In the pursuit of enhancing the fire safety of polyamide 6 (PA6), the addition of flame retardants generally leads to hydrogen bond dissociation, which results in detrimental effects on the ...mechanical properties of PA6 composites and impedes processing and application in the textile field. In this study, a macromolecular flame retardant, PPB, designed with hydrogen bond donor-acceptor spacing aligned with PA6, was synthesized to increase the number of hydrogen bonds. The addition of 10 wt% PPB to the PA6 matrix (PA6/PPB10) endowed the composite with the limiting oxygen index (LOI) increased to 31.6 % and V-0 rating in the vertical burning (UL-94) test. PA6/PPB10 also exhibited significant enhancement in tensile strength by 12.6 % compared to pure PA6 and demonstrated a superior ultraviolet protection factor (UPF) value of 573, greatly exceeding the value of 3 for PA6. The quenching effect, diluting effect in the gas phase, and hydrogen bond interactions between PPB and PA6 backbones imparted PA6/PPB composites with satisfactory flame retardancy and mechanical properties. As a representative example, PA6/PPB10 was melt-spun into filaments with a pleasing tenacity of 3.6 cN/dtex and self-extinguishing capability within 5 s after ignition, confirming the sustained comprehensive properties after spinning and drawing into filaments.
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•A flame retardant (PPB) with hydrogen bond spacing aligned with PA6 was synthesized.•PA6/PPB10 (containing 10 wt% PPB) achieved a LOI of 31.6 % and an UL94 V-0 rating.•PA6/PPB10 presented an increase of 12.6 % in the tensile strength compared to PA6.•PA6/PPB10 had an UPF value of 573, significantly exceeding the value of 3 for PA6.•PA6/PPB10 filaments presented both enhanced flame retardancy and high tenacity.
There is a great interest in developing microelectronic devices based on nanostructured conducting polymers that can selectively electro-couple analytes at high sensitivity and low power. ...Nanostructured conducting polymers have emerged as promising candidates for this technology due to their excellent stability with low redox potential, high conductivity, and selectivity endowed by chemical functionalization. However, it remains challenging to develop cost-effective and large-scale assembly approaches for functionalized conducting polymers in the practical fabrication of electronic devices. Here, we reported a straightforward wafer-scale assembly of nanostructured hexafluoroisopropanol functionalized poly(3,4-ethylenedioxythiophene) (PEDOT-HFIP) on smooth substrates. This approach is template-free, solution-processed, and adaptable to conductive and nonconductive substrates. By this approach, the nanostructured PEDOT-HFIPs could be easily integrated onto interdigitated electrodes with intimate ohmic contact. At the optimized space-to-volume ratio, we demonstrated a low-power, sensitive, and selective nerve agent sensing technology using this platform by detecting sarin vapor with a limit of detection (LOD) of 10 ppb and signal strength of 400 times the water interference at the same concentration, offering significant advantages over existing similar technologies. We envision that its easy scale-up, micro size, small power consumption, and combination of high sensitivity and selectivity make it attractive for various wearable platforms.
Two novel coumarin-substituted phthalocyanine dyes (
CAPc
and
CSPc
) with different linking units, using carboxylic groups as electron acceptor and injector, were designed, synthesized, and applied ...as panchromatic organic sensitizers in I
−
/I
3
−
-based dye-sensitized solar cells (DSSCs). The asymmetric coumarin–phthalocyanine dyad analogue (OAPc) and the symmetric coumarin-phthalocyanine dyad analogue (COPc) were also synthesized for comparison. The structure–property relationship for these dyes was investigated by absorption spectroscopy, cyclic voltammetry, and thermogravimetric analysis. The ultraviolet–visible (UV–Vis) absorption was dramatically affected by the nature of the linker. Notably, modulation of the π-conjugated coumarin–phthalocyanine dyad
CAPc
and
CSPc
resulted in a large red-shift (Q-band above 710 nm); in particular, the dyad
CAPc
showed remarkably intense absorption in the spectral window of 450–650 nm. Electrochemical data for the dyes indicated that the azo double-bond-linked coumarin–phthalocyanine dyad dyes possessed relatively low-lying
E
HOMO
values, which may be beneficial to suppress electron back-transfer from the conduction band of TiO
2
to oxidized dyes due to facile regeneration of the oxidized dye by the electrolyte. Thermogravimetric analysis showed that the three coumarin–phthalocyanine dyad sensitizers were stable above 200 °C. When the dyads were applied as light-harvesting sensitizers in dye-sensitized solar cells, the cell sensitized by
OAPc
showed the best power conversion efficiency of 2.4%.
