In this letter, a multiband rectifying metasurface is proposed. Two resonant modes are excited through the metasurface structure, and others are introduced by the trapezoidal patch while the resonant ...intensity is increased. Finally, RF energy in the quad-band can be captured by the metasurface with the four resonant modes. The rectification efficiency is analyzed at different conditions, and the optimal load and input power level of the system are obtained, which improves the synthetic rectification efficiency of the system. A 6 × 6 array is fabricated and measured. Experimental results show that the proposed rectifying metasurface can capture RF energy at 1.7 GHz, 2.4 GHz, 3.8 GHz, and 5.3 GHz. The peak RF to DC efficiency of the system is 72.1% at the incident power of 0 dBm. Compared with other reports, the proposed one can capture more bands of RF energy with relatively lower incident power level requirements and high efficiency. It may be applied to energy absorption scenarios in RF environments, such as wireless power transmission.
Modification with Au nanoparticles on the surface of semiconductor metal oxide (SMO) is a simple and effective mean to improve the sensing performance of pristine SMO sensor. ZnO nanorods are ...prepared via a simple precipitation reaction and subsequently modified by catalytic Au nanoparticles with effect on the surface through an ammonia deposition method. The gas response of sensor based on ZnO nanorods modified by Au nanoparticles is improved by 6.6 times to 100 ppm acetone at the optimal operating temperature of 172 °C, which is reduced from 219 °C for pristine ZnO sensor. Meanwhile, the response/recovery time is shortened to 1 s/20 s from 13 s/29 s. In addition, the sensing enhancement mechanism can be attributed to the electronic and chemical sensitization effects of Au nanoparticles.
Display omitted
•The synthesis of ZnO nanorods is simple and the modification of Au NPs is easy.•The response of Au-ZnO sensor is improved by 6.6 times to 100 ppm acetone.•Au-ZnO sensor exhibits lower working temperature and shorter response/recovery time.
This paper presents a 1.8-mW 2.4-GHz channelized receiver for ISM-band applications. Unlike traditional ISM-band radios which typically require a phase-locked loop (PLL) for channelization, we ...propose a modified sliding-IF receiver architecture with a suitable local oscillator (LO) frequency plan utilizing a temperature-compensated thin film bulk acoustic-wave resonator (FBAR). This strategy completely eliminates the need for a PLL by directly dividing down the fixed FBAR oscillator frequency. An inductor-less current-reuse balun LNA is proposed allowing a low-power wideband matching as well as noise cancelling. The frequency conversion is achieved by a hybrid mixer, which stacks a switching mixer on a switched-<inline-formula> <tex-math notation="LaTeX">g_{m} </tex-math></inline-formula> mixer for current reuse. It also features good voltage headroom and common-mode noise rejection. The FBAR-based Colpitts oscillator achieves the phase noise of −144 dBc/Hz at 3.5-MHz offset. The measured RX gain, noise figure, and in-band IIP 3 are 57.8 dB, 15.7 dB, and −18.5 dBm, respectively, without external crystal and on-chip inductors, which allows us to reduce the size and weight of the receiver system. It dissipates 0.86 mW (RX) and 0.92 mW (LO) from a single 1-V supply.
This paper proposes the development of a novel coagulant for dust suppression in open-cast mines. Specifically, pretreated sodium lignin sulfonate and acrylic acid were first cross-linked, then the ...graft copolymerization of the intermediate product (the cross-linking product) and acrylamide was conducted and finally the resulting gelatinous substances were crushed. During the reaction process, N,N’-methylene-bis-acrylamide and ammonium persulfate were used as the cross-linking agent and initiator, respectively. Subsequently, the functional groups, crystalline structure, and thermal stability of the dust coagulant were examined by means of Fourier transform infrared spectra measurements, X-ray diffraction spectra measurements, and differential scanning calorimeter analysis. Moreover, single-factor experiments were conducted to explore the optimal synthesis condition. According to the experimental results, the coagulant achieved its optimal dust suppression performance under the following conditions: the mass ratio of lignin to acrylic acid was 1:3, the mass ratio of lignin to acrylamide was 2:7, the content of the cross-linking agent was 0.9%, the mass ratio of initiator to acrylamide was 2:100, the reaction temperature was set as 60℃, and the pH value was set as 7. Finally, the coagulant was measured for its swelling kinetics, viscosity, film-forming hardness, peeling strength, and ability to suppress dust. It can be concluded that the coagulant exhibits a very high standard of both dust suppression and wind resistance.
