Essays on Quantitative Methods for Consequences of Political Institutions

In this dissertation, I develop and apply sophisticated Bayesian models to the analysis of institutional effects on electoral and legislative behavior in the policy making process. Leveraging the flexibility of Bayesian methods for statistical modeling, I deal with several methodological problems encountered by political scientists, and social scientists in general, in some established research agenda. This dissertation shows the improvement of the ability to evaluate the success of conflicting theories when these methodological issues are properly dealt with. The consequences of political institutions are investigated at three different levels in this dissertation: countries, political parties, and individual legislators. First of all, at the country level, I investigate whether there is a difference between the performances of democratic and nondemocratic regimes in social provision policy in 18 Latin American countries by focusing on the rarely changing property of political regimes. An appropriate model for the dynamic nature of rarely changing variables is built to thoroughly explore how democratic institutions improve social welfare. Second, at the party level, I develop a Bayesian structural equation model to examine the interdependence between party policy strategies and party support in multiparty systems, in an effort to illustrate the endogenous dynamics of multiparty systems. The results show that party manifestos do not provide clear-cut division of party policy positions. Instead, party labels are more important information than changes in party manifestos to the electorate. Finally, at the level of legislators, I focus on the role of the president and political parties in Brazilian legislative process, in which political exchanges between the government and legislature is an essential feature. By recognizing the existence of the non-ideological effect on voting behavior, I develop a random item-difficulty ideal-point model implied by the spatial voting model to analyze the relationship between coalition dynamics and party-based voting behavior of legislators

Endoscopic Optical Coherence Tomography for Clinical Gastroenterology

Optical coherence tomography (OCT) is a real-time optical imaging technique that is similar in principle to ultrasonography, but employs light instead of sound waves and allows depth-resolved images with near-microscopic resolution. Endoscopic OCT allows the evaluation of broad-field and subsurface areas and can be used ancillary to standard endoscopy, narrow band imaging, chromoendoscopy, magnification endoscopy, and confocal endomicroscopy. This review article will provide an overview of the clinical utility of endoscopic OCT in the gastrointestinal tract and of recent achievements using state-of-the-art endoscopic 3D-OCT imaging systems. Keywords: optical coherence tomography; optical biopsy; endoscopic imaging; Barrett’s esophagus; inflammatory bowel diseaseNational Institutes of Health (U.S.) (Grant R01-CA75289-17)National Institutes of Health (U.S.) (Grant R44-CA101067-06)National Institutes of Health (U.S.) (Grant R01-CA178636-01)National Institutes of Health (U.S.) (Grant R44EY022864-01)National Institutes of Health (U.S.) (Grant R01-EY011289-27)National Institutes of Health (U.S.) (Grant R01-NS057476-05)United States. Air Force Office of Scientific Research (Grant FA9550-12-1-0499)United States. Air Force Office of Scientific Research (Grant FA9550-10-1-0551

Embryo splitting can increase the quantity but not the quality of blastocysts

AbstractObjectiveIn this study, we investigated the developmental potential of single blastomeres that were obtained from 4-cell mice embryos that were split during the blastocyst stage.Materials and MethodsImprinting Control Region (ICR) mice (age: 6–8 weeks), were superovulated and mated with a single fertile male of the same strain. We obtained 2-cell embryos that were then cultured in 4 groups (×4) with Human tubal fluid (HTF) supplemented with 12% fetal bovine serum. When these embryos reached the 4-cell stage, their zonae pellucidae were removed and every single blastomere was isolated by repeated pipetting with Ca/Mg2+-free medium. The isolated blastomeres (study group) and the intact embryos (control group) were then cultured to determine the blastocyst formation rate and quality.ResultsWe collected a total of 936 embryos from 524 morphologically intact, top-grade embryos in the 4-cell stage from 80 stimulated mice. We used 356 of these embryos to isolate the blastomeres. The remaining 168 embryos were cultured as controls. A total of 1312 single blastomeres were obtained and cultured in vitro. Among these, 620 blastocysts were harvested from the original embryos compared with 136 blastocysts that were harvested from the control group. The overall blastocyst formation rate was 174.2% (620 blastocysts from 356 embryos) for the study group compared with 81.5% (136 blastocysts from 168 embryos) for the control group. The study group was 43.3% (268 of 620) top-grade blastocysts compared with 91% (152 of 168) of the control group. Taken together, the percentage of top-grade blastocysts obtained per original embryo in the split group was 75.4% (174.2%×43.3%) compared with 74.2% (81.5%×91%) for the control group.ConclusionsEmbryo splitting can increase the number of blastocysts. However, the percentage of available top-grade blastocysts is the same compared with nonsplit embryos. Embryo splitting may not be a cost-effective technique for the generation of high-quality mouse blastocysts

Improvement on thermal performance of a disk-shaped miniature heat pipe with nanofluid

The present study aims to investigate the effect of suspended nanoparticles in base fluids, namely nanofluids, on the thermal resistance of a disk-shaped miniature heat pipe [DMHP]. In this study, two types of nanoparticles, gold and carbon, in aqueous solution are used respectively. An experimental system was set up to measure the thermal resistance of the DMHP with both nanofluids and deionized [DI] water as the working medium. The measured results show that the thermal resistance of DMHP varies with the charge volume and the type of working medium. At the same charge volume, a significant reduction in thermal resistance of DMHP can be found if nanofluid is used instead of DI water

