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AMS Acta (8,187 recursos)
Repository of the University of Bologna.

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Mostrando recursos 221 - 240 de 311

221. The isometric deformability question for constant mean curvature surfaces with topology - Smyth, Brian; Tinaglia, Giuseppe
The paper treats the isometric deformability of non-simply-connected constant mean curvature surfaces which are neither assumed embedded nor complete. We prove that if a smooth oriented surface M immersed in R^3 admits a nontrivial isometric deformation with constant mean curvature H then every cycle in M has vanishing flux and, when H is not zero, also vanishing torque. The vanishing of all fluxes implies the existence of such an isometric deformation when H = 0. Our work generalizes to constant mean curvature surfaces a well-known rigidity result for minimal surfaces.

222. Comparing continuous treatment matching methods in policy evaluation - Adorno, Valentina; Bernini, Cristina; Pellegrini, Guido
The paper evaluates the statistical properties of two different matching estimators in the case of continuous treatment, using a Montecarlo experiment. The traditional generalized propensity score matching estimator is compared whit a new two steps matching estimator for the continuous treatment case, recently developed (Adorno, Bernini, Pellegrini, 2007). It compares treatment and control units similar in terms of their observable characteristics in both selection processes (the participation decision and the treatment level assignment), where the generalized propensity score matching estimator collapses the two processes into one single step matching. The results show that the two steps estimator has better finite...

223. Portfolio choice, behavioral preferences and equity home bias - Magi, Alessandro
We provide a plausible explanation of aggregate portfolio behavior, in a framework where economic agents have behavioral (narrow framing) preferences. The representative agent derives utility not only from consumption (standard models) but also from risky financial wealth fluctuations. Moreover, the investor frames the stock market risk narrowly and has loss averse preferences. We numerically solve, for the foreign equity share, a simple model of international portfolio choice, providing a possible explanation for the equity home bias puzzle. Only economic agents able to process correctly information deriving from stock markets exploit the diversification opportunities provided by international financial markets.

224. The Eulerian distribution on self evacuated involutions - Barnabei, Marilena; Bonetti, Flavio; Silimbani, Matteo
We present an extensive study of the Eulerian distribution on the set of self evacuated involutions, namely, involutions corresponding to standard Young tableaux that are fixed under the Sch¨utzenberger map. We find some combinatorial properties for the generating polynomial of such distribution, together with an explicit formula for its coefficients. Afterwards, we carry out an analogous study for the subset of self evacuated involutions without fixed points.

225. The signed Eulerian numbers on involutions - Barnabei, Marilena; Bonetti, Flavio; Silimbani, Matteo
We define an analogue of signed Eulerian numbers fn;k for involutions of the symmetric group and derive some combinatorial properties of this sequence. In particular, we exhibit both an explicit formula and a recurrence for fn;k arising from the properties of its generating function.

226. Combinatorial properties of the numbers of tableaux of bounded height - Barnabei, Marilena; Bonetti, Flavio; Silimbani, Matteo
We introduce an infinite family of lower triangular matrices ¡(s), where °s n;i counts the standard Young tableaux on n cells and with at most s columns on a suitable subset of shapes. We show that the entries of these matrices satisfy a three-term row recurrence and we deduce recursive and asymptotic properties for the total number ¿s(n) of tableaux on n cells and with at most s columns.

227. Arriving at equivalence. Making a case for comparable general reference corpora in Translation Studies. - Philip, Gill
When multilingual corpora are used in translation studies, it is usually assumed that they are either translated (parallel) or comparable, or both; and that their size and text composition are analogous. As general reference corpora become more widely available, it is inevitable that these too should be used to compare and contrast SL norms, thus extending the definition of comparability to include text collections whose size and content may vary considerably, and which are nevertheless considered representative of their languages. This paper addresses the contribution of comparable reference corpora to the identification of translation equivalence. Focusing in particular on native-speaker...

228. GIT quotients of projective spaces - Incensi, Francesca
We study the quotients for the diagonal action of SL3(C) on the product of n-fold of P^2(C): we are interested in describing how the quotient changes when we vary the polarization (i.e. the choice of an ample linearized line bundle). We illustrate the different techniques for the construction of a quotient, in particular the numerical criterion for semi-stability and the “elementary transformations” which are resolutions of precisely described singularities (case n = 6).

229. The CMC Dynamics Theorem in R^3 - Meeks, William H.; Tinaglia, Giuseppe
In this paper, we develop some new tools and theory that are useful in describing the geometry of properly embedded, constant mean curvature surfaces in R^3 with bounded second fundamental form. More precisely, we prove dynamics type results for the space of translational limits of such a surface. As a consequence of our main theorems, in subsequent papers we obtain rigidity results for certain properly embedded, constant mean curvature surfaces in R^3, as well as derive curvature estimates for complete, embedded, constant mean curvature surfaces in complete locally homogeneous three- manifolds.

