Real-time fault diagnosis for propulsion systems

Current research toward real time fault diagnosis for propulsion systems at NASA-Lewis is described. The research is being applied to both air breathing and rocket propulsion systems. Topics include fault detection methods including neural networks, system modeling, and real time implementations

Essays on Corporate Financial Reporting

This dissertation examines changes in managers’ financial reporting around two major corporate financing events, accelerated share repurchases (ASRs) and seasoned equity offerings (SEOs). The first essay provides evidence on managerial motives for initiating ASRs, a recent and important innovation in repurchase methods, by examining managers’ financial reporting behavior around ASRs and post-ASR performance. ASR firms report positive discretionary accruals in the quarter of the repurchase announcement and that the upward earnings management increases with the percentage of equity repurchased, initiation of the repurchase earlier in the quarter, and CEO’s bonus compensation as a fraction of total compensation. There is however a negative association between the ASR announcement returns and pre-repurchase positive discretionary accruals, suggesting that investors perceive the positive discretionary accruals as the result of managerial opportunism (i.e., boosting EPS) rather than managerial optimism (i.e., signaling undervaluation). Further, ASR announcements are not followed by an increase in operating performance. There is also no evidence of positive long-run abnormal stock performance during the post-ASR period. The results suggest that managers use ASRs along with positive discretionary accruals to manage reported EPS rather than to signal their favorable private information about firms’ prospects. The second essay examines the relation between firms’ financial constraints and their financial reporting during periods when they attempt to raise equity capital. Specifically, I investigate whether financially constrained firms tend to manage their earnings more aggressively around SEOs as compared to financially unconstrained firms. By using different measures of financial constraints, I document that constrained issuers, which cannot credibly signal the absence of aggressive earnings management, report higher income-increasing accruals than unconstrained issuers. I also find that investors correctly conjecture this greater earnings inflation and adjust issuers’ stock prices accordingly at the time of the offering. The evidence suggests that the aggressive earnings management by constrained issuers is not simply the result of managerial opportunism but rather a rational response to anticipated market behavior at offering announcements

Extensions of Picard 2-Stacks and the cohomology groups Ext^i of length 3 complexes

The aim of this paper is to define and study the 3-category of extensions of Picard 2-stacks over a site S and to furnish a geometrical description of the cohomology groups Ext^i of length 3 complexes of abelian sheaves. More precisely, our main Theorem furnishes (1) a parametrization of the equivalence classes of objects, 1-arrows, 2-arrows, and 3-arrows of the 3-category of extensions of Picard 2-stacks by the cohomology groups Ext^i, and (2) a geometrical description of the cohomology groups Ext^i of length 3 complexes of abelian sheaves via extensions of Picard 2-stacks. To this end, we use the triequivalence between the 3-category of Picard 2-stacks and the tricategory T^[-2,0](S) of length 3 complexes of abelian sheaves over S introduced by the second author in arXiv:0906.2393, and we define the notion of extension in this tricategory T^[-2,0](S), getting a pure algebraic analogue of the 3-category of extensions of Picard 2-stacks. The calculus of fractions that we use to define extensions in the tricategory T^[-2,0](S) plays a central role in the proof of our Main Theorem.Comment: 2 New Appendix: in the first Appendix we compute a long exact sequence involving the homotopy groups of an extension of Picard 2-stacks, and in the second Appendix we sketch the proof that the fibered sum of Picard 2-stacks satisfies the universal propert

Electrical System for Bioelectric Impedance using AD5933 Impedance Converter

Benchtop lab equipment, such as the HP4194A Precision Impedance Analyzer, offer accuracy and functionality but are often expensive and bulky. Although integrated circuits offer less functionality than benchtop equivalents, they can be a cheaper alternative for smaller applications. In this study, the AD5933 Impedance Converter was investigated as a low-cost option for impedance analysis of the bicep brachii. The AD5933 evaluation board was properly calibrated to measure human muscle by using an equivalent parallel circuit consisting of a 5 nF capacitor and a 1 kOhm resistor. Next, the impedance of the bicep was measured using the AD5933 as the experimental device and the HP4194A as the control device. A 2 volt peak-to- peak signal was generated for a 10 kHz to 100 kHz frequency range and the resulting impedance of the bicep was measured. The AD5933 recorded impedance curves qualitatively and quantitatively similar to those recorded by the HP4194A. Thus, the AD5933 was considered to be a low- cost alternative for impedance analysis in small-scale medical applications

