The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepare... 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 ...
Glass Transition Temperatures. Glass transition temperatures were determined via differential sca... more Glass Transition Temperatures. Glass transition temperatures were determined via differential scanning calorimetry using a TA Instruments Q1000. The values were determined from the 1 st cooling curve from 120 °C to-70 °C at 2 °C/min under inert nitrogen gas. Nematic to Isotropic Transition Temperature. The nematic to isotropic glass transition temperature for the 0.75 mol BDMT sample was determined via differential scanning calorimetry using a TA Instruments Q1000. The value was determined from the 2 nd heating curve from-70 °C to 250 °C at 2 °C/min under inert nitrogen gas. Degradation Temperatures. Degradation temperatures were obtained via thermogravimetric analysis (TGA) using a TA Instruments Q500 under nitrogen with a temperature ramp from 25 °C to 600 °C at a rate of 2 °C/min. Degradation temperature was determined from the onset of degradation from the derivative weight versus temperature curve. Summary of Mechanical Properties. The Young's modulus, yield stress, yield strain, soft elastic plateau, stress-at-failure, strain-at-failure, and toughness for the LCE films as a function of BDMT concentration (0-0.75 mol) and testing direction are reported in Table S1.
Laterally constrained arches driven between stable states by light, represent a unique space for ... more Laterally constrained arches driven between stable states by light, represent a unique space for compliant mechanism design. Exploiting mechanical multistability can overcome limitations of functional photomechanical actuators, which include limited repeatability, actuation speed, and positioning characteristics. Here, the addition of lateral constraints to an elastic bistable arch system is proposed as a method for toggling between bifurcated states by controlling the location of actinic irradiation. This approach expands the design space for photomechanical, mutistable structures and actuators. Arch behavior as a function of system parameters is simulated, including conditions leading to multistability. An experimental demonstration and exploration of a constrained photomechanical arch is also presented. It is expected that the concepts presented here could lead to innovations in areas such as energy harvesting, soft robotics, and multistable architected materials. 1. Introduction Bi-and multistable elements hold potential for a variety of applications in areas such as motion stabilization, mechanical or thermal energy harvesting, actuators, sensors, morphing surfaces and structures, and robotics [1-4]. These elements are a subset of a broader class of device elements termed compliant mechanisms. Compliant mechanisms make use of flexible components, rather than discrete, rigid links, and are designed to perform specified functions which combine both motion and force control [5]. These mechanisms are commonly employed in nature for the purpose of enhanced kinematics or accelerated motion (e.g. cicada ribs, hummingbird beaks, or the Venus flytrap [6-8]). By replacing multiple rigid elements with a smaller number of flexible components, compliant mechanisms offer integral, easy-to-fabricate structures with advantages that include, reduced wear and maintenance, lower overall device weight, and novel design strategies (e.g. in energy harvesting and energy dissipation applications) [1,5,9]. Realizations of these mechanisms using photomechanical materials, which convert light into mechanical work, is particularly intriguing because of the opportunity to induce spatially resolved, wireless actuation that can be actively controlled or designed to respond to environmental conditions. While the development of photochemically driven light responsive materials has been the focus of intense investigation [10-14], the utilization of these materials in functional compliant mechanisms [5] for smart structures and devices has not been extensively explored (see Ref. [15-18] for some notable exceptions).
Utilizing sequential layer-by-layer (LBL) coating and subsequent photopolymerization, we develope... more Utilizing sequential layer-by-layer (LBL) coating and subsequent photopolymerization, we developed circularpolarizing and free-standing mirrors with a broad reflection bandwidth. Photopolymerizable cholesteric liquid crystal (CLC) paints were first prepared by considering the intrinsic chirality and the coating viscoelasticity. The polymerstabilized nanostructures had finely tuned helical pitches that selectively reflected light over the entire visible wavelength range. The CLC films exhibited excellent thermomechanical properties and chemical stabilities, which enabled the preparation of patterned optical objects at macroscopic dimensions. The LBL coating and photopolymerization of the CLC paints demonstrated here can provide a simple solution for manufacturing flexible photonic devices with large areas at low cost.
Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties.... 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...
Directly transducing light into work is attractive for remotely powering soft mechanisms fabricat... more Directly transducing light into work is attractive for remotely powering soft mechanisms fabricated from photoresponsive polymers, but presents challenges for achieving reliable actuation within a control framework. Here, we utilize azobenzene-functionalized polyimides to fabricate actuators characterized by mechanically discrete states. Irradiation initiates the photochemically induced, quasistatic deformation to advance the actuator to the edge of instability. Following this latency, ultrafast snap through actuation (~10ms-scale) ensues. Restricting the role of control to the attainment of the edge of instability, strategies for achieving repetitive actuation via multiplexed irradiation are demonstrated. Approaches are examined for modulating the latency of the actuator using an all-optical strategy as well as mechanical design of the actuator. Prototypical assemblies of these actuators in arrays are used to fabricate morphable surfaces and structures, which is aided by the realization that the ultrafast actuation is characterized by a high power-density on the order of ~kW/m 3 .
dispersed in a liquid crystalline material usually affects the order of the system and the transi... more dispersed in a liquid crystalline material usually affects the order of the system and the transition temperature between various phases. If the dopants undergo photoisomerization between conformers with different shapes, the interactions with the liquid crystal molecules can be different for the material in the dark and during exposure to light of appropriate wavelength. This can be used to achieve isothermal photoinduced phase transitions (phototropism). With proper selection of materials components, both order-to-disorder and disorder-toorder photoinduced transition have been demonstrated. Isothermal order-increasing transitions have been observed recently using naphthopyran derivatives as dopants. We are investigating the changes in order parameter and transition temperature of liquid crystal mixtures containing naphthopyrans and how they are related to exposure conditions and to the concentration and molecular structure of the dopants. We are also studying the nature of the photoinduced phase transitions, and comparing the behavior with that of azobenzene-doped mixtures, in which exposure to light leads to a decrease, instead of an increase, in the order of the system.
Proceedings of the National Academy of Sciences, 2013
Significance Photomechanical effects in polymers are distinguished by the ease with which actinic... 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.
The photodriven oscillation of uniaxially aligned monodomain azo-LCNs was investigated as a funct... more The photodriven oscillation of uniaxially aligned monodomain azo-LCNs was investigated as a function of molecular alignment and temperature spanning a range of +/-40 of the glass transition temperature (T g). Monodomain azo-LCNs were synthesized between glass slide cells coated with Elvamide with an anti-parallel rubbing direction. In this work, multidimensional oscillations that include in plane bending and out of plane twisting are observed when the orientation of the axis is at intermediate angles to the long axis of the cantilever. The added dimensionality to the previously reported in plane oscillation is a result of a photoinduced shear gradient that causes twisting. The degree of twisting is shown to be dependent on both the polarization of the illuminating 442 nm light, and the orientation of the director to the cantilever geometry. Comparatively, rubbery azo-LCNs (e.g. systems heated > T g) show higher amplitude than glassy azo-LCN cantilevers. The relationship between the critical laser intensity and the concentration of azobenzene monomer for the photodriven oscillation behavior of azo-LCNs will also be discussed.
Synthetic approaches to prepare designer materials that localize deformation, by combining rigidi... more Synthetic approaches to prepare designer materials that localize deformation, by combining rigidity and compliance in a single material, have been widely sought. Bottom-up approaches, such as the self-organization of liquid crystals, offer potential advantages over top-down patterning methods such as photolithographic control of crosslink density, relating to the ease of preparation and fidelity of resolution. Here, we report on the directed self-assembly of materials with spatial and hierarchical variation in mechanical anisotropy. The highly nonlinear mechanical properties of the liquid crystalline elastomers examined here enables strain to be locally reduced 415-fold without introducing compositional variation or other heterogeneities. Each domain (Z0.01 mm 2) exhibits anisotropic nonlinear response to load based on the alignment of the molecular orientation with the loading axis. Accordingly, we design monoliths that localize deformation in uniaxial and biaxial tension, shear, bending and crack propagation, and subsequently demonstrate substrates for globally deformable yet locally stiff electronics.
