Direct field-to-pattern monolithic design of holographic metasurface via residual encoderdecoder convolutional neural network

Complex-amplitude holographic metasurfaces(CAHMs)with the flexibility in modulating phase and amplitude profiles have been used to manipulate the propagation of wavefront with an unprecedented level,leading to higher image-reconstruction quality compared with their natural counterparts.However,prevailing design methods of CAHMs are based on Huygens-Fresnel theory,meta-atom optimization,numerical simulation and experimental verification,which results in a consumption of computing resources.Here,we applied residual encoder-decoder convolutional neural network to directly map the electric field distributions and input images for monolithic metasurface design.A pretrained network is firstly trained by the electric field distributions calculated by diffraction theory,which is subsequently migrated as transfer learning framework to map the simulated electric field distributions and input images.The training results show that the normalized mean pixel error is about 3%on dataset.As verification,the metasurface prototypes are fabricated,simulated and measured.The reconstructed electric field of reverse-engineered metasurface exhibits high similarity to the target electric field,which demonstrates the effectiveness of our design.Encouragingly,this work provides a monolithic field-to-pattern design method for CAHMs,which paves a new route for the direct reconstruction of metasurfaces.

A Confocal Endoscope for Cellular Imaging

Since its inception, endoscopy has aimed to establish an immediate diagnosis that is virtually consistent with a histologic diagnosis. In the past decade, confocal laser scanning microscopy has been brought into endoscopy, thus enabling in vivo microscopic tissue visualization with a magnification and resolution comparable to that obtained with the ex vivo microscopy of histological specimens. The major challenge in the development of instrumentation lies in the miniaturization of a fiber-optic probe for microscopic imaging with micron-scale resolution. Here, we present the design and construction of a confocal endoscope based on a fiber bundle with 1.4-μm lateral resolution and 8-frames per second(fps) imaging speed. The fiber-optic probe has a diameter of 2.6 mm that is compatible with the biopsy channel of a conventional endoscope. The prototype of a confocal endoscope has been used to observe epithelial cells of the gastrointestinal tracts of mice and will be further demonstrated in clinical trials. In addition, the confocal endoscope can be used for translational studies of epithelial function in order to monitor how molecules work and how cells interact in their natural environment.

Eco-friendly PVA/Kaolin Clay Coating for Barrier Paper

The resistance of wood-fiber paper to water, grease, and water vapor is usually attained by immersing the base paper in hydrophobic oil, laminating with a plastic or metal film, or the application of a barrier coating. Oil impregnation and the addition of films may make the paper difficult to recycle or persistent in the environment owing to their strong binding force and nondegradability. Environmental concerns have attracted worldwide attention to eco-friendly barrier coatings. In this study, degradable polyvinyl alcohol(PVA) and kaolin clay pigment were used to prepare coatings that were applied to a base paper. By measuring the barrier properties of the coated paper, including the water absorptiveness(Cobb60 value), Hercules sizing degree, oil resistance(Kit rating), and water vapor transmission rate(WVTR), an optimal coating formulation and process were proposed. To examine the barrier mechanism of the PVA/kaolin clay coating, we characterized the coating microstructures using a scanning electron microscopy(SEM) and a mercury porosimeter. The results showed that the Cobb60 value and water vapor transmission rate of the coated paper decreased by 61.4% and 98.6%, respectively, compared with the base paper, for a pre-coating weight of 0.98 g/m^2 and a top-coating weight of about 3.23 g/m^2. Furthermore, the Hercules sizing degree rose by a factor of 337.2, while the oil resistance(Kit rating) increased from 0 to 12. The optimum drying temperature for a wet coating layer was found to be 170℃, and the optimum weight ratio of PVA to kaolin clay in the coating was determined to be 50∶50. It was assumed that the PVA/kaolin clay coating improved the smoothness of the paper considerably and decreased the pore size by filling the pores on the paper surface and forming an even film, thus enhancing the paper barrier performance. The coated paper also exhibited good repulpability.

