Inspection interval optimization for complex equipment in automotive manufacturing under dependent failures

Forschung im Ingenieurwesen - Inspection activities in automotive manufacturing play a crucial role in diagnosing and preventing unexpected failures by adopting the well-planned intervals....     

Interactions between serotypes of dengue highlight epidemiological impact of cross-immunity

Dengue, a mosquito-borne virus of humans, infects over 50 million people annually. Infection with any of the four dengue serotypes induces protective immunity to that serotype, but does not confer long-term protection against infection by other serotypes. The immunological interactions between serotypes are of central importance in understanding epidemiological dynamics and anticipating the impact of dengue vaccines. We analysed a 38-year time series with 12 197 serotyped dengue infections from a hospital in Bangkok, Thailand. Using novel mechanistic models to represent different hypothesized immune interactions between serotypes, we found strong evidence that infection with dengue provides substantial short-term cross-protection against other serotypes (approx. 1–3 years). This is the first quantitative evidence that short-term cross-protection exists since human experimental infection studies performed in the 1950s. These findings will impact strategies for designing dengue vaccine studies, future multi-strain modelling efforts, and our understanding of evolutionary pressures in multi-strain disease systems.     

Online measurement of particle size distribution during crystallization using ultrasonic spectroscopy

Particle growth during crystallization of paracetamol was monitored on-line using a new modified method based on ultrasonic spectroscopy. The model was earlier developed and tested with inert particles systems and accounts for low angle scattering and probe geometry. A graphic user interface was developed and integrated with the model based deconvolution algorithm for real-time data acquisition, analysis and display of results. The crystal growth and changes in size distribution were measured during the crystallization of paracetamol from paracetamol–isopropanol–water solution. A simplified pre-calibration procedure using acoustic velocity to estimate solution properties was established. The model based particle size distribution showed good agreement with offline measurements using laser diffraction analysis of a sample retrieved from the crystallizer.     

Perceived demands and musculoskeletal symptoms among employees of an Iranian petrochemical industry

As a part of a comprehensive ergonomics program, this study was conducted among employees of an Iranian petrochemical industry to determine the prevalence of musculoskeletal symptoms and to examine the relationship between perceived demands and reported symptoms. In this cross-sectional study, 928 randomly selected employees, corresponding to nearly 40% of all employees participated. Nordic Musculoskeletal Disorder Questionnaire and Job Content Questionnaire were used as collecting data tools. The results showed that 73% of the study population had experienced some form of symptoms from the musculoskeletal system during the last 12 months. Knees and lower back symptoms were the most prevalent problem among the employees studied. The results revealed that perceived physical demands were significantly associated with musculoskeletal symptoms (OR ranged from 1.45 to 2.33). Among the perceived physical demands, awkward working postures were most frequently associated with reported musculoskeletal symptoms. Association was also found between perceived psychological demands and reported symptoms. Conflicting demands, waiting on work from other people or departments, interruption that other make, working very fast and time pressure were psychological factors retained in the regression models with OR ≥ 1.49. Based on the findings, it could be concluded that any interventional program for preventing or reducing musculoskeletal symptoms among the petrochemical employees studied had to focus on reducing physical demands, particularly awkward working postures as well as psychological aspect of working environment.

Relevance to industry

In petrochemical industry where employees are involved in both static and dynamic activities, determination of musculoskeletal symptoms contributing factors can be considered as a basis for planning and implementing interventional ergonomics program for preventing musculoskeletal symptoms and improving working conditions.     

Determination of potash crystallization kinetics in a laboratory-scale continuous cooling crystallizer

Crystallization kinetics of KCl in a 21.8L continuous mixed-suspension-mixed-product-removal (CMSMPR) potash cooling crystallizer are determined using the method of s-plane analysis (Tavare, 1986). Feed saturated in refined potash, nearly saturated in NaCl and containing 0.75 g of MgSO₄ per 100 g of water is cooled from 54°C to 38°C by two concentric cooling coils. The crystallizer is brought to steady-state and then perturbed by a change in the crysallizer temperature from 38°C to 32°C. Samples are withdrawn every 15 minutes by means of a specially devised sample trap which permits representative sample removal. Samples are sized using sieve-analysis. The crystallization kinetics are correlated as B° = 49,618 G^0,982.     

Optimal bandwidth allocation for the data and feedback channels in MISO-FDD systems

In frequency-division duplex (FDD) systems, channel-state information (CSI) is estimated by the receiver and then fed back to the transmitter through a feedback link, which inevitably requires additional bandwidth and power. In this letter, we jointly study optimal bandwidth allocation between the data channel, modeled as a flat-fading multiple-input single-output (MISO) channel, and the feedback channel for maximum average throughput in the data channel using a beamforming scheme. We consider two models of the partial CSI at the transmitter (CSIT): the noisy CSIT, modeled as jointly Gaussian with the actual channel state, and the quantized CSIT. In the first model, we use distortion-rate theory to relate the CSIT accuracy to the feedback-link bandwidth. In the second model, we derive a lower bound on the achievable rate of the data channel based on the ensemble of a set of random quantization codebooks. We show that in the MISO flat-fading channel case, beamforming based on feedback CSI can achieve an average rate larger than the capacity without CSIT under a wide range of mobility conditions.     

Using Coal Fly Ash and Wastewater for Microwave Synthesis of LTA Zeolite

The reuse of industrial wastes from a coal‐fired power plant and a plasma electrolytic oxidation process was attempted to realize a zero discharge. The batch composition was adjusted by adding sodium hydroxide and sodium aluminate. A single‐mode microwave oven equipped with reflux condenser was used for crystallization under atmospheric pressure. The synthesized samples were characterized by X‐ray diffraction, scanning electron microscopy, BET, thermogravimetric analysis, and cation‐exchange capacity (CEC) measurement. Analytical results indicated that Na‐A zeolite with a defined maximum crystallinity could be successfully synthesized by hydrothermal treatment of fly ash with wastewater. Due to the high CEC, the product can be applied for gas purification and soil remediation processes.     

Transparent nanostructured coatings with UV-shielding and superhydrophobicity properties

Visible light transparent, UV-shielding and superhydrophobic nanostructured coatings have been successfully fabricated through a facile layer-by-layer deposition of TiO(2) and SiO(2) nanoparticles. The coatings are composed of an underlying UV-shielding TiO(2) layer and a top fully covered protective SiO(2) layer. The resulting coatings can block 100% of UVB and UVC and almost 85% of UVA. The fabricated surfaces have contact angles exceeding 165° after coating with organic PTES (1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane) molecules. The transparent superhydrophobic surfaces exhibit extremely strong UV stability. All coatings retain the initial UV-shielding and superhydrophobic properties even after exposure to 275 nm UV light with a light intensity of 75 mW cm(-2) for 12 h.     

A simplified approach to the operation of a batch crystallizer

A general model for a seeded cooling batch crystallizer based on first principles is developed, incorporating either size-dependent or size-independent growth rates. A simple approach is proposed to obtain temperature-time trajectories at constant supersaturation or nucleation rate, without resorting to optimization techniques. Cooling curves at constant supersaturation, which lead to a substantial improvement (a smaller coefficient of variation and a larger mean size) of the terminal crystal size distribution, can be determined even in the absence of precise nucleation and growth kinetics, whereas properties related to the crystal size distribution are sensitive to such kinetics. Experimental results for the potassium sulfate-water system, potash alum-water system, and hexamethylenetetramine in ethanol, methanol, and 2-propanol/water are predicted reasonably well by the model. Extension to any type of batch crystallization with super-saturation induced by means other than cooling, such as reactive precipitation and salting out, is briefly discussed.