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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

Periodic spacing between consecutive equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

We analyze three-years of data collected by a field-aligned airglow imaging system located at the Cerro Tololo Inter-American Observatory near La Serena, Chile to determine the occurrence of equatorial plasma bubbles (EPBs). On 317 of the 552 predominately clear nights of observations, structure indicative of EPBs is present. On 123 of these nights, multiple EPBs with periodic spacings were recorded with 88 nights showing 3 or more consecutive bubbles. We suggest that the periodic spacing of EPBs could be related to the properties of an underlying seed mechanism, namely gravity waves (GWs). The distribution of spacings compares favorably to the spectrum of GW induced traveling ionospheric disturbances (TIDs) measured by Vadas and Crowley (2010) from a similar geographic latitude in the northern hemisphere. Furthermore, the distribution of spacings decreases from 2006 through 2009, tracking the corresponding decrease in the thermospheric neutral temperature, Tn. As Tn decreases, GWs with larger horizontal wavelengths have smaller initial amplitudes and cannot propagate as easily to EPB seeding altitudes. Thus, our observations are consistent with GW theory.

Makela, J. J.; Vadas, S. L.; Muryanto, R.; Duly, T.; Crowley, G.

2010-07-01

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

GPS Observations of Plasma Bubbles and Scintillations over Equatorial Africa  

NASA Astrophysics Data System (ADS)

Sponsored in part by the International Heliophysical Year (IHY) program, Boston College, Air Force Research Laboratory (AFRL), and several universities in Africa have collaborated to deploy a network of GPS receivers throughout equatorial Africa, a region which has been largely devoid of ground-based ionospheric monitoring instruments. High date-rate GPS receivers capable of measuring Total Electron Content (TEC) and GPS scintillations were installed at Abidjan, Ivory Coast (5.3°N, 4.0°W, dip 3.5°S); Addis Ababa (9.0°N, 38.8°E, dip 0.1°N ); Bahir Dar, Ethiopia (26.1°N, 50.6°E, dip 20.1°N); Cape Verde (16.6°S, 22.9°W, dip 4.9°N); Ilorin, Nigeria (8.4°S, 4.7°E, dip 1.9°S); Kampala, Uganda (0.3°S, 32.6°E, dip 9.2°S); Lagos, Nigeria (6.5°N, 3.4°E, dip 3.1°S); Nairobi, Kenya (1.3°S, 36.8°W, dip 10.7°S); Nsukka, Nigeria (6.8°S, 7.4°W, dip 3.0°S); and Zanzibar, Tanzania (6.2°S, 39.2°E, dip 15.9°S). In this paper we report on the longitudinal, local time and seasonal occurrence of plasma bubbles and L band scintillations over equatorial Africa in 2009 and 2010, as a first step toward establishing the climatology of ionospheric irregularities over Africa. The scintillation intensity is obtained by measuring the standard deviation of normalized GPS signal power. The plasma bubbles are detected using an automated technique, whereby the GPS TEC is detrended to remove the diurnal variation and excursions exceeding a particular threshold are extracted for further analysis. A harmonic analysis (FFT) of these extracted events is performed to exclude wavelike features indicative of gravity waves or traveling ionospheric disturbances, and the remaining events are identified as plasma bubbles. Our findings suggest that the occurrence of plasma bubbles and L band scintillations over Africa are well correlated, but that some discrepancies in their morphologies are evident. While plasma bubbles and scintillations are generally observed during equinoctial periods, there are some longitudinal differences in their local time and seasonal occurrence statistics.

Carrano, C. S.; Valladares, C. E.; Semala, G. K.; Bridgwood, C. T.; Adeniyi, J.; Amaeshi, L. L.; Damtie, B.; D'Ujanga Mutonyi, F.; Ndeda, J. D.; Baki, P.; Obrou, O. K.; Okere, B.; Tsidu, G. M.

2010-12-01

5

Signatures of equatorial plasma bubbles in VHF satellite scintillations and equatorial ionograms  

NASA Astrophysics Data System (ADS)

Since their discovery in the 1970s, equatorial plasma bubbles (EPBs) have been invoked to explain the propagation of VHF signals on trans-equatorial circuits at night, and blamed for highly detrimental scintillation of VHF and GHz trans-ionospheric communications signals in equatorial regions. Over the last four decades, the properties of EPBs have been deduced by multiple techniques such as incoherent scatter radar, 630 nm airglow, depletions in GPS total electron content observations, VHF and GHz scintillations, and HF observations by ionosondes. The initiation and evolution of EPBs have by now been successfully modeled and a good understanding developed of the underlying physics. However, different communities tend to concentrate on a single observing technique, without regard to whether the different techniques provide a consistent physical picture. In contrast, this paper discusses two very different types of observations made on a night-by-night basis during the COPEX campaign of late 2002 in Brazil, namely, VHF scintillations and ionograms, and shows that the two methods of observation can provide a consistent interpretation of the properties of EPBs. For example, an EPB seen as an eastward drifting scintillation event can also be seen as an extra ionogram reflection trace that moves closer to and then away from the ionosonde site. The scintillations are attributed to strong gradients across the walls of an EPB, whereas the extra ionogram traces are attributed to oblique reflection of the ionosonde signals from the walls of the EPB.

McNamara, L. F.; Caton, R. G.; Parris, R. T.; Pedersen, T. R.; Thompson, D. C.; Wiens, K. C.; Groves, K. M.

2013-03-01

6

Coupling Processes in the Equatorial Spread F\\/Plasma Bubble Irregularity Development  

Microsoft Academic Search

\\u000a The plasma convection pattern of the evening sector equatorial ionosphere sets the condition for the plasma structuring through\\u000a instability processes leading to the Equatorial Spread F (ESF)\\/plasma bubble irregularity development and evolution. Vertical\\u000a coupling through upward propagating atmospheric waves controls\\/modifies the ionosphere-thermosphere interactive processes\\u000a that eventually lead to the irregularity development. Instabilities grow by the Rayleigh-Taylor mechanism at the bottom

Mangalathayil Ali Abdu; E. Alam Kherani

7

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

8

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

9

Geomagnetic conjugate observations of plasma bubbles and thermospheric neutral winds at equatorial latitudes  

NASA Astrophysics Data System (ADS)

Plasma bubbles are plasma-density depletion which is developed by the Rayleigh-Taylor instability on the sunset terminator at equatorial latitudes. They usually propagate eastward after the sunset. The eastward propagation of the plasma bubbles is considered to be controlled by background eastward neutral winds in the thermosphere through the F-region dynamo effect. However, it is not clear how the F-region dynamo effect contributes to the propagation of the plasma bubbles, because plasma bubbles and background neutral winds have not been simultaneously observed at geomagnetic conjugate points in the northern and southern hemispheres. In this study, geomagnetic conjugate observations of the plasma bubbles at low latitudes with thermospheric neutral winds were reported. The plasma bubbles were observed at Kototabang (0.2S, 100.3E, geomagnetic latitude (MLAT): 10.0S), Indonesia and at Chiang Mai (18.8N, 98.9E, MLAT: 8.9N), Thailand, which are geomagnetic conjugate stations, on 5 April, 2011 from 13 to 22 UT (from 20 to 05 LT). These plasma bubbles were observed in the 630-nm airglow images taken by using highly-sensitive all-sky airglow imagers at both stations. They propagated eastward with horizontal velocities of about 100-125 m/s. Background thermospheric neutral winds were also observed at both stations by using two Fabry-Perot interferometers (FPIs). The eastward wind velocities were about 70-130 m/s at Kototabang, and about 50-90 m/s at Chiang Mai. We estimated ion drift velocities by using these neutral winds observed by FPIs and conductivities calculated from the IRI and MSIS models. The estimated velocities were about 60-90 % of the drift velocities of plasma bubbles. This result shows that most of the plasma bubble drift can be explained by the F-region dynamo effect, and additional electric field effect may come in to play.

Fukushima, D.; Shiokawa, K.; Otsuka, Y.; Nishioka, M.; Kubota, M.; Tsugawa, T.; Nagatsuma, T.

2012-12-01

10

Insights from coordinated observations of neutral winds and equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

Installed in northeastern Brazil in 2009, the Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) comprises a suite of instruments to study the low-latitude ionosphere/thermosphere system. Two Fabry-Perot interferometers (FPIs) provide estimates of vector horizontal neutral winds in addition to the neutral temperature at an altitude of approximately 250 km. A wide-angle imaging system provides two-dimensional images of ionospheric structure, specifically equatorial plasma bubbles (EPBs). Finally, several Global Positioning System (GPS) receivers provide estimates of the background total electron content and scintillation environment imposed by these bubbles. We present results from the first three years of this experiment detailing the climatology of the neutral winds and temperatures during the transition from the deep solar minimum of 2008 towards the impending solar maximum. Furthermore, we discuss the coupling between the thermosphere and ionosphere through a coordinated analysis of neutral winds and the drift velocity of EPBs.

Makela, Jonathan J.; Meriwether, John; Buriti, Ricardo; Chapagain, Narayan; Fisher, Daniel

2012-07-01

11

Microsatellite missions to conduct midlatitude studies of equatorial ionospheric plasma bubbles  

NASA Astrophysics Data System (ADS)

Two missions presently under development by the United States Air Force Academy (USAFA), FalconSAT-2 and FalconSAT-3, include mission scientific objectives targeting the study of ionospheric F region plasma density depletions and topside bubbles associated with the so-called Equatorial Spread F (ESF) phenomena. The Miniature Electrostatic Analyzer (MESA), a USAFA-designed patch sensor that measures differential energy fluxes of electrons from 0.05 to 13 eV in six channels, is the primary experiment aboard FalconSAT-2, a 25-kg microsatellite intended for launch into an International Space Station (ISS) orbit via the Space Shuttle. Because the orbit will be approximately 360 km in altitude and of 52° inclination, FalconSAT-2 observations will complement those of low latitude missions (e.g., C/NOFS) and polar latitude, higher altitude missions (e.g., DMSP). Realistic internal magnetic field models demonstrate that field lines with apex heights of 1500 km (representing the upper altitude limit of equatorial plasma bubbles) may intersect the orbit plane at dip latitudes greater than 35°. Thus, FalconSAT-2 will be able to observe plasma depletions that have propagated poleward along the field lines and lower in altitude, depletions that may not be observed with the high altitude DMSP and the low latitude C/NOFS. Additionally, there may be opportunities for FalconSAT-2 to make simultaneous multipoint in situ measurements of large-scale plasma bubbles with other low altitude satellites, such as C/NOFS and DMSP. We will present a statistical analysis of the probability of making such measurements using nominal orbital parameters of the relevant spacecraft. Finally, a description of the FalconSAT-3 follow-on mission, including scientific objectives associated with seeking kinetic effects, is presented.

Krause, L. Habash; Enloe, C. L.; Haaland, R. K.; Golando, P.

12

Three-dimensional morphology of equatorial plasma bubbles deduced from measurements onboard CHAMP  

NASA Astrophysics Data System (ADS)

Total electron content (TEC) between Low-Earth-Orbit (LEO) satellites and the Global Navigation Satellite System (GNSS) satellites can be used to constrain the three-dimensional morphology of equatorial plasma bubbles (EPBs). In this study we investigate TEC measured onboard the Challenging Minisatellite Payload (CHAMP) from 2001 to 2005. We only use TEC data obtained when CHAMP passed through EPBs: that is, when in situ plasma density measurements at CHAMP altitude also show EPB signatures. The observed TEC gradient along the CHAMP track is strongest when the corresponding GNSS satellite is located equatorward and westward of CHAMP with elevation angles of about 40-60°. These elevation and azimuth angles are in agreement with the angles expected from the morphology of the plasma depletion shell proposed by Kil et al.(2009).

Park, J.; Lühr, H.; Noja, M.

2015-01-01

13

Evolution of equatorial ionospheric plasma bubbles and formation of broad plasma depletions measured by the C/NOFS satellite during deep solar minimum  

NASA Astrophysics Data System (ADS)

An unexpected feature revealed by the measurements of the Communication/Navigation Outage Forecasting System (C/NOFS) satellite is the presence of broad plasma depletions in the midnight-dawn sector during deep solar minimum. It has not been well understood what causes the broad plasma depletions and how equatorial plasma bubbles are related to the broad depletions. In this paper we present the C/NOFS measurements of equatorial plasma bubbles and broad depletions in a few cases. The ion density perturbations and enhanced ion vertical velocity are first identified in the topside F region at ˜2200 LT, suggesting that the plasma bubbles start to form earlier at lower altitudes. The observations show that the plasma bubbles observed in the midnight-dawn sector may originate in the evening sector. The plasma bubbles continue growing for more than 3.3 h, and the decay time of the bubbles is also longer than 3.3 h. The continuous growth of the plasma bubbles in the evening sector and the slow decay after midnight determine that most plasma bubbles become fully developed and are easily detected in the midnight-dawn sector. The plasma flow inside the bubbles remains strongly upward throughout the entire nighttime. We propose the following mechanism for the generation of wide plasma bubbles and broad depletions. A series of plasma bubbles is generated through the Rayleigh-Taylor instability process over a large longitudinal range. These plasma bubbles grow and merge to form a wide bubble (width of ˜700 km as observed), and multiple regular and/or wide bubbles can further merge to form broad plasma depletions (thousands of kilometers in longitude). The ion vertical drift inside each plasma bubble is driven by the polarization electric field and remains large after the bubbles have merged. This mechanism provides a reasonable interpretation of the large upward ion drift velocity inside the broad depletion region.

Huang, Chao-Song; de La Beaujardiere, O.; Roddy, P. A.; Hunton, D. E.; Pfaff, R. F.; Valladares, C. E.; Ballenthin, J. O.

2011-03-01

14

Microsatellite missions to conduct midlatitude studies of equatorial ionospheric plasma bubbles  

NASA Astrophysics Data System (ADS)

Two missions presently under development by the United States Air Force Academy (USAFA), FalconSAT-2 and FalconSAT-3, include mission scientific objectives targeting the study of ionospheric F region plasma density depletions and topside bubbles associated with the so-called Equatorial Spread F (ESF) phenomena. The Miniature Electrostatic Analyzer (MESA), a USAFA-designed patch sensor that measures differential energy fluxes of electrons from 0.1 eV to 13 eV in six channels, is the primary sensor aboard FalconSAT-2, a 25 kg microsatellite manifested for launch into an International Space Station (ISS) orbit via the Space Shuttle in January 2003. Because the orbit is approximately 360 km in altitude and of 52 degrees inclination, FalconSAT-2 observations will complement those of low latitude missions ( .g., C/NOFS) and high latitude, high altitude missions (e.g.,e DMSP). It is true that a 52 degree orbit appears rather high in inclination for study of ESF phenomena. However, realistic internal magnetic field models demonstrate that field lines with apex heights of 1500 km (representing the upper altitude limit of equatorial plasma bubbles) may intersect the orbit plane at dip latitudes greater than 35 degrees. Thus, FalconSAT-2 will be able to observe plasma depletions that have propagated poleward along the field lines and lower in altitude, depletions that may not be observed with the high altitude DMSP and the low latitude C/NOFS. Additionally, there may be opportunities for FalconSAT-2 to make simultaneous multipoint in situ measurements of large-scale plasma bubbles with other low altitude satellites, such as C/NOFS and DMSP. We will present a statistical analysis of the probability of making such measurements using nominal orbital parameters of the relevant spacecraft. Finally, a brief description of the FalconSAT-3 follow-on mission, including scientific objectives associated with seeking kinetic effects, will be included in the paper.

Habash Krause, L.; Haaland, R.; Enloe, C.; Golando, P.

15

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide-angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry-Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night-to-night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Chapagain, Narayan P.; Makela, Jonathan J.; Meriwether, John W.; Fisher, Daniel J.; Buriti, Ricardo A.; Medeiros, Amauri F.

2012-06-01

16

Plasma waves observed inside plasma bubbles in the equatorial F region  

NASA Astrophysics Data System (ADS)

Plasma waves have been detected within and around density depletions in the topside equatorial F region by the electric and magnetic field sensors of the Extremely Low Frequency Wave Analyzer (ELFWA) instrument which is part of the Low-Altitude Satellite Studies of Ionospheric Irregularities experiment on the Combined Release and Radiation Effects Satellite. The plasma waves include both electrostatic waves that have a small magnetic field component and electromagnetic waves propagating in the extraordinary mode. Thus they are not simply zero-frequency irregularities as generally assumed by previous investigators who were working without the benefit of high-sensitivity ac magnetic field measurements. The waves exhibit no resonances or cutoffs at characteristic frequencies of the plasma within the range of the ELFWA which is 2-125 Hz. They occur from late evening to early morning primarily at altitudes around 400-500 km. An example has been observed as high as 1500 km. The waves are associated with plasma depletions from a factor of 2 to a factor of 80 less than the surrounding density. The observations indicate that the waves are related to equatorial spread F.

Koons, H. C.; Roeder, J. L.; Rodriguez, P.

1997-03-01

17

Investigation of low-latitude ionospheric irregularities and their relationship to equatorial plasma bubbles using Sanya VHF radar  

NASA Astrophysics Data System (ADS)

A VHF radar has been set up at Sanya (18.34° N, 109.62° E, geomagnetic latitude 7.04°N), China in 2009. On the basis of the E, valley and F region irregularity observations detected by the Sanya VHF radar during equinoctial months, we focus on the simultaneous observations of E region irregularities disruption and valley region irregularities generation during the presence of post-sunset F region bubble structures. We stress that both the low latitude the E region irregularities (ERI) disruption and valley region irregularities (VRI) generation are associated with the development of post-sunset equatorial plasma bubble (EPB) structures. It is suggested that the electric field coupling from the unstable equatorial F region to low-latitude E and valley region could trigger and inhibit the occurrence of irregularities, depending on the polarity of the polarization electric field associated with the bifurcation of equatorial plasma bubbles. The mapping of upward/eastward and downward/eastward electric field associated with the west-tilted and east-tilted bubble structures, may be responsible for the disruption of E region irregularities, and the generation of valley region irregularities, respectively. However, more observations from multi instruments will be required to confirm such a scenario that the multi bifurcated EPBs play crucial roles for the simultaneous occurrence of low latitude ERI disruption and VRI generation.

Ning, B.; Li, G.; Hu, L.

2011-12-01

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

The day-to-day occurrence of equatorial plasma bubbles measured from Vanimo, Papua New Guinea  

NASA Astrophysics Data System (ADS)

An analysis of the occurrence of Equatorial Plasma Bubbles (EPBs) detected using a ground-based Global Positioning System (GPS) receiver located at Vanimo in South-east Asia will be presented. The 3-year (2000-2002) dataset employed shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The low-latitude ionosonde station at Vanimo is used in conjunction with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the equinox period. A superposed epoch analysis of the ionosonde data reveals that the height, and the change in height, of the F layer is 1 standard deviation (1?) larger on the days for which EPBs were detected, compared to non-EPB days. These results are interpreted using the generalized Rayleigh-Taylor (R-T) plasma instability growth rate, for which stronger upward drift of the lower-altitude F-layer plasma promotes faster growth of EPBs after sunset. These results are then compared to the results of the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM), which surprisingly show strong similarities to the observations, despite only using geomagnetic and solar activity inputs. The TIEGCM is also used to directly calculate the hourly flux-tube integrated R-T growth rate. A superposed epoch analysis reveals that the modeled R-T growth rate is a little less than 1? higher on average for EPB days compared to non-EPB days. The implication of this result is that the TIEGCM generates almost enough day-to-day variability in order to account for the day-to-day EPB occurrence observed during the equinox. This result isn't necessarily expected due to the model's limited altitude coverage of 100-700 km (depending on solar activity) and the lack of ionospheric observation inputs. It is thought that the remaining variability could originate from either lower altitudes (e.g. atmospheric gravity waves from the troposphere) or from higher altitudes (resulting from coupling with the magnetosphere and solar wind), or potentially both. It is concluded that the continuing advancement of numerical modeling of the thermosphere and ionosphere, coupled with altitudes above and below, is required to better understand the day-to-day EPB occurrence.

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

2013-12-01

20

Electron density and electron temperature in the valley between the equatorial E and F regions during the presence of plasma bubbles - Some recent rocket observations  

NASA Astrophysics Data System (ADS)

Rocket measurements of electron density and electron temperature made from Brazil show that the electron density and electron temperatures in the valley region between the equatorial E and F regions get modified during the onset of plasma bubbles. During one of the launches 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. Recently a Brazilian VS-30 rocket was launched from the equatorial rocket launching station CLBI in Natal, Brazil carrying a Langmuir probe operated 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. These profiles are compared with model electron density and temperature profiles as well as with electron density and temperature profiles observed during other rocket launches under conditions of no plasma bubbles in the F-region.

Muralikrishna, Polinaya; Batista, Inez S.; Domingos, Sinval; Goreti dos Santos Aquino, Maria

2012-07-01

21

A study of seeding, amplification, and development of equatorial plasma bubbles, using a cluster of instruments in the Pacific sector  

NASA Astrophysics Data System (ADS)

The problem of understanding the day-to-day variability in the development of equatorial plasma bubbles (EPBs) requires observations that are made with a cluster of instruments, which can provide a space-time description of the seeding, amplification, and growth of EPBs. Toward achieving this objective, we are operating a cluster of instruments, which provide the necessary, complementary set of measurements. Seeding information is extracted primarily from total electron content (TEC) variations versus longitude, which is determined by receiving beacon radio signals from the Communications/Navigation Outage Forecasting System (C/NOFS) satellite, and from ionogram signatures using two spaced ionosondes. Amplification of the seed is monitored using TEC measurements made on successive C/NOFS passes, and EPB development is determined from backscatter measurements using a five-beam radar. Both temporal development and longitudinal drift can be determined from these multi-beam measurements. In this presentation, we will summarize some of the recent results from this study. In particular, we show how the development and character of the large-scale wave structure in the bottomside F layer determine the subsequent development of EPBs.

Tsunoda, Roland; Yamamoto, Mamoru; Thampi, Smitha; Trang Nguyen, Thu; Bubenik, David

2012-07-01

22

Continuous generation and two-dimensional structure of equatorial plasma bubbles observed by high-density GPS receivers in Southeast Asia  

NASA Astrophysics Data System (ADS)

High-density GPS receivers located in Southeast Asia (SEA) were utilized to study the two-dimensional structure of ionospheric plasma irregularities in the equatorial region. The longitudinal and latitudinal variations of tens of kilometer-scale irregularities associated with equatorial plasma bubbles (EPBs) were investigated using two-dimensional maps of the rate of total electron content change index (ROTI) from 127 GPS receivers with an average spacing of about 50-100 km. The longitudinal variations of the two-dimensional maps of GPS ROTI measurement on 5 April 2011 revealed that 16 striations of EPBs were generated continuously around the passage of the solar terminator. The separation distance between the subsequent onset locations varied from 100 to 550 km with 10 min intervals. The lifetimes of the EPBs observed by GPS ROTI measurement were between 50 min and over 7 h. The EPBs propagated 440-3000 km toward the east with velocities of 83-162 m s-1. The longitudinal variations of EPBs by GPS ROTI keogram coincided with the depletions of 630 nm emission observed using the airglow imager. Six EPBs were observed by GPS ROTI along the meridian of Equatorial Atmosphere Radar (EAR), while only three EPBs were detected by the EAR. The high-density GPS receivers in SEA have an advantage of providing time continuous descriptions of latitudinal/longitudinal variations of EPBs with both high spatial resolution and broad geographical coverage. The spatial periodicity of the EPBs could be associated with a wavelength of the quasiperiodic structures on the bottomside of the F region which initiate the Rayleigh-Taylor instability.

Buhari, S. M.; Abdullah, M.; Hasbi, A. M.; Otsuka, Y.; Yokoyama, T.; Nishioka, M.; Tsugawa, T.

2014-12-01

23

An attempt to trigger ionospheric bubbles and equatorial spread F with the double barium cloud technique  

Microsoft Academic Search

An experiment is described that is expected to trigger an ionospheric bubble in the equatorial F region, i.e. the rise of a flux tube with low plasma content from the bottom of the post sunset F region. The disturbance which will be applied to this region by means of sounding rockets consists of two barium plasma injections at an altitude

G. Haerendel

1979-01-01

24

Simultaneous observations of equatorial plasma depletion by IMAGE and ROCSAT-1 satellites  

Microsoft Academic Search

(1) Simultaneous observations of the equatorial ionosphere by the ROCSAT-1 and IMAGE satellites were used to study zonal propagation characteristics of equatorial plasma bubbles. IMAGE far ultraviolet (FUV) nighttime images have indicated signatures of depression in the brightness of equatorial airglow arcs. Using the list of airglow brightness depression events observed by IMAGE, we surveyed ROCSAT-1 Ionospheric Plasma and Electrodynamics

Chin S. Lin; Thomas J. Immel; Huey-Ching Yeh; Stephen B. Mende; J. L. Burch

2005-01-01

25

Occurrence probability and amplitude of equatorial ionospheric irregularities associated with plasma bubbles during low and moderate solar activities (2008-2012)  

NASA Astrophysics Data System (ADS)

present a statistical analysis of the occurrence probability of equatorial spread F irregularities measured by the Communication/Navigation Outage Forecasting System satellite during 2008-2012. We use different criteria (plasma density perturbations, ?N, and relative density perturbations, ?N/N0) to identify the occurrence of ionospheric irregularities. The purpose of this study is to determine whether the occurrence probability of irregularities is the same for different criteria, whether the patterns of irregularity occurrence vary with solar activity and with local time, and how the patterns of irregularity occurrence are correlated with ionospheric scintillation. It is found that the occurrence probability of irregularities and its variation with local time are significantly different when different identification criteria are used. The occurrence probability based on plasma density perturbations is high in the evening sector and becomes much lower after midnight. In contrast, the occurrence probability based on relative density perturbations is low in the evening sector but becomes very high after midnight in the June solstice. We have also compared the occurrence of ionospheric irregularities with scintillation. The occurrence pattern of the S4 index and its variation with local time are in good agreement with the irregularity occurrence based on plasma density perturbations but are significantly different from those based on relative density perturbations. This study reveals that the occurrence pattern of equatorial ionospheric irregularities varies with local time and that only the occurrence probability of irregularities based on plasma density perturbations is consistent with the occurrence of scintillation at all local times.

Huang, Chao-Song; La Beaujardiere, O.; Roddy, P. A.; Hunton, D. E.; Liu, J. Y.; Chen, S. P.

2014-02-01

26

Observations of the Topside Ionosphere Plasma Bubbles in the Separate Plasma Component (He+): Model Estimations  

NASA Astrophysics Data System (ADS)

The question about an opportunity to detect the topside plasma bubbles of equatorial origin in their separate plasma component (He+) is investigated. There are the indications [1, 2, 3, 4] that there is genetic connection between the He+ density depletions (subtroughs) and the equatorial plasma bubbles. For validation of this idea the characteristic times of the main aeronomy and electrodynamics processes, in which the plasma bubbles and their minor ion component (He+) are involved, have been calculated and compared among themselves. The conditions and factors, connected with solar activity, which are more favorable in the detection of the topside ionosphere plasma bubbles as He+ depletions, were under consideration. The numerical calculations, obtained in SAMIS3 model (3D model of equatorial spread F) and kindly presented by J. Huba (USA) [5], were used for this study. It was revealed that the plasma bubbles, reaching the "ceiling" heights, can exist within several days and that there is principal opportunity to observe them in the separate plasma component (He+). [1] L.N. Sidorova, Adv. Space Res. 33, 850 (2004). [2] L.N. Sidorova, Adv. Space Res. 39, 1284 (2007). [3] L.N. Sidorova, Geomag. and Aeronomy, Intern. 48, 56 (2008). [4] L.N. Sidorova, S.V. Filippov, J. Atm. Solar-Terr. Phys. 86, 83-91, doi: 10.1016/j.jastp.2012.06.013 (2012). [5] J.D. Huba, G. Joyce, J. Krall, Geophys. Res. Lett. 35, L10102, doi:10.1029/2008GL033509 (2008).

Sidorova, Larisa; Filippov, Sergey

2013-04-01

27

Geomagnetic equatorial anomaly in zonal plasma flow  

NASA Technical Reports Server (NTRS)

The observation of a geomagnetic signature in the zonal eastward plasma flow, which is a striking feature of the equatorial ionosphere in the evening quadrant is reported. These observations were derived fronm (E x B)/B-squared measurements made with the cylindrical double-floating-probe experiment carried on the Dynamics Explorer 2 satellite. The signature consists of a crest-trough-crest effect in the latitude dependence of the eastward plasma flow with the crests at + or - 8 dip latitude and the trough nearly centered at the dip equator at all geographic longitudes. This phenomenon can be readily interpreted in terms of the altitude dependence of the F region dynamo electric field, and it is related to dip equator signatures in the plasma density and the magnetic declination which have been reported earlier.

Aggson, T. L.; Herrero, F. A.; Mayr, H. G.; Brace, L. H.; Maynard, N. C.

1987-01-01

28

Plasma bubble detection in the DEMETER micro-satellite data  

NASA Astrophysics Data System (ADS)

The occurrence of plasma bubbles is the most important phenomenon that affects the night time equatorial ionosphere resulting in strong and localized drops of the plasma density with often very sharp boundaries. Besides its own interest for ionospheric physics this phenomenon is also of significant practical importance since it disrupts HF communication and GPS signal reception. In the frame of a French ANR funded project to model the rise and development of plasma bubbles we have searched for specific disturbances of the low latitude ionosphere that might be considered as "precursors" of plasma bubbles, possibly leading, under favourable conditions, to an instable ionosphere. To this aim, we have manually selected and classified typical events observed on data from two instruments on board the DEMETER satellite, IAP (Plasma analyzer) and ISL (Langmuir probe experiment). We present in this poster the various types of events and show that one of them appears to be associated with the later occurrence of plasma bubbles. From the first list of events recorded during an ~ 18 month period we will discuss in detail the plasma disturbances and present initial results of a statistical study.

Onishi, T.; Nguyen, C.-T.; Berthelier, J.-J.

2012-04-01

29

Three-dimensional high-resolution plasma bubble modeling  

NASA Astrophysics Data System (ADS)

Equatorial plasma bubble (EPB) is a well-known phenomenon in the equatorial ionospheric F region. As it causes severe scintillation in the amplitude and phase of radio signals, it is important to understand and forecast the occurrence of EPB from a space weather point of view. The development of EPB is known as a evolution of the generalized Rayleigh-Taylor instability. Numerical modelings of the instability on the equatorial two-dimensional plane have been conducted since the late 1970's, and the nonlinear evolution of the instability has been clearly presented. Recently, three-dimensional (3D) modelings became popular tools for further understanding of the development of EPB such as 3D structure of EPB, meridional wind effects and gravity wave seeding. One of the biggest advantages of the 3D model is that the off-equatorial E region which is coupled with the equatorial F region can be included in the model. It is known from observations that the conductance of the off-equatorial E region controls the growth rate of the Rayleigh-Taylor instability, that is, sudden decrease of the E-region conductance around the sunset accelerates the evolution of the instability. We have developed a new 3D high-resolution model for EPB, and studied internal structure of EPB and the contribution of the off-equatorial E region. As it is necessary to use high-order numerical schemes to capture sharp plasma density gradient of EPB, we adopted the CIP scheme which can keep the third-order accuracy in time and space. The simulated EPB has asymmetrical density gradients at east and west walls, and the growth rate changes significantly depending on the condition of the off-equatorial E region. In the future, we will integrate the high-resolution model into whole atmosphere-ionosphere coupled model (GAIA) to study the growth of EPB under the realistic background conditions.

Yokoyama, Tatsuhiro; Shinagawa, Hiroyuki; Jin, Hidekatsu

30

Seasonal/longitudinal variations of the topside plasma bubbles occurrence  

NASA Astrophysics Data System (ADS)

The present study deals with the seasonal and longitudinal (s/l) variations of the plasma bubble occurrence probability. Topside ionosphere plasma bubbles, seen as He+ density depletions of the topside ionosphere ( 1000 km) deeply inside the plasmasphere (L 1.3-3) (Sidorova, Adv. Space Res., 2004, 2007), are considered. He+ density depletions were obtained from ISS-b space-craft data (1978-80, F10.7 200) for the post-sunset hours under winter, summer and equinoctial condition in the interval of 25° -50° INVLAT for Southern and Northern hemispheres. The ob-tained statistics were compared with the s/l statistics of the equatorial F-region irregularities (EFI), based on the AE-E (McClure et al., JGR, 1998), OGO-6 (Basu et al., Radio. Sci., 1976) and ROCSAT (Su et al., JGR, 2006) data. Moreover, ESF and RSF (range spread-F) statistics, obtained (Maruyama and Matuura, JGR, 1980, 1884) from ISS-b data, and plasma bubble statistics, obtained (Watanabe and Oya, JGG, 1986) from Hinotori data (1981, 650 km), were taken for comparison. EFI, ESF (RSF) and plasma bubble statistics were obtained above the equatorial region within ±20° DIPLAT under the same solar activity conditions. It was revealed that the main statistical maxima of the mentioned above equatorial F-region irregularities are well enough reflected in the s/l statistical plots of the He+ density depletions of the both hemispheres. The best conformity was obtained during the equinox periods, the worst one -during solstice periods, when the most dramatic insolation differences take place for the different hemispheres.

Sidorova, Larisa

31

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

32

Longitudinal structure of plasma bubbles over South American Continent observed by GNSS TEC mapping  

NASA Astrophysics Data System (ADS)

Total electron contents (TEC) from the equatorial to low-middle latitude ionosphere over South American Continent have been monitored by ground-based GNSS receiving network RBMC/IBGE, LISN, IGS and RAMSAC since December 2012. It was possible to monitor spatial and temporal variations of TEC over South America with a spatial resolution of 150 -500 km and by 10 minutes time interval. Plasma bubble formation, development and longitudinal drifting modes were successfully monitored. Equidistant several bubbles (longitudinal separation of 500-1000 km) with a large latitudinal extension (> 2000 km) were frequently observed during the November to February season in 2013. Diagnostics of the equatorial plasma bubbles using TEC mapping technique will be presented and discussed.

Takahashi, Hisao; De Paula, Eurico; Shiokawa, Kazuo; Otsuka, Yuichi; Marcos Denardini, Clezio; Nogueira, Paulo; Wrasse, Cristiano M.; Paulino, Igo; Costa, Sonia; Ivo, Andre; Gomes, Vitor C.

33

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

34

Plasma bubbles in the topside ionosphere: Estimations of the survival possibility  

NASA Astrophysics Data System (ADS)

The question about the survival possibility and the life duration of the topside ionosphere equatorial spread F (ESF) plasma bubbles observed in the separate ion component (He+) is investigated. For this aim the main aeronomy processes, in which plasma bubbles and their He+ ions are involved, were under consideration. It was obtained that the main competition takes place between the He+ loss reactions (He+-N2 reaction) and the uplift during linear growth phase (~10 min) of the Rayleigh-Taylor (R-T) instability, when the plasma bubbles are forming. It was revealed that the ambipolar diffusion of the He+ ions inside the plasma bubble is the fastest (~1-2 min) in the altitude region up to 500 km and becomes slower (~1 h) above 500 km. On the other hand, the plasma bubbles seen in He+ density are pretty stable structures against the cross-field (Bohm) diffusive collapse. It was concluded that the ESF plasma bubbles, reaching the “ceiling” heights, can exist for a night and several morning hours (~10-13 h) and that there is a principal opportunity to observe them in the separate ion component (He+).

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

2014-11-01

35

DRIFT-DISSIPATIVE PLASMA INSTABILITY AND EQUATORIAL SPREAD F  

Microsoft Academic Search

Electrostatic oscillations of a plasma drifting across a magnetic field are considered. The convective instability that arises in a medium containing a gradient of electron concentration is investigated for the case when charge-particle motions are dominated by collisions. The proposal that this instability is the amplification mechanism for producing the irregularities responsible for ionospheric spread-F conditions at equatorial latitudes is

D. M. Cunnold

1969-01-01

36

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

37

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

38

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

39

Topside Ionosphere Plasma Bubbles Seen in He+ Density: Results and Problems  

NASA Astrophysics Data System (ADS)

He (+) density depletions, considered as fossil equatorial plasma bubble signatures, were involved in this study. They are usually detected in the topside ionosphere (approx. 1000 km) deeply inside the plasmasphere (L=1.3-3). a) The question about an opportunity to detect the topside plasma bubbles of equatorial origin in their separate plasma component (He (+) ) is investigated. There are the indications [Sidorova, ASR, 2004, 2007; Sidorova and Filippov, JASTP, 2012] that there is genetic connection between the He (+) density depletions and the equatorial plasma bubbles. For validation of this idea the characteristic times of the main photochemical and electro-dynamical processes, in which the plasma bubbles and their minor ion component (He (+) ) are involved, have been calculated and compared. The model estimations, obtained in SAMIS3 (3D model of equatorial spread F) and kindly presented by J. Huba (USA), are also used for the investigation. It was revealed that the plasma bubbles, reaching the “ceiling” heights, can exist within 2-3 days and that there is principal opportunity to observe them in the separate plasma component (He (+) ). (b) The longitudinal statistics of the He (+) density depletions (P), calculated for all seasons and both hemispheres (20-50(°) INVLAT), were obtained. It was revealed that the most of the P plots have “wave-like” structure with well-defining four peaks. The peaks are the most pronounced in the NH during March equinox/December solstice and in the SH during March equinox/June solstice. Similar wave number 4 longitudinal structure has recently been found in the low-latitude ionosphere density distribution [Immel et al., GRL, 2006; England et al., GRL, 2006; Jin et al., JGR, 2008]. It is assumed that the longitudinal plasma density variations appear due to the modulated vertical ?×? drift. It is supposed that solar thermal tides excited in the troposphere induce zonal perturbation electric fields, which are added to the background F-region dynamo field, modulating the ionosphere fountain process. If the hypothesis about an equatorial origin of He (+) density depletions is true, we can suppose that such 4-peaked structure projected to the topside ionosphere are reflected in their longitudinal statistics. Perhaps this idea can be very useful for explanation of the obtained results. The results of this pioneer study suggest new investigation questions, based mainly on data lacking.

Sidorova, Larisa; Filippov, Sergey

40

Mesospheric gravity waves and ionospheric plasma bubbles observed during the COPEX campaign  

NASA Astrophysics Data System (ADS)

During the Conjugate Point Experiment (COPEX) campaign performed at Boa Vista (2.80?N;60.70?W, dip angle21.7?N) from October to December 2002, 15 medium-scale gravity waves in the OHNIR airglow images were observed. Using a Keogram image analysis, we estimate their parameters. Most of the waves propagate to Northwest, indicating that their main sources are Southeast of Boa Vista. Quasi-simultaneous plasma bubble activities in the OI 630 nm images were observed in seven cases. The distances between the bubble depletions have a linear relationship with the wavelengths of the gravity waves observed in the mesosphere, which suggests a direct contribution of the mesospheric medium-scale gravity waves in seeding the equatorial plasma bubbles.

Paulino, I.; Takahashi, H.; Medeiros, A. F.; Wrasse, C. M.; Buriti, R. A.; Sobral, J. H. A.; Gobbi, D.

