Compressive Response of Composites Under Combined Fire and Compression Loading

The thermal buckling of an axially restrained composite column that is exposed to a heat flux due to fire is studied by both analytical and experimental means. The column is exposed to fire from one-side and the resulting heat damage, the charred layer formation and non-uniform transient temperature distribution are calculated by the thermal model developed by Gibson et al. (Revue de l’Institute Francais du Petrole 50:69–74, 1995). For the thermal buckling analysis, the mechanical properties of the fire-damaged (charred) region are considered negligible; the degradation of the elastic properties with temperature (especially near the glass transition temperature of the matrix) in the undamaged layer, is accounted for by using experimental data for the elastic moduli. Due to the non-uniform stiffness and the effect of the ensuing thermal moment, the structure behaves like an imperfect column, and responds by bending rather than buckling in the classical Euler (bifurcation) sense. Another important effect of the non-uniform temperature is that the neutral axis moves away from the centroid of the cross section, resulting in another moment due to eccentric loading, which would tend to bend the structure away from the fire. In order to verify the mechanical response, the compressive buckling behavior of the same material subjected to simultaneous high intensity surface heating and axial compressive loading were investigated experimentally. Fire exposure was simulated by subjecting the surface of rectangular specimens to radiant heating in a cone calorimeter. Heat flux levels of 25 kW/m², 50 kW/m² and 75 kW/m² were studied. All specimens exhibited buckling and subsequent catastrophic failure, even at compressive stresses as low as 3.5 MPa under a surface heat flux of 25 kW/m². Details of the experimental procedure, including modifications made to a cone calorimeter to allow simultaneous mechanical loading are presented.     

Can Web services scale up?

In the past, only major Internet players such as Amazon, eBay, and Google were interested in deploying large-scale Web services. However, this is changing rapidly as all sorts of companies and governmental organizations are suddenly looking toward Web services as a platform that might support a wide range of demanding applications. This emerging trend presents developers with a new challenge: building Web services solutions that scale. In a nutshell, a scalable system is one that can flexibly accommodate growth in its client base. Such systems typically run on a clustered computer or in a large data center and must be able to handle high loads or sudden demand bursts and a vast number of users. They must reliably respond even in the event of failures or reconfiguration. Ideally, they're self-managed and automate as many routine services such as backups and component upgrades as possible. Many settings also require security against attempted intrusions and distributed denial-of-service (DDoS) attacks. At a glance, today's Web services standards seem to answer these needs. However, a more probing analysis reveals many critical limitations.     

Functionally Graded Stitched Laminates: Illustration on the Example of a Double Cantilever Beam

Although stitched laminates have been shown effective in preventing delamination failure, the presence of stitches results in a degraded in-plane strength and stiffness in such structures. The solution suggested in the paper is based on using stitches only in a part of the structure where they serve as arrestors of delamination cracks, while the part subject to considerable in-plane loading could remain unstitched. This approach, that could be called “functionally graded stitching,” is considered on the example of a double cantilever beam (DCB) with a preexisting delamination crack that has penetrated into the stitched region of the beam. As is shown in the paper, the distribution of stitches in a functionally graded DCB (and in any other laminated structure) should be chosen to prevent three major failure modes. These modes include the failure of the stitches, bending failure of the unstitched delaminated section of the structure, and continuous crack propagation through the stitched region. The results obtained in the paper for the static problem clearly illustrate the feasibility of using functionally graded stitched laminates retaining in-plane strength and stiffness, while providing barriers to delamination cracks in less loaded regions of the structure. Additionally, the approach to the solution of the dynamic problem presented in the paper may be applied to the analysis of fatigue delamination cracks in partially stitched structures.     

A review of experiences with reliable multicast

By understanding how real users have employed reliable multicast in real distributed systems, we can develop insight concerning the degree to which this technology has matched expectations. This paper reviews a number of applications with that goal in mind. Our findings point to trade‐offs between the form of reliability used by a system and its scalability and performance. We also find that to reach a broad user community (and a commercially interesting market) the technology must be better integrated with component and object‐oriented systems architectures. Looking closely at these architectures, however, we identify some assumptions about failure handling which make reliable multicast difficult to exploit. Indeed, the major failures of reliable multicast are associated with attempts to position it within object‐oriented systems in ways that focus on transparent recovery from server failures. The broader opportunity appears to involve relatively visible embeddings of these tools into object‐oriented architectures enabling knowledgeable users to make trade‐offs. Fault‐tolerance through transparent server replication may be better viewed as an unachievable holy grail. Copyright © 1999 John Wiley & Sons, Ltd.     

Two-dimensional inverse problem of diffusion tomography: the approach applicable for small inclusions

A method for solving the two-dimensional inverse problems of optical diffusion tomography is proposed. The method is especially designed for the imaging of small inclusions embedded in the backgrounds of strongly scattering media. Numerical simulations show that the results are stable with respect to external noise at the boundary of the sample. The location of an inclusion is obtained with an accuracy of the order of several photon transport mean-free paths in the medium in cases both with and without noise in the scattering data used for the solution of the inverse problem.     

An agent-based current differential relay for use with a utilityintranet

This paper proposes an agent-based current differential relay for use with a communication network. Agents are software processes capable of searching for information in networks, interacting with pieces of equipment and performing tasks on behalf of their owners (relays). Results illustrating the performance of the agent-based differential method proposed acting within a communication structure are presented for different traffic conditions. These results also show that a dedicated utility intranet is a viable and recommended option as a communication media for the proposed scheme     

Modelling the mechanics of partially mineralized collagen fibrils,fibres and tissue

Progressive stiffening of collagen tissue by bioapatite mineral is important physiologically, but the details of this stiffening are uncertain. Unresolved questions about the details of the accommodation of bioapatite within and upon collagen''s hierarchical structure have posed a central hurdle, but recent microscopy data resolve several major questions. These data suggest how collagen accommodates bioapatite at the lowest relevant hierarchical level (collagen fibrils), and suggest several possibilities for the progressive accommodation of bioapatite at higher hierarchical length scales (fibres and tissue). We developed approximations for the stiffening of collagen across spatial hierarchies based upon these data, and connected models across hierarchies levels to estimate mineralization-dependent tissue-level mechanics. In the five possible sequences of mineralization studied, percolation of the bioapatite phase proved to be an important determinant of the degree of stiffening by bioapatite. The models were applied to study one important instance of partially mineralized tissue, which occurs at the attachment of tendon to bone. All sequences of mineralization considered reproduced experimental observations of a region of tissue between tendon and bone that is more compliant than either tendon or bone, but the size and nature of this region depended strongly upon the sequence of mineralization. These models and observations have implications for engineered tissue scaffolds at the attachment of tendon to bone, bone development and graded biomimetic attachment of dissimilar hierarchical materials in general.     

Edge Mashups for Service-Oriented Collaboration

This paper presents the Live Distributed Objects platform that makes it possible to combine hosted content with P2P protocols in a single object-oriented framework.