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With the rapid development of sensor technology and artificial intelligence, the video gesture recognition technology under the background of big data makes human–computer interaction more natural and flexible, bringing the richer interactive experience to teaching, on-board control, electronic games etc. To perform robust recognition under the conditions of illumination change, background clutter, rapid movement, and partial occlusion, an algorithm based on multi-level feature fusion of two-stream convolutional neural network is proposed, which includes three main steps. Firstly, the Kinect sensor obtains red–green–blue-depth (RGB-D) images to establish a gesture database. At the same time, data enhancement is performed on the training set and test set. Then, a model of multi-level feature fusion of a two-stream convolutional neural network is established and trained. Experiments show that the proposed network model can robustly track and recognise gestures under complex backgrounds (such as similar complexion, illumination changes, and occlusion), and compared with the single-channel model, the average detection accuracy is improved by 1.08%, and mean average precision is improved by 3.56%.

The past few years have witnessed the great success of artificial metamaterials with effective medium parameters to control electromagnetic waves. Herein, we present a scheme to achieve broadband microwave low specular reflection with uniform backward scattering by using a coding metasurface, which is composed of a rational layout of subwavelength coding elements, via an optimization method. We propose coding elements with high transparency based on ultrathin doped silver, which are capable of generating large phase differences (∼180°) over a wide frequency range by designing geometric structures. The electromagnetic diffusion of the coding metasurface originates from the destructive interference of the reflected waves in various directions. Numerical simulations and experimental results demonstrate that low reflection is achieved from 12 to 18 GHz with a high angular insensitivity of up to ±40° for both transverse electric and transverse magnetic polarizations. Furthermore, the excellent visible transparency of the encoding metasurface is promising for various microwave and optical applications such as electronic surveillance, electromagnetic interference shielding, and radar cross-section reduction.

This paper proposes a spatial scanning method based on emission source microscopy (ESM), which extends the scanning point distribution from two-dimension (2D) plane to three-dimension (3D) volume space. A commonly used method is the planar scanning, which can determine the radiation source in the industrial field, but the increasing number of electronic devices, uneven shapes and other reasons make plane scanning difficult or require a higher price. Based on the characteristics of linear operation of ESM algorithm and Fourier transform, the three-dimensional scanning method obtained can better solve the shortcomings of planar 2D scanning. The simulation results show that under the same sampling point, the electric field data collected in three planes can also accurately locate the position of the radiation source.

Vaccine administration by subcutaneous or intramuscular injection is the most commonly prescribed route for inoculation, however, it is often associated with some deficiencies such as low compliance, high professionalism, and risk of infection. Therefore, the application of microneedles for vaccine delivery has gained widespread interests in the past few years due to its high compliance, minimal invasiveness, and convenience. This review focuses on recent advances in the development and application of microneedles for vaccination based on different delivery strategies, and introduces the current status of microneedle-mediated vaccination in clinical translation. The prospects for its application including opportunities and challenges are further discussed.

Manufacturer-retailer relationships are often cited as an important determinant in product distribution. By coordinating the channel and aligning incentives, relationships can significantly affect both manufacturers’ and retailers’ profits and contribute to market concentration. However, empirical evidence is scarce because relationships are usually trade secrets. I study how beer manufacturers leverage their relationships with retailers to promote new products in the U.S. hard cider market. I present novel empirical evidence of mutual preferential treatments between manufacturers and retailers in assortment choices and wholesale pricing. I interpret the finding as pair-specific relationships sustained through repeated interactions, and use industry regulations on trade and wholesale pricing to address alternative mechanisms, including non-linear contracts. I estimate a structural model of consumer demand, retail and wholesale pricing, and assortment that incorporates the relationships. The results show that the relationships increase Anheuser-Busch InBev’s and MillerCoors’ new cider availability by 17.7% and 7.2%, respectively, and present a double win to both the manufacturers and retailers.

In this paper, a high-gain, low radar cross-section (RCS) and dual-frequency microstrip antenna is designed. The radome with a symmetrical two-layer frequency selective surface (FSS) is adopted to achieve the RCS reduction in a wide range of frequencies while maintaining the radiation characteristics. The FSS structure used in this work is a 5 × 5 array, composed of two layers of metal patches printed on both sides of the F4B substrate (e r = 2.65 and the thickness is 1.0mm). The associated simulation results show that the S parameter is less affected by the new antenna after loading the radome. The gain of the antenna is increased by 5.1 dB, which improves the radiation pattern of the antenna. At the same time, in the range of 2.0–18.0 GHz, the in-band and out-of-band RCS reduction of the antenna is more than 2.0 dB and the maximum reduction attains 15.0 dB.

