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History of Hearing Aids
No full text[Introduction] Trumpets made of horns and hands cupped around the ear served to amplify sound since the days of hunter gatherers – a precursor to hearing aids of sorts. These devices remained fairly unchanged in principle until the 19th century. Today, hearing aids are much more than devices that simply amplify sound. Today’s hearing aids are complex instruments that combine amplification with cutting edge signal processing to enhance speech, reduce noise, cancel feedback, analyze acoustic environments, and link back to various IoT devices at home. Today, we enjoy miniaturization of electronics ranging from cell phones to pocket speakers. Miniaturization of electronics as we witness today can be attributed to several historical events such as the development of transistors (Mudry, 6) and World War II (Misa, 253). This paper will connect the history of electronics miniaturization and the development of hearing aid technology to argue that there was an inseparable bidirectional relationship between the two domains
Developing Plasma Spectroscopy and Imaging Diagnostics to Understand Astrophysically-Relevant Plasma Experiments: Megameters, Femtometers, and Everything in Between
Get PDFOne of the main attractions of using laboratory experiments as a proxy to study solar and astrophysical plasmas is the ability to build diagnostics that directly measure things. This cannot be done on actual solar and astrophysical plasmas as they are either i) extremely distant, ii) in an extreme environment, or iii) both. Fortunately, the lack of intrinsic scales in the MHD equations means that a plasma created in the laboratory with similar β, S, and magnetic topology will evolve similarly to its astrophysical analogs. Thus the use of diagnostics in the laboratory to understand the evolution of laboratory plasmas can assist in understanding complicated astrophysical plasma dynamics.
This thesis is broken up into three main areas. The first is about the development of and results from two new custom X-ray scintillator detectors and a CMOS camera repurposed into an X-ray spectrometer mounted on the Caltech Astrophysical Jet Experiment. Next, water-ice grain growth in a cold dusty plasma is quantified by analyzing the frames in a movie recorded by an ultra-high-speed camera. Finally, the development of and results from a custom, motorized Laser-Induced Fluorescence diagnostic that measures the temperature and flow speed of neutral argon atoms in the dusty plasma experiment are presented.
Two custom-built X-ray scintillator detectors mounted on the jet experiment detect a burst of hard X-rays establishing that this burst occurs simultaneously with a fast magnetic reconnection event taking place in the T = 2 eV plasma. A repurposed windowless CMOS camera acting as an X-ray spectrometer confirms the burst consists of non-mono-energetic photons around 6 keV energy. This magnetic reconnection event is triggered after the jet undergoes an ideal MHD kink instability which accelerates the jet laterally inducing a fast-growing secondary Rayleigh-Taylor instability. The Rayleigh-Taylor instability causes the ideal MHD treatment of the jet to be violated when it pinches the jet diameter past c/ωpi causing it to break apart. As it breaks apart, a burst of hard X-rays are detected. These findings lead to the conclusion that an inductive electric field arises at the location of the reconnection event that accelerates a small fraction of electrons to keV energy despite the plasma being so collisional that acceleration is unexpected. This theory leads to the hypothesis that the fine structure of solar prominences consists of many Litz-wire like strands of plasma each on the order of a few ion skin depths in diameter, as opposed to the traditional picture of one monolithic arch.
Analysis of a high-speed video of ice grains growing from 20 to 80 µm inside the dusty plasma experiment leads to the conclusion that the charged ice grains in the experiment grow via accretion of water molecules. The video challenges the common astrophysical assumption that the dusts in dusty plasmas are spherical as they are clearly seen to be elongated, fractal structures in the movie. Another commonly made assumption is that the grains grow via agglomerating collisions and that this results in the grains having a power law dependence on radius. Video of the grains in the Caltech experiment shows a log-normal dependence and absolutely no evidence of agglomerating collisions; or even a case of two grains approaching with a large relative velocity, and then scattering. It is believed that the grains have a large negative charge resulting in strong mutual repulsion and this, combined with their nearly non-existent relative velocities due to undergoing oscillatory motion by a relatively coherent wave, prevents them from agglomerating. This combined with a detailed study of Coulomb repulsion between the grains leads to the conclusion that direct accretion of water molecules is likely the dominant contribution to the observed ice grain growth.
