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Showing papers in "Journal of Applied Physics in 2023"


Journal ArticleDOI
TL;DR: In this paper , the authors present the pore collapse simulations of cylindrical pores in TATB for a wide range of pore sizes and shock strengths that trigger viscoplastic collapses that occur almost entirely perpendicular to the shock direction for weak shocks and hydrodynamic-like collapses for strong shocks.
Abstract: Atomistic and continuum scale modeling efforts have shown that the shock-induced collapse of porosity can occur via a wide range of mechanisms dependent on pore morphology, the shockwave pressure, and material properties. The mechanisms that occur under weaker shocks tend to be more efficient at localizing thermal energy but do not result in high, absolute temperatures or spatially large localizations compared to mechanisms found under strong shock conditions. However, the energetic material 1,3,5-trinitro-2,4,6-triaminobenzene (TATB) undergoes a wide range of collapse mechanisms that are not typical of similar materials, leaving the collapse mechanisms and the resultant energy localization from the collapse, i.e., hotspots, relatively uncharacterized. Therefore, we present the pore collapse simulations of cylindrical pores in TATB for a wide range of pore sizes and shock strengths that trigger viscoplastic collapses that occur almost entirely perpendicular to the shock direction for weak shocks and hydrodynamic-like collapses for strong shocks that do not break the strong hydrogen bonds of the TATB basal planes. The resulting hotspot temperature fields from these mechanisms follow trends that differ considerably from other energetic materials; hence, we compare them under normalized temperature values to assess the relative efficiency of each mechanism to localize energy. The local intra-molecular strain energy of the hotspots is also assessed to better understand the physical mechanisms behind the phenomena that lead to a latent potential energy.

6 citations


Journal ArticleDOI
TL;DR: In this article , the current trends in magnetocaloric materials research, highlighting the families of alloys and compounds that are gaining attention in the recent years, are discussed and an overview of novel approaches that can be used to analyze these properties.
Abstract: Magnetocaloric refrigeration has remained a promising alternative to conventional refrigeration for the last few decades. The delay in reaching the market is significantly based on materials’ related issues, such as hysteresis/reversibility, mechanical stability, or formability. This perspective paper shows the current trends in magnetocaloric materials research, highlighting the families of alloys and compounds that are gaining attention in the recent years. It also includes an overview of novel approaches that can be used to analyze these properties that could improve the applicability of magnetocaloric materials.

6 citations


Journal ArticleDOI
TL;DR: In this paper , the authors demonstrate non-reciprocal critical current in 65nm thick polycrystalline and epitaxial Nb thin films patterned into tracks and find that tracks of width 4μm provide the largest supercurrent diode efficiency of up to ≈30%, with the effect reducing or disappearing in the widest tracks of 10μm.
Abstract: We demonstrate nonreciprocal critical current in 65 nm thick polycrystalline and epitaxial Nb thin films patterned into tracks. The nonreciprocal behavior gives a supercurrent diode effect, where the current passed in one direction is a supercurrent and the other direction is a normal state (resistive) current. We attribute fabrication artifacts to creating the supercurrent diode effect in our tracks. We study the variation of the diode effect with temperature and the magnetic field and find a dependence with the width of the Nb tracks from 2 to 10 μm. For both polycrystalline and epitaxial samples, we find that tracks of width 4 μm provide the largest supercurrent diode efficiency of up to ≈30%, with the effect reducing or disappearing in the widest tracks of 10 μm. We propose a model based on the limiting contributions to the critical current density to explain the track width dependence of the induced supercurrent diode effect. It is anticipated that the supercurrent diode will become a ubiquitous component of the superconducting computer.

4 citations


Journal ArticleDOI
TL;DR: In this article , the state-of-the-art and challenges in designing ICT-based molecules and materials for optical applications are discussed, and the underlying theories used to quantify the magnitude of ICT and NLO response are mentioned.
Abstract: Tuning of intramolecular charge transfer (ICT) in a molecule could be used to modulate its linear and nonlinear optical (NLO) response properties. Over the years, the ICT process in the so-called “push–pull” molecules in which electron donor (D) and acceptor (A) groups are connected either directly or through a π-electron bridge has been used for emission color tuning, modulating absorption maxima, optimizing first or higher order hyperpolarizabilities, and two-photon absorption (TPA), among others. As ICT is the functional basis of many optoelectronic and semiconductor devices, optimizing the parameters involved in this process as well as modeling the effect of the environment and intermolecular interaction are crucial for these applications. NLO processes such as second harmonic generation, sum-frequency generation, and TPA have been used extensively for numerous technological applications, such as optical switching, optical limiting, bioimaging, and biophotonics. Recently, through-bond and through-space ICT have been employed to tune the reverse intersystem crossing that facilitates thermally activated delayed fluorescence for fabricating next-generation organic light-emitting diodes. Aggregation-induced emission of ICT molecules either alone or in combination with the other phenomenon, such as TPA, could be useful in many optical applications. In this perspective, the state-of-the-art and challenges in designing ICT-based molecules and materials for optical applications will be discussed. The underlying theories used to quantify the magnitude of ICT and NLO response are mentioned, followed by a discussion on the latest development and scope of using these molecules and materials for optical applications.

