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  1. Maximizing fossil fuel displacement and limiting atmospheric carbon dioxide levels require a high efficiency of carbon incorporation in bioenergy systems. The availability of biomass carbon is a constraint globally, and strategies to increase the efficiency of bioenergy production and biogenic carbon use are needed. Previous studies have shown that “energy upgrading” of biomass by coupling with renewable electricity through electrocatalytic hydrogenation offers a potential pathway to near full petroleum fuel displacement in the U.S., even when annual U.S. biomass production is limited to 1.2 billion dry tonnes. Commercialization of such technology requires economic feasibility. A technoeconomic model of decentralized, depot-based pyrolysis with electrocatalytic hydrogenation and centralized upgrading (Py-ECH), producing liquid hydrocarbon fuel is presented and compared to a cellulosic ethanol pathway using consistent assumptions. Using a discounted cash flow approach, a minimum fuel selling price (MFSP) of $3.62 per gallon gasoline equivalent (GGE) or $0.96 per gasoline liter equivalent (GLE) is estimated for Py-ECH fuel derived from corn stover, considering n th plant economics and a fixed internal rate of return of 10%. This is comparable to the MFSP for cellulosic ethanol from fermentation with the same feedstock ($3.71 per GGE or $0.98 per GLE) and is in the rangemore »of gasoline prices over the last 20 years of $1 per GGE ($0.26 per GLE) to $4.44 per GGE ($1.17 per GLE) in 2018. Optimization studies on depot sizing identified a trade-off between transportation and economies-of-scale costs, with an optimum size of 500 tpd. Sensitivity analyses showed that electricity cost, raw material costs, bio-oil yields, and cell efficiencies are the key parameters that affect the Py-ECH MFSP. With system improvements, a pathway to less than $3 per GGE or $0.79 per GLE is articulated for liquid hydrocarbon fuel from corn stover using Py-ECH.« less
    Free, publicly-accessible full text available May 31, 2023
  2. Abstract The effects of pyroclastic density currents (PDCs) can be devastating, so understanding their internal dynamics and evolution is important for hazard assessment. We use damaged trees located around Mount St. Helens (USA) as proxy for the dynamic pressure ( P dyn ) of the PDC erupted on 18 May 1980. We recorded the location, distribution, and foliage preservation of damaged trees within the medial and distal parts of the devastated forest. Sub-meter resolution aerial photographs from a month after the eruption allow distinction between standing trees that retained foliage from those that were stripped. Heights of standing trees were estimated from the measured lengths of their shadows. The number of standing trees was counted within defined areas along the propagation paths of PDCs. From the measured tree heights, we estimated tree toppling stresses from P dyn . Overall, P dyn of the PDC head within the medial to distal portions of the blowdown zone ranged from 10 to 35 kPa. P dyn likely waned with distance, as shown by the increased number of standing trees in the outer parts of the devastated area. In addition, we find clusters of standing trees on the lee sides of some hills. We proposemore »that these clusters survived because they were primarily impacted by lower dynamic pressures extant within the PDC body, with foliage retention or stripping as a function of the P dyn evolution in the PDC body. We estimate that P dyn of the body was less than the estimated maximum P dyn of the PDC head by 12 ± 4 kPa.« less
    Free, publicly-accessible full text available April 1, 2023
  3. We consider Markov chain Monte Carlo (MCMC) algorithms for Bayesian high-dimensional regression with continuous shrinkage priors. A common challenge with these algorithms is the choice of the number of iterations to perform. This is critical when each iteration is expensive, as is the case when dealing with modern data sets, such as genome-wide association studies with thousands of rows and up to hundreds of thousands of columns. We develop coupling techniques tailored to the setting of high-dimensional regression with shrinkage priors, which enable practical, non-asymptotic diagnostics of convergence without relying on traceplots or long-run asymptotics. By establishing geometric drift and minorization conditions for the algorithm under consideration, we prove that the proposed couplings have finite expected meeting time. Focusing on a class of shrinkage priors which includes the ‘Horseshoe’, we empirically demonstrate the scalability of the proposed couplings. A highlight of our findings is that less than 1000 iterations can be enough for a Gibbs sampler to reach stationarity in a regression on 100,000 covariates. The numerical results also illustrate the impact of the prior on the computational efficiency of the coupling, and suggest the use of priors where the local precisions are Half-t distributed with degree of freedom largermore »than one.« less
    Free, publicly-accessible full text available March 28, 2023
  4. Abstract We present a nearly complete rapid neutron-capture process ( r -process) chemical inventory of the metal-poor ([Fe/H] = −1.46 ± 0.10) r -process-enhanced ([Eu/Fe] = +1.32 ± 0.08) halo star HD 222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 ≤ Z ≤ 90, including elements rarely detected in r -process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The r -process elements from Ba to Pb, including all elements at the third r -process peak, exhibit remarkable agreement with the solar r -process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends frommore »Ga to Se, Nb through Cd, and In through Te. The r -process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the r -process. The lanthanide fraction, log X La = −1.39 ± 0.09, is typical for r -process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar r -process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations.« less
    Free, publicly-accessible full text available June 1, 2023
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