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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2018)

Since its introduction in 1956, hard disk drives have become one of the dominant products in the industry of data storage. The capacity of the hard disk drives must keep evolving to store the exploding data generated in the era of big data. This demand pushes the development of technologies including heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR) and bit-patterned media (BPM) to increase the areal density beyond 1Tb/in2. In the development of these technologies, it is essential to have a clear understanding of the dynamics and nanoscale heat transfer behavior across the head-disk interface.

In this dissertation, dynamics and nano-scale heat transfer in the head disk interface are discussed. Experimental study of nano-scale heat transfer is conducted with the specifically designed static touchdown experiment. Simulation strategy that incorporates the wave-based phonon conduction theory was also developed.

In the flying condition, correlation between the temperature and head disk spacing was found at both passive flying stage and modulation stage. When the flying height increases due to either disk surface microwaviness or contact induced modulation, head temperature will increase, with a slight time delay, indicating the existence of a cooling effect as the head approaches the disk.

The static touchdown experiment, which decouples the complicated air bearing from the nano-scale interface was further designed and performed. The heat transfer behavior across a closing nano-scale gap between head and disk was observed and measured. Experimental and simulation results showed general agreement with the theoretical predictions of the wave based theory for radiation and phonon conduction. The effect of different factors including humidity, air pressure, lubricant layer and disk substrate in the static touchdown experiment were also studied separately.

Furthermore, the dynamics of HAMR condition was studied with waveguide heads. The laser induced protrusion was found to be around 1~2 nm in height.

The findings of this dissertation could be applied to future HAMR head/media design, and the static touchdown experiment could be potentially improved to be a new approach to measure material conduction coefficient and emissivity with high special resolution.

    Cover page: Study of Dynamics and Nanoscale Heat Transfer of Head Disk Interface in Hard Disk Drives
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2021)
    Microplastics (MPs) are an environmental problem of growing concern. Aquatic sediments are considered as a final sink for MPs, but dredging can remobilize sedimentary MPs into both aquatic and terrestrial ecosystems. Although dredging is globally used for waterway deepening and ecological restoration, the environmental impacts of dredging on MP pollutants has not been previously assessed. In this study, Nile Red staining combined with micro-FTIR methods showed sediments containing high MP concentrations (6060-37610 n/kg·DW) from urban/suburban segments of a plain river network in Southeast China. The dredged sediments were stored in piles on farmlands, whereby MPs were subsequently dispersed to surrounding soils and surface waters while awaiting a permanent disposal option. MP concentrations in the soils surrounding the pile were higher in the dry season (wind dispersion), while MP concentrations in waters downstream of the piles were higher in the wet season (rainfall/runoff erosion). Whether dredge sediments are finally used to fertilize farmland, as fill material for coastal land reclamation or dumped into the ocean, MPs have the potential for remobilization into the environment causing concerns with aquatic food webs, agricultural production and human health. Therefore, disposal of dredge sediments containing MPs requires careful assessment to minimize potential environmental impacts.
      Cover page: Transport and fate of microplastics from riverine sediment dredge piles: Implications for disposal
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2021)
      Microplastics (MPs) in marine and terrestrial environments have been intensively studied, but the dynamics of airborne MPs remains limited. Existing studies on atmospheric MPs are mostly derived from collection of atmospheric deposition, whereas direct measurements of airborne MPs are scarce. However, the abundance of airborne MPs is more relevant for evaluating human inhalation exposure risk. Herein, airborne MPs in indoor and outdoor environments from urban and rural areas of a coastal city in eastern China were investigated. MP concentrations (mean±SD) in indoor air (1583 ± 1180 n/m3) were an order of magnitude higher than outdoor air (189 ± 85 n/m3), and airborne MP concentrations in urban areas (224 ± 70 n/m3) were higher than rural areas (101 ± 47 n/m3). MPs smaller than 100 µm dominated airborne MPs, and the predominant shape of airborne MPs was fragments, as opposed to fibers. The larger MP size fractions contained a higher proportion of fibers, whereas the smaller size fractions were nearly exclusively composed of fragments. The health risk caused by ubiquitous airborne MPs should not be discounted as the maximum annual outdoor exposure of airborne MPs can reach 1 million/year, while indoor exposure may be even higher due to higher indoor airborne MP concentrations.
        Cover page: Airborne microplastics in indoor and outdoor environments of a coastal city in Eastern China
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2020)
        An amendment to this paper has been published and can be accessed via a link at the top of the paper.
          Cover page: Author Correction: Robust estimation of bacterial cell count from optical density
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