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Open Access Publications from the University of California

Scholarly Works (11 results)

  • Article
  • Peer Reviewed
Faculty Publications (2008)
The double-gyre circulation, formulated in terms of the quasigeostrophic equations, has a symmetry about the basin midlatitude (y → −y, ψ → −ψ), which is absent in a formulation based on the shallow-water equations. As a result, the shallow-water model does not have the pitchfork bifurcation structures that, in the case of the quasigeostrophic model, connect together multiple solution branches with elongated and contracted recirculation gyres. For the shallow-water model, solution branches with elongated recirculation gyres are disconnected, and a one-parameter bifurcation analysis is unable to detect their existence. The deeply penetrating jet solution branches do, however, continue to exist, and can be found using a bifurcation analysis couched in terms of two parameters. An effective pair of parameters is the viscosity and a parameter controlling the symmetry of the wind stress profile. A bifurcation analysis with these parameters reveals the existence of new solution branches that were not found in previous bifurcation analyses of the shallow-water model. The new solutions have a jet extension that penetrates farther eastward and that is more stable than the jet-up and jet-down solutions found in previous studies. Furthermore, the origin of the low-frequency variability at low viscosities is associated with a sequence of bifurcations originating from one of the new steady-state solution branches. In particular, the eigenmode analysis of the new branch reveals that a so-called gyre mode is at the origin of the model’s low-frequency variability at decadal time scales.
    Cover page: Elongation and Contraction of the Western Boundary Current Extension in a Shallow-Water Model: A Bifurcation AnalysisCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    Faculty Publications (2007)

    The steady state bifurcation structure of the double-gyre wind-driven ocean circulation is examined in a shallow water model where the upper layer is allowed to outcrop at the sea surface. In addition to the classical jet-up and jet-down multiple equilibria, we find a new regime in which one of the equilibrium solutions has a large outcropping region in the subpolar gyre. Time dependent simulations show that the outcropping solution equilibrates to a stable periodic orbit with a period of 8 months. Co-existing with the periodic solution is a stable steady state solution without outcropping.

    A numerical scheme that has the unique advantage of being differentiable while still allowing layers to outcrop at the sea surface is used for the analysis. In contrast, standard schemes for solving layered models with outcropping are non-differentiable and have an ill-defined Jacobian making them unsuitable for solution using Newton’s method. As such, our new scheme expands the applicability of numerical bifurcation techniques to an important class of ocean models whose bifurcation structure had hitherto remained unexplored.

      Cover page: Bifurcation structure of a wind-driven shallow water model with layer-outcroppingCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2021)
      Gratitude and optimism are positive psychological dispositions associated with beneficial outcomes. To examine their associations with physiological and psychological experiences in daily life, we examined data from an Ecological Momentary Assessment study (N = 4,825), including blood pressure, heart rate, and reports of stress, health behaviors, and thoughts. Trait gratitude and trait optimism both predicted lower heart rate and blood pressure, better sleep quality, more exercise, less stress, more positive expectations and reflections, and greater feelings of appreciation toward others. However, gratitude and optimism were not completely overlapping constructs: Gratitude was a stronger predictor of felt appreciation toward others and pleasantness when reflecting on the best part of the day, whereas optimism was a stronger predictor of sleep quality, lower stress, and lower unpleasantness when reflecting on the worst part of the day. These associations reveal both similar and differential influences of positive dispositions on psychological and physiological outcomes that provide insight into health consequences. (PsycInfo Database Record (c) 2021 APA, all rights reserved).
        Cover page: Comparing Daily Physiological and Psychological Benefits of Gratitude and Optimism Using a Digital PlatformCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2022)
        [This corrects the article DOI: 10.1007/s42761-022-00112-x.].
          Cover page: Correction to: Asymmetrical Effects of Sleep and Emotions in Daily Life
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2023)

          Background

          Sleep can have consequential effects on people's health and well-being, and these effects may vary among younger and older adults.

          Purpose

          The goal of the present study was to investigate how sleep relates to physiologic and stress responses in daily life across adulthood.

          Methods

          We used an Ecological Momentary Assessment method in a large sample of participants (N = 4,359; Mage = 46.75, SD = 12.39; 69.30% male, 29.85% female) who completed morning sleep diaries, reported subjective stress, and recorded their heart rate and blood pressure for 21 days. Sleep was assessed with self-reports of duration, efficiency, and quality.

          Results

          Using multilevel modeling, between-person analyses showed that sleep duration, efficiency, and quality were negatively related to morning heart rate and stress, such that people who slept longer, more efficiently, or better experienced lower heart rate and stress compared to those who slept shorter, less efficiently, or worse. Within-person analyses showed that sleep duration, efficiency, and quality predicted morning heart rate, blood pressure (though less consistently), and stress. That is, people experienced lower heart, blood pressure, and stress following nights when they slept longer, more efficiently, or better than they typically did. These within-person relationships were moderated by age, such that the effects of better and longer sleep on lower morning heart rate, blood pressure, and stress were stronger among younger than older adults.

