Dual mechanism for an online retailer

While posted price and auction have typically been seen as alternatives to each other, we observe Web stores selling a product at a posted price and simultaneously running auctions for the identical product, a phenomenon that has not been studied fully. In this article, we study a dual mechanism, where an online retailer combines the two conventional mechanisms (posted price and auction) for multiple units of a product. We demonstrate that the dual mechanism can be used to achieve market segmentation when customers discount the expected utility of auctions. We characterize the customer’s decision rule and formulate a retailer’s profit function under the dual mechanism. Finally, we compare the performance of three selling mechanisms (posted price, auction, and dual) through computational experiments.     

Finding the optimal CSP inventory level for multi-echelon system in Air Force using random effects regression model

Determining the optimal inventory level of CSP (concurrent spare parts) is crucial at the time of acquisition of new aircrafts. Most of the existing optimal CSP models do not take into account the time varying characteristics of CSP even though their demand rates are sensitive to such variation. In this paper, we introduce the CSP inventory model using a two stage approach. At the first stage, we use a random effects model to predict the expected demand of CSP in a multi-echelon system consisting of depot and bases based on CSPs varying characteristics with time. At the second stage, we find the optimal inventory level of CSP by using the optimization algorithm with various constraints under limited budget. The study is expected to contribute to the Air Force establishing the optimal national defense procurement policy for CSP of aircrafts.     

Random effects Weibull regression model for occupational lifetime

High job turnover rate can cause many problems and each company needs proper strategies to prevent the brain-drain of its manpower. For effective human resource management, predicting the occupational life expectancy or the mean residual life of those who are to leave and join another company is important. In this paper, we propose a random effects Weibull regression model for forecasting the occupational lifetime of the employees who join another company, based on their characteristics. Advantage of using such a random effects model is the ability of accommodating not only the individual characteristics of each employee but also the uncertainty that cannot be explained by individual factors. We apply the proposed model to the occupational lifetime data obtained from the company affiliated to general trading in Korea. From our analyses, we can infer the characteristics of those who have a relatively longer occupational lifetime as follows: the managing director level, relatively old, those who entered the company earlier, high school graduates, those who were involved in technical service, and married female employees. Accordingly, effective human resources management policy is necessary to retain those who are good but want to leave and those who stay but need more improvement for the betterment of the company.     

Forecasting both time varying MTBF of fighter aircraft module and expected demand of minor parts

A fundamental aspect of inventory management of fighter aircraft is to forecast the demand of minor parts installed in the main module. Most of the existing inventory models do not take into account the time-varying characteristics of modules composed of minor parts even though the demand rate of minor parts is sensitive to the conditions of module. In this paper, we propose random-effects regression models to forecast the mean time between failure (MTBF) of modules and the expected demand for the minor parts in the module based on time-varying characteristics of modules. Subsequently, we show how they can be applied to find necessary seasonal demand of minor parts. Our study is expected to contribute to ROKAF (Republic of Korea Air Force) in terms of providing base information for inventory policy for minor parts.     

Hierarchical forecasting based on AR-GARCH model in a coherent structure

This paper compares the accuracy of the aggregate forecasting with the bottom-up forecasting based on AR-GARCH model for the return rate of simulated Dow Jones Industrial Average. Most of the existing stock price index studies did not consider the hierarchical structure and often missed the coherent relationships between individual components. In this experiment, we simulated 30 coherent components based on AR(2)-GARCH(1, 1) model. Then we evaluated the performance of both forecasting methods ignoring the coherent structure. The results of our experiment indicated that the accuracy of forecasting method varied depending on the correlation degree of 30 coherent components, however the data noise did not significantly influenced the performance of hierarchical forecasting method.     

Effects of developing agents and activator on the diffraction efficiencies in a reversal bleached transmission hologram derived from Slavich PFG-01

The effects of developing agents and activators in the reversal bleach upon the diffraction efficiencies of a Slavich PFG-01 plate to be used for recording transmission holograms were studied. The plates were developed using four different developers: MSC, AAC, PSC, and HSC. The four developers were derived from different developing agents of metol, l-ascorbic acid, phenidone, and hydroquinone, respectively. Sodium carbonate was added to the developer as an activator that accelerates the development by keeping the developer alkaline. A maximum diffraction efficiency of 89.0% was obtained when the AAC developer was used.     

