Interfacial properties of polyelectrolyte–cellulose systems. II. Electrokinetic properties of cellulose fibers with adsorbed monolayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on pulp (DP) fibers with or without irreversibly adsorbed monolayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties of these fibers, such as the amount of adsorbed polymer, the polymer molecular weight (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and the pH of the streaming medium (KCl solution), were examined. As the amount of adsorbed polymer increased, the negative zeta potential of the fibers decreased until the polarity of the zeta potential was reversed to the positive side. A marked change in the value of zeta potential was not observed when the formation of the saturated monolayer was completed. The zeta potential also varied in proportion to an increase in the amount of polymer adsorbed. Experimental results are interpreted with reference to the origin of the surface charge, the amphoteric nature of the surface, the modes of adsorption, and the adsorbed polymer chain configuration. Possible effects of the adsorbed monolayer formation on the structural change of the electric double layer at the fiber surface are discussed. It is concluded that the formation of a monolayer of cationic polyelectrolytes on the negatively charged cellulose fibers under the condition of k₁ > k₂ (part I) provides a means to arbitrarily control the charge of the fibers until formation of a saturated monolayer.     

Polymer blends of polyethersulfone with all aromatic liquid crystalline co-polyester

Polymer blends of polyethersulfone (PES) with an all aromatic liquid crystalline co-polyester (LCP) were investigated. In addition, PES oligomers with the reactive functions end groups (?ONa) were added as a third component to the above blends in order to improve their properties. Flexural properties, such as modulus and strength, and dynamic viscoelastic properties, such as dynamic storage elasticity (E′) and loss tangent (tan δ), of the blends were measured. The morphology of blends was characterized using a differential scanning calorimeter (DSC) and a scanning electron microscope (SEM). Of the flexural properties, the modulus of PES increased almost linearly with increasing LCP content. However, strength decreased as LCP content increased to 20 wt%. In contrast, the addition of the PES oligomers had little effect on modulus, but strength was clearly improved. Regarding dynamic viscoelastic properties, the oligomer-containing blends exhibited complex behavior. Regarding morphologies, SEM analysis revealed that the LCP was not fibrous in the core of the blend containing 40 wt% or less, but the addition of the PES oligomers made LCP fibrous even in blends with low LCP content. It was concluded that the PES oligomers with reactive functional groups acted as a compatibilizer in polymer blends of PES/LCP.     

Modeling and analysis of passive viscoelastic-legged rimless wheel that generates measurable period of double-limb support

Limit cycle walking including passive-dynamic walkers is generally modeled as a nonlinear hybrid dynamical system with state jumps. The inelastic collision model is usually derived on the assumption that the rear leg leaves the ground immediately after landing of the fore leg. This model is, however, inappropriate in the case of compliant-legged walkers. This paper then reconsiders the traditional collision model and discusses the conditions for transition to double-limb support (DLS) motion, which is not instantaneous through investigations of passive dynamic walking of a viscoelastic-legged rimless wheel. First, we experimentally confirm that measurable period of DLS motion emerges after landing of the fore leg, and develop the corresponding mathematical model. Second, we numerically analyze the fundamental properties of the generated passive-dynamic gaits. Furthermore, we discuss the conditions for transition to DLS motion and specify the computational procedures.     

Dietary cyanidin 3-O-β-d-glucoside increases ex vivo oxidation resistance of serum in rats

The effect of dietary cyanidin 3-O-β-d-glucoside (C3G), a typical anthocyanin pigment, on the generation of thiobarbituric acid reactive substances (TBARS) during serum formation ex vivo and susceptibility of serum to further lipid peroxidation was studied in rats. Rats were fed a diet containing C3G (2 g/kg) for 14 d. Feeding C3G resulted in a significant decrease in generation of TBARS during serum formation. The serum from the C3G-fed group showed a significantly lower susceptibility to further lipid peroxidation provoked by 2,2′-azobis (2-amidinopropane)hydrochloride or Cu²⁺ than that of the control group. No significant differences were observed in serum phospholipid, triglyceride, esterified cholesterol, and free fatty acid concentrations between the control and the C3G-fed groups. Concentrations of endogenous antioxidants remaining in the serum after blood coagulation were not affected by the C3G feeding. These results demonstrate that feeding C3G increases the ex vivo oxidation resistance of the serum without affecting serum endogeneous antioxidant levels, and reduces the TBARS generated during serum formation without changing the concentrations of serum lipids.     

Numerical analysis of electrochemical characteristics and heat/species transport for planar porous-electrode-supported SOFC

In this work, a fully three-dimensional mathematical model for planar porous-electrode-supported (PES) solid oxide fuel cell (SOFC) has been constructed to simulate the steady state electrochemical characteristics and multi-species/heat transport. The variation of chemical species concentrations, temperature, potential, current and current density for two types of PES-SOFC developed by central research institute of electric power industry (CRIEPI) of Japan are studied in the co-flow pattern. In the numerical computation, the governing equations for continuity, momentum, mass, energy and electrical charge conservation are solved simultaneously using the finite volume method. Activation, ohmic, and concentration polarizations are considered as the main sources of irreversibility. The Butler–Volmer equation, Ohm's law, and Darcy's gas model with constant porosity and permeability are used to determine the polarization over-potential, respectively. The output voltages measured in experiments and calculated using the above models agree well. For the cell using the same material and manufacturing process, the results show the type-II PES-SOFC is with better performance. However, the electrolyte of type-II PES-SOFC should be with higher maximum ionic conductivity. Furthermore, these results will be used to evaluate the overall performance of a PES-SOFC stack, and to significantly help optimize their design and operation in practical applications.     