2011-07-01

41

The current system associated with the boundary of plasma bubbles  

NASA Astrophysics Data System (ADS)

The current system associated with the boundary of plasma bubbles in the Earth's magnetotail has been studied by employing Cluster multipoint observations. We have investigated the currents in both the dipolarization front (DF, leading edge of the plasma bubble) and the trailing edge of the plasma bubble. The distribution of currents at the edge indicates that there is a current circuit in the boundary of a plasma bubble. The field-aligned currents in the trailing edge of the plasma bubble are flowing toward the ionosphere (downward) on the dawnside and away from the ionosphere (upward) on the duskside, in the same sense as region-1 current. Together with previous studies of the current distributions in the DF and magnetic dip region, we have obtained a more complete picture of the current system surrounding the boundary of plasma bubble. This current system is very similar to the substorm current wedge predicted by MHD simulation models but with much smaller scale.

Sun, Wei-Jie; Fu, Suiyan; Pu, Zuyin; Parks, George K.; Slavin, James A.; Yao, Zhonghua; Zong, Qiu-Gang; Shi, Quanqi; Zhao, Duo; Cui, Yanbo

2014-12-01

42

Cluster and Double Star multipoint observations of a plasma bubble  

Microsoft Academic Search

Depleted flux tubes, or plasma bubbles, are one possible explanation of bursty bulk flows, which are transient high speed flows thought to be responsible for a large proportion of flux transport in the magnetotail. Here we report observations of one such plasma bubble, made by the four Cluster spacecraft and Double Star TC-2 around 14:00 UT on 21 September 2005,

A. P. Walsh; A. N. Fazakerley; A. D. Lahiff; M. Volwerk; A. Grocott; M. W. Dunlop; A. T. Y. Lui; L. M. Kistler; M. Lester; C. Mouikis; Z. Pu; C. Shen; J. Shi; M. G. G. T. Taylor; E. Lucek; T. L. Zhang; I. Dandouras

2009-01-01

43

Ionospheric Plasma Bubbles observed at 29 degree south  

NASA Astrophysics Data System (ADS)

Ionospheric plasma bubbles have been observed by airglow OI6300 imaging technique at the Southern Space Observatory San Martino da Serra 29 S 54 W Brazil since 2004 The bubbles plasma depletion along the magnetic field line are frequently observed in a period from September to March during the southern spring equinox to autumn equinox seasons The frequency of occurrence avarege of eight bobbles for the period and its seasonal dependency are presented and compared to the observations of other locations

Goulart, H. O.; Grellmann, E. A.; Wrasse, C. M.; Makita, K.; Takahashi, H.; Schuch, N. J.

44

Oscillating plasma bubbles. III. Internal electron sources and sinks  

SciTech Connect

An internal electron source has been used to neutralize ions injected from an ambient plasma into a spherical grid. The resultant plasma is termed a plasma 'bubble.' When the electron supply from the filament is reduced, the sheath inside the bubble becomes unstable. The plasma potential of the bubble oscillates near but below the ion plasma frequency. Different modes of oscillations have been observed as well as a subharmonic and multiple harmonics. The frequency increases with ion density and decreases with electron density. The peak amplitude occurs for an optimum current and the instability is quenched at large electron densities. The frequency also increases if Langmuir probes inside the bubble draw electrons. Allowing electrons from the ambient plasma to enter, the bubble changes the frequency dependence on grid voltage. It is concluded that the net space charge density in the sheath determines the oscillation frequency. It is suggested that the sheath instability is caused by ion inertia in an oscillating sheath electric field which is created by ion bunching.

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

2012-08-15

45

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

46

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

47

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

48

Occurrence characteristics of plasma bubble derived from global ground-based GPS receiver networks  

Microsoft Academic Search

Occurrence characteristic of plasma bubble was studied using ground-based GPS receiver networks. The occurrence rate of plasma bubble derived from the global GPS network has higher spatial and temporal resolution than that derived from the other observational techniques because of its wide coverage of the observation. The physical characteristics of plasma bubble occurrence were studied in detail with this novel

M. Nishioka; A. Saito; T. Tsugawa

2008-01-01

49

C/NOFS satellite observations of equatorial ionospheric plasma structures supported by multiple ground-based diagnostics in October 2008  

NASA Astrophysics Data System (ADS)

In early October 2008, the C/NOFS satellite orbited near the magnetic equator at its perigee altitude of ˜400 km at dusk in the Peruvian sector. This provided an ideal opportunity for a comparison, under the current very low solar flux condition, of equatorial ionospheric disturbances observed with the Communication/Navigation Outage Forecasting System (C/NOFS) in situ measurements and ground-based observations available near Jicamarca Observatory. The primary objective was the comparison of plasma density disturbances measured by a Planar Langmuir Probe (PLP) instrument on the C/NOFS satellite with VHF scintillation activity at Ancon near Jicamarca for this period. Here we discuss in detail two extreme cases: one in which severe in situ disturbances were accompanied by mild scintillation on a particular day, namely, 10 October while there was little in situ disturbance with strong scintillation on 5 October. This apparent contradiction was diagnosed further by a latitudinal ground-based GPS network at Peruvian longitudes, a Digisonde, and the incoherent scatter radar (ISR) at Jicamarca. The crucial distinction was provided by the behavior of the equatorial ionization anomaly (EIA). The EIA was well-developed on the day having severe in situ disturbances (10 Oct). This led to lower equatorial plasma density and total electron content (TEC) at the equator and consequently reduced the scintillations detected at Ancon. On the other hand, on the day with severe scintillations (5 Oct), the EIA was not so well developed as on 10 October, leading to relatively higher equatorial plasma density and TEC. Consequently the severe scintillations at Ancon were likely caused by ionospheric structure located below the altitude of C/NOFS. The NRL SAMI2 model was utilized to gain a greater understanding of the role of neutral winds and electric fields in reproducing the TEC as a function of latitude for both classes of irregularities. Spectral studies with high resolution in situ PLP data were also performed. The power law spectra within the plasma bubbles showed two slopes: the low frequency slope being ˜-5/3 and the high frequency ˜-5 with a break around ? = 70 m. This particular type of two-slope spectra may be related to the extremely low solar activity and its impact on ion composition and temperature.

Nishioka, M.; Basu, Su.; Basu, S.; Valladares, C. E.; Sheehan, R. E.; Roddy, P. A.; Groves, K. M.

2011-10-01

50

Dependence of electron trapping on bubble geometry in laser-plasma wakefield acceleration  

SciTech Connect

The effect of bubble shape in laser-plasma electron acceleration was investigated. We showed the general existence of an ellipsoid bubble. The electromagnetic field in this bubble and its dependence on bubble shape were determined through theory. The electron-trapping cross-section for different bubble aspect ratios was studied in detail. When the shape of the bubble was close to spherical, the trapping cross-section reached to the maximum. When the bubble deviated from a spherical shape, the cross-section decreased until electron injection no longer occurred. These results were confirmed by particle-in-cell simulation.

Li, X. F.; Yu, Q.; Huang, S.; Zhang, F.; Kong, Q., E-mail: qkong@fudan.edu.cn [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education, Institute of Modern Physics, Fudan University, Shanghai 200433 (China); Gu, Y. J. [Applied Ion Beam Physics Laboratory, Key Laboratory of the Ministry of Education, Institute of Modern Physics, Fudan University, Shanghai 200433 (China); Institute of Physics of the ASCR, ELI-Beamlines Project, Na Slovance 2, 18221 Prague (Czech Republic); Kawata, S. [Department of Advanced Interdisciplinary Sciences, Utsunomiya University, 7-1-2 Yohtoh, Utsunomiya 321-8585 (Japan)

2014-07-15

51

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

52

Measurements of the Correlation between Plasma Bubble Dynamics and Electron Trapping in a Laser Wakefield Accelerator  

NASA Astrophysics Data System (ADS)

Generation of conically emitted second harmonic radiation has recently been observed in a laser wakefield accelerator experiment at the Naval Research Laboratory. This second harmonic is the result of frequency mixing within the sheath surrounding a fully cavitated plasma region, ``plasma bubble,'' created by the pondermotive force of a laser. Using this second harmonic signature, we have indirectly studied the dynamics of a plasma bubble. It has been observed that the plasma bubble dynamics are strongly correlated to the generation of electrons. Specifically, the onset of the bubble is connected to the generation of off-axis electrons, while forward accelerated electrons have been observed when the conical distribution of second harmonic is broken, signifying the disruption of the plasma bubble. Further results on bubble dynamics and its connection to electron beam production will be presented.

Kaganovich, Dmitri; Helle, Michael; Gordon, Daniel; Ting, Antonio

2010-11-01

53

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

54

Design and Construction of the Plasma Bubble Expansion Experiment  

NASA Astrophysics Data System (ADS)

We will present the design and construction of a new compact coaxial magnetized plasma gun and its associated hardware systems. The plasma gun will be used for experimental studies of ``magnetic bubble'' expansion into a pre-existing lower density background plasma on the HELCAT facility at UNM. These experiments will address key nonlinear plasma physics issues pertinent to plasma models of the formation and evolution of extra-galactic radio lobes. The gun will be powered by a 120?F 10kV ignitron-switched capacitor bank. High pressure gas, controlled by a gas valve system, will be puffed into an annular gap between inner and outer coaxial electrodes. An applied high voltage ionizes the gas and creates a radial current sheet. The ˜ 100kA discharge current generates toroidal flux, and an external magnet will provide poloidal ``bias'' flux. This poster will describe in detail the design and construction of the various power systems for the new plasma gun source.

Zhang, Y.; Lynn, A. G.; Hsu, S. C.; Gilmore, M.; Watts, Christopher

2007-11-01

55

Morphology of the postsunset vortex in the equatorial ionospheric plasma drift  

NASA Astrophysics Data System (ADS)

postsunset vortex in the equatorial ionosphere exhibits clockwise plasma motions after sunset in longitude (time) and altitude coordinates when the equatorial ionosphere is viewed looking northward. We describe the typical morphology of the postsunset vortex using incoherent scatter radar observations at Jicamarca in Peru during the previous solar maximum (2000-2002). A pronounced vortical plasma motion appears around 1700 LT along with the onset of the prereversal enhancement (PRE). The center of this vortex is located near an altitude of 270 km. A smaller-scale vortex also appears about 0.5 ~ 1 h later at higher altitudes. However, the morphology and occurrence time of this small vortex depend on the characteristics of the coherent backscatter region. We find that the earlier vortex is the major feature of the postsunset vortices because it is repeatable, associated with the PRE, and independent to the occurrence of the coherent backscatter region.

Lee, Woo Kyoung; Kil, Hyosub; Kwak, Young-Sil; Paxton, Larry J.

2015-01-01

56

Searching for quark-gluon plasma (QGP) bubble effects at RHIC\\/LHC  

Microsoft Academic Search

Since the early eighties, we have shared with van Hove the following view: If a quark-gluon plasma were produced in high energy heavy ion colliders, then its hadronization products would likely come from small bubbles of plasma localized in phase space. We develop a model based on HIJING, to which we added a ring of adjoining multiple bubbles in the

S. J. Lindenbaum; R. S. Longacre; M. Kramer

2003-01-01

57

Bubbles  

NASA Astrophysics Data System (ADS)

Vanitas vanitatum et omnia vanitas: bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, and many others. Some recent results on a "blinking bubble" micropump and vapor bubbles in sound fields are outlined. The last section describes Leonardo da Vinci's observation of the non-rectlinear ascent of buoyant bubbles and justifies the name Leonardo's paradox recently attributed to this phenomenon.

Prosperetti, Andrea

2004-06-01

58

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

59

KINETIC THEORY OF EQUILIBRIUM AXISYMMETRIC COLLISIONLESS PLASMAS IN OFF-EQUATORIAL TORI AROUND COMPACT OBJECTS  

SciTech Connect

The possible occurrence of equilibrium off-equatorial tori in the gravitational and electromagnetic fields of astrophysical compact objects has been recently proved based on non-ideal magnetohydrodynamic theory. These stationary structures can represent plausible candidates for the modeling of coronal plasmas expected to arise in association with accretion disks. However, accretion disk coronae are formed by a highly diluted environment, and so the fluid description may be inappropriate. The question is posed of whether similar off-equatorial solutions can also be determined in the case of collisionless plasmas for which treatment based on kinetic theory, rather than a fluid one, is demanded. In this paper the issue is addressed in the framework of the Vlasov-Maxwell description for non-relativistic, multi-species axisymmetric plasmas subject to an external dominant spherical gravitational and dipolar magnetic field. Equilibrium configurations are investigated and explicit solutions for the species kinetic distribution function are constructed, which are expressed in terms of generalized Maxwellian functions characterized by isotropic temperature and non-uniform fluid fields. The conditions for the existence of off-equatorial tori are investigated. It is proved that these levitating systems are admitted under general conditions when both gravitational and magnetic fields contribute to shaping the spatial profiles of equilibrium plasma fluid fields. Then, specifically, kinetic effects carried by the equilibrium solution are explicitly provided and identified here with diamagnetic energy-correction and electrostatic contributions. It is shown that these kinetic terms characterize the plasma equation of state by introducing non-vanishing deviations from the assumption of thermal pressure.

Cremaschini, Claudio; Ková?, Ji?í; Slaný, Petr; Stuchlík, Zden?k [Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava, Bezru?ovo nám.13, CZ-74601 Opava (Czech Republic); Karas, Vladimír [Astronomical Institute, Academy of Sciences, Bo?ní II, CZ-14131 Prague (Czech Republic)

2013-11-01

60

Equatorial ionospheric plasma structures observed with the C/NOFS satellite and multiple ground-based diagnostics in October 2008  

NASA Astrophysics Data System (ADS)

Comparison of equatorial ionospheric disturbances observed with C/NOFS in-situ measurements and ground-based observations is performed on two days in Oct 2008. Electron density at 400-850km altitudes in the equatorial ionosphere is measured with a Planar Langmuir Probe (PLP) on the Communications/ Navigation Outage Forecast System (C/NOFS) satellite, which was launched in April 2008 in order to monitor and forecast ionospheric scintillation. In early October, 2008, the C/NOFS satellites flew over the American sector around the dip equator at the perigee altitude at dusk. On 5 Oct, strong 250MHz scintillation occurred at the Ancon SCINDA site without much electron density disturbance in C/NOFS measurements. On the other hand, on 10 Oct., lower scintillations were observed with severe electron density disturbance in C/NOFS data. On 5 Oct, the bottom-side irregularities did not reach the C/NOFS perigee altitude. Latitudinal total electron content (TEC) profiles obtained by Low-latitude Ionospheric Sensor Network (LISN) over South America shows smaller latitudinal gradient of TEC on 5 Oct. than on 10 Oct. The under developed Equatorial Ionization Anomaly (EIA) at dusk on 5 Oct can be an evidence of the absence of irregularity upwelling. The high TEC at the dip equator would enhance the scintillation level on 5 Oct. On 10 Oct, the upwelling of the irregularities was also observed by 50MHz radar backscatter observations at Jicamarca. Latitudinal TEC profile of LISN shows well-developed EIA. This allowed the irregularity bubbles to reach the C/NOFS perigee height. LISN-TEC also shows lower values around the equator, which could contribute to lower scintillation levels. Such day-to-day variability of irregularities remains an unresolved issue during solar minimum as well. We will try to understand this variability better by obtaining spectral measurements of high-resolution in-situ data to provide insight into plasma processes, optical and digisonde observations to provide information regarding the bottom-side of the F-region and using observed vertical drifts to model electron density profiles using the SAMI2 model for comparison with the TEC.

Nishioka, M.; Basu, S.; Valladares, C. E.; Roddy, P. A.; Groves, K. M.; Makela, J. J.

2009-12-01

61

Experimental and Modeling Analysis of the Single Micro Bubble Generation by Micro Plasma in Water  

NASA Astrophysics Data System (ADS)

A single micro bubble (maximum diameter 50 to 600 ?m) is shown to be formed by a single nanosecond duration micro plasma in liquid. The micro scale corona plasma discharges are created at the tip of a micro-electrode with high energy density. Discharge conditions are controllable with tip diameter 1um, applied voltage 5 kV to 10 kV, discharge duration 10 ns to 1 ?s and discharge energy 1 mJ to 50 mJ per pulse. The energy input from the micro plasma to generate the micro bubble and to support its growth vary, which leads to variations in the rate of growth, maximum diameter, and the number of growth-collapse cycles of the micro bubble. These micro plasma based micro bubbles are visualized using a microscope based shadow graph system and two high speed cameras. The micro plasma discharge is captured with nano-second gating using an ICCD and the micro bubble generation and growth is recorded using million fps CCD video camera. The micro bubbles are found repeatedly generated. A Payleigh-Plesset model for growth and collapse of cavity bubble are compared to micro bubble videos and used to estimate the time dependent pressure, temperature and mass of the micro bubbles.

Xiao, Peng; Staack, David

2012-10-01

62

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

SciTech Connect

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. [Department of Physics and Institute for Fusion Studies, University of Texas, Austin, Texas 78712 (United States)

2013-01-15

63

Plasmas sustained in bubbles in water: optical emission and excitation mechanisms  

NASA Astrophysics Data System (ADS)

Plasmas in bubbles in water are being investigated for their ability to produce chemically reactive species for water purification and medical treatment. The gas forming the bubble is potentially a design parameter for water purification as the type and rate of production of active species may be controllable by the type of gas in the bubble. In this paper, we report on a computational investigation of the dynamics of plasmas in bubbles in water sustained in different gases. Images, optical spectra and plasma properties are discussed for plasmas in bubbles of N2, Ar and He in water, and compared to experiments. The differences in plasma dynamics and spatial distribution of the plasma (e.g., volume discharge or surface hugging) when using different gases depend in large part on the electron energy relaxation length, and the rate of diffusion of water vapour into the interior of the bubble. Electron impact dissociative excitation of water vapour, electron impact excitation of dissociation products and excitation transfer from the plasma excited injected bubble gases to water vapour all contribute to plasma emission. Variations in the contributions of these processes are responsible for differences in the observed optical spectra and differences in radical production.

Tian, Wei; Tachibana, Kunhide; Kushner, Mark J.

2014-02-01

64

Deformation of plasma bubbles and the associated field aligned current system during substorm recovery phase  

NASA Astrophysics Data System (ADS)

Multiple plasma bubbles have been detected by CLUSTER satellites on August 15th 2001 in midtail (˜-18 Re). Those bubbles can be classified into two types. Type-I bubbles are similar to those bubbles in previous studies [ Sergeev et al., 1996; Walsh et al., 2009]. Unlike type-I bubbles, the trailing parts/tails of type-II bubbles are much more dynamic than their leading parts/heads and have larger the flux transfer rate. The leading parts of type-II bubbles were suffering a deceleration process and the interaction between the leading and trailing parts will lead to the intensification of |B| and Bz and also a flow shear layer at the trailing parts. Those shear flows cause the twist of magnetic field line, the enhancement of x and y components magnetic field and the generation of field aligned current system. Enhancement of electric field fluctuations also can be found at the trailing parts of type-II bubbles. The corresponding ionospheric signatures were also detected by ground geomagnetic stations. We suggested that the type-II bubbles are bubbles in their late evolution stage and our results are important in understanding the evolution of plasma bubble or fast flow and the transportation of energy from magnetotail to ionosphere.

Pang, Y.; Lin, M. H.; Deng, X. H.; Zhou, M.; Huang, S. Y.

2012-09-01

65

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

66

The Equatorial Ionosphere During Solar Minimum -- C/NOFS Observations of Deep Plasma Depletions at Sunrise  

NASA Astrophysics Data System (ADS)

The Communication/Navigation Forecasting System (C/NOFS) satellite was launched in April 2008 into an equatorial orbit at an altitude between 400 and 850 km, to study the equatorial ionosphere as well as irregularities within it. The satellite sensors measure the following parameters: ambient and fluctuating ion densities; ion and electron temperatures; neutral winds, AC and DC electric and magnetic fields. C/NOFS is circling the Earth at a time when the solar cycle is the lowest it has been since the beginning of the space age. In this talk, we stress the findings that are unique to solar minimum conditions. The plasma density is the smallest seen in the past half century. The pre-reversal enhancement in the upward plasma drift, which is responsible for early evening irregularities, is rarely seen. Instead, plasma irregularities form mostly after midnight. An unexpected feature in the data concerns deep plasma depletions observed at sunrise. They are seen at all satellite altitudes and associated with ionospheric irregularities. Dawn depletions are more frequent in the America-Africa sector and in the Indonesia sector. Dawn depletions are also observed in other data sets, in particular in data from DMSP morning passes, and the CHAMP satellite. This fact confirms that they are real and not an artifact of the plasma instrument. It also allows measuring the N-S extent of the dawn depletions - we find that they are typically 50 x 14 degrees in the N-S and E-W directions respectively, but they can be much wider in longitude. We postulate that they are caused by upward plasma drifts, which are seen in the C/NOFS and ground-based data.

de La Beaujardiere, O.; Roddy, P.; Retterer, J.; Su, Y.; Hunton, D.; Kelley, M.; Pfaff, R.

2009-05-01

67

Penetration Electric Field Generated Plasma Bubbles Tracked by VEFI and PLP on C/NOFS and Associated Scintillations  

NASA Astrophysics Data System (ADS)

Plasma bubbles and scintillations were observed at the appropriate longitudes, namely in the Atlantic-sector, during the initial main phase (Basu et al., Radio Science, 2010) of complex CME-driven moderate magnetic storms that had a minimum Dst of - 60 nT at approximately 2300 UT on 3 August 2010. Fortunately, the C/NOFS satellite was near-perigee in this longitude sector during dusk and was able to intercept what was almost certainly the same bubble in two consecutive orbits. This allowed us to utilize the high resolution dc and ac electric fields from VEFI and plasma density measurements from PLP to track the evolution of the electric field and plasma density structure for the first time to elucidate the variability in the spectral characteristics in a freshly generated and mature bubble. In addition to the two-sloped density structure observed by Rodrigues et al. ( GRL, 2009), the most significant finding was the persistence of the electric field structuring at high frequencies observed in both dc and ac measurements. Such high frequency structures and their dynamics have great significance for the interpretation of radar measurements (Hysell et al., GRL, 2009) and for testing the predictions of instability theories at meter and sub-meter scale irregularities (Huba and Ossakow, JGR, 1979). The scintillation measurements at the Atlantic SCINDA sites, namely, Cape Verde closer to the magnetic equator in the Northern Hemisphere and Ascension Island near the southern crest of the equatorial anomaly shed light on the belt width of scintillations during a moderate magnetic storm in a period where climatologically scintillations are almost non-existent.

Basu, S.; Costa, E.; Pfaff, R. F.

2011-12-01

68

Towards understanding plasma formation in liquid water via single bubble studies  

NASA Astrophysics Data System (ADS)

Plasma-in-water based technological approaches offer great potential to addressing a wide range of contaminants threatening the safety of freshwater reserves. Widespread application of plasma-based technologies, however require a better understanding of plasma formation processes in water and the nature of the plasma-driven chemistry in solution. In this paper, we survey the scope of the threat to freshwater via contamination from a variety of sources, the status of conventional treatment technologies, the promise of plasma-based water purification, and the pathway to understanding plasma formation in water through the study of single bubble breakdown physics. Plasma formation in bubbles lie at the heart of plasma formation in liquid water. We present findings from ongoing research at the University of Michigan aimed at understanding the nature of plasma formation in bubbles, which provides an avenue for not only understanding breakdown conditions, but also insight in reducing the magnitude of the breakdown voltage. These experiments also establish an approach to a standardized apparatus for the study of plasma discharges in bubbles. We also discuss approaches to controlling plasma-induced chemistry in liquid water.

Foster, John E.; Sommers, Bradley; Gucker, Sarah

2015-01-01

69

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

70

Plasmas in Multiphase Media: Bubble Enhanced Discharges in Liquids and Plasma/Liquid Phase Boundaries  

SciTech Connect

In this research project, the interaction of atmospheric pressure plasmas with multi-phase media was computationally investigated. Multi-phase media includes liquids, particles, complex materials and porous surfaces. Although this investigation addressed fundamental plasma transport and chemical processes, the outcomes directly and beneficially affected applications including biotechnology, medicine and environmental remediation (e.g., water purification). During this project, we made advances in our understanding of the interaction of atmospheric pressure plasmas in the form of dielectric barrier discharges and plasma jets with organic materials and liquids. We also made advances in our ability to use computer modeling to represent these complex processes. We determined the method that atmospheric pressure plasmas flow along solid and liquid surfaces, and through endoscopic like tubes, deliver optical and high energy ion activation energy to organic and liquid surfaces, and produce reactivity in thin liquid layers, as might cover a wound. We determined the mechanisms whereby plasmas can deliver activation energy to the inside of liquids by sustaining plasmas in bubbles. These findings are important to the advancement of new technology areas such as plasma medicine

Kushner, Mark Jay [University of Michigan] [University of Michigan

2014-07-10

71

Field-Reversed Bubble in Deep Plasma Channels for High-Quality Electron Acceleration  

NASA Astrophysics Data System (ADS)

We study hollow plasma channels with smooth boundaries for laser-driven electron acceleration in the bubble regime. Contrary to the uniform plasma case, the laser forms no optical shock and no etching at the front. This increases the effective bubble phase velocity and energy gain. The longitudinal field has a plateau that allows for monoenergetic acceleration. We observe as low as 10-3 rms relative witness beam energy uncertainty in each cross section and 0.3% total energy spread. By varying the plasma density profile inside a deep channel, the bubble fields can be adjusted to balance the laser depletion and dephasing lengths. Bubble scaling laws for the deep channel are derived. Ultrashort pancakelike laser pulses lead to the highest energies of accelerated electrons per Joule of laser pulse energy.

Pukhov, A.; Jansen, O.; Tueckmantel, T.; Thomas, J.; Kostyukov, I. Yu.

2014-12-01

72

Field-reversed bubble in deep plasma channels for high-quality electron acceleration.  

PubMed

We study hollow plasma channels with smooth boundaries for laser-driven electron acceleration in the bubble regime. Contrary to the uniform plasma case, the laser forms no optical shock and no etching at the front. This increases the effective bubble phase velocity and energy gain. The longitudinal field has a plateau that allows for monoenergetic acceleration. We observe as low as 10^{-3} rms relative witness beam energy uncertainty in each cross section and 0.3% total energy spread. By varying the plasma density profile inside a deep channel, the bubble fields can be adjusted to balance the laser depletion and dephasing lengths. Bubble scaling laws for the deep channel are derived. Ultrashort pancakelike laser pulses lead to the highest energies of accelerated electrons per Joule of laser pulse energy. PMID:25541776

Pukhov, A; Jansen, O; Tueckmantel, T; Thomas, J; Kostyukov, I Yu

2014-12-12

73

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

74

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

75

Holographic Study Of Bubble Dissolution In Human Plasma  

NASA Astrophysics Data System (ADS)

When a deep-sea diver returns to the surface, he may suffer decompression sickness (commonly known as the bends). The disease occurs when the excess inert gas that dissolves in tissues during the dive (N2 or He) forms bubbles. The standard treatment is rapid recompression in order to redissolve the bubbles. The diver is placed in a hyperbaric chamber, which is then pressurized to a point where symptoms are relieved; this pressure is maintained for an arbitrary period presumed adequate to fully dissolve all bubbles. The pressure is then reduced gradually until atomospheric pressure is reached. If all has gone well, the diver experiences no residual effects.

Buckles, Richard G.; Cox, M. E.; Eckenhoff, J. B.

1981-05-01

76

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

77

Can HF heating generate ESF bubbles?  

NASA Astrophysics Data System (ADS)

The injection of powerful HF waves into the ionosphere can lead to strong electron heating followed by a pressure perturbation which can locally reduce the plasma density. In the postsunset equatorial ionosphere, density perturbations can provide the seed to generate equatorial spread F (ESF) bubbles. In this paper, a modified version of the SAMI3/ESF ionosphere code is used to model the density depletions created by HF heating and to determine if ESF bubbles can be artificially generated. It is found that HF heating primarily redistributes plasma along the geomagnetic field and does not significantly perturb the flux tube integrated conductivities. Thus, HF heating does not appear to be a viable method to seed or generate ESF bubbles.

Zawdie, K. A.; Huba, J. D.

2014-12-01

78

Comparison of drift velocities of nighttime equatorial plasma depletions with the ambient plasma drifts and the thermospheric neutral winds  

NASA Astrophysics Data System (ADS)

This study is for the first time to analyze satellite observations and compare the plasma depletion drifts with the ambient plasma drifts and the neutral winds in the post-sunset equatorial ionosphere. The local time and latitude variations of the drift velocities of O+ plasma depletions at 350--400 km altitude are derived from the observations of the Far Ultraviolet Imager (FUV) operated on the IMAGE satellite during March 10-June 7, 2002. The variations are compared with the simultaneous measurements of the ion drift velocities and the neutral winds by the ROCSAT-1 and the CHAMP satellites for a similar time period. The analysis shows that the zonal drift velocity of plasma depletions is smaller than both the ambient ion zonal drift velocity and the neutral zonal wind at 18-20 hour magnetic local time and after 21 hour the variations of these velocities are similar. The analysis also shows that the difference of the plasma depletion drift with the background is small at low latitudes. This is the first-ever satellite comparison of the plasma depletion drift with the ambient plasma drift as well as the neutral wind for a global scale, explaining many previous observations at single locations. Furthermore, the zonal drift velocity of the depletion is found in this study to have a large latitudinal gradient specifically at 12°-18° magnetic latitude, which again does not match the ambient ion drift and the neutral wind. This latitudinal difference has been reported by previous studies, but these studies use models and they only compare the depletion drifts with the modeled neutral winds. This study compares the satellite observations, and compares with both the neutral winds and the plasma drifts. The study provides a measure of the difference that has never been provided before by any study using global observations. It has been suggested that vertical polarization electric fields inside the plasma depletions are responsible for the eastward drift of the depletion structures. The difference in the latitudinal gradients seen here in this study could also be explained by the polarization electric fields. For the C-shaped depletion, the polarization electric fields drive a westward drift of plasma particles inside the depletion and this drift velocity changes with increasing latitude. Consequently, the depletion drifts eastward and the depletion drift has a larger latitudinal gradient than the ambient plasma drift.

Liu, G.; England, S.; Frey, H. U.; Immel, T. J.; Lin, C. S.; Pacheco, E.; Haeusler, K.; Doornbos, E.

2013-12-01

79

Nonlinear oscillations of gas bubbles submerged in water: implications for plasma breakdown  

NASA Astrophysics Data System (ADS)

Gas bubbles submerged in a dielectric liquid and driven by an electric field can undergo dramatic changes in both shape and volume. In certain cases, this deformation can enhance the distribution of the applied field inside the bubble as well as decrease the internal gas pressure. Both effects will tend to facilitate plasma formation in the gas volume. A practical realization of these two effects could have a broad impact on the viability of liquid plasma technologies, which tend to suffer from high voltage requirements. In this experiment, bubbles of diameter 0.4-0.7 mm are suspended in the node of a 26.4 kHz underwater acoustic standing wave and excited into nonlinear shape oscillations using ac electric fields with amplitudes of 5-15 kV cm-1. Oscillations of the deformed bubble are photographed with a high-speed camera operating at 5130 frames s-1 and the resulting images are decomposed into their axisymmetric spherical harmonic modes, Y_l^0 , using an edge detection algorithm. Overall, the bubble motion is dominated by the first three even modes l = 0, 2 and 4. Electrostatic simulations of the deformed bubble's internal electric field indicate that the applied field is enhanced by as much as a factor of 2.3 above the nominal applied field. Further simulation of both the pure l = 2 and l = 4 modes predicts that with additional deformation, the field enhancement factors could reach as much as 10-50.

Sommers, B. S.; Foster, J. E.

2012-10-01

80

A search for seeds of equatorial plasma irregularities: Results from ground- and balloon-borne optical measurements  

NASA Astrophysics Data System (ADS)

It has been shown that the daytime upper atmosphere in low- and equatorial-latitudes ';prepares' conditions suitable for the generation of ionospheric plasma irregularities after sunset. It has also been suggested that waves in the daytime lower thermosphere could potentially be responsible for the generation of nighttime plasma irregularities. To investigate this connection, an INDO-US collaborative Balloon and ground campaign was carried out on 8 March 2010 from Hyderabad, India. Its primary goal was to investigate daytime mesosphere and lower thermosphere wave dynamics. The balloon carried a high-resolution (0.2nm), wide-field (80°) ultraviolet spectrograph and observed OI 297.2 nm dayglow emissions, which recorded waves of scale sizes less than 100 km in the zonal direction. Ground-based optical, radio, and magnetic measurements included OI 557.7 nm dayglow emissions which showed waves whose periodicities have been estimated to be in the range of 14 - 35 minutes. These suggest a maximum phase speeds of these waves to be around 90 ms-1. Waves of such periodicities were also seen to be present over the equator in the equatorial electrojet on that day. Furthermore, a strong spread-F was recorded at the magnetic equatorial station, Trivendrum, starting at 2010 LT indicating that plasma irregularities were generated. We will describe the experiment and the results in the context of characteristics of waves which are potentially capable of forming seeds for the generation of equatorial plasma irregularities in the nighttime. This work was supported by NSF grant AGS-1315354 and ONR grant N000014-13-1-0266.

Chakrabarti, S.; Duggirala, P.; Baumgardner, J. L.; Singh, R.; Laskar, F.; Mendillo, C.; Cook, T.; Narayanan, R.; Pant, T. K.

2013-12-01

81

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

82

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

SciTech Connect

Self-injection of background electrons in plasma wakefield accelerators in the highly nonlinear bubble regime is analyzed using particle-in-cell and semi-analytic modeling. It is shown that the return current in the bubble sheath layer is crucial for accurate determination of the trapped particle trajectories.

Yi, S. A.; Khudik, V.; Siemon, C.; Shvets, G. [Department of Physics and Institute for Fusion Studies, University of Texas at Austin, One University Station C1500, Austin, Texas (United States)

2012-12-21

83

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

84

Design of a Compact Coaxial Magnetized Plasma Gun for Magnetic Bubble Expansion Experiments  

NASA Astrophysics Data System (ADS)

We will discuss the design of a compact coaxial magnetized plasma gun and its associated hardware systems in detail. The plasma gun will be used for experimental studies of magnetic bubble expansion into a lower pressure background plasma, as a model for extragalactic radio lobes. The gun is powered by an ignitron-switched capacitor bank. High-pressure gas will be puffed into an annular gap between inner and outer coaxial electrodes. An applied high voltage ionizes the gas and creates a radial current sheet. The 100kA discharge current generates toroidal flux; poloidal flux is provided by using an external bias magnet. The axial JxB force ejects plasma out of the gun. If the JxB force exceeds the magnetic tension of the poloidal flux by a sufficient amount then a detached magnetized plasma will be formed. The poster will discuss the plasma bubble formation system including the power system, gas valve control system, bias flux power system, and the magnetic probe diagnostic in detail. Experimental data will be provided.

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

2008-11-01

85

Handling cycle slips in GPS data during ionospheric plasma bubble events  

NASA Astrophysics Data System (ADS)

During disturbed ionospheric conditions such as the occurrence of plasma bubbles, the phase and amplitude of the electromagnetic waves transmitted by GPS satellites undergo rapid fluctuations called scintillation. When this phenomenon is observed, GPS receivers are more prone to signal tracking interruptions, which prevent continuous measurement of the total electron content (TEC) between a satellite and the receiver. In order to improve TEC monitoring, a study was conducted with the goal of reducing the effects of signal tracking interruptions by correcting for "cycle slips," an integer number of carrier wavelengths not measured by the receiver during a loss of signal lock. In this paper, we review existing cycle-slip correction methods, showing that the characteristics associated with ionospheric plasma bubbles (rapid ionospheric delay fluctuations, data gaps, increased noise, etc.) prevent reliable correction of cycle slips. Then, a reformulation of the "geometry-free" model conventionally used for ionospheric studies with GPS is presented. Geometric information is used to obtain single-frequency estimates of TEC variations during momentary L2 signal interruptions, which also provides instantaneous cycle-slip correction capabilities. The performance of this approach is assessed using data collected on Okinawa Island in Japan during a plasma bubble event that occurred on 23 March 2004. While an improvement in the continuity of TEC time series is obtained, we question the reliability of any cycle-slip correction technique when discontinuities on both GPS legacy frequencies occur simultaneously for more than a few seconds.

Banville, S.; Langley, R. B.; Saito, S.; Yoshihara, T.

2010-12-01

86

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

87

Coordinated in situ measurements of plasma irregularities and ground based scintillation observations at the crest of equatorial anomaly  

NASA Astrophysics Data System (ADS)

First comparison of in situ density fluctuations measured by the DEMETER satellite with ground based GPS receiver measurements at the equatorial anomaly station Bhopal (geographic coordinates (23.2°N, 77.6°E); geomagnetic coordinates (14.29°N, 151.12°E) for the low solar activity year 2005, are presented in this paper. Calculation of the diurnal maximum of the strength of the equatorial electrojet, which can serve as precursor to ionospheric scintillations in the anomaly region is also done. The Langmuir Probe experiment and Plasma Analyzer onboard DEMETER measure the electron and ion densities respectively. Irregularities in electron density distribution cause scintillations on transionospheric links and there exists a close relationship between an irregularity and scintillation. In 40% of the cases, DEMETER detects the irregularity structures (dNe/Ne ? 5% and dNi/Ni (O+) ? 5%) and GPS L band scintillations (S4 ? 0.2) are also observed around the same time, for the low solar activity period. It is found that maximum irregularity intensity is obtained in the geomagnetic latitude range of 10-20° for both electron density and ion density. As the GPS signals pass through this irregularity structure, scintillations are recorded by the GPS receiver installed at the equatorial anomaly station, Bhopal it is interesting to note that in situ density fluctuations observed on magnetic flux tubes that pass over Bhopal can be used as indicator of ionospheric scintillations at that site. Many cases of density fluctuations and associated scintillations have been observed during the descending low solar activity period. The percentage occurrence of density irregularities and scintillations shows good correspondence with diurnal maximum of the strength of electrojet, however this varies with different seasons with maximum correspondence in summer (up to 66%) followed by equinox (up to 50%) and winter (up to 46%). Also, there is a threshold value of EEJ strength to produce density irregularities ((dNe/Ne)max ? 5%) and for moderate to strong scintillations (S4 ? 0.3) to occur. For winter this value is found to be ?40 nT whereas for equinox and summer it is around 50 nT.

Sarkar, Shivalika; Gwal, A. K.

2014-08-01

88

The Role of Bubbles in the Transport of Particles From the Plasma Sheet to the Inner Magnetosphere (Invited)  

NASA Astrophysics Data System (ADS)

Essentially the whole closed-field-line region of the magnetosphere is stratified, with layers of highest PV5/3 on field lines that stretch far into the tail and lowest PV5/3 deep in the inner magnetosphere. (Here V is the volume of a flux tube containing a unit of magnetic flux.) The magnetosphere is like an atmosphere with heavy gases on the bottom and lighter ones on the top. The entropy parameter PV5/3 is strictly conserved in ideal MHD. Transport nevertheless occurs between layers, because a non-ideal process like a patch of reconnection can create a bubble of low PV5/3 that propagates rapidly earthward, forming a bursty bulk flow. During that rapid earthward motion, the earthward boundary of the bubble forms a dipolarization front, where the magnetic field switches from the background stretched configuration to a more dipolar shape inside the bubble. A thin layer of high-PV5/3 flux tubes gets pushed earthward ahead of the bubble (known feature of dipolarization fronts). The bubble slows after it reaches the region where the PV5/3 of the surrounding medium matches its own, and it is sometimes observed to oscillate about an equilibrium position. While bubbles have obvious effects in the plasma sheet, their effects on the inner magnetosphere are much less obvious. Gradient/curvature drift, which is strong in the inner magnetosphere, causes higher-energy ions in the bubble to drift west compared to the bubble center and lower-energy ions and electrons to drift east. Thus the bubble blends into its surroundings. This picture of transport by bubbles has become well established for the plasma sheet, but conventional ring current models do not consider it, envisaging injection as a result of an increase in global convection. The key question is: do bubbles have any observable signatures in the storm-time ring current? Results will be presented from RCM-E runs designed to answer this question.

