993 research outputs found
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Electrospun Piezoelectric Polymer Nanofiber Layers for Enabling in Situ Measurement in High-Performance Composite Laminates
This article highlights the effects from composite manufacturing parameters on fiber-reinforced composite laminates modified with layers of piezoelectric thermoplastic nanofibers and a conductive electrode layer. Such modifications have been used for enabling in situ deformation measurement in high-performance aerospace and renewable energy composites. Procedures for manufacturing high-performance composites are well-known and standardized. However, this does not imply that modifications via addition of functional layers (e.g., piezoelectric nanofibers) while following the same manufacturing procedures can lead to a successful multifunctional composite structure (e.g., for enabling in situ measurement). This article challenges success of internal embedment of piezoelectric nanofibers in standard manufacturing of high-performance composites via relying on composite process specifications and parameters only. It highlights that the process parameters must be revised for manufacturing of multifunctional composites. Several methods have been used to lay up and manufacture composites such as electrospinning the thermoplastic nanofibers, processing an inter digital electrode (IDE) made by conductive epoxy-graphene resin, and prepreg autoclave manufacturing aerospace grade laminates. The purpose of fabrication of IDE was to use a resin type (HexFlow RTM6) for the conductive layer similar to that used for the composite. Thereby, material mismatch is avoided and the structural integrity is sustained via mitigation of downgrading effects on the interlaminar properties. X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and scanning electron microscopy analyses have been carried out in the material characterization phase. Pulsed thermography and ultrasonic C-scanning were used for the localization of conductive resin embedded within the composite laminates. This study also provides recommendations for enabling internally embedded piezoelectricity (and thus health-monitoring capabilities) in high-performance composite laminates
Proposal for realizing Majorana fermions in chains of magnetic atoms on a superconductor
We propose an easy-to-build easy-to-detect scheme for realizing Majorana fermions at the ends of a chain of magnetic atoms on the surface of a superconductor. Model calculations show that such chains can be easily tuned between trivial and topological ground states. In the latter, spatially resolved spectroscopy can be used to probe the Majorana fermion end states. Decoupled Majorana bound states can form even in short magnetic chains consisting of only tens of atoms. We propose scanning tunneling microscopy as the ideal technique to fabricate such systems and to probe their topological properties
Quasiparticle Interference on the Surface of Topological Crystalline Insulator Pb(1-x)Sn(x)Se
Topological crystalline insulators represent a novel topological phase of
matter in which the surface states are protected by discrete point
group-symmetries of the underlying lattice. Rock-salt lead-tin-selenide alloy
is one possible realization of this phase which undergoes a topological phase
transition upon changing the lead content. We used scanning tunneling
microscopy (STM) and angle resolved photoemission spectroscopy (ARPES) to probe
the surface states on (001) PbSnSe in the topologically
non-trivial (x=0.23) and topologically trivial (x=0) phases. We observed
quasiparticle interference with STM on the surface of the topological
crystalline insulator and demonstrated that the measured interference can be
understood from ARPES studies and a simple band structure model. Furthermore,
our findings support the fact that PbSnSe and PbSe have
different topological nature.Comment: 5 pages, 4 figure
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Microwave-Assisted Rapid Synthesis of Reduced Graphene Oxide-Based Gum Tragacanth Hydrogel Nanocomposite for Heavy Metal Ions Adsorption
This work aims to address the effectiveness and challenges of non-destructive testing (NDT) by active infrared thermography (IRT) for the inspection of aerospace-grade composite samples and seeks to compare uncooled and cooled thermal cameras using the signal-to-noise ratio (SNR) as a performance parameter. It focuses on locating impact damages and optimising the results using several signal processing techniques. The work successfully compares both types of cameras using seven different SNR definitions, to understand if a lower-resolution uncooled IR camera can achieve an acceptable NDT standard. Due to most uncooled cameras being small, lightweight, and cheap, they are more accessible to use on an unmanned aerial vehicle (UAV). The concept of using a UAV for NDT on a composite wing is explored, and the UAV is also tracked using a localisation system to observe the exact movement in millimetres and how it affects the thermal data. It was observed that an NDT UAV can access difficult areas and, therefore, can be suggested for significant reduction of time and cost
Chemical evolution of primary and formation of secondary biomass burning aerosols during daytime and nighttime
Organic matter (OM) can constitute more than half of
fine particulate matter (PM) and affect climate and
human health. Natural and man-made biomass burning
is an important contributor to primary and secondary
OM (POA and SOA) with an increasing trend.