230. Adverb use in EFL student writing: from learner dictionary to text production - Philip, Gill
Adverbs, especially those occurring in adverb+adjective collocations, play a central role in the language that advanced learners are expected to produce in their argumentative writing. However submodifying adverbs of degree such as ‘closely’, ‘deeply’, ‘strongly’ and ‘widely’ have been identified as being problematic for learners of English: Italian learners over-use very and really to the virtual exclusion of any other adverb (Philip 2007). This situation is due in part to the EFL curriculum, but monolingual and bilingual learner’s dictionaries appear to do little to address the issue. This contribution examines the treatment of lexical adverbs of degree in the five...

231. On the Characteristic Direction of Real Hypersurfaces in C^(N+1) and a Symmetry Result - Martino, Vittorio; Montanari, Annamaria
In this paper we show the following property of a non Levi flat real hypersurface in C^(n+1): if the unit characteristic direction T is a geodesic, then it is an eigenvector of the second fundamental form and the relative eigenvalue is constant. As an application we prove a symmetry result, of Alexandrov type, for compact hypersurfaces in C^(n+1) with positive constant Levi mean curvature.

232. Integral Formulas for a Class of Curvature PDE'S and Application to Isoperimetric Inequalities and to Symmetry Problems - Martino, Vittorio; Montanari, Annamaria
We prove integral formulas for closed hypersurfaces in C^(n+1); which furnish a relation between elementary symmetric functions in the eigenvalues of the complex Hessian matrix of the defining function and the Levi curvatures of the hypersurface. Then we follow the Reilly approach to prove an isoperimetric inequality. As an application, we obtain the "Soap Bubble Theorem" for star- shaped domains with positive and constant Levi curvatures bounding the classical mean curvature from above.

233. Self-evaluation test for student guidance: the case of the University of Bologna - Matteucci, Mariagiulia; Mignani, Stefania; Ricci, Roberto
In this work, the theme of student guidance in the university context is outlined. In order to introduce the competence evaluation for student guidance, a new guidance project based on self-evaluation tests of the University of Bologna (Italy) is presented. In the paper, the issues of item specification and test calibration are explored, with reference to item response theory models. Models are for multiple-choice and binary items and they assume that a single ability is responsible for the student performance in the test. The test calibration is conducted for the Statistics Faculty and the results are discussed, together with the...

234. Adverb use in EFL student writing - Philip, Gill
Adverbs, especially those occurring in adverb+adjective collocations, play a central role in the language that advanced learners are expected to produce in their argumentative writing. However submodifying adverbs of degree such as ‘closely’, ‘deeply’, ‘strongly’ and ‘widely’ have been identified as being problematic for learners of English: Italian learners over-use very and really to the virtual exclusion of any other adverb (Philip 2007). This situation is due in part to the EFL curriculum, but monolingual and bilingual learner’s dictionaries appear to do little to address the issue. This contribution examines the treatment of lexical adverbs of degree in the five...

235. Metaphorical Keyness in Specialised Corpora - Philip, Gill
What is more important in text: the topical content, or the manner in which topical content is presented? While statistically-generated key words tell us about a text’s content, the inter-relation between these words and the message of the text can be difficult to ascertain. One method of doing so is to observe the inter-relation of key words with evaluative language: in this case, metaphor. Metaphors are notoriously difficult to locate in corpora, but this paper sets out a method for their semi-automatic identification, and demonstrates how their interaction with keywords is both systematic and pervasive. Studying the interaction of key...

236. Review of Hoey (2005)Lexical Priming - Philip, Gill
Book review of Hoey (2005) Lexical Priming. Describes and discusses presentation of contents and the implications of this novel approach to linguiatic theory.

237. Idioms - Philip, Gill
Encyclopedia entry for "Idioms"

238. “Non una donna in politica, ma una donna politica”: Women’s Political Language in an Italian Context - Philip, Gill
This study examines the metaphors used by women politicians in Italy. Similarities and differences between the metaphors which occur are analysed, using a corpus of political communiqués, speeches and interviews spanning the period June 2006 - May 2007.

239. “…and I dropped my jaw with fear”: The role of corpora in teaching phraseology - Philip, Gill
How can the effects of corpora on the language learning process be effectively assessed? This is an old question which is, however, just as important now as it was ten or twenty years ago. Does corpus use aid students in a measurable way? How does corpus use affect students’ subsequent language use? Is there a marked qualitative difference between the work of students who make use of corpora in their studies and those who do not? Does corpus use necessarily lead to an improvement in students’ language production? This research reports an ongoing study into phraseological production in advanced learner writing...

240. Which RPI-norms are the supremum of standard RPI-norms? - Baggio, Silvano
We settle some open problems regarding RPI-norms, i.e. norms (on a convenient subspace of differentiable real functions) that are invariant under differentiable reparametrizations. More precisely, we clarify some key points on how RPI-norms can be approximated using standard RPI-norms. We first prove that the sum of two standard RPI-norms is the supremum of a set of standard RPI-norms. This allows us to study a class of RPI-norms that can be expressed as the sup of standard ones. Finally, we give a positive answer to an open question on the existence of RPI-norms that are not the sup of standard RPI-norms.

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