The application of selective resonant tunneling model is extended from d ϩ t fusion to other ligh... more The application of selective resonant tunneling model is extended from d ϩ t fusion to other light nucleus fusion reactions, such as d ϩ d fusion and d ϩ 3 He. In contrast to traditional formulas, the new formula for the cross-section needs only a few parameters to fit the experimental data in the energy range of interest. The features of the astrophysical S-function are derived in terms of this model. The physics of resonant tunneling is discussed.
High-temperature piezoelectric (1−x)BiScO3−xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64,... more High-temperature piezoelectric (1−x)BiScO3−xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64, and 0.65) near the morphotropic phase boundary were fabricated. A thermal depoling experiment was used to investigate the stability of polarization at the temperature range from 200° to 460°C. The results indicated that samples with rhombohedral phase began to depole when the temperature was higher than 300°C, while samples with a tetragonal phase showed good resistance to thermal depoling up to 440°C, close to their Curie temperature.
Recently, a new family of piezoelectric perovskite materials based on the solid solution (1−x)BiS... more Recently, a new family of piezoelectric perovskite materials based on the solid solution (1−x)BiScO3–xPbTiO3 was developed. This system was found to have a Curie temperature higher than 450°C and excellent piezoelectric properties near the MPB composition. Niobium, as a donor dopant in the piezoelectric system Pb(Zr,Ti)O3 and other lead-based perovskite materials, has commonly been used to increase the electrical resistivity, dielectric, and piezoelectric properties. In the current work, the effect of niobium substitution in the BS–PT system has been reported. The results of niobium additions in the BS–PT system showed no large enhancement of the piezoelectric properties. Niobium doping also led to lower Curie temperatures and higher dielectric loss. Further grain size effects in niobium-doped BS–PT compositions provided experimental evidence of significant extrinsic contributions to the piezoelectric properties in this system.
A modified citrate precursor method, combining the advantages of the nitrate autocombustion metho... more A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba0. 70Sr0. 30TiO3 powders. Slight agglomerated and homogenized BST ...
We have previously described methodology that makes it possible to genetically encode a wide arra... more We have previously described methodology that makes it possible to genetically encode a wide array of unnatural amino acids in both prokaryotic and eukaryotic organisms. Here, we report the systematic optimization of a Saccharomyces cerevisiae expression system for the production of mutant proteins containing unnatural amino acids. Modifications include significant increases in both the expression levels of the orthogonal Escherichia coli amber suppressor tRNA CUA and cognate aminoacyl-tRNA synthetase (aaRS) pair, and expression of the target protein gene using a strong transcriptional promoter, optimized codons and elevated plasmid copy numbers. With this new system, a number of unnatural amino acids, including the photocrosslinkers p-benzoylphenylalanine and p-azidophenylalanine, and the chemically reactive amino acids, p-acetylphenylalanine and p-propargyloxyphenylalanine, were incorporated into human superoxide dismutase (hSOD) in yeast in good yields (maximally ∼6-8 mg/l of culture in most cases). Mass spectrometric analysis of the hSOD mutants was performed with high dynamic range using multiple reaction monitoring that provided new insights into the factors that control the fidelity of unnatural amino acid incorporation.
Systems in which resources are shared can be operated either with reservation schedulers or as qu... more Systems in which resources are shared can be operated either with reservation schedulers or as queueing systems. While reservation systems are the only option to support future start-time requests, both types of systems can be used when users want resources at the earliest available opportunity. The objective of this work is to determine the conditions under which a reservation scheduler is required versus when a queueing system is sufficient. The problem was motivated by a communication network service. A new scheduled dynamic circuit service that uses a reservation scheduler is being offered. It differs from plain old telephony service (POTS), which is operated as a queueing system. Three models of reservation systems are analyzed: (i) finitewindow reservation system model, (ii) infinite-window reservation system model, and (iii) synchronized-server model. Our main finding is that if the number of servers is small, a reservation scheduler is required in both blocking-mode and waiting-mode systems. In blocking-mode systems, users should specify multiple start-time options in reservation requests to lower blocking rate while simultaneously operating the system at high utilization. In waiting-mode systems with small numbers of servers, since high-utilization system operation will cause large waiting times, a reservation system is preferred as it will allow customers to carry out other activities between their times of request and allocated start times rather than wait in a queue.
