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1

Gravity Wave Seeding of Equatorial Plasma Bubbles  

NASA Technical Reports Server (NTRS)

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Singh, Sardul; Johnson, F. S.; Power, R. A.

1997-01-01

2

Multipoint observations of equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

This paper compares evening sector measurements by the Jicamarca unattended long-term studies of the ionosphere and atmosphere (JULIA) radar, the Ancon scintillation monitor, and plasma density sensors on Defense Meteorological Satellite Program (DMSP) satellites. During more than half of the 110 nights of JULIA operations in 1998 and 1999, backscatter was observed from plumes extending above the layer of bottomside spread F. On 98% of the nights with no plumes, the S4 index measured at Ancon was <0.8. On ˜90% nights with plumes, S4 > 0.8. DMSP F14 crossed the magnetic equator within 7.5° longitude of Ancon near the 2100 local time (LT) meridian on 61 nights. During 32 overpasses, DMSP detected no equatorial plasma bubbles (EPBs), and JULIA detected no plumes. DMSP encountered EPBs on only 9 of the remaining 29 nights when JULIA observed plumes. Two plumes detected by JULIA on 15 April 1999 did not coincide with nearby EPBs crossed by the two satellites on the same evening. We also compared the seasonally averaged percent of nights with S4 ? 0.8 at Ancon with the percent of orbits in which a DMSP satellite detected EPBs. Data were accumulated between May 1994 and the first quarter of 2001. On a global scale at solar minimum, DMSP encountered very few EPBs. In years near solar maximum the two data sets were well correlated. However, there were more nights with S4 ? 0.8 at Ancon than EPB encounters by DMSP satellites. This discrepancy reflects the effects of different sampling intervals and the fact that about a third of the plumes fail to reach the DMSP altitude. Still, a correlation coefficient of 0.88 indicates that EPB detection at 840 km is a good indicator that scintillation activity is occurring near the spacecraft's longitude at the Earth's surface. The data also suggest that bubbles are often generated in bursts rather than at nearly uniform intervals.

Burke, W. J.; Huang, C. Y.; Valladares, C. E.; Machuzak, J. S.; Gentile, L. C.; Sultan, P. J.

2003-05-01

3

Occurrence of equatorial plasma bubbles over Kolhapur  

NASA Astrophysics Data System (ADS)

This paper reports the nightglow observations of OI 630.0 nm emissions, made by using all sky imager operating at low latitude station Kolhapur (16.8°N, 74.2°E and dip lat. 10.6°N) during high sunspot number years of 24th solar cycle. The images are analyzed to study the nocturnal, seasonal and solar activity dependence occurrence of plasma bubbles. We observed EPBs in images regularly during a limited period 19:30 to 02:30 LT and reach maximum probability of occurrence at 22:30 LT. The observation pattern of EPBs shows nearly no occurrence during the month of May and it maximizes during the period October-April. The equinox and solstice seasonal variations in the occurrence of plasma bubbles show nearly equal and large differences, respectively, between years of 2010-11 and 2011-12.

Sharma, A. K.; Nade, D. P.; Nikte, S. S.; Patil, P. T.; Ghodpage, R. N.; Vhatkar, R. S.; Rokade, M. V.; Gurubaran, S.

2014-08-01

4

Season-Longitude Variability of Equatorial Plasma Bubble Occurrence  

Microsoft Academic Search

We compare season-longitude distributions of > 8300 equatorial plasma bubbles (EPBs) observed during the last solar cycle with predictions of two simple models. Both models are based on considerations of parameters controlling the linear growth rate of the generalized Rayleigh -Taylor instability in the context of finite windows of opportunity during the prereversal enhancement periods near suns et. Tsunoda (1985)

W. J. Burke; C. Y. Huang; L. C. Gentile; L. Bauer

5

Guest investigator program study: Physics of equatorial plasma bubbles  

NASA Technical Reports Server (NTRS)

Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. Our research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz, 1976; Ott, 1978; Kelley and Ott, 1978). Our results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study and modeling of SM-D electric field instrument (EFI) measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge-shaped plasma bubbles. The second topic was pursued because the inability to predict the day-to-day occurrence of plasma bubbles indicated inadequate knowledge of the physics of plasma bubbles. An understanding of bubble formation requires an understanding of the roles of the various terms in the linearized growth rate of the collisional Rayleigh-Taylor instability. In our study, we examined electric-field perturbations found in SM-D EFI data and found that the seeding is more likely to be produced in the E region rather than the F region. The results of this investigation are presented in the Appendix of this report and will be submitted for publication in the Journal of Geophysical Research.

Tsunoda, Roland T.

1994-01-01

6

Guest investigator program study: Physics of equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. Our research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz, 1976; Ott, 1978; Kelley and Ott, 1978). Our results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study and modeling of SM-D electric field instrument (EFI) measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge-shaped plasma bubbles. The second topic was pursued because the inability to predict the day-to-day occurrence of plasma bubbles indicated inadequate knowledge of the physics of plasma bubbles. An understanding of bubble formation requires an understanding of the roles of the various terms in the linearized growth rate of the collisional Rayleigh-Taylor instability. In our study, we examined electric-field perturbations found in SM-D EFI data and found that the seeding is more likely to be produced in the E region rather than the F region. The results of this investigation are presented in the Appendix of this report and will be submitted for publication in the Journal of Geophysical Research.

Tsunoda, Roland T.

1994-10-01

7

Correlative study of plasma bubbles, evening equatorial ionization anomaly, and equatorial prereversal E × B drifts at solar maximum  

Microsoft Academic Search

Previous ground observations have revealed a correlation that exists between equatorial plasma bubbles, evening equatorial ionization anomaly (EIA), and prereversal E × B drift velocity using latitudinal arrays of ionospheric sounders, such as in the Indian and American regions. Besides the ground measurements, the space-based observations also provide a convenient way to study the global-scale variations. On the basis of

Guozhu Li; Baiqi Ning; Libo Liu; Biqiang Zhao; Xinan Yue; S.-Y. Su; Sarita Venkatraman

2008-01-01

8

Nonlinear evolution of equatorial spread F. 3. Plasma bubbles generated by structured electric fields  

Microsoft Academic Search

Observations have shown that in some cases equatorial spread F (ESF) irregularities including plasma bubbles are related to temporal and spatial structures of electric fields. It has been conjectured that the electric field structures may be responsible to production of ESF bubbles. We present here numerical results of electric field effects in nonlinear evolution of ESF. In our simulations we

Chao-Song Huang; Michael C. Kelley

1996-01-01

9

Plasma bubbles and irregularities in the equatorial ionosphere  

Microsoft Academic Search

Using the Atmosphere Explorer satellite AE-C, we observe large-scale (10- to >200-km) irregular biteouts of up to three orders of magnitude in the ion concentration N⁠in the nighttime equatorial F region associated with small-scale inhomogeneities in Nâ. Similar phenomena were reported by Hanson and Sanatani but without the more complete plasma diagnostics present on AE. Simultaneous plasma velocity observations

J. P. McClure; W.B. Hanson; J. H. Hoffman

1977-01-01

10

Guest investigator program study: Physics of equatorial plasma bubbles. Final report  

SciTech Connect

Plasma bubbles are large-scale (10 to 100 km) depletions in plasma density found in the night-time equatorial ionosphere. Their formation has been found to entail the upward transport of plasma over hundreds of kilometers in altitude, suggesting that bubbles play significant roles in the physics of many of the diverse and unique features found in the low-latitude ionosphere. In the simplest scenario, plasma bubbles appear first as perturbations in the bottomside F layer, which is linearly unstable to the gravitationally driven Rayleigh-Taylor instability. Once initiated, bubbles develop upward through the peak of the F layer into its topside (sometimes to altitudes in excess of 1000 km), a behavior predicted by the nonlinear form of the same instability. While good general agreement has been found between theory and observations, little is known about the detailed physics associated with plasma bubbles. This research activity centered around two topics: the shape of plasma bubbles and associated electric fields, and the day-to-day variability in the occurrence of plasma bubbles. The first topic was pursued because of a divergence in view regarding the nonlinear physics associated with plasma bubble development. While the development of perturbations in isodensity contours in the bottomside F layer into plasma bubbles is well accepted, some believed bubbles to be cylinder-like closed regions of depleted plasma density that floated upward leaving a turbulent wake behind them (e.g., Woodman and LaHoz; Ott; Kelley and Ott). The authors' results, summarized in a paper submitted to the Journal of Geophysical Research, consisted of incoherent scatter radar measurements that showed unambiguously that the depleted region is wedgelike and not cylinderlike, and a case study of SM-D electric field instrument measurements that showed that the absence of electric-field perturbations outside the plasma-depleted region is a distinct signature of wedge-shaped plasma bubbles.

Tsunoda, R.T.

1994-10-01

11

Height variation of electron temperature associated with equatorial plasma bubbles - some recent rocket observations  

NASA Astrophysics Data System (ADS)

In-situ measurements made from Brazil recently using rocket-borne swept-bias Langmuir Probes show that the electron temperatures in the valley region between the equatorial E and F regions get modified before the onset of plasma bubbles. During one of the post sunset launches made on 18-th December 1995 from the equatorial rocket launching station CLA in Alcântara, Brazil the Langmuir probe measured abnormally large electron temperatures below the F-region just before the onset of plasma bubbles but temperatures became normal soon after the onset of bubbles. Later on 2-nd December 2011 a Brazilian VS-30 single stage rocket was launched from the equatorial rocket launching station CLBI in Natal, Brazil carrying a Langmuir probe operating alternately in swept and constant bias modes to measure both electron temperature and electron density respectively. The ground equipments operated before and during the rocket launch clearly showed the presence of plasma bubbles above the F-region. At the time of launch the bubble activity was at its peak. The electron density and temperature height profiles could be estimated from the LP data up to the rocket apogee altitude of 139km. During the rocket upleg and downleg the valley region showed the presence electron temperatures as high as 2000 degree K while the temperatures expected from the existing models are around 500 degree K. A two stage VS-30/Orion rocket was launched on 8-th December soon after sunset carrying a Langmuir Probe operating alternately in swept and constant bias modes to measure the electron density and electron temperature, mainly in the valley between the E and F regions. At the time of launch ground equipments operated at equatorial stations showed ionospheric conditions favorable for the generation of plasma bubbles. These profiles are compared with model electron density and temperature profiles as well as with electron density and temperature profiles observed under conditions of no plasma bubbles.

Muralikrishna, P.; Batista, I. S.; Domingos, S.; Aquino, M. G.

2013-05-01

12

Nonlinear evolution of equatorial spread F. 3. Plasma bubbles generated by structured electric fields  

NASA Astrophysics Data System (ADS)

Observations have shown that in some cases equatorial spread F (ESF) irregularities including plasma bubbles are related to temporal and spatial structures of electric fields. It has been conjectured that the electric field structures may be responsible to production of ESF bubbles. We present here numerical results of electric field effects in nonlinear evolution of ESF. In our simulations we have modeled electric field structures in both time and space. It is found that the temporal structures, including the prereversal enhancement, of the eastward electric field cause motion of the F layer in the vertical direction, but they cannot produce spatial structures of F region plasma. In contrast, plasma bubbles are produced when spatial structures of electric field are used as input in the simulations. The spatially irregular electric fields initiate plasma perturbations in the bottomside F region, then the perturbations are amplified by the Rayleigh-Taylor instability and evolve into topside plasma bubbles. It is concluded that spatial structures of electric field are needed for seeding of ESF bubbles. It is shown also that electric fields generated by E region gravity waves can result in production of F region bubbles.

Huang, Chao-Song; Kelley, Michael C.

1996-01-01

13

Electron temperature enhancements in nighttime equatorial ionosphere under the occurrence of plasma bubbles  

NASA Astrophysics Data System (ADS)

Simultaneous in-situ measurements of electron density and temperature in the nighttime equatorial region were performed by a rocket experiment launched under solar minimum and geomagnetic quiet conditions from the station of Alcântara (2.24°S; 44.24°W), Brazil, on Dec. 18, 1995, 21:17 LT. These measurements detected during the upleg flight a large overheated area around the base of density profile. The presence of plasma bubbles was revealed during the downleg phase, as well as temperature enhancements detected preferentially at altitudes where plasma depletions are found. It was assumed that the region traversed by the rocket during the downleg was preceded before the bubble's onset by a large overheating as observed during the upleg flight. Analyzing this framework under the light of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), as well as a 2D numerical code that simulate the growth of an instability and the evolution of thermal energy inside a bubble, we found that despite an overheated area in the F-region bottomside can disturb the electron density profile around the altitude interval where such heat is deposited, it seems not have a direct influence over parameters responsible for the bubble onset. Additionally, the phenomenon of the intra-bubble thermal enhancement could be formed due to the convection of hot-electron fluid transported from the overheated region surrounding the base of the F-region to upper altitudes by the underlying mechanism of bubble generation.

de Meneses, F. C.; Klimenko, M. V.; Klimenko, V. V.; Alam Kherani, E.; Muralikrishna, P.; Xu, Jiyao; Hasbi, A. M.

2013-10-01

14

Equatorial plasma bubbles studied using African slant total electron content observations  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubbles (EPBs) are field-aligned depletions of F-region ionospheric plasma density that grow from irregularities caused by the generalized Rayleigh-Taylor instability mechanism in the postsunset equatorial sector. Although they have been studied for some decades, they continue to be an important subject of both experimental and theoretical investigations because of their effects on trans-ionospheric radio communications. In this work, calibrated data of slant total electron content (sTEC) taken every 10 min from EGNOS System Test Bed Brazzaville (Congo), Douala (Cameroon), Lome (Togo) and N'Djamena (Chad), and International GNSS Service Ascension Island, Malindi (Kenya), and Libreville (Gabon), stations are used to detect plasma bubbles in the African equatorial region during the first 6 months of 2004. To identify these irregularities, the trend of every curve of sTEC against time is subtracted from the original data. The size of the EPBs is estimated by measuring its amplitude in the de-trended time variation of sTEC.

Portillo, A.; Herraiz, M.; Radicella, S. M.; Ciraolo, L.

2008-04-01

15

Electric field observations of equatorial bubbles  

NASA Technical Reports Server (NTRS)

Results from the double floating probe experiment performed on the San Marco D satellite are presented, with emphasis on the observation of large incremental changes in the convective electric field vector at the boundary of equatorial plasma bubbles. Attention is given to isolated bubble structures in the upper ionospheric F regions; these observed bubble encounters are divided into two types - type I (live bubbles) and type II (dead bubbles). Type I bubbles show varying degrees of plasma depletion and large upward velocities range up to 1000 km/s. The geometry of these bubbles is such that the spacecraft orbit may cut them where they are tilting either eastward or (more often) westward. Type II bubbles exhibit plasma density depletion but no appreciable upward convection. Both types of events are usually surrounded by a halo of plasma turbulence, which can extend considerably beyond the region of plasma depletion.

Aggson, T. L.; Maynard, N. C.; Hanson, W. B.; Saba, Jack L.

1992-01-01

16

Equatorial spread F and plasma bubbles: Preliminary results from the COPEX campaign  

NASA Astrophysics Data System (ADS)

The Conjugate Point Equatorial Experiment (COPEX) was conducted in Brazil from October 1 to December 10, 2002. The configuration of the experiment was planed in such a way that the equipments should be located in three sites along a magnetic meridian, one at the magnetic equator and the other two at magnetically conjugate points. The magnetic conjugate points should be located such that the conjugate E layers were field line mapped to the F layer peak, or to the bottomside, over the magnetic equator. The three selected locations were Campo Grande (20.5 S, 54.7 W, southern conjugate point); Boa Vista (2.8 N, 60.7 W, northern conjugate point) and Cachimbo (9.5 S, 54.8 W, magnetic equatorial point). Various instruments such as Digital Portable Sounders (DPS-4), optical imagers, GPS receivers for scintillation monitoring and for TEC measurements, magnetometers, HF receivers and a 50 MHz radar were operated during the campaign. The campaign was coordinated by the Aeronomy group at the Brazilian National Institute for Space Research (Instituto Nacional de Pesquisas Espaciais- INPE), in collaboration with the Brazilian Air Force group from CTA (Centro Técnico Aeroespacial) and with international groups from the Center for Atmospheric Research, University of Massachusetts Lowell (Lowell, MA, USA), the Air Force Research Laboratory Space Vehicles Directorate (AFRL/VSBX, Hanscom AFB, MA, USA), and the Japanese group from the Communication Research Laboratory (CRL), Tokyo. The data collected during the campaign are been used to study the equatorial spread F (ESF), a phenomena that produces large turbulent like variations of electron density at F region heights producing large index of refraction variations. ESF occurs in association with the plasma depleted flux tubes, known as plasma bubbles, which develop at the dusk hours into vertically extended formations extending to 1500 km over the magnetic equator and thousands of kilometers ( 25 ) into the low latitude ionosphere on either side. They consist of irregularity structures of scale sizes varying from 10's of centimeters to 100's of kilometers. These affect HF communications, as well as the satellite signals used for the many practical applications in our daily life: point to point communications, satellite to ground communications, navigation systems based on GPS satellites, geodesy and over-the-horizon radars. ESF is initiated by plasma instability processes operating at the F layer bottomside and grows into the topside ionosphere. In this paper we will present some preliminary results of analysis of the multi instrument data sets aiming at a better understanding of the possible causes of the day-to-day variability of the equatorial spread F.

Batista, I.; Abdu, M.; Reinisch, B.; de Paula, E.; Groves, K.

2003-04-01

17

Optical observations of the development of secondary instabilities on the eastern wall of an equatorial plasma bubble  

Microsoft Academic Search

Optical evidence is presented for the growth of a local secondary plasma instability on the eastern wall of an equatorial plasma bubble observed from the Haleakala Volcano, Hawaii (geographic: 20.71 N, 203.83 E; geomagnetic: 21.31 N, 271.45 E). Typically, only the western wall of depletions at tropical latitudes are susceptible to secondary structuring. This event occurs during a minor geomagnetic

J. J. Makela; M. C. Kelley; M. J. Nicolls

2006-01-01

18

Faith in a seed: on the origins of equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

Our faith in the seeds of equatorial plasma irregularities holds that there will generally always be density perturbations sufficient to provide the seeds for irregularity development whenever the Rayleigh-Taylor instability is active. When the duration of the time of the Rayleigh-Taylor instability is short, however, the magnitude of the seed perturbations can make a difference in whether the irregularities have a chance to grow to a strength at which the nonlinear development of plumes occurs. In addition, the character of the resulting irregularities reflects the characteristics of the initial seed density perturbation, e.g., their strength, spacing, and, to some extent, their spatial scales, and it is important to know the seeds to help determine the structure of the developed irregularities. To this end, we describe the climatology of daytime and early-evening density irregularities that can serve as seeds for later development of plumes, as determined from the Planar Langmuir Probe (PLP) plasma density measurements on the C/NOFS (Communication and Navigation Outage Forecast System) satellite mission, presenting their magnitude as a function of altitude, latitude, longitude, local time, season, and phase in the solar cycle (within the C/NOFS observation era). To examine some of the consequences of these density perturbations, they are used as initial conditions for the PBMOD PBMOD (Retterer, 2010a) 3-D irregularity model to follow their potential development into larger-amplitude irregularities, plumes, and radio scintillation. "Though I do not believe that a pla[sma bubble] will spring up where no seed has been, I have great faith in a seed. Convince me that you have a seed there, and I am prepared to expect wonders." - Henry David Thoreau

Retterer, J. M.; Roddy, P.

2014-05-01

19

Equatorial bubbles updrafting at supersonic speeds  

NASA Technical Reports Server (NTRS)

Plasma and electric field observations from two satellite encounters with equatorial plasma bubbles updrafting at velocities of about 2 km/s are presented. These large, upward velocities are consistent with an adaptation of Chandrasekhar's model for the motion of plasma blobs supported against gravity by a magnetic field. Vector magnetic field measurements, available during one of the bubble encounters show a perturbation of about 150 nT, directed radially outward from the earth, near the western wall of deepest plasma depletion. This magnetic variation is too large to be caused by simple shunting of the g x B current along the bubble's edge. Rather, it is Alfvenic in nature, radiating from a generator located near the magnetic equator, in the plasma outside the bubble's leading edge. A heuristic model of a depleted flux tube with constant circular cross section moving upward through a background plasma predicts most of the measurements' qualitative features.

Aggson, Thomas L.; Burke, William J.; Maynard, Nelson C.; Hanson, William B.; Anderson, Philip C.; Slavin, James A.; Hoegy, Walter R.; Saba, Jack L.

1992-01-01

20

Distributions of TEC Fluctuations and Losses of Lock Associated with Equatorial Plasma Bubbles  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubbles (EPBs) are local depletions of the electron density in the ionosphere. Due to field-aligned irregularities (FAIs) with various spatial scales, EPBs affect wide-band radio waves and cause scintillations in GPS navigation system. Strong scintillation can cause a GPS receiver to lose lock on GPS signals because of rapid variations of signal amplitude and phase, and limit the availability of carrier phase measurements. Since the scintillation is caused by Fresnel diffraction, the spatial scale of FAIs that causes the scintillation of GPS signals is about 2-300 m. Therefore, loss of phase lock (LOL) on GPS signals is a reference of hundred-meter-scale FAIs. As EPBs are also associated with fluctuations of the total electron content (TEC), the enhancement of Rate of TEC change index (ROTI) occurs around EPBs. Assuming that the altitude of the ionosphere is about 400 km, the velocity of the pierce point of the GPS radio wave at the ionospheric altitude is approximately 70 m/s around the zenith. Thus, ROTI averaged during 5 minutes is a reference of ten-kilometer-scale fluctuations. In this study, we analyzed LOL and 5-min. ROTI associated with EPBs to examine the spatial and temporal scales of electron density disturbances associated with EPBs. We selected 11 EPBs from 630-nm airglow images obtained by all-sky imager at Sata, Japan, in 2001. LOL and ROTI are obtained from GPS data from GPS Earth Observation Network (GEONET) of Japan, which consists of more than 1000 GPS receivers. As a result, it is shown that both LOL and the enhancement of ROTI are observed in 8 events out of 11 events. The distributions of LOL are approximately consistent with the areas in which the ionospheric electron density is depleted. The enhancements of ROTI are observed in the vicinities of EPBs. The enhancement of ROTI expands especially in the west side of EPBs. After the EPBs pass through, therefore, LOLs are vanished but the enhancements of ROTI last a while. This result shows that the hundred-meter-scale irregularities are distributed within EPBs while the ten-kilometer-scale disturbances are located around EPBs. Such huge EPBs as to be observed in Japan will appear in solar maximum periods. Therefore it is important to prepare against the next solar maximum by examining characteristics of the EPBs. Fortunately, LOL and the enhancement of ROTI are treated as indicators of these huge EPBs since most of the EPBs are associated with them. Examinations of these EPBs must be progressed further.

Nakata, H.; Kikuchi, H.; Tsugawa, T.; Otsuka, Y.; Takano, T.; Shimakura, S.; Shiokawa, K.; Ogawa, T.

2009-12-01

21

Development of intermediate scale structure near the peak of the F region within an equatorial plasma bubble  

NASA Astrophysics Data System (ADS)

observations are used to study the evolution of intermediate scale (~100 m-few kilometers) irregularities through growth of the Rayleigh-Taylor (R-T) instability on the bottom side of the post-sunset equatorial F region during magnetically quiet periods. Amplitude scintillations on a VHF signal from a geostationary satellite, recorded by spaced receivers at an equatorial station, are used to compute as a function of local time: (1) the coherence scale length for spatial variations of intensity in the ground scintillation pattern, which is linked with the spectrum of the intermediate scale irregularities near the peak of the equatorial F region that contribute the most to the observed scintillations; and (2) the "random velocity", which accounts for the de-correlation of the spaced receiver signals. The relationship between the coherence scale length and the random velocity for saturated scintillations at different local times suggests that (1) the random velocity is linked with fluctuations in the drift velocity of the irregularities caused by the perturbation electric fields associated with the R-T instability rather than structural changes in the intermediate scale irregularities, (2) the spectrum of intermediate scale irregularities in the equatorial F peak region tends to be shallowest after the decay of the perturbation electric fields associated with the R-T instability, and (3) evolution of intermediate-scale irregularity spectrum in the equatorial plasma bubble near the equatorial F region peak depends on season and solar flux. These have implications for observation of low-latitude L-band scintillations.

Bhattacharyya, A.; Kakad, B.; Sripathi, S.; Jeeva, K.; Nair, K. U.

2014-04-01

22

Equatorial plasma bubble rise velocities in the Indian sector determined from multistation scintillation observations  

SciTech Connect

The velocity of plasma-bubble rise over the magnetic equator is calculated on the basis of simultaneous measurements of the onset times of postsunset VHF scintillations from the Japanese satellite ETS-2, obtained at a meridian array of four Indian stations during February 1980. The data and calculation results are presented in tables and graphs and discussed in detail. It is found that bubble velocities increase with altitude, varying in the ranges 128-416, 38-327, and 15-200 m/sec at altitudes 450-550, 550-1140, and 1140-1270 km, respectively. These results are shown to be in good agreement with satellite and radar measurements and with F-layer vertical drift velocities. 17 refs.

Dabas, R.S.; Reddy, B.M. (National Physical Laboratory, New Delhi (India))

1990-04-01

23

Middle atmospheric gravity wave signatures and occurrence of equatorial plasma bubble during low solar activity  

NASA Astrophysics Data System (ADS)

A. Taori1, V. Kamalakar2, L. M. Joshi1, S. Sripathi3, A. K. Patra1 and S. V. B. Rao2 1. National Atmospheric Research Laboratory, Gadanki, India. 2. Dept. of Physics, S. V. University, Tirupati, India. 3. Indian Institute of Geomagnetism, Panvel, Navi Mumbai, India. In this investigation, we use simultaneous Rayleigh lidar and VHF radar data to investigate the middle atmospheric wave characteristics during the night when VHF radar exhibit plasma plume structures at ionospheric altitudes during 2007 and 2009 (when solar activity was at its minimum). We present two cases of nearby nights of observations, 17 and 20 February 2007 and 21 and 22 February 2009; with one night exhibiting the occurrence of F-region plasma bubble (EPB) structures in data while other night does not. We note that short period (<2 hr wave periods) were propagating upwards and exhibited large amplitudes at 70-75 km altitudes, on the nights when EPB occurred. Also, the average temporal spacing between the plume structures was found to be comparable to that of the short period gravity wave periods at mesospheric altitudes. We also note signature of similar periodicity in E-region FAI drift velocity, suggesting the occurrence of gravity wave induced E-region electric fields. These observations strongly suggest a role of gravity waves in the observed structures in EPBs. Our investigation also reveal that not only the F-layer height but also the amplitudes of short period (<2 hr wave periods) middle atmospheric waves are important for the generation of EPB.

Taori, Alok

2012-07-01

24

Modeling studies of equatorial plasma fountain and equatorial anomaly  

NASA Astrophysics Data System (ADS)

The importance of diffusion, electrodynamic drift, amd neutral wind on the generation and modulation of the equatorial plasma fountain of the Earth's ionosphere is studied using the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) for the ionosphere above Jicamarca (77 degW) under magnetically quiet (Ap = 4) equinoctial conditions (day 264) at medium solar activity (F10.7 = 145). The study also investigates the effects of the fountain, which include the equatorial anomaly. The F-region vertical E x B drift velocity measured at the equatorial station Jicamarca is used to represent the electrodynamic drift. The neutral wind is obtained from the HWM90 thermospheric wind model. As expected, the F-region electrodynamic drift generates the plasma fountain and the anomaly, which are symmetric with respect to the equator. The neutral wind makes the fountain and the anomaly asymmetric, with larger plasma flow (towards the hemisphere of stronger poleward wind) and stronger anomaly crest occurring in opposite hemispheres. The paper also addresses many important (some new) features which are related to the fountain. The features are: (1) the possibility of existence of an additional layer (called the G-layer) in the equatorial ionosphere, (2) the reverse plasma fountain, (3) the equatorial anomaly in vertical ionospheric electron content (IEC), (4) the presence (in Nmax) and absence (in IEC) of noon bite-out, (5) the occurrence of nighttime increase in ionization, and (6) plasma bubbles and spread-F.

Balan, N.; Bailey, G. J.

25

An analysis of the quiet time day-to-day variability in the formation of postsunset equatorial plasma bubbles in the Southeast Asian region  

NASA Astrophysics Data System (ADS)

Presented is an analysis of the occurrence of postsunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The three year data set shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is ˜1 standard deviation (1?) larger on the days for which EPBs were detected, compared to non-EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux-tube integrated Rayleigh-Taylor (R-T) instability linear growth rate. A SEA reveals that the modeled R-T growth rate is 1? higher on average for EPB days compared to non-EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM's success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F10.7). Geomagnetic activity varies the modeled high-latitude plasma convection and the associated Joule heating that affects the low-latitude F region dynamo, and consequently the equatorial upward plasma drift.

Carter, B. A.; Yizengaw, E.; Retterer, J. M.; Francis, M.; Terkildsen, M.; Marshall, R.; Norman, R.; Zhang, K.

2014-04-01

26

Theory of Rayleigh-Taylor bubbles in the equatorial ionosphere  

Microsoft Academic Search

A theory of rising bubbles (or sharp density depletions) in the equatorial ionosphere is presented. Both ion inertia and ion-neutral collisions are included. In the collision-dominated case the bubble velocity is independent of its size, while in the collisionless case it is proportional to the square root of the bubble size.

Edward Ott

1978-01-01

27

Modeling gravity wave initiation of equatorial bubbles with SAMI3  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory three-dimensional simulation code SAMI3/ESF is used to study the response of the post-sunset ionosphere to gravity waves, including the effect of the vertical wind component of the wave. We show that gravity waves can seed equatorial instabilities if the waves are on magnetic field lines that map to the bottomside of the equatorial F layer. This can occur for gravity waves at altitudes below 200 km, i.e., gravity waves do not need to propagate to high altitudes (above 300 km) to seed ESF bubbles. We also show that the phase relationship of interhemispheric gravity waves can enhance or suppress the triggering of equatorial spread F bubbles. Research supported by NASA and NRL Base Funds.

Huba, J. D.; Krall, J.; Wu, T.; Fritts, D. C.

2013-12-01

28

Gravity wave initiation of equatorial spread F\\/plasma bubble irregularities based on observational data from the SpreadFEx campaign  

Microsoft Academic Search

The data from ground based experiments conducted during the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical model calculations, to investigate the precursor conditions, and especially, the role of gravity waves, in the instability initiation leading to equatorial spread F development. Data from a digisonde and a 30 MHz coherent back-scatter radar operated at an equatorial

M. A. Abdu; E. Alam Kherani; I. S. Batista; E. R. de Paula; D. C. Fritts; J. H. A. Sobral

2009-01-01

29

Model computations of radio wave scintillation caused by equatorial ionospheric bubbles  

Microsoft Academic Search

In situ data measured on board AE satellites and rockets reveal spiky and wedgelike electron density structures inside the equatorial ionospheric bubbles. Two models are constructed to simulate the initial stage and fully developed stage of a bubble. Effects of radio propagation through such bubbles are simulated by solving the parabolic equation numerically. The results show that even though the

A. W. Wernik; C. H. Liu; K. C. Yeh

1980-01-01

30

Near-simultaneous plasma structuring in the midlatitude and equatorial ionosphere during magnetic superstorms  

NASA Astrophysics Data System (ADS)

Near simultaneous formation of ionospheric plasma density structures at middle and equatorial latitudes during the intense magnetic storms of October 29-31, 2003, July 15, 2000, and March 30-31, 2001 is investigated. The evolution of these structures is explored by measuring amplitude scintillation of satellite signals at 250 MHz, determining zonal irregularity drifts and by detecting equatorial plasma bubbles with DMSP satellites. During abrupt decreases of SYM-H (1-minute resolution Dst) that signify the penetration of high latitude electric fields, an impulsive onset of scintillation occurs at Hanscom AFB (HAFB), a sub-auroral location, as well as in the equatorial region where the early evening period corresponds to the time of scintillation onset at midlatitudes. The onset of equatorial scintillation is delayed from that at midlatitudes by about 20 minutes which can be accounted for by considering instantaneous electric field penetration and plasma instability growth time of equatorial irregularities.

Basu, S.; Basu, Su.; Groves, K. M.; MacKenzie, E.; Keskinen, M. J.; Rich, F. J.

2005-04-01

31

Comparing Plasma Bubble occurrence rates between CHAMP and GRACE observations  

Microsoft Academic Search

Based on the multi-year data base of CHAMP Planar Langmuir Probe (PLP) data and GRACE K-Band Ranging (KBR1B) data, typical feature of inospheric irregularities are studied at alti-tudes of CHAMP (400km) and GRACE (500km). The phenomena we are focusing on are the equatorial plasma bubbles (EPBs). Their typical seasonal\\/longitudinal distribution of EPBs occurrence rate often been shown. Here we present

Chao Xiong; Claudia Stolle; Hermann Luehr; S. Y. Ma

2010-01-01

32

The impact of gravity waves rising from convection in the lower atmosphere on the generation and nonlinear evolution of equatorial bubble  

Microsoft Academic Search

The nonlinear evolution of equatorial F-region plasma bubbles under varying ambient ionospheric conditions and gravity wave seeding perturbations in the bottomside F-layer is studied. To do so, the gravity wave propagation from the convective source region in the lower atmosphere to the thermosphere is simulated using a model of gravity wave propagation in a compressible atmosphere. The wind perturbation associated

E. Alam Kherani; M. A. Abdu; E. R. de Paula; D. C. Fritts; J. H. A. Sobral; F. C. de Meneses Jr.

2009-01-01

33

Oscillating plasma bubbles. II. Pulsed experiments  

SciTech Connect

Time-dependent phenomena have been investigated in plasma bubbles which are created by inserting spherical grids into an ambient plasma and letting electrons and ions form a plasma of different parameters than the ambient one. There are no plasma sources inside the bubble. The grid bias controls the particle flux. There are sheaths on both sides of the grid, each of which passes particle flows in both directions. The inner sheath or plasma potential develops self consistently to establish charge neutrality and divergence free charge and mass flows. When the electron supply is restricted, the inner sheath exhibits oscillations near the ion plasma frequency. When all electrons are excluded, a virtual anode forms on the inside sheath, reflects all ions such that the bubble is empty. By pulsing the ambient plasma, the lifetime of the bubble plasma has been measured. In an afterglow, plasma electrons are trapped inside the bubble and the bubble decays as slow as the ambient plasma. Pulsing the grid voltage yields the time scale for filling and emptying the bubble. Probes have been shown to modify the plasma potential. Using pulsed probes, transient ringing on the time scale of ion transit times through the bubble has been observed. The start of sheath oscillations has been investigated. The instability mechanism has been qualitatively explained. The dependence of the oscillation frequency on electrons in the sheath has been clarified.

Stenzel, R. L.; Urrutia, J. M. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States)

2012-08-15

34

Near Synchronous Plasma Structuring in the Middle and Equatorial Ionosphere During Intense Magnetic Storms  

NASA Astrophysics Data System (ADS)

Near simultaneous formation of plasma density structures in the ionosphere at middle and equatorial latitudes during intense magnetic storms is investigated. The magnetic storms of July 15, 2000, March 30-31, 2001 and October 29 - 31, 2003 are studied. These storms are characterized by minimum SYM-H (1-min Dst) values of -350 nT, -420 nT and -400 nT respectively. The evolution of plasma density structures in the midlatitude and the equatorial ionosphere is investigated by measuring amplitude scintillation of satellite signals at 250 MHz and L-band, phase fluctuations of GPS signals and by detecting equatorial plasma bubbles with DMSP satellites. It is shown that at the time of the fast rate of change of SYM-H, an impulsive onset of scintillation occurs at Hanscom AFB, a sub-auroral station, and the associated plasma structures in the equatorial ionosphere are observed in the specific longitude sector for which the early evening period corresponds to the time of rapid SYM-H variation, as shown earlier for moderate storms (Basu et al., JGR, 2001). From continuous measurements of scintillation of signals from geostationary satellites and phase fluctuations of GPS signals, it is found that the onset of equatorial plasma structures is delayed by about 20 minutes from the onset of midlatitude scintillation. This delay is discussed in the framework of instantaneous storm-time electric field penetration from high latitudes to middle to equatorial latitudes and the instability growth time of sub-km scale irregularities. It is also shown that during intense storms, the equatorward neutral wind can cause the post-sunset plasma drift in the equatorial region to be as large as 200 m/sec in the westward direction in contrast to the quiet time drift of 100 m/sec in the eastward direction.

Basu, S.; Groves, K. M.; MacKenzie, E.; Keskinen, M. J.; Rich, F.

2004-12-01

35

Plasma turbulence in the equatorial ionospheric F region  

NASA Astrophysics Data System (ADS)

Equatorial spread F is a spectacular phenomenon in which the equatorial region ionosphere is reshaped after sunset. The plasma instabilities responsible for equatorial spread F are fascinating since they occur on time scales ranging from seconds to hours and length scales from centimeters to tens of kilometers. The plasma irregularities that occur in the F region also influence the performance and reliability of space borne and ground based electronic systems and may cause the disruption of satellite operations, communications, navigation, and electrical power distribution grids, leading to potentially broad economic losses. The ionospheric model equations that describe these plasma instabilities display different dynamical behavior based on the value of the ion-neutral collision frequency. The transition occurs at the so-called inertial regime of the ionosphere, where the model equations are similar to the Navier Stokes equations except applied to inhomogeneous fluids. A general analytic solution does not exist for these nonlinear equations; however, a numerical model is developed by maintaining charge neutrality in the vicinity of a circular bubble rising from the collisional to the inertial regime. Using this model, we are able to determine the location of the inertial regime as a function of local time, longitude, season, and solar cycle. The model results determine that the regime occurs generally from about 2000 and 2100 local time and 500-900 km apex height. Also, the model predicts that solar minimum periods are generally more conducive for inertial effects than solar maximum periods. Time series analysis performed on Dynamics Explorer II ion density data show that a turbulent cascade form in the inertial regime predicted by the model. Intermediate scale density power spectra all obey k-5/3 spectra scaling when measured in altitude and local time windows predicted by our model as failing within the inertial regime. Meanwhile, density power spectra for data lying outside the inertial regime take on a range of power laws between k-0.75 and k-2.2 . Applying a wavelet transform, we are able to show that large depletions are necessary for inertial regime flows to exist.

McDaniel, Rickey Dale

36

Investigation of the role of gravity waves in the generation of equatorial bubbles  

NASA Technical Reports Server (NTRS)

The following areas of interest in this progress report are: (1) the continuation of software development in the examination of F-region gravity-wave power using in-situ data from the Atmosphere Explorer (AE-E); (2) the inquiry into the use of the San Marco data for the study of the initiation and growth of bubbles, particularly when the satellite passes through the early evening hours at relatively high altitudes, and the development of bubbles using not only the San Marco data but includes the use of airglow observations made in Hawaii; and (3) the promising development in the observation of distinct well formed waves at about 400 km altitude in the equatorial region. These waves look very much like waves seen over the polar cap that are attributed to internal gravity waves in the neutral atmosphere driving ionization up and down the magnetic field lines. These equatorial waves show no modulation of the total ion concentration.

Johnson, Francis S.; Coley, William R.

1995-01-01

37

Radio-tomographic images of postmidnight equatorial plasma depletions  

NASA Astrophysics Data System (ADS)

the first time, equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radiotomography. High-resolution (~10 km) reconstructions of electron density were derived from total electron content (TEC) measurements provided by a receiver array in Peru. TEC data were obtained from VHF/UHF signals transmitted by the Coherent Electromagnetic Radio Tomography (CERTO) beacon on the C/NOFS satellite. EPDs generated premidnight were observed near dawn. On one night, the bubble densities were highly reduced, 100-1000 km wide, and embedded within a layerlike ionosphere. Three nights later, the EPDs exhibited similar features but were embedded in a locally uplifted ionosphere. The C/NOFS in situ instruments detected a dawn depletion where the reconstruction showed lifted EPDs, implying that the postmidnight electric fields raised sections of ionosphere to altitudes where embedded/reactivated fossil EPDs were detected as dawn depletions. Satellites flying under domelike distortions of the ionosphere may observe these distortions as broad plasma decreases (BPDs).

Hei, Matthew A.; Bernhardt, Paul A.; Siefring, Carl L.; Wilkens, Matthew R.; Huba, Joseph D.; Krall, Jonathan F.; Valladares, Cesar E.; Heelis, Roderick A.; Hairston, Marc R.; Coley, W. Robin; Chau, Jorge L.; De La Jara, Cesar

2014-01-01

38

Tomographic imaging and characterization of ionospheric equatorial plasma irregularities with the Global Ultraviolet Imager  

NASA Astrophysics Data System (ADS)

This dissertation develops a technique for reconstructing multidimensional images of the electron density of the Earth's ionosphere using spectroscopic measurements obtained from the Global Ultraviolet Imager (GUVI). This work combines a novel image processing approach, models of GUVI observations as tomographic reconstruction problems, and new studies of equatorial plasma irregularities and the global F-region ionosphere. The image processing component of the research involves the development of a computationally efficient, edge-preserving regularization technique incorporating projection on convex sets (POCS) in order to solve the limited-angle tomographic image reconstruction problem. The algebraic reconstruction technique was specifically tailored to reconstruct the shapes of plasma irregularities while also recovering the altitude and longitude profile of the background ionosphere, all using data with a low signal-to-noise ratio. GUVI observation geometry is discretely modeled and a linear algebraic relationship is derived between GUVI brightness measurements and ionospheric electron density values. The specific formulation of the problem varies to accommodate the physics of different latitude regions of the ionosphere in order to allow the three-dimensional observation geometry to be cast as a two-dimensional limited-angle tomography problem. The experimental aspect explores the equatorial plasma bubble imaging capabilities of this technique and its scientific impact. Retrievals of altitude and longitude profiles allow for characterization of plasma bubbles based on their structure and depth of depletion. This information can then be used in coordinated studies of plasma bubbles with groundbased imaging systems. These coordinated studies both serve to validate the reconstructed images and to provide complementary information for a more complete understanding of plasma bubble events.

Comberiate, Joseph Michael

39

Equatorial F-Region plasma depletion drifts: latitudinal and seasonal variations  

NASA Astrophysics Data System (ADS)

The equatorial ionospheric irregularities have been observed, in the past few years, by different techniques (e.g. ground-based radar, digisonde, GPS, optical instruments and in situ satellite and rocket instrumentation) and its time evolution and propagation characteristics can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. At present, one of the most powerful optical techniques to study the large-scale ionospheric irregularities is the all-sky imaging photometer system, which normally measures the strong F-region nightglow 630 nm emission from atomic oxygen. The monochromatic OI 630 nm emission images usually show quasi north-south magnetic field aligned intensity depletion bands, which are the bottomside optical signatures of large-scale F-region plasma irregularities (also called plasma bubbles). The zonal drift velocities of the plasma bubbles can be inferred from the space-time displacement of the dark structures (low intensity regions) seen on the images. In this study, images obtained with an all-sky imaging photometer, using the OI 630 nm nightglow emission, from Cachoeira Paulista (22.7° S, 45° W, 15.8° S dip latitude), Brazil, have been used to determine the nocturnal monthly and latitudinal variation characteristics of the zonal plasma bubble drift velocities in the low latitude (16.7°S to 28.7°S) region. The east and west walls of the plasma bubble show a different evolution with time. The method used here is based on the western wall of the bubble, which presents a more stable behavior. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-90 model to investigate the thermosphere-ionosphere coupling. Salient features from this study are presented and discussed.

Fagundes, P. R.; Pimenta, A. A.; Sahai, Y.; Bittencourt, J. A.; Abalde, J. R.

2003-04-01

40

Vortex bubble formation in pair plasmas.  

PubMed

It is shown that delocalized vortex solitons in relativistic pair plasmas with small temperature asymmetries can be unstable for intermediate intensities of the background electromagnetic field. Instability leads to the generation of ever-expanding cavitating bubbles in which the electromagnetic fields are zero. The existence of such electromagnetic bubbles is demonstrated by qualitative arguments based on a hydrodynamic analogy, and by numerical solutions of the appropriate nonlinear Schrödinger equation with a saturating nonlinearity. PMID:23944600

Berezhiani, V I; Shatashvili, N L; Mahajan, S M; Aleksi?, B N

2013-07-01

41

Plasma bubbles in the topside ionosphere: solar activity dependence  

NASA Astrophysics Data System (ADS)

The present study deals with the He+ density depletions, observed during a high solar activity at the topside ionosphere heights. There are the indications that plasma bubbles, produced by Rayleigh-Taylor instability at the bottomside of ionosphere, could rise up to the topside ionosphere and plasmasphere. Maryama and Matuura (1984), using ISS-b spacecraft data (high solar activity - F10.7=200, 1978-80), have seen the plasma bubbles in Ne density over equator at 1100 km heights in 46 cases in 1700 passes (3%). However, there is distinctly another picture in He+ density depletions according to ISS-b spacecraft data for the same period. They occur in the topside ionosphere over low- and middle- latitudinal regions (L=1.3-3) in 11% of the cases (Karpachev, Sidorova, 2002; Sidorova, 2004, 2007). The detailed study of the He+ density depletion characteristics was done. It was noted that the He+ density depletions are mostly seen in the evening-night sector (18-05 LT) from October till May. It was like to the peculiarities of the Equatorial Spread-F (ESF), usually associated with plasma bubble. The monthly mean He+ density depletion statistics, plotted in LT versus month, was compared with the similar plots for ESF statistics, obtained by Abdu and colleagues (2000) from ground-based ionograms over Brazilian regions for the period of the same solar activity. It was revealed good enough correlation (R=0.67). Also depletion values as function of LT were compared with the vertical plasma drift velocity variations, obtained for the same period from AE-E spacecraft and IS radar (Jicamarca) data. Striking similarity in development dynamics was revealed for the different seasons. It was concluded, that the He+ density depletions should be considered as originating from equatorial plasma bubbles. It seems the plasma bubbles, reaching the topside ionosphere altitudes, are mostly seen not in electron density but in He+ density as depletions. According to publications, many cases of the He+ density depletions were revealed on OGO-4, OGO-6, Oreol-1 and DE-2 spacecraft data. The most of these cases occur during high and maximal solar activity periods, when the He+ density layer is very well developed at the topside ionosphere heights (Wilford et al., 2003). Using the model of the plasma bubble formation as suggested by Woodman and La Hoz (1976), it was shown that the topside plasma bubbles, seen in He+ density, are rather typical phenomena for the topside ionosphere for high solar activity epoch. REFERENCE Abdu, M.A., J.H.A. Sobral, I.S. Batista, Equatorial spread F statistics in the american longitudes: some problems relevant to ESF description in the IRI scheme, Adv. Space Res., vol. 25, pp. 113-124, 2000. Karpachev, A.T. and L.N. Sidorova, Occurrence probability of the light ion trough and subtrough in ??+ density on season and local time, Adv. Space Res., vol. 29, pp. 999-1008, 2002. Maryama, T. and N. Matuura, Longitudinal variability of annual changes in activity of equatorial spread F and plasma bubbles, J. Geophys. Res., 89(A12), 10,903-10,912, 1984. Sidorova, L.N., He+ density topside modeling based on ISS-b satellite data, Adv. Space Res., vol. 33, pp. 850-854, 2004. Sidorova, L.N., Plasma bubble phenomenon in the topside ionosphere, Adv. Space Res., Special issue (COSPAR), doi: 10.1016/j.asr.2007.03.067, 2007. Wilford, C.R., R.J. Moffett, J.M. Rees, G.J. Bailey, Comparison of the He+ layer observed over Arecibo during solar maximum and solar minimum with CTIP model results, J. Geophys. Res., vol. 108, A12, pp. 1452, doi:10.1029/2003JA009940, 2003. Woodman, R.F. and C. La Hoz, Radar observations of F-region equatorial irregularities, J. Geophys. Res., vol. 81, pp. 5447-5466, 1976.

