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Events on Tuesday, February 1st, 2011

Chaos & Complex Systems Seminar
"Spatial and Temporal Variability in Groundwater Chemistry: Is There Any Such Thing as a "Representative" Sample?"
Time: 12:00 pm
Place: 4274 Chamberlin Hall
Speaker: Jean Bahr, UW-Madison Dept of Geoscience
Abstract: The dissolved constituents found in groundwater have been of interest for over two centuries. In fact many of the early developments in analytical chemistry were motivated by requests from physicians who were interested in the composition of springs and spas that had presumed therapeutic benefits. More recently, public attention to groundwater chemistry has focused on constituents that are associated with health hazards such as arsenic and hexavalent chromium. In addition to its relevance to human health, water chemistry data provide hydrogeologists with clues to the complex subsurface structures and processes that control groundwater flow and water-rock interactions. A major challenge to interpreting these data is posed by the spatial and temporal variability of measured concentrations. This talk will discuss several case studies in which high resolution sampling and tracer experiments have been used to document the effects of complex flow fields and subsurface reactions on the chemical signatures we observe in groundwater samples.
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"How do Galaxies get their Gas?"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Dusan Keres, UC Berkeley
Abstract: Most galaxies are actively star forming at all epochs. However, observations of dense, galactic gas indicate that, at any epoch, there is not enough gas in galaxies to support evolution of star formation activity over time. This suggests that galactic gas is being replenished from the intergalactic medium.&lt;br&gt;<br>
I use fully cosmological hydrodynamic simulations to study the gas supply into galactic component from high redshift to present. At high redshift &amp;quot;smooth&amp;quot; infall of cold filamentary gas dominates the gas supply of all galaxies. This &amp;quot;cold mode accretion&amp;quot; is unlike the accretion in the standard model of galaxy formation in which cooling of the hot halo atmospheres is a source of gas supply to galaxies. Cold mode accretion is a major driver of very active star formation of high-z galaxies enabling such activity to proceed for a significant fraction of the Hubble time. Gas accretion rates at a given halo and galaxy mass decrease with time, causing the drop in star formation rates. At low redshift hot virialized gas can cool in some of the halos, but cold gaseous clouds that form from infalling filaments can dominate gas supply in galaxies such as Milky Way.&lt;br&gt;<br>
In this talk I will describe properties, physics and consequences of cold gas accretion as well as predictions for the observational probes of cold halo gas that can provide strong constraints on the models. I will also discuss remaining open questions and future directions in the studies of galactic gas accretion, including additional physical processes, new computational methods and observations with upcoming facilities.&amp;quot;&lt;br&gt;<br>
Host: Professor Heinz
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