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Internet of Things (IoT) is hard to deploy adequate security defenses due to the diversity of architectures as well as the limited computing and storage capabilities, which makes it more vulnerable to malware. With the massive deployment of IoT devices, how to accurately identify and classify the malware variants is crucial to IoT security. However, existing methods of IoT malware classification generally support specific platform or require complex models to achieve higher accuracies. To solve these problems, this paper proposes an IoT malware classification method based on Lightweight Convolutional Neural Networks (LCNN). First, the malware binaries are converted into multidimensional markov images. Then, the LCNN is designed with two new operations, depthwise convolution and channel shuffle, for malware images classification. Compared with other deep learning based methods such as VGG16, the designed LCNN can greatly reduce trainable parameters while maintaining accuracy. The generated model of LCNN is only about 1MB, while that of VGG16 is 552.57MB. The average accuracies of the proposed method are higher than that of gray images on multiple IoT malware datasets, all of which are over 95%. Compared with the state-of-the-art low-level features based methods, the average accuracy of the proposed method is 99.356% on the Microsoft dataset even if the model is tiny. The results show that the proposed method is not only suitable for IoT environments but also has high accuracy.

The high-performance and aberration-free broadband acoustic lens holds promise for extensive applications, yet remains challenged. In this work, a scheme is proposed, and the experimental demonstration of a planar acoustic Luneburg lens capable of focusing broadband sound ranging from 1 to 3 kHz (relative bandwidth approaching to 100%) in an aberration-free manner is presented. Concretely, plane sound within the frequency range incident from one side can be concentrated on a same point on the opposite edge of the Luneburg lens. The demanded refractive indexes of the lens are obtained from the component space coil acoustic metamaterials, which can easily manipulate the refractive index by adjusting a structural parameter. The prototype of the proposed Luneburg lens is fabricated by three-dimensional printing technology and experimentally characterized in a two-dimensional acoustic measuring platform. The measured results are consistently in good agreement with those from the numerical simulations. Finally, the proposed Luneburg lens is employed to construct a wide-angle acoustic reflector, which can produce a strong echo propagating in the direction exactly opposite to the incident wave. These results facilitate potential possibilities for developing more acoustic functional devices capable of manipulating broadband sound.

Compression tests were performed at room temperature to investigate the effects of hydrogenation temperature on compressive properties of Ti6Al4V alloy treated by continuous multistep hydrogenation treatment (CMHT). Pressure-composition isotherms and microstructures were also studied. Results showed that the equilibrium hydrogen pressure increased, and the hydrogen absorption rate decreased with the increase of hydrogenation temperature. The amounts of β phase and α” martensite increased first and then decreased when Ti6Al4V alloy was treated by four times CMHT with the increase of hydrogenation temperature. Hydrogenation temperature played a different role on the compressive properties of CMHT-treated Ti6Al4V alloy. The ultimate compression of Ti6Al4V alloy treated by 11 times CMHT at 850 °C increased by 83.3 % as compared to the as-received Ti6Al4V alloy. The compressive properties of Ti6Al4V alloy were dependent on the amounts of different phases and microstructures when Ti6Al4V alloy was treated by CMHT at different temperatures.

The effects of continuous multistep hydrogenation treatment (CMHT) on the room-temperature compressive properties of Ti6Al4V alloy were investigated through compression tests. The pressure-composition isotherms of Ti6Al4V alloy hydrogenated at 850 °C with different CMHT numbers were also studied. Results show that CMHT number has different effects on microstructures and compressive properties of Ti6Al4V alloy. When CMHT number increased, the amounts of α phase and α′ martensite decreased, the amount of α″ martensite increased first and then decreased, the number of β phase increased. When the CMHT number was one, δ hydrides precipitated at phase boundary. With the increase of CMHT number, δ hydrides precipitated not only at α phase, but also at β phase. The ultimate compression decreased first up to a minimum, and then increased gradually up to a maximum, finally decreased with the increase of CMHT number. The ultimate compression of Ti6Al4V alloy with eight times CMHT increased by 83.83% as compared to the as-received Ti6Al4V alloy, which was the highest ultimate compression among those of all CMHT-treated Ti6Al4V alloys. Reasons for the distinct effects of CMHT number on the room-temperature compressive properties were discussed.