Sidorova, L.

2009-04-01

42

Inertially confined plasma in an imploding bubble  

NASA Astrophysics Data System (ADS)

Models of spherical supersonic bubble implosion in cavitating liquids predict that it could generate temperatures and densities sufficient to drive thermonuclear fusion. Convincing evidence for fusion is yet to be shown, but the transient conditions generated by acoustic cavitation are certainly extreme. There is, however, a remarkable lack of observable data on the conditions created during bubble collapse. Only recently has strong evidence of plasma formation been obtained. Here we determine the plasma electron density, ion-broadening parameter and degree of ionization during single-bubble sonoluminescence as a function of acoustic driving pressure. We find that the electron density can be controlled over four orders of magnitude and exceed 1021cm-3-comparable to the densities produced in laser-driven fusion experiments-with effective plasma temperatures ranging from 7,000 to more than 16,000K. At the highest acoustic driving force, we find that neutral Ar emission lines no longer provide an accurate measure of the conditions in the plasma. By accounting for the temporal profile of the sonoluminescence pulse and the potential optical opacity of the plasma, our results suggest that the ultimate conditions generated inside a collapsing bubble may far exceed those determined from emission from the transparent outer region of the light-emitting volume.

Flannigan, David J.; Suslick, Kenneth S.

2010-08-01

43

Estimation of the initial amplitude of perturbation and its use in numerical simulation of plasma bubbles  

NASA Astrophysics Data System (ADS)

This work describes an experimental method for the calculation of the initial amplitude of plasma bubble seed perturbation in the bottomside F layer from ionograms. The observations show that after sunset the ionograms exhibit irregularities in the base of the F trace. In the context of the plasma depletion in the bottomside F-layer, the irregularities in ionograms can be seen like isodensity contour in evolution (in space and time). The initial amplitudes, calculated using the methodology, were used to simulate plasma bubbles through the use of flux corrected transport method with Boris-Book's flux limiter for the spatial integration and a predictor-corrector method for the direct time integration of the continuity equation of {O}^{+} and the SOR method for electric potential equation. Generalized Rayleigh-Taylor instability plays a predominant role in the evolution of long-wavelength irregularities in the equatorial ionosphere. This instability is influenced by the vertical density gradient at bottom of the F layer, and the magnitude and shape of the density perturbation that seeds the instability. The code is tested with different enhanced evening eastward electric fields to study the influences of pre-reversal enhancement in the zonal electric field on plasma bubble formation and development. The values of the zonal electric fields are based on Digisonde observations over the dip equatorial station of Cachimbo (9.5° S, 54.8° W) during the 2002 COPEX (Conjugate Point Equatorial Experiment) campaign in Brazil.

Batista, Inez S.; Carrasco, Alexander J.; Abdu, Mangalathayil A.

2012-07-01

44

Longitudinal and seasonal dependence of nighttime equatorial plasma density irregularities during solar minimum detected on the C\\/NOFS satellite  

Microsoft Academic Search

This letter investigates equatorial ionospheric plasma irregularitiesPresents longitudinal\\/seasonal dependence of equatorial plasma irregularitiesGoal: to help understand ionospheric irregularities in predicting scintillation

E. Dao; M. C. Kelley; P. Roddy; J. Retterer; J. O. Ballenthin; O. de La Beaujardiere; Y.-J. Su

2011-01-01

45

Equatorial ionospheric vertical plasma drift model over the Brazilian region  

Microsoft Academic Search

Comparison between equatorial inospheric F region vertical plasma drift from satellite measurements (Fejer et al., 1995), for the Brazilian longitude sector, and the drifts derived from ionosonde measurements around sunset shows significant differences on the prereversal peak behavior during solstices of high solar activity periods. Using ionosonde measurements around sunset and satellite measurements at other local times, we constructed an

I. S. Batista; R. T. de Medeiros; M. A. Abdu; J. R. de Souza; G. J. Bailey; E. R. de Paula

1996-01-01

46

Plasma wave excitation on meteor trails in the equatorial electrojet  

Microsoft Academic Search

The unusual properties of meteor echoes recently observed at Jicamarca (Chapin and Kudeki, 1994) are attributed to the growth and propagation of plasma irregularities along meteor trails deposited within the equatorial electrojet. It is suggested that trails at electrojet heights must carry intense discharge currents that excite two-stream and\\/or gradient drift instabilities for irregularity growth. The direction of electron motion

Elaine Chapin; Erhan Kudeki

1994-01-01

47

Quiet-Time Variability of Equatorial Nighttime Plasma Irregularities (Invited)  

NASA Astrophysics Data System (ADS)

Equatorial spread F and scintillations constitute one the most dynamic processes in the Earth's upper atmosphere. The plasma irregularities responsible for equatorial spread F and scintillations cover a very broad range of spatial and temporal scales. Over the last several decades extensive experimental and modeling studies have provided detailed information on the morphology and generation mechanisms of these irregularities. This includes their variation with altitude, season, longitude and solar flux, and dependence on plasma drifts and thermospheric neutral winds, atmospheric tides and gravity waves, and travelling ionospheric disturbances. On the other hand, relatively little progress has been made in determining the dominant processes responsible for the complex variability of these irregularities on time scales shorter than a month. In this presentation, we first briefly review the main physical processes responsible for the generation of equatorial plasma irregularities during geomagnetically quiet times. Then, we use ground-based observations and results from numerical models to discuss the possible roles of different processes on the short-term variability of equatorial spread F and scintillations. Finally, we suggest new experimental and modeling efforts for improved understanding of low latitude nighttime irregularities.

Fejer, B. G.

2013-12-01

48

The Ionospheric Bubble Index deduced from magnetic field and plasma observations onboard Swarm  

NASA Astrophysics Data System (ADS)

In the post-sunset tropical ionospheric F-region plasma density often exhibits depletions, which are usually called equatorial plasma bubbles (EPBs). In this paper we give an overview of the Swarm Level 2 Ionospheric Bubble Index (IBI), which is a standard scientific data of the Swarm mission. This product called L2-IBI is generated from magnetic field and plasma observations onboard Swarm, and gives information as to whether a Swarm magnetic field observation is affected by EPBs. We validate the performance of the L2-IBI product by using magnetic field and plasma measurements from the CHAMP satellite, which provided observations similar to those of the Swarm. The L2-IBI product is of interest not only for ionospheric studies, but also for geomagnetic field modeling; modelers can de-select magnetic data which are affected by EPBs or other unphysical artifacts.

Park, J.; Noja, M.; Stolle, C.; Lühr, H.

2013-11-01

49

Characterization of equatorial plasma depletions detected from derived GPS data in South America  

NASA Astrophysics Data System (ADS)

The equatorial plasma bubbles (EPBs) have been studied using slant total electron content (sTEC) derived from GPS data. The sTEC has been calculated from data measured at 15 International GNSS Service (IGS) stations located from 90°W to 30°W, covering the ionospheric equatorial anomaly at the American sector, for the years 2000, 2001, 2004, 2005 and 2008. The Ionospheric Bubbles Seeker (IBS) application has been used to detect and characterize the sTEC depletions associated to the EPBs. This technique bases its analysis on the time-variation of the sTEC and the population variance of this time-variation. The default configuration has been used and an EPB has been considered when a sTEC depletion was greater than 5 TEC units (TECu). The hourly occurrence shows the well-known maximum number of depletions after the post-sunset. The monthly occurrence of the EPBs is also analyzed and compared with previous studies. The International Reference Ionosphere model (IRI) has been used to calculate the equatorial vertical drift (EVD) and the peak densities of the E- and F-layers (NmE and NmF2, respectively). The EVD variation has been compared with the seasonal variation of the EPB. A discussion between the yearly mean occurrence EPBs rate and the solar activity is included. The variation of the yearly mean depth and duration of the sTEC depletions with the solar activity conditions and its relation with the ionospheric characteristics given by the IRI model has been also studied.

Magdaleno, S.; Herraiz, M.; de La Morena, B. A.

2012-01-01

50

Scintillations, plasma drifts, and neutral winds in the equatorial ionosphere after sunset  

Microsoft Academic Search

An equatorial campaign was conducted during September 25 to October 7, 1994, to investigate the neutral and plasma dynamics in the equatorial ionosphere after sunset in relation to the day-to-day variability of the occurrence of equatorial spread F (ESF). The campaign was organized under the auspices of National Science Foundation's Multi-Instrumented Studies of the Equatorial Thermosphere Aeronomy program (MISETA), which

S. Basu; E. Kudeki; C. E. Valladares; E. J. Weber; H. P. Zengingonul; S. Bhattacharyya; R. Sheehan; M. A. Biondi; H. Kuenzler; J. Espinoza

1996-01-01

51

Features of highly structured equatorial plasma irregularities deduced from CHAMP observations  

NASA Astrophysics Data System (ADS)

In this study five years of CHAMP (Challenging Mini-satellite Payload) fluxgate magnetometer (FGM) data is used to investigate the characteristics of Equatorial Plasma Bubbles (EPBs). We filtered the FGM data by using band-passes with four different cut-off periods to get the EPBs with different maximum spatial scale sizes in the meridional plane ranging from 76-608 km. Associated with the EPB observations at about 400 km, the typical altitude of CHAMP during the year 2000-2005, we also investigate the post-sunset equatorial vertical plasma drift data from ROCSAT-1 (Republic of China Satellite 1). Since the height of the F-layer is highly correlated with the vertical plasma drift and solar flux, we sorted the ROCSAT-1 data into different groups by F10.7. From the integrated vertical drift we have estimated the post-sunset uplift of the ionosphere. By comparing the properties of EPB occurrence for different scale sizes with the global distribution of plasma vertical uplift, we have found that EPBs reaching higher altitudes are more structured than those which are sampled by CHAMP near the top side of the depleted fluxtube. Such a result is in accord with 3-D model simulations (Aveiro and Hysell, 2010). Small-scale EPB structures are observed by CHAMP when the irregularities reach apex heights of 800 km and more. Such events are encountered primarily in the Brazilian sector during the months around November, when the post-sunset vertical plasma drift is high.

Xiong, C.; Lühr, H.; Ma, S. Y.; Stolle, C.; Fejer, B. G.

2012-08-01

52

Space Weather in the Equatorial Ionosphere  

Microsoft Academic Search

The `scintillations' observed on signals received in the equatorial region from GPS satellites are due to plasma instabilities in the F region of the ionosphere, also detected as spread F. These instabilities give rise to depletions of ionisation or `bubbles'. The occurrence of these events and their relation to the equatorial electrojet are reviewed. Possibilities of short-term forecasting are examined

R. J. Stening

2003-01-01

53

Phenomenological theory of laser-plasma interaction in ``bubble'' regime  

Microsoft Academic Search

The electron trapping in the ``bubble'' regime of laser-plasma interaction as proposed by Pukhov and Meyer-ter-Vehn [A. Pukhov and J. Meyer-ter-Vehn, Appl. Phys. B 74, 355 (2002)] is studied. In this regime the laser pulse generates a solitary plasma electron cavity: the bubble. It is free from the cold plasma electrons and runs with nearly light velocity. The present work

I. Kostyukov; A. Pukhov; S. Kiselev

2004-01-01

54

Mathematical modeling of plasma drifts over equatorial low latitude regions  

NASA Astrophysics Data System (ADS)

This paper presents a mathematical model to simulate ionospheric plasma drifts at equatorial low latitude regions by coupling of E- and F-regions. The governing non-linear differential equations (of elliptic and parabolic nature) are solved numerically through finite-difference schemes and obtained neutral winds and electric fields. The temperature and electron density profiles are generated utilizing MSIS-86 atmospheric model. The continuity equation is employed to obtain night-time E-region density profile using measured ionograms at Trivandrum (India). The computed vertical and zonal plasma drifts are comparable with measured Jacamarca plasma drifts with little variations during noon and evening times. The plasma drifts at Trivandrum (8.5° N, 76.5° E, dip 0.5° N) are compared with those of Jicamarca (12° S, 76.9° W, dip 2° N). Neutral wind simulations of present model agree well with those of horizontal wind model (HWM-93). The post-sunset enhancement and its reversal are also discussed.

Sundaresan, S.; Nageswara Rao, B.

2010-09-01

55

Plasma core at the center of a sonoluminescing bubble  

NASA Astrophysics Data System (ADS)

Considering high temperature and pressure during single bubble sonoluminescence collapse, a hot plasma core is generated at the center of the bubble. In this paper a statistical mechanics approach is used to calculate the core pressure and temperature. A hydrochemical model alongside a plasma core is used to study the bubble dynamics in two host liquids of water and sulfuric acid 85 wt % containing Ar atoms. Calculation shows that the extreme pressure and temperature in the plasma core are mainly due to the interaction of the ionized Ar atoms and electrons, which is one step forward to sonofusion. The thermal bremsstrahlung mechanism of radiation is used to analyze the emitted optical energy per flash of the bubble core.

Bemani, F.; Sadighi-Bonabi, R.

2013-01-01

56

Plasma core at the center of a sonoluminescing bubble.  

PubMed

Considering high temperature and pressure during single bubble sonoluminescence collapse, a hot plasma core is generated at the center of the bubble. In this paper a statistical mechanics approach is used to calculate the core pressure and temperature. A hydrochemical model alongside a plasma core is used to study the bubble dynamics in two host liquids of water and sulfuric acid 85 wt % containing Ar atoms. Calculation shows that the extreme pressure and temperature in the plasma core are mainly due to the interaction of the ionized Ar atoms and electrons, which is one step forward to sonofusion. The thermal bremsstrahlung mechanism of radiation is used to analyze the emitted optical energy per flash of the bubble core. PMID:23410423

Bemani, F; Sadighi-Bonabi, R

2013-01-01

57

Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging  

NASA Astrophysics Data System (ADS)

Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions.

Lynn, K. J. W.; Otsuka, Y.; Shiokawa, K.

2011-12-01

58

Ionospheric plasma bubble zonal drift over the tropical region: a study using OI 630 nm emission all-sky images  

NASA Astrophysics Data System (ADS)

With the advances in all-sky imaging technology for nightglow emission studies, the F-region OI 630 nm emission has become an important tool for ionospheric/ thermospheric coupling studies. At tropical regions, the all-sky imaging observations of the OI 630 nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale Fregion plasma- irregularities (plasma bubbles). By observing the motion of the intensity depleted bands it is possible to infer the ionospheric plasma bubble zonal velocity. All-sky images from São João do Cariri (7.4°S, 36.5°W), and Cachoeira Paulista (22.7°S, 45°W), Brazil, between December 1999 and February 2000 (summer in the southern hemisphere) are analysed in order to investigate the nocturnal and latitudinal behavior of the ionospheric plasma bubble zonal drifts. The data set included 16 nights from São João do Cariri (equatorial region) and 24 nights from Cachoeira Paulista (low latitude). An interesting characteristic observed is significant latitudinal variations in the ionospheric plasma bubble zonal drifts in the tropical region between 20:00-22:00 local time. The averaged result of the latitudinal analyses has revealed two peaks in the ionospheric plasma bubble zonal drifts. One peak is located near the magnetic equator (~150 m/s), occurring between 21:00 and 22:00 LT. Another peak in the ionospheric plasma bubble zonal drifts is located at approximately 18° S latitude (~140 m/s), occurring between 20:00 and 22:00 LT. The valley in the latitudinal variations is located approximately near 10°S (~120 m/s) and this reduction in the ionospheric plasma bubble zonal drift is attributed to a reduction in the zonal neutral wind. A comparison of the observed latitudinal variations in the ionospheric plasma bubble zonal drifts with the zonal winds obtained from the HWM-90 model reveals a good agreement. We find that the increase in electron density within the Equatorial Anomaly was sufficient to account for the observed reduction in the zonal winds. The observed development and motion of the nighttime F-region irregularities in the tropical region are presented and discuss ed in this work.

Pimenta, A.; Bittencourt, J.; Fagundes, P.; Sahai, Y.; Buriti, R.; Takahashi, H.; Taylor, M.

59

Equatorial plasma fountain and its effects: Possibility of an additional layer  

Microsoft Academic Search

The importance of diffusion, perpendicular electrodynamic drift, and neutral wind on the generation and modulation of the equatorial plasma fountain of the Earth's ionosphere is studied using the Sheffield University plasmasphere-ionosphere model for the ionosphere above Jicamarca under magnetically quiet equinoctial conditions at medium solar activity. The effects of the fountain, which include the equatorial anomaly, are also investigated. As

N. Balan

1995-01-01

60

Plasma Driven Implosions of a Bubble-Liner  

Microsoft Academic Search

Thin bubbles (? < 1 ?m) are imploded by a coaxial snowplough. The current sheet remains separated from the dense part of the bubble-liner, the latter compressing a deuterium plasma to ion densities > 1020 ions\\/cm3. Cylindrical and quasi-spherical implosions are obtained. Results of Schlieren and soft X-ray photography are reported. The application of the spherical implosions to the generation

A. Bortolotti; J. G. Linhart; J. Krava´rik

1994-01-01

61

Oscillating plasma bubbles. IV. Grids, geometry, and gradients  

SciTech Connect

Plasma bubbles are created in an ambient plasma. The bubble is formed inside a cavity bounded by a negatively biased grid. Ions are injected through the grid and neutralized by electrons from either the background plasma or an internal electron emitter. The external electron supply is controlled by the grid bias relative to the external plasma potential. When the electron flux is restricted to the ion flux, the sheath of the bubble becomes unstable and causes the plasma potential to oscillate near the ion plasma frequency. The exact frequency depends on the net space charge density in the bubble sheath. The frequency increases with density and grid voltage, provided the grid forms a parallel equipotential surface. The present investigation shows that when the Debye length becomes smaller than the grid openings the electron flux cannot be controlled by the grid voltage. The frequency dependence on grid voltage and density is modified creating frequency and amplitude jumps. Low frequency sheath oscillations modulate the high frequency normal oscillations. Harmonics and subharmonics are excited by electrons in an ion-rich sheath. When the plasma parameters vary over the bubble surface, the sheath may oscillate at different frequencies. A cavity with two isolated grids has been used to investigate anisotropies of the energetic electron flux in a discharge plasma. The frequency dependence on grid voltage is entirely different when the grid controls the energetic electrons or the bulk electrons. These observations are important to several fields of basic plasma physics, such as sheaths, sheath instabilities, diagnostic probes, current, and space charge neutralization of ion beams.

Stenzel, R. L. [Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547 (United States); Urrutia, J. M. [Urrutia Scientific, Van Nuys, California 91406 (United States)

2012-08-15

62

Ionospheric plasma bubble zonal drifts over the tropical region: a study using OI 630nm emission all-sky images  

NASA Astrophysics Data System (ADS)

In tropical regions, all-sky imaging observations of the OI 630nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large-scale F-region plasma irregularities (plasma bubbles). By observing the west-east motion of the intensity depleted bands it is possible to infer the ionospheric plasma bubble zonal velocity. All-sky images from Sa~o Joa~o do Cariri (7.4°S, 36.5°W) and from Cachoeira Paulista (22.7°S, 45.0°W), Brazil, between December 1999 and February 2000 (summer in the southern hemisphere), are analyzed in order to investigate the nocturnal and latitudinal behavior of the ionospheric plasma bubble zonal drift velocities. The data set included 12 nights from Sa~o Joa~o do Cariri (equatorial region) and 12 nights from Cachoeira Paulista (low latitude). An interesting characteristic observed is the significant latitudinal variations in the ionospheric plasma bubble zonal drifts in the tropical region, between 20:00-22:00 local time. The average result of the latitudinal analyses has revealed two peaks in the ionospheric plasma bubble zonal drift velocities. One peak is located near the magnetic equator (~160m/s), occurring between 21:00 and 22:00 LT, and another peak is located at approximately 19°S latitude (~150m/s), occurring between 20:00 and 22:00 LT. The valley in the latitudinal variations is located approximately near 10°S(~120m/s) and this reduction in the ionospheric plasma bubble zonal drifts is attributed to a reduction in the zonal neutral wind velocities. A comparison of the observed latitudinal variations in the ionospheric plasma bubble zonal drifts with the zonal winds obtained from the HWM-90 model reveals good agreement. We find that the increase in electron density within the Equatorial Ionospheric Anomaly was sufficient to account for the observed reduction in the zonal wind velocities. The observed development and motion of the nighttime F-region irregularities in the tropical region are presented and discussed in this paper.

Pimenta, A. A.; Bittencourt, J. A.; Fagundes, P. R.; Sahai, Y.; Buriti, R. A.; Takahashi, H.; Taylor, M. J.

2003-07-01

63

First in situ observations of equatorial ionospheric bubbles by Indian satellite SROSS-C2 and simultaneous multisatellite scintillations  

NASA Astrophysics Data System (ADS)

The first observation of equatorial ionospheric irregularities by RPA probe of the Indian low Earth orbiting satellite SROSS-C2 is presented in this paper. Amplitude scintillations of medium Earth orbiting Global Positioning System (GPS) satellites and geostationary FLEETSATCOM (244 MHz, 73°E) and INMARSAT (1.5 GHz, 65°E) signals recorded simultaneously at Calcutta (lat: 22.97° N, long: 88.50°E geographic; dip: 32°N) are used for a coordinated study of equatorial F region irregularities in the Indian zone. Cases of ionospheric irregularities identified from the SROSS-C2 records obtained during the initial one-and-a-half years since its launch in May 1994 have been analyzed. Some events of in situ ion density irregularities are compared with scintillations simultaneously observed on the transionospheric satellite links. Intense bite-outs of ion density (maximum relative irregularity amplitude ?N/N ˜ 65%) were detected on one occasion (October 29, 1994) coupled with deep fadings (S4 ˜ 1 at VHF, ˜0.52 at L-band, and ˜0.69 at GPS L1 frequency) on ground-based satellite links. An estimate of scintillation indices from the observed in situ density deviations compares well with the ground-based measurements. The development of intense equatorial bubbles even on a day like October 29, 1994, under low solar activity conditions, may be attributed to a prompt penetration of magnetospheric electric field equatorwards during the main phase of a magnetic storm in progress [maximum negative excursion of Dst ˜ -127 nT at 1600UT (2100MLT) with a dDst/dt rate -37 nT/hr at 1300-1400UT (1800-1900MLT)]. The drift velocity and spatial extent of these irregularities have been estimated from ground-based observations.

Paul, A.; Ray, S.; Dasgupta, A.; Garg, S. C.

2002-10-01

64

Temperature structure of plasma bubbles in the low latitude ionosphere around 600 km altitude  

Microsoft Academic Search

The electron temperature inside plasma bubbles at a height of 600 km was first measured by means of Japan's seventh scientific satellite Hinotori which is an equator orbiting satellite with an inclination of 31 deg. During the period between June 1981 and February 1982, 724 plasma bubbles were detected and studied. The electron temperature inside the plasma bubbles is either

K.-I. Oyama; K. Schlegel; S. Watanabe

1988-01-01

65

Laser-Induced Plasma In a Water Bubble  

SciTech Connect

In this work we present a theoretical study concerning the Laser Induced Breakdown Spectroscopy (LIBS) in water. The strong influence of chemical processes on the fluid dynamic expansion has been investigated. To this aim a fluid dynamic code has been developed and coupled with a chemical model, considering the plasma inside the bubble in local thermodynamic equilibrium (LTE)

Casavola, A.; Pesce, L. [Dipartimento di Chimica, Universita di Bari (Italy); Colonna, G. [CNR-IMIP, Bari section (Italy); Capitelli, M. [Dipartimento di Chimica, Universita di Bari (Italy); CNR-IMIP, Bari section (Italy)

2005-05-16

66

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this automation allows the drift velocities of each bubble to be determined as a function of magnetic latitude, which will give us the capability of retrieving geophysically important parameters such as the electric field, which are believed to vary rapidly with magnetic latitude.

Park, S. H.; England, S. L.; Immel, T. J.; Frey, H. U.; Mende, S. B.

2007-11-01

67

Space Weather in the Equatorial Ionosphere  

Microsoft Academic Search

The ‘scintillations’ observed on signals received in the equatorial region from GPS satellites are due to plasma instabilities\\u000a in the F region of the ionosphere, also detected as spread F. These instabilities give rise to depletions of ionisation or\\u000a ‘bubbles’. The occurrence of these events and their relation to the equatorial electrojet are reviewed. Possibilities of short-term\\u000a forecasting are examined

R. J. Stening

2003-01-01

68

Investigation of the role of gravity waves in the generation of equatorial bubbles. Technical progress report, 1 May 1994-28 February 1995  

SciTech Connect

The following areas of interest in this progress report are: (1) the continuation of software development in the examination of F-region gravity-wave power using in-situ data from the Atmosphere Explorer (AE-E); (2) the inquiry into the use of the San Marco data for the study of the initiation and growth of bubbles, particularly when the satellite passes through the early evening hours at relatively high altitudes, and the development of bubbles using not only the San Marco data but includes the use of airglow observations made in Hawaii; and (3) the promising development in the observation of distinct well formed waves at about 400 km altitude in the equatorial region. These waves look very much like waves seen over the polar cap that are attributed to internal gravity waves in the neutral atmosphere driving ionization up and down the magnetic field lines. These equatorial waves show no modulation of the total ion concentration.

Johnson, F.S.; Coley, W.R.

1995-02-01

69

Visualization of plasma bubble accelerators using Frequency-Domain Shadowgraphy  

NASA Astrophysics Data System (ADS)

We report on generation of relativistic electron beams in the wake of a relativistically intense laser pulse traversing a 1.7 mm long atmospheric density helium gas jet. The plasma wake structure is recovered using a Frequency-Domain Holography (FDH) and Frequency-Domain Shadowgraphy (FDS). As the gas density changes, the accelerated electron beams show variations in cross-section area, divergence, total charge, and peak energy. FDH phase reconstruction shows discontinuities and large phase jumps due to plasma electrons blown out by the pump pulse, probe pulse refraction, and nonlinear propagation in plasma. However, FDS amplitude reconstruction shows bright spots that yield information about bubble formation and evolution.

Dong, P.; Reed, S. A.; Yi, S. A.; Kalmykov, S. Y.; Shvets, G.; Downer, M. C.; Matlis, N. H.; Leemans, W. P.; McGuffey, C.; Bulanov, S. S.; Chvykov, V.; Kalintchenko, G.; Krushelnick, K.; Maksimchuk, A.; Matsuoka, T.; Thomas, A. G. R.; Yanovsky, V.

2010-06-01

70

OI 630 nm imaging observations of equatorial plasma depletions at 16° S dip latitude  

Microsoft Academic Search

F-region plasma irregularities associated with the night-time equatorial ionosphere continue to be the subject of intensive observational, theoretical, and simulation studies. The scale sizes of these irregu- larities span a scale from tens of centimeters as obtained with the ALTAIR radar (TSUNODA et al., 1979), to several tens of kilometres observed using radio beacon scintillation measurements. Those ir- regularities which

Y. Sahai; J. Aarons; M. Mendillo; J. Baumgardner; J. A. Bittencourt; H. Takahashi

1994-01-01

71

Seeding of equatorial plasma depletions by polarization electric fields from middle latitudes: Experimental evidence  

Microsoft Academic Search

It is well-known that large wedges of depleted plasma often form in the equatorial ionosphere after sunset. Irregularities in and around these depletions cause scintillation on trans-ionospheric radio paths, as well as strong VHF backscatter. The ultimate stage of depletion growth is controlled by a collisional interchange instability. However, the initiation stages remain the subject of debate. Depletions formed in

E. S. Miller; J. J. Makela; M. C. Kelley

2009-01-01

72

Simulated wave number 4 structure in equatorial F-region vertical plasma drifts  

Microsoft Academic Search

This article investigates the wave number 4 longitudinal structure in equatorial vertical E × B plasma drifts (V$\\\\perp$), using the Theoretical Ionospheric Dynamo Model, Institute of Geology and Geophysics, Chinese Academy of Sciences, Version II model and the DE3 tide wind from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)\\/TIMED Doppler interferometer (TIDI) observations. We simulate this longitudinal structure and

Zhipeng Ren; Weixing Wan; Jiangang Xiong; Libo Liu

2010-01-01

73

Equatorial electric field observations  

NASA Technical Reports Server (NTRS)

The paper reports both dc and ac measurements of equatorial electric fields from the San Marco D satellite. These measurements were performed with double floating probe sensors and have yielded a surprising number of new phenomena and effects in regions of equatorial spread-F. Among the phenomena observed are unexpected large-amplitude Rayleigh-Taylor updrafting velocities in equatorial bubbles.

Aggson, T. L.; Hanson, W. B.; Herrero, F. A.; Maynard, N. C.; Pfaff, R. F.; Saba, J. L.; Tsunoda, R. T.

1993-01-01

74

Thermosphere and F-region plasma dynamics in the equatorial region  

NASA Technical Reports Server (NTRS)

The dynamics of the equatorial thermosphere and the F-region plasma are reviewed, highlighting some features observed with the San Marco satellite, the AE-E, and the DE-2, as well as with ground-based facilities at Arecibo and Jicamarca. Particular attention is given to the midnight temperature maximum and related phenomena, and to results on zonal neutral and plasma flows at F-region heights.

Herrero, F. A.; Spencer, N. W.; Mayr, H. G.

1993-01-01

75

Plasma bubble registration at altitudes of the topside ionosphere: Numerical evaluations  

NASA Astrophysics Data System (ADS)

The possibility of registering a plasma bubble at altitudes of the topside ionosphere based on its minor species He+ were studied. The characteristic times of the main aeronomic and electrodynamic processes, in which a bubble and its ion component He+ are involved, were calculated and compared. The recombination processes of helium ions in a bubble, the vertical transfer of a plasma bubble as a whole, and the diffusion transfer of the plasma bubble minor constituent (He+) were considered. The characteristic times of ambipolar and transverse (Bohm) diffusion were calculated when the diffusion transfer was estimated. The effect of the photoionization processes on plasma bubble dissipation were estimated based on the He+ bubble ion component. It was shown that the bubble filling characteristic time with an average He+ depletion to the He+ ambient density is ˜24 h. It was concluded that such a prolonged bubble lifetime makes it possible to register a plasma bubble reliably over approximately two days. However, it has been noted that only a residual plasma bubble structure, i.e., its trace visible in He+ ions, will apparently be registered during most prolonged observations.

Sidorova, L. N.; Filippov, S. V.

2014-05-01

76

Self-consistent Theory of Young Plasma Bubbles: Kinetic and 3D Aspects  

Microsoft Academic Search

One of the major problems in modeling bursty transport of plasma and magnetic flux in the Earth's magnetotail is incomplete description of the elementary unit of that transport, the localized entropy-depleted flux tube or plasma bubble, which may convect much faster than the rest of the tail plasmas because of the buoyancy effect. Particularly unclear is the bubble formation process,

M. I. Sitnov; P. N. Guzdar; A. V. Divin; M. Swisdak

2006-01-01

77

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

Microsoft Academic Search

We experimentally study the micro dynamics of the laser induced plasma bubble in a dusty plasma liquid formed by negatively charged dust particles suspended in a low pressure rf Ar glow discharge. The plume from the ablation of the suspended dust particles pushes away dust particle and generates a dust-free plasma bubble. It then travels downward. The spatio-temporal evolution of

Lee-Wen Teng; Chen-Yu Tsai; Yu-Ping Tseng; Lin I

2008-01-01

78

Fast Magnetic Reconnection in Laser-Produced Plasma Bubbles  

SciTech Connect

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pileup at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfven time.

Fox, W.; Bhattacharjee, A.; Germaschewski, K. [Center for Integrated Computation and Analysis of Reconnection and Turbulence, and Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of New Hampshire, Durham, New Hampshire 03824 (United States)

2011-05-27

79

Comparison of the ionospheric plasma turbulence over seismic and equatorial regions.  

NASA Astrophysics Data System (ADS)

Many strong earthquakes which are objects of interest in investigations of the changes registered in the electric field in the ELF frequency range (1 Hz - 1250 Hz) in the ionospheric plasma, occurs in the equatorial region. In order to determine, if the observed disturbances are connected with the coupling between the ground and the ionosphere in the seismic active region, it is necessary to analyse and compare plasma instability phenomena occurring in the equatorial F-region ionosphere and are known as equatorial spread F (ESF) to changes before earthquakes because their character is very similar. The aim of this paper is the analysis of changes in the electromagnetic ELF field, registered by the French micro-satellite DEMETER over epicentres of three selected strong earthquakes with magnitude bigger than 6, which took place in: Sichuan, Chile and Haiti. A comparison between those cases and changes observed by the same satellite over the equatorial region in the similar time of year is presented. The analysis of the data, was conducted with the Fourier, wavelet and bispectral methods. The last one gives answer to question, whether the changes localized with the spectral analysis are nonlinear. Further processing consists the determination of the power spectrum and its slope, which allows to determine the type of turbulence which was inducted by the three wave interaction. The last stage of the presented research, was finding the characteristic remarks of changes, by calculation of the probability density function (PDF) and calculation of its characteristic values such as kurtosis and skewness.

Kosciesza, M.; Blecki, J.; Parrot, M.; Wronowski, R.

2012-04-01

80

Bubbles  

NSDL National Science Digital Library

Learners engage in a scientific investigation to answer the question, "Are free-floating bubbles always round?" By experimenting with different-shaped bubble wands and then reading a nonfiction book to support their findings, learners collect evidence to answer the question and then share their findings with others by creating a poster.

Morgan, Emily; Ansberry, Karen

2007-01-01

81

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

SciTech Connect

We experimentally study the micro dynamics of the laser induced plasma bubble in a dusty plasma liquid formed by negatively charged dust particles suspended in a low pressure rf Ar glow discharge. The plume from the ablation of the suspended dust particles pushes away dust particle and generates a dust-free plasma bubble. It then travels downward. The spatio-temporal evolution of the dust density fluctuation surrounding the bubble is monitored by directly tracking dust motion through optical video microscopy. The micro dynamics of the bubble associated dust acoustic type solitary oscillation in the wake field is investigated and discussed.

Teng, L.-W.; Tsai, C.-Y.; Tseng, Y.-P.; I Lin [Department of Physics, National Central University, Jhungli, Taiwan 32001 (China)

2008-09-07

82

Equatorial plasma convection from global simulations of the Earth's magnetosphere  

Microsoft Academic Search

The convection of plasma in the closed field region of the Earth's magnetosphere is an important consequence and a diagnostic of the coupling of solar wind momentum and energy into the magnetosphere. In the outer regions the nature of the flow can help to distinguish between different coupling processes; for example, between (1) a global reconnection process between closed geomagnetic

C. M. Mobarry; J. A. Fedder; J. G. Lyon

1996-01-01

83

Equatorial F region vertical plasma drifts during solar maxima  

Microsoft Academic Search

Incoherent scatter radar measurements at Jicamarca are used to study the effects of large solar fluxes and magnetic activity on the F region vertical plasma drifts. The average drifts from the two last solar maxima are almost identical except in the late afternoon-early evening sector where their variations with solar flux and magnetic activity are strongly season dependent. The average

B.G. Fejer; E.R. de Paula; I. S. Batista; E. Bonelli; R.F. Woodman

1989-01-01

84

Field-aligned 777.4-nm composite airglow images of equatorial plasma depletions  

Microsoft Academic Search

We present a powerful tool to analyze two-dimensional field-aligned images of equatorial plasma depletions taken from mid-latitudes. By shifting each individual image by the sum of the longitudinal offsets obtained by performing a cross-correlation between successive images, a single composite image can be formed for the entire night. It is shown that these field-aligned composite images give information on the

J. J. Makela; M. C. Kelley

2003-01-01

85

A plasma temperature anomaly in the equatorial topside ionosphere  

Microsoft Academic Search

A study of the thermal structure of the low-latitude (30°N to 30°S) ionosphere under equinoctial conditions at low, medium, and high solar activity has been carried out using the Sheffield University plasmasphere-ionosphere model (SUPIM) and Hinotori satellite observations. The study reveals the existence of an anomaly in the plasma (electron and ion) temperature in the topside ionosphere during the evening-midnight

N. Balan; K.-I. Oyama; S. Fukao; S. Watanabe; M. A. Abdu

1997-01-01

86

Characterization of single and colliding laser-produced plasma bubbles using Thomson scattering and proton radiography  

NASA Astrophysics Data System (ADS)

Time-resolved measurements of electron and ion temperatures using Thomson scattering have been combined with proton radiography data for comprehensive characterization of individual laser-produced plasma bubbles or the interaction of bubble pairs, where reconnection of azimuthal magnetic fields occurs. Measurements of ion and electron temperatures agree with lasnex simulations of single plasma bubbles, which include the physics of magnetic fields. There is negligible difference in temperatures between a single plasma bubble and the interaction region of bubble pairs, although the ion temperature may be slightly higher due to the collision of expanding plasmas. These results are consistent with reconnection in a ?˜8 plasma, where the release of magnetic energy (<5% of the electron thermal energy) does not appreciably affect the hydrodynamics.

Rosenberg, M. J.; Ross, J. S.; Li, C. K.; Town, R. P. J.; Séguin, F. H.; Frenje, J. A.; Froula, D. H.; Petrasso, R. D.

2012-11-01

87

Equatorial Spacecraft-Plasma Interaction Phenomenon Observed With DE 2  

NASA Technical Reports Server (NTRS)

Data from the retarding potential analyzer and ion drift meter on Dynamics Explorer 2 indicate that an unusual spacecraft-plasma interaction phenomenon occurs at times when the spacecraft velocity vector becomes nearly aligned with the local geomagnetic field lines. The primary signature of the interaction is a transient increase in the ion collection currents obtained with these instruments, up to approximately 15% in magnitude and typically a few tens of seconds duration. This signature is indicative of an increase in the net ion and electron currents to the satellite and is accompanied by a small positive increase in the spacecraft potential relative to the plasma. We present here a case study covering six of the strongest such events observed with DE 2 and discuss a possible physical mechanism. We suggest in particular that what might be called a collisional electron snowplow effect may be occurring, and we derive a simple numerical model based on this scenario. Least squares fitting is employed to test the model and to derive new estimates of the ambient ion concentration at times when the measurements are being perturbed by the interaction.

Cragin, B. L.; Hanson, W. B.

1993-01-01

88

Equatorial F region vertical plasma drifts during solar maxima  

SciTech Connect

Incoherent scatter radar measurements at Jicamarca are used to study the effects of large solar fluxes and magnetic activity on the F region vertical plasma drifts. The average drifts from the two last solar maxima are almost identical except in the late afternoon-early evening sector where their variations with solar flux and magnetic activity are strongly season dependent. The average evening winter (May--August) drifts appear to remain almost constant after a certain solar flux level is reached but increase with magnetic activity. The equinoctial evening drifts increase systematically with solar-flux but decrease with magnetic activity. Very large prereversal enhancement velocities, up to about 80 m/s, were often observed during the 1978--1981 equinoctial periods when the solar flux was very high. Comparison of incoherent scatter radar drifts with vertical velocities inferred from ionosonde observations indicate that the latter technique substantially underestimates the plasma drifts during periods of large solar fluxes except during winter. {copyright} American Geophysical Union 1989

Fejer, B.G. (Center for Atmospheric and Space Sciences, Utah State University, Logan (USA)); de Paula, E.R. (Center for Atmospheric and Space Sciences, Utah State University, Logan (USA) Instituto de Pesquisas Espaciais, Sao Jose dos Campos, Sao Paul, (Brazil)); Batista, I.S. (Instituto de Pesquisas Espaciais, Sao Jose dos Campos, Sao Paulo, (Brazil)); Bonelli, E. (Departamento de Fisica, Universidade Federal do Rio Grande do Norte, Natal, (Brazil)); Woodman, R.F. (Instituto Geofisico del Peru, Lima (Peru))

1989-09-01

89

Modified Bubble Core Fields and Bubble Shape in Laser Driven Plasma  

NASA Astrophysics Data System (ADS)

Bubble core fields as well bubble shape modification due to the nondepleted electrons inside the bubble is investigated theoretically. It is found that the slope of transverse fields are reduced significantly, however, the slope of longitudinal electric field, which plays a key role on electrons acceleration in bubble, changes little. Moreover a modified longitudinal compressed bubble shape leads to a shorter dephasing distance which makes the electrons acceleration energy reduced to some extent. As a comparison we perform particle-in-cell simulations whose results are consistent with that of our theoretical consideration.

Wu, Hai-Cheng; Xie, Bai-Song

2013-04-01

90

Response to ''Comment on 'Scalings for radiation from plasma bubbles''' [Phys. Plasmas 18, 034701 (2011)  

SciTech Connect

In the preceding Comment, Corde, Stordeur, and Malka claim that the trapping threshold derived in my recent paper is incorrect. Their principal argument is that the elliptical orbits I used are not exact solutions of the equation of motion in the fields of the bubble. The original paper never claimed this--rather I claimed that the use of elliptical orbits was a reasonable approximation, which I based on observations from particle-in-cell simulations. Integration of the equation of motion for analytical expressions for idealized bubble fields (either analytically [I. Kostyukov, E. Nerush, A. Pukhov, and V. Seredov, Phys. Rev. Lett. 103, 175003 (2009)] or numerically [S. Corde, A. Stordeur, and V. Malka, ''Comment on 'Scalings for radiation from plasma bubbles,' '' Phys. Plasmas 18, 034701 (2011)]) produces a trapping threshold wholly inconsistent with experiments and full particle-in-cell (PIC) simulations (e.g., requiring an estimated laser intensity of a{sub 0{approx}}30 for n{sub e{approx}}10{sup 19} cm{sup -3}). The inconsistency in the particle trajectories between PIC and the numeric model used by the comment authors arises due to the fact that the analytical fields are only approximately true for ''real'' plasma bubbles, and lack certain key features of the field structure. Two possible methods of resolution to this inconsistency are either to find ever more complicated but accurate models for the bubble fields or to find approximate solutions to the equations of motion that capture the essential features of the self-consistent electron trajectories. The latter, heuristic approach used in my recent paper produced a threshold that is better matched to experimental observations. In this reply, I will also revisit the problem and examine the relationship between bubble radius and electron momentum at the point of trapping without reference to a particular trajectory.

Thomas, A. G. R. [Centre for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2011-03-15

91

Electromagnetic Analysis of ITER Diagnostic Equatorial Port Plugs During Plasma Disruptions  

SciTech Connect

ITER diagnostic port plugs perform many functionsincluding structural support of diagnostic systems under high electromagnetic loads while allowing for diagnostic access to the plasma. The design of diagnostic equatorial port plugs (EPP) are largely driven by electromagnetic loads and associate responses of EPP structure during plasma disruptions and VDEs. This paper summarizes results of transient electromagnetic analysis using Opera 3d in support of the design activities for ITER diagnostic EPP. A complete distribution of disruption loads on the Diagnostic First Walls (DFWs), Diagnostic Shield Modules (DSMs) and the EPP structure, as well as impact on the system design integration due to electrical contact among various EPP structural components are discussed.

Y. Zhai, R. Feder, A. Brooks, M. Ulrickson, C.S. Pitcher and G.D. Loesser

2012-08-27

92

Analytic model of electromagnetic fields around a plasma bubble in the blow-out regime  

NASA Astrophysics Data System (ADS)

An analytic model of the electric and magnetic fields surrounding the nonlinear plasma ``bubble'' formed around the high-current electron bunch in a plasma wakefield accelerator is developed. The model, justified by the results of particle-in-cell simulations, accurately captures the thin high-density plasma sheath and extended return current layer surrounding the bubble. The resulting global fields inside and outside the bubble are used to investigate electron self-injection in a plasma with a smooth density gradient. It is shown that accurate description of the current/density sheaths is crucial for quantitative description of self-injection.

Yi, S. A.; Khudik, V.; Siemon, C.; Shvets, G.

2013-01-01

93

Coordinated airborne and satellite measurements of equatorial plasma depletions  

SciTech Connect

A series of experiments was conducted in December 1979 to investigate the structure of plasma depletions in the low latitude, nightime ionosphere. The measurements included all sky imaging photometer (ASIP), ionosonde and amplitude scintillation observations from the AFGL Airborne Ionospheric Observatory (AIO), and in situ ion density measurements from the Atmosphere Explorer (AE-E) Bennett Ion Mass Spectrometer (BIMS). The AIO performed two flights along the Ascension Island (-18/sup 0/ MLAT) magnetic meridian: one in the southern hemisphere and one near the Ascension conjugate point in the northern hemisphere. During these flights, measurements from the AE-E satellite at 434 km altitude are compared with simultaneous remote ionospheric measurements from the AIO. Density biteouts of approximately one order of magnitude in the dominant ion O/sup +/, were mapped to lower altitudes along magnetic field lines for comparison with 6300-A and 7774-A O I airglow depletions. Because of the different airglow production mechanisms (dissociative recombination of O/sup +//sub 2/ for 6300 A and radiative recombination of O/sup +/ for 7774 A) the 6300-A depletions reflect plasma depletions near the bottomside of the F layer, while those at 7774 A are located near the peak of the layer. The O/sup +/ biteouts map directly into the 7774-A airglow depletions in the same hemisphere and also when traced into the opposite hemisphere, which indicates magnetic flux tube alignment over north-south distances of approx.2220 km. The 6300-A (bottomside) depletions are wider in longitude than the 7774-A (F-peak) depletions near the equatorward edge of the Appleton anomaly. This difference in topside and bottomside structure is used to infer large-scale structure near the anomaly and to relate this to structure, commonly observed near the magnetic equator by the ALTAIR radar.

Weber, E.J.; Brinton, H.C.; Buchau, J.; Moore, J.G.

1982-12-01

94

Formation of bubbles, blobs, and surface cusps in complex plasmas.  

PubMed

Investigations of the dynamical evolution of a complex plasma, in which a vertical temperature gradient compensates gravity, were carried out. At low power the formation of microparticle bubbles, blobs, and spraying cusps was observed. This activity can be turned on and off by changing control parameters, such as the rf power and the gas pressure. Several observational effects indicate the presence of surface tension, even at small "nanoscales" of a few 100's of particles. By tracing the individual microparticle motion the detailed (atomistic) dynamics can be studied as well as the pressure dependence of the forces. A possible mechanism that could drive the observed phenomena is analogous to the Rayleigh-Taylor instability. PMID:19659088

Schwabe, M; Rubin-Zuzic, M; Zhdanov, S; Ivlev, A V; Thomas, H M; Morfill, G E

2009-06-26

95

Longitudinal Variability of Plasma Structuring in the Equatorial and Middle Latitudes During Magnetically Quiet and Disturbed Times - A Global MIT Coupling Issue  

Microsoft Academic Search

The synoptic global views of the equatorial anomaly provided by the GUVI instrument on TIMED has shed new light on the longitudinal variability of equatorial plasma structure first studied with the OGO - 6 satellite almost 30 years ago (Basu et al., Radio Sci., 1976). The eastward electric field at the magnetic equator during the post-sunset hours drives the equatorial

S. Basu; C. Valladres; S. McDonald; K. Groves

2005-01-01

96

The bubble regime of laser plasma acceleration: monoenergetic electrons and the scalability  

NASA Astrophysics Data System (ADS)

The bubble regime of electron acceleration in ultra-relativistic laser plasma is considered. It has been shown that the bubble can produce ultra-short dense bunches of electrons with quasi-monoenergetic energy spectra. The first experiment in this regime done at LOA has confirmed the peaked electron spectrum (Faure J et al 2004 Nature at press). The generated electron bunch may have density an order of magnitude higher than that of the background plasma. The bubble is able to guide the laser pulse over many Rayleigh lengths, thus no preformed plasma channel is needed for high-energy particle acceleration in the bubble regime. In this work we discuss a simple analytical model for the bubble fields as well as the scaling laws.