Wolf, R.; Yang, J.; Toffoletto, F.; Sazykin, S. Y.

2013-12-01

89

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

90

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

91

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

92

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

93

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

PubMed Central

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 × 1018 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

2014-01-01

94

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

95

Observation of F region irregularities near a northern equatorial anomaly crest during solar minimum using ionosonde, GPS receiver, and satellites  

NASA Astrophysics Data System (ADS)

For solar minimum, the spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA) are simultaneously analyzed to investigate F region irregularities for the first time. The data were observed using the Chungli ionosonde, YMSM GPS receiver, and DMSP satellites during 1996. It is found that in the observed ionograms, the frequency spread F (FSF) usually comes after the range spread F (RSF) in a series of nighttime spread F events. This results in that the maximum occurrence of RSF appears before that of FSF in the nighttime variations in occurrence probabilities. Moreover, the seasonal variation for RSF is close to that for FSF. Both have a board maximum in the J-months and a secondary maximum in December. These indicate that RSF and FSF should be regarded as one type of spread F, which is the all spread F (ASF) in this study. Because the equatorial plasma bubbles occur infrequently during solar minimum, the F region irregularities forming ASF are not related to the equatorial spread F. On the other hand, the similarity in seasonal occurrence between ASF and medium-scale traveling ionospheric disturbances (MSTIDs) demonstrates that the F region irregularities near the EIA crest are mainly generated by the gradient drift instability driven by MSTIDs. The irregularities, generated by MSTIDs, mostly occur in the bottom side of the F region. Consequently, the events of significant GPS phase fluctuations and plasma bubble near the EIA crest are rare during 1996.

Lee, C.-C.; Chen, W. S.; Chu, F. D.

2013-06-01

96

Electric field and plasma density measurements in the strongly driven daytime equatorial electrojet. I - The unstable layer and gradient drift waves. II - Two-stream waves  

NASA Technical Reports Server (NTRS)

The results of electric field and plasma density measurements in the strongly driven daytime equatorial electrojet over Peru, made during the March 1983 Condor electrojet experiment from Punta Lobos, Peru, are discussed together with the rocket instrumentation used for the measurements and the pertinent payload dynamics. The overall characteristics of the irregularity layer observed in situ in the electrojet are described. Special consideration is given to the waves generated by the gradient drift instability (observed between 90 and 106.5 km) and to primary and secondary two-stream waves detected by the two probes on the topside between 103 and 111 km, where the electron current was considered to be strongest.

Pfaff, R. F.; Kelley, M. C.; Kudeki, E.; Fejer, B. G.; Baker, K. D.

1987-01-01

97

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

98

Calculation of Magnetospheric Equilibria and Evolution of Plasma Bubbles with a New Finite-Volume MHD/Magnetofriction Code  

NASA Astrophysics Data System (ADS)

We present a finite-volume MHD code for simulations of magnetospheric dynamics of the plasma sheet and the inner magnetosphere. The code uses staggered non-uniform Cartesian grids to preserve the divergence-free magnetic fields, along with various numerical approximations and flux limiters for the plasma variables. The code can be initialized with empirical magnetic field models, such as the Tsyganenko models along with pressure information from either the Tsyganenko-Mukai models, or observational data, such as DMSP pressure maps. Artificial "friction term" can be added to the momentum equation, which turns the MHD code into "magnetofriction" code which can be used to construct approximate equilibrium solutions. We demonstrate some applications for our code, in both the "magnetofriction" and MHD mode, including relaxation of the empirical models to equilibrium and the evolution of a plasma bubble in the near magnetotail. The latter MHD simulation results exhibit oscillations about their equilibrium position in agreement with recent observations.

Silin, I.; Toffoletto, F.; Wolf, R.; Sazykin, S. Y.

2013-12-01

99

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

100

Midnight reversal of ionospheric plasma bubble eastward velocity to westward velocity during geomagnetically quiettime: Climatology and its model validation  

NASA Astrophysics Data System (ADS)

In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles - WTB - occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station São João do Cariri (Geographic 7.45°S, 36.5°W, dip ˜20°S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between ˜20 and 40 ms-1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July-September. No WTB have been observed from November until April in all years 2001-2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.

Sobral, José H. A.; de Castilho, Vivian M.; Abdu, M. A.; Takahashi, Hisao; Paulino, I.; Gasparelo, Ulisses A. C.; Arruda, Daniela C. S.; Mascarenhas, Matheus; Zamlutti, C. J.; Denardini, C. M.; Koga, Daiki; de Medeiros, A. F.; Buriti, R. A.

2011-07-01

101

An energy-efficient process for decomposing perfluorooctanoic and perfluorooctane sulfonic acids using dc plasmas generated within gas bubbles  

NASA Astrophysics Data System (ADS)

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are environmentally harmful and persistent substances. Their decomposition was investigated using dc plasmas generated within small gas bubbles in a solution. The plasma characteristics including discharge voltage, voltage drop in the liquid, plasma shape and the emission spectrum were examined with different gases. The decomposition rate and energy efficiency were evaluated by measuring the concentration of fluoride and sulfate ions released from PFOA/PFOS molecules. The concentration of fluoride ions and energy efficiency in the treatment of a PFOS solution were 17.7 mg l-1 (54.8% of the initial amount of fluorine atoms) and 26 mg kWh-1, respectively, after 240 min of operation. The addition of scavengers of hydroxyl radicals and hydrated electrons showed little effect on the decomposition. The decomposition processes were analyzed with an assumption that positive species reacted with PFOA/PFOS molecules at the boundary of the plasma-solution surface. This type of plasma showed a much higher decomposition energy efficiency compared with energy efficiencies reported in other studies.

Yasuoka, K.; Sasaki, K.; Hayashi, R.

2011-06-01

102

An equatorial scintillation model  

NASA Astrophysics Data System (ADS)

Radiowave scintillation in the presence of natural and/or high altitude nuclear disturbances has the potential to disrupt numerous transionospheric radio and radar systems. This report develops a model characterizing the plasma density irregularities that produce scintillation in the naturally disturbed equatorial F layer. The model has been incorporated into Program WBMOD along with subroutines for computing both link geometry and scintillation indices, the latter by means of phase screen diffraction theory. The model is based on similarly extensive analysis of Wideband data from two equatorial stations. It describes irregularities at an effective height of 350 km that are isotropic across the geomagnetic field and elongated by a factor of 50 along the field and whose one dimensional spatial power spectrum obeys a single regime power law with a (negative) spectral index of 1.5. The height-integrated spectral strength of the irregularities is modeled as a function of solar epoch (sunspot number), the angle between the sunset terminator and the geomagnetic field line through the equatorial F layer point in question (a measure of seasonal and longitudinal variation), time after E-layer sunset on that field line, and the F-layer magnetic apex latitude of the point. The report also highlights a factor missing from complete characterization of the joint seasonal/longitudinal variation of scintillation, thought to depend upon thermospheric neutral winds.

Fremouw, E. J.; Robins, R. E.

1985-09-01

103

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

104

Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly  

NASA Astrophysics Data System (ADS)

scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.

Lima, G. R. T.; Stephany, S.; Paula, E. R.; Batista, I. S.; Abdu, M. A.; Rezende, L. F. C.; Aquino, M. G. S.; Dutra, A. P. S.

2014-06-01

105

Equatorial spread F initiation and growth from satellite traces as revealed from conjugate point observations in Brazil  

NASA Astrophysics Data System (ADS)

better understanding of the precursor conditions for the instability growth is very important for identifying the causes of day-to-day variability in the equatorial spread F (ESF)/plasma bubble irregularity development. We investigate here the satellite trace (S-trace) in the ionograms, a precursor to the postsunset ESF occurrence, as observed by Digisondes operated at an equatorial and two magnetic conjugate sites in Brazil during a 66 day observational campaign (Conjugate Point Equatorial Experiment 2002). The satellite traces first occur at the equatorial site, and sequentially, after a variable delay of approximately 20 to 50 min, they are observed nearly simultaneously over the two conjugate sites. The evening prereversal enhancement in the zonal electric field/vertical drift is found to control its development. Using a three-dimensional simulation code based on collisional interchange instability mechanism, it is shown that the observed S-trace occurrence sequence is fully consistent with the instability initiation over the equator with the field-aligned plasma depletion vertical growth marked by latitudinal expansion of its extremities to conjugate locations. The delay in the S-trace occurrence at the conjugate sites (a measure of the nonlinear growth of the instability for plasma depletion) is controlled also by field line parallel (meridional) neutral wind. The relationship between the S-trace and the large-scale wave structure in the F layer, another widely known characterization of the precursor condition for the ESF development, is also clarified.

Abdu, M. A.; Kherani, E. A.; Batista, I. S.; Reinisch, B. W.; Sobral, J. H. A.

2014-01-01

106

MAPPING AGE-RELATED ELASTICITY CHANGES IN PORCINE LENSES USING BUBBLE-BASED ACOUSTIC RADIATION FORCE  

PubMed Central

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 1 mm 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

2007-01-01

107

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

108

Automatic analysis, identification, and classification of Equatorial Spread-F in the ionograms  

NASA Astrophysics Data System (ADS)

F-region large-scale irregularities, also called plasma bubbles, are one of the most interesting equatorial ionospheric phenomena. These irregularities are generated in the equatorial region and afterwards extend to lower latitudes. They are one of the important topics of investigation of equatorial ionosphere electrodynamics and, therefore, are subject to intense theoretical and experimental research. The ionosonde is the most used scientific equipment to study the ionosphere and the F-region. Multiple echoes recorded on ionograms are the signature of these irregularities in the ionograms, usually called Spread-F. Spread-F is classified into three types: range, frequency, and mixed. Thus, automatic identification and classification of Spread- F is important in ionospheric studies, because studies usually involve the analysis and interpretation of large numbers of ionograms. The main objective of this paper is to present a new computational tool, based on fuzzy relation, designed to automatically identify and classify the occurrence of Spread-F in ionograms. The test was conducted in ionograms recorded in the Brazilian sector ((São José dos Campos (23.2(°) S, 45.9(°) W, dip latitude 17.6(°) S - low latitude) and Palmas (10.2(°) S, 48.2(°) W, dip latitude 5.5(°) S - near the magnetic equatorial)). The automatic identification and classification of Spread-F occurrence were compared with those obtained manually and good agreement was found.

Pillat, Valdir Gil; Fagundes, Paulo Roberto; Guimaraes, Lamartine N. F.

109

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

110

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

111

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

112

Spatiotemporal variability and propagation of equatorial noise observed by Cluster  

E-print Network

; published 31 December 2002. [1] We report a multipoint case study of the electromagnetic equatorial noise et Plane´taires, Ve´lizy, France Received 5 November 2001; revised 20 March 2002; accepted 2 May 2002 plasma waves propagating in the close vicinity of the geomagnetic equatorial plane at frequencies from

Santolik, Ondrej

113

Japan contribution to studies of low-latitude and equatorial ionosphere over Southeast Asia  

NASA Astrophysics Data System (ADS)

A dense observation network to study ionosphere is deployed over Southeast Asian countries of Indonesia, Thailand, and Vietnam. The Equatorial Atmosphere Radar (EAR) at Kototabang, Indonesia is the center facility, and supporting instruments, i.e., an ionosonde, a VHF ionosphere radar, an optical imager, a GPS scintillation receiver, a magnetometer, a meteor radar, etc. are collocated. NICT operates the ionosonde network SEALION (South East Asian Low-latitude IOnosonde Network) that meridionally extends from the EAR site to Chumphong and Chiang Mai in Thailand, and two more sites (Baq Liu and Phy Thuy) in Vietnam. Additional facilities are an MF radar at Pameungpeuk, Indonesia, and an optical imager at Darwin, Australia. We have been observing plasma bubbles since 2001, that, for example, contributed clarification of time- spatial structures of the phenomena, their relationship to the pre-reversal enhancement, control of bubble occurrence by the meridional winds, etc. We are starting studies of their seeding by means of atmospheric waves that propages from the lower atmosphere, too. In 2008, Nagoya University will soon install three Fabry-Perot interferometers at the EAR site, Chiang Mai, and Darwin. We also have a plan to install digital beacon receivers in some of these sites. Next research program that follows CPEA (Coupling Processes in the Equatorial Atmosphere, 2001-2007) is under planning now. Our main facilities cover ± 10° of geomagnetic latitude, where the magnetic declination is relatively small, and the geomagnetic equator is in the geographic northern hemisphere. We will review our achievements, and show on-going efforts and future plans. Collaboration with the C/NOFS satellite, and comparisons to results from the American sector should be beneficial for global-scale understanding of the equatorial ionosphere/atmosphere.

Yamamoto, M.; Ishii, M.; Otsuka, Y.; Shiokawa, K.; Saito, A.; Tsuda, T.; Fukao, S.

2008-12-01

114

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). PMID:24740256

Shanahan, Martin E. R.; Sefiane, Khellil

2014-01-01

115

Guided radio-wave propagation in the equatorial ionosphere according to the topside sounding onboard Interkosmos-19  

NASA Astrophysics Data System (ADS)

In addition to normal vertical-incident ionogram traces, strongly remote (up to 2000 km) traces of HF-radio-signal reflections observed on topside-sounder ionograms of the Interkosmos-19 satellite obtained in the equatorial ionosphere are presented. Such traces are connected with waveguides (ducts). These waveguides are field-aligned irregularities of the ionospheric plasma with electron density depletions of a few percent and cross-field dimension of a few to several kilometers. Ray tracing confirms this supposition and allows an estimate of typical waveguide parameters: diameter ?10-15 km and amplitude |?N/N|?10%, where N is the electron density. The waveguide traces usually start at the cutoff frequencies of the main traces. However, sometimes they begin at much lower frequencies which indicates the satellite was transitioning through an equatorial plasma bubble during the recording of the ionogram. The X-mode of ducted echoes is more distinct then the O-mode. Only one ducted trace is usually observed on the Interkosmos-19 ionograms; a second conjugate trace is rarely recorded. The same is true for combination modes which is a combination of an oblique-incidence and guided propagation. Waveguides are observed at all heights of Interkosmos-19 (500-1000 km) inside the equatorial anomaly region (from -40° to +40° Dip). Waveguides are usually associated with other irregularities of various sizes in the equatorial ionosphere, some of which cause additional traces and spread F on the topside-sounding ionograms. Ducted-echo characteristics observed with Interkosmos-19 are different from those observed earlier with the Alouette and ISIS satellites. This difference is discussed. It is shown that the ionospheric plasma irregularities responsible for the waveguides are observed much more often during nighttime than during daytime.

Karpachev, A. T.; Zhbankov, G. A.; Kuleshova, V. P.; Telegin, V. A.

2014-12-01

116

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

117

Spread F - an old equatorial aeronomy problem finally resolved?  

NASA Astrophysics Data System (ADS)

One of the oldest scientific topics in Equatorial Aeronomy is related to Spread-F. It includes all our efforts to understand the physical mechanisms responsible for the existence of ionospheric F-region irregularities, the spread of the traces in a night-time equatorial ionogram - hence its name - and all other manifestations of the same. It was observed for the first time as an abnormal ionogram in Huancayo, about 70 years ago. But only recently are we coming to understand the physical mechanisms responsible for its occurrence and its capricious day to day variability. Several additional techniques have been used to reveal the spatial and temporal characteristics of the F-region irregularities responsible for the phenomenon. Among them we have, in chronological order, radio star scintillations, trans-equatorial radio propagation, satellite scintillations, radar backscatter, satellite and rocket in situ measurements, airglow, total electron content techniques using the propagation of satellite radio signals and, recently, radar imaging techniques. Theoretical efforts are as old as the observations. Nevertheless, 32 years after their discovery, Jicamarca radar observations showed that none of the theories that had been put forward could explain them completely. The observations showed that irregularities were detected at altitudes that were stable according to the mechanisms proposed. A breakthrough came a few years later, again from Jicamarca, by showing that some of the "stable" regions had become unstable by the non-linear propagation of the irregularities from the unstable to the stable region of the ionosphere in the form of bubbles of low density plasma. A problem remained, however; the primary instability mechanism proposed, an extended (generalized) Rayleigh-Taylor instability, was too slow to explain the rapid development seen by the observations. Gravity waves in the neutral background have been proposed as a seeding mechanism to form irregularities from which the instability would grow, but the former are difficult to observe as a controlling parameter. Their actual role still needs to be determined. More recently, radar observations again have shown the existence of horizontal plasma drift velocities counter streaming the neutral wind at the steep bottom of the F-region which produces a fast growing instability from which a generalized Rayleigh-Taylor instability can grow. The mechanisms proposed would explain the rapid development of the large and medium scale irregularities that have been observed, including some seen only by radars. Nevertheless, a proper quantitative theoretical mechanism that would explain how these irregularities break into the very important meter scale ones, responsible for the radar echoes, needs to be developed. This paper makes a selective historical review of the observations and proposed theories since the phenomenon was discovered to our current understanding.

Woodman, R. F.

2009-05-01

118

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

119

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

120

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

121

Guided radio-wave propagation in the equatorial ionosphere according to the Intercosmos-19 and Alouette/ISIS satellites  

NASA Astrophysics Data System (ADS)

In addition to normal vertical-incident ionogram traces, strongly remote (up to 2000 km), traces of HF-radio-signal reflections observed on topside-sounder ionograms of the Interkosmos-19 satellite obtained in the equatorial ionosphere are presented. Such traces are connected with waveguides (ducts). These waveguides are field-aligned irregularities of ionospheric plasma with electron density depletion of a few percent and cross-field dimension of a few to several kilometers. Ray tracing confirms this supposition and allows an estimate of the typical parameters of the waveguides. The waveguide traces usually start at the cutoff frequency of the main trace. However, sometimes they begin at much lower frequencies which indicate the waveguides are located in plasma bubbles. Only one ducted trace is usually observed on the Interkosmos-19 ionograms; a second conjugate trace is rarely recorded. Waveguides are observed at all heights of Interkosmos-19 (500-1000 km) inside the equatorial anomaly region (from -40 to +40 degrees DipLat). Ducted-echo characteristics observed with the Interkosmos-19 are different from those observed earlier with the Alouette and ISIS satellites. This difference is discussed. It is shown that the ionospheric plasma irregularities responsible for the waveguides are observed much more often during nighttime than during daytime.

Karpachev, Alexander; Zhbankov, Gennadii; Telegin, Viktor; Kuleshova, Valentina

122

PHYSICAL REVIEW E 86, 056407 (2012) Characterization of single and colliding laser-produced plasma bubbles using Thomson  

E-print Network

plasma, where the release of magnetic energy (thermal energy) does not appreciablyPHYSICAL REVIEW E 86, 056407 (2012) Characterization of single and colliding laser-produced plasma. J. Town,2 F. H. S´eguin,1 J. A. Frenje,1 D. H. Froula,3 and R. D. Petrasso1 1 Plasma Science

123

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

124

Low-latitude scintillation occurrences around the equatorial anomaly crest over Indonesia  

NASA Astrophysics Data System (ADS)

We investigated low-latitude ionospheric scintillation in Indonesia using two GPS receivers installed at Bandung (107.6° E, 6.9° S; magnetic latitude 17.5° S) and Pontianak (109.3° E, 0.02° S; magnetic latitude 8.9° S). This study aimed to characterise climatological and directional ionospheric scintillation occurrences, which are useful not only for the physics of ionospheric irregularities but also for practical use in GNSS (global navigation satellite system)-based navigation. We used the deployed instrument's amplitude scintillation (S4 index) data from 2009, 2010, and 2011; the yearly SSN (sunspot-smoothed numbers) were 3.1, 16.5, and 55.9, respectively. In summary, (1) scintillation occurrences in the post-sunset period (18:00-01:00 LT) during equinox months (plasma bubble season) at the two sites can be ascribed to the plasma bubble; (2) using directional analyses of the two sites, we found that the distribution of scintillation occurrences is generally concentrated between the two sites, indicating the average location of the EIA (equatorial ionisation anomaly) crest; (3) scintillation occurrence enhancements for the two sites in field-aligned directions are herein reported for the first time by ground-based observation in a low-latitude region; (4) distribution of scintillation occurrences at Pontianak are concentrated in the southern sky, especially in the southwest direction, which is very likely associated with the plasma bubble tilted westward with increasing latitude; and (5) scintillation occurrence in the post-midnight period in the non-plasma-bubble season is the most intriguing variable occurring between the two sites (i.e. post-midnight scintillations are observed more at Bandung than Pontianak). Most of the post-midnight scintillations observed at Bandung are concentrated in the northern sky, with low elevation angles. This might be due to the amplitude of irregularities in certain directions, which may be effectively enhanced by background density enhancement by the EIA and because satellite-receiver paths are longer in the EIA crest region and in a field-aligned direction.

Abadi, P.; Saito, S.; Srigutomo, W.

2014-01-01

125

The Colorado Equatorial Sundial  

Microsoft Academic Search

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

R. H. Garstang

1996-01-01

126

Equatorial MST radars: Further consideration  

NASA Technical Reports Server (NTRS)

The results presented give additional support to the need of equatorial MST radars in order to obtain more information on the nature of equatorial waves in the MST region. Radar deduced winds such as obtained at Jicamarca for periods of months indicate that with these data the full range of equatorial waves, with time scales of seconds to years, can be studied.

Lagos, P.

1983-01-01

127

Height dependence of spread F bubble drift velocities  

NASA Technical Reports Server (NTRS)

Vertical bubble velocities in equatorial spread F have been investigated analytically by Ott (1978), Osakow and Chaturvedi (1978), all of whom found a proportionality of the vertical velocity to bubble depletion density. The paper presents radar data from two equatorial sites which support theoretical predictions that vertical drift velocities of spread F bubbles increase with height on the bottomside of the F layer. This increase is shown to result from the proportionality of bubble drift velocity to density depletion amplitude, which itself increases with height. The measured rate of increase is found to be dU/dh equals about 2 m/s km. It is concluded that this is consistent with numerical simulation results within a factor of 2.

Hudson, M. K.; Balsley, B. B.

1979-01-01

128

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

129

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

130

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

131

Mercury Bubbles  

Microsoft Academic Search

I HAVE on several occasions noticed the beautiful bubbles described by Mr. Wright and Sir William Crookes (pp. 8 and 37). On each occasion I was purifying mercury in the following way. I half filled a rather large Woulffe's bottle with mercury and poured on to it weak nitric acid. Then, in order to keep, the whole in a state

A. T. Hare

1908-01-01

132

Equatorial scintillations - A review  

NASA Technical Reports Server (NTRS)

Scintillation observations of equatorial irregularities by techniques such as in situ, radar backscatter, airglow, and total electron content are reviewed, with an emphasis on GHz measurements. New aspects of the spread-F analysis from ionograms are mentioned, followed by a discussion of scintillation morphology, and the longitudinal control of the equatorial scintillations is emphasized. A coordinated multitechnique observation of the equatorial irregularities is described in detail, the study being divided into two parts: (1) an examination of the large field-aligned irregularity structures and their association with discrete patches of scintillation activity, and (2) an investigation of the coexistence of km-scale-irregularities with meter scales and a description of the evolution of the irregularity and scintillation spectra during the various phases of irregularity generation and decay. Unsolved problems are also reviewed, e.g., it is stated that the effects of steep spatial gradients in the electron density structures and their subsequent erosion on both CW and pulse propagation need to be evaluated both from the point of view of theory and experiments.

Basu, S.; Basu, S.

1981-01-01

133

Equatorial Electrojet Observations in the African Continent  

NASA Astrophysics Data System (ADS)

Although Satellite observations in the African sector show unique equatorial ionospheric structures that can severely impact navigation and communication systems, the study of ionospheric disturbances in this region is difficult due to the lack of ground-based instruments. This has created a gap in global understanding of the physics behind the evolution and formation of plasma irregularities in the equatorial region, which imposes limitations on ionospheric density modeling efforts. Therefore, in order to have a more complete global understanding of equatorial ionosphere motion, the international space science community has begun to develop an observational infrastructure in the African sector. This includes the deployment of a number of arrays of small instruments, including the AMBER magnetometer array, through the International Heliophysical Year (IHY) cooperative program with the United Nations Basic Space Science (UNBSS) program. Two AMBER magnetometers have been deployed successfully at Adigrat (~6°N magnetic) in Ethiopia and at Medea in Algeria (28°N magnetic), and became fully operational on 03 August 2008. The remaining two AMBER magnetometers will be deployed soon in Cameroon and Namibia. One of the prime scientific objectives of AMBER is to understand the processes governing electrodynamics of the equatorial ionosphere as a function of latitude, local time, magnetic activity, and season in the African region. The most credible driving mechanism of ionospheric plasma (E × B drift) can be estimated using two magnetometers, one right at the equator and the other about 6 off the equator. Therefore, using the AMBER magnetometer at Adigrat and the INTERMAGNET magnetometer located at Addis Ababa (0.9°N magnetic) in Ethiopia, the equatorial electrojet (E × B drift) activities in that longitudinal sector of the African continent is estimated. The paper also presents the comparison between the estimated vertical drift and the drift values obtained from the vector electric field instrument observation onboard the C/NOFS satellite. The evolution of equatorial ionospheric irregularities will also be presented using data from the growing number of ground- and space-based (on Low-Earth-Orbit (LEO) satellites) GPS receivers in the African region.

Yizengaw, E.; Moldwin, M. B.; Mebrahtu, A.; Damtie, B.; Pfaff, R.; Zesta, E.

2008-12-01

134

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

135

Equatorial oceanography. [review of research  

NASA Technical Reports Server (NTRS)

United States progress in equatorial oceanography is reviewed, focusing on the low frequency response of upper equatorial oceans to forcing by the wind. Variations of thermocline depth, midocean currents, and boundary currents are discussed. The factors which determine sea surface temperature (SST) variability in equatorial oceans are reviewed, and the status of understanding of the most spectacular manifestation of SST variability, the El Nino-Southern Oscillation phenomenon, is discussed. The problem of observing surface winds, regarded as a fundamental factor limiting understanding of the equatorial oceans, is addressed. Finally, an attempt is made to identify those current trends which are expected to bear fruit in the near and distant future.

Cane, M. A.; Sarachik, E. S.

1983-01-01

136

In-situ observation of abnormal electron temperure in the F-region valley associated with the prereversal enhancement in the vertical plasma drift  

NASA Astrophysics Data System (ADS)

During one of the post sunset rocket launches made on 18-th December 1995 from the equatorial rocket launching station CLA in Alcântara, Brazil a 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. 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, probably associated with the prereversal enhancement in the vertical plasma drift. 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 during the rocket launch clearly showed the rapid rise of the F-region base indicating the prereversal enhancement of the F-region vertical drift. At the time of launch the bubble activity was also 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 of electron temperatures as high as 2000 ºK while the temperatures expected from the existing models are around 500 ºK. A two stage VS-30/Orion rocket was again launched on 8-th December 2012 soon after sunset carrying a Langmuir Probe operating alternately in swept and constant bias modes. At the time of launch ground equipments operated at equatorial stations showed rapid rise in the base of the F-layer and creating ionospheric conditions favorable for the generation of plasma bubbles. Electron temperatures as high as 3500ºK were observed in the valley region during the rocket upleg and downleg. 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, Polinaya; Batista, Inez S.; Odriozola, Siomel

137

On the Geometrical Aspects of GPS Scintillations during the Conjugate Point Equatorial Experiment (copex) Campaign in Brazil  

NASA Astrophysics Data System (ADS)

We examine the geometrical aspects of GPS scintillations at three locations in Brazil during the Oct-Dec 2002 Conjugate Point Equatorial Experiment (COPEX): Boa Vista (2.85N, 60.70°W, dip 12.60°N); Alta Floresta (9.87°S, 56.1°W, dip 0.75°S); and Campo Grande (20.47°S, 54.66°W, dip 10.77°S). Previous authors [Muella et al., 2008; de Paula et al., 2010] have established the association between the GPS scintillations during the campaign and equatorial plasma bubbles generated by plasma interchange instabilities after sunset. Our aim is to demonstrate the effect of satellite motion and the direction of signal propagation with respect to the magnetic field on the depth and rate of signal fading, both of which affect the probability of scintillation-induced loss of lock on the GPS signals and degrade GPS positioning accuracy [Humphreys et al., 2010; Carrano et al., 2010]. We report on the behavior of the scintillation intensity index (S4) and the intensity decorrelation time (?) as a function of dip latitude, local time, and the speed and direction at which the line of sight scans through the drifting plasma irregularities. We remove the geometrical effects using weak scatter diffraction theory to estimate the turbulent intensity and spatial decorrelation length in the magnetic west-east direction. From these parameters, it is possible to infer the depth and rate of signal fading for any propagation geometry in the region, a capability which is needed for modeling GPS scintillation impacts on GPS positioning accuracy.

Carrano, C. S.; Valladares, C. E.; Groves, K.

2011-12-01

138

Characterization of breakdown and sustaining of a discharge in a gas bubble in water  

Microsoft Academic Search

Breakdown mechanism in water are not well understood. In the present study, we focus both on the ignition and propagation of the plasma in a bubble\\/water bi-phasic medium, as well as on the sustaining of DC plasmas in a gas bubble. Two geometries are studied : either the bubble is localized in a water filled capillary, or it is surrounded

P. Ceccato; A. Rousseau

2008-01-01

139

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

140

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

141

Structure and dynamics of the wake of bubbles and its relevance for bubble interaction  

NASA Astrophysics Data System (ADS)

The flow in the wake of single and two interacting air bubbles freely rising in water is studied experimentally using digital-particle-image-velocimetry in combination with high-speed recording. The experiments focus on ellipsoidal bubbles of diameter of about 0.4-0.8 cm which show spiraling, zigzagging, and rocking motion during their rise in water, which was seeded with small tracer particles for flow visualization. Under counterflow conditions in the vertical channel, the bubbles are retained in the center of the observation region, which allows the wake oscillations and bubble interaction to be observed over several successive periods. By simultaneous diffuse illumination in addition to the light sheet, we were able to record both the path and shape oscillations of the bubble, as well as the wake structure in a horizontal and vertical cross section. The results show that the zigzagging motion is coupled to a regular generation and discharge of alternate oppositely oriented hairpin-like vortex structures. Associated with the wake oscillation, the bubble experiences a strong asymmetric deformation in the equatorial plane at the inversion points of the zigzag path. The zigzag motion is superimposed on a small lateral drift of the bubble, which implies the existence of a net lift force. This is explained by the observed different strength of the hairpin vortices in the zig and zag path; a seemingly familiar phenomenon was found in recent numerical results of the sphere wake flow. For spiraling bubbles the wake is approximately steady to an observer moving with the bubble. It consists of a twisted pair of streamwise vortex filaments which are wound in a helical path and are attached to the bubble base at an asymmetrical position. The minor axis of the bubble is tilted in the tangential plane as well as in the radial plane toward the spiral center. Due to the pressure field induced by the asymmetrically attached wake two components of the lift force exist, one that causes the lateral motion and the other a centripetal force that keeps the bubble on a circular path. A mechanism is proposed to explain the reason for one bubble to spiral or to zigzag. Experiments with two simultaneous released bubbles show that bubble interaction is strongly triggered by the wake dynamics. Once a bubble is captured in the wake of a rocking bubble, it accelerates and rises via successive jumps until they collide. The jumps are explained by the upwards induction effect of the ring-like heads of the hairpin vortices being shed from the leading bubble. The final collision and repulsion thereafter abruptly enlarges the wake for a short moment, which is suggested to be one major contribution to the amplification of turbulence production in bubbly flows.

Brücker, Christoph

1999-07-01

142

Digital ionosonde observations during equatorial spread F  

NASA Astrophysics Data System (ADS)

Equatorial spread F data taken with a digital ionosonde/HF radar located at Huancayo, Peru, are presented and discussed. A modified phenomenology is developed which used the system's ability to do echo location. The onset of irregularities is seen to occur in the east and to move westward, while inside this large-scale structure the plasma is found to drift eastward. A very curious difference has been identified between spread F observations with the ionosonde and with the VHF radar at Jicamarca. At VHF, spread F onset often occurs when the ionosphere is rising, whereas in all five examples presented the digital ionosonde detected onset when the apparent ionosphere motion was downward. The result even held on the one night of common data taking. The effect could be instrumental, but maybe related to the considerable orographic differences in the two sites. During one night, data were obtained simultaneously with the HF radar, a rocket, and the Jicamarca VHF radar; comparisons of these data are discussed in detail. Additional evidence is presented that acoustic gravity waves play a role in the development of equatorial spread F and in the formation of detached plumes. To be self-consistent, the gravity waves must come from nearby sources such as the tropical rain forest to the east of Jicamarca.

Argo, P. E.; Kelley, M. C.

1986-05-01

143

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

144

Vortex centrifugal bubbling reactor  

Microsoft Academic Search

The vortex centrifugal bubbling apparatus is considered as a basis for a new type of multiphase vortex centrifugal bubbling reactor. In this device, a highly dispersed gas–liquid mixture is produced in the field of centrifugal forces inside the vortex chamber. The operation of the vortex centrifugal bubbling apparatus is based on the rotation of liquid by the tangential entry of

A. O. Kuzmin; M. Kh. Pravdina; A. I. Yavorsky; N. I. Yavorsky; V. N. Parmon

2005-01-01

145

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

146

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

147

Asymmetric propagation of flare-generated shocks in the heliospheric equatorial plane  

Microsoft Academic Search

A numerical simulation study is presented in this paper in terms of a two-dimensional, two-component MHD Inodel, concerning the propagation of flare-generated shocks in the heliospheric equatorial plane. The numerical results show that the spiral interplanetary magnetic field and the heliospheric plasma sheet in the equatorial plane have a significant influence on the shock propagation. When the shock source lies

Y. Q. Hu

1998-01-01

148

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

149

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

150

Bubble domain circuit organization  

NASA Technical Reports Server (NTRS)

An on-chip bubble domain circuit organization. One or more storage registers are connected to a propagation path whereby data in the form of magnetic bubble domains (bubbles) may be transferred into and out of the storage registers. The propagation path includes a generator for producing the initial bubbles which are expanded into any desired number of new bubbles by a unique multiple output replicator. A unique input decoder is utilized to determine to which storage register the bubbles from the replicator will be directed along the propagation path. Those bubbles not selected may be annihilated. An output decoder utilizing essentially the same decoding scheme as the input decoder, selectively receives bubbles from the storage register. A transfer and replicate switch is utilized between the storage register and output decoder to selectively transfer bubbles to the output decoder. The output decoder may collapse all of the bubbles from certain storage registers so that only the information from the selected storage register reaches the detector. The detectors in turn produce the chip output signal. External control electronics are utilized to control the selective operation of the various devices utilized in the propagation path.

Chen, Thomas T. (Inventor)

1977-01-01

151

C/NOFS Satellite Electric Field and Plasma Density Observations of Plasma Instabilities Below the Equatorial F-Peak -- Evidence for Approximately 500 km-Scale Spread-F "Precursor" Waves Driven by Zonal Shear Flow and km-Scale, Narrow-Banded Irregularities  

NASA Technical Reports Server (NTRS)

As solar activity has increased, the ionosphere F-peak has been elevated on numerous occasions above the C/NOFS satellite perigee of 400km. In particular, during the month of April, 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set (to our knowledge): The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second new result (for C/NOFS) is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is below the F -peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field component of these waves is strongest in the zonal direction. These waves are strongly correlated with simultaneous observations of plasma density oscillations and appear both with, and without, evidence of larger-scale spread-F depletions. These km-scale, quasi-coherent waves strongly resemble the bottomside, sinusoidal irregularities reported in the Atmosphere Explorer satellite data set by Valladares et al. [JGR, 88, 8025, 1983]. We interpret these new observations in terms of fundamental plasma instabilities associated with the unstable, nighttime equatorial ionosphere.

Pfaff, R.; Freudenreich, H.; Klenzing, J.; Liebrecht, C.; Valladares, C.

2011-01-01

152

Soap and Bubbles  

NSDL National Science Digital Library

The first Web site, from The Soap and Detergent Association, is called Soaps and Detergents (1). Visitors learn about the chemistry of soap and detergent, their history, how they're manufactured, and more. The easily read text and fun illustrations make this site a great place to start for this topic. The next site, called Bubble Engineering (2), is provided by Bubble Town. The page describes the physics of a cone-shaped bubble blowing device and how its shape reduces the velocity of air being blown through but not the volume of air moving through it. Other links on the site describe what the contents of the best bubble soap mixture. The third site is provided by Kevin Dunn of Hampden-Sydney College Department of Chemistry called Lye Soap (3). The site describes how soap was invented, the chemistry of lye and soap, how to make your own lye, and more. The fourth site highlighted is part of LessonPlansPage.com called Looking at Bubbles (4). The site, which is a lesson plan, is geared towards students between grades 6 and 8. The main objective of the chemistry activity is to explore what things can be added to soap to make the bubbles last longer. All procedures are provided to view online or to print. The Art and Science of Bubbles (5) Web site is maintained by the Soap and Detergent Association. Many great features can be found on this and other pages within the site, including washing hands with soap, the history and chemistry of soaps and detergents, the environmentally smart way of using and disposing of cleaning products, and more. The sixth site related to soap is entitled Bubble Games (6), which is maintained by bubbles.org. Three free games are offered here including Tic-Tac-Bubble, Bubblechase, and Bubble Wrap, which counts how many bubbles you can pop in twenty seconds. Next, from the Homeschooling page of About.com comes the Soap Power (7) activity. This unique lesson plan details how to power a model boat using soap as a result of its surface tension. Lastly, the Bubble Hydrodynamics (8) Web site is maintained by bubbleology.com. Visitors get an introduction to bubble hydrodynamics and also learn about the relationship between temperature and bubbles, surfactants and bubbles, and even oscillations and bubbles.

Brieske, Joel A.

2002-01-01

153

Magnetic bubble materials.  

PubMed

Physicists, materials scientists, and engineers combined to bring solid-state bubble devices into the computer memory and recording marketplace. Devices with smaller bubbles are being developed for increased data capacity and lower cost. Epitaxial garnet films made by isothermal dipping in molten solutions helped put the technology in place and will probably satisfy the material needs of future devices with bubbles scaled down from 2 to 0.5 micrometer in size. PMID:17772820

Giess, E A

1980-05-23

154

Bubbles: Using Controls  

NSDL National Science Digital Library

In this experiment, learners use JOY liquid detergent and glycerin to make the largest bubble they can that lasts 15 seconds. They blow the bubbles in a Teaching Tank, a narrow tank that is commercially available, which allows them to easily measure and monitor the bubbles. Results are collected and graphed by learners. Questions and teaching notes are included to encourage learners to consider what the multiple variables are, and what the effects of sugar, corn syrup, or other sweeteners are on their bubbles.

2012-06-26

155

A Bubble Full of Sunshine  

NSF Publications Database

... 05-030A Bubble Full of Sunshine Temperatures inside bursting bubbles can be four times hotter than ... of Illinois have determined that temperatures inside gas bubbles collapsing in a liquid reach ...

