Archivio della ricerca dell'Università di Modena e Reggio Emiliahttps://iris.unimore.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Tue, 20 Aug 2019 14:33:46 GMT2019-08-20T14:33:46Z10311Generalization possibilities of autocatalytic absolute enantioselective synthesishttp://hdl.handle.net/11380/612113Titolo: Generalization possibilities of autocatalytic absolute enantioselective synthesis
Abstract: A simple empirical formula enables the quantitative description of chiral autocatalysis. This formula was used for the prediction of the number of consecutive autocatalytic reaction cycles needed to obtain a high enantiomeric excess without chiral auxiliary or an asymmetric physical field (absolute enantioselective synthesis). The results show, that even less selective Soai-type systems can be used for absolute enantioselective synthesis, which, therefore, appears to be a fairly general phenomenon. (c) 2006 Published by Elsevier Ltd.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/11380/6121132006-01-01T00:00:00ZDouble wells: Nevanlinna analyticity, distributional borel sum and asymptoticshttp://hdl.handle.net/11380/612353Titolo: Double wells: Nevanlinna analyticity, distributional borel sum and asymptotics
Abstract: We consider the energy levels of a Stark family, in the parameter j, of quartic double wells with perturbation parameter g: H(g, j) = p(2) + x(2)(1 - gx)(2) - j (gx - 1/2). For non-even j (and for the symmetric case j = 0) we prove analyticity in the full Nevanlinna disk Rg(-2) > R(-1) of the g(2)-plane, as predicted by Crutchfield. By means of an approximation we give a heuristic estimate of the asymptotic small g behaviour, showing the relation between the avoided crossings and the failure of the usual perturbation series.
Mon, 01 Jan 1996 00:00:00 GMThttp://hdl.handle.net/11380/6123531996-01-01T00:00:00ZA lifetime prediction method based on Cumulative Flaw Length Theoryhttp://hdl.handle.net/11380/1012317Titolo: A lifetime prediction method based on Cumulative Flaw Length Theory
Abstract: Ultrasonic pulse velocity testing (UPVT) was carried out to perform non-destructive quality control of refractory plates. Used in conjunction with fracture mechanics, ultrasonic velocity measurements have proved a powerful technique for detecting, positioning and sizing internal voids and cracks in the samples, originated from the manufacturing process. Two cordierite-mullite refractory compositions exhibiting different microstructure and crack propagation behaviour were characterized through their lifetime during which they were subjected to thermal shock loading. In this paper, a new statistical method is proposed which allows to estimate the lifetime when the stress state that will be applied in service (loading) and the scattering of the ultrasonic velocity data in the as-received state are known. Since this lifetime prediction method is based on a non-destructive technique, it could be implemented into a code in an automatic quality control device for continuous lifetime estimation. The correlation between crack propagation behaviour and thermal shock resistance is discussed and semi-empirical models were developed to predict the service life of refractory plates from the measured values of ultrasonic velocities on as-received samples.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11380/10123172012-01-01T00:00:00ZHorn of singularities for the Stark-Wannier laddershttp://hdl.handle.net/11380/613240Titolo: Horn of singularities for the Stark-Wannier ladders
Abstract: We prove that the small field asymptotic behaviour of the Stark-Wannier ladders near the real direction is generically highly singular. This result is in agreement with the conjecture of a chaotic behaviour of the lifetime of the states because of infinitely many crossings.
Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/11380/6132401991-01-01T00:00:00ZAbsence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentialshttp://hdl.handle.net/11380/613061Titolo: Absence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentials
Abstract: We prove the absence of the absolutely continuous spectrum for the operator -d(2)/dx(2) + Sigma(j epsilon Z)alpha delta'(x - j) + fx, > 0 and alpha not equal 0, by means of the crystal momentum representation and the Howland's criterion for Floquet-type operators.
Sun, 01 Jan 1995 00:00:00 GMThttp://hdl.handle.net/11380/6130611995-01-01T00:00:00ZSingular continuous spectrum in a class of random Schroedinger operatorshttp://hdl.handle.net/11380/612564Titolo: Singular continuous spectrum in a class of random Schroedinger operators
Abstract: For a class of random Schrodinger operators in L2(R(d)) H(omega) = -DELTA + SIGMA(j is-an-element-of Z(d)) q(j)(omega) f(x - j) where q(j) are continuous independent identically distributed bounded random variables and f has a power decay and defined sign, in any energy interval the singular continuous spectrum is either empty or with positive Lebesgue measure. As a consequence, the proof of localization for a class of random but deterministic one-dimensional operators is shifted to showing that the singular continuous spectrum has null Lebesgue measure.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/11380/6125641993-01-01T00:00:00ZA statistical approach for the assessment of reliability in ceramic materials from ultrasonic velocity measurement: Cumulative Flaw Length Theoryhttp://hdl.handle.net/11380/623736Titolo: A statistical approach for the assessment of reliability in ceramic materials from ultrasonic velocity measurement: Cumulative Flaw Length Theory
Abstract: A primary objective of statistical fracture approach is to predict the probability of failure of a component for an arbitrary stress state when the failure statistics are known. This study introduces the fundamentals and application of a new approach to characterize the mechanical behaviour of high temperature ceramic materials, including refractory materials, by coupling non-destructive methods, in particular ultrasonic velocity measurement, and the Batdorf statistical fracture theory. A new approach, termed Cumulative Flaw Length Theory (CFLT), has been developed for the case of macroscopically homogeneous isotropic materials containing randomly oriented microcracks uniformly distributed in a location subjected to non-uniform multiaxial stresses. A function representing the number of cracks per unit volume is estimated based on the histograms of ultrasonic velocity measurements. This function is used without additional assumptions to determine the probability of fracture under an arbitrary stress condition. Two different cordierite-mullite high temperature ceramic materials were characterized under the assumptions of this theory to provide experimental evidence to support the model.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/11380/6237362009-01-01T00:00:00ZStability of the molecular structurehttp://hdl.handle.net/11380/629038Titolo: Stability of the molecular structure
Abstract: We prove the stability of the molecular structure given by a bidimensional nonlinear model for a stochastic perturbation. In particular, for a small stochastic perturbation, the racemisation effect doesn't happen when during the validity timew of the model
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/11380/6290382009-01-01T00:00:00ZAbsence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentialshttp://hdl.handle.net/11380/8622Titolo: Absence of the absolutely continuous spectrum for Stark-Bloch operators with strongly singular periodic potentials
Abstract: We correct here the proof of the boundedness of the coupling term X given by us in a previous paper (1995 J. Phys. A: Math. Gen. 28 1101-6).
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/11380/86221998-01-01T00:00:00ZOne-dimensional many point interactions and stability of eigenvalueshttp://hdl.handle.net/11380/613241Titolo: One-dimensional many point interactions and stability of eigenvalues
Abstract: n/a
Tue, 01 Jan 1991 00:00:00 GMThttp://hdl.handle.net/11380/6132411991-01-01T00:00:00Z