Energy is the backbone of a country's economy and development. The potential contribution of renewable energy technology to energy stability, climate change mitigation and economic growth is immense. Biogas, is a renewable energy resource and enriched with methane, produced through the breakdown of organic matters (anaerobically). The large quantity of livestock has significant contributions in Pakistan's economy, and also having a high potential for production of biogas. Therefore, this study was conducted in 6 southern districts of Khyber Pakhtunkhwa province of Pakistan, to identify the expected willingness of households for adopting any biogas system. A sum of 360 households (livestock-farmers) was selected for data collection by the procedure of equal allocation. The identification of the influencing factors on the household's willingness to adopt any biogas system was determined through probit analysis. It has been validated from the research outcomes of probit analysis that the selected household's qualification, electricity shortfall on daily basis and its impact on children's education and female work, awareness of the selected household's about the biogas utilization and its benefits as well as the availability of space have demonstrated their significance and relationship with the household's willingness to adopt biogas system. The overall model is statistically significant at 1% significance level and confirmed the impact of socioeconomic features as the prominent factors for the household's decision to adopt a biogas system. This study suggests the public awareness, which has more significant impact on identifying the household's adoption behavior. Similarly, adequate investments both at the private and public level, should be encouraged for promoting biogas technology. At the same time, the government's fiscal policy should be subsidized which will encourage the lower-income populations' participation in adopting and installing biogas plants.

A novel approach to generating ultra-wideband (UWB) impulses based on a Mach–Zehnder modulator (MZM) and a Fabry–Perot semiconductor optical amplifier (FP-SOA) is proposed and demonstrated. Both the carrier dynamic behavior of SOA and the feedback of FP cavity are exploited to generate a pair of polarity-reversed doublet-like impulses. Simulations and experiments are carried out to verify the UWB generation. In the experiment, the fractional bandwidths of the negative-doublet-like and the positive-doublet-like impulses are 100% and 108%, respectively. The bit error rate (BER) performance of the UWB before and after a span of 19-km standard single mode fiber (SSMF) transmission is also investigated and error-free performance can be achieved for each condition. Finally the UWB wireless transmission over a span of 10 cm is investigated.

We propose and experimentally demonstrate a microwave photonic filter based on an electro-optic phase modulator (EOPM) and a Fabry–Perot semiconductor optical amplifier (FP-SOA). A microwave photonic filter with a single passband between 0 and 40 GHz is obtained. The center frequency, the −3 dB bandwidth and the −30 dB bandwidth of the microwave photonic filter are 18.3, 3.184 and 4.005 GHz respectively. Correspondingly, the shape factor, which is defined as the ratio of the −30 dB bandwidth to the −3 dB bandwidth, is 1.26, and the Q factor, which is defined as the ratio of center frequency to the −3 dB bandwidth of the microwave passband, is 5.75. The achieved microwave passband can be fitted by an 8th order super-Gaussian shape.

We propose and experimentally demonstrate two simple solutions for power-efficient ultra-wideband (UWB) radio frequency (RF) system assisted by an electrical bandpass filter (EBPF). In the first solution, any optical Gaussian pulse with enough bandwidth is transmitted over optical fiber link, and then converted to a power-efficient UWB pulse by an EBPF with a passband of 3.1–10.6 GHz. The transmission and modulation of UWB signal is processed in optical domain, whereas the generation of UWB is processed in electrical domain. Both UWB modulations of on-off keying (OOK) and binary phase shift keying (BPSK) are experimentally demonstrated. In the second solution, the EBPF is used to convert any electrical waveform to a power-efficient UWB pulse. Then the electrical UWB pulse is converted to an optical UWB pulse with a Mach-Zehnder modulator (MZM), and then distributed over long haul fiber link. These two solutions embody the advantages of both low-loss longhaul transmission of optical fiber and mature electrical circuits. And the millimeter-wave UWB signal is also demonstrated.

Multifunctional microwave photonic filters (MWPFs) have potential applications in flexible and various microwave signal processing. The authors propose and demonstrate a MWPF, including all-pass filter, band-pass filter and notch filter based on a single fibre Bragg grating. A high Q band-pass filter with a Q factor of 235 and a rejection ration exceeding 30 dB, and a notch filter with a flat top and a rejection ratio exceeding 25 dB are experimentally achieved.

