Defect Detection Limits for Additively Manufactured Parts Using Current Thermography Techniques

Additive manufacturing (AM) will support NASA in their moon and mars missions by reducing the amount of redundant equipment carried into space and by providing crew members with the flexibility to design and create parts as needed. The ability to monitor the quality of these additively manufactured parts is critical, especially when using recycled or in-situ materials as NASA plans to do. This project assesses the possibility of detecting small, shallow AM defects with existing active thermography techniques. An axisymmetric, numerical model was created in COMSOL to simulate the heat transfer within AM structures during active thermography. The effects of surface convection, heat conduction through the subsurface defect, and radiative in-depth absorption were included in the model. The simulation results estimate the minimum detectable defect diameter for a given defect depth using a common thermography technique. Additionally, the data demonstrates conditions for which 1D thermography models may be applied to 3D systems

An AGN Identification for 3EG J2006-2321

We present a multiwavelength analysis of the high-energy gamma-ray source 3EG J2006-2321. The flux of this source above 100 MeV is shown to be variable on time scales of days and months. Optical observations and careful examination of archived radio data indicate that its radio counterpart is PMN J2005-2310, a flat-spectrum radio quasar with a 5-GHz flux density of 260 mJy. Study of the $V=18.7$ optical counterpart indicates a redshift of 0.833 and variable linear polarization. No X-ray source has been detected near the position of PMN J2005-2310, but an X-ray upper limit is derived from ROSAT data. This upper limit provides for a spectral energy distribution with global characteristics similar to those of known gamma-ray blazars. Taken together, these data indicate that 3EG J2006-2321, listed as unidentified in the 3rd EGRET Catalog, is a member of the blazar class of AGN. The 5-GHz radio flux density of this blazar is the lowest of the 68 EGRET-detected AGN. The fact that EGRET has detected such a source has implications for unidentified EGRET sources, particularly those at high latitudes ($|b|>30^{\circ}$), many of which may be blazars.Comment: 22 pages, 6 figures. To appear in ApJ v569 n1, 10 April 200

The Educational Case for a Simulated Lunar Base

An in depth study of interest in an addition to the science curriculum of the Worcester Public schools. The proposed addition is for a space science curriculum that can be combined with a simulated lunar exhibit

Effect of Lunar Dust Simulant on Human Epithelial Cell Lines

The purpose of this project is to assess the potential toxicity of lunar dust to cause the release of pro-inflammatory cytokines by human lung cells. Some of this dust is on the scale of 1-2 micrometers and could enter the lungs when astronauts track dust into the habitat and inhale it. This could be a serious problem as NASA plans on going back to the moon for an extended period of time. Literature shows that quartz, which has a known cytoxicity, can cause acute cases of silicosis within 6 months, and in most cases cause silicosis after 3 years. The activation of lunar dust through impacts creates surface based radicals which, upon contact with water create hydroxl radicals and peroxyl radicals which are very reactive and potentially might even be as cytotoxic as quartz. These radicals could then react with lung cells to produce pro-inflammatory mediators such as interleukin-6 and interleukin-8, and TNF-alpha

Spectral Absorption Coefficient of Additive Manufacturing Polymers

As NASA turns to additive manufacturing processes, there is a need to ensure that the parts they produce are reliable. This is especially true when creating parts in space, where resources are limited and failure could result in catastrophe. Active thermography has shown potential as a non-destructive quality assurance technique for additive manufacturing processes. Heat transfer models used in active thermography techniques require accurate material property measurements in order to extract useful information about the system, including defect location. The spectral absorption coefficient, which determines the depth at which radiative power is absorbed into a surface, is a material property necessary for performing active thermography on AM polymers. This paper presents measurements of spectral absorption coefficients of polymers commonly used in additive manufacturing. Spectral absorption coefficients for fully dense PLA, ABS, and Nylon 12 samples are reported. Future work is needed to measure the spectral absorption coefficients of different materials and colored filaments commonly used in additive manufacturing

John Nelson Armstrong folder of correspondence

The folder of correspondence labeled John Nelson Armstrong has been digitized and the original order maintained. The correspondence between J. N. Armstrong, N. B. Hardeman, Foy E. Wallace, and J. W. Shepherd is discussing the premillennialism teaching of R. H. Boll and others

Modelling the removal of an earth bund to maximise seawater ingress into a coastal wetland

Weed infestation is a critical management issue for maintaining the natural values of coastal wetlands across the world. Widespread use of herbicides to control weeds has resulted in environmental issues in the past and has led to the search for more natural control methods such as using saline water. This study investigates management options to restore the natural flow regimes between freshwater wetlands and seawater by removing a bund which was built to grow ponded pasture. The study was carried out in the Mungalla wetland in Queensland, which is an important Nywaigi aboriginal community asset for recreation, cultural and economic activities. The study used modelling and monitoring methods to (a) assess how effective the earth bund was in excluding seawater and (b) the extent to which seawater could enter the wetland without the bund. Eleven scenarios were investigated to estimate seawater ingress under different tide, onshore wind, low atmospheric pressure and sea level rise (SLR) conditions. Results show that removal of the bund reinstated periodic tidal ingress into the wetland. Seawater intrusion was also shown to increase when there were onshore winds and/or low atmospheric pressure associated with cyclones. The greatest impact was under future SLR, where large increases in the inundation frequency and extent are likely to cause a shift in the wetland vegetation towards native salt tolerant species. Findings of this study are useful for examining the potential impact of various management interventions that are being considered for wetland system repair. For example, the removal or height adjustment of tidal barriers, dredging of silted streams, removal of weeds from choked streams and reintroduction of tidal flows to control weed infestation, improve water quality and restore natural values to the wetlands

