skip to main content

Attention:

The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 5:00 PM ET until 11:00 PM ET on Friday, June 21 due to maintenance. We apologize for the inconvenience.


Search for: All records

Creators/Authors contains: "Xiao, Yao"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Free, publicly-accessible full text available September 1, 2024
  2. Abstract

    Recent technological advances have contributed to the rapid increase in algorithmic complexity of applications, ranging from signal processing to autonomous systems. To control this complexity and endow heterogeneous computing systems with autonomous programming and optimization capabilities, we propose aunified, end-to-end, programmable graph representation learning(PGL) framework that mines the complexity of high-level programs down to low-level virtual machine intermediate representation, extracts specific computational patterns, and predicts which code segments run best on a core in heterogeneous hardware. PGL extracts multifractal features from code graphs and exploits graph representation learning strategies for automatic parallelization and correct assignment to heterogeneous processors. The comprehensive evaluation of PGL on existing and emerging complex software demonstrates a 6.42x and 2.02x speedup compared to thread-based execution and state-of-the-art techniques, respectively. Our PGL framework leads to higher processing efficiency, which is crucial for future AI and high-performance computing applications such as autonomous vehicles and machine vision.

     
    more » « less
  3. Abstract Number: 381 Working Group: Instrumentation and Methods Abstract The phase state of atmospheric aerosol particles – solid, semi-solid, or liquid – influences their ability to take up water and participate in heterogeneous chemical reactions. Changes in phase state have been predicted by glass transition temperature (Tg) and viscosity; however, direct measurements of these properties is challenging for sub-micron particles. Historically, bulk measurements have been used, but this does not account for particle-to-particle variation or the impacts of particle size. Melting temperature (Tm) is the most significant predictor of Tg, and the two properties can be related through the Boyer-Beaman rule. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the Tm of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene-derived epoxydiols (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its Tm. The direct measurements are compared with model predictions based on molecular composition from hydrophilic interaction liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOF-MS) analysis. We compared the Tm of the SOA particles formed from IEPOX uptake onto acidic ammonium sulfate particles created at 30, 65, and 80% relative humidity (RH), and found that increasing RH from 30 to 80% led to an overall decrease in average Tm, indicating less viscous particles at higher RH conditions. Our measurements with this technique will allow for more accurate representations of the phase state of aerosols in the atmosphere. 
    more » « less
    Free, publicly-accessible full text available October 2, 2024
  4. The ability of an atmospheric aerosol to take up water or to participate in heterogeneous reactions is highly influenced by its phase state – solid, semi-solid, or liquid. These changes in phase state can be predicted by glass transition temperature (Tg), as particles at temperatures below their Tg will show solid properties, while increasing the temperature above their Tg will allow for semi-solid and eventually liquid properties. Historically, measurements of the Tg of bulk materials have been studied in order to model the phase states of aerosols in the atmosphere; however, these methods only permit an estimation of aerosol Tg based on their bulk chemical composition. Determining the Tg of individual particles will allow for more accurate model predictions of aerosol phase state. Herein, we apply a recently developed method utilizing a nano-thermal analysis (nanoTA) module coupled to an atomic force microscope (AFM), to determine the Tg of individual secondary organic aerosol (SOA) particles generated from the reactive uptake of isoprene epoxydiol (IEPOX) onto acidic ammonium sulfate aerosol particles. NanoTA works by using a specialized AFM probe which can be heated while in contact with a particle of interest. As the temperature increases, the probe deflection will first increase due to thermal expansion of the particle followed by a decrease at its melting temperature (Tm). The Tg of the particle can then be determined from Tm using the Boyer–Beaman rule. We compared the Tg of IEPOX-derived SOA particles generated at relative humidity (RH) of 30, 65, and 80%, and found that increasing RH from 30 to 80% led to a decrease in average Tg of 22 K, indicating less viscous particles at higher RH conditions. Our measurements with this technique will allow for more accurate representations of the phase state of aerosols in the atmosphere. 
    more » « less
    Free, publicly-accessible full text available October 2, 2024
  5. Abstract Number: 453 Working Group: Aerosol Chemistry Abstract Secondary organic aerosol (SOA) is composed of a significant fraction of low-volatility high-molecular-weight oligomer products. These species can affect particle viscosity, morphology, and mixing timescales, yet they are not very well understood. While strides have been made in elucidating oligomer formation mechanisms, their degradation is less studied. Previous work suggests that the presence of oligomers may suppress particle mass loss during atmospheric aging by slowing the production high-volatility fragments from monomers. Our work investigates the effects of relative humidity (RH) on oligomer formation in SOA and the effects of hydroxyl radical (·OH) exposure on oligomer degradation. To probe these questions, SOA is generated by the reactive uptake of isoprene epoxydiols (IEPOX) onto acidic ammonium sulfate aerosol in a 2-m3 steady-state chamber, followed by exposure to ·OH in an oxidation flow reactor. We investigate SOA formation at 30-80% RH, which is above and below the deliquescence point of ammonium sulfate. We examine the evolution of SOA bulk chemical composition as well as single-particle physicochemical properties over the course of aging using mass spectrometry-, spectroscopy-, and microscopy-based techniques. An optimized matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) method is used to identify and track the presence of oligomers in SOA over the course of aging. Our research will provide insight about the formation and degradation of oligomers in the atmosphere, which will allow better modeling of their impact on climate. 
    more » « less
  6. Heterogeneous hydroxyl radical (•OH) oxidation is an important aging process for isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) that alters its chemical composition. It was recently demonstrated that heterogeneous •OH oxidation can age single-component particulate methyltetrol sulfates (MTSs), causing ∼55% of the SOA mass loss. However, our most recent study of freshly generated IEPOX-SOA particulate mixtures suggests that the lifetime of the complete IEPOX-SOA mixture against heterogeneous •OH oxidation can be prolonged through the fragmentation of higher-order oligomers. Published studies suggest that the heterogeneous •OH oxidation of IEPOX SOA could affect the organic atmospheric aerosol budget at varying rates, depending on aerosol chemical composition. However, heterogeneous •OH oxidation kinetics for the full IEPOX-SOA particulate mixture have not been reported. Here, we exposed freshly generated IEPOX-SOA particles to heterogeneous oxidation by •OH under humid conditions (relative humidity ∼57%) for 0−15 atmospheric-equivalent days of aging and derived an effective heterogeneous •OH rate coefficient (kOH) of 2.64 ± 0.4 × 10−13 cm^3 molecules−1 s−1. While ∼44% of particulate organic mass of nonoxidized IEPOX-SOA was consumed over the entire 15 day aging period, only <7% was consumed during the initial 10 aging days. By molecular-level chemical analysis, we determined oligomers were consumed at a faster rate (by a factor of 2−4) than monomers. Analysis of aerosol physicochemical properties shows that IEPOX-SOA has a core−shell morphology, and the shell becomes thinner with •OH oxidation. In summary, this study demonstrates that heterogeneous •OH oxidation of IEPOX-SOA particles is a dynamic process in which aerosol chemical composition and physicochemical properties play important roles. 
    more » « less
    Free, publicly-accessible full text available October 19, 2024
  7. Abstract

