Analysis of Selective Laser Sintering print parameter modelling methodologies for energy input minimisation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Mechatronics at Massey University, Albany, New Zealand

Additive Manufacturing (AM) is the name given to a series of processes used to create solids, layer upon layer, from 3 Dimensional (3D) models. As AM experiences rapid growth there exists an opportunity for Selective Laser Sintering (SLS) to expand into markets it has not previously accommodated. One of the ways SLS can accomplish this is by expanding the range of materials that can be processed into useful products, as currently only a small number of materials are available when compared to other AM technologies. One of the biggest barriers to the adoption of materials is the danger inherent to high-energy processes such as SLS. The aim of this research was to identify opportunities to improve current methods for modelling the relationship between material specifications, and printing parameters. This was achieved by identifying existing models used to determine printing parameters for a new material, identifying weaknesses in current modelling processes, conducting experimentation to explore the validity of these weaknesses, and exploring opportunities to improve the model to address these weaknesses. The current models to determine printer parameters to achieve successful sintering include both the Sintering Window (SW) and the Energy Melt Ratio (EMR). These two models are complementary, and both are required to establish all common print parameters. They include both thermal and physical powder properties, but do not include any optical properties. This is significant because the nature of the SLS printing process relies on concentrated delivery of laser energy to achieve successful sintering. Analysis of two similar polyamide powders, one black and one white, identified that the two powders were similar thermally and physically, which meant the models predicted that they should both sinter successfully utilizing the same set of print parameters. Results of the experimental trials showed that no trials involving the white powder sintered successfully, and trials involving the black powder suffered from issues with either insufficient energy to successfully remove parts without damage, or excessive energy causing excess powder to bond to the part. Further experimentation was carried out to investigate the differences in optical properties using Fourier Transform Infrared Spectroscopy (FTIR) and Spectrofluorophotometry. FTIR revealed that there was a difference in absorption as a material property, indicating that differences in laser energy absorption could explain the results seen in the trials. Spectrofluorophotometry revealed minimal differences in fluorescence of the powders, suggesting it an unlikely source of energy loss. Future work is recommended to research a standardised form of testing setup that can be used to categorize the reflectance of a material, as current work relies on proprietary experimental setups. Finding methods of classifying the laser absorption that is easily available to operators would enable refinement of the EMR equation to reflect the energy losses during printing, and remove another barrier for adoption of new materials

Critique of network management systems and their practicality

Networks have become an integral part of the computing landscape, forming a global interconnection of a staggering number of heterogeneous systems and services. Current research focuses on policy based management and autonomous systems and involves the utilisation of very different languages and technologies in concert. This paper examines four current proposals for autonomous network management and analyses them using architectural modelling, against a measure of practicality, as expressed by scalability, reliability and maintainability. © 2010 IEEE

