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Open Access Publications from the University of California

Scholarly Works (21 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2018)

Automatic speech recognition (ASR) and speaker recognition (SRE) are two important fields of research in speech technology. Over the years, many efforts have been made on improving recognition accuracies on both tasks, and many different technologies have been developed. Given the close relationship between these two tasks, researchers have proposed different ways to introduce techniques developed for these tasks to each other.

In the first half of this thesis, I explore ways to improve speaker recognition performance using state-of-the-art speech recognition acoustic models, and then research alternative ways to perform speaker adaptation of deep learning models for ASR using speaker identity vector (i-vector). Experiments from this work shows that ASR and SRE are beneficial to each other and can be used to improve their performance.

In the second part of the thesis, I aim to build joint model for speech and speaker recognition. To implement this idea, I first build an open-source experimental framework, TIK, that connects well-known deep learning toolkit Tensorflow and speech recognition toolkit Kaldi. After reproducing state-of-the-art speech and speaker recognition performance using TIK, I then developed a unified model, JointDNN, that is trained jointly for speech and speaker recognition. Experimental results show that the joint model can effectively perform ASR and SRE tasks. In particular, experiments show that the JointDNN model is more effective in speaker recognition than x-vector system, given a limited amount of training data.

    Cover page: Combining Speech and Speaker Recognition - A Joint Modeling Approach
    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2021)

    ABSTRACTOptical phased arrays (OPAs), by controlling the phase and/or amplitude of optical emitter structure (e.g., grating coupler, 45-degree vertical coupler), have been widely used in applications such as light detection and ranging (LIDAR), imaging, and free-space communication systems. OPAs in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) regime, therefore, will be a good candidate for realizing thermal or gas-sensing, LIDAR with a lower level of turbulence. Here, based on our previous work, we propose an integrated non-mechanical OPAs-based beam steering system using a germanium-silicon optical platform. In the functional device part, we utilize vertical germanium via emitter and grating emitter arrays at MWIR and LWIR, respectively. Also, considering the fabrication complexity, we are now demonstrating a phase-change-material (PCM) assisted grating emitter to realize MWIR beam steering. Besides, we collaborated with AIM Photonics, demonstrating a large-scale lateral emitter array by foundry-based fabrication. For the light source part, Quantum Cascade Lasers (QCLs) are the only electrically pumped semiconductor light sources that can operate at room temperature over the entire MWIR/LWIR spectral range. We collaborate with other research groups and a commercial company to grow QCL wafers We design the III-V material QCL laser integration part with the germanium-silicon platform, to guarantee the good mode transition between III-V mesa and germanium waveguide. The integrated process will rely on the emerging micro-transfer-printing technology. We have already made some testing preparation work for this fabrication process.

      Cover page: Integrated Multi-spectral Non-Mechanical Light-Detection-and-Ranging Beam Steering Devices and Systems Using Optical Phased Array
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2019)
      We report the experimental results of fatigue behavior of ultralow-binder-content inorganic-organic hybrid (IOH) based on lunar soil simulant, which may be viewed as a "lunar cement". Under the same loading condition, the fatigue life of the IOH is superior to typical steel-reinforced concrete, especially when the stress amplitude is relatively high. Fatigue damage mostly occurs in the binder phase, followed by rapid cleavage-like failure. The important material parameters include filler type, filler particle size, and filler-binder bonding.
        Cover page: Fatigue Behavior of Inorganic-Organic Hybrid “Lunar Cement”
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2024)
        Australian mega-wildfires in the summer of 2019-2020 injected smoke into the stratosphere, causing strong ozone depletion in the lower stratosphere. Here, we model the smoke plume and reproduce its unexpected trajectory toward the middle stratosphere at ~35-kilometer altitude. We show that a smoke-charged vortex (SCV) induced and maintained by absorbing aerosols played a key role in lofting pollutants from the lower stratosphere and nearly doubled the southern hemispheric aerosol burden in the middle stratosphere. The SCV caused a redistribution of stratospheric aerosols, which boosted heterogeneous chemistry in the middle stratosphere and enhanced ozone production, compensating for up to 70% of the ozone depletion in the lower stratosphere. As global warming continues, we expect a growing frequency and importance of SCVs in promoting the impacts of wildfires on stratospheric aerosols and chemistry.
          Cover page: Smoke-charged vortex doubles hemispheric aerosol in the middle stratosphere and buffers ozone depletionCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2011)

          Objective and design

          Cystic fibrosis transmembrane conductance regulator (CFTR) regulates infection and inflammation. In this study, we investigated whether a lack of functional CFTR in neutrophils would promote lipopolysaccharide (LPS)-induced lung inflammation and injury.

          Materials and methods

          CFTR-inhibited or F508del-CFTR-mutated neutrophils were stimulated with LPS and cultured to evaluate production of cytokines and NF-κB activation. Wild-type mice were reconstituted with F508del neutrophils or bone marrow and then intratracheally challenged with LPS to observe lung inflammatory response.

          Results

          Pharmacologic inhibition and genetic mutation of CFTR in neutrophils activated NF-κB and facilitated macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor-α (TNF-α) production. Wild-type mice reconstituted with F508del neutrophils and bone marrow had more severe lung inflammation and injury after LPS challenge compared to wild-type mice receiving wild-type neutrophils or bone marrow reconstitution.

