ABSTRACT
We present a critical comparison of the dielectric properties of three models of water-TIP4P/2005, TIP4P/2005f, and TTM3F. Dipole spatial correlation is measured using the distance dependent Kirkwood function along with one-dimensional and two-dimensional dipole correlation functions. We find that the introduction of flexibility alone does not significantly affect dipole correlation and only affects É(ω) at high frequencies. By contrast the introduction of polarizability increases dipole correlation and yields a more accurate É(ω). Additionally, the introduction of polarizability creates temperature dependence in the dipole moment even at fixed density, yielding a more accurate value for dÉ/dT compared to non-polarizable models. To better understand the physical origin of the dielectric properties of water we make analogies to the physics of polar nanoregions in relaxor ferroelectric materials. We show that É(ω, T) and τD(T) for water have striking similarities with relaxor ferroelectrics, a class of materials characterized by large frequency dispersion in É(ω, T), Vogel-Fulcher-Tammann behaviour in τD(T), and the existence of polar nanoregions.
ABSTRACT
We have measured plasma and cerebrospinal fluid (CSF) concentrations of nociceptin, the endogenous agonist of the orphan opioid receptor-like receptor (ORL-1). We studied two groups of ten patients presenting for elective Caesarean section (Group E) or in established labour and requiring combined spinal epidural anaesthesia for pain relief (Group L). Nociceptin was identified in all CSF samples with mean +/- SD concentrations of 52.49 +/- 34.25 and 63.39 +/- 33.26 pg/ml in groups E and L, respectively. Nociceptin was identified in 16/20 plasma samples with mean +/- SD concentrations of 7.59 +/- 21.58 and 13 73 +/- 23.79 pg/ml in groups E and L, respectively. CSF concentrations were significantly higher than plasma concentrations and there were no differences between groups E and L. These data report the first measurements of CSF nociceptin in man and show no association with the acute pain of labour.
