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Coding is an effective method of designing wideband metabsorber, but the resultant metabsorbers are usually associated with complicated shapes that hinders clear physics understanding of the wideband principle behind the scene. This study presents characteristic mode analysis (CMA) of two types of coding metabsorber composed of single-layer and bilateral resonators, respectively, generated by the genetic algorithm optimization methods. Compared with the conventional single-layer design, CMA results illustrate the wideband principle of the bilateral design introducing additional absorption modes. With a fractional bandwidth of 143.5%, the proposed bilateral metabsorber measures an absorption bandwidth of 5.9–35.9 GHz for 90% absorptance. CMA provides a low-threshold method to analyze the metabsorber with complicated resonators, thereby paving the way for the physical-oriented coding optimization improvement. [ABSTRACT FROM AUTHOR]

Hole concentration of 2-D hole gas (2DHG) on (110) diamond is higher than that on other faces, making it the best choice for power device application. Detailed analysis of atomic layer deposition (ALD) Al2O3/(110) C–H diamond interface structure is of vital importance. MOSFETs with thin (10 nm) and thick (100 nm) ALD Al2O3 layer were made in this study. The microstructure of Al2O3 on (110) C–H diamond was analyzed. Abrupt interface of ALD Al2O3/C–H diamond was observed through high resolution transmission electron microscope (HRTEM). Cascode structure using diamond MOSFETs and enhancement mode silicon MOSFET is fabricated and its high performance is confirmed. [ABSTRACT FROM AUTHOR]

Traditional monocular vision localization methods are usually suitable for short-range area and indoor relative positioning tasks. This paper presents MGG, a novel monocular global geolocation method for outdoor long-range targets. This method takes a single RGB image combined with necessary navigation parameters as input and outputs targets’ GPS information under the Global Navigation Satellite System (GNSS). In MGG, we first design a camera pose correction method via pixel mapping to correct the pose of the camera. Then, we use anchor-based methods to improve the detection ability for long-range targets with small image regions. Next, the local monocular vision model (LMVM) with a local structure coefficient is proposed to establish an accurate 2D-to-3D mapping relationship. Subsequently, a soft correspondence constraint (SCC) is presented to solve the local structure coefficient, which can weaken the coupling degree between detection and localization. Finally, targets can be geolocated through optimization theory-based methods and a series of coordinate transformations. Furthermore, we demonstrate the importance of focal length on solving the error explosion problem in locating long-range targets with monocular vision. Extensive experiments on the challenging KITTI dataset as well as applications in outdoor environments with targets located at a long range of up to 150 meters show the superiority of our method. [ABSTRACT FROM AUTHOR]

Decomposition work of Loran-C resultant waves propagating in the Earth-ionosphere waveguide is concentrated on in this article. Resultant waves of different Earth–ionosphere models are predicted by the FDTD method first. The inverse fast Fourier transform (IFFT) spectral-division technique combined with a filtering process is employed to estimate the delays of different wave-propagation modes in the resultant waves, whereas the amplitudes are solved with the least-square method. Finally, accurate field strengths and delays of different modes (ground waves and skywaves of diverse hops) are obtained, which are important for Loran-C receivers to optimize their performances. [ABSTRACT FROM AUTHOR]

A CdTe/PbTe heterojunction (HJ) yields two-dimensional electron gas (2DEG) with a high electron density and mobility. Ultrahigh-speed and room-temperature operating mid-infrared photodetectors are developed with the 2DEG. The photoresponse of the detectors originates from the intrinsic response of PbTe by virtue of the conduction-band and valence-band alignment of the HJ. The extremely short rise and decay photoresponse time demonstrate a major advantage of the 2DEG. At λ = 3.0 μm and a bias voltage of 100 mV, the responsivity and detectivity reach 0.94 A/W and 2 × 1010 Jones, respectively. The excellent performance of the detectors renders promising applications in novel mid-infrared frequency detection systems. [ABSTRACT FROM AUTHOR]

