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Open Access Publications from the University of California

Scholarly Works (5 results)

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

This dissertation examines rock art from 20 sites in the District of Huánuco, in the Central Andes of Peru. The art spans the history of human occupation in the Andes; from approximately the seventh millennium BCE to the sixteenth century CE. When analyzed diachronically, the paintings elucidate changing social practices, as they relate to the relations between people and the creation of anthropogenic landscapes. As markings on stone, pictographs served to advertise territorial connections, but also reveal the primary importance of the land in instantiating and negotiating social relations for the Pre-Columbian peoples of Huánuco.

Episodes of painting were identified through a combination of stratigraphic analysis, revealed through an examination of instances of superposition, and the existence of stylistic relationships evident in an analysis of the formal qualities of the art. Chronology was subsequently revealed using stylistic seriation, cross-dating between sites, and analyzing the styles and motifs in comparison with art from other, more securely dated materials. This combined methodology allowed the chronological placement of the art to be determined without damaging or altering it.

The data were analyzed through the lens of Andean ethnographies and ethnohistories that relate to the themes depicted, and in combination with archaeological data from within and outside the study area. This analysis revealed the multifaceted functions of rock art, as well as illuminating some of the changing social trends and cosmological beliefs in the region. Some of the main themes that emerged from this analysis are an early focus on animals shifting to a focus on camelids as they were domesticated, the sharing of motifs and themes with Amazonian peoples beginning in the Preceramic Period (3000-1800 BCE), and a later emphasis on anthropomorphic figures that are interpreted as the founding ancestors of local social groups beginning in the Early Intermediate Period (200-700 CE).

The dissertation demonstrates that the creation of rock art was a practice that was far more actively engaged in the initiation, documentation, and negotiation of the social arrangements of Andean people than has heretofore been acknowledged or understood.

    Cover page: Transformational Refractions of Social Messages in the Rock Art of Huánuco, PeruCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    We present a systematic study of the phenomena of number squeezing and fragmentation for a repulsive Bose-Einstein condensate (BEC) in a three-dimensional double-well potential over a range of interaction strengths and barrier heights, including geometries that exhibit appreciable overlap in the one-body wave functions localized in the left and right wells. We compute the properties of the condensate with numerically exact, full-dimensional path-integral ground-state (PIGS) quantum Monte Carlo simulations and compare with results obtained from using two- and eight-mode truncated basis models. The truncated basis models are found to agree with the numerically exact PIGS simulations for weak interactions, but fail to correctly predict the amount of number squeezing and fragmentation exhibited by the PIGS simulations for strong interactions. We find that both number squeezing and fragmentation of the BEC show nonmonotonic behavior at large values of interaction strength a. The number squeezing shows a universal scaling with the product of number of particles and interaction strength (Na), but no such universal behavior is found for fragmentation. Detailed analysis shows that the introduction of repulsive interactions not only suppresses number fluctuations to enhance number squeezing, but can also enhance delocalization across wells and tunneling between wells, each of which may suppress number squeezing. This results in a dynamical competition whose resolution shows a complex dependence on all three physical parameters defining the system: interaction strength, number of particles, and barrier height.
      Cover page: Number-squeezed and fragmented states of strongly interacting bosons in a double well
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2018)
      Inducing superconductivity in a topological insulator can lead to novel quantum effects. However, experimental approaches to turn a topological insulator into a superconductor are limited. Here, we report on superconductivity in topological insulator Bi_{0.91}Sb_{0.09} induced via focused ion-beam deposition of a Pt thin film. The superconducting phase exhibits a Berezinski-Kosterlitz-Thouless transition, demonstrative of its two-dimensional character. From the in-plane upper critical field measurements, we estimate the superconducting thickness to be ∼17  nm for a 5.5-μm-thick sample. Our results provide evidence that the interface superconductivity could originate from the surface states of Bi_{0.91}Sb_{0.09}.
        Cover page: Onset of a Two-Dimensional Superconducting Phase in a Topological-Insulator–Normal-Metal Bi1-xSbx/Pt Junction Fabricated by Ion-Beam Techniques
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2011)
        Magnetic resonance imaging has revolutionized the detection of structural abnormalities in patients with epilepsy. However, many focal abnormalities remain undetected in routine visual inspection. Here we use an automated, surface-based method for quantifying morphometric features related to epileptogenic cortical malformations to detect abnormal cortical thickness and blurred gray-white matter boundaries. Using MRI morphometry at 3T with surface-based spherical averaging techniques that precisely align anatomical structures between individual brains, we compared single patients with known lesions to a large normal control group to detect clusters of abnormal cortical thickness, gray-white matter contrast, local gyrification, sulcal depth, jacobian distance and curvature. To assess the effects of threshold and smoothing on detection sensitivity and specificity, we systematically varied these parameters with different thresholds and smoothing levels. To test the effectiveness of the technique to detect lesions of epileptogenic character, we compared the detected structural abnormalities to expert-tracings, intracranial EEG, pathology and surgical outcome in a homogeneous patient sample. With optimal parameters and by combining thickness and GWC, the surface-based detection method identified 92% of cortical lesions (sensitivity) with few false positives (96% specificity), successfully discriminating patients from controls 94% of the time. The detected structural abnormalities were related to the seizure onset zones, abnormal histology and positive outcome in all surgical patients. However, the method failed to adequately describe lesion extent in most cases. Automated surface-based MRI morphometry, if used with optimized parameters, may be a valuable additional clinical tool to improve the detection of subtle or previously occult malformations and therefore could improve identification of patients with intractable focal epilepsy who may benefit from surgery.
          Cover page: Detection of Epileptogenic Cortical Malformations with Surface-Based MRI Morphometry
          • Article
          • Peer Reviewed
          UC Lab Fees Research Program (LFRP) Funded Publications (2020)
            Cover page: Laboratory equation of state measurements of the carbon envelopes of white dwarf stars
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