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Direction of arrival (DOA) estimation using the improved unfolded coprime array (IUFCA) subject to array motion isdiscussed in this study. Unfolded coprime array (UFCA) consists of two uniform linear subarrays, and the two subarrays are arranged at different sides of theaxis, which leads to a large number of holes in the difference co-array (DCA). With array motion and DCA synthesis,part of the holes can be filled, but there are still holes in the center which lead to the virtual arrays separated.By analyzing the hole positions in the synthetic DCA generated by UFCA motion, the authors improve the originalUFCA by relocating some physical elements, then the two dominantconsecutive DCA segments in the positive and negative sides can be connected. The expression of synthetic DCA is analyzed, and the closed-form expression of theuniform degree of freedom (uDOF) subject to IUFCA motion is studied. Simulation results show that IUFCA motion can obtain a largenumber of uDOFs, which leads to better DOA estimation performance and more identifiable signals compared with existingcoprime array configurations.

This article proposed a novel hybrid-connected boost converter (HCBC) with ultrahigh step-up and ultralow voltage stress. At the input part, a traditional interleaved boost converter structure is adopted based on dual coupled inductors, which can reduce the input current ripple and ease the current stress flowing through main switches and magnetic elements. Then, the voltage doubling capacitors embedded in this circuit can lift voltage and clamp the voltage stress on switches. Therefore, it will not only increase the voltage gain, but also recycle the leakage energy of coupled inductor to alleviate the voltage spikes across the power switches. At the output, the dual secondary windings of coupled inductors are connected in series and combined with a capacitor-diode to form a voltage multiplier module, which is stacked on the output for higher voltage gain. The working principle and steady-state performance of the proposed converter are analyzed in detail, and a 400-W experimental prototype based on HCBC is built to verify the correctness of theoretical analysis.

Bioclogging is a commonly encountered operational issue that lowers hydraulic conductivity and the overall performance of the infiltration systems. In this paper, a novel processing for alleviating bioclogging by filter media surface hydrophobic modification was presented. Two-dimensional porous media cells were used to observe the influence of hydrophobic modification on biofilm growth in the pore structure. Moreover, two continuous-flow columns packed with gravel, one of which half gravel was hydrophobically modified, were operated with artificial wastewater to verify the effect of hydrophobic modification on bioclogging alleviation. The results showed that the biofilm growth in the cell with hydrophobic modification was slow, and the biomass was less and liable to wipe off after hydrophobic treatment. Meanwhile, the hydraulic efficiency of the flow seepage field was also improved after hydrophobic treatment. The column tests results showed that the hydraulic conductivity of the filter bed with hydrophobic modification (Column B) decreased more slowly than that of another without hydrophobic modification (Column A). Column B had the hydraulic conductivity (k) of 0.66 cm/s in the final stage of the experiment, while the k of Column A was 0.14 cm/s. It verified that hydrophobic modification of partial filter media can alleviate the bioclogging problem of the infiltration systems to some extent. The results provide a new idea and potential technical support for solving bioclogging problem.

Loess has a strong water sensitivity, so loess landslides often transform into loess mudflows when water is added on the Chinese Loess Plateau, which results in high casualties and property loss of the Chinese government. In this study, a series of flume tests were designed to study the initiation of loess mudflows. The results reveal that the initiation modes of loess mudflows include large-scale mudflow and retrogressive toe sliding (Type A), and small-scale mudflow and retrogressive toe sliding (Type B). A model was used to analyze the test results that describe the effects of water flow on the potential for hillslope failure and liquefaction. It was found that the soil accumulation was unconditionally stable before a loess mudflow was formed, but as the rainfall continued, the water gradually infiltrated the soil, and the soil accumulation changed from unconditionally stable to unconditionally unstable. Thus, this led to different initiation modes during the tests. For Type A, the water preferentially infiltrated into the area with an uneven density and a large amount of water accumulated. The pore water pressure increased quickly and could not dissipate in time, so the loess liquefied. As the liquefaction area continued to expand and became larger, Type A occurred. Relatively speaking, Type B occurs in soil accumulations with relatively uniform densities. These results provide a certain scientific reference for the study of loess mudflows.

