bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of carboxylated and phosphonated single‐walled carbon nanotubes on the transport properties of sulfonated poly(styrene‐isobutylene‐styrene) membranes
Authors: Ruiz‐Colón Eduardo , Pérez‐Pérez Maritza , Suleiman David
Published: October 2018

This study discusses the effect of carboxylated (COOH) and phosphonated (PO3H2) single‐walled carbon nanotubes (SWCNTs) on the transport properties of sulfonated poly(styrene‐isobutylene‐styrene) (SO3H SIBS) as polymer nanocomposite membranes (PNMs) for direct methanol fuel cell (DMFC) and chemical and biological protective clothing (CBPC) applications. The properties were determined as a function of sulfonation level of SIBS, SWCNTs functionalization and loading. A comprehensive materials characterization study was performed to understand the interactions between the nanofillers and the functionalized polymer matrix, and to determine the effect of their incorporation on the resulting nanostructure of the PNMs. Results indicate that the sulfonation level is the variable that dictates nanofiller dispersion, mechanical properties, water absorption capabilities, morphology, and oxidative stability of SO3H SIBS. Meanwhile, the nanofiller loading and functionalization influenced the transport properties. The nanofillers reduced methanol permeation. PO3H2 SWCNTs increased the proton conductivity but at a high sulfonation level (i.e., 90 mol %), the ionic interconnectivity caused a more complex morphology decreasing the transport of protons. Optimal selectivity in transport properties were found with a sulfonation level of 61 mol % and a PO3H2 SWCNTs loading of 1.0 wt. % for DMFC and 0.5 wt. % for CBPC due to changes in morphology and the unique transport mechanism of permeants through the PNMs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2475–2495
Crosslinked colloids with cyclopropenium cations
Authors: Brucks Spencer D. , Steinman Noam Y. , Starr Rachel L. , Domb Abraham J. , Campos Luis M.
Published: October 2018

Chemical crosslinkers are commonly used to stabilize both natural and synthetic macromolecules, while providing opportunities to install functionality and modulate polymer architecture. Here, we introduce the aromatic cyclopropenium cation as a tri‐functional crosslinker of secondary amine‐containing polymers. The one‐step crosslinking reaction is rapid and requires no subsequent purification. When dispersed in aqueous media, the crosslinked polymers form spherical nanoparticles with highly positive charge that is maintained even in alkaline conditions. This synthetic strategy will enable the incorporation of cyclopropenium into a wide variety of macromolecules. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2641–2645
Development of a phenanthrodithiophene‐difluorobenzoxadiazole copolymer exhibiting high open‐circuit voltage in organic solar cells
Authors: Mori Hiroki , Takahashi Ryosuke , Nishihara Yasushi
Published: October 2018

A phenanthrodithiophene (PDT)‐difluorobenzoxadiazole (DFBO) copolymer, P‐PDT‐DFBO, was synthesized and characterized. Replacing a thiadiazole with an oxadiazole ring gives the synthesized polymer a highest occupied molecular orbital (HOMO) about 0.1 V lower, and lowest unoccupied molecular orbital energy levels lower than those of its benzothiadiazole (BT) counterpart, due to the more electron‐deficient oxadiazole. Furthermore, since oxadiazole has a larger dipole moment than BT, P‐PDT‐DFBO exhibits greater aggregation strength than previously reported for P‐PDT‐DFBT. The low‐lying HOMO level of P‐PDT‐DFBO gave about 0.1 V higher open‐circuit voltage (Voc), yielding over 0.9 V in a fabricated solar cell. From grazing incidence wide‐angle X‐ray diffraction analysis, P‐PDT‐DFBO formed a favorable face‐on orientation in both neat and blended films, indicating that the incorporation of an oxadiazole moiety can enhance Voc without any orientation change in the solid state. However, a P‐PDT‐DFBO‐based cell exhibited significantly lower Jsc and FF, and thus less power conversion efficiency, not >4.43%, due to its lower hole mobility than P‐PDT‐DFBT. One possible reason for poor performance may be the low crystallinity of P‐PDT‐DFBO in blended film. This may be caused by its strong aggregation tendency, leading to fast crystallization into a semiamorphous structure or to interference with the construction of long‐range ordered structure. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2646–2655
Direct through anionic, cationic, and radical active species: Terminal carbon–halogen bond for “controlled”/living polymerizations of styrene
Authors: Satoh Kotaro , Mori Yuya , Kamigaito Masami
Published: October 2018