Based on the latest geological, seismic, drilling and outcrop data, we studied the geological structure, tectonic evolution history and deformation process of the southwestern Sichuan fold-thrust belt to find out the potential hydrocarbon exploration areas in deep layers. During key tectonic periods, the southwestern Sichuan fold-thrust belt developed some characteristic strata and structural deformation features, including the Pre-Sinian multi-row N-S strike rifts, step-shaped platform-margin structures of Sinian Dengying Formation, the western paleo-uplift in the early stage of Late Paleozoic, the Late Paleozoic–Middle Triassic carbonate platform, foreland slope and forebulge during Late Triassic to Cretaceous, and Cenozoic multi-strike rejuvenated fold-thrusting structures. The fold-thrust belt vertically shows a double-layer structural deformation controlled by the salt layer in the Middle Triassic Leikoupo Formation and the base detachment layer at present. The upper deformation layer develops the NE-SW strike thrusts propagating toward basin in long distance, while the deeper deformation layer had near north-south strike basement-involved folds, which deformed the detachment and thrusting structures formed earlier in the upper layer, with the deformation strength high in south part and weak in north part. The southern part of the fold-thrust belt is characterized by basement-involved fold-thrusts formed late, while the central-northern part is dominated by thin-skin thrusts in the shallow layer. The Wuzhongshan anticlinal belt near piedmont is characterized by over-thrust structure above the salt detachment, where the upper over-thrusting nappe consists of a complicated fold core and front limb of a fault-bend fold, while the deep layer has stable subtle in-situ structures. Favorable exploration strata and areas have been identified both in the upper and deeper deformation layers separated by regional salt detachment, wherein multiple anticlinal structures are targets for exploration. Other potential exploration strata and areas in southwestern Sichuan fold-thrust belt include the deep Sinian and Permian in the Wuzhongshan structure, pre-Sinian rifting sequences and related structures, platform-margin belt of Sinian Dengying Formation, and Indosinian paleo-uplift in the east of the Longquanshan structure.

With low cost and high profit, fake IoT apps are an increasing risk to the security of the IoT ecosystem. In this article, we propose a novel fake IoT app detection method, referred as MSimDroid, based on multidimensional similarity to mitigate the threat. MSimDroid focuses on the distribution channels of fake apps, that is, app markets, and it consists of whole app similarity, resource similarity, code similarity, and their joint strategy. For similarity calculation, we design a distinctive algorithm based on the feature of different fake patterns. For joint strategy, which is the scheduler of multiple algorithms, it balances the accuracy and time consuming of MSimDroid. Experiments demonstrate that the accuracy of MSimDroid is more than 99.31% on ground-truth data set and 97.43% in the wild. The IoT apps from multiple well-known app markets reveal that the average proportion of fake apps is about 14.66%, and that of mixed-mode apps (including IoT and nonIoT apps) is 10.78%. Besides, it finds that about 0.58% of IoT apps suffer from malice, while the average ratio of mixed-mode apps is 1.06%.

Grain refinement is an effective method to improve the mechanical properties of magnesium (Mg) alloys. In the present research, the combination of multidirectional forging (MDF) and forward extrusion for sizing with decreasing temperature pass by pass was employed to deform as-cast AZ80 magnesium alloy billet with large size to obtain fine grains and homogeneous microstructure. It was found that with the increasing number of MDF passes, the average grain size decreases; the homogeneity of microstructures and the percentages of dynamic recrystallised grains increase simultaneously. After six-pass MDF, fine and homogeneous microstructure with an average grain size of 15 μm was achieved; however, grain refinement became very difficult with a further increase in the MDF pass number. After eight-pass MDF plus forward extrusion for sizing, excellent mechanical properties of large-scale AZ80 magnesium alloy billet were obtained. The tensile strength, the yield strength and the elongation of billet are 410 MPa, 292 MPa and 14%, respectively. Furthermore, during multitemperature MDF, the inverse of the square root of grain size and tensile yield strength fit well with the Hall–Petch relationship.

An isothermal closed-die forming process, including two forging procedures in which the female die of the final forging procedure is split into two parts, was developed, and a very complex component of magnesium alloy called the upper receiver was successfully produced. The obtained forged piece has higher mechanical properties and meets the standard of being safely used in special machines. Based on the FORGE software platform, finite element (FE) simulation was used to determine the preform shape, processing parameters, and forging procedure. A closed-die cavity was formed during the final forging procedure, which can effectively enhance the workability of magnesium alloy, refine the grain sizes, and increase the strength of the component. Importantly, the forged piece has homogeneous microstructures, and the ultimate tensile strength located at the lateral and bottom positions of the upper receiver is greater than 396 MPa and the minimum of the elongation ratio at fracture is 15%.

