Sulfonation of polyethylene membranes

The polyethylene membranes are hydrophilized under the action of chlorosulfonic acid. Such a hydrophilized membrane shows much better water permeability in comparison with the unmodified one. The ion-exchange capacity of the sulfonated membrane is taken as a measure for the hydrophilicity. The influences of the concentration of the sulfonating agent, temperature, and reaction time, on the ion-exchange capacity and water permeability, are investigated. It is shown that the increase in the degree of sulfonation does not always lead to an increase in the water permeability of the membrane. A lower concentration of the sulfonating agent and a lower temperature are to be chosen, so that only the surface and the inner walls of the pores are sulfonated. Sulfonation in the bulk leads to the deterioration of mechanical properties of the membrane without having any contribution to the increase in the water permeability of the membrane.     

Micro-injection moulding: Factors affecting the achievable aspect ratios

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The aspect ratios achievable in replicating micro features are one of the most important process characteristics and constitute a major manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research studies the effects of five process and one size factors on the achievable aspect ratios, and the role they play in producing micro components in different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed, holding pressure, the existence of air evacuation and the sizes of micro features. The study revealed that the barrel temperature and the injection speed are the key factors affecting the aspect ratios of micro features replicated in PP and ABS. In case of POM, in addition to these two factors, the mould temperature is also an important factor for improving the replication capabilities of the micro-injection moulding process. For all three materials, an increase of feature sizes improves the melt flow. However, the melt fill of micro features does not increase linearly with the increase of their sizes.     

Aliphatic–aromatic poly(azomethine)s with ester groups as thermotropic materials for opto(electronic) applications

We have explored the opto(electronic) and liquid crystal properties of a new series of semiconducting materials based on aliphatic–aromatic poly(azomethine)s. The structures of polymers were characterized by means of FTIR, ¹H, ¹³C NMR spectroscopy, and elemental analysis. UV–vis properties of the thin films of the polymers were investigated on the quartz substrate. The lowest optical energy gap (E_g) at 2.28 eV was found. The polymers were irradiated with a test dose of 2 Gy Co-60 gamma-rays to detect their thermoluminescence properties in the temperature range 25–200 °C. Mesomorphic behavior was investigated via differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) studies. Being into consideration backbone geometry, all polymers, excepted polymer PAZ2, obtained from poly(1,4-butanediol)bis(4-aminobenzoate) and 9-(2-ethylhexyl)carbazole-3,6-dicarboxaldehyde, exhibited liquid-crystalline properties. Moreover, the electrical characterizations of bulk heterojunction (BHJ) and bilayer devices with the following architecture ITO/PEDOT/PAZ:TiO₂/Al were investigated. Additionally, devices without and with TiO₂ layer such as ITO/PAZ/Al and ITO/TiO₂/PAZ/Al were prepared and investigation in the dark and during irradiation with light (under illumination 1000 W/m²). The sol–gel technique was applied to prepared TiO₂ layers and powders. Moreover, impedance spectroscopy at different temperatures for electrical properties measurement was used. Additionally, the compounds were tested using various AFM techniques such as Mode and Phase Imaging and local contrast force–distance curve measurement and roughness (Ra, Rms) along with skew and kurtosis are presented.     

Analysis of Xanthate Derivatives by Vacuum Ultraviolet Laser-Time-of-Flight Mass Spectrometry

A series of liquid O,S-dialkyl dithiocarbonates (xanthate esters) have been synthesized, and time-of-flight (TOF) mass spectra were recorded for their vapors using both ultraviolet (UV) and vacuum ultraviolet (VUV) laser excitation. These compounds are chemical derivatives of low vapor pressure xanthate salts which have found important commercial application as collectors in mineral sulfide flotation circuits. Our experiments demonstrate that esters ionized by short-wavelength VUV light can be detected by parent mass with high efficiency and minimal fragmentation. In contrast, the mass spectra of the same compounds obtained by UV light excitation exhibit a large number of low molecular mass peaks. A preliminary quantitative analysis of the composition of a gas-phase mixture of xanthate esters has also been achieved, which indicates possible subfemtomole detection limits.     

Nonstationary equivalent linearization of nonlinear continuous systems

This paper presents a technique for obtaining the nonstationary stochastic response of a nonlinear continuous system. The method of equivalent linearization is generalized to continuous systems subjected to nonstationary random excitation. This technique allows replacement of the original nonlinear system with a time-varying linear continuous system. A numerical implementation is also described. In this procedure, the linear replacement system is discretized by the finite element method. Application to systems satisfying the one-dimensional wave equation with a constitutive nonlinearity is discussed. Results are presented for nonlinear stress-strain laws of a strain-hardening type.     

A genetic approach to automatic neural network architecture optimization

The use of artificial neural networks for various problems has provided many benefits in various fields of research and engineering. Yet, depending on the problem, different architectures need to be developed and most of the time the design decision relies on a trial and error basis as well as on the experience of the developer. Many approaches have been investigated concerning the topology modelling, training algorithms, data processing. This paper proposes a novel automatic method for the search of a neural network architecture given a specific task. When selecting the best topology, our method allows the exploration of a multidimensional space of possible structures, including the choice of the number of neurons, the number of hidden layers, the types of synaptic connections, and the use of transfer functions. Whereas the backpropagation algorithm is being conventionally used in the field of neural networks, one of the known disadvantages of the technique represents the possibility of the method to reach saddle points or local minima, hence overfitting the output data. In this work, we introduce a novel strategy which is capable to generate a network topology with overfitting being avoided in the majority of the cases at affordable computational cost. In order to validate our method, we provide several numerical experiments and discuss the outcomes.

     

Monte Carlo algorithms for evaluating Sobol’ sensitivity indices

Sensitivity analysis is a powerful technique used to determine robustness, reliability and efficiency of a model. The main problem in this procedure is the evaluating total sensitivity indices that measure a parameter’s main effect and all the interactions involving that parameter. From a mathematical point of view this problem is presented by a set of multidimensional integrals. In this work a simple adaptive Monte Carlo technique for evaluating Sobol’ sensitivity indices is developed. A comparison of accuracy and complexity of plain Monte Carlo and adaptive Monte Carlo algorithms is presented. Numerical experiments for evaluating integrals of different dimensions are performed.     

Using audio to support animated route information in a hospital touch-screen kiosk

It can be difficult for both patients and staff to find particular locations within large, modern hospital building complexes. Interactive way-finding information on a touch-screen kiosk might remedy this, but numerous design issues face those developing appropriate interfaces. This paper discusses the decisions underlying a design which provided routes to 16 destinations in the UK’s third largest hospital, for both stair users and those wishing to avoid stairs. All routes included an animated map, photographs and text boxes with optional spoken output. Assessment methods included unobtrusive observation of kiosk users, analysis of computer logs, and interviews with reception staff who normally answered way-finding queries. Observation confirmed that people using the touch-screen reached their destinations. The computer logs over 10 weeks showed a stable daily average of 82 people interacting with the kiosk. Most way-finders (72%) retained the voice output but 28% turned it off, suggesting that modality choice is needed in multimedia interfaces for the public. This study highlighted beneficial side-effects of interactive way-finding kiosks, such as enabling patients to access relevant route information before visiting the hospital. This information could be provided via the internet or by including a printout of the relevant route with the appointment letter.