprae populations declined, occurred reduction in the reproductive vigor, and in the seed production, being these declines associated to strong sea erosion. In another hand, in one beach with population increase, there were little reproductive branches due to the occurrence of young stolons. Four patches never maturated fruits, being three of these located at small beaches. The fruit and seed productions in the patches showed values up to 40 fruits/m² and up to 140 seeds/m², respectively. Populations with great seed production were localized in areas adjacent to great coastal plains, which may represent potential seed sources for areas with small seed production in the island.