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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Independent Confirmation of the Pioneer 10 Anomalous Acceleration

I perform an independent analysis of radio Doppler tracking data from the Pioneer 10 spacecraft for the time period 1987-1994. All of the tracking data were taken from public archive sources, and the analysis tools were developed independently by myself. I confirm that an apparent anomalous acceleration is acting on the Pioneer 10 spacecraft, which is not accounted for by present physical models of spacecraft navigation. My best fit value for the acceleration, including corrections for systematic biases and uncertainties, is (8.60 plus or minus 1.34) x 10(exp -8) centimeters per second, directed towards the Sun. This value compares favorably to previous results. I examine the robustness of my result to various perturbations of the analysis method, and find agreement to within plus or minus 5%. The anomalous acceleration is reasonably constant with time, with a characteristic variation time scale of greater than 70 yr. Such a variation timescale is still too short to rule out on-board thermal radiation effects, based on this particular Pioneer 10 data set.

Markwardt, Craig B.↗
NASA NTRS1995

Anomalous carbonate precipitates: is the Precambrian the key to the Permian?

Late Permian reefs of the Capitan complex, west Texas; the Magnesian Limestone, England; Chuenmuping reef, south China; and elsewhere contain anomalously large volumes of aragonite and calcite marine cements and sea-floor crusts, as well as abundant microbial precipitates. These components strongly influenced reef growth and may have been responsible for the construction of rigid, open reefal frames in which bryozoans and sponges became encrusted and structurally reinforced. In some cases, such as the upper biostrome of the Magnesian Limestone, precipitated microbialites and inorganic crusts were the primary constituents of the reef core. These microbial and inorganic reefs do not have modern marine counterparts; on the contrary, their textures and genesis are best understood through comparison with the older rock record, particularly that of the early Precambrian. Early Precambrian reefal facies are interpreted to have formed in a stratified ocean with anoxic deep waters enriched in carbonate alkalinity. Upwelling mixed deep and surface waters, resulting in massive seafloor precipitation of aragonite and calcite. During Mesoproterozoic and early Neoproterozoic time, the ocean became more fully oxidized, and seafloor carbonate precipitation was significantly reduced. However, during the late Neoproterozoic, sizeable volumes of deep ocean water once again became anoxic for protracted intervals; the distinctive "cap carbonates" found above Neoproterozoic tillites attest to renewed upwelling of anoxic bottom water enriched in carbonate alkalinity and 12C. Anomalous late Permian seafloor precipitates are interpreted as the product, at least in part, of similar processes. Massive carbonate precipitation was favored by: 1) reduced shelf space for carbonate precipitation, 2) increased flux of Ca to the oceans during increased continental erosion, 3) deep basinal anoxia that generated upwelling waters with elevated alkalinities, and 4) further evolution of ocean water in the restricted Delaware, Zechstein, and other basins. Temporal coincidence of these processes resulted in surface seawater that was greatly supersaturated by Phanerozoic standards and whose only precedents occurred in Precambrian oceans.

Non-NASA Center↗
NASA NTRS2008

Did LMC X-3 Undergo a 'Her X-1-like' Anomalous Low State?

The black hole X-ray binary LMC X-3 has been monitored by the Rossi X-ray Timing Explorer (RXTE) from its launch to the present by the All-Sky Monitor (ASM). This well-sampled light curve is supplemented by frequent pointed observations with the PCA and HEXTE instruments which provide improved sensitivity, time resolution and spectral information. The long-term X-ray luminosity of the system is strongly modulated on timescales of hundreds of days. The mean 2-10 kev X-ray flux varies by a factor of more than 100 during this long-term cycle. This variability has been attributed to the precession of a bright, tilted, and warped accretion disk---the mechanism also invoked to explain the 35-day super-orbital period in the X-ray binary pulsar system Her X-1. The ASM light curve displays a unique episode, starting in December 2003, during which LMC X-3 displayed a very low, nearly constant flux, for about 80 days. This is markedly different from the typical low-flux excursions in LMC X-3, which smoothly evolve toward and then away from a minimum flux on about a 10-day time scale. The character of the long-term variability, as measured by amplitude and characteristic time scale, is not the same after this long low state as it was before. Similar shifts in long-term period and amplitude are seen after the so-called "anomalous low states" in Her X-1, when the 35-day X-ray modulation ceases for an unpredictable length of time. These similar shifts in the long-term amplitude and timescale in the two systems suggests they share a similar mechanism which gives rise to the anomalous low states

