This document details the investigation of the aeroelastic behavior of very high aspect ratio cylinders. The difficulty in this investigation lies in the fact that there are two important length scales: the aspect ratio and the Reynolds number. The primary goal is to develop a method that properly represents both length scales during testing. The secondary goal is to develop a method that quantifies the cylinder motion. This paper describes a wind tunnel technique designed to account for the aspect ratio and the Reynolds number of a very high aspect ratio cylinder. This paper also describes the data acquisition and analysis techniques developed here to quantify the motion. As demonstrations, these techniques are then used here to study the motions of two cylinders that are the same in all ways except cross-sectional shape.

Nanotechnologies are the fastest growing industry sector ever recorded. The US budget for nanotechnology is predicted to reach the 1 trillion dollar threshold in 2015, meaning that nanotechnologies will indeed be larger than all other technologies combined. High aspect ratio nanomaterials (HARN) become increasingly important in the nanotechnology industries, and show great promise, offering many advantages and improvements to a significant range of products. The main feature of HARN is the ratio of the width of a nanomaterial to its height which can be up to 1000, making the material fibre or platelet- shaped. However, this feature leads to comparison between HARN and other high aspect ratio materials including fibre shaped materials, such as asbestos fibres. Due to the structural similarities between fibrous HARN and asbestos the question arises- do HARN pose the same risk as asbestos? This project aimed to assess the potential of a range of HARN to cause similar pathological effects as asbestos fibres. In order to address this aim a panel of HARN was tested against the fibre pathogenicity paradigm in vivo by examining the pulmonary and pleural responses as well as in vitro to reveal the mechanism of cell/HARN interaction. The first part of the study focused on fibre-shaped HARN, including a panel of distinct length classes of silver nanowires (AgNW) which were injected directly into the pleural space, a target tissue for asbestos related diseases. Injection of high aspect ratio AgNW into the pleural space of mice revealed a length dependent inflammatory response in line with the fibre pathogenicity paradigm which explains fibre pathogenicity. AgNW from 5 μm in length and above led to a significant increase in granulocytes in the pleural space which is similar to that seen after treatment with long amosite asbestos. The use of additional HARN with different compositions allowed us to identify a threshold length for fibre-induced pleural inflammation, which is 5 μm. Frustrated phagocytosis has been stated as an important factor in the initiation of an inflammatory response after fibre exposure. A novel technique, backscatter scanning electron microscopy (BSEM), was used to study frustrated phagocytosis since it provides high-contrast detection of nanowires, allowing clear discrimination between the nanofibres and other cellular features. Using this technique we showed that the onset of inflammation does not correlate with the onset of frustrated phagocytosis, with a fibre length of ≥5 μm and ≥10 μm, respectively, leading to the conclusion that intermediate length fibres fully enclosed within macrophages as well as frustrated phagocytosis are associated with a proinflammatory state in the pleural space. We further showed that fibres compartmentalise in the mesothelial cells at the parietal pleura as well as in inflammatory cells in the pleural space. To investigate the mechanism of the lengthdependent inflammation caused by AgNW, the NALP3 inflammasome activation pathway was studied in vitro, however no clear correlation could be identified. We further aimed to investigate the threshold length of fibre-induced inflammation in the lung and the effect of fibre length on macrophage locomotion in an in vitro macrophage migration assay. Pharyngeal aspiration of AgNW resulted in a length dependent inflammatory response in the lungs with threshold at a fibre length of 14 μm. Shorter fibres including 3, 5 and 10 μm elicited no significant inflammation. This identified threshold length differs from that in the pleural space which may be explained by differences in clearance mechanism of deposited fibres from the airspaces compared to the pleural space. Particle clearance from the lung is partly performed by migration of particle-laden macrophages to the mucociliary escalator. We investigated if uptake of longer fibres leads to restricted mobility and showed that exposure to AgNW in the length of ≥ 5 μm resulted in impaired motility of macrophages in the wound closure assay. The second part of the study focused on HARN in the form of nanoplatelet-shaped particles since nanoplatelets may pose an unusual risk to the lungs and the pleural space because of their aerodynamic properties. We first derived the respirability of graphene nanoplatelets (GP) from the basic principles of the aerodynamic behaviour of plate-shaped particles which allowed us to calculate their aerodynamic diameter. This showed that the nanoplatelets, which were up to 25 μm in diameter, were respirable and so would deposit beyond the ciliated airways following inhalation. We therefore utilized models of pharyngeal aspiration and direct intrapleural installation of GP, as well as an in vitro model, to assess their inflammatory potential. These large but respirable GP were inflammogenic in both the lung and the pleural space at an acute timepoint although they decreased in their inflammatory potential over a 6 weeks period. Oxidation of GP in the lung tissue was investigated in order to identify if GP degraded over the 6 week period in the lung tissue and therefore showed reduced inflammogenicity. Raman spectroscopy was used to measure the oxidation state and revealed that no change occurred over the observed timeframe. The mechanism underlying acute GP inflammation was studied in THP-1 macrophages exposed to GP. These investigations showed that GP exposure led to significant expression of IL-1β, which could be blocked via a number of inhibitors related to the NALP3 inflammasome activation. This study highlights the importance of shape/length of HARN as a driver for in vivo and in vitro inflammogenicity by virtue of their respirable aerodynamic diameter, despite a considerable 2-dimensional size which leads to an inflammatory response when deposited in the distal lungs and the pleural space. The identification of the threshold length for nanofibre-induced pathogenicity in the pleura and the lung has important implications for the understanding of the structure–toxicity relationship for asbestos-induced mesothelioma. It also contributes to risk assessment by offering a template for production of safer synthetic nanofibres by the adoption of a benign-bydesign approach. The results of this work highlight the importance of testing new HARN to protect workers in nanotechnology industries and the public.

