Feasibility and Implementation of Self - Consolidating Concrete

This study focused on the construction and placement issues that are common among the production and utilization of self-consolidating concrete (SCC). Six distinct areas were looked at. Robustness and loss of passing ability were related to the change in water and high range water content. Mixes were batched and altered in such a way to determine the point when lack of robustness becomes unacceptable. The compaction, by vibration, of an SCC mix is not normally necessary, however may be needed under certain scenarios. A standard test for determining the static segregation resistance of SCC was altered to determine the effects of vibration duration. A foam layer was sometimes observed on the top of freshly cast SCC. It was found that this layer could be from certain material constituents, high fineness modulus of sand, High Range Water Reducer, or mix instabilities which are detrimental. A guideline for conducting trial batches in the laboratory was established. Field trips to ready-mix and precast plants producing SCC were conducted. SCC mixes can be replicated, in a production environment, although environmental and human factors can cause variability in the mix. SCC is more fluid than that of traditional vibrated concrete; it is believed to have a higher influence on the developed formwork pressure. Short and tall columns were erected and traditional vibrated concrete (TVC) as well as SCC mixes were cast in them. The lateral formwork pressure was recorded using sensors.;The results from this study show that a robust SCC mix can tolerate up to about a five percent increase in water content. A robust SCC mix can also be vibrated in short duration if need be. The generation of air and its migration of air with a fluid body of SCC were explored in order to determine how properties of the mix such as fineness modulus of the sand, mix instabilities, and HRWR (High Range Water Reducer) could cause this phenomenon. Guidelines for making and reproducing small batches of SCC in the laboratory were made and took into account the aggregates, chemical admixtures, the mixer, and batch sequence. The formwork pressures measured in short columns (47 in. head height) reached full hydrostatic pressure using TVC and SCC. The tall TVC and SCC columns (105 in. head height) tested did not reach hydrostatic pressure, but the pressure measured in the tall TVC column was significantly lower

Air-sea interaction in tropical atmosphere: influence of ocean mixing on atmospheric processes

One the major factors determining the development and evolution of atmospheric convection is the sea surface temperature and its variability. Results of this thesis show that state of atmospheric convection impacts the diurnal distribution of thermal energy in the upper ocean. Under calm and clear sky conditions a shallow warm layer of several meters depth develops on the surface of the ocean. This warm layer drives an anomalous flux from the ocean to the atmosphere. A novel Kelvin wave trajectory database based on satellite data is introduced in this study. The investigation of its data shows that substantial fraction of Kelvin waves is initiated as a result of interaction with another Kelvin wave. Two distinct categories are defined and analyzed: the two- and multiple Kelvin wave initiations, and a spin off initiation. Results show that primary forcing of such waves are high diurnal cycle and/or increased wind speed and latent heat flux at the ocean surface. Variability of the ocean surface and subsurface along Kelvin wave trajectories over Indian Ocean is investigated: wind speed and latent heat flux increase and a sea surface temperature anomaly decreases during a wave passage. It is also shown that Kelvin waves are longitude-diurnal cycle phase locked over the Maritime Continent. This cycle phase locking is such that it agrees with mean, local diurnal cycle of convection in the atmosphere. The strength of the longitude-diurnal cycle phase locking differs between non-blocked Kelvin waves, which make successful transition over the Maritime Continent, and blocked waves that terminate within it. The distance between the islands of Sumatra and Borneo agrees with the distance travelled by an average Kelvin wave in one day. This suggests that the Maritime Continent may act as a filter, favoring successful propagation waves, which are in phase with the local diurnal cycle of convection.Comment: PhD thesis, University of Warsa

Achieving fruit, juice, and vegetable recipe preparation goals influences consumption by 4th grade students

<p>Abstract</p> <p>Background</p> <p>Including children in food preparation activities has long been recommended as a method to encourage children's consumption, but has not been evaluated. Goal setting is also a common component of behavior change programs. This study assessed the impact of attaining goals to prepare fruit-juice or vegetable recipes on student fruit and vegetable consumption as part of a 10-week fruit and vegetable intervention for fourth grade students.</p> <p>Methods</p> <p>At six of the 10 sessions, students (n = 671) selected a fruit-juice or vegetable recipe to prepare at home before the next session. Students returned parent-signed notes reporting their child's goal attainment. Baseline and post consumption were assessed with up to four days of dietary recalls. Analyses included regression models predicting post consumption from the number of fruit-juice or vegetable recipe preparation goals attained, controlling for baseline consumption.</p> <p>Results</p> <p>In general, girls and Hispanic students achieved the most recipe preparation goals. For students with highest baseline fruit-juice consumption, post fruit-juice consumption was higher by about 1.0 serving for those achieving 2 or 3 fruit-juice recipe preparation goals. Post vegetable consumption was highest for students reporting the highest baseline vegetable consumption and who achieved two or three vegetable recipe preparation goals. In general, recipe goal setting was a useful procedure primarily for those with high baseline consumption.</p> <p>Conclusion</p> <p>This is one of the first reports demonstrating that home recipe preparation was correlated with dietary change among children.</p

Chemical screening to uncover small molecules that modulate neural stem cell self-renewal and differentiation

