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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The 77 day periodicity in the flare rate of cycle 22

The ocurrence times of major flares of solar cycle 22 are analyzed to detect periodicities. It is found that a periodicity of 77 d was in operation in the 15-m interval from 1988 November to 1990 February for six cycles. During the rest of 1990 no periodicity was discernible; however, it seems that the 77-d periodicity resumed in 1991. This 77-d period is interpreted as the third subharmonic of the fundamental period of about 25.5 d. In this interpretation, the 154-d periodicity is the sixth subharmonic. It is also found that when the 77-d periodicity or the 154-d periodicity is in operation the occurrence rate of major flares is much higher than is expected form the relative sunspot number.

Bai, T.↗
NASA NTRS1994

AH Cam: A metal-rich RR Lyrae star with the shortest known Blazhko period

Analysis of 746 new V-band observations of the RR Lyrae star AH Cam obtained during 1989 - 1992 clearly show that its light curve cannot be described by a single period. In fact, at first glance, the Fourier spectrum of the photometry resembles that of a double-mode pulsator, with peaks at a fundamental period of 0.3686 d and an apparent secondary period of 0.2628 d. Nevertheless, the dual-mode solution is a poor fit to the data. Rather, we believe that AH Cam is a single-mode RR Lyrae star undergoing the Blazhko effect: periodic modulation of the amplitude and shape of its light curve. What was originally taken to be the period of the second mode is instead the 1-cycle/d alias of a modulation sidelobe in the Fourier spectrum. The data are well described by a modulation period of just under 11 d, which is the shortest Blazhko period reported to date in the literature and confirms the earlier suggestion by Goranskii. A low-resolution spectrum of AH Cam indicates that it is relatively metal rich, with delta-S less than or = 2. Its high metallicity and short modulation period may provide a critical test of at least one theory for the Blazhko effect. Moskalik's internal resonance model makes specific predictions of the growth rate of the fundamental model vs fundamental period. AH Cam falls outside the regime of other known Blazhko variables and resonance model predictions, but these are appropriate for metal-poor RR Lyrae stars. If the theory matches the behavior of AH Cam for a metal-rich stellar model, this would bolster the resonance hypothesis.

Smith, Horace A.↗
NASA NTRS2001

NADH oxidase activity (NOX) and enlargement of HeLa cells oscillate with two different temperature-compensated period lengths of 22 and 24 minutes corresponding to different NOX forms

NOX proteins are cell surface-associated and growth-related hydroquinone (NADH) oxidases with protein disulfide-thiol interchange activity. A defining characteristic of NOX proteins is that the two enzymatic activities alternate to generate a regular period length of about 24 min. HeLa cells exhibit at least two forms of NOX. One is tumor-associated (tNOX) and is inhibited by putative quinone site inhibitors (e.g., capsaicin or the antitumor sulfonylurea, LY181984). Another is constitutive (CNOX) and refractory to inhibition. The periodic alternation of activities and drug sensitivity of the NADH oxidase activity observed with intact HeLa cells was retained in isolated plasma membranes and with the solubilized and partially purified enzyme. At least two activities were present. One had a period length of 24 min and the other had a period length of 22 min. The lengths of both the 22 and the 24 min periods were temperature compensated (approximately the same when measured at 17, 27 or 37 degrees C) whereas the rate of NADH oxidation approximately doubled with each 10 degrees C rise in temperature. The rate of increase in cell area of HeLa cells when measured by video-enhanced light microscopy also exhibited a complex period of oscillations reflective of both 22 and 24 min period lengths. The findings demonstrate the presence of a novel oscillating NOX activity at the surface of cancer cells with a period length of 22 min in addition to the constitutive NOX of non-cancer cells and tissues with a period length of 24 min.