This document is a response to the Kepler Project Call for White Papers. In it, we comment on the... more This document is a response to the Kepler Project Call for White Papers. In it, we comment on the potential for continuing asteroseismology of solar-type and red-giant stars in a 2-wheel Kepler Mission. These stars show rich spectra of solar-like oscillations. Our main conclusion is that by targeting stars in the ecliptic it should be possible to perform high-quality asteroseismology, as long as favorable scenarios for 2-wheel pointing performance are met. Targeting the ecliptic would potentially facilitate unique science that was not possible in the nominal Mission, notably from the study of clusters that are significantly brighter than those in the Kepler field. Our conclusions are based on predictions of 2-wheel observations made by a space photometry simulator, with information provided by the Kepler Project used as input to describe the degraded pointing scenarios. We find that elevated levels of frequency-dependent noise, consistent with the above scenarios, would have a significant negative impact on our ability to continue asteroseismic studies of solar-like oscillators in the Kepler field. However, the situation may be much more optimistic for observations in the ecliptic, provided that pointing resets of the spacecraft during regular desaturations of the two functioning reaction wheels are accurate at the ≤ 1 arcsec level. This would make it possible to apply a post-hoc analysis that would recover most of the lost photometric precision. Without this post-hoc correction-and the accurate re-pointing it requires-the performance would probably be as poor as in the Kepler-field case. Critical to our conclusions for both fields is the assumed level of pointing noise (in the short-term jitter and the longer-term drift). We suggest that further tests will be needed to clarify our results once more detail and data on the expected pointing performance becomes available, and we offer our assistance in this work.
Summary Realized gains from selection for resistance to the fungal disease fusiform rust caused b... 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...
We report here an analysis of the physical stellar parameters of the giant star HD 185351 using K... more We report here an analysis of the physical stellar parameters of the giant star HD 185351 using Kepler short-cadence photometry, optical and near infrared interferometry from CHARA, and high-resolution spectroscopy. Asteroseismic oscillations detected in the Kepler short-cadence photometry combined with an effective temperature calculated from the interferometric angular diameter and bolometric flux yield a mean density, ρ ⋆ = 0.0130 ± 0.0003 ρ ⊙ and surface gravity, log g = 3.280 ± 0.011. Combining the gravity and density we find R ⋆ = 5.35 ± 0.20 R ⊙ and M ⋆ = 1.99 ± 0.23 M ⊙. The trigonometric parallax and CHARA angular diameter give a radius R ⋆ = 4.97 ± 0.07 R ⊙. This smaller radius, when combined with the mean stellar density, corresponds to a stellar mass 1.60 ± 0.08 M ⊙ , which is smaller than the asteroseismic mass by 1.6-σ. We find that a larger mass is supported by the observation of mixed modes in our high-precision photometry, the spacing of which is consistent only for M ⋆ 1.8 M ⊙. Our various and independent mass measurements can be compared to the mass measured from interpolating the spectroscopic parameters onto stellar evolution models, which yields a model-based mass M ⋆,model = 1.87 ± 0.07 M ⊙. This mass agrees well with the asteroseismic value, but is 2.6-σ higher than the mass from the combination of asteroseismology and interferometry. The discrepancy motivates future studies with a larger sample of giant stars. However, all of our mass measurements are consistent with HD 185351 having a mass in excess of 1.5 M ⊙ .
