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NASA NTRS1976

New results from long-term observations of Cygnus X-1

Observations of Cyg X-1 between October 1974 and July 1975 reveal a persistent 5.6-day modulation of the 3-6 keV X-ray intensity, having a minimum in phase with superior conjunction of the HDE 226868 binary system. The modulation is found to be most pronounced just prior to the April-May 1975 increase of Cyg X-1, after which both the modulation and intensity are at their lowest values for the entire duration of the observations. These data imply that the X-ray emission from Cyg X-1 arises from the compact member of HDE 226868, and that the increase of April-May 1975 may have represented the depletion of accreting material which had not yet been mixed into a cylindrically symmetric accretion disk about the compact member.

Holt, S. S.↗

NASA NTRS1976

Observations of two X-ray flares and the nearby source MX 1716-31

Observations of the X-ray source MX 1716-31 by detectors aboard OSO-7 are described. During the study of the MX 1716-31 data, an X-ray flare was discovered which was probably associated with the source. The flare had a total duration of about 10 minutes and reached a peak intensity twice that of the Crab Nebula in the 3-10-keV range. A search for similar events elsewhere turned up one other flare with a position inconsistent with MX 1716-31. Those features of both flare events which are relevant for comparison with other short-lived X-ray phenomena are discussed.

Markert, T. H.↗

NASA NTRS1987

The recording and processing of pulsed laser diode spectra

A system capable of measuring and statistically analyzing wavelength and intensity fluctuations in pulsed laser diode output beams has been developed. The snapshot wavelength-intensity performance of laser diodes emitting discrete short-duration optical pulse is determined by isolating and recording individual pulses. Statistical processing of the resultant data generates information about the magnitude and/or frequency of occurrence of power variations or wavelength fluctuations in narrow optical bands. The system configuration along with plots depicting results based on measurements taken for various laser diodes are presented.

Fuhr, Peter L.↗

NASA NTRS1991

Origin of the burst of TeV gamma-rays from SN 1987 A

An electromagnetic origin of the TeV gamma-ray burst from SN 1987 A is proposed. The TeV gamma-rays result from inverse Compton scattering in the extreme Klein-Nishina limit of nuclear Co-56 gamma-ray lines and soft X-rays by monoenergetic TeV electrons. The model accounts for the observed time delay between the TeV burst and the peak X-ray intensity of about 3 days, and the different burst duration at TeV and X-ray energies.

Schlickeiser, R.↗

NASA NTRS1999

Polar UVI Observations of Auroral Oval Intensifications during a Transpolar Arc Event on December 7, 1996

The evolution of the northern hemisphere aurora is examined during a time when the Interplanetary Magnetic Field (IMF) makes three brief southward excursions after an extended period of northward IMF. POLAR UltraViolet Imager (UVI) provides images of the aurora while DMSP provides in situ measurements of precipitating particles, ionospheric plasma flows and ion density. Substorm-like events are correlated with northward turnings of the IMF, while the intensity of the ionospheric response is correlated with the duration of the southward IMF period prior to the northward turning. Observations indicate that when the transpolar arc reaches the highest latitudes it is located on a spatially narrow region of closed field lines which extends along the noon-midnight meridian. UV observations indicate a connection between the transpolar arc and the nightside auroral enhancements. Precipitating particles associated with both features are attributed to a plasma sheet boundary layer source in the magnetotail implying a magnetospheric connection between the transpolar arc and the nightside auroral oval intensification.

Cumnock, J. A.↗

NASA NTRS2016

Terral De Vicuna, a Foehnlike Wind in Semiarid Northern Chile: Meteorological Aspects and Implications for the Fulfillment of Chill Requirements in Deciduous Fruit Trees