156

Scaling electron acceleration in the bubble regime for upcoming lasers  

NASA Astrophysics Data System (ADS)

Electron acceleration in the laser-plasma bubble appeared to be the most successful regime of laser wake field acceleration in the last decade. The laser technology became mature enough to generate short and relativistically intense pulses required to reach the bubble regime naturally delivering quasi-monoenergetic bunches of relativistic electrons. The upcoming laser technology projects are promising short pulses with many times more energy than the existing ones. The natural question is how will the bubble regime scale with the available laser energy. We present here a parametric study of laser-plasma acceleration in the bubble regime using full three dimensional particle-in-cell simulations and compare numerical results with the analytical scalings from the relativistic laser-plasma similarity theory.

Jansen, O.; Tückmantel, T.; Pukhov, A.

2014-05-01

157

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

158

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

159

Gases in Tektite Bubbles.  

PubMed

Spectroscopic analysis of light produced by electrodeless discharge in a tektite bubble showed the main gases in the bubble to be neon, helium, and oxygen. The neon and helium have probably diffused in from the atmosphere, while the oxygen may be atmospheric gas incorporated in the tektite during its formation. PMID:17801113

O'keefe, J A; Lowman, P D; Dunning, K L

1962-07-20

160

Radio wave scintillations at equatorial regions  

NASA Technical Reports Server (NTRS)

Radio waves, passing through the atmosphere, experience amplitude and phase fluctuations know as scintillations. A characterization of equatorial scintillation, which has resulted from studies of data recorded primarily in South America and equatorial Africa, is presented. Equatorial scintillation phenomena are complex because they appear to vary with time of day (pre-and postmidnight), season (equinoxes), and magnetic activity. A wider and more systematic geographical coverage is needed for both scientific and engineering purposes; therefore, it is recommended that more observations should be made at earth stations (at low-geomagnetic latitudes) to record equatorial scintillation phenomena.

Poularikas, A. D.

1972-01-01

161

MJO, Equatorial Waves, and Tropical Cyclogenesis  

NSDL National Science Digital Library

This case study focuses on monitoring of the MJO and equatorial waves and their role in tropical cyclogenesis. Learners will use conceptual models to understand the structure of the MJO and equatorial waves. They will identify and monitor those circulations using geostationary satellite images. 850-hPa synoptic analysis is used to track equatorial Rossby and mixed Rossby-gravity waves. Focus is on May 2002, a period when an MJO and associated equatorial waves spawned sets of twin cyclones over the Indian Ocean. This case study is similar to a synoptic meteorology laboratory exercise but is designed for use in an online course.

Comet

2012-11-13

162

Anomalous opening of the Equatorial Atlantic due to an equatorial mantle thermal minimum  

Microsoft Academic Search

The geology of the Equatorial Atlantic is dominated by a broad east-west megashear belt where a cluster of large fracture zones offsets anomalously deep segments of the Mid-Atlantic Ridge (MAR). The origin and evolution of this megashear region may lie ultimately in an equatorial mantle thermal minimum. The notion of a mantle thermal minimum in the Equatorial Atlantic is supported

Enrico Bonatti

1996-01-01

163

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

164

Tribonucleation of bubbles  

PubMed Central

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

2014-01-01

165

Time-resolved characterization of a pulsed discharge in a stationary bubble  

NASA Astrophysics Data System (ADS)

In recent years, plasma generation in water has been proposed for the application of water treatment. The process efficiency is believed to be improved by the introduction of bubbles in the plasma active region. For further optimization, the initiating and developmental mechanisms of plasma inside bubbles need to be understood to a greater extent. In order to meet this necessity, we investigated pulsed electrical discharge inside a stationary bubble in water. This paper deals with the evolution of the discharge and of the bubble shape during discharge, investigated by electrical characterization and fast imaging. Only several microseconds after the application of the voltage pulse, plasma light is observed. Different phases are observed during plasma formation. The plasma is strongest at the bubble surface, causing the surrounding water to evaporate. This leads to both the formation of propagating streamers into the water and the expansion and collapse of the bubble. These observations show that plasma inside a bubble has the strongest activity at the bubble surface, making it attractive for water treatment.

Vanraes, P.; Nikiforov, A.; Lessiak, M.; Leys, C.

2012-12-01

166

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

167

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

168

Resent Status of ITER Equatorial Launcher Development  

SciTech Connect

The ITER equatorial launcher is divided into a front shield and a port plug. The front shield is composed of fourteen blanket shield modules so as to form three openings for the injection of mm-wave beams into plasma. Twenty-four waveguide transmission lines, internal shields, cooling pipes and so on are installed in the port plug. The transmission lines consist of the corrugated waveguides, miter bends and the free space propagation region utilizing two mirrors in front of the waveguide outlet. The analysis of mm-wave beam propagation in the region shows that the transmission efficiency more than 99.5% is attained. The high power experiments of the launcher mock-up have been carried out and the measured field patterns at each mirror and the outlet of the launcher are agreed with the calculations. It is concluded that the transmission line components in the launcher mock-up are fabricated as designed and the present mm-wave design in the launcher is feasible.

Takahashi, K.; Kajiwara, K.; Kasugai, A.; Oda, Y.; Kobayashi, N.; Sakamoto, K. [Japan Atomic Energy Agency, 801-1, Naka Ibaraki, 311-0193 (Japan)

2009-11-26

169

Gravity wave effects on postsunset equatorial F region stability  

NASA Astrophysics Data System (ADS)

The influence of gravity waves on the stability of the postsunset equatorial F region ionosphere is investigated numerically. For this investigation, we use the output of a direct numerical simulation of waves and turbulence in the mesosphere and lower thermosphere to force a simulation of ionospheric dynamics. Both simulations are cast in three dimensions. The effectiveness of the neutral-plasma coupling involved is generally thought to depend on the dynamo efficiency and spatial resonance of the forcing, which we evaluate. In our simulations, the postsunset equatorial ionosphere could be deformed by neutral waves after 5-15 min most severely when the wavefronts were aligned approximately with the magnetic meridian, despite the fact that the dynamo efficiency is modest even in that case. However, poor spatial resonance limits the subsequent growth of the deformations in our simulations, and the seeding of interchange instabilities does not occur. The coupled simulations predict the formation of intermediate layers in the equatorial valley region (150-250 km apex altitude) under some circumstances that could serve as telltales in nature of the presence of the kind of neutral forcing we simulate.

Hysell, D. L.; Jafari, R.; Fritts, D. C.; Laughman, B.

2014-07-01

170

Azimuthal plasma pressure gradient in quiet time plasma sheet  

Microsoft Academic Search

We have investigated the quiet-time azimuthal plasma pressure gradient in the plasma sheet at a radial distance of 10 RE to 12 RE using two THEMIS spacecraft that were in overlapping orbits during the 2008 THEMIS tail season. The equatorial plasma pressure is estimated by using the in-situ measurement of the plasma pressure and magnetic pressure based on pressure balance

X. Xing; L. R. Lyons; V. Angelopoulos; D. Larson; J. McFadden; C. Carlson; A. Runov; U. Auster

2009-01-01

171

Absolute electron density measurements in the equatorial ionosphere  

NASA Technical Reports Server (NTRS)

Accurate measurement of the electron density profile and its variations is crucial to further progress in understanding the physics of the disturbed equatorial ionosphere. To accomplish this, a plasma frequency probe was included in the payload complement of two rockets flown during the Condor rocket campaign conducted from Peru in March 1983. This paper presents density profiles of the disturbed equatorial ionosphere from a night-time flight in which spread-F conditions were present and from a day-time flight during strong electrojet conditions. Results from both flights are in excellent agreement with simultaneous radar data in that the regions of highly disturbed plasma coincide with the radar signatures. The spread-F rocket penetrated a topside depletion during both the upleg and downleg. The electrojet measurements showed a profile peaking at 1.3 x 10 to the 5th per cu cm at 106 km, with large scale fluctuations having amplitudes of roughly 10 percent seen only in the upward gradient in electron density. This is in agreement with plasma instability theory. It is further shown that simultaneous measurements by fixed-bias Langmuir probes, when normalized at a single point to the altitude profile of electron density, are inadequate to correctly parameterize the observed enhancements and depletions.

Baker, K. D.; Howlett, L. C.; Rao, N. B.; Ulwick, J. C.; Labelle, J.

1985-01-01

172

Fermi gamma -ray `bubbles' from stochastic acceleration of electrons  

NASA Astrophysics Data System (ADS)

Gamma-ray data from the Fermi-LAT show a bi-lobular structure extending up to 50 degrees above and below the Galactic centre, coincident with a possibly related structure in the ROSAT X-ray map. It has been argued that the gamma -rays arise due to inverse Compton scattering of relativistic electrons accelerated at plasma shocks present in the bubbles. We explore the alternative possibility that the relativistic electrons undergo stochastic 2nd-order Fermi acceleration in the entire volume of the bubbles by plasma wave turbulence. This turbulence is generated behind the outer shock and propagates into the bubble volume, leading to a non-trivial spatial variation of the electron spectral index. Rather than a constant volume emissivity as predicted in other models we find an almost constant surface brightness in gamma -rays and also reproduce the observed sharp edges of the bubbles. We comment on possible cross-checks in other channels.

Mertsch, Philipp; Sarkar, Subir

173

The thermodynamics of bubbles  

E-print Network

This paper outlines those concitions annanded by the laws of thermodynamics for equilibriza betwoen the vapor in a bubble and the surrounding liquid and then employs these concepts with a nucleation theory in an atteapt ...

Clark, John A.

1956-01-01

174

Black-hole bubbles  

SciTech Connect

If theories of high-energy physics such as spontaneous symmetry breaking and quantum chromodynamics are correct, then exploding black holes will be surrounded by phase-transition bubbles or fireballs, supported by the pressure of particles trapped inside a high-temperature phase. For quark-gas fireballs, where there is a hadron bag with a hole in it, this enhances the ..gamma..-ray emission by a factor of 69 which could lead to a feature in the ..gamma..-ray background around 200 MeV. For other bubbles there may be detectable electromagnetic pulses produced by the Rees mechanism when the bubble bursts, particularly for the inflated bubbles which result from the models suggested by the inflationary-universe scenario.

Moss, I.G.

1985-09-15

175

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

176

2012 Problem 8: Bubbles  

NASA Astrophysics Data System (ADS)

When a large number of bubbles exist in the water, an object may float on the surface or sink. The assumption of equivalent density is proposed in this article to explain the concrete example. According to the assumption, an object is floatable only if its density is less than the equivalent density of the water-bubble mixture. This conclusion is supported by the floating experiment and by measuring the pressure underwater to a satisfactory approximation.

Zhu, Kejing; Xia, Qing; Wang, Sihui; Zhou, Huijun

2015-10-01

177

Satellite traces: An ionogram signature for large-scale wave structure and a precursor for equatorial spread F  

Microsoft Academic Search

Although the source that controls day-to-day variability in the occurrence of equatorial plasma structure (i.e., equatorial spread F, or ESF) remains to be identified, progress is being made. There is evidence that the appearance of large-scale wave structure (LSWS) in the bottomside F layer, around the time of its post-sunset rise (PSSR), is a more-direct precursor of ESF than the

Roland T. Tsunoda

2008-01-01

178

Nonplanar mhd model for solar flare-generated disturbances in the heliospheric equatorial plane  

Microsoft Academic Search

An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier

S. T. Wu; M. Dryer; S. M. Han

1983-01-01

179

Equatorial Superrotation on Tidally Locked Exoplanets  

NASA Astrophysics Data System (ADS)

The increasing richness of exoplanet observations has motivated a variety of three-dimensional (3D) atmospheric circulation models of these planets. Under strongly irradiated conditions, models of tidally locked, short-period planets (both hot Jupiters and terrestrial planets) tend to exhibit a circulation dominated by a fast eastward, or "superrotating," jet stream at the equator. When the radiative and advection timescales are comparable, this phenomenon can cause the hottest regions to be displaced eastward from the substellar point by tens of degrees longitude. Such an offset has been subsequently observed on HD 189733b, supporting the possibility of equatorial jets on short-period exoplanets. Despite its relevance, however, the dynamical mechanisms responsible for generating the equatorial superrotation in such models have not been identified. Here, we show that the equatorial jet results from the interaction of the mean flow with standing Rossby waves induced by the day-night thermal forcing. The strong longitudinal variations in radiative heating—namely intense dayside heating and nightside cooling—trigger the formation of standing, planetary-scale equatorial Rossby and Kelvin waves. The Rossby waves develop phase tilts that pump eastward momentum from high latitudes to the equator, thereby inducing equatorial superrotation. We present an analytic theory demonstrating this mechanism and explore its properties in a hierarchy of one-layer (shallow-water) calculations and fully 3D models. The wave-mean-flow interaction produces an equatorial jet whose latitudinal width is comparable to that of the Rossby waves, namely the equatorial Rossby deformation radius modified by radiative and frictional effects. For conditions typical of synchronously rotating hot Jupiters, this length is comparable to a planetary radius, explaining the broad scale of the equatorial jet obtained in most hot-Jupiter models. Our theory illuminates the dependence of the equatorial jet speed on forcing amplitude, strength of friction, and other parameters, as well as the conditions under which jets can form at all.

Showman, Adam P.; Polvani, Lorenzo M.

2011-09-01

180

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. PMID:19547725

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

2008-01-01

181

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

182

Simulations of Hot Bubbles in the ICM  

E-print Network

We review the general properties of the intracluster medium (ICM) in clusters that host a cooling flow, and in particular the effects on the ICM of the injection of hot plasma by a powerful active galactic nucleus (AGN). It is observed that, in some cases, the hot plasma produces cavities in the ICM that finally detach and rise, perhaps buoyantly. The gas dynamics induced by the rising bubbles can help explain the absence of a cooled gas component in clusters with a cooling flow. This scenario is explored using numerical simulations.

A. Gardini; P. M. Ricker

2004-09-15

183

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

184

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

185

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

186

Effect of direct bubble-bubble interactions on linear-wave propagation in bubbly liquids  

NASA Astrophysics Data System (ADS)

We study the influence of bubble-bubble interactions on the propagation of linear acoustic waves in bubbly liquids. Using the full model proposed by Fuster and Colonius [J. Fluid Mech. 688, 253 (2011), 10.1017/jfm.2011.380], numerical simulations reveal that direct bubble-bubble interactions have an appreciable effect for frequencies above the natural resonance frequency of the average size bubble. Based on the new results, a modification of the classical wave propagation theory is proposed. The results obtained are in good agreement with previously reported experimental data where the classical linear theory systematically overpredicts the effective attenuation and phase velocity.

Fuster, D.; Conoir, J. M.; Colonius, T.

2014-12-01

187

The storm-time equatorial electrojet  

NASA Technical Reports Server (NTRS)

A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed and the large field depression, at the flight time, must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

1976-01-01

188

The storm-time equatorial electrojet  

NASA Technical Reports Server (NTRS)

A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed, and the large field depression at the flight time must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

Burrows, K.; Sastry, T. S. G.; Sampath, S.; Stolarik, J. D.; Usher, M. J.

1977-01-01

189

Genesis of Intraseasonal Oscillations and Equatorial Waves  

Microsoft Academic Search

The particular role of evaporation-wind feedback, and as well cumulus convection and dissipation, in the formation of the Madden-Julian 30-60-day intraseasonal oscillation (MJO) and equatorially trapped waves, including Kelvin, equatorial Rossby, mixed Rossby-gravity, and eastward inertio-gravity waves, has been studied using a global two-level primitive equation instability model. The evaporation has been specified through a bulk aerodynamic formula, and the

Jorgen S. Frederiksen

2002-01-01

190

The Fermi Bubbles  

NASA Astrophysics Data System (ADS)

The Fermi Bubbles are a pair of giant lobes at the heart of the Milky Way, extending roughly 50 degrees north and south of the Galactic Center, and emitting photons with energies up to 100 GeV. This previously unknown structure could be evidence for past activity of the central supermassive black hole, or enhanced star formation towards the inner Galaxy. We will describe the path to discovery of the Bubbles in multiwavelength data, from the first hints in microwave radiation measured by WMAP and X-rays from ROSAT, to the unveiling of their shape and spectrum using public gamma-ray data from the Fermi Gamma-ray Space Telescope, to more recent measurements by Planck and XMM-Newton. We will outline the current state of knowledge of the Bubbles' spectrum, morphology and internal structure, and discuss theoretical proposals and numerical simulations for their nature and origin.

Finkbeiner, Douglas P.

2015-01-01

191

Multivariate bubbles and antibubbles  

NASA Astrophysics Data System (ADS)

In this paper we develop models for multivariate financial bubbles and antibubbles based on statistical physics. In particular, we extend a rich set of univariate models to higher dimensions. Changes in market regime can be explicitly shown to represent a phase transition from random to deterministic behaviour in prices. Moreover, our multivariate models are able to capture some of the contagious effects that occur during such episodes. We are able to show that declining lending quality helped fuel a bubble in the US stock market prior to 2008. Further, our approach offers interesting insights into the spatial development of UK house prices.

Fry, John

2014-08-01

192

Bubbles from nothing  

SciTech Connect

Within the framework of flux compactifications, we construct an instanton describing the quantum creation of an open universe from nothing. The solution has many features in common with the smooth 6d bubble of nothing solutions discussed recently, where the spacetime is described by a 4d compactification of a 6d Einstein-Maxwell theory on S{sup 2} stabilized by flux. The four-dimensional description of this instanton reduces to that of Hawking and Turok. The choice of parameters uniquely determines all future evolution, which we additionally find to be stable against bubble of nothing instabilities.

Blanco-Pillado, Jose J.; Ramadhan, Handhika S.; Shlaer, Benjamin, E-mail: jose@cosmos.phy.tufts.edu, E-mail: handhika@cosmos.phy.tufts.edu, E-mail: shlaer@cosmos.phy.tufts.edu [Institute of Cosmology, Department of Physics and Astronomy, Tufts University, 212 College Ave, Medford, MA 02155 (United States)

2012-01-01

193

Magnetic bubble memories  

NASA Astrophysics Data System (ADS)

The role of magnetic bubble memories in systems is investigated by a review of their functions and construction. Propagation, which is achieved by varying localized magnetic field gradients, and detection, which is achieved by the magnetoresistive effect, are discussed. Board-level products, board or boxed subsystems, and custom designed systems are described, and military applications such as the PBM 90M (1 Mbyte module) for FHD replacement systems are presented. Other applications include security systems, computer terminals, and traffic control. Advantages of bubble systems are also summarized, and include the rugged nonvolatile storage medium, low cost, and high reliability.

Baker, K.

194

Drag Reduction by Bubble Oscillations  

E-print Network

Drag reduction in stationary turbulent flows by bubbles is sensitive to the dynamics of bubble oscillations. Without this dynamical effect the bubbles only renormalize the fluid density and viscosity, an effect that by itself can only lead to a small percentage of drag reduction. We show in this paper that the dynamics of bubbles and their effect on the compressibility of the mixture can lead to a much higher drag reduction.

T. S. Lo; Victor S. L'vov; Itamar Procaccia

2005-11-02

195

A possible origin of gamma rays from the Fermi Bubbles  

NASA Astrophysics Data System (ADS)

One of the most exciting discoveries of recent years is a pair of gigantic gamma-ray emission regions, the so-called Fermi bubbles, above and below the Galactic center. The bubbles, discovered by the Fermi space telescope, extend up to ?50° in Galactic latitude and are ?40° wide in Galactic longitude. The gamma-ray emission is also found to correlate with radio, microwave and X-rays emission. The origin of the bubbles and the associated non-thermal emissions are still not clearly understood. Possible explanations for the non-thermal emission include cosmic-ray injection from the Galactic center by high speed Galactic winds/jets, acceleration by multiple shocks or plasma turbulence present inside the bubbles, and acceleration by strong shock waves associated with the expansion of the bubbles. In this paper, I will discuss the possibility that the gamma-ray emission is produced by the injection of Galactic cosmic-rays mainly protons during their diffusive propagation through the Galaxy. The protons interact with the bubble plasma producing ?°-decay gamma rays, while at the same time, radio and microwave synchrotron emissions are produced by the secondary electrons/positrons resulting from the ?± decays.

Thoudam, Satyendra

2014-11-01

196

Inertial confinement fusion based on the ion-bubble trigger  

SciTech Connect

Triggering the ion-bubble in an inertial confinement fusion, we have developed a novel scheme for the fast ignition. This scheme relies on the plasma cavitation by the wake of an intense laser pulse to generate an ion-bubble. The bubble acts both as an intense electron accelerator and as an electron wiggler. Consequently, the accelerated electrons trapped in the bubble can emit an intense tunable laser light. This light can be absorbed by an ablation layer on the outside surface of the ignition capsule, which subsequently drills it and thereby produces a guide channel in the pellet. Finally, the relativistic electron beam created in the bubble is guided through the channel to the high density core igniting the fusion fuel. The normalized beam intensity and beam energy required for triggering the ignition have been calculated when core is heated by the e-beam. In addition, through solving the momentum transfer, continuity and wave equations, a dispersion relation for the electromagnetic and space-charge waves has been analytically derived. The variations of growth rate with the ion-bubble density and electron beam energy have been illustrated. It is found that the growth rates of instability are significantly controlled by the ions concentration and the e-beam energy in the bubble.

Jafari, S., E-mail: SJafari@guilan.ac.ir; Nilkar, M.; Ghasemizad, A. [Department of Physics, University of Guilan, Rasht 41335-1914 (Iran, Islamic Republic of); Mehdian, H. [Department of Physics and Institute for Plasma Research, Tarbiat Moallem University, Tehran 15614 (Iran, Islamic Republic of)

2014-10-15

197

Inertial confinement fusion based on the ion-bubble trigger  

NASA Astrophysics Data System (ADS)

Triggering the ion-bubble in an inertial confinement fusion, we have developed a novel scheme for the fast ignition. This scheme relies on the plasma cavitation by the wake of an intense laser pulse to generate an ion-bubble. The bubble acts both as an intense electron accelerator and as an electron wiggler. Consequently, the accelerated electrons trapped in the bubble can emit an intense tunable laser light. This light can be absorbed by an ablation layer on the outside surface of the ignition capsule, which subsequently drills it and thereby produces a guide channel in the pellet. Finally, the relativistic electron beam created in the bubble is guided through the channel to the high density core igniting the fusion fuel. The normalized beam intensity and beam energy required for triggering the ignition have been calculated when core is heated by the e-beam. In addition, through solving the momentum transfer, continuity and wave equations, a dispersion relation for the electromagnetic and space-charge waves has been analytically derived. The variations of growth rate with the ion-bubble density and electron beam energy have been illustrated. It is found that the growth rates of instability are significantly controlled by the ions concentration and the e-beam energy in the bubble.

Jafari, S.; Nilkar, M.; Ghasemizad, A.; Mehdian, H.

2014-10-01

198

Bubble size measurement in electroflotation  

Microsoft Academic Search

A feature of electroflotation is the ability to create very fine bubbles, which are known to improve flotation performance of fine particles. This study was aimed at determining the hydrogen bubble size generated as a function ofcurrent density and electrode geometry. Experiments were performed in a viewing cell that allowed direct visualization of hydrogen bubbles being generated and transported away

G. M. Evans; S. W. Donne

2010-01-01

199

Using Bubbles to Explore Membranes  

NSDL National Science Digital Library

In this activity, learners use bubbles to investigate the structure and unique properties of cell membranes. Bubbles serve as macroscopic models that mimic the cells' phospholipid bilayers. Learners also use the bubbles to form prokaryotic cells and eukaryotic cells. This inquiry type lab can be done as a group or cooperative learning experience. Materials listed are designed for a group of 30 learners.

Sandra Wardell

2009-01-01

200

Ideal magnetohydrodynamic simulation of magnetic bubble expansion as a model for extragalactic radio lobes  

SciTech Connect

Nonlinear ideal magnetohydrodynamic (MHD) simulations of the propagation and expansion of a magnetic ''bubble'' plasma into a lower density, weakly magnetized background plasma, are presented. These simulations mimic the geometry and parameters of the Plasma Bubble Expansion Experiment (PBEX) [A. G. Lynn, Y. Zhang, S. C. Hsu, H. Li, W. Liu, M. Gilmore, and C. Watts, Bull. Am. Phys. Soc. 52, 53 (2007)], which is studying magnetic bubble expansion as a model for extragalactic radio lobes. The simulations predict several key features of the bubble evolution. First, the direction of bubble expansion depends on the ratio of the bubble toroidal to poloidal magnetic field, with a higher ratio leading to expansion predominantly in the direction of propagation and a lower ratio leading to expansion predominantly normal to the direction of propagation. Second, a MHD shock and a trailing slow-mode compressible MHD wavefront are formed ahead of the bubble as it propagates into the background plasma. Third, the bubble expansion and propagation develop asymmetries about its propagation axis due to reconnection facilitated by numerical resistivity and to inhomogeneous angular momentum transport mainly due to the background magnetic field. These results will help guide the initial experiments and diagnostic measurements on PBEX.

Liu Wei; Li Hui; Li Shengtai [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Hsu, Scott C. [Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Lynn, Alan G. [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 (United States)

2008-07-15

201

Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)  

NASA Astrophysics Data System (ADS)

veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earth’s space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earth’s magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

Veenadhari, B.; Alex, S.

2006-11-01

202

Seismo-ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements  

NASA Astrophysics Data System (ADS)

We report the processes and results of statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a period of 6 years (2005-2010), in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which represent relative equatorial electron density increase, were performed for each region. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low-latitude region can accompany observable precursory and concurrent EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling is consistent with our observation, and the possibility of earthquake prediction using the EIA intensity variation is discussed.

Ryu, K.; Lee, E.; Chae, J. S.; Parrot, M.; Pulinets, S.

2014-10-01

203

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

204

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

205

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

206

Bubbly Little Star  

NASA Technical Reports Server (NTRS)

In this processed Spitzer Space Telescope image, baby star HH 46/47 can be seen blowing two massive 'bubbles.' The star is 1,140 light-years away from Earth.

The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are formed by starlight scattered by surrounding dust.

These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. The red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.

Whenever astronomers observe a star, or snap a stellar portrait, through the lens of any telescope, they know that what they are seeing is slightly blurred. To clear up the blurring in Spitzer images, astronomers at the Jet Propulsion Laboratory developed an image processing technique for Spitzer called Hi-Res deconvolution.

This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When scientists applied this image processing technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.

This infrared image is a three-color composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.

2007-01-01

207

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.; Mart?nez, H.; Rangel, J.; Reyes, P. G.

2013-07-01

208

DNA denaturation bubbles at criticality  

E-print Network

The equilibrium statistical properties of DNA denaturation bubbles are examined in detail within the framework of the Peyrard-Bishop-Dauxois model. Bubble formation in homogeneous DNA is found to depend crucially on the presence of nonlinear base-stacking interactions. Small bubbles extending over less than 10 base pairs are associated with much larger free energies of formation per site than larger bubbles. As the critical temperature is approached, the free energy associated with further bubble growth becomes vanishingly small. An analysis of average displacement profiles of bubbles of varying sizes at different temperatures reveals almost identical scaled shapes in the absence of nonlinear stacking; nonlinear stacking leads to distinct scaled shapes of large and small bubbles.

Theodorakopoulos, Nikos

2008-01-01

209

Simulations of the equatorial thermosphere anomaly: Geomagnetic activity modulation  

NASA Astrophysics Data System (ADS)

modulation of geomagnetic activity on the equatorial thermosphere anomaly (ETA) in thermospheric temperature under the high solar activity condition is investigated using the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations. The model simulations during the geomagnetically disturbed interval, when the north-south component of the interplanetary magnetic field (Bz) oscillates between southward and northward directions, are analyzed and also compared with those under the quiet time condition. Our results show that ionospheric electron densities increase greatly in the equatorial ionization anomaly (EIA) crest region and decrease around the magnetic equator during the storm time, resulting from the enhanced eastward electric fields. The impact of both the direct heat deposition at high latitudes and the modulation of the storm time enhanced EIA crests on the ETA are subsequently studied. The increased plasma densities over the EIA crest region enhance the field-aligned ion drag that accelerates the poleward meridional winds and consequently their associated adiabatic cooling effect. This process alone produces a deeper temperature trough over the magnetic equator as a result of the enhanced divergence of meridional winds. Moreover, the enhanced plasma-neutral collisional heating at higher latitudes associated with the ionospheric positive storm effect causes a weak increase of the ETA crests. On the other hand, strong changes of the neutral temperature are mainly confined to higher latitudes. Nevertheless, the changes of the ETA purely due to the increased plasma density are overwhelmed by those associated with the storm time heat deposition, which is the major cause of an overall elevated temperature in both the ETA crests and trough during the geomagnetically active period. Associated with the enhanced neutral temperature at high latitudes due to the heat deposition, the ETA crest-trough differences become larger under the minor geomagnetic activity condition than under the quiet time condition. However, when geomagnetic activity is further elevated, the ETA crests tend to be masked by high temperatures at middle and high latitudes.

Lei, Jiuhou; Wang, Wenbin; Thayer, Jeffrey P.; Luan, Xiaoli; Dou, Xiankang; Burns, Alan G.; Solomon, Stanley C.

2014-08-01

210

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

211

Are Bursty Bulk Flows MHD Bubbles? The Magnetospheric Constellation Mission  

NASA Astrophysics Data System (ADS)

Recently, 3D simulations of the magnetosphere have been shown to exhibit a behavior that appears to be a global realization of the MHD plasma bubble phenomenon discussed by Chen and Wolf. Bubble formation and dynamics appears to be a candidate mechanism for the production of bursty bulk flows, a term that is derived purely from observations from lone spacecraft in the magnetotail. Reaching closure between theory and observation for such a three-dimensionally structured, dynamic phenomenon will require constellation-class observations having extent and resolution in space and time commensurate with global simulations, i.e. ~ 1-2 RE and ~ 10 sec. We treat magnetic bubbles as representative of the general class of possible magnetospheric dynamical structures that can practically be studied only using a distributed constellation of spacecraft to obtain vector field "streamline" movies of the magnetotail plasma flow, magnetic field, and energetic particle fluxes. Relevant capabilities of the NASA Magnetospheric Constellation Mission (MCM) are summarized.

Moore, T. E.; Spence, H. E.; Goodrich, C. C.; Kepko, E. L.

2003-04-01

212

Polarizing bubble collisions  

SciTech Connect

We predict the polarization of cosmic microwave background (CMB) photons that results from a cosmic bubble collision. The polarization is purely E-mode, symmetric around the axis pointing towards the collision bubble, and has several salient features in its radial dependence that can help distinguish it from a more conventional explanation for unusually cold or hot features in the CMB sky. The anomalous ''cold spot'' detected by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such a collision, and the Planck satellite and other proposed surveys will measure the polarization on it in the near future. The detection of such a collision would provide compelling evidence for the string theory landscape.

Czech, Bart?omiej; Larjo, Klaus; Levi, Thomas S.; Sigurdson, Kris [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1 (Canada); Kleban, Matthew, E-mail: czech@phas.ubc.ca, E-mail: mk161@nyu.edu, E-mail: larjo@phas.ubc.ca, E-mail: tslevi@phas.ubc.ca, E-mail: krs@phas.ubc.ca [CCPP, Department of Physics, New York University, New York, NY 10003 (United States)

2010-12-01

213

Equatorial waves in the stratosphere of Uranus  

NASA Technical Reports Server (NTRS)

Analyses of radio occultation data from Voyager 2 have led to the discovery and characterization of an equatorial wave in the Uranus stratosphere. The observed quasi-periodic vertical atmospheric density variations are in close agreement with theoretical predictions for a wave that propagates vertically through the observed background structure of the stratosphere. Quantitative comparisons between measurements obtained at immersion and at emersion yielded constraints on the meridional and zonal structure of the wave; the fact that the two sets of measurements are correlated suggests a wave of planetary scale. Two equatorial wave models are proposed for the wave.

Hinson, David P.; Magalhaes, Julio A.

1991-01-01

214

Digital hf radar observations of equatorial spread-F  

SciTech Connect

Modern digital ionosondes, with both direction finding and doppler capabilities can provide large scale pictures of the Spread-F irregularity regions. A morphological framework has been developed that allows interpretation of the hf radar data. A large scale irregularity structure is found to be nightward of the dusk terminator, stationary in the solar reference frame. As the plasma moves through this foehn-wall-like structure it descends, and irregularities may be generated. Localized upwellings, or bubbles, may be produced, and they drift with the background plasma. The spread-F irregularity region is found to be best characterized as a partly cloudy sky, due to the patchiness of the substructures. 13 references, 16 figures.

Argo, P.E.

1984-01-01

215

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

216

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

217

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

218

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

219

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

220

Condor equatorial electrojet campaign: Radar results  

Microsoft Academic Search

A review of the experimental and theoretical background to the Condor equatorial electrojet compaign is followed by the presentation and discussion of VHF radar interferometer and HF radar backscatter data taken concurrently with two rocket in situ experiments reported in companion papers (Pfaff et al., this issue (a, b). Both experiments were conducted in strongly driven periods with the on-line

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

1987-01-01

221

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

222

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

223

Helium bubble bursting in tungsten  

SciTech Connect

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 [University of California, Berkeley, California 94720 (United States); Juslin, Niklas [University of Tennessee, Knoxville, Tennessee 37996 (United States); Wirth, Brian D., E-mail: bdwirth@utk.edu [University of Tennessee, Oak Ridge National Laboratory, Knoxville, Tennessee 37996 (United States)

2013-12-28

224

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

225

Equatorial ionospheric electrodynamics observations in the African and American longitudinal sectors  

NASA Astrophysics Data System (ADS)

Recent ground- and space-based observations have shown dramatic longitudinal differences in equatorial ionospheric electrodynamics, such as enhanced generation of F-region plasma irregularities and the 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 peak in large scale plasma depletion activity (zonal width, depletion level, and spacing) is maximal, in which no other region of the globe showed similar characteristics. Indeed, the most recent in situ density observations from the Communication/Navigation Outage Forecast System (C/NOFS) satellite also reveal similar maximal density depletion activities in Africa. However, the dearth of ground-based instrumentation in the region makes it difficult to confirm the ground-based signatures of these unique equatorial ionospheric structures, ultimately leading the investigation of their physics into speculation. 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 the AMBER magnetometers network, have been deployed in the region. One 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, which includes the evolution and formation of equatorial anomaly. This paper presents initial results from the AMBER magnetometer network and compares electrodynamics results in the Africa sector 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 infers the F-region vertical plasma drift (ExB drift) from the ground, the ground- and space-based GPS network monitor the structure of plasma at low/mid-latitudes. Finally, comparisons between the ground-based magnetometer estimated drift and the vertical ExB drift observations measured by probes on the C/NOFS satellite are presented.

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

2009-12-01

226

Non-trough foF2 enhancements at near-equatorial dip latitudes , P. M. Vila2  

E-print Network

° magnetic latitude zone. We report this new morphology, concentrating on foF2 enhancements of two types: near-equatorial crests (which travel either northwards or southwards) and magnetic ®eld-aligned domes controlled by a balance between EUV production, photochemical loss and the divergence of plasma ¯ux. Gravity

Boyer, Edmond

227

Bubble, bubble, flow and Hubble: large scale galaxy flow from cosmological bubble collisions  

NASA Astrophysics Data System (ADS)

We study large scale structure in the cosmology of Coleman-de Luccia bubble collisions. Within a set of controlled approximations we calculate the effects on galaxy motion seen from inside a bubble which has undergone such a collision. We find that generically bubble collisions lead to a coherent bulk flow of galaxies on some part of our sky, the details of which depend on the initial conditions of the collision and redshift to the galaxy in question. With other parameters held fixed the effects weaken as the amount of inflation inside our bubble grows, but can produce measurable flows past the number of efolds required to solve the flatness and horizon problems.

Larjo, Klaus; Levi, Thomas S.

2010-08-01

228

Stable tridimensional bubble clusters in multi-bubble sonoluminescence (MBSL).  

PubMed

In the present work, stable clusters made of multiple sonoluminescent bubbles are experimentally and theoretically studied. Argon bubbles were acoustically generated and trapped using bi-frequency driving within a cylindrical chamber filled with a sulfuric acid aqueous solution (SA85w/w). The intensity of the acoustic pressure field was strong enough to sustain, during several minutes, a large number of positionally and spatially fixed (without pseudo-orbits) sonoluminescent bubbles over an ellipsoidally-shaped tridimensional array. The dimensions of the ellipsoids were studied as a function of the amplitude of the applied low-frequency acoustic pressure (PAc(LF)) and the static pressure in the fluid (P0). In order to explain the size and shape of the bubble clusters, we performed a series of numerical simulations of the hydrodynamic forces acting over the bubbles. In both cases the observed experimental behavior was in excellent agreement with the numerical results. The simulations revealed that the positionally stable region, mainly determined by the null primary Bjerknes force (F?Bj), is defined as the outer perimeter of an axisymmetric ellipsoidal cluster centered in the acoustic field antinode. The role of the high-frequency component of the pressure field and the influence of the secondary Bjerknes force are discussed. We also investigate the effect of a change in the concentration of dissolved gas on the positional and spatial instabilities through the cluster dimensions. The experimental and numerical results presented in this paper are potentially useful for further understanding and modeling numerous current research topics regarding multi-bubble phenomena, e.g. forces acting on the bubbles in multi-frequency acoustic fields, transient acoustic cavitation, bubble interactions, structure formation processes, atomic and molecular emissions of equal bubbles and nonlinear or unsteady acoustic pressure fields in bubbly media. PMID:24974006

Rosselló, J M; Dellavale, D; Bonetto, F J

2015-01-01

229

Waveguide radio-wave propagation in the equatorial ionosphere according to the Interkosmos-19 data  

NASA Astrophysics Data System (ADS)

Additional strongly remote (up to 2000 km) radio-signal reflection traces on Intercosmos-19 ionograms obtained in the equatorial ionosphere have been considered. These traces, as a rule, begin at frequencies slightly lower than the main trace cutoff frequencies, which indicates that an irregularity with a decreased plasma density exists here. The waveguide stretched along the magnetic-field line is such an inhomogeneity in the equatorial ionosphere. The ray tracing confirm that radio waves propagate in a waveguide and make it possible to determine the typical waveguide parameters: -? N e ? 10%, with a diameter of 15-20 km. Since the waveguide walls are smooth, an additional trace is always recorded distinctly even in the case in which main traces were completely eroded by strong diffusivity. Only one additional trace (of the radio signal X mode) is usually observed one more multiple trace is rarely recorded. Waveguides can be observed at all altitudes of the equatorial ionosphere at geomagnetic latitudes of ±40°. The formation of waveguides is usually related to the formation of different-scale irregularities in the nighttime equatorial ionosphere, which result in the appearance of other additional traces and spread F.

Karpachev, A. T.; Zhbankov, G. A.; Telegin, V. A.

2014-03-01

230

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

231

A prediction for bubbling geometries  

E-print Network

We study the supersymmetric circular Wilson loops in N=4 Yang-Mills theory. Their vacuum expectation values are computed in the parameter region that admits smooth bubbling geometry duals. The results are a prediction for the supergravity action evaluated on the bubbling geometries for Wilson loops.

