International Journal for Numerical Methods in Engineering, 1999
This paper is aimed at developing a nonlocal theory for obtaining numerical approximation to a bo... more This paper is aimed at developing a nonlocal theory for obtaining numerical approximation to a boundary value problem describing damage phenomena in a brittle composite material. The mathematical homogenization method based on double scale asymptotic expansion is generalized to account for damage effects in heterogeneous media. A closed form expression relating local fields to the overall strain and damage is derived. Nonlocal damage theory is developed by introducing the concept of nonlocal phase fields (stress, strain, free energy density, damage release rate, etc.) in a manner analogous to that currently practiced in concrete [7], , with the only exception being that the weight functions are taken to be C 0 continuous over a single phase and zero elsewhere. Numerical results of our model were found to be in good agreement with experimental data of 4-point bend test conducted on composite beam made of Blackglas TM /Nextel 5-harness satin weave.
Proceedings of The National Academy of Sciences, 2000
A microfluidic platform for the construction of microscale components and autonomous systems is p... more A microfluidic platform for the construction of microscale components and autonomous systems is presented. The platform combines liquid-phase photopolymerization, lithography, and laminar flow to allow the creation of complex and autonomous microfluidic systems. The fabrication of channels, actuators, valves, sensors, and systems is demonstrated. Construction times can be as short as 10 min, providing ultrarapid prototyping of microfluidic systems.
Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscop... more Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.
IEEE/ASME Journal of Microelectromechanical Systems, 2002
Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydr... more Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydrogel components are fabricated inside microchannels using a liquid phase polymerization process. In-channel processing greatly simplifies device construction, assembly, and operation since the functional components are fabricated in situ and can perform both sensing and actuation functions. Two in situ photopolymerization techniques, "laminar stream mode" and "mask mode," have been
Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscop... more Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.
Why is it that e-businesses have not performed in line with expectations in the past years? Despi... more Why is it that e-businesses have not performed in line with expectations in the past years? Despite very optimistic projections for business-to-business (B2B) e-commerce not long ago, businesses have been very cautious in embracing this technology. One of the critical factors playing a major role is the risk associated with online commerce. Thus, a framework for evaluating online risks is needed to analyze the impact of e-business in the B2B world. The traditional process of buying and selling can be viewed as a model with conventional risk mitigation instruments including escrow, insurance, and contracts. As global B2B trade progresses using the e-business as its medium of choice, an array of new business models, new processes, new fulfillment needs, new services, and new technologies have emerged, resulting in a new set of online risks. These new online risks have created an imbalance in the traditional buying and selling process. Against this backdrop, we present a new framework for examining the various risks in the online B2B buying and selling process.
International Journal for Numerical Methods in Engineering, 1999
This paper is aimed at developing a nonlocal theory for obtaining numerical approximation to a bo... more This paper is aimed at developing a nonlocal theory for obtaining numerical approximation to a boundary value problem describing damage phenomena in a brittle composite material. The mathematical homogenization method based on double scale asymptotic expansion is generalized to account for damage effects in heterogeneous media. A closed form expression relating local fields to the overall strain and damage is derived. Nonlocal damage theory is developed by introducing the concept of nonlocal phase fields (stress, strain, free energy density, damage release rate, etc.) in a manner analogous to that currently practiced in concrete [7], , with the only exception being that the weight functions are taken to be C 0 continuous over a single phase and zero elsewhere. Numerical results of our model were found to be in good agreement with experimental data of 4-point bend test conducted on composite beam made of Blackglas TM /Nextel 5-harness satin weave.
Proceedings of The National Academy of Sciences, 2000
A microfluidic platform for the construction of microscale components and autonomous systems is p... more A microfluidic platform for the construction of microscale components and autonomous systems is presented. The platform combines liquid-phase photopolymerization, lithography, and laminar flow to allow the creation of complex and autonomous microfluidic systems. The fabrication of channels, actuators, valves, sensors, and systems is demonstrated. Construction times can be as short as 10 min, providing ultrarapid prototyping of microfluidic systems.
Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscop... more Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.
IEEE/ASME Journal of Microelectromechanical Systems, 2002
Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydr... more Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydrogel components are fabricated inside microchannels using a liquid phase polymerization process. In-channel processing greatly simplifies device construction, assembly, and operation since the functional components are fabricated in situ and can perform both sensing and actuation functions. Two in situ photopolymerization techniques, "laminar stream mode" and "mask mode," have been
Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscop... more Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.
Why is it that e-businesses have not performed in line with expectations in the past years? Despi... more Why is it that e-businesses have not performed in line with expectations in the past years? Despite very optimistic projections for business-to-business (B2B) e-commerce not long ago, businesses have been very cautious in embracing this technology. One of the critical factors playing a major role is the risk associated with online commerce. Thus, a framework for evaluating online risks is needed to analyze the impact of e-business in the B2B world. The traditional process of buying and selling can be viewed as a model with conventional risk mitigation instruments including escrow, insurance, and contracts. As global B2B trade progresses using the e-business as its medium of choice, an array of new business models, new processes, new fulfillment needs, new services, and new technologies have emerged, resulting in a new set of online risks. These new online risks have created an imbalance in the traditional buying and selling process. Against this backdrop, we present a new framework for examining the various risks in the online B2B buying and selling process.
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Papers by Qing Yu