Preparation of Ultrafine Starch Particle and its Application in Paper Coating

Despite its biodegradability, adequate cohesive strength and comparatively low cost, the use of cooked starch as a paper coating binder is limited due to its high viscosity and serious negative impact on the gloss. Starch-based bio-latex with size in the nanometer or sub-micrometer range has been developed recently to overcome these shortcomings. In this study, ultrafine starch particle(UFSP) was prepared by mechanical milling using a DYNO mill in combination with light chemical pretreatment. Model coating colors containing different dosages of UFSP were applied to base paper and the properties of the coated papers were evaluated. The results showed that the UFSP was disc-shaped with a median particle diameter of 167 nm. Water retention capacity of the coating colors was improved considerably with the addition of UFSP, i.e., the water retention value decreased by nearly 40% when styrene-butadiene latex was replaced by UFSP at a dosage of 3 pph(per hundred parts of pigment). The high shear rate viscosities of the coating colors containing no more than 2 pph of USFP were similar to that of the control coating color at shear strain rate higher than 2000 s^(-1). The properties and performances of the coated papers were comparable to the control coated paper with single synthesized latex binder. The gloss and the print gloss of paper samples with or without USFP were 59.7% and 58.2%, 79.0% and 78.8%, respectively. Surface strength of paper samples with or without USFP were 0.96 and 0.90 m/s, respectively, while the ink absorptivity values were 34% and 33%. This study demonstrates a promising approach to obtain submicrometer sized starch for paper coating.

Effects of active molecules of Korean pine seed on rodent health and implications for forest regeneration

After maturation, Korean pine (Pinus koraiensis Siebold & Zucc.) seeds often cannot disperse to reach a suitable germination site. It is therefore difficult to naturally regenerate by itself and relies on animal dispersal. Squirrels hoard pine seeds as winter food and Korean pine seeds stored for overwintering might become the source of regeneration of the species. From field observations, the pine seeds are the food preference for squirrels during autumn in the Lesser Khingan Mountains in Northeast China. Such preference by squirrels has been attributed to high seed energy content and the ease of seed storage. However, it may also be expected from nutritional aspects that a coevolutionary relationship between squirrels and Korean pine species could be partially explained by the effect of active seed components and their physiological regulatory effects on squirrels. To test this hypothesis, control experiments were carried out to examine the modulatory effects of Korean pine nut oil (PNO) on intestinal microbiota, inflammatory profile and oxidative stress in mice. The results showed that, compared with mice fed a high-fat diet, PNO significantly improved the physical and the healthy state of mice. Histological analysis of the liver and epididymal fat tissue showed that PNO alleviated liver and adipocyte lesions, and inflammation caused by high-fat diets. PNO also significantly decreased atherosclerotic index and ameliorate serum lipid accumulation to prevent cardiovascular disease, which effect the positive control SG group. Moreover, PNO elevated superoxide dismutase and glutathione peroxidase enzyme activities and reduced malondialdehyde levels in the serum. 16S rRNA sequencing showed that PNO restored intestinal microbiota composition, significantly increasing the relative abundance of Lactobacillus and Akkermansia bacteria. These results suggest that Korean pine seeds not only provide adequate fat, protein and energy for squirrels, but also promote physical health and improve body immunity.

Correction to:Effects of active molecules of Korean pine seed on rodent health and implications for forest regeneration

Correction to:J.For.Res.https://doi.org/10.1007/s11676-021-01380-2 In the Original publication,the author has found that Table 8 has been inadvertently published with errors due to incorrect calculation.The corrected Table 8 is provided below:Eff ect of PNO supplements on serum lipid levels and the atherosclerosis index TC,TG and LDL-C levels increased,while the HDL-C levels decreased notably in the HFD group compared to the ND group(P<0.01;Table 8).After supplementation with PNO,serum lipid(TG,TC)levels of mice in the M-PNO and H-PNO groups decreased;the diff erences were statistically signifi cant compared with those in the HFD group(P<0.05).Furthermore,PNO supplements signifi-cantly improved HDL-C levels and decreased LDL-C levels(P<0.01).

Hydrogen-rich Saline Reduces Atherogenesis in Apolipoprotein E Knockout Mice Fed a High-fat Diet by Inhibiting the Non-HDL-mediated Arterial Inflammation and Promoting the Expression of Genes Involving Reverse Cholesterol Transport