Non-NASA Center↗
DOE OSTI2023

The Intrinsic 150‐Day Periodicity of the Southern Hemisphere Extratropical Large‐Scale Atmospheric Circulation

Abstract The variability of the Southern Hemisphere (SH) extratropical large‐scale circulation is dominated by the Southern Annular Mode (SAM), whose timescale is extensively used as a key metric in evaluating state‐of‐the‐art climate models. Past observational and theoretical studies suggest that the SAM lacks any internally generated (intrinsic) periodicity. Here, we show, using observations and a climate model hierarchy, that the SAM has an intrinsic 150‐day periodicity. This periodicity is robustly detectable in the power spectra and principal oscillation patterns (aka dynamical mode decomposition) of the zonal‐mean circulation, and in hemispheric‐scale precipitation and ocean surface wind stress. The 150‐day period is consistent with the predictions of a new reduced‐order model for the SAM, which suggests that this periodicity is associated with a complex interaction of turbulent eddies and zonal wind anomalies, as the latter propagate from low to high latitudes. These findings present a rare example of periodic oscillations arising from the internal dynamics of the extratropical turbulent circulations. Based on these findings, we further propose a new metric for evaluating climate models, and show that some of the previously reported shortcomings and improvements in simulating SAM's variability connect to the models' ability in reproducing this periodicity. We argue that this periodicity should be considered in evaluating climate models and understanding the past, current, and projected Southern Hemisphere climate variability.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Spatially Quasi-Periodic Water Waves of Infinite Depth

Abstract We formulate the two-dimensional gravity-capillary water wave equations in a spatially quasi-periodic setting and present a numerical study of solutions of the initial value problem. We propose a Fourier pseudo-spectral discretization of the equations of motion in which one-dimensional quasi-periodic functions are represented by two-dimensional periodic functions on a torus. We adopt a conformal mapping formulation and employ a quasi-periodic version of the Hilbert transform to determine the normal velocity of the free surface. Two methods of time-stepping the initial value problem are proposed, an explicit Runge–Kutta (ERK) method and an exponential time-differencing (ETD) scheme. The ETD approach makes use of the small-scale decomposition to eliminate stiffness due to surface tension. We perform a convergence study to compare the accuracy and efficiency of the methods on a traveling wave test problem. We also present an example of a periodic wave profile containing vertical tangent lines that is set in motion with a quasi-periodic velocity potential. As time evolves, each wave peak evolves differently, and only some of them overturn. Beyond water waves, we argue that spatial quasi-periodicity is a natural setting to study the dynamics of linear and nonlinear waves, offering a third option to the usual modeling assumption that solutions either evolve on a periodic domain or decay at infinity.

Wilkening, Jon (ORCID:0000000327827596)↗
DOE OSTI2021

Very Large Array imaging rules out precessing radio jets in three DES–SDSS-selected candidate periodic quasars

ABSTRACT Periodic quasars have been suggested as candidates for hosting binary supermassive black holes (SMBHs), although alternative scenarios remain possible to explain the optical light-curve periodicity. To test the alternative hypothesis of precessing radio jet, we present deep 6 GHz radio imaging conducted with NSF’s Karl G. Jansky Very Large Array (VLA) in its C configuration for the three candidate periodic quasars, DES J024703.24−010032.0, DES J024944.66−000036.8, and DES J025214.67−002813.7. Our targets were selected based on their optical variability using 20 yr long multicolour light curves from the Dark Energy Survey (DES) and the Sloan Digital Sky Survey (SDSS). The new VLA observations show that all three periodic quasars are radio-quiet with the radio loudness parameters measured to be $R\equiv f_{6\, {\rm cm}}/f_{{\rm 2500}}$ of ≲1.0–1.5 and the k-corrected luminosities νLν[6 GHz] of ≲5–21 × 1039 erg s−1. They are in stark contrast to previously known periodic quasars proposed as binary SMBH candidates such as the blazar OJ 287 and PG1302−102. Our results rule out optical emission contributed from precessing radio jets as the origin of the optical periodicity in the three DES–SDSS-selected candidate periodic quasars. Future continued optical monitoring and complementary multiwavelength observations are still needed to further test the binary SMBH hypothesis as well as other competing scenarios to explain the optical periodicity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Searching for quasar candidates with periodic variations from the Zwicky Transient Facility: results and implications