Pukhov, A.; Gordienko, S.; Kiselev, S.; Kostyukov, I.

2004-12-01

97

Model study of the plasma cave in the equatorial ionization anomaly region  

NASA Astrophysics Data System (ADS)

Recently observations show plasma cave associated with latitudinal variation of perpendicular ExB drift in the equatorial ionization anomaly (EIA) by using in-situ measurements of dynamic explore-2 (DE-2) and IRI model. In this study, ion drifts taken by ROCSAT-1 indicate similar latitudinal (altitudinal) variations to those seen by DE-2 at EIA region. The variations of ion drifts are compared with ExB drift observations at Jicamarca and show some similarities. The observed drifts taken from ROCSAT-1 and Jicamarca are used to drive the SAMI-2 model simulations and feature of plasma cave is successfully reproduced. We study the relationship between the latitudinal/altitudinal variations of perpendicular ExB drifts and the modeled plasma cave features to understand the underlying physical mechanism.

Chen, Y.; Lin, C.; Chen, C.; Liu, J. G.; Oyama, K.; Lee, I.

2013-12-01

98

Bubble Bubble  

NSDL National Science Digital Library

With magic bubble solution, a boy discovers that he can blow any kind of bubble imaginable: a kangaroo, a bird, a car, or a boat. Mercer Mayer's colorful illustrations enliven this engaging tale of mysterious bubbles.

Mayer, Mercer

2009-11-11

99

Electrons trajectories around a bubble regime in intense laser plasma interaction  

SciTech Connect

Some typical electrons trajectories around a bubble regime in intense laser plasma interaction are investigated theoretically. By considering a modification of the fields and ellipsoid bubble shape due to the presence of residual electrons in the bubble regime, we study in detail the electrons nonlinear dynamics with or without laser pulse. To examine the electron dynamical behaviors, a set of typical electrons, which locate initially at the front of the bubble, on the transverse edge and at the bottom of the bubble respectively, are chosen for study. It is found that the range of trapped electrons in the case with laser pulse is a little narrower than that without laser pulse. The partial phase portraits for electrons around the bubble are presented numerically and their characteristic behaviors are discussed theoretically. Implication of our results on the high quality electron beam generation is also discussed briefly.

Lu, Ding; Xie, Bai-Song; Ali Bake, Muhammad; Sang, Hai-Bo [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China)] [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Zhao, Xue-Yan [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China) [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Wu, Hai-Cheng [Center for Applied Physics and Technology, Peking University, Beijing 100084 (China)] [Center for Applied Physics and Technology, Peking University, Beijing 100084 (China)

2013-06-15

100

Equatorial 150 km echoes and daytime F region vertical plasma drifts in the Brazilian longitude sector  

NASA Astrophysics Data System (ADS)

Previous studies showed that conventional coherent backscatter radar measurements of the Doppler velocity of the so-called 150 km echoes can provide an alternative way of estimating ionospheric vertical plasma drifts during daytime hours (Kudeki and Fawcett, 1993; Chau and Woodman, 2004). Using observations made by a small, low-power 30 MHz coherent backscatter radar located in the equatorial site of São Luís (2.59° S, 44.21° W; -2.35° dip lat), we were able to detect and monitor the occurrence of 150 km echoes in the Brazilian sector. Using these measurements we estimated the local time variation of daytime vertical ionospheric drifts in the eastern American sector. Here, we present a few interesting cases of 150 km-echoes observations made by the São Luís radar and estimates of the diurnal variation of vertical drifts. These cases exemplify the variability of the vertical drifts in the Brazilian sector. Using same-day 150 km-echoes measurements made at the Jicamarca Radio Observatory in Peru, we also demonstrate the variability of the equatorial vertical drifts across the American sector. In addition to first estimates of the absolute vertical plasma drifts in the eastern American (Brazilian) sector, we also present observations of abnormal drifts detected by the São Luís radar associated with the 2009 major sudden stratospheric warming event.

Rodrigues, F. S.; Shume, E. B.; de Paula, E. R.; Milla, M.

2013-10-01

101

Magnetic Bubble Expansion Experimental Investigation Using a Compact Coaxial Magnetized Plasma Gun  

NASA Astrophysics Data System (ADS)

The poster will first discuss the construction and improved design of a compact coaxial magnetized plasma gun. The plasma gun is used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, which as a model for extragalactic radio lobes and solar coronal mass ejections. In this experiment, the plasma bubble's density, electron temperature, and propagation speed are measured by using a multiple-tipped langmuir probe. Also a three axis B-dot probe array is used to measure the magnetic field in three dimensions during the expansion process. In this poster experiment setup and data will be provided. Finally the comparison with the simulation result will be made.

Zhang, Yue; Lynn, Alan; Hsu, Scott; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher

2009-11-01

102

Comparison of the plasma pressure distributions over the equatorial plane and at low altitudes under magnetically quiet conditions  

NASA Astrophysics Data System (ADS)

The distribution of plasma pressure over the equatorial plane is compared with the plasma pressure and the position of the electron precipitation boundaries at low altitudes under the conditions of low geomagnetic activity. The pressure at the equatorial plane is determined using data of the THEMIS international five-satellite mission; the pressure at low altitudes, using data of the DMSP satellites. Plasma pressure isotropy and the validity of the condition of the magnetostatic equilibrium at a low level of geomagnetic activity are taken into account. Plasma pressure in such a case is constant along the magnetic field line and can be considered a "natural tracer" of the field line. It is shown that the plasma ring surrounding the Earth at geocentric distances of ˜6 to ˜10-12 R E is the main source of the precipitations in the auroral oval.

Antonova, E. E.; Vorobjev, V. G.; Kirpichev, I. P.; Yagodkina, O. I.

2014-05-01

103

Space weather phenomena in the equatorial ionosphere  

NASA Astrophysics Data System (ADS)

Our increasing dependence on space-based technological systems requires that we understand the factors that determine "space weather", which affects the operation of satellites as well as space-based communication and navigation systems. The latter are particularly vulnerable to conditions in the dip equatorial ionosphere where geometry of the geomagnetic field creates conditions for the growth of certain plasma instabilities, which produce sub-kilometer scale structure in the ionospheric plasma that are capable of scattering VHF and higher frequency radio waves. The phenomenon of the equatorial plasma bubble (EPB) that occurs in the postsunset equatorial and low latitude ionosphere is therefore an important component of space weather in this region. Forecasting of this space weather phenomenon involves not only the identification of ambient conditions responsible for the day-to-day variation in its occurrence and spatial structure during magnetically quiet periods but also understanding the influence of solar variability on these conditions. This paper discusses briefly our present understanding of the role played by certain parameters of the equatorial ionosphere in the development of EPBs and the influence of solar activity on the equatorial ionosphere, in the context of its role in the generation of ionospheric irregularities that may be detrimental to the operation of space-based communication and navigation systems.

Bhattacharyya, Archana

2013-03-01

104

Energy enhancement of proton acceleration in combinational radiation pressure and bubble by optimizing plasma density  

SciTech Connect

The combinational laser radiation pressure and plasma bubble fields to accelerate protons are researched through theoretical analysis and numerical simulations. The dephasing length of the accelerated protons bunch in the front of the bubble and the density gradient effect of background plasma on the accelerating phase are analyzed in detail theoretically. The radiation damping effect on the accelerated protons energy is also considered. And it is demonstrated by two-dimensional particle-in-cell simulations that the protons bunch energy can be increased by using the background plasma with negative density gradient. However, radiation damping makes the maximal energy of the accelerated protons a little reduction.

Bake, Muhammad Ali; Xie Baisong [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, Beijing Normal University, Beijing 100875 (China); College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Shan Zhang [Department of Mathematics and Physics, Shijiazhuang Tiedao University, Shijiazhuang 050043 (China); Hong Xueren [College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China); Wang Hongyu [Department of Physics, Anshan Normal University, Anshan 114005 (China); Shanghai Bright-Tech Information Technology Co. Ltd, Shanghai 200136 (China)

2012-08-15

105

Radio-Tomographic Images of Post-midnight Equatorial Plasma Depletions  

NASA Astrophysics Data System (ADS)

For the first time, post-midnight equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radio-tomography. High-resolution (~10 km × 10 km) electron-density reconstructions were created from total electron content (TEC) data using an array of receivers sited in Peru and the Multiplicative Algebraic Reconstruction Technique (MART) inversion algorithm. TEC data were obtained from the 150 and 400 MHz signals transmitted by the CERTO beacon on the C/NOFS satellite. In-situ electron density data from the C/NOFS CINDI instrument and electron density profiles from the UML Jicamarca ionosonde were used to generate an initial guess for the MART inversion, and also to constrain the inversion process. Observed EPDs had widths of 100-1000 km, spacings of 300-900 km, and often appeared 'pinched off' at the bottom. Well-developed EPDs appeared on an evening with a very small (4 m/s) Pre-Reversal-Enhancement (PRE), suggesting that postmidnight enhancements of the vertical plasma drift and/or seeding-induced uplifts (e.g. gravity waves) were responsible for driving the Rayleigh-Taylor Instability into the nonlinear regime on this night. On another night the Jicamarca ISR recorded postmidnight (~0230 LT) Eastward electric fields nearly twice as strong as the PRE fields seven hours earlier. These electric fields lifted the whole ionosphere, including embedded EPDs, over a longitude range ~14° wide. CINDI detected a dawn depletion in exactly the area where the reconstruction showed an uplifted EPD. Strong Equatorial Spread-F observed by the Jicamarca ionosonde during receiver observation times confirmed the presence of ionospheric irregularities.

Hei, M. A.; Bernhardt, P. A.; Siefring, C. L.; Wilkens, M.; Huba, J. D.; Krall, J.; Valladares, C. E.; Heelis, R. A.; Hairston, M. R.; Coley, W. R.; Chau, J. L.

2013-12-01

106

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime  

SciTech Connect

An electron density bubble driven in a rarefied uniform plasma by a slowly evolving laser pulse goes through periods of adiabatically slow expansions and contractions. Bubble expansion causes robust self-injection of initially quiescent plasma electrons, whereas stabilization and contraction terminate self-injection thus limiting injected charge; concomitant phase space rotation reduces the bunch energy spread. In regimes relevant to experiments with hundred terawatt- to petawatt-class lasers, bubble dynamics and, hence, the self-injection process are governed primarily by the driver evolution. Collective transverse fields of the trapped electron bunch reduce the accelerating gradient and slow down phase space rotation. Bubble expansion followed by stabilization and contraction suppresses the low-energy background and creates a collimated quasi-monoenergetic electron bunch long before dephasing. Nonlinear evolution of the laser pulse (spot size oscillations, self-compression, and front steepening) can also cause continuous self-injection, resulting in a large dark current, degrading the electron beam quality.

Kalmykov, S. Y.; Shadwick, B. A.; Umstadter, D. P. [Department of Physics and Astronomy, University of Nebraska - Lincoln, Lincoln, Nebraska 68588-0299 (United States); Beck, A.; Lefebvre, E. [CEA, DAM, DIF, Arpajon F-91297 (France); Yi, S. A.; Khudik, V. N.; Downer, M. C. [Department of Physics, C1500, niversity of Texas at Austin, Austin, Texas 78712 (United States)

2011-05-15

107

Spread F Plasma Bubble Vertical Rise Velocities Determined from Spaced Ionosonde Observations.  

National Technical Information Service (NTIS)

Systematic time differences in the onsets of spread F-events in the ionograms were observed between a magnetic equatorial station and a low latitude station in Brazil. It is assumed that the spread F-irregularities occur in strongly field aligned plasma b...

M. A. Abdu R. T. Demedeiros J. H. A. Sobral J. A. Bittencourt

1982-01-01

108

Phase transition to an opaque plasma in a sonoluminescing bubble.  

PubMed

Time-resolved spectrum measurements of a sonoluminescing Xe bubble reveal a transition from transparency to an opaque Planck blackbody. As the temperature is <10?000??K and the density is below liquid density, the photon scattering length is 10?000 times too large to explain its opacity. We resolve this issue with a model that reduces the ionization potential. According to this model, sonoluminescence originates in a new phase of matter with high ionization. Analysis of line emission from Xe* also yields evidence of phase segregation for this first-order transition inside a bubble. PMID:21770508

Kappus, Brian; Khalid, Shahzad; Chakravarty, Avik; Putterman, Seth

2011-06-10

109

Phase Transition to an Opaque Plasma in a Sonoluminescing Bubble  

NASA Astrophysics Data System (ADS)

Time-resolved spectrum measurements of a sonoluminescing Xe bubble reveal a transition from transparency to an opaque Planck blackbody. As the temperature is <10000K and the density is below liquid density, the photon scattering length is 10 000 times too large to explain its opacity. We resolve this issue with a model that reduces the ionization potential. According to this model, sonoluminescence originates in a new phase of matter with high ionization. Analysis of line emission from Xe* also yields evidence of phase segregation for this first-order transition inside a bubble.

Kappus, Brian; Khalid, Shahzad; Chakravarty, Avik; Putterman, Seth

2011-06-01

110

Modelling chemical reactions in dc plasma inside oxygen bubbles in water  

NASA Astrophysics Data System (ADS)

Plasmas generated inside oxygen bubbles in water have been developed for water purification. Zero-dimensional numerical simulations were used to investigate the chemical reactions in plasmas driven by dc voltage. The numerical and experimental results of the concentrations of hydrogen peroxide and ozone in the solution were compared with a discharge current between 1 and 7 mA. Upon increasing the water vapour concentration inside bubbles, we saw from the numerical results that the concentration of hydrogen peroxide increased with discharge current, whereas the concentration of ozone decreased. This finding agreed with the experimental results. With an increase in the discharge current, the heat flux from the plasma to the solution increased, and a large amount of water was probably vaporized into the bubbles.

Takeuchi, N.; Ishii, Y.; Yasuoka, K.

2012-02-01

111

Plasma Driven Implosions of a Bubble-Liner  

Microsoft Academic Search

Thin bubbles (delta 1020 ions\\/cm3. Cylindrical and quasi-spherical implosions are obtained. Results of Schlieren and soft X-ray photography are reported. The application of the spherical implosions to the generation of an intense hohlraum radiation and to fibre super-pinches are discussed.

A. Bortolotti; J. G. Linhart; J. Kravárik; P. Kubes

1994-01-01

112

HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEWTRON DETECTORS  

SciTech Connect

OAK B202 HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEWTRON DETECTORS. Bubble detectors, which can detect neutrons with a spatial resolution of 5 to 30 {micro}, are a promising approach to high-resolution imaging of NIF target plasmas. Gel bubble detectors were used in successful proof-of-principle imaging experiments on OMEGA. Until recently, bubble detectors appeared to be the only approach capable of achieving neutron images of NIF targets with the desired 5 {micro} spatial resolution in the target plane. In 2001, NIF reduced the required standoff distance from the target, so that diagnostic components can now be placed as close as 10 cm to the target plasma. This will allow neutron imaging with higher magnification and may make it possible to obtain 5 {micro}m resolution images on NIF using deuterated scintillators. Having accomplished all that they can hope to on OMEGA using gel detectors, they suggested that the 2002 NLUF shots be used to allow experimental tests of the spatial resolution of the CEA-built deuterated scintillators. The preliminary CEA data from the June 2002 run appears to show the spatial resolution using the deuterated scintillator detector array is improved over that obtained in earlier experiments using the proton-based scintillators. Gel detectors, which consist of {approx} 10 {micro}m diameter drops of bubble detector liquid suspended in an inactive support gel that occupies {approx} 99% of the detector volume, were chosen for the initial tests on OMEGA since they are easy to use. The bubbles could be photographed several hours after the neutron exposure. Imaging NIF target plasmas at neutron yields of 10{sup 15} will require a higher detection efficiency detector. Using a liquid bubble chamber detector should result in {approx} 1000 times higher neutron detection efficiency which is comparable to that possible using scintillation detectors. A pressure-cycled liquid bubble detector will require a light scattering system to record the bubble locations a few microseconds after the neutron exposure when the bubbles have grown to be {approx} 10 {micro}m in diameter. The next major task planned under this grant will be to perform experimental tests to determine how accurately the spatial distribution of the bubble density can be measured under the conditions expected in NIF. The bubble density will be large enough to produce significant overlap in the two-dimensional images, so that they will need to be able to measure bubbles behind bubbles. One of the goals of these tests is to determine if a simple light transmission approach is feasible. One of the concerns at very high bubble densities is that light scattered out of the path can be rescattered back into the transmitted light path by bubbles in neighboring paths.

FISHER,RK

2002-10-01

113

Generation of intense ultrashort midinfrared pulses by laser-plasma interaction in the bubble regime  

SciTech Connect

As an intense laser pulse propagates through an underdense plasma, the strong ponderomotive force pushes away the electrons and produces a trailing plasma bubble. In the meantime the pulse itself undergoes extreme nonlinear evolution that results in strong spectral broadening toward the long-wavelength side. By experiment we demonstrate that this process can be utilized to generate ultrashort midinfrared pulses with an energy three orders of magnitude larger than that produced by crystal-based nonlinear optics. The infrared pulse is encapsulated in the bubble before exiting the plasma, hence is not absorbed by the plasma. The process is analyzed experimentally with laser-plasma tomographic measurements and numerically with three-dimensional particle-in-cell simulation. Good agreement is found between theoretical estimation, numerical simulation, and experimental results.

Pai, C.-H.; Chang, Y.-Y.; Ha, L.-C.; Xie, Z.-H.; Chen, Y.-M.; Wang, J. [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China); Lin, M.-W.; Chen, S.-Y. [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Lin, J.-M. [Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Department of Physics, National Chung Cheng University, Chia-Yi 62102, Taiwan (China); Tsaur, G. [Department of Mathematics, Tunghai University, Taichung 40704, Taiwan (China); Chu, H.-H.; Chen, S.-H. [Department of Physics, National Central University, Jhongli 32001, Taiwan (China); Lin, J.-Y. [Department of Physics, National Chung Cheng University, Chia-Yi 62102, Taiwan (China)

2010-12-15

114

Supra-bubble regime for laser acceleration of coldelectron beams in tenuous plasma  

SciTech Connect

Relativistic electrons can be accelerated by an ultraintense laser pulse in the "supra-bubble" regime, that is, in the blow-out regime ahead of the plasma bubble (as opposed to the conventional method, when particles remain inside the bubble). The acceleration is caused by the ponderomotive force of the pulse, via the so-called snow-plow mechanism. The maximum energy gain, ?? ~ ?g a, is attained when the particle Lorentz factor ? is initially about ?g/a, where ?g is the pulse group speed Lorentz factor, and a is the laser parameter, proportional to the laser field amplitude. The scheme operates at a ? ?g, yielding ?? of up to that via wakefield acceleration for the same plasma and laser parameters, ?? ~ ?2g. The interaction length is shorter than that for the wake field mechanism but grows with the particle energy, hindering acceleration in multiple stages.

V.I. Geyko, I.Y. Dodin, and N.J. Fisch G.M. Fraiman

2009-01-18

115

The Quantitative Analysis of Active Species Generated by Direct Current Plasma within Oxygen Bubbles  

NASA Astrophysics Data System (ADS)

In this research, concentrations of hydrogen peroxide and dissolved ozone generated by direct current plasma within oxygen bubbles in water were measured. The current magnitude and water conductivity were changed from 1 to 7mA, and from 1 to 100 ?S/cm, respectively. The highest efficiency of hydrogen peroxide generation was 0.64g/kWh at 7mA with 100?S/cm solution. The concentration of dissolved ozone decreased with increasing the discharge current, and was almost zero when the current was higher than 5mA. Non-dimensional simulation revealed that the water vapor concentration in bubbles strongly affects the generation of active species. With a large current, the amount of water vaporized into the bubbles enlarged due to a large heat flux from plasma.

Ishii, Yoko; Ando, Mizuki; Takeuchi, Nozomi; Ikeda, Kei; Yasuoka, Koichi

116

Extreme longitudinal variability of plasma structuring in the equatorial ionosphere on a magnetically quiet equinoctial day  

NASA Astrophysics Data System (ADS)

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22-23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American-Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground- and space-based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX, and a chain of GPS receivers are used in combination with the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) model to explore the relationship between the large-scale ionization distribution and small-scale irregularities at low latitudes in both the scintillating and nonscintillating longitude sectors. Our analysis shows that there are significant differences in the evolution of the ionization distributions during the evening hours, which are likely the result of differences in the daytime and postsunset vertical plasma drift in the two sectors. This study demonstrates the importance of USU-GAIM as a new tool for investigating longitudinal as well as day-to-day variability that is observed in the large-scale distribution of the ionosphere and how this relates to the occurrence of scintillation.

McDonald, Sarah E.; Basu, Sunanda; Basu, Santimay; Groves, Keith M.; Valladares, Cesar E.; Scherliess, Ludger; Thompson, Donald C.; Schunk, Robert W.; Sojka, Jan J.; Zhu, Lie

2006-12-01

117

Estimation of the initial amplitude of plasma bubble seed perturbation from ionograms  

NASA Astrophysics Data System (ADS)

This work gives the description of an experimental method for the calculation of the initial amplitude of plasma bubble seed perturbation in the bottomside F layer from ionograms. The observations show that after sunset the ionograms exhibit irregularities in the base of the F trace. In the context of the plasma depletion in the bottomside F-layer, the irregularities in ionograms can be seen like isodensity contour in evolution (in space and time). The initial amplitudes, calculated using the methodology, vary between 0.03 and 0.08. The ionograms analyzed were obtained from the station of Cachimbo (9.5°S, 54.8°W) during COPEX campaign in Brazil. The methodology can be useful for application in numerical simulation of plasma bubbles in which actual ionospheric parameters are used.

Carrasco, A. J.; Batista, I. S.

2012-04-01

118

3-D effects in magnetic reconnection of laser-produced plasma bubbles  

NASA Astrophysics Data System (ADS)

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles. It is of great interest to extend previous 2-D simulations [1] to understand the full 3-D evolution of the bubbles. This 3-D evolution, studied by PIC simulations, includes the 3-D spherical expansion of the bubbles and 3-D geometry of the interaction, including the formation of isolated magnetic nulls and null-null lines. In cylindrical 3-D geometry, we study the dynamics of long-wavelength kink instabilities and short-wavelength lower-hybrid instabilities in the return currents, over a range of parameters characteristic of the experiments. Observational signatures of 3-D dynamics in the experiments will be discussed.[4pt] [1] W. Fox, A. Bhattacharjee, K. Germaschewski, Phys. Rev. Lett. 106, 215003 (2011).

Fox, W.; Mollica, F.; Bhattacharjee, A.; Germaschewski, K.

2011-11-01

119

The equatorial ionosphere over Brazilian region from ground based and satellite data  

NASA Astrophysics Data System (ADS)

The equatorial ionosphere is characterized by various phenomena such as the instability pro-cesses that originate the equatorial electrojet, the equatorial ionization anomaly and the iono-spheric irregularities and plasma bubbles that can cause severe interference in the trans-ionospheric propagation of electromagnetic waves. Over the Brazilian region a set of ground based diagnose equipments has being providing data for more than three decades, that allowed a fairly good understanding of the climatology and of the main characteristics and peculiarities of the ionospheric phenomena over the region. Recent satellite missions, such as the Formosat 3/COSMIC, have provided a significant database that can be explored to give a more com-plete picture of the equatorial ionosphere. In this work we discuss the importance of these two datasets for the ionospheric studies over the equatorial region and present some results for the Brazilian region.

Batista, Inez S.; Abdu, Mangalathayil Ali; Vogel Ely, Claudia

120

Multi-wavelength Emission from the Fermi Bubbles. I. Stochastic Acceleration from Background Plasma  

NASA Astrophysics Data System (ADS)

We analyze processes of electron acceleration in the Fermi bubbles in order to define parameters and restrictions of the models, which are suggested for the origin of these giant radio and gamma-ray structures. In the case of the leptonic origin of the nonthermal radiation from the bubbles, these electrons should be produced somehow in situ because of the relatively short lifetime of high-energy electrons, which lose their energy by synchrotron and inverse-Compton processes. It has been suggested that electrons in bubbles may be accelerated by shocks produced by tidal disruption of stars accreting onto the central black hole or a process of re-acceleration of electrons ejected by supernova remnants. These processes will be investigated in subsequent papers. In this paper, we focus on in situ stochastic (Fermi) acceleration by a hydromagnetic/supersonic turbulence, in which electrons can be directly accelerated from the background plasma. We showed that the acceleration from the background plasma is able to explain the observed fluxes of radio and gamma-ray emission from the bubbles, but the range of permitted parameters of the model is strongly restricted.

Cheng, K. S.; Chernyshov, D. O.; Dogiel, V. A.; Ko, C. M.

2014-07-01

121

Experimental study of plasma bubble expansion as a model for extragalactic radio lobes  

NASA Astrophysics Data System (ADS)

Recent work in plasma astrophysics has suggested that magnetic energy features prominently in the large-scale evolution of active galaxies. The Plasma Bubble Expansion Experiment (PBEX) at UNM will conduct laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form extra-galactic radio lobe structures. A newly-built pulsed coaxial gun will form and inject magnetized plasma bubbles into a lower pressure weakly-magnetized background plasma formed by the helicon and/or hot cathode source in HELCAT, a 4 m long and 50 cm diameter linear plasma device. Plasma properties can be adjusted such that important dimensionless parameters are relevant to the astrophysical context. Ideal MHD simulations of the experiment have indicated the strong possibility of MHD shocks appearing. This poster will provide an overview of the physics goals, experimental design/status, and coordinated theory/modeling of PBEX.

Hsu, Scott; Lynn, Alan G.; Zhang, Yue; Liu, Wei; Li, Hui; Watts, Christopher; Gilmore, Mark

2008-04-01

122

Analytic model of electron self-injection in a plasma wakefield accelerator in the strongly nonlinear bubble regime  

NASA Astrophysics Data System (ADS)

We study self-injection into a plasma wakefield accelerator in the blowout (or bubble) regime, where the bubble evolves due to background density inhomogeneities. To explore trapping, we generalize an analytic model for the wakefields inside the bubble [1] to derive expressions for the fields outside. With this extended model, we show that a return current in the bubble sheath layer plays an important role in determining the trapped electron trajectories. We explore an injection mechanism where bubble growth due to a background density downramp causes reduction of the electron Hamiltonian in the co-moving frame, trapping the particle in the dynamically deepening potential well [2]. Model calculations agree quantitatively with PIC simulations on the bubble expansion rate required for trapping, as well as the range of impact parameters for which electrons are trapped. This is an improvement over our previous work [3] using a simplified spherical bubble model, which ignored the fields outside of the bubble and hence overestimated the expansion rate required for trapping. [4pt] [1] W. Lu et al., Phys. Plasmas 13, 056709 (2006).[0pt] [2] S. Kalmykov et al., Phys. Rev. Lett 103, 135004 (2009).[0pt] [3] S.A. Yi et al., Plasma Phys. Contr. Fus. 53, 014012 (2011).

Yi, Sunghwan; Khudik, Vladimir; Shvets, Gennady

2012-10-01

123

SEARCHING FOR QUARK - GLUON PLASMA (QGP) BUBBLE EFFECTS AT RHIC / LHC.  

SciTech Connect

Since the early eighties, we have shared with Leon Van Hove the view that if a QGP were produced in high energy heavy ion colliders that its hadronization products would likely come from small localized in phase space bubbles of plasma. In previous papers we have discussed the case where one to at most a few separated bubbles were produced. In this paper we develop a model based on HIJING to which we added a ring of adjoining multi bubble production, which we believe is a higher cross-section process which dominates the near central rapidity region. We have performed simulations which were designed to be tested by the expected first to become available suitable test data, namely the forthcoming RHIC STAR detector data on 65Gev/n Au colliding with 65 Gev/n Au. We took into account background effects and resonance effects so that a direct comparison with the data, and detailed test of these ideas could be made in the near future. Subsequently 100 Gev/n Au on 100 Gev/n Au forthcoming data can be tested, and of course these techniques, suitably modified by experience can be applied to it and eventually to LHC. We concluded that two charged particle correlations versus the azimuthal angle {Delta}{phi}; vs the opening angle, and vs psuedorapidity {eta}, can detect important bubble signals in the expected background, with statistical significances of 5 - 20{sigma}, provided the reasonably conservative assumptions we have made for bubble production occur. We also predicted charge fluctuation suppressions which increase with the bubble signal, and range from {approx} 5% to 27% in the simulations performed. We demonstrated reasonably that in our model, these charge suppression effects would not significantly be affected by resonances.

LINDENBAUM,S.J.; LONGACRE,R.S.; KRAMER,M.

2003-03-01

124

Gravity wave and tidal influences on equatorial spread F based on observations during the Spread F Experiment (SpreadFEx)  

Microsoft Academic Search

The Spread F Experiment, or SpreadFEx, was performed from September to November 2005 to define the potential role of neutral atmosphere dynamics, primarily gravity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles extending to higher altitudes. A description of the SpreadFEx campaign motivations, goals, instrumentation, and structure, and an overview of the

D. C. Fritts; S. L. Vadas; D. M. Riggin; M. A. Abdu; I. S. Batista; H. Takahashi; A. Medeiros; F. Kamalabadi; H.-L. Liu; M. J. Taylor

2008-01-01

125

Parametrization of spectra of plasma bubble induced VHF satellite scintillations and its geophysical significance  

NASA Astrophysics Data System (ADS)

An important component of ionospheric plasma irregularity studies in the Indian low latitudes involves the study of the plasma bubbles which produce intense scintillations of the transionospheric satellite signals. Many such plasma bubble induced (PBI) scintillation events were identified while recording 244 MHz signal from the geostationary satellite Fleetsat (73°E) at Delhi (28.6°N, 77.2°E) during March-April 1991. This type of scintillations represents changes in plasma processes. These scintillations are spectrally analyzed using an autoregressive (AR) scheme, which is equivalent to maximum entropy method of spectrum analysis, amenable to extracting optimum spectral content from short data lengths (20 - 40 s). Each spectrum is assigned a level of detectability using the final prediction error (FPE) derived from the optimum filter order required to resolve the spectrum. Lower detectability together with a higher order filter indicate a higher level of coherence for the plasma irregularities (discrete structures). Consistent patterns for these scintillations emerge from the present analysis as follows: (1) the initial and final phases of a scintillation patch display quasiperiodic oscillations. Their corresponding spectra show dominant (Gaussian shaped) spectral features with detectability levels of -6 dB to -12 dB and requiring a higher order (>6) AR filter for their spectral resolution. These are most likely associated with discrete filament-like or sheet-like plasma structures that exist near the bubble walls. (2) Two main features of the scintillation spectra could be positively associated with the well-developed plasma bubble stage: (a) spectra displaying a power-law process with a single component spectral slope between 1.6 to 3.0. Generally such spectra are resolved with a 2nd order filter and have a 1 dB to 6 dB of detectability. (b) Spectra displaying a double slope, indicating an inner and an outer scale regime for the power-law irregularities. These spectra are resolved with higher order filters (>3 but <7) and possess detectability levels of -1 dB to 3 dB. These spectra display finer spectral changes, perhaps indicative of the nature of continuously evolving plasma irregularities. As an example, an analysis of a single scintillation patch is presented to highlight the geophysical significance of the present approach. Some important parameters used in the AR scheme of spectral analysis are given in the Appendix.

Vijayakumar, P. N.; Pasricha, P. K.

1997-03-01

126

Extreme longitudinal variability of plasma structuring in the equatorial ionosphere on a magnetically quiet equinoctial day  

Microsoft Academic Search

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22-23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American-Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground- and space-based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX,

Sarah E. McDonald; Sunanda Basu; Santimay Basu; Cesar E. Valladares; Ludger Scherliess; Donald C. Thompson; Jan J. Sojka; Lie Zhu

2006-01-01

127

Extreme longitudinal variability of plasma structuring in the equatorial ionosphere on a magnetically quiet equinoctial day  

Microsoft Academic Search

We investigate the extreme longitudinal variability of equatorial scintillation under quiet magnetic conditions during 22–23 March 2002. Scintillation Network Decision Aid (SCINDA) observations show intense activity in the South American–Atlantic sector during local evening hours, whereas an absence of scintillation is seen in the far east Asian sector. Ground- and space-based measurements from SCINDA, the Global Ultraviolet Imager (GUVI), TOPEX,

Sarah E. McDonald; Sunanda Basu; Santimay Basu; Keith M. Groves; Cesar E. Valladares; Ludger Scherliess; Donald C. Thompson; Robert W. Schunk; Jan J. Sojka; Lie Zhu

2006-01-01

128

Evidence of cold bubble-like structure in START density limit plasmas  

SciTech Connect

Cold bubble (CB) structures were observed in START density limit studies for the first time in a low aspect ratio tokamak. They seem related to minor and major disruption processes, clearly identified here as a trigger to those events. Enormous discrepancies on the CB velocities in several devices are reported. This shows that the physical mechanisms related to the time scales for its propagation should be revised. Several models related to CB formation and its role in the disruptive process or just in a plasma with the presence of sawteeth qualitatively predict a great part of the observations.

Ribeiro, C., E-mail: celso_ribeiro@hotmail.co [Universidade Nova de Lisboa Campus da Caparica, Departamento de Fisica, Faculdade de Ciencias e Tecnologia (Portugal); Jenkins, I.; Martin, R.; Sykes, A.; Walsh, M. J. [Culham Science Centre, UKAEA-Euratom Fusion Association (United Kingdom)

2008-09-15

129

Evidence of cold bubble-like structure in START density limit plasmas  

NASA Astrophysics Data System (ADS)

Cold bubble (CB) structures were observed in START density limit studies for the first time in a low aspect ratio tokamak. They seem related to minor and major disruption processes, clearly identified here as a trigger to those events. Enormous discrepancies on the CB velocities in several devices are reported. This shows that the physical mechanisms related to the time scales for its propagation should be revised. Several models related to CB formation and its role in the disruptive process or just in a plasma with the presence of sawteeth qualitatively predict a great part of the observations.

Ribeiro, C.; Jenkins, I.; Martin, R.; Sykes, A.; Walsh, M. J.

2008-09-01

130

Zonal drift velocities of the ionospheric plasma bubbles over brazilian region using oi630nm airglow digital images  

NASA Astrophysics Data System (ADS)

The zonal drift velocities of the ionospheric plasma bubbles over the Brazilian region are analyzed in this study that is based on OI630nm airglow digital images. These digital images were obtained by an all-sky imager system between October 1998 and August 2000, at Cachoeira Paulista (22.5°S, 45°W), a low latitude region. In this period, 138 nights of OI 630 nm airglow experiments were carried out of which 30 nights detected the ionospheric plasma bubbles. These 30 nights correspond to magnetically quiet days (?K_P<24+) and were grouped according approximately to their season. KEY WORDS: Imager System, Ionospheric Plasma Bubbles, Zonal drift velocities, OI630nm.

Arruda, D. C. S.; Sobral, J. H. A.; Abdu, M. A.; Castilho, V. M.; Takahashi, H.

131

The Longitudinal Variation of Equatorial Electrodynamics Observations  

NASA Astrophysics Data System (ADS)

The uneven distribution of ground-based instruments due to the large ocean coverage in the equatorial regions hinders our ability to obtain a global understanding of the dynamics and structure of the equatorial ionosphere. In Africa, which has been mostly devoid of ground-based instruments, the ionospheric density structure has been traditionally estimated by model interpolation over vast geographic areas. Recent ground- and space-based observations have shown that geomagnetic storms can have dramatic longitudinal differences in equatorial ionospheric electrodynamics, such as enhanced generation of F-region plasma irregularities, and super fountain effect at low latitudes. For example, satellite observations have shown very unique equatorial ionospheric density structures in the African region. The African region is the longitude sector where the occurrence of large scale bubble activity (zonal width, depletion level, and spacing) peaks. No other region in the globe shows similar characteristics. One of the possible driving mechanisms that govern the equatorial electrodynamics is the vertical ExB drift, which strongly affects the structure and dynamics of the ionosphere in the low/mid-latitude region. According to the observations performed at different longitudes, using recently deployed limited ground-based instruments, the vertical ExB drift has significant longitudinal differences. This paper presents initial results of vertical ExB drifts observed at three different longitudes: East African, West African, and West American sectors. The drift is estimated using a pairs of ground-based magnetometers technique. In the African sector stations from the AMBER, INTERMAGNET, and MAGDAS, and in the American sector SAMBA and LISN magnetometer arrays have been used for this study. Finally, the comparison between the magnetometer estimated ExB drift and the vertical drift observations (VEFI and IVM) on board C/NOFS satellites have also been performed, showing promising results.

Yizengaw, E.; Zesta, E.; Moldwin, M.; Valladares, C. E.; Damtie, B.; Mebrahtu, A.; Biouele, C. M.; Yumoto, K.; Pfaff, R. F.; Heelis, R. A.

2010-12-01

132

Measurements of equatorial plasma depletion velocity using 630 nm airglow imaging over a low-latitude Indian station  

NASA Astrophysics Data System (ADS)

report the east-west velocity measurements of the equatorial plasma depletion (EPD) from Gadanki (13.5°N, 79.2°E, dip latitude 6.5°N) estimated using the airglow imaging of O(1D) 630 nm airglow emission during the years 2012-2013. Our measured EPD velocity values are significantly smaller than earlier reported values from low-latitude stations in India. The measured nocturnal EPD velocity variations are compared with recent empirical model given by England and Immel (2012). We note that during March-April months, our measurements agree very well with the empirical model while minor differences are noted in other months. We also note the differences between our measurements and horizontal wind model. We believe that these differences suggest the deviation of electrodynamics associated with EPD from the one occurring in the background thermospheric altitudes.

Taori, A.; Sindhya, A.

2014-01-01

133

Review of multitechnique observations of equatorial irregularities  

NASA Astrophysics Data System (ADS)

Studies of the nighttime F-region equatorial irregularities are presented. Co-ordinate measurements of in-situ satellites, VHP radar backscatter, total electron content and scintillation measurements were used to determine the relationship between the extended 3-m irregularity structures (plasma depletions or bubbles) and bursts of scintillation activity during their development and decay phases. The large-scale feature of plasma depletions in the equatorial region is illustrated in two-dimensional maps of 6300 Angstrom emission obtained by an all-sky imaging photometer. A connection between the steep spatial gradient in electron density, a feature of the onset phase of irregularity generation, and intense GHz scintillations is discussed in Basu et al. (1980). The presence of the steep gradient structure is indicative of plausible plasma instability processes at work; it is not clear, however, if thermal fluctuations in the ionosphere can be amplified to generate such steep spatial structures in electron density, or if a separate seed mechanism (Roettger, 1978; Klostermeyer, 1978) is necessary.

Basu, S.; Aarons, J.

134

Laboratory generated magnetized plasma bubbles as a means to understanding coronal mass ejections  

NASA Astrophysics Data System (ADS)

We have begun a series of laboratory experiments using the combined Helicon-Cathode (HelCat) plasma facility, and the Plasma Bubble Experiment (PBeX). These devices can generate CME like structures injected into a background plasma medium. The goal of this research is to substantiate, through a series of basic plasma experiments and corroborative numerical modeling, the fundamental physics of coronal mass ejection (CME) interaction with the solar wind flow in the Sun's outer corona. Results of these laboratory experiments will be compared with the University of Michigan state-of-the-art 3D BATS-R-US MHD numerical code, which has been used to perform simulations of the propagation of CMEs into a background solar wind. The results will be compared in a systematic way to validate the numerical model under controlled laboratory settings, allowing it to be applied with greater confidence to a more realistic but less well-understood solar setting. Initial laboratory simulation results will be presented.

Lynn, A. G.; Watts, C.; Manchester, W. B.

2009-12-01

135

Comparison of equatorial plasma mass densities deduced from field line resonances observed at ground for dipole and IGRF models  

NASA Astrophysics Data System (ADS)

technique to remotely sense the plasma mass density in magnetosphere using field line resonance frequencies detected by ground-based magnetometers has become more and more popular in the last few years. In this paper we examine the error that would be committed at low and middle latitudes (L < 4) in estimating the equatorial plasma mass density if dipole field lines are assumed instead of the more realistic representation given by International Geomagnetic Reference Field (IGRF) lines. It is found that the use of the centered dipole model may result in an error in the inferred density appreciably larger than what is usually assumed. In particular, it has a significant longitudinal dependence being, for example, greater than +30% in the Atlantic sector and about -30% at the opposite longitude sector for field lines extending to a geocentric distance of 2 Earth radii. This may result in an erroneous interpretation of the longitudinal variation in plasmaspheric density when comparing results from ground-based arrays located at different longitudes. We also propose simple modifications of the standard technique, such as the use of an effective dipole moment or the eccentric dipole model, which allow to keep using the dipole field geometry but with a significant error reduction.

Vellante, M.; Piersanti, M.; Pietropaolo, E.

2014-04-01

136

Two-fluid simulations of shock wave propagation and shock-bubble interaction in collisionless plasma  

NASA Astrophysics Data System (ADS)

The propagation of collisionless shock waves and the influence of the space-charge field on the development of fluid instabilities induced by a collisionless shock wave are investigated by solving the two-fluid plasma equations numerically in two space-dimensions. A second-order accurate Riemann solver is employed to sharply capture the shock wave and contact discontinuity. First, a series of shock-tube problems is solved to verify the method. The shock structure similar to that obtained in a previous particle-in-cell (PIC) simulation is reproduced. However, it is found that the shock wave propagates at speeds higher than the PIC results for high initial density ratios at the shock tube diaphragm. Second, the interactions between a collisionless shock wave of Mach number 1.6 and an isolated cylindrical bubble of Atwood number 0.81 are investigated. It is found that in addition to the well-known Richtmyer-Meshkov instability, filamentary fluid-instability is induced at the bubble interface introducing turbulence in the region ahead of the shock wave.

Mori, Koichi

2012-03-01

137

Plasma-assisted laser ablation of tungsten: Reduction in ablation power threshold due to bursting of holes/bubbles  

SciTech Connect

Nanosecond laser ablation of tungsten (W) exposed to helium plasma is investigated using optical emission spectroscopy. Submicrometer-sized holes/bubbles are formed on the surface of W when it was exposed to the helium plasma at a sufficiently high temperature (> or approx. 1500-1600 K). The emissions from a virgin W (before the helium plasma irradiation) cannot be detected when the fluence is <1 J/cm{sup 2}; however, the threshold fluence for the detection of neutral W emission after it was exposed to the helium plasma is {approx}0.2 J/cm{sup 2}. The physical mechanism of laser-induced bursting of holes/bubbles is proposed for achieving a significant reduction in ablation power threshold.

Kajita, Shin; Ohno, Noriyasu; Takamura, Shuichi; Sakaguchi, Wataru; Nishijima, Dai [Japan Atomic Energy Agency, Mukoyama 801-1, Naka, Ibaraki 311-0193 (Japan); EcoTopia Science Institute, Nagoya University, Nagoya 464-8603 (Japan); Aichi Institute of Technology, Yakusa-cho, Toyota 470-0392 (Japan); Graduate School of Engineering, Nagoya University, Nagoya 464-8603 (Japan); National Institute of Advanced Industrial Science and Technology, Saga 841-0052 (Japan)

2007-12-24

138

Electron self-injection into an evolving plasma bubble: toward a dark current free GeV-scale laser plasma accelerator  

NASA Astrophysics Data System (ADS)

A bubble of electron density created by the radiation pressure of a short laser pulse can travel with the driver over many centimeters and accelerate electrons trapped from the ambient plasma to a few GeV. Nonlinear refraction and depletion of the driving pulse cause variations of the bubble shape and potentials; these, in turn, can either stimulate or extinguish electron self-injection and thus directly affect the process of electron beam formation and determine its final characteristics. The new results [1] show that in low-density plasmas relevant to the next generation of GeV-scale laser- plasma accelerators, expansion of the bubble triggers self- injection. The bucket stabilization and contraction stops injection and thus limits electron beam charge and duration. Laser spot size oscillations caused by nonlinear refraction can induce the desired sequence of bubble expansion and shrinkage. Periodic repetition of the sequence, however, can degrade the beam quality [2]. Using dense plasma slabs in the role of nonlinear lenses helps stabilize the bubble pulsations, achieve phase space rotation, and produce a quasi-monoenergetic bunch well before the de-phasing limit [3]. 3D particle-in-cell simulations complemented with the Hamiltonian diagnostics of electron phase space demonstrate robustness of the concept over a broad range of parameters. Modeling also shows that a single- shot non- collinear optical probing (frequency-domain tomography [4]) can facilitate direct observation of bubble evolution and associate it with the observed electron beam characteristics.[4pt] [1] S. Kalmykov et al., PRL 103, 135004 (2009).[0pt] [2] S. Y. Kalmykov et al., New J. Phys. 12, 045019 (2010).[0pt] [3] S. Y. Kalmykov et al., Plasma Phys. Control. Fusion 52(9) (2010) (in press).[0pt] [4] P. Dong et al., New J. Phys. 12, 045016 (2010).

Kalmykov, Serguei

2010-11-01

139

Insights in the laser-induced breakdown spectroscopy signal generation underwater using dual pulse excitation — Part I: Vapor bubble, shockwaves and plasma  

NASA Astrophysics Data System (ADS)

Plasma and vapor bubble formation and evolution after a nanosecond laser pulse delivered to aluminum targets inside water were studied by fast photography. This technique was also applied to monitor the plasma produced by a second laser pulse and for different interpulse delays. The bubble growth was evident only after 3 ?s from the first laser pulse and the bubble shape changed during expansion and collapse cycles. The evolution and propagation of the initial shockwave and its reflections both from the back sample surface and cell walls were detected by Schlieren photography. The primary plasma develops in two phases: violent particle expulsion and ionization during the first ?s, followed by slow plasma growth from the ablation crater into the evolving vapor bubble. The shape of the secondary plasma strongly depends on the inner bubble pressure whereas the particle expulsion into the expanded bubble is much less evident. Both the primary and secondary plasma have similar duration of about 30 ?s. Detection efficiency of the secondary plasma is much reduced by light refraction at the curved bubble-water interface, which behaves as a negative lens; this leads to an apparent reduction of the plasma dimensions. Defocusing power of the bubble lens increases with its expansion due to the lowering of the vapor's refraction index with respect to that of the surrounding liquid (Lazic et al., 2012 [1]). Smell's reflections of secondary plasma radiation at the expanded bubble wall redistribute the detected intensity on a wavelength-dependent way and allow gathering of the emission also from the external plasma layer that otherwise, would not enter into the optical system.

Lazic, V.; Laserna, J. J.; Jovicevic, S.

2013-04-01

140

On the Azimuthal Variation of Core Plasma in the Equatorial Magnetosphere  

NASA Technical Reports Server (NTRS)

Previous results of plasmapause position surveys have been synthesized into a description of the underlying global distribution of plasmasphere-like or core plasma densities unique to a steady state magnetosphere. Under these steady conditions, the boundary between high- and low-density regions is taken to represent the boundary between diurnal near-corotation and large-scale circulation streamlines that traverse the entire magnetosphere. Results indicate a boundary that has a pronounced bulge in the dusk sector that is rotated westward and markedly reduced in size at increased levels of geomagnetic activity (and presumably magnetospheric convection). The derived profile is empirical confirmation of an underlying 'tear drop' distribution of core plasma, which is valid only for prolonged steady conditions and is somewhat different from that associated with the simple superposition of sunward flow and corotation, both in its detailed shape and in its varying orientation. Variation away from the tear drop profile suggests that magnetospheric circulation departs from a uniform flow field, having a radial dependence with respect to the Earth that is qualitatively consistent with electrostatic shielding of the convection electric field and which is rotated westward at increased levels of geophysical activity.

