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The field electron emission properties of carbon nanotube (CNT) films composed of densely packed and highly aligned CNTs were investigated. The CNT films were produced by a continuous film casting process and are spooled into long lengths with the CNTs aligned lengthwise in the film. The anisotropic nature of the CNT film morphology was confirmed by performing specific conductivity measurements in directions both parallel and perpendicular to the aligned CNT microstructure. Field emission experiments were performed on 5 and 10 mm wide films that were mechanically cut into small samples and then vertically mounted so that the emission occurred from the film edge. The films were mounted with the aligned CNT microstructure oriented either parallel or perpendicular to the direction of the applied electric field. The highest emission currents were produced by films mounted in the parallel alignment configuration. Additional experiments were performed on films that were folded, which eliminated surface irregularities at the film edge due to the cutting process. SEM imaging performed at the ridge of the folded film before and after field emission (FE) experiments showed that films mounted in the parallel alignment configuration had minimal surface damage after FE, while films mounted in the perpendicular alignment configuration showed substantial damage. The effective emission area and field enhancement factor were extracted from the FE data using the orthodox Fowler–Nordheim theory. Folded CNT film cathodes mounted in the parallel alignment configuration produced the highest emission currents, while demonstrating a larger emission area and lower field enhancement factor. [ABSTRACT FROM AUTHOR]

This work seeks to understand how the topography of a surface can be engineered to control secondary electron emission (SEE) for multipactor suppression. Two unique, semi-empirical models for the secondary electron yield (SEY) of a micro-porous surface are derived and compared. The first model is based on a two-dimensional (2D) pore geometry. The second model is based on a three-dimensional (3D) pore geometry. The SEY of both models is shown to depend on two categories of surface parameters: chemistry and topography. An important parameter in these models is the probability of electron emissions to escape the surface pores. This probability is shown by both models to depend exclusively on the aspect ratio of the pore (the ratio of the pore height to the pore diameter). The increased accuracy of the 3D model (compared to the 2D model) results in lower electron escape probabilities with the greatest reductions occurring for aspect ratios less than two. In order to validate these models, a variety of micro-porous gold surfaces were designed and fabricated using photolithography and electroplating processes. The use of an additive metal-deposition process (instead of the more commonly used subtractive metal-etch process) provided geometrically ideal pores which were necessary to accurately assess the 2D and 3D models. Comparison of the experimentally measured SEY data with model predictions from both the 2D and 3D models illustrates the improved accuracy of the 3D model. For a micro-porous gold surface consisting of pores with aspect ratios of two and a 50% pore density, the 3D model predicts that the maximum total SEY will be one. This provides optimal engineered surface design objectives to pursue for multipactor suppression using gold surfaces. [ABSTRACT FROM AUTHOR]

This paper studies field emission (FE) from a single carbon nanotube (CNT) fiber with different anode-cathode (AK) gap distances. It is found that the field enhancement factor depends strongly on the finite AK gap distance, due to the combination of geometrical effects and possible fiber morphology change. The geometrical effects of AK gap distance on the field enhancement factor are confirmed using COMSOL simulations. The slope drop in the Fowler-Northeim (FN) plot of the FE data in the high voltage is related to the electrical contact resistance between the CNT fiber and the substrate. It is found that even a small series resistance to the field emitter (<30% of the emission gap impedance) can strongly modify the FE characteristics in the high voltage regime, inducing a strong deviation from the linear FN plot. [ABSTRACT FROM AUTHOR]

The authors forgot to include the following disclaimer in Acknowledgements section. [ABSTRACT FROM AUTHOR]

In sentences such as "Some dogs are mammals," the literal semantic meaning ("Some and possibly all dogs are mammals") conflicts with the pragmatic meaning ("Not all dogs are mammals," known as a scalar implicature). Prior work has shown that adults vary widely in the extent to which they adopt the semantic or pragmatic meaning of such utterances, yet the underlying reason for this variation is unknown. Drawing on theoretical models of scalar implicature derivation, we explore the hypothesis that the cognitive abilities of executive function (EF) and theory of mind (ToM) contribute to this observed variation. In Experiment 1, we show that individuals with better ToM are more likely to compute a scalar implicature and adopt the pragmatic meaning of an utterance; however, EF makes no unique contribution to scalar implicature comprehension after accounting for ToM. In Experiment 2, we replicate this finding and assess whether it generalizes to the comprehension of other pragmatic phenomena such as indirect requests (e.g., "It's hot in here" uttered to ask for something to be done) and metaphor (e.g., "to harvest courage"). This is the first evidence that differences in ToM are associated with pragmatic competence in neurotypical adults across distinct pragmatic phenomena., (© 2021 Cognitive Science Society, Inc.)

