Development and application of ferrihydrite-modified diatomite and gypsum for phosphorus control in lakes and reservoirs

A novel phosphorus (P) adsorbent, ferrihydrite-modified diatomite (FHMD) was developed and characterized in this study. The FHMD was made through surface modification treatments, including NaOH treatment and ferrihydrite deposition on raw diatomite. In the NaOH treatment, surface SiO2 was partially dissolved in the NaOH solution. The dissolved Si contributed to form stable 2-line ferrihydrite, which deposited into the larger mesopores and macropores of the diatomite. The 2-line ferrihydrite not only deposited into the pores of the diatomite but also aggregated on the surface. Filling the larger mesopores and macropores of the diatomite and aggregation on the diatomite surface with 0.24 g Fe/g of 2-line ferrihydrite resulted in a specific surface area of 211.1 m2/g for the FHMD, which is an 8.5-fold increase over the raw diatomite (24.77 m2/g). The surface modification also increased the point of zero charge (pHPZC) values to 10 for the FHMD from 5.8 for the raw diatomite. Effects of the formation process parameters such as concentrations of FeCl2, NaOH, and drying temperature on the formation mechanism and crystalline characteristics of FHMD were studied by using X-ray absorption near-edge structure (XANES) spectroscopy. The spectra were recorded in both the total electron yield (TEY) and the fluorescence yield (FY) modes to investigate the chemical nature of Fe and Si on the surface and in the bulk of ferrihydrite-modified diatomite, respectively. It was found that only the surface SiO2 was partially dissolved in the NaOH solution with stirring and heating, whereas the bulk of diatomite seemed to be preserved. The dissolved Si was incorporated into the structure of ferrihydrite to form the 2-line Si-containing ferrihydrite. The crystalline degree of ferrihydrite increased with the increasing FeCl2 concentration and the Brunauer-Emmett-Teller (BET) specific surface area of FHMD decreased with the increasing FeCl2 concentration. The NaOH solution of higher concentration partially dissolved more surface SiO2 and the crystalline degree of ferrihydrite decreased with the increase in NaOH concentration. The dehydroxylation on the surface of FHMD occurred in the high temperature calcination, causing an energy shift in the Si L-edge spectra to the high energy side and an increase in the crystalline degree of ferrihydrite. In this study, the optimal synthesis conditions for the FHMD with the least crystalline degree and the highest surface area were found to be as the follows: 100 mL of 0.5M FeCl2 solution, 6M NaOH solution and the drying temperature of 50 ºC. Phosphorus adsorption behavior and adsorption mechanism of FHMD were investigated in the research. The Langmuir model best described the P adsorption data for FHMD. Because of increased surface area and surface charge, the maximum adsorption capacity of FHMD at pH 4 and pH 8.5 was increased from 10.2 mg P/g and 1.7 mg P/g of raw diatomite to 37.3 mg P/g and 13.6 mg P/g, respectively. Phosphorus showed the best affinity of adsorption onto FHMD among common anions. K-edge P XANES spectra demonstrate that P is not precipitated with Fe (III) of FHMD, but adsorbed on the surface layer of FHMD. Phosphorus removal from lake water and limiting phosphorus release from sediment by FHMD was examined. Phosphorus removal from lake water proceeded primarily through P adsorption onto the surface of FHMD. When a dose of FHMD of 250 mg/L was applied to lake water, a total phosphorus (TP) removal efficiency of 88% was achieved and a residual TP concentration was 17.0 µg/L which falls within the oligotrophic TP range (3.0-17.7 µg/L). FHMD settled down to the bottom of the 43 cm high cylinder within 6 hours, which suggested that retention time of FHMD in the 5.5 m of Jackfish lake water column was close to the equilibrium time of P adsorption onto FHMD (72 hours). During the 30-day anoxic incubation period, TP concentrations in lake water treated by 400, 500 and 600 mg/L of FHMD showed a slight decrease and maximum TP concentrations remained at levels lower than 15 µg/L. The addition of FHMD resulted in a marked increase in Fe-P fraction, a pronounced decrease in labile-P and organic-P fractions, and stable Al-P, Ca-P and residual-P fractions. The effect of FHMD on limiting P release was comparable with those of the combination of FHMD and alum solutions with logarithmic ratios of Al to mobile P of 0.5 and 0.8. FHMD not only can effectively remove P from lake water but also keep a strong P-binding capacity under anoxic conditions and competition for P with alum at high amounts. The role of gypsum on stabilizing sediment and the optimum dose of gypsum were investigated. The effectiveness of gypsum in stabilizing sediment was proved by the fact that at the same agitation speed, turbidities and soluble reactive P (SRP) concentrations of samples treated with gypsum were much lower than those of sample without gypsum. The optimal thickness of the gypsum layer was found to be 0.8 cm. Combined application of FHMD and gypsum to P control was investigated in the research. It was found in the 30-day incubation of lake water and sediment treated by FHMD and gypsum that no P release seemed to occur regardless of oxic or anoxic conditions. In order to investigate the 120-day effects of FHMD and gypsum on the P control under anoxic and agitation conditions a lab-scale artificial aquarium was established in an environmental chamber. Daily oscillation of a metal grid did not yield the sediment resuspension due to the gypsum stabilization. The combined application of FHMD and gypsum resulted in a 1 g/L increase in the SO42- concentration in the 120-day aquarium compared with that in the control aquarium; however it did not affect the total kjeldahl nitrogen (TKN) concentrations in both the control aquarium and the 120-day aquarium. The addition of FHMD and gypsum enhanced total alkalinity in the 120-day aquarium, thereby improving buffering capacity of lake water. Under anoxic conditions and sediment resuspension conditions, relative to a large increase in total P (TP) concentrations in the control aquarium, TP concentrations in the 120-day aquarium stayed relatively stable, fluctuating within the range of 9.1-13.3 µg/L. Relative to control sediment, Fe-P was significantly enhanced during the 60-day incubation; however, Fe-P did not appear to increase significantly in the second 60-day incubation. Labile-P and organic-P decreased with sediment depths in both control aquarium and test aquariums; however, Al-P, Ca-P and residue-P increased with sediment depth. Lower Al-P is observed in treatment aquariums than in control sediment. As an effective P adsorbent, FHMD showed a high adsorption capacity as well as a significantly higher affinity for P than other anions. A combined application of FHMD and gypsum effectively reduced sediment resuspension and maintained TP levels within the oligotrophic range under anoxic conditions in the laboratory-scale artificial aquarium