Gallagher, D. L.; Craven, P. D.; Comfort, R. H.; Moore, T. E.

1995-01-01

141

Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil  

NASA Astrophysics Data System (ADS)

The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 min and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (EIA) and post-sunset plasma enhancement (PS-EIA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in EIA and PS-EIA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles.

Takahashi, H.; Costa, S.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. G.; Paula, E.; Nogueira, P.; Denardini, C. M.; Becker-Guedes, F.; Wrasse, C. M.; Ivo, A. S.; Gomes, V. C. F.; Gargarela, W.; Sant'Anna, N.; Gatto, R.

2014-08-01

142

Observations and Simulations of Formation of Broad Plasma Depletions Through Merging Process  

NASA Technical Reports Server (NTRS)

Broad plasma depletions in the equatorial ionosphere near dawn are region in which the plasma density is reduced by 1-3 orders of magnitude over thousands of kilometers in longitude. This phenomenon is observed repeatedly by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite during deep solar minimum. The plasma flow inside the depletion region can be strongly upward. The possible causal mechanism for the formation of broad plasma depletions is that the broad depletions result from merging of multiple equatorial plasma bubbles. The purpose of this study is to demonstrate the feasibility of the merging mechanism with new observations and simulations. We present C/NOFS observations for two cases. A series of plasma bubbles is first detected by C/NOFS over a longitudinal range of 3300-3800 km around midnight. Each of the individual bubbles has a typical width of approx 100 km in longitude, and the upward ion drift velocity inside the bubbles is 200-400 m/s. The plasma bubbles rotate with the Earth to the dawn sector and become broad plasma depletions. The observations clearly show the evolution from multiple plasma bubbles to broad depletions. Large upward plasma flow occurs inside the depletion region over 3800 km in longitude and exists for approx 5 h. We also present the numerical simulations of bubble merging with the physics-based low-latitude ionospheric model. It is found that two separate plasma bubbles join together and form a single, wider bubble. The simulations show that the merging process of plasma bubbles can indeed occur in incompressible ionospheric plasma. The simulation results support the merging mechanism for the formation of broad plasma depletions.

Huang, Chao-Song; Retterer, J. M.; Beaujardiere, O. De La; Roddy, P. A.; Hunton, D.E.; Ballenthin, J. O.; Pfaff, Robert F.

2012-01-01

143

Multi-instrument analysis of plasma parameters in Saturn's equatorial, inner magnetosphere using corrections for corrections for spacecraft potential and penetrating background radiation  

NASA Astrophysics Data System (ADS)

We use a forward modeling program to derive one-dimensional isotropic plasma characteristics in Saturn's inner, equatorial magnetosphere using a novel correction for the spacecraft potential and penetrating background radiation. The advantage of this fitting routine is the simultaneous modeling of plasma data and systematic errors when operating on large data sets, which greatly reduces the computation time and accurately quantifies instrument noise. The data set consists of particle measurements from the electron spectrometer (ELS) and the ion mass spectrometer (IMS), which are part of the Cassini Plasma Spectrometer (CAPS) instrument suite on board the data are limited to peak ion flux measurements within ±10°magnetic latitude and 3-15 geocentric equatorial radial distance (RS). Systematic errors such as spacecraft charging and penetrating background radiation are parameterized individually in the modeling and are automatically addressed during the fitting procedure. The resulting values are in turn used as cross calibration between IMS and ELS, where we show a significant improvement in magnetospheric electron densities and minor changes in the ion characteristics due to the error adjustments. adjustments. Preliminary results show ion and electron densities in close agreement, consistent with charge neutrality throughout Saturn's inner magnetosphere and confirming the spacecraft potential to be a common influence on IMS and ELS. Comparison of derived plasma parameters with results from previous studies using CAPS data and the Radio and Plasma Wave Science investigation yields good agreement.

Livi, R.; Goldstein, J.; Burch, J. L.; Crary, F.; Rymer, A. M.; Mitchell, D. G.; Persoon, A. M.

2014-05-01

144

Concurrence of monoenergetic electron beams and bright X-rays from an evolving laser-plasma bubble.  

PubMed

Desktop laser plasma acceleration has proven to be able to generate gigaelectronvolt-level quasi-monoenergetic electron beams. Moreover, such electron beams can oscillate transversely (wiggling motion) in the laser-produced plasma bubble/channel and emit collimated ultrashort X-ray flashes known as betatron radiation with photon energy ranging from kiloelectronvolts to megaelectronvolts. This implies that usually one cannot obtain bright betatron X-rays and high-quality electron beams with low emittance and small energy spread simultaneously in the same accelerating wave bucket. Here, we report the first (to our knowledge) experimental observation of two distinct electron bunches in a single laser shot, one featured with quasi-monoenergetic spectrum and another with continuous spectrum along with large emittance. The latter is able to generate high-flux betatron X-rays. Such is observed only when the laser self-guiding is extended over 4 mm at a fixed plasma density (4 × 10(18) cm(-3)). Numerical simulation reveals that two bunches of electrons are injected at different stages due to the bubble evolution. The first bunch is injected at the beginning to form a stable quasi-monoenergetic electron beam, whereas the second one is injected later due to the oscillation of the bubble size as a result of the change of the laser spot size during the propagation. Due to the inherent temporal synchronization, this unique electron-photon source can be ideal for pump-probe applications with femtosecond time resolution. PMID:24711405

Yan, Wenchao; Chen, Liming; Li, Dazhang; Zhang, Lu; Hafz, Nasr A M; Dunn, James; Ma, Yong; Huang, Kai; Su, Luning; Chen, Min; Sheng, Zhengming; Zhang, Jie

2014-04-22

145

Ionospheric bubbles detection algorithms: Analysis in low latitudes  

NASA Astrophysics Data System (ADS)

Plasma depletions (or bubbles) are strong reductions in the ionospheric F-region plasma density due to the appearance of a Rayleigh-Taylor instability in the post-sunset, producing severe radio signal disruptions when crossing them. Most of the plasma depletions are confined on the Appleton Anomaly region, which also shows the presence of strong scintillations activity. Therefore, stations located in the vicinity of the geomagnetic equator are expected to be frequently affected by the presence of plasma depletions. This paper provides a comparison between the plasma depletion detection results achieved using two algorithms: one developed by the National Institute for Aerospace Technology and the University Complutense of Madrid and one developed by GMV. Six equatorial stations distributed all over the world and different solar activity and seasonal conditions have been selected to analyze the algorithms’ response to different plasma depletions characteristics. A regional behavior analysis of the plasma depletion occurrence and characteristics is also provided.

Magdaleno, S.; Cueto, M.; Herraiz, M.; Rodríguez-Caderot, G.; Sardón, E.; Rodríguez, I.

2013-04-01

146

HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEUTRON DETECTORS, Final Report for the Period November 1, 1999 - February 28, 2001  

SciTech Connect

OAK B202 HIGH SPATIAL RESOLUTION IMAGING OF INERTIAL FUSION TARGET PLASMAS USING BUBBLE NEUTRON DETECTORS. Bubble detectors, which can detect neutrons with a spatial 5 to 30 {micro}, are the most promising approach to imaging NIF target plasmas with the desired 5 {micro} spatial resolution in the target plane. Gel bubble detectors are being tested to record neutron images of ICF implosions in OMEGA experiments. By improving the noise reduction techniques used in analyzing the data taken in June 2000, we have been able to image the neutron emission from 6 {center_dot} 10{sup 13} yield DT target plasmas with a target plane spatial resolution of {approx} 140 {micro}. As expected, the spatial resolution was limited by counting statistics as a result of the low neutron detection efficiency of the easy-to-use gel bubble detectors. The results have been submitted for publication and will be the subject of an invited talk at the October 2001 Meeting of the Division of Plasma Physics of the American Physical Society. To improve the counting statistics, data was taken in May 2001 using a stack of four gel detectors and integrated over a series of up to seven high-yield DT shots. Analysis of the 2001 data is still in its early stages. Gel detectors were chosen for these initial tests since the bubbles can be photographed several hours after the neutron exposure. They consist of {approx} 5000 drops ({approx} 100 {micro} in diameter) of bubble detector liquid/cm{sup 3} suspended in an inactive support gel that occupies {approx} 99% of the detector volume. Using a liquid bubble chamber detector and a light scattering system to record the bubble locations a few microseconds after the neutron exposure when the bubbles are {approx} 10 {micro} in diameter, should result in {approx} 1000 times higher neutron detection efficiency and a target plane resolution on OMEGA of {approx} 10 to 50 {micro}.

FISHER,RK

2003-02-01

147

Equatorial ionospheric electrodynamics observations in the African sector using recently deployed magnetometer and GPS networks  

NASA Astrophysics Data System (ADS)

Recent ground-and space-based observations have shown that geomagnetic storms can have dramatic longitudinal differences in equatorial ionospheric electrodynamics, such as enhanced generation of F-region plasma irregularities and super fountain effect at low latitudes. For example, satellite observations have shown very unique equatorial ionospheric density struc-tures in the African region. The African region is the longitude sector where the peak in large scale bubble activity (zonal width, depletion level, and spacing) is maximum. No other region in the globe shows similar characteristics. Most recent in situ density observations from C/NOFS also reveal similar maximal bubble activities in Africa. However, the dearth of ground-based in-strumentation in the region makes it impossible to confirm these unique equatorial ionospheric structures from the ground and that leads the investigation of the physics into speculative dead ends. This initiated several open questions, which include: What are the possible governing mechanisms that create unique equatorial structures in Africa? In order to answer such open questions, recently limited progress has been made and very few ground-based instruments, including AMBER magnetometers and ACORN GPS network, have been either deployed in the region or in process. Some of many objectives of AMBER magnetometers network, in coordination with ground-and space-based GPS receiver observations, is to understand the fundamental electrodynamics that govern equatorial ionospheric motion and the penetration of ULF Pc5 wave into equatorial latitudes and its impact on the equatorial electrodynamics. This paper presents initial results from AMBER magnetometer network. The initial electro-dynamics result in Africa is also compared with similar observations in the American sector. The electron density structure in response to the electrodynamics is also investigated using the available ground-based GPS receivers in the region as well as data from GPS receivers on board LEO satellites. While AMBER observes the F -region plasma drift mechanism (E×Bdrift), the ground-and space-based GPS network monitor the structure of plasma at low/mid-latitudes. Finally, the comparison between the magnetometer estimated E × Bdrift and the vertical drift observations on board C/NOFS satellites shows promise. Similarly, solar wind dynamic pressure driven Pc5 signature have also been detected by ground-based magnetometers in the region. The Pc5 wave signature that we observed on the ground at the equatorial stations has also been detected by space-based observation such as GOES, and C/NOFS spacecrafts.

Yizengaw, Endawoke

148

Equatorial Sundial  

NSDL National Science Digital Library

In this activity, learners make an equatorial sundial, which is simple to construct and teaches fundamental astronomical concepts. Learners use the provided template and a straw to build the sundial. Then, learners take the sundial outside on a sunny day and measure the time at least fours time in one day. They also compare these measurements to the "clock" time. Learners can experiment with their sundials during different months as well. This lesson guide includes background information about Nabta, an Egyptian Stonehenge.

Observatory, Mcdonald

2008-01-01

149

Airborne studies of equatorial F layer ionospheric irregularities  

SciTech Connect

Radio wave and optical experiments were conducted onboard a U.S. Air Force research aircraft in March 1977 and March 1978 at low magnetic latitudes to investigate the effects of F region electron density amplitude. Scintillation measurements were used to monitor the development and motion of F region 6300-A O I airglow depletions, spread F, and scintillation producing irregularities that are all associated with low-density bubbles in the postsunset equatorial ionosphere. The 6300-A airglow depletions are the bottomside signature of low plasma density within the bubbles. Examples of multiple airglow depletions and their relation to variations in the F layer virtual height (h'F) and to the occurrence of amplitude scintillations on 250-MHz satellite signals are described. Estimates of the average bottomside electron density, from simultaneous ionosonde measurements and 6300-A airglow intensities, show electron density decreases of approx.66% within the bubbles. These decreases are approximately the same for bubbles observed at the magnetic equator and near Ascension Island (18 /sup 0/S magnetic latitude). The measurements at Ascension Island show that airglow depletions extend away from the magnetic equator into the southern 6300-A intertropical arc. Variations in the maximum poleward extent of airglow depletions and of associated ionospheric irregularities that give rise to amplitude scintillations were observed. These latitudinal variations are interpreted, using field line mapping considerations, as variations in the maximum altitude of plasma bubbles over the magnetic equator. A north-south flight confirms that the overall pattern of airglow depletions and associated ionospheric irregularities extends continuously across the magnetic equator to +-15/sup 0/ magnetic latitude.

Weber, E.J.; Buchau, J.; Moore, J.G.

1980-09-01

150

Gravity wave and tidal influences on equatorial spread F based on observations during the Spread F Experiment (SpreadFEx)  

NASA Astrophysics Data System (ADS)

The Spread F Experiment, or SpreadFEx, was performed from September to November 2005 to define the potential role of neutral atmosphere dynamics, primarily gravity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles extending to higher altitudes. A description of the SpreadFEx campaign motivations, goals, instrumentation, and structure, and an overview of the results presented in this special issue, are provided by Fritts et al. (2008a). The various analyses of neutral atmosphere and ionosphere dynamics and structure described in this special issue provide enticing evidence of gravity waves arising from deep convection in plasma bubble seeding at the bottomside F layer. Our purpose here is to employ these results to estimate gravity wave characteristics at the bottomside F layer, and to assess their possible contributions to optimal seeding conditions for ESF and plasma instability growth rates. We also assess expected tidal influences on the environment in which plasma bubble seeding occurs, given their apparent large wind and temperature amplitudes at these altitudes. We conclude 1) that gravity waves can achieve large amplitudes at the bottomside F layer, 2) that tidal winds likely control the orientations of the gravity waves that attain the highest altitudes and have the greatest effects, 3) that the favored gravity wave orientations enhance most or all of the parameters influencing plasma instability growth rates, and 4) that gravity wave and tidal structures acting together have an even greater potential impact on plasma instability growth rates and plasma bubble seeding.

Fritts, D. C.; Vadas, S. L.; Riggin, D. M.; Abdu, M. A.; Batista, I. S.; Takahashi, H.; Medeiros, A.; Kamalabadi, F.; Liu, H.-L.; Fejer, B. G.; Taylor, M. J.

2008-10-01

151

Equatorial Guinea.  

PubMed

Attention in this discussion of Equatorial Guinea is directed to the following: the people, history, geography, government, political conditions, the economy, foreign relations, and relations between the US and Equatorial Guinea. The population was estimated at 304,000 in 1983 and the annual growth rate was estimated in the range of 1.7-2.5. The infant mortality rate is 142.9/1000 with a life expectancy of 44.4 years for males and 47.6 years for females. The majority of the Equatoguinean people are of Bantu origin. The largest tribe, the Fang, is indigenous to the mainland, although many now also live on Bioko Island. Portuguese explorers found the island of Bioko in 1471, and the Portuguese retained control until 1778, when the island, adjacent islets, and the commercial rights to the mainland between the Niger and Ogooue Rivers were ceded to Spain. Spain lacked the wealth and the interest to develop an extensive economic infrastructure in Equatorial Guinea during the 1st half of this century, but the Spanish did help Equatorial Guinea achieve 1 of the highest literacy rates in Africa. They also founded a good network of health care facilities. In March 1968, under pressure from Guinean nationalists, Spain announced that it would grant independence to Equatorial Guinea as rapidly as possible. A referendum was held on August 11, 1968, and 63% of the electorate voted in favor of the constitution, which provided for a government with a general assembly and presidentially appointed judges in the Supreme Court. After the coup in August 1979, power was placed in the hands of a Supreme Military Council. A new constitution came into effect after a popular vote in August 1982, abolishing the Supreme Military Council. Under the terms of the constitution, the president was given extensive powers. By the end of 1983, a 60-member Chamber of Representatives of the people had been formed. The government, which is credited with restoring greater personal freedom, is regarded favorably by the populace. The economy is based on 3 products -- cacao, wood, and coffee. These are exported to spain and other European countries. There is little industry, and the local market for industrial products is small. The government wants to expand the role of free enterprise and to promote foreign investment. The potential exists for a viable ariculture-based, export-oriented economy. The US provides over $1 million annually in economic assistance, primarily in the field of agricultural development to assist in production of cash and food crops. PMID:12178092

1984-06-01

152

A method for determining the drift velocity of plasma depletions in the equatorial ionosphere using far-ultraviolet spacecraft observations: initial results  

NASA Astrophysics Data System (ADS)

The Far-Ultraviolet Imager (IMAGE-FUV) on-board the NASA IMAGE satellite has been used to observe plasma depletions in the nightside equatorial ionosphere. Observations from periods around spacecraft apogee, during which equatorial regions are visible for several hours, have allowed the velocity of these plasma depletions to be determined. A new method for determining the velocity of these depletions using an image analysis technique, Tracking Of Airglow Depletions (TOAD), has been developed. TOAD allows the objective identification and tracking of depletions. The automation of this process has also allowed for the tracking of a greater number of depletions than previously achieved without requiring any human input, which shows that TOAD is suitable for use with large data sets and for future routine monitoring of the ionosphere from space. Furthermore, this allows the drift velocities of each depletion to be determined as a function of magnetic latitude as well as local time. Previous ground-based airglow observations from a small number of locations have indicated that the drift velocities of depletions may vary rapidly with magnetic latitude. Here we shall present the first results from TOAD of this shear in drift velocities from our global sample of depletion drift velocities.

England, S. L.; Immel, T. J.; Park, S. H.; Frey, H. U.; Mende, S. B.

2007-12-01

153

Coordinated study of equatorial scintillation and in situ and radar observations of nighttime F region irregularities  

NASA Technical Reports Server (NTRS)

A coordinated set of Atmospheric Explorer E (AE-E) satellite in situ, VHF radar backscatter, and scintillation measurements performed during 1977 over a common ionospheric volume is used to study the relationship between the plasma depletions or bubbles, the extended 3-m irregularity structures known as plumes, and bursts of scintillation activity or patches in the nighttime equatorial F region. The implications of the observed spatial structures and the level of ambient concentration on the generation of 3-m irregularities and scintillation modeling are discussed.

Basu, S.; Basu, S.; Mcclure, J. P.; Hanson, W. B.; Aarons, J.

1980-01-01

154

Rice Convection Model simulation of the substorm-associated injection of an observed plasma bubble into the inner magnetosphere: 2. Simulation results  

NASA Astrophysics Data System (ADS)

We present results from a Rice Convection Model simulation of the early expansion phase of a substorm that occurred 22 July 1998. The theoretical basis of the simulation is the idea that the plasma injected into the inner magnetosphere during a substorm primarily consists of a low-content plasma bubble, which is made up of flux tubes with lower values of the entropy parameter PV 5/3 than their neighbors. As discussed in an accompanying paper, to simulate this event, we carefully tailor model inputs to fit Geotail observations of the bubble at X GSM ? -9 R E . We find that both potential and induction electric fields play important roles in transporting and energizing the particles during the event. The potential electric field associated with Birkeland currents that flow along the east and west sides of the bubble (i.e., the substorm current wedge) is characterized by a localized strengthening of the westward auroral ionospheric electric field within the bubble, as well as the production of a region of enhanced westward flow just Equatorward of the diffuse electron aurora. The inner edge of the modeled plasma sheet assumes a dented-in form that is similar in shape to the injection boundary proposed many years ago on observational grounds. Flux tubes that are pushed earthward ahead of the bubble at onset form a sharp pressure peak near local midnight and geosynchronous orbit, and the particles on those tubes contribute significantly to the injection of particles into the inner magnetosphere.

Zhang, J.-C.; Wolf, R. A.; Spiro, R. W.; Erickson, G. M.; Sazykin, S.; Toffoletto, F. R.; Yang, J.

2009-08-01

155

Mapping age-related elasticity changes in porcine lenses using bubble-based acoustic radiation force.  

PubMed

Bubble-based acoustic radiation force aims to measure highly localized tissue viscoelastic properties. In the current investigation, acoustic radiation force was applied to laser-induced bubbles to measure age-related changes in the spatial distribution of elastic properties within in vitro porcine lenses. A potential in vivo technique to map lens elasticity is crucial to understanding the onset of presbyopia and develop new treatment options. Bubble-based acoustic radiation force was investigated as a technique to measure the spatial elasticity distribution of the lens in its natural state without disrupting the lens capsule. Laser-induced optical breakdown (LIOB) generated microbubbles in a straight line across the equatorial plane of explanted porcine lenses with 1mm lateral spacing. Optical breakdown occurs when sufficiently high threshold fluence is attained at the focus of femtosecond pulsed lasers, inducing plasma formation and bubble generation. A two-element confocal ultrasonic transducer applied 6.5 ms acoustic radiation force-chirp bursts with the 1.5 MHz outer element while monitoring bubble position within the lens using pulse-echoes with the 7.44 MHz inner element. A cross-correlation method was used to measure bubble displacements and determine exponential time constants of the temporal responses. Maximum bubble displacements are inversely proportional to the local Young's modulus, while time constants are indicative of viscoelastic properties. The apparent spatial elasticity distributions in 41 porcine lenses, ranging from 4 months to 5 years in age, were measured using bubble-based acoustic radiation force. Bubble displacements decrease closer to the porcine lens center, suggesting that the nucleus is stiffer than the cortex. Bubble displacements decrease with increasing lens age, suggesting that porcine lenses become stiffer with age. Bubble-based acoustic radiation force may be well-suited as a potential in vivo technique to spatially map elastic properties of the lens and guide therapeutic procedures aimed at restoring accommodation. PMID:17141220

Erpelding, Todd N; Hollman, Kyle W; O'Donnell, Matthew

2007-02-01

156

Bubble Mania  

NSDL National Science Digital Library

In this math lesson, learners practice measurement skills as they examine a soap bubble print. Learners follow a recipe to make a soap bubble solution. They use the soapy solution to blow large bubbles with a plastic drinking straw until the bubbles pop, leaving behind circular prints. Learners find the diameter, circumference, and area of the bubble print.

Pbs

2012-01-01

157

Vertical neutral wind in the equatorial F-region deduced from electric field and ion density measurements  

NASA Astrophysics Data System (ADS)

Direct current (DC) electric field and ion density measurements near density depletion regions (that is, equatorial plasma bubbles) are used to estimate the vertical neutral wind speed. The measured zonal electric field in a series of density depletions crossed by the San Marco D satellite at 01.47-01.52 Universal Time (UT) on 25 October 1988, can be explained if a downward neutral wind of 15-30 m/s exists. Simultaneously, the F-region plasma was moving downward at a speed of 30-50 m/s. These events appear in the local time sector of 23.00-23.15 in which strong downward neutral winds may occur. Indeed, airglow measurements suggest that downward neutral velocities of 25-50 m/s are possible at time near midnight in the equatorial F-region.

Laakso, Harri; Aggson, Thomas L.; Herrero, F. A.; Pfaff, Robert F.; Hanson, William B.

1995-05-01

158

Electron Self-Injection into an Evolving Plasma Bubble: The Way to a Dark Current Free GeV-Scale Laser Accelerator  

SciTech Connect

A time-varying electron density bubble created by the radiation pressure of a tightly focused petawatt laser pulse traps electrons of ambient rarefied plasma and accelerates them to a GeV energy over a few-cm distance. Expansion of the bubble caused by the shape variation of the self-guided pulse is the primary cause of electron self-injection in strongly rarefied plasmas (n{sub e{approx}}10{sup 17} cm{sup -3}). Stabilization and contraction of the bubble extinguishes the injection. After the bubble stabilization, longitudinal non-uniformity of the accelerating gradient results in a rapid phase space rotation that produces a quasi-monoenergetic bunch well before the de-phasing limit. Combination of reduced and fully self-consistent (first-principle) 3-D PIC simulations complemented with the Hamiltonian diagnostics of electron phase space shows that the bubble dynamics and the self-injection process are governed primarily by the driver evolution; collective transverse fields of the trapped electron bunch reduce the accelerating gradient, slow down phase space rotation, and result in a formation of monoenergetic electron beam with higher energy than test-particle modeling predicts.

Kalmykov, S. Y.; Shadwick, B. A. [Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, NE 68588-0299 (United States); Beck, A.; Lefebvre, E. [CEA, DAM, DIF, Bruyeres-le-Chatel, 91297 Arpajon Cedex (France); Yi, S. A.; Khudik, V.; Downer, M. C. [Department of Physics, C1500, University of Texas at Austin, Austin, TX 78712 (United States)

2010-11-04

159

Dark-current-free petawatt laser-driven wakefield accelerator based on electron self-injection into an expanding plasma bubble  

NASA Astrophysics Data System (ADS)

A dark-current-free plasma accelerator driven by a short (<=150 fs) self-guided petawatt laser pulse is proposed. The accelerator uses two plasma layers, one of which, short and dense, acts as a thin nonlinear lens. It is followed by a long rarefied plasma (~1017 electrons cm-3) in which background electrons are trapped and accelerated by a nonlinear laser wakefield. The pulse overfocused by the plasma lens diffracts in low-density plasma as in vacuum and drives in its wake a rapidly expanding electron density bubble. The expanding bubble effectively traps initially quiescent electrons. The trapped charge given by quasi-cylindrical three-dimensional particle-in-cell (PIC) simulations (using the CALDER-Circ code) is ~1.3 nC. When laser diffraction saturates and self-guiding begins, the bubble transforms into a bucket of a weakly nonlinear non-broken plasma wave. Self-injection thus never resumes, and the structure remains free of dark current. The CALDER-Circ modelling predicts a few ? mm mrad normalized transverse emittance of electron beam accelerated in the first wake bucket. Test-particle modelling of electron acceleration over 9 cm (using the quasistatic PIC code WAKE) sets the upper limit of energy gain 2.6 GeV with ~2% relative spread.

Kalmykov, S. Y.; Yi, S. A.; Beck, A.; Lifschitz, A. F.; Davoine, X.; Lefebvre, E.; Khudik, V.; Shvets, G.; Downer, M. C.

2011-01-01

160

Bubble dielectrophoresis  

Microsoft Academic Search

The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements,

T. B. Jones; G. W. Bliss

1977-01-01

161

Modeling Equatorial Spread F Generated by HF Heating  

NASA Astrophysics Data System (ADS)

Equatorial spread F (ESF) bubbles are created from a Rayleigh-Taylor like instability in the equatorial ionosphere after sunset. Simulations with the Sami is Another Model of the Ionosphere/Equatorial Spread F (SAMI3/ESF) model have demonstrated that relatively small density perturbations in the ionosphere can create large enough instabilities post sunset to generate ESF bubbles. Similar density perturbations are generated from the injection of powerful HF waves into the ionosphere; the HF heating leads to strong electron heating followed by a depletion of electrons in the heated region. HF heating effects in the ionosphere have previously been studied using a version of SAMI3/ESF modified to include a simple heating source. We use the modified SAMI3/ESF to study the creation and growth of ESF bubbles caused by the injection of powerful HF waves into the ionosphere. In particular, we examine under what conditions an HF heater can create a density depletion that triggers ESF.

Zawdie, K.; Huba, J. D.

2013-12-01

162

Plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions, from polarimeter observations  

Microsoft Academic Search

Amplitude scintillation and Faraday rotation angle fluctuations of satellite VHF beacon registered by electronic polarimeters operated at two magnetically east-west spaced stations 110 km apart were analyzed for equinoctial and summer months of 1982-83, to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances. The scintillation patch occurrences, and TEC fluctuations representing plasma

M. A. Abdu; I. S. Batista; J. H. A. Sobral; E. R. Depaula; I. J. Kantor

1984-01-01

163

Characterizing the 10 November 2004 storm-time middle-latitude plasma bubble event in Southeast Asia using multi-instrument observations  

Microsoft Academic Search

The development and dynamics of ionospheric plasma bubble (PB) irregularity during the super storm of 7–11 November 2004 are investigated using the data from a multi-instrument network operated in Southeast Asia. Analysis of fluctuations in Global Positioning System total electron content (GPS TEC), ionosonde, GPS scintillation, and in situ satellite density data indicates a series of intense PB-associated irregularities at

Guozhu Li; Baiqi Ning; Biqiang Zhao; Libo Liu; Weixing Wan; Feng Ding; J. S. Xu; J. Y. Liu; K. Yumoto

2009-01-01

164

Buoyant Bubbles  

NSDL National Science Digital Library

What keeps bubbles and other things, like airplanes, floating or flying in the air? In this activity, learners blow bubbles and wave 3x5 cards above, below and on different sides of the bubbles to keep them afloat as long as possible. The Did You Know section explains the Bernoulli principle: how waving cards above the bubbles helps keep them afloat because faster moving air exerts less pressure to push the bubbles down. The activity can be extended by having learners wave their bubbles through an obstacle course they design themselves.

Science, Lawrence H.

2009-01-01

165

Growth and decay of a post-sunset equatorial anomaly at low latitudes: Control of E×B, neutral winds and daytime electrojet strength  

NASA Astrophysics Data System (ADS)

Analyzing the 2 months ionospheric electron content (IEC) data acquired during a high solar activity period from a network of a stations whose sub-ionospheric points at 420 km were located within ± 1° of 84° meridian and covering a latitude belt of 3 21°N (magnetic), it has been shown that following sunset a fresh equatorial anomaly develops in continuation to the decaying daytime equatorial anomaly (DEA) in the low latitude belt. The occurrence of this post-sunset equatorial anomaly (PEA) is although a regular phenomenon but large day-to-day variations are seen in its strength (crest to trough ratio) and the latitude extent, PEA develops fully within 2 3 h of sunset and then decays. During its development crest of anomaly clearly shows a pole-ward movement and during decay it shows substantial equator-ward movement. While the trough of PEA is always seen over the magnetic equator, the crest of fully developed anomaly may be seen to lie at latitudes anywhere between 12°N and 21°N magnetic or more on different days. Thus the development and decay of PEA produce large latitudinal disturbance of F-region plasma in the lower latitude belt in the post-sunset hours and the occurrence of various low latitude phenomenon observed in IEC, e.g. post-sunset IEC decreases at equatorial latitudes, post-sunset IEC enhancements at 12°N or higher latitudes, pre-midnight IEC enhancements at equatorial latitudes, etc., have been attributed to the systematic development and decay of PEA. Also, the occurrence and development of PEA has been found to play an important role in the onset of equatorial plasma bubble associated ionospheric irregularities and their latitudinal growth. The equatorial ionization anomaly (EIA) is primarily caused by the ExB drifts whereas meridional winds in association with E×B drifts also seems to play some role in determining the crest of PEA.

Dabas, R. S.; Singh, Lakha; Garg, S. C.; Das, Rupesh M.; Sharma, Kavita; Vohra, V. K.

2006-09-01

166

Bubble dielectrophoresis  

NASA Technical Reports Server (NTRS)

The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements, static-levitation experiments, and dynamic-force measurements.

Jones, T. B.; Bliss, G. W.

1977-01-01

167

Soap Bubbles  

NSDL National Science Digital Library

Learners explore three-dimensional geometric frames including cubes and tetrahedrons, as they create bubble wands with pipe cleaners and drinking straws. Then they investigate how soap film flows into a state of minimum energy when they lift the wand up from the bubble solution. Learners also see how light reflection and interference create shimmering colors in the bubbles.

Exploratorium, The

2011-12-07

168

Best Bubbles  

NSDL National Science Digital Library

In this activity, learners experiment with creating various types of bubble solutions and testing which ingredients form longer-lasting bubbles. Learners investigate how surface tension works and the importance of using a surfactant to make bubbles. This activity includes a video about NASA astronaut Don Pettit, who used candy corn to conduct science experiments during his stint aboard the International Space Station.

Saltz, Austen

2010-01-01

169

Recalcitrant bubbles  

PubMed Central

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles).

Shanahan, Martin E. R.; Sefiane, Khellil

2014-01-01

170

Recalcitrant bubbles  

NASA Astrophysics Data System (ADS)

We demonstrate that thermocapillary forces may drive bubbles against liquid flow in `anomalous' mixtures. Unlike `ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just `downstream' of the minimum in surface tension. The exponential trend for bubbles in `anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles).

Shanahan, Martin E. R.; Sefiane, Khellil

2014-04-01

171

First observations of SBAS\\/WAAS scintillations: Using collocated scintillation measurements and all-sky images to study equatorial plasma bubbles  

Microsoft Academic Search

The first observations of amplitude scintillations on a Space Based Augmentation System (SBAS) satellite signal are presented. The scintillations occurred on the signal transmitted by a Wide Area Augmentation Satellite (WAAS) on 8–9 September 2004 from 2250–0045 LT. The GPS receiver that measured the scintillations is located on Haleakala, Hawaii (geomagnetic: 21.3°N, 271.4°E). With a maximum S4 = 0.35, corresponding

B. M. Ledvina; J. J. Makela

2005-01-01

172

Gravity wave initiation of equatorial spread F\\/plasma bubble irregularities based on observational data from the SpreadFEx campaign  

Microsoft Academic Search

The data from ground based experiments con- ducted during the 2005 SpreadFEx campaign in Brazil are used, with the help of theoretical model calculations, to in- vestigate the precursor conditions, and especially, the role of gravity waves, in the instability initiation leading to equa- torial spread F development. Data from a digisonde and a 30 MHz coherent back-scatter radar operated

M. A. Abdu; E. Alam Kherani; I. S. Batista; E. R. de Paula; D. C. Fritts; J. H. A. Sobral

2009-01-01

173

Equatorial Radar System.  

National Technical Information Service (NTIS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan...

S. Rukao T. Tsuda T. Sato S. Kato

1989-01-01

174

Equatorial radar system  

Microsoft Academic Search

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active

S. Rukao; T. Tsuda; T. Sato; S. Kato

1989-01-01

175

Bubble Suspension  

NSDL National Science Digital Library

In this activity, learners observe as soap bubbles float on a cushion of carbon dioxide gas. Learners blow bubbles into an aquarium filled with a slab of dry ice. Learners will be amazed as the bubbles hover on the denser layer of carbon dioxide gas, then begin to expand and sink before freezing on the dry ice. Use this activity to discuss sublimation, density, and osmosis as well as principles of buoyancy, semipermeability, and interference.

Exploratorium, The

2011-10-11

176

Big Bubbles  

NSDL National Science Digital Library

How do you measure a bubble when it's floating? You can't really, but in this activity, learners can measure the diameter of the ring of suds a bubble leaves on a flat surface. The fun is blowing up the bubbles as big as possible with a straw. Then comes the measuring. This activity can be used to connect science and math, and makes a great rainy day or indoor lunch activity.

Science, Lawrence H.

2010-01-01

177

Bubble Combustion  

NASA Technical Reports Server (NTRS)

A method of energy production that is capable of low pollutant emissions is fundamental to one of the four pillars of NASA s Aeronautics Blueprint: Revolutionary Vehicles. Bubble combustion, a new engine technology currently being developed at Glenn Research Center promises to provide low emissions combustion in support of NASA s vision under the Emissions Element because it generates power, while minimizing the production of carbon dioxide (CO2) and nitrous oxides (NOx), both known to be Greenhouse gases. and allows the use of alternative fuels such as corn oil, low-grade fuels, and even used motor oil. Bubble combustion is analogous to the inverse of spray combustion: the difference between bubble and spray combustion is that spray combustion is spraying a liquid in to a gas to form droplets, whereas bubble combustion involves injecting a gas into a liquid to form gaseous bubbles. In bubble combustion, the process for the ignition of the bubbles takes place on a time scale of less than a nanosecond and begins with acoustic waves perturbing each bubble. This perturbation causes the local pressure to drop below the vapor pressure of the liquid thus producing cavitation in which the bubble diameter grows, and upon reversal of the oscillating pressure field, the bubble then collapses rapidly with the aid of the high surface tension forces acting on the wall of the bubble. The rapid and violent collapse causes the temperatures inside the bubbles to soar as a result of adiabatic heating. As the temperatures rise, the gaseous contents of the bubble ignite with the bubble itself serving as its own combustion chamber. After ignition, this is the time in the bubble s life cycle where power is generated, and CO2, and NOx among other species, are produced. However, the pollutants CO2 and NOx are absorbed into the surrounding liquid. The importance of bubble combustion is that it generates power using a simple and compact device. We conducted a parametric study using CAVCHEM, a computational model developed at Glenn, that simulates the cavitational collapse of a single bubble in a liquid (water) and the subsequent combustion of the gaseous contents inside the bubble. The model solves the time-dependent, compressible Navier-Stokes equations in one-dimension with finite-rate chemical kinetics using the CHEMKIN package. Specifically, parameters such as frequency, pressure, bubble radius, and the equivalence ratio were varied while examining their effect on the maximum temperature, radius, and chemical species. These studies indicate that the radius of the bubble is perhaps the most critical parameter governing bubble combustion dynamics and its efficiency. Based on the results of the parametric studies, we plan on conducting experiments to study the effect of ultrasonic perturbations on the bubble generation process with respect to the bubble radius and size distribution.

Corrigan, Jackie

2004-01-01

178

The role of the equatorial electrojet in the evening ionosphere  

NASA Astrophysics Data System (ADS)

The role of the equatorial E region in the electrodynamics of the evening ionosphere is examined. The influence and reaction of the electrojet current on the equatorial ionosphere at sunset are investigated using a field-line-integrated 1D electrodynamic model. The 1D time-varying model predicts the divergence of the horizontal current of the equatorial electrojet for a given time variation of the horizontal electric field. The negative divergence of the horizontal current during the evening hours provides a net upward current out of the equatorial E region into the integrated ionosphere of higher equatorial altitudes and equivalent latitudes. This upward current affects the vertical electric field magnitudes and subsequent horizontal plasma drifts of the overlying ionosphere. It is proposed that the equatorial electrojet current near sunset has a significant role in the determination of the postsunset enhancement of the horizontal electric field.

Haerendel, G.; Eccles, J. V.

1992-02-01

179

Magnetic Bubbles  

NASA Astrophysics Data System (ADS)

Bubbles in liquids driven by a sound field are used in many disciplines: for example bubbles clean surfaces in ultrasonic water bathes, they catalyze unique chemical reactions in sonochemistry, and under special conditions even create light. However, conventional bubbles have a major limitation when placed in an acoustic field: it is extremely hard to control their position. Here we present a new type of bubble that has permanent magnetization originating from a shell of self-assembled nanoparticles, so that magnetic fields can be used to control the bubble's position independently. We will report on the recipe and the experiment to study bubble oscillations in weak magnetic fields. The magnetic susceptibility of the bubbles is proportional to their surface area,?=(9±3x10-6m)r^2, where r is the radius. Also they are compressible in moderate acoustic fields and induce a microstreaming flow with a toroidal vortex at the upper pole of the bubble. Similar microstreaming flows have been used to transport and rupture cells at small scales. Thus we envision applications in manipulation of biological materials and in microfluidic devices using acoustic and magnetic forces.

Zhao, Xue; Quinto-Su, Pedro; Ohl, Claus-Dieter

2008-11-01

180

Bubble Tray  

NSDL National Science Digital Library

In this activity, learners use simple materials to create giant bubbles. Learners will explore what gives bubbles their shape, what makes them break or last, what causes the colors and patterns in the soap film, and why do they change? Use this activity to introduce the concepts of surface tension and interference.

Exploratorium, The

2012-06-26

181

Bubble Trouble  

NSDL National Science Digital Library

In this activity on page 15 of the PDF, learners measure the amount of bubbles that they make using a detergent. Learners investigate whether adding Epsom salt to the solution affects its "sudsiness"--an important attribute of soap, since sudsy bubbles help soap clean greasy dirt. Use this activity to explore how chemicals can change a material's properties and how substances dissolve.

Society, American C.

2011-01-01

182

Bubble dielectrophoresis  

Microsoft Academic Search

The force due to polarization exerted on dielectric particles, vapor or gas bubbles, and voids in insulating dielectric liquids is an example of dielectrophoresis. This force is directly proportional to the gradient of the electric field intensity. Bubbles and voids are attracted into regions of lower electric field intensity, while dielectric particles (with higher relative polarizability) are attracted into regions

T. B. Jones; G. W. Bliss

1977-01-01

183

Nonlinear evolution of equatorial spread F. 1. On the role of plasma instabilities and spatial resonance associated with gravity wave seeding  

Microsoft Academic Search

We have used a computer simulation to study properties of large-scale equatorial F region irregularities produced by gravity waves by separating such different processes as the spatial resonance effect and the Rayleigh-Taylor instability. Our purpose is to show their relative importance in the production of strong ionization perturbations. When a gravity wave propagates perpendicular to the magnetic field, it generates

Chao-Song Huang

1996-01-01

184

Long wavelength irregularities in the equatorial electrojet  

Microsoft Academic Search

We have used the radar interferometer technique at Jicamarca to study in detail irregularities with wavelengths of a few kilometers generated in the unstable equatorial electrojet plasma during strong type 1 conditions. In-situ rocket observations of the same instability process are discussed in a companion paper. These large scale primary waves travel essentially horizontally and have large amplitudes. The vertical

Erhan Kudeki; Donald T. Farley; Bela G. Fejer

1982-01-01

185

Linear Theory of Equatorial Spread F  

Microsoft Academic Search

A fluid dispersion relation for the drift and interchange (Rayleigh-Taylor) modes in a collisional plasma forms the basis for a linear theory of equatorial spread F. The collisional drift mode growth rate will exceed the growth rate of the Rayleigh-Taylor mode at short perpendicular wavelengths and density gradient scale lengths, and the drift mode can grow on top side as

Mary K. Hudson; Charles F. Kennel

1975-01-01

186

Equatorial vertical plasma drifts and the measured and IRI model-predicted F2-layer parameters above Ouagadougou during solar minimum  

NASA Astrophysics Data System (ADS)

In this paper, hourly median value of ionosonde measurements: peak height F2-layer (hmF2), F2-layer critical frequency (foF2) and propagation factor M3000F2made at near-equatorial dip latitude, Ouagadougou, Burkina Faso (12°N, 1.5°W; dip: 1.5°N) and relevant F2-layer parameters: thickness parameter (Bo), electron temperature (Te), ion temperature (Ti), total electron content (TEC) and electron density (Ne) (at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial electrodynamicson the diurnal structure of F2-layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. It is demonstrated that the month-by-month morphological patterns between vertical E × B drifts and F2-layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F2-layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-Bo, IRI-Te and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Examination of the association between measured foF2, hmF2 and M3000F2illustrates consistent much more smaller correlation coefficients with no systematic linkage.

Oyekola, O. S.

2012-06-01

187

An Experimental System for Laboratory Simulation of Equatorial Electrojet Instabilities.  

National Technical Information Service (NTIS)

An experimental system which simulates the essential characteristics of the equatorial electrojet plasma is described. A description of the components of the system is given. Preliminary results of equilibrium and instability characteristics, the latter o...

P. I. John Y. C. Saxena

1975-01-01

188

Cauldron Bubbles  

NSDL National Science Digital Library

In this activity, learners mix up a bubbly brew and examine density. Learners explore how they can make different materials fall and rise in water using oil, water, and salt. Learners can experiment using other materials like sugar and sand.

Boston, Wgbh

2003-01-01

189

Tiny Bubbles.  

National Technical Information Service (NTIS)

SINCE DECOMPRESSION SICKNESS (DCS) was first described, the elusive nature of its pathophysiology has been a challenge. It is generally thought that intravascular and extravascular bubbles arc responsible for a host of downstream effects that cause the co...

R. T. Mahon

2010-01-01

190

Equatorial ionospheric response to the August 18,2003 geomagnetic storm  

NASA Astrophysics Data System (ADS)

The response of equatorial ionosphere-thermosphere system during geomagnetic disturbances is one of the important issues in space weather studies. Complementary ionospheric sounding measurements from three stations, viz., Palmas (10.2°S, 48.2°W; dip latitude 5.7°S) and Sao Jose dos Campos (23.2°S, 45.9°W; dip latitude 17.6°S), Brazil, and Ho Chi Minh City (10.5°N, 106.3°E; dip latitude 2.9°N), Vietnam, are presented for the period August 16 to 20, 2003. All the three stations are equipped with the Canadian Advanced Digital Ionosonde (CADI) and the Brazilian sector lags by 10 hours in local time the Vietnamese sector. The period selected for the present study related to storm effects on equatorial F-region electron density and irregularities includes the intense geomagnetic storm on August 18 (SSC 1421 UT on 17/08; ? Kp=52+; Ap=108; | Dst|max=168 at 1600 UT). A comparative study of the F-region ionospheric data from the two sectors for both the quiet and disturbed conditions are presented and discussed in terms of magnetospheric disturbance related dynamics of equatorial F-region irregularities in this communication. It should be pointed out that on the magnetically disturbed night of September 18-19, the Brazilian sector shows the development of large-scale ionospheric plasma irregularities or plasma bubbles, whereas the Vietnam data indicates suppression of ionospheric irregularities. Also, several global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread longitudinal TEC changes during the different phases of the storm.

Sahai, Y.; Fagundes, P. R.; Becker-Guedes, F.; Lima, W. L. C.; Lan, H. T.; MacDougall, J. W.; Pi, X.; Bolzan, M. J. A.; Abalde, J. R.; Pimenta, A. A.

191

Summary and future of ionospheric observations with the Equatorial Atmosphere Radar (EAR) in Indonesia  

NASA Astrophysics Data System (ADS)

Equatorial ionospheric observation with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20°S, 100.32°E, 10.36°S dip latitude) has been conducted since 2001, and its unique observational data has been obtained for almost one solar cycle. The EAR is sensitive to 3-m scale ionospheric irregularities, which can be regarded as a tracer of equatorial spread F (ESF) or plasma bubbles. ESF is one of the long-standing subjects in the low-latitude ionosphere particularly because plasma irregularities associated with ESF cause severe scintillation on satellite signals which results in communication/navigation outages. The rapid beam steering capability of the active phased array system of the EAR, along with simultaneous ground-based and satellite observations, has revealed important aspects such as spatial/temporal structures of ESF and other intriguing phenomena. During solar maximum period, ESF plumes are observed just after sunset and traverse eastward until around midnight. During solar minimum period, on the other hand, the radar backscatter echoes are commonly observed around or after midnight and traverse westward, which are quite similar to the midlatitude-type irregularities observed with the MU radar in Japan. As the EAR is located at 10.36°S dip latitude, the E-region altitude illuminated by the EAR is coupled with the F-region altitude above the dip equator along a magnetic flux tube, which enables us to study the electrodynamic coupling between the E and F regions. We will summarize observational results with the EAR during the previous solar cycle, and discuss future potential of the ionospheric observation with the EAR.

Yokoyama, Tatsuhiro; Yamamoto, Mamoru; Fukao, Shoichiro

2012-07-01

192

Bubble Suspension  

NSDL National Science Digital Library

This activity from the Exploratorium illustrates the principles of buoyancy, semipermeability, and interference as soap bubbles float on a cushion of carbon dioxide gas. Dry ice, gloves, and adult supervision are required to view the beautiful effect. The site also includes an explanation of the physics involved and other quick experiments that can be done with bubbles. This activity is part of Exploratorium's Science Snacks series.

2006-07-16

193

Stereoisomer Bubbles  

NASA Astrophysics Data System (ADS)

Undergraduate organic chemistry students are given a simple method to determine the stereochemical relationships between several molecules with more than one chiral center. The four groups around each chiral center are assigned Cahn-Ingold-Prelog priorities, and these numbers encircled in "bubbles". Subsequent structure manipulations by the allowed Fisher projection rotations involve only these four number bubbles to make R or S assignments. A table of relationships (identical, diastereomer, or enantiomer) between all the molecules is then generated.

