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Modeling in computer vision has long been dominated by convolutional neural networks (CNNs). Recently, in light of the excellent performance of self-attention mechanism in the language field, transformers tailored for visual data have drawn significant attention and triumphed over CNNs in various vision tasks. These vision transformers heavily rely on large-scale pre-training to achieve competitive accuracy, which not only hinders the freedom of architectural design in downstream tasks like object detection, but also causes learning bias and domain mismatch in the fine-tuning stages. To this end, we aim to get rid of the "pre-train and fine-tune" paradigm of vision transformer and train transformer based object detector from scratch. Some earlier works in the CNNs era have successfully trained CNNs based detectors without pre-training, unfortunately, their findings do not generalize well when the backbone is switched from CNNs to a vision transformer. Instead of proposing a specific vision transformer based detector, in this work, our goal is to reveal the insights of training vision transformer based detectors from scratch. In particular, we expect those insights to help other researchers and practitioners, and inspire more interesting research in other fields, such as remote sensing, visual-linguistic pre-training, etc. One of the key findings is that both architectural changes and more epochs play critical roles in training vision transformer based detectors from scratch. Experiments on the MS COCO dataset demonstrate that vision transformer based detectors trained from scratch can also achieve similar performance to their counterparts with ImageNet pre-training. [ABSTRACT FROM AUTHOR]

Rapeseed is a crucial oil crop globally, and in recent years, abiotic stress has increasingly affected its growth, development, yield, and quality. Salt stress is a significant abiotic factor that restricts crop production. The EPF gene family is vital in managing salt stress by controlling stomatal development and opening, which reduces water loss and increases plant salt tolerance. To explore the features of the EPF gene family in Brassica napus and their expression under salt stress, this study utilized Arabidopsis EPF protein sequences as seed sequences, including their PF17181 and PF16851 domains. A total of 27 members of the EPF gene family were detected within the rapeseed genome. The study examined the physicochemical properties, gene structure, phylogenetic relationships, and collinearity of BnEPFs. Through transcriptomes, we employed the qPCR method to determine the relative expression levels of BnEPF genes potentially associated with rapeseed stress resistance under both non-salt and salt stress conditions. Subsequently, we assessed their influence on rapeseed plants subjected to salt stress. During salt stress conditions, all BnEPF genes displayed a downregulation trend, indicating their potential impact on stomatal development and signal transduction pathways, consequently improving rapeseed's resistance to salt stress. The study findings establish a basis for exploring the roles of BnEPFs and offer candidate genes for breeding stress-resistant varieties and enhancing the yield in rapeseed. [ABSTRACT FROM AUTHOR]

Numerous advanced and lightweight signal processing methods have been presented for single-channel speech enhancement (SE). It is imperative to carefully explore how to efficiently combine, integrate, and balance these methods. This paper proposes a more effective and less resource-intensive SE system, focused on the integration and adaptation of several approaches, especially the temporal cepstrum smoothing (TCS). First, a more robust fundamental frequency estimator is employed within TCS, mitigating the performance limitations caused by the inaccuracy of the original estimator. Additionally, a harmonic enhancement mechanism is introduced, effectively recovering the weak harmonic components. By incorporation of the modified TCS in the a posteriori speech presence probability estimation, the unbiased minimum mean square error noise power spectral density estimator can be refined. The modified TCS is also utilized for the a priori signal-to-noise ratio estimation. Moreover, this paper enhances the log-spectral amplitude estimator by applying both super-Gaussian speech priors and speech presence uncertainty for further improvement. Experimental evaluations demonstrate that the proposed method yields an improvement in speech quality while maintaining modest computational and storage requirements. Furthermore, the proposed system exhibits comparable performance to several baseline systems based on lightweight deep neural networks. [ABSTRACT FROM AUTHOR]

Background: Immunogenic cell death (ICD) is a process in which dying cells stimulate an immune response. It is a regulated form of cell death that can remodel the tumor microenvironment (TME) and activate the immune system, making immunotherapy more effective. This work was designed to identify prognostic gene features associated with ICD in cervical cancer (CC). Methods: Based on CC datasets and a set of ICD‐related genes obtained from public databases, we first filtered out ICD‐related genes unrelated to CC survival using univariate analysis. Subsequently, LASSO regression and multivariate Cox regression analysis were employed to develop prognostic feature genes based on ICD. For the construction and validation of the model, eight genes (CXCL1, IL1B, TNF, YKT6, PDIA3, ROCK1, CXCR3, and CLEC9A) were chosen. A nomogram was created to forecast the prognosis of CC individuals, and Kaplan–Meier curves were utilized to explore the survival disparities among different risk groups of CC individuals. Results: ssGSEA analysis was employed to investigate immune differences between two risk groups, revealing that the low‐risk group exhibited elevated levels of immune cell infiltration, enhanced activation of immune function, and a higher immunophenoscore compared with the other group, which highlighted the relevance of ICD to TME. Conclusion: We constructed a prognostic model based on genetic biomarkers of ICD for prognostic prediction of CC patients. Our model demonstrated excellent discriminative and calibration capabilities, providing a valuable tool for prognostic prediction and assessing the potential efficacy of immunotherapy in CC. [ABSTRACT FROM AUTHOR]

