291 research outputs found
Analysis of boost converter in continuous conduction mode and discontinuous conduction mode
No full textThis thesis discusses a boost converter using continuous conduction mode and discontinuous conduction mode. The first part of the thesis analyzes a boost converter using continuous conduction mode with voltage mode control. A switch network which eases the analysis of the boost converter is modeled. Important transfer functions are analyzed in detail to figure out the trade-off between input variables and specifications of the boost converter. Several types of compensators are discussed to build a stable system when feedback is included. The second part of the thesis addresses a boost converter using discontinuous conduction mode. The advantages, such as fast tracking and high gain bandwidth, of using discontinuous conduction mode over continuous conduction mode are discussed.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2020-05-01The student, Hyun Jae Ko, accepted the attached license on 2018-04-24 at 12:42.The student, Hyun Jae Ko, submitted this Thesis for approval on 2018-04-24 at 12:48.This Thesis was approved for publication on 2018-04-25 at 08:32.DSpace SAF Submission Ingestion Package generated from Vireo submission #12449 on 2018-08-31 at 17:21:25Made available in DSpace on 2018-09-04T20:36:53Z (GMT). No. of bitstreams: 2
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Previous issue date: 2018-04-25Embargo set by: Seth Robbins for item 107304
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107304
Lift date: 2020-09-04T20:42:08Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 107304 on 2020-09-05T09:15:13Z
Influence of Luting Materials and Methods and the Restoration Surface on the Amount of Cement Remnants in Implant Restorations
No full textThis study aimed to investigate the effects of the luting methods on the amount of cement remnants in implant restorations and to determine the restoration surface with the maximum amount of residual cement. Forty abutments and crowns were divided into 4 groups as follows: TB group, luting with zinc oxide-eugenol cement; TBV group, luting with zinc oxide-eugenol cement after application of a separating agent over the transmucosal area of the abutment; PI group, luting with methacrylate cement; and PIV group, luting with methacrylate cement after application of a separating agent. After cementation, all the quadrants of the specimens were photographed, and the amount and location of the cement remnants were statistically analyzed (P <= .05). The amount of cement remnants was significantly smaller in the groups with a separating agent. The type of luting material did not significantly affect the results. Cement remnants were more abundant on the mesial and distal sides than on the buccal and lingual sides of the restoration.N
EXPERIMENTAL-STUDY ON MASS-TRANSFER FROM A CIRCULAR-CYLINDER IN PULSATING FLOW
No full textLaboratory measurements were made of local mass transfer from a cylinder, which is placed in a pulsating free stream, U = U-0(1 + A(0) cos 2 pi f(p)t). Low turbulence-intensity wind tunnel experiments were conducted for small and moderate Reynolds numbers, 4500 less than or equal to Re-d less than or equal to 12450. Pulsation was generated by means of an acoustic speaker. Mass transfer rates were measured by employing the naphthalene sublimation technique. The present results for non-pulsating flows (A(0) = 0.0) were shown to be consistent with the published data. For pulsating approach flows, plots were constructed to illustrate the distribution of the Sherwood number, Sh, as a function of the azimuthal angle theta measured from the front stagnation point. In the zone of attached boundary layer, the effect of pulsation on Sh is meager. Sh decreases monotonically from the maximum value at the front stagnation point to the minimum value near the separation point theta approximate to 80-90 degrees. In general, Sh increases appreciably with increasing theta, after passing the separation point. The curve of Sh contains a secondary minimum point at around theta approximate to 130-150 degrees. The general magnitude of Sh increases, as A(0) increases. The augmentation of mass transfer is more pronounced for large f(p), such that the flow lock-on phenomenon takes place. At large Re-d, the relative influence of pulsation on Sh weakens
Oxygen saturation and perfusion index from pulse oximetry in adult volunteers with viable incisors
No full textObjective: Evaluation of pulp vitality is an important diagnostic procedure in dentistry. Conventional techniques for measurement of pulp vitality, including thermal stimulation, electrical stimulation, or direct dentin stimulation, are frequently associated with false positive or false negative results. Recently, oxygen saturation from pulse oximetry has been utilized in the evaluation of pulp vitality. Perfusion index (PI) data calculated from photoplethysmography have been widely used to evaluate peripheral perfusion. The combination of oxygen saturation and PI may aid in the accurate measurement of pulp vitality. We aimed to investigate the baseline values of oxygen saturation and PI using pulse oximetry in adult volunteers. Material and methods: Fifteen adult volunteers with viable incisors were tested. To measure PI, a fabricated oxygen sensor was applied to an incisor without a pulp lesion while oxygen saturation was simultaneously measured in the finger. Oxygen saturation and PI were continuously measured with customized software. The normal reference values of oxygen saturation and PI were obtained by analyzing the recorded data. Results: Pulse oximetry showed relatively stable, objective, and accurate oxygen saturation results. The tooth oxygen saturation ranged from 97% to 100%. The PI ranged from 0.3% to 0.5%, and PI and oxygen saturation showed relatively consistent values across subjects. Conclusions: Although there are some limitations to our study, these results may prove useful for detecting teeth with impaired vitality and non-invasively differentiating between necrotic and vital pulp.N
