Economics-Based Optimization of Unstable Flows

As an example for the optimization of unstable flows, we present an economics-based method for deciding the optimal rates at which vehicles are allowed to enter a highway. It exploits the naturally occuring fluctuations of traffic flow and is flexible enough to adapt in real time to the transient flow characteristics of road traffic. Simulations based on realistic parameter values show that this strategy is feasible for naturally occurring traffic, and that even far from optimality, injection policies can improve traffic flow. Moreover, the same method can be applied to the optimization of flows of gases and granular media.Comment: Revised version of ``Optimizing Traffic Flow'' (cond-mat/9809397). For related work see http://www.parc.xerox.com/dynamics/ and http://www.theo2.physik.uni-stuttgart.de/helbing.htm

Glucksman Fellowship Program Student Research Reports

Shourya Ghosh, under the supervision of Edward Altman, does a statistical comparison of credit ratings from Moody’s and Standard & Poor’s to see whether there are any consistent biases between the two rating agencies. Kenneth McDermid, under the direction of Jeffrey Wurgler, investigates the performance of hedge funds and confirms that institutions with fewer assets and more concentrated portfolios outperform the others and that the out-performance is the result of selection ability. Joe Mellet, under the supervision of David Yermack, examines the market’s reaction to 320 special dividend announcements made in October, November, and December of 2012 in response to the looming tax increases and finds significant Cumulative Abnormal Returns (CARs) in the days surrounding the dividend announcement.

From supported membranes to tethered vesicles: lipid bilayers destabilisation at the main transition

We report results concerning the destabilisation of supported phospholipid bilayers in a well-defined geometry. When heating up supported phospholipid membranes deposited on highly hydrophilic glass slides from room temperature (i.e. with lipids in the gel phase), unbinding was observed around the main gel to fluid transition temperature of the lipids. It lead to the formation of relatively monodisperse vesicles, of which most remained tethered to the supported bilayer. We interpret these observations in terms of a sharp decrease of the bending rigidity modulus $\kappa$ in the transition region, combined with a weak initial adhesion energy. On the basis of scaling arguments, we show that our experimental findings are consistent with this hypothesis.Comment: 11 pages, 3 figure

Glucksman Fellowship Program Student Research Reports

The Glucksman Institute for Research in Securities Markets awards fellowships each year to outstanding second year Stern MBA students to work on independent research projects under a faculty member's supervision. Four research projects completed by the Glucksman Fellows of 2011-2012 are included in this special issue of the Finance Department Working Paper Series. These papers focus on important topics in empirical financial economics. Samuel Welt, under the supervision of William Silber, analyzes the economic and political factors that determine the magnitude of increases in the debt ceiling voted by Congress. Karen Shortt, under the direction of Aswath Damodaran , investigates the relationship between corporate environmental performance and abnormal stock price movements of a firm. Oren Livne, under the supervision of Alexander Ljungqvist, provides an overview of the evolution of the private company secondary marketplace in the United States, and evaluates the ability of secondary market data to predict share price changes post IPO. Ismael Orenstein, under the supervision of Yakov Amihud, analyzes the impact of the Federal Reserve’s Quantitative Easing (QE) program on the relative pricing of treasury securities. These papers, reflecting the research effort of four outstanding Stern MBA students, are summarized in more detail in the Table of Contents on the next page

First- and second-order transitions of the escape rate in ferrimagnetic or antiferromagnetic particles

Quantum-classical escape-rate transition has been studied for two general forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles. It is found that the range of the first-order transition is greatly reduced as the system becomes ferrimagnetic and there is no first-order transition in almost compensated antiferromagnetic particles. These features can be tested experimentally in nanomagnets like molecular magnets.Comment: 11 pages, 3 figures, to appear in Europhys. Let

Low-Temperature Dephasing in Disordered Conductors: the Effect of ``1/f'' Fluctuations

Electronic quantum effects in disordered conductors are controlled by the dephasing rate of conduction electrons. This rate is expected to vanish with the temperature. We consider the very intriguing recently reported apparent saturation of this dephasing rate in several systems at very low temperatures. We show that the ``standard model'' of a conductor with static defects can {\em not} have such an effect. However, allowing some dynamics of the defects may produce it.Comment: 6page

Filling a silo with a mixture of grains: Friction-induced segregation

We study the filling process of a two-dimensional silo with inelastic particles by simulation of a granular media lattice gas (GMLG) model. We calculate the surface shape and flow profiles for a monodisperse system and we introduce a novel generalization of the GMLG model for a binary mixture of particles of different friction properties where, for the first time, we measure the segregation process on the surface. The results are in good agreement with a recent theory, and we explain the observed small deviations by the nonuniform velocity profile.Comment: 10 pages, 5 figures, to be appear in Europhys. Let

On the lowest energy excitations of one-dimensional strongly correlated electrons

It is proven that the lowest excitations $E_{low}(k)$ of one-dimensional half-integer spin generalized Heisenberg models and half-filled extended Hubbard models are $\pi$-periodic functions. For Hubbard models at fractional fillings $E_{low}{(k+ 2 k_f)} = E_{low}(k)$, where $2 k_f= \pi n$, and $n$ is the number of electrons per unit cell. Moreover, if one of the ground states of the system is magnetic in the thermodynamic limit, then $E_{low}(k) = 0$ for any $k$, so the spectrum is gapless at any wave vector. The last statement is true for any integer or half-integer value of the spin.Comment: 6 Pages, Revtex, final versio

Quantum gravity as a group field theory: a sketch

We give a very brief introduction to the group field theory approach to quantum gravity, a generalisation of matrix models for 2-dimensional quantum gravity to higher dimension, that has emerged recently from research in spin foam models.Comment: jpconf; 8 pages, 9 figures; to appear in the Proceedings of the Fourth Meeting on Constrained Dynamics and Quantum Gravity, Cala Gonone, Italy, September 12-16, 200