Publications

Spectroscopic Classification of DES14C3gqv from Keck

Regulatory control circuits for stabilizing long-term anabolic product formation in yeast

Abstract Engineering living cells for production of chemicals, enzymes and therapeutics can burden cells due to use of limited native co-factor availability and/or expression burdens, totalling a fitness deficit compared to parental cells encoded through long evolutionary trajectories to maximise fitness. Ultimately, this discrepancy puts a selective pressure against fitness-burdened engineered cells under prolonged bioprocesses, and potentially leads to complete eradication of high-performing engineered cells at the population level. Here we present the mutation landscapes of fitness-burdened yeast cells engineered for vanillin-β-glucoside production. Next, we design synthetic control circuits based on transcriptome analysis and biosensors responsive to vanillin-β-glucoside pathway intermediates in order to stabilize vanillin-β-glucoside production over ∼55 generations in sequential passage experiments. Furthermore, using biosensors with two different modes of action we identify control circuits linking vanillin-β-glucoside pathway flux to various essential cellular functions, and demonstrate control circuits robustness and 92% higher vanillin-β-glucoside production, including 5-fold increase in total vanillin-β-glucoside pathway metabolite accumulation, in a fed-batch fermentation compared to vanillin-β-glucoside producing cells without control circuits.

Inorganic Nanotubes: A Novel Platform for Nanofluidics

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Stablecoins: illusions, claims, and facts

Ultrafast XUV ARPES Studies of Electron and Exciton Dynamics in the Transition-Metal Dichalcogenide MoSe2

We exploit ultrafast extreme-UV angle-resolved photoemission spectroscopy (XUV ARPES) for sensitive studies of non-equilibrium carrier dynamics in MoSe2. The experiments reveal inter-valley scattering and provide first evidence for the observation of band-gap excitons in ARPES.

Signature of a Magnetar Central Engine from the Multiband Afterglow of GRB 151027A Associated with a Supernova

Abstract We report multiwavelength observations and theoretical modeling of the afterglow of gamma-ray burst (GRB) 151027A. The object exhibits a complete evolutionary sequence, including prompt gamma-ray and optical emission, an initial optical onset bump, an optical rebrightening, a late-time supernova bump, an X-ray flare, and two distinct X-ray plateaus. GRB 151027A exhibits nearly all characteristic features observed in GRB afterglows. Such a rich set of features within a single event is exceptionally rare. We show that the first X-ray plateau followed by a rapid decay can be attributed to the collapse of a newly formed magnetar to form a black hole. The second X-ray plateau can be explained by fallback accretion. We find that the energy-injection model successfully reproduces the optical rebrightening of GRB 151027A. The late-time optical bump is well described by a 56 Ni-powered supernova light curve. GRB 151027A presents a complete physical picture for GRB phenomenology, whereas reconstructing such a comprehensive picture previously required the statistical analysis of multiple GRBs.

Automated multi-model reconstruction from single-particle electron microscopy data

Management Partnerships: Improving Patient Care in Healthcare Organizations of the Future

The hospital of the future will have to be part of a system or network which will provide a continuum of care in primary care services, acute in-patient care and post-hospital care. Additionally, hospitals will become increasingly diversified and, at the same time, integrated, not only horizontally but more importantly, vertically. This amalgamation will be achieved either by acting alone or by a joint venture with another group, through shared services or through contract management. Technology and computerization will play an even larger role than currently, and there will be tremendous demands placed on the micro and macro levels of management partnership.

Drought Influences the Accuracy of Simulated Ecosystem Fluxes: A Model-Data Meta-analysis for Mediterranean Oak Woodlands

The caddisfly<i>Dicosmoecus gilvipes</i>: making a case for a functional role

Most caddisfly larvae build cases of silk and a variety of collected materials. Multiple functions, including protection from predators, resistance to entrainment by high flows, and improved respiration, have been suggested for caddisfly cases. We investigated the functional role of cases built by Dicosmoecus gilvipes, a limnephilid caddisfly. In this species, the 1st- through 4th-instar larvae build cases with plant material and attach Douglas-fir needles as lateral extensions that resemble vanes on an arrow. We tested whether the lateral extensions and entire case deterred predators by manipulating lateral extensions and case presence for larvae exposed to large steelhead trout. No larva with a case (with or without lateral extensions) was consumed during the experiment, whereas all larvae without a case were consumed. We tested whether lateral extensions provided stability against overturning and entrainment by manipulating presence of lateral extensions and subjecting larvae to turbulent flow conditions. Once dislodged, larvae with lateral extensions experienced fewer revolutions and regained their footing faster than those without extensions. Our results suggest lateral extensions provide stability against overturning in fast flow and may improve the ability of larvae to forage efficiently in turbulent flow conditions. Other caddisfly species build lateral extensions on their case, and the extensions may provide similar benefits for these taxa.