Studies in the pyrolysis of some benzyl bromides

The work described in subsequent pages arose from certain difficulties in the current knowledge of the bond dissociation energies (D) of compounds of the type C₆H₅CH₂-X. For the reaction C₆H₅CH₂-X → C₆H₅CH₂ - + X – D k.cals. (1) we can write D(C₆H₅CH₂-X) = ΔHf(C₆H₅CH₂-) + ΔHf(X-) - ΔHf(C₆H₅CH₂-X) (2) where ΔHf is the heat of formation of a chemical entity. It has been the task of many recent researches to evaluate (D) for different compounds. Since the last two terms in the thermochemical equation are often known, a determination of D(C₆H₅CH₂-X) permits the heat of formation of the benzyl radical to be evaluated. It is obviously necessary that a consistent scheme should produce a single value for ΔHf(C₆H₅CH₂-) and one which is independent of the nature of X. Early work in this field by Szwarc had produced such agreement, but recent more detailed work, threw doubt on his findings for D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D(C₆H₅CH₂-H). Since his values were claimed to be cross-checked through (2), it was clear that his work on the determination of D (C₆H₅CH₂-Br)⁴ might also be in error, for it was claimed to agree with his toluene results. The pyrolysis of bromides in the presence of excess toluene has been the main kinetic practised by Szwarc, and benzyl bromide is one of many bromides which have been investigated by him. In theory the method requires that the primary dissociation R – Br → R- + Br- (3) shall be followed by the inhibition of secondary processes by reactions R- + C₆H₅CH₃ → RH + C₆H₅CH₂- (4) Br- + C₆H₅Ch₃ → HBr + C₆H₅CH₂- (5) 2C₆H₅CH₂- → C₆H₅CH₂CH₂C₆H₅ (6) Swarc claimed that the method showed the decompositions to have a first order dependence on RBr concentration, and that the temperature dependence of the velocity constant followed an equation log₁₀k = log₁₀A – E/4.57T for the most extensively investigated cases. He laid stress on the fact that the values of A he obtained were close to 10¹³ sec⁻¹, which is the expected value for a first order reaction, and hence that he was observing the dissociation process (3). As usual in this field the energy of activation E was taken as the bond dissociation energy. Justification for this assumption will be considered in the next section. Benzyl bromide was one of the compounds Szwarc investigated more extensively and the results conformed with the above generalisations. In case of several other bromides the published results do not justify his assumption that the temperature independent factor would be found to have the value 10¹³ sec⁻¹ under a more exhaustive scrutiny. These items prompted a re-examination of the whole toluene carrier gas technique as applied to benzyl bromide. In one form of this technique, and probably the most widely used version, a stream of toluene vapour entrains the halide Rbr by passage over the surface of the latter. Although temperatures above the dew point of toluene were advocated by Szwarc, elementary considerations suggested that solution of toluene in the Rbr could not be prevented by this and uniformity of entrainment would suffer greatly. Varying concentrations of reactant would result and kinetic deductions would be invalidated. As described in later pages, some simple experiments showed this suspicion about the toluene carrier gas technique to be correct. In view of this end and the chemical uncertainties quoted earlier, there seemed a need to re-investigate the pyrolysis of benzyl bromide fairly extensively. In later pages the details of such work are given together with work on the chlorobenzyl bromides. Before dealing with the practical aspects of the work a short survey of the relevant previous investigations and kinetic techniques used is given

Retinotectal circuitry of larval zebrafish is adapted to detection and pursuit of prey

Retinal axon projections form a map of the visual environment in the tectum. A zebrafish larva typically detects a prey object in its peripheral visual field. As it turns and swims towards the prey, the stimulus enters the central, binocular area, and seemingly expands in size. By volumetric calcium imaging, we show that posterior tectal neurons, which serve to detect prey at a distance, tend to respond to small objects and intrinsically compute their direction of movement. Neurons in anterior tectum, where the prey image is represented shortly before the capture strike, are tuned to larger object sizes and are frequently not direction-selective, indicating that mainly interocular comparisons serve to compute an object's movement at close range. The tectal feature map originates from a linear combination of diverse, functionally specialized, lamina-specific, and topographically ordered retinal ganglion cell synaptic inputs. We conclude that local cell-type composition and connectivity across the tectum are adapted to the processing of locationdependent, behaviorally relevant object features

A design of experiments (DoE) approach to optimize cryogel manufacturing for tissue engineering applications

Marine origin polymers represent a sustainable and natural alternative to mammal counterparts regarding the biomedical application due to their similarities with proteins and polysaccharides present in extracellular matrix (ECM) in humans and can reduce the risks associated with zoonosis and overcoming social- and religious-related constraints. In particular, collagen-based biomaterials have been widely explored in tissue engineering scaffolding applications, where cryogels are of particular interest as low temperature avoids protein denaturation. However, little is known about the influence of the parameters regarding their behavior, i.e., how they can influence each other toward improving their physical and chemical properties. Factorial design of experiments (DoE) and response surface methodology (RSM) emerge as tools to overcome these difficulties, which are statistical tools to find the most influential parameter and optimize processes. In this work, we hypothesized that a design of experiments (DoE) model would be able to support the optimization of the collagen-chitosan-fucoidan cryogel manufacturing. Therefore, the parameters temperature (A), collagen concentration (B), and fucoidan concentration (C) were carefully considered to be applied to the Boxâ Behnken design (three factors and three levels). Data obtained on rheological oscillatory measurements, as well as on the evaluation of antioxidant concentration and adenosine triphosphate (ATP) concentration, showed that fucoidan concentration could significantly influence collagen-chitosan-fucoidan cryogel formation, creating a stable internal polymeric network promoted by ionic crosslinking bonds. Additionally, the effect of temperature significantly contributed to rheological oscillatory properties. Overall, the condition that allowed us to have better results, from an optimization point of view according to the DoE, were the gels produced at −80ºC and composed of 5% of collagen, 3% of chitosan, and 10% fucoidan. Therefore, the proposed DoE model was considered suitable for predicting the best parameter combinations needed to develop these cryogels.This research was funded by the Portuguese Foundation for Science and Technology (FCT) for Ph.D. fellowship (D.N.C.) under the scope of the doctoral program Tissue Engineering, Regenerative Medicine and Stem Cells, ref. PD/BD/143044/2018, for postdoctoral fellowship (C.G.), ref. SFRH/BPD/94277/2013. This work has been partially funded by ERDF under the scope of the Atlantic Area Program through project EAPA_151/2016 (BLUEHUMAN)