High-frame-rate 3-D ultrasound imaging technology combined with super-resolution processing method can visualize 3-D microvascular structures by overcoming the diffraction-limited resolution in every spatial direction. However, 3-D super-resolution ultrasound imaging using a full 2-D array requires a system with a large number of independent channels, the design of which might be impractical due to the high cost, complexity, and volume of data produced. In this study, a 2-D sparse array was designed and fabricated with 512 elements chosen from a density-tapered 2-D spiral layout. High-frame-rate volumetric imaging was performed using two synchronized ULA-OP 256 research scanners. Volumetric images were constructed by coherently compounding nine-angle plane waves acquired at a pulse repetition frequency of 4500 Hz. Localization-based 3-D super-resolution images of two touching subwavelength tubes were generated from 6000 volumes acquired in 12 s. Finally, this work demonstrates the feasibility of 3-D super-resolution imaging and super-resolved velocity mapping using a customized 2-D sparse array transducer. [ABSTRACT FROM AUTHOR]

Mode coupling vibration of a multilayered ZnO thin film bulk acoustic wave resonator (FBAR) with its c-axis along the wave propagation direction operating at the fundamental thickness-shear (TSh) mode is studied in this paper. The accurate dispersion curve from 3-D piezoelectric theory indicates that the operating TSh mode could couple to the flexural mode, which influences the performance of a sensing resonator and needs to be eliminated through the so-called frequency spectrum analysis. Frequency spectra of coupling vibration in this FBAR can be obtained by substituting the displacement solutions consisting of the mode branches in the dispersion curve into several weak boundary conditions, which gives the integral boundary conditions across the plate thickness at the side edge of FBARs. The results show that the content of mode couplings to spurious modes depends on the plate length/thickness ratios. The character of desirable values of plate aspect ratios under which the operating TSh mode dominates among all modes is stated specifically, which provides fundamental guidance to the design of structural parameters of FBARs. [ABSTRACT FROM AUTHOR]

A number of acoustic super-resolution techniques have recently been developed to visualize microvascular structure and flow beyond the diffraction limit. A crucial aspect of all ultrasound (US) super-resolution (SR) methods using single microbubble localization is time-efficient detection of individual bubble signals. Due to the need for bubbles to circulate through the vasculature during acquisition, slow flows associated with the microcirculation limit the minimum acquisition time needed to obtain adequate spatial information. Here, a model is developed to investigate the combined effects of imaging parameters, bubble signal density, and vascular flow on SR image acquisition time. We find that the estimated minimum time needed for SR increases for slower blood velocities and greater resolution improvement. To improve SR from a resolution of $\lambda $ /10 to $\lambda $ /20 while imaging the microvasculature structure modeled here, the estimated minimum acquisition time increases by a factor of 14. The maximum useful imaging frame rate to provide new spatial information in each image is set by the bubble velocity at low blood flows (<150 mm/s for a depth of 5 cm) and by the acoustic wave velocity at higher bubble velocities. Furthermore, the image acquisition procedure, transmit frequency, localization precision, and desired super-resolved image contrast together determine the optimal acquisition time achievable for fixed flow velocity. Exploring the effects of both system parameters and details of the target vasculature can allow a better choice of acquisition settings and provide improved understanding of the completeness of SR information. [ABSTRACT FROM AUTHOR]

A lossy-mode resonance (LMR) refractive index (RI) sensor with a few layer transition metal dichalcogenides (TMDs) is proposed. Contrasting with traditional surface plasmon resonance (SPR) sensors, the LMR sensor can support both transverse magnetic (TM) and transverse electric (TE) polarizations, while the traditional SPR sensors can only operate for TM polarization. Through theoretical calculation and simulation, we find that the proposed LMR sensor can realize higher sensitive and narrower full width half maximum (FWHM), and the most attractive character is figure-of-merit (FOM) with 1582 RIU−1, which is a significant improvement compared to the existing LMR sensors and is even 40% higher than the best graphene-based SPR sensors. We trust that the proposed LMR sensor can be extensively applied in optical sensing technology, chemical biomolecular detection, and so on. [ABSTRACT FROM AUTHOR]

