Distribution planning for multi-echelon networks considering multiple sourcing and lateral transshipments

Nowadays, due to the increasing complexity of business environment, especially demand uncertainty, supply chain managers need to establish more-effective sourcing and distribution strategies to ensure high customer service and low stock costs. To overcome this challenge multi-echelon network structures and alternative distribution strategies such as lateral transshipments and multiple sourcing should be considered in inventory optimisation models. In this article, we propose a scenario-based modelling approach to solve a two-stage multi-echelon inventory optimisation problem with a non-stationary demand. The model is based on a distribution requirements planning (DRP) approach and minimises the expected total cost that is composed of the fixed allocation, inventory holding, procurement, transportation, and back-ordering costs. Alternative inventory optimisation models, including the lateral transshipment strategy and multiple sourcing, are thus built, and the corresponding stochastic programmes are solved using the sample average approximation method. Through a numerical investigation conducted with several generated instances and an empirical investigation based on the case of a major French retailer’s distribution network, we show the substantial benefit of lateral transshipments and multiple sourcing in reducing the expected total costs of the distribution network.     

Improving the Out-Coupling of a Metal-Metal Terahertz Frequency Quantum Cascade Laser Through Integration of a Hybrid Mode Section into the Waveguide

A hybrid mode section is integrated into the end of the metal-metal waveguide of a terahertz (THz) frequency quantum cascade laser (QCL) by removing sub-wavelength portions of the top metal layer. This allows a hybrid mode to penetrate into the air, which reduces the effective index of the mode and improves the out-coupling performance at the facet. The transmission of the hybrid section is further increased by ensuring its length fulfills the criterion for constructive interference. These simple modifications to a 2.5-THz metal-metal QCL waveguide result in a significant increase in the output emission power. In addition, simulations show that further improvements in out-coupling efficiency can be achieved for lower frequencies with effective refractive indices close to the geometric mean of the indices of the metal-metal waveguide and air.     

The effect of insulation layers on pavement strength during non-freeze–thaw season

This paper examines the effect of integrating insulation layers on pavement strength using falling weight deflectometer testing data conducted on an instrumented test road in Edmonton, Alberta, Canada. The insulated sections of this road consisted of a -metre-thick bottom ash layer and two polystyrene layers at thicknesses of 5 and 10 cm, while the adjacent conventional section functioned as the control section (CS). For the purpose of strength comparison, the effective modulus and structural number of insulated sections were compared to a conventional CS in a non-freeze–thaw season. The durations of pavement freezing, recovering and fully recovered (non-freeze–thaw) periods were established by monitoring the moisture variations in different pavement layers. The results indicated that using insulation layers generally reduces pavement strength, and this reduction is more pronounced in the insulated section with thicker polystyrene.     

Surface versus bulk activity of lysozyme deposited on hydrogel contact lens materials in vitro

Purpose

To determine and compare the levels of surface versus bulk active lysozyme deposited on several commercially available hydrogel contact lens materials.

A comparative study of dip coating and spray pyrolysis methods for synthesizing ITO nanolayers by using Ag colloidal sol

Indium tin oxide (ITO) films were deposited on glass substrates by dip-coating and thermal pyrolysis methods. Sn (IV) is often used in the spray method as a precursor salt, but in this research we have employed a new procedure that uses Sn (II) and In(NO₃)₃ for preparation of transparent conductive thin films. Then, colloidal Ag was deposited on the ITO layers in order to compare the two synthesis methods, and the structural and electrical properties of the resultant films were investigated by FESEM, XRD, and four-terminal resistometry. The obtained films are polycrystalline with a preferred orientation of (200). The XRD patterns of the films indicate that in both films, the Sn phase is crystallized separately from In₂O₃. The presence of a Sn peak and the overall low intensity of XRD peaks suggest relative crystallization of ITO structure. For this reason, Ag films were deposited by dip coating method using a colloidal sol. By analyzing the XRD patterns of Ag-ITO films after eliminating the Sn peak, the increased intensity of the peaks confirmed the relatively good crystallization of the ITO films. The results show that the films with a sheet resistance as low as 2 × 10^?2 Ω·cm, which is beneficial for solar cells, were achieved.     

