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Open Access Publications from the University of California

Scholarly Works (12 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2012)
Electromagnetic methods, particularly magnetotelluric (MT) sounding, are often used to detect fluids in the crust and upper mantle. Recently, MT studies on land have focused on the deep structure of the San Andreas fault (SAF) in central California. One of these studies found a region of high conductivity, interpreted as a local abundance of pore fluid, southwest of the fault at depths corresponding to the lower crust and upper mantle. The study also identified a change in the connection of this deep conductor to the root of the SAF as their measurements moved along the strike of the fault. It was proposed that a change in access of fluids to the deep extension of the fault, as evidenced by the modeled resistivity of the region, is responsible for the observed change in behavior of both earthquakes and non-volcanic tremor along the central Californian segment of the SAF. As an effort to extend knowledge of the resistivity structure into the offshore environment of central California, as well as to better constrain the interpretations made onshore, the Marine Electromagnetic Research Group at the Scripps Institution of Oceanography collected marine MT and controlled-source electromagnetic (CSEM) data there. Our single profile of data extends an existing profile of land data. In this dissertation I interpret both profiles of MT data, land and marine, jointly. Inversions of the amphibious dataset produce a resistivity model that is similar to previous results. However, upon closer inspection it was found that the marine data and the land data solicit antithetical structures. I suspected this to be caused by distortion from bathymetry that varies in three dimensions (3D), which is a problem because our 2D models assume that the earth is uniform in the horizontal dimension perpendicular to our profile. Few numerical methods exist to calculate the effects of 3D bathymetry in the necessary detail, so I improved upon an established thin-sheet technique to allow for higher resolution models. With this method I estimated how the effects of 3D bathymetry along our profile deviate from those predicted by an analogous 2D model. The effects are significant relative to the data errors used in inversion. As a test, I created synthetic data from both 2D and 3D bathymetric models, and invert them with a 2D inversion algorithm. Surprisingly, the inversion of 2D data did not recover the simple model used to create the synthetic data. Anomalous structures were introduced that weakly resembled those found in the models derived from actual data. Inversion of the 3D data made matters worse; the same artifacts found with 2D data became more extreme and their resemblance to the features in the results from actual data was enhanced. I concluded that the results from applying the established 2D inversion scheme on the actual data cannot be trusted, as is likely the case for the work on the same data that was previously published by others. The thin-sheet modeling suggests that future interpretations must at least take into account the known 3D bathymetric variations that occur off our profile
    Cover page: Electromagnetic imaging of the crust and upper mantle across the continental margin in central California
    • Thesis
    • Peer Reviewed
    UC Riverside Electronic Theses and Dissertations (2012)

    ABSTRACT

    Recurrent selection for drought and heat tolerance among hybrids of perennial ryegrass (Lolium perenne L.) with meadow fescue (Festuca pratensis Huds.), was used to develop turf-type populations with a marked increase in stress tolerance. Increased tolerance was associated with the presence of an introgression of F. pratensis chromatin on chromosome 3 of L. perenne. To determine if root characteristics were responsible for the improved stress tolerance, a greenhouse study was conducted to compare sister lines of Festulolium both with or without the introgression; the recurrent backcross parent; a representative F. pratensis; and turf-type tall fescue (Festuca arundinacea Schreb.) grown under well-watered conditions in 5.1-cm diam. x 160-cm long tubes containing sand. Two separate 120-day experiments revealed that F. pratensis produced deeper roots, more root biomass, and a higher root:shoot, while the industry standard, F. arundinacea, ranked at or near the lowest value. For the hybrids and ryegrass, the root parameters were intermediate between the 2 fescues, with no statistically significant difference among the 3 lines tested. The results indicate that in the tested Festulolium turf, drought and heat tolerance were not a consequence of increased root depth or root biomass as reported in previous reports for forage-type intergeneric hybrids of ryegrass and fescue.