In this work, we examined the synthesis of novel block (co)polymers by mechanistic transformation through anionic, cationic, and radical living polymerizations using terminal carbon–halogen bond as the dormant species. First, the direct halogenation of growing species in the living anionic polymerization of styrene was examined with CCl4 to form a carbon–halogen terminal, which can be employed as the dormant species for either living cationic or radical polymerization. The mechanistic transformation was then performed from living anionic polymerization into living cationic or radical polymerization using the obtained polymers as the macroinitiator with the SnCl4/n‐Bu4NCl or RuCp*Cl(PPh3)/Et3N initiating system, respectively. Finally, the combination of all the polymerizations allowed the synthesis block copolymers including unprecedented gradient block copolymers composed of styrene and p‐methylstyrene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 465–473
On the morphological behavior of ABC miktoarm stars containing poly(cis 1,4‐isoprene), poly(styrene), and poly(2‐vinylpyridine)
Authors: Chernyy Sergey , Mahalik Jyoti P. , Kumar Rajeev , Kirkensgaard Jacob Judas Kain , Arras Matthias M. L. , Kim Hyeyoung , Schulte Lars , Ndoni Sokol , Smith Gregory S. , Mortensen Kell , Sumpter Bobby G. , Russell Thomas P. , Almdal Kristoffer
Published: October 2018

Fundamental understanding of microphase separation in ABC miktoarm copolymers is vital to access a plethora of nonconventional morphologies. Miktoarm stars based on poly(cis 1,4‐isoprene) (I), poly(styrene) (S), and poly(2‐vinylpyridine) (V) are model systems, which allow systematic studies of the effects of composition, chemical microstructure, and temperature on the thermodynamics of microphase separation. Eleven ISV‐x (I:S:V = 1:1:x, v:v:v) miktoarm copolymers were synthesized by anionic polymerization affording well‐defined copolymers with a variable V arm. Equilibrium bulk morphologies of all samples, as evidenced by small‐angle X‐ray scattering, transmission electron microscopy (TEM), and self‐consistent field theory, showed a systematic transition from lamellae (x ≈ 0–0.2) to [8.8.4] tiling (x ≈ 0.6–0.9) to cylinders in undulating lamellae (x ≈ 2–4) and, finally, to hexagonally packed core–shell cylinders (x ≈ 5–8). Chemical microstructure of the I arm [poly(cis 1,4‐isoprene)] versus poly(3,4‐isoprene) is shown to play important role in affecting morphological behavior. To reconcile differences between ISV‐x star morphologies reported in the literature and those reported herein, even for the same composition, effects of the microstructure of I arm on the Flory–Huggins parameter between I and V arms were taken into account in a qualitative manner. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1491–1504
Thermal, mechanical, and topographical evaluation of nonstoichiometric α‐cyclodextrin/poly(ε‐caprolactone) pseudorotaxane nucleated poly(ε‐caprolactone) composite films
Authors: Narayanan Ganesh , Caydamli Yavuz , Tekinalp Halil , Matai Ishita , Boy Ramiz , Chung Ching‐Chang , Shen Jialong , Gupta Bhupender S. , Tonelli Alan E.
Published: October 2018

Three pseudorotaxanes (PpR) comprised of poly (ε‐caprolactone) (PCL) and α‐cyclodextrin (α‐CD) with varying stoichiometric ratios were synthesized and characterized. Wide‐angle X‐ray diffraction (WAXD) and thermogravimetric (TGA) analyses provided conclusive evidence for complexation between the guest PCL and host α‐CD. The as‐synthesized and characterized PpRs were used at 10 and 20% concentrations as nucleants to promote the bulk PCL crystallization in composite films. Both WAXD and TGA provided evidence for intact PpR structures in the composite films. Isothermal differential scanning calorimetric (I‐DSC) analyses, performed at various crystallization temperatures demonstrated significant differences in the crystallization patterns among the composite films. In addition, I‐DSC analyses showed higher Avrami constant values (n) in the PpR‐nucleated composite PCL films (n ~ 3), indicating 3‐dimensional crystal growth. In the case of neat PCL films, however, lower n values indicated crystal growth in 1‐dimensions or 2‐dimensions. Moreover, atomic force microscopic analyses showed large crests and pits in PpR‐nucleated PCL composites, with irregular morphologies leading to higher surface roughness. To the contrary, the crests and pits were much smaller in the neat PCL films, resulting in lower surface roughness values. Finally, mechanical testing revealed higher tensile strength for PpR‐nucleated PCL composites films, demonstrating larger load bearing capabilities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1529–1537
Advancing the computational methodology of rigid rod and semiflexible polymer systems: A new solution to the wormlike chain model with rod‐coil copolymer calculations
Authors: Hannon Adam F. , Joseph Kline R. , DeLongchamp Dean
Published: October 2018

A wormlike chain model for rod type blocks in a rod‐coil diblock copolymer is implemented in the self‐consistent field theory (SCFT) formalism. A pseudo‐spectral method is used to solve for the single‐chain partition function of this copolymer system. Orientation degrees of freedom are discretized using Lebedev sphere rules such that orientation integrations are carried out through a Lebedev quadrature, an approach not used previously in tandem with the pseudo‐spectral method. Phase behavior in the rigid‐rod limit as a function of rod segment volume fraction, Flory–Huggins interaction parameter
χ, degree of polymerization
N, and rod contour length ratio
β are examined in detail in one and two dimensions. Examples extending to three dimensions are included. Semiflexible behavior via the rod bending rigidity
κ is explored. An approximation is used for rigid‐rods that do not need spherical harmonics leading to increased speed in finding equilibrium morphologies. The results show that standing vertical structures may be more easily produced with rigid‐rod blocks compared to coil‐coil lamellae, an important feature in nanolithographic applications. Suggestions are made for using the model in future molecular orientation studies where the model can be used with inverse search methods to measure the values of the model parameters for the real systems. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 29–39
Glass transition broadening via nanofiller‐contiguous polymer network in aromatic thermosetting copolyester nanocomposites
Authors: Bakir Mete , Meyer Jacob L. , Sutrisno Andre , Economy James , Jasiuk Iwona
Published: October 2018