3 citations


Journal ArticleDOI
TL;DR: In this article , the nature and stability of the defects generated by atoms knocked-out by particle irradiation at near threshold energies were determined based on density-functional simulations, and a low probability for Ga (O) defect recombination was shown.
Abstract: Gallium oxide is an emerging wide-bandgap semiconductor with promise for applications in space systems that may be exposed to energetic particles. We use molecular dynamics simulations, based on first principles density-functional methods, to determine the nature and stability of the defects generated by atoms knocked-out by particle irradiation at near threshold energies (found to be [Formula: see text] for Ga and [Formula: see text] for O). For Ga atoms, several types of low energy knock-out events result in defect complexes, but the final structures depend critically on the initial displacement direction. In contrast, a vacancy plus a peroxide linkage occurs in all types of low energy knock-out events of O atoms. Based on energy-barrier calculations, there is a low (high) probability for Ga (O) defect recombination. The electronic structure of residual, relaxed defects generated by Ga knock-outs reveals defect levels near the band edges.

3 citations


Journal ArticleDOI
TL;DR: In this article , a chiral periodic metasurface based on plasmonic nanodisks and nanorods arranged asymmetrically in a unit cell is proposed.
Abstract: Compact planar photonic elements serving for efficient control over the polarization of light are of paramount importance in photonics. Here, we propose a design of a chiral periodic metasurface based on plasmonic nanodisks and nanorods arranged asymmetrically in a unit cell. Using the finite-difference time-domain analysis, we show that the collective lattice resonance harnessed by the diffraction coupling of the plasmonic unit cells is the heart of the revealed resonant 38% circular dichroism effect. The circular dichroism enhancement of the considered structure is improved using the deep-learning-assisted optimization of the metasurface design.

2 citations


Journal ArticleDOI
TL;DR: In this paper , the authors proposed a magnonic co-processor for special task data processing, which is based on the natural property of an active ring circuit to self-adjust to the resonant frequency.
Abstract: In this work, we consider the possibility of building a magnonic co-processor for special task data processing. Its principle of operation is based on the natural property of an active ring circuit to self-adjust to the resonant frequency. The co-processor comprises a multi-path active ring circuit where the magnetic part is a mesh of magnonic waveguides. Each waveguide acts as a phase shifter and a frequency filter at the same time. Being connected to the external electric part, the system naturally searches for the path which matches the phase of the electric part. This property can be utilized for solving a variety of mathematical problems including prime factorization, bridges of the Konigsberg problem, traveling salesman, etc. We also present experimental data on the proof-of-the-concept experiment demonstrating the spin wave signal re-routing inside a magnonic matrix depending on the position of the electric phase shifter. The magnetic part is a 3 × 3 matrix of waveguides made of single-crystal yttrium iron garnet Y3Fe2(FeO4)3 films. The results demonstrate a prominent change in the output power at different ports depending on the position of the electric phase shifter. The described magnonic co-processor is robust, deterministic, and operates at room temperature. The ability to exploit the unique physical properties inherent in spin waves and classical wave superposition may be translated into a huge functional throughput that may exceed [Formula: see text] operations per meter squared per second for [Formula: see text] magnetic mesh. Physical limits and constraints are also discussed.

2 citations


Journal ArticleDOI
TL;DR: In this paper , the lattice particle method is used to decompose the grain domain into discrete material particles that are regularly packed according to the underlying atomic lattice, and nonlocal interactions are introduced between material particles and top-down approaches are used to relate model parameters to the material physical constants.
Abstract: In this paper, novel nonlocal reformulations of the conventional continuum-based models for modeling the thermoelastic behavior of cubic crystals based on a recently developed lattice particle method are presented. Like molecular dynamics simulation, the lattice particle method decomposes the grain domain into discrete material particles that are regularly packed according to the underlying atomic lattice. Nonlocal interactions are introduced between material particles and top-down approaches are used to relate model parameters to the material physical constants. Three equivalency assumptions are used in the top-down approach, namely, energy equivalency for the mechanical model, heat transfer rate equivalency for the thermal model, and thermal strain equivalency for the thermal-mechanical coupling model. Different from coordinates transformation used in the conventional continuum-based models, lattice rotation is adopted in the lattice particle method to equivalently represent the material anisotropy while explicitly capturing the crystallographic orientation. Two most common Bravais cubic lattices are studied, i.e., the body-centered cubic lattice and the face-center cubic lattice. The validity and prediction accuracy of the developed models are established by comparing the predicted displacements and temperature results with solutions of conventional continuum theories using the finite element method.

