339 research outputs found

    Economic lot sizing with imperfect rework derived without derivatives

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    This paper presents an algebraic method for solving economic production quantity (EPQ) model with imperfect rework. Conventional method for deriving optimal lot size is by using differential calculus on the cost function with the need to prove optimality first. Recent articles proposed algebraic approach to the solution of classic economic order quantity (EOQ) and EPQ model without reference to the use of derivatives. This note extends them to an EPQ model taking into consideration an imperfect rework of defective items. We demonstrate that the optimal lot size and the expected production-inventory cost for such a realistic EPQ model can be derived without derivatives

    The joint influence of quality assurance and postponement on a hybrid multi-item manufacturing-delivery decision-making

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    The present research explores the collective influence of quality assurance and postponement on a hybrid multiproduct replenishing-delivery decision-making. Assume the required multiproduct has a standard (common) component, and our replenishing-delivery model has incorporated a two-phase postponement strategy. The first phase makes all standard components and hires an external supplier to partially provide the required parts to cut short the needed uptime. In contrast, the second phase fabricates the finished multiproduct in sequence. To ensure the desired merchandise quality, we apply a quality-assurance action to the in-house processes to screen and remove scrap items and rework the repairable defects in both stages. Upon completing each merchandise, these products are transported to the customer in n fixed-quantity shipment in fixed-time intervals. We employ math modeling and formulating approaches to gain the overall supply-chain operating expenses comprising subcontracting, fabricating, stock holding, transportation, and customer holding costs. By minimizing system operating expenses, this research determines the optimal replenishing-delivery policy. Lastly, we give a numerical example to demonstrate our study’s applicability and usefulness/capability for facilitating managerial decision-making

    Unparticles and Holographic Renormalization Group

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    We revisit the unparticle interactions and propagators from the AdS-CFT point of view, and we show how the contact terms and their renormalization group flow appear in the context of the holographic renormalization. We study both vector unparticles and unfermions, uncovering the relevant boundary conditions and renormalization group flows.Comment: 12 pages, version to appear in JHE

    Proton conduction in a phosphonate-based metal-organic framework mediated by intrinsic “free diffusion inside a sphere”

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    Understanding the molecular mechanism of proton conduction is crucial for the design of new materials with improved conductivity. Quasi-elastic neutron scattering (QENS) has been used to probe the mechanism of proton diffusion within a new phosphonate-based metal–organic framework (MOF) material, MFM-500(Ni). QENS suggests that the proton conductivity (4.5 × 10–4 S/cm at 98% relative humidity and 25 °C) of MFM-500(Ni) is mediated by intrinsic “free diffusion inside a sphere”, representing the first example of such a mechanism observed in MOFs

    Vitamin D deficiency and anemia: a cross-sectional study

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    Vitamin D has been suggested to have an effect on erythropoiesis. We sought to evaluate the prevalence of anemia in a population of individuals with vitamin D deficiency compared with those with normal levels in a population of a large integrated healthplan. A cross-sectional analysis in the period 1 January 2004 through 31 December 2006 of subjects with documented concurrent levels of 25-hydroxyvitamin D and hemoglobin were evaluated. Vitamin D deficiency was defined as <30 ng/mL and anemia was defined as a hemoglobin <11 g/dL. A total of 554 subjects were included in the analysis. Anemia was present in 49% of 25-hydroxyvitamin D-deficient subjects compared with 36% with normal 25-hydroxyvitamin D levels (p < 0.01). Odds ratio for anemia in subjects with 25-hydroxyvitamin D deficiency using logistic regressions and controlling for age, gender, and chronic kidney disease was 1.9 (95% CI 1.3–2.7). 25-hydroxyvitamin D-deficient subjects had a lower mean Hb (11.0 vs. 11.7; p = 0.12 ) and a higher prevalence of erythrocyte stimulating agent use (47% vs. 24%; p < 0.05). This study demonstrates an association of vitamin D deficiency and a greater risk of anemia, lower mean hemoglobin, and higher usage of erythrocyte-stimulating agents. Future randomized studies are warranted to examine whether vitamin D directly affects erythropoiesis
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