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Open Access Publications from the University of California

Scholarly Works (103 results)

  • Article
  • Peer Reviewed
UCLA Previously Published Works (2016)
Abstract. The authors present an analytical model for wind-driven free drift of sea ice that allows for an arbitrary mixture of ice and open water. The model includes an ice–ocean boundary layer with an Ekman spiral, forced by transfers of wind-input momentum both through the sea ice and directly into the open water between the ice floes. The analytical tractability of this model allows efficient calculation of the ice velocity provided that the surface wind field is known and that the ocean geostrophic velocity is relatively weak. The model predicts that variations in the ice thickness or concentration should substantially modify the rotation of the velocity between the 10 m winds, the sea ice, and the ocean. Compared to recent observational data from the first ice-tethered profiler with a velocity sensor (ITP-V), the model is able to capture the dependencies of the ice speed and the wind/ice/ocean turning angles on the wind speed. The model is used to derive responses to intensified southerlies on Arctic summer sea ice concentration, and the results are shown to compare closely with satellite observations.
    Cover page: An analytical model for wind-driven Arctic summer sea ice drift
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2021)
    Superhydrophobic (SHPo) surfaces have been investigated vigorously since around 2000 due in large part to their unique potential for hydrodynamic frictional drag reduction without any energy or material input. The mechanisms and key factors affecting SHPo drag reduction have become relatively well understood for laminar flows by around 2010, as has been reviewed before [Lee et al. Exp Fluids 57:176 (2016)], but the progress for turbulent flows has been rather tortuous. While improved flow tests made positive SHPo drag reduction in fully turbulent flows more regular since around 2010, such a success in a natural, open water environment was reported only in 2020 [Xu et al. Phys Rev Appl 13:034056 (2020b)]. In this article, we review studies from the literature about turbulent flows over SHPo surfaces, with a focus on experimental studies. We summarize the key knowledge obtained, including the drag-reduction mechanism in the turbulent regime, the effect of the surface roughness morphology, and the fate and role of the plastron. This review is aimed to help guide the design and application of SHPo surfaces for drag reduction in the large-scale turbulent flows of field conditions. Graphic abstract: [Figure not available: see fulltext.]
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2005)

      A novel laser that utilizes a silicon waveguide bonded to AlGaInAs quantum wells is demonstrated. This wafer scale fabrication approach allows the optical waveguide to be defined by CMOS-compatible silicon processing while optical gain is provided by III-V materials. The AlGaInAs quantum well structure is bonded to the silicon wafer using low temperature oxygen plasma-assisted wafer bonding. The optically pumped 1538 nm laser has a pulsed threshold of 30 mW and an output power of 1.4 mW. (c) 2005 Optical Society of America.

        Cover page: Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum well
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2015)
        Hyperammonemia is less severe in arginase 1 deficiency compared with other urea cycle defects. Affected patients manifest hyperargininemia and infrequent episodes of hyperammonemia. Patients typically suffer from neurological impairment with cortical and pyramidal tract deterioration, spasticity, loss of ambulation, seizures and intellectual disability; death is less common than with other urea cycle disorders. In a mouse model of arginase I deficiency, the onset of symptoms begins with weight loss and gait instability, which progresses toward development of tail tremor with seizure-like activity; death typically occurs at about 2 weeks of life. Adeno-associated viral vector gene replacement strategies result in long-term survival of mice with this disorder. With neonatal administration of vector, the viral copy number in the liver greatly declines with hepatocyte proliferation in the first 5 weeks of life. Although the animals do survive, it is not known from a functional standpoint how well the urea cycle is functioning in the adult animals that receive adeno-associated virus. In these studies, we administered [1-13C] acetate to both littermate controls and adeno-associated virus-treated arginase 1 knockout animals and examined flux through the urea cycle. Circulating ammonia levels were mildly elevated in treated animals. Arginine and glutamine also had perturbations. Assessment 30 min after acetate administration demonstrated that ureagenesis was present in the treated knockout liver at levels as low at 3.3% of control animals. These studies demonstrate that only minimal levels of hepatic arginase activity are necessary for survival and ureagenesis in arginase-deficient mice and that this level of activity results in control of circulating ammonia. These results may have implications for potential therapy in humans with arginase deficiency.
          Cover page: Minimal ureagenesis is necessary for survival in the murine model of hyperargininemia treated by AAV-based gene therapy
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2006)

          We report a novel laser architecture, the hybrid silicon evanescent laser (SEL), that utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. The silicon waveguide is fabricated on a silicon-on-insulator wafer using a complimentary metal-oxide-semiconductor-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature 02 plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum temperature for CW operation is 60 degrees C. The maximum single-sided fiber-coupled CW output power at room temperature is 4.5 mW.

