Thesis (Ed.M.)--Boston University / This study is an effort to discover whether the flash-card method or the Study-Test Method of My Spelling is more effective in teaching spelling in Grade Five.

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This project researched the fungal and bacterial communities (i.e. biofilms) found on concrete infrastructure in Georgia. Various microbial communities were sampled from four geographically separated sites. The species present in these biofilms were identified through DNA analysis and cultured for testing. A new, rapid test method was developed to accurately simulate field growth conditions in a laboratory environment. Using the newly developed test method, these communities were grown on small mortar tiles, which varied in w/cm, surface roughness, cement type (including photocatalytic cement), and supplementary cementing materials. This research determined that photocatalytic cement was the most effective in decreasing biofilm growth under artificial daylight, but did not increase or decrease growth when not exposed to light. The next most effective ways to decrease growth were lowering w/cm and decreasing surface roughness. The supplementary cementing materials examined did not increase or decrease biofilm growth.

Today, distinct approaches are required when designing timber structures and their joints in the event of fire. Considering that the steel fasteners have temperature dependent properties and that the surrounding wooden construction is also affected by the fire due to occurrence of charring during fire exposure, these types of joints are complicated to design.  This study includes an overview of existing knowledge in the subject, where a literature survey has been conducted to enlighten current design procedures, previous research, and available test methods for axially loaded screw joints in wooden structures exposed to fire. The literature survey has been supplemented with an interview survey, in which six respondents’ knowledge in the subject and desires for future studies have played the main role.  The results from this study clearly indicates that the existing knowledge regarding axially loaded screw joints in wooden structures exposed to fire is insufficient. Today’s standards for the design of these types of joints are incomplete with respect to the referred joint arrangement and there are no explicit test methods for determination of the strength of these joints under fire exposure. A few previous studies have been carried out and the results from these have proven to be difficult to interpret since the experimental set-up was not consistent between the fire tests. This complicates the process of determining which factor has the greatest impact on the strength of the joint and the main underlying causes generating a collapse of the structure. The interview survey further strengthens the perception, based on the literature survey, that there is a lack of knowledge in the subject.  By mapping the existing knowledge in the subject it has been possible to identify deficiencies in current information and, finally, creating and proposing a test method for future tests of axially loaded screw joints in wooden structures exposed to fire. The proposed test method is influenced by existing test methods and design conditions for structures at normal temperatures. The development of this test method has its primary purpose in the ambition that the knowledge of axially loaded screw joints in fire exposed wooden structures can be expanded.

Sedan 1951 har Tetra Pak tillverkat livsmedelsförpackningar, formsprutningsverktyg och fyll-ningsmaskinerna för livsmedelsförpackningar. En del livsmedelsförpackningar som t.ex. gräddeoch yoghurt kan ha en formsprutad topp av plast. Det är nödvändigt att den formsprutade plas-ten stelnar så snabbt som möjligt. För att minska tiden för stelning så används formverktygmed hög värmeledningsförmåga, detta för att få stabila detaljer och ändå göra det möjligt atthålla en hög produktion. En acceptabel livslängd på verktygen uppnås genom att de ytbeläggs.Ytbeläggningen består dels av en hårdanodiserad yta, ett lager av teflon. Dessvärre har teflonen sämre värmeledningsförmåga än metaller som formverktygen är tillverkad i. I detta arbetehar en metod för att avgöra hur mycket ytbeläggningen påverkar värmeledningen utvecklats.Resultaten av arbetet kommer användas för att kunna göra nya materialval. Under projektetutvecklas en testrigg där testerna visar att verktyg utan ytbeläggning har en värmelednings-förmåga som är 24% bättre än för belagda verktyg. Därmed finns det mycket att vinna på attanvända en annan ytbeläggning. / Tetra Pak has since 1951 manufactured food packaging, injection molding tools and fillingmachines for food packaging. Some of the food packaging as for cream and yogurt may havea injection molded plastic top. It is necessary that the injection molded plastic solidifies asquickly as possible. In order to reduce the time for solidification, molding tools with highthermal conductivity are used, in order to obtain stable details and still make it possible tokeep a high production. To achieve an acceptable tool life, they are coated. The surface coatingconsists partly of a hard anodized surface and a layer of teflon. Unfortunately, teflon has worsethermal conductivity than metals that the molding tools are made of. In this project, a methodto determine how much the surface coating affect the thermal conductivity is being developed.The results of the project will be used to make new material choices. During the project, atest rig is developed where the tests show that tools without surface coating have a thermalconductivity that is 24% better than for coated tools. That means there are a lot to gain byselect a new surface coating.

Insulated Gate Bipolar Transistors (IGBTs) are popular power electronic switching devices with several advantages. However, they have been known to fail in the field when subjected to significant variations in power dissipation – known as power cycling. In the work presented here, a novel alternating-current (AC) power cycling test method for IGBTs together with their free-wheeling diodes is proposed and verified. A review of previous work revealed that the parameter that most affects IGBT lifetime under power cycling conditions is the variation in its junction-case temperature difference. Through simulation, the behaviour of a conventional single phase inverter (H-bridge) using simple pulse width modulation (PWM) control was quantified, and the effect of switching frequency and load power factor was studied. Results of the simulations and literature review were used to develop design criteria for a new AC test circuit. The new AC test circuit (a modified version of the conventional H-bridge) was then designed and its performance compared to the criteria and to the simulation results of the conventional circuit. The circuit was then built and its performance was validated. The circuit complied with the performance criteria, in particular the desired variation in 7jc, to an adequate degree of accuracy. The proposed test circuit is novel for several reasons. The stresses on devices used in a conventional H-bridge using a high power factor inductive load are reproduced using a low power factor inductive load, considerably reducing the energy cost of running such a test. IGBT switching losses are not actively reduced, as is normal practice, but instead are actively increased to generate the required losses. Free-wheeling diodes are also tested, but do not have significant switching losses, as the nature of the test circuit dictates that these be transferred to the IGBTs. The main drawback of the proposed test circuit is that a larger number of devices are needed; however, this tradeoff is necessary to obtain the energy cost savings provided by this circuit.

