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The yellow river basin (YRB) plays a crucial role in maintaining national ecological security, and controlling desertification is a critical factor in strengthening the foundation for the high-quality development of the basin. However, there are fewer studies on the spatiotemporal patterns of desertification change in different regions of the YRB, and the mechanisms affecting desertification change are not yet clear. The objective of this article was to construct a desertification difference index (DDI) to characterize the degree of desertification in the YRB based on surface Albedo and normalized difference vegetation index. We analyzed the spatiotemporal patterns of desertification in different regions of the YRB. We used geographical detector and correlation analyses to screen out the main drivers affecting desertification change. We found that the DDI increased significantly at a rate of 0.5 × 10−3/a from 2001 to 2021, indicating a slowing down trend of desertification in the YRB. The spatial concentration of desertification was a high degree of agglomeration and significant spatial autocorrelation. Precipitation (PRE) and surface radiation were the primary factors influencing desertification in the YRB. The most important factor influencing desertification in the upstream of the YRB and midstream of the YRB areas was PRE. However, human footprint has exacerbated desertification in the downstream of the YRB. This article aims to reveal the driving mechanisms behind desertification in the YRB. The objective is to provide a reference for combating desertification and improving the ecological environment in the region.

The Yellow River basin (YRB) is a major ecological functional area in China, and its ecological safety development and change have extremely significant impacts on the natural environment and human society. However, existing studies on the YRB lack spatiotemporal characteristics analysis and prediction of ecological safety with vegetation as the core. Therefore, this study proposes to construct an ecological safety index (ESI) of the YRB based on the comprehensive multidimensional ecological safety evaluation system “vigor-pressure-state-response,” using the normalized difference vegetation index, vegetation carbon sink indicator parameters, temperature, precipitation, the digital elevation model, population density, and the per capita gross domestic product from 2000 to 2020. The spatiotemporal characteristics of the ESI were then analyzed for the YRB, and a long-term and short-term memory network model was constructed to predict the ESI trend of the YRB over the next 10 years. According to the results, from 2000 to 2020, the ESI of the YRB showed a fluctuating upward trend, and the annual average of the ESI changed abruptly in 2015 due to drastic changes in hazardous areas. The ESI in most areas of the YRB showed a significant upward trend, the stability of ESI changes was weak in some areas, and the overall spatial distribution showed significant positive spatial agglomeration characteristics. Further, the response of ESI to landscape complexity in different reaches of the YRB varied. Most of the middle reaches were positively correlated with landscape complexity, while most of the upper and lower reaches were not significantly or negatively correlated. Notably, over the next 10 years, YRB's ESI growth will slow down, with areas with degradation increasing, areas with significant growth decreasing, and areas currently showing stability improvement.

Global Positioning System (GPS) spoofing attacks have attracted more attention as one of the most effective GPS attacks. Since the signals from an authentic satellite and the spoofer undergo different attenuation, the captured envelope of fake GPS signals exhibits distinctive transmission characteristics due to short transmission paths. This can be utilized for GPS spoofing detection. The existing technique for GPS spoofing are either computationally too expensive, require specialize hardware/software updates, or are not accurate enough. To solve these issues, we propose a light-weight GPS spoofing detection method based on a dynamic threshold and captured signal envelope. We validate the proposed technique using experiments based on actual GPS signals and hardware. The relation between envelope characteristics and the distance between a GPS transmitter and receiver are revealed. Inspired by the uncovered relation, a threshold approach towards the detection of GPS spoofing is developed. The proposed approach features a dynamic threshold determined by the dispersion value of a signal envelope's variance instead of a fixed threshold to maximize detection performance in multiple attack scenarios. The results show that the proposed technique can effectively detect GPS spoofing attacks with better accuracy and lower computational complexity as compared to existing techniques.

