Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Merced Electronic Theses and Dissertations (2017)

This study focuses on the development of (La(0.6)Sr(0.4))(0.95)Co(0.2)Fe(0.8)O(3-d) LSCF-based cathodes for solid oxide fuel cells, with the purpose of lowering operating temperature and improving cell performance for commercialization. The first part of the study investigated the effects of using Co3O4 as a sintering aid, which was shown to enhance grain growth and interconnectivity and to dramatically lower cell impedance for both LSCF and LSCF- Gd(0.1)Ce(0.9)O(2-d) (gadolinia-doped ceria; GDC) composite cathodes. Co3O4 concentration was optimized for both the functional layer and the current collecting layer of the cathode. The second portion of the study explores the relationship between electrode layer thickness and cell impedance. It was shown that increasing functional layer thickness beyond a limiting value increases cell impedance, and that both ohmic resistance and polarization resistance asymptotically decrease with increasing thickness of the current collecting layer. Optimal thicknesses were found for each of the electrode layers. Finally, ultra-thin layers of yttria-doped ceria were deposited via atomic layer deposition (ALD) onto the functional layer of bilayer LSCF-GDC/LSCF cathodes as well as pure LSCF cathodes. It was shown that for both sets of cells, ohmic resistance initially increased with YDC deposition, but that subsequent increases in YDC thickness had an inverse relationship with ohmic resistance. This behavior has been observed in previous studies, and prolonged heat treatment will be needed to fully realize the benefits of the functionalization. Polarization resistance was negatively affected by YDC functionalization for both sets of cells due to a blocking of oxygen reaction sites on the surface of the LSCF electrode. In summary, Co3O4 concentration and electrode layer thickness were optimized to maximize performance for LSCF-based cathodes, and ALD functionalization was investigated as a method for further improving cathode performance.

    Cover page: OPTIMIZATION OF MICROSTRUCTURE AND COMPOSITION AND THE EFFECTS OF ATOMIC LAYER DEPOSITION SURFACE TREATMENT ON LSCF-BASED CATHODES FOR INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS
    • Article
    • Peer Reviewed
    Western Journal of Emergency Medicine: Integrating Emergency Care with Population Health, Volume 19, Issue 3 (2018)

    Introduction: The objective was to determine if pregnant women visiting the emergency department (ED) are tested for substance use as frequently as non-pregnant women.

    Methods: We captured all ED visits over a six-year period (2010-2016) from a single community hospital and identified women of childbearing age, defined for our study as 11-50 years old. We collected demographic data including age in years, ethnicity, body mass index, marital status, disposition, last encounter department, method of arrival, and day of week. An independent binary variable was created based on whether the woman was tested for alcohol or drugs (amphetamines, barbiturates, benzodiazepines, cannabis, cocaine, opioids) during her visit. We then compared rates of testing for substance use by pregnancy status. 

    Results: We identified 61,222 ED visits by women of childbearing age (range 11-50, mean 30.5, standard deviation 9.6) over a six-year period from 2010-2016. Of the 57,360 non-pregnant women, 4.14% were tested compared to 1.04% of the 3,862 pregnant women tested with a relative risk of 0.25 (p<0.001, 95% confidence interval [CI] [0.183-0.341]). The most highly tested chief complaints for all women – psychiatric or substance use concerns – showed pregnant women were still 37% and 54% less likely to be tested, respectively (risk ratio [RR] 0.46, 95% CI [0.19-1.13]; RR 0.63, 95% CI [0.41-0.96]). Beyond pregnancy status, we found no significant interaction between patient demographics and substance use testing.

    Conclusion: Pregnant women presenting to the ED were 75% less likely to be tested for drug or alcohol use than non-pregnant women. Our study showed only pregnancy status as a statistically significant variable in drug- and alcohol-screening rates when pregnant and non-pregnant patient chief complaints and demographics were compared. Increased attention to the screening of pregnant women for substance use may be necessary to provide adequate care and intervention to this population.

