The Cohen-Macaulay representation type of arithmetically Cohen-Macaulay varieties

We show that all reduced closed subschemes of projective space that have a Cohen-Macaulay graded coordinate ring are of wild Cohen-Macaulay type, except for a few cases which we completely classify.Comment: Completely new version. The main result now covers reducible subschemes and cones. Many proofs have been simplified and correcte

ACM bundles on del Pezzo surfaces

ACM rank 1 bundles on del Pezzo surfaces are classified in terms of the rational normal curves that they contain. A complete list of ACM line bundles is provided. Moreover, for any del Pezzo surface $X$ of degree less or equal than six and for any $n\geq 2$ we construct a family of dimension $\geq n-1$ of non-isomorphic simple ACM bundles of rank $n$ on $X$

Do process innovations boost SMEs productivity growth?

In this paper we explore in depth the effect of process innovations on total factor productivity growth for small and medium enterprises (SMEs), taking into account the potential endogeneity problem that may be caused by self selection into these activities. First, we analyse whether the ex-ante most productive SMEs are those that start introducing process innovations; then, we test whether process innovations boost SMEs productivity growth using matching techniques to control for the possibility that selection into introducing process innovations may not be a random process. We use a sample of Spanish manufacturing SMEs for the period 1991-2002, drawn from the Encuesta sobre Estrategias Empresariales. Our results show that the introduction of process innovations by a first-time process innovator yields an extra productivity growth as compared to a non-process innovator, and that the life span of this extra productivity growth has an inverted U-shaped form. En este artículo se exploran los posibles efectos de la introducción de innovaciones de proceso en el crecimiento de la productividad de las pequeñas y medianas empresas (PYMES). Para ello se presta especial atención a la existencia de un problema de selección no aleatorio en la implementación de tales innovaciones. En primer lugar, se analiza si son aquellas empresas ex-ante más productivas las que introducen innovaciones de proceso. A continuación, se utilizan técnicas de matching para contrastar si la implementación de innovaciones de proceso acelera el crecimiento de la productividad de las PYMES. La utilización de técnicas de matching permite controlar la posible existencia de un proceso de selección no aleatorio en la implementación de innovaciones de proceso. El análisis empírico se lleva cabo usando una muestra de PYMES manufactureras españolas extraída de la Encuesta sobre Estrategias Empresariales. Nuestros resultados muestran que la implementación de innovaciones de proceso por parte de PYMES sin experiencia previa en la introducción de tales innovaciones, produce un crecimiento extra de la productividad de estas PYMES en comparación con el de aquellas PYMES que no implementan innovaciones de proceso. Adicionalmente, nuestros resultados sugieren la existencia de una relación en forma de U invertida entre el crecimiento extra de la productividad y el tiempo transcurrido desde la introducción de la innovación de proceso.innovaciones de proceso, PTF, dominancia estocástica, técnicas de matching. process innovations, TFP, stochastic dominance, matching techniques.

Information systems offshore outsourcing: a descriptive analysis

Purpose - The present paper has as its aim to deepen in the study of Information Systems Offshore Outsourcing, proposing three essential steps to make this decision: weighing up the advantages and risks of Offshore Outsourcing; analysing the taxonomy of this phenomenon; and determining its current geography. Design/Methodology/Approach - With that objective in mind, it was decided to base the research work on the literature about this topic and the review of reports and statistics coming from different sources (consultants, the press, public institutions, etc.). Findings - Offshore Outsourcing has grown vertiginously in recent years. Its advantages exceed even those of onshore outsourcing, though it also involves greater risks derived from the (cultural and physical) distance existing between customer and provider. Various types of services and customer-provider relationships hide under the umbrella of Offshore Outsourcing; i.e. it is not a homogeneous phenomenon. The main Offshore Outsourcing customers can be found in the USA and Europe, mainly in the UK but also in other countries such as Germany and France. As for provider firms, most of them are located in Asia −outstandingly in India but also in China and Russia. At present, there are important providers scattered in other continents as well. Originality/Value - The conclusions suggest that the range of potential Offshore Outsourcing destinations must be widened and that the search for a provider cannot be based exclusively on cost savings; other considerations such as quality, security and proximity of the provider must also be taken into consideration. That is precisely the reason why the study of new countries like Spain as Offshore Outsourcing destinations is proposed

ACM sheaves on the double plane

The goal of this paper is to start a study of aCM and Ulrich sheaves on non-integral projective varieties. We show that any aCM vector bundle of rank two on the double plane is a direct sum of line bundles. As a by-product, any aCM vector bundle of rank two on a sufficiently high dimensional quadric hypersurface also splits. We consider aCM and Ulrich vector bundles on a multiple hyperplanes and prove the existence of such bundles that do not split, if the multiple hyperplane is linearly embedded into a sufficiently high dimensional projective space. Then we restrict our attention to the double plane and give a classification of aCM sheaves of rank at most $3/2$ on the double plane and describe the family of isomorphism classes of them.Comment: 33 pages; Major changes in Section 3, 4 and 7; several typos corrected; Comments welcom

Light trapping within the grooves of 1D diffraction gratings under monochromatic and sunlight illumination

The Rayleigh-Modal method is used to calculate the electromagnetic field within the grooves of a perfectly conducting, rectangular-shaped 1D diffraction grating. An \emph{enhancement coefficient} ($\eta$) is introduced in order to quantify such an energy concentration. Accordingly, $\eta >$1 means that the amount of electromagnetic energy present within the grooves is larger than that one will have, over the same volume, if the diffraction grating is replaced by a perfectly reflecting mirror. The results in this paper show that $\eta$ can be as large as several decades at certain, often narrow, ranges of wavelengths. However, it reduces to approximately 20% under sunlight illumination. In this latter case, such values are achieved when the \textit{optical spacing} between the grooves $dn$ is greater than 500 nm, where $d$ is the groove spacing and $n$ is the refractive index of the substance within the grooves. For $dn$ smaller than 500 nm the enhancement coefficient turns negligibly small.Comment: This paper contains 11 pages and 4 figures, and will be published elsewher