The glass transition is a genuine imprint of temperature‐dependent structural relaxation dynamics of backbone chains in amorphous polymers, which can also reflect features of chemical transformations induced in macromolecular architectures. Optimization of thermophysical properties of polymer nanocomposites beyond the state of the art is contingent on strong interfacial bonding between nanofiller particles and host polymer matrix chains that accordingly modifies glass transition characteristics. Contemporary polymer nanocomposite configurations have demonstrated only marginal glass transition temperature shifts utilizing conventional polymer matrix and functionalized nanofiller combinations. We present nanofiller‐contiguous polymer network with aromatic thermosetting copolyester nanocomposites in which carbon nanofillers covalently conjugate with cure advancing crosslinked backbone chains through functional end‐groups of constituent precursor oligomers upon an in situ polymerization reaction. Via thoroughly transformed backbone chain configuration, the polymer nanocomposites demonstrate unprecedented glass transition peak broadening by about 100 °C along with significant temperature upshift of around 80 °C. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1595–1603
Role of adsorbed chain rigidity in reinforcement of polymer nanocomposites
Authors: Yang Siyang , Hassan Mohammed , Akcora Pinar
Published: October 2018

The thermomechanical behavior of polymer nanocomposites is mostly governed by interfacial properties which rely on particle–polymer interactions, particle loading, and dispersion state. We recently showed that poly(methyl methacrylate) (PMMA) adsorbed nanoparticles in poly(ethylene oxide) (PEO) matrices displayed an unusual thermal stiffening response. The molecular origin of this unique stiffening behavior resulted from the enhanced PEO mobility within glassy PMMA chains adsorbed on nanoparticles. In addition, dynamic asymmetry and chemical heterogeneities existing in the interfacial layers around particles were shown to improve the reinforcement of composites as a result of good interchain mixing. Here, the role of chain rigidity in this interfacially controlled reinforcement in PEO composites is investigated. We show that particles adsorbed with less rigid polymers improve the mechanical properties of composites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2019,57, 9–14
Formations of belonging inAustralia: The role of nostalgia in experiences of time and place
Authors: Cuervo Hernán , Cook Julia
Published: October 2018

Although residential mobility has been studied at length, residentialimmobilityhas been addressed comparatively rarely. In this article, we draw on interviews conducted with 35 participants aged 38–39 in 2012 in Victoria, Australia, in which they were asked to reflect on their lives over the previous 20 years, focusing specifically on those who have remained in or returned to the areas in which they grew up. We focus on the role of nostalgia in the participants' experiences of and relationships with place, finding that far from signifying a purely, or even predominantly, melancholic experience their expressions of nostalgia held the power to enliven the present, even while anchoring them to the past. We contend that nostalgia can form an integral part of practices that reconcile continuity and change and produce feelings of familiarity and comfort, which buffer individuals against the uncertainties associated with wider contexts shaped by rapid social change.
GPUs as boosters to analyze scalar and vector fields in quantum chemistry
Authors: Hernández‐Esparza Raymundo , Vázquez‐Mayagoitia Álvaro , Soriano‐Agueda Luis‐Antonio , Vargas Rubicelia , Garza Jorge
Published: October 2018

The analysis of scalar and vector fields in quantum chemistry is an essential task for the computational chemistry community, where such quantities must be evaluated rapidly to perform a particular study. For example, the atoms in molecules approach proposed by Bader has become popular; however, this method demands significant computational resources to compute the involved tasks in short times. In this article, we discuss the importance of graphics processing units (GPU) to analyze electron density, and related fields, implementing several scalar, and vector fields within the graphics processing units for atoms and molecules (GPUAM) code developed by a group of the Universidad Autónoma Metropolitana in México City. With this application, the quantum chemistry community can perform demanding computational tasks on a desktop, where CPUs and GPUs are used to their maximum capabilities. The performance of GPUAM is tested in several systems and over different GPUs, where a GPU installed in a workstation converts it to a robust high‐performance computing system.
Solvation thermodynamics of neutral and charged solutes using the solvation‐layer interface condition continuum dielectric model
Authors: Mehdizadeh Rahimi Ali , Molavi Tabrizi Amirhossein , Goossens Spencer , Knepley Matthew G. , Bardhan Jaydeep P.
Published: October 2018

