Lines on the Dwork Pencil of Quintic Threefolds

We present an explicit parametrization of the families of lines of the Dwork pencil of quintic threefolds. This gives rise to isomorphic curves which parametrize the lines. These curves are 125:1 covers of certain genus six curves. These genus six curves are first presented as curves in P^1*P^1 that have three nodes. It is natural to blow up P^1*P^1 in the three points corresponding to the nodes in order to produce smooth curves. The result of blowing up P^1*P^1 in three points is the quintic del Pezzo surface dP_5, whose automorphism group is the permutation group S_5, which is also a symmetry of the pair of genus six curves. The subgroup A_5, of even permutations, is an automorphism of each curve, while the odd permutations interchange the two curves. The ten exceptional curves of dP_5 each intersect each of the genus six curves in two points corresponding to van Geemen lines. We find, in this way, what should have anticipated from the outset, that the genus six curves are the curves of the Wiman pencil. We consider the family of lines also for the cases that the manifolds of the Dwork pencil become singular. For the conifold the genus six curves develop six nodes and may be resolved to a P^1. The group A_5 acts on this P^1 and we describe this action.Comment: 48 pages, 2 figure

An Ensemble Framework for Detecting Community Changes in Dynamic Networks

Dynamic networks, especially those representing social networks, undergo constant evolution of their community structure over time. Nodes can migrate between different communities, communities can split into multiple new communities, communities can merge together, etc. In order to represent dynamic networks with evolving communities it is essential to use a dynamic model rather than a static one. Here we use a dynamic stochastic block model where the underlying block model is different at different times. In order to represent the structural changes expressed by this dynamic model the network will be split into discrete time segments and a clustering algorithm will assign block memberships for each segment. In this paper we show that using an ensemble of clustering assignments accommodates for the variance in scalable clustering algorithms and produces superior results in terms of pairwise-precision and pairwise-recall. We also demonstrate that the dynamic clustering produced by the ensemble can be visualized as a flowchart which encapsulates the community evolution succinctly.Comment: 6 pages, under submission to HPEC Graph Challeng

Short dynamic fibrils in sunspot chromospheres

Sunspot chromospheres display vigorous oscillatory signature when observed in chromospheric diagnostics like the strong Ca II lines and H-alpha. New high-resolution sunspot observations from the Swedish 1-m Solar Telescope show the ubiquitous presence of small-scale periodic jet-like features that move up and down. This phenomenon has not been described before. Their typical width is about 0.3 arcsec and they display clear parabolic trajectories in space-time diagrams. The maximum extension of the top of the jets is lowest in the umbra, a few 100 km, and progressively longer further away from the umbra in the penumbra, with the longest more than 1000 km. These jets resemble dynamic fibrils found in plage regions but at smaller extensions. LTE inversion of spectro-polarimetric Ca II 8542 observations enabled for a comparison of the magnetic field inclination and the properties of these short jets. We find that the most extended of these jets also have longer periods and tend to be located in regions with more horizontal magnetic fields. This is a direct observational confirmation of the mechanism of long-period waves propagating along inclined magnetic fields into the solar chromosphere. This mechanism was identified earlier as the driver of dynamic fibrils in plage, part of the mottles in quiet Sun, and type I spicules at the limb. The sunspot dynamic fibrils that we report here represent a new class of manifestation of this mechanism. They are not the same as the transient penumbral and umbral micro-jets reported earlier.Comment: animations of figures can be found at http://folk.uio.no/rouppe/dfsunspot

Designs of magnetic atom-trap lattices for quantum simulation experiments

We have designed and realized magnetic trapping geometries for ultracold atoms based on permanent magnetic films. Magnetic chip based experiments give a high level of control over trap barriers and geometric boundaries in a compact experimental setup. These structures can be used to study quantum spin physics in a wide range of energies and length scales. By introducing defects into a triangular lattice, kagome and hexagonal lattice structures can be created. Rectangular lattices and (quasi-)one-dimensional structures such as ladders and diamond chain trapping potentials have also been created. Quantum spin models can be studied in all these geometries with Rydberg atoms, which allow for controlled interactions over several micrometers. We also present some nonperiodic geometries where the length scales of the traps are varied over a wide range. These tapered structures offer another way to transport large numbers of atoms adiabatically into subwavelength traps and back.Comment: 9 pages, 10 figure