Lesko, Melanie J.

1996-05-01

194

Exploring Bubbles  

NASA Astrophysics Data System (ADS)

Bubbles provide an enjoyable and festive medium through which to teach many concepts within the science topics of light, color, chemistry, force, air pressure, electricity, buoyancy, floating, density, among many others. In order to determine the nature of children's engagement within a museum setting and the learning opportunities of playing with bubbles, I went to a children's interactive museum located in a metropolitan city in the Northeastern part of the United States.

O'Geary, Melissa A.

195

Bubble diagnostics  

DOEpatents

The present invention is intended as a means of diagnosing the presence of a gas bubble and incorporating the information into a feedback system for opto-acoustic thrombolysis. In opto-acoustic thrombolysis, pulsed laser radiation at ultrasonic frequencies is delivered intraluminally down an optical fiber and directed toward a thrombus or otherwise occluded vessel. Dissolution of the occlusion is therefore mediated through ultrasonic action of propagating pressure or shock waves. A vapor bubble in the fluid surrounding the occlusion may form as a result of laser irradiation. This vapor bubble may be used to directly disrupt the occlusion or as a means of producing a pressure wave. It is desirable to detect the formation and follow the lifetime of the vapor bubble. Knowledge of the bubble formation and lifetime yields critical information as to the maximum size of the bubble, density of the absorbed radiation, and properties of the absorbing material. This information can then be used in a feedback system to alter the irradiation conditions.

Visuri, Steven R. (Livermore, CA) [Livermore, CA; Mammini, Beth M. (Walnut Creek, CA) [Walnut Creek, CA; Da Silva, Luiz B. (Danville, CA) [Danville, CA; Celliers, Peter M. (Berkeley, CA) [Berkeley, CA

2003-01-01

196

Equatorial Coordinates Model  

NSDL National Science Digital Library

The Equatorial Coordinates model displays the position of a star in equatorial (Right Ascension/Declination --- RA/Dec) coordinates. The horizon is shown along with the four cardinal directions (N, E, S, and W). The Latitude slider changes the latitude of the observer which is shown by the change in the (teal) celestial pole relative to the northern horizon. The position of the star can be changed by using the Right Ascension and Declination sliders. Once these coordinates are selected, pressing the play button will put the star, celestial grid, and the equatorial coordinates in motion to simulate the 23 hour and 56 minute motion of stars in the night sky. Equatorial Coordinates model is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_astronomy_EquatorialCoordinates.jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the plot and selecting "Open EJS Model" from the pop-up menu item.

Belloni, Mario; Timberlake, Todd

2009-11-14

197

On the occurrence of equatorial F-region irregularities during solar minimum using radio occultation measurements  

NASA Astrophysics Data System (ADS)

The technique of radio occultation (RO) is demonstrated to be a powerful tool for studying equatorial F-region irregularities (EFIs) associated with equatorial plasma bubbles. The extensive 4.9 year RO dataset of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites was employed in this study and contains EFI observations under a wide variety of solar and geomagnetic conditions. From an analysis of the EFI occurrence dependence on season/longitude, it is found that the EFI occurrence statistics largely match those reported previously, with the exception of an equinoctial EFI occurrence maximum in the American sector that is absent from previous studies. It is revealed that this maximum is due to enhanced EFI occurrence near the South Atlantic anomaly, where EFIs are expected to be suppressed by particle precipitation. An investigation into the solar activity dependence of the EFI occurrence characteristics revealed significant increases in the range of local times and latitudes with solar activity for most longitude sectors and seasons. Finally, the EFI suppression and enhancement effects of storm-time electric fields are also investigated using the COSMIC data.

Carter, B. A.; Zhang, K.; Norman, R.; Kumar, V. V.; Kumar, Sushil

2013-02-01

198

Tiny Bubbles  

NSDL National Science Digital Library

In this activity, which can be performed as a demonstration by the teacher or by the students themselves, carbon dioxide is generated in a fish tank using sodium bicarbonate and vinegar. The students can observe as the accumulating carbon dioxide extinguishes candles of different heights, marking rising levels of CO2 in the tank. They can also blow soap bubbles (which contain air) into the tank and observe them floating on the denser CO2 at first, then sinking as the gas diffuses through the soap film that forms the bubbles.

Dolphin, Glenn

199

Study of Equatorial Scintillations.  

National Technical Information Service (NTIS)

Observations of the amplitude scintillations produced by the F-region in equatorial areas are presented. The equipment used for conducting the observations is described. The use of transmissions from the ATS-1, ATS-3, and ATS-5 for obtaining data is descr...

J. Pomalaza R. Woodman G. Tisnado E. Nakasone

1972-01-01

200

Effects of equatorially trapped ions on refilling of the plasmasphere  

NASA Technical Reports Server (NTRS)

The kinetic aspects of shock formation in response to the equatorial heating of ions are reported by means of small-scale kinetic simulations of countersteaming plasma flows along a spatially varying magnetic field having the features of the dipolar magnetic field lines. Attention is given to the trapping of the field-aligned flowing ions in response to the simulated equatorial heating of ions and the associated self-consistent structures in the electric potentials and the f-plasma flow pattern. Trapping is found to lead to the formation of electrostatic shocks, which propagate away from the 'equator' as seen in the hydrodynamic model of Singh and Torr (1990). The shocks form near the mirror points of the 'equatorially' heated ions. The second stage of the refilling with equatorially trapped ions is reported. A variety of structures in density and temperature distributions as the refilling proceeds slowly is found.

Singh, Nagendra; Chan, C. B.

1992-01-01

201

Leverage bubble  

NASA Astrophysics Data System (ADS)

Leverage is strongly related to liquidity in a market and lack of liquidity is considered a cause and/or consequence of the recent financial crisis. A repurchase agreement is a financial instrument where a security is sold simultaneously with an agreement to buy it back at a later date. Repurchase agreement (repo) market size is a very important element in calculating the overall leverage in a financial market. Therefore, studying the behavior of repo market size can help to understand a process that can contribute to the birth of a financial crisis. We hypothesize that herding behavior among large investors led to massive over-leveraging through the use of repos, resulting in a bubble (built up over the previous years) and subsequent crash in this market in early 2008. We use the Johansen-Ledoit-Sornette (JLS) model of rational expectation bubbles and behavioral finance to study the dynamics of the repo market that led to the crash. The JLS model qualifies a bubble by the presence of characteristic patterns in the price dynamics, called log-periodic power law (LPPL) behavior. We show that there was significant LPPL behavior in the market before that crash and that the predicted range of times predicted by the model for the end of the bubble is consistent with the observations.

Yan, Wanfeng; Woodard, Ryan; Sornette, Didier

2012-01-01

202

Tiny Bubbles.  

ERIC Educational Resources Information Center

A simple oxygen-collecting device (easily constructed from glass jars and a lid) can show bubbles released by water plants during photosynthesis. Suggestions are given for: (1) testing the collected gas; (2) using various carbon dioxide sources; and (3) measuring respiration. (DH)

Kim, Hy

1985-01-01

203

Latitudinal extension of equatorial scintillations measured with a network of GPS receivers  

NASA Astrophysics Data System (ADS)

A latitudinally-spaced network of GPS receivers extending within Colombia, Peru and Chile has served to provide a measurement of the latitudinal extension of scintillations and TEC depletions associated with equatorial plasma bubbles. These observations were obtained with five Leica GPS receivers managed by Boston College and five additional receivers that are operated by other institutions. The BC receivers are controlled by specially-designed software that performs real-time calculations of the scintillation S4 index using the L1 signal. First, we present case-study events in which we correlate the GPS-determined largest magnetic latitude of scintillations, the maximum latitude where TEC depletions are observed and the altitude extension of radar plumes measured concurrently with the JULIA radar. We also show the statistics of scintillations and latitudinal profiles of TEC gathered during the first 6 months of operations of the GPS receiver at Bogota. We observe an almost perfect correlation between scintillations and TEC depletions. We confirm that the maximum latitude of scintillations (and TEC depletions) map quite well to the apex altitude of the radar plumes measured by JULIA. We also compare the location of the northern crest of the equatorial anomaly and the latitude of scintillations, and demonstrate that for 90% of the days between August 2001 and February 2002 scintillations are bounded by the limits of the anomaly crests. The anomaly peaks are the regions where the more intense GPS scintillations and the deepest depletions are seen. We have also correlated the value of the S4 index with the density profiles detected at the magnetic equator by the digisonde operating at Jicamarca. We conclude that the intense S4 values at an anomaly location such as Bogota are attributed to a higher altitude of the equatorial F-region instead of the depth of the local value of the TEC depletion.

Valladares, C.; Sheehan, R.; Basu, S.; Hagan, M.

2003-04-01

204

Equatorial African climate teleconnections  

NASA Astrophysics Data System (ADS)

Teleconnections between equatorial African climate and the surrounding circulation are examined using a convective index over the Congo River Basin in March to May (MAM) and July to September (JAS) seasons. Its influence on the wider region is determined through lag correlation and cross-wavelet analysis. During seasons of deeper convection, easterly winds weaken over the tropical Atlantic (anomalous flow toward Africa), whilst upper westerly winds weaken over southern Africa (in JAS). We view this as zonal overturning with ascent over the equatorial African lowlands and Congo River Basin that spreads moisture to the North African Sahel, with influence from the Pacific El Niño. Another facet of our study is the relationship between East African highlands rainfall and the Indian Ocean circulation. We find coupling between the Indian Ocean Rossby wave, a thermocline oscillation and Walker cell over the Indian Ocean that induces shifts in rainfall, particularly in the October to December season.

Jury, M. R.; Matari, E.; Matitu, M.

2009-03-01

205

Equatorial radar system  

Microsoft Academic Search

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar will be built in Pontianak, West Kalimantan, Indonesia (0.03 deg N, 109.29 deg E). The system is a 47-MHz monostatic Doppler radar with an active phased array configuration

Shoichiro Fukao; Toshitaka Tsuda; Toru Sato; Susumu Kato

1990-01-01

206

Photon Bubbles and Ion Acceleration in a Plasma Dominated by the Radiation Pressure of an Electromagnetic Pulse  

NASA Astrophysics Data System (ADS)

The stability of a thin plasma foil accelerated by the radiation pressure of a high intensity electromagnetic (e.m.) pulse is investigated analytically and with particle in cell numerical simulations. It is shown that the onset of a Rayleigh-Taylor-like instability can lead to transverse bunching of the foil and to broadening of the energy spectrum of fast ions. The use of a properly tailored e.m. pulse with a sharp intensity rise can stabilize the foil acceleration.

Pegoraro, F.; Bulanov, S. V.

2007-08-01

207

Late Pliocene equatorial Pacific  

Microsoft Academic Search

Late Pliocene foraminiferal Mg\\/Ca and ?18O records from Ocean Drilling Program Hole 806B in the western equatorial Pacific (WEP) reveal warm pool climate evolution during the onset of Northern Hemisphere glaciation, 3.1–2.3 Myr B.P. Mg\\/Ca data indicate an average late Pliocene sea surface temperature (SST) of 27.8°C, a small long-term cooling of 0.3°C between 3.1 and 2.3 Ma, and a

Martín Medina-Elizalde; David W. Lea

2010-01-01

208

Late Pliocene equatorial Pacific  

Microsoft Academic Search

Late Pliocene foraminiferal Mg\\/Ca and delta18O records from Ocean Drilling Program Hole 806B in the western equatorial Pacific (WEP) reveal warm pool climate evolution during the onset of Northern Hemisphere glaciation, 3.1-2.3 Myr B.P. Mg\\/Ca data indicate an average late Pliocene sea surface temperature (SST) of 27.8°C, a small long-term cooling of 0.3°C between 3.1 and 2.3 Ma, and a

Martín Medina-Elizalde; David W. Lea

2010-01-01

209

Cross-equatorial structures of equatorially trapped nonlinear Rossby waves  

NASA Astrophysics Data System (ADS)

Analysis of the Sea Surface Height (SSH) from satellite altimeters has shown that equatorially trapped Rossby waves exhibit asymmetric cross-equatorial structures; their northern extrema are much larger in magnitude than their southern counterparts. Such asymmetry is inconsistent with the classical theory for the first baroclinic, first meridional equatorially trapped Rossby mode, which predicts that SSH and zonal velocity are symmetric in latitude and the meridional velocity is latitudinally antisymmetric (Matsuno, 1966). Chelton et al. (2003) attributed the observed asymmetry to the mean-shear-induced modifications of first meridional mode Rossby waves. The present paper examines nonlinear rectification of cross-equatorial wave structures in the presence of different zonal mean currents. Nonlinear traveling Rossby waves embedded in shears are calculated numerically in a 1.5-layer model. Nonlinearity is shown to increase the cross-equatorial asymmetry substantially making the northern extrema even more pronounced. However, nonlinearity only slightly increases the magnitude of the westward phase speed.

Zhou, Cheng; Boyd, John P.

2013-11-01

210

Equatorial radar system  

NASA Astrophysics Data System (ADS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active phased array configuration similar to that of the MU radar in Japan, which has been in successful operation since 1983. It will have a PA product of more than 5 x 10(9) sq. Wm (P = average transmitter power, A = effective antenna aperture) with sensitivity more than 10 times that of the MU radar. This system configuration enables pulse-to-pulse beam steering within 25 deg from the zenith. As is the case of the MU radar, a variety of sophisticated operations will be made feasible under the supervision of the radar controller. A brief description of the system configuration is presented.

Rukao, S.; Tsuda, T.; Sato, T.; Kato, S.

1989-04-01

211

Equatorial radar system  

NASA Technical Reports Server (NTRS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar, called the Equatorial Radar, will be built in Pontianak, Kalimantan Island, Indonesia (0.03 N, 109.3 E). The system is a 47 MHz monostatic Doppler radar with an active phased array configuration similar to that of the MU radar in Japan, which has been in successful operation since 1983. It will have a PA product of more than 5 x 10(9) sq. Wm (P = average transmitter power, A = effective antenna aperture) with sensitivity more than 10 times that of the MU radar. This system configuration enables pulse-to-pulse beam steering within 25 deg from the zenith. As is the case of the MU radar, a variety of sophisticated operations will be made feasible under the supervision of the radar controller. A brief description of the system configuration is presented.

Rukao, S.; Tsuda, T.; Sato, T.; Kato, S.

1989-01-01

212

Photon bubbles and ion acceleration in a plasma dominated by the radiation pressure of an electromagnetic pulse.  

PubMed

The stability of a thin plasma foil accelerated by the radiation pressure of a high intensity electromagnetic (e.m.) pulse is investigated analytically and with particle in cell numerical simulations. It is shown that the onset of a Rayleigh-Taylor-like instability can lead to transverse bunching of the foil and to broadening of the energy spectrum of fast ions. The use of a properly tailored e.m. pulse with a sharp intensity rise can stabilize the foil acceleration. PMID:17930836

Pegoraro, F; Bulanov, S V

2007-08-10

213

Magnetic Dipole Inflation with Cascaded ARC and Applications to Mini-Magnetospheric Plasma Propulsion  

NASA Technical Reports Server (NTRS)

Mini-Magnetospheric Plasma Propulsion (M2P2) seeks to create a plasma-inflated magnetic bubble capable of intercepting significant thrust from the solar wind for the purposes of high speed, high efficiency spacecraft propulsion. Previous laboratory experiments into the M2P2 concept have primarily used helicon plasma sources to inflate the dipole magnetic field. The work presented here uses an alternative plasma source, the cascaded arc, in a geometry similar to that used in previous helicon experiments. Time resolved measurements of the equatorial plasma density have been conducted and the results are discussed. The equatorial plasma density transitions from an initially asymmetric configuration early in the shot to a quasisymmetric configuration during plasma production, and then returns to an asymmetric configuration when the source is shut off. The exact reasons for these changes in configuration are unknown, but convection of the loaded flux tube is suspected. The diffusion time was found to be an order of magnitude longer than the Bohm diffusion time for the period of time after the plasma source was shut off. The data collected indicate the plasma has an electron temperature of approximately 11 eV, an order of magnitude hotter than plasmas generated by cascaded arcs operating under different conditions. In addition, indirect evidence suggests that the plasma has a beta of order unity in the source region.

Giersch, L.; Winglee, R.; Slough, J.; Ziemba, T.; Euripides, P.

2003-01-01

214

Lightning over Equatorial Africa  

NASA Technical Reports Server (NTRS)

These two images were taken 9 seconds apart as the STS-97 Space Shuttle flew over equatorial Africa east of Lake Volta on December 11, 2000. The top of the large thunderstorm, roughly 20 km across, is illuminated by a full moon and frequent bursts of lightning. Because the Space Shuttle travels at about 7 km/sec, the astronaut perspectives on this storm system becomes more oblique over the 9-second interval between photographs. The images were taken with a Nikon 35 mm camera equipped with a 400 mm lens and high-speed (800 ISO) color negative film. Images are STS097-351-9 and STS097-351-12, provided and archived by the Earth Science and Image Analysis Laboratory, Johnson Space Center. Additional images taken by astronauts can be viewed at NASA-JSC's Gateway to Astronaut Photography of Earth at http://eol.jsc.nasa.gov/

2002-01-01

215

Late Pliocene equatorial Pacific  

NASA Astrophysics Data System (ADS)

Late Pliocene foraminiferal Mg/Ca and ?18O records from Ocean Drilling Program Hole 806B in the western equatorial Pacific (WEP) reveal warm pool climate evolution during the onset of Northern Hemisphere glaciation, 3.1-2.3 Myr B.P. Mg/Ca data indicate an average late Pliocene sea surface temperature (SST) of 27.8°C, a small long-term cooling of 0.3°C between 3.1 and 2.3 Ma, and a glacial-interglacial (G-I) SST range of 2°C throughout this time interval. For comparison, Pleistocene SSTs at this site over the last 0.9 Myr average 27.7°C with a G-I range of 3°C. Orbital-scale variability in Hole 806B SSTs during the late Pliocene occurs predominantly at ˜100 ka, in contrast to foraminiferal ?18O records, which show a dominant 41 kyr period. Variability at a 41 kyr period, out of phase with local annual insolation changes driven by obliquity, is also observed in the new WEP SST record. The WEP SST record suggests that an ˜3°C equatorial Pacific SST zonal gradient prevailed during the late Pliocene, compatible with a weaker Walker circulation. Adjustment of Hole 806B SSTs for past changes in seawater Mg/Ca suggests that SSTs higher than 30°C prevailed at 3 Myr B.P., followed by a progressive cooling of the warm pool through the late Pliocene. The characteristics of late Pliocene tropical climate evolution suggest that atmospheric greenhouse gas forcing played a major role in driving the observed G-I SST changes.

Medina-Elizalde, Martín; Lea, David W.

2010-05-01

216

Ventilation of the equatorial Atlantic  

NASA Astrophysics Data System (ADS)

The equatorial oxygen maximum at intermediate depth (300m-700m) is a characteristic feature of the observed water mass distribution of the tropical Atlantic, but it is not well reproduced in biogeochemical models. Here we analyze long-term moored velocity and oxygen observations as well as shipboard hydrographic and current sections acquired along 23°W, which cover the depth range of the oxygen minimum zones of the eastern tropical North and South Atlantic. The mean flow field from shipboard observations shows the presence of the equatorial intermediate current system (EICS) with strongest eastward flow at 2°N/S and westward flow in between. The moored zonal velocity data show high-baroclinic mode equatorial deep jet (EDJ) oscillations at a period of about 4.5 years. Equatorial oxygen observations which do not resolve or cover a full 4.5-yr EDJ cycle nevertheless reveal large variability, with oxygen concentrations locally spanning a range of more than 60 ?mol/kg. We study the effect of the EICS and EDJs on the equatorial oxygen concentration by forcing an advection-diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed EDJ cycle superimposed on the mean EICS. The advection-diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere. The respective role of mean advection, EDJs, and other possible processes in shaping the mean oxygen distribution of the equatorial Atlantic at intermediate depth is discussed.

Brandt, Peter; Greatbatch, Richard J.; Claus, Martin; Didwischus, Sven-Helge; Hahn, Johannes

2013-04-01

217

Diagnosing temperature change inside sonoluminescing bubbles by calculating line spectra.  

PubMed

With the numerical calculation of the spectrum of single bubble sonoluminescence, we find that when the maximum temperature inside a dimly luminescing bubble is relatively low, the spectral lines are prominent. As the maximum temperature of the bubble increases, the line spectrum from the bright bubble weakens or even fades away relative to the background continuum. The calculations in this paper effectively interpret the observed phenomena, indicating that the calculated results, which are closely related to the spectrum profile, such as temperature and pressure, should be reliable. The present calculation tends to negate the existence of a hot plasma core inside a sonoluminescing bubble. PMID:19905449

An, Yu; Li, Chaohui

2009-10-01

218

Shock-wave propagation in a sonoluminescing gas bubble  

NASA Technical Reports Server (NTRS)

The motion of the bubble radius and of the air trapped inside the bubble during sonoluminescence are determined self-consistently by coupling the solution of the Rayleigh-Plesset equation governing the bubble radius to the solution of Euler's equations for the motion of air in the bubble. Results are presented for three slightly different conditions of excitation, in two of which shocks are formed during the collapse of the bubble, and in which such high temperatures are attained that the air is ionized. Estimates are made of the duration and intensity of the light then radiated by the plasma.

Wu, C. C.; Roberts, Paul H.

1993-01-01

219

Substorm currents in the equatorial magnetotail  

NASA Astrophysics Data System (ADS)

We have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed from these variations, and systems of field-aligned currents were deduced. During the growth phase to the maximum phase of the taillike reconfiguration of the near-Earth magnetic field, a positive divergence (away from the equatorial plane) of the westward equatorial current occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the premidnight to early morning MLT sector. The field-aligned current associated with these divergences flows into the ionosphere in the late evening to premidnight MLT sector and flows away from the ionosphere in the premidnight to early morning MLT sector. This flow direction pattern is the same as that of the region 2 field-aligned current system. During the expansion phase a field-aligned current that is distinctive to the growth phase field-aligned current is generated in the same near-Earth plasma sheet region. The field-aligned current flows away from the ionosphere in the late evening to premidnight MLT sector and flows into the ionosphere in the premidnight to morning MLT sector. These field-aligned currents are due to a change in a sign of the divergence of the westward equatorial current. This flow direction pattern is same as that of the region 1 field-aligned current system and also of the current-wedge model. This region 1 sense field-aligned current develops first near midnight at about 5 min after the expansion phase onset (as determined from the ground-based magnetometer data), is delayed by 10-25 min farther away from midnight in the evening and morning MLTs, and continues until the end of geomagnetic depolarization at the site of either GOES 5 or GOES 6, whichever is located closer to midnight. We have also determined the presence of a radial current that flows toward the earth in the late evening to premidnight sector and flows away from the Earth in the midnight to morning sector. The intensity of the radial currents increases before the expansion phase. Consequently, the patterns of field-aligned currents associated with various substorm phases are the superposition of currents driven by multiple sources with different temporal variations. We have identified at least three different, but related sources of field-aligned currents during the growth and expansion phases. These sources are related to the divergence of the westward flowing equatorial current and to distributions of pressure and magnetic field gradients that evolve in the magnetotail. These patterns include the current-wedge model during the expansion phase. When combined, these complicated systems support the basic region 1 to region 2 field-aligned current flow pattern.

Iijima, T.; Watanabe, M.; Potemra, T. A.; Zanetti, L. J.; Kan, J. R.; Akasofu, S.-I.

1993-10-01

220

Calculations of equatorial scintillations at VHF and gigahertz frequencies based on a new model of the disturbed equatorial ionosphere  

Microsoft Academic Search

The weak scattering, thin screen theory of scintillation of radio stars and satellites has been applied, in a mathematically rigorous way, to the observations of the plasma density structure deduced from rocket and radar measurements during equatorial spread F conditions. It is shown that bottomside spread F is capable of producing moderate scintillation at VHF, but not at gigahertz frequencies.

Emanoel Costa; M. C. Kelly

1976-01-01

221

Traveling planetary wave ionospheric disturbances and their role in the generation of equatorial spread-F and GPS phase fluctuations during the last extreme low solar activity and comparison with high solar activity  

NASA Astrophysics Data System (ADS)

This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region virtual height rise during the E×B electric field pre-reversal enhancement (PRE), near sunset hours. We also studied their role in the generation of equatorial spread F (ESF) and GPS phase fluctuations during periods of the last extreme low solar activity (LSA) of January 2009 to April 2010 (F10.7bar=73). A comparison is made with periods of high solar activity (HSA) in 2003 and 2004 near equatorial region. The ionospheric irregularities investigated are medium (bottom-side) and large (plasma bubble) scales. Ionospheric F region oscillations with period of days are due to the TPWIDs, which play an important role in producing favorable or unfavorable conditions for equatorial ionospheric irregularities, changing the electron vertical profile and F region height. In this paper, we present simultaneous ionospheric sounding (ionosonde) and GPS vertical total electron content (vTEC) observations carried out near equatorial region (Palmas 10.2°S, 48.2°W) and low latitude region (São José dos Campos 23.2°S, 45.9°W; located under the southern crest of the equatorial ionospheric anomaly), Brazil. Observations show that the occurrence of fresh ESF during LSA and HSA and fresh GPS phase fluctuations at equatorial region follow the trend of day-to-day variations in the F region virtual height, which are due to electric field PRE modulated by TPWID wave like oscillations. During LSA, the altitude of 250 km acts as a threshold height for the generation of fresh ionospheric irregularities, whereas during HSA, the threshold height is 300 km. The observations also found a strong increase in the generation of fresh ionospheric irregularities from October 2009 to March 2010 during LSA and from September 2003 to March 2004 during the HSA. Furthermore, in LSA, the period of fresh ionospheric irregularities was less than during HSA, though both periods followed a similar seasonal pattern. In the low-latitude, we observed more ESFs than phase fluctuations because ionosonde is more sensitive than GPS. We also observed periods with and without day-to-day oscillations in the F region virtual height. The observations made by GPS stations and ionosondes in the equatorial region, for much of the period analyzed, presented similar results with regard to the generation of equatorial ionospheric irregularities. In the low latitude, some nights of January, February, October, and December 2009 also showed a similarity.

de Abreu, A. J.; Fagundes, P. R.; Bolzan, M. J. A.; Gende, M.; Brunini, C.; de Jesus, R.; Pillat, V. G.; Abalde, J. R.; Lima, W. L. C.

2014-09-01

222

Optical emissions in a sonoluminescing bubble  

NASA Astrophysics Data System (ADS)

We study how the mechanism of spontaneous decay of atoms (or molecules) in a sonoluminescing bubble (SLB) can be affected by the high density and high temperature environment resulting from the rapid collapse of the gas bubble immediately prior to light emission. We present a detailed study of the density of states of photons in multiple-layered spheres, which mimic various stages of a SLB. In particular, we found that the spontaneous decay rate could be strongly enhanced in the presence of a thin plasma shell inside the bubble, which was predicted recently in numerical hydrodynamic simulations of a SLB.

Chen, T. W.; Leung, P. T.; Chu, M.-C.

2000-11-01

223

Equatorial radar system  

NASA Astrophysics Data System (ADS)

A large clear air radar with the sensitivity of an incoherent scatter radar for observing the whole equatorial atmosphere up to 1000 km altitude is now being designed in Japan. The radar will be built in Pontianak, West Kalimantan, Indonesia (0.03 deg N, 109.29 deg E). The system is a 47-MHz monostatic Doppler radar with an active phased array configuration similar to that of the MU radar in Japan, which has been in successful operation since 1983. It will have a PA product of about 3 x 10 to the 9th W sq m (P = average transmitter power, A = effective antenna aperture) with a sensitivity of approximately 10 times that of the MU radar. This system configuration enables pulse-to-pulse beam steering within 20 deg from the zenith. As is the case of the MU radar, a variety of operations will be made feasible under the supervision of the radar controller. A brief description of the system configuration is presented.

Fukao, Shoichiro; Tsuda, Toshitaka; Sato, Toru; Kato, Susumu

224

The Colorado Equatorial Sundial  

NASA Astrophysics Data System (ADS)

The University of Colorado received from Mr. and Mrs. J. H. Tippit in 1995 a large equatorial sundial in memory of one of their sons, John Garrey Tippit, who graduated from the University of Colorado and was killed in a construction accident in 1969. The sundial is installed in the quadrangle in front of our main Norlin Library. The sundial is made of a large slab of Colorado rose-red granite, mined a few miles from Boulder. It is approximately 185 cm in diameter and 16 cm thick. The gnomon is a steel rod 7.6 cm in diameter and 205 cm in total length. The total mass, estimated from the average densities of granite and steel, is about 1400 kg, and this large mass made it impossible to make slight adjustments to the setup after installation. The sundial carries the motto "Knowledge and time abide in the same place". The sundial can be read to an accuracy of about one minute. We are making a large number of checks of the time; after allowing for the longitude and the equation of time the residuals are up to about three minutes, depending on whether one is using the winter or summer side and on whether it is morning or afternoon. We intend to analyze the errors after we have made checks for about a year.

Garstang, R. H.

1996-05-01

225

Occurrence of Equatorial F Region Irregularities: Evidence for Tropospheric Seeding  

NASA Technical Reports Server (NTRS)

We present a new gap-free version of the seasonal and longitudinal 0 (s/l) variations of P(sub EFI), the equatorial F region irregularity (EFI) occurrence probability, based on data from the AE-E spacecraft. The agreement of this and three earlier partial P(sub EFI) patterns verifies all four. We reinterpret another earlier gap-ridden pattern, that of D(bar)(sub RSF), a topside ionogram index of average darkening by range spread F. We compare it with P(sub EFI) and, using ionosonde radio science considerations, we conclude that D(bar)(sub RSF) = P(sub EFI) times a factor depending on the average number of topside plasma bubbles visible to the ionosonde. The s/l variations of D(baar)(sub RSF) thus imply s/l variations in the average spacing of bubbles, whose seeds have an occurrence probability pattern P(sub seed). For discussion we assume P(sub EFI) = P(sub inst)P(sub seed) is the pattern of F region instability. The P(sub EFI) pattern, which is by definition independent of seed and/or bubble spacing, is far too complex to be explained by the dominant paradigm, that of changes in P(sub inst) by simple changes in the F region altitude and/or north-south asymmetry. We examine evidence behind this dominance, and find it unconvincing. Both the asymmetry and sunset-node/altitude hypotheses of 1984 and 1985, respectively, seem to be partly based on misunderstood data, and their features appear displaced in time and space from those of our repeatable P(sub EFI) pattern. In contrast, if P(sub seed) variations influence the P(sub EFI) pattern and depend on thermospheric gravity waves from tropospheric convection near the dip equator, then the seasonal maxima (minima) Of P(sub EFI) could be explained, since they all occur above relatively warm (cold) surface features, where convection is maximal (minimal). Also, the hypothesis of the dominance of the P(sub seed) term could explain an unusual December/January P(sub EFI) maximum in the deep, wide, normal Pacific minimum in the one data set obtained in El Nino years. Based on the experiments we consider, we predict that the s/l variations Of P(sub seed) will be found to be similar to those of P(sub EFI) and largely to explain them. Finally, we find reasons, based on the similarity of the D(sub RSF) variations to s/l patterns of the average scintillation index, for not using, as is commonly done, such scintillation patterns as substitutes for P(sub EFI) or P(sub inst) patterns.

McClure, J. P.; Singh, S.; Bamgboye, D. K.; Johnson, F. S.; Kil, Hyosub

1998-01-01

226

Equatorial F-layer heights, evening prereversal electric field, and night E-layer density in the American sector: IRI validation with observations  

NASA Astrophysics Data System (ADS)

The equatorial F-layer height variations resulting from the variabilities in the zonal electric fields and winds and associated variability in ionospheric dynamo strength are important factors in determining the distribution and structuring of the electron density of the equatorial ionization anomaly (EIA) region. Especially, the evening enhancement in the F-layer heights and the associated prereversal enhancement in the zonal electric field due to the F-layer dynamo are believed to provide the most basic precondition for the equatorial spread F/ plasma bubble irregularity (ESF) generation. A realistic description by the International Reference Ionosphere (IRI) of the quiet time equatorial F-layer heights is therefore of fundamental importance for applications related to the studies of the ESF and EIA variabilities. The existing IRI description scheme (that uses the CCIR coefficients) appears to represent the equatorial F-layer peak density ( N mF 2/ƒ oF2) better than the peak height ( h mF2) and the heights of specific densities, the largest disagreement with observations being verified during the evening hours. Digisonde data from the three permanent stations in Brazil: São Luis (2.33°S, 44.2°W, dip angle: -.5°); Fortaleza (3.9°S, 38.45°W, dip angle: -9°); and Cachoeira Paulista (22.6°S, 315°E; dip angle: -28°) and from Jicamarca (12°S, 76.9°W; dip latitude: 1°N) in Peru have been analysed, to determine the quiet time mean behavior of the key F-layer parameters as a function of local time, season, and solar activity. These are complemented by data from the three conjugate point stations: Boa Vista (02.8°N; 60.66°W, dip angle: 22.5°) in the north and Campo Grande (20.45°S; 54.65°W, dip angle: -22.5°) in the south, and an equatorial station, Cachimbo (9.47°S; 54.83°W, dip angle: -3.9°) that were operated during the 2002 COPEX (Conjugate Point Experiment) campaign conducted in Brazil. The data for São Luis and Jicamarca are used to evaluate the longitudinal differences in the prereversal F-layer vertical drift, arising from the large magnetic declination angle difference that characterize these Brazilian and Peruvian longitude sectors. An attempt is made to characterize and quantify any systematic difference that exists between the mean behavioral patterns of the critical parameters as described by the IRI and those observed, with an objective to improve the IRI prediction capability.

Abdu, M. A.; Batista, I. S.; Reinisch, B. W.; Carrasco, A. J.

2004-01-01

227

Ventilation of the equatorial Atlantic by the equatorial deep jets  

NASA Astrophysics Data System (ADS)

Equatorial deep jets (EDJs) are a prominent flow feature of the equatorial Atlantic below the Equatorial Undercurrent down to about 3000 m. Here we analyze long-term moored velocity and oxygen observations, as well as shipboard hydrographic and current sections acquired along 23°W and covering the depth range of the oxygen minimum zones of the eastern tropical North and South Atlantic. The moored zonal velocity data show high-baroclinic mode EDJ oscillations at a period of about 4.5 years. Equatorial oxygen observations which do not resolve or cover a full 4.5-yr EDJ cycle nevertheless reveal large variability, with oxygen concentrations locally spanning a range of more than 60?mol kg-1. We study the effect of EDJs on the equatorial oxygen concentration by forcing an advection-diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed EDJ cycle. The advection-diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere. The model produces a 4.5-yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature, implying a net eastward oxygen flux. The comparison of available observations and basin-mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by EDJ oscillations. The respective role of mean advection, EDJs, and other possible processes in shaping the mean oxygen distribution of the equatorial Atlantic at intermediate depth is discussed.

Brandt, Peter; Greatbatch, Richard J.; Claus, Martin; Didwischus, Sven-Helge; Hormann, Verena; Funk, Andreas; Hahn, Johannes; Krahmann, Gerd; Fischer, Jürgen; KöRtzinger, Arne

2012-12-01

228

Soap Bubbles and Logic.  

ERIC Educational Resources Information Center

Introduces questions and activities involving soap bubbles which provide students with experiences in prediction and logic. Examines commonly held false conceptions related to the shapes that bubbles take and provides correct explanations for the phenomenon. (ML)

Levine, Shellie-helane; And Others

1986-01-01

229

Soap-bubble growth  

Microsoft Academic Search

A simple theory describing the dynamics of two-dimensional arrays of soap bubbles is proposed, and compared with a recent experiment. The average area of bubbles scales linearly at late times. Agreement with experiment is satisfactory, although not conclusive.

M. Marder

1987-01-01

230

Preheating in bubble collisions  

SciTech Connect

In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatic oscillation of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually highly inelastic. The cosmological implications of this result are discussed.

Zhang Jun; Piao Yunsong [College of Physical Sciences, Graduate School of Chinese Academy of Sciences, Beijing 100049 (China)

2010-08-15

231

Air Bubbles in Ice  

Microsoft Academic Search

The opacity of ice formed from water containing dissolved air is due to the presence of bubbles of air in the ice. Both bubble concentration and sizes were found to depend on the rate of freezing. Bulk water saturated with air at 0°C was found to freeze into ice containing about six bubbles per mm3 when freezing proceeded at 0.5

A E Carte

1961-01-01

232

Oscillations of soap bubbles  

Microsoft Academic Search

Oscillations of droplets or bubbles of a confined fluid in a fluid environment are found in various situations in everyday life, in technological processing and in natural phenomena on different length scales. Air bubbles in liquids or liquid droplets in air are well-known examples. Soap bubbles represent a particularly simple, beautiful and attractive system to study the dynamics of a

U. Kornek; F. Müller; K. Harth; A. Hahn; S. Ganesan; L. Tobiska; R. Stannarius

2010-01-01

233

Soap Bubbles in Reverse  

Microsoft Academic Search

WHEN sulphuric acid sodium sulphate solution containing surface-active material is dropped into water, bubbles approximately 5 mm. in diameter sinking through water may be observed. Such bubbles are spherical shells of air, with a sphere of acid sodium sulphate within and water outside. They are, in fact, soap bubbles in reverse. Instead of a two-surfaced film of soapy solution in

Leslie Rose

1946-01-01

234

Soap Films and Bubbles.  

ERIC Educational Resources Information Center

Develops and explains a format for a workshop which focuses on soap films and bubbles. The plan consists of: a discussion to uncover what children know about bubbles; explanations of the demonstration equipment; the presentation itself; the assembly of the workshop kit; and time to play with the bubbles. (ML)

Rice, Karen

1986-01-01

235

Study of Sun-Earth interactions using equatorial VHF scintillation in the Indian region  

NASA Astrophysics Data System (ADS)

Plasma density irregularities in the ionosphere (associated with ESF, plasma bubbles and Spo-radic E layers) cause scintillations in various frequency ranges. VHF radio wave scintillation technique is extensively used to study plasma density irregularities of sub-kilometre size . Ef-fects of magnetic and solar activity on ionospheric irregularities are studied so as to ascertain their role in the space weather of the near earth environment in space. Indian Institute of Ge-omagnetism operated a ground network of 13 stations monitoring amplitude scintillations on 244/251 MHz (FLEETSAT 73° E) signals in placecountry-regionIndia for more than a decade under AICPITS. At present VHF scintillation is being recorded at Mumbai by monitoring 251 MHz signal transmitted by geostationary satellite UFO2(71.2 E). sampling at 20 Hz. During CAWSES campaign (March-April 2006, low sunspot period) occurrence of daytime scintilla-tions was observed higher than the nighttime scintillations. This could be due to the fact that during low sunspot years occurrence of spread-F is limited to a narrow latitude region near the dip equator. To study solar cycle association of scintillations, long series of simultaneous amplitude scintillation data for period Jan 1989 to Dec 2000 at Indian low-latitude stations Tirunelveli/Trivandrum, close to dip equator, Pondicherry/Karur, located at the fringe of elec-trojet, Mumbai (dip lat. 13.5o N), a temperate station and Ujjain (dip lat. 18.6o N), close to anomaly crest region are utilized. Nighttime scintillation occurrence is solar activity dependent. Equatorial scintillations are inhibited with increase in geomagnetic activity.

Banola, Sridhar

236

ORIGIN OF THE FERMI BUBBLE  

SciTech Connect

Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10 kpc in diameter north and south of the Galactic center. The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A*, with a capture rate 3 x 10{sup -5} yr{sup -1} and energy release {approx}3 x 10{sup 52} erg per capture can produce very hot plasma {approx}10 keV with a wind velocity {approx}10{sup 8} cm s{sup -1} injected into the halo and heat up the halo gas to {approx}1 keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to {approx}TeV, which produce radio emission via synchrotron radiation and gamma rays via inverse Compton scattering with the relic and the galactic soft photons.

Cheng, K.-S.; Chernyshov, D. O.; Dogiel, V. A. [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Ko, C.-M.; Ip, W.-H. [Institute of Astronomy, National Central University, Chung-Li 32054, Taiwan (China)

2011-04-10

237

Studies on equatorial shock formation during plasmaspheric refilling  

NASA Technical Reports Server (NTRS)

Investigations based on small-scale simulations of microprocesses occurring when a magnetic flux tube refills with a cold plasma are summarized. Results of these investigations are reported in the following attached papers: (1) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: The Role of Ion Beam-Driven Instabilities'; and (2) 'Numerical Simulation of Filling a Magnetic Flux Tube with a Cold Plasma: Effects of Magnetically Trapped Hot Plasma'. Other papers included are: 'Interaction of Field-Aligned Cold Plasma Flows with an Equatorially-Trapped Hot Plasma: Electrostatic Shock Formation'; and 'Comparison of Hydrodynamic and Semikinetic Treatments for a Plasma Flow along Closed Field Lines'. A proposal for further research is included.

Singh, N.

1994-01-01

238

Bubble Manipulation by Self Organization of Bubbles inside Ultrasonic Wave  

NASA Astrophysics Data System (ADS)

Microbubble manipulation using ultrasonic waves is a promising technology in the fields of future medicine and biotechnology. For example, it is considered that bubble trapping using ultrasonic waves may play an important role in drug or gene delivery systems in order to trap the drugs or genes in the diseased tissue. Usually, when bubbles are designed so that they carry payloads, such as drug or gene, they tend to be harder than free bubbles. These hard bubbles receive a small acoustic radiation force, which is not sufficient for bubble manipulation. In this paper, a novel method of microbubble manipulation using ultrasonic waves is proposed. This method uses seed bubbles in order to manipulate target bubbles. When the seed bubbles are introduced into the ultrasonic wave field, they start to oscillate to produce a bubble aggregation of a certain size. Then the target bubbles are introduced, the target bubbles attach around the seed bubbles producing a bubble mass with bilayers (inner layer: seed bubbles, outer layer: target bubbles). The target bubbles are manipulated as a bilayered bubble mass. Basic experiments are carried out using polyvinyl chloride (PVC) shell bubbles. No target bubbles are trapped when only the target bubbles are introduced. However, they are trapped if the seed bubbles are introduced in advance.

Yamakoshi, Yoshiki; Koganezawa, Masato

2005-06-01

239

Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes  

NASA Astrophysics Data System (ADS)

The Plasma Bubble Expansion Experiment (PBEX) is conducting laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (˜10 kV, ˜100 kA, ˜2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. Experimental data from plasma bubble injection into a background plasma, particularly magnetic probe measurements, will be discussed. [4pt] [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).

Lynn, Alan; Zhang, Yue; Hsu, Scott

2010-11-01

240

Gravity Wave Initiation of Equatorial Spread F: A Case Study  

Microsoft Academic Search

Jicamarca radar backscatter maps 1980), and nonlinear simulations (Ossakow et al., were made during four consecutive nights in March 1979) confirm the basic concept that plasma 1979. Two of these maps displayed single depletions or bubbles are colocated with radar towering plumes extending to nearly 1000-kin backscatter plumes and that they originate on the altitude. On a third night, discussed

M. C. Kelley; M. F. Larsen; C. LaHoz; J. P. McClure

1981-01-01

241

Acoustical observation of bubble oscillations induced by bubble popping.  

PubMed

Acoustic measurements of aqueous foams show three distinct radiation mechanisms that contribute to the sound pressure field: oscillations of a bubble surface that precede popping due to the instability of thin liquid film, impulsive radiation due to bursts of bubbles, and oscillations from neighboring bubbles excited by a burst bubble. The movies captured by a fast camera confirm that the bubbles adjacent to a breaking bubble oscillate under the influence of the pressure generated by the burst bubble. The spectra of resulting transient sounds fall in the range of 2-8 kHz and those from bubble oscillations correlate well with the bubble size. PMID:17500901

Ding, Junqi; Tsaur, Felicia W; Lips, Alex; Akay, Adnan

2007-04-01

242

Equatorial zonal circulations: Historical perspectives  

NASA Astrophysics Data System (ADS)

The changing perceptions on zonal circulations in the equatorial belt are traced for (a) stratospheric wind regimes, and (b) vertical-zonal circulation cells in the troposphere. (a) Observations from the Krakatoa eruption 1883 and Berson's 1908 expedition to East Africa, along with later soundings over Batavia (Jakarta) led to the notion of "Krakatoa easterlies" around 30 km (10 mb) and "Berson westerlies" around 20 km (50 mb). Prompted by contrary observations since the late 1950s, this dogma was replaced by the notion of easterlies alternating with westerlies in the equatorial stratosphere at a rhythm of about 26 months. (b) Stimulated by Bjerknes' postulate of a "Walker circulation" along the Pacific Equator, a multitude of such cells have been hypothesized at other longitudes, in part from zonal contrasts of temperature and cloudiness. Essential for the diagnosis of equatorial zonal circulation cells is the continuity following the flow between the centers of ascending and subsiding motion. Evaluation of the recent NCEP-NCAR and ECMWF Reanalysis upper-air datasets reveals equatorial zonal circulation cells over the Pacific all year round, over the Atlantic only in boreal winter, and over the Indian Ocean only in autumn, all being seasons and oceanic longitudes with strong zonal flow in the lower troposphere.

Hastenrath, Stefan

2007-04-01

243

Equatorial scintillation and systems support  

Microsoft Academic Search

The need to nowcast and forecast scintillation for the support of operational systems has been recently identified by the interagency National Space Weather Program. This issue is addressed in the present paper in the context of nighttime irregularities in the equatorial ionosphere that cause intense amplitude and phase scintillations of satellite signals in the VHF\\/UHF range of frequencies and impact

S. Basu; E. J. Weber; M. Smitham; H. Kuenzler; C. E. Valladares; R. Sheehan; E. MacKenzie; J. A. Secan; P. Ning; W. J. McNeill; D. W. Moonan; M. J. Kendra

1997-01-01

244

Deep, cross-equatorial eddies  

Microsoft Academic Search

The question of how deep ocean eddies can cross the equator is addressed with the aid of analytical and numerical models. We focus on the possibility that deep ocean (lens-like) eddies can cross the equator via deep cross equatorial channels on the ocean floor. We first examine the behavior of solid balls (i.e., free particles) in a meridional parabolic channel

Sergey Borisov; Doron Nof

1998-01-01

245

Substorm currents in the equatorial magnetotail  

Microsoft Academic Search

We have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed

T. Iijima; M. Watanabe; T. A. Potemra; L. J. Zanetti; J. R. Kan; S.-I. Akasofu

1993-01-01

246

Study of zonal large scale wave structure (LSWS) and equatorial scintillation with low-latitude GRBR network over Southeast Asia and African sectors  

NASA Astrophysics Data System (ADS)

The day-to-day variability of Equatorial Spread-F, when and where the equatorial plasma bubbles (EPBs) may initiate, were the challenging problems that puzzling the space weather researchers for several decades. The zonal large scale wave structure (LSWS) at the base of F-layer is the earliest manifestation of seed perturbation for the evolution of EPBs by R-T instability processes, hence, found to play deterministic role on the development of ESF. Yet, only a little is known about LSWS with lack of sufficient observations, primarily because of inability to detect the LSWS with the currently existing instruments except with steerable incoherent scatter radar such as ALTAIR radar. This situation, however, was recently changed with launch of C/NOFS in a unique low-inclination (13 ^{o}) orbit. With the availability of CERTO beacon transmissions from C/NOFS in a near equatorial orbit, it is now possible to detect and resolve the roles by LSWS on a regular basis. A ground based low-latitude GNU Radio Beacon Receiver (GRBR) Network has been recently established that provide coverage of Southeast Asia, Pacific and African low-latitude regions. Recent observations suggest that these wave structures with zonal wave lengths varying between 200 and 800 km can be earliest detected even before E-region sunset and found to grow significantly after sunset, probably, aided by the polarization electric fields. Further, these zonal structures consistently found to be aligned with field lines for several hundreds of kilometers and EPBs were found to grow from the westward walls of upwellings. The characteristic differences on the strength of LSWS between the Asian and African longitudes were identified during the recent increasing solar activity and discussed in this paper.