ABSTRACT We conduct a systematic search for quasars with periodic variations from the archival photometric data of the Zwicky Transient Facility by cross-matching with the quasar catalogues of the Sloan Digital Sky Survey and Véron-Cetty and Véron. We first select out 184 primitive periodic candidates using the generalized Lomb–Scargle periodogram and autocorrelation function and then estimate their statistical significance of periodicity based on two red-noise models, i.e. damped random walk (DRW) and single power-law (SPL) models. As such, we finally identify 106 (DRW) and 86 (SPL) candidates with the most significant periodic variations out of 143 700 quasars. We further compare DRW and SPL models using Bayes factors, which indicate a relative preference of the SPL model for our primitive sample. We thus adopt the candidates identified with SPL as the final sample and summarize its basic properties. We extend the light curves of the selected candidates by supplying other archival survey data to verify their periodicity. However, only three candidates (with 6–8 cycles of periods) meet the selection criteria. This result clearly implies that, instead of being strictly periodic, the variability must be quasi-periodic or caused by stochastic red-noise. This exerts a challenge to the existing search approaches and calls for developing new effective methods.

Chen, Yong-Jie (ORCID:0000000342807673)↗
NASA NTRS1985

Secondary periodicities of microbursts of TeV gamma rays from the Crab pulsar

Observations were made during the past several years on the Crab pulsar using the Ooty atmospheric Cerenkov array with the aim of detecting possible emission of ultra high energy gamma rays by the pulsar. During the course of these observations, it was found that the Crab pulsar emits TeV gamma rays in bursts of short duration. The microbursts of TeV gamma rays from the Crab pulsar, which were seen in the data of at least three years, also reveal interesting secondary periodicities. It was noticed at first that some bursts could be connected with the others that occurred during the same night or during the next two nights with integral number of cycles of periods 43 + or - 1 minute. Ten possible periods in the vicinity of 43 minutes were determined for all the combinations of bursts for each year. The best values of periods thus obtained were different from year to year. But when, instead of the real time, the number of Crab cycles elapsed between the bursts was used as the unit of time, two values of burst periods - 77460 and 77770 Crab cycles - were found to be significant in the data of at least two years. A Monte Carlo simulation using 1500 trial periods chosen randomly within + or - 5 minutes of the original burst period did not reveal any value of the period as significant.

Vishwanath, P. R.↗
NASA NTRS1985

Light variations of Periodic Comet Halley beyond 7 AU

The present examination of brightness data on the Periodic Comet Halley over the October 1982-February 1984 period, for evidence concerning nucleus rotation period and projected cross section area, notes variations of up to 5:1 in intrinsic brightness. Application of a period-determination technique has failed to yield a clear choice for the true rotation period among a large number of peaks in the spectrum, some of which virtually coincide with the sun's rotation period and its submultiples. It is found that rotation periods longer than about 1 day are the most likely; it is suggested that the observed light curve is a composition of periodic and erratic variations.

Sekanina, Z.↗
NASA NTRS1989

A search for five month solar induced periodicity in the stratosphere

Recent studies of solar UV spectra and various indices of solar activity indicate a strong period at about 5 months. In the 10.7 cm solar radio flux (F10.7), a conventional index for the solar EUV and UV variabilities, the spectral power of the 5 month period is comparable to the well known 27 day solar period. However, in the solar UV flux at 205 nm, directly measured from the Nimbus-7 SBUV spectrometer, the (spectral) power of the 5 month period is about half that of the 27 day period. This paper examines the possible impact of the 5 month solar period on ozone and temperature at various pressure levels in the stratosphere and discusses the implications of differences in solar forcing at the 27 day and 5 month periods. It is shown that ozone, both in the lower and the upper stratosphere, has a measurable response to solar UV forcing at 27 days. Such a solar response is not observed at 5 month period because of a relatively weaker 5 month solar UV component in the solar signal and a strong interference from dynamical signals associated with planetary wave activity.

