Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Tidal”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

TOI-503: The First Known Brown-dwarf Am-star Binary from the TESS Mission

We report the discovery of an intermediate-mass transiting brown dwarf (BD), TOI-503b, from the TESS mission. TOI-503b is the first BD discovered by TESS, and it has circular orbit around a metallic-line A-type star with a period of P=3.6772±0.0001 days. The light curve from TESS indicates that TOI-503b transits its host star in a grazing manner, which limits the precision with which we measure the BD’s radius R(b) = 1.34(+0.26, -0.15)R(J). We obtained high resolution spectroscopic observations with the FIES, Ondrejov, PARAS, Tautenburg, and TRES spectrographs, and measured the mass of TOI-503b to be M(b)=53.7±1.2 M(J). The host star has a mass of M(*)=1.80±0.06M(ʘ), a radius of R(*)=1.70±0.05R(ʘ), an effective temperature of T(eff)=7650±160 K, and a relatively high metallicity of 0.61±0.07 dex. We used stellar isochrones to derive the age of the system to be ∼180 Myr, which places its age between that of RIK 72b (a ∼10 Myr old BD in the Upper Scorpius stellar association) and AD 3116b (a ∼600 Myr old BD in the Praesepe cluster). Given the difficulty in measuring the tidal interactions between BDs and their host stars, we cannot precisely say whether this BD formed in situ or has had its orbit circularized by its host star over the relatively short age of the system. Instead, we offer an examination of plausible values for the tidal quality factor for the star and BD. TOI-503b joins a growing number of known short-period, intermediate-mass BDs orbiting main sequence stars, and is the second such BD known to transit an A star, after HATS-70b. With the growth in the population in this regime, the driest region in the BD desert (35–55M(J) sin i) is reforesting.

Jan Subjak↗
NASA NTRS1993

Vertical Ocean Loading Amplitudes From VLBI Measurements

Vertical ocean loading amplitudes are determined by analysis of IRIS geodetic VLBI data. Vertical ocean loading amplitudes can thus be inferred from VLBI data at a level which improves the overall model, but detailed assessment of individual tidal components is presently obscured by inadequacies in modeling other tidal effects.

ocean↗
NASA NTRS2019

A New Class of Flares from Accreting Supermassive Black Holes

Accreting supermassive black holes (SMBHs) can exhibit variable emission across the electromagnetic spectrum and over a broad range of timescales. The variability of active galactic nuclei (AGNs) in the ultraviolet and optical is usually at the few tens of per cent level over timescales of hours to weeks1. Recently, rare, more dramatic changes to the emission from accreting SMBHs have been observed, including tidal disruption events2,3,4,5, ‘changing look’ AGNs6,7,8,9 and other extreme variability objects10,11. The physics behind the ‘re-ignition’, enhancement and ‘shut-down’ of accretion onto SMBHs is not entirely understood. Here we present a rapid increase in ultraviolet–optical emission in the centre of a nearby galaxy, marking the onset of sudden increased accretion onto a SMBH. The optical spectrum of this flare, dubbed AT 2017bgt, exhibits a mix of emission features. Some are typical of luminous, unobscured AGNs, but others are likely driven by Bowen fluorescence—robustly linked here with high-velocity gas in the vicinity of the accreting SMBH. The spectral features and increased ultraviolet flux show little evolution over a period of at least 14 months. This disfavours the tidal disruption of a star as their origin, and instead suggests a longer-term event of intensified accretion. Together with two other recently reported events with similar properties, we define a new class of SMBH-related flares. This has important implications for the classification of different types of enhanced accretion onto SMBHs.

