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Open Access Publications from the University of California

Recent Work

Lawrence Berkeley National Laboratory (Berkeley Lab) has been a leader in science and engineering research for more than 70 years. Located on a 200 acre site in the hills above the Berkeley campus of the University of California, overlooking the San Francisco Bay, Berkeley Lab is a U.S. Department of Energy (DOE) National Laboratory managed by the University of California. It has an annual budget of nearly $480 million (FY2002) and employs a staff of about 4,300, including more than a thousand students.

Berkeley Lab conducts unclassified research across a wide range of scientific disciplines with key efforts in fundamental studies of the universe; quantitative biology; nanoscience; new energy systems and environmental solutions; and the use of integrated computing as a tool for discovery. It is organized into 17 scientific divisions and hosts four DOE national user facilities. Details on Berkeley Lab's divisions and user facilities can be viewed here.

Solar conversion of CO2 to formate

(2019)

The Statement of Work for this CRADA was initially focused on optimization of a photoelectrochemical device, to be constructed using expertise in the Joint Center for Artificial Photosynthesis (JCAP) at LBNL, for transformation of CO2 into formate using a new catalyst developed by TCRDL. The work was to be jointly performed by LBNL and TCRDL at LBNL, and to involve an 18 month stay by a TCRDL researcher, Dr. Takeo Arai, at LBNL. Due to a family emergency this plan had to be cancelled after 6 months, and was replaced by a new work plan involving synchrotron studies that could be performed without requiring exchange of personnel.

Cover page of The Connection between Resonances and Bound States in the Presence of a Coulomb Potential

The Connection between Resonances and Bound States in the Presence of a Coulomb Potential

(2019)

© 2018 American Chemical Society. The connection between resonant metastable states and bound states with changing potential strength in the presence of a Coulomb potential is fundamentally different from the case of short-range potentials. This phenomenon is central to the physics of dissociative recombination of electrons with molecular cations. Here, it is verified computationally that there is no direct connection between the resonance pole of the S-matrix and any pole in the bound state spectrum. A detailed analysis is presented of the analytic structure of the scattering matrix, in which the resonance pole remains distinct in the complex k-plane while a new state appears in the bound state spectrum. A formulation of quantum-defect theory is developed based on the scattering matrix, which nonetheless exposes a close analytic relation between the resonant and bound state poles and thereby reveals the connection between quantum-defect theory and analytic S-matrix theory in the complex energy and momentum planes. One-channel and multichannel versions of the expressions with numerical examples for simple models are given, and the formalism is applied to give a unified picture of ab initio electronic structure and scattering calculations for e-O2 + and e-H2 + scattering.

Cover page of Exploratory analysis of high-resolution power interruption data reveals spatial and temporal heterogeneity in electric grid reliability

Exploratory analysis of high-resolution power interruption data reveals spatial and temporal heterogeneity in electric grid reliability

(2019)

© 2019 Modern grid monitoring equipment enables utilities to collect detailed records of power interruptions. These data are aggregated to compute publicly reported metrics describing high-level characteristics of grid performance. The current work explores the depth of insights that can be gained from public data, and the implications of losing visibility into heterogeneity in grid performance through aggregation. We present an exploratory analysis examining three years of high-resolution power interruption data collected by archiving information posted in real-time on the public-facing website of a utility in the Western United States. We report on the size, frequency and duration of individual power interruptions, and on spatio-temporal variability in aggregate reliability metrics. Our results show that metrics of grid performance can vary spatially and temporally by orders of magnitude, revealing heterogeneity that is not evidenced in publicly reported metrics. We show that limited access to granular information presents a substantive barrier to conducting detailed policy analysis, and discuss how more widespread data access could help to answer questions that remain unanswered in the literature to date. Given open questions about whether grid performance is adequate to support societal needs, we recommend establishing pathways to make high-resolution power interruption data available to support policy research.

Cover page of Leaf age effects on the spectral predictability of leaf traits in Amazonian canopy trees

Leaf age effects on the spectral predictability of leaf traits in Amazonian canopy trees

(2019)

© 2019 Recent work has shown that leaf traits and spectral properties change through time and/or seasonally as leaves age. Current field and hyperspectral methods used to estimate canopy leaf traits could, therefore, be significantly biased by variation in leaf age. To explore the magnitude of this effect, we used a phenological dataset comprised of leaves of different leaf age groups -developmental, mature, senescent and mixed-age- from canopy and emergent tropical trees in southern Peru. We tested the performance of partial least squares regression models developed from these different age groups when predicting traits for leaves of different ages on both a mass and area basis. Overall, area-based models outperformed mass-based models with a striking improvement in prediction observed for area-based leaf carbon (C area ) estimates. We observed trait-specific age effects in all mass-based models while area-based models displayed age effects in mixed-age leaf groups for P area and N area . Spectral coefficients and variable importance in projection (VIPs) also reflected age effects. Both mass- and area-based models for all five leaf traits displayed age/temporal sensitivity when we tested their ability to predict the traits of leaves of other age groups. Importantly, mass-based mature models displayed the worst overall performance when predicting the traits of leaves from other age groups. These results indicate that the widely adopted approach of using fully expanded mature leaves to calibrate models that estimate remotely-sensed tree canopy traits introduces error that can bias results depending on the phenological stage of canopy leaves. To achieve temporally stable models, spectroscopic studies should consider producing area-based estimates as well as calibrating models with leaves of different age groups as they present themselves through the growing season. We discuss the implications of this for surveys of canopies with synchronised and unsynchronised leaf phenology.