          Conclusion

          These findings suggest that daily variations in sleep show immediate associations with stress and physiologic responses, but these daily variations have a stronger relationship among younger compared to older adults.
            Cover page: Examining Daily Associations Among Sleep, Stress, and Blood Pressure Across Adulthood.Creative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2022)
            Sleep is an important process that can influence and be influenced by daily events and emotions. We examined the bidirectional relationships between sleep, daily events, and emotions with a daily diary method completed by 181 mothers (M age = 41.91, SD = 5.06). They answered morning and evening questionnaires for 1 week at three different points in time separated by nine months each, 21 days in total. Measures of sleep quality and emotional experiences each morning were assessed, and they reported on their best and worst experience of the day, peak emotional responses to these events, and affect in the evening. Sleep behavior, including total sleep time and sleep efficiency, was objectively quantified using wrist actigraphy. Multilevel modeling analyses showed that longer sleep duration and better subjective quality predicted greater positive emotions and lower negative emotions upon waking, and lower levels of peak perceived stressfulness, but not peak positivity ratings. Daily experiences did not predict sleep duration. Conversely, negative affect in the evening and greater peak perceived stressfulness during the day predicted worse sleep quality that night, whereas positive affect and positive events were not related to sleep. Although correlational, these findings suggest that good sleep can improve waking affect and help mitigate the impact of stressful experiences but does not amplify responses to the positive events of the day. In turn, daily perceived stress reactivity impairs sleep quality. These novel findings show stronger bidirectional relationships between sleep with daily stress, than sleep with daily positivity.

            Supplementary information

            The online version contains supplementary material available at 10.1007/s42761-022-00112-x.
              Cover page: Asymmetrical Effects of Sleep and Emotions in Daily Life
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2021)
              Non-collinear spin structures in materials that combine perpendicular and in-plane magnetic anisotropies are of great technological interest for microwave and spin wave-assisted magnetization switching. [Co/Pt] multilayers are well-known perpendicular anisotropy materials that have the potential to pin the magnetization of a soft magnetic layer, such as permalloy (Py), that has in-plane anisotropy, thereby forming a magnetic exchange spring. Here we report on multilayered [Co/Pt]/Pt/Py films, where an additional ultrathin Pt spacer has been included to control the coupling between the sub-units with in-plane and perpendicular magnetic anisotropy. Vector network analyser (VNA)-ferromagnetic resonance (FMR) measurements were made to obtain a complete picture of the resonant conditions, while the dynamical response of the sub-units was probed by synchrotron-based element- and phase selective x-ray detected FMR (XFMR). For all samples, only slight pinning of the dynamic magnetization of the Py by the [Co/Pt] was noted, and the FMR results were dominated by the 50 nm thick Py layer. Out-of-plane VNA-FMR maps reveal the presence of additional modes, e.g. a perpendicular standing spin-wave (PSSW) state. However, as the magnetic field is reduced below the saturation field, the PSSW state morphs continuously through a series of canted standing spin-wave (CSSW) states into a horizontal standing spin-wave (HSSW) state. The PSSW, CSSW and HSSW states are well described using a multilayer model of the Py film. The observation of CSSW modes is of particular relevance to microwave assisted magnetic recording, where microwave excitation stimulates precession of a soft layer canted out of plane by a pulsed magnetic field.
                Cover page: Canted standing spin-wave modes of permalloy thin films observed by ferromagnetic resonance
                • Article
                Electric Grid (2011)
                  Cover page: Extreme Events Phase 2
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2011)
                  Background

                  We investigate the accuracy of different similarity approaches for clustering over two million biomedical documents. Clustering large sets of text documents is important for a variety of information needs and applications such as collection management and navigation, summary and analysis. The few comparisons of clustering results from different similarity approaches have focused on small literature sets and have given conflicting results. Our study was designed to seek a robust answer to the question of which similarity approach would generate the most coherent clusters of a biomedical literature set of over two million documents.

                  Methodology

                  We used a corpus of 2.15 million recent (2004-2008) records from MEDLINE, and generated nine different document-document similarity matrices from information extracted from their bibliographic records, including titles, abstracts and subject headings. The nine approaches were comprised of five different analytical techniques with two data sources. The five analytical techniques are cosine similarity using term frequency-inverse document frequency vectors (tf-idf cosine), latent semantic analysis (LSA), topic modeling, and two Poisson-based language models – BM25 and PMRA (PubMed Related Articles). The two data sources were a) MeSH subject headings, and b) words from titles and abstracts. Each similarity matrix was filtered to keep the top-n highest similarities per document and then clustered using a combination of graph layout and average-link clustering. Cluster results from the nine similarity approaches were compared using (1) within-cluster textual coherence based on the Jensen-Shannon divergence, and (2) two concentration measures based on grant-to-article linkages indexed in MEDLINE.

                  Conclusions

                  PubMed's own related article approach (PMRA) generated the most coherent and most concentrated cluster solution of the nine text-based similarity approaches tested, followed closely by the BM25 approach using titles and abstracts. Approaches using only MeSH subject headings were not competitive with those based on titles and abstracts.

                    Cover page: Clustering More than Two Million Biomedical Publications: Comparing the Accuracies of Nine Text-Based Similarity ApproachesCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2020)
                    Insulating antiferromagnets have recently emerged as efficient and robust conductors of spin current. Element-specific and phase-resolved x-ray ferromagnetic resonance has been used to probe the injection and transmission of ac spin current through thin epitaxial NiO(001) layers. The spin current is found to be mediated by coherent evanescent spin waves of GHz frequency, rather than propagating magnons of THz frequency, paving the way towards coherent control of the phase and amplitude of spin currents within an antiferromagnetic insulator at room temperature.
                      Cover page: Coherent Transfer of Spin Angular Momentum by Evanescent Spin Waves within Antiferromagnetic NiO
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