University of California, Berkeley
  • Berkeley, CA, United States
Recent publications
Sea Water Air Conditioning (SWAC) technology uses deep ocean water to cool buildings. It is a non-intermittent renewable thermal energy used directly without any transformation. It may replace other air-conditioning systems powered by electrical energy (mechanical vapor compression thermodynamic cycle) or powered by other renewable energies (solar heating and cooling systems). Despite its theoretical appeal as a solution to help achieve net-zero carbon emissions, and the existence of successful deployments, SWAC technology remains scarce worldwide mainly due to its investment cost (CAPEX). One reason for this failure to scale might be the absence of experimental data detailing energy performance of SWAC systems in real-world, commercial settings. Here is presented the performance of an existing 2.4 MW SWAC system, operated by The Brando resort on the atoll of Tetiaroa in French Polynesia. Under a tropical climate, experimental results show that the Coefficient of Performance (COP) of the SWAC system can reach 20 to 150 depending on the secondary loop length, compared with conventional vapor compression systems that peak at around 5 for the most efficient. To put this in terms of carbon emissions avoided, conventional unitary split systems running in similar hotels on neighboring islands in French Polynesia (COP around 3.5) emit some 860 Tons/year compared to the estimated 225 Tons/year emitted (approximated with the emissions factor of French Polynesia in 2019) operating the Tetiaroa SWAC.
Consumer reactions to COVID-19 pandemic disruptions have been varied, including modifications in spending frequency, amount, product categories and delivery channels. This study analyzes spending data from a sample of 720 U.S. households during the start of deconfinement and early vaccine rollout to understand changes in spending and behavior one year into the pandemic. This paper finds that overall spending is similar to pre-pandemic levels, except for a 28% decline in prepared food spending. More educated and higher income households with children have shifted away from in-person spending, whereas politically conservative respondents are more likely to shop in-person and via pickup.
Fiber-reinforced polymer (FRP) composites are increasingly popular due to their superior strength to weight ratio. In contrast to significant recent advances in automating the FRP manufacturing process via 3D printing, quality inspection and defect detection remain largely manual and inefficient. In this paper, we propose a new approach to automatically detect, from microscope images, one of the major defects in 3D printed FRP parts: fiber-deficient areas (or equivalently, resin-rich areas). From cross-sectional microscope images, we detect the locations and sizes of fibers, construct their Voronoi diagram, and employ α-shape theory to determine fiber-deficient areas. Our Voronoi diagram and α-shape construction algorithms are specialized to exploit typical characteristics of 3D printed FRP parts, giving significant efficiency gains. Our algorithms robustly handle real-world inputs containing hundreds of thousands of fiber cross-sections, whether in general or non-general position.
Intra-individual variability of steady-state evoked potentials (ssEPs) is correlated with attention fluctuations and reveals the participant’s ability to sustain attention. We previously presented an analytical method to measure the variation of discrete Fourier measurements at the frequency of interest extracted from ssEP data and to model the Fourier estimates on the two-dimensional complex plane with an ellipse. In this paper, we will introduce the ratio of the major to minor axes of the ellipse, which we call the Length-to-Width Ratio (LWR), as an index of individual ability to control attention and show how to calculate the confidence interval of the LWR to be able to compare the LWR between conditions within a participant as well as between participants within or between studies. The method will enable us to find out the most sensitive electroencephalography electrode to attention fluctuation, to explore the neural correlates of attention, to differentiate cases with inconsistent control of attention from normal participants, and to objectively monitor the effects of therapeutic interventions on attention.