Medical students are known to be at a greater risk of psychological disorders compared to the general population. However, their rate of help-seeking behavior is low. The purpose of this study was to ...explore the influencing factors of attitudes towards psychological help-seeking among Chinese medical students and to examine its gender differences.
A total of 3,453 medical students from three medical colleges in Hainan Province, China, completed anonymous questionnaires that included socio-demographic attributes, the Family APGAR Index, the General Health Questionnaire (GHQ-20), and the Attitudes Towards Seeking Professional Psychological Help Short Form (ATSPPH-SF). Associations between predictor variables and attitudes towards help-seeking were explored using multivariate linear regression, and regression models with interaction terms were employed to test gender difference.
The mean score on ATSPPH-SF Scale was 15.04 ± 3.45, with males scoring significantly lower than females (14.34 vs. 15.64, P < 0.0001). For both male and female groups, psych knowledge, mental health status, family function and help-seeking utility perception significantly influenced attitudes toward psychological help-seeking. Furthermore, having more than once psycho-help experiences was positively correlated with women's attitudes. Significant interactions were found between gender and mental health status.
Attitude towards seeking psychological help was relatively negative among Chinese medical students. The implementation of interventions should take into account the at-risk population, especially the males and individuals with poor mental health.
Due to the growing use of composite materials in aircraft structures, Aircraft Smart Composite Skins (ASCSs) which have the capability of impact monitoring for large-scale composite structures need ...to be developed. However, the impact of an aircraft composite structure is a random transient event that needs to be monitored on-line continuously. Therefore, the sensor network of an ASCS and the corresponding impact monitoring system which needs to be installed on the aircraft as an on-board device must meet the requirements of light weight, low power consumption and high reliability. To achieve this point, an Impact Region Monitor (IRM) based on piezoelectric sensors and guided wave has been proposed and developed. It converts the impact response signals output from piezoelectric sensors into Characteristic Digital Sequences (CDSs), and then uses a simple but efficient impact region localization algorithm to achieve impact monitoring with light weight and low power consumption. However, due to the large number of sensors of ASCS, the realization of lightweight sensor network is still a key problem to realize an applicable ASCS for on-line and continuous impact monitoring. In this paper, three kinds of lightweight piezoelectric sensor networks including continuous series sensor network, continuous parallel sensor network and continuous heterogeneous sensor network are proposed. They can greatly reduce the lead wires of the piezoelectric sensors of ASCS and they can also greatly reduce the monitoring channels of the IRM. Furthermore, the impact region localization methods, which are based on the CDSs and the lightweight sensor networks, are proposed as well so that the lightweight sensor networks can be applied to on-line and continuous impact monitoring of ASCS with a large number of piezoelectric sensors. The lightweight piezoelectric sensor networks and the corresponding impact region localization methods are validated on the composite wing box of an unmanned aerial vehicle. The accuracy rate of impact region localization is higher than 92%.
Abstract
Stellar white-light flares are believed to play an essential role in the physical and chemical properties of the atmosphere of the surrounding exoplanets. Here we report an optical ...monitoring campaign on the nearby flaring system EI Cnc carried out by the Ground-based Wide Angle Camera (GWAC) and its dedicated follow-up telescope. A superflare, coming from the brighter component EI CncA, was detected and observed, in which four components are required to properly model the complex decay light curve. The lower limit of flare energy in the
R
− band is estimated to be 3.3 × 10
32
erg. A total of 27 flares are additionally detected from the GWAC archive data with a total duration of 290 hr. The inferred cumulative flare frequency distribution follows a quite shallow power-law function with a slope of
β
= − 0.50 ± 0.03 over the energy range between 10
30
and 10
33
erg, which reinforces the trend that stars cooler than M4 show enhanced superflare activity. The flares identified in EI Cnc enable us to extend the
τ
–
E
relationship previously established in the white-light superflares of solar-type stars down to an energy as low as ∼10
30
erg (i.e., by 3 orders):
τ
∝
E
0.42±0.02
, which suggests a common flare mechanism for stars with a type from M to solar-like and implies an invariant of
B
1/3
υ
A
in the white-light flares.