Flowtable-Free Routing for Data Center Networks: A Software-Defined Approach

The paradigm shift toward SDN has exhibited the following trends: (1) relying on a centralized and more powerful controller to make intelligent decisions, and (2) allowing a set of relatively dumb switches to route packets. Therefore, efficiently looking up the flowtables in forwarding switches to guarantee low latency becomes a critical issue. In this paper, following the similar paradigm, we propose a new routing scheme called KeySet which is flowtable-free and enables constant-time switching at the forwarding switches. Instead of looking up long flowtables, KeySet relies on a residual system to quickly calculate routing paths. A switch only needs to do simple modular arithmetics to obtain a packet's forwarding output port. Moreover, KeySet has a nice fault- tolerant capability because in many cases the controller does not need to update flowtables at switches when a failure occurs. We validate KeySet through extensive simulations by using general as well as Facebook fat-tree topologies. The results show that the KeySet outperforms the KeyFlow scheme [1] by at least 25% in terms of the length of the forwarding label. Moreover, we show that KeySet is very efficient when applied to fat-trees

Endoscopic optical coherence tomography for clinical studies in the gastrointestinal tract

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references.Optical coherence tomography (OCT) performs micrometer-scale, cross-sectional and three dimensional imaging by measuring the echo time delay of backscattered light. OCT imaging is performed using low-coherence interferometry. With the development of Fourier domain detection techniques and fiber-optic based OCT endoscopes, high speed internal body imaging was enabled, which makes OCT suitable for clinical research in the human gastrointestinal (GI) tract. Endoscopic OCT imaging is challenging because fast and stable optical scanning must be implemented inside a small imaging probe to acquire useable volumetric information from internal human bodies. Although several studies have shown the use of endoscopic OCT in human gastrointestinal tracts as a real-time surveillance tool, the capability of OCT has not yet been fully explored in endoscopic applications and OCT is not well accepted as a standard imaging modality for GI clinics due to hardware limitations and lack of comprehensive clinical evidences. This thesis presents a number of clinical studies using endoscopic OCT that provide solutions to clinical problems in the GI tract supported by statistically significant results and the development of ultrahigh speed endoscopic OCT system that enables advanced OCT imaging applications. In collaboration with medical partners, the structural features in the diseased esophagus identified from OCT images are compared before and immediately after different ablative therapies, and features that predict the treatment response are investigated. Working in collaboration with industrial partners, an ultrahigh speed endoscopic OCT imaging system is constructed for clinical research in gastroenterology. Distally actuated imaging catheters are developed, enabling the visualization of the detailed three-dimensional (3D) structure in the gastrointestinal tract. Finally, clinical pilot studies are conducted and demonstrate the utility of the ultrahigh speed endoscopic OCT imaging for broader surveillance coverage, pathology detection, and dye-less contrast enhancement. The convergence of 3D spatial resolution, imaging speed, field of view, and minimally invasive access enabled by endoscopic OCT are unmatched by most other biomedical imaging techniques. Though still in its early stage of clinical validation, endoscopic OCT may have a profound impact on human healthcare and industrial inspection by enabling visualization and quantification of 3D microstructure in situ and in real time.by Tsung-Han Tsai.Ph.D

Signatures of afterglows from light dark matter boosted by supernova neutrinos in current and future large underground detectors

Supernova neutrino boosted dark matter (SN$\nu$ BDM) and its afterglow effect have been shown to be a promising signature for beyond Standard Model (bSM) physics. The time-evolution feature of SN$\nu$ BDM allows for possibly direct inference of DM mass $m_\chi$, and results in significant background suppression with improving sensitivity. This paper extends the earlier study and provides a general framework for computing the SN$\nu$ BDM fluxes for a supernova that occurs at any location in our galaxy. A bSM $U(1)_{L_\mu-L_\tau}$ model with its gauge boson coupling to both DM and the second and third generation of leptons is considered, which allows for both DM-$\nu$ and DM-$e$ interactions. Detailed analysis of the temporal profile, angular distribution, and energy spectrum of the SN$\nu$ BDM are performed. Unique signatures in SN$\nu$ BDM allowing extraction of $m_\chi$ and detail features that contain information of the underlying interaction type are discussed. Expected sensitivities on the above new physics model from Super-Kamiokande, Hyper-Kamiokande, and DUNE detections of BDM events induced by the next galactic SN are derived and compared with the existing bounds.Comment: 17 pages, 15 figures, 1 table, 5 appendice

Piezoelectric-transducer-based miniature catheter for ultrahigh-speed endoscopic optical coherence tomography

We developed a piezoelectric-transducer- (PZT) based miniature catheter with an outer diameter of 3.5 mm for ultrahigh-speed endoscopic optical coherence tomography (OCT). A miniaturized PZT bender actuates a fiber and the beam is scanned through a GRIN lens and micro-prism to provide high-speed, side-viewing capability. The probe optics can be pulled back over a long distance to acquire three-dimensional (3D) data sets covering a large area. Imaging is performed with 11 μm axial resolution in air (8 μm in tissue) and 20 μm transverse resolution, at 960 frames per second with a Fourier domain mode-locked laser operating at 480 kHz axial scan rate. Using a high-speed data acquisition system, endoscopic OCT imaging of the rabbit esophagus and colon in vivo and human colon specimens ex vivo is demonstrated