Extreme idealism and equilibrium in the Hotelling-Downs model of political competition

In the classic Hotelling-Downs model of political competition there is (almost always) no pure strategy equilibrium with three or more potential strategic candidates where the distribution of voters’ preferred policies are single-peaked. I study the effect of introducing two idealist candidates who are non-strategic (i.e., fixed to their policy platform), to an unlimited number of potential strategic entrants. I present results that hold for a non-degenerate class of cases: (i) For any equilibrium, it must be that the left-most and right-most candidates (i.e., extremists) are idealists; (ii) Hotelling’s Law fails: in any equilibrium, candidates do not share their policy platforms, which instead are spread out across the policy space; (iii) Characterizations for symmetric and asymmetric single-peaked distributions of voters’ ideal policy preferences. Equilibria where many strategic candidates enter exist only if the distribution of voter preferences is asymmetric

An alternate proton acceptor for excited-state proton transfer in green fluorescent protein: Rewiring GFP

The neutral form of the chromophore in wild-type green fluorescent protein (wtGFP) undergoes excited-state proton transfer (ESPT) upon excitation, resulting in characteristic green (508 nm) fluorescence. This ESPT reaction involves a proton relay from the phenol hydroxyl of the chromophore to the ionized side chain of E222, and results in formation of the anionic chromophore in a protein environment optimized for the neutral species (the I* state). Reorientation or replacement of E222, as occurs in the S65T and E222Q GFP mutants, disables the ESPT reaction and results in loss of green emission following excitation of the neutral chromophore. Previously, it has been shown that the introduction of a second mutation (H148D) into S65T GFP allows the recovery of green emission, implying that ESPT is again possible. A similar recovery of green fluorescence is also observed for the E222Q/H148D mutant, suggesting that D148 is the proton acceptor for the ESPT reaction in both double mutants. The mechanism of fluorescence emission following excitation of the neutral chromophore in S65T/H148D and E222Q/H148D has been explored through the use of steady state and ultrafast time-resolved fluorescence and vibrational spectroscopy. The data are contrasted with those of the single mutant S65T GFP. Time-resolved fluorescence studies indicate very rapid (<1 ps) formation of I* in the double mutants, followed by vibrational cooling on the picosecond time scale. The time-resolved IR difference spectra are markedly different to those of wtGFP or its anionic mutants. In particular, no spectral signatures are apparent in the picosecond IR difference spectra that would correspond to alteration in the ionization state of D148, leading to the proposal that a low-barrier hydrogen bond (LBHB) is present between the phenol hydroxyl of the chromophore and the side chain of D148, with different potential energy surfaces for the ground and excited states. This model is consistent with recent high-resolution structural data in which the distance between the donor and acceptor oxygen atoms is =2.4 Å. Importantly, these studies indicate that the hydrogen-bond network in wtGFP can be replaced by a single residue, an observation which, when fully explored, will add to our understanding of the various requirements for proton-transfer reactions within proteins

Viewpoint consistency in Z and LOTOS: A case study

Specification by viewpoints is advocated as a suitable method of specifying complex systems. Each viewpoint describes the envisaged system from a particular perspective, using concepts and specification languages best suited for that perspective. Inherent in any viewpoint approach is the need to check or manage the consistency of viewpoints and to show that the different viewpoints do not impose contradictory requirements. In previous work we have described a range of techniques for consistency checking, refinement, and translation between viewpoint specifications, in particular for the languages LOTOS and Z. These two languages are advocated in a particular viewpoint model, viz. that of the Open Distributed Processing (ODP) reference model. In this paper we present a case study which demonstrates how all these techniques can be combined in order to show consistency between a viewpoint specified in LOTOS and one specified in Z. Keywords: Viewpoints; Consistency; Z; LOTOS; ODP

E-cigarettes : the extent and impact of complementary dual-use

The highly controversial e-cigarette industry has generated considerable policy debate and mixed regulatory responses worldwide. Surprisingly, an issue that has been largely ignored is the categorisation of e-cigarettes as substitutes or (dynamic) complements for conventional smoking. We conduct an online survey of US participants finding that 37% of e-cigarette users view them primarily as complementary. We use this result along-side publicly available data to calibrate a cost-benefit analysis, estimating that complementarity reduces the potential costsavings of e-cigarettes by as much as 57% (or $3.3-4.9bn p.a.) relative to case with zero complementarity

Relaxation Dynamics of Pseudomonas aeruginosa Re^I(C)O_3(α-diimine)(HisX)^+ (X=83, 107, 109, 124, 126)Cu-^(II) Azurins

Photoinduced relaxation processes of five structurally characterized Pseudomonas aeruginosa Re^I(CO)_3(α-diimine)(HisX) (X = 83, 107, 109, 124, 126)Cu^(II) azurins have been investigated by time-resolved (ps−ns) IR spectroscopy and emission spectroscopy. Crystal structures reveal the presence of Re-azurin dimers and trimers that in two cases (X = 107, 124) involve van der Waals interactions between interdigitated diimine aromatic rings. Time-dependent emission anisotropy measurements confirm that the proteins aggregate in mM solutions (D2O, KPi buffer, pD = 7.1). Excited-state DFT calculations show that extensive charge redistribution in the ReI(CO)_3 → diimine ^3MLCT state occurs: excitation of this ^3MLCT state triggers several relaxation processes in Re-azurins whose kinetics strongly depend on the location of the metallolabel on the protein surface. Relaxation is manifested by dynamic blue shifts of excited-state ν(CO) IR bands that occur with triexponential kinetics: intramolecular vibrational redistribution together with vibrational and solvent relaxation give rise to subps, 2, and 8−20 ps components, while the ~10^2 ps kinetics are attributed to displacement (reorientation) of the Re^I(CO)_3(phen)(im) unit relative to the peptide chain, which optimizes Coulombic interactions of the Re^I excited-state electron density with solvated peptide groups. Evidence also suggests that additional segmental movements of Re-bearing β-strands occur without perturbing the reaction field or interactions with the peptide. Our work demonstrates that time-resolved IR spectroscopy and emission anisotropy of Re^I carbonyl−diimine complexes are powerful probes of molecular dynamics at or around the surfaces of proteins and protein−protein interfacial regions

Multi-attribute decision by sampling : an account of the attraction, compromise and similarity effects

Consumers’ choices are typically influenced by choice context in ways that standard models cannot explain. We provide a concise explanation of the attraction, compromise and similarity effects. Value is assumed to be determined by simple dominance relations between choice options and sampled comparators, and selection of comparators is assumed to be systematically influenced by the choice options. In one experiment, participants viewed differing selections of market options prior to choice. The classic context effects appeared and disappeared as predicted. In the second experiment, individuals’ sampling distributions of market options were influenced by the choice set as predicted by the model