High-order synchronization of hair cell bundles
No full textAuditory and vestibular hair cell bundles exhibit active mechanical oscillations at natural frequencies that are typically lower than the detection range of the corresponding end organs. We explore how these noisy nonlinear oscillators mode-lock to frequencies higher than their internal clocks. A nanomagnetic technique is used to stimulate the bundles without an imposed mechanical load. The evoked response shows regimes of high-order mode-locking. Exploring a broad range of stimulus frequencies and intensities, we observe regions of high-order synchronization, analogous to Arnold Tongues in dynamical systems literature. Significant areas of overlap occur between synchronization regimes, with the bundle intermittently flickering between different winding numbers. We demonstrate how an ensemble of these noisy spontaneous oscillators could be entrained to efficiently detect signals significantly above the characteristic frequencies of the individual cells. © The Author(s) 20161
Flow and mass transfer measurements for a flat plate of finite thickness in pulsating flow
No full textLaboratory measurements were made of flow and mass transfer over a blunt flat plate of finite thickness, which is placed in a pulsating free stream, U-infinity = U-0(1 + A(0) cos 2 pi f(p)t). Low turbulence-intensity wind tunnel experiments were conducted for small and moderate Reynolds numbers, 770 less than or equal to Re-H less than or equal to 8000. Pulsation was generated by means of an acoustic speaker. The majority of experiments were carried out in the ranges of f(p) = 20.0-80.0 Hz and A(0) less than or equal to 0.15. Flow properties were measured by I-type and split-film probes. Mass transfer rates were measured by employing the naphthalene sublimation technique. The present results for non-pulsation flows (A(0) = 0.0) were shown to be consistent with the published data. For pulsating approach flows, results are provided for the distributions of the wall static pressure, the longitudinal mean velocity and turbulent intensity, and the Sherwood number, Sh, as a function of the stream-wise distance x* measured from the leading-edge separation point. As A(0) or f(p) increases, the time-mean reattachment length is reduced significantly. This implies that the height and length of the separation bubble shrink simultaneously; the position where C-p is recovered moves upstream, and the minimum value of C-p decreases; the reverse flow is intensified; and a substantial augmentation of turbulent energy is discernible. In the separation bubble, the effect of pulsation on Sh is conspicuous. Sit decreases monotonically from the separation point to the minimum value near the secondary separation point, and Sh increases appreciably with increasing x*, after passing the secondary separation point to the maximum value at the reattachment point: and afterward, Sh decreases. The secondary separation point and the position where Sit has a maximum move further upstream, as A(0) or f(p) increases. At large Re-H, the relative influence of pulsation on Sh weakens. (C) 1998 Elsevier Science Ltd. All rights reserved
Scalable ultrasmall three-dimensional nanowire transistor probes for intracellular recording
No full text© 2019, The Author(s), under exclusive licence to Springer Nature Limited.New tools for intracellular electrophysiology that push the limits of spatiotemporal resolution while reducing invasiveness could provide a deeper understanding of electrogenic cells and their networks in tissues, and push progress towards human–machine interfaces. Although significant advances have been made in developing nanodevices for intracellular probes, current approaches exhibit a trade-off between device scalability and recording amplitude. We address this challenge by combining deterministic shape-controlled nanowire transfer with spatially defined semiconductor-to-metal transformation to realize scalable nanowire field-effect transistor probe arrays with controllable tip geometry and sensor size, which enable recording of up to 100 mV intracellular action potentials from primary neurons. Systematic studies on neurons and cardiomyocytes show that controlling device curvature and sensor size is critical for achieving high-amplitude intracellular recordings. In addition, this device design allows for multiplexed recording from single cells and cell networks and could enable future investigations of dynamics in the brain and other tissue
Carbonate-coordinated cobalt co-catalyzed BiVO4/WO3 composite photoanode tailored for CO2 reduction to fuels
No full textWe report here that cobalt carbonate (Co-Ci) is a tailored oxygen evolution electrocatalyst (OEC) from water on BiVO4/WO3 composite photoanode to drive photoelectrochemical reduction of CO2 to fuels on a Cu cathode. For water oxidation, Co-Ci/BiVO4/WO3 performed best in CO2-saturated KHCO3 (KCi, pH 7) electrolyte recording an exceptional photocurrent of 3.5mA/cm2 at 1.23VRHE under 1sun illumination, and an onset potential of 0.2VRHE. In the photoanode-driven CO2 reduction, the Co-Ci/BiVO4/WO3 (photoanode)-Cu (cathode) system showed stable photocurrent and 51.9% faradaic efficiency (against water reduction to H2) for CO and C1-C2 hydrocarbons, whereas the best known OEC cobalt phosphate (Co-Pi) was less stable and gave only 22.4% faradaic efficiency. Due to its high stability and CO2 reduction selectivity, the Co-Ci assisted system produced 11 times larger amount of CH4 than the Co-Pi assisted system in a continuous operation. &copy; 2015.close1
자가발전 유연 전자 시스템 구현을 위한 고성능 유연 압전 음성센서 및 에너지 하베스터 개발
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2020.8,[x, 105 p. :]Chapter 1.