2 citations


Journal ArticleDOI
TL;DR: In this paper , a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permallioy film with a nonmagnetic spacer layer.
Abstract: We present a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy film with a nonmagnetic spacer layer. The thermal spin-wave spectra were recorded by BLS as a function of the magnetic field applied along the symmetry direction of the ASI sample. Magneto-optic Kerr effect magnetometry was used to measure the hysteresis loops in the same orientation as the BLS measurements. The frequency and the intensity of several spin-wave modes detected by BLS were measured as a function of the applied magnetic field. Micromagnetic simulations enabled us to identify the modes in terms of their frequency and spatial symmetry and to extract information about the existence and strength of the dynamic coupling, relevant only to a few modes of a given hybrid system. Using this approach, we suggest a way to understand if the dynamic coupling between ASI and film modes is present or not, with interesting implications for the development of future three-dimensional magnonic applications and devices.

2 citations


Journal ArticleDOI
TL;DR: In this article , the authors present and discuss practical techniques for formulating effective models to describe the low-energy electronic properties of bilayer graphene systems, and show that such effective models are constructed from a collection of appropriate single-layer Bloch states of two graphene layers.
Abstract: We present and discuss practical techniques for formulating effective models to describe the low-energy electronic properties of bilayer graphene systems. We show that such effective models are constructed from a collection of appropriate single-layer Bloch states of two graphene layers. In general, the obtained effective models allow the construction of a so-called moiré band structure. However, it is not the result of an irreducible representation of a translation symmetry group of the bilayer lattices except for the commensurate bilayer configurations. We also point out that the commensurate bilayer configurations are classified into three categories depending on the divisibility of the difference between two commensurate integer indices by 3. The electronic band structure of three lattice configurations, one for each category, is shown. Especially by combining with a real-space calculation, we validate the working ability of constructed effective models for generic bilayer graphene systems by showing that the effects of interlayer sliding are diminished by twisting. This result is consistent with the invariance of effective models under the interlayer sliding operation.

2 citations


DOI
TL;DR: In this article , a thin plate structure with an acoustic black hole (ABH) sub-unit was proposed to reorient the flexural wave. And the results show that the ABH beam-plate structure can effectively control the propagation direction of flexural waves, which provides a modern design idea and method for the manipulation and energy harvesting of the flexuric wave.
Abstract: This letter presents a thin plate structure with an acoustic black hole (ABH) sub-unit to reorient the flexural wave. Different from the previously reported flexural wave metasurface, ABH sub-units are introduced into thin plates in this work, which can control the group velocity of flexural waves and realize their efficient transmission. According to generalized Snell's law, the mechanism of phase shift of transmitted waves across subwavelength sub-units is theoretically revealed. An analysis of the ABH sub-units is established by the finite element method. The deflection and focusing effect of flexural waves are demonstrated. Furthermore, adjusting the black hole section can quickly obtain the transmission phase response in the range of 2π, and it can accurately predict the phase shift and amplitude of the transmitted wave. The results show that the ABH beam-plate structure can effectively control the propagation direction of flexural waves, which provides a modern design idea and method for the manipulation and energy harvesting of the flexural wave.

Journal ArticleDOI
TL;DR: In this paper , the development and characterization of an atom chip for magnetic trapping of cold [Formula: see text] atoms was described. Butts from an U-magneto-optical trap, after optical pumping, were directly trapped in the magnetic trap of the atom chip.
Abstract: In this work, we report the development and characterization of an atom chip for magnetic trapping of cold [Formula: see text] atoms. For fabrication of the atom chip, a silicon substrate was used after depositing an insulating layer of silica ([Formula: see text]) on it. An adhesive chromium layer was further deposited on this substrate before the deposition of the final layer of gold. On this gold coated substrate, a z-shaped gold wire (cross section, [Formula: see text]) was fabricated by a photo-chemical machining method. The chip wire was tested for current–voltage characteristics for its reliable operation in magnetic trapping. The atoms from an U-magneto-optical trap, after optical pumping, were directly trapped in the magnetic trap of the atom chip.

