538 research outputs found
Economical error estimates for block implicit methods for ODEs via deferred correction
No full textDeferred correction is a widely used tool for improving the numerical approximation to the solution of ODE problems [J.R. Cash, WSSIA 2 (1993) 113; J.R. Cash, M.H. Wright, SIAM J. Sci. Statist. Comput. 12 (1991) 971; M. Lentini, V. Pereyra, Math. Comp. 28 (1974) 981; B. Lindberg, BIT 20 (1980) 486; V. Pereyra, Numer. Math. 8 (1966) 376; V. Pereyra, Numer. Math. 10 (1967) 316; H.J. Stetter, Numer. Math. 29 (1978) 425; H.J. Stetter, in: Lecture Notes in Math. vol. 630, Springer, 1978, pp. 245-258; R.D. Skeel, SIAM J. Numer. Anal. 19 (1981) 171; R.D. Skeel, Numer. Math. 48 (1986) 1; P. Zadunaisky, Numer. Math. 27 (1976) 21]. Indeed, it allows to estimate the error due to the use of discrete methods. Such an estimate may be a global one, in the case of continuous BVPs, or a local one, when IVPs are to be approximated [L. Brugnano, in: Lecture Notes in Math., vol. 1196, Springer, 1997, pp. 78-89; L. Brugnano, D. Trigiante, Solving Differential Problems by Multistep Initial and Boundary Value Methods, Gordon and Breach, 1998]. Recently, it has been implemented in the computational code BiM [L. Brugnano, C. Magherini, J. Comput. Appl. Math. 164-165 (2004) 145, web page: http://math.unifi.it/~brugnano/BiM/index.html] for the numerical solution of stiff ODE-IVPs. In this paper we analyze deferred correction in connection with the methods used in that code, resulting in an overall simplification of the procedure, due to the properties of the underlying methods. The analysis is then extended to more general methods
On the construction and properties of m-step methods for FDEs
No full textIn this paper we consider the numerical solution of fractional differential equations by means of m-step recursions. The construction of such formulas can be obtained in many ways. Here we study a technique based on the rational approximation of the generating functions of fractional backward differentiation formulas (FBDFs). Accurate approximations lead to the definition of methods which simulate the underlying FBDF, with important computational advantages. Numerical experiments are presented
Tribunal Administratif de Versailles, 13 septembre 1994, Req. n° 901090 et 905003 ; M. Lamy-Rested, Président ; M. Baranes, Rapporteur ; M. Gonzalès, Commissaire du Gouvernement ; Me Magherini et Me Lepage-Jessua, avocats.
No full textTribunal Administratif de Versailles, 13 septembre 1994, Req. n° 901090 et 905003 ; M. Lamy-Rested, Président ; M. Baranes, Rapporteur ; M. Gonzalès, Commissaire du Gouvernement ; Me Magherini et Me Lepage-Jessua, avocats. In: Droit et Ville, tome 39, 1995. «Construction, nuisances et cadre de vie», Neuvièmes Assises «Justice-Construction », Cour d’Appel de Paris, le 29 novembre 1994. pp. 255-257
Parameters affecting the performance of the c-class wingsail
No full textWing sails offer a different design challenge to those of more conventional soft sail rigs. This study was undertaken in order to assess which parameters influence wingsail performance of C-Class catamarans, and to what extent, the results from the wind tunnel can be applied in the design developments of future wingsails. A combined wing sail and C- class catamaran was tested in the low-speed section of the 7’ x 5’ wind tunnel at the University of Southampton. Testing assessed the appropriate settings for the movable element of the multiple-element wing sail as well as heeling angle,trampoline porosity, spanwise camber distribution and gap at the foot of the wingsail. Both upwind and downwind conditions were considered through measurement of driving force, heeling force, heeling and yawl moments. The results demonstrate that low heel angles improve overall performance and that the gap underneath the wingsail foot adversely affects the generation of lift by the sail. An airfoil shaped trampoline is suggested in order to benefit both a reduced gap and a better control over the heel. For heavy wind condition, negative twist at the tip of the wingsail allows higher boat speed
Shooting methods for a PT-symmetric periodic eigenvalue problem
No full textWe present a rigorous analysis of the performance of some one-step discretization schemes for a class of PT-symmetric singular boundary eigenvalue problem which encompasses a number of different problems whose investigation has been inspired by the 2003 article of Benilov et al. (J Fluid Mech 497:201-224, 2003). These discretization schemes are analyzed as initial value problems rather than as discrete boundary problems, since this is the setting which ties in most naturally with the formulation of the problem which one is forced to adopt due to the presence of an interior singularity. We also devise and analyze a variable step scheme for dealing with the singular points. Numerical results show better agreement between our results and those obtained from small-ε asymptotics than has been shown in results presented hitherto