The terral de Vicuña is a warm and dry wind that flows down the Elqui Valley in north-central Chile typically at dawn and early morning. Given that most terral episodes occur in austral winter when chill accumulation by deciduous fruit trees proceeds, negative effects on agriculture may be expected. During 11 (2004-14) winters a meteorological characterization of terral winds and the assessment of their impact on chill accumulation, by the modified Utah Model and the Dynamic Model, were performed. Within this period, 67 terral days (TD) were identified as those in which nighttime to early morning wind direction and speed, air temperature, and relative humidity reached defined thresholds on an hourly basis (terral hours). Most frequent TD featured 6-9 consecutive terral hours; duration is considered here as a proxy for their intensity. Synoptic-scale meteorological analysis shows that 65% of moderate and strong terral events develop as a cold, migratory anticyclone drifts poleward of the study area, coinciding with the onset of a midtropospheric ridge over central Chile, bringing southwest winds on top of the Andes (approximately 500-hPa level). The remaining 35% are either associated with 500-hPa easterlies (foehn like), with prefrontal conditions ahead of a trough driving northwest 500-hPa winds, or with transitional 500-hPa westerlies.Assessments of chill accumulation during TD show that, although present average and cold winter conditions do not represent a major TD hazard to local agriculture, lower chill accumulation associated with anomalously high nocturnal temperatures could be significantly more important during present and future warmer winters.

agriculture↗

NASA NTRS2016

Temporal Characteristics and Energy Deposition of Pulsating Auroral Patches

We present a careful statistical analysis of pulsating aurora (PA) using all-sky green line (557.7 nm) images obtained at 3.3 Hz. Six well-defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on-time and off-time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term pulsating is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

Humberset, B. K.↗

NASA NTRS2016

Predicting Real-Time Safety of the National Airspace System

To gain the situational awareness necessary for informed decision making regarding avoidance of airspace hazards, each operator must consolidate operations-relevant information from disparate sources and apply extensive domain knowledge to correctly interpret not just the current state of the NAS but forecast its (combined) evolution over the duration of the operation. This time- and workload-intensive process is periodically repeated throughout the operation so that changes can be managed in a timely manner.The imprecision, inaccuracies, inconsistency, and incompleteness of the incoming data further challenges the process. To facilitate informed decision making, this paper presents a model-based framework for the textitautomated real-time monitoring and prediction of possible effects of airspace hazards on the safety of the National Airspace System (NAS). First, hazards to flight are identified and transformed into sms, that is, quantities of interest that could be evaluated based on available data and are predictive of an unsafe event. The sms and associated thresholds that specify when an event transitions from emphsafe to emphunsafe are combined with models of airspace operations and aircraft dynamics. The framework can include any hazard to flight that can be modeled quantitatively. Models can be detailed and complex, or they can be considerably simplifed, as appropriate to the application. Real-time NAS safety monitoring and prediction begins with an estimate of the state of the NAS using the dynamic models. Given the state estimate and a probability distribution of future inputs to the NAS, we can then predict the evolution of the NAS - the future state - and the occurrence of hazards and unsafe events. The entire probability distribution of airspace sms is computed, not just point estimates, without significant assumptions regarding the distribution type andor parameters. We demonstrate our overall approach through a simulated scenario in which we predict the occurrence of some unsafe events and show how these predictions evolve in time as flight operations progress. Predictions accounting for common sources of uncertainty are included and it is shown how the predictions improve in time, become more confident, and change dynamically as new information is made available to the prediction algorithm.

safety↗

NASA NTRS1985

Measurements of light background at large depth in the ocean

The mean intensity of Cerenkov emission from the products of K(40) decay and bioluminescence was measured at depths to 5 km. The intensity of ocean light background is found to depend upon depth and at the 5 km level is equal on averaged to 300 + or - 60 quanta/sq cms into spatial angle of 2 pi sterradian in transparency window. The amplitudes, duration and number of BL flashes were measured at various depths. The intensive flashes due to BL are shown to be observed rather seldom at depths over 4 km.

Bannykh, A. E.↗

NASA NTRS1987

Criteria of interplanetary parameters causing intense magnetic storms (Dst of less than -100 nT)

An analysis of ISEE-3 field and plasma data shows that 10 intense magnetic storms that occurred in 1979 were caused by long-duration, large-amplitude (13-30 nT) and negative (less than -10 nT) IMF Bz events associated with interplanetary duskward-electric fields of greater than 5 mV/m. The results suggest that these criteria may be used as predictors of intense storms. A study of opposite polarity (northward) Bz events with the same criteria shows that their occurrence is similar both in number and in their relationship to interplanetary disturbances. The amplitudes of the storms were not found to vary with shock strengths.