The interaction of a rectangular turbulent jet with a free surface for three jet-exit aspect ratios is experimentally investigated using Particle Image Velocimetry (PIV). The jet exits from a sharp edged rectangular orifice plate, parallel to the free surface and has a jet width of d = 10 mm. Aspect ratios of 1, 2 and 4 are studied with a fixed offset of 3d from the free surface. Reynolds and Froude numbers based on the bulk velocity are 6900 and 1.27 respectively. Detailed 2-D velocity fields are captured using the PIV in the central x-y plane for 0 < x/d < 23.5. The distribution of Reynolds shear stresses and turbulent kinetic energy show that they are suppressed in the vicinity of the free surface due to confinement. There was a significant effect of nozzle geometry on the reattachment point and recirculation region of the jets. / May 2016

The focus of this research was to investigate the use of functionalized/non-functionalized multi walled carbon nanotubes (MWCNTs) as reinforcements for the Portland cement paste. The unique geometrical characteristics of the carbon nanotubes (CNTs), as well as its unique mechanical properties such as high strength, ductility and stiffness, were the vital motivation for this study. In this research, we combined this unique material (CNTs) with concrete which is the most used man-made material. When compared to other composite materials, a limited amount of research has been conducted on the CNTs/cement composites. In order to investigate how the aspect ratio of functionalized/non-functionalized MWCNTs affects the mechanical properties of cementitious composites, ten different mixes of the MWCNTs/cement composites were prepared and tested. The different batches had a fixed water/cement ratio of 0.4, and variations of MWCNTs length, concentration and surface treatment. The cement nanocomposites were cast in small-scale specimens (beams) for the three-point flexural testing. Four major mechanical properties were evaluated at ages of 7, 14, and 28 days from the casting day: the maximum flexural strength, ultimate strain capacity (ductility), modulus of elasticity, and modulus of toughness. The results for the different nanocomposite batches were compared with the plain cement (reference) batch. The mechanical testing results showed that at 28 days almost all of the MWCNTs composites increased the flexural strength of the cement nanocomposites. At 28 days, the long MWCNTs increased the flexural strength more than the short MWCNTs. In general, the ultimate strain (ductility) of the short MWCNTs nanocomposites was higher than the ultimate strain of the long MWCNTs nanocomposites. The flexural strength of short 0.2 percent MWNT and long 0.04 percent MWNT (OH) increased by 269 percent and 83 percent, respectively, compared to the plain cement sample at 28 days. The highest ductility at 28 days for the short 0.1 percent MWNT and the short 0.2 percent MWNT was 86 percent and 81 percent, respectively. Clear evidence was obtained from the SEM images for micro-crack bridging; many of the MWCNTs were stretching across the micro-cracks. In conclusion, CNTs as nano reinforcements, can effectively improve certain mechanical properties of the cement paste composites.