Benny Trakhtenbrot↗
NASA NTRS2021

Magma Ocean Evolution of the TRAPPIST-1 Planets

Recent observations of the potentially habitable planets TRAPPIST-1 e, f, and g suggest that they possess large water mass fractions of possibly several tens of wt% of water, even though the host star’s activity should drive rapid atmospheric escape. These processes can photolyze water, generating free oxygen and possibly desiccating the planet. After the planets formed, their mantles were likely completely molten with volatiles dissolving and exsolving from the melt. In order to understand these planets and prepare for future observations, the magma ocean phase of these worlds must be understood. To simulate these planets, we have combined existing models of stellar evolution, atmospheric escape, tidal heating, radiogenic heating, magma ocean cooling, planetary radiation, and water-oxygen-iron geochemistry. We present Magm Oc, a versatile magma ocean evolution model, validated against the rocky Super-Earth GJ 1132b and early Earth. We simulate the coupled magma ocean-atmospheric evolution of TRAPPIST-1 e, f, and g for a range of tidal and radiogenic heating rates, as well as initial water contents between 1 and 100 Earth oceans. We also reanalyze the structures of these planets and find they have water mass fractions of 0–0.23, 0.01–0.21, and 0.11–0.24 for planets e, f, and g, respectively. Our model does not make a strong prediction about the water and oxygen content of the atmosphere of TRAPPIST-1 e at the time of mantle solidification. In contrast, the model predicts that TRAPPIST-1 f and g would have a thick steam atmosphere with a small amount of oxygen at that stage. For all planets that we investigated, we find that only 3 ́5% of the initial water will be locked in the mantle after the magma ocean solidified.

Exoplanets↗
NASA NTRS2019

Probing boson stars with extreme mass ratio inspirals

We propose to use gravitational waves from extreme mass ratio inspirals (EMRI), composed of a boson star and a supermassive black hole in the center of galaxies, as a new method to search for boson stars. Gravitational waves from EMRI have the advantage of being long-lasting within the frequency band of future space-based interferometer gravitational wave detectors and can accumulate large signal-to-noise ratio (SNR) for very sub-solar mass boson stars. Compared to gravitational waves from boson star binaries, which fall within the LIGO band, we find that much larger ranges of the mass and compactness of boson stars, as well as the underlying particle physics parameter space, can be probed by EMRI. We take tidal disruption of the boson stars into account and distinguish those which dissolve before the inner-most-stable-circular-orbit (ISCO) and those which dissolve after it. Due to the large number of cycles recorded, EMRIs can lead to a very precise mass determination of the boson star and distinguish it from standard astrophysical compact objects in the event of a signal. Tidal effects in inspiralling binary systems, as well as possible correlated electromagnetic signals, can also serve as potential discriminants.

Huai-Ke Guo↗
NASA NTRS2022

Rapid Glacier Retreat Rates Observed in West Antarctica

The Pope, Smith, and Kohler glaciers, in the Amundsen Sea Embayment of West Antarctica, have experienced enhanced ocean-induced ice-shelf melt, glacier acceleration, ice thinning, and grounding line retreat in the past thirty years. Here we present observations of the grounding line retreat of these glaciers since 2014 using a constellation of interferometric radar satellites combined with precision surface elevation data. We find that the grounding lines develop spatially-variable, kilometre-scale, tidally-induced migration zones. After correction for tidal effects, we detect a sustained pattern of retreat coincident with high melt rates of un-grounded ice, marked by episodes of more rapid retreat. In 2017, Pope Glacier retreated 3.5 km in 3.6 months, or 11.7 km/yr. In 2016-2018, Smith West retreated at 2 km/yr and Kohler at 1.3 km/yr. While the retreat slowed down in 2018-2020, these retreat rates are faster than anticipated by numerical models on yearly time scales. We hypothesize that the rapid retreat is caused by un-represented, vigorous ice-ocean interactions acting within newly-formed cavities at the ice-ocean boundary.

Climate change↗
NASA NTRS2022

Technical Note: On Seasonal Variability of the M2 Tide

Seasonal variability of the M2 ocean tide can be detected at many ports, perhaps most. Examination of the cluster of tidal constituents residing within the M2 tidal group can shed light on the physical mechanisms underlying seasonality. In the broadest terms these are astronomical, frictional–advective interactions, and climate processes; some induce annual modulations and some semiannual, in amplitude, phase, or both. This note reviews how this occurs and gives an example from each broad category. Phase conventions and their relationship with causal mechanisms, as well as nomenclature, are also addressed.

