5 research outputs found
Use of PVDF Wire Sensors for Leakage Localization in a Fluid-Filled Pipe
The detection and location of pipeline leakage can be deduced from the time difference between the arrival leak signals measured by sensors placed at the pipe access points on either side of a suspected leak. Progress has been made in this area to offer a potential improvement over the conventional cross-correlation method for time delay estimation. This paper is concerned with identifying suitable sensors that can be easily deployed to monitor the pipe vibration due to the propagation of leak noise along the pipeline. In response to this, based on the low-frequency propagation characteristics of leak noise in our previous study, polyvinylidene fluoride (PVDF) wire sensors are proposed as a potential solution to detect the pipeline leak signals. Experimental investigations were carried out at a leak detection pipe rig built in the Chinese Academy of Sciences. Their performances for leak detection were shown in comparison with hydrophones. It is suggested that with special considerations given to aspects pertaining to non-intrusive deployment and low cost, the PVDF wire sensors are of particular interest and may lead to a promising replacement for commercial leak noise transducers
On image fusion of ground surface vibration for mapping and locating underground pipeline leakage: an experimental investigation
This paper is concerned with imaging techniques for mapping and locating underground pipeline leakage. Ground surface vibrations induced by the propagating axisymmetric wave can be measured by an array of acoustic/vibration sensors, with the extraction of magnitude information used to determine the position of leak source. A method of connected graph traversal is incorporated into the vibroacoustic technique to obtain the spatial image with better accuracy compared to the conventional magnitude contour plot. Measurements are made on a dedicated cast iron water pipe by an array of seven triaxial geophones. The spectral characteristics of the propagation of leak noise signals from underground water pipes to the ground surface are reported. Furthermore, it is demonstrated that suspicious leakage areas can be readily identified by extracting and fusing the feature patterns at low frequencies where leak noise dominates. The results agree well with the real leakage position in the underground pipeline
Experimentally Validated Structures of Supported Metal Nanoclusters on MoS<sub>2</sub>
In
nanometer clusters (NCs), each atom counts. It is the specific
arrangement of these atoms that determines the unique size-dependent
functionalities of the NCs and hence their applications. Here, we
employ a self-consistent, combined theoretical and experimental approach
to determine atom-by-atom the structures of supported Pt NCs on MoS<sub>2</sub>. The atomic structures are predicted using a genetic algorithm
utilizing atomistic force fields and density functional theory, which
are then validated using aberration-corrected scanning transmission
electron microscopy. We find that relatively small clusters grow with
(111) orientation such that Pt[11Ì…0] is parallel to MoS<sub>2</sub>[100], which is different from predictions based on lattice-match
for thin-film epitaxy. Other 4d and 5d transition metals show similar
behavior. The underpinning of this growth mode is the tendency of
the NCs to maximize the metal–sulfur interactions rather than
to minimize lattice strain
High Triplet Energy Level Achieved by Tuning the Arrangement of Building Blocks in Phosphorescent Polymer Backbones for Furnishing High Electroluminescent Performances in Both Blue and White Organic Light-Emitting Devices
A high triplet energy level (<i>E</i><sub>T</sub>) of ca. 2.83 eV has been achieved in a novel polymer backbone through
tuning the arrangement of two kinds of building blocks, showing enhanced
hole injection/transporting capacity. Based on this new polymer backbone
with high <i>E</i><sub>T</sub>, both blue and white phosphorescent
polymers were successfully developed with a trade-off between high <i>E</i><sub>T</sub> and enhanced charge-carrier transporting ability.
In addition, their photophysical features, electrochemical behaviors,
and electroluminescent (EL) properties have been characterized in
detail. Benefitting from the advantages associated with the novel
polymer backbone, the blue phosphorescent polymers show top-ranking
EL performances with a maximum luminance efficiency (η<sub>L</sub>) of 15.22 cd A<sup>–1</sup>, corresponding to a power efficiency
(η<sub>P</sub>) of 12.64 lm W<sup>–1</sup>, and external
quantum efficiency (η<sub>ext</sub>) of 6.22% and the stable
Commission Internationale de L’Eclairage (CIE) coordinates
of (0.19, 0.38). Furthermore, blue–orange (B–O) complementary-colored
white phosphorescent polymers based on this novel polymer backbone
were also obtained showing encouraging EL efficiencies of 12.34 cd
A<sup>–1</sup>, 9.59 lm W<sup>–1</sup>, and 4.10% in
the optimized WOLED together with exceptionally stable CIE coordinates
of (Δ<i>x</i> = 0.014, Δ<i>y</i> =
0.010) in a wide driving voltage range from 4 to 16 V. All of these
attractive EL results achieved by these novel phosphorescent polymers
show the great potential of this new polymer backbone in developing
highly efficient phosphorescent polymers
Gold-like activity copper-like selectivity of heteroatomic transition metal carbides for electrocatalytic carbon dioxide reduction reaction.
An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO2RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we report the eCO2RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH4) current density of -421.63 mA/cm2 and a CH4 faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W2C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO2 to produce CH4 in a 700-h process under one sun illumination with a CO2RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO2 and cleavage of the C-O bond-the most energy consuming elementary steps in other catalysts such as copper-become nearly spontaneous at the W2C surface. This results in instantaneous formation of adsorbed CO-an important reaction intermediate-and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential