Petites déformations de droites dans le plan projectif réel

Résumé SoitD une famille deN droites dans le plan projectif réelRP ², telle que chaque point appartient au plus à deux droites. Le but de ce travail est l'étude de la topologie des courbes algébriques non singulières obtenues en faisant des petites déformations deD et la construction des algorithmes qui permettent de calculer le nombre de composantes connexes et le type topologique de ces courbes. De plus cet article contient les résultats du programme qui réalise ces algorithmes par un ordinateur dens les casN<-6.

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Riassunto SiaD un insieme diN rette nel piano proiettivo realeRP ², tale che ciascuna retta incontra tutte le altre e tutti i punti d'intersezione sono punti doppi. Lo scopo di questo lavoro è di studiare la topologia delle curve algebriche non singolari ottenute mediante piccole deformazioni diD e di costruire gli algoritmi che permettono di calcolare il numero di componenti connesse e il tipo topologico di queste curve. Inoltre nel lavoro sono contenuti i risultati del programma che realizza su calcolatore tali algoritmi perN<-6.

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/laUn petit d'un petit c'est un ovale…/ra (Van Rooten:Mots d'heures gousses et rames)     

Acoustical design and experimental verification of school music rooms: A case study

This paper presents an approach to acoustical design and the results of a survey in music rooms in an Italian public school (Liceo Statale “Alfano I” in Salerno, Italy). The locations selected are devoted to orchestral performances and to recording.     

A note on the divergence of geodesic rays in manifolds without conjugate points

Let (M, g) be a compact Riemannian manifold without conjugate points and let be its universal covering endowed with the pullback of the metric g by the covering map. We show that geodesic rays in which meet an axis of a covering isometry diverge from this axis. This result generalizes well known results by Morse and Hedlund in the context of globally minimizing geodesics in the universal covering of compact surfaces.      

Dyotropic rearrangement of alpha-lactone to beta-lactone: a computational study of small-ring halolactonisation

Transition structures have been optimised using the B3LYP/6-31+G* density functional level method, in vacuum and in implicit (PCM) and explicit (DFT/MM) aqueous solvation, for the degenerate rearrangement of the alpha-lactone derived by the formal addition of Cl(+) to acrylate anion and for the dyotropic rearrangement of this to the beta-lactone. Despite being lower in energy than the alpha-lactone, there is no direct pathway to the beta-lactone from the acrylate chloronium zwitterion, which is the transition structure for the degenerate rearrangement. This may be rationalised by consideration of the unfavorable angle of attack by the carboxylate nucleophile on the beta-position; attack on the alpha-position involves a less unfavorable angle. Formation of the beta-lactone may occur by means of a dyotropic rearrangement of the alpha-lactone. This involves a high energy barrier for the acrylate derived alpha-lactone, but dyotropic rearrangement of the beta,beta-dimethyl substituted alpha-lactone to the corresponding beta-lactone involves a much lower barrier, estimated at about 46 kJ mol(-1) in water, and is predicted to be a facile process.     

Multigram synthesis of a water-soluble porphyrazine and derived seco-porphyrazine labeling agents

Porphyrazine III has been synthesized on a large scale (18.4 g), with minimal chromatographic purification by employing a novel one-pot, 3-step sequence. Two dinitrile precursors I and II, the latter of which consisted of a mixture of geometric isomers, were transformed, via the corresponding pyrroline diimines, into a mixture of III and the octa-Ar1-porphyrazine. Isolated macrocycle III was subsequently transformed into IV, a water-soluble seco-porphyrazine suitable for the labeling of biological vectors.     

The Role of Lateral Tension in Calcium-Induced DPPS Vesicle Rupture

We assess the role of lateral tension in rupturing anionic dipalmitoylphosphatidyserine (DPPS), neutral dipalmitoylphosphatidylcholine (DPPC), and mixed DPPS-DPPC vesicles. Binding of Ca(2+) is known to have a significant impact on the effective size of DPPS lipids and little effect on the size of DPPC lipids in bilayer structures. In the present work we utilized laser transmission spectroscopy (LTS) to assess the effect of Ca(2+)-induced stress on the stability of the DPPS and DPPC vesicles. The high sensitivity and resolution of LTS has permitted the determination of the size and shape of liposomes in solution. The results indicate a critical size after which DPPS single shell vesicles are no longer stable. Our measurements indicate Ca(2+) promotes bilayer fusion up to a maximum diameter of ca. 320 nm. These observations are consistent with a straightforward free-energy-based model of vesicle rupture involving lateral tension between lipids regulated by the binding of Ca(2+). Our results support a critical role of lateral interactions within lipid bilayers for controlling such processes as the formation of supported bilayer membranes and pore formation in vesicle fusion. Using this free energy model we are able to infer a lower bound for the area dilation modulus for DPPS (252 pN/nm) and demonstrate a substantial free energy increase associated with vesicle rupture.     

Estimating technical and allocative efficiency in the public sector: A nonparametric analysis of Dutch schools

Public sector output provision is influenced not only by discretionary inputs but also by exogenous environmental factors. In this paper, we extended the literature by developing a conditional DEA estimator of allocative efficiency that allows a decomposition of overall cost efficiency into allocative and technical components while simultaneously controlling for the environment. We apply the model to analyze technical and allocative efficiency of Dutch secondary schools. The results reveal that allocative efficiency represents a significant 37 percent of overall cost efficiency on average, although technical inefficiency is still the dominant part. Furthermore, the results show that the impact of environment largely differs between schools and that having a more unfavorable environment is very expensive to schools. These results highlight the importance of including environmental variables in both technical and allocative efficiency analysis.     

Chemical, energetic, and geometric heterogeneity of device-quality (1 0 0) surfaces of single crystalline silicon after HFaq etching

An analysis, based on angle-resolved X-ray photoelectron spectroscopy, multiple-internal-reflection infrared spectroscopy, and atomic force microscopy, of device-quality (1 0 0)silicon surfaces after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH₂and SiH₃ terminations, but contains sub-stoichiometric oxidized silicon. The analysis shows moreover the existence of a form of reduced silicon, not consistent with the currently accepted picture of the native HF_aq-etched surface.