Common carp (Cyprinus carpio L.) alters its feeding niche in response to changing food resources: direct observations in simulated ponds

We used customized fish tanks as model fish ponds to observe grazing, swimming, and conspecific social behavior of common carp (Cyprinus carpio) under variable food-resource conditions to assess alterations in feeding niche. Different food and feeding situations were created by using only pond water or pond water plus pond bottom sediment or pond water plus pond bottom sediment and artificial feeding. All tanks were fertilized twice, prior to stocking and 2 weeks later after starting the experiment to stimulate natural food production. Common carp preferred artificial feed over benthic macroinvertebrates, followed by zooplankton. Common carp did not prefer any group of phytoplankton in any treatment. Common carp was mainly benthic in habitat choice, feeding on benthic macroinvertebrates when only plankton and benthic macroinvertebrates were available in the system. In the absence of benthic macroinvertebrates, their feeding niche shifted from near the bottom of the tanks to the water column where they spent 85% of the total time and fed principally on zooplankton. Common carp readily switched to artificial feed when available, which led to better growth. Common carp preferred to graze individually. Behavioral observations of common carp in tanks yielded new information that assists our understanding of their ecological niche. This knowledge could be potentially used to further the development of common carp aquaculture

Advanced polymeric membranes as biomaterials based on marine sources envisaging the regeneration of human tissues

The self-repair capacity of human tissue is limited, motivating the arising of tissue engineering (TE) in building temporary scaffolds that envisage the regeneration of human tissues, including articular cartilage. However, despite the large number of preclinical data available, current therapies are not yet capable of fully restoring the entire healthy structure and function on this tissue when significantly damaged. For this reason, new biomaterial approaches are needed, and the present work proposes the development and characterization of innovative polymeric membranes formed by blending marine origin polymers, in a chemical free cross-linking approach, as biomaterials for tissue regeneration. The results confirmed the production of polyelectrolyte complexes molded as membranes, with structural stability resulting from natural intermolecular interactions between the marine biopolymers collagen, chitosan and fucoidan. Furthermore, the polymeric membranes presented adequate swelling ability without compromising cohesiveness (between 300 and 600%), appropriate surface properties, revealing mechanical properties similar to native articular cartilage. From the different formulations studied, the ones performing better were the ones produced with 3 % shark collagen, 3% chitosan and 10% fucoidan, as well as with 5% jellyfish collagen, 3% shark collagen, 3% chitosan and 10% fucoidan. Overall, the novel marine polymeric membranes demonstrated to have promising chemical, and physical properties for tissue engineering approaches, namely as thin biomaterial that can be applied over the damaged articular cartilage aiming its regeneration.The authors would like to acknowledge the Portuguese Foundation of Science and Technology (FCT) for Ph.D. fellowship (D. N. Carvalho, under the scope of doctoral program TERM&SC, ref. PD/BD/143044/2018), post-doctoral fellowship (L.C. Rodrigues, ref. SFRH/BPD/93697/2013) and research project with ref. PTDC/CTM-CTM/29813/2017-(POCI-01-0145-FEDER-029813). The authors also thank Jellagen Ltd. (UK) for the provision of purified jellyfish collagen and Julio Maroto (Fundación CETMAR, Vigo, Spain) for the kind offer of the squid pens for chitosan production.This work has been partially funded by ERDF under the scope of the Atlantic Area Program through project EAPA_151/2016 (BLUEHUMAN)

Motivation for or from bilingual education? A comparative study of learner views in the Netherlands

Teaching and Teacher Learning (ICLON

Mammals of Aransas County, Texas

p. 165-198 : map ; 24 cm.Includes bibliographical references