Analysis of inverse synthetic aperture radar imaging in the presence of time-varying plasma sheath

The plasma sheath can induce radar signal modulation,causing not only ineffective target detection,but also defocusing in inverse synthetic aperture radar(ISAR)imaging.In this paper,through establishing radar echo models of the reentry object enveloped with time-varying plasma sheath,we simulated the defocusing of ISAR images in typical environment.Simulation results suggested that the ISAR defocusing is caused by false scatterings,upon which the false scatterings’formation mechanism and distribution property are analyzed and studied.The range of false scattering correlates with the electron density fluctuation frequency.The combined value of the electron density fluctuation and the pulse repetition frequency jointly determines the Doppler of false scattering.Two measurement metrics including peak signal-to-noise ratio and structural similarity are used to evaluate the influence of ISAR imaging.

Grenvillian and early Paleozoic polyphase metamorphism recorded by eclogite and host garnet mica schist in the North Qaidam orogenic belt

The North Qaidam orogenic belt(NQOB) is generally considered to be an early Paleozoic ultrahigh pressure metamorphic belt,but increasing reports of the Neoproterozoic magmatic and metamorphic events indicate that the NQOB probably also experienced the assembly of the Rodinia.However,the Neoproterozoic evolution of the NQOB is not well constrained due to the sparse records and ambiguous nature of the Neoproterozoic metamorphism.In order to reveal the multi-orogenic history of the NQOB,an integrated study of petrology,phase equilibrium modelling and geochronology was conducted on an epidote eclogite and host garnet mica schist from the Yuka–Luofengpo terrane.New zircon and monazite U–Pb ages show that the protolith of the garnet mica schist was deposited during 994–920 Ma and experienced Neoproterozoic(920–915 Ma) and early Paleozoic(451–447 Ma) polyphase metamorphism together with the enclosed eclogite.Relic omphacite inclusions were first identified in garnet and early Paleozoic zircon domains from the garnet mica schist,which provide solid evidence for the early Paleozoic eclogite facies metamorphism of the mica schist.Similar early Paleozoic peak P–T conditions of >27.4 kbar/613–670 ℃ and 30.2–30.8 kbar/646–655 ℃ were obtained for the garnet mica schist and enclosed eclogite,respectively,indicating that eclogites and their host paragneisses in this region underwent continental deep subduction as a coherent metamorphic terrane in early Paleozoic.The peak P–T conditions of the Neoproterozoic metamorphism were roughly constrained at 7.7–12.0 kbar and 634–680 ℃ for the garnet mica schist,based on stability field of mineral inclusions in Neoproterozoic zircons domains in P–T pseudosection,the relic garnet core composition and Ti-in-zircon thermometer.The high thermal gradients(16–37 ℃/km) defined by presently our and previously reported P–T conditions indicate that the Neoproterozoic metamorphism likely occurred in continental collision setting at >945–890 Ma.Since the Grenvillian syn-orogenic granitic magmatism and metamorphism(ca.1.0–0.9 Ga) in the NQOB are much younger than the Grenvillian orogeny in the central part of Rodinia,the Qaidam Block was probably located at the north margin of Rodinia in Neoproterozoic.

Inverse synthetic aperture radar range profile compensation of plasma-sheath-enveloped reentry object

The scattering points in a plasma sheath characterized with coupled velocities can cause pulse compression mismatching,which results in displacement and energy diffusion in the onedimension range profile.To solve this problem,we deduce the echo model of the plasma-sheathenveloped reentry object.By estimating the coupled velocities,we propose a compensation method to correct the defocus of an inverse synthetic aperture radar(ISAR)image in range dimension to improve the quality of the ISAR images.The simulation results suggest that the echoes from different regions of the surface of the reentry object have various coupling velocities,and the higher the coupled velocity,the more serious the displacement and energy diffusion in the range dimension.Our proposed method can correct the range dimension aberration.Two measurement metrics were used to evaluate the improvement of the compensation method.

Demonstration of an on-chip TE-pass polarizer using a silicon hybrid plasmonic grating

An on-chip, high extinction ratio transverse electric(TE)-pass polarizer using a silicon hybrid plasmonic grating is proposed and experimentally demonstrated. Utilizing plasmonics to manipulate the effective index and mode distribution, the transverse magnetic mode is reflected and absorbed, while the TE mode passes through with relatively low propagation loss. For a 6-μm-long device, the measurement result shows that the extinction ratio in the wavelength range of 1.52 to 1.58 μm varies from 24 to 33.7 dB and the insertion loss is 2.8–4.9 dB. Moreover,the structure exhibits large alignment tolerance and is compatible with silicon-on-insulator fabrication technology.

