Climatic control of Mississippi River flood hazard amplified by river engineering.

Over the past century, many of the world's major rivers have been modified for the purposes of flood mitigation, power generation and commercial navigation. Engineering modifications to the Mississippi River system have altered the river's sediment levels and channel morphology, but the influence of these modifications on flood hazard is debated. Detecting and attributing changes in river discharge is challenging because instrumental streamflow records are often too short to evaluate the range of natural hydrological variability before the establishment of flood mitigation infrastructure. Here we show that multi-decadal trends of flood hazard on the lower Mississippi River are strongly modulated by dynamical modes of climate variability, particularly the El Niño-Southern Oscillation and the Atlantic Multidecadal Oscillation, but that the artificial channelization (confinement to a straightened channel) has greatly amplified flood magnitudes over the past century. Our results, based on a multi-proxy reconstruction of flood frequency and magnitude spanning the past 500 years, reveal that the magnitude of the 100-year flood (a flood with a 1 per cent chance of being exceeded in any year) has increased by 20 per cent over those five centuries, with about 75 per cent of this increase attributed to river engineering. We conclude that the interaction of human alterations to the Mississippi River system with dynamical modes of climate variability has elevated the current flood hazard to levels that are unprecedented within the past five centuries.

Transflective spatial terahertz wave modulator.

Spatial light modulators can digitally manipulate the amplitude, phase, and polarization of light. Their counterparts in the terahertz band are highly pursued to meet the requirements of numerous applications such as wireless communications and biomedical detection. Here, we propose a spatial terahertz wave modulator based on a liquid-crystal-integrated metadevice. The modulator consists of 8 × 8 pixels. The liquid crystal layer is sandwiched between an asymmetric split ring resonator array and pixelated interdigital electrodes. Fano resonance occurs for the transmitted wave, while the reflected wave is perfectly absorbed. By separately driving the liquid crystal with pixelated interdigital electrodes, both the Fano resonance and absorption peak can be continuously tuned due to the variation in the environmental refractive index. This work provides a transflective spatial terahertz wave modulator that can dynamically reconfigure a terahertz wavefront.

Liquid crystal integrated metalens with dynamic focusing property.

Metalenses are developing fast towards versatile and integrated terahertz (THz) apparatuses, while tunable ones are highly pursued. Here, we propose a strategy that integrates dielectric metasurfaces with liquid crystals (LCs) to realize the dynamic focal spot manipulation. The silicon pillar meta-units of the metasurface are properly selected to generate different phase profiles for two orthogonal linear polarizations, permitting a laterally or axially altered focal spot. After LCs integrated, polarization-multiplexed focusing can be achieved via electrically varying the LC orientations. We demonstrate two metalenses with distinct functions. For the first one, the uniformly aligned LC works as a polarization converter, and further switches the focal length by altering the bias. For the second one, an LC polarization grating is utilized for rear spin-selective beam deflection. Consequently, a THz port selector is presented. This work supplies a promising method towards active THz elements, which may be widely applied in THz sensing, imaging, and communication.

3D porous graphene-assisted capsulized cholesteric liquid crystals for terahertz power visualization.

We demonstrate a high-efficiency visualized terahertz (THz) power meter based on the THz-photothermochromism of capsulized cholesteric liquid crystals (CCLCs) embedded in three-dimensional porous graphene (3DPG). The graphene is a broadband perfect absorber for THz radiation and transfers heat efficiently, and its black background is beneficial for color measurement. Quantitative visualization of THz intensity up to 2.8×102mW/cm2 is presented. The minimal detectable THz power is 0.009 mW. With multi-microcapsule analysis, the relationship between THz power and the average hue value of CCLCs achieves linearity. The device can convert THz radiation to visible light and is lightweight, cheap, and easy to use.

Liquid crystal tunable terahertz lens with spin-selected focusing property.

We propose and demonstrate an active spin-selected lens with liquid crystal (LC) in the terahertz (THz) range. The lens is a superposition of two geometric phase lenses with separate centers and conjugated phase profiles. Its digitalized multidirectional LC orientations are realized via a dynamic micro-lithography-based photo-patterning technique and sandwiched by two graphene-electrode-covered silica substrates. The specific lens can separate the focusing spots of incident light with opposite circular polarizations. Its focusing performance from 0.8 to 1.2 THz is characterized using a scanning near-field THz microscope system. The polarization conversion efficiency varies from 32.1% to 70.2% in this band. The spin-selected focusing functions match well with numerical simulations. Such lens exhibits the merit of dynamic functions, low insertion loss and broadband applicability. It may inspire various practical THz apparatuses.

Comprehensive comparison of multiple quantitative near-infrared spectroscopy models for Aspergillus flavus contamination detection in peanut.