XTH genes are key genes that regulate the hydrolysis and recombination of XG components and plays role in the structure and composition of plant cell walls. Therefore, clarifying the changes that occur in XTHs during plant defense against abiotic stresses is informative for the study of the plant stress regulatory mechanism mediated by plant cell wall signals. XTH proteins in Arabidopsis thaliana was selected as the seed sequences in combination with its protein structural domains, 80 members of the BnXTH gene family were jointly identified from the whole genome of the Brassica napus ZS11, and analyzed for their encoded protein physicochemical properties, phylogenetic relationships, covariance relationships, and interoperating miRNAs. Based on the transcriptome data, the expression patterns of BnXTHs were analyzed in response to different abiotic stress treatments. The relative expression levels of some BnXTH genes under Al, alkali, salt, and drought treatments after 0, 6, 12 and 24 h were analyzed by using qRT-PCR to explore their roles in abiotic stress tolerance in B. napus. BnXTHs showed different expression patterns in response to different abiotic stress signals, indicating that the response mechanisms of oilseed rape against different abiotic stresses are also different. This paper provides a theoretical basis for clarifying the function and molecular genetic mechanism of the BnXTH gene family in abiotic stress tolerance in rapeseed. [ABSTRACT FROM AUTHOR]

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A falling film flow test facility is designed and constructed to investigate the effect of tube spacing and tube material on the falling film transition mode. In the experiment, water is used as the falling film working liquid, copper and fluoroplastic are used as the tube materials, the tube spacing is set to 14 mm and 20 mm, and the diameter of the test tube is 20 mm. The analysis of the four observed transition modes and Reynolds number (Re) shows that the column modes in droplet to droplet-column and droplet-column to column transition modes are stretched, and the sheet modes in the column to column-sheet transition modes have gaps after the tube spacing increases. The Re of the two tube spacings is similar for droplet to droplet-column (D-DC) and droplet-column to column (DC-C) transition modes. For column to column-sheet (C-CS) and column-sheet to sheet (CS-S) modes, the Re of the tube spacing of 20 mm is higher than that of the tube spacing of 14 mm. After the copper tube is replaced with a fluoroplastic tube, the falling film flow rate distribution is uneven, and the columnar mode in the column to column-sheet (C-CS) transition mode and the partial sheet mode in the column-sheet to sheet (CS-S) transition mode deviated from one side of the fluoroplastic tube surface. For D-DC and DC-C transition modes, the Re of copper tube and fluoroplastic tube is similar. For C-CS and CS-S transition modes, the Re of fluoroplastic tube is higher than that of the copper tube. In order to facilitate the subsequent study of tube spacing and tube materials, a new prediction model of transition mode is established, and the literature data is considered to introduce the prediction model to enhance the application range. The Re prediction deviations of the model for the four transition modes are within ± 20%. This work provides a new research idea for the subsequent study of falling film flow with different tube materials and tube spacing. [ABSTRACT FROM AUTHOR]

Intuitive and comfortable physical human–robot interaction (pHRI) can be realized by changing impedance/admittance parameters corresponding to human interaction. However, this dynamic adjustment may result in drastically changed system dynamics, which usually give rise to system instability. We introduce a power envelope regulation strategy designed to constrain the variability of admittance parameters, thereby ensuring system passivity and mitigating the risk of instability. Then, sliding mode control (SMC) is employed to yield stable and robust performance. A new sliding surface is proposed based on feedback linearization, which shows improved tracking performance and stability compared to a conventional sliding surface. The effectiveness of the proposed sliding surface and associated control is theoretically validated. Notably, our modified sliding surface works universally, regardless of the order of the desired admittance equation. The trade-off between system chattering and robustness is effectively managed using a variable–boundary approach, which dynamically adjusts system constraints to optimize performance. In addition, a control algorithm combining acceleration feedback and sliding mode is proposed, showing improved robustness and tracking accuracy performance compared with applying the proposed SMC algorithm exclusively. The efficacy of these methodologies is substantiated through numerical simulations and empirical experiments. [ABSTRACT FROM AUTHOR]

Concentric circular microphone arrays have been used in a wide range of applications, such as teleconferencing systems and smarthome devices for speech signal acquisition. Such arrays are generally designed with omnidirectional sensors, and the associated beamformers are fully steerable but only in the sensors' plane. If operated in the three-dimensional space, the performance of those arrays would suffer from significant degradation if the sound sources are out of the sensors' plane, which happens due to the incomplete spatial sampling of the sound field. This paper addresses this issue by presenting a new method to design concentric circular microphone arrays using both omnidirectional microphones and bidirectional microphones (directional sensors with dipole-shaped patterns). Such arrays are referred to as superarrays as they are able to achieve higher array gain as compared to their traditional counterparts with omnidirectional sensors. It is shown that, with the use of bidirectional microphones, the spatial harmonic components that are missing in the traditional arrays are compensated back. A beamforming method is then presented to design beamformers that can achieve frequency-invariant beampatterns with high directivity and are fully steerable in the three-dimensional space. Simulations and real experiments validate the effectiveness and good properties of the presented method. [ABSTRACT FROM AUTHOR]

Gibberellin (GAs) plays an important regulatory role in the development and growth of pineapple (Ananas comosus (L.) Merr.). Bioinformatics was used to confirm the differential expression of GA2 gibberellin oxidase gene AcGA2oxs in the pineapple genome, which laid the foundation for exploring its role in pineapple. In this study, 42 GA2ox genes (AcGA2oxs) were identified in the pineapple genome, named from AcGA2ox1 to AcGA2ox42, and divided into four groups according to phylogenetic analysis. We also analyzed the gene structure, conserved motifs and chromosome localization of AcGA2oxs. AcGA2oxs within the same group had similar gene structure and motifs composition. Collinear analysis and cis-element analysis provided the basis for understanding the evolution and function of GA2ox genes in pineapple. In addition, we selected different tissue parts to analyze the expression profile of AcGA2oxs, and the results show that 41 genes were expressed, except for AcGA2ox18. AcGA2ox18 may not be expressed in these sites or may be pseudogenes. qRT-PCR (real-time fluorescence quantitative PCR) was used to detect the relative expression levels of the GA2ox gene family under different concentrations of GA3 treatment, and it was found that AcGA2ox gene expression was upregulated in different degrees under GA3 treatment. These results provide useful information for further study on the evolution and function of the GA2ox family in pineapple. [ABSTRACT FROM AUTHOR]