Journal ArticleDOI
TL;DR: In this paper , a silicon nitride nanopore-based sensing system was used to measure tau and tubulin monomers and their aggregations in salt solution at a single molecule level.
Abstract: In this study, a silicon nitride nanopore-based sensing system was used to measure tau and tubulin monomers and their aggregations in salt solution at a single molecule level. Nanopores (6–30 nm) were fabricated on silicon nitride membranes supported by silicon substrates using a combination of focused ion beam milling and ion beam sculpting. When a charged protein molecule in the salt solution passes through a nanopore driven by an applied voltage, the protein molecule increases pore resistivity, which induces an ionic current drop that can be measured. The current drop amplitude is directly proportional to the local excluded volume of the protein molecule in the nanopore. We measured the monomers and aggregations of tau and tubulin proteins at biased voltages from 60 to 210 mV in a solution of pH 7.0–10. Our results showed that (1) the nanopore method was able to differentiate tau and tubulin proteins in their monomer and aggregated forms by their excluded volumes; (2) the most probable aggregation form was dimer for α- and β-tubulin and pentamer for αβ tubulin plus tau under experimental conditions; (3) the protein excluded volumes measured by the nanopore method depended on the applied voltage, and this observation could be explained by the nonuniform charge distribution of proteins. The monomer and aggregated proteins were further analyzed using atomic force spectroscopy (AFM), and protein volumes estimated by AFM were consistent with nanopore results.

Journal ArticleDOI
TL;DR: In this paper , a transient conducting model for the double Schottky barrier (DSB) is proposed by quantifying the charge trapping processes of the interface states, and the proposed model is validated by a satisfying agreement between experimentally measured current responses and simulation results of ZnO varistors.
Abstract: ZnO varistors are widely employed for overvoltage protections and surge absorptions due to their excellent nonlinear current–voltage characteristics originating from double Schottky barriers (DSBs). In most cases, they are operating under moderate ac voltages, while calculating the transient current responses of DSBs remains a challenge, impeding the development of condition assessments. In this paper, a transient conducting model for the DSB is proposed by quantifying the charge trapping processes of the interface states. The DSB is found to quickly reach a quasi-steady state, where the interfacial charge stabilizes with only small modulations at a relatively high level above the dc equilibrium value, even though the applied ac voltage varies in time and polarity. This is the result of efficient charge trapping and slow de-trapping by grain boundary interface states. For charge compensation under the time-varying voltage, the width of the two depletion regions of the DSB shows periodic changes. The proposed model is validated by a satisfying agreement between experimentally measured current responses and simulation results of ZnO varistors. The findings of this study provide a perspective on investigating the time-varying conducting systems and open avenues for condition assessments of nonlinear conducting devices.

Journal ArticleDOI
TL;DR: In this paper , the authors review famous solutions for the reconstruction in terms of the photon propagation models and inverse reconstruction algorithms to make an overall understanding for the methods of OMT reconstruction.
Abstract: As a high-sensitivity and non-invasive technique, optical molecular tomography (OMT) can locate and visualize tissue quantitatively in three dimensions by collecting surface photons generated from luminescent biomarkers. It has great potential for tumor detection, surgery guidance, and pharmacokinetics research studies. However, due to the limited measurable surface photons and the highly scattered feature of photons, the reconstruction of OMT is highly ill-posed and ill-conditioned, which limits the performance in practice. To improve the accuracy of OMT, plenty of studies focus on precisely modeling photon propagation and accurately reconstructing light source. Since these methods are carried out based on different theories, we review famous solutions for the reconstruction in terms of the photon propagation models and inverse reconstruction algorithms to make an overall understanding for the methods of OMT reconstruction. Additionally, some prospects are listed to provide possible research orientation that may benefit future research.

Journal ArticleDOI
TL;DR: In this paper , structural, magnetic, and interfacial spin transport properties of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron sputtering were reported.
Abstract: We report the structural, magnetic, and interfacial spin transport properties of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron sputtering. High crystallinity was achieved by growing the films on gadolinium gallium garnet substrates either at high temperatures, or at room temperature followed by thermal annealing, above 750 °C in both cases. The films display large perpendicular magnetic anisotropy (PMA) induced by compressive strain, and tunable structural and magnetic properties through growth conditions or the substrate lattice parameter choice. The ferrimagnetic compensation temperature ([Formula: see text]) of selected TbIG films was measured through the temperature-dependent anomalous Hall effect in Pt/TbIG heterostructures. In the studied films, [Formula: see text] was found to be between 190 and 225 K, i.e., approximately 25-60 K lower than the bulk value, which is attributed to the combined action of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with large PMA and highly tunable properties reported here can provide a suitable material platform for a wide range of spintronic experiments and device applications.