Lastly, a Laser-Induced Fluorescence diagnostic has been developed for the dusty plasma experiment. Whereas the first two projects rely on passive detection instruments, the LIF diagnostic actively uses a pump beam to excite atoms in the plasma, and then detects the resulting emission. The diagnostic is motorized and automated with Labview so that the plasma volume can be scanned in three dimensions. Argon neutral temperature is measured to be slightly above room temperature on the Caltech experiment and the PK4 experimental setup at Baylor University. Challenges such as the lack of absolute calibration of diode lasers and wavelength drift due to slight changes in ambient room conditions are overcome to measure sub-linewidth bulk neutral flow speeds on the order of 1-2 m/s with resolution on the order of 2/3 of a meter per second. The competing influences of a density gradient and wavelength dependent absorption broadening mechanism are separated and quantified. High-speed video shows that introducing an argon flow to a cloud of ice grains causes the cloud of ice grains to move and change shape. This motion is analyzed and found to show agreement with neutral LIF flow measurements. Surprisingly, when the flow ceases, the ice grain cloud reverts to its original location and shape.</p
Higher-Order RNA and DNA Hubs Shape Genome Organization in the Nucleus
Get PDFAlthough the entire genome is present within the nucleus of every cell, distinct genes need to be accessed and expressed in different cellular conditions. Accordingly, the nucleus of each cell is a highly organized arrangement of DNA, RNA, and protein that is dynamically assembled and regulated in different cellular states. These dynamic nuclear structures are largely arranged around functionally related roles and often occur across multiple chromosomes. These include large nuclear bodies (i.e., nucleolus, nuclear speckle), smaller nuclear bodies (i.e., Cajal bodies and histone locus bodies), and gene-gene interactions (i.e., transcription compartments and loops). Yet, what molecular components are involved in establishing this dynamic organization have been largely unknown due to a lack of methods to measure the RNA and DNA components of nuclear bodies and their spatial arrangements in the nucleus. Here, we present Split-Pool Recognition of Interactions by Tag Extension (SPRITE), which enables genome-wide detection of higher-order interactions within the nucleus. In the second chapter, we introduce SPRITE and recapitulate known structures identified by proximity ligation and identify additional interactions occurring across larger distances, including two hubs of inter-chromosomal interactions that are arranged around the nucleolus and nuclear speckles. We show that a substantial fraction of the genome exhibits preferential organization relative to these nuclear bodies. Our results generate a global model whereby nuclear bodies act as inter-chromosomal hubs that shape the overall packaging of DNA in the nucleus. In the third chapter, we provide a detailed experimental protocol for performing SPRITE and an automated computational pipeline for analyzing SPRITE data. Finally, in the fourth chapter, we present a dramatically improved implementation of the SPRITE method that enables comprehensive mapping of all classes of RNA in the nucleus, from abundant RNAs encoded from DNA repeats to low abundance RNAs such as nascent pre-mRNAs and lncRNAs. We find that RNAs localize broadly across the nucleus, with individual RNAs localizing within discrete territories ranging from nuclear bodies to individual topologically associated domains. We uncover that nascent mRNAs interact in structures corresponding to nascent mRNA chromosome territories and compartments. Together, these results uncover a central and widespread role for non-coding RNA in demarcating 3D nuclear structures within the nucleus.</p
Effects of Sensory Experience on Early Stages of Olfactory Processing in the Fruit Fly
Get PDFPlasticity is widely studied across different sensory systems and behavioral paradigms, but the underlying mechanisms are varied and incompletely understood. Previous work in the fruit fly Drosophila melanogaster reported changes in odor preference and walking behavior after chronic odor exposure during early adulthood. Here, we investigated the hypothesis that changes in behavior reflect changes in how odors are encoded in the first two layers of the fly olfactory circuit. We chronically exposed flies to naturalistic odor stimuli that selectively and robustly activate a single olfactory receptor neuron (ORN) class. We then performed targeted intracellular recordings from genetically identified second-order olfactory projection neurons (PNs) that either receive direct input from the activated ORN class, or receive indirect activity (via local lateral circuitry), during chronic odor exposure. In addition, we used existing reagents to create a novel optical method to characterize ORN-PN synaptic strength. We find that the fly antennal lobe is resistant to plasticity, with a few exceptions. Of the odors we tested, we find that rearing in trans-2-hexenal, a leaf aldehyde that selectively activates ab4a ORNs, weakly enhanced odor responses in some PNs. The effects of rearing on PNs were not explained by ORN odor responses or changes in ORN-PN synaptic strength. We find evidence that lateral excitation may increase across glomeruli following rearing, suggesting that some odors may alter PN responses globally. We discuss possible reasons for differences between our observations and prior work on olfactory plasticity in this circuit, which has been conducted primarily in the context of exposures to much higher, non-naturalistic concentrations of odor. Our results point to the stability of insect sensory circuits in the face of large perturbations in the sensory environment.
