Enhancing wastewater remediation by drinking water treatment residual-augmented floating treatment wetlands.

In this study, the involvement of aluminum-based drinking water treatment residual (DWTR) as substrate in floating treatment wetland (FTW) to enhance its treatment performance was firstly proposed and trialed. A laboratory scale DWTR-FTW fed with synthetic wastewater containing COD, nitrogen (N), phosphorus (P) and mineral salts was operated in three stages of unplanted (1-30 days), planted (31-60 days) and aerated (61-135 days) modes. The results showed that the average removal rates of COD, total nitrogen (TN), total phosphorus (TP) in stage 3 were 88%, 85%, and 90.2%, respectively, indicating the outstanding purification performance of DWTR-FTW in comparison of traditional FTWs. The embedded DWTR enriches the biomass and robustly adsorbs P, while aeration supplies sufficient dissolved oxygen for the microorganism. The results revealed that 7.022 g P was accumulated in DWTR, which is 400 times higher than that in sediment and plants during the experimental period, reflecting that DWTR adsorption is the major P removal pathway in DWTR-FTW. Overall, DWTR-FTW could significantly remove pollutants, especially P, and provide an alternative pathway to enhance purification performance of FTW.

The aggregation of Fe3+ and their d-d radiative transitions in ZnSe:Fe3+ nanobelts by CVD growth.

Transition metal (TM) doped II-VI semiconductors have attracted great attention due to their luminescence and diluted magnetism. In this study, the Fe3+-doped ZnSe nanobelts (NBs) were grown by a facile CVD method. The surface morphology observed via SEM is smooth and clean and the elemental composition measured via EDS confirms that the Fe3+ ions were incorporated into ZnSe NBs successfully. The micro-Raman scattering spectra demonstrate that the as-prepared NBs have the zinc blende structure. Furthermore, the Raman spectra of the Fe3+-doped NBs were compared with those of pure and Fe2+-doped reference samples. The former with a higher signal-to-noise ratio, an enhanced 2LO mode, a stronger LO mode redshift and a larger intensity ratio of LO/TO mode as well as the lower acoustic phonon modes confirms the better crystallization and the stronger electron-phonon coupling on Fe3+-incorporation. The emission of single Fe3+ ion, assigned to the 4T1 → 6A1 transition, was observed at about 570 nm. Moreover, increasing the doping concentration of Fe3+ ions caused the formation of different Fe-Fe coupled pairs in the lattice, which emitted light at about 530-555 nm for an antiferromagnetic-coupled pair, possibly due to the stacking faults and at about 620-670 nm for a ferromagnetic-coupled pair.

[Ventilator-associated pneumonia among premature infants <34 weeks' gestational age in neonatal intensive care unit in China: a multicenter study].

Objective: To investigate the incidence and pathogen distribution of ventilator-associated pneumonia (VAP) among preterm infants admitted to level Ⅲ neonatal intensive care units (NICU) in China. Method: A prospective study was conducted in 25 level Ⅲ NICU, enrolling all preterm infants <34 weeks gestational age admitted to the participating NICU within the first 7 days of life from May 2015 to April 2016. Chi-square test, t test and Mann-Whitney U test were used for statistical analysis. Result: A total of 7 918 patients were enrolled, within whom 4 623(58.4%) were males. The birth weight was (1 639±415) g and the gestational age was (31.4±2.0) weeks; 4 654(58.8%) infants required non-invasive mechanical ventilation and 2 154(27.2%) required intubation. Of all the mechanically ventilated patients, VAP occurred in 95 patients. The overall VAP rate was 7.0 episodes per 1 000 ventilator days, varying from 0 to 34.4 episodes per 1 000 ventilator days in different centers. The incidence of VAP was 9.6 and 6.0 per 1 000 ventilator days in children's hospitals and maternity-infant hospitals respectively, without significant differences (t=1.002, P=0.327). Gram-negative bacilli (76 strains, 91.6%) were the primary VAP microorganisms, mainly Acinetobacter baumannii (24 strains, 28.9%), Klebsiella pneumonia (23 strains, 27.7%), and Pseudomonas aeruginosa (10 strains, 12.0%). Conclusion: The incidence of VAP in China is similar to that in developed counties, with substantial variability in different NICU settings. More efforts are needed to monitor and evaluate the preventable factors associated with VAP and conduct interventions that could effectively reduce the occurrence of VAP.

Theory of low-power ultra-broadband terahertz sideband generation in bi-layer graphene.

In a semiconductor illuminated by a strong terahertz (THz) field, optically excited electron-hole pairs can recombine to emit light in a broad frequency comb evenly spaced by twice the THz frequency. Such high-order THz sideband generation is of interest both as an example of extreme nonlinear optics and also as a method for ultrafast electro-optical modulation. So far, this phenomenon has only been observed with large field strengths (~10 kV cm(-1)), an obstacle for technological applications. Here we predict that bi-layer graphene generates high-order sidebands at much weaker THz fields. We find that a THz field of strength 1 kV cm(-1) can produce a high-sideband spectrum of about 30 THz, 100 times broader than in GaAs. The sidebands are generated despite the absence of classical collisions, with the quantum coherence of the electron-hole pairs enabling recombination. These remarkable features lower the barrier to desktop electro-optical modulation at THz frequencies, facilitating ultrafast optical communications.

