Block diagonalization (BD) is a precoding technique that eliminates interuser interference in downlink multiuser multiple-input multiple-output (MIMO) systems. With the assumptions that all users ...have the same number of receive antennas and utilize all receive antennas when scheduled for transmission, the number of simultaneously supportable users with BD is limited by the ratio of the number of base station transmit antennas to the number of user receive antennas. In a downlink MIMO system with a large number of users, the base station may select a subset of users to serve in order to maximize the total throughput. The brute-force search for the optimal user set, however, is computationally prohibitive. We propose two low-complexity suboptimal user selection algorithms for multiuser MIMO systems with BD. Both algorithms aim to select a subset of users such that the total throughput is nearly maximized. The first user selection algorithm greedily maximizes the total throughput, whereas the criterion of the second algorithm is based on the channel energy. We show that both algorithms have linear complexity in the total number of users and achieve around 95% of the total throughput of the complete search method in simulations
Herein, we first design a fast low‐pressure ultraviolet light irradiation strategy for easily regenerating the nearly equivalent surface vacancies. Taking the defective Bi2O2CO3 nanosheets as an ...example, nearly equal amount of oxygen vacancies can be regenerated under UV light irradiation. Synchrotron‐radiation quasi in situ X‐ray photoelectron spectra disclose the Bi sites in the O‐defective Bi2O2CO3 nanosheets can act as the highly active sites, which not only help to activate CO2 molecules, but also contribute to stabilizing the rate‐limiting COOH* intermediate. Also, in situ Fourier transform infrared spectroscopy and in situ mass spectrometry unravel the UV light irradiation contributes to accelerating CO desorption process. As a result, the O‐defective Bi2O2CO3 nanosheets achieve a stability up to 2640 h over 110 cycling tests and a high evolution rate of 275 μmol g−1 h−1 for visible‐light‐driven CO2 reduction to CO.
Regenerative surface vacancies could be repeatedly created by external conditions like UV light irradiation. These regenerative surface vacancies can significantly improve the cycling stability and eventually realize both high catalytic activity and long‐term stability.
Multiuser spatial multiplexing is a downlink transmission technique that uses linear transmit precoding to multiplex multiple users and precancel interuser interference. In such a system, the spatial ...degrees of freedom are used for interference mitigation and generally come at the expense of diversity gain. This paper proposes two precoding methods that use extra transmit antennas, beyond the minimum required, to provide additional degrees of diversity. The approach taken is to solve for a unitary transmit precoder, under a zero interuser interference constraint, that minimizes an upper bound on the symbol error rate (SER) for each user. Solutions where all transmit antennas are employed, as well as subsets of antennas (to reduce analog components), are described. Numerical results confirm a dramatic improvement in terms of SER and mutual information over single-user multiple-input multiple-output (MIMO) methods and static allocation methods. For example, the proposed techniques achieve a signal-to-noise ratio (SNR) improvement of 6-10 dB at an uncoded SER of 10 -3 , with only one extra transmit antenna
Heavy metal contamination in soil has attracted great attention worldwide. In situ stabilization has been considered an effective way to remediate soils contaminated by heavy metals. In the present ...research, a multiple-modified biochar (BCM) was prepared to stabilize Cd and Cu contamination in two different soils: a farmland soil (JYS) and a vegetable soil (ZZS). The results showed that BCM was a porous-like flake material and that modification increased its specific surface area and surface functional groups. The incubation experiment indicated that BCM decreased diethylenetriaminepentaacetic (DTPA)-extractable Cd and Cu by 92.02% and 100.00% for JYS and 90.27% and 100.00% for ZZS, respectively. The toxicity characteristic leaching procedure (TCLP)-extractable Cd and Cu decreased 66.46% and 100.00% for JYS and 46.33% and 100.00% for ZZS, respectively. BCM also reduced the mobility of Cd and Cu in soil and transformed them to more stable fractions. In addition, the application of BCM significantly increased the soil dehydrogenase, organic matter content and available K (p < 0.05). These results indicate that BCM has great potential in the remediation of Cd- and Cu-contaminated soil.
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•Multiple modifications improved the specific surface area and surface active groups of biochar.•BCM efficiently reduced the bioavailability Cd and Cu.•BCM reduced the leachability of Cd and Cu.•BCM transformed Cd and Cu to a more stable fraction.•BCM improved the properties of Cd- and Cu-contaminated soils.