Aim Hydrogen(dihydrogen,H2) is an effective antioxidant to reduce oxidative stress and oxidative stress is implicated in atherogene-sis.In this study we examined whether hydrogen-saturated saline can prevent atherosclerosis in apolipoprotein E knockout(apoE-/-) mice fed either chowdiet or high-fat diet,and characterized the underlying molecular mechanisms.Methods and Results The atherosclerotic lesion formation displayed by oil red O staining positive area was reduced significantly in either aortic root section or aortic arch en face in hydrogen administrated apoE-/-mice fed either chowdiet or high-fat diet,compared to the control.Plasma analysis by enzymatic method showed that total cholesterol(TC) and non-high-density lipoprotein cholesterol(non-HDL-C)were remarkably decreased by treatment with hydrogen.Western blot analysis revealed a significant decrease of both plasma apoli-poprotein B(apoB) level and hepatic expression of apoB after hydrogen treatment,suggesting hydrogen could downregulate the expression of the major protein constituent of non-HDL.In addition,spectrophotometric measurement showed that plasma levels of malondi-aldehyde(MDA) and serum amyloid Awas decreased and paraoxonase-1 activity was increased in mice treated with hydrogen,suggesting plasma lipid oxidation and peroxidation was impaired by hydrogen treatment.Besides,the MDA content of the non-HDL,whichseparated by ultracentrifugation from the plasma of mice treated with and without hydrogen,was reduced by hydrogen,suggesting the oxidation of non-HDL was impaired by hydrogen.Moreover,we found hydrogen treatment significantly suppressed the production of tumor necrosis factor-α(TNF-α) and interleukin-6 in RAW264.7 macrophages after stimulation with the isolated non-HDL,suggesting hydrogen reduces atherogenesis by inhibiting non-high-density lipoprotein(HDL)-mediated inflammation.Furthermore,immunohis-tochemistry of aortic valve sections revealed that hydrogen attenuated lesion formation by suppressing the expression of several proin-flammatory factors and decreasing vessel wall infiltration of macrophages,indicating hydrogen-treatment reduces arterial inflammation.Besides,real-time PCR and western blot analysis disclosed that the expression of several transporter genes involved in the process ofreverse cholesterol transport,including hepatic scavenger receptor class B type I(SR-BI),ATP-binding cassette(ABC) transporters ABCG8,ABCB4,ABCB11,and macrophage SR-BI,were all induced by hydrogen treatment.Conclusion These results re-vealed that administration of hydrogen-rich saline reduces atherogenesis in apoE-/-mice fed a high-fat diet by inhibiting the non-HDL-mediated arterial inflammation and promoting the expression of genes involving reverse cholesterol transport.

Miura origami based reconfigurable polarization converter for multifunctional control of electromagnetic waves

Polarization is one of the basic characteristics of electromagnetic(EM)waves,and its flexible control is very important in many practical applications.At present,most of the multifunction polarization metasurfaces are electrically tunable based on PIN and varactor diodes,which are easy to operate and have strong real-time performance.However,there are still some problems in them,such as few degrees of freedom of planar structure control,complex circuit,bulky sample,and high cost.In view of these shortcomings,this paper proposes a Miura origami based reconfigurable polarization conversion metasurface for multifunctional control of EM waves.The interaction between the electric dipoles is changed by adjusting the folding angleθ,thereby tuning the operating frequency of the polarization conversion and the polarization state of the reflected wave.This mechanical control method brings more degrees of freedom to manipulate EM waves.And the processed sample is with lightweight and low cost.To verify the performance of the proposed origami polarization converter,a Miura origami structure loaded with metal split rings is designed and fabricated.The operating frequency of the structure can be tuned in different folding states.In addition,by controlling the folding angleθ,linear-to-linear and linear-to-circular polarization converters can be realized at different folding states.The proposed Miura origami polarization conversion metasurface provides a new idea for reconfigurable linear polarization conversion and multifunctional devices.

Completely spin-decoupled geometric phase of a metasurface

Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.

Polarization singularities in planar electromagnetic resonators with rotation and mirror symmetries

In this work,we apply the group representation theory to systematically study polarization singularities in the inplane components of the electric fields supported by a planar electromagnetic(EM)resonator with generic rotation and reflection symmetries.We reveal the intrinsic connections between the symmetries and the topological features,i.e.,the spatial configuration of the in-plane fields and the associated polarization singularities.The connections are substantiated by a simple relation that links the topological charges of the singularities and the symmetries of the resonator.To verify,a microwave planar resonator with the D8group symmetries is designed and numerically simulated,which demonstrates the theoretical findings well.Our discussions can be applied to generic EM resonators working in a wide EM spectrum,such as circular antenna arrays,microring resonators,and photonic quasi-crystals,and provide a unique symmetry perspective on many effects in singular optics and topological photonics.

Switchable chiral mirror based on PIN diodes

Chiral mirrors can produce spin selective absorption for left-handed circularly polarized(LCP) or right-handed circularly polarized(RCP) waves. However, the previously proposed chiral mirror only absorbs the designated circularly polarized(CP) wave in the microwave frequency band, lacking versatility in practical applications.Here, we propose a switchable chiral mirror based on a pair of PIN diodes. The switchable chiral mirror has four working states, switching from the handedness-preserving mirror to the LCP mirror, RCP mirror, and perfect absorber. The basis of these advances is to change the chirality of two-dimensional(2D) chiral metamaterials and the circular conversion dichroism related to it, which is the first report in the microwave frequency band.Surface current distributions shed light on how switchable chiral mirrors work by handedness-selective excitation of reflective and absorbing electric dipole modes. Energy loss distributions verify the working mechanism. The thickness of the switchable chiral mirror is one-tenth of the working wavelength, which is suitable for integrated manufacturing. The measurement results are in good agreement with the simulation results.

