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Open Access Publications from the University of California

Scholarly Works (7 results)

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

This dissertation is a study of the climatological mean seasonal cycle of the ventilation of the ocean. Firstly, I have developed a computationally efficient 4-D variational assimilation system, called CYCLOCIM. It assimilates monthly mean temperature and salinity data from the World Ocean Atlas, transient CFC-11 and CFC-12, and natural radiocarbon measurements for the deep ocean from the GLODAPv2 database. CYCLOCIM is a new variational assimilation system that is specifically designed for the problem of estimating the climatological seasonal cycle of the residual mean circulation. I independently obtain the modeled overturning circulation, and the meridional heat and fresh water transport that largely agree with existing studies. Moreover, CYCLOCIM improves the model fit to the observation in the upper ocean compared to previous studies that ignored the seasonal cycle. The main product of the assimilation system is a set of 12 monthly data-constrained of tracer transport operators. I then calculate transit-time distribution (TTD) using the monthly transport operators to quantify ``Stommel's demon'', that is, the seasonality of the ventilation in the main thermocline. The study provides an accurate estimate of effective subduction and obduction months and maps of the water fraction in the main thermocline was last transported from or will be first transported back to the surface. For example, subduction occurs mainly in the Southern Ocean (64%), which lasts from June to November and peaks in September (21%) and October (20%). Moreover, the subduction happens in the North Pacific (12%) and the North Atlantic (16%), which lasts from January to April and peaks in March (15%). Obduction occurs mainly in ACC region (48%), which starts from April to November and peaks in August. The upwelling regions of the tropical ocean is the secondary primary obduction region, which upwell 35% of the water back to surface and lasts the whole year. Furthermore, I have applied the TTD method to estimate the ventilation of the deep water masses. The formation of NADW, AABW, PDW, IDW occurs mainly in the surface of the Southern Ocean (respectively, 15%, 69%, 56% and 53%) and the Atlantic Ocean (respectively, 84%, 39%, 37% and 41%) during winter and spring in both hemisphere.

    Cover page: The seasonally varying ventilation of the ocean: a model-data synthesis
    • Thesis
    • Peer Reviewed
    UC San Diego Electronic Theses and Dissertations (2016)

    A new distance and force detection platform has been realized based on nanoparticle-nanofiber optic platform. The detection of distance is based on recording the scattering intensity of nanoparticle which is directly related with its distance away from the nanofiber. If there is a well characterized compressible polymer layer between nanoparticle and nanofiber, the force applied on the nanoparticle can be known based with the scattering intensity.

    In order to fulfill the force sensing platform, two relationships have been established beforehand: one is uniform and stable polymer film on the nanofiber; another is an accurate calibration of the relationship between distance and scattering intensity. Firstly, different molecular weights of polyethylene glycol have been covalently grafted on the tin oxide nanofiber based on silane chemistry. Force-indentation under different ionic condition and tip modification show the steric force dominate the repulsion between nanofiber and AFM tip within the height of the polymer brush. Secondly, an easy method has been developed to link a single nanoparticle on the end of the AFM tip. A laser excitation system has been integrated with a bioscope AFM platform to directly record the relationship with distance with scattering intensity. Comparison with the reference nanoparticle on the nanofiber nearby show there is no influence of AFM tip on the scattering intensity of plasmonic nanoparticles in the evanescent field of the nanofiber.

    With these two baselines, PEG layer has been sandwiched between nanoparticle and nanofiber and provide mechanical feedback for the force applied on the nanoparticle. With laser excitation and bioscope AFM system, a detail calibration of distance and force with the scattering intensity has been demonstrated. The distance sensitivity is measured to be down to angstrom-level; the force sensitivity is multiplied with the spring constant to be down to 160 fN. The new force sensing platform has been used to detect the miroflow force applied on the nanoparticles with active bacteria, the average stress is compared with AFM cantilever system and show higher force sensitivity due to its smaller size and lower damping coefficient. Acoustical frequency signatures from AFM tip modulation and cardiomyocytes beating have also been identified using the force sensing platform with an acoustic sensitivity of -30 dB. With the ability to tune mechanical response of the compressible fiber cladding, detect forces from multiple nanoscale sites on a single fiber, and a geometry that can be inserted into small volumes, the new force sensing platform will become a valuable tool for biomechanical and intracellular studies.

      Cover page: Coupled Plasmonic Nanoparticle-Nanofiber Optic Force Transducers
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2017)

      Objective

      Adolescents with attention-deficit/hyperactivity disorder (ADHD) are at increased risk for alcohol and marijuana use. This study's objective is to describe adolescents' ADHD-specific reasons for marijuana use, knowledge of ADHD-specific alcohol risks, and reported subspecialty provider messaging/education regarding alcohol use among adolescents with ADHD.

      Methods

      Youths with ADHD aged 12 to 18 years completed a survey about alcohol and marijuana use, ADHD-specific reasons for marijuana use, knowledge of ADHD-specific alcohol risks, and reported provider messaging/education regarding alcohol use. We assessed knowledge toward substance use using descriptive statistics. We used χ and t tests to determine whether knowledge or provider messaging/education differed by sociodemographic characteristics.

      Results

      Of the 96 participants, 61.5% were male, average age was 15.7 years; 31.3% reported past-year alcohol use and 20.8% reported past-year marijuana use. The majority (65.2%) said "no/don't know" to both "Can alcohol make ADHD symptoms worse?" and "Can alcohol interfere or get in the way of the medications you take?" Older participants were more likely to correctly answer the medication question "yes." Despite most (74%) participants reporting that their provider asked about alcohol use, few youth reported that their providers gave specific messages/education that alcohol could make ADHD symptoms worse (9.4%) or interfere with ADHD medications (14.6%); older participants and past-year alcohol users were more likely to have received these alcohol-specific messages.