Journal ArticleDOI
TL;DR: In this article , the authors present a systematic study of multiple PSSW modes in NiFe films, where both the sample thickness and the cap layer material are varied and show that a simple analysis based on the Kittel rigid pinning model yields an exchange stiffness constant that varies with thickness, mode number, and capping layer material.
Abstract: The exchange stiffness constant is recognized as one of the fundamental properties of magnetic materials, though its accurate experimental determination remains a particular challenge. In thin films, resonance measurements exploiting perpendicular standing spin waves (PSSWs) are increasingly used to extract this parameter, typically through a determination of the first-order PSSW mode. Here, we present a systematic study of multiple PSSW modes in NiFe films, where both the sample thickness and the cap layer material are varied. The results show that a simple analysis based on the Kittel rigid pinning model yields an exchange stiffness constant that varies with thickness, mode number, and capping layer material. This finding is clearly inconsistent with physical expectation that the exchange stiffness constant of a material is single valued for a particular set of thermodynamic conditions. Using a more general exchange boundary condition, we show, through a comprehensive set of micromagnetic simulations, that a dynamic pinning mechanism originally proposed by Wigen is able to reproduce the experimental results using a single value of Aex. Our findings support the utility of short wavelength, higher order PSSWs to determine the Aex of thin films and show that the value of Aex obtained has a weak dependency on the material immediately adjacent to the magnetic layer.

Journal ArticleDOI
TL;DR: In this paper , the authors present some physical insights into enhancing the magnetic stability of 2D magnets. And they present the advanced understanding of magnetic stability in 2D materials, which provides new opportunities for further advancement in a wide variety of applications.
Abstract: Recently, two-dimensional (2D) magnets have drawn substantial attention from researchers for their fascinating properties and great application potential in the fields of biomedicine, data storage, signal transfer, and energy conversion. However, the low Curie/Néel temperature of 2D magnets hinders their application. In this Perspective, we present some physical insights into enhancing the magnetic stability of 2D magnets. First, the microscope theoretical model of 2D magnets is introduced. Then, we review and analyze several effective and commonly used methods for enhancing the magnetic stability of 2D magnets. Finally, we present the perspective and summary. This Perspective presents the advanced understanding of magnetic stability in 2D materials, which can provide new opportunities for further advancement in a wide variety of applications.

Journal ArticleDOI
TL;DR: In this article , the authors present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics, and they show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of neutrals change the spatiotemporal evolution of the discharge.
Abstract: The dynamics of the neutral atoms in Hall thrusters affects several plasma processes, from ionization to electrons' mobility. In the context of Hall thruster's particle-in-cell (PIC) modeling, the neutrals are often treated kinetically, similar to the plasma species, and their interactions with themselves and the ions are resolved using the direct-simulation Monte–Carlo (DSMC) algorithm. However, the DSMC approach is computationally resource demanding. Therefore, modeling the neutrals as a 1D fluid has been also pursued in simulations that do not involve the radial coordinate and, hence, do not resolve the neutrals' radial expansion. In this article, we present an extensive study on the sensitivity of the PIC simulations of Hall thruster discharge to the model used for the neutral dynamics. We carried out 1D axial PIC simulations with various fluid and kinetic models of the neutrals as well as self-consistent quasi-2D axial-azimuthal simulations with different neutrals’ fluid descriptions. Our results show that the predictions of the simulations in either 1D or 2D configurations are highly sensitive to the neutrals' model, and that different treatments of the neutrals change the spatiotemporal evolution of the discharge. Moreover, we observed that considering the ion-neutral collisions causes a significant variation in the neutral temperature, thus requiring that the neutrals' energy equation to be included as well in their fluid system of equations. Finally, the self-consistent axial-azimuthal simulations highlighted that a neutrals’ model based on the continuity conservation equation only is not an appropriate choice and leads to physically unexpected high-frequency global discharge oscillations.

