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Handwritten Text Recognition has achieved an impressive performance in public benchmarks. However, due to the high inter- and intra-class variability between handwriting styles, such recognizers need to be trained using huge volumes of manually labeled training data. To alleviate this labor-consuming problem, synthetic data produced with TrueType fonts has been often used in the training loop to gain volume and augment the handwriting style variability. However, there is a significant style bias between synthetic and real data which hinders the improvement of recognition performance. To deal with such limitations, we propose a generative method for handwritten text-line images, which is conditioned on both visual appearance and textual content. Our method is able to produce long text-line samples with diverse handwriting styles. Once properly trained, our method can also be adapted to new target data by only accessing unlabeled text-line images to mimic handwritten styles and produce images with any textual content. Extensive experiments have been done on making use of the generated samples to boost Handwritten Text Recognition performance. Both qualitative and quantitative results demonstrate that the proposed approach outperforms the current state of the art. [ABSTRACT FROM AUTHOR]

Shear horizontal (SH) waves are commonly generated by periodic permanent magnet (PPM) electromagnetic acoustic transducers (EMATs) in metallic media. Conventional PPM EMATs generate ultrasonic waves, which simultaneously propagate both forward and backward. This can be an undesirable characteristic, since the backward wave can be eventually reflected, reaching the receiver transducer where it can mix with the signal of interest. This limitation can be overcome using two side-shifted PPM arrays and racetracks coils to generate SH waves in a single direction. That design relies on the EMAT wavefront diffraction to produce constructive and destructive interference, but produces unwanted backward traveling sidelobes. Here, we present a different design, which uses a conventional PPM array and a dual linear-coil array. The concept was numerically simulated, the main design parameters were assessed and the unidirectional EMAT was experimentally evaluated on an aluminum plate, generating the SH0-guided wave mode nominally in a single direction. The amplitude ratio of the generated waves at the enhanced to the weakened side is above 20 dB. Since the wavefronts from the two sources are perfectly aligned, no obvious backward sidelobes are present in the acoustic field, which can significantly reduce the probability of false alarm of an EMAT detection system. [ABSTRACT FROM AUTHOR]

Periodic permanent magnet (PPM) array electromagnetic acoustic transducers (EMATs) can efficiently generate and receive shear horizontal (SH) ultrasonic waves. Conventional PPM EMATs typically generate waves which simultaneously propagate both forward and backward. This can complicate the received signals and make it difficult to locate the position of scatterers. Unidirectional generation of ultrasounds can be achieved if two ultrasonic sources are separated by a predefined distance and are excited with the proper delay. Relying on this principle, EMATs have been previously designed aiming to generate other modes of ultrasonic waves. The main challenge when extending this conception to an SH-wave EMAT is how to restrict each coil to its specific magnet array. We present the concept of a unidirectional SH EMAT consisting of two racetrack coils and two interlaced PPM arrays, that are slightly shifted sideways, in such a way that the generated wavefronts still properly interfere. The design was fabricated and experimentally evaluated in an aluminum plate generating the SH0 guided wave mode. The forward to backward generated wave ratio is above 20 dB and well agrees with finite element simulations. [ABSTRACT FROM AUTHOR]

In this article, a class of wideband transmit arrays (TAs), composed of cascaded anisotropic impedance surfaces (AISs), for circularly polarized (CP) multibeam generation from a single feed horn are reported. The dispersionless phase compensation is achieved by the Berry phase (BP) via imposing a spatially dependent rotation angle on the TA unit cells. A homogenized model for the BPTA unit cell is proposed and utilized for obtaining a wideband response by tailoring the dispersive properties of the AIS layers. Two modeling methods, an analytical vectorial field analysis and a full-wave strategy incorporating the homogenized model, were employed to efficiently evaluate the performance of the BPTAs. In order to validate the proposed unit cell and the modeling methodologies, a Q-band single-beam BPTA is demonstrated, which achieves a peak gain of 30.2 dBi and a 1 dB bandwidth of 11.1% within which the axial ratio is smaller than 2 dB. Furthermore, by employing the intersection approach for pattern synthesis, several Q-band BPTAs supporting multiple concurrent symmetric/asymmetric CP pencil beams and circular-shaped flat-top beams are designed. A BPTA prototype for producing quad CP pencil beams with unequal gain values was fabricated and characterized, yielding good performance with an overall operational bandwidth of about 11%. The proposed BPTAs are promising candidates for point-to-multipoint communication and point-to-multiregional coverage in wideband millimeter-wave communications for wireless and satellite applications. [ABSTRACT FROM AUTHOR]

