图片丢失啦 SPECIAL TOPIC — 80th Anniversary of Northwestern Polytechnical University (NPU)

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1. Heteroclinic cycles in a new class of four-dimensional discontinuous piecewise affine systems
徐文静, 徐伟, 蔡力
中国物理B    2018, 27 (11): 110201-110201.   DOI: 10.1088/1674-1056/27/11/110201
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It is a huge challenge to give an existence theorem for heteroclinic cycles in the high-dimensional discontinuous piecewise systems (DPSs). This paper first provides a new class of four-dimensional (4D) two-zone discontinuous piecewise affine systems (DPASs), and then gives a useful criterion to ensure the existence of heteroclinic cycles in the systems by rigorous mathematical analysis. To illustrate the feasibility and efficiency of the theory, two numerical examples, exhibiting chaotic behaviors in a small neighborhood of heteroclinic cycles, are discussed.

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2. Some new advance on the research of stochastic non-smooth systems
徐伟, 王亮, 冯进钤, 乔艳, 韩平
中国物理B    2018, 27 (11): 110503-110503.   DOI: 10.1088/1674-1056/27/11/110503
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Due to the extensive applicability in real life, the non-smooth system with random factors attracted much attention in past two decades. A lot of methods and techniques have been proposed to research these systems by scholars. In this paper, we will summarize some new research advance on the stochastic non-smooth systems. The existing results about the stochastic vibro-impact system, the stochastic friction system, and the stochastic hysteretic system are introduced respectively. Some conclusions and outlook are given at the end.

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3. Three-dimensional modulations on the states of polarization of light fields
李鹏, 吴东京, 刘圣, 章毅, 郭旭岳, 齐淑霞, 李渝, 赵建林
中国物理B    2018, 27 (11): 114201-114201.   DOI: 10.1088/1674-1056/27/11/114201
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Light fields with spatially structured states of polarization (SoPs) are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile, the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional (3D) modulations on the SoPs of light fields. The recent progress and novel implementations based on 3D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3D structured SoP and intensity distributions, namely, 3D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science, quantum optics, and so on.

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4. Cascaded tilted fiber Bragg grating for enhanced refractive index sensing
姜碧强, 毕芷瑄, 王守恒, 席特立, Kaiming Zhou, Lin Zhang, 赵建林
中国物理B    2018, 27 (11): 114220-114220.   DOI: 10.1088/1674-1056/27/11/114220
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We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating (TFBG) for enhanced refractive index sensing. The TFBG is UV-inscribed in series in ordinary single-mode fiber (SMF) and reduced-diameter SMF with the same tilt angle, and then excites two sets of superposed spectral combs of cladding modes. The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF, enabling an enlarged range and a higher accuracy of refractive index measurement. The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.

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5. Effect of the fluctuant acoustic channel on the gain of a linear array in the ocean waveguide
谢磊, 孙超, 蒋光禹, 刘雄厚, 孔德智
中国物理B    2018, 27 (11): 114301-114301.   DOI: 10.1088/1674-1056/27/11/114301
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The inhomogenous ocean waveguide, which leads the amplitude and phase of the signal arriving at a hydrophone array to fluctuate, is one of the causes that make the array gain deviate from its ideal value. The relationship between the array gain and the fluctuant acoustic channel is studied theoretically. The analytical expression of the array gain is derived via an acoustic channel transfer function on the assumption that the ambient noise field is isotropic. The expression is expanded via the Euler formula to give an insight into the effect of the fluctuant acoustic channel on the array gain. The result demonstrates that the amplitude fluctuation of the acoustic channel transfer functions has a slight effect on the array gain; however, the uniformity of the phase difference between the weighting coefficient and the channel transfer function on all the hydrophones in the array is a major factor that leads the array gain to further deviate from its ideal value. The numerical verification is conducted in the downslope waveguide, in which the gain of a horizontal uniform linear array (HLA) with a wide-aperture operating in the continental slope area is considered. Numerical result is consistent with the theoretical analysis.