We demonstrate that the solvation‐layer interface condition (SLIC) continuum dielectric model for molecular electrostatics, combined with a simple solvent‐accessible‐surface‐area (SASA)‐proportional model for nonpolar solvent effects, accurately predicts solvation entropies of neutral and charged small molecules. The SLIC/SASA model has only seven fitting parameters in total and achieves this accuracy using a training set with only 20 compounds. Despite this simplicity, solvation free energies and entropies are nearly as accurate as those predicted by the more sophisticated Langevin dipoles solvation model. Surprisingly, the model automatically reproduces the negligible contribution of electrostatics to the solvation of hydrophobic compounds. Opportunities for improvement include nonpolar solvation, anion solvation entropies, and heat capacities. More molecular realism may be needed for these quantities. To enable a future, explicit‐solvent‐based assessment of the SLIC/SASA implicit‐solvent model, we predict solvation entropies for the Mobley test set, which are available as Supporting Information.
Charged‐cell periodic DFT simulations via an impurity model based on density embedding: Application to the ionization potential of liquid water
Authors: Tölle Johannes , Severo Pereira Gomes André , Ramos Pablo , Pavanello Michele
Published: October 2018

Calculations of charged systems in periodic boundary conditions (PBC) are problematic because there are spurious interactions between the charges in different periodic images that can affect the physical picture. In addition, the intuitive limit of Coulomb interactions decaying to zero as the interacting charges are placed at infinite separation no longer applies, and for example total energies become undefined. Leveraging subsystem density functional theory (also known as density embedding) we define an impurity model that embeds a finite neutral or charged subsystem within an extended (infinite) surrounding subsystem. The combination of the impurity model and a consistent choice of the Coulomb reference provides us with an algorithm for evaluating the ionization potential (IP) in extended systems. We demonstrate our approach in a pilot calculation of the IP of liquid water, based on a configuration from a prior ab initio molecular dynamics (AIMD) simulation of liquid water (Genova et al., J. Chem. Phys. 2016, 144, 234105). The calculations with the impurity model capture the broadening on the ionization energies introduced by the interactions between the water molecules. Furthermore, the calculated average IP value (10.5 eV) compare favorably to experiments (9.9‐10.06 eV) and very recent simulations based on the GW approximation (10.55 eV), while at the same time outperforming density embedding calculations carried out with a naïve handling of the electrostatic interactions (about 7 eV).
Partition potential for hydrogen bonding in formic acid dimers
Authors: Gómez Sara , Oueis Yan , Restrepo Albeiro , Wasserman Adam
Published: October 2018

The ground‐state energy and density of 4 low‐energy conformations of the formic acid dimer were calculated via partition density functional theory (PDFT). The differences between isolated and PDFT monomer densities display similar deformation patterns for primary and secondary hydrogen bonds (HBs) among all 4 dimers. In contrast, the partition potential shows no transferable features in the bonding regions. These observations highlight the global character of the partition potential and the cooperative effect that occurs when a dimer is bound via more than 1 HB. We also provide numerical confirmation of the intuitive (but unproven) observation that fragment deformation energies are larger for systems with larger binding energies.
Multireference exciplex binding energies: Basis set convergence and error
Authors: Krueger Rachel A. , Blanquart Guillaume
Published: October 2018

In multichromophore systems, characterization of electronic structure requires characterization of exciplexes, electron‐hole pairs delocalized over multiple molecules. Computing exciplex binding energy requires an accurate description of both the noncovalent interactions between the chromophores and their excited electronic states. The critical role of basis set selection for accurate description of noncovalent interactions is well known, but for some of the most accurate excited‐state methods, basis set dependence is incompletely understood. In this work, the impact of basis set size and diffuseness on CASSCF/NEVPT2 binding energies is determined for three systems in their lowest singlet excited states: the benzene excimer, the cis‐butadiene‐benzene exciplex, and the benzene‐naphthalene exciplex. We demonstrate that excellent CBS binding energies may be obtained using the moderately‐sized jun‐cc‐pV(D + d)Z and jun‐cc‐pV(T + d)Z basis sets and a simple N−3 model. Repeating this procedure with the N = 3, 4 basis sets from the most diffuse basis set family applied to each system yields a binding energy of 56.6 ± 1.2 kJ/mol for the benzene excimer and binding energies of 11.1 ± 0.5 kJ/mol and 19.2 ± 1.7 kJ/mol for the cis‐butadiene‐benzene exciplex and the benzene‐naphthalene exciplex, respectively.
Controlling the Charge Density Wave Transition in Monolayer TiSe2: Substrate and Doping Effects
Authors: Kolekar Sadhu , Bonilla Manuel , Diaz Horacio Coy , Hashimoto Makato , Lu Donghui , Batzill Matthias
Published: October 2018

