T-duality and Actions for Non-BPS D-branes

We employ T-duality to restrict the tachyon dependence of effective actions for non-BPS D-branes. For the Born-Infeld part the criteria of T-duality and supersymmetry are satisfied by a simple extension of the D-brane Born-Infeld action.Comment: Latex, 11 page

Open and Closed Supermembranes with Winding

Motivated by manifest Lorentz symmetry and a well-defined large-N limit prescription, we study the supersymmetric quantum mechanics proposed as a model for the collective dynamics of D0-branes from the point of view of the 11-dimensional supermembrane. We argue that the continuity of the spectrum persists irrespective of the presence of winding around compact target-space directions and discuss the central charges in the superalgebra arising from winding membrane configurations. Along the way we comment on the structure of open supermembranes.Comment: Contribution to the proc. Strings '97, 10 pages, LaTeX, uses espcrc

Consistent truncation of d = 11 supergravity on AdS_4 x S^7

We study the system of equations derived twenty five years ago by B. de Wit and the first author [Nucl. Phys. B281 (1987) 211] as conditions for the consistent truncation of eleven-dimensional supergravity on AdS_4 x S^7 to gauged N = 8 supergravity in four dimensions. By exploiting the E_7(7) symmetry, we determine the most general solution to this system at each point on the coset space E_7(7)/SU(8). We show that invariants of the general solution are given by the fluxes in eleven-dimensional supergravity. This allows us to both clarify the explicit non-linear ansatze for the fluxes given previously and to fill a gap in the original proof of the consistent truncation. These results are illustrated with several examples.Comment: 41 pages, typos corrected, published versio

Magnetic flux density and the critical field in the intermediate state of type-I superconductors

To address unsolved fundamental problems of the intermediate state (IS), the equilibrium magnetic flux structure and the critical field in a high purity type-I superconductor (indium film) are investigated using magneto-optical imaging with a 3D vector magnet and electrical transport measurements. The least expected observation is that the critical field in the IS can be as small as nearly 40% of the thermodynamic critical field $H_c$. This indicates that the flux density in the \textit{bulk} of normal domains can be \textit{considerably} less than $H_c$, in apparent contradiction with the long established paradigm, stating that the normal phase is unstable below $H_c$. Here we present a novel theoretical model consistently describing this and \textit{all} other properties of the IS. Moreover, our model, based the rigorous thermodynamic treatment of observed laminar flux structure in a tilted field, allows for a \textit{quantitative} determination of the domain-wall parameter and the coherence length, and provides new insight into the properties of all superconductors.Comment: 5 pages, 5 figure

CONTRIBUTIONS TO THE HISTORY OF BOTANY AND EXPLORATION IN MALAYSIA-7

Barchewitz reached the islet of Leti,in the southwestern Moluccas,on September 2, 1714;he returned to Europe in September 1720, having represented the East India Company on Leti for six years.Like so many of his contemporaries he wrote a book on his life's adventures.This work appeared in 1730 and proved a success. A second, slightly enlarged, edition followed in 1751,entitled "Neu-vermehrte Ost-Indianische Reise- Beschreibung."Barchewitz is the earliest author on the natural history of Leti and -he paid attention to a number of plants.The present note is mainly a survey of the botany contained in his book.Ernst Christoph Barchewitz was born at the close of the 17th century at Grosz-Sommerda near Erfurt.He was bound apprentice to a tawer at Erfurt but soon preferred to travel ("Wanderschaft") with his brother to Holland.He visited the larger towns,learned at the Hague the art of dressing and the barber's craft,and became the valet de chambre of the Imperial Ambassador,Baron von Heems,whom he accompanied to Austria and the southern Netherlands.He ended his service at Delft Where he enlisted with the East India Company.As a soldier he embarked at Hellevoetsluis on the "Voorburg," sailing April 1, 1711.The treatment on board he judged to be fair; his only objection was that he had to drink water whereas wine would have seemed very suitable.After a stay at Batavia (December 20,1711 till January 29, 1712),he was garrisoned on Banda, where he remained till August 15, 1714. He left when he was appointed Corporal of Leti.The following pertains to the second edition of Barchewitz's book, the pages referred to are cited between brackets.All quotations have been translated