Gonzalez, Walter D.↗

NASA NTRS2012

Optical Frequency Optimization of a High Intensity Laser Power Beaming System Utilizing VMJ Photovoltaic Cells

An effective form of wireless power transmission (WPT) has been developed to enable extended mission durations, increased coverage and added capabilities for both space and terrestrial applications that may benefit from optically delivered electrical energy. The high intensity laser power beaming (HILPB) system enables long range optical 'refueling" of electric platforms such as micro unmanned aerial vehicles (MUAV), airships, robotic exploration missions and spacecraft platforms. To further advance the HILPB technology, the focus of this investigation is to determine the optimal laser wavelength to be used with the HILPB receiver, which utilizes vertical multi-junction (VMJ) photovoltaic cells. Frequency optimization of the laser system is necessary in order to maximize the conversion efficiency at continuous high intensities, and thus increase the delivered power density of the HILPB system. Initial spectral characterizations of the device performed at the NASA Glenn Research Center (GRC) indicate the approximate range of peak optical-to-electrical conversion efficiencies, but these data sets represent transient conditions under lower levels of illumination. Extending these results to high levels of steady state illumination, with attention given to the compatibility of available commercial off-the-shelf semiconductor laser sources and atmospheric transmission constraints is the primary focus of this paper. Experimental hardware results utilizing high power continuous wave (CW) semiconductor lasers at four different operational frequencies near the indicated band gap of the photovoltaic VMJ cells are presented and discussed. In addition, the highest receiver power density achieved to date is demonstrated using a single photovoltaic VMJ cell, which provided an exceptionally high electrical output of 13.6 W/sq cm at an optical-to-electrical conversion efficiency of 24 percent. These results are very promising and scalable, as a potential 1.0 sq m HILPB receiver of similar construction would be able to generate 136 kW of electrical power under similar conditions.

Raible, Daniel E.↗

DOE OSTI2022

Two-XUV-photon double ionization of neon

Two XUV-photon double ionization of Ne, induced by an intense few-pulse attosecond train with a ~ 4 fs envelope duration is investigated experimentally and theoretically. The experiment is performed at ELI-ALPS utilizing the recently constructed 10 Hz gas phase high-order harmonic generation SYLOS GHHG-COMPACT beamline. A total pulse energy up to ~1 {\mu}J generated in Argon in conjunction with high reflectivity optics in the XUV region, allowed the observation of the doubly charged state of Ne induced by 40 eV central XUV photon energies. The interaction of the intense attosecond pulse train with Ne is also theoretically studied via a second-order time dependent perturbation theory equations-of-motion. Further, the results of this work, combined with the feasibility of conducting XUV-pump-XUV-probe experiments, constitute a powerful tool for many potential applications. Those include attosecond pulse metrology as well as time resolved investigations of the dynamics underlying direct and sequential double ionization and their electron correlation effects.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2024

Generation of attosecond gigawatt soft x-ray pulses through coherent Thomson backscattering

Collision between relativistic electron sheets and counterpropagating laser pulses is recognized as a promising way to produce intense attosecond x rays through coherent Thomson backscattering (TBS). In a double-layer scheme, the electrons in an ultrathin solid foil are first pushed out by an intense laser driver and then interact with the laser reflected off a second foil to form a high-density relativistic electron sheet with vanishing transverse momentum. However, the repulsion between these concentrated electrons can increase the thickness of the layer, reducing both its density and subsequently the coherent TBS. Here, we present a systematic study on the evolution of the flying electron layer and find that its resulting thickness is determined by the interplay between the intrinsic space-charge expansion and the velocity compression induced by the drive laser. How the laser driver, the target areal density, the reflector, and the collision laser intensity affect the properties of the produced x rays is explored. Multidimensional particle-in-cell simulations indicate that employing this scheme in the nonlinear regime has the potential to stably produce soft x rays with several gigawatt peak power in hundreds of terawatt ultrafast laser facilities. The pulse duration can be tuned to tens of attoseconds. Here, this compact and intense attosecond x-ray source may have broad applications in attosecond science.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Femtosecond electronic structure response to high intensity XFEL pulses probed by iron X-ray emission spectroscopy

We report the time-resolved femtosecond evolution of the K-shell X-ray emission spectra of iron during high intensity illumination of X-rays in a micron-sized focused hard X-ray free electron laser (XFEL) beam. Detailed pulse length dependent measurements revealed that rapid spectral energy shift and broadening started within the first 10 fs of the X-ray illumination at intensity levels between 10 17 and 10 18 W cm -2 . We attribute these spectral changes to the rapid evolution of high-density photoelectron mediated secondary collisional ionization processes upon the absorption of the incident XFEL radiation. These fast electronic processes, occurring at timescales well within the typical XFEL pulse durations (i.e., tens of fs), set the boundary conditions of the pulse intensity and sample parameters where the widely-accepted ‘probe-before-destroy’ measurement strategy can be adopted for electronic-structure related XFEL experiments.

