Effect of lithium nitrate on the reaction between opal aggregate and sodium and potassium hydroxides in concrete over a long period of time

Alkali-silica reaction (ASR) is a reaction between amorphous or poorly crystallized siliceous phase, present in aggregates, and sodium and potassium hydroxides in the pore solution of concrete. Chemical admixtures such as lithium compounds are known to have high potential of inhibiting ASR. The aim of this study was to determine the effect of lithium nitrate on ASR in mortars containing high reactive opal aggregate over a long period of time. Mortar bar expansion tests were performed and microstructures of mortar bars were observed by scanning electron microscopy coupled with an energy dispersive X-ray microanalyser. Results from this study showed that effectiveness of lithium nitrate in mitigating ASR was limited over a long period of time. A larger amount of ASR gel which was formed in the presence of lithium nitrate indicated that the deterioration processes intensify within longer periods of time, which so far has not been observed in literature. Microscopic observation confirmed the presence of alkali-silica gel and delayed ettringite in mortars with lithium nitrate.

Surface modification of AZ91 magnesium alloy using GTAW technology

In this study, surface remelting treatment of the AZ91 magnesium alloy by means of welding using a non-consumable electrode in an inert gas shield was carried out. Three variants of surface treatment were used, i.e. the single torch variant with a single heat source without cooling down the samples, the single torch variant with a single heat source and a cooling system with liquid nitrogen, and the double welding torch variant with a double heat source in the torches operating in a tandem configuration. Experimental verification of the applied apparatus solutions was based on both macro- and microstructural assessment of the obtained effects. Comparative analysis of the variants used and the obtained microstructural results allowed the authors to indicate the deficiencies and limitations of particular solutions and to single out the best solution that would be useful for modifying the surface layers of magnesium alloys, as well as other materials having a strong oxygen affinity.

Financial optimisation of the scheduling for the multi-stage project

The paper analyses the problem of discounted cash flow maximising for the resource-constrained project scheduling from the project contractor’s perspective. Financial optimisation for the multi-stage project is considered. Cash outflows are the contactor’s expenses related to activity execution. Cash inflows are the client’s payments for the completed milestones. To solve the problem, the procedure of backward scheduling taking into account contractual milestones is proposed. The effectiveness of this procedure, as used to generate solutions for the simulated annealing algorithm, is verified with use of standard test instances with additionally defined cash flows and contractual milestones.

Iterative sliding mode observer for sensorless control of five-phase permanent magnet synchronous motor

Due to the star connection of the windings, the impact of the third harmonic which does not exist in three-phase permanent magnet synchronous motor (PMSM) cannot be ignored in five-phase PMSM. So the conventional sensorless control methods for three-phase PMSM cannot be applied for five-phase PMSM directly. To achieve the sensorless control for five-phase PMSM, an iterative sliding mode observer (ISMO) is proposed with the consideration of the third harmonic impact. First, a sliding mode observer (SMO) is designed based on the fivephase PMSM model with the third harmonic to reduce the chattering and obtain the equivalent signal of the back electromotive force (EMF). Then, an adaptive back EMF observer is built to estimate the motor speed and rotor position, which eliminates the low-pass filter and phase compensation module and improves the estimation accuracy. Meanwhile, by iteratively using the SMO in one current sampling period to adjust the sliding mode gains, the sliding mode chattering and estimation errors of motor speed and rotor position are further reduced. Besides, the stability of the SMO and the adaptive back EMF observer are demonstrated in detail by Lyapunov stability criteria. Experiment results verify the effectiveness of the proposed observer for sensorless control of five-phase PMSM.

FPGA implementation of logarithmic versions of Baum-Welch and Viterbi algorithms for reduced precision hidden Markov models

This paper presents a programmable system-on-chip implementation to be used for acceleration of computations within hidden Markov models. The high level synthesis (HLS) and “divide-and-conquer” approaches are presented for parallelization of Baum-Welch and Viterbi algorithms. To avoid arithmetic underflows, all computations are performed within the logarithmic space. Additionally, in order to carry out computations efficiently – i.e. directly in an FPGA system or a processor cache – we postulate to reduce the floating-point representations of HMMs. We state and prove a lemma about the length of numerically unsafe sequences for such reduced precision models. Finally, special attention is devoted to the design of a multiple logarithm and exponent approximation unit (MLEAU). Using associative mapping, this unit allows for simultaneous conversions of multiple values and thereby compensates for computational efforts of logarithmic-space operations. Design evaluation reveals absolute stall delay occurring by multiple hardware conversions to logarithms and to exponents, and furthermore the experiments evaluation reveals HMMs computation boundaries related to their probabilities and floating-point representation. The performance differences at each stage of computation are summarized in performance comparison between hardware acceleration using MLEAU and typical software implementation on an ARM or Intel processor.

Computational modeling of creep in complex plane for reinforced materials

Computational modeling for predicting the steady state creep behavior is presented in complex plane for reinforced materials by complex variable method. Both the fiber and matrix simultaneously creep at elevated temperatures and loading. We suppose that one dimension of the short fiber is small enough in comparison with the other two (see Fig. 1). In this formulation, plane stress state is used. Finally, displacement rate behaviors are predicted using compatibility, equilibrium, constitutive, and governing equations by complex variable method. One of the considerable applications of the method is in nano-composites analysis in elasticity or plasticity research.

The optimal online control of the instantaneous power and the multiphase source’s current

The paper presents the new optimal real-time control algorithm of the power source. The minimum of the square-instantaneous current was assumed as an optimal criterion, with an additional constraint on source instantaneous power. The mathematical model of a multiphase source was applied as a voltage-current convolution in the discrete time domain. The resulting control algorithm was the recursive digital filter with infinite recursion.