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Open Access Publications from the University of California

Scholarly Works (13 results)

  • Article
Working Papers (2000)

INCISIM is a computer program that simulates the occurrence of highway incidents, the dispatching of emergency vehicles, and the traffic flow on the network. INCISIM can represent multiple types of emergency vehicles, include highway patrol cars, freeway service patrol trucks, tow trucks operating from fixed bases, highway maintenance vehicles, and fire trucks. Incidents are represented by type classifications (corresponding to computer-aided-dispatch codes) and profiles (defining duration and magnitude of incidents). Delay is calculated as a function of these variables, along with traffic flows and highway capacities. INCISIM produces a complete log of incidents that occurred during the simulation along with statistics on highway delays.

    Cover page: INCISM: Users Manual
    • Thesis
    • Peer Reviewed
    UC San Diego Electronic Theses and Dissertations (2021)

    Shock wave focusing can lead to extreme thermodynamic conditions, and applications have been extended to a variety of areas such as civil engineering and medical treatment. Among all numerical approaches, geometrical shock dynamics (GSD) is a model capable of efficiently predicting the position, shape and strength of a shock. Compared to the traditional Euler method that solves the inviscid Euler equations, GSD is a reduced-order model derived from the method of characteristics that is more computationally efficient since it only considers the motion of the shock front instead of the entire flow field.

    Whitham’s original theory of GSD successfully relates the change of area upon the shock front to the shock motion with an assumption of a uniform state behind the shock, so it is able to accurately predict the behavior of a shock wave with constant properties behind it. However, the truncation of the post-shock flow term discredits its application to shock waves with decaying properties behind (e.g., in the case of blast waves). In this study three two-dimensional GSD models were first reviewed with a focus on how the post-shock flow effect is accounted for. It turned out that the completeness of the post-shock flow term determines the accuracy of GSD for blast waves, but prior knowledge of the particular blast is required to achieve full completeness. The point-source GSD (PGSD) model thus stands out since it encodes the analytical solution to blast propagation and is independent of the initial energy content of the point-explosion. Then a general framework based on PGSD was proposed aiming at efficiently solving the irregular reflection phase of blast focusing problems. Lagrangian simulations were thus performed for the symmetric interaction between two cylindrical blasts and compared to the experimental results. An agreement in attenuation of the maximum pressure at the Mach stem was observed but an overestimation of the Mach stem growth at its early stage by PGSD was also seen. To address this issue, an alternative model called PGSDSS was developed that combines PGSD and the shock-shock approximate theory for cylindrical shock reflection off a straight surface.

    Another advantage of PGSD is its capability to be extended to three dimensions. Unlike the traditional three-dimensional GSD studies using triangulated meshes, in this study the shock surface is represented by a point cloud arranged in an octree data structure, such that a fast k-nearest neighbor search is possible without the need of connectivity information. Differential geometric properties required by PGSD are obtained by computing the moving least squares (MLS) surface that approximates the underlying shock surface. The resulting MLS-PGSD model was utilized to investigate first the propagation of a single spherical micro-blast in air and then its reflection off a solid wall. A good agreement of the blast front contour at different time instants with the experimental results was reached.