Aerosol mass spectrometry (AMS) and Fourier
transform infrared spectroscopy (FTIR) are two
complementary methods of identifying the complex
chemical composition of OM in terms of mass fragments
and functional groups, respectively. AMS offers a
relatively higher temporal resolution compared to FTIR
(performed on PTFE filters). However, the interpretation
of AMS mass spectra remains complicated due to the
extensive molecular fragmentation.
In this study, we used collocated AMS and FTIR
measurements to better understand the evolution of
biomass burning POA and SOA due to different
mechanisms of chemical aging (e.g., homogeneous gasphase
oxidation and heterogeneous reactions). Primary
emissions from wood and pellet stoves were injected
into a 10 m3 environmental chamber located at the
Center for Studies of Air Qualities and Climate Change (CSTACC)
at ICE-HT/FORTH. Primary emissions were aged
using hydroxyl and nitrate radicals with atmospherically
relevant exposures. PM1 was analyzed by a highresolution
time-of-flight (HR-ToF) and was also collected
on PTFE filters over 20-minute periods before and after
aging for off-line FTIR analysis.
AMS and FTIR measurements agreed well with
regards to the concentration of OM and some biomass
burning tracers (levoglucosan and lignin; Yazdani A.,
2020b) and the OM:OC ratio. Chamber wall loss rates
were estimated using AMS OM concentration and were
used to split the contribution of POA and SOA. The
estimated FTIR and AMS spectra of SOA produced by
reactions of biomass burning volatile organic compounds
(VOCs) with OH were found to have prominent acid
signatures. Organonitrates, on the other hand, appeared
to be important for SOA produced by the nitrate radical.
We found that with continued aging, SOA evolves and
becomes similar to the oxygenated OA (OOA) in the
atmosphere. We also found that POA composition also
evolves with aging. Our estimates show that up to 10 %
of POA mass undergoes aging. Biomass burning tracers
such as lignin and levoglucosan in addition to
hydrocarbons are among the POA compounds that are
lost the most in biomass burning POA (up to 6 times more
than OM decrease due to chamber wall losses; Fig. 1).
This diminution is observed for both semi-volatile
(levoglucosan and hydrocarbons) and non-volatile
(lignin) POA species, implying the importance of gasparticle
partitioning, heterogeneous reactions, and
photolysis for POA evolution in the atmosphere. This
result can be important since chemical transport models
usually do not consider POA heterogeneous reactions.
Figure 1. Trends of individual AMS mass fragments (with
contribution to OM> 0.3 %) during aging with UV
(starting from time zero). All mass fragments have been
normalized by their concentration before the with start
of aging and corrected for the chamber wall losses.
Important mass fragments are shown in color.
This work was supported by the project PyroTRACH (ERC-
2016-COG) funded from H2020-EU.1.1. - Excellent
Science - European Research Council (ERC), project ID
726165 and funding from the Swiss National Science
Foundation (200021_172923).
References
Yazdani, A., Dudani, N., Takahama, S., Bertrand, A.,
Prévôt, A. S. H., El Haddad, I., and Dillner, A. M.:
Characterization of Primary and Aged Wood Burning and
Coal Combustion Organic Aerosols in Environmental
Chamber and Its Implications for Atmospheric Aerosols,
Atmospheric Chemistry and Physics Discussions, pp. 1–
32
Differentiating between primary and secondary organic aerosols of biomass burning in an environmental chamber with FTIR and AMS
Fine particulate matter (PM) affects visibility, climate and public health. Organic matter (OM), which is hard to characterize due to its complex chemical composition, can constitute more than half of the PM. Biomass burning from residential wood burning, wildfires, and prescribed burning is a major source of OM with an ever-increasing importance.
Aerosol mass spectrometry (AMS) and Fourier transform infrared spectroscopy (FTIR) are two complementary methods of identifying the chemical composition of OM. AMS measures the bulk composition of OM with relatively high temporal resolution but provides limited parent compound information. FTIR, carried out on samples collected on Teflon filters, provides detailed functional groupinformation at the expense of relatively low temporal resolution.
