ENTIRE-REGION CONSTITUTIVE RELATION FOR TRELOAR'S DATA

Hyperelastic materials can experience a large deformation process. A constitutive relation suitable for an entire region from small, moderate, to large deformations is of great importance for practical applications such as fracture problems. Treloar's data are first investigated, and the tension curve is divided into three regimes: small-to-moderate regime, strain-hardening regime, and limiting-chain regime. Next, the modeling theory of hyperelastic materials is introduced, and the tensile behaviors of basic energy functions are analyzed for different deformation regimes. Finally, a successive procedure is suggested to establish an entire-region constitutive relation and then applied to Treloar's data. The present constitutive relation can maintain the initial shear modulus while the experimental data are satisfactorily predicted. The present procedure is simple and feasible and hence applicable to other hyperelastic materials when their entire-region constitutive relations are studied based on experimental data.

[The clinical characteristics of 346 patients with IgG4-related disease]

Objective: To analyze the clinical characteristics of IgG₄-related disease (IgG₄-RD)so as to improve the understanding of IgG₄-RD in China. Methods: IgG₄-RD patients were recruited from Peking Union Medical College Hospital between January 2011 and January 2016. All patients were followed-up for more than 6 months. The demographic characteristics, symptoms, organ involvements, laboratory examinations and treatment efficacy were evaluated and analyzed. Results: A total of 346 patients were finally enrolled, including 230 males (66.5%) and 116 females (33.5%). The mean age of disease onset was (53.8±14.2) years old. The mostly common involved organs were lymph nodes (56.4%) and submandibular glands (52.6%). Other affected organs and manifestations included: swelling of the lacrimal glands (46.5%), autoimmune pancreatitis (38.4%), pulmonary involvement (28.0%), sclerosing cholangitis (25.4%), naso-sinusitis (23.4%), parotid gland swelling (21.7%), retroperitoneal fibrosis (19.9%), large arteries involvement (9.5%), kidney involvement (obstructive nephropathy caused by retroperitoneal fibrosis was excluded) (6.9%), skin lesions (6.4%). Rare features consisted of thyroid glands, pituitary glands, gastrointestinal tract, pachymeningitis, pericardium, sclerosing mediastinitis and orchitis. The majority of patients had multi-organ involvement, such as 74.3% patients with 3 and more, 18.2% and 7.5% patients with 2 and single organ involvement respectively. The average IgG₄-RD responder index (IgG₄-RD RI) was 13.21±5.70. History of allergy was found in 172 (49.7%) patients. As to the laboratory tests, elevated serum IgG₄ levels were confirmed in 285 (94.1%) patients, which was positively correlated with IgG₄-RD RI. There were 33.5% patients receiving monotherapy of glucocorticoid, 52.6% treated with glucocorticoids combined with immunosuppressive agents, 4.9% patients with immunosuppressant only, and 9.0% patients with mild disease not receiving medication. The majority (336, 97.1%) patients improved the above regimens. Conclusion: IgG₄-RD is a systemic fibro-inflammatory disease with multiple organ involvement. The mostly common involved organs include lymph node, submandibular glands, and pancreas. Glucocorticoids and immunosuppressive agents were effective for IgG₄-RD.

Ethylene Methyl Acrylate Copolymer Toughened Poly(lactic acid) Blends: Phase Morphologies, Mechanical and Rheological Properties

The ethylene methyl acrylate copolymer (EMA), for the first time, was melt blended with poly(lactic acid) (PLA) by a twin-screw extruder to toughen PLA. The phase morphologies, mechanical, and rheological properties of the PLA/EMA blends with six weight ratios were investigated. The results showed that the addition of EMA improves the toughness of PLA at the expense of the tensile strength, flexural strength and modulus to a certain degree, and results in the transition from brittle fracture of PLA into ductile fracture. The droplet-matrix morphology is observed in the PLA/EMA blends, in which the mean diameter of EMA droplets increases and its distribution widens gradually with increasing the EMA content. The PLA/EMA blends with three weight ratios (90/10, 80/20, and 70/30) display different characteristic linear viscoelastic properties in the low frequency region, which were investigated in terms of their complex viscosity, storage modulus, and Cole-Cole plots. The interfacial tension between the PLA and EMA is calculated using the Palierne model conducted on the 80/20 PLA/EMA blend, and the calculated result is 3.3 mN/m.

