Constitutive equations in Cosserat elasticity

Summary A new theory for the constitutive equations in Cosserat elasticity is proposed. It is based on the assumption that the rotation vector depending on the displacement vector should be coupled with a rotation vector independent of the displacement vector. This eliminates the indeterminancies in stress and couple-stress encountered earlier.     

Polyvinyl butyral as a dispersant for barium titanate in a non-aqueous suspension

Polyvinyl butyral (PVB) was used as a dispersant for BaTiO₃ in a toluene-methanol system and its efficiency was evaluated by measuring the zeta potential and by a rheological study of the suspension. Addition of only 1.6 vol % low-molecular-weight (50 000) PVB is effective in making a well-dispersed suspension. But a lower concentration (0.6 vol %) of high-molecular-weight (200 000) PVB is necessary to stabilize the suspension due to the longer chain length of the polymer, which enhances steric stabilization. Dispersion of BaTiO₃ by PVB is better in a reverse azeotropic composition of toluene-methanol (72.427.6) than in an azeotropic composition.     

A replenishment policy for perishable products with non-linear holding cost under stochastic supply lead time

The development and application of inventory models for deteriorating items is one of the main concerns of subject matter experts. The inventory models developed in this field have focused mainly on supply chains under the assumption of constant lead time. In this study, we develop an inventory model for a main class of deteriorating items, namely perishable products, under stochastic lead time assumption. The inventory system is modeled as a continuous review system (r, Q). Demand rate per unit time is assumed to be constant over an infinite planning horizon and the shortages could be backordered completely. For modeling the deterioration process, a non-linear holding cost is considered. Taking into account the stochastic lead time as well as a non-linear holding cost makes the mathematical model more complicated. We customize the proposed model for a uniform distribution function that could be tractable to solve optimally by means of an exact approach. We then solve an example taken from the literature to demonstrate the applicability and effectiveness of the proposed model. Finally, by doing several sensitivity analyses for the key parameters of the model, some managerial insights are proposed.     

Simultaneous coordination of capacity building and price decisions in a decentralized supply chain

In this paper, we investigate the simultaneous coordination of price and capacity building decisions in a dyadic supply chain. This problem is a combination of capacity reservation problem and pricing problem. While the coordination of supply chain with stochastic demand and fixed prices has received much attention in the literature, price-dependent and stochastic demand has been less considered. We study the latter case where a price-setting retailer faces a linear decreasing demand with respect to price. To capture the uncertainty of the demand, we add a stochastic variable to the demand function. In addition, we incorporate production rate and inventory cost on the supplier side. We propose Revenue Sharing Reservation Contract with Penalty (RSRP) as a coordination mechanism to align the price and capacity decisions. We then extend the model to include multiple retailers which are geographically dispersed. We next conduct a comprehensive numerical example with an extensive sensitivity analysis to understand the behavior and robustness of the supply chain under a RSRP, and finally, we draw some managerial implications.     

Synthesis of polypyrrole/indium tin oxide nanocomposites via miniemulsion polymerization

Polypyrrole/indium tin oxide nanocomposites were synthesized via in situ miniemulsion polymerization of pyrrole monomer in the presence of indium tin oxide nanoparticles. Different nanocomposites were synthesized by different loadings of nano indium tin oxide. The morphology and nanoparticles distribution of the nanocomposites were characterized by electron microscopy. The results of XRD and TEM analysis showed that indium tin oxide nanoparticles were well placed in the polymeric structure of latex. FTIR analysis was used for the characterization of synthesized polypyrrole and its nanocomposites. TGA analysis was performed to investigate the thermal behavior of pristine polypyrrole and its nanocomposites. Conductivities of nanocomposites were measured by 4-point probe method and compared to the neat polymer.     

Dimensional analysis on the evaporation and condensation of refrigerant R-134a in minichannel plate heat exchangers

Two-phase flow analysis for the evaporation and condensation of refrigerants within the minichannel plate heat exchangers is an area of ongoing research, as reported in the literatures reviewed in this article. The previous studies mostly correlated the two-phase heat transfer and pressure drop in these minichannel heat exchangers using theories and empirical correlations that had previously been established for two-phase flows in conventional macrochannels. However, the two-phase flow characteristics within micro/minichannels may be more sophisticated than conventional macrochannels, and the empirical correlations for one scale may not work for the other one. The objective of this study is to investigate the parameters that affect the two-phase heat transfer within the minichannel plate heat exchangers, and to utilize the dimensional analysis technique to develop appropriate correlations. For this purpose, thermo-hydrodynamic performance of three minichannel brazed-type plate heat exchangers was analyzed experimentally in this study. These heat exchangers were used as the evaporator and condenser of an automotive refrigeration system where the refrigerant R-134a flowed on one side and a 50% glycol–water mixture on the other side in a counter-flow configuration. The heat transfer coefficient for the single-phase flow of the glycol–water mixture was first obtained using a modified Wilson plot technique. The results from the single-phase flow analysis were then used in the two-phase flow analysis, and correlations for the refrigerant evaporation and condensation heat transfer were developed. Correlations for the single-phase and two-phase Fanning friction factors were also obtained based on a homogenous model. The results of this study showed that the two-phase theories and correlations that were established for conventional macrochannel heat exchangers may not hold for the minichannel heat exchangers used in this study.     

Nanostructured cigarette wrapper encapsulated PDMS-RGO sandwiched composite for high performance EMI shielding applications

Here, we report a unique hybrid sandwich-type composite structure consisting of waste cigarette wrapper (CW) inserted in polydimethylsiloxane (PDMS) and reduced graphene oxide (RGO) composite matrix that displays a high EMI shielding effectiveness (SE) of ~50.79 dB in the extended Ku-band. The function of the inserted CW is to facilitate the multiple reflections and heat dissipation as it contains an Al coating. The interior of CW in the composite as well as the three-dimensional conductive networks of RGO throughout the PDMS matrix facilitates the microwave absorption through conductive dissipation and heat dissipation. Thus, an absorption-multiple reflection-absorption pathway is followed due to the combination of three sandwiched layers, that is, PDMS-RGO, CW, and PDMS-RGO. The sandwich architecture of the hybrid PDMS nanocomposite containing both CW and RGO displays a superior EMI SE over the nanocomposite that only contains RGO as filler in PDMS matrix. Moreover, the fabricated composite displays a high thermal conductivity which helps to dissipate the radiated microwave energy via a Joule heating effect. Thus, the fabricated lightweight and flexible hybrid composite structure could be an efficient microwave absorber which offers an attractive and cost-effective alternative approach to metal based conventional EMI shielding materials.