A 6 weeks pot culture experiment was carried out to investigate the stabilization effects of a modified biochar (BCM) on metals in contaminated soil and the uptake of these metals by wheat seedlings. ...The results showed that the application of BCM significantly increased the soil fertility, the biomass of wheat seedling roots increased by more than 50%, and soil dehydrogenase (DHA) and catalase (CAT) activities increased by 369.23% and 12.61%, respectively. In addition, with the application of BCM, the diethylenetriaminepentaacetic acid extractable (DTPA-extractable) Cd, Pb, Cu and Zn in soil were reduced from 2.34 to 0.38 mg/kg, from 49.27 to 25.65 mg/kg, from 3.55 mg/kg to below the detection limit and from 4.05 to 3.55 mg/kg, respectively. Correspondingly, the uptake of these metals in wheat roots and shoots decreased by 62.43% and 79.83% for Cd, 73.21% and 66.32% for Pb, 57.98% and 68.92% for Cu, and 40.42% and 43.66% for Zn. Furthermore, BCM application decreased the abundance and alpha diversity of soil bacteria and changed the soil bacterial community structure dramatically. Overall, BCM has great potential for the remediation of metal-contaminated soils, but its long-term impact on soil metals and biota need further research.
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•Modified biochar (BCM) significantly reduced activity of metals in the soil.•BCM inhibited the uptake of metals by wheat seedlings.•BCM improved soil properties and increased soil enzyme activity.•BCM decreased soil bacterial diversity and changed the soil bacterial community.
The sum capacity of a Gaussian broadcast MIMO channel can be achieved with dirty paper coding (DPC). However, algorithms that approach the DPC sum capacity do not appear viable in the forseeable ...future, which motivates lower complexity interference suppression techniques. Block diagonalization (BD) is a linear preceding technique for downlink multiuser MIMO systems. With perfect channel knowledge at the transmitter, BD can eliminate other users' interference at each receiver. In this paper, we study the sum capacity of BD with and without receive antenna selection. We analytically compare BD without receive antenna selection to DPC for a set of given channels. It is shown that (1) if the user channels are orthogonal to each other, then BD achieves the same sum capacity as DPC; (2) if the user channels lie in the same subspace, then the gain of DPC over BD can be upper bounded by the minimum of the number of transmit and receive antennas. These observations also hold for BD with receive antenna selection. Further, we study the ergodic sum capacity of BD with and without receive antenna selection in a Rayleigh fading channel. Simulations show that BD can achieve a significant part of the total throughput of DPC. An upper bound on the ergodic sum capacity gain of DPC over BD is proposed for easy estimation of the gap between the sum capacity of DPC and BD without receive antenna selection.
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•The gut microbiome profile of a rat model of MNNG-induced gastric carcinogenesis was analyzed.•Changes in gut microbiota composition were detected by 16S rRNA gene ...sequencing.•Bacterial species richness increased and diversity decreased during gastric carcinogenesis progression.•The most significant changes were occurred at the precancerous lesion of GC stage.•Gut microbiome changes in the rat gastric carcinogenesis model were similar to those in human.
Although many studies have examined changes in gut microbiota composition in gastric carcinogenesis to clarify the mechanism of action of anticancer drugs, it is unclear whether animal models of gastric carcinogenesis adequately reflect the disease in humans.
To address this issue, the present study investigated changes in the gut microbiome profile of a rat model of gastric carcinogenesis established using a combination of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), sodium salicylate, irregular fasting, and ranitidine. The rats were divided into control (Normal), chronic non-atrophic gastritis (CNAG), chronic atrophic gastritis (CAG), precancerous lesion of gastric cancer (PLGC), and gastric cancer (GC) groups according to histopathological features. Gut microbiome in gastric carcinogenesis profiling was performed by 16S rRNA gene sequencing of rat feces samples.
We found that gut bacterial species richness increased whereas species diversity decreased during gastric carcinogenesis, with the most significant changes detected in the PLGC group. Gut microbiota community composition differed across groups, with the greatest similarities observed between CNAG and CAG groups and between PLGC and GC groups. There were significant differences in taxonomic representation at the phylum level: the PLGC group had the highest ratio of Firmicutes/Bacteroidetes whereas the GC group had the highest abundance of Proteobacteria and Actinobacteria.
These results indicate that changes in the gut microbiome in a rat model of MNNG-induced gastric carcinogenesis are similar to those observed in humans, thus providing a useful tool for evaluating the efficacy and mechanism of action of novel monotherapies or drug combinations for the treatment of gastric carcinogenesis.