Actual airborne time (AAT) is the time between actual wheels-off and actual wheels-on of a flight. Given the ever-growing demand for air travel and growing flight delays, understanding the behavior of AAT is increasingly important for on time performance and delay propagation. Of particular interest is the comparison on AAT in different countries with varying air route structures, air traffic management systems, weather, and geography. This paper performs the first comparative empirical analysis of AAT behavior, focusing on the U.S. and China. The focus is on how AAT is affected by origin-destination (OD) distance, the possible pressure to reduce AAT from other parts of flight operations, hub status of departure/arrival airports, enroute and terminal traffic conditions, and convective weather. Econometric models are developed to quantify the impacts of factors on AAT behavior in China and the U.S., separately. The estimation results show that in both countries AAT is highly correlated with OD distance. Flight time in China is longer than that in the U.S. given the same OD distance which indicates a low effective speed may be the result of a low aircraft speed, or due to the flight experiencing metering, rerouting, holding or vectoring in Chinese airspace. In addition, we find that a flight has limited capability to make up for pre-departure delay. Sensitivity analysis of AAT to flight length and aircraft utilization is further conducted. Given the more abundant civil airspace, flexible routing networks, and efficient air traffic flow management (ATFM) procedures, we performed a counterfactual analysis to investigate how Chinese AATs would change if they were governed by the U.S. model. We find that this would result in significant efficiency gains for the Chinese air traffic system. On average, 13 min of AAT per flight would be saved. Systemwide fuel saving would amount to 326 million gallons with CO2 emission reduction of 2.7 million tons and direct airline operating cost saving of over $1.3 billion in 2016.
Drawing from two waves (∼1.5–2.5 years apart) of longitudinal data, the current study investigated the bidirectional associations between self-regulatory skills and mathematics achievement among a socioeconomically diverse sample of school-age Chinese American children from immigrant families (N = 258; 48.1% girls; ages 5.8–9.1 years; first to third grades at Wave 1). Children’s self-regulatory skills were assessed with task-based measures of attention focusing, inhibitory control, behavioral persistence, and comprehensive executive function as well as parent- and teacher-reported effortful control. Multiple regressions showed that behavioral persistence and parent-reported effortful control positively predicted math achievement over time. Math achievement positively predicted comprehensive executive function over time. These effects were found when controlling for child age, sex, generation status, family socioeconomic status, parents’ cultural orientations, and prior levels of math achievement or self-regulation. The prospective relation of math achievement predicting comprehensive executive function remained significant after a false discovery rate correction.
Black carbon is a product of the incomplete combustion of carbonaceous fuels and has significant adverse effects on climate change, air quality, and human health. China has been a major contributor to global anthropogenic black carbon emissions. This study develops a black carbon inventory in China, using 2015 as the base year, and projects annual black carbon emissions in China for the period 2016–2050, under two scenarios: a Reference scenario and an Accelerated Reduction scenario. The study estimates that the total black carbon emissions in China in 2015 were 1100 thousand tons (kt), with residential use being the biggest contributor, accounting for more than half of the total black carbon emissions, followed by coke production, industry, agricultural waste burning, and transportation. This study then projects the total black carbon emissions in China in 2050 to be 278 kt in the Reference scenario and 86 kt in the Accelerated Reduction Scenario. Compared to the Reference scenario, the Accelerated Reduction scenario will achieve much faster and deeper black carbon reductions in all the sectors. The dramatic reductions can be attributed to the fuel switching in the residential sector, faster implementation of high-efficiency emission control measures in the industry, transportation, and coke production sectors, and faster phase-out of agricultural waste open burning. This analysis reveals the high potential of black carbon emission reductions across multiple sectors in China through the next thirty years.
As the largest polity worldwide to legalize cannabis, California has implemented uniquely high environmental and land use standards for cannabis agriculture. To date, however, regulations have suffered from low compliance rates, especially among smaller, “legacy” farms that existed prior to legalization. Meanwhile, both licensed and unlicensed farms are increasing in size, thus increasing environmental pressures. Is there a way to achieve environmental objectives, farmer compliance, and an equitable transition away from illegal markets? In the largest US survey of cannabis farmers to date, we found farmers are open to strong environmental protections yet face significant barriers in meeting regulatory requirements. We present this opinion article to suggest several strategies to ameliorate compliance barriers by reducing associated learning, financial, and psychological costs. Taken together, these strategies present an unprecedented opportunity to model a new kind of agriculture centered on small-farm production and environmental stewardship—a model that indicates new directions for agriculture beyond cannabis.