Optical coherent dot-product chip for sophisticated deep learning regression

Optical implementations of neural networks(ONNs)herald the next-generation high-speed and energy-efficient deep learning computing by harnessing the technical advantages of large bandwidth and high parallelism of optics.However,due to the problems of the incomplete numerical domain,limited hardware scale,or inadequate numerical accuracy,the majority of existing ONNs were studied for basic classification tasks.Given that regression is a fundamental form of deep learning and accounts for a large part of current artificial intelligence applications,it is necessary to master deep learning regression for further development and deployment of ONNs.Here,we demonstrate a silicon-based optical coherent dot-product chip(OCDC)capable of completing deep learning regression tasks.The OCDC adopts optical fields to carry out operations in the complete real-value domain instead of in only the positive domain.Via reusing,a single chip conducts matrix multiplications and convolutions in neural networks of any complexity.Also,hardware deviations are compensated via in-situ backpropagation control provided the simplicity of chip architecture.Therefore,the OCDC meets the requirements for sophisticated regression tasks and we successfully demonstrate a representative neural network,the AUTOMAP(a cutting-edge neural network model for image reconstruction).The quality of reconstructed images by the OCDC and a 32-bit digital computer is comparable.To the best of our knowledge,there is no precedent of performing such state-of-the-art regression tasks on ONN chips.It is anticipated that the OCDC can promote the novel accomplishment of ONNs in modern AI applications including autonomous driving,natural language processing,and scientific study.

High-Efficiency Rescue of Equine Infectious Anemia Virus from a CMV-Driven Infectious Clone

Dear Editor,Equine infectious anemia virus(EIAV)belongs to the macrophage-tropic lentiviruses family and infects mainly equines,including horses,donkeys and mules.EIAV shares many similar characteristics in its viral biology and host-virus immune regulation with other lentiviruses,such as human immunodeficiency virus type 1(HIV-1)and simian immunodeficiency virus(SIV),and has been accepted as a model for the study of other lentiviruses,especially HTV-1(Craigo and Montelaro 2013).Specifically,in the 1970s,Chinese scientists developed an attenuated EIAV vaccine and by using this vaccine,China has successfully controlled EIAV prevalence.This vaccine provides a meaningful reference for lentivirus research(Wang et al.2016).

An ultra-compact polarization-insensitive slot-strip mode converter

Integrated waveguides with slot structures have attracted increasing attention due to their advantages of tight mode confinement and strong light-matter interaction.Although extensively studied,the issue of mode mismatch with other strip waveguide-based optical devices is a huge challenge that prevents integrated waveguides from being widely utilized in large-scale photonic-based circuits.In this paper,we demonstrate an ultra-compact low-loss slot-strip converter with polarization insensitivity based on the multimode interference(MMI)effect.Sleek sinusoidal profiles are adopted to allow for smooth connection between the slot and strip waveguide,resulting reflection reduction.By manipulating the MMI effect with structure optimization,the self-imaging positions of the TE0 and TM0 modes are aligned with minimized footprint,leading to low-loss transmission for both polarizations.The measurement results show that high coupling efficiencies of−0.40 and−0.64 dB are achieved for TE_(0) and TM_(0) polarizations,respectively.The device has dimensions as small as 1.1μm×1.2μm and composed of factory-available structures.The above characteristics of our proposed compact slot-strip converter makes it a promising device for future deployment in multi-functional integrated photonics systems.

Low-loss hybrid plasmonic TM-pass polarizer using polarization-dependent mode conversion

A low-loss hybrid plasmonic transverse magnetic(TM)-pass polarizer has been demonstrated utilizing polarization-dependent mode conversion.Taking advantage of the silicon hybrid plasmonic slot waveguide(HPSW),the unwanted transverse electric(TE)fundamental mode can be efficiently converted first to a TM higher-order mode and then suppressed by a power combiner,while the retained TM fundamental mode can pass through with negligible influence.Since the HPSW feature both strong structural asymmetry and a small interaction area in the cross-section between the metal and optical field,the optimized insertion loss of the device is as low as 0.4 d B.At the wavelength of 1550 nm,the extinction ratio is 28.3 d B with a moderate footprint of 2.38μm×10μm.For the entire C band,the average reflection of the TE mode is suppressed below-14 d B,and the extinction ratio is over 18.6 d B.This work provides another more efficient and effective approach for better on-chip polarizers.

Study of a 560-mm-long stripline kicker for HIT 10 MeV electron accelerator

Purpose A stripline kicker is required for Harbin Institute of Technology(HIT)10 MeV electron accelerator to scan electrons horizontally in two directions,and the maximum deflecting angle is 65 mrad.In this study,a 560-mm-long stripline kicker was designed to achieve good field uniformity and odd mode impedance matching.Methods In order to reduce power reflections and meet field uniformity requirement,we optimized the cross section of the kicker main body.Design and optimization of the stripline kicker were finished by CST.Results The field uniformity is 2%in the 60 mm(x)×80 mm(y)region,as required.Considering impedance matching and manufacturing,the transmission odd mode impedance was finally chosen to 45Ω,which indicated a reflecting loss of less than−50 dB below 1 MHz.The maximum field is less than 7 MV/m with a maximum pulse voltage of±22 kV between the two electrodes when the electrons pass through the kicker.Conclusions The physical design of the stripline kicker has been finished,and the simulation results satisfied the requirements.

Strategies for training optical neural networks

Deep learning has flourished in different areas in recent years,such as computer vision and natural language processing.However,with the end of Moore’s law,these applications that rely heavily on computing power are facing bottlenecks.Optical neural networks(ONNs)[1]use light to perform calculations[2,3]featuring high speed and low energy consumption,and they are widely regarded as the next-generation applicationspecific integrated circuit(ASIC)[4,5]for artificial intelligence.