Sensitive determination of carbohydrates labelled with p-nitroaniline by capillary electrophoresis with photometric detection using a 406 nm light-emitting diode

p-Nitroaniline was explored as a derivatising reagent for UV absorbance detection of carbohydrates after separation by CE. This derivatising agent has three advantages: first, it has excellent water solubility; second, it has high molar absorptivity; and third, it is possible to obtain sensitive detection using a UV or blue light-emitting diode (LED) as the light source. The labelling reaction took less than 30 min to complete with high reaction yield. The separation process was modelled and optimised using an artificial neural network. Nine carbohydrates were separated by a CE system within 16 min using a 0.17 M boric acid buffer at pH 9.7. On-column LED detection at 406 nm allowed the detection of carbohydrates with good detection limits (<1.1 microM or 8.8 fmol) and reproducible quantification in the concentration range of 2.6-200 microM. This method was applied successfully to the determination of component carbohydrates in some food samples.     

Ultrasound‐assisted dispersive micro‐solid‐phase extraction based on N‐doped mesoporous carbon and high‐performance liquid chromatographic determination of 1‐hydroxypyrene in urine samples

In this research, a new ultrasound‐assisted dispersive micro‐solid‐phase extraction method based on N‐doped mesoporous carbon sorbent followed by high‐performance liquid chromatography equipped with diode array detector for trace measurement of 1‐hydroxypyrene as a metabolite of exposure to polycyclic aromatic hydrocarbons was optimized. Herein, the hard template method was used for the preparation of N‐doped mesoporous carbon sorbent. The prepared sorbent was characterized using the Brunauer–Emmett–Teller method, transmission electron microscopy, and elemental analysis. Parameters affecting the extraction of the target metabolite were investigated using the Box–Behnken design method. Considering optimum parameters, the plotted calibration curve for 1‐hydroxypyrene was linearly correlated with the concentration span of 0.1–50 μg/L for urine media. The accuracy of the optimized procedure was examined through the relative recovery tests on the fortified urine specimens. The relative recoveries fell between 95 and 101%. The method detection limit of the proposed procedure was also calculated to be 0.03 μg/L.     

Broad sub-continuum resonances and the case for finite-energy sum-rules

There is a need to go beyond the narrow resonance approximation for QCD sum-rule channels which are likely to exhibit sensitivity to broad resonance structures. We discuss how the first two Laplace sum rules are altered when one goes beyond the narrow resonance approximation to include possible subcontinuum resonances with nonzero widths. We show that the corresponding first two finite energy sum rules are insensitive to the widths of such resonances, provided their peaks are symmetric and entirely below the continuum threshold. We also discuss the reduced sensitivity of the first two finite energy sum rules to higher dimensional condensates, and show these sum rules to be insensitive to dimension condensates containing at least one pair. We extract the direct single-instanton contribution to the sum rule for the longitudinal component of the axial-vector correlation function from the known single-instanton contribution to the lowest Laplace sum rule for the pseudoscalar channel. Finally, we demonstrate how inclusion of this instanton contribution to the finite-energy sum rule leads to both a lighter quark mass and to more phenomenologically reasonable higher-mass-resonance contributions within the pseudoscalar channel. Received: 15 September 1997 / Revised version: 15 November 1997 / Published online: 26 February 1998     

Stress analysis of orthotropic planes weakened by cracks

The stress fields in an orthotropic infinite plane containing Volterra type climb and glide edge dislocations are derived. The dislocation solutions are utilized to formulate integral equations for dislocation density functions on the surfaces of smooth cracks. The integral equations are of Cauchy singular type and are solved for several different cases of crack configurations and arrangements. The results are used to evaluate modes I and II stress intensity factors for multiple smooth cracks.     

Dry Reforming of Methane by DC Spark Discharge with a Rotating Electrode

A novel type of plasma reactor having a rotating electrode is proposed for CO₂ reforming of methane without catalyst at room temperature and atmospheric pressure. Results indicated that employing rotating ground electrode leads to a stable discharge for any period of time. Effects of feed composition, feed flow rate, applied power and electrodes separation on the carbon dioxide and methane conversions as well as the products selectivity were investigated. Increasing CO₂/CH₄ molar ratio in the feed favors the reagents conversion and consequently promotes the formation of hydrogen and carbon monoxide. If the target product is hydrogen, it is proposed to operate the reactor at CO₂/CH₄ = 1 molar ratio and if the target product is carbon monoxide then CO₂/CH₄ = 3 molar ratio is the preferred option for feed composition. This reactor system has advantages of stable operation and high conversion ability. Also, the obtained syngas with flexible molar ratio of H₂ to CO is suitable for vast industrial applications.     

A memetic algorithm for minimizing the total weighted completion time on a single machine under linear deterioration

In this paper, we consider the problem of minimizing the total weighted completion time on a single machine. Jobs processing times are increasing linear function of start times. First, we present some new dominance properties for this NP-hard problem. And next, using these properties, we develop a memetic algorithm for the problem. The results of computational experiments show the good performance of the proposed algorithm.     

A branch and bound algorithm for hybrid flow shop scheduling problem with setup time and assembly operations

A hybrid flow shop scheduling problem (HFSP) with assembly operations is studied in this paper. In the considered problem, a number of products of the same kind are produced. Each product is assembled using a set of several parts. At first, the parts are produced in a hybrid flow shop and then they are assembled in an assembly stage to produce products. The considered objective is to minimize the completion time of all products (makespan). This problem has been proved strongly NP-hard, so in order to solve it, a hierarchical branch and bound algorithm is presented. Also, some lower and upper bounds are developed to increase the efficiency of the proposed algorithm. The numerical experiments are used to evaluate the performance of the proposed algorithm.     

Solving a new stochastic multi-mode p-hub covering location problem considering risk by a novel multi-objective algorithm

In this paper, we develop a novel stochastic multi-objective multi-mode transportation model for hub covering location problem under uncertainty. The transportation time between each pair of nodes is an uncertain parameter and also is influenced by a risk factor in the network. We extend the traditional comprehensive hub location problem by considering two new objective functions. So, our multi-objective model includes (i) minimization of total current investment costs and (ii) minimization of maximum transportation time between each origin–destination pair in the network. Besides, a novel multi-objective imperialist competitive algorithm (MOICA) is proposed to obtain the Pareto-optimal solutions of the problem. The performance of the proposed solution algorithm is compared with two well-known meta-heuristics, namely, non-dominated sorting genetic algorithm (NSGA-II) and Pareto archive evolution strategy (PAES). Computational results show that MOICA outperforms the other meta-heuristics.     

Conversion of ketones to trisubstituted olefins under neutral conditions

Phenylaziridine hydrazones react at 140°–160°C to provide sterically congested trisubstituted olefins in good yield.