Recursos de colección

Caltech Authors (143.226 recursos)

Repository of works by Caltech published authors.

Group = Resnick Sustainability Institute

Mostrando recursos 1 - 20 de 169

  1. Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis Copolymerization

    Lin, Tzu-Pin; Chang, Alice B.; Chen, Hsiang-Yun; Liberman-Martin, Allegra L.; Bates, Christopher M.; Voegtle, Matthew J.; Bauer, Christina A.; Grubbs, Robert H.
    Control over polymer sequence and architecture is crucial to both understanding structure–property relationships and designing functional materials. In pursuit of these goals, we developed a new synthetic approach that enables facile manipulation of the density and distribution of grafts in polymers via living ring-opening metathesis polymerization (ROMP). Discrete endo,exo-norbornenyl dialkylesters (dimethyl DME, diethyl DEE, di-n-butyl DBE) were strategically designed to copolymerize with a norbornene-functionalized polystyrene (PS), polylactide (PLA), or polydimethylsiloxane (PDMS) macromonomer mediated by the third-generation metathesis catalyst (G3). The small-molecule diesters act as diluents that increase the average distance between grafted side chains, generating polymers with variable grafting density....

  2. Hyper-Selective Plasmonic Color Filters

    Fleischman, Dagny; Sweatlock, Luke A.; Murakami, Hirotaka; Atwater, Harry
    The subwavelength mode volumes of plasmonic filters are well matched to the small size of state-of-the-art active pixels (~ 1 µm) in CMOS image sensor arrays used in portable electronic devices. Typical plasmonic filters exhibit broad (> 100 nm) transmission bandwidths. Dramatically reducing the peak width of filter transmission spectra would allow for the realization of CMOS hyperspectral imaging arrays, which demand the FWHM of transmission peaks to be less than 30 nm. We find that the design of 5 layer metal-insulator-metal-insulator-metal structures gives rise to multi-mode interference phenomena that suppresses spurious transmission features gives rise to a single narrow...

  3. Directed Evolution of a Bright Near-Infrared Fluorescent Rhodopsin Using a Synthetic Chromophore

    Herwig, Lukas; Rice, Austin J.; Bedbrook, Claire N.; Zhang, Ruijie K.; Lignell, Antti; Cahn, Jackson K. B.; Renata, Hans; Dodani, Sheel C.; Cho, Inha; Cai, Long; Gradinaru, Viviana; Arnold, Frances H.
    By engineering a microbial rhodopsin, Archaerhodopsin-3 (Arch), to bind a synthetic chromophore, merocyanine retinal, in place of the natural chromophore all-trans-retinal (ATR), we generated a protein with exceptionally bright and unprecedentedly red-shifted near-infrared (NIR) fluorescence. We show that chromophore substitution generates a fluorescent Arch complex with a 200-nm bathochromic excitation shift relative to ATR-bound wild-type Arch and an emission maximum at 772 nm. Directed evolution of this complex produced variants with pH-sensitive NIR fluorescence and molecular brightness 8.5-fold greater than the brightest ATR-bound Arch variant. The resulting proteins are well suited to bacterial imaging; expression and stability have not been...

  4. Non-conventional fluorescent biogenic and synthetic polymers without aromatic rings

    Ye, Ruquan; Liu, Yuanyue; Zhang, Haoke; Su, Huifang; Zhang, Yilin; Xu, Liguo; Hu, Rongrong; Kwok, Ryan T. K.; Wong, Kam Sing; Lam, Jacky W. Y.; Goddard, William A., III; Tang, Ben Zhong
    Non-conventional fluorescent materials without aromatic structures have attracted much research attention in recent years. However, the working mechanism responsible for their fluorescence remains mysterious. Here we decipher the origin of fluorescence by studying the photophysical properties of a series of non-aromatic biogenic and synthetic peptides. An experimental study suggests that the turn-on fluorescence in the aggregation state/condensed phase is associated with the communication of amide groups, where hydrogen bonds are playing a critical role in bringing these functionalities into close proximity. This explanation is further justified by the study of the hierarchical influence on fluorescence and applied to biomimetic polymers...

