Sulla riducibilità delle curve algebriche sghembe ottenute per «piccola variazione» sopra superficie algebriche irriducibili

Riassunto In questa Nota viene data una condizione per stabilire se, partendo da una curva algebrica sghemba riducibile situata sopra una superficie algebrica irriducibile di ordine qualunque ed operando per ?piccola variazione? sulla superficie stessa, sia possibile ottenere una curva algebrica sghemba irriducibile o, se irriducibile, abbia a contenere una o più componenti della curva data.

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Résumé On donne une condition pour vérifier s’il est possible, à partir d’une courbe algébrique gauche réductible placée sur une surface algébrique irréductible d’ordre quelconque et en opérant par ?petite variation? sur la même surface, d’obtenir une courbe algébrique gauche, irréductible ou, si réductible, contenant une ou plusieurs composantes de la courbe donnée.

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Lavoro eseguito nell’ambito dell’attività del Gruppo di ricerca n. 26 del Comitato Nazionale per la Matematica del C.N.R. per l’anno accademico 1964–65.     

Momentum dependent vertices σγγ, σργ and σρρ the NJL scalar hidden by chiral symmetry

We calculate the momentum dependence of three particle verticesσγγ, σργ andσρρ in the context of a Nambu Jona Lasinio type model. We show how they influence the processesγγ→σ→ππ, ρ→γσ andγγ→ρρ and how chiral symmetry shadows the presence of theσ.     

Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers

The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25–170 °C) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27–44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/~35 °C/n/~115 °C/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above T_NI. The phase diagram is asymmetric and does not alter above T_NI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b_LC=0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.This paper is dedicated to Prof. Fischer on the occasion of his 75th birthday.     

Versatile synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of 2-alkynylbenzyl alcohols

An easy synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of readily available 2-alkynylbenzyl alcohols under neutral conditions is reported. Reactions were carried out at 70-100°C in the presence of catalytic amounts (1-2%) of PdI₂ in conjunction with 2 equiv. of KI for 1.5-24 h. The preference towards the 5-exo-dig cyclization mode (leading to 1,3-dihydroisobenzofurans) or the 6-endo-dig cyclization mode (leading to isochromenes) turned out to be dependent on the substitution pattern of the substrate as well as reaction conditions. In several cases, by properly adjusting the reaction conditions, the same substrate could be selectively converted into either the dihydroisobenzofuran or the 1H-isochromene derivative.     

Density functional theory study of the trans-trans-cis (TTC)-->trans-trans-trans (TTT) isomerization of a photochromic spiropyran merocyanine

Density Functional Theory (DFT) calculations have been performed on the TTC-->TTT isomerization reaction of the open forms of the 1',3'-dihydro-8-bromo-6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-(2H)indole (8-Br-6-nitro-BIPS) system. The calculations were carried out in vacuo and in methylene chloride solution at different temperatures. Results are compared with the available experimental values of free energy difference and activation energy in solution.     

Studium der Verbrennung fester Brennstoffe mittels differenz-thermischer Analyse

Zusammenfassung Über die Anwendbarkeit der differenz-thermischen Analyse zur Untersuchung fester Brennstoffe wurde berichtet. Aus den Thermogrammen kann man für verschiedene feste Brennstoffe den Anfang der Verbrennung, den Entzündungspunkt, ablesen und die Wärmemenge bewerten, die beim Brennen freigesetzt wird. Durch Vergleich mit der Verbrennungswärme eines bekannten, festen Brennstoffes wurden die Reaktionswärmen beim Verbrennen fünf fester Brennstoffe bestimmt, und zwar für Braunkohle, Lignit, Elektrodengraphit, Petrolkoks und für normalen metallurgischen Hochofenkoks. Die Verbrennungsgeschwindigkeit in Abhängigkeit von der Temperatur wurde festgestellt, die Konstante der Verbrennungsgeschwindigkeit und die Reaktionsordnung errechnet. Bei geringen Brennstoffmengen, wenn man die Sauerstoffkonzentration als konstant annehmen kann, ist die Verbrennung fester Brennstoffe eine Reaktion erster Ordnung. Bei niedrigeren Temperaturen überwiegt jedoch der kinetische, bei höheren Temperaturen der Diffusionscharakter der Reaktion. Aus den Versuchen geht hervor, daß sich die differenzthermische Analyse in einigen Fällen erfolgreich anwenden läßt; aber bei komplizierteren Prozessen versagt bzw. kann sie bloß als Ergänzungsanalyse angewendet werden.

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Summary A report is given of the applicability of differential thermal analysis to the investigation of solid fuels. Information regarding the start of the combustion and the ignition point can be read from the thermograms for various solid fuels and the quantity of heat estimated that is set free during the burning. By comparison with the heat of combustion of a known solid fuel, the heats of reaction on combustion were determined of five solid fuels, namely lignite, brown coal, electrode graphite, petroleum coke and normal metallurgical blast furnace coke. The speed of combustion in relation to the temperature was determined, and the constants for the combustion velocity and the reaction order were calculated. If the oxygen concentration is taken to be constant in the case of small amounts of combustibles, the combustion of solid fuels is a first order reaction. However, at lower temperatures, the kinetic character of the reaction predominates, while at higher temperature the diffuse character is predominant. The experiments show that the differential thermal analysis can be applied with success in some instances; but it fails in more complicated processes, or it may be applied merely as a supplementary analysis.