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6. Discrete state space method and modal extension method based impact sound synthesis model
田旭华, 陈克安, 张燕妮, 李晗, 胥健
中国物理B    2018, 27 (11): 114302-114302.   DOI: 10.1088/1674-1056/27/11/114302
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The efficient and accurate synthesis of physical parameter-controllable impact sounds is essential for sound source identification. In this study, an impact sound synthesis model of a cylinder is proposed based on discrete state space (DSS) method and modal extension method (MEM). This model is comprised of the whole three processes of the physical interaction, i.e., the Hertz contact process, the transient structural response process, and the sound radiation process. Firstly, the modal expanded DSS equations of the contact system are constructed and the transient structural response of the cylinder is obtained. Then the impact sound of the cylinder is acquired using improved discrete Raleigh integral. Finally, the proposed model is verified by comparing with existing models. The results show that the proposed impact sound synthesis model is more accurate and efficient than the existing methods and easy to be extended to the impact sound synthesis of other structures.

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7. Three-dimensional human thermoregulation model based on pulsatile blood flow and heating mechanism
党思娜, 薛红军, 张晓燕, 瞿珏, 钟诚文, 陈思宇
中国物理B    2018, 27 (11): 114402-114402.   DOI: 10.1088/1674-1056/27/11/114402
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A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors' thermal models. The following improvements are necessary in real situations:ellipsoids and elliptical cylinders are used to adequately approximate body geometry, divided into 18 segments and five layers; the core layer consists of the organs; the pulsation of the heart cycle, the pulsatile laminar flow, the peripheral resistance, and the thermal effect of food are considered. The model is calculated by adopting computational fluid dynamics (CFD) technology, and the results of the model match with the experimental data. This paper can give a reasonable explanation for the temperature fluctuations.

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8. Effect of the asymmetric geometry on the wake structures of a pitching foil
朝黎明, 潘光, 张栋
中国物理B    2018, 27 (11): 114701-114701.   DOI: 10.1088/1674-1056/27/11/114701
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The two-dimensional wake produced by a time-periodic pitching foil with the asymmetric geometry is investigated in the present work. Through numerically solving nonlinear Navier-Stokes equations, we discuss the relationship among the kinematics of the prescribed motion, the asymmetric parameter K ranged as -1 ≤ K ≤ 1, and the types of the wakes including the mP+nS wake, the Bénard-von Kármán wake, the reverse Bénard-von Kármán wake, and the deviated wake. Compared with previous studies, we reveal that the asymmetric geometry of a pitching foil directly affects the foil's wake structures. The numerical results show that the reverse Bénard-von Kármán wake is easily deviated at K<0, while the symmetry-breaking of the reverse Bénard-von Kármán wake is delayed at K>0. Through the vortex dynamic method, we understand that the initial velocity of the vortex affected by the foil's asymmetry plays a key role in the deviation of the reverse Bénard-von Kármán wake. Moreover, we provide a theoretical model to predict the wake deviation of the asymmetric foil.

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9. Effect of elasticity mismatch on cell deformation and migration: A phase-field study
尹元枫, 邢辉, 臧渡洋, 金克新
中国物理B    2018, 27 (11): 116201-116201.   DOI: 10.1088/1674-1056/27/11/116201
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The phase-field model for cell migration is used to study the effect of elasticity mismatch on the migration dynamics of multiple cells in a confluent monolayer, where one tagged cell is embedded by a number of normal cells and both types of cells are supposed to have the same properties except elasticity. Our results show that a larger elasticity mismatch leads to a larger difference in shape change between the tagged cell and the normal cells. We find that the bursts of velocity always fall behind the peak of the perimeter, and the shape change of the tagged cell results in the accelerated motion of the tagged cell in the whole process. Moreover, the variation of the averaging cell perimeter ratio Ltag/Lnormal with the increase of the elasticity ratio γtag/γnormal for different active velocities|va|is analyzed. We find that Ltag/Lnormal decreases with the increase of γtag/γnormal, following a simple power law function. Our results highlight the important role played by the cell elasticity mismatch in cell deformation and migration.

