Inside Money, Procyclical Leverage, and Banking Catastrophes

We explore a model of the interaction between banks and outside investors in which the ability of banks to issue inside money (short-term liabilities believed to be convertible into currency at par) can generate a collapse in asset prices and widespread bank insolvency. The banks and investors share a common belief about the future value of certain long-term assets, but they have different objective functions; changes to this common belief result in portfolio adjustments and trade. Positive belief shocks induce banks to buy risky assets from investors, and the banks finance those purchases by issuing new short-term liabilities. Negative belief shocks induce banks to sell assets in order to reduce their chance of insolvency to a tolerably low level, and they supply more assets at lower prices, which can result in multiple market-clearing prices. A sufficiently severe negative shock causes the set of equilibrium prices to contract (in a manner given by a cusp catastrophe), causing prices to plummet discontinuously and banks to become insolvent. Successive positive and negative shocks of equal magnitude do not cancel; rather, a banking catastrophe can occur even if beliefs simply return to their initial state. Capital requirements can prevent crises by curtailing the expansion of balance sheets when beliefs become more optimistic, but they can also force larger price declines. Emergency asset price supports can be understood as attempts by a central bank to coordinate expectations on an equilibrium with solvency.Comment: 31 pages, 10 figure

Transport of ferrihydrite nanoparticles in saturated porous media: role of ionic strength and flow rate

The use of nanoscale ferrihydrite particles, which are known to effectively enhance microbial degradation of a wide range of contaminants, represents a promising technology for in situ remediation of contaminated aquifers. Thanks to their small size, ferrihydrite nanoparticles can be dispersed in water and directly injected into the subsurface to create reactive zones where contaminant biodegradation is promoted. Field applications would require a detailed knowledge of ferrihydrite transport mechanisms in the subsurface, but such studies are lacking in the literature. The present study is intended to fill this gap, focusing in particular on the influence of flow rate and ionic strength on particle mobility. Column tests were performed under constant or transient ionic strength, including injection of ferrihydrite colloidal dispersions, followed by flushing with particle-free electrolyte solutions. Particle mobility was greatly affected by the salt concentration, and particle retention was almost irreversible under typical salt content in groundwater. Experimental results indicate that, for usual ionic strength in European aquifers (2 to 5 mM), under natural flow condition ferrihydrite nanoparticles are likely to be transported for 5 to 30 m. For higher ionic strength, corresponding to contaminated aquifers, (e.g., 10 mM) the travel distance decreases to few meters. A simple relationship is proposed for the estimation of travel distance with changing flow rate and ionic strength. For future applications to aquifer remediation, ionic strength and injection rate can be used as tuning parameters to control ferrihydrite mobility in the subsurface and therefore the radius of influence during field injection

Inapproximability of the Standard Pebble Game and Hard to Pebble Graphs

Pebble games are single-player games on DAGs involving placing and moving pebbles on nodes of the graph according to a certain set of rules. The goal is to pebble a set of target nodes using a minimum number of pebbles. In this paper, we present a possibly simpler proof of the result in [CLNV15] and strengthen the result to show that it is PSPACE-hard to determine the minimum number of pebbles to an additive $n^{1/3-\epsilon}$ term for all $\epsilon > 0$, which improves upon the currently known additive constant hardness of approximation [CLNV15] in the standard pebble game. We also introduce a family of explicit, constant indegree graphs with $n$ nodes where there exists a graph in the family such that using constant $k$ pebbles requires $\Omega(n^k)$ moves to pebble in both the standard and black-white pebble games. This independently answers an open question summarized in [Nor15] of whether a family of DAGs exists that meets the upper bound of $O(n^k)$ moves using constant $k$ pebbles with a different construction than that presented in [AdRNV17].Comment: Preliminary version in WADS 201

Local phase space control and interplay of classical and quantum effects in dissociation of a driven Morse oscillator

This work explores the possibility of controlling the dissociation of a monochromatically driven one-dimensional Morse oscillator by recreating barriers, in the form of invariant tori with irrational winding ratios, at specific locations in the phase space. The control algorithm proposed by Huang {\it et al.} (Phys. Rev. A {\bf 74}, 053408 (2006)) is used to obtain an analytic expression for the control field. We show that the control term, approximated as an additional weaker field, is efficient in recreating the desired tori and suppresses the classical as well as the quantum dissociation. However, in the case when the field frequency is tuned close to a two-photon resonance the local barriers are not effective in suppressing the dissociation. We establish that in the on-resonant case quantum dissociation primarily occurs via resonance-assisted tunneling and controlling the quantum dynamics requires a local perturbation of the specific nonlinear resonance in the underlying phase space.Comment: 12 pages, 6 figures (reduced quality), submitted to Phys. Rev.

