Browsing by Subject "Stability"

Now showing 1 - 5 of 5
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    Characterization and Measurement of Hybrid Gas Journal Bearings
    (2012-08-28) Lawrence, Tom Marquis; Kemple, Marvin D.; Decca, Ricardo; Joglekar, Yogesh; Petrache, Horia; Akay, Hassan; Krousgrill, Charles Morton
    This thesis concentrates on the study of hybrid gas journal bearings (bearings with externally pressurized mass addition). It differs from most work in that it goes back to “basics” to explore the hydrodynamic phenomena in the bearing gap. The thesis compares geometrically identical bearings with 2 configurations of external pressurization, porous liners where mass-addition compensation is varied by varying the liner’s permeability, and bushings with 2 rows of 6 feedholes where the mass-addition compensation is varied by the feedhole diameter. Experimentally, prototype bearings with mass-addition compensation that spans 2 orders of magnitude with differing clearances are built and their aerostatic properties and mass addition characteristics are thoroughly tested. The fundamental equations for compressible, laminar, Poiseuille flow are used to suggest how the mass flow “compensation” should be mathematically modeled. This is back-checked against the experimental mass flow measurements and is used to determine a mass-addition compensation parameter (called Kmeas) for each prototype bushing. In so doing, the methodology of modeling and measuring the mass addition in a hybrid gas bearing is re-examined and an innovative, practical, and simple method is found that makes it possible to make an “apples-to-apples” comparison between different configurations of external pressurization. This mass addition model is used in conjunction with the Reynolds equation to perform theory-based numerical analysis of virtual hybrid gas journal bearings (CFD experiments). The first CFD experiments performed use virtual bearings modeled to be identical to the experimental prototypes and replicate the experimental work. The results are compared and the CFD model is validated. The ontological significance of appropriate dimensionless similitude parameters is re-examined and a, previously lacking, complete set of similitude factors is found for hybrid bearings. A new practical method is developed to study in unprecedented detail the aerostatic component of the hybrid bearings. It is used to definitively compare the feedhole bearings to the porous liner bearings. The hydrostatic bearing efficiency (HBE) is defined and it is determined that the maximum achievable hydrostatic bearing efficiency (MAHBE) is determined solely by the bearing’s mass addition configuration. The MAHBE of the porous liner bearings is determined to be over 5 times that of the feedhole bearings. The method also presents a means to tune the Kmeas to the clearance to achieve the MAHBE as well as giving a complete mapping of the hitherto misunderstood complex shapes of aerostatic load versus radial deflection curves. This method also rediscovers the obscure phenomenon of static instability which is called in this thesis the “near surface effect” and appears to be the first work to present a practical method to predict the range of static instability and quantify its resultant stiffness fall-off. It determines that porous liner type bearings are not subject to the phenomenon which appears for feedhole type bearings when the clearance exceeds a critical value relative to its mass-addition compensation. The standing pressure waves of hydrostatic and hybrid bearings with the 2 configurations of external pressurization as well as a geometrically identical hydrodynamic bearing are studied in detail under the methodology of the “CFD microscope”. This method is used to characterize and identify the development, growth, and movement of the pressure wave extrema with increased hydrodynamic action (either increasing speed or increasing eccentricity). This method is also used to determine the “cause” of the “near surface effect”. A gedanken experiment is performed based on these results which indicates that a bearing with a “stronger aerostatic strength” component should be more stable than one with a low aerostatic strength component. Numerical instability “speed limits” are found that are also related to the hydrostatic strength of the bearing. The local conditions in the standing waves are characterized in terms of their local Mach number, Knudsen number, Reynolds number, and Taylor Number. It is concluded that low eccentricity bearing whirl can be attributed to the off load-line orientation of the bearing load force caused by the overlay of the hydrodynamic bearing standing wave onto the hydrostatic bearing wave of the hybrid bearing, whereas it is hypothesized that aperiodic and random self-excited vibration which occurs at high eccentricity, as reported in the literature, is probably due to shock waves, turbulence, near surface effect, and slip at local areas of the standing wave.
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    Characterization of pre-analytical sample handling effects on a panel of Alzheimer's disease–related blood-based biomarkers: Results from the Standardization of Alzheimer's Blood Biomarkers (SABB) working group
    (Wiley, 2022) Verberk, Inge M. W.; Misdorp, Els O.; Koelewijn, Jannet; Ball, Andrew J.; Blennow, Kaj; Dage, Jeffrey L.; Fandos, Noelia; Hansson, Oskar; Hirtz, Christophe; Janelidze, Shorena; Kang, Sungmin; Kirmess, Kristopher; Kindermans, Jana; Lee, Ryan; Meyer, Matthew R.; Shan, Dandan; Shaw, Leslie M.; Waligorska, Teresa; West, Tim; Zetterberg, Henrik; Edelmayer, Rebecca M.; Teunissen, Charlotte E.; Neurology, School of Medicine
    Introduction: Pre-analytical sample handling might affect the results of Alzheimer's disease blood-based biomarkers. We empirically tested variations of common blood collection and handling procedures. Methods: We created sample sets that address the effect of blood collection tube type, and of ethylene diamine tetraacetic acid plasma delayed centrifugation, centrifugation temperature, aliquot volume, delayed storage, and freeze–thawing. We measured amyloid beta (Aβ)42 and 40 peptides with six assays, and Aβ oligomerization-tendency (OAβ), amyloid precursor protein (APP)699-711, glial fibrillary acidic protein (GFAP), neurofilament light (NfL), total tau (t-tau), and phosphorylated tau181. Results: Collection tube type resulted in different values of all assessed markers. Delayed plasma centrifugation and storage affected Aβ and t-tau; t-tau was additionally affected by centrifugation temperature. The other markers were resistant to handling variations. Discussion: We constructed a standardized operating procedure for plasma handling, to facilitate introduction of blood-based biomarkers into the research and clinical settings.
