284 research outputs found
Spectroscopic surface scattering of confined acoustic phonons in silicon nanostructures
No full textThe specularity of phonons at rough crystal surfaces is a fundamental aspect of phonon transport in nanostructures. It directly impacts engineering problems such as heat conduction in nanostructures and dissipation in nanomechanical resonators. At room temperature, the available guidance from theory is limited to fully diffuse transport under the condition of small surface roughness. Recent experiments in thermal transport suggest that there may exist large gaps in understanding phonon interactions with rough surfaces, especially when the roughness dimensions are comparable to phonon wavelengths. To consider such refinements, this thesis focuses on spectroscopic measurements of specularity in silicon nanostructures with well-characterized surface morphologies. We employ a femtosecond laser pump-probe setup to excite and detect confined acoustic phonons (∼ 18 - 200 GHz) in freely- suspended silicon membranes and nanowires. Surface scattering dominates intrinsic Akhiezer damping at frequencies > 60 GHz, thereby enabling us to probe phonon-boundary interactions over wavelengths ∼ 42 - 140 nm. To quantitatively understand the dependence of boundary scattering on RMS roughness and correlation length, we obtained detailed statistics of the surfaces using HRTEM and AFM imaging. For silicon membranes, we find that both Ziman and perturbation approach for roughness scattering successfully explain the nearly specular reflection of ∼ 0.1 THz phonons from surface with ∼ 1-nm scale roughness. The measured phonon specularities for silicon nanowires, however, are significantly lower in comparison to membranes for the frequency range ν ∼ 18−100 GHz. The reduction in specularity is caused by additional scattering from multiple surfaces introduced in a nanowire. Using a remarkably simple normalization scheme, we show that the scattering from multiple surfaces can be effectively decoupled. The magnitudes of the (normalized) phonon lifetimes are in good quantitative agreement with the predictions of Ziman approach but does not perfectly explain the frequency dependence. The τ ∼ ν^−1.7 dependence observed in our experiments is suggestive of weak phonon localization which cannot be understood within the existing framework of single scattering (or equivalently first Born approximation). This work helps to advance the fundamental understanding of phonon scattering at the surfaces of nanostructures.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-12-01The student, Dhruv Gelda, accepted the attached license on 2018-11-15 at 12:58.The student, Dhruv Gelda, submitted this Dissertation for approval on 2018-11-15 at 13:10.This Dissertation was approved for publication on 2018-11-15 at 16:13.DSpace SAF Submission Ingestion Package generated from Vireo submission #13089 on 2019-02-08 at 11:39:00Made available in DSpace on 2019-02-08T18:39:46Z (GMT). No. of bitstreams: 3
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Previous issue date: 2018-11-15Embargo set by: Seth Robbins for item 109938
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Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 109938
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Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 109938
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Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 109938
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Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 109938 on 2021-02-09T10:15:21Z
Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies
No full textHigh-frequency surface acoustic waves (SAWs) in the GHz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanism in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic Bragg reflectors (DABRs) in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than five times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can enable future measurements of intrinsic damping in SAWs at 100 GHz.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2019-05-01The student, Dhruv Gelda, accepted the attached license on 2017-01-31 at 12:44.The student, Dhruv Gelda, submitted this Thesis for approval on 2017-01-31 at 13:04.This Thesis was approved for publication on 2017-01-31 at 15:56.DSpace SAF Submission Ingestion Package generated from Vireo submission #10551 on 2018-08-14 at 16:00:20Made available in DSpace on 2018-08-14T21:37:12Z (GMT). No. of bitstreams: 3
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Previous issue date: 2017-01-31Embargo set by: Seth Robbins for item 106497
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CYTOLOGICAL, ULTRASOUND AND BIOCHEMICAL CORRELATION IN HASHIMOTO’S THYROIDITIS, FARIDABAD, INDIA: A RETROSPECTIVE CROSS-SECTIONAL ANALYSIS.