This article demonstrates a 10.23-15.7-GHz varactor-tuned microstrip bandpass filter (BPF) with fully controllable center frequency, bandwidth, and transmission zeros. The concept of cascading a ...tunable low-pass unit together with a tunable high-pass unit is adopted to achieve the reconfigurable BPF. A comprehensive loss analysis is carried out to determine the preferable circuit topologies for low-pass filter (LPF) and high-pass filter (HPF), respectively. This not only overcomes the limitation of low quality factor of varactor at high frequency, but also contributes to a highly flexible reconfigurability of the BPF. A reconfigurable LPF using defected ground structure (DGS) and a quasi-elliptic HPF using microstrip technology are then proposed to demonstrate the improved BPF performance at high frequency. The measured results show that the designed BPF is capable of operating in five working modes, with a center frequency tuning range from 10.23 to 15.7 GHz and a fractional bandwidth (FBW) tuning range from 32.48% to 95.76%. The minimum in-band insertion loss reaches 2.55 dB. A steep cutoff characteristic and ultrawide stopband with high rejection level are successfully achieved and are well preserved during the whole tuning process, demonstrating the superiority of the designed BPF.
In this article, a novel 1.05-1.25 GHz filtering antenna feeding network with reconfigurable frequency and polarization is proposed. It simply consists of a reconfigurable in-/out-of-phase filtering ...power divider and a 90° hybrid coupler. By controlling the varactors in the in-/out-of-phase reconfigurable filtering power divider (RFPD) without any switch component, the proposed three-port feeding network offers continuous reconfigurable filtering responses with four switchable output patterns including equal power dividing with phase difference of negative or positive 90° and single-ended output at either output port. With this proposed feeding network connecting to a regular dual-polarized antenna, the resulted antenna system can easily realize reconfigurable polarization of vertical polarization (V-LP), horizontal polarization (H-LP), LHCP, and RHCP, in addition to its reconfigurable filtering responses. A prototype using microstrip technology is designed, fabricated, and measured to demonstrate the proposed technique. Good agreement between the simulated and measured results is obtained. The measured results show that the feeding network covers a frequency range of 1.05-1.25 GHz, and the errors of phase difference and amplitude imbalance are less than 5 and 0.5 dB, respectively. The resulted antenna beams can be freely switched in four polarization states with good performance.
4D printing is inspired by embedded product designs to produce stimuli-responsive consumables fabricated by available commercial 3D printers. Although significant progress on smart material ...performance has been made and different studies have focused on new strategies and process improvements in typical additive manufacturing. Herein, the proposed review article discusses material arrangements for 4D printing, highlighting the structural evolvement mechanism, the behavior of deformation, and their prospective implementation with respect. Starting from a generalized idea, and fundamental workflow, together with a graphical manifestation of the 4D printing concept, and 4D printing for shape-memory materials (SMMs), self-fitting wearables based on shape memory alloys (SMAs) are reviewed exclusively. Furthermore, the capabilities of single and multiple materials mechanisms for shape-shifting behavior are summarized. Finally, we explored the future application potential under succeeding context: SMA-based knitted garments, transforming food, and relevant sectors wise development and proceedings with the advancement in smart materials. We determined our review by aiming our future directions such as the “dream it and make it feasible” technology.
Graphical abstract
High radix Booth encodings provide significant decrease on the number of partial products in the multiplication. However, due to the generation on hard multiples, additional delay and power are ...incurred, which in turn hampers the use of high radix Booth encodings. In this brief, an approximate radix-256 Booth encoding is proposed to circumvent the generation on hard multiples. A partial encoding approach is used to produce partial product pairs, which can be obtained easily by simple shifting and complementing operations. The exact encoding values are thus replaced by the sum of each corresponding partial product pair. A 16 <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> 16-bit multiplier with proposed approximate radix-256 Booth encoding has been implemented for performance evaluation. Compared with the traditional radix-4 Booth encoding multiplier, the proposed design achieves 42.39%, 7.03%, 26.00% reduction in area, delay, and power, respectively. Additionally, 2-D discrete cosine transform (DCT) system with proposed multiplier is demonstrated as an application. 33.51% and 24.15% reduction on area and power consumption are obtained respectively with a penalty of 6.42dB peak signal to noise ratio loss in average when compared with the traditional design.