During our optical stimulation experiments, we find that driving Chrimson expression may abolish odor responses in some ORNs. We include sample data highlighting this observation in a population of pb1a olfactory neurons. Lastly, we include antennal local field potential recordings in response to a variety of odor concentrations to help guide future experiments seeking isointense odor panels.</p
On-Chip Photonic Devices for Coupling to Color Centers in Silicon Carbide
Get PDFOptical quantum networks are important for global use of quantum computers, and secure quantum communication. Those networks require storage devices for synchronizing or making queues of processing transferred quantum information. Practical quantum information networks should minimize loss of transmitted data (photons) and have high efficiency mapping when writing data on memories (solid state qubits). This requires strong light-matter interaction that is enabled by coupling qubits to optical cavities.
The first half of the thesis focuses on emerging candidates for promising qubits in silicon carbide (SiC). The optical and quantum properties of these color centers are discussed with focus on divacancies in 4H-SiC due to their long spin coherence time. Optically detected magnetic resonance of divacancies is shown, an essential technique for reading out the qubit state using the intensity of optical emission.
The second half of the thesis focuses on hybrid photonic devices for coupling to silicon carbide qubits. Hybrid devices are made of another layer of high refractive index material other than the qubit hosting material. Evanescent coupling to qubits close to the surface can be achieved without damaging the host material. Mainly the silicon (Si) on 4H-SiC hybrid ring resonator architecture is discussed starting from design, simulation to fabrication. The fabrication includes Si membrane transfer that is an important step to create a light confining layer on 4H-SiC. The final ring resonator device shows quality factors as high as 23000.</p
Simulations of Conic Cusp Formation, Growth, and Instability in Electrified Viscous Liquid Metals on Flat and Curved Surfaces
No full textIt is well known that above a critical field strength sufficiently large to overcome damping by capillary forces, the free surface of a perfectly conducting liquid will spontaneously deform into one or more sharp protrusions known as conic cusps. Such cusps undergo tip sharpening while rapidly accelerating toward regions of highest electric field strength, eventually giving rise to beams of ions and/or charged droplets . These charged beams form the basis for liquid metal ion sources (LMIS) commonly used in focused ion beam systems, scanning ion microscopy, micromilling, ion mass spectrometry, implantation, and lithography. During the past few decades, there has been growing interest in optimizing the formation, growth, and stability of conic cusps in liquid metals for a new class of efficient and highly miniaturizable satellite micropropulsion devices consisting of microarrays of externally wetted solid needles coated with a film of liquid metal propellant. The thrust levels generated by such microarrays is suitable for propulsion of small satellites and precision pointing maneuvers for larger satellites.