      Cover page: Numerical Study of Shock Focusing Phenomena Using Geometrical Shock Dynamics
      • Article
      • Peer Reviewed
      LBL Publications (2023)
      Millifluidics, the manipulation of liquid flow in millimeter-sized channels, has been a revolutionary concept in chemical processing and engineering. The solid channels that contain the liquids, though, are not flexible in their design and modification, and prevent contact with the external environment. All-liquid constructs, on the other hand, while flexible and open, are imbedded in a liquid environment. Here, we provide a route to circumvent these limitations by encasing the liquids in a hydrophobic powder in air that jams on the surface, containing and isolating flowing fluids, offering flexibility and adaptability in design, as manifest in the ability to reconfigure, graft, and segment the constructs. Along with the open nature of these powder-contained channels that allow arbitrary connections/disconnections and substance addition/extraction, numerous applications can be opened in the biological, chemical, and material arenas.
        Cover page: Open millifluidics based on powder-encased channels
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2023)
        Non-fullerene acceptors based organic solar cells represent the frontier of the field, owing to both the materials and morphology manipulation innovations. Non-radiative recombination loss suppression and performance boosting are in the center of organic solar cell research. Here, we developed a non-monotonic intermediate state manipulation strategy for state-of-the-art organic solar cells by employing 1,3,5-trichlorobenzene as crystallization regulator, which optimizes the film crystallization process, regulates the self-organization of bulk-heterojunction in a non-monotonic manner, i.e., first enhancing and then relaxing the molecular aggregation. As a result, the excessive aggregation of non-fullerene acceptors is avoided and we have achieved efficient organic solar cells with reduced non-radiative recombination loss. In PM6:BTP-eC9 organic solar cell, our strategy successfully offers a record binary organic solar cell efficiency of 19.31% (18.93% certified) with very low non-radiative recombination loss of 0.190 eV. And lower non-radiative recombination loss of 0.168 eV is further achieved in PM1:BTP-eC9 organic solar cell (19.10% efficiency), giving great promise to future organic solar cell research.
          Cover page: 19.31% binary organic solar cell and low non-radiative recombination enabled by non-monotonic intermediate state transitionCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2021)
          Prostaglandin D2 (PGD2) signals through the G protein-coupled receptor (GPCR) CRTH2 to mediate various inflammatory responses. CRTH2 is the only member of the prostanoid receptor family that is phylogenetically distant from others, implying a nonconserved mechanism of lipid action on CRTH2. Here, we report a crystal structure of human CRTH2 bound to a PGD2 derivative, 15R-methyl-PGD2 (15mPGD2), by serial femtosecond crystallography. The structure revealed a "polar group in"-binding mode of 15mPGD2 contrasting the "polar group out"-binding mode of PGE2 in its receptor EP3. Structural comparison analysis suggested that these two lipid-binding modes, associated with distinct charge distributions of ligand-binding pockets, may apply to other lipid GPCRs. Molecular dynamics simulations together with mutagenesis studies also identified charged residues at the ligand entry port that function to capture lipid ligands of CRTH2 from the lipid bilayer. Together, our studies suggest critical roles of charge environment in lipid recognition by GPCRs.
            Cover page: Molecular basis for lipid recognition by the prostaglandin D2 receptor CRTH2
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2024)
            For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability.
              Cover page: Rational molecular and device design enables organic solar cells approaching 20% efficiency.
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2020)

              Background

              We sought to determine whether circulating inflammatory biomarkers were associated with the frequent exacerbator phenotype in stable COPD patients ie, those with two or more exacerbations in the previous year.

              Methods

              Eighty-eight stable, severe, COPD patients (4 females) were assessed for exacerbation frequency, pulmonary function, fraction of expired nitric oxide (FENO); inflammatory variables were measured in venous blood. Logistic regression assessed associations between the frequent exacerbator phenotype and systemic inflammation.

              Results

              Compared with infrequent exacerbators, frequent exacerbators (n=10; 11.4%) had greater serum concentration (median (25th-75th quartile)) of serum amyloid A (SAA; 134 (84-178) vs 71 (38-116) ng/mL; P=0.024), surfactant protein D (SP-D; 15.6 (9.0-19.3) vs 8.5 (3.6-14.9) ng/mL; P=0.049) and interleukin-4 (IL-4; 0.12 (0.08-1.44) vs 0.03 (0.01-0.10) pg/mL; P=0.001). SAA, SP-D and IL-4 were not significantly correlated with FEV1%predicted or FVC %predicted. After adjusting for sex, age, BMI, FEV1/FVC and smoking pack-years, only SAA remained independently associated with the frequent exacerbator phenotype (OR 1.49[1.09-2.04]; P=0.012). The odds of being a frequent exacerbator was 18-times greater in the highest SAA quartile (≥124.1 ng/mL) than the lowest SAA quartile (≤44.1 ng/mL) (OR 18.34[1.30-258.81]; P=0.031), and there was a significant positive trend of increasing OR with increasing SAA quartile (P=0.008). For SAA, the area under the receiver operating characteristic curve was 0.721 for identification of frequent exacerbators; an SAA cut-off of 87.0 ng/mL yielded an 80% sensitivity and 61.5% specificity.

