The application of proportional hazards and frailty models to multistage processes surveillance

Monitoring industrial and service processes with the purpose of improving the product reliability has been largely addressed in the literature. The surveillance procedures have been proposed with the concentration on single-stage processes with independent quality characteristics. However, the cascade property in multistage processes entails specific monitoring methods which take into account the dependency structure among quality variables in successive stages of a process. This is referred to as regression-adjustment that justifies the heterogeneity in the study population and thus leads to optimal monitoring of multistage processes. In general, it is not straightforward to adjust a quality variable for the effect of all influential covariates because measuring such covariates requires great financial cost and time effort or possibly one may have no prior information about such values. However, ignoring such covariates introduces unobserved heterogeneity which diminishes the detection power of a monitoring scheme. Moreover, the existence of a censoring mechanism results in having more complicated picture due to the inaccurate recording of some data. As a result, the proportional hazards and the frailty models are used to effectively account for both the observed and unobserved heterogeneity. Several monitoring procedures are devised which enable to justify the censoring issue as well. The comparison of the procedures reveals that the cumulative sum (CUSUM) control chart outweighs the competing counterparts.     

Thermal Coherence Tomography: Depth-Resolved Imaging in Parabolic Diffusion-Wave Fields Using the Thermal-Wave Radar

Energy transport in diffusion-wave fields is gradient driven and therefore diffuse, yielding depth-integrated responses with poor axial resolution. Using matched filter principles, a methodology is proposed enabling these parabolic diffusion-wave energy fields to exhibit energy localization akin to propagating hyperbolic wave fields. This not only improves the axial resolution, but also allows for deconvolution of individual responses of superposed axially discrete sources, opening a new field of depth-resolved subsurface thermal coherence tomography using diffusion waves. The depth-resolved nature of the developed methodology is verified through experiments carried out on phantoms and biological samples. The results suggest that thermal coherence tomography can resolve deep structural changes in hard dental and bone tissues, allowing for remote detection of early dental caries and potentially early osteoporosis.     

Efficient cooperative multicarrier underwater acoustic communication over the Persian Gulf channel

Real-time and reliable transmission with high data rate is one of the most crucial design issues in underwater acoustic (UWA) communications. This paper is part of an operational project in the Persian Gulf which is known as a shallow water channel worldwide. Building on the promising combination of cooperative and multicarrier techniques, we first address the design of an efficient UWA communication system over the Persian Gulf channel. We assume sparse and frequency-selective Rician fading, non-white correlated Gaussian ambient noise, and non-uniform Doppler distortion among subcarriers. Based on the extensive field measurements, we adopt a comprehensive channel model including modified sound speed profile, modified absorption coefficient, reflections from the surface and bottom of the sea, and modified ambient noise model. In our work, carrier frequency is efficiently determined based on the system and environmental parameters. In addition, a simple criterion for Doppler scale calculation is proposed. Moreover, based on the approximate auto-correlation function of the ambient noise, whitening filter is utilized at the receiver. In many applications of underwater acoustic sensors network (UW-ASN), nodes may not be big enough to have more than one antenna. Therefore, to achieve spatial diversity, cooperation between nodes can be a proper alternate method. In another part of this research, toward a proper approach that each node operates under full-duplex mode, we address a cooperative virtually-aided transmission scenario which is called cooperative multiple input single output. Simulation results demonstrate that our proposed models can significantly improve the bit error rate performance of UW-ASN in the Persian Gulf channel.     

Silver-zinc oxide nanocomposite: From synthesis to antimicrobial and anticancer properties

A green method by Verbascum speciosum was used to synthesize zinc oxide nanoparticles (ZnO NPs). ZnO NPs were coated with silver to synthesize Ag–ZnO nanocomposite (NCs). The physicochemical properties of Ag–ZnO NCs were analyzed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. The FTIR indicated the peak of Zn–O vibration and some hydroxyl and carboxyl groups. PXRD analyses confirmed the synthesis of ZnO NPs and Ag–ZnO NCs. Due to the size of the crystallite obtained from PXRD, solid-phase sizes (from FESEM and TEM images), and dynamic sizes from DLS, agglomeration was observed. The Ag–ZnO NCs showed a negative charge surface (?49.3 mV). Ag–ZnO NCs had a high antibacterial activity towards two most important infectious bacteria (i.e., Escherichia coli and Staphylococcus aureus) and anticancer activity against human liver-carcinoma cells (HepG2). Later, it depended on time and concentration of Ag–ZnO NCs. The cytotoxicity properties of Ag–ZnO NCs were also studied against NIH-3T3 as a normal cell, where the results verified the lower cell toxicities of nanocomposite than the HepG2.     

