Publications

To accurately describe gene expression and computationally model animal transcriptional networks, it is essential to determine the changing locations of cells in developing embryos. Using automated image analysis methods, we provide the first quantitative description of temporal changes in morphology and gene expression at cellular resolution in whole embryos, using the Drosophila blastoderm as a model. Analyses based on both fixed and live embryos reveal complex, previously undetected three-dimensional changes in nuclear density patterns caused by nuclear movements prior to gastrulation. Gene expression patterns move, in part, with these changes in morphology, but additional spatial shifts in expression patterns are also seen, supporting a previously proposed model of pattern dynamics based on the induction and inhibition of gene expression. We show that mutations that disrupt either the anterior/posterior (a/p) or the dorsal/ ventral (d/v) transcriptional cascades alter morphology and gene expression along both the a/p and d/v axes in a way suggesting that these two patterning systems interact via both transcriptional and morphological mechanisms. Our work establishes a new strategy for measuring temporal changes in the locations of cells and gene expression patterns that uses fixed cell material and computational modeling. It also provides a coordinate framework for the blastoderm embryo that will allow increasingly accurate spatio-temporal modeling of both the transcriptional control network and morphogenesis.

Multi-tenant transactional databases frequently observe contention on shared data, leading to a need for performance isolation. Databases typically provide performance isolation via a request rate limit or quota per tenant, but this approach can lead to system underutilization. Traditionally, fair sharing has been applied to achieve both performance isolation and high utilization in other domains. In this paper, we address the problem of fair sharing for transactions, which introduces new challenges because client requests do not acquire resources all at once. We propose DRFT, the first fair transaction scheduling algorithm that ensures both the share guarantee and strategy-proofness by accurately accounting for transactional resource usage. We evaluate DRFT on a range of standard benchmarks and real-world workloads, showing that it ensures fairness with less than a 5% throughput overhead compared to state-of-the-art scheduling policies.

Technologically important mechanical properties of engineering materials often degrade at low temperatures. One class of materials that defy this trend are CrCoNi-based medium- and high-entropy alloys, as they display enhanced strength, ductility, and toughness with decreasing temperature. Here we show, using in situ straining in the transmission electron microscope at 93 K (−180 °C) that their exceptional damage tolerance involves a synergy of deformation mechanisms, including twinning, glide of partials and full dislocations, extensive cross-slip, and multiple slip activated by dislocation and grain-boundary interactions. In particular, massive cross-slip occurs at the early stages of plastic deformation, thereby promoting multiple slip and dislocation interactions. These results indicate that the reduced intensity of thermal activation of defects at low temperatures and the required increase of applied stress for continued plastic flow, together with high lattice resistance, play a pivotal role in promoting the concurrent operation of multiple deformation mechanisms, which collectively enable the outstanding mechanical properties of these alloys.

ABSTRACT SN 2008es is one of the rare cases of a Type II superluminous supernova (SLSN), showing no narrow features in its early-time spectra, and therefore, its powering mechanism is under debate between circumstellar interaction (CSI) and magnetar spin-down. Late-time data are required for better constraints. We present optical and near-infrared (NIR) photometry obtained from Gemini, Keck, and Palomar Observatories from 192 to 554 d after explosion. Only broad H α emission is detected in a Gemini spectrum at 288 d. The line profile exhibits red-wing attenuation relative to the early-time spectrum. In addition to the cooling SN photosphere, an NIR excess with blackbody temperature ∼1500 K and radius ∼1016 cm is observed. This evidence supports dust condensation in the cool dense shell being responsible for the spectral evolution and NIR excess. We favour CSI, with ∼2–3 M⊙ of circumstellar material (CSM) and ∼10–20 M⊙ of ejecta, as the powering mechanism, which still dominates at our late-time epochs. Both models of uniform density and steady wind fit the data equally well, with an effective CSM radius ∼1015 cm, supporting the efficient conversion of shock energy to radiation by CSI. A low amount (≲0.4 M⊙) of 56Ni is possible but cannot be verified yet, since the light curve is dominated by CSI. The magnetar spin-down powering mechanism cannot be ruled out, but is less favoured because it overpredicts the late-time fluxes and may be inconsistent with the presence of dust.

