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An integrating model which, based on a review of the most recent
theoretical and empirical studies, offers an overall view of the factors
affecting the adoption of Advanced Manufacturing Technologies (AMTs) is
presented. The model is intended to be a base for the managers′ analysis
of the implementation of AMTs, and enables the four areas affecting
adoption (Industry, Firm, Technology and Supply) to be approached in a
more integrated way.

PurposeTo explore the relationship between the dimensions of supply chain flexibility and firm performance in a sample of automotive suppliers.Design/methodology/approachEmpirical survey of a representative sample of 126 Spanish automotive suppliers during the months of September and October 2003. Data gathered through a mail survey to purchasing managers by using a structured questionnaire. Spearman correlation coefficients were used to analyse the relationship between the different supply chain flexibility dimensions, between supply chain flexibility dimensions and firm performance dimensions, and between supply chain flexibility dimensions and environmental uncertainty dimensions. A multivariate analysis studied the determinants of supply chain flexibility.FindingsThe research has found a positive relation between a superior performance in flexibility capabilities and firm performance, although flexibility dimensions are not equally important for firm performance. On the other hand, the results show that companies enhance more the basic flexibility capabilities (at the shop floor level) than aggregate flexibility capabilities (at the customer‐supplier level). However, aggregate flexibility capabilities are more positively related to firm performance than basic flexibility capabilities. Thus, companies might miss opportunities to improve competitiveness by underestimating customer‐supplier flexibility capabilities. Finally, the results indicate that flexibility capabilities are enhanced in supply chains with higher environmental uncertainty, technological complexity, and mutual understanding, but with lower interdependence among the agents involved in the supply chain.Research limitations/implicationsThere are other factors not included in the model that could impact the relationship between flexibility, supply chain characteristics and firm performance. On the other hand, the research has used cross‐sectional data, which are limited in order to explain causal relationships. Another limitation of the research is that we did not use any secondary data (like manual financial reports) to crosscheck firm performance.Practical implicationsThe results of the research contribute to a better understanding of the forces and constraints that companies face with flexibility capabilities.Originality/valueThe paper analyses the relationship between supply chain flexibility dimensions and firm performance. The model provides a framework of supply chain flexibility dimensions that may be used as a test base for further research.

Develops and tests an integrated check‐list to assess manufacturing changes towards lean production. Using the results from a survey to manufacturing plants located in the Spanish region of Aragon, analyzes which lean production indicators are more used to assess the company's improvements in their production systems, and the determinants on the use of these indicators.

Crowdsourcing systems are evolving into a powerful tool of choice to deal with repetitive or lengthy human-based tasks. Prominent among those is Amazon Mechanical Turk, in which Human Intelligence Tasks, are posted by requesters, and afterwards selected and executed by subscribed (human) workers in the platform. Many times these HITs serve for research purposes. In this context, a very important question is how reliable the results obtained through these platforms are, in view of the limited control a requester has on the workers' actions. Various control techniques are currently proposed but they are not free from shortcomings, and their use must be accompanied by a deeper understanding of the workers' behavior. In this work, we attempt to interpret the workers' behavior and reliability level in the absence of control techniques. To do so, we perform a series of experiments with 600 distinct MTurk workers, specifically designed to elicit the worker's level of dedication to a task, according to the task's nature and difficulty. We show that the time required by a worker to carry out a task correlates with its difficulty, and also with the quality of the outcome. We find that there are different types of workers. While some of them are willing to invest a significant amount of time to arrive at the correct answer, at the same time we observe a significant fraction of workers that reply with a wrong answer. For the latter, the difficulty of the task and the very short time they took to reply suggest that they, intentionally, did not even attempt to solve the task. ; AS was supported in part by grants PGC2018-098186-B-I00 (BASIC, FEDER/MICINN- AEI, https://www.ciencia.gob.es/portal/site/MICINN/aei), PRACTICO-CM (Comunidad de Madrid, https://www.comunidad.madrid/servicios/educacion/convocatorias-ayudas-investigacion), and CAVTIONS-CM-UC3M (Comunidad de Madrid/Universidad Carlos III de Madrid, https://www.comunidad.madrid/servicios/educacion/convocatorias-ayudas-investigacion). AFA was supported by the Regional Government of Madrid (CM) grant 347 EdgeData-CM (P2018/TCS4499) cofounded by FSE & FEDER (https://www.comunidad.madrid/servicios/educacion/convocatorias-ayudas-investigacion), NSF of China grant 61520106005 (http://www.nsfc.gov.cn/english/site_1/index.html) and the Ministry of Science and Innovation (https://www.ciencia.gob.es/portal/site/MICINN/aei) grant PID2019-109805RB-I00 (ECID) cofounded by FEDER. The funders has no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Incoherent transport of excitations in one-dimensional disordered lattices with pairs of traps placed at random is studied by numerically solving the corresponding master equation. Results are compared to the case of lattices with the same concentration of unpaired traps, and it is found that pairing of traps causes a slowdown of the decay rate of both the mean square displacement and the survival probability of excitations. We suggest that this result is due to the presence of larger trap-free segments in the lattices with paired disorder, which implies that pairing of traps causes less disruption on the dynamics of excitations. In the conclusion we discuss the implications of our work, placing it in a more general context. ; This work is partially supported by Universidad Complutense through project PR161/93-4811. A.S. is partially supported by DGICyT (Spain) Grant No. PB92- 0248, by MEC (Spain)/Fulbright, and by the European Union Network ERBCHRXCT930413. Work at Los Alamos is performed under the auspices ofthe U.S. DOE. ; Publicado