A low-complexity multimode transmission technique for downlink multiuser multiple-input-multiple-output (MIMO) systems with block diagonalization (BD) is proposed. The proposed technique adaptively ...configures the number of data streams for each user by adjusting its number of active receive antenna and switching between single-stream beamforming and multistream spatial multiplexing, as a means to exploit the multimode switching diversity. We consider a highly loaded system where there are a large number of users, hence a subset of users need to be selected. Joint user and antenna selection has been proposed as a multiuser multimode switching technique, where the optimal subset of receive antennas and users are chosen to maximize the sum throughput. The brute-force search, however, is prohibitively complicated. In this paper, two low-complexity near-optimal user/antenna selection algorithms are developed. The first algorithm aims at maximizing a capacity lower bound, derived in terms of the sum Frobenius norm of the channel, while the second algorithm greedily maximizes the sum capacity. We analytically evaluate the complexity of the proposed algorithms and show that it is orders of magnitude lower than that of the exhaustive search. Simulation results demonstrate that the proposed algorithms achieve up to 98% of the sum throughput of the exhaustive search, for most system configurations, while the complexity is substantially reduced.
Purpose
Sediment contaminated with metals constitutes a worldwide environmental problem. Biochar-based materials are widely applied in soil/sediment remediation due to their high adsorption capacity ...and cost-effectiveness. In this study, multiple modified biochar (BCM) were used to stabilize metals in contaminated river sediment.
Materials and methods
BCM was mixed with metal-contaminated river sediment at doses of 0%, 1%, 2% and 3% (w/w, represented as CK, BCM1, BCM2 and BCM3, respectively). Changes in the availability, leachability and fractions of metals and in sediment chemical properties and enzyme activities (catalase, dehydrogenase) were analysed.
Results and discussion
Results showed that the application of BCM effectively reduced the levels of diethylenetriaminepentaacetic (DTPA)-extractable, CaCl
2
-extractable and toxicity characteristic leaching procedure (TCLP)-extractable metals in the sediment. In the BCM3 treatment, DTPA-extractable, levels of CaCl
2
-extractable and TCLP-extractable metals decreased by 56.61%, 98.20% and 23.57% for Cd, 99.99%, 97.04% and 71.15% for Cu and 82.21%, 97.77% and 55.27% for Ni, respectively. The levels of DTPA-extractable and TCLP-extractable Pb decreased 69.60% and 69.24%, respectively, and the levels of CaCl
2
-extractable and TCLP-extractable Zn decreased 49.81% and 55.27%, respectively. In addition, BCM application (BCM3) transformed the acid-soluble Cu, Cd and Ni to a more stable fraction, and the levels of acid-soluble Cd and Ni decreased by 28.23% and 5.81%, respectively. The level of acid-soluble Cu was below the detection limit, and reducible Cu was decreased 0.60% in the BCM3 treatment. However, the influence of BCM on the fractions of Pb and Zn was not significant (
p
< 0.05). In addition, the levels of organic matter, available P and NH
4
+
-N in the treated sediment were significantly increased compared with those undergoing CK treatment. BCM has insignificant influence on sediment pH, available K and NO
3
-N levels and sediment enzyme activity.
Conclusions
BCM simultaneously reduced the bioavailability and leachability of multiple metals in contaminated sediment. These results suggest that BCM has great potential for the remediation of sediments contaminated with metals.
In this study, a biochar-supported polycarboxylic acid-functionalized nanoiron oxide-encapsulated composite (BC@nFe-CA) was synthesized by the pyrolysis of rice husk biomass, nZVI reductive ...deposition and surface functionalization under mild conditions for Cd(II), EDTA and Cd-EDTA wastewater treatment. Physical and chemical properties of BC@nFe-CA were characterized by various spectral techniques; the effects of initial pH, contact time, initial concentration, etc., and the mechanism on Cd(II) and EDTA adsorption by BC@nFe-CA were explored by batch experiments and spectral techniques. The isotherm results indicated that Langmuir model can well describe the equilibrium data with the maximum BC@nFe-CA adsorption capacities of 63.84 mg g
−1
toward Cd(II) and 50.27 mg g
−1
for EDTA at pH 5.5 (± 0.5) and 40 °C, and the Cd(II) and EDTA adsorption process was quick, endothermic and spontaneous. Furthermore, Cd-EDTA decomplexation experiment was carried out in the presence of H
2
O
2
and BC@nFe-CA to evaluate the dominant catalytic role of reactive oxygen species (ROS). It was found that ROS generated in the BC@nFe-CA/H
2
O
2
system was responsible for Cd-EDTA decomplexation. The stabilization energies of BC@nFe-CA loaded with Cd(II) and EDTA were analyzed by density functional theory (DFT) calculation, and the possible decomplexation pathway of Cd-EDTA was proposed. Finally, high-purity (approximately 99.8%) cadmium salt crystals were obtained through the pickling-oxidation-evaporation crystallization (POEC) process. This work develops a feasible route for the application of rice husk biomass, unravels the interaction of BC@nFe-CA with Cd(II), EDTA and Cd-EDTA under various conditions, and provides deep insight into Cd-EDTA decomplexation in the presence of BC@nFe-CA and ROS.
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