T his paper builds on Granovetter's distinction between strong and weak ties [Granovetter, M. S. 1973. The strength of weak ties. Amer. J. Sociol. 78(6) 1360-1380] in order to respond to recent calls for a more dynamic and processual understanding of networks. The concepts of potential and latent tie are deductively identified, and their implications for understanding how and why networks emerge, evolve, and change are explored. A longitudinal empirical study conducted with companies operating in the European motorsport industry reveals that firms take strategic actions to search for potential ties and reactivate latent ties in order to solve problems of network redundancy and overload. Examples are given, and their characteristics are examined to provide theoretical elaboration of the relationship between the types of tie and network evolution. These conceptual and empirical insights move understanding of the managerial challenge of building effective networks beyond static structural contingency models of optimal network forms to highlight the processes and capabilities of dynamic relationship building and network development. In so doing, this paper highlights the interrelationship between search and redundancy and the scope for strategic action alongside path dependence and structural influences on network processes.Key words: network evolution; interorganizational ties; network overload; redundancy; exploration; potential and latent ties History: Published online in Articles in Advance May 17, 2011. IntroductionThere has been increasing interest in the nature of organizational network ties and their implications for knowledge creation and sharing (Ahuja 2000;McEvily and Zaheer 1999;Muthusamy and White 2005;Powell et al. 1996;Uzzi 1996Uzzi , 1997. Research has suggested that close and dense networks characterized by embedded relationships (strong ties) facilitate the sharing of highly contextual and complex knowledge by developing trust and creating common values and norms Nobeoka 2000, Uzzi 1997). Dense networks are contrasted with sparse networks that are seen as less effective at transferring tacit and embedded knowledge, but they allow firms to avoid redundancy and find novel and heterogeneous forms of knowledge by relying on more distant and sporadic contacts (weak ties) (Burt 1992). A third stream of research recombines these conflicting views and recognizes the potential of network configurations that mesh cohesion and structural holes, strong and weak ties, and proximity and diversity (Levin and Cross 2004, Nooteboom 2000, Obstfeld 2005. Questions of how to efficiently manage networks remain, however, because the strengthening of network ties leads to increased redundancy (Maurer and Ebers 2006), whereas continuing to extend the network is costly in terms of search and can lead to network overload, i.e., the constraints faced by actors in managing and sustaining a large number of contacts (Steier and Greenwood 2000, Elfring andHulsink 2007). Our understanding of how these challenges of network redu...

The concept of learning in networks has received scant attention within extant theories. Where learning has been applied to networks, different terms have emerged, which have generated confusion and prevented a full understanding of its complex and processual nature. Most importantly, the literature tends to focus either on the learning of single actors rather than the collaboration processes among a group of firms or on the mechanistic processes through which learning is stored at the network level. The paper attempts to make sense of current and past conceptualizations of learning both at the organizational and network levels and provides new insights into how interorganizational learning may be further explored. Interorganizational learning is indeed a complex phenomenon, and future scholars should pay more attention to the underlying processes that constitute it and its multilevel nature. Three interrelated processes are proposed here: learning to collaborate, learning to share knowledge, and learning to create interorganizational knowledge. These processes constitute the building blocks through which interorganizational learning occurs and can be regarded as “deutero” learning processes. Copyright © 2012 John Wiley & Sons, Ltd.

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Our previous data demonstrated profound anti-tumor and anti-metastatic effects of p62 (sqstm1) DNA vaccine in rodents with various types of transplantable tumors. Testing anti-cancer medicine in dogs as an intermediary step of translational research program provides two major benefits. First, clinical data collected in target animals is required for FDA/USDA approval as a veterinary anti-cancer drug or vaccine. It is noteworthy that the veterinary community is in need of novel medicine for the prevention and treatment of canine and feline cancers. The second more important benefit of testing anti-cancer vaccines in dogs is that spontaneous tumors in dogs may provide invaluable information for human trials. Here, we evaluated the effect(s) of p62 DNA vaccine on mammary tumors of dogs. We found that p62 DNA vaccine administered i.m. decreased or stabilized growth of locally advanced lesions in absence of its overall toxic effects. The observed antitumor activity was associated with lymphocyte infiltration and tumor encapsulation via fibrotic reaction. This data justifies both human clinical trials and veterinary application of p62 DNA vaccine.