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10. Ab initio molecular dynamics simulations of nano-crystallization of Fe-based amorphous alloys with early transition metals
汪姚岑, 张岩, Yoshiyuki Kawazoe, 沈军, 曹崇德
中国物理B    2018, 27 (11): 116401-116401.   DOI: 10.1088/1674-1056/27/11/116401
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The addition of early transition metals (ETMs) into Fe-based amorphous alloys is practically found to be effective in reducing the α-Fe grain size in crystallization process. In this paper, by using ab initio molecular dynamics simulations, the mechanism of the effect of two typical ETMs (Nb and W) on nano-crystallization is studied. It is found that the diffusion ability in amorphous alloy is mainly determined by the bonding energy of the atom rather than the size or weight of the atom. The alloying of B dramatically reduces the diffusion ability of the ETM atoms, which prevents the supply of Fe near the grain surface and consequently suppresses the growth of α-Fe grains. Moreover, the difference in grain refining effectiveness between Nb and W could be attributed to the larger bonding energy between Nb and B than that between W and B.

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11. Metastable phase separation and rapid solidification of undercooled Co40Fe40Cu20 alloy
白晓军, 汪姚岑, 曹崇德
中国物理B    2018, 27 (11): 116402-116402.   DOI: 10.1088/1674-1056/27/11/116402
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The metastable liquid phase separation and rapid solidification behaviors of Co40Fe40Cu20 alloy were investigated by using differential thermal analysis (DTA) in combination with glass fluxing and electromagnetic levitation (EML) techniques. The critical liquid phase separation undercooling for this alloy was determined by DTA to be 174 K. Macrosegregation morphologies are formed in the bulk samples processed by both DTA and EML. It is revealed that undercooling level, cooling rate, convection, and surface tension difference between the two separated phases play a dominant role in the coalescence and segregation of the separated phases. The growth velocity of the (Fe,Co) dendrite has been measured as a function of undercooling up to 275 K. The temperature rise resulting from recalescence increases linearly with the increase of undercooling because of the enhancement of recalescence. The slope change of the recalescence temperature rise versus undercooling at the critical undercooling also implies the occurrence of liquid demixing.

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12. Spin Seebeck effect and spin Hall magnetoresistance in the Pt/Y3Fe5O12 heterostructure under laser-heating
王拴虎, 李刚, 王建元, 田颖异, 张洪瑞, 邹吕宽, 孙继荣, 金克新
中国物理B    2018, 27 (11): 117201-117201.   DOI: 10.1088/1674-1056/27/11/117201
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In the previous study of longitudinal spin Seebeck effect (LSSE), the thermal gradient was often generated by inserting the sample between the cool bath and the hot bath. For practical use, this method is too cumbersome to be easily integrated into modern electrical circuits. Since the laser can be easily focused into a small region, it will be more convenient and friendly to the integrated circuit. In this paper, we systematically investigate the LSSE and spin Hall magnetoresistance (SMR) of the Pt/Y3Fe5O12 heterostructure under focused laser-heating. We find that the extremely large voltage of inverse spin Hall effect (VISHE) can be obtained by reducing the diameter of laser or increasing the number of light spots. Meanwhile, even under the illumination of the ultraviolet light which will excite the electron from the valence band to the conduction band in yttrium iron garnet (YIG), the magnitude of SMR is nearly constant. It indicates that the spin transport behavior of the adjacent Pt is independent of the electron configuration of YIG. The laser-heating method to generate LSSE will be very promising for modern integrated electronic circuits and will promote the application of spin caloritronics in practice.

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13. Twin boundary dominated electric field distribution in CdZnTe detectors
董江鹏, 介万奇, 余竞一, 郭榕榕, Christian Teichert, Kevin-P Gradwohl, 张滨滨, 罗翔祥, 席守智, 徐亚东
中国物理B    2018, 27 (11): 117202-117202.   DOI: 10.1088/1674-1056/27/11/117202
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The performance of CdZnTe X/γ-ray detectors is strongly affected by the electric field distribution in terms of charge transport and charge collection. Factors which determine the electric field distribution are not only electric contact, but also intrinsic defects, especially grown-in twin boundaries. Here, the electric field distribution around twin boundaries is investigated in a CdZnTe bicrystal detector with a {111}-{111} twin plane using the Pockels electro-optic effect. The results of laser beam induced current pulses are also obtained by the transient current technique, and we discuss the influence of the twin boundary on the electric field evolution. These studies reveal a significant distortion of the electric field, which is attributed to the buildup of space charges at twin boundaries. Also, the position of these space charge regions depends on the polarity of the detector bias. An energy band model based on the formation of an n-n+-n junction across the twin boundary has been established to explain the observed results.