Foreign-accented non-native speakers sometimes face negative biases compared to native speakers. Here we report an advantage in how comprehenders process the speech of non-native compared to native speakers. In a series of four experiments, we find that under-informative sentences are interpreted differently when attributed to non-native compared to native speakers. Specifically, under-informativeness is more likely to be attributed to inability (rather than unwillingness) to say more in non-native as compared to native speakers. This asymmetry has implications for learning: under-informative teachers are more likely to be given a second chance in case they are non-native speakers of the language (presumably because their prior under-informativeness is less likely to be intentional). Our results suggest strong effects of non-native speech on social-pragmatic inferences. Because these effects emerge for written stimuli, they support theories that stress the role of expectations on non-native comprehension, even in the absence of experience with foreign accents. Finally, our data bear on pragmatic theories of how speaker identity affects language comprehension and show how such theories offer an integrated framework for explaining how non-native language can lead to (sometimes unexpected) social meanings., Competing Interests: Declaration of competing interest None., (Copyright © 2019. Published by Elsevier B.V.)

Spatially resolved wavefront measurements are presented during nonlinear self-collapse and provide the first detailed characterization of wavefront evolution during filament formation. The wavefront dynamics of key nonlinear processes including Kerr self-focusing, ionization and plasma defocusing, and dynamic spatial replenishment are identified and resolved in both the filament core and reservoir regions. These results are analyzed and interpreted with respect to numerical simulations and provide insight into fundamental aspects of filamentation. They also inform applications based on phase manipulation, such as external beam guiding, and present a new method for measuring the nonlinear index of refraction, n 2 .

Utterances produced by foreign-accented speakers are often judged as less credible, more vague, and more difficult to understand compared to those produced by native speakers. Some theoretical accounts argue that listeners have different expectations about the speech of non-native speakers. Other accounts argue that non-native speech is processed differently to the extent that a foreign accent taxes intelligibility and introduces additional processing load. Here we test the role of expectations for the processing of native vs. non-native speech in written texts where accents cannot be directly perceived (and thus affect processing load). In Experiment 1, native comprehenders gave higher ratings to the meaning of under-informative sentences ("Some people have noses with two nostrils") when they believed that the sentences were produced by non-native compared to native speakers. This difference was larger the more likely individual participants were to interpret under-informative sentences pragmatically (as opposed to logically). In Experiment 2, the tendency to forgive sins of information omission was shown to depend on the presumed L2 proficiency of non-native speakers. Experiment 3 replicated and extended the major finding. Since intelligibility of the sentences was identical across types of speakers, these findings provide support for the role of expectations for non-native speech comprehension, as well as for broader models of language processing that argue for a role of speaker identity., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The controlled interaction of two high intensity beams opens new degrees of freedom for manipulating electromagnetic waves in air. The growing number of applications for laser filaments requires fine control of their formation and propagation. We demonstrate, experimentally and theoretically, that the attraction and fusion of two parallel ultrashort beams with initial powers below the critical value (70% P critical ), in the regime where the non-linear optical characteristics of the medium become dominant, enable the eventual formation of a filament downstream. Filament formation is delayed to a predetermined distance in space, defined by the initial separation between the centroids, while still enabling filaments with controllable properties as if formed from a single above-critical power beam. This is confirmed by experimental and theoretical evidence of filament formation such as the individual beam profiles and the supercontinuum emission spectra associated with this interaction.

During communication, hearers try to infer the speaker's intentions to be able to understand what the speaker means. Nevertheless, whether (and how early) preschoolers track their interlocutors' mental states is still a matter of debate. Furthermore, there is disagreement about how children's ability to consult a speaker's belief in communicative contexts relates to their ability to track someone's belief in non-communicative contexts. Here, we study young children's ability to successfully acquire a word from a speaker with a false belief; we also assess the same children's success on a traditional false belief attribution task. We show that the ability to consult the epistemic state of a speaker during word learning develops between the ages of three and five. We also show that false belief understanding in word-learning contexts proceeds similarly to standard belief-attribution contexts when the tasks are equated. Our data offer evidence for the development of mind-reading abilities during language acquisition.