A novel wideband quasi-Chebyshev bandpass filter (BPF) with steep skirt selectivity and extended upper stopband is presented. It is comprised of two microstrip-to-microstrip vertical transitions with nonuniform slotline sections, which cascaded directly by a nonuniform microstrip connecting line. In terms of odd-/even-mode analysis, the in-band six poles which make up the wideband bandwidth can be explicitly derived. Moreover, the Chebyshev equal-ripple filtering responses with prescribed specifications can be conveniently achieved in desired passband by adopting synthesis theory. In order to suppress the second and third spurious harmonics, a modified circuit model based on synthesis method is further proposed. Two additional transmission zeros (TZs) TZ3, TZ4 can be generated at $3f_{0}$ and $5f_{0}$ respectively by adjusting impedance ratio of slotline stubs properly under the condition of $\theta _{\mathrm {s1}} = \theta /4$ and $\theta _{\mathrm {s2}} = \theta /2$ , which widen the upper stopband bandwidth greatly and enhance harmonic rejection level effectively. Meanwhile, combing with the inherent periodic finite-frequency TZ5, TZ6 and TZ7, the upper stopband could be extended to $6.22f_{0}$ with rejection level better than 14.6 dB. Besides, a pair of finite-frequency TZ1 and TZ2 caused by source-load coupling occur at both sides of passband to sharpen the cutoff slope of skirts remarkably. For verification, a prototype is fabricated and measured, the experimental results agree well with the theoretical predictions, which verify the validity of proposed method.

Full-color display is a primary challenge for the commercialization of quantum dots (QDs). In this study, we utilize the spectral narrowing phenomenon of microcavities to fabricate the red, green and blue quantum dot light-emitting diodes (QLEDs) with a single QD layer. This work theoretically analyses the role of microcavities in adjusting the emitting color of QLEDs. By enhanced microcavity and properly chosen spacer thickness, the spectral selectivity shifts, realizing the full-color-tunability of QLEDs. The tunable experimental spectra of microcavity QLEDs are observed, in excellent agreement with our theoretical design. Benefiting from the spectral narrowing of microcavity and the narrow spectra of QDs, a high color purity with full width at half maximum (FWHM) of 18 to 25 nm is realized, leading to a color gamut ratio of 104.8% compared to National Television System Committee (NTSC) standard. The light extraction is also enhanced by constructive interference and the Purcell effect in the microcavity. Moreover, in the fabrication of red, green, and blue pixels, patterning the transparent cathode has better feasibility and lower damage relative to patterning the light-emitting layer.

High-heeled shoes of excessive height can severely injure shoe users. Such shoes may cause various injuries, including musculoskeletal pain, osteoarthritis, and hallux valgus. A physician can estimate an appropriate heel height limitation for an individual wearer by touching calcaneus to estimate deformation of the calcaneal varus. It would typically be impractical for a woman to seek the professional assistance of her physician when buying high-heeled shoes. A novel system was developed in this study for evaluating the maximum safe height of high-heeled shoes for female wearers. In this study, images of Achilles tendons, medial longitudinal arches, lateral longitudinal arches, and plantar pressure distributions served as the inputs in the proposed system. After the system had been trained with those images, the system could output the maximum height of high-heeled shoes for each individual wearer. In this study, two crucial methods were used for performing the evaluating system. First, Basic CNN, VGG16, and MobileNetV2 were used to evaluate images of feet. Through the experiments, the proposed artificial intelligence (AI) model achieved an accuracy of 0.88. Next, a statistics algorithm was used to modify the results obtained from the AI model. Subsequently, the error of the system declined. The mean absolute error of the proposed system which was used for evaluating the maximum height of high-heeled shoes was 1.21 cm, which is less than the typical increment for commercially available high-heeled shoes.

Under the computational integral imaging-based security system, the application of Deoxyribonucleic Acid (DNA) encoding algorithm will cause silhouettes in the cipher image, thereby reducing the security of the system. To solve this problem, we introduced a cellular automata-based DNA (CA-DNA) algorithm, which effectively hides the distribution information of the original scene. It can prevent attackers from obtaining any valid information based on the statistical characteristics of the image, which makes our encryption system more security. At the same time, an improved high-resolution reconstruction algorithm is applied to achieve a high-quality decrypted scene. We conducted relevant experiments to certificate the effectiveness of proposed method. Experimental results verify that the scheme has high security and robustness.

