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Effect of electric field on mechanical behavior of vertically-aligned carbon nanotube structures
No full textHere, we summarize various reports on the mechanical response of vertically aligned carbon nanotubes forest (CNTF) structures under an applied electric field. Quasi-static compression tests on CNTF structures show a dramatic strengthening by application of the electric field both in low-strain (linear) and high strain (nonlinear) regimes. The CNTF structures also show a finite hysteresis, i.e., energy dissipation, in stress–strain behavior during a loading–unloading cycle. Tests demonstrate that the application of an electric field can tailor the energy absorption capacity of CNTF structures. In practice, the energy absorption capacity of CNTF structures increases by several folds when the loading and unloading (under quasi-static strain rates) are performed in the presence and the absence of the electric field, respectively. However, the improvement in the energy absorption capacity decreases drastically at higher strain rates. Additionally, applying an electric field improves the creep resistance of the CNTF structures. Overall, the summarized studies show promising electro-mechanical properties of CNTF structures which are helpful in developing the next generation of nano-and micro-electro-mechanical devices and sensors
Non-local contribution from small scales in galaxy–galaxy lensing: comparison of mitigation schemes
Full text linkRecent cosmological analyses with large-scale structure and weak lensing measurements, usually referred to as 3 × 2pt, had to discard a lot of signal to noise from small scales due to our inability to accurately model non-linearities and baryonic effects. Galaxy–galaxy lensing, or the position–shear correlation between lens and source galaxies, is one of the three two-point correlation functions that are included in such analyses, usually estimated with the mean tangential shear. However, tangential shear measurements at a given angular scale θ or physical scale R carry information from all scales below that, forcing the scale cuts applied in real data to be significantly larger than the scale at which theoretical uncertainties become problematic. Recently, there have been a few independent efforts that aim to mitigate the non-locality of the galaxy–galaxy lensing signal. Here, we perform a comparison of the different methods, including the Y-transformation, the point-mass marginalization methodology, and the annular differential surface density statistic. We do the comparison at the cosmological constraints level in a combined galaxy clustering and galaxy–galaxy lensing analysis. We find that all the estimators yield equivalent cosmological results assuming a simulated Rubin Observatory Legacy Survey of Space and Time (LSST) Year 1 like set-up and also when applied to DES Y3 data. With the LSST Y1 set-up, we find that the mitigation schemes yield ∼1.3 times more constraining S8 results than applying larger scale cuts without using any mitigation scheme
α-Fe2O3-based artificial synaptic RRAM device for pattern recognition using artificial neural networks
Full text linkWe report on the α -Fe2O3-based artificial synaptic resistive random access memory device, which is a promising candidate for artificial neural networks (ANN) to recognize the images. The device consists of a structure Ag/α-Fe2O3/FTO and exhibits non-volatility with analog resistive switching characteristics. We successfully demonstrated synaptic learning rules such as long-term potentiation, long-term depression, and spike time-dependent plasticity. In addition, we also presented off-chip training to obtain good accuracy by backpropagation algorithm considering the synaptic weights obtained from α-Fe2O3 based artificial synaptic device. The proposed α-Fe2O3-based device was tested with the FMNIST and MNIST datasets and obtained a high pattern recognition accuracy of 88.06% and 97.6% test accuracy respectively. Such a high pattern recognition accuracy is attributed to the combination of the synaptic device performance as well as the novel weight mapping strategy used in the present work. Therefore, the ideal device characteristics and high ANN performance showed that the fabricated device can be useful for practical ANN implementation
Wavelet Analysis of Near-Field Ground Motions from the Mw 7.8 2015 Gorkha Earthquake
No full textThe 2015 Nepal earthquake was one of the strongest quakes to strike the landlocked Himalayan country. The earthquake resulted in strong ground motions that severely affected various structures in the region. The unreinforced masonry structures were destroyed. Recorded ground motions from only five stations are available in the public domain. However, characterizing these ground motions in the time domain does not provide any information about the sequence of frequencies and amplitudes arriving at the station, which are key to understanding structural damage. The continuous wavelet transforms (CWT) are useful for such improved characterization of ground motions, as they provide a 3D view of time, frequency, and amplitude, thus enabling a comprehensive understanding of the damage potential of the ground motions. In this paper, recorded near-field ground motions from the earthquake are analyzed in the time and frequency domains. It is observed that the response spectra show a very wide acceleration sensitive region and some ground motions contain significant velocity pulses, both of which strongly influence structural damage. Further, it is observed that CWTs properly represent the critical characteristics of ground motions which can be correlated with the observed non-uniform damage to the built environment. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd
A Novel and Sustainable Approach to Enhance the Li-Ion Storage Capability of Recycled Graphite Anode from Spent Lithium-Ion Batteries