A REVISION OF THE GENUS ARCHIDENDRON F. MUELL. (MIMOSACEAE)

1. The present paper is the author's second revision of the genus Archidendron.The validity of the genus is briefly discussed.2. The genus has its centre of speciation in New Guinea. The number of speciestreated is 31, not counting a few insufficiently known species. A key is given to thespecies and varieties, which are described.3. The following are new species or varieties: Archidendron affine De Wit,A. calliandrum De Wit, A. dies-Christi De Wit, A. nervosum De Wit, A. parviflorumvar. longipes De Wit, and A. trifoliolatum De Wit.4. New combinations are: Archidendron gogolense (K. Schum. & Laut.) De Wit(basonym: Hansemannia gogolense K. Schum. & Laut.) and A.lucyi var. schleohterii(Harms) De Wit (basonym: Archidendron schlechterii Harms).

Autonomy vs. control: Quality assurance and governmental policy in Flanders

Higher education in Flanders has seen some major changes in the 1990s. One of the key elements of the new higher education regulations was the quality assessment system. This exemplified best the government's policy of granting all institutions of higher education autonomy, making them responsible for their policies, while still keeping the quality of higher education somewhat under governmental control. In this article, we focus on the tension between the government's aim of improving and controlling the quality of higher education and universities ' concern for their autonomy. We describe the Flemish government's view on issues of quality in higher education and confront these with an account on the basis of case studies of how the quality assurance system was actually implemented in universities. We conclude that the model of the "market state" or the "evaluative state" is only realised partially in Flanders. The government is still interventionist when it comes to key policy issue

Special complex manifolds

We introduce the notion of a special complex manifold: a complex manifold (M,J) with a flat torsionfree connection \nabla such that (\nabla J) is symmetric. A special symplectic manifold is then defined as a special complex manifold together with a \nabla-parallel symplectic form \omega . This generalises Freed's definition of (affine) special K\"ahler manifolds. We also define projective versions of all these geometries. Our main result is an extrinsic realisation of all simply connected (affine or projective) special complex, symplectic and K\"ahler manifolds. We prove that the above three types of special geometry are completely solvable, in the sense that they are locally defined by free holomorphic data. In fact, any special complex manifold is locally realised as the image of a holomorphic 1-form \alpha : C^n \to T^* C^n. Such a realisation induces a canonical \nabla-parallel symplectic structure on M and any special symplectic manifold is locally obtained this way. Special K\"ahler manifolds are realised as complex Lagrangian submanifolds and correspond to closed forms \alpha. Finally, we discuss the natural geometric structures on the cotangent bundle of a special symplectic manifold, which generalise the hyper-K\"ahler structure on the cotangent bundle of a special K\"ahler manifold.Comment: 24 pages, latex, section 3 revised (v2), modified Abstract and Introduction, version to appear in J. Geom. Phy

Contrasting growth responses in lamina and petiole during neighbor detection depend on differential auxin responsiveness rather than different auxin levels.

Foliar shade triggers rapid growth of specific structures that facilitate access of the plant to direct sunlight. In leaves of many plant species, this growth response is complex because, although shade triggers the elongation of petioles, it reduces the growth of the lamina. How the same external cue leads to these contrasting growth responses in different parts of the leaf is not understood. Using mutant analysis, pharmacological treatment and gene expression analyses, we investigated the role of PHYTOCHROME INTERACTING FACTOR7 (PIF7) and the growth-promoting hormone auxin in these contrasting leaf growth responses. Both petiole elongation and lamina growth reduction are dependent on PIF7. The induction of auxin production is both necessary and sufficient to induce opposite growth responses in petioles vs lamina. However, these contrasting growth responses are not caused by different auxin concentrations in the two leaf parts. Our work suggests that a transient increase in auxin levels triggers tissue-specific growth responses in different leaf parts. We provide evidence suggesting that this may be caused by the different sensitivity to auxin in the petiole vs the blade and by tissue-specific gene expression