The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepared using unpolarized UV light (U–PSCLC), such as reflection bandwidth broadening and either red or blue tuning of the reflection peak, has... more
The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepared using unpolarized UV light (U–PSCLC), such as reflection bandwidth broadening and either red or blue tuning of the reflection peak, has been previously reported. Herein, recent efforts to use a polarized single argon‐ion laser beam to create PSCLCs (L–PSCLCs) with higher‐order reflections are described. The L–PSCLCs exhibit a primary reflection peak in the near‐infrared (NIR) regime and a second‐order reflection band with a narrow bandwidth in the visible regime that results from a deformed in‐plane CLC helical structure. The initial positions of the reflection bands are adjusted by the chiral dopant concentrations of the CLC mixture, and red, green, and blue reflection colors from the second‐order Bragg reflection are demonstrated. The primary and the second‐order reflection bands can be shifted to longer wavelengths by application of a DC electric field. The reflection efficiency of ...
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Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties. The director orientation within an LCE can be spatially localized into voxels [three-dimensional (3-D) volume elements] via photoalignment... more
Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties. The director orientation within an LCE can be spatially localized into voxels [three-dimensional (3-D) volume elements] via photoalignment surfaces. Here, we prepare nanocomposites in which both the orientation of the LCE and single-walled carbon nanotube (SWNT) are locally and arbitrarily oriented in discrete voxels. The addition of SWNTs increases the stiffness of the LCE in the orientation direction, yielding a material with a 5:1 directional modulus contrast. The inclusion of SWNT modifies the thermomechanical response and, most notably, is shown to enable distinctive electromechanical deformation of the nanocomposite. Specifically, the incorporation of SWNTs sensitizes the LCE to a dc field, enabling uniaxial electrostriction along the orientation direction. We demonstrate that localized orientation of the LCE and SWNT allows complex 3-D shape transformations to be electrically tri...
Research Interests: Chemical Engineering, Pharmacology, Neuroscience, Physiology, Biophysics, and 15 moreMaterials Science, Inorganic Chemistry, Computational Biology, Biotechnology, Plant Biology, Carbon Nanotube, Medicine, Anisotropy, Polymer, Nanocomposite, Composite Material, Liquid Crystal, Elastomer, LCE, and Electrostriction
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Significance Photomechanical effects in polymers are distinguished by the ease with which actinic light can be regulated to contactlessly trigger the magnitude and directionality of mechanical adaptivity with spatio-temporal control. The... more
Significance Photomechanical effects in polymers are distinguished by the ease with which actinic light can be regulated to contactlessly trigger the magnitude and directionality of mechanical adaptivity with spatio-temporal control. The materials examined to date have not demonstrated power densities or actuation speeds necessary for applications seeking to exploit the promise of wirelessly triggered actuation. Using mechanical design, we employ two classes of azobenzene-functionalized polymers and demonstrate contactless snap-through of bistable arches realizing orders-of-magnitude enhancement in the actuation rates (∼10 2 mm/s) and powers (∼1 kW/m 3 ) under moderate irradiation intensities (<<100 mW/cm 2 ). The experimental characterization of the snap-through is supported with modeling that elucidates the effect of geometry, mechanical properties, and photogenerated strain on the actuation rate and energy output.
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Summary Realized gains from selection for resistance to the fungal disease fusiform rust caused by Cronartium quercuum f. sp. fusiforme were estimated using data from five field trials planted on large rectangular plots in high... more
Summary Realized gains from selection for resistance to the fungal disease fusiform rust caused by Cronartium quercuum f. sp. fusiforme were estimated using data from five field trials planted on large rectangular plots in high rust-hazard sites. These five realized gain trials, planted as a Best Management Practices study (BMP), compared resistant and susceptible mixtures of families from the first-generation breeding population of slash pine (Pinus elliottii var. elliottii Engelm.) in southeastern North America. Analyses of variance (Proc Mixed using REML in SAS), conducted to test the significance of realized gains and interactions contrasting resistant with susceptible seedlots, detected important and highly significant realized gains in both rust resistance and mid-rotation yield. Significant gains were obtained for rust resistance at age 5 and stand yield at age 16 with high stability across sites and across silvicultural treatments, indicating that gains in rust resistance an...
