20 research outputs found
A GPU-accelerated simulator for the DEM analysis of granular systems composed of clump-shaped elements
We discuss the use of the Discrete Element Method (DEM) to simulate the
dynamics of granular systems made up of elements with nontrivial geometries.
The DEM simulator is GPU accelerated and can handle elements whose shape is
defined as the union with overlap of diverse sets of spheres with
user-specified radii. The simulator can also handle complex materials since
each sphere in an element can have its own Young's modulus , Poisson ratio
, friction coefficient , and coefficient of restitution CoR. To
demonstrate the simulator, we produce a "digital simulant" (DS), a replica of
the GRC-1 lunar simulant. The DS follows an element size distribution similar
but not identical to that of GRC-1. We validate the predictive attributes of
the simulator via several numerical experiments: repose angle, cone
penetration, drawbar pull, and rover incline-climbing tests. Subsequently, we
carry out a sensitivity analysis to gauge how the slope vs. slip curves change
when the element shape, element size, and friction coefficient change. The
paper concludes with a VIPER rover simulation that confirms a recently proposed
granular scaling law. The simulation involves more than 11 million elements
composed of more than 34 million spheres of different radii. The simulator
works in the Chrono framework and utilizes two GPUs concurrently. The GPU code
for the simulator and all numerical experiments discussed are open-source and
available on GitHub for reproducibility studies and unfettered use and
distribution.Comment: Main text 28 pages, including 27 figures. Submitted to Engineering
with Computer
Computation of Flapping-Wing Fluid–Structure Interaction
This thesis is on computational fluid–structure interaction (FSI) analysis of bioinspired wing flapping, based on an actual locust in wind tunnel. The wing motion is partially prescribed from high-speed video recordings of the locust. The computational analysis is performed with the Sequentially Coupled FSI (SCFSI) method as well as (full) FSI modeling. The thesis features using the Space–Time Slip Interface (ST-SI) technique to address the computational challenge created by near topology changes. Furthermore, we explore the possibility of using in the analysis the ST Isogeometric Analysis (ST-IGA) with NURBS basis functions in space. We start that exploration by conducting a developed-flow computation for the starting positions of the wings. The work provides a valuable way in studying insects of different species with flapping wings, and in understanding the aerodynamic performance of different bioinspired aerial vehicles. The core computational technology is the ST Variational Multiscale (ST-VMS) method, which is a moving-mesh method that allows us maintain mesh quality and resolution near fluid–structure interfaces and offers accurate solutions in both space and time. In addition, techniques including ST-SI method, ST-IGA method and mesh-moving based on elasticity equations (JBS), are employed in the computation
Characterization of Lignin Compounds at the Molecular Level: Mass Spectrometry Analysis and Raw Data Processing
Lignin is the second most abundant natural biopolymer, which is a potential alternative to conventional fossil fuels. It is also a promising material for the recovery of valuable chemicals such as aromatic compounds as well as an important biomarker for terrestrial organic matter. Lignin is currently produced in large quantities as a by-product of chemical pulping and cellulosic ethanol processes. Consequently, analytical methods are required to assess the content of valuable chemicals contained in these complex lignin wastes. This review is devoted to the application of mass spectrometry, including data analysis strategies, for the elemental and structural elucidation of lignin products. We describe and critically evaluate how these methods have contributed to progress and trends in the utilization of lignin in chemical synthesis, materials, energy, and geochemistry
The mechanism of trans-δ-viniferin inhibiting the proliferation of lung cancer cells A549 by targeting the mitochondria
Trans-δ-viniferin (TVN), as a natural extract, is a resveratrol dimer with attractive biological activities, particularly its anti-tumor character. However, the mechanism of TVN interfering with cancerous proliferation has not been fully understood. Herein in this study, we found that TVN could trigger cancerous mitochondrial membrane potential (ΔΨm) reduction, with intracellular reactive oxidative species (ROS) level increasing, leading to apoptosis, which makes TVN a promising candidate for lung cancer cells A549 treatment. Therefore, this study provides TVN as an option to meet the demand for higher antitumor availability with lower biotoxicity and other clinical applications
Characterization of Lignin Compounds at the Molecular Level
Lignin is the second most abundant natural biopolymer, which is a potential alternative to conventional fossil fuels. It is also a promising material for the recovery of valuable chemicals such as aromatic compounds as well as an important biomarker for terrestrial organic matter. Lignin is currently produced in large quantities as a by-product of chemical pulping and cellulosic ethanol processes. Consequently, analytical methods are required to assess the content of valuable chemicals contained in these complex lignin wastes. This review is devoted to the application of mass spectrometry, including data analysis strategies, for the elemental and structural elucidation of lignin products. We describe and critically evaluate how these methods have contributed to progress and trends in the utilization of lignin in chemical synthesis, materials, energy, and geochemistry.Peer Reviewe
Using a Bayesian-Inference Approach to Calibrating Models for Simulation in Robotics
In robotics, simulation has the potential to reduce design time and costs,
and lead to a more robust engineered solution and a safer development process.
