Selective Heat Sintering Versus Laser Sintering: Comparison of Deposition Rate, Process Energy Consumption and Cost Performance

The Selective Heat Sintering (SHS) process has become available as a low cost alternative to Laser Sintering (LS) for the additive deposition of polymer objects. While both processes belong to the powder bed fusion variant of Additive Manufacturing (AM) technology, their operating principles vary significantly: SHS employs a thermal print head to selectively fuse material powder, whereas the LS approach utilizes a laser beam coupled with a galvanometer. Based on a series of build experiments, this research compares these technology variants along three dimensions of process efficiency: deposition rate (measured in cm³/h), specific process energy consumption (MJ/kg) and specific cost ($/cm³). To ensure that both platforms are assessed under the condition of efficient technology utilization, an automatic build volume packing algorithm is employed to configure a subset of build experiments. Beyond reporting absolute and relative process performance, this paper additionally investigates how sensitive the compared processes are to a variation in the degree of capacity utilization and discusses the application of different levels of indirect cost in models of low cost AM.Mechanical Engineerin

How Can Material Jetting Systems Be Upgraded for More Efficient Multi-Material Additive Manufacturing

Multi-material Additive Manufacturing (AM) platforms are able to build up components from multiple materials in a single layer-by-layer process. It is expected that this capability will enable the manufacturing of functional structures within products, such as conductive tracks or optical pathways, resulting in radically novel products with unprecedented degrees of functional density. An important variant of commercially available multi-material AM technology is material jetting, which is currently in commercial use for the manufacture of prototypes and design studies. This paper presents a detailed process model of build-time, energy consumption and production cost for the Stratasys Objet 260 Connex system, analyzing the contemporaneous deposition of two different types of photopolymers (Veroclear RGD810 and Tangoblack FLX973). By using this process model to anticipate the effects of various upgrades to the investigated system, such as a larger build volume and a higher deposition speed, this forward-looking paper explores pathways to enhancing the value proposition of such multi-material systems through incremental technology improvement.Mechanical Engineerin

Energy Inputs to Additive Manufacturing: Does Capacity Utilization Matter?

The available additive manufacturing (AM) platforms differ in terms of their operating principle, but also with respect to energy input usage. This study presents an overview of electricity consumption across several major AM technology variants, reporting specific energy consumption during the production of dedicated test parts (ranging from 61 to 4849 MJ per kg deposited). Applying a consistent methodology, energy consumption during single part builds is compared to the energy requirements of full build experiments with multiple parts (up to 240 units). It is shown empirically that the effect of capacity utilization on energy efficiency varies strongly across different platforms.Mechanical Engineerin

Small scale structure and mixing at the edge of the Antarctic vortex

Small scale correlations and patterns in the chemical tracers measured from the NASA ER-2 aircraft in the 1987 AAOE campaign can be used to investigate the structure of the edge of the polar vortex and the chemically perturbed region within it. Examples of several types of transport processes can be found in the data. Since ClO and O3 have similar vertical gradients and opposite horizontal gradients near the chemically perturbed region, the correlation between ClO and O3 can be used to study the extent of horizontal transport at the edge of the chemically perturbed region. Horizontal transport dominates the correlation for a latitude band up to 4 degrees on each side of the boundary. This implies a transition zone containing a substantial fraction of the mass of the total polar vortex. Similar horizontal transport can be seen in other tracers as well. It has not been possible to distinguish reversible transport from irreversible mixing. One manifestation of the horizontal transport is that the edge of the chemically perturbed region is often layered rather than a vertical curtain. This can be seen from the frequent reversed vertical gradients of NO2, caused by air with high NO2 overlapping layers with lower mixing ratios. Water and NO2 are positively correlated within the chemically perturbed region. This is the opposite sign to the correlation in the unperturbed stratosphere. The extent of the positive correlation is too great to be attributed solely to horizontal mixing. Instead, it is hypothesized that dehydration and descent are closely connected on a small scale, possibly due to radiative cooling of the clouds that also cause ice to fall to lower altitudes