Richard D Ray↗
NASA NTRS2022

Atmospheric Lunar Tide in the Low Latitude Thermosphere-Ionosphere

We present simultaneous, independent measurements of the atmospheric semidiurnal lunar tide in neutral winds and plasma velocities from NASA's Ionospheric Connection Explorer, and in atomic oxygen 135.6 nm airglow measured by the Global-scale Observations of the Limb and Disk. Westward tidal winds near 115 km at the magnetic equator occur during part of the upward phase of the in-situ plasma drift. Vertical motions associated with the field-aligned plasma velocity occur away from the magnetic equator. The morphology of the lunar tide, and the phasing between the airglow and plasma velocities are consistent with E × B drift as a mechanism for linking neutral wind and plasma perturbations. This work provides the first observational quantification of global-scale E- and F-region coupling through E × B and field-aligned vertical drifts. Plain Language Summary: Tidal winds propagating upward from the neutral atmosphere influence ionospheric dynamo electric fields and vertical plasma drifts. However, these mechanisms have never been fully identified in comprehensive and simultaneous measurements spanning the ionosphere-thermosphere-mesosphere (ITM) system. The atmospheric lunar tide is an effective marker of ITM coupling because it originates at Earth's surface, propagates vertically, and is fully sampled in daytime-only and post-sunset satellite measurements. We utilize measurements from two new NASA missions to track the lunar tide in neutral and plasma velocities, and in an electron density proxy. Our work provides observational confirmation, and quantitative estimates of F-region vertical plasma motions driven by neutral winds and electrodynamical forces

Ruth S. Lieberman↗
NASA NTRS2023

A High-Eccentricity Warm Jupiter Orbiting TOI-4127

We report the discovery of TOI-4127 b, which is a transiting, Jupiter-sized exoplanet on a long period (P=56.39879 +0.00010 -0.00010 days) and a high-eccentricity orbit around a late F-type dwarf star. This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data and was later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical (R p =1.096 +0.039 -0.032 R J , M p =2.30 +0.11 -0.11 M J ) and orbital parameters of the exoplanet. Given its high orbital eccentricity (𝓮=0.7471 +0.0078 -0.0086 ), TOI-4127 b is a compelling candidate for studies of warm Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI-4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration.

Exoplanet astronomy↗
NASA NTRS2024

A Low Density Ocean Inside Titan Inferred From Cassini Data

The Cassini mission has provided measurements of the gravity of several moons of Saturn, as well as an estimate of the tidal response, expressed as the degree 2 Love number k 2 , of its largest moon, Titan. The first estimates of Titan’s Love number were larger than pre-Cassini expectations. Interior modeling suggested it may be explained with a dense ocean, but interpretation remained unclear. We have analyzed Cassini tracking data to determine Titan’s gravity field and its Love number. Our gravity results are consistent with earlier studies, but we find a lower Love number for Titan of k 2 =0.375±0.06. This lower value follows from an elaborate investigation of the tidal effects. We show that a dense ocean is not implied by the obtained Love number; instead, a water or ammonia ocean is more likely. A lower density ocean can increase the likeliness of contact between the silicate core and ocean, which can leach minerals into the ocean and could promote its habitability.

Sander Goossens↗
NASA NTRSDate not supplied

Cold Ocean Planets: Exoplanet Analogs of Our Solar System’s Icy Moons?