Few studies have quantified the combined effects of silvicultural treatments and genetic improvem... more Few studies have quantified the combined effects of silvicultural treatments and genetic improvement on unit area production of full-sib family blocks of loblolly (Pinus taeda L.) and slash pine (P. elliottii Engelm. var. elliotttii). Efficient operational deployment of genetic materials requires an understanding of possible site and silvicultural treatment interactions to maximize yield potential. We examined genotype (family) by environmental interactions (G  E) through age 5 years using a factorial experiment consisting of silvicultural treatment intensity (operational versus intensive), planting density (1334 versus 2990 trees ha À1) and families (seven elite full-sib loblolly and six elite full-sib slash pine families). In January of 2000, randomized complete block, split-plot experiments were installed at two locations for each species in southeast Georgia and northeast Florida. Five years after planting, both loblolly and slash pine demonstrated significant interactions among several factors: genotype  location (p < 0.028 and p < 0.016, respectively), genotype  silvicultural treatment intensity (p < 0.055 and p < 0.059), and silvicultural treatment intensity  density (p < 0.002 and p < 0.001) for basal area (BA) and standing stem volume (VOL). Genotype  silvicultural treatment interactions were positive, with the best overall performing families responding the greatest to intensive treatment. There were changes in slash pine family rankings between locations, which were partly explained by reductions in growth associated with a combination of fusiform rust infection [Cronartium quercum (Berk.) Miyabe ex Shirai f. sp. fusiforme] and wind damage from the 2004 hurricane season. No three-way interactions, which included family, were evident and all genetic sources were stable across the contrasting planting densities. At age 5, loblolly pine outperformed slash pine (p < 0.0001), especially under the intensive silvicultural intensity. While loblolly performance was similar whether deployed in mixtures or pure family blocks, slash pine tended to be more productive in intimate mixtures than when grown in pure family blocks (p = 0.0754 for aboveground biomass).
Abstract: Predicted breeding values were validated using realized gains estimated from large-rect... 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 ...
The dynamic electro‐optic (EO) response of polymer‐stabilized cholesteric liquid crystals prepare... 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 ...
Glass Transition Temperatures. Glass transition temperatures were determined via differential sca... more Glass Transition Temperatures. Glass transition temperatures were determined via differential scanning calorimetry using a TA Instruments Q1000. The values were determined from the 1 st cooling curve from 120 °C to-70 °C at 2 °C/min under inert nitrogen gas. Nematic to Isotropic Transition Temperature. The nematic to isotropic glass transition temperature for the 0.75 mol BDMT sample was determined via differential scanning calorimetry using a TA Instruments Q1000. The value was determined from the 2 nd heating curve from-70 °C to 250 °C at 2 °C/min under inert nitrogen gas. Degradation Temperatures. Degradation temperatures were obtained via thermogravimetric analysis (TGA) using a TA Instruments Q500 under nitrogen with a temperature ramp from 25 °C to 600 °C at a rate of 2 °C/min. Degradation temperature was determined from the onset of degradation from the derivative weight versus temperature curve. Summary of Mechanical Properties. The Young's modulus, yield stress, yield strain, soft elastic plateau, stress-at-failure, strain-at-failure, and toughness for the LCE films as a function of BDMT concentration (0-0.75 mol) and testing direction are reported in Table S1.