No full textBackground
Hashimoto’s thyroiditis, an autoimmune disorder that impairs thyroid hormone production via antibody-mediated destruction of thyroid cells, affects women more frequently and presents symptoms like weight gain and fatigue. This study investigates the correlation between cytomorphological, biochemical, and radiological findings in diagnosing this condition, utilizing Fine Needle Aspiration Cytology (FNAC) as a key diagnostic tool.
Materials and methods
A retrospective analysis of cytological, radiological, and biochemical parameters was done for 84 patients who underwent FNAC for Hashimoto’s Thyroiditis. The blood concentration of thyroid hormones was evaluated by the Thyroid Function Test (TFT). Thyroid ultrasound was done using a high-frequency linear ultrasound transducer.
Results
This study found Hashimoto's thyroiditis more common in females (95%) and primarily in those aged 20-40 years. Biochemical hypothyroidism (Thyroid function test) was observed in 50% of the selected patients, euthyroidism was observed in about 43% of the patients, and hyperthyroidism was observed in 7 % of the patients. Cytological findings showed mild, moderate, and dense lymphocytic infiltration in 32.15%, 41.66%, and 26.20% of patients across Grades I, II, and III, respectively. Moreover, 51% of the patients were affected with diffuse thyroiditis, 35% of the patients were affected with goiter, 8% of the patients were affected with thyroid nodules, and the remaining 6% of the patients were seen to be normal in the ultrasound findings.
Conclusion
Hashimoto’s Thyroiditis is more prevalent in females, with elevated biochemical results linked to higher FNAC grades. Early detection of diffuse thyroiditis using ultrasound assists in predicting the disease before clinical signs appear. Integrating biochemical, cytology, and ultrasound findings can identify subclinical hypothyroidism.
Recommendation
For early detection and precise staging of Hashimoto’s Thyroiditis, integrating cytomorphological, biochemical, and radiological diagnostics is advised. Future research should aim at refining treatment strategies based on these findings
Ethics: What is the decent thing?
No full textWhat is the decent thing? As VW feels the fallout from breaking its promises, architects Irena Bauman, author of How to be a Happy Architect, and Dhruv Sookhoo, ethics investigator, tackle some everyday ethical dilemmas
Hybrid adaptive chassis control for vehicle lateral stability in the presence of uncertainty
No full textTo guarantee the safety of passengers in a wide range of driving situations, vehicle lateral stability should be achieved in the presence of nonlinear dynamics (consequence of critical maneuvers) and uncertainty (consequence of uncertain parameters). This paper designs a hybrid adaptive strategy to attain vehicle stability in these situations. The design is based on a piecewise affine (PWA) description of the vehicle model where partitions describe both the linear and the nonlinear regimes, and where parametric uncertainties are handled by estimators for the control gains that can adapt to different conditions acting on the system. Comparisons with strategies that merely exploits the linear region of the vehicle dynamics are provided for different driving conditions, and performance improvements of the proposed methodology are assessed.Accepted Author ManuscriptTeam Bart De Schutte
The Proposed Tiebreaker Rule in OECD/G20 BEPS Action 6: A Critical Examination of the Possible Motives and Means, and a Potential Alternative
No full textIn this article, the author critically examines the proposed tiebreaker rule in the OECD’s Final Report on Action 6 of the Base Erosion and Profit Shifting (BEPS) project, and the motives behind the proposal. The author concludes by suggesting an alternative, which he argues is a more effective means to achieve the intended ends
Role of Gray Scale Ultrasound and Colour Doppler in Evaluation of Thyroid Nodules with Pathological Correlation
No full text
Three Essays in Law and Finance
