Digital micromirror devices for laser-based manufacturing

Digital Micromirror Devices (DMDs), containing arrays of around one million individually-controllable ~10µm square mirrors, provide an extremely cost-effective and practical method to modulate the spatial beam profile of a pulsed laser source for both additive and subtractive laser processing and printing. When demagnified by a factor of ~100 in one dimension (hence ~10,000 in area) a ~1mJ/cm2 laser pulse reflected from the mirrors on the DMD surface that are switched to the 'on' position, attains a fluence of ~10J/cm2 at the workpiece, which is more than sufficient to ablate most materials of interest to the laser-manufacturing community. More familiar in the context of high values of magnification by the laser projection industry, reversing the role to use them for equally high values of demagnification opens up a wealth of possibilities for ablation, multiphoton polymerization, security marking and fabrication of features that perhaps surprisingly can be well below the wavelength of the laser used. Of key relevance is that very high-resolution patterning can be achieved by a single laser pulse, and step-and-repeat processes, when combined with the refresh rates of the DMD pattern that are currently at the 30kHz level, open up the possibility of processing areas of up to 1cm2 per second with micron-scale resolution where each ~100µm x 100µm area patterned per pulse can display arbitrary pixelated content. We will discuss the application of DMD-baser laser processing to the following areas of interest to the laser-manufacturing community

Values and value in design

Relatively little is known about how concepts of human values and value interact during the construction design process. Whilst researchers of value management have expounded in this context upon the complexity of the design process, problem-solving and sense-making, little is said about the alignment and reconciliation of multiple-stakeholder values and value judgements. An abductive reasoning and a grounded theory approach was adopted that iterated between literature and empirical observation to obtain new insights. The initial phase created a values and value framework and Value in Design (VALiD) approach through seven unstructured interviews, a design workshop, four Schwartz Values Surveys (with 545 participants) and 55 semi-structured interviews. The values and value parts were then separately implemented, developed and validated through action research on five live education capital projects, involving over 250 participants. Subsequently, a middle-range theory of values and value is proposed through theoretical triangulation. This draws on seven related theories to provide greater explanatory pluralism, uncover hidden phenomena and enable convergence. The research findings are significant in focusing soft value management on underlying stakeholder values and subjective value judgements. A more nuanced and intertwined relationship between stakeholder values, attitudes, behaviours and qualities during the design process is offered that promotes compromise and sense-making

Kinetics of reduction of a Resazurin-based photocatalytic activity ink

The kinetics of reduction of a Resazurin, Rz,-based photocatalyst activity indicator ink, paii, on a commercial sample of self-cleaning glass, Activ™ is examined; the latter has ca. a 15nm compact coating of anatase TiO2 which serves as the active photocatalyst layer. The rate of dye reduction is reduced significantly by the presence of ambient O2. In the absence of O2, the measured change in film absorbance due to Rz, d Δ Abs/dt, was found to be independent of both [Rz] and film thickness, b. It is shown that this translates to the rate of dye reduction, d[Rz]/dt, being independent of the concentration of the Rz in the ink film, [Rz], and inversely proportional to film thickness, b. The observed kinetics are rationalised in terms of a kinetic model in which the rate determining step is the reduction of photocatalyst surface-adsorbed Rz by photo-generated surface electrons, with all photocatalyst surface sites occupied by Rz. Further work suggests that, if the kinetics of the photocatalysed reduction of the Rz paii were diffusion-controlled, then the decay in [Rz] would be first order and dependent upon b-2

Nanomaterial structure determination using XUV diffraction

Diffraction using coherent XUV radiation is used to study the structure of nanophotonic materials, in this case an ordered array of 196nm spheres. Crystal structure and defects are visible, and the nanomaterial dielectric constant determined

Governance, cooperation and coordination in large inter-organisational project networks: a viable system perspective

Purpose: This study aims to further the understanding of multi-level analysis in inter-organisational relationships by investigating the interplay of governance, cooperation and coordination in inter-organisational projects (IOPs) on sub-system and project levels. Design/methodology/approach: The authors use the Viable Systems Model as a framework to analyse inter-organisational project governance, cooperation and coordination by adopting a multiple-case study. Findings: The findings illustrate how governance and coordination mechanisms exhibit a filter-down effect on lower sub-systems while cooperation influence is confined within each sub-system. While remarking the importance of specific sub-systems on the overall project performance, the interplay of governance, cooperation and coordination across sub-systems appears to be complex, with governance influencing cooperation and coordination, whereas cooperation and coordination influence each other with an incremental effect. Originality/value: This study defines two propositions that explain how multiple levels of analysis (project and sub-systems) can support the governance of large inter-organisational projects. The authors elaborate theory on the interplay of inter-organisational project governance, cooperation and coordination

Organizational configurations of temporary multi-organizations delivering megaprojects: Insights from five megaprojects in China

Temporary multi-organizations (TMOs) are individual temporary client organizations that are jointly established and owned by multiple shareholders to undertake the predefined purposes in megaproject delivery. We conduct in-depth analysis of the organizational configurations of TMOs through a multi-case study of five megaprojects in China. We believe establishing a TMO is a multi-factorial decision and propose two types of TMO – integrated and independent – based on distinct motives for their establishment. Different TMO structuring processes of integrated and independent TMOs further give rise to distinctive patterns of TMO configuration. Based on the analysis of TMOs’ intra- and inter-organizational configurations, two patterns of organizational configuration – tightly- and loosely-coupled networks – emerge inductively from the data, and we highlight the dynamic nature of TMO configuration. This paper offers guidance to practitioners on designing and structuring TMOs and dealing with intra- and inter-organizational relations

Transport processes in wavy walled channels

Due to their complex shape, wavy walled geometries are capable of inducing unsteady and even chaotic flows at low Reynolds numbers. The convective effects of the unsteady motion significantly enhances heat and mass transport in the fluid. Because of this, wavy walled channels are commonly used in applications such as heat exchangers. Despite their common use however, a systematic investigation of the dependence of the fluid flow and heat transfer on the geometric parameters of the channel does not exist. In many heat exchanger applications, the working fluid contains suspended particulates. When cooling these particle laden flows, thermophoretic forces induced on the particles by thermal gradients in the fluid result in their deposition along the cooler walls. This process, known as fouling, leads to the formation of a porous layer, which reduces the effectiveness of the cooler. One application in which fouling is a significant issue is exhaust gas recirculation (EGR) used in diesel and gasoline engines to reduce nitrogen oxides (NOx) emissions. The heat exchanger used in this process experiences rapid degradation in performance from fouling caused by the high concentration of soot particles entrained in the exhaust gas. Recently, engine manufacturers have begun using wavy walled heat exchangers as empirical evidence suggests that this geometry is less prone to fouling. However, a limited amount of research has been performed to understand how this geometry reduces fouling and the dependence of this reduction on the geometric parameters of the channel. In this work we use computational modeling to investigate the effect of asymmetric wavy walled channel geometries on laminar fluid flow and heat/mass transfer. To this end, we develop a computational model based on the lattice Boltzmann method, explicit finite differences and Brownian dynamics to simulate unsteady viscous flow and heat/mass transport in wavy walled channel geometries and use this model to systematically examine these processes. Furthermore, we investigate the formation of deposit layers resulting from thermophoretic deposition of particulates transported by the flow onto the channel walls and probe how this process can be mitigated using a wavy wall geometry. The results from our studies are important for designing laminar heat/mass exchangers utilizing unsteady flows for enhancing transport processes. Additionally these results provide valuable information necessary to develop heat exchangers which are less prone to fouling.Ph.D