The geodesic orbit property is useful and interesting in Riemannian geometry. It implies homogeneity and has important classes of Riemannian manifolds as special cases. Those classes include weakly symmetric Riemannian manifolds and naturally reductive Riemannian manifolds. The corresponding results for indefinite metric manifolds are much more delicate than in Riemannian signature, but in the last few years important corresponding structural results were proved for geodesic orbit Lorentz manifolds. Here, we carry out a major step in the structural analysis of geodesic orbit Lorentz nilmanifolds. Those are the geodesic orbit Lorentz manifolds M=G/H such that a nilpotent analytic subgroup of G is transitive on M. Suppose that there is a reductive decomposition g=h⊕n (vector space direct sum) with n nilpotent. When the metric is nondegenerate on [n,n], we show that n is abelian or 2-step nilpotent (this is the same result as for geodesic orbit Riemannian nilmanifolds), and when the metric is degenerate on [n,n], we show that n is a Lorentz double extension corresponding to a geodesic orbit Riemannian nilmanifold. In the latter case, we construct examples to show that the number of nilpotency steps is unbounded.
Excitation in MRI is traditionally done at the Larmor frequency, where the energy of each radiofrequency photon corresponds to the energy difference between two spin states. However, if multiple radiofrequencies are employed, then multiphoton excitation can also occur when the sum or difference of multiple photon frequencies equals the Larmor frequency. Although multiphoton excitation has been known since the early days of NMR, it has been relatively unexplored in MRI. In this work, equations and principles for multiphoton selective RF pulse design in imaging are presented and experimentally demonstrated. In particular, the case where there are radiofrequency fields in both the traditional xy-direction and non-traditional z-direction is considered. To produce the z-direction radiofrequency field, an additional uniform coil was added to a clinical MRI scanner. Using this coil, two-photon slice-selective pulses were designed to be equivalent to traditional pulses, producing similar excitation, slice profiles, and in vivo images. Being the result of a combination of multiple radiofrequency fields instead of just one, two-photon pulses have more flexibility in how their parameters can be changed. Although individual multiphoton excitations are less efficient than their traditional counterparts, when the z-direction radiofrequency field is spatially non-uniform, multiple multiphoton resonances can be simultaneously used at different locations to produce simultaneous multislice excitation with the same pulse duration but less tissue heating than a naive implementation. In particular, non-uniform z-direction radiofrequency fields with negligible added tissue heating provided by oscillating the MRI scanner's gradient fields at kilohertz frequencies were used to excite multiple slices simultaneously with less high-frequency xy-direction radiofrequency power. For an example three-slice excitation, we achieve half the xy-direction radiofrequency power compared to the naïve approach of adding three single-slice pulses. For conventional or unconventional applications, multiphoton excitation may be of interest when designing new MRI systems.
We examined the role of different types of similarity in both analogical reasoning and recognition memory. On recognition tasks, people more often falsely report having seen a recombined word pair (e.g., flower: garden) if it instantiates the same semantic relation (e.g., is a part of) as a studied word pair (e.g., house: town). This phenomenon, termed relational luring, has been interpreted as evidence that explicit relation representations-known to play a central role in analogical reasoning also impact episodic memory. We replicate and extend previous studies, showing that relation-based false alarms in recognition memory occur after participants encode word pairs either by making relatedness judgments about individual words presented sequentially, or by evaluating analogies between pairs of word pairs. To test alternative explanations of relational luring, we implemented an established model of recognition memory, the Generalized Context Model (GCM). Within this basic framework, we compared representations of word pairs based on similarities derived either from explicit relations or from lexical semantics (i.e., individual word meanings). In two experiments on recognition memory, best-fitting values of GCM parameters enabled both similarity models (even the model based solely on lexical semantics) to predict relational luring with comparable accuracy. However, the model based on explicit relations proved more robust to parameter variations than that based on lexical similarity. We found this same pattern of modeling results when applying GCM to an independent set of data reported by Popov, Hristova, and Anders (2017). In accord with previous work, we also found that explicit relation representations are necessary for modeling analogical reasoning. Our findings support the possibility that explicit relations, which are central to analogical reasoning, also play an important role in episodic memory.