Dielectric properties of mirin in the microwave frequency range

Dielectric properties of mirin (sweet rice wine for seasoning) at the microwave frequency range of 300–3000 MHz and temperature range of 5–70 °C were measured. The effects of temperature, frequency and liquid concentration on dielectric properties were investigated. Dielectric constant and loss factor were related to frequency by using the modified Cole–Cole equation. The important parameters such as relaxation wavelength, static dielectric constant and ionic conductivity were determined numerically under experimental conditions. It was concluded that the index of spread in the relaxation times depended on mirin concentration and it spread with increasing concentration. Penetration depth was calculated based on the collected dielectric properties data and it had a trough at mixture ratio (v/v) of 1:1 (original:water). The relationship between dielectric properties and temperature was determined at 915 MHz and 2450 MHz for commercial significance.     

Differential expression of MHC class II antigens and cathepsin L by subtypes of cortical epithelial cells in the rat thymus: an immunoelectron microscopic study

To better comprehend the thymic microenvironment, it is necessary to identify the antigenic profile of cortical thymic epithelial cells (cTECs) that are involved in the development of major histocompatibility complex (MHC)-restricted T cells. Ultrastructurally, cTECs can be classified into four morphologically distinct subtypes: subcapsular/perivascular (EC1), pale (EC2), intermediate (EC3) and dark (EC4) cells. Several immunohistochemical studies were done on cTECs at the light and electron microscopic levels, but not with reference to the above subtypes. In the present paper, we analysed the expression of MHC class II antigen and cathepsin L by individual cTEC subtypes at the electron microscopic level. We show that (1) MHC class II antigens are expressed on the cell surfaces except on the basal surface of EC1, both on the cell surface and in intracytoplasmic vacuoles of EC2, and only in the intracytoplasmic vacuoles of EC3 and EC4, and (2) that cathepsin L is expressed strongly and uniformly throughout the cytoplasm of EC2, but weakly and non-uniformly in the cytoplasm of EC1, EC3 and EC4. These results show that MHC class II antigen expression and cathepsin L expression is heterogeneous in cTEC subtypes and suggest that EC2 might play a significant role in the development of CD4+ T cells.     

A sulphur matrix complex,elastic fibril composed of a fine core of amorphous elastin and microfibrils was largely accumulated in the aortic intima of aged rats

We examined elastic fibrils in the aortic intima of aged rats with elastin staining, elastase digestion and X-ray microanalysis. The innermost elastic lamina, heavily stained by a brief treatment with azure II-toluidine blue without heating, was thin and fragmented, and an amorphous substance that stained weakly to moderately was accumulated in the thick subendothelial space of 26-28-month-old rat aortas. The substance was always present in the intimas; to a large extent in the aged rats but rarely in 5-month-old rats, and disappeared after digestion with elastase. The amorphous substance was identified as elastic fibrils approximately 0.1-0.2 microm in diameter under an electron microscope with tannic acid-uranyl acetate/lead citrate staining. Elastase digestion revealed that elastic fibrils were composed of a number of microfibrils, which were 10-12 nm in diameter, in and around a fine core of amorphous elastin. X-ray microanalysis revealed a clear peak of sulphur in the elastic fibrils.     

Bacterial cellulose membrane as separation medium

A thin membrane of bacterial cellulose (BC) obtained from Acetobacter culture was tested for its performance as a dialysis membrane in aqueous systems. The BC membrane showed superior mechanical strength to that of a dialysis-grade regenerated cellulose membrane, allowing the use of a thinner membrane than the latter. As a result, the BC membrane gave higher permeation rates for poly(ethylene glycols) as probe solutes. The cutoff molecular weight of the original BC membrane, significantly greater than that of regenerated cellulose, could be modified by concentrated alkali treatments of the membrane. The nature of the change at the ultrastructural level caused by the alkali treatments was studied by X-ray diffraction and scanning electron microscopy. © 1993 John Wiley & Sons, Inc.     

Immunohistochemical localization of HLA-DR-positive cells in unerupted and erupted normal and carious human teeth

Class II major histocompatibility complex (MHC) antigen-expressing cells are generally associated with the early phase of the immune response. We have studied the distribution of class II-expressing cells in developing, normal, and carious human teeth to clarify when human pulp acquires an immunologic defense potential and how this reacts to dental caries. Antigen-expressing cells were identified immunohistochemically by means of HLA-DR monoclonal antibody. In the pulp of unerupted developing teeth, numerous HLA-DR-positive cells were distributed mainly in and around the odontoblast layer. In erupted teeth, HLA-DR-positive cells were located, for the most part, just beneath the odontoblast layer, with slender cytoplasmic processes extending into the layer. Superficial caries lesions caused an aggregation of HLA-DR-positive cells in dental pulp corresponding to the lesion. In teeth with deeper caries lesions, this aggregation of cells expanded to include the odontoblast layer. Also noted were HLA-DR-positive cells lying along the pulp-dentin border, with cytoplasmic processes projecting deep into the dentinal tubules, where they co-localized with odontoblast processes. These findings suggest that: (1) human dental pulp is equipped with immunologic defense potential prior to eruption; (2) in the initial stage of caries infection, an immunoresponse mediated by class-II-expressing cells is initiated in human dental pulp; and (3) HLA-DR-positive cells trespass deep into dentinal tubules as the caries lesion advances.