Localization-based ultrasound super-resolution imaging using microbubble contrast agents and phase-change nanodroplets has been developed to visualize microvascular structures beyond the diffraction limit. However, the long data acquisition time makes the clinical translation more challenging. In this study, fast acoustic wave sparsely activated localization microscopy (fast-AWSALM) was developed to achieve super-resolved frames with subsecond temporal resolution, by using low-boiling-point octafluoropropane nanodroplets and high frame rate plane waves for activation, destruction, as well as imaging. Fast-AWSALM was demonstrated on an in vitro microvascular phantom to super-resolve structures that could not be resolved by conventional B-mode imaging. The effects of the temperature and mechanical index on fast-AWSALM were investigated. The experimental results show that subwavelength microstructures as small as $190~\mu \text{m}$ were resolvable in 200 ms with plane-wave transmission at a center frequency of 3.5 MHz and a pulse repetition frequency of 5000 Hz. This is about a 3.5-fold reduction in point spread function full-width-half-maximum compared to that measured in the conventional B-mode, and two orders of magnitude faster than the recently reported AWSALM under a nonflow/very slow flow situations and other localization-based methods. Just as in AWSALM, fast-AWSALM does not require flow, as is required by current microbubble-based ultrasound super-resolution techniques. In conclusion, this study shows the promise of fast-AWSALM, a super-resolution ultrasound technique using nanodroplets, which can generate super-resolution images in milliseconds and does not require flow. [ABSTRACT FROM AUTHOR]

Ultrasound super-resolution techniques use the response of microbubble (MB) contrast agents to visualize the microvasculature. Techniques that localize isolated bubble signals first require detection algorithms to separate the MB and tissue responses. This work explores the three main MB detection techniques for super-resolution of microvasculature. Pulse inversion (PI), differential imaging (DI), and singular value decomposition (SVD) filtering were compared in terms of the localization accuracy, precision, and contrast-to-tissue ratio. MB responses were simulated based on the properties of Sonovue and using the Marmottant model. Nonlinear propagation through tissue was modeled using the k-Wave software package. For the parameters studied, the results show that PI is most appropriate for low frequency applications, but also most dependent on transducer bandwidth. SVD is preferable for high frequency acquisition where localization precision on the order of a few microns is possible. PI is largely independent of flow direction and speed compared to SVD and DI, so is appropriate for visualizing the slowest flows and tortuous vasculature. SVD is unsuitable for stationary MBs and can introduce a localization error on the order of hundreds of microns over the speed range 0–2 mm/s and flow directions from lateral (parallel to probe) to axial (perpendicular to probe). DI is only suitable for flow rates >0.5 mm/s or as flow becomes more axial. Overall, this study develops an MB and tissue nonlinear simulation platform to improve understanding of how different MB detection techniques can impact the super-resolution process and explores some of the factors influencing the suitability of each. [ABSTRACT FROM AUTHOR]

Surface plasmon polaritons (SPPs) with noble metals lose the capacity to confine the optical field in the long wavelength region, while surface phonon polaritons (SPhPs) in polar dielectrics show greater ability to achieve high local field, sub-diffraction confinement, and low optical losses in the mid-IR to THz spectral ranges. We propose a hybrid structure based on SPhPs mode with CsI and SPPs mode with graphene in THz spectral ranges. The characteristics of the coupling of these two modes have been analyzed and strong coupling has been confirmed theoretically. The results are applied to an intensity-interrogated terahertz sensor; the highest imaging sensitivity as high as 954 RIU−1 and a large figure of merit of 74 740 RIU−1 have been demonstrated. The results could find potential applications in gas detection in the THz band. [ABSTRACT FROM AUTHOR]