Reef–shoal reservoirs are important reservoir types of the Changxing–Feixianguan Formation located in the eastern Kaijiang–Liangping trough, Sichuan Basin, China. Understanding the reef–shoal combinations and the reservoirs characteristics are significant for oil and gas exploration in this area. According to field profiles, drilling and seismic data, the reef–shoal development state of Changxing-Feixianguan Formation was sorted out and counted, two main types of complete reef–shoal combination and incomplete reef–shoal combination had been identified based on whether reef or shoal development in the Changxing Formation and shoal development in the Feixianguan Formation, Ten secondary combination models were identified within these main combinations. To analyze the reservoir characteristics, core observations and descriptions, thin section identifications, and physical property testing were selected to match reef–shoal combinations, results show the favorable combination was mainly represented by the complete combination, of which the reservoir performance was relatively good. The platform margin reef facies and platform margin shoal facies constituted the most favorable reservoir facies zone, wherein reef–shoal reservoirs were mainly developed in the high-stand system tract within the sequence, and strong dolomitization was mostly developed at the top of the reef–shoal reservoirs. The formation of high-quality reservoirs was often controlled by the dual factors of sedimentation and diagenesis.

Carbon nanotubes/iron oxyhydroxide (CNTs/FeOOH) three-dimensional hybrid with shell/core nanostructure is designed as a binder-free electrode for the flexible supercapacitor (SC) application. The coiled and dense CNT forest is preferentially fabricated on flexible carbon fiber cloth (CC) by chemical vapor deposition (CVD) and employed as a highly conductive carrier for electrodeposition growth of FeOOH. The average diameter and length of the single CNT are 30–60 nm and 2–3 μm. The shell/core structured CNTs/FeOOH three-dimensional hybrid maintains the consistent interconnecting network morphology, contributing to overcoming the problem of poor conductivity of FeOOH and the transmission of electron channels and the diffusion of electrolyte ions. The CNTs/FeOOH hybrid exhibits a high mass-specific capacitance of 824 F g−1 (or 0.59 F cm−2) in 1 M Na2SO4 electrolyte at 0.5 mA cm−2. By increasing the FeOOH deposition weight, the enhanced area-specific capacitance of 0.892 F cm−2 (or 564 F g−1) is obtained at 0.5 mA cm−2, and the enhanced capacitance retention can reach 96% after 3000 charge/discharge cycles. Besides, a flexible SC is fabricated using the CNTs/FeOOH hybrid electrode and carboxymethyl cellulose (CMC)/Na2SO4 gel electrolyte. The SC displays an energy density as high as 13.33 Wh kg−1 at a power density of 1000 W kg−1. The SC device shows large bending deformation, and these SC devices pack can drive a red diode to work. These results provide such a shell/core structured CNTs/FeOOH three-dimensional hybrid that can be used as potential and low-cost electrode material for flexible SC.

Multidirectional forging (MDF) of Mg-Gd-Y-Nd-Zr alloy was performed under decreasing temperature condition. The grain refinement, microstructure and mechanical properties homogeneity of Mg-Gd-Y-Nd-Zr alloy during MDF process were investigated. The results show that the grain refinement mechanism of Mg-Gd-Y-Nd-Zr alloy during MDF process was dynamic recrystallization. The dynamic precipitations were observed after MDF process, which were mainly located at the grain boundaries and had a significant influence on the grain refinement, and the amount of dynamic precipitations increased as the MDF passes increase. The microstructure of the billet was not homogeneous due to the deformation and temperature inhomogeneity during MDF process. Optimization MDF process has been proposed, which benefited the microstructure homogeneity and reduced the amount of the dynamic precipitations. Based on the optimization MDF process, the elongation to fracture significantly increased.

We have demonstrated an acoustic metamaterial (AM) metalens with the anisotropic refractive index cavities based on the space-coiling units. Compared to that based on conventional Fabry-P e rot (FP) resonance, the proposed space-coiling units significantly downsize the thickness of the AM metalens. In the cavities, we further demonstrated a strong resonant tunneling compression effect, which can be used to substantially magnify the evanescent waves to realize subwavelength imaging. Imaging experiments have shown that the objects located at a considerably enlarged distance away from the input surface of the AM metalens can be imaged with a subwavelength spatial resolution. The proposed AM metalens may facilitate potential applications in acoustic super-resolution imaging and focusing devices.

