THE ECONOMICS OF MOBILE INTERNATIONAL ROAMING

International roaming is a hot topic in the telecommunications industry. Many countries have witnessed a downward trend in mobile domestic prices. On the contrary, international roaming prices remained reluctant to follow the domestic trend. In Europe, the service has been regulated with price cap since 2007, and regulation is maintained for years to come. The existing literature on the economics of international roaming has focused on theoretical modelling, which assumes a uniform retail price (i.e. common across visited networks). The main finding is that wholesale and retail prices rise with the number of visited networks. Additionally, vertical merger is found unprofitable; and home network steering does not cause downward pressure on wholesale prices. We found that the assumption of uniform retail pricing leads to results that are inconsistent with wholesale competition because visited networks appear in the demand as complements rather than substitutes. We present theoretical models that match the existing literature’s findings, and compare results to the case whereby the retail price is discriminatory (i.e. differs by visited networks). With discriminatory retail, substitutability of networks reduces prices, and the incentive for vertical merger exists. In a steering game, steering is found able to reduce wholesale prices; and networks alliances are formed in equilibrium. The empirical literature on international roaming is limited to few industry studies. We use an aggregated dataset on prices and quantities for networks visited by roamers from one major mobile provider whose subscribers travel a lot across the world, Etisalat. The study period witnessed a retail price shift from discriminatory to uniform. The main findings are: (1) competition, as measured by the number of visited networks, reduces wholesale price; (2) traffic steering is effective, especially towards preferred networks (alliance and cross-owned); (3) only alliance networks offer wholesale discounts; and (4) demand is more elastic than crude industry studies

Effect of halloysite aluminosilicate clay nanotube incorporation into bonding agents on shear bond strength to human dentin

Indiana University-Purdue University Indianapolis (IUPUI)In adhesive dentistry, obtaining a good bond is a fundamental goal. It has been suggested that filler addition to the adhesives would increase the bonding strength of the adhesive layer. Halloysite aluminosilicate nanotubes (HNTs) are biocompatible, hydrophilic, durable, and have high mechanical strength. These advantages make them good candidates to be used as reinforcing agents for improving the properties of dental adhesives. The objective of this study was to evaluate the effect of incorporating HNTs into a commercial two-step etch-and-rinse adhesive system or one-step self-etch adhesive system on dentin shear bond strength. HNTs were incorporated into the two commercial adhesive systems in 0 wt%, 5 wt%, 10 wt%, and 20 wt%. The commercial control adhesives and the experimental adhesives were used to bond occlusal dentin of 120 extracted human molar teeth and then tested for shear bond strength by a universal testing machine with a semi-circular edge at a crosshead speed of 1.0 mm/min. Debonded specimens were examined under light microscopy to evaluate the fracture pattern. Resin-dentin interface were evaluated under scanning electron microscopy (SEM) after bonding dentin slabs using commercial control adhesives and experimental adhesive that showed numerically highest shear bond strength from each adhesive system. Two-way ANOVA was used to evaluate the effects of adhesive system and nanofiller content on shear bond strength. Pair-wise comparisons between groups were made using Fisher's (LSD) (p < 0.05). For the self-etch adhesive system, only incorporation of 5 wt% showed a significant increase in shear bond strength to dentin compared with the commercial control group. For the etch-and-rinse adhesive system, there was no significant difference in shear bond strength between HNTs filled adhesives groups and the commercial control group. Resin-dentin interface SEM evaluation showed nanotubes infiltrated into dentinal tubules. In conclusion, incorporating the self-etch adhesive system with 5 wt% HNTs increased the bond strength to dentin. Incorporation of up to 10 wt% filler concentration into both the self-etch and the etch-and-rinse adhesive systems did not adversely affect the bond strength to dentin or the handling properties. HNTs can penetrate along with resin tags into dentinal tubules, which could expand the use of their unique properties