Numerical methods for transient solutions of machine repair problems

This paper reviews and compares two types of numerical methods of computing transient probabilities of finite Markovian queues (particularly the machine repair problem). A brief review of each method is followed by numerical examples of small and moderate size machine repair problems. The results demonstrate the feasibility of applying numerical techniques for obtaining transient solutions to Markovian queueing problems.     

Copolymerization of butyl acrylate with styrene in presence on ZnCl2

Summary Copolymers of butyl acrylate-styrene were prepared in presence of ZnCl₂. The formation of a complex was determined by infrared spectroscopy. The copolymers were characterized by IR, NMR and by solubility. The study of their structure as a function of the initial monomer composition and the analysis of UV spectra showing varying intensity of the carbonyl peaks confirmed the presence of an alternating copolymer. The reactivity ratios of the two monomers were determined and found to be 0.1 for both butyl acrylate and styrene.     

Target optimization for a 10-MeV E-beam neutron converter

Accelerator-based target design and optimization is an approach for neutron generation. The target plays an important role for a neutron source on an electron accelerator. For optimizing a neutron source using 10 MeV electron beams of Rhodotron-TT200, Pb, Ta, or W alloys with Be were calculated as photo-neutron converter. The neutron yield, flux and energy were simulated using the MCNPX code. The results indicate that a 10 MeV electron beam is capable of producing high-intensity neutron flux of 1013n·cm–2·s–1 with average energy of 0.8 MeV.     

Stresses in buried conduits caused by freezing front

A laboratory experiment modeling the buried conduit problem was performed to study the stress changes in the conduit as a result of frost penetration in the soil. The model consisted of a large-scale soil container insulated on all sides except the top. The level and temperature of the ground water in the container, and the end restraints of the buried conduit, could be controlled. The model was placed in a cold room where the air temperature could be reduced to ?25°C. The experimental results, supplemented by the available field data, demonstrate the influence of soil freezing on pipe bending stresses. Maximum frost depth, which can vary with the rate of freezing even for comparable air freezing indexes, is a significant soil thermal parameter that correlates with pipe stresses. Availability of ground water significantly increases pipe stresses while pipe-end restraints tend to decrease them slightly. The results suggest that the water expulsion by the advancing freezing front causes loss of soil stiffness due to the increased pore water pressures and decreased effective stresses in the soil.     

Application of Dispersive Liquid–Liquid Micro-extraction Using Mean Centering of Ratio Spectra Method for Trace Determination of Mercury in Food and Environmental Samples

In the present study, dispersive liquid–liquid micro-extraction has been applied for trace extraction and determination of mercury (Hg) ions in environmental samples. The mean centering of ratio spectra method was used to optimize the experimental parameters affecting the extraction of Hg. The factors influencing the extraction procedure such as type and volume of extracting and disperser solvent, concentration of chelating reagent, pH, salt effect, and centrifuge time were investigated and optimized. Under the optimized conditions, the limit of detection of the method was 0.15 μg l^?1 and enrichment factor was 39. The calibration curve was linear in the range of 0.5–100 μg l^?1 with a correlation of determination (R ²) of 0.998. The relative standard deviation for determination of 40 μg l^?1 of Hg(II) was 2.6 % (n?=?5). The proposed method was applied for the determination of Hg in pine leaf, sea and river fish, sand, and water samples as indicators of environmental pollution and cigarette with satisfactory analytical results. In comparison with other methods, the proposed method is very simple, easy, rapid, and sensitive for determination of Hg at trace levels in complex matrices.     

Alkali ash material: a novel fly ash-based cement

The United States generates 110 million t of coal ash annually. Approximately 70 million t of this coal ash is fly ash, of which 27% is recycled and the remaining 73% is landfilled. Disposal of such a huge quantity of ash poses a significant environmental problem. A new cementitious material has been developed, called alkali ash material (AAM), which is used to produce concrete for construction. AAM can be used to create a variety of concrete strengths and could revolutionize the concrete product manufacturing industry due to its economic advantage. AAM contains 40-95% Class F fly ash and is used as cement to bind sand, stone, and fibers creating concrete. AAM concrete has been tested for strength, durability, mechanical properties, and, most importantly, economic viability. AAM concrete is economically and technically viable for many construction applications. Some properties include rapid strength gain (90% of ultimate in 1 d), high ultimate strengths (110 MPa or 16,000 psi in 1 d), excellent acid resistance, and freeze-thaw durability. AAM's resistance to chemical attack, such as sulfuric (H2SO4), nitric (HNO3), hydrochloric (HCl), and organic acids, is far better than portland cement concrete. AAM is resistant to freeze-thaw attack based on ASTM C-666 specifications. Potential immediate applications of AAM are blocks, pipe, median barriers, sound barriers, and overlaying materials. Eventual markets are high strength construction products, bridge beams, prestressed members, concrete tanks, highway appurtenances, and other concrete products.     

