Phase behaviour and dynamics in primitive models of molecular ionic liquids

The phase behaviour and dynamics of molecular ionic liquids are studied using primitive models and extensive computer simulations. The models account for size disparity between cation and anion, charge location on the cation, and cation-shape anisotropy, which are all prominent features of important materials such as room-temperature ionic liquids. The vapour-liquid phase diagrams are determined using high-precision Monte Carlo simulations, setting the scene for in-depth studies of ion dynamics in the liquid state. Molecular dynamics simulations are used to explore the structure, single-particle translational and rotational autocorrelation functions, cation orientational autocorrelations, self diffusion, viscosity, and frequency-dependent conductivity. The results reveal some of the molecular-scale mechanisms for charge transport, involving molecular translation, rotation, and association.Comment: 15 pages, 7 figure

Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard sphere solvents

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios $x$ in the range $1/5 \leq x \leq 5$, and with volumes between one and twenty times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio $x$ should be more soluble than an oblate solute with aspect ratio $1/x$. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend is observed in the case of hydrophobic solvation. To help interpret the simulation results, comparison is made with a scaled-particle theory that requires prior knowledge of a solute-solvent interfacial tension and the pure-solvent equation of state, which parameters are obtained from simulation results for spherical solutes. The theory shows excellent agreement with simulation results over the whole range of solute elongations considered.Comment: 10 pages, 10 figure

Security and privacy in online social networking: Risk perceptions and precautionary behaviour

A quantitative behavioural online study examined a set of hazards that correspond with security- and privacy settings of the major global online social network (Facebook). These settings concern access to a user's account and access to the user's shared information (both security) as well as regulation of the user's information-sharing and user's regulation of others' information-sharing in relation to the user (both privacy). We measured 201 non-student UK users' perceptions of risk and other risk dimensions, and precautionary behaviour. First, perceptions of risk and dread were highest and precautionary behaviour was most common for hazards related to users' regulation of information-sharing. Other hazards were perceived as less risky and less precaution was taken against these, even though they can lead to breaches of users' security or privacy. Second, consistent with existing theory, significant predictors of perceived risk were attitude towards sharing information on Facebook, dread, voluntariness, catastrophic potential and Internet experience; and significant predictors of precautionary behaviour were perceived risk, control, voluntariness and Internet experience. Methodological implications emphasise the need for non-aggregated analysis and practical implications emphasise interventions to promote safe online social-network use

Influence of the 5' intron in the control of acetylcholinesterase gene expression during myogenesis.

During myogenesis, marked increases in both acetylcholinesterase (AChE) and its encoding mRNA are observed. The intron in the AChE gene between non-coding exon 1 [T.L. Rachinsky, S. Camp, Y. Li, T.J. Ekstrom, M. Newton, P. Taylor, Molecular cloning of mouse acetylcholinesterase: tissue distribution of alternatively spliced mRNA species, Neuron 5 (1990) 317-327] and start-site containing exon 2 [A. Mutero, S. Camp, P. Taylor, Promoter elements of the mouse acetylcholinesterase gene, J. Biol. Chem. 270 (4) (1995) 1866-1872] appears to be responsible for the enhanced expression of the enzyme upon myoblast to myotube differentiation. Deletion of a 255 bp sequence within the first intron of the AChE gene abolishes the increase in cell-associated activity observed with differentiation. To study the involvement of the intronic region in post-transcriptional processing of AChE message, we used real time RT-PCR to quantify spliced and unspliced message levels in myoblasts and myotubes. We observe a 200-fold increase of the fully spliced mRNA associated with myotube formation, while the increase in the unspliced mRNA retaining either intron 1 or intron 2 is only 5 to 15-fold. We have generated knockout mice without the conserved region of intron 1. The mice show a phenotype where skeletal muscle, hematopoietic and central nervous system AChE expression differ with the greatest effect existing in the disappearance of skeletal muscle expression [S. Camp, L Zhang, M. Marquez, B. de La Torre, J.M. Long, G. Bucht, P. Taylor, Acetylcholinesterase (AChE) gene modification in transgenic animals: functional consequences of selected exon and regulatory region deletion, VIII IMC Proceedings]

Frequency noise and intensity noise of next-generation gravitational-wave detectors with RF/DC readout schemes

The sensitivity of next-generation gravitational-wave detectors such as Advanced LIGO and LCGT should be limited mostly by quantum noise with an expected technical progress to reduce seismic noise and thermal noise. Those detectors will employ the optical configuration of resonant-sideband-extraction that can be realized with a signal-recycling mirror added to the Fabry-Perot Michelson interferometer. While this configuration can reduce quantum noise of the detector, it can possibly increase laser frequency noise and intensity noise. The analysis of laser noise in the interferometer with the conventional configuration has been done in several papers, and we shall extend the analysis to the resonant-sideband-extraction configuration with the radiation pressure effect included. We shall also refer to laser noise in the case we employ the so-called DC readout scheme.Comment: An error in Fig. 10 in the published version in PRD has been corrected in this version; an erratum has been submitted to PRD. After correction, this figure reflects a significant difference in the ways RF and DC readout schemes are susceptible to laser noise. In addition, the levels of mirror loss imbalances and input laser amplitude noise have also been updated to be more realistic for Advanced LIG