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Cover page of Osmotic and activity coefficients for five lithium salts in three non–aqueous solvents

Osmotic and activity coefficients for five lithium salts in three non–aqueous solvents

(2019)

© 2018 Elsevier Ltd To obtain osmotic coefficients, a classic static–view apparatus was used to measure the difference between the vapor pressure of a solvent and that of its salt solution at 25 °C. Vapor–pressure lowering was measured for solutions containing a lithium salt (LiCl, LiBr, LiNO3, LiPF6 and LITFSI) dissolved in a non–aqueous solvent (dimethyl carbonate, dimethyl sulfoxide and acetonitrile) that may be used in a lithium–ion battery. The osmotic–coefficient data are represented by Archer's extended Pitzer equation. Mean ionic activity coefficients for the salts are calculated from the osmotic–coefficient data.

Cover page of TOUGH-UDEC: A simulator for coupled multiphase fluid flows, heat transfers and discontinuous deformations in fractured porous media

TOUGH-UDEC: A simulator for coupled multiphase fluid flows, heat transfers and discontinuous deformations in fractured porous media

(2019)

© 2019 Elsevier Ltd A numerical simulator entitled TOUGH-UDEC is introduced for the analysis of coupled thermal-hydraulic-mechanical processes in fractured porous media. Two existing well-established codes, TOUGH2 and UDEC, are coupled to model multiphase fluid flows, heat transfers, and discontinuous deformations in fractured porous media by means of discrete fracture representation. TOUGH2 is widely used for the modeling of heat transfers and multiphase multicomponent fluid flows, and UDEC is a well-known distinct element code for rock mechanics. The two codes are solved sequentially, with coupling parameters passed to each equation at specific intervals. After solving thermal-hydraulic equations within the TOUGH2 code, pressure and temperature information is imported into the UDEC model. After solving the mechanical equation within the UDEC code the calculated fracture apertures are converted to the equivalent permeability and porosity values for a TOUGH2 flow analysis. The solution is calculated by iteratively following an explicit sequence for numerical efficiency. Verifications are presented to demonstrate the capabilities of the coupled TOUGH-UDEC simulator. Three application examples of (1) shear dilation due to increased pore pressure, (2) thermal stress and (3) CO 2 injection, show that the new simulator can be an effective tool for geoengineering applications involving shear activation of fractures and faults.

Cover page of Thermomechanical residual stress evaluation in multi-crystalline silicon solar cells of photovoltaic modules with different encapsulation polymers using synchrotron X-ray microdiffraction

Thermomechanical residual stress evaluation in multi-crystalline silicon solar cells of photovoltaic modules with different encapsulation polymers using synchrotron X-ray microdiffraction

(2019)

© 2019 Elsevier B.V. Photovoltaic (PV) module reliability issues, due to silicon cell cracking, are gaining more and more attention due to increasing demand for solar power and reduction of cell thickness to reduce cost. Recent reports show significant effect of encapsulation polymer material on cell cracks leading to the idea of tailoring encapsulation materials for more reliable PV modules. This paper investigates the effect of encapsulation modulus on the cell residual stress using Synchrotron scanning X-ray microdiffraction (µSXRD), which has been proven to be an effective technique to probe the stress in silicon solar cells, especially once they are encapsulated. The post lamination residual stress in the encapsulated multi-crystalline silicon (mc-Si) solar cells was reported for the first time using µSXRD in this manuscript and provide quantitative evaluation of the effect of encapsulation modulus on the cell residual stress. Further, simple approximate finite element (FE) model was also developed to evaluate the effect of the encapsulation polymer on the cell stress. The FE simulations predict the trend of the stress variation with encapsulation polymer modulus very well. Dynamic mechanical analysis and rheological testing of the encapsulation polymers was also performed to correlate the polymer behaviour with the experimental and simulated stresses. Both experimental and simulation results show a similar trend of significant cell stress variation with encapsulation polymer modulus. In the case of external loading, the temperature of load application is observed to be very significant as it dictates the elastic state of the encapsulant, leading to critical conclusion that the encapsulant needs to be selected based on elastic behaviour over the temperature history of the encapsulant during module fabrication and operation. The results and discussion presented are expected to be very useful for development of more reliable PV modules.

Cover page of A nano-photonic filter for near infrared radiative heater

A nano-photonic filter for near infrared radiative heater

(2019)

© 2019 Infrared (IR) radiative heating is a highly desirable method for heating as compared to convective heating due to the unprecedented control of radiative energy transfer, leading to a significant increase in energy efficiency. The greatest challenge however with IR radiative heating is its low penetration depth due to the strong IR absorption by the water content in the substance to be heated. Near IR (NIR) heating can circumvent this problem as it has greater penetration depths. The proposed nano-photonic design for NIR filter (or effective selective emitter) has transmissivity of more than 70% in NIR and less than 15% in both visible and IR wavelengths as opposed to currently available IR heaters, which have high emissivity across all wavelengths. This NIR filter can be applied to any radiative heating source to transform it into a NIR radiative heater. We demonstrate this with a simple prototype by applying it in front of tungsten-based incandescent lamp where significant reduction in white glow (glare) was observed. Potential application of this NIR filter would be in heating in both building and industrial sectors where the ability to provide localized heating could lead to significant energy savings. In addition, NIR selective emitters can be applied for power generation by supplying thermophotovoltaics (TPV) with photons at the right wavelengths, which will increase the efficiency of TPV.