The emergence of optical Internet of Things (optical-IoT) for sixth-generation (6G) networks has been envisaged to relieve the bandwidth congestion in the conventional radio frequency (RF) channel, and to support the ever-increasing number of smart devices. Among the plethora of device innovations deemed essential for fortifying the development, herein we report on the visible-to-near-infrared color-conversion luminescent-dyes based on lead sulphide quantum dots (PbS QDs), so as to achieve an eye-safe high-speed optical link. The solution-processed PbS QDs exhibited strong absorption in the visible range, radiative recombination lifetime of 6.4 $\mu$s, as well as high photoluminescence quantum yield of up to 88%. Our proof-of-principle demonstration based on an orthogonal frequency-division multiplexing (OFDM) modulation scheme established an infrared data transmission of 0.27 Mbit/s, readily supporting an indoor optical-IoT system, and shed light on the possibility for PbS-integrated transceivers in supporting remote access control of multiple nodes. We further envisaged that our investigations could find applications in future development of solution-processable PbS-integrated luminescent fibers, concentrators, and waveguides for high-speed optical receivers.

A novel dual-band patch antenna operating at 28/38 GHz is proposed for multiple-input multiple-output (MIMO) communication systems in this paper. The antenna utilizes substrate integrated waveguide (SIW) transmission line as the feed by means of a coupling slot on the SIW. A square patch antenna functions as the radiator for 28 GHz. The inductive loading, which presents as a pair of shorting pins in this design, achieves the impedance matching for 28 GHz-band. Etched on the square patch, the proposed H-shaped slot makes the radiator to performance as an antenna containing two radiating arms and thus introduces another resonant frequency at 38 GHz. Directions of the surface current on the paired arms are identical and produce a reasonable radiation pattern for 38 GH-band. Simulated results declare that the antenna achieves an S11

Near infrared to visible up-conversion devices have every growing demand in a myriad of industrial sectors including photovoltaics, energy harvesting, medicine and imaging. Here we have demonstrated an up-conversion device which utilizes quantum dots for both infrared absorption and visible emission. The band structure of the device is designed and optimized with well-constructed carrier transport and blocking layers. The achieved up-conversion device exhibits an impressive conversion efficiency of over 6 %, with a high near infrared on-off ratio of over 104. The device demonstrates a potential new approach for an up-conversion device designed solely on quantum dots with high efficiency.

In this article, a compact broadband circularly polarized (CP) antenna with non-planar reflector is presented. In this antenna, two fan-shaped cross-dipoles as the primary radiator and a stepped ground as a reflector are proposed to generate a broadband CP radiation. Besides, four L-shaped patches are introduced to effectively extend the bandwidth (BW) and extract a gain improvement together with the stepped ground. The measured -10 dB impedance BW is 132.08 % (1.36-6.65 GHz) and 3 dB axial ratio (AR) BW is 128.6% (1.39-6.4 GHz), closely with the simulated AR BW 136.73% (1.18-6.28 GHz), showing the proposed antenna features a wider bandwidth, comparing with other broadband CP antennas using similar structures. Due to the compact structure, the overall size of the proposed antenna is only 0.27λl×0.27λl©0.12λl (where λl is the free-space wavelength at 1.36 GHz). The proposed antenna has a wide application scope, such as the wireless network and satellite telecommunications.

The Sommerfeld Integrals (SIs) are re-visited in the presence of half-spaces under the assumption of γ0 ≈ iλ being valid for low-frequency propagation in order to investigate the near-field due to a Horizontal Magnetic Dipole (HMD). Analytical expressions are derived for the excited waves over a planar homogeneous conducting ground or sea surface, and a numerical Finite Element Method (FEM) approach is also exploited to validate its correctness and effectiveness. The proposed method is additionally verified by late released experimental data, and it is shown that the results for various simplified expressions qualitatively corroborate the conclusions found in published papers. The proposed formulas can be used as a valuable tool for the study of the properties of near-field propagations from a loop antenna.

Soybeans have the characteristics of balanced amino acid species and high nutritional value. In this article, the feasibility of the identification soybean from three typical origins (Argentina, the United States and China) by interval partial least squares (iPLS) optimized terahertz (THz) spectroscopy combined with chemometrics was investigated. Firstly, the THz frequency-domain spectrum was optimized using iPLS. Then, 168 soybean samples were selected as the correction set, and soybean origin identification models were respectively built using the extreme learning machine (ELM), genetic algorithm support vector machine (GA-SVM), and artificial bee colony algorithm support vector machine (ABC-SVM) combined with 8 pre-processing techniques. Finally, the models were verified through 57 samples of the test set and the comprehensive identification accuracy rate of the ABC-SVM model reached 94.74%. The experimental results showed that after iPLS optimization and appropriate pre-processing technique, THz spectroscopy and chemometrics could accurately identify the origin of soybean.