Boyd, Patricia t.↗
NASA NTRS2009

The Anomalous Low State of LMC X-3

Archival RXTE ASM and PCA observations of the black hole binary LMC X-3 reveal a dramatic and extended low state lasting from December 8, 2003 until March 18, 2004, unprecedented both in its Low luminosity (Lx(2-10keV)=4.2x 1035 ergs s-1, approximately 4 times fainter than ever before seen from LMC X-3 in its low/hard state, and representing 0.15% of its X-ray luminosity during the high/soft state); and Long duration (approximately equal to 100 days, as compared with 5-20 days for 'normal' low/hard state excursions). During this anomalous low state no significant variability is observed on timescales of days-weeks, and the spectrum is well described by a simple power law with index 1.7 plus or minus 0.2. We examine the variability characteristics of LMC X-3 before and after this event using conventional and topological methods, and show that with the exception of the anomalous low state itself the long-term behavior of the source in topological phase space can be completely described in terms of a well-understood nonlinear dynamics system known as the Duffing oscillator, implying that the accretion disk in LMC X-3 is a driven, dissipative system with two solutions competing for control of its time evolution. This work shows that dynamical information and constraints revealed by topological analysis methods can provide a valuable addition to traditional studies of accretion disk behavior.

Smale, A. P.↗
NASA NTRS2010

Explanation of Anomalous Behavior Observed in Impedance Eduction Techniques Using Measured Data

Several enhancements that improve the accuracy and robustness of an impedance eduction technique that use an automatic optimizer are presented. These enhancements are then used to launch an intensive investigation into the cause of anomalous behavior that occurs for a small number of test conditions. This anomalous behavior is investigated for both a hardwall insert and a conventional liner. The primary conclusions of the study are that: (1) for the hard wall insert, the anomalies are due to narrow peaks in the objective function, (2) For the conventional liner, the anomalies are due to the presence of an extremely flat objective function, and (3) the anomalies appear to be triggered by inconsistencies between the duct propagation model and the measured data. At high frequencies, the duct propagation model may need to include the effects of higher-order duct modes, whereas at low frequencies, the effects of the mean boundary layer may have to be included.

Watson, Willie R.↗
NASA NTRS2014

Anomalous Transport of High Energy Cosmic Rays in Galactic Superbubbles

High-energy cosmic rays may exhibit anomalous transport as they traverse and are accelerated by a collection of supernovae explosions in a galactic superbubble. Signatures of this anomalous transport can show up in the particles' evolution and their spectra. In a continuous-time-random- walk (CTRW) model assuming standard diffusive shock acceleration theory (DSA) for each shock encounter, and where the superbubble (an OB stars association) is idealized as a heterogeneous region of particle sources and sinks, acceleration and transport in the superbubble can be shown to be sub-diffusive. While the sub-diffusive transport can be attributed to the stochastic nature of the acceleration time according to DSA theory, the spectral break appears to be an artifact of transport in a finite medium. These CTRW simulations point to a new and intriguing phenomenon associated with the statistical nature of collective acceleration of high energy cosmic rays in galactic superbubbles.

