3,945 research outputs found
High-frequency data observations from space shuttle main engine low pressure fuel turbopump discharge duct flex joint tripod failure investigation
Observations made by Marshall Space Flight Center (MSFC) engineers during their participation in the Space Shuttle Main Engine (SSME) low pressure fuel turbopump discharge duct flex joint tripod failure investigation are summarized. New signal processing techniques used by the Component Assessment Branch and the Induced Environments Branch during the failure investigation are described in detail. Moreover, nonlinear correlations between frequently encountered anomalous frequencies found in SSME dynamic data are discussed. A recommendation is made to continue low pressure fuel (LPF) duct testing through laboratory flow simulations and MSFC-managed technology test bed SSME testing
Variational Integrators for the Gravitational N-Body Problem
This paper describes a fourth-order integration algorithm for the
gravitational N-body problem based on discrete Lagrangian mechanics. When used
with shared timesteps, the algorithm is momentum conserving and symplectic. We
generalize the algorithm to handle individual time steps; this introduces
fifth-order errors in angular momentum conservation and symplecticity. We show
that using adaptive block power of two timesteps does not increase the error in
symplecticity. In contrast to other high-order, symplectic, individual
timestep, momentum-preserving algorithms, the algorithm takes only forward
timesteps. We compare a code integrating an N-body system using the algorithm
with a direct-summation force calculation to standard stellar cluster
simulation codes. We find that our algorithm has about 1.5 orders of magnitude
better symplecticity and momentum conservation errors than standard algorithms
for equivalent numbers of force evaluations and equivalent energy conservation
errors.Comment: 31 pages, 8 figures. v2: Revised individual-timestepping description,
expanded comparison with other methods, corrected error in predictor
equation. ApJ, in pres
Variational Integrators for Almost-Integrable Systems
We construct several variational integrators--integrators based on a discrete
variational principle--for systems with Lagrangians of the form L = L_A +
epsilon L_B, with epsilon << 1, where L_A describes an integrable system. These
integrators exploit that epsilon << 1 to increase their accuracy by
constructing discrete Lagrangians based on the assumption that the integrator
trajectory is close to that of the integrable system. Several of the
integrators we present are equivalent to well-known symplectic integrators for
the equivalent perturbed Hamiltonian systems, but their construction and error
analysis is significantly simpler in the variational framework. One novel
method we present, involving a weighted time-averaging of the perturbing terms,
removes all errors from the integration at O(epsilon). This last method is
implicit, and involves evaluating a potentially expensive time-integral, but
for some systems and some error tolerances it can significantly outperform
traditional simulation methods.Comment: 14 pages, 4 figures. Version 2: added informative example; as
accepted by Celestial Mechanics and Dynamical Astronom
Application of multispectral radar and LANDSAT imagery to geologic mapping in death valley
Side-Looking Airborne Radar (SLAR) images, acquired by JPL and Strategic Air Command Systems, and visible and near-infrared LANDSAT imagery were applied to studies of the Quaternary alluvial and evaporite deposits in Death Valley, California. Unprocessed radar imagery revealed considerable variation in microwave backscatter, generally correlated with surface roughness. For Death Valley, LANDSAT imagery is of limited value in discriminating the Quaternary units except for alluvial units distinguishable by presence or absence of desert varnish or evaporite units whose extremely rough surfaces are strongly shadowed. In contrast, radar returns are most strongly dependent on surface roughness, a property more strongly correlated with surficial geology than is surface chemistry
Comparison of Gravitational Wave Detector Network Sky Localization Approximations
Gravitational waves emitted during compact binary coalescences are a
promising source for gravitational-wave detector networks. The accuracy with
which the location of the source on the sky can be inferred from gravitational
wave data is a limiting factor for several potential scientific goals of
gravitational-wave astronomy, including multi-messenger observations. Various
methods have been used to estimate the ability of a proposed network to
localize sources. Here we compare two techniques for predicting the uncertainty
of sky localization -- timing triangulation and the Fisher information matrix
approximations -- with Bayesian inference on the full, coherent data set. We
find that timing triangulation alone tends to over-estimate the uncertainty in
sky localization by a median factor of for a set of signals from
non-spinning compact object binaries ranging up to a total mass of , and the over-estimation increases with the mass of the system. We
find that average predictions can be brought to better agreement by the
inclusion of phase consistency information in timing-triangulation techniques.
However, even after corrections, these techniques can yield significantly
different results to the full analysis on specific mock signals. Thus, while
the approximate techniques may be useful in providing rapid, large scale
estimates of network localization capability, the fully coherent Bayesian
analysis gives more robust results for individual signals, particularly in the
presence of detector noise.Comment: 11 pages, 7 Figure
Ocean warming-acidification synergism undermines dissolved organic matter assembly.
Understanding the influence of synergisms on natural processes is a critical step toward determining the full-extent of anthropogenic stressors. As carbon emissions continue unabated, two major stressors--warming and acidification--threaten marine systems on several scales. Here, we report that a moderate temperature increase (from 30°C to 32°C) is sufficient to slow--even hinder--the ability of dissolved organic matter, a major carbon pool, to self-assemble to form marine microgels, which contribute to the particulate organic matter pool. Moreover, acidification lowers the temperature threshold at which we observe our results. These findings carry implications for the marine carbon cycle, as self-assembled marine microgels generate an estimated global seawater budget of ~1016 g C. We used laser scattering spectroscopy to test the influence of temperature and pH on spontaneous marine gel assembly. The results of independent experiments revealed that at a particular point, both pH and temperature block microgel formation (32°C, pH 8.2), and disperse existing gels (35°C). We then tested the hypothesis that temperature and pH have a synergistic influence on marine gel dispersion. We found that the dispersion temperature decreases concurrently with pH: from 32°C at pH 8.2, to 28°C at pH 7.5. If our laboratory observations can be extrapolated to complex marine environments, our results suggest that a warming-acidification synergism can decrease carbon and nutrient fluxes, disturbing marine trophic and trace element cycles, at rates faster than projected
Family Conflict Observations and Outcomes among Adopted School-Age Children with Lesbian, Gay, and Heterosexual Parents
Children’s externalizing problems are associated with family conflict among children and their biological parents, yet these linkages have remained unexamined among adoptive or lesbian and gay parent families. Investigating family processes facilitative of adjustment among adoptees, who face unique developmental challenges, is warranted. This multimethod study of 96 (26 lesbian, 29 gay, 41 heterosexual parent) adoptive families examined observations of adoptive family conflict and associations with child adjustment and feelings about adoption (children’s Mage = 8 years). The sample was recruited from 5 private, domestic infant adoption agencies across the United States. Parents and children reported about children’s externalizing problems and feelings about adoption, respectively. Observations of family conflict interaction were rated from videotaped family discussions. Family interactions were associated with children’s behavioral and adoption-specific adjustment, yet analysis of variance and hierarchical linear modeling analyses revealed no differences by parental sexual orientation in family dynamics (i.e., negativity/conflict, positive affect, cohesiveness) or child outcomes. Parents generally reported children to have few externalizing behaviors. Children reported positive feelings, moderate preoccupation, and low negativity about their adoption. These findings extend the family systems literature about conflict and child development among diverse families with sexual minority parents and adopted children. Practitioners who work with adoptive and sexual minority parent families can encourage positive and cohesive family interactions in supporting children’s adjustment. (PsycINFO Database Record (c) 2019 APA, all rights reserved
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