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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2019)

In this thesis, we focused on investigating novelty modules integrated into popular detection network for assisting it to learn attentive representations for several practical applications in objects detection and instance segmentation tasks, including universal object detection and 3D medical image segmentation tasks. For universal object detection task, despite increasing efforts on universal representations for visual recognition, few have addressed object detection. In this thesis, we develop an effective and efficient universal object detection system that is capable of working on various image domains, from human faces and traffic signs to medical CT images. Unlike multi-domain models, this universal model does not require prior knowledge of the domain of interest. This is achieved by the introduction of a new family of adaptation layers, based on the principles of squeeze and excitation, and a new domain-attention mechanism. In the proposed universal detector, all parameters and computations are shared across domains, and a single network processes all domains all the time. Experiments, on a newly established universal object detection benchmark of 11 diverse datasets, show that the proposed detector outperforms a bank of individual detectors, a multi-domain detector, and a baseline universal detector, with a 1.3 parameter increase over a single-domain baseline detector. For 3D medical images segmentation tasks, although high resolution 3D medical images offer abundant detail information of human body parts and allow early detection of small lesions, due to the limitation of GPU memory, most methods either use down-sampled 3D volume as input, which significantly affects the detectability of small lesions, or use 2.5D networks to crop out neighboring image slices at original resolution, which loses context information along z direction. Both ways can significantly affect the performance of final model. In this paper, we propose a cross-slice spatial and channel attention module, which can maintain spatial resolution of input data, and effectively utilize context information along z direction of 3D volume. In order to get higher quality mask prediction, a cascade mask refinement module is designed to provide an objectiveness pixel-wise attention map for input feature maps. Furthermore, our scheme allows us to utilize the pretrained 2D detection models to achieve good results even with limited amount of training data, which is often met in medical applications and imposes big challenge to many deep learning methods. By utilizing the two novel modules, we achieve state-of-art performance 74.10 dice per case on Liver Tumor Segmentation Challenge(LiTS), which outperforms previous year challenge winner by 6.7 points and rank as 1st on leader board of LiTS benchmark upon submission of this paper.

    Cover page: Attentive representations for objects detection and instance segmentation
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2024)
    In July to August 2022, Pakistan suffered historic flooding while record-breaking heatwaves swept southern China, causing severe socioeconomic impacts. Similar extreme events have frequently coincided between two regions during the past 44 years, but the underlying mechanisms remain unclear. Using observations and a suite of model experiments, here, we show that the upper-tropospheric divergent wind induced by convective heating over Pakistan excites a barotropic anomalous anticyclone over eastern China, which further leads to persistent heatwaves. Atmospheric model ensemble simulation indicates that this dynamic pathway linking Pakistan flooding and East Asian heatwaves is intrinsic to the climate system, largely independent of global sea surface temperature forcing. This dynamic connection is most active during July to August when convective variability is large over Pakistan and the associated divergent flow excites barotropic Rossby waves that propagate eastward along the upper troposphere westerly waveguide. This robust waveguide and the time delay offer hopes for improved subseasonal prediction of extreme events in East Asia.
      Cover page: Dynamic pathway linking Pakistan flooding to East Asian heatwaves.
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2013)
      Abstract Background Accurate determination of genetic ancestry is of high interest for many areas such as biomedical research, personal genomics and forensics. It remains an important topic in genetic association studies, as it has been shown that population stratification, if not appropriately considered, can lead to false-positive and -negative results. While large association studies typically extract ancestry information from available genome-wide SNP genotypes, many important clinical data sets on rare phenotypes and historical collections assembled before the GWAS area are in need of a feasible method (i.e., ease of genotyping, small number of markers) to infer the geographic origin and potential admixture of the study subjects. Here we report on the development, application and limitations of a small, multiplexable ancestry informative marker (AIM) panel of SNPs (or AISNP) developed specifically for this purpose. Results Based on worldwide populations from the HGDP, a 41-AIM AISNP panel for multiplex application with the ABI SNPlex and a subset with 31 AIMs for the Sequenome iPLEX system were selected and found to be highly informative for inferring ancestry among the seven continental regions Africa, the Middle East, Europe, Central/South Asia, East Asia, the Americas and Oceania. The panel was found to be least informative for Eurasian populations, and additional AIMs for a higher resolution are suggested. A large reference set including over 4,000 subjects collected from 120 global populations was assembled to facilitate accurate ancestry determination. We show practical applications of this AIM panel, discuss its limitations for admixed individuals and suggest ways to incorporate ancestry information into genetic association studies. Conclusion We demonstrated the utility of a small AISNP panel specifically developed to discern global ancestry. We believe that it will find wide application because of its feasibility and potential for a wide range of applications.
        Cover page: Inference of human continental origin and admixture proportions using a highly discriminative ancestry informative 41-SNP panel
        • Article
        • Peer Reviewed
        LBL Publications (2022)
        Glycine, the simplest amino acid, is considered a promising functional biomaterial owing to its excellent biocompatibility and strong out-of-plane piezoelectricity. Practical applications require glycine films to be manufactured with their strong piezoelectric polar 〈001〉 direction aligned with the film thickness. Based on the recently-developed solidification approach of a polyvinyl alcohol (PVA) and glycine aqueous solution, in this work, we demonstrate that the crystal orientation of the as-synthesized film is determined by the orientation of glycine crystal nuclei. By controlling the local nucleation kinetics via surface curvature tuning, we shifted the nucleation site from the edge to the middle of the liquid film, and thereby aligned the 〈001〉 direction vertically. As a result, the PVA-glycine-PVA sandwich film exhibits the highest aver-age piezoelectric coefficient d33 of 6.13 ± 1.13 pC N-1. This work demonstrates a promising kinetic approach to achieve crystallization and property control in a scalable biocrystal manufacturing process.