An effective strategy based on optical tunneling is developed to significantly improve the efficiency of quantum dots light-emitting diodes (QLEDs) and perovskite light-emitting diodes (PeLEDs). Contrary to the common impression that the hole transport layers (HTL) with low refractive index will severely confine lights according to Snell's law, optical tunneling unlocks a channel to extract the lights through HTL. In this work, we demonstrate the light beyond the critical angle still has a chance to penetrate into the substrate and finally emit outside the device. An optical tunneling model is also presented here to quantitatively describe the light extraction through optical tunneling and reveal related factors. Applying a thin HTL (thickness = 10 nm) and a high-index substrate (refractive index = 2) in the typical device architecture (Glass/ITO/PEDOT:PSS/EML/TPBi/LiF/Al), substrate modes can be improved from 18% to 60%. Therefore, optical tunneling followed by EES is believed to be a cost-effective strategy to enhance light extraction efficiency. This work unravels the potential to further significantly improve the efficiency of QLEDs and PeLEDs.

Cerenkov luminescence tomography (CLT) is a promising imaging modality in the field of optical molecular imaging (OMI), which successfully bridges the OMI and tradition nuclear medical imaging and provides the location and quantitative analysis of the distribution of radionuclide probes inside the biological objects. As the CLT is an inherent highly ill-posed inverse problem, it is still a challenge to obtain an accurate reconstruction result. Here, we proposed a novel reconstruction framework based on stacking denoising autoencoders (SDAE), which serve as one famous structure of the artificial neural network (ANN). In our framework, the initial permission region is the whole domain and then a traditional reconstruction algorithm is used to reconstruct each node's energy. Then these nodes are clustered into two regions: permission region and non-permission region, and the permission region is used to start a new reconstruction loop where a new result can be obtained. The procedures above are repeated before the result meets the stop conditions. The numerical simulation experiments, physical phantom experiments and in vivo experiments are all carried out to validate the feasibility and potential of our framework. Results demonstrate that the proposed framework can indeed achieve a good performance in CLT reconstruction.

The waveguide traveling-wave power combiner (WTWPC) falls into the category of asymmetrical non-isolated power combiners, and, therefore, the active load modulation occurring within the combiner was investigated. Proper manipulation of active load modulation gave rise to a two-step design method for the combiner. The first step formulated the specifications of the combiner in terms of active load impedance at its input ports, which determined the objective scattering parameters of the combiner, as well as the desired coherent excitation signals. The second step established a versatile equivalent circuit model to provide a mapping relation between the scattering parameters and the physical dimensions of the combiner. The proposed equivalent circuit method not only offered a close-to-reality description of the existing type of traveling-wave power combiners but also broke new ground for combiner variants that accommodate the more general driving amplifiers. A Q-band quasi-planar traveling-wave waveguide spatial combined amplifier was built to demonstrate the proposed method. The measured P-1dB bandwidth of the prototype was 6 GHz (33-39 GHz).

In this paper, a new class of shielded half-mode substrate integrated waveguide (SD-HMSIW) and shielded quarter-mode substrate integrated waveguide (SD-QMSIW) filtering power dividers (FPDs) have been presented. The proposed prototypes are capable of splitting/combining power and selecting frequency simultaneously. The SD-HMSIW and SD-QMSIW resonant cavities combine the features of compact size, high-quality factor, and low loss. To the best of author's knowledge, it is the first time employing the shielded SIW structure for FPD designs. The six prototype circuits with pure or hybrid SD-HMSIW/SD-QMSIW resonators are designed and fabricated to validate the proposed concept. Multilayered structures are implemented to minimize the dimensions of the FPDs further. Transmission zeros distributing near the operating passband are introduced by cross-coupling mechanism. Both measured and simulated results indicate that the proposed FPDs with the shielded SIW structures exhibit not only filtering performance, but also the good magnitude and phase imbalance characteristics in the operating frequency band.