Isotropic and Anisotropic Regimes of the Field-Dependent Spin Dynamics in Sr2IrO4: Raman Scattering Studies

A major focus of experimental interest in Sr2IrO4 has been to clarify how the magnetic excitations of this strongly spin-orbit coupled system differ from the predictions of anisotropic 2D spin-1/2 Heisenberg model and to explore the extent to which strong spin-orbit coupling affects the magnetic properties of iridates. Here, we present a high-resolution inelastic light (Raman) scattering study of the low energy magnetic excitation spectrum of Sr2IrO4 and doped Eu-doped Sr2IrO4 as functions of both temperature and applied magnetic field. We show that the high-field (H>1.5 T) in-plane spin dynamics of Sr2IrO4 are isotropic and governed by the interplay between the applied field and the small in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya interaction. However, the spin dynamics of Sr2IrO4 at lower fields (H<1.5 T) exhibit important effects associated with interlayer coupling and in-plane anisotropy, including a spin-flop transition at Hc in Sr2IrO4 that occurs either discontinuously or via a continuous rotation of the spins, depending upon the in-plane orientation of the applied field. These results show that in-plane anisotropy and interlayer coupling effects play important roles in the low-field magnetic and dynamical properties of Sr2IrO4.Comment: 8 pages, 4 figures, submitte

Constitutional Cases 2011: An Overview

The last year was a high-profile one for the Court in constitutional matters: Two cases, PHS and the Securities Reference, are especially noteworthy, not just for their political significance, but for their likely impact on constitutional jurisprudence in years to come. Several other decisions concerning freedom of association, equality rights and Aboriginal rights also reflected important developments in their respective areas, and in one case underscored deep divisions on the Court. Notably, 2011 was a year of unusual unanimity on the Court in the constitutional area: The justices agreed in all but four constitutional cases. That said, where the justices split, a core group comprising the Chief Justice and Justices Binnie, Charron, Rothstein and Cromwell were most likely to sign on to the majority opinion. Continuing a trend in recent years, the more liberal Justices LeBel, Fish and Abella found the mselves writing separately relatively frequently, as did the especially independent-minded Justice Deschamps. For the second year in a row, Prime Minister Stephen Harper will have a chance to change the face of the Court given the retirement of Justice Deschamps. With the appointment of her successor, Justice Wagner, Mr. Harper has appointed five justices, making 2012 the first year of a “Harper Court”. With two approaching mandatory retirements, by the time of the next federal election Mr. Harper will have had an opportunity to appoint a clear majority of justices, who will shape the jurisprudence of the Court for years to come

Constitutional Cases 2011: An Overview

The last year was a high-profile one for the Court in constitutional matters: Two cases, PHS and the Securities Reference, are especially noteworthy, not just for their political significance, but for their likely impact on constitutional jurisprudence in years to come. Several other decisions concerning freedom of association, equality rights and Aboriginal rights also reflected important developments in their respective areas, and in one case underscored deep divisions on the Court. Notably, 2011 was a year of unusual unanimity on the Court in the constitutional area: The justices agreed in all but four constitutional cases. That said, where the justices split, a core group comprising the Chief Justice and Justices Binnie, Charron, Rothstein and Cromwell were most likely to sign on to the majority opinion. Continuing a trend in recent years, the more liberal Justices LeBel, Fish and Abella found the mselves writing separately relatively frequently, as did the especially independent-minded Justice Deschamps. For the second year in a row, Prime Minister Stephen Harper will have a chance to change the face of the Court given the retirement of Justice Deschamps. With the appointment of her successor, Justice Wagner, Mr. Harper has appointed five justices, making 2012 the first year of a “Harper Court”. With two approaching mandatory retirements, by the time of the next federal election Mr. Harper will have had an opportunity to appoint a clear majority of justices, who will shape the jurisprudence of the Court for years to come

Constitutional Cases 2011: An Overview

This paper provides an overview of the constitutional decisions of the Supreme Court of Canada released in the calendar year 2011. It was a high-profile one for the Court in constitutional matters: Two cases, PHS and the Securities Reference, are especially noteworthy, not just for their political significance, but their likely impact on constitutional jurisprudence in years to come. Several other decisions concerning freedom of association, equality rights and Aboriginal rights also reflected important developments in their respective areas, and in one case underscored deep divisions on the Court.Notably, 2011 was a year of unusual unanimity on the Court in the constitutional area: the justices agreed in all but four constitutional cases. That said, where the justices split, a core group comprising of the Chief Justice and Binnie, Charron, Rothstein and Cromwell JJ. were most likely to sign-on to the majority opinion. Continuing a trend in recent years, the more liberal LeBel, Fish and Abella JJ. found themselves writing separately relatively frequently, as did the especially independently-minded Deschamps J.For the second year in a row, Prime Minister Stephen Harper will have a chance to change the face of the Court given the retirement of Deschamps J. With the appointment of successor, Mr. Harper has appointed five justices, making 2012 the first year of a “Harper Court.” With two justices approaching mandatory retirements, by the time of the next federal election Mr. Harper will have had an opportunity to appoint a clear majority of justices, who will shape the jurisprudence of the Court for years to come