The effect of chitosan coating incorporated with ethanolic extract of propolis on the quality of refrigerated chicken fillet

Chitosan is considered as a functional packaging component for maintaining the quality and increasing the shelf life of perishable foods include meat, poultry, fish, dairy products, and all cooked leftovers. The present study was conducted to evaluate edible coating of chitosan (2%) containing ethanolic extract of propolis (1% and 2%) on microbiological (mesophilic aerobic, psychrotrophic, lactic acid bacteria, coliforms, and Staphylococcus aureus counts), chemical (TBARS, TVN and Peroxide values) and sensory (odor, color, texture, taste, and overall acceptance) properties of chicken fillet. Microbial analysis showed that coating had a significant reducing effect on growth of bacteria during 12 days at 4 °C. Besides, the increase of TBARS, Total volatile nitrogen, and peroxide value of samples coated by chitosan and ethanolic extract of propolis was less than control group. According to our results, chitosan and propolis can be used to enhance the shelf life of fillet and maintain its quality.

Practical applications

Propolis is used for infections caused by bacteria, viruses, fungus, and by single‐celled organisms called protozoans. Propolis is also used as an antioxidant and anti‐inflammatory agent. Ethanol extract of propolis improve the properties of chitosan edible coating in chicken fillet preservation. The chitosan coating incorporated with ethanolic extract of propolis can improve the microbial, chemical, and sensory quality of food and enhance the shelf life of them by synergistic effects.     

Hydroxymethylfurfural in fruit puree and juice: preconcentration and determination using microextraction method coupled with high-performance liquid chromatography and optimization by Box–Behnken design

In the present study, a sensitive and rapid method for separation and determination of hydroxymethylfurfural (HMF) in fruit puree and juices was proposed. Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC) was used for extraction and quantitative determination of HMF in fruit puree and juices. The effective parameters such as the type and volume of extraction and dispersive solvents, pH and salt amount (NaCl) were studied and optimized with the aid of response surface methodology based on Box–Behnken design to obtain the best condition for HMF extraction. At the optimized conditions, parameter values were 60 µL extracting solvent, 600 µL dispersive solvent, 2 g NaCl and pH 5. Repeatability of the method, described as the relative standard deviation, was 3.1% (n?=?6) and the recovery was 98.4%. The limit of detection and limit of quantitation were 1.47 and 5.28 µg L^?1, respectively. The merit figures of DLLME–HPLC–UV method showed that the proposed method can be noticed as a new, fast and good alternative method for investigation of HMF in various fruit puree and juice samples.     

Role of salt in Iranian ultrafiltered Feta cheese: Some textural and physicochemical changes during ripening

The effect of NaCl (0–4%) on the ripening of Iranian ultrafiltered (UF)‐Feta cheese was assessed over 120 days of ripening at 4 °C. Whey percentage, whey salt, whey pH, cheese pH and textural properties of hardness and cohesiveness were monitored, and experimental modelling performed using response surface methodology. Texture, pH and whey percentage were significantly affected by NaCl and ripening. The maximum whey of 22% was recorded at the end of ripening period. Texture of this cheese becomes harder during ripening confirming cheese pH and whey percentage being the major determining factors. Cheese samples were more elastic than viscous with cohesiveness values of 0.6–0.9.     

GC/MS analysis and in vitro antioxidant activity of essential oil and methanol extracts of Thymus caramanicus Jalas and its main constituent carvacrol

Chemical composition of the essential oil, antioxidant activity (DPPH and β-carotene/linoleic acid assays), and total phenolic content (Folin–Ciocalteu assay) of aerial parts of Thymus caramanicus were determined. The highest radical-scavenging activity (DPPH test) was shown by the polar subfraction of the methanol extract (IC₅₀ = 43.0 μg/ml) which was also higher than that of butylated hydroxytoluene (BHT, IC₅₀ = 19.7 μg/ml). However, it was the nonpolar subfraction of the methanol extract that showed the highest inhibition (84.4%), as assessed by the β-carotene/linoleic acid assay, which was only slightly lower than that shown by BHT (93.3%). The antioxidant activities of the essential oil main component (carvacrol) were also evaluated for comparison. Total phenolic content of the polar subfraction, as gallic acid equivalents, was 124.3 μg/mg. Essential oil extracted from the aerial parts by hydrodistillation was analysed by GC and GC/MS. Fifteen constituents, representing 99.3% of the oil, were identified, of which the major ones, carvacrol (85.9%), thymol (3.3%), p-cymene (3.2%), γ-terpinene (1.8%) and borneol (1.3%), accounted for 95.6% of the oil.