Choice under Uncertainty with the Best and Worst in Mind: Neo-additive Capacities

The concept of a non-extreme-outcome-additive capacity (neo-additive capacity ) is introduced. Neo-additive capacities model optimistic and pessimistic attitudes towards uncertainty as observed in many experimental studies. Moreover, neo-additive capacities can be applied easily in economic problems, as we demonstrate by examples. This paper provides an axiomatisation of Choquet expected utility with neo-capacities in a framework of purely subjective uncertainty.

The a-MEU Model: A Comment

In [7] Ghirardato, Macheroni and Marinacci (GMM) propose a method for distinguishing between perceived ambiguity and the decision-maker's reaction to it. They study a general class of preferences which they refer to as invariant biseparable. This class includes CEU and MEU. They axiomatize a subclass of a-MEU preferences. If attention is restricted to finite state spaces, we show that any a-MEU preference relation, satisfies GMM's axioms if and only if a = 0 or 1, that is, the preferences must be either maxmin or maxmax. We show by example that these axioms may be satisfied when the state space is [0,1].Ambiguity, multiple priors, invariant biseparable, Clarke derivative, ambiguity-preference.

Sequential two-player games with ambiguity

Author's pre-printIf players' beliefs are strictly nonadditive, the Dempster–Shafer updating rule can be used to define beliefs off the equilibrium path. We define an equilibrium concept in sequential two-person games where players update their beliefs with the Dempster–Shafer updating rule. We show that in the limit as uncertainty tends to zero, our equilibrium approximates Bayesian Nash equilibrium. We argue that our equilibrium can be used to define a refinement of Bayesian Nash equilibrium by imposing context-dependent constraints on beliefs under uncertainty.ESRC senior research fellowship scheme, H5242750259

Information and ambiguity: herd and contrarian behaviour in financial markets

“The final publication is available at Springer via http://dx.doi.org/10.1007/s11238-012-9334-3”The paper studies the impact of informational ambiguity on behalf of informed traders on history-dependent price behaviour in a model of sequential trading in nancial markets. Following Chateauneuf, Eichberger and Grant (2006), we use neo-additive capacities to model ambiguity. Such ambiguity and attitudes to it can engender herd and contrarian behaviour, and also cause the market to break down. The latter, herd and contrarian behaviour, can be reduced by the existence of a bid-ask spread.Research in part funded by ESRC grant RES-000-22-0650

Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation

The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(II) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(II) complex. Pt(II) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(II) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-ditBu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)(tBu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02–0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COOiPr)2bpy)(3,5-di-tBu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(II) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(II) complexes in general

Effects of disorder on carrier transport in Cu2SnS3

In recent years, further improvements in the efficiency of Cu2ZnSn S,Se 4 photovoltaic devices have been hampered due to several materials issues, including cation disorder. Cu2SnS3 is a promising new absorber material that has attracted significant interest in recent years. However, similar to CZTS, Cu2SnS3 displays cation disorder. In this work, we develop synthetic techniques to control the disorder in Cu2SnS3 thin films. By manipulating the disorder in this material, we observe crystal structure changes and detect improvements in the majority carrier hole transport. However, when the minority carrier electron transport was investigated using optical pump terahertz probe spectroscopy, minimal differences were observed between the ordered and disordered Cu2SnS3. By combining these results with first principles and Monte Carlo theoretical calculations, we are able to conclude that even ostensibly ordered Cu2SnS3 displays minority carrier transport properties corresponding to the disordered structure. The presence of extended planar defects in all samples, observed in TEM imaging, suggests that disorder is present even when it is not detectable using traditional structural characterization methods. The results of this study highlight some of the challenges to the further improvement of Cu2SnS3 based photovoltaics, and have implications for other disordered multinary semiconductors such as CZT