Rheological Behavior of Immiscible PS/PMMA Blends during Dynamic Plasticating Extrusion

PS/PMMA blends were prepared using a twin screw extruder and then extruded using an electromagnetic dynamic plasticating extruder equipped with a specially designed split die. During dynamic plasticating extrusion, the dynamic rheological behavior of PS/PMMA blends was investigated. The extrudates were cooled immediately and collected for morphology measurements using a scanning electron microscope (SEM). Results show that the average shear stress decreases with the introduction of vibration force field into the whole extrusion process, and reaches a minimum at the vibration amplitude of 0.15 mm and the vibration frequency of 5 Hz. At the same shear stress, the melt viscosity of the blend under dynamic plasticating extrusion is lower than that under static extrusion and decreases with vibration intensity. With increasing vibration intensity, the power-law index of the blend melt has a tendency to increase. The drop size of the dispersed phase in 25/75 PS/PMMA blend decreases at a faster rate with an increase of shear stress, compared with that in 75/25 PS/PMMA blends, correspondingly, the melt viscosity of 25/75 PS/PMMA blend has a stronger shear rate dependence. During dynamic plasticating extrusion, a negative deviation from the additivity rule is observed for the studied blend compositions.

Spreading of completely wetting or partially wetting power-law fluid on solid surface

This study investigated the drop-spreading dynamics of pseudo-plastic and dilatant fluids. Experimental results indicated that the spreading law for both fluids is related to rheological characteristics or power exponent n. For the completely wetting system, the evolution of the wetting radius over time can be expressed by the power law R = atm, where the spreading exponent m of the dilatant fluids is >0.1 and the spreading exponent m of pseudo-plastic fluids is <0.1. The strength of non-Newtonian effects is positively correlated to the extent of deviation from the theoretical value 0.1 of m for Newtonian fluids. For the partially wetting system, the power law on the time dependence of the wetting radius no longer holds; therefore, an exponential power law, R = Req(1-exp(-at(m)/Req)), is proposed, where Req denotes the equilibrium radius of drop and a is a coefficient. Comparing experimental data with the exponential power law revealed that both are in good agreement.

Spreading dynamics and dynamic contact angle of non-Newtonian fluids

The spreading dynamics of power-law fluids, both shear-thinning and shear-thickening fluids, that completely or partially wet solid substrate was investigated theoretically and experimentally. An evolution equation for liquid-film thickness was derived using a lubrication approximation, from which the dynamic contact angle versus the contact line moving velocity relationship was evaluated. In the capillary spreading regime, film thickness h is proportional to xi3/(n+2) (xi is the distance from the contact line), whereas in the gravitational regime, h is proportional to xi1/(n+2), relating to the rheological power exponent n. The derived model fit the experimental data well for a shear-thinning fluid (0.2% w/w xanthan solution) or a shear-thickening fluid (7.5% w/w 10 nm silica in polypropylene glycol) on a completely wetted substrate. The derived model was extended using Hoffmann's proposal for partially wetting fluids. Good agreement was also attained between model predictions and the shear-thinning fluid (1% w/w cmc solution) and shear-thickening fluid (10% w/w 15 nm silica) on partially wetted surfaces.

Advective flow in spherical floc

Numerous structural models of flocs, such as homogeneous model or radially-varying model, were proposed in literature for predicting the extent of advective flow on the intrafloc transport processes. This work probed the three-dimensional structure of original and chemically flocculated wastewater flocs using the fluorescence in situ hybridization (FISH) and the confocal laser scanning microscope (CLSM) techniques, from which the spherical mesh model on real floc structure was constructed. Simulation results revealed that if an average characteristic of sludge floc, such as porosity or drag force correction factor of sludge floc is of concern, both homogeneous or radially-varying models may be able to apply, particularly for those flocs that were closely compacted. However, the detailed flow patterns inside real floc are much more tortuous than those of the homogeneous or radially-varying models. If local hydrodynamic environment within the floc is of interest, then only the complicated structural model with real floc could be applicable.

Fragmentation of wastewater sludge floc by planar ice front

Floc size has substantial impact on sludge dewaterability, which might be increased or reduced after freezing and thawing. It is commonly assumed that floc size would be increased by low-speed freezing, with a planar ice front rejecting most flocs ahead of it to form large aggregates. We demonstrate in this work that an advancing planar ice front can not only engulf an activated sludge floc of size 3030 mum, but also fragment it. During floc freezing, when the ice engulfed a thin layer of floc, the latter would be pulled apart vertically by the action of the former. This particular portion of floc was then axially elongated and fixed in the frozen layer, with accumulated force pushing upward. In the present test the floc's vertical length was increased by over 92% and its width decreased by 37% over freezing. The force measurement and floc morphology tracking revealed that the force gradient that pulled apart the floc was 0.0027 N/m. The floc under investigation was fragmented at the point where the normal stress acting on the interior network exceeded 8 Pa.

