A comparative study of hygroscopic moisture content,electrical conductivity and ion chromatography for salt assessment in plasters of historical buildings

It has long been known that highly soluble salts or hydrate-forming salts can damage porous building material. There is a real challenge to provide salt assessment in compliance with good monuments diagnosis and restoration practices. The salts present in the masonry can be analysed qualitatively and quantitatively by means of several techniques. Nowadays, the standard analytical equipment as ion chromatography (IC) found in several laboratories is a reliable method for analysing a large variety of anions and cations in solutions (or building materials water extracts), in order to meet international standards and regulations. However, preliminary study and diagnosis of soluble salt present in monuments do not necessarily require such a precise (SD < 5%) and sensitive (ppm or ppb range) analyses. Some simple-to-use techniques, such as hygroscopic moisture content (HMC) and electrical conductivity (EC) of extracted salt solutions, are widely in use to provide indications on the presence of salts.This paper presents a comparison of salt assessment obtained by IC, HMC and EC methods, and provides the domain of their application to specific questions linked to the damaged building diagnosis and preservation.The comparison of the results obtained by IC, EC and HMC analyses highlights the limits of the EC method in providing quantitative information on soluble salt content. The EC technique seems to require some cautions when used for materials containing other high soluble phases such as portlandite. On the other hand, the HMC technique seems to be very useful in the field of historical masonry investigation since it can provide reliable semi-quantitative distribution of hygroscopic salts.     

Investigations on printed elastic resistors containing carbon nanotubes

This paper presents the results of authors investigations on elaboration of a new thick film composition filled with carbon nanotubes (CNTs). The polymer composition consists of polymer vehicle, which is the solution of organic resin in certain combination of solvents, and functional phase—carbon nanotubes well dispersed in the vehicle. The pastes were applied with screen-printing on several substrates and temperature cured. The properties of obtained layers were characterized. Series of samples were prepared with different amount of CNTs to evaluate electrical properties. Changes in resistance were investigated during periodic mechanical and temperature stresses, realized through cyclical bending and rapid temperature change. Tensometric effect was also investigated. Investigations have proved that polymer composites based on carbon nanotubes exhibit high resilience to stress factors. Resistance change in function of temperature was also investigated to evaluate temperature coefficient of resistance (TCR). All this aspects are important for elastic resistors fabrication in printed electronics microcircuits. Resistance and noise measurements in cryostats have also been involved. 1/f type noise has been observed. Noise intensity, calculated in decade frequency bands, rises significantly with increasing temperature. Activation energies of thermally activated noise sources (TANS) have been revealed using low-frequency noise spectroscopy. Relatively large value of negative TCR has been obtained from resistance versus temperature curve. Calculated dimensionless sensitivity is similar to that observed in cryogenic temperature sensors. However, bulk noise intensity of resistive layer is larger than obtained for lead containing RuO₂ based resistive layers.     

Stability analysis of stiffened plates by finite strips

The stability analysis of stiffened plates by means of the finite strip method is presented. The studies are based on the thin shallow theory, giving nonlinear strain displacement relations, but linear curvature displacement relations. The nonlinear equilibrium equations are obtained by the principle of incremental virtual work, using finite strip discretization. The higher order strip with one internal nodal line is applied. It is shown that considerable improvements can be obtained using this kind of strip. It is especially true for the postbuckling analysis. Numerical examples of the strength of stiffened plates in compression are carried out, covering a range of plate and stiffener slenderness.     

The Design of Genetically Optimized Self-Organizing Neural Networks with Polynomial and Fuzzy Polynomial Neurons

In this study, we introduce and investigate a class of neural architectures of self-organizing neural networks (SONNs) that is based on a genetically optimized multilayer perceptron with polynomial neurons (PNs) or fuzzy polynomial neurons (FPNs), develop a comprehensive design methodology involving mechanisms of genetic optimization, and carry out a series of numeric experiments. We distinguish between two kinds of SONN architectures: (a) PN-based and (b) FPN-based SONNs. The augmented genetically optimized SONN (gSONN) results in a structurally optimized structure and comes with a higher level of flexibility in comparison to the one encountered in the conventional SONN. The genetic algorithm (GA)-based design procedure being applied at each layer of SONN leads to the selection of preferred nodes (PNs or FPNs) with specific local characteristics (such as the number of input variables, the order of the polynomial, and a collection of the specific subset of input variables) available within the network.     

Hybrid DPWM implementation using coarse and fine programmable ADLL

In the paper we propose a novel architecture and implementation of 11-bit Digital Pulse Width Modulator (DPWM) circuit based on previously known building blocks. Linearized Class-AD Double-sided (LADD) algorithm has been used to calculate the DPWM signals of the 11-bit resolution hybrid DPWM for a Class-AD digital audio amplifier. Noise-shaping process is used to support high fidelity with practical values of time resolution. The proposed DPWM circuit is composed of 8-bit counter and Analog Delay Locked Loop (ADLL) using 4-bit tapped delay line. A dual ADLL employing coarse and fine programmable delay element is used to adjust the delay time of delay line and lock it to required time. The coarse- as well as fine-delay lines are implemented as a cascade of variable-delay elements based on shunt capacitor delay element or single-ended Schmitt trigger. The proposed 11-bit DPWM circuit, at a switching frequency of 352.8 kHz and clock generator frequency of 90.3 MHz allows us to attain SNR of 120 dB and THD of the output signal less than 0.1% within the audio baseband and modulation index M=0.95. Basic verification of circuit manufacturability and simulation results (Monte Carlo analysis) for real CMOS process are presented.     

A simple model for explosive combustion of premixed natural gas with air in a bubbling fluidized bed of inert sand

The combustion of premixed natural gas and air has been studied in a bubbling fluidized bed of inert particles. The temperature of the solids was carefully monitored, using 8 thermocouples, immersed in the bed at different heights. The observed temperature profiles were used to find the height above the distributor at which most of the combustion occurred and on this basis a clear distinction could be made between combustion above the bed and inside the bed. The region where most of the heat of combustion is evolved depends on the average bed temperature. If this temperature is low, the gases burn above the bed or just under its upper surface, but at higher temperatures the process is located close to the distributor. Rapid fluctuations in the measured temperature and pressure indicate that the process inside the bed is not a steady one. The model developed here assumes that combustion takes place inside bubbles of premixed gases, as they move through the bed. A detailed chemical kinetic model was used to calculate the induction period for ignition. The model can predict the height above the distributor at which bubbles should ignite and explode. Comparison of the experimental results with the modeling calculations indicates that the course taken by the process depends on temperature. At the lowest temperatures, the gases burn above the bed. In the high temperature range, where the bubbles ignite is determined by the induction period. At intermediate temperatures the location of the reaction is determined by the depth of the bed and bubble size, with ignition spreading from above the bed to bubbles, which are about to leave, but are still in the bed. That bubbles explode at different heights up the bed is reflected in the acoustic signals registered above and below the bed. The associated changes in the composition of the flue gases are also very characteristic.