Differential capacitance of ionic liquids according to lattice-gas mean-field model with nearest-neighbor interactions

The Bragg-Williams free energy is used to incorporate nearest-neighbor interactions into the lattice gas model of a solvent-free ionic liquid near a planar electrode. We calculate the differential capacitance from solutions of the mean-field consistency relation, arriving at an explicit expression in the limit of a weakly charged electrode. The two additional material parameters that appear in the theory -- the degree of nonideality and the resistance to concentration changes of each ion type -- give rise to different regimes that we identify and discuss. As the nonideality parameter, which becomes more positive for stronger nearest-neighbor attraction between like-charged ions, increases and the electrode is weakly charged, the differential capacitance is predicted to transition through a divergence and subsequently adopt negative values just before the ionic liquid becomes structurally unstable. This is associated with the spontaneous charging of an electrode at vanishing potential. The physical origin of the divergence and the negative sign of the differential capacitance is a nonmonotonic relationship between surface potential and surface charge density, which reflects the formation of layered domains alternatingly enriched in counterions and coions near the electrode. The decay length of this layered domain pattern, which can be many times larger than the ion size, is reminiscent of the recently introduced concept of "underscreening".Comment: 24 pages, 7 figures, version of record published in The Journal of Chemical Physic

Somatic Symptoms, but Not Nonsomatic Symptoms, of Depression are Associated with Insulin Resistance: National Health and Nutrition Examination Survey (NHANES) 2005-2010

poster abstractWhile there is a well-established link between depression and type 2 diabetes, depressive symptoms have received little attention in this literature. To begin to address this gap, we examined relationships among the somatic and nonsomatic symptoms of depression and insulin resistance, which is involved in the development of type 2 diabetes. Participants were 4,834 adults (mean age = 44.3 years, 50% female, 19% African American, 20% Mexican American) who participated in the 2005-2010 waves of NHANES – a survey of a large representative sample of the U.S. population. Participants with the following conditions were excluded: diabetes, cardiovascular disease, liver disease, kidney disease, or pregnancy. Depressive symptoms were measured using the Patient Health Questionnaire (PHQ-9), and somatic and nonsomatic subscales were derived based on confirmatory factor analysis. Our index of insulin resistance was the homeostatic model assessment (HOMA) score, which we computed from fasting plasma glucose and insulin levels. Separate regression analyses (adjusted for age, sex, race-ethnicity, education, BMI, and NHANES sample design) demonstrated positive relationships between PHQ-9 total (B=0.04, SEB=0.01, p<0.0001), somatic (B=0.07, SEB=0.02, p=0.0004), and nonsomatic (B=0.06, SEB=0.02, p=0.0004) scores and HOMA score. When the subscales were entered simultaneously into a regression model, the somatic score (B=0.05, SEB=0.02, p=0.03), but not the nonsomatic score (B=0.03, SEB=0.02, p=0.06), remained associated with HOMA score. A significant interaction was found for race-ethnicity, and further analyses demonstrate that the somatic symptoms of depression are only significantly associated with HOMA among Caucasians (B=0.07, SEB=0.02, p=0.02). Our cross-sectional findings suggest that the relationship between depression and insulin resistance may be driven by the somatic symptoms of depression and that this relationship may only be present only occur in Caucasians. The findings suggest that Caucasian adults with the somatic symptoms of depression may be at an elevated risk of type 2 diabetes

Antisymmetric solitons and their interactions in strongly dispersion-managed fiber-optic systems

By means of the variational approximation (VA), a system of ordinary differential equations (ODEs) is derived to describe the propagation of antisymmetric solitons in a multi-channel (WDM) optical fiber link subject to strong dispersion management. Results are reported for a prototypical model including two channels. Using the VA technique, conditions for stable propagation of the antisymmetric dispersion-managed (ASDM) solitons in one channel are found, and complete and incomplete collisions between the solitons belonging to the different channels are investigated. In particular, it is shown that formation of a bound inter-channel state of two ASDM solitons is possible under certain conditions (but may be easily avoided). The VA predictions for the single- and two-channel systems are compared with direct simulations of the underlying partial differential equations. In most cases, the agreement is very good, but in some cases (very closely spaced channels) the collision may destroy the ASDM solitons. The timing-jitter suppression factor (JSF) for the ASDM soliton in one channel, and the crosstalk timing jitter induced by collision between the solitons belonging to the different channels are also estimated analytically. In particular, the JSF for the ASDM soliton may be much larger than for its fundamental-soliton counterpart in the same system.Comment: 15 pages, 10 figures, accepted for publication in Optics Communication