              Conclusion

              In stable COPD patients, SAA was independently associated with the frequent exacerbator phenotype, suggesting that SAA may be a useful serum biomarker to inform progression or management in COPD.
                Cover page: Serum Amyloid A in Stable COPD Patients is Associated with the Frequent Exacerbator Phenotype
                • Article
                • Peer Reviewed
                LBL Publications (2019)
                Controlling ferroic orders (ferroelectricity, ferromagnetism and ferroelasticity) by optical methods is a significant challenge due to the large mismatch in energy scales between the order parameter coupling strengths and the incident photons. Here, we demonstrate an approach to manipulate multiple ferroic orders in an epitaxial mixed-phase BiFeO3 thin film at ambient temperature via laser illumination. Phase-field simulations indicate that a light-driven flexoelectric effect allows the targeted formation of ordered domains. We also achieved precise sequential laser writing and erasure of different domain patterns, which demonstrates a deterministic optical control of multiferroicity at room temperature. As ferroic orders directly influence susceptibility and conductivity in complex materials, our results not only shed light on the optical control of multiple functionalities, but also suggest possible developments for optoelectronics and related applications.
                  Cover page: Deterministic optical control of room temperature multiferroicity in BiFeO3 thin films
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2020)
                  Magnetoelectric coupling at room temperature in multiferroic materials, such as BiFeO3, is one of the leading candidates to develop low-power spintronics and emerging memory technologies. Although extensive research activity has been devoted recently to exploring the physical properties, especially focusing on ferroelectricity and antiferromagnetism in chemically modified BiFeO3, a concrete understanding of the magnetoelectric coupling is yet to be fulfilled. We have discovered that La substitutions at the Bi-site lead to a progressive increase in the degeneracy of the potential energy landscape of the BiFeO3 system exemplified by a rotation of the polar axis away from the 〈111〉pc towards the 〈112〉pc discretion. This is accompanied by corresponding rotation of the antiferromagnetic axis as well, thus maintaining the right-handed vectorial relationship between ferroelectric polarization, antiferromagnetic vector and the Dzyaloshinskii-Moriya vector. As a consequence, La-BiFeO3 films exhibit a magnetoelectric coupling that is distinctly different from the undoped BiFeO3 films.
                    Cover page: Manipulating magnetoelectric energy landscape in multiferroics
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2020)
                    Magnetoelectric coupling at room temperature in multiferroic materials, such as BiFeO3, is one of the leading candidates to develop low-power spintronics and emerging memory technologies. Although extensive research activity has been devoted recently to exploring the physical properties, especially focusing on ferroelectricity and antiferromagnetism in chemically modified BiFeO3, a concrete understanding of the magnetoelectric coupling is yet to be fulfilled. We have discovered that La substitutions at the Bi-site lead to a progressive increase in the degeneracy of the potential energy landscape of the BiFeO3 system exemplified by a rotation of the polar axis away from the 〈111〉pc towards the 〈112〉pc discretion. This is accompanied by corresponding rotation of the antiferromagnetic axis as well, thus maintaining the right-handed vectorial relationship between ferroelectric polarization, antiferromagnetic vector and the Dzyaloshinskii-Moriya vector. As a consequence, La-BiFeO3 films exhibit a magnetoelectric coupling that is distinctly different from the undoped BiFeO3 films.
                      Cover page: Manipulating magnetoelectric energy landscape in multiferroics
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