Temporal trends and transport within and around the Antarctic polar vortex during the formation of the 1987 Antarctic ozone hole

During AAOE in 1987 an ER-2 high altitude aircraft made twelve flights out of Punta Arenas, Chile (53 S, 71 W) into the Antarctic polar vortex. The aircraft was fitted with fast response instruments for in situ measurements of many trace species including O3, ClO, BrO, NO sub y, NO, H2O, and N2O. Grab samples of long-lived tracers were also taken and a scanning microwave radiometer measured temperatures above and below the aircraft. Temperature, pressure, and wind measurements were also made on the flight tracks. Most of these flights were flown to 72 S, at a constant potential temperature, followed by a dip to a lower altitude and again assuming a sometimes different potential temperature for the return leg. The potential temperature chosen was 425 K (17 to 18 km) on 12 of the flight legs, and 5 of the flight legs were flown at 450 K (18 to 19 km). The remaining 7 legs of the 12 flights were not flown on constant potential temperature surfaces. Tracer data have been analyzed for temporal trends. Data from the ascents out of Punta Arenas, the constant potential temperature flight legs, and the dips within the vortex are used to compare tracer values inside and outside the vortex, both with respect to constant potential temperature and constant N2O. The time trend during the one-month period of August 23 through September 22, 1987, shows that ozone decreased by 50 percent or more at altitudes form 15 to 19 km. This trend is evident whether analyzed with respect to constant potential temperature or constant N2O. The trend analysis for ozone outside the vortex shows no downward trend during this period. The analysis for N2O at a constant potential temperature indicates no significant trend either inside or outside the vortex; however, a decrease in N2O with an increase in latitude is evident

Predicting phase resetting due to multiple stimuli

We generalized the phase resetting curve (PRC) to a more realistic case of neural oscillators receiving two or more inputs per cycle. The PRC tabulates the transient change in the firing period of a neuron due to an external perturbation, such as a presynaptic stimulus. We used a conductance-based model neuron to estimate experimentally the two-stimulus PRC and compared the results against our mathematical prediction based on the assumption of instantaneous recurrent stimulation. Within the limits of the recurrent stimulation assumptions, we found that the newly introduced prediction for the two-stimulus PRC matched experimental measurements. Our new results open the possibility of a more realistic approach to predicting phase-locked modes in neural networks, such as the synchronous activity of large networks during epileptic seizures

Mn Interstitial Diffusion in (Ga,Mn)As

We present a combined theoretical and experimental study of the ferromagnetic semiconductor (Ga,Mn)As which explains the remarkably large changes observed on low temperature annealing. Careful control of the annealing conditions allows us to obtain samples with ferromagnetic transition temperatures up to 159 K. Ab initio calculations, and resistivity measurements during annealing, show that the observed changes are due to out-diffusion of Mn interstitials towards the surface, governed by an energy barrier of about 0.7-0.8 eV. The Mn interstitial is a double donor resulting in compensation of charge carriers and suppression of ferromagnetism. Electric fields induced by high concentrations of substitutional Mn acceptors have a significant effect on the diffusion.Comment: 5 pages, 4 figures, submitted to Physical Review Letter

Large-scale variations in ozone and polar stratospheric clouds measured with airborne lidar during formation of the 1987 ozone hole over Antarctica