Takuya Okuda

2008-02-11

232

Bubbles are rational Pierre Lescanne  

E-print Network

Bubbles are rational Pierre Lescanne Universit´e de Lyon, ´Ecole normale sup´erieure de Lyon, CNRS of equilibrium in the theory of infinite sequential games, bubbles and escalations are rational for economic coinduction to properly reason on infinite games. This way we refine the notion of rationality. Keywords

Paris-Sud XI, Université de

233

Lithospheric Flexural Modeling of Iapetus' Equatorial Ridge  

NASA Astrophysics Data System (ADS)

Iapetus, which is one of Saturn's ball-shaped satellites, has some unique features in the Solar System. This satellite has a mean radius of 735 km, and there is an approximately 20-kilometer-high mountain lying precisely on its equator. The mountain is known as an "equatorial ridge" since it makes Iapetus appear walnut shaped. The origin of the equatorial ridge is attributed to several hypotheses, including different endogenesis and exogenesis processes. In this work, we attempted to construct a flexural model of the equatorial ridge using elastic lithosphere theory. The equatorial ridge is treated as a linear load which exerts uniform force on Iapetus' hard shell (i.e. elastic lithosphere of Iapetus). To calculate the deflection of surface, we use the Digital Terrain Model (DTM) data of Iapetus' leading side published by Giese et al. (2008). Giese et al. also pointed out that the elastic lithospheric thickness of Iapetus must exceed 100 km to support the ridge without deflecting. However, we found possible evidence in the DTM data that implied deflection. There are two sites of surface depression on the northern side of the equatorial ridge. The few-kilometer deflection implies a thinner lithosphere than previous suggested. Assume that the thickness of elastic lithosphere is only 5% below of the radius of Iapetus, so the flat-Earth and one-plate condition could adapt to the flexure model of Iapetus. Based on analysis of the distance between a bulge and the ridge, the calculated lithospheric thickness is 6-10 km. The new result seems controversial, but the modeled surface profile is highly consistent with numerical ridge DTM profile extracted from Giese et al. (2008). Thinner lithosphere also supports the contraction model proposed by Sandwell and Schubert (2010) since the bucking harmonic degree increases. In the other hand, the transformation layer between hard shell and plastic inner core may need constraint on thermal history or crystal form of ice. In conclusion, The flexural model of Iapetus' equatorial ridge reveals the possibility of thinner hard shell, fits the surface profile, and supplies more clues to the origin of Iapetus, the interesting satellite in the Solar System.

Zheng, W.; Ip, W.-H.; Teng, L. S.

2012-04-01

234

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. PMID:22267872

Kapl, Mario; Byrtus, Marek; Jüttler, Bert

2011-01-01

235

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

236

Bubble formation in microgravity  

NASA Technical Reports Server (NTRS)

An extensive experimental program was initiated for the purpose of understanding the mechanisms leading to bubble generation during fluid handling procedures in a microgravity environment. Several key fluid handling procedures typical for PCG experiments were identified for analysis in that program. Experiments were designed to specifically understand how such procedures can lead to bubble formation. The experiments were then conducted aboard the NASA KC-135 aircraft which is capable of simulating a low gravity environment by executing a parabolic flight attitude. However, such a flight attitude can only provide a low gravity environment of approximately 10-2go for a maximum period of 30 seconds. Thus all of the tests conducted for these experiments were designed to last no longer than 20 seconds. Several experiments were designed to simulate some of the more relevant fluid handling procedures during protein crystal growth experiments. These include submerged liquid jet cavitation, filling of a cubical vessel, submerged surface scratch, attached drop growth, liquid jet impingement, and geysering experiments. To date, four separate KC-135 flight campaigns were undertaken specifically for performing these experiments. However, different experiments were performed on different flights.

Antar, Basil N.

1996-01-01

237

Squeezing through: capsule or bubble?  

E-print Network

In this fluid dynamics video, we compare the deformation of two flexible particles as they propagate through a sudden constriction of a liquid filled channel under constant-flux flow: a gas bubble, and a capsule formed by encapsulating a liquid droplet in a cross-linked polymeric membrane. Both bubble and capsule adopt highly contorted configurations as they squeeze through the constriction, exhibit broadly similar features over a wide range of flow rates, and rupture for sufficiently high flow rates. However, at flow rates prior to rupture, certain features of the deformation allow bubble and capsule to be distinguished: bubbles exhibit a tip-streaming singularity associated with critical thinning of the rear of the bubble, while the capsule membrane wrinkles under large compressive stresses induced by the constriction.

Dawson, Geoffrey

2013-01-01

238

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles  

PubMed Central

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble’s origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications. PMID:18601556

Karpiouk, Andrei B.; Aglyamov, Salavat R.; Bourgeois, Frederic; Ben-Yakar, Adela; Emelianov, Stanislav Y.

2008-01-01

239

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

240

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

241

Onset conditions for equatorial spread F  

Microsoft Academic Search

The problem of day-to-day variability in the occurrence of equatorial spread F (ESF) is addressed using multidiagnostic observations and semiempirical modeling. The observational results are derived from a two-night case study of ESF onset conditions observed at Kwajalein Atoll (Marshall Islands) using the ALTAIR incoherent scatter radar and all-sky optical imaging techniques. The major difference between nights when ESF instabilities

Michael Mendillo; Jeffrey Baumgardner; Xiaoqing Pi; Peter J. Sultan; Roland Tsunoda

1992-01-01

242

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

243

Breaking of balanced and unbalanced equatorial waves.  

PubMed

A clear-cut signature of a wave-breaking event is irreversible modification of the mean flow. In this paper, we provide examples of different breaking mechanisms and show that breaking scenario of equatorial waves in the beta-plane shallow water model is determined by the degree of balance between the zonal component of the Coriolis force and the pressure gradient. Our analysis is based on a specially designed numerical method which guarantees two essential conditions to simulate nonlinear equatorial waves: (i) the scheme converges toward weak solutions including shocks and (ii) preserves the steadiness of balanced stationary solutions. This allows for accurate diagnostics of Lagrangian invariants of motion such as passive tracer density or potential vorticity. For unbalanced waves, the lack of balance leads to shock formation in finite time. In shock fronts, the variation of the dissipation rate induces a nonadvective potential vorticity flux and violates the local potential vorticity conservation valid for smooth solutions. This dissipative breaking mechanism is generic for unbalanced waves and is associated with enhanced mixing. For long, balanced (Rossby) waves, breaking consists in appearance of recirculation regions. It results in the formation of propagating patterns, the equatorial modons, which trap fluid particles. Such breaking occurs during the propagation of Rossby wave packets with positive geopotential anomaly and is strengthened by decreasing fluid depth. The modons are robust and collide quasielastically with Kelvin waves. PMID:15836268

Bouchut, F; Le Sommer, J; Zeitlin, V

2005-03-01

244

The Dynamics of Equatorial Atmospheric Angular Momentum  

NASA Astrophysics Data System (ADS)

The physical processes that drive intraseasonal equatorial atmospheric angular momentum (EAAM) fluctuations are examined with data from an aquaplanet GCM run and with NCEP/NCAR reanalysis data. The GCM has an all-ocean lower boundary with a zonally symmetric sea surface temperature field. The EAAM budget is dominated by the equatorial bulge torque in both the GCM and in observations. For the GCM and the atmosphere, both components of the EAAM vector exhibit a strong spectral peak near a period of 10 days. An analysis with the linearized shallow water model equations on the sphere shows that this 10-day period can be interpreted as arising from the westward propagation of a free, antisymmetric, zonal wavenumber one, Rossby wave. The amplitude fluctuations of the EAAM vector are found to be related to tropical convection in both the GCM and the atmosphere. For the GCM, this convection is associated with an equatorial mixed Rossby-gravity wave. In the atmosphere, in addition to mixed Rossby-gravity waves, EAAM amplitude fluctuations are also related to both the Madden-Julian Oscillation (MJO) and to constructive and destructive interference between the propagating and stationary components of EAAM vector. The latter two processes arise because of the large, nonzero, seasonal mean values of the components of the EAAM vector. The above findings collectively suggest that the latent heat release in the tropics excites poleward Rossby wave propagation which alters the amplitude of the EAAM vector.

Feldstein, S. B.

2003-12-01

245

Study of Equatorial Atmosphere with the Equatorial Atmosphere Radar (EAR) under the CPEA project  

NASA Astrophysics Data System (ADS)

The Coupling Processes in the Equatorial Atmosphere CPEA is a six-year 2001-2007 research project of Japan to study dynamical and electrodynamical coupling processes in the equatorial atmosphere CPEA seeks pioneer research by means of primarily ground-based observations in the Indonesian equatorial region The main facility for CPEA is the Equatorial Atmosphere Radar EAR located right at the equator in West Sumatra Indonesia We continue continuous observations with the EAR since June 2001 and have studied atmospheric waves and structures in the troposphere lower-stratosphere and in the ionosphere thermosphere We review results based on observations with the EAR and other instruments developed during CPEA Some of our research topics are shown below begin itemize item Propagation and breaking of Kelvin waves are studied in the troposphere and lower-stratosphere Gravity-wave generation from the tropospheric convection is detected with the EAR rasiosondes and weather radars item Vertical motion and laminar structure of the atmosphere is studied by the vertical-wind mode observations and the frequency domain radar interferometric imaging FII techniques with the EAR In October-November 2005 we conducted an observation campaign for cirrus with a 95-GHz cloud radar radiosondes and a lidar item The equatorial spread F ESF is measured as 3-m scale irregularity echoes with the EAR Pulse-to-pulse beam steerability of the EAR helped much to reveal spatial structures and time evolution of the

Yamamoto, M.; Hashiguchi, H.; Yamamoto, M. K.; Fukao, S.

246

A possible origin of gamma rays from the Fermi Bubbles  

E-print Network

One of the most exciting discoveries of recent years is a pair of gigantic gamma-ray emission regions, the so-called Fermi bubbles, above and below the Galactic center. The bubbles, discovered by the Fermi space telescope, extend up to $\\sim 50^\\circ$ in Galactic latitude and are $\\sim 40^\\circ$ wide in Galactic longitude. The gamma-ray emission is also found to correlate with radio, microwave and X-rays emission. The origin of the bubbles and the associated non-thermal emissions are still not clearly understood. Possible explanations for the non-thermal emission include cosmic-ray injection from the Galactic center by high speed Galactic winds/jets, acceleration by multiple shocks or plasma turbulence present inside the bubbles, and acceleration by strong shock waves associated with the expansion of the bubbles. In this paper, I will discuss the possibility that the gamma-ray emission is produced by the injection of Galactic cosmic-rays mainly protons during their diffusive propagation through the Galaxy. Th...

Thoudam, Satyendra

2014-01-01

247

Anatomy of bubbling solutions  

E-print Network

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 gravitational solution is dual to, but it does determine it enough so that vevs of all single trace 1/2 BPS operators in that state are uniquely determined to leading order in the large N limit. These are precisely the vevs encoded in the asymptotics of the LLM solutions. We extract these vevs for operators up to dimension 4 using holographic renormalization and KK holography and show exact agreement with the field theory expressions.

Kostas Skenderis; Marika Taylor

2008-05-23

248

Equatorial balance model for planetary scale dynamics  

NASA Astrophysics Data System (ADS)

As slow dynamics often dominate in geophysical fluid models, it is desirable to filter out fast motions by constructing simplified `balanced' models; the most notable example is the quasi-geostrophic model for mid-latitude dynamics. Attempts to derive similar balance models for the tropics have not been entirely successful, as Kelvin waves, which contribute significantly to tropical low-frequency variability, are generally filtered out. In the long-wave limit of the equatorial wave theory, both Kelvin and Rossby waves are slow relative to inertia-gravity and mixed-Rossby-gravity waves, and thus a balance model in this regime should retain Kelvin waves to capture the slow dynamics accurately. In the present study, an asymptotic expansion is used to systematically derive a family of balance models for the shallow water equations on the equatorial beta-plane, with anisotropy (ratio of meridional to zonal scale) as the small parameter. In the weakly nonlinear, small Froude number limit, we recover the traditional linear long-wave model of Gill (1980) at leading order, while the higher order terms in the expansion introduce nonlinearity and dispersion for Rossby waves. The method is shown to be applicable to the fully nonlinear regime (i.e Froude number approaching unity), as well as linearly stratified models. The slow dynamics in the nonlinear balance model are characterized by an advective timescale and small horizontal divergence, which is in agreement with the `balanced' view of equatorial dynamics (e.g. Charney 1963) where vortical motions dominate. As Gill's long-wave model emerges from the nonlinear balance model in the small Froude number limit, our theory then suggests that the equatorial long-wave theory is fully consistent with the balanced view of equatorial dynamics. In addition to the adiabatic models, we also consider a case where a diabatic heat source is present, with the aim of further clarifying the role of diabatic heating in large scale balanced dynamics in the tropics. References: Charney, J. G., 1963, J. Atmos. Sci. 20: 607-609. Gill, A. E., 1980. Q. J. Roy. Meteor. Soc. 106: 447-462.

Chan, Ian; Shepherd, Theodore

2013-04-01

249

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

250

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

251

On the multifaceted role played by the Neutral Wind in the Equatorial Electrodynamics during Magnetically Disturbed times  

NASA Astrophysics Data System (ADS)

A disturbance dynamo was observed in the magnetic equatorial region of the Asian subcontinent on May 31, 2005, one day after an intense magnetic storm of relatively short duration. At first sight, there was nothing unusual about the event on that particular day as the ground-based magnetograms revealed very strong reduction in the normal mid-day electrojet with the essential disappearance of the Equatorial Ionization Anomaly, as revealed by the Total Electron Content (TEC) data. A closer look at the ionosonde data however revealed that, contrary to conventional thinking, the zonal electric field had remained eastward for most of the day in spite of the evidence for westward currents. There was, in addition, a clear mid afternoon amplification of the eastward zonal field followed by a westward turning field after 1600 IST. This electric field oscillation triggered a depletion in the equatorial TEC, but without an accompanying modulation of the TEC in the anomaly crest region. Interestingly, the equatorial TEC returned to its pre-depletion value when the plasma came through the downward phase of its oscillation. We argue that these observations can be explained by two important disturbed dynamo neutral wind properties that have not been emphasized before, namely,(1) the neutral wind circulation cell due to Joule heating did not reach the magnetic equator but came close enough to it to essentially kill the equatorial fountain effect while maintaining an eastward zonal field; (2) a weakening of the high latitude-driven Hadley cell circulation in the mid-afternoon hours could have easily produced the observed equatorial F region zonal electric field oscillation creating a situation that was highly reminiscent of the equatorial `Pre-Reversal-Enhancement' signature normally observed near the terminator instead of the mid-afternoon

Choudhary, Raj Kumar; St-Maurice, Jean-Pierre; Ambili, M. K.; Sridharan, R.

2012-07-01

252

Post-testicular development of a novel membrane substructure within the equatorial segment of ram, bull, boar, and goat spermatozoa as viewed by atomic force microscopy.  

PubMed

Atomic force microscopy has been used to investigate changes in the plasma membrane overlying the head region of mammalian spermatozoa (bull, boar, ram, goat, stallion, mouse, and monkey) during post-testicular development, after ejaculation, and after exocytosis of the acrosomal vesicle. On ejaculated ram, bull, boar, and goat spermatozoa the postacrosomal plasma membrane has a more irregular surface than that covering the acrosome. The equatorial segment, by contrast, is relatively smooth except for an unusual semicircular substructure within it that has a coarse uneven appearance. This substructure (referred to as the equatorial subsegment) is situated adjacent to the boundary between the postacrosomal region and the equatorial segment itself and seems to be confined to the order Artiodactyla as it has not been observed on stallion, mouse, or monkey spermatozoa. The equatorial subsegment develops during epididymal maturation, and following induction of the acrosome reaction with Ca(2+) ionophore A23187, its topography changes from a finely ridged appearance to that resembling truncated papillae. A monoclonal antibody to the equatorial subsegment binds only to permeabilized spermatozoa, suggesting that the subsegment is related to the underlying perinuclear theca that surrounds the sperm nucleus. A role for the equatorial subsegment in mediating fusion with the oolemma at fertilization is discussed. PMID:12217657

Ellis, Darren J; Shadan, Sadaf; James, Peter S; Henderson, Robert M; Edwardson, J Michael; Hutchings, Amanda; Jones, Roy

2002-06-01

253

Aspherical bubble dynamics and oscillation times  

SciTech Connect

The cavitation bubbles common in laser medicine are rarely perfectly spherical and are often located near tissue boundaries, in vessels, etc., which introduce aspherical dynamics. Here, novel features of aspherical bubble dynamics are explored by time-resolved photography and numerical simulations. The growth-collapse period of cylindrical bubbles of large aspect ratio (length:diameter {approximately}20) differs only slightly from twice the Rayleigh collapse time for a spherical bubble with an equivalent maximum volume. This fact justifies using the temporal interval between the acoustic signals emitted upon bubble creation and collapse to estimate the maximum bubble volume. As a result, hydrophone measurements can provide an estimate of the bubble size and energy even for aspherical bubbles. The change of the oscillation period of bubbles near solid walls and elastic (tissue-like) boundaries relative to that of isolated spherical bubbles is also investigated.

Vogel, A.; Noack, J. [Meizinisches Laserzentrum Luebeck (Germany); Chapyak, E.J.; Godwin, R.P. [Los Alamos National Lab., NM (United States)

1999-06-01

254

Transient bubbles, bublets and breakup  

NASA Astrophysics Data System (ADS)

The non-spherical nature of the collapse of bubbles has important ramifications in many practical situations such as ultrasonic cleaning, tanning of leather, and underwater explosions. In particular the high speed liquid jet that can thread a collapsing bubble is central to the functional performance. An impressive photographic record of a liquid jet was obtained by Crum using a bubble situated in the vicinity of a platform oscillating vertically at a frequency of 60 Hz. A boundary integral method is used to model this situation and is found to closely mimic some of the observations. However, a slight variation of parameters or a change in the phase of the driving frequency can lead to dramatically different bubble behaviour, a feature also observed by Crum.

Keen, Giles; Blake, John

1999-11-01

255

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

256

Heating the bubbly gas of galaxy clusters with weak shocks and sound waves  

E-print Network

Using hydrodynamic simulations and a technique to extract the rotational component of the velocity field, we show how bubbles of relativistic gas inflated by AGN jets in galaxy clusters act as a catalyst, transforming the energy carried by sound and shock waves to heat. The energy is stored in a vortex field around the bubbles which can subsequently be dissipated. The efficiency of this process is set mainly by the fraction of the cluster volume filled by (sub-)kpc scale filaments and bubbles of relativistic plasma.

S. Heinz; E. Churazov

2005-07-01

257

Modeling the Local Bubble  

NASA Astrophysics Data System (ADS)

Modeling the Local Bubble is one of those activities fraught with danger. It is very easy to be too naive, to fail to consider the dependence of the model on assumptions about the nearby ambient state, or the likelihood of such a structure. It is similarly easy to become so caught up in the details of the vicinity that it is unclear where to begin a necessarily idealized modeling effort. And finally, it is important to remember that the data we have may in some cases be lying to us, and that we have not yet learned to read their facial expressions quite carefully enough. That said, I've tried in this paper to be helpful to those who may wish to take the risks. I surveyed the very most basic stories that the data seem to tell, and pointed out the standard coincidences that may be telling us a lot about what is happening, but may turn out once again to have been just coincidences. I've described 5 distinct conceptions that in one flavor or another pretty well survey the collection of mental images that have so far been carried by those who've attempted models. One may be right, or something entirely different may be more appropriate. It's at least vital to realize that a conception comes first, followed by a simplified model of details. I've also included a long list of questions directed at observers. Some have partial answers, some one wouldn't know today quite how to approach. But it is a list that students of the soft x-ray background, interstellar absorption lines, possible instrumentation, and the heliosphere may wish to review from time to time, just to see whether they can figure out how to be more helpful. There is another list for modelers, things the models must address, however-so-flimsily if necessary, because there are strong observational constraints (and stronger ones coming) on what can and cannot be present in the local ISM. To that I've added a few remarks concerning x-ray emission coming from beyond the Local Bubble, and another few on how x-ray emission from within the solar system might be contaminating what we see. That last bit is new, exciting, and possibly wrong, but it is an example of the ongoing wariness I believe one has to take toward the facts in the case. By the way, Dieter, it really was a great meeting.

Cox, D. P.

258

On the Necessity and Feasibility of an Equatorial Magnetospheric Constellation  

NASA Technical Reports Server (NTRS)

Synthesizing multi-point in-situ observations from the magnetosphere is the only way that we can retain an accurate knowledge of the driving mechanisms of convection and energy flow while "imaging" its vast volume. In addition to measuring the wavenumber of plasma instabilities thus opening up for study a previously unexplored domain of space plasma physics the Constellation mission can afford us a view of the rapid topological reconfigurations and the energy circulation throughout the astrophysical laboratory closest to human space activity. In this paper we argue that the deployment of approximately 80 autonomous micro-satellites (probes) to monitor the Earth's magnetosphere and measure the plasma and magnetic field in the near-equatorial magnetosphere is a necessary and sufficient condition for answering long standing, high priority questions regarding magnetospheric stability and dynamics. The proposed mission concept is technically feasible and fiscally modest. The probes can be raised from a Geosynchronous Transfer orbit to their final elliptical orbits with perigee approximately 3R(sub E)and apogees ranging from 12 to 42 R(sub E) by a single dispenser propelled by an ion engine. Each probe will weigh approximately 5 kg. The mission can form a cornerstone of an incrementally deployed Solar Terrestrial Probe Line Magnetospheric Constellation, as it requires no new technologies in the areas of spacecraft subsystems and instruments, but some development in the areas of dispenser design, probe packaging, mechanical release and spin-up. The technology developed can be utilized by follow-on Constellation class missions as well.

Angelopoulos, V.; Carlson, C. W.; Curtis, D. W.; Harvey, P.; Lin, R. P.; Mozer, F. S.; Pankow, D. H.; Raeder, J.; Russell, C. T.

1998-01-01

259

Climate Response of the Equatorial Pacific to Global Warming.  

E-print Network

??The climate response of the equatorial Pacific to increased greenhouse gases is investigated using numerical experiments from five climate models participating in the Intergovernmental Panel… (more)

Di Nezio, Pedro N.

2008-01-01

260

Dynamics of resonantly interacting equatorial waves  

NASA Astrophysics Data System (ADS)

In this paper we explore some dynamical features on the non-linear interactions among equatorial waves. The shallow-water equation model with the equatorial ?-plane approximation is used for this purpose. The Galerkin method is applied to the governing equations with the basis functions given by the eigensolutions of the linear problem. From the phase space expansion of two particular integrals of motion of the system, quadratic to lowest order, some constraints are obtained which the coupling coefficients must satisfy in order to ensure the invariance of such integrals. From the numerical evaluation of the coupling coefficients, these constraints are used to determine the possible resonant triads among equatorial waves. Numerical integrations of the resonant three-wave problem show that the energy of the waves in a resonant triad evolves periodically in time, with the period and amplitude of the energy oscillations dependent on the magnitude of the initial amplitudes of the waves and the way in which the initial energy is distributed among the triad components. The high-frequency modes are found to be energetically more active than the low-frequency modes. The latter tend to act as `catalytic' components in a resonant triad. Integrations of the problem of two resonant triads coupled by a single mode point out the importance of gravity waves in the intertriad energy exchanges, suggesting the significance of these modes in the redistribution of energy throughout the atmospheric motion spectrum. The results also show that the intertriad energy exchanges provided by the highest frequency mode of two triads occur in a longer time-scale than the intratriad interactions. Therefore, these results also suggest the importance of the high-frequency modes in the generation of the low-frequency variability (intraseasonal and even longer term) of the atmospheric flow.

Raupp, Carlos F. M.; Dias, Pedro L. Silva

2006-03-01

261

The Physics of Ion Decoupling in Magnetized Plasma Explosions  

SciTech Connect

When a finite pulse of plasma expands into a magnetized background plasma, MHD predicts the pulse expel background plasma and its B-field - i.e. cause a magnetic 'bubble'. The expanding plasma is confined within the bubble, later to escape down the B-field lines. MHD suggests that the debris energy goes to expelling the B-field from the bubble volume and kinetic energy of the displaced background. For HANEs, this is far from the complete story. For many realistic HANE regimes, the long mean-free-path for collisions necessitates a Kinetic Ion Simulation Model (KISM). The most obvious effect is that the debris plasma can decouple and slip through the background plasma. The implications are: (1) the magnetic bubble is not as large as expected and (2) the debris is no longer confined within the magnetic bubble.

Hewett, D; Larson, D; Brecht, S

2011-02-08

262

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

263

An equatorial coronal hole at solar minimum  

NASA Technical Reports Server (NTRS)

The large transequatorial coronal hole that was observed in the solar corona at the end of August 1996 is presented. It consists of a north polar coronal hole called the 'elephant's trunk or tusk'. The observations of this coronal hole were carried out with the coronal diagnostic spectrometer onboard the Solar and Heliospheric Observatory (SOHO). The magnetic field associated with the equatorial coronal hole is strongly connected to that of the active region at its base, resulting in the two features rotating at almost the same rate.

Bromage, B. J. I.; DelZanna, G.; DeForest, C.; Thompson, B.; Clegg, J. R.

1997-01-01

264

Equatorial Oscillations in Jupiter's and Saturn's Atmospheres  

NASA Technical Reports Server (NTRS)

Equatorial oscillations in the zonal-mean temperatures and zonal winds have been well documented in Earth's middle atmosphere. A growing body of evidence from ground-based and Cassini spacecraft observations indicates that such phenomena also occur in the stratospheres of Jupiter and Saturn. Earth-based midinfrared measurements spanning several decades have established that the equatorial stratospheric temperatures on Jupiter vary with a cycle of 4-5 years and on Saturn with a cycle of approximately 15 years. Spectra obtained by the Composite Infrared Spectrometer (CIRS) during the Cassini swingby at the end of 2000, with much better vertical resolution than the ground-based data, indicated a series of vertically stacked warm and cold anomalics at Jupiter's equator; a similar structurc was seen at Saturn's equator in CIRS limb measurements made in 2005, in the early phase of Cassini's orbital tour. The thermal wind equation implied similar patterns of mean zonal winds increasing and decreasing with altitude. On Saturn the peak-to-pcak amplitude of this variation was nearly 200 meters per second. The alternating vertical pattern of wanner and colder cquatorial tcmperatures and easterly and westerly tendencies of the zonal winds is seen in Earth's equatorial oscillations, where the pattern descends with time, The Cassini Jupiter and early Saturn observations were snapshots within a limited time interval, and they did not show the temporal evolution of the spatial patterns. However, more recent Saturn observations by CIRS (2010) and Cassini radio-occultation soundings (2009-2010) have provided an opportunity to follow the change of the temperature-zonal wind pattern, and they suggest there is descent, at a rate of roughly one scale height over four years. On Earth, the observed descent in the zonal-mean structure is associated with the absorption of a combination of vertically propagating waves with easlerly and westerly phase velocities. The peak-to-peak zonal wind amplitude in the oscillation pattern and the rate of descent constrain the absorbed wave flux of zonal momentum. On Saturn this is approximately 0.05 square meters per square seconds, which is comparable to if not greater than that associated with the terrestrial oscillations. We discuss possible candidates for the absorbed waves on Saturn. On Earth the wave forcing of the equatorial oscillation generales secondary circulations that can affcct the temperature and wind structure at latitudes well away from the equator, and we discuss possible evidence of that on Saturn.

Flasar, F. Michael; Guerlet, S.; Fouchet, T.; Schinder, P. J.

2011-01-01

265

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

266

Fading of Jupiter's South Equatorial Belt  

NASA Technical Reports Server (NTRS)

One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma

2011-01-01

267

Bubble instability in overheated liquid Helium-3  

NASA Astrophysics Data System (ADS)

The generation and the growth of vapor bubbles in metastable liquid Helium-3 are studied. The finite diffuse layer of vapor bubble, the temperature dependence of the surface tension and the relaxation processes are taken into consideration. We show that the growth of bubble in overheated liquid Helium-3 is significantly influenced by the memory effects caused by the dynamic Fermi-surface distortions. In particular, the increase of bubble is strongly hindered and accompanied by the characteristic oscillations of the bubble radius. The oscillations of the bubble radius disappear in a short relaxation-time limit where the memory effects are negligible.

Kolomietz, V. M.

2014-11-01

268

IRON PHOTOCHEMISTRY IN SEAWATER FROM THE EQUATORIAL PACIFIC  

EPA Science Inventory

The photochemistry of iron in surface waters, and its implications to iron bioavailability, was examined on two cruises to the equatorial Pacific. ecktop incubations were performed with equatorial seawater to which iron was added in various chemical forms. esults showed clear diu...

269

Eastern equatorial Pacific response to three composite westerly wind types  

Microsoft Academic Search

It has been suggested recently that episodes of westerly wind near the international date line in the western Pacific tend to fall into one of four types. Three of the types have enough equatorial zonal wind variation to be able to induce an eastern Pacific response by forcing equatorial waves. In this note we examine the central and eastern Pacific

Benjamin S. Giese; D. E. Harrison

1991-01-01

270

Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone  

E-print Network

Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone Eric Gehrie,1 outcrops in high latitudes. We present dissolved argon data that distinguishes a diapycnally ventilated), Subsurface ocean argon disequilibrium reveals the equatorial Pacific shadow zone, Geophys. Res. Lett., 33, L

Archer, David

271

Ethnic diversity deflates price bubbles.  

PubMed

Markets are central to modern society, so their failures can be devastating. Here, we examine a prominent failure: price bubbles. Bubbles emerge when traders err collectively in pricing, causing misfit between market prices and the true values of assets. The causes of such collective errors remain elusive. We propose that bubbles are affected by ethnic homogeneity in the market and can be thwarted by diversity. In homogenous markets, traders place undue confidence in the decisions of others. Less likely to scrutinize others' decisions, traders are more likely to accept prices that deviate from true values. To test this, we constructed experimental markets in Southeast Asia and North America, where participants traded stocks to earn money. We randomly assigned participants to ethnically homogeneous or diverse markets. We find a marked difference: Across markets and locations, market prices fit true values 58% better in diverse markets. The effect is similar across sites, despite sizeable differences in culture and ethnic composition. Specifically, in homogenous markets, overpricing is higher as traders are more likely to accept speculative prices. Their pricing errors are more correlated than in diverse markets. In addition, when bubbles burst, homogenous markets crash more severely. The findings suggest that price bubbles arise not only from individual errors or financial conditions, but also from the social context of decision making. The evidence may inform public discussion on ethnic diversity: it may be beneficial not only for providing variety in perspectives and skills, but also because diversity facilitates friction that enhances deliberation and upends conformity. PMID:25404313

Levine, Sheen S; Apfelbaum, Evan P; Bernard, Mark; Bartelt, Valerie L; Zajac, Edward J; Stark, David

2014-12-30

272

Initial conditions for bubble universes  

SciTech Connect

The ''bubble universes'' of Coleman and De Luccia play a crucial role in string cosmology. Since our own Universe is supposed to be of this kind, bubble cosmology should supply definite answers to the long-standing questions regarding cosmological initial conditions. In particular, it must explain how an initial singularity is avoided, and also how the initial conditions for inflation were established. I argue that the simplest nonanthropic approach to these problems involves a requirement that the spatial sections defined by distinguished bubble observers should not be allowed to have arbitrarily small volumes. Casimir energy is a popular candidate for a quantum effect which can ensure this, but (because it violates energy conditions) there is a danger that it could lead to nonperturbative instabilities in string theory. I make a simple proposal for the initial conditions of a bubble universe, and show that my proposal ensures that the system is nonperturbatively stable. Thus, low-entropy conditions can be established at the beginning of a bubble universe without violating the second law of thermodynamics and without leading to instability in string theory. These conditions are inherited from the ambient spacetime.

McInnes, Brett [Department of Mathematics, National University of Singapore, 2 Science Drive 2, Singapore 117543 (Singapore)

2008-06-15

273

Initial Conditions for Bubble Universes  

E-print Network

The "bubble universes" of Coleman and De Luccia play a crucial role in string cosmology. Since our own Universe is supposed to be of this kind, bubble cosmology should supply definite answers to the long-standing questions regarding cosmological initial conditions. In particular, it must explain how an initial singularity is avoided, and also how the initial conditions for Inflation were established. We argue that the simplest non-anthropic approach to these problems involves a requirement that the spatial sections defined by distinguished bubble observers should not be allowed to have arbitrarily small volumes. Casimir energy is a popular candidate for a quantum effect which can ensure this, but [because it violates energy conditions] there is a danger that it could lead to non-perturbative instabilities in string theory. We make a simple proposal for the initial conditions of a bubble universe, and show that our proposal ensures that the system is non-perturbatively stable. Thus, low-entropy conditions can be established at the beginning of a bubble universe without violating the Second Law of thermodynamics and without leading to instability in string theory. These conditions are inherited from the ambient spacetime.

Brett McInnes

2007-05-29

274

Ethnic diversity deflates price bubbles  

PubMed Central

Markets are central to modern society, so their failures can be devastating. Here, we examine a prominent failure: price bubbles. Bubbles emerge when traders err collectively in pricing, causing misfit between market prices and the true values of assets. The causes of such collective errors remain elusive. We propose that bubbles are affected by ethnic homogeneity in the market and can be thwarted by diversity. In homogenous markets, traders place undue confidence in the decisions of others. Less likely to scrutinize others’ decisions, traders are more likely to accept prices that deviate from true values. To test this, we constructed experimental markets in Southeast Asia and North America, where participants traded stocks to earn money. We randomly assigned participants to ethnically homogeneous or diverse markets. We find a marked difference: Across markets and locations, market prices fit true values 58% better in diverse markets. The effect is similar across sites, despite sizeable differences in culture and ethnic composition. Specifically, in homogenous markets, overpricing is higher as traders are more likely to accept speculative prices. Their pricing errors are more correlated than in diverse markets. In addition, when bubbles burst, homogenous markets crash more severely. The findings suggest that price bubbles arise not only from individual errors or financial conditions, but also from the social context of decision making. The evidence may inform public discussion on ethnic diversity: it may be beneficial not only for providing variety in perspectives and skills, but also because diversity facilitates friction that enhances deliberation and upends conformity. PMID:25404313

Levine, Sheen S.; Apfelbaum, Evan P.; Bernard, Mark; Bartelt, Valerie L.; Zajac, Edward J.; Stark, David

2014-01-01

275

Initial conditions for bubble universes  

NASA Astrophysics Data System (ADS)

The “bubble universes” of Coleman and De Luccia play a crucial role in string cosmology. Since our own Universe is supposed to be of this kind, bubble cosmology should supply definite answers to the long-standing questions regarding cosmological initial conditions. In particular, it must explain how an initial singularity is avoided, and also how the initial conditions for inflation were established. I argue that the simplest nonanthropic approach to these problems involves a requirement that the spatial sections defined by distinguished bubble observers should not be allowed to have arbitrarily small volumes. Casimir energy is a popular candidate for a quantum effect which can ensure this, but (because it violates energy conditions) there is a danger that it could lead to nonperturbative instabilities in string theory. I make a simple proposal for the initial conditions of a bubble universe, and show that my proposal ensures that the system is nonperturbatively stable. Thus, low-entropy conditions can be established at the beginning of a bubble universe without violating the second law of thermodynamics and without leading to instability in string theory. These conditions are inherited from the ambient spacetime.

McInnes, Brett

2008-06-01

276

Observations of the generation of eastward equatorial electric fields near dawn  

NASA Astrophysics Data System (ADS)

We report and discuss interesting observations of the variability of electric fields and ionospheric densities near sunrise in the equatorial ionosphere made by instruments onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite over six consecutive orbits. Electric field measurements were made by the Vector Electric Field Instrument (VEFI), and ionospheric plasma densities were measured by Planar Langmuir Probe (PLP). The data were obtained on 17 June 2008, a period of solar minimum conditions. Deep depletions in the equatorial plasma density were observed just before sunrise on three orbits, for which one of these depletions was accompanied by a very large eastward electric field associated with the density depletion, as previously described by de La Beaujardière et al. (2009), Su et al. (2009) and Burke et al. (2009). The origin of this large eastward field (positive upward/meridional drift), which occurred when that component of the field is usually small and westward, is thought to be due to a large-scale Rayleigh-Taylor process. On three subsequent orbits, however, a distinctly different, second type of relationship between the electric field and plasma density near dawn was observed. Enhancements of the eastward electric field were also detected, one of them peaking around 3 mV m-1, but they were found to the east (later local time) of pre-dawn density perturbations. These observations represent sunrise enhancements of vertical drifts accompanied by eastward drifts such as those observed by the San Marco satellite (Aggson et al., 1995). Like the San Marco measurements, the enhancements occurred during winter solstice and low solar flux conditions in the Pacific longitude sector. While the evening equatorial ionosphere is believed to present the most dramatic examples of variability, our observations exemplify that the dawn sector can be highly variable as well.

Kelley, M. C.; Rodrigues, F. S.; Pfaff, R. F.; Klenzing, J.

2014-09-01

277

Approximations for acoustically excited bubble cluster dynamics  

NASA Astrophysics Data System (ADS)

In this paper the effect of interaction on the expansion of a bubble in a regular monodisperse cluster is investigated. By a geometric construction a two-dimensional ordinary differential equation with an exact expression for first-order bubble interactions is derived for an n-bubble model. An approximate equation is derived for the rapid expansion of the bubble which can be solved yielding an analytic expression for the collapse of a bubble which undergoes inertial cavitation. It is then demonstrated that the maximum volume of a bubble in a cluster is considerably less than that of a single bubble. This result is of significance as typically the dispersion relationship, the wave speed and the co-efficient of attenuation are calculated using a single bubble model and summed for the total number of bubbles to yield the void fraction. Furthermore it is shown that the maximum radius of a bubble in the cluster is considerably smaller than that of a single bubble, yet the duration of the collapse phase is only weakly dependent on the number of bubbles. Hence, it is conjectured that the likelihood of fragmentation due to Rayleigh-Taylor instability is reduced. The results from the analysis are in good agreement with full numerical simulations of multi-bubble dynamics, as well as experimental observations

Sinden, D.; Stride, E.; Saffari, N.

2012-03-01

278

Equatorial radius of the earth: A dynamical determination  

NASA Technical Reports Server (NTRS)

An interesting variation on the familiar method of determining 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 parameters are GM = 3,986008 + or - 4 X 1014 cu cm/sec/sec which includes the relative mass of atmosphere approximately 0.000001 x GM, the equatorial gravity gamma sub e = 978,030.9 milligals (constrained in this solution by the Potsdam Correction of 13.67 milligals as the Potsdam Correction is more directly, or less indirectly, measurable than the equatorial gravity) and an ellipsoidal flattening of f = 1/298.255.

Khan, M. A.

1972-01-01

279

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, including magnetic probe measurements and high-speed camera imaging, will be presented. [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).

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

2008-11-01

280

Ionic physisorption on bubbles induced by pulsed ultra-sound.  

PubMed

Ion flotation processes involve the use of bubbles in order to separate ionic species from a mixed solution. Due to bubble interfaces we may assume null curvature at the molecular scale, where selective ion adsorption might be more easily investigated than with liquid-liquid extraction. In contrast to a classical flotation set-up, where bubbles are introduced via a glass frit, we use here a controlled sono-device generating cavitation bubbles which are initially absolutely clean. Moreover we have a faster process with a smaller device. The liquid phase resulting from the coalescence of the overflowing foam is enriched in some ions versus the initial brine. We show here that this effect follows the Hofmeister series and can be attributed to a weak adsorption of hydrated ions at the surfactant-water interface. The selectivity of alkali metals physisorbed at interfaces is analysed through the concentrations of competing ions remaining in solution by inductively coupled plasma optical emission spectrometry. Cationic selectivity, which is independent of the method for obtaining a foam, is discussed via the Gibbs free energy difference for bulk to hydrated surfactant monolayer. Relative values of effective adsorption energies are determined versus sodium ions taken as reference and correspond to 1-3% of the total hydration free energy. PMID:20931120

Toquer, Guillaume; Zemb, Thomas; Shchukin, Dmitry; Möhwald, Helmut

2010-11-21

281

Scintillations associated with bottomside sinusoidal irregularities in the equatorial F region  

NASA Technical Reports Server (NTRS)

Multisatellite scintillation observations and spaced receiver drift measurements are presented for a category of equatorial F region plasma irregularities characterized by nearly sinusoidal waveforms in the ion number density. The observations were made at Huancayo, Peru, and the measurements at Ancon, Peru, associated with irregularities observed by the Atmospheric-Explorer-E satellite on a few nights in December 1979. Utilizing ray paths to various geostationary satellites, it was found that the irregularities grow and decay almost simultaneously in long-lived patches extending at least 1000 km in the east-west direction.

