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Open Access Publications from the University of California

Scholarly Works (14 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2024)

Cooling is essential for human lives. Refrigeration that relies on the traditional vapor-compressor system has been developed for more than a century, but it still has unavoidable disadvantages such as low efficiency, noise, leakage of ozone-depleting agents and failure to meet the cooling demands of modern technologies. Electrocaloric cooling, which can be accomplished with the reversible electric field-driven polarization change and the associated adiabatic temperature change of electrocaloric materials, is one of the emerging solid-state cooling technologies that has the potential to replace the traditional one. Therefore, this dissertation aims to develop efficient electrocaloric cooling from both the material and the device aspects.

Poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer is a relaxor ferroelectric material exhibiting giant electrocaloric effect at room temperature. The excellent electrocaloric performances, high breakdown strength and flexible character of the terpolymer material render it promising potential to be used for constructing practical solid-state refrigerators. This dissertation starts from a detailed introduction of fabricating high-quality P(VDF-TrFE-CFE) thin films with various phase compositions. To understand the connections between films’ electrocaloric performances and the fabrication processes, and to determine the molecular origin of the electrocaloric activity of this terpolymer, multiple characterizations have been conducted on a pool of terpolymer films processed from different conditions. The core characterization couples the Fourier transform infrared with a high-voltage source to operandoly observe the dipole switching mechanism of P(VDF-TrFE-CFE) under an electrical field. It is found that the polar short trans sequences (T3Gs) along the molecular chains can be reversibly switched by the electric field, which is responsible for the giant electrocaloric effect.

A solid-state electrocaloric cooler named self-regenerative heat pump (SRHP) is constructed using the P(VDF-TrFE-CFE) film stacks with enhanced adiabatic temperature change. The SRHP exploits the concurrent electrocaloric and electrostrictive effects of P(VDF-TrFE-CFE), automatically synchronizing the material’s thermodynamic cycle with a mechanical heat transfer mechanism for refrigeration purposes. Therefore, the need for any external driving facilities for actuations is eliminated. The SRHP is composed of a cascade of six film stacks. A polyimide backing layer stuck on top of each film stack transforms the irregular in-plane electrostrictive expansion of the films under the field into a large out-of-plane actuation to make good thermal contact with the bottom film stacks. The SRHP with consecutive stages working in antiphase of their electrocaloric cycles achieves unidirectional heat transfer and refrigeration of the heat source. Finally, the SRHP achieves a cooling of 8.8 K below the ambient temperature in 30 s, a temperature lift of 14.2 K, and a maximum specific cooling power of 1.52W/g, corresponding to a 0.78 W cooling power over an active cooling area of 4.52 cm². The performances rank the SRHP the best electrocaloric solid-state cooler made of polymer materials.