Chandra, S.↗
NASA NTRS1992

Short- and intermediate-period oxygen-rich Miras

Available IR photometry and the period-IR luminosity relationship are used to analyze a nearly complete sample of oxygen-rich Miras at Galactic latitudes with /b/ greater than 30 deg. In agreement with previous kinematic studies, a marked difference is found in the spatial distributions between the stars with periods less than and those with periods greater than 300 d. For stars with periods in the range 300-400 d, the exponential scale height from the Galactic plane is close to 240 pc, the projected surface density is about 100/sq kpc, and the local space density is about 210/cu kpc. The progenitors of the Miras with periods greater than 300 d appear to be disk dwarfs with typical main-sequence masses of between 1.0 and 1.2 solar masses. The masses of the main-sequence progenitors of the short-period Miras are 1.1 solar masses or less. The duration of the Mira phase for the intermediate-period stars is estimated to be about 20,000 yr, somewhat longer than other recent estimates. Both short- and intermediate-period oxygen-rich Miras characteristically lose mass at about 10 exp -7 solar mass/yr.

Jura, M.↗
NASA NTRS1992

'Intermittent' solar periodicities

The signal from a stable periodicity can seem to be intermittent when it is partially masked by an unmodelled window function or when the data set is too short to resolve closely spaced periodicities. By taking this into account, short-lived periodicities in solar data can be reinterpreted as evidence for continuously periodic behavior. The periodic sources are located in the solar interior and caused by global oscillation modes. The convective envelope acts as the window for these sources. Recent reports of seven periodicities from 100 to 1000 days are compared with this model. Precise long-term values for the periodicities are predicted and they agree closely with observations. Some elements are suggested that might explain the well-documented 155-day periodicity. Conventional filtering methods to suppress effects of the 11-year cycle are criticized as inadequate.

Wolff, Charles L.↗
NASA NTRS1994

Periodic intensity variations in sulfur emissions from the Io plasma torus

In November and December 1988, we acquired 157 spectra of (S II) lambda 6731 emissions from the Io plasma torus with a Fabry-Perot interferometer at the McMath-Pierce Solar Telescope facility on Kitt Peak. A major goal of this experiment was to extend our earlier studies of intensity variations in the plasma torus. Our earlier analysis (F. L. Roesler, F. Scherb, and R. J. Oliversen, 1984, of (S III) lambda 9531 emission spectra acquired in April 1982 had shown that the intensity of torus emissions varied periodically with a period of 10.20 +/- 0.06 hr (1-sigma uncertainty level), slightly longer than Jupiter's System 3 rotational period of 9.925 hr. We present here an reanalysis of our 1982 data revealing, in addition to the 10.20-hr period, a clear secondary periodicity at 9.95 +/- 0.906 hr. By constrast, we show that our new (S II) lambda 6731 data have a single period of 10.14 +/- 0.03 hr. which is neither the System 3 period nor the proposed 'System 4' period of 10.224 hr.

Woodward, R. Carey, Jr.↗
NASA NTRS1995

Revised predictions of long-period ocean tidal effects on Earth's rotation rate

The rotational response of Earth to long-period tidal forces, embodied in a 'zonal response function,' can be expected to vary with frequency because of variable contributions by the oceans, mantle, and core. The zonal response function has been estimated from 9 years of International Radio Interferometric Surveying (IRIS) universal time (UT1) data and compared with theoretical predictions, using a spherical harmonic tide model to compute the oceans' dynamic response, at semiannual, monthly, fortnightly, and 9-day lunisolar tidal frequencies. Different amounts of mantle anelasticity have been considered for both the oceanic and soild earth responses; predictions have been made assuming axial core-mantle coupling which is either complete or absent. Additionally, an extensive recalibration of the ocean model's frictional parameters was performed using constraints derived in part from Space92 polar motion data; zonal response function predictions have also been made employing this recalibrated ocean tide model. Our results indicate that any amount of core coupling can be ruled out at a fortnightly period and probably at a 9-day period, but not at a monthly period. Our results also suggest that the mantle responds purely elastically at a 9-day period but may behave increasingly anelastically at longer periods. A simple dispersive rule is postulated for periods ranging up to the 14-month Chandler wobble period.

