Reviewing Our Goals in Theological Field Education

When students set clear goals for their learning in their learning covenants, recognizing where they are in their formation and where they need to be and taking into account their ministry context, better learning results. The students have a clear focus for their ministry and learning. I dare to believe that the same will be true for us. Sharpening the overall goals for our programs will lead to better learning. Then, when we take time to evaluate how we are doing, we will know where we want to be and if we have made it

Theological Reflective Practice: A Key Tool for Contemporary Ministry

The pace of modern ministry often leaves little time or space to plan or assess strategies already in motion or stop long enough to consider the implication of our pastoral actions. These demands work against the thoughtful integration of context, theology, and practice in ministry. The capacity for reflection is of growing importance given the complexity of ministry in an increasingly pluralistic world

Going outside the system: Gödel and the “I-it” structure of experience

It has often been argued that Gödel’s first incompleteness theorem has major implications for our understanding of the human mind. Gödel himself hoped that the results of his theorem, combined with Turning’s work on computers and phenomenological analysis, would establish that the human mind contains an element totally different from a finite combinatorial mechanism. Decades of attempts to establish this by reasoning about Gödel’s theorem and Turing’s work are now widely taken to be unsuccessful. The present article, in accord with Gödel’s suggestion, adds extended phenomenological analysis to the discussion. It also focuses on the “going outside the system” step central to Gödel’s method of proof, rather than on the implications of the theorem itself. Analysis of the “I-it” intentional structure, held by phenomenology to underlie all ordinary experience, yields a simple model that (i) resolves long-standing conceptual problems associated with the “I-it”, the most basic structure of phenomenology, (ii) clarifies the “going outside” step crucial to Gödel’s method of proof, (iii) avoids conceptual problems associated with this step, (iv) identifies the step as an instance of a natural pre-mathematical operation of ordinary thought, and (v) suggests that the step itself is intrinsically non-algorithmic. Logical analysis of role of this step in Gödel’s proof then shows, independently of phenomenological considerations, that anything (human or not) that can prove Gödel’s theorem soundly by his method cannot be entirely algorithmic. Further implications for the nature of the mind are then suggested

The self-excitation damping ratio: A chatter criterion for time-domain milling simulations

Regenerative chatter is known to be a key factor that limits the productivity of high speed machining. Consequently, a great deal of research has focused on developing predictive models of milling dynamics, to aid engineers involved in both research and manufacturing practice. Time-domain models suffer from being computationally intensive, particularly when they are used to predict the boundary of chatter stability, when a large number of simulation runs are required under different milling conditions. Furthermore, to identify the boundary of stability each simulation must run for sufficient time for the chatter effect to manifest itself in the numerical data, and this is a major contributor to the inefficiency of the chatter prediction process. In the present article, a new chatter criterion is proposed for time-domain milling simulations, that aims to overcome this draw-back by considering the transient response of the modeled behavior, rather than the steady-state response. Using a series of numerical investigations, it is shown that in many cases the new criterion can enable the numerical prediction to be computed more than five times faster than was previously possible. In addition, the analysis yields greater detail concerning the nature of the chatter vibrations, and the degree of stability that is observed

Vibration absorbers for chatter suppression: A new analytical tuning methodology

Vibration absorbers have been widely used to suppress undesirable vibrations in machining operations, with a particular emphasis on avoiding chatter. However, it is well known that for vibration absorbers to function effectively their stiffness and damping must be accurately tuned based upon the natural frequency of the vibrating structure. For general vibration problems, suitable tuning strategies were developed by Den Hartog and Brock over 50 years ago. However, the special nature of the chatter stability problem means that this classical tuning methodology is no longer optimal. Consequently, vibration absorbers for chatter mitigation have generally been tuned using ad hoc methods, or numerical or graphical approaches. The present article introduces a new analytical solution to this problem, and demonstrates its performance using time domain milling simulations. A 40-50% improvement in the critical limiting depth of cut is observed, compared to the classically tuned vibration absorber. © 2006 Elsevier Ltd. All rights reserved

The effect of Duffing-type non-linearities and Coulomb damping on the response of an energy harvester to random excitations

Linear energy harvesters can only produce useful amounts of power when excited close to their natural frequency. Due to the uncertain nature of ambient vibrations, it has been hypothesised that such devices will perform poorly in real-world applications. To improve performance, it has been suggested that the introduction of non-linearities into such devices may extend the bandwidth over which they perform effectively. In this study, a magnetic levitation device with non-linearities similar to the Duffing oscillator is considered. The governing equations of the device are formed in which the effects of friction are considered. Analytical solutions are used to explore the effect that friction can have on the system when it is under harmonic excitations. Following this, a numerical model is formed. A differential evolution algorithm is used alongside experimental data to identify the relevant parameters of the device. The model is then validated using experimental data. Monte Carlo simulations are then used to analyse the effect of coulomb damping and Duffing-type non-linearities when the device is subjected to broadband white noise and coloured noise excitations. </jats:p

Chatter, process damping, and chip segmentation in turning: A signal processing approach

An increasing number of aerospace components are manufactured from titanium and nickel alloys that are difficult to machine due to their thermal and mechanical properties. This limits the metal removal rates that can be achieved from the production process. However, under these machining conditions the phenomenon of process damping can be exploited to help avoid self-excited vibrations known as regenerative chatter. This means that greater widths of cut can be taken so as to increase the metal removal rate, and hence offset the cutting speed restrictions that are imposed by the thermo-mechanical properties of the material. However, there is little or no consensus as to the underlying mechanisms that cause process damping. The present study investigates two process damping mechanisms that have previously been proposed in the machining literature: the tool flank/workpiece interference effect, and the short regenerative effect. A signal processing procedure is employed to identify flank/workpiece interference from experimental data. Meanwhile, the short regenerative model is solved using a new frequency domain approach that yields additional insight into its stabilising effect. However, analysis and signal processing of the experimentally obtained data reveals that neither of these models can fully explain the increases in stability that are observed in practice. Meanwhile, chip segmentation effects were observed in a number of measurements, and it is suggested that segmentation could play an important role in the process-damped chatter stability of these materials