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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2012)

Experimental and analytical investigations were conducted to provide insight into the nonlinear cyclic response of moderate aspect ratio reinforced concrete structural walls. Five large-scale cantilever structural wall specimens, subjected to combined constant axial load and reversed cyclic lateral loading, were designed, constructed, instrumented, and tested. The wall specimens were designed to yield in flexure prior to loss of lateral load capacity. Primary test variables included aspect ratio (1.5 and 2.0), axial load level (0.025Agf'c and 0.10Agf'c), and wall shear stress level.

Test results showed that substantial loss of lateral load capacity was observed for a variety of reasons, such as diagonal tension, diagonal compression, sliding shear, concrete crushing, and buckling of vertical reinforcement. Test results also indicated that significant strength loss was impacted by wall aspect ratio, axial load level, and wall shear stress level. Although various failure modes were observed for five wall specimens, drift ratio at substantial loss of lateral load capacity was approximately 3.0% for all tests. The average contribution of nonlinear shear deformations to the top lateral displacement varied between approximately 20 and 50%, with lower values for the aspect ratio 2.0 walls.

Modeling parameters recommended by ASCE 41-06 and FEMA 356, including effective flexural and shear stiffness values, deformation capacities, and residual strengths, are compared with the corresponding values derived from test results. Current modeling approaches, including both uncoupled (P-M and V independent) and coupled (interaction between P-M and V) models, were used to assess their ability to capture the measured responses for the moderate aspect ratio structural walls. The investigation indicates that both models overestimate lateral load capacity and lateral stiffness, but with notable differences. In general, results for the uncoupled models are less consistent with the test results, indicating that coupled models are needed to adequately capture the responses of moderate aspect ratio walls. The primary shortcoming of the coupled model was the lack of cyclic material models. The detailed response information obtained from the heavily instrumented walls tested in this study provide essential data to develop robust analytical models, including models that account for cyclic nonlinear shear-flexure interaction.

    Cover page: Experimental and Analytical Studies of Moderate Aspect Ratio Reinforced Concrete Structural Walls
    • Thesis
    • Peer Reviewed
    UC Riverside Electronic Theses and Dissertations (2018)

    Citrus greening disease, also known as Huanglongbing (HLB), is posing a worldwide threat to the multi-billion dollars citrus industry. Currently, there are no cures for infected plants while containment of the spread of disease is heavily dependent on early detection of infected hosts for quarantine. The pathogen responsible for causing the disease is the bacteria Candidatus Liberibacter asiaticus (CLas). Thus, it is imperative that disease management strategies address current demands for accurate, timely, and robust disease detection and diagnosis minimize the spread of disease. By adopting a novel detection strategy targeting a recently discovered secreted protein biomarker, SDE1, which is unique to CLas, we hope to overcome the challenges faced by current detection methods, such as nucleic acid-based and symptom-based which have been found prone to false negatives and mis-diagnoses, respectively. To do this, we have worked to procure and characterize the antibodies specific for the novel HLB biomarker. In the process of characterizing the anti-SDE1 antibodies, we have also developed a specific and sensitive enzyme-linked immunosorbent assay (ELISA) for high-throughput and point-of-laboratory analysis of citrus plant samples. With the final goal of using the anti-SDE1 antibodies to develop sensitive, facile, and specific HLB detection method, we have integrated these antibodies into nanoscale electrical biosensor platforms. Using the novel semiconducting carbon nanomaterials, reduced graphene oxide (RGO) and single-walled carbon nanotubes (SWNTs), as the electrical transducer element for our biosensors, we have developed chemiresistive biosensors that demonstrate specificity and sensitivity to the SDE1 biomarker in simple phosphate buffer and in plant extracts.

