Cooperative Transmission in Mobile Wireless Sensor Networks with Multiple Carrier Frequency Offsets: A Double-Differential Approach

As a result of the rapidly increasing mobility of sensor nodes, mobile wireless sensor networks (MWSNs) would be subject to multiple carrier frequency offsets (MCFOs), which result in time-varying channels and drastically degrade the network performance. To enhance the performance of such MWSNs, we propose a relay selection (RS) based double-differential (DD) cooperative transmission scheme, termed RSDDCT, in which the best relay sensor node is selected to forward the source sensor node’s signals to the destination sensor node with the detect-and-forward (DetF) protocol. Assuming a Rayleigh fading environment, first, exact closed-form expressions for the outage probability and average bit error rate (BER) of the RSDDCT scheme are derived. Then, simple and informative asymptotic outage probability and average BER expressions at the large signal-to-noise ratio (SNR) regime are presented, which reveal that the RSDDCT scheme can achieve full diversity. Furthermore, the optimum power allocation strategy in terms of minimizing the average BER is investigated, and simple analytical solutions are obtained. Simulation results demonstrate that the proposed RSDDCT scheme can achieve excellent performance over fading channels in the presence of unknown random MCFOs. It is also shown that the proposed optimum power allocation strategy offers substantial average BER performance improvement over the equal power allocation strategy

A Cooperative Mobile Satellite Communication System with the Dynamic Space-Time Coding

Channels of mobile satellite communications are affected by multipath fading and shadowing attenuation. At the same time, diversity gains are believed to improve the transmission reliability in fading channels. Considering that the traditional Space-Time Coding (STC) is not suitable for the cooperative mobile satellite communication, in this paper, a new cooperative mobile satellite communication system is proposed based on the Dynamic Space-Time Coding (D-STC). The transmitting energy of the proposed scheme is saved by avoiding forwarding erroneous signals in cooperative users. Meanwhile, this system benefits from diversity gains and the transmission is robust. Additionally, a closed-form expression of the outage probability for the proposed scheme is derived, and then it is demonstrated that this scheme is much better than the existing noncooperative scheme and schemes with traditional STCs in the outage performance. Finally, the analytical result is supported and validated by numerical simulations

A Parallel Decoding Algorithm for Short Polar Codes Based on Error Checking and Correcting

We propose a parallel decoding algorithm based on error checking and correcting to improve the performance of the short polar codes. In order to enhance the error-correcting capacity of the decoding algorithm, we first derive the error-checking equations generated on the basis of the frozen nodes, and then we introduce the method to check the errors in the input nodes of the decoder by the solutions of these equations. In order to further correct those checked errors, we adopt the method of modifying the probability messages of the error nodes with constant values according to the maximization principle. Due to the existence of multiple solutions of the error-checking equations, we formulate a CRC-aided optimization problem of finding the optimal solution with three different target functions, so as to improve the accuracy of error checking. Besides, in order to increase the throughput of decoding, we use a parallel method based on the decoding tree to calculate probability messages of all the nodes in the decoder. Numerical results show that the proposed decoding algorithm achieves better performance than that of some existing decoding algorithms with the same code length

A Versatile Bonding Method for PDMS and SU-8 and Its Application towards a Multifunctional Microfluidic Device

This paper reports a versatile and irreversible bonding method for poly(dimethylsiloxane) (PDMS) and SU-8. The method is based on epoxide opening and dehydration reactions between surface-modified PDMS and SU-8. A PDMS replica is first activated via the low-cost lab equipment, i.e., the oxygen plasma cleaner or the corona treater. Then both SU-8 and plasma-treated PDMS samples are functionalized using hydrolyzed (3-aminopropyl)triethoxysilane (APTES). Ultimately, the samples are simply brought into contact and heated to enable covalent bonding. The molecular coupling and chemical reactions behind the bonding occurring at the surfaces were characterized by water contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis. The reliability of bonded PDMS-SU-8 samples was examined by using tensile strength and leakage tests, which revealed a bonding strength of over 1.4 MPa. The presented bonding method was also applied to create a metal-SU-8-PDMS hybrid device, which integrated SU-8 microfluidic structures and microelectrodes. This hybrid system was used for the effective trapping of microparticles on-chip, and the selective releasing and identification of predefined trapped microparticles. The hybrid fabrication approach presented here, based on the PDMS-SU-8 bonding, enables multifunctional integration in complex microfluidic devices

Convergence Gain in Compressive Deconvolution: Application to Medical Ultrasound Imaging