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14. Subwavelength asymmetric Au-VO2 nanodisk dimer for switchable directional scattering
张汉谋, 尚武云, 陆华, 肖发俊, 赵建林
中国物理B    2018, 27 (11): 117301-117301.   DOI: 10.1088/1674-1056/27/11/117301
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We propose an asymmetric Au-VO2 nanodisk dimer for realizing a switchable directional scattering. Specifically, the directional scattering can be triggered on/off through controlling the phase transition of the VO2 nanodisk from metallic to semiconductor state. More strikingly, an obvious directional scattering with the directivity of~40 dB is achieved under the metallic state of VO2 nanodisk. This tunable directional scattering is further explained with an interference model where the Au and VO2 nanodisks are treated as two weakly interacting electric dipoles. The phase transition controlled scattering patterns of asymmetric Au-VO2 nanodisk dimer are then well interpreted from the phase difference between these two dipoles.

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15. Coupling-induced spectral splitting for plasmonic sensing with ultra-high figure of merit
陆华, 范奕村, 戴思清, 毛东, 肖发俊, 李鹏, 赵建林
中国物理B    2018, 27 (11): 117302-117302.   DOI: 10.1088/1674-1056/27/11/117302
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We investigate a kind of spectral splitting effect in a plasmonic multilayer system, which consists of stacked Al2O3 and SiO2 layers, a thin metal film, and a dielectric prism substrate. The results illustrate that an obvious peak appears in the center of the surface plasmon resonance (SPR)-induced reflection spectral dip in the structure with the SiO2/Al2O3/SiO2 layers. This spectral splitting response can be regarded as an electromagnetically induced transparency (EIT) like effect, which is attributed to the coupling and interference between the SPR on the metal film and guided-mode resonance (GMR) in the Al2O3 layer. The theoretical calculations agree well with the numerical simulations. It is also found that the reflection spectrum will be further split by the introduction of another Al2O3 layer into the multilayer structure. The reintroduced GMR in the Al2O3 layer changes the coupling and interference process between the SPR and GMR field, giving rise to the generation of ultra-narrow reflection dip. Especially, the spectral splitting can facilitate the realization of plasmonic sensors with ultra-high figure of merit (583), which is about 5 times larger than that of traditional SPR sensors. These results will provide a new avenue to the light field manipulation and optical functionalities, especially biochemical and environmental sensing.

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16. Review of photoinduced effect in manganite films and their heterostructures
李欣谕, 赵龙, 魏向洋, 李豪, 金克新
中国物理B    2018, 27 (11): 117501-117501.   DOI: 10.1088/1674-1056/27/11/117501
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Light-matter interaction plays an important role in the non-equilibrium physics, especially in strongly correlated electron systems with complex phases. Photoinduced effect can cause the variation in the physical properties and produce some emergent phases. As a classical archetype, manganites have received much attention due to their colossal magnetoresistance (CMR) effect and the strong interaction of charge, spin, orbital, and lattice degrees of freedom. In this paper, we give an overview of photoinduced effect in manganites and their heterostructures. In particular, some materials, including ZnO, Si, BiFeO3 (BFO), titanate-based oxides, and 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) have been integrated with manganites. Heterostructures composed of these materials display some exciting and intriguing properties. We do hope that this review offers a guiding idea and more meaningful physical phenomena will be discovered in active areas of solid state physics and materials science.

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17. Review of photoresponsive properties at SrTiO3-based heterointerfaces
闫虹, 张兆亭, 王拴虎, 金克新
中国物理B    2018, 27 (11): 117804-117804.   DOI: 10.1088/1674-1056/27/11/117804
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The two-dimensional electron gas at SrTiO3-based heterointerfaces has received a great deal of attention in recent years owing to their potential for the exploration of emergent physics and the next generation of electronics. One of the most fascinating aspects in this system is that the light, as a powerful external perturbation, can modify its transport properties. Recent studies have reported that SrTiO3-based heterointerfaces exhibit the persistent photoconductivity and can be tuned by the surface and interface engineering. These researches not only reveal the intrinsic physical mechanisms in the photoresponsive process, but also highlight the ability to be used as a tool for novel all-oxide optical devices. This review mainly contraposes the studies of photoresponse at SrTiO3-based heterointerfaces.