Basu, S.; Basu, S.; Valladares, C. E.; Dasgupta, A.; Whitney, H. E.

1986-01-01

282

Components of rainy seasons variability in Equatorial East Africa : onset, cessation, rainfall frequency and intensity  

E-print Network

1 Components of rainy seasons variability in Equatorial East Africa : onset, cessation, rainfall rainfall variables is analysed over Equatorial East Africa (Kenya and northeastern Tanzania). At station

Boyer, Edmond

283

Bursting Bubbles and Bilayers  

PubMed Central

This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition - in particular, poly (ethylene glyclol) (PEG) - is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the “brush” regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented, including those involving microbubbles to deliver cargo into a cell, and those - not necessarily involving microubbles - to release cargo from a phospholipid vesicle (or reverse sonoporation). It is shown that the rate of (reverse) sonoporation from liposomes correlates with phospholipid bilayer phase behavior, liquid-disordered phases giving appreciably faster release than liquid-ordered phases. Moreover, liquid-disordered phases exhibit evidence of two release mechanisms, which are described well mathematically by enhanced diffusion (possibly via dilation of membrane phospholipids) and irreversible membrane disruption, whereas liquid-ordered phases are described by a single mechanism, which has yet to be positively identified. The ability to tune release kinetics with bilayer composition makes reverse sonoporation of phospholipid vesicles a promising methodology for controlled drug delivery. Moreover, nesting of microbubbles inside vesicles constitutes a truly “theranostic” vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery. PMID:23382772

Wrenn, Steven P.; Dicker, Stephen M.; Small, Eleanor F.; Dan, Nily R.; Mleczko, Micha?; Schmitz, Georg; Lewin, Peter A.

2012-01-01

284

Bursting bubbles and bilayers.  

PubMed

This paper discusses various interactions between ultrasound, phospholipid monolayer-coated gas bubbles, phospholipid bilayer vesicles, and cells. The paper begins with a review of microbubble physics models, developed to describe microbubble dynamic behavior in the presence of ultrasound, and follows this with a discussion of how such models can be used to predict inertial cavitation profiles. Predicted sensitivities of inertial cavitation to changes in the values of membrane properties, including surface tension, surface dilatational viscosity, and area expansion modulus, indicate that area expansion modulus exerts the greatest relative influence on inertial cavitation. Accordingly, the theoretical dependence of area expansion modulus on chemical composition-- in particular, poly (ethylene glyclol) (PEG)--is reviewed, and predictions of inertial cavitation for different PEG molecular weights and compositions are compared with experiment. Noteworthy is the predicted dependence, or lack thereof, of inertial cavitation on PEG molecular weight and mole fraction. Specifically, inertial cavitation is predicted to be independent of PEG molecular weight and mole fraction in the so-called mushroom regime. In the "brush" regime, however, inertial cavitation is predicted to increase with PEG mole fraction but to decrease (to the inverse 3/5 power) with PEG molecular weight. While excellent agreement between experiment and theory can be achieved, it is shown that the calculated inertial cavitation profiles depend strongly on the criterion used to predict inertial cavitation. This is followed by a discussion of nesting microbubbles inside the aqueous core of microcapsules and how this significantly increases the inertial cavitation threshold. Nesting thus offers a means for avoiding unwanted inertial cavitation and cell death during imaging and other applications such as sonoporation. A review of putative sonoporation mechanisms is then presented, including those involving microbubbles to deliver cargo into a cell, and those--not necessarily involving microubbles--to release cargo from a phospholipid vesicle (or reverse sonoporation). It is shown that the rate of (reverse) sonoporation from liposomes correlates with phospholipid bilayer phase behavior, liquid-disordered phases giving appreciably faster release than liquid-ordered phases. Moreover, liquid-disordered phases exhibit evidence of two release mechanisms, which are described well mathematically by enhanced diffusion (possibly via dilation of membrane phospholipids) and irreversible membrane disruption, whereas liquid-ordered phases are described by a single mechanism, which has yet to be positively identified. The ability to tune release kinetics with bilayer composition makes reverse sonoporation of phospholipid vesicles a promising methodology for controlled drug delivery. Moreover, nesting of microbubbles inside vesicles constitutes a truly "theranostic" vehicle, one that can be used for both long-lasting, safe imaging and for controlled drug delivery. PMID:23382772

Wrenn, Steven P; Dicker, Stephen M; Small, Eleanor F; Dan, Nily R; Mleczko, Micha?; Schmitz, Georg; Lewin, Peter A

2012-01-01

285

Unorthodox bubbles when boiling in cold water  

NASA Astrophysics Data System (ADS)

High-speed movies are taken when bubbles grow at gold surfaces heated spotwise with a near-infrared laser beam heating water below the boiling point (60-70 °C) with heating powers spanning the range from very low to so high that water fails to rewet the surface after bubbles detach. Roughly half the bubbles are conventional: They grow symmetrically through evaporation until buoyancy lifts them away. Others have unorthodox shapes and appear to contribute disproportionately to heat transfer efficiency: mushroom cloud shapes, violently explosive bubbles, and cavitation events, probably stimulated by a combination of superheating, convection, turbulence, and surface dewetting during the initial bubble growth. Moreover, bubbles often follow one another in complex sequences, often beginning with an unorthodox bubble that stirs the water, followed by several conventional bubbles. This large dataset is analyzed and discussed with emphasis on how explosive phenomena such as cavitation induce discrepancies from classical expectations about boiling.

Parker, Scott; Granick, Steve

2014-01-01

286

Removal of hydrogen bubbles from nuclear reactors  

NASA Technical Reports Server (NTRS)

Method proposed for removing large hydrogen bubbles from nuclear environment uses, in its simplest form, hollow spheres of palladium or platinum. Methods would result in hydrogen bubble being reduced in size without letting more radioactivity outside reactor.

Jenkins, R. V.

1980-01-01

287

Unorthodox bubbles when boiling in cold water.  

PubMed

High-speed movies are taken when bubbles grow at gold surfaces heated spotwise with a near-infrared laser beam heating water below the boiling point (60-70?°C) with heating powers spanning the range from very low to so high that water fails to rewet the surface after bubbles detach. Roughly half the bubbles are conventional: They grow symmetrically through evaporation until buoyancy lifts them away. Others have unorthodox shapes and appear to contribute disproportionately to heat transfer efficiency: mushroom cloud shapes, violently explosive bubbles, and cavitation events, probably stimulated by a combination of superheating, convection, turbulence, and surface dewetting during the initial bubble growth. Moreover, bubbles often follow one another in complex sequences, often beginning with an unorthodox bubble that stirs the water, followed by several conventional bubbles. This large dataset is analyzed and discussed with emphasis on how explosive phenomena such as cavitation induce discrepancies from classical expectations about boiling. PMID:24580324

Parker, Scott; Granick, Steve

2014-01-01

288

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view to the west, from between the cloud layers and over the patchy white clouds to the east of the hotspot. This is probably an area where moist convection is occurring over large horizontal distances, similar to the atmosphere over the equatorial ocean on Earth. The clouds are high and thick, and are observed to change rapidly over short time scales.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

1997-01-01

289

The morphological catalogue of galaxies equatorial survey  

NASA Technical Reports Server (NTRS)

We present 865 redshifts of galaxies located in the equatorial strip delta between -17.5 deg and -2.5 deg in the right ascension range between 20 h and 5 h. Redshifts have been obtained for the complete sample of all 833 galaxies in the Morphological Catalog of Galaxies with magnitudes brighter than m = 14.5 (corresponding approximately to m(Zwicky) = 15.0). This sample also includes three galaxies from other sources with more reliable magnitudes, satisfying this limit, and 29 fainter galaxies, usually companions of the galaxies in the magnitude limited sample. Our maps of a very large volume of nearby space demonstrate a variety of coherent large scale structures which include large voids, 20-50/h Mpc in diameter and large walls at least 70/h Mpc across.

Huchra, John; Latham, David W.; Da Costa, L. N.; Pellegrini, P. S.; Willmer, C. N. A.

1993-01-01

290

Climatic trends of the equatorial undercurrent: A backup mechanism for sustaining the equatorial Pacific production  

NASA Astrophysics Data System (ADS)

The Equatorial Undercurrent (EUC) is the major source of iron to the equatorial Pacific and it is sensitive to climatic changes as other components of the tropical Pacific. This work proposes a methodology based on a Lagrangian approach aimed at understanding the changes in the transport of iron rich waters to the EUC in a future climate change scenario, using climate model data from an Earth system model. A selected set of regions from the northern and southern extra-equatorial Pacific has been chosen. These regions are characterized by the presence of iron sources from continental shelf processes like the Papua New Guinea region and atmospheric deposition like the northern subtropical gyre. The trajectories that reach the EUC during the 20th and the 21st century departing from these areas have been analyzed using a set of statistics designed to determine variations in the amount of transport and in the travel times of the water masses. The transport of waters to the EUC from the north Pacific subtropical gyre and from the Bismarck Sea is projected to increase during the 21st century. The increase is particularly significant for water masses from the northern subtropical gyre, with travel times lower than 10 years in the second half of the 21st century. This increased interaction between the extra-tropics and the EUC may bring additional iron-rich waters in the high-nutrient low-chlorophyll region of the equatorial Pacific compatibly with the significant increase of the simulated net primary production found in the biogeochemical model, thus partly offsetting the anticipated decrease of production implied by the surface warming.

Ruggio, Raffaele; Vichi, Marcello; Paparella, Francesco; Masina, Simona

2013-07-01

291

PARTON BUBBLE MODEL FOR TWO PARTICLE ANGULAR CORRELATIONS AT RHIC/LHC.  

SciTech Connect

In an earlier paper we developed a bubble model, based on a view we had shared with van Hove for over two decades. Namely, that if a quark-gluon plasma is produced in a high energy heavy ion collider, then its hadronization products would likely be emitted from small bubbles localized in phase space containing plasma. In this paper we refined the model to become a parton bubble model in which each localized bubble contains initially 3-4 partons which are almost entirely gluons forming a gluon hot spot. We greatly expanded the transverse momentum interval investigated, and thus are able to treat recombination effects within each bubble. We again utilize two particle correlations as a sensitive method for detecting the average bubble substructure. In this manuscript we make many predictions for angular correlations detectable at RHIC and which will be later modified to LHC conditions. Some early available low precision correlation analyses is qualitatively explained. However a critical consistency test of the model can be made with high precision data expected in the near future.

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

2006-06-27

292

Analysis of a pulsed discharge within single bubbles in water under synchronized conditions  

NASA Astrophysics Data System (ADS)

Synchronized generation of single bubbles and an underwater discharge in the bubbles was performed using pulsed injection of feed gas with a piezoelectric valve. The differences in the discharge appearance and the after-effect on the bubble were systematically studied with different kinds of gases. In molecular gases such as N2 and O2, surface discharge along the inner bubble surface predominated and the disturbance caused wrinkles on the bubble surface, while in rare gases, such as He, Ne and Ar, a large hump formed on the smooth surface due to a rather volumetric discharge. When the input power was increased, the discharge sometimes caused the collapse of a single bubble, producing smaller bubbles. It was observed by emission spectra that excited species of OH, H and O radicals were produced in the discharge plasma. The emission intensity ratio of the H? line to the OH band was larger in He and Ne gases than in other gases, suggesting differences in the dissociation channels.

Tachibana, Kunihide; Takekata, Yuki; Mizumoto, Yusuke; Motomura, Hideki; Jinno, Masafumi

2011-06-01

293

Microfluidics with ultrasound-driven bubbles  

Microsoft Academic Search

Microstreaming from oscillating bubbles is known to induce vigorous vortex flow. Here we show how to harness the power of bubble streaming in an experiment to achieve directed transport flow of high velocity, allowing design and manufacture of microfluidic MEMS devices. By combining oscillating bubbles with solid protrusions positioned on a patterned substrate, solid beads and lipid vesicles are guided

P. Marmottant; J. P. Raven; H. Gardeniers; J. G. Bomer; S. Hilgenfeldt

2006-01-01

294

Pulsed electrogeneration of bubbles for electroflotation  

Microsoft Academic Search

Fine bubbles of the size required for many processes such as electroflotation can be generated by electrolysis. A large number of factors such as electrode material, electrode surface\\/morphological properties, pH and current density affect the gas bubble size distribution. This work is aimed at studies on the effect of interrupted current (pulsed) electrolysis on the generation of gas bubbles. A

N. K. Khosla; S. Venkatachalam; P. Somasundaran

1991-01-01

295

Frictional drag reduction by bubble injection  

NASA Astrophysics Data System (ADS)

The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.

Murai, Yuichi

2014-07-01

296

Possible applications of bubble acoustics in Nature  

Microsoft Academic Search

Gas bubbles are the most potent naturally-occurring entities that influence the acoustic environment in liquids. Upon entrainment under breaking waves, waterfalls, or rainfall over water, each bubble undergoes small amplitude decaying pulsations with a natural frequency that varies approximately inversely with the bubble radius, giving rise to the 'plink' of a dripping tap or the roar of a cataract. When

T. G. Leighton; D. C. Finfer

297

Radiation Damping at a Bubble Wall  

E-print Network

The first order phase transition proceeds via nucleation and growth of true vacuum bubbles. When charged particles collide with the bubble they could radiate electromagnetic wave. We show that, due to an energy loss of the particles by the radiation, the damping pressure acting on the bubble wall depends on the velocity of the wall even in a thermal equilibrium state.

Jae-weon Lee; Kyungsub Kim; Chul H. Lee; Ji-ho Jang

1999-09-27

298

Radiation Damping at a Bubble Wall  

Microsoft Academic Search

The first order phase transition proceeds via nucleation and growth of true vacuum bubbles. When charged particles collide with the bubble they could radiate electromagnetic wave. We show that, due to an energy loss of the particles by the radiation, the damping pressure acting on the bubble wall depends on the velocity of the wall even in a thermal equilibrium

Jae-weon Lee; Kyungsub Kim; Chul H. Lee; Ji-ho Jang

1999-01-01

299

Radiation Damping at a Bubble Wall  

E-print Network

The first order phase transition proceeds via nucleation and growth of true vacuum bubbles. When charged particles collide with the bubble they could radiate electromagnetic wave. We show that, due to an energy loss of the particles by the radiation, the damping pressure acting on the bubble wall depends on the velocity of the wall even in a thermal equilibrium state.

Lee, J; Lee, C H; Jang, J; Lee, Jae-weon; Kim, Kyungsub; Lee, Chul H.; Jang, Ji-ho

1999-01-01

300

Marangoni bubble motion in zero gravity  

Microsoft Academic Search

It is shown experimentally that the Marangoni phenomenon is a primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low-gravity environment. In such two-phase flow systems, local variations in bubble surface tension are caused by a temperature gradient in the liquid. Shearing stresses thus generated at the bubble surface lead to convection in both

R. L. Thompson; K. J. de Witt

1979-01-01

301

MARANGONI BUBBLE MOTION PHENOMENON IN ZERO GRAVITY  

Microsoft Academic Search

The Marangoni phenomenon is shown to be the primary mechanism for the movement of a gas bubble in a nonisothermal liquid in a low-gravity environment. In such a two-phase system, local variations in surface tension at the bubble surface are caused by a temperature gradient in the liquid. Shearing stresses thus generated at the bubble surface lead to convection in

R. L. THOMPSON; K. J. DeWITT; T. L. LABUS

1980-01-01

302

Soap bubbles in paintings: Art and science  

Microsoft Academic Search

Soap bubbles became popular in 17th century paintings and prints primarily as a metaphor for the impermanence and fragility of life. The Dancing Couple (1663) by the Dutch painter Jan Steen is a good example which, among many other symbols, shows a young boy blowing soap bubbles. In the 18th century the French painter Jean-Simeon Chardin used soap bubbles not

F. Behroozi

2008-01-01

303

Effect of sodium dodecyl sulfate (SDS) on bubble characteristics and ozone transfer in a bubble column  

Microsoft Academic Search

The rising of ozone?containing bubbles in a bubble column was examined by a high?speed micro video camera. The shape of the bubbles shifted from spherical to ellipsoidal during their rise along the column. The experimental observation indicated that the average diameter at the X?axis of the bubbles was markedly increased after the bubbles left the diffuser because the gas pressure

Young Ku

2007-01-01

304

Ice bubbles confirm big chill  

SciTech Connect

Clues buried in Greenland`s icesheet indicate that during the last ice age, the climate repeatedly warmed sharply, only to slide into a renewed chill lasting thousands of years. New indicators derived from trapped bubbles of ancient gases, nitrogen and methane, indicate that these were indeed catastrophic events. This article describes the research and adjunct issues.

Kerr, R.A.

1996-06-14

305

The Trouble With Bubble Gum  

NSDL National Science Digital Library

Most students are totally unaware of the amount of sugar in bubble gum and don't know that they are literally eating sugar in huge amounts. In this chapter, the author is concerned with finding out what happens to the weight of gum when it is chewed, whic

Richard Konicek-Moran

2010-03-12

306

Bubble-driven inertial micropump  

NASA Astrophysics Data System (ADS)

The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel, or continues to grow axially when it reaches the reservoir. In the non-axial regime, the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section, but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical principles of the pump, a phenomenological one-dimensional model is developed and solved. A linear array of micropumps has been built using silicon-SU8 fabrication technology that is used to manufacture thermal inkjet printheads. Semi-continuous pumping across a 2 mm-wide channel has been demonstrated experimentally. Measured net flow with respect to viscosity variation is in excellent agreement with simulation results.

Torniainen, Erik D.; Govyadinov, Alexander N.; Markel, David P.; Kornilovitch, Pavel E.

2012-12-01

307

Electrolysis Bubbles Make Waterflow Visible  

NASA Technical Reports Server (NTRS)

Technique for visualization of three-dimensional flow uses tiny tracer bubbles of hydrogen and oxygen made by electrolysis of water. Strobe-light photography used to capture flow patterns, yielding permanent record that is measured to obtain velocities of particles. Used to measure simulated mixing turbulence in proposed gas-turbine combustor and also used in other water-table flow tests.

Schultz, Donald F.

1990-01-01

308

Hot toroidal and bubble nuclei  

NASA Astrophysics Data System (ADS)

As nuclear temperature increases, the surface-tension coefficient decreases and the Coulomb repulsion is effective in pushing the nuclear matter outward, leading to the formation of toroidal and bubble nuclei. The threshold temperatures above which these nuclei are stable against symmetry-preserving distortions are obtained. They are found to decrease with the mass number.

Wong, C.-Y.

1985-11-01

309

Breaking waves, turbulence and bubbles  

NASA Astrophysics Data System (ADS)

The air-sea fluxes of heat, momentum, and gases are to a large extent affected by wave-induced turbulence in the near-surface ocean layer, and are generally increased over the fluxes in a law-of-the-wall type boundary layer. However, air-bubbles generated during the wave breaking process may affect the density stratification and in turn reduce turbulence intensity in the near-surface layer. The turbulence field beneath surface waves is rather complex and provides great challenges for detailed observations. We obtained high resolution near-surface velocity profiles, bubble cloud measurements and video recordings of the breaking activity in a coastal strait. Conditions ranged from moderate to strong wind forcing with wind speed ranging from 5 m/s to 20 m/s. Estimates of the dissipation rates of turbulence kinetic energy are calculated from the in-situ velocity measurements. We find dissipation rates, fluctuating by more than two orders of magnitude, are closely linked to the air-fraction associated with micro-bubbles. Combining these turbulence estimates and the bubble cloud characteristics we infer differences in the strength of wave breaking and its effect on wave-induced mixing and air-sea exchange processes.

Gemmrich, Johannes; Vagle, Svein; Thomson, Jim

2014-05-01

310

The Coming Law School Bubble  

ERIC Educational Resources Information Center

In this article, the author explains how forty years of politicized hiring in the law schools has left its destructive mark. The results are potentially catastrophic: Market forces and internal law school policies may be combining to produce a legal education bubble the likes of which the country has never seen. (Contains 11 footnotes.)

Krauss, Michael I.

2011-01-01

311

Phase and coherence of longitudinally separated equatorial ionospheric scintillation  

NASA Astrophysics Data System (ADS)

This paper presents the first calculation of phase and coherence of cross-wavelet transform applied on longitudinally separated VHF and L-band equatorial ionospheric scintillation. The cross-wavelet analysis has utilized scintillation observations made over equatorial South America and Christmas Island. Part of the results of this study has been reported recently in the Geophysical Research Letters by Shume and Mannucci (2013). The phase and coherence analysis were employed on pairs of scintillation observations separated by longitudes thereby to develop VHF and L-band scintillation (and equatorial spread F) forecast tools west of observation sites.

Shume, E. B.; Mannucci, A. J.

2013-12-01

312

Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion  

NASA Astrophysics Data System (ADS)

This paper provides the theoretical basis for energetic vapor bubble implosions induced by a standing acoustic wave. Its primary goal is to describe, explain, and demonstrate the plausibility of the experimental observations by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] of thermonuclear fusion for imploding cavitation bubbles in chilled deuterated acetone. A detailed description and analysis of these data, including a resolution of the criticisms that have been raised, together with some preliminary HYDRO code simulations, has been given by Nigmatulin et al. [Vestnik ANRB (Ufa, Russia) 4, 3 (2002); J. Power Energy 218-A, 345 (2004)] and Lahey et al. [Adv. Heat Transfer (to be published)]. In this paper a hydrodynamic shock (i.e., HYDRO) code model of the spherically symmetric motion for a vapor bubble in an acoustically forced liquid is presented. This model describes cavitation bubble cluster growth during the expansion period, followed by a violent implosion during the compression period of the acoustic cycle. There are two stages of the bubble dynamics process. The first, low Mach number stage, comprises almost all the time of the acoustic cycle. During this stage, the radial velocities are much less than the sound speeds in the vapor and liquid, the vapor pressure is very close to uniform, and the liquid is practically incompressible. This process is characterized by the inertia of the liquid, heat conduction, and the evaporation or condensation of the vapor. The second, very short, high Mach number stage is when the radial velocities are the same order, or higher, than the sound speeds in the vapor and liquid. In this stage high temperatures, pressures, and densities of the vapor and liquid take place. The model presented herein has realistic equations of state for the compressible liquid and vapor phases, and accounts for nonequilibrium evaporation/condensation kinetics at the liquid/vapor interface. There are interacting shock waves in both phases, which converge toward and reflect from the center of the bubble, causing dissociation, ionization, and other related plasma physics phenomena during the final stage of bubble collapse. For a vapor bubble in a deuterated organic liquid (e.g., acetone), during the final stage of collapse there is a nanoscale region (diameter ˜100nm) near the center of the bubble in which, for a fraction of a picosecond, the temperatures and densities are extremely high (˜108K and ˜10g/cm3, respectively) such that thermonuclear fusion may take place. To quantify this, the kinetics of the local deuterium/deuterium (D/D) nuclear fusion reactions was used in the HYDRO code to determine the intensity of the fusion reactions. Numerical HYDRO code simulations of the bubble implosion process have been carried out for the experimental conditions used by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] at Oak Ridge National Laboratory. The results show good agreement with the experimental data on bubble fusion that was measured in chilled deuterated acetone.

Nigmatulin, Robert I.; Akhatov, Iskander Sh.; Topolnikov, Andrey S.; Bolotnova, Raisa Kh.; Vakhitova, Nailya K.; Lahey, Richard T.; Taleyarkhan, Rusi P.

2005-10-01

313

Theory of supercompression of vapor bubbles and nanoscale thermonuclear fusion  

SciTech Connect

This paper provides the theoretical basis for energetic vapor bubble implosions induced by a standing acoustic wave. Its primary goal is to describe, explain, and demonstrate the plausibility of the experimental observations by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] of thermonuclear fusion for imploding cavitation bubbles in chilled deuterated acetone. A detailed description and analysis of these data, including a resolution of the criticisms that have been raised, together with some preliminary HYDRO code simulations, has been given by Nigmatulin et al. [Vestnik ANRB (Ufa, Russia) 4, 3 (2002); J. Power Energy 218-A, 345 (2004)] and Lahey et al. [Adv. Heat Transfer (to be published)]. In this paper a hydrodynamic shock (i.e., HYDRO) code model of the spherically symmetric motion for a vapor bubble in an acoustically forced liquid is presented. This model describes cavitation bubble cluster growth during the expansion period, followed by a violent implosion during the compression period of the acoustic cycle. There are two stages of the bubble dynamics process. The first, low Mach number stage, comprises almost all the time of the acoustic cycle. During this stage, the radial velocities are much less than the sound speeds in the vapor and liquid, the vapor pressure is very close to uniform, and the liquid is practically incompressible. This process is characterized by the inertia of the liquid, heat conduction, and the evaporation or condensation of the vapor. The second, very short, high Mach number stage is when the radial velocities are the same order, or higher, than the sound speeds in the vapor and liquid. In this stage high temperatures, pressures, and densities of the vapor and liquid take place. The model presented herein has realistic equations of state for the compressible liquid and vapor phases, and accounts for nonequilibrium evaporation/condensation kinetics at the liquid/vapor interface. There are interacting shock waves in both phases, which converge toward and reflect from the center of the bubble, causing dissociation, ionization, and other related plasma physics phenomena during the final stage of bubble collapse. For a vapor bubble in a deuterated organic liquid (e.g., acetone), during the final stage of collapse there is a nanoscale region (diameter {approx}100 nm) near the center of the bubble in which, for a fraction of a picosecond, the temperatures and densities are extremely high ({approx}10{sup 8} K and {approx}10 g/cm{sup 3}, respectively) such that thermonuclear fusion may take place. To quantify this, the kinetics of the local deuterium/deuterium (D/D) nuclear fusion reactions was used in the HYDRO code to determine the intensity of the fusion reactions. Numerical HYDRO code simulations of the bubble implosion process have been carried out for the experimental conditions used by Taleyarkhan et al. [Science 295, 1868 (2002); Phys. Rev. E 69, 036109 (2004)] at Oak Ridge National Laboratory. The results show good agreement with the experimental data on bubble fusion that was measured in chilled deuterated acetone.

Nigmatulin, Robert I.; Akhatov, Iskander Sh.; Topolnikov, Andrey S.; Bolotnova, Raisa Kh.; Vakhitova, Nailya K.; Lahey, Richard T. Jr.; Taleyarkhan, Rusi P. [Institute of Mechanics, Ufa Branch of the Russian Academy of Sciences, 6 Karl Marx Street, Ufa 450000 (Russian Federation); Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907-1290 (United States)

2005-10-01

314

Bubble Universe Dynamics After Free Passage  

E-print Network

We consider bubble collisions in single scalar field theories with multiple vacua. Recent work has argued that at sufficiently high impact velocities, collisions between such bubble vacua are governed by 'free passage' dynamics in which field interactions can be ignored during the collision, providing a systematic process for populating local minima without quantum nucleation. We focus on the time period that follows the bubble collision and provide evidence that, for certain potentials, interactions can drive significant deviations from the free-passage bubble profile, thwarting the production of bubbles with different field values.

Pontus Ahlqvist; Kate Eckerle; Brian Greene

2014-12-26

315

Bubble departure size in flow boiling  

NASA Astrophysics Data System (ADS)

Flow boiling experiments were conducted in a vertical annular channel to study bubble departure characteristics. Deionized water was used as the working fluid, and the tests were performed at atmospheric pressure. Bubble departure diameters were obtained from the images which were captured by a high-speed digital camera. The relationship between bubble contact diameter and departure diameter was discussed. A new model base on force balance analysis, taking bubble contact diameter into account for predicting bubble departure diameter is proposed in this study. A good agreement between predicted and measured results is achieved.

Guan, Peng; Jia, Li; Yin, Liaofei; Tan, Zetao

2014-12-01

316

Tiny Bubbles in my BEC  

SciTech Connect

Ultracold atomic gases provide a unique way for exploring many-body quantum phenomena that are inaccessible to conventional low-temperature experiments. Nearly two decades ago the Bose-Einstein condensate (BEC) - an ultracold gas of bosons in which almost all bosons occupy the same single-particle state - became experimentally feasible. Because a BEC exhibits superfluid properties, it can provide insights into the behavior of low-temperature helium liquids. We describe the case of a single distinguishable atom (an impurity) embedded in a BEC and strongly coupled to the BEC bosons. Depending on the strength of impurity-boson and boson-boson interactions, the impurity self-localizes into two fundamentally distinct regimes. The impurity atom can behave as a tightly localized 'polaron,' akin to an electron in a dielectric crystal, or as a 'bubble,' an analog to an electron bubble in superfluid helium. We obtain the ground state wavefunctions of the impurity and BEC by numerically solving the two coupled Gross-Pitaevskii equations that characterize the system. We employ the methods of imaginary time propagation and conjugate gradient descent. By appropriately varying the impurity-boson and boson-boson interaction strengths, we focus on the polaron to bubble crossover. Our results confirm analytical predictions for the polaron limit and uncover properties of the bubble regime. With these results we characterize the polaron to bubble crossover. We also summarize our findings in a phase diagram of the BEC-impurity system, which can be used as a guide in future experiments.

Blinova, Alina A. [Los Alamos National Laboratory

2012-08-01

317

Plasma Clouds in the Magnetosphere  

Microsoft Academic Search

Previous equatorial observations of the magnetospheric plasma [Gringauz, 1961; Frank, 1967 a, b, c, 1970; Vasyliunas, 19'6.8; Frank and Owens, 1970] have been made from spacecraft that made rapid but infrequent traversals of the region between 5 and 20 Rr or, as for the Vela spacecraft Bame et al., 1967], remained at great distances. The ATS I observations [Freeman and

S. E. DeForest; C. E. McIlwain

1971-01-01

318

Study of the equatorial ionosphere behavior over Brazilian region during the last two solar minima  

NASA Astrophysics Data System (ADS)

The recent solar cycle 23-24 presented an unusually deep and long lasting minimum activity period. The impact of this solar minimum on the system magnetosphere-thermosphere-ionosphere has been the subject of several studies. In this study we use the measurements by digisondes installed in the Brazilian sector to investigate the climatology of the ionospheric parameters over Sao Luis (2.33 S degrees, 44.2 W degrees, dip angle: -6.7), an equatorial site, and over Cachoeira Paulista (23S degrees, 45 W degrees, dip angle: -37), a location over the southern crest of the equatorial ionospheric anomaly (EIA). The ionograms were manually scaled in order to extract the ionospheric parameters: hmF2 (the F2 layer peak height, in km) and foF2 (the F2 layer critical frequency, in MHz). The critical frequency is related to the peak electron density of the F2-layer, NmF2, where: NmF2= 1.24 x 1010 (foF2)2 el.m-3. We determine the monthly average values of these parameters to investigate the local time and the seasonal dependence on the solar activity. We also compare the ionospheric behavior during the last two solar minima period: the solar cycle 22-23 (1996) and the solar cycle 23-24 (2008-2009). It is observed that in general the plasma densities and F-region heights are lower in the recent solar minimum, compared to the last one, especially for lower latitude region. In addition, we observe the occurrence of F-region plasma irregularities around local midnight and during post-midnight hours, which present morphological features that are distinct from typical irregularities associated with post sunset equatorial spread-F. We discuss the dependence of the ionospheric behavior on the solar flux.

Nicoli Candido, C. M.; Batista, I. S.

2013-12-01

319

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view from the southwest looking northeast, from an altitude just above the high haze layer. The streaks in the lower cloud leading towards the hotspot are visible. The upper haze layer is mostly flat, with notable small peaks that can be matched with features in the lower cloud. In reality, these areas may represent a continuous vertical cloud column.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

1997-01-01

320

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view from above and to the south of the visualized area, showing the entire model. The entire region is overlain by a thin, transparent haze. In places the haze is high and thick, especially to the east (to the right of) the hotspot.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

1997-01-01

321

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view to the northeast, from between the cloud layers and above the streaks in the lower cloud leading towards the hotspot. The hotspot is clearly visible as a deep blue feature. The cloud streaks end near the hotspot, consistent with the idea that clouds traveling along these streak lines descend and evaporate as they approach the hotspot. The upper haze layer is slightly bowed upwards above the hotspot.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

1997-01-01

322

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view to the southeast, from between the cloud layers and over the north center of the region. The tall white clouds in the lower cloud deck are probably much like large terrestrial thunderclouds. They may be regions where atmospheric water powers vertical convection over large horizontal distances.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

1997-01-01

323

Three dimensional Visualization of Jupiter's Equatorial Region  

NASA Technical Reports Server (NTRS)

Frames from a three dimensional visualization of Jupiter's equatorial region. The images used cover an area of 34,000 kilometers by 11,000 kilometers (about 21,100 by 6,800 miles) near an equatorial 'hotspot' similar to the site where the probe from NASA's Galileo spacecraft entered Jupiter's atmosphere on December 7th, 1995. These features are holes in the bright, reflective, equatorial cloud layer where warmer thermal emission from Jupiter's deep atmosphere can pass through. The circulation patterns observed here along with the composition measurements from the Galileo Probe suggest that dry air may be converging and sinking over these regions, maintaining their cloud-free appearance. The bright clouds to the right of the hotspot as well as the other bright features may be examples of upwelling of moist air and condensation.

This frame is a view to the northeast, from between the cloud layers and above the streaks in the lower cloud leading towards the hotspot. The upper haze layer has some features that match the lower cloud, such as the bright streak in the foreground of the frame. These are probably thick clouds that span several tens of vertical kilometers.

Galileo is the first spacecraft to image Jupiter in near-infrared light (which is invisible to the human eye) using three filters at 727, 756, and 889 nanometers (nm). Because light at these three wavelengths is absorbed at different altitudes by atmospheric methane, a comparison of the resulting images reveals information about the heights of clouds in Jupiter's atmosphere. This information can be visualized by rendering cloud surfaces with the appropriate height variations.

The visualization reduces Jupiter's true cloud structure to two layers. The height of a high haze layer is assumed to be proportional to the reflectivity of Jupiter at 889 nm. The height of a lower tropospheric cloud is assumed to be proportional to the reflectivity at 727 nm divided by that at 756 nm. This model is overly simplistic, but is based on more sophisticated studies of Jupiter's cloud structure. The upper and lower clouds are separated in the rendering by an arbitrary amount, and the height variations are exaggerated by a factor of 25.

The lower cloud is colored using the same false color scheme used in previously released image products, assigning red, green, and blue to the 756, 727, and 889 nanometer mosaics, respectively. Light bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue hotspot in the center is a hole in the lower cloud with an overlying thin haze.

The images used cover latitudes 1 to 10 degrees and are centered at longitude 336 degrees west. The smallest resolved features are tens of kilometers in size. These images were taken on December 17, 1996, at a range of 1.5 million kilometers (about 930,000 miles) by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

1997-01-01

324

Formation of the equatorial thermosphere anomaly trough: Local time and solar cycle variations  

NASA Astrophysics Data System (ADS)

This paper evaluates the formation and behavior of the equatorial thermosphere anomaly (ETA) trough in neutral temperature and mass density using the National Center for Atmospheric Research thermosphere-ionosphere electrodynamics general circulation model under quiet geomagnetic activity and March equinox conditions. The driving mechanism for the generation of the ETA trough in the model is field-aligned ion drag. In our simulations, during the daytime, field-aligned ion drag on the north-south flanks of the magnetic equator causes a divergence in meridional winds, leading to an upward change in vertical winds, adiabatic cooling, and a reduction in neutral temperature of about 30 K over the magnetic equator near 400 km. This response closely links ETA behavior to variations in the equatorial ionosphere anomaly (EIA) associated with local time and solar cycle. As the EIA begins to disappear in the evening, the processes in the ETA mechanism recede, causing the ETA trough to subside. The ETA trough is not completely eliminated until about after 23:00 LT. In our simulations, the trough becomes more prominent as the solar cycle progresses from low (F10.7=80) to high (F10.7=180), in agreement with observations. The neutral-ion collision frequency (proportional to variations in electron density) controls ETA day-to-night and solar cycle variations, while plasma scale height and gradients in electron number density and plasma temperature produce a secondary structure in ETA local time behavior that varies with solar cycle levels.

Hsu, Vicki W.; Thayer, Jeffrey P.; Lei, Jiuhou; Wang, Wenbin

2014-12-01

325

Equatorial Energy Accumulation and Emanation Regions: Impacts of a Zonally Varying Basic State  

Microsoft Academic Search

Previous studies have suggested that the regions of mean anomalous perturbation kinetic energy which exist in the vicinity of the equatorial upper-tropospheric westerlies are the result of the propagation of extratropical synoptic and low frequency waves through the equatorial `westerly duet' where a subsequent wave energy convergence occurs. The proposition that these perturbed equatorial regions may arise from remote equatorial

Peter J. Webster; Hai-Ru Chang

1988-01-01

326

Scenarios regarding the lead of equatorial sea surface temperature over global ice volume  

Microsoft Academic Search

Recent proxy evidences indicate that the equatorial sea surface temperature (SST) may have led global ice volume by ?3 kyr during the late Pleistocene glacial cycles. Given the short timescales of equatorial dynamics, equatorial climate variability is characterized by a timescale of no more than a few years. It would seem somewhat surprising therefore that the equatorial ocean and atmosphere

Yosef Ashkenazy; Eli Tziperman

2006-01-01

327

Scenarios regarding the lead of equatorial sea surface temperature over global ice volume  

Microsoft Academic Search

Recent proxy evidences indicate that the equatorial sea surface temperature (SST) may have led global ice volume by ~3 kyr during the late Pleistocene glacial cycles. Given the short timescales of equatorial dynamics, equatorial climate variability is characterized by a timescale of no more than a few years. It would seem somewhat surprising therefore that the equatorial ocean and atmosphere

Yosef Ashkenazy; Eli Tziperman

2006-01-01

328

Generation of Bubbly Suspensions in Low Gravity  

NASA Technical Reports Server (NTRS)

Generation of a uniform monodisperse bubbly suspension in low gravity is a rather difficult task because bubbles do not detach as easily as on Earth. Under microgravity, the buoyancy force is not present to detach the bubbles as they are formed from the nozzles. One way to detach the bubbles is to establish a detaching force that helps their detachment from the orifice. The drag force, established by flowing a liquid in a cross or co-flow configuration with respect to the nozzle direction, provides this additional force and helps detach the bubbles as they are being formed. This paper is concerned with studying the generation of a bubbly suspension in low gravity in support of a flight definition experiment titled "Behavior of Rapidly Sheared Bubbly Suspension." Generation of a bubbly suspension, composed of 2 and 3 mm diameter bubbles with a standard deviation <10% of the bubble diameter, was identified as one of the most important engineering/science issues associated with the flight definition experiment. This paper summarizes the low gravity experiments that were conducted to explore various ways of making the suspension. Two approaches were investigated. The first was to generate the suspension via a chemical reaction between the continuous and dispersed phases using effervescent material, whereas the second considered the direct injection of air into the continuous phase. The results showed that the reaction method did not produce the desired bubble size distribution compared to the direct injection of bubbles. However, direct injection of air into the continuous phase (aqueous salt solution) resulted in uniform bubble-diameter distribution with acceptable bubble-diameter standard deviation.