Utility-maximization Resource Allocation for Device-to-Device Communication Underlaying Cellular Networks

Device-to-device(D2D) underlaying communication brings great benefits to the cellular networks from the improvement of coverage and spectral efficiency at the expense of complicated transceiver design. With frequency spectrum sharing mode, the D2D user generates interference to the existing cellular networks either in downlink or uplink. Thus the resource allocation for D2D pairs should be designed properly in order to reduce possible interference, in particular for uplink. In this paper, we introduce a novel bandwidth allocation scheme to maximize the utilities of both D2D users and cellular users. Since the allocation problem is strongly NP-hard, we apply a relaxation to the association indicators. We propose a low-complexity distributed algorithm and prove the convergence in a static environment. The numerical result shows that the proposed scheme can significant improve the performance in terms of utilities.The performance of D2D communications depends on D2D user locations, the number of D2D users and QoS(Quality of Service) parameters

Imaging Neural Activity in the Primary Somatosensory Cortex Using Thy1-GCaMP6s Transgenic Mice

The mammalian brain exhibits marked symmetry across the sagittal plane. However, detailed description of neural dynamics in symmetric brain regions in adult mammalian animals remains elusive. In this study, we describe an experimental procedure for measuring calcium dynamics through dual optical windows above bilateral primary somatosensory corticies (S1) in Thy1-GCaMP6s transgenic mice using 2-photon (2P) microscopy. This method enables recordings and quantifications of neural activity in bilateral mouse brain regions one at a time in the same experiment for a prolonged period in vivo. Key aspects of this method, which can be completed within an hour, include minimally invasive surgery procedures for creating dual optical windows, and the use of 2P imaging. Although we only demonstrate the technique in the S1 area, the method can be applied to other regions of the living brain facilitating the elucidation of structural and functional complexities of brain neural networks

Longitudinal Optogenetic Motor Mapping Revealed Structural and Functional Impairments and Enhanced Corticorubral Projection after Contusive Spinal Cord Injury in Mice

Current evaluation of impairment and repair after spinal cord injury (SCI) is largely dependent on behavioral assessment and histological analysis of injured tissue and pathways. Here, we evaluated whether transcranial optogenetic mapping of motor cortex could reflect longitudinal structural and functional damage and recovery after SCI. In Thy1-Channelrhodopsin2 transgenic mice, repeated motor mappings were made by recording optogenetically evoked electromyograms (EMGs) of a hindlimb at baseline and 1 day and 2, 4, and 6 weeks after mild, moderate, and severe spinal cord contusion. Injuries caused initial decreases in EMG amplitude, losses of motor map, and subsequent partial recoveries, all of which corresponded to injury severity. Reductions in map size were positively correlated with motor performance, as measured by Basso Mouse Scale, rota-rod, and grid walk tests, at different time points, as well as with lesion area at spinal cord epicenter at 6 weeks post-SCI. Retrograde tracing with Fluoro-Gold showed decreased numbers of cortico- and rubrospinal neurons, with the latter being negatively correlated with motor map size. Combined retro- and anterograde tracing and immunostaining revealed more neurons activated in red nucleus by cortical stimulation and enhanced corticorubral axons and synapses in red nucleus after SCI. Electrophysiological recordings showed lower threshold and higher amplitude of corticorubral synaptic response after SCI. We conclude that transcranial optogenetic motor mapping is sensitive and efficient for longitudinal evaluation of impairment and plasticity of SCI, and that spinal cord contusion induces stronger anatomical and functional corticorubral connection that may contribute to spontaneous recovery of motor function