Bund removal to re-establish tidal flow, remove aquatic weeds and restore coastal wetland services—North Queensland, Australia

The shallow tidal and freshwater coastal wetlands adjacent to the Great Barrier Reef lagoon provide a vital nursery and feeding complex that supports the life cycles of marine and freshwater fish, important native vegetation and vital bird habitat. Urban and agricultural development threaten these wetlands, with many of the coastal wetlands becoming lost or changed due to the construction of artificial barriers (e.g. bunds, roads, culverts and floodgates). Infestation by weeds has become a major issue within many of the wetlands modified (bunded) for ponded pasture growth last century. A range of expensive chemical and mechanical control methods have been used in an attempt to restore some of these coastal wetlands, with limited success. This study describes an alternative approach to those methods, investigating the impact of tidal reinstatement after bund removal on weed infestation, associated changes in water quality, and fish biodiversity, in the Boolgooroo lagoon region of the Mungalla wetlands, East of Ingham in North Queensland. High resolution remote sensing, electrofishing and in-water logging was used to track changes over time– 1 year before and 4 years after removal of an earth bund. With tides only penetrating the wetland a few times yearly, gross changes towards a more natural system occurred within a relatively short timeframe, leading to a major reduction in infestation of olive hymenachne, water hyacinth and salvina, reappearance of native vegetation, improvements in water quality, and a tripling of fish diversity. Weed abundance and water quality does appear to oscillate however, dependent on summer rainfall, as changes in hydraulic pressure stops or allows tidal ingress (fresh/saline cycling). With an estimated 30% of coastal wetlands bunded in the Great Barrier Reef region, a passive remediation method such as reintroduction of tidal flow by removal of an earth bund or levee could provide a more cost effective and sustainable means of controlling freshwater weeds and improving coastal water quality into the future

Anomalous thermal expansion in 1D transition-metal cyanides: what makes the novel trimetallic cyanide Cu1/3Ag1/3Au1/3CN behave differently?

The structural dynamics of a quasi-one-dimensional (1D) mixed-metal cyanide, Cu1/3Ag1/3Au1/3CN, with intriguing thermal properties is explored. All the current known related compounds with straight-chain structures, such as group 11 cyanides CuCN, AgCN, AuCN and bimetallic cyanides MxM’1-xCN (M, M’ = Cu, Ag, Au), exhibit 1D negative thermal expansion (NTE) along the chains and positive thermal expansion (PTE) perpendicular to them. Cu1/3Ag1/3Au1/3CN exhibits similar PTE perpendicular to the chains, however PTE, rather than NTE, is also observed along the chains. In order to understand the origin of this unexpected behavior, inelastic neutron scattering (INS) measurements were carried out, underpinned by lattice-dynamical density-functional-theory (DFT) calculations. Synchrotron-based pair-distribution-function (PDF) analysis and 13C solid-state nuclear-magnetic-resonance (SSNMR) measurements were also performed to build an input structural model for the lattice dynamical study. The results indicate that transverse motions of the metal ions are responsible for the PTE perpendicular to the chains, as is the case for the related group 11 cyanides. However NTE along the chain due to the tension effect of these transverse motions is not observed. As there are different metal-to-cyanide bond lengths in Cu1/3Ag1/3Au1/3CN, the metals in neighboring chains cannot all be truly co-planar in a straight-chain model. For this system, DFT-based phonon calculations predict small PTE along the chain due to low-energy chain-slipping modes induced by a bond-rotation effect on the weak metallophilic bonds. However the observed PTE is greater than that predicted with the straight-chain model. Small bends in the chain to accommodate truly co-planar metals provide an alternative explanation for thermal behavior. These would mitigate the tension effect induced by the transverse motions of the metals and, as temperature increases and the chains move further apart, a straightening could occur resulting in the observed PTE. This hypothesis is further supported by unusual evolution in the phonon spectra, which suggest small changes in local symmetry with temperature

A cost-reducing extracorporeal membrane oxygenation (ECMO) program model: a single institution experience.

BACKGROUND: The worldwide demand for ECMO support has grown. Its provision remains limited due to several factors (high cost, complicated technology, lack of expertise) that increase healthcare cost. Our goal was to assess if an intensive care unit (ICU)-run ECMO model without continuous bedside perfusionists would decrease costs while maintaining patient safety and outcomes. METHOD: A new ECMO program was implemented in 2010, consisting of dedicated ICU multidisciplinary providers (ICU-registered nurses, mid-level providers and intensivists). In year one, we introduced an education platform, new technology and dedicated space. In year two, continuous bedside monitoring by perfusionists was removed and new management algorithms designating multidisciplinary providers as first responders were established. The patient safety and cost benefit from the removal of the continuous bedside monitoring of the perfusionists of this new ECMO program was retrospectively reviewed and compared. RESULTS: During the study period, 74 patients (28 patients in year 1 and 46 patients in year 2) were placed on ECMO (mean days: 8 ± 5.7). The total annual hospital expenditure for the ECMO program was significantly reduced in the new model ($234,000 in year 2 vs.$600,264 in year 1), showing a 61% decrease in cost. This cost decrease was attributed to a decreased utilization of perfusion services and the introduction of longer lasting and more efficient ECMO technology. We did not find any significant changes in registered nurse ratios or any differences in outcomes related to ICU safety events. CONCLUSION: We demonstrated that the ICU-run ECMO model managed to lower hospital cost by reducing the cost of continuous bedside perfusion support without a change in outcomes