TiSe2 is an exciting material because it can be tuned between superconducting and charge density wave (CDW) transitions. In the monolayer limit, TiSe2 exhibits a sizable energy gap in the CDW phase that makes it a promising quantum material. It is shown that interfacing a single layer of TiSe2 with dissimilar van der Waals materials enables control of its properties. Using angle‐resolved photoemission spectroscopy, the energy gap opening is analyzed as a function of temperature for TiSe2 monolayers supported on different van der Waals substrates. A substantial increase in the CDW transition temperature of ≈45 K is observed on MoS2 compared to graphite (highly oriented pyrolytic graphite) substrates. This control of the CDW in monolayer TiSe2 is suggested to arise from varying charge screening of the unconventional CDW of TiSe2 by the substrate. In addition, the suppression of CDW order and a complete closing of the energy gap by electron doping of monolayer TiSe2 is demonstrated. Regulating the many‐body physics phenomena in monolayer TiSe2 lays the foundation of modifying TiSe2 in, for example, artificial van der Waals heterostructures and thus creates a new approach for utilizing the quantum states of TiSe2 in device applications.
Cooperative autonomous search, grasping, and delivering in a treasure hunt scenario by a team of unmanned aerial vehicles
Authors: Spurný Vojtěch , Báča Tomáš , Saska Martin , Pěnička Robert , Krajník Tomáš , Thomas Justin , Thakur Dinesh , Loianno Giuseppe , Kumar Vijay
Published: October 2018

This paper addresses the problem of autonomous cooperative localization, grasping and delivering of colored ferrous objects by a team of unmanned aerial vehicles (UAVs). In the proposed scenario, a team of UAVs is required to maximize the reward by collecting colored objects and delivering them to a predefined location. This task consists of several subtasks such as cooperative coverage path planning, object detection and state estimation, UAV self‐localization, precise motion control, trajectory tracking, aerial grasping and dropping, and decentralized team coordination. The failure recovery and synchronization job manager is used to integrate all the presented subtasks together and also to decrease the vulnerability to individual subtask failures in real‐world conditions. The whole system was developed for the Mohamed Bin Zayed International Robotics Challenge (MBZIRC) 2017, where it achieved the highest score and won Challenge No. 3—Treasure Hunt. This paper does not only contain results from the MBZIRC 2017 competition but it also evaluates the system performance in simulations and field tests that were conducted throughout the year‐long development and preparations for the competition.
Data‐driven mobility risk prediction for planetary rovers
Authors: Skonieczny Krzysztof , Shukla Dhara K. , Faragalli Michele , Cole Matthew , Iagnemma Karl D.
Published: October 2018

Mobility assessment and prediction continues to be an important and active area of research for planetary rovers, with the need illustrated by multiple examples of high slip events experienced by rovers on Mars. Despite slip versus slope being one of the strongest and most broadly used relationships in mobility prediction, this relationship is nonetheless far from precisely predictable. Although the literature has made significant advances in the predictability of average mobility, the other key related aspect of the problem is the risk caused by edge cases. A key contribution of this study is a metric for explicitly assessing mobility risk based on data‐driven nonparametric slip versus slope relationships. The data‐driven approach is meant to address limitations of past model‐based approaches. The metric is informed by past work in terramechanics relating drawbar pull (i.e., net traction) to slip: High slip fraction (HSF), defined as the proportion of slip data points above 20%. Another contribution is a low complexity mobility prediction framework, the autonomous soil assessment system. Field tests demonstrate that, for sand and gravel, rover trafficability becomes nonlinear and highly variable above the 20% slip threshold. HSF is shown to be a useful metric for categorizing rover‐terrain interactions into low, medium, or high risk, correctly and consistently. Furthermore, the metric is shown to be useful for early detection of potentially hazardous changes in rover‐terrain conditions. The combination of HSF with an appropriately sized queue structure for modeling slip versus slope enables an appropriate balance between responsiveness and stability.
Shared autonomy for low‐cost underwater vehicles
Authors: Lawrance Nicholas , DeBortoli Robert , Jones Dylan , McCammon Seth , Milliken Lauren , Nicolai Austin , Somers Thane , Hollinger Geoffrey
Published: October 2018

This field report presents an overview of the development and testing of a semi‐autonomous underwater vehicle (sAUV). The work presented here is aimed at bridging the gap between current remotely operated vehicles and autonomous research platforms by developing shared autonomy capabilities for low‐cost underwater vehicles. We use commercially available components and open‐source software interfaces to provide a wider range of capabilities for underwater autonomy research at a lower cost than previously available systems. We describe the overall structure of the system, discuss its capabilities, and provide results demonstrating system performance. We place particular emphasis on shared autonomy, where a human operator is assisted in controlling an underwater tethered vehicle. We present three capabilities developed for the sAUV: (a) an assisted control mode that provides a variable level of assistance using an on‐line estimate of user skill level, (b) a planner to generate paths that avoid tether entanglement, and (c) a sonar processing algorithm that identifies informative sonar images for selecting features for 3D scene reconstruction. The vehicle has been deployed on five off‐shore and near‐shore marine field deployments since 2015, and this report includes selected results from four of those trials to demonstrate the capabilities and limitations of the sAUV system.
Evaluating flow management as a strategy to recover an endangered sturgeon species in the Upper Missouri River, USA
Authors: Erwin Susannah O. , Bulliner Edward A. , Fischenich J. Craig , Jacobson Robert B. , Braaten Patrick J. , DeLonay Aaron J.
Published: October 2018