      Cover page: Evaluation of Turf-Type Intergeneric Hybrids of Lolium perenne with Festuca pratensis for Improved Stress Tolerance
      • Thesis
      • Peer Reviewed
      UCLA Electronic Theses and Dissertations (2016)

      Background: Cardiac complications are the leading cause of long-term non-graft related mortality following liver transplantation. While the Scientific Registry of Transplant Recipients (SRTR) reports multiple risk factors for post-operative mortality, there are currently no cardiac specific risk factors included in the survival models. Cirrhotic cardiomyopathy, a spectrum of cardiovascular changes associated with end stage liver disease including diastolic dysfunction (DD), is well described. Left atrial volume index (LAVI) is an echocardiographic measure of DD, and has been associated with mortality in many populations. Unlike transmitral inflow velocities which are load dependent, LAVI is considered to be a more sensitive and stable measurement of DD. To date, there is limited data evaluating the effect of LAVI on mortality following liver transplantation. The aims of this study were to determine whether LAVI is an independent predictor of post-liver transplant mortality, and whether LAVI improves the ability to predict mortality beyond known risk factors.

      Methods: We performed a retrospective cohort study of patients ≥ 18 years of age who underwent liver transplantation between July 2011 and June 2014 at the University of California, Los Angeles, and who had their preoperative transthoracic echocardiograms performed at our center. The primary outcome was time to mortality, and the primary predictor was LAVI, dichotomized at 28ml/m2. Known risk factors of post liver transplant mortality identified from the SRTR database were collected as covariates. A multivariable Cox regression model was built using a backwards stepwise selection procedure to assess the effect of LAVI on post-operative mortality.

      Results: Of the 254 patients included in our analysis, 48 deaths occurred over the follow-up period (median: 17.5 months). In a multivariable model including re-transplantation, physiologic MELD score (dichotomized at the sample median of 33), preoperative mechanical ventilation, previous malignancy, and HCV, LAVI was not a statistically significant predictor of mortality (HR: 0.99, p=0.99, 95% CI: 0.56, 1.77). Given that advanced liver disease is associated with cirrhotic cardiomyopathy, we explored whether the effect of LAVI on mortality differed as a function of MELD score. In a multivariable model including the covariates listed above, there was a statistically significant interaction between LAVI and MELD score (p=0.007). Specifically, for patients with MELD scores ≥ 33, LAVI ≥ 28 ml/m2 was associated with increased mortality (HR=2.4, p=0.032, 95% CI 1.1, 5.4). However, for patients with MELD scores < 33, LAVI was not associated with mortality (HR: 0.44, p=0.08, 95% CI 0.18, 1.1). The C-statistic for the model including LAVI and the interaction was 0.73, statistically significantly greater than the C-statistic of 0.67 for the model excluding these terms, thus demonstrating an improvement in the predictive ability of that model.

      Discussion: This is the first study to examine the effect of LAVI as a predictor of post-liver transplant mortality using a multivariable model. We demonstrated that LAVI had a significant impact on mortality among patients with high MELD scores, whereas this effect was not observed among patients with lower MELD scores. Liver transplant recipients with high LAVI values and high MELD scores may represent patients with advanced cirrhotic cardiomyopathy who may be at an increased risk of postoperative mortality. This may have important consequences for the selection of liver transplant recipients.

