Publications

From social networks to language modeling, the growing scale and importance of graph data has driven the development of numerous new graph-parallel systems (e.g., Pregel, GraphLab). By restricting the computation that can be expressed and introducing new techniques to partition and distribute the graph, these systems can efficiently execute iterative graph algorithms orders of magnitude faster than more general data-parallel systems. However, the same restrictions that enable the performance gains also make it difficult to express many of the important stages in a typical graph-analytics pipeline: constructing the graph, modifying its structure, or expressing computation that spans multiple graphs. As a consequence, existing graph analytics pipelines compose graph-parallel and data-parallel systems using external storage systems, leading to extensive data movement and complicated programming model. To address these challenges we introduce GraphX, a distributed graph computation framework that unifies graph-parallel and data-parallel computation. GraphX provides a small, core set of graph-parallel operators expressive enough to implement the Pregel and PowerGraph abstractions, yet simple enough to be cast in relational algebra. GraphX uses a collection of query optimization techniques such as automatic join rewrites to efficiently implement these graph-parallel operators. We evaluate GraphX on real-world graphs and workloads and demonstrate that GraphX achieves comparable performance as specialized graph computation systems, while outperforming them in end-to-end graph pipelines. Moreover, GraphX achieves a balance between expressiveness, performance, and ease of use.

Co-based oxides are suitable electrode materials for the electrocatalytic oxygen evolution reaction (OER) with promising activity and stability, in addition to being widely available and relatively cheap. We investigate OER on Co3O4(001) and β-CoOOH (011̅2) surfaces using density functional theory calculations (DFT). We construct surface Pourbaix diagrams and investigate the theoretical overpotential for the elementary steps involved in OER on these surfaces. We show that inclusion of the Hubbard-U correction to DFT (DFT+U) is necessary to recover experimentally observed trends in the activity for the strongly correlated cobalt oxides. We find that the inclusion of the Hubbard-U correction lowers the activity of both Co3O4(001) and β-CoOOH(011̅2) when compared to results from pure DFT. In addition, the Hubbard-U correction shifts the location of Co3O4 and β-CoOOH from the strong binding leg to the weak binding leg of the OER volcano plot. The calculations also suggest that the theoretical overpotentials for Co3O4 and β-CoOOH are very nearly the same. We ascribe this to a similar local coordination environment of the active Co site in Co3O4 and CoOOH under OER conditions.

We present optical and infrared (IR) light curves of the enshrouded massive binary NaSt1 (WR 122) with observations from Palomar Gattini-IR (PGIR), the Zwicky Transient Facility (ZTF), the Katzman Automatic Imaging Telescope (KAIT), and the All-Sky Automated Survey for Supernovae (ASAS-SN). The optical and IR light curves span between 2014 July and 2020 Oct., revealing periodic, sinusoidal variability from NaSt1 with a $P=305.2\pm1.0$ d period. We also present historical IR light curves taken between 1983 July and 1989 May that also indicate NaSt1 exhibits long-term IR variability on timescales of $\sim$decades. Fixed-period sinusoidal fits to the recent optical and IR light curves show that amplitude of NaSt1's variability is different at different wavelengths and also reveal significant phase offsets of $\sim18$ d between the ZTF $r$ and PGIR $J$ light curves.We interpret the $\sim300$ d period of the observed variability as the orbital period of a binary system in NaSt1. Assuming a circular orbit and adopting a range of combined stellar mass values in the range 20-100 M$_\odot$ in NaSt1, we estimate orbital separations of $\sim2$-4 au. We suggest that the sinusoidal photometric variability of NaSt1 may arise from variations in the line-of-sight optical depth toward circumstellar optical/IR emitting regions throughout its orbit due to colliding-wind dust formation. We provide an interpretation on the nature of NaSt1 and speculate that the mass-transfer process may have been triggered by Roche-lobe overflow (RLOF) during an eruptive phase of a Ofpe/WN9 star. Lastly, we claim that NaSt1 ceased RLOF mass transfer $\lesssim3400$ yr ago.

Lignin samples isolated from Miscanthus giganteus using organosolv processes were treated with vanadium catalysts that were previously developed in our group. We demonstrate that the catalyst with high β-O-4′ bond-cleaving activity in dimeric lignin models was also effective in depolymerizing actual lignin. Molecular weight-lowering was evidenced by gel permeation chromatography (GPC), whereas 2D NMR experiments showed that β-O-4′ linkages were selectively cleaved in the degradation process, just as in the case of lignin models. Monophenolic degradation products were also formed, and the individual molecules were identified and quantified by GC/MS.

