In this article, the problem of training federated learning (FL) algorithms over a realistic wireless network is studied. In the considered model, wireless users execute an FL algorithm while ...training their local FL models using their own data and transmitting the trained local FL models to a base station (BS) that generates a global FL model and sends the model back to the users. Since all training parameters are transmitted over wireless links, the quality of training is affected by wireless factors such as packet errors and the availability of wireless resources. Meanwhile, due to the limited wireless bandwidth, the BS needs to select an appropriate subset of users to execute the FL algorithm so as to build a global FL model accurately. This joint learning, wireless resource allocation, and user selection problem is formulated as an optimization problem whose goal is to minimize an FL loss function that captures the performance of the FL algorithm. To seek the solution, a closed-form expression for the expected convergence rate of the FL algorithm is first derived to quantify the impact of wireless factors on FL. Then, based on the expected convergence rate of the FL algorithm, the optimal transmit power for each user is derived, under a given user selection and uplink resource block (RB) allocation scheme. Finally, the user selection and uplink RB allocation is optimized so as to minimize the FL loss function. Simulation results show that the proposed joint federated learning and communication framework can improve the identification accuracy by up to 1.4%, 3.5% and 4.1%, respectively, compared to: 1) An optimal user selection algorithm with random resource allocation, 2) a standard FL algorithm with random user selection and resource allocation, and 3) a wireless optimization algorithm that minimizes the sum packet error rates of all users while being agnostic to the FL parameters.
This letter investigates a power allocation problem in a downlink single-input single-output non-orthogonal multiple access (NOMA) system. Our goal is to maximize the sum rate of users subject to ...minimum user rate requirements. We rigorously prove the optimal user decoding order, and show that the sum rate maximization problem is convex, which guarantees the globally optimal solution. Numerical results validate the performance gain by the proposed NOMA compared with conventional schemes.
Crowd counting is the task of estimating people numbers in crowd images. Modern crowd counting methods employ deep neural networks to estimate crowd counts via crowd density regressions. A major ...challenge of this task lies in the perspective distortion, which results in drastic person scale change in an image. Density regression on the small person area is in general very hard. In this work, we propose a perspective-aware convolutional neural network (PACNN) for efficient crowd counting, which integrates the perspective information into density regression to provide additional knowledge of the person scale change in an image. Ground truth perspective maps are firstly generated for training; PACNN is then specifically designed to predict multi-scale perspective maps and encode them as perspective-aware weighting layers in the network to adaptively combine the outputs of multi-scale density maps. The weights are learned at every pixel of the maps such that the final density combination is robust to the perspective distortion. We conduct extensive experiments on the ShanghaiTech, WorldExpo'10, UCF_CC_50, and UCSD datasets, and demonstrate the effectiveness and efficiency of PACNN over the state-of-the-art.
The unfrozen water content has a significant impact on the mechanical and thermal properties of saline soils during freezing, and their electrical properties measured by electromagnetic sensors can ...be a promising proxy of the unfrozen water content. This paper investigated the electrical properties and their relationship with the unfrozen water content of saline lean clay. Specimens with increasing concentration of sodium chloride were prepared for assessing their initial freezing points and unfrozen water content by the cooling test and the nuclear magnetic resonance relaxometry, respectively. In addition, the apparent dielectric permittivity and bulk electrical conductivity were measured by sensors based on frequency-domain reflectometry in the electrical property test. A significant variation was observed in both the apparent dielectric permittivity and bulk electrical conductivity of saline lean clay near the initial freezing point. They generally decreased linearly with decreasing temperatures above their initial freezing points and then dropped according to a power curve with temperatures below their initial freezing points. The bulk electrical conductivity of saline lean clay depended on salt concentration and ion conductive pathway, with the latter being dominant at temperatures below its initial freezing point. A new empirical equation was proposed for estimating unfrozen water content based on the apparent dielectric permittivity and initial salt concentration, and independent data validated its applicability of similar soils at relatively low salt concentrations. The proposed equation could be useful for the evaluation of the unfrozen water content of saline lean clay via the apparent dielectric permittivity and initial salt concentration.