Categorizing suppliers for development investments in construction: application of DEA and RFM concept

Supplier development plays a significant role in the cost, quality and delivery improvements of construction projects. However, there is limited research on analytical methods of categorizing and prioritizing a high number of suppliers for effective allocation of scarce development resources. This research aims to develop an objective model to categorize a general contractor’s suppliers. To do so, we use three concepts from different research backgrounds – recency, frequency and monetary value (RFM); data envelopment analysis (DEA); and the customer pyramid – and add the number of projects (P) shared with each supplier as a context-related variable to build a novel RFMP model. The model categorizes suppliers into four levels of the supplier pyramid, utilizing historical data on supplier–contractor transactions. To test the model in practice, we adopt a case study of an international construction company in Finland. The results reveal that a supplier’s RFMP score reflects its contribution to the contractor’s business; therefore, development investments should vary, based on a supplier’s position in the supplier pyramid. This research contributes to the knowledge on supply chain management in construction by combining three approaches – RFM, DEA and the customer pyramid – into a single objective model to categorize suppliers for effective development investments.     

The role of knowledge about user behaviour in demand response management of domestic hot water usage

Load balancing is an important topic in smart grid systems. Dynamic pricing is a common approach to achieve a better balance between renewable energy production and energy usage. This assumes that individual households adapt their energy usage patterns based on energy prices. However, the actual behaviour of consumers in a household is an uncertain factor that might influence the effectiveness of pricing strategies. In this paper, we investigate to what extent knowledge about actual user behaviour can contribute to local optimization of energy usage. We use simulations to study whether a smart heating system that applies a pre-heating strategy for domestic water during periods of low prices can benefit from good predictions of the user behaviour, in financial terms or in terms of energy saving. Also, we use the simulations to investigate the effect of different goal temperatures for the pre-heating strategy. The results show that pre-heating does not make a difference with respect to the energy efficiency, but that during cold months, pre-heating can result in a financial benefit. In addition, we calculate what certainty about the user behaviour is needed to be able to effectively use pre-heating during the warmer summer month. These results can help to design residential energy optimization systems.     

Phase transformation studies on the a-C coating under repetitive impacts

The phase transformation of hydrogen-free amorphous carbon (a-C) coating on tungsten high speed steel (SKH2) substrates under repetitive impact testing has been studied. The a-C coated disc was impacted by the chromium molybdenum steel (SCM420) pin at several different impact loads and impact cycles (up to 100,000) under lubricated conditions. The results show that the sp³ fractions of impacted a-C coating obtained from the surface of impact craters are significantly increased with impact cycles due to decreasing ID/IG ratio. This means that the amorphization of a-C coating also increased after several impact cycles. As for the full-width at half maximum (FWHM) of G peak characterization, it is shown that the hardness of impacted a-C coating is higher than the as-received. From the observation of surface roughness using atomic force microscopy (AFM), it is supposed that increasing sp³ fractions and the hardness of the impacted a-C coating during impact correlate to the reduction of surface roughness. In addition, the tribochemical reaction to the environment during impact occurred at the mating material, where the transfer layer adhered, as well as in the wear debris. This is due to the oxidation of ferrum (Fe) to magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) phases with predominant peak at about 680 cm⁻¹ and 1317 cm⁻¹, respectively. The formation of Fe₃O₄ and α-Fe₂O₃ phases was revealed from Raman spectroscopy and the existence of oxide elements was verified by energy dispersive X-ray spectroscopic (EDS) analysis. Increasing the G peak position, together with a concomitant decrease of their width, it is believed that the structural transformation from sp³ to sp² is taking place within the wear debris and leads to the graphitization process at a higher contact pressure. It was suggested that the high contact pressure is not just only corresponding to the applied normal impact load, but it is also exerted by an oil lubricant during impact. A high contact pressure can significantly reduce the graphitization temperature and substantially accelerate the graphitization process. However, a significant phase transformation of the transfer layer on the SCM420 pin does not intensely occur because it is mainly coming from the surface layer of the impacted a-C coating, where the sp³ content increases and no wear debris is observed inside it.     

Preconcentration and determination of chromium in water with flame atomic absorption spectrometry by thiourea-formaldehyde as chelating resin

Thiourea-formaldehyde chelating resin is synthesized simply and rapidly from thiourea and formaldehyde by condensation polymerization and characterized by IR spectra and studied for the preconcentration and determination of trace Cr(III) ion from solution samples. The optimum pH value for sorption of the metal ion was 6.5. The sorption capacity of resin for Cr(III) was determined. The chelating resin can be reused for 20 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 96% was obtained for the metal ion with 0.5M HNO₃ as eluting agent. The equilibrium adsorption data of Cr(III) on modified resin were analyzed by Langmuir, Freundlich and Temkin models. Based on equilibrium adsorption data the Langmuir, Freundlich and Temkin constants were determined as 0.016, 0.040 and 0.074 at pH 6.5 and 20°C. The method was applied for chromium ion determination from river water sample.