Dogan G.,Theiss Research |
Dogan G.,U.S. National Institute of Standards and Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2017
We propose an efficient algorithm to minimize an anisotropic surface energy generalizing the Geodesic Active Contour model for image segmentation. In this energy, the weight function may depend on the normal of the curve/surface. Our algorithm is Lagrangian, but nonparametric. We only use the node and connectivity information for computations. Our approach provides a flexible scheme, in the sense that it allows to easily incorporate the generalized gradients proposed recently, especially those based on the H1 scalar product on the surface. However, unlike these approaches, our scheme is applicable in any number of dimensions, such as surfaces in 3d or 4d, and allows weighted H1 scalar products, with weights may depending on the normal and the curvature. We derive the second shape derivative of the anisotropic surface energy, and use it as the basis for a new weighted H1 scalar product. In this way, we obtain a Newton-type method that not only gives smoother flows, but also converges in fewer iterations and much shorter time. © Springer International Publishing AG 2017.
Wheeler D.,Theiss Research |
Moffat T.P.,U.S. National Institute of Standards and Technology |
Josell D.,U.S. National Institute of Standards and Technology
Journal of the Electrochemical Society | Year: 2013
Extreme bottom-up superfilling of annular through-silicon-vias (TSV) during copper electrodeposition has been reported wherein metal deposits on the bottom surface of the TSV with negligible deposition on its sidewalls or the field around it. The growth mode derives from a suppressor species that generates critical behavior manifesting as a negative differential resistance that, when coupled with a resistive electrolyte, yields bottom-up filling of recessed surface features. This paper models the observed phenomenon, the predictions capturing the full dynamics of the bottom-up filling process. The model considers the impact of the potential drop in the resistive electrolyte between the reference electrode and workpiece and the gradients of metal ion and rate-suppressing additive that accompany TSV filling. The predictions provide insight into the temporal and spatial variations of concentrations and overpotential that drive the bottom-up metal deposition process. © 2013 The Electrochemical Society. All rights reserved.
Smit P.,Technical University of Delft |
Janssen T.,Theiss Research |
Holthuijsen L.,Technical University of Delft |
Smith J.,U.S. Army
Coastal Engineering | Year: 2014
Non-hydrostatic models such as Surface WAves till SHore (SWASH) resolve many of the relevant physics in coastal wave propagation such as dispersion, shoaling, refraction, dissipation and nonlinearity. However, for efficiency, they assume a single-valued surface and therefore do not resolve some aspects of breaking waves such as wave overturning, turbulence generation, and air entrainment. To study the ability of such models to represent nonlinear wave dynamics and statistics in a dissipative surf zone, we compare simulations with SWASH to flume observations of random, unidirectional waves, incident on a 1:30 planar beach. The experimental data includes a wide variation in the incident wave fields, so that model performance can be studied over a large range of wave conditions. Our results show that, without specific calibration, the model accurately predicts second-order bulk parameters such as wave height and period, the details of the spectral evolution, and higher-order statistics, such as skewness and asymmetry of the waves. Monte Carlo simulations show that the model can capture the principal features of the wave probability density function in the surf zone, and that the spectral distribution of dissipation in SWASH is proportional to the frequency squared, which is consistent with observations reported by earlier studies. These results show that relatively efficient non-hydrostatic models such as SWASH can be successfully used to parametrize surf zone wave processes. © 2013 Elsevier B.V.
Cramer B.S.,Theiss Research |
Miller K.G.,Rutgers University |
Barrett P.J.,Victoria University of Wellington |
Wright J.D.,Rutgers University
Journal of Geophysical Research: Oceans | Year: 2011
We reconstruct trends in ice volume and deep ocean temperature for the past 108 Myr, resolving variations on timescales of ∼2 Myr and longer. We use a sea level record as a proxy for ice volume, a benthic foraminiferal Mg/Ca bf record as a proxy for temperature, and a benthic foraminiferal δ18Obf record as a proxy for both. This allows us to construct dual estimates of temperature and ice volume variations for the interval 10-60Ma: extracting temperature from δ18Obf by using sea level as a proxy for ice volume to constrain the δ18Osw component, and extracting seawater δ18Osw (which reflects ice volume) from δ18Obf by using Mg/Cabf to constrain the temperature component. Each of these approaches requires numerous assumptions, but the range of plausible solutions are concordant on timescales >2 Myr and within an uncertainty of 2C temperature and 0.4‰ δ 18Osw. The agreement between the two approaches for the last 50 Myr provides empirical justification for the use of δ 18Obf, Mg/Cabf, and sea level records as robust climate proxies. Our reconstructions indicate differences between deep ocean cooling and continental ice growth in the late Cenozoic: cooling occurred gradually in the middle-late Eocene and late Miocene-Pliocene while ice growth occurred rapidly in the earliest Oligocene, middle Miocene, and Plio-Pleistocene. These differences are consistent with climate models that imply that temperatures, set by the long-term CO2 equilibrium, should change only gradually on timescales >2 Myr, but growth of continental ice sheets may be rapid in response to climate thresholds due to feedbacks that are not yet fully understood. Copyright 2011 by the American Geophysical Union.
Burko L.M.,Alabama A&M University |
Burko L.M.,Theiss Research |
Khanna G.,University of Massachusetts Dartmouth
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013
We consider the importance of the second-order dissipative self-force for gravitational wave dephasing for an extreme or intermediate mass ratio system moving along a quasicircular Schwarzschild orbit. For the first-order self-force we use the fully relativistic force in the Lorenz gauge for eternally circular geodesics. The second-order self-force is modeled by its 3.5 post-Newtonian counterpart. We evolve the system using the osculating orbits method, and obtain the gravitational waveforms, whose phase includes all the terms - within our approximation (and using the self-force along circular geodesics) - that are independent of the system's mass ratio. The partial dephasing due to the second-order dissipative self-force is substantially smaller than that of the first-order conservative self-force, although they are both at the same order in the mass ratio. © 2013 American Physical Society.
