86 research outputs found
iPINNs: Incremental learning for Physics-informed neural networks
Physics-informed neural networks (PINNs) have recently become a powerful tool
for solving partial differential equations (PDEs). However, finding a set of
neural network parameters that lead to fulfilling a PDE can be challenging and
non-unique due to the complexity of the loss landscape that needs to be
traversed. Although a variety of multi-task learning and transfer learning
approaches have been proposed to overcome these issues, there is no incremental
training procedure for PINNs that can effectively mitigate such training
challenges. We propose incremental PINNs (iPINNs) that can learn multiple tasks
(equations) sequentially without additional parameters for new tasks and
improve performance for every equation in the sequence. Our approach learns
multiple PDEs starting from the simplest one by creating its own subnetwork for
each PDE and allowing each subnetwork to overlap with previously learned
subnetworks. We demonstrate that previous subnetworks are a good initialization
for a new equation if PDEs share similarities. We also show that iPINNs achieve
lower prediction error than regular PINNs for two different scenarios: (1)
learning a family of equations (e.g., 1-D convection PDE); and (2) learning
PDEs resulting from a combination of processes (e.g., 1-D reaction-diffusion
PDE). The ability to learn all problems with a single network together with
learning more complex PDEs with better generalization than regular PINNs will
open new avenues in this field
Compositional Analysis of Lignocellulosic Feedstocks. 2. Method Uncertainties
The most common procedures for characterizing the chemical components
of lignocellulosic feedstocks use a two-stage sulfuric acid hydrolysis
to fractionate biomass for gravimetric and instrumental analyses.
The uncertainty (i.e., dispersion of values from repeated measurement)
in the primary data is of general interest to those with technical
or financial interests in biomass conversion technology. The composition
of a homogenized corn stover feedstock (154 replicate samples in 13
batches, by 7 analysts in 2 laboratories) was measured along with
a National Institute of Standards and Technology (NIST) reference
sugar cane bagasse, as a control, using this laboratory's suite of
laboratory analytical procedures (LAPs). The uncertainty was evaluated
by the statistical analysis of these data and is reported as the standard
deviation of each component measurement. Censored and uncensored versions
of these data sets are reported, as evidence was found for intermittent
instrumental and equipment problems. The censored data are believed
to represent the ābest caseā results of these analyses,
whereas the uncensored data show how small method changes can strongly
affect the uncertainties of these empirical methods. Relative standard
deviations (RSD) of 1ā3% are reported for glucan, xylan, lignin,
extractives, and total component closure with the other minor components
showing 4ā10% RSD. The standard deviations seen with the corn
stover and NIST bagasse materials were similar, which suggests that
the uncertainties reported here are due more to the analytical method
used than to the specific feedstock type being analyzed
Combined inactivation of the Clostridium cellulolyticum lactate and malate dehydrogenase genes substantially increases ethanol yield from cellulose and switchgrass fermentations
<p>Abstract</p> <p>Background</p> <p>The model bacterium <it>Clostridium cellulolyticum </it>efficiently degrades crystalline cellulose and hemicellulose, using cellulosomes to degrade lignocellulosic biomass. Although it imports and ferments both pentose and hexose sugars to produce a mixture of ethanol, acetate, lactate, H<sub>2 </sub>and CO<sub>2</sub>, the proportion of ethanol is low, which impedes its use in consolidated bioprocessing for biofuels production. Therefore genetic engineering will likely be required to improve the ethanol yield. Plasmid transformation, random mutagenesis and heterologous expression systems have previously been developed for <it>C. cellulolyticum</it>, but targeted mutagenesis has not been reported for this organism, hindering genetic engineering.</p> <p>Results</p> <p>The first targeted gene inactivation system was developed for <it>C. cellulolyticum</it>, based on a mobile group II intron originating from the <it>Lactococcus lactis </it>L1.LtrB intron. This markerless mutagenesis system was used to disrupt both the paralogous <smcaps>L</smcaps>-lactate dehydrogenase (<it>Ccel_2485; ldh</it>) and <smcaps>L</smcaps>-malate dehydrogenase (<it>Ccel_0137; mdh</it>) genes, distinguishing the overlapping substrate specificities of these enzymes. Both mutations were then combined in a single strain, resulting in a substantial shift in fermentation toward ethanol production. This double mutant produced 8.5-times more ethanol than wild-type cells growing on crystalline cellulose. Ethanol constituted 93% of the major fermentation products, corresponding to a molar ratio of ethanol to organic acids of 15, versus 0.18 in wild-type cells. During growth on acid-pretreated switchgrass, the double mutant also produced four times as much ethanol as wild-type cells. Detailed metabolomic analyses identified increased flux through the oxidative branch of the mutant's tricarboxylic acid pathway.</p> <p>Conclusions</p> <p>The efficient intron-based gene inactivation system produced the first non-random, targeted mutations in <it>C. cellulolyticum</it>. As a key component of the genetic toolbox for this bacterium, markerless targeted mutagenesis enables functional genomic research in <it>C</it>. <it>cellulolyticum </it>and rapid genetic engineering to significantly alter the mixture of fermentation products. The initial application of this system successfully engineered a strain with high ethanol productivity from cellobiose, cellulose and switchgrass.</p
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