Publications

We study a repeated game with asymmetric information about a dynamic state of nature. In the course of the game, the better informed player can communicate some or all of his information with the other. Our model covers costly and/or bounded communication. We characterize the set of equilibrium payoffs, and contrast these with the communication equilibrium payffs, which by definition entail no communication costs.

Optical transport capacities have grown significantly in the last decade to meet the increased demands on communications networks. This growth has been achieved both by increases in individual channel rates, which are based on time division multiplexing (TDM), and by increased channel counts, through the use of dense wavelength division multiplexing (DWDM). Yet increasing optical transport capacity alone is insufficient to scale the network; the underlying data needs to be delivered from numerous geographically diverse originating locations to similarly diverse terminating locations, requiring increasing switching capacity to facilitate this networking need. Since the growth in the individual TDM channel rates is driven by the capabilities of electronics, it is reasonable to expect that the switching capacity of electronics will tend to track this trend, although because of the challenges in high data rate interconnects it is unlikely to exceed it. This leaves the challenge of managing the increased bandwidth attained through the use of DWDM. Management of this bandwidth in the optical layer is an attractive proposition if eliminating unnecessary high-speed electronics in the path of an optical signal can reduce the complexity of the network and the associated equipment costs. These optical bandwidth management elements are classified according to the degree of switching, as either reconfigurable optical add/drop multiplexers (ROADM) or wavelength selective cross-connects (WSXC), analogous to the add/drop multiplexers and digital cross-connects of the TDM domain. We generalize these elements and describe whether the switching provides functions that are multicolored, colorless, or colored, and whether the channels are fixed data rate or rateless. We review the wavelength selective switch (WSS) components that perform the necessary switching function and present two successful technology platforms that can be used to construct them: planar lightwave circuits (PLC) and micro-electromechanical systems (MEMS). We also discuss future directions for WSS technologies and device functionality to more flexibly manage bandwidth in the optical layer. © 2006 Lucent Technologies Inc.

Electron dynamics in metallic clusters are examined using a time-dependent density functional theory that includes a “memory term,” i.e., attempts to describe temporal nonlocal correlations. Using the Iwamoto, Gross, and Kohn exchange-correlation XC kernel, we construct a translationally invariant memory action from which an XC potential is derived that is translationally covariant and exerts zero net force on the electrons. An efficient and stable numerical method to solve the resulting Kohn-Sham equations is presented. Using this framework, we study memory effects on electron dynamics in spherical jellium gold clusters. We find memory significantly broadens the surface plasmon absorption line, yet considerably less than measured in real gold clusters, attributed to the inadequacy of the jellium model. Memory effects on nonlinear spectroscopy are studied as well: a real-time pump-probe setup is used to study the temporal decay profile of the plasmon, finding a fast decay followed by slower tail; and in high harmonic generation, we show that memory narrows and redshifts emission lines.

The cellular cytoskeleton is a complex dynamical network that constantly remodels as cells divide and move. This reorganization process occurs not only at the cell membrane, but also in the cell interior (bulk). During locomotion, regulated actin assembly near the plasma membrane produces lamellipodia and filopodia. Therefore, most in vitro experiments explore phenomena taking place in the vicinity of a surface. To understand how the molecular machinery of a cell self-organizes in a more general way, we studied bulk polymerization of actin in the presence of actin-related protein 2/3 complex and a nucleation promoting factor as a model for actin assembly in the cell interior separate from membranes. Bulk polymerization of actin in the presence of the verprolin homology, cofilin homology, and acidic region, domain of Wiskott-Aldrich syndrome protein, and actin-related protein 2/3 complex results in spontaneous formation of diffuse aster-like structures. In the presence of fascin these asters transition into stars with bundles of actin filaments growing from the surface, similar to star-like structures recently observed in vivo. The transition from asters to stars depends on the ratio [fascin]/[G actin]. The polarity of the actin filaments during the transition is preserved, as in the transition from lamellipodia to filopodia. Capping protein inhibits star formation. Based on these experiments and kinetic Monte Carlo simulations, we propose a model for the spontaneous self-assembly of asters and their transition into stars. This mechanism may apply to the transition from lamellipodia to filopodia in vivo.

The job chains model of local labor market change is a demand-driven analytic device for estimating the effects of new job creation. This paper explores the effects of restricting supply, i.e., limiting job access, on the model’s primary outcomes: vacancy chain multipliers, welfare effects, and distributional impacts. Major sources of labor supply are the local unemployed, out of the labor force and in-migrants. Three simulations are reported relating to (1) restricting new jobs to current local residents (i.e., no in-migrants), (2) restricting new jobs to current residents in the first round of hiring only, and (3) restricting hiring to local unemployed/out of labor force on the first round alone. The results are compared to the basic model that assumes no supply-side restrictions. In terms of chain length, welfare effects, distributional impacts, and policy palatability, first-round restrictions on in-migrants would seem to be the most plausible option. However, as an economic development strategy, well-targeted demand-side initiatives would still seem to be preferable.

The second edition of Bentley Layton’s A Coptic Grammar with Chrestomathy and Glossary: Sahidic Dialect, so quickly replacing the first of 2000, can only be viewed with gratification, answering as it does the evident demand that it must imply. The main improvement and real expansion of the present edition is in its Index of Citations. (“Revised and Expanded With an Index of Citations”: the question of what constitutes “revision” — see Glenn E. Snyder’s review in RBL 3 (2005) — and the valency-grammar snag of whether “expanded with” can be seen as an alternative construction to “expanded by”, need hardly be addressed here. However, a list, technically easy to compile, of additions, omissions and replacements could have prevented misunderstanding and forestalled protest.) The Index of Citations is especially useful for Shenoute؛ in fact, it can serve as the basis of a “Shenoutean sub-grammar” (e.g. in isolating exclusively or predominantly Shenoutean usage — consider the Conjunctive, p. 283, or adnominal xe- in negative environment, §483). But it also brings home rather sharply a striking imbalance in documentation, as well as the programmatic limitations of the Grammar’s corpus database, already commented on in reviews of the first edition. One regrets that the author has not exploited the rare opportunity of a new edition coming out so soon after the first, to provide at the least some highlights for the grammatical usage of more Sahidic texts, from the Pistis Sophia to non-literary sources (including documents and such specialized textemes as medical prescriptions) and such “Late Sahidic” genres as martyrologies and other patristic sources, and cases like Drescher’s Legends, which are grammatically distinctive and probably illuminating for their glimpses into Coptic colloquial usage.