We have calculated total internal heating rates and depths to possible subsurface oceans for 17 planets that were previously characterized as rocky worlds but that are best described as Cold Ocean Planets. These low-mass exoplanets have equilibrium surface temperatures and/or densities that are consistent with icy surfaces and a substantial H2O content. While all planets in our study are likely to be covered in ice, estimated internal heating rates from tidal and radiogenic sources are large enough that they may harbor internal oceans and exhibit explosive cryovolcanism in the form of geyser-like plumes at their surfaces. Several of the icy moons in our solar system may thus serve as small-scale analogs of the Cold Ocean Planets in our study. We find that geological activity rates on these worlds are likely to exceed geological activity rates on Jupiter’s moon Europa and that several planets are likely to experience enhanced geological activity that exceeds that on Io. Owing to these planets’ thin ice shells, their expected high rates of internal heating, and their potential for tidally-induced explosive cryovolcanism, the identification of water vapor absorption features, especially given the expected time-variability of water vapor output during eruptions, could allow for the detection of geyser-like plumes on Trappist-1f, Proxima Cen b, and LHS 1140 b. Our study suggests that Cold Ocean Planets are habitable worlds at which the detection of explosive cryovolcanism could serve as indirect evidence of the presence of oceans beneath a layer of surface ice. Analyses of observational data from next-generation space telescopes and upcoming ground-based extremely large telescopes, and designs for future telescopic missions, should be undertaken with these results in mind.

Lynnae C Quick↗
NASA NTRS1966

Gravitational shielding and absorption.

Gravitational shielding and absorption, examining tidal effects induced in solid sphere by another sphere, analogy to electromagnetic fields, etc

ELECTROMAGNETIC FIELD↗
NASA NTRS1998

Mechanisms underlying very-low-frequency RR-interval oscillations in humans

BACKGROUND: Survival of post-myocardial infarction patients is related inversely to their levels of very-low-frequency (0.003 to 0.03 Hz) RR-interval variability. The physiological basis for such oscillations is unclear. In our study, we used blocking drugs to evaluate potential contributions of sympathetic and vagal mechanisms and the renin-angiotensin-aldosterone system to very-low-frequency RR-interval variability in 10 young healthy subjects. METHODS AND RESULTS: We recorded RR intervals and arterial pressures during three separate sessions, with the patient in supine and 40 degree upright tilt positions, during 20-minute frequency (0.25 Hz) and tidal volume-controlled breathing after intravenous injections: saline (control), atenolol (0.2 mg/kg, beta-adrenergic blockade), atropine sulfate (0.04 mg/kg, parasympathetic blockade), atenolol and atropine (complete autonomic blockade), and enalaprilat (0.02 mg/kg, ACE blockade). We integrated fast Fourier transform RR-interval spectral power at very low (0.003 to 0.03 Hz), low (0.05 to 0. 15 Hz), and respiratory (0.2 to 0.3 Hz) frequencies. Beta-adrenergic blockade had no significant effect on very-low- or low-frequency RR-interval power but increased respiratory frequency power 2-fold. ACE blockade had no significant effect on low or respiratory frequency RR-interval power but modestly (approximately 21%) increased very-low-frequency power in the supine (but not upright tilt) position (P<0.05). The most profound effects were exerted by parasympathetic blockade: Atropine, given alone or with atenolol, abolished nearly all RR-interval variability and decreased very-low-frequency variability by 92%. CONCLUSIONS: Although very-low-frequency heart period rhythms are influenced by the renin-angiotensin-aldosterone system, as low and respiratory frequency RR-interval rhythms, they depend primarily on the presence of parasympathetic outflow. Therefore the prognostic value of very-low-frequency heart period oscillations may derive from the fundamental importance of parasympathetic mechanisms in cardiovascular health.