Converting normal insulators into topological insulators via tuning orbital levels

Tuning the spin-orbit coupling strength via foreign element doping and/or modifying bonding strength via strain engineering are the major routes to convert normal insulators to topological insulators. We here propose an alternative strategy to realize topological phase transition by tuning the orbital level. Following this strategy, our first-principles calculations demonstrate that a topological phase transition in some cubic perovskite-type compounds CsGeBr$_3$ and CsSnBr$_3$ could be facilitated by carbon substitutional doping. Such unique topological phase transition predominantly results from the lower orbital energy of the carbon dopant, which can pull down the conduction bands and even induce band inversion. Beyond conventional approaches, our finding of tuning the orbital level may greatly expand the range of topologically nontrivial materials

Sequence Design for Cognitive CDMA Communications under Arbitrary Spectrum Hole Constraint

To support interference-free quasi-synchronous code-division multiple-access (QS-CDMA) communication with low spectral density profile in a cognitive radio (CR) network, it is desirable to design a set of CDMA spreading sequences with zero-correlation zone (ZCZ) property. However, traditional ZCZ sequences (which assume the availability of the entire spectral band) cannot be used because their orthogonality will be destroyed by the spectrum hole constraint in a CR channel. To date, analytical construction of ZCZ CR sequences remains open. Taking advantage of the Kronecker sequence property, a novel family of sequences (called "quasi-ZCZ" CR sequences) which displays zero cross-correlation and near-zero auto-correlation zone property under arbitrary spectrum hole constraint is presented in this paper. Furthermore, a novel algorithm is proposed to jointly optimize the peak-to-average power ratio (PAPR) and the periodic auto-correlations of the proposed quasi-ZCZ CR sequences. Simulations show that they give rise to single-user bit-error-rate performance in CR-CDMA systems which outperform traditional non-contiguous multicarrier CDMA and transform domain communication systems; they also lead to CR-CDMA systems which are more resilient than non-contiguous OFDM systems to spectrum sensing mismatch, due to the wideband spreading.Comment: 13 pages,10 figures,Accepted by IEEE Journal on Selected Areas in Communications (JSAC)--Special Issue:Cognitive Radio Nov, 201

Characterization of dendritic morphology and neurotransmitter phenotype of thoracic descending propriospinal neurons after complete spinal cord transection and GDNF treatment

After spinal cord injury (SCI), poor regeneration of damaged axons of the central nervous system (CNS) causes limited functional recovery. This limited spontaneous functional recovery has been attributed, to a large extent, to the plasticity of propriospinal neurons, especially the descending propriospinal neurons (dPSNs). Compared with the supraspinal counterparts, dPSNs have displayed significantly greater regenerative capacity, which can be further enhanced by glial cell line-derived neurotrophic factor (GDNF). In the present study, we applied a G-mutated rabies virus (G-Rabies) co-expressing green fluorescence protein (GFP) to reveal Golgi-like dendritic morphology of dPSNs. We also investigated the neurotransmitters expressed by dPSNs after labeling with a retrograde tracer Fluoro-Gold (FG). dPSNs were examined in animals with sham injuries or complete spinal transections with or without GDNF treatment. Bilateral injections of G-Rabies and FG were made into the 2nd lumbar (L2) spinal cord at 3 days prior to a spinal cord transection performed at the 11th thoracic level (T11). The lesion gap was filled with Gelfoam containing either saline or GDNF in the injury groups. Four days post-injury, the rats were sacrificed for analysis. For those animals receiving G-rabies injection, the GFP signal in the T7-9 spinal cord was visualized via 2-photon microscopy. Dendritic morphology from stack images was traced and analyzed using a Neurolucida software. We found that dPSNs in sham injured animals had a predominantly dorsal-ventral distribution of dendrites. Transection injury resulted in alterations in the dendritic distribution with dorsal-ventral retraction and lateral-medial extension. Treatment with GDNF significantly increased the terminal dendritic length of dPSNs. The density of spine-like structures was increased after injury, and treatment with GDNF enhanced this effect. For the group receiving FG injections, immunohistochemistry for glutamate, choline acetyltransferase (ChAT), glycine, and GABA was performed in the T7-9 spinal cord. We show that the majority of FG retrogradely-labeled dPSNs were located in the Rexed Lamina VII. Over 90% of FG-labeled neurons were glutamatergic, with the other three neurotransmitters contributing less than 10% of the total. To our knowledge this is the first report describing the morphologic characteristics of dPSNs and their neurotransmitter expressions, as well as the dendritic response of dPSNs after transection injury and GDNF treatment