    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2022)
    Stretchable electroluminescent (EL) devices are obtained by partitioning a large emission area into areas specifically for stretching and light-emission (island-bridge structure). Buckled and textile structures are also shown effective to combine the conventional light emitting diode fabrication with elastic substrates for structure-enabled stretchable EL devices. Meanwhile, intrinsically stretchable EL devices which are characterized with uniform stretchability down to microscopic scale are relatively less developed but promise simpler device structure and higher impact resistance. The challenges in fabricating intrinsically stretchable EL devices with high and robust performance are in many facets, including stretchable conductors, emissive materials, and compatible processes. For the stretchable transparent electrode, ionically conductive gel, conductive polymer coating, and conductor network in surface of elastomer are all proven useful. The stretchable EL materials are currently limited to conjugated polymers, conjugated polymers with surfactants and ionic conductors added to boost stretchability, and phosphor particles embedded in elastomer matrices. These emissive materials operate under different mechanisms, require different electrode materials and fabrication processes, and the corresponding EL devices face distinctive challenges. This review aims to provide a basic understanding of the materials meeting both the mechanical and electronic requirements and important techniques to fabricate the stretchable EL devices.
      Cover page: Structures and Materials in Stretchable Electroluminescent Devices
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2015)
      Tuberous sclerosis complex (TSC) is an autosomal dominant disorder caused by mutations in either TSC1 or TSC2. TSC has high frequency of osseous manifestations such as sclerotic lesions in the craniofacial region. However, an animal model that replicates TSC craniofacial bone lesions has not yet been described. The roles of Tsc1 and the sequelae of Tsc1 dysfunction in bone are unknown. In this study, we generated a mouse model of TSC with a deletion of Tsc1 in neural crest-derived (NCD) cells that recapitulated the sclerotic craniofacial bone lesions in TSC. Analysis of this mouse model demonstrated that TSC1 deletion led to enhanced mTORC1 signaling in NCD bones and the increase in bone formation is responsible for the aberrantly increased bone mass. Lineage mapping revealed that TSC1 deficient NCD cells overpopulated the NCD bones. Mechanistically, hyperproliferation of osteoprogenitors at an early postnatal stage accounts for the increased osteoblast pool. Intriguingly, early postnatal treatment with rapamycin, an mTORC1 inhibitor, can completely rescue the aberrant bone mass, but late treatment cannot. Our data suggest that enhanced mTOR signaling in NCD cells can increase bone mass through enlargement of the osteoprogenitor pool, which likely explains the sclerotic bone lesion observed in TSC patients.
        Cover page: Neural Crest‐Specific TSC1 Deletion in Mice Leads to Sclerotic Craniofacial Bone Lesion
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2018)
        A large-scale sub-5 nm nanofabrication technique is developed based on double layer anodized aluminium oxide (AAO) porous membrane masking. This technique also provides a facile route to form multilayer nano-arrays (metal nanoarrays sandwiched by AAO membranes), which is very challenging for other techniques. Normally the AAO mask has to be sacrificed, yet in this work it is preserved as a part of the nanostructure. The preserved AAO layers as the support for the second/third layer of the metal arrays provide a high-refractive index background for the multilayer metal arrays. This background concentrates the local E-field more significantly and results in a much higher Surface-Enhanced Raman Spectroscopy (SERS) signal than single layer metal arrays. This technique may lead to the advent of an inexpensive, reproducible, highly sensitive SERS substrate. Moreover, the physical essence of the plasmonic enhancement is unveiled by finite element method based numerical simulations. Enhancements from the gaps and the multilayer nanostructure agree very well with the experiments. The calculated layer-by-layer electric field distribution determines the contribution from different layers and provides more insights into the 3D textured structure.
          Cover page: Multi-layer nanoarrays sandwiched by anodized aluminium oxide membranes: an approach to an inexpensive, reproducible, highly sensitive SERS substrate
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2016)
          Calcium/calmodulin-dependent protein kinase (CCaMK) has been shown to play an important role in abscisic acid (ABA)-induced antioxidant defense and enhance the tolerance of plants to drought stress. However, its downstream molecular events are poorly understood. Here, we identify a NAC transcription factor, ZmNAC84, in maize (Zea mays), which physically interacts with ZmCCaMK in vitro and in vivo. ZmNAC84 displays a partially overlapping expression pattern with ZmCCaMK after ABA treatment, and H2O2 is required for ABA-induced ZmNAC84 expression. Functional analysis reveals that ZmNAC84 is essential for ABA-induced antioxidant defense in a ZmCCaMK-dependent manner. Furthermore, ZmCCaMK directly phosphorylates Ser-113 of ZmNAC84 in vitro, and Ser-113 is essential for the ABA-induced stimulation of antioxidant defense by ZmCCaMK. Moreover, overexpression of ZmNAC84 in tobacco (Nicotiana tabacum) can improve drought tolerance and alleviate drought-induced oxidative damage of transgenic plants. These results define a mechanism for ZmCCaMK function in ABA-induced antioxidant defense, where ABA-produced H2O2 first induces expression of ZmCCaMK and ZmNAC84 and activates ZmCCaMK. Subsequently, the activated ZmCCaMK phosphorylates ZmNAC84 at Ser-113, thereby inducing antioxidant defense by activating downstream genes.
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2015)
            Ras GTPase-activating proteins (RasGAPs) inhibit signal transduction initiated through the Ras small GTP-binding protein. However, which members of the RasGAP family act as negative regulators of T cell responses is not completely understood. In this study, we investigated potential roles for the RasGAPs RASA1 and neurofibromin 1 (NF1) in T cells through the generation and analysis of T cell-specific RASA1 and NF1 double-deficient mice. In contrast to mice lacking either RasGAP alone in T cells, double-deficient mice developed T cell acute lymphoblastic leukemia/lymphoma, which originated at an early point in T cell development and was dependent on activating mutations in the Notch1 gene. These findings highlight RASA1 and NF1 as cotumor suppressors in the T cell lineage.
