The picosecond time-resolved Stokes shift of the laser dye, coumarin 480 (I) is studied in neutral (Triton X-100, TX), cationic (cetyltrimethylammonium bromide, CTAB), and anionic (sodium dodecyl sulfate, SDS) micelles. Above critical micellar concentration (cmc) for all three micelles I exhibits wavelength dependent fluorescence decays and a distinct growth at the long wavelengths. The time dependent Stokes shift studies indicate that the water molecules in the Stern layer of the micelles relax on the time scale 180−550 ps, which is slower than the subpicosecond relaxation dynamics observed in ordinary bulk water.

The picosecond time-resolved Stokes shift of the laser dye coumarin 480 (I) is studied in Aerosol OT-heptane reverse micelles at various concentrations of water. On addition of water to a n-heptane solution of I containing 0.09 M AOT, the emission spectrum of I exhibits a prominent shoulder at 480 nm which is ascribed to the dye molecules in the water pool of the reverse micelles. In n-heptane, the fluorescence decays of I at short and long wavelengths are identical, which rules out any time-resolved Stokes shift. On addition of water to the AOT/heptane system, the decay at long wavelengths exhibit a distinct growth on the nanosecond time scale. This and the time-dependent Stokes shift indicate that the water molecules in the water pool of the AOT reverse micelles undergo slow relaxation on the nanosecond time scale.

Intramolecular charge transfer (ICT) processes of the neutral fluorescence probe, nile red, I, confined in the water pool of aerosol-OT (AOT) reverse micelle in n-heptane, is studied using picosecond emission spectroscopy. Utilizing the solvatochromism of nile red, only those probe molecules inside the reverse micelle are selectively excited. It is observed that while in aqueous solutions the lifetime (τf) of nile red is 650 ps, inside the reverse micelles τf increases to 3.73 ns in reverse micelle and to 2.06 ns at the highest water content of the microemulsion (w o = 32). With increase in the water-to-surfactant ratio, w o, as the water pool swells in size, the lifetime and quantum yield of emission decrease and the rate of the ICT process of nile red increases. However, the magnitude of the change (at most 8 times) in the rate of the ICT process of nile red compared to that of ordinary water is much smaller than the several thousandfold decrease observed in the solvation dynamics of water in the water pool relative to bulk water. It is proposed that while the solvation dynamics in the water pool is governed by the dielectric relaxation time, dynamics of the ICT process is controlled by the static polarity of the medium.

Managers and researchers alike have long recognized the importance of corporate textual risk disclosures. Yet it is a nontrivial task to discover and quantify variables of interest from unstructured text. In this paper, we develop a variation of the latent Dirichlet allocation topic model and its learning algorithm for simultaneously discovering and quantifying risk types from textual risk disclosures. We conduct comprehensive evaluations in terms of both conventional statistical fit and substantive fit with respect to the quality of discovered information. Experimental results show that our proposed method outperforms all competing methods, and could find more meaningful topics (risk types). By taking advantage of our proposed method for measuring risk types from textual data, we study how risk disclosures in 10-K forms affect the risk perceptions of investors. Different from prior studies, our results provide support for all three competing arguments regarding whether and how risk disclosures affect the risk perceptions of investors, depending on the specific risk types disclosed. We find that around two-thirds of risk types lack informativeness and have no significant influence. Moreover, we find that the informative risk types do not necessarily increase the risk perceptions of investors—the disclosure of three types of systematic and liquidity risks will increase the risk perceptions of investors, whereas the other five types of unsystematic risks will decrease them. Data, as supplemental material, are available at http://dx.doi.org/10.1287/mnsc.2014.1930 . This paper was accepted by Alok Gupta, special issue on business analytics.

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