          Conclusions

          Lack of functional CFTR in neutrophils can promote LPS-induced acute lung inflammation and injury.
            Cover page: Role of CFTR expressed by neutrophils in modulating acute lung inflammation and injury in mice
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2024)
            Abstract: Multiphase oxidation of sulfur dioxide (SO2) is an important source of sulfate in the atmosphere. There are, however, concerns that protons produced during SO2 oxidation may cause rapid acidification of aerosol water and thereby quickly shut down the fast reactions favored at high pH. Here, we show that the sustainability of sulfate production is controlled by the competing effects of multiphase buffering and acidification, which can be well described by a characteristic buffering time, τbuff. Both GEOS‐Chem simulations and observations show that globally, τbuff is long enough (days) to sustain sulfate production over most populated regions, where the acidification of aerosol water is counteracted by the strong buffering effect of NH4+/NH3. Our results highlight the importance of anthropogenic ammonia emissions and pervasive human influences in shaping the chemical environment of the atmosphere.
              Cover page: Multiphase Buffering by Ammonia Sustains Sulfate Production in Atmospheric AerosolsCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2021)
              Airborne transmission by droplets and aerosols is important for the spread of viruses. Face masks are a well-established preventive measure, but their effectiveness for mitigating SARS-CoV-2 transmission is still under debate. We show that variations in mask efficacy can be explained by different regimes of virus abundance and related to population-average infection probability and reproduction number. For SARS-CoV-2, the viral load of infectious individuals can vary by orders of magnitude. We find that most environments and contacts are under conditions of low virus abundance (virus-limited) where surgical masks are effective at preventing virus spread. More advanced masks and other protective equipment are required in potentially virus-rich indoor environments including medical centers and hospitals. Masks are particularly effective in combination with other preventive measures like ventilation and distancing.
                Cover page: Face masks effectively limit the probability of SARS-CoV-2 transmission
                • Article
                • Peer Reviewed
                UC Irvine Previously Published Works (2018)
                Polycyclic aromatic hydrocarbons like benzo(a)pyrene (BaP) in atmospheric particulate matter pose a threat to human health because of their high carcinogenicity. In the atmosphere, BaP is mainly degraded through a multiphase reaction with ozone, but the fate and atmospheric transport of BaP are poorly characterized. Earlier modeling studies used reaction rate coefficients determined in laboratory experiments at room temperature, which may overestimate/underestimate degradation rates when applied under atmospheric conditions. Moreover, the effects of diffusion on the particle bulk are not well constrained, leading to large discrepancies between model results and observations. We show how regional and global distributions and transport of BaP can be explained by a new kinetic scheme that provides a realistic description of the temperature and humidity dependence of phase state, diffusivity, and reactivity of BaP-containing particles. Low temperature and humidity can substantially increase the lifetime of BaP and enhance its atmospheric dispersion through both the planetary boundary layer and the free troposphere. The new scheme greatly improves the performance of multiscale models, leading to better agreement with observed BaP concentrations in both source regions and remote regions (Arctic), which cannot be achieved by less-elaborate degradation schemes (deviations by multiple orders of magnitude). Our results highlight the importance of considering temperature and humidity effects on both the phase state of aerosol particles and the chemical reactivity of particulate air pollutants.
                  Cover page: Temperature effect on phase state and reactivity controls atmospheric multiphase chemistry and transport of PAHs
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2023)
                    Cover page: Extremely low-volatility organic coating leads to underestimation of black carbon climate impactCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2023)
                    Abstract. The Amazon Basin is frequently influenced by transatlantic transport of African dust plumes during its wet season (January–April), which not only interrupts the near-pristine atmospheric condition in that season, but also provides nutrient inputs to the Amazon rainforest upon deposition. In this study, we use the chemical transport model GEOS-Chem to investigate the impact of the export of African mineral dust to the Amazon Basin during the period of 2013–2017, constrained by multiple datasets obtained from the AErosol RObotic NETwork (AERONET), MODIS, as well as the Cayenne site and the Amazon Tall Tower Observatory (ATTO) site in the Amazon Basin. With an optimized particle mass size distribution (PMSD) of dust aerosols, the model captures observed aerosol optical depth (AOD) well in terms of both the mean value and the decline rate of the logarithm of AOD over the Atlantic Ocean along the transport path (AOaTP), implying consistency with the observed export efficiency of African dust along the transatlantic transport. With an annual emission of 0.73±0.12 Pg yr−1, African dust entering the Amazon Basin during the wet season accounts for 40±4.5 % (up to 70 %) of surface aerosol mass concentrations over the basin. Observed dust peaks over the Amazon Basin are generally associated with relatively higher African dust emissions (including the Sahara and the Sahel) and longer lifetimes of dust along the transatlantic transport, i.e., higher export efficiency of African dust across the Atlantic Ocean. The frequency of dust events during the wet season is around 18 % when averaged over the Amazon Basin, with maxima of over 60 % at the northeastern coast. During the dust events, AOD over most of the Amazon Basin is dominated by dust. Based on dust deposition, we further estimate annual inputs of 52±8.7, 0.97±0.16, and 21±3.6 mg m−2 yr−1 for iron, phosphorus, and magnesium, respectively, into the Amazon rainforest, which may to some extent compensate for the hydrologic losses of nutrients in the forest ecosystem.
                      Cover page: The export of African mineral dust across the Atlantic and its impact over the Amazon BasinCreative Commons 'BY-ND' version 4.0 license
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