Master of Science

thesisA standard lumped parameter model for an inertial vibration energy harvester consists of a proof mass, spring, and damper(s). This model can also be described with a proof mass, viscous damping element for parasitic mechanical losses, and a generalized transducer that applies some force to the mass damper system. The transducer may contain restorative spring elements and energy extraction elements to harvest power. Currently the framework to relate vibration input to an optimal transducer architecture does not exist. Previous work has shown that for some inputs nonlinear transducer architectures can result in an increased power output. This paper outlines a mathematical framework needed in order to find the optimal transducer architecture for a given vibration input. This framework defines the theoretical upper limit that any inertial transducer can harvest from a given vibration input in the presence of viscous mechanical damping. This framework is then applied to three cases of standard input types. The first application is a single sinusoid input. The transducer architecture found is the expected result, a linear spring with matched resonance to the input, and an energy extraction element, that behaves as a linear viscous damper, with matched impedance to the mechanical damping. The second application of this framework is an input of two sinusoids both having equal magnitude but different frequencies. The resulting optimal transducer is dependent on the difference in the frequencies of the two signals. This optimal transducer is often not realizable with a passive system, as it is inherently time dependent. For all cases of frequency separation between the two sinusoidal inputs, the upper limit for the energy generated is found to be twice that of a linear harvester tuned to the lower of the two frequencies. The third application is for an input whose frequency changes linearly in time (i.e. a swept sinusoid). The optimal transducer architecture for this input is found to be completely time dependent. However for the case when the change in the input frequency is much slower than the period of the system, the transducer can be approximated by a linear spring whose stiffness changes in time

Alterations in Platelet Function and Cell-Derived Microvesicles in Recently Menopausal Women: Relationship to Metabolic Syndrome and Atherogenic Risk

A woman’s risk for metabolic syndrome (MS) increases at menopause, with an associated increase in risk for cardiovascular disease. We hypothesized that early menopause-related changes in platelet activity and concentrations of microvesicles derived from activated blood and vascular cells provide a mechanistic link to the early atherothrombotic process. Thus, platelet functions and cellular origin of blood-borne microvesicles in recently menopausal women (n = 118) enrolled in the Kronos Early Estrogen Prevention Study were correlated with components of MS and noninvasive measures of cardiovascular disease [carotid artery intima medial thickness (CIMT), coronary artery calcium (CAC) score, and endothelial reactive hyperemic index (RHI)]. Specific to individual components of the MS pentad, platelet number increased with increasing waist circumference, and platelet secretion of ATP and expression of P-selectin decreased with increasing blood glucose (p = 0.005) and blood pressure (p < 0.05), respectively. Waist circumference and systolic blood pressure were independently associated with monocyte- and endothelium-derived microvesicles (p < 0.05). Platelet-derived and total procoagulant phosphatidylserine-positive microvesicles, and systolic blood pressure correlated with CIMT (p < 0.05), but not with CAC or RHI. In summary, among recently menopausal women, specific platelet functions and concentrations of circulating activated cell membrane-derived procoagulant microvesicles change with individual components of MS. These cellular changes may explain in part how menopause contributes to MS and, eventually, to cardiovascular disease

Recombinant tissue-type plasminogen activator versus a novel dosing regimen of urokinase in acute pulmonary embolism: a randomized controlled multicenter trial

AbstractThrombolysis of acute pulmonary embolism can be accomplished more rapidly and safely with 100 mg of recombinant human tissue-type plasminogen activator (rt-PA) (Activase) than with a conventional dose of urokinase (Abbokinase) given as a 4,400-U/kg bolus dose, followed by 4,400 U/kg per h for 24 h. To determine the effects of a more concentrated urokinase dose administered over a shorter time course, this trial enrolled 90 patients with baseline perfusion lung scans and angiographically documented pulmonary embolism. They were randomized to receive either 100 mg/2 h of rt-PA or a novel dosing regimen of urokinase: 3 million U/2 h with the initial 1 million U given as a bolus injection over 10 min. Both drugs were delivered through a peripheral vein.To assess efficacy after initiation of therapy, repeat pulmonary angiograms at 2 h were performed in 87 patients and then graded in a blinded manner by a panel of six investigators. Of the 42 patients allocated to rt-PA therapy, 79% showed angiographic improvement at 2 h, compared with 67% of the 45 patients randomized to urokinase therapy (95% confidence interval for the difference in these proportions [rt-PA minus urokinase] is −6.6% to 30.4%; p = 0.11). The mean change in perfusion lung scans between baseline and 24 h was similar for both treatments. Three patients (two treated with rt-PA and one with urokinase) had an intracranial hemorrhage, which was fatal in one.The results indicate that a 2-h regimen of rt-PA and a new dosing regimen of urokinase exhibit similar efficacy and safety for treatment of acute pulmonary embolism

Characteristics and Risk Factors of Cancer Associated Venous Thromboembolism

The objective of this study was to examine the differences in commonly associated characteristics and risk factors of venous thromboembolism (VTE) between patients with and without cancer in a VTE population

Differences in Thrombotic Risk Factors in Black and White Women with Adverse Pregnancy Outcome

Black women have an increased risk of adverse pregnancy outcomes and the characteristics of thrombotic risk factors in this population are unknown. The objective of this study was to examine the racial differences in thrombotic risk factors among women with adverse pregnancy outcomes

Actin polymerization stabilizes α4β1 integrin anchors that mediate monocyte adhesion

Leukocytes arrested on inflamed endothelium via integrins are subjected to force imparted by flowing blood. How leukocytes respond to this force and resist detachment is poorly understood. Live-cell imaging with Lifeact-transfected U937 cells revealed that force triggers actin polymerization at upstream α4β1 integrin adhesion sites and the adjacent cortical cytoskeleton. Scanning electron microscopy revealed that this culminates in the formation of structures that anchor monocyte adhesion. Inhibition of actin polymerization resulted in cell deformation, displacement, and detachment. Transfection of dominant-negative constructs and inhibition of function or expression revealed key signaling steps required for upstream actin polymerization and adhesion stabilization. These included activation of Rap1, phosphoinositide 3-kinase γ isoform, and Rac but not Cdc42. Thus, rapid signaling and structural adaptations enable leukocytes to stabilize adhesion and resist detachment forces