In the Upper Missouri River, Fort Peck and Garrison Dams limit the length of free‐flowing river available to the endangered pallid sturgeon. These barriers restrict the upstream migration of adults and downstream larval dispersal. A one‐dimensional (1D) modelling framework is currently in use to evaluate reservoir operation alternatives and to simulate drift of dispersing free embryos for different flow regimes and reservoir stages. This paper presents the results of a large‐scale tracer experiment conducted in 2016 and associated modelling performed to evaluate flow management scenarios that might aid species recovery. Breakthrough curves from the tracer experiment were used to infer the 1D longitudinal dispersion coefficient from a parameter optimization procedure. Simulations generated using the calibrated 1D advection–dispersion model were compared with field observations of the passive tracer and with larval fish collected during a previous experiment in 2007. When used with the appropriate range of dispersion coefficients, the 1D modelling framework agrees well with the available direct measurements of larval drift distances. Although we cannot unequivocally state whether insufficient length of free‐flowing river alone is causing recruitment failure, given the current thermal regime and our understanding of pallid sturgeon development, the time required for pallid sturgeon to transition to the benthos and initiate feeding might exceed the duration of drift available given constraints of reservoir operations.
Simulating the effect of environmental flow duration on seedling emergence from riparian seed banks of the Upper Hunter River, New South Wales
Authors: Stone Luke , Fryirs Kirstie , Leishman Michelle
Published: October 2018

Passive riparian revegetation techniques are important tools in river rehabilitation. However, the utility of the sediment seed bank as a passive riparian regeneration option is poorly understood. After modelling a range of flows for field‐surveyed cross sections, a glasshouse seedling emergence experiment was undertaken to compare the effects of simulated flow duration on seedling emergence of desirable riparian species that occur on benches of the gravel‐bedded Hunter River near Muswellbrook, New South Wales. The duration of inundation did have an effect (although not always significant) on seed germination for most species. The most successful simulated flood conditions differed among species, with the control treatment (no inundation) resulting in the most germination for only two of the 10 species examined. These findings suggest that although environmental flows for the sole purpose of stimulating the riparian seed bank in order to facilitate regeneration of desirable riparian species would be largely ineffective and complicated by differing inundation responses among species, seed bank stimulation using environmental flows could be a value‐added benefit from flows allocated for other purposes. As such, consideration of flow duration is worthy of inclusion in environmental flow allocation planning.
Counting Hamilton cycles in sparse random directed graphs
Authors: Ferber Asaf , Kwan Matthew , Sudakov Benny
Published: October 2018

Let be the random directed graph on n vertices where each of the possible arcs is present independently with probability p. A celebrated result of Frieze shows that if then typically has a directed Hamilton cycle, and this is best possible. In this paper, we obtain a strengthening of this result, showing that under the same condition, the number of directed Hamilton cycles in is typically . We also prove a hitting‐time version of this statement, showing that in the random directed graph process, as soon as every vertex has in‐/out‐degrees at least 1, there are typically directed Hamilton cycles.
Spanning universality in random graphs
Authors: Ferber Asaf , Nenadov Rajko
Published: October 2018

A graph is said to be ‐universal if it contains every graph with n vertices and maximum degree at most Δ as a subgraph. Dellamonica, Kohayakawa, Rödl and Ruciński used a “matching‐based” embedding technique introduced by Alon and Füredi to show that the random graph is asymptotically almost surely ‐universal for , a threshold for the property that every subset of Δ vertices has a common neighbor. This bound has become a benchmark in the field and many subsequent results on embedding spanning graphs of maximum degree Δ in random graphs are proven only up to this threshold. We take a step towards overcoming limitations of former techniques by showing that is almost surely ‐universal for .
Using classroom observations to evaluate science teaching: Implications of lesson sampling for measuring science teaching effectiveness across lesson types
Authors: Mikeska Jamie N. , Holtzman Steven , McCaffrey Daniel F. , Liu Shuangshuang , Shattuck Tamara
Published: October 2018

Despite the prevalent use of observational measures in teacher evaluation systems, research has only recently begun to take into account how aspects of the instructional environment and lesson sampling design may interact with teachers’ scores on these measures. Instead, one assumption guiding current evaluation systems is that the variation in teachers’ instructional practices captured by the lessons sampled is a valid measure of their teaching quality. Our study investigates this assumption by examining whether scores from observational measures of science teachers’ instructional practices vary depending on lesson type. Results show that science teachers’ scores on certain observational measures vary across lab and nonlab lessons, suggesting that the claims one can make about science teaching effectiveness are dependent on the particular types of lessons observed. Given the increasing prominence and use of observational measures within evaluation systems, it is imperative to ensure that the observed lessons adequately represent variation in a teacher’s practice and are not subject to undue instability from the types of lessons included in the sample, especially in science where there are clear distinctions in the instructional practices teachers employ across lab and nonlab lessons. Implications for measuring science teaching quality are discussed.
What is engineering? Elaborating the nature of engineering for K‐12 education
Authors: Pleasants Jacob , Olson Joanne K.
Published: October 2018