BnIPT gene family members in Brassica napus and analyzing their expression under different exogenous hormones and abiotic stress treatments to provide a theoretical basis for clarifying their functions and molecular genetic mechanisms in nitrogen deficiency stress tolerance of B. napus. Using the Arabidopsis IPT protein as the seed sequence, combined with the IPT protein domain PF01715, 26 members of the BnIPT gene family were identified from the whole genome of the rape variety ZS11. Additionally, the physicochemical properties and structures, phylogenetic relationships, synteny relationships, protein–protein interaction network, and gene ontology enrichment were analyzed. Based on transcriptome data, the expression patterns of the BnIPT gene under different exogenous hormone and abiotic stress treatments were analyzed. We used the qPCR method to identify the relative expression level of BnIPT genes that may be related to the stress resistance of rapeseed in transcriptome analysis under normal nitrogen (N: 6 mmol·L−1) and nitrogen deficiency (N: 0) conditions and analyzed its effect on rapeseed under nitrogen deficiency stress role in tolerance. In response to nitrogen deficiency signals, the BnIPT gene showed a trend of up-regulation in shoots and down-regulation in roots, indicating that it may affect the process of nitrogen transport and redistribution to enhance the stress resistance of rapeseed to respond to the nitrogen deficiency stress. This study provides a theoretical basis for clarifying the function and molecular genetic mechanism of the BnIPT gene family in nitrogen deficiency stress tolerance in rape. [ABSTRACT FROM AUTHOR]

Polystyrene (PS) is generally considered as a passive optical material that is transparent to light with wavelengths longer than 300 nm. In practice, PS micro- and nanospheres with uniform sizes are usually used to build photonic crystals based on self-assembly mechanism. Here, we demonstrate experimentally that PS microspheres supporting whispery gallery modes can be transformed into multimode light sources by laser irradiation. We show that a PS microsphere placed on a silica substrate can be lighted up when it is consecutively irradiated by using a 488-nm continuous wave laser beam with a pumping power above a threshold. Broadband luminescence emitted from the PS microsphere increases rapidly to a maximum value and decreases gradually with increasing irradiation time, implying the generation and degradation of a certain luminescent material upon laser irradiation. However, the PS microsphere is found to be damaged by high temperature based on morphology examination. By replacing the silica substrate with a thin silver film, the threshold laser power for lighting up a PS microsphere is dramatically reduced. More importantly, we can see enhanced luminescence intensities from the whispery gallery modes supported by the PS microsphere, which becomes an efficient multimode light source. Interestingly, the threshold laser power can be further lowered by inserting a molybdenum disulfide monolayer in between the PS microsphere and the silver film. As a result, the PS microsphere remains nearly unchanged except the formation of the luminescence material. Our findings open a new horizon for the interaction of polymer with laser light by exploiting the optical resonances supported by micro- and nanoparticles and pave the way for constructing photonic devices based on laser-induced luminescent materials in polymers. [ABSTRACT FROM AUTHOR]

Strong light–matter interaction has attracted great interest due to its potential applications in photonic and plasmonic devices. So far, many studies focus on micro‐ and nanocavities with three‐dimensional confinement of light. Here, we investigate the coupling between the surface waves supported by a dielectric‐metal heterostructure and the excitons in a two‐dimensional material. It is revealed that the transverse‐electric (TE) polarized waves excited in the dielectric‐metal heterostructure possess significantly enhanced in‐plane electric field on the surface of the dielectric layer. This unique property makes it possible to realize strong photon–exciton coupling with the excitons in a two‐dimensional material. By using a tungsten disulfide (WS2)/silicon nitride (Si3N4)/silver (Ag) heterostructure, we demonstrate the strong coupling of the TE polarized waves with the two excitons (both A and B excitons) in the WS2 monolayer, creating TE polarized polaritons propagating in the heterostructure. The strong photon–exciton coupling is revealed in the angle‐resolved reflection or scattering spectra with a Rabi splitting larger than the average damping rate of the TE polarized wave and the exciton. Our findings open new horizons for manipulating light–matter interaction in two‐dimensional nanostructures and indicate the potential applications of such propagating polaritons in photonic and plasmonic devices. [ABSTRACT FROM AUTHOR]

Accurate and reliable parcel-level apple orchard mapping is required for many precise agriculture application models, including planting suitability evaluation, standardized production, and personal agricultural operation loan approval. However, in hilly areas where smallholder management predominates, the highly fragmented and heterogeneous agricultural landscape means that fine parcel-level apple orchard mapping remains challenging. This paper proposes a parcel-level apple orchard mapping method based on feature-level spatiotemporal data fusion, which is suitable for hilly areas where smallholder management predominates. First, a hierarchical strategy that simulates human image cognition processing was used to extract redundant candidate parcels from a very high spatial resolution (VHR) image (Google Earth image with a spatial resolution of 0.6 m). Second, deep learning models, including a Depth-wise Asymmetric Bottleneck Network (DABNet) and long short-term memory (LSTM), were used to extract implicit spatial and time series features of the parcels. Third, the implicit features extracted by the deep learning models were formatted into meta-features, which then formed the feature space together with the morphological and geographical features of the parcel. Fourth, based on the constructed parcel feature space, a random forests (RF) model was used to classify candidate parcels. The experiment was carried out in the town of Guanli, southwest of Qixia city, Shandong Province, China: 21,123 apple orchard parcels were extracted from 31,235 candidate parcels. The overall accuracy (OA) of the parcel-level mapping result was 0.919. The parcel features were combined according to their types, and the performance of different feature combinations for parcel classification was further compared, demonstrating that the proposed meta-features had a stronger spatial information description capability than traditional features. Moreover, the mean decrease in the accuracy (MDA) index was used to evaluate the importance of each feature. And spatial-information-related meta-features were revealed to play the most important role in parcel classification. This method provides methodological references for parcel-level orchard mapping in hilly areas where smallholder management predominates and can be applied to improve the monitoring of orchards in such areas. [ABSTRACT FROM AUTHOR]