Solar extreme ultraviolet (EUV) radiation, the solar wind, and solar energetic particles (SEPs) are variable sources of ionization and heating to the Martian atmosphere. Mars Atmosphere Volatile Evolution’s (MAVEN's) elliptical orbit provides a means to characterize these solar drivers immediately upstream of Mars. We have calculated the energy fluxes of EUV, solar wind, and SEPs while MAVEN is outside of the Martian induced magnetosphere. By time‐averaging observations over 2–5 month periods, we reduced short‐term variability to resolve seasonal and solar cycle trends. For the duration spanning the declining phase of solar cycle 24 and three Mars years, the calculated energy fluxes in units of 10⁹ eV/cm²/s were 650–1,400 for EUV, 77–180 for solar wind ions, 2.4–7.4 for solar wind electrons, 0.01–2.7 for SEP ions, and 0–0.4 for SEP electrons. We estimated the fraction of these energy fluxes that would reach the atmosphere and determined that precipitating particle fluxes on the dayside would need to exceed 10¹² eV/cm²/s to compare to EUV. We also predicted that SEPs may impart as much or more energy flux than solar wind electrons on the nightside during periods of strong and weak coronal mass ejection activity. We then discussed and decoupled seasonal variation from the solar drivers to reveal trends and outliers as a function of solar cycle. Finally, we compared MAVEN observations during a weak solar cycle to prior estimates of EUV, solar wind, and SEPs from the young sun, and identified times when MAVEN‐observed peak energy fluxes were close to the steady‐state energy fluxes of the ancient solar system.
Species whose ranges encompass substantial environmental variation should experience heterogeneous selection, potentially resulting in local adaptation. Repeated covariation between phenotype and environment across ecologically similar species inhabiting similar environments provides strong evidence for adaptation. Lesser Antillean anoles present an excellent system in which to study repeated local adaptation because most species are widespread generalists occurring throughout environmentally heterogenous island landscapes. We leveraged this natural replication to test the hypothesis that intraspecific variation in phenotype (coloration and morphology) is consistently associated with environment across nine species of bimaculatus series anoles. We measured dorsal coloration from 173 individuals from six species and 16 morphological traits from 883 individuals from nine species, spanning their island ranges. We identified striking, but incomplete, parallelism in dorsal coloration associated with annual precipitation in our study species. By contrast, we observed significant patterns of morphological isolation-by-environment in only two species and no signal of parallel morphological evolution. Collectively, our results reveal strong divergent natural selection by environment on dorsal coloration but not morphology.
This article examines To T, or Not To T?, a solo play by D’Lo, a queer transmasculine Sri Lankan Tamil American performance artist and comedian. Considering the Super Aunty character, I examine how aunties orient diasporic life towards multiple modes of belonging and exclusion. Specifically, I explore how Aunty Discipline directed toward the queer diasporic child is vital in creating future hetero-reproductive diasporic subjects, then consider the intimacies of fictive kinship through the term ‘fam’. The queer diasporic body is a text on which others enact diasporic meanings, but D’Lo uses that very queer body to actively reimagine and re-image family and community, thereby infusing these spaces with his own queer ontologies and epistemologies.