TG/DSC tests of hydrogenated TC21 alloys were carried out. Effects of temperature and holding time on the residual hydrogen contents of hydrogenated TC21 alloys and their microstructures were analyzed. Results show hydrogen atoms begin to release from the hydrogenated TC21 alloys when the heating temperature reaches 500 °C. Release of hydrogen from the hydrogenated TC21 alloy appears at the heating temperature in the range of 500 °C to 700 °C. The area of the endothermic peak of the hydrogenated alloy is consistent with its hydrogen content. The residual hydrogen contents in the alloys dehydrogenated at different temperatures all decrease with the increase of holding time. When the hydrogenated TC21 alloy is dehydrogenated at 700 °C, hydrogen has not been removed completely when the holding time reaches 8 h because of its low dehydrogenation rate. Hydrogen can be removed completely when the alloys are dehydrogenated at 750 °C for 4 h or 800 °C for 2 h. The grains in all dehydrogenated TC21 alloys are effectively refined compared with those in the as-received alloy. With the increase of holding time, the grains in the alloys dehydrogenated at different temperatures all grow up. The optimal dehydrogenation temperature of hydrogenated TC21 alloy is 750 °C.

Mechanical tests were carried out at room temperature to reveal the effect of hydrogen content (0.2–1.2 wt.%) on the compressive properties of TC21 alloy. Results show that different hydrogen contents have distinct effects on microstructures and compressive properties of TC21 alloy. With the increase of hydrogen content, the amounts of α phase and acicular α′ martensite phase decrease, while the amounts of β phase and δ hydride increase, δ hydrides distribute along phase/grain boundaries first and then precipitate in β phase. As hydrogen content increases, the yield strength and microhardness decrease first and then increase, and the ultimate compressive strength decreases. The ultimate compression changes little first, and then increases up to a maximum, and finally decreases with the increase of hydrogen content. The optimum hydrogen content is about 0.9 wt.%, with which TC21 alloy exhibits higher plasticity and lower flow stress. Moreover, the fracture mode of TC21 alloys with hydrogen content less than 1.0 wt.% is a ductile fracture, while the fracture mode of the alloy with 1.2 wt.% hydrogen is a transgranular brittle fracture caused by hydride. Reasons for the distinct effect of hydrogen content on the room-temperature compressive properties are discussed. Keywords: TC21 alloy, Hydrogen content, Compressive properties, Microstructure, Fractography

The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy (OM) and X-ray diffraction (XRD). The results show that the hydrogen absorption reaction occurred during the hydrogen absorption process of TC21 titanium alloy can be divided into two different stages according to the hydrogen absorption kinetics. After hydrogenation, the microstructure of TC21 titanium alloy changes obviously. Just a little hydrogen will change the contrast of transformed β phase. The contrast of α phase darkens when the hydrogen content in TC21 titanium alloy exceeds 0.5% (mass fraction). The phase/grain boundaries become ambiguous or even vanished, and β phase becomes the main phase instead of α phase when the hydrogen content reaches 0.625%. Moreover, α phase disappears when the hydrogen content reaches 1.065%. Additionally, the XRD analysis shows that α′ martensite and FCC δ hydride appear in the hydrogenated alloy. According to the microstructures and XRD analysis, the schematic diagrams of hydrogen diffusion process in TC21 titanium alloy were established.

In recent years, malware attacks have become serious security threats and have caused huge losses. Due to the rapid growth of malware variants, how to quickly and accurately classify malware is critical to cyber security. As traditional methods based on machine learning are limited by feature engineering and difficult to process vast amounts of malware quickly, malware classification based on malware images and deep learning has become an effective solution. However, the accuracy rate of existing method based on gray images and deep learning (GDMC) still needs to be improved. Moreover, it is heavily dependent on the amount of training dataset. To improve the accuracy, this paper proposes a byte-level malware classification method based on markov images and deep learning referred to as MDMC. The main step in MDMC is converting malware binaries into markov images according to bytes transfer probability matrixs. Then the deep convolutional neural network is used for markov images classification. The experiments are conducted on two malware datasets, the Microsoft dataset and the Drebin dataset. The average accuracy rates of MDMC are respectively 99.264% and 97.364% on the two datasets. Further experiments on different proportions of training dataset and testing dataset also show that MDMC has better performance than GDMC.

Compression tests were performed at room temperature to investigate the effects of cyclic thermo-hydrogen processing (CTHP) on microstructural and mechanical properties of Ti6Al4V alloy. It was found that the amount of β-phase in the microstructure of the alloy increased significantly under CTHP. Moreover, the ultimate compression of the alloy increased first and then started to decrease with the increasing number of CTHP cycles. The ultimate compression of the CTHP 2-treated Ti6Al4V alloy was improved by 22% as compared to Ti6Al4V alloy without hydrogen and reached 42%. Furthermore, with the increasing number of CTHP cycles, yield strength and yield ratio decreased first and then increased slightly; however, no conspicuous change in compressive strength was noticed.

