Publications

The optical absorption properties of free-standing InAs nanomembranes of thicknesses ranging from 3 nm to 19 nm are investigated by Fourier transform infrared spectroscopy. Stepwise absorption at room temperature is observed, arising from the interband transitions between the subbands of 2D InAs nanomembranes. Interestingly, the absorptance associated with each step is measured to be ∼1.6%, independent of thickness of the membranes. The experimental results are consistent with the theoretically predicted absorptance quantum, A Q = πα/n c for each set of interband transitions in a 2D semiconductor, where α is the fine structure constant and n c is an optical local field correction factor. Absorptance quantization appears to be universal in 2D systems including III–V quantum wells and graphene.

Catalysis research at the U.S. Department of Energy’s (DOE’s) National Laboratories covers a wide range of research topics in heterogeneous catalysis, homogeneous/molecular catalysis, biocatalysis, electrocatalysis, and surface science. Because much of the work at National Laboratories is funded by DOE, the research is largely focused on addressing DOE’s mission to ensure America’s security and prosperity by addressing its energy, environmental, and nuclear challenges through transformative science and technology solutions. The catalysis research carried out at the DOE National Laboratories ranges from very fundamental catalysis science, funded by DOE’s Office of Basic Energy Sciences (BES), to applied research and development (R&D) in areas such as biomass conversion to fuels and chemicals, fuel cells, and vehicle emission control with primary funding from DOE’s Office of Energy Efficiency and Renewable Energy. National Laboratories are home to many DOE Office of Science national scientific user facilities that provide researchers with the most advanced tools of modern science, including accelerators, colliders, supercomputers, light sources, and neutron sources, as well as facilities for studying the nanoworld and the terrestrial environment. National Laboratory research programs typically feature teams of researchers working closely together, often joining scientists from different disciplines to tackle scientific and technical problems using a variety of tools and techniques available at the DOE national scientific user facilities. Along with collaboration between National Laboratory scientists, interactions with university colleagues are common in National Laboratory catalysis R&D. In some cases, scientists have joint appointments at a university and a National Laboratory. This ACS Catalysis Virtual Special Issue {http://pubs.acs.org/page/accacs/vi/doe-national-labs} was motivated by Christopher Jones and Rhea Williams, who sent out the invitations to all of DOE’s National Laboratories where catalysis research is conducted. All manuscripts submitted went through the standard rigorous peer review required for publication in ACS Catalysis. A total of 29 papers are published in this virtual special issue, which features some of the recent catalysis research at 11 of DOE’s National Laboratories: Ames Laboratory (Ames), Argonne National Laboratory (ANL), Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL), Lawrence Livermore National Laboratory (LLNL), National Energy Technology Laboratory (NETL), National Renewable Energy Laboratory (NREL), Oak Ridge National Laboratory (ORNL), Pacific Northwest National Laboratory (PNNL), Sandia National Laboratory (SNL), and SLAC National Accelerator Laboratory (SLAC). In this preface, we briefly discuss the history and impact of catalysis research at these particular DOE National Laboratories, where the majority of catalysis research continues to be conducted.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CrCoNi-based high-entropy alloys have demonstrated outstanding mechanical properties, particularly at cryogenic temperatures. Here we investigate the fatigue-crack propagation properties of the equiatomic, single-phase, face-centered cubic, medium-entropy alloy (MEA), CrCoNi, that displays exceptional strength, ductility and toughness, all of which are enhanced at cryogenic temperatures. Fatigue-crack growth is examined, at a load ratio of 0.1 over a wide range of growth rates, from ~10−11 to >10−7 m/cycle, at room (293 K) and cryogenic (198 K, 77 K) temperatures for two grain sizes (~7 and 68 µm), with emphasis on near-threshold behavior. We find that the ΔK th fatigue thresholds are increased with decreasing temperature and increasing grain size: from 5.7 MPa√m at 293 K to 8 MPa√m at 77 K in the fine-grained alloy, and from 9.4 MPa√m at 293 K to 13.7 MPa√m at 77 K in the coarse-grained alloy. Mechanistically, transgranular cracking at 293 K transitions to a mixture of intergranular and transgranular at cryogenic temperatures, where the increased propensity of nano-twins appears to inhibit growth rates by deflecting the crack path. However, the main factor affecting near-threshold behavior is roughness-induced crack closure from interference between the crack flanks, which is enhanced by the rougher fracture surfaces at low temperatures, particularly in the coarser-grained microstructure. Fatigue-crack propagation behavior in CrCoNi is comparable to nickel-based superalloys but is superior to that of the high-entropy CrMnFeCoNi (Cantor) alloy and many high-strength steels, making the CrCoNi alloy an excellent candidate material for safety-critical applications, particularly involving low temperatures.

