Integrated Calendar

Equatorially trapped waves account for a large portion of the perturbations within the tropical atmosphere and ocean. In the atmosphere, these disturbances are coupled to convection and determine a significant amount of rainfall variability on synoptic to intraseasonal time scales. Numerical models used for both weather and climate forecasting universally still have great difficulty simulating these convectively coupled disturbances. We assess the quantitative precipitation forecasts (QPF) skill of NOAA's Global Forecast System (GFS) and the European Centre for Medium Range Weather Forecasting Integrated Forecast System (IFS) operational models used for short term forecasts out to 10 days. Forecast skill was assessed by comparison with virtually independent GPM and CMORPH satellite precipitation estimates. Skill was quantified using a variety of metrics including pattern correlations for various latitude bands, temporal correlation at individual grid points, and space-time spectra of forecast precipitation over the global tropics and extratropics. Results reveal that, in general, initial conditions are reasonably well estimated in both forecast systems, as indicated by relatively good scores for the 6-12 hour forecasts. Since precipitation estimates are not directly assimilated into these systems, this indicates that the initialization of dynamical and thermodynamical fields is able to produce a reasonable QPF field, at least for the larger scales. We present evidence that the specification of the mass circulation rather than the moisture field is the primary source of this initial skill. Model skill is substantially better overall in the extratropics, however, tropical QPF in both systems is not considered useful by typical metrics much beyond a few days. A portion of this lack of tropical skill in can be traced back to inadequate treatment of equatorial wave activity coupled to convection. It is also demonstrated that extratropical forecast skill is positively correlated to preceding tropical skill, strongly suggesting that improvements in the treatment of tropics will lead to improved extratropical forecasts on the weekly and longer timescale.

A holy grail of nano-technology is to create truly complex, multi-component structures by self-assembly. Most self-assembly has focused on the creation of "structural complexity". In my talk, I will discuss "Addressable Complexity": the creation of structures that contain hundreds or thousands of distinct building blocks that all have to find their place in a 3D structure. Experiments on “DNA bricks” have demonstrated the feasibility of making such structures. Simulation and theory yield surprising insights that suggest design principles for brick structures. Interestingly, the design principles are different for DNA origami.

In the history of many families, all that remains about the fate of an ancestor for whom all traces were lost are rumors, often in conflicting versions. One of the most gratifying pleasures of a genealogical quest is to unveil the true story. Two examples taken from the lecturer’s personal history will demonstrate this.

GABAA receptors mediate two forms of signaling in the brain: phasic and tonic. Phasic signaling (e.g., IPSCs) is mediated by synaptic GABAA receptors, while tonic signaling (e.g., tonic current or tonic conductance) is mediated by extrasynaptic GABAA receptors. Tonic current is expressed in a cell-type specific manner and is mediated by heterogeneous and plastic GABAA receptors. These receptors are activated by ambient GABA that originates from vesicular and non-vesicular sources and is regulated by different GABA transporter systems.
Tonic GABAA conductance is commonly referred as tonic inhibition. We found that ambient GABA can actually excite adult hippocampal interneurons. In these cells, the GABAA reversal potential is depolarizing, making baseline tonic GABAA conductance excitatory. Increasing the tonic conductance enhances shunting-mediated inhibition, which eventually overpowers the excitation. Because hippocampal interneurons are the key to setting the network rhythms this mechanism allows bidirectional control of network synchronization by tonic GABAA receptor-mediated signaling.
We also show that tonic GABAA conductance decreases the membrane time constant (τm) and improves the temporal fidelity of EPSP-spike coupling. Long-term potentiation (LTP) induced by different stimulation patterns is differently affected by tonic GABAA conductance.
Our findings thus point to an important role of extrasynaptic signaling mediated by GABAA receptors in brain computations.