TC21 alloy was hydrogenated at different temperatures, and its hydrogen absorption characteristic, hydrogen content, hydrogen absorption kinetics, microstructural evolution and mechanism of hydride formation were investigated. Results show that under the same initial hydrogen pressure, hydrogen absorption rate of TC21 alloy is very slow and hydrogen content of the alloy is close to zero when hydrogenation temperature is lower than 500 °C. The initial hydrogen absorption rate achieves the maximum value at 600 °C. Hydrogen content increases first, then increases up to a maximum at 600 °C and decreases last with the increase of temperature. Hydrogen absorption reactions reach equilibrium faster when temperature increases. Hydrogen absorption reaction occurred during hydrogen absorption process of TC21 alloy is a complicated process which contains different stages according to hydrogen absorption kinetics. Hydrogenation temperature has a significant effect on microstructural evolution of TC21 alloy. With the addition of 0.68 wt.%H in the alloy, β transus temperature drops below 750 °C but still higher than 650 °C. HCP α2 phase and FCC δ hydride appear in the specimens hydrogenated at 550 °C and 650 °C according to XRD and TEM analyses. The morphologies of δ hydrides in the alloy hydrogenated at different temperatures are not identical, acicular δ hydrides exist in the alloy hydrogenated at 550 °C, while large amount of lamellar δ hydrides exist in the alloy hydrogenated at 650 °C. Furthermore, the formation mechanism of δ hydride is discussed, results reveal that δ hydrides precipitate directly in β phase at high temperature, and the most appropriate temperature for the precipitation of δ hydrides in β phase is 600 °C.

Unidirectional acoustic transmission has been investigated in an asymmetric bull’s eye structure, which consistes of a subwavelength hole with concentric grooves on one side of a thin steel plate. When acoustic waves impinge normally on the groove side of the asymmetric structure, a strong acoustic transmitted energy flux is observed in the frequency range of 400–450 kHz, while there is no obvious transmitted energy flux in the same frequency range if the acoustic waves impinge normally on the other side. Thus, a remarkable unidirectional acoustic transmission behavior is exhibited by the current structure. With changing the period of the grooves, it is found that the transmitted acoustic energy flux keeps unchanged while the frequency of the transmitted waves can be modified. The experiments are performed, which has confirmed the unidirectional acoustic transmission behavior in the asymmetric bulls eye structure. The asymmetric bull’s eye structure may have potential application in ultrasound diagnosis and therapy.

The solid grain size, degree of spheroidization, contiguity and practical liquid fraction of Mg–Zn–Y–Zr alloys reheated from the as-cast and extruded states are characterized and compared. Thixoforming tests are performed to examine thixoformability of the as-cast and extruded alloys. Tensile mechanical properties for Mg–Zn–Y–Zr alloys thixoformed from the as-cast and extruded alloys are also determined. Reheating from the extruded alloy has been shown to produce ideal, fine semi-solid structures, in which completely spheroidal primary solid grains are essentially free of entrapped liquid. However, the as-cast alloy exhibits non-uniform microstructures with a large amount of entrapped liquid, which are less spheroidal compared with the extruded alloy in the semi-solid state. The grain coarsening rate is relatively low in the extruded alloy than that in the as-cast alloy during reheating. During thixoforming, despite the low liquid fraction, the fine and spheroidal solid grains are weakly connected and slide over each other without any plastic deformation in the extruded alloy. Therefore, the as-cast alloy which has heterogeneous and coarse solid grains is not as thixoformable as the extruded alloy. The tensile mechanical properties for Mg–Zn–Y–Zr alloys thixoformed from the extruded alloy are better than those of Mg–Zn–Y–Zr alloys thixoformed from the as-cast alloy.

Hot workability of conventional magnesium alloys, such as AZ61, AZ80 and ZK60, have been proposed or reported in previous literature. However, no detailed investigation has been conducted regarding the hot workability of as-cast Mg–Zn–Y–Zr alloy. The hot deformation characteristics of as-cast Mg–Zn–Y–Zr alloy were investigated using constitutive equations and processing maps at temperatures between 200 and 400 °C and strain rates ranging from 0.001 to 1 s −1 . Backward extrusion of the component with multi-hole was carried out to evaluate the workability of Mg–Zn–Y–Zr alloy at elevated temperatures. The results show that the flow stress has been found to be strongly dependent on temperature as well as strain rate. By means of regression analysis for the Arrhenius type equation of flow behavior, the apparent average activation energy of deformation was determined as 251.228 KJ/mol, and the stress exponent was 6.231. The processing map technique was utilized to determine the practical processing parameters. The reasonable process parameters of as-cast Mg–Zn–Y–Zr alloy were deformation temperatures of 350–400 °C and stain rates of 0.001–0.1 s −1 . The reproduction of Mg–Zn–Y–Zr alloy components with multi-hole was shown to be good, and no problem was experienced in filling during backward extrusion using reasonable process parameters.