However, the use of simulators is predicated on the availability of good
models. This contribution is concerned with improving the quality of these
models via calibration, which is cast herein in a Bayesian framework. First, we
discuss the Bayesian machinery involved in model calibration. Then, we
demonstrate it in one example: calibration of a vehicle dynamics model that has
low degree of freedom count and can be used for state estimation, model
predictive control, or path planning. A high fidelity simulator is used to
emulate the ``experiments'' and generate the data for the calibration. The
merit of this work is not tied to a new Bayesian methodology for calibration,
but to the demonstration of how the Bayesian machinery can establish
connections among models in computational dynamics, even when the data in use
is noisy. The software used to generate the results reported herein is
available in a public repository for unfettered use and distribution.Comment: 19 pages, 42 figure
Degradation of DEET and Caffeine under UV/Chlorine and Simulated Sunlight/Chlorine Conditions
Photoactivation
of aqueous chlorine could promote degradation of
chlorine-resistant and photochemically stable chemicals accumulated
in swimming pools. This study investigated the degradation of two
such chemicals, <i>N</i>,<i>N</i>-diethyl-3-methylbenzamide
(DEET) and caffeine, by low pressure ultraviolet (UV) light and simulated
sunlight (SS) activated free chlorine (FC) in different water matrices.
Both DEET and caffeine were rapidly degraded by UV/FC and SS/FC but
exhibited different kinetic behaviors. The degradation of DEET followed
pseudo-first-order kinetics, whereas the degradation of caffeine accelerated
with reaction. Mechanistic study revealed that, under UV/FC, ·OH
and Cl· were responsible for degradation of DEET, whereas ClO·
related reactive species (ClOrrs), generated by the reaction between
FC and ·OH/Cl·, played a major role in addition to ·OH
and Cl· in degrading caffeine. Reaction rate constants of DEET
and caffeine with the respective radical species were estimated. The
imidazole moiety of caffeine was critical for the special reactivity
with ClOrrs. Water matrix such as pH had a stronger impact on the
UV/FC process than the SS/FC process. In saltwater matrix under UV/FC
and SS/FC, the degradation of DEET was significantly inhibited, but
the degradation of caffeine was much faster than that in nonsalty
solutions. The interaction between Br<sup>–</sup> and Cl<sup>–</sup> may play an important role in the degradation of caffeine
by UV/FC in saltwater. Reaction product analysis showed similar product
patterns by UV/FC and SS/FC and minimal formation of chlorinated intermediates
and disinfection byproducts
Altered gut mycobiome in patients with end-stage renal disease and its correlations with serum and fecal metabolomes
Abstract Background The relationship between the gut mycobiome and end-stage renal disease (ESRD) remains largely unexplored. Methods In this study, we compared the gut fungal populations of 223 ESRD patients and 69 healthy controls (HCs) based on shotgun metagenomic sequencing data, and analyzed their associations with host serum and fecal metabolites. Results Our findings revealed that ESRD patients had a higher diversity in the gut mycobiome compared to HCs. Dysbiosis of the gut mycobiome in ESRD patients was characterized by a decrease of Saccharomyces cerevisiae and an increase in various opportunistic pathogens, such as Aspergillus fumigatus, Cladophialophora immunda, Exophiala spinifera, Hortaea werneckii, Trichophyton rubrum, and others. Through multi-omics analysis, we observed a substantial contribution of the gut mycobiome to host serum and fecal metabolomes. The opportunistic pathogens enriched in ESRD patients were frequently and positively correlated with the levels of creatinine, homocysteine, and phenylacetylglycine in the serum. The populations of Saccharomyces, including the HC-enriched Saccharomyces cerevisiae, were frequently and negatively correlated with the levels of various toxic metabolites in the feces. Conclusions Our results provided a comprehensive understanding of the associations between the gut mycobiome and the development of ESRD, which had important implications for guiding future therapeutic studies in this field
Rapid Disinfection by Peracetic Acid Combined with UV Irradiation
This study proposes a novel disinfection
process by sequential
application of peracetic acid (PAA) and ultraviolet light (UV), on
the basis of elucidation of disinfection mechanisms under UV/PAA.
Results show that hydroxyl radicals, generated by UV-activated PAA,
contribute to the enhanced inactivation of Escherichia
coli under UV/PAA compared to PAA alone or UV alone.
Furthermore, the location of hydroxyl radical generation is a critical
factor. Unlike UV/H<sub>2</sub>O<sub>2</sub>, which generates hydroxyl
radicals mainly in the bulk solution, the hydroxyl radicals under
UV/PAA are produced close to or inside E. coli cells, due to PAA diffusion. Therefore, hydroxyl radicals exert
significantly stronger disinfection power under UV/PAA than under
UV/H<sub>2</sub>O<sub>2</sub> conditions. Pre-exposing E. coli to PAA in the dark followed by application
of UV (i.e., a PAA-UV/PAA process) promotes diffusion of PAA to the
cells and achieves excellent disinfection efficiency while saving
more than half of the energy cost associated with UV compared to simultaneous
application of UV and PAA. The effectiveness of this new disinfection
strategy has been demonstrated not only in lab water but also in wastewater
matrices