On finitely recursive programs

Disjunctive finitary programs are a class of logic programs admitting function symbols and hence infinite domains. They have very good computational properties, for example ground queries are decidable while in the general case the stable model semantics is highly undecidable. In this paper we prove that a larger class of programs, called finitely recursive programs, preserves most of the good properties of finitary programs under the stable model semantics, namely: (i) finitely recursive programs enjoy a compactness property; (ii) inconsistency checking and skeptical reasoning are semidecidable; (iii) skeptical resolution is complete for normal finitely recursive programs. Moreover, we show how to check inconsistency and answer skeptical queries using finite subsets of the ground program instantiation. We achieve this by extending the splitting sequence theorem by Lifschitz and Turner: We prove that if the input program P is finitely recursive, then the partial stable models determined by any smooth splitting omega-sequence converge to a stable model of P.Comment: 26 pages, Preliminary version in Proc. of ICLP 2007, Best paper awar

Quantum causal histories

Quantum causal histories are defined to be causal sets with Hilbert spaces attached to each event and local unitary evolution operators. The reflexivity, antisymmetry, and transitivity properties of a causal set are preserved in the quantum history as conditions on the evolution operators. A quantum causal history in which transitivity holds can be treated as ``directed'' topological quantum field theory. Two examples of such histories are described.Comment: 16 pages, epsfig latex. Some clarifications, minor corrections and references added. Version to appear in Classical and Quantum Gravit

The elixir (or burden) of youth? Exploring differences in innovation between start-ups and established firms

Despite the widely acknowledged role of start-ups in economic development, little is known about their innovative activities compared with those of established firms. Drawing on a sample of 12,209 UK firms, we differentiate between services and manufacturing firms and, using a matching estimator approach, demonstrate that start-ups differ significantly from established firms in their innovation activities. We find that in services, being a start-up increases the likelihood of product innovations. However, in manufacturing, we find no significant differences in the likelihood of product innovation between start-ups and established firms. When examining the returns to innovation, we find that start-ups have a significant advantage both in services and in manufacturing. We explore the implications of these results for theory and policy

Managing Unsolicited Ideas for R&D

Existing academic and popular literature suggests that unsolicited ideas, the non-contractual and voluntary submission of innovation-related information from external sources to the firm, offer the promise of a bountiful and low-cost tool to sustain and extend firms' R&D efforts. Yet, in practice, many organizations find it difficult to deal with unsolicited ideas because of high quantity, low quality, and the need to transfer IP ownership. This article identifies a range of practices that allow organizations to meet these challenges and therefore realize some of the potential of unsolicited ideas for R&D

Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology

Quantum fields are investigated in the (2+1)-open-universes with non-trivial topologies by the method of images. The universes are locally de Sitter spacetime and anti-de Sitter spacetime. In the present article we study spacetimes whose spatial topologies are a torus with a cusp and a sphere with three cusps as a step toward the more general case. A quantum energy momentum tensor is obtained by the point stripping method. Though the cusps are no singularities, the latter cusps cause the divergence of the quantum field. This suggests that only the latter cusps are quantum mechanically unstable. Of course at the singularity of the background spacetime the quantum field diverges. Also the possibility of the divergence of topological effect by a negative spatial curvature is discussed. Since the volume of the negatively curved space is larger than that of the flat space, one see so many images of a single source by the non-trivial topology. It is confirmed that this divergence does not appear in our models of topologies. The results will be applicable to the case of three dimensional multi black hole\cite{BR}.Comment: 17 pages, revtex, 3 uuencoded figures containe

Coping with Open Innovation: Responding to the Challenges of External Engagement in R&D

Open innovation often requires wholesale changes to the nature of R&D. However, academic research and managerial practice have paid little attention to the challenges that individuals face in the daily pursuit of open innovation. As a result, there is little understanding of how individuals cope with open innovation, and which organizational practices can support them in this role. Drawing on the experiences of R&D professionals, this article identifies four specific challenges and coping strategies of individuals engaged in open innovation. It proposes a range of open innovation practices that organizations can implement to better equip their staff to undertake effective external engagement

Satélites de Monitoramento: CD-ROM para o ensino de sensoriamento remoto.

O CD-ROM Satélites de Monitoramento apresenta textos, figuras, tabelas e mapas que ilustram, a partir de uma interface de fácil acesso, os principais instrumentos de sensoriamento remoto que contribuem para o conhecimento dos diferentes aspectos da agricultura e do meio ambiente do Brasil

2+12+1 Covariant Lattice Theory and t'Hooft's Formulation

We show that 't Hooft's representation of (2+1)-dimensional gravity in terms of flat polygonal tiles is closely related to a gauge-fixed version of the covariant Hamiltonian lattice theory. 't Hooft's gauge is remarkable in that it leads to a Hamiltonian which is a linear sum of vertex Hamiltonians, each of which is defined modulo $2 \pi$. A cyclic Hamiltonian implies that ``time'' is quantized. However, it turns out that this Hamiltonian is {\it constrained}. If one chooses an internal time and solves this constraint for the ``physical Hamiltonian'', the result is not a cyclic function. Even if one quantizes {\it a la Dirac}, the ``internal time'' observable does not acquire a discrete spectrum. We also show that in Euclidean 3-d lattice gravity, ``space'' can be either discrete or continuous depending on the choice of quantization. Finally, we propose a generalization of 't Hooft's gauge for Hamiltonian lattice formulations of topological gravity dimension 4.Comment: 10 pages of text. One figure available from J.A. Zapata upon reques