The compressive deconvolution (CD) problem represents a class of efficient models that is appealing in high-resolution ultrasound image reconstruction. In this paper, we focus on designing an improved CD method based on the framework of a strictly contractive Peaceman⁻Rechford splitting method (sc-PRSM). By fully excavating the special structure of ultrasound image reconstruction, the improved CD method is easier to implement by partially linearizing the quadratic term of subproblems in the CD problem. The resulting subproblems can obtain closed-form solutions. The convergence of the improved CD method with partial linearization is guaranteed by employing a customized relaxation factor. We establish the global convergence for the new method. The performance of the method is verified via several experiments implemented in realistic synthetic data and in vivo ultrasound images

Application of Modified Biochar in the Treatment of Pesticide Wastewater by Constructed Wetland

To explore the synergistic effects of modified biochar in the purification of herbicide-containing wastewater, the effect of biochar addition on the removal effect of the herbicide atrazine in wastewater was verified by the addition of biochar bags in a small reed bed-constructed wetland in the laboratory. The results showed that the addition of sulfuric acid-modified biochar could increase the removal rate of atrazine in wastewater from 50% to 70%, and the COD elimination rate in wastewater was from 66.7% to 86.7%. The addition of biochar to the constructed reed bed wetland improved the removal efficiency of total nitrogen and total phosphorus in the wastewater, and the outlet water from the constructed wetland reached the Class III level of China’s surface water quality standard (the inlet water was inferior to Class V). The experimental design met the requirements of low-cost, generalized atrazine-containing wastewater treatment and thus could have the potential for wide application. The results reflected the application potential of modified biochar as a synergist in the treatment of herbicide wastewater in constructed wetlands

Ecological risk assessment of glyphosate and its possible effect on bacterial community in surface sediments of a typical shallow Lake, northern China

Glyphosate is a widely used herbicide worldwide and its prevalent presence in aquatic ecosystems poses a threat to living organisms. This study evaluated potential ecological risk of glyphosate to sediment-dwelling organisms and assessed the probable effect of glyphosate on structure and predicated function of sediment-attached bacterial communities from a large shallow lake in northern China based on 16S rRNA high-throughput sequencing. Results suggested that glyphosate showed a medium to high concentration (up to 8.63 mg/kg) and chronic risk to sediment-dwelling organisms (10% samples exhibiting medium to high risk quotient), especially in sites nearby farmland and residential areas in August. Bacterial community identification based on 16S rRNA sequence indicated some species of dominant phylum Proteobacteria and Campilobacterota (e.g., Steroidobacteraceae, Thiobacillus, Gallionellaceae, Sulfurimonadaceae) were stimulated while some species of dominant phylum Actinobacteriota, Acidobacteriota and Firmicutes (e.g., Nocardioidaceae, Microtrichales, Vicinamibacteraceae, Paenisporosarcina) were inhibited by glyphosate accumulation. The stimulating species were related to sulfur-oxidizing, sulfate-, iron-, or nitrate-reducing bacteria; The inhibiting species were related to plant bacterial endophytes, polyphosphate-accumulating organisms (PAOs) and denitrifers. Correspondingly, promoted bacterial metabolic functions of “sulfite respiration”, “nitrogen respiration”, “aromatic compound degradation” and “nitrification” but suppressed “cellulolysis”, “manganese oxidation”, “anoxygenic photoautotrophy S oxidizing” and “nitrate denitrification” were predicated on functional annotation of prokaryotic taxa. Although these results could only partly suggest the impacts of glyphosate on the bacterial communities due to the lack of actual results from control experiments, the identified Steroidobacteraceae could be thought as a bioindicator in the future mechanism study for the ecological effect and bioremediation of glyphosate. This work intends to arise the concern about the depletion of biodiversity and bacterial metabolic functions with contribution of glyphosate in part in eutrophic lakes

Application of Modified Biochar in the Treatment of Pesticide Wastewater by Constructed Wetland

To explore the synergistic effects of modified biochar in the purification of herbicide-containing wastewater, the effect of biochar addition on the removal effect of the herbicide atrazine in wastewater was verified by the addition of biochar bags in a small reed bed-constructed wetland in the laboratory. The results showed that the addition of sulfuric acid-modified biochar could increase the removal rate of atrazine in wastewater from 50% to 70%, and the COD elimination rate in wastewater was from 66.7% to 86.7%. The addition of biochar to the constructed reed bed wetland improved the removal efficiency of total nitrogen and total phosphorus in the wastewater, and the outlet water from the constructed wetland reached the Class III level of China’s surface water quality standard (the inlet water was inferior to Class V). The experimental design met the requirements of low-cost, generalized atrazine-containing wastewater treatment and thus could have the potential for wide application. The results reflected the application potential of modified biochar as a synergist in the treatment of herbicide wastewater in constructed wetlands