Re-Framing the Slaughter: Remembering the Rwandan Genocide

This project looks at both official and silenced discourse pertaining to Rwandan genocide remembrance. I look specifically at discourse at museums, memorials, memoir, and film. I argue that the Rwandan state exists in the midst of a political conflict that has produced dual memories of victimization. While the genocidal violence inflicted on Tutsi should be commemorated as uniquely cruel and inhumane, many Hutu experienced similar acts of genocide in the 1972 Burundian genocide and in eastern Congo at the hands of the Rwandan Patriotic Front. The Rwandan state faces the challenge of rebuilding in a context in which both sides have memories of victimization, but only groups that follow the government narrative are given a voice

The macroscopic volume changes of selected polymers subjected to uniform tensile deformation

High density polyethylene (PE), polycarbonate (PC), and polymethylmethacrylate (PMMA) were subjected to uniaxial tensile deformation up to the onset of instability or necking. Simultaneous readings of longitudinal extension and transverse contraction (width and thickness) were obtained continuously during the loading period. From these data, plots of longitudinal versus “average” transverse strain were produced and it was found that the trends were neither constant nor linear over the full strain range employed. Additional plots of per cent volume change versus longitudinal strain indicate that the PMMA and PC show a maximum volume increase of about 0.6% while PE shows a maximum volume decrease on the order of 2.5%. Similar volume decreases have been noted by others and it would appear that structural changes are the most likely cause of this behavior.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38099/1/760120608_ftp.pd

Heat treatment of cold extruded polycarbonate: Some implications for design engineers

Polycarbonate was subjected to various combinations of mechanical - thermal histories to investigate such effects on subsequent tensile mechanical properties. This was accomplished by "cold extruding" the material initially; nominal "reductions in area" of 18, 40 and 64% were used. Cold extruded bars were then heat treated at three temperature levels, all being less than Tg (150[deg]C) of polycarbonate. As compared with the material that was only cold extruded, it was found that in general, heat treating tends to raise the yield stress while lowering the tensile strength, elastic modulus and stress at fracture. The results suggest that a desired combination of properties may be obtainable by the use of a cold work - heat treating sequence.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22085/1/0000509.pd

Cold extrusion and cold drawing of polymeric rod: The influence on subsequent tensile and compressive mechanical properties

Nylon 6-6, polycarbonate and high density polyethylene were extruded and drawn through a 40% reduction die in one pass at room temperature. Certain mechanical properties of the extrudate were measured by subsequent tension and compression tests. For both forming processes and for all three polymers, the tensile true stress-true strain curve is raised compared with the behavior of the original material while the comparable compressive curve is lowered. It was also found that the onset of tensile instability was extended to larger tensile strains when these polymers were first cold worked by extruding or drawing. The elastic modulus was increased when PC was extruded or drawn while this property exhibited a decrease, due to cold working, for both other polymers.All three materials exhibited pronounced directional effects when subjected to compressive loading both parallel to and perpendicular to the longitudinal axis of the extrudate. In a qualitative manner this seems to correlate with greater chain alignment brought about by the forced flow through the die throat.Exploratory temperature measurements indicate that a maximum rise of 20 deg F resulted for this severe reduction of area; this would not cause the glass transition temperature of the PC and Nylon to be exceeded.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34200/1/0000489.pd