Dickman, S. R.↗
NASA NTRS1995

Periodicities of solar flare and its relations

Daily flare index during period between March 1975 and May 1978, were studied by using power spectral analysis method. There are periodicities between 4.5 days to 21.7 days. Our results confirm the periodicity around 12.5 days found by several authors. This periodicity was attributed to the rotation of solar core. Long term periodicities were given where 88 and 320 days periodicities were confirmed. The relation between these periodicities and other solar activities periodicity were given.

Hady, Ahmed A.↗
NASA NTRS1995

Solar wind plasma periodicities observed at 1 AU by IMP 8

The IMP 8 spacecraft has been in Earth orbit since 1973, gathering plasma data over one complete 22-year solar cycle. These data are being examined to look for periodicities at time scales ranging from several hours to the entire span of the data set. A 1.3-year periodicity in the radial speed observed by IMP 8 and Voyager 2 has already been reported for the years from 1987 to 1993. The periodogram method, useful for unevenly sampled data such as the IMP 8 plasma data, has been used to search for other periods. It is interesting to note that the 13-year period is not present in the out-of-the-ecliptic component of the velocity (Vz), although a 1-year period is very obvious both visually and on the periodogram. Both components show a very strong peak associated with the 11-year solar cycle variation. This work will be extended to the thermal speed (a measure of the wind's temperature) and density, although the frequent correlations between these parameters and the velocity are expected to cause similar results. Additionally, the fine resolution data will be examined for shorter time periods than are visible using the hourly average data which are appropriate for longer periods. A comparison with periods observed at other spacecraft may also be made.

Paularena, K. I.↗
NASA NTRS1998

Studies of Long Period Variability in Neutron Star HMXB Systems

The purpose of this effort was to investigate the long term, quasi-periodic variability of the X-ray emission from the accreting X-ray pulsars LMC X-4 and SMC X-1. These high mass X-ray binary (HMXB) sources are known to vary in a nearly periodic fashion with cycle lengths of about 30 and 60 days respectively. The prevailing model for such behavior is that it is due to the precession of a tilted accretion disk around the neutron star which is the source of the X-ray emission. As the disk precesses, it periodically obscures the emitting region, resulting in reduced flux as observed at the Earth. The obscuration is not strictly periodic, as the disk precession period changes as the total mass and size of the disk change through variable accretion processes. This model is well established for the long-period variability in the X-ray pulsar Her X-1. With this work, my collaborators and I sought to test whether this model works for LMC X-4 and SMC X-1. Observations with the pointed instruments on the Rossi X-ray Timing Explorer (RXTE) were carried out in order to observe changes in the X-ray spectrum and total flux which were correlated with the long period cycles in these objects. One of the main predictions of the precessing disk model is that the periods of low emission are caused not by changes in the central source, but by increased absorption of that flux as seen at the Earth. Such behavior would be observed in the X-ray spectrum as a relative lack of low energy X-rays (which are more easily absorbed) as compared to high energy X-rays. This is what was observed for SMC X-1, landing strong support to the precessing disk model for this system. For LMC X-1, however, the absorption was consistent with zero at the time of minimum flux. The entire spectrum appeared to be equally reduced. This is not supporting evidence for the model. However, it also does not rule out a precessing disk. If at the time of minimum flux, the intervening disk is so thick that no flux, even high energy X-rays, can penetrate, and if there is material above the disk which can scatter X-rays, then a small scattered spectrum will be seen which is indistinguishable from the unobscured source flux. This is quite possibly the case in LMC X-1.

Heindl, William A.↗
NASA NTRS2010

Examining Periodic Solar-Wind Density Structures Observed in the SECCHI Heliospheric Imagers

We present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as approximately equals 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper analyzed the alpha-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.

Viall, Nicholeen M.↗