Laterally constrained arches driven between stable states by light, represent a unique space for ... more Laterally constrained arches driven between stable states by light, represent a unique space for compliant mechanism design. Exploiting mechanical multistability can overcome limitations of functional photomechanical actuators, which include limited repeatability, actuation speed, and positioning characteristics. Here, the addition of lateral constraints to an elastic bistable arch system is proposed as a method for toggling between bifurcated states by controlling the location of actinic irradiation. This approach expands the design space for photomechanical, mutistable structures and actuators. Arch behavior as a function of system parameters is simulated, including conditions leading to multistability. An experimental demonstration and exploration of a constrained photomechanical arch is also presented. It is expected that the concepts presented here could lead to innovations in areas such as energy harvesting, soft robotics, and multistable architected materials. 1. Introduction Bi-and multistable elements hold potential for a variety of applications in areas such as motion stabilization, mechanical or thermal energy harvesting, actuators, sensors, morphing surfaces and structures, and robotics [1-4]. These elements are a subset of a broader class of device elements termed compliant mechanisms. Compliant mechanisms make use of flexible components, rather than discrete, rigid links, and are designed to perform specified functions which combine both motion and force control [5]. These mechanisms are commonly employed in nature for the purpose of enhanced kinematics or accelerated motion (e.g. cicada ribs, hummingbird beaks, or the Venus flytrap [6-8]). By replacing multiple rigid elements with a smaller number of flexible components, compliant mechanisms offer integral, easy-to-fabricate structures with advantages that include, reduced wear and maintenance, lower overall device weight, and novel design strategies (e.g. in energy harvesting and energy dissipation applications) [1,5,9]. Realizations of these mechanisms using photomechanical materials, which convert light into mechanical work, is particularly intriguing because of the opportunity to induce spatially resolved, wireless actuation that can be actively controlled or designed to respond to environmental conditions. While the development of photochemically driven light responsive materials has been the focus of intense investigation [10-14], the utilization of these materials in functional compliant mechanisms [5] for smart structures and devices has not been extensively explored (see Ref. [15-18] for some notable exceptions).
Utilizing sequential layer-by-layer (LBL) coating and subsequent photopolymerization, we develope... more Utilizing sequential layer-by-layer (LBL) coating and subsequent photopolymerization, we developed circularpolarizing and free-standing mirrors with a broad reflection bandwidth. Photopolymerizable cholesteric liquid crystal (CLC) paints were first prepared by considering the intrinsic chirality and the coating viscoelasticity. The polymerstabilized nanostructures had finely tuned helical pitches that selectively reflected light over the entire visible wavelength range. The CLC films exhibited excellent thermomechanical properties and chemical stabilities, which enabled the preparation of patterned optical objects at macroscopic dimensions. The LBL coating and photopolymerization of the CLC paints demonstrated here can provide a simple solution for manufacturing flexible photonic devices with large areas at low cost.
Liquid crystal elastomers (LCEs) exhibit anisotropic mechanical, thermal, and optical properties.... 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...
Directly transducing light into work is attractive for remotely powering soft mechanisms fabricat... more Directly transducing light into work is attractive for remotely powering soft mechanisms fabricated from photoresponsive polymers, but presents challenges for achieving reliable actuation within a control framework. Here, we utilize azobenzene-functionalized polyimides to fabricate actuators characterized by mechanically discrete states. Irradiation initiates the photochemically induced, quasistatic deformation to advance the actuator to the edge of instability. Following this latency, ultrafast snap through actuation (~10ms-scale) ensues. Restricting the role of control to the attainment of the edge of instability, strategies for achieving repetitive actuation via multiplexed irradiation are demonstrated. Approaches are examined for modulating the latency of the actuator using an all-optical strategy as well as mechanical design of the actuator. Prototypical assemblies of these actuators in arrays are used to fabricate morphable surfaces and structures, which is aided by the realization that the ultrafast actuation is characterized by a high power-density on the order of ~kW/m 3 .
dispersed in a liquid crystalline material usually affects the order of the system and the transi... more dispersed in a liquid crystalline material usually affects the order of the system and the transition temperature between various phases. If the dopants undergo photoisomerization between conformers with different shapes, the interactions with the liquid crystal molecules can be different for the material in the dark and during exposure to light of appropriate wavelength. This can be used to achieve isothermal photoinduced phase transitions (phototropism). With proper selection of materials components, both order-to-disorder and disorder-toorder photoinduced transition have been demonstrated. Isothermal order-increasing transitions have been observed recently using naphthopyran derivatives as dopants. We are investigating the changes in order parameter and transition temperature of liquid crystal mixtures containing naphthopyrans and how they are related to exposure conditions and to the concentration and molecular structure of the dopants. We are also studying the nature of the photoinduced phase transitions, and comparing the behavior with that of azobenzene-doped mixtures, in which exposure to light leads to a decrease, instead of an increase, in the order of the system.
