Anaerobic fermentation of xylose by pichia stipitis: The effect of forced cycling of ph

Xylose fermentation by Pichia stipitis was examined using a two-stage batch process. The cells were first grown aerobically on D-xylose (5 g/L), whereafter additional xylose (10 g/L) was added and fermented during anaerobic conditions (T=30°C). The optimum pH value for a fermentation with constant pH was found to be 4.5 (maximum specific ethanol production rate 0.21 g/(g h). Forced square wave cycling of the pH between 4 and 5, and 3.5 and 5.5 (cycle time 30 min) during the fermentation stage resulted in a fermentation rate lower than the maximum rate, but with unchanged ethanol yields.     

Comments on "Compression of the ECG by Prediction or Interpolation and Entropy Encoding"

A recent paper1 discusses prediction and interpolation for data compression of ECG. This communication points out that both methods can be viewed as linear filtering. They are therefore equivalent and give the same result in terms of the amount of data compression achieved.     

Mechanical properties and morphology of flax fiber reinforced melamine‐formaldehyde composites

The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber‐matrix interface. In contrast, melamine‐formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this Paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM), it is found that microcracking takes place mainly in the fiber cell walls and not at the fiber‐matrix interface. This suggests that the fiber‐matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements.     

Influence of chemical composition on the rheological behavior of condensation reaction resins

In this paper, the chemorheological and dynamic mechanical behavior of melamine‐formaldehyde (MF) resins of four different formaldehyde/melamine (F/M) molar ratios (1.25, 1.5 1.75 and 2.00) are investigated. MF resins polymerize via a polycondensation reaction involving formation of up to 10 wt% of H₂O on cure. This typically results in rapid and extensive foaming of the resin when it is cured under atmospheric pressure. Experimental adaptation for the foaming behavior of MF resins is used to gather rheological information concerning the curing kinetics and the mechanical response of neat MF resins of different molar ratios. Likewise, the procedures developed allow curing of the resins under atmospheric pressure, hence allowing volatile evacuation as occurs during venting procedures (commonly used during compression molding of MF molding compounds) or as a result of absorption by hydrophilic fillers or substrates. The results show that increased moisture content in the B‐stage leads to faster reaction rates and greater foaming. Gelation and vitrification times are identified for each molar ratio, and are found to increase with decreasing molar ratio. The dynamic mechanical behavior of carefully molded neat MF samples of different molar ratios is studied using DMTA. T_g is found to be 200°C for the resin with the lowest formaldehyde content (F/M = 1.25), and around 230°C for the other resins. The storage shear modulus above T_g is studied, and the results show that the crosslink density increases with increasing molar ratio.     

Microstructure and stiffness analysis of a new ternary melamine-formaldehyde composite

A new ternary planar random fiber composite manufactured under the name RMC (Reinforced Melamine Compound) is studied. Microstructure and stiffness of the random glass fiber-reinforced and particulate-filled melamine-formaldehyde composite processed by compression molding from RMC molding compounds are analyzed. Glass fiber bundles in a mixture of melamine-formaldehyde resin with various size of filler particulates outside the bundle space, and small size particulates inside the bundle space are found from scanning electron microscopy (SEM) and optical micrographs. The tensile modulus of the particulate-filled matrix is modeled using equations of Halpin and Tsai, and Lewis and Nielsen. The tensile modulus of the resin/filler/fiber composite is calculated using the Halpin-Tsai equation followed by a randomization procedure employing the averaging concept of Nielsen and Chen. Fiber bundles rather than single fibers are assumed as the reinforcing unit. Parameter ? representing the reinforcing efficiency is discussed for the case of stiffness in the direction transverse to the bundles orientation. Predicted values of the tensile modulus are in good agreement with experimental results for various compositions. Different resin/filler/fiber compositions are characterized using the calculated tensile modulus values together with merit indices introduced for the purpose of tailoring the composite toward minimized weight and material cost.     

Visualization and coding in three-dimensional image processing

A system for calculating orthographic views of three-dimensional objects from a confocal microscope has been implemented in a high-level language. It is used on a regular basis in a number of projects and on different computers. The system enables the user to filter the original data and make a selection of which points and parts of the objects to show in a projective view. The information to be shown is coded in a compact format that is well suited for projection calculations. Several display principles were implemented that enhance different aspects of the objects.     