99 GENERAL AND MISCELLANEOUS↗

NASA NTRS1975

Temporal X-ray astronomy with a pinhole camera

Preliminary results from the Ariel-5 all-sky X-ray monitor are presented, along with sufficient experiment details to define the experiment sensitivity. Periodic modulation of the X-ray emission was investigated from three sources with which specific periods were associated, with the results that the 4.8 hour variation from Cyg X-3 was confirmed, a long-term average 5.6 day variation from Cyg X-1 was discovered, and no detectable 0.787 day modulation of Sco X-1 was observed. Consistency of the long-term Sco X-1 emission with a shot-noise model is discussed, wherein the source behavior is shown to be interpretable as approximately 100 flares per day, each with a duration of several hours. A sudden increase in the Cyg X-1 intensity by almost a factor of three on 22 April 1975 is reported, after 5 months of relative source constancy. The light curve of a bright nova-like transient source in Triangulum is presented, and compared with previously observed transient sources. Preliminary evidence for the existence of X-ray bursts with duration less than 1 hour is offered.

Holt, S. S.↗

NASA NTRS1976

Temporal X-ray astronomy with a pinhole camera

Preliminary results from the Ariel-5 All-Sky X-Ray Monitor are presented, along with sufficient experiment details to define the experiment sensitivity. Periodic modulation of the X-ray emission is investigated from three sources with which specific periods have been associated, with the results that the 4.8 h variation from Cyg X-3 is confirmed, a long-term average 5.6 day variation from Cyg X-1 is discovered, and no detectable 0.787 day modulation of Sco X-1 is observed. Consistency of the long-term Sco X-1 emission with a 'shot-noise' model is discussed, wherein the source behavior is shown to be interpretable as about 100 'flares' per day, each with a duration of several hours. A sudden increase in the Cyg X-1 intensity by almost a factor of three on 22 April 1975 is reported, after 5 months of relative source constancy. The light curve of a bright nova-like transient source in Triangulum is presented, and compared with previously observed transient sources. Preliminary evidence for the existence of X-ray 'bursts' with duration less than 1 h is offered, with the caveat that there is not yet any supporting evidence to guarantee that the effect is truly astronomical.

Holt, S. S.↗

NASA NTRS1971

Tone-burst technique measures high-intensity sound absorption

Tone-burst technique, in which narrow-bandwidth, short-duration sonic pulse is propagated down a standing-wave tube, measures sound absorbing capacity of materials used in jet engine noise abatement. Technique eliminates effects of tube losses and yields normal-incidence absorption coefficient of specimen.

Powell, J. G.↗

NASA NTRS2003

Spatial Analysis of Great Lakes Regional Icing Cloud Liquid Water Content

Abstract Clustering of cloud microphysical conditions, such as liquid water content (LWC) and drop size, can affect the rate and shape of ice accretion and the airworthiness of aircraft. Clustering may also degrade the accuracy of cloud LWC measurements from radars and microwave radiometers being developed by the government for remotely mapping icing conditions ahead of aircraft in flight. This paper evaluates spatial clustering of LWC in icing clouds using measurements collected during NASA research flights in the Great Lakes region. We used graphical and analytical approaches to describe clustering. The analytical approach involves determining the average size of clusters and computing a clustering intensity parameter. We analyzed flight data composed of 1-s-frequency LWC measurements for 12 periods ranging from 17.4 minutes (73 km) to 45.3 minutes (190 km) in duration. Graphically some flight segments showed evidence of consistency with regard to clustering patterns. Cluster intensity varied from 0.06, indicating little clustering, to a high of 2.42. Cluster lengths ranged from 0.1 minutes (0.6 km) to 4.1 minutes (17.3 km). Additional analyses will allow us to determine if clustering climatologies can be developed to characterize cluster conditions by region, time period, or weather condition. Introduction

Ryerson, Charles C.↗