Energy harvesting form ambient vibrational energy for the goal of operating low-power consumption electronic devices has widely researched during the last decade years for enabling wireless applications. The purpose of this effort is to provide remote and sustainable source of electricity to recharge storage components such as capacitors and batteries. One of the most researched areas is the utilization of piezoelectric materials which have piezoelectric effect to convert mechanical and vibrational energy such as bending, stretching, and pressing into useful electric energy. The area of piezoelectric energy harvesting embraces material science, mechanics, and electric circuitry. The ultimate goal of these research is making high-performance piezoelectric energy harvesters to power the low-power consuming electronics by using the ambient vibrational and mechanical energy available in our environment. If this dream can be achieved, the maintenance price for periodic battery replacements as well as the requirement of an outer power sources could be noticeably decreased. This part introduces the principle of piezoelectricity, piezoelectric materials, and electric energy generation in piezoelectric materials.
Chapter 2.
In this chapter, a self-powered flexible piezoelectric acoustic sensor (f-PAS) inspired by basilar membrane in human cochlea was demonstrated. The f-PAS covered the voice frequency spectrum via the combination of its low quality (Q) factor and multi-resonant frequency tuning, exhibiting four to eight times higher sensitivity than the conventional condenser sensor. Our piezoelectric acoustic sensor with a thin membrane design produced sufficient output voltages by the distinct resonant movement of the Pb[Zr0.52Ti0.48]O3(PZT) membrane under the minute acoustic sound stimuli. Multiple sensor channels were integrated in a single f-PAS chip with a size of 1.5 × 3 cm2, which acquire multi-tunable piezoelectric signals without any external power. A linear response of the resonance frequency of the curved piezoelectric membrane was theoretically investigated by a finite element method (FEM) calculation. Low Q factors from corresponding channels were achieved by optimal membrane thickness and channel length.
Chapter 3.
In this chapter, a new platform of machine learning-based speaker recognition was demonstrated, via the flexible piezoelectric acoustic sensor (f-PAS) with a highly sensitive multi-resonant frequency band. The resonant self-powered f-PAS was fabricated by mimicking the operating mechanism of the basilar membrane in the human cochlear. The f-PAS acquired abundant voice information from the multi-channel sound inputs. The standard TIDIGITS dataset were recorded by the f-PAS and converted to frequency components by using a Fast Fourier Transform (FFT) and a Short-Time Fourier Transform (STFT). The machine learning based Gaussian Mixture Model (GMM) was designed by utilizing the most highest and second highest sensitivity data among multi-channel outputs, exhibiting outstanding speaker recognition rate of 97.5 % with error rate reduction of 75 % compared to that of the reference MEMS microphone.
Chapter 4.
Flexible piezoelectric energy harvesters (f-PEHs) have been regarded as an overarching candidate for achieving self-powered electronic systems for environmental sensors and biomedical devices using the self-sufficient electrical energy. In this research, we realize a flexible high-output and lead-free piezoelectric energy harvester by using the aerosol deposition (AD) method and the laser lift-off (LLO) process. We also investigated the comprehensive biocompatibility of the lead-free piezoceramic device using ex-vivo ionic elusion and in-vivo bioimplantation, as well as in-vitro cell proliferation and histologic inspection. The fabricated LiNbO3-doped (K,Na)NbO3(KNN) thin film-based flexible energy harvester exhibited an outstanding piezoresponse, and output performance up to an open-circuit voltage of ~140V and a short-circuit current of ~1.8μA under normal bending and release deformation, which is the best record among previously reported flexible lead-free piezoelectric energy harvesters. Although both the KNN and PZT devices showed short-term biocompatibility in cellular and histological studies, excessive Pb toxic ions were eluted from the PZT in human serum and tap water. Moreover, the KNN-based flexible energy harvester was implanted into a porcine chest, and generated up to ~5V and 700nA from the heartbeat motion, comparable to the output of previously reported lead-based flexible energy harvesters. This work can compellingly serve to advance the development of piezoelectric energy harvesting for actual and practical biocompatible self-powered biomedical applications beyond restrictions of lead-based materials in long-term physiological and clinical aspects.
Chapter 5.
In this chapter, the structure of the basilar membrane inside the human cochlea was inspired to produce a voice sensor. In a flexible electronic device such as an flexible energy harvester, flexible acoustic sensor, flexible pressure sensor, substrate having a uniform film thickness is used. However, in this study, the thickness of the substrate has a structure with a constant gradient thickness. In particular, the high frequency is sensed in the narrow part and the low frequency is sensed in the wide part, and has a structure for maximizing it. In the basilar membrane inside the cochlea, the narrow part has a thick thickness, and the wide part has a thin thickness, so it has an advantage of having a wider frequency coverage. This is because the thickness and the resonance frequency become proportional by the resonance frequency formula. In this experiment, polyimide (PI) liquid was poured into an aluminum mold of an inclined shape to harden it, and it was removed and used as a gradual substrate. The post-process including the transfer process, is based on the previously used method.한국과학기술원 :신소재공학과
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