Optimization of Porosity in Cold Spray Produced Copper and Zinc Coatings

Since its invention in 1981, the cold spray (CS) additive manufacturing (AM) process has been studied and optimized to produce well-adhered, dense material coatings. CS can operate at a wide range of temperatures if the feed material remains in a solid state. Copper and zinc were studied to characterize and understand the effects of heating element voltage, travel speed, and standoff distance on deposit porosity, grain size, microhardness, and coating thickness. Samples were sprayed on 3.2 mm x 25 mm x 150 mm 6061 aluminum substrates. Sections were taken from the middle of the samples to represent steady-state conditions. Sample sections were polished and imaged with optical microscopy before being etched and imaged again. Sample sections were repolished for Vickers microhardness testing. Results from the copper CS deposits show that porosity, grain size, and microhardness can be controlled in the variable range, (69%-100% voltage to a heating element, 33-251 mm/min travel speed, and 4.2-15.2 mm standoff distance) of the study however, copper porosity results exclude travel speed as a variable which goes against other research in the field, suggesting some physical phenomenon was not accounted for in the study. Results from the zinc CS deposits show that porosity can be controlled in the variable range of the study and that optimal processing parameters to produce minimal porosity (1.5%) are 94% heating element voltage, 69 mm/min nozzle travel speed, and 9.7 mm standoff distance. There was no correlation in zinc grain size data or microhardness data from any of the tested processing parameters. Thickness results from both tested materials indicate a strong correlation with the studied processing parameters and thickness can be controlled

Investigations of Nanoscale Variations in Spin and Charge Transport in Manganites and Organic Semiconductors Using Spin Polarized Scanning Tunneling Spectroscopy

Spintronics is a new class of spin-dependent electronics with great potential for nonvolatile memory and logic technology. Additionally, spintronics may be combined with optoelectronic applications to achieve higher efficiency and novel capabilities. All of these developments require growth and characterization of new materials to polarize and transport electron spin currents. In this context, spin-polarized and non spin-polarized spatially resolved conductance measurements performed by scanning tunneling microscopy (STM) are effective means to investigate the spin and charge quantum transport in magnetic and organic systems, particularly for systems that are prone to phase separations and complex magnetic properties, such as the colossal magnetoresistive (CMR) manganites La1-xCaxMnO3 (LCMO) that are known to exhibit intrinsic electronic heterogeneity due to strong electronic correlation and competing orders in the ground state. Additionally, STM measurements can provide direct information about the band structure and mobility of the organic semiconductor 8-hydroxyquinoline aluminum (Alq3) in the Alq3/LCMO heterostructures to further understand their performance in spintronic devices. The manganite compound La1-xCaxMnO3 (LCMO) with a bulk doping level x = 0.3 is a ferromagnetic metal with a relatively high Curie temperature Tc = 270K. This system is promising for spintronic device applications, and may be used as a spin current injector because of the gapped band structure for minority spins, a property known as half-metallicity. On the other hand, even in this bulk ferromagnetic metallic phase, inherent electronic inhomogeneity at microscopic scales is expected. To further study this effect, we have investigated x = 0.3 LCMO thin films using scanning tunneling microscopy in spectroscopic mode under varied temperature, magnetic field and spin polarization of the tunneling current. Spatially resolved maps of tunneling conductance taken with non polarized Pt/Ir tip show variations on the scale of a few hundred nanometers in size in the bulk ferromagnetic state, which are believed to be the result of intrinsic inhomogeneity of the manganites due to their tendency toward phase separation. Maps of tunneling conductance taken with spin-polarized Cr coated tips are consistent with the convolution of the LCMO and Cr density of states, and below the Tc of LCMO the spin-polarized tunnel junction can be described as a spin valve configuration. The electronic homogeneity in the material increases above the magnetic ordering temperature, or with application of magnetic field in the bulk ferromagnetic state. We identified gaps in the conductance at two separate characteristic energies. The first gap of energy approximately 0.6 eV is believed to arise from a ferromagnetic insulator (FI) surface phase due to its disappearance above the Curie temperature (Tc) and the dependence of gap energy on relative tip and sample magnetic orientation. The surface phase may be stabilized by Ca deficiency at the LCMO surface, corroborated by x-ray photoemission spectroscopy (XPS). Second, we observe a nearly temperature independent and spatially varying gap of approximately 0.4 eV for all zero-field tunneling spectra, which is believed to be associated with the psuedogap (PG) phenomena in the manganites. Application of a magnetic field converts the regions of PG phenomena to FI, in conjunction with an increase in the homogeneity of the lm conductance. These findings suggest that the PG phenomena arise from electronic inhomogeneity in the manganite film, in agreement with theoretical investigations, and that the vertical and lateral electronic inhomogeneity, along with its dependence on temperature and applied magnetic field, has important implications for use of these materials in high-density nanoscale spintronic devices. We have also successfully deposited and investigated Alq3/LCMO heterostructures of varying thicknesses to investigate charge transport in Alq3. Bulk Alq3 structural properties are preserved down to 10 nm in thickness with a -0.3 eV offset in band energies. The lack of band bending between LCMO and Alq3 is suggestive of a shift in the preferred isomer from meridinial to facial at the interface. The absence of polaron states from our STM studies implies the relative unimportance of polarons in Alq3 for this heterostructure. In addition, the measured mobilities on the order of 10-5cm2(Vs)-1 for electrons and holes in Alq3 lms deposited on heated LCMO substrates more closely resemble values of the intrinsic mobility estimated from the muon spin relaxation measurements than those from studies of the bulk LED structures, suggesting that superior film conductivity close to the fundamental limit is possible with a heated substrate during sublimation.</p