Deadly dialogues:The Magherini case and police brutalities in Italy
No full textPurpose: This paper looks at police brutalities in Italy. In particular, the discussion focusses on the case of the death of Riccardo Magherini, who was stopped by the Corpo dei Carabinieri (CC), a branch of the Italian Army operating as a police force, on the 3rd of March 2014. The paper focusses on the way the police agents involved in the Magherini trial, both witnesses and defendants, made sense of the case. Their answers to the questions put to them by case lawyers or judges during the first trial in February 2016 will be closely examined. Design/methodology/approach: Discussion of the case will rely on material drawn from court files. The Carabinieris internal reports on the incident and the court transcription of the agents questioning will form the basis for an ethnographic analysis of the case. The author will then use the case analysis as the starting point for a broader discussion on police culture. While ethnography generally consists of direct on-the-ground participant observation Geertz 1992, the author’s methodology of using legal transcripts and reports can nevertheless be considered ethnographical. Findings: Discussion will consider the importance of an ethical element to the internal culture of the Italian police forces which influences their street practice. Italian police have an ethical approach in that they believe their role is to be able separate good from bad and protect society from the bad. Moreover they have operated within a context of impunity which has produced over time a critical threshold according to which specific individuals and groups deemed as dangerous classes are considered outside the realm of normal civilised society and as such can be treated differently in contemporary Italy. Originality/value: The originality of this paper relates to two distinct elements. The first one concerns the context analysed, as the peculiarities of the Italian police are hardly known to the larger international public. The second aspect relates to the specificity of a case. Magherini was not a marginal person, he was an Italian citizen, but he suffered from a brutality that caused his death. The dynamics of this outcome will be closely analysed.</p
Short-term recursions for fractional differential equations
No full textThis paper deals with the numerical solution of Fractional Differential Equations by means of m-step recursions. For the construction of such formulas, we study a technique based on a rational approximation of the generating functions of Fractional Backward Differentiation Formulas (FBDFs). The so-defined methods simulate very well the properties of the underlying FBDFs with important computational advantages. This fact becomes particularly evident especially in the case when they are used for solving problems arising from the semi-discretization of fractional partial differential equations
Potassium currents in periglomerular cells of frog olfactory bulb in vitro
No full textVoltage-activated currents have been recorded from periglomerular cells in thin slices of frog olfactory bulb. Cells were examined with whole-cell patch clamp methods. The voltage-dependent potassium currents were studied after pharmacological block of inward currents. Depolarising steps from -130 mV gave an early transient, A-type, outward current and a delayed rectifier K+ current (IKV). The two currents could be isolated on the basis of the differences in their kinetic properties. The A-current developed following a third-order kinetics when the membrane was depolarised to potentials more positive than -40 mV after preconditioning to potentials more negative than -60 mV. Once activated (tau a 2.5 ms at 0 mV), IA inactivated following a single exponential (tau ha about 60 ms). IKV activated with a second-order kinetics above -30 mV with a time constant of 4 ms at 0 mV. IA and IKV were sensitive, respectively, to 4-aminopyridine (4-AP) and tetraethylammonium (TEA)
Potassium currents in periglomerular cells of frog olfactory bulb in vitro
No full textVoltage-activated currents have been recorded from periglomerular cells in thin slices of frog olfactory bulb. Cells were examined with whole-cell patch clamp methods. The voltage-dependent potassium currents were studied after pharmacological block of inward currents. Depolarising steps from -130 mV gave an early transient, A-type, outward current and a delayed rectifier K+ current (IKV). The two currents could be isolated on the basis of the differences in their kinetic properties. The A-current developed following a third-order kinetics when the membrane was depolarised to potentials more positive than -40 mV after preconditioning to potentials more negative than -60 mV. Once activated (tau a 2.5 ms at 0 mV), IA inactivated following a single exponential (tau ha about 60 ms). IKV activated with a second-order kinetics above -30 mV with a time constant of 4 ms at 0 mV. IA and IKV were sensitive, respectively, to 4-aminopyridine (4-AP) and tetraethylammonium (TEA)
- …