Lithium‐sulfur (Li−S) battery with the advantages of high theoretical capacity and low cost is a promising technology for advanced energy storage. However, poor conductivity of the sulfur cathode, huge volume expansion, shuttling effect and sluggish catalytic conversion of lithium polysulfide hinder its commercialization. Herein, a 3D hierarchical porous carbon loaded with atomically dispersed Fe‐N4 was developed as a sulfur cathode, which not only offers enhanced electronic conductivity, but also alleviates volume expansion. Moreover, density functional theory calculation results suggest that the Fe‐N4 sites are favorable to enhance the diffusion and promote the conversion of lithium polysulfide. Consequently, lithium‐sulfur battery with 3D hierarchical porous carbon as the sulfur cathode exhibit good capacity and cycling performance, where a high initial specific capacity of 1289.3 mAh g−1 can be delivered at 0.1 C, and a capacity loss of only 0.025 % per cycle can be achieved for 1000 cycles at 2.0 C. [ABSTRACT FROM AUTHOR]

Modern top-performing object detectors depend heavily on backbone networks, whose advances bring consistent performance gains through exploring more effective network structures. In this paper, we propose a novel and flexible backbone framework, namely CBNet, to construct high-performance detectors using existing open-source pre-trained backbones under the pre-training fine-tuning paradigm. In particular, CBNet architecture groups multiple identical backbones, which are connected through composite connections. Specifically, it integrates the high- and low-level features of multiple identical backbone networks and gradually expands the receptive field to more effectively perform object detection. We also propose a better training strategy with auxiliary supervision for CBNet-based detectors. CBNet has strong generalization capabilities for different backbones and head designs of the detector architecture. Without additional pre-training of the composite backbone, CBNet can be adapted to various backbones (i.e., CNN-based vs. Transformer-based) and head designs of most mainstream detectors (i.e., one-stage vs. two-stage, anchor-based vs. anchor-free-based). Experiments provide strong evidence that, compared with simply increasing the depth and width of the network, CBNet introduces a more efficient, effective, and resource-friendly way to build high-performance backbone networks. Particularly, our CB-Swin-L achieves 59.4% box AP and 51.6% mask AP on COCO test-dev under the single-model and single-scale testing protocol, which are significantly better than the state-of-the-art results (i.e., 57.7% box AP and 50.2% mask AP) achieved by Swin-L, while reducing the training time by $6\times $. With multi-scale testing, we push the current best single model result to a new record of 60.1% box AP and 52.3% mask AP without using extra training data. Code is available at https://github.com/VDIGPKU/CBNetV2 . [ABSTRACT FROM AUTHOR]

This paper presents a broad-band and broad-angle anisotropic reflective polarization converting metasurface (PCMS) for C- and X-band applications, which is composed of square split ring resonators. Such PCMS can be used in a wide range of applications such as satellite antennas, navigation systems, and biomedical devices, to name but a few. The performance of the presented PCMS is analyzed theoretically, numerically, and experimentally. The results at normal and oblique incidences demonstrate that the PCMS achieves broad-band linear polarization (LP) transformation within an operating bandwidth of 5.3 GHz (5.3–10.6 GHz), covering the C-band and a portion of the X-band. The broad-band performance of the PCMS sustains from 0 ∘ to 60 ∘ . Moreover, the PCMS achieves polarization conversion for circularly polarized (CP) waves in the same bands. The polarization conversion ratio is more than 90 % for both LP and CP incident waves. [ABSTRACT FROM AUTHOR]

Gallium (Ga) emerges as a promising material in plasmonics mainly due to its extraordinary properties, such as changeable material phase, tunable plasmon resonances across the ultraviolet to near‐infrared spectral range, and remarkable chemical stability. Here, the efficient white light emission from gallium oxide (Ga2O3) nanoparticles doped with liquid Ga nanodots, which are fabricated by using a laser‐induced oxidation method is reported. The quantum efficiency of Ga/Ga2O3 hybrid nanoparticles is found to be ≈1.3%, which is nearly two orders of magnitude larger than that of liquid Ga nanoparticles. It is revealed that the existence of Schottky barrier and hotspots in Ga/Ga2O3 nanoparticles plays a crucial role in enhancing the quantum efficiency. As an example of practical applications, high‐quality optical data storage is demonstrated by exploiting the controllable formation of Ga/Ga2O3 nanoparticles on a platform of disordered Ga nanoislands. These results suggest the potential applications of Ga/Ga2O3 hybrid nanoparticles in the development of nanoscale light sources and data storage devices. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth study and analysis of human action recognition in dancesport video images through chaotic system equations. A novel fractional-order chaotic system model with hidden multistability is constructed. Since this fractional-order chaotic system has no equilibrium point, the equilibrium point stability analysis is not required. The effect of system parameters on the multistability characteristics of the fractional-order chaotic system is investigated in depth by using the control variable method and nonlinear dynamic tools. In addition, the system has a special property of offset incremental control, which makes the system more widely and practically useful in engineering applications. Finally, circuit simulation experiments and hardware circuit experiments are conducted for the fractional-order chaotic system, and the results are consistent with the corresponding theoretical analysis. The system architecture of the mobile augmented reality-based ethnic dynamic art display system is designed, and the system architecture adopts a hierarchical design. The experimental results show that the design method of the mobile augmented reality-based dynamic art display system proposed in this thesis can meet the purpose of expanding the ways of dancesport display, and the system designed in this thesis is customizable and the synthesized images have a high sense of realism. [ABSTRACT FROM AUTHOR]

