Association between COMT Val158Met genotype and EEG alpha peak frequency tested in two independent cohorts

Item does not contain fulltextThis study could not confirm the association between the Catechol-O-Methyltransferase Val158Met polymorphism (COMT) and electroencephalographic (EEG) alpha peak frequency (APF) in two independent cohorts of 187 (96 depressed and 91 healthy participants) and 413 healthy participants. If COMT and APF play a role in depression or antidepressant treatment response, they do not have a shared pathway. We emphasize the importance of publishing null-findings for obtaining more accurate overall estimates of genetic effects

Modeling the initial, fast Sea-Surface Height decay of Agulhas ring “Astrid"

The early Sea-Surface Height (SSH) decay of an Agulhas ring is studied using a circular symmetric, equivalent barotropic idealization of ring Astrid, which was measured during the first MARE-cruise. Observations indicate that the SSH of Agulhas rings most rapidly decays just after shedding. It is found that the observed initial fast decay of ring Astrid can be recovered by a numerical model and that a mixed baroclinic/barotropic instability accounts for most of the observed decay of SSH.In addition, a series of numerical experiments is presented in which the effects on the decay of ring strength, barotropic component, diameter, radial profile, ?, and cooling were investigated. In all cases discussed, rings are linearly unstable to an m=2 mode. The evolution of the first 10 days is well predicted by a linear stability analysis. Further growth of the m=2 mode leads in most cases to split-up of the ring. The SSH decay of the rings is associated with a conversion from available potential energy of the parent ring to kinetic energy of nearly barotropic higher modes. Most of the energy release is associated with the m=2 mode. Also, the parent ring features an energy conversion from its barotropic to its baroclinic components.A strong barotropic component associated with a corotating ring is essential for SSH decay to occur. Counterrotating rings may feature SSH increase by energy conversion from the baroclinic to the barotropic component. For corotating rings SSH decay becomes weaker when the instability develops less vigorous. The simulation of ring Astrid shows that tracer loss from the core scales well with the decay of SSH. In the thermocline the associated mixing of fluid occurs preferably at the extremes of the elongating ring. At the deepest levels mixing is associated with dispersion through Rossby-wave radiation

Observations of a young Agulhas ring, Astrid, during MARE in March 2000

The MARE project studies the effects of inter-ocean exchange between the Indian and Atlantic Ocean, via Agulhas rings, on the Atlantic meridional overturning circulation. The field programme of MARE concentrates on the study of the decay and modification of a single Agulhas ring named Astrid, formed in January 2000. The ring was clearly visible in the analysis of satellite altimetry data, and surface drifters confirmed the anti-cyclonic rotation. During a detailed survey of this 2-month-old ring in March 2000, it appeared that the water mass properties of this ring only differed from the surrounding water above the 12°C isotherm. The observed fine-structure near its boundary suggested that exchange of water with its surroundings already had started. Observations with a lowered acoustic Doppler current profiler showed that the ring had a significant barotropic component, additional to the baroclinic flow around its warm centre. Meteorological observations indicated that during the summer survey the ring was losing heat to the atmosphere. This heat loss maintained convective mixing in the surface mixed layer. Compared to other reported rings, Astrid had a very large kinetic energy, a property probably characteristic for very young Agulhas rings. In other aspects Astrid did not differ strongly from the other rings, although Astrid was slightly larger than their typical ‘average’ size