Abstract Solid‐state packing plays a defining role in the properties of a molecular organic material, but it is difficult to elucidate in the absence of single crystals that are suitable for X‐ray diffraction. Herein, we demonstrate the coupling of divergent synthesis with microcrystal electron diffraction (MicroED) for rapid assessment of solid‐state packing motifs, using a class of chiral nanocarbons—expanded helicenes—as a proof of concept. Two highly selective oxidative dearomatizations of a readily accessible helicene provided a divergent route to four electron‐deficient analogues containing quinone or quinoxaline units. Crystallization efforts consistently yielded microcrystals that were unsuitable for single‐crystal X‐ray diffraction, but ideal for MicroED. This technique facilitated the elucidation of solid‐state structures of all five compounds with <1.1 Å resolution. The otherwise‐inaccessible data revealed a range of notable packing behaviors, including four different space groups, homochirality in a crystal for a helicene with an extremely low enantiomerization barrier, and nanometer scale cavities.

This paper proposes an adaptive near-hover position controller for quadcopters, which can be deployed to quadcopters of very different mass, size and motor constants, and also shows rapid adaptation to unknown disturbances during runtime. The core algorithmic idea is to learn a single policy that can adapt online at test time not only to the disturbances applied to the drone, but also to the robot dynamics and hardware in the same framework. We achieve this by training a neural network to estimate a latent representation of the robot and environment parameters, which is used to condition the behaviour of the controller, also represented as a neural network. We train both networks exclusively in simulation with the goal of flying the quadcopters to goal positions and avoiding crashes to the ground. We directly deploy the same controller trained in the simulation without any modifications on two quadcopters in the real world with differences in mass, size, motors, and propellers with mass differing by 4.5 times. In addition, we show rapid adaptation to sudden and large disturbances up to one-third of the mass of the quadcopters. We perform an extensive evaluation in both simulation and the physical world, where we outperform a state-of-the-art learning-based adaptive controller and a traditional PID controller specifically tuned to each platform individually. Video results can be found at https://youtu.be/U-c-LbTfvoA.

Abstract Mono‐ and diterpenoids are of great industrial and medical value as specialty chemicals and pharmaceuticals. Production of these compounds in microbial hosts, such as Escherichia coli, can be limited by intracellular levels of the polyprenyl diphosphate precursors, geranyl diphosphate (GPP), and geranylgeranyl diphosphate (GGPP). To alleviate this limitation, we constructed synthetic operons that express three key enzymes for biosynthesis of these precursors: (1) DXS,1‐deoxy‐ d ‐xylulose‐5‐phosphate synthase; (2) IPPHp, IPP isomerase from Haematococcus pluvialis ; and (3) one of two variants of IspA, FPP synthase that produces either GPP or GGPP. The reporter plasmids pAC‐LYC and pACYC‐IB, which encode enzymes that convert either FPP or GGPP, respectively, to the pigment lycopene, were used to demonstrate that at full induction, the operon encoding the wild‐type FPP synthase and mutant GGPP synthase produced similar levels of lycopene. To synthesize di‐ or monoterpenes in E. coli using the GGPP and GPP encoding operons either a diterpene cyclase [casbene cyclase ( Ricinus communis L ) and ent ‐kaurene cyclase ( Phaeosphaeria sp. L487)] or a monoterpene cyclase [3‐carene cyclase ( Picea abies )] was coexpressed with their respective precursor production operon. Analysis of culture extracts or headspace by gas chromatography‐mass spectrometry confirmed the in vivo production of the diterpenes casbene, kaur‐15‐ene, and kaur‐16‐ene and the monoterpenes α‐pinene, myrcene, sabinene, 3‐carene, α‐terpinene, limonene, β‐phellandrene, α‐terpinene, and terpinolene. Construction and functional expression of GGPP and GPP operons provides an in vivo precursor platform host for the future engineering of di‐ and monoterpene cyclases and the overproduction of terpenes in bacteria. © 2004 Wiley Periodicals, Inc.