Non-NASA Center↗
NASA NTRS1997

Ventilation during simulated altitude, normobaric hypoxia and normoxic hypobaria

To investigate the possible effect of hypobaria on ventilation (VE) at high altitude, we exposed nine men to three conditions for 10 h in a chamber on separate occasions at least 1 week apart. These three conditions were: altitude (PB = 432, FIO2 = 0.207), normobaric hypoxia (PB = 614, FIO2 = 0.142) and normoxic hypobaria (PB = 434, FIO2 = 0.296). In addition, post-test measurements were made 2 h after returning to ambient conditions at normobaric normoxia (PB = 636, FIO2 = 0.204). In the first hour of exposure VE was increased similarly by altitude and normobaric hypoxia. The was 38% above post-test values and end-tidal CO2 (PET(CO2) was lower by 4 mmHg. After 3, 6 and 9 h, the average VE in normobaric hypoxia was 26% higher than at altitude (p < 0.01), resulting primarily from a decline in VE at altitude. The difference between altitude and normobaric hypoxia was greatest at 3 h (+ 39%). In spite of the higher VE during normobaric hypoxia, the PET(CO2) was higher than at altitude. Changes in VE and PET(CO2) in normoxic hypobaria were minimal relative to normobaric normoxia post-test measurements. One possible explanation for the lower VE at altitude is that CO2 elimination is relatively less at altitude because of a reduction in inspired gas density compared to normobaric hypoxia; this may reduce the work of breathing or alveolar deadspace. The greater VE during the first hour at altitude, relative to subsequent measurements, may be related to the appearance of microbubbles in the pulmonary circulation acting to transiently worsen matching. Results indicate that hypobaria per se effects ventilation under altitude conditions.

NASA Discipline Environmental Health↗
NASA NTRS1995

'Non-hypotensive' hypovolaemia reduces ascending aortic dimensions in humans

1. The notion that small, 'non-hypotensive' reductions of effective blood volume alter neither arterial pressure nor arterial baroreceptor activity is pervasive in the experimental literature. We tested two hypotheses: (a) that minute arterial pressure and cardiac autonomic outflow changes during hypovolaemia induced by lower body suction in humans are masked by alterations in breathing, and (b) that evidence for arterial baroreflex engagement might be obtained from measurements of thoracic aorta dimensions. 2. In two studies, responses to graded lower body suction at 0 (control), 5, 10, 15, 20 and 40 mmHg were examined in twelve and ten healthy young men, respectively. In the first, arterial pressure (photoplethysmograph), R-R interval, and respiratory sinus arrhythmia amplitude (complex demodulation) were measured during uncontrolled and controlled breathing (constant breathing frequency and tidal volume). In the second, cross-sectional areas of the ascending thoracic aorta were calculated from nuclear magnetic resonance images. 3. Lower body suction with controlled breathing resulted in an increased arterial pulse pressure at mild levels (5-20 mmHg; ANOVA, P < 0.05) and a decreased arterial pulse pressure at moderate levels (40 mmHg; ANOVA, P < 0.05). Both R-R intervals and respiratory sinus arrhythmia were negatively related to lower body suction level, whether group averages (general linear regression, r > 0.92) or individual subjects (orthogonal polynomials, 12 of 12 subjects) were assessed. 4. Aortic pulse area decreased progressively and significantly during mild lower body suction, with 47% of the total decline occurring by 5 mmHg. 5. These results suggest that small reductions of effective blood volume reduce aortic baroreceptive areas and trigger haemodynamic adjustments which are so efficient that alterations in arterial pressure escape detection by conventional means.

NASA Discipline Cardiopulmonary↗
NASA NTRS2005

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging: Measurement for URSA Minor - 3

This article presents a measurement of the proper motion of the Ursa Minor dwarf spheroidal galaxy determined from images taken with the Hubble Space Telescope in two distinct fields. Each field contains a quasi-stellar object that serves as the "reference point". Integrating the motion of Ursa Minor in a realistic potential for the Milky Way produces orbital elements. The perigalacticon and apogalacticon are 40 (10, 76) and 89 (78, 160) kpc, respectively, where the values in the parentheses represent the 95% confidence intervals derived from Monte Carlo experiments. The eccentricity of the orbit is 0.39 (0.09, 0.79), and the orbital period is 1.5 (1.1, 2.7) Gyr. The orbit is retrograde and inclined by 124 degrees (94 deg, 36 deg ) to the Galactic plane. Ursa Minor is not a likely member of a proposed stream of galaxies on similar orbits around the Milky Way, nor is the plane of its orbit coincident with a recently proposed planar alignment of galaxies around the Milky Way. Comparing the orbits of Ursa Minor and Carina shows no reason for the different star formation histories of these two galaxies. Ursa Minor must contain dark matter to have a high probability of having survived disruption by the Galactic tidal force until the present.

FLUX RESIDUALS↗