Leaky cavity modes in metasurfaces:a route to low-loss wideband anomalous dispersion

Metasurfaces have provided unprecedented degrees of freedom in manipulating electromagnetic waves upon interfaces.In this work,we first explore the condition of wide operating bandwidth in the view of reflective scheme,which indicates the necessity of anomalous dispersion.To this end,the leaky cavity modes(LCMs)in the metaatom are analyzed and can make effective permittivity inversely proportional to frequency.Here we employ the longitudinal Fabry-Perot(F-P)resonances and transverse plasmonic resonances to improve the LCMs efficiency.It is shown that the order of F-P resonance can be customized by the plasmonic modes,that is,the F-P cavity propagation phase should match the phase delay of surface currents excited on the meta-atom.The nth order F-P resonance will multiply the permittivity by a factor of n,allowing larger phase accumulation with increasing frequencies and forming nonlinear phase distribution which can be applied in weak chromatic-aberration focusing design.As a proof-of-concept,we demonstrate a planar weak chromatic-aberration focusing reflector with a thickness ofλ_(0)∕9 at 16.0-21.0 GHz.This work paves a robust way to advanced functional materials with anomalous dispersion and can be extended to higher frequencies such as terahertz,infrared,and optical frequencies.

Six-channel programmable coding metasurface simultaneously for orthogonal circular and linear polarizations

Metasurfaces have intrigued long-standing research interests and developed multitudinous compelling applications owing to their unprecedented capability for manipulating electromagnetic waves,and the emerging programmable coding metasurfaces(PCMs)provide a real-time reconfigurable platform to dynamically implement customized functions.Nevertheless,most existing PCMs can only act on the single polarization state or perform in the limited polarization channel,which immensely restricts their practical application in multitask intelligent metadevices.Herein,an appealing strategy of the PCM is proposed to realize tunable functions in co-polarized reflection channels of orthogonal circularly polarized waves and in co-polarized and cross-polarized reflection channels of orthogonal linearly polarized waves from 9.0 to 10.5 GHz.In the above six channels,the spindecoupled programmable meta-atom can achieve high-efficiency reflection and 1-bit digital phase modulation by selecting the specific ON/OFF states of two diodes,and the phase coding sequence of the PCM is dynamically regulated by the field-programmable gate array to generate the desired function.A proof-of-concept prototype is constructed to verify the feasibility of our methodology,and numerous simulation and experimental results are in excellent agreement with the theoretical predictions.This inspiring design opens a new avenue for constructing intelligent metasurfaces with higher serviceability and flexibility,and has tremendous application potential in communication,sensing,and other multifunctional smart metadevices.

Virtual metasurfaces:reshaping electromagnetic waves in distance

Metasurface has provided unprecedented freedoms in manipulating electromagnetic(EM) waves, exhibiting fascinating functions. Conventionally, these functions are implemented right on metasurfaces, where spatial modulations on EM wave amplitudes or phases are achieved by meta-atoms. This study proposes the concept of virtual metasurface(VM), which is formed by arrays of foci away from the entity metasurface. Unlike conventional metasurfaces, spatial modulations on the amplitudes or phases of EM waves occur in the air, with a focal length distance from the entity metasurface. As a proof of concept, we demonstrated a transmissive VM. The entity metasurface consists of transmissive focusing metasurface tiles(TFMTs) with the same focal length. Two TFMTs were designed with phase difference π to enable the most typical checkerboard configuration. The TFMTs were assembled to form the entity metasurface, whereas their foci formed the VM. Due to the π phase difference among adjacent foci, EM propagation along the normal direction was cancelled, leading to four tilted far-field beams. The concept of VM can be readily extended to higher frequencies from terahertz to optical regimes and may find wide applications in communication, camouflage, and other fields.