Fluorecent staining for study of extracellular polymeric substances in membrane biofouling layers

Membrane biofouling by microbial products adversely impacts the feasibility of adopting membrane bioreactors (MBRs) for treating wastewater. The fouling layer structure determines the pressure drop across the fouling layer. Three-dimensional distributions of nucleic acids, proteins, alpha-D-GLUCOPYRANOSE POLYSACCHARIDES, AND B-D-glucopyranose polysaccharides in the fouling layer formed on a mixed cellulose ester membrane were generated utilizing a quadruple staining protocol combined with confocal laser scanning microscopy (CLSM). For the first time, this study constructed a three-dimensional volumetric grids model representing the fouling layer structure on the basis of a series of CLSM images. Quantitative structural information about the fouling layer was extracted from the CLSM images.

Micromechanics of wastewater sludge floc: Force–deformation relationship at cyclic freezing and thawing

This study examined shape changes in two typical wastewater flocs subjected to cyclic freezing and thawing and the associated force exerted by the ice front. While freezing, the engulfing ice front gradually pulled the floc apart. Subsequent thawing only partially restored the floc's shape. By the Maxwell model, used to interpret gross shape deformations, both flocs were visco-elastic objects exhibiting time-varying rheological characteristics which were more viscous than elastic. Detailed observations of floc 1 deformation demonstrated a two-stage force-displacement relationship. Following 1 cycle of freezing and thawing, the interior structure of the floc deteriorated and the force required to elongating a unit length of floc decreased by 60%. The original floc 2 had a dense "core" and loose "tail"; the core was more resistant to deformation under normal stress than the loose tail. Although both flocs had similar shapes and sizes and were acquired from the same activated sludge stream at a wastewater treatment plant, their rheological behaviors differed substantially. A comprehensive theoretical model for freezing and thawing processes should incorporate these rheological characteristics as they corresponded to observed structural changes and reduction in bound water content in sludge following a cyclic treatment of freezing and thawing.

Diffusion coefficient of Brownian particle in rough micro-channel

This study examines the feasibility of using of the lattice Boltzmann method to determine how the surface roughness of a quadrate channel affects the diffusion coefficient of Brownian particle(s). The surface was represented by a regular array of spheres. Surface roughness reduced the diffusion coefficient of the Brownian particle(s) because of a change in the velocity autocorrelation function decay and in pressure. Additionally, the neighboring particles increased the diffusion coefficient of Brownian particle.

Force of a gas bubble on a foreign particle in front of a freezing interface

We monitored the formation and development of a single gas bubble on the surface of a spherical particle of size 1.676 mm under unidirectional freezing and thawing (4.6-5.0 microm/s) and for the first time quantitatively estimated the force exerted on this particle by measuring the deformation of an attached elastic stick. The bubble would nucleate and grow on the particle surface closest to the ice front, while the force curve for a freezing-thawing cycle presented a hysteresis characteristic. This force was much greater than in the case without a bubble, and hence it dominated the engulfment process in the present freezing tests. The bubble force increased with increasing bubble size and was shown to be mainly attributable to the elastic force by the deformed bubble shape. Comments were made on the need to incorporate the role of bubbles in predicting the critical velocity to freeze a suspension with high dissolved gas content.

Structure of conditioned sludge flocs

Free settling tests, small-angle light scattering, microtome-slicing techniques, and confocal laser scanning microscopy were performed to examine how the cationic flocculation or freezing and thawing affected the floc structure. The floc size, internal pore size, mass fractal dimensions determined from free-settling test or small angle light scattering test, aeral porosity, boundary fractal dimension and Sierpinski carpet fractal dimension of pore boundary from 2D slices, and the volume porosity, compactness, and the pores' box-counting fractal dimension from 3D reconstructed image, were estimated and compared. Cationic flocculation would produce large flocs with internal pores of shape resembling a long "tube" with rough surface. Freezing and thawing would produce flocs with internal pores with lower aspect ratio and a smoother boundary.

Thermal drying of wastewater sludge with crack formation

We examined in this work the drying characteristics of wastewater sludge. The drying flux of the constant-rate period for sludge cake could be up to 40% higher than that from a sand bed. Owing to the considerable volume shrinkage of cake, cracks would form and develop on the crack surface, which yielded three-dimensional but rather than the one-dimensional cake structure assumed in conventional drying theories. The crack length was fully developed in the first 30 min of drying, while the width of crack increased linearly with time. Using these data the drying flux from the cracks was estimated. Enhanced drying flux was noticeable which depended on the crack shape and the crossflow velocity.

Advective Flow and Floc Permeability

This work monitored advection flow through a floc by bubble tracking. Close examination of the motion of a swarm of hydrogen bubbles that passed over a free-falling floc allowed the extent of advection flow to be estimated at 53% for the original activated sludge floc, and 12% for the flocculated floc. The interior permeability of the sludge flocs was estimated from this information. The fluid force exerted on the falling floc was also considered.