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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2020)

Ultrasound technologies can be applied to a variety of applications, such as medical

imaging/therapeutics, materials assessment, flow rate measurement and others. Piezoelectric

micromachined ultrasonic transducers (PMUTs) have advantages over the traditional bulk

transducers in wide bandwidth, small size, and low cost. This work proposes to boost

PMUT’s acoustic performance further including vibrational amplitude, acoustic pressure and

electromechanical coupling by using the pinning boundary structure and to explore various

new applications.

The equivalent circuit model for pinned boundary PMUTs has been developed and validated

with simulation results in terms of mode shape and displacement of the piezoelectric

diaphragm under the alternative electrical voltage inputs. Prototype devices with pinned

boundary are then fabricated without adding any fabrication complexity as compared to the

conventional fabrication process of PMUTs by modifying the mask designs. Fabrication

limitation of PMUTs with low resonant frequency is also investigated by fabricating

prototype chips that operate at a resonant frequency of 338 kHz in air to experimentally detect

objects at 22 cm away. Furthermore, testing results show a measured 2.5 times improvement

in center displacement and 3.3 times improvement in the pressure output as compared with

those PMUTs based on the traditional design with clamped boundary. The measured mode

shape deformation results match well with the analytical and simulation results and a dualelectrode

pinned PMUT structure is proposed to enable a single chip for both transmitting

and receiving functionality without sacrificing the improved acoustic performance.

In the area of practical applications, a tilt angle sensing chip based on the PMUT device has

been demonstrated based on the amplitude of signals from the receiver PMUT. It is found

that the measured sensing results match well with theoretical predictions with an average

error of ±0.7 degree within the tilting range of plate between -8 to 8 degrees. A wireless

power transfer system is then proposed based on a pinned ring PMUT transmitting array to

provide a maximum efficiency of 57% at a focus point 2.7 mm away at a resonant frequency

of 250 kHz.

  • 1 supplemental PDF
Cover page: Pinned boundary piezoelectric micromachined ultrasonic transducers (PMUT)
  • Article
  • Peer Reviewed
UC Davis Previously Published Works (2021)
Air pollution control has become the top priority of China's "green development" concept since 2013. The Chinese government has enacted a range of policies and statutes to control contaminant emissions and improve air quality. On the basis of the national air quality ground observation database, the spatial and temporal distribution of air quality index value (AQI), fine particulate matter (PM2.5), coarse particles (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) were explored in 336 cities throughout China from 2014 to 2019. AQI and most pollutants (except O3) decreased in concentrations from 2014 to 2019. In 2019, all cities except Henan reached the level 2 of the ambient air quality index, and six cities had a lower ambient air quality index and reached the level 1. Spatially, higher pollutant concentrations were concentrated in large city clusters, whereas the areas with high O3 concentration were found across the country. Furthermore, central heating was shown to have a negative impact on air quality. The observed AQI value, PM2.5, PM10, SO2, NO2, and CO concentrations were highest in north and northwest China and Henan province in central China. The correlations among pollutants suggest that the main sources of pollutants are fossil fuel combustion, industrial production, and motor vehicle emissions. The influence of meteorological factors on air quality, long-distance transportation, and the transformations of pollutants should be explored in future research.

Supplementary information

The online version contains supplementary material available at 10.1007/s11869-021-01043-5.
    Cover page: Spatio-temporal analysis of urban air pollutants throughout China during 2014–2019
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2023)
    In many plant species, petal abscission can be considered the final step of petal senescence. Cytokinins (CKs) are powerful suppressors of petal senescence; however, their role in petal abscission is ambiguous. Here, we observed that, in rose (Rosa hybrida), biologically active CK is accumulated during petal abscission and acts as an accelerator of the abscission process. Using a combination of reverse genetics, and molecular and biochemical techniques, we explored the roles of a LESION SIMULATING DISEASE1 (LSD1) family member RhLOL1 interacting with a bHLH transcription factor RhILR3 in CK-induced petal abscission. Silencing RhLOL1 delays rose petal abscission, while the overexpression of its ortholog SlLOL1 in tomato (Solanum lycopersicum) promotes pedicel abscission, indicating the conserved function of LOL1 in activating plant floral organ abscission. In addition, we identify a bHLH transcription factor, RhILR3, that interacts with RhLOL1. We show that RhILR3 binds to the promoters of the auxin signaling repressor auxin/indole-3-acetic acid (Aux/IAA) genes to inhibit their expression; however, the interaction of RhLOL1 with RhILR3 activates the expression of the Aux/IAA genes including RhIAA4-1. Silencing RhIAA4-1 delays rose petal abscission. Our results thus reveal a RhLOL1-RhILR3 regulatory module involved in CK-induced petal abscission via the regulation of the expression of the Aux/IAA genes.
      Cover page: The RhLOL1–RhILR3 module mediates cytokinin‐induced petal abscission in rose
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2016)
      Roses are one of the most important cut flowers among ornamental plants. Rose flower longevity is largely dependent on the timing of petal shedding occurrence. To understand the molecular mechanism underlying petal abscission in rose, we performed transcriptome profiling of the petal abscission zone during petal shedding using Illumina technology. We identified a total of 2592 differentially transcribed genes (DTGs) during rose petal shedding. Gene ontology term enrichment and pathway analysis revealed that major biochemical pathways the DTGs were involved in included ethylene biosynthesis, starch degradation, superpathway of cytosolic glycolysis, pyruvate dehydrogenase and TCA cycle, photorespiration and the lactose degradation III pathway. This suggests that alterations in carbon metabolism are an important part of rose petal abscission. Among these DTGs, approximately 150 genes putatively encoding transcription factors were identified in rose abscission zone. These included zinc finger, WRKY, ERF, and Aux/IAA gene families, suggesting that petal abscission involves complex transcriptional reprogramming. Approximately 108 DTGs were related to hormone pathways, of which auxin and ethylene related DTGs were the largest groups including 52 and 41 genes, respectively. These also included 12 DTGs related to gibberellin and 6 DTGs in jasmonic acid pathway. Surprisingly, no DTGs involved in the biosynthesis/signaling of abscisic acid, cytokinin, brassinosteroid, and salicylic acid pathways were detected. Moreover, among DTGs related to auxin, we identified an Aux/IAA gene RhIAA16 that was up-regulated in response to petal shedding. Down-regulation of RhIAA16 by virus-induced gene silencing in rose promoted petal abscission, suggesting that RhIAA16 plays an important role in rose petal abscission.
        Cover page: Transcriptome Profiling of Petal Abscission Zone and Functional Analysis of an Aux/IAA Family Gene RhIAA16 Involved in Petal Shedding in Rose
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