A balanced microstrip quad-band bandpass filter (BPF) employing balanced microstrip/slotline (MS) transition structures and two pairs of folded asymmetric short stub-loaded resonators (ASSLRs) is presented in this paper. The center frequencies of the four differential-mode (DM) passbands can be controlled by changing the electrical length ratio of each ASSLR. Meanwhile, the fractional bandwidths (FBWs) can be adjusted by controlling the coupling gaps between the resonators and interdigital coupled line. High selectivity of the four DM passbands is achieved by introducing eight transmission zeros (TZs). Moreover, the DM passbands are independent from the common-mode (CM) responses, which significantly simplifies the design procedure. In order to validate the design strategies, a balanced quad-band BPF centered at 2.54/ 3.46/ 4.5/ 5.2 GHz was fabricated and a good agreement between the simulated and measured results is observed.

In this paper, we propose a method to increase the robustness of 2D/3D optical image encryption using the dilated deep convolutional neural network (CNN). In order to solve the problem that encrypted images suffer from some attacks in practical application, we utilize a fast and effective CNN denoiser based on the principle of deep learning. The CNN improves the robustness of the algorithm by improving the resolution of the reconstructed images. Besides, CNN has a high performance against blur and occlusion attacks. We introduce the pixel scrambling method to enhance the security level of the encryption by the private key of pixel scrambling operation. The proposed method can not only realize the encryption of a two-dimensional image but also implement three-dimensional image encryption by combining the integral imaging technology. Double random phase encoding in the fractional Fourier domain is selected for experimental verification, and the results show the capability for robustness, noise immunity, and security of the proposed method.

Fluorescent quantum rods (QRs) have received much attention recently because of their properties of polarized light emission with narrow full width at half-maximum. Therefore, QRs can be used in liquid crystal display (LCD) backlight, as an active polarizer. In order to emit light with a high degree of polarization (DOP), QRs need to be controlled and aligned along one direction on large-scaled devices. However, most of the proposed effective alignment approaches cannot be applied to a large area. In this paper, we report for the first time the contact ink-jet printing (CIJP) method to align CdSe/CdS core/shell QRs. With the ink being printed, the QRs can align along the fluid ink flow direction resulting in aligned QRs along printing direction and forming a film with a high DOP of 42%. Furthermore, CIJP can realize arbitrarily large area fabrication without reducing DOP value. It is expected that this method can be utilized to print on large-scaled substrates directly to fabricate polarized optoelectronic devices, and further applied to LCD backlights and any other applications where polarized light is needed.

The plasmonic surface is made of metallic surface with deep sub-wavelength decorations, which are designed to mimic the surface plasmon polaritons at lower frequency. Recently, high-order modes in some special structures are analyzed. In order to analyze the dispersion problem of high-order modes of complex lossless structures faster and simpler, a convenient and simple method using the average input wave impedance obtained by a field-network joint solution is proposed. Meanwhile, based on Forster's reactance theorem, high-order modes of the complex structure always exist. Then, the dispersion curves of the high-order modes calculated using proposed method are in perfect match with the simulated results, which can verify the effectiveness and correctness of the proposed method. Additionally, the simulated and experimentally measured electric field distribution of high-order modes have great agreement. Using the proposed method, one can quickly obtain dispersion curve of a plasmonic structure to verify or estimate structure design. Hence, the proposed method may make a big step forward for obtaining the special dispersion relations.

A balanced microstrip quad-band bandpass filter (BPF) with independently controllable frequencies, controllable fractional bandwidths (FBWs) and high selectivity is designed in this paper. The proposed BPF is achieved by employing two pairs of folded asymmetric stub-loaded resonators (FASLRs) and balanced microstrip/slotline transition structures (MSTSs). The center frequencies of the four differential-mode (DM) passbands can be controlled independently by changing the electrical lengths of each FASLR. A novel interdigital coupled line is firstly proposed to enhance source-load coupling further, which contributes to a higher selectivity. Meanwhile, the DM passbands are independent of the CM responses, which significantly simplifies the design procedure. In addition, eight transmission zeros (TZs) are generated to improve the selectivity of the four passbands obviously. The measured results of the fabricated balanced BPF centered at 2.48/3.45/5.17/5.78 GHz agree well with the simulated ones, which validates the proposed design method well.