This thesis addresses the formation, growth, and instability of conic cusp formations in perfectly conducting, electrified viscous liquids on flat and curved surfaces. We use finite element simulations based on the arbitrary Lagrangian-Eulerian (ALE) method for coupling the vacuum and liquid domains across the accelerating interface. The simulations in Chapters 2–4 describe the evolution of liquid flow subject to electric field distributions generated by opposing flat parallel and solid electrodes. In particular, we examine in Chapter 2 the growth of a small liquid protuberance on an otherwise flat viscous liquid layer of perfectly conducting fluid subject to an initial uniform electric field. Previous studies in the literature have established that tip sharpening proceeds via a self-similar process in two distinct limits: the Stokes regime at Re = 0 and the inviscid regime Re → ∞. These simulations, conducted at fixed capillary number Ca and for 0.1 ≤ Re ≤ 50,000, which span the viscous to inviscid regimes, demonstrate that the conic tip always undergoes self-similar growth irrespective of Reynolds number. Field self-enhancement due to conic cusp tip sharpening is shown to generate divergent power law growth in finite time (so-called blowup behavior) of the interfacial and volumetric forces acting at the advancing tip. The computed blow up exponents at the tip surface associated with the various terms in the Navier-Stokes equation and interface normal stress condition reveal the different forces at play as Re increases. Rescaling of the tip shape by the capillary stress exponent yields excellent collapse onto a universal conic tip shape with interior half-angle dependent on the magnitude of the Maxwell stress. The simulations clearly show that the interior cone angle adopts values both above and below the Taylor cone angle value of 49.3°. Additional details of the modeled flow dispel prevailing misconceptions that dynamic cones resemble conventional Taylor cones or that viscous stresses at finite Re can be neglected. In Chapter 3, we demonstrate how the rapid acceleration of the curved liquid interface also generates a thin surface boundary layer with very high local strain rate in the vicinity of the conic tip. The value of the surface vorticity along the moving interface is shown to be in excellent agreement with theoretical predictions. More importantly, the results in Chapters 2 and 3 demonstrate that the velocity streamlines are always at an oblique angle to the moving interface, contrary to commonly held belief that the streamlines always lie tangent to the moving boundary. In Chapter 4, we extend the simulations to include variation of the capillary number and find that for sufficiently high Re and Ca, the advancing interface develops significant oscillations. Fourier analysis of these interface oscillations indicates that the extracted instability wavelength characteristic of flows at smaller values of Re tends to exceed the simplified theoretical prediction based on inviscid flow. By contrast, the extracted instability wavelength for the largest values of Re examined tends to fall below the inviscid prediction.
In Chapter 5, we explore the effect of substrate curvature on the flow and stability of electrified films by examining the behavior of a thin viscous film of perfectly conducting liquid on two types of curved surfaces. These shapes, which include a solid conical needle with a spherical cap tip and a solid parabolic needle, are intended to mimic substrates used in some externally wetted microemitter arrays in LMIS systems. For the simulations in Chapter 5, the needle is situated below a counter electrode perforated with a circular aperture. The films are shown to develop both on-axis and off-axis cusp-like protrusions depending on the parameter range examined. In particular, the formation of off-axis protrusions are directly traced to substrate shapes which manifest an abrupt change in curvature, as present in a solid conical needle with a spherical cap tip. The simulations reported here are anticipated to help optimize fabrication of externally wetted needle shapes for use in a variety of LMIS systems.</p
Cell-Selective Proteomic Profiling in Complex Biological Systems
Get PDFCells within biological systems are constantly adjusting their protein synthesis in response to various environmental changes. To study the rapid cellular regulations in complex biological systems, global proteomic profiling provides important information on system-level regulations, yet physiological properties characteristic of individual cellular subpopulations could be hidden under the characterization. Instead, cell-selective proteomic profiling allows researchers to reveal the heterogeneities in biological systems with phenotypically and even genetically distinct subpopulations under different microenvironments.
Chapter 1 describes the development of bioorthogonal noncanonical amino acid tagging (BONCAT) for proteomic profiling with resolution in both space and time: its initial role is protein labeling with temporal resolution via pulse-addition of noncanonical amino acid, which could be recognized by endogenous aminoacyl tRNA-synthetase (aaRS), into systems of interest; later on, mutant aaRSs are identified through mutant synthetase library screening, which allows for efficient incorporation of various types of noncanonical amino acids that could hardly be activated by endogenous machineries. The identification and exploitation of mutant aaRSs allow sensitive cellular selectivity during protein labeling. With unprecedented spatiotemporal resolution of BONCAT, and the advancement in high-resolution mass spectrometry and computational algorithms, BONCAT is a powerful technique for selective proteomic profiling to study physiological regulations in a wide range of complex biological systems.