Ram Sudarsanam, Tulasi; Yamamoto, Mamoru; Gurubaran, Subramanian; Tsunoda, Roland

2012-07-01

247

Microfluidic bubble logic.  

PubMed

We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low-Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro-bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation. PMID:17289994

Prakash, Manu; Gershenfeld, Neil

2007-02-01

248

Microfluidic Bubble Logic  

NASA Astrophysics Data System (ADS)

We demonstrate universal computation in an all-fluidic two-phase microfluidic system. Nonlinearity is introduced into an otherwise linear, reversible, low Reynolds number flow via bubble-to-bubble hydrodynamic interactions. A bubble traveling in a channel represents a bit, providing us with the capability to simultaneously transport materials and perform logical control operations. We demonstrate bubble logic AND/OR/NOT gates, a toggle flip-flop, a ripple counter, timing restoration, a ring oscillator, and an electro bubble modulator. These show the nonlinearity, gain, bistability, synchronization, cascadability, feedback, and programmability required for scalable universal computation. With increasing complexity in large-scale microfluidic processors, bubble logic provides an on-chip process control mechanism integrating chemistry and computation.

Prakash, Manu; Gershenfeld, Neil

2007-02-01

249

Bubble column bioreactors  

Microsoft Academic Search

The present article investigates the behavior of bubble column bioreactors with yeast culture media in the absence of cells.\\u000a To aid in the assessment of these reactors the following properties were estimated and partly theoretically treated: relative\\u000a mean gas hold-up, bubble swarm velocity, bubble size, gas\\/liquid interfacial area, energy requirement for aeration, oxygen\\u000a transfer coefficient across the gas\\/liquid interface and

K. Schügerl; J. Lücke; U. Oels

250

Gas bubble detector  

NASA Technical Reports Server (NTRS)

A gas bubble detector having a modulated IR source focused through a bandpass filter onto a venturi, formed in a sample tube, to illuminate the venturi with modulated filtered IR to detect the presence of gas bubbles as small as 0.01 cm or about 0.004 in diameter in liquid flowing through the venturi. Means are provided to determine the size of any detected bubble and to provide an alarm in the absence of liquid in the sample tube.

Mount, Bruce E. (Inventor); Burchfield, David E. (Inventor); Hagey, John M. (Inventor)

1995-01-01

251

Planar Soap Bubbles  

Microsoft Academic Search

The generalized soap bubble problem seeks the least perimeter way to enclose\\u000aand separate n given volumes in R^m. We study the possible configurations for\\u000aperimeter minimizing bubble complexes enclosing more than two regions. We prove\\u000athat perimeter minimizing planar bubble complexes with equal pressure regions\\u000aand without empty chambers must have connected regions. As a consequence, we\\u000ashow that

RICHARD PAUL; DEVEREAUX VAUGHN

1998-01-01

252

Measuring the Response of Bubble Neutron Detectors Using DT Accelerators  

Microsoft Academic Search

Bubble neutron detectors appear to be an attractive approach for measuring the high energy neutron tail created by knock-on alpha-fuel ion collisions in a DT plasma. Measurement of the DT neutron energy spectrum above ~16 MeV will provide diagnostic information on the spatial and energy distributions of confined alpha particles in the plasma core of ITER. Bubble detectors are designed

J. Liptac; R. K. Fisher; E. Morse; A. Belian

1998-01-01

253

Errors in position-fixing by GPS in an environment of strong equatorial scintillations in the Indian zone  

NASA Astrophysics Data System (ADS)

The signal-to-noise ratio (SNR) of the L1 (1.6 GHz) transmission from the GPS and GLONASS satellites has been recorded at Calcutta (22.58°N, 88.38°E geographic; 32°N magnetic dip, 17.35°N dip latitude) since 1999 by a stand-alone coarse acquisition (C/A) code Ashtec receiver. The receiver usually tracks 10-15 satellites, sampling different sections of the ionosphere at different look angles from the station. Simultaneously, L-band (1.5 GHz) signals from geostationary INMARSAT (65°E) (350 km subionospheric point: 21.08°N, 86.59°E geographic; 28.74°N magnetic dip, 15.33°N dip latitude) and VHF (244 MHz) from FLEETSATCOM (73°E) (350 km subionospheric point: 21.10°N, 87.25°E geographic; 28.65°N magnetic dip, 15.28°N dip latitude) are also recorded. Calcutta is situated under the northern crest of the equatorial anomaly in the Indian longitude sector. The SNR of many GPS and GLONASS links, particularly in the southern sky and near overhead, has been found to scintillate frequently in between the local sunset and midnight hours. Scintillations of satellite signals near overhead are caused by irregularities in electron density distribution in an environment of high ambient ionization occurring near the crest of the equatorial anomaly. For the links at lower elevation angles in the southern sky, scintillations occur when satellites are viewed "end-on" through the field-aligned plasma bubbles. During periods of intense scintillations, in the high sunspot number years 1999-2002, it has frequently been observed that seven or eight GPS/GLONASS satellite links out of 15 may simultaneously show scintillations in excess of 10 dB. This paper presents an example of the above when the position determined with GPS shows fluctuations to the extent of 11 m in latitude and 8 m in longitude under such an environment.

Dasgupta, A.; Ray, S.; Paul, A.; Banerjee, P.; Bose, A.

2004-02-01

254

Studies on equatorial shock formation during plasmaspheric refilling  

NASA Technical Reports Server (NTRS)

During the grant period starting August 1, 1992, our major effort has been on examining the presence of equatorially trapped hot plasma on plasmaspheric refilling. We performed one-dimensional PIC simulations of cold plasmas expanding into a hot plasma, consisting of hot anisotropic ions and warm isotropic electrons, trapped in a region of minimum magnetic field. Simulations showed that the electric potential barrier built up by the anisotropy of the hot ion population facilitates in the formation of electrostatic shocks when the cold ion beams begin to come into contact with the hot plasma. The shock formation occurs even when the cold ion beams are highly supersonic with respect to the ion-acoustic speed. This finding is interesting because equatorial shock formation during the early stage of plasmaspheric refilling has been debated over about two decades. In the past ion-ion instability has been invoked as the main mechanism for the coupling between the cold ion beams approaching the equator from the conjugate ionspheres. This coupling occurs when the beams are sufficiently slow; the beam velocity being less than three times the ion-acoustic speed. In the presence of hot plasma, the beams slow down by the potential barrier. The slowing down and the reflection process lead to the formation of the electrostatic shock even for highly supersonic ion beams. The mixing of hot and cold plasma was also studied.

Singh, Nagendra

1993-01-01

255

Evaporation, Boiling and Bubbles  

ERIC Educational Resources Information Center

Evaporation and boiling are both terms applied to the change of a liquid to the vapour/gaseous state. This article argues that it is the formation of bubbles of vapour within the liquid that most clearly differentiates boiling from evaporation although only a minority of chemistry textbooks seems to mention bubble formation in this context. The…

Goodwin, Alan

2012-01-01

256

Let Them Blow Bubbles.  

ERIC Educational Resources Information Center

Describes a series of activities and demonstrations involving the science of soap bubbles. Starts with a recipe for bubble solution and gives instructions for several activities on topics such as density, interference colors, optics, static electricity, and galaxy formation. Contains some background information to help explain some of the effects.…

Korenic, Eileen

1988-01-01

257

Market bubbles and crashes  

Microsoft Academic Search

Episodes of market crashes have fascinated economists for centuries. Although many academics, practitioners and policy makers have studied questions related to collapsing asset price bubbles, there is little consensus yet about their causes and effects. This review and essay evaluates some of the hypotheses offered to explain the market crashes that often follow asset price bubbles. Starting from historical accounts

Taisei Kaizoji; Didier Sornette

2008-01-01

258

Soap bubbles. 1  

Microsoft Academic Search

I consider the chemistry, physics, and computer graphics of soap bubbles. I focus on the physics of soap films, which are, after all, what bubbles are made of. I see what happens when soap dissolves in water and discuss some surprising properties of soap films

A. Glassner

2000-01-01

259

The Vacuum Bubble Nucleation  

SciTech Connect

We study the nucleation of a vacuum bubble via the vacuum-to-vacuum tunneling transition in curved spacetime. We consider Coleman-de Luccia's semiclassical approximation at zero temperature in pure Einstein theory of gravity and the theory with nonminimal coupling. We discuss the dynamics of a nucleated vacuum bubble.

Lee, Bum-Hoon [Department of Physics and Center for Quantum Spacetime, Sogang University Seoul 121-742 (Korea, Republic of); Lee, Wonwoo [Center for Quantum Spacetime, Sogang University, Seoul 121-742 (Korea, Republic of)

2009-07-10

260

The Fermi bubbles revisited  

NASA Astrophysics Data System (ADS)

We analyze 60 months of all-sky data from the Fermi-LAT. The Fermi bubble structures discovered previously are clearly revealed by our analysis. With more data, hence better statistics, we can now divide each bubble into constant longitude slices to investigate their gross ?-ray spectral morphology. While the detailed spectral behavior of each slice derived in our analysis is somewhat dependent on the assumed background model, we find, robustly, a relative deficit in the flux at low energies (i.e., hardening) toward the top of the south bubble. In neither bubble does the spectrum soften with longitude. The morphology of the Fermi bubbles is also revealed to be energy-dependent: at high energies they are more extended. We conclude from the gamma-ray spectrum at high latitudes that a low energy break in the parent cosmic ray population is required in both leptonic and hadronic models. We briefly discuss possible leptonic and hadronic interpretations of this phenomenology.

Yang, Rui-zhi; Aharonian, Felix; Crocker, Roland

2014-07-01

261

Drivers of Quiet-Time Equatorial Evening Electrodynamics  

NASA Astrophysics Data System (ADS)

The sources of plasma convection in the evening equatorial ionosphere are examined in terms of geomagnetic-field-line-integrated electric conductivities and wind-driven electric currents, using the coupled National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General-Circulation Model (NCAR TIE-GCM) and the Global Ionosphere-Plasmasphere (GIP) model. It is important to identify the regions where thermospheric winds, through ionospheric dynamo action, have the greatest influence on this convection, in order to understand the sources of variability of the vertical plasma velocity, including the pre-reversal enhancement (PRE). At night, the largest field-line-integrated Pedersen conductivity is found on field lines that pass through the lower F region around the latitudes of the peaks of the equatorial ionization anomaly (EIA), typically 15 degrees magnetic latitude, corresponding to field lines with a apex heights of around 750 km for moderate solar activity levels. Thermospheric winds in the lower F region near the EIA peaks have a strong influence on the properties of the PRE, while F-region winds nearer the magnetic equator have less influence. The day-time ionospheric dynamo and the day-time equatorial electrojet have relatively little influence on the PRE.

Richmond, A. D.; Fang, T.

2013-12-01

262

Hydrodynamical similarities between bubble column and bubbly pipe flow  

Microsoft Academic Search

The hydrodynamical similarities between the bubbly flow in a bubble column and in a pipe with vertical upward liquid flow are investigated. The system concerns air\\/water bubbly flow in a vertical cylinder of 14.9 cm inner diameter. Measurements of the radial distribution of the liquid velocity, gas fraction and the bubble velocity and size are performed using laser Doppler anemometry

Robert F. Mudde; Takayuki Saito

2001-01-01

263

Mounting and application of bubble display system: bubble cosmos  

Microsoft Academic Search

In this paper, we propose the soap bubble display method that the image can be projected to the real soap bubbles that white smoke entered. The position and the size of soap bubbles tossed in the air are detected with the camera. By projecting the image only to the position with the projector, the soap bubble display is realized. And

Masahiro Nakamura; Go Inaba; Jun Tamaoki; Kazuhito Shiratori; Junichi Hoshino

2006-01-01

264

Bubbles, Bubbles: Integrated Investigations with Floating Spheres  

ERIC Educational Resources Information Center

In this article, the author describes integrated science and mathematics activities developed for fourth-grade students to explore and investigate three-dimensional geometric shapes, Bernoulli's principle, estimation, and art with and through bubbles. Students were engaged in thinking and reflection on the questions their teachers asked and were…

Reeder, Stacy

2007-01-01

265

Bubbles, Bubbles: Integrated Investigations with Floating Spheres  

Microsoft Academic Search

In this article, the author describes integrated science and mathematics activities developed for fourthgrade students to explore and investigate three-dimensional geometric shapes, Bernoulli's principle, estimation, and art with and through bubbles. Students were engaged in thinking and reflection on the questions their teachers asked and were also encouraged to use prior knowledge to make conjectures about what they believed would

Stacy Reeder

2007-01-01

266

Interplay Between the Equatorial Geophysical Processes  

NASA Astrophysics Data System (ADS)

r_sridharanspl@yahoo.com With the sun as the main driving force, the Equatorial Ionosphere- thermosphere system supports a variety of Geophysical phenomena, essentially controlled by the neutral dynamical and electro dynamical processes that are peculiar to this region. All the neutral atmospheric parameters and the ionospheric parameters show a large variability like the diurnal, seasonal semi annual, annual, solar activity and those that are geomagnetic activity dependent. In addition, there is interplay between the ionized and the neutral atmospheric constituents. They manifest themselves as the Equatorial Electrojet (EEJ), Equatorial Ionization Anomaly (EIA), Equatorial Spread F (ESF), Equatorial Temperature and Wind Anomaly (ETWA). Recent studies have revealed that these phenomena, though apparently might show up as independent ones, are in reality interlinked. The interplay between these equatorial processes forms the theme for the present talk.

Sridharan, R.

2006-11-01

267

On near-tail bubble penetration into geosynchronous altitude  

NASA Astrophysics Data System (ADS)

Dipolarization of the magnetic field at the near-Earth tail is usually associated with the local reduction of pV5/3 compared to that of the background, where p is the plasma pressure and V is the volume of the unit magnetic flux tube. This can be interpreted as a bubble, which can propagate earthward by the interchange process. How deep such a bubble can penetrate earthward, and what is the critical factor are critical questions that need to be answered. In this paper, we examine these issues by comparing near-tail observations by inner probes of THEMIS with geosynchronous magnetic observations by GOES. We identified a number of bubble events associated with near-tail dipolarization, which we call “tail bubble,” and checked geosynchronous disturbances. We find a statistical trend that geosynchronous disturbance is more likely to occur when associated with (or when hit by) an earthward moving tail bubble with a more-depleted pV5/3. We estimated the background pV5/3 profile statistically and used it to determine expected equilibrium (or stop) positions for earthward moving bubbles where the bubble's pV5/3 is equal to that of the background. Statistically, we find that the equilibrium position is more inward for tail bubbles with a lower pV5/3, for which the probability of causing geosynchronous disturbance is higher. For example, the probability of a tail bubble being associated with geosynchronous disturbance is 75% if the bubble's equilibrium position is <8 RE. However, for all the events studied here, the bubble equilibrium positions are still outside the geosynchronous altitude. Although this result may be subject to change due to the uncertainty in estimating pV5/3 and the limited number of the events identified near geosynchronous altitude, we suggest that an overshooting of the penetrating bubbles beyond equilibrium positions is a possible explanation.

Kim, H.-S.; Lee, D.-Y.; Ohtani, S.; Park, M.-Y.; Ahn, B.-H.

2012-07-01

268

Tribonucleation of bubbles.  

PubMed

We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rubbing force and velocity exceed a certain threshold. Direct observation through a transparent solid shows that each bubble in the trail results from the early coalescence of several microscopic bubbles, themselves detaching from microscopic gas pockets forming between the solids. From a detailed study of the wear tracks, with atomic force and scanning electron microscopy imaging, we conclude that these microscopic gas pockets originate from a local fracturing of the surface asperities, possibly enhanced by chemical reactions at the freshly created surfaces. Our findings will be useful either for preventing undesired bubble formation or, on the contrary, for "writing with bubbles," i.e., creating controlled patterns of microscopic bubbles. PMID:24982169

Wildeman, Sander; Lhuissier, Henri; Sun, Chao; Lohse, Detlef; Prosperetti, Andrea

2014-07-15

269

Aerator Combined With Bubble Remover  

NASA Technical Reports Server (NTRS)

System produces bubble-free oxygen-saturated water. Bubble remover consists of outer solid-walled tube and inner hydrophobic, porous tube. Air bubbles pass from water in outer tube into inner tube, where sucked away. Developed for long-term aquaculture projects in space. Also applicable to terrestrial equipment in which entrained bubbles dry membranes or give rise to cavitation in pumps.

Dreschel, Thomas W.

1993-01-01

270

Speculations on Nonlinear Speculative Bubbles  

Microsoft Academic Search

This paper reviews a variety of issues related to speculative bubbles, especially those involving nonlinear dynamics. Models of irrational bubbles, rational bubbles, and bubbles arising from heterogeneous agents with varying degrees of knowledge or rationality are examined. The latter are shown to be prone to nonlinear dynamics with catastrophic discontinuities, chaos, and other forms of complex phenomena. Empirical evidence regarding

J. Barkley Rosser

1997-01-01

271

Rotating bubble membrane radiator  

DOEpatents

A heat radiator useful for expelling waste heat from a power generating system aboard a space vehicle is disclosed. Liquid to be cooled is passed to the interior of a rotating bubble membrane radiator, where it is sprayed into the interior of the bubble. Liquid impacting upon the interior surface of the bubble is cooled and the heat radiated from the outer surface of the membrane. Cooled liquid is collected by the action of centrifical force about the equator of the rotating membrane and returned to the power system. Details regarding a complete space power system employing the radiator are given.

Webb, Brent J. (West Richland, WA); Coomes, Edmund P. (West Richland, WA)

1988-12-06

272

Viscosity Destabilizes Sonoluminescing Bubbles  

NASA Astrophysics Data System (ADS)

In single-bubble sonoluminescence (SBSL) microbubbles are trapped in a standing sound wave, typically in water or water-glycerol mixtures. However, in viscous liquids such as glycol, methylformamide, or sulphuric acid it is not possible to trap the bubble in a stable position. This is very peculiar as larger viscosity normally stabilizes the dynamics. Suslick and co-workers call this new mysterious state of SBSL “moving-SBSL.” We identify the history force (a force nonlocal in time) as the origin of this destabilization and show that the instability is parametric. A force balance model quantitatively accounts for the observed quasiperiodic bubble trajectories.

Toegel, Ruediger; Luther, Stefan; Lohse, Detlef

2006-03-01

273

Viscosity destabilizes sonoluminescing bubbles.  

PubMed

In single-bubble sonoluminescence (SBSL) microbubbles are trapped in a standing sound wave, typically in water or water-glycerol mixtures. However, in viscous liquids such as glycol, methylformamide, or sulphuric acid it is not possible to trap the bubble in a stable position. This is very peculiar as larger viscosity normally stabilizes the dynamics. Suslick and co-workers call this new mysterious state of SBSL "moving-SBSL." We identify the history force (a force nonlocal in time) as the origin of this destabilization and show that the instability is parametric. A force balance model quantitatively accounts for the observed quasiperiodic bubble trajectories. PMID:16605826

Toegel, Ruediger; Luther, Stefan; Lohse, Detlef

2006-03-24

274

Modelling the equatorial emission in a microquasar  

NASA Astrophysics Data System (ADS)

The jets in a microquasar are modelled using a three-dimensional relativistic hydrocode (PLUTO), with the aim of investigating the appearance of equatorial radio emission. A dynamical mechanism is explored whereby the bow shocks of the jets strongly affect the equatorial regions. The presence of an extended disc is assumed and its role proves to be important in producing equatorial emission. As a concrete example, we focus on the SS 433 microquasar, one of the most intensively studied objects in the Galaxy, for which equatorial emission has been repeatedly detected during the last decade.

Smponias, T.; Kosmas, T. S.

2011-04-01

275

Aerosol Transport Over Equatorial Africa  

NASA Technical Reports Server (NTRS)

Long-range and inter-hemispheric transport of atmospheric aerosols over equatorial Africa has received little attention so far. Most aerosol studies in the region have focussed on emissions from rain forest and savanna (both natural and biomass burning) and were carried out in the framework of programs such as DECAFE (Dynamique et Chimie Atmospherique en Foret Equatoriale) and FOS (Fires of Savanna). Considering the importance of this topic, aerosols samples were measured in different seasons at 4420 meters on Mt Kenya and on the equator. The study is based on continuous aerosol sampling on a two stage (fine and coarse) streaker sampler and elemental analysis by Particle Induced X-ray Emission. Continuous samples were collected for two seasons coinciding with late austral winter and early austral spring of 1997 and austral summer of 1998. Source area identification is by trajectory analysis and sources types by statistical techniques. Major meridional transports of material are observed with fine-fraction silicon (31 to 68 %) in aeolian dust and anthropogenic sulfur (9 to 18 %) being the major constituents of the total aerosol loading for the two seasons. Marine aerosol chlorine (4 to 6 %), potassium (3 to 5 %) and iron (1 to 2 %) make up the important components of the total material transport over Kenya. Minimum sulfur fluxes are associated with recirculation of sulfur-free air over equatorial Africa, while maximum sulfur concentrations are observed following passage over the industrial heartland of South Africa or transport over the Zambian/Congo Copperbelt. Chlorine is advected from the ocean and is accompanied by aeolian dust recirculating back to land from mid-oceanic regions. Biomass burning products are transported from the horn of Africa. Mineral dust from the Sahara is transported towards the Far East and then transported back within equatorial easterlies to Mt Kenya. This was observed during austral summer and coincided with the dying phase of 1997/98 El Nino.

Gatebe, C. K.; Tyson, P. D.; Annegarn, H. J.; Kinyua, A. M.; Piketh, S.; King, M.; Helas, G.

1999-01-01

276

Multiscale Organization of Equatorial Waves  

NASA Astrophysics Data System (ADS)

This contribution will discuss some observational aspects of the organization of equatorial rainfall systems. It is well-known that convective disturbances in the tropics occur over a very broad spectrum of scales, ranging from individual cumulus cells to planetary scale features such as the Madden-Julian Oscillation (MJO). It is also observed that the larger scale features are composed of smaller scale equatorial waves, so that for example the "envelope" of the MJO is often comprised of eastward propagating Kelvin, and westward inertio- gravity waves. The envelopes of these waves are in turn are comprised of a broad spectrum of mesoscale features, which are predominantly westward propagating. While it is certainly evident that the larger envelopes must be creating a favorable environment for the higher frequency activity within them, the precise mechanisms for this modulation are still a subject of debate, as is the inverse role of the mesoscale disturbances in the upscale transfer of energy. Interestingly, a census of a large number of individual MJOs shows that they are comprised of a wide variety of smaller scale disturbance types from case to case, suggesting that parameterization of their upscale impacts of might be feasible. A majority of the westward propagating features move much too quickly (greater than 20 m/s) to be explained solely by advection. A space-time spectrum of high resolution satellite cloudiness data shows an overall dominance of westward over eastward power, especially at higher zonal wavenumbers and frequencies. In particular, a spectral peak extends from the previously well-documented large scale westward inertio-gravity peak into the westward portion of the mesoscale region, with a dispersion relationship representative of pure gravity waves. These westward gravity waves are strongly modulated by the diurnal cycle, especially over the continents. Understanding the precise role of these scale interactions is likely a crucial step towards the improved simulation of equatorial disturbances in models.

Kiladis, G. N.; Tulich, S.

2008-12-01

277

Gravity-driven bubbly flows  

Microsoft Academic Search

? Abstract Gravity-driven bubbly flows are a specific class of flows, where all action is provided by gravity. An industrial example,is formed,by the so-called bubble column: a vertical cylinder filled with liquid through,which,bubbles,flow that are introduced at the bottom of the cylinder. On the bubble scale, gravity gives rise to buoyancy of individual bubbles. On larger scales, gravity acts on

Robert F. Mudde

2005-01-01

278

Lift force in bubbly suspensions  

Microsoft Academic Search

Closure relations are presented for the lift coefficient for ordered arrays of 2-D and 3-D bubbles at various bubble volume fractions. These were determined via lattice Boltzmann simulations of bubble rise in periodic boxes, where the bubbles were also subjected to shear. The single-bubble lift coefficient, determined by low-shear computational experiments, varies in a systematic manner with the aspect ratio

Krishnan Sankaranarayanan; Sankaran Sundaresan

2002-01-01

279

Steepened structures in equatorial spread F. 2: Theory  

NASA Technical Reports Server (NTRS)

This paper investigates the properties of a one-dimensional fluid model of plasma convection in the equatorial F region ionosphere. The model equations are similar in form to Burgers equation except for additional higher-order spatial derivatives. Like Burgers equation, solution to the model have the form of propagating, shocklike structures. Numerical simulations of the model closely resemble the steepened structures observed by sounding rocket plasma density probes within equatorial spread F. Simulated denstiy power spectra, like the spectra computed from in situ data, seem to possess power law forms with a break at wavelengths of about 100 m. The precise wavenumber of the spectral break is determined by the ambipolar diffusion coefficient. The model predicts that electric field fluctuations perpendicular to the direction of plasma steepening should be proportional to the plasma density fluctuations. Electric field fluctuations parallel to the steepening will be due primarily to the ambipolar field and have a Boltzmann relationship with density (square of the absolute value of delta E) approximately equal to (K(exp 2))(square of the absolute value of (delta n/n)). At wavelengths less than about 300 m, the ambipolar field should be the dominant component of the total field intensity.

Hysell, D. L; Seyler, C. E.; Kelley, M. C.

1994-01-01

280

Chemistry in Soap Bubbles.  

ERIC Educational Resources Information Center

Describes a laboratory experiment in which common chemical gases are trapped inside soap bubbles. Examines the physical and chemical properties of the gases such as relative density and combustion. (Author/MM)

Lee, Albert W. M.; Wong, A.; Lee, H. W.; Lee, H. Y.; Zhou, Ning-Huai

2002-01-01

281

Visualization of bubble behavior and bubble diameter correlation for NH 3–H 2O bubble absorption  

Microsoft Academic Search

The objectives of this paper are to visualize the bubble behavior for an ammonia–water absorption process, and to study the effect of key parameters on ammonia–water bubble absorption performance. The orifice diameter, orifice number, liquid concentration and vapor velocity are considered as the key parameters. The departing bubbles tend to be spherical for surface tension dominant flow, and the bubbles

Yong Tae Kang; T. Nagano; Takao Kashiwagi

2002-01-01

282

Colloquium: Soap bubble clusters  

NASA Astrophysics Data System (ADS)

Soap bubble clusters and froths model biological cells, metallurgical structures, magnetic domains, liquid crystals, fire-extinguishing foams, bread, cushions, and many other materials and structures. Despite the simplicity of the governing principle of energy or area minimization, the underlying mathematical theory is deep and still not understood, even for rather simple, finite clusters. Only with the advent of geometric measure theory could mathematics treat surfaces which might have unprescribed singularities and topological complexities. In 1884, Schwarz gave a rigorous mathematical proof that a single round soap bubble provides the least-area way to enclose a given volume of air. Similarly, the familiar double bubble provides the absolute least-area way to enclose and separate the two given volumes of air, although the proof did not come until 2000 and has an interesting story, as this Colloquium explains in some detail. Whether a triple soap bubble provides the least-area way to enclose and separate three given volumes of air remains an open conjecture today. Even planar bubble clusters remain mysterious. In about 200 B.C. Zenodorus essentially proved that a circle provides the least-perimeter way to enclose a single given area. The planar double and triple bubbles were proved minimizing recently. The status of the planar four-bubble remains open today. In most spaces other than Euclidean space, even the best single bubble remains unproven. One exception is Gauss space, which is of much interest to probabilists and should be more familiar to physicists. General “isoperimetric” problems of minimizing area for given volume occur throughout mathematics and play an important role in differential geometry and analysis, including Perelman’s proof of the Poincaré conjecture.

Morgan, Frank

2007-07-01

283

Bubble coalescence in magmas  

NASA Technical Reports Server (NTRS)

The most important factors governing the nature of volcanic eruptions are the primary volatile contents, the ways in which volatiles exsolve, and how the resulting bubbles grow and interact. In this contribution we assess the importance of bubble coalescence. The degree of coalescence in alkali basalts has been measured using Image Analysis techniques and it is suggested to be a process of considerable importance. Binary coalescence events occur every few minutes in basaltic melts with vesicularities greater than around 35 percent.

Herd, Richard A.; Pinkerton, Harry

1993-01-01

284

Central Equatorial Pacific Experiment (CEPEX)  

SciTech Connect

The Earth's climate has varied significantly in the past, yet climate records reveal that in the tropics, sea surface temperatures seem to have been remarkably stable, varying by less than a few degrees Celsius over geologic time. Today, the large warm pool of the western Pacific shows similar characteristics. Its surface temperature always exceeds 27[degree]C, but never 31[degree]C. Heightened interest in this observation has been stimulated by questions of global climate change and the exploration of stabilizing climate feedback processes. Efforts to understand the observed weak sensitivity of tropical sea surface temperatures to climate forcing has led to a number of competing ideas about the nature of this apparent thermostat. Although there remains disagreement on the processes that regulate tropical sea surface temperature, most agree that further progress in resolving these differences requires comprehensive field observations of three-dimensional water vapor concentrations, solar and infrared radiative fluxes, surface fluxes of heat and water vapor, and cloud microphysical properties. This document describes the Central Equatorial Pacific Experiment (CEPEX) plan to collect such observations over the central equatorial Pacific Ocean during March of 1993.

Not Available

1993-01-01

285

Reduced gradient bubble model.  

PubMed

An approach to decompression modeling, the reduced gradient bubble model (RGBM), is developed from the critical phase hypothesis. The phase limit is introduced, extended, and applied within bubble-nucleation theory proposed by Yount. Much is different in the RGBM algorithm, on both theoretical and applied sides, with a focus on permissible bubble excesses rather than just dissolved gas buildup, something of a departure from traditional models. Overall, the approach is conservative, with changes in parameter settings affording flexibility. Marginal profiles permitted by tables and meters are restricted by the bubble algorithm. Highlighted features of the conservative algorithm include: (1) reduced no-stop time limits from the varying-permeability model (VPM); (2) short safety stops (or shallow swimming ascents) in the 10-20 feet of sea water (fsw) zone; (3) ascent and descent rates of 60 fsw/min, or slower; (4) restricted repetitive exposures, particularly beyond 100 fsw, based on reduced permissible bubble excess; (5) restricted spike (shallow-to-deep) exposures based on excitation of additional micronuclei; (6) restricted multi-day activity based on regeneration of micronuclei; (7) consistent treatment of altitude diving within model framework; (8) algorithm linked to bubble-nucleation theory and experiment. Coupled to medical reports about the long term effects of breathing pressurized gases and shortcomings in dissolved gas models, conservative modeling seems prudent. PMID:2276850

Wienke, B R

1990-11-01

286

Collision of counterpropagating laser-excited wake bubbles  

NASA Astrophysics Data System (ADS)

The collision of wake bubbles behind two counterpropagating laser pulses in rarefied plasma is investigated using particle-in-cell simulation. Special attention is paid to the highly nonlinear dynamics of the electrons in the interaction region. It is found that, as the two bubbles approach each other and collide, the electrons in the interaction region first oscillate in a periodic fashion, forming a quasistationary dense electron density ripple with fairly regular spatial structure. At longer times, the electron motion becomes chaotic, and the density grating is gradually smeared. The electrons escape in the transverse direction, and eventually the two bubbles merge to form a single one. The transition of the electron motion from regular to chaotic is confirmed by analytical modeling using test electrons moving in counterpropagating planar electromagnetic waves. The findings shed light on the dynamics of wake-bubble collisions and the complex behavior induced by multiple laser pulses in plasmas.

Deng, Z. G.; Yang, L.; Zhou, C. T.; Yu, M. Y.; Ying, H. P.; Wang, X. G.

2014-06-01

287

Tungsten surface evolution by helium bubble nucleation, growth and rupture  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations reveal sub-surface mechanisms likely involved in the initial formation of nanometre-sized ‘fuzz’ in tungsten exposed to low-energy helium plasmas. Helium clusters grow to over-pressurized bubbles as a result of repeated cycles of helium absorption and Frenkel pair formation. The self-interstitials either reach the surface as isolated adatoms or trap at the bubble periphery before organizing into prismatic <1?1?1> dislocation loops. Surface roughening occurs as single adatoms migrate to the surface, prismatic loops glide to the surface to form adatom islands, and ultimately as over-pressurized gas bubbles burst.

Sefta, Faiza; Hammond, Karl D.; Juslin, Niklas; Wirth, Brian D.

2013-07-01

288

Statistical equilibrium of bubble oscillations in dilute bubbly flows.  

PubMed

The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium (or initial) radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general (nonimpulsive) forcing and strong two-way coupled bubbly flows are briefly discussed. PMID:19547725

Colonius, Tim; Hagmeijer, Rob; Ando, Keita; Brennen, Christopher E

2008-04-01

289

Statistical equilibrium of bubble oscillations in dilute bubbly flows  

PubMed Central

The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium (or initial) radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general (nonimpulsive) forcing and strong two-way coupled bubbly flows are briefly discussed.

Colonius, Tim; Hagmeijer, Rob; Ando, Keita; Brennen, Christopher E.

2008-01-01

290

Colliding with a crunching bubble  

SciTech Connect

In the context of eternal inflation we discuss the fate of Lambda = 0 bubbles when they collide with Lambda< 0 crunching bubbles. When the Lambda = 0 bubble is supersymmetric, it is not completely destroyed by collisions. If the domain wall separating the bubbles has higher tension than the BPS bound, it is expelled from the Lambda = 0 bubble and does not alter its long time behavior. If the domain wall saturates the BPS bound, then it stays inside the Lambda = 0 bubble and removes a finite fraction of future infinity. In this case, the crunch singularity is hidden behind the horizon of a stable hyperbolic black hole.

Freivogel, Ben; Freivogel, Ben; Horowitz, Gary T.; Shenker, Stephen

2007-03-26

291

Shear flow effects at the onset of equatorial spread F  

NASA Astrophysics Data System (ADS)

Experiments were conducted during the NASA EQUIS II sounding rocket campaign on Kwajalein Atoll to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on August 7 and 15, 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets yielded lower thermospheric wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. Strong plasma shear flow was evident in both experiments. Bottom-type scattering layers were observed below the shear nodes in westward-drifting plasma strata. The layers were often patchy and distributed periodically in space. We attribute the patchiness to large-scale waves which modulate the layers. The large-scale waves may also serve as seed irregularities for ESF. A three-dimensional electrodynamic model is constructed that can reproduce the observed shear flow. Based on the model, we calculate the linear growth rate for the collisional shear instability and show that it can compete with the generalized Rayleigh Taylor instability. A scenario where the former generates the large-scale waves and initiates the latter is discussed.

Hysell, D.; Larsen, M.; Swenson, C.; Barjatya, A.; Wheeler, T.

2006-05-01

292

Equatorial ionosphere 'fountain- effect' above imminent earthquake epicenter  

NASA Astrophysics Data System (ADS)

Existence of lithosphere-ionosphere interaction is known for a long time, but it does not mean that the ionospheric morphology above areas of earthquakes preparation is investigated sufficiently well. It was shown that seismo-precursor variations of the atmosphere electricity cause appropriate electric field at the ionospheric heights, which being added to existing natural field may both increase or decrease its action on the ionospheric plasma characteristics: drifts, aeronomy, plasma chemistry, ion composition etc. Anomalous variations appear inside whole ionosphere volume from the lowest boundary of Earth's plasma shell (100 km) up to 1000km and higher. Under fortunate coincidence seismo-precursor electric field can generate natural ionosphere phenomena, 'fountain- effect', leading to Appleton anomaly in the equatorial ionosphere over future earthquake position. Our basic idea is to take into account dependence of the observable effects on a geographical position of the earthquake epicenter. As for low latitudes it is proved by specificity of formation and dynamics of equatorial ionosphere (seismogenic ""fountain" effect , first of all), and also by features of earth crust structure close to the equator (mainly meridionally alongated tectonic faults). Ionospheric effects of low-latitude earthquakes were not investigated separately so far though rather semo-active zones are located namely at low latitudes: India, Peru, Oceania. We used the data of topside sounding of ALOUETTE-1 and ISS-b satellites, and also data of ground-based vertical sounding stationary stations Kodaikanal, Huancayo, Djibouti etc. and records of the total electron content (TEC).

Ruzhin, Yu.; Depueva, A. H.; Devi, M.

2003-04-01

293

Bubbles of Metamorphosis  

NASA Astrophysics Data System (ADS)

Metamorphosis presents a puzzling challenge where, triggered by a signal, an organism abruptly transforms its entire shape and form. Here I describe the role of physical fluid dynamic processes during pupal metamorphosis in flies. During early stages of pupation of third instar larvae into adult flies, a physical gas bubble nucleates at a precise temporal and spatial location, as part of the normal developmental program in Diptera. Although its existence has been known for the last 100 years, the origin and control of this ``cavitation'' event has remained completely mysterious. Where does the driving negative pressure for bubble nucleation come from? How is the location of the bubble nucleation site encoded in the pupae? How do molecular processes control such a physical event? What is the role of this bubble during development? Via developing in-vivo imaging techniques, direct bio-physical measurements in live insect pupal structures and physical modeling, here I elucidate the physical mechanism for appearance and disappearance of this bubble and predict the site of nucleation and its exact timing. This new physical insight into the process of metamorphosis also allows us to understand the inherent design of pupal shell architectures in various species of insects.

Prakash, Manu

2011-11-01

294

Swarm SCARF equatorial electric field inversion chain  

NASA Astrophysics Data System (ADS)

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere. Since the EEF is the primary driver of the low-latitude ionospheric current system, the observed magnetic measurements can then be inverted for the EEF. This paper details the algorithm for recovering the EEF from Swarm geomagnetic field measurements. The equatorial electric field estimates are an official Swarm level-2 product developed within the Swarm SCARF (Satellite Constellation Application Research Facility). They will be made freely available by ESA after the commissioning phase.

Alken, P.; Maus, S.; Vigneron, P.; Sirol, O.; Hulot, G.

2013-11-01

295

Time dependent response of equatorial ionospheric electric fields to magnetospheric disturbances  

Microsoft Academic Search

We use extensive radar measurements of F region vertical plasma drifts and auroral electrojet indices to determine the storm time dependence of equatorial zonal electric fields. These disturbance drifts result from the prompt penetration of high latitude electric fields and from the dynamo action of storm time winds which produce largest perturbations a few hours after the onset of magnetic

Ludger Scherliess

1995-01-01

296

Study of electron trapping by a transversely ellipsoidal bubble in the laser wake-field acceleration  

SciTech Connect

We present electron trapping in an ellipsoidal bubble which is not well explained by the spherical bubble model by [Kostyukov et al., Phys. Rev. Lett. 103, 175003 (2009)]. The formation of an ellipsoidal bubble, which is elongated transversely, frequently occurs when the spot size of the laser pulse is large compared to the plasma wavelength. First, we introduce the relation between the bubble size and the field slope inside the bubble in longitudinal and transverse directions. Then, we provide an ellipsoidal model of the bubble potential and investigate the electron trapping condition by numerical integration of the equations of motion. We found that the ellipsoidal model gives a significantly less restrictive trapping condition than that of the spherical bubble model. The trapping condition is compared with three-dimensional particle-in-cell simulations and the electron trajectory in test potential simulations.

Cho, Myung-Hoon [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Natural Science, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of); Kim, Young-Kuk; Hur, Min Sup [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)] [School of Electrical and Computer Engineering, UNIST, BanYeon-Ri 100, Ulju-gun, Ulsan 689-798 (Korea, Republic of)

2013-09-15

297

Atmospheric-pressure microplasma in dielectrophoresis-driven bubbles for optical emission spectroscopy.  

PubMed

The manipulation of bubbles and the ignition of microplasma within a 200 nL bubble at atmospheric pressure and in an inert silicone oil environment were achieved. Driven by dielectrophoresis (DEP), bubble generation, transportation, mixing, splitting, and expelling were demonstrated. This process facilitated the preparation of various bubbles with tuneable gas compositions. Different gas bubbles, including air, argon (Ar), helium (He), and Ar/He mixtures, were manipulated and ignited to the plasma state by dielectric barrier discharge (DBD) within a 50 ?m-high gap between parallel plates. Moving and splitting the atmospheric-pressure microplasma in different gas bubbles were achieved by DEP. The excited light of the microplasma was recorded by an optical spectrometer for the optical emission spectroscopy (OES) analyses. The characteristic peaks of air, Ar, and He were observed in the DEP-driven microplasma. With the capability to manipulate bubbles and microplasma, this platform could be used for gas analyses in the future. PMID:22878730

Fan, Shih-Kang; Shen, Yan-Ting; Tsai, Ling-Pin; Hsu, Cheng-Che; Ko, Fu-Hsiang; Cheng, Yu-Ting

2012-10-01

298

On the effects of scintillation of low-latitude bubbles on transionospheric paths of propagation  

NASA Astrophysics Data System (ADS)

A previously developed scintillation propagation model for L band signals on transionospheric paths has been further extended to describe the effects caused by the localized structure of plasma bubbles in the low-latitude ionosphere. This takes into account quasi-deterministic and random structures typical of bubbles. The model can produce signal statistical moments (power spectra, correlation functions, scintillation index, etc.) and generate random time series including the case of through bubble propagation. The simulated random time series of the field demonstrate the characteristic nonstationary behavior caused by the presence and motion of the bubble structures through the path of propagation, showing that strong enhancements of the scintillation index (S4) can occur depending on the parameters of the bubble and the path. Modeling results are compared with scintillation records due to bubbles passing through GPS signal paths to a receiver at Douala, Cameroon. This shows good agreement providing validation for the bubble and propagation model.

Zernov, Nikolay N.; Gherm, Vadim E.; Strangeways, Hal J.

2009-02-01

299

Do stops slow down electroweak bubble walls?  

NASA Astrophysics Data System (ADS)

We compute the wall velocity in the MSSM. We therefore generalize the SM equations of motion for bubble walls moving through a hot plasma at the electroweak phase transition and calculate the friction terms which describe the viscosity of the plasma. We give the general expressions and apply them to a simple model where stops, tops and W bosons contribute to the friction. In a wide range of parameters including those which fulfil the requirements of baryogenesis we find a wall velocity of order v w?10 -2 much below the SM value.

John, P.; Schmidt, M. G.

2001-03-01

300

Unsteady Thermocapillary Migration of Bubbles.  

National Technical Information Service (NTIS)

Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubb...

L. H. Dill R. Balasubramaniam

1988-01-01

301

Bubbles and Biosensors  

NSDL National Science Digital Library

Students work in groups to create soap bubbles on a smooth surface, recording their observations from which they formulate theories to explain what they see (color swirls on the bubble surfaces caused by refraction). Then they apply this theory to thin films in general, including porous films used in biosensors, listing factors that could change the color(s) that become visible to the naked eye, and learn how those factors can be manipulated to give information on gene detection. Finally (by experimentation or video), students see what happens when water is dropped onto the surface of a Bragg mirror.

Vu Bioengineering Ret Program

302

Fluid Dynamics of Bubbly Liquids  

NASA Technical Reports Server (NTRS)

Experiments have been performed to study the average flow properties of inertially dominated bubbly liquids which may be described by a novel analysis. Bubbles with high Reynolds number and low Weber number may produce a fluid velocity disturbance that can be approximated by a potential flow. We studied the behavior of suspensions of bubbles of about 1.5 mm diameter in vertical and inclined channels. The suspension was produced using a bank of 900 glass capillaries with inner diameter of about 100 microns in a quasi-steady fashion. In addition, salt was added to the suspension to prevent bubble-bubble coalescence. As a result, a nearly monodisperse suspension of bubble was produced. By increasing the inclination angle, we were able to explore an increasing amount of shear to buoyancy motion. A pipe flow experiment with the liquid being recirculated is under construction. This will provide an even larger range of shear to buoyancy motion. We are planning a microgravity experiment in which a bubble suspension is subjected to shearing in a couette cell in the absence of a buoyancy-driven relative motion of the two phases. By employing a single-wire, hot film anemometer, we were able to obtain the liquid velocity fluctuations. The shear stress at the wall was measured using a hot film probe flush mounted on the wall. The gas volume fraction, bubble velocity, and bubble velocity fluctuations were measured using a homemade, dual impedance probe. In addition, we also employed a high-speed camera to obtain the bubble size distribution and bubble shape in a dilute suspension. A rapid decrease in bubble velocity for a dilute bubble suspension is attributed to the effects of bubble-wall collisions. The more gradual decrease of bubble velocity as gas volume fraction increases, due to subsequent hindering of bubble motion, is in qualitative agreement with the predictions of Spelt and Sangani for the effects of potential-flow bubble-bubble interactions on the mean velocity. The ratio of the bubble velocity variance to the square of the mean is 0(0.1). For these conditions Spelt and Sangani predicted that the homogeneous suspension would be unstable and clustering into horizontal rafts will take place. Evidence for bubble clustering is obtained by analysis of video images. The liquid velocity variance is larger than would be expected for a homogeneous suspension and the liquid velocity frequency spectrum indicates the presence of velocity fluctuations that are slow compared with the time for the passage of an individual bubble. These observations provide further evidence for bubble clustering.

Tsang, Y. H.; Koch, D. L.; Zenit, R.; Sangani, A.; Kushch, V. I.; Spelt, P. D. M.; Hoffman, M.; Nahra, H.; Fritz, C.; Dolesh, R.

2002-01-01

303

Asset Float and Speculative Bubbles  

Microsoft Academic Search

We model the relationship between asset float (tradeable shares) and speculative bubbles. Investors with heterogeneous beliefs and short-sales constraints trade a stock with limited float because of insider lockups. A bubble arises as price overweighs optimists' beliefs and investors anticipate the option to resell to those with even higher valuations. The bubble's size depends on float as investors anticipate an

HARRISON HONG; JOSÉ SCHEINKMAN; WEI XIONG

2006-01-01

304

The Home Zone: Bubble Shapes  

NSDL National Science Digital Library

Few can resist a bubble wand and a brightly colored bottle of bubble solution. Although playing with bubbles might seem like just a fun outdoor activity, it is also an opportunity to explore some interesting science concepts related to soap, light, and color.

Damonte, Kathleen

2003-05-01

305

Cohesion of Bubbles in Foam  

ERIC Educational Resources Information Center

The free-energy change, or binding energy, of an idealized bubble cluster is calculated on the basis of one mole of gas, and on the basis of a single bubble going from sphere to polyhedron. Some new relations of bubble geometry are developed in the course of the calculation. (BB)

Ross, Sydney

1978-01-01

306

Equatorial spread F modeling: Multiple bifurcated structures, secondary instabilities, large density `bite-outs,' and supersonic flows  

NASA Astrophysics Data System (ADS)

The Naval Research Laboratory has recently developed a new two-dimensional code to study equatorial spread F (ESF): NRLESF2. The code uses an 8th order spatial interpolation scheme and the partial donor cell method. This allows the model to capture very sharp gradients over ~ 4 grid cells and to assess the impact of numerical diffusion on the dynamics of `bubble' evolution. Simulation results are presented that show new and complex ESF bubble dynamics: multiple bifurcations, secondary instabilities, density `bite-outs' of over three orders of magnitude, and supersonic flows within low density channels (V $\\simeq$ few km/s). These results are consistent with radar and satellite observations, as well as optical images. It is also shown that numerical diffusion can inhibit bubble bifurcation and the development of small-scale structure.