Nahra, Henry K.; Hoffmann, Monica I.; Hussey, Sam; Bell, Kimberly R.

2000-01-01

329

Molecular dynamics simulation of deuterium trapping and bubble formation in tungsten  

NASA Astrophysics Data System (ADS)

The interaction between plasma particles and tungsten as plasma facing material is one of the critical issues in successfully using tungsten in Tokamak reactors environment. The deuterium bombardment of monocrystalline tungsten was modeled by molecular dynamics simulation using LAMMPS code and Tersoff type interatomic potential. The deuterium trapping rate, implantation depth, and the stopping time in tungsten at several temperatures ranging from 600 to 2000 K bombarded by 5-100 eV deuterium atoms were simulated. Deuterium bubble formation at near tungsten surface was also studied. Irradiated monocrystalline tungsten became amorphous state prior to deuterium cluster formation, and gas bubbles were observed in the 600, 900, and 1200 K tungsten samples. The formation of gas bubbles were caused by the near surface deuterium super-saturation region and the subsequent plastic deformation induced by the local high gas pressure.

Yang, Xue; Hassanein, Ahmed

2013-03-01

330

Dynamics of the equatorial undercurrent and its determination  

E-print Network

This study focuses on the zonal weakening, eastern termination and seasonal variations of the Atlantic equatorial undercurrent (EUC). The main and most original contribution of the dissertation is a detailed analysis of ...

Wacongne, Sophie

1988-01-01

331

Eastern Equatorial Pacific Ocean Sedimentation: Investigating Constant Flux Proxies  

E-print Network

Age-model derived sediment mass accumulation rates (MARs) are consistently higher than 230Th-normalized MARs in the Equatorial Pacific Ocean during the past 25 ka. The offset, being highest in the Panama Basin, suggests sediment redistribution...

Singh, Ajay 1980-

2012-12-03

332

Equatorial Spread F On West African Ionograms : Evolution From 15-minute Resolution Profile Sequences  

NASA Astrophysics Data System (ADS)

Centre-equatorial nighttime profile sequences at OUAGADOUGOU (Burkina, +1.2 magnetic latitude) illustrate in 15 minute-interpolated detail the ESF occurrence pat- terns and the layer -isodensity curves. ESF occurrence contours (LT by Day Number) traced for 5 minute-running averages had been obtained for the December 1994 to November 1995 year (Farges and Vila, 2002). Further detailed height-time changes of ESF traces during series of magnetically quiet nights obtained from KORHOGO ( Ivory Coast, - 2.3 magnetic latitude) and DAKAR (Senegal, + 4.5 magnetic latitude) help interpreting the equatorial source (mostly OUAGADOUGOU) and the lateral magnetic field-aligned transfers. Interpolating the respective behaviours at our three stations in latitude and time we situate the ESF 2D patches onto the changing F layer density background, that typically presents three sawtooth-like altitude phases after Subset, around O1 LT, and at presunrise hours. These detailed body-of-F layer and unstable ESF patch motions allow to discuss the middle-scale magnetic field-aligned morphologies of the bottomside F layer and ESF evolution.Three kinds of local ESF mechanisms can be separated from the "fossil patch" clouds : i) - Rayleigh-Taylor Bubbles of afew 10 to a few 100 km transverse size, often grown from the visible shear at F layer bottom; ii) - local neutral wave gradient-triggered instability, of (a few meters to) a few km vertical range scales, and iii) - coupling instability triggers. These results are in remarkable agreement with the behaviour that can be expected from the newly-discovered ESF dynamics (e.g. Zhargham and Seyler, 1987) ; Hysell and Burcham, 1998).

Adohi, J. P.; Sambou, E.; Houngninou, E.; Kone, E.; Vila, P.

333

An almost two-dimensional approach to type 2 irregularities in the equatorial electrojet  

SciTech Connect

A recently developed theory of almost two-dimensional turbulence, is applied to E {times} B fluctuations in the E region equatorial electrojet. This theory of plasma turbulence in an external magnetic field extends strictly two-dimensional theory to include weak phase variations along the magnetic field. Based on the direct interaction approximation of Kraichnan, it describes the tendency of spectra energy to transfer nonlinearly towards modes with high k{sub {parallel}} despite strong linear damping of these modes. Here, the authors discuss application of this theory to the aspect angle k{sub {parallel}}/k of fluctuations at 3-m scales, for which radar backscatter measurements have been made. Allowing for uncertainty in characterizing the plasma turbulence, they find good agreement except at the lowest altitudes of the electrojet.

Albert, J.M. (Air Force Geophysics Lab., Hanscom AFB, MA (United States)); Similon, P.L. (Yale Univ., New Haven, CT (United States)); Sudan, R.N. (Cornell Univ., Ithaca, NY (United States))

1991-09-01

334

Catastrophic ape decline in western equatorial Africa.  

PubMed

Because rapidly expanding human populations have devastated gorilla (Gorilla gorilla) and common chimpanzee (Pan troglodytes) habitats in East and West Africa, the relatively intact forests of western equatorial Africa have been viewed as the last stronghold of African apes. Gabon and the Republic of Congo alone are thought to hold roughly 80% of the world's gorillas and most of the common chimpanzees. Here we present survey results conservatively indicating that ape populations in Gabon declined by more than half between 1983 and 2000. The primary cause of the decline in ape numbers during this period was commercial hunting, facilitated by the rapid expansion of mechanized logging. Furthermore, Ebola haemorrhagic fever is currently spreading through ape populations in Gabon and Congo and now rivals hunting as a threat to apes. Gorillas and common chimpanzees should be elevated immediately to 'critically endangered' status. Without aggressive investments in law enforcement, protected area management and Ebola prevention, the next decade will see our closest relatives pushed to the brink of extinction. PMID:12679788

Walsh, Peter D; Abernethy, Kate A; Bermejo, Magdalena; Beyers, Rene; De Wachter, Pauwel; Akou, Marc Ella; Huijbregts, Bas; Mambounga, Daniel Idiata; Toham, Andre Kamdem; Kilbourn, Annelisa M; Lahm, Sally A; Latour, Stefanie; Maisels, Fiona; Mbina, Christian; Mihindou, Yves; Obiang, Sosthène Ndong; Effa, Ernestine Ntsame; Starkey, Malcolm P; Telfer, Paul; Thibault, Marc; Tutin, Caroline E G; White, Lee J T; Wilkie, David S

2003-04-10

335

An equatorial temperature and wind anomaly (ETWA)  

NASA Technical Reports Server (NTRS)

Data obtained from the WATS (Wind and Temperature Spectrometer) and LP (Langmuir Probe) experiments on board DE-2 (Dynamic Explorer) during high solar activity show evidence of anomalous latitudinal variations in the zonal winds and temperature at low latitudes. The zonal winds exhibit a broad maximum centered around the dip equator, flanked by minima on either side around 25 degrees; while the temperature exhibits a pronounced bowl-shaped minimum at the dip equator which is flanked by maxima. The two minima in the zonal winds and the corresponding maxima in the temperature are nearly collocated with the crests of the well known Equatorial Ionization Anomaly (EIA). The maximum in the zonal winds and the minimum in the gas temperature are collocated with the trough of the EIA. The differences between the maxima and minima in temperature and zonal winds, on many occasions, are observed to exceed 100 K and 100 m/s, respectively. The characteristics of this new phenomenon have eluded present day empirical models of thermospheric temperature and winds. The connection among these variables can be understood from the ion-neutral drag effect on the motions of the neutrals that in turn affect their energy balance.

Raghavarao, R.; Wharton, L. E.; Spencer, N. W.; Mayr, H. G.; Brace, L. H.

1991-01-01

336

Condor equatorial electrojet campaign: Radar results  

SciTech Connect

A review of the experimental and theoretical background to the Condor equatorial electrojet compaign is followed by the presentation and discussion of VHF radar interferometer and HF radar backscatter data taken concurrently with two rocket in situ experiments reported in companion papers (Pfaff et al., this issue (a, b). Both experiments were conducted in strongly driven periods with the on-line radar interferometer displaying signatures of what has been interpreted in earlier radar work (Kudeki et al., 1982) as kilometer scale gradient drift waves. Low-frequency density fluctuations detected by in situ rocket sensors confirm the earlier interpretation. VHF radar/rocket data comparisons also indicate the existence of a turbulent layer in the upper portion of the daytime electrojet at about 108 km altitude driven purely by the two-stream instability. Nonlinear mode coupling of linearly growing two-stream waves to linearly damped 3-m vertical modes could account for the radar echoes scattered from this layer, which showed no indication of large-scale gradient drift waves. Nonlinear mode coupling may therefore compete with the wave-induced anomalous diffusion mechanism proposed recently by Sudan (1983) for the saturation of directly excited two-stream waves. Nighttime radar data show a bifurcated layer with the two parts having comparable echo strength but oppositely directed zonal drift velocities. The lower layer shows narrow backscatter spectra; the upper layer is characterized by kilometer scale waves and vertically propagating type 1 waves.

Kudeki, E.; Fejer, B.G.; Farley, D.T.; Hanuise, C.

1987-12-01

337

Lagrangian sources of frontogenesis in the equatorial Atlantic front  

NASA Astrophysics Data System (ADS)

Estimating the processes that control the north equatorial sea surface temperature (SST)-front on the northern edge of the cold tongue in the tropical Atlantic is a key issue for understanding the dynamics of the oceanic equatorial Atlantic and the West African Monsoon. Diagnosis of the frontogenetic forcings on a realistic high-resolution simulation was used to identify the processes involved in the formation and evolution of the equatorial SST-front. The turbulent forcing associated with the mixed-layer turbulent heat flux was found to be systematically frontolytic while the dynamic forcing associated with currents was found to be frontogenetic for the equatorial SST-front. Nevertheless, the low-frequency component of the turbulent forcing was frontogenetic and initiated the SST-front which was then amplified and maintained by the leading dynamic forcing. This forcing was mainly driven by the meridional convergence of the northern South Equatorial Current (nSEC) and the Guinea Current, which points out the essential role played by the circulation in the equatorial SST-front evolution. The quasi-biweekly variability of the equatorial SST-front and its forcings were found to be more strongly coupled to the wind energy flux ( WEF) than to the surface wind stress. In fact the WEF controlled the convergence/divergence of the nSEC and Guinea Current and thus the meridional component of the leading dynamic forcing. The WEF explains the equatorial SST-front development better than the wind does because it is a coupled ocean-atmosphere process.

Giordani, Hervé; Caniaux, Guy

2014-12-01

338

On the West Atlantic Ocean Equatorial boundary layer  

NASA Astrophysics Data System (ADS)

The equatorial Ocean shows a different dynamics compared to off-equatorial regions and it can be therefore interpreted as a boundary layer. It presents a current system that is strongly coherent in zonal direction and time, constituted by stacked alternating zonal currents known as Equatorial Deep Jets. Internal wave activity in the equatorial belt is high, and presents sudden transitions in polarization and mixing properties (van Haren, 2005). Surprisingly, the causes and feeding mechanisms of these equatorial features are still poorly understood. In this work, data collected in a CTD/LADCP transect between 0°and 2°N in the deep West Equatorial Atlantic Ocean, off the Brazilian coast, are used for a study on non traditional equatorial geostrophy, where full Coriolis force is taken into account (Gerkema et al., 2008). For the same area, measurements from a series of one year moored ADCPs and current meters are also considered, with special attention to the observed internal wave field . Low latitude dynamics asks for a robust interpretation and in situ measurements as the ones presented here can provide us with a partial, but direct view of the processes taking place in this unique region. Hans van Haren, (2005). Sharp near-equatorial transitions in inertial motions and deep-ocean step-formation. Geophys. Res. Lett., 32(1), L01605, doi:10.1029/2004GL021630 Theo Gerkema, Zimmermann, J. T. F., Maas, L. R. M., and van Haren, H. (2008). Geophysical and astrophysical fluid dynamics beyond the traditional approximation. Rev. Geophys., 46, RG2004, doi:10.1029/2006RG000220

Rabitti, A.; van Haren, H.; Gerkema, T.; Maas, L. R. M.

2012-04-01

339

Ionospheric irregularities and storm-induced equatorial and high-latitude effects at the anomaly crest region  

NASA Astrophysics Data System (ADS)

IEC information received through VHF RB measurements has been analyzed over the anomaly crest region of Guwahati (92° E, 26° N, 15° N geo.mag) along with a few low/low-mid latitude observations for understanding the roles of influx of plasma to anomaly crest regions, from equatorward and poleward processes during geomagnetically disturbed situations. The conditions leading to inflow of plasma to equatorial anomaly crest region or inhibition of such processes have been described in the paper through systematic analysis of disturbed day (free from sudden commencements) ionospheric electron content (IEC) variations at different temporal situtions. The storm-induced effects in relation to the development of the above conditions have also been examined for moderate and moderately severe isolated storm cases. Finally the paper deals with a few severe storms. The storm-triggered IEC features indicate inhibition or suppression of plasma dumping process at anomaly crests, through equatorial anomaly phenomenon. During winter and many equinoxial storms, the compression effect pushes this station away from the region where effective dumping of ionization from the equator is expected. Diffusion of plasma from the polar region to the crest area has also been observed through penetration of the eastward electric field during many disturbed situations. Depletion of noontime density during winter and equinoxial months and enhancement of the same during summer geomagnetically active situations are examined through anomaly compression (or inhibition) process as well as plasma replenishment through the equatorward wind.

Devi, M.; Barbara, A. K.; Barman, M.

1996-03-01

340

Large-scale Electric Field Structures in the Daytime Equatorial Electrojet Oobserved From Alcontara, Brazil  

NASA Astrophysics Data System (ADS)

During the Guar Rocket/Radar Campaign conducted from August-October, 1994, three NASA rockets were launched from Alcontara, Brazil that returned detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet. The electric field and plasma density data reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (~10-15 mV/m) in the zonal direction, considerable structure (~5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields, in a manner suggested by Kudeki et al. [JGR, 90, p. 429, 1985] to explain backscatter radar spectral asymmetries. The largest amplitude waveforms imply scales of ~0.5-1.5 km, although the spectrum of irregularities is quite broad, extending to less than 10m. Indeed, evidence for secondary two stream and gradient drift waves is also observed. For each flight, simultaneous VHF CUPRI backscatter vertical echoes also show the presence of both large scale waves and secondary 3 m structures within the same regions. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves in the daytime equatorial electrojet.

Pfaff, R. F.; Freudenreich, H.; Swartz, W.

2001-05-01

341

First Observations of a Foreshock Bubble: Implications for Global Magnetospheric Dynamics and Particle Acceleration  

NASA Astrophysics Data System (ADS)

Here, we present unprecedented, multipoint observations of a recently predicted astrophysical plasma phenomenon, foreshock bubbles, which have not been identified previously in situ. First modeled and described in Omidi et al. [JGR, 2010], foreshock bubbles are kinetic phenomena that develop when plasma in Earth's quasi-parallel shock region, known as the foreshock, interacts with a discontinuity in the IMF. Foreshock bubbles develop a central, core region, which is characterized by low density and magnetic field strength, hot plasma temperatures, and highly deflected, sometimes even sunward, plasma flows. The expanding core region is surrounded by a compression layer of enhanced density and field strength that culminates in a fast magnetosonic shock on the upstream edge of the bubble, since it acts as a barrier to the upstream solar wind. The entire bubble structure scales with the foreshock region (order of 10 RE), grows in time, and is convected with the solar wind, such that if a foreshock bubble forms upstream of the bow shock on Earth's dayside, it will impact the magnetosheath and magnetosphere resulting in rapid expansion and compression of the entire system. Additionally, since foreshock bubbles consist of two, converging shocks, they should be particularly efficient at accelerating particles. For the observations, NASA's THEMIS spacecraft are used in conjunction with NOAA-GOES and the THEMIS ground magnetometer network to observe this new phenomenon and its effects on the magnetosphere. Using two spacecraft in the foreshock region, we clearly show that the events in question are fully consistent with the predictions of Omidi et al. [JGR, 2010], and the events exhibit several key inconsistencies with another, similar, and well-established foreshock phenomenon, hot flow anomalies. We discuss the events' global effects on the magnetosphere using two spacecraft along the dayside magnetopause, GOES at geosynchronous orbit, and ground magnetometers across North America, all of which clearly observe the global disturbance resulting from the foreshock bubble's impact. We finish with details on the observations of the energetic ions and electrons accelerated in the foreshock bubble, potentially by a combination of first and second order Fermi and shock drift acceleration processes. Solar wind ions are clearly isotropized and accelerated by the event, while solar wind electrons are also isotropized and accelerated up to ~10 keV, producing a suprathermal flux enhancement of up to two orders of magnitude. We conclude on a most interesting note, namely that this new phenomena is common and should play a role in energetic particle acceleration at collisionless, quasi-parallel shocks throughout the Universe.

Turner, D. L.; Omidi, N.; Sibeck, D. G.; Angelopoulos, V.

2011-12-01

342

Influence of Assimilation of Subsurface Temperature Measurements on Simulations of Equatorial Undercurrent and South Equatorial Current Along the Pacific Equator  

NASA Technical Reports Server (NTRS)

Equatorial Pacific current and temperature fields were simulated with and without assimilation of subsurface temperature measurements for April 1992 - March 1995, and compared with moored bouy and research vessel current measurements.

Halpern, David; Leetmaan, Ants; Reynolds, Richard W.; Ji, Ming

1997-01-01

343

Soap bubbles in paintings: Art and science  

NASA Astrophysics Data System (ADS)

Soap bubbles became popular in 17th century paintings and prints primarily as a metaphor for the impermanence and fragility of life. The Dancing Couple (1663) by the Dutch painter Jan Steen is a good example which, among many other symbols, shows a young boy blowing soap bubbles. In the 18th century the French painter Jean-Simeon Chardin used soap bubbles not only as metaphor but also to express a sense of play and wonder. In his most famous painting, Soap Bubbles (1733/1734) a translucent and quavering soap bubble takes center stage. Chardin's contemporary Charles Van Loo painted his Soap Bubbles (1764) after seeing Chardin's work. In both paintings the soap bubbles have a hint of color and show two bright reflection spots. We discuss the physics involved and explain how keenly the painters have observed the interaction of light and soap bubbles. We show that the two reflection spots on the soap bubbles are images of the light source, one real and one virtual, formed by the curved surface of the bubble. The faint colors are due to thin film interference effects.

Behroozi, F.

2008-12-01

344

THE DEPTHS OF HYDROGEN AND HELIUM BUBBLES IN TUNGSTEN: A COMPARISON  

E-print Network

THE DEPTHS OF HYDROGEN AND HELIUM BUBBLES IN TUNGSTEN: A COMPARISON K. O. E. HENRIKSSON,* K of self-trapping and defect trapping of hydrogen and helium implanted into tungsten has been investigated-facing materials contain heavy chemical ele- ments, e.g., tungsten, since energy loss in the plasma is proportional

Krasheninnikov, Arkady V.

345

Ionospheric responses to the October 2003 superstorm: Longitude/local time effects over equatorial low and middle latitudes  

NASA Astrophysics Data System (ADS)

Ionospheric responses to the major magnetic storm disturbances of October 2003 are investigated using database selected in the Brazilian and Japanese-Asian longitude sectors. Data obtained from latitudinally spaced digisondes in the equatorial and low-latitude sites in Brazil and from the Asian and Japanese ionosonde network, the total electron content data from the extensive Japanese GPS receiver chain, and magnetometer data from the Pacific equatorial electrojet stations are analyzed during the period 28-31 October. Prompt penetrating (PP) dawn-dusk polar cap electric fields produce large F region plasma uplift on the dayside and eveningside, while the associated westward electric field on the nightside produces large downdraft of the F region plasma, and causes development of westward electrojet current, observed for the first time. Episodes of PP electric field effects appear to be of larger intensity over Brazil than over Asian longitudes. Equatorial anomaly, development due to undershielding as well as overshielding electric fields, was observed in the Brazilian and in the Asian sectors. Disturbance dynamo electric field causes large nighttime F layer uplifts that are modulated by strong meridional winds in both sectors. The disturbance electric field local time variation patterns are compared with the results of recent global model (MTIEGCM) simulation by Richmond et al. (2003) and validated in some cases. Transients of transequatorial winds, flipping direction from southward to northward, in the widely separated longitude sectors, were diagnosed to be present toward the final recovery phase of the storm. These results are presented and discussed in this paper.

Abdu, Mangalathayil A.; Maruyama, Takashi; Batista, Inez S.; Saito, Susumo; Nakamura, Maho

2007-10-01

346

Unsteady thermocapillary migration of bubbles  

NASA Astrophysics Data System (ADS)

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 bubble in a microgravity environment and is restricted to situations wherein the flow is sufficiently slow such that inertial terms in the Navier-Stokes equation and convective terms in the energy equation may be safely neglected (i.e., both Reynolds and Marangoni numbers are small). The resulting linear equations were solved analytically in the Laplace domain with the Prandtl number of the liquid as a parameter; inversion was accomplished numerically using a standard IMSL routine. In the asymptotic long-time limit, the theory agrees with the steady-state theory of Young, Goldstein, and Block. The theory predicts that more than 90 percent of the terminal steady velocity is achieved when the smallest dimensionless time, i.e., the one based upon the largest time scale-viscous or thermal-equals unity.

Dill, Loren H.; Balasubramaniam, R.

347

Equatorial and quasi-equatorial gravitational lensing by Kerr black hole pierced by a cosmic string  

E-print Network

In the present paper, we study numerically the equatorial lensing and quasiequatorial lensing by Kerr black hole pierced by a cosmic string in the strong deflection limit. We calculate the strong deflection limit coefficients and the deflection angle, which are found to depend closely on the cosmic string parameter $\\beta$ and dimensionless spin $a_{*}$. The magnification and positions of relativistic images are also computed in the strong deflection limit and a two-dimensional lens equation is derived. The most important and outstanding effect is that the caustics drift away from the optical axis and shift in the clockwise direction with respect to the Kerr black hole. For fixed $a_{*}$ of the black hole, the caustics drift farther away from the optical axis for a large value of $\\beta$. And for fixed $\\beta$, they drift farther for high $a_{*}$. We also obtain the intersections of the critical curves with the equatorial plane, which decrease with $a_{*}$ and $\\beta$. In particular, we obtain a quantity $\\bar{\\mu}_{k+1}/\\bar{\\mu}_{k}$, which is independent of the black hole spin and mass. Thus, through measuring it, one is allowed to determine the value of $\\beta$ from astronomical observations.

Shao-Wen Wei; Yu-Xiao Liu

2012-04-05

348

Isostatic compensation of equatorial highlands on Venus  

NASA Technical Reports Server (NTRS)

Spherical harmonic models for Venus' global topography and gravity incorporating Magellan data are used to test isostatic compensation models in five 30 deg x 30 deg regions representative of the main classes of equatorial highlands. The power spectral density for the harmonic models obeys a power-law scaling with spectral slope Beta approximately 2 (Brown noise) for the topography and Beta approximately 3 (Kaula's law) for the geoid, similar to what is observed for Earth. The Venus topography spectrum has lower amplitudes than Earth's which reflects the dominant lowland topography on Venus. Observed degree geoid to topography ratios (GTRs) on Venus are significantly smaller than degree GTRs for uncompensated topography, indicative of substantial compensation. Assuming a global Airy compensation, most of the topography is compensated at depths greater than 100 km, suggesting a thick lithosphere on Venus. For each region considered we obtain a regional degree of compensation C from a linear regression of Bouguer anomaly versus Bouguer gravity data. Geoid anomaly (N) versus topography variation (h) data for each sample were compared, in the least-squares sense, to theoretical correlations for Pratt, Airy, and thermal thinning isostasy models yielding regional GTR, zero-elevation crustal thickness (H), and zero elevation thermal lithosphere thickness (y(sub L(sub 0)), respectively. We find the regional compensation to be substantial (C approximately 52-80%), and the h, N data correlations in the chosen areas can be explained by isostasy models applicable on the Earth and involving variations in crustal thickness (Airy) and/or lithospheric (thermal thinning) thickness. However, a thick crust and lithosphere (y(sub L(sub 0)) approximately 300 km) must be assumed for Venus.

Kucinskas, Algis B.; Turcotte, Donald L.

1994-01-01

349

A Drying Trend in Central Equatorial Africa  

NASA Astrophysics Data System (ADS)

There has been considerable uncertainty about changes in rainfall over central equatorial Africa over the past three decades due to a lack of reliable rainfall data in the region. This region contains the northern portion of the Albertine Rift, which is one of the world's hotspots for biodiversity, and within this region there is an exploding human population dependent on rainfed agriculture. Both the human population and conservation/preservation areas are becoming increasingly sensitive to changes in rainfall. There now exists an accurate, high-resolution, satellite based precipitation dataset, African Rainfall Climatology version 2 (ARC2), for the region that provides daily rainfall estimates from 1983 to the present. Here we show significant declines in monthly and annual rainfall in west-central Uganda, which exists in the far northeastern portion of the Rift, from 1983-2012. The decrease in annual rainfall was 110 mm per decade. Therefore, the current annual rainfall of approximately 1,200 mm is less than 80% of the annual rainfall three decades ago. The drying trend most likely extended westward into the Congo Basin. There were significant increasing (decreasing) trends in light-rainfall (heavy-rainfall) days over the period. Using results from previous studies, Indian Ocean warming and increasing carbonaceous aerosols from biomass burning in tropical Africa, are explored as potential causes of the drying trend. The aim of the study is not to find the fingerprint of local and regional anthropogenic forcings on the drying trend, but our results suggest that those forcings could be a leading cause of the drying trend.

Diem, J.; Hartter, J.; Ryan, S. J.; Palace, M. W.

2013-12-01

350

Observations of Neutral and Electron Structure in the Equatorial Mesosphere by Rocket and Radar During EQUIS-2/LEMMA  

NASA Astrophysics Data System (ADS)

The NASA EQUIS-2 rocket campaign was conducted in August-September 2004 from USAKA/RTS on Roi-Namur, Marshall Islands (9 N, 168 E). One part of the program was dedicated to neutral and plasma density fluctuations in the equatorial mesosphere and lower thermosphere. The objective was to detect layers of small scale structures that can be associated with mesospheric VHF radar echoes observed frequently at equatorial and low latitudes. One instrumented rocket and three passive falling spheres were launched successfully on September 20, 2004, supported by ALTAIR UHF radar observing incoherent backscatter from ~85-700 km. We give an overview of the investigation and present first results that include the comparison of in situ and radar electron density profiles, neutral temperature and wind structure, and characteristics of neutral and electron fluctuation layers.

Lehmacher, G. A.; Croskey, C. L.; Mitchell, J. D.; Friedrich, M.; Luebken, F.; Rapp, M.; Kudeki, E.; Fritts, D. C.

2005-05-01

351

Dynamics of a Tethered Bubble Alexey O. Maksimov 1  

E-print Network

bubble on a solid surface [3] differs from single-bubble SL. The forced oscillation of a gas bubble can using an acoustically driven tethered gas bubble. Clearly the forced oscillation of a tethered gas Abstract. Small gas bubbles adhering to solids occur in a range of manufacturing processes, including

Sóbester, András

352

Ostwald Ripening in Multiple-Bubble Nuclei  

E-print Network

The ostwald ripening of bubbles is studied by molecular dynamics simulations involving up to 679 million Lennard-Jones particles. Many bubbles appear after depressurizing a system that is initially maintained in the pure-liquid phase, and the coarsening of bubbles follows. The self-similarity of the bubble-size distribution function predicted by Lifshitz-Slyozov-Wagner theory is directly confirmed. The total number of bubbles decreases asymptotically as $t^{-x}$ with scaling exponent $x$. As the initial temperature increases, the exponent changes from $x=3/2$ to $1$, which implies that the growth of bubbles changes from interface-limited (the $t^{1/2}$ law) to diffusion-limited (the $t^{1/3}$ law) growth.

Watanabe, Hiroshi; Inaoka, Hajime; Ito, Nobuyasu

2014-01-01

353

Ostwald Ripening in Multiple-Bubble Nuclei  

E-print Network

The ostwald ripening of bubbles is studied by molecular dynamics simulations involving up to 679 million Lennard-Jones particles. Many bubbles appear after depressurizing a system that is initially maintained in the pure-liquid phase, and the coarsening of bubbles follows. The self-similarity of the bubble-size distribution function predicted by Lifshitz-Slyozov-Wagner theory is directly confirmed. The total number of bubbles decreases asymptotically as $t^{-x}$ with scaling exponent $x$. As the initial temperature increases, the exponent changes from $x=3/2$ to $1$, which implies that the growth of bubbles changes from interface-limited (the $t^{1/2}$ law) to diffusion-limited (the $t^{1/3}$ law) growth.

Hiroshi Watanabe; Masaru Suzuki; Hajime Inaoka; Nobuyasu Ito

2014-07-01

354

BUBBLE DYNAMICS AT GAS-EVOLVING ELECTRODES  

SciTech Connect

Nucleation of bubbles, their growth by diffusion of dissolved gas to the bubble surface and by coalescence, and their detachment from the electrode are all very fast phenomena; furthermore, electrolytically generated bubbles range in size from ten to a few hundred microns; therefore, magnification and high speed cinematography are required to observe bubbles and the phenomena of their growth on the electrode surface. Viewing the action from the front side (the surface on which the bubbles form) is complicated because the most important events occur close to the surface and are obscured by other bubbles passing between the camera and the electrode; therefore, oxygen was evolved on a transparent tin oxide "window" electrode and the events were viewed from the backside. The movies showed that coalescence of bubbles is very important for determining the size of bubbles and in the chain of transport processes; growth by diffusion and by coalescence proceeds in series and parallel; coalescing bubbles cause significant fluid motion close to the electrode; bubbles can leave and reattach; and bubbles evolve in a cycle of growth by diffusion and different modes of coalescence. An analytical solution for the primary potential and current distribution around a spherical bubble in contact with a plane electrode is presented. Zero at the contact point, the current density reaches only one percent of its undisturbed value at 30 percent of the radius from that point and goes through a shallow maximum two radii away. The solution obtained for spherical bubbles is shown to apply for the small bubbles of electrolytic processes. The incremental resistance in ohms caused by sparse arrays of bubbles is given by {Delta}R = 1.352 af/kS where f is the void fraction of gas in the bubble layer, a is the bubble layer thickness, k is the conductivity of gas free electrolyte, and S is the electrode area. A densely populated gas bubble layer on an electrode was modeled as a hexagonal array of dielectric spheres. Accurately machined lucite spheres were placed one at a time in one end of a hexagonal cell which simulated the unit cell of such an array. The resistance as a function of gas bubble layer packing density sharply increased as close packing was approached. Because the interaction of the fields around bubbles closely spaced in the direction perpendicular to the current dominates the added resistance, and because there is a tri-modal distribution of bubble sizes in a bubble layer, the Distribution Model of Meredith and Tobias (16), derived for three dimensional gas dispersions, approximately predicted the conductivity of a bubble layer at void fractions greater than 0.3. At moderate-to-high current densities, the bubble layer in a cell having an interelectrode gap of half a centimeter could increase the ohmic resistance by as much as 20 percent.

Sides, Paul J.

1980-12-01

355

Ostwald ripening in multiple-bubble nuclei  

NASA Astrophysics Data System (ADS)

The Ostwald ripening of bubbles is studied by molecular dynamics simulations involving up to 679 × 106 Lennard-Jones particles. Many bubbles appear after depressurizing a system that is initially maintained in the pure-liquid phase, and the coarsening of bubbles follows. The self-similarity of the bubble-size distribution function predicted by Lifshitz-Slyozov-Wagner theory is directly confirmed. The total number of bubbles decreases asymptotically as t-x with scaling exponent x. As the initial temperature increases, the exponent changes from x = 3/2 to 1, which implies that the growth of bubbles changes from interface-limited (the t1/2 law) to diffusion-limited (the t1/3 law) growth.

Watanabe, Hiroshi; Suzuki, Masaru; Inaoka, Hajime; Ito, Nobuyasu

2014-12-01

356

Scattering measurements from a dissolving bubble.  

PubMed

A laboratory-scale study on acoustic scattering from a single bubble undergoing dissolution in undersaturated fresh water is presented. Several experiments are performed with the acoustic source driven with five-cycle tone bursts, center frequency of 120 kHz, to insonify a single bubble located on axis of the combined beam of the set of transducers. The bubble is placed on a fine nylon thread located in the far field of the transducer set, arranged in bistatic configuration, in a tank filled with undersaturated water. Backscattered waveforms from the bubble target are acquired every few seconds for several hours until the bubble has completely dissolved, and detailed dissolution curves are produced from the acoustic data. The rate of bubble dissolution is calculated using the solution developed by Epstein and Plesset [J. Chem. Phys. 18, 1505-1509 (1950)]. The results of the experiments performed are in agreement with the calculations. PMID:22712899

Kapodistrias, George; Dahl, Peter H

2012-06-01

357

Ostwald ripening in multiple-bubble nuclei.  

PubMed

The Ostwald ripening of bubbles is studied by molecular dynamics simulations involving up to 679 × 10(6) Lennard-Jones particles. Many bubbles appear after depressurizing a system that is initially maintained in the pure-liquid phase, and the coarsening of bubbles follows. The self-similarity of the bubble-size distribution function predicted by Lifshitz-Slyozov-Wagner theory is directly confirmed. The total number of bubbles decreases asymptotically as t(-x) with scaling exponent x. As the initial temperature increases, the exponent changes from x = 3/2 to 1, which implies that the growth of bubbles changes from interface-limited (the t(1/2) law) to diffusion-limited (the t(1/3) law) growth. PMID:25527953

Watanabe, Hiroshi; Suzuki, Masaru; Inaoka, Hajime; Ito, Nobuyasu

2014-12-21

358

The quest for the most spherical bubble: experimental setup and data overview  

NASA Astrophysics Data System (ADS)

We describe a recently realized experiment producing the most spherical cavitation bubbles today. The bubbles grow inside a liquid from a point plasma generated by a nanosecond laser pulse. Unlike in previous studies, the laser is focussed by a parabolic mirror, resulting in a plasma of unprecedented symmetry. The ensuing bubbles are sufficiently spherical that the hydrostatic pressure gradient caused by gravity becomes the dominant source of asymmetry in the collapse and rebound of the cavitation bubbles. To avoid this natural source of asymmetry, the whole experiment is therefore performed in microgravity conditions (ESA, 53rd and 56th parabolic flight campaign). Cavitation bubbles were observed in microgravity (˜0 g), where their collapse and rebound remain spherical, and in normal gravity (1 g) to hyper-gravity (1.8 g), where a gravity-driven jet appears. Here, we describe the experimental setup and technical results, and overview the science data. A selection of high-quality shadowgraphy movies and time-resolved pressure data is published online.

Obreschkow, Danail; Tinguely, Marc; Dorsaz, Nicolas; Kobel, Philippe; de Bosset, Aurele; Farhat, Mohamed

2013-04-01

359

Bubble effect on Kelvin-Helmholtz' instability  

E-print Network

We derive boundary conditions at interfaces (contact discontinuities) for a class of Lagrangian models describing, in particular, bubbly flows. We use these conditions to study Kelvin-Helmholtz' instability which develops in the flow of two superposed layers of a pure incompressible fluid and a fluid containing gas bubbles, co-flowing with different velocities. We show that the presence of bubbles in one layer stabilizes the flow in some intervals of wave lengths.

Sergey L. Gavrilyuk; Henri Gouin; Vladimir M. Teshukov

2008-01-16

360

Bubble, Drop and Particle Unit (BDPU)  

NASA Technical Reports Server (NTRS)

This section of the Life and Microgravity Spacelab (LMS) publication includes the following articles entitled: (1) Oscillatory Thermocapillary Instability; (2) Thermocapillary Convection in Multilayer Systems; (3) Bubble and Drop Interaction with Solidification Front; (4) A Liquid Electrohydrodynamics Experiment; (5) Boiling on Small Plate Heaters under Microgravity and a Comparison with Earth Gravity; (6) Thermocapillary Migration and Interactions of Bubbles and Drops; and (7) Nonlinear Surface Tension Driven Bubble Migration

1998-01-01

361

DNA Bubble Life Time in Denaturation  

E-print Network

We have investigated the denaturation bubble life time for a homogeneous as well as for a heterogeneous DNA within a Poland-Scheraga model. It is shown that at criticality the bubble life time for a homogeneous DNA is finite provided that the loop entropic exponent c>2 and has a scaling dependence on DNA length for c<2. Heterogeneity in the thermodynamical limit makes the bubble life time infinite for any entropic exponent.

Zh. S. Gevorkian; Chin-Kun Hu

2010-10-11

362

Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions  

NASA Astrophysics Data System (ADS)

A form of range-time plots derived from ionograms taken from a standard digital ionosondes, situated at the low latitude sites of Vanimo, Port Moresby and Darwin, exhibit bursts of spread F at the center of descending and ascending off-angle reflectors. This particular type of event has since been identified with the passage of optically imaged ionospheric plasma depletions (bubbles) over a Darwin ionosonde. This paper describes the process for producing this form of range-time display and its relationship to ionospheric height, satellite traces and range spread F as seen on individual ionograms. First hop satellite traces are proposed to be via direct reflection from the steep electron density gradients at the base of bubbles while second hop satellite traces then involve a single additional ground reflection. Measurements of night equatorial drift velocity were made from the range-time displays and found to be in the range 20-220 m/s peaking at approximately 90-100 m/s in good agreement with values derived from drift measurements made by a variety of other types of equipment.

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

2013-06-01

363

Experimental and Numerical Studies of Magnetic Bubble Expansion as a Model for Extra-Galactic 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) will conduct laboratory experiments and coordinated numerical modeling 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. Experiments will be conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A new pulsed coaxial gun will form and inject magnetized plasma bubbles into a lower pressure background plasma formed by the helicon and/or hot cathode source in HELCAT. Experimental parameters will be adjusted so that important dimensionless parameters are relevant to the astrophysical context. Preliminary magnetic probe measurements and MHD modeling will be presented.

Lynn, A. G.; Zhang, Y.; Hsu, S. C.; Li, H.; Li, W.; Gilmore, M.; Watts, Christopher

2007-11-01

364

Modeling bubble clusters in compressible liquids  

NASA Astrophysics Data System (ADS)

We present a new model to simulate the behaviour of bubble clouds in compressible liquids. The method uses a volume-averaged approach and defines the pressure and void fraction relative to a computational cell. Inside the cell, a generalisation of the Keller-Miksis equation is derived in order to take into account the presence of (one or more) nearby spherical bubbles as well as liquid compressibility effect on the bubble interface motion. The method converges to previous models in two distinct limits. First, it reproduces the bubble radius evolution and pressure disturbances induced by a single bubble subjected to a given far field pressure, irrespective of the relative size of the bubble compared to the grid size. Second, it converges to continuum models based on Ensemble-averaged equations when there are many bubbles in a cell. The main advantage of the model is that it allows to access to the instantaneous pressure profiles in the liquid rather than the averaged behaviour. The local pressures generated and scattered by bubble dynamics is important for predicting the peak pressures that can be locally achieved in some points of the liquid when violent bubble collapses are encountered.