No full textThis dissertation explores three topics at the intersection of law and finance. It emphasizes how the structure of the legal profession and contractual choices made in bylaws and charters have significant effects on corporate governance. The first essay, “The Market for General Counsel,” studies the hiring, firing, demographics, and politics of general counsels (GCs) in American public companies. I use an original dataset tracking the background and career trajectories of over three thousand GCs at publicly traded U.S. companies to establish that a majority of inhouse counsel are outsiders without previous connections to their employers. I also document several trends in the market for GCs, including the rise of women GCs and the increasing Democratic tilt of inhouse counsel. GCs are twice as likely to be terminated from their position as CEOs, and their tenures have substantially decreased since the 1990s. Outsider GCs are more likely to be fired at any point in their tenure than insiders or pseudo-outsiders, and this relationship between insider status and firing persists after controlling for litigation around the time of the GC’s departure.The second essay, “Does Bankruptcy Priority Matter? Evidence From India” examines the effect of a 2019 decision by the Indian Supreme Court introducing bankruptcy priority. I find that banking stocks exhibited positive abnormal returns around the time of the decision. This effect was concentrated in banks with toxic balance sheets as well as state-operated banks. Debtors also seemed to have benefitted from the advent of absolute priority: firms with high costs of debt had positive abnormal returns around the time of the court’s decision. This evidence is consistent with the salutary effects of strong creditor rights predicted by economic theory, and could inform U.S. debates about the desirability of bankruptcy priority. The final essay, “The Rise of Dual-Class Stock IPOs is co-authored with Ofer Eldar, Yael Hochberg, and Lubomir Litov. In this essay, we create a novel dataset to examine the recent increase in the popularity of dual-class stock IPOs. We create a novel taxonomy for controlling shareholders at dual-class firms, and show that the rise of dual-class stock IPOs has been driven by founder-controlled firms. Founders’ wedge has increased over time with an increase in founder bargaining power, as proxied by greater availability of private capital and technological shocks that reduced firms’ need for external financing. Chapter One: The Market for General Counsel This paper presents the first systematic descriptive study of the market for general counsel (GCs) in publicly traded U.S. companies. Using a hand-collected dataset, I track the backgrounds and careers of 3,409 GCs, and establish basic facts about the hiring, firing, demographics, and politics of inhouse counsel. Most GCs are outsiders to their companies, not having previously worked in subordinate positions within the legal department or served as external counsel. I find that the share of women GCs has risen sharply over time, with GCs now about five times as likely to be female as chief executive officers (CEOs). GCs have also become more Democratic-leaning over time, in sharp contrast to business-side employees such as CEOs. GC tenures have decreased over time, and GCs are twice as likely to be fired from their positions as CEOs. Outsider GCs are especially likely to be fired from their position, controlling for biographical details, firm financials, and securities litigation against the firm. Chapter Two: Does Bankruptcy Priority Matter? Evidence from IndiaThis paper offers empirical evidence to demonstrate the economic value of bankruptcy priority. Since bankruptcy priority has been the law of the land in the United States for eight decades, most existing arguments for or against bankruptcy priority have been theoretical. I exploit the quasi-natural setting of a 2019 decision by the Indian Supreme Court to investigate the effects of the introduction of bankruptcy priority. I find that banking stocks exhibited positive abnormal returns around the time of the decision. This effect was concentrated in banks with toxic balance sheets as well as state-operated banks. Debtors also seem to have benefitted from the introduction of absolute priority: firms with higher cost of debt experienced positive abnormal returns around the time of the decision. This evidence is consistent with the salutary effects of strong creditor rights predicted by economic theory, and could inform U.S. debates about the desirability of bankruptcy priority. Chapter Three: The Rise of Dual-Class Stock IPOs We create a novel dataset to examine the recent rise in dual-class IPOs. We document that dual-class firms have different types of controlling shareholders and wedges between voting and economic rights, and that the increasing popularity of dual-class structures is driven by founder-controlled firms. We find that founders’ wedge is greater when founders have stronger bargaining power. The increase in founder control over time is due to greater availability of private capital and technological shocks that reduced firms’ needs for external financing. Stronger bargaining power is also associated with a lower likelihood of sunset provisions that terminate dual-class structures
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