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College Place, WA, United States

Haynal S.,College Place | Haynal H.,Walla Walla University
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2013

Recent research presents a technique to enumerate all valid assignments of 'twiddle factors' for power-of-two fast Fourier transform (FFT) flow graphs. Brute-force search employing state-of-the-art Boolean satisfiability (SAT) solvers can then be used to find FFT algorithms within this large solution space which have desirable characteristics. Surprisingly, this approach has discovered FFT algorithms requiring fewer operations than the split-radix algorithm even when all twiddle factors are nth roots of unity. This paper reviews and then extends this prior research to examine fast discrete convolution algorithms when implemented via FFT and inverse FFT (IFFT) algorithms. In particular, we find that the combination of FFT and IFFT algorithms in fast convolution permits greater freedom when selecting valid twiddle factor assignments. We exploit this freedom and use SAT solvers to find new fast convolution algorithms with the lowest operation counts known. © 2013 IEEE. Source

Parizek B.R.,College Place | Walker R.T.,Pennsylvania State University
Earth and Planetary Science Letters | Year: 2010

Ice-sheet grounding lines are sensitive to initial conditions and to small perturbations in boundary conditions, based on new model results coupling ocean and ice flow. To study ice-ocean dynamics near ice-stream grounding lines, we couple an ocean-plume model that simulates ice-shelf basal melting with a two-dimensional, isothermal model of ice-stream and ice-shelf flow. The notable results of the coupled model experiments are to reveal grounding-line migration sensitivities to i) specific aspects of modeling-derived and history-dependent initial conditions, ii) to the overall melt magnitude, and iii) to a positive feedback between focused melting and local slopes of basal ice that is eventually stabilized by buttressing for lengthening ice shelves. These interactions can lead to multiple steady states for ice flow over a bed that shallows in the along-flow direction and have an important bearing on the effects of bedrock bumps.When in the vicinity of bedrock highs, grounding lines tend to rapidly advance or retreat towards the basal asperity. A significant delay or cessation of (de)glaciation occurs once the grounding line reaches the leeward side of the bedrock crest. However, while bedrock bumps can offer stability in the grounding zone, minor changes in ocean conditions can easily offset their effect through basal melting feedbacks. © 2010 Elsevier B.V. Source

Dustin Becker C.,Maui Forest Bird Recovery Project | Mounce H.L.,Maui Forest Bird Recovery Project | Rassmussen T.A.,Maui Forest Bird Recovery Project | Rassmussen T.A.,College Place | And 2 more authors.
Endangered Species Research | Year: 2010

The Critically Endangered (IUCN) Maui parrotbill Pseudonestor xanthophrys, an endemic Hawaiian honeycreeper, is restricted to a single population of about 500 individuals. During 3 breeding seasons (2006 to 2008) we found and monitored 17 Maui parrotbill nests from 13 pairs. Eggs and incubating females were confirmed for 12 of the nests, but only 4 fledged successfully. Severe weather led to nest abandonment in 5 cases. Two nests were depredated, and 1 nest had an egg that failed to hatch. Three pairs renested after failures. We used logistic linear regression and ANOVA to evaluate 300 h of observations to assess the effects of parental investment behavior and weather on nest fate. Female time incubating, a significant factor explaining nest fate, did not differ by time of day, but averaged 12 min h-1 less for failed than for successful nests. Male provisioning rates to adult females and chick feeding rates by parents were also significantly related to nest success. Male vocalizations near the nest did not differ by nest fate. Establishment of a second population is a key step in the recovery of Maui parrotbills, and a small captive population has been established. Although limited, our data suggest that collection of Maui parrotbill eggs and/or nestlings up to 1 wk old from nests for captive rearing, especially in advance of severe winter storms, would have minimal effects on the population. © Inter-Research 2010. Source

Subramaniam K.,University of Florida | Gotesman M.,University of Florida | Smith C.E.,College Place | Steckler N.K.,University of Florida | And 3 more authors.
Diseases of Aquatic Organisms | Year: 2016

Megalocytiviruses, such as infectious spleen and kidney necrosis virus (ISKNV), induce lethal systemic diseases in both ornamental and food fish species. In this study, we investigated an epizootic affecting Nile tilapia Oreochromis niloticus cultured in the US Midwest. Diseased fish displayed lethargy, gill pallor, and distension of the coelomic cavity due to ascites. Histopathological examination revealed a severe systemic abundance of intravascular megalocytes that were especially prominent in the gills, kidney, spleen, liver, and intestinal submucosa. Transmission electron microscopic examination revealed abundant intracytoplasmic polygonal virions consistent with iridovirus infection. Comparison of the full-length major capsid protein nucleotide sequences from a recent outbreak with a remarkably similar case that occurred at the same facility many years earlier revealed that both epizootics were caused by ISKNV. A comparison of this case with previous reports suggests that ISKNV may represent a greater threat to tilapia aquaculture than previously realized. © Inter-Research 2016. Source

Walker R.T.,Pennsylvania State University | Christianson K.,Pennsylvania State University | Christianson K.,St. Olaf College | Parizek B.R.,College Place | And 2 more authors.
Earth and Planetary Science Letters | Year: 2012

The motion of Bindschadler Ice Stream, West Antarctica, is dominated by sliding over a nearly plastic bed, according to analysis of kinematic GPS data using a new viscoelastic flowline model. Inversions of time-averaged velocity data with viscous ice-flow models can be consistent with multiple sliding laws, but propagation of velocity perturbations in a viscoelastic model can distinguish between sliding laws with different exponents. We develop such a model and apply it to a time series of velocity for the tidally modulated flow of Bindschadler Ice Stream (formerly Ice Stream D). Observed velocity perturbations are found to be consistent with a flow-law exponent m≥ 8, which indicates basal motion with a relatively weak till bed; lower exponents consistent with motion dominated by deformation within the ice over a hard or frozen bed are found to be unlikely. This result suggests that Bindschadler Ice Stream would respond rapidly and significantly to any future loss of buttressing from the Ross Ice Shelf. © 2011 Elsevier B.V.. Source

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