Barghouty, Nasser F.↗
NASA NTRS2015

Petrology of Anomalous Eucrite QUE 94484

Most mafic achondrites are broadly "eucritic", being composed of ferroan low-Ca clinopyroxene, high-Ca plagioclase, a silica phase, ilmenite and accessory phases. Their characteristics indicate that eucrite-like basalts formed on asteroids of similar composition under similar petrologic conditions (T, P, fO2). Some eucrite-like basalts have isotopic compositions and petrologic characteristics consistent with formation on different parent asteroids (e.g., Ibitira, NWA 011). Others show small isotopic differences but no distinguishing petrological characteristics (e.g., Caldera, Pasamonte). We have begun a study of anomalous eucrite-like achondrites in an effort to seek resolution to the issues: Did the eucrite parent asteroid fail to homogenize via a magma-ocean stage, thus explaining outliers like Pasamonte? How many parent asteroids are represented by these basalts? Here we present preliminary petrologic information on anomalous basaltic eucrite QUE 94484.

Mittlefehldt, D. W.↗
NASA NTRS2015

Anomalous Cases of Astronaut Helmet Detection

An astronaut's helmet is an invariant, rigid image element that is well suited for identification and tracking using current machine vision technology. Future space exploration will benefit from the development of astronaut detection software for search and rescue missions based on EVA helmet identification. However, helmets are solid white, except for metal brackets to attach accessories such as supplementary lights. We compared the performance of a widely used machine vision pipeline on a standard-issue NASA helmet with and without affixed experimental feature-rich patterns. Performance on the patterned helmet was far more robust. We found that four different feature-rich patterns are sufficient to identify a helmet and determine orientation as it is rotated about the yaw, pitch, and roll axes. During helmet rotation the field of view changes to frames containing parts of two or more feature-rich patterns. We took reference images in these locations to fill in detection gaps. These multiple feature-rich patterns references added substantial benefit to detection, however, they generated the majority of the anomalous cases. In these few instances, our algorithm keys in on one feature-rich pattern of the multiple feature-rich pattern reference and makes an incorrect prediction of the location of the other feature-rich patterns. We describe and make recommendations on ways to mitigate anomalous cases in which detection of one or more feature-rich patterns fails. While the number of cases is only a small percentage of the tested helmet orientations, they illustrate important design considerations for future spacesuits. In addition to our four successful feature-rich patterns, we present unsuccessful patterns and discuss the cause of their poor performance from a machine vision perspective. Future helmets designed with these considerations will enable automated astronaut detection and thereby enhance mission operations and extraterrestrial search and rescue.

Dolph, Chester↗
NASA NTRS2016

The Diversity of Anomalous HEDs: Isotopic Constraints on the Connection of EET 92023, GRA 98098, and Dhofar 700 With Vesta

The possibility for multiple parent bodies, instead of a common parent body of Vesta, for eucrites has been suggested based on the variable oxygen isotopic composition observed in some eucrites.. Recently, we added an extra dimension to the discussion based on the (epsilon)54Cr composition of the same eucrites with known (delta)17O to compare with the normal eucrites. The combined (delta)17O and (epsilon)54Cr isotope systematics for Pasamonte, PCA 91007, A-881394, and Ibitira indicate their likely origin from multiple different parent bodies than the normal eucrites. Often the qualifier anomalous is used to identify HEDs with (delta)17O values that deviate significantly (>3(sigma)) from the mean HED (delta)17O. However, variations in eucrites and diogenites also include unique geochemical characteristics such as bulk composition, trace element abundances, or volatile concentrations, in addition to (delta)17O. Here, we investigate three such geochemically anomalous HEDs: Elephant Moraine (EET) 92023, Graves Nunataks (GRA) 98098, and Dhofar 700. In addition, to verify the homogeneity of (epsilon)54Cr observed for normal HEDs thus far, a set of seven eucrites and diogenites considered normal samples were also investigated.