Orographic drag associated with lee waves trapped at an inversion

The drag produced by 2D orographic gravity waves trapped at a temperature inversion and waves propagating in the stably stratified layer existing above are explicitly calculated using linear theory, for a two-layer atmosphere with neutral static stability near the surface, mimicking a well-mixed boundary layer. For realistic values of the flow parameters, trapped lee wave drag, which is given by a closed analytical expression, is comparable to propagating wave drag, especially in moderately to strongly non-hydrostatic conditions. In resonant flow, both drag components substantially exceed the single-layer hydrostatic drag estimate used in most parametrization schemes. Both drag components are optimally amplified for a relatively low-level inversion and Froude numbers Fr ≈ 1. While propagating wave drag is maximized for approximately hydrostatic flow, trapped lee wave drag is maximized for l_2 a = O(1) (where l_2 is the Scorer parameter in the stable layer and a is the mountain width). This roughly happens when the horizontal scale of trapped lee waves matches that of the mountain slope. The drag behavior as a function of Fr for l_2 H = 0.5 (where H is the inversion height) and different values of l2a shows good agreement with numerical simulations. Regions of parameter space with high trapped lee wave drag correlate reasonably well with those where lee wave rotors were found to occur in previous nonlinear numerical simulations including frictional effects. This suggests that trapped lee wave drag, besides giving a relevant contribution to low-level drag exerted on the atmosphere, may also be useful to diagnose lee rotor formation

A Hamiltonian Formulation for Long Internal Waves

A novel canonical Hamiltonian formalism is developed for long internal waves in a rotating environment. This includes the effects of background vorticity and shear on the waves. By restricting consideration to flows in hydrostatic balance, superimposed on a horizontally uniform background of vertical shear and vorticity, a particularly simple Hamiltonian structure arises, which can be thought of as describing a nonlinearly coupled infinite collection of shallow water systems. The kinetic equation describing the time evolution of the spectral energy of internal waves is subsequently derived, and a stationary Kolmogorov solution is found in the high frequency limit. This is surprisingly close to the Garrett--Munk spectrum of oceanic internal waves

On the tensile behavior of high density polyethylene subjected to cold rolling

High density polyethylene was cold rolled to produce a series of specimens having from zero to 50% cold work. For those worked beyond 20%, the absolute thickness recovery was relatively constant. X-Ray diffraction studies indicated that significant changes in the original structure also occurred in specimens cold worked beyond 20% and that increasing c-axis orientation was coincident with greater cold work.From the fully recovered specimens, tensile behavior was studied for two strain rates. The early portions of the true stress-true strain curves vary as the degree of initial cold rolling increases; this is reflected in different values of the elastic modulus which exhibits a minimum with material cold rolled about 25%.Tensile instability or necking is delayed as the degree of initial cold working increases but little variation was observed in regard to the tensile strength. The findings pertain for both strain rates. Regarding specimens of similar "structural" condition, say for example 15% cold work, higher strain rates correlate with greater strength and lower strain at instability.In a qualitative manner, comparative behavior between this polymer and ductile metals is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34199/1/0000488.pd

Large-amplitude mesospheric response to an orographic wave generated over the Southern Ocean Auckland Islands (50.7°S) during the DEEPWAVE project

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) project was conducted over New Zealand and the surrounding regions during June and July 2014, to more fully understand the generation, propagation, and effects of atmospheric gravity waves. A large suite of instruments collected data from the ground to the upper atmosphere (~100 km), with several new remote-sensing instruments operating on board the NSF Gulfstream V (GV) research aircraft, which was the central measurement platform of the project. On 14 July, during one of the research flights (research flight 23), a spectacular event was observed as the GV flew in the lee of the sub-Antarctic Auckland Islands (50.7°S). An apparent ship wave pattern was imaged in the OH layer (at ~83.5 km) by the Utah State University Advanced Mesospheric Temperature Mapper and evolved significantly over four successive passes spanning more than 4 h. The waves were associated with orographic forcing generated by relatively strong (15-20 m/s) near-surface wind flowing over the rugged island topography. The mountain wave had an amplitude T_ ~ 10 K, a dominant horizontal wavelength ~40 km, achieved a momentum flux exceeding 300 m2 s-2, and eventually exhibited instability and breaking at the OH altitude. This case of deep mountain wave propagation demonstrates the potential for strong responses in the mesosphere arising from a small source under suitable propagation conditions and suggests that such cases may be more common than previously believed. © 2016. American Geophysical Union. All Rights Reserved