The design and fabrication of multi-layer amperometric electrochemical glucose sensors is dependent upon the diffusional kinetics of the chemical/biochemical species which contribute to the sensor’s response. Conside...
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The design and fabrication of multi-layer amperometric electrochemical glucose sensors is dependent upon the diffusional kinetics of the chemical/biochemical species which contribute to the sensor’s response. Considerable effort has been carried out to coat the working electrode with appropriate glucose flux-limiting membranes which is pertinent for superior in vivo performance, and hence requires a careful understanding of the participating species within the sensor cross-sectional architecture. This contribution reports the computational modeling of Clark’s first generation amperometric glucose sensor coated with an electro-polymerized glucose oxidase (GOx) layer along with a layer of polyurethane (PU) employed to reduce the glucose-influx in order to generate linear operation over the normal physiological glucose range in vivo . The model was programmed using MATLAB and utilizes the finite-difference method for the solution to the enzymatic reaction-based diffusion equations. Additionally, experimental devices were fabricated, tested and compared with the simulated results. The simulation of these devices have been shown to align well with experimentally fabricated devices in terms of amperometric current density. The increase in device linearity with the addition of the outer glucose-flux limiting PU membrane corroborate our experimental findings reported in this study which can be used as a powerful analytical tool in designing high–performance next generation implantable glucose sensors.
We present an overview of work in the Ruoff group on graphene-based and graphene-derived materials in energy storage systems (EES). With high electrical conductivity and surface area, graphene-based materials are bein...
We present an overview of work in the Ruoff group on graphene-based and graphene-derived materials in energy storage systems (EES). With high electrical conductivity and surface area, graphene-based materials are being intensively studied as electrode material or support material in ultracapacitors and batteries. Graphene-based materials with different physicochemical properties have been studied including chemically reduced graphene oxide,[1] thermally reduced graphene oxide,[2] microwave exfoliated graphite oxide (MEGO),[3] and activated microwave-expanded graphite oxide ('a-MEGO').[4] Our recent work based on a highly porous graphene-derived carbon material showed that extremely high specific surface area can be obtained by an activation process, which allows for extensive formation of an electrochemical double layer (EDL) and a high gravimetric capacitance in a symmetric ultracapacitor. In addition, activated graphene-based materials showed significantly improved performance in terms of energy density approaching that of conventional lead-acid batteries.[4, 5] Other studies of highly porous graphene-derived materials in EES including Li-ion capacitors and Li-S batteries will also be presented, along with current efforts in our group on graphene-based and graphene–derived materials for electrical energy storage. REFERENCES 1. Stoller, M.D., et al., Graphene-Based Ultracapacitors. Nano Letters, 2008. 8(10): p. 3498-3502. 2. Zhu, Y.W., et al., Exfoliation of Graphite Oxide in Propylene Carbonate and Thermal Reduction of the Resulting Graphene Oxide Platelets. ACS Nano, 2010. 4(2): p. 1227-1233. 3. Zhu, Y.W., et al., Microwave assisted exfoliation and reduction of graphite oxide for ultracapacitors. Carbon, 2010. 48(7): p. 2118-2122. 4. Zhu, Y.W., et al., Carbon-Based Supercapacitors Produced by Activation of Graphene. science, 2011. 332(6037): p. 1537-1541. 5. Kim, T., et al., Activated graphene-based carbons as supercapacitor electrodes with macro- and mesopores.
Although several magnetic resonance studies address the Mg acceptor in GaN, there are few reports on Mg doping in the alloys, where hole production depends strongly on the Al or In content. Our electron paramagnetic r...
Although several magnetic resonance studies address the Mg acceptor in GaN, there are few reports on Mg doping in the alloys, where hole production depends strongly on the Al or In content. Our electron paramagnetic resonance (EPR) measurements of the p-type alloys suggest that the Mg impurity retains the axial symmetry, characteristic of a p-type dopant in both alloys; however, In and Al produce additional, different characteristics of the acceptor. In InGaN, the behavior is consistent with a lowering of the acceptor level and increasing hole density as In concentration increases. For AlGaN, the amount of neutral Mg decreases with increasing Al content, which is attributed to different kinetics of hydrogen diffusion thought to occur in samples with higher Al mole fraction.
