Gas and dust in the Beta Pictoris Moving Group as seen by the Herschel Space Observatory

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us to comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel PACS observations of young stellar associations. Aims. This work aims at studying the properties of discs in the Beta Pictoris Moving Group (BPMG) through far-IR PACS observations of dust and gas. Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100 and 160 microns of 19 BPMG members, together with spectroscopic observations of four of them. Spectroscopic observations were centred at 63.18 microns and 157 microns, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content. Results. We have detected far-IR excess emission toward nine BPMG members, including the first detection of an IR excess toward HD 29391.The star HD 172555, shows [OI] emission, while HD 181296, shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55 to 264 K, with low dust masses (6.6*10^{-5} MEarth to 0.2 MEarth) and radii from blackbody models in the range 3 to 82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component.Comment: 12 pages, 7 figures, 6 table

Diffeomorphisms and families of Fourier-Mukai transforms in mirror symmetry

Assuming the standard framework of mirror symmetry, a conjecture is formulated describing how the diffeomorphism group of a Calabi-Yau manifold Y should act by families of Fourier-Mukai transforms over the complex moduli space of the mirror X. The conjecture generalizes a proposal of Kontsevich relating monodromy transformations and self-equivalences. Supporting evidence is given in the case of elliptic curves, lattice-polarized K3 surfaces and Calabi-Yau threefolds. A relation to the global Torelli problem is discussed.Comment: Approx. 20 pages LaTeX. One reference adde

An item's status in semantic memory determines how it is recognized: Dissociable patterns of brain activity observed for famous and unfamiliar faces

Are all faces recognized in the same way, or does previous experience with a face change how it is retrieved? Previous research using human scalp-recorded Event-Related Potentials (ERPs) demonstrates that recognition memory can produce dissociable brain signals under a variety of circumstances. While many studies have reported dissociations between the putative ‘dual processes’ of familiarity and recollection, a growing number of reports demonstrate that recollection itself may be fractionated into component processes. Many recognition memory studies using lexical materials as stimuli have reported a left parietal ERP old/new effect for recollection; however, when unfamiliar faces are recollected, an anterior effect can be observed. This paper addresses two separate hypotheses concerning the functional significance of the anterior old/new effect: perceptual retrieval and semantic status. The perceptual retrieval view is that the anterior effect reflects reinstatement of perceptual information bound up in an episodic representation, while the semantic status view is that information not represented in semantic memory pre-experimentally elicits the anterior effect instead of the left parietal effect. We tested these two competing accounts by investigating recognition memory for unfamiliar faces and famous faces in two separate experiments, in which same or different pictures of studied faces were presented as test items to permit brain activity associated with retrieving face and perceptual information to be examined independently. The difference in neural activity between same and different picture hits was operationalized as a pattern of activation associated with perceptual retrieval; while the contrast between different picture hits and correct rejection of new faces was assumed to reflect face retrieval. In Experiment 1, using unfamiliar faces, the anterior old/new effect (500–700msec) was observed for face retrieval but not for perceptual retrieval, challenging the perceptual retrieval hypothesis. In Experiment 2, using famous faces, face retrieval was associated with a left parietal effect (500–700msec), supporting the semantic representation hypothesis. A between-subjects analysis comparing scalp topography across the two experiments found that the anterior effect observed for unfamiliar faces is dissociable from the left parietal effect found for famous faces. This pattern of results supports the hypothesis that an item's status in semantic memory determines how it is recognized

On complex surfaces diffeomorphic to rational surfaces

In this paper we prove that no complex surface of general type is diffeomorphic to a rational surface, thereby completing the smooth classification of rational surfaces and the proof of the Van de Ven conjecture on the smooth invariance of Kodaira dimension.Comment: 34 pages, AMS-Te

Topological quantum D-branes and wild embeddings from exotic smooth R^4

This is the next step of uncovering the relation between string theory and exotic smooth R^4. Exotic smoothness of R^4 is correlated with D6 brane charges in IIA string theory. We construct wild embeddings of spheres and relate them to a class of topological quantum Dp-branes as well to KK theory. These branes emerge when there are non-trivial NS-NS H-fluxes where the topological classes are determined by wild embeddings S^2 -> S^3. Then wild embeddings of higher dimensional $p$-complexes into S^n correspond to Dp-branes. These wild embeddings as constructed by using gropes are basic objects to understand exotic smoothness as well Casson handles. Next we build C*-algebras corresponding to the embeddings. Finally we consider topological quantum D-branes as those which emerge from wild embeddings in question. We construct an action for these quantum D-branes and show that the classical limit agrees with the Born-Infeld action such that flat branes = usual embeddings.Comment: 18 pages, 1 figur

On semistable principal bundles over a complex projective manifold, II

Let (X, \omega) be a compact connected Kaehler manifold of complex dimension d and E_G a holomorphic principal G-bundle on X, where G is a connected reductive linear algebraic group defined over C. Let Z (G) denote the center of G. We prove that the following three statements are equivalent: (1) There is a parabolic subgroup P of G and a holomorphic reduction of the structure group of E_G to P (say, E_P) such that the bundle obtained by extending the structure group of E_P to L(P)/Z(G) (where L(P) is the Levi quotient of P) admits a flat connection; (2) The adjoint vector bundle ad(E_G) is numerically flat; (3) The principal G-bundle E_G is pseudostable, and the degree of the charateristic class c_2(ad(E_G) is zero.Comment: 15 page

The Ethics of Corporate Governance

How should corporate directors determine what is the right decision? For at least the past 30 years the debate has raged as to whether shareholder value should take precedence over corporate social responsibility when crucial decisions arise. Directors face pressure, not least from ethical investors, to do the good thing when they seek to make the right choice. Corporate governance theory has tended to look to agency theory and the need of boards to curb excessive executive power to guide directors' decisions. While useful for those purposes, agency theory provides only limited guidance. Supplementing it with the alternatives - stakeholder theory and stewardship theory - tends to put directors in conflict with their legal obligations to work in the interests of shareholders. This paper seeks to reframe the discussion about corporate governance in terms of the ethical debate between consequential, teleological approaches to ethics and idealist, deontological ones, suggesting that directors are - for good reason - more inclined toward utilitarian judgments like those underpinning shareholder value. But the problems with shareholder value have become so great that a different framework is needed: strategic value, with an emphasis on long-term value creation judged from a decidedly utilitarian standpoint