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Research Interests: Genetics, Forestry, Silviculture, Forest Ecology And Management, Biology, and 15 moreAgroforestry, Forest Ecology, Biological Sciences, Seasonality, Environmental Sciences, Genotype X Environment Interaction, Pinus elliottii, Aboveground biomass, Slash Pine, Pinus Taeda, Loblolly Pine, Southeastern United States, Genetic Improvement, Basal Area, and Plant density
Abstract: Predicted breeding values were validated using realized gains estimated from large-rectangular-plot field trials from the first generation breeding population of slash pine (Pinus elliottii var. elliottii Engelm.) in the... more
Abstract: Predicted breeding values were validated using realized gains estimated from large-rectangular-plot field trials from the first generation breeding population of slash pine (Pinus elliottii var. elliottii Engelm.) in the Southeast. These 43 realized gain trials ...
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A total of 2561 slash pine ( Pinus elliottii Engelm. var. elliottii) grafts were topgrafted in the winter of 2003 and evaluated in January of 2004. The objectives of this study were to understand the effect of the genetic material and... more
A total of 2561 slash pine ( Pinus elliottii Engelm. var. elliottii) grafts were topgrafted in the winter of 2003 and evaluated in January of 2004. The objectives of this study were to understand the effect of the genetic material and crown position on survival and flowering response of topgrafts. Also, the effects of geographic direction, branch order, and scion age on topgraft response were assessed. Topgrafting was an effective tool for promoting both female and male strobili. The genetic material (scion and interstock clones) and the crown position had large effects on the promotion of female flowering and topgraft survival. More than 23% of the total variation in female flowering and 16.3% of the total variation in topgraft survival were due to differences among scion clones and among interstock clones, respectively. The highest survival rate was reached by grafting in the mid-top followed by the top crown position. Grafting in the top of the crown was highly superior in promot...
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It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC)... more
It has previously been shown that for polymer-stabilized cholesteric liquid crystals (PSCLCs) with negative dielectric anisotropy, the position and bandwidth of the selective reflection notch can be controlled by a direct-current (DC) electric field. The field-induced deformation of the polymer network that stabilizes the devices is mediated by ionic charges trapped in or near the polymer. A unique and reversible electro-optic response is reported here for relatively thin films (≤5 μm). Increasing the DC field strength redshifts the reflection notch to longer wavelength until the reflection disappears at high DC fields. The extent of the tuning range is dependent on the cell thickness. The transition from the reflective to the clear state is due to the electrically controlled, chirped pitch across the small cell gap and not to the field-induced reorientation of the liquid crystal molecules themselves. The transition is reversible. By adjusting the DC field strength, various reflecti...
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Photomechanical effects in materials can directly convert light stimulus into mechanical work.
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Amoroso demonstrate the power of our data by estimating the high-resolution trawling footprint on seafloor habitat. Yet we argue that a coarser grid is required to understand full ecosystem impacts. Vessel tracking data allow us to... more
Amoroso demonstrate the power of our data by estimating the high-resolution trawling footprint on seafloor habitat. Yet we argue that a coarser grid is required to understand full ecosystem impacts. Vessel tracking data allow us to estimate the footprint of human activities across a variety of scales, and the proper scale depends on the specific impact being investigated.
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Liquid crystalline elastomers (LCEs) are soft, anisotropic materials that exhibit large shape transformations when subjected to various stimuli. Here we demonstrate a facile approach to enhance the out-of-plane work capacity of these... more
Liquid crystalline elastomers (LCEs) are soft, anisotropic materials that exhibit large shape transformations when subjected to various stimuli. Here we demonstrate a facile approach to enhance the out-of-plane work capacity of these materials by an order of magnitude, to nearly 20 J/kg. The enhancement in force output is enabled by the development of a room temperature polymerizable composition used both to prepare individual films, organized via directed self-assembly to retain arrays of topological defect profiles, as well as act as an adhesive to combine the LCE layers. The material actuator is shown to displace a load >2500× heavier than its own weight nearly 0.5 mm.