        Cover page: The Association Between Left Atrial Volume Index and Liver Transplant Survival
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2024)
        OBJECTIVE: Given the critical need for efficient and tailored suicide screening for youth presenting in the emergency department (ED), this study establishes validated screening score thresholds for the Computerized Adaptive Screen for Suicidal Youth (CASSY) and presents an example of a suicide risk classification pathway. METHODS: Participants were primarily from the Study One derivation cohort of the Emergency Department Screen for Teens at Risk for Suicide (ED-STARS) enrolled in collaboration with Pediatric Emergency Care Applied Research Networks (PECARN). CASSY scores corresponded to the predicted probabilities of a suicide attempt in the next 3 months and risk thresholds were classified as minimal (<1%), low (1%-5%), moderate (5%-10%), and high (>10%). CASSY scores were compared to risk thresholds derived from clinical consensus and ED complaints and dispositions. CASSY risk thresholds were also examined as predictors of future suicide attempts in the Study Two validation cohort of ED-STARS. RESULTS: A total of 1452 teens were enrolled with a median age of 15.2 years, 59.5% were female, 55.6% were White, 22% were Black, 22.3% were Latinx, and 42.8% received public assistance. The clinical consensus suicide risk groups were strongly associated with the CASSY-predicted risk thresholds. Suicide attempts in the Study Two cohort occurred at a frequency consistent with the CASSY-predicted thresholds. CONCLUSIONS: The CASSY can be a valuable tool in providing patient-specific risk probabilities for a suicide attempt at 3 months and tailor the threshold cutoffs based on the availability of local mental health resources. We give an example of a clinical risk pathway, which should include segmentation of the ED population by medical versus psychiatric chief complaint.
          Cover page: Management of suicidal risk in the emergency department: A clinical pathway using the computerized adaptive screen for suicidal youth.
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2023)
          Suicide is the second leading cause of death among adolescents. As nearly 20% of adolescents visit emergency departments (EDs) each year, EDs have an opportunity to identify previously unrecognized suicide risk. A novel Computerized Adaptive Screen for Suicidal Youth (CASSY) was shown in a multisite study to be predictive for suicide attempts within 3 months. This study uses site-specific data to estimate the cost of CASSY implementation with adolescents in general EDs. When used universally with all adolescents who are present and able to participate in the screening, the average cost was USD 5.77 per adolescent. For adolescents presenting with non-behavioral complaints, the average cost was USD 2.60 per adolescent. Costs were driven primarily by time and personnel required for the further evaluation of suicide risk for those screening positive. Thus, universal screening using the CASSY, at very low costs relative to the cost of an ED visit, can facilitate services needed for at-risk adolescents.
            Cover page: The Cost of Universal Suicide Risk Screening for Adolescents in Emergency Departments.
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2020)
            The purpose of this study was to include youth, parents, researchers, and clinicians in the identification of feasible and acceptable strategies for teen suicide screening in the pediatric emergency department (ED). Concept mapping methodology was used to elicit stakeholder responses. Regarding the most important result of suicide screening for teens in the pediatric ED, suicide prevention and education for parents, friends, and community members was rated easiest to implement, while short- and long-term follow-up and treatment was rated most important. In terms of successful suicide screening for teens in the pediatric ED, provision of resources and information was rated most feasible, and a safe, friendly, private screening environment was rated most important. The concept maps can be used to align suicide risk screening with the priorities and recommendations of pediatric ED stakeholders.
              Cover page: Successful Suicide Screening in the Pediatric Emergency Department: Youth, Parent, Researcher, and Clinician Perspectives
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2021)

              Background

              Differences in risk and protective factors (e.g., victimization, abuse, social support) have been used to explain elevated rates of suicidal ideation and suicide attempts in sexual minority youth (SMY) relative to heterosexual peers. However, little is known regarding how risk and protective factors may explain suicide risk differences among subgroups of SMY. The aims of this study were to 1) examine differences in prevalence and severity for suicide risk and protective factors among SMY, and 2) explore whether risk and protective factors are differentially associated with suicidal ideation and suicide attempts for SMY subgroups.

              Methods

              Participants were 6,423 adolescents (ages 12-17) recruited from 14 Emergency Departments across the United States who completed an assessment of suicide risk and protective factors. SMY were 20% of the sample (n = 1,275) and categorized as bisexual (8%), gay/lesbian (2%), mostly straight (5%), or other sexual minority (5%).

              Results

              Bisexual youth had elevated rates of suicidal ideation and attempts, more risk factors (e.g., bullying victimization, depression), and fewer protective factors (e.g., parent-family connectedness, positive affect) relative to mostly straight and other sexual minority youth. Bisexual and gay/lesbian youth only differed in parent-family connectedness (lower among bisexual youth). Depression and parent-family connectedness had weaker associations with suicidal ideation for bisexual youth.