The method of embedded cold-pressing joining could achieve the joining of sheets with different thickness and the joining of dissimilar sheets. Besides, it could meet the lightweight request easily. This article expounded the joining mechanism of this method deeply. To expound the joining mechanism of this method, this article has taken aluminum and stainless steel as examples. In addition, numerical stimulation studies of different hole types’ connecting processes had shown that it was easier to reach plastic yield conditions for aluminum and deform it under the same load conditions. The deformation achieved was significantly greater than that for stainless steel. The width increment of the joining parts increased with the increase of the load pressures; however, the thickness changes of the joining parts behaved in an opposite manner. When the pressing volume of the punch reached 2.4 mm, with the width increment of aluminum sheets of the square hole reaching 2.78 mm, which was the maximum width increment, followed by the hexagonal hole, and the round hole being a minimum. Hole type had a small influence on the width of stainless steel sheets. The experimental results of different hole type joining process indicated that compared with round hole and hexagonal hole, the filling of the square hole was relatively difficult. In case of unreasonable process schemes, defects such as “fake joining,” “offset loading” and “hole deformation” would occur. Thus, this article provided a theoretical basis for the scheme establishment and quality control of the embedded cold-pressing joining process.

The present work deals with the microstructural evolution and mechanical properties of 7A09 aluminium alloy in four different conditions, including as-received, annealed, cold-extruded and heat treated conditions. The results indicate that 7A09 alloy treated by annealing can be backward extruded successfully at room temperature with an extrusion ratio of 4. After annealing, although the degree of recrystallisation increases, unrecrystallised grains still exist. Associated with the decrease in tensile strength is an increase in ductility in the 7A09 alloy during annealing. Backward extrusion at room temperature indicates that the strengths of the alloy are moderately improved at the expense of decrease in ductility. After heat treatment (T6), fine precipitates uniformly distribute in the alloy and are very effective in restricting dislocation movement during deformation. Good ultimate tensile strength (590 MPa) is obtained for the alloy treated by heat treatment (T6), with a yield strength of 522 MPa and an elongation to fracture of 10%. The tensile properties of 7A09 alloy in the heat treated condition are a little better than those of 7A09 alloy in the as-received condition. Moreover, dimensional accuracy and surface roughness of 7A09 alloy treated by backward extrusion at room temperature plus heat treatment are also satisfied with the requirement.

Acoustic Zero-index metamaterials (ZIMs) have attracted much attention recently due to their rich physics and practical applications. The principle of e-near-zero electromagnetics metamaterials equals valid for that of density-near-zero (DNZ) acoustic metamaterials. In this paper, we design a simple 2D membrane-network structure behaving as DNZ metamaterials for airborne sound. The lumped-circuit model of the metamaterial unit cell exhibits a significant resonance. Further parameter retrievals find that the effective mass density approaches zero at the frequency near the resonance. By using both full-wave simulations and lumped-circuit simulations, the unique transmission property of the metamaterial slab at the DNZ frequency is demonstrated in which the phase velocity and the wavelength approach infinity. We further investigate the extraordinary sound transmission induced by the proposed DNZ metamaterials such as efficient cloaking effect, perfect transmission in waveguides with sharp bends and wave splitter. Different from the previous schemes, no extreme parameters are required and the unit cell of membrane-network DNZ metamaterial is in deep subwavelength scale. The microstructure of the membrane network is comparatively simple, and its lump-circuit model provides a convenient way to construct the unit cell for achieving DNZ at the designed frequency. The near-zero effective density has been ascribed to the first order of the air-membrane resonance and hence the disappearance of density because the restoring force from the membrane adds a negative term to the effective mass.

