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We present 40 new 10Be exposure ages of moraines and other glacial deposits left behind by the southeastern sector of the Laurentide Ice Sheet (LIS) in southern New England and New York, summarize the regional moraine record, and interpret the dataset in the context of previously published deglaciation chronologies. The regional moraine record spans the Last Glacial Maximum (LGM), with the outermost ridge of the terminal complex dating to ~26–25 ka, the innermost ridge of the terminal complex dating to ~22 ka, and a series of smaller recessional limits within ~50 km of the terminal complex dating to ~21–20.5 ka. The chronology generally agrees with independent age constraints from radiocarbon and glacial varves. A few inconsistencies among ages from cosmogenic-nuclide measurements and those from other dating methods are explained by geologic scatter where several bedrock samples and boulders from the outer terminal moraine exhibit nuclide inheritance, while exposure ages on large moraines are likely affected by postdepositional disturbance. The exposure-age chronology places the southeastern sector of the LIS at or near its maximum extent from ~26 to 21 ka, which is broadly consistent with the LGM sea-level lowstand, local and regional temperature indicators, and local summer insolation. The net change in LIS extent represented by this chronology occurred more slowly (<5 to 25 m yr-1) than retreat through the rest of New England, consistent with a slow general rise in insolation and modeled summer temperature. We conclude that the major pulse of LIS deglaciation and accelerated recession, recorded by dated glacial deposits north of the moraines discussed here, did not begin until after atmospheric CO2 increased at ~18 ka, marking the onset of Termination 1. [ABSTRACT FROM AUTHOR]

We consider the spatially-dependent diffusion tensors that maximize the rate of convergence to equilibrium of solutions to the heat equation in inhomogeneous media. We formulate a variational problem for the optimal spectral gap, subject to an Lp constraint on the diffusion tensors, and solve a relaxed version of this variational problem. This provides an upper bound for the optimal spectral gap. The solution is characterized in terms of the extremals of Sobolev and Poincaré type inequalities. To illustrate this result, we give a presentation of the one-dimensional case. In this case, we can adapt the known closed solution of a related eigenvalue problem to write the solution to the relaxed variational problem, arriving at an expression for the upper bound on the optimal spectral gap. The sharpness of this upper bound is then investigated by comparison to numerical simulations. [ABSTRACT FROM AUTHOR]

The concept of bubbleless aeration with microporous hollow fiber membranes is tested in a system that does not require external energy input, other than pressurizing oxygen, and is designed to add oxygen to surface waters. Microporous hollow fiber membranes, potted at one end and connected to an oxygen supply, with the other end individually sealed, were installed vertically in a flume to simulate their performance in rivers and lakes. The gas-filled fibers tend to rise vertically due to buoyancy, while bending downstream due to the drag force exerted by the flowing water. When operated at differential pressures of up to 3 atm during the experiments, this cross-flow configuration resulted in high rates of gas transfer with no supplemental energy input. Gas-transfer coefficients were found to depend on cross-flow velocity and internal gas pressure for the tested fibers. Two possible applications for passive hollow fiber membrane aeration are considered, and contrasted with traditional methods of aeration.