We study electronic transport properties of disordered polymers in a quasi-one-dimensional model with fully three-dimensional interaction potentials. We consider such quasi-one-dimensionallattices in the presence of both uncorrelated and short-range correlated impurities. In our procedure, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to a Schrodinger equation that is exactly solvable in the momentum representation. By choosing an appropriate potential with the same spectral structure as the physical one, we obtain a discrete set of algebraic equations that can be mapped onto a tight-binding-like equation. We then show that the reflection coefficient of a pair of impurities placed at neighboring sites (dimer defect) vanishes for a particular resonant energy. When there is a finite number of such defects randomly distributed over the whole lattice, we find that the transmission coefficient is almost unity for states close to the resonant energy, and that those states present a very large localization length. Multifractal analysis techniques applied to very long systems demonstrate that these states are truly extended in the thermodynamic limit. These results are obtained with parameters taken from actual physical systems such as polyacetylene, and thus reinforce the possibility of verifying experimentally theoretical predictions about the absence of localization in quasi-one-dimensional disordered systems. ; Work at Madrid is supported by UCM through Project No. PR161/93-4811. Work at Leganes is supported by the DGICyT (Spain) through Project No. PB92-0248, and by the European Union Human Capital and Mobility Programme through Contract No. ERBCHRXCT930413. ; Publicado

We study resonant tunneling in B-8-doped diodes grown by Si-molecular beam epitaxy. A Thomas-Fermi approach is used to obtain the conduction-band modulation. Using a scalar Hamiltonian within the effective-mass approximation we demonstrate that the occurrence of negative differential resistance (NDR) only involves conduction-band states, whereas interband tunneling effects seem to be negligible. Our theoretical results are in very good agreement with recent experimental observations of NDR in this type of diode. ; F. D.-A. acknowledges support from UCM through project PR 161/93-4811. A. S. acknowledges partial support from c.I.c. y T. (Spain) through project PB92-0248 and by the European Union Human Capital and Mobility Programme through contract ERBCHRXCT930413. ; Publicado

We study resonant tunnelling through double-barrier structures under an applied bias voltage, in which nonlinearities due to self-interaction of electrons in the barrier regions are included. As an approximation, we concern ourselves with thin barriers simulated by 8-function potentials. This approximation allows for an analytical expression of the transmission probability through the structure. We show that the typical peaks due to resonant tunneling decrease and broaden as non linearity increases. The main conclusion is that nonlinear effects degrade the peak-to-valley ratio but improve the maximum operation frequency of the resonant tunnelling devices. ; FD.-A. acknowledges support from UCM through project PR161193-4811. A.S. acknowledges partial support from e.1.e. y T. (Spain) through project PB92-0248 and from the European Union Human Capital and Mobility Programme through contract ERBCHRXCT930413. ; Publicado

