Elaboration of small‐diameter vascular prostheses—Selection of appropriate sterilisation method

The aim of study is the elaboration of semi‐biodegradable, multilayered tubular structures as substitutes for the reconstruction of small diameter vascular prostheses (<6 mm). The inert external layer of the prostheses will be fabricated via the melt electrospinning of poly (l ‐lactide‐co‐glycolide) (PLGA). The middle layer will be constructed from polypropylene (PP); the first prototype will be produced via melt electrospinning and the second using the melt blowing technique. The general aim of this stage of the research is the selection of a sterilisation technique that is appropriate for semi‐biodegradable, multilayered tubular structures. For this purpose, single tubular structures created via the melt electrospinning of PLGA or PP and melt blown tubular structures of PP were elaborated. The influence of steam, ethylene‐oxide (EO), and radiation sterilisation techniques on the elaborated microstructure of tubular structures was analyzed during this study. The effect of each sterilisation technique was evaluated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy/energy‐dispersive X‐ray spectroscopy analysis (SEM/EDS). The changes in average molecular weight (M_w) and crystallinity index (CI) of the PLGA tubular structures after EO and steam sterilisation were evaluated. The EO and steam sterilisation resulted in the complete destruction of PLGA tubular structures. Only the radiation sterilisation (accelerated electrons) did not influence on PLGA tubular structures morphology as well as thermal and chemical properties. FTIR and SEM/EDS analysis indicated that no changes in the chemical properties of PP tubular structures after each sterilisation occurred. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40812.     

One-dimensional axial simulation of electric double layer overlap effects in devices combining micro- and nanochannels

This paper presents a numerical steady-state model of ion transport in micro- and nanofluidic devices with widely varying geometric scale, such as transitions between micro- and nanochannels. Finite element or finite volume simulation of such problems is challenging, due to the number of elements needed to produce a satisfactory mesh. Here, only the lengthwise channel dimension is meshed; standard analytical approximations are used to incorporate cross-channel properties. Singularly perturbed cases are built up by continuation. The method is shown to reproduce our previously reported measurements of electric double-layer effects on conductivity, ion concentration, and ion enhancement and depletion. Comparison with 2-D simulations reported in the literature shows that effects on accuracy due to the 1-D approximation are small. The model incorporates analytical models of surface charge density taken from the literature. This enables predictive simulation with reasonable accuracy using published parameter values, or these values may be tuned based on experiment to give improved results. Use of the model for iterative design and parameter estimation is demonstrated.     

An alternative formulation of the geometric stiffness matrix for plate elements

A simplified formulation of the geometric stiffness matrix for plate elements is presented. In this formulation the transverse displacement is defined along the element boundary but not for the element interior as with the usual formulation. As such the formulation is particularly suitable for use with hybrid stress or discrete Kirchhoff methods which are also based on boundary approximation of the transverse displacement.

The simplicity, computational economy and accuracy obtained with the formulation compare favorably with the usual order formulation.     

Study of spray cooling of a pressure vessel head of a boiling water reactor

The present paper deals with a theoretical analysis of the spray cooling of a Reactor Pressure Vessel (RPV) head in a Boiling Water Reactor (BWR). To this end a detailed computational model has been developed. The model predicts the trajectories, diameters and temperatures of subcooled droplets moving in saturated vapor. The model has been validated through comparison with experimental data, in which droplet temperatures were measured as functions of the distance that they cover in saturated vapor from the moment they leave the sprinkler outlet to the moment they impact on the RPV head inner wall. The calculations are in very good agreement with measurements, confirming the model adequacy for the present study. The model has been used for a parametric study to investigate the influence of several parameters on the cooling efficiency of the spray system. Based on the study it has been shown that one of the main parameters that govern the temperature increase in a subcooled droplet is its initial diameter. Comparisons are also made between conclusions from the theoretical model and observations made through flow and temperature measurements in the plant (Forsmark 1 and 2). One of these observations is that the rate at which the RPV head temperature decreases on the way down from hot to cold standby is constant and independent of the sprinkling flow rate as long as the flow rate is above a certain minimum value. Accordingly, the theoretical model shows that if one assumes that the cooling of the RPV head is through a water film built on the inner wall due to sprinkling, the heat removal rate is only very weakly dependent on the sprinkling flow rate.     

Thin plate elements with relaxed Kirchhoff constraints

An analysis of thin plates by C⁰ elements is presented. The fundamental part of it is the formulation of a set of constraints that relate the rotational degrees of freedom to the translational degrees of freedom and which are weaker than the usual Kirchhoff constraints. A penalty term associated with these constraints is then introduced instead of the usual expression for the shear strain energy. It is shown that the approach is effective for both quadrilateral and triangular elements.     

Acrylamide formation in low-fat potato snacks and its correlation with colour development.

A recipe and technological process for the production of low-fat potato snacks (7% fat) was developed at the Institute of Food Technology of Plant Origin (Agricultural University of Poznan) using a combination of extrusion and a roasting process. Due to the character of the product, the level of acrylamide was analysed. At the same time, the influence of temperature and time of heating on acrylamide levels were monitored, as well as the correlation between colour development and acrylamide content. The level of acrylamide in low-fat potato snacks was 489 +/- 26 microg kg(-1), which is comparable to French fries, crackers and cookies but almost three times less than in potato chips, as analysed by other authors. It was also shown that temperature and heating time have a significant influence on acrylamide formation, with temperature having a stronger effect than time. Measurement of colour and acrylamide content at different temperatures and roasting times showed that there is a substantial correlation between lightness (L*), redness (a*), yellowness (b*) and acrylamide concentration as a function of time: r(2) = -0.995, r(2) = 0.996, r(2) = 0.998, respectively. Graduated increases in roasting temperature showed a correlation between lightness (L*) or redness (a*) and acrylamide concentration: r(2) = -0.947 and r(2) = 0.968. Yellowness (b*) was not correlated with acrylamide content as a function of temperature.     

Diffusion with simultaneous immobilization in polymer–dye systems. I. Diffusion of the cationic dye anilana red BL in the anionically modified polyester fiber dilana

The diffusion coefficient of the cationic dye Anilana Red BL in the anionically modified polyester fiber Dilana has been calculated regarding a general diffusion-immobilization model. In the model the mobile species are distinguished from the immobilized ones. In computations of Sand's equation and experimentally determined sorption isotherm of the dye in the fiber, the rate-of-dyeing curve and the concentration profiles of the dye in the same fiber were employed. The diffusion coefficient of the mobile species of Anilana Red BL in the fiber is two orders of magnitude higher than the average diffusion coefficient obtained from Hill's equation and the apparent diffusion coefficient calculated by the Boltzmann–Matano method.     

Circulating fluid-bed reactor for coal pyrolysis

A high temperature coal pyrolysis reactor was developed and its operation demonstrated on a scale of 8 t/h. Pyrolysis is performed in a circulating fluidized bed reactor at 850–950°C. The developed process was integrated into smokeless fuel production technology and tested. Experimental data and reactor performance are presented.