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We report on electrically-induced, large magnitude (>300 nm), and reversible tuning of the selective reflection in polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy nematic liquid... more
We report on electrically-induced, large magnitude (>300 nm), and reversible tuning of the selective reflection in polymer stabilized cholesteric liquid crystals (PSCLCs) prepared from negative dielectric anisotropy nematic liquid crystal hosts. The electrically-induced blue shift in the selective reflection of the PSCLCs is distinguished from our prior reports of bandwidth broadening and red-shifting tuning of the selective reflection in PSCLCs. The dominant factor in delineating the electro-optic response of the PSCLCs detailed here are the preparation conditions. Specifically, long exposure to UV intensity exceeding 250 mW cm(-2). Other factors are shown to contribute to the response, including the type and concentration of photoinitiator.
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Light is distinguished as a contactless energy source for microscale devices as it can be directed from remote distances, rapidly turned on or off, spatially modulated across length scales, polarized, or varied in intensity. Motivated in... more
Light is distinguished as a contactless energy source for microscale devices as it can be directed from remote distances, rapidly turned on or off, spatially modulated across length scales, polarized, or varied in intensity. Motivated in part by these nascent properties of light, transducing photonic stimuli into macroscopic deformation of materials systems has been examined in the last half-century. Here we report photoinduced motion (photomotility) in monolithic polymer films prepared from azobenzene-functionalized liquid crystalline polymer networks (azo-LCNs). Leveraging the twisted-nematic orientation, irradiation with broad spectrum ultraviolet–visible light (320–500 nm) transforms the films from flat sheets to spiral ribbons, which subsequently translate large distances with continuous irradiation on an arbitrary surface. The motion results from a complex interplay of photochemistry and mechanics. We demonstrate directional control, as well as climbing.
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We report the pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy, supported by density functional... more
We report the pressure-induced crystallographic transitions and optical behavior of MAPbI3 (MA=methylammonium) using in situ synchrotron X-ray diffraction and laser-excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin-orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO3 -type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase-mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction.
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Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous... more
Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous property can be attributed to the presence of both interstitial oxygen and cation vacancies, that create diffusion paths which computational studies suggest are less tortuous and have lower activation energies for migration than in stoichiometric compounds. In this work, neutron diffraction of Nd(28+x)/3AlxSi6-xO26 (0 ≤ x ≤ 1.5) single crystals identified the locations of oxygen interstitials, and allowed the deduction of a dual-path conduction mechanism that is a natural extension of the single-path sinusoidal channel trajectory arrived at through computation. This discovery provides the most thorough understanding of the O(2-) transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture o...
Research Interests: Biochemistry, Genetics, Biophysics, Chemistry, Inorganic Chemistry, and 15 moreBiotechnology, Solid Oxide Fuel Cells, Infectious Diseases, Neutron Diffraction, Chemical Physics, Medicine, Diffusion, SOFC, Mechanism, Conductivity, CHEMICAL SCIENCES, Ionic Conductivity, Oxide, Transport Mechanism, and Electrolyte
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Melilite, a tetrahedral-layered structure, shows strong anisotropic oxygen ion conduction at intermediate temperatures, which can be controlled by increasing the number of interstitial oxygen and reducing the size of interlayer cations.
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Research Interests: Botany, Genetics, Biology, Innate immunity, Medicine, and 15 moreBiological Sciences, Plant diseases, Fusarium, Phenotype, Analysis of Variance, Canker, Genetic variation, Pinus Taeda, Loblolly Pine, Genetic Resistance, Plant Disease Resistance, BASIDIOMYCOTA, Inheritance Patterns, Genetic Correlation, and Gall
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Measurements of 500 Sun-like stars show that their properties differ from those predicted by stellar population models.