The primary scientific goal of ICARUS (Investigation of Coronal AcceleRation and heating of solar wind Up to the Sun), a mother-daughter satellite mission, proposed in response to the ESA “Voyage 2050” Call, will be to determine how the magnetic field and plasma dynamics in the outer solar atmosphere give rise to the corona, the solar wind, and the entire heliosphere. Reaching this goal will be a Rosetta Stone step, with results that are broadly applicable within the fields of space plasma physics and astrophysics. Within ESA’s Cosmic Vision roadmap, these science goals address Theme 2: “How does the Solar System work?” by investigating basic processes occurring “From the Sun to the edge of the Solar System”. ICARUS will not only advance our understanding of the plasma environment around our Sun, but also of the numerous magnetically active stars with hot plasma coronae. ICARUS I will perform the first direct in situ measurements of electromagnetic fields, particle acceleration, wave activity, energy distribution, and flows directly in the regions in which the solar wind emerges from the coronal plasma. ICARUS I will have a perihelion altitude of 1 solar radius and will cross the region where the major energy deposition occurs. The polar orbit of ICARUS I will enable crossing the regions where both the fast and slow winds are generated. It will probe the local characteristics of the plasma and provide unique information about the physical processes involved in the creation of the solar wind. ICARUS II will observe this region using remote-sensing instruments, providing simultaneous, contextual information about regions crossed by ICARUS I and the solar atmosphere below as observed by solar telescopes. It will thus provide bridges for understanding the magnetic links between the heliosphere and the solar atmosphere. Such information is crucial to our understanding of the plasma physics and electrodynamics of the solar atmosphere. ICARUS II will also play a very important relay role, enabling the radio-link with ICARUS I. It will receive, collect, and store information transmitted from ICARUS I during its closest approach to the Sun. It will also perform preliminary data processing before transmitting it to Earth. Performing such unique in situ observations in the area where presumably hazardous solar energetic particles are energized, ICARUS will provide fundamental advances in our capabilities to monitor and forecast the space radiation environment. Therefore, the results from the ICARUS mission will be extremely crucial for future space explorations, especially for long-term crewed space missions.
The dynamical structure of ecological communities results from interactions among taxa that change with shifts in species composition in space and time. However, our ability to study the interplay of ecological and evolutionary processes on community assembly remains relatively unexplored due to the difficulty of measuring community structure over long temporal scales. Here, we made use of a geological chronosequence across the Hawaiian Islands, representing 50 years to 4.15 million years of ecosystem development, to sample 11 communities of arthropods and their associated plant taxa using semi-quantitative DNA metabarcoding. We then examined how ecological communities changed with community age by calculating quantitative network statistics for bipartite networks of arthropod-plant associations. The average number of interactions per species (linkage density), ratio of plant to arthropod species (vulnerability), and uniformity of energy flow (interaction evenness) increased significantly in concert with community age. The index of specialization H2 ' has a curvilinear relationship with community age. Our analyses suggest that younger communities are characterized by fewer but stronger interactions, while biotic associations become more even and diverse as communities mature. These shifts in structure became especially prominent on East Maui (~0.5 my) and older volcanos, after enough time had elapsed for adaptation and specialization to act on populations in situ. Such natural progression of specialization during community assembly is likely impeded by the rapid infiltration of non-native species, with special risk to younger or more recently disturbed communities that are composed of fewer specialized relationships.
Earthquake focal mechanisms, determined with P‐wave polarities and S/P amplitude ratios, are primary data for analyzing fault zone geometry, sense of slip, and the crustal stress field. Solving for the focal mechanisms of small earthquakes is often challenging because phase arrivals and first‐motion polarities are hard to be separated from noise. To overcome this challenge, we implement convolutional‐neural‐network algorithms (Ross, Meier, & Hauksson, 2018, Ross, Meier, Hauksson, & Heaton, 2018, https://doi.org/10.1029/2017jb015251, https://doi.org/10.1785/0120180080) to detect additional phases and polarities. Using both existing and these new data, we build a high‐quality focal mechanism catalog of 297,478 events that occurred from 1981 to 2021 in southern California with the HASH method of Hardebeck and Shearer (2002), https://doi.org/10.1785/0120010200, Hardebeck and Shearer (2003), https://doi.org/10.1785/0120020236. The new focal mechanism catalog is overall consistent with the standard catalog (Yang et al., 2012, https://doi.org/10.1785/0120110311) but includes 40% more focal mechanisms, and is more consistent with moment tensor solutions derived using waveform‐fitting methods. We apply the new catalog to identify changes in focal mechanism properties caused by the occurrences of large mainshocks such as the 2010 Mw7.2 El Mayor‐Cucapah and 2019 Mw7.1 Ridgecrest earthquakes. Such changes may be associated with co‐seismic stress drops, post‐seismic deformation processes, and static stress changes on a regional scale. The new high‐resolution catalog will contribute to improved understanding of the crustal stress field, earthquake triggering mechanisms, fault zone geometry, and sense of slip on the faults in southern California.