The application of selective resonant tunneling model is extended from d ϩ t fusion to other ligh... more The application of selective resonant tunneling model is extended from d ϩ t fusion to other light nucleus fusion reactions, such as d ϩ d fusion and d ϩ 3 He. In contrast to traditional formulas, the new formula for the cross-section needs only a few parameters to fit the experimental data in the energy range of interest. The features of the astrophysical S-function are derived in terms of this model. The physics of resonant tunneling is discussed.
High-temperature piezoelectric (1−x)BiScO3−xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64,... more High-temperature piezoelectric (1−x)BiScO3−xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64, and 0.65) near the morphotropic phase boundary were fabricated. A thermal depoling experiment was used to investigate the stability of polarization at the temperature range from 200° to 460°C. The results indicated that samples with rhombohedral phase began to depole when the temperature was higher than 300°C, while samples with a tetragonal phase showed good resistance to thermal depoling up to 440°C, close to their Curie temperature.
Recently, a new family of piezoelectric perovskite materials based on the solid solution (1−x)BiS... more Recently, a new family of piezoelectric perovskite materials based on the solid solution (1−x)BiScO3–xPbTiO3 was developed. This system was found to have a Curie temperature higher than 450°C and excellent piezoelectric properties near the MPB composition. Niobium, as a donor dopant in the piezoelectric system Pb(Zr,Ti)O3 and other lead-based perovskite materials, has commonly been used to increase the electrical resistivity, dielectric, and piezoelectric properties. In the current work, the effect of niobium substitution in the BS–PT system has been reported. The results of niobium additions in the BS–PT system showed no large enhancement of the piezoelectric properties. Niobium doping also led to lower Curie temperatures and higher dielectric loss. Further grain size effects in niobium-doped BS–PT compositions provided experimental evidence of significant extrinsic contributions to the piezoelectric properties in this system.
A modified citrate precursor method, combining the advantages of the nitrate autocombustion metho... more A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba0. 70Sr0. 30TiO3 powders. Slight agglomerated and homogenized BST ...
We have previously described methodology that makes it possible to genetically encode a wide arra... more We have previously described methodology that makes it possible to genetically encode a wide array of unnatural amino acids in both prokaryotic and eukaryotic organisms. Here, we report the systematic optimization of a Saccharomyces cerevisiae expression system for the production of mutant proteins containing unnatural amino acids. Modifications include significant increases in both the expression levels of the orthogonal Escherichia coli amber suppressor tRNA CUA and cognate aminoacyl-tRNA synthetase (aaRS) pair, and expression of the target protein gene using a strong transcriptional promoter, optimized codons and elevated plasmid copy numbers. With this new system, a number of unnatural amino acids, including the photocrosslinkers p-benzoylphenylalanine and p-azidophenylalanine, and the chemically reactive amino acids, p-acetylphenylalanine and p-propargyloxyphenylalanine, were incorporated into human superoxide dismutase (hSOD) in yeast in good yields (maximally ∼6-8 mg/l of culture in most cases). Mass spectrometric analysis of the hSOD mutants was performed with high dynamic range using multiple reaction monitoring that provided new insights into the factors that control the fidelity of unnatural amino acid incorporation.
Systems in which resources are shared can be operated either with reservation schedulers or as qu... more Systems in which resources are shared can be operated either with reservation schedulers or as queueing systems. While reservation systems are the only option to support future start-time requests, both types of systems can be used when users want resources at the earliest available opportunity. The objective of this work is to determine the conditions under which a reservation scheduler is required versus when a queueing system is sufficient. The problem was motivated by a communication network service. A new scheduled dynamic circuit service that uses a reservation scheduler is being offered. It differs from plain old telephony service (POTS), which is operated as a queueing system. Three models of reservation systems are analyzed: (i) finitewindow reservation system model, (ii) infinite-window reservation system model, and (iii) synchronized-server model. Our main finding is that if the number of servers is small, a reservation scheduler is required in both blocking-mode and waiting-mode systems. In blocking-mode systems, users should specify multiple start-time options in reservation requests to lower blocking rate while simultaneously operating the system at high utilization. In waiting-mode systems with small numbers of servers, since high-utilization system operation will cause large waiting times, a reservation system is preferred as it will allow customers to carry out other activities between their times of request and allocated start times rather than wait in a queue.
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Papers by Shawn Chen