Strong influences of climate and land-cover changes on terrestrial ecosystems urgently need to re-estimate forest carbon turnover time (τforest), i.e., the residence time of carbon (C) in the living ...forest carbon reservoir in China, to reduce uncertainties in ecosystem carbon sinks under ongoing climate change. However, in absence of accurate carbon loss (e.g., forest litterfall), τforest estimate based on the non-steady-state assumption (NSSA) in forest ecosystems across China is still unclear. In this study, thus, we first compiled a litterfall dataset with 1025 field observations, and applied a Random Forest (RF) algorithm with the linkage of gridded environmental variables to predict litterfall from 2000 to 2019 with a fine spatial resolution of 1 km and a temporal resolution of one year. Finally, τforest was also estimated with the data-driven litterfall product. Results showed that RF algorithm could well predict the spatial and temporal patterns of forest litterfall with a model efficiency of 0.58 and root mean square error of 78.7 g C m−2 year−1. Mean litterfall was 205.4 ± 1.1 Tg C year−1 (mean ± standard error) with a significant increasing trend of 0.65 ± 0.14 Tg C year−2 from 2000 to 2019 (p < 0.01), indicating an increasing carbon loss from litterfall. Mean τforest was 26.2 ± 0.1 years with a significant decreasing trend of −0.11 ± 0.02 years (p < 0.01) from 2000 to 2019. Climate change dominated the inter-annual variability of τforest in high latitude areas, and land-cover change dominated the regions with intensive human activities. These findings suggested that carbon loss from vegetation to the atmosphere becomes more quickly in recent decades, with significant implication for vegetation carbon cycling-climate feedbacks. Meanwhile, the developed litterfall and τforest datasets can serve as a benchmark for biogeochemical models to accurately estimate global carbon cycling.
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•Forest carbon turnover time was estimated based on Random Forest-based litterfall.•Total litterfall was 205.4 ± 1.1 Tg C year−1.•Mean forest carbon turnover time was 26.2 ± 0.1 years.•Litterfall and carbon turnover time can serve as benchmark for biogeochemical models.
The effective conversion of carbon dioxide (CO2) into cyclic carbonates requires porous materials with high ionic content and large specific surface area. Herein, we developed a new systematic ...post-synthetic modification strategy for synthesizing imidazolium-based hypercrosslinked ionic polymers (HIPs) with high ionic content (up to 2.1 mmol g−1) and large specific surface area (385 m2 g−1) from porous hypercrosslinked polymers (HCPs) through addition reaction and quaternization. The obtained HIPs were efficient in CO2 capture and conversion. Under the synergistic effect of high ionic content, large specific surface area, and plentiful micro/mesoporosity, the metal-free catalyst HCP-CH2-ImCl-1 exhibited quantitative selectivities, high catalytic yields, and good substrate compatibility for the conversion of CO2 into cyclic carbonates at atmospheric pressure (0.1 MPa) in a shorter reaction time in the absence of cocatalysts, solvents, and additives. High catalytic yields (styrene oxide, 120 °C, 8 h, 94% yield; 100 °C, 20 h, 93% yield) can be achieved by appropriately extending the reaction times at low temperature, and the reaction times are shorter than other porous materials under the same conditions. This work provides a new strategy for synthesizing an efficient metal-free heterogeneous catalyst with high ionic content and a large specific surface area from HCPs for the conversion of CO2 into cyclic carbonates. It also demonstrates that the ionic content and specific surface area must be coordinated to obtain high catalytic activity for CO2 cycloaddition reaction.
Digital Multiplier is a fundamental component in many digital signal processing (DSP) systems, which takes up the most part of the computational resources. As many DSP applications have an inherent ...tolerance for inexact computations, approximate multiplication is considered as an appropriate substitution to obtain energy-performance-accuracy tradeoffs, especially in those applications that require high energy-efficiency in computing. Meanwhile, reducing the supply voltage is proved to be an efficient way to further lower the total energy consumption. In this paper, a novel approximate 4-2 compressor and its circuit implementation is proposed for error-resilient multiplication with a low supply voltage. Simulation results indicate that the approximate multiplier with our proposed approximate 4-2 compressor consumes the least energy per operation with the same computational accuracy when compared with other multipliers for the operand length of 8 bits. It achieves 26.7% reduction on energy-delay product (EDP) when compared with the exact multiplication.
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