A Reduced Landau-de Gennes Study for Nematic Equilibria in Three-Dimensional Prisms

We model nematic liquid crystal configurations inside three-dimensional prisms, with a polygonal cross-section and Dirichlet boundary conditions on all prism surfaces. We work in a reduced Landau-de Gennes framework, and the Dirichlet conditions on the top and bottom surfaces are special in the sense, that they are critical points of the reduced Landau-de Gennes energy on the polygonal cross-section. The choice of the boundary conditions allows us to make a direct correspondence between the three-dimensional Landau-de Gennes critical points and pathways on the two-dimensional Landau-de Gennes solution landscape on the polygonal cross-section. We explore this concept by means of asymptotic analysis and numerical examples, with emphasis on a cuboid and a hexagonal prism, focusing on three-dimensional multistability tailored by two-dimensional solution landscapes

Hierarchies of Critical Points of a Landau-de Gennes Free Energy on Three-Dimensional Cuboids

We investigate critical points of a Landau-de Gennes (LdG) free energy in three-dimensional (3D) cuboids, that model nematic equilibria. We develop a hybrid saddle dynamics-based algorithm to efficiently compute solution landscapes of these 3D systems. Our main results concern (a) the construction of 3D LdG critical points from a database of 2D LdG critical points and (b) studies of the effects of cross-section size and cuboid height on solution landscapes. In doing so, we discover multiple-layer 3D LdG critical points constructed by stacking 3D critical points on top of each other, novel pathways between distinct energy minima mediated by 3D LdG critical points and novel metastable escaped solutions, all of which can be tuned for tailor-made static and dynamic properties of confined nematic liquid crystal systems in 3D.Comment: 28 pages,10 figure

Nematic liquid crystals in a rectangular confinement : solution landscape, and bifurcation

We study the solution landscape and bifurcation diagrams of nematic liquid crystals confined on a rectangle, using a reduced two-dimensional Landau–de Gennes framework in terms of two geometry-dependent variables: half short edge length λ and aspect ratio b . First, we analytically prove that, for any b with a small enough λ or for a large enough b with a fixed domain size, there is a unique stable solution that has two line defects on the opposite short edges. Second, we numerically construct solution landscapes by varying λ and b , and report a novel X state, which emerges from saddle-node bifurcation and serves as the parent state in such a solution landscape. Various new classes are then found among these solution landscapes, including the X class, the S class, and the L class. By tracking the Morse indices of individual solutions, we present bifurcation diagrams for nematic equilibria, thus illustrating the emergence mechanism of critical points and several effects of geometrical anisotropy on confined defect patterns

Effect of cooling pad installation on indoor airflow distribution in a tunnel-ventilated laying-hen house

Extra cooling pads on the sidewalls are needed for larger poultry houses using tunnel ventilation system. Preliminary study showed that the airflow velocity going through different aisles varies greatly when the extra pads are installed at the end of sidewalls, making a “[”-shape air inlet. Combined with field tests, the CFD (computational fluid dynamics) technology was used to study the uniformity of airflow distribution in a tunnel-ventilated laying-hen house. The air distribution was first monitored in a layer house to find the main reason resulting in the variations of airflows in different aisles. Then CFD simulations were carried out with different distances (D=2 m, 3 m or 4 m) between the pads on end-wall and the extra pads on side walls. The field test showed that airflow streams from the different groups of cooling pads collided vertically at the house corners, mixed with each other, then flew towards the center of the house. This was the main reason that the wind speed in the middle aisle was much higher than in other aisles, leaving large zones of lower ventilation in the aisles adjacent to the sidewalls. The results of CFD simulations indicated that air distributions could be significantly improved when the extra pieces of pads were moved away for an appropriate distance from the end cooling pads. As far as conventional poultry house with a span of 12 m, the air speeds in different aisles were more uniform when this distance was about 3 m

Multistability for nematic liquid crystals in cuboids with degenerate planar boundary conditions

We study nematic configurations within three-dimensional (3D) cuboids, with planar degenerate boundary conditions on the cuboid faces, in the Landau–de Gennes framework. There are two geometry-dependent variables: the edge length of the square cross-section, λ, and the parameter h, which is a measure of the cuboid height. Theoretically, we prove the existence and uniqueness of the global minimizer with a small enough cuboid size. We develop a new numerical scheme for the high-index saddle dynamics to deal with the surface energies. We report on a plethora of (meta)stable states, and their dependence on h and λ, and in particular how the 3D states are connected with their two-dimensional counterparts on squares and rectangles. Notably, we find families of almost uniaxial stable states constructed from the topological classification of tangent unit-vector fields and study transition pathways between them. We also provide a phase diagram of competing (meta)stable states as a function of λ and h

New control strategy against temperature sudden-drop in the initial stage of pad cooling process in poultry houses