What is engineering? What do engineers do? How is engineering related to, but distinct from, science? These questions all relate to the nature of engineering (NOE), and as engineering is incorporated into K‐12 education across the United States, the NOE is becoming increasingly important for students and teachers. While many policy documents call for students to learn more about the structure of the engineering discipline, little has been done to define the NOE construct. This paper presents key dimensions of the NOE via a framework synthesized from studies of the engineering discipline from philosophical, historical, and sociological perspectives, as well as perspectives from within the engineering field. The framework identifies and elaborates nine features of engineering, each of which capture an important aspect of the NOE. For teachers, these features serve as points of entry for discussing NOE ideas with students. For researchers, the features provide a set of constructs to guide future inquiries into teachers’ and students’ NOE knowledge.
Applying the ambitious science teaching framework in undergraduate biology: Responsive talk moves that support explanatory rigor
Authors: Grinath Anna S. , Southerland Sherry A.
Published: October 2018

Orchestrating opportunities for students to engage in scientific talk in the classroom is challenging for most teachers and even more so for novice teaching assistants (TAs) who typically instruct introductory science laboratories at the postsecondary level. This study was designed to understand how TA moves are related to instances of scientific discourse in the classroom (meaning discourse that includes a high degree of explanatory rigor). For this, we examined the enactment of a planned “elicitation discussion” that took place in 26 sections of a general biology laboratory for nonscience majors. Our research was driven by two‐related questions: What patterns of discourse emerged? What TA discursive moves were related to high levels of explanatory rigor in student talk? Using conversation analysis, four distinct patterns of discourse were identified, each representing different levels of explanatory rigor. Regression analysis revealed that the type of question the TA used to initiate classroom talk was not significantly related to the students’ explanatory rigor. Rather, the most important aspect of TA talk for elevating the explanatory rigor of student discourse was TA responses to student contributions to TA's initiating questions. The implications of these findings for TA professional development are discussed.
Immunosuppression Agent Cyclosporine Reduces Self-Renewal and Vessel Regeneration Potentiation of Human Endothelial Colony Forming Cells
Authors: Sim Seen-Ling , Alexis Josue , Roy Edwige , Shafiee Abbas , Khosrotehrani Kiarash , Patel Jatin
Published: October 2018

Endothelial colony forming cells (ECFC) and mesenchymal stem cells (MSC) combined have great potential to be used for cell therapy of ischemic vascular diseases. However, to improve allogeneic stem cell engraftment the use of immunosuppression, such as cyclosporine has been suggested. Our aim was to assess the impact of cyclosporine on hind limb revascularisation upon MSC and ECFC combination therapy. Balb/c immunocompetent mice subjected to hind limb ischemia (right femoral artery ligation) were given both human ECFC and MSC (weekly intramuscular injections) with or without cyclosporine (daily injection). Surprisingly, mice receiving cyclosporine had a significant decrease in reperfusion based on laser Doppler imaging compared to vehicle controls and had poorer limb survival. In vitro, the downstream calcineurin target NFATC4 was highly expressed in the self-renewing fraction of ECFCs. ECFCs cultured with cyclosporine had reduced colony formation capacity and tube formation in Matrigel. Lastly, ECFC displayed increased proliferation and loss of capacity for long term culture when in the presence of cyclosporine clearly showing a loss of quiescence and progenitor function. Our findings demonstrate the deleterious impact of cyclosporine on ECFC function, with significant impact on ECFC-based allogeneic cellular therapy. Stem Cells Translational Medicine  2019;8:162&7
Matoy jirofo, masaka lavany: Rural–urban migrants' livelihood strategies through the lens of the clove commodity cycle in Madagascar
Authors: Tilghman Laura M.
Published: October 2018

Residents of many African cities face economic uncertainty due to high rates of under‐ and unemployment and lack of government support. In response, many urban Africans have fortified their links to rural areas as a strategy to weather uncertainty and reduce vulnerability. Scholars have documented high rates of ownership of rural resources (e.g., land, housing, and livestock) by people living in cities as proof of the strength of rural–urban linkages in Africa. In this article, I argue that the use of rural resources to reduce urban expenditures or increase income cannot be assumed and depends on the social relationships between city and village residents. I draw on twenty‐four months of ethnographic fieldwork with rural–urban migrants in northeastern Madagascar. I focus on the clove season of 2011–12, a spectacular moment in which high yields and prices created a market boom for this agricultural commodity. While many urban migrants had claimed access to clove trees, not all of these individuals were successful in actually accessing the clove crop or the income generated from its sale during the 2011–12 season. Exploring the winners and losers in this commodity boom reveals that investing in social relationships with rural family and friends has important economic consequences for urban migrants.
Moral imaginings of the market and the state in contemporary China
Authors: Kuever Erika
Published: October 2018