Abstract The luminosities ( L ) and velocity dispersions ( σ ) of the extinction-corrected Balmer emission lines of giant H ii regions in nearby galaxies exhibit a tight correlation (∼0.35 dex scatter). There are few constraints, however, on whether giant H ii regions at significant look-back times follow an L – σ relation, given the angular resolution and sensitivity required to study them individually. We measure the luminosities and velocity dispersions of H α and H β emission from 11 H ii regions in Sp1149, a spiral galaxy at redshift ( z ) z = 1.49 multiply imaged by the MACS J1149 galaxy cluster. Sp1149 is also the host galaxy of the first-known strongly lensed supernova with resolved images, SN Refsdal. We employ archival Keck I OSIRIS observations, and newly acquired Keck I MOSFIRE and Large Binocular Telescope LUCI long-slit spectra of Sp1149. When we use the GLAFIC simply parameterized lens model, we find that the H α luminosities of the H ii regions at z = 1.49 are a factor of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>6.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.9</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> brighter than predicted by the low-redshift L – σ relation we measure from Very Large Telescope MUSE spectroscopy. If the lens model is accurate, then the H ii regions in Sp1149 differ from their low-redshift counterparts. We identify an H ii region in Sp1149 that is dramatically brighter (by 2.03 ± 0.44 dex) than our low-redshift L – σ relation predicts given its low velocity dispersion. Finally, the H ii regions in Sp1149 are consistent, perhaps surprisingly, with the z ≈ 0 star-forming locus on the Baldwin–Phillips–Terlevich diagram.

Reductive eliminations to form alkyl–nitrogen bonds are rare, and examples of this reaction from isolated complexes containing simple, unstabilized primary alkyl groups have not been observed. We report the synthesis of stable neopentylpalladium(II) anilido and methyleneamido complexes that undergo reductive elimination to form the C(sp3)–N bonds in N-neopentyl anilines and N-neopentyl imines, respectively. The synthesis and isolation of these complexes were enabled by weak chelation of palladium by P,O ancillary ligands. DFT calculations suggest that neopentylpalladium(II) complexes undergo reductive elimination by a concerted mechanism resembling a migration of the alkyl ligand to the nitrogen either following initial dissociation of the oxygen donor or in concert with lengthening of the Pd–O bond, depending on the identities of the reacting and ancillary ligands.

Water vapor sorption data and nitrogen sorption data for MOF-303 synthesized by solvothermal, reflux, vessel and microwave method.

SUMMARY In combination with advanced mechanistic modeling and the generation of high-quality multi-dimensional data sets, machine learning is becoming an integral part of understanding and engineering living systems. Here we show that mechanistic and machine learning models can complement each other and be used in a combined approach to enable accurate genotype-to-phenotype predictions. We use a genome-scale model to pinpoint engineering targets and produce a large combinatorial library of metabolic pathway designs with different promoters which, once phenotyped, provide the basis for machine learning algorithms to be trained and used for new design recommendations. The approach enables successful forward engineering of aromatic amino acid metabolism in yeast, with the new recommended designs improving tryptophan production by up to 17% compared to the best designs used for algorithm training, and ultimately producing a total increase of 106% in tryptophan accumulation compared to optimized reference designs. Based on a single high-throughput data-generation iteration, this study highlights the power of combining mechanistic and machine learning models to enhance their predictive power and effectively direct metabolic engineering efforts.