Purpose -The literature on interfirm networks devotes scant attention to the ways collaborating firms combine and integrate the knowledge they share and to the subsequent learning outcomes. This study aims to investigate how motorsport companies use network ties to share and recombine knowledge and the learning that occurs both at the organizational and dyadic network levels.Design/methodology/approach -The paper adopts a qualitative and inductive approach with the aim of developing theory from an in-depth examination of the dyadic ties between motorsport companies and the way they share and recombine knowledge.Findings -The research shows that motorsport companies having substantial competences at managing knowledge flows do so by getting advantage of bridging ties. While bridging ties allow motorsport companies to reach distant and diverse sources of knowledge, their strengthening and the formation of relational capital facilitate the mediation and overlapping of that knowledge.Research limitations/implications -The analysis rests on a qualitative account in a single industry and does not take into account different types of inter-firm networks (e.g. alliances; constellations; consortia etc.) and governance structures. Cross-industry analyses may provide a more fine-grained picture of the practices used to recombine knowledge and the ideal composition of inter-firm ties.Practical implications -This study provides some interesting implications for scholars and managers concerned with the management of innovation activities at the interfirm level. From a managerial point of view, the recognition of the different roles played by network spanning connections is particularly salient and raises issues concerning the effective design and management of interfirm ties.Originality/value -Although much of the literature emphasizes the role of bridging ties in connecting to diverse pools of knowledge, this paper goes one step further and investigates in more depth how firms gather and combine distant and heterogeneous sources of knowledge through the use of strengthened bridging ties and a micro-context conducive to high quality relationships.

Interventional radiology and cardiology are widespread employed techniques for diagnosis and treatment of several pathologies because they avoid the majority of the side-effects associated with surgical treatments, but are known to increase the radiation exposure to patient and operators. In recent years many studies treated the exposure of the operators performing cardiological procedures. The aim of this work is to study the exposure condition of the medical staff in some selected interventional radiology procedures. The Monte Carlo simulations have been employed with anthropomorphic mathematical phantoms reproducing the irradiation scenario of the medical staff with two operators and the patient. A personal dosemeter, put on apron, was modelled for comparison with measurements performed in hospitals, done with electronic dosemeters, in a reduced number of interventional radiology practices. Within the limits associated to the use of numerical anthropomorphic models to mimic a complex interventional procedure, the personal dose equivalent, Hp(10), was evaluated and normalised to the simulated Kerma-Area Product, KAP, value, indeed the effective dose has been calculated. The Hp(10)/KAPvalue of the first operator is about 10 μSv/Gy.cm2, when ceiling shielding is not used. This value is calculated on the trunk and it varies of +/−30% moving the dosemeter to the waist or to the neck. The effective dose, normalised to the KAP value, varies between 0.03 and 0.4 μSv/Gy.cm2. Considering all the unavoidable approximation of this kind of investigations, the comparisons with hospital measurement and literature data showed a good agreement allowing to use of the present results for dosimetric characterisation of interventional radiology procedures.

BackgroundPET/CT has recently been shown to be a viable alternative to traditional post-infusion imaging methods providing good quality images of 90Y-laden microspheres after selective internal radiation therapy (SIRT). In the present paper, first we assessed the quantitative accuracy of 90Y-PET using an anthropomorphic phantom provided with lungs, liver, spine, and a cylindrical homemade lesion located into the hepatic compartment. Then, we explored the accuracy of different computational approaches on dose calculation, including (I) direct Monte Carlo radiation transport using Raydose, (II) Kernel convolution using Philips Stratos, (III) local deposition algorithm, (IV) Monte Carlo technique (MCNP) considering a uniform activity distribution, and (V) MIRD (Medical Internal Radiation Dose) analytical approach. Finally, calculated absorbed doses were compared with those obtained performing measurements with LiF:Mg,Cu,P TLD chips in a liquid environment.ResultsOur results indicate that despite 90Y-PET being likely to provide high-resolution images, the 90Y low branch ratio, along with other image-degrading factors, may produce non-uniform activity maps, even in the presence of uniform activity. A systematic underestimation of the recovered activity, both for the tumor insert and for the liver background, was found. This is particularly true if no partial volume correction is applied through recovery coefficients. All dose algorithms performed well, the worst case scenario providing an agreement between absorbed dose evaluations within 20%. Average absorbed doses determined with the local deposition method are in excellent agreement with those obtained using the MIRD and the kernel-convolution dose calculation approach.Finally, absorbed dose assessed with MC codes are in good agreement with those obtained using TLD in liquid solution, thus confirming the soundness of both calculation approaches. This is especially true for Raydose, which provided an absorbed dose value within 3% of the measured dose, well within the stated uncertainties.ConclusionsPatient-specific dosimetry is possible even in a scenario with low true coincidences and high random fraction, as in 90Y–PET imaging, granted that accurate absolute PET calibration is performed and acquisition times are sufficiently long. Despite Monte Carlo calculations seeming to outperform all dose estimation algorithms, our data provide a strong argument for encouraging the use of the local deposition algorithm for routine 90Y dosimetry based on PET/CT imaging, due to its simplicity of implementation.

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