          Cover page: Orientation-controlled crystallization of γ-glycine films with enhanced piezoelectricityCreative Commons 'BY-NC' version 4.0 license
          • Article
          • Peer Reviewed
          UC Merced Previously Published Works (2022)
          Density functional theory calculations are combined with time-resolved photoluminescence experiments to identify the species responsible for the reversible trapping of holes following photoexcitation of InP/ZnSe/ZnS core/shell/shell quantum dots (QDs) having excess indium in the shell [P. Cavanaugh et al., J. Chem. Phys. 155, 244705 (2021)]. Several possible assignments are considered, and a substitutional indium adjacent to a zinc vacancy, In3+/VZn 2-, is found to be the most likely. This assignment is consistent with the observation that trapping occurs only when the QD has excess indium and is supported by experiments showing that the addition of zinc oleate or acetate decreases the extent of trapping, presumably by filling some of the vacancy traps. We also show that the addition of alkyl carboxylic acids causes increased trapping, presumably by the creation of additional zinc vacancies. The calculations show that either a single In2+ ion or an In2+-In3+ dimer is much too easily oxidized to form the reversible traps observed experimentally, while In3+ is far too difficult to oxidize. Additional experimental data on InP/ZnSe/ZnS QDs synthesized in the absence of chloride demonstrates that the reversible traps are not associated with Cl-. However, a zinc vacancy adjacent to a substitutional indium is calculated to have its highest occupied orbitals about 1 eV above the top of the valence band of bulk ZnSe, in the appropriate energy range to act as reversible traps for quantum confined holes in the InP valence band. The associated orbitals are predominantly composed of p orbitals on the Se atoms adjacent to the Zn vacancy.
          • 1 supplemental PDF
          Cover page: Identity of the reversible hole traps in InP/ZnSe core/shell quantum dots
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2024)
          Conductive hydrogels have a remarkable potential for applications in soft electronics and robotics, owing to their noteworthy attributes, including electrical conductivity, stretchability, biocompatibility, etc. However, the limited strength and toughness of these hydrogels have traditionally impeded their practical implementation. Inspired by the hierarchical architecture of high-performance biological composites found in nature, we successfully fabricate a robust and sensitive conductive nanocomposite hydrogel through self-assembly-induced bridge cross-linking of MgB2 nanosheets and polyvinyl alcohol hydrogels. By combining the hierarchical lamellar microstructure with robust molecular B─O─C covalent bonds, the resulting conductive hydrogel exhibits an exceptional strength and toughness. Moreover, the hydrogel demonstrates exceptional sensitivity (response/relaxation time, 20 milliseconds; detection lower limit, ~1 Pascal) under external deformation. Such characteristics enable the conductive hydrogel to exhibit superior performance in soft sensing applications. This study introduces a high-performance conductive hydrogel and opens up exciting possibilities for the development of soft electronics.
            Cover page: Robust and sensitive conductive nanocomposite hydrogel with bridge cross-linking-dominated hierarchical structural design.
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2024)
            The sensitivity of soil organic carbon (SOC) decomposition in seasonally frozen soils, such as alpine ecosystems, to climate warming is a major uncertainty in global carbon cycling. Here we measure soil CO2 emission during four years (2018-2021) from the whole-soil warming experiment (4 °C for the top 1 m) in an alpine grassland ecosystem. We find that whole-soil warming stimulates total and SOC-derived CO2 efflux by 26% and 37%, respectively, but has a minor effect on root-derived CO2 efflux. Moreover, experimental warming only promotes total soil CO2 efflux by 7-8% on average in the meta-analysis across all grasslands or alpine grasslands globally (none of these experiments were whole-soil warming). We show that whole-soil warming has a much stronger effect on soil carbon emission in the alpine grassland ecosystem than what was reported in previous warming experiments, most of which only heat surface soils.
              Cover page: Whole-soil warming leads to substantial soil carbon emission in an alpine grassland.
              • Article
              • Peer Reviewed
              UC Riverside Previously Published Works (2019)
              Semiconductive transition metal dichalcogenides (TMDs) have been considered as next generation semiconductors, but to date most device investigations are still based on microscale exfoliation with a low yield. Wafer scale growth of TMDs has been reported but effective doping approaches remain challenging due to their atomically thick nature. This work reports the synthesis of wafer-scale continuous few-layer PtSe2 films with effective doping in a controllable manner. Chemical component analyses confirm that both n-doping and p-doping can be effectively modulated through a controlled selenization process. The electrical properties of PtSe2 films have been systematically studied by fabricating top-gated field effect transistors (FETs). The device current on/off ratio is optimized in two-layer PtSe2 FETs, and four-terminal configuration displays a reasonably high effective field effect mobility (14 and 15 cm2 V−1 s−1 for p-type and n-type FETs, respectively) with a nearly symmetric p-type and n-type performance. Temperature dependent measurement reveals that the variable range hopping is dominant at low temperatures. To further establish feasible application based on controllable doping of PtSe2, a logic inverter and vertically stacked p–n junction arrays are demonstrated. These results validate that PtSe2 is a promising candidate among the family of TMDs for future functional electronic applications.
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2023)
                Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.
                  Cover page: Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications.
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