On quiver Grassmannians and orbit closures for representation-finite algebras

We show that Auslander algebras have a unique tilting and cotilting module which is generated and cogenerated by a projective-injective; its endomorphism ring is called the projective quotient algebra. For any representation- nite algebra, we use the projective quotient algebra to construct desingularizations of quiver Grassmannians, orbit closures in representation varieties, and their desingularizations. This generalizes results of Cerulli Irelli, Feigin and Reineke

E-learning e università: risultati e sviluppi di un progetto di formazione in ambito accademico.

Nell’articolo si riflette sui possibili impieghi della tecnologia al fine di promuovere una formazione di alto livello facilmente fruibile, inclusiva e adattabile ai bisogni degli utenti, alla luce dei risultati del PELT - Progetto E-Learning Trasversale -, nella sua terza e ultima fase di attuazione. Si descrivono gli obiettivi, le attività e i risultati delle prime due fasi: dalla progettazione di strumenti quantitativi e qualitativi adeguati all’implementazione dell’indagine conoscitiva - questionari, interviste semistrutturate, focus group interdisciplinari- ai risultati parziali, confrontati con quelli di una precedente indagine del 2004 sull’innovazione didattica all'Università di Pisa. Tra le riflessioni che emergono, alcune riguardano la terminologia utilizzata nei corsi FaD, che tende rapidamente a diventare obsoleta, altre evidenziano gli aspetti costruttivisti e sociali dell’E-Learning, altre ancora si soffermano sulle sue potenzialità in situazioni e contesti problematici, come i poli penitenziari universitari. A quest'ultimo riguardo, si considerano anche le importanti potenzialità dei corsi di italiano L2 on line per i detenuti stranieri, sia all’interno del carcere sia nella prospettiva del loro reinserimento nel mondo del lavoro e nella società

Propionate-induced relaxation in rat mesenteric arteries: a role for endothelium-derived hyperpolarising factor

Short chain fatty acids, including propionate, are generated in the caecum and large intestine, and when absorbed may elicit localised increases in intestinal blood flow. We sought to assess the mechanism by which propionate caused vasorelaxation. Propionate-mediated relaxation of noradrenaline-preconstricted rat mesenteric small arteries (RMSAs, i.d. 200–300 μm) was studied using small vessel myography. Propionate (1–30 mm) produced a concentration-dependent relaxation. Relaxation induced by 10 mm propionate (the approximate EC50) was almost abolished by endothelial denudation, although a marked relaxation to a very high concentration of propionate (50 mm) persisted in the absence of the endothelium. In endothelium-intact RMSAs, relaxation to 10 mm propionate was almost abolished by elevating [K+]o to 25 mm, but was unaffected by 100 μm Nω-nitro-l-arginine methyl ester (l-NAME) (68 ± 4 vs. 66 ± 3 % in controls, n = 35), or by 1 μm indomethacin (60 ± 4 vs. 61 ± 7 % in controls, n = 15). In the presence of l-NAME, relaxation to 10 mm propionate was significantly and markedly (i.e. > 50 %) inhibited by 50 μm Ba2+ and by the combination of 100 nm charybdotoxin and 100 nm apamin. A similar effect on propionate-mediated relaxation was also exerted by 100 μm ouabain, and by the combination of 50 μm barium with ouabain. Relaxation was also significantly and markedly inhibited by pre-treatment of RMSAs with 100 nm thapsigargin or 10 μm cyclopiazonic acid (CPA). The results demonstrate that 10 mm propionate relaxes RMSAs via endothelium-derived hyperpolarising factor (EDHF). The observation that relaxation by propionate is inhibited by thapsigargin and CPA suggests that this action of propionate involves the release of endothelial cell Ca2+ stores

The SPHINX Enigma in Critical VoIP Infrastructures: Human or Botnet?

Abstract---Sphinx was a monster in Greek mythology devouring those who could not solve her riddle. In VoIP, a new service in the role of Sphinx provides protection against SPIT (Spam over Internet Telephony) by discriminating human callers from botnets. The VoIP Sphinx tool uses audio CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) that are controlled by an anti-SPIT policy mechanism. The design of the Sphinx service has been formally verified for the absence of side-effects in the VoIP services (robustness), as well as for its DoS-resistance. We describe the principles and innovations of Sphinx, together with experimental results from pilot use cases. Keywords---SPIT; VoIP; CAPTCHA; Botnet; Security. I

Synthesis, Cyclic Voltammetric and Electrospray Mass Spectrometric Studies of a Series of Tris-Substituted 1,2-Dithiolene Complexes of Tungsten and Molybdenum

Ten new nonsymmetric dithiolenes of the general formula [RR′(C2S2)3M were synthesized, from the corresponding l,3-dithiol-2-ones, or from the corresponding mixed benzoins and tetraphosphorus decasulfide. The redox properties of these ten complexes together with those of the symmetric ones with R = R′ = Ph and M = Mo or W, were investigated by cyclic voltammetry. Two processes were only observed, assigned to C â†' C1− and C1− â†' C2− (C the complex), for which the quasi-reversible E1/2 potentials are highly dependent on the nature of the central metal ion, and for the same metal on the nature of the ligand and on the substituents on the phenyl rings. The ease by which the complexes are reduced is most likely the reason they give ESMS (negative mode) spectra, in spite of the fact they are neutral in solution. The process of this reduction and the parameters affecting it are investigated and discussed. © 1995, American Chemical Society. All rights reserved

First examples of homogeneous catalytic cyclotrimerization and polymerization of phenylacetylene and copolymerization of phenylacetylene and norbonene with dinuclear complexes containing unbridged metal-metal quadruple bond

First examples of application of dinuclear complexes containing unbrigded metal-metal quadruple bond as catalysts in cyclotrimerization, oligomerization and polymerization of substituted acetylene are reported. The d4-d4 dinuclear complexes (Bu4N)2[Re2X8] (1) (1a, X = Cl; 1b, X = Br and 1c, X = I) show low activity and the complex [Mo2Cl4(MeOH)2(PPh3)2] (2) medium activity in cyclotrimerization and oligomerization of phenylacetylene (PA). In contrast, the tungsten-based d4-d4, complex Na4[W2Cl8] (3) exhibits high polymerization activity (polymer yield above 90%) and ca 75% cis-selectivity in tetrahydrofuran. The activity and cis-stereoselectivity of these single-component catalysts decrease in the order 3 ≫ 2 ≫ 1, which is proportional to the metal-metal quadruple bond propensity towards ligand addition reactions. Complex 3 induces metathesis polymerization of norbornene (NBE) to poly(cyclopentene-1,3-diylvinylene) with 82% cis-selectivity and copolymerization of PA and NBE to almost all-cis high-molecular-weight copolymer containing cyclopentene-1,3-diyl-vinylene units, which is free of longer sequences of both PA and NBE units. This suggests that also homopolymerization of PA with 3 proceeds by the metathesis mechanism and that the PA/NBE copolymer structure is close to the alternating one