Journal ArticleDOI
TL;DR: In this paper , the electrical properties of semi-insulating GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn) grown by hydride vapor phase epitaxy are presented.
Abstract: The electrical properties of semi-insulating GaN substrates doped with iron (Fe), carbon (C), or manganese (Mn) grown by hydride vapor phase epitaxy are presented. Hall effect measurements were performed at temperatures ranging from 300 to 800 K. At all of the investigated temperatures, the Mn-doped samples exhibited the highest resistivity. The Fe-doped samples showed n-type conduction, whereas the C-doped samples and the Mn-doped sample with a Mn concentration of 1 × 1019 cm−3 showed p-type conduction. A detailed analysis of the temperature dependence of the carrier concentration showed that all of the impurities formed acceptor levels at EC −(0.59–0.61) eV for Fe, at EV +(0.90–1.07) eV for C, and at EV +1.55 eV for Mn. The Mn-doped sample with a Mn concentration of 8 × 1017 cm−3 showed a negative Hall coefficient (suggesting n-type conduction) at high temperatures, contradicting the formation of acceptor levels by Mn. We successfully explained the negative value by considering the conduction of both holes and electrons with different mobilities. On the basis of the results, we calculated the relationship between the resistivity and doping concentration for each dopant. The calculations indicated that the highest resistivity can be realized in Mn-doped GaN with an optimized doping concentration (depending on the residual donor concentration). All of the dopants can effectively realize high resistivity at room temperature. Mn is an effective dopant for attaining high resistivity, especially at high temperatures (e.g., 800 K).

Journal ArticleDOI
TL;DR: In this paper, a high-resolution survey on a rampart of a Xi'an defensive wall in demand of urgent protection is presented, and the results indicate density anomalies inside the rampart with unprecedented levels of precision.
Abstract: Muography is a rapidly developing and non-destructive tomographic technology that uses cosmic ray muons. Due to the natural presence and deeper penetration of cosmic ray muons, scientists have performed various pioneer studies in fields, such as customs security, the internal imaging of volcanoes, scientific archaeology, and others. With unique advantages, muography has gained increasing attention from archaeologists as a novel and innovative tool to investigate large-scale archaeological sites. This approach may be especially helpful for identifying endangered cultural relics and monuments. In the work, we employ a compact, rugged, and portable muon imaging system, CORMIS (COsmic Ray Muon Imaging System), deployed at up to six measurement locations to perform a case study of three-dimensional muography in Xi’an city, China. Cultural cities, such as Xi’an, have long histories and could benefit from innovative techniques used to investigate, conserve, and protect large historical sites. In this paper, we present in detail a high resolution survey on a rampart of a Xi’an defensive wall in demand of urgent protection. The survey data are carefully processed with advanced statistical methods newly introduced in muography, and the results indicate density anomalies inside the rampart with unprecedented levels of precision. The density anomalies are potential safety hazards and need to be eliminated as soon as possible. The successful implementation of this survey significantly encourages more engagement on the tangible application of high-precision 3D muography in archaeological investigations and protection projects around the world.

Journal ArticleDOI
TL;DR: In this article , a double-layer acoustic metasurface (DAM) composed of a fixed LAM and a rotatable upper UAM is proposed for the generation of mode-reconfigurable acoustic orbital angular momentum (OAM).
Abstract: In this paper, a double-layer acoustic metasurface (DAM) composed of a fixed lower acoustic metasurface (LAM) and a rotatable upper acoustic metasurface (UAM) is proposed for the generation of mode-reconfigurable acoustic orbital angular momentum (OAM). The UAM and LAM are divided into multiple sections, in which the hybrid structures combining cascaded Helmholtz resonators and a straight pipe are adopted to achieve specific phase compensation. By rotating the UAM, the incident acoustic plane wave can be efficiently converted into the vortex acoustic waves of reconfigurable topological charges ranging from −5 to +5 with distinguishable purity. Furthermore, the influences of the parameters on the purity of the generated topological charges have been investigated and discussed, such as the distance between LAM and UAM, rotatable angle error, and operating frequency. With the capability of reconfigurable OAM modes, the proposed DAM can be used to efficiently increase capacity or to conveniently switch between different channels in underwater vortex acoustic communications.

Journal ArticleDOI
TL;DR: In this paper , the acoustic properties of a laser filament coupled with a donut-shaped signal beam are exploited for free-space optical communication (FSO) through clouds and fog, which requires low energy, is resilient to noise and is unaffected by the filament.
Abstract: Dynamic media such as atmospheric clouds and fog form a formidable barrier to light propagation for free-space optical communication (FSO). To overcome such an obstacle, we propose to make use of the acoustic properties of a laser filament coupled together with a donut-shaped signal beam. A filament generated by an ultrafast laser is accompanied by an acoustic wave that clears a cylindrical chamber around the filament’s plasma column that can mimic a transmission channel. We present a method to couple a Laguerre–Gauss beam through the obstacle-free channel. We image and measure the transmitted signal carried by the structured beam to demonstrate an efficient method for FSO through cloudy conditions, which requires low energy, is resilient to noise, and is unaffected by the filament.

