Residual stresses in amorphous alumina films synthesized by ion beam assisted deposition

A set of experiments was conducted to determine the origin of residual stresses in amorphous Al2O3 films formed by ion beam assisted deposition. Samples were deposited during bombardment by Ne, Ar, or Kr over a narrow range of energies, E, and a wide range of ion‐to‐atom arrival rate ratios, R. Films were characterized in terms of composition, thickness, density, crystallinity, microstructure, and residual stress. Film composition was independent of ion beam parameters and residual stress was independent of thickness over the range 200–1200 nm. Stress varied strongly with ion beam parameters and gas content. Residual stress and gas content saturated at a normalized energy of ∼20 eV/atom or an R of ∼0.05. Where residual stress varied linearly with RE1/2, results are consistent with an atom peening model, but saturation at high R or RE1/2 is inconsistent with such a model. Stress due to gas pressure in existing voids explains neither the functional dependence on gas content nor the magnitude of the observed stress. A probable explanation for the behavior of stress is gas incorporation into the matrix, where the amount of incorporated gas is controlled by trapping. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70865/2/JAPIAU-77-7-3029-1.pd

Aspirin inhibits the acute venodilator response to furosemide in patients with chronic heart failure

OBJECTIVES: We sought to determine the effect of aspirin on the venodilator effect of furosemide in patients with chronic heart failure (CHF) BACKGROUND: Furosemide has an acute venodilator effect preceding its diuretic action, which is blocked by nonsteroidal anti-inflammatory drugs. The ability of therapeutic doses of aspirin to block this effect of furosemide in patients with CHF has not been studied. For comparison, the venodilator response to nitroglycerin (NTG) was also studied. METHODS: Eleven patients with CHF were randomized to receive placebo, aspirin at 75 mg/day or aspirin at 300 mg/day for 14 days in a double-blind, crossover study. The effect of these pretreatments on the change in forearm venous capacitance (FVC) after 20 mg of intravenous furosemide was measured over 20 min by using venous occlusion plethysmography. In a second study, the effect of 400 μg of sublingual NTG on FVC was documented in 11 similar patients (nine participated in the first study). RESULTS: Mean arterial pressure, heart rate and forearm blood flow did not change in response to furosemide. After placebo pretreatment, furosemide caused an increase in FVC of 2.2% (95% confidence interval [CI] −0.9% to 5.2%; mean response over 20 min). By comparison, FVC fell by −1.1% (95% CI −4.2% to 1.9%) after pretreatment with aspirin at 75 mg/day, and by −3.7% (95% CI −6.8% to −0.7%) after aspirin at 300 mg/day (p = 0.020). In the second study, NTG increased FVC by 2.1% (95% CI −1.6% to 5.8%) (p = 0.95 vs. furosemide). CONCLUSIONS: In patients with CHF, venodilation occurs within minutes of the administration of intravenous dose of furosemide. Our observation that aspirin inhibits this effect further questions the use of aspirin in patients with CHF

Role of ion beam assisted deposition in the synthesis and fracture of metal-ceramic multilayers

Multilayer metal-ceramic films have the potential to serve as strong, tough and environmentally resistant films and coatings for a wide variety of applications. They derive their properties from the multilayer structure (architecture), the microstructure and, hence, mechanical properties of the individual layers and the stress state of the film. However, in order to realize the potential of microlaminates, these features (architecture, microstructure and stress) must be controlled. Ion beam assisted deposition (IBAD) holds the promise to provide this control. In an effort to understand how IBAD can control mechanical properties of films, single trilayer and five-bilayer metal-ceramic, Al-Al2O3 films were fabricated on ductile metal substrates using IBAD over a range of thicknesses and normalized energies. Results of bending and tension experiments revealed that the stress state is critical in determining the fracture strain (ductility) of the film. A residual compressive stress is beneficial and can be formed in the oxide phase by bombardment of the film with Ar during deposition. The behavior of film stress correlates well with Ar gas incorporation and the film consists of a high density of small cavities. Gas incorporation into the cavities or the surrounding matrix may be responsible for the observed residual compressive stress. The density of surface cracks at high strains is a function of the film architecture, film strength and the interfacial shear strength. Use of a multilayer structure reduces the crack density over a monolithic oxide film by increasing the strain needed to form through-thickness cracks and by increasing the intrinsic strength of the brittle layers by decreasing their thickness. Ion bombardment of the metal layers resulted in radiation damage and grain size refinement, both of which result in a stronger film and a lower crack density. It was shown that architecture, microstructure and stress are the key ingredients in microlaminate properties and are uniquely controllable by IBAD.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31878/1/0000828.pd

Clara Goldiner - Senior Internship Reflection

This summer I interned with the New York City Department of Housing Preservation and Development (HPD) in the research department. HPD is the department of the goverment of New York City responsible for developing and maintaining the city\u27s stock of affordable housing. The main focus of my internship was a project that I worked on expanding on a study that the department I was working with had conducted. The project focused on comparing New York City neighborhood quality and seeing if low-income New Yorkers who were given access to public housing were living in better neighborhoods a few years later