            Cover page: A continuous-wave hybrid AlGaInAs-silicon evanescent laser
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2013)
            Sensitive probing of temperature variations on nanometre scales is an outstanding challenge in many areas of modern science and technology. In particular, a thermometer capable of subdegree temperature resolution over a large range of temperatures as well as integration within a living system could provide a powerful new tool in many areas of biological, physical and chemical research. Possibilities range from the temperature-induced control of gene expression and tumour metabolism to the cell-selective treatment of disease and the study of heat dissipation in integrated circuits. By combining local light-induced heat sources with sensitive nanoscale thermometry, it may also be possible to engineer biological processes at the subcellular level. Here we demonstrate a new approach to nanoscale thermometry that uses coherent manipulation of the electronic spin associated with nitrogen-vacancy colour centres in diamond. Our technique makes it possible to detect temperature variations as small as 1.8 mK (a sensitivity of 9 mK Hz(-1/2)) in an ultrapure bulk diamond sample. Using nitrogen-vacancy centres in diamond nanocrystals (nanodiamonds), we directly measure the local thermal environment on length scales as short as 200 nanometres. Finally, by introducing both nanodiamonds and gold nanoparticles into a single human embryonic fibroblast, we demonstrate temperature-gradient control and mapping at the subcellular level, enabling unique potential applications in life sciences.
              Cover page: Nanometre-scale thermometry in a living cell
              • Article
              • Peer Reviewed
              UC Santa Barbara Previously Published Works (2006)

              We present the design and fabrication of a novel laser structure, the hybrid silicon evanescent laser. This structure utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. With this structure, the optical mode is predominantly confined in the passive silicon waveguide and is evanescently coupled to the AlGaInAs strained QWs. The optimal design of the optical waveguide for delivering sufficient optical gain to reach the lasing threshold, while confining most of the optical mode in the silicon waveguide, for efficiently coupling the output power into silicon passive devices, is described. The silicon waveguide is fabricated on a silicon-on-insulator (SOI) wafer using a CMOS-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature O-2 plasma-assisted wafer bonding. We demonstrate optically pumped silicon evanescent lasers operating continuous wave (CW) up to 60 degrees C. The lasers emit a wavelength of 1.5 mu m with a minimum threshold of 23 mW and a maximum single-sided fiber-coupled CW output power of 4.5 mW at the room temperature.

                Cover page: Design and fabrication of optically pumped hybrid silicon-AlGaInAs evanescent lasers
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2021)
                We present measurements of spatially and temporally resolved electron temperature in high-energy-density plasmas using gated x-ray pinhole imagers. A 2D image of bremsstrahlung x-ray self-emission from laser-driven plasma plumes is detected at the same time through two pinholes covered with different filter materials. By comparing the attenuated signal through each filter, a spatially resolved electron temperature as low as 0.1 keV can be estimated. Measurements of the plasma plume taken from different directions indicate that imaging through extended plasmas has a negligible effect on the temperature estimates. Methods for estimating the expected signal, selecting filters, and incorporating the response of the detector are discussed.
                  Cover page: Measurements of electron temperature in high-energy-density plasmas using gated x-ray pinhole imagingCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  LBL Publications (2020)
                  Correlated electrons give rise to both exotic electronic and magnetic properties in rare-earth nickelates. Here we present evidence of the interfacial coupling between two nickelate systems, EuNiO_{3} (ENO) and LaNiO_{3} (LNO), with different electronic and magnetic properties but with compatible structural registry giving rise to an electrostructural transition, unobserved in each constituent. Nominally, LNO remains in a paramagnetic-metallic R3[over ¯]c phase while orthorhombic ENO undergoes antiferromagnetic and insulating transitions. However, the ENO/LNO heterostructure displays a uniform rotational symmetry set by an entwined interface. This leads to an anomalous reduction of bond disproportionation in the ENO layer through the metal to insulator transition and concomitantly charge disproportionation opens the gap accompanied by antiferromagnetic ordering. Our results resolve a long-standing question in the physics of rare-earth nickelates, herein demonstrating that charge and bond disproportionation are competing mechanisms for the charge localization process in the rare-earth nickelate system.
                    Cover page: Direct Evidence of the Competing Nature between Electronic and Lattice Breathing Order in Rare-Earth Nickelates
                    • Article
                    • Peer Reviewed
                    UC San Francisco Previously Published Works (2015)

                    Background and objectives

                    South Africa has a markedly skewed representation where the majority of blood (62%) is presently collected from an ethnically White minority. This study seeks to identify culturally specific factors affecting motivation of donors in South Africa.

                    Materials and methods

                    We performed a qualitative study to evaluate motivators and deterrents to blood donation among Black South Africans. A total of 13 focus groups, comprising a total of 97 Black South Africans, stratified by age and geographic location were conducted. Transcripts of the interviews were analysed using a coding framework by Bednall & Bove.

                    Results

                    Participants made 463 unique comments about motivators focusing primarily on promotional communications (28%), incentives (20%) and prosocial motivation (16%). Participants made 376 comments about deterrents which focused primarily on fear (41%), negative attitudes (14%) and lack of knowledge (10%).

                    Conclusion

                    Although prosocial motivation (altruism) was the most frequently mentioned individual motivator, promotional communication elicited more overall comments by participants. As reported by many authors, fear and lack of awareness were strong deterrents, but scepticism engendered by perceived racial discrimination in blood collection were unique to the South African environment.
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