We generated mice in which a functional RAG2:GFP fusion gene is knocked in to the endogenous RAG2 locus. In bone marrow and thymus, RAG2:GFP expression occurs in appropriate stages of developing B and T cells as well as in immature bone marrow IgM+ B cells. RAG2:GFP also is expressed in IgD+ B cells following cross-linking of IgM on immature IgM+ IgD+ B cells generated in vitro. RAG2:GFP expression is undetectable in most immature splenic B cells; however, in young RAG2:GFP mice, there are substantial numbers of splenic RAG2:GFP+ cells that mostly resemble pre-B cells. The latter population decreases in size with age but reappears following immunization of older RAG2:GFP mice. We discuss the implications of these findings for current models of receptor assembly and diversification.

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

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The objective of this study is to investigate particle deformation and bonding over a wide range of impact conditions, cold spraying of spherical Ti-6Al-4V powders was carried out with nitrogen as process gas onto titanium grade II, Ti-6Al-4V, and aluminum and magnesium alloy substrates. The bond strength was assessed by applying a modified cavitation test. The corresponding impact morphologies and fracture morphologies, as obtained after cavitation testing, were studied by scanning electron microscopy. The investigations demonstrate that bonding and adhesion of spherical Ti-6Al-4V particles depend strongly on substrate properties. Higher bond strength is achieved for material combinations that show lower differences in properties (density, hardness, thermal and mechanical properties), e.g., in the case of Ti-6Al-4V on Ti and Ti-6Al-4V substrates. This is attributed to more pronounced formation of adiabatic shear instabilities for more compatible material combinations.

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Cold spraying (CS) has been widely explored over the last decade due to its low process temperature and limited thermal effect on spray materials. As a solid-state process, the inherent deficiencies of traditional thermal spraying such as oxidation, decomposition and grain growth are avoided. This article summarizes the research work on the fabrication of composites and nanostructured coatings by the promising CS process. After a brief introduction to CS and its deposition mechanisms, the preparation methods of spray powders are classified. Different methods are appropriate for particles of various properties, and the tendency is to design composite powders by combined methods in order to create coatings with specified properties. Then the co-deposition mechanism of composite particles as well as research findings on metal-metal, metal-ceramic and metal-intermetallic composite coatings are reviewed concerning the deposition characteristics, microstructure and its relation to properties. Moreover, CS has been used to deposit a variety of nanostructured materials, including metals, metal-ceramic composites, and even ceramics, retaining their nanocrystalline nature in the coating without grain growth or phase transformation. Finally, the potential applications of CS and issues to be addressed in coating deposition are discussed.

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