The Dynamics of Knowledge-intensive Sectors' Knowledge Base: Evidence from Biotechnology and Telecommunications

In this paper, we present a methodology to represent and measure knowledge which takes into account knowledge heterogeneity and its sectoral level theoretical and empirical implications in knowledge intensive environments. We draw on work on recombinant knowledge, extending the approach to include the way the dynamics of technological knowledge creation evolves according to a life cycle; testing the existence of concepts such as technological paradigms; mapping the characteristics of the search process in the phases of exploration and exploitation during this technology life cycle and detecting the differences in sectoral evolution that can be explained by the properties of the knowledge base. We use European Patent Office data (1981–2005) to propose some operational metrics for the knowledge base and its evolution in two knowledge intensive sectors: biotechnology and telecommunications. Our empirical results show that there are interesting and meaningful differences across sectors, which are linked to the different phases of the technology life cycles.     

Gold Nanoparticle‐Based Sensors Activated by External Radio Frequency Fields

A novel molecular beacon (a nanomachine) is constructed that can be actuated by a radio frequency (RF) field. The nanomachine consists of the following elements arranged in molecular beacon configuration: a gold nanoparticle that acts both as quencher for fluorescence and a localized heat source; one reporter fluorochrome, and; a piece of DNA as a hinge and recognition sequence. When the nanomachines are irradiated with a 3 GHz RF field the fluorescence signal increases due to melting of the stem of the molecular beacon. A control experiment, performed using molecular beacons synthesized by substituting the gold nanoparticle by an organic quencher, shows no increase in fluorescence signal when exposed to the RF field. It may therefore be concluded that the increased fluorescence for the gold nanoparticle‐conjugated nanomachines is not due to bulk heating of the solution, but is caused by the presence of the gold nanoparticles and their interaction with the RF field; however, existing models for heating of gold nanoparticles in a RF field are unable to explain the experimental results. Due to the biocompatibility of the construct and RF treatment, the nanomachines may possibly be used inside living cells. In a separate experiment a substantial increase in the dielectric losses can be detected in a RF waveguide setup coupled to a microfluidic channel when gold nanoparticles are added to a low RF loss liquid. This work sheds some light on RF heating of gold nanoparticles, which is a subject of significant controversy in the literature.     

Stationary straight cracks in quasicrystals

Stationary straight cracks in quasicrystals in linear elastic setting are under scrutiny. The analysis is developed by using Stroh formalism which is modified to account for a totally degenerate eigenvalue problem: in fact, the fundamental matrix of the governing equations of motion admits a repeated eigenvalue corresponding to a single eigenvector. Cases of a semi-infinite rectilinear crack loaded along its margins and a crack of finite length under remote loading conditions are considered. Standard and phason stresses display square-root singularities at crack tip. The latter stresses represent peculiar microstructural inner actions occurring in quasicrystals and are determined by rearrangements assuring quasi-periodicity of the atomic tiling—modes described by a vector field, called phason field, collecting the local degrees of freedom exploited by the atoms within the material elements. Energy release rate increases with the coupling parameter between displacement and phason fields.     

Synthesis and characterization of 4H-SiC on C-plane sapphire by C60 and Si molecular beam epitaxy

4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000-1100 °C) with relative high deposition rate by using fullerene (C₆₀) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼ 165 nm/h was achieved.     

Predicting the size-dependent tissue accumulation of agents released from vascular targeted nanoconstructs

Vascular targeted nanoparticles have been developed for the delivery of therapeutic and imaging agents in cancer and cardiovascular diseases. However, at authors’ knowledge, a comprehensive systematic analysis on their delivery efficiency is still missing. Here, a computational model is developed to predict the vessel wall accumulation of agents released from vascular targeted nanoconstructs. The transport problem for the released agent is solved using a finite volume scheme in terms of three governing parameters: the local wall shear rate $S$ , ranging from $10$ to $200\,\mathrm{s}^{-1}$ ; the wall filtration velocity $V_f$ , varying from $10^{-9}$ to $10^{-7}\,\mathrm{m}/\mathrm{s}$ ; and the agent diffusion coefficient $D$ , ranging from $10^{-12}$ to $10^{-9}\,\mathrm{m}^2/\mathrm{s}$ . It is shown that the percentage of released agent adsorbing on the vessel walls in the vicinity of the vascular targeted nanoconstructs reduces with an increase in shear rate $S$ , and with a decrease in filtration velocity $V_f$ and agent diffusivity $D$ . In particular, in tumor microvessels, characterized by lower shear rates ( $S = 10\,\mathrm{s}^{-1}$ ) and higher filtration velocities ( $V_f=10^{-7}\,\mathrm{m}/\mathrm{s}$ ), an agent with a diffusivity $D = 10^{-12}\,\mathrm{m}^2/\mathrm{s}$ (i.e. a 50 nm particle) is predicted to deposit on the vessel wall up to $30~\%$ of the total released dose. Differently, drug molecules, exhibiting a smaller size and much higher diffusion coefficient ( $D = 10^{-9}\,\mathrm{m}^2/\mathrm{s}$ ), are predicted to accumulate up to $70~\%$ . In healthy vessels, characterized by higher $S$ and lower $V_f$ , the largest majority of the released agent is redistributed directly in the circulation. These data suggest that drug molecules and small nanoparticles only can be efficiently released from vascular targeted nanoconstructs towards the diseased vessel walls and tissue.     

A revised virtual crack closure technique for physically consistent fracture mode partitioning

The virtual crack closure technique (VCCT) is a well-established method for computing the energy release rate when analysing fracture problems via the finite element method. For mixed-mode fracture problems, the VCCT is also commonly used to partition the fracture modes, i.e. to determine the energy release rate contributions related to the three classical fracture modes. A perhaps little known fact, however, is that in some circumstances the standard VCCT predicts physically inconsistent, negative values for the modal contributions to the energy release rate. Focusing on I/II mixed-mode problems, this paper presents a revised VCCT which furnishes a physically consistent partitioning of fracture modes by associating the mode I and II contributions to the amounts of work done in a suitably defined two-step process of closure of the virtually extended crack. Deeper investigation pinpoints the origins of the physically inconsistent predictions of the standard VCCT in the lack of energetic orthogonality between the crack-tip force components used to compute the modal contributions. Further insight into the problem is offered by a geometric construction, which introduces the ‘ellipse of crack-tip flexibility’. In closing, the phenomena of contact, interpenetration, and friction between the crack surfaces are briefly touched upon.     

On the Presence of the Out–of–Plane Singular Mode Induced by Plane Loading With K<Subscript>II</Subscript> = K<Subscript>I</Subscript> = 0

Previous studies by a number of researchers demonstrated that in the case of a plane crack subjected to shear loading conditions characterized by a remote stress intensity factor, K_II, a three-dimensional singular mode (called mode O or out-of-plane mode) develops at the crack tip. This singular mode occurs due to the primary shear loading and Poisson’s effect. Similar to mode III, the O-mode is associated with the transverse shear stress components. Recent theoretical and numerical studies have also demonstrated a strong presence of this singular mode in plates weakened by pointed V-notches. Therefore, it was suggested that O-mode can play an important role in fracture initiation, particularly at large opening angles (above 102.6°) when the applied mode II is non-singular.