Fuster, Daniel; Colonius, Tim

2010-11-01

365

Experiments with electron bubbles in liquid helium  

NASA Astrophysics Data System (ADS)

When a free electron is injected into liquid helium, it forms a microscopic bubble essentially free of helium atoms. The electron bubble is an excellent textbook example of a quantum mechanical particle confined in a potential well. The bubble is also a powerful tool to study superfluidity. In this dissertation, we describe various experiments on electron bubbles using standard ultrasonic techniques. By using a focused sound wave, we create a region in liquid helium where the pressure was negative. The bubble becomes unstable, and can grow without limit when the ambient pressure is lower than some critical value. This macroscopic bubble can then be detected by light scattering. The critical pressure of the bubble depends on many factors. For example, a bubble containing an electron in an excited state has a lower magnitude of critical pressure, and is therefore easier to explode than a bubble with the electron in the ground state. Similarly, bubbles trapped on vortices are easier to explode than normal, untrapped bubbles. In our experiments, we injected electrons in liquid helium by either a field emission tip or a radioactive beta source. We investigated the different experimental conditions under which the bubbles were trapped on vortices. We measured the difference of critical pressures between bubbles on and off vortices as a function of temperature. In the course of our experiments, we were able to detect electrons that were formed by the Penning ionization of dimers. At temperatures lower than 1 K, we have discovered new objects that can be exploded very easily. These objects depend on different experimental parameters in a complicated way, and are not completely understood. In a second series of experiments, we used infrared radiation to excite the electron bubbles. By analyzing the data carefully, we estimated the lifetime of these excited state bubbles; and concluded that the decay mechanism is non-radiative in nature. We also studied the effect of infrared radiation on bubbles trapped on vortices. Finally, we measured the current arising from the secondary ionization of the beta particles emitted from a radioactive source. The current had an interesting dependence on different experimental parameters, especially temperature and electric field.

Ghosh, Ambarish

366

Fission gas bubble behaviour in uranium dioxide  

NASA Astrophysics Data System (ADS)

A theoretical model developed to study the gas bubble evolution in nuclear materials has been used to analyze experiments on uranium dioxide irradiated to low burnups (0.1 and 0.4 at%), in which fission gas bubble size distributions were measured following out-of-pile isothermal anneals. Following irradiation, the UO 2 was annealed for 1 or 6 h each at temperatures between 1303 and 1973 K and then thinned for transmission electron microscopy observation of the bubble size distributions. The model is based on the assumption, that the coalescence of the moving bubbles is the main mechanism defining gas porosity development under these conditions. The gas bubbles are assumed to be in equilibrium and their motion is assumed to be caused by random migration. The calculations show that the observed bubble size distributions may be reproduced on the base of the bubble growth mechanisms considered. The joint action of bubble surface and volume diffusion mechanisms can explain both the general nature of the experimental distributions and their perculiarities, in particularly the bimodal bubble size distribution observed after annealing at 1673 K. The choice of appropriate values as input parameters into the model is discussed.

Chkuaseli, V. F.; Matzke, Hj.

367

Bubble and spherical air shell formation dynamics.  

PubMed

We studied the formation dynamics of air bubbles emitted from a nozzle submerged in aqueous glycerol solutions of different viscosities. We describe the evolution of the bubbling regimes by using the air flow rate as a control parameter and the time between successive bubbles as a dynamical variable. Some results concerning bubbling coalescence were emulated with a combination of simple maps. We also observed the formation of air shells surrounding liquid drops inside the liquid, known as antibubbles. The antibubbling conditions were related to an intermittent regime. PMID:12513583

Tufaile, A; Sartorelli, J C

2002-11-01

368

Breaking Bubble Rafts: Modeling material failure  

NASA Astrophysics Data System (ADS)

Bubble rafts have long been of interest as a model two-dimensional system for the study of general amorphous systems, ranging from metallic glasses to foams and potentially geophysical flows. Consisting of a single layer of gas-bubbles on an aqueous substrate, bubble rafts allow for excellent control over bubble size, size distribution, bubble solution composition, and for the tracking and characterizing of each bubble in the system. The individual bubbles serve as the model for the "particles" in other complex flows, such as molecules or grains. Additionally, bubble rafts have been used in a wide-range of flow geometries and with varied methods of confinement. These features of bubble rafts have provided insight in a range of issues related to the visco-elastic nature of foams and other complex fluids. In this talk, we will present results from a relatively new configuration: uniaxial extension. At relatively low speeds, the system exhibits pinch-off behaviour that is consistent with a fluid-like response. Two types of pinch-off are observed: double-cone and long-thread. The appearance of either mode is dependent on the pulling speed and system size. As the speed of extension is increased, the system exhibits classic fracture behaviour. We will report on our characterization of these transitions, with a focus on connecting to potential microscopic origins of the different modes.

Dennin, M.

2011-12-01

369

Dynamics of Vapour Bubbles in Nucleate Boiling. 1; Basic Equations of Bubble Evolution  

NASA Technical Reports Server (NTRS)

We consider the behaviour of a vapour bubble formed at a nucleation site on a heated horizontal wall. There is no forced convection of an ambient liquid, and the bubble is presumably separated from the wall by a thin liquid microlayer. The energy conservation law results in a variational equation for the mechanical energy of the whole system consisting of the bubble and liquid. It leads to a set of two strongly nonlinear equations which govern bubble expansion and motion of its centre of mass. A supplementary equation to find out the vapour temperature follows from consideration of heat transfer to the bubble, both from the bulk of surrounding liquid and through the microlayer. The average thickness of the microlayer is shown to increase monotonously with time as the bubble meniscus spreads along the wall. Bubble expansion is driven by the pressure head between vapour inside and liquid far away from the bubble, with due allowance for surface tension and gravity effects. It is resisted by inertia of liquid being placed into motion as the bubble grows. The inertia originates also a force that presses the bubble to the wall. This force is counteracted by the buoyancy and an effective surface tension force that tends to transform the bubble into a sphere. The analysis brings about quite a new formulation of the familiar problem of bubble growth and detachment under conditions of nucleate pool boiling.

Buyevich, Yu A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

1995-01-01

370

The Behavior of Micro Bubbles and Bubble Cluster in Ultrasound Field  

NASA Astrophysics Data System (ADS)

Ultrasound is widely applied in the clinical field today, such as ultrasound imaging, Extracorporeal Shock Wave Lithotripsy (ESWL) and so on. It is essential to take a real understanding of the dynamics of micro bubbles and bubble cluster in these applications. Thus we numerically simulate them in ultrasound field in this paper. In the numerical simulation, we consider the thermal behavior inside the bubble and the pressure wave phenomena in the bubble cluster in detail, namely, the evaporation and condensation of liquid at the bubble wall, heat transfer through the bubble wall, diffusion of non-condensable gas inside the bubble and the compressibility of liquid. Initial cluster radius is to 0.5[mm], bubble radius is 1.7[mm], void fraction is 0.1[ambient pressure is 101.3[kPa], temperature is 293[K] and the amplitude of ultrasound is 50[kPa]. We simulate bubble cluster in ultrasound field at various frequencies and we obtain the following conclusions. 1) The maximum pressure inside bubble cluster reaches 5[MPa] and this is much higher than that of a bubble. 2) Bubble cluster behaves like a rigid body acoustically when the frequency of ultrasound is much higher than its natural frequency.

Yoshizawa, Shin; Matsumoto, Yoichiro

2001-11-01

371

Validation of Bubble Distribution Measurements of the ABS Acoustic Bubble Spectrometer with High Speed Video Photography  

Microsoft Academic Search

Abstract Measurement,of the bubble size distribution in a liquid is very important for cavitation inception studies. In this paper we describe an acoustics based device, the ABS Acoustic Bubble Spectrometer? that measures bubble size distributions and void fractions in liquids based on the ,measurement ,of sound ,propagation through the tested liquid. Short monochromatic,bursts of sound at different frequencies are generated

G. L. Chahine; K. M. Kalumuck; J Y Cheng; G. S. Frederick

372

Equatorial Winds on Saturn and the Stratospheric Oscillation  

NASA Technical Reports Server (NTRS)

The zonal jets on the giant planets are generally thought to be stable with time. Recently, there are still some debates about the general thought. Here, we report a significant temporal variation of the equatorial jet at high-altitude on Saturn. Long-term (2004-2009) observations by Cassini reveal that wind speed at the 60-mbar level increased from 270 m/s in 2004 to 290 m/s in 2008, while the wind speed has been mostly constant over time at the 500-mbar level in the southern equatorial region. The Cassini observations further reveal that the equatorial jet intensified approximately 60 m/s in the stratosphere (1-5 mbar) from 2005 to 2008. The fact that the wind acceleration is weaker at the 60-mbar level (approximately 20 m/s) than at the 1-mbar level (approximately 60 m/s) demonstrates that the equatorial oscillation is damped when it propagates downwards to the tropopause around 60 mbar. The direct measurement of the varying equatorial jet around the tropopause also serves as a key boundary condition when deriving the thermal wind fields in the stratosphere.

Li, Liming; Jian, Xun; Ingersoll, Andrew P.; DelGenio, Anthony D.; Porco, Carolyn C.; West, Robert A.; Vasavada, Ashwin R.; Ewald, Shawn P.; Conrath, Barney J.; Gierasch, Peter J.; Simon-Miller, Amy A.; Nixon, Conor A.; Achterberg, Richard K.; Orton, Glenn S.; Fletcher, Leigh N.; Baines, Kevin H.

2011-01-01

373

Fluid mechanics of bubble capture by the diving bell spider  

E-print Network

The water spider, a unique member of its species, is used as inspiration for a bubble capture mechanism. Bubble mechanics are studied in the pursuit of a biomimetic solution for transporting air bubbles underwater. Careful ...

Brooks, Alice (Alice P.)

2010-01-01

374

Colorful Demos with a Long-Lasting Soap Bubble.  

ERIC Educational Resources Information Center

Describes several demonstrations that feature interaction of light with soap bubbles. Includes directions about how to produce a long-lasting stationary soap bubble with an easily changeable size and describes the interaction of white light with the bubble. (DDR)

Behroozi, F.; Olson, D. W.

1994-01-01

375

Equatorial Density Irregularity Structures at Intermediate Scales and Their Temporal Evolution  

NASA Technical Reports Server (NTRS)

We examine high resolution measurements of ion density in the equatorial ionosphere from the AE-E satellite during the years 1977-1981. Structure over spatial scales from 18 km to 200 m is characterized by the spectrum of irregularities at larger and smaller scales and at altitudes above 350 km and below 300 km. In the low-altitude region, only small amplitude large-scale (lambda greater than 5 km) density modulations are often observed, and thus the power spectrum of these density structures exhibits a steep spectral slope at kilometer scales. In the high-altitude region, sinusoidal density fluctuations, characterized by enhanced power near 1-km scale, are frequently observed during 2000-0200 LT. However, such fluctuations are confined to regions at the edges of larger bubble structures where the average background density is high. Small amplitude irregularity structures, observed at early local time hours, grow rapidly to high-intensity structures in about 90 min. Fully developed structures, which are observed at late local time hours, decay very slowly producing only-small differences in spectral characteristics even 4 hours later. The local time evolution of irregularity structure is investigated by using average statistics for low-(1% less than sigma less than 5%) and high-intensity (sigma greater than 10%) structures. At lower altitudes, little chance in the spectral slope is seen as a function of local time, while at higher attitudes the growth and maintenance of structures near 1 km scales dramatically affects the spectral slope.

Kil, Hyosub; Heelis, R. A.

1998-01-01

376

Neural basis of economic bubble behavior.  

PubMed

Throughout human history, economic bubbles have formed and burst. As a bubble grows, microeconomic behavior ceases to be constrained by realistic predictions. This contradicts the basic assumption of economics that agents have rational expectations. To examine the neural basis of behavior during bubbles, we performed functional magnetic resonance imaging while participants traded shares in a virtual stock exchange with two non-bubble stocks and one bubble stock. The price was largely deflected from the fair price in one of the non-bubble stocks, but not in the other. Their fair prices were specified. The price of the bubble stock showed a large increase and battering, as based on a real stock-market bust. The imaging results revealed modulation of the brain circuits that regulate trade behavior under different market conditions. The premotor cortex was activated only under a market condition in which the price was largely deflected from the fair price specified. During the bubble, brain regions associated with the cognitive processing that supports order decisions were identified. The asset preference that might bias the decision was associated with the ventrolateral prefrontal cortex and the dorsolateral prefrontal cortex (DLPFC). The activity of the inferior parietal lobule (IPL) was correlated with the score of future time perspective, which would bias the estimation of future price. These regions were deemed to form a distinctive network during the bubble. A functional connectivity analysis showed that the connectivity between the DLPFC and the IPL was predominant compared with other connectivities only during the bubble. These findings indicate that uncertain and unstable market conditions changed brain modes in traders. These brain mechanisms might lead to a loss of control caused by wishful thinking, and to microeconomic bubbles that expand, on the macroscopic scale, toward bust. PMID:24468106

Ogawa, A; Onozaki, T; Mizuno, T; Asamizuya, T; Ueno, K; Cheng, K; Iriki, A

2014-04-18

377

Problem Solving: Bubble Gum Contest  

NSDL National Science Digital Library

This professional development video clip presents students engaged in The Common Core Practice Standard #1âMake sense of problems and persevere in solving them. The learners gather data for a bubble gum contest, as part of a larger activity involving recording data and writing up results. Students understand the problem and persevere with the task as they independently go to other classrooms to conduct their survey. Additional resources include a video transcript, teaching tips, and a link to a professional development reflection activity based upon the video.

Boston, Wghb

2013-01-01

378

Bubbling in unbounded coflowing liquids.  

PubMed

An investigation of the stability of low density and viscosity fluid jets and spouts in unbounded coflowing liquids is presented. A full parametrical analysis from low to high Weber and Reynolds numbers shows that the presence of any fluid of finite density and viscosity inside the hollow jet elicits a transition from an absolute to a convective instability at a finite value of the Weber number, for any value of the Reynolds number. Below that critical value of the Weber number, the absolute character of the instability leads to local breakup, and consequently to local bubbling. Experimental data support our model. PMID:16605912

Gañán-Calvo, Alfonso M; Herrada, Miguel A; Garstecki, Piotr

2006-03-31

379

Tether radiation in Juno-type and circular-equatorial Jovian orbits  

NASA Astrophysics Data System (ADS)

Wave radiation by a conductor carrying a steady current in both a polar, highly eccentric, low perijove orbit, as in NASA's planned Juno mission, and an equatorial low Jovian orbit (LJO) mission below the intense radiation belts, is considered. Both missions will need electric power generation for scientific instruments and communication systems. Tethers generate power more efficiently than solar panels or radioisotope power systems (RPS). The radiation impedance is required to determine the current in the overall tether circuit. In a cold plasma model, radiation occurs mainly in the Alfvén and fast magnetosonic modes, exhibiting a large refraction index. The radiation impedance of insulated tethers is determined for both modes and either mission. Unlike the Earth ionospheric case, the low-density, highly magnetized Jovian plasma makes the electron gyrofrequency much larger than the plasma frequency; this substantially modifies the power spectrum for either mode by increasing the Alfvén velocity. Finally, an estimation of the radiation impedance of bare tethers is considered. In LJO, a spacecraft orbiting in a slow downward spiral under the radiation belts would allow determining magnetic field structure and atmospheric composition for understanding the formation, evolution, and structure of Jupiter. Additionally, if the cathodic contactor is switched off, a tether floats electrically, allowing e-beam emission that generate auroras. On/off switching produces bias/current pulses and signal emission, which might be used for Jovian plasma diagnostics.

Sanchez-Torres, A.; Sanmartin, J. R.

2011-12-01

380

Model study on the formation of the equatorial mass density anomaly in the thermosphere  

NASA Astrophysics Data System (ADS)

The equatorial mass density anomaly (EMA) is a fascinating phenomenon in the equatorial upper atmosphere. In this study, we investigate the generation mechanism of the EMA using the ground-to-topside model of the atmosphere and ionosphere for aeronomy (GAIA). The GAIA model is a self-consistent global model of the atmosphere and ionosphere covering the height range from the ground surface to the exobase. It can reproduce the observed EMA structure at 300-400 km heights. Our results show that the EMA structure can extend down to 200 km height. The EMA during daytime is caused by the in situ diurnal tide and the upward propagating terdiurnal tide. About half of the magnitude of the EMA is generated by the upward propagating terdiurnal tide from the lower atmosphere. This is the first report concerning the importance of the upward propagating tide for EMA formation. The in situ diurnal tide in the thermosphere is also essential for EMA formation. The in situ diurnal tide is modified by the momentum exchange between the plasma and the neutral atmosphere. This is seen as the enhanced upward flow of the neutral atmosphere along the dip equator in the 200-400 km height region, which has a profound effect on the latitudinal distributions of the atmospheric composition, temperature, pressure, and density in the thermosphere.

Miyoshi, Y.; Fujiwara, H.; Jin, H.; Shinagawa, H.; Liu, H.; Terada, K.

2011-05-01

381

Bistability between equatorial and axial dipoles during magnetic field reversals.  

PubMed

Numerical simulations of the geodynamo in the presence of heterogeneous heating are presented. We study the dynamics and the structure of the magnetic field when the equatorial symmetry of the flow is broken. If the symmetry breaking is sufficiently strong, the m=0 axial dipolar field is replaced by a hemispherical magnetic field, dominated by an oscillating m=1 magnetic field. Moreover, for moderate symmetry breaking, a bistability between the axial and the equatorial dipole is observed. In this bistable regime, the axial magnetic field exhibits chaotic switches of its polarity, involving the equatorial dipole during the transition period. This new scenario for magnetic field reversals is discussed within the framework of Earth's dynamo. PMID:23003961

Gissinger, Christophe; Petitdemange, Ludovic; Schrinner, Martin; Dormy, Emmanuel

2012-06-01

382

Dynamics of Vapour Bubbles in Nucleate Boiling. 2; Evolution of Thermally Controlled Bubbles  

NASA Technical Reports Server (NTRS)

The previously developed dynamic theory of growth and detachment of vapour bubbles under conditions of nucleate pool boiling is applied to study motion and deformation of a bubble evolving at a single nucleation site. The bubble growth is presumed to be thermally controlled, and two components of heat transfer to the bubble are accounted of: the one from the bulk of surrounding liquid and the one due to heat conduction across a liquid microlayer formed underneath the bubble. Bubble evolution is governed by the buoyancy and an effective surface tension force, both the forces making the bubble centre of mass move away from the wall and, thus, assisting its detachment. Buoyancy-controlled and surface-tension-controlled regimes are considered separately in a meticulous way. The duration of the whole process of bubble evolution till detachment, the rate of growth, and the bubble departure size are found as functions of time and physical and operating parameters. Some repeatedly observed phenomena, such as an influence of gravity on the growth rate, are explained. Inferences of the model agree qualitatively with available experimental evidence, and conclusions pertaining to the dependence on gravity of the bubble radius at detachment and the whole time of the bubble development when being attached to the wall are confirmed quantitatively.

Buyevich, Yu A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

1995-01-01

383

Plasma pressure distribution in the surrounding the Earth plasma ring and its role in the magnetospheric dynamics  

NASA Astrophysics Data System (ADS)

We analyzed the characteristics of the plasma region surrounding the Earth at the geocentric distances between 6 and 15RE using the data of THEMIS mission from April 2007 to September 2012. The obtained averaged distributions of plasma pressure, of pressure anisotropy, and of magnetic field near the equatorial plane showed the presence of a ring-shaped structure surrounding the Earth. It was found that for quiet geomagnetic conditions the plasma pressure is nearly isotropic for all magnetic local times at geocentric distances >6RE. Taking into consideration that the minimal values of the magnetic field at the field lines near noon are shifted from the equatorial plane, we estimate the value of plasma beta parameter in the region of minimal values of the magnetic field using the Tsyganenko-2001 magnetic field model. It was found that the values of plasma beta parameter are of the order of unity for the nightside part of the ring-shaped structure in the equatorial plane and for the region of minimal values of the magnetic field in the dayside, indicating that the ring-shaped structure should play an active role in the magnetic field distortion. Comparison of obtained distribution of plasma pressure at the equatorial plane with the values of plasma pressure at low altitudes, showed that the considerable part of the auroral oval can be mapped into the analyzed plasma ring. The role of the high-beta plasma ring surrounding the Earth for Earth-Sun System disturbances is discussed.

Antonova, E. E.; Kirpichev, I. P.; Stepanova, M. V.

2014-08-01

384

Bubble Growth and Detachment from a Needle  

Microsoft Academic Search

The release of bubbles from an underwater nozzle or orifice occurs in large number of applications, such as perforated plate columns, blood oxygenators and various methods of water treatment. It is also a widely used method in laboratory research on multiphase flow and acoustics for generating small bubbles in a controlled fashion. We studied experimentally the growth and pinch-off of

Michael Shusser; Edmond Rambod; Morteza Gharib

1999-01-01

385

Fearless versus fearful speculative financial bubbles  

NASA Astrophysics Data System (ADS)

Using a recently introduced rational expectation model of bubbles, based on the interplay between stochasticity and positive feedbacks of prices on returns and volatility, we develop a new methodology to test how this model classifies nine time series that have been previously considered as bubbles ending in crashes. The model predicts the existence of two anomalous behaviors occurring simultaneously: (i) super-exponential price growth and (ii) volatility growth, that we refer to as the “fearful singular bubble” regime. Out of the nine time series, we find that five pass our tests and can be characterized as “fearful singular bubbles”. The four other cases are the information technology Nasdaq bubble and three bubbles of the Hang Seng index ending in crashes in 1987, 1994 and 1997. According to our analysis, these four bubbles have developed with essentially no significant increase of their volatility. This paper thus proposes that speculative bubbles ending in crashes form two groups hitherto unrecognized, namely those accompanied by increasing volatility (reflecting increasing risk perception) and those without change of volatility (reflecting an absence of risk perception).

Andersen, J. V.; Sornette, D.

2004-06-01

386

The Minnaert Bubble: An Acoustic Approach  

ERIC Educational Resources Information Center

We propose an "ab initio" introduction to the well-known Minnaert pulsating bubble at graduate level. After a brief recall of the standard stuff, we begin with a detailed discussion of the radial movements of an air bubble in water. This discussion is managed from an acoustic point of view, and using the Lagrangian rather than the Eulerian…

Devaud, Martin; Hocquet, Thierry; Bacri, Jean-Claude; Leroy, Valentin

2008-01-01

387

Drops and Bubble in Materials Science  

NASA Technical Reports Server (NTRS)

The formation of extended p-n junctions in semiconductors by drop migration, mechanisms and morphologies of migrating drops and bubbles in solids and nucleation and corrections to the Volmer-Weber equations are discussed. Bubble shrinkage in the processing of glass, the formation of glass microshells as laser-fusion targets, and radiation-induced voids in nuclear reactors were examined.

Doremus, R. H.

1982-01-01

388

Modeling the Motion of a Rising Bubble  

Microsoft Academic Search

It is well known that an air bubble in water with a diameter between 1.3mm and 50mm does not move straight up as might be expected, but instead zigzags or spirals. We have developed an apparatus to study this phenomenon using digital video capture. Air bubbles are formed at the bottom of a rectangular Plexiglas tank three feet high with

Ryan Greer; E. A. George; P. A. Voytas

2002-01-01

389

Continuous-data FIFO bubble shift register  

NASA Technical Reports Server (NTRS)

Simple loop first-in-first-out (FIFO) bubble memory shift register has continuous storage capability. Bubble shift register simplifies chip-control electronics by enabling all control functions to be alined at same bit. FIFO shift register is constructed from passive replicator and annihilator combinations.

Chen, T. T.

1977-01-01

390

Modeling bubble clusters in compressible liquids  

Microsoft Academic Search

We present a new model to simulate the behaviour of bubble clouds in compressible liquids. The method uses a volume-averaged approach and defines the pressure and void fraction relative to a computational cell. Inside the cell, a generalisation of the Keller-Miksis equation is derived in order to take into account the presence of (one or more) nearby spherical bubbles as

Daniel Fuster; Tim Colonius

2010-01-01

391

Experimental characterisation of bubbly flow using MRI  

E-print Network

-phase pipe flow up to a Reynolds number of 12,000. By employing a compressed sensing reconstruction, images were acquired at a rate of 188 fps. Images were then acquired of bubbly flow for the entire range of voidages for which bubbly flow was possible (up...

Tayler, Alexander B.

2011-11-08

392

Measuring the surface tension of soap bubbles  

NASA Technical Reports Server (NTRS)

The objectives are for students to gain an understanding of surface tension, to see that pressure inside a small bubble is larger than that inside a large bubble. These concepts can be used to explain the behavior of liquid foams as well as precipitate coarsening and grain growth. Equipment, supplies, and procedures are explained.

Sorensen, Carl D.

1992-01-01

393

Topical review Sonoluminescence: how bubbles glow  

Microsoft Academic Search

We review recent attempts to elucidate the phenomenon of sonoluminescence in terms of fundamental principles. We focus mainly on the processes which generate the light, but other relevant facts, such as the bubble dynamics, must also be considered for the understanding of the physics involved. Our emphasis is on single bubble sonoluminescence which in recent years has received much attention,

DOMINIK HAMMER; LOTHAR FROMMHOLD

2001-01-01

394

Bubble structures in He irradiated metals  

Microsoft Academic Search

Transmission electron microscopy is used to investigate the spatial arrangement of gas bubbles produced in the metals, Cu, Ni, Au, stainless steel and Ti irradiated with He at temperatures ? 300 K. For metals having a high degree of crystalline perfection within grains, a gas bubble superlattice is formed at high He doses in every case investigated. A study is

P. B. Johnson; D. J. Mazey; J. H. Evans

1983-01-01

395

New approaches to hard bubble suppression  

NASA Technical Reports Server (NTRS)

Description of a new double-layer method for the suppression of hard bubbles that is more versatile than previously reported suppression techniques. It is shown that it may be possible to prevent hard bubble generation without recourse to exchange coupling of multilayer films.

Henry, R. D.; Besser, P. J.; Warren, R. G.; Whitcomb, E. C.

1973-01-01

396

The Interaction of Two Underwater Explosion Bubbles  

NASA Astrophysics Data System (ADS)

The interaction between two growing and collapsing underwater explosion bubbles is studied experimentally and numerically. In the experiments, the bubbles are generated by detonating small Lead Azide explosive charges submerged in a transparent water tank, and the resulting interactions are photographed using a high-speed camera. The parametric studies include simultaneous detonation of two charges of different sizes, and detonation of identically sized charges at staggered times. When the time delay between detonations is significant, the collapsing first bubble forms a jet directed away from the expanding second bubble and then re-expands nonspherically. During the re-expansion of the first bubble, a micro-jet forms in the second bubble. Eventually this micro-jet pierces the side of the second bubble farthest from the first and vortex rings are formed. Numerical simulations of the interaction phenomena are achieved using a boundary element method. By partitioning the system into computational sub-domains it is possible to replicate many relevant physical details including jet formation, fluid-fluid impact, and bubble re-expansion after complete jet penetration. The numerical results are in qualitative agreement with the experimental findings.

Milligan, Charles; Duncan, James

1996-11-01

397

Mixture segregation by an inertial cavitation bubble  

Microsoft Academic Search

Pressure diffusion is a mass diffusion process forced by pressure gradients. It has the ability to segregate two species of a mixture, driving the densest species toward high pressure zones, but requires very large pressure gradients to become noticeable. An inertial cavitation bubble develops large pressure gradients in its vicinity, especially as the bubble rebounds at the end of its

R. Grossier; O. Louisnard; Y. Vargas

2007-01-01

398

The Interaction of Two Underwater Explosion Bubbles  

Microsoft Academic Search

The interaction between two growing and collapsing underwater explosion bubbles is studied experimentally and numerically. In the experiments, the bubbles are generated by detonating small Lead Azide explosive charges submerged in a transparent water tank, and the resulting interactions are photographed using a high-speed camera. The parametric studies include simultaneous detonation of two charges of different sizes, and detonation of

Charles Milligan; James Duncan

1996-01-01

399

Moving with Bubbles: A Review of the Interactions between Bubbles and the Microorganisms that Surround them.  

PubMed

Bubbles are ubiquitous in biological environments, emerging during the complex dynamics of waves breaking in the open oceans or being intentionally formed in bioreactors. From formation, through motion, until death, bubbles play a critical role in the oxygenation and mixing of natural and artificial ecosystems. However, their life is also greatly influenced by the environments in which they emerge. This interaction between bubbles and microorganisms is a subtle affair in which surface tension plays a critical role. Indeed, it shapes the role of bubbles in mixing or oxygenating microorganisms, but also determines how microorganisms affect every stage of the bubble's life. In this review, we guide the reader through the life of a bubble from birth to death, with particular attention to the microorganism-bubble interaction as viewed through the lens of fluid dynamics. PMID:25096288

Walls, Peter L L; Bird, James C; Bourouiba, Lydia

2014-12-01

400

Bubble coalescence in turbulent flows: A mechanistic model for turbulence-induced coalescence applied to microgravity bubbly pipe flow  

Microsoft Academic Search

A mechanistic model for bubble coalescence in turbulent flow is presented. The model is developed in two steps, which are essentially separable. In the first, expressions put forward earlier for the collision frequency and coalescence probability of equal bubbles during turbulence-driven, high-Reynolds-number collisions are extended to unequal bubbles and to take account of bubble–turbulence and bubble–bubble interactions. In the second,

A. M Kamp; A. K Chesters; C Colin; J Fabre

2001-01-01

401

Dynamics of exploding plasmas in a large magnetized plasma  

NASA Astrophysics Data System (ADS)

The dynamics of an exploding laser-produced plasma in a large ambient magneto-plasma was investigated with magnetic flux probes and Langmuir probes. Debris-ions expanding at super-Alfvénic velocity (up to MA=1.5) expel the ambient magnetic field, creating a large (>20 cm) diamagnetic cavity. We observe a field compression of up to B /B0=1.5 as well as localized electron heating at the edge of the bubble. Two-dimensional hybrid simulations reproduce these measurements well and show that the majority of the ambient ions are energized by the magnetic piston and swept outside the bubble volume. Nonlinear shear-Alfvén waves (?B/B0>25%) are radiated from the cavity with a coupling efficiency of 70% from magnetic energy in the bubble to the wave.

Niemann, C.; Gekelman, W.; Constantin, C. G.; Everson, E. T.; Schaeffer, D. B.; Clark, S. E.; Winske, D.; Zylstra, A. B.; Pribyl, P.; Tripathi, S. K. P.; Larson, D.; Glenzer, S. H.; Bondarenko, A. S.

2013-01-01

402

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet  

NASA Technical Reports Server (NTRS)

We have conducted a detailed study of the cloud features in the strong southern equatorial wind jet near 7.5 S planetographic latitude. To understand the apparent variations in average zonal wind jet velocity at this latitude [e.g.. 1,2,3], we have searched for variations iIi both feature latitude and velocity with longitude and time. In particular, we focused on the repetitive chevron-shaped dark spots visible on most dates and the more transient large anticyclonic system known as the South Equatorial Disturbance (SED). These small dark spots are interpreted as cloud holes, and are often used as material tracers of the wind field.

Simon-Miller, A. A.; Rogers, John H.; Gierasch, Peter J.; Choi, David; Allison, Michael; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

403

Analysis of Bubbly Lubrication in Journal Bearings  

NASA Astrophysics Data System (ADS)

The effect of air bubbles evenly distributed in lubricating oil on the bearing performances is analyzed theoretically. The Reynolds equation for the bubbly lubricant in a steady-state and isothermal condition is solved with an iterative numerical method. Surface tension and the radius of bubble are taken into account in the analysis. It is assumed that bubbles move along streamlines and do not split apart or coalesce. The density and the viscosity of air-oil mixture are treated as functions of oil film pressure and the volume fraction of air. Numerical results show that the load carrying capacity of a journal bearing increases as bubbles in the supplied lubricant become smaller or the surface tension is getting larger. The load carrying capacity increases as the volume fraction increases up to a critical volume fraction that gives maximum load carrying capacity. Beyond the critical volume fraction, it decreases as the volume fraction increases.

Choi, Song; Kim, Kyung Woong

404

Phosphorus geochemistry of equatorial Pacific sediments  

NASA Astrophysics Data System (ADS)

Understanding phosphorus (P) geochemistry and burial in oceanic sediments is important because of the role of P for modulating oceanic productivity on long timescales. We investigated P geochemistry in seven equatorial Pacific sites over the last 53 m.y., using a sequential extraction technique to elucidate sedimentary P composition and P diagenesis within the sediments. The dominant P-bearing component in these sediments is authigenic P (61-86% of total P), followed in order of relative dominance by iron-bound P (7-17%), organic P (3-12%), adsorbed P (2-9%), and detrital P (0- 1 %). Clear temporal trends in P component composition exist. Organic P decreases rapidly in younger sediments in the eastern Pacific (the only sites with high sample resolution in the younger intervals), from a mean concentration of 2.3 ?mol P/g sediment in the 0-1 Ma interval to 0.4 ?mol/g in the 5- 6 Ma interval. Over this same time interval, decreases are also observed for iron-bound P (from 2.1 to 1.1 ?mol P/g) and adsorbed P (from 1.5 to 0.7 ?mol P/g). These decreases are in contrast to increases in authigenic P (from 6.0-9.6 ?mol P/g) and no significant changes in detrital P (0.1 ?mol P/g) and total P (12 ?mol P/g). These temporal trends in P geochemistry suggest that (1) organic matter, the principal shuttle of P to the seafloor, is regenerated in sediments and releases associated P to interstitial waters, (2) P associated with iron-rich oxyhydroxides is released to interstitial waters upon microbial iron reduction, (3) the decrease in adsorbed P with age and depth probably indicates a similar decrease in interstitial water P concentrations, and (4) carbonate fluorapatite (CFA), or another authigenic P-bearing phase, precipitates due to the release of P from organic matter and iron oxyhydroxides and becomes an increasingly significant P sink with age and depth. The reorganization of P between various sedimentary pools, and its eventual incorporation in CFA, has been recognized in a variety of continental margin environments, but this is the first time these processes have been revealed in deep-sea sediments. Phosphorus accumulation rate data from this study and others indicates that the global pre-anthropogenic input rate of P to the ocean (20 × 10 10 mol P/yr) is about a factor of four times higher than previously thought, supporting recent suggestions that the residence time of P in the oceans may be as short as 10,000-20,000 years.

Filippelli, Gabriel M.; Delaney, Margaret Lois

1996-05-01

405

Gas bubble dynamics in soft materials.  

PubMed

Epstein and Plesset's seminal work on the rate of gas bubble dissolution and growth in a simple liquid is generalized to render it applicable to a gas bubble embedded in a soft elastic solid. Both the underlying diffusion equation and the expression for the gas bubble pressure were modified to allow for the non-zero shear modulus of the medium. The extension of the diffusion equation results in a trivial shift (by an additive constant) in the value of the diffusion coefficient, and does not change the form of the rate equations. But the use of a generalized Young-Laplace equation for the bubble pressure resulted in significant differences on the dynamics of bubble dissolution and growth, relative to an inviscid liquid medium. Depending on whether the salient parameters (solute concentration, initial bubble radius, surface tension, and shear modulus) lead to bubble growth or dissolution, the effect of allowing for a non-zero shear modulus in the generalized Young-Laplace equation is to speed up the rate of bubble growth, or to reduce the rate of bubble dissolution, respectively. The relation to previous work on visco-elastic materials is discussed, as is the connection of this work to the problem of Decompression Sickness (specifically, "the bends"). Examples of tissues to which our expressions can be applied are provided. Also, a new phenomenon is predicted whereby, for some parameter values, a bubble can be metastable and persist for long times, or it may grow, when embedded in a homogeneous under-saturated soft elastic medium. PMID:25382720

Solano-Altamirano, J M; Malcolm, John D; Goldman, Saul

2014-12-01

406

Mechanism of single-bubble sonoluminescence.  

PubMed

Considering almost all the effective processes of physics and chemical reaction in our numerical computation model, we investigate the mechanism of single bubble sonoluminescence (SBSL). For those sonoluminescing single bubbles in water at its flashing phase, the numerical simulation reveals that if the temperature inside the bubble is not high enough which may result in the plenty oxygen molecules and OH radicals undissociated, such as the case of a single argon bubble in 20 degrees C or 34 degrees C water, the radiative attachment of electrons to oxygen molecules and OH radicals contributes most to the SBSL; if the temperature inside the bubble is higher which makes most of the water vapor inside the bubble dissociate into oxygen and hydrogen atoms, such as the case of an argon bubble or a helium bubble in 0 degrees C water, the radiative attachment of electrons to oxygen and hydrogen atoms dominates the SBSL; if the temperature is still higher, such as the case of a xenon bubble in 0 degrees C water, the contribution from electron-neutral atom bremsstrahlung and electron-ion bremsstrahlung and recombination would be comparable with the contribution from the radiative attachment of electrons to oxygen and hydrogen atoms, and they together dominate the SBSL. For sonoluminescing single bubbles in those low vapor pressure liquids, such as in 85 wt.% sulphuric acid, the electron-neutral atom bremsstrahlung and the electron-ion bremsstrahlung and recombination contribute most to the continuous spectrum part of SBSL. The present calculation also provides good interpretations to those observed phenomena, such as emitted photon numbers, the width of optical pulses, the blackbody radiation like spectra. The temperature fitted by the blackbody radiation formula is very different from that calculated by the gas dynamics equations. Besides, the effect of chemical dissociation on the shock wave is also discussed. PMID:17025536

An, Yu

2006-08-01

407

Bubble creation and collapse during excimer laser ablation of weak absorbing polymers  

NASA Astrophysics Data System (ADS)

We present evidence suggesting that XeCl laser ablation of a weakly absorbing poly-methyl-methacrylate (PMMA) polymer, done by chemical, thermal bond breaking of the polymer chain or optical breakdown of the material, which involves plasma generation, creates a cloud of small asymmetric near the surface bubbles, which subsequently expand and aggregate during the same laser pulse duration or in subsequent pulses depending on the laser pulse energy. When a critical volume is reached each bubble collapses in a high pressure and temperature central point and rebounds ejecting a hot jet of material on the non-irradiated area of the polymer and creating craters on the surface. A characteristic bipolar pressure wave corresponding to the bubble collapse, explosion and rebound is observed. The number density of the craters on the surface is a function of the laser pulse sequence number and the laser pulse energy density.

Efthimiopoulos, T.; Kiagias, H.; Christoulakis, S.; Merlemis, N.

2008-06-01

408

Observation of Microhollows Produced by Bubble Cloud Cavitation  

NASA Astrophysics Data System (ADS)

When an ultrasonic wave with sound pressure less than the threshold level of bubble destruction irradiates microbubbles, the microbubbles aggregate by an acoustic radiation force and form bubble clouds. The cavitation of bubble clouds produces a large number of microhollows (microdips) on the flow channel wall. In this study, microhollow production by bubble cloud cavitation is evaluated using a blood vessel phantom made of N-isopropylacrylamide (NIPA) gel. Microbubble dynamics in bubble cloud cavitation is observed by a microscope with a short pulse light emitted diode (LED) light source. Microhollows produced on the flow channel wall are evaluated by a confocal laser microscope with a water immersion objective. It is observed that a mass of low-density bubbles (bubble mist) is formed by bubble cloud cavitation. The spatial correlation between the bubble mist and the microhollows shows the importance of the bubble mist in microhollow production by bubble cloud cavitation.

Yamakoshi, Yoshiki; Miwa, Takashi

2012-07-01

409

Magma mixing enhanced by bubble ascent  

NASA Astrophysics Data System (ADS)

Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization has been divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of magma has commonly been attributed to shear and folding movements between two liquids of distinct viscosities. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of magma mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket, or bubble trapped within the