Influence of accelerated curing on the compressive strength of polymer-modified concrete

In recent building practice, rapid construction is one of the principal requisites. Furthermore, in designing concrete structures, compressive strength is the most significant of all parameters. While 3-d and 7-d compressive strength reflects the strengths at early phases, the ultimate strength is paramount. An effort has been made in this study to develop mathematical models for predicting compressive strength of concrete incorporating ethylene vinyl acetate (EVA) at the later phases. Kolmogorov-Smirnov (KS) goodness-of-fit test was used to examine distribution of the data. The compressive strength of EVA-modified concrete was studied by incorporating various concentrations of EVA as an admixture and by testing at ages of 28, 56, 90, 120, 210, and 365 d. An accelerated compressive strength at 3.5 hours was considered as a reference strength on the basis of which all the specified strengths were predicted by means of linear regression fit. Based on the results of KS goodness-of-fit test, it was concluded that KS test statistics value (D) in each case was lower than the critical value 0.521 for a significance level of 0.05, which demonstrated that the data was normally distributed. Based on the results of compressive strength test, it was concluded that the strength of EVA-modified specimens increased at all ages and the optimum dosage of EVA was achieved at 16% concentration. Furthermore, it was concluded that predicted compressive strength values lies within a 6% difference from the actual strength values for all the mixes, which indicates the practicability of the regression equations. This research work may help in understanding the role of EVA as a viable material in polymer-based cement composites.     

Cavity cutting efficiency of a Bioglass<Superscript>TM</Superscript> and alumina powder combination utilized in an air abrasion system

This study investigated the attempt to replace alumina in the air abrasion system with an alternative material that is effective at cutting and also has remineralization potential. The powder samples were randomized into three groups: group 1—alumina (composed of aluminium and oxygen), group 2—45S5 (composed of 45% silica, 24.5% calcium oxide, 24.5% sodium oxide and 6% phosphorus pentoxide in weight percentage) and group 3—alumina + 45S5. Thirty human enamel blocks and microscope glass slides of 0.5 mm thickness were randomly divided into these three groups. The time taken to cut a hole through the glass slide and for the cutting of human enamel blocks was recorded, the cutting time was fixed at 15 s. The depths of the cavities were measured using a periodontal probe and the enamel blocks were then analysed by scanning electron microscope (SEM). The mean time taken to cut a hole through the microscope glass slide was 2.96, 23.01 and 3.02 s for groups 1, 2 and 3, respectively. After cutting the human enamel blocks, the mean cavity depths produced were measured to be 2.5, 1.0 and 2.0 mm for groups 1, 2 and 3, respectively. The SEM micrographs revealed that the cavities formed by 45S5 were more conical in shape, whereas cavities produced by alumina and alumina + 45S5 were more cylindrical. The combined use of alumina and 45S5 has demonstrated a promising cutting efficiency and it has the potential to achieve effective cutting with the possibility of the remineralization.     

Optimal maintenance policy for equipment subject to random deterioration and random failure A modern control theory approach

The stochastic version of Pontryagin's maximum principle is applied to determine an optimal maintenance policy of equipment subject to random deterioration. The deterioration of the equipment with age is modelled as a random process. Next the model is generalized to include random catastrophic failure of the equipment. The optimal maintenance policy is derived for two special probability distributions of time to failure of the equipment, namely, exponential and Weibull distributions Both the salvage value and deterioration rate of the equipment are treated as state variables and the maintenance as a control variable. The result is illustrated by an example.     

Reliability modelling and evaluation of phased mission systems

A reliability model for phased mission systems is developed. First, the mission phase change times are assumed to be known in advance. Next, these times are assumed as random variables and a method of solution is presented. The solution procedure is illustrated by an illustrative example. It is seen that for large systems, an analytical expression for mission system reliability becomes quite involved and requires a computation procedure.     

An application of modern control theory to a time-dependent queuing system for optimal operation

‘ Bang-bang ’ optimal closed-loop service policy for a time dependent M/M/l queuing system is derived using optimal control theory. The policy is based on probabilistic (and not stochastic) behaviour of the queue. Computational results are obtained for an illustrative example with non-bang-bang service policy using the conjugate gradient algorithm with bounded control variables. It is interesting to note that the optimal service policy is not sensitive to the arrival rate but to the mean service cost of a customer.     

