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BEYOND SEMICLASSICAL GRAVITY: QUANTUM STRESS TENSOR FLUCTUATIONS IN THE VACUUM
No full textAbstract: Large vacuum fluctuations of a quantum stress tensor can be described by the asymptotic behavior of its probability distribution. Here we focus on stress tensor operators which have been averaged with a sampling function in time. The Minkowski vacuum state is not an eigenstate of the time-averaged operator, but can be expanded in terms of its eigenstates. We calculate the probability distribution and the cumulative probability distribution for obtaining a given value in a measurement of the time-averaged operator taken in the vacuum state. In these calculations, we use the normal ordered square of the time derivative of a massless scalar field in Minkowski spacetime as an example of a stress tensor operator. We analyze the rate of decrease of the tail of the probability distribution for different temporal sampling functions, such as compactly supported functions and the Lorentzian function. We find that the tails decrease relatively slowly, as exponentials of fractional powers, in agreement with previous work using the moments of the distribution. Our results lead additional support to the conclusion that large vacuum stress tensor fluctuations are more probable than large thermal fluctuations, and may have observable effects.Thesis (Ph.D.)--Tufts University, 2018.Submitted to the Dept. of Physics.Advisor: Lawrence Ford.Committee: Alexander Vilenkin, Mark Hertzberg, Ken Olum, Peter Love, and Jen-Tsung Hsiang.Keywords: Theoretical physics, Quantum physics, and Particle physics
Ultrasound Transducers for a Simplified Martian Acoustic Anemometer
No full textAbstract: The selection, modeling and verification of ultrasonic transducers in an ultrasound transmit - receive system are described. The system is applied to the measurement of wind speed in an acoustic anemometry application. The target environment for the final system is the surface of Mars, which requires operation in approximately 6 mbar CO2. Four transducers are tested as part of this work: Kobitone and PUI piezoelectric transducers, and custom "CAP1" and capacitive micromachined ultrasound (cMUT) transducers from VN Instruments and Tufts University, respectively. Tukey - windowed linear chirp acoustic signal is chosen and analyzed using cross frequency techniques. A model for the full system frequency response, which includes the control electronics, electromechanical coupling of the transducers and attenuation of sound, is provided and verified. Transducers are also characterized using LDV (Laser Doppler Vibrometry) and input impedance measurement. For PUI transducers, the model provides a peak value within 5% of the measured value in air and in 6 mbar CO2. Time delay are also predicted to have a value within 10% difference from the calculated distance in atmospheric air for all the transducer tested.Thesis (M.S.)--Tufts University, 2018.Submitted to the Dept. of Mechanical Engineering.Advisor: Robert White.Committee: Jason Rife, Brian Tracey, and Don Banfield.Keyword: Mechanical engineering
An In-Situ Microcroaxial Fabrication and Attachment Strategy
No full textAbstract: Micro-coaxial cables (MCCs), with an outer diameter of 100 μm or less, enable a new microelectronics packaging platform that will reduce the time required to design and fabricate complex multi-chip microelectronic assemblies. Low-inductance MCCs for power distribution and 30-75 Ω MCCs for signal distribution, eliminate the need for lengthy simulations and fabrication processes, as in board design of photo-lithographically patterned microchips, because each individually shielded MCC provides sufficient isolation to prevent electro-magnetic interference (EMI) and crosstalk. The in-situ fabrication method presented here utilizes only conventional wire bonding and microfabrication techniques, providing a high-feasibility path toward a new interconnect paradigm based on MCCs. Each cable measured consists of a 25.4 μm gold bond wire coated first with a dielectric and then a 5.0 μm thick gold shield. For power distribution, the dielectrics evaluated are 1.0 μm thick Parylene C dielectric and 100 nm thick HfO2. Their characteristic impedances are measured to be 3.2-5.9 Ω and 0.11-0.18 Ω, respectively. A third MCC, appropriate for signals, has a 38 μm thick Parylene C dielectric and a characteristic impedance of 39-68 Ω. For a wire pitch of 0.51 mm cross-talk is -62 dB at 1 GHz for micro-coax. Cross-talk increases to -30 dB at 26.5 GHz.Thesis (M.S.)--Tufts University, 2018.Submitted to the Dept. of Mechanical Engineering.Advisors: Robert White, and Caprice Gray.Committee: Marc Hodes.Keywords: Packaging, Electrical engineering, and Mechanical engineering
Silk-based Tissue Engineered Constructs to Improve Tissue Regeneration and Vascularization with Stem Cells
No full textAbstract: A silk-based hydrogel system was explored to evaluate the effects of substrate stiffness and cyclic stretch on human mesenchymal stem cell (hMSCs) differentiation. The hydrogel fibers were highly tunable, elastic and supported the survival and growth of encapsulated hMSCs. The hMSCs in silk hydrogel fibers at 50 kPa and 150 kPa both transferred from a multipotent stem cell state to a pre-osteoblast/adipocyte state in static culture. With cyclic stretching, osteo-differentiation was enhanced, while adipo-differentiation was suppressed. A new method to generate a tunable, anisotropic 3D porous scaffold with branching networks to enhance vascularization in vitro and direct anastomosis in vivo was also developed. Branched channels were generated in the silk-based scaffolds with proper endothelialization. Silk fibers in the scaffold aligned with a specific direction and achieved anisotropic diffusion of molecules with different sizes. These new silk-based tissue engineered constructs can integrate physical and chemical cues for desired stem cell differentiation to improve tissue regeneration.Thesis (M.S.)--Tufts University, 2018.Submitted to the Dept. of Biomedical Engineering.Advisors: Lauren Black III, and David Kaplan.Committee: Emmanuel Tzanakakis.Keyword: Biomedical engineering