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    Concrete services usage on child placement stability: Propensity score matched effects
    (Elsevier, 2020-11) Winters, Drew E.; Pierce, Barbara J.; Imburgia, Teresa M.; School of Social Work
    Background: Experiencing poverty and financial difficulties are significant barriers to outcomes of permanency and placement stability. This is particularly true for children who are in out of home placements. The provision of concrete services is intended to meet concrete needs of families to address this barrier. However, little is known about how concrete services meet the needs of families in need of these services or if the use of concrete services is a viable treatment for children who are in out of home placements. Methods: The present study examined differences between those who received and those who did not receive concrete services on factors of stability, child and caregiver traumatic stress, number of placements, and current out of home placement. Regression analysis examined the association between amount of concrete service spending and permanency. Then to test concrete services as an intervention for children in a current out of home placement, we used propensity score matching to match participants on characteristics that predicted whether they would receive concrete services. We then ran a hierarchical regression to test the treatment condition of concrete services with children who are in a current out of home placement. Results: Participants who received concrete services were at a much higher level of need with significantly higher levels of traumatic stress and number of placements and lower levels of placement stability. The amount of money spent on concrete services was associated with increases in placement stability. And, children in a current out of home placement had an increase in placement stability when they received concrete services. Conclusions: The present study is the first to evidence concrete service as a treatment for placement stability for children in current out of home placements. Spending on concrete services in addition to child welfare services improves a child's current placement stability. This is an important finding with implications for improving child welfare services' approach to those in their care with financial burdens.
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    Stability of MRI metrics in the advanced research core of the NCAA-DoD concussion assessment, research and education (CARE) consortium
    (Springer Nature, 2018-08) Nencka, Andrew S.; Meier, Timothy B.; Wang, Yang; Muftuler, L. Tugan; Wu, Yu-Chien; Saykin, Andrew J.; Harezlak, Jaroslaw; Brooks, M. Alison; Giza, Christopher C.; Difiori, John; Guskiewicz, Kevin M.; Mihalik, Jason P.; LaConte, Stephen M.; Duma, Stefan M.; Broglio, Steven; McAllister, Thomas; McCrea, Michael A.; Koch, Kevin M.; Radiology and Imaging Sciences, School of Medicine
    The NCAA-DoD Concussion Assessment, Research, and Education (CARE) consortium is performing a large-scale, comprehensive study of sport related concussions in college student-athletes and military service academy cadets. The CARE "Advanced Research Core" (ARC), is focused on executing a cutting-edge investigative protocol on a subset of the overall CARE athlete population. Here, we present the details of the CARE ARC MRI acquisition and processing protocol along with preliminary analyzes of within-subject, between-site, and between-subject stability across a variety of MRI biomarkers. Two experimental datasets were utilized for this analysis. First, two "human phantom" subjects were imaged multiple times at each of the four CARE ARC imaging sites, which utilize equipment from two imaging vendors. Additionally, a control cohort of healthy athletes participating in non-contact sports were enrolled in the study at each CARE ARC site and imaged at four time points. Multiple morphological image contrasts were acquired in each MRI exam; along with quantitative diffusion, functional, perfusion, and relaxometry imaging metrics. As expected, the imaging markers were found to have varying levels of stability throughout the brain. Importantly, between-subject variance was generally found to be greater than within-subject and between-site variance. These results lend support to the expectation that cross-site and cross-vendor advanced quantitative MRI metrics can be utilized to improve analytic power in assessing sensitive neurological variations; such as those effects hypothesized to occur in sports-related-concussion. This stability analysis provides a crucial foundation for further work utilizing this expansive dataset, which will ultimately be freely available through the Federal Interagency Traumatic Brain Injury Research Informatics System.
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    Towards Better Diabetes Therapeutics: Designing a More Stable Insulin Analog
    (2023-03) Sambou Oumarou, Oumoul Ghaniyya Faiza; Weiss, Michael; Georgiadis, Millie M.; Hoang, Quyen Q.; Sims, Emily
    Insulin is a hormone that plays a central role in the regulation of human metabolism, and as a drug, is used in the treatment of diabetes mellitus. Hyperglycemia characterizes this condition due to a range of reasons from impaired insulin production by pancreatic beta cells to abnormalities resulting in resistance to insulin action. Depending on time and mechanism of action, the main types of insulin analogs are basal and prandial. Basal insulin analogs are slow-acting insulins that maintain a continuous basal level of insulin in the bloodstream. Prandial insulin analogs are fast-acting and their therapeutic goal is to avoid immediate and late post-prandial hyperglycemia. Most analogs face the problem of chemical degradation and amyloid-like fibril formation (fibrillation) in delivery devices. Thus, many modifications have been made to insulin in the effort to make it more stable and faster-acting. This thesis aims to study the effects of modifications that could be used to design an insulin analog with improved chemical and physical properties, while maintaining biological activity. We studied six amino-acid substitutions to native human insulin in different combinations: desB1 , AB2 , EB3, EA8 , EA14, and EB29. Analogs of the protein were chemically synthesized. Then, fibrillation and circular dichroism assays were performed using purified proteins. The results suggested that EB3 and EA14 are stabilizing modifications that prevent fibril formation, whereas EA8 and EA14 increase the structural stability of an analog. Our findings also suggested that certain modifications in isolation may not impact overall stability, but when combined with others, may show detectable effects, which is why EA8 and EA14 became the focus of further experiments. Cell-based activity assays indicated that all the analogs had similar biological activities. Future work will assess chemical degradation, solubility, amide proton exchange (as monitored by NMR), and mitogenicity.