•Analyze the influence of temperature and salt concentration on the electrical properties of frozen saline soil•Apparent dielectric permittivity depends on temperature and salt concentration at temperature below initial freezing point•Bulk electrical conductivity mainly depends on ion conductive pathway at temperature below initial freezing point•Propose and validate a new model for the unfrozen water content of frozen saline soil
Diffusion-based salient region detection has recently received intense research attention. In this paper, we present some effective improvements concerning two important aspects of diffusion-based ...methods: the construction of the diffusion matrix and the seed vector. First, we construct a two-layer sparse graph, which is generated by connecting each node to its neighboring nodes and the most similar node that shares common boundaries with its neighboring nodes. Compared with the most frequently used two-layer neighborhood graph, our graph not only effectively uses local spatial relationships, but also removes dissimilar redundant nodes. Second, we use the spatial variance of superpixel clusters to obtain the seed vector and, compared with the previously most-used boundary prior, our approach can better distinguish saliency seeds from the background seeds, especially when salient objects appear near the image boundaries. Finally, we calculate two preliminary saliency maps using the saliency and background seed vectors, and more accurate results are obtained using the manifold ranking diffusion method. Integrating these two diffusion-based saliency maps, we obtain the final saliency map. Extensive experiments in which we compare our method with 20 existing state-of-the-art methods on five benchmark data sets: ASD, DUT-OMRON, ECSSD, MSRA5K, and MSRA10K, show that the proposed method performs better in terms of various evaluation metrics.
The fate of diverse antibiotic resistance genes (ARGs) in anaerobic digestion (AD) system under different temperature remains largely unknow. This study employed the shotgun metagenomic sequencing ...and 16S rRNA amplicon sequencing approaches and investigated the shifts of composition and abundance of more than 1360 ARGs, as well as microbial community, in a temperature-raising AD system (from 35 °C to 55 °C) treating municipal sewage sludge. Results suggested that the six ARGs, inlcuding macB, tetA(58), bcrA, evgS, mtrA, and oleC, were predominated in digested sludge. More than 407ARG subtypes (30%) could be largely reduced under high temperature condition. Thermophilic AD (55 °C) provided a better removal for tetracycline, macrolide, penam, fluoroquinolone, acridine dye, and peptide resistance genes when compared to mesophilic AD (35 °C). The removal rates of these genes reached 29.7%–32.3%. In addition, at the end of thermophilic digestion process, the relative abundance of Firmicutes increased (from 18.22% to 74.89%), while Proteobacteria and Chloroflexi both decreased, from 36.39% to 6.80% and 20.29%–2.64%. This study further proposed the underlying mechanisms of effective elimination of ARGs under high temperature by: (1) the reduction of genes encoding antibiotic efflux pump, (2) the promotion of sludge biomass degradation rate, (3) the loss of microbial community diversity in AD systems, and (4) the inactivation of multidrug-resistant bacteria. The significance of current study is in characterizing the fate of ARGs across AD process, which allows to correlate diverse genetic properties with digesters’ operational condition. Results provided an insight into the manipulation of AD technology (e.g. temperature) to efficiently remove ARGs from municipal sewage sludge.
•Fate of ARGs in a temperature-raising anaerobic digester was investigated.•More than 1360 ARG subtypes were identified by metagenomics approach.•Effective reduction of ARGs under thermophilic condition was confirmed.•Underlying mechanisms of ARGs removal were proposed.
The excellent properties of plastics make them widely used all over the world. However, when plastics enter the environmental medium, microplastics will inevitably be produced due to physical, ...chemical and biological factors. Studies have shown that microplastics have been detected in terrestrial, aquatic and atmospheric environments. In addition, the presence of microplastics will provide a new artificial adhesion substrate for biofilms. It has been proved that the formation of biofilms could significantly change some properties of microplastics. Some studies have found that microplastics attached with biofilms have higher environmental risks and eco-toxicity. Therefore, considering the widespread existence of microplastics and the ecological risks of microplastic biofilms, the physical and chemical properties of biofilms on microplastics and their impact on microplastics in aqueous environment are worth reviewing. In this paper, we comprehensively reviewed representative studies in this area. Firstly, this study reviews that the existence of biofilms could change the transport and deposition of microplastics. Subsequently, the presence of biofilms would enhance the ability of microplastics to accumulate pollutant, such as persistent organic pollutants, heavy metals and antibiotics. Moreover, the effect of biofilms on microplastics enrichment of harmful microorganisms is summarized. Finally, some future research needs and strategies are proposed to better understand the problem of biofilms on microplastics.
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•Microplastics enter terrestrial, aquatic and atmospheric environment through a variety of pathways.•Microplastics have impacts on creatures and humans.•Biofilms on microplastics have unique physicochemical properties.•The existence of biofilm affects microplastics in aqueous environment.
