The untrustworthy Web services revolution

The commoditization of the Web is bringing tremendous benefits, but also some serious risks. The benefits are obvious: Web-based technologies are becoming a universal standard. At the same time, however, the economics of the Web favor an untrustworthy technology base. The key driver for this concern is service-oriented architectures. Major database products, embedded systems platforms, and turnkey solutions in areas ranging from process planning to supply-chain and customer-relations management are adopting a service-oriented approach.     

Analytical models of sandwich plates with piezoelectric strip-stiffeners

A theory of sandwich plates with composite-material facings and piezoelectric strip-stiffeners bonded to the surface or embedded in the facings is developed. The stiffeners bonded to the surfaces are modeled using either the plane stress assumption or a first-order shear deformable theory. The former approach is appropriate if the stiffeners represent thin strips, while the latter method can be used in the case where the stiffeners are relatively deep. The stiffeners embedded in the facings in the form of piezoelectric strips are considered using the plane stress assumption.     

Optimum distribution of smart stiffeners in sandwich plates subjected to bending or forced vibrations

The problems of optimum distribution of active stiffeners manufactured from piezoelectric or shape memory alloy materials and bonded to or embedded within the facings of a sandwich plate are considered. The sandwich plate consists of thin composite or isotropic facings which are in the state of plane stress and a thick shear deformable core. The amplitude of forced vibrations of the plate is reduced using symmetric couples of piezoelectric stiffeners subjected to out-of-phase dynamic voltages. Shape memory alloy stiffeners are used to reduce bending deformations. In the latter case, a desirable effect is achieved by activating the stiffeners on one side of the middle surface. Optimum design is considered based on the requirement of minimal transverse static or dynamic deflections subject to a constraint on the volume of smart stiffeners. The variables employed in the process of optimization are the ratios of the cross-sectional areas of the stiffeners in each direction to their respective spacings. It is shown, that, dependent on the load, materials, and geometry, optimum design can significantly reduce deflections, i.e. enhance the strength, of sandwich plates.     

A Gel‐Based Model of Selective Cell Motility: Implications for Cell Sorting,Diagnostics, and Screening

The ability to precisely control cell‐loaded material systems is essential for in vitro testing of novel therapeutics poised to advance to clinic. In this report, unique patterns of cell migration are devised into an in vitro gel‐in‐gel model for the purpose of obtaining cell response data to potentially therapeutic chemical agonists. The model consists of co‐cultures in a cell‐loaded microgel invading an acellular “sorting” gel. Material properties including biophysical and chemical compositions of the sorting gel are carefully controlled to guide a desired cell‐specific behavior, leading to massive tumor cell invasion by amoeboid migration mechanisms. Optical transparency enables straightforward and high‐throughput measurements of outgrowth response in the presence of either chemical and photoradiation therapy. Important dosing and drug sensitivity information are obtained with the gel‐in‐gel model using no more than a light microscope, without further need for arduous genomic or proteomic screening of the tissue samples.     

Injectability of Biosynthetic Hydrogels: Consideration for Minimally Invasive Surgical Procedures and 3D Bioprinting

Injectable hydrogels are often preferred when designing carriers for cell therapy or developing new bio-ink formulations. Biosynthetic hydrogels, which are a class of materials made with a hybrid design strategy, can be advantageous for endowing injectability while maintaining biological activity of the material. The chemical modification required to make these gels injectable by specific crosslinking pathways can be challenging and also make the hydrogels inhospitable to cells. Therefore, most efforts to functionalize biosynthetic hydrogel precursors toward injectability in the presence of cells try to balance between chemical and biological functionality, in order to preserve cell compatibility while addressing the injectability design challenges. Accordingly, hydrogel crosslinking strategies have evolved to include the use of photoinitiated “click” chemistry or bio-orthogonal reactions with rapid gelation kinetics and minimal cyto-toxicity required when working with cell-compatible hydrogel systems. With many new injectable biosynthetic materials emerging, their impact in cell-based regenerative medicine and bioprinting is also becoming more apparent. This review covers the main strategies that are used to endow biosynthetic polymers with injectability through rapid, cyto-compatible physical or covalent crosslinking and the main considerations for using the resulting injectable hydrogels in cell therapy, tissue regeneration, and bioprinting.     

Thermomechanical wrinkling and strength of sandwich panels with nanoscale or microscale randomly reinforced core

Abstract

Wrinkling represents one of the failure modes in sandwich structures, although in practical designs the loss of strength and global buckling often occur at lower compressive loads. However, the properties of both polymeric matrix in the facings as well as the polymeric core degrade under an elevated temperature. As a consequence, wrinkling that does not present a problem at the room temperature may become a dominant mode of failure at elevated temperatures. In this article, we suggest that a reinforcement of the core material with stiff random nanoscale or microscale reinforcements may alleviate wrinkling. The solution accounts for the thermal loading history and the effect of temperature on the stiffness of the materials of the core and facings. While nano or microscale reinforcements increase the capacity of the structure to resist wrinkling, the strength of the core may be compromised due to the presence of such inclusions in the core material. Accordingly, the residual stresses in the reinforced core are evaluated using a finite-element method and accounting for the effect of temperature on the properties and stresses. It is demonstrated that both wrinkling and the core strength analyses should account for the effect of temperature on the material properties.     

The league of SuperNets

The author proposes a major effort to transform the Internet into a league of SuperNets. Doing so offers the promise of revolutionary new business opportunities, and could save the emerging Web services technology area from a snarl of reliability and security problems. We can slash the costs of operating big networks, roll out new kinds of applications with real-time properties, and start to build other kinds of applications for purposes like controlling the restructured electrical power grid or managing military assets on a battlefield. Unfortunately, however, the proposal departs drastically from the way that the Internet is currently evolving. The technical side of the issue is likely to be the easy part; the problem centers on the politics of the Internet sector and the community that controls its future. Yet, the payoff could be so great that I want to argue for a community response. If we all get behind a common vision, we can make it a reality.     

Computing approximate blocking probabilities for a class ofall-optical networks

We study a class of all-optical networks using wavelength-division multiplexing (WDM) and wavelength routing, in which a connection between a pair of nodes in the network is assigned a path and a wavelength on that path. Moreover, on the links of that path no other connection can share the assigned wavelength. Using a generalized reduced load approximation scheme we calculate the blocking probabilities for the optical network model for two routing schemes: fixed routing and least loaded routing     

Response of spatially tailored structures to thermal loading

The paper presents the formulation and analysis of composite plates serving as STATs, i.e., spatially tailored advanced thermal structures where the distribution of the constituent phases varies throughout the surface as well as through the thickness. This is an extension of the well-known concept of functionally graded materials (FGM) and structures with the constituent phases varying only in the latter direction. As a result of two- or three-dimensional grading it is possible to optimize the response and properties of the structure providing multitask and multi-scale optimization. The response of plates with two- or three-dimensional grading to an arbitrary thermal loading is elucidated, including the conditions that result in thermal bending versus thermal instability.