Price Discrimination between Retailers with and without Market Power

Some retail markets are more competitive than others. A manufacturer with market power in the wholesale market who sells his product to competing retailers in cities and monopolistic ones in each of various towns must set the wholesale price difference between towns and cities to be smaller than the transportation cost to prevent “grey market” arbitrage. If he uses linear pricing, the town retail price will be even higher than under single-retailer double marginalization. Two-part tariffs do not solve the problem as they would if there were a single retailer, because the wholesale unit price must be higher than marginal cost to prevent arbitrage to the cities. If transportation costs are low, price discrimination is difficult and two- part tariffs come to resemble inefficient linear monopoly pricing. High transportation costs allow greater efficiency in contracting, and this can outweigh the negative direct effect on welfare.price discrimination, double marginalization, retail network, transportation costs, two-part tariffs, vertical restraints

Measurement of microvascular cerebral blood volume changes over the cardiac cycle with ferumoxytol-enhanced T2* MRI

PURPOSE This feasibility study investigates the non-invasive measurement of microvascular cerebral blood volume (BV) changes over the cardiac cycle using cardiac-gated, ferumoxytol-enhanced MRI. METHODS Institutional review board approval was obtained and all subjects provided written informed consent. Cardiac gated MR scans were prospectively acquired on a 3.0T scanner in 22 healthy subjects using -weighted sequences with 2D-EPI and 3D spiral trajectories. Images were collected before and after the intravenous administration of 2 doses of ferumoxytol (1 mg FE/kg and 4 mg FE/kg). Cardiac cycle-induced (1/ ) changes (Δ ) and BV changes (ΔBV) throughout the cardiac cycle in gray matter (GM) and white matter (WM) were quantified and differences assessed using ANOVA followed by post hoc analysis. RESULTS Δ was found to increase in a dose-dependent fashion. A significantly larger increase was observed in GM compared to WM in both 2D and 3D acquisitions (P < 0.050). In addition, Δ increased significantly (P < 0.001) post versus pre-contrast injection in GM in both MRI acquisitions. Mean GM Δ derived from 2D-EPI images was 0.14 ± 0.06 s pre-contrast and 0.33 ± 0.13 s after 5 mg FE/kg. In WM, Δ was 0.19 ± 0.06 s pre-contrast, and 0.23 ± 0.06 s after 5 mg FE/kg. The fractional changes in BV throughout the cardiac cycle were 0.031 ± 0.019% in GM and 0.011 ± 0.008% in WM (P < 0.001) after 5 mg FE/kg. CONCLUSION Cardiac-gated, ferumoxytol-enhanced MRI enables characterization of microvascular BV changes throughout the cardiac cycle in GM and WM tissue of healthy subjects