Full text linkThe ubiquitous manufacturing of lithium-ion batteries (LIBs) due to high consumer demand produces inevitable e-waste that imposes severe environmental and resource sustainability challenges. In this work, the charge storage capability and Li-ion kinetics of the recovered water-leached graphite (WG) anode from spent LIBs are enhanced by using an optimized amount of recycled graphene nanoflakes (GNFs) as an additive. The WG@GNF anode exhibits an initial discharge capacity of 400 mAh g-1 at 0.5C with 88.5% capacity retention over 300 cycles. Besides, it delivers an average discharge capacity of 320 mAh g-1 at 500 mA g-1 over 1000 cycles, which is 1.5-2 times higher than that of WG. The sharp increase in electrochemical performance is due to the synergistic effects of Li-ion intercalation into the graphite layers and Li-ion adsorption into the surface functionalities of GNF. Density functional theory calculations reveal the role of functionalization behind the superior voltage profile of WG@GNF. Besides, the unique morphology of spherical graphite particles trapping into graphene nanoflakes provides mechanical stability over long-term cycling. This work explains an efficient strategy to upgrade the electrochemical compatibility of recovered graphite anode from spent LIBs toward next-generation high-energy-density LIBs
Unique Chiro-optical Properties of the Weakly-2D (R-/S-MBA)2CuBr4 Hybrid Material
Full text linkWe establish that the formally 0D (R-/S-MBA)2CuBr4, containing R-/S-α-methyl benzylamine (R-/S-MBA) connected to highly distorted CuBr4 tetrahedral units in alternating layers, possesses extraordinary chiro-optical properties. The concentration and path length-independent chiral anisotropy factor, gCD, for this compound is the highest in the orange-red part of the visible spectrum reported so far from any hybrid material, arising from a chirality transfer from the organic component to the inorganic layer through the extensive asymmetric hydrogen bonding network and electronic coupling, driving the CuBr4 tetrahedral units to follow the 21-screw axis. This sensitivity in the orange-red part of the visible spectrum is achieved by incorporating bromine in the copper coordination sphere, which significantly red-shifts the band edge absorption to ∼710 nm compared to ∼490 nm reported for the chloride analogue. DFT/TDDFT calculations allow us to understand the underlying electronic structure responsible for its remarkable optical properties. We find that this compound gets a partial 2D character, crucial for its broadband chiro-optical properties, arising from Cu-Br···Br-Cu interactions connecting the otherwise isolated CuBr4 units
Tailoring cavity coupled plasmonic substrates for SERS applications
Full text linkSurface-enhanced Raman spectroscopy (SERS) has been effectively used in biosensing applications due to its high sensitivity and specificity. Enhancing the coupling of light into plasmonic nanostructures can lead to engineered SERS substrates with improved sensitivity and performance. In the current study, we demonstrate a cavity-coupled structure that assists in enhancing the light-matter interaction leading to an improved SERS performance. Using numerical simulations, we demonstrate that the cavity-coupled structures can either enhance or suppress the SERS signal depending on the cavity length and the wavelength of interest. Furthermore, the proposed substrates are fabricated using low-cost large-area techniques. The cavity-coupled plasmonic substrate consists of a layer of gold nanospheres on an indium tin oxide (ITO)-Au-glass substrate. The fabricated substrates exhibit nearly a 9 times improvement in SERS enhancement as compared to the uncoupled substrate. The demonstrated cavity-coupling approach can also be used for enhancing other plasmonic phenomena like plasmonic trapping, plasmon-enhanced catalysis, and nonlinear signal generation
Ultracool dwarfs candidates based on 6 yr of the Dark Energy Survey data
Full text linkWe present a sample of 19 583 ultracool dwarf candidates brighter than z ≤23 selected from the Dark Energy Survey DR2 coadd data matched to VHS DR6, VIKING DR5, and AllWISE covering ∼ 480 deg2. The ultracool candidates were first pre-selected based on their (i–z), (z–Y), and (Y–J) colours. They were further classified using a method that compares their optical, near-infrared, and mid-infrared colours against templates of M, L, and T dwarfs. 14 099 objects are presented as new L and T candidates and the remaining objects are from the literature, including 5342 candidates from our previous work. Using this new and deeper sample of ultracool dwarf candidates we also present: 20 new candidate members to nearby young moving groups and associations, variable candidate sources and four new wide binary systems composed of two ultracool dwarfs. Finally, we also show the spectra of 12 new ultracool dwarfs discovered by our group and presented here for the first time. These spectroscopically confirmed objects are a sanity check of our selection of ultracool dwarfs and photometric classification method
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Full text linkA test of spatial coincidence between CHIME FRBs and IceCube TeV energy neutrinos
No full textWe search for a spatial association between the Canadian Hydrogen Mapping Intensity Experiment (CHIME) FRBs and IceCube neutrinos detected in the TeV energy range, by counting the total number of neutrino-FRB pairs with angular separations of <3 degrees, as well as within the observed neutrino error circle. This number constitutes the total signal events, which is then compared to the total background, corresponding to the null hypothesis of no spatial association. The background was obtained from the total neutrino-FRB matches in off-source angular windows with the same solid angle as the signal window. We do not find any statistically significant excess compared to the background. Therefore, we conclude that there is no evidence for an angular correlation between the IceCube neutrinos in the TeV energy range and CHIME FRBs. For each of these searches, we report 90% Bayesian credible interval upper limits on the observed FRB-induced neutrinos