Isomeric biphenyldicarboxylic acids have been prepared from halobenzoic acids and aryl boronic acids using an inverse biphasic modification of the Suzuki coupling reaction. In this modification of the Suzuki coupling ...Isomeric biphenyldicarboxylic acids have been prepared from halobenzoic acids and aryl boronic acids using an inverse biphasic modification of the Suzuki coupling reaction. In this modification of the Suzuki coupling reaction, both reactants and products are contained in the aqueous phase, with palladium catalyst contained in the organic phase. A phase transfer catalyst is used to contact reactants and catalyst. Multiple cycles, in which the catalyst/organic solvent is contacted with fresh aqueous reactants, generating products with no loss of efficiency, are demonstrated. We believe that this is the first demonstration of Suzuki coupling to produce biphenyldicarboxylic acids, in this case useful as monomers for the production of condensation polymers.展开更多
Carrier diffusion is of paramount importance in many semiconductor devices,such as solar cells,photodetectors,and power electronics.Structural defects prevent such devices from reaching their full performance potentia...Carrier diffusion is of paramount importance in many semiconductor devices,such as solar cells,photodetectors,and power electronics.Structural defects prevent such devices from reaching their full performance potential.Although a large carrier diffusion length indicates high material quality,it also implies increased carrier depletion by an individual extended defect(for instance,a dislocation)and obscures the spatial resolution of neighboring defects using optical techniques.For commonly utilized photoluminescence(PL)imaging,the spatial resolution is dictated by the diffusion length rather than by the laser spot size,no matter the spot is at or below the diffraction limit.Here,we show how Raman imaging of the LO phonon-plasmon-coupled mode can be used to recover the intrinsic spatial resolution of the optical system,and we demonstrate the effectiveness of the technique by imaging defects in GaAs with diffraction-limited optics,achieving a 10-fold improvement in resolution.Furthermore,by combining Raman and PL imaging,we can independently and simultaneously determine the spatial dependence of the electron density,hole density,radiative recombination rate,and non-radiative recombination rate near a dislocation-like defect,which has not been possible using other techniques.展开更多
Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C--O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficien...Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C--O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide （SnO2） nanoparticles and edge-oxidized graphene oxide （eo-GO） sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO2 reduction compared to SnO2 and commercialized TiO2 （P25）, respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.展开更多
An invasive population of Burmese pythons(Python molurus bivittatus)is established across several thousand square kilometers of southern Florida and appears to have caused precipitous population declines among several...An invasive population of Burmese pythons(Python molurus bivittatus)is established across several thousand square kilometers of southern Florida and appears to have caused precipitous population declines among several species of native mammals.Why has this giant snake had such great success as an invasive species when many established reptiles have failed to spread?We scored the Burmese python for each of 15 literature-based attributes relative to predefined comparison groups from a diverse range of taxa and provide a review of the natural history and ecology of Burmese pythons relevant to each attribute.We focused on attributes linked to spread and magnitude of impacts rather than establishment success.Our results suggest that attributes related to body size and generalism appeared to be particularly applicable to the Burmese python’s success in Florida.The attributes with the highest scores were:high reproductive potential,low vulnerability to predation,large adult body size,large offspring size and high dietary breadth.However,attributes of ectotherms in general and pythons in particular(including predatory mode,energetic efficiency and social interactions)might have also contributed to invasion success.Although establishment risk assessments are an important initial step in prevention of new establishments,evaluating species in terms of their potential for spreading widely and negatively impacting ecosystems might become part of the means by which resource managers prioritize control efforts in environments with large numbers of introduced species.展开更多
The Gierer-Meinhardt reaction-diffusion model is analyzed using a spectralcollocation method. This reaction-diffusion system is governed by activator and inhibitorconcentrations. Initially, the system is considered in...The Gierer-Meinhardt reaction-diffusion model is analyzed using a spectralcollocation method. This reaction-diffusion system is governed by activator and inhibitorconcentrations. Initially, the system is considered in one dimension and thenin two dimensions;numerical results are presented for both cases. The algorithmiccomplexity and accuracy are compared to those of a moving finite element method.Finally, observations are made concerning when to use the proposed spectral methodas opposed to the established moving mesh method.展开更多