Preliminary field measurements have shown substantial temperature sudden-drop (ΔTsd) at bird level in the initial stage of pad cooling process in arid regions of China. Such sudden temperature fluctuation can cause thermal stress to laying hens and this problem is attracting increasing concerns. The purpose of this study was to develop a new control strategy (NCS) to avoid or minimize ΔTsd while simplify the operational process. Theoretical calculation and field test were conducted in this study. The key ambient thermal factor affecting ΔTsd was analysed by calculating temperature drop of cooled air existing the cooling pad (ΔTd). A countermeasure was applied by controlling the wetted pad area at each startup of the water supply pump. Field test was carried out to demonstrate application of the NCS in a poultry house. The theoretical arithmetic results showed that ambient relative humidity (RHo) was the main factor affecting ΔTd, and ΔTsd occurred when RHo ≤ 60%. Temperature fluctuation at the bird level (Tdb,b) could be controlled within 4°C when the wetted pad area increased by 25%. The NCS operated based on RHo that was divided into three regions. For RHo \u3e 80%, the pump would not be turned on because of poor cooling effect. For 60% \u3c RHo \u3c 80%, no ΔTsd would occur and the pump would be controlled by “on-off” regulation. For RHo ≤ 60%, ΔTsd occurred and the pump was turned on intermittently. Then, 4-stage cooling would be applied. Results of the field test were generally consistent with the theoretical simulation with regards to alleviation of ΔTsd that was controlled within 3.5°C. Further field verification of the NCS on the flock health and production performance is warranted

Spatial and Diurnal Variations of Particulate Matter Concentration of a Pilot-Scale Aviary Layer House in Winter

Laying hen production plays an important role in particulate matter (PM) emissions which potentially cause air pollution and adverse health effect on animals and workers. Aviary cage-free (CF) egg production systems have been attracting increasing attention due to concerns over animal welfare and increased market demand. While studies have been conducted to characterize PM concentrations and emissions of aviary CF houses with litter floor, few reports are available of this information for aviary CF layer houses equipped with slat floor. In this study, PM concentrations – both spatial and diurnal patters inside a pilot-scale aviary CF layer house (1,800 laying hens, LxWxH of 28.2 x 9.0 x 3.0 m) in northern China were measured under winter conditions. Daily mean PM2.5, PM10, and TSP levels were found to be 0.19±0.11, 1.05±0.65, 2.90±2.07 mg/m3, respectively, which were considerably lower than those reported in previous studies of aviary CF houses with litter floor in cold weather. Daytime PM concentrations were significantly higher than those at night primarily due to differences in animal activity and feed supply. The average PM10 and TSP concentrations during light period (5:00-21:00 h) were 1.34 mg/m3 and 3.75 mg/m3, amounting to 279% and 304% of those during the dark period (21:00-5:00h), respectively. Spatial variations for PM10 and TSP were observed in the experimental hen house due to non-uniform distribution of ventilation air and localized generation of the constituents. Higher TSP concentrations (4.26 mg/m3) were found at worker respiratory level (2.0 m) as compared to floor level (0.5 m, 3.00 mg/m3). TSP concentration at one end of the house (west) was found to be 28.3% and 86.9% higher than the middle and the opposite (east) end. This spatial variation characteristic points out the importance of multi-location sampling when assessing indoor air quality and aerial emissions (for cross ventilation). Data from this study will be useful for future improvement of the housing ventilation design and operation. Future study should also assess PM concentrations of the housing style under warm seasons

The Histone Demethylases Jhdm1a/1b Enhance Somatic Cell Reprogramming in a Vitamin-C-Dependent Manner

SummaryReprogramming of somatic cells into induced pluripotent stem cells (iPSCs) resets the epigenome to an embryonic-like state. Vitamin C enhances the reprogramming process, but the underlying mechanisms are unclear. Here we show that the histone demethylases Jhdm1a/1b are key effectors of somatic cell reprogramming downstream of vitamin C. We first observed that vitamin C induces H3K36me2/3 demethylation in mouse embryonic fibroblasts in culture and during reprogramming. We then identified Jhdm1a/1b, two known vitamin-C-dependent H3K36 demethylases, as potent regulators of reprogramming through gain- and loss-of-function approaches. Furthermore, we found that Jhdm1b accelerates cell cycle progression and suppresses cell senescence during reprogramming by repressing the Ink4/Arf locus. Jhdm1b also cooperates with Oct4 to activate the microRNA cluster 302/367, an integral component of the pluripotency machinery. Our results therefore reveal a role for H3K36me2/3 in cell fate determination and establish a link between histone demethylases and vitamin-C-induced reprogramming

Genomic and phenotypic analyses reveal Paenibacillus polymyxa PJH16 is a potential biocontrol agent against cucumber fusarium wilt

In recent years, bacterial-based biocontrol agents (BCA) have become a new trend for the control of fungal diseases such as fusarium wilt that seriously threaten the yield and quality of cucumber, which are transmitted through infested soil and water. This study was set out with the aim of figuring the mechanism of the isolated rhizobacterial strain Paenibacillus polymyxa PJH16 in preventing Fusarium oxysporum f. sp. cucumerinum (Foc). Biocontrol and growth-promoting experiments revealed that bacterial strain causes effective inhibition of the fungal disease through a significant growth-promoting ability of plants, and had activities of β-1,3-glucanase, cellulase, amylase and protease. It could produce siderophore and indole-3-acetic acid, too. Using the high-throughput sequencing tool PacBio Sequel II system and the database annotation, the bacterial strain was identified as P. polymyxa PJH16 and contained genes encoding for presence of biofilm formation, antimicrobial peptides, siderophores and hydrolyases. From comparing data between the whole genome of P. polymyxa PJH16 with four closely related P. polymyxa strains, findings revealed markedly the subtle differences in their genome sequences and proposed new antifungal substances present in P. polymyxa PJH16. Therefore, P. polymyxa PJH16 could be utilized in bioengineering a microbial formulation for application as biocontrol agent and bio-stimulant, in the future