Proceedings of the National Academy of Sciences, 2013
Significance Photomechanical effects in polymers are distinguished by the ease with which actinic... 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.
The photodriven oscillation of uniaxially aligned monodomain azo-LCNs was investigated as a funct... more The photodriven oscillation of uniaxially aligned monodomain azo-LCNs was investigated as a function of molecular alignment and temperature spanning a range of +/-40 of the glass transition temperature (T g). Monodomain azo-LCNs were synthesized between glass slide cells coated with Elvamide with an anti-parallel rubbing direction. In this work, multidimensional oscillations that include in plane bending and out of plane twisting are observed when the orientation of the axis is at intermediate angles to the long axis of the cantilever. The added dimensionality to the previously reported in plane oscillation is a result of a photoinduced shear gradient that causes twisting. The degree of twisting is shown to be dependent on both the polarization of the illuminating 442 nm light, and the orientation of the director to the cantilever geometry. Comparatively, rubbery azo-LCNs (e.g. systems heated > T g) show higher amplitude than glassy azo-LCN cantilevers. The relationship between the critical laser intensity and the concentration of azobenzene monomer for the photodriven oscillation behavior of azo-LCNs will also be discussed.
Synthetic approaches to prepare designer materials that localize deformation, by combining rigidi... more Synthetic approaches to prepare designer materials that localize deformation, by combining rigidity and compliance in a single material, have been widely sought. Bottom-up approaches, such as the self-organization of liquid crystals, offer potential advantages over top-down patterning methods such as photolithographic control of crosslink density, relating to the ease of preparation and fidelity of resolution. Here, we report on the directed self-assembly of materials with spatial and hierarchical variation in mechanical anisotropy. The highly nonlinear mechanical properties of the liquid crystalline elastomers examined here enables strain to be locally reduced 415-fold without introducing compositional variation or other heterogeneities. Each domain (Z0.01 mm 2) exhibits anisotropic nonlinear response to load based on the alignment of the molecular orientation with the loading axis. Accordingly, we design monoliths that localize deformation in uniaxial and biaxial tension, shear, bending and crack propagation, and subsequently demonstrate substrates for globally deformable yet locally stiff electronics.
This document is a response to the Kepler Project Call for White Papers. In it, we comment on the... more This document is a response to the Kepler Project Call for White Papers. In it, we comment on the potential for continuing asteroseismology of solar-type and red-giant stars in a 2-wheel Kepler Mission. These stars show rich spectra of solar-like oscillations. Our main conclusion is that by targeting stars in the ecliptic it should be possible to perform high-quality asteroseismology, as long as favorable scenarios for 2-wheel pointing performance are met. Targeting the ecliptic would potentially facilitate unique science that was not possible in the nominal Mission, notably from the study of clusters that are significantly brighter than those in the Kepler field. Our conclusions are based on predictions of 2-wheel observations made by a space photometry simulator, with information provided by the Kepler Project used as input to describe the degraded pointing scenarios. We find that elevated levels of frequency-dependent noise, consistent with the above scenarios, would have a significant negative impact on our ability to continue asteroseismic studies of solar-like oscillators in the Kepler field. However, the situation may be much more optimistic for observations in the ecliptic, provided that pointing resets of the spacecraft during regular desaturations of the two functioning reaction wheels are accurate at the ≤ 1 arcsec level. This would make it possible to apply a post-hoc analysis that would recover most of the lost photometric precision. Without this post-hoc correction-and the accurate re-pointing it requires-the performance would probably be as poor as in the Kepler-field case. Critical to our conclusions for both fields is the assumed level of pointing noise (in the short-term jitter and the longer-term drift). We suggest that further tests will be needed to clarify our results once more detail and data on the expected pointing performance becomes available, and we offer our assistance in this work.