              Limitations

              Emergency departments were not nationally representative. Study design was cross-sectional, preventing causal inferences.

              Conclusions

              Interventions seeking to mitigate risk factors and promote protective factors are greatly needed for SMY and may benefit from tailoring to address unique stressors for sexual minority subgroups.
                Cover page: Risk and protective factors for suicide among sexual minority youth seeking emergency medical services
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2020)

                Objective

                Adolescents at risk for suicide are highly heterogeneous in terms of psychiatric and social risk factors, yet there has been little systematic research on risk profiles, which would facilitate recognition and the matching of patients to services. Our primary study aims were to identify latent class profiles of adolescents with elevated suicide risk, and to examine the association of these profiles with mental health service use (MHSU).

                Method

                Participants were 1,609 adolescents from the Emergency Department Screen for Teens at Risk for Suicide (ED-STARS) cohort. Participants completed baseline surveys assessing demographics, MHSU, and suicide risk. Telephone follow-up interviews were conducted at 3 months to assess suicide attempts. Participants met pre-established baseline criteria for suicide risk.

                Results

                Using latent class analysis, we derived 5 profiles of elevated suicide risk with differing patterns of eight risk factors: history of multiple suicide attempts, past-month suicidal ideation, depression, alcohol and drug misuse, impulsive-aggression, and sexual and physical abuse. In comparison to adolescents who did not meet baseline criteria for suicide risk, each profile was associated with increased risk of a suicide attempt within 3 months. The MHSU was lowest for adolescents fitting profiles with previous (but no recent) suicidal thoughts and behavior, and for adolescents from racial and ethnic minority groups.

                Conclusion

                Adolescents at elevated risk for suicide present to emergency departments with differing profiles of suicide risk. MHSU varies across these profiles and by race/ethnicity, indicating that targeted risk recognition and treatment linkage efforts may be necessary to reach some adolescents at risk.
                  Cover page: Five Profiles of Adolescents at Elevated Risk for Suicide Attempts: Differences in Mental Health Service Use
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2019)

                  Objective

                  To compare the longitudinal course of family functioning in offspring of parents with bipolar disorder (BD), offspring of parents with non-BD psychopathology, and offspring of healthy control (HC) parents.

                  Method

                  Offspring of parents with BD (256 parents and 481 offspring), parents without BD (82 parents and 162 offspring), and HC parents (88 parents and 175 offspring) 7 to 18 years of age at intake, from the Bipolar Offspring Study (BIOS), were followed for an average of 4.3 years. Family functioning was evaluated using the child- and parent-reported Family Adaptability and Cohesion Scale-II and the Conflict Behavior Questionnaire. The data were analyzed using multivariate multilevel regression, generalized linear estimating equation models, and path analysis.

                  Results

                  Families of parents with BD and parents with non-BD psychopathology showed lower cohesion and adaptability and higher conflict compared with HC families. There were no significant differences in cohesion and adaptability between families of parents with psychopathology. The effect of parental psychopathology on family functioning was mediated by parental psychosocial functioning and, to a lesser extent, offspring disorders. In all 3 groups, parent-reported family conflict was significantly higher than child-reported conflict. Across groups, family cohesion decreased over follow-up, whereas conflict increased.

                  Conclusion

                  Any parental psychopathology predicted family impairment. These results were influenced by the offspring's age and were mediated by parental psychosocial functioning and, to a lesser degree, by offspring psychopathology. These findings emphasize the need to routinely assess family functioning in addition to psychopathology and provide appropriate interventions to parents and offspring.
                    Cover page: A Longitudinal Study of Family Functioning in Offspring of Parents Diagnosed With Bipolar Disorder
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2023)
                      Creative Commons 'BY-NC-ND' version 4.0 license
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