Concentration and mass dependence of transport coefficients and correlation functions in binary mixtures with high mass-asymmetry

Correlation functions and transport coefficients of self-diffusion and shear viscosity of a binary Lennard-Jones mixture with components differing only in their particle mass are studied up to high values of the mass ratio $\mu$, including the limiting case $\mu=\infty$, for different mole fractions $x$. Within a large range of $x$ and $\mu$ the product of the diffusion coefficient of the heavy species $D_{2}$ and the total shear viscosity of the mixture $\eta_{m}$ is found to remain constant, obeying a generalized Stokes-Einstein relation. At high liquid density, large mass ratios lead to a pronounced cage effect that is observable in the mean square displacement, the velocity autocorrelation function and the van Hove correlation function

Phase diagrams of classical spin fluids: the influence of an external magnetic field on the liquid-gas transition

The influence of an external magnetic field on the liquid-gas phase transition in Ising, XY, and Heisenberg spin fluid models is studied using a modified mean field theory and Gibbs ensemble Monte Carlo simulations. It is demonstrated that the theory is able to reproduce quantitatively all characteristic features of the field dependence of the critical temperature T_c(H) for all the three models. These features include a monotonic decrease of T_c with rising H in the case of the Ising fluid as well as a more complicated nonmonotonic behavior for the XY and Heisenberg models. The nonmonotonicity consists in a decrease of T_c with increasing H at weak external fields, an increase of T_c with rising H in the strong field regime, and the existence of a minimum in T_c(H) at intermediate values of H. Analytical expressions for T_c(H) in the large field limit are presented as well. The magnetic para-ferro phase transition is also considered in simulations and described within the mean field theory.Comment: 14 pages, 12 figures (to be submitted to Phys. Rev. E

Chemosensory Cues to Conspecific Emotional Stress Activate Amygdala in Humans

Alarm substances are airborne chemical signals, released by an individual into the environment, which communicate emotional stress between conspecifics. Here we tested whether humans, like other mammals, are able to detect emotional stress in others by chemosensory cues. Sweat samples collected from individuals undergoing an acute emotional stressor, with exercise as a control, were pooled and presented to a separate group of participants (blind to condition) during four experiments. In an fMRI experiment and its replication, we showed that scanned participants showed amygdala activation in response to samples obtained from donors undergoing an emotional, but not physical, stressor. An odor-discrimination experiment suggested the effect was primarily due to emotional, and not odor, differences between the two stimuli. A fourth experiment investigated behavioral effects, demonstrating that stress samples sharpened emotion-perception of ambiguous facial stimuli. Together, our findings suggest human chemosensory signaling of emotional stress, with neurobiological and behavioral effects

Up Close It Feels Dangerous: 'Anxiety' in the Face of Risk

Motivated by individuals' emotional response to risk at different time horizons, we model an 'anxious' agent - one who is more risk averse with respect to imminent risks than distant risks. Such preferences describe well-documented features of 1) individual behavior, 2) equilibrium prices, and 3) institutions. In particular, we derive implications for financial markets, such as overtrading and price anomalies around announcement dates, as well as a downward-sloping term structure of risk premia, which are found empirically. Since such preferences can lead to dynamic inconsistencies with respect to risk trade-offs, we show that costly delegation of investment decisions is a strategy used to cope with 'anxiety.