Corbynizmin Yükselişi ve Çöküşü

In an era when the traditional centre-left parties have constantly lost ground to rising right-wing populist movements, Jeremy Corbyn’s Labour Party was increasingly portrayed as a left-wing alternative to both pro-austerity incumbent parties that rule out redistributive policies and right-wing populism fuelled by the grievances of the masses targeting the traditional political elites. Corbyn managed to mobilize a vast section of the society by becoming Europe’s biggest left-wing party in terms of membership and increased its votes in the 2017 election, especially by gaining youth support. Nevertheless, the 2019 election constituted an immense fall. Regarding his political discourse both during the electoral campaigns and the serious challenges he faced, Corbyn could be identified as a left-wing populist. To be more specific, Corbyn is a democratic socialist who usually resorted to left-wing populist means within a social democratic party, and failed in his efforts to transform both the British mainstream politics and the Labour in the end.Geleneksel merkez sol partilerin yükselen sağ popülist hareketlere karşı sürekli zemin kaybettiği bir tarihsel evrede, Jeremy Corbyn'in İşçi Partisi, hem yeniden dağıtım politikalarını dışlayan kemer sıkma yanlısı iktidar partilerine, hem de kitlelerin siyasi elitlere yönelik memnuniyetsizliğinden güç alan sağ popülizme karşı bir sol alternatif olarak tasvir edildi. Britanya İşçi Partisi üye sayısı bakımından Avrupa'nın en büyük sol partisi haline gelerek toplumun geniş bir kesimini harekete geçirmeyi başardı ve 2017 seçimlerinde özellikle gençlerin desteğini alarak oylarını arttırdı. Buna karşılık 2019 seçimleri muazzam bir düşüşe sahne oldu. Corbyn, seçim kampanyaları sırasındaki siyasi söylemi ve karşılaştığı zorluklara verdiği yanıtlar bakımından bir sol popülist olarak tanımlanabilir. Daha açık ifade etmek gerekirse, Corbyn, sosyal demokrat bir parti içinde genellikle sol popülist araçlara başvuran ve sonunda hem İngiliz ana akım siyasetini hem de İşçi Partisi'ni dönüştürme çabalarında başarısız olmuş bir demokratik sosyalisttir

Cargo adaptors regulate stepping and force generation of mammalian dynein-dynactin.

Cytoplasmic dynein is an ATP-driven motor that transports intracellular cargos along microtubules. Dynein adopts an inactive conformation when not attached to a cargo, and motility is activated when dynein assembles with dynactin and a cargo adaptor. It was unclear how active dynein-dynactin complexes step along microtubules and transport cargos under tension. Using single-molecule imaging, we showed that dynein-dynactin advances by taking 8 to 32-nm steps toward the microtubule minus end with frequent sideways and backward steps. Multiple dyneins collectively bear a large amount of tension because the backward stepping rate of dynein is insensitive to load. Recruitment of two dyneins to dynactin increases the force generation and the likelihood of winning against kinesin in a tug-of-war but does not directly affect velocity. Instead, velocity is determined by cargo adaptors and tail-tail interactions between two closely packed dyneins. Our results show that cargo adaptors modulate dynein motility and force generation for a wide range of cellular functions

Dielectric Characterization of Coastal Cartilage Chondrocytes

BACKGROUND: Chondrocytes respond to biomechanical and bioelectrochemical stimuli by secreting appropriate extracellular matrix proteins that enable the tissue to withstand the large forces it experiences. Although biomechanical aspects of cartilage are well described, little is known of the bioelectrochemical responses. The focus of this study is to identify bioelectrical characteristics of human costal cartilage cells using dielectric spectroscopy. METHODS: Dielectric spectroscopy allows non-invasive probing of biological cells. An in house computer program is developed to extract dielectric properties of human costal cartilage cells from raw cell suspension impedance data measured by a microfluidic device. The dielectric properties of chondrocytes are compared with other cell types in order to comparatively assess the electrical nature of chondrocytes. RESULTS: The results suggest that electrical cell membrane characteristics of chondrocyte cells are close to cardiomyoblast cells, cells known to possess an array of active ion channels. The blocking effect of the non-specific ion channel blocker gadolinium is tested on chondrocytes with a significant reduction in both membrane capacitance and conductance. CONCLUSIONS: We have utilized a microfluidic chamber to mimic biomechanical events through changes in bioelectrochemistry and described the dielectric properties of chondrocytes to be closer to cells derived from electrically excitably tissues. GENERAL SIGNIFICANCE: The study describes dielectric characterization of human costal chondrocyte cells using physical tools, where results and methodology can be used to identify potential anomalies in bioelectrochemical responses that may lead to cartilage disorders