    Elastomers generally possess low Young's modulus and high failure strain, which are widely used in soft robots and intelligent actuators. However, elastomers generally lack diverse functionalities, such as stimulated shape morphing, and a general strategy to implement these functionalities into elastomers is still challenging. Here, a microfluidic 3D droplet printing platform is developed to design composite elastomers architected with arrays of functional droplets. Functional droplets with controlled size, composition, position, and pattern are designed and implemented in the composite elastomers, imparting functional performances to the systems. The composited elastomers are sensitive to stimuli, such as solvent, temperature, and light, and are able to demonstrate multishape (bow‐ and S‐shaped), multimode (gradual and sudden), and multistep (one‐ and two‐step) deformations. Based on the unique properties of droplet‐embedded composite elastomers, a variety of stimuli‐responsive systems are developed, including designable numbers, biomimetic flowers, and soft robots, and a series of functional performances are achieved, presenting a facile platform to impart diverse functionalities into composite elastomers by microfluidic 3D droplet printing.

     
    more » « less
  8. Atmospheric aerosols are key contributors to cloud condensation nuclei (CCN) and ice nucleating particle (INP) formation, which can offset positive radiative forcing. Aerosol particles can undergo many cycles of droplet activation and subsequent drying before their removal from the atmosphere through dry or wet deposition. Cloud-aerosol-precipitation interactions are affected by cloud droplet or ice crystal formation, which is related to the physicochemical properties of aerosol particles. Isoprene-derived secondary organic aerosol (iSOA) is an abundant component aerosol and has been previously found in INPs and cloud water residues, and it includes both soluble and insoluble residues in its particle matrix. Currently, most of our understanding of iSOA is derived from studying the soluble residues, but there has been a measurement gap for characterizing the insoluble residues. These measurements are needed as previous research has suggested that insoluble components could be important with respect to CCN and INP formation. Herein, a unique approach is utilized to collect the insoluble residues of SOA in ~3 µm droplets collected from a Spot Sampler from Aerosol Devices, Inc. iSOA is generated by reactive uptake of IEPOX onto acidic seed particles (ammonium sulfate + sulfuric acid) in a humidified atmospheric chamber under dark conditions. Droplets are impacted directly on a substrate or in a liquid medium to study the roles of insoluble residues from both single-particle and bulk perspectives. A suite of microspectroscopy techniques, including Raman and optical photothermal infrared (O-PTIR) spectroscopy, are used to probe the chemical composition of the residues. Atomic force microscopy – photothermal infrared (AFM-PTIR) spectroscopy and Nanoparticle Tracking Analysis (NTA) are used to measure the size distributions of the residues. These insights may help understand the properties of residues from cloud droplet evaporation and subsequent cloud-aerosol-precipitation interactions in the atmosphere. 
    more » « less
  9. Abstract

    Strong and tough bio‐based fibers are attractive for both fundamental research and practical applications. In this work, strong and tough hierarchical core–shell fibers with cellulose nanofibrils (CNFs) in the core and regenerated silk fibroins (RSFs) in the shell are designed and prepared, mimicking natural spider silks. CNF/RSF core–shell fibers with precisely controlled morphology are continuously wet‐spun using a co‐axial microfluidic device. Highly‐dense non‐covalent interactions are introduced between negatively‐charged CNFs in the core and positively‐charged RSFs in the shell, diminishing the core/shell interface and forming an integral hierarchical fiber. Meanwhile, shearing by microfluidic channels and post‐stretching induce a better ordering of CNFs in the core and RSFs in the shell, while ordered CNFs and RSFs are more densely packed, thus facilitating the formation of non‐covalent interactions within the fiber matrix. Therefore, CNF/RSF core–shell fibers demonstrate excellent mechanical performances; especially after post‐stretching, their tensile strength, tensile strain, Young's modulus, and toughness are up to 635 MPa, 22.4%, 24.0 GPa, and 110 MJ m−3, respectively. In addition, their mechanical properties are barely compromised even at −40 and 60 °C. Static load and dynamic impact tests suggest that CNF/RSF core–shell fibers are strong and tough, making them suitable for advanced structural materials.

     
    more » « less