Granular materials composed of different-sized grains may experience undesired segregation.Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes.For these re...Granular materials composed of different-sized grains may experience undesired segregation.Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes.For these reasons,the segregation phenomena have been intensively studied in the last decades,and a lot of models have been provided by many researchers.However,these models are mainly based on empirical relations rather than physical considerations.This paper aims to confirm the main assumptions made by Volpato,Tirapelle,and Santomaso(2020)in their percolation theory by means of DEM simulations.The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains,and simulations are performed for a range of tilting frequencies and size ratios.The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions.展开更多
With the wide applications of nanomaterials in an array of industries, more concerns are being raised about the occupational health and safety of nanoparticles in the workplace, and implications ofnanotech- nology on ...With the wide applications of nanomaterials in an array of industries, more concerns are being raised about the occupational health and safety of nanoparticles in the workplace, and implications ofnanotech- nology on the environment and living systems. Studies on environmental, health and safety （EHS） issues of nanomaterials play a significant role in public acceptance, and eventual sustainability, of nanotechnol- ogy. We present research results on three aspects of the EHS studies： characterization and measurement of nanoparticles, nanoparticle emission and exposure at workplaces, and control and abatement of nanoparticle release using filtration technology. Measurement of nanoparticle agglomerates using a newly developed instrument, the Universal Nanoparticle Analyzer, is discussed. Nanoparticle emission and exposure measurement results for carbon nanotubes in the manufacture of nanocomposites and for silicon nanoparticles in their production at a pilot scale facility are presented. Filtration of nanoparticles and nanoparticle agglomerates are also studied.展开更多
Photo-polymerization is at the foundation of many industries such as dentistry,coatings,adhesives,and stereolithography 3D printing.However,the organic cationic photo-initiators currently used are toxic,expensive,and ...Photo-polymerization is at the foundation of many industries such as dentistry,coatings,adhesives,and stereolithography 3D printing.However,the organic cationic photo-initiators currently used are toxic,expensive,and difficult to tune with respect to the wavelength of light required to initiate polymerization reactions.For example,current stereolithography 3D printing resins are unstable under sunlight.Here,we demonstrate that less expensive and non-toxic titania quantum dots made via the scalable flame spray pyrolysis technology can photo-polymerize epoxy when exposed to UVC(not present in sunlight on Earth),while being insensitive to UVA(present in natural sunlight on Earth)leading to resins that are photo-stable during end use.We use NMR and FTIR to demonstrate that photo-polymerization is catalyzed under UVC but not UVA,and nanoindentation to monitor the mechanical stability of epoxy films during postpolymerization UVA exposure.This approach allows precise control over the wavelengths of light under which photo-polymerization can and cannot occur,and is also transferable to other photo-catalytic reactions.展开更多
文摘Granular materials composed of different-sized grains may experience undesired segregation.Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes.For these reasons,the segregation phenomena have been intensively studied in the last decades,and a lot of models have been provided by many researchers.However,these models are mainly based on empirical relations rather than physical considerations.This paper aims to confirm the main assumptions made by Volpato,Tirapelle,and Santomaso(2020)in their percolation theory by means of DEM simulations.The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains,and simulations are performed for a range of tilting frequencies and size ratios.The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions.
基金supported by the NSF grant(award ID:1056479) on "Real Time Measurement of Agglomerated or Aggregated Airborne Nanoparticles Released From a Manufacturing Process and Their Transport Characteristics"the NIEHS grant # 1RC2ES018741 -01(sub-grant 100029-D) on "Hazard Assessment and Risk Estimation of Inhaled Nanomaterials Exposure"+1 种基金the support of members of the Center for Filtration Research:3M,Boeing Commercial Airplanes,Cummins Filtration,Donaldson Co.,Inc.,Entegris,Inc.,Hollingsworth & Vose Co.,MANN+HUMMEL,GMBH,MSP Corp.,Samsung Electronics Co.,Ltd,Shigematsu Works Co.,Ltd,TS1 Inc.,and W.L.Core & Associates,Inc.and affiliate member NIOSHthe Characterization Facility,University of Minnesota,which receives partial support from NSF through the MRSEC program
文摘With the wide applications of nanomaterials in an array of industries, more concerns are being raised about the occupational health and safety of nanoparticles in the workplace, and implications ofnanotech- nology on the environment and living systems. Studies on environmental, health and safety （EHS） issues of nanomaterials play a significant role in public acceptance, and eventual sustainability, of nanotechnol- ogy. We present research results on three aspects of the EHS studies： characterization and measurement of nanoparticles, nanoparticle emission and exposure at workplaces, and control and abatement of nanoparticle release using filtration technology. Measurement of nanoparticle agglomerates using a newly developed instrument, the Universal Nanoparticle Analyzer, is discussed. Nanoparticle emission and exposure measurement results for carbon nanotubes in the manufacture of nanocomposites and for silicon nanoparticles in their production at a pilot scale facility are presented. Filtration of nanoparticles and nanoparticle agglomerates are also studied.
文摘Photo-polymerization is at the foundation of many industries such as dentistry,coatings,adhesives,and stereolithography 3D printing.However,the organic cationic photo-initiators currently used are toxic,expensive,and difficult to tune with respect to the wavelength of light required to initiate polymerization reactions.For example,current stereolithography 3D printing resins are unstable under sunlight.Here,we demonstrate that less expensive and non-toxic titania quantum dots made via the scalable flame spray pyrolysis technology can photo-polymerize epoxy when exposed to UVC(not present in sunlight on Earth),while being insensitive to UVA(present in natural sunlight on Earth)leading to resins that are photo-stable during end use.We use NMR and FTIR to demonstrate that photo-polymerization is catalyzed under UVC but not UVA,and nanoindentation to monitor the mechanical stability of epoxy films during postpolymerization UVA exposure.This approach allows precise control over the wavelengths of light under which photo-polymerization can and cannot occur,and is also transferable to other photo-catalytic reactions.
