Classical and accelerated evaluation of neutron escape probability

Neutron escape probability from a monodimensional plane medium is determined by resorting to the integral neutron transport equation.Both a projection procedure and an appropriate variational approach, yielding an acceleration of the convergence rate, are employed; their numerical results are reported and discussed.The theory is presented in a general form, since it can be applied directly to many basic problems in other branches of applied sciences.

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Riassunto La probabilità di fuga di un neutrone da un mezzo monodimensionale piano viene determinata nell'ambito della teoria integrale del trasporto. Vengono impiegati sia un procedimento proiezionale classico, che un opportuno metodo variazionale in grado di produrre un'accelerazione della velocità di convergenza; i relativi risultati numerici sono riportati e discussi. La teoria è esposta nella sua forma generale, in quanto può essere applicata direttamente a diversi problemi di base in altri rami delle scienze applicate.

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Work supported by the National Group for Mathematical Physics of C.N.R.     

The normodistributive expansion of a category

Summary Starting from a categoryC, verifying certain hypotheses, we define a categoryC ^♯ called normodistributive expansion ofC. The categoryC ^♯is orthoquaternary, then canonical isomorphisms between subquotients ofC ^♯ are composable. This is a generalization of the construction of the distributive expansion ε^♯ of an exact catagory ε, which can be applied to a larger class of categories (including the category of groups).

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Riassunto Partendo da una categoriaC, che verifica certe ipotesi, si costruisce una categoriaC ^♯ detta espansione normodistributiva diC. La categoriaC ^♯ risulta essere orto-quaternaria, quindi gli isomorfismi canonici fra i suoi subquozienti sono componibili. Si è così generalizzato il passaggio da una categoria esatta ε alla sua espansione distributiva ε^♯, al caso di una famiglia più vasta di catagorie comprendente, fra le altre, quella (non esatta) dei gruppi.

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Lavoro eseguito nell’ambito dei gruppi di ricerca matematici del C.N.R.     

Hypervalent iodine as good leaving group: oxidative rearrangement of 1-IODO-2-methoxy-2-arylalkanes.

A new example of the good leaving group properties of hypervalent iodine is reported: oxidative rearrangement of 1-iodo-2-methoxy-2-arylalkanes 1 (R=alkyl) provides, via 1,2-aryl shift, alkyl benzyl ketones 3 in good yields.     

The carbonyl-carbonyl coupling route to penems : a stepwise analysis

Preparation and reactivity of novel azetidinyl(phosphoranylidene)acetates implicated in penem synthesis is discussed     

Multilevel parametrization for aerodynamical optimization of 3D shapes

We introduce and discuss a combination of methods and options that aim at the aerodynamical optimization of a flow around an arbitrary aircraft shape. The flow is governed by the Euler equations, discretized by a mixed element-volume method on a fixed unstructured tetrahedrization. The shape parametrization relies on the skin of the above mesh through a hierarchical representation. Descent-type and one-shot algorithms are devised and adapted to the solution of a few model problems.     

Über eine Modifikation der kolorimetrischen Bestimmung von Guanidingruppen mit dem Nitroprussiatreagens

Zusammenfassung Die Guanidingruppen in der Substanz P₇ und in Arginin lassen sich mit Nitroprussiat, Cyanoferrat(III) und Natronlauge bestimmen. Die Verwendung eines Lösungsmittelgemisches aus Isopropanol und Wasser verhindert die Bildung unlöslicher Niederschläge und erhöht in beträchtlichem Maß die Farbintensität und damit die Empfindlichkeit der Methode.

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A modification of the colorimetric determination of guanidine groups with the nitroprusside reagent

Summary The guanidine groups in the substance P₇ (dichlorohydrate of 2,4-diguanidino-phenyl-lauryl ester monohydrate) and in arginine may be determined by means of nitroprussiate, cyanoferrate(III) and caustic soda solution. The employment of a solvent mixture consisting of isopropanol and water prevents the formation of insoluble precipitates and enhances to a high degree the color intensity and hence the sensitivity of the method.