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Résumé On présente une étude sur l'application de l'analyse thermique différentielle à l'étude des combustibles solides. On peut estimer sur les enregistrements le début de la combustion, le point d'inflammation et apprécier la quantité de chaleur libérée quand ils brûlent. En comparant avec la chaleur de combustion d'un combustible solide connu, on a déterminé les chaleurs de réaction accompagnant la combustion de 5 combustibles solides ainsi que pour la tourbe, le lignite, le graphite pour électrodes, le coke de pétrole et le coke métallurgique normal des hauts fourneaux. On a établi la vitesse de combustion suivant la température et calculé la constante de vitesse de la combustion et l'ordre de la réaction. Pour de faibles quantités de combustible, si l'on peut admettre constante la concentration d'oxygène, la combustion du combustible solide suit une réaction du premier ordre. Pour les températures plus basses, le caractère cinétique de la réaction domine et pour les températures plus élevées, le caractère d'une diffusion. On déduit de l'expérience que l'analyse thermique différentielle peut s'appliquer avec plein succès dans certains cas. Toutefois, pour des processus compliqués, elle se trouve mise en échec ou ne peut s'appliquer simplement que comme analyse de complément.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.     

The Reversibility of UV‐B Induced Alterations in Optical Properties of the Rabbit Cornea Depends on Dose of UV Irradiation

Solar UVB radiation evokes photokeratitis, accompanied by increased corneal hydration and changes in corneal transparency, resulting in increased light absorption. Corneal optical properties are disturbed and visual acuity decreased. The aim of this study was to investigate the reversibility of these UVB‐induced changes. Rabbit corneas were irradiated with UVB doses of 0.5 J cm^?2 or 1.01 J cm^?2 during 4 days. Some rabbits were sacrificed after the last irradiation and some 2 months later. Corneas were investigated spectrophotometrically for light absorption, and corneal hydration was evaluated by central corneal thickness with an ultrasonic pachymeter. Corneal impression cytologies were examined immunohistochemically for proinflammatory cytokines and malondialdehyde. The increased corneal light absorption, hydration and the staining of immunohistochemical markers found in corneas after irradiation returned to normal values during 2 months in corneas irradiated with the lower UVB dose. In contrast, in corneas irradiated with the higher UVB dose, a moderate but statistically significant increase in corneal light absorption, hydration and positive immunohistochemical stainings remained as residual changes. This was in contrast to normal corneas, where the staining of proinflammatory cytokines as well as malondialdehyde was negative. In conclusion, the reversibility of UVB‐induced disturbances was dependent on UVB dose.     

Nuovi risultati nella teoria diametrale delle superficie algebriche

Riassunto Nella presente Nota metto in rilievo anzitutto una corrispondenza [1, (n−1)²] che sussiste fra i piani diametrali di una superficie algebrica di ordinen e le corrispondenti direzioni coniugate e ne deduco la proprietà che i piani diametrali si dispongono a gruppi di (n−1)² piani paralleli. Ciò posto, procedo alla ricerca dei piani diametrali autoconiugati e mutuamente coniugati della superficie in riferimento al comportamento della stessa superficie con il piano all’infinito ponendo particolare riguardo alle superficie di ordinen (pari) aventi in comune con il piano all’infinito una conica contatan/2 volte (quadriche generalizzate).

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Résumé Dans cette Note j’établis avant tout, une correspondance [1, (n−1)²] qui existe pour les plans diamétraux d’une surface algébrique générale d’ordren et les correspondantes directions conjuguées et j’en déduis la propriété que les plans diamétraux de la surface se disposent en groupes de (n−1)² plans parallèles. Cela posé, je proiede à la recherche des plaus diamétraux autoconjugués et mutuellement conjugués de la surface à l’égard de la nature de la courbe d’intersection de la surface avec le plan à l’infini, considerant particulièrment les surfaces d’ordren (pair) qui recontrent le plan à l’infini suivant une conique comptéen/2 fois (quadriques généralisées).

     

Sulla classificazione delle curve algebriche sghembe in base alla determinazione di tutti i multilateri sghembi connessi per ogni ordine e genere

Riassunto In questa Nota si dà un metodo per ottenere il numero ed i tipi di multilateri sghembi di ordinen e generep dati, conn+p−1 vertici di connessione e che sono casi limite di curve algebriche sghembe irriducibili.

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Résumé Dans la prèsente Note on donne une méthode pour obtenir le nombre et les types des multilatères gauches d'ordren e de genrep donnés, ayantn+p−1 sommets de connexion, et qui sont des cas limites de courbes gauches algébriques irriductibles.