We have recently proved that the serial coupling of RP and zwitterionic hydrophilic interaction LC with mass spectrometric detection is a versatile and reliable technique to simultaneously separate polar and apolar compounds in complex samples, for example, phenols in wine. In order to evaluate the system suitability for long‐term usage, the robustness of a method based on the serial coupling of RP and zwitterionic hydrophilic interaction LC was evaluated after one year of analyses comprising >1100 injections. The retention time and peak shape of phenol standards and phenols in a red wine were compared to the values previously published. Phenol retention times were shifted <30 s. However, the peak widths were increased, partially due to the deterioration of the stationary phases. Nevertheless, the method was still highly reliable for the analysis of phenols in wine. 相似文献
Considering the inherent connection between supplier selection and inventory management in supply chain networks, this article presents a multi-period inventory lot-sizing model for a single product in a serial supply chain, where raw materials are purchased from multiple suppliers at the first stage and external demand occurs at the last stage. The demand is known and may change from period to period. The stages of this production–distribution serial structure correspond to inventory locations. The first two stages stand for storage areas for raw materials and finished products in a manufacturing facility, and the remaining stages symbolize distribution centers or warehouses that take the product closer to customers. The problem is modeled as a time-expanded transshipment network, which is defined by the nodes and arcs that can be reached by feasible material flows. A mixed integer nonlinear programming model is developed to determine an optimal inventory policy that coordinates the transfer of materials between consecutive stages of the supply chain from period to period while properly placing purchasing orders to selected suppliers and satisfying customer demand on time. The proposed model minimizes the total variable cost, including purchasing, production, inventory, and transportation costs. The model can be linearized for certain types of cost structures. In addition, two continuous and concave approximations of the transportation cost function are provided to simplify the model and reduce its computational time. 相似文献
Abstract We prove that every serial ring R has the isolation property: every isolated point in any theory of modules over R is isolated by a minimal pair. Using this we calculate the Krull–Gabriel dimension of the module category over serial rings. For instance, we show that this dimension cannot be equal to 1. 相似文献
In this paper, a transform approach is used for polycyclic and serial codes over finite local rings in the case that the defining polynomials have no multiple roots. This allows us to study them in terms of linear algebra and invariant subspaces as well as understand the duality in terms of the transform domain. We also make a characterization of when two polycyclic ambient spaces are Hamming-isometric. 相似文献
In the present study, an easy and efficient method based on the serial coupling of analytical reversed‐phase and zwitterionic hydrophilic interaction liquid chromatography was developed for the simultaneous separation of polar and nonpolar phenols occurring in wine. The zwitterionic hydrophilic column was connected in series to the reversed‐phase one via a T‐piece, with which the ACN content in eluent of the second dimension was increased, in order to cope the solvent strength incompatibility between the two columns. The final mobile phase at low‐flow rate (≤0.5 mL/min), high‐ACN content (90%), and low‐salt concentration was directed to an ESI‐TOF‐MS , for high accurate mass detections. The developed method was applied for the identification of target phenols in several wines. Retention time and peak width intra‐ and interday repeatability studies proved the reliability of the method for the simultaneous analysis of all the polar and nonpolar analytes in wine. The serial reversed‐phase/zwitterionic hydrophilic interaction liquid chromatography coupling offered the possibility to enlarge the number of identified compounds and it represents a valid approach for nontarget analysis of complex samples by a single injection. 相似文献
We consider a heuristic for serial production systems with random yields and rigid demand: all usable units exiting a stage move forward. We calculate optimal lots and corresponding expected costs for binomial, interrupted-geometric, and all-or-nothing yields. Our method is that it makes it easy to analyze large systems. 相似文献
Natural convection mass transfer rates at both vertical and horizontal serially connected tubes were reported using the electrochemical technique involving the measurement of limiting currents for the deposition of copper on copper cylinders from acidified cupric sulphate solutions. Measurements were carried out with: (a) one tube active; (b) two tube surfaces active; (c) three tube surfaces active.
The electrolyte concentration and a number of serial connections of tubes were varied to provide a range of GrSc extending from 5.3×108 to 9.5×1011. The mass transfer rates at serially connected horizontal cylinders were in good agreement with mass transfer data in the literature. Correlation of results covered both laminar and turbulent conditions separately. The mass transfer rates at serially connected vertical cylinders were controlled by the boundary layer development at the multi-electrodes. The results for vertical electrodes, which are single, serially connected two and three electrodes, were separately correlated in the turbulent region.
The results illustrate the important effect of boundary layer development in determining current distribution in multi-electrode electrochemical cells. 相似文献