As Moore's law has marched forward, progressively shrinking chip designs at a consistent pace, the manufacturing of those chips has raced to keep up. Through advances in lithography hardware and software, we now are in the realm of the single-digit-nanometer design nodes at leading chip foundries. This paper will review the method of Inverse Lithography Technology (ILT), which is the preferred computational method for photolithography. Indeed photolithographic masks were the first metasurfaces, and still the most important metasurface, economically, used in memory chips, storage, and microprocessors. Moreover, photolithographic mask designers were the early adopters of the mathematical optimization in optics, creating ILT, specifying intended wafer patterns and metrics, and using the mathematical machinery of level sets, functional derivatives, and adjoints to drive the mask design process.

peer reviewed

We have identified a progenitor candidate in archival Hubble Space Telescope (HST) images for the Type Ic supernova (SN Ic) SN 2017ein in NGC 3938, pinpointing the candidate's location via HSTTarget of Opportunity imaging of the SN itself. This would be the first identification of a stellar-like object as a progenitor candidate for any SN Ic to date. We also present observations of SN 2017ein during the first ~49 days since explosion. We find that SN 2017ein most resembles the well-studied SN Ic SN 2007gr. We infer that SN 2017ein experienced a total visual extinction of A_V ≈ 1.0–1.9 mag, predominantly because of dust within the host galaxy. Although the distance is not well known, if this object is the progenitor, it was likely of high initial mass, ~47–48 M⊙ if a single star, or ~60–80 M⊙ if in a binary system. However, we also find that the progenitor candidate could be a very blue and young compact cluster, further implying a very massive (>65 M⊙) progenitor. Furthermore, the actual progenitor might not be associated with the candidate at all and could be far less massive. From the immediate stellar environment, we find possible evidence for three different populations; if the SN progenitor was a member of the youngest population, this would be consistent with an initial mass of ~57 M⊙. After it has faded, the SN should be reobserved at high spatial resolution and sensitivity, to determine whether the candidate is indeed the progenitor.

Here, experiments and analysis revealing the unique defense mechanisms of the coelacanth, a lobe‐finned fish termed a “living fossil”, are reported, as it was considered to be extinct until 1938, but extant for 400 million years. This defense is provided by primitive elasmoid scales having a rare double‐twisted Bouligand structure of lamellae which provides extraordinary resistance to deformation without failure. Distinct from other elasmoid scales, the collagen fibrils in the coelacanth fish scales form bundles which are embedded in a matrix comprising fibers arranged perpendicular to the layered (double‐twisted Bouligand) structure that provide added rigidity and resistance to deformation. Using in situ synchrotron small‐angle X‐ray scattering during uniaxial tensile testing, the deformation mechanisms of the collagen are identified in terms of fibril stretching, reorientation, sliding, bending, and delamination. The unique structure of the coelacanth scales, distinct from modern elasmoid scales such as the carp, provides a variety of mechanisms to arrest cracking, making it an outstanding damage‐tolerant material to resist predator attacks.

We present SAM 3D, a generative model for visually grounded 3D object reconstruction, predicting geometry, texture, and layout from a single image. SAM 3D excels in natural images, where occlusion and scene clutter are common and visual recognition cues from context play a larger role. We achieve this with a human- and model-in-the-loop pipeline for annotating object shape, texture, and pose, providing visually grounded 3D reconstruction data at unprecedented scale. We learn from this data in a modern, multi-stage training framework that combines synthetic pretraining with real-world alignment, breaking the 3D "data barrier". We obtain significant gains over recent work, with at least a 5:1 win rate in human preference tests on real-world objects and scenes. We will release our code and model weights, an online demo, and a new challenging benchmark for in-the-wild 3D object reconstruction.

Hybrid nanocatalysts consisting of metal nanoparticle-semiconductor junctions offer an interesting platform to study the role of metal-oxide interfaces and hot electron flows in heterogeneous catalysis. Here, we report that hot carriers generated upon photon absorption significantly impact the catalytic activity of CO oxidation. We found that Pt-CdSe-Pt nanodumbbells exhibit a higher turnover frequency by a factor of 2 during irradiation by light with energy higher than the bandgap of CdSe, while the turnover rate on bare Pt nanoparticles did not depend on light irradiation. We found that Pt nanoparticles deposited on a GaN substrate under light irradiation exhibit changes in catalytic activity of CO oxidation that depends on the type of doping of the GaN. We suppose that hot electrons are generated upon the absorption of photons by the semiconducting nanorods or substrates, whereafter the hot electrons are injected into the Pt nanoparticles, resulting in the change in catalytic activity. The results imply that hot carrier flows generated during light irradiation significantly influence the catalytic activity of CO oxidation, leading to potential applications as a hot electron-based catalytic actuator.