      Cover page: Carbon Nanomaterial-Based Chemiresistive Biosensors for Detection of Secretory Protein Biomarkers of Citrus Greening Disease
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2021)
      Molybdenum disulfide (MoS2) features a band gap of 1.3 eV (indirect) to 1.9 eV (direct). This tunable band gap renders MoS2 a suitable conducting channel for field-effect transistors (FETs). In addition, the highly sensitive surface potential in MoS2 layers allows the feasibility of FET applications in biosensors, where direct immobilization and detection of biological molecules are conducted in wet conditions. In this work, we report, for the first time, the degradation of chemical vapor deposition (CVD) grown MoS2 FET-based sensors in the presence of phosphate buffer and water, which caused false positive response in detection. We conclude the degradation was originated by physical delamination of MoS2 thin films from the SiO2 substrate. The problem was alleviated by coating the sensors with a 30 nm thick aluminum oxide (Al2O3) layer using atomic layer deposition technique (ALD). This passive oxide thin film not only acted as a protecting layer against the device degradation but also induced a strong n-doping onto MoS2, which permitted a facile method of detection in MoS2 FET-based sensors using a low-power mode chemiresistive I-V measurement at zero gate voltage (Vgate = 0 V). Additionally, the oxide layer provided available sites for facile functionalization with bioreceptors. As immunoreaction plays a key role in clinical diagnosis and environmental analysis, our work presented a promising application using such enhanced Al2O3-coated MoS2 chemiresistive biosensors for detection of HIgG with high sensitivity and selectivity. The biosensor was successfully applied to detect HIgG in artificial urine, a complex matrix containing organics and salts.
        Cover page: Effect of Al2O3 Passive Layer on Stability and Doping of MoS2 Field-Effect Transistor (FET) Biosensors
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2018)
        Nb2O5 is a Li+ intercalation metal oxide that is of current interest for lithium ion battery electrodes. The electrophoretic deposition (ED) of Nb2O5 thin-films from aqueous, NbOx colloidal solutions is reported here. For films ranging in thickness from 38 to 144 nm, the mass loading of Nb2O5 on the electrode is correlated with the coulometry of ED using quartz crystal microbalance gravimetry. Crystalline, phase pure films of orthorhombic, T-Nb2O5, are obtained by postdeposition calcination. These films exhibit unusually high specific capacities for Li+-based energy storage as a consequence of ≈70% porosity. For example, a 60 nm thick film displays a specific capacity, Csp, of 420 mAh/g at 5 A/g and 220 mAh/g at 50 A/g, which can be compared with the theoretical Faradaic capacity of 202 mAh/g. T-Nb2O5 films also have a specific energy density in the range from 770-486 Wh/kg, and a specific power density in the range from 9 to 90 kW/kg. These excellent energy storage metrics are attributed to augmentation of the Faradaic capacity by high double-layer capacities enabled by the mesoporous structure of these films.
          Cover page: Electrophoretic Deposition of Mesoporous Niobium(V)Oxide Nanoscopic Films
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2015)
          Results of the studies are reported relating to application of the silanized nanostructured zirconia, electrophoretically deposited onto indium tin oxide (ITO) coated glass for covalent immobilization of the monoclonal antibodies (anti-CYFRA-21-1). This biosensing platform has been utilized for a simple, efficient, noninvasive, and label-free detection of oral cancer via cyclic voltammetry technique. The results of electrochemical response studies conducted on bovine serum albumin (BSA)/anti-CYFRA-21-1/3-aminopropyl triethoxy silane (APTES)/ZrO2/ITO immunoelectrode reveal that this immunoelectrode can be used to measure CYFRA-21-1 (oral cancer biomarker) concentration in saliva samples, with a high sensitivity of 2.2 mA mL ng-1, a linear detection range of 2-16 ng mL-1, and stability of six weeks. The results of these studies have been validated via enzyme-linked immunosorbent assay.
            Cover page: Biofunctionalized Nanostructured Zirconia for Biomedical Application: A Smart Approach for Oral Cancer Detection
            • Article
            • Peer Reviewed
            UC Riverside Previously Published Works (2017)
            The citrus industry is facing an unprecedented crisis due to Huanglongbing (HLB, aka citrus greening disease), a bacterial disease associated with the pathogen Candidatus Liberibacter asiaticus (CLas) that affects all commercial varieties. Transmitted by the Asian citrus psyllid (ACP), CLas colonizes citrus phloem, leading to reduced yield and fruit quality, and eventually tree decline and death. Since adequate curative measures are not available, a key step in HLB management is to restrict the spread of the disease by identifying infected trees and removing them in a timely manner. However, uneven distribution of CLas cells in infected trees and the long latency for disease symptom development makes sampling of trees for CLas detection challenging. Here, we report that a CLas secreted protein can be used as a biomarker for detecting HLB infected citrus. Proteins secreted from CLas cells can presumably move along the phloem, beyond the site of ACP inoculation and CLas colonized plant cells, thereby increasing the chance of detecting infected trees. We generated a polyclonal antibody that effectively binds to the secreted protein and developed serological assays that can successfully detect CLas infection. This work demonstrates that antibody-based diagnosis using a CLas secreted protein as the detection marker for infected trees offers a high-throughput and economic approach that complements the approved quantitative polymerase chain reaction-based methods to enhance HLB management programs.
              Cover page: A Pathogen Secreted Protein as a Detection Marker for Citrus Huanglongbing.
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2024)

              Importance

              Before surgery, the best strategy for managing patients who are taking renin-angiotensin system inhibitors (RASIs) (angiotensin-converting enzyme inhibitors or angiotensin receptor blockers) is unknown. The lack of evidence leads to conflicting guidelines.

              Objective

              To evaluate whether a continuation strategy vs a discontinuation strategy of RASIs before major noncardiac surgery results in decreased complications at 28 days after surgery.

              Design, setting, and participants

              Randomized clinical trial that included patients who were being treated with a RASI for at least 3 months and were scheduled to undergo a major noncardiac surgery between January 2018 and April 2023 at 40 hospitals in France.

              Intervention

              Patients were randomized to continue use of RASIs (n = 1107) until the day of surgery or to discontinue use of RASIs 48 hours prior to surgery (ie, they would take the last dose 3 days before surgery) (n = 1115).

              Main outcomes and measures

              The primary outcome was a composite of all-cause mortality and major postoperative complications within 28 days after surgery. The key secondary outcomes were episodes of hypotension during surgery, acute kidney injury, postoperative organ failure, and length of stay in the hospital and intensive care unit during the 28 days after surgery.

              Results

              Of the 2222 patients (mean age, 67 years [SD, 10 years]; 65% were male), 46% were being treated with angiotensin-converting enzyme inhibitors at baseline and 54% were being treated with angiotensin receptor blockers. The rate of all-cause mortality and major postoperative complications was 22% (245 of 1115 patients) in the RASI discontinuation group and 22% (247 of 1107 patients) in the RASI continuation group (risk ratio, 1.02 [95% CI, 0.87-1.19]; P = .85). Episodes of hypotension during surgery occurred in 41% of the patients in the RASI discontinuation group and in 54% of the patients in the RASI continuation group (risk ratio, 1.31 [95% CI, 1.19-1.44]). There were no other differences in the trial outcomes.

              Conclusions and relevance

              Among patients who underwent major noncardiac surgery, a continuation strategy of RASIs before surgery was not associated with a higher rate of postoperative complications than a discontinuation strategy.

              Trial registration

              ClinicalTrials.gov Identifier: NCT03374449.
                Cover page: Continuation vs Discontinuation of Renin-Angiotensin System Inhibitors Before Major Noncardiac Surgery
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