As-cast Mg–Zn–Y–Zr magnesium alloy is subjected to forward extrusion in different conditions. The results show that mechanical properties of Mg–Zn–Y–Zr alloy remarkably deteriorate when extrusion temperature increases from 400 °C to 450 °C because of grain coarsening. Significant improvement in mechanical properties of the alloy can be obtained with increasing extrusion ratio from 0 to 25. However, when the extrusion ratio increases from 25 to 100, the mechanical properties of the alloy almost remain the same. The retardation of recrystallisation in the alloy is dominated by the presence of Mg–Zn–Y particles. Solution treatment at 510 °C (T4) causes complete recrystallisation and decrease of mechanical properties. Aging at 160 °C (T5) causes increase in both strengths and ductility of extruded alloy. In isothermal backward extrusion, the as-cast Mg–Zn–Y–Zr alloy exhibits an excellent workability at temperatures from 250 °C to 400 °C with a extrusion rate of 10 mm/s. Temperatures higher than 400 °C are not suitable for forming of the alloy because of heavy oxidation.

The Mg–5.3 wt.%Zn–1.13 wt.%Nd–0.51 wt.%La–0.28 wt.%Pr–0.79 wt.%Zr alloy prepared by direct chill casting is subjected to hot extrusion. The effects of extrusion ratio and temperature on microstructure and tensile mechanical properties have been studied. The results indicate coarse grains of as-cast alloys are refined with extrusion ratio increasing from 0 to 9. The eutectic constituents are elongated along extrusion direction. However, further increase of extrusion ratio has a little influence on grain refinement and the improvement of mechanical properties of the alloy. Dynamic recrystallisation is the main mechanism of grain refinement during hot extrusion. Raising extrusion temperature results in grain coarsening. Grain shape becomes more equiaxed-like with raising extrusion temperature. At the same time, mechanical properties decrease with the increase of extrusion temperature.

The synthesis of diethyl carbonate (DEC) from ethyl carbamate and ethanol was investigated over a series of double metal oxides. Among the catalysts, ZnO-PbO showed the best catalytic activity and the highest DEC yield was 20.6%. Furthermore, ZnO-PbO had an excellent reusability. According to the results of XRD measurement, IR and element analysis, ZnO and PbO in ZnO-PbO catalyst were separately converted to Zn(NCO)2(NH3)2 and metal Pb during the reaction, indicating that the mixture of Zn(NCO)2(NH3)2 and metal Pb may be the real active composition for DEC synthesis and ZnO-PbO is the precursor. In addition, a possible reaction mechanism for DEC synthesis was proposed.

In the paper, target detection and imaging from refraction photonic crystal (NR-PC) slab lens is studied by the finite-difference time-domain (FDTD) method. Numerical simulation shows that, there is a transmission peak with a value far greater than unit, resulting from the mini-forbidden bands and resonance excitation at the resonance frequency of 0.3068 ( a / λ ). When a target is placed at the focus point (F 2 ) of the NR-PC lens, its image and great amplitude could be formed in the vicinity of the point source through the focusing of backscattered optical wave from the target. Further investigation demonstrates that the lens-combined scanning scheme provides higher refocusing resolution than lens-fixed and non-dynamic scanning scheme for square target detection and imaging.

Thixoforging requires feedstock having a non-dendritic, equiaxed microstructure, which in some cases can be obtained by the recrystallization and partial (RAP) melting route. Based on the RAP route, squeeze casting–solid extrusion followed by partial melting is proposed to obtain the semi-solid feedstock for thixoforging. After squeeze casting–solid extrusion, unrecrystallized grains were elongated along the extrusion direction. As the temperature rises into the semi-solid regime, there is a sudden increase in the appearance of spheroidal grains. The occurrence of recrystallized grains is closely associated with the location of the first liquid to form above the solidus. Grain coarsening in the semi-solid state can be described by classical LSW equation in Ostwald ripening. The coarsening rate does decrease with increasing solid fraction, f s , for f s less than approximately 0.70, and then increases again with further increasing f s . With prolonged holding time, the grains coarsen and mechanical properties of thixoforged components decrease. Moreover, the AZ91D-RE thixoforged from starting materials produced by squeeze casting–solid extrusion followed by reheating at 570 °C for 5 min have extremely fine and uniform microstructure. The tensile mechanical properties of squeeze casting–solid extrusion formed AZ91D-RE are better than those of AZ91D-RE thixoforged from starting materials produced by squeeze casting–solid extrusion followed by partial melting.

The characteristics of two-target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens are studied by using the two-dimensional finite-difference time-domain method. It is demonstrated that due to the influence of the mini-forbidden band and resonance excitation effect, high transmissivity will appear at the normalized resonance frequency of 0.3068 when the lightwave goes through the NR-PC lens. Meanwhile, the use of the NR-PC lens may introduce at least fourfold improvement of the refocusing resolution, if compared to the directly backscattered lightwave without using the NR-PC lens. In addition, by giving a defination for two-target minimum distinguishable distance, we further investigate the performance of two-target detection and imaging system using the proposed focus-scanning scheme. The results show that the smaller the size of the target pair is, the weeker the interference between the two targets will be, which results in a better performance in the minimum distinguishable distance.