Incoherent exciton dynamics in one-dimensional perfect lattices with traps at sites arranged according to aperiodic deterministic sequences is studied. We focus our attention on Thue-Morse and Fibonacci systems as canonical examples of self-similar aperiodic systems. Solving numerically the corresponding master equation we evaluate the survival probability and the mean-square displacement of an exciton initially created at a single site. Results are compared to systems of the same size with the same concentration of traps randomly as well as periodically distributed over the whole lattice. Excitons progressively extend over the lattice on increasing time and, in this sense, they act as a probe of the particular arrangements of traps in each system considered. The analysis of the characteristic features of their time decay indicates that exciton dynamics in self-similar aperiodic arrangements of traps is quite close to that observed in periodic ones, but differs significantly from that corresponding to random lattices. We also report on characteristic features of exciton motion suggesting that Fibonacci and Thue-Morse orderings might be clearly observed by appropriate experimental measurements. In the conclusions we comment on the implications of our work on the way towards a unified theory of the ordering of matter. ; This work is partially supported by Universidad Complutense through Project No. PRI61/93-4811. A.S. is partially supported by DGICyT (Spain) Grant No. PB92-0248, by MEC (Spain)/Fulbright, and by the European Union Network ERBCHRXCT930413. Work at Los Alamos is performed under the auspices of the U .S. DOE. ; Publicado

We theoretically study electron transport in disordered, quantum-well-based, semiconductor superlattices with structural short-range correlations. Our system consists of equal-width square barriers and quantum wells with two different thicknesses. The two kinds of quantum wells are randomly distributed along the growth direction. Structural correlations are introduced by adding the constraint that one of the wells always appears in pairs. We show that such correlated disordered superlattices exhibit a strong enhancement of their dc conductance as compared to usual random ones, giving rise to quasi-ballistic-electron transport. Interestingly, this phenomenon is also detected in superlattices with random fluctuations of the well thicknesses. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder and, most important, that it should be clearly observed even in the presence of imperfections ; Work at Madrid was supported by UCM through Project No. PR161/93-4811. Work at Leganes was supported by the DGICyT (Spain) through Project No. PB92-0248, and by the European Union Human Capital and Mobility Programme through Contract No. ERBCHRXCT930413. ; Publicado

We study the relationship between the electronic spectrum structure and the configurational order of onedimensional quasiperiodic systems. We take the Fibonacci case as a specific example, but the ideas outlined here may be useful to accurately describe the energy spectra of general quasiperiodic systems of technological interest. Our main result concerns the minimization of the information entropy as a characteristic feature associated with quasiperiodic arrangements. This feature is shown to be related to the ability of quasiperiodic systems to encode more information, in the Shannon sense, than periodic ones. In the conclusion we comment on interesting implications of these results on further developments on the issue of quasiperiodic order. ; This work is partially supported by UCM under Project No. PR161/93-481l. A.S. is partially supported by DGICyT (Spain) through Project No. PB92-0248, and by the European Union Human Capital and Mobility Programme through Contract No. ERBCHRXCT930413 ; Publicado

We study how the influence of structural correlations in disordered systems manifests itself in experimentally measurable magnitudes, focusing on dc conductance of semiconductor supedattices with general potential profiles. We show that the existence of bands of extended states in these structures gives rise to very noticeable peaks in the finite-temperature dc conductance as the chemical potential is moved through the bands or as the temperature is increased from zero. On the basis of these results we discuss how dc conductance measurements can provide information on the location and width of the bands of extended states. Our predictions can be used to demonstrate experimentally that structural correlations inhibit the localization effects of disorder. ; Work at Leganes is supported by the Direccion General de Investigacion Cientifica y Tecnica (Spain) through project PB92-0248, and by the European Union Human Capital and Mobility Programme through Contract No. ERBCHRXCT930413. Work at Madrid is supported by U niversidad Complutense through Project No. PR161/93-4811. ; Publicado

We derive a discrete Hamiltonian describing a Fibonacci superlattice in which the electronic potential is taken to be an array of equally spaced 0 potentials, whose strengths modulate the chemical composition in the growth direction. In this model both diagonal and off-diagonal elements of the Hamiltonian matrix become mutually related through the potential strengths. The corresponding energy spectrum and related magnitudes, such as the Lyapunovcoefficient, transmission coefficient, and Landauer resistance, exhibit a highly fragmented, self-similar nature. We investigate the influence of the underlying spectrum structure on the dc conductance at different temperatures obtaining analytical expressions which relate special features of the dc conductance with certain parameters that characterize the electronic spectrum of Fibonacci superlattices. ; A.S. is partially supported by DGICyT (Spain) through Project No. PB92-0248, and by European Union through NETWORK nonlinear Spatio-Temporal Structures in Semiconductors, Fluids, and Oscillator Ensembles. ; Publicado