Carfentrazone-ethyl Pond Dissipation and Efficacy on Floating Plants

Carfentrazone-ethyl (CE) is a reduced risk herbicide that is currently being evaluated for the control of aquatic weeds. Greenhouse trials were conducted to determine efficacy of CE on water hyacinth ( Eichhornia crassipes (Mart.) Solms- Laub.), water lettuce ( Pistia stratiotes L.), salvinia ( Salvinia minima Baker) and landoltia (Landoltia punctata (G. Mey.) Les & D. J. Crawford ) . CE controlled water lettuce, water hyacinth and salvinia at rates less than the maximum proposed use rate of 224 g ha -1 . Water lettuce was the most susceptible to CE with an EC 90 of 26.9 and 33.0 g ha -1 in two separate trials. Water hyacinth EC 90 values were calculated to be 86.2 to 116.3 g ha -1 , and salvinia had a similar susceptibility to water hyacinth with an EC 90 of 79.1 g ha -1 . Landoltia was not adequately controlled at the rates evaluated. In addition, CE was applied to one-half of a 0.08 ha pond located in North Central, Florida to determine dissipation rates in water and hydrosoil when applied at an equivalent rate of 224 g ha -1 . The half-life of CE plus the primary metabolite, CE-chloropropionic acid, was calculated to be 83.0 h from the whole pond, and no residues were detected in water above the limit of quantification (5 μg L -1 ) 168 h after treatment. CE dissipated rapidly from the water column, did not occur in the sediment above the levels of quantification, and in greenhouse studies effectively controlled three species of aquatic weeds at relatively low rates.(PDF contains 6 pages.

SMA CO(2-1) Observations of CG30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow

We present interferometric observations in the 12CO (2-1) line and at 1.3 mm dust continuum of the low-mass protostellar binary system in the cometary globule CG30, using the Submillimeter Array. The dust continuum images resolve two compact sources (CG30N and CG30S), with a linear separation of ~8700 AU and total gas masses of ~1.4 and ~0.6 M_sun, respectively. With the CO images, we discover two high-velocity bipolar molecular outflows, driven by the two sources. The two outflows are nearly perpendicular to each other, showing a quadrupolar morphology. The northern bipolar outflow extends along the southeast (redshifted, with a velocity up to ~23 km/s) and northwest (blueshifted, velocity up to ~30 km/s) directions, while the southern pair has an orientation from southwest (blueshifted, velocity up to 13 km/s) to northeast (redshifted, velocity up to ~41 km/s). The outflow mass of the northern pair, driven by the higher mass source CG30N, is ~9 times larger than that of the southern pair. The discovery of the quadrupolar molecular outflow in the CG30 protobinary system, as well as the presence of other quadrupolar outflows associated with binary systems, demonstrate that the disks in (wide) binary systems are not necessarily co-aligned after fragmentation.Comment: 12 pages, 3 figures, to be published by ApJL in October 200

Predict-and-recompute conjugate gradient variants

The standard implementation of the conjugate gradient algorithm suffers from communication bottlenecks on parallel architectures, due primarily to the two global reductions required every iteration. In this paper, we introduce several predict-and-recompute type conjugate gradient variants, which decrease the runtime per iteration by overlapping global synchronizations, and in the case of our pipelined variants, matrix vector products. Through the use of a predict-and-recompute scheme, whereby recursively updated quantities are first used as a predictor for their true values and then recomputed exactly at a later point in the iteration, our variants are observed to have convergence properties nearly as good as the standard conjugate gradient problem implementation on every problem we tested. It is also verified experimentally that our variants do indeed reduce runtime per iteration in practice, and that they scale similarly to previously studied communication hiding variants. Finally, because our variants achieve good convergence without the use of any additional input parameters, they have the potential to be used in place of the standard conjugate gradient implementation in a range of applications.Comment: This material is based upon work supported by the NSF GRFP. Code for reproducing all figures and tables in the this paper can be found here: https://github.com/tchen01/new_cg_variant

A spectrum adaptive kernel polynomial method

The kernel polynomial method (KPM) is a powerful numerical method for approximating spectral densities. Typical implementations of the KPM require an a prior estimate for an interval containing the support of the target spectral density, and while such estimates can be obtained by classical techniques, this incurs addition computational costs. We propose an spectrum adaptive KPM based on the Lanczos algorithm without reorthogonalization which allows the selection of KPM parameters to be deferred to after the expensive computation is finished. Theoretical results from numerical analysis are given to justify the suitability of the Lanczos algorithm for our approach, even in finite precision arithmetic. While conceptually simple, the paradigm of decoupling computation from approximation has a number of practical and pedagogical benefits which we highlight with numerical examples

Length summation in noise

To investigate the effect of background noise on visual summation, we measured the contrast detection thresholds for targets with or without a white noise mask in luminance contrast. The targets were Gabor patterns placed at 3° eccentricity to either the left or right of the fixation and elongated along an arc of the same radius to ensure equidistance from fixation for every point along the long axis. The task was a spatial two-alternative forced-choice (2AFC) paradigm in which the observer had to indicate whether the target was on the left or the right of the fixation. The threshold was measured at 75% accuracy with a staircase procedure. The detection threshold decreased with target length with slope −1/2 on log-log coordinates for target lengths between 30′ and 300′ half-height full-width (HHFW), defining a range of ideal matched-filter summation extending up to about 200′ (or about 16× the center width of the Gabor targets). The summation curves for different noise contrasts were shifted copies of each other. For the threshold versus mask contrast (TvN) functions, the target threshold was constant for noise levels up to about −22 dB, then increased with noise contrast to a linear asymptote on log-log coordinates. Since the “elbow” of the target threshold versus noise function is an index of the level of the equivalent noise experienced by the visual system during target detection, our results suggest that the signal-to-noise ratio was invariant with target length. We further show that a linear-nonlinear-linear gain-control model can fully account for these results with far fewer parameters than a matched-filter model