Flow reversal triggers discontinuous shear thickening response across an erodible granular bed in a Couette-Poiseuille-like flow.

Granular rheology is experimentally investigated in a vertical Couette-Poiseuille-like channel flow of photoelastic disks, where an erodible bed is sheared intermittently by an upward-moving shear band and a gravity-induced reverse flow. The shear band conforms to the existing nonlocal Eyring-like rheology but the bed exhibits discontinuous shear thickening from the Bagnold inertial regime near the band-bed interface to the Herschel-Bulkley plastic regime near the static wall. This newly discovered bed rheology is rate dependent and is associated with the fragility of the contact networks indicated by the statistics of local stress states inferred from the material photoelastic responses.

Enhanced flow rate by the concentration mechanism of Tetris particles when discharged from a hopper with an obstacle.

We apply a holistic two-dimensional (2D) Tetris-like model, where particles move based on prescribed rules, to investigate the flow rate enhancement from a hopper. This phenomenon was originally reported in the literature as a feature of placing an obstacle at an optimal location near the exit of a hopper discharging athermal granular particles under gravity. We find that this phenomenon is limited to a system of sufficiently many particles. In addition to the waiting room effect, another mechanism able to explain and create the flow rate enhancement is the concentration mechanism of particles on their way to reaching the hopper exit after passing the obstacle. We elucidate the concentration mechanism by decomposing the flow rate into its constituent variables: the local area packing fraction ϕ_{l}^{E} and the averaged particle velocity v_{y}^{E} at the hopper exit. In comparison to the case without an obstacle, our results show that an optimally placed obstacle can create a net flow rate enhancement of relatively weakly driven particles, caused by the exit-bottleneck coupling if ϕ_{l}^{E}>ϕ_{o}^{c}, where ϕ_{o}^{c} is a characteristic area packing fraction marking a transition from fast to slow flow regimes of Tetris particles. Utilizing the concentration mechanism by artificially guiding particles into the central sparse space under the obstacle or narrowing the hopper exit angle under the obstacle, we can create a manmade flow rate peak of relatively strongly driven particles that initially exhibit no flow rate peak. Additionally, the enhanced flow rate can be maximized by an optimal obstacle shape, particle acceleration rate toward the hopper exit, or exit geometry of the hopper.

Status and prospects of the application of root exudates in the restoration of polluted or desertated soil.

Ecological and environmental problems including heavy metal pollution have received increasing concerns. Given the shortage of physical and chemical remediation methods in high cost and secondary pollution, using plants and microorganisms for joint remediation of environment has become one of the most important strategies. Root exudates are an important medium for information and nutrient exchange between plants and soil. The roles of plant root exudates in remediation of polluted and degradated soil have been widely studied. In this review, we described the composition, secretion mechanism and functions of root exudates and summarized the functions of root exudate in heavy metal absorption, allelopathy, interaction between roots and rhizosphere microorga-nisms, and changes in soil physical and chemical properties. The progress, challenges and prospect of applying root exdudates and rhizosphere microorganisms in the remediation of ecology and environment have also been discussed. This review could provide theoretical support for the application of plant-microorganism based environmental remediation.

Energy Balance-Related Behaviors and Body Mass Index in Asian School-Aged Children With Congenital Heart Disease.

BACKGROUND: Overweight/obesity is a substantial global public health concern, which can be caused by genetic factors and energy balance-related behaviors (EBRBs). If it occurs in children with congenital heart disease (CCHD), it can yield an extra burden on their health. Most studies on CCHD have taken place in Western societies, leaving Asian populations understudied, especially children. OBJECTIVE: We sought (1) to determine body mass index distribution among school-aged CCHD in Taiwan, (2) to ascertain whether the body mass index of CCHD differs from that of the general population, (3) to describe EBRBs in CCHD, and (4) to identify factors associated with underweight and overweight/obesity among CCHD. METHODS: In this cross-sectional study, 97 child-parent dyads (53.6% boys; mean age, 9.73 years; 25.8% moderate-to-severe heart conditions) were enrolled. Self-administered questionnaires were used to collect demographics, medical factors, food frequency, physical activity, and sedentary behaviors. Anthropometric measurements were taken in the hospital. Independent predictors of EBRBs and health conditions were calculated through logistic regression analysis. RESULTS: Among Taiwanese CCHD, 19.6% were underweight and 14.4% were overweight/obese. Children with moderate-to-severe heart defects were more often underweight. Body mass index did not differ between CCHD and children in the general population. More complex heart defects and asthma were associated with being underweight, whereas sedentary behaviors, cardiomegaly, and the New York Heart Association classification II to IV were associated with being overweight/obese. CONCLUSIONS: Sedentary lifestyle is seemingly the only EBRB correlated with being overweight. Physical activity programs for children may help prevent and treat overweight or obesity in Asian CCHD, similar to Western countries.