Risk and Resilience in Child Emotion Regulation: Investigating Intimate Partner Violence, Parenting Stress, and Social Support in a Home Visiting Program for Young Mothers
No full textAbstract: This thesis examined intimate partner violence (IPV), parenting stress, mothers' perceptions of social support, and children's emotion regulation in a sample that may be at risk for IPV. It also investigated whether the Healthy Families Massachusetts (HFM) home visiting program moderated relations between mothers' perceptions of social support and child emotion regulation, as social support has been shown to be a valuable protective factor against IPV. A non-significant trend suggested that sexual coercion positively predicted child emotion dysregulation, though parenting stress and social support did not moderate the relations between IPV and child emotion regulation. In addition, a non-significant trend found that the home visiting program moderated relations between mothers' perceptions of social support and child emotion dysregulation, suggesting that HFM's home visiting services may be valuable in promoting social support for the mother. These findings suggest resilience in the presence of adversity among young families experiencing IPV. Future studies might examine factors behind resilience, such as how strengths within the mother (self-advocacy skills, positive parenting, and healthy coping mechanisms) might buffer negative effects of IPV, and how home visiting programs promote these strengths.Thesis (M.A.)--Tufts University, 2018.Submitted to the Dept. of Child Development.Advisor: M. Easterbrooks.Committee: Ellen Pinderhughes, and Rachel Cohen.Keyword: Social research
Cost-effectiveness of colorectal cancer screening in Ukraine.
No full textBackground: Colorectal cancer is one of the most common cancers worldwide and is associated with high mortality when detected at a later stage. There is a paucity of studies from low and middle income countries to support the cost-effectiveness of colorectal cancer screening. We aim to analyze the cost-effectiveness of colorectal cancer screening compared to no screening in Ukraine, a lower-middle income country.Springer Open
A semi-synthetic regulon enables rapid growth of yeast on xylose.
No full textNutrient assimilation is the first step that allows biological systems to proliferate and produce value-added products. Yet, implementation of heterologous catabolic pathways has so far relied on constitutive gene expression without consideration for global regulatory systems that may enhance nutrient assimilation and cell growth. In contrast, natural systems prefer nutrient-responsive gene regulation (called regulons) that control multiple cellular functions necessary for cell survival and growth. Here, in Saccharomyces cerevisiae, by partially- and fully uncoupling galactose (GAL)-responsive regulation and metabolism, we demonstrate the significant growth benefits conferred by the GAL regulon. Next, by adapting the various aspects of the GAL regulon for a non-native nutrient, xylose, we build a semi-synthetic regulon that exhibits higher growth rate, better nutrient consumption, and improved growth fitness compared to the traditional and ubiquitous constitutive expression strategy. This work provides an elegant paradigm to integrate non-native nutrient catabolism with native, global cellular responses to support fast growth
Spiritual Development in Childhood and Adolescence.
No full textOriginal commentary and annotations of sources on the topic of "Spiritual Development in Childhood and Adolescence"
This Could Be Heaven or This Could Be Hell: Escape and Anxiety in the Cinematic Hotel.
No full textAn in-depth look at the role of the hotel in contemporary American cinema through four films - The Shining, Psycho, The Grand Budapest Hotel, and Lost in Translation - and how they depict the hotel as a paradoxical site of both fantasy and distress
Engineering an In Vitro Silk-Based Intestinal Model Using Topographical Features.
No full textMillions of people worldwide are affected by intestinal diseases, which can severely affect people’s quality of lives. Options to study intestinal functions and associated diseases are limited by existing models: cell co-cultures, microfluidic systems, organoid models, animal studies, and other in vitro systems. To replicate the in vivo functions of the intestines, we aimed to recreate the physical environment of the small intestinal niche through the incorporation of crypt- and villus-like structures in our current 3D tissue engineered intestinal model. With the goal of promoting the self-renewal of the intestinal epithelium, we seeded enteroids on patterned silk scaffolds. We aimed to look at the impact of the topographical features and the 3D geometry of the intestines of the intestinal epithelium formation and maturation. We’ve also used a novel method to create these topographical features through 3D printing, which is more efficient, quicker, and more cost efficient than the standard photolithography. In the further development of the model, we have demonstrated the ability of 3D printing to create villus- and crypt-like features. In addition, the possibility of incorporating these features in silk hydrogel and film coated silk sponges was also pursued. With initial seeding we have demonstrated the possibility of enteroids to adhere and proliferate to the featured silk hydrogel scaffolds and the formation of a polarized epithelial cell layer on the villus-like features. Through future works, we will be able to develop an in vitro physiologically relevant intestinal model that can be used for evaluating treatment cascades and screening orally delivered pharmaceuticals