Localised knowledge spillovers vs. innovative milieux: Knowledge “tacitness” reconsidered

Abstract. This article provides a critical discussion of the recent econometric literature on "localised knowledge spillovers" and the related notion of tacit knowledge. The basic claim of the article is that the increasing, and more or less automatic reliance of industrial geographers upon such econometric evidence and theoretical concepts to support their work on industrial districts, hi-tech agglomerations and, more broadly, local innovation systems is not well placed and risks to generate conceptual confusion and to distort research agendas. Following some recent advances in the economics of knowledge, the article also suggests that more research efforts should instead be devoted to exploring how knowledge is actually transmitted, among whom, at what distance, and on the basis of which codebooks.     

Transient subharmonic and ultraharmonic acoustic emission during dissolution of free gas bubbles

This work concerns the study of free gas bubble behavior, a basic step in contrast agent study. In order to improve the understanding of microbubble-ultrasound interaction, we propose an acoustic dynamic observation of microbubble behavior performed by a high frame-rate acquiring and processing system. Results from ultrasonic observations of free gas microbubbles are discussed and compared with theoretical simulation. Peculiar radio frequency (RF) echo signals back-propagated from bubbles during dissolution up to their destruction are shown and their behavior is discussed. In particular, the different orders of subharmonic emissions related to changes in bubble sizes during dissolution were observed.     

Effects of noise stress on EFS-mediated cholinergic and inhibitory NANC responses in tracheae from normal and sensitized guinea-pigs

1 The aim of the present research was to study the cholinergic and inhibitory non-adrenergic-non-cholinergic (NANC) responses obtained with electrical field stimulation (EFS) of tracheal tissues from sham- and noise-exposed guinea-pigs. A comparison was also made between normal and ovalbumin (OA)-sensitized animals. 2 In proximal tracheae pretreated with indomethacin (3 microM), propranolol (1 microM), alpha-chymotrypsin (2 U ml-1) and L-NAME (0.1 mM), frequency-dependent responses to EFS (0.1 ms width; 20 V, 0.1-100 Hz, 15 s train duration) were obtained, both contractile and relaxing in nature. The contractile responses were abolished by atropine (1 microM), and did not vary significantly between sham- and noise-exposed guinea-pigs, or between normal and sensitized animals. The NANC relaxing responses, present in spite of the pre-treatment of the tissues with L-NAME and alpha-chymotrypsin, and almost completely abolished by tetrodotoxin (TTX) treatment (10 microM), appeared to be enhanced in noise-exposed guinea-pigs, with respect to sham-exposed animals, but only when the animals were not OA-sensitized. 3 In distal tracheae contracted with histamine (10 microM), the study of the whole inhibitory NANC response (pre-treatment with propranolol, but not with alpha-chymotrypsin and L-NAME), which was mainly TTX-sensitive, revealed a statistically non-significant difference between sham- and noise-exposed guinea-pigs, both normal and OA-sensitized. When distal tracheae were preincubated with alpha-chymotrypsin (2 U ml-1) and L-NAME (0.1 mM), in addition to propranolol, a significant residual inhibitory NANC response to EFS was observed. Surprisingly, in this case, similarly to the evidence obtained in proximal tracheae, a significantly enhanced response was revealed in noise-exposed guinea-pigs with respect to sham-exposed animals. 4 The noise-induced enhancement of the relaxant response disappeared when the tissues were pretreated with the A2 purinergic antagonist 3,7-dimethyl-1-propargylxanthine (DMPX, 1 microM), while it persisted in the presence of the A1 antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 nM). 5 The above data indicate that, while not modifying the cholinergic and the whole inhibitory NANC response to EFS, noise stress selectively influences an inhibitory component of the NANC system in guinea-pig trachea with a mechanism probably involving an enhanced neurally mediated release of adenosine, which relaxes the smooth muscle via A2 receptors. This effect appears to be lacking or masked in sensitized guinea-pigs.     

Stable and transient subharmonic emissions from isolated contrast agent microbubbles

Ultrasound contrast agents (UCAs) have been widely studied in recent years in order to improve and develop new, sophisticated imaging techniques for clinical applications. In order to improve the understanding of microbubble-ultrasound interactions, an acoustic dynamic characterization of UCA microbubble behavior was performed in this work using a high frame-rate acquiring and processing system. This equipment is connected to a commercial scanner that provides RF beam-formed data with a frame-rate of 30 Hz. Acquired RF sequences allows us to follow the dynamics of cavitation mechanisms in its temporal evolution during different insonifying conditions. The experimental setup allowed us to keep the bubbles free in a spatial region of the supporting medium, thus avoiding boundary effects that can alter the ultrasound field and the scattered echo from bubbles. The work focuses on the study of subharmonic emission from an isolated bubble of contrast agent. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the stand still of the subharmonic emission, was detected at 3.3 MHz and 5 MHz excitation frequencies. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. An experimental procedure was devised in order to investigate these behaviors and several sequences of RF echo signals and the related spectra, acquired from an isolated bubble in different insonation conditions, are presented and discussed in this paper.     

Electromagnetic Modeling of the Jacket in Cable-in-Conduit Conductors

Most magnets designed for thermonuclear fusion experiments rely on the cable-in-conduit conductor technology. These cables are made of several hundreds or thousands of multifilamentary superconducting strands. The strands are refrigerated by a flow of liquid helium in forced convection through a conduit, usually made of aluminum or stainless steel. The complexity of the manufacturing techniques makes it very difficult to perform direct voltage measurements inside the jacket of these cables. Voltage taps are usually placed on the jacket outer surface, deriving relevant information about the inner cable electrical characteristics. In the present study, an electromagnetic model is presented that allows us to take into account the presence of the jacket and its interactions with the superconducting cable. Some unexpected qualitative behaviors of the voltage signals detected on the jacket, whose interpretation is currently under debate in the scientific community, are reproduced by the model.     

Direct data‐driven design of switching controllers

Switching linear models can be used to represent the behavior of hybrid, time‐varying, and nonlinear systems, while generally providing a satisfactory trade‐off between accuracy and complexity. Although several control design techniques are available for such models, the effect of modeling errors on the closed‐loop performance has not been formally evaluated yet. In this paper, a data‐driven synthesis scheme is thus introduced to design optimal switching controllers directly from data, without needing a model of the plant. In particular, the theory will be developed for piecewise affine controllers, which have proven to be effective in many real‐world engineering applications. The performance of the proposed approach is illustrated on some benchmark simulation case studies.