Experimental observation of electron-hole recollisions.

An intense laser field can remove an electron from an atom or molecule and pull the electron into a large-amplitude oscillation in which it repeatedly collides with the charged core it left behind. Such recollisions result in the emission of very energetic photons by means of high-order-harmonic generation, which has been observed in atomic and molecular gases as well as in a bulk crystal. An exciton is an atom-like excitation of a solid in which an electron that is excited from the valence band is bound by the Coulomb interaction to the hole it left behind. It has been predicted that recollisions between electrons and holes in excitons will result in a new phenomenon: high-order-sideband generation. In this process, excitons are created by a weak near-infrared laser of frequency f(NIR). An intense laser field at a much lower frequency, f(THz), then removes the electron from the exciton and causes it to recollide with the resulting hole. New emission is predicted to occur as sidebands of frequency f(NIR) + 2nf(THz), where n is an integer that can be much greater than one. Here we report the observation of high-order-sideband generation in semiconductor quantum wells. Sidebands are observed up to eighteenth order (+18f(THz), or n = 9). The intensity of the high-order sidebands decays only weakly with increasing sideband order, confirming the non-perturbative nature of the effect. Sidebands are strongest for linearly polarized terahertz radiation and vanish when the terahertz radiation is circularly polarized. Beyond their fundamental scientific significance, our results suggest a new mechanism for the ultrafast modulation of light, which has potential applications in terabit-rate optical communications.

Atomic-scale magnetometry of distant nuclear spin clusters via nitrogen-vacancy spin in diamond.

The detection of single nuclear spins is an important goal in magnetic resonance spectroscopy. Optically detected magnetic resonance can detect single nuclear spins that are strongly coupled to an electron spin, but the detection of distant nuclear spins that are only weakly coupled to the electron spin has not been considered feasible. Here, using the nitrogen-vacancy centre in diamond as a model system, we numerically demonstrate that it is possible to detect two or more distant nuclear spins that are weakly coupled to a centre electron spin if these nuclear spins are strongly bonded to each other in a cluster. This cluster will stand out from other nuclear spins by virtue of characteristic oscillations imprinted onto the electron spin decoherence profile, which become pronounced under dynamical decoupling control. Under many-pulse dynamical decoupling, the centre electron spin coherence can be used to measure nuclear magnetic resonances of single molecules. This atomic-scale magnetometry should improve the performance of magnetic resonance spectroscopy for applications in chemical, biological, medical and materials research, and could also have applications in solid-state quantum computing.

Preserving electron spin coherence in solids by optimal dynamical decoupling.

To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is first vital to overcome the problem of spin decoherence due to their coupling to the noisy environment. Dynamical decoupling, which uses stroboscopic spin flips to give an average coupling to the environment that is effectively zero, is a particularly promising strategy for combating decoherence because it can be naturally integrated with other desired functionalities, such as quantum gates. Errors are inevitably introduced in each spin flip, so it is desirable to minimize the number of control pulses used to realize dynamical decoupling having a given level of precision. Such optimal dynamical decoupling sequences have recently been explored. The experimental realization of optimal dynamical decoupling in solid-state systems, however, remains elusive. Here we use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50 K to room temperature. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 mus; it would otherwise be about 0.04 mus without control or 6.2 mus under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Optimal dynamical decoupling may be applied to other solid-state systems, such as diamonds with nitrogen-vacancy centres, and so lay the foundation for quantum coherence control of spins in solids at room temperature.

Broadband coherent emission observed in polycrystalline CdSSe nanowires under high excitation.

Polycrystalline CdSSe nanowires were prepared with a low-temperature physical evaporation method. Structural analysis combining HRTEM with XRD demonstrate that these as-prepared wires have a hexagonal wurtzite structure with a polycrystalline nature. Locally excited optical measurements show that though these wires can still act as waveguide cavities, their polycrystalline nature will induce a significant redshift of the emitted light during its transportation along them. Power dependent photoluminescence measurement shows that these polycrystalline wires can achieve broadband coherent emission at the band-edge band under high excitation, which shows marked contrast with the much narrower and multimode spectra observed in the single-crystalline nanowires with the same elemental composition. Time-resolved photoluminescence further confirms the occurrence of coherent emission in these wires, which originates from the electron-hole plasma (EHP) recombination of high-density carriers generated under high excitation. These kinds of polycrystalline alloy nanowires with broadband coherent emission should have potential uses in nano-scaled wavelength tunable light-emitting devices.

The influence of preamplifiers on the piezoelectric sensor's dynamic property.

A charge amplifier or a voltage amplifier can be used as a signal conditioning circuit between a piezoelectric element and a meter or a data acquisition board. The outputs of the piezoelectric sensor are in an open-circuit state and a short-circuit state if a voltage amplifier and a charge amplifier are used, respectively. When the electrodes are in different states, the piezoelectric element has rather different stiffness and thus different sensor resonant frequency. This phenomenon is theoretically analyzed in detail and validated by a carefully designed experiment. The results indicate that a much wider range of working frequency is achieved when a voltage amplifier is used.