Huba, J. D.; Joyce, G.

2007-04-01

307

Downward Mapping of Equatorial Ionospheric Electric Fields.  

National Technical Information Service (NTIS)

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions. Numerical solutions are shown and are compared with the corresponding ones for high latitudes. It is found that ionospheric electric fields can map dow...

W. D. Gonzalez S. L. G. Dutra A. L. C. Gonzalez A. E. C. Pereira

1985-01-01

308

Rocket Measurement of the Equatorial Electrojet.  

National Technical Information Service (NTIS)

Four Nike-Apache rockets, equipped with cesium vapor magnetometers, were launched in the equatorial electrojet region in March 1965. The rocket launched at the magnetic equator during the period of maximum electrojet current flow detected a 220-gamma disc...

B. M. Shuman

1970-01-01

309

What's in the Bubbles?  

NSDL National Science Digital Library

The purpose of this assessment probe is to elicit students' ideas about particles during a change in state. The probe is designed to find out if students recognize that the bubbles formed when water boils are the result of liquid water changing into water vapor. This free selection also includes the Table of Contents, Foreword, Preface, and Index.

Eberle, Francis; Tugel, Joyce; Keeley, Page

2007-01-01

310

Bubble fusion: Preliminary estimates  

SciTech Connect

The collapse of a gas-filled bubble in disequilibrium (i.e., internal pressure {much_lt} external pressure) can occur with a significant focusing of energy onto the entrapped gas in the form of pressure-volume work and/or acoustical shocks; the resulting heating can be sufficient to cause ionization and the emission of atomic radiations. The suggestion that extreme conditions necessary for thermonuclear fusion to occur may be possible has been examined parametrically in terms of the ratio of initial bubble pressure relative to that required for equilibrium. In this sense, the disequilibrium bubble is viewed as a three-dimensional ``sling shot`` that is ``loaded`` to an extent allowed by the maximum level of disequilibrium that can stably be achieved. Values of this disequilibrium ratio in the range 10{sup {minus}5}--10{sup {minus}6} are predicted by an idealized bubble-dynamics model as necessary to achieve conditions where nuclear fusion of deuterium-tritium might be observed. Harmonic and aharmonic pressurizations/decompressions are examined as means to achieve the required levels of disequilibrium required to create fusion conditions. A number of phenomena not included in the analysis reported herein could enhance or reduce the small levels of nuclear fusions predicted.

Krakowski, R.A.

1995-02-01

311

Double Bubble? No Trouble!  

ERIC Educational Resources Information Center

Describes a soap-solution activity involving formation of bubbles encasing the students that requires only readily available materials and can be adapted easily for use with various grade levels. Discusses student learning outcomes including qualitative and quantitative observations and the concept of surface tension. (JRH)

Shaw, Mike I.; Smith, Greg F.

1995-01-01

312

Soap bubbles and crystals  

Microsoft Academic Search

The Plateau problem is a famous problem in the shape of bubbles. The author’s solution to this problem by the introduction\\u000a of geometric measure theory is described. The context of Cyril Stanley Smith’s work on the shape of grains and crystals is\\u000a introduced.

Jean E. Taylor

2006-01-01

313

Colloquium: Soap bubble clusters  

Microsoft Academic Search

Soap bubble clusters and froths model biological cells, metallurgical structures, magnetic domains, liquid crystals, fire-extinguishing foams, bread, cushions, and many other materials and structures. Despite the simplicity of the governing principle of energy or area minimization, the underlying mathematical theory is deep and still not understood, even for rather simple, finite clusters. Only with the advent of geometric measure theory

Frank Morgan

2007-01-01

314

Oscillations of soap bubbles  

NASA Astrophysics Data System (ADS)

Oscillations of droplets or bubbles of a confined fluid in a fluid environment are found in various situations in everyday life, in technological processing and in natural phenomena on different length scales. Air bubbles in liquids or liquid droplets in air are well-known examples. Soap bubbles represent a particularly simple, beautiful and attractive system to study the dynamics of a closed gas volume embedded in the same or a different gas. Their dynamics is governed by the densities and viscosities of the gases and by the film tension. Dynamic equations describing their oscillations under simplifying assumptions have been well known since the beginning of the 20th century. Both analytical description and numerical modeling have made considerable progress since then, but quantitative experiments have been lacking so far. On the other hand, a soap bubble represents an easily manageable paradigm for the study of oscillations of fluid spheres. We use a technique to create axisymmetric initial non-equilibrium states, and we observe damped oscillations into equilibrium by means of a fast video camera. Symmetries of the oscillations, frequencies and damping rates of the eigenmodes as well as the coupling of modes are analyzed. They are compared to analytical models from the literature and to numerical calculations from the literature and this work.

Kornek, U.; Müller, F.; Harth, K.; Hahn, A.; Ganesan, S.; Tobiska, L.; Stannarius, R.

2010-07-01

315

The Liberal Arts Bubble  

ERIC Educational Resources Information Center

The author expresses his doubt that the general higher education bubble will burst anytime soon. Although tuition, student housing, and book costs have all increased substantially, he believes it is still likely that the federal government will continue to pour billions into higher education, largely because Americans have been persuaded that it…

Agresto, John

2011-01-01

316

Bubble nucleation in liquids  

Microsoft Academic Search

A review of theoretical and experimental aspects of homogeneous and heterogeneous bubble nucleation (valuable in LNG studies) covers recent developments in nucleation theory, which include hydrodynamic and diffusion constraints, gas-phase nonidealities, and heterogeneous nucleation. Large superheating may be involved in the dangerous and destructive contact vapor explosions observed in metallurgical and paper smelt processing and pose a potential hazard in

Milton Blander; Joseph L. Katz

1975-01-01

317

Bubble Chamber Site  

NSDL National Science Digital Library

This substantial site features a large number of photos of bubble chamber (BC) tracks, many with a discussion of the physics. There is a description of how the BC works and also useful tutorial on reading BC pictures. The high quality of the images and the explanations of the events that are shown make this site especially valuable.

2006-06-19

318

Bubble fusion: Preliminary estimates  

NASA Astrophysics Data System (ADS)

The collapse of a gas-filled bubble in disequilibrium (i.e., internal pressure much less than external pressure) can occur with a significant focusing of energy onto the entrapped gas in the form of pressure-volume work and/or acoustical shocks; the resulting heating can be sufficient to cause ionization and the emission of atomic radiations. The suggestion that extreme conditions necessary for thermonuclear fusion to occur may be possible has been examined parametrically in terms of the ratio of initial bubble pressure relative to that required for equilibrium. In this sense, the disequilibrium bubble is viewed as a three-dimensional 'sling shot' that is 'loaded' to an extent allowed by the maximum level of disequilibrium that can stably be achieved. Values of this disequilibrium ratio in the range 10(exp -5) to 10(exp -6) are predicted by an idealized bubble-dynamics model as necessary to achieve conditions where nuclear fusion of deuterium-tritium might be observed. Harmonic and aharmonic pressurizations/decompressions are examined as means to achieve the required levels of disequilibrium required to create fusion conditions. A number of phenomena not included in the analysis reported herein could enhance or reduce the small levels of nuclear fusions predicted.

Krakowski, R. A.

319

Substorm currents in the equatorial magnetotail  

SciTech Connect

The authors have determined characteristics of magnetospheric equatorial currents during substorms from the vector magnetic field data acquired with the GOES 5 and GOES 6 satellites, separated about 1.9 hours in MLT in geosynchronous orbit. These data have been used to determine the local time (azimuthal) and radial variation of the equatorial current. The divergence of the equatorial current was computed from these variations, and systems of field-aligned currents were deduced. During the growth phase to the maximum phase of the taillike reconfiguration of the near-Earth magnetic field, a positive divergence (away from the equatorial plane) of the westward equatorial current occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the late evening to premidnight MLT sector, and a negative divergence (away from the equatorial plane) occurs in the premidnight to early morning MLT sector. This flow direction pattern is the same as that of the region 2 field-aligned current system. The authors have also determined the presence of a radial current that flows toward the earth in the late evening to premidnight sector and flows away from the Earth in the midnight to morning sector. The intensity of the radial currents increases before the expansion phase. Consequently, the patterns of field-aligned currents associated with various substorm phases are the superposition of currents driven by multiple sources with different temporal variations. They have identified at least three different but related sources of field-aligned currents during the growth and expansion phases. These sources are related to the divergence of the westward flowing equatorial current and to distributions of pressure and magnetic field gradients that evolve in the magnetotail. When combined, these complicated systems support the basic region 1 to region 2 field-aligned current flow pattern. 22 refs., 12 figs., 1 tab.

Iijima, T.; Watanabe, M. [Univ. of Tokyo (Japan); Potemra, T.A.; Zanetti, L.J. [John Hopkins Univ., Laurel, MD (United States); Kan, J.R.; Akasofu, S.I. [Univ. of Alaska, Anchorage, AK (United States)

1993-10-01

320

Spread F Bubbles: Nonlinear Rayleigh-Taylor Mode in Two Dimensions  

Microsoft Academic Search

Analytic results on the nonlinear evolution of the Rayleigh-Taylor instability into equatorial spread F bubbles are presented. The nonlinear saturation amplitude and k spectrum of the inertia-dominated Rayleigh-Taylor instability is computed in two dimensions (east-west and vertical). Analogous to the collisional case, the dominant nonlinearity is found to be two dimensional. The linearly most unstable modes which are primarily horizontal

Mary K. Hudson

1978-01-01

321

Swarm Equatorial Electric Field Inversion Chain  

NASA Astrophysics Data System (ADS)

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere, in order to recover the EEF. We will present preliminary estimates of the EEF using the first Swarm geomagnetic field measurements, and compare them with independently measured electric fields from the JULIA ground-based radar in Peru.

Alken, Patrick; Maus, Stefan; Vigneron, Pierre; Sirol, Olivier; Hulot, Gauthier

2014-05-01

322

Signature of anisotropic bubble collisions  

SciTech Connect

Our universe may have formed via bubble nucleation in an eternally inflating background. Furthermore, the background may have a compact dimension--the modulus of which tunnels out of a metastable minimum during bubble nucleation--which subsequently grows to become one of our three large spatial dimensions. When in this scenario our bubble universe collides with other ones like it, the collision geometry is constrained by the reduced symmetry of the tunneling instanton. While the regions affected by such bubble collisions still appear (to leading order) as disks in an observer's sky, the centers of these disks all lie on a single great circle, providing a distinct signature of anisotropic bubble nucleation.

Salem, Michael P. [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155 (United States)

2010-09-15

323

Experimental investigation of laser enhancement of single-bubble sonoluminescence  

NASA Astrophysics Data System (ADS)

A single air bubble in degassed ultrapure water was acoustically levitated in a cylindrical resonator and made to sonoluminescence. A Nd:YAG nanosecond laser was fired synchronously and focused onto the bubble at the moment when the bubble was emitting photons. The laser enhancement on single bubble sonoluminescence was investigated by detecting the change in the brightness of the sonoluminescence when the laser was on and off. Laser induced background signal overshadows the sonoluminescence signal at strong laser power, possibly from the Raman effect or the plasma formation. At a low laser power of 1.7 mJ per pulse, a 5--9% increase in sonoluminescence intensity was found, while the relative standard deviation in the amplitudes of sonoluminescence pulses was found to be about 45%. Therefore, a definitive answer to the question of the laser enhancement of sonoluminescence cannot be given.

Cao, Guohua

324

Undulations on the Equatorial Edge of the Auroral Oval  

NASA Astrophysics Data System (ADS)

We present 5 events with observation of the evolution of large scale auroral undulations imaged by IMAGE FUV. Auroral undulations are large scale wave structures seen at the equatorial edge of the auroral oval during enhanced geomagnetic activity. They develop close to, or during the maximum of strength of the ring current. As the auroral undulations propagate westward along the duskside, their amplitude is growing. When they enter the plasmasphere further west, the auroral undulations are seen to reduce in amplitude, and vanish. DMSP F13 data shows velocity shears in the plasma close to the crest of the undulations, where the velocity shears are due to the establishment of SAPS channels. Observations of the precipitating energetic ion flux show an excellent latitudinal overlap with the location and extent of the auroral undulation. We suggest that the large scale auroral undulations are a consequence of the Kelvin-Helmholtz instability, and that energetic ions constitute the plasma population that is modulated.

Daae, M.; Østgaard, N.; Lewis, W. S.

2008-12-01

325

Planetary waves in the equatorial mesosphere and ionosphere measurements  

NASA Astrophysics Data System (ADS)

Mesosphere-ionosphere coupling through signature of planetary waves is investigated from equatorial meteor wind, obtained at São João do Cariri-PB (7.4°S, 36.5°W), from four magnetometer data and from evening F region vertical plasma drift measurements, obtained by digital ionospheric sounder (DPS-4) at Fortaleza (3.9°S, 38.4°W). To examine the temporal variations in meteor winds, magnetometer data and in vertical plasma drifts we used the S-transform method. The spectral analysis shows distinct power spectrum with peaks with low-frequency oscillations, which are associated with planetary waves, mainly those with period near 2 days and 6-7 days. The presence of these periodic variations, in these three different types of data, suggests that ionosphere has been modulated by mesospheric oscillations with period of planetary waves.

Lima, L. M.; Araujo, L. R.; Takahashi, H.; Batista, P. P.; Batista, I. S.; Silva, M. F.

2013-05-01

326

Energy effects in bubble nucleation  

SciTech Connect

Bubble size and number produced by desorption are important considerations for certain industrial processes such as flotation, gas stripping, and some types of chemical reactions and mass transfer. The size and number of bubbles produced by the desorption of supersaturated gases from water are shown to be a primary function of the energy available for bubble formation in a flowing system; this energy is that not dissipated in turbulence and friction. The number of nucleation sites is greatly increased when certain impurities are present, particularly surface-active agents. Low saturation pressures can produce very large numbers of very small bubbles when added energy is provided for discharge. High gas concentrations produce excess large bubbles which pass up rapidly through the much slower rising bubble mass. A combination of low saturation pressure followed by higher pressure for flow, such as by liquid pumping, results in bubble characteristics which can be controlled for applications.

Jackson, M.L. (Univ. of Idaho, Moscow, ID (United States). Dept. of Chemical Engineering)

1994-04-01

327

Shock wave and cavitation bubble measurements of ultrashort-pulse laser-induced breakdown in water  

Microsoft Academic Search

Laser-induced breakdown (LIB) has long been used in ophthalmic microsurgery as a mechanism for disruption of tissue. The goal of this surgery has been precise tissue cutting by plasma formation and a minimization of collateral damage due to shock wave and cavitation bubble formation. We investigate the strength of the shock wave emission, the size of the cavitation bubble, and

Daniel X. Hammer; Robert J. Thomas; Martin Frenz; E. Duco Jansen; Gary D. Noojin; Sarah J. Diggs; Joachim Noack; Alfred Vogel; Benjamin A. Rockwell

1996-01-01

328

Ring Bubbles of Dolphins  

NASA Technical Reports Server (NTRS)

The article discusses how dolphins create and play with three types of air-filled vortices. The underlying physics is discussed. Photographs and sketches illustrating the dolphin's actions and physics are presented. The dolphins engage in this behavior on their own initiative without food reward. These behaviors are done repeatedly and with singleminded effort. The first type is the ejection of bubbles which, after some practice on the part of the dolphin, turn into toroidal vortex ring bubbles by the mechanism of baroclinic torque. These bubbles grow in radius and become thinner as they rise vertically to the surface. One dolphin would blow two in succession and guide them to fuse into one. Physicists call this a vortex reconnection. In the second type, the dolphins first create an invisible vortex ring in the water by swimming on their side and waving their tail fin (also called flukes) vigorously. This vortex ring travels horizontally in the water. The dolphin then turns around, finds the vortex and injects a stream of air into it from its blowhole. The air "fills-out" the core of the vortex ring. Often, the dolphin would knock-off a smaller ring bubble from the larger ring (this also involves vortex reconnection) and steer the smaller ring around the tank. One other dolphin employed a few other techniques for planting air into the fluke vortex. One technique included standing vertically in the water with tail-up, head-down and tail piercing the free surface. As the fluke is waved to create the vortex ring, air is entrained from above the surface. Another technique was gulping air in the mouth, diving down, releasing air bubbles from the mouth and curling them into a ring when they rose to the level of the fluke. In the third type, demonstrated by only one dolphin, the longitudinal vortex created by the dorsal fin on the back is used to produce 10-15 foot long helical bubbles. In one technique she swims in a curved path. This creates a dorsal fin vortex since centrifugal force has to be balanced by a lift-like force. She then re-traces her path and injects air into the vortex from her blowhole. She can even make a ring reconnect from the helix. In the second technique, demonstrated a few times, she again swims in a curved path, releases a cloud or group of bubbles from her blowhole and turns sharply away (Which presumably strengthens the vortex). As the bubbles encounter the vortex, they travel to the center of the vortex, merge and, in a flash, elongate along the core of the vortex. In all the three types, the air-water interface is shiny smooth and stable because the pressure gradient in the vortex flow around the bubble stabilizes it. A lot of the interesting physics still remains to be explored.

Shariff, Karim; Marten, Ken; Psarakos, Suchi; White, Don J.; Merriam, Marshal (Technical Monitor)

1996-01-01

329

Measurements of fast neutrons by bubble detectors  

NASA Astrophysics Data System (ADS)

Neutron bubble detectors have been studied using Am-Be and D-D neuron sources, which give limited energy information. The Bubble Detector Spectrometer (BDS) have six different energy thresholds ranging from 10 KeV to 10 Mev. The number of bubbles obtained in each measurement is related to the dose (standardized response R) equivalent neutrons through sensitivity (b / ?Sv) and also with the neutron flux (neutrons per unit area) through a relationship that provided by the manufacturer. Bubble detectors were used with six different answers (0.11 b/ ?Sv, 0093 b/?Sv, 0.14 b/?Sv, 0.17 b/?Sv, 0051 b/?Sv). To test the response of the detectors (BDS) radiate a set of six of them with different energy threshold, with a source of Am-Be, placing them at a distance of one meter from it for a few minutes. Also, exposed to dense plasma focus Fuego Nuevo II (FN-II FPD) of ICN-UNAM, apparatus which produces fusion plasma, generating neutrons by nuclear reactions of neutrons whose energy emitting is 2.45 MeV. In this case the detectors were placed at a distance of 50 cm from the pinch at 90° this was done for a certain number of shots. In both cases, the standard response is reported (Dose in ?Sv) for each of the six detectors representing an energy range, this response is given by the expression Ri = Bi / Si where Bi is the number of bubbles formed in each and the detector sensitivity (Si) is given for each detector in (b / ?Sv). Also, reported for both cases, the detected neutron flux (n cm-2), by a given ratio and the response involves both standardized R, as the average cross section sigma. The results obtained have been compared with the spectrum of Am-Be source. From these measurements it can be concluded that with a combination of bubble detectors, with different responses is possible to measure the equivalent dose in a range of 10 to 100 ?Sv fields mixed neutron and gamma, and pulsed generated fusion devices.

Castillo, F.; Leal, B.; Martìnez, H.; Rangel, J.; Reyes, P. G.

2013-07-01

330

Measurements of fast neutrons by bubble detectors  

SciTech Connect

Neutron bubble detectors have been studied using Am-Be and D-D neuron sources, which give limited energy information. The Bubble Detector Spectrometer (BDS) have six different energy thresholds ranging from 10 KeV to 10 Mev. The number of bubbles obtained in each measurement is related to the dose (standardized response R) equivalent neutrons through sensitivity (b / {mu}Sv) and also with the neutron flux (neutrons per unit area) through a relationship that provided by the manufacturer. Bubble detectors were used with six different answers (0.11 b/ {mu}Sv, 0093 b/{mu}Sv, 0.14 b/{mu}Sv, 0.17 b/{mu}Sv, 0051 b/{mu}Sv). To test the response of the detectors (BDS) radiate a set of six of them with different energy threshold, with a source of Am-Be, placing them at a distance of one meter from it for a few minutes. Also, exposed to dense plasma focus Fuego Nuevo II (FN-II FPD) of ICN-UNAM, apparatus which produces fusion plasma, generating neutrons by nuclear reactions of neutrons whose energy emitting is 2.45 MeV. In this case the detectors were placed at a distance of 50 cm from the pinch at 90 Degree-Sign this was done for a certain number of shots. In both cases, the standard response is reported (Dose in {mu}Sv) for each of the six detectors representing an energy range, this response is given by the expression R{sub i}= B{sub i} / S{sub i} where B{sub i} is the number of bubbles formed in each and the detector sensitivity (S{sub i}) is given for each detector in (b / {mu}Sv). Also, reported for both cases, the detected neutron flux (n cm{sup -2}), by a given ratio and the response involves both standardized R, as the average cross section sigma. The results obtained have been compared with the spectrum of Am-Be source. From these measurements it can be concluded that with a combination of bubble detectors, with different responses is possible to measure the equivalent dose in a range of 10 to 100 {mu}Sv fields mixed neutron and gamma, and pulsed generated fusion devices.

Castillo, F.; Martinez, H. [Laboratorio de Espectroscopia, Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 48-3, 62251, Cuernavaca Morelos (Mexico); Leal, B. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510, Ciudad Universitaria, Mexico D. F. (Mexico); Rangel, J. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510, Ciudad Universitaria, Mexico D. F (Mexico); Reyes, P. G. [Facultad de Ciencias, Universidad Autonoma del Estado de Mexico, Instituto Literario 100, Col. Centro, 50000, Toluca Estado de Mexico (Mexico)

2013-07-03

331

Equatorial scintillations in relation to the development of ionization anomaly  

NASA Astrophysics Data System (ADS)

The irregularities in the electron density distribution of the ionosphere over the equatorial region frequently disrupt space-based communication and navigation links by causing severe amplitude and phase scintillations of signals. Development of a specification and forecast system for scintillations is needed in view of the increased reliance on space-based communication and navigation systems, which are vulnerable to ionospheric scintillations. It has been suggested in recent years that a developed equatorial anomaly in the afternoon hours, with a steep gradient of the F-region ionization or Total Electron Content (TEC) in the region between the crest and the trough, may be taken as a precursor to scintillations on transionospheric links. Latitudinal gradient of TEC measured using Faraday Rotation technique from LEO NOAA 12/14 transmissions during the afternoon hours at Calcutta shows a highly significant association with L-band scintillations recorded on the INMARSAT link, also from Calcutta, during the equinoxes, August through October 2000, and February through April 2001.

The daytime equatorial electrojet is believed to control the development of the equatorial anomaly and plays a crucial role in the subsequent development of F-region irregularities in the post-sunset hours. The diurnal maximum and integrated value (integrated from the time of onset of plasma influx to off-equatorial latitudes till local sunset) of the strength of the electrojet in the Indian longitude sector shows a significant association with post-sunset L-band scintillations recorded at Calcutta during the two equinoxes mentioned earlier.

Generation of equatorial irregularities over the magnetic equator in the post-sunset hours is intimately related to the variation of the height of the F-layer around sunset. Ionosonde data from Kodaikanal, a station situated close to the magnetic equator, has been utilized to calculate the vertical drift of the F-layer over the magnetic equator for the period August through October 2000. The post-sunset F-region height rise over the magnetic equator shows a remarkable correspondence with the occurrence of scintillations at Calcutta located near the northern crest of the equatorial anomaly.

Existence of a flat-topped ionization distribution over the magnetic equator around sunset has been suggested as a possible indication of occurrence of post-sunset scintillations. Width of the latitudinal distribution of ionization obtained from DMSP satellite shows some correspondence with post-sunset L-band scintillations. During the period of observation of the present study (August through October 2000, and February through April 2001), it has been observed that although the probability of occurrence of scintillations is high on days with flat-topped ion density variation over the equator, there are cases when no scintillations were observed even when a pronounced flat top variation was recorded.

Ray, S.; Paul, A.; Dasgupta, A.

2006-07-01

332

Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements  

Microsoft Academic Search

Simultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low

C.A. Gonzales; M.C. Kelley; B.G. Fejer; J.F. Vickrey; R.F. Woodman

1979-01-01

333

Sonoluminescence, sonochemistry and bubble dynamics of single bubble cavitation  

NASA Astrophysics Data System (ADS)

The amount of hydroxyl radicals produced from a single cavitation bubble was quantified by terephthalate dosimetry at various frequencies and pressure amplitudes, while the dynamics of the single bubble was observed by stroboscopic and light-scattering methods. Also, sonoluminescence (SL), sonochemiluminescence (SCL) of luminol, and sodium atom emission (Na*) in the cavitation field were observed. The amount of hydroxyl radicals per cycle as well as the intensity of SL was proportional to pressure amplitude at every frequency performed, and it decreased with increasing frequency. When the single bubble was dancing with a decrease in pressure amplitude, however, the amount of hydroxyl radicals was greater than that for the stable bubble at the higher pressure amplitude and did not significantly decrease with frequency. Furthermore, SCL and Na* were detected only under unstable bubble conditions. These results imply that the instability of bubbles significantly enhances sonochemical efficiency for non-volatile substances in liquid phase.

Hatanaka, Shin-ichi

2012-09-01

334

Anatomy of bubbling solutions  

Microsoft Academic Search

We present a comprehensive analysis of holography for the bubbling solutions of Lin-Lunin-Maldacena. These solutions are uniquely determined by a coloring of a 2-plane, which was argued to correspond to the phase space of free fermions. We show that in general this phase space distribution does not determine fully the 1\\/2 BPS state of N = 4 SYM that the

Kostas Skenderis; Marika Taylor

2007-01-01

335

Bubble dynamics in drinks  

NASA Astrophysics Data System (ADS)

This study introduces two physical effects known from beverages: the effect of sinking bubbles and the hot chocolate sound effect. The paper presents two simple "kitchen" experiments. The first and second effects are indicated by means of a flow visualization and microphone measurement, respectively. To quantify the second (acoustic) effect, sound records are analyzed using time-frequency signal processing, and the obtained power spectra and spectrograms are discussed.

Brou?ková, Zuzana; Trávní?ek, Zden?k; Šafa?ík, Pavel

2014-03-01

336

Inside a Collapsing Bubble: Sonoluminescence and the Conditions During Cavitation  

NASA Astrophysics Data System (ADS)

Acoustic cavitation, the growth and rapid collapse of bubbles in a liquid irradiated with ultrasound, is a unique source of energy for driving chemical reactions with sound, a process known as sonochemistry. Another consequence of acoustic cavitation is the emission of light [sonoluminescence (SL)]. Spectroscopic analyses of SL from single bubbles as well as a cloud of bubbles have revealed line and band emission, as well as an underlying continuum arising from a plasma. Application of spectrometric methods of pyrometry as well as tools of plasma diagnostics to relative line intensities, profiles, and peak positions have allowed the determination of intracavity temperatures and pressures. These studies have shown that extraordinary conditions (temperatures up to 20,000 K; pressures of several thousand bar; and heating and cooling rates of >1012 K s1) are generated within an otherwise cold liquid.

Suslick, Kenneth S.; Flannigan, David J.

2008-05-01

337

Effect of bubble deformation on the properties of bubbly flows  

Microsoft Academic Search

Direct numerical simulations of the motion of 27 three-dimensional deformable buoyant bubbles in periodic domains are presented. The full Navier Stokes equations are solved by a parallelized finite-difference\\/front-tracking method that allows a deformable interface between the bubbles and the suspending fluid and the inclusion of surface tension. The Eötvös number is taken as equal to 5, so that the bubbles

Bernard Bunner; Grétar Tryggvason

2003-01-01

338

Dynamic simulation of bubbly flow in bubble columns  

Microsoft Academic Search

Gas–liquid bubbly flow in two-dimensional bubble columns is studied by numerical simulation. An Eulerian–Eulerian two-fluid model is used to describe the time-dependent motion of the liquid driven by small, spherical gas bubbles injected at the bottom of the columns. The simulations are able to capture the large scale structures as observed experimentally in the laboratory. The numerical results, which include

Y. Pan; M. P. Dudukovic; M. Chang

1999-01-01

339

In Search of the Big Bubble  

ERIC Educational Resources Information Center

Freely rising air bubbles in water sometimes assume the shape of a spherical cap, a shape also known as the "big bubble". Is it possible to find some objective function involving a combination of a bubble's attributes for which the big bubble is the optimal shape? Following the basic idea of the definite integral, we define a bubble's surface as…

Simoson, Andrew; Wentzky, Bethany

2011-01-01

340

Effect of frothers on bubble size  

Microsoft Academic Search

The size of bubbles in flotation cells was measured using the UCT bubble size meter and the HUT bubble size analyser. While both methods provided similar critical coalescence concentration (CCC) values for the three tested frothers, they also revealed important differences. Using the HUT bubble size analyser, which does not impose any lower bubble size limit, it was possible to

Rodrigo A. Grau; Janusz S. Laskowski; Kari Heiskanen

2005-01-01

341

Acoustic Measurements Bubbles in Biological Tiessure  

Microsoft Academic Search

An acoustic based instrument, the ABS Acoustic Bubble Spectrometer®© (ABS), was investigated for the detection and quantification of bubbles in biological media. These include viscoelastic media (blood), materials of varying density (bone in tissue), non-homogenous distribution of bubbles (intravenous bubbly flow), and bubbles migrating in tissue (decompression sickness, DCS). The performance of the ABS was demonstrated in a series of

Georges L. CHAHINE; Michel TANGUAY; Greg LORAINE

2009-01-01

342

Gamma rays from Fermi bubbles as due to diffusive injection of Galactic cosmic rays  

NASA Astrophysics Data System (ADS)

Recent detailed analysis of the Fermi-LAT data has discovered two giant ?-ray emission regions, the so-called Fermi bubbles, extending up to ~50° in Galactic latitude above and below the Galactic center with a width of ~40° in longitude. The origin of the ?-ray emission is not clearly understood. Here, we discuss the possibility that the ?-rays can be the result of diffusive injection of Galactic cosmic-ray protons during their propagation through the Galaxy. In the model, we consider that the bubbles are slowly expanding, and cosmic rays undergo much slower diffusion inside the bubbles than in the averaged Galaxy. Moreover, we consider that cosmic rays inside the bubbles suffer losses from adiabatic expansion, and also from inelastic collisions with the bubble plasma producing pion-decay ? rays. We show that this simple model can explain some of the important properties of Fermi bubbles such as the measured ?-ray intensity profile, the energy spectrum and the measured luminosity.

Thoudam, Satyendra

2014-04-01

343

Bubble Measuring Instrument and Method  

NASA Technical Reports Server (NTRS)

Method and apparatus are provided for a non-invasive bubble measuring instrument operable for detecting. distinguishing, and counting gaseous embolisms such as bubbles over a selectable range of bubble sizes of interest. A selected measurement volume in which bubbles may be detected is insonified by two distinct frequencies from a pump transducer and an image transducer, respectively. The image transducer frequency is much higher than the pump transducer frequency. The relatively low-frequency pump signal is used to excite bubbles to resonate at a frequency related to their diameter. The image transducer is operated in a pulse-echo mode at a controllable repetition rate that transmits bursts of high-frequency ultrasonic signal to the measurement volume in which bubbles may be detected and then receive, the echo. From the echo or received signal, a beat signal related to the repetition rate may be extracted and used to indicate the presence or absence of a resonant bubble. In a preferred embodiment, software control maintains the beat signal at a preselected frequency while varying the pump transducer frequency to excite bubbles of different diameters to resonate depending on the range of bubble diameters selected for investigation.

Kline-Schoder, Robert (Inventor); Magari, Patrick J. (Inventor)

2002-01-01

344

Bubble Measuring Instrument and Method  

NASA Technical Reports Server (NTRS)

Method and apparatus are provided for a non-invasive bubble measuring instrument operable for detecting, distinguishing, and counting gaseous embolisms such as bubbles over a selectable range of bubble sizes of interest. A selected measurement volume in which bubbles may be detected is insonified by two distinct frequencies from a pump transducer and an image transducer. respectively. The image transducer frequency is much higher than the pump transducer frequency. The relatively low-frequency pump signal is used to excite bubbles to resonate at a frequency related to their diameter. The image transducer is operated in a pulse-echo mode at a controllable repetition rate that transmits bursts of high-frequency ultrasonic signal to the measurement volume in which bubbles may be detected and then receives the echo. From the echo or received signal, a beat signal related to the repetition rate may be extracted and used to indicate the presence or absence of a resonant bubble. In a preferred embodiment, software control maintains the beat signal at a preselected frequency while varying the pump transducer frequency to excite bubbles of different diameters to resonate depending on the range of bubble diameters selected for investigation.

Kline-Schoder, Robert (Inventor); Magari, Patrick J. (Inventor)

2002-01-01

345

Bubble measuring instrument and method  

NASA Technical Reports Server (NTRS)

Method and apparatus are provided for a non-invasive bubble measuring instrument operable for detecting, distinguishing, and counting gaseous embolisms such as bubbles over a selectable range of bubble sizes of interest. A selected measurement volume in which bubbles may be detected is insonified by two distinct frequencies from a pump transducer and an image transducer, respectively. The image transducer frequency is much higher than the pump transducer frequency. The relatively low-frequency pump signal is used to excite bubbles to resonate at a frequency related to their diameter. The image transducer is operated in a pulse-echo mode at a controllable repetition rate that transmits bursts of high-frequency ultrasonic signal to the measurement volume in which bubbles may be detected and then receives the echo. From the echo or received signal, a beat signal related to the repetition rate may be extracted and used to indicate the presence or absence of a resonant bubble. In a preferred embodiment, software control maintains the beat signal at a preselected frequency while varying the pump transducer frequency to excite bubbles of different diameters to resonate depending on the range of bubble diameters selected for investigation.

Kline-Schoder, Robert (Inventor); Magari, Patrick J. (Inventor)

2003-01-01

346

Bubble Measuring Instrument and Method  

NASA Technical Reports Server (NTRS)

Method and apparatus are provided for a non-invasive bubble measuring instrument operable for detecting, distinguishing, and counting gaseous embolisms such as bubbles over a selectable range of bubble sizes of interest. A selected measurement volume in which bubbles may be detected is insonified by two distinct frequencies from a pump transducer and an image transducer, respectively. The image transducer frequency is much higher than the pump transducer frequency. The relatively low-frequency pump signal is used to excite bubbles to resonate at a frequency related to their diameter. The image transducer is operated in a pulse-echo mode at a controllable repetition rate that transmits bursts of high-frequency ultrasonic signal to the measurement volume in which bubbles may be detected and then receives the echo. From the echo or received signal, a beat signal related to the repetition rate may be extracted and used to indicate the presence or absence of a resonant bubble. In a preferred embodiment, software control maintains the beat signal at a preselected frequency while varying the pump transducer frequency to excite bubbles of different diameters to resonate depending on the range of bubble diameters selected for investigation.

Kline-Schoder, Robert (Inventor); Magari, Patrick J. (Inventor)

2002-01-01

347

Helium bubble bursting in tungsten  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations have been used to systematically study the pressure evolution and bursting behavior of sub-surface helium bubbles and the resulting tungsten surface morphology. This study specifically investigates how bubble shape and size, temperature, tungsten surface orientation, and ligament thickness above the bubble influence bubble stability and surface evolution. The tungsten surface is roughened by a combination of adatom "islands," craters, and pinholes. The present study provides insight into the mechanisms and conditions leading to various tungsten topology changes, which we believe are the initial stages of surface evolution leading to the formation of nanoscale fuzz.

Sefta, Faiza; Juslin, Niklas; Wirth, Brian D.

2013-12-01

348

Equatorially coordinated lanthanide single ion magnets.  

PubMed

The magnetic relaxation dynamics of low-coordinate Dy(III) and Er(III) complexes, namely three-coordinate ones with an equatorially coordinated triangle geometry and five-coordinate ones with a trigonal bipyramidal geometry, have been exploited for the first time. The three-coordinate Er-based complex is the first equatorially coordinated mononuclear Er-based single-molecule magnet (SMM) corroborating that simple models can effectively direct the design of target SMMs incorporating 4f-elements. PMID:24625001

Zhang, Peng; Zhang, Li; Wang, Chao; Xue, Shufang; Lin, Shuang-Yan; Tang, Jinkui

2014-03-26

349

A discussion on the effect of bubble induced liquid velocity on the mass transfer performance of bubbles in bubble plumes  

Microsoft Academic Search

The effect of the bubble induced liquid velocity on the mass transfer performance of bubbles in bubble plumes has been studied numerically. A two-way coupling Euler-Lagrange method was adopted for the modeling of bubble plumes with mass transfer. The dissolution of air (nitrogen and oxygen, mainly considered) in bubble plumes with micro bubbles, 100mum<=d0<=1mm, was simulated. The results show that

Xiaobo Gong; Shu Takagi; Yoichiro Matsumoto

2006-01-01

350

Mapping a bubble at dip equator and anomaly with oblique ionospheric soundings of range spread F  

SciTech Connect

Multiple ionospheric sounders are employed in the first attempt to detect and map remotely an equatorial bubble near the dip equator and simultaneously near the Appleton anomaly crest. The sounders also provide latitudinal profiles of electron density through {+-} 30{degrees} dip latitude (DIPLAT). Conditions are solar maximum and low Kp. Using oblique range spread F (RSF) echoes from the bubble boundaries, four sounders located near the dip equator detect a single isolated bubble at ranges as great as a 1020 km and track it for 2.25 hours at 5-min intervals as it drifts eastward through 15{degrees} geomagnetic longitude (MLONG). Maximum velocity is 185 m/s, and width is 375 km. Near the northern anomaly crest, a sounder at 20.3{degrees} DIPLAT observes the western boundary for a duration of 1 hour concurrently with and magnetically conjugate to the equatorial observations. The boundary here has nearly the same drift velocity and MLONG as at the equator, implying that the boundary location and velocity are nearly independent of altitude above the dip equator. Subsequently, in the south a sounder at 19.9{degrees} DIPLAT observes the bubble to have a velocity approximately half that seen by other stations and a MLONG that is at least 3{degrees} west of the others. This difference may be related to the north-south asymmetry of the anomaly crest, which is at the location of the northern sounder but equatorward of the southern sounder, although the two are at the same DIPLAT. The onset of the bubble is recorded in the first appearance of RSF at 1915 local mean time; 20 min later the bubble boundary appears and begins accelerating eastward, the movement occurring within about 5 min of electric field reversal as inferred from F layer vertical motion. 30 refs., 8 figs.

Whalen, J.A. [Phillips Laboratory, Hanscom Air Force Base, MA (United States)] [Phillips Laboratory, Hanscom Air Force Base, MA (United States)

1996-03-01

351

Bubble Formation of Vortices in a Liquid Helium Bubble Chamber.  

National Technical Information Service (NTIS)

It is believed that vorticity was produced in liquid helium II and used to nucleate bubble formation. Most of the bubbles appear to be round, and many have their outer edges near the inside wall of the glass cylinder. Many more vortices are detected at lo...

M. H. Edwards R. M. Cleary W. M. Fairbank

1965-01-01

352

Bubble levitation and translation under single-bubble sonoluminescence conditions  

NASA Astrophysics Data System (ADS)

Bubble levitation in an acoustic standing wave is re-examined for conditions relevant to single-bubble sonoluminescence. Unlike a previous examination [Matula et al., J. Acoust. Soc. Am. 102, 1522-1527 (1997)], the stable parameter space [Pa,R0] is accounted for in this realization. Forces such as the added mass force and drag are included, and the results are compared with a simple force balance that equates the Bjerknes force to the buoyancy force. Under normal sonoluminescence conditions, the comparison is quite favorable. A more complete accounting of the forces shows that a stably levitated bubble does undergo periodic translational motion. The asymmetries associated with translational motion are hypothesized to generate instabilities in the spherical shape of the bubble. A reduction in gravity results in reduced translational motion. It is hypothesized that such conditions may lead to increased light output from sonoluminescing bubbles.

Matula, Thomas J.

2003-08-01

353

New mechanism for bubble nucleation: Classical transitions  

SciTech Connect

Given a scalar field with metastable minima, bubbles nucleate quantum mechanically. When bubbles collide, energy stored in the bubble walls is converted into kinetic energy of the field. This kinetic energy can facilitate the classical nucleation of new bubbles in minima that lie below those of the 'parent' bubbles. This process is efficient and classical, and changes the dynamics and statistics of bubble formation in models with multiple vacua, relative to that derived from quantum tunneling.

Easther, Richard [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Giblin, John T. Jr [Department of Physics, Kenyon College, Gambier, Ohio 43022 (United States); Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON N2L 2Y5 (Canada); Hui Lam; Lim, Eugene A. [ISCAP and Physics Department, Columbia University, New York, 10027 (United States)

2009-12-15

354

Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes  

NASA Astrophysics Data System (ADS)

The Plasma Bubble Expansion Experiment (PBEX) has begun laboratory experiments and coordinated nonlinear MHD simulations to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (˜10 kV, ˜100 kA, ˜2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Experimental parameters can be adjusted so that important dimensionless parameters are relevant to the astrophysical context. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. First experimental data from plasma bubble injection into a background plasma, including magnetic probe measurements and high-speed camera imaging, will be presented. [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008). Supported by NSF-AST/DOE grant AST-0613577 and LANL LDRD.

Lynn, Alan; Zhang, Yue; Hsu, Scott; Li, Hui; Liu, Wei; Gilmore, Mark; Watts, Christopher

2009-05-01

355

Effects of pulse width on nascent laser-induced bubbles for underwater laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

The reason for the significant advantage offered by long-pulse (150 ns) irradiation in underwater laser-induced breakdown spectroscopy (LIBS) is investigated from the point of view of the behavior of nascent cavitation bubbles. Shadowgraphs of nascent bubbles generated by pulsed laser irradiation of Cu targets in water were observed for two different pulse widths, 20 ns and 150 ns. It is clearly seen that the nascent bubble is formed at the leading edge of the laser pulse profile, regardless of the pulse width. Bubbles generated by a 20-ns pulse are characterized by a flat-shape filled with dense matter with intense optical emission, which is in contrast to more hemispherical low-density bubbles observed under the irradiation by a 150-ns pulse. The behavior of the nascent bubbles is consistent with the behavior of the later plasma in the bubbles, which is crucial for observation of well-defined atomic spectral lines for underwater LIBS.

Sakka, Tetsuo; Tamura, Ayaka; Matsumoto, Ayumu; Fukami, Kazuhiro; Nishi, Naoya; Thornton, Blair

2014-07-01

356

Relation Between Ionospheric Plasma Irregularities at High Latitudes and Auroral Phenomena  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities at low-latitudes, known as equatorial plasma bubbles, tend to occur preferably at post-sunset hours when the vertical plasma velocity during the pre-reversal enhancement is particularly strong. Recently, significant occurrence rates of plasma irregularities have also been reported in the high-latitude regions. Their generation mechanisms are quite different and at present still not fully understood. As these irregularities tend to cluster in three prominent regions of the polar area - cusp, polar cap, and pre-midnight substorm onset sector - we investigate their characteristics for these regions separately. One suggestion for high-latitude irregularity generation is ionisation by soft electron precipitations. These beams of soft electrons are commonly accompanied by bursts of small-scale field-aligned currents (FAC). In a superposed epoch analysis we investigate the relation between the occurrences of plasma irregularities and collocated small-scale FACs. In the cusp, a clear coincidence of the two phenomena is observed. Conversely, in the polar cap small-scale FACs are not so frequent. Therefore we suggest a transport of the irregularities from the cusp region into the polar cap by the general anti-sunward plasma convection pattern. In order to discuss possible relations between plasma irregularities detected in the pre-midnight sector and substorm phases we also compare the event times with the substorm catalogue of Frey and Mende (2006).

Ritter, P.; Park, J.; Luhr, H.

2012-12-01

357

Identifying equatorial ionospheric irregularities using in situ ion drifts  

NASA Astrophysics Data System (ADS)

Previous climatological investigations of ionospheric irregularity occurrence in the equatorial ionosphere have utilized in situ measurements of plasma density to identify the presence of an irregularity. Here we use the Morlet wavelet and C/NOFS to isolate perturbations in meridional ion drifts and generate irregularity occurrence maps as a function of local time, longitude, season, and solar activity. For the low solar activity levels in 2008, the distributions identified by velocity perturbations follow normalized density perturbation (?N/N) maps with large occurrences after midnight into dawn over all longitudes. The velocity and normalized density occurrence maps contract in both local time and longitude with increasing solar activity. By 2011 irregularities are confined to particular longitudes expected by alignment and a few hours of local time after sunset. The variation in the occurrence of the late night irregularities with solar activity is consistent with the presence of gravity wave seeding.

Stoneback, R. A.; Heelis, R. A.

2014-04-01

358

Seeding and layering of equatorial spread F by gravity waves  

SciTech Connect

Studies dating back more than 15 years have presented evidence that atmospheric gravity waves play a role in initiating nighttime equatorial F region instabilities. This paper analyzes a spectabular spread F event that for the first time demonstrates a layering which, the authors argue, is controlled by a gravity wave effect. The 50-km vertical wavelength of a gravity wave which they have found is related theoretically to a plasma layering irregularity that originated at low altitudes and then was convected, intact, to higher altitudes. Gravity waves also seem to have determined bottomside intermediate scale undulations, although this fact is not as clear in the data. The neutral wind dynamo effect yields wave number conditions on the gravity wave's ability to modulate the Rayleigh-Taylor instaiblity process. Finally, after evaluating the gravity wave dispersion relation and spatial resonance conditions, we estimate the properties of the seeding wave.

Hysell, D.L.; Kelley, M.C.; Swartz, W.E. (Cornell University, Ithaca, NY (United States)); Woodman, R.F. (Inst. Geofisico del Peru, Lima (Peru))

1990-10-01

359

Attempt to monitor the equatorial undercurrent  

SciTech Connect

The geostrophic balance is used to compare integrals of the observed density distribution with transports of the equatorial undercurrent measured directly during the Hawaii to Tahiti shuttle experiment. The scatter of the relationship is large, making the relation useless for monitoring purposes. The reason for the failure lies in the fast response of the density structure to anomalous upwelling or downwelling.

Wyrtki, K.

1983-01-20

360

An improved model of equatorial scintillation  

Microsoft Academic Search

One of the main limitations of the modeling work that went into the equatorial section of the Wideband ionospheric scintillation model (WBMOD) was that the data set used in the modeling was limited to two stations near the dip equator (Ancon, Peru, and Kwajalein Island, in the North Pacific Ocean) at two fixed local times (nominally 1000 and 2200). Over

J. A. Secan; R. M. Bussey; E. J. Fremouw; Sa. Basu

1995-01-01

361

Dynamical variability in Saturn Equatorial Atmosphere  

Microsoft Academic Search

Historical ground-based and recent HST observations show that Saturn's Equatorial Atmosphere is the region where the most intense large-scale dynamical variability took place at cloud level in the planet. Large-scale convective storms (nicknamed the ``Great White Spots\\

A. Sánchez-Lavega; S. Pérez-Hoyos; R. Hueso; J. F. Rojas; R. G. French

2003-01-01

362

Equion, an Equatorial Ionospheric Irregularity Experiment  

Microsoft Academic Search

This paper describes a coordinated rocket and ground-based study to investigate equatorial spread F irregularities. Measurements by the Jicamarca backscatter radar, ionosondes, and airglow instrumentation and of radio scintillations were correlated with high spatial resolution measurements of electron densities, particle fluxes, and VLF-ELF fields from a rocket probe. Experimentally, we find that (l) very high positive and negative electron density

F. A. Morse; B. C. Edgar; H. C. Koons; C. J. Rice; W. J. Heikkila; J. H. Hoffman; B. A. Tinsley; J. D. Winningham; A. B. Christensen; R. F. Woodman; J. Pomalaza; N. R. Teixeira

1977-01-01

363

First observational evidence for opposite zonal electric fields in equatorial E and F region altitudes during a geomagnetic storm period  

NASA Astrophysics Data System (ADS)

The strong westward electrojet and simultaneous upward drift of the equatorial ionospheric peak observed over South-East Asia and Indian equatorial regions during the prolonged Dst minimum phase of an intense geomagnetic storm during 14-15 December 2006 are investigated for the altitudinal variation of zonal electric field polarity using ground based and space-borne observations. The results show first observational evidence for simultaneous existence of daytime westward and eastward zonal electric fields at equatorial E and F region altitudes, respectively, in a wide longitude sector. While the westward electric fields at E region altitudes cause westward electrojet, at the same time, the eastward zonal electric fields at F region altitudes cause the upward drift of the equatorial ionospheric peak and reinforcement of the equatorial ionization anomaly (EIA) even in the topside ionosphere (˜660 km). The reversal of the electric fields is found to occur at ˜280 km height. A clear bifurcation of F region plasma at ˜280 km is evident in the iso-electron density contours due to these oppositely polarized zonal electric fields, which manifests as an unusually deep cusp between F1 and F2 layers on equatorial ionograms.