International R&D Spillovers: A Re-Examination

Coe and Helpman(1995) have measured the extent to which technology spills over between industrialized countries through the particular channel of trade flows. This paper re-examines two particular features of their study. First, we suggest that their functional form of how foreign R&D affects domestic productivity via imports is probably incorrect. We provide an alternative model which turns out to be more accurate, both theoretically and empirically. Second, we take into account two new potential channels of technology transfer: inward FDI and technology sourcing, as proxied by outward FDI. The empirical results show that outward FDI flows and imports flows are two simultaneous channels through which technology is internationally diffused. Inward FDI flows are not a significant channel of technology transfer. The hypothesis of technology sourcing associated with MNEs activities abroad is therefore confirmed while the widespread belief that inward FDI is a major channel of technology transfer is rejected.

The Determinants of Venture Capital: Additional Evidence

This paper attempts to identify and evaluate the main determinants of venture capital (VC). We develop a theoretical model where macroeconomic conditions, technological opportunity, and the entrepreneurial environment affect the demand and supply of VC. The quantitative results, based on a panel dataset of 16 OECD countries from 1990 to 2000, show that VC intensity is pro-cyclical. Interest rates affect more the demand side of VC (entrepreneurs) than the supply side. Indicators of technological opportunity, such as the stock of knowledge and the number of triadic patents affect positively and significantly the relative level of VC. Labour market rigidities reduce the impact of the GDP growth rate and of the stock of knowledge, whereas a minimum level of entrepreneurship is required in order to have a positive effect of the available stock of knowledge on VC intensity. --Venture Capital,Technological Opportuniy,Entrepreneurship,Labour Market Regidities

The Sources of Knowledge and the Value of Academic Patents

This paper aims at contributing to the literature on the determinants of patent value in two respects. It first puts forward new potential determinants of patent value which are mainly related to the identification of the institutional sources of knowledge and the geographical scope of patenting strategy. Second, it aims at validating the traditional and new determinants of patent value with academic patents. The empirical analysis focuses on 208 patent families applied by six main Belgian Universities. The patent value is approximated by the number of forward patent citations. The estimates confirm the role of most traditional determinants of patent value (e.g., backward citation and family size). Further, the new indicators underline the importance of identifying the institutional sources of knowledge. They provide a more in-depth view on the way non patent citations, backward patent citations, co-assignees, and the geographical scope for protection determine patent value. Policy implications emerge from these results, such as the benefit of local and international collaboration between public research organisations and the need to convince academic researchers with a high scientific profile in terms of publications to crystallize their tacit knowledge into high value academic patents.Patent value, patent indicators, knowledge sources

Measuring Innovation Competencies and Performances: A Survey of Large Firms in Belgium

Based on original survey data, this paper provides evidence on firms' innovation competencies and performances in Belgium. The relationship with firm size and technological opportunity is systematically evaluated. The first conclusion is that firms recognize the strategic importance of innovation but fail to undertake the "practical" steps to develop it. Large firms globally better master innovation competencies. However, small firms allocate the largest share of profits to finance innovative projects. In terms of performances, small and large firms, as opposed to medium ones, show the best results for their R&D investments and patent applications. It is also shown that the share of turnover due to incremental innovation is the highest within small firms, while technological breakthroughs are more important within large firms. There is a positive relation between technological opportunity and innovation competencies, R&D investments and patent applications. Services firms have relatively weak records on all innovation indicators but perform well concerning human resources, educational activities and the management of market information. Foreign firms invest significantly less in R&D than local firms. Finally costs- and risks-related barriers to innovation are the most important to all firms, whatever the size and technological opportunity.Innovation competencies, Innovation performances, Barriers to innovation, Survey data