      Cover page: Substance Use in Pregnant Women Using the Emergency Department: Undertested And Overlooked?Creative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2015)
      Catalysis in protein tyrosine phosphatases (PTPs) involves movement of a protein loop called the WPD loop that brings a conserved aspartic acid into the active site to function as a general acid. Mutation of the tryptophan in the WPD loop of the PTP YopH to any other residue with a planar, aromatic side chain (phenylalanine, tyrosine, or histidine) disables general acid catalysis. Crystal structures reveal these conservative mutations leave this critical loop in a catalytically unproductive, quasi-open position. Although the loop positions in crystal structures are similar for all three conservative mutants, the reasons inhibiting normal loop closure differ for each mutant. In the W354F and W354Y mutants, steric clashes result from six-membered rings occupying the position of the five-membered ring of the native indole side chain. The histidine mutant dysfunction results from new hydrogen bonds stabilizing the unproductive position. The results demonstrate how even modest modifications can disrupt catalytically important protein dynamics. Crystallization of all the catalytically compromised mutants in the presence of vanadate gave rise to vanadate dimers at the active site. In W354Y and W354H, a divanadate ester with glycerol is observed. Such species have precedence in solution and are known from the small molecule crystal database. Such species have not been observed in the active site of a phosphatase, as a functional phosphatase would rapidly catalyze their decomposition. The compromised functionality of the mutants allows the trapping of species that undoubtedly form in solution and are capable of binding at the active sites of PTPs, and, presumably, other phosphatases. In addition to monomeric vanadate, such higher-order vanadium-based molecules are likely involved in the interaction of vanadate with PTPs in solution.
        Cover page: Conservative Tryptophan Mutants of the Protein Tyrosine Phosphatase YopH Exhibit Impaired WPD-Loop Function and Crystallize with Divanadate Esters in Their Active Sites
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2024)
        OBJECTIVES: To differentiate invasive lepidic predominant adenocarcinoma (iLPA) from adenocarcinoma in situ (AIS)/minimally invasive adenocarcinoma (MIA) of lung utilizing visual semantic and computer-aided detection (CAD)-based texture features on subjects initially diagnosed as AIS or MIA with CT-guided biopsy. MATERIALS AND METHODS: From 2011 to 2017, all patients with CT-guided biopsy results of AIS or MIA who subsequently underwent resection were identified. CT scan before the biopsy was used to assess visual semantic and CAD texture features, totaling 23 semantic and 95 CAD-based quantitative texture variables. The least absolute shrinkage and selection operator (LASSO) method or forward selection was used to select the most predictive feature and combination of semantic and texture features for detection of invasive lung adenocarcinoma. RESULTS: Among the 33 core needle-biopsied patients with AIS/MIA pathology, 24 (72.7%) had invasive LPA and 9 (27.3%) had AIS/MIA on resection. On CT, visual semantic features included 21 (63.6%) part-solid, 5 (15.2%) pure ground glass, and 7 (21.2%) solid nodules. LASSO selected seven variables for the model, but all were not statistically significant. Volume was found to be statistically significant when assessing the correlation between independent variables using the backward selection technique. The LASSO selected tumor_Perc95, nodule surround, small cyst-like spaces, and volume when assessing the correlation between independent variables. CONCLUSIONS: Lung biopsy results showing noninvasive LPA underestimate invasiveness. Although statistically non-significant, some semantic features showed potential for predicting invasiveness, with septal stretching absent in all noninvasive cases, and solid consistency present in a significant portion of invasive cases.
          Cover page: Predicting Invasiveness in Lepidic Pattern Adenocarcinoma of Lung: Analysis of Visual Semantic and Radiomic Features.
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2022)
          Type Ia supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a very low brightness of −10.5 AB absolute magnitude, revealing a hitherto unseen plateau in the B band that results in a rapid redward colour evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing B-band flux is best explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed B − V colour evolution of the supernova also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colours are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended subsonic mixing processes in some normal type Ia SN explosions.
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2023)
            SN 2018aoz is a Type Ia SN with a B-band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN 2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on Hα and He i favor a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O i] and He i disfavors a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN 2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe ii] and [Ni ii]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1D models are incompatible with the infant-phase excess emission, B max - V max color, and weak strength of nebular-phase [Ca ii]. Although the explosion processes of SN 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear to be normal after ∼1 day.
              Cover page: The Origin and Evolution of the Normal Type Ia SN 2018aoz with Infant-phase Reddening and Excess EmissionCreative Commons 'BY' version 4.0 license
              Top