Harmonious developments of electrical and mechanical performances are crucial for stretchable sensors in structural health monitoring (SHM) of flexible aircraft such as aerostats and morphing ...aircrafts. In this study, we prepared a highly durable ternary conductive nanocomposite made of polydimethylsiloxane (PDMS), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) to fabricate stretchable strain sensors. The nanocomposite has excellent electrical and mechanical properties by intensively optimizing the weight percentage of conducting fillers as well as the ratio of PDMS pre-polymer and curing agent. It was found that the nanocomposite with homogeneous hybrid filler of 1.75 wt % CB and 3 wt % MWCNTs exhibits a highly strain sensitive characteristics of good linearity, high gauge factor (GF ~ 12.25) and excellent durability over 10⁵ stretching-releasing cycles under a tensile strain up to 25% when the PDMS was prepared at the ratio of 12.5:1. A strain measurement of crack detection for the aerostats surface was also employed, demonstrating a great potential of such ternary nanocomposite used as stretchable strain sensor in SHM.
Modern structures on aircraft make increasing use of large-scale composite structures. Quantitative damage monitoring for composites, including damage occurrence, number, localization, and size ...estimation, will help reduce maintenance costs, improve fleet management efficiency through condition-based maintenance, and potentially more rapidly enable new material systems and structural concepts by integrating health monitoring into the design itself. With the advantage of easily interpretable, intuitive, and accurate imaging result, the delay-and-sum imaging algorithm is frequently researched and applied to damage monitoring. However, when it is applied to multidamage monitoring in large-scale composites, the consumed time and computation resource are too much for pixel value calculation. Besides, due to the material anisotropy and existence of bolt holes and stiffeners in the researched complex carbon fiber composite laminate, propagation mechanism of Lamb wave is quite complicated, which makes the conventional localization result not accurate by delay-and-sum algorithm according to the point with pixel peak value. What is more, the imaging quality is deteriorated with concurrence of multiple damages, and thus, quantitative damage information cannot be extracted. Hence, the damage index merging algorithm is introduced for quick damage identification and damage merging in every subarea divided by piezoelectric sensor array. The delay-and-sum imaging algorithm is performed afterward only in subareas identified with damages, which significantly improves the efficiency of damage imaging for large-scale composites. The nonlinear normalization of pixel values compensates the deterioration of multidamage imaging quality. Then, a weighted average algorithm is introduced for more accurate localization. A further damage size level estimation is realized with probabilities by extracting the image pixel peak value. Experiments with six damages simultaneously on the complex carbon fiber laminate verify the effectiveness of the proposed quantitative multidamage monitoring algorithm with localization error below 2 cm and correct damage number and size level estimation.
A broadband antenna with simultaneous flat gain and filtering characteristic is proposed in this paper. To achieve a flat gain response, rectangle slots and a bandpass filter are loaded on the ...antipodal Vivaldi antenna. The loaded rectangle slots adjust the phase of the surface currents to widen the operating bandwidth, as well as reduce the far-field radiation cancellation of the reverse currents in the end-fire direction, thus improving the gain. In addition, a bandpass filter is added to the antenna to further equalize the currents amplitude and suppress out-of-band signals. The measured results show that the proposed antenna achieves an impedance bandwidth of 101.9% (3.99–12.28 GHz) and an out-of-band suppression level of 15.5 dBi in the upper stopband. What is more, an extremely low gain fluctuation of ± 0.464 dBi is realized in the 4–12 GHz. Compared with conventional broadband antennas, the antenna features simple structure and better performance, which achieves broadband with simultaneous flat gain response and filtering characteristic. The proposed antenna may be applied in high-precision radar sensing system.
PDF