Chapter 2 describes the application of the BONCAT method in cell-selective proteomic profiling in Pseudomonas aeruginosa biofilms. In this work, we targeted an iron-starved subpopulation in biofilms and compared its proteomic profile with that of the entire system. Key gene and pathway regulations in the subpopulation are found through the analysis of the proteomic data, which suggest that iron-starved cells shift their priority towards housing keeping pathways, adapt an energy- and resources-saving mode to cope with their harsh local environmental conditions, and get prepared to disperse for better survival. Analysis of poorly studied proteins highly upregulated in the subpopulation led to the discovery of a previously uncharacterized protein (PA14_52000) that is potentially related to iron acquisition. The transposon insertion mutant PA14_52000::tn showed significantly enhanced pyoverdine production in rich medium and reduced biofilm formation.
Chapter 3 describes the study of physiological regulations in Bacillus subtilis K-state subpopulation via BONCAT. A subset of B. subtilis cells, typically 10% - 20% of the entire population, enter K-state in a stochastic manner. With the low level of K-state entry rate and high randomness, we challenged BONCAT to specifically capture gene and pathway regulations in K-state cells and compared the proteomic profiling with that of the entire population. Regardless of the difficulties of selective protein labeling inherent in the system, our results indicate that BONCAT has high specificity and resolution in proteomic profiling for minor subpopulations and proteins with low overall absolute abundance. We found multiple pathways and genes characteristic of K-state regulated differentially from the entire population, either significantly up- or down-regulated. Proteins that are uncharacterized or previously known for functions irrelevant of K-state are highly abundant in the subpopulation, providing new insight toward their alternative functions critical for K-state cells and future investigation directions of K-state study.</p
Improved Tools for Point-of-Care Nucleic Acid Amplification Testing
Get PDFThere is a critical need for improved diagnostic tools to detect infectious diseases, especially in low-resource regions. A sample-to-answer point-of-care nucleic acid amplification test (NAAT) would be incredibly valuable for many different applications (e.g. COVID-19, Chlamydia/Gonorrhoeae, Influenza, Ebola, Zika/Chikungunya/Dengue, etc.). However, sample preparation (purification of pure nucleic acids) is a challenging bottleneck. In Chapter 2, commercial NA extraction methods were studied and improved. In Chapter 3, commercial stocks of SARS-CoV-2 RNA used in FDA emergency-use authorizations were found to be inaccurate and were independently quantified using reverse transcription digital PCR. In Chapter 4, a 3D printed meter-mix device was developed for initial processing prior to the sample preparation device. In Chapter 5, a 3D printed sample-to-device interface was prototyped to facilitate loading multi-volume SlipChip devices with purified template mixed with LAMP reactants. In Chapters 6-7, advancements were made for image processing of commercial chips to study digital LAMP reactions. In Chapter 8, additional tools were developed towards sample-to-answer point-of-care NAAT including a sample preparation module, amplification module, cell-phone readout, and automated base station
Phonon Anharmonicity at the Limits of Perturbation Theory
Get PDFPhonons, as the building blocks of solid-state physics, have been studied for almost one hundred years. The harmonic model is helpful when introducing the concepts and offering a basic physics picture of atomic vibrations. However, there are many properties that cannot be explained by the harmonic model or its extension to the quasiharmonic approximation (QHA), which ignores the pure temperature dependence of phonon frequencies. The rapid development of materials science requests a deep understanding of the phonon behaviors at elevated temperatures, where phonon-phonon interactions, as a main source of phonon anharmonicity, account for a number of abnormal phonon behaviors and the thermodynamical properties of many materials. In this thesis, I present the phonon anharmonicity in metals of Pd and Pt, the metallic compound FeGe2, and the polar material NaBr to show the limitation of the harmonic or QH model and the importance of taking anharmonic effects into consideration.