It is of great significance to study the time-dependent mechanical properties of loess, as loess landslides are closely related to them. The purpose of this study is to investigate the effect of moisture content on instantaneous and time-dependent deformation, strength and failure behaviors of undisturbed loess specimens from Nangou in Yan'an City, Shanxi Province, China, via triaxial shearing tests and multi-loading triaxial creep tests under moisture contents of 5%, 10%, 17% and 22%. The results show that the time-dependent deformation of loess increase with the moisture content, while the time-dependent deformation rate decreases slowly. The soil deformation is divided into four stages based on the peak strain rate. Furthermore, the instantaneous and long-term strength of loess decrease with increasing moisture content, and the instantaneous strength decreases more than the long-term strength. The failure mode of undisturbed loess changes from shear failure to homogeneous failure with increasing moisture content; when the failure mode is shear failure, the thickness of the shear band that forms at the specimen surface over time is smaller than the corresponding thickness that forms instantaneously. Finally, the macroscopic morphology and microstructure of loess specimens were considered together to analyze the effect of moisture content on the instantaneous and long-term mechanical behavior of loess and to discuss the process of loess deformation to failure.

This study presents a non-isolated step-up inverter without leakage current for low-voltage renewable energy generation such as photovoltaic (PV) cells grid connection. From the structure of the proposed inverter, the negative terminal of the PV array is directly linked with the grid neutral, so the common mode voltage of the parasitic capacitance can be kept constant and the leakage current will not be generated in theory. Moreover, this transformerless inverter can produce an AC output voltage higher than the input DC voltage, which will reduce the sizes of the generation system. A switching modulation strategy carrier-based is analysed in detail when the input inductor current is operated in discontinuous conduction mode. The operation modes of the proposed inverter are also discussed, respectively, in positive and negative half line cycles. Finally, a digital experimental prototype is tested in the laboratory, and the experimental results are consistent with the theoretical analysis.

In this paper, an integrated step-up inverter without transformer is investigated for photovoltaic (PV) power generation. The proposed topology can be derived by combining a traditional boost converter with a single-phase full bridge dc–ac converter. The main features of the integrated inverter are: First, the leakage current caused by the solar cell array-to-ground parasitic capacitance can be theoretically reduced to zero due to the characteristics of the converter configuration, which can improve the efficiency and the reliability of the PV generation system; second, the output ac voltage of the proposed inverter can be higher than the input dc voltage, which is capable of connecting low voltage PV panels to the grid; third, only five active switches are used in the presented inverter, and those switching devices can be synchronously driven by various sinusoidal pulsewidth modulation methods based on the carrier; therefore, the proposed inverter is compact and with curtailed cost. The working principle and analysis of the proposed integrated inverter are elaborated. Finally, simulation and experimental results are obtained in a lab prototype, which agree well with the theoretical analysis.

Combined applications of mixed biomaterial amendments and polyacrylamide (MBAP) to maize in semiarid areas have the potential to improve soil physical properties such that improved crop performance may be obtained under deficient irrigation management. In this study, three MBAP applications were C0 (conventional N fertilization application) and C2 and C4 (MBAP applied at rates of 2 and 4 t ha−1, respectively); three irrigation levels were W3 (nearly full irrigation, 85%–100% of field capacity), W2 (light deficit irrigation, 65%–75% of field capacity), and W1 (medium deficit irrigation, 55%–65% of field capacity). Under the same irrigation level, the MBAP significantly decreased soil bulk densities and increased soil hydraulic conductivities and soil water contents. The effects of irrigation levels on soil bulk densities and soil saturated hydraulic conductivities were not significant. Consequently, MBAP improved soil conditions for maize growth and increased grain and biomass yields, especially at the two deficit irrigation levels. Compared with that of C0, grain yields for C2 and C4 were increased by 52.8% and 39.3% under W2, and by 23.5% and 13.7% under W1, respectively. The MBAP and irrigation had significant interaction effects on evapotranspiration during sowing to jointing and on plant heights at 32 d after sowing. The incorporation of MBAP (2 t ha−1) and chemical fertilizer (111.8 kg N ha−1) resulted in the greatest yields under light deficit irrigation and seemed the best approach to improve soil physical properties and sustain maize productivity using limited water resources in dryland regions.