Analysis Of Conservation Practices In The Blackland Prairie Region Of Mississippi And Construction Of A Predictor For Locating New Sites For Conservation Efforts

Mississippi’s Blackland Prairie has been reduced below 10% of pre-Columbian extent, with few conservation practices in place. To determine efficacy of current restoration practices, plant species at remnant sites were compared with those at restoration sites. Analyses using multivariate statistical approaches revealed no generalizable patterns among four available remnants versus two available restoration sites. Thus, the aim of this project shifted to evaluating methods of identifying Blackland Prairie remnants or potential restoration sites. Location data for Blackland Prairie plant species and potentially informative environmental variables were used to develop geographic information system (GIS)-based habitat models. The best models were selected for validation against a second set of data collected from random points on public lands across the survey region. Validation surveys also were used to explore trends in predictive success and to aid in increasing accuracy through inclusion of other variables. Models incorporating soil characteristics had the highest predictive success

Scaffolding Middle and High School Students’ Engineering Design Experiences: Quality Problem-SCOPEing Promoting Successful Solutions

Highly proficient expert engineers begin the iterative process of design by thoroughly investigating the design problem. Engineering students are often distracted by surface details, leading to a faulty conception of the problem and inappropriate solution strategies. Adequate problem-scoping is arguably the most important step in the design process. To address this issue, the researchers developed an instructional framework to help teachers scaffold students’ cognitive and metacognitive processes during the problem-scoping phase of a design challenge. The purpose of this quasi-experimental study was to investigate the impact that scaffolded instruction related to the SCOPE process had on students’ solution success during a design challenge. The SCOPE process is used to help teachers scaffold students’ design experiences during a tower design challenge and increase the overall effectiveness of their design efforts. Students in this study (N = 802) were separated into treatment and control groups. Using hierarchical multiple regression, the SCOPE process accounted for 40.4% (ΔR2 = .404) of the variability of the design score, which was statistically significant (p \u3c .001). The results indicate that students who received scaffolded instruction from their teachers related to the SCOPE process during the design experience performed better on the design challenge

Older people’s participation and engagement in falls prevention interventions: Comparing rates and settings

Objective: Falls among older people remain a major public health issue. The purpose of this article was to facilitate accurate interpretation of the existing evidence-base and facilitate robust planning of future fall prevention randomised controlled trials (RCTs). Method: Two systematic reviews were further developed that evaluated older people’s participation and engagement in RCTs to prevent falls in both community and institutional settings. It is argued that there is a need to differentiate between: 1) Acceptance rates versus recruitment rates, i.e. respectively the proportion of older people willing to participate in the RCTs versus those willing and included; 2) Rates of recruitment and participation in institutional settings distinguishing between nursing care facilities versus hospitals. Results: For community settings (n = 78), the median rates were 41.3% (22.0 - 63.5%) for recruitment and 70.7% (64.2 - 81.7%) for acceptance. For institutional settings (n = 25), the median rates were 48.5% (38.9 - 84.5%) for recruitment and 88.7% (81.2 - 95.4%) for acceptance. In comparing trials from nursing care facilities and hospitals, recruitment and acceptance rates were remarkably similar, though the remaining data - attrition, adherence, and whether adherence acted as a moderator on the effectiveness of the intervention on trial outcomes - was only available from trials from nursing care facilities. Conclusion: Researchers are encouraged to be more inclusive in trials and to conduct more RCTs in hospitals to prevent falls. A consensus on how to define successful engagement with trials and uptake and adherence to trial interventions remains desired