Plusieurs études ont montré que dans les accidents réels, la vitesse d’impact de la tête n’est que rarement normale à la surface et présente une composante tangentielle non négligeable. Aucune norme, à l’heure actuelle ne propose de choc oblique avec enregistrement de l’accélération en translation et en rotation de la fausse tête. Un aspect essentiel de cette recherche a été d’aborder les descriptions d’accidents réels impliquant un motocycliste et un véhicule afin d’évaluer les conditions aux limites de la tête juste avant impact, en termes de vecteur vitesse et de localisation d’impact. Cette étude a permis d’établir le vecteur vitesse possible et de l’angle d’impact de la tête du motocycliste en situation. Une méthode de test pour évaluer le casque a été proposée. Les tests d'impact obliques, sont effectués avec une vitesse d’impact de 8.5 m/s sur une enclume inclinée de 45° permettant la rotation autour de l’axe Y X et Z. Les accélérations 6-D sont implémentés dans le modèle SUFEHM afin d’extraire la déformation axonal maximale et le risque lésionnel. Cette fusion de la méthode expérimentale et numérique donne un avantage par rapport aux normes conventionnelles, tant en termes de conditions d’impact qu’en termes de critère de blessure de la tête. / It is well know that in case of accident the head does not only impact perpendicularly to the impacted structure but presents an oblique impact condition. However none of the today helmet standards do integrate oblique impacts with the recording of the dummy head rotational acceleration. An essential aspect of the present research is to simulate real world accident and to compute the victim’s kinematic in order to extract the head impact conditions. In collaboration with University Florence (Italy) 19 cases were considered and it was shown that the head impact velocity vector presents a significative angle. A novel helmet test method has been proposed. Helmeted headfoml is impacting a 45° inclined anvil at a speed of 8.5 m/s and the 6D acceleration versus time curves are introduced into an existing head FEM in order to compute the axon strains and to derive the brain injury risk.

Electric mobility scooters are increasing in popularity and are used extensively by individuals with mobility impairments to conduct activities of daily living. Scientific literature on the safety and efficacy of scooters in winter conditions is sparse and the current technical standards for scooters do not mandate testing in these conditions. This study paves the way for more rigorous standard testing by: 1) Describing a novel, motion-capture based method to quantify the tractive performance of scooters; 2) Describing methods to create a wide variety of simulated winter conditions; 3) Presenting pilot-test results of a scooter driven in these winter conditions. The outcomes of this study are significant because it is the first study to evaluate the performance of a scooter in winter conditions. Furthermore, it constitutes the first phase of a broader initiative to develop a rigorous, new winter test method for scooters and drive improvements in safety, performance and design.

Electric mobility scooters are increasing in popularity and are used extensively by individuals with mobility impairments to conduct activities of daily living. Scientific literature on the safety and efficacy of scooters in winter conditions is sparse and the current technical standards for scooters do not mandate testing in these conditions. This study paves the way for more rigorous standard testing by: 1) Describing a novel, motion-capture based method to quantify the tractive performance of scooters; 2) Describing methods to create a wide variety of simulated winter conditions; 3) Presenting pilot-test results of a scooter driven in these winter conditions. The outcomes of this study are significant because it is the first study to evaluate the performance of a scooter in winter conditions. Furthermore, it constitutes the first phase of a broader initiative to develop a rigorous, new winter test method for scooters and drive improvements in safety, performance and design.

Austenitic stainless steels have a major problem during solution annealing or welding in the temperature range of 500-800 &deg / C due to the formation of chromium carbide, which causes chromium depleted areas along grain boundaries. This means that the structure has become sensitized to intergranular corrosion. Susceptibility to intergranular corrosion can be determined by means of destructive acid tests or by nondestructive electrochemical potentiokinetic reactivation (EPR) tests. The EPR test, which provides quantitative measurements, can be practiced as single loop or double loop. Single loop EPR method for AISI 304 and 304L type stainless steels was standardized / however double loop EPR (DLEPR) method has not been validated yet. In this study, the degree of sensitization was examined in AISI 304L and 316L type steels by DLEPR method whose experiments have been carried out on sensitive and nonsensitive steels to examine and determine the detailed parameters / solution temperature, concentration and scan rate of the DLEPR method. In order to determine the degree of sensitization, oxalic acid, Huey and Streicher tests were carried out and revealed microstructures and measurements of weight loss by the acid tests were then correlated with DLEPR method results, as a first step towards standardization of DLEPR method for 316L steels. Best agreement was provided with test parameters which are 1M H2SO4 + 0.005M KSCN at 3 V/hr scan rate with 30 &deg / C solution temperature. It was concluded that specimens can be classified as step, dual and ditch, if the Ir:Ia ratios were obtained to be between 0 to 0.15, 0.15 to 4.0 and 4.0 to higher respectively.