Aluminum alloy can obtain good forming effect and strength after age forming. The addition of an ultrasonic field in the two-stage age forming process could have a positive effect on the forming performance and microstructure. In this study, we aimed to combine the ultrasonic vibration and two-stage age forming. The application of ultrasonic waves could reduce the rebound rate of aluminum alloy component. When the ultrasound application time was 6 h, the minimum rebound rate was 40.2%. The higher the two-stage aging temperature with the aid of ultrasound, the lower the rebound rate. Ultrasonic energy shortened the time for the Guinier Preston zones (GP zones) to reach the stable η phases during the age forming process and refined the η phases in the grains. With the extension of the ultrasonic application time, the strength showed a trend from declined to rose, and the elongation increased. The higher the two-stage aging temperature, the larger and coarser the size of the grains, and the strength of the aluminum alloy component will decrease. [ABSTRACT FROM AUTHOR]

Design and analysis of a dual-band polarization converting metasurface is presented in this letter. The proposed converter, which consists of two square split ring resonators, exhibits peak resonances at frequencies of 5.6, 7.3, 8.8, 15.1, and 15.9 GHz. The surface behaves as a polarization converter for linearly polarized incident waves in two frequency ranges, i.e., 5.4–9.0 GHz with a polarization conversion ratio (PCR) ≥ 93 %, and 14.6–16.1 GHz with a PCR ≥ 99 %). The size and thickness of the unit cell are, respectively, 0.126 λo and 0.057 λo, where λo is the largest wavelength (corresponding to the lower frequency). The mechanism of polarization conversion is studied by examining the surface currents for all the resonance frequencies. Both simulated and experimental results reveals that the polarization converter can be utilized in C-, X- and Ku-band applications. [ABSTRACT FROM AUTHOR]

Spatial information is important for human perception of speech and sound signals. However, this information is often either distorted or completely neglected in noise reduction because it is challenging, to say the least, to achieve optimal noise reduction and accurate spatial information preservation at the same time. This paper studies the problem of binaural speech enhancement. By jointly diagonalizing the speech and noise correlation matrices, we present a method to construct the noise reduction filter as a linear combination of different eigenvectors, which span a certain subspace of the entire space. A different dimension of the subspace gives a different trade-off between noise reduction and speech/noise spatial information preservation. On the one side, if the dimension is equal to 1, maximum noise reduction is achieved but at the price of significant spatial information distortion. On the other extreme, if the dimension of the subspace is equal to that of the entire space, spatial information is accurately preserved but at the cost of no noise reduction. Therefore, one can achieve different levels of compromises between the amount of noise reduction and the level of speech/noise spatial information preservation by adjusting the dimension of the used subspace. [ABSTRACT FROM AUTHOR]

A method for designing wideband Fabry–Perot resonator antennas (FPRAs) using multilayer partially reflective surface (PRS) is presented. The proposed partially reflecting structure employs a pair of closely spaced PRSs to obtain a positive reflection phase gradient over a wide range of frequencies. Each PRS layer is composed of complementary square apertures and patches printed on either side of a thin dielectric sheet. The distance between the two PRS layers is only λo/12λo being wavelength at the center frequency of 13 GHz). Due to the presence of strong couplings between the two PRS layers, the designed PRS unit cell gives a positive reflection phase gradient from 11 to 15 GHz, thereby forming the basis of a wideband FPRA. Based on the proposed PRS, a compact FPRA with overall dimensions of 2.4λo × 2.4λo × 0.66λo is designed and experimentally validated, which gives a 3 dB gain bandwidth and a maximum realized gain of 32.3% and 14 dBi, respectively. [ABSTRACT FROM AUTHOR]

This paper studies signal models for microphone array beamforming in the short-time-Fourier-transform (STFT) domain with long acoustic impulse responses. The major contributions are as follows. First, the signal modeling problem is investigated in the STFT domain and a general decomposition is proposed for the convolved source signal. Second, new insights into the array manifold are presented: the STFT of the windowed acoustic impulse response from the source to the sensors. Third, the structure of the reference signal is analyzed: it can be viewed as the output of a beamformer without considering the noise in the observation signal. Fourth, based on the new perspectives and decomposition, a signal model is derived based on the use of the superdirective beamformer. Finally, three performance measures are defined, based on which three optimal/suboptimal signal models are derived and their performance is assessed under different acoustic environments and analysis window lengths. The performance of the well-known minimum variance distortionless response (MVDR) beamformer is evaluated, which justifies the properties of the developed signal models. [ABSTRACT FROM AUTHOR]

Differential microphone arrays (DMAs), which are responsive to the differential acoustic pressure fields, have been used in a wide range of applications related to audio and speech. The core part of a DMA is the so-called differential beamformer, which is generally designed by placing a number of nulls in its beampattern to attenuate noise from some directions. But the presence of these nulls may cause some great issues, e.g., leading to suboptimal performance if the interference/noise is incident from directions other than the nulls’ directions, and making the beamformer less robust to sensors’ self noise and array imperfections. To overcome these problems, this letter is devoted to the design of differential beamformers with no nulls in its beampattern. A design method and its multistage implementation are presented and analyzed. An improved solution is then developed, which is able to form frequency-invariant beampatterns with no nulls in the frequency range of speech signals. Simulations are provided to illustrate the properties of the developed methods. [ABSTRACT FROM AUTHOR]