We theoretically and experimentally demonstrate a novel scheme of bandwidth-variable ultra-wideband (UWB) monocycle generation, using a semiconductor-optical-amplifier (SOA)-based nonlinear optical loop mirror (NOLM). In our scheme, the probe light is split into two parts by the NOLM, and both of them are phase modulated by the pump light due to the cross-phase modulation in the SOA. An extra phase difference between these two parts is also introduced by tuning the polarization controller within the loop. When both parts interfere at the NOLM output port, the phase modulation is converted to the intensity modulation with a UWB monocycle waveform. In addition, the bandwidth of the UWB spectrum is variable by tuning the optical delay line within the loop.

We theoretically and experimentally demonstrate a scheme to implement bipolar millimeter-wave (MMW) ultrawideband (UWB) monocycles using a nonlinear optical loop mirror (NOLM). A 20-GHz optical clock as the probe light and a Gaussian pulse as the pump light are launched into the NOLM for cross-phase modulation (XPM). At the reflection and transmission ports of the NOLM, a pair of polarity-reversed MMW-Gaussian pulses is generated due to constructive and destructive interferences. They are then mixed with proper time delay and orthogonal polarization states. Thus, a photonic MMW-UWB monocycle is obtained. By adjusting the time delay between the reflection and transmission ports of the NOLM, bipolar MMW-UWB pulses are generated.

We experimentally demonstrate an arbitrary-order bandwidth-tunable differentiator using a programmable optical pulse shaper, which is based on spatial diffraction and liquid crystal modulation. The impact of bandwidth of optical pulse shaper on output power and pulsewidth of differentiation is theoretically analyzed. In the experiment, all first-order, second-order, and third-order differentiators with bandwidths of 80, 160, and 320 GHz are obtained with average deviations of less than 4.2%. The differentiation of pseudorandom nonreturn-to-zero (NRZ) signals at 10 and 20 Gbit/s is also discussed.

The finite element static analysis software Algor is used to simulate and analyze the engine connecting rod, and the distribution diagram of the change of stress and displacement is obtained. Theoretically, the force analysis of engine connecting rod is carried out, which provides a necessary theoretical basis for further structural design and optimization of engine connecting rod.

We propose and demonstrate a scheme to implement photonic multi-shape ultra-wideband (UWB) signal generation using a semiconductor optical amplifier (SOA) based nonlinear optical loop mirror (NOLM). By employing the cross phase modulation (XPM) effect, cross gain modulation (XGM), or both, multi-shape UWB waveforms are generated including monocycle, doublet, triplet, and quadruplet pulses. Both the shapes and polarities of the generated pulses are flexible to adjust, which may be very useful in UWB pulse shape modulation and pulse polarity modulation.

We propose and demonstrate a novel scheme of ultra-wideband (UWB) doublet pulse generation using a semiconductor optical amplifier (SOA) based polarization-diversified loop (PDL) without any assistant light. In our scheme, the incoming gaussian pulse is split into two parts by the PDL, and each of them is intensity modulated by the other due to cross-gain modulation (XGM) in the SOA. Then, both parts are recombined with incoherent summation to form a UWB doublet pulse. Bi-polar UWB doublet pulse generation is demonstrated using an inverted gaussian pulse injection. Moreover, pulse amplitude modulation of UWB doublet is also experimentally demonstrated. Our scheme shows some advantages, such as simple implementation without assistant light and single optical carrier operation with good fiber dispersion tolerance.

We theoretically design a power-efficient ultra-wideband pulse generator by combining three monocycle pulses with different weights. We also experimentally demonstrate a feasible scheme to generate such power-efficient ultra-wideband waveforms using cross-phase modulation in a single semiconductor optical amplifier. The designed ultra-wideband pulse fully satisfies the requirements for the spectral mask specified by the Federal Communications Commission with high power efficiency. In the experiment, a power-efficient ultra-wideband waveform with a pulse duration of 310 ps is achieved, and the power efficiency is greatly improved compared with that of a single monocycle pulse or a mixture of two monocycles.

We experimentally demonstrate an all-optical temporal differentiator using a high resolution optical arbitrary waveform shaper, which is based on liquid crystal on silicon switching elements, and both amplitude and phase of the spectrum are programmable. By designing specific transfer functions with the optical waveform shaper, we obtain first-, second-, and third-order differentiators for periodic pulses with small average errors. We also theoretically analyze the bandwidth limitation of optical waveform shaper on the differentiator.