Publications

Restoring degraded peat soils presents an attractive, but largely untested, climate change mitigation approach. Drained peat soils used for agriculture can be large greenhouse gas sources. By restoring subsided peat soils to managed, impounded wetlands, significant agricultural emissions are avoided, and soil carbon can be sequestered and protected. Here, we synthesize 36 site-years of continuous carbon dioxide and methane flux data from a mesonetwork of eddy covariance towers in the Sacramento-San Joaquin Delta in California, USA to compute carbon and greenhouse gas budgets for drained agricultural land uses and compare these to restored deltaic wetlands. We found that restored wetlands effectively sequestered carbon and halted soil carbon loss associated with drained agricultural land uses. Depending on the age and disturbance regime of the restored wetland, many land use conversions from agriculture to restored wetland resulted in emission reductions over a 100-year timescale. With a simple model of radiative forcing and atmospheric lifetimes, we showed that restored wetlands do not begin to accrue greenhouse gas benefits until nearly a half century, and become net sinks from the atmosphere after a century. Due to substantial interannual variability and uncertainty about the multi-decadal successional trajectory of managed, restored wetlands, ongoing ecosystem flux measurements are critical for understanding the long-term impacts of wetland restoration for climate change mitigation.

We exploit the complementary strengths of vision and proprioception to develop a point-goal navigation system for legged robots, called VP-Nav. Legged systems are capable of traversing more complex terrain than wheeled robots, but to fully utilize this capability, we need a high-level path planner in the navigation system to be aware of the walking capabilities of the low-level locomotion policy in varying environments. We achieve this by using proprioceptive feedback to ensure the safety of the planned path by sensing unexpected obstacles like glass walls, terrain properties like slipperiness or softness of the ground and robot properties like extra payload that are likely missed by vision. The navigation system uses onboard cameras to generate an occupancy map and a corresponding cost map to reach the goal. A fast marching planner then generates a target path. A velocity command generator takes this as input to generate the desired velocity for the walking policy. A safety advisor module adds sensed unexpected obstacles to the occupancy map and environment-determined speed limits to the velocity command generator. We show superior performance compared to wheeled robot baselines, and ablation studies which have disjoint high-level planning and low-level control. We also show the real-world deployment of VP-Nav on a quadruped robot with onboard sensors and computation. Videos at https://navigation-locomotion.github.io

The Sloan Digital Sky Survey-II (SDSS-II) has embarked on a multi-year project to identify and measure light curves for intermediate-redshift (0.05 < z < 0.35) Type Ia supernovae (SNe Ia) using repeated five-band (ugriz) imaging over an area of 300 sq. deg. The survey region is a stripe 2.5° wide centered on the celestial equator in the Southern Galactic Cap that has been imaged numerous times in earlier years, enabling construction of a deep reference image for the discovery of new objects. Supernova imaging observations are being acquired between September 1 and November 30 of 2005-7. During the first two seasons, each region was imaged on average every five nights. Spectroscopic follow-up observations to determine supernova type and redshift are carried out on a large number of telescopes. In its first two three-month seasons, the survey has discovered and measured light curves for 327 spectroscopically confirmed SNe Ia, 30 probable SNe Ia, 14 confirmed SNe Ib/c, 32 confirmed SNe II, plus a large number of photometrically identified SNe Ia, 94 of which have host-galaxy spectra taken so far. This paper provides an overview of the project and briefly describes the observations completed during the first two seasons of operation.

ABSTRACT Optical spectropolarimetry of the normal thermonuclear supernova (SN) 2019np from −14.5 to +14.5 d relative to B-band maximum detected an intrinsic continuum polarization (pcont) of 0.21 ± 0.09 per cent at the first epoch. Between days −11.5 and +0.5, pcont remained ∼0 and by day +14.5 was again significant at 0.19 ± 0.10 per cent. Not considering the first epoch, the dominant axis of ${\rm Si\, {\small II}}$ λ6355 was roughly constant staying close the continuum until both rotated in opposite directions on day +14.5. Detailed radiation-hydrodynamical simulations produce a very steep density slope in the outermost ejecta so that the low first-epoch pcont ≈ 0.2 per cent nevertheless suggests a separate structure with an axis ratio ∼2 in the outer carbon-rich (3.5–4) × 10−3 M⊙. Large-amplitude fluctuations in the polarization profiles and a flocculent appearance of the polar diagram for the ${\rm Ca\, {\small II}}$ near-infrared triplet (NIR3) may be related by a common origin. The temporal evolution of the polarization spectra agrees with an off-centre delayed detonation. The late-time increase in polarization and the possible change in position angle are also consistent with an aspherical 56Ni core. The pcont and the absorptions due to ${\rm Si\, {\small II}}$ λ6355 and ${\rm Ca\, {\small II}}$ NIR3 form in the same region of the extended photosphere, with an interplay between line occultation and thermalization producing p. Small-scale polarization features may be due to small-scale structures, but many could be related to atomic patterns of the quasi-continuum; they hardly have an equivalent in the total-flux spectra. We compare SN 2019np to other SNe and develop future objectives and strategies for SN Ia spectropolarimetry.

Abstract Taxadien‐5α‐hydroxylase and taxadien‐5α‐ol O ‐acetyltransferase catalyze the oxidation of taxadiene to taxadien‐5α‐ol and subsequent acetylation to taxadien‐5α‐yl‐acetate in the biosynthesis of the blockbuster anticancer drug, paclitaxel (Taxol®). Despite decades of research, the promiscuous and multispecific CYP725A4 enzyme remains a major bottleneck in microbial biosynthetic pathway development. In this study, an interdisciplinary approach was applied for the construction and optimization of the early pathway in Saccharomyces cerevisiae , across a range of bioreactor scales. High‐throughput microscale optimization enhanced total oxygenated taxane titer to 39.0 ± 5.7 mg/L and total taxane product titers were comparable at micro and minibioreactor scale at 95.4 ± 18.0 and 98.9 mg/L, respectively. The introduction of pH control successfully mitigated a reduction of oxygenated taxane production, enhancing the potential taxadien‐5α‐ol isomer titer to 19.2 mg/L, comparable with the 23.8 ± 3.7 mg/L achieved at microscale. A combination of bioprocess optimization and increased gas chromatography‐mass spectrometry resolution at 1 L bioreactor scale facilitated taxadien‐5α‐yl‐acetate detection with a final titer of 3.7 mg/L. Total oxygenated taxane titers were improved 2.7‐fold at this scale to 78 mg/L, the highest reported titer in yeast. Critical parameters affecting the productivity of the engineered strain were identified across a range of scales, providing a foundation for the development of robust integrated bioprocess control systems.