Time difference of arrival (TDOA) estimation, which often serves as the fundamental step for a source localization or a beamforming system, has a significant practical importance in a wide spectrum of applications. To deal with reverberation, the TDOA estimation problem is often transformed into one of identifying the relative acoustic impulse responses. This letter presents a method to efficiently identify the relative acoustic impulse response between two microphones for TDOA estimation based on the so-called Kronecker product decomposition. By decomposing the relative impulse response into a series of Kronecker products of shorter filters, the original channel identification problem with a long impulse response is converted into one of identifying a number of short filters. Since the TDOA information is embedded only in the direct path of the relative impulse response, the dimension of the Kronecker product decomposition can be very small and, as a result, the developed algorithm is expected to work well in real environments with a small number of data snapshots. [ABSTRACT FROM AUTHOR]

Reverberation impairs not only the speech quality, but also intelligibility. The weighted-prediction-error (WPE) method, which estimates the late reverberation component based on a multichannel linear predictor, is by far one of the most effective algorithms for dereverberation. Generally, the WPE prediction filter in every short-time-Fourier-transform (STFT) subband has to be long enough to estimate accurately the late reverberation component. As a consequence, WPE is computationally expensive, which makes it difficult to implement into real-time embedded or edge computing devices. Moreover, WPE is sensitive to additive noise and its performance may suffer from dramatic degradation even in environments where the signal-to-noise ratio (SNR) is high. To address these drawbacks, this letter proposes to decompose the multichannel linear prediction filter as a Kronecker product of a temporal (interframe) prediction filter and a spatial filter. An iterative algorithm is then developed to optimize the two filters. In comparison with the original WPE algorithm, the presented method not only exhibits better performance in terms of dereverberation and robustness to additive noise, as there are fewer parameters to estimate for a given number of observation signal samples, but is also computationally more efficient, since the dimensions of the covariance matrices after Kronecker product decomposition are smaller. [ABSTRACT FROM AUTHOR]

Differential beamformers with small-size microphone arrays are very attractive for audio and speech signal acquisition thanks to their high directivity and frequency-invariant spatial responses. However, such beamformers often suffer from significant white noise amplification at low frequencies, which makes their implementation in real-world systems challenging. One widely used way to circumvent this issue is to increase the number of microphones in the design of a given order differential beamformer, leading to the so-called robust differential beamformer in which the redundancy provided by the additional sensors are used to improve the white noise gain (WNG). But even with this robust solution, white noise amplification at low frequencies still exists. In this article, instead of trying to improve WNG, we adopt a method to render the white noise in such a way that it affects less the perception of the speech signal of interest. Specifically, we propose a binaural differential beamforming method in which a differential beamformer is designed with two sub-beamforming filters that simultaneously generates two outputs, one for the left ear and the other for the right ear. Motivated by psychoacoustic experiments, we design these two filters in such a way that they are orthogonal so that the coherence between the white noise at the binaural outputs is minimized while the coherence between diffuse noise is maximized. With the proposed binaural differential beamformers, the desired signal components and (amplified) white noise at the binaural differential beamformer's outputs are rendered into different directions or zones. Consequently, the human perception system can better distinguish the desired signal from white noise for improved speech intelligibility. The superiority of the proposed binaural beamforming technique is justified by simulations, experiments, as well as listening tests. [ABSTRACT FROM AUTHOR]

Differential beamforming combined with microphone arrays can be used in a wide range of applications related to acoustic and speech signal acquisition and recovery. A practical and useful method for designing differential beamformers is the so-called null-constrained method, which was developed based on linear arrays and requires only the nulls' information from the target directivity pattern. While it is effective and easy to use, this method is found not suitable for designing steerable differential beamformers with circular arrays. This paper reexamines this technique in the context of circular differential microphone arrays. By analyzing the properties of the circular array topology, the null-constrained method is extended to include symmetric constraints, which is inherent in the design of circular arrays. This extension yields a design method for fully steerable differential beamformers that require only minimum information from the target beampattern. Simulations justify the theoretical analysis and demonstrate the good properties of the developed method. [ABSTRACT FROM AUTHOR]

The shift of Fano resonances has been widely exploited to realize biomedical sensing, optical filtering, and optical switching. Here, the formation of Fano resonances in the scattering spectra of silicon nanoparticles excited by surface plasmon polaritons is reported and the modification of Fano lineshapes is demonstrated. It is revealed that the subradiant and superradiant modes responsible for the formation of Fano resonance originate from the coherent interaction of the electric and magnetic dipoles excited in the silicon nanoparticle with their mirror images induced by a thin metal film. The modification of the asymmetry parameter q can be realized by simply adjusting the angle of the incident light or by slightly varying the environment refractive index. The tuning of the q value is accompanied by the variation of the field enhancement factors and manifested in the color change of the scattered light. The strongest enhancement of both electric and magnetic fields can be achieved at the point of contact between the silicon nanoparticle and the metal film for the symmetric Fano lineshape (q ≈ 0). These findings indicate the potential applications of such a hybrid metal–dielectric system in sensing, color display, and strong light–matter interaction. [ABSTRACT FROM AUTHOR]