In contemporary China, the site of endemic food scandals and persistent anxiety about the quality and safety of products, moral imaginings of the market implicate state actors and institutions. In articulating perceived injustices, Chinese consumer‐citizens resort not to the “mutual rights and obligations” of buyers and sellers specified in the Consumer Law but to ideals of fairness that include the role of the state in regulating the market. The law defines the normative rights and obligations of consumers and sellers, but citizens largely reject this depoliticized formulation, instead expressing expectations of state action that mirror a moral economy framework. This understanding of the persistence of fake and dangerous goods as a manifestation of poor governance allows for a rereading of Marx's famous maxim. For Marx, the commodity disguises an exploitative relationship between buyers and sellers, but in societies characterized by industrial production, the state mediates interactions between producers and consumers through regulation and the law. Demands from Chinese consumer‐citizens that the state curtail the production and sale of fake and dangerous goods and punish bad actors reveal an understanding of the modern state's role in the production of the commodity. They also illustrate the importance of the historical context of the state–citizen relationship in framing moral claims.
Assessing the influence of treatment nonadherence on noninferiority trials using the tipping point approach
Authors: Kim Mimi , Wang Cuiling , Xue Xiaonan
Published: October 2018

In noninferiority (NI) trials, an ongoing methodological challenge is how to handle in the analysis the subjects who are nonadherent to their assigned treatment. Some investigators perform the intent‐to‐treat (ITT) as the primary analysis and the per‐protocol (PP) analysis as sensitivity analysis, whereas others do the reverse since ITT results may be anticonservative in the NI setting. But even when there is agreement between the ITT and PP approaches, NI of the experimental therapy to the comparator is not guaranteed. We propose that a tipping point method be used to further assess the impact of nonadherence on the results of a NI trial. In this approach, data from the nonadherers obtained after treatment discontinuation is not used, and their outcomes under the counterfactual situation of complete adherence are considered missing. The tipping point analysis indicates how sensitive the NI trial results are to the values of these missing counterfactual outcomes. The advantages of this approach are that a model or mechanism for the missing outcomes does not have to be assumed, and all subjects who were randomized are included in the analysis. We consider both binary and continuous outcomes and propose extensions to accommodate different types of nonadherence. The methods are illustrated with examples from two NI trials, one to evaluate different doses of radiation therapy to treat painful bone metastases and the other to compare treatments for reducing depression in adolescents.
The use of weight adjusted for height rather than body mass index to assess growth trajectory: Results from a population‐based cohort
Authors: Araújo Joana , Ramos Elisabete , Mishra Gita D. , Severo Milton
Published: October 2018

We compared different growth models parameterizations regarding (i) adjustment of weight‐for‐height, as denoted by body mass index (BMI); (ii) adjustment for different covariates, ie, age or height; and (iii) the use of different smoothing methods, ie, polynomial, fractional polynomial, or linear splines. A total of 11 459 measurements of weight and height from 719 participants were used, obtained from the EPITeen cohort at 13, 17, and 21 years, and extracted from child health books. The individual growth curves were modeled using mixed‐effects polynomial, fractional polynomial, and linear splines, and each model parameterization included as covariate age or height. The goodness‐of‐fit of the model parametrizations was compared using the relative squared error (RSE) and the relative absolute error (RAE). The adjustment of weight‐for‐height as denoted by BMI was found to be biased, especially for extreme values of height and presented the worst fit indexes from all model parameterizations tested (RSE = 12.46%; RAE = 22.63%). Regardless of the smoothing method, the weight‐for‐height retrieved the best fit indexes in comparison to the adjustment for age. With regard to the smoothing methods and comparing weight‐for‐height model parameterizations, the fractional polynomial model performed better (RSE = 0.75%; RAE = 5.70%), followed by linear splines (RSE = 0.77%; RAE = 5.82%), and conventional polynomial (RSE = 0.91%; RAE = 6.82%). Therefore, growth modeling in pediatric age should be based on the modeling of weight‐for‐height because the use of BMI leaves residual confounding for height. Regarding the smoothing methods, although differences were relatively small, the fractional polynomials performed better in comparison to conventional polynomials and linear splines.
Picoanalysis of Drugs in Biofluids with Quantitative Label‐Free Surface‐Enhanced Raman Spectroscopy
Authors: Turzhitsky Vladimir , Zhang Lei , Horowitz Gary L. , Vitkin Edward , Khan Umar , Zakharov Yuri , Qiu Le , Itzkan Irving , Perelman Lev T.
Published: October 2018

The enormous increase of Raman signal in the vicinity of metal nanoparticles allows surface‐enhanced Raman spectroscopy (SERS) to be employed for label‐free detection of substances at extremely low concentrations. However, the ultimate potential of label‐free SERS to identify pharmaceutical compounds at low concentrations, especially in relation to biofluid sensing, is far from being fully realized. Opioids are a particular challenge for rapid clinical identification because their molecular structural similarities prevent their differentiation with immunolabeling approaches. In this paper, a new method called quantitative label‐free SERS (QLF‐SERS) which involves the formation of halide‐conjugated gold nanoclusters trapping the analyte of interest near the SERS hot spots is reported, and it is demonstrated that it yields a 105 fold improvement in the detection limit over previously reported results for the entire class of clinically relevant opioids and their metabolites. Measurements of opioid concentrations in multicomponent mixtures are also demonstrated. QLF‐SERS has comparable detection limits as currently existing laboratory urine drug testing techniques but is significantly faster and inexpensive and, therefore, can be easily adapted as part of a rapid clinical laboratory routine.