Journal ArticleDOI
TL;DR: In this paper , the authors present a review of the use of Figures-of-merit (FoM) for determining how a given pyroelectric material will behave in a PIRD.
Abstract: Pyroelectric infrared detectors (PIRDs) have a number of advantages over other IR sensors, including room-temperature operation, wide wavelength sensitivity, and low cost, leading to their use in many applications and a market expected to reach U.S.$68 million by 2025. Physical models that can be used to accurately predict the performances of PIRDs of different types are reviewed in detail. All polar dielectrics exhibit the pyroelectric effect, so there are many materials potentially available for use in PIRDs. Traditionally, a range of “figures-of-merit” (FoMs) are employed to aid the selection of the best material to use in a given application. These FoMs, and their utility in determining how a given pyroelectric material will behave in a PIRD, are reviewed in the light of the physical models and the availability of dielectric data, which cover the frequency ranges of greatest interest for PIRDs (0.1–100 Hz). The properties of several pyroelectric materials are reviewed, and models are derived for their dielectric properties as functions of frequency. It is concluded, first, that the availability of full-frequency dielectric data is highly desirable if accurate predictions of device performance are to be obtained from the models and that second, the FoMs have practical utility in only very limited circumstances. Thus, they must be used with considerable care and circumspection. The circumstances under which each FoM is likely to give a good prediction for utility are discussed. The properties of some recently researched pyroelectric materials, including lead-containing single crystals in the Pb[(Mg⅓Nb⅔)xTi1−x]O3 system and Na½Bi½TiO3–K½Bi½TiO3 based lead-free crystals and ceramics, are reviewed in the light of this, and their properties and potential for device applications compared with the industry-standard material, LiTaO3. It is concluded that while there is potential for significant device performance improvements by using improved materials, especially with the PMN-PT-based materials, factors such as temperature stability, uniformity, and ease-of-processing are at least as important as device performance in determining material utility. The properties reported for the new lead-free materials do not, as yet, promise a performance likely to compete with LiTaO3 for mm-scale detectors, a material that is both readily available and lead-free.

Journal ArticleDOI
TL;DR: In this paper , the authors reviewed the materials science of moiré superlattices with a focus on the structural properties of the interface and its structural-property relationships and gave an outlook on their applications in quantum electronics and optoelectronics.
Abstract: Moiré lattices formed in twisted and lattice-mismatched van der Waals heterostructures have emerged as a platform to engineer the novel electronic and excitonic states at the nanoscale. This Perspective reviews the materials science of moiré heterostructures with a focus on the structural properties of the interface and its structural–property relationships. We first review the studies of the atomic relaxation and domain structures in moiré superlattices and how these structural studies provide critical insights into understanding the behaviors of quantum-confined electrons and excitons. We discuss the general frameworks to manipulate moiré structures and how such control can be harnessed for engineering new phases of matter and simulating various quantum phenomena. Finally, we discuss routes toward large-scale moiré heterostructures and give an outlook on their applications in quantum electronics and optoelectronics. Special emphasis will be placed on the challenges and opportunities of the reliable fabrication and dynamical manipulation of moiré heterostructures.

Journal ArticleDOI
TL;DR: In this paper , an improved hybrid quantum-classic convolutional neural network (HQC-CNN) with fast training speed, lightweight, and high performance is proposed, which can effectively classify meningiomas, glioma, pituitary, and no tumor with a classification accuracy of 97.8%.
Abstract: The efficiency of quantum computing has recently been extended to machine learning, which has made a significant impact on quantum machine learning. The hybrid structure of quantum and classical ones has developed into the most successful application mode currently due to noisy intermediate scale quantum limitations. In this paper, an improved hybrid quantum-classic convolutional neural network (HQC-CNN) with fast training speed, lightweight, and high performance is proposed. Its convolution layer realizes feature mapping through parameterized quantum circuit, while other layers keep classic operation and finally complete the task of four classifications of brain tumors. The experiment in this paper is based on kaggle brain tumor magnetic resonance imaging public dataset. The final experimental results show that HQC-CNN can effectively classify meningioma, glioma, pituitary, and no tumor with a classification accuracy of 97.8%. When compared to numerous well-known landmark models, HQC-CNN has obvious advantages.