Deep, sub-wavelength acoustic patterning of complex and non-periodic shapes on soft membranes supported by air cavities.

Arbitrary patterning of micro-objects in liquid is crucial to many biomedical applications. Among conventional methodologies, acoustic approaches provide superior biocompatibility but are intrinsically limited to producing periodic patterns at low resolution due to the nature of standing waves and the coupling between fluid and structure vibrations. This work demonstrates a near-field acoustic platform capable of synthesizing high resolution, complex and non-periodic energy potential wells. A thin and viscoelastic membrane is utilized to modulate the acoustic wavefront on a deep, sub-wavelength scale by suppressing the structural vibration selectively on the platform. Using 3 MHz excitation (λ∼ 500 µm in water), we have experimentally validated such a concept by realizing patterning of microparticles and cells with a line resolution of 50 µm (one tenth of the wavelength). Furthermore, massively parallel patterning across a 3 × 3 mm2 area has been achieved. This new acoustic wavefront modulation mechanism is powerful for manufacturing complex biologic products.

Publisher's Note: Relaxation-type nonlocal inertial-number rheology for dry granular flows [Phys. Rev. E 96, 062909 (2017)].

This corrects the article DOI: 10.1103/PhysRevE.96.062909.

Relaxation-type nonlocal inertial-number rheology for dry granular flows.

We propose a constitutive model to describe the nonlocality, hysteresis, and several flow features of dry granular materials. Taking the well-known inertial number I as a measure of sheared-induced local fluidization, we derive a relaxation model for I according to the evolution of microstructure during avalanche and dissipation processes. The model yields a nonmonotonic flow law for a homogeneous flow, accounting for hysteretic solid-fluid transition and intermittency in quasistatic flows. For an inhomogeneous flow, the model predicts a generalized Bagnold shear stress revealing the interplay of two microscopic nonlocal mechanisms: collisions among correlated structures and the diffusion of fluidization within the structures. In describing a uniform flow down an incline, the model reproduces the hysteretic starting and stopping heights and the Pouliquen flow rule for mean velocity. Moreover, a dimensionless parameter reflecting the nonlocal effect on the flow is discovered, which controls the transition between Bagnold and creeping flow dynamics.

The role of orthographic neighborhood size effects in Chinese word recognition.

Previous studies about the orthographic neighborhood size (NS) in Chinese have overlooked the morphological processing, and the co-variation between the character frequency and the the NS. The present study manipulated the word frequency and the NS simultaneously, with the leading character frequency controlled, to explore their influences on word lexical decision (Experiment 1) and naming (Experiment 2). The results showed a robust effect that words with a larger NS produced shorter reaction time than those with a smaller NS, irrespective of the word frequency and the tasks. This facilitative effect may occur due to a semantic network formed by neighbor words, resulting in the semantic activation to accelerate the word recognition. Moreover, the comparison of the effect sizes of word frequency between the two tasks showed that lexical decision responses demonstrated a larger word frequency effect, indicating that the sub-word processing was involved in the multi-character word recognition.

A mixed contact model for an immersed collision between two solid surfaces.

Experimental evidence shows that the presence of an ambient liquid can greatly modify the collision process between two solid surfaces. Interactions between the solid surfaces and the surrounding liquid result in energy dissipation at the particle level, which leads to solid-liquid mixture rheology deviating from dry granular flow behaviour. The present work investigates how the surrounding liquid modifies the impact and rebound of solid spheres. Existing collision models use elastohydrodynamic lubrication (EHL) theory to address the surface deformation under the developing lubrication pressure, thereby coupling the motion of the liquid and solid. With EHL theory, idealized smooth particles are made to rebound from a lubrication film. Modified EHL models, however, allow particles to rebound from mutual contacts of surface asperities, assuming negligible liquid effects. In this work, a new contact mechanism, 'mixed contact', is formulated, which considers the interplay between the asperities and the interstitial liquid as part of a hybrid rebound scheme. A recovery factor is further proposed to characterize the additional energy loss due to asperity-liquid interactions. The resulting collision model is evaluated through comparisons with experimental data, exhibiting a better performance than the existing models. In addition to the three non-dimensional numbers that result from the EHL analysis--the wet coefficient of restitution, the particle Stokes number and the elasticity parameter--a fourth parameter is introduced to correlate particle impact momentum to the EHL deformation impulse. This generalized collision model covers a wide range of impact conditions and could be employed in numerical codes to simulate the bulk motion of solid particles with non-negligible liquid effects.