Sanborn, M. E.↗
NASA NTRS2017

Petrology of Anomalous Mafic Achondrite Polymict Breccia Pasamonte

The most common asteroidal igneous meteorites are eucrite-type basalts and gabbros - rocks composed of ferroan pigeonite and augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal [1]. These rocks are thought to have formed on a single asteroid, widely considered to be 4 Vesta, along with howardites and diogenites [1, 2]. High precision O-isotopic analyses have shown that some eucrites have small, well-resolved O-isotopic differences from the group mean [3-5]. These Oanomalous eucrites are thought to hail from asteroidal parents that are distinct from that of eucrites [5]. Three O-anomalous eucrites are PCA 82502, PCA 91007 (paired) and Pasamonte, all of which have the same O-isotopic composition [5, 6]. Our petrologic studies have shown that PCA 82502 and PCA 91007 have well-resolved anomalies in low-Ca pyroxene Fe/Mn compared to eucrites [6]. Divalent Mn and Fe are homologous species that do not greatly fractionate during igneous processes; mafic mineral Fe/Mn can be used to fingerprint parent object sources [7]. Previous petrological studies of Pasamonte [8-10] have not yielded sufficiently precise Fe/Mn ratios to allow distinction of anomalies of the scale of those found for the PCA basalts. We have begun petrological study of Pasamonte for comparison with our results on normal and anomalous eucrites [6], and to constrain its origin.

Mittlefehldt, D. W.↗
NASA NTRSDate not supplied

Preliminary 3D Simulations of Anomalous Thermocouple Coupling to Surface Electric Fields

Anomalous measurements from subsurface thermocouples have been observed during re-entry of the Orion capsule (EFT-1 plugs). These measurements are considered anomalous because the amplitude and frequency of the inferred temperature modulations are too large to be due to plausible heating processes. Consequently, it is believed the anomalies are caused by electrical interference generated by the re-entry plasma. Quantifying these effects requires several steps: modeling the external plasma flows, modeling the plasma-surface interaction, and finally modeling the surface-thermocouple coupling. This paper addresses this last step using 3D finite element simulations of a wire embedded in a weakly conductive medium.

thermocouple anomaly↗
NASA NTRS2014

Anomalous Expansion of Coronal Mass Ejections During Solar Cycle 24 and Its Space Weather Implications

The familiar correlation between the speed and angular width of coronal mass ejections (CMEs) is also found in solar cycle 24, but the regression line has a larger slope: for a given CME speed, cycle 24 CMEs are significantly wider than those in cycle 23. The slope change indicates a significant change in the physical state of the heliosphere, due to the weak solar activity. The total pressure in the heliosphere (magnetic + plasma) is reduced by approximately 40%, which leads to the anomalous expansion of CMEs explaining the increased slope. The excess CME expansion contributes to the diminished effectiveness of CMEs in producing magnetic storms during cycle 24, both because the magnetic content of the CMEs is diluted and also because of the weaker ambient fields. The reduced magnetic field in the heliosphere may contribute to the lack of solar energetic particles accelerated to very high energies during this cycle.

coronal mass ejections↗
NASA NTRS2023

Metrics for Anomalous Charging currents in Polymer Tantalum Capacitors

Anomalous charging currents (ACC) in polymer tantalum capacitors may appear as a temporary short circuit that can last for dozens of milliseconds, cause failures to the parts, or cause malfunctions to fast operating electronic systems. Currently, there is no standard technique or set of metrics to evaluate the level of ACC which compares results obtained by different users and manufacturers. In this work, ACC in different types of capacitors were characterized by analysis of current transients during the constant voltage ramp or power surge testing (PST) techniques. It is shown that although the shape of transients may vary at different test conditions, the transfer charge and energy remain practically the same. The level of ACC is characterized by the energy dissipated in the part during PST. Variations of the dissipated energy with moisture content, test temperature, and voltage are evaluated. Effects of different reflow soldering conditions and long-term (up to 3000 hours) storage at 125 °C are discussed.

polymer tantalum capacitor↗