Summary Realized gains from selection for resistance to the fungal disease fusiform rust caused b... 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...
We report here an analysis of the physical stellar parameters of the giant star HD 185351 using K... more We report here an analysis of the physical stellar parameters of the giant star HD 185351 using Kepler short-cadence photometry, optical and near infrared interferometry from CHARA, and high-resolution spectroscopy. Asteroseismic oscillations detected in the Kepler short-cadence photometry combined with an effective temperature calculated from the interferometric angular diameter and bolometric flux yield a mean density, ρ ⋆ = 0.0130 ± 0.0003 ρ ⊙ and surface gravity, log g = 3.280 ± 0.011. Combining the gravity and density we find R ⋆ = 5.35 ± 0.20 R ⊙ and M ⋆ = 1.99 ± 0.23 M ⊙. The trigonometric parallax and CHARA angular diameter give a radius R ⋆ = 4.97 ± 0.07 R ⊙. This smaller radius, when combined with the mean stellar density, corresponds to a stellar mass 1.60 ± 0.08 M ⊙ , which is smaller than the asteroseismic mass by 1.6-σ. We find that a larger mass is supported by the observation of mixed modes in our high-precision photometry, the spacing of which is consistent only for M ⋆ 1.8 M ⊙. Our various and independent mass measurements can be compared to the mass measured from interpolating the spectroscopic parameters onto stellar evolution models, which yields a model-based mass M ⋆,model = 1.87 ± 0.07 M ⊙. This mass agrees well with the asteroseismic value, but is 2.6-σ higher than the mass from the combination of asteroseismology and interferometry. The discrepancy motivates future studies with a larger sample of giant stars. However, all of our mass measurements are consistent with HD 185351 having a mass in excess of 1.5 M ⊙ .
Few studies have quantified the combined effects of silvicultural treatments and genetic improvem... more Few studies have quantified the combined effects of silvicultural treatments and genetic improvement on unit area production of full-sib family blocks of loblolly (Pinus taeda L.) and slash pine (P. elliottii Engelm. var. elliotttii). Efficient operational deployment of genetic materials requires an understanding of possible site and silvicultural treatment interactions to maximize yield potential. We examined genotype (family) by environmental interactions (G  E) through age 5 years using a factorial experiment consisting of silvicultural treatment intensity (operational versus intensive), planting density (1334 versus 2990 trees ha À1) and families (seven elite full-sib loblolly and six elite full-sib slash pine families). In January of 2000, randomized complete block, split-plot experiments were installed at two locations for each species in southeast Georgia and northeast Florida. Five years after planting, both loblolly and slash pine demonstrated significant interactions among several factors: genotype  location (p < 0.028 and p < 0.016, respectively), genotype  silvicultural treatment intensity (p < 0.055 and p < 0.059), and silvicultural treatment intensity  density (p < 0.002 and p < 0.001) for basal area (BA) and standing stem volume (VOL). Genotype  silvicultural treatment interactions were positive, with the best overall performing families responding the greatest to intensive treatment. There were changes in slash pine family rankings between locations, which were partly explained by reductions in growth associated with a combination of fusiform rust infection [Cronartium quercum (Berk.) Miyabe ex Shirai f. sp. fusiforme] and wind damage from the 2004 hurricane season. No three-way interactions, which included family, were evident and all genetic sources were stable across the contrasting planting densities. At age 5, loblolly pine outperformed slash pine (p < 0.0001), especially under the intensive silvicultural intensity. While loblolly performance was similar whether deployed in mixtures or pure family blocks, slash pine tended to be more productive in intimate mixtures than when grown in pure family blocks (p = 0.0754 for aboveground biomass).
Abstract: Predicted breeding values were validated using realized gains estimated from large-rect... 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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Papers by Timothy White