A joint field experiment between NASA and NOAA was conducted during August to September 1987 to obtain in situ and remote measurements of key gases and aerosols from aircraft platforms during the formation of the ozone (O3) hole over Antarctica. The ER-2 (advanced U-2) and DC-8 aircraft from the NASA Ames Research Center were used in this field experiment. The NASA Langley Research Center's airborne differential absorption lidar (DIAL) system was operated from the DC-8 to obtain profiles of O3 and polar stratospheric clouds in the lower stratosphere during long-range flights over Antarctica from August 28 to September 29, 1987. The airborne DIAL system was configured to transmit simultaneously four laser wavelengths (301, 311, 622, and 1064 nm) above the DC-8 for DIAL measurements of O3 profiles between 11 to 20 km ASL (geometric altitude above sea level) and multiple wavelength aerosol backscatter measurements between 11 to 24 km ASL. A total of 13 DC-8 flights were made over Antarctica with 2 flights reaching the South Pole. Polar stratospheric clouds (PSC's) were detected in multiple thin layers in the 11 to 21 km ASL altitude range with each layer having a typical thickness of less than 1 km. Two types of PSC's were found based on aerosol backscattering ratios: predominantly water ice clouds (type 2) and clouds with scattering characteristics consistent with binary solid nitric acid/water clouds (type 1). Large-scale cross sections of O3 distributions were obtained. The data provides additional information about a potentially important transport mechanism that may influence the O3 budget inside the vortex. There is also some evidence that strong low pressure systems in the troposphere are associated with regions of lower stratospheric O3. This paper discusses the spatial and temporal variations of O3 inside and outside the polar vortex region during the development of the O3 hole and relates these data to other measurements obtained during this field experiment

Development of bone marrow lesions is associated with adverse effects on knee cartilage while resolution is associated with improvement - a potential target for prevention of knee osteoarthritis: a longitudinal study

INTRODUCTION: To examine the relationship between development or resolution of bone marrow lesions (BMLs) and knee cartilage properties in a 2 year prospective study of asymptomatic middle-aged adults. METHODS: 271 adults recruited from the Melbourne Collaborative Cohort Study, underwent a magnetic resonance imaging scan (MRI) of their dominant knee at baseline and again approximately 2 years later. Cartilage volume, cartilage defects and BMLs were determined at both time points. RESULTS: Among 234 subjects free of BMLs at baseline, 33 developed BMLs over 2 years. The incidence of BMLs was associated with progression of tibiofemoral cartilage defects (OR 2.63 (95% CI 0.93, 7.44), P = 0.07 for medial compartment; OR 3.13 (95% CI 1.01, 9.68), P = 0.048 for lateral compartment). Among 37 subjects with BMLs at baseline, 17 resolved. Resolution of BMLs was associated with reduced annual loss of medial tibial cartilage volume (regression coefficient -35.9 (95%CI -65, -6.82), P = 0.02) and a trend for reduced progression of medial tibiofemoral cartilage defects (OR 0.2 (95% CI 0.04, 1.09), P = 0.06). CONCLUSIONS: In this cohort study of asymptomatic middle-aged adults the development of new BMLs was associated with progressive knee cartilage pathology while resolution of BMLs prevalent at baseline was associated with reduced progression of cartilage pathology. Further work examining the relationship between changes and BML and cartilage may provide another important target for the prevention of knee osteoarthritis

The understated turn: Emerging interests and themes in Canadian posthumanist geography

This is the final version. Available on open access from Wiley via the DOI in this recordPosthumanist geography is a broad tradition incorporating a range of intersecting theoretical approaches including assemblage theory, actor‐network theory, new materialisms, affect theory, neo‐vitalism, political ecology, post‐phenomenology, and non‐representational theory—as well as contributions from a number of theoretically progressive subject fields such as new mobilities, relational thinking, sensory and performance studies, biosocial and biopolitics studies, and science and technology studies. The specificities of and differences between these traditions and fields aside, common to posthumanism is a scepticism of human exceptionalism. Here, the sovereign human subject is decentred, and in doing so, posthumanist work acknowledges the agencies of a full array of human and non‐human actors and forces. Recognizing that there are important “geographies to (the discipline of) geography,” this paper identifies and reviews some of the key posthumanist interests and themes that have emerged over recent years quietly and organically in Canadian geography, namely posthumanist (i) Indigenous geographies; (ii) animal and natures geographies; (iii) health, wellbeing, and disability geographies; (iv) affective and atmospheric geographies; and (v) non‐representational and creative methodologies. The paper concludes with some thoughts on the nature and strengths of Canadian posthumanist geography, and on some possibilities for future advancement