A nonconforming mixed-element (tetrahedral/hexahedral) discontinuous Galerkin time-domain (DGTD) method with a perfectly matched layer (PML) absorber is proposed to analyze the electromagnetic scattering from doubly periodic structures. An efficient auxiliary differential equation (ADE)-based PML implementation is presented with transformed field variables introduced by the time-domain periodic boundary conditions (PBCs). The proposed PML implementation performs well in absorbing the waves with high-order Floquet modes. Additionally, a mixed-order DGTD method is introduced to improve the proposed PML implementation’s long-term stability and reduce the total computational cost. Based on the mixed tetrahedral and hexahedral grids, the nonconforming DGTD method can provide accurate field distribution near complex scattering geometries while simultaneously reducing the degrees of freedom (DoF) in the rest of the computational domain, including the open space and PML regions. Finally, electromagnetic simulations are presented to demonstrate the applicability, accuracy, and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, we first propose a very interesting and practical problem, pattern matching in a distributed mobile environment. Pattern matching is a well-known problem and extensive research has been conducted for performing effective and efficient search. However, previous proposed approaches assume that data are centrally stored, which is not the case in a mobile environment (e.g., mobile phone networks), where one person's pattern could be separately stored in a number of different stations, and such a local pattern is incomplete compared with the global pattern. A simple solution to pattern matching over a mobile environment is to collect all the data distributed in base stations to a data center and conduct pattern matching at the data center afterwards. Clearly, such a simple solution will raise huge amount of communication traffic, which could cause the communication bottleneck brought by the limited wireless bandwidth to be even worse. Therefore, a communication efficient and search effective solution is necessary. In our work, we present a novel solution which is based on our well-designed weighted bloom filter (WBF), called, D istributed Incomplete pattern matching ( DI-matching), to find target patterns over a distributed mobile environment. Specifically, to save communication cost and ensure pattern matching in distributed incomplete patterns, we use WBF to encode a query pattern and disseminate the encoded data to each base station. Each base station conducts a local pattern search according to the received WBF. Only qualified IDs and corresponding weights in each base station are sent to the data center for aggregation and verification. Through non-trivial theoretical analysis and extensive empirical experiments on a real city-scale mobile networks data set, we demonstrate the effectiveness and efficiency of our proposed solutions. [ABSTRACT FROM PUBLISHER]

RFID tag identification is a crucial problem in UHF RFID systems. Traditional tag identification algorithms can be classified into two categories, ALOHA-based and tree-based. Both of them are inefficient due to the incidental high coordination cost. In this paper, we bring CSMA into UHF RFID systems to enhance tag read rate by reducing coordination cost. However, it is not straightforward due to the simple hardware design of passive RFID tags, which is unable to sense the transmissions or collisions of other tags. To tackle this challenge, we propose receiver-based CSMA (RCSMA) in this paper. In RCSMA, the reader notifies the tags channel condition. According to different sensing results of reader's notifications, the tags take corresponding actions, e.g., random back off. RCSMA does not require special RFID tag hardware design. An absorbing Markov chain model is presented to analyze the performance of RCSMA and shown to be consistent with the simulation results. Compared with optimized ALOHA-based algorithms and optimized tree-based algorithms, RCSMA can enhance the tag read rate by 30-70 percent under different reader and tag data rates. [ABSTRACT FROM AUTHOR]

RFID has been gaining popularity due to its variety of applications, such as inventory control and localization. One important issue in RFID system is tag identification. In RFID systems, the tag randomly selects a slot to send a Random Number (RN) packet to contend for identification. Collision happens when multiple tags select the same slot, which makes the RN packet undecodable and thus reduces the channel utilization. In this paper, we redesign the RN pattern to make the collided RNs decodable. By leveraging the collision slots, the system performance can be dramatically enhanced. This novel scheme is called DDC, which is able to directly decode the collisions without exact knowledge of collided RNs. In the DDC scheme, we modify the RN generator in RFID tag and add a collision decoding scheme for RFID reader. We implement DDC in GNU Radio and USRP2 based testbed to verify its feasibility. Both theoretical analysis and testbed experiment show that DDC achieves 40 percent tag read rate gain compared with traditional RFID protocol. [ABSTRACT FROM PUBLISHER]

The elastic waves generated by traditional meander- line coil electromagnetic acoustic transducers (EMATs) propagate in two directions, overlapping the echo signals from defects with the same distances, and the defect echo signal is hard to distinguish from the edge-reflected signal when the EMATs are near the edge of a specimen. In this paper, a unidirectional EMAT with two meander-line coils is proposed. A finite element model is used to simulate the directivity of the Rayleigh and shear vertical waves generated by these EMATs. Six transducers are fabricated using the printed circuit technique. The unidirectional Rayleigh wave and shear vertical wave are tested, and the results agree well with the simulation. [ABSTRACT FROM AUTHOR]

Electromagnetic ultrasonic (EMU) Lamb waves excited by electromagnetic acoustic transducers (EMATs) possess many advantages in NDT. However, their characteristic multi-modes and dispersion are disadvantageous for inspection and restrict further improvements in their real applications. By deducing the excitation equation of EMU Lamb waves, the primary design parameters of EMATs and the characteristic equation of Lamb waves are combined, and excitation curves based on the excitation equation are plotted to aid the design of EMATs. The excitation characteristic of EMU Lamb waves on different thickness of plates is analyzed according to the excitation curves. The influence of multi-modes of EMU Lamb waves is minimized by choosing reasonable operating points and operating zones to excite a single-mode Lamb wave or multi-mode Lamb waves with identical or approximate propagation velocities. The influence of dispersion is minimized by searching corresponding points whose slope of group velocity tends to zero. The validity of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]