              Cover page: Cutting Edge: Codeletion of the Ras GTPase-Activating Proteins (RasGAPs) Neurofibromin 1 and p120 RasGAP in T Cells Results in the Development of T Cell Acute Lymphoblastic Leukemia
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2024)
              Stretchable electrodes are an essential component in soft actuator systems. In particular, Joule heating electrodes (JHEs) are required for thermal actuation systems. A highly stretchable, patternable, and low-voltage operating JHE based on hybrid layers of silver nanowires (AgNWs) and carbon nanotubes (CNTs) is reported. The conductive layers were applied on a locally pre-strained bistable electroactive polymer (BSEP) membrane to form a wrinkled conductive surface with a low resistance of 300 Ω/sq, and subsequently patterned to a serpentine trace by laser engraving. The resistance of the resulting electrode remains nearly unchanged up to ~80-90% area strain. By applying a voltage of 7 - 9 V to the electrode, the temperature of the BSEP membrane increased to more than 60 °C, well above the polymer's phase transition temperature of 46 °C, thereby lowering its modulus by a factor of 103. An electronic Braille device based on the JHEs on a BSEP membrane was assembled with a diaphragm chamber. The electrode was patterned into 3 × 2 individually addressable pixels according to the standard U.S. Braille cell format. Through Joule heating of the pixels and local expansion of the BSEP membrane using a small pneumatic pressure, the pixels deformed out of the plane by over 0.5 mm to display specific Braille letters. The Braille content can be refreshed for 20,000 cycles at the same operating voltage.
                Cover page: Deformable Joule Heating Electrode Based on Hybrid Layers of Silver Nanowires and Carbon Nanotubes and its Application in a Refreshable Multi‐Cell Braille DisplayCreative Commons 'BY-NC' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2017)
                Trimethylation of histone H3K36 is a chromatin mark associated with active gene expression, which has been implicated in coupling transcription with mRNA splicing and DNA damage response. SETD2 is a major H3K36 trimethyltransferase, which has been implicated as a tumor suppressor in mammals. Here, we report the regulation of SETD2 protein stability by the proteasome system, and the identification of SPOP, a key subunit of the CUL3 ubiquitin E3 ligase complex, as a SETD2-interacting protein. We demonstrate that SPOP is critically involved in SETD2 stability control and that the SPOP/CUL3 complex is responsible for SETD2 polyubiquitination both in vivo and in vitro ChIP-Seq analysis and biochemical experiments demonstrate that modulation of SPOP expression confers differential H3K36me3 on SETD2 target genes, and induce H3K36me3-coupled alternative splicing events. Together, these findings establish a functional connection between oncogenic SPOP and tumor suppressive SETD2 in the dynamic regulation of gene expression on chromatin.
                  Cover page: SPOP-containing complex regulates SETD2 stability and H3K36me3-coupled alternative splicingCreative Commons 'BY-NC' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2024)
                  BACKGROUND: The relationship between insulin resistance-related indices and the outcomes of acute ischemic stroke (AIS) is still unclear. This study aimed to explore the association between the Apo B/Apo A-1 ratio and the Prognostic Nutritional Index (PNI) with the 90-day outcomes of AIS. METHODS: A total of 2011 AIS patients with a 3-month follow-up were enrolled in the present study from January 2017 to July 2021. Multivariate logistic regression modeling was performed to analyze the relationship between Apo B/Apo A-1 ratio, PNI, and AIS poor outcomes. The mediating effect between the three was analyzed using the Bootstrap method with PNI as the mediating variable. RESULTS: Among the 2011 included AIS patients, 20.3% had a poor outcome. Patients were categorized according to quartiles of Apo B/Apo A-1 ratio and PNI. Multivariate logistic regression revealed that the fourth Apo B/Apo A-1 ratio quartile had poorer outcomes than the first quartile (OR 1.75,95%CL 1.21-2.53, P=0.003), and the fourth PNI quartile exhibited a lower risk of poor outcomes than the first quartile (OR 0.40, 95%CL 0.27-0.61, P<0.001). PNI displayed a significant partially mediating effect (21.4%) between the Apo B/Apo A-1 ratio and poor AIS outcomes. CONCLUSION: The Apo B/Apo A-1 ratio is a risk factor for poor AIS outcomes, whereas PNI acts as a protective factor. The association between the ApoB/ApoA-1 ratio and poor AIS outcomes was partially mediated by PNI.
                    Cover page: Association Apo B/Apo a-1 Ratio and Prognostic Nutritional Index with 90-Day Outcomes of Acute Ischemic Stroke.
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2024)
                    Relaxor ferroelectric polymers exhibiting a giant electrocaloric effect (ECE) can potentially be used to create next-generation solid-state coolers. Under an electric field, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer goes through a large dipolar entropy change producing a high adiabatic temperature change (ΔTECE). This work resolves the molecular origins of the large entropy change behind the electric field-induced dipole switching. A Fourier transform infrared spectroscopy equipped with a high voltage source is used to operandoly observe the characteristic molecular vibrational modes. A short-range trans (T) conformation of the CF2-CH2 dyads interrupted by a gauche (G) conformation, e.g., TTTG in the terpolymer chain, undergoes a dynamic transformation that leads to a corresponding ΔTECE whenever an electric field is applied. The molecular dynamics simulation also proves that the energy barrier that the transformation from TTTGs into a long T sequence overcomes is smaller than that for all other conformations. A mixed solvent system is used to obtain T3G-enriched terpolymer films exhibiting a 4.02 K ΔTECE at 60 MVm−1 and these films are employed to manufacture a 2-layer-cascaded cooling device that achieves a 6.7 K temperature lift, the highest reported value for a 2-layer cascaded device made of fluoropolymers.
                      Cover page: Operando Investigation of the Molecular Origins of Dipole Switching in P(VDF‐TrFE‐CFE) Terpolymer for Large Adiabatic Temperature ChangeCreative Commons 'BY' version 4.0 license
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