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18. Metamaterials and metasurfaces for designing metadevices: Perfect absorbers and microstrip patch antennas
刘亚红, 赵晓鹏
中国物理B    2018, 27 (11): 117805-117805.   DOI: 10.1088/1674-1056/27/11/117805
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In the past twenty years, electromagnetic metamaterials represented by left-handed metamaterials (LHMs) have attracted considerable attention due to the unique properties such as negative refraction, perfect lens, and electromagnetic cloaks. In this paper, we present a comprehensive review of our group's work on metamaterials and metasurfaces. We present several types of LHMs and chiral metamaterials. As a two-dimensional equivalent of bulk three-dimensional metamaterials, metasurfaces have led to a myriad of devices due to the advantages of lower profile, lower losses, and simpler to fabricate than bulk three-dimensional metamaterials. We demonstrate the novel microwave metadevices based on metamaterials and metasurfaces:perfect absorbers and microwave patch antennas, including novel transmission line antennas, high gain resonant cavity antennas, wide scanning phased array antennas, and circularly polarized antennas.

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19. Effects of filler loading and surface modification on electrical and thermal properties of epoxy/montmorillonite composite
贾梓睿, 高振国, 兰笛, 成永红, 吴广磊, 吴宏景
中国物理B    2018, 27 (11): 117806-117806.   DOI: 10.1088/1674-1056/27/11/117806
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Epoxy-based composites containing montmorillonite (MMT) modified by silylation reaction with γ-aminopropyltriethoxysilane (γ-APTES) and 3-(glycidyloxypropyl) trimethoxysilane (GPTMS) are successfully prepared. The effects of filler loading and surface modification on the electrical and thermal properties of the epoxy/MMT composites are investigated. Compared with the pure epoxy resin, the epoxy/MMT composite, whether MMT is surface-treated or not, shows low dielectric permittivity, low dielectric loss, and enhanced dielectric strength. The MMT in the epoxy/MMT composite also influences the thermal properties of the composite by improving the thermal conductivity and stability. Surface functionalization of MMT not only conduces to the better dispersion of the nanoparticles, but also significantly affects the electric and thermal properties of the hybrid by influencing the interfaces between MMT and epoxy resin. Improved interfaces are good for enhancing the electric and thermal properties of nanocomposites. What is more, the MMT modified with GPTMS rather than γ-APTES is found to have greater influence on improving the interface between the MMT filler and polymer matrices, thus resulting in lower dielectric loss, lower electric conductivity, higher breakdown strength, lower thermal conductivity, and higher thermal stability.

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20. An infrared and visible image fusion method based uponmulti-scale and top-hat transforms
何贵青, 张琪琦, 纪佳琪, 董丹丹, 张海曦, 王珺
中国物理B    2018, 27 (11): 118706-118706.   DOI: 10.1088/1674-1056/27/11/118706
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The high-frequency components in the traditional multi-scale transform method are approximately sparse, which can represent different information of the details. But in the low-frequency component, the coefficients around the zero value are very few, so we cannot sparsely represent low-frequency image information. The low-frequency component contains the main energy of the image and depicts the profile of the image. Direct fusion of the low-frequency component will not be conducive to obtain highly accurate fusion result. Therefore, this paper presents an infrared and visible image fusion method combining the multi-scale and top-hat transforms. On one hand, the new top-hat-transform can effectively extract the salient features of the low-frequency component. On the other hand, the multi-scale transform can extract high-frequency detailed information in multiple scales and from diverse directions. The combination of the two methods is conducive to the acquisition of more characteristics and more accurate fusion results. Among them, for the low-frequency component, a new type of top-hat transform is used to extract low-frequency features, and then different fusion rules are applied to fuse the low-frequency features and low-frequency background; for high-frequency components, the product of characteristics method is used to integrate the detailed information in high-frequency. Experimental results show that the proposed algorithm can obtain more detailed information and clearer infrared target fusion results than the traditional multi-scale transform methods. Compared with the state-of-the-art fusion methods based on sparse representation, the proposed algorithm is simple and efficacious, and the time consumption is significantly reduced.

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