BACKGROUND: Aspergillus flavus is a major pollutant in moldy peanuts, and it has a large influence on the taste of food. The secondary metabolites of Aspergillus flavus, including aflatoxin B1 (AFB1) and aflatoxin B2 (AFB2), are highly toxic and can expose humans to high risk. The total mold count (TMC) is an important index to determine the contamination degree and hygiene quality of peanut. RESULTS: Quantitative calibration models were established based on full-band wavelengths and characteristic wavelengths, combined with chemometric methods, to explore the feasibility of the use of near-infrared spectroscopy (NIRS) for rapid detection of the TMC in peanuts. The successive projection algorithm (SPA) and elimination of uninformative variables (UVE) algorithms were used to extract the characteristic wavelengths. In comparison, the model built by original spectrum, selected with the UVE algorithm, gave the best result, with a correlation coefficient in a prediction set (RP ) of 0.9577, a root mean square error for the prediction set (RMSEP) of 0.2336 Log CFU/g, and a residual predictive deviation (RPD) of 3.5041. CONCLUSIONS: The results showed that NIRS is a rapid, practicable method for the quantitative detection of peanut Aspergillus flavus contamination. It is a promising method for detecting moldy peanuts and increasing peanut safety. © 2019 Society of Chemical Industry.

Liquid-crystal-integrated metadevice: towards active multifunctional terahertz wave manipulations.

Active terahertz elements with multifunction are highly expected in security screening, nondestructive evaluation, and wireless communications. Here, we propose an innovative terahertz metadevice that exhibits distinguishing functions for transmitted and reflected waves. The device is composed of a thin liquid crystal layer sandwiched by Au comb electrodes and a dual-ring resonator array. For transmission mode, the metadevice manifests the electromagnetically induced transparency analog. For reflection mode, it works as a perfect absorber. The comb electrodes actuate the in-plane switching of liquid crystals, making the metadevice actively tuned. 60 GHz frequency tuning of an electromagnetically induced transparency analog and 15% modulation depth of the absorption are demonstrated. Such modulations can be realized in the millisecond scale. The in-plane switching driving mode avoids the electrode connections among separate resonators, thus freeing the design of the metadevice. The proposed work may pave a bright road towards various active multifunctional terahertz apparatuses.

Terahertz vortex beam generator based on a photopatterned large birefringence liquid crystal.

A terahertz (THz) q-plate is proposed and demonstrated to generate THz vortex beams. It is composed of a large birefringence liquid crystal (LC) with spatially-varying director distribution sandwiched by two pieces of fused silica glass. A polarization-sensitive alignment agent is photopatterned to carry out the specific LC director distribution. THz vortex beams with different topological charges are characterized with a THz digital holographic imaging system. The intensity and phase distributions consistent with theoretical analyses are obtained. Besides, an eight-lobed intensity distribution is observed corresponding to the vertical polarization component of a cylindrical vector beam. This work may inspire novel THz applications.

Human disturbances dominated the unprecedentedly high frequency of Yellow River flood over the last millennium.

A warming climate may increase flood hazard through boosting the global hydrological cycle. However, human impact through modifications to the river and its catchment is not well quantified. Here, we show a 12,000-year-long record of Yellow River flood events by synthesizing sedimentary and documentary data of levee overtops and breaches. Our result reveals that flood events in the Yellow River basin became almost an order of magnitude more frequent during the last millennium than the middle Holocene and 81 ± 6% of the increased flood frequency can be ascribed to anthropogenic disturbances. Our findings not only shed light on the long-term dynamics of flood hazards in this world's most sediment-laden river but also inform policy of sustainable management of large rivers under anthropogenic stress elsewhere.

A novel binary pipette splitting sediment subsampling method for improving reproducibility in laser-diffraction particle-size analysis.

Laser-diffraction analysis has been established as one of the standard methods for particle-size distribution (PSD) measurement. However, the uncertainty when analyzing naturally heterogeneous sediment is poorly constrained for the lack of control on one of its largest error sources simply originating from subsampling. Here, we introduce a novel subsampling method, binary pipette splitting (BPS), and verify its precision by using sediment samples from ten flood-layer deposits that have formed in the wake of Hurricane Florence (2018). The BPS approach avoids extracting from only a fixed part of the suspended fluid but considers all the suspended sediment, resulting in the generation of twin subsamples. The median coefficient of variation (COV) for D10, D50, and D90 of subsamples obtained using BPS is 4%, 3%, and 2%, respectively. These values are significantly smaller than the corresponding values of 18%, 15%, and 13% obtained using the conventional pipette subsampling method. Therefore, the new BPS method represents a significant improvement in producing statistically identical subsamples for laser-diffraction particle-size analysis. •The binary pipette splitting (BPS) subsampling method dramatically improves the reproducibility of subsampling wet sediment.