In vitro expanded neural stem cells provide an important cellular model to explore mechanisms of neural development, for modelling of disease, and in the longer term may have applications in new types of stem cell-based therapies. However, our ability to steer neural stem (NS) cell lines into specific desired lineages in vitro remains limited. PDGFRα is one of the earliest markers of the transition of neural stem cells to oligodendrocyte progenitors. I established and characterised a novel set of mouse NS cell lines that report the activation of PDGFRα via expression of an H2B:GFP ‘knock-in’. Three clonal ‘PG1’ cell lines were fully characterised. Under self-renewing conditions I found <1% of NS cell express the H2B:GFP reporter but this increases to ~15-20% following induction of differentiation. Using this cellular model system I carried out a high-content chemical screen of a diverse collection of 463 pharmacologically active small molecule modulators of ‘stem cell pathways’ and kinase inhibitors, to identify those capable of modulating NS cell self-renewal and differentiation. I did not uncover any small molecules capable of promoting OPC lineage specification. However, I found multiple HDAC inhibitors that were highly effective in blocking the activation of PDGFRα, a finding that mirrors published studies implicating HDAC inhibition in the later differentiation of OPCs to oligodendrocytes. Three further compounds, Nigericin (an ionophore), Withaferin (a steroidal lactone) and NFkB inhibitor also completely blocked OPC commitment. I focused on the specific cellular responses and downstream molecular events triggered by these molecules and tested their differentiation potential on human NS cells and malignant glioblastoma-derived NS cells

A Time-Orbiting Potential Trap for Bose-Einstein Condensate Interferometry

We describe a novel atom trap for Bose-Einstein condensates of 87Rb to be used in atom interferometry experiments. The trap is based on a time-orbiting potential waveguide. It supports the atoms against gravity while providing weak confinement to minimize interaction effects. We observe harmonic oscillation frequencies omega_x, omega_y, omega_z as low as 2 pi times (6.0,1.2,3.3) Hz. Up to 2 times 10^4 condensate atoms have been loaded into the trap, at estimated temperatures as low as 850 pK. We anticipate that interferometer measurement times of 1 s or more should be achievable in this device.Comment: 9 pages, 3 figure

Quasi-classical cyclotron resonance of Dirac fermions in highly doped graphene

Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasi-classical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m = E_F/v_F^2.Comment: 6 pages, 4 figure

Electronic and Vibrational Properties of gamma-AlH3

Aluminum hydride (alane) AlH_3 is an important material in hydrogen storage applications. It is known that AlH_3 exists in multiply forms of polymorphs, where $\alpha$-AlH_3 is found to be the most stable with a hexagonal structure. Recent experimental studies on $\gamma$-AlH_3 reported an orthorhombic structure with a unique double-bridge bond between certain Al and H atoms. This was not found in $\alpha$-AlH_3 or other polymorphs. Using density functional theory, we have investigated the energetics, and the structural, electronic, and phonon vibrational properties for the newly reported $\gamma$-AlH_3 structure. The current calculation concludes that $\gamma$-AlH_3 is less stable than $\alpha$-AlH_3 by 2.1 KJ/mol. Interesting binding features associated with the unique geometry of $\gamma$-AlH3 are discussed from the calculated electronic properties and phonon vibrational modes. The binding of H-s with higher energy Al-p,d orbitals is enhanced within the double-bridge arrangement, giving rise to a higher electronic energy for the system. Distinguishable new features in the vibrational spectrum of $\gamma$-AlH_3 were attributed to the double-bridge and hexagonal-ring structures.Comment: 18 pages, 9 figures, submited to PR

Excitonic Properties of Low-Band-Gap Lead-Tin Halide Perovskites

The MAPb1–xSnxI3 (x = 0–1) (MA = methylammonium) perovskite family comprises a range of ideal absorber band gaps for single- and multijunction perovskite solar cells. Here, we use spectroscopic measurements to reveal a range of hitherto unknown fundamental properties of this materials family. Temperature-dependent transmission results show that the temperature of the tetragonal to orthorhombic structural transition decreases with increasing tin content. Through low-temperature magnetospectroscopy, we show that the exciton binding energy is lower than 16 meV, revealing that the dominant photogenerated species at typical operational conditions of optoelectronic devices are free charges rather than excitons. The reduced mass increases approximately proportionally to the band gap, and the mass values (0.075–0.090me) can be described with a two-band k·p perturbation model extended across the broad band gap range of 1.2–2.4 eV. Our findings can be generalized to predict values for the effective mass and binding energy for other members of this family of materials

Subsurface oceanic structure associated with atmospheric convectively coupled equatorial Kelvin waves in the eastern Indian Ocean

Atmospheric convectively coupled equatorial Kelvin waves (CCKWs) are a major tropical weather feature strongly influenced by ocean–atmosphere interactions. However, prediction of the development and propagation of CCKWs remains a challenge for models. The physical processes involved in these interactions are assessed by investigating the oceanic response to the passage of CCKWs across the eastern Indian Ocean and Maritime Continent using the NEMO ocean model analysis with data assimilation. Three-dimensional life cycles are constructed for “solitary” CCKW events. As a CCKW propagates over the eastern Indian Ocean, the immediate thermodynamic ocean response includes cooling of the ocean surface and subsurface, deepening of the mixed layer depth, and an increase in the mixed layer heat content. Additionally, a dynamical downwelling signal is observed two days after the peak in the CCKW westerly wind burst, which propagates eastward along the Equator and then follows the Sumatra and Java coasts, consistent with a downwelling oceanic Kelvin wave with an average phase speed of 2.3 m s −1. Meridional and vertical structures of zonal velocity anomalies are consistent with this framework. This dynamical feature is consistent across distinct CCKW populations, indicating the importance of CCKWs as a source of oceanic Kelvin waves in the eastern Indian Ocean. The subsurface dynamical response to the CCKWs is identifiable up to 11 days after the forcing. These ocean feedbacks on time scales longer than the CCKW life cycle help elucidate how locally driven processes can rectify onto longer time-scale processes in the coupled ocean–atmosphere system