A critical review of ash slagging mechanisms and viscosity measurement for low-rank coal and bio-slags

Gasification or combustion of coal and biomass is the most important form of power generation today. However, the use of coal/biomass at high temperatures has an inherent problem related to the ash generated. The formation of ash leads to a problematic phenomenon called slagging. Slagging is the accumulation of molten ash on the walls of the furnace, gasifier, or boiler and is detrimental as it reduces the heat transfer rate, and the combustion/gasification rate of unburnt carbon, causes mechanical failure, high-temperature corrosion and on occasions, superheater explosions. To improve the gasifier/combustor facility, it is very important to understand the key ash properties, slag characteristics, viscosity and critical viscosity temperature. This paper reviews the content, compositions, and melting characteristics of ashes in differently ranked coal and biomass, and discusses the formation mechanism, characteristics, and structure of slag. In particular, this paper focuses on low-rank coal and biomass that have been receiving increased attention recently. Besides, it reviews the available methodologies and formulae for slag viscosity measurement/prediction and summarizes the current limitations and potential applications. Moreover, it discusses the slagging behavior of different ranks of coal and biomass by examining the applicability of the current viscosity measurement methods to these fuels, and the viscosity prediction models and factors that affect the slag viscosity. This review shows that the existing viscosity models and slagging indices can only satisfactorily predict the viscosity and slagging propensity of high-rank coals but cannot predict the slagging propensity and slag viscosity of low-rank coal, and especially biomass ashes, even if they are limited to a particular composition only. Thus, there is a critical need for the development of an index, or a model or even a measurement method, which can predict/measure the slagging propensity and slag viscosity correctly for all low-rank coal and biomass ashes.     

Pharmacotherapeutics and molecular docking studies of alpha-synuclein modulators as promising therapeutics for Parkinson’s disease

Parkinson’s disease (PD) is an age-related neurodegenerative ailment that affects dopamine-producing neurons in a specific area of the brain called the substantia nigra of the ventral midbrain. It is clinically characterized by movement disorder and marked with unusual synaptic protein alpha-synuclein accumulation in the brain. To date, only a few Food and Drug Administration (FDA) approved drugs are available on the market for the treatment of PD. Nonetheless, these drugs show parasympathomimetic related adverse events and remarkably higher toxicity; hence, it is important to find more efficacious molecules to treat PD. In our study, We chosen 22 natural compounds as inhibitors that potentially block the alpha-synuclein clump—the pathological hallmark of PD—and provide new avenues for its treatment. Most of these molecules exhibited good pharmacokinetic behaviors, making them decisively favorable drug candidates to cure PD. Molecular docking studies were performed to investigate the binding interactions between natural compounds and alpha-synuclein as anti-Parkinson drug targets. Among the examined compounds, curcumin and piperine emerged as promising phytochemicals with the highest binding affinity, key residual stable bindings and showed a good inhibitory features. Thus, the present study indicates that curcumin and piperine hold the potential to be developed as treatment options against PD. Experimental validations are needed for insights into their mechanism of action and potential clinical application.     

INFLUENCE OF DESIGN AND OPERATING CONDITIONS ON THE SYSTEM PERFORMANCE OF A TWO-STAGE ADSORPTION CHILLER

This article aims at clarifying the possible design and operating conditions for silica gel-water adsorption refrigeration cycles driven by near-ambient temperature waste heat sources (between 45 and 75°C) with relatively small regenerating temperature lifts (15 to 45 K). A two-stage silica gel-water advanced adsorption chiller is introduced and a simulation model of the chiller was developed to analyze the influence of operating and design conditions on the system performance (coefficient of performance, COP, and cooling capacity). It was hypothesized that the proposed chiller can be driven by low temperature waste heat at 55°C to produce effective cooling. Simulation results show that the operating conditions such as cycle time and hot and cooling water inlet temperature have an influential effect on cooling capacity and COP. COP is proportional to cycle time and heat transfer coefficient as well as inversely proportional to the cooling water inlet temperature, while there are optimum values of hot water temperature and silica gel weight for maximum COP. Cooling capacity mainly improves with the addition of silica gel weight and decreases as cooling water temperature increases. Simulation results also revealed that the system performance can be improved significantly by setting the design and operating conditions optimally.     

Joint effect of test effort and learning factor on software reliability and optimal release policy

This paper presents a realistic approach for software reliability growth modelling incorporating the joint effect of test effort and learning factor. The error detection process in software is described using a non-homogeneous Poisson process. Maximum likelihood estimates of the reliability growth parameters are obtained using a numerical method. Optimal release policies for cost and reliability are discussed. Finally, an example using real-life data is presented for illustration and comparison     

Moorland soil erosion and spectral reflectance

Abstract

The dramatic increase in erosion on Glaisdale Moor in the North York Moors is mapped using aerial photographs for 1973, 1978 and 1983. The erosion provides a focus for a quantitative analysis of the relationships between spectral reflectance and ground variables in areas of peat, bare soil and vegetation.