Thesis: B.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1976 / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / B.S. / B.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

The response of light-frame timber shear walls to lateral forces is the focus of the dissertation. The objective of this study was to obtain performance characteristics of shear walls with various aspect ratios and overturning restraint via experimental testing and analytical modeling. Presented are the test data of monotonic and cyclic tests on fifty-six light-frame timber shear walls with aspect ratios of 4:1, 2:1, 1:1, and 2:3. Overturning restraint conditions represent engineered construction and conventional construction practices. The walls representative of the engineered construction were attached to the base by means of tie-down anchors and shear bolts. As opposed to engineered construction, conventionally built walls were secured to the base by nails or shear bolts only. The specimens were tested in a horizontal position with oriented strandboard (OSB) sheathing on one side. To obtain conservative estimates, no dead load was applied in the wall plane during the tests. The nail-edge distance across the top and bottom plates varied from 10 mm (3/8 in.) to 19 mm (3/4 in.). Twelve walls were repaired after the initial tests and re-tested. A mechanics-based model was advanced to predict the racking resistance of conventional multi-panel shear walls using simple formulae. The deflections of engineered and conventional shear walls were predicted using the energy method combined with empirical formulae to account for load-deformation characteristics of sheathing-to-framing connections and overturning restraint. The proposed formulae were validated through comparison with test results obtained during this study. The results of the study serve to further development of a mechanics-based methodology for design of shear walls accounting for various wall configurations and boundary conditions. / Ph. D.

Fluvial channel geometry is controlled by the interaction of a number of geologic and hydraulic variables. The width of mixed alluvial-bedrock channels generally is a function of discharge, with variations due to local conditions. The aspect ratio (width/depth) of channels is heavily influenced by substrate size and erodibility. How channel width and aspect ratio vary as a function of other variables, such as structure, lithology, slope, large scale valley topography, and rock uplift, has not been fully quantified. The New River is ideal for examining these relationships because it shows considerable variability in width and aspect ratio and flows through three structurally and lithologically distinct geologic provinces. Through these provinces, the New River does not follow the expected trends of channel widening with increasing drainage area. Topographic maps show that channel width of the New River has a significant variation that far outscores an overall widening downstream. Aspect ratios for the New River are also large, approaching 500. We collected a field data set of 29 sites of the river's channel geometry, along with characteristics of bedrock, sediment, and confinement. Fifteen of the 29 sites are bedrock reaches. The data set allows empirical analysis of how width and aspect ratio of the New River are related to different variables, including slope, discharge, flow velocity, curvature, trend, bedrock type, and structure. Sediment characteristics and confinement of the channel do not affect channel morphology. Bedrock is shown to affect channel width directly through the percent of bedrock exposed in the channel and indirectly through the modified rock mass strength, rock hardness, obliquity to regional strike, dip orientation, and degree of joint intersection. / Master of Science

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This paper describes a promising fabrication technique for rapid replication of high aspect ratio microstructured molds for UV embossing. The process involves casting silicone rubber on a microstructured master, replicating an epoxy mold using the PDMS rubber mold and finally, metallizing the surfaces of the epoxy mold by electroless plating nickel (EN). The preliminary study suggests that this technique is feasible for rapid replication of high aspect ratio molds for UV embossing. Uniform molds can be replicated rapidly through this technique making the process economical and accessible. / Singapore-MIT Alliance (SMA)

An in vivo study with 19 rabbits was completed. Half of the exposed rabbits had a magnetic field placed externally over their right lung. Magnetic resonance images of the lungs were acquired to determine the iron concentrations in the right and left lung of each animal. The right/left ratio increased in the middle and basal regions of the lung. With further optimization, this technique could be an effective method for targeted drug delivery. Additionally, the feasibility of increasing the length of high aspect ratio particles for improved targeted drug delivery was explored. An ultrasonic nozzle was pulsed into a large evaporation chamber. Individual particles were found to be double the original length. However, due to locally increased humidity the droplets were not dried, except with the use of an orifice to rapidly accelerate and break apart the larger droplets. The complications associated with this method make it an undesirable and unfeasible method of creating longer particles.