Optimal spatial sampling of light rigorously requires that identical photoreceptors be arranged in perfectly regular arrays in two dimensions. Examples of such perfect arrays in nature include the compound eyes of ins...
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Optimal spatial sampling of light rigorously requires that identical photoreceptors be arranged in perfectly regular arrays in two dimensions. Examples of such perfect arrays in nature include the compound eyes of insects and the nearly crystalline photoreceptor patterns of some fish and reptiles. Birds are highly visual animals with five different cone photoreceptor subtypes, yet their photoreceptor patterns are not perfectly regular. By analyzing the chicken cone photoreceptor system consisting of five different cell types using a variety of sensitive microstructural descriptors, we find that the disordered photoreceptor patterns are “hyperuniform” (exhibiting vanishing infinite-wavelength density fluctuations), a property that had heretofore been identified in a unique subset of physical systems, but had never been observed in any living organism. Remarkably, the patterns of both the total population and the individual cell types are simultaneously hyperuniform. We term such patterns “multihyperuniform” because multiple distinct subsets of the overall point pattern are themselves hyperuniform. We have devised a unique multiscale cell packing model in two dimensions that suggests that photoreceptor types interact with both short- and long-ranged repulsive forces and that the resultant competition between the types gives rise to the aforementioned singular spatial features characterizing the system, including multihyperuniformity. These findings suggest that a disordered hyperuniform pattern may represent the most uniform sampling arrangement attainable in the avian system, given intrinsic packing constraints within the photoreceptor epithelium. In addition, they show how fundamental physical constraints can change the course of a biological optimization process. Our results suggest that multihyperuniform disordered structures have implications for the design of materials with novel physical properties and therefore may represent a fruitful area for future research
Two derivatives of tetraphenylethene (TPE) were synthesized through one step cross McMurry coupling reaction. Both luminogens exhibit aggregation-induced emission (AIE) and crystallization induced emission enhancement...
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Two derivatives of tetraphenylethene (TPE) were synthesized through one step cross McMurry coupling reaction. Both luminogens exhibit aggregation-induced emission (AIE) and crystallization induced emission enhancement (CIEE). The emissions of both luminogens could be switched between blue and green through reversible modulation of morphology with thermal, organic solvent fuming and mechanical stimuli. Thus we provide a possible design strategy for emission switching materials.
A search in the Thomson Reuters Web of Knowledge in January 2012,with the terms"organic solar cells/organic photovoltaics"was used to compile a list of 8962 papers written by 15374 individual authors(excludi...
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A search in the Thomson Reuters Web of Knowledge in January 2012,with the terms"organic solar cells/organic photovoltaics"was used to compile a list of 8962 papers written by 15374 individual authors(excluding reviews and conference proceedings).Solar cell data and bibliographic information was extracted from each of these papers(26 data fields)to create an overview of all OPV data reported to that date.1 The rate of publications shows a rapid exponential increase over a little more than a decade underlining the massive interest in this field of *** of the interesting findings is that there seems to be a universal correlation between the maximum power conversion efficiency(PCEMAX)and the short circuit current(JSC)which holds for all types of PV technologies(except for a few GaAs type cells).
The pronounced variation of the optical reflectance R of nanometer thin VO 2 films with temperature T at the phase transition recently has triggered interest in the development of compact thermo-optical sensors that ...
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ISBN:
(纸本)9781467363846
The pronounced variation of the optical reflectance R of nanometer thin VO 2 films with temperature T at the phase transition recently has triggered interest in the development of compact thermo-optical sensors that utilize optical fiber technology. Its immunity against electromagnetic interference effects makes this approach suited for an optical detection of local areas with increased temperature, i.e. so called hot spots, inside of high power transformers. Optical reflectance of thin VO 2 -films as function of T throughout the hysteretic phase transition is reported in this work. A modified version of the Preisach hysteresis model is utilized, and combined with experimental optical data. Suited VO 2 film thickness values and wavelengths range for optimum sensor operation can be extracted. The achievable temperature range, as confirmed by experimental observations, is consistent with requirements that apply for power transformers of the first group, according to NBR 5416 (ABNT).
Three types of silica materials with different morphology, specifically SiO2 hollow microspheres, mesoporous silica, and silica aerogel were tested as potential precursors for synthesis of silicon nano- and meso-struc...
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