A balanced planar quasi-Yagi antenna integrated with a bandpass filtering response is presented in this paper. The proposed balanced antenna consists of a balanced stepped-impedance microstrip-slotline transition structure, a driver dipole, a parasitic strip, and a bandpass filtering unit. A good differential-mode (DM) passband selectivity is formed by inserting a microstrip stub-loaded resonator (SLR) in the feed line of the quasi-Yagi antenna. This integration enables the antenna to achieve both compact size and high frequency selectivity. By controlling the dimensions of SLR, the central frequency and fractional bandwidth (FBW) can be easy to be adjusted. Meanwhile, the microstrip-slotline transition structure can achieve a good wideband common-mode (CM) suppression without affecting the DM ones, thus simplify the design procedure. The proposed antenna with low cross-polarization level and high CM rejection is found to be comparable to the conventional quasi-Yagi antenna. Furthermore, there are two radiation nulls on both sides of the passband to improve the selectivity effectively. In order to validate its practicability, the balanced antenna is designed and fabricated. The experimental results exhibit that the designed balanced filtering antenna features good filtering response, low cross-polarization level, and high CM rejection.

To mitigate the contradiction between scarcity spectrum resources and heavily wireless services, cognitive radio (CR) has been proposed to improve spectrum utilization through allowing CR users to access licensed channels opportunistically. In large-scale networks, spectrum status is not the same at different locations due to the heterogeneity of CR network (CRN). To cope with such heterogeneity, some noncooperative spectrum sensing and distributed cooperative sensing algorithms were proposed. Such spectrum decision results will be exploited in this paper, in order to draw the spectrum map of the entire largescale CRN. The proposed spectrum mapping scheme contains three processing steps, and a boundary CR users searching algorithm using kennel function based supportive vector machine is adopted to improve the performance of the proposed scheme. The simulation results show that radial basis function kennel performs the best in the proposed scheme, and when accuracy threshold θα = 0.95 and filtration threshold θf = 0.02, the proposed scheme can draw a spectrum map with the accuracy 99.3% using only about 28% CR users performing spectrum sensing. Furthermore, the number of CR users and energy detection threshold have little effects on the performance of the proposed scheme.

A novel dual-transformation simplified real frequency technique is proposed in this paper to synthesize a broadband Doherty power amplifier (DPA). The proposed method can realize the co-design of the carrier and peaking output matching networks to achieve dual-impedance transformation at back-off (BO) and saturation simultaneously. To realize this method, a generalized driving point function with different loads of the matching network is proposed, and weight factors are adopted to combine the separate target functions to form a united one. Compared with conventional designs, no initial guess is required and additional compensating lines are eliminated to improve the performance of the DPA. Based on the proposed technique, a broadband DPA is designed and fabricated across 2.2-3.7 GHz (51% fractional bandwidth). The measurement results show that the designed DPA has a 6-dB BO efficiency of 45%-53% and a saturated output power of 43-44.6 dBm over 1.5 GHz bandwidth. Various modulated signals including 80-MHz long-term evolution-advanced signal and concurrent dual-band signal are employed to validate the DPA. In this way, the DPA can achieve an average efficiency of 45.3%-55.9% at 6.5-dB BO with the adjacent channel leakage ratio levels better than -48.6 dBc by utilizing digital predistortion.

We propose a liquid-crystal-based reconfigurable chiral metasurface absorber and numerically investigate its chiro-optical properties. The chiral metasurface absorber consists of a metal-insulator-metal structure with the substrate, which can strongly absorb a circularly polarized wave of one spin state and reflects that of the opposite spin, resulting a strong circular dichroism (CD). A birefringent liquid crystal (LC) is exploited to serve as the insulator layer in the metal-insulator-metal structure. We could then vary the circular state of the incident light by controlling the alignment of the LC molecules, hence inversing the CD. The simulation results show that the CD will change the sign as the LC molecules are realigned from 0° to 90°. The absorption efficiency for the specific circularly polarized wave is larger than 80% and the CD is nearly 70%. The simple and compact design of our proposed chiral metasurface absorber is especially favorable for integration, and such a reconfigurable chiral absorber could find many potential applications in biological detection/sensing, polarimetric imaging, and optical communications.