Journal ArticleDOI
TL;DR: In this paper , the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence), on the ablation depth, surface oxidation, topography, and ultimately on the secondary electron yield were investigated.
Abstract: Ultrashort-pulse laser processing of copper is performed in air to reduce the secondary electron yield (SEY). By UV (355 nm), green (532 nm), and IR (1064 nm) laser-light induced surface modification, this study investigates the influence of the most relevant experimental parameters, such as laser power, scanning speed, and scanning line distance (represented as accumulated fluence) on the ablation depth, surface oxidation, topography, and ultimately on the SEY. Increasing the accumulated laser fluence results in a gradual change from a Cu[Formula: see text]O to a CuO-dominated surface with deeper micrometer trenches, higher density of redeposited surface particles from the plasma phase, and a reduced SEY. While the surface modifications are less pronounced for IR radiation at low accumulated fluence ([Formula: see text] J/cm[Formula: see text]), analogous results are obtained for all wavelengths when reaching the nonlinear absorption regime, for which the SEY maximum converges to 0.7. Furthermore, independent of the extent of the structural transformations, an electron-induced surface conditioning at 250 eV allows a reduction of the SEY maximum below unity at doses of 5×10-4 C/mm[Formula: see text]. Consequently, optimization of processing parameters for application in particle accelerators can be obtained for a sufficiently low SEY at controlled ablation depth and surface particle density, which are factors that limit the surface impedance and the applicability of the material processing for ultrahigh vacuum systems. The relations between processing parameters and surface features will provide guidance in treating the surface of vacuum components, especially beam screens of selected magnets of the Large Hadron Collider or of future colliders.

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TL;DR: In this article , a deep neural network (DNN) with multiple hidden layers is constructed to surrogate the fluid model to investigate the discharge characteristics of atmospheric helium dielectric barrier discharges (DBDs) with very high computational efficiency.
Abstract: Numerical simulation is an essential way to investigate the discharge behaviors of atmospheric low-temperature plasmas (LTPs). In this study, a deep neural network (DNN) with multiple hidden layers is constructed to surrogate the fluid model to investigate the discharge characteristics of atmospheric helium dielectric barrier discharges (DBDs) with very high computational efficiency, working as an example to show the ability and validity of DNN to explore LTPs. The DNN is trained by the well-formed training datasets obtained from a verified fluid model, and a designed loss function coupled in the DNN program is continuously optimized to achieve a better prediction performance. The predicted data show that the essential discharge characteristics of atmospheric DBDs such as the discharge current waveforms, spatial profiles of charged particles, and electric field can be yielded by the well-trained DNN program with great accuracy only in several seconds, and the predicted evolutionary discharge trends are consistent with the previous simulations and experimental observations. Additionally, the constructed DNN shows good generalization performance for multiple input attributes, which indicates a great potential promise for vastly extending the range of discharge parameters. This study provides a useful paradigm for future explorations of machine learning-based methods in the field of atmospheric LTP simulation without high-cost calculation.

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TL;DR: In this paper , the terahertz (THz) detectors based on field effect transistor (FET) with the graphene channel (GC) and a floating metal gate (MG) separated from the GC by a black-phosphorus (b-P) or black-arsenic (bAs) barrier layer are evaluated.
Abstract: We evaluate the terahertz (THz) detectors based on field-effect transistor (FET) with the graphene channel (GC) and a floating metal gate (MG) separated from the GC by a black-phosphorus (b-P) or black-arsenic (b-As) barrier layer. The operation of these GC-FETs is associated with the heating of the two-dimensional electron gas in the GC by impinging THz radiation leading to thermionic emission of the hot electrons from the GC to the MG. This results in the variation of the floating gate potential, which affects the source–drain current. At the THz radiation frequencies close to the plasmonic resonance frequencies in the gated GC, the variation of the source–drain current and, hence, the detector responsivity can be resonantly large.

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TL;DR: An organic-inorganic hybrid electrochromic device was fabricated by combining the films of hydrothermally synthesized tungsten oxide (WO3) with electrodeposited polypyrrole as mentioned in this paper .
Abstract: An organic–inorganic hybrid electrochromic device was fabricated by combining the films of hydrothermally synthesized tungsten oxide (WO3) with electrodeposited polypyrrole. Before making a device, these deposited thin films were characterized using scanning electron microscopy, infrared spectroscopy, and Raman spectroscopy techniques. Thereafter, a solid-state organic–inorganic electrochromic device was fabricated, which shows reversible switching between coloration and bleaching states with a very small external bias voltage (±1 V) and excellent cyclic stability up to 500 s with a negligible amount of transmission loss. In situ electrochemical studies show that the device has enhanced switching speed (1.1/1.8 s), and optical contrast of more than 47% at the wavelength of 650 nm. Furthermore, the optimized electrochromic device displays enhanced coloration efficiency up to ∼304 cm2/C. All these results open a new door for increasing the performance of a single-layered device by combining it with complementary electrodes.