The knowledge of speech presence probability (SPP) plays an essential role in noise estimation and speech enhancement. Single channel SPP estimation and centralized multi-channel SPP estimation have been well studied. However, how to estimate SPP in wireless acoustic sensor networks (WASNs) remains a great challenge and few efforts can be found in this topic, particularly for WASN applications with multiple speakers. Accordingly, this paper is devoted to the problem of SPP estimation in WASNs and it presents a distributed model-based SPP estimation method for multi-speaker detection, which does not need any fusion center. A distributed k-means clustering method is first used to cluster the nodes into subnetworks, which detect different speakers. For each node in the subnetwork, the speech and noise power spectral densities are estimated locally by using a model-based method, then a distributed SPP estimator is developed and applied in every subnetwork. A distributed consensus method is used to obtain the distributed clustering and the distributed SPP estimation. Simulation results show that the proposed distributed clustering method can assign nodes into subnetworks based on their noisy observations. Moreover, the proposed distributed SPP estimator achieves robust speech detection performance under different noise conditions. [ABSTRACT FROM AUTHOR]

An ultraminiaturized frequency selective surface (FSS) based on 2.5-D convoluted structure is proposed. 2-D convoluted lines in the form of square spirals are incorporated with vertical vias to give a unit cell size which is only 2.7% of the free-space wavelength at resonance frequency of 2.8 GHz. Transverse-electric (TE) and transverse-magnetic (TM) resonators are combined to synthesize the proposed FSS unit cell resulting in a polarization-independent 2.5-D FSS. Moreover, the designed FSS provides a stable frequency response for incidence angles, up to 75°, for both the TE and TM polarizations. An equivalent circuit model is also developed to provide physical insights into the working mechanism of the proposed FSS. Transmission characteristics of the FSS are analyzed using full-wave simulations and equivalent circuit modeling. A prototype FSS is fabricated and measured utilizing ${S}$ -band waveguide setup where a good consistency between the measured and simulated frequency responses validates the design process. [ABSTRACT FROM AUTHOR]

Placental oxidative stress is present throughout the duration of pregnancy, but it is when oxidative stress exceeds the normal physiological level that complications can occur. Trophoblast cell lines are commonly utilized for oxidative stress research due to their distinct uniform cell population and easy-to-apply interventions. However, conflicting results are often reported when different oxidative stress cell models are used. In this study, the aim was to characterize the intracellular and extracellular metabolite profiles of different oxidative stress cell models commonly used in the research of pregnancy complications. HTR8/SVneo human trophoblast cell lines were treated with five different oxidative stress-inducing conditions: Hypoxia (1% oxygen); hypoxia and reoxygenation; cobalt chloride (CoCl2; 300 µmol/l); sodium nitroprusside (SNP; 2.5 mmol/l); and the serum of women with preeclampsia (10% v/v). Intracellular metabolites were extracted from cells and extracellular metabolites were collected from spent media for metabolomic analysis via gas chromatography-mass spectrometry. The results demonstrated that there were distinct differences in the intracellular and extracellular metabolome between the different cell models. Meanwhile, treatments with exogenous drugs, such as CoCl2 and SNP, resulted in more similar metabolite profiles. These disparities between the different oxidative stress cell models will have implications for the applications of these results, and highlight the need for the standardization of oxidative stress cell models in obstetric research. [ABSTRACT FROM AUTHOR]

Wide angular coverage antennas despite being a requirement for many recent safety applications are a design challenge. Applications like Automotive Radars, GPS and telemetry all need an antenna with wide half-power beamwidths in both principal planes. A novel broadbeam aperture-coupled step-walled rectangular dielectric resonator antenna is proposed. The antenna consists of a central widest ceramic plate with two plates on each side with decreased widths creating stepped or staircase like walls. The dielectric resonator is centered over the feed slot. Two modes T E 111 x and T E 113 x are simultaneously excited. The antenna is shown to yield broadbeam radiation patterns at frequencies between Mode-I and Mode-III resonances. To validate the principal, a prototype is fabricated and measured. The antenna has measured operating frequency band ranging from 5.75 GHz to 7.23 GHz with broadbeam frequency band from 6.1 to 6.6 GHz. The measured xoz and yoz beamwidths range from 120 ∘ to 132 ∘ with measured gain from 4.5 dB to 5.5 dB in the broadbeam band. [ABSTRACT FROM AUTHOR]

An ultraminiaturized bandstop frequency-selective surface (FSS) utilizing two-dimensional (2-D) tapered meandering lines (TML) along with vertical vias is proposed. Full-wave simulations, equivalent circuit modeling, and analytical results are presented for the designed FSS. A prototype 2.5-D TML-FSS is fabricated, and its performance is measured in an anechoic chamber for various incident angles in both the transverse-electric (TE) and transverse-magnetic (TM) polarizations. Measured results are in agreement with the simulated ones, indicating the authenticity of the design process. Unit cell size of the proposed FSS is only $\text{2.9}\%$ of the free-space wavelength at resonant frequency and has a fractional bandwidth of $\text{20.9}\%$. Furthermore, the proposed design is modified to convoluted 2.5-D TML-FSS and interdigitated 2.5-D TML-FSS to give different unit cell sizes in terms of wavelength with different fractional bandwidths. [ABSTRACT FROM AUTHOR]

The design of variable span linear filters for noise reduction involves a generalized eigenvalue decomposition problem that is of high computational complexity. In order to address this issue, this work proposes a recursive algorithm that computes the filter weights with streaming signal data. Specifically, the inverse square root of the noise covariance matrix is recursively computed with a rank-one update strategy, and the generalized eigenvalues and eigenvectors are approached with the projection approximation subspace tracking method. Numerical simulations show that the proposed recursive method is able to achieve satisfactory performance with significantly lower complexity as compared to the batch algorithm. [ABSTRACT FROM AUTHOR]