Tulasi Ram, S.; Balan, N.; Veenadhari, B.; Gurubaran, S.; Ravindran, S.; Tsugawa, T.; Liu, H.; Niranjan, K.; Nagatsuma, T.

2012-09-01

364

Tuning bubbly structures in microchannels.  

PubMed

Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row ("dripping"), to multiple rows ("alternating"), to densely packed bubbles ("bamboo" and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate stable nitrogen bubbles in aqueous surfactant solution and stable droplets in oil containing dissolved surfactant. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters. PMID:22655008

Vuong, Sharon M; Anna, Shelley L

2012-06-01

365

Why Are Bubbles So Colorful?  

NSDL National Science Digital Library

In this activity, learners explore why they can see colors in bubbles and why they change. Learners also examine what thin slits do to light and how this phenomenon is similar to that of bubbles and oil slicks. Note: This activity works best outside in the sunlight.

America, Optical S.

2008-01-01

366

Bursting Bubbles and Air Pollution.  

National Technical Information Service (NTIS)

Photographic studies of small bubbles bursting at the surface of fresh and sea water have shown that aersols are produced through the breakup of minute water jets formed by the collapse of the bubble cavities. It is the purpose of the report to show a few...

A. H. Woodcock

1965-01-01

367

Tuning bubbly structures in microchannels  

PubMed Central

Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row (“dripping”), to multiple rows (“alternating”), to densely packed bubbles (“bamboo” and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate stable nitrogen bubbles in aqueous surfactant solution and stable droplets in oil containing dissolved surfactant. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters.

Vuong, Sharon M.; Anna, Shelley L.

2012-01-01

368

Acoustic Behavior of Vapor Bubbles  

NASA Technical Reports Server (NTRS)

In a microgravity environment vapor bubbles generated at a boiling surface tend to remain near it for a long time. This affects the boiling heat transfer and in particular promotes an early transition to the highly inefficient film boiling regime. This paper describes the physical basis underlying attempts to remove the bubbles by means of pressure radiation forces.

Prosperetti, Andrea; Oguz, Hasan N.

1996-01-01

369

Bubble nucleation in stout beers  

Microsoft Academic Search

Bubble nucleation in weakly supersaturated solutions of carbon dioxide---such as champagne, sparkling wines, and carbonated beers---is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology

W. T. Lee; J. S. McKechnie; M. G. Devereux

2011-01-01

370

Gas bubbles in shaped sapphire  

Microsoft Academic Search

Shaped sapphire single crystals almost always contain a typical defect: small bubbles also known as “micro-voids”. The goal of this paper is to review the existing literature and give a survey of our recent work on this specific defect. As a conclusion to our review we propose a mechanism for bubble formation and its occurrence and distribution in shaped sapphire.The

O. M. Bunoiu; Th. Duffar; I. Nicoara

2010-01-01

371

Equatorial Radius of the Earth a Dynamical Determination.  

National Technical Information Service (NTIS)

An interesting variation on the familiar method of determi-ning the earth's equatorial radius a sub e, from a knowledge of the earth's equatorial gravity is suggested. The value of equatorial radius thus found is 6378,142 + or - 5 meters. The associated p...

M. A. Khan

1972-01-01

372

Triangular bubble spline surfaces  

PubMed Central

We present a new method for generating a Gn-surface from a triangular network of compatible surface strips. The compatible surface strips are given by a network of polynomial curves with an associated implicitly defined surface, which fulfill certain compatibility conditions. Our construction is based on a new concept, called bubble patches, to represent the single surface patches. The compatible surface strips provide a simple Gn-condition between two neighboring bubble patches, which are used to construct surface patches, connected with Gn-continuity. For n?2, we describe the obtained Gn-condition in detail. It can be generalized to any n?3. The construction of a single surface patch is based on Gordon–Coons interpolation for triangles. Our method is a simple local construction scheme, which works uniformly for vertices of arbitrary valency. The resulting surface is a piecewise rational surface, which interpolates the given network of polynomial curves. Several examples of G0, G1 and G2-surfaces are presented, which have been generated by using our method. The obtained surfaces are visualized with reflection lines to demonstrate the order of smoothness.

Kapl, Mario; Byrtus, Marek; Juttler, Bert

2011-01-01

373

Triangular bubble spline surfaces.  

PubMed

We present a new method for generating a [Formula: see text]-surface from a triangular network of compatible surface strips. The compatible surface strips are given by a network of polynomial curves with an associated implicitly defined surface, which fulfill certain compatibility conditions. Our construction is based on a new concept, called bubble patches, to represent the single surface patches. The compatible surface strips provide a simple [Formula: see text]-condition between two neighboring bubble patches, which are used to construct surface patches, connected with [Formula: see text]-continuity. For [Formula: see text], we describe the obtained [Formula: see text]-condition in detail. It can be generalized to any [Formula: see text]. The construction of a single surface patch is based on Gordon-Coons interpolation for triangles.Our method is a simple local construction scheme, which works uniformly for vertices of arbitrary valency. The resulting surface is a piecewise rational surface, which interpolates the given network of polynomial curves. Several examples of [Formula: see text], [Formula: see text] and [Formula: see text]-surfaces are presented, which have been generated by using our method. The obtained surfaces are visualized with reflection lines to demonstrate the order of smoothness. PMID:22267872

Kapl, Mario; Byrtus, Marek; Jüttler, Bert

2011-11-01

374

Bubbles under stress.  

PubMed

We present an experimental and theoretical investigation of a system composed of two soap bubbles strained between two parallel solid surfaces. The two-bubble cluster can be found in several configurations. The existence and stability of each of these states is studied as a function of the distance between the two facing surfaces. The change of this distance can induce a transition from one configuration to another; we observe that most transitions are subcritical, showing that the system is often trapped in states where the minimum of free energy is only local. The hysteretic transitions are responsible for the dissipation of elastic energy. The existence of more than one stable states for given boundaries conditions combined with the absence of thermalization means that the history of the system has to be taken into account and that there is no unique stress-strain relation. In the present system, because of its simplicity, a complete quantitative analysis of these general processes is obtained. The presented results may contribute to a better understanding of the dynamics of more complex systems such as foams or granular materials where similar processes are at work. PMID:15011058

Bohn, S

2003-06-01

375

Bubble formation in microgravity  

NASA Technical Reports Server (NTRS)

Two KC-135 flight campaigns have been conducted to date which are specifically dedicated to study bubble formation in microgravity. The first flight was conducted during March 14-18, 1994, and the other during June 20-24, 1994. The results from the June 1994 flight have not been analyzed yet, while the results from the March flight have been partially analyzed. In the first flight three different experiments were performed, one with the specific aim at determining whether or not cavitation can take place during any of the fluid handling procedures adopted in the shuttle bioprocessing experiments. The other experiments were concerned with duplicating some of the procedures that resulted in bubble formation, namely the NCS filling procedure and the needle scratch of a solid surface. The results from this set of experiments suggest that cavitation did not take place during any of the fluid handling procedures. The results clearly indicate that almost all were generated as a result of the breakup of the gas/liquid interface. This was convincingly demonstrated in the scratch tests as well as in the liquid fill tests.

Antar, Basil N.

1994-01-01

376

Equatorial spread F studies using SAMI3 with two-dimensional and three-dimensional electrostatics  

NASA Astrophysics Data System (ADS)

This letter presents a study of equatorial F region irregularities using the NRL SAMI3/ESF model, comparing results using a two-dimensional (2-D) and a three-dimensional (3-D) electrostatic potential solution. For the 3-D potential solution, two cases are considered for parallel plasma transport: (1) transport based on the parallel ambipolar field, and (2) transport based on the parallel electric field. The results show that the growth rate of the generalized Rayleigh-Taylor instability is not affected by the choice of the potential solution. However, differences are observed in the structures of the irregularities between the 2-D and 3-D solutions. Additionally, the plasma velocity along the geomagnetic field computed using the full 3-D solution shows complex structures that are not captured by the simplified model. This points out that only the full 3-D model is able to fully capture the complex physics of the equatorial F region.

Aveiro, H. C.; Huba, J. D.

2013-12-01

377

Wave Forcing of Saturn's Equatorial Oscillation  

NASA Technical Reports Server (NTRS)

Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn.

Flasar, F. M.; Schlinder, P. J.; Guerlet, S.; Fouchet, T.

2011-01-01

378

Nonlinear evolution of equatorial spread F. 2. Gravity wave seeding of Rayleigh-Taylor instability  

Microsoft Academic Search

We have performed numerical simulations of nonlinear evolution of the Rayleigh-Taylor instability in equatorial spread F (ESF) under different conditions. Our main purpose is to explain the generation of multiple plumes on the west wall of a plasma upwelling and the relationship between gravity waves and large scale ESF irregularities. We have studied ESF structures resulting from one-dimensional or two-dimensional

Chao-Song Huang

1996-01-01

379

Observations of solute effects on bubble formation  

SciTech Connect

The authors have studied the effects of solute, in particular aqueous electrolyte, on bubble formation at capillary orifices and frits at varying gas flow rates. Using a stroboscope, video microscope, and rotating mirror, they have obtained pictures which show how bubble formation involves the interaction of bubbles at the orifice. These interactions depend on the value of the surface elasticity E due to positively (ethanol) or negatively (NaCl) adsorbed solute. At low flow rates consecutive bubbles do not interact. Each bubble detaches and leaves the orifice region before the next one starts forming. A intermediate flow rates the more closely spaced, consecutive bubbles begin to interact. In pure liquids there is no barrier to bubble coalescence and the detached bubble is fed by the subsequent bubble as this starts to grow. The process may be repeated several times before the original bubble has risen out of range. In solutions where E is large enough bubble coalescence is inhibited. Instead of feeding into the detached bubble the following bubble pushes it aside, and the bubbles appear to bounce off each other. Bouncing may give rise to a characteristic sequence of larger and smaller bubbles if the emerging bubbles break off prematurely from the orifice due to the inertia of the original bubble. The transition from feeding to bouncing depends critically on E of the solution and leads to a smaller average bubble size for large E values. At high flow rates detached bubbles are invariably fed by several subsequent ones. At very high flow rates the bubbling becomes chaotic, but the interaction of bubbles after leaving the orifice area produces smaller bubbles in solutions. Bouncing is more likely to occur with narrow and irregular capillaries. The dramatically different appearance of gas-sparged columns in salt water and freshwater has its origin in the difference between assemblies of pores showing mainly feeding (freshwater) or bouncing (salt water).

Hofmeier, U.; Yaminsky, V.V.; Christenson, H.K. [Australian National Univ., Canberra (Australia)] [Australian National Univ., Canberra (Australia)

1995-09-01

380

Evidence for a Rayleigh-Taylor type instability and upwelling of depleted density regions during equatorial spread F  

Microsoft Academic Search

Recent rocket probe, barium cloud and radar measurements conducted during equatorial spread F conditions are interpreted in terms of a Rayleigh-Taylor gravitational instability operating on the bottomside of the F peak. The persistent theoretical problems associated with strong radar echoes typically observed in patch-like structures at high altitudes are explained in terms of regions of depleted plasma density which buoyantly

M. C. Kelley; G. Haerendel; H. Kappler; A. Valenzuela; B. B. Balsley; D. A. Carter; W. L. Ecklund; C. W. Carlson; B. Haeusler; R. Torbert

1976-01-01

381

Solar and geomagnetic activity control on equatorial VHF Scintillations in the Indian region  

NASA Astrophysics Data System (ADS)

The ionospheric plasma density irregularities are responsible for scintillation of trans-equatorial radio signals. VHF radio wave Scintillation technique is extensively used to study plasma density irregularities of sub-km size. A ground network of 14 stations were operated by Indian Institute of Geomagnetism (and one station at Waltair) under All India coordinated Programme of Ionospheric and Thermospheric Studies (AICPITS), monitoring amplitude scintillations of 244/250 MHz signal from FLEETSAT (73° E) in India for more than a solar cycle. Effect of solar and geomagnetic activity on scintillation is studied in detail. Using long series of simultaneous amplitude scintillation data at different stations for the period 1989-2000, solar cycle association of scintillation is studied. Boundary of the equatorial belt of scintillation is determined using the entire network data. Geomagnetic control on the width of the scintillation belt is studied from the latitudinal variations of scintillation occurrence separately for geomagnetic quiet and disturbed days and also for the groups of days with low, medium and high Kp values. Kp and Ap indices, characterizing the geomagnetic activity which are shown extensively related to the dynamic properties of the plasma from the sun, are examined for their association with the scintillations. It is noticed that with increase in geomagnetic activity at low and equatorial regions scintillation occurrence is inhibited. Scintillation activity under different magnetic storm conditions is studied using Dst index and classification of the various geomagnetic storms into 3 types of Aaron's criteria (Radio Science,1991), satisfying in about 70 % of cases.

Banola, S.; Maurya, R. N.; Prasad, D. S. V.; Rama Rao, P. S. V.

382

Experimental determination of bubble size distributions in bubble columns: prediction of mean bubble diameter and gas hold up  

Microsoft Academic Search

Bubble diameters were measured photographically in a bubble column, which was operating in the homogeneous regime with air and aqueous isopropanol solutions. The bubble size data were determined for several values of the superficial gas velocity, and used to fit bubble size distributions. The gas hold up was measured under the same conditions and its values were calculated from the

P. L. C. Lage; R. O. Espósito

1999-01-01

383

THE FERMI BUBBLES. II. THE POTENTIAL ROLES OF VISCOSITY AND COSMIC-RAY DIFFUSION IN JET MODELS  

SciTech Connect

The origin of the Fermi bubbles recently detected by the Fermi Gamma-ray Space Telescope in the inner Galaxy is mysterious. In the companion paper Guo and Mathews (Paper I), we use hydrodynamic simulations to show that they could be produced by a recent powerful active galactic nucleus (AGN) jet event. Here, we further explore this scenario to study the potential roles of shear viscosity and cosmic-ray (CR) diffusion on the morphology and CR distribution of the bubbles. We show that even a relatively low level of viscosity ({mu}{sub visc} {approx}> 3 g cm{sup -1} s{sup -1}, or {approx}0.1%-1% of Braginskii viscosity in this context) could effectively suppress the development of Kelvin-Helmholtz instabilities at the bubble surface, resulting in smooth bubble edges as observed. Furthermore, viscosity reduces circulating motions within the bubbles, which would otherwise mix the CR-carrying jet backflow near bubble edges with the bubble interior. Thus viscosity naturally produces an edge-favored CR distribution, an important ingredient to produce the observed flat gamma-ray surface brightness distribution. Generically, such a CR distribution often produces a limb-brightened gamma-ray intensity distribution. However, we show that by incorporating CR diffusion that is strongly suppressed across the bubble surface (as inferred from sharp bubble edges) but is close to canonical values in the bubble interior, we obtain a reasonably flat gamma-ray intensity profile. The similarity of the resulting CR bubble with the observed Fermi bubbles strengthens our previous result in Paper I that the Fermi bubbles were produced by a recent AGN jet event. Studies of the nearby Fermi bubbles may provide a unique opportunity to study the potential roles of plasma viscosity and CR diffusion on the evolution of AGN jets and bubbles.

Guo Fulai; Mathews, William G. [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Dobler, Gregory [Kavli Institute for Theoretical Physics, University of California, Santa Barbara Kohn Hall, Santa Barbara, CA 93106 (United States); Oh, S. Peng, E-mail: fulai@ucolick.org [Department of Physics, University of California, Santa Barbara Kohn Hall, Santa Barbara, CA 93106 (United States)

2012-09-10

384

Surface bubble nucleation stability.  

PubMed

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobized silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this parameter space, occurring for gas concentrations of approximately 100%-110%. Below the nanobubble region we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles. PMID:21405411

Seddon, James R T; Kooij, E Stefan; Poelsema, Bene; Zandvliet, Harold J W; Lohse, Detlef

2011-02-01

385

Constrained Vapor Bubble  

NASA Technical Reports Server (NTRS)

The nonisothermal Constrained Vapor Bubble, CVB, is being studied to enhance the understanding of passive systems controlled by interfacial phenomena. The study is multifaceted: 1) it is a basic scientific study in interfacial phenomena, fluid physics and thermodynamics; 2) it is a basic study in thermal transport; and 3) it is a study of a heat exchanger. The research is synergistic in that CVB research requires a microgravity environment and the space program needs thermal control systems like the CVB. Ground based studies are being done as a precursor to flight experiment. The results demonstrate that experimental techniques for the direct measurement of the fundamental operating parameters (temperature, pressure, and interfacial curvature fields) have been developed. Fluid flow and change-of-phase heat transfer are a function of the temperature field and the vapor bubble shape, which can be measured using an Image Analyzing Interferometer. The CVB for a microgravity environment, has various thin film regions that are of both basic and applied interest. Generically, a CVB is formed by underfilling an evacuated enclosure with a liquid. Classification depends on shape and Bond number. The specific CVB discussed herein was formed in a fused silica cell with inside dimensions of 3x3x40 mm and, therefore, can be viewed as a large version of a micro heat pipe. Since the dimensions are relatively large for a passive system, most of the liquid flow occurs under a small capillary pressure difference. Therefore, we can classify the discussed system as a low capillary pressure system. The studies discussed herein were done in a 1-g environment (Bond Number = 3.6) to obtain experience to design a microgravity experiment for a future NASA flight where low capillary pressure systems should prove more useful. The flight experiment is tentatively scheduled for the year 2000. The SCR was passed on September 16, 1997. The RDR is tentatively scheduled for October, 1998.

Huang, J.; Karthikeyan, M.; Plawsky, J.; Wayner, P. C., Jr.

1999-01-01

386

Space plasma physics research  

NASA Technical Reports Server (NTRS)

During the course of this grant, work was performed on a variety of topics and there were a number of significant accomplishments. A summary of these accomplishments is included. The topics studied include empirical model data base, data reduction for archiving, semikinetic modeling of low energy plasma in the inner terrestrial magnetosphere and ionosphere, O(+) outflows, equatorial plasma trough, and plasma wave ray-tracing studies. A list of publications and presentations which have resulted from this research is also included.

Comfort, Richard H.; Horwitz, James L.

1993-01-01

387

Equatorial aeronomy - I; Proceedings of the Sixth International Symposium on Equatorial Aeronomy, Aguadilla, PR, July 17-23, 1980  

NASA Astrophysics Data System (ADS)

Papers on equatorial aeronomy are presented, covering the following general areas: electric fields, coupling processes, neutral atmosphere, ionospheric D- and F-regions, F-region irregularities, equatorial electrojets and their irregularities, transequatorial radio propagation, and geomagnetic fields. Specific topics covered include: (1) internal structure of the equatorial ionospheric dynamo, (2) electromagnetic interactions between high and low latitudes shown by computer simulation movies, (3) direct measurements of electron density, temperature, and ion composition in an equatorial spread-F ionosphere, (4) simultaneous meteor radar observations at Monpazier, France and Punta Borinquen, PR, and (5) a review of the equatorial electrojet instability in light of recent developments in HF radar measurements.

Matsushita, S.; Balsley, B.; Rishbeth, H.

1981-06-01

388

Resonance properties of soluble gas bubbles  

Microsoft Academic Search

Soluble gas bubbles in a liquid experiencing radial oscillations created by an acoustic field are considered. It is shown that the resonance frequency of large soluble gas bubbles practically coincides with the natural frequency of gas bubbles as determined by the Minnaert formula. In the case of small gas bubbles, the presence of capillary effects and solubility of the gas

Nail S. Khabeev

2006-01-01

389

Sound Waves in Water Containing Vapor Bubbles  

Microsoft Academic Search

The rapid evaporation or condensation of a vapor bubble when out of equilibrium compared to the slow dissolving or growth of an air bubble results in quite different propagation properties of sound waves through water containing one or the other types of bubbles. Adapting a method developed by Foldy in his treatment of the air bubble case, we derive an

G. T. Trammell

1962-01-01

390

Period-adding route in sparkling bubbles  

Microsoft Academic Search

Chains of bubbles are seen rising along the wall whenever champagne is poured into a glass. The careful observation of a given bubble chain often reveals that the interbubble distance suddenly changes during the degassing process, indicating different bubbling regimes in this elusive phenomenon of effervescence. We report the transitions between these different bubbling regimes that present sequences of multiple

Gérard Liger-Belair; Alberto Tufaile; Bertrand Robillard; Philippe Jeandet; José Carlos Sartorelli

2005-01-01

391

Bubble Growth in Lunar Basalts  

NASA Astrophysics Data System (ADS)

Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth Planet. Sci. Lett. 181, 251. (2) Liu Y, Zhang YX, Behrens H (2005) J. Volcanol. Geotherm. Res. 143, 219. (3) Murase T, McBirney A (1970) Science 167, 1491. (4) Proussevitch AA, Sahagian DL (1998) J. Geophys. Res. 103, 18223. (5) Saal AE, Hauri EH, Cascio ML, et al. (2008) Nature 454, 192. (6) Zhang YX, Stolper EM (1991) Nature 351, 306.

Zhang, Y.

2009-05-01

392

Sonoluminescing Air Bubbles Rectify Argon  

NASA Astrophysics Data System (ADS)

The dynamics of single bubble sonoluminescence (SBSL) strongly depends on the percentage of inert gas within the bubble. We propose a theory for this dependence, based on a combination of principles from sonochemistry and hydrodynamic stability. The nitrogen and oxygen dissociation and subsequent reaction to water soluble gases implies that strongly forced air bubbles eventually consist of pure argon. Thus it is the partial argon (or any other inert gas) pressure which is relevant for stability. The theory provides quantitative explanations for many aspects of SBSL.

Lohse, Detlef; Brenner, Michael P.; Dupont, Todd F.; Hilgenfeldt, Sascha; Johnston, Blaine

1997-02-01

393

Sonoluminescing Air Bubbles Rectify Argon  

SciTech Connect

The dynamics of single bubble sonoluminescence (SBSL) strongly depends on the percentage of inert gas within the bubble. We propose a theory for this dependence, based on a combination of principles from sonochemistry and hydrodynamic stability. The nitrogen and oxygen dissociation and subsequent reaction to water soluble gases implies that strongly forced air bubbles eventually consist of pure argon. Thus it is the partial argon (or any other inert gas) pressure which is relevant for stability. The theory provides quantitative explanations for many aspects of SBSL. {copyright} {ital 1997} {ital The American Physical Society}

Lohse, D.; Hilgenfeldt, S. [Fachbereich Physik der Universitaet Marburg, Renthof 6, 35032 Marburg (Germany)] [Fachbereich Physik der Universitaet Marburg, Renthof 6, 35032 Marburg (Germany); Brenner, M.P. [Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Dupont, T.F. [Department of Computer Science, University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Computer Science, University of Chicago, Chicago, Illinois 60637 (United States); Johnston, B. [Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States)

1997-02-01

394

Moon influence on equatorial atmospheric angular momentum  

NASA Astrophysics Data System (ADS)

The variation of the equatorial atmospheric angular momentum function, coordinated with respect to a star-fixed system, is investigated in relation with the lunar tide. We isolate the rapid fluctuations, below 30 days, where Moon motion has a possible influence. First we notice that pressure term and wind term are almost proportional, by contrast to celestial seasonal band (S1). This would mean that, in this frequency band, the torque of the atmosphere on the solid Earth mostly results from the equatorial bulge. Spectrum reveals sharp lunar tidal peaks at 13.66 days (O1 diurnal tide in the terrestrial frame) and 13.63 days, reflecting the Moon influence on meridional circulation. We also observe powerful episodic fluctuations between 5 and 8 days (up to 10 mas), possibly resulting from non linear effect of the O1 tide, or tidal waves 2Q1 (6.86 days) and ?1 (7.095 days).

Bizouard, Christian; Zotov, Leonid; Sidorenkov, Nikolay

2014-05-01

395

Metallic ions in the equatorial ionosphere  

NASA Technical Reports Server (NTRS)

Four positive ion composition measurements of the equatorial E region made at Thumba, India, are presented. During the day, the major ions between 90 and 125 km are NO(+) and O2(+). A metallic ion layer centered at 92 km is observed, and found to contain Mg(+), Fe(+), Ca(+), K(+), Al(+), and Na(+) ions. The layer is explained in terms of a similarly shaped latitude distribution of neutral atoms which are photoionized and charge-exchanged with NO(+) and O2(+). Three body reactions form molecular metallic ions which are rapidly lost by dissociative ion-electron recombination. Nighttime observations show downward drifting of the metallic ion layer caused by equatorial dynamo effects. These ions react and form neutral metals which exchange charges with NO(+) and O2(+) to produce an observed depletion of those ions within the metallic ion region.

Aikin, A. C.; Goldberg, R. A.

1972-01-01

396

Equatorial Kelvin waves do not vanish  

NASA Technical Reports Server (NTRS)

In the last several years many scientists have been using poorly resolved coupled models to study the ENSO. It has been very common to state that an ENSO cycle found in a model cannot have oceanic Kelvin waves as a mechanism because such waves do not exist in an ocean model with coarse grid spaing. In this note it is demonstrated that equatorial Kelvin waves can exist in models with coarse grids.

O'Brien, James J.; Parham, Fred

1992-01-01

397

The Equatorial Electrojet as seen from Satellites.  

NASA Astrophysics Data System (ADS)

The equatorial electrojet is a thin electric current in the ionosphere over the dip equator around 100 to 115 km altitude normally flowing in an eastward direction. It has a distinct magnetic signature that can be clearly identified in most passes in the scalar and vector magnetic field measurements from magnetometers on board satellites. Two things will be presented; the effect filtering has on the morphology of the electrojet signature and a detailed study of longitudinal variation of the amplitude of the electrojet.

McCreadie, H.

2002-05-01

398

Time variability of Indian Ocean equatorial currents  

NASA Astrophysics Data System (ADS)

As part of the INDEX program we have obtained two records from current meters each of 6-month duration, from a single depth (500 m) and location (0°, 55°40'E) in the equatorial Indian Ocean. Spectral analysis for periods shorter than 500 h reveals features consistent with other equatorial measurements in the Indian and Atlantic oceans, features which follow from the disappearance of the mid-latitude inertial peak and its replacement by a sum of equatorially trapped waves. Certain comparisons with a model spectrum of such waves due to ERIKSEN ( Journal of Geophysical Research, 85, 3285-3303, 1980) are noted. Longer-period variations cannot be analyzed statistically with such short records. Nevertheless, it is interesting that in the spring of two different years the zonal velocity changes abruptly (in 1 to 2 weeks) from near zero to 25 cm s -1 westward. There is a clear need for much longer measurements to examine the possible relationship between this variability and seasonal forcing due to the monsoons. Spectra of the higher frequency motions are not discernably different before and after this transition.

Knox, R. A.

1981-03-01

399

Vapor Bubble Nucleation: A Microscopic Phenomenon  

Microsoft Academic Search

In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit\\u000a were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble\\u000a formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion\\u000a force. Bubble nucleation by

Ho-Young Kwak

2004-01-01

400

Nonclassical Thermomigration of an Air Bubble  

NASA Astrophysics Data System (ADS)

We study air bubbles confined in capillaries with a temperature gradient. Classically, air bubbles move in a temperature gradient due to decreased surface tension at higher temperatures, creating a net surface traction towards the cold pole, pushing the bubble towards the hot pole for mass conservation. Here we report non-classical thermo-migration of confined air bubbles: in the presence of surfactant the bubbles can go the other way.

Michler, Dominik; Sprik, Rudolf; Schall, Peter; Bonn, Daniel

2012-02-01

401

Bottomside sinusoidal irregularities in the equatorial F region. II - Cross-correlation and spectral analysis  

NASA Technical Reports Server (NTRS)

Equatorial bottomside sinusoidal (BSS) irregularities have been studied by applying techniques of cross-correlation and spectral analysis to the Atmosphere Explorer data set. The phase of the cross-correlations of the plasma number density is discussed and the two drift velocity components observed using the retarding potential analyzer and ion drift meter on the satellite are discussed. Morphology is addressed, presenting the geographical distributions of the occurrence of BSS events for the equinoxes and solstices. Physical processes including the ion Larmor flux, interhemispheric plasma flows, and variations in the lower F region Pedersen conductivity are invoked to explain the findings.

Cragin, B. L.; Hanson, W. B.; Mcclure, J. P.; Valladares, C. E.

1985-01-01

402

A Bubble Full of Sunshine  

NSF Publications Database

... inside gas bubbles collapsing in a liquid reach roughly 20,000 degrees Kelvin?four times hotter than ... the discovery by blasting the liquid with intense sound waves and measuring "sonoluminescence," the ...

403

Smashing Bubbles and Vanishing Sugar.  

ERIC Educational Resources Information Center

Science activities with soap bubbles for primary school children are described in this article. Another activity involves children in determining the whereabouts of sugar as it dissolves in water. (SA)

Ward, Alan

1979-01-01

404

Bubbles in Liquid: Euromech 7.  

National Technical Information Service (NTIS)

A convention was held in Grenoble during April 23 to 26, 1968 to discuss the mechanics of liquids containing bubbles. Summaries are given of selected presentations and discussions which have special relevance to problems dealing with adiabatic flow in foa...

C. Reuterswaerd

1975-01-01

405

Bubble nucleation in stout beers.  

PubMed

Bubble nucleation in weakly supersaturated solutions of carbon dioxide-such as champagne, sparkling wines, and carbonated beers-is well understood. Bubbles grow and detach from nucleation sites: gas pockets trapped within hollow cellulose fibers. This mechanism appears not to be active in stout beers that are supersaturated solutions of nitrogen and carbon dioxide. In their canned forms these beers require additional technology (widgets) to release the bubbles which will form the head of the beer. We extend the mathematical model of bubble nucleation in carbonated liquids to the case of two gases and show that this nucleation mechanism is active in stout beers, though substantially slower than in carbonated beers and confirm this by observation. A rough calculation suggests that despite the slowness of the process, applying a coating of hollow porous fibers to the inside of a can or bottle could be a potential replacement for widgets. PMID:21728549

Lee, W T; McKechnie, J S; Devereux, M G

2011-05-01

406

Holography in small bubble chambers  

SciTech Connect

This chapter reports on an experiment to determine the total charm cross section at different incident momenta using the small, heavy liquid bubble chamber HOBC. Holography in liquid hydrogen is also tested using the holographic lexan bubble chamber HOLEBC with the aim of preparing a future holographic experiment in hydrogen. The high intensity tests show that more than 100 incident tracks per hologram do not cause a dramatic effect on the picture quality. Hydrogen is more favorable than freon as the bubble growth is much slower in hydrogen. An advantage of holography is to have the maximum resolution in the full volume of the bubble chamber, which allows a gain in sensitivity by a factor of 10 compared to classical optics as 100 tracks per hologram look reasonable. Holograms are not more difficult to analyze than classical optics high-resolution pictures. The results show that holography is a very powerful technique which can be used in very high resolution particle physics experiments.

Lecoq, P.

1984-01-01

407

Rayleigh-Taylor and wind-driven instabilities of the nighttime equatorial ionosphere  

NASA Technical Reports Server (NTRS)

A thorough re-examination has been made of the Rayleigh-Taylor instability in the nighttime equatorial ionosphere from approximately 100 km to the bottomside F region. The following effects have been taken into account explicitly in various combinations: (1) the eastward drift of the ionosphere caused by the nighttime polarization electric field, (2) the eastward nighttime neutral wind, and (3) recombination in the F and E regions. It was found that, well below the bottomside F region, the Rayleigh-Taylor mode can be unstable and is driven by an eastward neutral wind rather than by gravitational drift. Formation of ionospheric bubbles below the bottomside F region is consistent with the observation of lower ionospheric ions in F region ionospheric holes; furthermore, seasonal and shorter term variations in spread-F occurrence may be associated with variations in the neutral wind and polarization electric field.

Chiu, Y. T.; Straus, J. M.

1979-01-01

408

Driving bubbles out of glass  

NASA Technical Reports Server (NTRS)

Surface tension gradient in melt forces gas bubbles to surface, increasing glass strength and transparency. Conventional chemical and buoyant fining are extremely slow in viscous glasses, but tension gradient method moves 250 um bubbles as rapidly as 30 um/s. Heat required for high temperature part of melt is furnished by stationary electrical or natural-gas heater; induction and laser heating are also possible. Method has many applications in industry processes.

Mattox, D. M.

1981-01-01

409

Global Specification of the Post-Sunset Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

The Special Sensor Ultraviolet Limb Imager (SSULI) on the Defense Meteorological Satellite Program (DMSP) is used to specify the post-sunset Equatorial Ionization Anomaly. Ultraviolet emission profiles of 135.6 nm and 91.1 nm emissions from O++ e recombination are measured in successive altitude scans along the orbit of the satellite. The overlapping sample geometry provides for a high resolution reconstruction of the ionosphere in altitude and latitude for each pass of the satellite. Emission profiles are ingested by the Global Assimilation of Ionospheric Measurements (GAIM) space weather model, which was developed by Utah State University and is run operationally at the Air Force Weather Agency (AFWA). The resulting specification of the equatorial ionosphere reveals significant variability in the postsunset anomaly, which is reflective of the driving space weather processes, namely, electric fields and neutral winds. Significant longitudinal and day-to-day variability in the magnitude (or even existence) of the post-sunset anomaly reveal the influence of atmospheric tides and waves as well as geomagnetic disturbances on the pre-reversal enhancement of the electric field. Significant asymmetry between anomaly crests reveals the influence of atmospheric tides and waves on meridional neutral winds. A neutral wind parallel to the magnetic field line pushes plasma up (or down) the field lines, which raises (or lowers) the altitude of the crests and modifies the horizontal location and magnitude of the crests. The variability in the post-sunset anomaly is one of the largest sources of error in ionospheric specification models. The SSULI instrument provides critical data towards the reduction of this specification error and the determination of key driver parameters used in ionospheric forecasting. Acknowledgements: This research was supported by the USAF Space and Missile Systems Center (SMC), the Naval Research Laboratory (NRL) Base Program, and the Office of Naval Research (ONR).

Coker, C.; Dandenault, P. B.; Dymond, K.; Budzien, S. A.; Nicholas, A. C.; Chua, D. H.; McDonald, S. E.; Metzler, C. A.; Walker, P. W.; Scherliess, L.; Schunk, R. W.; Gardner, L. C.; Zhu, L.

2012-12-01

410

The equatorial ionospheric scintillations during geomagnetic storms  

NASA Astrophysics Data System (ADS)

Geomagnetic storms and disturbances are thought to play an important role for initiation of the ionospheric scintillations. Scintillation manifest itself in rapid fluctuation of the phase and intensity of a radio signal that has passed through the Earth's ionosphere, typically on a satellite-to-ground propagation channel. Mechanisms of ionospheric scintillation are better understood than its morphology and serious efforts were made to find the empirical relationships in terms of different geomagnetic indices for their forcasting. Such relationships can help to avoid blackouts and distortions in VLF communication due to ionospheric irregularities. We used the different geomagnetic indices, the ionospheric parameters, and the Bz-component of the interplanetary magnetic field (IMF) to study scintillation activity at the dip latitudes. The relationship between the equatorial ionospheric scintillations and the IMF Bz, Dst, Kp, AU, and AL indices is demonstrated. It is shown that in parallel with much used of Dst- index other indices are also suitable for study of scintillation activity. For example, Kp as planetary index carries information about auroral electrojets also and we can see that no scintillation activity when Kp decreases during positive IMF Bz. This means that the auroral electrojets depicted by the AU, and AL-indices and connected with the field-aligned currents (FAC) are decreased and moved to pole ward. The positive IMF Bz is likely to be the factor that inhibits the equator ward penetration of the high latitude electric field. The negative IMF Bz enhances the auroral electric fields and they can penetrate to the equatorial ionosphere. The examples presented in our study allow us to assume that the southward IMF Bz by the Region 1 FAC can form an additional eastward current system at the equatorial ionosphere. Under these conditions the virtual height h'F rises to high altitudes and when it drops the scintillations can be generated. It may be safely suggested that source of this phenomenon is the solar wind electric field responcible for the auroral and equatorial ionosphere coupling. Other processes such as tides, earthquakes etc. can change the ionospheric height also and may play a role in the generation of the ionospheric scintillations. From a practical point of view, the relationships between the solar wind and the ionospheric parameters can be used for the prediction of scintillations, if one takes into account the time delay between the IMF Bz and the equatorial ionospheric data.

Biktash, L.

411

Optimization of the ITER electron cyclotron equatorial launcher for improved heating and current drive functional capabilities  

NASA Astrophysics Data System (ADS)

The design of the ITER Electron Cyclotron Heating and Current Drive (EC H&CD) system has evolved in the last years both in goals and functionalities by considering an expanded range of applications. A large effort has been devoted to a better integration of the equatorial and the upper launchers, both from the point of view of the performance and of the design impact on the engineering constraints. However, from the analysis of the ECCD performance in two references H-mode scenarios at burn (the inductive H-mode and the advanced non-inductive scenario), it was clear that the EC power deposition was not optimal for steady-state applications in the plasma region around mid radius. An optimization study of the equatorial launcher is presented here aiming at removing this limitation of the EC system capabilities. Changing the steering of the equatorial launcher from toroidal to poloidal ensures EC power deposition out to the normalized toroidal radius ? ? 0.6, and nearly doubles the EC driven current around mid radius, without significant performance degradation in the core plasma region. In addition to the improved performance, the proposed design change is able to relax some engineering design constraints on both launchers.

Farina, D.; Henderson, M.; Figini, L.; Saibene, G.

2014-06-01

412

FEASTING BLACK HOLE BLOWS BUBBLES  

NASA Technical Reports Server (NTRS)

A monstrous black hole's rude table manners include blowing huge bubbles of hot gas into space. At least, that's the gustatory practice followed by the supermassive black hole residing in the hub of the nearby galaxy NGC 4438. Known as a peculiar galaxy because of its unusual shape, NGC 4438 is in the Virgo Cluster, 50 million light-years from Earth. These NASA Hubble Space Telescope images of the galaxy's central region clearly show one of the bubbles rising from a dark band of dust. The other bubble, emanating from below the dust band, is barely visible, appearing as dim red blobs in the close-up picture of the galaxy's hub (the colorful picture at right). The background image represents a wider view of the galaxy, with the central region defined by the white box. These extremely hot bubbles are caused by the black hole's voracious eating habits. The eating machine is engorging itself with a banquet of material swirling around it in an accretion disk (the white region below the bright bubble). Some of this material is spewed from the disk in opposite directions. Acting like high-powered garden hoses, these twin jets of matter sweep out material in their paths. The jets eventually slam into a wall of dense, slow-moving gas, which is traveling at less than 223,000 mph (360,000 kph). The collision produces the glowing material. The bubbles will continue to expand and will eventually dissipate. Compared with the life of the galaxy, this bubble-blowing phase is a short-lived event. The bubble is much brighter on one side of the galaxy's center because the jet smashed into a denser amount of gas. The brighter bubble is 800 light-years tall and 800 light-years across. The observations are being presented June 5 at the American Astronomical Society meeting in Rochester, N.Y. Both pictures were taken March 24, 1999 with the Wide Field and Planetary Camera 2. False colors were used to enhance the details of the bubbles. The red regions in the picture denote the hot gas. Credits: NASA and Jeffrey Kenney and Elizabeth Yale (Yale University)

2002-01-01

413

Abnormal fb Es enhancements in equatorial Es layers during magnetic storms of solar cycle 23  

NASA Astrophysics Data System (ADS)

We have analyzed the behavior of blanketing frequency of the Es layer (fb Es) occurring at an equatorial station covering the days before, during and subsequent to 24 intense and very intense magnetic storms (Dst?-100nT) that occurred during the solar cycle 23. The fb Es was measured by digital ionosonde over São Luís, Brazil (2.33° S, 44.2° W, dip: -4.5°). Our analysis shows that there are significant changes in the fb Es, mainly during the recovery phase of magnetic storms, characterized by occurrence of peaks that exceed the ambient background values. Also, these peaks are associated to other types of sporadic E layer than the Esq (a non-blanketing layer detected due the plasma irregularities in the equatorial electrojet), which in turn means competing mechanisms. The results are discussed in terms of the statistics of the abnormal enhancement taking into account the phase of the magnetic storm.

Resende, L. C. A.; Denardini, C. M.; Batista, I. S.

2013-09-01

414

Progress of the ITER equatorial vis/IR wide angle viewing system optical design  

SciTech Connect

The equatorial vis/IR wide angle viewing system is present in four ITER diagnostic equatorial ports. This instrument will cover a large field of view with high spatial and temporal resolutions, to provide real time temperature measurements of plasma facing components, spectral data in the visible range, information on runaway electrons, and pellet tracking. This diagnostic needs to be reliable, precise, and long lasting. Its design is driven by both the tokamak severe environment and the high performances required for machine protection. The preliminary design phase is ongoing. Paramount issues are being tackled, relative to wide spectral band optical design, material choice, and optomechanical difficulties due to the limited space available for this instrument in the ports, since many other diagnostics and services are also present. Recent progress of the diagnostic optical design and status of associated R and D are presented.

Davi, M.; Corre, Y.; Guilhem, D.; Jullien, F.; Reichle, R.; Salasca, S.; Travere, J. M. [Association Euratom CEA, CEA/DSM/IRFM, Cadarache, 13108 Saint-Paul-lez-Durance (France); Cal, E. de la; Manzanares, A.; Pablos, J. L. de [Association Euratom CIEMAT, Av. Complutense 22, 28040 Madrid (Spain); Migozzi, J. B. [JBM Optique, 11 Av. de la division Leclerc, 92310 Sevres (France)

2008-10-15

415

The role of the equatorial electrojet in the evening ionosphere  

Microsoft Academic Search

The role of the equatorial E region in the electrodynamics of the evening ionosphere is examined. The influence and reaction of the electrojet current on the equatorial ionosphere at sunset are investigated using a field-line-integrated 1D electrodynamic model. The 1D time-varying model predicts the divergence of the horizontal current of the equatorial electrojet for a given time variation of the

G. Haerendel; J. V. Eccles

1992-01-01

416

Electric fields in the equatorial ionosphere derived from CHAMP satellite magnetic field measurements  

Microsoft Academic Search

The day-time eastward equatorial electric field (EEF) in the E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring the EEF. However, there is a severe lack of high

Patrick Alken; Stefan Maus

2009-01-01

417

Equatorially trapped waves in varying basic states: Structures and lateral forcing processes  

Microsoft Academic Search

Linear shallow water equations on an equatorial beta-plane are used to theoretically investigate the effects of atmospheric basic state on equatorial waves. With different varying basic states, three main topics are addressed: eigenfrequencies and meridional structures of free equatorial waves; mechanism of equatorial Rossby wave trapping; and equatorial wave responses to transient extratropical forcings. The free Rossby wave is shown

Chi-Dong Zhang

1989-01-01

418

Measurement of Bubble Size Distribution Based on Acoustic Propagation in Bubbly Medium  

NASA Astrophysics Data System (ADS)

Acoustic properties are strongly affected by bubble size distribution in a bubbly medium. Measurement of the acoustic transmission becomes increasingly difficulty as the void fraction of the bubbly medium increases due to strong attenuation, while acoustic reflection can be measured more easily with increasing void fraction. The ABS Acoustic Bubble Spectrometer^, an instrument for bubble size measurement that is under development tries to take full advantage of the properties of acoustic propagation in bubbly media to extract bubble size distribution. Properties of both acoustic transmission and reflection in the bubbly medium from a range of short single-frequency bursts of acoustic waves at different frequencies are measured in an effort to deduce the bubble size distribution. With the combination of both acoustic transmission and reflection, assisted with validations from photography, the ABS Acoustic Bubble Spectrometer^ has the potential to measure bubble size distributions in a wider void fraction range.

Wu, Xiongjun; Hsiao, Chao-Tsung; Choi, Jin-Keun; Chahine, Georges

2013-03-01

419

The equatorial electrojet satellite and surface comparison  

NASA Technical Reports Server (NTRS)

The OGO 4 and 6 (POGO) magnetic field results for the equatorial electrojet indicate that while the present models are approximately correct, the possibility of a westward component must be incorporated. The scatter diagrams of POGO amplitudes and surface data show a correlation. The ratios between the amplitudes estimated from surface data and those at 400 km altitude are as follows: India 5 to 8, East Africa (Addis Ababa) 4, Central Africa 3, West Africa (Nigeria) 3, South America (Huancayo) 5, and Philippines 5. The variation in the ratio is due to the conductivity structure of the earth in various zones.

Cain, J. C. (editor); Sweeney, R. E. (editor)

1972-01-01

420

Possible Cross Equatorial Influence of the Northeast Monsoon on the Equatorial Westerlies over Indonesia.  

National Technical Information Service (NTIS)

Objectively analysed surface, 700 and 200 mb winds of nine winters are used to study the possible cross equatorial influence of the northern winter monsoon on the zonal wind along 10 deg S in the Indonesia-Arafura Sea region and to prepare a nine-year mon...

K. A. Shield

1985-01-01

421

OH Production Enhancement in Bubbling Pulsed Discharges  

SciTech Connect

The generation of active species, such as H{sub 2}O{sub 2}, O{sup *}, OH*, HO{sub 2}*, O{sub 3}, N{sub 2}{sup *}, etc, produced in aqueous solutions by HV pulsed discharges was studied in order to find the most efficient way in waste water treatment taking into account that these species are almost stronger oxidizers than ozone. Plasma was generated inside gas bubbles formed by the argon, air and oxygen gas flow between the special designed electrodes. The pulse width and pulse frequency influence was studied in order to increase the efficiency of the OH active species formation. The produced active species were investigated by optical emission spectroscopy and correlated with electrical parameters of the discharges (frequency, pulse width, amplitude, and rise and decay time).

Lungu, Cristian P.; Porosnicu, Corneliu; Jepu, Ionut; Chiru, Petrica; Zaroschi, Valentin; Lungu, Ana M. [National Institute for Laser, Plasma and Radiation Physics, Bucharest, 077125 (Romania); Saito, Nagahiro; Bratescu, Maria; Takai, Osamu [Ecotopia Science Institute, Nagoya University, Nagoya, 464-8603 (Japan); Velea, Theodor; Predica, Vasile [R and D National Institute for Nonferous and Rare Metals, Pantelimon, Jud. Ilfov, 077145 (Romania)

2010-10-13

422

Cell death from bursting bubbles: role of cell attachment to rising bubbles in sparged reactors.  

PubMed

Bursting bubbles are thought to be the dominant cause of cell death in sparged animal or insect cell cultures. Cells that die during the bubble burst can come from three sources: cells suspended near the bubble; cells trapped