  5. Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

    Brown, Ana M.; Sundararaman, Ravishankar; Narang, Prineha; Schwartzberg, Adam M.; Goddard, William A., III; Atwater, Harry A.
    Ultrafast pump-probe measurements of plasmonic nanostructures probe the nonequilibrium behavior of excited carriers, which involves several competing effects obscured in typical empirical analyses. Here we present pump-probe measurements of plasmonic nanoparticles along with a complete theoretical description based on first-principles calculations of carrier dynamics and optical response, free of any fitting parameters. We account for detailed electronic-structure effects in the density of states, excited carrier distributions, electron-phonon coupling, and dielectric functions that allow us to avoid effective electron temperature approximations. Using this calculation method, we obtain excellent quantitative agreement with spectral and temporal features in transient-absorption measurements. In both our...

  6. A potassium tert-butoxide and hydrosilane system for ultra-deep desulfurization of fuels

    Toutov, Anton A.; Salata, Mike; Fedorov, Alexey; Yang, Yun-Fang; Liang, Yong; Cariou, Romain; Betz, Kerry N.; Couzijn, Erik P. A.; Shabaker, John W.; Houk, Kendall N.; Grubbs, Robert H.
    Hydrodesulfurization (HDS) is the process by which sulfur-containing impurities are removed from petroleum streams, typically using a heterogeneous, sulfided transition metal catalyst under high H_2 pressures and temperatures. Although generally effective, a major obstacle that remains is the desulfurization of highly refractory sulfur-containing heterocycles, such as 4,6-dimethyldibenzothiophene (4,6-Me_2DBT), which are naturally occurring in fossil fuels. Homogeneous HDS strategies using well-defined molecular catalysts have been designed to target these recalcitrant S-heterocycles; however, the formation of stable transition metal sulfide complexes following C–S bond activation has largely prevented catalytic turnover. Here we show that a robust potassium (K) alkoxide (O)/hydrosilane (Si)-based (‘KOSi’)...

  7. Convexification of AC optimal power flow

    Gan, Lingwen; Low, Steven H.
    This overview paper summarizes the key elements of semidefinite relaxations of the optimal power flow problem, and discusses several open challenges.

  8. Optimal decentralized primary frequency control in power networks

    Zhao, Changhong; Low, Steven
    We augment existing generator-side primary frequency control with load-side control that are local, ubiquitous, and continuous. The mechanisms on both the generator and the load sides are decentralized in that their control decisions are functions of locally measurable frequency deviations. These local algorithms interact over the network through nonlinear power flows. We design the local frequency feedback control so that any equilibrium point of the closed-loop system is the solution to an optimization problem that minimizes the total generation cost and user disutility subject to power balance across entire network. With Lyapunov method we derive a sufficient condition for any...

  9. Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes

    Savoie, Brett M.; Webb, Michael A.; Miller, Thomas F., III
    Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li^+ conductivity remains a barrier to technological viability. SPEs are designed to maximize Li^+ diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly(ethylene oxide) (PEO), the most widely used SPE, exhibits Li^+ diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using...

  10. An Efficient and Incentive Compatible Mechanism for Wholesale Electricity Markets

    Xu, Yunjian; Low, Steven H.
    Being widely used in many deregulated wholesale electricity markets, the locational marginal pricing (LMP) mechanism is known to achieve social optimality in a competitive market. When profit-maximizing generators act strategically to manipulate prices; however, LMP may lead to high loss of economic efficiency. In this paper, we apply the Vickrey-Clarke–Groves (VCG) mechanism to wholesale electricity markets. We show that the VCG mechanism minimizes the total cost at a truth-telling dominant strategy equilibrium. We establish an important comparative result that the VCG mechanism always results in higher per-unit electricity prices than the LMP mechanism under any given set of reported supply...