Acoustic source localization (ASL) is a fundamental yet still challenging signal processing problem in sound acquisition, speech communication, and human–machine interfaces. Many ASL algorithms have been developed, such as the steered response power (SRP), the SRP-phase transform, the minimum variance distortionless response, the multiple signal classification (MUSIC), the householder transform-based methods, to name but a few. Most of those algorithms require hundreds or even thousands of snapshots to produce one reliable estimate, which make them difficult to track moving sources. Moreover, not much efforts have been reported in the literature to show the intrinsic relationships among those methods. This paper deals with the ASL problem with its focal point placed on how to achieve ASL with a short frame of acoustic signal (corresponding to a single snapshot in the frequency domain). It reformulates the ASL problem from the perspective of geometric projection. Four types of power functions are proposed, leading to several different algorithms for ASL. By analyzing those power functions, we show the equivalence between the popularly used conventional algorithms and our methods, which provides some new insights into the conventional algorithms. The relationships among different algorithms are discussed, which make it easy to comprehend the pros and cons of each of those methods. Experiments in real acoustic environments corroborate the theoretical analysis, which in turn justifies the contribution of this paper. [ABSTRACT FROM AUTHOR]

Microphone arrays are typically used in room acoustic environments to acquire high fidelity audio and speech signals while suppressing noise, interference, and reverberation. In many application scenarios, interference and reverberation may mainly come from a certain region, and it is therefore necessary to develop beamformers that can preserve signals of interest while minimizing the power of signals coming from the region where interference and reverberation dominate. For this purpose, this paper first reexamines the so-called front-to-back ratio and the classical supercardioid beamformer. To deal with the white noise amplification problem and the limited directivity factor associated with the supercardioid beamformer, a set of reduced-rank beamformers are deduced by using the well-known joint diagonalization technique, which can make compromises between the front-to-back ratio and the amount of white noise amplification or the directivity factor. Then, the definition of the front-to-back ratio is extended to a generalized version, from which another set of reduced-rank beamformers and their regularized versions are developed. Simulations are conducted to illustrate the properties and advantages of the proposed beamformers. [ABSTRACT FROM AUTHOR]

This letter deals with the problem of differential beamforming with microphone arrays of arbitrary planar geometry. By approximating the beampattern with the Jacobi-Anger expansion, it develops an algorithm that can form any specified frequency-invariant beampattern with a microphone array of any planar geometry as long as the sensors' coordinates are given and the spacing between neighboring sensors is smaller than the smallest wavelength. This method is rather general and it can be used to design differential beamformers with linear, circular, and concentric circular differential microphone arrays as well as differential arrays of arbitrary planar geometry where sensors are placed in any specified positions. [ABSTRACT FROM AUTHOR]

The maximum directivity (MD) beamformer with spherical microphone arrays has many salient features in processing broadband acoustic and speech signals while suppressing noise and reverberation; but it is sensitive to sensors' self-noise and mismatch among these sensors. One effective way to deal with this sensitivity is by increasing the number of microphones, thereby improving the so-called white noise gain (WNG), but this increase may lead to many other design issues in terms of cost, array aperture, and possibly other performance degradation. This paper is tackling this sensitivity problem and presents a flexible high directivity (HD) beamforming algorithm. By approximating the ideal directivity pattern and the beamformer's beampattern with spherical harmonic series, the relationship between the two is obtained. This relationship is subsequently used to deduce a flexible HD beamformer, which can improve the WNG while achieving a directivity factor (DF) between the DF of an Nth-order MD beamformer and that of an ( N − 1 ) th-order MD one. Also derived is the analytical link between the DF and a tuning parameter and the link between the WNG and this parameter. Based on these links, one can easily determine the optimal value of the tuning parameter once the value of the DF or the WNG is specified. [ABSTRACT FROM AUTHOR]

This paper develops an approach to beamforming with small spacing uniform linear microphone arrays based on the null-steering (NS) principle. It first formulates the beamforming problem from the conventional mean-squared error (MSE) criterion and its normalized version. Several NS algorithms are then derived for beamforming with the constraint of placing nulls to either a single direction or multiple angles. The difference and relationships between different algorithms are discussed and their performances are evaluated. These algorithms can be used to design either fixed or adaptive beamformers. In the former case, the resulting beamformers work as differential microphone arrays (DMAs) since they exhibit frequency-invariant beampatterns and their directivity factors are high with a given number of sensors. In the latter case, the resulting beamformers can be viewed as a combination of DMAs and single-channel noise reduction since they do not only exhibit frequency-invariant beampatterns but also can achieve noise reduction based on the noise statistics. [ABSTRACT FROM AUTHOR]

Artificial control of colors based on plasmonic and dielectric nanostructures is not only interesting for fundamental research, but also important for practical applications. Apart from spatial resolution, chromaticity, angular independence, and dynamical color-tuning have emerged as the most desirable functions for structural color. Here, it is shown theoretically that the orientations of the electric or magnetic dipoles induced in a silicon nanoparticle can be manipulated by using an evanescent wave excited by s- or p-polarized light, and it is experimentally demonstrated that the scattering light color can be controlled by simply varying the polarization of the illumination light. It is revealed that the excitation of a silicon nanoparticle using an evanescent wave is equivalent to that of using both the incident and reflected light, enabling the manipulation of the scattering light color by controlling the orientations of the electric and magnetic dipoles. In addition, an enhanced scattering light intensity and a completely dark background are achieved by using evanescent wave excitation. More importantly, a color-tuning display with a spatial resolution close to the optical diffraction limit, and a good chromaticity on an array of silicon nanopillars fabricated on a silica substrate is demonstrated, which are compatible with the current fabrication technology of silicon chips. [ABSTRACT FROM AUTHOR]