We demonstrate an all optical approach that can surprisingly offer the possibility of yielding much more information than one would expect,pertinent to the carrier recombination dynamics via both radiative and nonradi...We demonstrate an all optical approach that can surprisingly offer the possibility of yielding much more information than one would expect,pertinent to the carrier recombination dynamics via both radiative and nonradiative processes when only one dominant deep defect level is present in a semiconductor material.By applying a band-defect state coupling model that explicitly treats the inter-band radiative recombination and Shockley-Read-Hall(SRH)recombination via the deep defect states on an equal footing for any defect center occupation fraction,and analyzing photoluminescence(PL)as a function of excitation density over a wide range of the excitation density(e.g.,5-6 orders in magnitude),in conjunction with Raman measurements of the LO-phonon plasmon(LOPP)coupled mode,nearly all of the key parameters relevant to the recombination processes can be obtained.They include internal quantum efficiency(IQE),minority and majority carrier density,inter-band radiative recombination rate(Wr),minority carrier nonradiative recombination rate(Wnr),defect center occupation fraction(f)),defect center density(Nt),and minority and majority carrier capture cross-sections(σt andσtM).While some of this information is thought to be obtainable optically,such as IQE and the Wr/Wnr ratio,most of the other parameters are generally considered to be attainable only through electrical techniques,such as current-voltage(Ⅰ-Ⅴ)characteristics and deep level transient spectroscopy(DLTS).Following a procedure developed herein,this approach has been successfully applied to three GaAs double-heterostructures that exhibit two distinctly different nonradiative recombination characteristics.The method greatly enhances the usefulness of the simple PL technique to an unprecedented level,facilitating comprehensive material and device characterization without the need for any device processing.展开更多
We analyze a Markov cellular automaton that models the spread of viruses that often progress to a chronic condition, such as human immunodeficiency virus （HIV） or hep- atitis C virus （HCV）. We show that the comple...We analyze a Markov cellular automaton that models the spread of viruses that often progress to a chronic condition, such as human immunodeficiency virus （HIV） or hep- atitis C virus （HCV）. We show that the complex dynamical system produces a Markov process at the later stages, whose eigenvectors corresponding to the eigenvalue 1 have physical significance for the long-term prognosis of the virus. Moreover we show that drug treatment leads to chronic conditions that can be modeled by Markov shifts with more optimal eigenveetors.展开更多
文摘Isomeric biphenyldicarboxylic acids have been prepared from halobenzoic acids and aryl boronic acids using an inverse biphasic modification of the Suzuki coupling reaction. In this modification of the Suzuki coupling reaction, both reactants and products are contained in the aqueous phase, with palladium catalyst contained in the organic phase. A phase transfer catalyst is used to contact reactants and catalyst. Multiple cycles, in which the catalyst/organic solvent is contacted with fresh aqueous reactants, generating products with no loss of efficiency, are demonstrated. We believe that this is the first demonstration of Suzuki coupling to produce biphenyldicarboxylic acids, in this case useful as monomers for the production of condensation polymers.
基金supported by ARO/MURI(W911NF-10-1-0524)ARO/Electronics(W911NF-16-1-0263)+2 种基金supported by the National Natural Science Foundation of China(Grant No.51702245)support from the China Scholarship Council for his visit at UNCCthe support of a Bissell Distinguished Professorship at UNCC.
文摘Carrier diffusion is of paramount importance in many semiconductor devices,such as solar cells,photodetectors,and power electronics.Structural defects prevent such devices from reaching their full performance potential.Although a large carrier diffusion length indicates high material quality,it also implies increased carrier depletion by an individual extended defect(for instance,a dislocation)and obscures the spatial resolution of neighboring defects using optical techniques.For commonly utilized photoluminescence(PL)imaging,the spatial resolution is dictated by the diffusion length rather than by the laser spot size,no matter the spot is at or below the diffraction limit.Here,we show how Raman imaging of the LO phonon-plasmon-coupled mode can be used to recover the intrinsic spatial resolution of the optical system,and we demonstrate the effectiveness of the technique by imaging defects in GaAs with diffraction-limited optics,achieving a 10-fold improvement in resolution.Furthermore,by combining Raman and PL imaging,we can independently and simultaneously determine the spatial dependence of the electron density,hole density,radiative recombination rate,and non-radiative recombination rate near a dislocation-like defect,which has not been possible using other techniques.
文摘Artificial photosynthesis uses a catalyst to convert CO2 into valuable hydrocarbon products by cleaving the C--O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide （SnO2） nanoparticles and edge-oxidized graphene oxide （eo-GO） sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO2 reduction compared to SnO2 and commercialized TiO2 （P25）, respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.