  11. Environment-economy tradeoff for Beijing-Tianjin-Hebei’s exports

    Zhao, Hongyan; Zhang, Qiang; Huo, Hong; Lin, Jintai; Liu, Zhu; Wang, Haikun; Guan, Dabo; He, Kebin
    The trade of goods among regions or nations associated with large environmental consequences. Yet balancing economic gains and environmental consequences induced by trade is still hindered by a lack of quantification of these two factors, especially for the environmental problems those are more locally oriented, such as the atmospheric pollution. Based on an environmental input–output analysis for 2010, we contrast economic gains (value added) against atmospheric pollutant emissions (sulfur dioxide (SO_2), nitric oxide (NO_x), primary fine particulate matter (PM_(2.5)) and non-methane volatile organic compounds (NMVOC)) and the widely concerned CO2 emissions associated with international and interprovincial exports from Beijing–Tianjin–Hebei (BTH),...

  12. Understanding the energy consumption and greenhouse gas emissions and the implication for achieving climate change mitigation targets

    Liu, Zhu; Feng, Kuishuang; Davis, Steven J.; Guan, Dabo; Chen, Bin; Hubacek, Klaus; Yan, Jinyue
    [No abstract]

  13. New provincial CO_2 emission inventories in China based on apparent energy consumption data and updated emission factors

    Shan, Yuli; Liu, Jianghua; Liu, Zhu; Xu, Xinwanghao; Shao, Shuai; Wang, Peng; Guan, Dabo
    This study employs “apparent energy consumption” approach and updated emissions factors to re-calculate Chinese provincial CO_2 emissions during 2000–2012 to reduce the uncertainty in Chinese CO_2 emission estimates for the first time. The study presents the changing emission-socioeconomic features of each provinces as well. The results indicate that Chinese provincial aggregated CO_2 emissions calculated by the apparent energy consumption and updated emissions factors are coincident with the national emissions estimated by the same approach, which are 12.69% smaller than the one calculated by the traditional approach and IPCC default emission factors. The provincial aggregated CO_2 emissions increased from 3160 million...

  14. Consumption-based emission accounting for Chinese cities

    Mi, Zhifu; Zhang, Yunkun; Guan, Dabo; Shan, Yuli; Liu, Zhu; Cong, Ronggang; Yuan, Xiao-Chen; Wei, Yi-Ming
    Most of China’s CO_2 emissions are related to energy consumption in its cities. Thus, cities are critical for implementing China’s carbon emissions mitigation policies. In this study, we employ an input-output model to calculate consumption-based CO_2 emissions for thirteen Chinese cities and find substantial differences between production- and consumption-based accounting in terms of both overall and per capita carbon emissions. Urban consumption not only leads to carbon emissions within a city’s own boundaries but also induces emissions in other regions via interregional trade. In megacities such as Shanghai, Beijing and Tianjin, approximately 70% of consumption-based emissions are imported from other...

  15. Alkali metal hydroxide–catalyzed C(sp)–H bond silylation

    Toutov, Anton A.; Betz, Kerry N.; Schuman, David P.; Liu, Wen-Bo; Fedorov, Alexey; Stoltz, Brian M.; Grubbs, Robert H.
    Disclosed is a mild, scalable, and chemoselective catalytic cross-dehydrogenative C–H bond functionalization protocol for the construction of C(sp)–Si bonds in a single step. The scope of the alkyne and hydrosilane partners is substantial, providing an entry point into various organosilane building blocks and additionally enabling the discovery of a number of novel synthetic strategies. Remarkably, the optimal catalysts are NaOH and KOH.

