Publications

Abstract This study investigated pupillary and behavioral responses to an emotional word valence identification paradigm among 32 pre-/early pubertal and 34 mid-/late pubertal typically developing children and adolescents. Participants were asked to identify the valence of positive, negative, and neutral words while pupil dilation was assessed using an eyetracker. Mid-/late pubertal children showed greater peak pupillary reactivity to words presented during the emotional word identification task than pre-/early pubertal children, regardless of word valence. Mid-/late pubertal children also showed smaller sustained pupil dilation than pre-/early pubertal children after the word was no longer on screen. These findings were replicated controlling for participants' age. In addition, mid-/late pubertal children had faster reaction times to all words, and rated themselves as more emotional during their laboratory visit compared to pre-/early pubertal children. Greater recall of emotional words following the task was associated with mid-/late pubertal status, and greater recall of emotional words was also associated with higher peak pupil dilation. These results provide physiological, behavioral, and subjective evidence consistent with a model of puberty-specific changes in neurobehavioral systems underpinning emotional reactivity.

Magnetic force microscopy probes were obtained via the solution phase electrochemical deposition of cobalt nanostructures at the probe apexes. Single tips were fabricated in an atomic force microscope fluid cell. Multiple tips were produced in a single batch with an alternating potential in an electrochemical cell. The probes achieve 50nm spatial resolution.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We demonstrate the selective, pulsed-laser deposition of hexagonal GaS and monoclinic Ga2S3 films on sapphire substrates from a single Ga2S3 target in high-vacuum conditions. Growth at substrate temperatures below 550 °C causes GaS film formation, which indicates non-stoichiometric transfer from the target to the film. Surprisingly, stoichiometric transfer occurs at substrate temperatures above 650 °C with monoclinic Ga2S3 as the preferred, higher S-content phase. Through a series of growth and annealing experiments, we show that GaS nucleation under S-deficient conditions leads to the preferred growth of this layered, hexagonal phase below 550 °C. Furthermore, GaS films annealed above 650 °C under high vacuum are transformed to Ga2S3, reflecting the greater stability of the monoclinic phase. By first growing Ga2S3 at a higher temperature and subsequently growing GaS at a lower temperature, we can fabricate GaS/Ga2S3 heterostructures in a single growth process.

The paper describes an analog current mode realization of Discrete-Time Cellular Neural Networks (DTCNNs) with high cell density, which have local analog and local logic memory. Hence, some important parts of the CNN Universal Machine concept are implemented. The computation speed can be adjusted simply to the application by changing the clock rate. The circuit components are described in detail and SPICE level 2 simulation results are given for the ORBIT 2.0 /spl mu/m process. A layout has been designed for a chip with 12 by 12 cells on a square grid realizing a one-neighborhood with 9 feedback and 9 control coefficients. The cell size is 619 /spl mu/m by 425 /spl mu/m and the simulated speed is between 1 MHz and 10 MHz depending on the minimum value of the state current. For the latter this leads to a simulated performance of 25.9 10/sup 9/ XPS for a single chip operation with an effective area of 0.379 cm/sup 2/ and a worst case power consumption of 0.86 W. Another important feature of the chip is its capability for a spatial cascaded connection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Abstract not Available.

We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.