      Conclusion

      Many youth with ADHD are unaware of the risks of alcohol use in relation to ADHD and providers are not consistently discussing these risks in the context of clinical ADHD care.
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2017)
        Ultrasensitive nanomechanical instruments, including the atomic force microscope (AFM)1-4 and optical and magnetic tweezers5-8, have helped shed new light on the complex mechanical environments of biological processes. However, it is difficult to scale down the size of these instruments due to their feedback mechanisms9, which, if overcome, would enable high-density nanomechanical probing inside materials. A variety of molecular force probes including mechanophores10, quantum dots11, fluorescent pairs12,13 and molecular rotors14-16 have been designed to measure intracellular stresses; however, fluorescence-based techniques can have short operating times due to photo-instability and it is still challenging to quantify the forces with high spatial and mechanical resolution. Here, we develop a compact nanofibre optic force transducer (NOFT) that utilizes strong near-field plasmon-dielectric interactions to measure local forces with a sensitivity of <200 fN. The NOFT system is tested by monitoring bacterial motion and heart-cell beating as well as detecting infrasound power in solution.
          Cover page: Nanofibre optic force transducers with sub-piconewton resolution via near-field plasmon–dielectric interactions
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2017)
          Ultrasensitive nanomechanical instruments, including the atomic force microscope (AFM)1-4 and optical and magnetic tweezers5-8, have helped shed new light on the complex mechanical environments of biological processes. However, it is difficult to scale down the size of these instruments due to their feedback mechanisms9, which, if overcome, would enable high-density nanomechanical probing inside materials. A variety of molecular force probes including mechanophores10, quantum dots11, fluorescent pairs12,13 and molecular rotors14-16 have been designed to measure intracellular stresses; however, fluorescence-based techniques can have short operating times due to photo-instability and it is still challenging to quantify the forces with high spatial and mechanical resolution. Here, we develop a compact nanofibre optic force transducer (NOFT) that utilizes strong near-field plasmon-dielectric interactions to measure local forces with a sensitivity of <200 fN. The NOFT system is tested by monitoring bacterial motion and heart-cell beating as well as detecting infrasound power in solution.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2016)

            Background

            In an effort to reduce barriers to screening for alcohol use in pediatric primary care, the National Institute on Alcoholism and Alcohol Abuse (NIAAA) developed a two-question Youth Alcohol Screening Tool derived from population-based survey data. It is unknown whether this screening tool, designed for use with general populations, accurately identifies risk among youth with chronic medical conditions (YCMC). This growing population, which comprises nearly one in four youth in the US, faces a unique constellation of drinking-related risks.

            Method

            To validate the NIAAA Youth Alcohol Screening Tool in a population of YCMC, we performed a cross-sectional validation study with a sample of 388 youth ages 9-18 years presenting for routine subspecialty care at a large children's hospital for type 1 diabetes, persistent asthma, cystic fibrosis, inflammatory bowel disease, or juvenile idiopathic arthritis. Participants self-administered the NIAAA Youth Alcohol Screening Tool and the Diagnostic Interview Schedule for Children as a criterion standard measure of alcohol use disorders (AUD). Receiver operating curve analysis was used to determine cut points for identifying youth at moderate and highest risk for an AUD.

            Results

            Nearly one third of participants (n = 118; 30.4%) reported alcohol use in the past year; 86.4% (106) of past year drinkers did not endorse any AUD criteria, 6.8% (n = 8) of drinkers endorsed a single criterion, and 6.8% of drinkers met criteria for an AUD. Using the NIAAA tool, optimal cut points found to identify youth at moderate and highest risk for an AUD were ≥ 6 and ≥12 drinking days in the past year, respectively.

            Conclusions

            The NIAAA Youth Alcohol Screening Tool is highly efficient for detecting alcohol use and discriminating disordered use among YCMC. This brief screen appears feasible for use in specialty care to ascertain alcohol-related risk that may impact adversely on health status and disease management.
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2023)

              Introduction

              COVID-19 vaccines are safe, effective, and widely available, but many adults in the U.S. have not been vaccinated for COVID-19. This study examined the associations between behavioral and social drivers of vaccination with COVID-19 vaccine uptake in the U.S. adults and their prevalence by region.

              Methods

              A nationally representative sample of U.S. adults participated in a cross-sectional telephone survey in August-November 2021; the analysis was conducted in January 2022. Survey questions assessed self-reported COVID-19 vaccine initiation, demographics, and behavioral and social drivers of vaccination.

              Results

              Among the 255,763 respondents, 76% received their first dose of COVID-19 vaccine. Vaccine uptake was higher among respondents aged ≥75 years (94%), females (78%), and Asian non-Hispanic people (94%). The drivers of vaccination most strongly associated with uptake included higher anticipated regret from nonvaccination, risk perception, and confidence in vaccine safety and importance, followed by work- or school-related vaccination requirements, social norms, and provider recommendation (all p<0.05). The direction of association with uptake varied by reported level of difficulty in accessing vaccines. The prevalence of all of these behavioral and social drivers of vaccination was highest in the Northeast region and lowest in the Midwest and South.

              Conclusions

              This nationally representative survey found that COVID-19 vaccine uptake was most strongly associated with greater anticipated regret, risk perception, and confidence in vaccine safety and importance, followed by vaccination requirements and social norms. Interventions that leverage these social and behavioral drivers of vaccination have the potential to increase COVID-19 vaccine uptake and could be considered for other vaccine introductions.
                Cover page: Behavioral and Social Drivers of COVID-19 Vaccination in the United States, August–November 2021
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