Objective: To understand which anthropometric diagnostic criteria best discriminate higher from lower risk of death in children and explore programme implications. Design: A multiple cohort individual data meta-analysis of mortality risk (within six months of measurement) by anthropometric case definitions. Sensitivity, specificity, informedness and inclusivity in predicting mortality, face validity and compatibility with current standards and practice were assessed and operational consequences modelled. Setting: Community-based cohort studies in 12 low-income countries between 1977 and 2013 in settings where treatment of wasting was not widespread. Participants: Children aged 6 to 59 months. Results: Of the 12 anthropometric case definitions, four (weight-for-age Z-score (WAZ) <-2), (mid-upper-arm circumference (MUAC) <125 mm), (MUAC <115 mm or WAZ <-3), and (WAZ <-3) had the highest informedness in predicting mortality. A combined case definition (MUAC <115 mm or WAZ <-3) was better at predicting deaths associated with weight-for-height Z-score (WHZ) <-3 and concurrent wasting and stunting (WaSt) than the single WAZ <-3 case-definition. After assessment of all criteria, the combined case definition performed best. The simulated workload for programmes admitting based on MUAC <115 mm or WAZ <-3, when adjusted with a proxy for required intensity and/or duration of treatment, was 1.87 times larger than programmes admitting on MUAC <115 mm alone. Conclusions: A combined case definition detects nearly all deaths associated with severe anthropometric deficits suggesting that therapeutic feeding programmes may achieve higher impact (prevent mortality and improve coverage) by using it. There remain operational questions to examine further before wide-scale adoption can be recommended.
Sensitivity studies of the i process have identified the region around ¹³⁵I as a bottleneck for the neutron capture flow. Nuclear properties such as the Maxwellian-averaged cross section (MACS) are key to constrain the uncertainties in the final abundance patterns. From the ¹²⁴Sn(α, pγ)¹²⁷Sb reaction we are able to indirectly measure the nuclear level density and γ-ray strength function for ¹²⁷Sb using the Oslo method. From these two quantities we can calculate the MACS for the ¹²⁶Sb(n, γ)¹²⁷Sb reaction using the Hauser-Feshbach formalism, constrain its uncertainties and compare it to libraries such as JINA REACLIB, TENDL and BRUSLIB.
Background Understanding the predictors of adverse clinical outcomes following incident Clostridiodes difficile infection (CDI) can help clinicians identify which patients are at risk of complications and help prioritize the provision of their care. In this study, we assessed the associations between epidemiologic case definition categories and adverse clinical outcomes in patients with CDI in San Francisco County, California. Methods We conducted a retrospective cohort study using CDI surveillance data (n = 3274) from the California Emerging Infections Program for the time period 2016 to 2020. After independent associations were established, two multivariable logistic and log-binomial regression models were constructed for the final statistical analysis. Result The mean cumulative incidence of CDI cases was 78.8 cases per 100,000 population. The overall recurrence rate and the 30-day all-cause mortality rate were 11.1% and 4.5%, respectively. After adjusting for potential confounders, compared to the community associated CDI cases, healthcare facility onset (AOR = 3.1; 95% CI [1.3–7]) and community-onset-healthcare facility associated (AOR = 2.4; 95% CI [1.4–4.3]) CDI cases were found to have higher odds of all-cause 30-day mortality. Community onset-healthcare facility-associated CDI case definition category was found to be significantly associated with an increased risk of recurrence of CDI (ARR = 1.7; 95% CI [1.2–2.4]). Conclusion Although the incidence of community-associated CDI cases has been rising, the odds of all-cause 30-day mortality and the risk of recurrent CDI associated with these infections are lower than healthcare facility onset and community-onset healthcare facility-associated CDI cases.
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Fernando de Juan
  • Department of Physics
Despina Lymperopoulou
  • Department of Plant and Microbial Biology
Peter Hosemann
  • Department of Nuclear Engineering
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