Complexity of Strong Implementability

We consider the question of implementability of a social choice function in a classical setting where the preferences of finitely many selfish individuals with private information have to be aggregated towards a social choice. This is one of the central questions in mechanism design. If the concept of weak implementation is considered, the Revelation Principle states that one can restrict attention to truthful implementations and direct revelation mechanisms, which implies that implementability of a social choice function is easy to check. For the concept of strong implementation, however, the Revelation Principle becomes invalid, and the complexity of deciding whether a given social choice function is strongly implementable has been open so far. In this paper, we show by using methods from polyhedral theory that strong implementability of a social choice function can be decided in polynomial space and that each of the payments needed for strong implementation can always be chosen to be of polynomial encoding length. Moreover, we show that strong implementability of a social choice function involving only a single selfish individual can be decided in polynomial time via linear programming

Credit rationing and pass-through in supply chains: theory and evidence from Bangladesh

Traders are often blamed for high prices, prompting government regulation. We study the effects of a government ban of a layer of financing intermediaries in edible oil supply chain in Bangladesh during 2011-12. Contrary to the predictions of a standard model of an oligopolistic supply chain, the ban caused downstream wholesale and retail prices to rise, and pass-through of the changes in imported crude oil price to fall. These results can be explained by an extension of the standard model to incorporate trade credit frictions, where intermediaries expand credit access of downstream traders.https://people.bu.edu/dilipm/publications/Edoilaeja.pdfFirst author draf

Credit Rationing and Pass-Through in Supply Chains: Theory and Evidence from Bangladesh

We extend standard models of price pass-through across multiple layers of intermediaries in a supply chain with imperfect competition to incorporate credit rationing. To test against a standard model without credit rationing, we study the effects of a policy reform in Bangladesh's edible oils supply chain during 2011-12 which banned a layer of financing intermediaries. The standard model predicts higher pass-through of international prices to wholesale prices after the reform, while the credit rationing model predicts the opposite if the resulting credit contraction is strong enough. Evidence from a difference-in-difference estimation rejects the standard model. Our estimates imply that the regulatory effort to reduce market power of financing intermediaries ended up raising consumer prices by restricting access to credit of downstream traders

Serpentine polymorphism: A quantitative insight from first-principles calculations

Single-walled chrysotile nanotubes [...] of increasing size (up to 5004 atoms per unit cell, corresponding to a radius of 205 Å) have been modelled at the Density Functional level of theory. For the first time, it is demonstrated that the (n, -n) and (n, n) series present a minimum energy structure at a specific radius (88.7 and 89.6 Å, respectively, referring to the neutral surface), corresponding to a rolling vector of (60, -60) and (105, 105), respectively. The minima are nearly overlapped and are lower in energy than the corresponding slab of lizardite (the flat-layered polymorph of chrysotile) by about 3.5 kJ mol-1 per formula unit. In both cases, the energy profile presents a shallow minimum, where radii in the range of 63 to 139 Å differ in energy by less than 0.5 kJ mol-1 per formula unit. The energy of larger nanotubes has a trend that slowly converges to the limit of the flat lizardite slab. Structural quantities such as bond distances and angles of nanotubes with increasing size asymptotically converge to the flat slab limit, with no discontinuities in the surrounding of the minimum energy structures. However, analysis of the elongation of a rectangular pseudo-unit cell along the nanotube circumference indicates that the main factor that leads lizardite to curl in tubes is the elastic strain caused by the mismatch between the lattice parameters of the two adjacent tetrahedral and octahedral sheets. It is also shown in this study that the curvature of the layers in one of the lately proposed models of antigorite, the "wavy-layered" polymorph of chrysotile, falls within the range of radii of minimum energy for the nanotubes. These findings provide quantitative insights into the peculiar polymorphism of these three phyllosilicates. They show also that chrysotile belongs to those families of inorganic nanotubes that present a minimum in their strain energy profile at a specific range of radii, which is lower in energy with respect to their flat equivalent

Taking the detour

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115976/1/jhm2424.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/115976/2/jhm2424-sup-0001-suppinfo.pd

Low-temperature behaviour of ammonium ion in buddingtonite [N(D/H) 4 AlSi 3 O 8 ] from neutron powder diffraction

The structural response of buddingtonite [N(D/H) 4 AlSi 3 O 8 ] on cooling has been studied by neutron diffraction. Data have been collected from 280 K down to 11 K, and the crystal structure refined using the Rietveld method. Rigid-body constraints were applied to the ammonium ion to explore the structural properties of ammonium in the M-site cavities at low-temperature. Low-temperature saturation is observed for almost all the lattice parameters. From the present in situ low-temperature neutron diffraction studies, there is no strong evidence of orientational order–disorder of the ammonium ions in buddingtonite.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46909/1/269_2004_Article_425.pd