Evaluation of Efficiency of Polymerization,Surface Roughness,Porosity and Adaptation of Flowable and Sculptable Bulk Fill Composite Resins

A new category of commercial bulk fill composite resins (CRs) enables the placement of 4-mm-thick layers as an alternative to the traditional time-consuming incremental technique. The purpose of the present study was to compare the efficiency of the polymerization, adaptation and porosity of two high-viscosity ‘sculptable’ bulk fill CRs (Filtek™ Bulk Fill (3M™ ESPE, St. Paul, MN, USA) and Tetric EvoCeram^® Bulk Fill (Ivoclar Vivadent AG, Schwan, Liechtenstein)) and two low-viscosity ‘flowable’ bulk fill CRs (SureFil^® SDR™ flow (Dentsply Sirona, Charlotte, NC, USA) and Tetric EvoFlow^® Bulk Fill (Ivoclar Vivadent AG, Schaan, Liechtenstein)). Cylindrical samples of the bulk fill CRs (4 mm height × 10 mm diameter) were analyzed by Fourier-transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Additionally, occlusal cavities were prepared in twelve extracted human molars and restored with the bulk fill CRs (n = 3 for each CR). The adaptation and porosity of the bulk fill CRs were evaluated by X-ray microcomputed tomography (µCT) with a 3D morphometric analysis, and the adaptation was also analyzed by scanning electron microscopy (SEM) on longitudinal vestibulo-oral sections of the restored teeth. The AFM analysis demonstrated that the surface roughness of the SureFil^® SDR™ flow was higher than that of the Tetric EvoFlow^® Bulk Fill and that the surface roughness of Filtek™ Bulk Fill was higher than that of Tetric EvoCeram^® Bulk Fill. µCT and SEM confirmed that the flowable bulk fill CRs had excellent adaptation to the cavity walls. The 3D morphometric analysis showed the highest and lowest degrees of porosity in Filtek™ Bulk Fill and Tetric EvoFlow^® Bulk Fill, respectively. In general, the flowable bulk fill CRs exhibited better adaptation, a higher efficiency of polymerization and lower porosity than the sculptable materials.     

A zigzag‐type one‐dimensional coordination polymer formed by (2,2‐di­methyl‐1,3‐propane­di­amine)­bis­(iso­nico­tin­ato)­platinum(II) and copper nitrate

The title compound, catena‐poly­[[[tri­aqua‐2κ³O‐(2,2‐dimethyl‐1,3‐propane­di­am­ine)‐1κ²N,N′‐μ‐isonicotinato‐1:2κ²N:O‐copper(II)­plati­num(II)]‐μ‐isonicotinato‐2:1′κ²O:N] dinitrate], {[CuPt(C₆H₄NO₂)₂(C₅H₁₄N₂)(H₂O)₃](NO₃)₂}_n, obtain­ed from equimolar (dmpda)Pt^II(isonic)₂ (where dmpda is 2,2‐di­methyl‐1,3‐propane­di­amine and isonic is isonicotinate) and copper(II) nitrate, has been found to be a one‐dimensional coordination polymer of the zigzag‐type.     

Properties of stable nonstoichiometric nanoceria produced by thermal plasma

Thermally stable blue nonstoichiometric nanoceria was produced by feeding nanoceria with an average size of 50 nm into a DC thermal plasma reactor. The effects of different plasma power levels and atmospheres were investigated. XRD results showed the ceria lattice parameter increased with plasma power. SEM and TEM results showed that the shape of nanoparticles changed after plasma treatment; the blue nonstoichiometric nanoceria had highly regular shapes such as triangular pyramids and polyhedral in contrast to the irregular shape of the raw nanoceria. Significant downshift was found in the Raman spectra of the plasma products, with a 7.9-cm^?1 shift compared with raw nanoceria, which was explained by the reduction of Ce⁴⁺. X-ray photoelectron spectroscopy results showed that the Ce³⁺ fraction increased from 14% in the raw nanoceria to 38–39% for the product CeO_2-x , indicating the high reduction state on the ceria surface. It was determined that this blue nonstoichiometric nanoceria was stable up to 400 °C in air, but the color changed to pale yellow after 4 h at 500 °C in air indicating oxidation to CeO₂. Additionally, this novel stable nano-CeO_2-x caused a red shift in the UV-visible absorption results; a 48-nm red shift occurred for the nonstoichiometric nanoceria produced at 15 kW compared with the raw nanoceria. The band gap was calculated to be 2.5 eV while it was 3.2 eV for the raw nanoceria, indicating that this novel stable blue nonstoichiometric nanoceria should be a promising material for optical application.     

Effect of thermal annealing sequence on the crystal phase of HfO2 and charge trap property of Al2O3/HfO2/SiO2 stacks

In this study, we investigated the effect of a post annealing sequence on the HfO₂ crystal phase and the memory window of charge trap devices with TiN-Al₂O₃-HfO₂-SiO₂-Si stacks. The charge trap dielectrics of HfO₂ were deposited by atomic layer deposition and were annealed in an oxygen environment with or without Al₂O₃ blocking oxides. X-ray diffraction analysis showed that, after thermal annealing, the predominant crystal phase of HfO₂ is divided into tetragonal and monoclinic phase depending on the presence or absence of Al₂O₃ blocking oxide. In addition, deconvolution of X-ray diffraction spectra showed that, with increasing annealing temperature, the fraction of the tetragonal phase in the HfO₂ film was enhanced with the Al₂O₃ blocking oxide, while it was reduced without the Al₂O₃ blocking oxide. Finally, measurements of program/erase and increase-step-pulse programming showed that the charge trap efficiency and the memory window of the charge trap devices increased with decreasing fraction of tetragonal HfO₂.