  16. Unequal household carbon footprints in China

    Wiedenhofer, Dominik; Guan, Dabo; Liu, Zhu; Meng, Jing; Zhang, Ning; Wei, Yi-Ming
    Households’ carbon footprints are unequally distributed among the rich and poor due to differences in the scale and patterns of consumption. We present distributional focused carbon footprints for Chinese households and use a carbon-footprint-Gini coefficient to quantify inequalities. We find that in 2012 the urban very rich, comprising 5% of population, induced 19% of the total carbon footprint from household consumption in China, with 6.4 tCO_2/cap. The average Chinese household footprint remains comparatively low (1.7 tCO_2/cap), while those of the rural population and urban poor, comprising 58% of population, are 0.5–1.6 tCO_2/cap. Between 2007 and 2012 the total footprint from...

  17. Atomic H-Induced Mo_2C Hybrid as an Active and Stable Bifunctional Electrocatalyst

    Fan, Xiujun; Liu, Yuanyue; Peng, Zhiwei; Zhang, Zhenhua; Zhou, Haiqing; Zhang, Xianming; Yakobson, Boris I.; Goddard, William A., III; Guo, Xia; Hauge, Robert H.; Tour, James M.
    Mo_2C nanocrystals (NCs) anchored on vertically aligned graphene nanoribbons (VA-GNR) as hybrid nanocatalysts (Mo_2C-GNR) are synthesized through the direct carbonization of metallic Mo with atomic H treatment. The growth mechanism of Mo2C NCs with atomic H treatment is discussed. The Mo_2C-GNR hybrid exhibits highly active and durable electrocatalytic performance for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). For HER, in an acidic solution the Mo_2C-GNR has an onset potential of 39 mV and a Tafel slope of 65 mV dec^(-1), in a basic solution Mo_2C-GNR has an onset potential of 53 mV, and Tafel slope of 54...

  18. Gate-Variable Mid-Infrared Optical Transitions in a (Bi_(1-x)Sb_x)_2Te_3 Topological Insulator

    Whitney, William S.; Brar, Victor Watson; Ou, Yunbo; Shao, Yinming; Davoyan, Artur R.; Basov, Dimitri N.; He, Ke; Xue, Qi-Kun; Atwater, Harry A.
    We report mid-infrared spectroscopy measurements of ultrathin, electrostatically gated (Bi_(1-x)Sb_x)_2Te_3 topological insulator films, in which we observe several percent modulation of transmittance and reflectance as gating shifts the Fermi level. Infrared transmittance measurements of gated films were enabled by use of an epitaxial lift-off method for large-area transfer of topological insulator films from infrared-absorbing SrTiO3 growth substrates to thermal oxidized silicon substrates. We combine these optical experiments with transport measurements and angle-resolved photoemission spectroscopy to identify the observed spectral modulation as a gate-driven transfer of spectral weight between both bulk and 2D topological surface channels and interband and intraband channels....

  19. Substantial global carbon uptake by cement carbonation

    Xi, Fengming; Davis, Steven J.; Ciais, Philippe; Crawford-Brown, Douglas; Guan, Dabo; Pade, Claus; Shi, Tiemao; Syddall, Mark; Lv, Jie; Ji, Lanzhu; Bing, Longfei; Wang, Jiaoyue; Wei, Wei; Yang, Keun-Hyeok; Lagerblad, Björn; Galan, Isabel; Andrade, Carmen; Zhang, Ying; Liu, Zhu
    Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO_2 emissions from all industrial process and fossil-fuel combustion in 2013. Considerable attention has been paid to quantifying these industrial process emissions from cement production, but the natural reversal of the process—carbonation—has received little attention in carbon cycle studies. Here, we use new and existing data on cement materials during cement service life, demolition, and secondary use of concrete waste to estimate regional and global CO_2 uptake between 1930 and 2013 using an analytical model describing carbonation chemistry. We find that carbonation of cement materials over their...

  20. Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

    Liu, Yuanyue; Xiao, Hai; Goddard, William A., III
    Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weak...

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