Throughout the history of Li-ion batteries, cathode materials with high energy density have been sought from well-ordered oxide compounds in which lithium and other cations occupy distinct sites within an oxygen FCC framework.[1,2] In contrast, cation-disordered materials have received only a limited attention as cathodes because lithium diffusion tends to be limited by their structure, resulting in poor cycling performance.[3] However, recent studies have shown that cation-disordered materials can in fact deliver higher energy densities than the ordered materials once enough excess lithium ( x &gt; 0.1 in Li1+ x TM1- x O2, TM: transition metal) is introduced to their structure, opening a new search space for high energy density Li-ion cathodes.[4,5] The understanding of disordered cathodes was first made with percolation theory which links the composition of a compound to the population of Li diffusion channels with low barriers.[4,5] In rocksalt-type oxides, Li diffusion takes place between two octahedral sites through a face-sharing tetrahedral site. Li+ ion in this tetrahedral site in the activate state in diffusion, whose electrostatic energy largely determines the diffusion barrier. Hence, (i) the oxidation states of species in the face-sharing octahedral sites and (ii) the tetrahedron height, along which the activated Li+ ion relaxes away the strong electrostatic repulsion from face-sharing octahedral species, largely determine the activity of a Li diffusion channel. [4] In the disordered rocksalt structure with small tetrahedron heights, it was found that only the diffusion channel through which an activated Li+ ion shares faces with no transition metal ions (0-TM channels) has low Li diffusion barriers. However, for the 0-TM channel to dominate macroscopic Li diffusion, the channel must be percolating in a crystal structure, such that every Li hopping occurs through the channel. Percolation theory predicts that Li excess introduces such 0-TM percolation, and hence Li-excess disordered cathodes should allow for facile Li diffusion.(Fig. 1a)[4] Consistent to the theory, recently developed cation-disordered Li-excess cathodes (e.g. Li1.211Mo0.467Cr0.3O2, Li1.3Mn0.4Nb0.3O2) deliver high capacity and energy density with facile Li diffusion.[4,6] However, percolation theory alone cannot completely guide the design of high capacity disordered cathodes because it does not take redox process into account. While percolation theory predicts higher Li-excess contents should lead to better disordered cathodes, higher Li excess necessarily leads to lower transition metal contents hence their redox capacity.[7] Therefore, unless transition metals can exchange multiple electrons or oxygen redox can reversibly occur, the electron-storage capacity should decrease with Li excess, which is unwanted. In this presentation, we explain how lithium excess can affect both Li diffusion and redox process in disordered cathodes using percolation theory and ligand field theory, respectively.(Fig. 1b, 1c)[4,8] Based on this understanding, we will show that Li diffusion and redox process in the materials are highly correlated hence need to be considered simultaneously. We further demonstrate how such complete understanding can be used to explain the performance of recently developed high capacity disordered cathodes (e.g. Li-Ni-Ti-Mo oxides) and to design improved disordered cathode materials.[7,8] References [1] K. Kang, Y. S. Meng, J. Bréger, C. P. Grey, G. Ceder, Science 311, 977–980 (2006). [2] M. M. Thackeray, P. J. Johnson, L. A. De Picciotto, P. G. Bruce, J. B. Goodenough, Mater. Res. Bull.19, 179–187 (1984). [3] M. N. Obrovac, O. Mao, J. R. Dahn, Solid State Ion.112, 9–19 (1998). [4] J. Lee, A. Urban, X. Li, D. Su, G. Hautier, G. Ceder, Science 343, 519–522 (2014). [5] A. Urban, J. Lee, G. Ceder, Adv. Energy Mater.4, 1400478 (2014). [6] N. Yabuuchi et al., PNAS 112, 7650–7655 (2015). [7] J. Lee, D.-H. Seo, M. Balasubramania, N. Twu, X. Li, G. Ceder, Energy Environ. Sci.8, 3255 (2015). [8] D.-H. Seo‡, J. Lee‡, A. Urban, R. Malik, SY. Kang, G. Ceder, Nature Chem., in press (2016) (‡ equal contribution) Figure 1

We review the development of virtual tests for high-temperature ceramic matrix composites with textile reinforcement. Success hinges on understanding the relationship between the microstructure of continuous-fiber composites, including its stochastic variability, and the evolution of damage events leading to failure. The virtual tests combine advanced experiments and theories to address physical, mathematical, and engineering aspects of material definition and failure prediction. Key new experiments include surface image correlation methods and synchrotron-based, micrometer-resolution 3D imaging, both executed at temperatures exceeding 1,500°C. Computational methods include new probabilistic algorithms for generating stochastic virtual specimens, as well as a new augmented finite element method that deals efficiently with arbitrary systems of crack initiation, bifurcation, and coalescence in heterogeneous materials. Conceptual advances include the use of topology to characterize stochastic microstructures. We discuss the challenge of predicting the probability of an extreme failure event in a computationally tractable manner while retaining the necessary physical detail.

Fish, reptiles, and mammals can possess flexible dermal armor for protection. Here we seek to find the means by which Nature derives its protection by examining the scales from several fish ( Atractosteus spatula , Arapaima gigas , Polypterus senegalus, Morone saxatilis, Cyprinius carpio) , and osteoderms from armadillos, alligators, and leatherback turtles. Dermal armor has clearly been developed by convergent evolution in these different species. In general, it has a hierarchical structure with collagen fibers joining more rigid units (scales or osteoderms), thereby increasing flexibility without significantly sacrificing strength, in contrast to rigid monolithic mineral composites. These dermal structures are also multifunctional, with hydrodynamic drag (in fish), coloration for camouflage or intraspecies recognition, temperature and fluid regulation being other important functions. The understanding of such flexible dermal armor is important as it may provide a basis for new synthetic, yet bioinspired, armor materials.

Abstract The Wide Field InfraRed Survey Telescope ( WFIRST ) was the highest-ranked large space-based mission of the 2010 New Worlds , New Horizons decadal survey. It is now a NASA mission in formulation with a planned launch in the mid 2020s. A primary mission objective is to precisely constrain the nature of dark energy through multiple probes, including Type Ia supernovae (SN Ia). Here, we present the first realistic simulations of the WFIRST SN survey based on current hardware specifications and using open-source tools. We simulate SN light curves and spectra as viewed by the WFIRST wide-field channel (WFC) imager and integral field channel (IFC) spectrometer, respectively. We examine 11 survey strategies with different time allocations between the WFC and IFC, two of which are based upon the strategy described by the WFIRST Science Definition Team, which measures SN distances exclusively from IFC data. We propagate statistical and, crucially, systematic uncertainties to predict the Dark Energy Task Force figure of merit (FoM) for each strategy. Of the strategies investigated, we find the most successful to be WFC focused. However, further work in constraining systematics is required to fully optimize the use of the IFC. Even without improvements to other cosmological probes, the WFIRST SN survey has the potential to increase the FoM by more than an order of magnitude from the current values. Although the survey strategies presented here have not been fully optimized, these initial investigations are an important step in the development of the final hardware design and implementation of the WFIRST mission.