Click chemistry‐type crosslinking of a low‐conductivity polyethylene copolymer ternary blend for power cable insulation

High‐voltage direct‐current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high‐voltage power cable insulation – low‐density polyethylene (LDPE) – is usually crosslinked with peroxides, a process that releases unwanted by‐products. Hence, by‐product‐free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry‐type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co‐monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co‐monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 °C. Instead, at 200 °C rapid curing is possible, leading to thermosets with a low direct‐current electrical conductivity of about 10^?16 S cm^?1 at an electric field of 20 kV mm^?1 and 70 °C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide‐cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. © 2019 Society of Chemical Industry     

Rheokinetical behavior of melamine-formaldehyde resins

The effects of cure temperature and amount of catalyst on the rheokinetical behavior of a melamine-formaldehyde (MF) thermosetting system is investigated using a dynamic mechanical technique similar in nature to Torsion Impregnated Cloth Analysis (TICA) and Torsional Braid Analysis (TBA). The proposed name of the used technique is Torsional Substrate Analysis (TSA). Isothermal cures of the resin are carried out from 115°C to 160°C for varying amounts of catalyst. Each TSA measurement exposes several transitions. First, a glass-to-liquid transition during the heatup procedure is seen, indicated by sharp peaks of the loss shear modulus, G″, and loss tangent, tanδ. Later, vitrification is seen, indicated by a second G″ maximum. Finally, a completion of shift to a diffusion controlled cure reaction occurs, shown as a storage shear modulus, G′, plateau. The rheokinetical data is used to construct Time-Temperature-Transformation (TTT) cure diagrams, for each level of catalyst. High pressure differential scanning calorimetry (HPDSC) measurements are carried out in order to estimate the fractional conversion of samples that have been cured isothermally for times corresponding to a second tanδ maximum, the second G″ maximum, and the G′ plateau. The fractional conversion is determined by the residual entalphy technique. The HPDSC measurements do not give a clear answer whether the second tanδ maximum corresponds to gelation or not. It is therefore likely that TSA, like similar techniques, is not capable to detect gelation. A glass transition temperature of 130°C and 150°C is found to correspond to a fractional conversion of 0.65 and ～0.80, respectively. Preliminary measurements suggest that the maximum glass transition temperature, T_{g ∞}, of the investigated MF resin is at least 180°C.     

Interleukin-35 Prevents Development of Autoimmune Diabetes Possibly by Maintaining the Phenotype of Regulatory B Cells

The anti-inflammatory role of regulatory B cells (Breg cells) has been associated with IL-35 based on studies of experimental autoimmune uveitis and encephalitis. The role of Breg cells and IL-35⁺ Breg cells for type 1 diabetes (T1D) remains to be investigated. We studied PBMCs from T1D subjects and healthy controls (HC) and found lowered proportions of Breg cells and IL-35⁺ Breg cells in T1D. To elucidate the role of Breg cells, the lymphoid organs of two mouse models of T1D were examined. Lower proportions of Breg cells and IL-35⁺ Breg cells were found in the animal models of T1D compared with control mice. In addition, the systemic administration of recombinant mouse IL-35 prevented hyperglycemia after multiple low dose streptozotocin (MLDSTZ) injections and increased the proportions of Breg cells and IL-35⁺ Breg cells. A higher proportion of IFN-γ⁺ cells among Breg cells were found in the PBMCs of the T1D subjects. In the MLDSTZ mice, IL-35 administration decreased the proportions of IFN-γ⁺ cells among the Breg cells. Our data illustrate that Breg cells may play an important role in the development of T1D and that IL-35 treatment prevents the development of hyperglycemia by maintaining the phenotype of the Breg cells under an experimental T1D condition.     

Fiber orientation in multilayer tubes processed by a conical extruder

A new extruder design has been developed for the coextrusion of two-layer annular sections. The extruder consists of a conical stator-rotor-stator assembly, which performs extrusion from each side of the rotor. Flow within this assembly is fully three-dimensional, with helicoidal streamlines in the vicinity of the rotor and the die entry region. Fiber orientation is created in a circumferential direction by these helicoidal streamlines; close to the inner and outer surfaces of the tube, the fibers are parallel to the main extrusion direction, whereas in the mid-thickness, they are oriented in the circumferential direction. It is demonstrated that the amount of orientation depends on rotor speed and die design. When using a short die and high rotor speed, an increased fraction of fibers are oriented in the circumferential direction. Polym. Compos. 25:331–341, 2004. © 2004 Society of Plastics Engineers.