Oil exploitation and the environmental Kuznets curve

This study refers to a panel estimation of an environmental Kuznets curve (EKC) for oil to determine the factors most affecting oil exploitation in 38 oil-producing countries during 1990–2000. Control variables such as oil reserves, oil price, population, political rights, and the Gini index were used to determine its contribution to the main EKC model. The empirical results fully support the existence of an EKC for oil exploitation. Furthermore, the result indicates that the proved oil reserves has a significant and positive role in oil production, but oil price and population do not significantly affect crude oil production. Also, increased freedoms and a better income distribution will reduce the rate of oil exploitation. Thus, policies aiming at enhancing democratic society and better income distribution would be more compatible with sustainability.     

Determination of Pb2+ ions by a modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and nanosilica

A novel carbon paste ion selective electrode for determination of trace amount of lead was prepared. Multi-walled carbon nanotubes (MWCNTs) and nanosilica were used for improvement of a lead carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The electrode composition of 20 wt% paraffin oil, 57% graphite powder, 15% ionophore (thiram), 5% MWCNTs, and 3% nanosilica showed the stable potential response to Pb²⁺ ions with the Nernstian slope of 29.8 (±0.2) mV decade^?1 over a wide linear concentration range of 10^?7–10^?2 mol L^?1. The electrode has fast response time, and long term stability (more than 2 months). The proposed electrode was used to determine the concentration of lead ions in waste water and black tea samples.     

An integrated multi-criteria Taguchi computer simulation-DEA approach for optimum maintenance policy and planning by incorporating learning effects

Modelling the maintenance activities could be complex and non-linear system which consists of different parameters. In this paper, a new approach for maintenance policy and planning problem is developed. First, maintenance activities are simulated by incorporating learning effects. Production and maintenance functions are estimated using historical data. Then, simulation is carried out for different scenarios which are combinations of periodic maintenance and different policies. Several outputs including machines and operators’ availability, reliability, efficiency and queue length are computed. Since the problem is multi-criteria, data envelopment analysis method is used to select the preferred policy. In order to show the applicability of the proposed approach, the data for a series production line is used and different scenarios with different policies are investigated. Since many scenarios are needed to be simulated, Taguchi orthogonal array design is used to reduce the number of scenarios. The proposed approach of this study would help managers to identify the preferred strategy considering and investigating various parameters and policies. This is the first study that introduces an integrated multi-criteria approach for optimum maintenance policy and planning.     

Freeze–thaw performance of base course treated with carboxylated styrene–butadiene emulsion–Portland cement

Freeze–thaw (FT) cycles and moisture susceptibility are important factors influencing the geotechnical characteristics of soil–aggregates. Given the lack of published information on the behaviour of base course materials stabilised with styrene butadiene emulsions (SBE) and cement–SBE-treated base (CSBETB) under environmental conditions, especially freezing and thawing, this study investigated the effects of these additives on the CSBETB performance. The primary goal was to evaluate the resistance of CSBETB to moisture damage by performing FT, Marshall conditioning and AASHTO T-283 tests and to evaluate the long-term stripping susceptibility of CSBETB while also predicting the liquid antistripping additives to assess the mixture’s durability and workability. Specimens were stabilised with Portland cement, SBE and a Portland cement–SBE mixture and cured for 7 days, and their short- and long-term performances were studied. Test evaluation results show that the additions of additives increase the resistance of the mixtures to moisture damage. Results of durability tests performed for determining the resistance of compacted specimens to repeated FT cycles indicate that the specimen with the 4% cement–8% SBE mixture significantly improves water absorption, volume changes and weight losses. This indicates the effectiveness of this additive as a road base stabiliser with excellent engineering properties.