Frozen soils, especially seasonally frozen soils, have a great impact on the seismic performance of bridge pile foundations. To account for this impact on pile foundations during seismic events, it ...is necessary to evaluate the mechanical properties of naturally frozen soil samples. This paper focuses on the mechanical properties of naturally frozen silty soils at a relatively high strain rate. High quality specimens of both permafrost and seasonally frozen soils were prepared by block sampling and machining. Both horizontal and vertical specimens were prepared to investigate the effect of specimen orientation. Unconfined compression tests were performed at temperatures ranging from −0.7°C to −11.6°C, at a constant deformation rate corresponding to a strain rate of 0.001/s. Testing results including soil characteristics and mechanical properties such as stress–strain curves, compressive strength, yield strength, modulus of elasticity, strain values at unconfined compressive and yield strength, and strain value at which 50% of the compressive strength is achieved are presented. The impact of temperature, dry density, water content, and specimen orientation on the mechanical properties is discussed. For permafrost, the ultimate compressive strength of horizontal specimens is substantially higher than that of vertical specimens at the same testing temperature and this strength anisotropy is likely due to ice wedge formation, commonly observed in lowland permafrost. In general, the ultimate compressive strength of naturally frozen specimens is lower than that found in previous studies for remolded frozen silty soils.
•Naturally frozen ground samples•specimen orientation considered•Testing at relatively high strain rate
The change of soil macropores, especially fissures, due to freeze-thaw (F-T) has important implications for soil engineering properties such as hydraulic conductivity and compressibility. This paper ...describes a quantitative study of the soil macropore changes due to F-T by using three-dimensional (3D) X-ray Computed Tomography (CT). Saturated lean clay specimens were subjected to unidirectional F-T under different water-supply conditions for acquiring 3D X-ray CT images before and after F-T. The CT imagery data were filtered and processed for obtaining parameters such as transverse-sectional macro-porosity, macropore size, transverse-sectional fissure porosity, and longitudinal-sectional fissure orientation frequency distribution. It was found that F-T alters the transverse-sectional macro-porosity and macropore size significantly, the changes are different across the specimen height. Moreover, the changes in the transverse-sectional fissure porosity and longitudinal-sectional fissure orientation frequency distribution vary along with the specimen height. More horizontal fissures form in the unfrozen zone or near the freezing front, depending on water-supply conditions. Pore water pressure data confirm that, besides water migration, soil particles also migrate from the unfrozen zone to the freezing front during freezing with water-supply due to piping. The macropore structural changes help understand the F-T impact on soil engineering properties such as hydraulic permeability and compressibility.
•Describe the filtering and processing of CT images to reveal macropore changes of clay.•Freeze-thaw increases the transverse-sectional macro-porosity and macropore size.•The fissure porosity and fissure orientation vary along with the specimen height.•Reveal that soil particles migration due to piping during freezing.
Adsorption of tetracycline antibiotics from aqueous solutions by a multi-walled carbon nanotube (MWCNT) loaded iron metal-organic framework (MIL-53(Fe)) composite was studied. The adsorbent was ...characterized by environmental scanning electron microscope, energy dispersive X-ray spectroscopy, brunauer-emmett-teller, thermogravimetric analysis, X-ray diffraction, fourier transform infrared spectrum, and X-ray photoelectron spectrum. The adsorption kinetics of tetracycline hydrochloride (TCN), oxytetracycline hydrochloride (OTC), and chlortetracycline hydrochloride (CTC) were all well fitted to the pseudo-second-order equation as well as the adsorption isotherms could be well delineated via Langmuir equations. The main influencing factors such as pH and ionic strength were studied in detail. At initial pH of 7.0, maximum adsorption capacity of TCN, OTC and CTC on MWCNT/MIL-53(Fe) was 364.37, 325.59, 180.68 mg·g−1 at 25 °C, which was 1.25, 8.28 and 3.34 times than that of single MWCNT, respectively. The adsorption capacity of TCS for this adsorbent was in the order: TCN > OTC > CTC, which was determined by the adsorbate molecule magnitude. In addition, π-π adsorbate-adsorbent interactions played an important role during the adsorption process. The excellent reusability and great water stability indicated the potential application of this novel composite in the removal of TCS from aqueous solutions.
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•Multi-walled carbon nanotube modified MIL-53(Fe) was used to remove antibiotic tetracycline for the first time.•MWCNT/MIL-53(Fe) showed the highest adsorption capacity for TCN, OTC and CTC, respectively.•π-π interactions were possible mechanism for adsorptive removal of TCN, OTC and CTC.•MWCNT/MIL-53(Fe) with great water stability was suggested as a reusable and efficient adsorbent.
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