Development of an FMCW LADAR Source Chip using MEMS-Electronic-Photonic Heterogeneous Integration

We present a modular integration platform, combining active and passive photonic devices with CMOS integrated electronics. Based on this integration platform, an integrated Frequency Modulated Continuous Wave (FMCW) Laser Detection and Ranging (LADAR) source chip is being developed. Such a LADAR source chip can be used in miniaturized 3D imaging systems for defense and consumer electronics applications. In this paper, we discuss the integration approach, the performance of select individual components, and experimental results on a bench top LADAR model system.

Empirical basis for treatment.

Enantio- and Diastereodivergent Cyclopropanation of Allenes by Directed Evolution of an Iridium-Containing Cytochrome

Alkylidene cyclopropanes (ACPs) are valuable synthetic intermediates because of their constrained structure and opportunities for further diversification. Although routes to ACPs are known, preparations of ACPs with control of both the configuration of the cyclopropyl (<i>R</i> vs <i>S</i>) group and the geometry of the alkene (<i>E</i> vs <i>Z</i>) are unknown. We describe enzymatic cyclopropanation of allenes with ethyl diazoacetate (EDA) catalyzed by an iridium-containing cytochrome (Ir(Me)-CYP119) that controls both stereochemical elements. Two mutants of Ir(Me)-CYP119 identified by 6-codon (6c, VILAFG) saturation mutagenesis catalyze the formation of (<i>E</i>)-ACPs with -93% to >99% ee and >99:1 <i>E</i>/<i>Z</i> ratio with just three rounds of 96 mutants. By four additional rounds of mutagenesis, an enzyme variant was identified that forms (<i>Z</i>)-ACPs with up to 94% ee and a 28:72 <i>E/Z</i> ratio. Computational studies show that the orientation of the carbene unit dictated by the mutated positions accounts for the stereoselectivity.

⁴⁰ Ar/ ³⁹ Ar age constraints on ore deposition and cooling of the Bushveld Complex, South Africa

The UG-2 chromitite layer in the upper critical zone of the Rustenburg Layered Suite is one of the prominent platinum-group element enrichment zones of the c . 2.06 Ga Bushveld Complex (South Africa). Eleven biotite crystals were selected from a production concentrate from the Impala Platinum mine and degassed incrementally with a CO 2 laser. The apparent age spectra display widely varying characteristics, ranging from essentially 100% concordant to strongly discordant (in some cases undulatory) as a result of various degrees of chloritization of the grains. The least discordant spectra (seven grains, 90–100% 39 Ar released) yield integrated and plateau ages ranging from 2037 to 2049 Ma (relative to the Fish Canyon sanidine standard at 28.02 Ma) and share a weighted mean age of 2042.4 ± 3.2 Ma (2σ, excluding systematic errors). This age is slightly younger than existing constraints from U–Pb dating ( c . 2055–2061 Ma), which seem to indicate a cooling rate of around 20 °C/Ma. However, the recently inferred c . 1% bias between currently used calibrations of the 40 Ar/ 39 Ar and U–Pb systems implies a very rapid cooling rate for the Bushveld Complex between 700 and &lt;500 °C. The possibility of subtle bias as a result of recoil artefacts must be considered. In all cases, the heterogeneous age spectra yielded older apparent plateau ages, revealing the likelihood for erroneous conclusions to be drawn from less complete data sets.

Effect of lattice vibrations on the ordering tendencies in substitutional binary alloys

The effect of lattice vibrations on the ordering tendencies and phase stability of substitutional binary alloys is analyzed. The alloy Hamiltonian is cast onto an Ising-like Hamiltonian through a cluster expansion of the vibrational free energy computed in the harmonic approximation. The temperature dependence of the vibrational effective cluster interactions (VECI's) is found for a general d-dimensional alloy. Analytic results for the VECI's for d=1 are derived. It is argued that the vibrations can have pronounced effects on the phase diagram and on the short-range order at high temperatures.

Rh1−x Pd x Nanoparticle Composition Dependence in CO Oxidation by NO

Bimetallic 15 nm Pd-core Rh-shell Rh1−x Pd x nanoparticle catalysts have been synthesized and studied in CO oxidation by NO. The catalysts exhibited composition-dependent activity enhancement (synergy) in CO oxidation in high NO pressures. The observed synergetic effect is attributed to the favorable adsorption of CO on Pd in NO-rich conditions. The Pd-rich bimetallic catalysts deactivated after many hours of oxidation of CO by NO. After catalyst deactivation, product formation was proportional to the Rh molar fraction within the bimetallic nanoparticles. The deactivated catalysts were regenerated by heating the sample in UHV. This regeneration suggests that the deactivation was caused by the adsorption of nitrogen atoms on Pd sites. TOF of CO2 as a function of Pd molar fraction for Rh1−x Pd x nanocrystals at 230 °C (before deactivation) and 250 °C (after deactivation) in 80 Torr NO, 8 Torr CO, and 672 Torr He. At 230 °C, prior to deactivation, the Pd-rich catalysts were more active for CO2 production than the Rh-rich catalysts.

Magnetic Properties of Obsidians from the Southwestern U.S