4D printing of Magnetic Shape Memory Alloys

Magnetic shape memory alloys (MSMA) are ferromagnetic materials exhibiting a plastic reversible transformation when subjected to a magnetic field. This transformation occurs within few milliseconds, making them good candidates for ultra-fast actuators. Previous studies have reported an increase of the shape memory effect in bamboo-like Ni-Mn-Ga structures. Thus, 3D Printing, using Laser Powder Bed Fusion (l-PBF), is a potential manufacturing approach to fabricate near-net-shape textured MSMAs structures. This study investigates the influence of l-PBF process parameters (laser power, scan speed, hatch spacing and scanning strategy) on the relative density and the microstructure of bulk and lattice specimens made from a gas atomised Ni-Mn-Ga powder doped with excess Mn. The as-built bulk samples showed a high relative density, up to 98% with a homogenous 14M structure and a ferromagnetic behaviour. The residual porosity in the bulk material is mainly due to gas voids, lack of fusion and cracking. Fabrication of lattice structures at a low laser power (70W) and scan speed (450 mm/s) resulted in a significant decrease in cracking. The effect of process parameters on the strut’s geometry was also investigated, in addition the influence of the lattice geometries on the magnetic properties. Microstructural analysis revealed a layered microstructure with a stripe-like surface relief that originated from the presence of martensitic twins within the sample. Further work will focus on developing a new design to enhance the magnetic properties.France-UK Dstl PhD Schem

The Effects of The Content Enhancement Model in College Algebra

The purpose of this study was to investigate The Content Enhancement Model in the field of college algebra in a mid-western community college. The Content Enhancement Model is a teaching technique that teachers use to help students acquire the content information by helping them identify, organize, comprehend, and memorize material. This study investigated the effects of The Content Enhancement Model on the college algebra achievement, mathematics confidence levels and students' perceived value of the Content Enhancement Routines on their college algebra achievement. This study used a quasi-experimental design with control and experimental groups. Gender was also a factor. The Content Enhancement Routines included Concept Diagram, Concept Comparison, and Concept Anchoring. The topics used in these routines included function, domain, slope, linear functions, and quadratic functions. The Content Enhancement Organizers included Course, Unit, and Lesson. The organizers were used for an introductory function unit, linear function unit and quadratic function unit in a college algebra course. Statistically significant differences in mean algebra achievement post-test scores were found between students in the control and experimental groups in favor of the experimental group using the ANOVA. Significant differences were also found in algebra achievement posttest scores on a sub-topic, slope in favor of the experimental group. This study supports the use of the Content Enhancement Model as an effective way to increase overall algebra achievement in a community college setting

Spatial ecology of wolves in Scandinavia : From spatio-temporal dynamics of wolf pairs to wolf population dynamics

PHD in applied ecology, 2016Understanding how spatial and temporal variations shape populations is necessary to develop trustworthy conservation and management planning. In this thesis, I used individual-based long-term monitoring data of the grey wolf (Canis lupus) collected in Scandinavia during its recolonization phase since the early 1990’s. My main goal was to identify how habitat could affect the demography of this social carnivore species living in packs. Packs are generally composed of a territorial breeding pair and their offspring. Because the pair plays an important role in the pack, they are generally considered as the functional unit of wolf populations. I therefore focused my analyses on the territorial pair. My results suggest that wolf pairs generally avoided habitat characterized by humans when establishing a territory. Wolf pair bond duration was short (on average 3 consecutive winters), and dissolutions were mostly caused by humans. Furthermore, I showed that the effect of wolf culling (i.e. legal harvest) on population growth was complex. Culling interacted with the intrinsic characteristics of the species and other causes of mortality making any predictions of the effect of culling rather challenging. However, I found that temporal pair bond stability was a better predictor of growth rate than individual culling mortality. Additionally, I found that interspecific competition with brown bears (Ursus arctos) could have contributed to shape spatial patterns of wolf recolonization. The spatio-temporal avoidance of bears by wolves could occur at several scales, from decisions on territory establishment to the habitat selected by wolves within their home ranges. My results showed how data from long-term monitoring programs can be used to provide key information linking demography with habitat in a social large carnivore. In this thesis, I also highlighted the importance of a functional unit (i.e. the wolf pair for wolves) for the population dynamics of a socially-living species. I therefore recommend monitoring, management and conservation programs to further focus their actions at the level of the wolf pair.For å kunne utvikle gode planer for bevaring og forvaltning av en art, er det nødvendig å forstå hvordan variasjoner i tid og rom kan forme populasjoner. I denne doktorgraden har jeg benyttet data fra langtidsstudier av ulv (Canis lupus), som er samlet inn i Skandinavia etter dens rekolonisering på begynnelsen av 1990-tallet. Mine hovedmål var å finne ut hvordan habitat kunne påvirke demografien til denne sosiale flokk-levende rovdyrarten. Flokkene er stort sett sammensatt av et revirhevdende ynglende par og deres avkom. Siden det revirhevdende paret spiller en viktig rolle i flokken, er de ofte sett på som den funksjonelle enheten av ulvebestanden. Jeg har derfor valgt å fokusere analysene mine på de revirhevdende parene. Ulveparene unngikk i hovedsak habitater som var påvirket av mennesker når de etablerte et revir. Tiden ei tispe og en hann klarte å holde sammen som et revirhevdende par viste seg å være kort (gjennomsnittlig 3 påfølgende vintre), og oppløsningen av paret var som oftest forårsaket av mennesker. Videre fant jeg ut at effekten av uttak (lisensjakt, skadefelling eller ekstraordinært uttak) på populasjonsveksten var sammensatt, da det også er andre årsaker (f.eks. innavl, illegal jakt, sykdom) som påvirker populasjonsvekst, noe som gjorde det vanskelig å finne effekten av selve uttaket. Jeg fant derimot ut at evnen parene hadde til å holde sammen over tid var en bedre faktor for å forutse populasjonsveksten enn dødelighet forårsaket av uttak. I tillegg fant jeg ut at konkurranse med brunbjørn (Ursus arctos) kan ha påvirket det romlige mønsteret for rekoloniseringen av ulv. At ulven unngår bjørn i både tid og rom kan forekomme på flere skalaer, helt fra avgjørelsen om hvor de skal etablere et revir, til habitatvalg innenfor det etablerte reviret. Mine resultater viser hvordan data fra langtidsstudier av ulv kan bli brukt for å gi viktig informasjon som setter demografi i sammenheng med habitat hos et sosialt rovdyr. I denne syntesen får jeg også frem viktigheten av en funksjonell enhet (det revirhevende paret hos ulver) for populasjonsdynamikken til en sosial art. Jeg anbefaler derfor overvåknings- og forvaltningsprogram til i fremtiden å ha fokus på par-nivå