Inelastic neutron scattering (INS) was used to measure the phonon density of states (DOS) in fcc Pd and Pt metal at temperatures from 7 K to 1576 K. Both phonon-phonon interactions and electron-phonon interactions were calculated by methods based on density functional theory (DFT) and were consistent with the measured shifts and broadenings of phonons with temperature. Contributions to the entropy from phonons and electrons were assessed and summed to obtain excellent agreement with prior calorimetric data. The QH entropy is positive for both phonons and electrons but larger for phonons. The anharmonic phonon entropy is negative in Pt, but in Pd it changes from positive to negative with increasing temperature.
Phonon dispersions in a single crystal of FeGe2 with the C16 structure at 300, 500, and 635 K were measured by INS. Phonon DOS were also measured on polycrystalline FeGe2 from 325 to 1050 K, and the Fe partial DOS was obtained from polycrystalline 57FeGe2 at 300 K using nuclear resonant inelastic X-ray scattering (NRIXS). The dominant feature in the temperature dependence of the phonon spectrum is thermal broadening of high-energy modes. The energy shifts of the low- and high-energy parts of the spectrum were almost the same. DFT calculations performed with the QHA gave results in moderate agreement with the experimental thermal energy shifts, although the isobaric Grüneisen parameter calculated from the quasiharmonic model was smaller than that from measurements. The thermal broadening of the phonon spectrum and dispersions, especially at high energies, indicates a cubic anharmonicity to second order that should also induce phonon shifts. There are cancellations of different anharmonic contributions to energy shifts, giving average phonon shifts in moderate agreement to calculations with the QHA. The different parts of the large phonon contribution to the entropy are separated for FeGe2, showing modest but interpretable anharmonic contributions.
All phonons in a single crystal of NaBr were measured by INS at temperatures of 10, 300 and 700 K. Even at 300 K the phonons, especially the longitudinal optical (LO) phonons, showed large shifts in frequencies, and showed large broadenings in energy owing to anharmonicity. The QHA was an unqualified failure for predicting the temperature dependence of phonon frequencies, even at 300K, and it predicted a thermal expansion that was in error by a factor of four. Ab initio computations that included both anharmonicity and quasiharmonicity successfully predicted both the temperature dependence of phonons and the large thermal expansion of NaBr. The frequencies of LO phonon modes decrease significantly with temperature owing to the real part of the phonon self-energy from explicit anharmonicity. The origin of the large cubic anharmonicity was identified with nearest-neighbor Na-Br bonds. Anharmonicity is not a small correction to the QHA predictions of thermal expansion and thermal phonon shifts, but anharmonicity dominates the behavior.
New spectral features were found in phonon dispersions of NaBr at 300 K. Ab initio calculations based on anharmonic perturbation theory also showed these spectral features as "many-body effects". Their physical origin is better elucidated with a Langevin model, similar that in recent work in optomechanics. The transverse optic (TO) part of the new features originates from phonon intermodulation between the transverse acoustic (TA) and TO phonons. The LO spectral features originate from three-phonon coupling between the TA modes and the TO lattice modes.</p
Suspended Trace Air-Gap Resonators for Low Loss Superconducting Circuits
Get PDFQuantum memories and networks for distributed quantum information processing require links between the microwave, mechanical, and optical domains. Coherent integration of long-lived superconducting qubits (SCQs) with optomechanical and photonic devices (OMPDs) remains an outstanding challenge. We present a step towards coherent integration using a suspended trace air-gap resonator (STAR): a superconducting resonator on a silicon-on-insulator (SOI) substrate with the signal trace suspended by silicon tethers above and between galvanically connected ground metal planes. As a result, the electric field energy is closely confined within the microwave structure, yielding lower crosstalk compared to conventional coplanar waveguides (CPW). An order of magnitude improvement in the quality factors for STAR over previous work on SOI is achieved, in a transverse cross-sectional area that is an order of magnitude more compact. Electric field participation in lossy bulk dielectrics, a dominant source of energy leakage in previous measurements of aluminum CPW resonators on SOI, is virtually eliminated in STAR. The loss from the metal-air interface now dominates, but can be reduced by several factors using superconductors with better surface properties. Most importantly, STAR fabrication is compatible with Josephson junction and air-bridge deposition for highly coherent integration of SCQs and OMPDs to realize proposals for quantum information storage and networking.</p