Continuous use of diversion-based irrigation has been associated with an increase in the frequency of loess landslides on the South Jingyang Platform, Shaanxi, China. A loess landslide event with a maximum sliding distance of 278 m occurred near the village of Miaodian on May 26, 2015. This landslide event was characterized by four individual landslides. Field investigations, geological exploration, numerical simulation, isotropically consolidated undrained (ICU) triaxial tests, and ring shear tests were conducted to identify its initiation and movement mechanisms. The ICU tests revealed that saturated loess samples were highly liquefiable. High pore water pressure was quickly produced and deviation stress increased the highest value even at low values of axial strain. Geological investigations revealed that cracks penetrated into the saturated zone from the ground surface, and simulation results revealed that these cracks played a dominant role in the infiltration of surface water and led to a rise in the groundwater table. When the infiltration recharge exceeds the holding capacity of the paleosol, the latter behaves as aquifuge under relatively undrained conditions. This process results in the accumulation of water at the bottom of the loess layer, thereby contributing to soil liquefaction and landslide initiation. The ring shear tests revealed that the saturated sand layer of the landslide substrates was subjected to easily inducible high pore water pressure under undrained conditions which led to the thrusting of the sand layer onto the deposit surface and explains the high speed and long runout distance of this landslide.

High group delay dispersion (GDD) is often required for ultrafast laser applications. To achieve GDD level higher than -10000 fs2 in a single mirror setting is difficult due to the high sensitivity to unavoidable production inaccuracies. To overcome the problem, total internal reflection (TIR) based dispersive mirrors have been proposed in theory. In this paper, we report our continuous effort to further design, fabricate and measure TIR based dispersive mirrors.

Loess landslides exhibit strong interactions with the terrace sediments of the Jing River on the South Jingyang Platform, Jingyang, Xi'an, China. Analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface, accompanied by other terrace sediments of carrying. This led to the formation of a thrust nappe structure over a long distance. We performed ring shear tests to examine the shear behavior of this sand layer, with the finding that saturated sand was highly susceptible to liquefaction-induced failure. The groundwater level of the study area is high, resulting in near-saturation of the sand layer. Therefore, topographic interferences contributed additional variables and increased interaction complexities. Simulations indicated that the liquefied sand layer was compressed and forced. Due to the absence of constraints, the sand layer near the bottom of the slope was sheared out over a relatively short distance. On the other hand, particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground. Finally, an initiation-movement model of loess flowslides is proposed. It describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides. Collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands. The landslide experienced four stages as they moved: scraping collisions, floating scrapes, folded thrusts, and nappe accumulation.

An accurate model for the silicon refractive index including its temperature and wavelength dependence is critically important for many disciplines of science and technology. Currently, such a model for temperatures above 22°C in the optical communication bands is not available. The temperature dependence in the spectral response of integrated echelle grating filters made in silicon-on-insulator is solely determined by the optical properties of the slab waveguide, making it largely immune to dimensional uncertainties. This feature renders the echelle filters a reliable tool to evaluate the thermo-optic properties of silicon. Here we investigate the temperature dependence of silicon echelle filters for the wavelength range of both O and C bands, measured between 22°C to 80°C. We show that if a constant thermo-optic coefficient of silicon is assumed for each band, as is common in the literature, the predictions show an underestimate of up to 10% in the temperature-induced channel wavelength shift. We propose and assess a model of silicon refractive index that encompasses both the wavelength and temperature dependence of its thermo-optic coefficients. We start from literature data for bulk silicon and further refine the model using the echelle filter measurement results. This model is validated through accurate predictions of device channel wavelengths and their temperature dependence, including the quadratic term, over a wide wavelength and temperature range. This work also demonstrates a new high-precision method for characterizing the optical properties of a variety of materials.

Two-dimensional (2-D) direction of arrival (DOA) estimation exploiting interlaced uniform planar array (IUPA) motion is discussed in this paper, and a Discrete Fourier Transform cascading Taylor Expansion (DFT-TE) algorithm is proposed. Specifically, the proposed IUPA structure possesses larger inter-element spacing than traditional uniform planar array (UPA), and it can mitigate the mutual coupling effectively. Simultaneously, the proposed IUPA structure is suitable for array motion. The synthetic IUPA generated by IUPA motion can offer more available array sensors and better DOA estimation performance than synthetic UPA and synthetic sparse uniform planar array (SUPA). Furthermore, considering the high computational complexity of 2-D DOA estimation, we propose the DFT-TE method. The DFT-TE method requires neither eigenvalue decomposition nor search operation. It gets the initial angles by employing the direct DFT method, and obtains the offset compensation for refined estimates by utilizing the Taylor Expansion method and total least squares (TLS) criterion. The proposed method has lower complexity and better estimation performance than the traditional 2-D DFT cascading search (DFT-S) method. Simulation results verify the effectiveness and advantages of the IUPA structure and DFT-TE method.