Root, mycorrhiza and earthworm interactions: their effects on soil structuring processes, plant and soil nutrient concentration and plant biomass

Earthworms, arbuscular mycorrhiza fungi (AMF) and roots are important components of the belowground part of terrestrial ecosystem. However, their interacting effects on soil properties and plant growth are still poorly understood. A compartmental experimental design was used in a climate chamber in order to investigate, without phosphorus (P) addition, the single and combined effects of earthworms (Allolobophora chlorotica), AMF (Glomus intraradices) and roots (Allium porrum) on soil structure, nutrient concentration and plant growth. In our experimental conditions, plant roots improved soil structure stability (at the level of macroaggregates) whereas earthworms decreased it. AMF had no effect on soil structure stability but increased P transfer from the soil to the plant and significantly increased plant biomass. Earthworms had no direct influence on P uptake or plant biomass, and the N/P ratio measured in the shoots indicated that P was limiting. Interactions between AMF and earthworms were also observed on total C and N content in the soil and on total root biomass. Their effects varied temporally and between the different soil compartments (bulk soil, rhizosphere and drilosphere). After comparison with other similar studies, we suggest that effects of earthworms and AMF on plant production may depend on the limiting factors in the soil, mainly N or P. Our experiment highlights the importance of measuring physical and chemical soil parameters when studying soil organism interactions and their influence on plant performanc

Quantum superposition principle and generation of ultrashort optical pulses

We discuss the propagation of laser radiation through a medium of quantum prepared {\Lambda}-type atoms in order to enhance the insight into the physics of QS-PT generator suggested in Phys. Rev. A 80, 035801 (2009). We obtain analytical results which give a qualitatively corerct description of the outcoming series of ultrashort optical pulses and show that for the case of alkali vapor medium QS-PT generation may be implemented under ordinary experimental conditions

The effects of an organic phosphate compound (Bayer 21

Call number: LD2668 .T4 1959 M5

In-situ alloying laser powder bed fusion of Ni-Mn-Ga magnetic shape memory alloy using liquid Ga

Ni-Mn-Ga-based magnetic shape memory alloys can exhibit large magnetic field induced strains (MFIS). Recently, additive manufacturing techniques, especially laser powder bed fusion (L-PBF), have been successfully used to manufacture functional polycrystalline Ni-Mn-Ga with complex geometries, such as ‘bamboo-grained’ lattice structures. However, previous approaches of L-PBF of Ni-Mn-Ga have used pre-alloyed powders, which can limit the compositional freedom of the manufactured devices. This study explores, for the first time, the feasibility of an in-situ L-PBF alloying approach using a powder blend of elemental Ni, Mn, and Ga. Promising results were obtained despite the significant differences between the elemental Ni and Mn powders and the liquid Ga. The microstructure of the as-built sample showed distinct stripe patterns from the 14 M structure confirmed by XRD analysis. Heat-treatment significantly improved chemical homogeneity, dissolved the Ni-rich phase but couldn’t dissolve MnO hindering the shape memory effect