Prediction of total volatile basic nitrogen (TVB-N) content of chilled beef for freshness evaluation by using viscoelasticity based on airflow and laser technique.

Viscoelasticity experiments were performed to detect the total volatile basic nitrogen (TVB-N) content of chilled beef for freshness evaluation. The growth trend of TVB-N was further analyzed with prolonged storage time. A six-element viscoelastic model was then established by fitting deformation data through universal global optimization. The viscoelastic parameters, including elasticity moduli E1, E2, E3, and viscosity coefficients η1, η2, η3, were applied to build models of TVB-N content prediction using partial least squares regression (PLSR) and support vector machine regression (SVR). Results showed that the SVR model performed better than the PLSR model, with a correlation coefficient in the prediction set of 0.89 and a root mean squared error in the prediction set of 1.47 mg/100 g. These results demonstrated for the first time that the viscoelasticity based on airflow and laser technique combined with chemometrics can be used for the fast, nondestructive detection of TVB-N concentration for meat freshness assessment.

Broadband achromatic metalens in terahertz regime.

Achromatic focusing is essential for broadband operation, which has recently been realised from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element. Here, we propose an achromatic metalens with C-shaped unit elements working from 0.3 to 0.8 THz with a bandwidth of approximately 91% over the centre frequency. The designed metalens possesses a high working efficiency of more than 68% at the peak and a relatively high numerical aperture of 0.385. We further demonstrate the robustness of our C-shaped metalens, considering lateral shape deformations and deviations in the etching depth. Our metalens design opens an avenue for future applications of terahertz meta-devices in spectroscopy, time-of-flight tomography and hyperspectral imaging systems.

Chirality invertible superstructure mediated active planar optics.

Active planar optical devices that can dynamically manipulate light are highly sought after in modern optics and nanophotonics. The geometric phase derived from the photonic spin-orbit interaction provides an integrated strategy. Corresponding elements usually suffer from static functions. Here, we introduce an inhomogeneously self-organized anisotropic medium featured by photo-invertible chiral superstructure to realize geometric phase elements with continuously tunable working spectrum and light-flipped phase profile. Via preprograming the alignment of a cholesteric liquid crystal mixed with a photo-responsive chiral dopant, we demonstrate light-activated deflector, lens, Airy beam and optical vortex generators. Their polychromatic working bands are reversibly tuned in an ultra-broadband over 1000 nm covering green to telecomm region. The chirality inversion triggers facile switching of functionalities, such as beam steering, focusing/defocusing and spin-to-orbital angular momentum conversion. This work offers a platform for advanced adaptive and multifunctional flat optics with merits of high compactness, low loss and broad bandwidth.

Anatomy of Mississippi Delta growth and its implications for coastal restoration.

The decline of several of the world's largest deltas has spurred interest in expensive coastal restoration projects to make these economically and ecologically vital regions more sustainable. The success of these projects depends, in part, on our understanding of how delta plains evolve over time scales longer than the instrumental record. Building on a new set of optically stimulated luminescence ages, we demonstrate that a large portion (~10,000 km2) of the late Holocene river-dominated Mississippi Delta grew in a radially symmetric fashion for almost a millennium before abandonment. Sediment was dispersed by deltaic distributaries that formed by means of bifurcations at the coeval shoreline and remained active throughout the life span of this landform. Progradation rates (100 to 150 m/year) were surprisingly constant, producing 6 to 8 km2 of new land per year. This shows that robust rates of land building were sustained under preindustrial conditions. However, these rates are several times lower than rates of land loss over the past century, indicating that only a small portion of the Mississippi Delta may be sustainable in a future world with accelerated sea-level rise.

Cluster of human infections with avian influenza A (H7N9) cases: a temporal and spatial analysis.

OBJECTIVES: This study aims to describe the spatial and temporal characteristics of human infections with H7N9 virus in China using data from February 2013 to March 2014 from the websites of every province's Population and Family Planning Commission. METHODS: A human infection with H7N9 virus dataset was summarized by county to analyze its spatial clustering, and by date of illness onset to analyze its space-time clustering using the ESRI® Geographic Information System (GIS) software ArcMap™ 10.1 and SatScan. RESULTS: Based on active surveillance data, the distribution map of H7N9 cases shows that compared to the rest of China, the areas from near the Yangtze River delta (YRD) to farther south around the Pearl River delta (PRD) had the highest densities of H7N9 cases. The case data shows a strong space-time clustering in the areas on and near the YRD from 26 March to 18 April 2013 and a weak space-time clustering only in the areas on and near the PRD between 3 and 4 February 2014. However, for the rest of the study period, H7N9 cases were spatial-temporally randomly distributed. CONCLUSIONS: Our results suggested that the spatial-temporal clustering of H7N9 in China between 2013 and 2014 is fundamentally different.