Assessment worlds colliding? Negotiating between discourses of assessment on an online open course

Using the badged open course, Taking your first steps into Higher Education, this case study examines how assessment on online open courses draws on concepts of assessment used within formal and informal learning. Our experience was that assessment used within open courses, such as massive open online courses, is primarily determined by the requirements of quality assurance processes to award a digital badge or statement of participation as well as what is technologically possible. However, this disregards much recent work in universities that use assessment in support of learning. We suggest that designers of online open courses should pay greater attention to the relationship of assessment and learning to improve participant course completion

Microexpression detection in undergraduate students

Microexpressions, facial expressions lasting for less than half a second, are a common but unnoticed occurrence. The accuracy of microexpression detection, and college major choice, have both been linked with personality. This led to the hypothesis that different majors should have different levels of accuracy in detection. A convenience sample of 121 undergraduate students, of different majors, was given a short survey about microexpression detection. 10 frontal headshots, portraying examples of 7 different microexpressions, were shown on a screen. Participants were asked to identO, the expressions by choosing from a provided list on the survey. There was no statistical significance in microexpression detection among majors, [F(3,118) = 0.92, p = 0.90], or between gender, t(118) = 1.23, p = 0.22. However, there was a statistically significant correlation between gender with the identification of contempt and disgust. While our results conflict with research that has already been done on emotion/microexpression detection, it is possible that another study with a larger sample could achieve results similar to existing research

SCOPE Process: Fostering Students\u27 Design Outcome Effectiveness

The purpose of this article is to help Technology and Engineering Educators scaffold engineering design and problem-solving experiences so that students taking technology and engineering courses will develop an improved ability to design. Technology and Engineering Education seems to increasingly focus on problem-solving, design, and engineering. Technology and Engineering Education is not the only discipline with this focus. The fact that both Science and Technology and Engineering Education are similarly focused on the teaching and learning of engineering begs the question of what separates technology and engineering educators from science educators in the teaching of engineering? Lewis (2004) cautioned that the introduction of engineering signaled the discipline turning away from more practical, blue-collar knowledge, towards white-collar academic traditions. Lewis (2004) highlighted John Dewey\u27s argument that manual training was a gateway for students to integrate math and science

Examining the functions of prison critical incidents: a preliminary qualitative analysis of public reporting

Purpose: The current study explored the function of crisis incidents in prisons within the UK and US. The incidents reviewed included riots and hostage-incidents, focusing only on information that was available publically. It did not intend to capture official reports not in the public domain. Design/methodology/approach: Publically available information on incidents were systematically reviewed. Functional assessment and grounded theory were employed to examine background factors, triggers and maintaining factors. Twenty-five crisis incidents were analysed (UK = 10 and US = 15) from the past 30 years. It was predicted that crisis incidents would be motivated by negative and positive reinforcement, with negative more evidenced than positive. Precipitating factors (i.e. triggers) were predicted to include negative emotions, such as frustration and anger. Findings: Similarities in triggers and background factors were noted between hostage taking and riot incidents. Positive reinforcement was primarily indicated. Riots appeared driven by a need to communicate, to secure power, rights, control and/or freedom whereas for hostage taking these functions extended to capture the removal of negative emotions, to inflict pain, to punish/gain revenge, to effect a release, to manage boredom, and to promote positive emotions. Research limitations/implications: The study is preliminary and focused on the reporting of incidents in publically available sources; consequently, the data is secondary in nature and further limited by sample size. Nevertheless, it highlights evidence for similarities between types of crisis incidents but also some important potential differences. The need to understand the protective factors preventing incidents and minimising harm during incidents is recommended. Originality/value: This is an under-researched area. The study contributes to the field not only by focusing on providing a detailed analysis of an under-used source (public reporting) but by also identifying where gaps in research remain. The results demonstrate the value in understanding incidents through their motivation, particularly in distinguishing between negative and positive reinforcement