Graphene has emerged as a potential plasmonic material for the development of optical devices in terahertz (THz) frequency in the past few years. It is shown that the double-layer graphene can support surface plasmon polaritons (SPPs), which is similar to the long-range SPP of a thin metal layer. By coupling the SPPs of the double-layer graphene with the dielectric planar waveguide (PWG) modes, a THz biochemical sensor is proposed in this paper. Strong coupling between the two modes will occur in the hybrid structure due to the strong resonances, and the sensitivity of the sensor is greatly improved due to the high quality factors of both PWG and double-layer graphene SPPs modes. The proposed sensor has achieved the state-of-art sensitivity of 292 RIU−1, which is nearly doubled compared to the sensitivity of the double-layer graphene SPPs sensor (140 RIU−1) and almost nine times of a conventional graphene SPPs sensor (33 RIU−1). We believe that the proposed biochemical sensor can be used well in THz chemical and biological detection. [ABSTRACT FROM AUTHOR]

Bloch surface wave (BSW) is a surface state excited within the truncate defect layer at the surface of a dielectric 1-D photonic crystal (1DPC), which has been suggested as an attractive alternative to surface plasmon resonance (SPR) in chemical and biological sensors. In this paper, we propose an intensity-sensitive BSW sensor based on the truncate 1DPC with graphene. By optimizing the thickness of the defect layer and the layer number of graphene, the maximum intensity sensitivity of biosensor can surpass 3.5\times 10^4 /RIU, which is greater than that for the conventional BSW or SPR sensors. With such excellent and interesting performance, we believe that the structure can be useful for many important applications in the field of chemical and biological sensors in the future. [ABSTRACT FROM PUBLISHER]

We fabricate Si-based blocked impurity band (BIB) terahertz detectors using p-dopant through a standard silicon device fabrication technology. Comparison of photoresponse of the detectors under alternate operating mode and conventional operation mode (COM) is made. We demonstrate that the detectors can achieve high responsivity through positive bias on the active layer side, namely, alternate operating mode (AOM). The response of the detectors terminates at wavelength of 35~\mu \textm (8.57 THz) under AOM; on the contrary, the response is cutoff at 31~\mu \textm (9.68 THz) with a positive bias on the blocking layer, namely, COM. The relative responsivity at 0.6 V under AOM is 2.3 times of that under COM. By developing an energy band model, we find that the response difference under the two modes originates from the change of band offsets. The electric field in the blocking layer under AOM is much smaller than COM and most of the voltage drops in the active layer under AOM, which leads to the bigger multiplication of the photon-generated carriers than COM. By analyzing the origination of the dark current under the AOM, a method to improve the performance of BIB detectors under AOM is proposed. [ABSTRACT FROM AUTHOR]

Textual documents created and distributed on the Internet are ever changing in various forms. Most of existing works are devoted to topic modeling and the evolution of individual topics, while sequential relations of topics in successive documents published by a specific user are ignored. In this paper, in order to characterize and detect personalized and abnormal behaviors of Internet users, we propose Sequential Topic Patterns (STPs) and formulate the problem of mining User-aware Rare Sequential Topic Patterns (URSTPs) in document streams on the Internet. They are rare on the whole but relatively frequent for specific users, so can be applied in many real-life scenarios, such as real-time monitoring on abnormal user behaviors. We present a group of algorithms to solve this innovative mining problem through three phases: preprocessing to extract probabilistic topics and identify sessions for different users, generating all the STP candidates with (expected) support values for each user by pattern-growth, and selecting URSTPs by making user-aware rarity analysis on derived STPs. Experiments on both real (Twitter) and synthetic datasets show that our approach can indeed discover special users and interpretable URSTPs effectively and efficiently, which significantly reflect users’ characteristics. [ABSTRACT FROM PUBLISHER]