基金supported by the Department of the Interior’s Office of Insular Affairsthe Vero Beach office of the US Fish and Wildlife Service+4 种基金the US Geological Survey’s Greater Everglades Priority Ecosystem Science and Invasive Species programsEverglades National Parksupported by Davidson Collegethe Associated Colleges of the Souththe J.E.and Majorie B.Pittman Foundation.
文摘An invasive population of Burmese pythons(Python molurus bivittatus)is established across several thousand square kilometers of southern Florida and appears to have caused precipitous population declines among several species of native mammals.Why has this giant snake had such great success as an invasive species when many established reptiles have failed to spread?We scored the Burmese python for each of 15 literature-based attributes relative to predefined comparison groups from a diverse range of taxa and provide a review of the natural history and ecology of Burmese pythons relevant to each attribute.We focused on attributes linked to spread and magnitude of impacts rather than establishment success.Our results suggest that attributes related to body size and generalism appeared to be particularly applicable to the Burmese python’s success in Florida.The attributes with the highest scores were:high reproductive potential,low vulnerability to predation,large adult body size,large offspring size and high dietary breadth.However,attributes of ectotherms in general and pythons in particular(including predatory mode,energetic efficiency and social interactions)might have also contributed to invasion success.Although establishment risk assessments are an important initial step in prevention of new establishments,evaluating species in terms of their potential for spreading widely and negatively impacting ecosystems might become part of the means by which resource managers prioritize control efforts in environments with large numbers of introduced species.
基金the NSF Grant DMS-0453600.Special thanks are due to the Hong Kong Baptist University for their generous accommodations,specifically Dr.Tao Tang for his time and support.Also we would like to thank Dr.Graeme Fairweather for his guidance throughout this project,and Dr.Greg Fasshauer for his suggestions and contributions.
文摘The Gierer-Meinhardt reaction-diffusion model is analyzed using a spectralcollocation method. This reaction-diffusion system is governed by activator and inhibitorconcentrations. Initially, the system is considered in one dimension and thenin two dimensions;numerical results are presented for both cases. The algorithmiccomplexity and accuracy are compared to those of a moving finite element method.Finally, observations are made concerning when to use the proposed spectral methodas opposed to the established moving mesh method.
基金This work was authored in part by the National Renewable Energy Laboratory,operated by Alliance for Sustainable Energy,LLC,for the U.S.Department of Energy(DOE)under Contract No.DE-AC36-08GO28308,Funding provided by the U.S.Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies OfficeF.Z.also acknowledges Guangdong Basic and Applied Basic Research Foundation(2021A1515110170).
文摘We demonstrate an all optical approach that can surprisingly offer the possibility of yielding much more information than one would expect,pertinent to the carrier recombination dynamics via both radiative and nonradiative processes when only one dominant deep defect level is present in a semiconductor material.By applying a band-defect state coupling model that explicitly treats the inter-band radiative recombination and Shockley-Read-Hall(SRH)recombination via the deep defect states on an equal footing for any defect center occupation fraction,and analyzing photoluminescence(PL)as a function of excitation density over a wide range of the excitation density(e.g.,5-6 orders in magnitude),in conjunction with Raman measurements of the LO-phonon plasmon(LOPP)coupled mode,nearly all of the key parameters relevant to the recombination processes can be obtained.They include internal quantum efficiency(IQE),minority and majority carrier density,inter-band radiative recombination rate(Wr),minority carrier nonradiative recombination rate(Wnr),defect center occupation fraction(f)),defect center density(Nt),and minority and majority carrier capture cross-sections(σt andσtM).While some of this information is thought to be obtainable optically,such as IQE and the Wr/Wnr ratio,most of the other parameters are generally considered to be attainable only through electrical techniques,such as current-voltage(Ⅰ-Ⅴ)characteristics and deep level transient spectroscopy(DLTS).Following a procedure developed herein,this approach has been successfully applied to three GaAs double-heterostructures that exhibit two distinctly different nonradiative recombination characteristics.The method greatly enhances the usefulness of the simple PL technique to an unprecedented level,facilitating comprehensive material and device characterization without the need for any device processing.
文摘We analyze a Markov cellular automaton that models the spread of viruses that often progress to a chronic condition, such as human immunodeficiency virus （HIV） or hep- atitis C virus （HCV）. We show that the complex dynamical system produces a Markov process at the later stages, whose eigenvectors corresponding to the eigenvalue 1 have physical significance for the long-term prognosis of the virus. Moreover we show that drug treatment leads to chronic conditions that can be modeled by Markov shifts with more optimal eigenveetors.