We used the method of two-dimensional (2D) finite-difference time-domain (FDTD) to study the characteristics of optical-wave target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens in the paper. The theory of image resolution was introduced. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. And, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. And the application of NR-PC flat lens can be extended in optical area, especially in the detection and imaging of small target.

Two novel Cu(II) complexes were synthesized through the reaction of 2-aminomethyl pyridine (AMP) with CuCl 2 ·2H 2 O by changing the metal/ligand ratio. Their structures were thoroughly characterized by FT-IR, elemental analysis and X-ray diffraction method. The results revealed that complex 1 [Cu(AMP)Cl 2 ] consists of isolated binuclear molecules unit and displays distorted tetragonal pyramid. Complex 2 [Cu(AMP) 2 (H 2 O) 2 ]Cl 2 exhibits a octahedral geometry. The complexes were both evaluated as catalysts in the tetralin oxidation with TBHP as oxidant. Complex 1 showed high catalytic activity and selectivity towards α-tetralone under mild conditions. Thus, under the optimized conditions (acetonitrile 10 ml, catalyst 0.045 mmol, tetralin 4.5 mmol, 65% TBHP 22.5 mmol, T = 50 °C), the conversion of tetralin reached 89% with a selectivity of 71% towards α-tetralone. Compared with complex 1 , complex 2 displayed low catalytic activity mainly due to the strong steric hindrance from the two coordinated 2-aminomethyl pyridine molecules.

The characteristics of optical-wave target detection and imaging from a negative-refraction photonic crystal (NR-PC) flat lens are studied with a two-dimensional (2D) finite-difference time-domain (FDTD) method in the paper. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. Also, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. Therefore, the NR-PC flat lens will find many implications in optical area, especially in the detection and imaging of small targets.

The paper investigated a composite photonic crystal patch antenna by using the method of finite difference time domain (FDTD). The results show that there exists a wave resonance state at 2.635 GHz, where the real part of the permittivity and permeability are all negative; its refraction index is –1. The effect has largely enhanced the electromagnetic wave’s resonance intensity, and has improved the localized extent of electromagnetic energy obviously in such photonic crystal structure (PBG), resulting in a higher antenna gain, a lower return loss, and a better improvement of the antenna’s characteristics. Due to such the advantages, the use of patch antennas can be extended to such fields as mobile communication, satellite communication, aviation, etc.

In this paper, we use the theory of spontaneous emission of two-level atoms embedded in photonic crystals. The unavoidable existence of a localized field with a defect mode and its basic properties are confirmed, which enables one to study the inherent laws of spontaneous emission from doped media. We combine the theory of spontaneous emission with numerical simulation for studying stimulated emission in a doped localized field and conditions for increasing the emission. The inherent laws for the cases where transmissivity is larger than unity and the negative imaginary part of the complex refractive index in doped compound lattices appears are also studied. The analysis of two-dimensional nested rectangle photonic crystal fibers (PCFs) with and without active impurities was performed using the finite-difference time-domain (FDTD) method. We find that, when active impurities are introduced into photonic crystal fibers, the negative imaginary part of the complex refractive index appears and the doped mode with high quality factor and great mode density occurs in the photonic forbidden band, thus amplifying substantially the stimulated emission.

This paper presents state space closed forms and transfer function recursive algorithms for evenly distributed RC interconnect models and their even length-order (ELO) model reduction. The closed-forms have a computation complexity O (1). The characteristics of the ELO model simplification to its original model are revealed. It is shown that extremely high-order RC interconnects can be accurately approximated only by a tenth or higher order ELO model. The order may be reduced further when external ports are included and dominated. The results are useful to VLSI interconnect model reduction and design, and to control systems with a distributed transmission line.

In order to reveal the effect of hydrogen on the room-temperature plasticity of the titanium alloys TC4 and TC21, compression tests have been carried out at room temperature. Results show that an appropriate amount of hydrogen can improve the room-temperature plasticity of both the TC4 and TC21 alloys. The ultimate compression strain of the TC4 alloy containing a hydrogen concentration of 0.5 wt.% increases by 39% compared to the untreated material. For the TC21 alloy the ultimate compression strain is increased by 33% at a hydrogen concentration of 0.6 wt.%. The main reason for the improvement of hydrogen-induced room-temperature plasticity of the TC4 and TC21 alloys is discussed.