In this study, we used these two methods to better understand the evolution of biomass burning OM in the atmosphere with aging. For this purpose, primary emissions from wood and pellet stoves were injected into the Center for Studies of Air Qualities and Climate Change (C-STACC) environmental chamber at ICE-HT/FORTH. Primary emissions were aged using hydroxyl and nitrate radicals (with atmospherically relevant exposures) simulating atmospheric day-time and night-time oxidation. A time-of-flight (ToF) AMS reported the composition of non-refractory PM1 every three minutes and PM1 was collected on PTFE filters over 20-minute periods before and after aging for off-line FTIR analysis.
We found that AMS and FTIR measurements agreed well in terms of measured OM mass concentration, the OM:OC ratio, and concentration of biomass burning tracers – lignin and levoglucosan. AMS OM concentration was used to estimate chamber wall loss rates which were then used separate the contribution of primary and secondary organic aerosols (POA and SOA) to the aged OM. AMS mass spectra and FTIR spectra of biomass burning SOA and estimates of bulk composition were obtained by this procedure. FTIR and AMS spectra of SOA produced by OH oxidation of biomass burning volatile organic compounds (VOCs) were dominated by acid signatures. Organonitrates, on the other hand, appeared to be important in the SOA aged by the nitrate radical. The spectra from the two instruments also indicated that the signatures of certain compounds such as levoglucosan, lignin and hydrocarbons, which are abundant in biomass burning POA, diminish with aging significantly more than what can be attributed to chamber wall losses. The latter suggests biomass burning POA chemical composition might change noticeably due to heterogeneous reactions or partitioning in the atmosphere. Therefore, the common assumption of stable POA composition is only partially true. In addition, more stable biomass burning tracers should be used to be able to identify highly aged biomass burning aerosols in the atmosphere
Open Vocabulary Extreme Classification Using Generative Models
The extreme multi-label classification (XMC) task aims at tagging content with a subset of labels from an extremely large label set. The label vocabulary is typically defined in advance by domain experts and assumed to capture all necessary tags. However in real world scenarios this label set, although large, is often incomplete and experts frequently need to refine it. To develop systems that simplify this process, we introduce the task of open vocabulary XMC (OXMC): given a piece of content, predict a set of labels, some of which may be outside of the known tag set. Hence, in addition to not having training data for some labels-as is the case in zero-shot classification-models need to invent some labels on-the-fly. We propose GROOV, a fine-tuned seq2seq model for OXMC that generates the set of labels as a flat sequence and is trained using a novel loss independent of predicted label order. We show the efficacy of the approach, experimenting with popular XMC datasets for which GROOV is able to predict meaningful labels outside the given vocabulary while performing on par with state-of-the-art solutions for known labels
Chemical evolution of primary and secondary biomass burning aerosols during daytime and nighttime
Primary emissions from wood and pellet stoves were aged in an atmospheric simulation chamber under daytime and nighttime conditions. The aerosol was analyzed with the online Aerosol Mass Spectrometer (AMS) and offline Fourier transform infrared spectroscopy (FTIR). Measurements using the two techniques agreed reasonably well in terms of the organic aerosol (OA) mass concentration, OA:OC trends, and concentrations of biomass burning markers – lignin-like compounds and anhydrosugars. Based on the AMS, around 15 % of the primary organic aerosol (POA) mass underwent some form of transformation during daytime oxidation conditions after 6–10 hours of atmospheric exposure. A lesser extent of transformation was observed during the nighttime oxidation. The decay of certain semi-volatile (e.g., levoglucosan) and less volatile (e.g., lignin-like) POA components was substantial during aging, highlighting the role of heterogeneous reactions and gas-particle partitioning. Lignin-like compounds were observed to degrade under both daytime and nighttime conditions, whereas anhydrosugars degraded only under daytime conditions. Among the marker mass fragments of primary biomass burning OA (bbPOA), heavy ones (higher m/z) were relatively more stable during aging. The biomass burning secondary OA (bbSOA) became more oxidized with continued aging and resembled those of aged atmospheric organic aerosols. The bbSOA formed during daytime oxidation was dominated by acids. Organonitrates were an important product of nighttime reactions in both humid and dry conditions. Our results underline the importance of changes to both the primary and secondary biomass burning aerosols during their atmospheric aging. Heavier AMS fragments seldomly used in atmospheric chemistry can be used as more stable tracers of bbPOA and in combination with the established levoglucosan marker, can provide an indication of the extent of bbPOA aging
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