Borrelli C.,Rensselaer Polytechnic Institute |
Cramer B.S.,Theiss Research |
Katz M.E.,Rensselaer Polytechnic Institute
Paleoceanography | Year: 2014
We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning-38.5-Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene,-1-4-Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (-34-Ma) and the consequent development of a circumpolar proto-ACC. Key Points The opening of Southern Ocean gateways impacted global ocean circulation Late middle Eocene thermal differentiation between SCW and NCW NCW formation in the Labrador Sea starting around 38.5 Ma ©2014. American Geophysical Union. All Rights Reserved.
de Bakker A.T.M.,University Utrecht |
Herbers T.H.C.,Theiss Research |
Smit P.B.,Theiss Research |
Tissier M.F.S.,Technical University of Delft |
Ruessink B.G.,University Utrecht
Journal of Physical Oceanography | Year: 2015
A high-resolution dataset of three irregular wave conditions collected on a gently sloping laboratory beach is analyzed to study nonlinear energy transfers involving infragravity frequencies. This study uses bispectral analysis to identify the dominant, nonlinear interactions and estimate energy transfers to investigate energy flows within the spectra. Energy flows are identified by dividing transfers into four types of triad interactions, with triads including one, two, or three infragravity-frequency components, and triad interactions solely between short-wave frequencies. In the shoaling zone, the energy transfers are generally from the spectral peak to its higher harmonics and to infragravity frequencies. While receiving net energy, infragravity waves participate in interactions that spread energy of the short-wave peaks to adjacent frequencies, thereby creating a broader energy spectrum. In the short-wave surf zone, infragravity-infragravity interactions develop, and close to shore, they dominate the interactions. Nonlinear energy fluxes are compared to gradients in total energy flux and are observed to balance nearly completely. Overall, energy losses at both infragravity and short-wave frequencies can largely be explained by a cascade of nonlinear energy transfers to high frequencies (say, f > 1.5 Hz) where the energy is presumably dissipated. Infragravity-infragravity interactions seem to induce higher harmonics that allow for shape transformation of the infragravity wave to asymmetric. The largest decrease in infragravity wave height occurs close to the shore, where infragravity-infragravity interactions dominate and where the infragravity wave is asymmetric, suggesting wave breaking to be the dominant mechanism of infragravity wave dissipation. © 2015 American Meteorological Society.
Miller K.G.,Rutgers University |
Wright J.D.,Rutgers University |
Browning J.V.,Rutgers University |
Kulpecz A.,Rutgers University |
And 8 more authors.
Geology | Year: 2012
We obtained global sea-level (eustatic) estimates with a peak of ~22 m higher than present for the Pliocene interval 2.7-3.2 Ma from backstripping in Virginia (United States), New Zealand, and Enewetak Atoll (north Pacific Ocean), benthic foraminiferal 18O values, and Mg/Ca- δ18O estimates. Statistical analysis indicates that it is likely (68% confidence interval) that peak sea level was 22 ± 5 m higher than modern, and extremely likely (95%) that it was 22 ± 10 m higher than modern. Benthic foraminiferal δ18O values appear to require that the peak was <20-21 m. Our estimates imply loss of the equivalent of the Greenland and West Antarctic ice sheets, and some volume loss from the East Antarctic Ice Sheet, and address the longstanding controversy concerning the Pliocene stability of the East Antarctic Ice Sheet. © 2012 Geological Society of America.
Cramer B.S.,Theiss Research
Stratigraphy | Year: 2012
I reportmagnetic susceptibility point measurements on the lower Maastrichtian-lowermost Eocene section retrieved in a core taken near the GSSP for the Paleocene/Eocene boundary in the Dababiya Quarry (Upper Nile Valley, Egypt). This record of magnetic susceptibility supplements the visual core descriptions, with lower values corresponding to more calcareous intervals. Preliminary investigation suggests that cyclicity apparent in themagnetic susceptibility record is consistent with a response to variations in Earth's orbital eccentricity. This interpretation is consistent with biostratigraphy and would imply sedimentation rates varying in the range 6-11 m/Myr, with lower sedimentation rates associated with intervals of low susceptibility/high carbonate.
Agency: NSF | Branch: Continuing grant | Program: | Phase: | Award Amount: 45.90K | Year: 2012
This award supports theoretical research on topics related to gravitational waves. One of these is a study of the properties of extreme mass ratio binary inspirals where a stellar mass black hole orbits a supermassive black hole, emits gravitational waves, and eventually falls in. Such a system could be an important source for the Laser Interferometer Space Antenna (LISA) . Accurate calculation of the orbit of the stellar mass black hole and of the gravitational radiation produced require improved understanding of fundamental issues in Einsteins theory of general relativity such as the self-force on the small black hole due to the gravitational radiation it emits and how that changes the orbit. Another project is to develop a method to extract gravitational waveforms from large scale numerical simulations of (comparable mass) binary black hole systems.
Better understanding of gravitational wave sources and waveforms will maximize the discovery opportunities presented by ground-based gravitational wave detectors now operating and future space-based detectors. Undergraduate and graduate students will participate in this research. The PI plans to continue his program of public outreach and his involvement with nearby minority serving institutions.