Shape memory alloy-based 3D morphologically reconfigurable chiral metamaterial for tailoring circular dichroism by voltage control

Three-dimensional chiral materials with intrinsic chirality play a crucial role in achieving a strong chiral response and flexible light manipulation.Reconfigurable chirality through the 3D morphological transformation of chiral materials is significant for greater freedom in tailoring light but remains a challenge.Inspired by the unique 3D morphological memory capability of shape memory alloys(SMAs),we demonstrate and discuss a chiral resonator in the microwave regime that can realize reconfigurable chirality through 3D morphological transformation.The introduction of heating film realizes voltage control of SMA’s morphology for utilizing the temperature sensitivity of SMA better,enabling arbitrary control of circular dichroism(CD)flip and CD intensity.The qualitative and quantitative analysis of the surface current distribution of chiral enantiomers reveals that the chirality of metaatoms originates from the surge of electric dipole pxand electric quadrupole Q.It is worth mentioning that the proposed strategy to achieve reconfigurable chirality using 3D morphological transformations can be directly extended to other higher frequencies,such as visible,infrared,and terahertz bands.Significantly,our paradigm to study the relationship between complex 3D morphology and chirality holds potential for application in biosensing,spin detection,and spin-selective devices.

Design of concise robust control for longitudinal motionof YuKun

With the rapid development of the shipping industry,the safety and comfort of ship transportation have been paid more and more attention,and the pitch and heave motion of ships are the most serious factors.In this paper,the longitudinal motion mathematical model of YuKun is esta b lished.By assigning the zero-pole to the left half-plane and using the properties of the symmetric matrix,the shaping weighting functions matrix is designed to stabilize the multi-input multi-output(MIMO)system of YuKun.Finally,a new concise robust controller is designed using the steady output of the shaped system.The simulation results show that under the control of the concise robust controller,the pitch angle and heave of YuKun decrease by 79.9% and 86.2%,respectively.Theoretical analysis and simulation results show that the concise robust controller has a good control effect on the longitudinal motion of YuKun,and is simple and easy to use,with clear engineering significance.

Machine-learning-empowered multispectral metafilm with reduced radar cross section,low infrared emissivity,and visible transparency

For camouflage applications,the performance requirements for metamaterials in different electromagnetic spectra are usually contradictory,which makes it difficult to develop satisfactory design schemes with multispectral compatibility.Fortunately,empowered by machine learning,metamaterial design is no longer limited to directly solving Maxwell’s equations.The design schemes and experiences of metamaterials can be analyzed,summarized,and learned by computers,which will significantly improve the design efficiency for the sake of practical engineer-ing applications.Here,we resort to the machine learning to solve the multispectral compatibility problem of metamaterials and demonstrate the design of a new metafilm with multiple mechanisms that can realize small microwave scattering,low infrared emissivity,and visible transparency simultaneously using a multilayer back-propagation neural network.The rapid evolution of structural design is realized by establishing a mapping between spectral curves and structural parameters.By training the network with different materials,the designed network is more adaptable.Through simulations and experimental verifications,the designed architecture has good accuracy and robustness.This paper provides a facile method for fast designs of multispectral metafilms that can find wide applications in satellite solar panels,aircraft windows,and others.

Construction of cDNA library, nucleotide sequence and analysis of entire genome of classical swine fever virus strain Shimen

According to the previously published CSFV sequences, 18 pairs of primers have been designed and synthesized, which cover the entire genome of CSFV strain Shimen. Each cDNA fragment has been amplified by RT-PCR from the anticoagulant blood of strain Shimen infected pig. The PCR products have been cloned respectively and sequenced. Results show that the cDNA library of strain Shimen and its nucleotide sequence have been obtained. The genomic RNA of strain Shimen is 12 298 nucleotides in length, containing a 5’ and a 3’ noncoding region 373 and 231 nt long respectively. The center of genome is a single large open reading frame of 11 697 nt which encodes a polyprotein of 3 898 amino acids. The entire sequence of strain Shimen has also been compared with that of other CSFV strains.

Spin-selective corner reflector for retro-reflection and absorption by a circular dichroitic manner

Recently, we have witnessed an extraordinary spurt in attention toward manipulating electromagnetic waves by metasurfaces. Particularly, tailoring of circular polarization has attracted great amounts of interest in both microwave and optics regimes. Circular dichroism, an exotic chiroptical effect of natural molecules, has aroused discussion about this issue, yet it is still in its infancy. Herein, we initiate circular dichroism followed by controlling spin-selective wavefronts via chiral metasurfaces. An N-shaped chiral resonator loaded with two lumped resistors is proposed as the meta-atom producing an adequate phase gradient. Assisted by the ohmic dissipation of the introduced resistors, the effect of differential absorption provides an auxiliary degree of freedom for developing circularly polarized waves with a designated spin state. A planar corner reflector that can achieve retro-reflection and absorption for right-and left-handed circularly polarized incidence is theoretically simulated and experimentally observed at microwave frequency. Thus, our effort provides an alternative approach to tailoring electromagnetic waves in a circular dichroitic manner and may also find applications in multi-functional systems in optics and microwave regimes.

Remotely mind-controlled metasurface via brainwaves

The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.