The shear behavior of loess is closely related to its microstructural variation. Their relationship is of great significance to better understand the loess landslide mechanism. Consolidated-undrained triaxial tests were performed on natural loess from Yan'an, China, with various initial water contents under different confining pressures to investigate the shear behavior. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were conducted on the specimens before and after the triaxial tests to study the variations in microstructure and pore characteristics and their relationship with the shear behavior. The triaxial tests revealed three different failure modes (shearing, homogeneous and plastic failure) and the corresponding stress-strain response of specimens depending on confining pressure level and initial water content. The cohesion decreases exponentially with increasing initial water content whereas the internal friction angle decreases slightly. This effect is closely related to the weakening effect of water on the inter-particle cementation and water-air interface in loess. The macroscopic shear behavior of loess is essentially the result of the continuous adjustment and change in its microstructure system under loading and wetting. This variation process is related to the confining pressure, initial water content and failure mode of the specimen. This condition is manifested by the softening, dispersion, disintegration and reassembly of cementations, particle movement and rearrangement, the reduction and mutual transformation of the inter-aggregate pore populations larger than 0.05 μm in diameter (macropores and abundant mesopores decrease, small pores increase), and the generation and development of cracks under certain conditions.

The Datong Basin is part of the regionally extensive Fenwei Graben System, a major tectonic zone impacted by active tectonics and the resulting damage to life and infrastructure. The basin also contains the Shizhuang ground fissure system. In this study, the likely origin, surface extent, and fissure subsurface characteristics are explored by traditional methods: surveying, mapping, trenching, drilling, and seismic exploration. The Shizhuang ground fissure is located at the intersection of the Xiaoshikou fault and the southern Liuleng margin fault in Yingxian County. It has a length of 2.1 km, excellent continuity, and semi-elliptical surface morphology. The dislocation of strata induced by the fissure increases significantly as the depth increases. The strata bend downward and form typical traction structures near the fissure plane, indicating that the fissure has prominent synsedimentary fault characteristics. The fissure causes serious damage to houses, farmlands, roads, and public facilities, featuring large tensile cracks and vertical dislocations. The resulting data and interpretations indicate that: (1) the ground fissures connect to two major subsurface active faults, which lay the tectonic foundation for the fissure; (2) accelerated groundwater extraction has reactivated the underlying faults and exacerbated fissure development; and (3) mitigation is best achieved by cessation of excessive groundwater pumping, appropriate engineering design, and local avoidance for placement of critical structures. This paper provides a heretofore generally unknown example, promotes research on the mechanisms of fissures, and has guiding significance for disaster prevention and reduction in this area.

Background: Switchable glasses allow the control of light transmission—an attractive property for applications such as car sunroofs, aircraft windows, building windows, augmented reality, imaging, and displays. Commercialized switchable glasses have severe limitations, such as speed, cost, and operating conditions, among others. Microshutters, a type of switchable glass with very distinctive properties, are reviewed, as they are a technology that could significantly improve some or all of the shortcomings mentioned above. Aim: We will summarize the various types of microshutters and tentatively identify various critical designs, fabrication schemes, and performance criteria by the many research groups implementing them and investigating their properties. Approach: We will describe the various approaches used to control light transmission through microelectromechanical systems. It will compare their performances and comment on fabrication and implementation challenges. Conclusions: Microshutters have performance levels that could make them good candidates for switchable glasses. Many research groups have investigated various approaches to fabricate microshutters and have shown that they can be implemented reliably on a small scale, with fast actuation, low power, and high contrast and are relatively easy to manufacture. Work is needed to demonstrate that they can be scaled-up and still be economical to produce.

Thin films of high reflecting metal, such as Ag, have a high reflectance in the long-wavelength region. When they are combined with dielectric layers, it is possible, through thin film interference effects, to induce transmission in certain shorter wavelength regions. Thus, they are useful components for the design of long-wavelength cutoff filters with a broad rejection region. In this paper, metal/dielectric multilayer designs based on this principle are numerically investigated. Three designs with different cutoff wavelengths and with very broad transmission regions in the visible or near-IR spectral ranges are presented. An excellent rejection on the long-wavelength side extends beyond 20 μm. Experimental results for one of the designs produced in our magnetron sputtering system are given.

A cavity stabilized, SESAM mode-locked Cr4+:YAG laser capable of generating sub-100 fs pulses has been developed. Locking the 130-MHz pulse repetition frequency to that of a hydrogen maser-referenced frequency synthesizer provides a 30-nm wide frequency comb for the 1530-nm wavelength region. In conjunction with a pair of acetylene stabilized, external cavity diode lasers, this laser provides a high precision measurement tool for the determination of acetylene transition frequencies.