Resonant enhancement of two-photon absorption in substituted fluorene molecules

The degenerate and nondegenerate two-photon absorption (2PA) spectra for a symmetric and an asymmetric fluorene derivative were experimentally measured in order to determine the effect of intermediate state resonance enhancement (ISRE) on the 2PA cross section delta. The ability to tune the individual photon energies in the nondegenerate 2PA (ND-2PA) process afforded a quantitative study of the ISRE without modifying the chemical structure of the investigated chromophores. Both molecules exhibited resonant enhancement of the nonlinearity with the asymmetric compound showing as much as a twentyfold increase in delta. Furthermore, the possibility of achieving over a one order of magnitude enhancement of the nonlinearity reveals the potential benefits of utilizing ND-2PA for certain applications. To model ISRE, we have used correlated quantum-chemical methods together with the perturbative sum-over-states (SOS) expression. We find strong qualitative and quantitative correlation between the experimental and theoretical results. Finally, using a simplified three-level model for the SOS expression, we provide intuitive insight into the process of ISRE for ND-2PA.     

The evolution of manufacturing cells: An action research study

This study seeks to explain how and why manufacturing cells evolve over time. The purpose is to prevent many of the cellular manufacturing failures reported in industry. We conclude that manufacturing cells go through, somewhat overlapping, evolutionary stages before they begin to perform at the optimal level. It is important to recognize these evolutionary stages because they must be properly managed in order to reap the benefits of cell implementation efforts. In the first stage, both human and technical problems exist; however human problems dominate – requiring conflict management skills to resolve. In the second stage, human problems improve, and technical problems persist, requiring formal problem-solving methods to resolve. Finally, in the third stage, both human and technical problems improve, and cells begin to perform at the optimal level.     

Evolving networks for social optima in the “weakest link game”

Previous models have applied evolving networks based on node-level “copy and rewire” rules to simple two player games (e.g. the Prisoner’s Dilemma). It was found that such models tended to evolve toward socially optimal behavior. Here we apply a similar technique to a more tricky co-ordination game (the weakest link game) requiring interactions from several players (nodes) that may play several strategies. We define a variant of the game with several equilibria—each offering increasing social benefit. We found that the evolving network functions to select and spread more optimal equilibria while resisting invasion by lower ones. Hence the network acts as a kind of “social ratchet” selecting for increasing social benefit. Such networks have applications in peer-to-peer computing and may have implications for understanding social systems.

NONCOOPERATIVE MANAGEMENT OF THE NORTHEAST ATLANTIC COD FISHERY: A FIRST MOVER ADVANTAGE

The point of departure for this analysis is Bjørndal and Lindroos [2012], who developed an empirical bioeconomic model to analyze cooperative and noncooperative management of Northeast Atlantic cod. In their analysis, only constant strategies were analyzed for noncooperative games. In this paper, nonconstant strategies are considered. Moreover, the fishery in question is characterized by cooperative management. What may happen in the real world is that one nation breaks the cooperative agreement by fishing in excess of its quota. Often, it takes time for the other agent to detect this and respond. In this paper, we allow this kind of delayed response into a two‐agent noncooperative game so that, if country 2 exceeds its quota, there will be a time lag before this is detected by country 1; moreover, there may also be a delay until country 1 is able to respond. Results show that the outcome critically depends on the length of these two lags as well as initial conditions.     

Sphere packings, I

We describe a program to prove the Kepler conjecture on sphere packings. We then carry out the first step of this program. Each packing determines a decomposition of space into Delaunay simplices, which are grouped together into finite configurations called Delaunay stars. A score, which is related to the density of packings, is assigned to each Delaunay star. We conjecture that the score of every Delaunay star is at most the score of the stars in the face-centered cubic and hexagonal close packings. This conjecture implies the Kepler conjecture. To complete the first step of the program, we show that every Delaunay star that satisfies a certain regularity condition satisfies the conjecture.     

Sphere Packings, II

An earlier paper describes a program to prove the Kepler conjecture on sphere packings. This paper carries out the second step of that program. A sphere packing leads to a decomposition of R ³ into polyhedra. The polyhedra are divided into two classes. The first class of polyhedra, called quasi-regular tetrahedra, have density at most that of a regular tetrahedron. The polyhedra in the remaining class have density at most that of a regular octahedron (about 0.7209). Received April 24, 1995, and in revised form April 11, 1996.     

Two-photon spectroscopy and analysis with a white-light continuum probe

We present a powerful experimental tool and analysis for characterization of two-photon absorption (2PA) spectra. We demonstrate this method with ZnS and then apply it to organic dyes in solution. We also compare the results with those from other methods such as two-photon fluorescence spectroscopy. This femtosecond pump-probe method uses a white-light continuum (WLC) as the probe to produce a nondegenerate 2PA spectrum. The extreme chirp of the WLC requires that transmittance data be collected over a range of temporal delays between pump and probe pulses. These data then need to be corrected for the effects of this chirp as well as for the temporal walk-off of the pulses in the sample that result from the frequency nondegenerate nature of the experiment. We present a simple analytic solution for the transmitted fluence through the sample, which is applicable for most practical cases.     

Meaning and Control: Social Aspects of Science and Technology

Journal of the Operational Research Society -